bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling and simulation of planar flexible link manipulators with rigid
tip connections to revolute joints
Authors: Megahed S. M. , Hamza K. T.
Published: May 2004

This paper presents the basis of a mathematical model for simulation of planar flexible-link manipulators, taking into consideration the effect of higher stiffness zones at the link tips. The proposed formulation is a variation of the finite segment multi-body dynamics approach. The formulation employs a consistent mass matrix in order to provide better approximation than the traditional lumped masses often encountered in the finite segment approach. The formulation is implemented into a computational code and tested through three examples; cantilever beam, rotating beam and three-link manipulator.
In these examples, the length of the rigid tips at both sides of each link ranges from 0% to 6.25% of the whole link length. The zones of higher stiffness
at the link tips are treated as short rigid zones. The effect of the rigid zones is averaged along with some portions of the flexible links, thereby allowing further simplification
of the dynamic equations of motion. The simulation results demonstrate the effectiveness of the proposed modeling technique and show the importance of not ignoring the effect of the rigid tips.
Dynamic control of multi-arm co-operating manipulator systems
Authors: Swain Anjan Kumar , Morris Alan S.
Published: May 2004

This paper deseribes the control of multi-arm co-operating manipulator systems handling a common object. Inverse dynamics controllers with motive force compensation are developed for the co-operating fixed-base, free-floating, and free-flying space manipulator systems. Further, the relative performances of all the three configurations are compared on two tracking problems.
The dual-frequency sonar system of the mobile robot RAM-2
Authors: Martinez M. A. , Martinez J. L.
Published: May 2004

This paper deals with the design and development of a new perception system for controlling a set of ultrasonic transducers working at two different frequencies generated by a digital signal processor (DSP). Data gathering speed is increased by the simultaneous firing of sonars without crosstalk problems. The software and hardware implementation are presented as well as the results from the calibration process and the integration on board the mobile robot RAM-2. Finally, a demonstration of the use of the proposed equipment to wall-following via a fuzzy controller is described.
Reports & Surveys
Authors: Rudall B. H.
Published: May 2004

It is reported by the British Aerospace (BAE Systems) that their researchers have developed a revolutionary airborne computer system that, they claim, can land aircraft safely without the need of human air traffic controllers. The new system will allow a pilot to determine an aircraft's landing by pressing a button in the cockpit to initiate the computer system.
TQL: a query language for semistructured data based on the ambient logic
Authors: CARDELLI LUCA , GHELLI GIORGIO
Published: May 2004

The ambient logic is a modal logic that was proposed for the description of the structural and computational properties of distributed and mobile computation. The structural part of the ambient logic is, essentially, a logic of labelled trees, hence it turns out to be a good foundation for query languages for semistructured data, much in the same way as first-order logic is a fitting foundation for relational query languages. We define here a query language for semistructured data that is based on the ambient logic, and we outline an execution model for this language. The language turns out to be quite expressive. Its strong foundations and the equivalences that hold in the ambient logic are helpful in the definition of the language semantics and execution model.
Reo: a channel-based coordination model for component composition
Authors: ARBAB FARHAD
Published: May 2004

In this paper, we present Reo, which forms a paradigm for composition of software components based on the notion of mobile channels. Reo is a channel-based exogenous coordination model in which complex coordinators, called connectors, are compositionally built out of simpler ones. The simplest connectors in Reo are a set of channels with well-defined behaviour supplied by users. Reo can be used as a language for coordination of concurrent processes, or as a ‘glue language’ for compositional construction of connectors that orchestrate component instances in a component-based system. The emphasis in Reo is just on connectors and their composition, and not on the entities that connect to, communicate and cooperate through these connectors. Each connector in Reo imposes a specific coordination pattern on the entities (for example, components) that perform I/O operations through that connector, without the knowledge of those entities. Channel composition in Reo is a very powerful mechanism for construction of connectors. We demonstrate the expressive power of connector composition in Reo through a number of examples. We show that exogenous coordination patterns that can be expressed as (meta-level) regular expressions over I/O operations can be composed in Reo out of a small set of only five primitive channel types.
Introduction to special issue on concurrency and coordination: Selected work from the International Workshop ConCoord
Authors: SASSONE VLADIMIRO
Published: May 2004

This Special Issue of Mathematical Structures in Computer Science contains selected papers from ConCoord, the International Workshop on Concurrency and Coordination held in Lipari, Italy, on July 6–8, 2001 and associated to the 13th Lipari School for Computer Science Researchers on the Foundations of Wide Area Network Programming.
Give syntax a chance
Authors: BICKERTON DEREK
Published: May 2004

As an occasional visitor to the land of SLA, I found myself somewhat mystified by the approach of Truscott and Sharwood Smith (henceforth TSS). Unless I have totally misunderstood them, they are arguing against the separate existence of both a Language Acquisition Device (LAD) and a Universal Grammar (UG). But who ever thought they were two? Occasionally linguists may write about one rather than the other, but I have always assumed them to be the same thing appearing in different guises (like Christ and the Holy Ghost in Christian theology). If you have UG, why would you need LAD? Processing with the aid of UG seems the only way to go – to the extent that UG is available to SLA, an issue TSS does not directly address.
Between the input and the acquisition lies the shadow
Authors: HARRINGTON MICHAEL
Published: May 2004

