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51.
52.
Acidification of Norwegian surface waters, as indicated by elevated concentrations of sulfate and a corresponding reduction in acid neutralizing capacity and pH, is a result of emission and subsequent deposition of sulfur and nitrogen compounds. Episodic sea-salt deposition during severe weather conditions may increase the effects of acidification by mobilizing more toxic aluminum during such episodes. Changes in climatic conditions may increase the frequency and strength of storms along the coast thus interacting with acidification effects on chemistry and biota. We found that the North Atlantic Oscillation (NAO) is linked to sea-salt deposition and sea-salt induced water chemistry effects in five rivers. Particularly, toxic levels of aluminum in all rivers were significantly correlated with higher NAO index values. Further, temporal trends were studied by comparing tendencies for selected statistical indices (i.e. frequency distributions) with time. The selected indices exhibited strong correlations between the NAO index, sea-salt deposition and river data such as chloride, pH and inorganic monomeric aluminum, pointing at the influence of North Atlantic climate variability on water chemistry and water toxicity. The potentially toxic effects of sea-salt deposition in rivers seem to be reduced as the acidification is reduced. This suggests that sea-salt episodes have to increase in strength in order to give the same potential negative biological effects in the future, if acid deposition is further reduced. More extreme winter precipitation events have been predicted in the northwest of Europe as a result of climate change. If this change will be associated with more severe sea-salt episodes is yet unknown. 相似文献
53.
Aerosol lidar intercomparison in the framework of the EARLINET project. 1. Instruments 总被引:1,自引:0,他引:1
Matthais V Freudenthaler V Amodeo A Balin I Balis D Bösenberg J Chaikovsky A Chourdakis G Comeron A Delaval A De Tomasi F Eixmann R Hågård A Komguem L Kreipl S Matthey R Rizi V Rodrigues JA Wandinger U Wang X 《Applied optics》2004,43(4):961-976
In the framework of the European Aerosol Research Lidar Network to Establish an Aerosol Climatology (EARLINET), 19 aerosol lidar systems from 11 European countries were compared. Aerosol extinction or backscatter coefficient profiles were measured by at least two systems for each comparison. Aerosol extinction coefficients were derived from Raman lidar measurements in the UV (351 or 355 nm), and aerosol backscatter profiles were calculated from pure elastic backscatter measurements at 351 or 355, 532, or 1064 nm. The results were compared for height ranges with high and low aerosol content. Some systems were additionally compared with sunphotometers and starphotometers. Predefined maximum deviations were used for quality control of the results. Lidar systems with results outside those limits could not meet the quality assurance criterion. The algorithms for deriving aerosol backscatter profiles from elastic lidar measurements were tested separately, and the results are described in Part 2 of this series of papers [Appl. Opt. 43, 977-989 (2004)]. In the end, all systems were quality assured, although some had to be modified to improve their performance. Typical deviations between aerosol backscatter profiles were 10% in the planetary boundary layer and 0.1 x 10(-6) m(-1) sr(-1) in the free troposphere. 相似文献
54.
This paper presents an integrated approach to solve the buffer allocation problem in unreliable production lines so as to maximize the throughput rate of the line with minimum total buffer size. The proposed integrated approach has two control loops; the inner loop and the outer loop. While the inner loop control includes an adaptive tabu search algorithm proposed by Demir et al. [8], binary search and tabu search are proposed for the outer loop. These nested loops aim at minimizing the total buffer size to achieve the desired throughput level. To improve the efficiency of the proposed tabu search, alternative neighborhood generation mechanisms are developed. The performances of the proposed algorithms are evaluated by extensive computational experimentation, and the results are reported. 相似文献
55.
56.
3-Halobithienyls have been prepared through the Pd(PPh3)4-catalyzed coupling of thiopheneboronic acids with 2,4-dihalothiophenes. The ring-opening of the corresponding 3-lithiobithienyls obtained upon halogen-metal exchange with phenyllithium has been investigated. Compound 12 , 3′-iodo-2,2′,2″-terthienyl, was prepared in one step through the Pd(PPh3)4-catalyzed coupling of two equivalents of 2-thiopheneboronic acid with 2,3,5-triiodothiophene. Treatment of 12 with phenyllithium and methyl iodide gave a mixture of compounds 10 and 11 occurring in Berkheya and Cullumia species. 相似文献
57.
