Asymptotically optimal smoothing of averaged LMS estimates for regression parameter tracking

The sequence of estimates formed by the LMS algorithm for a standard linear regression estimation problem is considered. It is known since earlier that smoothing these estimates by simple averaging will lead to, asymptotically, the recursive least-squares algorithm. In this paper, it is first shown that smoothing the LMS estimates using a matrix updating will lead to smoothed estimates with optimal tracking properties, also in case the true parameters are slowly changing as a random walk. The choice of smoothing matrix should be tailored to the properties of the random walk. Second, it is shown that the same accuracy can be obtained also for a modified algorithm, SLAMS, which is based on averages and requires much less computations.     

Feedback linearization of a flexible manipulator near its rigid body manifold

It is shown that a ‘slow’ 2n-dimensional manifold exists in the 4n-dimensional state space of an n-link manipulator with n flexible joints. While the flexible manifold is not linearizable by feedback, its restriction to'the slow manifold is. A method is given for computing a feedback control which achieves an approximate linearization.     

Synchrotrons for hadron therapy: Part I

The treatment of cancer with accelerator beams has a long history with betatrons, linacs, cyclotrons and now synchrotrons being exploited for this purpose. Treatment techniques can be broadly divided into the use of spread-out beams and scanned ‘pencil’ beams. The Bragg-peak behaviour of hadrons makes them ideal candidates for the latter. The combination of precisely focused ‘pencil’ beams with controllable penetration (Bragg peak) and high, radio-biological efficiency (light ions) opens the way to treating the more awkward tumours that are radio-resistant, complex in shape and lodged against critical organs. To accelerate light ions (probably carbon) with pulse-to-pulse energy variation, a synchrotron is the natural choice. The beam scanning system is controlled via an on-line measurement of the particle flux entering the patient and, for this reason, the beam spill must be extended in time (seconds) by a slow-extraction scheme. The quality of the dose intensity profile ultimately depends on the uniformity of the beam spill. This is the greatest challenge for the synchrotron, since slow-extraction schemes are notoriously sensitive. This paper reviews the extraction techniques, describes methods for smoothing the beam spill and outlines the implications for the extraction line and beam delivery system     

螺旋线慢波结构色散特性与耦合阻抗测量系统误差分析

本文系作者研制的＂螺旋线慢波结构冷特性自动测量系统＂的补充,给出了此类系统测量误差的详细理论分析,并对典型数据进行了计算。结果表明色散特性（相光速比）的测量误差可小于0.5%,基波耦合阻抗的测量误差则可达15%。     

On the role of hydrogen in the stress corrosion cracking behavior of Q345R steel in HF vapor environment

The stress corrosion cracking (SCC) behavior of Q345R steel in hydrofluoric acid (HF) vapor environment was investigated. It is shown that Q345R has a high susceptibility to SCC in HF vapor environment, which is negatively correlated with the strain rate. Several different crack morphologies and cracking factors are verified: flat cracks in ferrite are associated with anodic dissolution triggered by micro-galvanic corrosion, and porous cracks at the pearlite and pearlite-ferrite interfaces are mainly influenced by hydrogen. The results of hydrogen charging tests show that pre-charging has little effect on the hydrogen embrittlement of Q345R steel, while in-situ charging leads to severe brittle fracture of the material, because hydrogen interacts with large number of moving dislocations generated by in-situ stretching process and penetrates more readily into the material. The synergistic relationship between hydrogen and dislocation motion is found to be the main mechanism for the transition from ductile to brittle fracture.     

Effects of polarisation on mechanical properties and stress corrosion cracking susceptibility of 7050 aluminium alloy

The effects of polarisation (including cathodic and anodic polarisation) on mechanical properties and stress corrosion cracking (SCC) susceptibility (I_SCC) of 7050 aluminium alloy have been investigated by means of polarisation and slow strain rate test. The results of cathodic polarisation experiments showed that the I_SCC increased with shifting negatively the polarisation potential when the cathodic potential E_C≧?1100 mV(SCE), while it decreased with shifting negatively the polarisation potential when the cathodic potential E_CI_SCC increased severely with increasing the polarisation potential. In addition, the extents for the effect of polarisation potential on I_SCC were different among the 7050 aluminium alloy under various aging states. Polarisation was of the biggest effect on the I_SCC of under aged state, the smallest effect of over aged state and the middle effect of peak aged state. The SCC mechanism of aluminium alloy was a combination of anodic dissolution and hydrogen embrittlement, and the effects of hydrogen on SCC increased with increasing the hydrogen concentration.     

Study on cyclic characteristics of silica gel–water adsorption cooling system driven by variable heat source

The fluctuation of heat source influences the performance of adsorption cooling systems greatly in practical applications. This paper mainly investigates the cyclic characteristics of silica gel–water adsorption cooling system under the condition of general variable heat source, in order to explore the system characteristics and access the related operation strategies. In this work, all practical variable heat sources are regarded as the combination of two different changes: the slow time-varying change (long change) and the fast time-varying change (short change). Based on a transient model of adsorption chiller verified by experiments, the characteristics of adsorption cooling system under both the two types of changes are presented. With the slow time-varying change, the heat source variation rate is a key factor that influences the system performance greatly. And for the fast time-varying change, concentration is being focused on the influence on chiller desorption process. The methods to minimize this effect, such as to change desorption time, is discussed. Moreover, the water tank capacity plays a very important role under both slow time-varying and fast time-varying heat sources. The analysis in this work will eventually contribute to operation strategies under different conditions and methods to decrease the influence of heat source fluctuation.     

等离子体加载大功率微波器件

评述等离子体加载微波管在理论和实验方面的最新进展。在微波管中数量可控的背景等离子体可改善其特性。研究结果清楚地证明 ,等离子体的存在可以显著增加非相对论微波振荡器和放大器的带宽、效率和功率容量 ,并允许工作于无引导磁场。     

Czochralski-grown nitrogen-doped silicon: Electrical properties of MOS structures; A positron annihilation study

Czochralski-grown nitrogen-doped (NCZ) silicon was studied using different methods. Measurements of interface traps density, effective generation lifetime and effective surface generation velocity were performed on selected Metal-Oxide-Semiconductor (MOS) structures. Application of the positron annihilation technique (PAS)—pulsed low energy positron system (PLEPS)—was focused on the detection of nitrogen-related defects in NCZ silicon in the near surface region. PAS—PLEPS technique gave relevant results on p-type NCZ silicon. Low sensitivity in the application to n-type NCZ silicon discriminates the PAS—PLEPS technique and should be alternated by other experimental technique. On the other hand, more pertinent measurement of generation lifetime was performed on MOS structures with n-type Si. Although the generation lifetime decreases in NCZ silicon, considerable lateral homogenization of the relaxation time was observed on the wafer.