Recent developments in magnetic levitation

New developments in magnetic levitation by tuned circuits are described. Suspension of relatively large weights at low frequencies is now possible. The system is extremely simple and therefore reliable. Owing to the high reliability and cylindrical symmetry, the levitation is suitable for magnetic bearings.     

Recent developments in power transistors

Power transistors capable of providing five watts output are now in production. Because these units are relatively non-linear in their characteristics, large signal graphical analysis of their behavior is necessary. To facilitate this, the static characteristics of the grounded base, grounded emitter, and grounded collector circuits are presented for several temperatures. Since power transistors are seldom driven with a high impedance source, the input voltages must be known as well as the input currents. These characteristics are drawn to indicate both simultaneously on one chart. The power that must be removed from the junction of these transistors requires that the mounting for the transistor be thermally adequate to remove the heat without allowing the temperature of the Junction to exceed its critical value. The temperature power relationship is discussed and the theoretical size requirements for a heat dissipator are shown for free air convection and forced convection.     

Recent developments in light-emitting-diode technology

This paper describes recent trends in LED technology. Emphasis is placed on the LED materials and device-fabrication technologies that have resulted in larger and brighter LED displays with a variety of colors, and on the monolithic red-emitting LED displays that are commonly employed as watch and calculator displays.     

Recent developments in micromachined silicon

This paper provides a review, directed at scientists and engineers concerned with microsystems technology, of advances in microelectromechanical systems (MEMS). The emphasis is on silicon technology, where the electrical properties of the material are exploited in circuitry and the mechanical properties are used in sensor and microstructure applications. Developments in surface micromachining are discussed, and applications in sensors, microelectronic devices, vacuum microanalysis systems, microfluidics, and optoelectronic subsystems are reviewed. Some emerging technologies are assessed and promising new research directions are identified     

Recent developments in feedback communication

The use of a noiseless feedback communication channel to improve both digital and analog transmission is discussed. The feedback channel is used in an iterative signaling procedure called center-of-gravity feedback. Suboptimum schemes having a less severe-feedback requirement are also treated.     

Accurate method for characterising single-mode fibres: theory and experiment

We present a direct method for determining the modal field from the far-field pattern of single-mode fibres having arbitrary index profiles. Analysis of experimental data shows that the method is relatively simple compared to other methods and gives accurate results.     

应用激光化学的发展近况

本文报导了近年来激光在化学中期应用取得进展的一些成功实例，并提出了激光化学在今后十年内一些看来很有前途的应用领域。请如激光分离同位素，激光提纯化学品，激光热解合成超细粉末材料，激光在分析化学中的应用，激光催化，激光化学沉积及重要化学药品的合成等。由所取得的成果可以予期，应用激光化学将会有一个美好的前景。     

Recent developments in lightwave network analysis

The widespread use of photonic systems having microwave modulation bandwidths, coupled with the inclusion of photonic components in microwave and millimetre-wave systems, is creating a demand for efficient characterisation techniques. In particular, new tools will be required for the measurement of fundamental quantities such as the microwave frequency response, bandwidth, gain and return loss of microwave photonic components. However, existing lightwave measurement techniques are primitive when compared with conventional RF and microwave network analysis. This paper provides a review of the theory and techniques used for the small-signal characterisation of microwave photonic components. State-of-the-art architectures for lightwave network analysers and the corresponding two-port calibration techniques are described     

Recent developments in rapid thermal processing

Rapid thermal annealing (RTA) with a short dwell time at maximum temperature is used with ion implantation to form shallow junctions and polycrystalline-Si gate electrodes in complementary, metal-oxide semiconductor (CMOS) Si processing. Wafers are heated by electric lamps or steady heat sources with rapid wafer transfer. Advanced methods use “spike anneals,” wherein high-temperature ramp rates are used for both heating and cooling while also minimizing the dwell time at peak temperature to nominally zero. The fast thermal cycles are required to reduce the undesirable effects of transient-enhanced diffusion (TED) and thermal deactivation of the dopants. Because junction profiles are sensitive to annealing temperature, the challenge in spike annealing is to maintain temperature uniformity across the wafer and repeatability from wafer to wafer. Multiple lamp systems use arrayed temperature sensors for individual control zones. Other methods rely on process chambers that are designed for uniform wafer heating. Generally, sophisticated techniques for accurate temperature measurement and control by emissivity-compensated infrared pyrometry are required because processed Si wafers exhibit appreciable variation in emissivity.     

