Response of a marine-terminating Greenland outlet glacier to abrupt cooling 8200 and 9300 years ago

Long-term records of Greenland outlet-glacier change extending beyond the satellite era can inform future predictions of Greenland Ice Sheet behavior. Of particular relevance is elucidating the Greenland Ice Sheet's response to decadal- and centennial-scale climate change. Here, we reconstruct the early Holocene history of Jakobshavn Isbræ, Greenland's largest outlet glacier, using 10Be surface exposure ages and 14C-dated lake sediments. Our chronology of ice-margin change demonstrates that Jakobshavn Isbræ advanced to deposit moraines in response to abrupt cooling recorded in central Greenland ice cores ca. 8,200 and 9,300 years ago. While the rapid, dynamically aided retreat of many Greenland outlet glaciers in response to warming is well documented, these results indicate that marine-terminating outlet glaciers are also able to respond quickly to cooling. We suggest that short lag times of high ice flux margins enable a greater magnitude response of marine-terminating outlets to abrupt climate change compared to their land-terminating counterparts

Earliest Holocene south Greenland ice sheet retreat within its late Holocene extent

Early Holocene summer warmth drove dramatic Greenland ice sheet (GIS) retreat. Subsequent insolation-driven cooling caused GIS margin readvance to late Holocene maxima, from which ice margins are now retreating. We use 10Be surface exposure ages from four locations between 69.4°N and 61.2°N to date when in the early Holocene south to west GIS margins retreated to within these late Holocene maximum extents. We find that this occurred at 11.1 ± 0.2 ka to 10.6 ± 0.5 ka in south Greenland, significantly earlier than previous estimates, and 6.8 ± 0.1 ka to 7.9 ± 0.1 ka in southwest to west Greenland, consistent with existing 10Be ages. At least in south Greenland, these 10Be ages likely provide a minimum constraint for when on a multicentury timescale summer temperatures after the last deglaciation warmed above late Holocene temperatures in the early Holocene. Current south Greenland ice margin retreat suggests that south Greenland may have now warmed to or above earliest Holocene summer temperatures

Ultraviolet Imaging of the Globular Cluster 47 Tucanae

We have used the Ultraviolet Imaging Telescope to obtain deep far-UV (1620 Angstrom), 40' diameter images of the prototypical metal-rich globular cluster 47 Tucanae. We find a population of about 20 hot (Teff > 9000 K) objects near or above the predicted UV luminosity of the hot horizontal branch (HB) and lying within two half-light radii of the cluster center. We believe these are normal hot HB or post-HB objects rather than interacting binaries or blue stragglers. IUE spectra of two are consistent with post-HB phases. These observations, and recent HST photometry of two other metal-rich clusters, demonstrate that populations with rich, cool HB's can nonetheless produce hot HB and post-HB stars. The cluster center also contains an unusual diffuse far-UV source which is more extended than its V-band light. It is possible that this is associated with an intracluster medium, for which there was earlier infrared and X-ray evidence, and is produced by C IV emission or scattered light from grains.Comment: 13 pages AASLaTeX including one postscript figure and one bitmapped image, JPEG format. Submitted to the Astronomical Jorunal. Full Postscript version available at http://www.astro.virginia.edu/~bd4r

UIT Detection of Hot Stars in the Globular Cluster NGC362

We used the Ultraviolet Imaging Telescope during the March 1995 Astro-2 mission to obtain a deep far-UV image of the globular cluster NGC 362, which was formerly thought to have an almost entirely red horizontal branch (HB). 84 hot (T_eff > 8500 K) stars were detected within a radius of 8'.25 of the cluster center. Of these, 43 have FUV magnitudes consistent with HB stars in NGC 362, and at least 34 are cluster members. The number of cluster members is made uncertain by background contamination from blue stars in the Small Magellanic Cloud (SMC). There are six candidate supra-HB stars which have probably evolved from the HB. We discuss the implications of these results for the production of hot blue stars in stellar populations.Comment: 10 pages AASLaTeX including one postscript figure and one compressed bitmap, .jpg format. To appear in Ap. J. Letters. Postscript version also available at http://www.astro.virginia.edu/~bd4r

Geological structure of the Sylmar basin: implications for slip distribution along the Santa Susana/hospital and mission hills fault system in the San Fernando Valley, CA, USA

