Showing papers by "University of Trento published in 1996"
TL;DR: In this paper, a construction of virtual fundamental classes of certain types of moduli spaces is proposed, where the fundamental classes can be expressed as a set of classes of modulus spaces.
Abstract: We suggest a construction of virtual fundamental classes of certain types of moduli spaces.
702 citations
TL;DR: This work investigates the low energy excitations of a dilute atomic Bose gas confined in a harmonic trap of frequency and interacting with repulsive forces and predicts the dispersion law of the noninteracting harmonic oscillator model.
Abstract: We investigate the low energy excitations of a dilute atomic Bose gas confined in a harmonic trap of frequency ${\ensuremath{\omega}}_{0}$ and interacting with repulsive forces. The dispersion law $\ensuremath{\omega}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}{\ensuremath{\omega}}_{0}({2n}^{2}+2n\ensuremath{\ell}+3n+\ensuremath{\ell}{)}^{1/2}$ for the elementary excitations is obtained for large numbers of atoms in the trap, to be compared with the prediction $\ensuremath{\omega}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}{\ensuremath{\omega}}_{0}(2n+\ensuremath{\ell})$ of the noninteracting harmonic oscillator model. Here $n$ is the number of radial nodes and $\ensuremath{\ell}$ is the orbital angular momentum. The effects of the kinetic energy pressure are estimated using a sum rule approach. Results are also presented for deformed traps and attractive forces.
630 citations
TL;DR: In this article, the authors introduce the approach of electrochemical impedance data interpretation by equivalent electrical circuits on organic coated metals showing some examples relevant to different metal substrates or coating cycles, and introduce a method to analyze the electrical models used to explain the impedance results.
411 citations
TL;DR: It is shown that the presence of vortices significantly increases the stability of the condensate in the case of attractive interactions, and the critical angular velocity for production of vorts is calculated.
Abstract: We solve the Gross-Pitaevskii equations for a dilute atomic gas in a magnetic trap, modeled by an anisotropic harmonic potential. We evaluate the wave function and the energy of the Bose-Einstein condensate as a function of the particle number, both for positive and negative scattering length. The results for the transverse and the vertical size of the cloud of atoms, as well as for the kinetic and potential energy per particle, are compared with the predictions of approximated models. We also compare the aspect ratio of the velocity distribution with experimental estimates available for $^{87}\mathrm{Rb}$. Vortex states are considered and the critical angular velocity for production of vortices is calculated. We show that the presence of vortices significantly increases the stability of the condensate in the case of attractive interactions. \textcopyright{} 1996 The American Physical Society.
385 citations
TL;DR: In this article, it was shown that the surface conditions chosen by Dabby and Paek are wrong and that the subsurface region is indeed hotter but only by a few degrees.
275 citations
TL;DR: By using a mean field approach, based on the Popov approximation, the temperature dependence of the condensate fraction of an interacting Bose gas confined in an anisotropic harmonic trap is calculated.
Abstract: By using a mean-field approach, based on the Popov approximation, we calculate the temperature dependence of the condensate fraction of an interacting Bose gas of N atoms confined in an anisotropic harmonic trap. For systems interacting with repulsive forces we find a significant decrease of the condensate fraction and of the critical temperature with respect to the predictions of the noninteracting model with the same value of N. An analytic result for the shift of the critical temperature holding to first order in the scattering length is also derived. \textcopyright{} 1996 The American Physical Society.
243 citations
TL;DR: In this paper, the elastic modulus (E), flexural strength (MOR), and Vickers hardness (H v ) increase with the amount of carbon in the oxycarbide glasses reaching the maximum values (E≃115 GPa, MOR≃550 MPa, and H v ≃9 GPa).
