23,482 research outputs found
Typed Norms for Typed Logic Programs
As typed logic programming becomes more mainstream, system building tools like partial deduction systems will need to be mapped from untyped languages to typed ones. It is important, however, when mapping techniques across that the new techniques should exploit the type system as much as possible. in this paper, we show how norms which play a crucial role in termination analysis, can be generated from the prescribed types of a logic program. Interestingly, the types highlight restrictions of earlier norms and suggest how these norms can be extended to obtain some very general and powerful notions of norm which can be used to measure any term in an almost arbitrary way. We see our work on norm derivation as a contribution to the termination analysis of typed logic programs which, in particular, forms an essential part of offline partial deduction systems
Generating Efficient, Terminating Logic Programs
The objective of control generation in logic programming is to automatically derive a computation rule for a program that is efficient and yet does not compromise program correctness. Progress in solving this important problem has been slow and, to date, only partial solutions have been proposed where the generated programs are either incorrect or inefficient. We show how the control generation problem can be tackled with a simple automatic transformation that relies on information about the depths of derivations. To prove correctness of our transform we introduce the notion of a semi delay recurrent program which generalises previous ideas in the termination literature for reasoning about logic programs with dynamic selection rules
Broken discs: warp propagation in accretion discs
We simulate the viscous evolution of an accretion disc around a spinning
black hole. In general any such disc is misaligned, and warped by the
Lense-Thirring effect. Unlike previous studies we use effective viscosities
constrained to be consistent with the internal fluid dynamics of the disc. We
find that nonlinear fluid effects, which reduce the effective viscosities in
warped regions, can promote the breaking of the disc into two distinct planes.
This occurs when the Shakura & Sunyaev dimensionless viscosity parameter alpha
is ~
45 degrees. The break can be a long-lived feature, propagating outwards in the
disc on the usual alignment timescale, after which the disc is fully co- or
counter-aligned with the hole. Such a break in the disc may be significant in
systems where we know the inclination of the outer accretion disc to the line
of sight, such as some X-ray binaries: the inner disc, and so any jets, may be
noticeably misaligned with respect to the orbital plane.Comment: 8 pages, 9 figures. Accepted for publication in MNRA
The Future of California Transportation Revenue
Stable, predictable, and adequate transportation revenues are needed if California is to plan and deliver an excellent transportation system. This report provides a brief history of transportation revenue policies and potential futures in California. It then presents projections of transportation revenue under the recently enacted Senate Bill 1, the Road Repair and Accountability Act of 2017. Those revenue projections are compared with projections of revenue should SB 1 be repealed by voters in the November 2018 election. State-generated transportation revenues will be higher under SB1 than if the act is repealed. For 2020, the mean projection is that the state will collect 6.6 billion without it, a difference of 8.6 billion with SB1 and 5.2 billion difference. The total of all state transportation revenue collected between 2018 and 2040, assuming no other revisions to transportation revenue programs during these years, will be about $100 billion less if SB 1 is repealed than if the law is retained. The final section of the report addresses public attitudes toward transportation tax and fee policies, since future any policy changes must be informed by public willingness to consider revenue increases and opinions about which taxes or fees would be most appropriate
GUT predictions for quark-lepton Yukawa coupling ratios with messenger masses from non-singlets
We propose new predictions from grand unified theories (GUTs) [applicable to both supersymmetric (SUSY) and non-SUSY models] for the ratios of quark and lepton Yukawa couplings. These new predictions arise from splitting the masses of the messenger fields for the GUT-scale Yukawa operators by Clebsch-Gordan factors from GUT symmetry breaking. This has the effect that these factors enter inversely in the predicted quark-lepton Yukawa coupling ratios, leading to new possible GUT predictions. We systematically construct the new predictions that can be realized in this way in SU(5) GUTs and Pati-Salam unified theories and discuss model building applications
The Impact of ZEV Adoption on California Transportation Revenue
Former California Governor Jerry Brown set an ambitious target for the state to reach five million zero-emission vehicles (ZEVs) by 2030. The policy is intended to reduce greenhouse gas emissions, but progress toward this target will also affect future state-generated transportation revenues collected from vehicle owners and operators. A central concern for policymakers is to estimate the magnitude of the revenue impact. We used a simple spreadsheet model to project future transportation revenue in California through 2040 under two scenarios. The first scenario assumes that ZEV ownership continues at its historical rate of net increase, approximately 26,000 vehicles per year (the “low-adoption scenario”). The second scenario assumes that California reaches its goal of five million ZEVs by 2030 (the “high-adoption scenario”). The projections are for light duty vehicles and do not address the possibility that heavy trucks may over time also adopt alternative fuels
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Data-Driven Generalized Integer Aperture Bootstrapping for Real-Time High Integrity Applications
A new method is developed for integer ambiguity
resolution in carrier-phase differential GPS (CDGPS) positioning.
