25,062 research outputs found
New nonlinear coherent states and some of their nonclassical properties
We construct a displacement operator type nonlinear coherent state and
examine some of its properties. In particular it is shown that this nonlinear
coherent state exhibits nonclassical properties like squeezing and
sub-Poissonian behaviour.Comment: 3 eps figures. to appear in J.Opt
Optimal detection of changepoints with a linear computational cost
We consider the problem of detecting multiple changepoints in large data
sets. Our focus is on applications where the number of changepoints will
increase as we collect more data: for example in genetics as we analyse larger
regions of the genome, or in finance as we observe time-series over longer
periods. We consider the common approach of detecting changepoints through
minimising a cost function over possible numbers and locations of changepoints.
This includes several established procedures for detecting changing points,
such as penalised likelihood and minimum description length. We introduce a new
method for finding the minimum of such cost functions and hence the optimal
number and location of changepoints that has a computational cost which, under
mild conditions, is linear in the number of observations. This compares
favourably with existing methods for the same problem whose computational cost
can be quadratic or even cubic. In simulation studies we show that our new
method can be orders of magnitude faster than these alternative exact methods.
We also compare with the Binary Segmentation algorithm for identifying
changepoints, showing that the exactness of our approach can lead to
substantial improvements in the accuracy of the inferred segmentation of the
data.Comment: 25 pages, 4 figures, To appear in Journal of the American Statistical
Associatio
Optical Spectroscopy of X-Mega targets in the Carina Nebula - VI. FO 15: a new O-Type double-lined eclipsing binary
We report the discovery of a new O-type double-lined spectroscopic binary
with a short orbital period of 1.4 days. We find the primary component of this
binary, FO 15, to have an approximate spectral type O5.5Vz, i.e. a
Zero-Age-Main-Sequence star. The secondary appears to be of spectral type
O9.5V. We have performed a numerical model fit to the public ASAS photometry,
which shows that FO 15 is also an eclipsing binary. We find an orbital
inclination of ~ 80 deg. From a simultaneous light-curve and radial velocity
solution we find the masses and radii of the two components to be 30 +/- 1 and
16 +/- 1 solar masses and 7.5 +/- 0.5 and 5.3 +/- 0.5 solar radii. These radii,
and hence also the luminosities, are smaller than those of normal O-type stars,
but similar to recently born ZAMS O-type stars. The absolute magnitudes derived
from our analysis locate FO 15 at the same distance as Eta Carinae. From
Chandra and XMM X-ray images we also find that there are two close X-ray
sources, one coincident with FO 15 and another one without optical counterpart.
This latter seems to be a highly variable source, presumably due to a
pre-main-sequence stellar neighbour of FO 15.Comment: 11 pages, 9 figures, 3 tables. Accepted for publication in MNRAS.
Higher resolution version available at
http://lilen.fcaglp.unlp.edu.ar/papers2006.htm
Phase properties of a new nonlinear coherent state
We study phase properties of a displacement operator type nonlinear coherent
state. In particular we evaluate the Pegg-Barnett phase distribution and
compare it with phase distributions associated with the Husimi Q function and
the Wigner function. We also study number- phase squeezing of this state.Comment: 8 eps figures. to appear in J.Opt
Ferromagnetic coupling of mononuclear Fe centers in a self-assembled metal-organic network on Au(111)
The magnetic state and magnetic coupling of individual atoms in nanoscale
structures relies on a delicate balance between different interactions with the
atomic-scale surrounding. Using scanning tunneling microscopy, we resolve the
self-assembled formation of highly ordered bilayer structures of Fe atoms and
organic linker molecules (T4PT) when deposited on a Au(111) surface. The Fe
atoms are encaged in a three-dimensional coordination motif by three T4PT
molecules in the surface plane and an additional T4PT unit on top. Within this
crystal field, the Fe atoms retain a magnetic ground state with easy-axis
anisotropy, as evidenced by X-ray absorption spectroscopy and X-ray magnetic
circular dichroism. The magnetization curves reveal the existence of
ferromagnetic coupling between the Fe centers
Spectra of Doubly Heavy Quark Baryons
Baryons containing two heavy quarks are treated in the Born-Oppenheimer
approximation. Schr\"odinger equation for two center Coulomb plus harmonic
oscillator potential is solved by the method of ethalon equation at large
intercenter separations. Asymptotical expansions for energy term and wave
function are obtained in the analytical form. Using those formulas, the energy
spectra of doubly heavy baryons with various quark compositions are calculated
analytically.Comment: 19 pages, latex2e, published at PRC61(2000)04520
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