Abstract: Silicon oxycarbide glasses have been fabricated, in the shape of thin rods suitable for flexural test experiments, by pyrolysis in an inert atmosphere at 1000 and 1200°C of sol-gel precursors containing Si-CH 3 and Si-H bonds The amount of carbon in the silicon oxycarbide network has been controlled by varying the carbon load in the precursor gel Density and surface area analysis revealed that all of the samples pyrolyzed at 1200°C were well-densified silicon oxycarbide glasses whereas for the glasses treated at 1000°C, compositions with low carbon loads showed the presence of a residual fine porous phase The elastic modulus (E), flexural strength (MOR), and Vickers hardness (H v ) increase markedly with the amount of carbon in the oxycarbide glasses reaching the maximum values (E≃115 GPa, MOR≃550 MPa, and H v ≃9 GPa) for samples with the highest carbon content The experimental elastic modulus values of the silicon oxycarbide glasses compare well with the theoretical estimations obtained using the Voigt and Reuss models assuming the disordered network formed by the corresponding thermodynamic compositions
176 citations
165 citations
TL;DR: NL-OOPS, a CASE tool that supports requirements analysis by generating object oriented models from natural language requirements documents by implementing an algorithm for the extraction of the objects and their associations for use in creating object models.
Abstract: This paper describes NL-OOPS, a CASE tool that supports requirements analysis by generating object oriented models from natural language requirements documents. The full natural language analysis is obtained using as a core system the Natural Language Processing System LOLITA. The object oriented analysis module implements an algorithm for the extraction of the objects and their associations for use in creating object models.
157 citations
01 Nov 1996
TL;DR: A new method for generating spatially-correlated random fields, called HYDRO_GEN, which can simulate fields of different nature, starting from weakly stationary fields with a prescribed covariance and ending with fractal fields.
Abstract: This paper describes a new method for generating spatially-correlated random fields. Such fields are often encountered in hydrology and hydrogeology and in the earth sciences. The method is based on two observations: (i) spatially distributed attributes usually display a stationary correlation structure, and (ii) the screening effect of measurements leads to the sufficiency of a small search neighborhood when it comes to projecting measurements and data in space. The algorithm which was developed based on these principles is called HYDRO_GEN, and its features and properties are discussed in depth. HYDRO_GEN is found to be accurate and extremely fast. It is also versatile: it can simulate fields of different nature, starting from weakly stationary fields with a prescribed covariance and ending with fractal fields. The simulated fields can display statistical isotropy or anisotropy.
153 citations
TL;DR: The pseudodynamic test method is intended as an efficient and powerful alternative to the shaking table test method and has been widely used in structural research as discussed by the authors. But it is not suitable for structural analysis.
Abstract: The pseudodynamic test method is intended as an efficient and powerful alternative to the shaking table test method. Since its inception, a variety of new testing techniques and numerical schemes have been developed to improve the efficiency and accuracy of the method. The main objective of this paper is to present the pseudodynamic test method from a user's perspective. With this objective in mind, an overview of the pseudodynamic test method is provided. Some of the most up‐to‐date developments, including substructure testing techniques, are illustrated with test examples. It is shown that while the method is definitely more complicated than conventional quasi‐static tests, it can be implemented and applied to structural research with a small incremental cost.
TL;DR: The results of an XPS study of sol-gel-derived silicon oxycarbide glasses are presented in this paper, where it was shown that the fracture surface is richer in carbon compared with the bulk.
TL;DR: Leucascandrolide A ((+)-1), a doubly O-bridged 18-membered macrolide of a new type, was isolated from a calcareous sponge as discussed by the authors.
