A novel tunable cascaded IIR microwave photonic filter

A new tunable cascaded infinite impulse response (IIR) microwave photonic filter is presented, based on a novel configuration in which a semiconductor optical amplifier (SOA) is inserted between two active recirculating delay line (RDL) loops. Due to wavelength conversion with cross-gain modulation (XGM) in SOA, interferences between light beams traveling different paths are canceled, ensuring a stable transmission. By employing this configuration, a cascaded IIR microwave photonic filter is firstly achieved. The free spectral range (FSR) and the Q factor are both increased significantly by adopting “vernier effect” technique in the IIR filter. The structure is also tunable by adjusting the length of one RDL loop.     

Effects of variation in modulator temperature during cryogenic modulation in comprehensive two‐dimensional gas chromatography

Many modulation systems in comprehensive 2D GC (GC×GC) are based on cryogenic methods. High trapping temperatures in these systems can result in ineffective trapping of the more volatile compounds, whilst temperatures that are too low can prevent efficient remobilisation of some compounds. To better understand the trapping and release of compounds over a wide range of volatilities, we have investigated a number of different constant temperature modulator settings, and have also examined a constant temperature differential between the cryo‐trap and the chromatographic oven. These investigations have led us to modify the temperature regulation capabilities of the longitudinally modulated cryogenic system (LMCS). In contrast to the current system, where the user sets a constant temperature for the cooling chamber, the user now sets the temperature difference between the cryo‐trap and the chromatographic oven. In this configuration, the cooling chamber temperature increases during the chromatographic run, tracking the oven temperature ramp. This produces more efficient, volatility‐dependent modulation, and increases the range of volatile compounds that can be analysed under optimal trap‐and‐release conditions within a single analytical run. This system also reduces cryogenic fluid consumption.     

Surface plasmon resonance biosensor based on water-soluble ZnO-Au nanocomposites

A wavelength modulation surface plasmon resonance biosensor based on ZnO-Au nanocomposites for the detection of human IgM was developed. Self-assembly technique has the advantages of flexibility, simplicity and the precise control of film component and was applied to the building of the sensor. The ZnO-Au nanocomposites are in a dumbbell-like shape and can be immobilized on the Au film through 1,6-hexanedithiol by covalent attachment. Meanwhile the activated ZnO nanocrystals can be used to connect protein. The biosensor based on ZnO-Au nanocomposites was used to detect human IgM. Some experimental conditions were examined and optimized. In the selected conditions, the modified biosensor exhibits a satisfactory response for human IgM in the concentration range of 0.30-20.00 μg mL⁻¹. However, the biosensor without ZnO-Au nanocomposites shows a response for human IgM in the concentration range of 1.25-20.00 μg mL⁻¹. Compared with the biosensor based on Au film, when the biosensor based on the ZnO-Au nanocomposites was applied, the sensitivity for determination of human IgM is significantly enhanced.     

Investigation of the magnetic properties of ferritin by AFM imaging with magnetic sample modulation

Individual ferritin molecules can be sensitively detected using magnetic sample modulation (MSM) combined with contact mode atomic force microscopy (AFM). To generate an oscillating magnetic field, an alternating current (AC) was applied to a solenoid placed within the base of the AFM sample stage. When a modulated electromagnetic field is applied to samples, ferromagnetic and paramagnetic nanomaterials are induced to vibrate. The flux of the AC electromagnetic field causes the ferritin samples to vibrate with corresponding rhythm and periodicity of the applied field. This motion can be detected and mapped using contact mode AFM with a soft, nonmagnetic cantilever. Changes in the phase and amplitude of the periodic motion of the sample are sensed by the tip to selectively map vibrating magnetic nanomaterials. Particle lithography was used to create nanopatterned test platforms of ferritin for MSM measurements. Regularly spaced structures of proteins provide precise reproducible dimensions for multiple successive surface measurements at dimensions of tens of nanometers. Figure Ring patterns of ferritin were used as nanoscale test platforms to characterize magnetic properties at the level of individual proteins with AFM imaging

一种基于Logistic映射的水声混沌信号测距方法

在浅海水声定位系统中,针对传统声呐信号持续时间长、效率低、正交性差的问题,提出了一种抗噪声、快速、窄带的水声混沌信号。通过推导Logistic混沌序列的混沌性和相关特性;并据此将具有混沌特性的相位信息对混沌序列进行调制。理论表明调制后的水声混沌信号具有正的Lyapunov指数、理想的相关性和窄带性。水域数据分析显示,水声混沌信号依旧表现出混沌性和窄带性;并且与同水域实验的m序列相比,定位精度提高了5 cm左右,信号时长缩短了73 ms,为海洋中动态目标的快速定位提供了参考。     

宽带多速率通用数字调制器的设计与实现

设计了宽带通用调制器结构,分析了该调制器硬件实现的关键技术,给出了基带脉冲成形数字滤波器、多速率插值的CIC滤波器及时钟信号产生的具体实现方法. 利用矢量信号分析仪对调制器进行了测试. 测试结果表明,该调制器可产生速率为0.5～50.0MS/s的通用数字调制信号,矢量幅度误差和频谱满足通信标准的要求.     

