5,064 research outputs found

    The Radio Emission from the Ultra-Luminous Far-Infrared Galaxy NGC 6240

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    We present new radio observations of the ``prototypical'' ultra-luminous far- infrared galaxy NGC~6240, obtained using the VLA at 20~cm in `B' configuration and at 3.6~cm in `A' configuration. These data, along with those from four previous VLA observations, are used to perform a comprehensive study of the radio emission from NGC~6240. Approximately 70\% (~3 x 1023^{23} W~Hzβˆ’1^{-1}) of the total radio power at 20 cm originates from the nuclear region ( <~ 1.5 kpc), of which half is emitted by two unresolved (R<Β 36pc)coresandhalfbyadiffusecomponent.Theradiospectrumofthenuclearemissionisrelativelyflat(R <~ 36 pc) cores and half by a diffuse component. The radio spectrum of the nuclear emission is relatively flat (\alpha=Β 0.6; =~ 0.6; S_{\nu} \propto \nu^{-\alpha}). The supernova rate required to power the diffuse component is consistent with that predicted by the stellar evolution models of Rieke \etal (1985). If the radio emission from the two compact cores is powered by supernova remnants, then either the remnants overlap and form hot bubbles in the cores, or they are very young ( <~ 100 yr). Nearly all of the other 30\% of the total radio power comes from an ``arm-like'' region extending westward from the nuclear region. The western arm emission has a steep spectrum (\alpha=Β 1.0),suggestiveofagingeffectsfromsynchrotronorinverseβˆ’Comptonlosses,andisnotcorrelatedwithstarlight;wesuggestthatitissynchrotronemissionfromashellofmaterialdrivenbyagalacticsuperwind.Inverseβˆ’Comptonscatteringoffarβˆ’infraredphotonsintheradiosourcesisexpectedtoproduceanXβˆ’rayfluxofΒ 2βˆ’6x10 =~ 1.0), suggestive of aging effects from synchrotron or inverse-Compton losses, and is not correlated with starlight; we suggest that it is synchrotron emission from a shell of material driven by a galactic superwind. Inverse-Compton scattering of far-infrared photons in the radio sources is expected to produce an X-ray flux of ~2-6 x 10^{-14}$ erg/s/cm2 in the 2-10 keV band. No significant radio emission is detected from or near the possible ultra-massive ``dark core'' hypothesized by Bland-Hawthorn, Wilson \& Tully (1991).Comment: 36 pages (text and tables) as an uuencoded compressed postscript file (figures available upon request), accepted for the ApJ (20 Nov issue), STScI preprint no. ?? -- May 199

    Effect of silver content on the structure and antibacterial activity of silver-doped phosphate-based glasses

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    Staphylococcus aureus can cause a range of diseases, such as osteomyelitis, as well as colonize implanted medical devices. In most instances the organism forms biofilms that not only are resistant to the body's defense mechanisms but also display decreased susceptibilities to antibiotics. In the present study, we have examined the effect of increasing silver contents in phosphate-based glasses to prevent the formation of S. aureus biofilms. Silver was found to be an effective bactericidal agent against S. aureus biofilms, and the rate of silver ion release (0.42 to 1.22 Β΅gΒ·mm–2Β·h–1) from phosphate-based glass was found to account for the variation in its bactericidal effect. Analysis of biofilms by confocal microscopy indicated that they consisted of an upper layer of viable bacteria together with a layer (20 Β΅m) of nonviable cells on the glass surface. Our results showed that regardless of the silver contents in these glasses (10, 15, or 20 mol%) the silver exists in its +1 oxidation state, which is known to be a highly effective bactericidal agent compared to that of silver in other oxidation states (+2 or +3). Analysis of the glasses by 31P nuclear magnetic resonance imaging and high-energy X-ray diffraction showed that it is the structural rearrangement of the phosphate network that is responsible for the variation in silver ion release and the associated bactericidal effectiveness. Thus, an understanding of the glass structure is important in interpreting the in vitro data and also has important clinical implications for the potential use of the phosphate-based glasses in orthopedic applications to deliver silver ions to combat S. aureus biofilm infections

    Randomized controlled trials in adult traumatic brain injury: A systematic review on the use and reporting of clinical outcome assessments

