Showing papers by "Technical University of Madrid published in 1999"

Climate change and world food security: a new assessment

Abstract: Building on previous work quantitative estimates of climate change impacts on global food production have been made for the UK Hadley Centre's HadCM2 greenhouse gas only ensemble experiment and the more recent HadCM3 experiment (Hulme et al., 1999). The consequences for world food prices and the number of people at risk of hunger as defined by the Food and Agriculture Organisation (FAO, 1988) have also been assessed. Climate change is expected to increase yields at high and mid-latitudes, and lead to decreases at lower latitudes. This pattern becomes more pronounced as time progresses. The food system may be expected to accommodate such regional variations at the global level, with production, prices and the risk of hunger being relatively unaffected by the additional stress of climate change. By the 2080s the additional number of people at risk of hunger due to climate change is about 80 million people (±10 million depending on which of the four HadCM2 ensemble members is selected). However, some regions (particularly the arid and sub-humid tropics) will be adversely affected. A particular example is Africa, which is expected to experience marked reductions in yield, decreases in production, and increases in the risk of hunger as a result of climate change. The continent can expect to have between 55 and 65 million extra people at risk of hunger by the 2080s under the HadCM2 climate scenario. Under the HadCM3 climate scenario the effect is even more severe, producing an estimated additional 70+ million people at risk of hunger in Africa.

Overview of Knowledge Sharing and Reuse Components: Ontologies and Problem-Solving Methods

Abstract: Ontologies and problem-solving methods are promising candidates for reuse in Knowledge Engineering. Ontologies define domain knowledge at a generic level, while problem-solving methods specify generic reasoning knowledge. Both type of components can be viewed as complementary entities that can be used to configure new knowledge systems from existing, reusable components. In this paper, we give an overview of approaches for ontologies and problem-solving methods.

An efficient inverse scattering algorithm for the design of nonuniform fiber Bragg gratings

Abstract: Presents an efficient method for the design of complex fiber Bragg gratings. The method relies on the synthesis of the impulse response of the grating by means of a differential layer-peeling algorithm. The algorithm developed takes into account all the multiple reflections inside the grating, giving an exact solution to the inverse scattering problem. Its low algorithmic complexity enables the synthesis of long fiber gratings. The method is illustrated by designing several filters with interest for optical fiber communication systems: dispersionless bandpass filters and second- and third order dispersion compensators.

Snakin-1, a Peptide from Potato That Is Active Against Plant Pathogens

Abstract: A new type of antimicrobial peptide, snakin-1 (SN1), has been isolated from potato tubers and found to be active, at concentrations <10 μM, against bacterial and fungal pathogens from potato and other plant species. The action of SN1 and potato defensin PTH1 was synergistic against the bacterium Clavibacter michiganensis subsp. sepedonicus and additive against the fungus Botrytis cinerea. Snakin-1 causes aggregation of both gram-positive and gram-negative bacteria. The peptide has 63 amino acid residues (M r 6,922), 12 of which are cysteines, and is unrelated to any previously isolated protein, although it is homologous to amino acid sequences deduced from cloned cDNAs that encode gibberellin-inducible mRNAs and has some sequence motifs in common with kistrin and other hemotoxic snake venoms. A degenerate oligonucleotide probe based on the internal sequence CCEECKC has been used to clone an SN1 cDNA. With the cDNA used as probe, one copy of the StSN1 gene per haploid genome has been estimated and expressi...

2 Origin and domestication

Abstract: Publisher Summary This chapter discusses the evolutionary origin of the members of Brassica coenospecies. Alloploid species— B. carinata , B. juncea and B. napus —originated multiple natural interspecific hybridizations. Natural hybridizations are always unidirectional as revealed by the studies on Fraction-I protein and cp DNA restriction patterns, which established that B. nigra and B. rapa are the cytoplasmic donors of B. carinata and B. juncea respectively, while in B. napus, there is a slightly altered B. oleracea cytoplasm. The close similarity in cp DNA of diploids and alloploids suggests that alloploids are of recent origin. A survey of rDNA of the allotetraploid species led to propose that B. juncea was the first to evolve and B. napus and B. carinata originated later. This agrees with the delayed entrance of B. oleracea in the agricultural world. Amount of DNA in tetraploids has not changed significantly since their origin, though there has been a reduction in nuclear size, probably because of the higher DNA density resulting from greater condensation of chromosome material. Nuclear DNA composition of alloploid species is closely related to the maternal cytoplasmic donors than to the male parents.

