Showing papers by "Brno University of Technology published in 2008"

High-performance current differencing transconductance amplifier and its application in precision current-mode rectification

Abstract: A CMOS-based circuit for realization of high-performance current differencing transconductance amplifier (CDTA) is demonstrated. The proposed circuit offers the advantages of a wide frequency bandwidth and very small input terminal impedance. The results of circuit simulations and an application example are given to illustrate the advantages of the proposed circuit for precise high-frequency signal rectification.

Water at polar and nonpolar solid walls (Review)

Abstract: Recent progress in simulating the properties of interfacial water at hard hydrophobic and hydrophilic surfaces is reviewed and compared to results for the air/water interface. The authors discuss static properties such as the equilibrium contact angle, the depletion layer thickness, and the orientation of interfacial water molecules. Relations between these properties, e.g., the relation between the contact angle and the thickness of the depletion layer which is experimentally observed on hydrophobic surfaces, are emphasized. For a hydrophilic sapphire surface, the authors discuss the influence of geometry and density of polar surface groups on the interfacial water structure. They discuss nonequilibrium effects arising in laminar shear flows, where the classic no-slip hydrodynamic boundary condition is violated at hydrophobic interfaces. They discuss the arising slip and relate it to static properties of the solid hydrophobic/water interface.

Review of the role of the interphase in the control of composite performance on micro- and nano-length scales

Abstract: In fiber reinforced composites (FRCs), exhibiting heterogeneous structure at multiple length scales, the interphase phenomena at various length scales were shown to be of pivotal importance for the control of the performance and reliability of such structures. Various models based on continuum mechanics were used to describe effects of the macro- and meso-scale interphase on the mechanical response of laminates and large FRC parts, satisfactorilly. At the micro-scale, the interphase is considered a 3D continuum with ascribed average properties. Number of continuum mechanics models was derived over the last 50 years to describe the stress transfer between matrix and individual fiber with realtively good success. In these models, the interphase was characterized by some average shear strength, τa, and elastic modulus, Ea. On the other hand, models for tranforming the properties of the micro-scale interphase around individual fiber into the mechanical response of macroscopic multifiber composite have not been generally successfull. The anisotropy of these composite structures are the main reasons causing the failure of these models. The strong thickness dependence of the elastic modulus of the micro-scale interphase suggested the presence of its underlying sub-structure. On the nano-scale, the discrete molecular structure of the polymer has to be considered. The term interphase, originally introduced for continuum matter, has to be re-defined to include the discrete nature of the matter at this length scale. The segmental immobilization resulting in retarded reptation of chains caused by interactions with solid surface seems to be the primary phenomenon which can be used to re-define term interphase on the nano-scale. Thus, the Rubinstein reptation model and a simple percolation model were used to describe immobilization of chains near solid nano-particles and to explain the peculiarities in the viscoleastic response of nano-scale “interphase.” It has also been shown that below 5 nm, Bernoulli–Euler continuum elasticity becomes not valid and higher-order elasticity along with the proposed reptation dynamics approach can provide suitable means for bridging the gap in modeling the transition between the mechanics of continuum matter at the micro-scale and mechanics of discrete matter at the nano-scale.

Effect of grain size on mechanical properties of 3y-tzp ceramics

Abstract: The dependence of mechanical properties of 3Y-TZP ceramics on their grain sizes in the range from 0.19 µm to 2.15 µm has been investigated. Vickers indentation tests were used to determine hardness and fracture toughness. The hardness decreased with increasing grain size. The fracture toughness was almost constant for ceramics with the grain size up to 0.40 µm and then grew with increasing grain size up to 7.8 MPam 0.5 for ceramics with grain size of 1.8 µm. Above this grain size a spontaneous transformation from tetragonal to monoclinic phase occurred. Ceramic samples with grain sizes of 0.30 µm and 0.78 µm yielded similar bending strength, 1020 and 1011 MPa, respectively. The microstructural coarsening required for achieving larger grain size resulted in a higher scatter of strength values, which was demonstrated by a lower Weibull modulus (13.0 vs. 7.54). The mechanical properties of nanocrystalline 3Y-zirconia ceramics coarsened to the grain size range from 0.085 to 0.70 µm were also investigated and compared. Differences in mechanical behaviour of investigated ceramics were observed and their possible causes discussed.

