Galactic archaeology: IMF and depletion in the "thin disk"

We determine the initial mass function (IMF) of the ``thin disk'' by means of a direct comparison between synthetic stellar samples (for different matching choices of IMF, star formation rate SFR and depletion) and a complete (volume-limited) sample of single stars near the galactic plane (|z| < 25pc), selected from the Hipparcos catalogue (d < 100pc, M_v < +4.0). Our synthetic samples are computed from first principles: stars are created with a random distribution of mass M_* and age t_* which follow a given (genuine) IMF and SFR(t_*). They are then placed in the HR diagram by means of a grid of empirically well-tested evolution tracks. The quality of the match (synthetic versus observed sample) is assessed by means of star counts in specific regions in the HR diagram. 7 regions are located along the MS (main sequence, mass sensitive), while 4 regions represent different evolved (age-sensitive) stages of the stars. The counts of evolved stars, in particular, give valuable evidence of the history of the ``thin disk'' (apparent) star formation and lift the ambiguities in models restricted to MS star counts.Comment: 10 pages, 3 figures, submitted to MNRA

Cooling system for high speed aircraft

The system eliminates the necessity of shielding an aircraft airframe constructed of material such as aluminum. Cooling is accomplished by passing a coolant through the aircraft airframe, the coolant acting as a carrier to remove heat from the airframe. The coolant is circulated through a heat pump and a heat exchanger which together extract essentially all of the added heat from the coolant. The heat is transferred to the aircraft fuel system via the heat exchanger and the heat pump. The heat extracted from the coolant is utilized to power the heat pump. The heat pump has associated therewith power turbine mechanism which is also driven by the extracted heat. The power turbines are utilized to drive various aircraft subsystems, the compressor of the heat pump, and provide engine cooling

Nonequilibrium quantum fluctuation relations for harmonic systems in nonthermal environments

We formulate exact generalized nonequilibrium fluctuation relations for the quantum mechanical harmonic oscillator coupled to multiple harmonic baths. Each of the different baths is prepared in its own individual (in general nonthermal) state. Starting from the exact solution for the oscillator dynamics we study fluctuations of the oscillator position as well as of the energy current through the oscillator under general nonequilibrium conditions. In particular, we formulate a fluctuation-dissipation relation for the oscillator position autocorrelation function that generalizes the standard result for the case of a single bath at thermal equilibrium. Moreover, we show that the generating function for the position operator fullfills a generalized Gallavotti-Cohen-like relation. For the energy transfer through the oscillator, we determine the average energy current together with the current fluctuations. Finally, we discuss the generalization of the cumulant generating function for the energy transfer to nonthermal bath preparations.Comment: 21 page

A STUDY OF SPACE-BASED SOLAR POWER SYSTEMS

Space-Based Solar Power (SBSP) is best defined as delivering meaningful amounts of energy without moving or employing mass between the transmitter and receiver. The current modus operandi for the Department of Defense (DoD) requires the delivery of energy by physical transport of fossil fuels or its derivatives, which is burdensome, costly, and dangerous in the face of threats. SBSP is known to be technically possible, with varying degrees of success, from ground-based wireless power transmission demonstrations; integrated solar collection, conversion, and transmission systems development; and microwave conversion and rectifying efficiency studies, but a full end-to-end SBSP system has yet to be realized. This thesis aims to explore SBSP's utility in DoD operations at the tactical edge, serving the warfighters at forward operating bases as well as expeditionary forces where power infrastructure is problematic or extant. A collection of SBSP research, studies, and articles was pored over to identify the major stakeholders for such a system, analyze their requirements, and identify a valid reference architecture to maximize the SBSP solution space. This thesis's conclusive results can serve as a baseline for further research in this field. The international community is already aggressively underway in SBSP system design, and the results herein highlight the need for the DoD to act as a leader in this space decisively and quickly.Civilian, Department of the NavyApproved for public release. Distribution is unlimited

An Integrated Picture of Star Formation, Metallicity Evolution, and Galactic Stellar Mass Assembly

We present an integrated study of star formation and galactic stellar mass assembly from z=0.05-1.5 and galactic metallicity evolution from z=0.05-0.9 using a very large and highly spectroscopically complete sample selected by rest-frame NIR bolometric flux in the GOODS-N. We assume a Salpeter IMF and fit Bruzual & Charlot (2003) models to compute the galactic stellar masses and extinctions. We determine the expected formed stellar mass density growth rates produced by star formation and compare them with the growth rates measured from the formed stellar mass functions by mass interval. We show that the growth rates match if the IMF is slightly increased from the Salpeter IMF at intermediate masses (~10 solar masses). We investigate the evolution of galaxy color, spectral type, and morphology with mass and redshift and the evolution of mass with environment. We find that applying extinction corrections is critical when analyzing galaxy colors; e.g., nearly all of the galaxies in the green valley are 24um sources, but after correcting for extinction, the bulk of the 24um sources lie in the blue cloud. We find an evolution of the metallicity-mass relation corresponding to a decrease of 0.21+/-0.03 dex between the local value and the value at z=0.77 in the 1e10-1e11 solar mass range. We use the metallicity evolution to estimate the gas mass of the galaxies, which we compare with the galactic stellar mass assembly and star formation histories. Overall, our measurements are consistent with a galaxy evolution process dominated by episodic bursts of star formation and where star formation in the most massive galaxies (>1e11 solar masses) ceases at z<1.5 because of gas starvation. (Abstract abridged)Comment: 48 pages, Accepted by the Astrophysical Journa

