10,662 research outputs found
Isostatic compression process converts polyaromatics into structural material
Isostatic compression process compacts certain powdered aromatic polymers into homogeneous materials that can be machined to form useful components, such as bearings. It provides for complete removal of air in the interstitial spaces surrounding the granules of the powdered polymer before the powder is subjected to isostatic compression
Electron impact excitation of N IV: calculations with the DARC code and a comparison with ICFT results
There have been discussions in the recent literature regarding the accuracy
of the available electron impact excitation rates (equivalently effective
collision strengths ) for transitions in Be-like ions. In the present
paper we demonstrate, once again, that earlier results for are
indeed overestimated (by up to four orders of magnitude), for over 40\% of
transitions and over a wide range of temperatures. To do this we have performed
two sets of calculations for N~IV, with two different model sizes consisting of
166 and 238 fine-structure energy levels. As in our previous work, for the
determination of atomic structure the GRASP (General-purpose Relativistic
Atomic Structure Package) is adopted and for the scattering calculations (the
standard and parallelised versions of) the Dirac Atomic R-matrix Code ({\sc
darc}) are employed. Calculations for collision strengths and effective
collision strengths have been performed over a wide range of energy (up to
45~Ryd) and temperature (up to 2.010~K), useful for applications in
a variety of plasmas. Corresponding results for energy levels, lifetimes and
A-values for all E1, E2, M1 and M2 transitions among 238 levels of N~IV are
also reported.Comment: This paper with 5 Figs. and 8 Tables will appear in MNRAS (2016
Solubility of Sulfur Dioxide in Sulfuric Acid
The solubility of sulfur dioxide in 50% (wt./wt.) sulfuric acid was evaluated by regular solution theory, and the results verified by experimental measurements in the temperature range of 25 C to 70 C at pressures of 60 to 200 PSIA. The percent (wt./wt.) of sulfur dioxide in 50% (wt./wt.) sulfuric acid is given by the equation %SO2 = 2.2350 + 0.0903P - 0.00026P 10 to the 2nd power with P in PSIA
Extreme ultraviolet emission lines of Ni XII in laboratory and solar spectra
Wavelengths for emission lines arising from 3s23p5-3s3p6 and 3s23p5-3s23p43d transitions in Ni XII have been measured in extreme ultraviolet spectra of the Joint European Torus(JET) tokamak. The 3s23p5 2P1/2-3s23p4(3P)3d 2D3/2 line is found to lie at 152.90 ± 0.02 A, a significant improvement over the previous experimental determination of 152.95 ± 0.5 A. This new wavelength is in good agreement with a solar identification at 152.84 ± 0.06 A, confirming the presence of this line in the solar spectrum. The Ni XII feature at 152.15 A may be a result only of the 3s23p5 2P3/2-3s23p4(3P)3d 2D5/2 transition, rather than a blend of this line with 3s23p5 2P3/2-3s23p (3P)3d 2P1/2, as previously suggested. Unidentified emission
lines at 295.32 and 317.61 A in solar flare spectra from the Skylab mission are tentatively identified as the 3s23p5 2P3/2-3s3p6 2S1/2 and 3s23p5 2P1/2-3s3p6 2S1/2 transitions in Ni XII, which have laboratory wavelengths of 295.33 and 317.50 A, respectively. Additional support for these identifications is provided by the line intensity ratio for the solar features, which shows good agreement between theory and observation
The platinum nuclei: concealed configuration mixing and shape coexistence
The role of configuration mixing in the Pt region is investigated. For this
chain of isotopes, the nature of the ground state changes smoothly, being
spherical around mass and and deformed around the
mid-shell N=104 region. This has a dramatic effect on the systematics of the
energy spectra as compared to the systematics in the Pb and Hg nuclei.
Interacting Boson Model with configuration mixing calculations are presented
for gyromagnetic factors, -decay hindrance factors, and isotope shifts.
The necessity of incorporating intruder configurations to obtain an accurate
description of the latter properties becomes evident.Comment: Accepted in Physical Review
The effect of ionization on the populations of excited levels of C IV and C V in tokamak edge plasmas
The main populating and depopulating mechanisms of the excited energy levels
of ions in plasmas with densities <1023-1024 m-3 are electron collisional
excitation from the ion's ground state and radiative decay, respectively, with
the majority of the electron population being in the ground state of the
ionization stage. Electron collisional ionization is predominately expected to
take place from one ground state to that of the next higher ionization stage.
However, the question arises as to whether, in some cases, ionization can also
affect the excited level populations. This would apply particularly to those
cases involving transient events such as impurity influxes in a laboratory
plasma. An analysis of the importance of ionization in populating the excited
levels of ions in plasmas typical of those found in the edge of tokamaks is
undertaken for the C IV and C V ionization stages. The emphasis is on those
energy levels giving rise to transitions of most use for diagnostic purposes.
Carbon is chosen since it is an important contaminant of JET plasmas; it was
the dominant low Z impurity before the installation of the ITER-like wall and
is still present in the plasma after its installation. Direct electron
collisional ionization both from and to excited levels is considered.
