Showing papers by "Polytechnic University of Catalonia published in 1986"

On the optimal station keeping control of halo orbits

Abstract: Techniques for computing and controlling a halo orbit are considered in this paper. It presents a semi-analytical theory for the halo orbits in the Restricted Three Bodies Problem (RTBP), that is valid and amenable to computation to any order. Results are presented up to order 11. The Floquet modes of the monodromy matrix are used to define a local optimal control procedure through the concepts of projection and gain functions.

High temperature incipient fluidization in mono and polydisperse systems

Abstract: Tests have been made on the behaviour of fluidized beds at high temperature (15-950°C). Bed materials used were silica sand of different sizes. Bed voidage at minimum fluidization conditions was found to be dependent on temperature rise and on increase in Reynolds number. Plots of bed voidage function, bed voidage and Ar versus Remf show a change in the behaviour at Reynolds numbers between approximately 0.75-2. This is explained in terms of a variation in the fluid flow pattern inside the bed: at very low Remf creeping flow exists, but at higher values of Reynolds number, separation of boundary layer takes place and a wake appears at the rear of the particle, creating a low pressure zone. This contributes to attractive forces between particles at the minimum fluidization conditions, decreasing the value of ϵmf. If Remf increases, the separation point moves towards the rear of the particle and the wake shrinks; attractive forces decrease, and ϵmf increases. Data on umf , both for monodisperse systems and ...

Structural and magnetic characterization of the lithiated iron oxide LixFe3O4

Abstract: The Rietveld profile‐analysis method is used to investigate the x‐ray diffraction pattern of lithiated Fe3O4. It is shown that, after exposure to air, pure magnetite coexists with a lithium‐inserted LixFe3O4 phase. The Mossbauer spectra at 300 and 4.2 K have been used to estimate the lithium content of the sample, the pure magnetite concentration, and the iron distribution over the available 16c and 16d sites of the spinel structure. Magnetization measurements from 4.2 to 120 K with an external magnetic field up to 150 kOe have been used to obtain the saturation magnetic moment, the magnetic anisotropy constants, and the susceptibility. It is concluded that a noncollinear spin structure should be present in Li0.5Fe3O4. These results indicate that there is no room‐temperature extrusion of iron even for x→2.0, but that on exposure to air LixFe3O4 samples with x>0.5 are oxidized at room temperature by delithiation.

Exchange interactions in BaFe12O19

Abstract: In the scope of the mean field approximation the nine nearest neighbour exchange interactions existing among the ferric ions in BaFe12O19 hexagonal ferrite have been determined from the experimental sublattice magnetizations. It is shown that these exchange interactions are well explained by means of the superexchange theory. It is also concluded that some direct exchange interaction does exist among the octahedral 4f VI ions. The calculated magnetization, paramagnetic susceptibility, and Curie temperature are in good agreement with the corresponding experimental values. The stability of the collinear Gorter-type magnetic structure of BaFe12O19 is discussed as well.

Neural Network Model with Rhythm-Assimilation Capacity

Abstract: Assimilation of a stimulus rhythm by certain nervous structures of vertebrate animals in a conditioning situation has been reported. A lateral-inhibition-type network of plastic pacemaker neurons is proposed to model such behavior. Through simulation, the network exhibits capacity to assimilate and encode in separate groups of neurons two successively presented frequencies. Learning of the second frequency does not disrupt memory of the first one. From the exploration of the effect of varying several factors upon the learning process?related to the connectivity, the intraneuronal functioning, the initial state, and the simulation conditions?it follows that the most influential factors are the proportion of excitatory connections over the total, the ratio between the ranges of the excitatory and the inhibitory connectivity, and the degree of intraneuronal randomness.

Uniform characterizations of non-uniform complexity measures

Abstract: The class PSPACE/ply of sets decided within polynomial space by machines with polynomial advices is characterized in several way: we give an algebraic characterization, a parallel model characterization. Finally we define a dual class and state some of its properties.

