492 research outputs found
Ion Charge States in Halo CMEs: What can we Learn about the Explosion?
We describe a new modeling approach to develop a more quantitative
understanding of the charge state distributions of the ions of various elements
detected in situ during halo Coronal Mass Ejection (CME) events by the Advanced
Composition Explorer (ACE) satellite. Using a model CME hydrodynamic evolution
based on observations of CMEs propagating in the plane of the sky and on
theoretical models, we integrate time dependent equations for the ionization
balance of various elements to compare with ACE data. We find that plasma in
the CME ``core'' typically requires further heating following filament
eruption, with thermal energy input similar to the kinetic energy input. This
extra heating is presumably the result of post eruptive reconnection. Plasma
corresponding to the CME ``cavity'' is usually not further ionized, since
whether heated or not, the low density gives freeze-in close the the Sun. The
current analysis is limited by ambiguities in the underlying model CME
evolution. Such methods are likely to reach their full potential when applied
to data to be acquired by STEREO when at optimum separation. CME evolution
observed with one spacecraft may be used to interpret CME charge states
detected by the other.Comment: 20 pages, accepted by Ap
Hubungan Tinggi Badan Dengan Ukuran Lebar Panggul Pada Mahasiswi Angkatan 2010 Fakultas Kedokteran Universitas Sam Ratulangi
: Body weight is one of growth indicators. The result of previous research show that women with less than 145 centimeter body weight are potentially has a pelvic stricture. Pelvic stricture is able to cause a coccygeal presentation that can cause natal death. The purpose is to know the correlation of body height and pelvic width which are distansia spinarum and distansia tuberum. The method of this research is observational – analytic using cross – sectional design. The study was conducted for three weeks. The amount of the subject is 80 subjects. The measure of body height and pelvic width of the subjects was being analyzed by the Pearson Correlation Analysis with α = 0,05. The result show that there was a significant correlation of body height and measure of distansia spinarum with correlation coefficient +0,479. In the other side, there was nothing significant correlation of body height and measure of distansia tuberum with correlation coefficient +0,088. Conclusion: There have significant correlation of body height and measure of distansia spinarum but there have no significant correlation of body height and measure of distansia tuberum
Fe XVII X-ray Line Ratios for Accurate Astrophysical Plasma Diagnostics
New laboratory measurements using an Electron Beam Ion Trap (EBIT) and an
x-ray microcalorimeter are presented for the n=3 to n=2 Fe XVII emission lines
in the 15 {\AA} to 17 {\AA} range, along with new theoretical predictions for a
variety of electron energy distributions. This work improves upon our earlier
work on these lines by providing measurements at more electron impact energies
(seven values from 846 to 1185 eV), performing an in situ determination of the
x-ray window transmission, taking steps to minimize the ion impurity
concentrations, correcting the electron energies for space charge shifts, and
estimating the residual electron energy uncertainties. The results for the
3C/3D and 3s/3C line ratios are generally in agreement with the closest theory
to within 10%, and in agreement with previous measurements from an independent
group to within 20%. Better consistency between the two experimental groups is
obtained at the lowest electron energies by using theory to interpolate, taking
into account the significantly different electron energy distributions.
Evidence for resonance collision effects in the spectra is discussed.