Distorted-wave Flexible Atomic Code calculations are performed to generate the
required ionization cross sections, due to a lack of atomic data in the
literature.Comment: 29 pages, 5 figures. This is an author-created, un-copyedited version
of an article accepted for publication in Journal of Physics B. IOP
Publishing Ltd is not responsible for any errors or omissions in this version
of the manuscript or any version derived from i
The Ever Changing Circumstellar Nebula Around UW Centauri
We present new images of the reflection nebula surrounding the R Coronae
Borealis Star, UW Cen. This nebula, first detected in 1990, has changed its
appearance significantly. At the estimated distance of UW Cen, this nebula is
approximately 0.6 ly in radius so the nebula cannot have physically altered in
only 8 years. Instead, the morphology of the nebula appears to change as
different parts are illuminated by light from the central star modulated by
shifting thick dust clouds near its surface. These dust clouds form and
dissipate at irregular intervals causing the well-known declines in the R
Coronae Borealis (RCB) stars. In this way, the central star acts like a
lighthouse shining through holes in the dust clouds and lighting up different
portions of the nebula. The existence of this nebula provides clues to the
evolutionary history of RCB stars possibly linking them to the Planetary
Nebulae and the final helium shell flash stars.Comment: To be published in ApJ Letters. 5 pages, 3 figures (2 in color
Long-term high fat feeding of rats results in increased numbers of circulating microvesicles with pro-inflammatory effects on endothelial cells
Obesity and type 2 diabetes lead to dramatically increased risks of atherosclerosis and CHD. Multiple mechanisms converge to promote atherosclerosis by increasing endothelial oxidative stress and up-regulating expression of pro-inflammatory molecules. Microvesicles (MV) are small ( < 1 μm) circulating particles that transport proteins and genetic material, through which they are able to mediate cell–cell communication and influence gene expression. Since MV are increased in plasma of obese, insulin-resistant and diabetic individuals, who often exhibit chronic vascular inflammation, and long-term feeding of a high-fat diet (HFD) to rats is a well-described model of obesity and insulin resistance, we hypothesised that this may be a useful model to study the impact of MV on endothelial inflammation. The number and cellular origin of MV from HFD-fed obese rats were characterised by flow cytometry. Total MV were significantly increased after feeding HFD compared to feeding chow (P< 0·001), with significantly elevated numbers of MV derived from leucocyte, endothelial and platelet compartments (P< 0·01 for each cell type). MV were isolated from plasma and their ability to induce reactive oxygen species (ROS) formation and vascular cell adhesion molecule (VCAM)-1 expression was measured in primary rat cardiac endothelial cells in vitro. MV from HFD-fed rats induced significant ROS (P< 0·001) and VCAM-1 expression (P= 0·0275), indicative of a pro-inflammatory MV phenotype in this model of obesity. These findings confirm that this is a useful model to further study the mechanisms by which diet can influence MV release and subsequent effects on cardio-metabolic health
A comparison of theoretical line intensity ratios for Ni XII with extreme ultraviolet observations from the JET tokamak
Recent R-matrix calculations of electron impact excitation rates in Ni XII are used to derive the emission line ratios R1 = I (154.17 Å)/I (152.15 Å), R2 = I (152.95 Å)/I (152.15 Å) and R3 = I (160.55 Å)/I (152.15 Å). This is the first time (to our knowledge) that theoretical emission line ratios have been calculated for this ion. The ratios are found to be insensitive to changes in the adopted electron density (Ne) when Ne >= 5 × 10^11 cm−3, typical of laboratory plasmas. However, they do vary with electron temperature (Te), with for example R1 and R3 changing by factors of 1.3 and 1.8, respectively, between Te = 10^5 and 10^6 K. A comparison of the theoretical line ratios with measurements from the Joint European Torus (JET) tokamak reveals very good agreement between theory and observation for R1, with an average discrepancy of only 7%. Agreement between the calculated and experimental ratios for R2 and R3 is less satisfactory, with average differences of 30 and 33%, respectively. These probably arise from errors in the JET instrument calibration curve. However, the discrepancies are smaller than the uncertainties in the R2 and R3 measurements. Our results, in particular for R1, provide experimental support for the accuracy of the Ni XII line ratio calculations, and hence for the atomic data adopted in their derivation
The Chandra X-ray Observatory Resolves the X-ray Morphology and Spectra of a Jet in PKS 0637-752
The core-dominated radio-loud quasar PKS 0637-752 (z = 0.654) was the first
celestial object observed with the Chandra X-ray Observatory, offering the
early surprise of the detection of a remarkable X-ray jet. Several observations
with a variety of detector configurations contribute to a total exposure time
with the Chandra Advanced CCD Imaging Spectrometer (ACIS; Garmire et al. 2000,
in preparation) of about 100ks. A spatial analysis of all the available X-ray
data, making use of Chandra's spatial resolving power of about 0.4 arcsec,
reveals a jet that extends about 10 arcsec to the west of the nucleus. At least
four X-ray knots are resolved along the jet, which contains about 5% of the
overall X-ray luminosity of the source. Previous observations of PKS 0637-752
in the radio band (Tingay et al. 1998) had identified a kpc-scale radio jet
extending to the West of the quasar. The X-ray and radio jets are similar in
shape, intensity distribution, and angular structure out to about 9 arcsec,
after which the X-ray brightness decreases more rapidly and the radio jet turns
abruptly to the north. The X-ray luminosity of the total source is log Lx ~
45.8 erg/s (2 - 10keV), and appears not to have changed since it was observed
with ASCA in November 1996. We present the results of fitting a variety of
emission models to the observed spectral distribution, comment on the
non-existence of emission lines recently reported in the ASCA observations of
PKS 0637-752, and briefly discuss plausible X-ray emission mechanisms.Comment: 24 pages, includes 8 figures, Accepted for publication in Ap
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