Abstract: Leucascandrolide A ((+)-1), a doubly O-bridged 18-membered macrolide of a new type, i.e., showing little C1-branching vs. extensive 1,3-dioxygenation and a peculiar side chain, was isolated from a calcareous sponge of a new genus, Leucascandra caveolata BOROJEVIC and KLAUTAU from the Coral Sea. Transesterification of (+)-1 gave the methyl ester 3, derived from the side chain, and the 5-hydroxy derivative (+)-2, derived from the macrolide portion and with the natural configuration at C(5) (axial). Mosher's MTPA esters 4 and 5 obtained from (+)-2 showed scattered Δδ = (δ(S) − δ(R)) data. However, inversion of the configuration at C(5) led, via ketone (+)-6, to the less encumbered 5-equatorial hydroxy derivative (+)-7, whose MTPA esters 8 and 9 gave consistent Δδ data, allowing the assignment of the absolute configuration of (+)-7, and hence of (+)-1. The structural novelty of (+)-1 and its powerful antifungal and cytotoxic activities are likely to renew interest in calcareous sponges, previously limited to scarcely biologically active 2-aminoimidazoles.
TL;DR: In this article, a very strong phonon sideband is coupled to the 5 D 0 ← 7 F 0 transition; a value of 0.11 is obtained for the electron-phonon coupling strength.
Abstract: 4ZnO · 3B 2 O 3 glasses undoped and doped with 0.5–2.5% Eu 3+ were studied using absorption, emission and excitation spectroscopies, fluorescence line narrowing, Raman scattering and lifetime measurements. The vibrational spectra of the undoped and doped glasses are very similar and indicate the presence of borate groups already observed in binary metaborate glasses. The Judd-Ofelt parameters and the asymmetry ratio derived from the f-f transitions of the Eu 3+ ion give information on the average local structure around the impurity ions. Crystal-field parameters obtained from site selective emission spectra are close to those found for various silicate glasses, and their major ratios are close to predictions of the Brecher and Riseberg model. A very strong phonon sideband is coupled to the 5 D 0 ← 7 F 0 transition; a value of 0.11 is obtained for the electron-phonon coupling strength. Comparison with Raman spectra indicates that the sideband is due to an Eu 3+ O stretching/BO 3 3− mode. No energy transfer is found in the most diluted samples.
TL;DR: In this article, absolute electron-scattering total cross sections for noble gas atoms (He, Ne, Ar, Kr, and Xe) and H, N, CO, NO, and 0, molecules have been measured at impact energies between 0.5 and 250eV by the linear transmission method with the same experimental set-up for all the investigated targets.
Abstract: Absolute electron-scattering total cross sections for noble gas atoms (He, Ne, Ar, Kr, and Xe) and H,, N, , CO, NO, and 0, molecules have been measured at impact energies between 0.5 and 250eV by the linear transmission method with the same experimental set-up for all the investigated targets. Generally, our total cross sections have been found to be in good agreement with other data with respect to shape. Some systematic discrepancies in magnitude still exist between results of different groups, especially at the lowest applied energies and in the energy range where the cross sections peak. At these energies, new measurements should be carried out before establishing a reference set of data.
TL;DR: In this article, a novel algorithm for the global optimization of functions (C-RTS) is presented, in which a combinatorial optimization method cooperates with a stochastic local minimizer.
Abstract: A novel algorithm for the global optimization of functions (C-RTS) is presented, in which a combinatorial optimization method cooperates with a stochastic local minimizer. The combinatorial optimization component, based on the Reactive Tabu Search recently proposed by the authors, locates the most promising “boxes”, in which starting points for the local minimizer are generated. In order to cover a wide spectrum of possible applications without user intervention, the method is designed with adaptive mechanisms: the box size is adapted to the local structure of the function to be optimized, the search parameters are adapted to obtain a proper balance of diversification and intensification. The algorithm is compared with some existing algorithms, and the experimental results are presented for a variety of benchmark tasks.
01 Jan 1996
TL;DR: For materials capable of attaining two phases, the free energy potential is a non-convex functional of the state variables as discussed by the authors, and absolute and relative minimizers of this functional are related to stable and metastable states, respectively.
Abstract: For materials capable of attaining two phases, the free energy potential is a non-convex functional of the state variables. Absolute and relative minimizers of this functional are related to stable and metastable states, respectively. Metastability explains the undercooling required for solid nucleation.
