Michelson干涉仪式光纤空气声传感器

介绍了一种用于直升机等低空目标探测的光纤空气声传感器.该传感器基于光纤Michelson干涉仪的原理,结合弹性盘片的应力应变理论分析和光纤粘接的工艺设计,采用相位载波解调技术进行信号解调.对比实验测试验证了这种声音探测技术可行性.传感器理论灵敏度为2.38 rad/Pa,实测灵敏度为1.5 rad/Pa,采用PGC相位解调理论最小可探测的最小声信号为6.7 μPa,即9.5 dB.传感器在20～300 Hz范围内响应基本平坦.结合声音传播规律分析并肯定其在实用中的可行性.     

用于光盘记录介质的“偶氮染料-聚合物”复合材料

由噻唑类偶氮染料和硝化纤维组成的复合材料涂布于玻璃载体上可用作光盘记录介质,测定这一记录介质的光学性质和物理性质,表明其具有良好的记录灵敏性和读写特性。     

高密度光数据存储技术的发展

讨论了信息技术发展中信息数据存储的重要性,比较了磁存储和光存储的各自特点,介绍了光盘存储技术的发展趋势和高度光盘存储技术的关键问题,进一步讨论了超高密度光存储的发展可能。     

并行多控制器光盘阵列系统

介绍了一种新型的并行多控制器光盘阵列系统。在传统的光盘阵列系统中,往往采用单一控制器控制多驱动器阵列系统,但主机对于连接的驱动器数目有特定限制,对阵列整体性能也有所限制。该系统中采用并行多阵列控制器组成光盘阵列。试验证明,采用该方法设计的光盘阵列相对于传统的光盘阵列系统可以有效地降低系统的复杂程度,取得良好的控制效果。     

Synchronous vibration parameters identification by tip timing measurements

The Blade Tip Timing (BTT) measurement system is a technique to measure vibration parameters of a rotating bladed disk. In particular for synchronous vibrations the BTT provides signals versus the rotation speed of the disk starting from the measurement of the time of arrival (TOA) of each blade under the tip timing probes. The signals must be post processed in order to obtain the interesting parameters of each blade vibration. The paper presents a method to extract the main parameters (amplitude and frequency) in resonance condition from the tip timing measurements. The proposed method is a revision of the already existing well known Two-Parameter Plot (2PP) method which requires a minimum of two probes. Improvements to the existing 2PP method are here suggested mainly in the part of engine order identification.The proposed method is then applied to the BTT measured signals coming from a rotating bladed disk excited at different engine orders. At the same time on the disk the vibration of one blade was detected by strain gauges. The strain gauges were calibrated and they provide the reference values of the vibration parameters. The vibration parameters derived by the proposed method are in agreement with those obtained by the strain gauges methodology.     

Capacitance of an elliptical disk on a semi-infinite dielectric material

Using an integral transform, the mixed boundary value problem of a conducting, elliptical disk on a dielectric half-space in an electric field is reduced to the solution of an integral equation. An analytical expression of the electric system capacitance is derived, which is a function of the eccentricity of the elliptical disk. The electric charge and electric stress distribute non-uniformly over the surface of the elliptical disk and display local singularities at the edge of the elliptical disk. The square root singularity of the electric field at the edge of the elliptical disk leads to the divergent of the resultant force on the elliptical disk, which is physically unrealistic. There likely exist geometrical constraint and/or field constraint to limit the presence of the square root singularity of the electric field. For any symmetric conductor in an infinite space that consists of air (vacuum) and a semi-infinite dielectric material with symmetric plane being in the interface between the air and the dielectric material, the electric potential in the space is independent of the dielectric constant of the dielectric material.     

Influence of periodic excitation on self-sustained vibrations of one disk rotors in arbitrary length journals bearings

Interaction of forced and self-sustained vibrations of one disk rotor is described by nonlinear finite-degree-of-freedom dynamical system. The shaft of the rotor is supported by two journal bearings. The combination of the shooting technique and the continuation algorithm is used to study the rotor periodic vibrations. The Floquet multipliers are calculated to analyze periodic vibrations stability. The results of periodic motions analysis are shown on the frequency response. The quasi-periodic motions are investigated. These nonlinear vibrations coexist with the periodic forced vibrations.     

Perpendicular magnetic recording—Its development and realization—

The principle of conventional magnetic recording is that magnetic fields are applied parallel to the plane of the magnetic medium. As described in this paper, the invention and development of a new method of placing the magnetized information perpendicular to the plane of the magnetic recording medium is presented. The yield in the mass production of high-density hard disk drives (HDDs) for perpendicular recording is much higher than that of HDDs for conventional recording. Consequently, it is estimated that as many as 75% of the 500 million HDDs to be shipped this year will use this technology.     

Scheduling sensor activity for information coverage of discrete targets in sensor networks

In this paper, we study the problem of scheduling sensor activity to cover a set of targets with known locations such that all targets can be monitored all the time and the network can operate as long as possible. A solution to this scheduling problem is to partition all sensors into some sensor covers such that each cover can monitor all targets and the covers are activated sequentially. In this paper, we propose to provide information coverage instead of the conventional sensing disk coverage for target. The notion of information coverage is based on estimation theory to exploit the collaborative nature of geographically distributed sensors. Due to the use of information coverage, a target that is not within the sensing disk of any single sensor can still be considered to be monitored (information covered) by the cooperation of more than one sensor. This change of the problem settings complicates the solutions compared to that by using a disk coverage model. We first define the target information coverage (TIC) problem and prove its NP‐completeness. We then propose a heuristic to approximately solve our problem. Simulation results show that our heuristic is better than an existing algorithm and is close to the upper bound when only the sensing disk coverage model is used. Furthermore, simulation results also show that the network lifetime can be significantly improved by using the notion of information coverage compared with that by using the conventional definition of sensing disk coverage. Copyright © 2008 John Wiley & Sons, Ltd.     

The period function of potential systems of polynomials with real zeros

We consider some analytic behaviors (convexity, monotonicity and number of critical points) of the period function of period annuli of the potential system and focus on the case when g(x) is a polynomial whose roots are all real. The main contributions of this paper are twofold: (i) analytic behaviors are given for the period functions of period annuli surrounding one or more and simple or degenerate equilibria; (ii) as a nontrivial application of the general conclusions in (i), a purely analytical and shorter proof is provided for a result for the case degg=4 recently obtained by Chengzhi Li and Kening Lu with some help of computer algebra [Chengzhi Li, Kening Lu, The period function of hyperelliptic Hamiltonian of degree 5 with real critical points, Nonlinearity 21 (2008) 465-483].