High-speed, low-noise metal–semiconductor–metal ultraviolet photodetectors based on GaN

Abstract: We present the fabrication and characterization of nonintentionally doped GaN and GaN:Mg Schottky metal–semiconductor–metal (MSM) photodetectors, grown on sapphire by metalorganic chemical vapor deposition. Low-leakage, Schottky contacts were made with Pt/Au. The devices are visible blind, with an ultraviolet/green contrast of about five orders of magnitude. The response times of the MSM devices were <10 ns and about 200 ns for GaN and GaN:Mg, respectively. The noise power spectral density remains below the background level of the system (10−24 A2/Hz) up to 5 V, for the undoped GaN MSM detector.

Ka)2

Abstract: Ontologies are becoming increasingly more important in many different areas, including the knowledge management area. In knowledge management, ontologies can be used as an instrument to make knowledge assets intelligently accessible to people in organizations through an Intranet or the Internet. Most enterprises agree that knowledge is an essential asset for success and survival on an increasingly competitive and global market. In this paper, we present an ontology-based approach through a large-scale initiative involving knowledge management for the knowledge-acquisition research community.

Heterologous Expression of a Plant Small Heat-Shock Protein Enhances Escherichia coli Viability under Heat and Cold Stress

Abstract: A small heat-shock protein (sHSP) that shows molecular chaperone activity in vitro was recently purified from mature chestnut (Castanea sativa) cotyledons. This protein, renamed here as CsHSP17.5, belongs to cytosolic class I, as revealed by cDNA sequencing and immunoelectron microscopy. Recombinant CsHSP17.5 was overexpressed in Escherichia coli to study its possible function under stress conditions. Upon transfer from 37°C to 50°C, a temperature known to cause cell autolysis, those cells that accumulated CsHSP17.5 showed improved viability compared with control cultures. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of cell lysates suggested that such a protective effect in vivo is due to the ability of recombinant sHSP to maintain soluble cytosolic proteins in their native conformation, with little substrate specificity. To test the recent hypothesis that sHSPs may be involved in protection against cold stress, we also studied the viability of recombinant cells at 4°C. Unlike the major heat-induced chaperone, GroEL/ES, the chestnut sHSP significantly enhanced cell survivability at this temperature. CsHSP17.5 thus represents an example of a HSP capable of protecting cells against both thermal extremes. Consistent with these findings, high-level induction of homologous transcripts was observed in vegetative tissues of chestnut plantlets exposed to either type of thermal stress but not salt stress.

High efficiency and high concentration in photovoltaics

Abstract: In this paper, we present the state-of-the-art of multijunction solar cells and the future prospects of this technology. Their use in terrestrial applications will likely be for concentrators operating at very high concentrations. Some trends are also discussed and we present a cost calculation showing that highly efficient cells under very high concentration would be able to produce electricity at costs competitive with electricity generation costs for some utilities.

Size effect and boundary conditions in the Brazilian test: Experimental verification

Abstract: The effect of both size specimen and boundary conditions on the splitting tensile strength, determined from the Brazilian test, were studied experimentally. A total of 110 splitting tests of granite and mortar specimens were performed, using cylindrical and prismatic specimens of sizes between 17 mm and 300 mm. To analyze the effect of the boundary conditions, the specimens were tested with different widths of load bearing strip in the range of size recommended by the standards. The influence of the rupture mode (stable or unstable crack propagation) on the splitting tensile strength was also explored. The results of the tests were compared with the theoretical predictions obtained from a closed form analytical expression based on the cohesive crack model. The validity of the classical limit strength theory for larger size specimens was also analyzed. The results indicate that the splitting tensile strength depends strongly on specimen size and on the boundary conditions of the test. As the size of the specimen increases and the relative width of the bearing strip decreases, the splitting strength tends asymptotically to the minimum value coincident with the tensile strength. The dependence of the Brazilian test on the specimen size and boundary conditions closely follows the predictions of the cohesive crack model.

