Showing papers by "University of Oviedo published in 2006"

Spin and molecular electronics in atomically generated orbital landscapes

Abstract: Ab initio computational methods for electronic transport in nanoscaled systems are an invaluable tool for the design of quantum devices. We have developed a flexible and efficient algorithm for evaluating I-V characteristics of atomic junctions, which integrates the nonequilibrium Green’s function method with density functional theory. This is currently implemented in the package SMEAGOL. The heart of SMEAGOL is our scheme for constructing the surface Green’s functions describing the current-voltage probes. It consists of a direct summation of both open and closed scattering channels together with a regularization procedure of the Hamiltonian and provides great improvements over standard recursive methods. In particular it allows us to tackle material systems with complicated electronic structures, such as magnetic transition metals. Here we present a detailed description of SMEAGOL together with an extensive range of applications relevant for the two burgeoning fields of spin and molecular electronics.

Bladder Cancer and Exposure to Water Disinfection By-Products through Ingestion, Bathing, Showering, and Swimming in Pools

Abstract: Bladder cancer has been associated with exposure to chlorination by-products in drinking water, and experimental evidence suggests that exposure also occurs through inhalation and dermal absorption. The authors examined whether bladder cancer risk was associated with exposure to trihalomethanes (THMs) through ingestion of water and through inhalation and dermal absorption during showering, bathing, and swimming in pools. Lifetime personal information on water consumption and water-related habits was collected for 1,219 cases and 1,271 controls in a 1998-2001 case-control study in Spain and was linked with THM levels in geographic study areas. Long-term THM exposure was associated with a twofold bladder cancer risk, with an odds ratio of 2.10 (95% confidence interval: 1.09, 4.02) for average household THM levels of >49 versus 35 micro g/day through ingestion had an odds ratio of 1.35 (95% confidence interval: 0.92, 1.99). The odds ratio for duration of shower or bath weighted by residential THM level was 1.83 (95% confidence interval: 1.17, 2.87) for the highest compared with the lowest quartile. Swimming in pools was associated with an odds ratio of 1.57 (95% confidence interval: 1.18, 2.09). Bladder cancer risk was associated with long-term exposure to THMs in chlorinated water at levels regularly occurring in industrialized countries.

The use of luminescent quantum dots for optical sensing

Abstract: Semiconductor nanocrystals, known as “quantum dots” (QDs), have demonstrated several remarkable, attractive optoelectronic characteristics especially suited to analytical applications in the (bio)chemical field. We review progress in exploiting the attractive luminescent properties of QDs in designing novel probes for chemical and biochemical optical sensing.

Search for neutral MSSM Higgs bosons at LEP

Abstract: The four LEP collaborations, ALEPH, DELPHI, L3 and OPAL, have searched for the neutral Higgs bosons which are predicted by the Minimal Supersymmetric standard model (MSSM). The data of the four collaborations are statistically combined and examined for their consistency with the background hypothesis and with a possible Higgs boson signal. The combined LEP data show no significant excess of events which would indicate the production of Higgs bosons. The search results are used to set upper bounds on the cross-sections of various Higgs-like event topologies. The results are interpreted within the MSSM in a number of “benchmark” models, including CP-conserving and CP-violating scenarios. These interpretations lead in all cases to large exclusions in the MSSM parameter space. Absolute limits are set on the parameter cosβ and, in some scenarios, on the masses of neutral Higgs bosons.

Fine-Tuning of Algorithms Using Fractional Experimental Designs and Local Search

Abstract: Researchers and practitioners frequently spend more time fine-tuning algorithms than designing and implementing them. This is particularly true when developing heuristics and metaheuristics, where the right choice of values for search parameters has a considerable effect on the performance of the procedure. When testing metaheuristics, performance typically is measured considering both the quality of the solutions obtained and the time needed to find them. In this paper, we describe the development of CALIBRA, a procedure that attempts to find the best values for up to five search parameters associated with a procedure under study. Because CALIBRA uses Taguchis fractional factorial experimental designs coupled with a local search procedure, the best values found are not guaranteed to be optimal. We test CALIBRA on six existing heuristic-based procedures. These experiments show that CALIBRA is able to find parameter values that either match or improve the performance of the procedures resulting from using the parameter values suggested by their developers. The latest version of CALIBRA can be downloaded for free from the website that appears in the online supplement of this paper at http://or.pubs.informs.org/Pages.collect.html.

