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排序方式: 共有325条查询结果,搜索用时 46 毫秒
41.
Humberto César Chaves Fernandes Idalmir de Souza Queiroz Júnior 《International Journal of Infrared and Millimeter Waves》1996,17(8):1391-1402
The Transverse Transmission Line (TTL) is used in the theory of the overlay shielded microstrip lines considering the superconductor strip on two semiconductor regions. The superconductor effect is included with the boundary condition of the surface impedance, that is related to the complex conductivity of the material, calculated from the advanced two-fluid model. Applying the moment method the complex propagation constant of the structure, including the phase constant and the attenuation constant, is obtained. Results are presented for the complex propagation constant, versus the frequency and the temperature, of this overlay superconducting microstrip lines. 相似文献
42.
Humberto César Chaves Fernandes Eduardo Armorim Martins de Souza Idalmir de Souza Queiroz Jr 《International Journal of Infrared and Millimeter Waves》1995,16(1):185-200
In this study, the effect of the metallization thickness in finlines on semiconcuctor substrate is researched. The propagation parameters are computed to measure the inluence of the metallization. The theory and numerical results are presented to the propagation constant and characteristic impedance of the bilateral and unilateral finlines. The full wave analysis of the transverse transmission line — TTL method is used to determine the electromagnetic fields of the structure in Fourier transform domain — FTD. Applying the suitable boundary conditions, the moment method and expanding the fields in a set of suitable bases functions, a homogeneous matrix system is obtained and the propagation constant is computed. The characteristic impedance is obtained using the relation of the voltage in the slot and the transmitted power by the structure.Computational programs are developed to obtain numerical results to the propagation parameters composed by the propagation constant and characteristic impedance.This work received financial support by CAPES and CNPq. 相似文献
43.
Jean-Louis Uribelarrea José Humberto De Queiroz Alain Pareilleux 《Applied biochemistry and biotechnology》1997,66(1):69-81
The aerobic growth ofSchizosaccharomyces pombe on mixtures of glucose and malate was investigated during continuous high cell density cultures with partial cell-recycle
using a membrane bioreactor. Determination of the specific metabolic rates relative to substrates and products allowed the
capacity of the yeast to metabolize malic acid under both oxidative metabolism (carbon limited cultures) and oxidofermentative
metabolism (carbon sufficient cultures) situations to be characterized. Under carbon limiting conditions, the specific rate
of malate utilization was dependent on the residual concentration and a limit for a purely oxidative breakdown without ethanol
formation was observed for a characteristic ratio between the rates of substrate consumption qm/qg of 1.63 g.g-1. In addition, the mass balance analysis revealed the incorporation of malic acid into biomass. In carbon excess environments,
the specific rate of malate utilization was dependent on both the residual malate and the specific rate of glucose consumption
indicating that in addition to its conversion into ethanol malate can be respiratively metabolized for qm/qg ratios higher
than 0.4 g.g-1. 相似文献
44.
Davies SG Garner AC Goddard EC Kruchinin D Roberts PM Rodriguez-Solla H Smith AD 《Chemical communications (Cambridge, England)》2006,(25):2664-2666
Conjugate addition of homochiral lithium amides to methyl 4-(N-benzyl-N-allylamino)but-2-enoate, chemoselective N-deprotection and concomitant cyclisation, followed by enolate functionalisation and deprotection allows access to syn- and anti-3,4-disubstituted aminopyrrolidines in > 98% d.e. and > 98% e.e. 相似文献
45.
Humberto C. Garcia Luiz F. C. de Oliveira Mauro C. C. Ribeiro 《Journal of Raman spectroscopy : JRS》2010,41(5):524-528
Raman and electronic spectra of the [3,5‐bis(dicyanomethylene)cyclopentane‐1,2,4‐trionate] dianion, the croconate violet (CV), are reported in solutions of ionic liquids based on imidazolium cations. Different normal modes of the CV anion, ν (CO), ν (CO) + ν (CC) + ν (CCN), and ν(C≡N), were used as probes of solvation characteristics of ionic liquids, and were compared with spectra of CV in common solvents. The spectra of CV in ionic liquids are similar to those in dichloromethane solution, but distinct from those in protic solvents such as ethanol or water. The UV–vis spectra of CV in ionic liquids strongly suggest π–π interactions between the CV anion and the imidazolium cation. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
46.
