The manual control of vehicles undergoing slow transitions in dynamic characteristics

The manual control was studied of a vehicle with slowly time-varying dynamics to develop analytic and computer techniques necessary for the study of time-varying systems. The human operator is considered as he controls a time-varying plant in which the changes are neither abrupt nor so slow that the time variations are unimportant. An experiment in which pilots controlled the longitudinal mode of a simulated time-varying aircraft is described. The vehicle changed from a pure double integrator to a damped second order system, either instantaneously or smoothly over time intervals of 30, 75, or 120 seconds. The regulator task consisted of trying to null the error term resulting from injected random disturbances with bandwidths of 0.8, 1.4, and 2.0 radians per second. Each of the twelve experimental conditons was replicated ten times. It is shown that the pilot's performance in the time-varying task is essentially equivalent to his performance in stationary tasks which correspond to various points in the transition. A rudimentary model for the pilot-vehicle-regulator is presented

The Enigmatic Radio Afterglow of GRB 991216

We present wide-band radio observations spanning from 1.4 GHz to 350 GHz of the afterglow of GRB 991216, taken from 1 to 80 days after the burst. The optical and X-ray afterglow of this burst were fairly typical and are explained by a jet fireball. In contrast, the radio light curve is unusual in two respects: (a) the radio light curve does not show the usual rise to maximum flux on timescales of weeks and instead appears to be declining already on day 1 and (b) the power law indices show significant steepening from the radio through the X-ray bands. We show that the standard fireball model, in which the afterglow is from a forward shock, is unable to account for (b) and we conclude that the bulk of the radio emission must arise from a different source. We consider two models, neither of which can be ruled out with the existing data. In the first (conventional) model, the early radio emission is attributed to emission from the reverse shock as in the case of GRB 990123. We predict that the prompt optical emission would have been as bright (or brighter) than 8th magnitude. In the second (exotic) model, the radio emission originates from the forward shock of an isotropically energetic fireball (10^54 erg) expanding into a tenuous medium (10^-4 cm^-3). The resulting fireball would remain relativistic for months and is potentially resolvable with VLBI techniques. Finally, we note that the near-IR bump of the afterglow is similar to that seen in GRB 971214 and no fireball model can explain this bump.Comment: ApJ, submitte

First observation of CO at 345 GHz in the atmosphere of Saturn with the JCMT. New constaints on its origin

International audienceWe have performed the first observation of the CO(3-2) spectral line in the atmosphere of Saturn with the James Clerk Maxwell Telescope. We have used a transport model of the atmosphere of Saturn to constrain the origin of the observed CO. The CO line is best-fit when the CO is located at pressures less than (15± 2) mbar with a mixing ratio of (2.5±0.6)×10-8 implying an external origin. By modelling the transport in Saturn's atmosphere, we find that a cometary impact origin with an impact 200-350 years ago is more likely than continuous deposition by interplanetary dust particles (IDP) or local sources (rings/satellites). This result would confirm that comet impacts are relatively frequent and efficient providers of CO to the atmospheres of the outer planets. However, a diffuse and/or local source cannot be rejected, because we did not account for photochemistry of oxygen compounds. Finally, we have derived an upper limit of 1×10-9 on the tropospheric CO mixing ratio

HI ``Tails'' from Cometary Globules in IC1396

IC 1396 is a relatively nearby (750 pc), large (>2 deg), HII region ionized by a single O6.5V star and containing bright-rimmed cometary globules. We have made the first arcmin resolution images of atomic hydrogen toward IC 1396, and have found remarkable ``tail''-like structures associated with some of the globules and extending up to 6.5 pc radially away from the central ionizing star. These HI ``tails'' may be material which has been ablated from the globule through ionization and/or photodissociation and then accelerated away from the globule by the stellar wind, but which has since drifted into the ``shadow'' of the globules. This report presents the first results of the Galactic Plane Survey Project recently begun by the Dominion Radio Astrophysical Observatory.Comment: 11 pages, 5 postscript figures, uses aaspp4.sty macros, submitted in uuencoded gzipped tar format, accepted for publication in Astrophysical Journal Letters, colour figures available at http://www.drao.nrc.ca/~schieven/news_sep95/ic1396.htm

Vortex Dynamics in Selfdual Maxwell-Higgs Systems with Uniform Background Electric Charge Density

We introduce selfdual Maxwell-Higgs systems with uniform background electric charge density and show that the selfdual equations satisfied by topological vortices can be reduced to the original Bogomol'nyi equations without any background. These vortices are shown to carry no spin but to feel the Magnus force due to the shielding charge carried by the Higgs field. We also study the dynamics of slowly moving vortices and show that the spin-statistics theorem holds to our vortices.Comment: 24 pages + 2 figures ( not included), Cu-TP-611, IASSNS-HEP-93/33, NSF-ITP-93-13

Etiology of pure tricuspid regurgitation based on anular circumference and leaflet area: Analysis of 45 necropsy patients with clinical and morphologic evidence of pure tricuspid regurgitation

