The epidemiology of fluorine, iodine, manganese, copper, cobalt, zinc, molybdenum, in soils, plants, animals and man

Thesis (M.A.)--Boston University, 1949. This item was digitized by the Internet Archive

Use of the Wetzel Grid in the study of growth and development, mental status and social adjustment of behavior deviates

Thesis (Ed.D.)--Boston University

Use of the Wetzel Grid in the study of growth and development, mental status and social adjustment of behavior deviates

Thesis (Ed.D.)--Boston University

Galaxy Formation by Galactic Magnetic Fields

Galaxies exhibit a sequence of various morphological types, i.e., the Hubble sequence, and they are basically composed of spheroidal components (elliptical galaxies and bulges in spiral galaxies) and disks. It is known that spheroidal components are found only in relatively massive galaxies with M=10^{10-12} M_sun, and all stellar populations in them are very old, but there is no clear explanation for these facts. Here we present a speculative scenario for the origin of the Hubble sequence, in which magnetic fields ubiquitously seen in galaxies have played a crucial role. We first start from a strange observational fact that magnetic field strengths observed in spiral galaxies sharply concentrate at a few microgauss, for a wide range of galaxy luminosity and types. We then argue that this fact and the observed correlation between star formation activity and magnetic field strength in spiral galaxies suggest that spheroidal galaxies have formed by starbursts induced by strong magnetic fields. Then we show that this idea naturally leads to the formation of spheroidal systems only in massive and high-redshift objects in hierarchically clustering universe, giving a simple explanation for various observations.Comment: 7 pages including 2 figures. Accepted by ApJ Letter

Distances to the high galactic latitude molecular clouds G192-67 and MBM 23-24

We report on distance determinations for two high Galactic latitude cloud complexes, G192-67 and MBM 23-24. No distance determination exists in the literature for either cloud. Thirty-four early type stars were observed towards the two clouds, more than half of which have parallaxes measured by the Hipparcos satellite. For the remaining stars we have made spectroscopic distance estimates. The data consist of high resolution echelle spectra centered on the Na I D lines, and were obtained over six nights at the Coude Feed telescope at Kitt Peak National Observatory. Interstellar absorption lines were detected towards some of the stars, enabling estimates of the distances to the clouds of 109 +/- 14 pc for G192-67, and of 139 +/- 33 pc for MBM 23-24. We discuss the relationship of these clouds to other ISM features such as the Local Hot Bubble and the local cavity in neutral hydrogen.Comment: 15 pages, 6 embedded figures, to be published in the ApJ Vol. 516, No.

Coherent acoustic vibration of metal nanoshells

Using time-resolved pump-probe spectroscopy we have performed the first investigation of the vibrational modes of gold nanoshells. The fundamental isotropic mode launched by a femtosecond pump pulse manifests itself in a pronounced time-domain modulation of the differential transmission probed at the frequency of nanoshell surface plasmon resonance. The modulation amplitude is significantly stronger and the period is longer than in a gold nanoparticle of the same overall size, in agreement with theoretical calculations. This distinct acoustical signature of nanoshells provides a new and efficient method for identifying these versatile nanostructures and for studying their mechanical and structural properties.Comment: 5 pages, 3 figure

Diffusive propagation of UHECR and the propagation theorem

We present a detailed analytical study of the propagation of ultra high energy (UHE) particles in extragalactic magnetic fields. The crucial parameter which affects the diffuse spectrum is the separation between sources. In the case of a uniform distribution of sources with a separation between them much smaller than all characteristic propagation lengths, the diffuse spectrum of UHE particles has a {\em universal} form, independent of the mode of propagation. This statement has a status of theorem. The proof is obtained using the particle number conservation during propagation, and also using the kinetic equation for the propagation of UHE particles. This theorem can be also proved with the help of the diffusion equation. In particular, it is shown numerically, how the diffuse fluxes converge to this universal spectrum, when the separation between sources diminishes. We study also the analytic solution of the diffusion equation in weak and strong magnetic fields with energy losses taken into account. In the case of strong magnetic fields and for a separation between sources large enough, the GZK cutoff can practically disappear, as it has been found early in numerical simulations. In practice, however, the source luminosities required are too large for this possibility.Comment: 16 pages, 13 eps figures, discussion of the absence of the GZK cut-off in strong magnetic field added, a misprint in figure 6 corrected, version accepted for publication in Ap

A Magnetized Local Supercluster and the Origin of the Highest Energy Cosmic Rays

A sufficiently magnetized Local Supercluster can explain the spectrum and angular distribution of ultra-high energy cosmic rays. We show that the spectrum of extragalactic cosmic rays with energies below $\sim 10^{20}$ eV may be due to the diffusive propagation in the Local Supercluster with fields of $\sim 10^{-8} - 10^{-7}$ Gauss. Above $\sim 10^{20}$ eV, cosmic rays propagate in an almost rectilinear way which is evidenced by the change in shape of the spectrum at the highest energies. The fit to the spectrum requires that at least one source be located relatively nearby at $\sim 10-15$ Mpc away from the Milky Way. We discuss the origin of magnetic fields in the Local Supercluster and the observable predictions of this model.Comment: 11 pages, 2 figures, submitted to PR

The Parker Instability in 3-D: Corrugations and Superclouds Along the Carina-Sagittarius Arm

Here we present three-dimensional MHD models for the Parker instability in a thick magnetized disk, including the presence of a spiral arm. The $B$-field is assumed parallel to the arm, and the model results are applied to the optical segment of the Carina-Sagittarius arm. The characteristic features of the undular and interchange modes are clearly apparent in the simulations. The undular mode creates large gas concentrations distributed along the arm. This results in a clear arm/inter-arm difference: the instability triggers the formation of large interstellar clouds inside the arms, but generates only small structures with slight density enhancements in the inter-arm regions. The resulting clouds are distributed in an antisymmetric way with respect to the midplane, creating an azimuthal corrugation along the arm. For conditions similar to those of the optical segment of the Carina-Sagittarius arm, it has a wavelength of about 2.4 kpc. This structuring can explain the origin of both HI superclouds and the azimuthal corrugations in spiral arms. The wavelength matches the corrugation length derived with the young stellar groups located in the optical segment of the Carina-Sagittarius arm. Keywords: Galaxy: kinematics and dynamics -- Galaxy: structure -- Instabilities -- ISM: clouds -- ISM: magnetic fields -- ISM: structure -- MHDComment: 29 pages, 12 figures, Latex, Accepted by the Astrophysical Journa