44,679 research outputs found
Strong eigenfunction correlations near the Anderson localization transition
We study overlap of two different eigenfunctions as compared with
self-overlap in the framework of an infinite-dimensional version of the
disordered tight-binding model. Despite a very sparse structure of the
eigenstates in the vicinity of Anderson transition their mutual overlap is
still found to be of the same order as self-overlap as long as energy
separation is smaller than a critical value. The latter fact explains
robustness of the Wigner-Dyson level statistics everywhere in the phase of
extended states. The same picture is expected to hold for usual d-dimensional
conductors, ensuring the form of the level repulsion at critical
point.Comment: 4 pages, RevTe
Notes and Discussion Piece: Status of the Topeka Shiner in Iowa
The Topeka shiner Notropis topeka is native to Iowa, Kansas, Minnesota, Missouri, Nebraska, and South Dakota and has been federally listed as endangered since 1998. Our goals were to determine the present distribution and qualitative status of Topeka shiners throughout its current range in Iowa and characterize the extent of decline in relation to its historic distribution. We compared the current (2016–2017) distribution to distributions portrayed in three earlier time periods. In 2016–2017 Topeka shiners were found in 12 of 20 HUC10 watersheds where they occurred historically. Their status was classified as stable in 21% of the HUC10 watersheds, possibly stable in 25%, possibly recovering in 8%, at risk in 33%, and possibly extirpated in 13% of the watersheds. The increasing trend in percent decline evident in earlier time periods reversed, going from 68% in 2010–11 to 40% in the most recent surveys. Following decades of decline, the status of Topeka shiners in Iowa appears to be improving. One potential reason for the reversal in the distributional decline of Topeka shiners in Iowa is the increasing number of oxbow restorations. Until a standardized monitoring program is established for Iowa, periodic status assessments such as this will be necessary to chronicle progress toward conserving this endangered fish species
Photon Echoes Produced by Switching Electric Fields
We demonstrate photon echoes in Eu:YSiO by controlling the
inhomogeneous broadening of the Eu
FD optical transition. This transition has
a linear Stark shift and we induce inhomogeneous broadening by applying an
external electric field gradient. After optical excitation, reversing the
polarity of the field rephases the ensemble, resulting in a photon echo. This
is the first demonstration of such a photon echo and its application as a
quantum memory is discussed.Comment: improved introduction, including theoretical outline of the relvant
quantum memory proposa
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Correlated analytical studies of organic material from the Tagish Lake carbonaceous chondrite
We report on correlated studies of organic material using SIMS, FIB-SEM, and TEM
Piecewise smooth systems near a co-dimension 2 discontinuity manifold: can one say what should happen?
We consider a piecewise smooth system in the neighborhood of a co-dimension 2
discontinuity manifold . Within the class of Filippov solutions, if
is attractive, one should expect solution trajectories to slide on
. It is well known, however, that the classical Filippov
convexification methodology is ambiguous on . The situation is further
complicated by the possibility that, regardless of how sliding on is
taking place, during sliding motion a trajectory encounters so-called generic
first order exit points, where ceases to be attractive.
In this work, we attempt to understand what behavior one should expect of a
solution trajectory near when is attractive, what to expect
when ceases to be attractive (at least, at generic exit points), and
finally we also contrast and compare the behavior of some regularizations
proposed in the literature.
Through analysis and experiments we will confirm some known facts, and
provide some important insight: (i) when is attractive, a solution
trajectory indeed does remain near , viz. sliding on is an
appropriate idealization (of course, in general, one cannot predict which
sliding vector field should be selected); (ii) when loses attractivity
(at first order exit conditions), a typical solution trajectory leaves a
neighborhood of ; (iii) there is no obvious way to regularize the
system so that the regularized trajectory will remain near as long as
is attractive, and so that it will be leaving (a neighborhood of)
when looses attractivity.
We reach the above conclusions by considering exclusively the given piecewise
smooth system, without superimposing any assumption on what kind of dynamics
near (or sliding motion on ) should have been taking place.Comment: 19 figure
Magnetic properties of iron pnictides from spin-spiral calculations
The wave-vector (q) and doping dependences of the magnetic energy, iron
moment, and effective exchange interactions in LaFeAsO, BaFe2As2, and SrFe2As2\
are studied by self-consistent LSDA calculations for co-planar spin spirals.
For the undoped compounds, the calculated total energy, E(q), reaches its
minimum at q corresponding to stripe anti-ferromagnetic order. In LaFeAsO, this
minimum becomes flat already at low levels of electron-doping and shifts to an
incommensurate q at delta=0.2, where delta is the number of additional
electrons (delta>0) or holes (delta<0) per Fe. In BaFe2As2 and SrFe2As2, stripe
order remains stable for hole doping down to delta=-0.3. Under electron doping,
on the other hand, the E(q) minimum shifts to incommensurate q already at
delta=0.1.Comment: 4 pages, 2 figures, International Conference on Magnetism, Karlsruhe,
July 26 - 31, 200
Radiation from a charged particle and radiation reaction -- revisited
We study the electromagnetic fields of an arbitrarily moving charged particle
and the radiation reaction on the charged particle using a novel approach. We
first show that the fields of an arbitrarily moving charged particle in an
inertial frame can be related in a simple manner to the fields of a uniformly
accelerated charged particle in its rest frame. Since the latter field is
static and easily obtainable, it is possible to derive the fields of an
arbitrarily moving charged particle by a coordinate transformation. More
importantly, this formalism allows us to calculate the self-force on a charged
particle in a remarkably simple manner. We show that the original expression
for this force, obtained by Dirac, can be rederived with much less computation
and in an intuitively simple manner using our formalism.Comment: Submitted to Physical Review
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