Showing papers by "Wrocław University of Technology published in 2003"
TL;DR: In this article, the authors presented several constructions of a censored stable process in an open set, i.e., a symmetric stable process which is not allowed to jump outside the boundary of the set.
Abstract: We present several constructions of a ``censored stable process'' in an open set D⊂R
n
, i.e., a symmetric stable process which is not allowed to jump outside D.
We address the question of whether the process will approach the boundary of D in a finite time – we give sharp conditions for such approach in terms of the stability index α and the ``thickness'' of the boundary. As a corollary, new results are obtained concerning Besov spaces on non-smooth domains, including the critical exponent case.
We also study the decay rate of the corresponding harmonic functions which vanish on a part of the boundary. We derive a boundary Harnack principle in C
1,1
open sets.
313 citations
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TL;DR: In this paper, the authors address the issue of modeling spot electricity prices and present a number of models proposed in the literature to fit a jump diffusion and a regime switching model to spot prices from the Nordic power exchange.
Abstract: In this paper we address the issue of modeling spot electricity prices. After summarizing the stylized facts about spot electricity prices, we review a number of models proposed in the literature. Afterwards we fit a jump diffusion and a regime switching model to spot prices from the Nordic power exchange and discuss the pros and cons of each one.
218 citations
TL;DR: The possibility of using some natural fats, rapeseed oil, olive oil and lard, as starting material for the preparation of neopentyl glycol (NPG) and trimethylol propane (TMP) esters is reported.
202 citations
TL;DR: A new class of very potent inhibitors of cytosol leucine aminopeptidase (LAP), a member of the metalloprotease family, is described and the key feature, which determines their selectivity, is structure at the P1' position.
Abstract: A new class of very potent inhibitors of cytosol leucine aminopeptidase (LAP), a member of the metalloprotease family, is described. The X-ray structure of bovine lens leucine aminopeptidase complexed with the phosphonic acid analogue of leucine (LeuP) was used for structure-based design of novel LAP inhibitors and for the analysis of their interactions with the enzyme binding site. The inhibitors were designed by modification of phosphonic group in the LeuP structure toward finding the substituents bound at the S' side of the enzyme. This resulted in two classes of compounds, the phosphonamidate and phosphinate dipeptide analogues, which were synthesized and evaluated as inhibitors of the enzyme. The in vitro kinetic studies for the phosphinate dipeptide analogues revealed that these compounds belong to the group of the most effective LAP inhibitors found so far. Their further modification at the P1 position resulted in more active inhibitors, hPheP[CH(2)]Phe and hPheP[CH(2)]Tyr (K(i) values 66 nM and 67 nM, respectively, for the mixture of four diastereomers). The binding affinities of these inhibitors toward the enzyme are the highest, if considering all compounds containing a phosphorus atom that mimic the transition state of the reaction catalyzed by LAP. To evaluate selectivity of the designed LAP inhibitors, additional tests toward aminopeptidase N (APN) were performed. The key feature, which determines their selectivity, is structure at the P1' position. Aromatic and aliphatic substituents placed at this position strongly interact with the LAP S1' binding pocket, while a significant increase in binding affinity toward APN was observed for compounds containing aromatic versus leucine side chains at the P1' position. The most selective inhibitor, hPheP[CH(2)]Leu, binds to LAP with 15 times higher affinity than to APN. One of the studied compounds, hPheP[CH(2)]Tyr, appeared to be very potent inhibitor of APN (K(i) = 36 nM for the mixture of four diastereomers). The most promising LAP inhibitors designed by computer-aided approach, the phosphonamidate dipeptide analogues, were unstable at pH below 12, because of the P-N bond decomposition, which excluded the possibility of determination of their binding affinities toward LAP.
185 citations
TL;DR: In this paper, the authors investigated how ammonia treatment of the surface can influence the activity of a viscose-based activated carbon cloth (ACC) for the oxidative retention of H2S and SO2 in humid air at 25 8C.
166 citations
TL;DR: A novel approach to harmonic and interharmonic analysis, based on the "subspace" methods, is proposed, and Min-norm harmonic retrieval method is an example of high-resolution eigenstructure-based methods.
