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91.
C.P. Marcel M. Rohde V.P. Masson T.H.J.J. Van der Hagen 《International Journal of Heat and Mass Transfer》2009,52(21-22):5046-5054
The use of supercritical water as coolant/moderator may induce oscillations in the supercritical light water reactor similar to the density wave oscillations observed in boiling water reactors (BWRs). In order to experimentally investigate the stability of supercritical reactors, a fluid-to-fluid downscaled facility is proposed. It is found that with an appropriate mixture of refrigerants R-125 and R-32, the dimensionless enthalpy and density of the supercritical water can be accurately matched for all relevant operational conditions of the reactor. Moreover, the inertia distribution, the friction factor distribution and the heat transfer mechanism are taken into account in the modeling. As a result of the proposed downscaling, the operational pressure, temperature and power are considerably smaller than those of a water-based system, which in turn helps reducing the construction and operational costs of a test facility. Finally, it is found that the often used modeling fluid supercritical CO2 cannot accurately represent supercritical water at reactor conditions. 相似文献
92.
Tjeerd A. L. Snoeren Remco M. P. Van Poecke Marcel Dicke 《Journal of chemical ecology》2009,35(9):1021-1031
The oxylipin pathway is commonly involved in induced plant defenses, and is the main signal-transduction pathway induced by
insect folivory. Herbivory induces the production of several oxylipins, and consequently alters the so-called ‘oxylipin signature’
in the plant. Jasmonic acid (JA), as well as pathway intermediates are known to induce plant defenses. Indirect defense against
herbivorous insects comprises the production of herbivore-induced plant volatiles (HIPVs). To unravel the precise oxylipin
signal-transduction underlying the production of HIPVs in Arabidopsis thaliana and the resulting attraction of parasitoid wasps, we used a multidisciplinary approach that includes molecular genetics,
metabolite analysis, and behavioral analysis. Mutant plants affected in the jasmonate pathway (18:0 and/or 16:0 -oxylipin
routes; mutants dde2-2, fad5, opr3) were studied to assess the effects of JA and its oxylipin intermediates 12-oxo-phytodienoate (OPDA) and dinor-OPDA (dnOPDA)
on HIPV emission and parasitoid (Diadegma semiclausum) attraction. Interference with the production of the oxylipins JA and OPDA altered the emission of HIPVs, in particular terpenoids
and the phenylpropanoid methyl salicylate, which affected parasitoid attraction. Our data show that the herbivore-induced
attraction of parasitoid wasps to Arabidopsis plants depends on HIPVs that are induced through the 18:0 oxylipin-derivative
JA. Furthermore, our study shows that the 16:0-oxylipin route towards dnOPDA does not play a role in HIPV induction, and that
the role of 18:0 derived oxylipin-intermediates, such as OPDA, is either absent or limited. 相似文献
93.
Multimodal Video Indexing: A Review of the State-of-the-art 总被引:5,自引:7,他引:5
Efficient and effective handling of video documents depends on the availability of indexes. Manual indexing is unfeasible for large video collections. In this paper we survey several methods aiming at automating this time and resource consuming process. Good reviews on single modality based video indexing have appeared in literature. Effective indexing, however, requires a multimodal approach in which either the most appropriate modality is selected or the different modalities are used in collaborative fashion. Therefore, instead of separately treating the different information sources involved, and their specific algorithms, we focus on the similarities and differences between the modalities. To that end we put forward a unifying and multimodal framework, which views a video document from the perspective of its author. This framework forms the guiding principle for identifying index types, for which automatic methods are found in literature. It furthermore forms the basis for categorizing these different methods. 相似文献
94.
95.
Roberto Hirata Junior Marcel Brun Junior Barrera Edward R. Dougherty 《Journal of Mathematical Imaging and Vision》2002,16(3):199-222
The design of an aperture operator is based on adequately constraining the spatial domain and the graylevel range in order to diminish the space of operators and, consequently, the estimation error. The design of a resolution constrained operator is based on adequately combining information from two or more different resolutions and has the same motivation, that is, diminish the space of operators to facilitate design. This paper joins these approaches and studies multiresolution design of aperture operators for grayscale images. Spatial resolution constraint, range resolution constraint and the combination of both constraints are characterized, and the error increase by using the constrained filter in place of the optimal unconstrained one is analyzed. Pyramidal multiresolution design involves applying the resolution constraint approach hierarchically, from the higher to the lower resolution space. These approaches are also characterized and their error increase analyzed. The system that has been implemented to design pyramidal multiresolution operators is described and has its complexity (memory and runtime) analyzed. Several simulations and two applications for deblurring are shown and compared to optimal linear filters. The results confirm the usefulness of the approach. 相似文献
96.