First-principles study of magnetism at grain boundaries in iron and nickel

Abstract: The geometric and magnetic structures of fully relaxed symmetrical tilt $\ensuremath{\Sigma}5(310)$ grain boundaries (GBs) in iron and $\ensuremath{\Sigma}5(210)$ GBs in nickel have been investigated using density-functional theory. We found for both GBs an enhancement of the local magnetic moments of atoms in the GB plane ($2.55\text{ }{\ensuremath{\mu}}_{B}$ for iron and $0.67\text{ }{\ensuremath{\mu}}_{B}$ for nickel) which is correlated with the larger local atomic volume compared to the bulk. At larger distances from the GB the variation of the local magnetic moments follows the changes in the exchange splitting in the spin-polarized local density of states imposed by the local variations in the atomic geometry. When Si and Sn impurity atoms in interstitial or substitutional positions appear at the $\ensuremath{\Sigma}5(310)$ GB in iron, the local magnetic moments of iron atoms are reduced for silicon and almost unchanged for tin. We also calculated the segregation enthalpies of both impurities and confirmed the experimental fact that silicon is a substitutional and tin an interstitial segregant; the calculated values of segregation enthalpy are in good agreement with experiment.

Investigation of heavy-metal accumulation in selected plant samples using laser induced breakdown spectroscopy and laser ablation inductively coupled plasma mass spectrometry

Abstract: Single-pulse Laser-Induced Breakdown Spectroscopy (LIBS) and Laser-Ablation Inductively Coupled Plasma Mass-Spectrometry (LA-ICP-MS) were applied for mapping the silver and copper distribution in Helianthus Annuus L. samples treated with contaminant in controlled conditions. For Ag and Cu detection the 328.07 nm Ag(I) and 324.75 nm Cu(I) lines were used, respectively. The LIBS experimental conditions (mainly the laser energy and the observation window) were optimized in order to avoid self-absorption effect in the measured spectra. In the LA-ICP-MS analysis the Ag 107 and Cu 63 isotopes were detected. The capability of these two analytical techniques for high-resolution mapping of selected trace chemical elements was demonstrated.

Combination of strongly and weakly constrained recognizers for reliable detection of OOVS

Abstract: This paper addresses the detection of OOV segments in the output of a large vocabulary continuous speech recognition (LVCSR) system. First, standard confidence measures from frame-based word- and phone-posteriors are investigated. Substantial improvement is obtained when posteriors from two systems - strongly constrained (LVCSR) and weakly constrained (phone posterior estimator) are combined. We show that this approach is also suitable for detection of general recognition errors. All results are presented on WSJ task with reduced recognition vocabulary.

Two-dimensional blind Bayesian deconvolution of medical ultrasound images

Abstract: A new approach to 2-D blind deconvolution of ultrasonic images in a Bayesian framework is presented. The radio-frequency image data are modeled as a convolution of the point-spread function and the tissue function, with additive white noise. The deconvolution algorithm is derived from statistical assumptions about the tissue function, the point-spread function, and the noise. It is solved as an iterative optimization problem. In each iteration, additional constraints are applied as a projection operator to further stabilize the process. The proposed method is an extension of the homomorphic deconvolution, which is used here only to compute the initial estimate of the point-spread function. Homomorphic deconvolution is based on the assumption that the point-spread function and the tissue function lie in different bands of the cepstrum domain, which is not completely true. This limiting constraint is relaxed in the subsequent iterative deconvolution. The deconvolution is applied globally to the complete radiofrequency image data. Thus, only the global part of the point-spread function is considered. This approach, together with the need for only a few iterations, makes the deconvolution potentially useful for real-time applications. Tests on phantom and clinical images have shown that the deconvolution gives stable results of clearly higher spatial resolution and better defined tissue structures than in the input images and than the results of the homomorphic deconvolution alone.

Novel Hardware Implementation of Adaptive Median Filters

Abstract: A new FPGA implementation for adaptive median filters is proposed. Adaptive median filters exhibit better filtering properties than standard median filters; however, their implementation cost is higher. Proposed architecture was optimized for throughput allowing 300 M pixels to be filtered per second. The best performance/cost ratio exhibits the adaptive median filter which utilizes filtering window 7x7 pixels and can suppress shot noise with intensity up to 60%. In addition to filtering, adaptive median filters can be also used as detectors of corrupted pixels (detection statistics).

