The difference periodic Ricati equation for the periodic predictionproblem

Gives a comprehensive treatment of several important aspects of the discrete-time periodic Riccati equation (DPRE) arising from the prediction problem for linear discrete-time periodic systems. The authors analyze the symmetric periodic positive semidefinite (SPPS) solution of the DPRE under appropriate assumptions of stabilizability and detectability of the periodic system. Among the results obtained are necessary and sufficient conditions for the existence and uniqueness of the SPPS solution and the stability of the resulting closed-loop system. Some of these results can be seen as extensions of the corresponding results for the time-invariant case; however, a number of them contain contributions to the time-invariant case as well. The paper also gives a numerical algorithm based on an iterative linearization procedure for computing the SPPS solution. The algorithm is a periodic version of Kleinman's algorithm for the time-invariant case     

Scanning electron microscopy studies of failure surfaces of short glass fibre — rubber composites

The failure surfaces of short-glass fibre reinforced rubber composites have been examined by scanning electron microscopy. The tensile, tear, flexing and abrasion modes have been studied. The different modes generate typical fracture surfaces depending on the nature of the test. The technical properties of the composites with and without reinforcing carbon-black filler have been explained on the basis of fracture modes. For comparison, mixes without fibre have also been studied.     

A 2-D five-noded finite element to model power singularity

A 2-D five-noded finite element which contains a singularity is developed. The new element is compatible with cubic standard isoparametric elements. The main advantage of using cubic isoparametric elements over quadratic elements is to reduce the number of elements required to model a structure for results of comparable accuracy. The element is tested on two different examples. In the first example, an edge crack problem is analyzed using two different meshes. The second example is a crack perpendicular to the interface problem which is solved for two different specific composites. The results obtained using the proposed element are compared with those obtained using other existing elements in the literature. Those comparisons demonstrate the superiority of the present technique in using less number of elements and nodes to produce accurate results.     

Dynamic active impedance for vibration suppression of Large Space Structures

This paper approaches the control of Large Space Structures (LSS) by modulating the impedance of a joint to obtain desired vibration suppression. The suppression of several vibration modes cannot be done efficiently with a constant gain control system, i.e. a constant joint impedance. A dynamic active impedance controller is required and is proposed herein for this purpose. The method is applied to a flexible beam which is modelled by the Euler-Bernoulli equation. The experimental set-up and its operation can emulate a typical slew manoeuvre about a fixed axis. The boundary conditions for the beam in this case are defined for a servomotor at one end and a free condition at the other end. The beam parameters are experimentally identified for the first three modes of vibration. Active impedances are determined separately for the rigid mode and the first three modes of vibration using a pole placement method. The four different active impedances are realized using gain scheduling while transitions between gains follow a cubic polynomial of time. The duration of application of each impedance is determined based on their respective settling time. Preliminary experiments establish the minimum duration for each transition from one active impedance to another in suppressing beam vibrations.     

Adaptive control of robot manipulators via velocity estimatedfeedback

An approach for designing robot controllers using state-space feedback is presented. The robot model parameters are assumed to be unknown and velocity measurements are assumed not to be available. This asymptotically stable control scheme combines an adaptive control law with a sliding observer and does not need additional assumptions on the variation of the inertia matrix eigenvalues. State observation and parameter adaptation are performed simultaneously. The adaptation law, the observer gains, and the control law are designed on the reduced order manifold which results from the invariance of the switching surface     

On the detection of card-sharing traffic through wavelet analysis and Support Vector Machines

In the last years, the interest in methods and techniques for circumventing the security of the available digital video broadcasting systems is continuously increasing. Digital TV providers are struggling to restrict access to their video contents only to authorized users, by deploying more and more sophisticated conditional access systems. At the state-of-the-art, the most significant menace is the card-sharing activity which exploits a known weakness allowing an authorized subscriber to provide access to digital contents to a potentially large group of unauthorized ones connected over a communication network. This is usually realized by using ad hoc customized devices. Detecting the presence of these illegal systems on a network, by recognizing their related traffic is an issue of primary importance. Unfortunately, to avoid the identification of such traffic, payload obfuscation strategies based on encryption are often used, hindering packet inspection techniques.This paper presents a strategy for the detection of card-sharing traffic, empowered by machine-learning-driven traffic classification techniques and based on the natural capability of wavelet analysis to decompose a traffic time series into several component series associated with particular time and frequency scales and hence allowing its observation at different frequency component levels and with different resolutions. These ideas have been used for the proof-of-concept implementation of an SVM-based binary classification scheme that relies only on time regularities of the traffic and not on the packet contents and hence is immune to payload obfuscation techniques.     

基于免疫算法的图像基元提取方法

借鉴免疫细胞的耐受成熟过程和克隆选择过程,将免疫算法引入基元提取问题,以椭圆提取为例对基于免疫算法的基元提取方法的实现方法进行了详细介绍。通过与RHT和SGA算法的比较实验及分析,说明该方法在噪声较多时具有收敛速度快、抗干扰能力强等优点,对图片进行的椭圆提取表明该算法的广泛适用性和实用价值。     

Polycarbonate-linear low density polyethylene blends: Thermal and dynamic-mechanical properties

Blends of polycarbonate (PC) and linear low density polyethylene (LLDPE) of different compositions, in the form of slabs obtained by melt extrusion, have been examined by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA).DSC measurements show that the melting, crystallization and glass transition temperatures of the two polymeric components in the blends are slightly affected by the composition. On the contrary, large differences are observed in the melting behaviour of layers cut at various depths, parallel to the slab surfaces of samples. This supports the occurrence of different crystal morphologies and distribution of the two components within the samples. The study of the crystallization kinetics from the melt blends shows that the crystallization processes of LLDPE are affected by the presence of PC.The dynamic mechanical analysis indicates that modulus, transitions and relaxational behaviour of the polymer components are scarcely affected by the composition. Some variations of the damping factor have been interpreted as due to the phase heterogeneity of the system, arising from the processing conditions and rheological behaviour of the blends.