Quantitative study of molecular N_2 trapped in disordered GaN:O films

The structure of disordered GaN:O films grown by ion-assisted deposition is investigated using x-ray absorption near-edge spectroscopy and Raman spectroscopy. It is found that between 4 and 21 % of the nitrogen in the films is in the form of molecular N_2 that interacts only weakly with the surrounding matrix. The anion to cation ratio in the GaN:O host remains close to unity, and there is a close correlation between the N_2 fraction, the level of oxygen impurities, and the absence of short-range order in the GaN:O matrix.Comment: 5 pages, 3 figure

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

Resonant x-ray scattering study on multiferroic BiMnO3

Resonant x-ray scattering is performed near the Mn K-absorption edge for an epitaxial thin film of BiMnO3. The azimuthal angle dependence of the resonant (003) peak (in monoclinic indices) is measured with different photon polarizations; for the $\sigma\to\pi'$ channel a 3-fold symmetric oscillation is observed in the intensity variation, while the $\sigma\to\sigma'$ scattering intensity remains constant. These features are accounted for in terms of the peculiar ordering of the manganese 3d orbitals in BiMnO3. It is demonstrated that the resonant peak persists up to 770 K with an anomaly around 440 K; these high and low temperatures coincide with the structural transition temperatures, seen in bulk, with and without a symmetry change, respectively. A possible relationship of the orbital order with the ferroelectricity of the system is discussed.Comment: 14 pages, 4 figure

Superclustering at Redshift Z=0.54

We present strong evidence for the existence of a supercluster at a redshift of z=0.54 in the direction of Selected Area 68. From the distribution of galaxies with spectroscopic redshifts we find that there is a large over-density of galaxies (a factor of four over the number expected in an unclustered universe) within the redshift range 0.530 < z < 0.555. By considering the spatial distribution of galaxies within this redshift range (using spectroscopic and photometric redshifts) we show that the galaxies in SA68 form a linear structure passing from the South-West of the survey field through to the North-East (with a position angle of approximately 35 deg East of North). This position angle is coincident with the positions of the X-ray clusters CL0016+16, RX J0018.3+1618 and a new X-ray cluster, RX J0018.8+1602, centered near the radio source 54W084. All three of these sources are at a redshift of approximately z=0.54 and have position angles, derived from their X-ray photon distributions, consistent with that measured for the supercluster. Assuming a redshift of 0.54 for the distribution of galaxies and a FWHM dispersion in redshift of 0.020 this represents a coherent structure with a radial extent of 31 Mpc, transverse dimension of 12 Mpc, and a thickness of approximately 4 Mpc. The detection of this possible supercluster demonstrates the power of using X-ray observations, combined with multicolor observations, to map the large scale distribution of galaxies at intermediate redshifts.Comment: 12 pages, 3 figures, Latex, aaspp4.sty, accepted for publication in Ap J Letters. Figure 3 and followup observations can be found at http://tarkus.pha.jhu.edu/~ajc/papers/supercluster

Radius Dependent Luminosity Evolution of Blue Galaxies in GOODS-N

We examine the radius-luminosity (R-L) relation for blue galaxies in the Team Keck Redshift Survey (TKRS) of GOODS-N. We compare with a volume-limited, Sloan Digital Sky Survey sample and find that the R-L relation has evolved to lower surface brightness since z=1. Based on the detection limits of GOODS this can not be explained by incompleteness in low surface-brightness galaxies. Number density arguments rule out a pure radius evolution. It can be explained by a radius dependent decline in B-band luminosity with time. Assuming a linear shift in M_B with z, we use a maximum likelihood method to quantify the evolution. Under these assumptions, large (R_{1/2} > 5 kpc), and intermediate sized (3 < R_{1/2} < 5 kpc) galaxies, have experienced Delta M_B =1.53 (-0.10,+0.13) and 1.65 (-0.18, +0.08) magnitudes of dimming since z=1. A simple exponential decline in star formation with an e-folding time of 3 Gyr can result in this amount of dimming. Meanwhile, small galaxies, or some subset thereof, have experienced more evolution, 2.55 (+/- 0.38) magnitudes. This factor of ten decline in luminosity can be explained by sub-samples of starbursting dwarf systems that fade rapidly, coupled with a decline in burst strength or frequency. Samples of bursting, luminous, blue, compact galaxies at intermediate redshifts have been identified by various previous studies. If there has been some growth in galaxy size with time, these measurements are upper limits on luminosity fading.Comment: 34 Total pages, 15 Written pages, 19 pages of Data Table, 13 Figures, accepted for publication in Ap

