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Showing papers by "Vienna University of Technology published in 1991"


Journal ArticleDOI
TL;DR: It is shown that standard multilayer feedforward networks with as few as a single hidden layer and arbitrary bounded and nonconstant activation function are universal approximators with respect to L p (μ) performance criteria, for arbitrary finite input environment measures μ.

5,593 citations


Journal ArticleDOI
TL;DR: Cross-phase and self-phase modulation are used for self-sustained mode locking of a high-power neodymium glass fiber laser.
Abstract: Cross-phase and self-phase modulation are used for self-sustained mode locking of a high-power neodymium glass fiber laser. Stable pulses with a FWHM as short as 70 fs and pulse energies of as much as 1 nJ are generated at a wavelength of 1.064 microm.

340 citations


Journal ArticleDOI
TL;DR: In this article, a miniaturized glucose sensor by means of thin-film technology is reported, which can be placed on glass or flexible polymer substrates by using a double working electrode array for reproducibility tests or differential measurements to suppress interferences.

224 citations


Journal ArticleDOI
TL;DR: In this paper, waste mycelia from several industrial fermentation plants (Aspergillus niger, Penicillium chrysogenum, Claviceps paspali) were used as a biosorbent for zinc ions from aqueous environments, both batchwise as well as in a column mode.
Abstract: Waste mycelia from several industrial fermentation plants (Aspergillus niger, Penicillium chrysogenum, Claviceps paspali) were used as a biosorbent for zinc ions from aqueous environments, both batchwise as well as in a column mode. With all mycelia testes, biosorption per biomass dry weight was a function of pH (increasing with increasing pH between 1.0 and 9.0), biomass concentration (decreasing at high biomass concentrations) and the zinc concentration. Under optimized conditions, A. niger and C. paspali were superior to P. chrysogenum. Treatment of A. niger biomass with NaOH further increased its biosorbent capacity. Desorption of biosorbed zinc was achieved by elution with 0.1 m HCl, best results being obtained with NaOH-treated A. niger. Such treatment did not affect the capacity for biosorption in repeated experiments. NaOH-treated A. niger mycelia were also successfully used in removal of zinc from polluted waters in Austria, thereby showing that the simultaneous presence of other naturally occurring ions does not affect biosorption.

160 citations


Journal ArticleDOI
TL;DR: Experimental results confirm the predictions of the theory and predict an intensity threshold for self-starting passive mode locking related to the linewidth of the first beat note of the power spectrum of the free-running laser output.
Abstract: We investigate the evolution of continuous-wave laser oscillation from free-running to mode-locked operation assuming a nonlinear device with an intensity-dependent transmittivity or reflectivity to be the mode-locking element. An intensity threshold for self-starting passive mode locking is predicted and related to the linewidth of the first beat note of the power spectrum of the free-running laser output. Experimental results confirm the predictions of the theory.

147 citations


Journal ArticleDOI
TL;DR: In this paper, the authors give a geometric construction of heteroclinic and homocliic orbits for singularly perturbed differential equations and derive analytical conditions for transversality.

138 citations


Journal ArticleDOI
TL;DR: A survey of experimental findings for Ce-Cu- and Yb-Cu based compounds is given in this paper, where a successful description of the observed behaviour is possible in terms of the Coqblin-Schrieffer model, which is based on the Anderson Hamiltonian which is more general than the Kondo Hamiltonian.
Abstract: A survey of experimental findings for Ce-Cu- and Yb-Cu-based compounds is given. Most of these compounds exhibit unusual physical properties as a consequence of various competing mechanisms such as a magnetic interaction of the Ruderman-Kittel-Kasuya-Yoshida type, Kondo interaction and crystal-field splitting. The ground-state properties are then dominated by whichever process surpasses the others. A successful description of the observed behaviour is possible in terms of the Coqblin-Schrieffer model, which is based on the Anderson Hamiltonian which is more general than the Kondo Hamiltonian.

