Bulletin of the Polish Academy of Sciences. Technical Sciences
A new class of externally positive 2D linear systems described by the general model and the Roesser model is introduced. It is shown that the 2D linear systems are externally positive if and only if their impulse responses are not negative. The relationship between external and (internal) positiveness of 2 D linear systems is also discussed.
A novel solution for fully-balanced transconductance amplifier controlled from body terminals is presented. The circuit operates from a single supply voltage of only 3V and exhibits very large frequency range.
This paper presents measuring and experimental results of A/D converters with current mode sigma delta modulators. The sigma delta modulator structures are composed of current mode blocks with transconductance amplifiers and their parasitic input capacitances. Sigma delta modulator structures were designed and simulated by using VLSISPICE COMPASS DESIGN program and finally designed by using UNCLE...
The MPEG-2 video coding standard provides the functionality of spatial scalability in an inefficient way. Therefore solutions based on subband decomposition gained a lot of interest very recently. In particular, this paper deals with scalable (hierarchical) coding of video at bitrates in the range af about 2-6 Mbps. The solution proposed in the paper is based on both temporal and spatial resolution...
In the paper, a computer program is presented, which is the aid for the design and prediction of operation of three basic configurations of PWM switch-mode power converters: Buck, Boost and Flyback. The design procedure is based on formulas presented in the literature. The time-domain simulation of current and voltage waveforms is performed with the use of semi-analytical recursive convolution algorithms...
A class of viscoplastic constitutive models relating strain rate to stress and state variables (of the type proposed by S.R.Bodner and Y.Partom) is considered and the monotonicity of the related operator is studied. It was shown earlier (1) that the considered operator is not of monotone type but the extended class of the monotone constitutive equations is introduced (clas LM) and evolution of total...
The presented method for 2D-curve detection, representation and analysis is based on the structural model of a shape being developed since the eighties and incorporates perceptual organization for curve segmentation, grouping, identification of distinct low-level perceptual entities known as shape primitives, as well as for grouping shape primitives into contour structures to form successive levels...
Scattering parameters for multiconductor lossy transmission line, directly in time-domain, have been derived. The parameters have the form of infinite fast convergent series. Only a few terms of those series are needed to obtain sufficient exactness and the number of terms is controlled. Some examples of simulation are presented.
An orthogonal all-pass structure of nth order is introduced. A recurrence expression giving nth order input all-pass function is derivered. An example of all-pass input function of the first, second and third order of the proposed structure is shown.
After a short review of image analysis methods that use deformable structures, this paper reveals that fast and accurate matching can be achieved by employing a variable-flexibility elastic model for image analysis. Methods discussed are illustrated by application examples, with particular emphasis on analysis of wheat grain X-ray images.
A special ASIC was designed to control the active heat sink with a Peltier heat pump according to the power consumption or temperature changes in a cooled chip. Two kinds of cooling are described and their simulation results are presented. Our proposal is to use such an ASIC as a standard cell in VLSI circuits or micromachine structures to control the thermal resistance between a silicon structure...
The paper investigates the existence and uniqueness of the weak solution to the initial boundary value problem for a system consisting of a hyperbolic-type partial differential equation with distributional coefficients and a collection of ordinary differential equations, modelling small vibrations of a mechanical system composed with an elastic body and a number of concentrated masses.
It is shown that in a nonhomogeneous isotropic elastic half-space with constant density and shear modulus and with Poisson ratio being bounded function of half-space depth belonging to the class [formula] the surface wave is unique.
The paper summarises the author's research on the preparation of dense beta-sialon materials using a combustion (SHS) method. The following aspects of sialon technology are discussed: the preparation of sialon powders, the powders characteristics, their processing and densification, as well as the characterisation of dense sialon polycrystals.
As an introduction to the publication dealing with research into advanced ceramic structural materials an outline of the main properties and apllications of these materials is given in the present essay.
A hydrothermal synthesis was used to prepare zirconia ultrafine powders stabilised with 6 mol % CaO. The influence of pH of a coprecipitation and crystalisation environment on the chemical composition and morphology of resultant powders was studied. Behaviour of the powders during compaction and sintering was characterised. The crystallisation mechanisms in the NaOH environment were discussed. Requirements...
The aim of the present paper was to demonstrate that a quantitative description of the microstructure of an advanced ceramic material can be efficiently obtained using modern computer-aided methods. Such a description is necessary for realistic modelling of properties and perhaps may lead to improvements in the technology of producing such materials.
The main objective of this paper is to explain the role of activators in silicon carbide sintering. On the basis of dihedral angle measuremets in model systems the authors postulate rejection of the S. Prochazka hypothesis saying that boron and carbon modify the grain-boundary and surface energy. Evolution of microstructure observed on model sinters and the data available in the literature enabled...
The paper presents the results of the computer aided quantitative analysis of the three groups of the ceramic composites: [formulas]. The methods of visualization and processing were elaborated and the representative microstructural characteristics for these materials have been thus obtained. The relationship between the microstructure and parameters of synthesis can be thus studied.
Sialon ceramics appear to be an attractive engineering material because of their excellent mechanical and thermal properties. Carbothermal production can be the most economical route for the production of the relevant sialon powders if some problems of multiphase composition are overcome. Thermodynamic calculations of the equilibrium composition in the Si-O-N-C and Al-O-N-C systems have been performed...