A note on the elliptic restricted three-body problem

Abstract: This work considers periodic solutions, arc-solutions (solutions with consecutive collisions) and double collision orbits of the plane elliptic restricted problem of three bodies for μ=0 when the eccentricity of the primaries,e p , varies from 0 to 1. Characteristic curves of these three kinds of solutions are given.

N-Alkylbetaines in Wool Dyeing

Abstract: The influence of N-alkylbetaines, with alkyl chain lengths from eight to 18 carbon atoms, on the dyeing of wool with acid dyes has been studied. In the first part of the study the presence of N-alkylbetaines was found to cause spectral changes of the dye in solution, and two clearly differentiated dissociation stages have been observed. These represent the formation of dye-betaine complexes and the solubilisation of these complexes in the betaine micelles. The second part of the study examined how the presence of betaines influenced dyeing kinetics. Generally N-alkylbetaines were found to increase the rate of dyeing, the type and amount of betaine present being important factors.

Saccharification of concentrated brewing bagasse slurries with dilute sulfuric acid for producing acetone-butanol by Clostridium acetobutylicum.

Abstract: A comprehensive kinetic study of the acid hydrolysis of concentrated brewing bagasse slurries was performed. The use of the simple series reaction model was found to be suitable when a "heterogeneous correction" (pseudosubstrate-inhibition) is taken into account in slurries with low liquid-to-biomass ratios. Rate constants are shown to be dependent not only on temperature and acid concentration but essentially also on the initial biomass concentration. Actual rate constants, activation energies, and acid and substrate reaction orders are reported for xylan, arabinan, and alpha-glucan acid saccharification. There is a threshold acid loading necessary to overcome the 80% conversion, but no threshold has been found to overcome the "neutralizing" property of cellulosic materials. Reversible acid capture from brewing bagasse has been postulated. The highest monosccharide concentration into hydrolyzates has been found (65 g/L) after 10 h treatment, but economic considerations led us to treat a mean-concentrated slurry (156 g/L) with 0.3M H(2)SO(4) at 96 degrees C, thus obtaining 45.5 g/L monosaccharides in 5 h with 50% less furfural content. After pH regulation only, growth of Clostridium acetobutylicum has been obtained, although complete sugar comsumption has not been achieved. Experiments are now underway to reach complete digestion and to investigate the increase of enzymic accessibility into residual substrate rich in cellulose.

Kinetics of Dyeing Acrylic Fibres with Cationic Dyes in the Presence of Polyethoxylated Amines

Abstract: The role of ethoxylated amines in retarding the rate of absorption of C.I. Basic Green 4 on acrylic fibres has been studied. The influence of degree of ethoxylation, amine concentration and application temperature have been studied. It has been found that these compounds act, in general, as retarders, the retarding effect increasing as the degree of ethoxylation decreases. The dyeing kinetics in the presence of these compounds obey the Williams, Landel and Ferry equation.

Pseudoclassical model of a particle with arbitrary spin.

Abstract: A pseudoclassical model for a free spinning particle with arbitrary spin is presented. It is a generalization of a previously studied model for spin one-half. Quantization of the Poincar\'e-invariant version of the model yields the Bargmann-Wigner equations while a tower of Levy-Leblond equations emerge from the Galilean-invariant version. Classicalization yields an invariant world line and the expected multipole structure in both cases.

