298 research outputs found
Discussion
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/117481/1/nyas00019.pd
Mechanism of cholesterol gallstone dissolution. III. Electrophoretic studies showing the correlation between the bile micellarcharge and the effect of alkyl amines as cholesterol gallstone dissolution rate accelerators
We have shown that the cholesterol monohydrate dissolution rate acceleration in chenodeoxycholic acid solutions due to the addition of hexylamine and octylamine may be directly related to their ability to bind to the negatively charged chenodeoxycholate micelles. Based on these results, we have proposed that the primary mechanism by which these amines accelerate the dissolution rate is by reducing the micellar charge. An independent test of the above hypothesis was carried out by measuring the electrophoretic mobility of chenodeoxycholate micelles as a function of the amine concentration utilizing the moving boundary electrophoresis method in the presence of and absence of 0.1 M sodium chloride. At the concentrations of hexylamine and octylamine which gave the same dissolution rate, J/A, i.e., at equal efficacy, the electrophoretic mobilities were found to be the same. These results verify our hypothesis that the primary mechanism by which these amines accelerate the dissolution rate is by reducing the micellar charge. In addition, particle microelectrophoresis studies showed no significant surface charge variation with cholesterol particles as a function of amine concentration.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23303/1/0000241.pd
The METCRAX II Field Experiment: A Study of Downslope Windstorm-Type Flows in Arizona\u2019s Meteor Crater
The second Meteor Crater Experiment (METCRAX II) was conducted in October 2013 at Arizona\u2019s Meteor Crater. The experiment was designed to investigate nighttime downslope windstorm 12type flows that form regularly above the inner southwest sidewall of the 1.2-km diameter crater as a southwesterly mesoscale katabatic flow cascades over the crater rim. The objective of METCRAX II is to determine the causes of these strong, intermittent, and turbulent inflows that bring warm-air intrusions into the southwest part of the crater. This article provides an overview of the scientific goals of the experiment; summarizes the measurements, the crater topography, and the synoptic meteorology of the study period; and presents initial analysis results
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An overview of ISCAT 2000
The Investigation of Sulfur Chemistry in the Antarctic Troposphere (ISCAT) took place over the timer period of 15 November to 31 December in the year 2000. The study location was the Amundsen Scott Station in Antarctica. ISCAT 2000 defines the second phase of a program designed to explore tropospheric chemistry in Antarctica. As in 1998, the 2000 ISCAT study revealed a strong oxidizing environment at South Pole (SP). During the 2000 investigation, however, the suite of measurements was greatly expanded. These new measurements established the recycling of reactive nitrogen as a critical component of this unique environment. This paper first presents the historical background leading up to the ISCAT 2000 observations; then it focuses on providing a summary of the year 2000 results and contrasts these with those recorded during 1998. Important developments made during the 2000 study included the recording of SP data for several species being emitted from the snowpack. These included NO, H 2O2 and CH2O. In this context, eddy-diffusion flux measurements provided the first quantitative estimates of the SP NO and NOx snow-to-atmosphere fluxes. This study also revealed that HNO 3 and HO2NO2 were major sink species for HOx and NOx radicals. And, it identified the critical factors responsible for SP NO levels exceeding those at other polar sites by nearly an order of magnitude. Finally, it reports on the levels of gas phase sulfur species and provides evidence indicating that the absence of DMS at SP is most likely due to its greatly shorten chemical lifetime in the near vicinity of the plateau. It is proposed that this is due to the influence of NO on the distribution of OH in the lower free troposphere over a region that extends well beyond the plateau itself. Details related to each of the above findings plus others can be found in the 11 accompanying Special Issue papers. © 2004 Elsevier Ltd. All rights reserved
Airborne sampling of aerosol particles: Comparison between surface sampling at Christmas Island and P-3 sampling during PEM-Tropics B
