Invariant manifolds and orbit control in the solar sail three-body problem

In this paper we consider issues regarding the control and orbit transfer of solar sails in the circular restricted Earth-Sun system. Fixed points for solar sails in this system have the linear dynamical properties of saddles crossed with centers; thus the fixed points are dynamically unstable and control is required. A natural mechanism of control presents itself: variations in the sail's orientation. We describe an optimal controller to control the sail onto fixed points and periodic orbits about fixed points. We find this controller to be very robust, and define sets of initial data using spherical coordinates to get a sense of the domain of controllability; we also perform a series of tests for control onto periodic orbits. We then present some mission strategies involving transfer form the Earth to fixed points and onto periodic orbits, and controlled heteroclinic transfers between fixed points on opposite sides of the Earth. Finally we present some novel methods to finding periodic orbits in circumstances where traditional methods break down, based on considerations of the Center Manifold theorem

7-Li(p,n) Nuclear Data Library for Incident Proton Energies to 150 MeV

We describe evaluation methods that make use of experimental data, and nuclear model calculations, to develop an ENDF-formatted data library for the reaction p + Li7 for incident protons with energies up to 150 MeV. The important 7-Li(p,n_0) and 7-Li(p,n_1) reactions are evaluated from the experimental data, with their angular distributions represented using Lengendre polynomial expansions. The decay of the remaining reaction flux is estimated from GNASH nuclear model calculations. The evaluated ENDF-data are described in detail, and illustrated in numerous figures. We also illustrate the use of these data in a representative application by a radiation transport simulation with the code MCNPX.Comment: 11 pages, 8 figures, LaTeX, submitted to Proc. 2000 ANS/ENS International Meeting, Nuclear Applications of Accelerator Technology (AccApp00), November 12-16, Washington, DC, US

The Infrared Continuum Sizes of Be Star Disks

We present an analysis of the near-infrared continuum emission from the circumstellar gas disks of Be stars using a radiative transfer code for a parametrized version of the viscous decretion disk model. This isothermal gas model creates predicted images that we use to estimate the HWHM emission radius along the major axis of the projected disk and the spatially integrated flux excess at wavelengths of 1.7, 2.1, 4.8, 9, and 18 ?m. We discuss in detail the effect of the disk base density, inclination angle, stellar effective temperature, and other physical parameters on the derived disk sizes and color excesses. We calculate color excess estimates relative to the stellar V -band flux for a sample of 130 Be stars using photometry from 2MASS and the AKARI infrared camera all-sky survey. The color excess relations from our models make a good match of the observed color excesses of Be stars. We also present our results on the projected size of the disk as a function of wavelength for the classical Be star ? Tauri, and we show that the model predictions are consistent with interferometric observations in the H, K', and 12 \mu m bands

Methods of Nature: Landscapes from the Gettysburg College Collection

Methods of Nature: Landscapes from the Gettysburg College Collection is the third annual exhibition curated by students enrolled in the Art History Methods course. The exhibition is an exciting academic endeavor and incredible opportunity for engaged learning, research, and curatorial experience. The five student curators are Molly Chason ’17, Leah Falk ’18, Shannon Gross ’17, Bailey Harper ’19 and Laura Waters ’19. The selection of artworks in this exhibition includes the depiction of landscape in the nineteenth- and twentieth-century French, American and East Asian cultural traditions in various art forms from traditional media of paintings and prints to utilitarian artifacts of porcelain and a paper folding fan. Landscape paintings in this exhibition are inspired by nature, specific locales and literature. Each object carries a distinctive characteristic, a mood, and an ambience. Collectively, they present a multifaceted view of the landscape in the heart and mind of the artists and intended viewers. [excerpt]https://cupola.gettysburg.edu/artcatalogs/1020/thumbnail.jp

