3,922 research outputs found
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
Surface Instabilities and Magnetic Soft Matter
We report on the formation of surface instabilities in a layer of
thermoreversible ferrogel when exposed to a vertical magnetic field. Both
static and time dependent magnetic fields are employed. Under variations of
temperature, the viscoelastic properties of our soft magnetic matter can be
tuned. Stress relaxation experiments unveil a stretched exponential scaling of
the shear modulus, with an exponent of beta=1/3. The resulting magnetic
threshold for the formation of Rosensweig-cusps is measured for different
temperatures, and compared with theoretical predictions by Bohlius et. al. in
J. Phys.: Condens. Matter., 2006, 18, 2671-2684.Comment: accepted to Soft Matte
Integrated results from the COPERNICUS and GALILEO studies.
OBJECTIVES: To report on the efficacy and safety of intravitreal aflibercept in patients with macular edema secondary to central retinal vein occlusion (CRVO) in an integrated analysis of COPERNICUS and GALILEO.
PATIENTS AND METHODS: Patients were randomized to receive intravitreal aflibercept 2 mg every 4 weeks or sham injections until week 24. From week 24 to week 52, all intravitreal aflibercept-treated patients in both studies and sham-treated patients in COPERNICUS were eligible to receive intravitreal aflibercept based on prespecified criteria. In GALILEO, sham-treated patients continued to receive sham treatment through week 52.
RESULTS: At week 24, mean gain in best-corrected visual acuity and mean reduction in central retinal thickness were greater for intravitreal aflibercept-treated patients compared with sham, consistent with individual trial results. At week 52, after 6 months of intravitreal aflibercept as-needed treatment in COPERNICUS, patients originally randomized to sham group experienced visual and anatomic improvements but did not improve to the extent of those initially treated with intravitreal aflibercept, while the sham group in GALILEO did not improve over week 24 mean best-corrected visual acuity scores. Ocular serious adverse events occurred in
CONCLUSION: This analysis of integrated data from COPERNICUS and GALILEO confirmed that intravitreal aflibercept is an effective treatment for macular edema following CRVO
Hybrid Rules with Well-Founded Semantics
A general framework is proposed for integration of rules and external first
order theories. It is based on the well-founded semantics of normal logic
programs and inspired by ideas of Constraint Logic Programming (CLP) and
constructive negation for logic programs. Hybrid rules are normal clauses
extended with constraints in the bodies; constraints are certain formulae in
the language of the external theory. A hybrid program is a pair of a set of
hybrid rules and an external theory. Instances of the framework are obtained by
specifying the class of external theories, and the class of constraints. An
example instance is integration of (non-disjunctive) Datalog with ontologies
formalized as description logics.
The paper defines a declarative semantics of hybrid programs and a
goal-driven formal operational semantics. The latter can be seen as a
generalization of SLS-resolution. It provides a basis for hybrid
implementations combining Prolog with constraint solvers. Soundness of the
operational semantics is proven. Sufficient conditions for decidability of the
declarative semantics, and for completeness of the operational semantics are
given
Multiscale modelling of vascular tumour growth in 3D: the roles of domain size & boundary condition
We investigate a three-dimensional multiscale model of vascular tumour growth, which couples blood flow, angiogenesis, vascular remodelling, nutrient/growth factor transport, movement of, and interactions between, normal and tumour cells, and nutrient-dependent cell cycle dynamics within each cell. In particular, we determine how the domain size, aspect ratio and initial vascular network influence the tumour's growth dynamics and its long-time composition. We establish whether it is possible to extrapolate simulation results obtained for small domains to larger ones, by constructing a large simulation domain from a number of identical subdomains, each subsystem initially comprising two parallel parent vessels, with associated cells and diffusible substances. We find that the subsystem is not representative of the full domain and conclude that, for this initial vessel geometry, interactions between adjacent subsystems contribute to the overall growth dynamics. We then show that extrapolation of results from a small subdomain to a larger domain can only be made if the subdomain is sufficiently large and is initialised with a sufficiently complex vascular network. Motivated by these results, we perform simulations to investigate the tumour's response to therapy and show that the probability of tumour elimination in a larger domain can be extrapolated from simulation results on a smaller domain. Finally, we demonstrate how our model may be combined with experimental data, to predict the spatio-temporal evolution of a vascular tumour
Modeling Single Electron Transfer in Si:P Double Quantum Dots
Solid-state systems such as P donors in Si have considerable potential for
realization of scalable quantum computation. Recent experimental work in this
area has focused on implanted Si:P double quantum dots (DQDs) that represent a
preliminary step towards the realization of single donor charge-based qubits.
This paper focuses on the techniques involved in analyzing the charge transfer
within such DQD devices and understanding the impact of fabrication parameters
on this process. We show that misalignment between the buried dots and surface
gates affects the charge transfer behavior and identify some of the challenges
posed by reducing the size of the metallic dot to the few donor regime.Comment: 11 pages, 7 figures, submitted to Nanotechnolog
Radio Astronomy
Contains reports on five research projects.National Science Foundation (Grant AST82-14296)National Aeronautics and Space Administration (Grant NAG W-373)National Aeronautics and Space Administration (Grant NAG5-537)U.S. Navy - Office of Naval Research (Contract N00014-84-C-2082)SM Systems and Research, Inc.Defense Advanced Research Project Agency (Contract MDA903-82-K-0521
The asymmetric radio remnant of SN 1987A
We present seven years of radio observations of SN 1987A made with the
Australia Telescope Compact Array. At 1.4, 2.4, 4.8 and 8.6 GHz, the flux
density of the radio remnant has increased monotonically since emission was
redetected 1200 days after the explosion. On day 3200, the remnant was
expanding at 2800 +/- 400 km/s, which we interpret as indicating significant
deceleration of the fastest moving ejecta. Since day 1787 the spectral index
has remained constant at alpha = -0.95 +/- 0.04. These observations are all
consistent with the shock having encountered a denser, shocked, component of
the progenitor's stellar wind. At the current rate of expansion, the shock is
expected to encounter the inner optical ring in the year 2006 +/- 3.
Using super-resolution, we have also obtained 9 GHz images of the remnant
(resolution approx 0".5) at four epochs. The emission is distributed around the
rim of a near-circular shell, but has become increasingly asymmetric with time.
There are two "hotspots" to the east and west, aligned along the major axis of
the optical ring. This morphology is most likely indicative of an axisymmetric
circumstellar medium into which the shock is expanding, consistent with present
understanding of the progenitor star and its environment.Comment: 45 pages, LaTeX, including 15 PostScript figures. To appear in "The
Astrophysical Journal", volume 479 (20 Apr 1997
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