多芯光纤折射率与内应力分布重构技术（特邀）

介绍了一种基于定量相位显微（Quantitative phase microscopy,QPM）法、Brace-K?hler补偿器（Brace-K?hler compensator,BKC）法与机器视觉技术的多芯光纤综合参数测试系统,并利用该系统获得了七芯光纤的折射率分布与几何结构,单模光纤的内应力分布图。采用横向测量方式的QPM法避免了截断光纤造成的损坏,采用改进的BKC法优化了光延迟量的获取方式,结合机器视觉技术,实现了多模块、高空间分辨率、快速准确的光纤参数测量,其中相对折射率差的精度约5×10?4量级,单模光纤内应力测量分辨率约0.5 MPa。通过与既有的光纤产品技术指标对比,证明了该系统具有测量准确性,测试结果为多芯光纤在传输和传感等多领域的应用提供了数据支撑。     

一种新型的认知无线电频谱空穴自适应检测算法

根据认知无线电实际频谱需求,通过对弱信号检测技术的研究,该文首次在认知无线电领域提出了一种基于三重矩阵累积估计的频谱空穴检测算法,该算法将频域块自适应滤波与矩阵重构、累积估计和频域平滑相结合实现弱信号检测。最后以QPSK调制信号为例进行了算法的计算机仿真,给出了性能分析。仿真结果表明该检测算法能够快速有效地实现弱信号检测并具有较高的检测概率,完全可以应用于认知无线电的频谱空穴检测。     

穴位神经刺激法治疗耳鸣的疗效观察

目的 :探讨穴位神经刺激法治疗耳鸣的疗效。方法 :穴位神经刺激组采用韩氏穴位神经刺激仪 (HANS)的穴位神经刺激法对 60例( 10 0耳 )进行耳鸣治疗 ,对照组应用ATP针、辅酶A针、维生素B1 针、维生素B1 2 针等药物进行耳鸣治疗。结果 :穴位神经刺激组 10 0耳 ,显效 :3 8耳 ( 3 8% ) ,有效 :46耳 ( 4 6% ) ,无效 :16耳 ( 16% ) ,总有效率为 84%。对照组 3 0例 ( 5 2耳 ) ,显效 :7耳 ( 13 .4% ) ,有效 :18耳 ( 3 4.6% ) ,无效 :2 7耳 ( 5 2 % ) ,总有效率为 48%。经统计学处理P <0 .0 1,两组疗效比较 ,穴位神经刺激组明显优于对照组 ,结论 :穴位神经刺激法是治疗耳鸣较为理想的方法     

Design of a Vlasov antenna with reflector

The Vlasov antenna, composed of a slant-cut radiator and a parabolic cylinder reflector, is designed by using vector diffraction theory. The experiential formulae on the antenna design are given. A C-band Vlasov antenna, composed of a cylindrical waveguide of 4.5?cm radius with 35° as the bevel-cut angle, and a reflector, was designed. The calculations and measurement results show that the antenna can work over a wide bandwidth (from 3.6?GHz to 5.6?GHz). The gain is about 21?dBi at 4?GHz and over 23?dBi at 5.6?GHz. The energy emission efficiency exceeds 90% at 4?GHz and the overall efficiency exceeds 88% in the range from 3.6?GHz to 5.6?GHz.     

皮秒级光控光开关研究现状

介绍了目前常用的几种光控光开关(M-Z型、平面反射型、光克尔型、NOLM型、频移型等)的工作原理、性能和应用;介绍了几类对全光开关研究有十分重要意义的新材料;最后探讨了关于如何能够更好的研究光控光开关的一些思路。     

电子断层成像技术在两种纳米材料中的应用

本文通过使用电子断层成像技术,分别对纳米金样品和纳米囊泡药物两种材料进行多角度成像研究,发现纳米金样品为圆盘状,并没有棒状结构,同时还测量了纳米金盘的厚度。纳米囊泡拟包含药物为膜状结构而非针状或棒状。多角度成像排除了二维电镜图片的假象,显示电子断层成像技术在纳米材料的应用前景。     

Tailoring zero chromatic dispersion into the 1.5?1.6 ?m low-loss spectral region of single-mode fibres

We have designed and fabricated single-mode silica fibres that have zero chromatic dispersion within the 1.5?1.6 ?m low-loss spectral region by controlling their waveguide dispersion and dopant-dependent material dispersion. These fibres have small core diameters and large core-cladding refractive-index differences, ?n = 0.018, corresponding to a 13 mole % GeO2 dopant concentration in the core. The zero-dispersion wavelength was shifted from ?0 = 1.375 ? to ?0 = 1.54 ? by decreasing the fibre core diameter from 7 ?m to 4.8 ?m. This ability to tailor the minimum dispersion wavelength to the ultra-low-loss region near 1.55 ?m is important for designing single-mode fibres for very long distance and very high capacity optical transmission.     

