35,252 research outputs found
Runtime Verification of Temporal Properties over Out-of-order Data Streams
We present a monitoring approach for verifying systems at runtime. Our
approach targets systems whose components communicate with the monitors over
unreliable channels, where messages can be delayed or lost. In contrast to
prior works, whose property specification languages are limited to
propositional temporal logics, our approach handles an extension of the
real-time logic MTL with freeze quantifiers for reasoning about data values. We
present its underlying theory based on a new three-valued semantics that is
well suited to soundly and completely reason online about event streams in the
presence of message delay or loss. We also evaluate our approach
experimentally. Our prototype implementation processes hundreds of events per
second in settings where messages are received out of order.Comment: long version of the CAV 2017 pape
On the Coexistence Magnetism/Superconductivity in the Heavy-Fermion Superconductor CePtSi
The interplay between magnetism and superconductivity in the newly discovered
heavy-fermion superconductor CePtSi has been investigated using the
zero-field SR technique. The SR data indicate that the whole muon
ensemble senses spontaneous internal fields in the magnetic phase,
demonstrating that magnetism occurs in the whole sample volume. This points to
a microscopic coexistence between magnetism and heavy-fermion
superconductivity.Comment: Final version, new figure structure, references correcte
Characterization of Active Main Belt Object P/2012 F5 (Gibbs): A Possible Impacted Asteroid
In this work we characterize the recently discovered active main belt object
P/2012 F5 (Gibbs), which was discovered with a dust trail > 7' in length in the
outer main belt, 7 months prior to aphelion. We use optical imaging obtained on
UT 2012 March 27 to analyze the central condensation and the long trail. We
find nuclear B-band and R-band apparent magnitudes of 20.96 and 19.93 mag,
respectively, which give an upper limit on the radius of the nucleus of 2.1 km.
The geometric cross-section of material in the trail was ~ 4 x 10^8 m^2,
corresponding to a dust mass of ~ 5 x 10^7 kg. Analysis of infrared images
taken by the Wide-Field Infrared Survey Explorer in September 2010 reveals that
the object was below the detection limit, suggesting that it was less active
than it was during 2012, or possibly inactive, just 6 months after it passed
through perihelion. We set a 1-sigma upper limit on its radius during this time
of 2.9 km. P/2012 F5 (Gibbs) is dynamically stable in the outer main belt on
timescales of ~ 1 Gyr, pointing towards an asteroidal origin. We find that the
morphology of the ejected dust is consistent with it being produced by a single
event that occurred on UT 2011 July 7 20 days, possibly as the result of
a collision with a small impactor.Comment: 29 pages, 5 figures. Accepted for publication in Ap
Regularization independent of the noise level: an analysis of quasi-optimality
The quasi-optimality criterion chooses the regularization parameter in
inverse problems without taking into account the noise level. This rule works
remarkably well in practice, although Bakushinskii has shown that there are
always counterexamples with very poor performance. We propose an average case
analysis of quasi-optimality for spectral cut-off estimators and we prove that
the quasi-optimality criterion determines estimators which are rate-optimal
{\em on average}. Its practical performance is illustrated with a calibration
problem from mathematical finance.Comment: 18 pages, 3 figure
Jet noise suppression by porous plug nozzles
Jet noise suppression data presented earlier by Maestrello for porous plug nozzles were supplemented by the testing of a family of nozzles having an equivalent throat diameter of 11.77 cm. Two circular reference nozzles and eight plug nozzles having radius ratios of either 0.53 or 0.80 were tested at total pressure ratios of 1.60 to 4.00. Data were taken both with and without a forward motion or coannular flow jet, and some tests were made with a heated jet. Jet thrust was measured. The data were analyzed to show the effects of suppressor geometry on nozzle propulsive efficiency and jet noise. Aerodynamic testing of the nozzles was carried out in order to study the physical features that lead to the noise suppression. The aerodynamic flow phenomena were examined by the use of high speed shadowgraph cinematography, still shadowgraphs, extensive static pressure probe measurements, and two component laser Doppler velocimeter studies. The different measurement techniques correlated well with each other and demonstrated that the porous plug changes the shock cell structure of a standard nozzle into a series of smaller, periodic cell structures without strong shock waves. These structures become smaller in dimension and have reduced pressure variations as either the plug diameter or the porosity is increased, changes that also reduce the jet noise and decrease thrust efficiency
Lingering grains of truth around comet 17P/Holmes
Comet 17P/Holmes underwent a massive outburst in 2007 Oct., brightening by a
factor of almost a million in under 48 hours. We used infrared images taken by
the Wide-Field Survey Explorer mission to characterize the comet as it appeared
at a heliocentric distance of 5.1 AU almost 3 years after the outburst. The
comet appeared to be active with a coma and dust trail along the orbital plane.
We constrained the diameter, albedo, and beaming parameter of the nucleus to
4.135 0.610 km, 0.03 0.01 and 1.03 0.21, respectively. The
properties of the nucleus are consistent with those of other Jupiter Family
comets. The best-fit temperature of the coma was 134 11 K, slightly
higher than the blackbody temperature at that heliocentric distance. Using
Finson-Probstein modeling we found that the morphology of the trail was
consistent with ejection during the 2007 outburst and was made up of dust
grains between 250 m and a few cm in radius. The trail mass was 1.2
- 5.3 10 kg.Comment: Accepted to ApJ. 2 tables, 4 figure
- …