Surfaces, submanifolds, and aligned Fox reimbedding in non-Haken 3-manifolds

Understanding non-Haken 3-manifolds is central to many current endeavors in 3-manifold topology. We describe some results for closed orientable surfaces in non-Haken manifolds, and extend Fox's theorem for submanifolds of the 3-sphere to submanifolds of general non-Haken manifolds. In the case where the submanifold has connected boundary, we show also that the boundary-connected sum decomposition of the submanifold can be aligned with such a structure on the submanifold's complement.Comment: 10 page

SWAS observations of comet 9P/Tempel 1 and Deep Impact

On 4 July 2005 at 1:52 UT the Deep Impact mission successfully completed its goal to hit the nucleus of 9P/Tempel 1 with an impactor, forming a crater on the nucleus and ejecting material into the coma of the comet. The 370 kg impactor collided with the sunlit side of the nucleus with a relative velocity of 10.2 km/s. NASA's Submillimeter Wave Astronomy Satellite (SWAS) observed the 1(10)-1(01) ortho-water ground-state rotational transition in comet 9P/Tempel 1 before, during, and after the impact. No excess emission from the impact was detected by SWAS. However, the water production rate of the comet showed large natural variations of more than a factor of three during the weeks before the impact.Comment: to appear in the proceedings of the IAU Symposium No. 231: "Astrochemistry - Recent Successes and Current Callenges". Typo corrected in author affiliation lis

THE HISTONES ASSOCIATED WITH CONDENSED AND EXTENDED CHROMATIN OF MOUSE LIVER

Histones were extracted from isolated mouse liver nuclei, and from mouse liver condensed and extended chromatin. Mouse liver histones were found to be very similar to those of calf thymus in their solubility properties, relative electrophoretic mobilities, and molecular weights as determined on SDS-polyacrylamide gels. Quantitative analysis by high-resolution gel electrophoresis demonstrated a remarkable similarity between the histones of condensed chromatin and those of extended chromatin. However, minor differences were found. A unique subspecies was found only in condensed chromatin histone and the relative amounts of fractions F2A1 and F2A2 differed in the two types of chromatin. The ratio of the parental to the acetylated form of F2A1 was identical in the two chromatin samples. Since DNA extracted from the condensed chromatin fraction consisted of approximately 50% satellite DNA, the general similarities between the histones of condensed and extended chromatin make it likely that even this simple, highly repetitive DNA is complexed with a number of histone subfractions

The Effect of CodY on stationary phase mutagenesis in Bacillus subtilis

We examine the notion that cells in conditions of stress accumulate mutation is in genes under selection via transcription processes. CodY is a global transcriptional regulator in many Gram positives, including soil and pathogenic microbes. In conditions of exponential growth and when branch chain amino acids and GTP are in abundance CodY acts as a transcriptional repressor of many metabolic operons. This transitional repression saves the cell energy and allows efficient use of resources. In conditions of starvation, CodY relieves repression of genes involved in acquisition of nutrients and degradation of carbon sources (genes under selection). Here, we compare the accumulation of mutations in genes under selection in wild type and CodY

Retrospective Application of Human Reliability Analysis for Oil and Gas Incidents: A Case Study Using the Petro-HRA Method

Human reliability analysis (HRA) may be performed prospectively for a newly designed system or retrospectively for an as-built system, typically in response to a safety incident. The SPAR-H HRA method was originally developed for retrospective analysis in the U.S. nuclear industry. As HRA has found homes in new safety critical areas, HRA methods developed predominantly for nuclear power applications are being used in novel ways. The Petro-HRA method represents a significant adaptation of the SPAR-H method for petroleum applications. Current guidance on Petro-HRA considers only prospective applications of the method, such as for review of new systems to be installed at offshore installations. In this paper, we review retrospective applications of Petro-HRA and analyze the Macando Oil Well-Deepwater Horizon accident as a case study

