20 research outputs found
Lattice screening of the polar catastrophe and hidden in-plane polarization in KNbO3/BaTiO3 interfaces
No full textWe have carried out first-principles simulations, based on density functional theory, to obtain the atomic and electronic structure of (001) BaTiO3/KNbO3 interfaces in an isolated slab geometry. We tried different types of structures including symmetric and asymmetric configurations and variations in the thickness of the constituent materials. The spontaneous polarization of the layer-by-layer non-neutral material (KNbO3) in these interfaces cancels out almost exactly the “built-in” polarization responsible for the electronic reconstruction. As a consequence, the so-called polar catastrophe is quenched and all the simulated interfaces are insulating. A model, based on the modern theory of polarization and basic electrostatics, allows an estimation of the critical thickness for the formation of the two-dimensional electron gas between 33 and 36 KNbO3 unit cells. We also demonstrate the presence of an unexpected in-plane polarization in BaTiO3 localized at the p-type TiO2/KO interface, even under in-plane compressive strains. We expect this in-plane polarization to remain hidden due to angular averaging during quantum fluctuations unless the symmetry is broken with small electric fields.We thank Massimiliano Stengel for useful discussions and a critical reading of the manuscript. This work was supported by the Spanish Ministery of Science and Innovation through the MICINN Grant FIS2009-12721-C04-02, by the Spanish Ministry of Education through the FPU fellowship AP2006-02958 (PAP), and by the European Union through the Project EC-FP7, Grant No. CP-FP 228989-2 “OxIDes.” The authors thankfully acknowledge the computer resources, technical expertise and assistance provided by the Red Española de Supercomputación. Calculations were also performed at the ATC group of the University of Cantabria
Instructional Development (2004 Fall Semester)
No full textUniversity of Minnesota Duluth. Instructional Development Service. (2004). Instructional Development (2004 Fall Semester). Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/228989
Positive Effect of an Internal Depolarization Field in Ultrathin Epitaxial Ferroelectric Films
No full textThe effect of intentionally introducing a large depolarization field in (001)-oriented, epitaxial Pb(Zr0.2TiO0.8)O3 (PZT) ultrathin films grown on La0.67Sr0.33MnO3 (LSMO) buffered SrTiO3 (STO) substrates is investigated. Inserting between 3 and 10 unit cells of STO between two 3 nm thick PZT films significantly influences the out-of-plane (c) lattice constant as well as the virgin domain state. Piezoresponse force microscopy images reveal a nanoscale (180°) polydomain structure in these films. In comparison, a “reference” single layer PZT sample (6 nm thick without STO spacer) exhibits an elongated PZT c-axis (0.416 nm) and is preferentially “down”-polarized with large regions of monodomain contrast. It shows asymmetric switching loops (i.e., imprint) coupled with sluggish domain switching under external bias. It is shown that the insertion of STO drives a monodomain to 180° polydomain transition in the as-grown state, which reduces the imprint by 80%. The insertion of the STO also profoundly improves dielectric leakage and hence the distribution of the applied electric field. Consequently, the critical pulse duration of the electric field required to initiate domain switching is reduced by two orders of magnitude relative to the reference sample. These results demonstrate the possibility of manipulating the depolarization field in such a way that it has positive effects on the ferroelectric behavior of ultrathin PZT films.Acknowledgements: G.L. and J.C. contributed equally to this work. G.L., J.C., and N.V. acknowledge support from ARC Discovery Project. N.V. acknowledges valuable discussions with Prof. P. Alpay and Prof. Anna Morozovska. C.L. and J.-M.T. thank support from the Swiss National Science Foundation division II. P.A.-P. and J.J. acknowledge the Spanish Ministry of Science and Innovation through the MICINN Grant FIS2012–37549-C05-04 and by the European Union through the project EC-FP7, Grant No. CP-FP 228989–2 “OxIDes.
Methods mathematical modeling shape flax seeds ®
No full textW artykule przedstawiono propozycję trzech metod matematycznego
modelowania kształtu nasion lnu z wykorzystaniem
krzywych parametrycznych, krzywych Béziera i krzywych
przekrojów poprzecznych. W metodzie 1 matematycznego
opisu kształtu nasion lnu zastosowano równania parametryczne
bryły z ostrym wierzchołkiem. W metodzie 2 zastosowano
równania parametryczne bryły z łukowym wierzchołkiem.
W metodzie 3 zastosowano równania parametryczne
krzywych Béziera i krzywych przekrojów poprzecznych.
Wybrane do modelowania nasiona sfotografowano w płaszczyźnie
XZ aparatem Panasonic LUMIX DMC-TZ3. Miarą
oceny była na ustalonej wysokości w płaszczyźnie XZ maksymalna
różnica odległości między krawędzią nasiona a krawędzią
modelu. Metoda z wykorzystaniem krzywych Béziera
i krzywych przekrojów poprzecznych może być stosowana do
matematycznego modelowania kształtu nasion lnu.The article presents of three methods of mathematical modeling
of the shape of flax seed with the use of parametric curves,
Bezier curves and curves of cross sections. In the method
1 mathematical description of the shape of the flax seed
used parametric equations with a sharp apex. In method 2
uses parametric equations topped with an arched apex. The
method 3 uses parametric equations of curves and Bezier curves
of cross sections. Selected to modeling seeds photographed
in the XZ plane Panasonic LUMIX DMC-TZ3 camera.
