Showing papers by "Technical University of Madrid published in 1998"

Applying watershed algorithms to the segmentation of clustered nuclei

Abstract: Cluster division is a critical issue in fluorescence microscopy-based analytical cytology when preparation protocols do not provide appropriate separation of objects. Overlooking clustered nuclei and analyzing only isolated nuclei may dramatically increase analysis time or affect the statistical validation of the results. Automatic segmentation of clustered nuclei requires the implementation of specific image segmentation tools. Most algorithms are inspired by one of the two following strategies: 1) cluster division by the detection of internuclei gradients; or 2) division by definition of domains of influence (geometrical approach). Both strategies lead to completely different implementations, and usually algorithms based on a single view strategy fail to correctly segment most clustered nuclei, or perform well just for a specific type of sample. An algorithm based on morphological watersheds has been implemented and tested on the segmentation of microscopic nuclei clusters. This algorithm provides a tool that can be used for the implementation of both gradient- and domain-based algorithms, and, more importantly, for the implementation of mixed (gradient- and shape-based) algorithms. Using this algorithm, almost 90% of the test clusters were correctly segmented in peripheral blood and bone marrow preparations. The algorithm was valid for both types of samples, using the appropriate markers and transformations.

A Survey of Agent-Oriented Methodologies

Abstract: This article introduces the current agent-oriented methodologies. It discusseswhat approacheshave been followed (mainly extending existing objectoriented and knowledge engineering methodologies), the suitability of these approaches for agent modelling, and some conclusions drawn from the survey.

The power of a pebble: exploring and mapping directed graphs

Abstract: Exploring and mapping an unknown environment is a fundamental problem that is studied in a variety of contexts. Many results have focused on finding efficient solutions to restricted versions of the problem. In this paper, we consider a model that makes very limited assumptions about the environment and solve the mapping problem in this general setting. We model the environment by an unknown directed graph G, and consider the problem of a robot exploring and mapping G. The edges emanating from each vertex are numbered from ‘1’ to ‘d’, but we do not assume that the vertices of G are labeled. Since the robot has no way of distinguishing between vertices, it has no hope of succeeding unless it is given some means of distinguishing between vertices. For this reason we provide the robot with a “pebble”—a device that it can place on a vertex and use to identify the vertex later. In this paper we show: (1) If the robot knows an upper bound on the number of vertices then it can learn the graph efficiently with only one pebble. (2) If the robot does not know an upper bound on the number of vertices n, then (log log n) pebbles are both necessary and sufficient. In both cases our algorithms are deterministic. C © 2002 Elsevier Science (USA)

Mixed Mode Fracture of Concrete under Proportional and Nonproportional Loading

Abstract: A novel testing procedure for mixed mode crack propagation in concrete is presented: four point bend of notched beams under the action of two independent force actuators. In contrast to classical procedures, this method allows nonproportional loading and crack trajectory modifications by changing the action of one actuator. Different experimental crack trajectories, under mixed mode and nonproportional loading, are presented together with the corresponding curves of load-CMOD and load-displacement. The tests were performed for three homotetic specimen sizes and two mixed mode loading conditions. The results are useful for checking the accuracy of mixed mode fracture analytical and numerical models. The models should predict the crack trajectory and a complete group of experimental records of load and displacements on several control points in the specimen.

High-performance GaN p-n junction photodetectors for solar ultraviolet applications

Abstract: The fabrication and characterization of ultraviolet photodetectors based on GaN p-n junctions is reported. The devices are grown by metalorganic vapour phase epitaxy on basal-plane sapphire substrates. These detectors are visible-blind with a sharp wavelength cut-off at 360 nm. The photocurrent is linear with incident power from up to , with a responsivity of at 360 nm. The device time response is dominated by the effective resistance-capacitance time constant, and a 105 ns response is estimated for very low load resistances. A comparison with the response of GaN photoconductor detectors is also presented. The application of these high-performance photodetectors for solar ultraviolet monitoring is described.