Technique for multiplying the repetition rates of periodic trains of pulses by means of a temporal self-imaging effect in chirped fiber gratings.

Abstract: We show that a temporal effect that is equivalent to the spatial self-imaging (Talbot) effect applies to the reflection of periodic signals from linearly chirped fiber gratings. The effect can be used for multiplying the repetition frequency of a given periodic pulse train without distorting the individual pulse characteristics. The practical limit on the frequency-multiplication factor depends only on the temporal width of the individual pulse. Thus we demonstrate that a suitable combination of well-known techniques for short-pulse generation, such as pulse mode locking, and the technique proposed here allows us to obtain short-pulse trains with ultrahigh repetition rates (in the terahertz regime). Results from simulations show good agreement with those predicted by theory.

Impulsive noise measurements and characterization in a UHF digital TV channel

Abstract: This paper presents the results of a study covering measurement and characterization of the wide-band impulsive noise present in a digital TV radio channel. Measurements were conducted at a frequency of 762 MHz in different outdoor and indoor environments using vertical and horizontal polarization. The measurement system was built on commercial equipment only. The calibration process, which is an important stage of this kind of measurements, is described. To analyze the measurements the impulsive noise has been modeled as a pulse train where the pulse amplitude, pulse duration and elapsed time between pulses are considered random variables. It has been found that the pulse duration and elapsed time between pulses is not dependent on the antenna polarization while the pulse amplitude is, especially in the case of the noise generated by a fluorescent lamp. It has also been found that the pulse duration of the noise measured in the outdoor environments presents some clustering features and is correlated with the pulse amplitudes. This correlation may be caused by a RF noise bandwidth that is larger than the bandwidth of the measurement system. The noise in busy streets presents larger pulse durations, larger amplitude, and shorter elapsed time between pulses that the noise measured in a pedestrian area. Several statistical tests have been done to find the distribution function that best fits these random variables. Power Rayleigh, lognormal, exponential, Poisson, and Gamma distributions have been tested. According to the assessment carried out, none of the distribution functions is adequate to model the pulse amplitudes or the elapsed time between pulses, while the pulse duration seems to be Gamma distributed.

Rate control and bit allocation for MPEG-4

Abstract: In previous years, an interest has developed in the coded representations of video signals allowing independent manipulation of semantically independent elements (objects). Along these lines, the ISO standard MPEG-4 enhances the traditional concept of the video sequence to convert it into a synchronized set of visual objects organized in a flexible way. The real-time generation of a bitstream according to this new paradigm, and suitable for its transmission through either fixed- or variable-rate channels, results in a challenging new bit allocation and rate control problem, which has to satisfy complex application requirements. This paper formalizes this new issue by focusing on the design of rate control systems for real-time applications. The proposed approach relies on the modelization of the source and the optimization of a cost criterion based on signal quality parameters. Different cost criteria are provided, corresponding to a set of relevant definitions of the object priority concept. Algorithms are introduced to minimize the average distortion of the objects, to guarantee desired qualities to the most relevant ones, and to keep constant ratios among the object qualities. The techniques have been applied to a coder implementing the MPEG-4 video verification model, showing good properties in terms of achievement of the control objectives.

