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61.
François Chapeau-Blondeau Christian Jeanguillaume 《Journal of Mathematical Imaging and Vision》2014,49(2):467-480
For photon emission tomography, the maximum likelihood (ML) estimator for image reconstruction is generally solution to a nonlinear equation involving the vector of measured data. No explicit closed-form solution is known in general for such a nonlinear ML equation, and numerical resolution is usually implemented, with a very popular iterative method formed by the expectation-maximization algorithm. The numerical character of such resolutions usually makes it difficult to obtain a general characterization of the performance of the ML solution. We show that the nonlinear ML equation can be replaced by an equivalent system of two dual linear equations nonlinearly coupled. This formulation allows us to exhibit explicit (to some extent) forms for the solutions to the ML equation, in general conditions corresponding to the various possible configurations of the imaging system, and to characterize their performance with expressions for the mean-squared error, bias and Cramér-Rao bound. The approach especially applies to characterize the ML solutions obtained numerically, and offers a theoretical framework to contribute to better appreciation of the capabilities of ML reconstruction in photon emission tomography. 相似文献
62.
Alper Sarıoğlan Ömer Tunç Savaşçı Ayşe Erdem-Şenatalar Vu Thu Ha Gilbert Sapaly Younès Ben Taârit 《Catalysis Letters》2007,118(1-2):123-128
MFI type inorganic carrier was used in two different cationic forms, hydrogen and calcium respectively. MFI-supported molybdenum
and rhenium catalysts were prepared. The activities of the catalysts were compared for the aromatization reaction of methane.
Higher activity values were attained with the catalysts supported on HZSM-5. Aromatics were also observed with the catalysts
supported on CaZSM-5, despite their deficiency in acid sites. Highly dispersed rhenium is expected to be formed with the use
of the inorganic carrier in calcium form. On the other hand, lower reaction rates were observed with rhenium supported on
CaZSM-5, in spite of the improved dispersion of the active rhenium species on this catalyst. This was interpreted in terms
of the critical role of the acid sites in the conversion of methane to aromatics, compared to the improved dispersion of the
active metal. 相似文献
63.
André Lourenço Hugo Plácido da Silva Carlos Carreiras Ana Priscila Alves Ana L. N. Fred 《Multimedia Tools and Applications》2014,70(1):433-460
With the advent of wearable sensing and mobile technologies, biosignals have seen an increasingly growing number of application areas, leading to the collection of large volumes of data. One of the difficulties in dealing with these data sets, and in the development of automated machine learning systems which use them as input, is the lack of reliable ground truth information. In this paper we present a new web-based platform for visualization, retrieval and annotation of biosignals by non-technical users, aimed at improving the process of ground truth collection for biomedical applications. Moreover, a novel extendable and scalable data representation model and persistency framework is presented. The results of the experimental evaluation with possible users has further confirmed the potential of the presented framework. 相似文献
64.
Hiba Messaoudi Fayçal Djazi Mohamed Litim Bahadır Keskin Maamar Slimane Djillali Bekhiti 《Journal of Adhesion Science and Technology》2020,34(20):2216-2244
AbstractCorrosion inhibitors based on environmentally friendly and harmless products are currently being studied and developed. The corrosion inhibition properties of caffeine (1,3,7-trimethylxanthine) on copper corrosion in aqueous chloride solution (3.5?wt.% NaCl) are analysed here using stationary and transient electrochemical methods, and a theoretical study based on density functional theory is carried out. Caffeine is a very competitive compared to the chemical inhibitors that are often used for copper protection. Electrochemical and impedance experiments reveal that the protective efficiency of caffeine reaches a value of 96% at a concentration of 10?2?mol L?1. Based on these results, the Langmuir model appears to be the best representation of the adsorption of caffeine onto the copper surface. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy and X-ray diffraction (XRD) were used to determine the surface morphology and the chemical composition of the copper surface in chloride media, in the absence and presence of caffeine. The results show the development of a mechanism of corrosion inhibition. In order to confirm the correlation between the inhibitory effect and the molecular structure of caffeine, quantum chemical parameters are used to calculate its electronic properties. 相似文献
65.
Claude Leger Lucie Fremont Didier Marion Ibrahim Nassour Marie-Françoise Desfarges 《Lipids》1981,16(8):593-600
This paper describes evidence of (n−3) and particularly of 22∶6 (n−3) fatty acid enrichment in trout lipoproteins as well
as in vitellogenin, egg lipovitellin and oil globule. Among the lipoproteins, HDL and LDL were the main forms of blood lipid
transport, whereas phospholipids and cholesteryl esters are the preferential chemical carriers for (n−3) fatty acid transport.
