Biodegradable Luminescent Silicon Quantum Dots for Two Photon Imaging Applications

Cadmium- and lead-based quantum dots are normally coated for biological applications, because their degradation may result in the release of toxic heavy metal ions. Here, we synthesize silicon quantum dots that are expected to biodegrade to non-toxic products. A chitosan coating is used to render the silicon quantum dots stable in storage conditions and biodegradable at physiological conditions. The applications of these particles are demonstrated in cellular imaging with single and two-photon excitation. These results open the door for a new generation of silicon quantum dots that may have a wide variety of applications derived from the flexibility of chitosan

Escherichia coli O157:H7 transcriptome datasets for comparison of RNA-seq and microarray platforms

Whole transcriptome analysis to investigate differential gene expression and regulatory adaption can be carried out on two different technological platforms: by probe hybridisation to microarrays or by RNAseq for deep sequencing. Since there are difference in terms of their genome coverage, sensitivity and cost, there is a requirement for robust comparisons to determine the platform of choice. Here, we present datasets for the whole transcriptional response verocytoxigenic Escherichia coli (VTEC) obtained from RNA-seq and microarray platforms in response to spinach, together with a comparison between the datasets (available at Array Express: E-MTAB-3249, E-MTAB-4120, E-MTAB-7441)

New observations of cool carbon stars in the halo

We report new results of our search for rare, cool carbon stars located at large distances from the galactic plane. Eighteen new C stars were discovered. Six are remarkable by showing the two peculiarities of a strong infrared excess at 12 microns and a large height above the Galactic plane, from 1.7 to 6 kpc. The number of C stars with these properties has been increased to 16. Mass-loss rates were tentatively estimated by assuming that all these 16 stars are Miras and by using the correlation between Mdot and the K-12 colour index. It is found that several stars have large mass loss, with median Mdot around 4E-06 solar mass per year. It would be desirable to detect their CO emission ... Eight stars might be at more than 30 kpc from the Sun, and two at the unprecedented distance of 150 kpc (this abstract has been abridged).Comment: 15 pages; accepted by Astronomy and Astrophysic

The Orbit of the Orphan Stream

We use recent SEGUE spectroscopy and SDSS and SEGUE imaging data to measure the sky position, distance, and radial velocities of stars in the tidal debris stream that is commonly referred to as the "Orphan Stream." We fit orbital parameters to the data, and find a prograde orbit with an apogalacticon, perigalacticon, and eccentricity of 90 kpc, 16.4 kpc and 0.7, respectively. Neither the dwarf galaxy UMa II nor the Complex A gas cloud have velocities consistent with a kinematic association with the Orphan Stream. It is possible that Segue-1 is associated with the Orphan Stream, but no other known Galactic clusters or dwarf galaxies in the Milky Way lie along its orbit. The detected portion of the stream ranges from 19 to 47 kpc from the Sun and is an indicator of the mass interior to these distances. There is a marked increase in the density of Orphan Stream stars near (l,b)=(253,49) deg., which could indicate the presence of the progenitor at the edge of the SDSS data. If this is the progenitor, then the detected portion of the Orphan Stream is a leading tidal tail. We find blue horizontal branch (BHB) stars and F turnoff stars associated with the Orphan Stream. The turnoff color is (g-r)_0=0.22. The BHB stars have a low metallicity of [Fe/H]=-2.1. The orbit is best fit to a halo potential with a halo plus disk mass of about 2.6x10^11 Solar masses, integrated to 60 kpc from the Galactic center. Our best fit is found with a logarithmic halo speed of v_halo=73+/-24 km/s, a disk+bulge mass of M(R< 60 kpc) = 1.3x10^11 Solar masses, and a halo mass of M(R< 60 kpc) = 1.4x10^11 Solar masses. The Orphan Stream is projected to extend to 90 kpc from the Galactic center, and measurements of these distant parts of the stream would be a powerful probe of the mass of the Milky Way (truncated).Comment: 17 Figures, ApJ accepte

‘Manic mums’ and ‘distant dads’? Gendered geographies of care and the journey to school

This is the post-print version of the final paper published in Health & Place. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2011 Elsevier B.V.Research in the geographies of care has identified the central role of mothers in caring for children, although much less explored are the experiences of men who also participate in care. Drawing upon research conducted in the UK with children and their families, this paper contributes to existing debates in the geographies of care by exploring a relatively new space of caring, namely the escort of primary school children to and from school and other settings. The paper explores mothers’ and fathers’ involvement in escorting children, the extent and nature of participation and also how distinct gendered forms of caring practices are established. In doing so, the paper also considers the importance of place and local cultures of parenting which inform these gendered carescapes

