CALCULATED ELECTRONIC AND MAGNETIC-STRUCTURES OF THE NEW TERNARY RARE-EARTH IRON NITRIDE ND2FE17N3

The electronic and magnetic structures of Nd2Fe17 and Nd2Fe17N3 have been calculated using the first-principle, spin-polarized orthogonalized linear combination of atomic orbitals method. Comparative studies of the two materials reveal important effects of the nitrogen atoms (at 9e site) on the electronic and magnetic structures. Results are presented for the total density of states, site-projected partial density of states and the spin magnetic moments on four nonequivalent Fe sites. The highest magnetic moments are found to be located on the 6c site for Nd2Fe17 and on the 9d site for Nd2Fe17N3, in agreement with the neutron and Mossbauer experiments. The variation trends of the magnetic moments on different Fe sites are discussed in terms of the separation between Fe and N atoms. Compared with Nd2Fe17, an increase in the exchange splitting of the Fe d band is found in Nd2Fe17N3, which accounts for its higher Curie temperature as observed in experiments. The calculated results show that the nitrogen atoms are charge acceptors in these compounds.

Hardness of covalent crystals

Based on the idea that the hardness of covalent crystal is intrinsic and equivalent to the sum of the resistance to the indenter of each bond per unit area, a semiempirical method for the evaluation of hardness of multicomponent crystals is presented. Applied to beta-BC2N crystal, the predicted value of hardness is in good agreement with the experimental value. It is found that bond density or electronic density, bond length, and degree of covalent bonding are three determinative factors for the hardness of a polar covalent crystal. Our method offers the advantage of applicability to a broad class of materials and initializes a link between macroscopic property and electronic structure from first principles calculation.

Genetic mapping of size-related quantitative trait loci (QTL) in the bay scallop (Argopecten irradians) using AFLP and microsatellite markers

We constructed genetic linkage maps for the bay scallop Argopecten irradians using AFLP and microsatellite markers and conducted composite interval mapping (CIM) of body-size-related traits. Three hundred seventeen AFLP and 10 microsatellite markers were used for map construction. The female parent map contained 120 markers in 15 linkage groups, spanning 479.6 cM with an average interval of 7.0 cM. The male parent map had 190 markers in 17 linkage groups, covering 883.8 cM at 7.2 cM per marker. The observed coverage was 70.4% for the female and 81.1% for the male map. Markers that were distorted toward the same direction were closely linked to each other on the genetic maps, suggesting the presence of genes important for survival. Six size-related traits, shell length, shell height, shell width, total weight, soft tissue weight, and shell weight, were measured for QTL mapping. The size data were significantly correlated with each other. We subjected the data, log transformed firstly, to a principle component analysis and use the first principle component for QTL mapping. CIM analysis revealed one significant QTL (LOD=2.69, 1000 permutation, P<0.05) in linkage group 3 on the female parent map. The mapping of size-related QTL in this study raises the possibility of improving the growth of bay scallops through marker-assisted selection. (c) 2007 Published by Elsevier B.V.

压力和铁含量对铁方镁石(Mg1-xFex)O(x<=0.25)弹性常数影响的第一性原理研究

By first principle methods based on density functional theory (DFT),the equation of state(EOS) and elastic constants of both periclase and ferropericlase are calculated. The pressure and iron doping effects on the elastic constants of ferropericlase are investigated systematically. Firstly, we calculate the elastic constants of periclase and compare the obtained results with experimental data and other theoretical calculations, which shows a encouraging consistence and demonstrates the practicability of first-principle methods. Secondly, by adding iron into periclase crystal model, we build up ferropericlase with iron contents ranging from 0% to 25% mole percent. The corresponding elastic constants are calculated in a large pressure range(0~120GPa). Emphatically, the strong correlation of 3d electrons in transitional elements, such as iron, is difficult to treat in first-principle methods for a long time. The current solution is to make additional correction. During the initial stage of this study, the strong correlation of 3d electrons in iron is not considered, and we observed that addition of iron decreases the volume of ferropericlase, which is totally contradictory to the experimental data. By applying LDA+U approximation in order to solve the strongly correlated 3d electron of iron, we observed the expansion of volume by iron as expected. On the basis of the LDA+U approximation, the elastic constants of ferropericlase are calculated. After a detailed analysis of data obtained from theoretical calculations, we have reached the following conclusions:(1)pressure imposes positive effects on all elastic constants, and the degree of effects is C11>C12>C44. (2) Iron has no distinctive effects on C11 and C12, although some fluctuations are observed around 60GPa. However, iron has obvious softening effects on C44 The softening effects on C44 are intensified as pressure increases. Above the 100GPa, the effects increase greatly, even surpasses the pressure's positive effects in ferropericlase crystal models with iron mole percent of having 12.5%, 18.75% and 25% iron content. (3)As to the modulus deprived from elastic constants, iron has no effect on the adiabatic bulk module BS, only a little fluctuation around 60GPa. We find iron's softening effects on shear modulus G. (4)We find out that, compared with low iron content, elastic constants with iron content approaching 25mole% is consistently fluctuated，which may be caused by the limitations of the LDA+U approximation method itself. (5)We investigate the pressure and Fe doping effects on elastic anisotropy factor（A=(2C44+C12-C11)/C11） of ferropericlase and find out that iron contents will lower the critical isotropic pressure. At the same pressure, when the pressure is below the isotropic pressure, iron softens the anisotropy factor ; when pressure surpasses the isotropic pressure, iron increases the anisotropy factor.

