1,376 research outputs found
Investigation of a mesospheric bore event over northern China
A mesospheric bore event was observed using an OH all-sky airglow imager (ASAI) at Xinglong (40.2° N, 117.4° E), in northern China, on the night of 8â9 January 2011. Simultaneous observations by a Doppler meteor radar, a broadband sodium lidar, and TIMED/SABER OH intensity and temperature measurements are used to investigate the characteristics and environment of the bore propagation and the possible relations with the Na density perturbations. The bore propagated from northeast to southwest and divided the sky into bright and dark halves. The calculations show that the bore has an average phase velocity of 68 m sâ1. The crests following the bore have a horizontal wavelength of ~ 22 km. These parameters are consistent with the hydraulic jump theory proposed by Dewan and Picard, as well as the previous bore reports. Simultaneous wind measurements from the Doppler meteor radar at Shisanling (40.3° N, 116.2° E) and temperature data from SABER on board the TIMED satellite are used to characterize the propagating environment of the bore. The result shows that a thermal-Doppler duct exists near the OH layer that supports the horizontal propagation of the bore. Simultaneous Na lidar observations at Yanqing (40.4° N, 116.0° E) suggest that there is a downward displacement of Na density during the passage of the mesospheric bore event.Q. Li, J. Xu, J. Yue, X. Liu, W. Yuan, B. Ning, S. Guan, and J. P. Younge
Independent Expert Scientific Panel â Report on Unconventional Oil and Gas
No abstract available
Ion beam analysis of microcrystalline quartz artifacts from the Reed Mound Site, Delaware County, Oklahoma
Ion beam analysis (IBA) has been a powerful, non-destructive tool for archaeological research worldwide for over four decades, yet its full potential is seldom realized in North American archaeology. Herein the potential of particle induced X-ray emission spectrometry (PIXE) as a tool for future Ozarks chert provenance studies is evaluated based on its ability to facilitate (1) discrimination of Ozarks chert materials from different geological formations and (2) identification of discrete groups of artifacts from the same geological formation. In addition, PIXE was also used to evaluate the elemental heterogeneity of Ozarks chert materials. Thirty chert (microcrystalline quartz) artifacts were visually sorted and classified according to macroscopic features characteristic of certain chert resources from particular Ozarks geological formations. The elemental concentrations obtained from PIXE analysis underwent multivariate statistical analyses in order to gain insight from the data. The results indicate that PIXE could be a useful tool for assigning Ozarks chert materials to their respective geological formations, and possibly for determining regional or sub-regional provenance
Scenarios of intermittent E. coli contamination from sewer overflows to shellfish growing waters: the Dart Estuary case study
Sewage overflows (SOs) and Combined Sewer Overflows (CSOs) significantly contribute to the bacterial contamination of coastal waters, which is of especial concern for aquaculture, a growing industry worldwide. Hydrodynamic and water quality models were used to investigate impacts of CSO discharge frequency and duration, river discharge and tides on Escherichia coli levels at shellfish farming sites in the Dart Estuary (UK), being the employed methodology generally applicable. High E. coli contamination occurred during neap tides and high river discharges due to higher retention and lower bacterial decay. Synchronicity of CSO spills affected the duration of the pollution episodes rather than peak concentrations, more influenced by discharges of the neighbouring CSOs. During peak discharges, E. coli concentrations could be 10 times higher than during average flows. CSO spills were more frequent when rainfall was >20 mm. Model outputs combined with rainfall forecasts can indicate microbiological contamination risk in the aquaculture sites.En prensa2,35
Sticky surface: sphere - sphere adhesion dynamics
Special Issue: Selected Papers from the The Fourth International Conference on Mathematical Modeling and Analysis of Populations in Biological Systems (ICMA IV), Texas Tech University, Lubbock, Texas, USA, 4-6 October 2013We present a multi-scale model to study the attachment of spherical particles with a rigid core, coated with binding ligands and suspended in the surrounding, quiescent fluid medium. This class of fluidimmersed adhesion is widespread in many natural and engineering settings, particularly in microbial surface adhesion. Our theory highlights how the micro-scale binding kinetics of these ligands, as well as the attractive/repulsive surface potential in an ionic medium affects the eventual macro-scale size distribution of the particle aggregates (flocs). The bridge between the micro-macro model is made via an aggregation kernel. Results suggest that the presence of elastic ligands on the particle surface lead to the formation of larger floc aggregates via efficient inter-floc collisions (i.e. non-zero sticking probability, g). Strong electrolytic composition of the surrounding fluid favours large floc formation as well. The kernel for the Brownian diffusion for hard spheres is recovered in the limit of perfect binding effectiveness (g -> 1) and in a neutral solution with no dissolved salts.Sarthok Sircara, John G.Younger and David M. Bort
The Self-Regulated Growth of Supermassive Black Holes
We present a series of simulations of the self--regulated growth of
supermassive black holes (SMBHs) in galaxies via three different fueling
mechanisms: major mergers, minor mergers, and disk instabilities. The SMBHs in
all three scenarios follow the same black hole fundamental plane (BHFP) and
correlation with bulge binding energy seen in simulations of major mergers, and
observed locally. Furthermore, provided that the total gas supply is
