Procesos funcionales y eficacia de la escuela : un modelo causal.

Investigar sobre la eficacia de la enseñanza, las características de los profesores, los métodos de la enseñanza, las conductas del profesor en el aula y los nuevos desarrollos en la investigación de la enseñanza. 615 profesores del segundo ciclo de la EGB pertenecientes a 91 centros escolares, 77 estatales y 14 privados. Elabora y contrasta empíricamente un modelo causal orientado a explicar la estructura de relaciones e influencias existentes entre determinados procesos funcionales que se desarrollan en los centros escolares y los resultados educativos que se obtienen en ellos. Analiza la incidencia que tienen aspectos como el trabajo en equipo y la planificación en el centro, el papel de la dirección como elemento dinamizador, la organización y el clima general del centro. Utiliza cuestionarios. La técnica utilizada en la contrastación empírica del modelo es el path analysis, dada su capacidad para desarrolar un análisis causal de los fenómenos. Los resultados educativos de los centros escolares dependen de la conjunción de tres series de influencias: las procedentes del origen social del alumnado, las ligadas a la actuación del profesorado en las aulas y las que ejerce el centro escolar como tal a través de su funcionamiento y del clima general que lo caracteriza.

Dynamic causal modeling applied to fMRI data shows high reliability

Sensitivity, specificity, and reproducibility are vital to interpret neuroscientific results from functional magnetic resonance imaging (fMRI) experiments. Here we examine the scan–rescan reliability of the percent signal change (PSC) and parameters estimated using Dynamic Causal Modeling (DCM) in scans taken in the same scan session, less than 5 min apart. We find fair to good reliability of PSC in regions that are involved with the task, and fair to excellent reliability with DCM. Also, the DCM analysis uncovers group differences that were not present in the analysis of PSC, which implies that DCM may be more sensitive to the nuances of signal changes in fMRI data.

Analysis of the calving pattern of herds in small-scale dairy systems in central Mexico

This study sets out to find the best calving pattern for small-scale dairy systems in Michoacan State, central Mexico. Two models were built. First, a linear programming model was constructed to optimize calving pattern and herd structure according to metabolizable energy availability. Second, a Markov chain model was built to investigate three reproductive scenarios (good, average and poor) in order to suggest factors that maintain the calving pattern given by the linear programming model. Though it was not possible to maintain the optimal linear programming pattern, the Markov chain model suggested adopting different reproduction strategies according to period of the year that the cow is expected to calve. Comparing different scenarios, the Markov model indicated the effect of calving interval on calving pattern and herd structure.

Modelling heterotachy in phylogenetic inference by reversible-jump Markov chain Monte Carlo

The rate at which a given site in a gene sequence alignment evolves over time may vary. This phenomenon-known as heterotachy-can bias or distort phylogenetic trees inferred from models of sequence evolution that assume rates of evolution are constant. Here, we describe a phylogenetic mixture model designed to accommodate heterotachy. The method sums the likelihood of the data at each site over more than one set of branch lengths on the same tree topology. A branch-length set that is best for one site may differ from the branch-length set that is best for some other site, thereby allowing different sites to have different rates of change throughout the tree. Because rate variation may not be present in all branches, we use a reversible-jump Markov chain Monte Carlo algorithm to identify those branches in which reliable amounts of heterotachy occur. We implement the method in combination with our 'pattern-heterogeneity' mixture model, applying it to simulated data and five published datasets. We find that complex evolutionary signals of heterotachy are routinely present over and above variation in the rate or pattern of evolution across sites, that the reversible-jump method requires far fewer parameters than conventional mixture models to describe it, and serves to identify the regions of the tree in which heterotachy is most pronounced. The reversible-jump procedure also removes the need for a posteriori tests of 'significance' such as the Akaike or Bayesian information criterion tests, or Bayes factors. Heterotachy has important consequences for the correct reconstruction of phylogenies as well as for tests of hypotheses that rely on accurate branch-length information. These include molecular clocks, analyses of tempo and mode of evolution, comparative studies and ancestral state reconstruction. The model is available from the authors' website, and can be used for the analysis of both nucleotide and morphological data.

