3,987 research outputs found
Intra-sexual competition alters the relationship between testosterone and ornament expression in a wild territorial bird
Open Access funded by Natural Environment Research Council Under a Creative Commons licensePeer reviewedPublisher PD
Multilevel Models with Stochastic Volatility for Repeated Cross-Sections: an Application to tribal Art Prices
In this paper we introduce a multilevel specification with stochastic
volatility for repeated cross-sectional data. Modelling the time dynamics in
repeated cross sections requires a suitable adaptation of the multilevel
framework where the individuals/items are modelled at the first level whereas
the time component appears at the second level. We perform maximum likelihood
estimation by means of a nonlinear state space approach combined with
Gauss-Legendre quadrature methods to approximate the likelihood function. We
apply the model to the first database of tribal art items sold in the most
important auction houses worldwide. The model allows to account properly for
the heteroscedastic and autocorrelated volatility observed and has superior
forecasting performance. Also, it provides valuable information on market
trends and on predictability of prices that can be used by art markets
stakeholders
Transporting Functions across Ornaments
Programming with dependent types is a blessing and a curse. It is a blessing
to be able to bake invariants into the definition of data-types: we can finally
write correct-by-construction software. However, this extreme accuracy is also
a curse: a data-type is the combination of a structuring medium together with a
special purpose logic. These domain-specific logics hamper any effort of code
reuse among similarly structured data.
In this paper, we exorcise our data-types by adapting the notion of ornament
to our universe of inductive families. We then show how code reuse can be
achieved by ornamenting functions. Using these functional ornament, we capture
the relationship between functions such as the addition of natural numbers and
the concatenation of lists. With this knowledge, we demonstrate how the
implementation of the former informs the implementation of the latter: the user
can ask the definition of addition to be lifted to lists and she will only be
asked the details necessary to carry on adding lists rather than numbers.
Our presentation is formalised in a type theory with a universe of data-types
and all our constructions have been implemented as generic programs, requiring
no extension to the type theory
Effects of experimental tail shortening on the phenotypic condition of barn swallows Hirundo rustica: Implications for tail-length evolution
Some studies have suggested that tail streamers in the barn swallow Hirundo rustica may have been elongated 10-12 mm by sexual selection, but according to other studies, the length of these feathers is at the aerodynamic optimum or very close to it. To shed light on this issue, outermost tail feathers were experimentally shortened in male and female barn swallows by 1, 11 or 21 mm. Changes in four physiological parameters commonly used to estimate phenotypic condition in birds (weight, erythrocyte sedimentation rate, blood leukocyte concentration and heterophil/lymphocyte ratio) were checked one month later. Health improved (blood leukocyte concentration decreased) in the group of birds with tails shortened by 11 mm (both males and females), but body condition deteriorated (weight decreased) compared to the other two experimental groups. There was no significant effect of tail-length manipulation on the other two physiological parameters. These contradictory results suggest trade-offs between components of phenotypic condition. Possible negative relationships between condition-related traits imply that using one or very few physiological parameters to estimate phenotypic condition might not be appropriate. The most plausible explanation for the turning point in phenotypic condition when streamers were shortened by 11 mm is that these feathers are 7-15 mm longer than the aerodynamic optimum in both sexes. Therefore, our results are consistent with the hypothesis that tail streamers have been elongated 10-12 mm by sexual selection. This conclusion disagrees with a previous study on the effect of experimental tail shortening on haematocrit, but the complexity of interpreting changes in haematocrit might account for this discrepancy. © 2014 The Authors.The study was funded by the Andalusian Regional Government (Acc. Coord. 2001) and by the Spanish Ministry of Science and Technology and the European Regional Development Fund (projects BOS2001-1717 and CGL2008-00137/BOS).Peer Reviewe
Intrahousehold Health Care Financing Strategy and the Gender Gap: Empirical Evidence from India