Despite recent renewed interest in the detection of tricuspid valve regurgitation by echocardiographic and Doppler techniques, little morphologic information is available on dysfunctioning tricuspid valves. This report describes 45 necropsy patients with clinical and morphologic evidence of pure(no element of stenosis) tricuspid regurgitation and provides morphometric observations (anular circumference, leaflet area) of the tricuspid valve useful in determining the etiology of pure tricuspid regurgitation. Of 45 patients, 24 (53%) had pure tricuspid regurgitation resulting from an anatomically abnormal valve (prolap9e in 7, papillary muscle dysfunction in 6, rheumatic disease in 5, Ebstein's anomaly in 3, infective endocarditis in 2, carcinoid tumor in 1), and 21(47%) had an anatomically normal valve with systolic pulmonary artery hypertension (cor pulmonary in 12, mitral stenosis in 9). Anular circumference was dilated (> 12 cm) in patients with various causes of pulmonary hypertension, floppy valve and Ebstein's tricuspid anomaly. Leaflet area was increased in floppy valve and Ebstein's anomaly.Of the 45 patients, 24 had pulmonary systolic artery pressure measurements available for correlation with tricuspid valve morphology. Pulmonary artery pressures accurately predicted morphologically normal from abnormal valves in 16 patients (89 %). Morphologic overlap occurred in six patients with pulmonary pressures of 41 to 54 mm Hg. Of these six, the additional knowledge of normal or dilated anular circumference correctly separated valves with normal and abnormal leaflets

Compositional Diversity of the Vestan Regolith Derived from Howardite Compositions and Dawn VIR Spectra

Howardite, eucrite and diogenite meteorites likely come from asteroid 4 Vesta [1]. Howardites - physical mixtures of eucrites and diogenites - are of two subtypes: regolithic howardites were gardened in the true regolith; fragmental howardites are simple polymict breccias [2]. The Dawn spacecraft imaged the howarditic surface of Vesta with the visible and infrared mapping spectrometer (VIR) resulting in qualitative maps of the distributions of distinct diogenite-rich and eucrite-rich terranes [3, 4]. We are developing a robust basis for quantitative mapping of the distribution of lithologic types using spectra acquired on splits of well-characterized howardites [5, 6]. Spectra were measured on sample powders sieved to <75 m in the laboratories of the Istituto di Astrofisica e Planetologia Spaziali and Brown University. Data reduction was done using the methods developed to process Dawn VIR spectra [4]. The band parameters for the ~1 and ~2 m pyroxene absorption features (hereafter BI and BII) can be directly compared to Dawn VIR results. Regolithic howardites have shallower BI and BII absorptions compared to fragmental howardites with similar compositions. However, there are statistically significant correlations between Al or Ca contents and BI or BII center wavelengths regardless of howardite subtype. Diogenites are poor in Al and Ca while eucrites are rich in these elements. The laboratory spectra can thus be directly correlated with the percentage of eucrite material contained in the howardites. We are using these correlations to quantitatively map Al and Ca distributions, and thus the percentage of eucritic material, in the current regolith of Vesta

The Broadband Afterglow of GRB980329

We present radio observations of the afterglow of the bright gamma-ray burst GRB980329 made between one month and several years after the burst, a re-analysis of previously published submillimeter data, and late-time optical and near-infrared (NIR) observations of the host galaxy. From the absence of a spectral break in the optical/NIR colors of the host galaxy, we exclude the earlier suggestion that GRB980329 lies at a redshift of z >~5. We combine our data with the numerous multi-wavelength observations of the early afterglow, fit a comprehensive afterglow model to the entire broadband dataset, and derive fundamental physical parameters of the blast-wave and its host environment. Models for which the ejecta expand isotropically require both a high circumburst density and extreme radiative losses from the shock. No low density model (n << 10 cm^{-3}) fits the data. A burst with a total energy of ~ 10^{51} erg, with the ejecta narrowly collimated to an opening angle of a few degrees, driven into a surrounding medium with density ~ 20 cm^{-3}, provides a satisfactory fit to the lightcurves over a range of redshifts.Comment: 27 pages, incl. 6 figures, minor revisions (e.g. added/updated references) Accepted by Ap

A multi-layer extension of the stochastic heat equation

Motivated by recent developments on solvable directed polymer models, we define a 'multi-layer' extension of the stochastic heat equation involving non-intersecting Brownian motions.Comment: v4: substantially extended and revised versio

Curie: Constraining Solar System Bombardment Using In Situ Radiometric Dating

The Curie mission would constrain the existence of the putative cataclysm by determining the age of samples directly sourced from the impact melt sheet of a major pre-Imbrium lunar basin. The measurements would also enable further understanding of lunar evolution by characterizing new lunar lithologies far from the Apollo and Luna landing sites, including the very low-Ti basalts in Mare Crisium and potential olivine rich lithologies in the margins of both Mare Nectaris and Mars Crisium. Equipped with a mass spectrometer and a LIBS, Curie would also be well-placed to survey volatile components of the lunar regolith, including surface-bound hydrogen