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61.
Pedro J. Castro Joaquim J. Barroso Rafael A. Corrêa 《Journal of Infrared, Millimeter and Terahertz Waves》2000,21(4):633-645
A study of the electrodynamical properties of a Ka-band gyrotron open resonator was experimentally conducted. Experiments were accomplished to measure resonant frequencies and their respective loaded quality factors for TE modes in the frequency range from 26 to 40 GHz. In particular, a perturbation technique was used to determine the axial, radial and azimuthal electric field profiles, as an identification method of the TE021 mode operating around 35 GHz. In any experimental event, good agreement with the values predicted by theory was found. 相似文献
62.
Humberto C. C. Fernandes Clenilson B. Fonseca 《Journal of Infrared, Millimeter and Terahertz Waves》2003,24(10):1729-1736
The phased array formed by microstrip antennas is analyzed using the full wave Transverse Transmission Line (TTL) method. For the microstrip patch resonator a set of equations that represents the electromagnetic fields in the x and z directions as function of the fields in the y direction are obtained applying the TTL method. The structure PBG (Photonic Band Gap) is analyzed using the homogenization theory, the objective is obtain the equivalent permittivity of structure. Numerical results of the radiation pattern for some phase excitation in a phased array are shown. 相似文献
63.
Tatiana A. Kolesnikova Dmitry A. Gorin Paulo Fernandes Stefanie Kessel Gennady B. Khomutov Andreas Fery Dmitry G. Shchukin Helmuth Möhwald 《Advanced functional materials》2010,20(7):1189-1195
A water suspension of nanocomposite microcapsules with embedded ZnO nanoparticles in the capsule shell is reported. The microcapsule morphology is characterized by confocal microscopy, TEM, SEM, and AFM before and after ultrasound treatment. A remarkably high capsule sensitivity to ultrasound is evidenced, and it is observed to grow with increasing number of ZnO nanoparticle layers in the nanocomposite shell. This effect is correlated with the mechanical properties of microcapsules measured with AFM. 相似文献
64.
Biologically Inspired and Magnetically Recoverable Copper Porphyrinic Catalysts: A Greener Approach for Oxidation of Hydrocarbons with Molecular Oxygen 下载免费PDF全文
César A. Henriques Auguste Fernandes Liane M. Rossi M. Filipa Ribeiro Mário J. F. Calvete Mariette M. Pereira 《Advanced functional materials》2016,26(19):3359-3368
An efficient synthetic method for magnetically recoverable hybrid copper porphyrinic nanomaterials is reported. These functionalized magnetic materials prove to be efficient bioinspired oxidation catalysts of olefins and thiols, using molecular oxygen as oxidant, in total absence of reductants and solvents, with the highest TON (turnover number) yet achieved for this reaction (≈200 000). A comparative study between homogeneous and heterogeneous oxidation of cyclohexene is discussed, revealing the heterogeneous system to be the most promising concerning stability and reusability of the catalysts. The full characterization of the magnetic hybrid porphyrinic nanomaterials, by transmission electron microscopy, flame atomic absorption spectrometry, thermogravimetry, N2 sorption, and infrared spectroscopy, is also described. 相似文献
65.
J. Galán T. Sánchez-Rodríguez C. Luján-Martínez M. Pedro R. G. Carvajal A. López-Martín 《Analog Integrated Circuits and Signal Processing》2010,62(1):1-8
A fourth-order low-pass channel filter for a zero-IF Bluetooth receiver is presented. It employs two cascaded multiple feedback
biquads and active resistors made by quasi-floating gate MOS transistors in triode region for highly linear continuous tuning.
Power consumption is strongly reduced using a gain-enhanced class-AB single-stage opamp together with a filter topology that
only requires a single opamp for each biquad. The filter has been fabricated in a 0.18 μm CMOS technology and consumes 290 μW
from a 1.2 V supply. 相似文献
66.
