Browsing by Subject "growth"

Now showing 1 - 20 of 26

Accretion onto Intermediate-Mass Black Holes in Dense Protogalactic Clouds
(2009-05) Milosavljevi?, Miloš; Couch, Sean M.; Bromm, Volker; Milosavljevi?, Miloš; Couch, Sean M.; Bromm, Volker
We present the first results from two-dimensional simulations of radiatively efficient accretion of metal-free gas onto intermediate-mass black holes. We fix the shape of the spectral energy distribution of the radiation produced near the event horizon and study the structure of the irradiated low-angular-momentum accretion flow over 3 orders of magnitude in radius from the black hole, 10(14)-10(17) cm for a 100 M(circle dot) black hole. The luminosity of the central source is made to be proportional to the rate at which gas accretes across the inner boundary, which we set just inside the sonic radius. We find that photoionization heating and radiation pressure modify the structure of the flow. When the ambient gas density is 10(7) cm(-3), accretion is intermittent and on average reduced to 32% of the Eddington-limited rate, over 2 orders of magnitude below the "Bondi" rate evaluated ignoring radiation, in agreement with theoretical models. Even if the vicinity of the black hole is supplied with high-density gas, accretion is rendered inefficient through heating and radiation pressure.
The Anatomy and Some of the Biological Aspects of the "American Mistletoe"
(University of Texas at Austin, 1909-03-15) University of Texas at Austin
Angular redistribution of nonlinear perturbations: A universal feature of nonuniform flows
(2010-06) Horton, W.; Kim, J. H.; Chagelishvili, G. D.; Bowman, J. C.; Lominadze, J. G.; Horton, W.
Classically, the net action of nonlinear turbulent processes is interpreted as either a direct or inverse cascade. However, in nonuniform/shear flows the dominant process is a nonlinear redistribution over wave number angle of perturbation spatial Fourier harmonics. We call this process a nonlinear transverse redistribution (NTR). This phenomenon is demonstrated for a simple two-dimensional constant shear (non-normal) flow by numerically simulating the nonlinear dynamics of coherent and stochastic vortical perturbations in the flow. NTR is a general feature of nonlinear processes that should manifest itself in nonuniform engineering, environmental, and astrophysical flows. The conventional characterization of turbulence in terms of direct and inverse cascades, which ignores NTR, appears to be misleading for shear flow turbulence. We focus on the action of nonlinear processes on the spectral energy. NTR redistributes perturbations over different quadrants of the wave number plane and the interplay of this nonlinear redistribution with linear phenomena becomes intricate: it can realize either positive or negative feedback. In the case of positive feedback, it repopulates the quadrants in wave number space where the shear flow induces linear transient growth.
Bayes And Empirical-Bayes Multiplicity Adjustment In The Variable-Selection Problem
(2010-10) Scott, James G.; Berger, James O.; Scott, James G.; Berger, James O.
This paper studies the multiplicity-correction effect of standard Bayesian variable-selection priors in linear regression. Our first goal is to clarify when, and how, multiplicity correction happens automatically in Bayesian analysis, and to distinguish this correction from the Bayesian Ockham's-razor effect. Our second goal is to contrast empirical-Bayes and fully Bayesian approaches to variable selection through examples, theoretical results and simulations. Considerable differences between the two approaches are found. In particular, we prove a theorem that characterizes a surprising aymptotic discrepancy between fully Bayes and empirical Bayes. This discrepancy arises from a different source than the failure to account for hyperparameter uncertainty in the empirical-Bayes estimate. Indeed, even at the extreme, when the empirical-Bayes estimate converges asymptotically to the true variable-inclusion probability, the potential for a serious difference remains.
Changes in Imja Tsho in the Mount Everest Region of Nepal
(2014-09) Somos-Valenzuela, M. A.; McKinney, D. C.; Rounce, D. R.; Byers, A. C.; Somos-Valenzuela, M. A.; McKinney, D. C.; Rounce, D. R.
Imja Tsho, located in the Sagarmatha ( Everest) National Park of Nepal, is one of the most studied and rapidly growing lakes in the Himalayan range. Compared with previous studies, the results of our sonar bathymetric survey conducted in September of 2012 suggest that its maximum depth has increased from 90.5 to 116.3 +/- 5.2 m since 2002, and that its estimated volume has grown from 35.8 +/- 0.7 to 61.7 +/- 3.7 million m(3). Most of the expansion of the lake in recent years has taken place in the glacier terminus-lake interface on the eastern end of the lake, with the glacier receding at about 52 m yr(-1) and the lake expanding in area by 0.04 km(2) yr(-1). A ground penetrating radar survey of the Imja-Lhotse Shar glacier just behind the glacier terminus shows that the ice is over 200 m thick in the center of the glacier. The volume of water that could be released from the lake in the event of a breach in the damming moraine on the western end of the lake has increased to 34.1 +/- 1.08 million m(3) from the 21 million m(3) estimated in 2002.
