Showing papers by "Technical University of Madrid published in 1992"

Prehydration and Priming Treatments that Advance Germination also Increase the Rate of Deterioration of Lettuce Seeds

Abstract: The objective was to quantify the germination and deterioration rates of lettuce seeds following a range of prehydratation and priming treatments. Both long and short imbibition durations in water as well as priming in osmotic solutions were investigated to determine whether the duration or osmotic potential of the treatment might affect the responses observed

New method of design of nonimaging concentrators

Abstract: A new method of designing nonimaging concentrators is presented and two new types of concentrators are developed. The first is an aspheric lens, and the second is a lens-mirror combination. A ray tracing of three-dimensional concentrators (with rotational symmetry) is also done, showing that the lens-mirror combination has a total transmission as high as that of the full compound parabolic concentrators, while their depth is much smaller than the classical parabolic mirror-nonimaging concentrator combinations. Another important feature of this concentrator is that the optically active surfaces are not in contact with the receiver, as occurs in other nonimaging concentrators in which the rim of the mirror coincides with the rim of the receiver.

An experimental and numerical study of cyclic deformation in metal-matrix composites

Abstract: The cyclic stress-strain characteristics of discontinuously reinforced metal-matrix composites are studied both experimentally and numerically The model systems used for investigation are aluminum alloys reinforced with SiC particulates and whiskers Finite element analyses of the fatigue deformation of the composite are performed within the context of axisymmetric unit cell formulations Two constitutive relations are used to characterize the matrix of the composite: the fully dense Mises model of an isotropically hardening elastic-viscoplastic solid and the Gurson model of a progressively cavitating elastic-viscoplastic solid (to simulate ductile matrix failure by the nucleation and growth of voids) The brittle reinforcement phase is modeled as elastic, and the interface between the ductile matrix and the reinforcement is taken to be perfectly bonded The analyses provide insights into the effects of reinforcement shape and concentration on (1) constrained matrix deformation under cyclic loading conditions, (2) cyclic hardening and saturation, (3) the onset and progression of plastic flow and cavitation within the matrix, and (4) cyclic ductility The numerical predictions of flow strength, strain hardening, evolution of matrix field quantities, and ductility under cyclic loading conditions are compared with those predicted for monotonic tensile deformation and with experimental observations

Sur l'adjonction d'une masse de Dirac á une forme régulière et semi-classique

Abstract: On montre que si L est une forme lineaire reguliere et semi-classique, alors la forme u=L + λδc ou c e C est quelconque, est encore reguliere et semi-classique pour tout λ e C en dehors d'un ensemble denombrable de valeurs singulieres. On donne l'equation differentielle lineaire du second ordre verifiee par chaque polynome de la suite orthogonale associee a u.

Global kinetics for n-heptane ignition at high pressures

Abstract: A kinetic mechanism of 1011 elementary reactions with 171 chemical species for n-heptane ignition is analysed and reduced to 4 global steps with adjusted rate coefficients to describe ignition at pressures around 40 atm. Two of these steps account for the high temperature branch and the other two for the low temperature branch of the ignition mechanism. The ignition delay time passes through a negative temperature dependence during the transition between the two branches. This is accounted for by the reversible third reaction step, which models the first and second O2-addition in the degenerated chain branching mechanism at low temperatures. Ignition delay times calculated with the adjusted 4-step model are compared to those from the detailed kinetics and experimental data. Finally the 4-step mechanism is analysed by asymptotic methods and explicit ignition delay time formulas are derived.

Asymptotic analysis of a cohesive crack: 1. Theoretical background

Abstract: A method to analyze the evolution of a cohesive crack, particularly appropriate for asymptotic analysis, is presented. Detailed descriptions of the zeroth order and first order asymptotic approaches are given and from these results the far field equivalent elastic crack theorem is derived. An analytically soluble example, the Griffith crack, and a simple model, the Dugdale model, are used to exemplify the results.

Characterization and Analysis of Thionin Genes

Abstract: The general designation of thionins has been proposed for a family of homologous proteins that have been isolated from different tissues in a wide range of plant taxa and have been variously named purothionins, viscotoxins, crambins, etc. (see Garcia-Olmedo et al., 1989). The possible involvement of thionins in plant defense was first suggested, on the basis of their in vitro toxicity to plant pathogens, by Fernandez de Caleya et al., (1972). Those observations had been prompted by earlier reports concerning the antimicrobial properties of these polypeptides (Stuart and Harris, 1942; Balls and Harris, 1944). Work on the thionins, which has been actively pursued over the past half-century, has been recently reviewed in detail (Garcia-Olmedo et al., 1989). For this reason. earlier work will only be partially summarized in the present chapter, which will focus on recent developments concerning thionin genes and their potential role in plant defense mechanisms.