Sub-word modeling of out of vocabulary words in spoken term detection

Abstract: This paper deals with comparison of sub-word based methods for spoken term detection (STD) task and phone recognition. The sub-word units are needed for search for out-of-vocabulary words. We compared words, phones and multigrams. The maximal length and pruning of multigrams were investigated first. Then two constrained methods of multigram training were proposed. We evaluated on the NIST STD06 dev-set CTS data. The conclusion is that the proposed method improves the phone accuracy more than 9% relative and STD accuracy more than 7% relative.

Antichain-Based Universality and Inclusion Testing over Nondeterministic Finite Tree Automata

Abstract: We propose new antichain-based algorithms for checking universality and inclusion of nondeterministic tree automata (NTA). We have implemented these algorithms in a prototype tool and our experiments show that they provide a significant improvement over the traditional determinisation-based approaches. We use our antichain-based inclusion checking algorithm to build an abstract regular tree model checking framework based entirely on NTA. We show the significantly improved efficiency of this framework through a series of experiments with verifying various programs over dynamic linked tree-shaped data structures.

Multi-instrumental Analysis of Tissues of Sunflower Plants Treated with Silver(I) Ions - Plants as Bioindicators of Environmental Pollution.

Abstract: The aim of this work is to investigate sunflower plants response on stressinduced by silver(I) ions. The sunflower plants were exposed to silver(I) ions (0, 0.1, 0.5,and 1 mM) for 96 h. Primarily we aimed our attention to observation of basic physiologicalparameters. We found that the treated plants embodied growth depression, coloured changes and lack root hairs. Using of autofluorescence of anatomical structures, such aslignified cell walls, it was possible to determine the changes of important shoot and rootstructures, mainly vascular bungles and development of secondary thickening. Thedifferences in vascular bundles organisation, parenchymatic pith development in the rootcentre and the reduction of phloem part of vascular bundles were well observable.Moreover with increasing silver(I) ions concentration the vitality of rhizodermal cellsdeclined; rhizodermal cells early necrosed and were replaced by the cells of exodermis.Further we employed laser induced breakdown spectroscopy for determination of spatialdistribution of silver(I) ions in tissues of the treated plants. The Ag is accumulated mainlyin near-root part of the sample. Moreover basic biochemical indicators of environmentalstress were investigated. The total content of proteins expressively decreased withincreasing silver(I) ions dose and the time of the treatment. As we compare the resultsobtained by protein analysis - the total protein contents in shoot as well as root parts - wecan assume on the transport of the proteins from the roots to shoots. This phenomenon canbe related with the cascade of processes connecting with photosynthesis. The secondbiochemical parameter, which we investigated, was urease activity. If we compared theactivity in treated plants with control, we found out that presence of silver(I) ions markedlyenhanced the activity of urease at all applied doses of this toxic metal. Finally we studiedthe effect of silver(I) ions on activity of urease in in vitro conditions.

SMS Encryption for Mobile Communication

Abstract: This paper deals with an SMS encryption for mobile communication. The transmission of an SMS in GSM network is not secure, therefore it is desirable to secure SMS by additional encryption. In the following text, there are compared differences in the use of symmetric and asymmetric cryptography for SMS transfer securing. In the next part, there is the description of design and implementation of the application for mobile phones, which encrypts and signs SMS using an asymmetric RSA cipher. At the end, there are described attacks on secured SMS and future extension of the application.

Comparative Studies of Diphenyl-Diketo-Pyrrolopyrrole Derivatives for Electroluminescence Applications

Abstract: Four different derivatives of diphenyl-diketo-pyrrolopyrrole (DPP) with alkyl side groups were synthesized to increase their solubility Quantum chemical calculations revealed that the substitution influenced molecular geometry and subsequently modified absorption and photoluminescence spectra The theoretical results were confirmed by experimental characterization With increasing phenyl torsion the vibrational structure was less pronounced and larger Stokes shift was observed Simultaneously, the molar absorption coefficient decreased as the deformation increased On the other hand, the measured fluorescence quantum yields were modified only slightly This indicates the possibility to prepare soluble derivatives without loss of quantum yields and to use these materials for construction of efficient and stable electroluminescent devices Furthermore, the electroluminescence of the thin layer devices based on the soluble low molecular DPPs were characterized and discussed

