Showing papers by "Technical University of Madrid published in 2001"

Variability and genetic structure of plant virus populations.

Abstract: Populations of plant viruses, like all other living beings, are genetically heterogeneous, a property long recognized in plant virology. Only recently have the processes resulting in genetic variation and diversity in virus populations and genetic structure been analyzed quantitatively. The subject of this review is the analysis of genetic variation, its quantification in plant virus populations, and what factors and processes determine the genetic structure of these populations and its temporal change. The high potential for genetic variation in plant viruses, through either mutation or genetic exchange by recombination or reassortment of genomic segments, need not necessarily result in high diversity of virus populations. Selection by factors such as the interaction of the virus with host plants and vectors and random genetic drift may in fact reduce genetic diversity in populations. There is evidence that negative selection results in virus-encoded proteins being not more variable than those of their hosts and vectors. Evidence suggests that small population diversity, and genetic stability, is the rule. Populations of plant viruses often consist of a few genetic variants and many infrequent variants. Their distribution may provide evidence of a population that is undifferentiated, differentiated by factors such as location, host plant, or time, or that fluctuates randomly in composition, depending on the virus.

Millions at risk: defining critical climate change threats and targets

Abstract: Agreements to mitigate climate change have been hampered by several things, not least their cost. But the cost might well be more acceptable if we had a clear picture of what damages would be avoided by different levels of emissions reductions, in other words, a clear idea of the pay off. The problem is that we do not. The Third Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) published this year (IPCC (2001a) and IPCC (2001b)) lists a wide range of potential impacts but has difficulty in discriminating between those that are critical in their nature and magnitude from those that are less important. Yet, the identification of critical impacts (e.g. ones that should be avoided at any reasonable cost) is obviously a key to addressing targets for mitigating climate change. Indeed, a central objective of the UN Framework Objective on Climate Change (UNFCCC) is to avoid “dangerous levels” of climate change that could threaten food security, ecosystems and sustainable development (areas of risk that are specifically mentioned in UNFCCC Article 2). For several years, we have been researching impacts in key areas of risk: hunger, water shortage, exposure to malaria transmission, and coastal flooding, as part of a global fast-track assessment (Parry and Livermore, 1999). 1 The results of our work have been reported widely and form a significant part of the IPCC's assessment of likely impacts (IPCC (2001a) and IPCC (2001b)). But they are scattered through different parts of the IPCC report and other literature and, before now, we have not brought them together. For this review, we have graphed our estimates of effects as a single measure: the additional millions of people who could be placed at risk as a result of different amounts of global warming ( Fig. 1). Full-size image (36K) - Opens new window Full-size image (36K) Fig. 1. Additional millions at risk due to climate change in 2050s and 2080s for hunger, coastal flooding, water shortage and malaria. The width of the curve indicates one standard deviation of variance around the mean, based on results from four HadCM2 experiments (Parry and Livermore, 1999; IPCC, 2000). Solid lines indicate model-based estimates. Dotted lines are inferred ( IPCC (2001a) and IPCC, 2001b. Climate change 2001: The Scientific Basis. Technical Summary of the Working Group I Report, Geneva, 2001.IPCC (2001b)) and intended as schematic. Stab. 450 (etc.)=stabilisation@450 ppmv (etc.). View Within Article The figure shows the increase in millions at risk due to higher temperatures for two time periods—2050s and 2080s. The analysis takes into account likely non-climate developments such as growth in population, and income and developments of technology, and these become important assumptions behind future trends in, for example, increases in crop yield and the building of coastal defences. These developments themselves have very great effects on the numbers at risk and represent a (non-climate change) reference case. The graph thus shows the additional millions at risk due specifically to estimated future changes in climate. But now for the caveats: the reference case is only for one future world (what the IPCC used to call a best estimate or “business-as-usual” future, now referred to as IS92a). More recently, the IPCC has explored a set of six different developmental pathways that the world may follow (IPCC, 2000), and the millions at risk in these alternative futures will certainly differ. Our work on these is in hand but will probably take a year to complete. We need also to emphasise that the graph is a global estimate which hides important regional variations and, so far, it is based on one model of future climate patterns (the UK's Hadley Centre second generation global climate model) ( Johns et al., 1997). While these are the only global impact estimates currently available, we need urgently to complete similar ones for different climate models and for a variety of development pathways. Five important points emerge from this figure. First, the curves of additional millions at risk generally become steeper over time. Less obviously, this results as much from a larger and more vulnerable exposed population in 2080 than in 2050, as from increases in temperature or inferred changes in precipitation and sea-level rise. For example, the remarkable steepness of the water shortage curve in 2080 is the outcome of very large city populations in China and India becoming newly at risk. In the case of hunger, however, the rising curve in 2080 stems from widespread heat stress of crops, while up to about 2050 lesser amounts of warming lead to yield gains in temperate regions that balance losses elsewhere and lead to only small net increases in hunger (Parry and Livermore, 1999). These complex interactions between exposure and climate change tell a clear story: there will be more millions at risk as time progresses. Secondly, the figure indicates how much we need to reduce emissions in order to draw-down significantly the numbers at risk. We have estimated effects assuming that atmospheric concentrations of CO2 are stabilised at 750 parts per million (ppmv) by 2250 and at 550 ppmv by 2150 (Arnell, in press). These are approximately equivalent, respectively, to 10 times and 20 times the reduction in emissions assumed in the Kyoto Protocol. The 750 ppmv target delays the damage but does not avoid it. By 2080, it would halve the number at risk from hunger and flooding, reduce the population at risk of malaria by perhaps a third and water shortage by about a quarter. But to bring risk levels down from hundreds to tens of millions would require a stabilisation target of about 550 ppmv. We have also indicated on the graph, but only in a schematic form, the approximate locations of 450, 650 and 1000 ppmv stabilisation pathways and their effect on millions at risk (IPCC (2001a) and IPCC (2001b)). Although impact analyses have not yet been conducted for these stabilisation levels, it appears that the 450 ppmv pathway would achieve very great reductions in millions at risk, although very high costs of mitigation would be incurred. It is precisely this kind of pay-off that needs to be analysed properly. A third conclusion is that information is now available that can help inform the selection of climate change targets. Thus far these targets, such as Kyoto, have been chosen in broadly a top–down manner, without clear knowledge of the impacts that would be avoided, and that has been partly their weakness. Now we may argue, for example, that in order to keep damages below an agreed tolerable level (for example, a given number of additional people at risk) global temperature increases would need to be kept below a given amount; and emissions targets could then be developed to achieve that objective. Fourthly, it is clear that mitigation alone will not solve the problem of climate change. Adaptation will be necessary to avoid, or at least reduce, much of the possible damage, and since we need many of the benefits of adaptation today, regardless of climate change in the future (e.g. increased drought protection of agriculture, improved flood defences, more efficient use of water, better malaria control), many of the adaptive strategies for climate change can be “win–win”. We need to find a blend of mitigation and adaptation to meet the challenge of climate change. Mitigation can buy time for adaptation (for example, delaying impacts until improved technology and management can handle them), and adaptation can raise thresholds of tolerance that need to be avoided by mitigation (for example, by increasing drought tolerance of crops). Considered separately, they appear inadequate to meet such a challenge, but combined they would make a powerful response.

Extended lexicographic goal programming: a unifying approach

Abstract: This article starts reviewing the satisficing philosophy of Goal Programming (GP) and interpreting their solutions from the point of view of the utility theory. This interpretation leads to a very general optimisation structure called Extended Lexicographic Goal Programming (ELGP). It is then demonstrated that there are a significant number of Multiple Criteria Decision Making (MCDM) approaches that, from a logical point of view, can be reduced to the ELGP structure. The paper ends assessing the theoretical and practical advantages of the proposed unified approach.

