156,582 research outputs found
How many electrons are needed to flip a local spin?
Considering the spin of a local magnetic atom as a quantum mechanical
operator, we illustrate the dynamics of a local spin interacting with a
ballistic electron represented by a wave packet. This approach improves the
semi-classical approximation and provides a complete quantum mechanical
understanding for spin transfer phenomena. Sending spin-polarized electrons
towards a local magnetic atom one after another, we estimate the minimum number
of electrons needed to flip a local spin.Comment: 3 figure
Extended Optical Model Analyses of Elastic Scattering and Fusion Cross Section Data for the 7Li+208Pb System at Near-Coulomb-Barrier Energies using the Folding Potential
Simultaneous analyses previously made for elastic scattering and
fusion cross section data for the Li+Pb system is extended to the
Li+Pb system at near-Coulomb-barrier energies based on the
extended optical model approach, in which the polarization potential is
decomposed into direct reaction (DR) and fusion parts. Use is made of the
double folding potential as a bare potential. It is found that the experimental
elastic scattering and fusion data are well reproduced without introducing any
normalization factor for the double folding potential and that both the DR and
fusion parts of the polarization potential determined from the
analyses satisfy separately the dispersion relation. Further, we find that the
real part of the fusion portion of the polarization potential is attractive
while that of the DR part is repulsive except at energies far below the Coulomb
barrier energy. A comparison is made of the present results with those obtained
from the Continuum Discretized Coupled Channel (CDCC) calculations and a
previous study based on the conventional optical model with a double folding
potential. We also compare the present results for the Li+Pb system
with the analysis previously made for the Li+Pb system.Comment: 7 figures, submitted to PR
Path methods for strong shift equivalence of positive matrices
In the early 1990's, Kim and Roush developed path methods for establishing
strong shift equivalence (SSE) of positive matrices over a dense subring U of
the real numbers R. This paper gives a detailed, unified and generalized
presentation of these path methods. New arguments which address arbitrary dense
subrings U of R are used to show that for any dense subring U of R, positive
matrices over U which have just one nonzero eigenvalue and which are strong
shift equivalent over U must be strong shift equivalent over U_+. In addition,
we show positive real matrices on a path of shift equivalent positive real
matrices are SSE over R_+; positive rational matrices which are SSE over R_+
must be SSE over Q_+; and for any dense subring U of R, within the set of
positive matrices over U which are conjugate over U to a given matrix, there
are only finitely many SSE-U_+ classes.Comment: This version adds a 3-part program for studying SEE over the reals.
One part is handled by the arxiv post "Strong shift equivalence and algebraic
K-theory". This version is the author version of the paper published in the
Kim memorial volume. From that, my short lifestory of Kim (and more) is on my
web page http://www.math.umd.edu/~mboyle/papers/index.htm
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