TL;DR: In this article, the first phase of a research project aimed at developing simple design criteria for semi-rigid steel frames in seismic zones is described, which consists of two series of tests on beam-to-column joints under cyclic reversal loading.
TL;DR: In vitro comparative cytotoxicity assays of these compounds show that for high cytotoxic activity, such as of 1in vivo, unsubstituted OHC(8a), HN(5),HN(6) moieties are needed in the natural B/D transoid configuration.
Abstract: Agelastatin A (1), an unusual alkaloid of the axinellid sponge Agelas dendromorpha from the Coral Sea, can be selectively acetylated (7) or methylated at OHC(8a) (4), peracetylated (8) or permethylated at OHC(8a), NH(5), and NH(6) (5), or, finally, subjected to C(9)C(8a) (14) or C(5b)C(8a) β-elimination (11–13), in a regiospecific manner or not, depending on the reaction conditions. Under acidic conditions, compound 12 adds H2O or MeOH, regioselectively though not endo/exo stereoselectively, giving transoid/cisoid mixtures 1/18 or 4/19, respectively. Similarly 11 or 13 add MeOH to give mixtures (−)-2/20 or 15/16, respectively. Compound 13 also adds AcOH giving mixture 8/17. The intermediate cisoid form obtained on treatment of 21 with H3O+ undergoes N(5)N(6) bridging affording pentacyclic 22 which constitutes a proof for the cisoid configuration. From conformational studies, rules are devised that allow assigning the configuration of these compounds from NMR data. In vitro comparative cytotoxicity assays of these compounds show that for high cytotoxic activity, such as of 1in vivo, unsubstituted OHC(8a), HN(5), HN(6) moieties are needed in the natural B/D transoid configuration.
TL;DR: In this article, ZrO 2 CeO 2 coatings were deposited on 304 stainless steel substrates by dip coating in alkoxide solution, and they were transparent and continuous at thickness below 700 nm.
01 Jan 1996
TL;DR: In this paper, the concept of hysteresis operator is outlined, and some simple models are illustrated, some differential equations with hystresis are also briefly discussed, and the results of the model are discussed.
Abstract: The concept of hysteresis operator is outlined, and some simple models are illustrated. Some differential equations with hysteresis are also briefly discussed.
TL;DR: It is argued that demixing and phase separation occur in the relaxation stage or thermal spike phase of the collision cascade, as a consequence of the positive heat of mixing.
Abstract: Ag/Fe bilayers deposited onto ${\mathrm{SiO}}_{2}$/Si substrates were irradiated at 20, 77, and 300 K with 300--750 keV Ar and Xe ions in order to study the ion-beam-induced mixing and phase formation in this thermally immiscible system. A combination of Rutherford backscattering spectroscopy (RBS), channeling, conversion electron M\"ossbauer spectroscopy (CEMS), and scanning tunneling microscopy (STM) was used to analyze the atomic transport at the interface and the resulting microstructure and morphology changes of the samples. In the CEMS measurements, a 13 nm thin $^{57}\mathrm{Fe}$ marker layer at the Ag/Fe interface was introduced in order to enhance the sensitivity to alterations of the interfacial composition. From the small amount of Ag atoms found to be dissolved in Fe and from the sharpness of the element profiles at the interface, we derived a very small mixing efficiency, which is significantly smaller than the prediction of the ballistic model. Since ballistic mixing is expected in any case, we argue that demixing and phase separation occur in the relaxation stage or thermal spike phase of the collision cascade, as a consequence of the positive heat of mixing. On the other hand, ion irradiation induces a large surface roughening of the Ag top layer as proven by STM. This effect is obviously due to recrystallization of Ag, which results in grain growth and texture formation along the direction of the impinging ion, as demonstrated by RBS/channeling measurements. \textcopyright{} 1996 The American Physical Society.
TL;DR: In this paper, a procedure for the evaluation of the double integrals involved in the symmetric BE method is proposed, which consists in a regularization via integration by parts and in a successive numerical evaluation of weakly singular integrals.