Size effect and boundary conditions in the brazilian test: theoretical analysis

Abstract: Splitting strength determined in the Brazilian test is assumed to be a property independent of size and uniquely related to the intrinsic material strength. However, as was experimentally demonstrated by various authors, the splitting strength depends on the specimen size. In this paper, the size effect in the Brazilian test is analyzed theoretically using a nonlinear fracture model based on cohesive crack concepts and the results obtained are compared with the classical strength limit approach. Two important variables are studied: the load-bearing strip and the geometry of the specimen. From the numerical results a closed form expression is proposed, dependent on the width of the bearing strip and on geometry. The results confirm that splitting strength decreases with the specimen size, tending towards an asymptotic solution for large size specimens. Within the size range analyzed (0.1 m to 2.5 m diameter for typical concrete) the splitting strength can vary by up to 25% in cylindrical specimens and by up to 35% in prismatic square section specimens, although this size effect is strongly dependent on the load-bearing strip. For widths of bearing strip smaller than 4% of the specimen diameter, the effect of the specimen size is negligible and the splitting strength approaches the tensile strength for any practical specimen size.

Cloning of two genes encoding potassium transporters in Neurospora crassa and expression of the corresponding cDNAs in Saccharomyces cerevisiae.

Abstract: Two Neurospora crassa genes, trk-1 and hak-1, encode K+ transporters that show sequence similarities to the TRK transporters described in Saccharomyces cerevisiae and Schizosaccharomyces pombe, and to the HAK transporters described in Schwanniomyces occidentalis and barley The N crassa TRK1 and HAK1 transporters expressed by the corresponding cDNAs in a trk1Δ trk2Δ mutant of S cerevisiae exhibited a high affinity for Rb+ and K+ Northern blot analysis and comparison of the kinetic characteristics of the two transporters in the trk1Δ trk2Δ mutant with the kinetic characteristics of K+ uptake in N crassa cells allowed TRK1 to be identified as the dominant K+ transporter and HAK1 as a transporter that is only expressed when the cells are K+ starved The HAK1 transporter showed a high concentrative capacity and is identified as the K+–H+ symporter described in N crassa, whereas TRK1 might be a K+ uniporter Although the co-existence of K+ transporters of the TRK and HAK types in the same species had not been reported formerly, we discuss whether this co-existence may be the normal situation in soil fungi

Ontological Reengineering for Reuse

Abstract: This paper presents the concept of Ontological Reengineering as the process of retrieving and transforming a conceptual model of an existing and implemented ontology into a new, more correct and more complete conceptual model which is reimplemented. Three activities have been identified in this process: reverse engineering, restructuring and forward engineering. The aim of Reverse Engineering is to output a possible conceptual model on the basis of the code in which the ontology is implemented. The goal of Restructuring is to reorganize this initial conceptual model into a new conceptual model, which is built bearing in mind the use of the restructured ontology by the ontology/application that reuses it. Finally, the objective of Forward Engineering is output a new implementation of the ontology. The paper also discusses how the ontological reengineering process has been applied to the Standard-Units ontology [18], which is included in a Chemical-Elements [12] ontology. These two ontologies will be included in a Monatomic-Ions and Environmental-Pollutants ontologies.

Design methodologies based on hardware description languages

Abstract: In this paper, we are presenting the basic methodology to be used in the design of a digital system, based on the use of hardware description languages. The most important stages of the design flow and the computer-aided design tools involved are presented, from the initial specification to the final implementation. The design flow described in the paper is based on a top-down approach, as this is the methodology currently used for most of the digital systems to face the current system complexity. Although all the concepts and methods are feasible for any kind of digital electronic system, application-specific integrated circuits are, in particular, considered as an application example in the paper. Most of the examples shown are written in VHSIC HDL, as it is an IEEE Standard and is one of the most commonly used.

Cyclic Siloxanes and Silsesquioxanes as Cores and Frameworks for the Construction of Ferrocenyl Dendrimers and Polymers

Abstract: Starting from 1,3,5,7-tetramethylcyclotetrasiloxane as core, novel ferrocenyl silicon-containing dendrimers have been constructed up to the third generation, which contains 16 peripheral ferrocene moieties. As precursors of these ferrocenyl dendritic molecules, Si— Cl- and Si— allyl-terminated cyclotetrasiloxane-based dendrimers were also built step by step, by the repetition of hydrosilylation and alkenylation reactions as growing steps. The dendritic structures have been confirmed by 1 H, 13 C and 29 Si NMR, infrared spectroscopy, elemental analysis, mass spectrometry and vapor-pressure osmometry. Solution electrochemical studies showed that all the ferrocenyl redox centers attached to the dendritic surface behave as independent, electronically isolated units, so that the dendrimers exchange all the electrons simultaneously at the same potential. We also describe the application of the first redox-active ferrocenyl polymer containing an octakis(dimethylsiloxy)octasilsesquioxane framework, as a mediator in the electrocatalytic oxidation of ascorbic acid. Copyright # 1999 John Wiley & Sons, Ltd.