Effect of irrigation on changes in the anthocyanin composition of the skin of cv Tempranillo (Vitis vinifera L) grape berries during ripening

Abstract: The impact of water availability on the yield and on the chemical composition in the skins of cv Tempranillo grapes at different phases of berry growth was studied over a 2 year period by determining changes in berry weight, °Brix, titratable acidity, pH and different phenolic compounds. The evolution of phenolic compounds during berry growth followed similar patterns to those reported by previous investigators. Over the 2 year study, concentrations of total phenols and total tannins in the skins were always higher for the non-irrigated than for the irrigated vines, though the differences were not significant on some sampling dates. Total anthocyanin concentrations in 1992 were significantly higher in the non-irrigated than in the irrigated grapes, except at veraison and harvest. In contrast, in 1993, concentrations were higher in the non-irrigated grapes on the first three sampling dates and in the irrigated grapes on the last three sampling dates, but with significant differences only on day 136 after budbreak. In the first year, anthocyanin concentrations for the non-irrigated grapes were higher than for the irrigated grapes, except at harvest, though the differences at harvest were not significant. However, in the second year, concentrations in the berries from the irrigated vines were significantly higher on most sampling dates. In both years, concentrations of the five anthocyanins at harvest were higher for the irrigated treatment, the treatment that produced higher berry weights and crop yields. © 2001 Society of Chemical Industry

Evaluation of ontologies

Abstract: The evaluation of ontologies is an emerging field. At present, there is an absence of a deep core of preliminary ideas and guidelines for evaluating ontologies. This paper presents a brief summary of previous work done on evaluating ontologies and the criteria (consistency, completeness, conciseness, expandability, and sensitiveness) used to evaluate and to assess ontologies. It also addresses the possible types of errors made when domain knowledge is structured in taxonomies in an ontology and in knowledge bases: circularity errors, exhaustive and nonexhaustive class partition errors, redundancy errors, grammatical errors, semantic errors, and incompleteness errors. It also describes the process followed to evaluate the standard-units ontology already published at the Ontology Server.

III nitrides and UV detection

Abstract: III nitrides have become the most exciting challenge in optoelectronic materials in the last decade. Their intrinsic properties and an intense technological effort have made possible the fabrication of reliable and versatile detectors for short wavelengths. In this work, materials and devices issues are considered to provide a full picture of the advances in nitride UV photodetection. First, basic structures like photoconductors, Schottky, p-i-n and metal-semiconductor-metal photodiodes and phototransistors are compared, with emphasis on their specific properties and performance limitations. The efforts in the design and fabrication of more advanced detectors, in the search for higher quantum efficiency, contrast, signal-to-noise or speed operation, are reviewed afterwards. Metal-insulator-semiconductor diodes, avalanche photodetectors and GaN array detectors for UV imaging are also described. Further device optimization is linked with present materials issues, mainly due to the nitride quality, which is a direct result of the substrate used. The influence of substrates and dislocations on detector behaviour is discussed in detail. As an example of AlGaN photodetector applications, monitoring of the solar UV-B radiation to prevent erythema and skin cancer is presented.

Ten years of genetic fuzzy systems: current framework and new trends

Abstract: Although fuzzy systems demonstrated their ability to solve different kinds of problems in various applications, there is an increasing interest on augmenting them with learning capabilities. Two of the most successful approaches to hybridise fuzzy systems with adaptation methods have been made in the realm of soft computing: neuro-fuzzy systems and genetic fuzzy systems hybridise the approximate reasoning method of fuzzy systems with the learning capabilities of neural networks and evolutionary algorithms. The article focuses on genetic fuzzy systems, paying special attention to genetic fuzzy rule based systems, giving a brief overview of the field.

Parallel execution of prolog programs: a survey

Abstract: Since the early days of logic programming, researchers in the field realized the potential for exploitation of parallelism present in the execution of logic programs. Their high-level nature, the presence of nondeterminism, and their referential transparency, among other characteristics, make logic programs interesting candidates for obtaining speedups through parallel execution. At the same time, the fact that the typical applications of logic programming frequently involve irregular computations, make heavy use of dynamic data structures with logical variables, and involve search and speculation, makes the techniques used in the corresponding parallelizing compilers and run-time systems potentially interesting even outside the field. The objective of this article is to provide a comprehensive survey of the issues arising in parallel execution of logic programming languages along with the most relevant approaches explored to date in the field. Focus is mostly given to the challenges emerging from the parallel execution of Prolog programs. The article describes the major techniques used for shared memory implementation of Or-parallelism, And-parallelism, and combinations of the two. We also explore some related issues, such as memory management, compile-time analysis, and execution visualization.

