Showing papers by "Wrocław University of Technology published in 2000"
TL;DR: The most widely applied methods for the production of composite materials and composite parts are based on casting techniques such as the squeeze casting of porous ceramic preforms with liquid metal alloys and powder metallurgy methods.
836 citations
TL;DR: In this article, the role of rapid prototyping technology in increasing the speed of tooling development is described and a comprehensive review of examples of rapid tooling indicates a major shift in tooling practice.
286 citations
TL;DR: This problem can be modelled as a hybrid flow shop scheduling problem with mixed no-wait/no-store constraints and mixed bottleneck/non-bottleneck machines and an approximation algorithm based on the tabu search approach is proposed.
220 citations
TL;DR: Fuzzy equivalents of all the classical capital budgeting (investment choice) methods are generalised or proposed to evaluate and compare projects in which the cash ows, duration time and required rate of return are given imprecisely, in the form of a fuzzy number.
195 citations
TL;DR: In this paper, a review of different models for computing the changes in flow stress depending on the deformation conditions is presented, and the models are divided into two main groups, each of them characterised by a different set of deformation parameters.
152 citations
TL;DR: In this paper, three distinct forms of modelling flux decline of cross flow filtration at constant transmembrane pressure (Δ P ) were examined, and the best fit to the data sets examined was obtained with the model developed previously by Field [9,10].
139 citations
TL;DR: In this article, it has been demonstrated that such products can be manufactured from waste such as aluminium and aluminium-alloy chips, and the method consists in the conversion of the chips directly into a finished product.
135 citations
TL;DR: In this article, the properties of porous membranes modified by action of nitrogen plasma were investigated and it was shown that modified ultrafiltration membranes are less prone to protein fouling than their untreated analogues.
132 citations
TL;DR: In this article, the authors study the feature of electricity returns by means of Hurst R=S analysis and show that the mechanism underlying the process of price returns is a strong mean-reverting mechanism.
Abstract: The price of electricity is extremely volatile, because electric power cannot be economically stored, end user demand is largely weather dependent, and the reliability of the grid is paramount. However, underlying the process of price returns is a strong mean-reverting mechanism. We study this feature of electricity returns by means of Hurst R=S analysis. c 2000 Elsevier Science B.V. All rights reserved.
120 citations
TL;DR: In this paper, an attempt was made to use alkaline-earth metal compounds as catalysts for alcoholysis reaction in terms of synthesis di(2-ethylhexyl) adipate and an oligomeric ester of neopentyl glycol.
Abstract: Some esters of carboxylic acids and polyhydric alcohols are environmental friendly lubricants of superior properties. This work presents an attempt to use alkaline-earth metal compounds as catalysts for alcoholysis reaction in terms of synthesis di(2-ethylhexyl) adipate and an oligomeric ester of neopentyl glycol. Magnesium methoxide, calcium oxide, calcium alkoxides and barium hydroxide appear to be active catalysts for transesterification. The mechanism of catalytic activity of these compounds in alcoholysis reaction has been proposed. Synthesised esters possess suitable physicochemical properties as lubricant oils.
113 citations
TL;DR: The formation of 3D structures on Si(100) wafers by means of anisotropic etching results from the interdependences of (100) plane etching rates and basic high-indexed planes as mentioned in this paper.
Abstract: The formation of 3D structures on Si(100) wafers by means of anisotropic etching results from the inter-dependences of (100) plane etching rates and basic high-indexed planes. The shapes of the figures obtained under anisotropic etching (holes or islands limited by the planes inclined to the surface at various well-defined angles) are considered in comparison with the etching rate values of various crystallographic planes. The best etchants and etching conditions for the formation of figures of the desired shape are presented in this paper.
TL;DR: A theory of charged excitons in a dilute two-dimensional (2D) electron gas in a high-magnetic field is presented in this paper, where three bound states (one singlet and two triplets) are found in a narrow and symmetric GaAs quantum well.