Stress Intensity factor, compliance and CMOD for a General Three-Point-Bend Beam

Abstract: New simple and general expressions for the stress intensity factor, compliance and crack mouth opening displacement for three-point bend specimens are computed. Inverse functions giving the crack length as a function of load-point displacement or crack mouth opening displacement are also included. The expressions are valid for any crack length and for any span-to-depth ratio larger than 2.5. The expressions are checked by comparing them to direct finite element computations and to available expressions by other authors. The accuracy of the new expression is equal to or better than available formulas when compared with finite element computations, and its range of applicability is much larger. Moreover, all the new expressions exhibit the correct asymptotic behaviour for very shallow and very deep cracks.

Microstructural factors controlling the strength and ductility of particle-reinforced metal-matrix composites

Abstract: A micromechanical model is developed to simulate the mechanical response in tension of particle-reinforced metal-matrix composites. The microstructure of the composite is represented as a three-dimensional array of hexagonal prisms with one reinforcement at the centre of each prism. The shape, volume fraction and state (either intact or broken) of the reinforcement is independent for each cell, so the interaction among all these factors could be studied. The tensile response of the composite is determined from the behaviour of the intact and damaged cells, the fraction of damaged cells being calculated on the assumption that the reinforcement strength follows the Weibull statistics. The model is used to determine the microstructural factors which provide optimum behaviour from the point of view of the tensile strength and ductility. The analyses included the effect of the matrix and reinforcement properties, the reinforcement volume fraction, the interaction between reinforcements of different shape and the heterogeneous distribution of the reinforcements within the composite.

Ultrashort pulsed gaussian light beams

Abstract: We find a family of solutions of the paraxial wave equation that represents ultrashort pulsed light beams propagating in free space. These pulsed beams have an arbitrary temporal form and a nearly Gaussian cross section, while modeling for the pulses emitted by mode-locked lasers with stable two-mirror resonators. We also study the effects arising from their spatiotemporal coupled behavior, such as pulse time delay, distortion, and a frequency shift toward the beam periphery. Time-varying diffraction (with diffraction reduction at the first instants of arrival of the pulsed beam at a given distance) and the dependence of the spatial distribution of energy on the pulse form are also described. These effects become important for pulsed beams with a few optical oscillations within the pulse envelope.

Inactivation of the sapA to sapF Locus of Erwinia chrysanthemi Reveals Common Features in Plant and Animal Bacterial Pathogenesis

Abstract: We investigated the role in pathogenesis of bacterial resistance to plant antimicrobial peptides. The sapA to sapF (for sensitive to antimicrobial peptides) operon from the pathogenic bacterium Erwinia chrysanthemi has been characterized. It has five open reading frames that are closely related (71% overall amino acid identity) and are in the same order as those of the sapA to sapF operon from Salmonella typhimurium. An E. chrysanthemi sap mutant strain was constructed by marker exchange. This mutant was more sensitive than was the wild type to wheat alpha-thionin and to snakin-1, which is the most abundant antimicrobial peptide from potato tubers. This mutant was also less virulent than was the wild-type strain in potato tubers: lesion area was 37% that of the control, and growth rate was two orders of magnitude lower. These results indicate that the interaction of antimicrobial peptides from the host with the sapA to sapF operon from the pathogen plays a similar role in animal and in plant bacterial pathogenesis.

A non-interactive methodology to assess farmers' utility functions: An application to large farms in Andalusia, Spain

Abstract: Summary This paper proposes a methodological approach for eliciting farmers' utility functions. The methodology is non-interactive, in that the parameters defining the utility function are obtained by observing the actual behaviour adopted by farmers without resorting to the use of questions on random lotteries. The methodology recognises that the farmer attempts to achieve several objectives, most of which are in conflict. The methodological approach is applied to a large farmer in the county of Vega de Cdrdoba, Spain. The primary empirical finding of this research was a satisfactory explanation of farmers' behaviour through a multi-attribute utility function with three attributes: working capital, risk and level of relative profitability.

Goal programming, compromise programming and reference point method formulations : linkages and utility interpretations

Abstract: This paper looks at connections between the multi-criteria techniques of goal programming, compromise programming, and the reference point method. The utility function structure of each method is examined and interpretation of the techniques in terms of pareto efficiency and the equilibrated nature of the solution is given. Means of ensuring pareto efficiency whilst maintaining as much as possible the equilibrated character are given for a certain class of model. Methods for ensuring conceptual correctness and computational accuracy by reducing reference point models to equivalent goal programmes are given. The findings are illustrated by means of an example.

