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91.
For agriculturally used areas, which are contaminated by the debris from a nuclear accident, the use of chemical amendmends (e.g. potassium chloride and lime) is among the most common soil-based countermeasures. These countermeasures are intended to reduce the plant uptake of radionuclides (mainly 137Cs and 90Sr) by competitive inhibition by chemically similar ions. So far, the impacts of countermeasures on soil solution composition - and thus, their effectiveness - have almost exclusively been established experimentally, since they depend on mineral composition and chemical characteristics of the soil affected. In this study, which focuses on caesium contamination, the well-established code PHREEQC was used as a geochemical model to calculate the changes in the ionic compositions of soil solutions, which result from the application of potassium or ammonium in batch equilibrium experiments. The simple ion exchange model used by PHREEQC was improved by taking into account selective sorption of Cs+, NH4+ and K+ by clay minerals. Calculations were performed with three different initial soil solution compositions, corresponding to particular soil types (loam, sand, peat). For loamy and sandy soils, our calculational results agree well with experimental data reported by Nisbet (Effectiveness of soil-based countermeasures six months and one year after contamination of five diverse soil types with caesium-134 and strontium-90. Contract Report NRPB-M546, National Radiation Protection Board, Chilton, 1995.). For peat, discrepancies were found indicating that for organic soils a reliable set of exchange constants of the relevant cations still has to be determined experimentally. For cesium, however, these discrepancies almost disappeared if selective sites were assumed to be inaccessible. Additionally, results of sensitivity analyses are presented by which the influence of the main soil parameters on Cs+ concentrations in solution after soil treatment has been systematically studied. It is shown that calculating the impacts of soil-based chemical countermeasures on soil solution chemistry using geochemical codes such as PHREEQC offers an attractive alternative to establishing these impacts by often time-consuming and site-specific experiments. 相似文献
92.
Quang Huy Nguyen Claude Kirchner Hélène Kirchner 《Journal of Automated Reasoning》2002,29(3-4):309-336
This paper presents the design, the implementation, and experiments of the integration of syntactic, conditional possibly associative-commutative term rewriting into proof assistants based on constructive type theory. Our approach is called external because it consists in performing term rewriting in a specific and efficient environment and checking the computations later in a proof assistant. Two typical systems are considered in this work: ELAN, based on the rewriting calculus, as the term rewriting-based environment, and Coq, based on the calculus of inductive constructions as the proof assistant. We first formalize the proof terms for deduction by rewriting and strategies in ELAN using the rewriting calculus with explicit substitutions. We then show how these proof terms can soundly be translated into Coq syntax where they can be directly type checked. For the method to be applicable for rewriting modulo associativity and commutativity, we provide an effective method to prove equalities modulo these axioms in Coq using ELAN. These results have been integrated into an ELAN-based rewriting tactic in Coq. 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.
HP Grocott ND Croughwell DW Amory WD White JL Kirchner MF Newman 《Canadian Metallurgical Quarterly》1998,65(6):1645-9; discussion 1649-50
BACKGROUND: The glial protein S100beta has been used to estimate cerebral damage in a number of clinical settings. The purpose of this investigation was to determine the correlation between cerebral microemboli and S100beta levels during cardiac operations. METHODS: Transcranial Doppler ultrasonography was used to measure emboli in the right middle cerebral artery. Emboli counts (n = 111) were divided into five time periods: (1) incision to aortic cannulation; (2) aortic cannulation to cross-clamp onset; (3) cross-clamp onset to cross-clamp release; (4) cross-clamp release to decannulation; and (5) decannulation to chest closure. The level of S100beta (n = 156) was measured at baseline, at the end of cardiopulmonary bypass, then 150 and 270 minutes after cross-clamp release. RESULTS: The level of S100beta correlated with age, cardiopulmonary bypass time, cross-clamp time, and number of emboli at time period 2. Although cardiopulmonary bypass time was univariately associated with S100beta level, it became nonsignificant in a multivariable model that included age and cross-clamp time. CONCLUSIONS: The correlation of S100beta level with emboli measured during cannulation (time period 2) supports the hypothesis that cannulation is a high-risk time period for cerebral injury. 相似文献
99.
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
100.
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