A Chandra Search for Coronal X Rays from the Cool White Dwarf GD 356

We report observations with the Chandra X-ray Observatory of the single, cool, magnetic white dwarf GD 356. For consistent comparison with other X-ray observations of single white dwarfs, we also re-analyzed archival ROSAT data for GD 356 (GJ 1205), G 99-47 (GR 290 = V1201 Ori), GD 90, G 195-19 (EG250 = GJ 339.1), and WD 2316+123 and archival Chandra data for LHS 1038 (GJ 1004) and GD 358 (V777 Her). Our Chandra observation detected no X rays from GD 356, setting the most restrictive upper limit to the X-ray luminosity from any cool white dwarf -- L_{X} < 6.0 x 10^{25} ergs/s, at 99.7% confidence, for a 1-keV thermal-bremsstrahlung spectrum. The corresponding limit to the electron density is n_{0} < 4.4 x 10^{11} cm^{-3}. Our re-analysis of the archival data confirmed the non-detections reported by the original investigators. We discuss the implications of our and prior observations on models for coronal emission from white dwarfs. For magnetic white dwarfs, we emphasize the more stringent constraints imposed by cyclotron radiation. In addition, we describe (in an appendix) a statistical methodology for detecting a source and for constraining the strength of a source, which applies even when the number of source or background events is small.Comment: 27 pages, 4 figures, submitted to the Astrophysical Journa

Chandra Phase-Resolved Spectroscopy of the Crab Pulsar

We present the first phase-resolved study of the X-ray spectral properties of the Crab Pulsar that covers all pulse phases. The superb angular resolution of the Chandra X-ray Observatory enables distinguishing the pulsar from the surrounding nebulosity, even at pulse minimum. Analysis of the pulse-averaged spectrum measures interstellar X-ray extinction due primarily to photoelectric absorption and secondarily to scattering by dust grains in the direction of the Crab Nebula. We confirm previous findings that the line-of-sight to the Crab is underabundant in oxygen, although more-so than recently measured. Using the abundances and cross sections from Wilms, Allen & McCray (2000) we find [O/H] = (3.33 +/-0.25) x 10**-4. Analysis of the spectrum as a function of pulse phase measures the low-energy X-ray spectral index even at pulse minimum -- albeit with large statistical uncertainty -- and we find marginal evidence for variations of the spectral index. The data are also used to set a new (3-sigma) upper limit to the temperature of the neutron star of log T(infinity) < 6.30.Comment: 20 Pages including 7 figures. Accepted for publication in the Astrophysical Journa

Feasibility of state of the art PET/CT systems performance harmonisation

Purpose The objective of this study was to explore the feasibility of harmonising performance for PET/CT systems equipped with time-of-flight (ToF) and resolution modelling/point spread function (PSF) technologies. A second aim was producing a working prototype of new harmonising criteria with higher contrast recoveries than current EARL standards using various SUV metrics. Methods Four PET/CT systems with both ToF and PSF capabilities from three major vendors were used to acquire and reconstruct images of the NEMA NU2-2007 body phantom filled conforming EANM EARL guidelines. A total of 15 reconstruction parameter sets of varying pixel size, post filtering and reconstruction type, with three different acquisition durations were used to compare the quantitative performance of the systems. A target range for recovery curves was established such that it would accommodate the highest matching recoveries from all investigated systems. These updated criteria were validated on 18 additional scanners from 16 sites in order to demonstrate the scanners' ability to meet the new target range. Results Each of the four systems was found to be capable of producing harmonising reconstructions with similar recovery curves. The five reconstruction parameter sets producing harmonising results significantly increased SUVmean (25%) and SUVmax (26%) contrast recoveries compared with current EARL specifications. Additional prospective validation performed on 18 scanners from 16 EARL accredited sites demonstrated the feasibility of updated harmonising specifications. SUVpeak was found to significantly reduce the variability in quantitative results while producing lower recoveries in smaller ( Conclusions Harmonising PET/CT systems with ToF and PSF technologies from different vendors was found to be feasible. The harmonisation of such systems would require an update to the current multicentre accreditation program EARL in order to accommodate higher recoveries. SUVpeak should be further investigated as a noise resistant alternative quantitative metric to SUVmax

User observations on information sharing (corporate knowledge and lessons learned)

The sharing of 'corporate knowledge' and lessons learned in the NASA aerospace community has been identified by Johnson Space Center survey participants as a desirable tool. The concept of the program is based on creating a user friendly information system that will allow engineers, scientists, and managers at all working levels to share their information and experiences with other users irrespective of location or organization. The survey addresses potential end uses for such a system and offers some guidance on the development of subsequent processes to ensure the integrity of the information shared. This system concept will promote sharing of information between NASA centers, between NASA and its contractors, between NASA and other government agencies, and perhaps between NASA and institutions of higher learning