5,981 research outputs found
Biomediation of Turbulence and Suspended Sediment Characteristics in Marsh Surface Flows - The Influence of Spartina anglica
Laboratory experimentation in a large aimular flume (radius 3 m, channel width
and water depth 0.4 m) has been conducted using a geometrically and dynamically
similar Spariina anglica mimic (canopy height 0.21 m, stem density 1000 stems
m~^) to investigate the influence of submerged Spartina on hydrodynamics under
unidirectional currents {Uh = 0.2 m s~*) and the impact upon the dynamics of
suspended cohesive sediments near the bed within the canopy.
The vertical distribution of canopy biomass strongly influences vertical profiles
of time-averaged velocity and turbulent quantities. An inflected velocity profile is
observed in the region 0.79 < z/h < 0.9 which generates shear, T K E and Reynolds
Stress peaks within vicinity of the canopy top. In this region T K E peaks at 15
times the levels observed in un-vegetated experiments. Flows at the canopy top are
strongly intermittent with extremely efficient downward momentum transfer, uf]
and ufz (stream-wise and vertical zero-mean fluctuating velocity) skewness are 0.5
and -0.5 indicating the presence of intermittent downward penetrating gusts. Near
the bed (0 < z/h < 0.3) mean flow velocities are reduced by 88 - 90% in comparison
to un-vegetated flows but turbulence intensities are strongly augmented by wake
shedding from vegetative elements. TKE in this region is approximately equal to
that in un-vegetated flows.
Novel field observations in a low energ>', estuarine fringing marsh site on the Tavy
Estuary, UK, with a vertical array of synchronous velocimeters and optical backscatter
sensors exhibit low velocities (<0.6 ra s"*) and suspension concentrations (<100
mg L"*) in agreement with laboratory simulations. While field observations of
near bed flows exhibit similarity to those measured in the laboratory, magnitudes
of time-averaged flow throughout the water column are so small that the velocity
profile appears constant over depth. Superimposed upon the low field velocities are
small wind generated waves ( < 0.05 m in height and with periods < 3 s) which have
a considerable impact on flow energy and stress estimates, but crucially, cannot be
replicated in the laboratory experiments. Dissipation rates within the laboratory
canopy are 70-200x10"'* m~^s"^ giving reduced Kohnogorov length scales of 0.04 -
0.14 mm. Field values for dissipation are generally of similar magnitude but peak
at up to 600 X10"** m~^s~^. Kolmogorov length scales are consequently 0.06 - 2.6
mm. Using natural intertidal mud, suspension concentrations of 100-200 mg L~*
have been sheared through the mimic canopy. Observations from a vertical array
of miniaturised OBS sensors suggests sediments are maintained in suspension twice
as long, under constant unidirectional currents, compared to un-vegetated flows. In
the field initial concentrations of 100 mg L~* quickly decay to background levels of
<20 mg L"* indicating the rapid setthng of material from suspension.
Use of a novel digital in-line holographic particle iinaging system and the development
of a particle tracking methodology has enabled the high resolution observation
of both sample size and settling velocities of suspended cohesive particles. Laboratory
observations of sample averaged size (74.5 - 111.7 mm) and settling rates (0.35
- 1 mm s~*) are in agreement with published estimates and the limited observational
data that exists for settling rates in marsh systems. Settling velocities estimated
in the field at 0.1 - 0.8 mm s~^. Significantly larger and fast settling aggregates
have been observed than previously recorded. In the narrow range of experimental
suspension concentrations and shear stresses utilised in the present experiments,
significant diff^erences in particle size and settling velocity between vegetated and
un-vegetated flows cannot be identified. Contrasting flux estimates using sample
averaged settling rates and concentrations with full spectral estimates derived from
the holographic particle imager indicate an error in the former fluxes of, on average,
62%. The range of settling rates observed during the pr^ent study raises questions
regarding the accurate representation of marsh surface settling fluxes in numerical
simulations. Large magnitude flux errors may have significant implications for
accurate accretion rates in numerical models of marsh sedimentation
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A survey of physical education in the elementary schools of Hampshire County, Massachusetts.