Candida antarctica Lipase B: An Ideal Biocatalyst for the Preparation of Nitrogenated Organic Compounds

Abstract: Candida antarctica lipase B (CAL-B) is a very effective catalyst for the production of amines and amides using different enzymatic procedures. Simplicity of use, low cost, commercial availability and recycling possibility make this lipase an ideal tool for the synthesis and resolution of a wide range of nitrogenated compounds that can be used for the production of pharmaceuticals and interesting manufactures in the industrial sector.

Intensity of tennis match play

Abstract: This review focuses on the characteristics of tennis players during match play and provides a greater insight into the energy demands of tennis. A tennis match often lasts longer than an hour and in some cases more than five hours. During a match there is a combination of periods of maximal or near maximal work and longer periods of moderate and low intensity activity. Match intensity varies considerably depending on the players' level, style, and sex. It is also influenced by factors such as court surface and ball type. This has important implications for the training of tennis players, which should resemble match intensity and include interval training with appropriate work to rest ratios.

Lipases: Useful biocatalysts for the preparation of pharmaceuticals

Abstract: Biocatalysis offers a clean and ecological way to perform chemical processes, in mild reaction conditions and with high degree of selectivity. The use of enzymes, specially lipases, in organic solvents proves an excellent methodology for the preparation of single-isomer chiral drugs. This review covers some general aspects and representative examples of the use of lipases for the enantioselective or regioselective preparation of alcohol and amine intermediates in the synthesis of pharmaceuticals.

A Molecular Energy Decomposition Scheme for Atoms in Molecules.

Abstract: An exact energy partition method based on a physically sound decomposition of the nondiagonal first-order and diagonal second-order density matrices put forward by Li and Parr (J. Chem. Phys. 1986, 84, 1704) is presented. The method splits the total energy into intra- and interatomic components and is applicable on quite general wave functions. To explore it numerically, the energy components of three test molecules (H2, N2, and LiH) have been computed using four different partitions of the charge density ρ(r) into atomic densities. Several aspects on the chemical bond and the relative importance of different components of the binding energy are analyzed. The merits of different partitions of ρ(r) are also discussed.

A continental scale evaluation of the role of limpet grazing on rocky shores

Abstract: It is critical for our knowledge of biodiversity and ecosystem processes to understand how individual species contribute to ecosystem processes and how these contributions vary in space and time. We used a manipulative field experiment in five locations over 17° of latitude [from southern Portugal to the Isle of Man (British Isles)] to determine the relative response of rocky intertidal algal assemblages released from control by the grazing of limpets. Response ratios showed that when limpets were removed there was a trend of effects from north to south. In the north, grazing had a strong effect on algal assemblages, but removing grazers reduced spatial variability in assemblages. In the south, the effect of limpet grazing was far weaker and removal of grazers had a much reduced impact on spatial variability. Here we show a clear trophic control of an ecosystem in that grazing by limpets not only determines macroalgal abundance overall but also modifies ecosystem stability via variability in cover of algae.

Antecedents of the difference in perceived risk between store brands and national brands

Abstract: Purpose – The present study sets out to analyze the effects that a set of variables related to purchasing behaviour has on the difference in perceived risk between store brands and national brands.Design/methodology/approach – The methodology proposed to achieve the objective consists of analyzing the existing relationship between different aspects relating to purchasing behaviour of the consumer and the difference in perceived risk between the two types of brands through a causal and integrated model. Such a model covers both the direct effects and the indirect effects caused by these variables jointly. In order to do so data were obtained from two groups of people, which has allowed for cross‐validation of the methodology used, which, in turn, permitted a greater generalization of the results.Findings – The variables which have proven to be most relevant when explaining this difference are the perceived quality of the store as opposed to that of the national brands, familiarity with the store brands and...

Interpreting and Testing the Scaling Property in Models where Inefficiency Depends on Firm Characteristics

Abstract: Let u ≥ 0 be technical inefficiency, let z be a set of variables that affect u, and let δ be the parameters of this relationship. The model satisfies the scaling property if u(z, δ) can be written as a scaling function h(z, δ) times a random variable u* that does not depend on z. This property implies that changes in z affect the scale but not the shape of u(z,δ). This paper reviews the existing literature and identifies models that do and do not have the scaling property. It also discusses practical advantages of the scaling property. The paper shows how to test the hypothesis of scaling, and other interesting hypotheses, in the context of the model of Wang, Journal of Productivity Analysis, 2002. Finally, two empirical examples are given.

The nature of the hydrogen bond: a synthesis from the interacting quantum atoms picture.

