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51.
Ikonen P.M.T. Saenz E. Gonzalo R. Tretyakov S.A. 《Antennas and Propagation, IEEE Transactions on》2007,55(10):2692-2700
We study the characteristics and radiation mechanism of antenna superstrates based on closely located periodical grids of loaded wires. An explicit analytical method based on the local field approach is used to study the reflection and transmission properties of such superstrates. It is shown that as a result of proper impedance loading there exists a rather wide frequency band over which currents induced to the grids cancel each other, leading to a wide transmission maximum. In this regime radiation is produced by the magnetic dipole moments created by circulating out-of-phase currents flowing in the grids. An impedance matrix representation is derived for the superstrates, and the analytical results are validated using full-wave simulations. As a practical application example we study numerically the radiation characteristics of dipole antennas illuminating finite-size superstrates. 相似文献
52.
Ultrasound image segmentation with shape priors: application to automatic cattle rib-eye area estimation. 总被引:1,自引:0,他引:1
Pablo Arias Alejandro Pini Gonzalo Sanguinetti Pablo Sprechmann Pablo Cancela Alicia Fernández Alvaro Gómez Gregory Randall 《IEEE transactions on image processing》2007,16(6):1637-1645
Automatic ultrasound (US) image segmentation is a difficult task due to the quantity of noise present in the images and the lack of information in several zones produced by the acquisition conditions. In this paper, we propose a method that combines shape priors and image information to achieve this task. In particular, we introduce knowledge about the rib-eye shape using a set of images manually segmented by experts. A method is proposed for the automatic segmentation of new samples in which a closed curve is fitted taking into account both the US image information and the geodesic distance between the evolving curve and the estimated mean rib-eye shape in a shape space. This method can be used to solve similar problems that arise when dealing with US images in other fields. The method was successfully tested over a database composed of 610 US images, for which we have the manual segmentations of two experts. 相似文献
53.
54.
Edgar Chávez José L. Marroquín Gonzalo Navarro 《Multimedia Tools and Applications》2001,14(2):113-135
Pivot-based algorithms are effective tools for proximity searching in metric spaces. They allow trading space overhead for number of distance evaluations performed at query time. With additional search structures (that pose extra space overhead) they can also reduce the amount of side computations. We introduce a new data structure, the Fixed Queries Array (FQA), whose novelties are (1) it permits sublinear extra CPU time without any extra data structure; (2) it permits trading number of pivots for their precision so as to make better use of the available memory. We show experimentally that the FQA is an efficient tool to search in metric spaces and that it compares favorably against other state of the art approaches. Its simplicity converts it into a simple yet effective tool for practitioners seeking for a black-box method to plug in their applications. 相似文献
55.
Pilar Manglano María Jesús Lagarda María Dolores Silvestre Carmen Vidal Gonzalo Clemente Rosaura Farr 《European Journal of Lipid Science and Technology》2005,107(11):815-823
A study is made of the effects of storage (time and temperature) on the lipid fraction of four milk‐based adapted infant formulas with basically the same composition, though differing in the iron salt added (lactate or sulfate) and/or the vitamin E source (α‐tocopherol or α‐tocopherol acetate). Peroxide value, hydroperoxide C18 percentage and thiobarbituric acid‐reactive substance (TBARS) content were used as indicators of lipid peroxidation. Fat contents remained stable throughout storage. Peroxide values increased from the first storage month and were affected by storage time, although they exhibited irregular behavior. Storage time and temperature affected hydroperoxide percentage, which was seen to be the earliest indicator of lipid oxidation, being measurable in newly manufactured formulas. TBARS values were only affected by storage time. No statistically significant differences were found among the four infant formulas for any of the lipid oxidation indicators. 相似文献
56.