However, cholesteryl esters were less important as esterified fatty acid carriers than in man. Taken together with the data
obtained in mammals, our results suggest that there may be a relationship between EFA activity and the distribution of the
EFA among the lipoprotein lipid fractions in vertebrates, irrespective of the EFA series. Administration of an (n−3) fatty
acid deficient diet for three months prior to trout spawning produced a significant increase in egg lipid content, primarily
as a result of the increase of the oil globule composed almost exclusively of triacylglycerols. This diet decreased the 22∶6
(n−3), as well as the (n−3) fatty acid contents of lipoproteins, lipovitellin, vitellogenin and the oil globule. In contrast,
the (n−3) fatty acid level was always higher in lipoproteins and lipovitellin than in the vitellogenin and the oil globule.
Moreover, the relative levels of 22∶6 (n−3) and total (n−3) fatty acids were quite similar in lipoproteins and lipovitellin
on the one hand, and in vitellogenin and the oil globule on the other. These findings suggest a direct relationship between
the two forms of plasma lipid transport and the two egg compartments. During ovogenesis, dietary lipids seemed to be diverted
from the adipose tissue and essentially deposited in the egg. 相似文献
66.
An acid-activated clay (Çanakkale montmorillonite from Turkey) was used to adsorb chlorophyll from hexane solutions. The phenomenon seems to be mainly driven by the interaction of chlorophyll with acid sites. The adsorption of chlorophyll on Brönsted acid sites was indicated by a characteristic infrared band for the -OH group at 3671 cm?1. The variations in the structure of clay mineral and chlorophyll during adsorption have been examined by differential thermal analysis, thermogravimetry and infrared spectroscopy of the activated clay before and after adsorption of chlorophyll. Oxidation of adsorbed chlorophyll was completed at quite a high temperature. 相似文献
67.
本文介绍一种新型气相色谱固定相——碳分子筛(KMS),其最大的优点是在常温下,单柱即可同时分离分析H_2、O_2、N_2、CO、CH_4、CO_2六种混合气体,柱子的保留值重现性好,峰形对称,柱效高。本文求得了在H_2和Ar作载气时KMS对上述六种气体的定性定量特性,配气的定量结果总的平均相对误差为3.67%。同时这种碳分子筛原料易得,制作简单,成本便宜。 相似文献
68.
69.
案例教学法在高校思想政治理论课中的运用,不仅有利于激发学生的学习兴趣,而且促进提高了思想政治理论课的教学效果.随着高校思想政治理论课教学的新一轮改革,从心理层面研究近因效应、名人效应、超限效应、共生效应、罗森塔尔效应、感动效应在思想政治理论课案例教学中的作用,并在实践中加以运用,是进一步提高思想政治理论课教学实效性的重要路径. 相似文献
70.
Yassine Slimani Sagar E. Shirsath Essia Hannachi Munirah A. Almessiere Moustafa M. Aouna Nouf E. Aldossary Ghulam Yasin Abdulhadi Baykal Bekir Ozçelik Ismail Ercan 《Journal of the American Ceramic Society》2021,104(11):5648-5658
Two phase-based nanocomposites consisting of dielectric barium titanate (BaTiO3 or BTO) and magnetic spinel ferrite Co0.5Ni0.5Nb0.06Fe1.94O4 (CNNFO) have been synthesized through solid state route. Series of (BaTiO3)1-x + (Co0.5Ni0.5Nb0.06Fe1.94O4)x nanocomposites with x content of 0.00, 0.25, 0.50, 0.75, and 1.00 were considered. The structure has been examined via X-rays diffraction (XRD) and indicated the occurrence of both perovskite BTO and spinel CNNFO phases in various nanocomposites. A phase transition from tetragonal BTO structure to cubic structure occurs with inclusion of CNNFO phase. The average crystallites size of BTO phase decreases, whereas that for the CNNFO phase increases with increasing x in various nanocomposites. The morphological observations revealed that the porosity is highly reduced, and the connectivity between grains is enhanced with increasing x content. The optical properties have been investigated by UV−vis diffuse reflectance spectroscopy. The deduced band gap energy (Eg) value is found to reduce with increasing the content of spinel ferrite phase. The magnetic as well as the dielectric properties were also investigated. The analysis showed that CNNFO ferrite phase greatly affects the magnetic properties and dielectric response of BTO material. The obtained findings can be useful to enhance the performances of magneto-dielectric composite-based systems. 相似文献