Propriétés magnétiques des ferrites hexagonaux: BaMg2-W et BaCo2-W

Abstract: Les deux composes oxydes, ferrimagnetiques a la temperature ambiante, BaMg2Fe16O27 et BaCo2Fe16O27 ont ete etudies. Les temperatures de Curie sont respectivement TC = (452 ± 3) °C et T′C = (490 ± 3) °C; l'utilisation de champs magnetiques intenses (150 kOe) a permis de determiner pour les deux composes, l'aimantation a saturation M0 et la susceptibilite superposee a haut champs χ. Dans le cas du compose magnetique axial BaMg2–W, l'application de la loi d'approche a la saturation nous a de plus permis d'obtenir le champ d'anisotropie magnetique Ha et d'en deduire la premiere constante d'anisotropie K1; des calculs d'energie magnetique dipolaire montrent que la forte anisotropie est principalement due a la contribution de cette energie magnetique dipolaire. The two room-temperature ferrimagnetic oxides, BaMg2Fe16O27 and BaCo2Fe16O27 are studied. The Curie temperatures are respectively TC = (452 ± 3) °C and T′C = (490 ± 3) °C; by using high magnetic fields (up to 150 kOe), we determine the saturation magnetization M0 and the high field susceptibility χ, for both the compounds. Moreover, in the case of the axial magnetic BaMg2–W compound, the magnetic anisotropy field Ha was obtained by application of the law of approach to saturation and the first constant of anisotropy K1 is deduced; calculations for the magnetic dipolar energy suggest the strong magnetic anisotropy to be mainly due to this dipolar magnetic energy contribution.

Bainitic transformation of steels

Abstract: Presentation des derniers resultats experimentaux: courbes TTT et etude microstructurale par microscopie electronique a balayage relatifs a la transformation bainitique de l'acier non allie (0,38 C-0,23 Si-1,4 Mn-0,22 Cr-0,18 Ni)

Optical bistability in two-beam interferometric devices with in-phase outputs

Abstract: Optical switching and bistability in interferometric systems result from the interplay of light interference and feedback. Usually, bistability is achieved with cavity structures in which feedback occurs because an intracavity parameter determining the internal intensity becomes intensity-dependent through a suitable physical mechanism.

A Finite Element Formulation for Geometrically Non Linear Problems Using a Secant Matrix

Abstract: An incremental finite element formulation for the analysis of geometrically non linear problems is developed. The incremental equations are obtained via the full incremental form of the principle of virtual displacements. This leads to the obtention of a non symmetric secant stiffness matrix which allows to compute the displacement increments in a direct iterative manner. It is shown how the secant matrix yields naturally the expression of the classic tangent matrix. In the last part of the paper the formulation is applied to the analysis of 3-D trusses using simple two node elements, and an example of application to a slender 3-D truss tower is presented.

Copolymer reactor operation for uniform product composition — analysis of continuous stirred-tank reactors

Abstract: This paper deals with the basic mass balance calculations for the analysis and operation of steady state continuous stirred-tank reactor (CSTR) cascades used in copolymer production. After a brief introduction on copolymer theory, a Skeist-type graphical analysis is presented where the relations between copolymer composition, feed composition and reactor conversion are studied. To do this, an equilibrium-stage approach is used, much in the same manner as in the study of separation processes. The graphical procedure is then extended to CSTR cascades. Two cases are considered. In the first, copolymer compositions occurring in each tank as well as the final copolymer composition distribution at the end of the cascade are calculated. In the second, an original method is developed to calculate the interstage feeds intended to compensate tank-to-tank drift in composition. After discussing the applicability and limitations in practical cases, two examples are given for copolymer emulsions.