Abstract: Modern frequency power converters generate a wide spectrum of harmonic components. Large converters systems can also generate noncharacteristic harmonics and interharmonics. Standard tools of harmonic analysis based on the Fourier transform assume that only harmonics are present and the periodicity intervals are fixed, while periodicity intervals in the presence of interharmonics are variable and very long. A novel approach to harmonic and interharmonic analysis, based on the "subspace" methods, is proposed. Min-norm harmonic retrieval method is an example of high-resolution eigenstructure-based methods. The Prony method as applied for signal analysis was also tested for this purpose. Both high-resolution methods do not show the disadvantages of the traditional tools and allow exact estimation of the interharmonics frequencies. To investigate the methods several experiments were performed using simulated signals, current waveforms at the output of a simulated frequency converter, and current waveforms at the output of an industrial frequency converter. For comparison, similar experiments were repeated using the fast Fourier transform (FFT). The comparison proved the superiority of the new methods. However, their computation is much more complex than FFT.
165 citations
TL;DR: It is concluded that neural detectors for rotor and stator faults as well as for rolling bearings and supply asymmetry faults can be developed based on measurement data acquired on-line in the drive system.
149 citations
TL;DR: In this paper, the authors consider Hermite functions with respect to the eigenfunctions of the harmonic oscillator L =−Δ+|x|2 and investigate their boundary behaviour and mapping properties.
135 citations
TL;DR: It is demonstrated that the behavior of wavelet transform of epileptic spikes across scales can constitute the foundation of a relatively simple yet effective detection algorithm.
Abstract: Interictal spikes and sharp waves in human EEG are characteristic signatures of epilepsy. These potentials originate as a result of synchronous pathological discharge of many neurons. The reliable detection of such potentials has been the long standing problem in EEG analysis, especially after long-term monitoring became common in investigation of epileptic patients. The traditional definition of a spike is based on its amplitude, duration, sharpness, and emergence from its background. However, spike detection systems built solely around this definition are not reliable due to the presence of numerous transients and artifacts. We use wavelet transform to analyze the properties of EEG manifestations of epilepsy. We demonstrate that the behavior of wavelet transform of epileptic spikes across scales can constitute the foundation of a relatively simple yet effective detection algorithm.
127 citations
TL;DR: Overall, the complexes of tris(2-carboxyethyl)phosphine (TCEP), a newly introduced thiol group protectant, were found to be rather weak, but the phosphorus pK(a) value for TCEP, 7.68, suggests that it can be a good buffer for studies at physiological pH.
Abstract: Acid-base properties and metal-binding abilities of tris(2-carboxyethyl)phosphine (TCEP), a newly introduced thiol group protectant, were studied in solution, using potentiometry, (1)H and (31)P NMR, and UV-vis spectroscopy, and also in the solid state by X-ray diffraction. Stability constants of complexes of the P-oxide of TCEP (TCEPO) were established by potentiometry. The list of metal ions studied included Ni(II), Cu(II), Zn(II), Cd(II), and Pb(II). Cu(II) catalyzed oxidation of TCEP to TCEPO. For all other systems ML complexes were found as major species at neutral pH with TCEP and TCEPO. Monoprotonated MHL species were also detected in weakly acidic conditions for all TCEP complexes and for the Pb(II) complex of TCEPO, while hydrolytic MH(-1)L complexes were found for TCEP at the weakly alkaline pH range. The NiL(4) complex was found to form at excess of TCEP. Overall, the complexes were found to be rather weak, with log beta(ML) values around 3-5 for TCEP and 1.5-2.5 for TCEPO. The phosphorus pK(a) value for TCEP, 7.68, suggests that it can be a good buffer for studies at physiological pH.
123 citations
TL;DR: It is indicated that desensitization rate is the fastest ligand-independent transition in the GABAAR gating scheme, and the pH dependencies of amplitudes were almost opposite, which resulted from a much shorter receptor exposure to agonist in the case of mIPSCs.
Abstract: Protons are the most ubiquitous and very potent modulators of the biological systems. Hydrogen ions are known to modulate GABAA receptors (GABAARs), but the mechanism whereby these ions affect IPSCs and the gating of GABAARs is not clear. In the present study we examined the effect of protons on miniature IPSCs (mIPSCs) and found that hydrogen ions strongly affected both their amplitude and time course. To explore the underlying mechanisms with resolution adequate to the time scale of synaptic transmission, we recorded current responses to ultrafast GABA applications at various pH. These experiments revealed that the major effect of protons on GABAAR gating is a strong enhancement of desensitization and binding rates at increasing pH. This analysis also indicated that desensitization rate is the fastest ligand-independent transition in the GABAAR gating scheme. Although proton effects on the time course of mIPSCs and current responses to saturating [GABA] were similar, the pH dependencies of amplitudes were almost opposite. Our quantitative analysis, based on model simulations, indicated that this difference resulted from a much shorter receptor exposure to agonist in the case of mIPSCs. Modeling of IPSCs as current responses to brief exponentially decaying GABA applications was sufficient to reproduce correctly the pH dependence of mIPSCs, and optimal fit was obtained for peak [GABA] of 1.5-3 mm and a clearance time constant of 0.075-0.125 msec. Our analysis indicates that, for these parameters of GABA transient, in control conditions (pH 7.2) mIPSCs are not saturated.
