Showing papers by "Brno University of Technology published in 2001"

Thin Film Colorimetric Interferometry

Abstract: Measurement technique for the study of very thin lubrication films down to one nanometer in a point contact between a steel ball and a transparent disc is used to explore the relationship between central and minimum film thickness and rolling speed at the interface between elastohydrodynamic and boundary lubrication for a series of lubricating fluids. This technique based on the colorimetric interferometry combines powerful film thickness mapping capabilities with high accuracy. It was confirmed that both hexadecane and mineral base oil obey the linear relationship between log central and minimum film thickness and log rolling speed predicted by elastohydrodynamic theory down to approximately one nanometer. Conversely, squalane and additive-treated mineral base oil showed film thickness enhancement at slow speeds caused by boundary layers formation within the lubricant film. Obtained experimental data was used for the determination of pressure-viscosity coefficients of test fluids. The measurement techniq...

Factors affecting successful implementation of high performance teams

Abstract: Agrees that the evidence of a vast array of research concerning teamwork is conclusive: teams are capable of outstanding performance and are the primary unit of performance for increasing numbers of organisations. Nevertheless, high performance teams (HPTs) are a rarity. Presents the results of collaborative research aimed at determining the factors affecting successful implementation of HPTs. The factors have been derived from literature on teamwork, quality management, and a review of case study literature. This research has led to the development of a model for the successful implementation of HPTs, which has been tested through a case study organisation. Furthermore, the results were used to develop an implementation program aimed at rejuvenating team performance in UK small‐ to medium‐sized enterprises.

Adsorption sites and ligand effect for CO on an alloy surface: a direct view.

Abstract: CO adsorption on a PtCo(111) surface was studied by scanning tunneling microscopy. Comparison of images with chemical contrast of Pt and Co and images showing the CO molecules indicates that CO resides exclusively on top of Pt sites and never on Co. CO bonding is highly sensitive to the chemical environment. The probability to find CO on a Pt atom increases drastically with the number of its Co nearest neighbors. Ab initio calculations show that this ligand effect is due to different positions of the center of the Pt d band.

Modal analysis of rib waveguide through finite element and mode matching methods

Abstract: Two mode solvers based on the finite element and the mode matching methods are compared by way of analyzing rib waveguides. Differences between the normalized propagation constants provided by the two methods are always less than 10−4 which is at least about one order of magnitude smaller than previously reported values. Results for lossy waveguides and field comparison are also presented.

Comparison of low stress creep properties of ferritic and austenitic creep resistant steels

Abstract: Creep tests at stresses below 30 MPa and temperatures from 923 to 1073 K were conducted on an austenitic AISI-316H creep resistant steel The helicoid spring specimen technique was used with the average test duration of ∼2000 h The results were compared to the results obtained on modified 9% Cr ferritic P-91 type creep resistant steel by the same experimental technique under comparable conditions The shapes of creep curves for both steels are rather similar, with a deep decrease in creep rate during primary stage followed by a secondary stage with constant strain rate Viscous creep (ie creep having the stress exponent close to one) was demonstrated in both steels under the loading conditions described above The secondary creep rate for AISI-316H is about two times lower than that of P-91 under the same testing conditions The difference can be easily explained by the difference in mean grain size of both materials, supposing that the diffusional creep is the prevailing deformation mechanism Unfortunately, it is not possible to identify creep mechanism clearly due to no possibility to obtain specimens with different grain size and the same microstructure Further, the creep mechanism identification is complicated by the fact, that the measured apparent activation energy is almost the same for both materials This result is in contradiction to the diffusion data published in the literature, where a considerably lower value of activation enthalpy in γ -phase than in α -phase have been reported for both volume and grain boundary diffusion

Design of the special fast reconfigurable chip using common fpga

Abstract: Some applications require chips with fast partial reconfiguration. These requirements are traditionally satisfied by a special chip design, but it is usually a very expensive solution. This paper describes a new approach. Special fast partially reconfigurable chip is implemented with a common FPGA. The format of the configuration bit stream is suggested and optimized according to the given task. Result chip offers many good properties, but some problems with scalability can appear.

Blends of polyvinylalcohol with collagen hydrolysate: thermal degradation and processing properties

Abstract: The blends of polyvinylalcohol with collagen hydrolysate were studied from the point of view of the effect of collagen hydrolysate on thermal degradation and processing properties. Elimination of deliberated acetic acid in reaction with NH 2 groups of CH can protect PVA against acidic catalysis of degradation. Using talc instead of silica can eliminate the crossliking effect in PVA-CH-silica blend when silica is used as antiblock agent. The obtained results make possible to use PVA/CH blends for blowing of biodegradable films with CH content up to 30 wt.%.