Detecting Extrasolar Planets with Integral Field Spectroscopy

Observations of extrasolar planets using Integral Field Spectroscopy (IFS), if coupled with an extreme Adaptive Optics system and analyzed with a Simultaneous Differential Imaging technique (SDI), are a powerful tool to detect and characterize extrasolar planets directly; they enhance the signal of the planet and, at the same time, reduces the impact of stellar light and consequently important noise sources like speckles. In order to verify the efficiency of such a technique, we developed a simulation code able to test the capabilities of this IFS-SDI technique for different kinds of planets and telescopes, modelling the atmospheric and instrumental noise sources. The first results obtained by the simulations show that many significant extrasolar planet detections are indeed possible using the present 8m-class telescopes within a few hours of exposure time. The procedure adopted to simulate IFS observations is presented here in detail, explaining in particular how we obtain estimates of the speckle noise, Adaptive Optics corrections, specific instrumental features, and how we test the efficiency of the SDI technique to increase the signal-to-noise ratio of the planet detection. The most important results achieved by simulations of various objects, from 1 M_J to brown dwarfs of 30 M_J, for observations with an 8 meter telescope, are then presented and discussed.Comment: 60 pages, 37 figures, accepted in PASP, 4 Tables adde

Surface Modification of an Experimental Silicone Rubber Maxillofacial Material to Improve Wettability

OBJECTIVES: Good wettability of maxillofacial prosthetic materials is important so hat a lubricating layer is formed with supporting tissues thus reducing patient discomfort. The purpose of the study was to surface modify an experimental silicone rubber material in order to improve wettability. METHODS : Samples of experimental silicone rubber were surface modified by first argon plasma treatment followed by chemisorption of ethyleneoxy functional silanes. These were compared with the same silicone rubber which had ethyleneoxy functional surfactants incorporated into the polymer matrix. In all cases contact angles, tear strength and water uptake were measured. RESULTS: Surface modified materials had comparable contact angles to surfactant modified silicone rubber, all being significantly lower than the unmodified material. Surface modified materials however had a significantly higher tear strength and lower water uptake in comparison to surfactant modified materials. CONCLUSION: Argon plasma treatment followed by chemisorption of ethyleneoxy functional silanes proved an effective way of improving the wettability of an experimental silicone rubber maxillofacial prosthetic material without altering bulk properties

An Inner Gaseous Disk around the Herbig Be Star MWC 147

We present high-spectral-resolution, optical spectra of the Herbig Be star MWC 147, in which we spectrally resolve several emission lines, including the [O I] lines at 6300 and 6363\deg. Their highly symmetric, double-peaked line profiles indicate that the emission originates in a rotating circumstellar disk. We deconvolve the Doppler-broadened [O I] emission lines to obtain a measure of emission as a function of distance from the central star. The resulting radial surface brightness profiles are in agreement with a disk structure consisting of a flat, inner, gaseous disk and a flared, outer, dust disk. The transition between these components at 2 to 3 AU corresponds to the estimated dust sublimation radius. The width of the double-peaked Mg II line at 4481\deg suggests that the inner disk extends to at least 0.10 AU, close to the corotation radius.Comment: accepted for ApJ Letters (Oct. 2010

Development of a stratospheric and mesospheric microwave temperature sounder experiment

A passive microwave spectrometer system for measuring global atmospheric temperature profiles from 0-75 km altitude was developed and analyzed. The system utilizes 12 channels near the 5 mm wavelength oxygen absorption band and is designed to provide global coverage by scanning perpendicular to the orbital track of a polar orbiting satellite. A significant improvement in the accuracy of theoretical atmospheric microwave transmittance functions was achieved through the development of a first-order approximation to overlapping line theory for the oxygen molecule. This approximation is particularly important in the troposphere and lower stratosphere where pressure-broadening blends nearby lines. Ground-based and aircraft observations of several resonances of stratospheric oxygen generally support the theory. The 23, 25, 29, and 31 atmospheric oxygen lines were measured and the frequencies of several such oxygen lines were measured with improved precision. The polarization and Zeeman splitting of the atmospheric 27 line was also observed