Multi-frequency harmonic arrays: initial experience with a novel transducer concept for nonlinear contrast imaging

Nonlinear contrast imaging modes such as second harmonic imaging (HI) and subharmonic imaging (SHI) are increasingly important for clinical applications. However, the performance of currently available transducers for HI and SHI is significantly constrained by their limited bandwidth. To bypass this constraint, a novel transducer concept termed multi-frequency harmonic transducer arrays (MFHA's) has been designed and a preliminary evaluation has been conducted. The MFHA may ultimately be used for broadband contrast enhanced HI and SHI with high dynamic range and consists of three multi-element piezo-composite sub-arrays (A-C) constructed so the center frequencies are 4f(A) = 2f(B) = f(C) (specifically 2.5/5.0/10.0 MHz and 1.75/3.5/7.0 MHz). In principle this enables SHI by transmitting on sub-array C receiving on B and, similarly, from B to A as well as HI by transmitting on A receiving on B and, likewise, from B to C. Initially transmit and receive pressure levels of the arrays were measured with the elements of each sub-array wired in parallel. Following contrast administration, preliminary in vitro HI and SHI signal-to-noise ratios of up to 40 dB were obtained. In conclusion, initial design and in vitro characterization of two MFHA's have been performed. They have an overall broad frequency bandwidth of at least two octaves. Due to the special design of the array assembly, the SNR for HI and SHI was comparable to that of regular B-mode and better than commercially available HI systems. However, further research on multi-element MFHA's is required before their potential for in vivo nonlinear contrast imaging can be assessed.     

改善高功率激光二极管阵列光束质量的一种新方法

根据波导模理论，推导了高功率激光二极管阵列的远场分布，根据其分布特点，设计了一种离轴外腔.运用这种外腔，在工作电流为17A时，光束的束宽积从自由运转时的1100mm·mrad减小到128mm·mrad，二极管阵列的光束质量提高了8.5倍左右，输出功率约为自由运转时的75%.     

二维全同Nb4团簇在Cu(100)表面的结构稳定性和电子性质

使用基于密度泛函理论的第一性原理赝势法和超原胞模型，研究了吸附在Cu(100)表面上的二维有序排列的幻数团簇Nb₄的结构稳定性及其电子结构性质.计算表明，四面体结构和平面的菱形结构的Nb₄团簇都可以稳定地吸附在Cu(100)表面上，这个体系很可能有重要的应用前景.在Cu(100)表面上，菱形结构的Nb₄比四面体结构的Nb₄更稳定，从Nb₄团簇的四面体结构到菱形结构，需经过的势垒高度约为0.94eV/团蔟.电子结构的计算表明，在Nb₄吸附后，Cu(100)表面与Nb₄团簇间有明显的电荷重新分布，表面Cu原子的电子态密度也明显改变. 关键词： 4团簇')" href="#">Nb₄团簇 有序排列 结构稳定性 从头计算     

Using light to bioactivate surfaces: A new way of creating oriented, active immunobiosensors

Ultraviolet light can be used to immobilize biomolecules onto thiol reactive surfaces in order to, e.g., make biosensors. The mechanism involves light-induced formation of free, reactive thiol groups in disulphide containing molecules. This technology allows for the creation of arrays of biomolecules with a high degree of reproducibility, circumventing the need for often expensive nano/micro-dispensing technologies. The ultimate size of the immobilized spots is defined by the focal area of the UV beam. Light-induced immobilization has the added benefit that the immobilized molecules will be spatially oriented and covalently bound to the surface. In this paper, we demonstrate the utility of a sensor array created with the new sensor technology when integrated into a microfluidic system. Protein arrays made using light-induced immobilization showed successful antigen/antibody binding in a flow cell allowing the visualisation of real time binding and enzyme activity. This new technology is ideal for the creation of protein/DNA microarrays, can replace present micro-dispensing arraying technologies and is ideal as a molecular imprinting technology.     

电化学刻蚀法制备LaB6场发射微尖锥阵列

采用电化学刻蚀方法,成功制备出单尖的六硼化镧、钼、钨及钨铼合金场发射冷阴极尖锥,并对这几种场发射单尖锥阴极的电子发射性能进行了测试比较.结果表明,LaB₆作为场发射阴极,具有良好的发射性能和稳定性.在〈111〉面单晶LaB₆基片上,用PECVD法沉积非晶硅作掩膜,制备出具有一定高度的LaB₆微尖锥场发射阵列,结果发现,LaB₆基底较为平整,尖锥阵列呈现出各向异性.该结论对LaB₆材料在场发射阴极方面的进一步研究具有重要的指导意义.     