A plasma surface treatment of polyester textile fabrics used for reinforcement of car tires

Abstract: Polyester tire cord surfaces have been modified by plasma at low temperature and atmospheric pressure The surface treatment has been executed by various nonequilibrium discharges, namely by barrier discharge, atmospheric pressure glow discharge and gliding arc The polymeric multicord sewing threads treated by this procedure have been used in the same form as in industry, ie, with the protecting oil films on their surface The surface properties have been investigated by electron spin resonance spectroscopy and by measuring their contact angle with various liquids; partially the zeta potential measurements have been used, too Further tests have been done at an industrial testing impregnation line using the common technology and conditions, on both plasma treated and untreated fibers Finally, the standard H-tests and peel-tests have been used to characterize the fiber adhesion to usual testing rubbers

Discrete retract principle for systems of discrete equations

Abstract: A power tool for investigation of various problems of ordinary differential equations as well as delayed differential equations is a retraction method. The development of this method is discussed here in the case of system discrete equations. Corresponding definition of a point of a type of strict egress for a given set with respect to the system of discrete equations Δ u ( k ) = F ( k, u ( k )) is given. In an example, it is shown that this definition cannot exactly copy the analogous one, known from the theory of ordinary differential equations. Conditions for existence of at least one solution with graph remaining in a given set are formulated. The proof is based on idea of a retract principle. In construction of a retract mapping, the property of continuous dependence on their initial data is used. Illustrative applications are considered too.

Data Driven Design of Filter Bank for Speech Recognition

Abstract: Filter bank approach is commonly used in feature extraction phase of speech recognition (e.g. Mel frequency cepstral coefficients). Filter bank is applied for modification of magnitude spectrum according to physiological and psychological findings. However, since mechanism of human auditory system is not fully understood, the optimal filter bank parameters are not known. This work presents a method where the filter bank, optimized for discriminability between phonemes, is derived directly from phonetically labeled speech data using Linear Discriminant Analysis. This work can be seen as another proof of the fact that incorporation of psychoacoustic findings into feature extraction can lead to better recognition performance.

Noise and scanning by local illumination as reliability estimation for silicon solar cells

Abstract: This paper presents two methods, namely those using noise and homogeneity measurements of a large area solar cells, for determining the local defects, which bring down efficiency and long reliability of single-crystal silicon solar cells. As a result of the non-uniformities (non-homogeneity) in the large junction area, local areas with lower built-in potentials at the junction lead to hot spots and reduced reliability. The two techniques can be used to give a precise description of the quality of the product technology. Correlations between noise and inhomogeneities for an ensemble of 30 silicon solar cell samples are given.

Carbon reduction reaction in the Y2O3–SiO2 glass system at high temperature

Abstract: In order to assess the role of carbon with respect to the grain boundary chemistry of Si3N4-based ceramics model experiments were performed. Y2O3–SiO2 glass systems with various amount of carbon (from 1 to 30 wt.%) were prepared by high-temperature treatment in a graphite furnace. High carbon activity of the furnace atmosphere was observed. EDX analysis proved the formation of SiC by the carbothermal reduction of SiO2 either in the melt or in the solid state. The melting temperature of the Y2O3–SiO2 system is strongly dependent on the amount of reduced SiO2. XRD analysis of the products documented the presence of Y2Si2O7, Y2SiO5 and Y2O3 crystalline phases in that order with an increasing amount of free C in the starting mixture. The reduction of Y2O3 was not confirmed.

Sensor networking

Abstract: This paper deals with sensor networking frameworks, namely interconnected fieldbuses and IEEE 1451 smart transducer interface architecture. The contribution begins with interconnected fieldbuses mediating an access from an Intranet to sensors; particularly, coupling architectures are treated both from the viewpoint of more classical interconnections of wide-area and local-area networks, and from the viewpoint of fieldbus domain. Next section of the paper reviews some concepts aimed at connecting sensors and actuators through low-level fieldbuses to Intranets or the Internet. The following section introduces the IEEE 1451 smart transducer interface for sensors and actuators as an emerging, standard-based networking framework. The kernel of the paper deals with the application of the discussed frameworks for a computer-based pressure measurement system as a real-world project, stressing both the intra-system and Internet connectivity issues.

On the formal correctness of the reaction kinetics model and its solution in HV circuit breakers after current zero

Abstract: Five necessary conditions for the so-called formal correctness of solutions of kinetic equations are formulated, which form a mathematical model of the reaction kinetics in HV circuit breakers after current zero for a given time-dependence of temperature and a given time-dependence of pressure or volume. The conditions are based on the mass action law, knowledge obtained from mathematical analysis of a system of ordinary differential equations, the principles of numerical analysis and the equilibrium-state principle of thermodynamics. Concrete solutions of kinetic equations are given and analysed for the products of SF6 dissociation and ionization. Two models are considered. In one model, the temperature drops from 10 000 to 2500 K, in the other it drops from 12 000 K to room temperature. A comparison of the time-dependent composition with the equilibrium composition is offered for both models.