The âmissing womenâ dilemma in India has sparked interest in investigating gender discrimination in the provision of health care in the country. No studies, however, have directly examined this discrimination in relation to household behavior in health care financing. We hypothesize that households who face tight budget constraints are more likely to spend their meager resources on hospitalization of boys rather than girls. We use the 60th Indian National Sample Survey and a multinomial logit model to test this hypothesis and to shed some light on this important but overlooked issue. The results reveal that while the gap in the probability of boysâ and girlsâ hospitalization and usage of household income and savings is relatively small, the gender gap in the probability of hospitalization and usage of scarce resources is very high. Ceteris paribus, the probability of boys to be hospitalized by financing from relatively scarce sources such as borrowing, sale of assets, help from friends, etc., is much higher than that of girls. Moreover, the results indicate that the gender gap deepens as we move from the richest to poorest households.gender discrimination, health care finance, hospitalization, India
Dependent Inductive and Coinductive Types are Fibrational Dialgebras
In this paper, I establish the categorical structure necessary to interpret
dependent inductive and coinductive types. It is well-known that dependent type
theories \`a la Martin-L\"of can be interpreted using fibrations. Modern
theorem provers, however, are based on more sophisticated type systems that
allow the definition of powerful inductive dependent types (known as inductive
families) and, somewhat limited, coinductive dependent types. I define a class
of functors on fibrations and show how data type definitions correspond to
initial and final dialgebras for these functors. This description is also a
proposal of how coinductive types should be treated in type theories, as they
appear here simply as dual of inductive types. Finally, I show how dependent
data types correspond to algebras and coalgebras, and give the correspondence
to dependent polynomial functors.Comment: In Proceedings FICS 2015, arXiv:1509.0282
Elaborating Inductive Definitions
We present an elaboration of inductive definitions down to a universe of
datatypes. The universe of datatypes is an internal presentation of strictly
positive families within type theory. By elaborating an inductive definition --
a syntactic artifact -- to its code -- its semantics -- we obtain an
internalized account of inductives inside the type theory itself: we claim that
reasoning about inductive definitions could be carried in the type theory, not
in the meta-theory as it is usually the case. Besides, we give a formal
specification of that elaboration process. It is therefore amenable to formal
reasoning too. We prove the soundness of our translation and hint at its
correctness with respect to Coq's Inductive definitions.
The practical benefits of this approach are numerous. For the type theorist,
this is a small step toward bootstrapping, ie. implementing the inductive
fragment in the type theory itself. For the programmer, this means better
support for generic programming: we shall present a lightweight deriving
mechanism, entirely definable by the programmer and therefore not requiring any
extension to the type theory.Comment: 32 pages, technical repor
Honest sexual signalling mediated by parasite and testosterone effects on oxidative balance
Extravagant ornaments evolved to advertise their bearers' quality, the honesty of the signal being ensured by the cost paid to produce or maintain it. The oxidation handicap hypothesis (OHH) proposes that a main cost of testosterone-dependent ornamentation is oxidative stress, a condition whereby the production of reactive oxygen and nitrogen species (ROS/RNS) overwhelms the capacity of antioxidant defences. ROS/RNS are unstable, very reactive by-products of normal metabolic processes that can cause extensive damage to key biomolecules (cellular proteins, lipids and DNA). Oxidative stress has been implicated in the aetiology of many diseases and could link ornamentation and genetic variation in fitness-related traits. We tested the OHH in a free-living bird, the red grouse. We show that elevated testosterone enhanced ornamentation and increased circulating antioxidant levels, but caused oxidative damage. Males with smaller ornaments suffered more oxidative damage than those with larger ornaments when forced to increase testosterone levels, consistent with a handicap mechanism. Parasites depleted antioxidant defences, caused oxidative damage and reduced ornament expression. Oxidative damage extent and the ability of males to increase antioxidant defences also explained the impacts of testosterone and parasites on ornamentation within treatment groups. Because oxidative stress is intimately linked to immune function, parasite resistance and fitness, it provides a reliable currency in the trade-off between individual health and ornamentation. The costs induced by oxidative stress can apply to a wide range of signals, which are testosterone-dependent or coloured by pigments with antioxidant properties
Categories without structures
The popular view according to which Category theory provides a support for
Mathematical Structuralism is erroneous. Category-theoretic foundations of
mathematics require a different philosophy of mathematics. While structural
mathematics studies invariant forms (Awodey) categorical mathematics studies
covariant transformations which, generally, don t have any invariants. In this
paper I develop a non-structuralist interpretation of categorical mathematics
and show its consequences for history of mathematics and mathematics education.Comment: 28 page
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