387 research outputs found
Electronic-structure-induced deformations of liquid metal clusters
Ab initio molecular dynamics is used to study deformations of sodium clusters
at temperatures K. Open-shell Na cluster has two shape
isomers, prolate and oblate, in the liquid state. The deformation is stabilized
by opening a gap at the Fermi level. The closed-shell Na remains magic also
at the liquid state.Comment: REVTex, 11 pages, no figures, figures (2) available upon request
(e-mail to hakkinen at jyfl.jyu.fi), submitted to Phys. Rev.
Limited diversity in natal origins of immature anadromous fish during ocean residency
Author Posting. © The Authors, 2009. This is the author's version of the work. It is posted here by permission of NRC Research Press for personal use, not for redistribution. The definitive version was published in Canadian Journal of Fisheries and Aquatic Sciences. 67 (2010): 1699-1707, doi:10.1139/F10-086.Variable migration patterns can play a significant role in promoting diverse life history traits among populations. However, population and stage specific movement patterns are generally unknown yet crucial aspects of life history strategies in many highly migratory species. We used a natural tag approach using geochemical signatures in otoliths to identify natal origins of one-year-old anadromous American shad (Alosa sapidissima) during ocean residency. Otolith signatures of migrants were compared to a database of baseline signatures from 20 source populations throughout their spawning range. Samples were dominated by fish from only two rivers, while all other potential source populations were nearly or completely absent. These data support the hypothesis that American shad exhibit diverse migratory behaviors and immature individuals from populations throughout the native range do not all mix on northern summer feeding grounds. Rather, our results suggest populations of anadromous fish are distributed heterogeneously at sea in the first year of life and thus may encounter different ocean conditions at a critical early life history stage.This work was funded by National Science Foundation grants OCE-0215905 and OCE-0134998 to SRT and by a WHOI Ocean Life Institute grant to BDW
Chaos in a double driven dissipative nonlinear oscillator
We propose an anharmonic oscillator driven by two periodic forces of
different frequencies as a new time-dependent model for investigating quantum
dissipative chaos. Our analysis is done in the frame of statistical ensemble of
quantum trajectories in quantum state diffusion approach. Quantum dynamical
manifestation of chaotic behavior, including the emergence of chaos, properties
of strange attractors, and quantum entanglement are studied by numerical
simulation of ensemble averaged Wigner function and von Neumann entropy.Comment: 9 pages, 18 figure
On the nature of cosmic rays above the Greisen--Zatsepin--Kuz'min cut off
A re-examination of the atmospheric cascade profile of the highest energy
cosmic ray is presented. The study includes air-shower simulations considering
different cross sections, particle multiplicity and variation of the
hadronic-event-generator to model interactions above 200 GeV. The analysis
provides evidence that a medium mass nucleus primary reproduces the shower
profile quite well. This result does not support the idea, increasingly popular
at present, that the highest energy particles are protons, derived from the
decay of supermassive relic particles. On the other hand, we show that debris
of relativistic super-heavy nuclei, which can survive a 100 Mpc journey through
the primeval radiation are likely to generate such a kind of cascade.Comment: Revised version, improvements per referee's suggestions. To be
published in Phys. Lett.
Parity violating target asymmetry in electron - proton scattering
We analyze the parity-violating (PV) components of the analyzing power in
elastic electron-proton scattering and discuss their sensitivity to the strange
quark contributions to the proton weak form factors. We point out that the
component of the analyzing power along the momentum transfer is independent of
the electric weak form factor and thus compares favorably with the PV beam
asymmetry for a determination of the strangeness magnetic moment. We also show
that the transverse component could be used for constraining the strangeness
radius. Finally, we argue that a measurement of both components could give
experimental information on the strangeness axial charge.Comment: 24 pages, Latex, 5 eps figures, submitted to Phys.Rev.
