Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2000. / Cataloged from PDF version of thesis. / Includes bibliographical references (page 61). / The goal of this thesis is to propose a layout for the Wallace Astrophysical Observatory (WAO) 24-inch optical system that would utilize the full potential of the telescope and a new CCD imaging instrument. An optical analysis of the 6.5-meter Magellan I telescope was first performed to determine the optimal mounting location for the Raymond and Beverly Sackler Magellan Instant Camera (MAGIC). The analysis method used for the Magellan I model was then applied to the WAO 24-inch telescope. The results of the optical analysis of the WAO 24-inch model suggest that the optimal layout would follow a Cassegrain model with a focal ratio of between 15.3 and 16.6 to obtain image sizes of approximately 1.0 arcsecond or less over a field of up to 26.4 arcminutes in diameter. / by Janet P. Wu. / S.B.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, June 2009. / "May 2008." Cataloged from PDF version of thesis. / Includes bibliographical references (p. 53-54). / The goal of this thesis is to upgrade the scientific capabilities of the 24" Cassegrain reflector telescope at the George R. Wallace, Jr. Astrophysical Observatory (Wallace Observatory), part of Massachusetts Institute of Technology (MIT). The upgrade consists of evaluating, designing and constructing the Wallace Astrophysical Observatory Camera (WAOcam), optimized for 24" telescope. A full 3D model of the 24" telescope and dome was created to find the size restrictions for WAOcam. An optical model was also developed to maximize the field of view of the camera detector. WAOcam was designed using SolidWorks (3D modeling Software), the parts files from the designing process were also used to machine the instrument. The manufacturing of the WAOcam involved using the following: Computer Numerical Control (CNC) lathe, CNC mill, drill press, and a Waterjet (cutting machine). The manufacturing process also required learning of Omax (software for the Waterjet) and MasterCam 9.1 (software for the CNC lathe and CNC mill). The resulting product is WAOcam, which consists of three modules: 1) vacuum dewar (houses a CCD detector), 2) shutter (controls when light hits the camera detector), and 3) filter wheel (modifies the light before hitting the detector). The remaining work left on the WAOcam is the installation of two additional modules: 1) a four port instrument rotator and 2) a field rotator. This upgrade will allow for occultation observations, strip scanning surveys, and Kuiper Belt Object (KBOs) astrometry to be obtained using the 24" telescope. / by Folkers Eduardo Rojas. / S.B.

Thesis (PhD) -- McMaster University, 1996. / Includes bibliographical references (p.260-271). Also available via World Wide Web.

>Magister Scientiae - MSc / Most stable and extremely low abundance neutron deficient nuclei with Z ≥ 34 are referred to as p-nuclei. Nearly all p-nuclei with A < 110 are most likely produced in the rp-process while almost all A > 110 are thought to be produced by the photodisintegration of s- and r- process seed nuclei. However, for some nuclear systems, these processes are not sufficient to explain their observed solar abundance. Results from calculations in ¹⁸ᴼTa generally provoke debates since several processes are able, sometimes exclusively, to reproduce the observed ¹⁸ᴼTa abundance in the cosmos, making it a unique case study. Some of the main sources of errors in the predicted reaction rates of ¹⁸ᴼTa arise due to the absence of nuclear data or due to large uncertainties in the nuclear properties such as the nuclear level densities (NLD) and gamma-ray strength functions (γSF) of ¹⁸ᴼ,¹⁸¹Ta. The NLD and γSF are primary ingredients for astrophysical reaction rate calculations based on the Hauser-Feshbach approach. These parameters need to be well understood to improve our understanding of ¹⁸ᴼTa production in astrophysical environments. In this thesis, new experimental data for the low-energy part of the γSF and NLD in ¹⁸ᴼ,¹⁸¹Ta were extracted, using the so-called Oslo method. An experiment was performed and the NaI(Tl) gamma-ray array and silicon particle telescopes at the Oslo cyclotron laboratory were utilized to measure particle-γ coincidence events from which the NLDs and γSFs are extracted below the neutron separation energy threshold Sn. A beam of ³He was used to populate excited states in ¹⁸ᴼ,¹⁸¹Ta through the inelastic scattering (³He,³He’𝛾) and the transfer reaction (³He,𝜶𝛾). Based on results from this measurements, the Maxwellian averaged (n, 𝛾) cross sections for the 179Ta(n, γ) and ¹⁸ᴼTa(n, 𝛾) reactions, at the s-process thermal energy of kT = 30 keV (i.e. a temperature of T = 3.5 × 10⁸ K) and p-process thermal energy of 215 keV (T = 2.5 × 10⁹ K), respectively, were computed with the TALYS reaction code. These results can be used to place the nuclear physics aspects of the large network abundance calculations on a solid footing and have potential to improve our understanding of the astrophysical processes and sites involved in the production of nature’s rarest isotope ¹⁸ᴼTa. / National Research Foundation (NRF)

No description available.