Inference on microsatellite mutation processes in the invasive mite, Varroa destructor, using reversible jump Markov chain Monte Carlo

Varroa destructor is a parasitic mite of the Eastern honeybee Apis cerana. Fifty years ago, two distinct evolutionary lineages (Korean and Japanese) invaded the Western honeybee Apis mellifera. This haplo-diploid parasite species reproduces mainly through brother sister matings, a system which largely favors the fixation of new mutations. In a worldwide sample of 225 individuals from 21 locations collected on Western honeybees and analyzed at 19 microsatellite loci, a series of de novo mutations was observed. Using historical data concerning the invasion, this original biological system has been exploited to compare three mutation models with allele size constraints for microsatellite markers: stepwise (SMM) and generalized (GSM) mutation models, and a model with mutation rate increasing exponentially with microsatellite length (ESM). Posterior probabilities of the three models have been estimated for each locus individually using reversible jump Markov Chain Monte Carlo. The relative support of each model varies widely among loci, but the GSM is the only model that always receives at least 9% support, whatever the locus. The analysis also provides robust estimates of mutation parameters for each locus and of the divergence time of the two invasive lineages (67,000 generations with a 90% credibility interval of 35,000-174,000). With an average of 10 generations per year, this divergence time fits with the last post-glacial Korea Japan land separation. (c) 2005 Elsevier Inc. All rights reserved.

Thermodynamic analysis of ferrous ion binding to Escherichia coli ferritin EcFtnA

Iron oxidation in the bacterial ferritin EcFtnA from Escherichia coli shows marked differences from its homologue human H-chain ferritin (HuHF). While the amino acid residues that constitute the dinuclear center in these proteins are highly conserved, EcFtnA has a third iron-binding site (C site) in close proximity to the dinuclear center that is seemingly responsible for these differences. Here, we describe the first thermodynamic study of Fe2+ binding to EcFtnA and its variants to determine the location of the primary ferrous ion-binding sites on the protein and to better understand the role of the third C site in iron binding. Isothermal titration calorimetric analyses of the wild-type protein reveal the presence of two main classes of binding sites in the pH range of 6.5-7.5, ascribed to Fe2+ binding, first at the A and then the B sites. Site-directed mutagenesis of ligands in the A, B, or C sites affects the apparent Fe2+-binding stoichiometries at the unaltered sites. The data imply some degree of inter- and intrasubunit negative cooperative interaction between sites. Unlike HuHF where only the A site initially binds Fe2+, both A and B sites in EcFtnA bind Fe2+, implying a role for the C site in influencing the binding of Fe2+ at the B site of the di-iron center of EcFtnA. The ITC equations describing a binding model for three classes of independent binding sites are reported here for the first time.

DNA variation in a 13-Mb region including the F9 gene: inferring the genealogical history and causal role of a hemophilia B mutation (IVS 5+13 A -> G)

About 5.5% of all UK hemophilia B patients have the base substitution IVS 5+13 A-->G as the only change in their factor (F)IX gene (F9). This generates a novel donor splice site which fits the consensus better than the normal intron 5 donor splice. Use of the novel splice site should result in a missense mutation followed by the abnormal addition of four amino acids to the patients' FIX. In order to explain the prevalence of this mutation, its genealogical history is examined. Analysis of restriction fragment length polymorphism in the 21 reference UK individuals (from different families) with the above mutation showed identical haplotypes in 19 while two differed from the rest and from each other. In order to investigate the history of the mutation and to verify that it had occurred independently more than once, the sequence variation in 1.5-kb segments scattered over a 13-Mb region including F9 was examined in 18 patients and 15 controls. This variation was then analyzed with a recently developed Bayesian approach that reconstructs the genealogy of the gene investigated while providing evidence of independent mutations that contribute disconnected branches to the genealogical tree. The method also provides minimum estimates of the age of the mutation inherited by the members of coherent trees. This revealed that 17 or 18 mutant genes descend from a founder who probably lived 450 years ago, while one patient carries an independent mutation. The independent recurrence of the IVS5+13 A-->G mutation strongly supports the conclusion that it is the cause of these patients' mild hemophilia.