In this paper a realistic directional channel model that is an extension of the COST 273 channel model is presented. The model uses a cluster of scatterers and visibility region generation based strategy with increased realism, due to the introduction of terrain and clutter information. New approaches for path-loss prediction and line of sight modeling are considered, affecting the cluster path gain model implementation. The new model was implemented using terrain, clutter, street and user mobility information for the city of Lisbon, Portugal. Some of the model’s outputs are presented, mainly path loss and small/large-scale fading statistics. 相似文献
67.
Structure and microstructure of yttria thin films grown by electron beam physical vapour deposition on a stationary Si (111) substrate at room temperature (RT), 500° and 700 °C, were investigated by the grazing-incidence X-ray diffraction and scanning electron microscopy, respectively. X-ray photoelectron spectroscopy provided information on the surface contamination from the atmosphere and the Y oxidation state. A strong effect of the deposition temperature and the vapour flux incidence angle was found. The film deposited at RT is polycrystalline with very fine grains of the body-centered cubic (bcc) crystallographic symmetry. An increase of deposition temperature results in a rapid growth of bcc grains with an improved crystalline structure. Moreover, the based-centered monoclinic phase appears for the deposition temperature of 700 °C. Preferred grain orientation (texture) with two main components, (400) and (622), was observed in the films deposited at 500 °C whereas no texture was found for 700 °C. The microstructure exhibits the columnar feather-like structure of different degrees of perfection which can be explained by the shadowing effects caused by an oblique vapour flux incidence angle. Surface morphology of the films is governed by a combination of the triangular and four-sided (square) columns. All films were found to be dense with a little porosity between the columns. 相似文献
68.
Köber M Sahagún E García-Mochales P Briones F Luna M Sáenz JJ 《Small (Weinheim an der Bergstrasse, Germany)》2010,6(23):2725-2730
The sticking effect between hydrophilic surfaces occurring at increasing relative humidity (RH) is an everyday phenomenon with uncountable implications. Here experimental evidence is presented for a counterintuitive monotonous decrease of the capillary adhesion forces between hydrophilic surfaces with increasing RH for the whole humidity range. It is shown that this unexpected result is related to the actual shape of the asperity at the nanometer scale: a model based on macroscopic thermodynamics predicts this decrease in the adhesion force for a sharp object ending in an almost flat nanometer-sized apex, in full agreement with experiments. This anomalous decrease is due to the fact that a significant growth of the liquid meniscus formed at the contact region with increasing humidity is hindered for this geometry. These results are relevant in the analysis of the dynamical behavior of nanomenisci. They could also have an outstanding value in technological applications, since the undesirable sticking effect between surfaces occurring at increasing RH could be avoided by controlling the shape of the surface asperities at the nanometric scale. 相似文献
69.
The fracture and fatigue behaviour of prototype automotive pistons produced in an aluminium alloy matrix composite in industrial
conditions has been studied. Fracture toughness increased when the testing temperature rose from 20° to 75°C and kept near
constant up to 250°C, when a significantly lower value was recorded. A change in the failure operating mechanism, which can
explain this trend, was observed by analysing the fracture surfaces in the scanning electron microscope. Room temperature
fatigue tests performed with R = 0.1 stress ratio led to an average value of the Paris law exponent higher than those reported in aluminium alloys but low
for an industrially produced brittle composite. A higher exponent and a much larger scattering were observed in those fatigue
tests carried out under R = 0.5 stress ratio. 相似文献
70.
Bernardo Mançano Fernandes 《Landscape Research》2019,44(7):892-907
ABSTRACTFrom the perspective of Brazilian agrarian geography, the conflicts generated by land tenure disputes have as protagonists the families of the Landless Workers’ Movement (Movimento dos Trabalhadores Rurais Sem Terra), traditional landowners, and agribusiness corporations. In this article, we present a reflection on land conflicts and the spatial and territorial production of latifundia, peasant smallholders, and large-scale agribusiness through studies of the landscapes of two municipalities in the state of São Paulo. Among the various tools for analysing territorial disputes, Google Earth can be used for local, regional, and international comparative studies of how landscapes have been transformed. Informed by traditional research, the article analyses a diversity of photographs, from satellite to field shots, as evidence of landscapes that express conflicting social relations in disputes over different models of social and territorial development. 相似文献