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排序方式: 共有216条查询结果,搜索用时 15 毫秒
31.
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
32.
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
33.
EPR spectra of SO-3 ion-radical in X-ray irradiated CsLiSO4 single crystals were used for the study of the ferroelastic phase transition at Tc = 203.0 K. The splitting (ΔH) of the SO3 line in the low-temperature ferroelastic phase has been interpreted as proportional to the square of the order parameter. The splitting shows the temperature dependence ΔH ∞ (Tc ? T) 1.01± 0.01 相似文献
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Direct measurements of the bulk flow of a ferrofluid in a uniform rotating magnetic field were obtained using the ultrasonic velocity profile method. The fluid was observed to corotate with the field in a rigid-body-like fashion throughout the bulk of the container, except near the air-fluid interface, where it was observed to counterrotate. The results were found in qualitative agreement with the spin diffusion theory of Zaitsev and Shliomis [J. Appl. Mech. Tech. Phys. 10, 696 (1969)]10.1007/BF00907424. 相似文献
37.
Aharonian F Akhperjanian AG Barres de Almeida U Bazer-Bachi AR Becherini Y Behera B Beilicke M Benbow W Bernlöhr K Boisson C Bochow A Borrel V Braun I Brion E Brucker J Brun P Bühler R Bulik T Büsching I Boutelier T Carrigan S Chadwick PM Charbonnier A Chaves RC Chounet LM Clapson AC Coignet G Costamante L Dalton M Degrange B Deil C Dickinson HJ Djannati-Ataï A Domainko W Drury LO Dubois F Dubus G Dyks J Egberts K Emmanoulopoulos D Espigat P Farnier C Feinstein F Fiasson A Förster A Fontaine G 《Physical review letters》2008,101(17):170402
In the past few decades, several models have predicted an energy dependence of the speed of light in the context of quantum gravity. For cosmological sources such as active galaxies, this minuscule effect can add up to measurable photon-energy dependent time lags. In this Letter a search for such time lags during the High Energy Stereoscopic System observations of the exceptional very high energy flare of the active galaxy PKS 2155-304 on 28 July 2006 is presented. Since no significant time lag is found, lower limits on the energy scale of speed of light modifications are derived. 相似文献
38.
Suiformes orthologous satellite DNAs as a hallmark of Pecari tajacu and Tayassu pecari (Tayassuidae) evolutionary rearrangements 总被引:1,自引:1,他引:0
In a broad general way, eukaryotic satellite DNA sequences are characterized by a highly dynamic molecular behavior due to concerted evolution that leads to rapid change between repeat sequences of different species, achieved by amplification of new variants during speciation or by gradual sequence evolution due to the accumulation of nucleotide substitutions. There are, although exceptions for this almost universal rule. We isolated variants from both the Mc1 and Ac2 pig (Sus scrofa, Suidae) satellite DNA families from the genomes of two Tayassuidae members: Pecari tajacu and Tayassu pecari, which have highly derived karyotypes. The presence of these sequences in both families’ genomes (Suidae and Tayassuidae) implies their existence in a common ancestor, what confers to the variants the status of orthology and the approximate age of, at least 40 million years.While at the molecular composition level these orthologous sequences are highly homologous, cross-species physical mapping revealed a completely different chromosomal location in Suidae versus Tayassuidae families, most probably, reflecting the high level of divergence and chromosomes evolution pathways after radiation of each family. Detailed comparative analysis of the satellites assignment on the peccary's chromosomes revealed its co-localization with homologous evolutionary breakpoints in both species, suggesting their involvement in the rearrangement events. The complex behavior of the repeats evolution in the pig/peccaries genomes is here clearly illustrated. These sequences are molecularly preserved for a considerable period of time and display slow rates of sequence change, but show a dynamic motion behavior throughout the peccary's genomes that accompanied the great architectonic reorganization of Tayassuidae chromosomes during evolution. 相似文献
39.
Microemulsion electrokinetic chromatography as a suitable tool for lipophilicity determination of acidic,neutral, and basic compounds 下载免费PDF全文
In the present work, several MEEKC systems are studied to assess their suitability for lipophilicity determination of acidic, neutral, and basic compounds. Thus, several microemulsion compositions over a wide range of pH values (from 2.0 to 12.0), containing heptane, 1?butanol and different types and amounts of surfactant (SDS or sodium cholate: from 1.3 to 3.3%) are characterized using Abraham's solvation model. The addition of acetonitrile (up to 10%) is also studied, since it increases the resolution of the technique for the most lipophilic compounds. The system coefficients obtained are very similar to those of the 1?octanol/water, used as the reference lipophilicity index, allowing simple and linear correlations between the 1?octanol/water partition values (log Po/w) and MEEKC mass distribution ratios (log kMEEKC). Variations in the microemulsion composition (aqueous buffer, surfactant, concentration of ACN) did not significantly affect the similarity of the MEEKC systems to log Po/w partition. 相似文献
40.
Sebastião PJ Simeão Carvalho P Chaves MR Nguyen HT Ribeiro AC 《The European physical journal. E, Soft matter》2006,20(1):55-61
We present a polarising optical microscopy study of the low-temperature anticlinic-like tilted mesophase of the liquid-crystal
compound octylphenyl-2-chloro-4-(p-cyano-benzoyloxy) (DB8Cl). This mesophase has been described as a bilayer smectic structure in which the molecules within each layer are organised
in an anticlinic way. The optical textures observed in samples with planar orientation show a double stripe pattern, with
the lines aligned parallel to the rubbing direction, characteristic of a double periodic modulation of the refractive index
of the material. The long-period modulation is temperature dependent and disappears for thin sample cells (< 5μm). The short-period
modulation is nearly independent of the thickness of the cells. The experimental results are analysed in terms of a model
which considers that there is a special distribution of the principal optical axis which may be in or out of the polariser-analyser
plane. The observed periodic variation of the principal optical axis could not be interpreted in terms of the original structure
proposed for this phase. DB8Cl presents a structure formed by dimers that can be viewed as flexible bent-core-like molecules, showing similarities with
phases found in banana-like systems, but exhibiting a much more complex structure. 相似文献