Development of a community e-portal constellation: Queensland Smart Region Initiative
A community e-portal facilitates dynamic (developing), value (financial and non-financial), constellation (collaborative networks), which supports community integration and economic growth. The OECD has identified that social cohesion rather than narrow economic gain is the most significant outcome for societies where all citizens, through learning and the transfer of knowledge, skills and attitudes, leads to becoming more effective and proactive participants in civil and economic processes. In this work, action research facilitated design, development, and implementation of a community-portal dynamic-value constellation to support networked value chains, community, and local government connectivity. The research gives insights through working closely with stakeholders. The research domain represents a novel value creation model, incorporating technologies and solutions in the context of virtual enterprises, partnerships and joint ventures and other market-driven value constellations, where partners dynamically come together in response to or in anticipation of new market opportunities. Such constellations, however, bring with them significant operational and logistical challenges, about which there has been very little prior knowledge
The effect of tannins in Korean Lespedeza and other feeds on milk production
This bulletin is a report on Department of Dairy Husbandry research project number 139 entitled 'Milk Production'--P. [2].Includes bibliographical references (page 8)
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Rh single atoms on TiO2 dynamically respond to reaction conditions by adapting their site.
Single-atom catalysts are widely investigated heterogeneous catalysts; however, the identification of the local environment of single atoms under experimental conditions, as well as operando characterization of their structural changes during catalytic reactions are still challenging. Here, the preferred local coordination of Rh single atoms is investigated on TiO2 during calcination in O2, reduction in H2, CO adsorption, and reverse water gas shift (RWGS) reaction conditions. Theoretical and experimental studies clearly demonstrate that Rh single atoms adapt their local coordination and reactivity in response to various redox conditions. Single-atom catalysts hence do not have static local coordinations, but can switch from inactive to active structure under reaction conditions, hence explaining some conflicting literature accounts. The combination of approaches also elucidates the structure of the catalytic active site during reverse water gas shift. This insight on the real nature of the active site is key for the design of high-performance catalysts
Illuminating trap density trends in amorphous oxide semiconductors with ultrabroadband photoconduction
Under varying growth and device processing conditions, ultrabroadband
photoconduction (UBPC) reveals strongly evolving trends in the defect density
of states (DoS) for amorphous oxide semiconductor thin-film transistors (TFTs).
Spanning the wide bandgap of amorphous InGaZnO (a-IGZO), UBPC identifies
seven oxygen-deep donor vacancy peaks that are independently confirmed by
energetically matching to photoluminescence emission peaks. The sub-gap DoS
from 15 different types of a-IGZO TFTs all yield similar DoS, except only
back-channel etch TFTs can have a deep acceptor peak seen at 2.2 eV below the
conduction band mobility edge. This deep acceptor is likely a zinc vacancy,
evidenced by trap density which becomes 5-6x larger when TFT wet-etch methods
are employed. Certain DoS peaks are strongly enhanced for TFTs with active
channel processing damage caused by plasma exposure. While Ar implantation and
He plasma processing damage are similar, Ar plasma yields more disorder showing
a 2x larger valence-band Urbach energy and two orders of magnitude increase in
the deep oxygen vacancy trap density. Changing the growth conditions of a-IGZO
also impacts the DoS, with zinc-rich TFTs showing much poorer electrical
performance compared to 1:1:1 molar ratio a-IGZO TFTs owing to the former
having a ~10xlarger oxygen vacancy trap density. Finally, hydrogen is found to
behave as a donor in amorphous indium tin gallium zinc oxide TFTs.Comment: 11 pages, 6 figure
SERS active colloidal nanoparticles for the detection of small blood biomarkers using aptamers