Introduction to the information system

Abstract: Planning a flexible manufacturing system is a complex process. It receives information from previous activities about the product to be manufactured and the amounts to be manufactured per time unit. With that information, a manufacturing system able to solve the posed manufacturing problem has to be designed. This implies two basic activities: planning the system layout and planning the execution process. Both planning activities are usually performed by stepwise refinement and are closely interrelated.

Identification of C-banded chromosomes in meiosis and the analysis of nucleolar activity in Avena byzantina C. Koch cv ‘Kanota’

Abstract: The Giemsa C-banding technique was used to identify individual meiotic and somatic chromosomes in 21 monosomic lines of Avena byzantina C. Koch cv ‘Kanota’ (genome designation AACCDD). The hexaploid complement is composed of three sets of seven chromosome pairs. The heterochromatin in the putative diploid progenitors is located at the telomeres (genome A), at the centromeric and interstitial regions (genome C), or more evenly spread throughout the set (genome D). Comparisons based on C-banding between A. byzantina and its diploid progenitor species allowed us to allocate individual chromosomes into specific genomes. The C-banding technique may be useful for interspecific chromosome pairing analyses. Nucleolar activity and competition were studied using a silver-staining procedure. Only three chromosome pairs showed nucleolar organizer regions, thus indicating that nucleolar competition occurs naturally in hexaploid oats.

Roughness-induced fatigue crack closure: a numerical study

Abstract: — A numerical study of the influence of crack surface roughness on fatigue crack closure is presented. Calculations are performed with a research oriented finite difference code suitably modified to study fatigue crack propagation and closure. A powerful algorithm of contact detection is used to ascertain the interaction between the crack surfaces and a penalty forces method is employed to avoid node-to-node and node-to-face penetration. The results indicate that the key controlling factor of roughness-induced fatigue crack closure is the tilt angle between crack branches and the average direction of crack propagation. Crack opening and closure loads increase with the tilt angle, and when plasticity effects are negligible, they are not affected by the crack branch length. Numerical results are also able to explain the large closure levels measured experimentally in 2124 Al alloy fatigue cracks.

Optimum cruise lift coefficient in initial design of jet aircraft

Abstract: shows the average lift during the ramp-down motion is the dominant factor in the decline of the total average lift at high amax. In the analysis in Ref. 1 a dynamic lift augmentation of AL = 1.5 was assumed, and this resulted in an ALV with a near 20% improvement in straight-and-level range over the conventional baseline vehicle. In Fig. 3c, an augmentation of AL = 1.5 was achieved at the highest pitch rate of K = 0.2 and a0 = 0 deg and for both cases of K = 0.05 and 0.1 for starting angles of aQ = 10 deg. The asssumption of Ref. 1 concerning the existence of augmentation parameters near 1.5 and above would appear then to have some justification. Any benefits that might be gained from augmented lift must be weighed against the penalty levied by the increase in dynamic drag loading. Figure 4 shows the total time-average drag coefficients for each test motion. Figure 4 clearly shows that decreasing amax is advantageous from the standpoint of average drag reduction. From Fig. 3c at the pitch rates of K = 0.05 and 0.1 and starting angles of 10 deg, a value of amax = 35 deg results in nearly optimum lift augmentation with respective AL values of 1.5 and 1.63. The corresponding average drag coefficient is seen in Fig. 4 to be near 0.7, which by some standards is large. Notice, however, that the average drag decreases rapidly with decreasing amax, and for amax = 25 deg and pitch rates of K = 0.05 and 0.1, the average drag coefficient has dropped to 0.3 and 0.24, respectively. At the same time, the lift augmentation remains well above unity and, from Fig. 3c, has values of 1.38 and 1.34, respectively. Thus for the rate of K = 0.1, decreasing amax from 35 to 25 deg results in a drop in the average lift of 18% (though still maintaining significant lift augmentation), whereas the average drag decreases over 60%. In the present study the pitch rate for the ramp-up and ramp-down motions was the same. For a stopping angle of amax = 25 deg the data of Fig. 3a indicate that the average lift during ramp up generally increases with pitch rate, whereas in Fig. 3b the average lift during ramp down decreases with pitch rate. There may then be some advantage in ramping up at a high rate followed by ramping down at a lower rate. In the motions studied in Ref. 1 the rate during pull-up was lower than that for pitch-down. Maintaining acceptable drag loading may be a limiting condition for defining airfoil motions for the purpose of utilizing augmented lift.

