Showing papers by "Technical University of Madrid published in 1984"
TL;DR: The history of the probability of extinction for the entire Phanerozoic, based on time series analysis, does not support the reported bipartite distribution of Van Valen, whereas the inertia or stability of the biotic system after the Late Permian crisis has increased.
Abstract: The temporal spacing and the magnitude of major extinctions over the past 250 and 570 million years, based on the use of different metrics of extinction probability, are analyzed by comparing deterministic and stochastic explanations. The best-fitting time series model is a stochastic autoregressive model that displays a pseudoperiodic behavior with a cycle length of 31 million years for the past 250 million years, regardless of the metric of extinction probability. The periodicity lengthens and weakens when the analysis is extended to the entire Phanerozoic. The history of the probability of extinction for the entire Phanerozoic, based on time series analysis, does not support the reported bipartite distribution of Van Valen. Rather, the probability of extinction has decreased uniformly over Phanerozoic time whereas the inertia or stability of the biotic system after the Late Permian crisis has increased.
75 citations
TL;DR: In this article, the authors show that the appropriate selection of constraints in the variational formulation of spectral estimation leads to new models and more freedom for the designer, and illustrate the relationships between the set of constraints and the underlying model in the procedure.
Abstract: In this paper we show that the appropriate selection of constraints in the variational formulation of spectral estimation leads to new models and more freedom for the designer. We also illustrate the relationships between the set of constraints and the underlying model in the procedure. The rest of the paper concentrates on obtaining maximum entropy ARMA models for spectral estimation, using cepstral constraints and correlation constraints simultaneously. The nonlinearity that these kinds of constraints introduce is avoided by a simple linearization, that provides an estimator which is easily implemented. Finally, some examples are given to illustrate the performance of the proposed method.
31 citations
TL;DR: In this paper, the steady-state and transient processes of the external heating of a flat plate under a convective flow are studied, with inclusion of the axial heat conduction through the plate.
30 citations
TL;DR: This theorem gives a relationship between the maximum geometrical concentration of a cylindrical concentrator and the angular field of view which is more restrictive than the general one when the collector is surrounded by a refractive medium.
Abstract: The conservation of etendue for general 2-D bundles of rays (not necessarily coplanar) is examined (a 2-D bundle of rays is that whose rays are distinguishable by giving each one two parameters). This is one of the integral invariants of Poincare and it is directly related to the Lagrange invariant. The application of this theorem to selected 2-D bundles of rays crossing an arbitrary cylindrical concentrator gives us a relationship between the maximum geometrical concentration of a cylindrical concentrator and the angular field of view which is more restrictive than the general one (i.e., the relationship is valid for an arbitrary concentrator) when the collector is surrounded by a refractive medium.
29 citations
TL;DR: In this article, an analysis of truncated bifacial compound parabolic concentrators filled with dielectric is presented based on ray tracing, and a panel based on such concentrators has been measured.
19 citations
TL;DR: In this article, the authors measured the deformation of unloaded water-saturated concrete samples and loaded water saturated concrete samples, assuming that microcracking is the dominant deformation mechanism in the transition range.
19 citations
TL;DR: In this article, a new general method of calculating the efficiency-concentration characteristic (including the direct determination of the maximum efficiency point) of a solar cell is presented, which is valid for any model which describes the dark current density-voltage characteristic of the cell, including the common single-exponential and doubleexponential models.
19 citations
14 citations
TL;DR: This work study the characteristics of the crossed compound parabolic concentrator, formed by the intersection of two cylindrical compoundParabolic concentrators (CPC).
Abstract: Static and quasi-static concentrators present interesting characteristics for obtaining photovoltaic solar energy. In this work we study the characteristics of the crossed compound parabolic concentrator, formed by the intersection of two cylindrical compound parabolic concentrators (CPC). Bifacial cells are used in this concentrator as a requirement for obtaining higher concentrations. Static and quasi-static concentrators see the sun as an extended source, so a simplified source model of radiance for the sky of Madrid is used. The figures of merit of a lossless concentrator are studied and the most important parameters influencing its optical behavior are discussed. We conclude that these concentrators obtain results that lead to a decrease in the cost of photovoltaic energy.
14 citations
TL;DR: In this article, the reduction of titanocene dithiocyanate in various solvents has been examined using the techniques of polarography, voltammetry, controlled potential electrolysis and cyclic voltammetric.
9 citations
TL;DR: This work derives the directional intercept factor of a cylindrical nonimaging concentrator called the Ideal Tubular Concentrator from the results obtained for axisymmetrical optical systems.
Abstract: Cylindrical concentrators are viewed as a limit case of toroidal concentrators with the purpose of applying to them some results obtained for axisymmetrical optical systems. This enables us to obtain easily the directional intercept factor of a cylindrical nonimaging concentrator called the Ideal Tubular Concentrator. A useful tool for designing new cylindrical concentrators is also derived.
TL;DR: A new type of domain in twisted-wedge negative nematics that allows the separation of ordinary and extraordinary beams that can be studied separately is reported.
Abstract: A new type of domain in twisted-wedge negative nematics is reported. The wedge shape allows the separation of ordinary and extraordinary beams that can be studied separately. In these conditions, at least five different regions can be detected depending on applied voltages and frequencies. Both rays are shown to, yield different diffraction patterns. The relative light intensity of several spots of these patterns is also studied.
