Results 1 - 10 of 54922
Results 1 - 10 of 54922. Search took: 0.048 seconds
|Sort by: date | relevance|
[en] A new retarding-grid electron spectrometer for conversion electron Moessbauer spectroscopy has been constructed. The structure and performance of the spectrometer are described in detail. The response functions for various settings of energy resolution have been determined using the energy spectrum of a very thin 57 Co source. The best energy resolution obtained is 0.3% at 7.3 keV with a detection efficiency of 1.2%/4π. (orig.)
[en] A newly conceived microscope, based on a pure quantum phenomenon, is an ideal tool to study atom by atom the topography and properties of surfaces. Applications are presented: surface ''reconstruction'' of silicon, lamellar compound study, etc... Spectroscopy by tunnel effect will bring important information on electronic properties; it is presented with an application on silicon
[fr]Un nouveau type de microscope vient de naitre, capable de fournir des images de surfaces avec un grossissement voisinant la centaine de millions. Baptise ''microscope a effet tunnel'', il fournit en effet des images de surfaces revelant leur structure atomique. Apres la mise au point d'un premier prototype par G. Binnig et H. Rohrer dans les laboratoires IBM de Zurich en 1981, de nombreux microscopes a effet tunnel ont ete construits dans le monde entier. Ils ont deja permis de preciser la structure de certaines surfaces de metaux ou de semi-conducteurs dont l'importance technologique vient de la miniaturisation de l'electronique moderne. Mais l'utilisation possible du microscope dans l'air ou en milieu aqueux ouvre aussi des perspectives importantes en chimie et en biologie. Grace a cet instrument, un grand pas vers une meilleure comprehension des proprietes electroniques locales des surfaces vient d'etre franchi par l'utilisation de la spectroscopie par effet tunnel
[en] The field inside and outside dielectrical cube, which can be used as tuning element in SHF-accelerating channels is obtained by numerical-analytical method based on equations of macroscopic electrodynamics in integro-differential form. Problems on accuracy of the results obtained are considered
[en] The Static X-ray Imager (SXI) at the National Ignition Facility (NIF) is a pinhole camera using a CCD detector to obtain images of hohlraum wall x-ray drive illumination patterns seen through the laser entrance hole (LEH). Carefully chosen filters combined with the CCD response allows recording images in the x-ray range of 3 to 5 keV with 60 (micro)m spatial resolution. The routines used to obtain the apparent size of the backlit LEH, and the location and intensity of beam spots are discussed and compared to predictions. A new soft x-ray channel centered at 870 eV (near the x-ray peak of a 300 eV temperature ignition hohlraum) is discussed.
[en] The physical quality of a digitised image is affected by non-digital processes in the imaging instrumentation and by digital processes in the computer. The spatial unsharpness depends on instrumental resolution and on the pixel size of the digital array. The image contrast depends on the properties of the imaging system and on the number of grey scales used in the digital sampling process. The possibility is examined of constructing formulae for spatial unsharpness, and for the analogous parameter in the intensity dimension, defined as threshold contrast, in terms of instrumental and digital components. Formulae are developed from simple principles and tested against the observed properties of computer simulated images. The conclusion is that the concepts and the formulae provide a basis for predicting the effects of digital processing on the total unsharpness and contrast of digitised images. (author)
[en] We have used a first-order reflectron lens in an optical tomographic atom probe in order to improve the mass resolution. Calculations have been performed to determine the effect of second-order errors in ion energy and incidence angle on the performance of the lens. By applying a correction procedure based on the results of these calculations, we have been able to improve experimental mass resolution by 30%
[en] To increase selectivity of activation autoradiography for the first time it has been suggested to use computer’s processing of time series of autoradiography images obtained while the sample is cooling. To preserve the spatial resolution of the method, the processing must involve all coaxial pixels of the series. For visualization of the obtained results a cross section method for generation of a set of metaimages has been developed. The generated metaimages characterize the spatial distribution of pixels for half-life values lying in the selected interval. The algorithm for testing the computational data compatibility within the preselected zone has been developed. The algorithm is based on analysis of frequency distribution of half-life values for pixels array composing the sample zone under testing. The normal distribution characterizes compatible data for homogeneous part of the sample. Using the frequency analysis, a method for generation of contrasted metaimages has been developed. The method is able to distinguish zones with half-life differences of about 1 h. (author)
[en] It is shown that laser femtosecond photoelectron projection microscopy based on megahertz-high repetition rate T1:sapphire femtosecond lasers is a universal tool to study practically every types of the samples with an ultrahigh spatial resolution. Two-photon photoelectron images of the diamond and silicon nanotips are briefly discussed. Ultrahigh spatial resolution images (with the resolution of up to 3 nm, which is, to the best of our knowledge, the best achieved at present spatial resolution of a photoelectron microscope) have been obtained for the ultrasharp silicon nanotips.
[en] We model the dynamical structure of M87 (NGC4486) using high spatial resolution long-slit observations of stellar light in the central regions, two-dimensional stellar light kinematics out to half of the effective radius, and globular cluster velocities out to eight effective radii. We simultaneously fit for four parameters: black hole mass, dark halo core radius, dark halo circular velocity, and stellar mass-to-light (M/L) ratio. We find a black hole mass of 6.4(±0.5) x 109 M sun (the uncertainty is 68% confidence marginalized over the other parameters). The stellar M/LV = 6.3 ± 0.8. The best-fit dark halo core radius is 14 ± 2 kpc, assuming a cored logarithmic potential. The best-fit dark halo circular velocity is 715 ± 15 km s-1. Our black hole mass is over a factor of 2 larger than previous stellar dynamical measures, and our derived stellar M/L ratio is two times lower than previous dynamical measures. When we do not include a dark halo, we measure a black hole mass and stellar M/L ratio that is consistent with previous measures, implying that the major difference is in the model assumptions. The stellar M/L ratio from our models is very similar to that derived from stellar population models of M87. The reason for the difference in the black hole mass is because we allow the M/L ratio to change with radius. The dark halo is degenerate with the stellar M/L ratio, which is subsequently degenerate with the black hole mass. We argue that dynamical models of galaxies that do not include the contribution from a dark halo may produce a biased result for the black hole mass. This bias is especially large for a galaxy with a shallow light profile such as M87, and may not be as severe in galaxies with steeper light profiles unless they have a large stellar population change with radius.