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51.
N. M. Miskovsky P. H. Cutler T. E. Feuchtwang A. A. Lucas 《Applied Physics A: Materials Science & Processing》1982,27(3):139-147
The effect of the multiple image interactions on theI–V characteristics and the reliability of the mean barrier approximation in calculating the current in MOM and MVM tunneling junctions are critically examined. It is demonstrated that the continued use of the uncorrected form of Simmons' original multiple-image force interaction in the analysis of tunneling junctions can lead to serious errors in both the current and the dynamic resistance. An extensive numerical analysis of planar junctions including the image potential suggests that the basic mean barrier approximation formulated by Simmons is essentially a thick barrier approximation. It also is shown that the conventional mean barrier approximation is a relatively poor approximation for the tunneling barriers of interest, and that it is not possible to establish a reliable a priori estimate of its range of validity.This research was supported in part by the NATO Research Grants Program, Grant No. 1902, Scientific Affairs Division, Brussels, Belgium 相似文献
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The kinematic approximation method has shown that the peak intensity and the full width at half maximum (FWHM) of stepped surfaces exhibit an oscillatory behavior for changing incident energy. This paper generalizes the kinematic approximation to an (N × 1) reconstructed surface with a distribution of various types of lateral displacements at a step. A particular solution of this model we call the fixed point solution, yields a clear intuitive understanding of these oscillations as well as an exact solution for the step density of any surface. The specific examples of (5 × 1) and (2 × 1) reconstruction are examined to show the striking differences between the reconstructed surface diffraction patterns. These differences make an examination of the half-maximum (HM) intensity position a powerful tool to determine the surface structure for any incommensurate stepped surface. 相似文献
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Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) is demonstrated to be a potentially
useful tool for the rapid identification of yeasts, the grouping of Candida albicans strains, and the monitoring of germ tube-specific markers. Co-crystallized with sinapinic acid as the MALDI matrix, intact
yeast cells yielded a sufficient number of medium-sized ions (4–15 kDa) in MALDI mass spectra to provide “mass signatures”
that were diagnostic of strain type. For most isolates, the mass signatures were affected by the growth medium, length of
incubation and the cell preparation method. While the overall past success of this methodology for fungal cells has been relatively
low compared to its application to bacteria, fixing the yeast cells in 50% methanol inactivated the cells, reduced cell aggregation
in aqueous suspension solution, and more importantly, it significantly improved the mass signature quality. This simple but
critical advance in sample treatment improved mass spectrometric signal-to-noise ratios and allowed the identification of
yeasts by a mass signature approach. Under optimized conditions, Candida species (C. albicans, C. glabrata, C. krusei, C. kefyr), Aspergillus species (A. terreus, A. fumigatus, A. syndowii) and other yeast genera (Cryptococcus neoformans, Saccharomyces cerevisiae and a Rhodotorula sp.) could be distinguished. Within the C. albicans species, several common ions in the m/z 5,000–10,000 range were apparent in the mass spectra of all tested strains. In addition to shared ions, the mass spectra
of individual C. albicans strains permitted grouping of the strains. Principal component analysis (PCA) was employed to confirm spectral reproducibility
and C. albicans strain grouping by mass signatures. Finally, C. albicans germ tubes produced MALDI-TOF mass signatures that differed from yeast forms of this species. This is a rapid, sensitive
and simple method for identifying yeasts, grouping strains and following the morphogenesis of C. albicans.
Figure 相似文献
56.
A procedure is explained to determined the amount of several pairs of diametrical loads applied to the outside boundary of
a ring when stresses at selected points of the inside or outside boundaries are known. Coefficients of influence are used,
following an approach similar to the one presented in a previous paper. Examples of application are given and the possible
increase in precision is shown when the number of points of measurements is larger than the number of loads to be determined. 相似文献
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