1,235 research outputs found
Algebras for parameterised monads
Parameterised monads have the same relationship to adjunctions with parameters as monads do to adjunctions. In this paper, we investigate algebras for parameterised monads. We identify the Eilenberg-Moore category of algebras for parameterised monads and prove a generalisation of Beck’s theorem characterising this category. We demonstrate an application of this theory to the semantics of type and effect systems
Optimized Spectrometers Characterization Procedure for Near Ground Support of ESA FLEX Observations: Part 1 Spectral Calibration and Characterisation
The paper presents two procedures for the wavelength calibration, in the oxygen telluric absorption spectral bands (O2-A, λc = 687 nm and O2-B, λc = 760.6 nm), of field fixed-point spectrometers used for reflectance and Sun-induced fluorescence measurements. In the first case, Ne and Ar pen-type spectral lamps were employed, while the second approach is based on a double monochromator setup. The double monochromator system was characterized for the estimation of errors associated with different operating configurations. The proposed methods were applied to three Piccolo Doppio-type systems built around two QE Pros and one USB2 + H16355 Ocean Optics spectrometers. The wavelength calibration errors for all the calibrations performed on the three spectrometers are reported and potential methodological improvements discussed. The suggested calibration methods were validated, as the wavelength corrections obtained by both techniques for the QE Pro designed for fluorescence investigations were similar. However, it is recommended that a neon emission line source, as well as an argon or mercury-argon source be used to have a reference wavelength closer to the O2-B feature. The wavelength calibration can then be optimised as close to the O2-B and O2-A features as possible. The monochromator approach could also be used, but that instrument would need to be fully characterized prior to use, and although it may offer a more accurate calibration, as it could be tuned to emit light at the same wavelengths as the absorption features, it would be more time consuming as it is a scanning approach
Homology of generalized partition posets
We define a poset of partitions associated to an operad. We prove that the
operad is Koszul if and only if the poset is Cohen-Macaulay.
In one hand, this characterisation allows us to compute the homology of the
poset. This homology is given by the Koszul dual operad. On the other hand, we
get new methods for proving that an operad is Koszul.Comment: Final version. To appear in JPA
Influence of distance, area, and cultural context in active commuting: Continental and insular children
Additionally, this study takes place thanks to funding from the University of Granada, Plan Propio de Investigación 2016, Excellence actions: Units of Excellence; Unit of Excellence on Exercise and Health (UCEES). To PACO project (Pedalea y Anda al Cole), from PROFITH group, University of Granada. To CONICYT PAI-MEC program, from Education Ministry of Chile and to Carmen Sainz Quinn of Granada University for English revision and correction of the document. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Commuting by walking or cycling is a way to increase physical activity levels. The objective of this article was to determine the modes of commuting to school and the distance and time of the way to school among children from Easter Island and from the mainland (Valparaíso), in Chile. A total of 666 children and adolescents aged 10 to 18 years old (208 from Easter Island and 458 from Valparaíso) participated and completed a valid questionnaire including data about age, gender, usual commuting mode to and from school, distance, and travel time. There are important differences in the mode of commuting between students of Valparaíso and Easter Island. Private transport is more commonly used in Valparaíso than in Easter Island (p<0.001). Furthermore, it was observed that cycling and public transportation are not used as mode of commuting in Valparaíso and Easter Island respectively. Students from Easter Island, who travel more distance and during more time, are more active than students from Valparaíso (going 24.8% and 17.6%; from: 61% and 28.8% respectively). This situation is influenced by the geographic context of the island, the distances from home to school, and the type of commuting, which fosters the level of active commuting. On the other hand, the passive modes of commuting to school are higher in the mainland urban setting of Valparaíso. It is necessary to study the diverse contexts of the Easter Island population, but, for now, the rural setting of Easter Island seems to be associated with a greater level of active commuting to school.This study was supported by the Spanish Ministry of Economy, Industry and Competitiveness and the European Regional Development Fund (DEP2016-75598-R, MINECO/FEDER, UE)
From parametricity to conservation laws, via Noether's Theorem
Invariance is of paramount importance in programming languages and in physics. In programming languages, John Reynolds' theory of relational parametricity demonstrates that parametric polymorphic programs are invariant under change of data representation, a property that yields "free" theorems about programs just from their types. In physics, Emmy Noether showed that if the action of a physical system is invariant under change of coordinates, then the physical system has a conserved quantity: a quantity that remains constant for all time. Knowledge of conserved quantities can reveal deep properties of physical systems. For example, the conservation of energy is by Noether's theorem a consequence of a system's invariance under time-shifting. In this paper, we link Reynolds' relational parametricity with Noether's theorem for deriving conserved quantities. We propose an extension of System Fω with new kinds, types and term constants for writing programs that describe classical mechanical systems in terms of their Lagrangians. We show, by constructing a relationally parametric model of our extension of Fω, that relational parametricity is enough to satisfy the hypotheses of Noether's theorem, and so to derive conserved quantities for free, directly from the polymorphic types of Lagrangians expressed in our system
Galactic winds driven by cosmic-ray streaming
Galactic winds are observed in many spiral galaxies with sizes from dwarfs up
to the Milky Way, and they sometimes carry a mass in excess of that of newly
formed stars by up to a factor of ten. Multiple driving processes of such winds
have been proposed, including thermal pressure due to supernova-heating, UV
radiation pressure on dust grains, or cosmic ray (CR) pressure. We here study
wind formation due to CR physics using a numerical model that accounts for CR
acceleration by supernovae, CR thermalization, and advective CR transport. In
addition, we introduce a novel implementation of CR streaming relative to the
rest frame of the gas. We find that CR streaming drives powerful and sustained
winds in galaxies with virial masses M_200 < 10^{11} Msun. In dwarf galaxies
(M_200 ~ 10^9 Msun) the winds reach a mass loading factor of ~5, expel ~60 per
cent of the initial baryonic mass contained inside the halo's virial radius and
suppress the star formation rate by a factor of ~5. In dwarfs, the winds are
spherically symmetric while in larger galaxies the outflows transition to
bi-conical morphologies that are aligned with the disc's angular momentum axis.
