8,022 research outputs found
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Surface Profiling of Natural Dust Devils
We present results from the first high-resolution near-surface profiles conducted on dust devil wind fields. These results are integrated with extensive geologic mapping to understand the factors that influence vortex generation and erosive efficacy
The oxidation and sublimation of graphite in simulated re-entry environments
Graphite oxidation and sublimation in simulated reentry environment
New calibration procedures for airborne turbulence measurements and accuracy of the methane fluxes during the AirMeth campaigns
Low-level flights over tundra wetlands in Alaska and Canada have been conducted during the Airborne Measurements of Methane Emissions (AirMeth) campaigns to measure turbulent methane fluxes in the atmosphere. In this paper we describe the instrumentation and new calibration procedures for the essential pressure parameters required for turbulence sensing by aircraft that exploit suitable regular measurement flight legs without the need for dedicated calibration patterns. We estimate the accuracy of the mean wind and the turbulence measurements. We show that airborne measurements of turbulent fluxes of methane and carbon dioxide using cavity ring-down spectroscopy trace gas analysers together with established turbulence equipment achieve a relative accuracy similar to that of measurements of sensible heat flux if applied during low-level flights over natural area sources. The inertial subrange of the trace gas fluctuations cannot be resolved due to insufficient high-frequency precision of the analyser, but, since this scatter is uncorrelated with the vertical wind velocity, the covariance and thus the flux are reproduced correctly. In the covariance spectra the â7â3 drop-off in the inertial subrange can be reproduced if sufficient data are available for averaging. For convective conditions and flight legs of several tens of kilometres we estimate the flux detection limit to be about 4mgmâ2dâ1 for wâ˛CH4â˛, 1.4gmâ2dâ1 for wâ˛CO2Ⲡand 4.2Wmâ2 for the sensible heat flux
Intrauterine repair of gastroschisis in fetal rabbits
Objective: Infants with gastroschisis (GS) still face severe morbidity. Prenatal closure may prevent gastrointestinal organ damage, but intrauterine GS repair (GSR) has not been established yet. Methods: In New Zealand White rabbits we developed and compared GS versus GSR: creation of GS was achieved by hysterotomy, right-sided laparotomy of the fetus and pressure on the abdominal wall to provoke evisceration. GSR was accomplished by careful reposition of eviscerated organs and a running suture of the fetal abdominal wall. For study purposes, 18 animals were divided equally into 3 groups: GS, GS with GSR after 2 h, and unmanipulated controls (C). Vitality was assessed by echocardiography. After 5 h all animals were sacrificed. Results: GSR inflicted no increased mortality, because all fetuses survived GS or GS with GSR. All fetuses with GS demonstrated significant evisceration of abdominal organs. In contrast, the abdominal wall of the fetuses from GSR was intact. Conclusion:The present animal model demonstrated the technical feasibility and success of an intrauterine repair of GS for the first time. However, further long-term studies (leaving GS and GSR in utero for several days) will be necessary to compare survival rates and intestinal injury, motility or absorption. The clinical application of GSR in utero remains a vision so far. Copyright (C) 2003 S. Karger AG, Basel
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A close encounter with a terrestrial dust devil
We report on an extremely well characterised encounter with a terrestrial dust devil, and its comparison with martian dust devils
Is Small Perfect? Size Limit to Defect Formation in Pyramidal Pt Nanocontacts
We report high resolution transmission electron microscopy and ab initio
calculation results for the defect formation in Pt nanocontacts (NCs). Our
results show that there is a size limit to the existence of twins (extended
structural defects). Defects are always present but blocked away from the tip
axes. The twins may act as scattering plane, influencing contact electron
transmission for Pt NC at room temperature and Ag/Au NC at low temperature.Comment: 4 pages, 3 figure
The relationship between Hippocampal asymmetry and working memory processing in combat-related PTSD: a monozygotic twin study