Abstract: A theory of charged excitons ${X}^{\ensuremath{-}}$ in a dilute two-dimensional (2D) electron gas in a high-magnetic field is presented. In contrast to previous calculations, three bound ${X}^{\ensuremath{-}}$ states (one singlet and two triplets) are found in a narrow and symmetric GaAs quantum well. The singlet and a ``bright'' triplet are the two optically active states observed in experiments. The bright triplet has the binding energy of about 1 meV, smaller than the singlet and a ``dark'' triplet. The interaction of bound ${X}^{\ensuremath{-}}\mathrm{'}\mathrm{s}$ with a dilute 2D electron gas is investigated using exact diagonalization techniques. It is found that the short-range character of the $e--{X}^{\ensuremath{-}}$ interactions effectively isolates bound ${X}^{\ensuremath{-}}$ states from a dilute $e--h$ plasma. This results in the insensitivity of the photoluminescence spectrum to the filling factor $\ensuremath{
u},$ and a rapid decrease of the oscillator strength of the dark triplet ${X}^{\ensuremath{-}}$ as a function of ${\ensuremath{
u}}^{\ensuremath{-}1}.$
TL;DR: In this article, the molecular structures of p-chlorophenol and p-bromophenol have been calculated with the MP2, DFT(hybrid), and HF methods using the extended 6-311++G(df, pd) basis set.
Abstract: The molecular structures of p-chlorophenol and p-bromophenol have been calculated with the MP2, DFT(hybrid), and HF methods using the extended 6-311++G(df, pd) basis set. The geometrical parameters of p-ClPh and pBrPh in the gas phase have not been reported as yet. The results show that substitution of phenol with σ-electron-withdrawing groups (Br and Cl) leads to small shortening of the C−C and C−O bonds and small changes in the CCC angles. The structural changes of the phenol ring are governed mainly by the electronegativity of the para-substituent and, to a lesser extend, by resonance factors. The FT-IR spectra of p-ClPh, p-BrPh, and their OD counterparts were measured in CCl4 and cyclohexane solutions in the frequency range of 3700−400 cm-1, and the integrated infrared intensities were determined. The theoretical harmonic frequencies and infrared intensities were calculated for all the molecules using the DFT and HF methods. The best overall agreement between the calculated and experimental spectra ha...
TL;DR: The problem is NP-complete and two heuristic algorithms are presented, which aim to find a schedule (processing order) which minimizes the maximum lateness criterion.
TL;DR: In this article, the authors present arguments why this is the case and present a number of standard financial tools cannot be readily applied to pricing and hedging electricity derivatives, and present arguments that the possibility of extreme price movements increases the risk of trading in electricity markets.
Abstract: The price of electricity is far more volatile than that of other commodities normally noted for extreme volatility. Demand and supply are balanced on a knife-edge because electric power cannot be economically stored, end user demand is largely weather dependent, and the reliability of the grid is paramount. The possibility of extreme price movements increases the risk of trading in electricity markets. However, a number of standard financial tools cannot be readily applied to pricing and hedging electricity derivatives. In this paper we present arguments why this is the case.
TL;DR: Quantitative EPR method was applied to characterise four types of humic acids derived from composts, soil, peat and soft brown coal, and it was recognised that the radical centres, which are enhanced by 'ammonia effect' are quenched in the formed HA-Cu(II) complexes.
TL;DR: Results from semi-empirical calculations combined with a proposed partial active site model showed a correlation between the experimental kinetic constants and the change in polarization of the pro-S Cbeta-H bond and heat of formation of the sigma complexes, thus making the electrophilic attack at the neutral aromatic ring plausible.
Abstract: Several fluoro- and chlorophenylalanines were found to be good substrates of phenylalanine ammonia-lyase (PAL/EC 4.3.1.5) from parsley. The enantiomerically pure L-amino acids were obtained in good yields by reaction of the corresponding cinnamic acids with 5M ammonia solution (buffered to pH 10) in the presence of PAL. The kinetic constants for nine different fluoro- and chlorophenylalanines do not provide a rigorous proof for but are consistent with the previously proposed mechanism comprising an electrophilic attack of the methylidene-imidazolone cofactor of PAL at the aromatic nucleus as a first chemical step. In the resulting Friedel-Crafts-type sigma complex the beta-protons are activated for abstraction and consequently the pro-S is abstracted by an enzymic base. Results from semi-empirical calculations combined with a proposed partial active site model showed a correlation between the experimental kinetic constants and the change in polarization of the pro-S Cbeta-H bond and heat of formation of the sigma complexes, thus making the electrophilic attack at the neutral aromatic ring plausible. Furthermore, while 5-pyrimidinylalanine was found to be a moderately good substrate of PAL, 2-pyrimidinylalanine was an inhibitor.
