2,349 research outputs found
Numerical Study of Wave Propagation in Uniaxially Anisotropic Lorentzian Backward Wave Slabs
The propagation and refraction of a cylindrical wave created by a line
current through a slab of backward wave medium, also called left-handed medium,
is numerically studied with FDTD. The slab is assumed to be uniaxially
anisotropic. Several sets of constitutive parameters are considered and
comparisons with theoretical results are made. Electric field distributions are
studied inside and behind the slab. It is found that the shape of the
wavefronts and the regions of real and complex wave vectors are in agreement
with theoretical results.Comment: 6 pages, figure
Correlates of substitution rate variation in mammalian protein-coding sequences
BACKGROUND: Rates of molecular evolution in different lineages can vary widely, and some of this
variation might be predictable from aspects of species' biology. Investigating such predictable rate
variation can help us to understand the causes of molecular evolution, and could also help to
improve molecular dating methods. Here we present a comprehensive study of the life history
correlates of substitution rate variation across the mammals, comparing results for mitochondrial
and nuclear loci, and for synonymous and non-synonymous sites. We use phylogenetic comparative
methods, refined to take into account the special nature of substitution rate data. Particular
attention is paid to the widespread correlations between the components of mammalian life
history, which can complicate the interpretation of results.
RESULTS: We find that mitochondrial synonymous substitution rates, estimated from the 9 longest
mitochondrial genes, show strong negative correlations with body mass and with maximum
recorded lifespan. But lifespan is the sole variable to remain after multiple regression and model
simplification. Nuclear synonymous substitution rates, estimated from 6 genes, show strong
negative correlations with body mass and generation time, and a strong positive correlation with
fecundity. In contrast to the mitochondrial results, the same trends are evident in rates of
nonsynonymous substitution.
CONCLUSION: A substantial proportion of variation in mammalian substitution rates can be
explained by aspects of their life history, implying that molecular and life history evolution are
closely interlinked in this group. The strength and consistency of the nuclear body mass effect
suggests that molecular dating studies may have been systematically misled, but also that methods
could be improved by incorporating the finding as a priori information. Mitochondrial synonymous
rates also show the body mass effect, but for apparently quite different reasons, and the strength
of the relationship with maximum lifespan provides support for the hypothesis that mtDNA
damage is causally linked to aging
Lights on a Ground of Darkness: An Evocation of a Place aud Time
Review of: "Lights on a Ground of Darkness: An Evocation of a Place and Time," by Ted Kooser
Tunneling of Cooper pairs across voltage biased asymmetric single-Cooper-pair transistors
We analyze tunneling of Cooper pairs across voltage biased asymmetric
single-Cooper-pair transistors. Also tunneling of Cooper pairs across two
capacitively coupled Cooper-pair boxes is considered, when the capacitive
coupling and Cooper pair tunneling are provided by a small Josephson junction
between the islands. The theoretical analysis is done at subgap voltages, where
the current-voltage characteristics depend strongly on the macroscopic
eigenstates of the island(s) and their coupling to the dissipative environment.
As the environment we use an impedance which satisfies Re[Z]<<R_Q and a few
LC-oscillators in series with Z. The numerically calculated I-V curves are
compared with experiments where the quantum states of mesoscopic SQUIDs are
probed with inelastic Cooper pair tunneling. The main features of the observed
I-V data are reproduced. Especially, we find traces of band structure in the
higher excited states of the Cooper-pair boxes as well as traces of multiphoton
processes between two Cooper-pair boxes in the regime of large Josephson
coupling.Comment: 9 pages, 9 figures, Revtex
Sunday Afternoon on the Porch: Reflections of a Small Town in Iowa, 1939–1942
Review of: "Sunday Afternoon on the Porch: Reflections of a Small Town in Iowa, 1939–1942," by Jim Heynen (text), and Everett W. Kuntz (photog.
The War Comes to Plum Street
Review of: "The War Comes to Plum Street," by Bruce C. Smith
American Dreaming, Global Realities: Rethinking U. S. Immigration History
Review of: "American Dreaming, Global Realities: Rethinking U.S. Immigration History," edited by Donna R. Gabaccia and Vicki L. Rui
Patriotism, Courage, & Sacrifice: Warren County\u27s Response to WW II
Review of: Patriotism, Courage, & Sacrifice: Warren County\u27s Response to WW II by Jerry K. Beatt
Negative reflections of electromagnetic waves in chiral media
We investigate the reflection properties of electromagnetic/optical waves in
isotropic chiral media. When the chiral parameter is strong enough, we show
that an unusual \emph{negative reflection} occurs at the interface of the
chiral medium and a perfectly conducting plane, where the incident wave and one
of reflected eigenwaves lie in the same side of the boundary normal. Using such
a property, we further demonstrate that such a conducting plane can be used for
focusing in the strong chiral medium. The related equations under paraxial
optics approximation are deduced. In a special case of chiral medium, the
chiral nihility, one of the bi-reflections disappears and only single reflected
eigenwave exists, which goes exactly opposite to the incident wave. Hence the
incident and reflected electric fields will cancel each other to yield a zero
total electric field. In another word, any electromagnetic waves entering the
chiral nihility with perfectly conducting plane will disappear.Comment: 5 pages, 5 figure
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