可变环境下的离散时间单部件可修系统

研究离散时间可修系统,讨论了一个可在不同环境下工作的单部件可修系统,其所处环境的改变服从马尔可夫更新过程;利用马尔可夫更新理论,得到了系统的可用度, 故障频度和可靠度等各项指标．     

THE CONSTRUCTION OF MULTITYPE CANONICAL MARKOV BRANCHING CHAINS IN RANDOM ENVIRONMENTS

The investigation for branching processes has a long history by their strong physics background, but only a few authors have investigated the branching processes in random environments. First of all, the author introduces the concepts of the multitype canonical Markov branching chain in random environment (CMBCRE) and multitype Markov branching chain in random environment (MBCRE) and proved that CMBCRE must be MBCRE, and any MBCRE must be equivalent to another CMBCRE in distribution. The main results of this article are the construction of CMBCRE and some of its probability properties.     

Contamination of outdoor settled dust by butyltins in Malta

The presence of compounds of tributyltin (TBT), dibutyltin (DBT) and monobutyltin (MBT) was determined in outdoor settled dust collected from several sites on the island of Malta, mainly from flat rooftops of school buildings. The dust was separated into three size fractions with diameters (µm) > 250, 125–250 and < 125, and the two finer fractions were analysed for butyltins using extraction with glacial acetic acid followed by derivatization/solvent extraction with sodium tetraethylborate in the presence of iso‐octane and quantitation by gas chromatography with flame photometric detection. The presence of TBT, DBT and MBT was established in most of the samples and TBT concentrations varied from non‐detectable (<5 ng Sn g^?1) to highs of 15.5 and 18.7 µg Sn g^?1 in Senglea and Marsaxlokk. TBT was generally found at concentrations significantly higher than reported hitherto in house dust collected from European homes. The geographical distribution of total organotins in both dust fractions suggests that TBT originates mainly from antifouling marine paint residues which contaminate the urban environment when ships' hulls are sand‐ or hydro‐blasted during maintenance and repair at the drydocks facility in Grand Harbour. Other significant sources of TBT are located at Marsaxlokk fishing port and Wied i?‐?urrieq creek, both hosting sizeable communities of fishermen and leisure boating. The data also suggest that the municipal solid waste landfill at Maghtab is an inland source of butyltins. We suggest that dust containing harmful butyltins could possibly be ingested to expose humans to a risk which is probably of concern especially for young children living close to the hotspots of contamination. Copyright © 2007 John Wiley & Sons, Ltd.     

Corrosion behavior of sputtered Cr-Si-Ni and Cr-Si-Ni-Al resistive films in 0.1 M NaOH

The corrosion behavior of magnetron sputtered Cr-Si-Ni and Cr-Si-Ni-Al resistive films had been investigated by means of the relative resistance change (ΔR/R), polarization measurements, AES, and SEM in 0.1 M NaOH solution at 25 °C and 50 °C, which simulated an alkaline environment. The results revealed that both the annealed Cr-Si-Ni and Cr-Si-Ni-Al films in Ar ambient exhibited good corrosion resistance and long-term reliability in 0.1 M NaOH solution at 25 °C, due to the formation of a protective oxide layer on the surface of two types of the films during corrosion. However, the corrosion properties of two types of the films became degraded rapidly with the solution temperature at 50 °C. The studies showed that the pro-formation of a protective oxide layer on the surface of two types of the films by annealing in air had an enhancing effect on the corrosion properties of the films in 0.1 M NaOH solution at 50 °C, and that Cr-Si-Ni-Al films by annealing in air had more improving effect on the corrosion resistance and long-term reliability than Cr-Si-Ni films.     

Tris-β-diketones and related keto derivatives for use as building blocks in supramolecular chemistry

The synthesis of three new tris-β-diketones and some derivatives is reported. In two cases facile alkaline hydrolysis of the diketone moieties yielded the corresponding keto compounds. These are readily functionalised to provide tripodal ligands.     

半直线上随机环境中可逗留随机游动的常返性

本文主要讨论了在独立但不同分布环境下，半直线上可逗留随机环境中随机游动的常返性和非常返性，并进一步研究了常返性中的正常返性和零常返性．     

Dynamic discrimination of convergence of the LMS time delay estimation in complicated noisy environments

For nonstationary signals, time constant can no longer represent the actual convergence performance of the adaptive delay estimation. A scheme is thus proposed for dynamically discriminating the convergence of the LMS time delay estimation to get an optimal estimate even under complicated noisy environments. Based on the fact that the filter output gets orthogonal to the estimation error only when an adaptive filter operates in its optimal condition, an approximate orthogonality constraint is derived for discriminating the practical adaptation’s convergence. This discrimination condition, which is obtained through the estimated mean-square values of related available variables at each iteration, can be updated in the adaptation process according to the varying statistic characteristics of observed signals. Thus, it can dynamically evaluate the quality of the adaptive solution and end the iteration opportunely. Simulation results are also included to demonstrate its effectiveness to give exact convergence results in both stationary and nonstationary cases.     

具时滞的捕食-食饵系统的一致持久性

研究周期环境下具时滞的Volterra-Lotka捕食-食饵系统。利用持久性理论，积分均值和微分不等式的方法。建立了关于一致持久的充分必要差别准确。得到新的结果。     

Sedimentary siloxanes: A depositional history

A Puget Sound sediment core has been quantitatively analyzed for organic silicon content, as derived from post-1945 release of poly(organo)-siloxanes (silicones). The sedimentary silicone data record and preserve at depth, a smeared event horizon, or first appearance of silicone in the sediment column. Core samples older than 50 years showed no detectable silicone as measured by a new procedure utilizing inductively coupled plasma (ICP) emission spectroscopy after solvent extraction to collect the silicone from gram-sized sediment core samples.