9,875 research outputs found
Magnetic Phases of Rare Earth Hexagonal Manganites
We describe the magnetic phases of hexagonal rare earth manganites RMnO3
using Landau theory. A minimal model based on four one-dimensional magnetic
order parameters is developed.Comment: 2 Pages, Proceedings of SCES'0
New structures in the proton-antiproton system
In the most recent measurements of the reaction
by the BABAR collaboration, new structures have been found with unknown origin.
We examine a possible relation of the most distinct peak to the recently
observed . Alternatively, we analyse possible explanations due to
the nucleon and thresholds. The latter
could explain a periodicity found in the data
Heat transfer between elastic solids with randomly rough surfaces
We study the heat transfer between elastic solids with randomly rough
surfaces. We include both the heat transfer from the area of real contact, and
the heat transfer between the surfaces in the noncontact regions. We apply a
recently developed contact mechanics theory, which accounts for the
hierarchical nature of the contact between solids with roughness on many
different length scales. For elastic contact, at the highest (atomic)
resolution the area of real contact typically consists of atomic (nanometer)
sized regions, and we discuss the implications of this for the heat transfer.
For solids with very smooth surfaces, as is typical in many modern engineering
applications, the interfacial separation in the non-contact regions will be
very small, and for this case we show the importance of the radiative heat
transfer associated with the evanescent electromagnetic waves which exist
outside of all bodies.Comment: 23 pages, 19 figure
Zoo of quantum phases and excitations of cold bosonic atoms in optical lattices
Quantum phases and phase transitions of weakly- to strongly-interacting
bosonic atoms in deep to shallow optical lattices are described by a {\it
single multi-orbital mean-field approach in real space}. For weakly-interacting
bosons in 1D, the critical value of the superfluid to Mott insulator (MI)
transition found is in excellent agreement with {\it many-body} treatments of
the Bose-Hubbard model. For strongly-interacting bosons, (i) additional MI
phases appear, for which two (or more) atoms residing in {\it each site}
undergo a Tonks-Girardeau-like transition and localize and (ii) on-site
excitation becomes the excitation lowest in energy. Experimental implications
are discussed.Comment: 12 pages, 3 figure
Ultrafast interatomic electronic decay in multiply excited clusters
An ultrafast mechanism belonging to the family of interatomic Coulombic decay
(ICD) phenomena is proposed. When two excited species are present, an ultrafast
energy transfer can take place bringing one of them to its ground state and
ionizing the other one. It is shown that if large homoatomic clusters are
exposed to an ultrashort and intense laser pulse whose photon energy is in
resonance with an excitation transition of the cluster constituents, the large
majority of ions will be produced by this ICD mechanism rather than by
two-photon ionization. A related collective-ICD process that is operative in
heteroatomic systems is also discussed.Comment: 4 pages, 3 figure
Theoretical study of electronic damage in single particle imaging experiments at XFELs for pulse durations 0.1 - 10 fs
X-ray free-electron lasers (XFELs) may allow to employ the single particle
imaging (SPI) method to determine the structure of macromolecules that do not
form stable crystals. Ultrashort pulses of 10 fs and less allow to outrun
complete disintegration by Coulomb explosion and minimize radiation damage due
to nuclear motion, but electronic damage is still present. The major
contribution to the electronic damage comes from the plasma generated in the
sample that is strongly dependent on the amount of Auger ionization. Since the
Auger process has a characteristic time scale on the order of femtoseconds, one
may expect that its contribution will be significantly reduced for attosecond
pulses. Here, we study the effect of electronic damage on the SPI at pulse
durations from 0.1 fs to 10 fs and in a large range of XFEL fluences to
determine optimal conditions for imaging of biological samples. We analyzed the
contribution of different electronic excitation processes and found that at
fluences higher than - photons/m (depending on the
photon energy and pulse duration) the diffracted signal saturates and does not
increase further. A significant gain in the signal is obtained by reducing the
pulse duration from 10 fs to 1 fs. Pulses below 1 fs duration do not give a
significant gain in the scattering signal in comparison with 1 fs pulses. We
also study the limits imposed on SPI by Compton scattering.Comment: 35 pages, 9 figures, 1 table, 2 appendixes, 45 reference
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