Bulk aerosol sampling of soluble ionic compounds from the NASA Wallops Island P-3 aircraft and a tower on Christmas Island during PEM-Tropics B provides an opportunity to assess the magnitude of particle losses in the University of New Hampshire airborne bulk aerosol sampling system. We find that most aerosol-associated ions decrease strongly with height above the sea surface, making direct comparisons between mixing ratios at 30 m on the tower and the lowest flight level of the P-3 (150 m) open to interpretation. Theoretical considerations suggest that vertical gradients of sea-salt aerosol particles should show exponential decreases with height. Observed gradients of Na+ and Mg2+, combining the tower observations with P-3 samples collected below 1 km, are well described by exponential decreases (r values of 0.88 and 0.87, respectively), though the curve fit underestimates average mixing ratios at the surface by 25%. Cascade impactor samples collected on the tower show that \u3e99% of the Na+ and Mg2+mass is on supermicron particles, 65% is in the 1–6 micron range, and just 20% resides on particles with diameters larger than 9 microns. These results indicate that our airborne aerosol sampling probes must be passing particles up to at least 6 microns with high efficiency. We also observed that nss SO42− and NH4+, which are dominantly on accumulation mode particles, tended to decrease between 150 and 1000 m, but they were often considerably higher at the lowest P-3 sampling altitudes than at the tower. This finding is presently not well understood
Observational and Modeling Analysis of Land–Atmopshere Coupling over Adjacent Irrigated and Rainfed Cropland during the GRAINEX Field Campaign
The Great Plains Irrigation Experiment (GRAINEX) was conducted in the spring and summer of 2018 to investigate Land-Atmosphere (L-A) coupling just prior to and through the growing season across adjacent, but distinctly unique, soil moisture regimes (contrasting irrigated and rainfed fields). GRAINEX was uniquely designed for the development and analysis of an extensive observational dataset for comprehensive process studies of L-A coupling, by focusing on irrigated and rainfed croplands in a ~100 x 100 km domain in southeastern Nebraska. Observation platforms included multiple NCAR EOL Integrated Surface Flux Systems and Integrated Sounding Systems, NCAR CSWR Doppler Radar on Wheels, 1200 radiosonde balloon launches from 5 sites, the NASA GREX airborne L-Band radiometer, and 75 University of Alabama-Huntsville Environmental Monitoring Economic Monitoring Sensor Hubs (EMESH mesonet stations). An integrated observational and modeling approach to advance knowledge of L-A coupling processes and precipitation impacts in regions of heterogeneous soil moisture will be presented. Specifically, through observation of land surface states, surface fluxes, near surface meteorology, and properties of the atmospheric column, an examination of the diurnal planetary boundary layer evolving characteristics will be presented. Results from a hierarchy of modeling platforms (e.g. single column, large-eddy, and mesoscale simulations) will also be presented to complement the observational findings. The modeling effort will generate high spatiotemporal resolution datasets to: 1) generate a multi-physics ensemble to test the robustness and potentially advance physical parameterizations in high resolution weather and climate models, 2) comparison of prescribed forcing from observations and those from offline land surface model simulations and high resolution operational analyses, 3) determine the ability of model simulations to reproduce observed boundary layer evolution, with particular attention to the processes that compose the L-A coupling chain and metrics (e.g. mixing ratio diagrams), and 4) in combination with observations, isolate the impacts of soil moisture heterogeneity on planetary boundary layer characteristics, cloud development, precipitation, mesoscale circulation patters and boundary layer development. Initial results from the observational and modeling analysis will be presented
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Assessing the accuracy of microwave radiometers and radio acoustic sounding systems for wind energy applications
To assess current remote-sensing capabilities for wind energy
applications, a remote-sensing system evaluation study, called XPIA
(eXperimental Planetary boundary layer Instrument Assessment), was held in
the spring of 2015 at NOAA's Boulder Atmospheric Observatory (BAO) facility.