Serological evidence of exposure to Rickettsia felis and Rickettsia typhi in Australian veterinarians

BACKGROUND: Rickettsia felis and Rickettsia typhi are emerging arthropod-borne zoonoses causing fever and flu-like symptoms. Seroprevalence and risk factors associated with exposure to these organisms was explored in Australian veterinarians. METHODS: One hundred and thirty-one veterinarians from across Australia were recruited to participate in a cross-sectional survey. Veterinarians provided a single blood sample and answered a questionnaire on potential risk factors influencing their exposure to R. felis and R. typhi. Indirect microimmunofluorescence antibody testing (IFAT) was used to identify evidence of serological exposure of the participants to R. felis and R. typhi. Results were analyzed and a logistical regression model performed to predict risk factors associated with seropositivity. RESULTS: In total, 16.0% of participants were seropositive to R. felis, 4.6% to R. typhi and 35.1% seropositive to both, where cross-reactivity of the IFAT between R. felis and R. typhi precluded a definitive diagnosis. Veterinarians residing within the south-eastern states of Victoria and Tasmania were at a higher risk of exposure to R. felis or generalised R. felis or R. typhi exposure. Older veterinarians and those that recommended flea treatment to their clients were found to be significantly protected from exposure. CONCLUSIONS: The high exposure to R. felis amongst veterinary professionals suggests that flea-borne spotted fever is an important cause of undifferentiated fever conditions that may not be adequately recognized in Australia

OPERATIONAL EFFICIENCY OF A U.S./CANADIAN WHEAT POOL: A GAME THEORY ANALYSIS

The problem of declining wheat prices and excess supply has been the subject of recent economic studies partly because it coincides with the Federal Agriculture Improvement and Reform (FAIR) Act of 1996, and partly because efforts to decrease supply domestically have led to increased imports from Canada. This paper develops a game theory optimization model of market efficiency and derives conditions under which voluntary pooling is sustained for U.S./Canadian durum and hard red spring wheat producers. Analysis reveals that U.S. and Canadian farmers can increase farm returns with efficiency gains from pooling and by internalizing benefits from grain blending and logistics. The model is used to analyze diverse factors affecting the sustainability of such a pool.Voluntary pooling, game theory, efficiency gains, durum and HRS wheat marketing, Crop Production/Industries, Marketing,

OPERATIONAL EFFICIENCY OF US/CANADA WHEAT POOL: A GAME THEORY ANALYSIS

This paper develops a game theory optimization model of market efficiency and derives conditions under which voluntary pooling is sustained for US/Canada durum and hard red spring wheat producers. Analysis reveals that United States and Canadian farmers can increase farm returns with efficiency gains from pooling and by internalizing benefits from grain blending and logistics. The model is used to analyze diverse factors affecting the sustainability of such a pool.Crop Production/Industries, Marketing,

ECONOMIC ANALYSIS OF THE PROPOSED NORTH DAKOTA WHEAT POOL

The ND Durum Wheat Pool may provide additional revenue to durum wheat producers by raising the domestic prices in the North American market with full cooperation from the Canadian Wheat Board. The pool also could provide additional revenue to its members by improving marketing efficiency. On the other hand, the ND Spring Wheat Pool is less likely to provide additional revenue to spring wheat producers by raising domestic prices, mainly because hard red spring and winter wheat are highly substitutable. Efficiency gains also could be smaller than for durum wheat.marketing pool, market power, efficiency gains, durum wheat, hard red spring wheat, pool price, organizational structure, operating costs, Marketing,

ECONOMIC ANALYSIS OF THE PROPOSED NORTH DAKOTA WHEAT POOL; SUMMARY

The ND Durum Wheat Pool may provide additional revenue to durum wheat producers by raising the domestic prices in the North American market with full cooperation from the Canadian Wheat Board. The pool also could provide additional revenue to its members by improving marketing efficiency. On the other hand, the ND Spring Wheat Pool is less likely to provide additional revenue to spring wheat producers by raising domestic prices, mainly because hard red spring and winter wheat are highly substitutable. Efficiency gains also could be smaller than for durum wheat.marketing pool, market power, efficiency gains, durum wheat, hard red spring wheat, pool price, organizational structure, operating costs, Marketing,