Direct synthesis of porous NiO nanowall arrays on conductive substrates for supercapacitor application

Porous NiO nanowall arrays (NWAs) grown on flexible Fe-Co-Ni alloy have been successfully synthesized by using nullaginite (Ni₂(OH)₂CO₃) as precursor and investigated as supercapacitor electrodes. In details, we adopted a simple hydrothermal method to realize Ni₂(OH)₂CO₃ NWAs and examined their robust mechanical adhesion to substrate via a long-time ultrasonication test. Porous NiO NWAs were then obtained by a post-calcination towards precursors at 500 °C in nitrogen atmosphere. Electrochemical properties of as-synthesized NiO NWAs were evaluated by cyclic voltammetry and galvanostatic charge/discharge; porous NiO NWAs electrode delivered a specific capacitance of 270 F/g (0.67 A/g); even at high current densities, the electrode could still deliver a high capacitance up to 236 F/g (13.35 A/g). Meanwhile, it exhibited excellent cycle lifetime with ∼93% specific capacitance kept after 4000 cycles. These results suggest that as-made porous NiO NWAs electrode is a promising candidate for future thin-film supercapacitors and other microelectronic systems.     

Microstructural characterization and optical polarization of glass with needle-like micro–nano silver oriented arrangement

Homogeneous glasses in the Na₂O–B₂O₃–Al₂O₃–SiO₂ system doped with proper amount of AgCl were obtained by melting at a temperature of 1450 °C. Then, with several steps of treatment, including crystallization, elongation and reduction, the glass with oriented arrangement of needle-like micro–nano silver particles was produced. The microstructure and the optical properties of the glass samples in different stages were studied by SEM-EDAX, FE-SEM and UV–Vis spectrum. The results showed that the glass after elongation and reduction exhibits excellent polarization performance in the wavelength range from 600 nm to 900 nm, with an extinction ratio larger than 45 dB. The glass only elongated shows also slight polarizing performance, which may result from the formation of filament structure of Ag during elongation processing.     

Aligned Nanorod Arrays: Additive and Emergent Properties

Studies of one-dimensional nanostructures of various types (such as quantum wires, nanorods, nanotubes and nanobelts) have progressed substantially during the past decade and have been reviewed by a number of authors. Here, we provide a concise overview of the synthesis and special properties of arrays of parallel nanorods, whose behavior is often quite distinct from that of individual nanorods of the same material. We show that the distinctive behavior of such nanorod arrays may occur due to their exhibiting either additive or emergent properties. The former originates from a simple amplification of some advantageous property shown by a single nanorod, thus making it usable in a practical device; while the latter necessarily involves the presence of the array, and would not be observable from a single nanorod. Nanorod arrays have been shown to have possible applications in diverse areas that include nanolasers, microcavities, surface enhanced Raman effect, photovoltaic cells, field emission sources, gas sensing, electrical discharge and in hydrophobic surfaces. We first present an overview of some of the physical and chemical synthesis strategies for nanorod arrays, followed by a brief review of their applications in the areas just mentioned.     

Proper generating trees and their internal path length

We find the generating function counting the total internal path length of any proper generating tree. This function is expressed in terms of the functions (d(t),h(t)) defining the associated proper Riordan array. This result is important in the theory of Riordan arrays and has several combinatorial interpretations.     

Growth of high-crystallinity uniform GaAs nanowire arrays by molecular beam epitaxy

The self-catalyzed growth of Ga As nanowires(NWs) on silicon(Si) is an effective way to achieve integration between group III–V elements and Si. High-crystallinity uniform Ga As NW arrays were grown by solid-source molecular beam epitaxy(MBE). In this paper, we describe systematic experiments which indicate that the substrate treatment is crucial to the highly crystalline and uniform growth of one-dimensional nanomaterials. The influence of natural oxidation time on the crystallinity and uniformity of Ga As NW arrays was investigated and is discussed in detail. The Ga As NW crystallinity and uniformity are maximized after 20 days of natural oxidation time. This work provides a new solution for producing high-crystallinity uniform III–V nanowire arrays on wafer-scale Si substrates. The highly crystalline uniform NW arrays are expected to be useful for NW-based optical interconnects and Si platform optoelectronic devices.