10,767 research outputs found
Keplerian discs around post-AGB stars: a common phenomenon?
Aims: We aim at showing that the broad-band SED characteristics of our sample
of post-AGB stars are best interpreted, assuming the circumstellar dust is
stored in Keplerian rotating passive discs.
Methods: We present a homogeneous and systematic study of the Spectral Energy
Distributions (SEDs) of a sample of 51 post-AGB objects. The selection criteria
to define the whole sample were tuned to cover the broad-band characteristics
of known binary post-AGB stars. The whole sample includes 20 dusty RV Tauri
stars from the General Catalogue of Variable Stars (GCVS). We supplemented our
own Geneva optical photometry with literature data to cover a broad range of
fluxes from the UV to the far-IR.
Results: All the SEDs display very similar characteristics: a large IR excess
with a dust excess starting near the sublimation temperature, irrespective of
the effective temperature of the central star. Moreover, when available, the
long wavelength fluxes show a black-body slope indicative of the presence of a
component of large mm sized grains.
Conclusions: We argue that in all systems, gravitationally bound dusty discs
are present. The discs must be puffed-up to cover a large opening angle for the
central star and we argue that the discs have some similarity with the passive
discs detected around young stellar objects. We interpret the presence of a
disc to be a signature for binarity of the central object, but this will need
confirmation by long-term monitoring of the radial velocities. We argue that
dusty RV Tauri stars are those binaries which happen to be in the Population II
instability strip.Comment: 29 pages, 5 figures, accepted for publication in A&
Infant cortex responds to other humans from shortly after birth
A significant feature of the adult human brain is its ability to selectively process information about conspecifics. Much debate has centred on whether this specialization is primarily a result of phylogenetic adaptation, or whether the brain acquires expertise in processing social stimuli as a result of its being born into an intensely social environment. Here we study the haemodynamic response in cortical areas of newborns (1–5 days old) while they passively viewed dynamic human or mechanical action videos. We observed activation selective to a dynamic face stimulus over bilateral posterior temporal cortex, but no activation in response to a moving human arm. This selective activation to the social stimulus correlated with age in hours over the first few days post partum. Thus, even very limited experience of face-to-face interaction with other humans may be sufficient to elicit social stimulus activation of relevant cortical regions
Experimental Quantum Private Queries with linear optics
The Quantum Private Query is a quantum cryptographic protocol to recover
information from a database, preserving both user and data privacy: the user
can test whether someone has retained information on which query was asked, and
the database provider can test the quantity of information released. Here we
introduce a new variant Quantum Private Query algorithm which admits a simple
linear optical implementation: it employs the photon's momentum (or time slot)
as address qubits and its polarization as bus qubit. A proof-of-principle
experimental realization is implemented.Comment: 4 pages, 2 figure
A Denotational Semantics for First-Order Logic
In Apt and Bezem [AB99] (see cs.LO/9811017) we provided a computational
interpretation of first-order formulas over arbitrary interpretations. Here we
complement this work by introducing a denotational semantics for first-order
logic. Additionally, by allowing an assignment of a non-ground term to a
variable we introduce in this framework logical variables.
