11,288 research outputs found
Nitrogen, Phosphorus, and Suspended Solids Concentrations in Tributaries to the Great Bay Estuary Watershed in 2013
Nitrogen, phosphorus, and sediment loads to the Great Bay Estuary are a growing concern. The Piscataqua Region Estuaries Partnership (PREP) calculates the nitrogen load from tributaries to the Great Bay Estuary for its State of Our Estuaries reports. Therefore, the purpose of this study was to collect representative data on nitrogen, phosphorus, and suspended sediment concentrations in tributaries to the Great Bay Estuary in 2013. The study design followed the tributary sampling design which was implemented by the New Hampshire Department of Environmental Services between 2001 and 2007 and by the University of New Hampshire between 2008 and 2012, so as to provide comparable data to the previous loading estimates
Environmental statistics and optimal regulation
Any organism is embedded in an environment that changes over time. The
timescale for and statistics of environmental change, the precision with which
the organism can detect its environment, and the costs and benefits of
particular protein expression levels all will affect the suitability of
different strategies-such as constitutive expression or graded response-for
regulating protein levels in response to environmental inputs. We propose a
general framework-here specifically applied to the enzymatic regulation of
metabolism in response to changing concentrations of a basic nutrient-to
predict the optimal regulatory strategy given the statistics of fluctuations in
the environment and measurement apparatus, respectively, and the costs
associated with enzyme production. We use this framework to address three
fundamental questions: (i) when a cell should prefer thresholding to a graded
response; (ii) when there is a fitness advantage to implementing a Bayesian
decision rule; and (iii) when retaining memory of the past provides a selective
advantage. We specifically find that: (i) relative convexity of enzyme
expression cost and benefit influences the fitness of thresholding or graded
responses; (ii) intermediate levels of measurement uncertainty call for a
sophisticated Bayesian decision rule; and (iii) in dynamic contexts,
intermediate levels of uncertainty call for retaining memory of the past.
Statistical properties of the environment, such as variability and correlation
times, set optimal biochemical parameters, such as thresholds and decay rates
in signaling pathways. Our framework provides a theoretical basis for
interpreting molecular signal processing algorithms and a classification scheme
that organizes known regulatory strategies and may help conceptualize
heretofore unknown ones.Comment: 21 pages, 7 figure
The iron K line complex in NGC1068: implications for X-ray reflection in the nucleus
We report a new analysis of ASCA data on the iron K line complex in NGC1068.
The line complex basically consists of three components, as previously
reported. A weak red wing of the 6.4 keV fluoresence iron K line is found. A
plausible explanation is Compton scattering in optically thick, cold matter
which can be identified with an obscuring torus or cold gas in the host galaxy.
We also show that this `Compton shoulder' should be observable with ASCA using
a simulated reflection spectrum. In order to explain the two higher energy
lines as well as the cold 6.4 keV line, we fit the ASCA data with a composite
model of cold and warm reflection. This shows that cold reflection dominates
the observed X-ray emission above 4 keV. The two higher energy lines have large
equivalent width with respect to the warm-scattered continuum, suggesting that
efficient resonant scattering operates. The line energies are systematically
lower than those expected from resonant lines for FeXXV and FeXXVI by 100 eV.
The redshifts may be due to either the ionized gas of the warm mirror receding
at a radial velocity of 4000-5000 km/s, or effects of Compton scattering in a
complicated geometry.Comment: 7 pages, 4 figures, to appear in MNRA
Dirty black holes: Symmetries at stationary non-static horizons
We establish that the Einstein tensor takes on a highly symmetric form near
the Killing horizon of any stationary but non-static (and non-extremal) black
hole spacetime. [This follows up on a recent article by the current authors,
gr-qc/0402069, which considered static black holes.] Specifically, at any such
Killing horizon -- irrespective of the horizon geometry -- the Einstein tensor
block-diagonalizes into ``transverse'' and ``parallel'' blocks, and its
transverse components are proportional to the transverse metric. Our findings
are supported by two independent procedures; one based on the regularity of the
on-horizon geometry and another that directly utilizes the elegant nature of a
bifurcate Killing horizon. It is then argued that geometrical symmetries will
severely constrain the matter near any Killing horizon. We also speculate on
how this may be relevant to certain calculations of the black hole entropy.Comment: 21 pages; plain LaTe
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