Recent developments in silicon optoelectronic devices

Due to the rapid growth of the internet and multi-media communication networks, there are urgent needs and tremendous commercial values in the development of optoelectronics integrated circuits (OEICs). This work reviews the recent developments and the prospect of silicon-based integrated optoelectronic circuits (Si-OEICs). The technological aspects of porous silicon and oxynitride devices for integrated optoelectronic applications are discussed. Some optoelectronic devices being realized with these technologies are described. Recent achievements indicate that the present constraints for using Si-based materials in optoelectronics are mainly technological rather than physical. Once these technological difficulties are resolved, the realization and applications of Si-OEICs will grow rapidly.     

Recent developments in magnetic bubble technology

In the year between the September 1970 AIME meeting in New York and the 1971 AIME meeting in San Francisco, rapid advancement of material and circuit technology for magnetic bubble-domain memory circuits has taken place. This paper summarizes the advancement in field-access circuits (10,000 bit propagation loops, a 3600 bit memory system, 10 megabit/ square inch density, and 1 MHz propagation) and the development of single-current propagation circuits which do not require a high-frequency rotating magnetic field.     

Recent developments in detection, imaging and classification for airborne maritime surveillance

The role of maritime patrol missions is to monitor large oceanic areas. The authors focus on a complete signal-processing sequence from the primary detection of the targets to their classification or recognition from an airborne radar. Contrary to the classical approach in which detection, tracking, imaging and classification are considered separately, here the authors propose an integrated strategy based on a close cooperation among all of them. Recent developments in high range resolution target detection are presented and their integration in the complete system is discussed to limit false alarms. High-resolution ISAR imaging of ships is then tackled and associated with a feature extraction process and a support vector machine classifier. A set of real data is used to illustrate the imaging and classification results.     

Recent developments and trends in bipolar analog arrays

Recent developments in bipolar analog arrays are reviewed. The use of tiles, their characteristics, and impact on design is evaluated. The progression from breadboarding to computer-aided simulation of array circuits with sophisticated transistor models is discussed. Design layout tools and functional libraries for the user are also reviewed in terms of their importance to analog array design. The increased use of arrays has revealed new problems and responses to them are discussed. Limitations of analog arrays with respect to full custom IC design are delineated. The paper concludes with a short discussion of future trends.     

Recent developments in hermetically coated optical fiber

Recent progress on the development of hermetically coated optical fiber is presented. This fiber provides improved fatigue resistance; high usable strength; and excellent resistance to hydrogen permeation, 25-90°C water, and corrosive chemicals such as hydrofluoric acid and boiling sodium hydroxide. These attributes make the hermetically coated fiber an excellent candidate for use in undersea cables and other special applications where a harsh environment prevails     

Recent developments in spectroscopy of quantum structures

Two spectroscopic techniques, modulated reflectance spectroscopy and surface photovoltage spectroscopy, are being used increasingly to probe the electronic structure of low-dimensional semiconductors. We have found improved versions of these techniques: soft contact electroreflectance and soft contact surface photovoltage which offer operational advantages as well as extend the range of these spectroscopies. We also provide analytic formulation for extracting the transition parameters from the measured surface photovoltage spectrum of a quantum structure.     

Recent developments in securing Internet routing protocols

Routing protocols distribute network topology information around the routers of a network. They are part of the critical network infrastructure, but are vulnerable to both internal and external attacks. In this paper, different routing protocols are first introduced, followed by reviews of routing protocol security publications in academia and industry. The general vulnerabilities and threats of routing protocols are then analysed. The two major protection countermeasures for both link-state routing protocols and distance-vector routing protocols are presented in detail. The popular hacking tools which can be used directly or customised to launch attacks are described. The product vendors of routing protocol security and the best practice adopted by network carriers and ISPs are investigated. The paper aims to provide an overview of Internet routing protocol security, and highlight areas for further research.