TL;DR: A collection of regular and singular Jacobian inverse kinematics algorithms that drive the end effector to a desirable position and orientation in the taskspace are presented.
Abstract: By a mobile manipulator we mean a robotic system composed of a non-holonomic mobile platform and a holonomic manipulator fixed to the platform. A taskspace of the mobile manipulator includes positions and orientations of its end effector relative to an inertial coordinate frame. The kinematics of a mobile manipulator are represented by a driftless control system with outputs. Admissible control functions of the platform along with joint positions of the manipulator constitute the endogenous configuration space. Endogenous configurations have a meaning of controls. A map from the endogenous configuration space into the taskspace is referred to as the instantaneous kinematics of the mobile manipulator. Within this framework, the inverse kinematic problem for a mobile manipulator amounts to defining an endogenous configuration that drives the end effector to a desirable position and orientation in the taskspace. Exploiting the analogy between stationary and mobile manipulators we present in the paper a colle...
TL;DR: The results are of general interest since they represent the first detailed quantitative structure-activity relationship study of the inhibition of an expressed farnesyl pyrophosphate synthase enzyme by bisphosphonate inhibitors and that the activity of these inhibitors can be predicted within about a factor of 3 by using 3D-QSAR techniques.
Abstract: We report the activities of 62 bisphosphonates as inhibitors of the Leishmania major mevalonate/isoprene biosynthesis pathway enzyme, farnesyl pyrophosphate synthase. The compounds investigated exhibit activities (IC50 values) ranging from ∼100 nM to ∼80 μM (corresponding to Ki values as low as 10 nM). The most active compounds were found to be zoledronate (whose single-crystal X-ray structure is reported), pyridinyl-ethane-1-hydroxy-1,1-bisphosphonates or picolyl aminomethylene bisphosphonates. However, N-alicyclic aminomethylene bisphosphonates, such as incadronate (N-cycloheptyl aminomethylene bisphosphonate), as well as aliphatic aminomethylene bisphosphonates containing short (n = 4, 5) alkyl chains, were also active, with IC50 values in the 200−1700 nM range (corresponding to Ki values of ∼20−170 nM). Bisphosphonates containing longer or multiple (N,N-) alkyl substitutions were inactive, as were aromatic species lacking an o- or m-nitrogen atom in the ring, or possessing multiple halogen substitutio...
TL;DR: In this paper, the authors investigated properties of functions which are harmonic with respect to -stable processes on d-sets such as the Sierpi«ski gasket or carpet, and they proved the Harnack inequality for such functions.
Abstract: We investigate properties of functions which are harmonic with respect to -stable processes on d-sets such as the Sierpi«ski gasket or carpet. We prove the Harnack inequality for such functions. For every process we estimate its transition density and harmonic measure of the ball. We prove continuity of the density of the harmonic measure. We also give some results on the decay rate of harmonic functions on regular subsets of the d-set. In the case of the Sierpi«ski gasket we even obtain the Boundary Harnack Principle.
TL;DR: A modification of the Newton algorithm applied to nonholonomic motion planning with energy optimization is discussed, which can be used to steer any driftless non holonomic systems particular free-floating objects, underactuated manipulators, mobile robots (with trailers).
Abstract: Discusses a modification of the Newton algorithm applied to nonholonomic motion planning with energy optimization. The energy optimization is performed either by optimizing motion in the null space of the Jacobian matrix derived from the nonholonomic system or coupling this motion with movement toward the goal. Resulting controls are smooth and easily generated by motors or thrusters. The two methods can be used, when kinematics are considered, to steer any driftless nonholonomic systems particular free-floating objects, underactuated manipulators, mobile robots (with trailers). Similarities and differences are also discussed in the Newton algorithm for holonomic and nonholonomic systems.
TL;DR: A white-light spectral interferometric technique employing a low-resolution spectrometer for measurement of the dispersion of the group and phase modal birefringence in an elliptical-core optical system over a wide spectral range is presented.