Incommensurate modulated structure of the ferromagnetic shape-memory Ni2MnGa martensite

The ferromagnetic shape memory (MSM) alloy Ni₂MnGa undergoes a martensitic transformation (MT) at T=220 K on cooling. The structure of this phase is studied by powder X-ray diffraction experiment. The analysis of the experimental data combined with the huge information reported in literature allowed to conclude that the Ni₂MnGa martensite shows an incommensurate modulated structure closely related to a five-fold layered superstructure. The symmetry of the basic structure is found to be orthorhombic. The structure is refined by Rietveld method with superspace group Immm(00γ)s00 having a=4.2187(1) Å, b=5.5534(1) Å and c=4.1899(1) Å and modulation vector q=0.4248(3)c*. The results show that the modulation is mainly related to the periodic shuffling of the atomic layers perpendicular to the c-axis of the orthorhombic basic structure.     

Magnetic study of two isotypic manganese chloro-sulfides: MnSbS2Cl and the new compound MnBiS2Cl

Among the MnPnQ₂X compounds (Pn: pnictide; Q: chalcogen; X: halogen), two isotypic chloro-sulfides, MnSbS₂Cl and MnBiS₂Cl, have been studied. MnBiS₂Cl is a new compound synthesized by solid state reaction at 500 °C. It is orthorhombic, space group Pnma, with a=9.502(2), b=3.8802(8), , , Z=4. Its X-ray single crystal study shows (001) waved layers of MnS₄Cl₂ octahedra, opposite edge-sharing along b, and corner-sharing along a. Similar magnetic susceptibilities for both compounds have been recorded, indicating high spin Mn²⁺ with anti-ferromagnetic exchange. Correlatively, specific heat versus temperature shows a magnetic transition at for the Sb-bearing compound, and a two-steps magnetic transition at 28 and 32 K for the Bi isotype. The magnetic structure of MnSbS₂Cl has been determined by neutron diffraction, revealing a magnetic ordering at 1.5 K with an incommensurate wave-vector along b (k=[0, 0.3838, 0]). Two modulation models, sinusoidal and helicoidal, give quite equivalent reliability factors (R_mag=0.0573 and 0.0586, respectively).     

Stable manifolds for all monic supercritical focusing nonlinear Schrödinger equations in one dimension

Standing wave solutions of the one-dimensional nonlinear Schrödinger equation

with are well known to be unstable. In this paper we show that asymptotic stability can be achieved provided the perturbations of these standing waves are small and chosen to belong to a codimension one Lipschitz surface. Thus, we construct codimension one asymptotically stable manifolds for all supercritical NLS in one dimension. The considerably more difficult -critical case, for which one wishes to understand the conditional stability of the pseudo-conformal blow-up solutions, is studied in the authors' companion paper Non-generic blow-up solutions for the critical focusing NLS in 1-d, preprint, 2005.

     

用于射频泄漏抑制的相位共轭电路设计

针对方向回溯天线中射频泄漏对相位共轭性能及波束指向性能影响的问题,提出了基于平衡结构的二次混频相位共轭结构,实现射频泄漏抑制。分析了传统相位共轭(phase-conjugating,PON)阵列中射频-中频(radio frequency-intermediate frequency,RF-IF)隔离度对相位共轭性能影响;并针对传统PON阵列射频泄漏抑制较差的问题,设计了基于平衡结构的阻性场效应管(field effect transistor,FET)混频电路来提高射频泄漏抑制指标和相位共轭性能;进一步设计了平衡型的二次混频相位共轭结构,利用跟踪锁相环和同相正交(in-phase/quadrature,IQ)调制结构促进RF-IF隔离。仿真结果表明,本文设计的平衡型二次混频相位共轭电路射频泄漏的抑制高于40 dB,且具有在射频输入功率低至-80 d Bm时,保持约4 dBm的稳定共轭信号输出。