133 citations


Journal ArticleDOI
TL;DR: In this article, the authors derive conditions for the optimality of a limit cycle in a dynamic economic system and to interpret them economically, using a fairly general two-state continuous-time nonlinear optimal control problem.
Abstract: The purpose of this paper is to derive conditions for the optimality of a limit cycle in a dynamic economic system and to interpret them economically. A fairly general two-state continuous-time nonlinear optimal control problem is considered. It turns out that for this class of models three different economic mechanisms can be identified as the possible source of limit cycles. One relates to an intertemporal substitution effect expressed in terms of complementarity over time, the second one is a dominating cross effect between the state variables of the system (i.e., the capital stocks in our model), and the third one is positive growth at the equilibrium.

130 citations


Journal ArticleDOI
TL;DR: Stability in passively mode-locked lasers in which pulse formation is dominated by the interplay between self-phase modulation and negative dispersion in separate cavity elements is found to depend sensitively on the magnitude of amplitude modulation relative to that of phase modulation.
Abstract: We present an analysis of passively mode-locked lasers in which pulse formation is dominated by the interplay between self-phase modulation and negative dispersion in separate cavity elements. Steady-state pulse parameters and stability issues are discussed. Stability in these solitary systems relies on some passive amplitude modulation, and the ultimate system performance is found to depend sensitively on the magnitude of amplitude modulation relative to that of phase modulation.

128 citations


Journal ArticleDOI
TL;DR: The generation of bandwidth-limited shoulder-free 125-fsec pulses by additive-pulse-compression mode locking of a neodymium glass laser is described, allowing stable pulse generation under the condition of large pulse shaping in the cavity.
Abstract: The generation of bandwidth-limited shoulder-free 125-fsec pulses by additive-pulse-compression mode locking of a neodymium glass laser is described. An all-fiber nonlinear amplifying loop mirror is employed as a fast saturable absorber and permits stable pulse generation under the condition of large pulse shaping in the cavity.

111 citations


Journal ArticleDOI
TL;DR: It can be concluded that manganese peroxidase plays the major role in the initial breakdown and decolorization of high molecular weight chlorolignin in bleach plant effluents by P. chrysosporium in vivo.

Journal ArticleDOI
TL;DR: In this article, the authors present an analysis of transonic solutions of the steady state 1-dimensional unipolar hydrodynamic model for semiconductors in the isoentropic case.
Abstract: We present an analysis of transonic solutions of the steady state 1-dimensional unipolar hydrodynamic model for semiconductors in the isoentropic case. The approach is based on construction of the orbits of the system in the electron density-electric field phase plane and on representation of discontinuous solutions of the hydrodynamic boundary value problem by a union of trajectory pieces. These pieces are related by shocks obeying jump and entropy conditions. A continuation argument in the length of the semiconductor device under consideration is applied to construct a continuum of sub- and transonic solutions, which contains at least one solution for every positive length. We also present numerical results illustrating the various possible solution profiles. For this we use a regularization of the problem, adding artificial diffusion to obtain singularly perturbed problems which are then solved numerically using continuation in the regularization parameter.

Journal ArticleDOI
TL;DR: Simulation de l'alliage Fe-Ni par quatre structures ordonnees, dont les energies totales sont obtenues en fonction du volume and du moment magnetique par calculs de structures de bandes en employant la methode du moment de spin fixe (fixe) (FSM).
Abstract: The Fe-Ni alloy is simulated by four ordered structures, whose total energies are obtained as a function of volume and magnetic moment by band-structure calculations employing the fixed-spin-moment (FSM) method. An analytic fit of these E(M,V) surfaces is made and permits an interpolation for varying Ni concentration. These parametrized surfaces allow the introduction of the thermodynamics of spin fluctuations. Among others, the following characteristic Invar properties are calculated: the magnetic contribution to the thermal expansion coefficient ${\mathrm{\ensuremath{\alpha}}}_{\mathit{m}}$, the critical pressure for the disappearance of magnetism ${\mathit{P}}_{\mathit{c}}$, the pressure dependence of the Curie temperature ${\mathit{dT}}_{\mathit{C}}$/dP, and the high-field susceptibility. These quantities agree well with experiment, especially their variation with Ni content. The key quantity is ${\mathrm{\ensuremath{\alpha}}}_{\mathit{m}}$, which shows a narrow minimum as a function of the Ni concentration before the \ensuremath{\alpha}\ensuremath{\rightarrow}\ensuremath{\gamma} (bcc\ensuremath{\rightarrow}fcc) phase transition occurs. Near the Invar composition the large negative contribution ${\mathrm{\ensuremath{\alpha}}}_{\mathit{m}}$ compensates the positive phonon part so that the total thermal expansion nearly vanishes near room temperature. The present combination of models provides new insight into the nature of the Invar effect.