Abstract: We present a white-light spectral interferometric technique employing a low-resolution spectrometer for measurement of the dispersion of the group and phase modal birefringence in an elliptical-core optical fiber over a wide spectral range. The technique utilizes a tandem configuration of a Michelson interferometer and the optical fiber to record a series of spectral interferograms and to measure the equalization wavelengths as a function of the optical path difference in the Michelson interferometer, or equivalently, the wavelength dependence of the group modal birefringence in the optical fiber. Applying a polynomial fit to the measured data, the wavelength dependence of the phase modal birefringence can also be determined.
TL;DR: The most dynamic accumulation of Al,Cd, Cr, Ni and Pb was observed for examined species and the highest differences in element concentrations for investigated sites were found for Ba, Cd, Mn and Ni.
Abstract: Accumulation of metals in deciduous tree foliage fromurban areas in western-south Poland was monitored duringthe vegetation season of 2000 year. Concentrations of Al,Ba, Ca, Cd, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Sr, Ti and Znwere measured in birch, willow, linden and maple leavesusing the ICP-AES method. Seasonal variations of metalconcentrations and their relations with sampling sitewere investigated. The most dynamic accumulation of Al,Cd, Cr, Ni and Pb was observed for examined species. Thehighest differences in element concentrations forinvestigated sites were found for Ba, Cd, Mn and Ni.Interelement correlations were investigated. In allfoliar samples synergistic relationships between Al–Crand Ca-Sr were found. Statistically significant negativecorrelations were observed only for Cd and Ti in birch leaves.
TL;DR: In this article, the effectivity of α-amylase, β-, β-, and glucoamylases on copolymers of butyl acrylate and pentaerhitrite triacrylate was evaluated.
TL;DR: In this article, polysulfone films were modified by ammonia, n-butylamine and allylamine remote plasma using various sample-toplasma distances and contact angle measurements, FTIR-ATR and XPS spectroscopy proved the presence of polar groups on the modified surface.
TL;DR: Selenamides, such as 2-phenyl-1,2-benzisoselenazol-3(2H)-one (ebselen) and its analogues, known as glutathione peroxidase mimics acting via active hydroperoxide intermediates, are efficient and selective oxidants.
TL;DR: It is shown that the rising phase and amplitude of GABA-evoked currents depend on desensitization and singly bound states, and there is evidence that preequilibration at low GABA concentrations reduce GABA- Evoked currents due to receptor trapping in a singlybound desensitized state.
Abstract: The time course of GABA-evoked currents is the main source of information on the GABAAreceptor gating. Since the kinetics of these currents depends on the transitions between several receptor confo...
TL;DR: In this paper, the influence of physicochemical properties (chemical composition, particle size distribution and resistivity) of fly ash on the collection efficiency was investigated in a single-stage electrostatic precipitator test facility.
TL;DR: Sequence alignments indicate that the EcR–RXR heterodimer is an important model for understanding how the FXR– RXRheterodimer binds to IR‐1 sites.
Abstract: Ecdysteroids initiate molting and metamorphosis in insects via a heterodimeric receptor consisting of the ecdysone receptor (EcR) and ultraspiracle (USP). The EcR–USP heterodimer preferentially mediates transcription through highly degenerate pseudo-palindromic response elements, resembling inverted repeats of 5′-AGGTCA-3′ separated by 1 bp (IR-1). The requirement for a heterodimeric arrangement of EcR–USP subunits to bind to a symmetric DNA is unusual within the nuclear receptor superfamily. We describe the 2.24 Å structure of the EcR–USP DNA-binding domain (DBD) heterodimer bound to an idealized IR-1 element. EcR and USP use similar surfaces, and rely on the deformed minor groove of the DNA to establish protein–protein contacts. As retinoid X receptor (RXR) is the mammalian homolog of USP, we also solved the 2.60 Å crystal structure of the EcR–RXR DBD heterodimer on IR-1 and found the dimerization and DNA-binding interfaces to be the same as in the EcR–USP complex. Sequence alignments indicate that the EcR–RXR heterodimer is an important model for understanding how the FXR–RXR heterodimer binds to IR-1 sites.
TL;DR: In this article, the results of examination of ion exchange capacity of solid and gel forms of humic acids of brown coals in respect to 17 metal ions were presented, including Pb, Ag, Hg, Cu, Ba and Cd.
TL;DR: In this paper, the effect of water adsorption at the pored surface of the glasses on the dielectric response was examined over wide temperature (−100 to +300 °C) and frequency (20 Hz-1 MHz) ranges.
TL;DR: In this article, a simple Ising spin model is proposed to describe the mechanism of advertising in a duopoly market, where the influence does not flow inward from the surrounding neighbors to the center site, but spreads outward from the center to the neighbors.
