260 research outputs found
Suicide inhibition of alpha-oxamine synthases:structures of the covalent adducts of 8-amino-7-oxononanoate synthase with trifluoroalanine
The suicide inhibition of the α-oxamine synthases by the substrate analog, L-trifluoroalanine was investigated. The inhibition resulted in the formation of a complex with loss of all three fluorine atoms. Decarboxylation and loss of fluoride occurred immediately after aldimine formation. The inherent flexibility could allow the difluorinated intermediate complex to adopt a suitable conformation. Decarboxylation in the normal mechanism occurs after formation of the ketoacid intermediate.link_to_subscribed_fulltex
Low-Tech Riparian and Wet Meadow Restoration Increases Vegetation Productivity and Resilience Across Semiarid Rangelands
Restoration of riparian and wet meadow ecosystems in semiarid rangelands of the western United States is a high priority given their ecological and hydrological importance in the region. However, traditional restoration approaches are often intensive and costly, limiting the extent over which they can be applied. Practitioners are increasingly trying new restoration techniques that are more costâeffective, less intensive, and can more practically scale up to the scope of degradation. Unfortunately, practitioners typically lack resources to undertake outcomeâbased evaluations necessary to judge the efficacy of these techniques. In this study, we use freely available, satellite remote sensing to explore changes in vegetation productivity (normalized difference vegetation index) of three distinct, lowâtech, riparian and wet meadow restoration projects. Case studies are presented that range in geographic location (Colorado, Oregon, and Nevada), restoration practice (Zeedyk structures, beaver dam analogs, and grazing management), and time since implementation. Restoration practices resulted in increased vegetation productivity of up to 25% and increased annual persistence of productive vegetation. Improvements in productivity with time since restoration suggest that elevated resilience may further enhance wildlife habitat and increase forage production. Longâterm, documented outcomes of conservation are rare; we hope our findings empower practitioners to further monitor and explore the use of lowâtech methods for restoration of ecohydrologic processes at meaningful spatial scales
Optical and Near-Infrared Observations of the Highly Reddened, Rapidly Expanding Type Ia Supernova 2006X in M100
We present extensive optical (UBVRI), near-infrared (JK) light curves and
optical spectroscopy of the Type Ia supernova (SN) 2006X in the nearby galaxy
NGC 4321 (M100). Our observations suggest that either SN 2006X has an
intrinsically peculiar color evolution, or it is highly reddened [E(B -
V)_{host} = 1.42+/-0.04 mag] with R_V = 1.48+/-0.06, much lower than the
canonical value of 3.1 for the average Galactic dust. SN 2006X also has one of
the highest expansion velocities ever published for a SN Ia. Compared with the
other SNe Ia we analyzed, SN 2006X has a broader light curve in the U band, a
more prominent bump/shoulder feature in the V and R bands, a more pronounced
secondary maximum in the I and near-infrared bands, and a remarkably smaller
late-time decline rate in the B band. The B - V color evolution shows an
obvious deviation from the Lira-Phillips relation at 1 to 3 months after
maximum brightness. At early times, optical spectra of SN 2006X displayed
strong, high-velocity features of both intermediate-mass elements (Si, Ca, and
S) and iron-peak elements, while at late times they showed a relatively blue
continuum, consistent with the blue U-B and B-V colors at similar epochs. A
light echo and/or the interaction of the SN ejecta and its circumstellar
material may provide a plausible explanation for its late-time photometric and
spectroscopic behavior. Using the Cepheid distance of M100, we derive a Hubble
constant of 72.7+/-8.2 km s^{-1} Mpc^{-1}(statistical) from the normalized
dereddened luminosity of SN 2006X. We briefly discuss whether abnormal dust is
a universal signature for all SNe Ia, and whether the most rapidly expanding
objects form a subclass with distinct photometric and spectroscopic properties.Comment: 48 pages, 20 figures and 11 tables. Accepted Version (ApJ, 2008,
March issue
Star Formation at From the Spitzer Large Area Survey with Hyper-Suprime-Cam (SPLASH)
Using the first 50% of data collected for the Spitzer Large Area Survey with
Hyper-Suprime-Cam (SPLASH) observations on the 1.8 deg Cosmological
Evolution Survey (COSMOS) we estimate the masses and star formation rates of
3398 star-forming galaxies at with a
substantial population up to . We find that the
strong correlation between stellar mass and star formation rate seen at lower
redshift (the "main sequence" of star-forming galaxies) extends to .
