370 research outputs found
Morphology and structure of soot emitted from various aircraft engines
International audienceWe present here an experimental characterization of the morphology, structure and chemical properties of soot particles emitted from various aircraft engines (CFM56-5C, -7B, SaM-146), and a combustor [Delhaye, 2008 ; Petzold, 2011]. Soot particles have been collected by direct impaction on electron microscope grids. Transmission electron microscopy (TEM) is used to determine the aggregates fractal dimension as well as soot primary particles and aggregates size distributions. The morphology, structure and texture of primary particles are also determined in addition to the elemental composition by the mean of X-ray energy dispersive spectrometry (XREDS)
Induced work function changes at Mg-doped MgO/Ag(001) interfaces: Combined Auger electron diffraction and density functional study
The properties of MgO/Ag(001) ultrathin films with substitutional Mg atoms in the interface metal layer have been investigated by means of Auger electron diffraction experiments, ultraviolet photoemission spectroscopy, and density functional theory (DFT) calculations. Exploiting the layer-by-layer resolution of the MgKL23L23 Auger spectra and using multiple scattering calculations, we first determine the interlayer distances as well as the morphological parameters of the MgO/Ag(001) system with and without Mg atoms incorporated at the interface. We find that the Mg atom incorporation drives a strong distortion of the interface layers and that its impact on the metal/oxide electronic structure is an important reduction of the work function (0.5 eV) related to band-offset variations at the interface. These experimental observations are in very good agreement with our DFT calculations which reproduce the induced lattice distortion and which reveal (through a Bader analysis) that the increase of the interface Mg concentration results in an electron transfer from Mg to Ag atoms of the metallic interface layer. Although the local lattice distortion appears as a consequence of the attractive (repulsive) Coulomb interaction between O2− ions of the MgO interface layer and the nearest positively (negatively) charged Mg (Ag) neighbors of the metallic interface layer, its effect on the work function reduction is only limited. Finally, an analysis of the induced work function changes in terms of charge transfer, rumpling, and electrostatic compression contributions is attempted and reveals that the metal/oxide work function changes induced by interface Mg atoms incorporation are essentially driven by the increase of the electrostatic compression effect
Correcting for static shift of magnetotelluric data with airborne electromagnetic measurements: a case study from Rathlin Basin, Northern Ireland
Galvanic distortions of
magnetotelluric (MT) data, such as the static-shift effect, are a known
problem that can lead to incorrect estimation of resistivities and erroneous
modelling of geometries with resulting misinterpretation of subsurface
electrical resistivity structure. A wide variety of approaches have been
proposed to account for these galvanic distortions, some depending on the
target area, with varying degrees of success. The natural laboratory for our
study is a hydraulically permeable volume of conductive sediment at depth,
the internal resistivity structure of which can be used to estimate reservoir
viability for geothermal purposes; however, static-shift correction is
required in order to ensure robust and precise modelling accuracy.We present here a possible method to employ frequency–domain electromagnetic
data in order to correct static-shift effects, illustrated by a case study
from Northern Ireland. In our survey area, airborne frequency domain electromagnetic (FDEM) data are regionally
available with high spatial density. The spatial distributions of the derived
static-shift corrections are analysed and applied to the uncorrected MT data
prior to inversion. Two comparative inversion models are derived, one with
and one without static-shift corrections, with instructive results. As
expected from the one-dimensional analogy of static-shift correction, at
shallow model depths, where the structure is controlled by a single local MT
site, the correction of static-shift effects leads to vertical scaling of
resistivity–thickness products in the model, with the corrected model showing
improved correlation to existing borehole wireline resistivity data. In turn,
as these vertical scalings are effectively independent of adjacent sites,
lateral resistivity distributions are also affected, with up to half a decade
of resistivity variation between the models estimated at depths down to
2000 m. Simple estimation of differences in bulk porosity, derived using
Archie's Law, between the two models reinforces our conclusion that the
suborder of magnitude resistivity contrasts induced by the correction of static
shifts correspond to similar contrasts in estimated porosities, and hence,
for purposes of reservoir investigation or similar cases requiring accurate
absolute resistivity estimates, galvanic distortion correction, especially
static-shift correction, is essential
Ultrafast imaging of the entire chest without ECG synchronisation or beta-blockade: to what extent can we analyse the coronary arteries?
Spectral Line-by-Line Pulse Shaping of an On-Chip Microresonator Frequency Comb
We report, for the first time to the best of our knowledge, spectral phase
characterization and line-by-line pulse shaping of an optical frequency comb
generated by nonlinear wave mixing in a microring resonator. Through
programmable pulse shaping the comb is compressed into a train of
near-transform-limited pulses of \approx 300 fs duration (intensity full width
half maximum) at 595 GHz repetition rate. An additional, simple example of
optical arbitrary waveform generation is presented. The ability to characterize
and then stably compress the frequency comb provides new data on the stability
of the spectral phase and suggests that random relative frequency shifts due to
uncorrelated variations of frequency dependent phase are at or below the 100
microHertz level.Comment: 18 pages, 4 figure
SAMPLE III SC.01 - Studying, sAmpling and Measuring of aircraft ParticuLate Emissions III: Specific Contract 01
Ultrasound- Versus Fluoroscopy-Guided Strategy for Transfemoral Transcatheter Aortic Valve Replacement Access: A Systematic Review and Meta-Analysis
Background:Access site vascular and bleeding complications remain problematic for patients undergoing transcatheter aortic valve replacement (TAVR). Ultrasound-guided transfemoral access approach has been suggested as a technique to reduce access site complications, but there is wide variation in adoption in TAVR. We performed a systematic review and meta-analysis to compare access site vascular and bleeding complications according to the Valve Academic Research Consortium-2 classification following the use of either ultrasound- or conventional fluoroscopy-guided transfemoral TAVR access.Methods:Medline, Embase, Web of Science, and The Cochrane Library were searched to November 2020 for studies comparing ultrasound- and fluoroscopy-guided access for transfemoral TAVR. A priori defined primary outcomes were extracted: (1) major, (2) minor, and (3) major and minor (total) access site vascular complications and (4) life-threatening/major, (5) minor, and (6) life-threatening, major, and minor (total) access site bleeding complications.Results:Eight observational studies (n=3875) were included, with a mean participant age of 82.8 years, STS score 5.81, and peripheral vascular disease in 23.5%. An ultrasound-guided approach was significantly associated with a reduced risk of total (Mantel-Haenszel odds ratio [MH-OR], 0.50 [95% CI, 0.35–0.73]), major (MH-OR, 0.51 [95% CI, 0.35–0.74]), and minor (MH-OR, 0.59 [95% CI, 0.38–0.91]) access site vascular complications. Ultrasound guidance was also significantly associated with total access site bleeding complications (MH-OR, 0.59 [95% CI, 0.39–0.90]). The association remained significant in sensitivity analyses of maximally adjusted minor and total vascular access site complications (MH-OR, 0.51 [95% CI, 0.29–0.90]; MH-OR, 0.44 [95% CI, 0.20–0.99], respectively).Conclusions:In the absence of randomized studies, our data suggests a potential benefit for ultrasound guidance to obtain percutaneous femoral access in TAVR
- …