Abstract: A simple Ising spin model which can describe the mechanism of advertising in a duopoly market is proposed. In contrast to other agent-based models, the influence does not flow inward from the surrounding neighbors to the center site, but spreads outward from the center to the neighbors. The model thus describes the spread of opinions among customers. It is shown via standard Monte Carlo simulations that very simple rules and inclusion of an external field—an advertising campaign—lead to phase transitions.
TL;DR: The Claisen rearrangement of chorismate to prephenate in the enzyme has been modelled here by a combined quantum mechanics/molecular mechanics (QM/MM) method, indicating that this is central to catalysis by the enzyme.
Abstract: Chorismate mutase provides an important test of theories of enzyme catalysis, and of modelling methods. The Claisen rearrangement of chorismate to prephenate in the enzyme has been modelled here by a combined quantum mechanics/molecular mechanics (QM/MM) method. Several pathways have been calculated. The sensitivity of the results to details of model preparation and pathway calculation is tested, and the results are compared in detail to previous similar studies and experiments. The potential energy barrier for the enzyme reaction is estimated at 24.5—31.6 kcal mol−1 (AMl/CHARMM), and 2.7—11.9 kcal mol−1 with corrections (e.g. B3LYP/6-31 + G(d)). In agreement with previous studies, the present analysis of the calculated paths provides unequivocal evidence of significant transition state stabilization by the enzyme, indicating that this is central to catalysis by the enzyme. The active site is exquisitely complementary to the transition state, stabilizing it more than the substrate, so reducing the barrier...
TL;DR: Titania and titania-silica aerogels have been prepared by sol-gel method The pH of their point of zero charge (pHPZC), SBET, volumes of the micro- and mesopores were determined Considering titania−silica aerosogels FTIR analyses were carried out Three phenol para-derivatives (p-chlorophenol, p-nitrophenol, 4-hydroxybenzoic acid) were chosen as model compounds in photodegradation processes as mentioned in this paper.
Abstract: Titania and titania–silica aerogels have been prepared by sol–gel method The pH of their point of zero charge (pHPZC), SBET, volumes of the micro- and mesopores were determined Considering titania–silica aerogels FTIR analyses were carried out Three phenol para-derivatives (p-chlorophenol, p-nitrophenol, 4-hydroxybenzoic acid) were chosen as model compounds in photodegradation processes All aerogels indicated photocatalytic activity However, titania aerogels were more efficient photocatalysts comparing to titania–silica aerogels The results can be explained by the percentage content of two phases (5, 10 and 20 wt% SiO2 in TiO2) The ratio of SiO2:TiO2 results in the presence of two separated phases that hinders photocatalytic processes The identified by-products of p-chlorophenol and p-nitrophenol degradation are hydroquinone, benzoquinone as well as chloride ions and nitrate ions, respectively The pHPZC of all catalysts changed between 62 and 67 Between the pHPZC and photoactivity there was no direct correlation The course of the photodegradation did not depend on surface area and pores volumes of the catalysts but on the kind of pollutant
TL;DR: In this paper, the results of Baryshnikov, Mayo and Taylor (1998) were applied to calculate non-arbitrage prices of a zero-coupon and coupon CAT bond.
Abstract: We apply the results of Baryshnikov, Mayo and Taylor (1998) to calculate non-arbitrage prices of a zero-coupon and coupon CAT bond. First, we derive pricing formulae in the compound doubly stochastic Poisson model framework. Next, we study 10-year catastrophe loss data provided by Property Claim Services and calibrate the pricing model. Finally, we illustrate the values of the CAT bonds tied to the loss data.
TL;DR: In this paper, the physico-chemical properties of ZrO 2, MgO and admixtured (stabilized) zirconium dioxide are presented. But the authors do not consider the effect of substitutions.
Abstract: The physico-chemical properties of ZrO 2 , MgO and admixtured (stabilized) zirconium dioxide are presented. The synthesis of stabilized ZrO 2 was conducted in a low-temperature process. The catalysts obtained on the basis of zirconium dioxide were monophase materials of a regular structure. The lattice parameter of the materials did not differ much from the standard value. The character of the surface active centers was being changed as a result of the admixturing. Synthesized monophase materials of catalytic properties, Zr-Mg-O and Zr-Mg-Y-O, have many strong Lewis centers at surfaces. There appeared not only the stabilization of the regular polymorphous structure of ZrO 2 , but also a modification of catalytic properties of the materials when the basic admixture (MgO and Y 2 O 3 ) was being introduced to basic zirconium dioxide. The authors present a mechanism of alcohol or aldehyde condensation to ketone at the surface of the materials with the participation of Lewis acidic centers.