The "Mysterious" Origin of Brown Dwarfs

Hundreds of brown dwarfs (BDs) have been discovered in the last few years in stellar clusters and among field stars. BDs are almost as numerous as hydrogen burning stars and so a theory of star formation should also explain their origin. The ``mystery'' of the origin of BDs is that their mass is two orders of magnitude smaller than the average Jeans' mass in star--forming clouds, and yet they are so common. In this work we investigate the possibility that gravitationally unstable protostellar cores of BD mass are formed directly by the process of turbulent fragmentation. Supersonic turbulence in molecular clouds generates a complex density field with a very large density contrast. As a result, a fraction of BD mass cores formed by the turbulent flow are dense enough to be gravitationally unstable. We find that with density, temperature and rms Mach number typical of cluster--forming regions, turbulent fragmentation can account for the observed BD abundance.Comment: 11 pages, 3 figures, ApJ submitted Error in equation 1 has been corrected. Improved figure

Research of metal solidification in zero-g state

An experiment test apparatus that allows metal melting and resolidification in the three seconds available during free fall in a drop tower was built and tested in the tower. Droplets (approximately 0.05 cm) of pure nickel and 1090 steel were prepared in this fashion. The apparatus, including instrumentation, is described. As part of the instrumentation, a method for measuring temperature-time histories of the free floating metal droplets was developed. Finally, a metallurgical analysis of the specimens prepared in the apparatus is presented

Out of sight, out of mind: An exploration of wastewater issues and possible solutions in and out of Montana

Larson, Keely, M.A., Spring 2023 Major:Environmental and Natural Resources Journalism Out of sight, out of mind: An exploration of wastewater issues and possible solutions in and out of Montana Chairperson: Dennis Swibold Co-Chairpersons: Nadia White, Sarah Halvorson This is a master’s project, featuring three stories, linked in theme. The first starts with a nationally scoped story about septic systems in resort towns and what happens when too many people want to visit areas like Cape Cod, the Florida Keys or, more locally, Seeley Lake, and overwhelm waste disposal methods. Often in these areas that are more remote, septic systems are the norm. Septic systems can be effective methods of waste disposal, but they must be maintained, which is not always the case. When nutrients from septic systems leach into groundwater, they can make their way into surface water as algal blooms, a nuisance that can sometimes be toxic and commonly keeps people out of the water, a problem for resort communities that rely on water recreation. Secondly, the project looks at a regional solution to another waste problem. A septage facility was proposed in Flathead County, Montana to address an issue septic pumpers and haulers were having – they didn’t have anywhere to dump their loads. As the prices of land continue to rise with a population influx and mirrored real estate prices in Montana, the land that pumpers and haulers typically used for land application is running low. Land application, or the act of disposing human waste as fertilizer onto a farm plot, has been practiced in one form or another for generations. Lastly, this project looks at a more political solution to growth, infrastructure and waste. Montana Governor Greg Gianforte released his budget before the 2023 legislature and earmarked $200 million for water and sewer infrastructure upgrades, with a goal of that money going towards larger municipalities to facilitate expansion. Local economists in Bozeman, Montana saw this money as a way of supporting growth while eventually lowering the cost of housing, something the city of Bozeman continues to deal with as a result of more people and wealth coming to the city

An introductory unit of tabulation for first-year typewriting

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

Dust-cooling--induced Fragmentation of Low-metallicity Clouds

Dynamical collapse and fragmentation of low-metallicity cloud cores is studied using three-dimensional hydrodynamical calculations, with particular attention devoted whether the cores fragment in the dust-cooling phase or not. The cores become elongated in this phase, being unstable to non-spherical perturbation due to the sudden temperature decrease. In the metallicity range of 10^{-6}-10^{-5}Z_sun, cores with an initial axis ratio >2 reach a critical value of the axis ratio (>30) and fragment into multiple small clumps. This provides a possible mechanism to produce low-mass stars in ultra-metal-poor environments.Comment: 4 pages, 3 figures, ApJ Letters in pres

On the rotating wave approximation in the adiabatic limit

I revisit a longstanding question in quantum optics; When is the rotating wave approximation justified? In terms of the Jaynes-Cummings and Rabi models I demonstrate that the approximation in general breaks down in the adiabatic limit regardless of system parameters. This is explicitly shown by comparing Berry phases of the two models, where it is found that this geometrical phase is strictly zero in the Rabi model contrary to the non-trivial Berry phase of the Jaynes-Cummings model. The source of this surprising result is traced back to different topologies in the two models.Comment: 8 pages, 3 figure

Mott insulator states of ultracold atoms in optical resonators

We study the low temperature physics of an ultracold atomic gas in the potential formed inside a pumped optical resonator. Here, the height of the cavity potential, and hence the quantum state of the gas, depends not only on the pump parameters, but also on the atomic density through a dynamical a.c.-Stark shift of the cavity resonance. We derive the Bose-Hubbard model in one dimension, and use the strong coupling expansion to determine the parameter regime in which the system is in the Mott-insulator state. We predict the existence of overlapping, competing Mott states, and bistable behavior in the vicinity of the shifted cavity resonance, controlled by the pump parameters. Outside these parameter regions, the state of the system is in most cases superfluid.Comment: 4 pages, 3 figures. Substantially revised version. To appear in Phys. Rev. Let

The Initial Mass Function of Low-Mass Stars and Brown Dwarfs in Taurus

By combining deep optical imaging and infrared spectroscopy with data from the Two-Micron All-Sky Survey (2MASS) and from previous studies (e.g., Briceno et al.), I have measured the Initial Mass Function (IMF) for a reddening-limited sample in four fields in the Taurus star forming region. This IMF is representative of the young populations within these fields for masses above 0.02 Msun. Relative to the similarly derived IMF for the Trapezium Cluster (Luhman et al.), the IMF for Taurus exhibits a modest deficit of stars above one solar mass (i.e., steeper slope), the same turnover mass (~0.8 Msun), and a significant deficit of brown dwarfs. If the IMF in Taurus were the same as that in the Trapezium, 12.8+/-1.8 brown dwarfs (>0.02 Msun) are expected in these Taurus fields where only one brown dwarf candidate is found. These results are used to test theories of the IMF.Comment: to be published in The Astrophysical Journal, 24 pages, 6 figures, also found at http://cfa-www.harvard.edu/~kluhman/taurus