Justified Generalization: Acquiring Procedures from Examples

This thesis describes an implemented system called NODDY for acquiring procedures from examples presented by a teacher. Acquiring procedures form examples involves several different generalization tasks. Generalization is an underconstrained task, and the main issue of machine learning is how to deal with this underconstraint. The thesis presents two principles for constraining generalization on which NODDY is based. The first principle is to exploit domain based constraints. NODDY demonstrated how such constraints can be used both to reduce the space of possible generalizations to manageable size, and how to generate negative examples out of positive examples to further constrain the generalization. The second principle is to avoid spurious generalizations by requiring justification before adopting a generalization. NODDY demonstrates several different ways of justifying a generalization and proposes a way of ordering and searching a space of candidate generalizations based on how much evidence would be required to justify each generalization. Acquiring procedures also involves three types of constructive generalizations: inferring loops (a kind of group), inferring complex relations and state variables, and inferring predicates. NODDY demonstrates three constructive generalization methods for these kinds of generalization.

Causality enabled compositional modelling of Bayesian networks

J. Keppens and Q. Shen. Causality enabled compositional modelling of Bayesian networks. Proceedings of the 18th International Workshop on Qualitative Reasoning, pages 33-40, 2004.

Cooperation between adsorbates accounts for the activation of atomic layer deposition reactions

Atomic layer deposition (ALD) is a technique for producing conformal layers of nanometre-scale thickness, used commercially in non-planar electronics and increasingly in other high-tech industries. ALD depends on self-limiting surface chemistry but the mechanistic reasons for this are not understood in detail. Here we demonstrate, by first-principle calculations of growth of HfO2 from Hf(N(CH3)2)4–H2O and HfCl4–H2O and growth of Al2O3 from Al(CH3)3–H2O, that, for all these precursors, co-adsorption plays an important role in ALD. By this we mean that previously-inert adsorbed fragments can become reactive once sufficient numbers of molecules adsorb in their neighbourhood during either precursor pulse. Through the calculated activation energies, this ‘cooperative’ mechanism is shown to have a profound influence on proton transfer and ligand desorption, which are crucial steps in the ALD cycle. Depletion of reactive species and increasing coordination cause these reactions to self-limit during one precursor pulse, but to be re-activated via the cooperative effect in the next pulse. This explains the self-limiting nature of ALD.

Quantum manifestations of scattering orbits in the scaled spectrum of a non-hydrogenic atom in crossed fields

Evidence for scattering closed orbits for the Rydberg electron of the singly excited helium atom in crossed electric and magnetic fields at constant scaled energy and constant scaled electric field strength has been found through a quantum calculation of the photo-excitation spectrum. A particular 3D scattering orbit in a mixed regular and chaotic region has been investigated and the hydrogenic 3D closed orbits composing it identified. To the best of our knowledge, this letter reports the first quantum calculation of the scaled spectrum of a non- hydrogenic atom in crossed fields.

Enhancing process insight in polymer extrusion by grey box modelling

Due to the complexity and inherent instability in polymer extrusion there is a need for process models which can be run on-line to optimise settings and control disturbances. First-principle models demand computationally intensive solution, while ‘black box’ models lack generalisation ability and physical process insight. This work examines a novel ‘grey box’ modelling technique which incorporates both prior physical knowledge and empirical data in generating intuitive models of the process. The models can be related to the underlying physical mechanisms in the extruder and have been shown to capture unpredictable effects of the operating conditions on process instability. Furthermore, model parameters can be related to material properties available from laboratory analysis and as such, lend themselves to re-tuning for different materials without extensive remodelling work.

A Unified Scheduler for Recursive and Task Dataflow Parallelism

Task dataflow languages simplify the specification of parallel programs by dynamically detecting and enforcing dependencies between tasks. These languages are, however, often restricted to a single level of parallelism. This language design is reflected in the runtime system, where a master thread explicitly generates a task graph and worker threads execute ready tasks and wake-up their dependents. Such an approach is incompatible with state-of-the-art schedulers such as the Cilk scheduler, that minimize the creation of idle tasks (work-first principle) and place all task creation and scheduling off the critical path. This paper proposes an extension to the Cilk scheduler in order to reconcile task dependencies with the work-first principle. We discuss the impact of task dependencies on the properties of the Cilk scheduler. Furthermore, we propose a low-overhead ticket-based technique for dependency tracking and enforcement at the object level. Our scheduler also supports renaming of objects in order to increase task-level parallelism. Renaming is implemented using versioned objects, a new type of hyper object. Experimental evaluation shows that the unified scheduler is as efficient as the Cilk scheduler when tasks have no dependencies. Moreover, the unified scheduler is more efficient than SMPSS, a particular implementation of a task dataflow language.

