4,244 research outputs found
Non-destructive measurement of the transition probability in a Sr optical lattice clock
We present the experimental demonstration of non-destructive probing of the
1S0-3P0 clock transition probability in an optical lattice clock with 87Sr
atoms. It is based on the phase shift induced by the atoms on a weak
off-resonant laser beam. The method we propose is a differential measurement of
this phase shift on two modulation sidebands with opposite detuning with
respect to the 1S0-1P1 transition, allowing a detection limited by the photon
shot noise. We have measured an atomic population of 10^4 atoms with a signal
to noise ratio of 100 per cycle, while keeping more than 95% of the atoms in
the optical lattice with a depth of 0.1 mK. The method proves simple and robust
enough to be operated as part of the whole clock setup. This detection scheme
enables us to reuse atoms for subsequent clock state interrogations,
dramatically reducing the loading time and thereby improving the clock
frequency stability.Comment: 4 pages, 5 figure
Magnetodielectric effect of Bi6Fe2Ti3O18 film under an ultra-low magnetic field
Good quality and fine grain Bi6Fe2Ti3O18 magnetic ferroelectric films with
single-phase layered perovskite structure have been successfully prepared via
metal organic decomposition (MOD) method. Results of low-temperature
magnetocapacitance measurements reveal that an ultra-low magnetic field of 10
Oe can produce a nontrivial magnetodielectric (MD) response in
zero-field-cooling condition, and the relative variation of dielectric
constants in magnetic field is positive, i.e., MD=0.05, when T<55K, but
negative with a maximum of MD=-0.14 when 55K<T<190K. The magnetodielectric
effect appears a sign change at 55K, which is due to transition from
antiferromagnetic to weak ferromagnetic; and vanishes abruptly around 190K,
which is thought to be associated with order-disorder transition of iron ion at
B site of perovskite structures. The ultra-low-field magnetodielectric
behaviour of Bi6Fe2Ti3O18 film has been discussed in the light of
quasi-two-dimension unique nature of local spin order in ferroelectric film.
Our results allow expectation on low-cost applications of detectors and
switches for extremely weak magnetic fields in a wide temperature range
55K-190K.Comment: 10 pages 4 figures, planned to submit to J. Phys.: Condensed Matte
Molecular and Ionic shocks in the Supernova Remnant 3C391
New observations of the supernova remnant 3C391 are in the H2 2.12 micron and
[Fe II] 1.64 micron narrow-band filters at the Palomar 200-inch telescope, and
in the 5-15 micron CVF on ISOCAM. Shocked H2 emission was detected from the
region 3C391:BML, where broad millimeter CO and CS lines had previously been
detected. A new H2 clump was confirmed to have broad CO emission, demonstrating
that the near-infrared H2 images can trace previously undetected molecular
shocks. The [Fe II] emission has a significantly different distribution, being
brightest in the bright radio bar, at the interface between the supernova
remnant and the giant molecular cloud, and following filaments in the radio
shell. The near-infrared [Fe II] and the mid-infrared 12-18 micron filter
images are the first images to reveal the radiative shell of 3C391. The
mid-infrared spectrum is dominated by bright ionic lines and H2 S(2) through
S(7). There are no aromatic hydrocarbons associated with the shocks, nor is
their any mid-infrared continuum, suggesting that macromolecules and very small
grains are destroyed. Comparing 3C391 to the better-studied IC443, both
remnants have molecular- and ionic-dominated regions; for 3C391, the
ionic-dominated region is the interface into the giant molecular cloud, showing
that the main bodies of giant molecular clouds contain significant regions with
densities 100 to 1000/cm^3 and a small filling factor with higher-density. The
molecular shocked region resolves into 16 clumps of H2 emission, with some
fainter diffuse emission but with no associated near-infrared continuum
sources. One of the clumps is coincident with a previously-detected OH 1720 MHz
maser. These clumps are interpreted as a cluster of pre-stellar, dense
molecular cores that are presently being shocked by the supernova blast wave
Radio continuum imaging of FIR luminous QSOs at z>6
We present sensitive imaging at 1.4 GHz of the two highest redshift