Presented here are observations, analysis and interpretation of five Fanaroff-Riley class I radio galaxies. Total intensity and polarised emission was observed in each source at 6 and 3 cm at angular resolutions of 16 to 2 arc seconds. These sources have a flux density greater than 1 Jy at 843 MHz, are 10-30 arc minutes in total angular extent, have redshifts between 0.011 and 0.035, are south of declination –43 degrees and have bright prominent jet structure. Images of the distribution of total intensity, polarised intensity and magnetic field configuration are presented and analysed. Physical properties in the jets and lobe are estimated using a number of different techniques. The observations have revealed a wide variety of structures, which imply many types of physical processes occurring in these sources, and different types of environments the jets travel through. The surface brightness distribution of some FR I radio galaxies with some characteristics of FR II galaxies are found to be consistent with the jets traveling through flat pressure gradients possibly caused by the presence of a cocoon surrounding the source. Analytical model imply jets with Mach numbers of 1-5, and jet velocities of approximately 1,000-20,000 km s-1 along most of the jets but mildly relativistic velocities 0.1-0.5c are indicated by Doppler boosting models at the base of most of the jets / Doctor of Philosophy (PhD)

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

La première partie de ce travail se propose de définir une nouvelle version du formalisme d'étude des instabilités MHD de pression dans les structures d'accrétion-éjection magnétisées. Ces processus se produisent dans des plasmas confinés magnétiquement et sont très contraignants dans le domaine de la fusion thermonucléaire mais leur influence est peu étudiée dans des contextes astrophysiques. Dans un cadre d'approximation éliminant les ondes magnétosoniques rapides nous avons développé un système d'équations général permettant de s'intéresser à la fois aux modes instables d'interchange et aux modes de ballooning. L'application de ce système à un jet cylindrique en rotation solide nous montre que le cisaillement magnétique conduit à la déstabilisation des parties internes de ces structures. En outre, tout en clarifiant cette problématique dans une certaine mesure, nous retrouvons que ces flots sont génériquement instables vis-à-vis des modes d'interchange. Par ailleurs, nous avons étudié les méthodes numériques de résolution des équations aux dérivées partielles et plus particulièrement celles de la MHD. A partir d'un algorithme d'intégration élémentaire, nous avons pu évaluer les effets de géométrie, de conditions aux limites et de dissipation artificielle sur le calcul numérique, à travers une série de tests classiques. L'étude de la production de rayons cosmiques de très haute énergie dans les gamma-ray bursts constitue la dernière partie du travail effectué. Dans ces objets, des processus de Fermi accélèrent des particules jusqu'à des énergies de 10 21 eV, lors du croisement de perturbations d'Alfvén relativistes. Une interaction de type faisceau-plasma, entre une coquille de plasma en mouvement relativiste et les baryons qui la traversent, génère ces fronts alfvéniques et un mécanisme de rétrodiffusion redistribue l'énergie disponible entre des perturbations alfvéniques progressive, régressive et des perturbations magnétosoniques.

A côté des processus de réactions thermonucléaires à l'œuvre dans les étoiles, ainsi que dans l'Univers primordial, les études de réactions nucléaires non thermiques induites par des particules accélérées dans divers sites astrophysiques occupent une place grandissante dans les préoccupations de l'astrophysique nucléaire. Des populations d'ions et d'électrons accélérés sont vraisemblablement produites dans de nombreux objets astrophysiques : à la surface du soleil et de toutes les étoiles de type solaire, à la limite de l'héliosphère, dans les vents soufflés par les étoiles massives, dans les ondes de choc générées par les explosions stellaires, au voisinage d'étoiles à neutrons et de trous noirs accrétant de la matière, dans les amas de galaxies etc. Les divers phénomènes non thermiques induits par ces particules peuvent nous fournir des informations de grande valeur pour comprendre la physique de ces objets. Ils nous renseignent également sur certaines propriétés du milieu interstellaire de notre galaxie, ou encore sur les conditions dans lesquelles le système solaire s'est formé. Ce mémoire discute en particulier de l'accélération de particules dans les ondes de choc des explosions stellaires, des phénomènes nucléaires associés aux éruptions des étoiles, dont le soleil, de certains effets des rayons cosmiques non relativistes sur le milieu interstellaire, ainsi que de l'origine des radioactivités de courte période dans le système solaire primitif.

Blazars are a type of Active Galaxy that emit strong astrophysical jets. The association of a HE gamma-ray flare from the blazar TXS 0506+056 to the IceCube-170922A neutrino event in 2017, opened the possibility to a link between these two events. In this thesis, we will look at the HE gamma-ray behavior of TXS 0506+056 using data obtained from the Fermi-LAT by taking into account the other set of neutrino events associated with this source from 2014-2015. We will investigate whether both neutrino events present with comparable HE gamma-ray behavior by analyzing the lightcurves and the spectra for a quiet state, the 2014-2015 period, and the flare centered around the neutrino event from 2017. The results of the analysis performed in this thesis show no strong indication of a change in the gamma-ray behaviour in these potential neutrino detections.