10,368 research outputs found
Spectral isometries on non-simple C*-algebras
We prove that unital surjective spectral isometries on certain non-simple
unital C*-algebras are Jordan isomorphisms. Along the way, we establish several
general facts in the setting of semisimple Banach algebras.Comment: 7 pages; paper available since July 201
Memory and rejuvenation in a spin glass
The temperature dependence of the magnetisation of a Cu(Mn) spin glass (
57 K) has been investigated using weak probing magnetic fields ( =
0.5 or 0 Oe) and specific thermal protocols. The behaviour of the zero-field
cooled, thermoremanent and isothermal remanent magnetisation on (re-)cooling
the system from a temperature (40 K) where the system has been aged is
investigated. It is observed that the measured magnetisation is formed by two
parts: (i) a temperature- and observation time-dependent thermally activated
relaxational part governed by the age- and temperature-dependent response
function and the (latest) field change made at a lower temperature, superposed
on (ii) a weakly temperature-dependent frozen-in part. Interestingly we observe
that the spin configuration that is imprinted during an elongated halt in the
cooling, if it is accompanied by a field induced magnetisation, also includes a
unidirectional excess magnetisation that is recovered on returning to the
ageing temperature.Comment: EPL style; 7 pages, 5 figure
X rays from old open clusters: M 67 and NGC 188
We have observed the old open clusters M 67 and NGC 188 with the ROSAT PSPC.
In M 67 we detect a variety of X-ray sources. The X-ray emission by a
cataclysmic variable, a single hot white dwarf, two contact binaries, and some
RS CVn systems is as expected. The X-ray emission by two binaries located below
the subgiant branch in the Hertzsprung Russell diagram of the cluster, by a
circular binary with a cool white dwarf, and by two eccentric binaries with
orbital period > 700 d is puzzling. Two members of NGC 188 are detected,
including the FK Com type star D719. Another possible FK Com type star,
probably not a member of NGC 188, is also detected.Comment: 10 pages, 5 figures. Accepted for publication on Astronomy &
Astrophysic
Magnetotransport in a bi-crystal film of La_0.7Sr_0.3MnO_3
Transport properties of an epitaxial film of La_0.7Sr_0.3MnO_3 (LSMO),
deposited epitaxially on a LaAlO_3 bi-crystal substrate having a misorientation
angle of 9.2 deg., have been studied.
The film was patterned into a meander containing 100 grain boundaries. The
resistivity of the sample exhibits two components; one originating from the
grain boundary regions, and one from the LSMO elements in the meander; the
latter contribution is similar to the resistivity of a reference epitaxial LSMO
film. The low (<0.5 T) and high (up to 6 T) field magnetoresistance was also
studied. The meander show a large low field magnetoresistance, increasing with
decreasing temperature, and a constant high field slope of the
magnetoconductance, results that are well explained by a two-step spin
polarized tunneling model.Comment: ICM2000 contribution - 6 pages, 3 figure
The Progeny of Stellar Dynamics and Stellar Evolution within an N-body model of NGC 188
We present a direct N-body simulation modeling the evolution of the old (7
Gyr) open cluster NGC 188. This is the first N-body open cluster simulation
whose initial binary population is directly defined by observations of a
specific open cluster: M35 (150 Myr). We compare the simulated color-magnitude
diagram at 7 Gyr to that of NGC 188, and discuss the blue stragglers produced
in the simulation. We compare the solar-type main sequence binary period and
eccentricity distributions of the simulation to detailed observations of
similar binaries in NGC 188. These results demonstrate the importance of
detailed observations in guiding N-body open cluster simulations. Finally, we
discuss the implications of a few discrepancies between the NGC 188 model and
observations and suggest a few methods for bringing N-body open cluster
simulations into better agreement with observations.Comment: Contributed talk at IAUS 266 'Star clusters: basic galactic building
blocks', R. de Grijs and J.R.D. Lepine, eds. 6 pages, 4 figure
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