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    As part of efforts to improve study design, the use of outcome measures in randomized controlled trials (RCTs) in traumatic brain injury (TBI) is receiving increasing attention. This review aimed to assess how clinical outcome assessments (COAs) have been used and reported in RCTs in adult TBI. Systematic literature searches were conducted to identify medium to large (n β‰₯ 100) acute and post-acute TBI trials published since 2000. Data were extracted independently by two reviewers using a set of structured templates. Items from the Consolidated Standards of Reporting Trials (CONSORT) 2010 Statement and CONSORT patient-reported outcomes (PRO) extension were used to evaluate reporting quality of COAs. Glasgow Outcome Scale/Extended (GOS/GOSE) data were extracted using a checklist developed specifically for the review. A total of 126 separate COAs were identified in 58 studies. The findings demonstrate heterogeneity in the use of TBI outcomes, limiting comparisons and meta-analyses of RCT findings. The GOS/GOSE was included in 39 studies, but implemented in a variety of ways, which may not be equivalent. Multidimensional outcomes were used in 30 studies, and these were relatively more common in rehabilitation settings. The use of PROs was limited, especially in acute study settings. Quality of reporting was variable, and key information concerning COAs was often omitted, making it difficult to know how precisely outcomes were assessed. Consistency across studies would be increased and future meta-analyses facilitated by (a) using common data elements recommendations for TBI outcomes and (b) following CONSORT guidelines when publishing RCTs

    Right to Serve, Right to Lead: Lives and Legacies of the USCT

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    This is a catalog for an exhibit that follows the evolution of African-American participation in the Civil War, from slaves, to contrabands, to soldiers of the United States Colored Troops (USCT), as well as the lives of black veterans beyond the war, and their ultimate military and social legacy. Using a variety of period items, it creates a narrative that stretches from the Antebellum Period to the current day. In doing so, the exhibit shows how black sacrifice on the battlefield redefined the war\u27s purpose throughout the divided nation, how Jim Crowe suppressed the memory of black participation after Reconstruction, and how the illustrious African-American military tradition left by the USCT endures to this day in their modern heirs

    Photodissociation of Non-Covalent Peptide-Crown Ether Complexes

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    Highly chromogenic 18-crown-6-dipyrrolylquinoxaline coordinates primary amines of peptides, forming non-covalent complexes that can be transferred to the gas-phase by electrospray ionization. The appended chromogenic crown ether facilitates efficient energy transfer to the peptide upon ultraviolet irradiation in the gas phase, resulting in diagnostic peptide fragmentation. Collisional-activated dissociation and infrared multiphoton dissociation of these non-covalent complexes result only in their disassembly with the charge retained on either the peptide or crown ether, yielding no sequence ions. Upon UV photon absorption the intermolecular energy transfer is facilitated by the fast activation timescale of ultraviolet photodissociation (<10 ns) and by the collectively strong hydrogen bonding between the crown ether and peptide, thus allowing effective transfer of energy to the peptide moiety before disruption of the intermolecular hydrogen bonds

    Grid cells on steeply sloping terrain: evidence for planar rather than volumetric encoding

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    Neural encoding of navigable space involves a network of structures centred on the hippocampus, whose neurons –place cells – encode current location. Input to the place cells includes afferents from the entorhinal cortex, which contains grid cells. These are neurons expressing spatially localised activity patches, or firing fields, that are evenly spaced across the floor in a hexagonal close-packed array called a grid. It is thought that grid cell grids function to enable the calculation of distances. The question arises as to whether this odometry process operates in three dimensions, and so we queried whether grids permeate three-dimensional space – that is, form a lattice – or whether they simply follow the environment surface. If grids form a three-dimensional lattice then a tilted floor should transect several layers of this lattice, resulting in interruption of the hexagonal pattern. We model this prediction with simulated grid lattices and show that on a 40-degree slope the firing of a grid cell should cover proportionally less of the surface, with smaller field size and fewer fields and reduced hexagonal symmetry. However, recording of grid cells as animals foraged on a 40-degree-tilted surface found that firing of grid cells was almost indistinguishable, in pattern or rate, from that on the horizontal surface, with if anything increased coverage and field number, and preserved field size. It thus appears unlikely that the sloping surface transected a lattice. However, grid cells on the slope displayed slightly degraded firing patterns, with reduced coherence and slightly reduced symmetry. These findings collectively suggest that the grid cell component of the metric representation of space is not fixed in absolute three-dimensional space but is influenced both by the surface the animal is on and by the relationship of this surface to the horizontal, supporting the hypothesis that the neural map of space is multi-planar rather than fully volumetric
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