1,701 research outputs found
Maintaining genetic integrity of coexisting wild and domestic populations : Genetic differentiation between wild and domestic Rangifer with long traditions of intentional interbreeding
The funding for the fieldwork and laboratory work for this study was provided by the ERC Advanced Grant 295458 Arctic Domus (PI D.G. Anderson). The writing and analysis was supported by ESRC ES-M0110548-1 JPI HUMANOR (PI D.G. Anderson). The sample set for Lake Nichatka was collected and deposited under a research programme of the Norwegian Institute for Nature Research. We thank Liv Midthjell for skilful laboratory analyses, Konstantin Klokov for help sourcing statistics on Russian reindeer populations, and Jan Heggenes for useful comments on an earlier version of this paper. A full list of project participants is in Appendix 2.Peer reviewedPublisher PD
The oxygen isotope effect on critical temperature in superconducting copper oxides
The isotope effect provided a crucial key to the development of the BCS
(Bardeen-Cooper-Schrieffer) microscopic theory of superconductivity for
conventional superconductors. In superconducting cooper oxides (cuprates)
showing an unconventional type of superconductivity, the oxygen isotope effect
is very peculiar: the exponential coefficient strongly depends on doping level.
No consensus has been reached so far on the origin of the isotope effect in the
cuprates. Here we show that the oxygen isotope effect in cuprates is in
agreement with the bisoliton theory of superconductivity.Comment: 3 pages including 4 figures; version 2 is with minor correction
Quantum coherence and carriers mobility in organic semiconductors
We present a model of charge transport in organic molecular semiconductors
based on the effects of lattice fluctuations on the quantum coherence of the
electronic state of the charge carrier. Thermal intermolecular phonons and
librations tend to localize pure coherent states and to assist the motion of
less coherent ones. Decoherence is thus the primary mechanism by which
conduction occurs. It is driven by the coupling of the carrier to the molecular
lattice through polarization and transfer integral fluctuations as described by
the hamiltonian of Gosar and Choi. Localization effects in the quantum coherent
regime are modeled via the Anderson hamiltonian with correlated diagonal and
non-diagonal disorder leading to the determination of the carrier localization
length. This length defines the coherent extension of the ground state and
determines, in turn, the diffusion range in the incoherent regime and thus the
mobility. The transfer integral disorder of Troisi and Orlandi can also be
incorporated. This model, based on the idea of decoherence, allowed us to
predict the value and temperature dependence of the carrier mobility in
prototypical organic semiconductors that are in qualitative accord with
experiments
Extension of Frohlich's method to 4-fermion interactions
Higher order terms of the transformed electron-phonon Hamiltonian, obtained
by performing the Frohlich's transformation, are investigated. The influence of
terms discarded by Frohlich (in particular those proportional to the third
power of electron-phonon coupling) on the effective Hamiltonian is examined. To
this end a second Frohlich-type transformation is performed, which yields,
among others, an effective 4-electron interaction. This interaction is reduced
to a form admitting solution of thermodynamics. The form of the coupling of the
4-electron interaction is found. By applying standard approximations, it is
shown that this interaction is attractive with interaction coupling given by -
D_{k_F}^6 / \omega_{k_F}^5, where D_{k} is electron-phonon coupling,
\omega_{k}$ is phonon energy and k_F is Fermi momentum.
The form of higher order terms of the original Frohlich-transformed H_{e-ph}
are also found, up to terms proportional to the 6-th power of the coupling,
that is up to those, which yield the effective 4-electron interactions.Comment: REVTeX4, 25 pages; major changes: added section and appendix about
the form of 4-fermion interaction coupling, typos correcte
Calculation of the energy spectrum of a two-electron spherical quantum dot
We study the energy spectrum of the two-electron spherical parabolic quantum
dot using the exact Schroedinger, the Hartree-Fock, and the Kohn-Sham
equations. The results obtained by applying the shifted-1/N method are compared
with those obtained by using an accurate numerical technique, showing that the
relative error is reasonably small, although the first method consistently
underestimates the correct values. The approximate ground-state Hartree-Fock
and local-density Kohn-Sham energies, estimated using the shifted-1/N method,
are compared with accurate numerical self-consistent solutions. We make some
perturbative analyses of the exact energy in terms of the confinement strength,
and we propose some interpolation formulae. Similar analysis is made for both
mean-field approximations and interpolation formulae are also proposed for
these exchange-only ground-state cases.Comment: 18 pages, LaTeX, 2 figures-ep
Proton Wires in an Electric Field: the Impact of Grotthuss Mechanism on Charge Translocation
We present the results of the modeling of proton translocation in finite
H-bonded chains in the framework of two-stage proton transport model. We
explore the influence of reorientation motion of protons, as well as the effect
of electric field and proton correlations on system dynamics. An increase of
the reorientation energy results in the transition of proton charge from the
surrounding to the inner water molecules in the chain. Proton migration along
the chain in an external electric field has a step-like character, proceeding
with the occurrence of electric field threshold-type effects and drastic
redistribution of proton charge. Electric field applied to correlated chains
induces first a formation of ordered dipole structures for lower field
strength, and than, with a further field strength increase, a stabilization of
states with Bjerrum D-defects. We analyze the main factors responsible for the
formation/annihilation of Bjerrum defects showing the strong influence of the
complex interplay between reorientation energy, electric field and temperature
in the dynamics of proton wire.Comment: 28 pages, 9 figure
Tensor polarization of deuterons passing through matter
It is shown that the magnitude of tensor polarization of the deuteron beam,
which arises owing to the spin dichroism effect, depends appreciably on the
angular width of the detector that registers the deuterons transmitted through
the target. Even when the angular width of the detector is much smaller than
the mean square angle of multiple Coulomb scattering, the beam's tensor
polarization depends noticeably on rescattering. When the angular width of the
detector is much larger than the mean square angle of multiple Coulomb
scattering (as well as than the characteristic angle of elastic nuclear
scattering), tensor polarization is determined only by the total reaction cross
sections for deuteron-nucleus interaction, and elastic scattering processes
make no contribution to tensor polarization.Comment: 18 pages, 3 figures, to be published in IO
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