Mesostructured Arrays of Nanometer‐spaced Gold Nanoparticles for Ultrahigh Number Density of SERS Hot Spots

A novel one‐trough synthesis via an air‐water interface is demonstrated to provide hexagonally packed arrays of densely spaced metallic nanoparticles (NPs). In the synthesis, a mesostructured polyoxometalate (POM)‐silicatropic template (PSS) is first self‐assembled at the air‐water interface; upon UV irradiation, anion exchange cycles enable the free‐floating PSS film to continuously uptake gold precursors from the solution subphase for diffusion‐controlled and POM‐site‐directed photoreduction inside the silica channels. NPs ≈ 2 nm can hence be homogeneously formed inside the silica‐surfactant channels until saturation. As revealed via X‐ray diffraction, small‐angle X‐ray scattering (SAXS), grazing incidence SAXS, and transmission electron microscopy, the Au NPs directed by the PSS template are arrayed into a 2D hexagonal lattice with inter‐channel spacing of 3.2 nm and a mean along‐channel NP spacing of 2.8 nm. This corresponds to an ultra‐high number density (≈10¹⁹ NPs cm^?3) of narrowly spaced Au NPs in the Au‐NP@PSS composite, leading to 3D densely deployed hot‐spots along and across the mesostructured POM‐silica channels for surface‐enhanced Raman scattering (SERS). Consequently, the Au‐NP@PSS composite exhibits prominent SERS with 4‐mercaptobenzoic acid (4‐MBA) adsorbed onto Au NPs. The best 4‐MBA detection limit is 5 nm , with corresponding SERS enhancement factors above 10⁸.     

Access algorithm for packetized wireless transmission in thepresence of cochannel interference

Packetized access has some potential advantages over conventional circuit-switched-based access methods because several signal sources can share the same radio channel using statistical multiplexing. We consider radio resource assignment algorithms for packetized access based on the packet-reservation multiple-access (PRMA) protocol in the presence of cochannel interference. The statistical multiplexing gain of packet access is limited by frequency reuse, especially when the reuse factor is low or duality requirement is high. We propose a fuzzy logic-based adaptive medium-access control (MAC) algorithm to improve packet-access efficiency. Computer simulations based on the example of packetized voice have confirmed that the proposed packet-access protocol can support a higher number of active users per radio port than that supported by random slot assignment     

Redshifting and broadening of quantum-well infrared photodetector'sresponse via impurity-free vacancy disordering

The partial intermixing of the well and barrier materials offers unique opportunities to shift locally the bandgap of quantum-well (QW) structures. We have demonstrated redshifting and broadening of the wavelength responses of bound-to-continuum GaAs and InP based quantum-well infrared photodetectors (QWIP's) after growth via impurity-free vacancy disordering (IFVD). A comprehensive set of experiments is conducted on QWIP's fabricated from both as-grown and multiple-quantum-well (MQW) structures. Compared to the as-grown detector, the peak spectral responses of the disordered detectors were shifted to longer wavelengths. The peak absolute response of the disordered GaAs based QWIP is lower by almost a factor of four. However, the responsivity characteristics of the disordered InP based QWIP show no major degradation. In general, with the spectral broadening taken into account, the overall performance of the disordered QWIP's has not dropped significantly. Thus, the postgrowth control of the QW composition profiles by impurity-free vacancy disordering offers unique opportunities to fine tune various aspects of a photodetector's response. Theoretical calculations of the absorption coefficient spectrum are in excellent agreement with the experimental data     

Optical gain of strained wurtzite GaN quantum-well lasers

A theory for the electronic band structure and the free-carrier optical gain of wurtzite-strained quantum-well lasers is presented. We take into account the strain-induced band-edge shifts and the realistic band structures of the GaN wurtzite crystals. The effective-mass Hamiltonian, the basis functions, the valence band structures, the interband momentum matrix elements, and the optical gain are presented with analytical expressions and numerical results for GaN-AlGaN strained quantum-well lasers. This theoretical model provides a foundation for investigating the electronic and optical properties of wurtzite-strained quantum-well lasers.     

