共查询到20条相似文献，搜索用时 31 毫秒
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An all-dielectric coaxial waveguide that can overcome problems of polarization rotation and pulse broadening in the transmission of optical light is presented here. It consists of a coaxial waveguiding region with a low index of refraction, bounded by two cylindrical, dielectric, multilayer, omnidirectional reflecting mirrors. The waveguide can be designed to support a single mode whose properties are very similar to the unique transverse electromagnetic mode of a traditional metallic coaxial cable. The new mode has radial symmetry and a point of zero dispersion. Moreover, because the light is not confined by total internal reflection, the waveguide can guide light around very sharp corners. 相似文献
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The Belousov-Zhabotinsky reagent and numerical simulations were used to show that under high-frequency stimuli, rotating spiral waves can be initiated in a homogeneous excitable medium in the vicinity of domain boundaries or inexcitable barriers with sharp corners. 相似文献
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An artificial crystal structure has been fabricated exhibiting a full three-dimensional photonic bandgap effect at optical communication wavelengths. The photonic crystal was constructed by stacking 0.7-micrometer period semiconductor stripes with the accuracy of 30 nanometers by advanced wafer-fusion technique. A bandgap effect of more than 40 decibels (which corresponds to 99.99% reflection) was successfully achieved. The result encourages us to create an ultra-small optical integrated circuit including a three-dimensional photonic crystal waveguide with a sharp bend. 相似文献
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GK Wong MS Kang HW Lee F Biancalana C Conti T Weiss PS Russell 《Science (New York, N.Y.)》2012,337(6093):446-449
Spiral twisting offers additional opportunities for controlling the loss, dispersion, and polarization state of light in optical fibers with noncircular guiding cores. Here, we report an effect that appears in continuously twisted photonic crystal fiber. Guided by the helical lattice of hollow channels, cladding light is forced to follow a spiral path. This diverts a fraction of the axial momentum flow into the azimuthal direction, leading to the formation of discrete orbital angular momentum states at wavelengths that scale linearly with the twist rate. Core-guided light phase-matches topologically to these leaky states, causing a series of dips in the transmitted spectrum. Twisted photonic crystal fiber has potential applications in, for example, band-rejection filters and dispersion control. 相似文献
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In otherwise profoundly akinetic rats that had been severely depleted of brain catecholamines, anticholinergic drugs caused excessive walking. The effect did not appear until 10 days after surgery and then increased with time, suggesting that a phenomenon analogous to denervation supersensitivity may be involved. If the animals walked into corners, they were unable to turn around or back out. Their gait (extremely short steps) was reminiscent of that of patients with Parkinson's disease. The results are consistent with a mutually antagonistic interaction between cholinergic and dopaminergic brain systems and emphasize certain complexities in this interaction. 相似文献
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Laser Rapid Prototyping of Photonic Band-Gap Microstructures 总被引：1，自引：0，他引：1
Three-dimensional periodic microstructures of aluminum oxide, which are important for creating photonic band-gap structures (PBGs), were fabricated by laser rapid prototyping by means of laser-induced direct-write deposition from the gas phase. The structures consisted of layers of parallel rods forming a face-centered tetragonal lattice with lattice constants of 66 and 133 micrometers. These structures showed transmission minima centered around 4 terahertz (75 micrometers) and 2 terahertz (150 micrometers), respectively. PBGs will allow precise control of the optical properties of materials, including lasers without threshold. 相似文献
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Wiltshire MC Pendry JB Young IR Larkman DJ Gilderdale DJ Hajnal JV 《Science (New York, N.Y.)》2001,291(5505):849-851
Magnetic resonance imaging and spectroscopy systems use coils, either singly or as arrays, to intercept radio-frequency (RF) magnetic flux from regions of interest, often deep within the body. Here, we show that a new magnetic material offers novel possibilities for guiding RF flux to the receiver coil, permitting a clear image to be obtained where none might otherwise be detectable. The new material contains microstructure designed according to concepts taken from the field of photonic band gap materials. In the RF range, it has a magnetic permeability that can be produced to specification while exhibiting negligible direct-current magnetism. The latter property is vital to avoid perturbing the static and audio-frequency magnetic fields needed to obtain image and spectral data. The concept offers a new paradigm for the manipulation of RF flux in all nuclear magnetic resonance systems. 相似文献
