3,555 research outputs found
Gain narrowing in few-atom systems
Using a density matrix approach, we study the simplest systems that display
both gain and feedback: clusters of 2 to 5 atoms, one of which is pumped. The
other atoms supply feedback through multiple scattering of light. We show that,
if the atoms are in each other's near-field, the system exhibits large gain
narrowing and spectral mode redistribution. The observed phenomena are more
pronounced if the feedback is enhanced. Our system is to our knowledge the
simplest exactly solvable microscopic system which shows the approach to laser
oscillation
Broad-band photometric colors and effective temperature calibrations for late-type giants. II. Z<0.02
(Abridged) We investigate the effects of metallicity on the broad-band
photometric colors of late-type giants, and make a comparison of synthetic
colors with observed photometric properties of late-type giants over a wide
range of effective temperatures (T_eff=3500-4800 K) and gravities (log
g=0.0-2.5), at [M/H]=-1.0 and -2.0. The influence of metallicity on the
synthetic photometric colors is generally small at effective temperatures above
\~3800 K, but the effects grow larger at lower T_eff, due to the changing
efficiency of molecule formation which reduces molecular opacities at lower
[M/H]. To make a detailed comparison of the synthetic and observed photometric
colors of late type giants in the T_eff--color and color--color planes, we
derive a set of new T_eff--log g--color relations based on synthetic
photometric colors, at [M/H]=-0.5, -1.0, -1.5, and -2.0. While differences
between the new T_eff--color relations and those available from the literature
are typically well within ~100 K, effective temperatures predicted by the
scales based on synthetic colors tend to be slightly higher than those
resulting from the T_eff--color relations based on observations, with the
offsets up to ~100 K. This is clearly seen both at [M/H]=-1.0 and -2.0,
especially in the T_eff--(B-V) and T_eff--(V-K) planes. The consistency between
T_eff--log g--color scales based on synthetic colors calculated with different
stellar atmosphere codes is very good, with typical differences being well
within \Delta T_eff~70 K at [M/H]=-1.0 and \Delta T_eff~40 K at [M/H]=-2.0.Comment: 20 pages, 11 figures, A&A accepte
Metallicity of M dwarfs III. Planet-metallicity and planet-stellar mass correlations of the HARPS GTO M dwarf sample
Aims. The aim of this work is the study of the planet-metallicity and the
planet-stellar mass correlations for M dwarfs from the HARPS GTO M dwarf
subsample
Methods. We use a new method that takes advantage of the HARPS
high-resolution spectra to increase the precision of metallicity, using
previous photometric calibrations of [Fe/H] and effective temperature as
starting values.
Results. In this work we use our new calibration (rms = 0.08 dex) to study
the planet-metallicity relation of our sample. The well-known correlation for
Giant planet FGKM hosts with metallicity is present. Regarding Neptunians and
smaller hosts no correlation is found but there is a hint that an
anti-correlation with [Fe/H] may exist. We combined our sample with the
California Planet Survey late-K and M-type dwarf sample to increase our
statistics but found no new trends. We fitted a power law to the frequency
histogram of the Jovian hosts for our sample and for the combined sample, f_p =
C10^\alpha[Fe/H], using two different approaches: a direct bin fitting and a
bayesian fitting procedure. We obtained a value for C between 0.02 and 0.04 and
for \alpha between 1.26 and 2.94.
Regarding stellar mass, an hypothetical correlation with planets was
discovered, but was found to be the result of a detection bias.Comment: Accepted for publication in A&A. 18 pages, 11 Figures, 12 Table
Metallicity of M dwarfs IV. A high-precision [Fe/H] and Teff technique from high-resolution optical spectra for M dwarfs
Aims. In this work we develop a technique to obtain high precision
determinations of both metallicity and effective temperature of M dwarfs in the
optical.
Methods. A new method is presented that makes use of the information of 4104
lines in the 530-690 nm spectral region. It consists in the measurement of
pseudo equivalent widths and their correlation with established scales of
[Fe/H] and .
Results. Our technique achieves a of 0.080.01 for [Fe/H],
9113 K for , and is valid in the (-0.85, 0.26 dex), (2800, 4100
K), and (M0.0, M5.0) intervals for [Fe/H], and spectral type
respectively. We also calculated the RMSE which estimates uncertainties
of the order of 0.12 dex for the metallicity and of 293 K for the effective
temperature. The technique has an activity limit and should only be used for
stars with . Our method is available
online at \url{http://www.astro.up.pt/resources/mcal}.Comment: Accepted in Astronomy and Astrophysics. Updated one important
reference in the introduction. Some typos correcte
Anisotropic 2D diffusive expansion of ultra-cold atoms in a disordered potential
We study the horizontal expansion of vertically confined ultra-cold atoms in
the presence of disorder. Vertical confinement allows us to realize a situation
with a few coupled harmonic oscillator quantum states. The disordered potential
is created by an optical speckle at an angle of 30{\deg} with respect to the
horizontal plane, resulting in an effective anisotropy of the correlation
lengths of a factor of 2 in that plane. We observe diffusion leading to
non-Gaussian density profiles. Diffusion coefficients, extracted from the
experimental results, show anisotropy and strong energy dependence, in
agreement with numerical calculations
Electrical characterization and modeling of benthic microbial fuel cells for energy harvesting
National audienceMicrobial fuel cell (MFC) is a promising energy harvester for supplying sensors in seafloors where solar, thermal and vibration sources are inadequate. Extensive efforts focus improvement of MFC biological and electrochemical capabilities while the electrical perspectives are poorly developed in literature. In order to promote MFC as energy scavenger, this paper explains the methods used to electrically characterize the specific MFC for seafloor conditions and the way to model its steady state operation close to the maximum power point. The method is applied to a compost-fed MCF delivering 5.7µW at 0.14V optimal output voltage. This work is the first step to efficiently apprehend the elaboration of an electrical harvesting interface
The role of insight teams in integrating diverse marketing information management techniques.
The full text version attached to this file is the authors final version. The final definitive publishers version can be found at http://dx.doi.org/10.1108/03090560810877187The purpose of this article is to address the viability of planning and executing the integration of four, often independent marketing information management techniques: competitive intelligence (CI), customer relationship management (CRM), data mining (DM) and market research (MR). A longitudinal, exploratory and descriptive case study is reported upon, covering a three year period during a critical development phase of a medium-size, national employer association which sought to improve the quality of marketing-based insights to its strategic planning capability as well as improve economic outcomes. A multi-year roadmap is presented and a key finding was that it is possible to achieve profitable and capability enhancing integration of diverse marketing information management techniques. Successful integration and the use of a highly focused cross functional team generated better market strategies and bottom line benefits. There are very few case studies published that demonstrate the successful evolution and integration of CI, CRM, DM and MR into the enterprise's strategy-making process. The unique element of this example was that it was achieved within the context of a medium-sized, national, not-for-profit employer association
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