Acquisition by Processing Theory (APT) is a unified account of language processing and learning that encompasses both L1 and L2 acquisition. Bold in aim and broad in scope, the proposal offers parsimony and comprehensiveness, both highly desirable in a theory of language acquisition. However, the sweep of the proposal is accompanied by an economy of description that makes it difficult to evaluate the validity of key learning claims, or even how literally they are to be interpreted. Two in particular deserve comment; the first concerns the learning mechanisms responsible for adding new L2 grammatical information, and the second the theoretical and empirical status of the activation concept used in the model.
Inflection, thematic roles and abstract Case
Authors: HERSCHENSOHN JULIA
Published: May 2004

This keynote article proposes a new model of language development based on processing, the sole mechanism of acquisition for the Acquisition by Processing Theory (APT). The language module – adapted from Jackendoff's distinction between integration (building complex structures) and interface (facilitating information transfer at the intersections of the sub-modules) – has phonological, syntactic and conceptual processors that interact with each other, working memory and lexical entries. On the one hand, the application of Jackendoff's model to language learning bridges a gap between syntactic theory and processing. On the other hand, its breadth sometimes brings together strange bedfellows, as, for example, minimalist syntax and APT's ‘clear affinities with connectionism’ (p. 17). In order to explore this hybrid model within a focused area, I will limit my comments to a discussion of features of I(nflection), Case and thematic (theta) roles, highlighting the question of how much syntactic theory APT needs. I will suggest that the model could profit from a greater exploitation of morphological input and its role in parameter setting.
Processing perspectives in SLA research and their compatibility
Authors: PIENEMANN MANFRED
Published: May 2004

Truscott and Sharwood-Smith's (henceforth T&SS's) paper offers an interesting set of hypotheses about one possible processing perspective in research on language acquisition. What is striking about this exposition of their model is that it ignores almost entirely the context of previous research on this issue. Embedding their exposition in its historical context would have in no way diminished the innovation entailed in their proposal. Instead it could have served as an instrument for ensuring conceptual parsimony, which in my view is flawed in this exposition.
Can the APT be a theory of Multiple Grammars and a minimal theory of parsing?
Authors: ROEPER TOM
Published: May 2004

This essay by Truscott and Sharwood-Smith is a valiant attempt with a laudable goal. It seeks to show how different perspectives and disciplines can capture what is happening in acquisition and notably in L2 acquisition. Nonetheless, I think that the results are much closer to an elaborated grammatical theory than an elaborated processing theory (thus it seems less important to me than to the authors to choose one label over the other). Their essential, sensible idea is that where different grammars provide independent analyses of constructions, both are computed (even where the lexical items belong to only one grammar). Therefore conflict is experienced which produces computational demands. However this is pure grammar – just a more sophisticated situation where, as I like to argue, the L2 person has Multiple Grammars (Roeper, 1999), creating more computational work as well. In this respect, the situation is no different from L1 acquisition, where the course of acquisition involves generation and maintenance of multiple grammars, some of which are shed and some retained in the Final State.
Growing syntactic structure and code-mixing in the weaker language: The Ivy Hypothesis
Authors: BERNARDINI PETRA , SCHLYTER SUZANNE
Published: May 2004

We present a hypothesis for a specific kind of code-mixing in young bilingual children, during the development of their two first languages, one of which is considerably weaker than the other. Our hypothesis, which we label the Ivy Hypothesis, is that, in the interaction meant to be in the weaker language, the child uses portions of higher syntactic structure lexically instantiated in the stronger language combined with lower portions in the weaker language. Code-mixing patterns were studied in five Swedish-French/Italian children aged 2–4. The parts of the code-mixed utterances reflected as much syntactic structure of each language as was used in monolingual utterances in the same recording of each child. This uneven development, which is due to different amounts of input of the two languages, can be accounted for by assuming that syntactic structure is acquired by building each language from the bottom up through lexical learning.
Voice onset time in bilingual German-Spanish children
Authors: KEHOE MARGARET M. , LLEÓ CONXITA , RAKOW MARTIN
Published: May 2004

This study examines the acquisition of the voicing contrast in German-Spanish bilingual children, on the basis of the acoustic measurement of Voice Onset Time (VOT). VOT in four bilingual children (aged 2;0–3;0) was measured and compared to VOT in three monolingual German children (aged 1;9–2;6), and to previous literature findings in Spanish. All measurements were based on word-initial stops extracted from naturalistic speech recordings. Results revealed that the bilingual children displayed three different patterns of VOT development: 1. Delay in the phonetic realization of voicing: two bilingual children did not acquire long lag stops in German during the testing period; 2. Transfer of voicing features: one child produced German voiced stops with lead voicing and Spanish voiceless stops with long lag voicing; and 3. No cross-language influence in the phonetic realization of voicing. The relevance of the findings for cross-linguistic interaction in bilingual phonetic/phonological development is discussed.
‘LEARNED STYLE’ IN TWO LESSING SETTINGS BY HAYDN
Authors: MIKUSI BALÁZS
Published: May 2004

