The Relative Age of the Thin and Thick Galactic Disks

We determine the relative ages of the open cluster NGC 188 and selected Hipparcos field stars by isochrone fitting, and compare them to the age of the thick disk globular cluster 47 Tuc. The best fit age for NGC 188 was determined to be $6.5 \pm 1.0$ Gyr. The solar metallicity Hipparcos field stars yielded a slightly older thin disk age, $7.5 \pm 0.7$ Gyr. Two slightly metal-poor (\feh = -0.22) field stars whose kinematic and orbital parameters indicate that they are members of the thin disk were found to have an age of $9.7\pm 0.6$ Gyr. The age for 47 Tuc was determined to be $12.5 \pm 1.5$ Gyr. All errors are internal errors due to the uncertainty in the values of metallicity and reddening. Thus, the oldest stars dated in the thin disk are found to be $2.8\pm 1.6$ Gyr younger than 47 Tuc. Furthermore, as discussed by \citet{Chb99} 47 Tuc has a similar age to three globular clusters located in the inner part of the Galactic halo, implying that star formation in the thin disk started within $2.8\pm 1.6$ Gyr of star formation in the halo.Comment: 26 pages, 11 figures, to appear in Ap

Early Surgery for Traumatic Spinal Cord Injury: Where Are We Now?

Study Design: Narrative review. Objective: There is a strong biological rationale to perform early decompression after traumatic spinal cord injury (SCI). With an enlarging clinical evidence base, most spine surgeons internationally now favor early decompression for the majority of SCI patients; however, a number of pertinent questions remain surrounding this therapy. Methods: A narrative review evaluating the status of early surgery for SCI. In particular, we addressed the following questions: (1) Which patients stand to benefit most from early surgery? 2) What is the most appropriate time threshold defining early surgery? Results: Although heterogeneity exists, the evidence generally seems to support early surgery. While the best evidence exists for cervical SCI, there is insufficient data to support a differential effect for early surgery depending on neurological level or injury severity. When comparing thresholds to define early versus late surgery-including a later threshold (48-72 hours), an earlier threshold (24 hours), and an ultra-early threshold (8-12 hours)-the 2 earlier time points seem to be associated with the greatest potential for improved outcomes. However, existing prehospital and hospital logistics pose barriers to early surgery in a significant proportion of patients. An overview of recommendations from the recent AOSpine guidelines is provided. Conclusion: In spite of increasing acceptance of early surgery post SCI, further research is needed to (1) identify subgroups of patients who stand to derive particular benefit-in particular to develop more evidence-based approaches for central cord syndrome and (2) investigate the efficacy and feasibility of ultra-early surgery targeting more aggressive timelines

Reply to “Comment on ‘Accurate and fast numerical solution of Poisson\u27s equation for arbitrary, space-filling Voronoi polyhedra: Near-field corrections revisited’ ”

This is a Reply to the Comment by Gonis and Zhang on our recent paper. They discuss supposed issues with our “accurate and fast numerical solution of Poisson’s equation for arbitrary Voronoi polyhedra” (VP)

Darling Harbour conservation and re-use with particular reference to Pyrmont Bridge

Part I of this thesis considers that part of Darling Harbour which lies south of Pyrmont Bridge in the City of Sydney. It traces the history of Darling Harbour from the time of the First Fleet through its development as: (i) a commercial port; (ii) the birthplace of Australian industry; and (iii) the largest railway Goodsyard in the State. Part I studies the present circumstances of the area and its potential. It examines the existing constraints upon the site and assesses the conflicting plans of various Australian, State and Local Government agencies. The question of conservation, or rather, the lack of conservation, is considered. Part II concludes by rejecting the proposal for the extension of longshore wharves south of Pyrmont Bridge and recommends the recycling of the Goodsyard for a major people oriented open space of regional significance together with a certain amount of housing and commercial development. Part II develops a proposal in which conservation is an essential and integral part. Without the retention of key historic structures like Pyrmont Bridge and the Darling Harbour Forwarding Station the proposal could not realise the full potential of Darling Harbour. The rpoposal envisages a Bicentennial waterfront park with a multitude of activities. Certain Government—owned land on the edge of the Goodsyard is earmarked for private development. Conservation includes the retention of Pyrmont Bridge, the Darling Harbour Forwarding Station, and the Corn Exchange and part of a railway shed. The success of the conservation proposals hinge on the construction of a pedestrian bridge link from Pyrmont Bridge to Market Street in the City Centre. Life and finance are injected into the conservation proposals by locating Paddy’s Market on the Bridge and the Sydney Maritime Museum and the Sydney Fishing Museum beneath it. The Museum of Applied Arts and Sciences operates the swing span and operates the "Pyrmont Bridge Stations". This thesis includes a brief statement on a management structure which has insured the conservation of other bridges in NSW, and concludes that conservation, the forgotten element in all current plans, is an essential ingredient for the future of Darling Harbour

Constitutive Extracellular Polysaccharide (EPS) Production by Specific Isolates of Crocosphaera watsonii

Unicellular dinitrogen (N2) fixing cyanobacteria have only recently been identified in the ocean and recognized as important contributors to global N2 fixation. The only cultivated representatives of the open ocean unicellular diazotrophs are multiple isolates of Crocosphaera watsonii. Although constituents of the genus are nearly genetically identical, isolates have been described in two size classes, large ∼5 μm and small ∼3 μm cell diameters. We show here that the large size class constitutively produces substantial amounts of extracellular polysaccharides (EPS) during exponential growth, up to 10 times more than is seen in the small size class, and does so under both N2 fixing and non-N2 fixing conditions. The EPS production exceeds the amount produced by larger phytoplankton such as diatoms and coccolithophores by one to two orders of magnitude, is ∼22% of the total particulate organic C in the culture, and is depleted in N compared to cellular material. The large difference in observed EPS production may be accounted for by consistently higher photochemical efficiency of photosystem II in the large (0.5) vs. small (∼0.35) strains. While it is known that Crocosphaera plays an important role in driving the biological carbon (C) pump through the input of new nitrogen (N) to the open ocean, we hypothesize that this species may also contribute directly to the C cycle through the constitutive production of EPS. Indeed, at two stations in the North Pacific Subtropical Gyre, ∼70% of large Crocosphaera cells observed were embedded in EPS. The evolutionary advantage of releasing such large amounts of fixed C is still unknown, but in regions where Crocosphaera can be abundant (i.e., the warm oligotrophic ocean) this material will likely have important biogeochemical consequences