双离子束溅射制备SiNx薄膜的光致发光性质

采用双离子束溅射法制备了SiNx薄膜，用XRD、XPS、FTIR等对薄膜的结构进行了表征，并且分析了样品的光致发光(PL)特性。发现在225nm的紫外光激发下，样品在室温下可发射高强度的可见光，峰位分别位于470nm、520nm和620nm，用能隙态模型讨论了可能的发光机理。     

The Existence of a Zero-Cross-Polarization Mode Through Rain

In this paper, it is shown that there exists a zero-cross-polarization mode through rain in which no cross polarization will be induced when orthogonally polarized signals are transmitted. This mode is derived based on a matrix model of the rain-induced depolarization effect for the linear case suggested by Chu [12]. It is also assumed that when the canting angles O of the raindrops are treated as a random variable, the received signal will have an amplitude equal to its expectation value weighted by the probability density of ?, f (). The zero-cross-polarization mode through rain will then be two orthogonal linear polarizations at an angle ?away from the conventional vertical and horizontal directions. The magnitude of ?can be determined if the statistical distribution of the canting angles is partially known. In fact, ?is determined by only two parameters, ?and ?eff, which can be obtained from measured data. It is also shown that whenf (?) is sysmetric about its mean value, the magnitude of ?will be exactly that mean value. Some data reported by Chu [12] for ?and ?eff provide an example. The results are also extended to the cases of circular polarizations and satellite communications.     

Influence of ZnO Inclusions on the Low-Temperature Thermoelectric Properties of CoSb3

CoSb₃ composites with different amounts of ZnO nanoparticles (2?wt.% to 12?wt.%) were prepared from nanosized ZnO (commercial) and micron-sized CoSb₃ (obtained via solid-state reaction) particles mixed in solution and freeze dried. The resulting powders were densified by spark plasma sintering. The samples were characterized by x-ray diffraction and scanning electron microscopy. It was found that ZnO forms micron-sized clusters at the grain boundaries of the matrix material. The thermoelectric properties (electrical resistivity, thermopower, and thermal conductivity) were measured in the 2?K to 300?K temperature range. Both the electrical and thermal conductivities were observed to decrease with increasing ZnO content. The dimensionless figure of merit ZT was improved by up to 30% at 300?K for the sample containing 2?wt.% ZnO.     

A fully integrated multi-band ED-mode pHEMT VCO using variable transformer and switched resonator

A systematic approach to the design of a reconfigurable LC-coupled voltage-controlled oscillator (VCO) is proposed in this article. The focus is on the choice of the reactive elements of the resonance tank which are most suitable to switch to the desired oscillation frequencies. The optimum Q of the tank will be determined by the selected component. We report a 0.5-µm enhancement–depletion (ED) mode pHEMT (HEMT, high-electron mobility transistor) multiple-frequency VCO, and the generation of multiple frequencies are achieved using switched resonator topology. LC-tank circuit is built by square transformers. By careful selection of the reactive elements, evenly distributed results showed at each designed band. The multi-band ED-mode pHEMT VCO showed the output power of ?4.7?dBm for 2?GHz band, ?6.67?dBm for 3.86?GHz band and ?5.9?dBm for 4.5?GHz band, respectively. The phase noises at 1?MHz offset frequency from carrier were ?112.8?dBc/Hz for 2?GHz, ?105?dBc/Hz for 3.86?GHz and ?103.3?dBc/Hz for 4.5?GHz, respectively. The total chip size is only 1.17?×?0.83?mm².     

AC Conductivity and Diffuse Reflectance Studies of Ag-TiO2 Nanoparticles

Silver (Ag)-TiO₂ nanoparticles synthesized by a low-temperature hydrothermal method in the anatase phase have been investigated by x-ray diffraction. Transmission electron microscopy has been used for morphological studies. Surface areas were studied by the Brunauer?CEmmett?CTeller method. Alternating-current (AC) conductivity and dielectric properties were studied for various dopant levels of 0.25?wt.%, 0.5?wt.%, and 1.0?wt.% at 300?K in the frequency range from 42?Hz to 5?MHz. AC conductivity and dielectric properties of TiO₂ nanoparticles were greatly affected by loading with Ag. At high frequencies, the materials showed high AC conductivity and low dielectric constant. Diffuse reflectance studies were carried out for various dopant levels at 300?K by ultraviolet?Cvisible (UV?CVis) spectroscopy. Considerable absorption of visible light by 0.5?wt.% and 1.0?wt.% Ag-TiO₂ nanoparticles was observed due to the decrease of the energy band gap on Ag loading.     

