The Soft-Collinear Bootstrap: N=4 Yang-Mills Amplitudes at Six and Seven Loops

Infrared divergences in scattering amplitudes arise when a loop momentum $\ell$ becomes collinear with a massless external momentum $p$. In gauge theories, it is known that the L-loop logarithm of a planar amplitude has much softer infrared singularities than the L-loop amplitude itself. We argue that planar amplitudes in N=4 super-Yang-Mills theory enjoy softer than expected behavior as $\ell \parallel p$ already at the level of the integrand. Moreover, we conjecture that the four-point integrand can be uniquely determined, to any loop-order, by imposing the correct soft-behavior of the logarithm together with dual conformal invariance and dihedral symmetry. We use these simple criteria to determine explicit formulae for the four-point integrand through seven-loops, finding perfect agreement with previously known results through five-loops. As an input to this calculation we enumerate all four-point dual conformally invariant (DCI) integrands through seven-loops, an analysis which is aided by several graph-theoretic theorems we prove about general DCI integrands at arbitrary loop-order. The six- and seven-loop amplitudes receive non-zero contributions from 229 and 1873 individual DCI diagrams respectively.Comment: 27 pages, 48 figures, detailed results including PDF and Mathematica files available at http://goo.gl/qIKe8 v2: minor corrections v3: figure 7 corrected, Lemma 2 remove

O ENFERMEIRO ATUANDO NA PREVENÇÃO DAS ÚLCERAS DE PRESSÃO

Las úlceras de decúbito fueron y siguen siendo un cuidado importante en la enfermería. Sin embargo, comprender hoy la práctica del cuidar solo es posible a partir de una visión holística, un cuidar que ve a la persona integralmente. Por ese motivo, cuando se habla de prevención de úlceras es preciso conocer la estructura de la piel y su función para comprender mejor los fundamentos de prevención y cuidados eficaces. La manutención de la integridad de la piel es responsabilidad del Enfermero. Los mecanismos que causan las úlceras son innumerables y precisan ser atenuados o prevenidos completamente para que la integridad cutánea sea mantenida. Ante eso trazamos como objeto de estudio: El conocimiento por la Enfermería de la Escala Predictiva de Braden en la prevención de las úlceras de presión. Y como problema el siguiente cuestionamiento: ¿Cómo la enfermería sistematiza la asistencia en la prevención de las úlceras de presión? Objetivos: Identificar lo que la Enfermería conoce al respecto de la Escala predictiva de Braden (“Escala pronóstica de Braden); Comparar lo que saben con lo que hacen para prevenir las úlceras de presión. Metodología: En cuanto al tipo se trata de un estudio de caso, descriptivo, y utilizaremos el abordaje cuantitativo. La pesquisa tuvo como escenario la Unidad de Terapia Intensiva de una institución pública, de medio porte, clasificada como hospital general.As úlceras de decúbito foram e continuarão sendo um cuidado importante na enfermagem. Porém, hoje compreender a prática do cuidar, só é possível a partir de uma visão holística, um cuidar que veja a pessoa integralmente. Por esse motivo, quando se fala em prevenção de úlceras é preciso conhecer a estrutura da pele e sua função para compreender melhor os fundamentos de prevenção e cuidados eficazes com pele. A manutenção da integridade da pele é responsabilidade do Enfermeiro. Os mecanismos que causam as úlceras são inúmeros e precisam ser atenuados ou prevenidos completamente para que a integridade cutânea seja mantida. Diante disso, traçamos como objeto de estudo: O conhecimento pela Enfermagem da Escala Preditiva de Braden na prevenção das úlceras de pressão. E como problema o seguinte questionamento: Como a enfermagem sistematiza a assistência na prevenção das úlceras de pressão? Objetivos: Identificar o que a Enfermagem conhece a respeito de Escala preditiva de Braden; Comparar o que sabem com o que fazem para prevenir as úlceras de pressão. Metodologia: quanto à tipologia trata-se de um estudo de caso, descritivo e utilizaremos a abordagem quantitativa. A pesquisa teve como cenário a Unidade de Terapia Intensiva, de uma instituição pública, de médio porte, classificada como hospital geral

Centrifugal Fan Performance With Distorted Inflows

Efforts to quantify degradation of the performance of a centrifugal fan subjected to distorted inflows are presented. The study centered on examination of pressure rise, efficiency, and onset of stall for a backwardly-inclined, airfoil-bladed fan. Nonuniform flow patterns were generated in an adjustable countervane damper assembly installed upstream of the inlet box, and systematic families of performance curves were generated. Results of these tests show that significant degradation in efficiency and pressure rise—as much as 10 to 15 percent—may result from moderately to severely distorted inflow patterns. Onset of stall was significantly influenced by severely distorted inflows.</jats:p

Structural Investigation of Sol-Gel-Derived Hybrid Siloxane-Oxide Materials Using ²⁹Si MAS-NMR Spectroscopy

ABSTRACTHybrid siloxane-oxide systems were prepared by sol-gel techniques. Siloxane precursors are either monomeric species, dimethyldiethoxysilane, or OH-terminated polydimethylsiloxanes. The oxide component is introduced via metallic alkoxides, M(OR)n (M=Si, Ti, Zr). Transparent materials from flexible to brittle gels, can be obtained over a large M/siloxane range. The structure of the various systems was investigated by 29Si MAS-NMR. The signals due to the difunctional Si units, (CH3)2SiO, depend strongly on the nature of M and on the M/siloxane ratio. Structural models are proposed, ranging from single phase systems with highly interconnected siloxane and oxide units, to nanocomposites made of polysiloxane chains crosslinked with oxide-based particles.</jats:p

Surface Chemical Structure of Sío2-TiO₂ Sol-Gel Powders

ABSTRACTAmorphous SiO2, TiO2 and x SiO2-(1-x) TiO2 powders, with nominal values of x=0.9, 0.7 and 0.5, have been prepared via sol-gel, using silicon tetrahoxysilane (TEOS) and titanium tetraisopropoxide Ti(OPri)4. X-ray photoelectron spectroscopy (XPS) and X-ray induced Auger electron spectroscopy (XAES) are used for studying the surface chemical structure of the powders as a function of the air thermal treatment temperature up to 1273 K. For the whole range of temperature, XPS and XAES signals indicate that silicon and titanium are present as Si4+ and Ti4+ oxides. From the line shape of the O 1s peak, it is possible to distinguish between the single O-Ti and O-Si bonds and to disclose also the presence of Si-O-Ti cross linking bonds that are supposed to act as bridges between SiO2 and TiO2 moieties. Starting from 873 K, the Si-O-Ti bonds are broken and formation of a low amount of new Ti-O and a higher amount of Si-O bonds takes place. Si/Ti atomic ratios obtained by curve fitting the O Is peaks and from Ti 2p3/2 and Si 2p peaks, confirm the silicon oxide surface enrichment. Furthermore, with increasing temperature, XAES data indicate the formation of crystalline phases.</jats:p