Al films, 80–85 nm in thickness and 10–30 μΩ cm in resistivity, are coated with Pd (8–40 nm). The bilayer is exposed to a hydrogen atmosphere of up to 4.0 kPa. The hydrogen concentration is calculated from the frequency change in a quartz crystal microbalance and the electrical resistance of the Pd film, the Al film and the bilayer is measured as function of hydrogen pressure. Concentration and resistance measurements indicate that the Pd coating enables the Al films to absorb hydrogen from the gas phase. 相似文献
57.
Emma OrtizIslas María Elena ManríquezRamírez Amarilis SosaMuoz Paola Almaguer Carlos Arias Patricia Guevara Gonzalo HernndezCortez Ma. Lucinda AguirreCruz 《IET nanobiotechnology / IET》2020,14(3):191
In the present work, the preparation, characterisation, and efficiency of two different silica nanostructures as release vehicles of Cisplatin are reported. The 1‐hexadeciltrimethyl‐ammonium bromide templating agent was used to obtain mesoporous silica nanoparticles which were later loaded with Cisplatin. While sol–gel silica was very fast prepared using an excess of acetic acid during the hydrolysis–condensation reactions of tetraethylorthosilicate and at the same time the Cisplatin was added. Several physicochemical techniques including spectroscopies, electronic microscopy, X‐ray diffraction, N2 adsorption–desorption were used to characterise the silica nanostructures. An in vitro Cisplatin release test was carried out using artificial cerebrospinal fluid. Finally, the toxicity of all silica nanostructures was tested using the C6 cancer cell line. The spectroscopic results showed the suitable stabilisation of Cisplatin into the two different silica nanostructures. A large surface area was obtained for the mesoporous silica nanoparticles, while low areas were obtained in the silica nanoparticles. Cisplatin was released faster from mesoporous silica channels than from inside of aggregates nanoparticles silica. Cisplatin alone, as well as, cisplatin released from both silica nanostructures exerted a toxic effect on cancer cells. In contrast, both silica structures without the drug did not exert any toxic effect.Inspec keywords: cellular biophysics, desorption, adsorption, biomedical materials, sol‐gel processing, silicon compounds, cancer, toxicology, nanofabrication, brain, condensation, mesoporous materials, nanoparticles, X‐ray diffraction, nanomedicine, drugs, aggregates (materials)Other keywords: mesoporous silica channels, silica‐based nanoparticles, cancer brain cells, silica nanostructures, 1‐hexadeciltrimethyl‐ammonium bromide, mesoporous silica nanoparticles, sol‐gel silica, C6 cancer cell line, in vitro cisplatin release test, C6 cancer cell line, acetic acid, hydrolysis‐condensation reactions, tetraethylorthosilicate, physicochemical techniques, electronic microscopy, X‐ray diffraction, N2 adsorption‐desorption, artificial cerebrospinal fluid, toxicity, toxic effect, N2 , SiO2 相似文献
58.
Local and global electrochemical impedances applied to the corrosion behaviour of an AZ91 magnesium alloy 总被引:1,自引:0,他引:1
The electrochemical behaviour of an AZ91 magnesium alloy was investigated in a low aggressive medium by means of local and global electrochemical impedance measurements. The results were compared to those obtained on a pure magnesium sample. It was possible to show the individual contribution of each phase constituting the alloy, and it was observed that the corrosion mechanism of the two phases was the same, controlled by the Mg dissolution. However, local impedance diagrams clearly indicated that the kinetics dissolution of the β-phase was slower than that of the α-phase, which was in good agreement with SEM observations. 相似文献
59.
The Reynolds number is interpreted as the ratio of phase volumes for the macroscopic and microscopic motions of molecules. Effect of the second virial coefficient on the critical Reynolds number was predicted and experimentally verified. The measurements were performed in a Hagen-Poiseuille flow of several gases (He, Ne, Ar, Kr, Xe, N2, CO2, and SF6). 相似文献
60.
Comments on the special issue of the American Psychologist (2000[Jan], Vol 55[1]) on positive psychology. The author points out that in this special issue the perspectives of psychologists of color were not represented. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献