A comparison between the MEXE and Pippard's methods of assessing the load carrying capacity of masonry arch bridges

The Military Engineering eXperimental Establishment (MEXE) method is a long established system of masonry arch load carrying capacity assessment. It has been subject to review in recent years and some shortcomings have been identified. There is now growing consensus that the current version of MEXE overestimates the load carrying capacity of short span bridges, but for spans over 12m it becomes increasingly conservative. In this paper Pippard’s elastic method and the MEXE method are used to investigate the significance of factors such as fill cover, ring thickness and effective width of arch barrel, and their effect upon the load-carrying capacity predictions in short and long span arches. Conclusions are drawn which establish directions of new research and offer guidance to assessors of short and long span masonry arch bridges

Measuring the Slope of the Dust Extinction Law and the Power Spectrum of Dust Clouds Using Differentially-Reddened Globular Clusters

We present 3 methods for measuring the Galactic dust extinction law slope R_V and a method for quantifying fine structure in dust clouds in the direction of differentially-reddened globular clusters. We apply these methods to the low- latitude globular cluster NGC4833 which displays variable extinction/reddening about a mean ~ 1. A set of Monte Carlo simulations is used to characterize the efficacy of the methods. The essence of the first 2 methods is to determine, for an assumed value of R_V, the relative visual extinction delta(A_V) of each cluster horizontal branch (HB) star with respect to an empirical HB locus; the locus is derived from the CMD of a subset of stars near the cluster center in which differential reddening is small. A star-by-star comparison of delta(A_V) from the (B-V,V) CMD with that from the (V-I,V) CMD is used to find the optimal R_V. In the third method, R_V is determined by minimizing the scatter in the HB in the (B-V, V) CMD after correcting the photometry for extinction and reddening using the Schlegel et al. (1998) dust maps. The weighted average of the results from 3 methods gives R_V = 3.0 +/- 0.4 for the dust towards NGC4833. The dust fine structure is quantified via the difference, Delta(A_V)_ij = [delta(A_V)]_i - [delta(A_V)]_j, between pairs of cluster HB stars (i,j) as a function of their angular separation r_ij. The variance of Delta(A_V)_ij is found to have a power- law dependence on angular scale: var(r) \propto r^(+0.9 +/- 0.1). This translates into an angular power spectrum P(kappa) \propto kappa^(-1.9 +/- 0.1) for r ~ 1' - 5', where kappa = 1/r. The dust angular power spectrum on small scales (from optical data) matches smoothly onto the larger-scale power spectrum derived from Schlegel et al.'s far-infrared map of the dust thermal emission.Comment: 36 pages, 15 figures, 1 table. Accepted for publication in the Astronomical Journal (July 2004

Alien Registration- Carmichael, Melbourne J. (Monticello, Aroostook County)

https://digitalmaine.com/alien_docs/33924/thumbnail.jp

Black Hole Masses and Star Formation Rates of z >1 Dust Obscured Galaxies (DOGs): Results from Keck OSIRIS Integral Field Spectroscopy

We have obtained high spatial resolution Keck OSIRIS integral field spectroscopy of four z~1.5 ultra-luminous infrared galaxies that exhibit broad H-alpha emission lines indicative of strong AGN activity. The observations were made with the Keck laser guide star adaptive optics system giving a spatial resolution of 0.1", or <1 kpc at these redshifts. These high spatial resolution observations help to spatially separate the extended narrow-line regions --- possibly powered by star formation --- from the nuclear regions, which may be powered by both star formation and AGN activity. There is no evidence for extended, rotating gas disks in these four galaxies. Assuming dust correction factors as high as A(H-alpha)=4.8 mag, the observations suggest lower limits on the black hole masses of (1 - 9) x 10^8 solar masses, and star formation rates <100 solar masses per year. The black hole masses and star formation rates of the sample galaxies appear low in comparison to other high-z galaxies with similar host luminosities. We explore possible explanations for these observations including, host galaxy fading, black hole growth, and the shut down of star formation.Comment: Accepted for publication in the Astronomical Journal. 12 pages, 6 figures, 5 table

Morphologies of High Redshift, Dust Obscured Galaxies from Keck Laser Guide Star Adaptive Optics

