Abstract. Mathematical formulae in academic texts significantly contribute to the overall semantic content of such texts, especially in the fields of Science, Technology, Engineering and Mathematics. Knowing the definitions of the identifiers in mathematical formulae is essential to understand the semantics of the formulae. Similar to the sense-making process of human readers, mathematical information retrieval systems can analyze the text that surrounds formulae to extract the definitions of identifiers occurring in the formulae. Several approaches for extracting the definitions of mathematical identifiers from documents have been proposed in recent years. So far, these approaches have been evaluated using different collections and gold standard datasets, which prevented comparative performance assessments. To facilitate future research on the task of identifier definition extraction, we make three contributions. First, we provide an automated evaluation framework, which uses the dataset and gold standard of the NTCIR-11 Math Retrieval Wikipedia task. Second, we compare existing identifier extraction approaches using the developed evaluation framework. Third, we present a new identifier extraction approach that uses machine learning to combine the wellperforming features of previous approaches. The new approach increases the precision of extracting identifier definitions from 17.85% to 48.60%, and increases the recall from 22.58% to 28.06%. The evaluation framework, the dataset and our source code are openly available at: https:// ident.formulasearchengine.com.

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The GPS receiver used for navigation on the Space Shuttle exhibits range rate noise which appears to result from scintillation of the satellite signals by irregularities in ionospheric plasma.The noise events cluster in geographic regions previously identified as susceptible to instability and disturbed ionospheric conditions. These mechanisms are reviewed in the context of the GPS observations . Range rate data continuously monitored during the free orbiting phase of several space shuttle missions reveals global scale distribution of ionospheric irregularities. Equatorial events cluster +/-20 degrees about the magnetic equator and polar events exhibit hemispheric asymmetry suggesting influence of off axis geomagnetic polar oval system. The diurnal, seasonal and geographic distribution is compared to previous work concerning equatorial spread F, Appleton anomaly and polar oval. The observations provide a succinct demonstration of the utility of space based ionospheric monitoring using GPS.e susceptability of GPS receivers to scintillation represents ' an unanticipated technical risk not factored into the selection of receivers for the United Stat€s spaee program.

In this paper we shall present the interaction mechanisms between the ISS and the surrounding plasma and give an overview of the PIM components. PIM predictions are compared with available data followed by a discussion of the variability of plasma parameters and the conductive area on the ISS.

Three years ago, a joint project was established by the Wright Aeronautical Division, Curtiss-Wright Corp., at the Jet and Flame Laboratory of New York University, to study the preparation and behavior of pyrophoric organometallic compounds. The aluminum alkyls have been one of the most interesting groups studied to date, from an ignition standpoint.Compounds capable of ready spontaneous ignition with air are of considerable potential importance for certain types of air-breathing power plants. Certain thermal theories of flame propagation suggest that the flame is propagated by virtue of continuous spontaneous ignition occurring on the leading edge of the flame front; in such a case, the time lapse before the flame appears-ignition delay-would be an important factor.Although aluminum alkyls have been known for some time, it has been only during the past few years that these compounds have been the subject of extensive research, largely because of the use of these compounds by Ziegler as catalysts for olefin polymerizations at low pressures. Preparation of Aluminum AlkylsA convenient method for the preparation of small quantities of these compounds involves a displacement reaction between aluminum metal and the alkyl compound of some less active metal (which can be readily prepared)-e.g., the reaction of dimethylmercury with an excess of aluminum yields trimethylaluminum and mercury (2) :Although this procedure gives good yields for lower members of the series, the decreased stability of the higher mercury alkyls limits its usefulness. The cost of such a method would be high.Recently Ziegler has developed several new methods of preparing aluminum alkyls using olefins as the starting reagents (10, 11).At about 100° C. lithium aluminum hydride reacts with ethylene and tetraethylaluminum lithium is formed:When this quaternary salt is treated with aluminum chloride, triethylaluminum is formed :This method has been used to prepare the corresponding η-propyl and n-hexyl com pounds.A more economical process for the large scale production of these compounds involves spraying aluminum into an atmosphere of hydrogen and an olefin (12): 172 METAL-ORGANIC COMPOUNDS Downloaded from pubs.acs.org by UNIV OF CALIFORNIA SAN DIEGO on 06/09/15. For personal use only.

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Numerous experimental investigations have been conducted over the past two years in an attempt to increase understanding of the arcing characteristics associated with anodized aluminum plates immersed in a plasma environment. The International Space Station (ISS), as well as the Extra-vehicular Mobility Unit (EMU) worn by ISS crew-members, utilize anodized aluminum components in many key areas. Photo-voltaic array driven charging of these components can cause arcs to be initiated when these components are exposed to the Low Earth Orbit (LEO) plasma environment. Arc generation can lead not only to damage of the anodized surface and generation of electromagnetic interference, but also to an electrical shock hazard for an astronaut in an EMU. Descriptions of multiple arc tests that apply to the ISS and EMU will be provided. Results of each test will be shown in a compiled form, due to the large number of arc events generated during a typical test campaign. Where appropriate, current and voltage waveforms associated with a single arc event will be shown in detail.

A model is presented that simulates the behavior of superthermal ions previously reported in the dayside ionosphere of Venus. The model considers effects of E×B and gradient drifts, charge exchange and collisions with the ambient neutral atmosphere and the possible effects of a wave‐particle (anomalous) scattering process. Results indicate that scattering processes are required if superthermal ions are the explanation for the observed “missing pressure” component in the day‐side Venus ionosphere. The scattering scale length required to match the “missing pressure” distribution is similar to the scale length previously predicted for growth of a lower hybrid beam instability.