Showing papers by "Technical University of Madrid published in 1987"
TL;DR: In this paper, the authors developed a methodology to identify the number of factors and to build a simplifying transformation to represent the multivariate time series process, which is the canonical transformation.
Abstract: This article studies how to identify hidden factors in multivariate time series process. This problem is important because, when the series are driven by a set of common factors, (a) a large number of parameters may be needed to obtain an adequate representation of the system and (b) the estimated parameters will be highly correlated. Therefore, a complex and badly defined relationship can appear when, in fact, a simpler and parsimonious model in terms of a few common factors can be operating. This article develops a methodology to identify the number of factors and to build a simplifying transformation to represent the series. It is proved that the number of factors is equal to the rank of the covariance matrices and the parameter matrices of the infinite moving average representation of the process. The eigenvectors of these matrices will provide the canonical transformation. The method is illustrated with one example, using series of the price of wheat in five provinces of Spain in the 19th ce...
255 citations
21 Jun 1987
TL;DR: In this paper, the influence of the tapped inductor turn ratio (λ) is analyzed in dc-to-dc converters derived from buck, boost and buck-boost topologies.
Abstract: Six different topologies of tapped-inductor dc-to-dc converters derived from buck, boost and buck-boost topologies are analyzed. Both dc and ac analysis in continuous and discontinuous operating modes are considered. The influence of the tapped inductor turn ratio (λ) is very important in the circuit behaviour. Particulary in the poles and zeros distribution of the transfer function. Some important conclusions about the dynamical characteristics of converters are derived from this study. Theoretical results are compared with those obtained from experiment carried out on some prototypes. Generalized conclusions are presented considering classical buck, boost and buck-boost (non tapped-inductor) as a particular case of these converters.
90 citations
TL;DR: The moisture, ash, free reducing sugar, starch, ether extractive, crude protein, amino acid and the heat energy contents of young and mature cladodes of Opuntia ficus-indica, with or without fruits, are described.
Abstract: The moisture, ash, free reducing sugar, starch, ether extractive, crude protein, amino acid and the heat energy contents of young and mature cladodes of Opuntia ficus-indica, with or without fruits, are described. The measurements were made in each of the following stages of development: vegetative growth (March), full vegetative development, and at the beginning of fructification (October). Independently of developmental stage (different cladode types) the highest values were reached always in young cladodes in the following months: moisture content in March and October; ash and free reducing sugars in March; starch and ether extractive in September and October; crude protein in March and July. Crude fibre was maximal in September and global heat energy in October. The nutritive and caloric value of cladodes are compared to other products used for livestock nutrition.
49 citations
TL;DR: In this paper, the effect of stress ratio on fatigue threshold in cold drawn eutectoid steel wires has been experimentally measured and the results showed that fatigue threshold decreases when yield strength increases in pearlitic steels.
42 citations
TL;DR: In this paper, a concentrating photovoltaic system has been built that uses Fresnel lenses of a potentially low cost design, and which employs a simple and robust method for bonding solar cells to the cooling tube.
41 citations
TL;DR: The chemical composition of the plant material and alcoholic fermentation were studied under controlled conditions and the potential ethanol production that could be obtained from prickly pear cultivation in various regions (arid, semi-arid and irrigated) is discussed.
Abstract: Using prickly pear cladodes and fruits and different yeast strains of the genus Saccharomyces, both the chemical composition of the plant material and alcoholic fermentation were studied under controlled conditions. Before fermentation, fresh or previously dried cladodes were hydrolysed using cellulose or acid (HCl). The yield was determined by measurement of ethanol production by gas-liquid chromatography. Two conversion indices, representing either the percentage of reducing sugars or the energy converted into ethanol, were considered. Using fresh or dried cladodes without fruits, the best results were always obtained after performing both types of hydrolysis. The enzymic method gave the highest sugar yield. However, ethanol production was similar to that obtained by acid hydrolysis of fresh cladodes, and only slightly higher than that of previously dried cladodes. The potential ethanol production that could be obtained from prickly pear cultivation in various regions (arid, semi-arid and irrigated) is discussed.
41 citations
TL;DR: In this paper, an analysis of an experiment aboard Spacelab-D1 on the mechanical stability of long liquid columns between coaxial equal discs is presented, and the effect of column slenderness, column rotation and disc vibration upon the liquid outer shape is studied.
32 citations
TL;DR: In this paper, the authors investigated the impedance of a monopole located off-axis on a disk and oriented in an arbitrary direction using hybrid method of moments/geometrical theory of diffraction (MM/GTD) techniques.
Abstract: The input impedance of a monopole located off-axis on a disk and oriented in an arbitrary direction is investigated using hybrid method of moments/geometrical theory of diffraction (MM/GTD) techniques. The equivalent currents method (ECM) and the uniform geometrical theory of diffraction (UTD) are used to ensure a proper treatment of each situation. A criterion for switching from UTD to ECM in the vicinity of the axial caustic is discussed. Measurements of impedance have been made in order to check the numerical results and are presented here, showing good agreement with theory.