Spitzer MIPS images in the Bootes field of the NOAO Deep Wide-Field Survey have revealed a class of extremely dust obscured galaxy (DOG) at z~2. The DOGs are defined by very red optical to mid-IR (observed-frame) colors, R - [24 um] > 14 mag, i.e. f_v (24 um) / f_v (R) > 1000. They are Ultra-Luminous Infrared Galaxies with L_8-1000 um > 10^12 -10^14 L_sun, but typically have very faint optical (rest-frame UV) fluxes. We imaged three DOGs with the Keck Laser Guide Star Adaptive Optics (LGSAO) system, obtaining ~0.06'' resolution in the K'-band. One system was dominated by a point source, while the other two were clearly resolved. Of the resolved sources, one can be modeled as a exponential disk system. The other is consistent with a de Vaucouleurs profile typical of elliptical galaxies. The non-parametric measures of their concentration and asymmetry, show the DOGs to be both compact and smooth. The AO images rule out double nuclei with separations of greater than 0.1'' (< 1 kpc at z=2), making it unlikely that ongoing major mergers (mass ratios of 1/3 and greater) are triggering the high IR luminosities. By contrast, high resolution images of z~2 SCUBA sources tend to show multiple components and a higher degree of asymmetry. We compare near-IR morphologies of the DOGs with a set of z=1 luminous infrared galaxies (LIRGs; L_IR ~ 10^11 L_sun) imaged with Keck LGSAO by the Center for Adaptive Optics Treasury Survey. The DOGs in our sample have significantly smaller effective radii, ~1/4 the size of the z=1 LIRGs, and tend towards higher concentrations. The small sizes and high concentrations may help explain the globally obscured rest-frame blue-to-UV emission of the DOGs.Comment: 9 pages, 7 figures, 2 tables, accepted for publication in the Astronomical Journa

Spatially Resolved Stellar Populations of Eight GOODS-South AGN at z~1

We present a pilot study of the stellar populations of 8 AGN hosts at z~1 and compare to (1) lower redshift samples and (2) a sample of nonactive galaxies of similar redshift. We utilize K' images in the GOODS South field obtained with the laser guide star adaptive optics (LGSAO) system at Keck Observatory. We combine this K' data with B, V, i, and z imaging from the ACS on HST to give multi-color photometry at a matched spatial resolution better than 100 mas in all bands. The hosts harbor AGN as inferred from their high X-ray luminosities (L_X > 10^42 ergs/s) or mid-IR colors. We find a correlation between the presence of younger stellar populations and the strength of the AGN, as measured with [OIII] line luminosity or X-ray (2-10 keV) luminosity. This finding is consistent with similar studies at lower redshift. Of the three Type II galaxies, two are disk galaxies and one is of irregular type, while in the Type I sample there only one disk-like source and four sources with smooth, elliptical/spheroidal morphologies. In addition, the mid-IR SEDs of the strong Type II AGN indicate that they are excited to LIRG (Luminous InfraRed Galaxy) status via galactic starbursting, while the strong Type I AGN are excited to LIRG status via hot dust surrounding the central AGN. This supports the notion that the obscured nature of Type II AGN at z~1 is connected with global starbursting and that they may be extincted by kpc-scale dusty features that are byproducts of this starbursting.Comment: 56 pages, 39 figures, accepted to A

Optical Morphology Evolution of Infrared Luminous Galaxies in GOODS-N

We combine optical morphologies and photometry from HST, redshifts from Keck, and mid-infrared luminosities from Spitzer for an optically selected sample of~800 galaxies in GOODS-N to track morphology evolution of infrared luminous galaxies (LIRGs) since redshift z=1. We find a 50% decline in the number of LIRGs from z~1 to lower redshift, in agreement with previous studies. In addition, there is evidence for a morphological evolution of the populations of LIRGs. Above z=0.5, roughly half of all LIRGs are spiral, the peculiar/irregular to spiral ratio is ~0.7, and both classes span a similar range of L_{IR} and M_B. At low-z, spirals account for one-third of LIRGs, the peculiar to spiral fraction rises to 1.3, and for a given M_B spirals tend to have lower IR luminosity than peculiars. Only a few percent of LIRGs at any redshift are red early-type galaxies. For blue galaxies (U-B < 0.2), M_B is well correlated with log(L_{IR}) with an RMS scatter (about a bivariate linear fit) of ~0.25 dex in IR luminosity. Among blue galaxies that are brighter than M_B = -21, 75% are LIRGs, regardless of redshift. These results can be explained by a scenario in which at high-z, most large spirals experience an elevated star formation rate as LIRGs. Gas consumption results in a decline of LIRGs, especially in spirals, to lower redshifts.Comment: 6 pages, 2 figures, accepted ApJ