BACKGROUND: PTSD is associated with reduction in hippocampal volume and abnormalities in hippocampal function. Hippocampal asymmetry has received less attention, but potentially could indicate lateralised differences in vulnerability to trauma. The P300 event-related potential component reflects the immediate processing of significant environmental stimuli and has generators in several brain regions including the hippocampus. P300 amplitude is generally reduced in people with PTSD. METHODS: Our study examined hippocampal volume asymmetry and the relationship between hippocampal asymmetry and P300 amplitude in male monozygotic twins discordant for Vietnam combat exposure. Lateralised hippocampal volume and P300 data were obtained from 70 male participants, of whom 12 had PTSD. We were able to compare (1) combat veterans with current PTSD; (2) their non-combat-exposed co-twins; (3) combat veterans without current PTSD and (4) their non-combat-exposed co-twins. RESULTS: There were no significant differences between groups in hippocampal asymmetry. There were no group differences in performance of an auditory oddball target detection task or in P300 amplitude. There was a significant positive correlation between P300 amplitude and the magnitude of hippocampal asymmetry in participants with PTSD. CONCLUSIONS: These findings suggest that greater hippocampal asymmetry in PTSD is associated with a need to allocate more attentional resources when processing significant environmental stimuli.Timothy Hall, Cherrie Galletly, C.R. Clark, Melinda Veltmeyer, Linda J. Metzger, Mark W. Gilbertson, Scott P. Orr, Roger K. Pitman and Alexander McFarlan
A Search for Distant Galactic Cepheids Toward l=60
We present results of a survey of a 6-square-degree region near l=60, b=0 to
search for distant Milky Way Cepheids. Few MW Cepheids are known at distances
>~ R_0, limiting large-scale MW disk models derived from Cepheid kinematics;
this work was designed to find a sample of distant Cepheids for use in such
models. The survey was conducted in the V and I bands over 8 epochs, to a
limiting I~=18, with a total of ~ 5 million photometric observations of ~ 1
million stars. We present a catalog of 578 high-amplitude variables discovered
in this field. Cepheid candidates were selected from this catalog on the basis
of variability and color change, and observed again the following season. We
confirm 10 of these candidates as Cepheids with periods from 4 to 8 days, most
at distances > 3 kpc. Many of the Cepheids are heavily reddened by intervening
dust, some with implied extinction A_V > 10 mag. With a future addition of
infrared photometry and radial velocities, these stars alone can provide a
constraint on R_0 to 8%, and in conjunction with other known Cepheids should
provide good estimates of the global disk potential ellipticity.Comment: 18 pages, 4 tables, 13 figures (LaTeX / AASTeX
Aerosol water parameterization: long-term evaluation and importance for climate studies
We scrutinize the importance of aerosol water for the aerosol optical depth
(AOD) calculations using a long-term evaluation of the EQuilibrium
Simplified Aerosol Model v4 for climate modeling. EQSAM4clim is
based on a single solute coefficient approach that efficiently parameterizes
hygroscopic growth, accounting for aerosol water uptake from the
deliquescence relative humidity up to supersaturation. EQSAM4clim extends the
single solute coefficient approach to treat water uptake of multicomponent
mixtures. The gasâaerosol partitioning and the mixed-solution water uptake
can be solved analytically, preventing the need for iterations, which is
computationally efficient. EQSAM4clim has been implemented in the global
chemistry climate model EMAC and compared to ISORROPIAÂ II on climate
timescales. Our global modeling results show that (I) our EMAC results of the
AOD are comparable to modeling results that have been independently evaluated
for the period 2000â2010, (II) the results of various aerosol properties of
EQSAM4clim and ISORROPIAÂ II are similar and in agreement with AERONET and
EMEP observations for the period 2000â2013, and (III) the underlying
assumptions on the aerosol water uptake limitations are important for derived
AOD calculations. Sensitivity studies of different levels of chemical aging
and associated water uptake show larger effects on AOD calculations for the
year 2005 compared to the differences associated with the application of the
two gasâliquidâsolid partitioning schemes. Overall, our study demonstrates
the importance of aerosol water for climate studies.</p
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