Using Global Analysis, Partial Specifications, and an Extensible Assertion Language for Program Validation and Debugging

Abstract: We present a framework for the application of abstract interpretation as an aid during program development, rather than in the more traditional application of program optimization. Program validation and detection of errors is first performed statically by comparing (partial) specifications written in terms of assertions against information obtained from static analysis of the program. The results of this process are expressed in the user assertion language. Assertions (or parts of assertions) which cannot be verified statically are translated into run-time tests. The framework allows the use of assertions to be optional. It also allows using very general properties in assertions, beyond the predefined set understandable by the static analyzer and including properties defined by means of user programs. We also report briefly on an implementation of the framework. The resulting tool generates and checks assertions for Prolog, CLP(R), and CHIP/CLP(fd) programs, and integrates compile-time and run-time checking in a uniform way. The tool allows using properties such as types, modes, non-failure, determinacy, and computational cost, and can treat modules separately, performing incremental analysis. In practice, this modularity allows detecting statically bugs in user programs even if they do not contain any assertions.

Distance-based consensus methods: a goal programming approach

Abstract: Several authors have proposed a social choice function based upon distance-consensus between different committee rankings. Under this framework, the total absolute disagreement between committees is minimised. The purpose of this paper is to formulate the underlying optimisation problem as a goal programming (GP) model. To do this, the following three GP formulations are proposed: (a) a linear weighting GP model, where consensus is established by the minimisation of the weighted aggregated disagreement, (b) a MINMAX GP model, where the consensus is defined as the minimisation of the maximum disagreement and (c) an extended GP model, which subsumes the two previous formulations as particular cases.

Minimal recurrence relations for connection coefficients between classical orthogonal polynomials: discrete case

Abstract: We present a simple approach in order to compute recursively the connection coefficients between two families of classical (discrete) orthogonal polynomials (Charlier, Meixner, Kravchuk, Hahn), i.e., the coefficients Cm(n) in the expression P n (X)= ∑ n m=0 C m (n)Q m (x) , where Pn(x) and Qm(x) belong to the aforementioned class of polynomials. This is SCV2 done by adapting a general and systematic algorithm, recently developed by the authors, to the discrete classical situation. Moreover, extensions of this method allow to give new addition formulae and to estimate Cm(n)-asymptotics in limit relations between some families.

Analysis and modelling of emotional speech in spanish

Abstract: The importance of speech prosody for conveying emotional information has been extensively underlined in the literature. Major elements such as pitch, tempo and stress are presented as the main acoustic correlates of emotion in human speech. Nevertheless, as several authors have shown, voice quality is also a relevant feature in emotion recognition. In this paper, we present the prosodic analysis, modelling and evaluation of the Spanish Emotional Speech Database including four emotions: happiness, sadness, cold anger and surprise. Our results show that, for Spanish, the contribution of prosody to the recognisability of the uttered emotion greatly varies from one to another, with sadness and surprise being more supra segmental, and happiness and cold anger being rather segmental.

Nonsinusoidal few-cycle pulsed light beams in free space

Abstract: We study a family of nonseparable solutions of the three-plus-one-dimensional paraxial wave equation in free space that represent ultrashort waveforms localized in time and space. We use them to develop a simple model for the spatiotemporal structure of ultrashort pulsed light beams, with only one or a few field oscillations of a nonsinusoidal nature. In the many-oscillation limit the model approaches the widely used separable models of modulated sinusoidal oscillations in time and of a Gaussian beam in space.