Global uniform input-to-state stabilization of large-scale interconnections of MIMO generalized triangular form switched systems

We solve the problem of global uniform input-to-state stabilization with respect to external disturbance signals for a class of large-scale interconnected nonlinear switched systems. The overall system is composed of switched subsystems each of which has the nonlinear MIMO generalized triangular form, which (in contrast to strict-feedback form) has non-invertible input–output maps. The switching signal is an arbitrary unknown piecewise constant function and the feedback constructed does not depend on the switching signal.     

Ultrasonic pulse shaping with optimal lag filters

Attempts to increase the resolution of ultrasound imaging apparata resulted in the desire for precise control over the shape of transmitted ultrasonic pulses. The shape of transmitted ultrasonic pulses can be controlled when a transducer is excited by a signal corresponding to a convolution filter. This article discusses a method of precise ultrasonic pulse shaping using lag filters. A lag filter f_l(t) is a convolution filter calculated for a time-shifted desired output waveform w(t): w(t) → w(t − l). An optimal lag filter is selected by trying all possible values of lag l and selecting a filter with the best performance. The filter coefficients can be calculated using a Fourier transform or least-squares criterion. The quality-limiting factors of the pulse shaping are the length of the filter and the accuracy of the actual excitation signal. The improvement of the pulse-shaping quality can be achieved by accounting for the amplifier transfer function or by accurate DAC-values-to-voltage mapping. The analysis of the experimental results indicates that the developed ultrasonic pulse-shaping technique provides a means for flexible control over the transmitted ultrasonic pulse waveform and frequency. The presented pulse-shaping technique is specially developed for cost effective ultrasound imaging devices utilizing a simplified beamformer composed of a single pair of input/output amplifiers. © 1999 John Wiley & Sons, Inc. Int J Imaging Syst Technol 10, 397–403, 1999     

Decentralized uniform finite-time stabilization of large-scale nonlinear networks by small-gain theorems

We solve the problem of decentralized uniform finite-time stabilization for a large-scale network of nonlinear systems in triangular form which are not feedback linearizable and whose input–output maps are not invertible. For this, we provide a new recursive design to satisfy the conditions of a certain modification of the small-gain theorems for the case of the uniform finite-time stability of large-scale networks. In the general case, we consider the general triangular form systems whose input–output links are surjections only. In addition, we consider the special case of the triangular form systems with polynomial integrators, which is also needed as the first step of the proof of our main result. In the latter case, the design becomes constructive, the decentralized stabilizers can be designed explicitly, and this is demonstrated by examples.     

Progress and challenges of 3D-printing technologies in the manufacturing of piezoceramics

Piezoceramic materials provide the foundation for essential components of modern engineering applications in the fields of acoustics, sensorics, biomedical devices, and microelectronics. With device miniaturization, the industrial requirements for piezoceramics with complex geometries and improved efficiencies has grown tremendously. Traditionally manufactured piezoceramics demonstrate great piezoelectric properties but poor shape conformity. Additive manufacturing (AM) technologies, being a successful contender in the field of technical ceramics, makes its way into piezoceramics production. AM technology applied to traditional piezoelectric materials has many obstacles to overcome, since typical piezoceramic products require complex and intricate shapes, and often consist of composite materials. As a solution to these problems, AM technology can be transformed into a robust fabrication tool. This review intends to outline the current state of the art of AM technologies applied to the manufacture of piezoceramic materials. Modern piezoceramic materials are described in detail, including the effects of doping and texturing. The properties of piezoceramics and their composites are compared for traditionally and additively manufactured devices. The piezolectric properties of the materials produced using different manufacturing methods are summarized in comprehensive tables and figures, where the emerging trends in physical characteristics are revealed. The pros and cons of AM technologies are discussed, and the problems to be addressed in future work are highlighted.     

Assessment of forest cover in Russia by combining a wall-to-wall coarse-resolution land-cover map with a sample of 30 m resolution forest maps

The process of gathering land-cover information has evolved significantly over the last decade (2000–2010). In addition to this, current technical infrastructure allows for more rapid and efficient processing of large multi-temporal image databases at continental scale. But whereas the data availability and processing capabilities have increased, the production of dedicated land-cover products with adequate accuracy is still a prerequisite for most users. Indeed, spatially explicit land-cover information is important and does not exist for many regions. Our study focuses on the boreal Eurasia region for which limited land-cover information is available at regional level.

The main aim of this paper is to demonstrate that a coarse-resolution land-cover map of the Russian Federation, the ‘TerraNorte’ map at 230 m × 230 m resolution for the year 2010, can be used in combination with a sample of reference forest maps at 30 m resolution to correctly assess forest cover in the Russian federation.

First, an accuracy assessment of the TerraNorte map is carried out through the use of reference forest maps derived from finer-resolution satellite imagery (Landsat Thematic Mapper (TM) sensor). A sample of 32 sites was selected for the detailed identification of forest cover from Landsat TM imagery. A methodological approach is developed to process and analyse the Landsat imagery based on unsupervised classification and cluster-based visual labelling. The resulting forest maps over the 32 sites are then used to evaluate the accuracy of the forest classes of the TerraNorte land-cover map. A regression analysis shows that the TerraNorte map produces satisfactory results for areas south of 65° N, whereas several forest classes in more northern areas have lower accuracy. This might be explained by the strong reflectance of background (i.e. non-tree) cover.

A forest area estimate is then derived by calibration of the TerraNorte Russian map using a sample of Landsat-derived reference maps (using a regression estimator approach). This estimate compares very well with the FAO FRA exercise for 2010 (1% difference for total forested area). We conclude that the TerraNorte map combined with finer-resolution reference maps can be used as a reliable spatial information layer for forest resources assessment over the Russian Federation at national scale.     

Global Stabilization of the Generalized MIMO Triangular Systems With Singular Input-Output Links

This work is devoted to the problem of global stabilization for a class of the general multi-input and multi-output (MIMO) triangular systems which are not feedback linearizable. To solve the problem, we develop a specific backstepping procedure and generalize some existing results. Since we deal with the global stabilization for the singular and MIMO case, the technique of the proof differs from the standard backstepping algorithms.