We developed a forward model using the Trishear module in MOVE to better understand the structure of the northwestern San Fernando Valley and the relationship among the Santa Susana, Hospital, Mission Hills and Northridge Hills faults. This study was motivated by the 1971 San Fernando earthquake and previous work that inferred a high slip rate on the Santa Susana fault, which is in apparent contrast to the lack of significant geomorphic expression of the fault in the Sylmar Basin region. We trenched the Mission Hills anticline from the crest to the base of slope and demonstrate that the Mission Hills anticline is an actively growing fault propagation fold. The associated thrust tip is either deeper than 15 m or sufficiently far to the south that the fault was not encountered in large diameter borings, but the minimum structural relief across the Mission Hills fault since the late Pleistocene is on the order of 37 m, suggesting a minimum uplift rate of 0.5 mm/yr. Our work presents a structural analysis that demonstrates how the Santa Susana fault system evolved in time, with the frontal thrust progressively migrating southward to the Mission Hills fault, and farther south to the Northridge Hills blind thrust. The progression of faulting towards the direction of vergence is compatible with the observed thrust front migration in the western Transverse Ranges of California, and other trust belts around the world

Microwave background anisotropies and non-linear structures II. Numerical computations

A new method for modelling spherically symmetric inhomogeneities is applied to the formation of clusters in an expanding Universe. We impose simple initial velocity and density perturbations of finite extent and we investigate the subsequent evolution of the density field. Photon paths are also calculated, allowing a detailed consideration of gravitational lensing effects and microwave background anisotropies induced by the cluster. We apply the method to modelling high-redshift clusters and, in particular, we consider the reported microwave decrement observed towards the quasar pair PC1643+4631 A&B. We also consider the effect on the primordial microwave background power spectrum due to gravitational lensing by a population of massive high-redshift clusters.Comment: 15 pages, 23 figures; Monthly Notices of the Royal Astronomical Society (MNRAS), in pres

Radio Recombination Lines in Galactic HII Regions

We report radio recombination line (RRL) and continuum observations of a sample of 106 Galactic HII regions made with the NRAO 140 Foot radio telescope in Green Bank, WV. We believe this to be the most sensitive RRL survey ever made for a sample this large. Most of our source integration times range between 6 and 90 hours which yield typical r.m.s. noise levels of 1.0--3.5 milliKelvins. Our data result from two different experiments performed, calibrated, and analyzed in similar ways. A CII survey was made at 3.5 cm wavelength to obtain accurate measurements of carbon radio recombination lines. When combined with atomic (CI) and molecular (CO) data, these measurements will constrain the composition, structure, kinematics, and physical properties of the photodissociation regions that lie on the edges of HII regions. A second survey was made at 3.5 cm wavelength to determine the abundance of 3He in the interstellar medium of the Milky Way. Together with measurements of the 3He+ hyperfine line we get high precision RRL parameters for H, 4He, and C. Here we discuss significant improvements in these data, with both longer integrations and newly observed sources.Comment: LaTeX, 50 pages with 11 figures. Accepted for publication in The Astrophysical Journal Supplement Serie

Higher diagnostic accuracy and cost-effectiveness using procalcitonin in the treatment of emergency medicine patients with fever (The HiTEMP study)

__Background:__ Fever is a common symptom in the emergency department(ED). Fever can be caused by bacterial infections, which are treated with antibiotics. Often, bacterial infections cannot be ruled out in the ED using standard diagnostics, and empiric antibiotic treatment is started. Procalcitonin(PCT) is a biomarker for bacterial infections, but its role in an undifferentiated ED population remains unclear. We hypothesize that PCT-guided therapy may reduce antibiotics prescription in undifferentiated febrile ED patients. The primary objectives of this study are to determine a) the efficacy, b) the safety of PCT-guided therapy, and c) the accuracy of the biomarker PCT for bacterial infections. The secondary objective is to study the cost-effectiveness of PCT-guided therapy. __Methods/design:__ This is a multicenter noninferiority randomized controlled trial. All adult ED patients with fever(≥38.2 °C) are randomized between standard care with and without the addition of a PCT level, after written informed consent. a) For efficacy, the reduction of patients receiving antibiotics is calculated, using a superiority analysis: differences between the PCT-guided group and control group are assessed using a Fisher's exact test, and a multivariable logistic regression analysis to account for the effects of demographic and medical variables on the percentage of febrile patients receiving antibiotics. b) Safety consists of a composite endpoint, defined as mortality, intensive care admission and ED return visit within 14 days. Noninferiority of PCT will be tested using a one-sided 95 % confidence interval for the difference in the composite safety endpoint between the PCT-guided and control groups using a noninferiority margin of 7.5 %. c) Accuracy of PCT and CRP for the diagnosis of bacterial infections will be reported, using the sensitivity, specificity, and the area under the receiver-operating-characteristic curve in the definitive diagnosis of bacterial infections. The sample size is 550 patients, which was calculated using a power analysis for all primary objectives. Enrollment of patients started in August 2014 and will last 2 years. __Discussion:__ PCT may offer a more tailor-made treatment to the individual ED patient with fever. Prospective costs analyses will reveal the economic consequences of implementing PCT-guided therapy in the ED. This trial is registered in the Dutch trial register:NTR4949