2,193 research outputs found
The O(3P) and N(4S) density measurement at 225 km by ultraviolet absorption and fluorescence in the Apollo-Soyuz test project
The densities of O(3P) and N(4S) at 225 km were determined during the Apollo Soyuz Test Project by a resonance absorption/fluorescence technique in which OI and NI line radiation produced and collimated on board the Apollo was reflected from the Soyuz back to the Apollo for spectral analysis. The two spacecraft maneuvered so that a range of observation angles of plus or minus 15 deg with respect to the normal to the orbital velocity vector was scanned. The measurements were made at night on two consecutive orbits at spacecraft separations of 150 and 500 m. The resulting relative counting rates as function of observation angle were compared to calculated values to determine the oxygen value. This value agrees with mass spectrometric measurements made under similar conditions. The nitrogen value is in good agreement with other measurements and suggests a smaller diurnal variation than is predicted by present models
Ultraviolet absorption: Experiment MA-059
A technique devised to permit the measurement of atmospheric species concentrations is described. This technique involves the application of atomic absorption spectroscopy and the quantitative observation of resonance fluorescence in which atomic or molecular species scatter resonance radiation from a light source into a detector. A beam of atomic oxygen and atomic nitrogen resonance radiation, strong unabsorbable oxygen and nitrogen radiation, and visual radiation was sent from Apollo to Soyuz. The density of atomic oxygen and atomic nitrogen between the two spacecraft was measured by observing the amount of resonance radiation absorbed when the line joining Apollo and Soyuz was perpendicular to their velocity with respect to the ambient atmosphere. Results of postflight analysis of the resonance fluorescence data are discussed
Comment on: “The measurement of tropospheric OH radicals by laser-induced fluorescence spectroscopy during the POPCORN Field Campaign” by Hofzumahaus et al. and “Intercomparison of tropospheric OH radical measurements by multiple folded long-path laser absorption and laser induced fluorescence” by Brauers et al.
Calibration of laser induced fluorescence (LIF) instruments
that measure OH is challenging because it is difficult to
reliably introduce a known amount of this reactive radical into a measurement apparatus. In a recent paper, Hofzumahaus et al., [1996] describe a novel and seemingly simple technique to accomplish this goal: they dissociate trace quantities of water vapor in air with a low pressure mercury (Hg) lamp to produce low concentrations (10^5 - 10^9 cm^(-3)) of OH (R1)
Constraints on Primordial Nongaussiantiy from the High-Redshift Cluster MS1054--03
The implications of the massive, X-ray selected cluster of galaxies
MS1054--03 at are discussed in light of the hypothesis that the
primordial density fluctuations may be nongaussian. We generalize the
Press-Schechter (PS) formalism to the nongaussian case, and calculate the
likelihood that a cluster as massive as MS1054 would appear in the EMSS. The
probability of finding an MS1054-like cluster depends only on \omegam and the
extent of primordial nongaussianity. We quantify the latter by adopting a
specific functional form for the PDF, denoted which tends to
Gaussianity for and show how is related to the more
familiar statistic the probability of fluctuations for a
given PDF relative to a Gaussian. We find that Gaussian initial density
fluctuations are consistent with the data on MS1054 only if \omegam\simlt
0.2. For \omegam\ge 0.25 a significant degree of nongaussianity is required,
unless the mass of MS1054 has been substantially overestimated by X-ray and
weak lensing data. The required amount of nongaussianity is a rapidly
increasing function of \omegam for 0.25 \le \omegam \le 0.45, with (T \simgt 7) at the upper end of this range. For a fiducial
\omegam=0.3, \omegal=0.7 universe, favored by several lines of evidence we
obtain an upper limit corresponding to a This
finding is consistent with the conclusions of Koyama, Soda, & Taruya (1999),
who applied the generalized PS formalism to low (z\simlt 0.1) and
intermediate (z\simlt 0.6) redshift cluster data sets.Comment: 15 pages, 11 figures, submitted to the Astrophysical Journal, uses
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Spin configurations in Co2FeAl0.4Si0.6 Heusler alloy thin film elements
We determine experimentally the spin structure of half-metallic
Co2FeAl0.4Si0.6 Heusler alloy elements using magnetic microscopy. Following
magnetic saturation, the dominant magnetic states consist of quasi-uniform
configurations, where a strong influence from the magnetocrystalline anisotropy
is visible. Heating experiments show the stability of the spin configuration of
domain walls in confined geometries up to 800 K. The switching temperature for
the transition from transverse to vortex walls in ring elements is found to