A sex attractant for males of the noctuid moth Athetis hospes

Abstract: A. Guerrero 1, R. Canela 2, M. Riba 2, M. Eizaguirre 2, R. Albajes 2 & V. Sarto 3 1Departamento de Qu{mica Orgcinica Biol6gica, C.S.LC., Jorge Girona Salgaclo 18-26, 08034 Barcelona; 2Instituto de Investigaci6n y Desarrollo Agrario de Li 3Departamento de Zoologia, Universidacl Aut6noma de Bellaterra, Barcelona, Spain Keywords: Athetis hospes, Noctuidae, Amphipyrinae, Sesamia nonagrioides, Mamestra oleracea, Mythimna (= Pseudaletia) unipuncta, sex attractant, (Z)-9-tetradecen-l-ol Introduction Athetis hospes Freyer is a bivoltine noctuid moth which spreads over several mediterranean countries (Goater, 1983). The larvae feed on vegetables and herbaceous plants (i.e. Plantago sp.) and although the data on this species are scarce, it may be cause of damage to crops. Here we describe that during field experiments designed to catch males of the noctuid moth Sesa- mia nonagrioides Lef., (Z)-9-tetradecen-l-ol (Z9-14:OH) has been found to be a good attractant for A. hospes. While Sz6cs et al. (1981, 1983) have reported that a blend of (Z)-7-dodecenyl acetate and (Z)-9-tetradecenyl acetate is a sex attractant for A. gluteosa Tr. and A. lepigone M6schl., the un- saturated alcohol has also been described by Ando et al. (1977) as attractant for males of A. dissimilis Hampson. Materials and methods Chemicals. Z9-14:OH and (Z)-11-hexadecen-1-ol (Zll-16:OH) were prepared, respectively, by Wittig reactions of 1-tetrahydropyraniloxynonylidene and 1-tetrahydropyraniloxyundecylidene triphenyl- phosphoranes with pentanal followed by acid hydrolysis. Acetylation of the resulting alcohols un- der conventional conditions furnished the cor- responding acetates. The stereochemical purity of the synthetic compounds was higher than 96% ae- cording to GLC analysis (SE-54 fused silica capil- lary column 50 m x 0.32 mm i.d.) using hydrogen as carrier gas. Stereochemically pure sample (100%) of Z9-14:OH was assessed by purification on HPLC (Spherisorb ODS-2 5ix 15x0.4 cm column, 1 ml/min using acetonitrile:water 90:10 as eluant). Field experiments. The required amount of test compound for each bait was mixed with 5 mg of paraffin wax to increase longevity in the field (Cue- vas et al., 1983), and dissolved in 1 ml of hexane. The solutions were transferred into closed poly- ethylene vials (3 cm x 1.1 cm i.d.) and these placed into Pherocon 1CP traps for the 1984 field tests. Pherocon Delta traps were used throughout the 1985 test season. The experiments conducted in July 20 to Oc- tober 19 1984, were originally designed to catch males of Sesamia nonagrioides and formulations were those with higher EAG activity. Some of the compounds tested had been shown to be effective attractants for S. cretica Led. (Arsura et al., 1977) and S. inferens Walk. (Nesbitt et al., 1976). Traps were placed at random in a maize field separated each other 30 m apart at about 1 m above ground. The moths captured were removed every 7 days, the sticky base replaced and the traps rerandomized. Three replicates per treatment were done. A second set of experiments, conducted in the summer of 1985, was specifically designed to con- firm the attractant character of Z9-14:OH toward A. hospes males. Field trapping was carried out as

Possibilities of the finite element viscous shell approach for analysis of sheet metal forming problems

Abstract: The viscous shell approach combines the use of visco-plastic flow and classical shell theories. The paper presents the general aspects of the viscous shell formulation for axisymmetric and general 3-D shell problems using finite elements. Details of treatment of coordenate updating, friction effects, strain hardening and extensions to include the elastic deformations are also given together with some examples of application to the forming of axisymmetrical thin sheets of metal under hemispherical punches.

Electron Polarization in Nuclear Reactions at High Density

Abstract: In most calculations of the enhancement factor of nuclear reactions at high density, the degenerate electrons have been treated as a uniform non-polarized background. In this paper, we check the validity of this assumption by computing the correction for finite electron polarizability. We compare our result with the recent work of Ichimaru and Utsumi (1983, 1984). We confirm that polarization effects are indeed small, in agreement with their 1984 paper. Moreover, we show that the uncertainty in the main contribution to the enhancement factor is of same order than the polarization correction. Electron polarization can then be safely neglected for example in deflagration scenarios for type I supernovae or in X-γ-ray burst models.