Abstract: The interacting quantum atoms approach [IQA, as presented by Blanco et al., J. Chem. Theory Comput. 1, 1096 (2005)] is applied to standard hydrogen bonded dimers. IQA is an interpretation tool based on a real space energy decomposition scheme fully consistent with the quantum theory of atoms in molecules. It provides a partition of every physical term present in the Hamiltonian into atomic and interatomic contributions. The procedure is orbital-free and self-contained, needing neither external references nor artificial intermediate states. Binding is the result of a competition between the destabilizing deformations suffered by the interacting fragments upon interaction and the stabilizing interaction energy itself. According to IQA, there is no incompatibility between the prevalent electrostatic image of hydrogen bonded systems and that favoring important covalent contributions. Depending on how we gather the different energetic terms, we may recover electrostatic or covalent pictures from the same under...

Human Resource Management as a Determining Factor in Organizational Learning

Abstract: The role of human resource management in learning organizations has been discussed by a number of researchers. It is suggested that some of the more traditional personnel functions of HR practitioners may be tailored to encourage a focus on learning and thus to help achieve organizational goals. However, there is a lack of empirical studies that explore the relationship between human resource management and organizational learning. This article aims to address this shortcoming. More specifically, the purpose of this article is to analyse the relation between four human resources practices (hiring, training, compensation and decision-making) and organizational learning. The hypotheses proposed were tested on a sample of 195 Spanish companies using the structural equation modelling technique. The results support that selective hiring, strategic training and employee participation in decision-making positively influence organizational learning.

Paleobiology and comparative morphology of a late Neandertal sample from El Sidrón, Asturias, Spain

Abstract: Fossil evidence from the Iberian Peninsula is essential for understanding Neandertal evolution and history. Since 2000, a new sample ≈43,000 years old has been systematically recovered at the El Sidron cave site (Asturias, Spain). Human remains almost exclusively compose the bone assemblage. All of the skeletal parts are preserved, and there is a moderate occurrence of Middle Paleolithic stone tools. A minimum number of eight individuals are represented, and ancient mtDNA has been extracted from dental and osteological remains. Paleobiology of the El Sidron archaic humans fits the pattern found in other Neandertal samples: a high incidence of dental hypoplasia and interproximal grooves, yet no traumatic lesions are present. Moreover, unambiguous evidence of human-induced modifications has been found on the human remains. Morphologically, the El Sidron humans show a large number of Neandertal lineage-derived features even though certain traits place the sample at the limits of Neandertal variation. Integrating the El Sidron human mandibles into the larger Neandertal sample reveals a north–south geographic patterning, with southern Neandertals showing broader faces with increased lower facial heights. The large El Sidron sample therefore augments the European evolutionary lineage fossil record and supports ecogeographical variability across Neandertal populations.

Brønsted Acid‐Catalyzed Nucleophilic Substitution of Alcohols

Abstract: Simple Bronsted acids such as p-toluenesulfonic acid monohydrate (PTS) or polymer-bound p-toluenesulfonic acid efficiently catalyze the direct nucleophilic substitution of the hydroxy group of allylic and benzylic alcohols with a large variety of carbon- and heteroatom-centered nucleophiles. Reaction conditions are mild, the process is conducted under an atmosphere of air without the need for dried solvents, and water is the only side product of the reaction.

The invasibility of marine algal assemblages: role of functional diversity and identity

Abstract: The emergence of the biodiversity-ecosystem functioning debate in the last decade has renewed interest in understanding why some communities are more easily invaded than others and how the impact of invasion on recipient communities and ecosystems varies. To date most of the research on invasibility has focused on taxonomic diversity, i.e., species richness. However, functional diversity of the communities should be more relevant for the resistance of the community to invasions, as the extent of functional differences among the species in an assemblage is a major determinant of ecosystem processes. Although coastal marine habitats are among the most heavily invaded ecosystems, studies on community invasibility and vulnerability in these habitats are scarce. We carried out a manipulative field experiment in tide pools of the rocky intertidal to test the hypothesis that increasing functional richness reduces the susceptibility of macroalgal communities to invasion. We selected a priori four functional groups on the basis of previous knowledge of local species characteristics: encrusting, turf, subcanopy, and canopy species. Synthetic assemblages containing one, two, three, or four different functional groups of seaweeds were created, and invasion by native species was monitored over an eight-month period. Cover and resource availability in the assemblages with only one functional group showed different patterns in the use of space and light, confirming true functional differences among our groups. Experimental results showed that the identity of functional groups was more important than functional richness in determining the ability of macroalgal communities to resist invasion and that resistance to invasion was resource-mediated.