TL;DR: In this article, the authors give sharp global estimates for the Green function and Martin kernel in Lipschitz domains, and apply the estimates to obtain short proofs of some classical results.
TL;DR: A continuous-time Hammerstein system, i.e., a system consisting of a nonlinear memoryless subsystem followed by a linear dynamic one, is identified and an algorithm to estimate the nonlinearity is presented and its pointwise convergence to the true characteristic is shown.
Abstract: A continuous-time Hammerstein system, i.e., a system consisting of a nonlinear memoryless subsystem followed by a linear dynamic one, is identified. The system is driven and disturbed by white random signals. The a priori information about both subsystems is nonparametric, which means that functional forms of both the nonlinear characteristic and the impulse response of the dynamic subsystem are unknown. An algorithm to estimate the nonlinearity is presented and its pointwise convergence to the true characteristic is shown. The impulse response of the dynamic part is recovered with a correlation method. The algorithms are computationally independent. Results of a simulation example are given.
TL;DR: In this article, a fractal approach is used to analyze financial time series by applying different degrees of time resolutions, which leads to the heterogenous market hypothesis (HMH), where different market participants analyze past events and news with different time horizons.
Abstract: A fractal approach is used to analyze financial time series by applying different degrees of time resolutions. This leads to the heterogenous market hypothesis (HMH), where different market participants analyze past events and news with different time horizons. A new general model for asset returns is studied in the framework of the fractal market hypothesis (FMH). It concerns capital market systems in which the conditionally exponential dependence (CED) property can be attached to each investor on the market.
TL;DR: The main results of the paper are sufficient conditions on a fuzzy preference relation allowing to reduce the problem of determining UND solutions to that of determining the optimal solutions of a classical linear programming problem.
TL;DR: In this paper, a step-by-step procedure for applying the response surface and SORM methods in estimating the reliability index associated with exceeding a certain allowable settlement level by a shallow foundation is presented.
TL;DR: In this article, a description of non-destructive strength characterization of concrete, using ultrasonic probes, and measuring surface wave velocity is presented, and the results of laboratory examination are described and examples of application of this measurement method in practice are given.
Abstract: The paper presents a description of non-destructive strength characterization of concrete, using ultrasonic probes, and of measuring surface wave velocity. Probes work at frequencies of 40 and 100 kHz, and they are equipped with an exponential waveguide, the end of which has a surface of ca. 1 mm2. A short characteristic of this type of probe is shown with an analysis of the influence of the inclination angle between the vertical and the examined surface as well as the influence of surface irregularities on ultrasonic wave propagation. The results of laboratory examination are described and examples of application of this measurement method in practice are given. It has been proved that this method has a number of advantages that are very useful in engineering practice.
TL;DR: In this article, the authors investigated the competitive transport of Zn(II, Cd(II), and Cr(VI) ions from acidic source phases through PIMs and supported liquid membranes (SLMs) containing TOA and tri-n-octylphosphine oxide (TOPO) as carriers.
Abstract: Competitive alkali metal cation transport across polymer inclusion membranes (PIMs) containing sym-(alkyl)dibenzo-16-crown-5-oxyacetic acid carriers provides excellent selectivity for Na+ transport with the total fluxes being strongly influenced by the length of the alkyl chain that is attached geminal to the functional side arm in the lariat ether. Removal of chromium(VI) anions by PIMs from acidic aqueous phases was also investigated. Using tri-n-octylamine (TOA) as the ion carrier, Cr(VI) was removed by a PIM to decrease the source phase metal concentration from 1.0 to 0.010 ppm after 30 hours of transport. Competitive transport of Cr(VI) and Cr(III) ions from acidic source phases through PIMs and supported liquid membranes (SLMs) containing TOA and tri-n-octylphosphine oxide (TOPO) as carriers was evaluated and a very high Cr(VI)/Cr(III) separation ratio of 4800 was achieved with a PIM containing TOA. Competitive transport of Zn(II), Cd(II), and Cr(VI) from acidic aqueous solutions through PIMs containing TOA was investigated. The selectivity order for metal ion transport was: HCrO4−>CdCl42−+CdCl3−>ZnCl42−+ ZnCl3−. Non-contact atomic force microscopy was used to obtain images of the pores in cellulose triacetate membranes containing a plasticizer.