Journal ArticleDOI
TL;DR: In this paper, two point snowmelt models are compared under different weather and snowpack conditions, and the results show that the performance of the bulk model depends on snow pack conditions.

Journal ArticleDOI
TL;DR: Femtosecond mode locking of a Ti:sapphire laser synchronously pumped by a mode-locked, frequency-doubled Nd:YLF laser and stable tunable 70-fs pulses are generated in a TEM(00) output without the need for stabilization of the cavity length.
Abstract: We report femtosecond mode locking of a Ti:sapphire laser synchronously pumped by a mode-locked, frequency-doubled Nd:YLF laser. Stable tunable 70-fs pulses are generated in a TEM00 output without the need for stabilization of the cavity length.

Journal ArticleDOI
TL;DR: In this article, the alkylation of toluene with methanol over HZSM-5 zeolites was studied in a continuously stirred tank reactor equipped with CaF2 windows, which allows the monitoring of the catalyst and the adsorption complexes under reaction conditions by means of IR spectroscopy.

Journal ArticleDOI
TL;DR: In this paper, a surface barrier detector for collecting the ejected and subsequently accelerated electrons was used to measure the electron emission from clean gold under impact of slow (< 1 au) heavy particles.

Journal ArticleDOI
TL;DR: Northern (RNA) hybridization with full copies of cbh1 and cbh2 genes indicated that the control of CBH I and CBH II biosyntheses by the carbon source operates mainly at the pretranslational level.
Abstract: Regulation of the formation and secretion of two cellulase components from Trichoderma reesei QM 9414, cellobiohydrolases I and II (CBH I and CBH II, respectively), by the carbon source was investigated. With monoclonal antibodies against CBH I and CBH II it was found that during cultivation on carbon sources which enable fast growth (glucose, glycerol, and fructose), no formation of CBH I occurred, whereas low levels of CBH II were formed. Lactose and cellulose, which allow comparably slower growth, promoted the formation of both CBH I and CBH II. However, noncarbohydrate carbon sources as citrate or acetate, which also enable only slow growth, did not promote the formation of CBH I or CBH II. The addition of glucose or glycerol to lactose- or cellulose-pregrown mycelia, on the other hand, only partially reduced the formation of CBH I. This reduction was also achieved by several other metabolizable and nonmetabolizable carbon compounds, e.g., fructose, galactose, beta-methylglucoside, 2-deoxyglucose, and rhamnose, as well as by transfer to no carbon source at all. This result indicates that the control of CBH I synthesis by the carbon source is due to induction and not to repression. The use of cycloheximide and 5-fluorouracil as inhibitors at and before translation, respectively, revealed a half-life for CBH I mRNA of at least several hours, which may, at least in part, account for the prolonged synthesis of some CBH I under these conditions. Northern (RNA) hybridization with full copies of cbh1 and cbh2 genes indicated that the control of CBH I and CBH II biosyntheses by the carbon source operates mainly at the pretranslational level. We conclude that the low rate of cellulase synthesis on glucose and some other carbon sources is due to the lack of an inducer and not to carbon source repression.

Journal ArticleDOI
TL;DR: In this article, the authors demonstrate the application of Li-CXS (fast lithium-beam-activated charge exchange spectroscopy) for measuring spatially and temporally resolved impurity ion concentrations in the TEXTOR tokamak edge plasma.
Abstract: We demonstrate the application of Li-CXS (fast lithium-beam-activated charge exchange spectroscopy) for measuring spatially and temporally resolved impurity ion concentrations in the TEXTOR tokamak edge plasma. After briefly describing the method of Li-CXS and its capabilities, we present a model for attenuation and atomic state population of an injected Li beam due to collisional interactions with the background plasma particles, taking into account up to eight excited LiI states for considering stepwise excitation-ionization processes. Measured impurity radiation characteristics resulting from Li-activated CX of C q+ (q=5, 6) in ohmically heated TEXTOR plasmas are evaluated with the above model and lead to the corresponding impurity ion concentrations within the TEXTOR edge region.

