2,420 research outputs found
Passive Evolution: Are the Faint Blue Galaxy Counts Produced by a Population of Eternally Young Galaxies?
A constant age population of blue galaxies, postulated in the model of
Gronwall & Koo (1995), seems to provide an attractive explanation of the excess
of very blue galaxies in the deep galaxy counts. Such a population may be
generated by a set of galaxies with cycling star formation rates, or at the
other extreme, be maintained by the continual formation of new galaxies which
fade after they reach the age specified in the Gronwall and Koo model. For both
of these hypotheses, we have calculated the luminosity functions including the
respective selection criteria, the redshift distributions, and the number
counts in the B_J and K bands. We find a substantial excess in the number of
galaxies at low redshift (0 < z < 0.05) over that observed in the CFH redshift
survey (Lilly et al. 1995) and at the faint end of the Las Campanas luminosity
function (Lin et al. 1996). Passive or mild evolution fails to account for the
deep galaxy counts because of the implications for low redshift determinations
of the I-selected redshift distribution and the r-selected luminosity function
in samples where the faded counterparts of the star-forming galaxies would be
detectable.Comment: 11 pages, LaTeX type (aaspp4.sty), 3 Postscript figures, submitted to
ApJ Letter
Chronic Idiopathic Thrombocytopenic Purpura: Effective preoperative preparation and long-term results of splenectomy
A retrospective review of 98 patients seen at Henry Ford Hospital from 1953 through 1977 demonstrated that splenectomy for chronic idiopathic thrombocytopenic purpura provided a good response which usually was sustained on long-term follow-up (72% at 15 years). Although splenectomy for this condition had a low mortality, morbidity was significant in patients older than 40 years. When compared to patients whose response to splenectomy was sustained, patients who relapsed had significantly lower platelet counts preoperatively both when they were untreated (mean: 9,194 per cc versus 18,524 per-cc) and/or when they were treated with steroids (mean: 85,647 per cc versus 142,590 per cc). Another significant risk factor for relapse was a longer interval from splenectomy to the maximum postoperative platelet count. In the immediate preoperative preparation of the patient for splenectomy, corticosteroids temporarily increased the platelet count, but high doses were necessary in many patients. A platelet count of greater than 40,000/cc usually was achieved with a dose of 60 to 80 mgs of prednisone per day for several days. Platelet infusion rarely was needed if patients were prepared adequately with steroids. There should be no hesitation to give large doses of steroids for a few days, and a delay in proceeding with the operation, once indicated, should be avoided. Because the response of the platelet count to splenectomy may be variable or fluctuating and late relapses can occur, patients should be re-evaluated periodically
Quantifying Variation across 16S rRNA Gene Sequencing Runs in Human Microbiome Studies
Recent microbiome research has incorporated a higher number of samples through more participants in a study, longitudinal studies, and metanalysis between studies. Physical limitations in a sequencing machine can result in samples spread across sequencing runs. Here we present the results of sequencing nearly 1000 16S rRNA gene sequences in fecal (stabilized and swab) and oral (swab) samples from multiple human microbiome studies and positive controls that were conducted with identical standard operating procedures. Sequencing was performed in the same center across 18 different runs. The simplified mock community showed limitations in accuracy, while precision (e.g., technical variation) was robust for the mock community and actual human positive control samples. Technical variation was the lowest for stabilized fecal samples, followed by fecal swab samples, and then oral swab samples. The order of technical variation stability was inverse of DNA concentrations (e.g., highest in stabilized fecal samples), highlighting the importance of DNA concentration in reproducibility and urging caution when analyzing low biomass samples. Coefficients of variation at the genus level also followed the same trend for lower variation with higher DNA concentrations. Technical variation across both sample types and the two human sampling locations was significantly less than the observed biological variation. Overall, this research providing comparisons between technical and biological variation, highlights the importance of using positive controls, and provides semi-quantified data to better understand variation introduced by sequencing runs
Cloning Hubble Deep Fields I: A Model-Independent Measurement of Galaxy Evolution
We present a model-independent method of quantifying galaxy evolution in
high-resolution images, which we apply to the Hubble Deep Field (HDF). Our
procedure is to k-correct all pixels belonging to the images of a complete set
of bright galaxies and then to replicate each galaxy image to higher redshift
by the product of its space density, 1/V_{max}, and the cosmological volume.
