1,085 research outputs found
Aquatic Vegetation, Largemouth Bass and Water Quality Responses to Low-Dose Fluridone Two Years Post Treatment
Whole-lake techniques are increasingly being used to selectively
remove exotic plants, including Eurasian watermilfoil
(
Myriophyllum spicatum
L.). Fluridone (1-methyl-3-phenyl-
5-[3-(trifluoromethyl)phenyl]-4(1
H
)-pyridinone), a systemic
whole-lake herbicide, is selective for Eurasian watermilfoil
within a narrow low concentration range. Because fluridone
applications have the potential for large effects on plant assemblages
and lake food webs, they should be evaluated at
the whole-lake scale. We examined effects of low-dose (5 to 8
ppb) fluridone applications by comparing submersed plant
assemblages, water quality and largemouth bass (
Micropterus
salmoides
) growth rates and diets between three reference
lakes and three treatment lakes one- and two-years post treatment.
In the treatment lakes, fluridone reduced Eurasian watermilfoil
cover without reducing native plant cover, although
the duration of Eurasian watermilfoil reduction varied among
treatment lakes. (PDF has 11 pages.
Temporal behavior of two-wave-mixing in photorefractive InP:Fe versus temperature
The temporal response of two-wave-mixing in photorefractive InP:Fe under a dc
electric field at different temperatures has been studied. In particular, the
temperature dependence of the characteristic time constant has been studied
both theoretically and experimentally, showing a strongly decreasing time
constant with increasing temperature
A strategy to qualify the performance of radiographic monitors
The purpose of this work was to compare standard desktop display systems with dedicated medical display systems. The set of image tests proposed by the American Association of Physicists in Medicine (AAPM TG18) was used to assess a Philips 107S desktop display system and a Siemens medical display. Three observers performed the subjective assessment, in a non-concerted manner. The objective assessment was performed using a CCD camera according to the AAPM TG18 procedure. The results clearly demonstrate the inadequacy of standard desktop display systems in the framework of diagnostic radiology. Moreover, a good correlation between the subjective and objective assessment methods was obtaine
Management of patient dose and image noise in routine pediatric CT abdominal examinations
The aim was to propose a strategy for finding reasonable compromises between image noise and dose as a function of patient weight. Weighted CT dose index (CTDIw) was measured on a multidetector-row CT unit using CTDI test objects of 16, 24 and 32cm in diameter at 80, 100, 120 and 140kV. These test objects were then scanned in helical mode using a wide range of tube currents and voltages with a reconstructed slice thickness of 5mm. For each set of acquisition parameter image noise was measured and the Rose model observer was used to test two strategies for proposing a reasonable compromise between dose and low-contrast detection performance: (1) the use of a unique noise level for all test object diameters, and (2) the use of a unique dose efficacy level defined as the noise reduction per unit dose. Published data were used to define four weight classes and an acquisition protocol was proposed for each class. The protocols have been applied in clinical routine for more than one year. CTDIvol values of 6.7, 9.4, 15.9 and 24.5mGy were proposed for the following weight classes: 2.5-5, 5-15, 15-30 and 30-50kg with image noise levels in the range of 10-15HU. The proposed method allows patient dose and image noise to be controlled in such a way that dose reduction does not impair the detection of low-contrast lesions. The proposed values correspond to high- quality images and can be reduced if only high-contrast organs are assesse
The Canada-UK Deep Submillimetre Survey: The Survey of the 14-hour field
We have used SCUBA to survey an area of 50 square arcmin, detecting 19
sources down to a 3sigma sensitivity limit of 3.5 mJy at 850 microns. We have
used Monte-Carlo simulations to assess the effect of source confusion and noise
on the SCUBA fluxes and positions, finding that the fluxes of sources in the
SCUBA surveys are significantly biased upwards and that the fraction of the 850
micron background that has been resolved by SCUBA has been overestimated. The
radio/submillmetre flux ratios imply that the dust in these galaxies is being
heated by young stars rather than AGN. We have used simple evolution models
based on our parallel SCUBA survey of the local universe to address the major
questions about the SCUBA sources: (1) what fraction of the star formation at
high redshift is hidden by dust? (2) Does the submillimetre luminosity density
reach a maximum at some redshift? (3) If the SCUBA sources are
proto-ellipticals, when exactly did ellipticals form? However, we show that the
observations are not yet good enough for definitive answers to these questions.
