Supporting ArcAngel in ProofPower

AbstractArcAngel is a specialised tactic language devised to facilitate and automate program developments using Morgan's refinement calculus. It is especially well-suited for the specification of high-level strategies to derive programs by construction, and equipped with a formal semantics that enables reasoning about tactics. In this paper, we present an implementation of ArcAngel for the ProofPower theorem prover. We discuss the underlying design, explain how it implements the semantics of ArcAngel, and examine differences in expressiveness and flexibility in comparison to ProofPower's in-built tactic language. ArcAngel supports backtracking through angelic choice; this is beyond the basic capabilities of ProofPower and many other main-stream theorem provers. The implementation is demonstrated with a non-trivial tactic example

Gamma Rays from Space

An overview of gamma rays from space is presented. We highlight the most powerful astrophysical explosions, known as gamma-ray bursts. The main features observed in detectors onboard satellites are indicated. In addition, we also highlight a chronological description of the efforts made to observe their high energy counterpart at ground level. Some candidates of the GeV counterpart of gamma-ray bursts, observed by Tupi telescopes, are also presented

Alignment of air showers produced by ultra-high energy cosmic rays at the Pierre Auger Observatory

We show that the energy-weighted angular (zenith, azimuth) distribution of extensive air showers (EAS), produced by Ultra High Energy (UHE) cosmic rays at the Pierre Auger Observatory (PAO), has a thrust axis almost transverse to the interplanetary magnetic field (IMF), with a thrust value $Tp \geq 0.64$ ( where 1.0 means a perfect alignment and 0.5 isotropy). This behavior strongly suggests an effect of the IMF on the charged shower particles, producing additional lateral scattering. We discuss the weakening of the Earth's magnetic field during geomagnetic storms (30\% of observational time) when the IMF becomes preponderant, strengthening the alignment.Comment: 6 pages, 6 figure

The Influence of Lateral Faults in the Nonlinear Analysis in an Alluvionar Valley

The nonlinear dynamic behavior of an alluvionar valley situated in São Sebastão region in Terceira island (Azores archipel) is performed. The Mohr-Coulomb model is used in this paper. A bidimensional cross-section with 1240 m long and 250 m depth is considered. The cross-section of the model is composed by layers having different type of ground, each one having their own geotechnical characteristics. The Distinct Element method is employed in this case. UDE Code is used. The size of Finite Elements has been tailored to the wavelength of the propagating waves through the layers. The objectives of this paper are: 1) The analysis of seismic response in terms of maximum values of shear strain at different spots along the depth; 2) The study of the influence of the lateral faults in the seismic response in terms of maximum values of shear strain and shear strain-stress relationship; 3) The analysis of the seismic response of the soils at different locations in terms of shear strain-stress relationship for “no fault” case. This is the first attempt to study the nonlinear behavior of this valley using a 2-D refined model. The UDEC code is used for studying, not only the nonlinear behavior of the soils, but also the influence of the faults to the seismic response of the soils

Exponentially small quantum correction to conductance

When time-reversal symmetry is broken, the average conductance through a chaotic cavity, from an entrance lead with $N_1$ open channels to an exit lead with $N_2$ open channels, is given by $N_1N_2/M$, where $M=N_1+N_2$. We show that, when tunnel barriers of reflectivity $\gamma$ are placed on the leads, two correction terms appear in the average conductance, and that one of them is proportional to $\gamma^{M}$. Since $M\sim \hbar^{-1}$, this correction is exponentially small in the semiclassical limit. Surprisingly, we derive this term from a semiclassical approximation, generally expected to give only leading orders in powers of $\hbar$. Even though the theory is built perturbatively both in $\gamma$ and in $1/M$, the final result is exact.Comment: 9 pages, 2 figure