The set of bright galaxies is itself selected from the HDF, because presently
the HDF provides the highest quality UV images of a redshift-complete sample of
galaxies (31 galaxies with I<21.9, \bar{z}=0.5, and for which V/V_{max} is
spread fairly). These galaxies are bright enough to permit accurate
pixel-by-pixel k-corrections into the restframe UV (\sim 2000 A). We match the
shot noise, spatial sampling and PSF smoothing of the HDF data, resulting in
entirely empirical and parameter-free ``no-evolution'' deep fields of galaxies
for direct comparison with the HDF. In addition, the overcounting rate and the
level of incompleteness can be accurately quantified by this procedure. We
obtain the following results. Faint HDF galaxies (I>24) are much smaller, more
numerous, and less regular than our ``no-evolution'' extrapolation, for any
interesting geometry. A higher proportion of HDF galaxies ``dropout'' in both U
and B, indicating that some galaxies were brighter at higher redshifts than our
``cloned'' z\sim0.5 population.Comment: 51 pages, 23 figures, replacement includes figures not previously
include
The erythromycin breath test as a predictor of cyclosporine blood levels
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109915/1/cptclpt1990126.pd
Mirror Images of String Cosmologies
A discrete symmetry of the four-dimensional string effective action is
employed to derive spatially homogeneous and inhomogeneous string cosmologies
from vacuum solutions of general relativity that admit two commuting spacelike
Killing vectors. In particular, a tilted Bianchi type V cosmology is generated
from a vacuum type VI_h solution and a plane wave solution with a bounded and
oscillating dilaton field is found from a type model. Further
applications are briefly discussed.Comment: 10 pages plain late
LESSONS FROM THE MOTORIZED MIGRATIONS
Ten experiments have been conducted to determine if cranes can be led on migration and if those so trained will repeat migrations on their own. Results have been mixed as we have experienced the mishaps common to pilot studies. Nevertheless, we have learned many valuable lessons. Chief among these are that cranes can be led long distances behind motorized craft (air and ground), and those led over most or the entire route will return north come spring and south in fall to and from the general area of training. However, they will follow their own route. Groups transported south and flown at intervals along the route will migrate but often miss target termini. If certain protocol restrictions are followed, it is possible to make the trained cranes wild, however, the most practical way of so doing is to introduce them into a flock of wild cranes. We project that it is possible to create or restore wild migratory flocks of cranes by first leading small groups from chosen northern to southern termini
Cardiogenic shock complicating acute myocardial infarction: The use of coronary angioplasty and the integration of the new support devices into patient management
Conventional therapy for cardiogenic shock complicating acute myocardial infarction continues to be associated with a high in-hospital mortality rate. Hemodynamic support with new mechanical devices and emergency coronary revascularization may alter the long-term prognosis for patients with this complication. Between July 1985 and March 1990, 68 patients presented to the University of Michigan with acute myocardial infarction and cardiogenic shock. Interventions performed included thrombolytic therapy (46%), intraaortic balloon pump counterpulsation (70%), cardiac catheterization (86%), coronary angioplasty (73%), emergency coronary artery bypass grafting/ventricular septal defect repair (15%), Hemopump insertion (11%), percutaneous cardiopulmonary support (4%) and ventricular assist device (3%).The 30-day survival rate was significantly better in patients who had successful angioplasty of the infarct-related artery than in patients with failed angioplasty (61% vs. 7%, p = 0.002) or no attempt at angioplasty (61% vs. 14%, p = 0.003). This difference was maintained over the 1-year follow-up period. The only clinical variable that predicted survival was age <65 years.The early use of the new support devices in 10 patients was associated with death in 8 (80%), but this poor outcome may reflect a selection bias for an especially high risk population. Collectively, these recent data continue to suggest that emergency revascularization with angioplasty may reduce the mortality rate, but further study is required to define optimal utilization and integration of new support devices
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