Reliability of power stations: Stochastic versus derated power approach

Consideration of the eventual forced outage of individual power stations leads to a large number of possible states of the power generating system, all with their own probability. It is possible to design a stochastic method to properly take into account all of these possibilities and to weigh them accordingly. In broader energy models, instead of these stochastic techniques that require a considerable amount of calculation time, mostly approximative static simplified methods are applied. Up till now, these simplified techniques have not been validated. The scope of this paper is to check their validity. Therefore, two approaches are compared: a complete stochastic approach and a method based on the derated power (which is the nominal power multiplied with the average availability) of the individual plants. The conclusion of this comparison is that derated power may be used in energy modelling instead of the complicated stochastic approach. The error made is very small and the correlation between the unserved load probability functions obtained by both methods is excellent. Copyright © 2004 John Wiley & Sons, Ltd.     

Development of a flickermeter for grid-connected wind turbines using a DSP-based prototyping system

The measurement of one of the power-quality problems (flicker), which may arise due to the presence of wind-turbine generators, is presented. This paper focuses on the design of a complete fully digital flickermeter relying on an in-house-developed measurement system, which features a data-acquisition system, using a C6711 DSP-based starter kit (DSK) and a field programmable gate array (FPGA). To study flicker produced during the wind turbine's continuous operation, special attention is given to the simulation of the voltage fluctuations on a fictitious grid.     

Sustained nitrite accumulation in a membrane‐assisted bioreactor (MBR) for the treatment of ammonium‐rich wastewater

A membrane‐assisted bioreactor (MBR) for sustained nitrite accumulation is presented, treating a synthetic wastewater with total ammonium nitrogen (TAN) concentrations of 1 kg N m^?3 at a hydraulic retention time down to 1 day. Complete biomass retention was obtained by microfiltration with submerged hollow fibre membranes. A membrane flux up to 189.5 dm³ day^?1 m^?2 could be maintained at a suction pressure below 100 kPa. Nitrification was effectively blocked at the nitrite stage (nitritation), and nitrate concentration was less than 29 g N m^?3. The rate of aeration was reduced to obtain a mixture of ammonium and nitrite, and after adjusting this rate the TAN/NO₂‐N ratio in the reactor effluent was kept around unity, making it suitable for further treatment by anaerobic oxidation of ammonium with nitrite. After increasing again the rate of aeration, complete nitrification to nitrate recovered after 11 days. It is suggested that nitrite accumulation resulted from a combination of factors. First, the dissolved oxygen (DO) concentration in the reactor was always limited with concentrations below 0.1 g DO m^?3, thereby limiting nitrification and preventing significant nitrate formation. The latter is attributed to the fact that ammonium‐oxidising bacteria cope better with low DO concentrations than nitrite oxidisers. Second, the MBR was operated at a high ammonia concentration of 7–54 g N m^?3, resulting in ammonia inhibition of the nitrite‐oxidising microorganisms. Third, a temperature of 35 °C was reported to yield a higher maximum growth rate for ammonium‐oxidising bacteria than for nitrite‐oxidising bacteria. Nitrite oxidisers were always present in the MBR but were out‐competed under the indicated process conditions, which is reflected in low concentrations of nitrate. Oxygen limitation was shown to be the most important factor to sustain nitrite accumulation. Nevertheless, nitritation was possible at ambient temperature (22–24 °C), lower ammonia concentration (<7 g N m^?3) and when using raw nitrogenous wastewater containing some biodegradable carbon. Overall, application of the MBR for nitritation was shown to be a reliable technology. © 2003 Society of Chemical Industry     

SQL Server Integration Services 2005中的模糊查找和模糊分组

简介 由于拼写错误、意外的缩略语和其他不规则问题，实际的数据是“有问题”的。因此，在数据仓储项目中，很大一部分的时间和金钱都花费在了数据提取、数据转换和数据加载（ETL，Extraction、Transformation、Loading）阶段。在ETL阶段，新数据被清理、标准化，并使其与现有数据一致。在Microsoft SQL Server 2005中可用的模糊查找和模糊分组转换，有助于使ETL过程在遇到若干种在交际数据中观测到的常见错误时更易复原。它们解决一般的匹配和分组问题，而无需特定于域的规则和脚本的专家集合。通过为您的域自定义模糊查找和模糊分组，您可以利用Business Intelligence Development Studio内的通用数据清理算法，并避免创建复杂的自定义规则和代码。     

Concave utility, transaction costs, and risk in measuring discounting of delayed rewards.

Research has consistently found that the decline in the present values of delayed rewards as delay increases is better fit by hyperbolic than by exponential delay-discounting functions. However, concave utility, transaction costs, and risk each could produce hyperbolic-looking data, even when the underlying discounting function is exponential. In Experiments 1 (N=45) and 2 (N=103), participants placed bids indicating their present values of real future monetary rewards in computer-based 2nd-price auctions. Both experiments suggest that utility is not sufficiently concave to account for the superior fit of hyperbolic functions. Experiment 2 provided no evidence that the effects of transaction costs and risk are large enough to account for the superior fit of hyperbolic functions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Irreversibility in the two-body hard-disk lorentz gas

Time-reversible modifications of Newton's equations of motion have been used to simulate irreversible isothermal shear flows. The modified equations have stable solutions for periodic systems with as few as two or three particles. These small-system solutions exhibit thermodynamic irreversibility, entropy production and realistic nonlinear constitutive behavior.     

The relation between methods of coping during adulthood with a history of childhood sexual abuse and current psychological adjustment.

With a community sample of 192 women who had been sexually abused during childhood, the investigators determined if methods of coping in adulthood with the aftermath of child sexual abuse were associated with current symptoms of psychological distress. Multiple regression analyses indicated that disengagement methods of coping with the sexual abuse accounted for unique variance in general psychological distress even after controlling for characteristics of the abuse and methods of coping with other stressors. Disengagement methods of coping were also used more often to deal with the stressful aspects of having been sexually abused than to deal with other stressful events. In contrast, engagement methods of coping were used more often to deal with the other stressors than with sexual abuse. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

DNA microarray enhancement using a continuously and discontinuously rotating microchamber

It is demonstrated that the most efficient way to enhance DNA microarray analysis consists of a maximal reduction of the total device volume (to keep the concentration of the available DNA as high as possible), combined with the creation of a strong lateral convective transport of the sample. In the present study, DNA microarray hybridizations are performed in a set of rotating, circular microchambers covering exactly the spotted area of the microarray and with a depth varying between 70 and 1.6 microm. Rotating the microchamber substrate while keeping the microarray stationary, the rotating microchamber bottom wall literally drags the sample past the microarray spots with a velocity which is independent of the fluid layer thickness. Interestingly, it was found that transporting the sample in a discontinuous mode (with stop periods of several minutes) not only yields a more stable and reproducible operation, it also yields significantly larger hybridization intensities (typically a factor of 2-3 larger) than a continuous rotation. This seems to be due to the fact that the velocity field disturbs the binding process at the binding site level. Working under limiting DNA sample mass conditions, the system yielded in a short, 30-min experiment already a 5-fold increase of the hybridization intensity, as compared to a conventional microscope slide/coverslip system operated overnight under diffusion-driven conditions. Compared to a commercial pump-around hybridization system, the gain was even more impressive, precisely due to the fact that the pump-around system requires larger volumes, which with a fixed amount of available genetic material leads to the application of more diluted samples.