Showing papers by "University of Alcalá published in 1983"
TL;DR: The existence of a nutrient threshold under which the Principle of Competitive Exclusion holds, is proven and the following very general result is proven: All solutions of a τ-periodic, dissipative, competitive system are either τ- periodic or approach a τ -periodic solution.
Abstract: A model of the competition of n species for a single essential periodically fluctuating nutrient is considered. Instead of the familiar Michaelis-Menten kinetics for nutrient uptake, we assume only that the uptake rate functions are positive, increasing and bounded above. Sufficient conditions for extinction are given. The existence of a nutrient threshold under which the Principle of Competitive Exclusion holds, is proven. For two species systems the following very general result is proven: All solutions of a τ-periodic, dissipative, competitive system are either τ-periodic or approach a τ-periodic solution. A complete description of the geometry of the Poincare operator of the two species system is given.
186 citations
TL;DR: When the whole medial collateral ligament is severed, there is a lateral displacement of the talus, which may be important in the diagnosis and surgical treatment of a torn medialateral ligament.
Abstract: The calcaneotibial and posterior talotibial ligaments slacken and the naviculotibial ligament tightens as the ankle plantarflexes; the reverse occurs in ankle extension. The naviculotibial ligament increases its length and the posterior talotibial ligament relaxes in abduction. The cutting of the posterior talotibial ligament repercutes on other parts of the medial collateral ligament. The cutting of other parts of the medial collateral ligament produces very little change on the posterior talotibial ligament. When the whole medial collateral ligament is severed, there is a lateral displacement of the talus. This may be important in the diagnosis and surgical treatment of a torn medial collateral ligament.
20 citations
TL;DR: In this article, the reduction of THF solutions of (η-C 5 H 5 ) 2 NbCl 2 with Na/Hg in the presence of various phosphines, phosphites, acetylenes or isocyanides gives complexes of the type ( η -C 5H 5 ), where L PMe 2 Ph, P(OMe) 3, PhCCPh, PhC-Ph, CNCy, CNPh, etc.
16 citations
TL;DR: Nine species of Hemerobiidae in six genera are described and their distributions given.
Abstract: Nine species of Hemerobiidae in six genera are described and their distributions given. Keys are provided for their identification and notes are given on biology and habitat preferences.
16 citations
TL;DR: The relationship between intrathymic erythropoiesis, degeneration of cortical lymphocytes and epithelial-reticular cells, and macrophage activity is discussed and related to a possible functional role of sex hormones in this phenomenon.
Abstract: Although previously described in other avian species, intrathymic erythropoiesis is a remarkable feature of the thymus of Sturnus unicolor. In discrete stages of the life cycle of this species, erythroblasts and mature erythrocytes occupy large areas of the thymic cortex and cortico-medullary border. Simultaneously, degenerated thymocytes and epithelial-reticular cells occur in the same areas. The relationship between intrathymic erythropoiesis, degeneration of cortical lymphocytes and epithelial-reticular cells, and macrophage activity is discussed and related to a possible functional role of sex hormones in this phenomenon.
15 citations
TL;DR: In this article, the rotational isomeric states model is applied to calculate dipole moments of polypeptides of the twenty natural α-amino acids in the random coil state.
10 citations
TL;DR: In this paper, the crystal and molecular structures of N -ethylnortropane-3-spiro-5′-oxazolidine-2′,4′-dione were determined by X-ray diffraction.
10 citations
TL;DR: In this paper, the birefringence of polydimethylsilmethylene (PDMSM) networks was found to be qualitatively similar to that of polyisobutylene.
Abstract: Elastomeric networks were prepared from polydimethylsilmethylene (PDMSM) [Si(CH3)2CH2], a polymer closely related to polydimethylsiloxane (PDMSO) [Si(CH3)2O] and polyisobutylene (PIB) [C(CH3)2CH2]. The birefringence of PDMSM in elongation was found to be qualitatively similar to that of PDMSO, in that there was no evidence for strain-induced crystallization. However, the values of the optical-configuration parameter Δa were considerably larger, and both Δa and its temperature coefficient are essentially the same as those of PIB. Swelling the PDMSM networks generally decreased Δa; the largest decreases, obtained as expected with the most nearly symmetrical diluent, were also approximately the same as those observed for PIB. Use of cyclic PDMSO pentamer as diluent in a PDMSM network was found to increase the birefringence, presumably because of orientational effects. Various network-diluent combinations involving the significantly anisotropic PDMSM and the more nearly isotropic PDMSO should be extremely useful for elucidating the nature of these intermolecular correlations. Results obtained from rotational isomeric state theory considerably underestimate both Δa and its temperature coefficient for PDMSM, as they do for PIB. Although the origin of the discrepancy is not necessarily the same for both polymers, the results on PDMSM suggest that the discrepancy for PIB is not due to the severe steric congestion known to be present in this polymer.
9 citations
TL;DR: In this paper, an intento de analisisis de la evolucion del comercio exterior espanol durante los siglos XVIII and XIX is presented, with the aim of mostrar su incidencia sobre la evoçion general del pais and comparar algunas de las conclusiones obtenidas con alguna of las teorias mas extendidas acerca de las interrelaciones entre el sector exterior and la economia en general.