increase with ring width, an effect attributed to structural changes and
consequent changes in magnetic anisotropy, which start to occur in the narrower
elements at lower temperatures.Comment: 4 pages, 4 figure
Polarization Diagnostics for Cool Core Cluster Emission Lines
The nature of the interaction between low-excitation gas filaments at ~104 K, seen in optical line emission, and diffuse X-ray emitting coronal gas at ~107 K in the centers of galaxy clusters remains a puzzle. The presence of a strong, empirical correlation between the two gas phases is indicative of a fundamental relationship between them, though as yet of undetermined cause. The cooler filaments, originally thought to have condensed from the hot gas, could also arise from a merger or the disturbance of cool circumnuclear gas by nuclear activity. Here, we have searched for intrinsic line emission polarization in cool core galaxy clusters as a diagnostic of fundamental transport processes. Drawing on developments in solar astrophysics, direct energetic particle impact induced polarization holds the promise to definitively determine the role of collisional processes such as thermal conduction in the ISM physics of galaxy clusters, while providing insight into other highly anisotropic excitation mechanisms such as shocks, intense radiation fields, and suprathermal particles. Under certain physical conditions, theoretical calculations predict of the order of 10% polarization. Our observations of the filaments in four nearby cool core clusters place stringent upper limits ( 0.1%) on the presence of emission line polarization, requiring that if thermal conduction is operative, the thermal gradients are not in the saturated regime. This limit is consistent with theoretical models of the thermal structure of filament interfacesPeer reviewe
Adiabatic Domain Wall Motion and Landau-Lifshitz Damping
Recent theory and measurements of the velocity of current-driven domain walls
in magnetic nanowires have re-opened the unresolved question of whether
Landau-Lifshitz damping or Gilbert damping provides the more natural
description of dissipative magnetization dynamics. In this paper, we argue that
(as in the past) experiment cannot distinguish the two, but that
Landau-Lifshitz damping nevertheless provides the most physically sensible
interpretation of the equation of motion. From this perspective, (i) adiabatic
spin-transfer torque dominates the dynamics with small corrections from
non-adiabatic effects; (ii) the damping always decreases the magnetic free
energy, and (iii) microscopic calculations of damping become consistent with
general statistical and thermodynamic considerations
Characterization of large genomic deletions in the FBN1 gene using multiplex ligation-dependent probe amplification
<p>Abstract</p> <p>Background</p> <p>Connective tissue diseases characterized by aortic aneurysm, such as Marfan syndrome, Loeys-Dietz syndrome and Ehlers Danlos syndrome type IV are heterogeneous and despite overlapping phenotypes, the natural history, clinical manifestations and interventional course for each diagnosis can be quite unique. The majority of mutations involved in the etiology of these disorders are missense and nonsense mutations. However, large deletions and duplications undetected by sequencing may be implicated in their pathogenesis, and may explain the apparent lack of genotype-phenotype correlation in a subset of patients. The objective of this study was to search for large pathogenic deletions and/or duplications in the <it>FBN1, TGFβR1</it>, and <it>TGFβR2 </it>genes using multiplex-ligation dependent probe amplification (MLPA) in patients with aortopathy, in whom no mutations in the <it>FBN1, TGFβR1</it>, and <it>TGFβR2 </it>genes were identified by sequencing.</p> <p>Methods</p> <p>The study included 14 patients from 11 unrelated families with aortic aneurysm. Of those, six patients (including 3 first-degree relatives), fulfilled the revised Ghent criteria for Marfan syndrome, and eight had predominantly aortic aneurysm/dilatation with variable skeletal and craniofacial involvement. MLPA for <it>FBN1, TGFβR1</it>, and <it>TGFβR2 </it>was carried out in all patients. A 385 K chromosome 15 specific array was used in two patients with a deletion of the entire <it>FBN1 </it>in order to define its size and boundaries.</p> <p>Results</p> <p>We identified two novel large deletions in the <it>FBN1 </it>gene in four patients of two unrelated families who met clinical diagnostic criteria for Marfan syndrome. One patient was found to have a <it>FBN1 </it>deletion encompassing exons 1-5. The other three patients had a 542 Kb deletion spanning the whole <it>FBN1 </it>gene and five additional genes (<it>SLC24A5, MYEF2, CTXN2, SLC12A1, DUT</it>) in the chromosome 15.</p> <p>Conclusions</p> <p>Our findings expand the number of large <it>FBN1 </it>deletions, and emphasize the importance of screening for large genomic deletions in connective tissue disorders featuring aortopathies, especially for those with classic Marfan phenotype.</p
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