Measure of assessment at a fixed height in plane XZ is maximum
difference in distance between the edge of the seed
and the edge of the model. Method using Bézier curves and
cross-sections can be used for mathematical modeling of the
shape of the flax seeds
Functional annotation chart showing differentially-expressed pathways in renal medulla tissue comparing HLP+ Apocynin treated versus untreated control groups.
No full text<p>The gene heading indicates number of genes mapped to an ontology category. The first ten pathways are common in the cortex and the medulla. P-value derived from Fisher's exact test and Benjamini multiple test correlation.</p
Ensaio de projeto performativo para pavilhão
No full textO presente trabalho discute sobre os processos digitais no projeto de arquitetura. Reflete sobre a colaboração das ferramentas de modelagem generativa, integradas à análise de performance, para a construção da informação no processo de projeto. O trabalho apresenta um ensaio projetual, realizado no âmbito da pesquisa conduzida no grupo SCP - Sistemas Contemporâneos de Projeto (www.gruposcp.org), dedicado ao desenvolvimento de um pavilhão de uso multifuncional para uso público, inserido em um vazio urbano da cidade de Vila Velha, Espírito Santo, Brasil. A pesquisa buscou explorar as possibilidades metodológicas do projeto generativo e performativo para estabelecer diálogos digitais entre a concepção formal e as informações pré-existentes no contexto — sociais, culturais, ambientais — através de processos explícitos e integrados. O método inclui o uso das programas computacionais Revit Architecture para modelagem do entorno; Rhinoceros e Grasshopper para modelagem generativa; plug-in DIVA for Grasshopper e Kangaroo para análise de performance integrada à concepção; e o plug-in Galapagos para aplicação de algoritmos evolutivos no processo de formação. O método possibilitou a otimização da forma em função dos condicionantes locais e das variáveis de performance, automatizando processos e reduzindo tempo de projeto. O projeto mediado pelos programas digitais colaborou para processos de conhecer-na-ação e refletir-na-ação, nos quais o conhecimento explícito, obtido no ato do fazer, realimenta o processo, permitindo teste, análise e ajuste no ato da concepção.This paper discusses the digital process in architectural design. It reflects on the collaboration of generative modeling tools, integrated with performance analysis, to construct information in the design process. The work approaches a design experiment, carried out by the Research Group Grupo SCP - Contemporary Design Systems (www.gruposcp.org)dedicated to the development of a multi-purpose pavilion for public use, inserted in an urban void of the city of Vila Velha, in the state of Espírito Santo, Brazil. The research sought to explore the methodological possibilities of generative and performative design to establish digital dialogues between the formal conception and the pre-existing information in context—social, cultural, environmental—through explicit and integrated processes. The method includes the use of computer programs and plugins as Revit Architecture for environment modeling; Rhinoceros and Grasshopper for generative modeling; the DIVA for Grasshopper plug-in and Kangaroo for design-integrated performance analysis; and the Galapagos plug-in to applying evolutionary algorithms in the formation process. The method enabled the optimization of a form according to local conditions and performance variables, automation of processes and reducing design time. The project mediated by the digital programs collaborated with processes of knowing-in-action and reflection-in-action, in which explicit knowledge, obtained in the act of doing, feeds back into the process, allowing testing, analysis and adjustment in the act of conception.O presente trabalho discute sobre os processos digitais no projeto de arquitetura. Reflete sobre a colaboração das ferramentas de modelagem generativa, integradas à análise de performance, para a construção da informação no processo de projeto. O trabalho apresenta um ensaio projetual, realizado no âmbito da pesquisa conduzida no grupo SCP - Sistemas Contemporâneos de Projeto (www.gruposcp.org), dedicado ao desenvolvimento de um pavilhão de uso multifuncional para uso público, inserido em um vazio urbano da cidade de Vila Velha, Espírito Santo, Brasil. A pesquisa buscou explorar as possibilidades metodológicas do projeto generativo e performativo para estabelecer diálogos digitais entre a concepção formal e as informações pré-existentes no contexto — sociais, culturais, ambientais — através de processos explícitos e integrados. O método inclui o uso das programas computacionais Revit Architecture para modelagem do entorno; Rhinoceros e Grasshopper para modelagem generativa; plug-in DIVA for Grasshopper e Kangaroo para análise de performance integrada à concepção; e o plug-in Galapagos para aplicação de algoritmos evolutivos no processo de formação. O método possibilitou a otimização da forma em função dos condicionantes locais e das variáveis de performance, automatizando processos e reduzindo tempo de projeto. O projeto mediado pelos programas digitais colaborou para processos de conhecer-na-ação e refletir-na-ação, nos quais o conhecimento explícito, obtido no ato do fazer, realimenta o processo, permitindo teste, análise e ajuste no ato da concepção
Schillers Schädel in Goethes Hand : das Terzinengedicht "Im ernsten Beinhaus war's" im Kontext von Goethes Gedächtnis-Poetik und -Politik
No full text'A school full of instructional experts': Shared instructional leadership in rural schools
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