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Recrystallization of the solid Cd(10)S(4)(SC(6)H(5))(12) from a solution of pyridine and N, N-di-methylformamide (DMF) results in the formation of the cluster Cd(32)S(14)(SC(6)H(5))(36)-DMF(4) as pale yellow cubes. The structure consists of an 82-atom CdS core that is a roughly spherical piece of the cubic sphalerite lattice approximately 12 angstroms in diameter. The four corners of the lattice are capped by hexagonal wurtzite-like CdS units, which results in an overall tetrahedral cluster approximately 15 angstroms in diameter. This cluster dissolves intact in tetrahydrofuran where its absorption spectrum reveals a sharp peak at 358 nanometers at room temperature and its emission spectra show a strong broad band at 500 nanometers. 相似文献
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戴思锐 《西南大学学报(自然科学版)》1988,(4)
本文分析了邻水县人口增长和居民食物结构改善对农畜产品需求增长的影响,得出了食物结构改善、质量提高是造成目前食物需求猛增的主要原因。提出了该县城乡居民食物结构的指导性方案。指出了食物消费宏观控制的基本着眼点是粮食的需求平衡,从农业生产的发展中增加食物的供给量,从对居民食物消费的调节中控制食物需求的总量增长,使二者达到协调。而控制居民食物消费膨胀的主要途径是校正消费行为的偏差,引导居民将一部分收入用于长期储蓄与生产性投资. 相似文献
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在计算机视觉领域中角点特征的提取具有相当重要的地位，因为角点包含了丰富的信息。本文的目的在于提取某类图像上的重要特征角点。其主要思路是首先利用角点检测方法提取图像中的角点之后，然后再通过Zernike矩和神经网络对它们进行筛选，从而达到自提取特征角点的目的。最后通过实验验证了本算法的有效性。尽管本文是针对某类图像进行了特征点提取的，但相信对于一般情况下的目标特征检测也具有一定的借鉴意义。 相似文献
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夏季气候炎热,城市周边的农家乐就遇到了很棘手的问题,游客人数锐减,生意惨淡,应该想办法解决这样的季节性经营问题,使农家乐走出夏季的经营困难. 相似文献
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加热炉炉管是直接式加热炉的关键部件，其壁厚直接影响加热炉的安全运行。分别对方箱炉和弹簧炉的炉管壁厚进行了测试，从分析数据得出结论：炉内单根炉管的腐蚀主要集中的炉管两头及靠近弯头部位０－９００ｍｍ范围内。 相似文献
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Preparation of photonic crystals made of air spheres in titania 总被引：3，自引：0，他引：3
Three-dimensional crystals of air spheres in titania (TiO2) with radii between 120 and 1000 nanometers were made by filling the voids in artificial opals by precipitation from a liquid-phase chemical reaction and subsequently removing the original opal material by calcination. These macroporous materials are a new class of photonic band gap crystals for the optical spectrum. Scanning electron microscopy, Raman spectroscopy, and optical microscopy confirm the quality of the samples, and optical reflectivity demonstrates that the crystals are strongly photonic and near that needed to exhibit band gap behavior. 相似文献
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Growth of thin films from atoms deposited from the gas phase is intrinsically a nonequilibrium phenomenon governed by a competition between kinetics and thermodynamics. Precise control of the growth and thus of the properties of deposited films becomes possible only after an understanding of this competition is achieved. Here, the atomic nature of the most important kinetic mechanisms of film growth is explored. These mechanisms include adatom diffusion on terraces, along steps, and around island corners; nucleation and dynamics of the stable nucleus; atom attachment to and detachment from terraces and islands; and interlayer mass transport. Ways to manipulate the growth kinetics in order to select a desired growth mode are briefly addressed. 相似文献
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Three-dimensional (3D) photonic crystals containing artificial point defects have been fabricated to emit light at optical communications wavelengths. They were constructed by stacking 0.7-micrometer-period gallium arsenide striped layers, resulting in a 3D "woodpile" photonic crystal. Indium-gallium arsenide-phosphide quantum-well layers emitting at a wavelength of 1.55 micrometers were incorporated in the center of the crystal. Samples having up to nine stacked layers were constructed, and artificial point-defect cavities of different sizes were formed in the light-emitting layer. Light emission was suppressed in the photonic crystal regions, whereas cavity modes were successfully observed at the point defects and were size dependent. 相似文献
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The current understanding of how birds fly must be revised, because birds use their hand-wings in an unconventional way to generate lift and drag. Physical models of a common swift wing in gliding posture with a 60 degrees sweep of the sharp hand-wing leading edge were tested in a water tunnel. Interactions with the flow were measured quantitatively with digital particle image velocimetry at Reynolds numbers realistic for the gliding flight of a swift between 3750 and 37,500. The results show that gliding swifts can generate stable leading-edge vortices at small (5 degrees to 10 degrees) angles of attack. We suggest that the flow around the arm-wings of most birds can remain conventionally attached, whereas the swept-back hand-wings generate lift with leading-edge vortices. 相似文献
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一维类梳状波导是由在一维主链上周期性接枝而形成的光子晶体，利用界面响应理论可导出波导的色散关系，据此分别讨论了这种光子晶体的带隙宽度与波导接枝参数之间的关系，接枝的介电常数和长度的变化将会使对带隙的宽度发生改变，通过数值计算发现，对于不同类型的接枝，参数变化引起的带隙宽度的变化趋势基本相同，而不同的参数产生的影响则有很大差别。特别的，当参数变化至某些特定点时带隙将会消失，这和其他类型的光子晶体完全不同，带隙的消失不是因为缺陷而仅仅是因为参数改变的影响。 相似文献