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The investigation of phase transformations in metastable ceramic systems such as zirconia often requires local phase analysis within the areas of interest. Electron backscatter diffraction is a suitable method in combination with focused ion beam sample preparation. The interaction between ion beam and sample has to be carefully considered. In case of metastable Y-PSZ and Mg-PSZ, phase transformations were observed after FIB preparation with 30?kV, 30?nA and 5° incidence angle. Damage was the dominating effect for angles of 72°. The expected local temperature increase due to the ion bombardment with 30?kV and 30?nA is 700?K for ZrO2. Thus, the observed phase transformations can be explained on the basis of the temperature increase in the corresponding Y-PSZ phase diagram. In case of Mg-PSZ, the transition temperature is 1083?°C. The local temperature increase was obviously lower. The excitation energy for the observed phase transformation was smaller than expected from the phase diagrams of the thermodynamic equilibrium. Using 5?kV, 4.8?nA and 5° incidence angle, no phase transformations and no damage were observed. Thus, these conditions are well suited for the FIB preparation of metastable zirconia. 相似文献
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Yachao Dong Christos T. Maravelias Norman F. Jerome 《Optimization and Engineering》2018,19(4):937-976
We study a maritime inventory routing problem, in which shipments between production and consumption nodes are carried out by a fleet of vessels. The vessels have specific capacities and can be chartered under different agreements. The inventory levels of all consumption nodes and some production nodes should be maintained within specified bounds; for the remaining production nodes, orders should be picked up within pre-defined time windows. We propose a discrete-time mixed-integer programming model. In the face of new information and uncertainty, this optimization model has to be re-solved, as the horizon is rolled forward. We discuss how to account for different sources of uncertainty. We present a rolling-horizon reoptimization framework that allows us to study different policies that impact the quality of the implemented solution, so we can identify the optimal set of policies. 相似文献
5.
Christos Theoharatos Apostolos Ifantis Nikolaos A. Laskaris George Economou 《Computers & Geosciences》2008,34(6):625-634
An exploratory data analysis (EDA) framework was developed in order to investigate the presence of possible correlations in the long-term geoelectric potential (LTGP) signal, prior to significant seismic events in Western Greece. Experimental data, which had been collected continuously within a 6-year period (1998–2003) at the earthquake signal-acquisition center of the University of Patras Seismological Laboratory (UPSL), were studied. The multidimensional scaling (MDS) technique was used to detect putative clustering tendencies in the ensemble of time-series (TS) segments that could indicate the existence of a possible correlation between the geoelectric signal structure and the impending seismic activity. The end result is a 2-dimensional point diagram with the geometry reflecting important signal characteristics, directly related with the underlying seismic events. In addition, the “appending technique”, a well-suited data analysis methodology was incorporated as a means of relating any other TS segment directly with the pre-computed, via the MDS, point diagram. Using the proposed EDA framework, we examined the presence of similar temporal patterns in the recorded geoelectric TS field, 10 days before the occurrence of the major earthquakes. The presented experimental results indicated clearly the validity of the introduced approach and, further, motivated the use of such advanced visualization schemes for charting precursor trends of significance seismicity. 相似文献
6.
Christos Bouras Agisilaos Konidaris 《International Journal of Communication Systems》2005,18(2):119-142
Redundant data transfers over the Web, can be mainly attributed to the repeated transfers of unchanged data. Web caches and Web proxies are some of the solutions that have been proposed, to deal with the issue of redundant data transfers. In this paper we focus on the efficient estimation and reduction of redundant data transfers over the Web. We first prove that a vast amount of redundant data is transferred in Web pages that are considered to carry fresh data. We show this by following an approach based on Web page fragmentation and manipulation. Web pages are broken down to fragments, based on specific criteria. We then deal with these fragments as independent constructors of the Web page and study their change patterns independently and in the context of the whole Web page. After the fragmentation process, we propose solutions for dealing with redundant data transfers. This paper has been based on our previous work on ‘Web Components’ but also on related work by other researchers. It utilises a proxy based, client/server architecture, and imposes changes to the algorithms executed on the Proxy server and on clients. We show that our proposed solution can considerably reduce the amount of redundant data transferred on the Web. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
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Abstract. In this paper we refer to the Temporal Precedence Problem on Pure Pointer Machines . This problem asks for the design of a data structure, maintaining a set of stored elements and supporting the following
two operations: insert and precedes . The operation insert (a) introduces a new element a in the structure, while the operation precedes (a,b) returns true iff element a was inserted before element b temporally. In [11] a solution was provided to the problem with worst-case time complexity O (log log n ) per operation and O(n log log n) space, where n is the number of elements inserted. It was also demonstrated that the precedes operation has a lower bound of Ω (log log n ) for the Pure Pointer Machine model of computation. In this paper we present two simple solutions with linear space and worst-case constant insertion
time. In addition, we describe two algorithms that can handle the precedes (a,b) operation in O (log log d ) time, where d is the temporal distance between the elements a and b . 相似文献
8.