A tutorial on wavelets from an electrical engineering perspective. I. Discrete wavelet techniques

Abstract: The objective of this paper is to present the subject of wavelets from a filter-theory perspective, which is quite familiar to electrical engineers. Such a presentation provides both physical and mathematical insights into the problem. It is shown that taking the discrete wavelet transform of a function is equivalent to filtering it by a bank of constant-Q filters, the non-overlapping bandwidths of which differ by an octave. The discrete wavelets are presented, and a recipe is provided for generating such entities. One of the goals of this tutorial is to illustrate how the wavelet decomposition is carried out, starting from the fundamentals, and how the scaling functions and wavelets are generated from the filter-theory perspective. Examples (including image compression) are presented to illustrate the class of problems for which the discrete wavelet techniques are ideally suited. It is interesting to note that it is not necessary to generate the wavelets or the scaling functions in order to implement the discrete wavelet transform. Finally, it is shown how wavelet techniques can be used to solve operator/matrix equations. It is shown that the "orthogonal-transform property" of the discrete wavelet techniques does not hold in numerical computations.

The role of unequal diffusivities in ignition and extinction fronts in strained mixing layers

Abstract: We have studied flame propagation in a strained mixing layer formed between a fuel stream and an oxidizer stream, which can have different initial temperatures. Allowing the Lewis numbers to deviate from unity, the problem is first formulated within the framework of a thermo-diffusive model and a single irreversible reaction. A compact formulation is then derived in the limit of large activation energy, and solved analytically for high values of the Damkohler number. Simple expressions describing the flame shape and its propagation velocity are obtained. In particular, it is found that the Lewis numbers affect the propagation of the triple flame in a way similar to that obtained in the studies of stretched premixed flames. For example, the flame curvature determined by the transverse enthalpy gradients in the frozen mixing layer leads to flame-front velocities which grow with decreasing values of the Lewis numbers. The analytical results are complemented by a numerical study which focuses on preferentialdiffusion effects on triple flames. The results cover, for different values of the fuel Lewis number, a wide range of values of the Damkohler number leading to propagation speeds which vary from positive values down to large negative values.

La planta ideal: revision del concepto, parametros definitorios e implementacion practica

Abstract: El objetivo de este articulo es examinar de una forma ordenada lo que constituye una planta ideal y como concretar este concepto en un programa operacional. Con el fin de alcanzar estos objetivos se discuten, en primer lugar, varios conceptos: la influencia de las practicas culturales en vivero sobre las caracteristicas de la planta, la fenologia de la misma, y los procesos implicados en la supervivencia y crecimiento en campo. A continuacion, se pasa revista a algunos de los posibles atributos de estado y de comportamiento de la planta que pueden servir para definir la planta ideal. Finalmente, se presentan las lineas maestras de lo que constituiria un programa operacional de planta ideal.

Accessibility, Network Efficiency, and Transport Infrastructure Planning:

Abstract: Most accessibility measures reported in the literature do not meet certain requirements of transport planners, as the results offered by these indicators are heavily influenced by the geographic location of the places. Peripheral locations invariably figure as being of low accessibility and consequently as possible receptors for new investments, even though they may already have a very good provision of transport infrastructure. In this paper an accessibility indicator is formulated that neutralizes the effect of geographic location. To this end, the customary notion of distance (length, time, or costs) is substituted by another which expresses the ease of access in terms of network efficiency. This indicator can be useful to assist decisions to invest in transport networks, as it is more sensitive than the potential model to the transport infrastructure needs of each individual region. It has been tested by application to the current Spanish Infrastructure Master Plan.