Journal ArticleDOI
TL;DR: In order to assess the importance of the conidial CBH II level for cellulase induction by cellulose, multiple copies of the chb2 gene were introduced into the T. reesei genome by cotransformation using PyrG as a marker.
Abstract: Monoclonal antibodies have been used to determine the presence of cellobiohydrolases I and II (CBH I and II), and endoglucanase I (EG I) on the surface of conidia from Trichoderma reesei QM 9414 and RUT C-30, and 8 other Trichoderma species. For this purpose, proteins were released from the conidial surface by treatment with a non-ionic detergent (Triton X-100 and β-octylglucoside), followed by SDS-PAGE/Western blotting and immunostaining. Both CBH I and II were clearly present, but — unlike in extracellular culture fluids from Trichoderma — CBH II was the predominant cellulase. In T. reesei EG I could not be detected. The higher producer strain T. reesei RUT C-30 exhibited a higher conidial level of CBH II than T. reesei QM 9414. In order to assess the importance of the conidial CBH II level for cellulase induction by cellulose, multiple copies of the chb2 gene were introduced into the T. reesei genome by cotransformation using PyrG as a marker. Stable multicopy transformants secreted the 2- to 4-fold level of CBH II into the culture medium when grown on lactose as a carbon source, but their CBH I secretion was unaltered. Upon growth on cellulose, both CBH I and CBH II secretion was enhanced. Those strain showing highest cellulase activity on cellulose also appeared to contain the highest level of conidial bound CBH II. CBH II was also the predominant conidial cellulase in various other Trichoderma sp. However, roughly the same amount of conidial bound CBH II was detected in all strains, although their cellulase production differed considerably.

Journal ArticleDOI
TL;DR: In this paper, the band structure, densities of states, partial charges, electron densities, and electric field gradients of Ba and Y are determined from first-principles calculations using the full-potential linearized-augmented-plane-wave method.
Abstract: The band structure, densities of states, partial charges, electron densities, and electric-field gradients (EFG's) of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{4}$${\mathrm{O}}_{8}$ are determined from first-principles calculations using the full-potential linearized-augmented-plane-wave method. Exchange and correlation effects are treated by the local-density approximation. The doubling of the copper-oxygen chains with respect to ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ affects the electronic structure, especially near the chain oxygen, which has a third copper neighbor. The charge distribution around this position is drastically changed, and consequently the asymmetry parameter of the EFG is increased from 0.3 to 1.0, while the principal EFG component becomes similar for all oxygen positions. The bonding characteristic of the double chains is illustrated by difference electron densities. The core-level shifts are estimated and agree with experimental data, which are available for Ba and Y.

Journal ArticleDOI
TL;DR: In this paper, a series of H-ZSM5 zeolites varying in Si/Al ratio were investigated for disproportionation of toluene and isomerization of xylene.

Journal ArticleDOI
TL;DR: Notably, the (Sternheimer antishielding) contribution from the core electrons--mainly from the Cu 3{ital p} semicore'' electrons--is found to be very small, and the agreement of the oxygen EFG components themselves with experiment is good.
Abstract: The origin of the electric-field gradients (EFG) at nuclear sites in the high-{ital T}{sub {ital c}} superconductor YBa{sub 2}Cu{sub 3}O{sub 7} is investigated theoretically by means of highly precise local-density full-potential linearized-augmented-plane-wave calculations. In all cases considered (i.e., at Cu, O, Ba, and Y nuclei), the theoretical predictions for the principal axis {ital V}{sub {ital z}{ital z}} and the anisotropy parameter {eta} of the EFG tensor agree well with available experiments and the results of Ambrosch-Draxl {ital et} {ital al}. The principal axis at O sites are found to lie in the direction of the Cu-O {ital dp}{sigma} bonding axis, and the oxygen {eta} values are largely determined by the internal anisotropy inside the oxygen spheres. This is consistent with the finding that the main contribution to the EFG at the Cu sites comes from the intrinsic quadrupole field provided by the nonspherical (internal) charge distributions surrounding each Cu atom arising from the strong anisotropic hybridization between Cu {ital d} and O {ital p} electrons. Surprisingly, the (Sternheimer antishielding) contribution from the core electrons--mainly from the Cu 3{ital p} semicore'' electrons--is found to be very small. Overall, the agreement of the oxygen EFG components themselves with experiment is good. Themore » calculated {ital V}{sub {ital z}{ital z}} values are within 20% of the experiment, except for Cu(2), which is only half of the observed value and results in a reversal of the relative magnitude of the EFG at Cu(1) and Cu(2) sites. This error may result from the inexact treatment of the 3{ital p} semicore states when they are allowed to relax and are described as band states. This is seen from the extreme sensitivity of the EFG to the calculated anisotropic charge distributions of the core electrons.« less