TL;DR: The limit of concentration for cylindrical concentrators whose collector rejects rays arriving at grazing angles is calculated and it is shown that the upper limit is achievable.
Abstract: The limit of concentration for cylindrical concentrators whose collector rejects rays arriving at grazing angles is calculated. Cylindrical concentrators having as cross section a 2-D optimal and ideal concentrator (CPC type) with restricted exit angle are analyzed. These concentrators do not achieve, in general, the upper limit but are very close to it. It is also shown that the upper limit is achievable. Finally, two 2-D concentrators with restricted exit angle are shown for the case when the collector is bifacial and specularly reflects the rejected rays.
01 Jan 1984
TL;DR: In this article, a theory is put forward which predicts the fatigue life of prestressing steel wires, based on fracture mechanics principles, and the theory is compared with experimental results, and residual stresses in the wires are also considered.
Abstract: Fatigue of prestressing steel is studied according to fracture mechanics principles. Initiation and propagation crack aspects are considered separately and analysed experimentally. From the data obtained a theory is put forward which predicts fatigue life of prestressing steel wires. Predictions are compared with experimental results. Residual stresses in the wires are also considered.
TL;DR: In this paper, a large activation energy analysis of the problem of thermal ignition of self-heating porous bodies is carried out by means of a regular perturbation method, and a correction to the well-known Frank-Kamenetskii estimate of the ignition limit is calculated, for symmetric bodies, by using similarity properties of the equations giving higher order terms in an expansion in powers of \/E (E = activation energy).
TL;DR: In this paper, the authors measured the propatation field in Metglas 2826 ribbons under stress at different temperatures (from t = 25 °C to t = 200 °C) and showed that propagation field depends on domain wall energy, γ, at constant temperature.
Abstract: Viscous damping parameter, β, and propatation field, H p , have been measured in Metglas 2826 ribbons under stress (from σ = 103 MPa to σ = 365 MPa) at different temperatures (from t = 25 °C to t = 200 °C) Results show that propagation field depends on domain wall energy, γ, at constant temperature. Viscous damping, β = β E + β R , (being β R relaxation damping and β E eddy current damping) depends on domain wall thickness, δ, and on parameter (μ o M s )2/ρ (ρ resistivity, μ o M s saturation magnetization) through β R and β E respectively.
TL;DR: Modal analysis and scattering matrix concepts at discontinuities have been applied to the design and optimization of open-ended waveguide applicators with several transverse discontinUities and the results obtained show how important improvements can be obtained in the match between the applicator and the tissues.
Abstract: Modal analysis and scattering matrix concepts at discontinuities have been applied to the design and optimization of open-ended waveguide applicators with several transverse discontinuities. The tissues are simulated by means of two dielectric layers, skin and fat. The results obtained show how important improvements can be obtained in the match between the applicator and the tissues.This method can also be applied to obtain applicators with increased depth of penetration, by controlling the discontinuities of the applicators.
TL;DR: It was concluded that the high injections cells show a more symmetric behaviour and that the low injection cells show slightly higher efficiencies, although good cells can be obtained with both bases.
01 Jan 1984
TL;DR: In this article, the authors have developed an equipment which, in its prototype stage, has allowed a study to be made of the possibilities of connecting photovoltaic arrays to the electric power mains through a suitable high power circuit.
Abstract: Abstrac As one of the possible applications of Photovoltaic Solar Energy, the Electronic Engineering Department of the Industrial Engineering College of Madrid has developed an equipment which, in its prototype stage, has allowed a study to be made of the possibilities of connecting photovoltaic arrays to the electric power mains through a suitable high-power circuit. An additional objective was that the interfacing unit should have the fewest elements possible with a view to optimizing the overall efficiency of the installation.
01 Jan 1984
TL;DR: In this paper, a microprocessor based control circuit using the MC6802, which generates all the control signals necessary for feeding AC motors was presented, based on the "Control Rose Theory" and the "Existential Function Modulation" (E.F.M).
Abstract: Abstrac. This paper presents a microprocessor based control circuit using the MC6802, which generates all the control signals necessary for feeding AC motors.
Basis on the ″Control Rose Theory″ and the ″Existential Function Modulation″ (E.F.M.) method suitable algorithms, which cancel a number of predetermined unwanted harmonics, for an Unrestricted Frequency Changer and a three phase bridge inverter have been developed.
Using these theories as a working tool, control circuits, specially adapted to fed AC motors are herewith presented.
01 Jan 1984
TL;DR: In this paper, les effets allelopathiques de ces substances au niveau des phytocenoses forestieres are discussed, and a discussion on the effet allelopathy of these substances is presented.
Abstract: Discussion sur les effets allelopathiques de ces substances au niveau des phytocenoses forestieres
TL;DR: In this article, a graphical design method for lossless and lossy gain-compensating networks is presented and the advantages of the new technique in the microwave band are discussed.
Abstract: A graphical design method for lossless and lossy gain-compensating networks is presented and the advantages of the new technique in the microwave band are discussed. The method is based on graphical equalization diagrams, whose construction rules are described, and saves computer time and cost. Using bipolar transistors with ƒT= 4·5 GHz, a three-stage ultra-broadband matched amplifier has been developed. The amplifier provides a gain of 23 dB in the 10 MHz-1·2 GHz band with low input and output VSWRs.