Barley BLZ1: a bZIP transcriptional activator that interacts with endosperm-specific gene promoters

Abstract: A cDNA encoding a bZIP transcription factor was obtained from barley endosperm and used to identify the corresponding gene from a genomic library. The gene, designated Blz1, contained six exons and five introns, plus a 442 nt-long 5'-untranslated leader sequence, and was located on chromosome 5H. The Blz1 mRNA was detected early in endosperm development and was also expressed in roots and leaves. The BLZ1 protein was a potent transcriptional activator in a yeast system; 85% of its activity was associated with the first 203 amino acid residues at the N-terminus, which included two acidic regions. Presumptive involvement of Blz1 in the regulation of gene expression in endosperm was ascertained by the DNA-binding properties of BLZ1 in electrophoretic mobility shift assays (EMSA) and by transient expression in barley developing endosperms, using, as effectors, Blz1 in both sense and anti-sense orientations. In the co-bombardment experiments, the beta-glucuronidase (GUS) reported gene responded to Blz1 if under the control of the endosperm-specific ltr1 promoter or under a synthetic promoter containing the endosperm box of gene Hor2. Sucrose synthase promoters Ss1 and Ss2 and synthetic promoters containing mutated sequences of Hor2 were unaffected in trans by Blz1.

Multifractal analysis of particle size distributions in soil

Abstract: Power-law scaling of particle size distributions in air, water, and soil have been frequently reported and are sometimes interpreted in the context of a fractal dimension to yield estimates of the ...

Comparison between sensory and instrumental measurements for mealiness assessment in apples. a collaborative test

Abstract: Definition and establishment of assessment procedures for mealiness of apple fruits using sensory and instrumental measurements were performed on 'Boskoop'. 'Cox's Orange Pippin' and 'Jonagold' samples with varying degrees of mealiness. The sensory procedure profiled mealiness as a loss of crispness, hardness, and juiciness, with an increase in the floury sensation in the mouth. High correlations between the sensory descripiors and instrumental parameters was shown through principal component analysis. The instrumental procedures (confined compression offruit cylinders and acoustic impulse response) gave coefficients of determination for juiciness and crispness of 0.85 and 0.71, respectively. This level of accuracy indicates the possihility of establishing

Emotional speech synthesis: from speech database to TTS.

Abstract: Modern Speech synthesisers have achieved a high degree of intelligibility, but can not be regarded as natural-sounding devices. In order to decrease the monotony of synthetic speech, the implementation of emotional effects is now being progressively considered. This paper presents a through study of emotional speech in Spanish, and its application to TTS, presenting a prototype system that simulates emotional speech using a commercial synthesiser. The design and recording of a Spanish database will be described and also the analysis of the emotional prosody (by fitting the data to a formal model). Using this collected data, a rule-based simulation of three primary emotions was implemented in the Text-to-Speech system. Finally, the assessment of the synthetic voice through perception experiments will classify the system as capable of producing quality voice with recognisable emotional effects.

Surface-wave damping in a brimful circular cylinder

Abstract: The natural frequencies and damping rates of surface waves in a circular cylinder with pinned-end boundary conditions are calculated in terms of the gravitational Reynolds and Bond numbers, C−1 and B, and the slenderness of the cylinder Λ, in the limit C→0. We consider higher-order approximations that include the effect of viscous dissipation in the Stokes boundary layers and the bulk. A comparison with clean-surface experiments by Henderson & Miles (1994) shows a satisfactory agreement except for the first axisymmetric mode, which exhibits a 26% discrepancy. The much larger dramatic discrepancy of former theoretical predictions is hereby improved and explained.

AlxGa1−xN:Si Schottky barrier photodiodes with fast response and high detectivity

Abstract: Gold and nickel Schottky barrier photovoltaic detectors have been fabricated on Si-doped AlxGa1−xN layers (0⩽x⩽0.22) grown on sapphire by metalorganic vapor phase epitaxy. Responsivity is independent of the Schottky metal or diode size, and also of the incident power in the range measured (10 mW/m2–2 kW/m2). A higher visible rejection has been observed in the spectral response of Au photodiodes (>103). Time response is resistance-capacitance limited, with time constants as short as 14 ns in Al0.22Ga0.78N diodes. Low frequency noise studies are also presented, and detectivities of 6.1×107 and 1.2×107 mHz1/2 W−1 are determined in GaN/Au and Al0.22Ga0.78N/Au detectors, at −2 V bias.