RESUMO
The results of He atom scattering experiments on KTa0.48Nb0.52O3(001) surfaces are presented and compared with similar experiments on mixed potassium tantalate/niobate perovskites with lower concentrations of Nb. The results are puzzling, unique and intriguing. Angular distributions of the He scattering intensities (the He surface diffraction pattern) are found to be very similar to those obtained from targets with lower Nb fractions. However, drift spectra (the intensity of the He specular reflection as a function of the He wave vector) are not. Whereas the drift spectra in the ã10ã azimuth do resemble those of the 0, 6 and 10% Nb fraction targets, in the ã11ã azimuth they are more similar to the strange drift spectra found from the 30% Nb-doped targets. Most intriguing are the surface temperature scans (the He specular intensity as a function of the target surface temperature); for they are quite distinct from those with lower Nb fractions. Finally, the inelastic He scattering experiments provide phonon dispersion results that are similar in most respects to those found for the lower Nb level samples. In particular, the most prominent feature is an Einstein-like mode at about 13.5 meV which spans the entire surface Brillouin zone in both ã10ã and ã11ã azimuths.
RESUMO
Helium atom scattering experiments have been carried out on the (001) surface of KTaO(3) doped with 6, 10 and 15% Nb, produced by cleaving in situ single crystal samples. Several phenomena were observed through He atom diffraction measurements, including metastable behavior immediately after cleaving, reconstruction of a fraction of the surface to (2 × 1) domains after thermally cycling the surface temperatures, and the distribution of step heights of terraces at the surface as multiples of the unit cell dimension of â¼ 4 Å. In addition, a large hysteresis effect was found in the (100) azimuth in the variation of surface reflectivity with surface temperature; a much smaller hysteresis effect was found in the (110) azimuth. The hysteresis effects appear for all Nb doping concentrations. Finally, small oscillations in the specular and Bragg diffraction intensities near the surface temperature 80 K were also observed.
Assuntos
Humanos , Masculino , Adulto , Lesões das Artérias Carótidas , Artéria Carótida Externa , Traumatismos Maxilofaciais , Boca , Lesões do Pescoço , Ferimentos por Arma de Fogo , Lesões das Artérias Carótidas , Emergências , Ossos Faciais , Maxila , Traumatismos Maxilofaciais , Pescoço , Lesões do Pescoço , Traumatismos Dentários , Vasos Sanguíneos/lesões , Ferimentos PenetrantesAssuntos
Humanos , Masculino , Adulto , Ferimentos por Arma de Fogo , Boca/lesões , Artéria Carótida Externa , Traumatismos Maxilofaciais/cirurgia , Lesões das Artérias Carótidas/cirurgia , Lesões do Pescoço/cirurgia , Pescoço/cirurgia , Ossos Faciais/lesões , Maxila/lesões , Traumatismos Maxilofaciais/etiologia , Traumatismos Maxilofaciais/diagnóstico , Vasos Sanguíneos/lesões , Traumatismos Dentários/etiologia , Ferimentos Penetrantes , Emergências , Lesões das Artérias Carótidas/etiologia , Lesões das Artérias Carótidas/diagnóstico , Lesões do Pescoço/etiologia , Lesões do Pescoço/diagnósticoRESUMO
Helium atom diffraction experiments carried out under ultrahigh vacuum conditions on a freshly cleaved (001) surface of KTaO3 reveal metastable features which decay over a period of several hours. The initial He diffraction pattern contains large scattering intensity satellite peaks very close to the specular reflection beam. As time from cleaving elapses, the satellite intensities diminish virtually to zero while the specular intensity increases, and the diffraction pattern evolves into one consistent with the (1x1) bulk termination surface. The data are compared with model calculations for scattering from a series of terraces at two heights with a distribution of terrace lengths [Surf. Sci. 384, 15 (1997)].
RESUMO
The purpose of this article is to describe our findings on barium enema in patients who have had incomplete colonoscopy. For patients undergoing colonoscopy and barium enema within 6-months of each other between 1991 and 1997, barium enemas were reevaluated for redundant anatomy as well as lesions. Seventy-seven women and 30 men underwent 108 barium enemas. The most common finding was a redundant colon in 68% (55/81) of study patients, but only 33% (9/27) of control (complete colonoscopy) patients.
Assuntos
Sulfato de Bário , Doenças do Colo/diagnóstico , Colonoscopia/métodos , Enema , Adulto , Idoso , Idoso de 80 Anos ou mais , Estudos de Casos e Controles , Terapia Combinada , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Valores de Referência , Reprodutibilidade dos Testes , Estudos Retrospectivos , Sensibilidade e EspecificidadeRESUMO
A spacelike hypersurface (condimension 1) in a Lorentzian manifold is called a maximal surface if it extremizes the hypervolume functional. Although maximal surfaces are superficially analogous to minimal hypersurfaces in Riemannian geometry, their properties can be dramatically different, as can be seen from the validity of Bernstein's theorem in all dimensions [Cheng, S.-Y. & Yau, S.-T. (1976) Ann. Math. 104, 407-419]. Here we establish a point of contact between maximal surfaces and minimal surfaces by solving the Dirichlet problem for acausal boundary data but using boundary curvature conditions similar to those of H. Jenkins and J. Serrin [(1968) J. Reine Angew. Math. 229, 170-187].