The Contribution of Thermally-pulsing Asymptotic Giant Branch and Red Supergiant Stars to the Luminosities of the Magellanic Clouds at 1-24 μm

We present the near-through mid-infrared flux contribution of thermally-pulsing asymptotic giant branch (TP-AGB) and massive red supergiant (RSG) stars to the luminosities of the Large and Small Magellanic Clouds (LMC and SMC, respectively). Combined, the peak contribution from these cool evolved stars occurs at ~3-4 μm, where they produce 32% of the SMC light, and 25% of the LMC flux. The TP-AGB star contribution also peaks at ~3-4 μm and amounts to 21% in both galaxies. The contribution from RSG stars peaks at shorter wavelengths, 2.2 μm, where they provide 11% of the SMC flux, and 7% for the LMC. Both TP-AGB and RSG stars are short lived, and thus potentially impose a large stochastic scatter on the near-IR derived mass-to-light (M/L) ratios of galaxies at rest-frame 1-4 μm. To minimize their impact on stellar mass estimates, one can use the M/L ratio at shorter wavelengths (e.g., at 0.8-1 μm). At longer wavelengths (≥8 μm), emission from dust in the interstellar medium dominates the flux. In the LMC, which shows strong polycyclic aromatic hydrocarbon (PAH) emission at 8 μm, TP-AGB and RSG contribute less than 4% of the 8 μm flux. However, 19% of the SMC 8 μm flux is from evolved stars, nearly half of which is produced by the rarest, dustiest, carbon-rich TP-AGB stars. Thus, star formation rates of galaxies, based on an 8 μm flux (e.g., observed-frame 24 μm at z = 2), may be biased modestly high, especially for galaxies with little PAH emission

The Contribution of Thermally-Pulsing Asymptotic Giant Branch and Red Supergiant Starts to the Luminosities of the Magellanic Clouds at 1-24 micrometers

We present the near-through mid-infrared flux contribution of thermally-pulsing asymptotic giant branch (TP-AGB) and massive red supergiant (RSG) stars to the luminosities of the Large and Small Magellanic Clouds (LMC and SMC, respectively). Combined, the peak contribution from these cool evolved stars occurs at approx 3 - 4 micron, where they produce 32% of the SMC light, and 25% of the LMC flux. The TP-AGB star contribution also peaks at approx 3 - 4 micron and amounts to 21% in both galaxies. The contribution from RSG stars peaks at shorter wavelengths, 2.2 micron, where they provide 11% of the SMC flux, and 7% for the LMC. Both TP-AGB and RSG stars are short lived, and thus potentially impose a large stochastic scatter on the near-IR derived mass-to-light (M/L) ratios of galaxies at rest-frame 1 - 4 micron. To minimize their impact on stellar mass estimates, one can use the M/L ratio at shorter wavelengths (e.g., at 0.8 - 1 micron). At longer wavelengths (much > 8 micron), emission from dust in the interstellar medium dominates the flux. In the LMC, which shows strong polycyclic aromatic hydrocarbon (PAH) emission at 8 micron, TP-AGB and RSG contribute less than 4% of the 8 micron flux. However, 19% of the SMC 8 micron flux is from evolved stars, nearly half of which is produced by the rarest, dustiest, carbon-rich TP-AGB stars. Thus, star formation rates of galaxies, based on an 8 micron flux (e.g., observed-frame 24 micron at z = 2), may be biased modestly high, especially for galaxies with little PAH emission

An apparatus for the electrodynamic containment of charged macroparticles

The dynamic moition of the ions contained in the trapped (199)Hg+ frequency standard contributes to the stability of the standard. In order to study these dynamics, a macroscopic analog of the (199)Hg+ trap is constructed. Containment of micron-sized particles in this trap allows direct visual observation of the particles' motion. Influenced by the confining fields and their own Coulomb repulsion, the particles can form stable arrays