ANTLR Tree Grammar Generator and Extensions

A computer program implements two extensions of ANTLR (Another Tool for Language Recognition), which is a set of software tools for translating source codes between different computing languages. ANTLR supports predicated- LL(k) lexer and parser grammars, a notation for annotating parser grammars to direct tree construction, and predicated tree grammars. [ LL(k) signifies left-right, leftmost derivation with k tokens of look-ahead, referring to certain characteristics of a grammar.] One of the extensions is a syntax for tree transformations. The other extension is the generation of tree grammars from annotated parser or input tree grammars. These extensions can simplify the process of generating source-to-source language translators and they make possible an approach, called "polyphase parsing," to translation between computing languages. The typical approach to translator development is to identify high-level semantic constructs such as "expressions," "declarations," and "definitions" as fundamental building blocks in the grammar specification used for language recognition. The polyphase approach is to lump ambiguous syntactic constructs during parsing and then disambiguate the alternatives in subsequent tree transformation passes. Polyphase parsing is believed to be useful for generating efficient recognizers for C++ and other languages that, like C++, have significant ambiguities

Custom Sky-Image Mosaics from NASA's Information Power Grid

yourSkyG is the second generation of the software described in yourSky: Custom Sky-Image Mosaics via the Internet (NPO-30556), NASA Tech Briefs, Vol. 27, No. 6 (June 2003), page 45. Like its predecessor, yourSkyG supplies custom astronomical image mosaics of sky regions specified by requesters using client computers connected to the Internet. Whereas yourSky constructs mosaics on a local multiprocessor system, yourSkyG performs the computations on NASA s Information Power Grid (IPG), which is capable of performing much larger mosaicking tasks. (The IPG is high-performance computation and data grid that integrates geographically distributed 18 NASA Tech Briefs, September 2005 computers, databases, and instruments.) A user of yourSkyG can specify parameters describing a mosaic to be constructed. yourSkyG then constructs the mosaic on the IPG and makes it available for downloading by the user. The complexities of determining which input images are required to construct a mosaic, retrieving the required input images from remote sky-survey archives, uploading the images to the computers on the IPG, performing the computations remotely on the Grid, and downloading the resulting mosaic from the Grid are all transparent to the use

Common spaceborne multicomputer operating system and development environment

A preliminary technical specification for a multicomputer operating system is developed. The operating system is targeted for spaceborne flight missions and provides a broad range of real-time functionality, dynamic remote code-patching capability, and system fault tolerance and long-term survivability features. Dataflow concepts are used for representing application algorithms. Functional features are included to ensure real-time predictability for a class of algorithms which require data-driven execution on an iterative steady state basis. The development environment supports the development of algorithm code, design of control parameters, performance analysis, simulation of real-time dataflow applications, and compiling and downloading of the resulting application

Precision measurement of the speed of propagation of neutrinos using the MINOS detectors

We report a two-detector measurement of the propagation speed of neutrinos over a baseline of 734 km. The measurement was made with the NuMI beam at Fermilab between the near and far MINOS detectors. The fractional difference between the neutrino speed and the speed of light is determined to be (v/c-1) = (1.0±1.1) × 10^−6, consistent with relativistic neutrinos

FONTES DE DISTORÇÕES DA REDE GEODÉSICA BRASILEIRA

The Brazilian Geodetic Network started to be established in the early 40’s,employing classical surveying methods, such as triangulation and trilateration. Withthe introduction of satellite positioning systems, such as TRANSIT and GPS, thatnetwork was densified. That data was adjusted by employing a variety of methods,yielding distortions in the network that need to be understood. In this work, weanalyze and interpret study cases in an attempt to understand the distortions in theBrazilian network. For each case, we performed the network adjustment employingthe GHOST software suite. The results show that the distortion is least sensitive tothe removal of invar baselines in the classical network. The network would be moreaffected by the inexistence of Laplace stations and Doppler control points, withdifferences up to 4.5 m.A Rede Geodésica Brasileira (RGB) começou a ser implantada no início da décadade 40, com base nos métodos geodésicos de triangulação e poligonação, atualmentedesignados como métodos clássicos de levantamento. Com o surgimento doposicionamento por satélites artificiais, tais como TRANSIT e GPS, adensou-se arespectiva rede. Ajustamentos realizados envolvendo estes diferentes métodos deposicionamento evidenciaram as distorções na RGB, levando deste modo ànecessidade de se entender melhor tais inconsistências. Este trabalho tem porfinalidade realizar estudos de caso para auxiliar a análise e a interpretação dedistorções na rede planimétrica brasileira. Para este estudo, utilizou-se o programaGHOST, o mesmo usado no ajustamento da RGB. Em cada caso, removeu-se umtipo de observação – azimutes astronômicos (estações de Laplace), linhas de baseinvar, pontos Doppler – e repetiu-se o ajustamento da rede. Com isso foi possívelavaliar a contribuição ou importância de cada tipo de observação para a rigidez darede. Ou seja, foi possível responder a seguinte pergunta: “Quanto maior seria adistorção da rede clássica se estes tipos de observação estivessem ausentes oufossem ponderados diferentemente?”. Resultados destes estudos de caso indicamque as maiores distorções horizontais na rede geodésica brasileira existiriam se nãohouvessem estações de Laplace, ou seja, com a remoção dos azimutes astronômicos. Neste caso, as distorções horizontais atingiriam valores de até 4,5 m.Menores distorções horizontais ocorreriam com a inexistência das bases de invar, ecom reponderamento das estações de Laplace ou se pontos de controle Dopplerfossem inexistentes, nesta ordem

On the use of repeat leveling for the determination of vertical land motion: artifacts, aliasing and extrapolation errors

Leveling remains the most precise technique for measuring changes in heights. However, for the purposes of determining vertical land motion (VLM), a time series of repeat leveling measurements is susceptible to artifacts and aliasing that may arise due to systematic errors, seasonal surface fluctuations, motions occurring during a survey, and any inconsistencies in the observation conditions among epochs. Using measurements from 10 repeat leveling surveys conducted twice yearly along a profile spanning ~40 km across the Perth Basin, Western Australia, we describe the observation, processing, and analysis methods required to mitigate these potential error sources. We also demonstrate how these issues may lead to misinterpretation of the VLM derived from repeat leveling and may contribute to discrepancies between geologically inferred rates of ground motion or those derived from other geodetic measurement techniques. Finally, we employ historical (~40‐year‐old) leveling data in order to highlight the errors that can arise when attempting to extrapolate VLM derived from a geodetic time series, particularly in cases where the long‐term motion may be nonlinear

The effect of EGM2008-based normal, normal-orthometric and Helmert orthometric height systems on the Australian levelling network

This paper investigates the normal-orthometric correction used in the definition of the Australian Height Datum, and also computes and evaluates normal and Helmert orthometric corrections for the Australian National Levelling Network (ANLN). Testing these corrections in Australia is important to establish which height system is most appropriate for any new Australian vertical datum. An approximate approach to assigning gravity values to ANLN benchmarks (BMs) is used, where the EGM2008-modelled gravity field is used to "re-construct" observed gravity at the BMs. Network loop closures (for first- and second-order levelling) indicate reduced misclosures for all height corrections considered, particularly in the mountainous regions of south eastern Australia. Differences between Helmert orthometric and normal-orthometric heights reach 44 cm in the Australian Alps, and differences between Helmert orthometric and normal heights are about 26 cm in the same region. Normal orthometric heights differ from normal heights by up to 18 cm in mountainous regions >2,000 m. This indicates that the quasigeoid is not compatible with normal-orthometric heights in Australia