宽带接入网的发展趋势与FTTH

通过分析中国电信宽带接入网的现状,并结合宽带业务需求的变化,研究宽带接入技术和宽带接入网的发展趋势,明确了光纤到用户(FTTH)将是宽带接入网发展的方向。     

A new procedure for treatment of oily slurry using geotextile filters

A new procedure to mitigate the environmental impacts and reduce the cost of disposal of oil slurry is present in this paper. Waste from the petroleum industry has a high environmental impact. Systems for oil–water separation have been used to mitigate the contamination potential of these types of effluents. At the outlet of these systems, the oil is skimmed-off the surface, while the slurry is removed from the base. Due to the high concentration of contaminants, the disposal of this slurry is an environmentally hazardous practice. Usually this type of waste is disposed of in tanks or landfills after removal from the industrial plant. Basically, the proposed procedure utilizes drying beds with geotextile filters to both reduce the water content in the slurry and obtain a less contaminated effluent. Laboratory tests were carried out to simulate the drying system. Four types of filters were analyzed: two non-woven geotextiles, one woven geotextile, and a sand filter.     

EPON系统中高效视频组播的实现方法

采用EPON系统的宽带接入网络可以为每个用户提供较高带宽,并且能较好地支持组播功能,是视频组播业务重要的用户接入手段。提供一种在EPON系统中实现高效率纽播的方法,充分发挥EPON网络点到多点结构的特点,使同一个组播组的用户共享一条流,从而提高下行带宽的利用率。     

Plasmon spectroscopy and imaging of individual gold nanodecahedra: a combined optical microscopy, cathodoluminescence, and electron energy-loss spectroscopy study

Imaging localized plasmon modes in noble-metal nanoparticles is of fundamental importance for applications such as ultrasensitive molecular detection. Here, we demonstrate the combined use of optical dark-field microscopy (DFM), cathodoluminescence (CL), and electron energy-loss spectroscopy (EELS) to study localized surface plasmons on individual gold nanodecahedra. By exciting surface plasmons with either external light or an electron beam, we experimentally resolve a prominent dipole-active plasmon band in the far-field radiation acquired via DFM and CL, whereas EELS reveals an additional plasmon mode associated with a weak dipole moment. We present measured spectra and intensity maps of plasmon modes in individual nanodecahedra in excellent agreement with boundary-element method simulations, including the effect of the substrate. A simple tight-binding model is formulated to successfully explain the rich plasmon structure in these particles encompasing bright and dark modes, which we predict to be fully observable in less lossy silver decahedra. Our work provides useful insight into the complex nature of plasmon resonances in nanoparticles with pentagonal symmetry.     

Surface plasmon resonance and magnetism of thiol-capped gold nanoparticles

Surface plasmon resonance measurements and magnetic characterization studies have been carried out for two types of thiol-capped gold nanoparticles (NPs) with similar diameters between 2.0 and 2.5?nm and different organic molecules linked to the sulfur atom: dodecanethiol and tiopronin. In addition, Au NPs capped with tetraoctyl ammonium bromide have also been included in the investigation since such capping molecules weakly interact with the gold surface atoms and, therefore, this system can be used as a model for naked gold NPs; such particles presented a bimodal size distribution with diameters around 1.5 and 5?nm. The plasmon resonance is non-existent for tiopronin-capped NPs, whereas a trace of such a feature is observed for NPs covered with dodecanethiol molecules and a bulk-like feature is measured for NPs capped with tetralkyl ammonium salts. These differences would indicate that the modification of the surface electronic structure of the Au NPs depends on the geometry and self-assembling capabilities of the capping molecules and on the electric charge transferred between Au and S atoms. Regarding the magnetization, dodecanethiol-capped NPs have a ferromagnetic-like behaviour, while the NPs capped with tiopronin exhibit a paramagnetic behaviour and tetralkyl ammonium-protected NPs are diamagnetic across the studied temperature range; straight chains with a well-defined symmetry axis can induce orbital momentum on surface electrons close to the binding atoms. The orbital momentum not only contributes to the magnetization but also to the local anisotropy, giving rise to permanent magnetism. Due to the domain structure of the adsorbed molecules, orbital momentum is not induced for tiopronin-capped NPs and the charge transfer only induces a paramagnetic spin component.     

Tunnelling spectra of individual magnetic endofullerene molecules

The manipulation of single magnetic molecules may enable new strategies for high-density information storage and quantum-state control. However, progress in these areas depends on developing techniques for addressing individual molecules and controlling their spin. Here, we report success in making electrical contact to individual magnetic N@C(60) molecules and measuring spin excitations in their electron tunnelling spectra. We verify that the molecules remain magnetic by observing a transition as a function of magnetic field that changes the spin quantum number and also the existence of non-equilibrium tunnelling originating from low-energy excited states. From the tunnelling spectra, we identify the charge and spin states of the molecule. The measured spectra can be reproduced theoretically by accounting for the exchange interaction between the nitrogen spin and electron(s) on the C(60) cage.     

Disposable magnetic DNA sensors for the determination at the attomolar level of a specific enterobacteriaceae family gene

Disposable magnetic DNA sensors using an enzyme-amplified strategy for the specific detection of a gene related to the Enterobacteriaceae bacterial family, based on the coupling of streptavidin-peroxidase to biotinylated lacZ gene target sequences, has been developed. A biotinylated 25-mer capture probe was attached to streptavidin-modified magnetic beads and hybridization with the biotinylated target was allowed to proceed. Then, a streptavidin-peroxidase polymer was attached to the biotinylated target, and the resulting modified magnetic beads were captured by a magnetic field on the surface of tetrathiafulvalene (TTF) modified gold screen-printed electrodes (Au/SPEs). The amperometric response obtained at -0.15 V after the addition of hydrogen peroxide was used to detect the hybridization process. In order to improve the sensitivity of the determination and reduce the assay time, different variables of the assay protocol were optimized. A low detection limit (5.7 fmol) with good stability (RSD = 7.1%, n = 10) was obtained. The DNA nonspecific adsorption at the magnetic beads was negligible, the obtained results thus demonstrating the possibility to detect the hybridization event with great specificity and sensitivity. The developed method was used for the analysis of Escherichia coli DNA fragments (326 bases) in polymerase chain reaction (PCR) amplicons extracted from a cell culture. As low as 2.5 aM asymmetric PCR product could be detected with the developed methodology.     

Color encoding for polychromatic single-channel optical pattern recognition

The common multichannel system for recognizing colored images is replaced by a color-encoded single-channel system. Amethod inspired by the Munsell color system is used for encoding the different colors as phase and amplitude functions. It is shown that for many practical cases the phase information part of the color code is sufficient for obtaining good results. An implementation based on a liquid-crystal television panel that works in a phase-modulation mode is suggested. Computer simulations that demonstrate the capabilities of the suggested method are given as well as a comparison with previously published multichannel performance.     

金属真空弧离子源引出强流离子束的数值模拟

为了引出更高强度、更高亮度的铀离子束,以满足重离子研究中心(Gesellschaft für SchwerionenforschungmbH,GSI)重离子同步加速器的需求,本文用三维的计算机程序KOBRA3-INP对金属真空弧离子源(Metalvapor vacuum arcion source,MEVVA)引出强流铀离子束在引出系统和后加速系统中的动力学特性进行了研究,讨论了离子源发射束流密度对引出束性能的影响.结果表明,束流损失主要发生在引出系统和后加速系统之间的漂移区;在假设漂移区束流被空间电荷中和的情况下,模拟结果和实验结果符合;在发射束流密度为180-230 mA/cm2范围内,经后加速的束流强度变化不大.