Journal ArticleDOI
01 Jun 1991-Zeolites
TL;DR: In this paper, the thermal decomposition of tetrapropylammonium fluorides in ZSM-5 crystals was studied by means of time resolved spectroscopy, and three different processes were observed, i.e., increasing of the mobility of the tetraplammonium cations and oligomerization of the template or parts of a template.

Journal ArticleDOI
TL;DR: The aim in this paper is to demonstrate the extensive applicability of several series relations occurring in Ramanujan's Notebook in the analysis of special data structures and algorithms.
Abstract: Using several transformation formulae from Ramanujan's second Notebook we achieve distribution results on random variables related to dynamic data structures (so-called “tries”). This continues research of Knuth, Flajolet and others via an approach that is completely new in this subject.

Journal ArticleDOI
TL;DR: In this paper, the catalytic activity of a series of alkali exchanged and alkali impregnated ZSM-5 zeolites in the alkylation of toluene with methanol was investigated.

Book ChapterDOI
01 Jan 1991
TL;DR: The semantics of Object/Behaviour diagrams is formally defined through a mapping into Predicate/Transition nets, which model the life cycles of objects through a set of states and activities.
Abstract: An object-oriented diagram technique is introduced for the design of information systems. Structural properties of objects are depicted in object diagrams. Dynamic properties are shown in behaviour diagrams. Object diagrams are based on semantic data model concepts. Behaviour diagrams are based on Petri nets and model the life cycles of objects through a set of states (places) and activities (transitions). The relationship between Object/Behaviour diagrams and Predicate/Transition nets is shown. The semantics of Object/Behaviour diagrams is formally defined through a mapping into Predicate/Transition nets.

Journal ArticleDOI
TL;DR: In this paper, the influence of local air temperature and albedo on snowmelt in the Austrian Alps is analyzed using a range of model parameters representing different snow cover conditions.
Abstract: Extrapolating meteorological data to the basin scale represents a major problem of spatial snowmelt modelling in alpine terrain. Within this study errors in air temperature introduced by regionalization are analyzed for the Sellrain region in the Austrian Alps. Albedo is simulated using a range of model parameters representing different snow cover conditions. The influence on snowmelt is assessed by simulating water equivalent at the site scale using estimated air temperatures and albedoes. Simulation results indicate that a bias in measured temperatures as produced by local effects may be significantly more important than interpolation errors. Uncertainty in albedo appears to affect snowmelt to a higher degree than air temperature.

Journal ArticleDOI
TL;DR: In this article, a collection of experimental results on electron emission from a clean gold surface bombarded by slow neutral atoms and singly or multiply charged ions, which have been obtained by measuring the corresponding emission statistics, are presented.
Abstract: We present a collection of experimental results on electron emission from a clean gold surface bombarded by slow neutral atoms and singly or multiply charged ions, which have been obtained by measuring the corresponding emission statistics. Apart from an intrinsic interest in the emission statistics themselves,our investigations provide a physically sound distinction between potential and kinetic emission processes, and at sufficiently low projectile energies they permit an unambiguous separation of both contributions. The threshold impact energy for kinetic emission can now be correctly determined and dependencies of the kinetic emission process on charge state and molecular composition of the projectiles can clearly be demonstrated. In their entirety our results provide new information on the relevant mechanisms for slow particle-induced electron emission.

Journal ArticleDOI
TL;DR: In this article, the existence and continuity of infinite series type Gaussian processes are proved via showing that under a global condition their partial sum processes converge uniformly over finite intervals with probability one.