Chemical Vapour Deposition of Amorphous Ru(P) Thin Films from Ru Trialkylphosphite Hydride Complexes
(2012-09) McCarty, W. Jeffrey; Yang, Xiaoping; Anderson, Lauren J. D.; Jones, Richard A.; McCarty, W. Jeffrey; Yang, Xiaoping; Anderson, Lauren J. D.; Jones, Richard A.
The ruthenium phosphite hydride complexes H2Ru(P(OR)(3))(4) (R = Me (1), Et (2), Pr-i (3)) were used as CVD precursors for the deposition of films of amorphous ruthenium-phosphorus alloys. The as-deposited films were X-ray amorphous and XPS analysis revealed that they were predominantly comprised of Ru and P in zero oxidation states. XPS analysis also showed the presence of small amounts of oxidized ruthenium and phosphorus. The composition of the films was found to depend on ligand chemistry as well as the deposition conditions. The use of H-2 as the carrier gas had the effect of increasing the relative concentrations of P and O for all films. Annealing films to 700 degrees C under vacuum produced films of polycrystalline hcp Ru while a flowing stream of H-2 resulted in polycrystalline hcp RuP.
Formation and Aging of Secondary Organic Aerosol from Toluene: Changes in Chemical Composition, Volatility, and Hygroscopicity
(2015) Ruiz, L. Hildebrandt; Paciga, A. L.; Cerully, K. M.; Nenes, A.; Donahue, N. M.; Pandis, S. N.; Ruiz, L. Hildebrandt
Secondary organic aerosol (SOA) is transformed after its initial formation, but this chemical aging of SOA is poorly understood. Experiments were conducted in the Carnegie Mellon environmental chamber to form secondary organic aerosol (SOA) from the photo-oxidation of toluene and other small aromatic volatile organic compounds (VOCs) in the presence of NOx under different oxidizing conditions. The effects of the oxidizing condition on organic aerosol (OA) composition, mass yield, volatility, and hygroscopicity were explored. Higher exposure to the hydroxyl radical resulted in different OA composition, average carbon oxidation state (OSc), and mass yield. The OA oxidation state generally increased during photo-oxidation, and the final OA OSc ranged from -0.29 to 0.16 in the performed experiments. The volatility of OA formed in these different experiments varied by as much as a factor of 30, demonstrating that the OA formed under different oxidizing conditions can have a significantly different saturation concentration. There was no clear correlation between hygroscopicity and oxidation state for this relatively hygroscopic SOA.
Formation Of The First Galaxies
(2012) Bromm, V.; Bromm, Volker
The emergence of the first stars and galaxies ended the cosmic dark ages, thus fundamentally transforming the simple initial state of the universe into one of ever increasing complexity. We will review the basic physics governing the formation of the first galaxies. Their properties sensitively depend on the feedback exerted by the first, Population III, stars, which in turn reflects how massive those stars were. The key goal is to derive their observational signature, to be probed with upcoming next-generation facilities, such as the James Webb Space Telescope.
Innovative Initiatives in Growth Management and Open Space Preservation: A National Study, PRP 145
(LBJ School of Public Affairs, 2003) Wilson, Robert H.; Paterson, Robert
Integral Field Unit Spectroscopy of the Stellar Disk Truncation Region of NGC 6155
(2010-06) Yoachim, Peter; Roskar, Rok; Debattista, Victor P.; Roskar, Rok
Like the majority of spiral galaxies, NGC 6155 exhibits an exponential surface brightness profile that steepens significantly at large radii. Using the VIRUS-P integral field unit spectrograph, we have gathered spatially resolved spectra of the system. Modifying the GANDALF spectral fitting routine for use on the complex stellar populations found in spirals, we find that the average stellar ages increase significantly beyond the profile break radius. This result is in good agreement with recent simulations that predict the outskirts of disk galaxies are populated through stellar migration. With the ability to bin multiple fibers, we are able to measure stellar population ages down to mu(V) similar to 24 mag arcsec(-2).
Letter to C.Barker Jorgenson from H.B. Stenzel on 1964-03-13
(1964-03-13) Stenzel, H.B.