Humberto C. Garcia Luiz F. C. de Oliveira Bruno G. Nicolau Mauro C. C. Ribeiro 《Journal of Raman spectroscopy : JRS》2010,41(12):1720-1724
Raman spectra of dilute solutions of acetonitrile in ionic liquids reveal the characteristic features of ionic liquids' polarity. This is accomplished by investigating the Raman bandshape of the ν (CN) band, corresponding to the CN stretching mode of CH3CN, which is a very sensitive probe of the local environment. The amphiphilic nature of the CH3CN molecule allows us to observe the effect of electron pair acceptor and electron pair donor characteristics on ionic liquids. It has been found that the overall polarity of nine different ionic liquids based on 1‐alkyl‐3‐methylimidazolium cations is more dependent on the anion than cation. The observed wavenumber shift of the ν (CN) band of CH3CN in ionic liquids containing alkylsulfate anions agrees with the significant different values previously measured for the dielectric constant of these ionic liquids. The conclusions obtained from the analysis of the ν (CN) band were corroborated by the analysis of the symmetric ν1 (CD3 ) stretching mode of deuterated acetonitrile in different ionic liquids. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
47.
Humberto Rafeiro Stefan Samko 《Journal of Mathematical Analysis and Applications》2010,365(2):483-497
Under the standard assumptions on the variable exponent p(x) (log- and decay conditions), we give a characterization of the variable exponent Bessel potential space Bα[Lp(⋅)(Rn)] in terms of the rate of convergence of the Poisson semigroup Pt. We show that the existence of the Riesz fractional derivative Dαf in the space Lp(⋅)(Rn) is equivalent to the existence of the limit . In the pre-limiting case we show that the Bessel potential space is characterized by the condition ‖α(I−Pε)f‖p(⋅)≦Cεα. 相似文献
48.
Cristiane Kalinke Paulo Roberto de Oliveira Marta Bonet San Emeterio Andreu Gonzlez‐Calabuig Manel del Valle Antonio Salvio Mangrich Luiz Humberto Marcolino Junior Mrcio F. Bergamini 《Electroanalysis》2019,31(11):2238-2245
Biochar is a charcoal produced from the biomass pyrolysis process that presents a highly porous and functionalized surface. In the present work an array of carbon paste electrodes (CPE) made of different forms of carbon (graphite, carbon nanotubes and activated biochar) was evaluated in the development of an electronic tongue for discrimination and stripping voltammetric determination of catechol (CAT), 4‐ethylcatechol (4‐EC) and 4‐ethylguaiacol (4‐EG) phenolic compounds. Morphological characterization of carbon materials and electrodes surfaces was performed by scanning electron microscopy (SEM) and semi‐quantitative elemental composition by energy dispersive spectroscopy (EDS). Electrochemical Impedance Spectroscopy (EIS) measurements were used for electrochemical characterization of electrodes. Cyclic voltammetry measurements were performed for the phenolic compounds evaluated using different concentrations. Principal component analysis (PCA) was performed to evaluate the qualitative analysis. Quantitative data modeling was done using artificial neural networks (ANN). The proposed sensor array presented analytical potentiality allowing the distinction and determination of CAT, 4‐EC and 4‐EG by using chemometric processing. The method showed sensibility, reproducibility and a good linearity (R2>0.9940) for three compounds evaluated. Spontaneous preconcentration of three compounds was possible using all three sensors, which can allow the application of these as passive samplers for remote determinations of phenolic compounds in wine and food samples. 相似文献
49.
We show that, by tuning interactions in nonintegrable vector nonlinear Schr?dinger equations modeling Bose-Einstein condensates and other relevant physical systems, it is possible to achieve a regime of elastic particlelike collisions between solitons. This would allow one to construct a Newton's cradle with solitons and supersolitons: localized collective excitations in solitary-wave chains. 相似文献
50.
Humberto Andre Potes-Lesoinne Fernando Ramirez-Alvarez Victor H. Perez-Gonzalez Sergio O. Martinez-Chapa Roberto Carlos Gallo-Villanueva 《Electrophoresis》2022,43(1-2):249-262
The survival of living beings, including humanity, depends on a continuous supply of clean water. However, due to the development of industry, agriculture, and population growth, an increasing number of wastewaters is discarded, and the negative effects of such actions are clear. The first step in solving this situation is the collection and monitoring of pollutants in water bodies to subsequently facilitate their treatment. Nonetheless, traditional sensing techniques are typically laboratory-based, leading to potential diminishment in analysis quality. In this paper, the most recent developments in micro- and nano-electrochemical devices for pollutant detection in wastewater are reviewed. The devices reviewed are based on a variety of electrodes and the sensing of three different categories of pollutants: nutrients and phenolic compounds, heavy metals, and organic matter. From these electrodes, Cu, Co, and Bi showed promise as versatile materials to detect a grand variety of contaminants. Also, the most commonly used material is glassy carbon, present in the detection of all reviewed analytes. 相似文献