far-infrared (FIR) luminous QSOs SDSS J114816.65+525150.2 (z=6.42) and SDSS
J104845.05+463718.3 (z=6.2). Radio continuum emission is detected from
J1148+5251 with S_{1.4} = 55 \pm 12 uJy, while J1048+4637 is marginally
detected with S_{1.4} = 26 \pm 12 uJy. Comparison of the radio and FIR
luminosities shows that both sources follow the radio-FIR correlation for star
forming galaxies, with implied (massive) star formation rates \sim 10^3 M_sun
year^{-1}, although we cannot rule-out as much as 50% of the FIR luminosity
being powered by the AGN. Five bright (> 22 mJy) radio sources are detected
within 8' of J1148+5251. This is a factor 30 more than expected for a random
field. Two sources have SDSS redshifts, including a z = 1.633 radio loud quasar
and a z = 0.05 radio galaxy. However, we do not find evidence for a galaxy
cluster in the SDSS data, at least out to z = 0.2. Considering the faint SDSS
magnitudes of the remaining radio sources, we conclude that the over-density of
radio sources could either be a statistical fluke, or a very large scale
structure (> 8 Mpc comoving) at z > 1. We also consider the possibility of
gravitational lensing by the closest (in angle) bright galaxy in the SDSS data
at z = 0.05, and conclude that the galaxy provides negligible magnification.Comment: aastex, 5 figures, 2 tables. to appear in the Astronomical Journa
Phase appearance or disappearance in two-phase flows
This paper is devoted to the treatment of specific numerical problems which
appear when phase appearance or disappearance occurs in models of two-phase
flows. Such models have crucial importance in many industrial areas such as
nuclear power plant safety studies. In this paper, two outstanding problems are
identified: first, the loss of hyperbolicity of the system when a phase appears
or disappears and second, the lack of positivity of standard shock capturing
schemes such as the Roe scheme. After an asymptotic study of the model, this
paper proposes accurate and robust numerical methods adapted to the simulation
of phase appearance or disappearance. Polynomial solvers are developed to avoid
the use of eigenvectors which are needed in usual shock capturing schemes, and
a method based on an adaptive numerical diffusion is designed to treat the
positivity problems. An alternate method, based on the use of the hyperbolic
tangent function instead of a polynomial, is also considered. Numerical results
are presented which demonstrate the efficiency of the proposed solutions
A Population of Faint Non-Transient Low Mass Black Hole Binaries
We study the thermal and viscous stability of accretion flows in Low Mass
Black Hole Binaries (LMBHBs). We consider a model in which an inner
advection-dominated accretion flow (ADAF) is surrounded by a geometrically thin
accretion disk, the transition between the two zones occurring at a radius
R_tr. In all the known LMBHBs, R_tr appears to be such that the outer disks
could suffer from a global thermal-viscous instability. This instability is
likely to cause the transient behavior of these systems. However, in most
cases, if R_tr were slightly larger than the estimated values, the systems
would be globally stable. This suggests that a population of faint persistent
LMBHBs with globally stable outer disks could be present in the Galaxy. Such
LMBHBs would be hard to detect because they would lack large amplitude
outbursts, and because their ADAF zones would have very low radiative
efficiencies, making the systems very dim. We present model spectra of such
systems covering the optical and X-ray bands.Comment: LateX, 37 pages, 11 figures; Accepted for publication in The
Astrophysical Journa
TINA Service Validation: The ErnesTINA project
While extensive work has been carried out with the goal of validating the TINA architecture and the TINA documents, little has been done yet for the validation of TINA services. This is the main focus of the ErnesTINA project. In the ErnesTINA project, we propose an integrated approach to facilitate the validation of TINA services by verifying at run-time that the service implementation has not violated and is not violating certain predefined properties. In this paper, we present the specification of the properties, the run-time observation of the distributed environment, the validation of the properties and finally the implementation of the concepts in a prototype
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