This article offers close readings of the part-song Die Beredsamkeit and the solo song Lob der Faulheit. The former seems to illustrate ‘eloquence’ on at least four levels by imitating the intonation of elevated speech, by invoking the so-called ‘learned style’ of music through the introduction of various contrapuntal procedures, by quoting some of the most elementary figures of musical rhetoric (such as the Halbzirkel and the tirata) and by constructing the whole of the work as a well-delivered oration consisting of introduction, statement, corroboration, refutation and reaffirmation. Lob der Faulheit, on the other hand, in which the singer finally proves unable to deliver the praise promised in the title, appears to be an extraordinarily sensitive representation of musical failure. The unnatural and forced character of the song is unmistakable in its intervallic and metric structure, and rises in the melody are invariably followed by precipitous falls. Beyond this straightforward musical illustration, the descending fourth that opens and closes the vocal line may also be programmatic in its seeming reference to the well-known contemporary saying, ‘es wird auf ein Lami hinaus laufen’ (it will run out on a Lami), a forecast of a bad end.
ON BWV849/2
Authors: KERMAN JOSEPH
Published: May 2004

Among the special features of Bachanalia: The Essential Listener’s Guide to Bach’s Well-Tempered Clavier – a well-meaning effort, though badly misconceived, in my view – are author Eric Lewin Altschuler’s picks for ‘The Top Ten Fugues’, ‘The Top Ten Subjects’, ‘The Superstar Four’ and so on.
EDITORIAL
Authors: Eisen Cliff , Dean Sutcliffe W.
Published: May 2004

Why Eighteenth-Century Music? Thirty years ago, eighteenth-century music research represented a scholarly vanguard: the field was at the forefront in source studies, in performance practice, in investigating local music history and even in its willingness to think critically about the ways it had defined itself historically. These successes were in no small part responsible for a fundamental shift in musicological studies, even if this shift, fed by methodologies derived from literary and critical theory, was more apparent in writings on nineteenth-century music. Perhaps the field of eighteenth-century music studies was slow to reposition itself in this new intellectual environment. Or perhaps there was a feeling that this music ‘could look after itself’, that it is the common property of all musicologists. Whatever the reason, research into music of the eighteenth century was eclipsed in terms of the number of publications, conferences and doctoral dissertations.
Förderung sozialer Kompetenzen im Kindergarten: Evaluation eines sozialen Problemlösetrainings zur universellen Prävention dissozialer Verhaltensprobleme
Authors: Beelmann Andreas
Published: May 2004

Zusammenfassung. Es wird über die Ergebnisse einer kontrollierten Evaluationsstudie zu einem sozialen Problemlösetraining berichtet. 36 Kindergartenkinder im Alter von vier bis sechs Jahren wurden im Rahmen eines Gruppenkurses mit 15 Sitzungen trainiert und mit einer unbehandelten Kontrollgruppe (n = 33) vor und drei Monate nach dem Training im Hinblick auf Verhaltensratings der Eltern (Mutter und Vater) und Erzieherinnen verglichen. Anhand von Angaben der Trainerinnen zum aufgabenbezogenen Verhalten der Kinder während der Sitzungen konnte zunächst eine gelungene Implementation des Programms festgestellt werden. Des Weiteren wurden geringe, aber über die drei Informanten hinweg konsistent positive Effekte beim prosozialen Verhalten der Kinder erzielt. Weniger deutlich waren die Wirkungen auf die Verhaltensprobleme der Kinder, wenngleich sich nach mütterlichen Angaben signifikant geringere Werte im dissozialen Verhalten ergaben. Insgesamt bestätigten sich die Ergebnisse neuerer Meta-Analysen, nach denen soziale Trainingsprogramme bei Risikogruppen wirksamer sind. Vor dem Hintergrund der relativ geringen Programmintensität, den sehr guten Implementationswerten und den positiven Befunden beim prosozialen Verhalten kann jedoch das hier evaluierte Programm auch als universelle Präventionsstrategie empfohlen werden.
Leitlinien zur Diagnostik und Psychotherapie
Authors: Döpfner Manfred , Esser Günter
Published: May 2004

Zusammenfassung. In dem Beitrag wird eine Übersicht über den Stand der Entwicklung von Leitlinien zur Diagnostik und Psychotherapie psychischer Störungen im Kindes- und Jugendalter gegeben. Die Funktionen, die Leitlinien übernehmen können, werden diskutiert und die Gütekriterien, die an Leitlinien angelegt werden sollten, werden dargestellt. Damit soll der Startschuss für die Entwicklung von Leitlinien für psychologische und psychotherapeutische Disziplinen im deutschen Sprachraum gegeben werden.
Leitlinien zur Diagnostik und Psychotherapie von Angst- und Phobischen Störungen im Kindes- und Jugendalter: Ein evidenzbasierter Diskussionsvorschlag
Authors: Schneider Silvia , Döpfner Manfred
Published: May 2004