Partial filling of a quantum dot intermediate band for solar cells

Abstract: This paper describes how to partially fill the intermediate band formed by the confined states of quantum dots with electrons. Efficiencies of up to 63.2% have been calculated in ideal cases for solar cells with this intermediate band. In order to achieve this, the barrier region is n-doped so that the electrons delivered by the donors fall into the otherwise empty intermediate band states. This method produces a fully space-charged structure whose electrostatic properties are studied in this paper, thus confirming the feasibility of the proposed method. Partial filling of the intermediate band is necessary to provide strong absorption in transitions from it to both the valence and the conduction bands.

WebODE: a scalable workbench for ontological engineering

Abstract: This paper presents WebODE as a workbench for ontological engineering that not only allows the collaborative edition of ontologies at the knowledge level, but also provides a scalable architecture for the development of other ontology development tools and ontology-based applications. First, we will describe the knowledge model of WebODE, which has been mainly extracted and improved from the reference model of METHONTOLOGY's intermediate representations. Later, we will present its architecture, together with the main functionalities of the WebODE ontology editor, such as its import/export service, translation services, ontology browser, inference engine and axiom generator, and some services that have been integrated in the workbench: WebPicker, OntoMerge and the OntoCatalogue.

Power factor correction: a survey

Abstract: New recommendations and future standards have increased the interest in power factor correction circuits. There are multiple solutions to this problem to obtain sinusoidal line current and in addition, a great number of circuits have been proposed with nonsinusoidal line current. In this paper, a review of the most interesting solutions for single phase applications is carried out. They are classified attending to the line current waveform, energy processing, number of switches, control loops, etc. The major advantages and disadvantages are highlighted and the field of application is found.

Growth, leaf morphology, water use and tissue water relations of Eucalyptus globulus clones in response to water deficit

Abstract: Changes in leaf size, specific leaf area (SLA), transpiration and tissue water relations were studied in leaves of rooted cuttings of selected clones of Eucalyptus globulus Labill. subjected to well-watered or drought conditions in a greenhouse. Significant differences between clones were found in leaf expansion and transpiration. There was a significant clone × treatment interaction on SLA. Water stress significantly reduced osmotic potential at the turgor loss point (Π 0 ) and at full turgor (Π 100 ), and significantly increased relative water content at the turgor loss point and maximum bulk elastic modulus. Differences in tissue water relations between clones were significant only in the mild drought treatment. Among clones in the drought treatments, the highest leaf expansion and the highest increase in transpiration during the experiment were measured in those clones that showed an early and large decrease in Π 0 and Π 100 .

Mechanical properties of directionally solidified Al2O3–ZrO2(Y2O3) eutectics

Abstract: The relationship between microstructure and mechanical properties was studied in Al2O3–ZrO2 eutectic rods The material, produced by directional solidification using the laser-heated float zone method, was formed mainly of colonies consisting of a fine interpenetrating or ordered network of ZrO2 and α-Al2O3 surrounded by a thick boundary region that contained pores and other defects The flexure strength of the eutectic rods was excellent (>11 GPa) owing to the small critical defect size and the high toughness (78 MPa m ) No microstructural changes were observed after about 1 h of exposure at 1700 K, and the eutectic oxide maintained a very high strength up to this temperature The nature of the critical defects that led to fracture, the toughening micromechanisms, and the differences between the longitudinal and transverse strength are discussed in the light of the microstructural features of the material

Knowledge-based models for emergency management systems

Abstract: This paper proposes the use of advanced knowledge models to support environmental emergency management as an adequate response to the current needs and technology. A generic architecture embodying the knowledge pieces required to manage emergencies in different kinds of problem scenarios is described. Simulation models of the physical system, integrated as part of the knowledge architecture, are also claimed to be adequate, both from the point of view of the knowledge model calibration and the training of the emergency personnel as well. The feasibility of the approach has been demonstrated with the application of the generic model to a particular real world problem: the management of flood emergencies in the Jucar river basin area (Spain). This work was developed in the framework of ARTEMIS, a European Commission research project.

