4,476 research outputs found
Electro-optic dual-comb interferometry over 40-nm bandwidth
Dual-comb interferometry is a measurement technique that uses two laser
frequency combs to retrieve complex spectra in a line-by-line basis. This
technique can be implemented with electro-optic frequency combs, offering
intrinsic mutual coherence, high acquisition speed and flexible repetition-rate
operation. A challenge with the operation of this kind of frequency comb in
dual-comb interferometry is its limited optical bandwidth. Here, we use
coherent spectral broadening and demonstrate electro-optic dual-comb
interferometry over the entire telecommunications C band (200 lines covering ~
40 nm, measured within 10 microseconds at 100 signal-to-noise ratio per
spectral line). These results offer new prospects for electro-optic dual-comb
interferometry as a suitable technology for high-speed broadband metrology, for
example in optical coherence tomography or coherent Raman microscopy
Revisiting the Hubble sequence in the SDSS DR7 spectroscopic sample: a publicly available bayesian automated classification
We present an automated morphological classification in 4 types
(E,S0,Sab,Scd) of ~700.000 galaxies from the SDSS DR7 spectroscopic sample
based on support vector machines. The main new property of the classification
is that we associate to each galaxy a probability of being in the four
morphological classes instead of assigning a single class. The classification
is therefore better adapted to nature where we expect a continuos transition
between different morphological types. The algorithm is trained with a visual
classification and then compared to several independent visual classifications
including the Galaxy Zoo first release catalog. We find a very good correlation
between the automated classification and classical visual ones. The compiled
catalog is intended for use in different applications and can be downloaded at
http://gepicom04.obspm.fr/sdss_morphology/Morphology_2010.html and soon from
the CasJobs database.Comment: A&A in press, english corrections from language editor adde
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ACA chefs adopt a school: An evaluation
This document summarises an evaluation of a cooking in schools initiative called Chefs Adopt a School (CAAS) which is delivered by the Academy of Culinary Arts.1 At present, sessions are provided all over England from Cumbria to Cornwall subject to demand and resources (with a few sessions being delivered in Scotland too). Annually, 21,000 children take part in the initiative. Delivered by professional chefs, the programme aim is to teach children about food, food provenance, health, nutrition and cookery. The evaluation was informed by a rapid systematic review of the existing literature on cooking in schools.
This research has been carried out at a time when cooking in schools is being put forward as a solution to improving diets and reducing obesity. It is currently the only evaluation of school cooking in the UK that measures outcomes that impact on health, such as: eating behaviour, cooking confidence and confidence asking for fruit, vegetables and ingredients at home. As such, it can inform future UK school cooking initiative interventions and evaluations. It also highlights the need to incorporate evaluation into school cooking initiatives, as findings provide valuable information necessary to fine tune an
intervention.
In the core programme, chefs link with local schools, usually primary, where they deliver 2-3 sessions to one year group within a school. This process is then repeated each year. Key issues covered include hygiene, healthy eating, an appreciation of food through the senses (particularly taste) and practical cooking/food preparation. The first session covers healthy eating and the sensory appreciation of food while the second and third sessions are practical
Optical bandgap engineering in nonlinear silicon nitride waveguides
Silicon nitride is awell-established material for photonic devices and
integrated circuits. It displays a broad transparency window spanning from the
visible to the mid-IR and waveguides can be manufactured with low losses. An
absence of nonlinear multi-photon absorption in the erbium lightwave
communications band has enabled various nonlinear optic applications in the
past decade. Silicon nitride is a dielectric material whose optical and
mechanical properties strongly depend on the deposition conditions. In
particular, the optical bandgap can be modified with the gas flow ratio during
low-pressure chemical vapor deposition (LPCVD). Here we show that this
parameter can be controlled in a highly reproducible manner, providing an
approach to synthesize the nonlinear Kerr coefficient of the material. This
holistic empirical study provides relevant guidelines to optimize the
properties of LPCVD silicon nitride waveguides for nonlinear optics
applications that rely on the Kerr effect
The bivariate gas-stellar mass distributions and the mass functions of early- and late-type galaxies at
We report the bivariate HI- and H-stellar mass distributions of local
galaxies in addition of an inventory of galaxy mass functions, MFs, for HI,
H, cold gas, and baryonic mass, separately into early- and late-type
galaxies. The MFs are determined using the HI and H conditional
distributions and the galaxy stellar mass function, GSMF. For the conditional
distributions we use the compilation presented in Calette et al. 2018. For
determining the GSMF from to
, we combine two spectroscopic samples from the SDSS at the redshift
range . We find that the low-mass end slope of the GSMF, after
correcting from surface brightness incompleteness, is ,
consistent with previous determinations. The obtained HI MFs agree with radio
blind surveys. Similarly, the H MFs are consistent with CO follow-up
optically-selected samples. We estimate the impact of systematics due to
mass-to-light ratios and find that our MFs are robust against systematic
errors. We deconvolve our MFs from random errors to obtain the intrinsic MFs.