Corn: Signed, Constant-Time Communication

Recent advances in cacheable technology and unstable theory have paved the way for lambda calculus. In this position paper, we verify the evaluation of hierarchical databases, demonstrates the unproven importance of hardware and architecture. In this work, we propose a novel algorithm for the deployment of Markov models (Corn), confirming that architecture and e-commerce are mostly incompatible

Neutrinos And Big Bang Nucleosynthesis

The early universe provides a unique laboratory for probing the frontiers of particle physics in general and neutrino physics in particular. The primordial abundances of the relic nuclei produced during the first few minutes of the evolution of the Universe depend on the electron neutrinos through the charged-current weak interactions among neutrons and protons (and electrons and positrons and neutrinos), and on all flavors of neutrinos through their contributions to the total energy density which regulates the universal expansion rate. The latter contribution also plays a role in determining the spectrum of the temperature fluctuations imprinted on the Cosmic Background Radiation (CBR) some 400 thousand years later. Using deuterium as a baryometer and helium-4 as a chronometer, the predictions of BBN and the CBR are compared to observations. The successes of, as well as challenges to the standard models of particle physics and cosmology are identified. While systematic uncertainties may be the source of some of the current tensions, it could be that the data are pointing the way to new physics. In particular, BBN and the CBR are used to address the questions of whether or not the relic neutrinos were fully populated in the early universe and, to limit the magnitude of any lepton asymmetry which may be concealed in the neutrinos.Comment: Accepted for publication in the Proceedings of Nobel Symposium 129, "Neutrino Physics"; to appear in Physics Scripta, eds., L Bergstrom, O. Botner, P. Carlson, P. O. Hulth, and T. Ohlsso

Chemical Evolution of Galaxies

Chemical evolution of galaxies brings together ideas on stellar evolution and nucleosynthesis with theories of galaxy formation, star formation and galaxy evolution, with all their associated uncertainties. In a new perspective brought about by the Hubble Deep Field and follow-up investigations of global star formation rates, diffuse background etc., it has become necessary to consider the chemical composition of dark baryonic matter as well as that of visible matter in galaxies.Comment: 6 pages, AAS LaTeX macros v5.0, Millennium Essay to appear in PASP, Feb 200

Chemical Properties of Star-Forming Emission Line Galaxies at z=0.1 - 0.5

We measure oxygen and nitrogen abundances for 14 star-forming emission line galaxies (ELGs) at 0.11<z<0.5 using Keck/LRIS optical spectroscopy. The targets exhibit a range of metallicities from slightly metal-poor like the LMC to super-solar. Oxygen abundances of the sample correlate strongly with rest-frame blue luminosities. The metallicity-luminosity relation based on these 14 objects is indistinguishable from the one obeyed by local galaxies, although there is marginal evidence (1.1sigma) that the sample is slightly more metal-deficient than local galaxies of the same luminosity. The observed galaxies exhibit smaller emission linewidths than local galaxies of similar metallicity, but proper corrections for inclination angle and other systematic effects are unknown. For 8 of the 14 objects we measure nitrogen-to-oxygen ratios. Seven of 8 systems show evidence for secondary nitrogen production, with log(N/O)> -1.4 like local spirals. These chemical properties are inconsistent with unevolved objects undergoing a first burst of star formation. The majority of the ELGs are presently ~4 magnitudes brighter and ~0.5 dex more metal-rich than the bulk of the stars in well-known metal-poor dwarf spheroidals such as NGC 205 and NGC 185, making an evolution between some ELGs and metal-poor dwarf spheroidals improbable. However, the data are consistent with the hypothesis that more luminous and metal-rich spheroidal galaxies like NGC 3605 may become the evolutionary endpoints of some ELGs. [abridged]Comment: 41 pages, w/12 figures, uses AASTeX aaspp4.sty, psfig.sty; To appear in The Astrophysical Journa

The Primordial Abundance of He4: An Update

We include new data in an updated analysis of helium in low metallicity extragalactic HII regions with the goal of deriving the primordial abundance of He4 (Y_P). We show that the new observations of Izotov et al (ITL) are consistent with previous data. However they should not be taken in isolation to determine (Y_P) due to the lack of sufficiently low metallicity points. We use the extant data in a semi-empirical approach to bounding the size of possible systematic uncertainties in the determination of (Y_P). Our best estimate for the primordial abundance of He4 assuming a linear relation between He4 and O/H is Y_P = 0.230 \pm 0.003 (stat) based on the subset of HII regions with the lowest metallicity; for our full data set we find Y_P = 0.234 \pm 0.002 (stat). Both values are entirely consistent with our previous results. We discuss the implications of these values for standard big bang nucleosynthesis (SBBN), particularly in the context of recent measurements of deuterium in high redshift, low metallicity QSO absorption-line systems.Comment: 26 pages, latex, 6 ps figure