Abstract: Este ensayo es un intento de analisis de la evolucion del comercio exterior espanol durante los siglos XVIII y XIX, que aspira a mostrar su incidencia sobre la evolucion general del pais y a comparar algunas de las conclusiones obtenidas con algunas de las teorias mas extendidas acerca de las interrelaciones entre el sector exterior y la economia en general. Se trata, naturalmente, de una version muy resumida de un proyecto de investigacion en curso, y cualquier demanda de informacion adicional sera atendida.
8 citations
TL;DR: The authors greatly appreciate the financial support received from Comision Asesora de lnvestigación Cientifica y Tecnica (CATECH) as discussed by the authors.
6 citations
TL;DR: In this paper, the average molar Kerr constants of polypeptides of the twenty natural α-aminoacids in the random coil state were calculated using the Rotational Isomeric States model with the values of energies, dipole moments and optical anisotropies of the repeating units.
Abstract: Calculations of average molar Kerr constants of polypeptides of the twenty natural α-aminoacids in the random coil state are presented. The computation was carried out according to the Rotational Isomeric States model with the values of energies, dipole moments and optical anisotropies of the repeating units reported elsewhere. In the case of homopolypeptides, the ratios /x extrapolated to x→∞ range approximately from −6000 to +5000 in units of 10−27V−2m5mol−1. Results obtained for ten actual proteins and three enzymes in the random coil state are also reported; their values of /x are very sensitive to the kind of aminoacid residues and to the sequence of those residues.
TL;DR: In this article, an assignment of relative configurations for the diastereomeric racemates (1R2R,1S2S) and (1S, 1S2R) of 3,3-dimethyl-1,2-diphenylbutan-1-ol through a comparative analysis of the respective chemical shifts induced by Eu(fod)3 in the 1H and 13C NMR spectra, and the corresponding conformational distribution.
Abstract: An assignment of relative configurations has been achieved for the diastereomeric racemates (1R2R,1S2S) and (1R2S,1S2R) of 3,3-dimethyl-1,2-diphenylbutan-1-ol through the comparative analysis of the respective chemical shifts induced by Eu(fod)3 in the 1H and 13C NMR spectra, and the corresponding conformational distribution.
TL;DR: Theoretical values of the mean-squared optical anisotropies (γ2 ), of random-coil polypeptides of the twenty natural α-amino acids by the use of the Rotational Isomeric State model are calculated in this article.
Abstract: Theoretical values of the mean-squared optical anisotropies (γ2 ), of random-coil polypeptides of the twenty natural α-amino- acids are calculated according to the Valence Optical Scheme by the use of the Rotational Isomeric State model. The contribution of each repeat unit to the anisotropic part of the polarizability tensor of the chain [math] was computed by addition of previously optimized bond polarizabilities. Values of (γ2 )1 for single peptide units (identified for this calculation with molecules of the formula CH3 -CO-NH-CH2 R, where R is the side chain of each aminoacid residue) range from 3.5 to 85.7 in units of 10–6 nm6 . The results of (γ2 )x /x in the limit of x → ∞ for homopolypeptides are roughly proportional to (γ2 )1 of the peptide unit. Ten actual proteins and there enzymes are also studied, their values of (γ2 )x /x are almost identical and do not depend on the sequence of aminoacids.
TL;DR: A review of the most important analytical techniques for determining metals such as lead, iron, vanadium, nickel, copper, chromium, cobalt and sodium which are present in crude oils and by-products is made in this paper.
Abstract: A review is made of the most important analytical techniques for determining metals such as lead, iron, vanadium, nickel, copper, chromium, cobalt and sodium which are present in crude oils and by-products. Techniques such as neutron activation, atomic absorption spectrometry, X-ray fluorescence, molecular spectrophotometry and inductively coupled emission (ICP) are discussed.
TL;DR: In la literatura economica sobre tipos de cambio pueden encontrarse diferentes teorias o explicaciones sobre la determination del valor de cotizacion de las monedas.
Abstract: En la literatura economica sobre tipos de cambio pueden encontrarse diferentes teorias o explicaciones sobre la determination del valor de cotizacion de las monedas. De todas ellas, las que gozan de mayor aceptacion son la teoria de la balanza de pagos, la teoria del mercado de cambios a futuros, la teoria keynesiana sobre determination del tipo de cambio, el reciente enfoque monetarista y, por ultimo, la traditional teoria de la paridad del poder adquisitivo.
TL;DR: The use of the CMOS-SOS technology, the MAS281 as microprocessor and total cold redundancy as architecture is selected as architecture for the Common Data Processing Unit of the CEPAC instrument of SOHO space-craft.
TL;DR: Using the embedding of the Hopf bundle into the trivial bundleS2×S3, this article obtained the Dirac-Wu-Yang regular vector potential onS3 from the T Hooft-Polyakov monopole field.
Abstract: Using the embedding of the Hopf bundle into the trivial bundleS2×S3, we obtain the Dirac-Wu-Yang regular vector potential onS3 from the ’t Hooft-Polyakov monopole field. Furthermore, it is shown that the electromagnetism bundleS3/Zn is aU1 reduced bundle ofS2×S3. From this bundle reduction and the connection one-form onS3/Zn we get the asymptotic behaviour of theSU2 n-monopole field. Axial symmetry, usually assumed for BPS monopoles, is obtained and the asymptotic behaviour ofn-monopole solutions of the Ernst equation is predicted.