Using the MFs, we calculate cosmic density parameters of all the baryonic
components. Baryons locked inside galaxies represent 5.4% of the universal
baryon content, while % of the HI and H mass inside galaxies reside
in late-type morphologies. Our results imply cosmic depletion times of H
and total neutral H in late-type galaxies of and 7.2 Gyr,
respectively, which shows that late type galaxies are on average inefficient in
converting H into stars and in transforming HI gas into H. Our results
provide a fully self-consistent empirical description of galaxy demographics in
terms of the bivariate gas--stellar mass distribution and their projections,
the MFs. This description is ideal to compare and/or to constrain galaxy
formation models.Comment: 37 pages, 17 figures. Accepted for publication in PASA. A code that
displays tables and figures with all the relevant statistical distributions
and correlations discussed in this paper is available here
https://github.com/arcalette/Python-code-to-generate-Rodriguez-Puebla-2020-result
Comparing PyMorph and SDSS photometry. II. The differences are more than semantics and are not dominated by intracluster light
The Sloan Digital Sky Survey pipeline photometry underestimates the
brightnesses of the most luminous galaxies. This is mainly because (i) the SDSS
overestimates the sky background and (ii) single or two-component Sersic-based
models better fit the surface brightness profile of galaxies, especially at
high luminosities, than does the de Vaucouleurs model used by the SDSS
pipeline. We use the PyMorph photometric reductions to isolate effect (ii) and
show that it is the same in the full sample as in small group environments, and
for satellites in the most massive clusters as well. None of these are expected
to be significantly affected by intracluster light (ICL). We only see an
additional effect for centrals in the most massive halos, but we argue that
even this is not dominated by ICL. Hence, for the vast majority of galaxies,
the differences between PyMorph and SDSS pipeline photometry cannot be ascribed
to the semantics of whether or not one includes the ICL when describing the
stellar mass of massive galaxies. Rather, they likely reflect differences in
star formation or assembly histories. Failure to account for the SDSS
underestimate has significantly biased most previous estimates of the SDSS
luminosity and stellar mass functions, and therefore Halo Model estimates of
the z ~ 0.1 relation between the mass of a halo and that of the galaxy at its
center. We also show that when one studies correlations, at fixed group mass,
with a quantity which was not used to define the groups, then selection effects
appear. We show why such effects arise, and should not be mistaken for physical
effects.Comment: 15 pages, 17 figures, accepted for publication in MNRAS. The PyMorph
luminosities and stellar masses are available at
https://www.physics.upenn.edu/~ameert/SDSS_PhotDec
Letter to Sonora Dodd from The A. M. Davis Company, May 23, 1911
Letter to Sonora Dodd from the A. M. Davis Company, with envelope.https://digitalcommons.whitworth.edu/fathers-day-correspondence/1003/thumbnail.jp
The high mass end of the stellar mass function: Dependence on stellar population models and agreement between fits to the light profile
We quantify the systematic effects on the stellar mass function which arise
from assumptions about the stellar population, as well as how one fits the
light profiles of the most luminous galaxies at z ~ 0.1. When comparing results
from the literature, we are careful to separate out these effects. Our analysis
shows that while systematics in the estimated comoving number density which
arise from different treatments of the stellar population remain of order < 0.5
dex, systematics in photometry are now about 0.1 dex, despite recent claims in
the literature. Compared to these more recent analyses, previous work based on
Sloan Digital Sky Survey (SDSS) pipeline photometry leads to underestimates of
rho_*(> M_*) by factors of 3-10 in the mass range 10^11 - 10^11.6 M_Sun, but up
to a factor of 100 at higher stellar masses. This impacts studies which match
massive galaxies to dark matter halos. Although systematics which arise from
different treatments of the stellar population remain of order < 0.5 dex, our
finding that systematics in photometry now amount to only about 0.1 dex in the
stellar mass density is a significant improvement with respect to a decade ago.
Our results highlight the importance of using the same stellar population and
photometric models whenever low and high redshift samples are compared.Comment: 18 pages, 17 figures, accepted for publication in MNRAS. The PyMorph
luminosities and stellar masses are available at
https://www.physics.upenn.edu/~ameert/SDSS_PhotDec
Phase-coherent lightwave communications with frequency combs
Fiber-optical networks are a crucial telecommunication infrastructure in
society. Wavelength division multiplexing allows for transmitting parallel data
streams over the fiber bandwidth, and coherent detection enables the use of
sophisticated modulation formats and electronic compensation of signal
impairments. In the future, optical frequency combs may replace multiple lasers
used for the different wavelength channels. We demonstrate two novel signal
processing schemes that take advantage of the broadband phase coherence of
optical frequency combs. This approach allows for a more efficient estimation
and compensation of optical phase noise in coherent communication systems,
which can significantly simplify the signal processing or increase the
transmission performance. With further advances in space division multiplexing
and chip-scale frequency comb sources, these findings pave the way for compact
energy-efficient optical transceivers.Comment: 17 pages, 9 figure
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