Constraining the Milky Way potential with a 6-D phase-space map of the GD-1 stellar stream

The narrow GD-1 stream of stars, spanning 60 deg on the sky at a distance of ~10 kpc from the Sun and ~15 kpc from the Galactic center, is presumed to be debris from a tidally disrupted star cluster that traces out a test-particle orbit in the Milky Way halo. We combine SDSS photometry, USNO-B astrometry, and SDSS and Calar Alto spectroscopy to construct a complete, empirical 6-dimensional phase-space map of the stream. We find that an eccentric orbit in a flattened isothermal potential describes this phase-space map well. Even after marginalizing over the stream orbital parameters and the distance from the Sun to the Galactic center, the orbital fit to GD-1 places strong constraints on the circular velocity at the Sun's radius V_c=224 \pm 13 km/s and total potential flattening q_\Phi=0.87^{+0.07}_{-0.04}. When we drop any informative priors on V_c the GD-1 constraint becomes V_c=221 \pm 18 km/s. Our 6-D map of GD-1 therefore yields the best current constraint on V_c and the only strong constraint on q_\Phi at Galactocentric radii near R~15 kpc. Much, if not all, of the total potential flattening may be attributed to the mass in the stellar disk, so the GD-1 constraints on the flattening of the halo itself are weak: q_{\Phi,halo}>0.89 at 90% confidence. The greatest uncertainty in the 6-D map and the orbital analysis stems from the photometric distances, which will be obviated by Gaia.Comment: 16 pages, 18 figures; accepted to ApJ; full resolution version is available at http://www.ast.cam.ac.uk/~koposov/files/gd1_fullres.pd

Applying scale-free mass estimators to the Local Group in Constrained Local Universe Simulations

We use the recently proposed scale-free mass estimators to determine the masses of the Milky Way (MW) and Andromeda (M31) galaxy in a dark matter only Constrained Local UniversE Simulation (CLUES). While these mass estimators work rather well for isolated spherical host systems, we examine here their applicability to a simulated binary system with a unique satellite population similar to the observed satellites of MW and M31. We confirm that the scale-free estimators work also very well in our simulated Local Group galaxies with the right number of satellites which follow the observed radial distribution. In the isotropic case and under the assumption that the satellites are tracking the total gravitating mass, the power-law index of the radial satellite distribution $N(<r)\propto r^{3-\gamma}$ is directly related to the host's mass profile $M(<r)\propto r^{1-\alpha}$ as $\alpha=\gamma-2$. The use of this relation for any given $\gamma$ leads to highly accurate mass estimations which is a crucial point for observer, since they do not know a priori the mass profile of the MW and M31 haloes. We discuss possible bias in the mass estimators and conclude that the scale-free mass estimators can be satisfactorily applied to the real MW and M31 system.Comment: 14 pages, 6 figures, 6 tables. Accepted in MNRAS 2012 March 29. Received 2012 March 29; in original form 2011 September 2

Tracing Sagittarius Structure with SDSS and SEGUE Imaging and Spectroscopy

We show that the Sagittarius dwarf tidal stream can be traced with very red K/M-giant stars selected from SDSS photometry. A subset of these stars are spectroscopically confirmed with SEGUE and SDSS spectra, and the distance scale of 2MASS and SDSS M giants is calibrated to the RR Lyrae distance scale. The absolute g band magnitude of the K/M-giant stars at the tip of the giant branch is M_g=-1.0. The line-of-sight velocities of the M giant and BHB stars that are spatially coincident with the Sgr dwarf tidal stream are consistent with those of previous authors, reinforcing the need for new models that can explain all of the Sgr tidal debris stream observations. We estimate stellar densities along the tidal tails that can be used to help constrain future models. The K/M-giant, BHB, and F-turnoff stars in the lower surface brightness tidal stream that is adjacent to the main leading Sgr dwarf tidal tail have velocities and metallicities that are similar to those of the stars in the leading tidal tail. The ratio of K/M giants to BHBs and BHBs to F-turnoff stars are also similar for both branches of the leading tidal tail. We show that there is an additional low-metallicity tidal stream near the Sgr trailing tidal tail.Comment: 19 figures, accepted for publication in ApJ, references update