There are, for example, acceptable models in which 10 times as much
high-redshift star formation is hidden by dust as is seen at optical
wavelengths, but also acceptable ones in which the amount of hidden star
formation is less than that seen optically. There are acceptable models in
which very little star formation occurred before a redshift of three (as might
be expected in models of hierarchical galaxy formation), but also ones in which
30% of the stars have formed by this redshift. The key to answering these
questions are measurements of the dust temperatures and redshifts of the SCUBA
sources.Comment: 41 pages (latex), 17 postscript figures, to appear in the November
issue of the Astronomical Journa
Olfactory CNG Channel Desensitization by Ca2+/CaM via the B1b Subunit Affects Response Termination but Not Sensitivity to Recurring Stimulation
SummaryCa2+/calmodulin-mediated negative feedback is a prototypical regulatory mechanism for Ca2+-permeable ion channels. In olfactory sensory neurons (OSNs), such regulation on the cyclic nucleotide-gated (CNG) channel is considered a major mechanism of OSN adaptation. To determine the role of Ca2+/calmodulin desensitization of the olfactory CNG channel, we introduced a mutation in the channel subunit CNGB1b in mice that rendered the channel resistant to fast desensitization by Ca2+/calmodulin. Contrary to expectations, mutant OSNs showed normal receptor current adaptation to repeated stimulation. Rather, they displayed slower response termination and, consequently, reduced ability to transmit olfactory information to the olfactory bulb. They also displayed reduced response decline during sustained odorant exposure. These results suggest that Ca2+/calmodulin-mediated CNG channel fast desensitization is less important in regulating the sensitivity to recurring stimulation than previously thought and instead functions primarily to terminate OSN responses
Red Parkes-Quasars: Evidence for Soft X-ray Absorption
The Parkes Half-Jansky Flat Spectrum Sample contains a large number of
sources with unusually red optical-to-near-infrared continua. If this is to be
interpreted as extinction by dust in the line-of-sight, then associated
material might also give rise to absorption in the soft X-ray regime. This
hypothesis is tested using broadband (0.1-2.4 keV) data from the {\it ROSAT}
All-Sky Survey provided by Siebert et al. (1998). Significant (
confidence level) correlations between optical (and near-infrared)--to--soft
X-ray continuum slope and optical extinction are found in the data, consistent
with absorption by material with metallicity and a range in gas-to-dust ratio
as observed in the local ISM. Under this simple model, the soft X-rays are
absorbed at a level consistent with the range of extinctions (
magnitudes) implied by the observed optical reddening. Excess X-ray absorption
by warm (ionised) gas, (ie. a `warm absorber') is not required.Comment: 23 pages of text, 3 figures, to appear in Jan 10 (1999) issue of The
Astrophysical Journa
A Detailed Record of Shallow Hydrothermal Fluid Flow in the Sierra Nevada Magmatic Arc from Low-ÎŽ18O Skarn Garnets
Garnet from skarns exposed at Empire Mountain, Sierra Nevada (California, United States) batholith, have variable ÎŽ18O values including the lowest known ÎŽ18O values of skarn garnet (â4.0â°) in North America. Such values indicate that surface-derived meteoric water was a significant component of the fluid budget of the skarn-forming hydrothermal system, which developed in response to shallow emplacement (âŒ3.3 km) of the 109 Ma quartz diorite of Empire Mountain. Values of ÎŽ18O, measured in situ across single garnet crystals by secondary ion mass spectrometry, vary considerably (up to 7â°) and sometimes abruptly, indicating variable mixing of meteoric, magmatic, and metamorphic water. Brecciation in the skarns and alteration of the Empire Mountain pluton suggests that fracture-enhanced permeability was a critical control on the depth to which surface waters penetrated to form skarns and later alter the pluton. Compared to other Sierran systems, much greater volumes of skarn rock suggest an exceptionally vigorous hydrothermal system that saw unusually high levels of decarbonation reaction progress, likely a consequence of the magma intruding relatively cold wallrocks inboard of the main locus of magmatism in the Sierran arc at that time
Revisiting the 'Missing Middle' in English Sub-National Governance
In the light of the new Coalition Governmentâs proposed ârescalingâ of sub-national governance away from the regional level, it is an opportune time to re-consider the strength and weaknesses of the city or sub-regional approach to economic development and to search, once more, for the âmissing middleâ in English Governance. In this context, the article initially assesses the case for city or sub regions as tiers of economic governance, before examining the lessons to be learnt from the experiences of the existing city regions in the North East of England. It argues that while contemporary plans to develop Local Enterprise Partnerships (LEPs) can be usefully considered within the context of the emerging city regional developments under the previous Labour Governments, a number of important challenges remain, particularly in relation to ensuring accountable structures of governance, a range of appropriate functions, adequate funding, and comprehensive coverage across a variety of sub-regional contexts. While the proposals of the new Government create the necessary âspaceâ to develop sub-regional bodies and offer genuine opportunities for both city and county LEPs, the scale of the sub-regional challenge should not be underestimated, particularly given the context of economic recession and major reductions in the public sector
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