The effects of transferring glacier-fed water to a clear-water river on production and food organisms of brown trout (Salmo trutta L.) were investigated in a mountain river, in southern Norway. Production in unregulated fluvial habitat was 271.5 g 100 m?2 yr?1 compared with 103.1 g 100 m?2 yr?1 in a glacier-fed reach of the river. This difference was due to low fish density and recruitment rate. The growth rate, at least for younger fish (2+ to 4+ age groups), was significantly higher in the regulated reach of the river. The main difference in food composition was the low abundance of crustaceans Eurycercus lamellatus and Gammarus lacustris in the regulated reach. Trichopterans were the main diet component in both sites. 相似文献
58.
Creativity is a cornerstone of what makes us human, yet the neural mechanisms underlying creative thinking are poorly understood. A recent surge of interest into the neural underpinnings of creative behavior has produced a banquet of data that is tantalizing but, considered as a whole, deeply self-contradictory. We review the emerging literature and take stock of several long-standing theories and widely held beliefs about creativity. A total of 72 experiments, reported in 63 articles, make up the core of the review. They broadly fall into 3 categories: divergent thinking, artistic creativity, and insight. Electroencephalographic studies of divergent thinking yield highly variegated results. Neuroimaging studies of this paradigm also indicate no reliable changes above and beyond diffuse prefrontal activation. These findings call into question the usefulness of the divergent thinking construct in the search for the neural basis of creativity. A similarly inconclusive picture emerges for studies of artistic performance, except that this paradigm also often yields activation of motor and temporoparietal regions. Neuroelectric and imaging studies of insight are more consistent, reflecting changes in anterior cingulate cortex and prefrontal areas. Taken together, creative thinking does not appear to critically depend on any single mental process or brain region, and it is not especially associated with right brains, defocused attention, low arousal, or alpha synchronization, as sometimes hypothesized. To make creativity tractable in the brain, it must be further subdivided into different types that can be meaningfully associated with specific neurocognitive processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
59.
This paper is motivated by the performance evaluation of circulating vertical conveyor systems (CVCSs). CVCSs are bulk queues of transportation type. These material handling systems feature generally distributed inter-arrival times, which can be longer than the bulk service time. This leads to interdependencies between the number of arrivals in consecutive service intervals and the number of loads in the queue. We propose a new discrete-time approach for the steady-state analysis of such bulk service queues of transportation type with general arrival and service processes and finite server and limited queue capacities. The approach is based on a finite Markov chain that generates complete probability distributions for the key performance measures, including the queue length, waiting time and departing batch size. The proposed approach is exact in the cases of discrete-time slots, e.g. as in communication systems. We investigate the discretisation error that arises if the approach is used as an approximation for the continuous time using a numerical comparison to a discrete-event simulation. Moreover, we examine the impact of arrival stream variability on the system performance and compare the positive effects of a higher frequency of server visits with the effects arising from larger pickup capacities. 相似文献
60.
Arild Hoff Henrik Andersson Marielle Christiansen Geir Hasle Arne Løkketangen 《Computers & Operations Research》2010,37(12):2041-2061
The purpose of this paper is to describe industrial aspects of combined fleet composition and routing in maritime and road-based transportation, and to present the current status of research in the form of a comprehensive literature review. First, presents a classification of problems, and then focuses on a basic definition of combined fleet composition and routing: the fleet size and mix vehicle routing problem. A basic mathematical formulation from the literature is presented. Further, the literature of extended and related problems is described and categorized. Surveys of application oriented research in road-based and maritime transportation conclude the review. Finally, we contrast the literature with aspects of industrial applications from a critical, but constructive stance. Major issues for future work are suggested. 相似文献