Although particle detachment is a common phenomenon associated with most tribological processes, it seldom occurs that each piece of elemental debris can be considered as the result of a single event. Such an association has been revealed by the systematic study of a specific system, where a pin of graphite is made to rub against thoroughly polished steel. While the discontinuous nature of the transfer film allows a quantitative assessment of the volume of transfer h
e to be made by 3D optical-profilometry, the linear dependence of the rate of particle detachment dh
e/dn (n=number of rubbing cycles) with the logarithm of sliding speed v strongly suggests the existence of a particular type of stick–slip, where each stick may lead to the detachment of a debris particle. The variations in size of these debris with environment as revealed by AFM, further suggest that the global rate of particle detachment is of the form: dh
e/dn=Nx
i
, where N is the number of stick–slip events per rubbing cycle, x the proportion of stick events leading to a cohesive rupture, and
i
the mean volume of an elemental particle. While this relation is apparently supported by most experimental results, its actual validation can only be made by experiments at the level of single (nanoscale) asperities, carried out under well-controlled experimental conditions. 相似文献
97.
Summary The evolution of scientific fields analyzed by co-word analysis and presented in strategic diagrams is simulated based on
the law of cumulative advantages - the probability of a new tie between two keywords depends positively on the frequencies
in which both keywords have taken part already. The results we get from simulations are compared with the results of real
scientific field evolution. We consider the high correspondence of both to be a proof of the working of the law of cumulative
advantages in the development of scientific fields and we believe that our research opens new possibilities for predictions
of the development of scientific fields. 相似文献
98.
Roland Guérin El Houssine El Ghadraoui Jean-Yves Pivan Jean Padiou Marcel Sergent 《Materials Research Bulletin》1984,19(10):1257-1270
Two new compounds Ni12Zr2P7 and Ni20Zr6P13 were synthesized in the NiZrP system by reacting the constituent elements. Ni12Zr2P7 is of the Fe12Zr2P7-type while Ni20Zr6P13 appears as a new structural type in the chemistry of transition metal phosphides. Its unit cell is hexagonal with space group P6̄ and contains one formula unit. The X-ray structure was studied from three-dimensional single-crystal counter data and was refined down to R = 0.040 for 221 independent reflections. The structure of Ni20Zr6P13 can be described as built up by two groups of three phosphorus trigonal prisms occupied by the zirconium atoms. In each group, the |ZrP6| prisms are linked together by common edges in order to generate triangular phosphorus sites occupied by nickel atoms. In addition, nickel atoms are also in tetrahedral and square-planar pyramidal phosphorus sites. A comparative study with the Fe2P- and Co4Hf2P3-type structures having the same metal/non metal ratio as in Ni12Zr2P7 and Ni20Zr6P13 is also discussed. A nearly temperature independent paramagetism and a metallic conduction deducted from magnetic and electrical measurements exhibit the metallic behavior for these new compounds. 相似文献
99.
New halide glasses based on cadmium halides as glass progenitors have been discovered. This paper describes fluoride glasses in the CdF2-BaF2-ZnF2 ternary system. Binary glasses CdxBa1?xF2 (0.45 < x < 0.52) have been obtained. The limits of the glassy area are: 5–55 % CdF2, 15–55 % BaF2, 0–60 % ZnF2. Numerous fluorides such as the alkali fluorides, AlF3, YbF3 and ThF4 may be included in the glass composition. Only thin glass samples may be prepared because of the high crystallization rate. The characteristic temperatures of the Cd0.3Ba0.4Zn0.3F2 glass are 290° C for TG, 330° C for TC and 620° C for TF. The optical transmission spectrum of a thin sample shows an extrinsic absorption band at around 9000 nm and the multiphonon IR absorption edge beyond 10500 nm. The optimization of these glasses will make them attractive materials for IR transmittance and IR optical fibres. The crystallization of the Cd0.5Ba0.5F2 glass results in two solid solutions Ba1?xCdxF2 and Cd1?xBaxF2 deriving from the fluorite structural type. Thus, cadmium fluoride glasses appear as the result of the disordering of the fluorite type structure in the same way as ZrF4-based glasses derive from the disordering of the ReO3-type structure. Both glasses may be described as the random insertion of cations into an aperiodic array of F? anions. 相似文献
100.
Hiscock Merrill; Kinsbourne Marcel; Caplan Bruce; Swanson James M. 《Canadian Metallurgical Quarterly》1979,88(1):27
Administered dichotic digit tasks requiring free report and selective listening, respectively, to 20 6–16 yr old hyperactive children. Ss received methylphenidate before 2 experimental sessions and a placebo before 2 control sessions. The stimulant did not improve free-report performance significantly; rather it facilitated or impaired performance, depending on how it affected the order in which stimuli were reported. Similarly, medication had no effect on overall selective-listening performance, but it increased the difficulty of switching attention from one ear to the other. Results demonstrate that stimulants may act to maintain selective attention and to inhibit channel switching. Listening asymmetry, that is, right-ear superiority, was influenced by task variables but not by stimulant medication. (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献