Population subdivision and molecular sequence variation: Theory and analysis of Drosophila ananassae data

Population subdivision complicates analysis of molecular variation. Even if neutrality is assumed, three evolutionary forces need to be considered: migration, mutation, and drift. Simplification can be achieved by assuming that the process of migration among and drift within subpopulations is occurring fast compared to Mutation and drift in the entire population. This allows a two-step approach in the analysis: (i) analysis of population subdivision and (ii) analysis of molecular variation in the migrant pool. We model population subdivision using an infinite island model, where we allow the migration/drift parameter Theta to vary among populations. Thus, central and peripheral populations can be differentiated. For inference of Theta, we use a coalescence approach, implemented via a Markov chain Monte Carlo (MCMC) integration method that allows estimation of allele frequencies in the migrant pool. The second step of this approach (analysis of molecular variation in the migrant pool) uses the estimated allele frequencies in the migrant pool for the study of molecular variation. We apply this method to a Drosophila ananassae sequence data set. We find little indication of isolation by distance, but large differences in the migration parameter among populations. The population as a whole seems to be expanding. A population from Bogor (Java, Indonesia) shows the highest variation and seems closest to the species center.

Stabilization of a helical water chain in a metal-organic host of a trinuclear Schiff base complex

Three heterometallic trinuclear Schiff base complexes, [{GuL(1)(H2O)}(2)Ni(CN)(4)]center dot 4H(2)O (1), [{CuL2(H2O)}(2)Ni(CN)(4)] (2), and [{CuL3(H2O)}(2)Ni(CN)(4)] (3) (HL1 = 7-amino-4-methyl-5-azahept-3-en-2-one, HL2 = 7-methylamino-4-methyl-5-azahept-3-en-2-one, and HL3 = 7-dimethylamino-4-methyl-5-azahept-3-en-2-one), were synthesized. All three complexes were characterized by elemental analysis, IR and UV spectroscopies, and thermal analysis. Two of them (1 and 3) were also characterized by single crystal X-ray crystallography. Complex 1 forms a hydrogen-bonded one-dimensional metal-organic framework that stabilizes a helical water chain into its cavity, but when any of the amine hydrogen atoms of the Schiff base are replaced by methyl groups, as in L 2 and L 3, the water chain, vanishes, showing explicitly the importance of the host-guest H-bonding interactions for the stabilization of a water cluster.

Design, synthesis and computational modelling of aromatic tweezer-molecules as models for chain-folding polymer blends

Novel 'tweezer-type' complexes that exploit the interactions between pi-electron-rich pyrenyl groups and pi-electron deficient diimide units have been designed and synthesised. The component molecules leading to complex formation were accessed readily from commercially available starting materials through short and efficient syntheses. Analysis of the resulting complexes, using the visible charge-transfer band, revealed association constants that increased sequentially from 130 to 11,000 M-1 as increasing numbers of pi-pi-stacking interactions were introduced into the systems. Computational modelling was used to analyse the structures of these complexes, revealing low-energy chain-folded conformations for both components, which readily allow close, multiple pi-pi-stacking and hydrogen bonding to be achieved. In this paper, we give details of our initial studies of these complexes and outline how their behaviour could provide a basis for designing self-healing polymer blends for use in adaptive coating systems. (C) 2008 Elsevier Ltd. All rights reserved.