TL;DR: In this paper, three types of reactive groups: methylthiourea, dithiocarbamate and guanyl thienourea are introduced into the structure of ion-exchange/coordinating resins having vinylbenzyl chloride/divinylbenzene matrix.
TL;DR: The calculations imply that the emanation coefficient of rocks may have a greater influence on radon concentration in underground waters than the contents of radium in the reservoir rocks.
01 Oct 2000
TL;DR: In this paper, a novel approach to harmonic and interharmonic analysis, based on the subspace methods, is proposed, which is an example of high-resolution eigenstructure-based methods.
Abstract: Modern frequency power converters generate a wide spectrum of harmonics 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 the 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 FFT. The comparison proved the superiority of the new methods. However, their computation is much more complex than FFT.
TL;DR: This article presents three BSM system concepts: ARCS, Teledesic, and Skybridge, chosen to present several technical aspects, i.e., how to use geostationary satellites in BSM, highly asymmetrical links, bandwidth on demand, beam diversity, spectrum efficiency, EMC aspects, etc.
Abstract: Recently, the interest in broadband satellite multimedia (BSM) systems has grown rapidly. Advancements in transmission technology have led to the availability of low-cost satellite earth terminals. The superior remote access capabilities of satellite networks are foreseen to provide broadband services to geographically diverse user groups. The desire to support a wide range of broadband services in satellite networks implies that many features present in terrestrial multimedia networks will also emerge in satellite networks. The interest in TCP/IP, DVB, and ATM is also demonstrated by the architecture of some proposed new satellite systems. Access to broadband services via satellites is one of the major issues and depends on the type of orbit of the satellite system. This is the motivation for discussing orbits and their features in this article. Different technical features can be achieved when the satellite system serves as an access system and when it serves as an access and core (transport) system. Broadband services need broadband frequency channels. The discussion about spectrum availability led to the conclusion that BSM systems can operate at higher bands, i.e., Ka and V, or they must use unique solutions to be compatible with the existing systems. The problem of electromagnetic compatibility is discussed in many places in this article. There is also a classification of user terminals and a list of services the BSM systems can offer. Of course, for each particular system this list depends on the features of the BSM system, which is selected by the designer and the future operator. Three types of protocols/platforms can be identified when BSM systems are considered. There are TCP/IP and ATM protocols and the DVB-S platform. This article presents three BSM system concepts: ARCS, Teledesic, and Skybridge. They have been chosen to present several technical aspects, i.e., how to use geostationary satellites in BSM, highly asymmetrical links, bandwidth on demand, beam diversity, spectrum efficiency, EMC aspects, etc. ARCS is a geostationary system with both links provided by the satellite. Many other BSM GSO systems plan to use similar concept (e.g., Direct PC), but only ARCS is well advanced in the standardization process and use of satellite links in both directions. Two other systems, Teledesic and Skybridge, use LEO orbits and are designed with a completely different architecture. Teledesic provides satellite access as well as a satellite core network, while Skybridge is a satellite access system. They differ in coverage, frequency utilization, constellation, and many other important parameters. Considering all this, presenting these three concepts, it is possible to show many technical issues. Other solutions of broadband multimedia systems based on high altitudes platform systems (HAPS) are also presented. The conclusion presents an opinion about the future of BSM systems.
TL;DR: In this article, Li et al. studied the distributions underlying insurance claims and found that the lognormal distribution seems to give a better fit than the Paretian one, while the lagged autocorrelation study reveals a mean-reverting structure of indices returns.
Abstract: Property claim services (PCS) provides indices for losses resulting from catastrophic events in the US. In this paper, we study these indices and take a closer look at distributions underlying insurance claims. Surprisingly, the lognormal distribution seems to give a better fit than the Paretian one. Moreover, lagged autocorrelation study reveals a mean-reverting structure of indices returns.
TL;DR: In this paper, the fabrication and properties of buried microheaters made inside low temperature co-fired ceramics (LTCC) structures are described, where laser cutting is used for meander pattern generation in dried Pt, PtAu or PdAg conductive pads.