significantly larger than the mass of the SMBH, its limiting mass is not
influenced by the amount of gas available or the efficiency of black hole
growth. This supports the assertion that SMBHs accrete until they reach a
critical mass at which feedback is sufficient to unbind the gas locally,
terminating the inflow and stalling further growth. At the same time, while
minor and major mergers follow the same projected correlations (e.g., the
and Magorrian relations), SMBHs grown via disk instabilities do
not, owing to structural differences between the host bulges. This finding is
supported by recent observations of SMBHs in pseudobulges and bulges in barred
systems, as compared to those hosted by classical bulges. Taken together, this
provides support for the BHFP and binding energy correlations as being more
"fundamental" than other proposed correlations in that they reflect the
physical mechanism driving the co-evolution of SMBHs and spheroids.Comment: 15 pages, 16 figures, accepted for publication in Ap
The ASTRA Spectrophotometer: A July 2004 Progress Report
A cross-dispersed spectrophotometer with CCD detector and its automated 0.5-m
telescope at the Fairborn Observatory, now under construction, should begin
observations in 6 to 9 months. The Citadel ASTRA Telescope will be able to
observe Vega the primary standard, make rapid measurements of the naked-eye
stars, use 10 minutes per hour to obtain photometric measurements of the
nightly extinction, and obtain high quality observations of V=10.5 mag. stars
in an hour. The approximate wavelength range is 3300-9000A with a resolution of
14A in first and 7A in second order. Filter photometric magnitudes and indices
will be calibrated in part for use as quality checks.
Science observations for major projects such as comparisons with model
atmospheres codes and for exploratory investigations should also begin in the
first year. The ASTRA team realizes to deal with this potential data flood that
they will need help to make the best scientific uses of the data. Thus they are
interested in discussing possible collaborations. In less than a year of normal
observing, all isolated stars in the Bright Star Catalog that can be observed
can have their fluxes well measured. Some A Star related applications are
discussed.Comment: 10 pages, 4 figures. Poster presented at IAU Symposium 224 "The A
Star Puzzle", 7-13 July 2004, Poprad, Slovaki
Cosmological Simulations of the Preheating Scenario for Galaxy Cluster Formation: Comparison to Analytic Models and Observations
We perform a set of non--radiative cosmological simulations of a preheated
intracluster medium in which the entropy of the gas was uniformly boosted at
high redshift. The results of these simulations are used first to test the
current analytic techniques of preheating via entropy input in the smooth
accretion limit. When the unmodified profile is taken directly from
simulations, we find that this model is in excellent agreement with the results
of our simulations. This suggests that preheated efficiently smoothes the
accreted gas, and therefore a shift in the unmodified profile is a good
approximation even with a realistic accretion history. When we examine the
simulation results in detail, we do not find strong evidence for entropy
amplification, at least for the high-redshift preheating model adopted here. In
the second section of the paper, we compare the results of the preheating
simulations to recent observations. We show -- in agreement with previous work
-- that for a reasonable amount of preheating, a satisfactory match can be
found to the mass-temperature and luminosity-temperature relations. However --
as noted by previous authors -- we find that the entropy profiles of the
simulated groups are much too flat compared to observations. In particular,
while rich clusters converge on the adiabatic self--similar scaling at large
radius, no single value of the entropy input during preheating can
simultaneously reproduce both the core and outer entropy levels. As a result,
we confirm that the simple preheating scenario for galaxy cluster formation, in
which entropy is injected universally at high redshift, is inconsistent with
observations.Comment: 11 pages, 13 figures, accepted for publication in Ap
Evolution of the Cluster Mass and Correlation Functions in LCDM Cosmology
The evolution of the cluster mass function and the cluster correlation
function from z = 0 to z = 3 are determined using 10^6 clusters obtained from
high-resolution simulations of the current best-fit LCDM cosmology (\Omega_m =
0.27, \sigma_8 = 0.84, h = 0.7). The results provide predictions for
comparisons with future observations of high redshift clusters. A comparison of
the predicted mass function of low redshift clusters with observations from
early Sloan Digital Sky Survey data, and the predicted abundance of massive
distant clusters with observational results, favor a slightly larger amplitude
of mass fluctuations (\sigma_8 = 0.9) and lower density parameter (\Omega_m =
0.2); these values are consistent within 1-\sigma with the current
observational and model uncertainties. The cluster correlation function
strength increases with redshift for a given mass limit; the clusters were more
strongly correlated in the past, due to their increasing bias with redshift -
the bias reaches b = 100 at z = 2 for M > 5 x 10^13 h^-1 M_sun. The
richness-dependent cluster correlation function, represented by the correlation
scale versus cluster mean separation relation, R0-d, is generally consistent
with observations. This relation can be approximated as R_0 = 1.7 d^0.6 h^-1
Mpc for d = 20 - 60 h^-1 Mpc. The R0-d relation exhibits surprisingly little
evolution with redshift for z < 2; this can provide a new test of the current
LCDM model when compared with future observations of high redshift clusters.Comment: 20 pages, 9 figures, accepted for publication in Ap
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