5,218 research outputs found
Real-time imaging required for optimal echocardiographic assessment of aortic valve calcification
Introduction Aortic valve calcification (AVC), even without haemodynamic significance, may be prognostically import as an expression of generalized atherosclerosis, but techniques for echocardiographic assessment are essentially unexplored. Methods Two-dimensional (2D) echocardiographic recordings (Philips IE33) of the aortic valve in short-axis and long-axis views were performed in 185 consecutive patients within 1 week before surgery for aortic stenosis (n = 109, AS), aortic regurgitation (n = 61, AR), their combination (n = 8) or dilation of the ascending aorta (n = 7). The grey scale mean (GSMn) of the aortic valve in an end-diastolic short-axis still frame was measured. The same frame was scored visually 15 as indicating that the aortic valve was normal, thick, or had mild, moderate or severe calcification. The visual echodensity of each leaflet was determined real time applying the same 5-grade scoring system for each leaflet, and the average for the whole valve was calculated. Finally, a similar calcification score for the whole valve based on inspection and palpation by the surgeon was noted. Results Visual assessment of real-time images using the proposed scoring system showed better correlation with the surgical evaluation of the degree of valve calcification (r = 0.83, P<0.001) compared to evaluation of stop frames by visual assessment (r = 0.66, P<0.001) or the GSMn score (r = 0.64, P<0.001). High inter- and intra-observer correlations were observed for real-time visual score (both intraclass correlation coefficient = 0.93). Conclusion Real-time evaluation of the level of AVC is superior to using stop frames assessed either visually or by dedicated computer grey scale measurement software
Electronic structure and chemical bonding in Ti4SiC3 investigated by soft x-ray emission spectroscopy and first principle theory
The electronic structure in the new transition metal carbide Ti4SiC3 has been
investigated by bulk-sensitive soft x-ray emission spectroscopy and compared to
the well-studied Ti3SiC2 and TiC systems. The measured high-resolution Ti L, C
K and Si L x-ray emission spectra are discussed with ab initio calculations
based on density-functional theory including core-to-valence dipole matrix
elements. The detailed investigations of the Ti-C and Ti-Si chemical bonds
provide increased understanding of the physical properties of these
nanolaminates. A strongly modified spectral shape is detected for the buried Si
monolayers due to Si 3p hybridization with the Ti 3d orbitals. As a result of
relaxation of the crystal structure and the charge-transfer from Ti (and Si) to
C, the strength of the Ti-C covalent bond is increased. The differences between
the electronic and crystal structures of Ti4SiC3 and Ti3SiC2 are discussed in
relation to the number of Si layers per Ti layer in the two systems and the
corresponding change of materials properties.Comment: 12 pages, 7 figures, 1 tabl
Electronic structure and chemical bonding in Ti2AlC investigated by soft x-ray emission spectroscopy
The electronic structure of the nanolaminated transition metal carbide Ti2AlC
has been investigated by bulk-sensitive soft x-ray emission spectroscopy. The
measured Ti L, C K and Al L emission spectra are compared with calculated
spectra using ab initio density-functional theory including dipole matrix
elements. The detailed investigation of the electronic structure and chemical
bonding provides increased understanding of the physical properties of this
type of nanolaminates. Three different types of bond regions are identified;
the relatively weak Ti 3d - Al 3p hybridization 1 eV below the Fermi level, and
the Ti 3d - C 2p and Ti 3d - C 2s hybridizations which are stronger and deeper
in energy are observed around 2.5 eV and 10 eV below the Fermi level,
respectively. A strongly modified spectral shape of the 3s final states in
comparison to pure Al is detected for the buried Al monolayers indirectly
reflecting the Ti 3d - Al 3p hybridization. The differences between the
electronic and crystal structures of Ti2AlC, Ti3AlC2 and TiC are discussed in