Very low-frequency measurements of flicker noise in silicon planar transistors

The noise-power spectrum from 0.01 to 10?4 Hz is measured using a progressive bandwidth-measuring method. The 1/f law is verified, and it is found that flicker noise may be represented in the common-emitter configuration by an input current generator iB given in terms of current collector Ie and current gain ? by iB2? = C?f/f Ie3/2/?2     

Development of a Measurement Method for the Thermal Conductivity of a Thick Film Prepared by a Screen-Printing Technique

We propose a method that allows us to evaluate the thermal conductivity of a conductive material that has thickness on the order of microns. The key feature of the proposed method is use of a complete thermoelectric device with electrodes and a substrate, while conventional methods measure the temperature gradient of thermoelectric materials directly without electrodes. The measured thermal conductivity of a ZnSb film annealed at 380°C in N₂ ambient for 16?min to 26?min is 1.2?W/m?K to 1.4?W/m?K. The measurement shows that thermoelectric film prepared by a screen-printing technique has lower thermal conductivity than bulk material (2.2?W/m?K to 2.4?W/m?K) because the screen-printing technique generates high porosity in the film. The lower measured thermal conductivity of the porous films compared with bulk material supports the reliability of the proposed measurement method.     

Dielectric Properties of Fluid-Saturated Bone

The dielectric relaxation of bovine femoral compact bone specimens in vitro, saturated with 0.9 percent NaCI solution is determined by applying a constant current pulse and measuring the change in voltage with time. For specimens in which the current is in the plane perpendicular to the length of the whole bone and along the radial direction (radial specimens), the relaxation is confined to the time domain, t50 ?s; for longitudinal specimens, the relaxation, if any, would be for t1 ?s. The long-time resistivity of the latter is ?45 to 48 ?m; for the radial specimens, it is ?3 to 4 times greater. The resistivity of the fluid is 0.72 ?m. The results indicate that the dielectric behavior of fluid-saturated compact bone in vitro, and, hence, possibly also of in vivo bone, is determined mostly by the fluid-fllled pores. This has implications that contradict some of the commonly accepted views on the electromechanical effect in bone.     

含铝的富硅二氧化硅薄膜的发光特性及结构

采用双离子束共溅射技术制备出掺铝的富硅二氧化硅复合薄膜(A1SiO)，采用荧光分光光度计对样品进行PL测试表明：A1SiO复合膜共有三个发光峰，分别在370nm、410nm、510nm处。发光峰的位置随铝含量的变化基本上没有改变，峰强随铝含量有变化，且510nm处的峰强随铝含量增加而增强。PLE结果表明：370nm和410nm的PL峰与样品中的氧空位缺陷有关，而510nm的PL峰则是由于铝的掺入改变了样品中的缺陷状态所致，是Al、Si、O共同而复杂的作用。     

A 5-GHz low-voltage and low-power CMOS LC voltage controlled oscillator for 802.11a wireless LAN applications

In this paper, a low phase noise and low power 5.15?GHz LC-tank VCO is presented and analysed. The phase noise achieved is??91,??116 and??126?dBc/Hz at 100?KHz, 1?MHz and 3?MHz offsets respectively from the carrier frequency of 5.15?GHz, with 1.8?V power supply voltage and giving a very low power consumption of about 2.5?mW by considering the proposed oscillator topology, which consumes less power than the classical oscillator using the traditional differential transconductor pair. A broad tuning range has been achieved by means of standard mode PMOS varactors. The tunability of the designed VCO covers 530?MHz, from 4.78?GHz up to 5.31?GHz. Predicted performance has been verified by analyses and simulations using ELDO-RF tool with 0.35?µm CMOS TSMC parameters.     

Energy Conservation via Antenna Scheduling in Fiber-Connected Femto Base Stations

We formulated the energy consumption of previously proposed broadband wireless access with fibre-connected massively distributed antennas (BWA-FMDA) architecture under a generalized framework and developed an optimization tool in a femtocell cluster based on coordinated multipoint transmission (femto-CoMP) to maximize energy efficiency by adjusting the number of transmission antennas and controlling transmission power in zero-forcing beamforming. Based on the analysis results, we group every two neighboring antennas in multiple femto-CoMP configurations and proposed a new network configuration scheme that uses antenna scheduling to simultaneously improve spectral and energy efficiency. Compared with standalone femtocells, the proposed scheme is shown in a typical office building to increase energy efficiency by 64?%?~?160?% and spectral efficiency by 2?%?~?36?%. Compared with our previous BWA-FMDA configurations, the new scheme is able to improve energy efficiency by 6?%?~?68?% and spectral efficiency by 15?%?~?55?%. The exact gain depends on network configurations and transmission power levels.     

On the structure of the superconducting ortho-II phase of YBa2Cu3O6.51

From the intensities of superstructure reflections, the structure of the ortho-II phase in YBa₂Cu₃O_5.51(5) (T_c=55.8K) was determined by single crystal x-ray diffraction. In the basal plane of the 2a×b×c supercell, the oxygen atoms order to alternating Cu?O?Cu and Cu?Cu chains. Due to the oxygen order, the barium and yttrium atoms are displaced in (100) direction in an antiferrodistortive way (Ba-shift: 0.046Å toward the Cu?O?Cu chains, Y-shift: 0.008Å toward the Cu?Cu chains). The apex oxygen and copper atoms of the superconducting planes are displaced in (001) direction. The Ba displacements are confirmed by anomalous scattering near the Ba?K absorption edge observed by synchrotron x-ray diffraction. A rigid ion model shows that the cation displacements stabilize the ortho-II structure by reducing its lattice energy.