Functionalized colloidal nanoparticles for SERS serve as a promising multifunctional assay component for blood biomarker detection. Proper design of these nanoprobes through conjugation to spectral tags, protective polymers, and sensing ligands can provide experimental control over the sensitivity, range, reproducibility, particle stability, and integration with biorecognition assays. Additionally, the optical properties and degree of electromagnetic SERS signal enhancement can be altered and monitored through tuning the nanoparticle shape, size, material and the colloid's local surface plasmon resonance (LSPR). Aptamers, synthetic affinity ligands derived from nucleic acids, provide a number of advantages for biorecognition of small molecules and toxins with low immunogenicity. DNA aptamers are simpler and more economical to produce at large scale, are capable of greater specificity and affinity than antibodies, are easily tailored to specific functional groups, can be used to tune inter-particle distance and shift the LSPR, and their intrinsic negative charge can be utilized for additional particle stability.1,2 Herein, a "turn-off" competitive binding assay platform involving two different plasmonic nanoparticles for the detection of the toxin bisphenol A (BPA) using SERS is presented. A derivative of the toxin is immobilized onto a silver coated magnetic nanoparticle (Ag@MNP), and a second solid silver nanoparticle (AgNP) is functionalized with the BPA aptamer and a Raman reporter molecule (RRM). The capture (Ag@MNP) and probe (AgNP) particles are mixed and the aptamer binding interaction draws the nanoparticles closer together, forming an assembly that results in an increased SERS signal intensity. This aptamer mediated assembly of the two nanoparticles results in a 100x enhancement of the SERS signal intensity from the RRM. These pre-bound aptamer/nanoparticle conjugates were then exposed to BPA in free solution and the competitive binding event was monitored by the decrease in SERS intensity
Discovery of an optical counterpart to the hyperluminous X-ray source in ESO 243-49
The existence of black holes of masses ~ 10^2-10^5 Msun has important
implications for the formation and evolution of star clusters and supermassive
black holes. One of the strongest candidates to date is the hyperluminous X-ray
source HLX1, possibly located in the S0-a galaxy ESO243-49, but the lack of an
identifiable optical counterpart had hampered its interpretation. Using the
Magellan telescope, we have discovered an unresolved optical source with R =
(23.80 +/- 0.25) mag and V = (24.5 +/- 0.3) mag within HLX1's positional error
circle. This implies an average X-ray/optical flux ratio ~ 500. Taking the same
distance as ESO243-49, we obtain an intrinsic brightness M_R = (-11.0 +/- 0.3)
mag, comparable to that of a massive globular cluster. Alternatively, the
optical source is consistent with a main-sequence M star in the Galactic halo
(for example an M4.4 star at ~ 2.5 kpc). We also examined the properties of
ESO243-49 by combining Swift/UVOT observations with stellar population
modelling. We found that the overall emission is dominated by a ~5 Gyr old
stellar population, but the UV emission at ~2000 Ang is mostly due to ongoing
star-formation at a rate of ~ 0.03 Msun/yr. The UV emission is more intense (at
least a 9-sigma enhancement above the mean) North East of the nucleus, in the
same quadrant as HLX1. With the combined optical and X-ray measurements, we put
constraints on the nature of HLX1. We rule out a foreground star and a
background AGN. Two alternative scenarios are still viable. HLX1 could be an
accreting intermediate-mass black hole in a star cluster, which may itself be
the stripped nucleus of a dwarf galaxy that passed through ESO243-49, an event
which might have caused the current episode of star formation. Or, it could be
a neutron star in the Galactic halo, accreting from an M4-M5 donor star.Comment: 7 pages, accepted by MNRAS. Several improvements from Oct 7 version:
stronger evidence of the optical counterpart; more accurate estimate of its
brightness (a factor of 2 brighter than previously estimated); use of a
larger set of Swift/UVOT data to measure the recent star formation rate in
ESO243-49; improved discussion and comparison of the competing scenario
Two little girls in blue: waltz song
https://digitalcommons.ithaca.edu/sheetmusic/1073/thumbnail.jp
Microwave Gaseous Discharges
Contains reports on five research projects.United States Atomic Energy Commission (Contract AT(30-1) 1842
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