relation to the number of Al layers per Ti layer in the two former systems and
the corresponding change of the unusual materials properties.Comment: 14 pages, 7 figures; PACS:78.70.En, 71.15.Mb, 71.20.-
WATCHING THE SKY NEW REALIZATIONS, NEW MEANINGS, AND SURPRIZING ASPECTS IN UNIVERSITY LEVEL ASTRONOMY
Abstract: Learning astronomy is challenging at all levels due to the highly specialized form of communication used to share knowledge. When taking astronomy courses at different levels at university, learners are exposed to a variety of representations that are intended to help them learn about the structure and complexity of the Universe. However, not much is known about the reflective awareness that these representations evoke. Using a simulation video that provides a vivid virtual journey through our Milky Way galaxy, the nature of this awareness is captured and categorised for an array of learners (benchmark by results obtained for experts). The results illustrate how the number and nature of new things grounded in dimensionality, scale, time and perspective reflective awareness can too easily be taken for granted by both teachers and learners
The Hamburg/ESO R-process Enhanced Star survey (HERES) IV. Detailed abundance analysis and age dating of the strongly r-process enhanced stars CS 29491-069 and HE 1219-0312
We report on a detailed abundance analysis of two strongly r-process
enhanced, very metal-poor stars newly discovered in the HERES project, CS
29491-069 ([Fe/H]=-2.51, [r/Fe]=+1.1) and HE 1219-0312 ([Fe/H]=-2.96,
[r/Fe]=+1.5). The analysis is based on high-quality VLT/UVES spectra and MARCS
model atmospheres. We detect lines of 15 heavy elements in the spectrum of CS
29491-069, and 18 in HE 1219-0312; in both cases including the Th II 4019 {\AA}
line. The heavy-element abundance patterns of these two stars are mostly
well-matched to scaled solar residual abundances not formed by the s-process.
We also compare the observed pattern with recent high-entropy wind (HEW)
calculations, which assume core-collapse supernovae of massive stars as the
astrophysical environment for the r-process, and find good agreement for most
lanthanides. The abundance ratios of the lighter elements strontium, yttrium,
and zirconium, which are presumably not formed by the main r-process, are
reproduced well by the model. Radioactive dating for CS 29491-069 with the
observed thorium and rare-earth element abundance pairs results in an average
age of 9.5 Gyr, when based on solar r-process residuals, and 17.6 Gyr, when
using HEW model predictions. Chronometry seems to fail in the case of HE
1219-0312, resulting in a negative age due to its high thorium abundance. HE
1219-0312 could therefore exhibit an overabundance of the heaviest elements,
which is sometimes called an "actinide boost"
Observation of a New Type of Low Frequency Waves at Comet 67P/Churyumov-Gerasimenko
We report on magnetic field measurements made in the innermost coma of
67P/Churyumov-Gerasimenko in its low activity state. Quasi-coherent,
large-amplitude (), compressional magnetic field
oscillations at 40 mHz dominate the immediate plasma environment of the
nucleus. This differs from previously studied comet-interaction regions where
waves at the cometary ion gyro-frequencies are the main feature. Thus classical
pick-up ion driven instabilities are unable to explain the observations. We
propose a cross-field current instability associated with newborn cometary ion
currents as a possible source mechanism.Comment: 6 pages, 3 Figure
Gene Expression and Immunohistochemistry in Adipose Tissue of HIV Type 1-Infected Patients with Nucleoside Analogue Reverse-Transcriptase Inhibitor-Associated Lipoatrophy