Zusammenfassung. Das Ziel der vorliegenden Arbeit ist, eine Diskussion über evidenzbasierte Leitlinien zur Diagnostik und Psychotherapie von Angst- und Phobischen Störungen des Kindes- und Jugendalters zu initiieren. In den letzten Jahren kam es zu wichtigen Fortschritten in der Klassifikation, klinischen Beschreibung und Epidemiologie dieser Störungsbilder, die zunächst einleitend vorgestellt werden. Eine reliable und valide Angstdiagnostik bei Kindern und Jugendlichen kann heute durch eine Kombination aus standardisierter Selbst- und Fremdbeurteilung gewährleistet werden. Die Zusammenschau der empirischen Befunde zur Psychotherapie macht deutlich, dass lediglich verschiedene Varianten standardisierter kognitiver Verhaltenstherapie mit und ohne Elterntraining als empirisch fundierte Psychotherapie bezeichnet werden können. Als möglicherweise wirksam zeigten sich nondirektive und psychodynamische Psychotherapien. Abschließend werden Rahmenbedingungen und Bausteine evidenzbasierter Psychotherapie der Angst- und Phobischen Störungen des Kindes- und Jugendalters dargestellt.
Infrared Auroral Emissions Driven by Resonant Electron Impact Excitation of NO Molecules
Authors: Campbell L. , Brunger M. J. , Petrovic Z. Lj. , Jelisavcic M. , Panajotovic R. , Buckman S. J.
Published: May 2004

Although only a minor constituent of the earth's upper atmosphere, nitric oxide (NO) plays a major role in infrared auroral emissions due to radiation from vibrationally excited (NO*) states. The main process leading to the production of these excited molecules was thought to be chemiluminescence, whereby excited nitrogen atoms interact with oxygen molecules to form vibrationally excited nitric oxide (NO*) and atomic oxygen. Here we show evidence that a different production mechanism for NO*, due to low energy electron impact excitation of NO molecules, is responsible for more than 30% of the NO auroral emission near 5 μm.
Decomposition of daily geomagnetic variations by using method of natural orthogonal component
Authors: Xu Wen‐Yao , Kamide Y.
Published: May 2004

In this paper the method of natural orthogonal components (NOC) is utilized to decompose the daily magnetic variation, expressing the variation as a summation of the eigenmodes. The results show that the first and second NOC eigenmodes represent the solar quiet daily variation, Sq, and the disturbance‐daily variation, SD, respectively. The third and fourth eigenmodes may be related to specific currents in the magnetosphere. Remarkable day‐to‐day (DTD) variations exist in the amplitudes of the eigenmodes. The combination of the eigenmodes reproduces the complicated characteristics in the DTD variation of the daily magnetic variation. The decomposition of the daily magnetic variation presented in this paper is helpful for understanding the mechanism of the daily variation and its DTD variation. In addition, this decomposition method provides a ground‐based monitoring of the current systems in several important regions of the near‐Earth space.
Variations of low‐latitude geomagnetic fields and Dst index caused by magnetospheric substorms
Authors: Huang Chao‐Song , Foster J. C. , Goncharenko L. P. , Reeves G. D. , Chau J. L. , Yumoto K. , Kitamura K.
Published: May 2004

We present observations of periodic magnetospheric substorms and corresponding ionospheric disturbances. Since the periodic substorms occur during a stable interplanetary magnetic field, we are able to identify which ionospheric signatures are caused solely by substorms. We find that the low‐latitude ionospheric electric field perturbation after substorm onsets is eastward on the dayside and westward on the nightside and that the ground magnetometer northward (H) deviations at middle and low latitudes show an increase (a positive bay) after each substorm onset, no matter whether the magnetometers are located on the dayside or on the nightside. The nightside magnetometer H deviations are closely correlated with the inner magnetospheric magnetic field Bz component during the dipolarization process. The Dst index shows a significant increase of 20–40 nT after each substorm onset. We propose that the increase in the magnetometer H field and Dst index in response to substorm onsets is related to the field dipolarization. In this scenario the nightside magnetosphere earthward of the near‐Earth neutral line is highly compressed during the dipolarization, and the magnetic flux density within the inner magnetosphere is greatly enhanced, resulting in an increase in the ground magnetometer H component and in Dst.
Advective controls on primary production in the stratified western Irish Sea: An eddy‐resolving model study
Authors: Holt Jason T. , Proctor Roger , Blackford Jerry C. , Allen J. Icarus , Ashworth Mike
Published: May 2004

The Proudman Oceanographic Laboratory Coastal Ocean Modelling System and the European Regional Seas Ecosystem Model are applied at eddy‐resolving (∼1.8 km) scales to the stratified region of the western Irish Sea to investigate the effects of advective transport processes on the ecosystem. We find currents can transport nutrient‐rich water into the otherwise nutrient‐depleted surface layer of the stratified region, fueling intermittent production throughout the summer. The currents involved fall into three classes: large‐scale wind and density‐driven circulation, smaller‐scale eddies, and tidally mediated dispersive phenomena; all appear to play a role in this area. A model experiment without ecosystem advection does not show the intermittent surface production; summer growth only occurs at the thermocline. This experiment gives a significantly lower total annual production of 110 ± 26 g C m−2 yr−1, compared with 150 ± 40 g C m−2 yr−1 for the full model, which is in better agreement with observational estimates of 140 g C m−2 yr−1. We calculate summer averages of the terms in the scalar transport equation, which show that advective transport of all nutrients dominates over vertical diffusion above the thermocline in most of the stratified region. The transport of nitrate, ammonia, and phosphate is significantly greater than the transport of silicate. This can be attributed to the lack of silicate recycling in the pelagic ecosystem. Only limited and anecdotal observational evidence exists to support these model results, which points to a need for observations of high spatial and temporal resolution to investigate these processes in conjunction with further model studies.
Sea surface salinity interannual variability in the western tropical Atlantic: An ocean general circulation model study
Authors: Ferry Nicolas , Reverdin Gilles
Published: May 2004

