5,938 research outputs found
Radiation counting technique allows density measurement of metals in high-pressure/ high-temperature environment
Radioactive tracers induced by neutron irradiation provide a gamma ray flux proportional to the density of a metal, allowing density measurement of these metals in extreme high-temperature and high-pressure environments. This concept is applicable to most metals, as well as other substances
Rapid Evolutionary Rewiring of a Structurally Constrained Eye Enhancer
SummaryBackgroundEnhancers are genomic cis-regulatory sequences that integrate spatiotemporal signals to control gene expression. Enhancer activity depends on the combination of bound transcription factors as well as—in some cases—the arrangement and spacing of binding sites for these factors. Here, we examine evolutionary changes to the sequence and structure of sparkling, a Notch/EGFR/Runx-regulated enhancer that activates the dPax2 gene in cone cells of the developing Drosophila eye.ResultsDespite functional and structural constraints on its sequence, sparkling has undergone major reorganization in its recent evolutionary history. Our data suggest that the relative strengths of the various regulatory inputs into sparkling change rapidly over evolutionary time, such that reduced input from some factors is compensated by increased input from different regulators. These gains and losses are at least partly responsible for the changes in enhancer structure that we observe. Furthermore, stereotypical spatial relationships between certain binding sites (“grammar elements”) can be identified in all sparkling orthologs—although the sites themselves are often recently derived. We also find that low binding affinity for the Notch-regulated transcription factor Su(H), a conserved property of sparkling, is required to prevent ectopic responses to Notch in noncone cells.ConclusionsRapid DNA sequence turnover does not imply either the absence of critical cis-regulatory information or the absence of structural rules. Our findings demonstrate that even a severely constrained cis-regulatory sequence can be significantly rewired over a short evolutionary timescale
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Treatment of Alaska-produced food products by ionizing radiation may
benefit the seafood and agricultural industries and the Alaskan consumer. A
feasibility study to evaluate the potential social and economic benefits and
risks as well as the costs of using the process in Alaska on Alaskan products is being coordinated
by the Institute of Northern Engineering. A research and development project to determine
effects on the quality o f Alaskan products could be the next phase in the introduction o f a new
food-preservation technique
to Alaska
Multibreather and vortex breather stability in Klein--Gordon lattices: Equivalence between two different approaches
In this work, we revisit the question of stability of multibreather
configurations, i.e., discrete breathers with multiple excited sites at the
anti-continuum limit of uncoupled oscillators. We present two methods that
yield quantitative predictions about the Floquet multipliers of the linear
stability analysis around such exponentially localized in space, time-periodic
orbits, based on the Aubry band method and the MacKay effective Hamiltonian
method and prove that their conclusions are equivalent. Subsequently, we
showcase the usefulness of the methods by a series of case examples including
one-dimensional multi-breathers, and two-dimensional vortex breathers in the
case of a lattice of linearly coupled oscillators with the Morse potential and
in that of the discrete model
A Feynman-Kac Formula for Anticommuting Brownian Motion
Motivated by application to quantum physics, anticommuting analogues of
Wiener measure and Brownian motion are constructed. The corresponding Ito
integrals are defined and the existence and uniqueness of solutions to a class
of stochastic differential equations is established. This machinery is used to
provide a Feynman-Kac formula for a class of Hamiltonians. Several specific
examples are considered.Comment: 21 page
Discrete breathers in systems with homogeneous potentials - analytic solutions
We construct lattice Hamiltonians with homogeneous interaction potentials
which allow for explicit breather solutions. Especially we obtain exponentially
localized solutions for -dimensional lattices with .Comment: 10 page
Photoinduced charge separation in Q1D heterojunction materials: Evidence for electron-hole pair separation in mixed-halide solids
Resonance Raman experiments on doped and photoexcited single crystals of
mixed-halide complexes (=Pt; =Cl,Br) clearly indicate charge
separation: electron polarons preferentially locate on PtBr segments while hole
polarons are trapped within PtCl segments. This polaron selectivity,
potentially very useful for device applications, is demonstrated theoretically
using a discrete, 3/4-filled, two-band, tight-binding, extended Peierls-Hubbard
model. Strong hybridization of the PtCl and PtBr electronic bands is the
driving force for separation.Comment: n LaTeX, figures available by mail from JTG ([email protected]
Competing Ground States of the New Class of Halogen-Bridged Metal Complexes
Based on a symmetry argument, we study the ground-state properties of
halogen-bridged binuclear metal chain complexes. We systematically derive
commensurate density-wave solutions from a relevant two-band Peierls-Hubbard
model and numerically draw the the ground-state phase diagram as a function of
electron-electron correlations, electron-phonon interactions, and doping
concentration within the Hartree-Fock approximation. The competition between
two types of charge-density-wave states, which has recently been reported
experimentally, is indeed demonstrated.Comment: 4 pages, 5 figures embedded, to appear in J. Phys. Soc. Jp
Short-range repulsion and isospin dependence in the KN system
The short-range properties of the KN interaction are studied within the
meson-exchange model of the Juelich group. Specifically, dynamical explanations
for the phenomenological short-range repulsion, required in this model for
achieving agreement with the empirical KN data, are explored. Evidence is found
that contributions from the exchange of a heavy scalar-isovector meson
(a_0(980)) as well as from genuine quark-gluon exchange processes are needed.
Taking both mechanisms into account a satisfactory description of the KN phase
shifts can be obtained without resorting to phenomenological pieces.Comment: 26 pages, 5 figure
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