Rational screening low-cost counter electrodes for dye-sensitized solar cells

Dye-sensitized solar cells have attracted intense research attention owing to their ease of fabrication, cost-effectiveness and high efficiency in converting solar energy. Noble platinum is generally used as catalytic counter electrode for redox mediators in electrolyte solution. Unfortunately, platinum is expensive and non-sustainable for long-term applications. Therefore, researchers are facing with the challenge of developing low-cost and earth-abundant alternatives. So far, rational screening of non-platinum counter electrodes has been hamstrung by the lack of understanding about the electrocatalytic process of redox mediators on various counter electrodes. Here, using first-principle quantum chemical calculations, we studied the electrocatalytic process of redox mediators and predicted electrocatalytic activity of potential semiconductor counter electrodes. On the basis of theoretical predictions, we successfully used rust (alpha-Fe2O3) as a new counter electrode catalyst, which demonstrates promising electrocatalytic activity towards triiodide reduction at a rate comparable to platinum.

High-resolution electron energy-loss spectroscopy of Ba Ti O 3∕ Sr Ti O 3 multilayers

The dielectric properties of BaTiO3 thin films and multilayers are different from bulk materials because of nanoscale dimensions, interfaces, and stress-strain conditions. In this study, BaTiO3/SrTiO3 multilayers deposited on SrTiO3 substrates by pulsed laser deposition have been investigated by high-energy-resolution electron energy-loss spectroscopy. The fine structures in the spectra are discussed in terms of crystal-field splitting and the internal strain. The crystal-field splitting of the BaTiO3 thin layer is found to be a little larger than that of bulk BaTiO3, which has been interpreted by the presence of the internal strain induced by the misfit at the interface. This finding is consistent with the lattice parameters of the BaTiO3 thin layer determined by the selected area diffraction pattern. The near-edge structure of the oxygen K edge in BaTiO3 thin layers and in bulk BaTiO3 are simulated by first-principle self-consistent full multiple-scattering calculations. The results of the simulations are in a good agreement with the experimental results. Moreover, the aggregation of oxygen vacancies at the rough BaTiO3/SrTiO3 interface is indicated by the increased [Ti]/[O] element ratio, which dominates the difference of dielectric properties between BaTiO3 layer and bulk materials.

Productive Knowledge of English Binomials by Japanese Learners of English

The purpose of this research is to reveal (1) which English binomials Japanese learners of English have productive knowledge of and (2) what strategies they use to produce English binomials when they do not know the binomials. One hundred and three Japanese learners of English with intermediate proficiency level completed an online survey of 44 binomials. The participants were given the first word of a binomial and asked to type a word following “and”. The target word was provided by more than 75% of participants for 19 of the 44 binomials, meaning that learners have productive knowledge for certain binomials. An analysis of errors suggested that the participants relied heavily on semantic relationships between items in binomials.However, the use of a semantic strategy for producing the second words often leads to non-binomial expressions. From these results we suggest that giving more input to learners, as well as teaching the “Me first” principle (Cooper & Ross, 1975) explicitly would help the learners to develop more accurate and effective strategies for uncertain or unfamiliar binomials.

Desenvolvimento de modelo de primeiros princípios para simulação dinâmica de uma coluna de destilação contínua

Trabalho Final de Mestrado para obtenção do grau de Mestre em Engenharia Química e Biológica

Heróis de palmo e meio: a intervenção psicossocial e a relação de ajuda no acolhimento institucional

Os Lares de Infância e Juventude têm como objetivo defender o superior interesse das crianças, desempenhando um papel fundamental no acompanhamento do seu desenvolvimento. Este dever concretiza-se substancialmente na definição e acompanhamento dos seus projetos de vida. Neste sentido, as práticas dos profissionais devem ir ao encontro das reais necessidades dos seus atores, numa ação adequada, desenhada e concertada, tendo sempre como principio básico o respeito pelas idiossincrasias de cada criança e jovem. O presente Relatório tem como objetivo apresentar o desenho e desenvolvimento de um projeto de intervenção psicossocial e relação de ajuda com crianças em acolhimento institucional, intitulado “Heróis de Palmo e Meio. A intervenção psicossocial e a relação de ajuda no acolhimento institucional”. Este projeto teve como grande finalidade a “Participação das crianças e das suas famílias na construção dos seus projetos de vida com base na compreensão da institucionalização”. Priorizando as necessidades e respeitando o critério de urgência, foram desenhados dois subprojectos com duas crianças e suas famílias, tentando sempre responder às suas necessidades individuais. Foram definidos alguns objetivos gerais comuns, assim como objetivos específicos, estratégias e ações adequadas a cada um dos subprojectos. Os resultados deste projeto revelam-se significativos, já que permitiram, quer às crianças, quer às famílias, desenvolver um processo de reflexão e consciencialização em torno da sua história de vida, compreensão da sua realidade e participação ativa no projeto de vida dos filhos, o que veio facilitar o caminho inicial do processo da mudança.