J.D. Thomas

Geometry and velocity structure of HD 44179’s bipolar jet

In this paper we analyse a set of 33 optical spectra, which were acquired with the ARCES echelle spectrograph (R = 38,000) on the 3.5-m telescope at the Apache Point Observatory. We examine the H{\alpha} profile in each of these observations in order to determine the geometry and velocity structure of the previously discovered bipolar jet, which originates from the secondary star of HD 44179 located at the centre of the Red Rectangle nebula. Using a 3D geometric model we are able to determine the orbital coverage during which the jet occults the primary star. During the occultation, part of the H{\alpha} line profile appears in absorption. The velocity structure of the jet was determined by modelling the absorption line profile using the Sobolev approximation for each orbital phase during which we have observations. The results indicate the presence of a wide angle jet, likely responsible for observed biconical structure of the outer nebula. Furthermore, we were able to determine a likely velocity structure and rule out several others. We find that the jet is comprised of low-density, high-velocity, central region and a higher-density, lower-velocity, conical shell.

Production, Characterization, and Measurement of H(D) Beams on the ORNL Merged‐Beams Experiment

Total cross section measurements of electron capture processes are being studied for low‐energy, Aq++H(D) collisions using the Ion‐Atom Merged‐Beams apparatus at the Multicharged Ion Research Facility (MIRF) at Oak Ridge National Laboratory (ORNL). On this apparatus, a modified Faraday cup detector is used to measure the intensity of the neutral beam. The conversion of the measured electrical current to the true neutral particle beam current is necessary to accurately determine the true cross section values. Inherent in this conversion process is the number of secondary electrons (γ) emitted from the surface of the detector upon impact of an atom. The method employed to determine γ and its role in the absolute electron capture measurements at ORNL‐MIRF are presented. With a recent upgrade to the apparatus, the neutral beam H(D) production technique has been improved and is discussed in detail in this paper.

Isotope Effects in Low Energy Ion‐Atom Collisions

Isotope effects for charge transfer processes have recently received increased attention. The ion‐atom merged‐beams apparatus at Oak Ridge National Laboratory is used to measure charge transfer for low energy collisions of multi‐charged ions with H and D and is therefore well suited to investigate isotope effects. The apparatus has been relocated and upgraded to accept high velocity beams from the 250 kV High Voltage Platform at the Multi‐Charged Ion Research Facility. The intense higher velocity multi‐charged ion beams allow, for the first time, measurements with both H and D from keV/u down to meV/u collision energies in the center‐of‐mass frame. When charge transfer occurs at relatively large inter‐nuclear distances (via radial couplings) the ion‐induced dipole attraction can lead to trajectory effects, causing differences in the charge transfer cross sections for H and D. A strong isotope effect (nearly a factor of two) has been observed in the cross section for Si4++H(D) below 0.1 eV/u. However, litt...

Forelimbs of Tyrannosaurus Rex: A pathetic vestigial organ or an integral part of a fearsome predator?

In this paper, we examine a first-year torque and angular acceleration problem to address a possible use of the forelimbs of Tyrannosaurus rex. A 1/40th-scale model (see Fig. 1) is brought to the classroom to introduce the students to the quandary: given that the forelimbs of T. rex were too short to reach its mouth, what function did the forelimbs serve? This issue crosses several scientific disciplines including paleontology, ecology, and physics, making it a great starting point for thinking “outside the box.” Noted paleontologist Kenneth Carpenter has suggested that the forelimbs of T. rex were an integral part of its predatory behavior. Given the large teeth of T. rex, it is assumed that they killed with their teeth. Lipkin and Carpenter1 have suggested that the forelimbs were used to hold a struggling victim (which had not been dispatched with the first bite) while the final, lethal bite was applied. If that is the case, then the forelimbs must be capable of large angular accelerations α in order to...