Mining State-Based Models from Proof Corpora

Interactive theorem provers have been used extensively to reason about various software/hardware systems and mathematical theorems. The key challenge when using an interactive prover is finding a suitable sequence of proof steps that will lead to a successful proof requires a significant amount of human intervention. This paper presents an automated technique that takes as input examples of successful proofs and infers an Extended Finite State Machine as output. This can in turn be used to generate proofs of new conjectures. Our preliminary experiments show that the inferred models are generally accurate (contain few false-positive sequences) and that representing existing proofs in such a way can be very useful when guiding new ones.Comment: To Appear at Conferences on Intelligent Computer Mathematics 201

Hipster: Integrating Theory Exploration in a Proof Assistant

This paper describes Hipster, a system integrating theory exploration with the proof assistant Isabelle/HOL. Theory exploration is a technique for automatically discovering new interesting lemmas in a given theory development. Hipster can be used in two main modes. The first is exploratory mode, used for automatically generating basic lemmas about a given set of datatypes and functions in a new theory development. The second is proof mode, used in a particular proof attempt, trying to discover the missing lemmas which would allow the current goal to be proved. Hipster's proof mode complements and boosts existing proof automation techniques that rely on automatically selecting existing lemmas, by inventing new lemmas that need induction to be proved. We show example uses of both modes

Discovery of an eccentric 30 days period in the supergiant X-ray binary SAX J1818.6-1703 with INTEGRAL

SAX J1818.6-1703 is a flaring transient X-ray source serendipitously discovered by BeppoSAX in 1998 during an observation of the Galactic centre. The source was identified as a High-Mass X-ray Binary with an OB SuperGiant companion. Displaying short and bright flares and an unusually very-low quiescent level implying intensity dynamical range as large as 1e3-4, the source was classified as a Supergiant Fast X-ray Transient. The mechanism triggering the different temporal behaviour observed between the classical SGXBs and the recently discovered class of SFXTs is still debated. The discovery of long orbits (>15 d) should help to discriminate between emission models and bring constraints. We analysed archival INTEGRAL data on SAX J1818.6-1703. We built short- and long-term light curves and performed timing analysis in order to study the temporal behaviour of SAX J1818.6-1703 on different time scales. INTEGRAL revealed an unusually long orbital period of 30.0+/-0.2 d and an elapsed accretion phase of ~6 d in the transient SGXB SAX J1818.6-1703. This implies an elliptical orbit and constraints the possible supergiant spectral type between B0.5-1I with eccentricities e~0.3-0.4 (for average fundamental parameters of supergiant stars). During the accretion phase, the source behaved like classical SGXBs. The huge variations of the observed X-ray flux can be explained through accretion of macro-clumps formed within the stellar wind. Our analysis strengthens the model which predicts that SFXTs behave as SGXBs but with different orbital parameters, thus different temporal behaviour.Comment: 4 pages, 3 figures, A&A Letter in press (subm. 17/10/2008 - accept. 15/11/2008

Evolution of the seroprevalence of pestivirus and respiratory viral infections in Spanish feedlot lambs

The presence of respiratory viruses and pestiviruses in sheep has been widely demon-strated, and their ability to cause injury and predispose to respiratory processes have been proven experimentally. A longitudinal observational study was performed to determine the seroprevalence of bovine parainfluenza virus type 3 (BPIV-3), bovine respiratory syncytial virus (BRSV), bovine herpesvirus type 1 (BHV-1) and pestiviruses in 120 lambs at the beginning and the end of the fattening period. During this time, the animals were clinically monitored, their growth was recorded, and post-mortem examinations were performed in order to identify the presence of pneumonic lesions in the animals. Seroconversion to all viruses tested except BHV-1 was detected at the end of the period. Initially, BPIV-3 antibodies were the most frequently found, while the most common seroconversion through the analysed period occurred to BRSV. Only 10.8% of the lambs showed no detectable levels of antibodies against any of the tested viruses at the end of the survey. In addition, no statistical differences were found in the presentation of respiratory clinical signs, pneumonic lesions nor in the production performance between lambs that seroconverted and those which did not, except in the case of pestiviruses. The seroconversion to pestiviruses was associated with a reduction in the final weight of the lambs

IGR J16393-4643: a new heavily-obscured X-ray pulsar

An analysis of the high-energy emission from IGR J16393-4643 (=AX J1639.0-4642) is presented using data from INTEGRAL and XMM-Newton. The source is persistent in the 20-40 keV band at an average flux of 5.1x10^-11 ergs/cm2/s, with variations in intensity by at least an order of magnitude. A pulse period of 912.0+/-0.1 s was discovered in the ISGRI and EPIC light curves. The source spectrum is a strongly-absorbed (nH=(2.5+/-0.2)x10^23 atoms/cm2) power law that features a high-energy cutoff above 10 keV. Two iron emission lines at 6.4 and 7.1 keV, an iron absorption edge >7.1 keV, and a soft excess emission of 7x10^-15 ergs/cm2/s between 0.5-2 keV, are detected in the EPIC spectrum. The shape of the spectrum does not change with the pulse. Its persistence, pulsation, and spectrum place IGR J16393-4643 among the class of heavily-absorbed HMXBs. The improved position from EPIC is R.A. (J2000)=16:39:05.4 and Dec.=-46:42:12 (4" uncertainty) which is compatible with that of 2MASS J16390535-4642137.Comment: 8 pages, 9 figures, accepted for publication in A&

Fitting of dust spectra with genetic algorithms - I. Perspectives & Limitations

Aims: We present an automatised fitting procedure for the IR range of AGB star spectra. Furthermore we explore the possibilities and boundaries of this method. Methods: We combine the radiative transfer code DUSTY with the genetic algorithm PIKAIA in order to improve an existing spectral fit significantly. Results: In order to test the routine we carried out a performance test by feeding an artificially generated input spectrum into the program. Indeed the routine performed as expected, so, as a more realistic test set-up, we tried to create model fits for ISO spectra of selected AGB stars. Here we were not only able to improve existing fits, but also to show that a slightly altered dust composition may give a better fit for some objects. Conclusion: The use of a genetic algorithm in order to automatise the process of fitting stellar spectra seems to be very promising. We were able to improve existing fits and further offer a quantitative method to compare different models with each other. Nevertheless this method still needs to be studied and tested in more detail.Comment: 9 pages, 5 figures, accepted for publication in Astronomy and Astrophysic