We show that damping of Alfven waves excited by streaming CRs provides a means
of heating the outflows to temperatures that scale with the square of the
escape speed. In larger haloes (M_200 > 10^{11} Msun), CR streaming is able to
drive fountain flows that excite turbulence. For halo masses M_200 > 10^{10}
Msun, we predict an observable level of H-alpha and X-ray emission from the
heated halo gas. We conclude that CR-driven winds should be crucial in
suppressing and regulating the first epoch of galaxy formation, expelling a
large fraction of baryons, and - by extension - aid in shaping the faint end of
the galaxy luminosity function. They should then also be responsible for much
of the metal enrichment of the intergalactic medium.Comment: 25 pages, 14 figures, accepted by MNRA
The 1-1000 micron SEDs of far-infrared galaxies
Galaxies selected at 170um by the ISO FIRBACK survey represent the brightest
\~10% of the Cosmic Infrared Background. Examining their nature in detail is
therefore crucial for constraining models of galaxy evolution. Here we combine
Spitzer archival data with previous near-IR, far-IR, and sub-mm observations of
a representative sample of 22 FIRBACK galaxies spanning three orders of
magnitude in infrared luminosity. We fit a flexible, multi-component, empirical
SED model of star-forming galaxies designed to model the entire ~1-1000um
wavelength range. The fits are performed with a Markov Chain Monte Carlo (MCMC)
approach, allowing for meaningful uncertainties to be derived. This approach
also highlights degeneracies such as between Td and beta, which we discuss in
detail. From these fits and standard relations we derive: L_IR, L_PAH, SFR,
tau_V, M_star, M_dust, Td, and beta. We look at a variety of correlations
between these and combinations thereof in order to examine the physical nature
of these galaxies. Our conclusions are supplemented by morphological
examination of the sources, and comparison with local samples. We find the bulk
of our sample to be consistent with fairly standard size and mass disk galaxies
with somewhat enhanced star-formation relative to local spirals, but likely not
bona fide starbursts. A few higher-z LIGs and ULIGs are also present, but
contrary to expectation, they are weak mid-IR emitters and overall are
consistent with star-formation over an extended cold region rather than
concentrated in the nuclear regions. We discuss the implications of this study
for understanding populations detected at other wavelengths, such as the bright
850um SCUBA sources or the faint Spitzer 24um sources.Comment: 19 pages, 20 figures, accepted for publication in MNRA
From Euclidean Geometry to Knots and Nets
This document is the Accepted Manuscript of an article accepted for publication in Synthese. Under embargo until 19 September 2018. The final publication is available at Springer via https://doi.org/10.1007/s11229-017-1558-x.This paper assumes the success of arguments against the view that informal mathematical proofs secure rational conviction in virtue of their relations with corresponding formal derivations. This assumption entails a need for an alternative account of the logic of informal mathematical proofs. Following examination of case studies by Manders, De Toffoli and Giardino, Leitgeb, Feferman and others, this paper proposes a framework for analysing those informal proofs that appeal to the perception or modification of diagrams or to the inspection or imaginative manipulation of mental models of mathematical phenomena. Proofs relying on diagrams can be rigorous if (a) it is easy to draw a diagram that shares or otherwise indicates the structure of the mathematical object, (b) the information thus displayed is not metrical and (c) it is possible to put the inferences into systematic mathematical relation with other mathematical inferential practices. Proofs that appeal to mental models can be rigorous if the mental models can be externalised as diagrammatic practice that satisfies these three conditions.Peer reviewe
Time-Variable Radio Recombination Line Emission in W49A
We present new Jansky Very Large Array (VLA) images of the central region of
the W49A star-forming region at 3.6~cm and at 7~mm at resolutions of 0\farcs15
(1650 au) and 0\farcs04 (440 au), respectively. The 3.6~cm data reveal new
morphological detail in the ultracompact \ion{H}{2} region population, as well
as several previously unknown and unresolved sources. In particular, source A
shows elongated, edge-brightened, bipolar lobes, indicative of a collimated
outflow, and source E is resolved into three spherical components. We also
present VLA observations of radio recombination lines at 3.6~cm and 7~mm, and
IRAM Northern Extended Millimeter Array (NOEMA) observations at 1.2~mm. Three
of the smallest ultracompact \ion{H}{2} regions (sources A, B2 and G2) all show
broad kinematic linewidths, with V40~km~s. A
multi-line analysis indicates that broad linewidths remain after correcting for
pressure broadening effects, suggesting the presence of supersonic flows.
Substantial changes in linewidth over the 21 year time baseline at both 3.6 cm
and 7 mm are found for source G2. At 3.6 cm, the linewidth of G2 changed from
31.71.8 km s to 55.62.7 km s, an increase of
23.93.4 km s. The G2 source was previously reported to have
shown a 3.6~cm continuum flux density decrease of 40\% between 1994 and 2015.
This source sits near the center of a very young bipolar outflow whose
variability may have produced these changes.Comment: 18 pages, 7 figures, Accepted for publication in The Astronomical
Journa
- …