1,109 research outputs found
Report on the formal specification and partial verification of the VIPER microprocessor
The formal specification and partial verification of the VIPER microprocessor is reviewed. The VIPER microprocessor was designed by RSRE, Malvern, England, for safety critical computing applications (e.g., aircraft, reactor control, medical instruments, armaments). The VIPER was carefully specified and partially verified in an attempt to provide a microprocessor with completely predictable operating characteristics. The specification of VIPER is divided into several levels of abstraction, from a gate-level description up to an instruction execution model. Although the consistency between certain levels was demonstrated with mechanically-assisted mathematical proof, the formal verification of VIPER was never completed
Fourier Series Formalization in ACL2(r)
We formalize some basic properties of Fourier series in the logic of ACL2(r),
which is a variant of ACL2 that supports reasoning about the real and complex
numbers by way of non-standard analysis. More specifically, we extend a
framework for formally evaluating definite integrals of real-valued, continuous
functions using the Second Fundamental Theorem of Calculus. Our extended
framework is also applied to functions containing free arguments. Using this
framework, we are able to prove the orthogonality relationships between
trigonometric functions, which are the essential properties in Fourier series
analysis. The sum rule for definite integrals of indexed sums is also
formalized by applying the extended framework along with the First Fundamental
Theorem of Calculus and the sum rule for differentiation. The Fourier
coefficient formulas of periodic functions are then formalized from the
orthogonality relations and the sum rule for integration. Consequently, the
uniqueness of Fourier sums is a straightforward corollary.
We also present our formalization of the sum rule for definite integrals of
infinite series in ACL2(r). Part of this task is to prove the Dini Uniform
Convergence Theorem and the continuity of a limit function under certain
conditions. A key technique in our proofs of these theorems is to apply the
overspill principle from non-standard analysis.Comment: In Proceedings ACL2 2015, arXiv:1509.0552
Radioactive disintegration spectra of some short-lived nuclides
The beta endpoint energies of several short=lived, low Z radioactive nuclides have been measured with an improved scintillation spectrometer. These values have been combined with recent half-life determinations to give the ft values
Hardware verification at Computational Logic, Inc.
The following topics are covered in viewgraph form: (1) hardware verification; (2) Boyer-Moore logic; (3) core RISC; (4) the FM8502 fabrication, implementation specification, and pinout; (5) hardware description language; (6) arithmetic logic generator; (7) near term expected results; (8) present trends; (9) future directions; (10) collaborations and technology transfer; and (11) technology enablers
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High Repetition Rate, LINAC-Based Nuclear Resonance Fluorescence FY 2008 Final Report
This summarizes the first year of a multi-laboratory/university, multi-year effort focusing on high repetition rate, pulsed LINAC-based nuclear resonance fluorescence (NRF) measurements. Specifically, this FY2008 effort centered on experimentally assessing NRF measurements using pulsed linear electron accelerators, operated at various repetition rates, and identifying specific detection requirements to optimize such measurements. Traditionally, interest in NRF as a detection technology, which continues to receive funding from DHS and DOE/NA-22, has been driven by continuous-wave (CW), Van de Graff-based bremsstrahlung sources. However, in addition to the relatively sparse present-day use of Van de Graff sources, only limited NRF data from special nuclear materials has been presented; there is even less data available regarding shielding effects and photon source optimization for NRF measurements on selected nuclear materials
Eutectic colony formation: A phase field study
Eutectic two-phase cells, also known as eutectic colonies, are commonly
observed during the solidification of ternary alloys when the composition is
close to a binary eutectic valley. In analogy with the solidification cells
formed in dilute binary alloys, colony formation is triggered by a
morphological instability of a macroscopically planar eutectic solidification
front due to the rejection by both solid phases of a ternary impurity that
diffuses in the liquid. Here we develop a phase-field model of a binary
eutectic with a dilute ternary impurity and we investigate by dynamical
simulations both the initial linear regime of this instability, and the
subsequent highly nonlinear evolution of the interface that leads to fully
developed two-phase cells with a spacing much larger than the lamellar spacing.
We find a good overall agreement with our recent linear stability analysis [M.
Plapp and A. Karma, Phys. Rev. E 60, 6865 (1999)], which predicts a
destabilization of the front by long-wavelength modes that may be stationary or
oscillatory. A fine comparison, however, reveals that the assumption commonly
attributed to Cahn that lamella grow perpendicular to the envelope of the
solidification front is weakly violated in the phase-field simulations. We show
that, even though weak, this violation has an important quantitative effect on
the stability properties of the eutectic front. We also investigate the
dynamics of fully developed colonies and find that the large-scale envelope of
the composite eutectic front does not converge to a steady state, but exhibits
cell elimination and tip-splitting events up to the largest times simulated.Comment: 18 pages, 18 EPS figures, RevTeX twocolumn, submitted to Phys. Rev.
Far-Infrared Line Imaging of the Starburst Ring in NGC 1097 with the Herschel/PACS Spectrometer
NGC 1097 is a nearby SBb galaxy with a Seyfert nucleus and a bright starburst
ring. We study the physical properties of the interstellar medium (ISM) in the
ring using spatially resolved far-infrared spectral maps of the circumnuclear
starburst ring of NGC 1097, obtained with the PACS spectrometer on board the
Herschel Space Telescope. In particular, we map the important ISM cooling and
diagnostic emission lines of [OI] 63 m, [OIII] 88 m, [NII] 122
m, [CII] 158 m and [NII] 205 m. We observe that in the [OI] 63
m, [OIII] 88 m, and [NII] 122 m line maps, the emission is
enhanced in clumps along the NE part of the ring. We observe evidence of rapid
rotation in the circumnuclear ring, with a rotation velocity of ~220^{-1}\mu\mu\mu\mu\mu\mu^{-3}$.Comment: Accepted for publication on the A&A Herschel Special Issu
Enhanced dust heating in the bulges of early-type spiral galaxies
Stellar density and bar strength should affect the temperatures of the cool
(T ~ 20-30 K) dust component in the inner regions of galaxies, which implies
that the ratio of temperatures in the circumnuclear regions to the disk should
depend on Hubble type. We investigate the differences between cool dust
temperatures in the central 3 kpc and disk of 13 nearby galaxies by fitting
models to measurements between 70 and 500 microns. We attempt to quantify
temperature trends in nearby disk galaxies, with archival data from
Spitzer/MIPS and new observations with Herschel/SPIRE, which were acquired
during the first phases of the Herschel observations for the KINGFISH (key
insights in nearby galaxies: a far-infrared survey with Herschel) sample. We
fit single-temperature modified blackbodies to far-infrared and submillimeter
measurements of the central and disk regions of galaxies to determine the
temperature of the component(s) emitting at those wavelengths. We present the
ratio of central-region-to-disk-temperatures of the cool dust component of 13
nearby galaxies as a function of morphological type. We find a significant
temperature gradient in the cool dust component in all galaxies, with a mean
center-to-disk temperature ratio of 1.15 +/- 0.03. The cool dust temperatures
in the central ~3 kpc of nearby galaxies are 23(+/-3)% hotter for morphological
types earlier than Sc, and only 9(+/-3)% hotter for later types. The
temperature ratio is also correlated with bar strength, with only strongly
barred galaxies having a ratio over 1.2. The strong radiation field in the high
stellar density of a galactic bulge tends to heat the cool dust component to
higher temperatures, at least in early-type spirals with relatively large
bulges, especially when paired with a strong bar.Comment: Accepted for publication on the A&A Herschel Special Issu
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