Relationship between pairing frequencies and genome affinity estimations in Aegilops ovata × Triticum aestivum hybrid plants.

Abstract: Meiotic associations at metaphase I have been analysed in Aegilops ovata × Triticum aestivum hybrid plants (genome constitution ABDUM) with low and high homoeologous pairing by using C-banding. Five different types of meiotic associations involving Aegilops and wheat genomes were identified. Pairing affinities between Aegilops and wheat genomes have been analysed from meiotic associations at metaphase I in low and high homoeologous pairing hybrid plants as well as from different meiotic configurations (bivalents and multivalents) in those hybrids with a high pairing mutant (phlb). Those kinds of distinguishable associations revealed the same relative order: AD-UM > A-D > U-M > AD-B > UM-B in both low and high homoeologous pairing hybrids. The mean number of associations per total associations (relative contribution) for the different distinguishable types of pairing was well maintained among hybrids with different levels of pairing (low and high) as well as in different meiotic configurations (bivalents and multivalents) in the high pairing plants. These results seem to indicate that the affinities expressed between the genomes that are in competition for pairing are independent of the meiotic configurations considered and on the level of pairing analysed.

Light-confining cavities for photovoltaic applications based on the angular-spatial limitation of the escaping beam.

Abstract: Integrating spheres are proposed as light-confining cavities for enhancing the absorption of light by devices such as solar cells, and also for making photovoltaic converters with cells of several band gaps. A new concept for achieving this light confinement by angular restriction of the escaping of rays, which avoids the requirement of having a small entry aperture and therefore concentrations on it that are much higher than those required on the solar cells, is proposed here.

Flavonoids in seed coats of Medicago arborea and M. strasseri (Leguminosae): Ecophysiological aspects

Abstract: Medicago arborea and M. strasseri are two leguminous species of great rusticity, valuables as ornamental and fodder plants. The high susceptibility to the fungal attack of their seeds limited those potential uses. Seven main flavonoids (Luteolin; Luteolin-7-glucoside; 7,3′,4′-Trihydroxyflavone; 7,3′,4′-Trihydroxyflavone 7-glucoside; 7,4′-Dihydroxyflavone; Quercetin-3-glucoside; Kaempferol-3-glucoside) were identified in the seed coats of both species. Their ecophysiological role is studied by bioassays: inhibition test of germination and radicle growth of Lactuca sativa and inhibition test of growth of Alternaria alternata and Pleospora herbarum fungus isolated from the seed coats.

A universal model for lossy and dispersive transmission lines for time domain CAD of circuits

Abstract: Branin's method of characteristics has been extended to obtain a universal equivalent model for lossy and dispersive transmission lines. Existing CAD software packages, such as SPICE, can be used for this implementation. The starting point for obtaining the model is the analog filters that approximate the characteristic impedance Z/sub 0/(s) and the propagation function F(s)=exp(- gamma l) of the transmission line. The circuits are synthesized using conventional network synthesis techniques. An examination of the validity of the model is carried out by analyzing an example of RLCG lines driven by bipolar logic gates and the distortion of a DC Gaussian pulse as it propagates along a microstrip line. >

Microbial corrosion of stainless steel.

Abstract: Stainless steel, developed because of their greater resistance to corrosion in different aggressive environments, have proved to be affected, however, by various processes and types of corrosion Some of these types of corrosion, mainly pitting, is activated and developed in the presence of microorganisms, which acting in an isolated or symbiotic way, according to their adaptation to the environment, create a favorable situation for the corrosion of these steel The microorganisms that are involved, mainly bacteria of both the aerobic and anaerobic type, modify the environment where the stainless steel is found, creating crevices, differential aeration zones or a more aggressive environment with the presence of metabolites In these circumstances, a local break of the passive and passivating layer is produced, which is proper to these types of steel and impedes the repassivation that is more favorable to corrosion In the study and research of these types of microbiologically influenced corrosion are found electrochemical techniques, since corrosion is fundamentally an electrochemical process, and microbiological techniques for the identification, culture, and evaluation of the microorganisms involved in the process, as well as in the laboratory or field study of microorganism-metal pairs Microstructural characterization studies of stainless steel have also been considered important, since it is known that the microstructure of steel can substantially modify their behavior when faced with corrosion As for surface analysis studies, it is known that corrosion is a process that is generated on and progresses from the surface The ways of dealing with microbiologically influenced corrosion must necessarily include biocides, which are not always usable or successful, the design of industrial equipment or components that do not favor the adherence of microorganisms, using microstructures in steel less sensitive to corrosion, or protecting the materials