恩平凹陷源外隆起区新近系油气成藏条件与定量评价

源外隆起区是珠江口盆地恩平凹陷近年勘探的重点区带,其石油地质条件区别于近洼陷带。综合利用地震、测井、油藏等资料,对隆起区成藏特征和富集规律展开研究,并提出了定量评价方法。隆起区以侧向长距离运移成藏为特征,多次跨断层运移为特色;断裂对油气晚期成藏具有控制作用。富足的供烃单元是油气远源富集的物质基础和动力来源,圈闭与主汇聚脊的组合构成良好的空间输导格架,圈闭捕获能力和运聚强度的时空匹配是富集的关键因素。研究提出了油柱高度序列法和SGR图版法两种定量评价方法,分别评价了隆起区油气运聚强度和富集潜力,有效指导了隆起区的勘探且具有推广价值。     

A microwave photonic phase-shifter based on wavelength conversion in a DFB laser

We propose and demonstrate a microwave photonic phase-shifter using a distributed-feedback laser-wavelength converter. Through carrier competition in the laser, information is passed from the input signal to the lasing mode. The frequency response of this conversion mechanism follows the intrinsic modulation response of the laser, which exhibits a large phase change near the relaxation frequency. Through current-control of the relaxation frequency, the phase of the wavelength-converted microwave output can be varied by more than 135/spl deg/ over a bandwidth of 1.8GHz. We further identify an operating regime that exhibits a large discrete phase shift of 114/spl deg/ at 3 GHz with negligible change in power.     

Planar array stack design aided by rapid prototyping in development of air-breathing PEMFC

The polymer electrolyte membrane fuel cell (PEMFC) is one of the most important research topics in the new and clean energy area. The middle or high power PEMFCs can be applied to the transportation or the distributed power system. But for the small power application, it is needed to match the power requirement of the product generally. On the other hand, the direct methanol fuel cell (DMFC) is one of the most common type that researchers are interested in, but recently the miniature or the micro-PEMFCs attract more attention due to their advantages of high open circuit voltage and high power density.     

Significantly enhanced charge conduction in electric double layer capacitors using carbon nanotube-grafted activated carbon electrodes

Carbon nanotube (CNT)-grafting by chemical vapor deposition was conducted to reduce the resistance of activated carbon fiber serving as an electrode for electric double layer capacitors. Sputtering deposition of Ni catalyst particles led to a uniform growth of CNTs on the carbon fiber surface through the tip-growth mechanism. Because sputtering deposition ensures little pore blockage (in comparison with wet-impregnation), the surface area decrease of the carbon fiber due to Ni loading was minimized. By using H₂SO₄ aqueous solution as the electrolyte, a capacitor cell assembled with the CNT-grafted fiber showed higher electron and electrolyte-ion conductivities relative to a cell assembled with the bare fiber. By increasing the discharging current density from 1 to 150 mA cm⁻², the bare fiber exhibited a capacitance loss of 17% while the CNT-grafted fiber showed a mitigated capacitance loss of only 7%. This developed CNT-grafting technique renders activated carbon fiber a promising electrode material for a variety of electrochemical applications.     

Centrifugal compressor blade optimization based on uniform design and genetic algorithms

An optimization approach to centrifugal compressor blade design, incorporating uniform design method (UDM), computational fluid dynamics (CFD) analysis technique, regression analysis method and genetic algorithms (GA), is presented. UDM is employed to generate the geometric information of trial samples whose performance is evaluated by CFD technique. Then, function approximation of sample information is performed by regression analysis method. Finally, global optimization of the approximative function is obtained by genetic algorithms. Taking maximum isentropic efficiency as objective function, this optimization approach has been applied to the optimum design of a certain centrifugal compressor blades. The results, compared with those of the original one, show that isentropic efficiency of the optimized impeller has been improved which indicates the effectiveness of the proposed optimization approach.     

珠江口盆地惠州26⁃6油气田有效气源岩分析

位于珠江口盆地的惠州26?6构造在中生界古潜山及古近系获得油气勘探重大突破,是该盆地古潜山及恩平组—文昌组凝析气勘探的首个规模发现。为进一步指导浅水富油区天然气勘探,应用天然气生成及分子碳同位素动力学技术,对惠州26?6油气田三级层序格架下的有效气源岩层进行系统研究。结果表明：惠州26洼文昌组六段（文六段）+五段（文五段）半深湖—深湖亚相烃源岩为惠州26?6油气田古潜山储层提供大量天然气,文五段半深湖—深湖亚相烃源岩为文昌组—恩平组储层提供一定量天然气,文昌组四段（文四段）半深湖—深湖亚相烃源岩为文昌组—恩平组提供少量天然气,上文昌组（文三段）和恩平组烃源岩基本不提供天然气;该气田属于阶段性累积聚气,成藏时间较晚,有效充注成藏期在10~0 Ma之间,目前仍处于有效充注阶段。这一新认识对于珠江口盆地富油区天然气勘探具有重要的指导意义。