University of Oxford

About: University of Oxford is a education organization based out in Oxford, Oxfordshire, United Kingdom. It is known for research contribution in the topics: Population & Context (language use). The organization has 99713 authors who have published 258108 publications receiving 12972806 citations. The organization is also known as: Oxford University & Oxon..

Phylogenies without fossils.

Abstract: Phylogenies that are reconstructed without fossil material often contain approximate dates for lineage splitting. For example, particular nodes on molecular phylogenies may be dated by known geographic events that caused lineages to split, thereby calibrating a molecular clock that is used to date other nodes. On the one hand, such phylogenies contain no information about lineages that have become extinct. On the other hand, they do provide a potentially useful testing ground for ideas about evolutionary processes. Here we first ask what such reconstructed phylogenies should be expected to look like under a birth-death process in which the birth and death parameters of lineages remain constant through time. We show that it is possible to estimate both the birth and death rates of lineages from the reconstructed phylogenies, even though they contain no explicit information about extinct lineages. We also show how such phylogenies can reveal mass extinctions and how their characteristic footprint can be distinguished from similar ones produced by density-dependent cladogenesis.

Taming the infinite chase: query answering under expressive relational constraints

Abstract: A crucial task in Knowledge Representation is answering queries posed over a knowledge base, represented as a set of facts plus a set of rules. In this paper we address the problem of answering conjunctive queries posed over knowledge bases where rules are an extension of Datalog rules, called Datalog∃ rules, that may have existentially quantified variables in the head; this kind of rules are traditionally called tuple-generating dependencies (TGDs) in the database literature, but they are broadly used in description logics and in ontological reasoning. In this setting, the chase algorithm is an important tool for query answering. So far, most of the research has concentrated on cases where the chase terminates. We define and study large classes of TGDs under which the query evaluation problems remain decidable even in case the chase does not terminate. We provide tight complexity bounds for such cases. Our results immediately extend to query containment.

Is cosmic acceleration slowing down

Abstract: We investigate the course of cosmic expansion in its recent past using the Constitution SN Ia sample, along with baryon acoustic oscillations (BAO) and cosmic microwave background (CMB) data. Allowing the equation of state of dark energy (DE) to vary, we find that a coasting model of the universe (q{sub 0}=0) fits the data about as well as Lambda cold dark matter. This effect, which is most clearly seen using the recently introduced Om diagnostic, corresponds to an increase of Om and q at redshifts z < or approx. 0.3. This suggests that cosmic acceleration may have already peaked and that we are currently witnessing its slowing down. The case for evolving DE strengthens if a subsample of the Constitution set consisting of SNLS+ESSENCE+CfA SN Ia data is analyzed in combination with BAO+CMB data. The effect we observe could correspond to DE decaying into dark matter (or something else)

Modeling contact angle hysteresis on chemically patterned and superhydrophobic surfaces

Abstract: We investigate contact angle hysteresis on chemically patterned and superhydrophobic surfaces, as the drop volume is quasistatically increased and decreased. We consider both two (cylindrical drops) and three (spherical drops) dimensions using analytical and numerical approaches to minimize the free energy of the drop. In two dimensions, we find, in agreement with other authors, a slip, jump, stick motion of the contact line. In three dimensions, this behavior persists, but the position and magnitude of the contact line jumps are sensitive to the details of the surface patterning. In two dimensions, we identify analytically the advancing and receding contact angles on the different surfaces, and we use numerical insights to argue that these provide bounds for the three-dimensional cases. We present explicit simulations to show that a simple average over the disorder is not sufficient to predict the details of the contact angle hysteresis and to support an explanation for the low contact angle hysteresis of suspended drops on superhydrophobic surfaces.

Division, Segmentation, and Interpellation: The Embodied Labors of Migrant Workers in a Greater London Hotel

Abstract: In this article, we explore the ways in which a divided and segmented migrant labor force is assembled to serve guests in a London hotel. We draw on previous studies of hotel work, as well as on cultural analyses of the ways in which employers and managers use stereotypical assumptions about the embodied attributes of workers to name workers as suitable for particular types of labor. We argue that a dual process of interpellation operates within service-sector workplaces that is reinforced and resisted in daily social practices and relationships between managers, workers, and guests in a hotel. The article, which draws on a case study of employment practices in a large London hotel, looks in detail at the micropolitics of everyday working lives, the representation of workers of different nationalities, and the performance of service work.