The method is novel in that it is (1) data-driven, (2) generalized
to include partial ambiguity resolution, and (3) amenable to a
full characterization of the prior and posterior distributions of
the three-dimensional baseline vector that results from CDGPS.
The technique is termed generalized integer aperture bootstrapping
(GIAB). GIAB improves the availability of integer
ambiguity resolution for high-integrity, safety-critical systems.
Current high-integrity CDGPS algorithms, such as EPIC and
GERAFS, evaluate the prior risk of position domain biases due to
incorrect integer ambiguity resolution without further validation
of the chosen solution. This model-driven approach introduces
conservatism which tends to reduce solution availability. Common
data-driven ambiguity validation methods, such as the ratio test,
control the risk of incorrect ambiguity resolution by shrinking
an integer aperture (IA), or acceptance region. The incorrect
fixing risk of current IA methods is determined by functional
approximations that are inappropriate for use in safety-of-life
applications. Moreover, generalized IA (GIA) methods incorrectly
assume that the baseline resulting from partial ambiguity resolution
is zero mean. Each of these limitations is addressed by
GIAB, and the claimed improvements are validated by Monte
Carlo simulation. The performance of GIAB is then optimized by
tuning the integer aperture size to maximize the prior probability
of full ambiguity resolution. GIAB is shown to provide higher
availability than EPIC for the same integrity requirements.Aerospace Engineering and Engineering Mechanic
Liquid oil painting: Free and forced convection in an enclosure with mechanical and thermal forcing
A fluid dynamics video is linked to this article, which have been submitted
to the Gallery of Fluid Motion as part of the 65th American Physical Society
meeting of the Division of Fluid Dynamics, held in San Diego, California, USA,
over 17-20 November 2012. The video serves to visualize flows generated in a
rectangular enclosure that are subjected to both mechanical and thermal forcing
through a common horizontal boundary. This system exhibits features consistent
with either horizontal convection or lid-driven cavity flows depending on the
ratio between thermal and mechanical stirring, and three different cases are
visualized in the linked videos.Comment: 2 video files attached, 4 pages, 1 figure. This article is submitted
accompanying a video submitted to the Gallery of Fluid Motion as part of the
65th Division of Fluid Dynamics meeting of the American Physical Society
(17-20 November, San Diego, CA, USA
A study of the porosity of nuclear graphite using small-angle neutron scattering
Small angle neutron scattering (SANS) measures porosity in nuclear graphites, including both open pores, caused by escaping decomposition gases, and internal cracks (in coke particles) generated by anisotropic thermal contraction along the c-direction (Mrozowski Cracks). Porosity changes on the length scale observable by SANS must control the development of internal stresses and hence of cracking in AGR graphite due to irradiation (both fast neutron displacements of carbon atoms and radiolytic corrosion by CO2). Such cracking may cause premature reactor shutdown. SANS measurements show that porosity is fractal on a length scale between ~0.2-300 nm, presumably due to Mrozowski cracks – because the fractal index of the SANS signal depends only on the porosity of the graphitic filler. We report here two novel uses of the SANS technique as applied to reactor graphite – contrast matching with D-toluene (to measure the fraction of the porosity open to the surface) and the temperature dependence of the scattering (to measure pore width changes up to 2000 °C). These results provide important new information on AGR graphite porosity and its evolution during irradiation
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