855 research outputs found
Correlations between the proton temperature anisotropy and transverse high-frequency waves in the solar wind
Correlations are studied between the power density of transverse waves having
frequencies between and normalized to the proton gyrofrequency in
the plasma frame and the ratio of the perpendicular and parallel temperature of
the protons. The wave power spectrum is evaluated from high-resolution 3D
magnetic field vector components, and the ion temperatures are derived from the
velocity distribution functions as measured in fast solar wind during the
Helios-2 primary mission at radial distances from the Sun between 0.3~AU and
0.9~AU. From our statistical analysis, we obtain a striking correlation between
the increases in the proton temperature ratio and enhancements in the wave
power spectrum. Near the Sun the transverse part of the wave power is often
found to be by more than an order of magnitude higher than its longitudinal
counterpart. Also the measured ion temperature anisotropy appears to be limited
by the theoretical threshold value for the ion-cyclotron instability. This
suggests that high-frequency Alfv\'{e}n-cyclotron waves regulate the proton
temperature anisotropy.Comment: Some references have been adde
Petrologic and geophysical study of the source of long wavelength crustal magnetic anomalies
The magnetic mineralogy and magnetic signature of banded ion formations, diagenetic (unmetamorphosed) and low grade banded iron formations, high-grade mineralogy, and phase equilibria of magnetite inorogenic magmers are discussed
Immunohistochemical characterization of the 'intimal proliferation' phenomenon in Sneddon's syndrome and essential thrombocythaemia
Cellular changes were immunocytochemically characterized in skin vessels of five patients with idiopathic generalized racemose livedo (Sneddon's syndrome), and one patient with localized racemose livedo associated with essential thrombocythaemia. Antibodies against alpha-smooth muscle-actin, tropomyosin, desmin, vimentin, factor VIII-related antigen, human endothelial cells (CD31), human macrophages (CD68), and HLA-DR positive cells (CR3/43) were used. Conventional light microscopy showed, in all cases, intimal thickening of ascending arteries and arterioles as a result of an accumulation of cells and extracellular hyalinized material. None of the specimens showed infiltration with polymorphonuclear leucocytes or macrophages. The cells in the region of the intimal hyperplasia showed intense positive immunostaining for alpha-smooth muscle actin and tropomyosin. Staining for the intermediate filament desmin was localized to the resident smooth muscle cells of the media, whereas staining for vimentin was found in all types of cells in both the intima and media. Positive immunostaining for factor VIII-related antigen and CD31 was strictly confined to the endothelial cells lining the narrowed lumina of the vessels. No positive staining with either antibody was observed in totally occluded vessels. Cells in the subintimal space did not show reactivity for CD68 in any of the specimens, but two cases showed solitary cells with positive staining for HLA-DR in this region. There were no differences in staining pattern between Sneddon's syndrome and essential thrombocythaemia with any of the antibodies. Our results support the assumption that the 'intimal proliferation' in both diseases is caused by colonization of the subendothelial space with contractile cells of possible smooth muscle origin.(ABSTRACT TRUNCATED AT 250 WORDS
Formation Heights of Extreme Ultraviolet Lines in an Active Region Derived by Correlation of Doppler Velocity and Magnetic Field
We study the correlation heights, which indicate the formation height of
Extreme Ultraviolet (EUV) lines in an active region using observations from the
EUV Imaging Spectrometer (EIS) and Solar Optical Telescope (SOT) on board
\emph{Hinode}. The nonlinear force-free field (NLFFF) optimization method is
adopted to extrapolate the 3D magnetic fields to higher layers. Three
subregions with different characteristics are selected in the active region for
this study. The results show that the formation heights in different subregions
vary with their different magnetic fields or velocity patterns. After solving
the line blending problem between the He {\sc \romannumeral 2} 256.32 \AA and
Si {\sc \romannumeral 10} 256.37 \AA lines by the double Gaussian curve
fitting, we find that the transition region lies higher in a strong magnetic
area. In a pre-flare heating area there possibly exist multithermal loops as
implied by comparing the Doppler velocity and the magnetic field on the solar
disk.Comment: 17 pages, 5 figures, 1 table, accepted for publication in Ap
A Model to Explore Responses of Spruce Stands to Air-Pollution Stress in Europe
Systems analysis has proven to be a suitable instrument for describing the processes taking place in pollution-damaged forest stands and for simulating the ecosystem behavior in various environmental situations. In a preliminary model showing the behavior of pollution-damaged spruce stands, site, air pollution, stand structure and management are taken into consideration. The target of this model consists of simulating system behavior under variable pollutant stressors and management strategies, and of serving as a basis for decision-making. The basic model is subdivided into the following submodels: "Forest stand" with management as well as external ecological factors and international modifications; "Leaf quantity/leaf fall"; "Net assimilation"; and "Dendromass distribution". A soil model from other authors is being incorporated. After a comparison with similar models, reference is made to further possibilities of application
Computation of Kolmogorov's Constant in Magnetohydrodynamic Turbulence
In this paper we calculate Kolmogorov's constant for magnetohydrodynamic
turbulence to one loop order in perturbation theory using the direct
interaction approximation technique of Kraichnan. We have computed the
constants for various , i.e., fluid to magnetic energy ratios
when the normalized cross helicity is zero. We find that increases from
1.47 to 4.12 as we go from fully fluid case to a situation when , then it decreases to 3.55 in a fully magnetic limit .
When , we find that .Comment: Latex, 10 pages, no figures, To appear in Euro. Phys. Lett., 199
Temperature anisotropy and differential streaming of solar wind ions -- Correlations with transverse fluctuations
We study correlations of the temperature ratio (which is an indicator for
perpendicular ion heating) and the differential flow of the alpha particles
with the power of transverse fluctuations that have wave numbers between 0.01
and 0.1 (normalized to , where is the proton inertial length).
We found that both the normalized differential ion speed, (where is the Alfv\'en speed) and the proton
temperature anisotropy, , increase when the
relative wave power is growing. Furthermore, if the normalized differential ion
speed stays below 0.5, the alpha-particle temperature anisotropy, , correlates positively with the relative power of
the transverse fluctuations. However, if is higher
than 0.6, then the alpha-particle temperature anisotropy tends to become lower
and attain even values below unity despite the presence of transverse
fluctuations of relatively high amplitudes. Our findings appear to be
consistent with the expectations from kinetic theory for the resonant
interaction of the ions with Alfv\'en/ion-cyclotron waves and the resulting
wave dissipation.Comment: 5 pages, 4 figures, accepted for publication in Astronomy and
Astrophysics journa
Gyrokinetic Simulations of Solar Wind Turbulence from Ion to Electron Scales
The first three-dimensional, nonlinear gyrokinetic simulation of plasma
turbulence resolving scales from the ion to electron gyroradius with a
realistic mass ratio is presented, where all damping is provided by resolved
physical mechanisms. The resulting energy spectra are quantitatively consistent
with a magnetic power spectrum scaling of as observed in \emph{in
situ} spacecraft measurements of the "dissipation range" of solar wind
turbulence. Despite the strongly nonlinear nature of the turbulence, the linear
kinetic \Alfven wave mode quantitatively describes the polarization of the
turbulent fluctuations. The collisional ion heating is measured at
sub-ion-Larmor radius scales, which provides the first evidence of the ion
entropy cascade in an electromagnetic turbulence simulation.Comment: 4 pages, 2 figures, submitted to Phys. Rev. Let
- …