Phytotoxicity of iron in relation to its solubility conditions and the effect of ionic strength

Abstract: The effect of iron on root elongation and seed germination of Lactuca sativa was investigated within the limits of the plant’s sensitivity to an acidic environment and iron solubility under experimental conditions. Because ionic strength was found to have phytotoxic effects, the same pH and ionic strength conditions were kept constant over the entire iron concentration range, so as to evaluate solely the effect of iron. 0.14 mM Fe 3+ was found to be the lowest effective concentration inhibiting root elongation. The low solubility of iron at a pH of 3 (the lowest value which could be applied for root elongation) excluded the testing of higher iron concentrations. Due to the lower sensitivity of seed germination to acidity, a pH of 2.6 could be applied in this case. The lowest effective iron concentration (the lowest applied concentration causing a significant decrease in germination as compared to the control, P < 0.05), EC50 (the concentration at which germination was 50% of that of the control specimens) and the completely effective iron concentration (the concentration that completely inhibited seed germination) were 0.6, 0.92 and 2.0 mM, respectively.

Size effect in fracture of sandwich structure components: Foam and laminate

Abstract: In the design of sandwich plates and shells for very large structures, such as ships in the range of 100 m length, it is very important to take the size effect on the nominal strength into account, and do so in a realistic, physically justified, manner. Before the size effect is addressed for a sandwich structure, it must be understood for its components — the foam core and the laminate skins. In the current practice, the size effects are automatically attributed to the randomness of material strength, as described by the Weibull theory. The purpose of this paper is to show that in both the foam and the laminate there are deterministic size effects, which are generally more pronounced. They are caused by stress redistribution and energy release due to the growth of large fractures or large cracking zones prior to attaining the maximum load. This deterministic size effect is verified and calibrated by new tests of notched specimens of rigid close-cell vinyl foam. A combined deterministic-probabilistic theory of size effect of the laminates is proposed and verified by extensive test data.

Material Identification Using Laser Spectroscopy and Pattern Recognition Algorithms

Abstract: We report on pattern recognition algorithms in discriminant analysis, which were used on Laser Induced Breakdown Spectroscopy (LIBS) spectra (intensity of signal against wavelength) for metal identification and sorting purposes. In instances where accurate elemental concentrations are not needed, discriminant analysis can be applied, to compare and match spectra of "unknown" samples to library spectra of calibration samples. This type of "qualitative" pattern recognition analysis has been used here for material identification and sorting. Materials of different matrix materials (e.g. Al, Cu, Pb, Zn, vitrification glass, steels, etc.) could be identified with 100% certainty, using Principle Component Analysis and the Mahalanobis Distance algorithms. The limits within which the Mahalanobis Distance indicate a match status of Yes, Possible or No were investigated. The factors, which dictate these limits in LIBS analysis, were identified - (i) spectrum reproducibility and (ii) the sample-to-sample homogeneity. If correctly applied the combination of pattern recognition algorithms and LIBS provide a useful tool for remote and in-situ material identification problems, which are of a more "identify-and-sort" nature (for example those in the nuclear industry).

Holographic confocal microscopy

Abstract: Application of incoherent holography for achievement of the depth-discriminated microscopic imaging was proved. The image quality described by the coherent transfer function is comparable with that of a conventional confocal microscope; the imaging speed can be substantially higher. The observed plane is imaged as a whole, continuously in time, without any scanning system. Besides the amplitude, the phase of the confocal image is reconstructed, carrying information about phase shifts inside the specimen. The depth discrimination property can be enhanced beyond the capability of a conventional confocal microscope by the use of a broad-band illumination.

Algorithmic s-z transformations for continuous-time to discrete-time filter conversion

Abstract: This paper introduces a so-called generalized Pascal matrix. Using this matrix, the coefficients of transfer functions of the continuous-time and discrete-time linear circuits can be converted on the assumption that both circuits are related by a general first-order s-z transformation. We explain the effective numerical procedure of computing all matrix elements for arbitrary first-order s-z transformation.

Type Analysis in Object-Oriented Petri Nets

Abstract: The paper considers the problem of an automatic type analysis in the context of the object-oriented Petri nets (OOPNs) associated with the PNtalk language. We describe the skeleton of one of the possible approaches to deriving the types of tokens that may get into particular places of OOPN-based models. We briefly discuss advantages and disadvantages and also possible alternatives to the described approach.

Two-axis micropositioning system with piezoelectric actuators and digital control

Abstract: The scanning table, which is controlled by a PZT control system that has been constructed, is presented. It is used for a fine manipulation of a probe in measurement of the profile of the laser beam focused by high NA lens e.g.. The whole system has been calibrated by a two-axis laser interferometer. Where the PZT control system and the interferometer were connected to the CAN network and the actual X-Y position was saved to the PC synchronously with the CAN network time stamps generated by the PZT control system. Precision about 300nm at the positioning system was reached.