2,612 research outputs found
First-principles theoretical evaluation of crystalline zirconia and hafnia as gate oxides for Si microelectronics
Parameters determining the performance of the crystalline oxides zirconia
(ZrO_2) and hafnia (HfO_2) as gate insulators in nanometric Si electronics are
estimated via ab initio calculations of the energetics, dielectric properties,
and band alignment of bulk and thin-film oxides on Si (001). With their large
dielectric constants, stable and low-formation-energy interfaces, large valence
offsets, and reasonable (though not optimal) conduction offsets (electron
injection barriers), zirconia and hafnia appear to have a considerable
potential as gate oxides for Si electronics.Comment: RevTeX 4 pages, 3 eps figure
alpha :a constant that is not a constant?
We review the observational information on the constancy of the fine
structure constant alpha. We find that small improvements on the measurement of
^{187}Re lifetime can provide significant progress in exploring the range of
variability suggested by QSO data. We also discuss the effects of a time
varying alpha on stellar structure and evolution. We find that radioactive
dating of ancient stars can offer a new observational window.Comment: 9 pages with 3 ps figures included, to appear on the Proc. of
ESO-CERN-ESA Symposium on Astronomy, Cosmology and Fundamental Physics,
Garching bei Munchen, Germany March 4-7, 200
Helioseismic tests of diffusion theory
We present a quantitative estimate of the accuracy of the calculated
diffusion coefficients, by comparing predictions of solar models with
observational data provided by helioseismology. By taking into account the
major uncertainties in building solar models we conclude that helioseismology
confirms the diffusion efficiency adopted in SSM calculations, to the 10%
level.Comment: 5 pages with 1 ps figure included, LaTeX file with l-aa.sty,
submitted to Astronomy and Astrophysic
Is G a conversion factor or a fundamental unit?
By using fundamental units c, h, G as conversion factors one can easily
transform the dimensions of all observables. In particular one can make them
all ``geometrical'', or dimensionless. However this has no impact on the fact
that there are three fundamental units, G being one of them. Only experiment
can tell us whether G is basically fundamental.Comment: 2 page
Which radius for the Sun?
The high accuracy reached by solar limb observations, by helioseismic
measurements and by Standard Solar Models (SSMs) calculations suggests that
general relativity corrections are included when discussing the solar radius.
The Allen value (R = 695.99 0.07 Mm) has to be reduced by 1.5
Km. This correction, which is small as compared with present accuracy, should
be kept in mind for future more precise measurements and/or calculations.Comment: Latex, 3 page
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