Interannual variability of sea surface salinity in the northwest tropical Atlantic is investigated in several ocean general circulation model eddy‐permitting simulations using different air‐sea freshwater forcing. The only simulation able to reproduce some features of the observed variability from 1989 to 1993, in particular in the northwest South American region up to 20°N, east of the Lesser Antilles, is one with no relaxation to a salinity climatology. The model variability results from advection of freshwater originating from the large South American continental shelf river runoff and has a seasonal cycle associated with the displacement of the intertropical convergence zone: Anomalies develop from March to May and then propagate to a larger area within the next months with the horizontal currents (where both geostrophic and Ekman currents contribute). Later on, from July to October, the anomalies are damped through entrainment across the mixed layer base. The vertical diffusion through the mixed layer base does not weaken when anomalously fresh surface water is present (i.e., no barrier layer effect). According to the European Centre for Medium‐Range Weather Forecasts ERA15 reanalysis, air‐sea freshwater fluxes have little impact on the large (over 0.5 practical salinity scale) sea surface salinity (SSS) variability in this region. In the model, eddy variability plays little role in the interannual SSS variability, maybe because of inadequate resolution resulting in too weak and too few North Brazil Current eddies.
Brazil Malvinas Frontal System as seen from 9 years of advanced very high resolution radiometer data
Authors: Saraceno Martín , Provost Christine , Piola Alberto R. , Bava José , Gagliardini Antonio
Published: May 2004

Surface thermal fronts in the southwestern Atlantic (SWA) Ocean are examined using 9 years (1987–1995) of advanced very high resolution radiometer data. Fronts are detected considering a gradient based edge detector. Sea surface temperature gradients are calculated from 4 km resolution 5‐day composite images covering the western Argentine Basin south of 30°S. Variability in the position and intensity of the fronts from seasonal to interannual timescales is characterized in six regions including different parts of the Brazil Current Front (BCF) and the Subantarctic Front (SAF): Shelf Break‐Brazil (SB‐B), Brazil Malvinas Collision (BM‐C), Brazil Current‐Overshoot (BC‐O), Shelf Break‐Malvinas (SB‐M), Malvinas Return Flow (MRF), and Falkland Escarpment (FE). Fronts in the SB‐B, SB‐M, MRF, and FE regions are controlled by the bathymetry. In the BM‐C region the BCF and SAF appear to merge as a single front. This front does not present large seasonal north‐south excursions as previously described, though it pivots seasonally around a fixed point located approximately at 39.5°S, 53.5°W, changing its orientation from N‐S in winter to NW‐SE in summer. Consequently, on average, the front intersects the 1000 m isobath at 38°30′S in summer and north of 37°S in winter. In the BC‐O region the BCF has a U‐shape centered at 53°W. The intensity of the fronts in each region except in the FE region presents large seasonal variability. In the SB‐B, BM‐C, and BC‐O regions the frontal intensity is highest (>0.35°C/km) during austral winter, the annual components explain 83, 67, and 71% of the total variance, respectively. In the SB‐M and MRF regions the SAF is most intense (>0.25°C/km) in summer and fall; the annual component of the intensity fluctuations explains 29 and 38% of the total variance, respectively. In the FE region the annual component of frontal intensity explains only 17% of the variability. In the six regions, important interannual variability is found. The Zapiola Rise (centered at 45°S, 43°W) appears as a gradient‐free region. Closed planetary potential vorticity contours in this area suggest it is dynamically isolated.
Chemical and meteorological characteristics associated with rapid increases of O3 in Houston, Texas
Authors: Berkowitz Carl M. , Jobson Tom , Jiang Guangfeng , Spicer Chester W. , Doskey Paul V.
Published: May 2004

We report here on measurements made from the 62nd story of the Williams Tower on the west side of Houston, Texas between 15 August and 15 September 2000. The time series of trace gases differ from those at many other urban sites in having very rapidly increasing spikes of O3, HCHO, and PAN. Measurements show that the highest O3 levels in Houston are not always those measured at the surface, and the extreme values may occur aloft. Plumes with high O3 appear to be produced largely from local sources and to have the potential to form additional O3. The ozone production efficiency (7 molecules of O3 produced per molecule of NOx consumed) when ΔO3/Δt ≥ 20 ppb per 15 min was found to be smaller than estimates made from observations directly downwind of the Ship Channel petrochemical plants (e.g., ∼12). Back trajectories show that simple straight line flow was associated with mean O3 levels of 56 ppb, in contrast to flow patterns associated with a decrease in wind speed or flow reversal, which were associated with mean values of 63 ppb and extremes in excess of 125ppb. VOC samples taken during periods when ΔO3/Δt ≥ 20 ppb per 15 min were elevated and in particular light olefins were more than a factor of 7 greater than the corresponding samples collected on other occasions. No significant increase in isoprene at the Williams Tower was associated with these episodes. When air passed over stack emissions in eastern Houston, rich in VOCs, a Lagrangian model simulated O3 production rates of ∼50 ppb hr−1.
Modeling spatial patterns of saturated areas: An evaluation of different terrain indices
Authors: Güntner Andreas , Seibert Jan , Uhlenbrook Stefan
Published: May 2004

