57,316 research outputs found
IUE observations of the chromospheric activity-age relation in young solar-type stars
Ultraviolet data obtained with the IUE spacecraft are presented for a dozen solar-type stars in the field. The stars are of spectral type F6 V - G1 V; on the basis of their high Li content, they range in age from 0.1 to 2.8 Gyr. The evolution of transition regions and chromospheric emission with stellar age is studied along with the surface distribution of magnetically active regions as revealed by rotational modulation of UV emission line fluxes
Rotational modulation of the chromospheric activity in the young solar-type star, X-1 Orionis
The IUE satellite was used to observe one of the youngest G stars (GO V) for which Duncan (1981) derives an age of 6 x 10 to the 8th power years from the Li abundance. Rotational modulation was looked for in the emission flux in the chromospheric and transition region lines of this star. Variations in the Ca 11 K-lines profile were studied with the CHF telescope at Mauna Kea. Results show that the same modulation of the emission flux of Ca 11 due to stellar rotation is present in the transition region feature of C IV and probably of He II. For other UV lines the modulation is not apparent, due to a more complex surface distribution of the active areas or supergranulation network, or a shorter lifetime of the conditions which give rise to these features, or to the uncertainities in the measured line strengths. The Mg II emission flux is constant to within + or - 3.4% implying a rather uniform distribution of Mg II emission areas. The Ca II emission not only shows a measurable variation in intensity but also variations in detailed line profile shape when observed at high resolution
Complete spatial characterization of an optical wavefront using a variable-separation pinhole pair
We present a technique for measuring the transverse spatial properties of an
optical wavefront. Intensity and phase profiles are recovered by analysis of a
series of interference patterns produced by the combination of a scanning
X-shaped slit and a static horizontal slit; the spatial coherence may be found
from the same data. We demonstrate the technique by characterizing high
harmonic radiation generated in a gas cell, however the method could be
extended to a wide variety of light sources.Comment: 4 pages, 3 figures, 1 tabl
Status of the ILC Main Linac BPM R&D
An introduction and the status of R&D activities for a high-resolution,
"cold" beam position monitor (BPM) and the related read-out electronics are
discussed. Two different BPM detector concepts, to be attached to the SC
quadrupole and located inside the ILC cryomodule, are currently under
investigation: A resonant dipole-mode cavity-style BPM pickup, developed at
Fermilab, and a re-entrant resonant coaxial waveguide BPM, designed by
CEA-Saclay. While the 1.5 GHz dipole-mode cavity BPM is still in the R&D phase,
the re-entrant BPM has already passed first beam tests, including its read-out
system. Furthermore, the LAPP group is developing radiation tolerant digital
read-out systems, which are tested at the CLIC test facility (CTF).Comment: LCWS / ILC08 conference contribution, 6 pages, 6 figure
A dynamic scheme for generating number squeezing in Bose-Einstein condensates through nonlinear interactions
We develop a scheme to generate number squeezing in a Bose-Einstein
condensate by utilizing interference between two hyperfine levels and nonlinear
atomic interactions. We describe the scheme using a multimode quantum field
model and find agreement with a simple analytic model in certain regimes. We
demonstrate that the scheme gives strong squeezing for realistic choices of
parameters and atomic species. The number squeezing can result in noise well
below the quantum limit, even if the initial noise on the system is classical
and much greater than that of a poisson distribution.Comment: 4 pages, 3 figure
Measurement based entanglement under conditions of extreme photon loss
The act of measuring optical emissions from two remote qubits can entangle
them. By demanding that a photon from each qubit reaches the detectors, one can
ensure than no photon was lost. But the failure rate then rises quadratically
with loss probability. In [1] this resulted in 30 successes per billion
attempts. We describe a means to exploit the low grade entanglement heralded by
the detection of a lone photon: A subsequent perfect operation is quickly
achieved by consuming this noisy resource. We require only two qubits per node,
and can tolerate both path length variation and loss asymmetry. The impact of
photon loss upon the failure rate is then linear; realistic high-loss devices
can gain orders of magnitude in performance and thus support QIP.Comment: Contains an extension of the protocol that makes it robust against
asymmetries in path length and photon los
Black hole thermodynamics from simulations of lattice Yang-Mills theory
We report on lattice simulations of 16 supercharge SU(N) Yang-Mills quantum
mechanics in the 't Hooft limit. Maldacena duality conjectures that in this
limit the theory is dual to IIA string theory, and in particular that the
behavior of the thermal theory at low temperature is equivalent to that of
certain black holes in IIA supergravity. Our simulations probe the low
temperature regime for N <= 5 and the intermediate and high temperature regimes
for N <= 12. We observe 't Hooft scaling and at low temperatures our results
are consistent with the dual black hole prediction. The intermediate
temperature range is dual to the Horowitz-Polchinski correspondence region, and
our results are consistent with smooth behavior there. We include the Pfaffian
phase arising from the fermions in our calculations where appropriate.Comment: 4 pages, 4 figure
Estimating fugitive bioaerosol releases from static compost windrows: feasibility of portable wind tunnel approach
An assessment of the fugitive release of bioaerosols from static compost piles
was conducted at a green waste composting facility in South East England; this
representing the initial stage of a programme of research into the influence of
process parameters on bioaerosol emission flux. Wind tunnel experiments
conducted on the surface of static windrows generated specific bioaerosol
emission rates (SBER2s) at ground level of between 13 - 22 x10 3 cfu/m 2 /s for
mesophilic actinomycetes and between 8 - 11 x10 3 cfu/m 2 /s for Aspergillus
fumigatus. Air dispersion modelling of these emissions using the SCREEN3 air
dispersion model in area source term mode was used to generate source depletion
curves downwind of the facility for comparative purposes
Constrained simulations of the Antennae Galaxies: Comparison with Herschel-PACS observations
We present a set of hydro-dynamical numerical simulations of the Antennae
galaxies in order to understand the origin of the central overlap starburst.
Our dynamical model provides a good match to the observed nuclear and overlap
star formation, especially when using a range of rather inefficient stellar
feedback efficiencies (0.01 < q_EoS < 0.1). In this case a simple conversion of
local star formation to molecular hydrogen surface density motivated by
observations accounts well for the observed distribution of CO. Using radiative
transfer post-processing we model synthetic far-infrared spectral energy
distributions (SEDs) and two-dimensional emission maps for direct comparison
with Herschel-PACS observations. For a gas-to-dust ratio of 62:1 and the best
matching range of stellar feedback efficiencies the synthetic far-infrared SEDs
of the central star forming region peak at values of ~65 - 81 Jy at 99 - 116
um, similar to a three-component modified black body fit to infrared
observations. Also the spatial distribution of the far-infrared emission at 70
um, 100 um, and 160 um compares well with the observations: >50% (> 35%) of the
emission in each band is concentrated in the overlap region while only < 30% (<
15%) is distributed to the combined emission from the two galactic nuclei in
the simulations (observations). As a proof of principle we show that parameter
variations in the feedback model result in unambiguous changes both in the
global and in the spatially resolved observable far-infrared properties of
Antennae galaxy models. Our results strengthen the importance of direct,
spatially resolved comparative studies of matched galaxy merger simulations as
a valuable tool to constrain the fundamental star formation and feedback
physics.Comment: 17 pages, 8 figures, 4 tables, submitted to MNRAS, including
revisions after first referee report, comments welcom
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