The semantics combines a number of well-known ideas from the areas of
semantics of imperative programming languages and logic programming. In the
resulting computational view conjunction corresponds to sequential composition,
disjunction to ``don't know'' nondeterminism, existential quantification to
declaration of a local variable, and negation to the ``negation as finite
failure'' rule. The soundness result shows correctness of the semantics with
respect to the notion of truth. The proof resembles in some aspects the proof
of the soundness of the SLDNF-resolution.Comment: 17 pages. Invited talk at the Computational Logic Conference (CL
2000). To appear in Springer-Verlag Lecture Notes in Computer Scienc
Fitness, Friendship, and Fun: University Sponsored Community PE Program
This paper describes a University-sponsored community physical education program and the feedback received about it from teachers, children, and the college students who oversaw it. The program, called Fitness, Friendship, and Fun, was staffed by 65 first-year student interns from the University of Dayton; four graduate assistants; and two university professors. It began with 65 male and female elementary students, primarily from the fifth and sixth grades at a nearby elementary school
Outlier Edge Detection Using Random Graph Generation Models and Applications
Outliers are samples that are generated by different mechanisms from other
normal data samples. Graphs, in particular social network graphs, may contain
nodes and edges that are made by scammers, malicious programs or mistakenly by
normal users. Detecting outlier nodes and edges is important for data mining
and graph analytics. However, previous research in the field has merely focused
on detecting outlier nodes. In this article, we study the properties of edges
and propose outlier edge detection algorithms using two random graph generation
models. We found that the edge-ego-network, which can be defined as the induced
graph that contains two end nodes of an edge, their neighboring nodes and the
edges that link these nodes, contains critical information to detect outlier
edges. We evaluated the proposed algorithms by injecting outlier edges into
some real-world graph data. Experiment results show that the proposed
algorithms can effectively detect outlier edges. In particular, the algorithm
based on the Preferential Attachment Random Graph Generation model consistently
gives good performance regardless of the test graph data. Further more, the
proposed algorithms are not limited in the area of outlier edge detection. We
demonstrate three different applications that benefit from the proposed
algorithms: 1) a preprocessing tool that improves the performance of graph
clustering algorithms; 2) an outlier node detection algorithm; and 3) a novel
noisy data clustering algorithm. These applications show the great potential of
the proposed outlier edge detection techniques.Comment: 14 pages, 5 figures, journal pape
Strong dust processing in circumstellar discs around 6 RV Tauri stars. Are dusty RV Tauri stars all binaries?
We present extended Spectral Energy Distributions (SEDs) of seven classical
RV Tauri stars, using newly obtained submillimetre continuum measurements and
Geneva optical photometry supplemented with literature data. The broad-band
SEDs show a large IR excess with a black-body slope at long wavelengths in six
of the seven stars, R Sct being the noticeable exception. This long wavelength
slope is best explained assuming the presence of a dust component of large
grains in the circumstellar material. We show that the most likely distribution
of the circumstellar dust around the six systems is that the dust resides in a
disc. Moreover, very small outflow velocities are needed to explain the
presence of dust near the sublimation temperature and we speculate that the
discs are Keplerian. The structure and evolution of these compact discs are as
yet not understood but a likely prerequisite for their formation is that the
dusty RV Tauri stars are binaries.Comment: 10 pages, will be published in A&
A Formalization of the Theorem of Existence of First-Order Most General Unifiers
This work presents a formalization of the theorem of existence of most
general unifiers in first-order signatures in the higher-order proof assistant
PVS. The distinguishing feature of this formalization is that it remains close
to the textbook proofs that are based on proving the correctness of the
well-known Robinson's first-order unification algorithm. The formalization was
applied inside a PVS development for term rewriting systems that provides a
complete formalization of the Knuth-Bendix Critical Pair theorem, among other
relevant theorems of the theory of rewriting. In addition, the formalization
methodology has been proved of practical use in order to verify the correctness
of unification algorithms in the style of the original Robinson's unification
algorithm.Comment: In Proceedings LSFA 2011, arXiv:1203.542
Coinductive soundness of corecursive type class resolution
This work has been supported by the EPSRC grant “Coalgebraic Logic Programming for Type Inference” EP/K031864/1-2, EU Horizon 2020 grant “RePhrase: Refactoring Parallel Heterogeneous Resource-Aware Applications - a Software Engineering Approach” (ICT-644235), and by COST Action IC1202 (TACLe), supported by COST (European Cooperation in Science and Technology)Horn clauses and first-order resolution are commonly used to implement type classes in Haskell. Several corecursive extensions to type class resolution have recently been proposed, with the goal of allowing (co)recursive dictionary construction where resolution does not terminate. This paper shows, for the first time, that corecursive type class resolution and its extensions are coinductively sound with respect to the greatest Herbrand models of logic programs and that they are inductively unsound with respect to the least Herbrand models. We establish incompleteness results for various fragments of the proof system.Postprin
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