A key component to understanding and predicting water fluxes and water quality in river basins is the spatial distribution of water‐saturated areas. There is limited knowledge on spatial patterns of saturated areas, their relation to landscape characteristics and processes, and the ability of hydrological models to represent the observed spatial patterns, particularly at the large scales most relevant for water resources management. In this study, saturated areas were mapped in two mesoscale (18 and 40 km2), humid temperate basins. Geobotanical and pedological criteria were used to achieve a consistent time‐integrated delineation of saturated areas. Using commonly available spatial data on landscape characteristics, various terrain indices were evaluated for their ability to predict the observed patterns. Quantitative performance criteria describing the agreement of modeled and observed spatial patterns included cell‐by‐cell and cell‐neighborhood approaches. Upslope contributing area was the most important single factor explaining the observed pattern. An improved pattern was obtained for the topographic wetness index (TOPMODEL index). However, the performance was markedly sensitive to the algorithms used for calculation of upslope contributing area and slope gradient. Other factors such as soil or climate were of less value for improving the predictions. The optimum spatial agreement of observed and modeled saturated areas was about 50% for a combined soil‐climate‐topographic index. Geological features (bedrock fractures) partly explained the residual pattern. Using an independent test catchment, it was shown that the index approach can be transferred to basins with similar physiographic characteristics for estimating the general pattern of saturated areas.
MLT cooling during stratospheric warming events
Authors: Cho Y.‐M. , Shepherd G. G. , Won Y.‐I. , Sargoytchev S. , Brown S. , Solheim B.
Published: May 2004

MLT (Mesosphere and Lower Thermosphere) airglow emission rates and temperatures have been monitored with a Spectral Airglow Temperature Imager (SATI), operated at Resolute Bay (74.68°N, 94.90°W). The 2001/2002 winter season data exhibits a major cooling event for both the O2 and OH emissions near the end of December, a mild event in mid February and a final cooling in early March. These temperature perturbations are compared with the UKMO stratospheric assimilated data for the Resolute Bay location and for zonally averaged data at 75°N, at two pressure levels, 3.16 hPa and 0.316 hPa. For the major event the 3.16 hPa zonally averaged temperature coincides in time with the MLT cooling. The O2 temperatures increase slightly, prior to the stratospheric warming, but after onset both emissions exhibit cooling; this is consistent with the TIME‐GCM/CCM3 predictions for the meridional circulation at high latitudes.
Simulations of magnetic fields generated by the Antarctic Circumpolar Current at satellite altitude: Can geomagnetic measurements be used to monitor the flow?
Authors: Vivier Frédéric , Maier‐Reimer Ernst , Tyler Robert H.
Published: May 2004

With a volume transport of ∼134 × 106 m3/s at the Drake Passage, the Antarctic Circumpolar Current (ACC) is the strongest ocean current. In the interest of estimating the secondary magnetic fields generated by the magnetohydrodynamic interaction of this flow with Earth's main field, we compare numerical results for the magnetic fields obtained using flow from three different ocean general circulation models. These simulations all expect detectable ocean signals in the magnetic records at ground and satellite altitude (400 km). The variability of this contribution is highly correlated with the ACC transport, a very important variable for climate studies. Observed magnetic fields could then be used, in principle, to derive an index of variability of the ACC. However given its small amplitude compared with other magnetic contributions, extracting the ocean's signal from observations remains a challenge at this time.
Origins of positive cloud‐to‐ground lightning flashes in the stratiform region of a mesoscale convective system
Authors: Lang Timothy J. , Rutledge Steven A. , Wiens Kyle C.
Published: May 2004

The origins of positive cloud‐to‐ground (+CG) lightning in the stratiform region of a leading‐line, trailing‐stratiform mesoscale convective system (MCS) are investigated. Platforms include radars, NLDN data, and a VHF 3‐D lightning mapping system. This study examines a small asymmetric MCS that occurred near the Colorado‐Kansas border in June 2000. In this storm 39 of the 269 +CGs produced over a nearly 5‐hour period came to ground within the stratiform region. Of these, 30 initiated in the leading convective line and propagated rearward before coming to ground. Nine other +CGs originated within the stratiform region. Stratiform +CGs were observed to propagate mostly horizontally through vertically thin layers. The observations suggest that stratiform charge is a conduit for +CG lightning from the convective line, and can initiate +CGs as well.
Effect of planetary rotation on distal tektite deposition on Mars
Authors: Wrobel Kelly E. , Schultz Peter H.
Published: May 2004

The rapid rotation of Mars creates a significant pseudoforce, known as the Coriolis force, that greatly modifies the flight paths and subsequent deposition of distal ejecta (ejecta with launch velocities of 3 km/s and greater). An accurate depiction of the effects of the Coriolis force requires the integration of the Coriolis terms directly into a series of spherical ballistic equations applied within a rotating reference frame. The resulting landing positions of radially ejected particles tend to form distinct wrapping patterns that are focused to specific areas in the hemisphere opposite from the source crater: around the pole for high‐latitude craters (45° in latitude and above) and in an equatorial band for low‐latitude craters (below 45° latitude). Consequently, particular locations on the surface receive deposits in stages: direct delivery of ejecta followed by deposits of higher‐velocity ejecta. This staged deposition leads to regions of enhanced ejecta accumulations where meters of material collect (millimeters would be predicted in nonrotational radial decay models). Thus high‐latitude craters could supply a considerable amount of distal products (tektites and melts) to polar locations, perhaps contributing to the dark circumpolar materials.
Flow resistance due to lateral momentum transfer in partially vegetated rivers
Authors: Helmiö Terhi
Published: May 2004