Several remote-sensing platforms were evaluated to determine their
suitability for the verification and validation processes used to test the
accuracy of numerical weather prediction models.The evaluation of these platforms was performed with respect to well-defined
reference systems: the BAO's 300 m tower equipped at six levels (50, 100, 150,
200, 250, and 300 m) with 12 sonic anemometers and six temperature (T) and relative
humidity (RH) sensors; and approximately 60 radiosonde launches.In this study we first employ these reference measurements to validate
temperature profiles retrieved by two co-located microwave radiometers (MWRs) as
well as virtual temperature (Tv) measured by co-located wind profiling radars
equipped with radio acoustic sounding systems (RASSs). Results indicate a mean
absolute error (MAE) in the temperature retrieved by the microwave radiometers
below 1.5 K in the lowest 5 km of the atmosphere and a mean absolute error
in the virtual temperature measured by the radio acoustic sounding systems
below 0.8 K in the layer of the atmosphere covered by these measurements (up
to approximately 1.6–2 km). We also investigated the benefit of the
vertical velocity correction applied to the speed of sound before computing
the virtual temperature by the radio acoustic sounding systems. We find that
using this correction frequently increases the RASS error, and that it
should not be routinely applied to all data.Water vapor density (WVD) profiles measured by the MWRs were also compared with
similar measurements from the soundings, showing the capability of MWRs to
follow the vertical profile measured by the sounding and finding a mean
absolute error below 0.5 g m−3 in the lowest 5 km of the atmosphere.
However, the relative humidity profiles measured by the microwave radiometer
lack the high-resolution details available from radiosonde profiles. An
encouraging and significant finding of this study was that the coefficient
of determination between the lapse rate measured by the microwave radiometer
and the tower measurements over the tower levels between 50 and 300 m ranged
from 0.76 to 0.91, proving that these remote-sensing instruments can provide
accurate information on atmospheric stability conditions in the lower
boundary layer
Solar Site Survey for the Advanced Technology Solar Telecope. I. Analysis of the Seeing Data
The site survey for the Advanced Technology Solar Telescope concluded
recently after more than two years of data gathering and analysis. Six
locations, including lake, island and continental sites, were thoroughly probed
for image quality and sky brightness. The present paper describes the analysis
methodology employed to determine the height stratification of the atmospheric
turbulence. This information is crucial because day-time seeing is often very
different between the actual telescope aperture (~30 m) and the ground. Two
independent inversion codes have been developed to analyze simultaneously data
from a scintillometer array and a solar differential image monitor. We show
here the results of applying them to a sample subset of data from May 2003,
which was used for testing. Both codes retrieve a similar seeing stratification
through the height range of interest. A quantitative comparison between our
analysis procedure and actual in situ measurements confirms the validity of the
inversions. The sample data presented in this paper reveal a qualitatively
different behavior for the lake sites (dominated by high-altitude seeing) and
the rest (dominated by near-ground turbulence).Comment: To appear in the Publications of the Astronomical Society of the
Pacific (PASP). Note: Figures are low resolution versions due to file size
limitation
Scalar flux profile relationships over the open ocean
Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 109 (2004): C08S09, doi:10.1029/2003JC001960.The most commonly used flux-profile relationships are based on Monin-Obukhov (MO) similarity theory. These flux-profile relationships are required in indirect methods such as the bulk aerodynamic, profile, and inertial dissipation methods to estimate the fluxes over the ocean. These relationships are almost exclusively derived from previous field experiments conducted over land. However, the use of overland measurements to infer surface fluxes over the ocean remains questionable, particularly close to the ocean surface where wave-induced forcing can affect the flow. This study investigates the flux profile relationships over the open ocean using measurements made during the 2000 Fluxes, Air-Sea Interaction, and Remote Sensing (FAIRS) and 2001 GasEx experiments. These experiments provide direct measurement of the atmospheric fluxes along with profiles of water vapor and temperature. The specific humidity data are used to determine parameterizations of the dimensionless gradients using functional forms of two commonly used relationships. The best fit to the Businger-Dyer relationship [ Businger, 1988 ] is found using an empirical constant of a q = 13.4 ± 1.7. The best fit to a formulation that has the correct form in the limit of local free convection [e.g., Wyngaard, 1973 ] is found using a q = 29.8 ± 4.6. These values are in good agreement with the consensus values from previous overland experiments and the Coupled Ocean-Atmosphere Response Experiment (COARE) 3.0 bulk algorithm [ Fairall et al., 2003 ]; e.g., the COARE algorithm uses empirical constants of 15 and 34.2 for the Businger-Dyer and convective forms, respectively. Although the flux measurements were made at a single elevation and local similarity scaling is applied, the good agreement implies that MO similarity is valid within the marine atmospheric surface layer above the wave boundary layer.The FAIRS work was supported by the
Office of Naval Research grant N00014-00-1-0403 while the GasEx work
was supported by the National Science Foundation grant OCE-9986724
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