DFT-based channel estimation in 2D-pilot-symbol-aided OFDM wireless systems

Abstract: An efficient channel estimation algorithm for OFDM in wireless applications has been proposed. Two-dimensional pilot-symbol assisted modulation (2D-PSAM) is employed in coherent OFDM for channel estimation and it is based on inserting known symbols spreaded throughout the 2D time-frequency grid. These scattered symbols are employed to perform an estimation of the channel's frequency response. At a first stage, if certain requirements are fulfilled, channel estimation in frequency dimension can be carried out with an efficient DFT-based algorithm, which provides an accurate estimation at time positions where pilot symbols are included. In the second step, linear interpolation is performed in the time direction. This scheme has been proven to be very successful in multicarrier HF communications systems.

Thermodynamic consistency of sub-bandgap absorbing solar cell proposals

Abstract: This paper proves, using thermodynamic arguments, that ideal multiple quantum well (MQW) solar cells cannot exceed the efficiency of ideal ordinary solar cells unless carriers in the well are pumped by the absorption of a second photon. In this case, the cells behave identically to the intermediate band (IB) solar cell that allows for sub-band photon absorption. It is also proven that the IB solar cell complies with the second law of thermodynamics and, in this way, the theoretical potential of this cell for achieving efficiencies of 63.2% as compared to the 40.7% of ordinary cells, is confirmed.

Tensile properties of Argiope trifasciata drag line silk obtained from the spider's web

Abstract: The tensile properties of Argiope trifasciata (Argiopidae) drag line silk retrieved from mooring threads in the web were characterized. Scanning electron microscope images were used to determine the cross-sectional area of the samples, allowing force-displacement plots to be rescaled as stress–strain curves and to characterize fracture surfaces. Twenty-eight samples were tested to obtain statistically significant values of the mechanical parameters (elastic modulus, stress and strain at the proportional limit, and tensile strength). The tensile strength of the material was subjected to a Weibull analysis—the first time that this has been attempted with a spider silk. A low value of the Weibull modulus, m = 3.4, was obtained, demonstrating that drag line monofilament does not have a sufficiently reliable tensile strength to function as an engineering material on its own. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2245–2251, 2001

Real-Time Spectrum Analysis in Microstrip Technology

Abstract: We report on a time-domain analog to the spatial far-field Fraunhofer diffraction using microstrip lines with chirped distributed Bragg coupling between the fundamental microstrip mode and the same but counter-propagating mode. The chirping of the microstrip impedance yields to linear group delays within the reflected bandwidth. Under the condition of a temporal equivalent of the spatial Fraunhofer inequality, the distortion of a frequency-limited pulse results in an output reflected signal whose complex envelope is, except a phase factor, proportional to the Fourier Transform of the input pulse envelope. This has important temporal applications and, in particular, the devices designed in this paper work as real-time energy spectral density analyzers.

Use of silane agents and poly(propylene-g-maleic anhydride) copolymer as adhesion promoters in glass fiber/polypropylene composites

Abstract: Two organofunctional silanes and a copolymer were used to increase the interfacial adhesion in glass fiber polypropylene (PP) reinforced composites. The performance of the coupling agents was investigated by means of mechanical property measurements, scanning electron microscopy (SEM), and dynamic mechanical analysis. The increased adhesion between the glass fibers and PP matrix observed with SEM resulted in an improvement of the mechanical and dynamic mechanical properties of the composites. Coupling achieved with the copolymer poly(propylene-g-maleic anhydride) (PP-g-MA) proved to be the most successful compared with 3-aminopropyltrimethoxysilane and 3-aminopropyltriethoxysilane. The combination of PP-g-MA with the silanes resulted in further property improvements because of the ability of the MA groups to react with the amino groups of the silanes.