19 citations
TL;DR: In this article, the cross section of the four leading processes of leptoquark production from superstring inspired E6 models in e-p colliders is calculated, and an important number of high PT events can be found in HERA for leptonquark masses as heavy as 200 GeV even in the case of couplings as small as 0.01.
19 citations
TL;DR: In this paper, the authors reviewed the expansion of river regulation and related scientific research in Spain since 1982 and found that the number of dams completed each year has decreased and moreover, the average size of reservoir has continued to decline.
Abstract: The expansion of river regulation and of related scientific research in Spain since 1982 is reviewed. The number of dams completed each year has decreased and, moreover, the average size of reservoir has continued to decline. It is the creation of many new, relatively small, irrigation reservoirs that is having the greatest impact on the fluvial systems. Recent legislation may promote greater involvement of scientists in the management of these systems not least in the setting of minimum ecological flows.
17 citations
TL;DR: In this article, the mixed carbonyl-phosphorus ligand monodentate xanthate complexes η5-C5H5Fe(CO)2(η1-SC(S)OEt)L (5a-5d), can be conveniently obtained by treatment of the dicarbonyl compound with the appropriate phosphine or phosphite ligand.
01 Dec 1987
TL;DR: In this article, a flow of a viscous fluid has a finite number of degrees of freedom, and can therefore be seen as a dynamical system, and a coherent structure can be thought of as a lower dimensional manifold in whose neighborhood the dynamic system spends a substantial fraction of its time.
Abstract: Any flow of a viscous fluid has a finite number of degrees of freedom, and can therefore be seen as a dynamical system. A coherent structure can be thought of as a lower dimensional manifold in whose neighborhood the dynamical system spends a substantial fraction of its time. If such a manifold exists, and if its dimensionality is substantially lower that that of the full flow, it is conceivable that the flow could be described in terms of the reduced set of degrees of freedom, and that such a description would be simpler than one in which the existence of structure was not recognized. Several examples are briefly summarized.
TL;DR: In this paper, a comparison of several analytical, approximate expressions proposed by various authors to calculate the fill factor and the efficiency of a sol ar cell is presented, referred to the conventional singleexponential solar cell model and it has been made by using a normalized nomenclature.
TL;DR: In this article, the authors showed that the number of basic problems to be used depends on the distribution of the points and on the chosen interpolation space, which here is not necessarily a polynomial space.
Abstract: In a paper in J.S.I.A.M., 8, (1960), p.33–42, Thacher and Mil ne showed how the solution of certain polynomial interpolation problems in R s can be constructed from the solutions of s+1 simpler problems. In the present paper we extend the method showing that the number of basic problems to be used depends on the distribution of the points and on the chosen interpolation space, which here is not necessarily a polynomial space.
TL;DR: A general implementation of CSP in Modula-2 is presented and low level and modularity facilities of this language have been used to develop a kernel thus allowing the use of comunication primitives and nondeterministic selection.
Abstract: Recently, a series of process communication schemes based on message exchanges have been developed. Hoare's CSP is perhaps the most interesting one and is the base for concurrent features of modern languages (e.g. ADA, Occam, etc.).Several concurrency mechanisms have already been implemented in Modula-2 (signals, COBEGIN..COEND structure, message exchanges, etc.) but they have not completely fulfilled the Hoare's CSP scheme.In this paper a general implementation of CSP in Modula-2 is presented. Low level and modularity facilities of this language have been used to develop a kernel thus allowing the use of comunication primitives and nondeterministic selection.The original CSP scheme has been slightly modified by using port names instead of process names to specify communication.
TL;DR: In this paper, the use of polynomial interpolation to approximate a function specified by samples taken at random moments satisfying a Poisson distribution with uniform mean sampling rate was studied.
TL;DR: Smoothing of plasma ablated from a laser target under weakly nonuniform irradiation is discussed in this article, where a quasisteady layer enclosing the critical surface (large pellet or focal spot, and long, low-intensity, shortwavelength pulse) is assumed.
TL;DR: In this article, an estimation of the influence of the radical group upon the reaction cross-section was made, and the results reveal a larger steric factor with the size of the alkyl group.
Abstract: Relative values of the total reaction cross-section for the crossed molecular beam K + RI → KI + R (R = CH3, C2H5, C3H7) reactions have been measured at low collision energies. An estimation of the influence of the radical group upon the reaction cross-section was made. At ET = 0·18 eV of collision energy we found 20A2, 30A2 and 39A2 for the propyl, ethyl and methyl reactions, respectively. These results reveal a larger steric factor with the size of the alkyl group. This is consistent with the (observed) increase in the backward character of the product (KI) centre of mass angular distributions as the reagents' alkyl group size increases.
TL;DR: A review of the available information about fracture at low temperatures of reinforced concrete materials, as well as incipient standards related with this subject is made in this paper. But no international standards have yet been developed to prevent brittle fracture under cryogenic conditions.
TL;DR: A mathematical model was created to simulate design operation of the CESA-I solar central receiver located near Almeria, Spain and the differences between real data from the plant data acquisition system and design values were big enough to justify an adjustment of the mathematical model to real conditions.