Abstract: A procedure for the evaluation of the double integrals involved in the symmetric BE method is proposed, which consists in a regularization via integration by parts and in a successive numerical evaluation of weakly singular integrals. The procedure is applicable to curved elements and higher order shape functions and lends itself to a fairly straightforward implementation. Continuity is required for displacement modelling, while tractions may be modelled as piece-wise continuous. Some example problems characterized by the presence of curved boundaries or of cracks are analyzed using the proposed technique to demonstrate its effectiveness.
TL;DR: In this article, an ion-sensitive field effect transistor (ISFET) was used in conjunction with an enzyme specific for this pollutant to sample atmospheric formaldehyde by dissolution in an aqueous solution followed by the monitoring of the aldehyde using an ISFET.
Abstract: This paper reports on a system for sampling atmospheric formaldehyde by dissolution in an aqueous solution followed by the monitoring of the aldehyde using an ion-sensitive field-effect transistor (ISFET) in conjunction with an enzyme specific for this pollutant. Formaldehyde dehydrogenase from Pseudomonas putida was chosen on the basis of its characteristics to be coupled to the ISFET transducer. This enzyme, using oxidized nicotinamide adenine dinucleoside (NAD) as cofactor, catalyses the oxidation of a molecule of formaldehyde with the parallel production of two protons, which are sensed by the ISFET. The working conditions were chosen to obtain a linear response of the sensor up to 200 μM formaldehyde. On the basis of the enrichment obtained by the sampling system, the detection limit of 10 μM formaldehyde in aqueous solution, achieved by the ISFET biosensor, corresponds to an atmospheric concentration of the formaldehyde in the ppb range.
TL;DR: In this paper, the authors examined the centre-of-mass velocity autocorrelation function of liquid water under room conditions through a mode-coupling approach developed to study monatomic liquids.
Abstract: The centre-of-mass velocity autocorrelation function of liquid water under room conditions is examined through a mode-coupling approach developed to study monatomic liquids The wavevector-dependent current correlations relevant to the theory are evaluated by computer simulations using a recently developed interaction potential, which accounts for the polarizability of the molecule The theory is found to reproduce all the relevant dynamical features of water Moreover, the analysis in terms of longitudinal and transverse contributions clarifies the origin of some peculiarities in the dynamics of this single-molecule correlation A discussion of the corresponding spectra is also given
TL;DR: In this article, a room temperature visible light emitting diodes based on porous silicon planar microcavities are reported. The electrical injection was provided by metal contacts (Schottky-like diode) and the performance of these structures with respect to standard porous silicon LEDs is presented and discussed.
TL;DR: This work discusses how intrinsic inconsistencies and negative results in social choice may be alleviated by plausible modifications of underlying assumptions and problem formulations, basically by the introduction of some impreciseness of a probabilistic, fuzzy and rough type.
TL;DR: In this paper, a simple lattice model describing the recombination dynamics in visible-light-emitting porous silicon is presented, where each occupied lattice site represents a Si crystal of nanometre size.
Abstract: A simple lattice model describing the recombination dynamics in visible-light-emitting porous silicon is presented. In the model, each occupied lattice site represents a Si crystal of nanometre size. The disordered structure of porous silicon is modelled by modified random percolation networks in two and three dimensions. Both correlated (excitons) and uncorrelated electron - hole pairs have been studied. Radiative and non-radiative processes as well as hopping between nearest-neighbour occupied sites are taken into account. By means of extensive Monte Carlo simulations, we show that the recombination dynamics in porous silicon is due to a dispersive diffusion of excitons in a disordered arrangement of interconnected Si quantum dots. The simulated luminescence decay for the excitons shows a stretched exponential lineshape while for uncorrelated electron - hole pairs a power-law decay is suggested. Our results successfully account for the recombination dynamics recently observed in experiments. The present model is a prototype for a larger class of models describing diffusion of particles in a complex disordered system.