12,600 research outputs found
Capture cross sections of the acceptor level of iron-boron pairs in p-type silicon by injection-level dependent lifetime measurements
Injection-level dependent recombination lifetime measurements of iron-diffused, boron-doped
silicon wafers of different resistivities are used to determine the electron and hole capture crosssections
of the acceptor level of iron-boron pairs in silicon. The relative populations of iron-boron
pairs and interstitial iron were varied by exposing the samples to different levels of illumination
prior to lifetime measurements. The components of the effective lifetime due to interstitial iron and
iron-boron pairs were then modeled with Shockley-Read-Hall statistics. By forcing the sum of the
modeled iron-boron and interstitial iron concentrations to equal the implanted iron dose, in
conjunction with the strong dependence of the shape of the lifetime curves on dopant density, the
electron and hole capture cross-sections of the acceptor level of iron-boron pairs have been
determined as (3±2)×10-14cm-2 and (2±1)×10-15cm-2
Patterson Function from Low-Energy Electron Diffraction Measured Intensities and Structural Discrimination
Surface Patterson Functions have been derived by direct inversion of
experimental Low-Energy Electron Diffraction I-V spectra measured at multiple
incident angles. The direct inversion is computationally simple and can be used
to discriminate between different structural models. 1x1 YSi_2 epitaxial layers
grown on Si(111) have been used to illustrate the analysis. We introduce a
suitable R-factor for the Patterson Function to make the structural
discrimination as objective as possible. From six competing models needed to
complete the geometrical search, four could easily be discarded, achieving a
very significant and useful reduction in the parameter space to be explored by
standard dynamical LEED methods. The amount and quality of data needed for this
analysis is discussed.Comment: 5 pages, 4 figure
PPM/NAR 8.4-GHz noise temperature statistics for DSN 64-meter antennas, 1982-1984
From August 1982 through November 1984, X-band downlink (8.4-GHz) system noise temperature measurements were made on the DSN 64-m antennas during tracking periods. Statistics of these noise temperature values are needed by the DSN and by spacecraft mission planners to assess antenna, receiving, and telemetry system needs, present performance, and future performance. These measurements were made using the DSN Mark III precision power monitor noise-adding radiometers located at each station. It is found that for DSS 43 and DSS 63, at the 90% cumulative distribution level, equivalent zenith noise temperature values fall between those presented in the earlier (1977) and present (1983) versions of DSN/Flight Project design documents. Noise temperatures measured for DSS 14 (Goldstone) are higher than those given in existing design documents and this disagreement will be investigated as a diagnostic of possible PPM or receiving system performance problems
Experimentally Attainable Optimal Pulse Shapes Obtained with the Aid of Genetic Algorithms
We propose a methodology to design optimal pulses for achieving quantum
optimal control on molecular systems. Our approach constrains pulse shapes to
linear combinations of a fixed number of experimentally relevant pulse
functions. Quantum optimal control is obtained by maximizing a multi-target
fitness function with genetic algorithms. As a first application of the
methodology we generated an optimal pulse that successfully maximized the yield
on a selected dissociation channel of a diatomic molecule. Our pulse is
obtained as a linear combination of linearly chirped pulse functions. Data
recorded along the evolution of the genetic algorithm contained important
information regarding the interplay between radiative and diabatic processes.
We performed a principal component analysis on these data to retrieve the most
relevant processes along the optimal path. Our proposed methodology could be
useful for performing quantum optimal control on more complex systems by
employing a wider variety of pulse shape functions.Comment: 7 pages, 6 figure
Critical connectedness of thin arithmetical discrete planes
An arithmetical discrete plane is said to have critical connecting thickness
if its thickness is equal to the infimum of the set of values that preserve its
-connectedness. This infimum thickness can be computed thanks to the fully
subtractive algorithm. This multidimensional continued fraction algorithm
consists, in its linear form, in subtracting the smallest entry to the other
ones. We provide a characterization of the discrete planes with critical
thickness that have zero intercept and that are -connected. Our tools rely
on the notion of dual substitution which is a geometric version of the usual
notion of substitution acting on words. We associate with the fully subtractive
algorithm a set of substitutions whose incidence matrix is provided by the
matrices of the algorithm, and prove that their geometric counterparts generate
arithmetic discrete planes.Comment: 18 pages, v2 includes several corrections and is a long version of
the DGCI extended abstrac
Intertemporal Substitution and the Liquidity Effect in a Sticky Price Model
The liquidity effect, defined as a decrease in nominal interest rates in response to a monetary expansion, is a major stylized fact of the business cycle. This paper seeks to understand under what conditions such an effect can be explained in a general equilibrium model with sticky prices and capital adjustment costs. The paper first confirms that, with separable preferences, a low degree of intertemporal substitution in consumption is a necessary condition for the existence of the liquidity effect. Contrary to this result, in a model with non-separable preferences and capital accumulation it takes an implausibly high degree of intertemporal substitution to produce a liquidity effect. The robustness of these results to alternative degrees of nominal rigidities, money demand properties and real rigidities is also analyzed.
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