Torque in mooring chain. Part 1: Background and theory

Chain in both its forms - common (or stud-less) and stud-link - has many engineering applications. It is widely used as a component in the moorings of offshore floating systems, where its ruggedness and corrosion resistance make it an attractive choice. Chain exhibits some interesting behaviour in that when straight and subject to an axial load it does not twist or generate any torque, but if twisted or loaded when in a twisted condition it behaves in a highly non-linear manner, with the torque dependent upon the level of twist and axial load. Clearly an understanding of the way in which chains may behave and interact with other mooring components (such as wire rope, which also exhibits coupling between axial load and generated torque) when they are in service is essential. However, the sizes of chain that are in use in offshore moorings (typical bar diameters are 75 mm and greater) are too large to allow easy testing. This paper, which is in two parts, aims to address the issues and considerations relevant to torque in mooring chain. The first part introduces a frictionless theory that predicts the resultant torques and 'lift' in the links as non-dimensionalized functions of the angle of twist. Fortran code is presented in an Appendix, which allows the reader to make use of the analysis. The second part of the paper presents results from experimental work on both stud-less (41 mm) and stud-link (20.5 and 56 mm) chains. Torsional data are presented in both 'constant twist' and 'constant load' forms, as well as considering the lift between the links.

Torque in mooring chain. Part 2: Experimental investigation

Chain is a commonly used component in offshore moorings where its ruggedness and corrosion resistance make it an attractive choice. Another attractive property is that a straight chain is inherently torque balanced. Having said this, if a chain is loaded in a twisted condition, or twisted when under load, it exhibits highly non-linear torsional behaviour. The consequences of this behaviour can cause handling difficulties or may compromise the integrity of the mooring system, and care must be taken to avoid problems for both the chain and any components to which it is connected. Even with knowledge of the potential problems, there will always be occasions where, despite the utmost care, twist is unavoidable. Thus it is important for the engineer to be able to determine the effects. A frictionless theory has been developed in Part 1 of the paper that may be used to predict the resultant torques and movement or 'lift' in the links as non-dimensional functions of the angle of twist. The present part of the paper describes a series of experiments undertaken on both studless and stud-link chain to allow comparison of this theoretical model with experimental data. Results are presented for the torsional response and link lift for 'constant twist' and 'constant load' type tests on chains of three different link sizes.

Assessment of long chain n-3 polyunsaturated fatty acid status and clinical outcome in adults receiving home parenteral nutrition

Background & aims: Long term parenteral nutrition rarely supplies the long chain n-3 polyunsaturated fatty acids (PUFA), eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA). The aim of this study was to assess long chain n-3 PUFA status in patients receiving home parenteral. nutrition (HPN). Methods: Plasma phospholipid fatty acids were measured in 64 adult HPN patients and compared with 54 age, sex and BMI matched controls. Logistic regression analysis was used to identify factors related to plasma fatty acid fractions in the HPN patients, and to identify factors associated with the risk of clinical. complications. Results: Plasma phospholipid fractions of EPA, DPA and DHA were significantly tower in patients receiving HPN. Factors independently associated with tow fractions included high parenteral energy provision, tow parenteral lipid intake, tow BMI and prolonged duration of HPN. Long chain n-3 PUFA fractions were not associated with incidence of either central venous catheter associated infection or central venous thrombosis. However, the fraction of EPA were inversely associated with plasma alkaline phosphatase concentrations. Conclusions: This study demonstrates abnormal long chain n-3 PUFA profiles in patients receiving HPN. Reduced fatty acid intake may be partly responsible. Fatty acid metabolism may also be altered. (C) 2008 Elsevier Ltd and European Society for Clinical Nutrition and Metabolism. All rights reserved.

Neoglycolipid probes prepared via oxime ligation for microarray analysis of oligosaccharide-protein interactions

Neoglycolipid technology is the basis of a microarray platform for assigning oligosaccharide ligands for carbohydrate-binding proteins. The strategy for generating the neoglycolipid probes by reductive amination results in ring opening of the core monosaccharides. This often limits applicability to short-chain saccharides, although the majority of recognition motifs are satisfactorily presented with neoglycolipids of longer oligosaccharides. Here, we describe neoglycolipids prepared by oxime ligation. We provide evidence from NMR studies that a significant proportion of the oxime-linked core monosaccharide is in the ring-closed form, and this form selectively interacts with a carbohydrate-binding protein. By microarray analyses we demonstrate the effective presentation with oxime-linked neoglycolipids of (1) Lewis(x) trisaccharide to antibodies to Lewisx, (2) sialyllactose analogs to the sialic acid-binding receptors, siglecs, and (3) N-glycans to a plant lectin that requires an intact N-acetylglucosamine core.