Letter to H.B. Stenzel from Arthur Wrigley on 1949-04-25
(1949-04-25) Wrigley, Arthur
Letter to H.B. Stenzel from C.Barker Jorgensen on 1964-03-18
(1964-03-18) Jorgensen, C.Barker
Letter to Henryk Stenzel from Norman D. Newell on 1948-01-12
(1948-01-12) Newell, Norman D.
Letter to Paul E. Chanley from H.B. Stenzel on 1965-01-28
(1965-01-28) Stenzel, Henryk B.
Letter to Robert M. Ingle from H.B. Stenzel on 1962-05-14
(1962-05-14) Stenzel, Henryk B.
Letter to T.P. Burnaby from H.B. Stenzel on 1966-06-02
(1966-06-02) Stenzel, Henryk B.
A Matrix Analysis of Growth Policy in Austin, PRP 58
(LBJ School of Public Affairs, 1983) Hadden, Susan G.; Cope, Glen H.
Methylosinus-Trichosporium Ob3B Mutants Having Constitutive Expression Of Soluble Methane Monooxygenase In The Presence Of High-Levels Of Copper
(1992-11) Phelps, Patricia A.; Agarwal, Sandeep K.; Speitel, Gerald E.; Georgiou, George; Phelps, Patricia A.; Agarwal, Sandeep K.; Speitel, Gerald E.; Georgiou, George
The methanotrophic bacterium Methylosinus trichosporium OB3b is unusually active in degrading recalcitrant haloalkanes such as trichloroethylene (TCE). The first and rate-limiting step in the degradation of TCE is catalyzed by a soluble methane monooxygenase (sMMO). This enzyme is not expressed when the cells are grown in the presence of copper at concentrations typically found in polluted groundwater. Under these conditions, M. trichosporium OB3b expresses a particulate form of the enzyme (pMMO), which has a narrow substrate specificity and does not degrade TCE at any significant rate. We have isolated M. trichosporium OB3b mutants that are deficient in pMMO and express sMMO constitutively in the presence of elevated concentrations of copper. One mutant (PP358) exhibited a TCE degradation rate which was almost twice as high as that of the wild-type strain grown under optimal conditions (without copper). All of the mutants lost the ability to express pMMO activity and to form stacked intracellular membranes characteristic of wild-type cells expressing pMMO.
A Novel Immunofluorescence Flow Cytometry Technique Detects The Expansion Of Brown Tides Caused By Aureoumbra Lagunensis To The Caribbean Sea
(2014-06) Koch, F.; Kang, Y.; Villareal, Tracy A.; Anderson, D. M.; Gobler, C. J.; Villareal, Tracy A.
During the past 3 decades, brown tides caused by the pelagophytes Aureococcus anophagefferens and Aureoumbra lagunensis have caused ecological and economic damage to coastal ecosystems across the globe. While blooms of A. lagunensis had previously been confined to Texas, in 2012, an expansive brown tide occurred on Florida's East Coast, causing widespread disruption within the Indian River and Mosquito Lagoons and generating renewed interest in this organism. A major impediment to detailed investigations of A. lagunensis in an ecosystem setting has been the absence of a rapid and reliable method for cell quantification. The combination of their small size (3 to 5 mu m) and nondescript extracellular features makes identification and enumeration of these cells with conventional methods a challenge. Here we report the development of an immunological-based flow cytometry method that uses a fluorescently labeled antibody developed against A. lagunensis. This method is species specific, sensitive (detection limit of 1.5 X 10(3) cells ml(-1)), precise (1% relative standard deviation of replicated samples), and accurate (108% +/- 8% recovery of spiked samples) over a wide range of cell concentrations. Furthermore, this method effectively quantifies A. lagunensis in both glutaraldehyde-and formalin-preserved samples, yields a high throughput of samples (similar to 35 samples h(-1)), and is cost-effective, making it an ideal tool for managers and scientists. This method successfully documented the recurrence of a brown tide bloom in Florida in 2013. Bloom densities were highest in June (>2.0 x 10(6) cells ml(-1)) and spanned >60 km from the Ponce de Leon inlet in the northern Mosquito Lagoon south to Titusville in the Indian River Lagoon. Low levels of A. lagunensis cells were found >250 km south of this region. This method also quickly and accurately identified A. lagunensis as the causative agent of a 2013 brown tide bloom in Guantanamo Bay, Cuba, and thus should prove useful for both quantifying the dynamics of ongoing blooms of A. lagunensis as well as documenting new outbreaks of this harmful alga.