The observed relation and scatter is consistent with a continued increase in
star formation rate at fixed mass in line with extrapolations from
lower-redshift observations. It is difficult to explain this continued
correlation, especially for the most massive systems, unless the most massive
galaxies are forming stars near their Eddington-limited rate from their first
collapse. Furthermore, we find no evidence for moderate quenching at higher
masses, indicating quenching either has not occurred prior to or
else occurs rapidly, so that few galaxies are visible in transition between
star-forming and quenched.Comment: ApJL, accepte
Crimmigration and Refugees: Bridging Visas, Criminal Cancellations and âLiving in the Communityâ as Punishment and Deterrence
Australiaâs status as the only state with a policy of mandatory indefinite detention of all unlawful non-citizens, including asylum seekers, who are within Australian territory is a fact that is both well-known and frequently cited. From its inception, mandatory immigration detention was touted as âthe method of deterrence for those seeking asylum onshoreâ and since then âmandatory detention has been at the forefront of a deterrence as control and control as deterrence discourseâ2. The imagined subjects of deterrence are frequently asylum seekers presented as âbogusâ or as economic migrants, and the sites for control are Australiaâs âimmigration programâ and borders. While these dual factors have animated the implementation and continuation of the policy for over 25 years, the contemporary practice and enforcement of detention in Australia presents a much more complex picture
The Lick AGN Monitoring Project: Reverberation Mapping of Optical Hydrogen and Helium Recombination Lines
We have recently completed a 64-night spectroscopic monitoring campaign at
the Lick Observatory 3-m Shane telescope with the aim of measuring the masses
of the black holes in 12 nearby (z < 0.05) Seyfert 1 galaxies with expected
masses in the range ~10^6-10^7M_sun and also the well-studied nearby active
galactic nucleus (AGN) NGC 5548. Nine of the objects in the sample (including
NGC 5548) showed optical variability of sufficient strength during the
monitoring campaign to allow for a time lag to be measured between the
continuum fluctuations and the response to these fluctuations in the broad
Hbeta emission, which we have previously reported. We present here the light
curves for the Halpha, Hgamma, HeII 4686, and HeI 5876 emission lines and the
time lags for the emission-line responses relative to changes in the continuum
flux. Combining each emission-line time lag with the measured width of the line
in the variable part of the spectrum, we determine a virial mass of the central
supermassive black hole from several independent emission lines. We find that
the masses are generally consistent within the uncertainties. The time-lag
response as a function of velocity across the Balmer line profiles is examined
for six of the AGNs. Finally we compare several trends seen in the dataset
against the predictions from photoionization calculations as presented by
Korista & Goad. We confirm several of their predictions, including an increase
in responsivity and a decrease in the mean time lag as the excitation and
ionization level for the species increases. Further confirmation of
photoionization predictions for broad-line gas behavior will require additional
monitoring programs for these AGNs while they are in different luminosity
states. [abridged]Comment: 37 pages, 18 figures and 15 tables, accepted for publication in the
Astrophysical Journa
ACR Appropriateness CriteriaÂź Non-Spine Bone Metastases
Abstract Bone is one of the most common sites of metastatic spread of malignancy, with possible deleterious effects including pain, hypercalcemia, and pathologic fracture. External beam radiotherapy (EBRT) remains the mainstay for treatment of painful bone metastases. EBRT may be combined with other local therapies like surgery or with systemic treatments like chemotherapy, hormonal therapy, osteoclast inhibitors, or radiopharmaceuticals. EBRT is not commonly recommended for patients with asymptomatic bone metastases unless they are associated with a risk of pathologic fracture. For those who do receive EBRT, appropriate fractionation schemes include 30?Gy in 10 fractions, 24?Gy in 6 fractions, 20?Gy in 5 fractions, or a single 8?Gy fraction. Single fraction treatment maximizes convenience, while fractionated treatment courses are associated with a lower incidence of retreatment. The appropriate postoperative dose fractionation following surgical stabilization is uncertain. Reirradiation with EBRT may be safe and provide pain relief, though retreatment might create side effect risks which warrant its use as part of a clinical trial. All patients with bone metastases should be considered for concurrent management by a palliative care team, with patients whose life expectancy is less than six months appropriate for hospice evaluation. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed every two years by a multidisciplinary expert panel. The guideline development and review include an extensive analysis of current medical literature from peer reviewed journals and the application of a well-established consensus methodology (modified Delphi) to rate the appropriateness of imaging and treatment procedures by the panel. In those instances where evidence is lacking or not definitive, expert opinion may be used to recommend imaging or treatment.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98458/1/jpm%2E2011%2E0512.pd
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