In the study of natural rivers, accurate conveyance estimation is challenging because of complex cross‐sectional geometry and variable flow resistance. The aim of this study was to investigate the additional friction factor due to lateral momentum transfer at the interface of vegetated and nonvegetated channel parts in two rivers: (1) the Rhine River, a large dredged river with partially vegetated floodplains, and (2) the River Päntäneenjoki, a small boreal lowland river with dense bank vegetation and an undulating longitudinal profile. The friction factors of the interfaces were computed backward from the topographical field data, while the measured depth‐flow regime data were computed with the help of an unsteady one‐dimensional (1‐D) flow model. Laboratory experiments were carried out to verify the effects of longitudinal spacing of plants on the friction factors. In the researched rivers the values of the friction factors at the interface were higher than the ones presented in the literature.
Feral horse demography and population growth in the Kaimanawa Ranges, New Zealand
Authors: Linklater Wayne L. , Cameron Elissa Z. , Minot Ed O. , Stafford Kevin J.
Published: May 2004

Although feral horses are a common management problem in numerous countries, detailed and long-term demographic studies are rare. We measured the age and sex structure, and pregnancy, birth and death rates in a population of 413 feral horses in New Zealand during 1994–98 and used them to construct a model simulating population growth. Survivorship increased with age (0–1 years old = 86.8%, 1–2 = 92.3%, 2–4 = 92.4%, ≥�4 years old = females 94%, males 97% per annum). Birth sex ratio parity, a slight female bias in the adult sex ratio (92 males per 100 females) and higher adult male survivorship indicated lower average survivorship for young males than females that was not detectable in mortality statistics. Pregnancy and foaling rates for mares ≥�2 years old averaged 79 and 49%, respectively. Foaling rates increased as mares matured (2–3-year-old mares = 1.9%, 3–4 = 20.0%, 4–5 = 42.1%, ≥�5 = 61.5% per annum). Young mares had higher rates of foetal and neonatal mortality (95% of pregnancies failed and/or were lost as neonatal foals in 2–3-year-old mares, 70.6% in 3–4, 43.2% in 4–5, and 31% in mares ≥�5 years old). Population growth was 9.6% per annum (9.5–9.8, 95% CI) without human-induced mortalities (i.e. r = 0.092). Our model, standardised aerial counts, and historical estimates of annual reproduction suggest that the historical sequence of counts since 1979 has overestimated growth by ~50% probably because of improvements in count effort and technique.
Heme axial methionine fluxionality in
Hydrogenobacter thermophilus
cytochrome
c
552
Authors: Zhong Linghao , Wen Xin , Rabinowitz Terry M. , Russell Brandy S. , Karan Elizabeth F. , Bren Kara L.
Published: May 2004

The heme group in paramagnetic (
S
= 1/2) ferricytochromes
c
typically displays a markedly asymmetric distribution of unpaired electron spin density among the heme pyrrole β substituents. This asymmetry is determined by the orientations of the heme axial ligands, histidine and methionine. One exception to this is ferricytochrome
c
552
from
Hydrogenobacter thermophilus
, which has similar amounts of unpaired electron spin density at the β substituents on all four heme pyrroles. Here, determination of the orientation of the magnetic axes and analysis of NMR line shapes for
H. thermophilus
ferricytochrome
c
552
is performed. These data reveal that the unusual electronic structure for this protein is a result of fluxionality of the heme axial methionine. It is proposed that the ligand undergoes inversion at the pyramidal sulfur, and the rapid interconversion between two diastereomeric forms results in the unusual heme electronic structure. Thus a fluxional process for a metal-bound amino acid side chain has now been identified.
MuSK is required for anchoring acetylcholinesterase at the neuromuscular junction
Authors: Cartaud Annie , Strochlic Laure , Guerra Manuel , Blanchard Benoît , Lambergeon Monique , Krejci Eric , Cartaud Jean , Legay Claire
Published: May 2004

At the neuromuscular junction, acetylcholinesterase (AChE) is mainly present as asymmetric forms in which tetramers of catalytic subunits are associated to a specific collagen, collagen Q (ColQ). The accumulation of the enzyme in the synaptic basal lamina strictly relies on ColQ. This has been shown to be mediated by interaction between ColQ and perlecan, which itself binds dystroglycan. Here, using transfected mutants of ColQ in a ColQ-deficient muscle cell line or COS-7 cells, we report that ColQ clusterizes through a more complex mechanism. This process requires two heparin-binding sites contained in the collagen domain as well as the COOH terminus of ColQ. Cross-linking and immunoprecipitation experiments in Torpedo postsynaptic membranes together with transfection experiments with muscle-specific kinase (MuSK) constructs in MuSK-deficient myotubes or COS-7 cells provide the first evidence that ColQ binds MuSK. Together, our data suggest that a ternary complex containing ColQ, perlecan, and MuSK is required for AChE clustering and support the notion that MuSK dictates AChE synaptic localization at the neuromuscular junction.
Affixin interacts with α-actinin and mediates integrin signaling for reorganization of F-actin induced by initial cell–substrate interaction
Authors: Yamaji Satoshi , Suzuki Atsushi , Kanamori Heiwa , Mishima Wataru , Yoshimi Ryusuke , Takasaki Hirotaka , Takabayashi Maki , Fujimaki Katsumichi , Fujisawa Shin , Ohno Shigeo , Ishigatsubo Yoshiaki
Published: May 2004