TL;DR: In this article, a system of integral equations (SIE) based on the uniquehess theorem that uses only electric equivalent currents (EEC) is formulated to analyze conducting bodies with apertures.
Abstract: A system of integral equations (SIE) based on the unique-hess theorem that uses only electric equivalent currents (EEC) is formulated to analyze conducting bodies with apertures. This SIE is compared with an SIE that uses both electric and magnetic equivalent currents (EMEC). In general, to solve both SIE's numerically difficult computations of Cauchy principal-value integrals with highly singular kernels are required. These integrals appear when computing electric (magnetic) fields created by magnetic (electric) currents. Their evaluation can be avoided using the EEC approach in many practical cases when the main interest is in the radiation patterns of aperture antennas. The two SIE's are compared by carrying out an analysis of rotationally symmetric horns using the moment method (MM) in its formulation for bodies of revolution. Numerical results of electric currents and radiation patterns are presented for small horns of various geometries. These results compare quite well with measurements for both SIE's. However, the central processing unit (CPU) time for the EEC formulation is an order of magnitude smaller than for the EMEC formulation.
TL;DR: In this article, the electrochemical properties of cationic complexes were studied in THF solution, using cyclic voltammetry and coulometry, showing that the products of the one-electron reduction are labile and the reduced species lose the ligand.
TL;DR: Chapman and Hall as mentioned in this paper showed that the primary amines of CoCl2 and FeCl3 with the carbonyl compounds acetylacetone (Hacac) and pyridyl carbaldehyde (pyc) yield complexes which contain the Schiff bases from the condensation of the amines and the carbenyl groups.
Abstract: FeCl3 and the primary amines 2-aminobenzimidazole (abi) and 2(2′-aminophenyl)benzimidazole (apbi) give complexes for which spectroscopic and magnetic data suggest a pentacoordinate [FeCl4]. The reactions of complexes of primary amines of CoCl2 and FeCl3 with the carbonyl compounds acetylacetone (Hacac) and pyridylcarbaldehyde (pyc) yield complexes which contain the Schiff bases from the condensation of the amines and the carbonyl groups. Analytical data indicate formulae [CoCl2(abiacac)2], [CoCl2(abipyc)], [FeCl3(abiacac)], [FeCl3(abipyc)2] and [FeCl3(apbipyc)] for the complexes. The cobalt(II) complexes are pseudo-tetrahedral, while the iron complexes are tetra-, penta-, or hexa-coordinate, as deduced from spectroscopic and magnetic measurements. © 1987 Chapman and Hall Ltd.
TL;DR: The reductive electrochemistry of compounds of the type Cp★Fe(CO)2L has been examined by polarography, cylic voltammetry and coulometry as mentioned in this paper.
TL;DR: A general recurrence interpolation formula due to Gasca and Lopez-Carmona (J. Approx. Th. 34 (1982)) is studied by means of elimination techniques in linear systems as discussed by the authors.
TL;DR: In this paper, the analytical solution for the different shapes that a bidimensional liquid bridge in a gravity field may adopt is reviewed, criticizing the well-known limit of Heywang, and the work is shown in the context of a wider-scope program to model the fluid-mechanical behaviour of molten bridges in the floating zone and related techniques of crystal growth, which has blossomed with the advent of microgravity platforms.
TL;DR: The paper enumerates the allowable combinations of decipherable boolean functions of certain types, namely functions of a given number of message and key bits, based upon decipherable functions property of being one-to-one.
Abstract: The paper enumerates the allowable combinations of decipherable boolean functions of certain types, namely functions of a given number of message and key bits. Such an enumeration is based upon decipherable functions property of being one-to-one. Formulas for finding the number of decipherable boolean functions are also given.
01 Dec 1987
TL;DR: A possible model for the inception of vorticity ejections in the viscous sublayer of a turbulent rectangular channel is presented in this paper, where it is shown that this part of the flow is dominated by protruding strong shear layers of z-vorticity.
Abstract: A possible model for the inception of vorticity ejections in the viscous sublayer of a turbulent rectangular channel is presented. It was shown that this part of the flow is dominated by protruding strong shear layers of z-vorticity, and it was proposed as a mechanism for their maintenance and reproduction which is essentially equivalent to that responsible for the instability of 2-D Tollmien-Schlichting waves. The efforts to isolate computationally a single structure for its study have failed up to now, since it appears that single structures decay in the absence of external forcing, but a convenient computation model was identified in the form of a long and narrow periodic computational box containing at each moment only a few structures. Further work in the identification of better reduced systems is in progress.
TL;DR: In this paper, an efficient harmonic-balance technique for determining the steady-state response of nonlinear circuits to multitone input signals is presented, which is an approach for calculating the Jacobian matrix associated with the Newton Raphson algorithm.
Abstract: An efficient harmonic-balance technique for determining the steady-state response of nonlinear circuits to multitone input signals is presented. Its main feature is an approach for calculating the Jacobian matrix associated with the Newton Raphson algorithm which significantly reduces its computational cost.