BackgroundLong-term use of both zidovudine (AZT) and stavudine (d4T) is associated with lipoatrophy, but it occurs possibly through different mechanisms MethodsSurgical biopsy specimens of subcutaneous adipose tissue were obtained from 18 human immunodeficiency virus type 1 (HIV-1)-infected lipoatrophic patients (the LA+ group) who were treated with either zidovudine (the AZT+LA+ group; n=10) or stavudine (the d4T+LA+ group; n=8) and from 10 nonlipoatrophic HIV-1-infected patients (the LAâ group) who received antiretroviral therapy. Mitochondrial DNA (mtDNA) copy numbers, gene expression, and immunohistochemistry data were analyzed ResultsmtDNA copy numbers were significantly reduced in the LA+ group, compared with the LAâ group, and in the d4T+LA+ group, compared with the AZT+LA+ group. The ratio of mtDNA-encoded cytochrome COX3 to nuclear DNA-encoded COX4 expression was significantly lower in the LA+ group than in the LAâ group. Compared with the LAâ group, the LA+ group had significantly lower expression of genes involved in adipogenesis (SREBP1cand CEBPB) lipid (fatty acid synthase), and glucose (GLUT4) metabolism. Expression of genes involved in mitochondrial biogenesis (PGC1B) apoptosis (FAS) inflammation (IL1B) oxidative stress (PCNA and SOD1) and lamin B was significantly higher in the LA+ group than in the LAâ group. The d4T+LA+ group had significantly lower expression of genes involved in mitochondrial biogenesis (POLG1) energy metabolism (the COX3/COX4 ratio), adipogenesis (SREBP1c and CEBPA) perilipin, and hexokinase than did the AZT+LA+ group. There were 7-fold more macrophages in adipose tissue specimens obtained from patients in the LA+ group, compared with the LAâ group ConclusionsLipoatrophy is characterized by mtDNA depletion, inflammation, and signs of apoptosis. Changes were more profound in the d4T+LA+ group than in the AZT+LA+ grou
Cyclic AMP impairs the rapid effect of insulin to enhance cell-surface insulin-binding capacity in rat adipocytes
Electronic structure investigation of Ti3AlC2, Ti3SiC2, and Ti3GeC2 by soft-X-ray emission spectroscopy
The electronic structures of epitaxially grown films of Ti3AlC2, Ti3SiC2 and
Ti3GeC2 have been investigated by bulk-sensitive soft X-ray emission
spectroscopy. The measured high-resolution Ti L, C K, Al L, Si L and Ge M
emission spectra are compared with ab initio density-functional theory
including core-to-valence dipole matrix elements. A qualitative agreement
between experiment and theory is obtained. A weak covalent Ti-Al bond is
manifested by a pronounced shoulder in the Ti L-emission of Ti3AlC2. As Al is
replaced with Si or Ge, the shoulder disappears. For the buried Al and
Si-layers, strongly hybridized spectral shapes are detected in Ti3AlC2 and
Ti3SiC2, respectively. As a result of relaxation of the crystal structure and
the increased charge-transfer from Ti to C, the Ti-C bonding is strengthened.
The differences between the electronic structures are discussed in relation to
the bonding in the nanolaminates and the corresponding change of materials
properties.Comment: 15 pages, 8 figure
HE 0557-4840 - Ultra-Metal-Poor and Carbon-Rich
We report the discovery and high-resolution, high S/N, spectroscopic analysis
of the ultra-metal-poor red giant HE 0557-4840, which is the third most
heavy-element deficient star currently known. Its atmospheric parameters are
T_eff = 4900 K, log g = 2.2, and [Fe/H]= -4.75. This brings the number of stars
with [Fe/H] < -4.0 to three, and the discovery of HE 0557-4840 suggests that
the metallicity distribution function of the Galactic halo does not have a
"gap" between [Fe/H] = -4.0, where several stars are known, and the two most
metal-poor stars, at [Fe/H] ~ -5.3. HE 0557-4840 is carbon rich - [C/Fe] = +1.6
- a property shared by all three objects with [Fe/H] < -4.0, suggesting that
the well-known increase of carbon relative to iron with decreasing [Fe/H]
reaches its logical conclusion - ubiquitous carbon richness - at lowest
abundance. We also present abundances (nine) and limits (nine) for a further 18
elements. For species having well-measured abundances or strong upper limits,
HE 0557-4840 is "normal" in comparison with the bulk of the stellar population
at [Fe/H] ~ -4.0 - with the possible exception of Co. We discuss the
implications of these results for chemical enrichment at the earliest times, in
the context of single ("mixing and fallback") and two-component enrichment
models. While neither offers a clear solution, the latter appears closer to the
mark. Further data are required to determine the oxygen abundance and improve
that of Co, and hence more strongly constrain the origin of this object.Comment: Submitted to Astrophysical Journal. 52 pages (41 text, 11 figures
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