Deciphering the biosynthesis pathway of the antitumor thiocoraline from a marine actinomycete and its expression in two Streptomyces species

Abstract: Thiocoraline is a thiodepsipeptide antitumor compound produced by two actinomycetes Micromonospora sp. ACM2-092 and Micromonospora sp. ML1, isolated from two marine invertebrates (a soft coral and a mollusc) found of the Indian Ocean coast of Mozambique. By using oligoprimers derived from nonribosomal peptide synthetase (NRPS) consensus sequences, six PCR fragments containing putative NRPS adenylation domains were amplified from the chromosome of Micromonospora sp. ML1. Insertional inactivation of each adenylation domain showed that two of them generated nonproducing mutants, thereby indicating that these domains were involved in thiocoraline biosynthesis. Sequencing of a 64.6 kbp DNA region revealed the presence of 36 complete open reading frames (ORFs) and two incomplete ones. Heterologous expression of a region of about 53 kbp, containing 26 of the ORFs, in Streptomyces albus and S. lividans led to the production of thiocoraline in these streptomycetes. Surprisingly, the identified gene cluster contains more NRPS modules than expected on the basis of the number of amino acids of thiocoraline. TioR and TioS would most probably constitute the NRPS involved in the biosynthesis of the thiocoraline backbone, according to the colinearity of the respective modules. It is proposed that two other NRPSs, TioY and TioZ, could be responsible for the biosynthesis of a small peptide molecule which could be involved in regulation of the biosynthesis of thicoraline in Micromonospora sp. ML1. In addition, a pathway is proposed for the biosynthesis of the unusual starter unit, 3-hydroxy-quinaldic acid.

Comparison of step length estimators from weareable accelerometer devices.

Abstract: Wearable accelerometry provides easily portable systems that supply real-time data adequate for gait analysis. When they do not provide direct measurement of a spatio- temporal parameter of interest, such as step length, it has to be estimated with a mathematical model from indirect sensor measurements. In this work we are concerned with the accelerometry-based estimation of the step length in straight line human walking. We compare five step length estimators. Measurements were taken from a group of four adult men, adding up a total of 800m per individual of walking data. Also modifications to these estimators are proposed, based on biomechanical considerations. Results show that this modifications lead to improvements of interest over previous methods. I. INTRODUCTION Gait analysis is frequently calculated by means of video- based recording of markers placed at end-points of all or a subset of body segments. However, this equipment is not easily portable, it requires off-line digitizing that can be time consuming and automated real-time systems which can be costly. This makes these systems impractical for use by the average clinician in daily practice. Other measurement de- vices such as force-plates, electro-goniometres or electrodes to measure EMG signals (1) are not designed for usability. Conversely, accelerometry provides easily portable sys- tems that supply real-time data. In addition, these systems come at a decreased cost when compared to video motion analysis systems, making them easily available to a wide range of clinics. Precision and repetibility characteristics of accelerometry make it adequate for gait analysis (2), and it has been widely used recently, mainly in ambulatory diagnostic (3), (4), (5), (6), (7). However, such systems do not provide direct measure of several spatio-temporal parameters of interest such as step length, walking distance or walking velocity. Instead, they have to be estimated with a mathematical model from indirect sensor measurements. Specifically, in this work we are concerned with the accelerometry-based estimation of the step length in straight line human walking. For instance, there exist empirical relations between the step length and the maximum and minimum vertical ac- celeration of the body's center of mass (COM) (8). More frequently it is accepted a linear relation of the step length with the step frequency (9). Finally, clinical studies show that

The aureolic acid family of antitumor compounds: structure, mode of action, biosynthesis, and novel derivatives

Abstract: Members of the aureolic acid family are tricyclic polyketides with antitumor activity which are produced by different streptomycete species. These members are glycosylated compounds with two oligosaccharide chains of variable sugar length. They interact with the DNA minor groove in high-GC-content regions in a nonintercalative way and with a requirement for magnesium ions. Mithramycin and chromomycins are the most representative members of the family, mithramycin being used as a chemotherapeutic agent for the treatment of several cancer diseases. For chromomycin and durhamycin A, antiviral activity has also been reported. The biosynthesis gene clusters for mithramycin and chromomycin A(3) have been studied in detail by gene sequencing, insertional inactivation, and gene expression. Most of the biosynthetic intermediates in these pathways have been isolated and characterized. Some of these compounds showed an increase in antitumor activity in comparison with the parent compounds. A common step in the biosynthesis of all members of the family is the formation of the tetracyclic intermediate premithramycinone. Further biosynthetic steps (glycosylation, methylations, acylations) proceed through tetracyclic intermediates which are finally converted into tricyclic compounds by the action of a monooxygenase, a key event for the biological activity. Heterologous expression of biosynthetic genes from other aromatic polyketide pathways in the mithramycin producer (or some mutants) led to the isolation of novel hybrid compounds.