The linking of integrin to cytoskeleton is a critical event for an effective cell migration. Previously, we have reported that a novel integrin-linked kinase (ILK)–binding protein, affixin, is closely involved in the linkage between integrin and cytoskeleton in combination with ILK. In the present work, we demonstrated that the second calponin homology domain of affixin directly interacts with α-actinin in an ILK kinase activity–dependent manner, suggesting that integrin–ILK signaling evoked by substrate adhesion induces affixin–α-actinin interaction. The overexpression of a peptide corresponding to the α-actinin–binding site of affixin as well as the knockdown of endogenous affixin by small interference RNA resulted in the blockade of cell spreading. Time-lapse observation revealed that in both experiments cells were round with small peripheral blebs and failed to develop lamellipodia, suggesting that the ILK–affixin complex serves as an integrin-anchoring site for α-actinin and thereby mediates integrin signaling to α-actinin, which has been shown to play a critical role in actin polymerization at focal adhesions.
NG2-expressing cells in the subventricular zone are type C–like cells and contribute to interneuron generation in the postnatal hippocampus
Authors: Aguirre Adan A. , Chittajallu Ramesh , Belachew Shibeshih , Gallo Vittorio
Published: May 2004

The subventricular zone (SVZ) is a source of neural progenitors throughout brain development. The identification and purification of these progenitors and the analysis of their lineage potential are fundamental issues for future brain repair therapies. We demonstrate that early postnatal NG2-expressing (NG2+) progenitor cells located in the SVZ self-renew in vitro and display phenotypic features of transit-amplifier type C–like multipotent cells. NG2+ cells in the SVZ are highly proliferative and express the epidermal growth factor receptor, the transcription factors Dlx, Mash1, and Olig2, and the Lewis X (LeX) antigen. We show that grafted early postnatal NG2+ cells generate hippocampal GABAergic interneurons that propagate action potentials and receive functional glutamatergic synaptic inputs. Our work identifies Dlx+/Mash1+/LeX+/NG2+/GFAP-negative cells of the SVZ as a new class of postnatal multipotent progenitor cells that may represent a specific cellular reservoir for renewal of postnatal and adult inhibitory interneurons in the hippocampus.
Coalignment of plasma membrane channels and protrusions (fibripositors) specifies the parallelism of tendon
Authors: Canty Elizabeth G. , Lu Yinhui , Meadows Roger S. , Shaw Michael K. , Holmes David F. , Kadler Karl E.
Published: May 2004

The functional properties of tendon require an extracellular matrix (ECM) rich in elongated collagen fibrils in parallel register. We sought to understand how embryonic fibroblasts elaborate this exquisite arrangement of fibrils. We show that procollagen processing and collagen fibrillogenesis are initiated in Golgi to plasma membrane carriers (GPCs). These carriers and their cargo of 28-nm-diam fibrils are targeted to previously unidentified plasma membrane (PM) protrusions (here designated “fibripositors”) that are parallel to the tendon axis and project into parallel channels between cells. The base of the fibripositor lumen (buried several microns within the cell) is a nucleation site of collagen fibrillogenesis. The tip of the fibripositor is the site of fibril deposition to the ECM. Fibripositors are absent at postnatal stages when fibrils increase in diameter by accretion of extracellular collagen, thereby maintaining parallelism of the tendon. Thus, we show that the parallelism of tendon is determined by the late secretory pathway and interaction of adjacent PMs to form extracellular channels.
A pathway of neuregulin-induced activation of cofilin-phosphatase Slingshot and cofilin in lamellipodia
Authors: Nagata-Ohashi Kyoko , Ohta Yusaku , Goto Kazumichi , Chiba Shuhei , Mori Reiko , Nishita Michiru , Ohashi Kazumasa , Kousaka Kazuyoshi , Iwamatsu Akihiro , Niwa Ryusuke , Uemura Tadashi , Mizuno Kensaku
Published: May 2004

Cofilin mediates lamellipodium extension and polarized cell migration by stimulating actin filament dynamics at the leading edge of migrating cells. Cofilin is inactivated by phosphorylation at Ser-3 and reactivated by cofilin-phosphatase Slingshot-1L (SSH1L). Little is known of signaling mechanisms of cofilin activation and how this activation is spatially regulated. Here, we show that cofilin-phosphatase activity of SSH1L increases ∼10-fold by association with actin filaments, which indicates that actin assembly at the leading edge per se triggers local activation of SSH1L and thereby stimulates cofilin-mediated actin turnover in lamellipodia. We also provide evidence that 14-3-3 proteins inhibit SSH1L activity, dependent on the phosphorylation of Ser-937 and Ser-978 of SSH1L. Stimulation of cells with neuregulin-1β induced Ser-978 dephosphorylation, translocation of SSH1L onto F-actin–rich lamellipodia, and cofilin dephosphorylation. These findings suggest that SSH1L is locally activated by translocation to and association with F-actin in lamellipodia in response to neuregulin-1β and 14-3-3 proteins negatively regulate SSH1L activity by sequestering it in the cytoplasm.