Ionic and electronic structure of sodium clusters up to N=59
We determined the ionic and electronic structure of sodium clusters with even
electron numbers and 2 to 59 atoms in axially averaged and three-dimensional
density functional calculations. A local, phenomenological pseudopotential that
reproduces important bulk and atomic properties and facilitates structure
calculations has been developed. Photoabsorption spectra have been calculated
for , , and to
. The consistent inclusion of ionic structure considerably
improves agreement with experiment. An icosahedral growth pattern is observed
for to . This finding is supported by
photoabsorption data.Comment: To appear in Phys. Rev. B 62. Version with figures in better quality
can be requested from the author
Four-fermion heavy quark operators and light current amplitudes in heavy flavor hadrons
We introduce and study the properties of the "color-straight" four-quark
operators containing heavy and light quark fields. They are of the form (\bar
b\Gamma_b b)(\bar q\Gamma_q q) where both brackets are color singlets. Their
expectation values include the bulk of the nonfactorizable contributions to the
nonleptonic decay widths of heavy hadrons. The expectation values of the
color-straight operators in the heavy hadrons are related to the momentum
integrals of the elastic light-quark formfactors of the respective heavy
hadron. We calculate the asymptotic behavior of the light-current formfactors
of heavy hadrons and show that the actual decrease is 1/(q^2)^3/2 rather than
1/q^4. The two-loop hybrid anomalous dimensions of the four-quark operators and
their mixing (absent in the first loop) are obtained. Using plausible models
for the elastic formfactors, we estimate the expectation values of the
color-straight operators in the heavy mesons and baryons. Improved estimates
will be possible in the future with new data on the radiative decays of heavy
hadrons. We give the Wilson coefficients of the four-fermion operators in the
1/m_b expansion of the inclusive widths and discuss the numerical predictions.
Estimates of the nonfactorizable expectation values are given.Comment: 51 pages. The case of flavor-singlet operators is added for the
two-loop anomalous dimension
Energetics, forces, and quantized conductance in jellium modeled metallic nanowires
Energetics and quantized conductance in jellium modeled nanowires are
investigated using the local density functional based shell correction method,
extending our previous study of uniform in shape wires [C. Yannouleas and U.
Landman, J. Phys. Chem. B 101, 5780 (1997)] to wires containing a variable
shaped constricted region. The energetics of the wire (sodium) as a function of
the length of the volume conserving, adiabatically shaped constriction leads to
formation of self selecting magic wire configurations. The variations in the
energy result in oscillations in the force required to elongate the wire and
are directly correlated with the stepwise variations of the conductance of the
nanowire in units of 2e^2/h. The oscillatory patterns in the energetics and
forces, and the correlated stepwise variation in the conductance are shown,
numerically and through a semiclassical analysis, to be dominated by the
quantized spectrum of the transverse states at the narrowmost part of the
constriction in the wire.Comment: Latex/Revtex, 11 pages with 5 Postscript figure
Radiative Decay of a Long-Lived Particle and Big-Bang Nucleosynthesis
The effects of radiatively decaying, long-lived particles on big-bang
nucleosynthesis (BBN) are discussed. If high-energy photons are emitted after
BBN, they may change the abundances of the light elements through
photodissociation processes, which may result in a significant discrepancy
between the BBN theory and observation. We calculate the abundances of the
light elements, including the effects of photodissociation induced by a
radiatively decaying particle, but neglecting the hadronic branching ratio.
Using these calculated abundances, we derive a constraint on such particles by
comparing our theoretical results with observations. Taking into account the
recent controversies regarding the observations of the light-element
abundances, we derive constraints for various combinations of the measurements.
We also discuss several models which predict such radiatively decaying
particles, and we derive constraints on such models.Comment: Published version in Phys. Rev. D. Typos in figure captions correcte
Using the past to constrain the future: how the palaeorecord can improve estimates of global warming
Climate sensitivity is defined as the change in global mean equilibrium
temperature after a doubling of atmospheric CO2 concentration and provides a
simple measure of global warming. An early estimate of climate sensitivity,
1.5-4.5{\deg}C, has changed little subsequently, including the latest
assessment by the Intergovernmental Panel on Climate Change.
The persistence of such large uncertainties in this simple measure casts
doubt on our understanding of the mechanisms of climate change and our ability
to predict the response of the climate system to future perturbations. This has
motivated continued attempts to constrain the range with climate data, alone or
in conjunction with models. The majority of studies use data from the
instrumental period (post-1850) but recent work has made use of information
about the large climate changes experienced in the geological past.
In this review, we first outline approaches that estimate climate sensitivity
using instrumental climate observations and then summarise attempts to use the
record of climate change on geological timescales. We examine the limitations
of these studies and suggest ways in which the power of the palaeoclimate
record could be better used to reduce uncertainties in our predictions of
climate sensitivity.Comment: The final, definitive version of this paper has been published in
Progress in Physical Geography, 31(5), 2007 by SAGE Publications Ltd, All
rights reserved. \c{opyright} 2007 Edwards, Crucifix and Harriso
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