Effect of normal stress on the ideal shear strength in covalent crystals

Abstract: Critical shear stress under the superimposed hydrostatic and uniaxial normal stress conditions of C, Si, Ge, and SiC is evaluated by ab initio density functional theory calculations to investigate the response of ideal shear strength (ISS) to superimposed normal stresses in covalent crystals. We find a substantial difference in the responses of ISS to normal stress among the covalent crystals examined; e.g., hydrostatic compression increases the ISS of C but decreases that of Si, Ge, and SiC. The ISS is mostly a highly nonlinear and anisotropic function of normal stress. The results thus indicate that normal stresses can significantly affect the critical shear stress, which is crucial to interpreting experimental observations of crystal deformation, e.g., dislocation nucleation in nanoindentation.

Comprehensive two-dimensional liquid chromatography in the analysis of antioxidant phenolic compounds in wines and juices

Abstract: A novel comprehensive two-dimensional liquid chromatographic (LC×LC) system was developed for the quantification of antioxidant phenolic compounds in wine and juice. The system allows parts of the sample that are well separated in the first column to pass directly to the detector after the first column, while the rest of the sample proceeds to the second column. The optimised LC×LC system employed a combination of two C18 columns, the latter column with an ion-pair reagent (tetrapentylammonium bromide). The relative standard deviations (RSD) for the retention times were better than 0.01% in the first dimension and on average 6.3% in the second. The RSD values of the peak volumes varied from 3% (protocatechuic acid) to 13% (caffeic acid, n = 3, 10 μg/ml).

A Formal Model for Network-Wide Security Analysis

Abstract: Network designers perform challenging tasks with so many configuration options that it is often hard or even impossible for a human to predict all potentially dangerous situations. In this paper, we introduce a formal method approach for verification of security constraints on networks with dynamic routing protocols in use. A unifying model based on packet-filters is employed for modelling of network behaviour. Over this graph model augmented with filtering rules over edges verification of reachability properties can be made. In our approach we also consider topology changes caused by dynamic routing protocols.

Measurements of light scattering in an integrated microfluidic waveguide cytometer

Abstract: An integrated microfluidic planar optical waveguide system for measuring light scattered from a single scatterer is described This system is used to obtain 2D side-scatter patterns from single polystyrene microbeads in a fluidic flow Vertical fringes in the 2D scatter patterns are used to infer the location of the 90-deg scatter (polar angle) The 2D scatter patterns are shown to be symmetrical about the azimuth angle at 90 deg Wide-angle comparisons between the experimental scatter patterns and Mie theory simulations are shown to be in good agreement A method based on the Fourier transform analysis of the experimental and Mie simulation scatter patterns is developed for size differentiation

Computing simulations over tree automata: efficient techniques for reducing tree automata

Abstract: We address the problem of computing simulation relations over tree automata. In particular, we consider downward and upward simulations on tree automata, which are, loosely speaking, analogous to forward and backward relations over word automata. We provide simple and efficient algorithms for computing these relations based on a reduction to the problem of computing simulations on labelled transition systems. Furthermore, we show that downward and upward relations can be combined to get relations compatible with the tree language equivalence, which can subsequently be used for an efficient size reduction of nondeterministic tree automata. This is of a very high interest, for instance, for symbolic verification methods such as regular model checking, which use tree automata to represent infinite sets of reachable configurations. We provide experimental results showing the efficiency of our algorithms on examples of tree automata taken from regular model checking computations.

Sintering densification curve: A practical approach for its construction from dilatometric shrinkage data

Abstract: This article summarizes the usage of high-temperature dilatometry in ceramic processing and powder technology with special attention on the description of the sintering process. A practical method for transformation of dilatometric shrinkage data into densification curves (the dependence of the sample density on sintering temperature or time) is described in detail. A new automatic procedure to recalculate sintering shrinkage data allowing the plot of the densification curve has been developed, which is presented here.

Vysoké učení technické v brně

Abstract: The aim of this trim’s thesis is to reveal possibilities and demonstrate parallelization of computation on graphics processors. The paper presents descriptions of available development tools, and then one of them is selected to implement MD5 encryption algorithm and neural network for optical character recognition. Its performance is then compared to its parallel equivalent for conventional processors. In conclusion, problems encountered during development are described, and ways of avoiding them are discussed.