Christos C. Agrafiotis Chrysoula Pagkoura Souzana Lorentzou Margaritis Kostoglou Athanasios G. Konstandopoulos 《Catalysis Today》2007,127(1-4):265-277
The present work summarizes the recent activities of our laboratory in the field of solar-aided hydrogen production with structured monolithic solar reactors. This reactor concept, “transferred” from the well-known automobile exhaust catalytic after-treatment systems, employs ceramic supports optimized to absorb effectively solar radiation and develop sufficiently high temperatures, that are coated with active materials capable to perform/catalyze a variety of “solar-aided” reactions for the production of hydrogen such as water splitting or natural gas reforming. Our work evolves in an integrated approach starting from the synthesis of active powders tailored to particular hydrogen production reactions, their deposition upon porous absorbers, testing of relevant properties of merit such as thermomechanical stability and hydrogen yield and finally to the design, operation simulation and performance optimization of structured monolithic solar hydrogen production reactors. This approach, among other things, has culminated to the world's first closed, solar-thermochemical cycle in operation that is capable of continuous hydrogen production employing entirely renewable and abundant energy sources and raw materials – solar energy and water, respectively – without any CO2 emissions and holds, thus, a significant potential for large-scale, emissions-free hydrogen production, particularly for regions of the world that lack indigenous resources but are endowed with ample solar energy. 相似文献
9.
Makris Angela P.; Rush Craig R.; Frederich Robert C.; Taylor Alisia C.; Kelly Thomas H. 《Canadian Metallurgical Quarterly》2007,15(2):123
Modafinil is indicated for the management of excessive daytime sleepiness; however, recent studies have examined a broad range of potential uses. Given that clinical uses of modafinil may be expanding, this study compared modafinil and d-amphetamine effects on subjective and performance measures. Across 11 sessions, 11 healthy adults were tested after oral doses of placebo (5 sessions), modafinil (1.75 mg/kg, 3.50 mg/kg, or 7.00 mg/kg), and d-amphetamine (0.035 mg/kg, 0.070 mg/kg, 0.140 mg/kg) under double-blind, randomized conditions. Assessments of cognitive performance and subjective effects were completed before drug administration, 30 min after drug administration, and at hourly intervals after drug administration for 5 hr. Modafinil increased ratings on the Amphetamine and Morphine Benzedrine Group scales of the Addiction Research Center Inventory (ARCI) and increased ratings on the Vigor and Total Positive scales of the Profile of Mood States. d-Amphetamine increased visual analog ratings of feeling stimulated and liking the drug and increased ratings on the Morphine Benzedrine Group scale of the ARCI. Both medications significantly reduced visual analog scale ratings of feeling sleepy, and modafinil decreased ratings on the ARCI Pentobarbital-Chlorpromazine-Alcohol Group scale. Both medications sustained performance that deteriorated across time on the Sternberg Number Recognition Test. Modafinil also enhanced performance rate on the Digit-Symbol Substitution Task above baseline levels and increased response rate on the Repeated Acquisition of Response Sequences Task. These results suggest that modafinil engenders alerting effects and increases performance in healthy non-sleep-deprived individuals comparable with that of d-amphetamine. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
10.
The authors examined students' understanding of hypotheses as beliefs that can be empirically verified. Thirty second graders and 30 sixth graders considered cases of disagreement about foods and colors that reflected either alternative hypotheses or different preferences. Their task was to decide whether the validity of each expressed belief could be determined and to justify their decision. Younger students considered both hypotheses and preferences as empirically verifiable, whereas older students were better able to recognize in some cases that preferences are legitimately variable. This lack of distinction may reflect limited metaconceptual ability or a deterministic epistemological view, both of which might interfere with the understanding of the hypothesis-testing process. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献