Renormalized values for the absolute cross sections of the 3C and 3D lines are
obtained by combining previously published results, and shown to be in
agreement with the predictions of converged R-matrix theory. This work
establishes consistency between results from independent laboratories and
improves the reliability of these lines for astrophysical diagnostics. Factors
that should be taken into account for accurate diagnostics are discussed,
including electron energy distribution, polarization, absorption/scattering,
and line blends.Comment: 29 pages, including 7 figure
Accelerated Electrons in Cassiopeia A: An Explanation for the Hard X-ray Tail
We propose a model for the hard X-ray (> 10 keV) emission observed from the
supernova remnant Cas A. Lower hybrid waves are generated in strong (mG)
magnetic fields, generally believed to reside in this remnant, by shocks
reflected from density inhomogeneities. These then accelerate electrons to
energies of several tens of keV. Around 4% of the x-ray emitting plasma
electrons need to be in this accelerated distribution, which extends up to
electron velocities of order the electron Alfven speed, and is directled along
magnetic field lines. Bremsstrahlung from these electrons produces the observed
hard x-ray emission. Such waves and accelerated electrons have been observed in
situ at Comet Halley, and we discuss the viability of the extrapolation from
this case to the parameters relevant to Cas A.Comment: 20 pages, 3 figures, aasTeX502, accepted in Ap
The Magnetorotational Instability in Core Collapse Supernova Explosions
We investigate the action of the magnetorotational instability (MRI) in the
context of iron-core collapse. Exponential growth of the field on the rotation
time scale by the MRI will dominate the linear growth process of field line
"wrapping" with the same characteristic time. We examine a variety of initial
rotation states, with solid body rotation or a gradient in rotational velocity,
that correspond to models in the literature. A relatively modest value of the
initial rotation, a period of ~ 10 s, will give a very rapidly rotating PNS and
hence strong differential rotation with respect to the infalling matter. We
assume conservation of angular momentum on spherical shells. Results are
discussed for two examples of saturation fields, a fiducial field that
corresponds to Alfven velocity = rotational velocity and a field that
corresponds to the maximum growing mode of the MRI. Modest initial rotation
velocities of the iron core result in sub-Keplerian rotation and a
sub-equipartition magnetic field that nevertheless produce substantial MHD
luminosity and hoop stresses: saturation fields of order 10^{15} - 10^{16} G
develop within 300 msec after bounce with an associated MHD luminosity of about
10^{52} erg/s. Bi-polar flows driven by this MHD power can affect or even cause
the explosions associated with core-collapse supernovae.Comment: 42 pages, including 15 figures. Accepted for publication in ApJ. We
have revised to include an improved treatment of the convection, and some
figures have been update
Coronal versus photospheric abundances of stars with different activity levels
We report a detailed analysis of the coronal abundance of 4 stars with
varying levels of activity and with accurately known photospheric abundances.
The coronal abundance is determined here using a line flux analysis and a full
determination of the differential emission measure. Photospheric abundance
values are taken from literature works. Previous coronal abundance
determinations have generally been compared to solar photospheric abundances;
from this a number of general properties have been inferred, such as the
presence of a coronal metal depletion with an inverse First Ionization
Potential correlated with activity level. Here we show that, when coronal
abundances are compared with real photospheric values for the individual stars,
the resulting pattern can be very different. Also, we present evidence that, in
some cases, the coronal metal abundance may not be uniform in the corona; in
particular it can vary with the temperature of the emitting plasma.Comment: 10 pages, Online material: 8 pages (online material is included in
the file). Accepted by A&
Determining the Elemental and Isotopic Composition of the preSolar Nebula from Genesis Data Analysis: The Case of Oxygen
We compare element and isotopic fractionations measured in solar wind samples
collected by NASA's Genesis mission with those predicted from models
incorporating both the ponderomotive force in the chromosphere and conservation
of the first adiabatic invariant in the low corona. Generally good agreement is
found, suggesting that these factors are consistent with the process of solar
wind fractionation. Based on bulk wind measurements, we also consider in more
detail the isotopic and elemental abundances of O. We find mild support for an
O abundance in the range 8.75 - 8.83, with a value as low as 8.69 disfavored. A
stronger conclusion must await solar wind regime specific measurements from the
Genesis samples.Comment: 6 pages, accepted by Astrophysical Journal Letter
On Collisionless Electron-Ion Temperature Equilibration in the Fast Solar Wind
We explore a mechanism, entirely new to the fast solar wind, of electron
heating by lower hybrid waves to explain the shift to higher charge states
observed in various elements in the fast wind at 1 A.U. relative to the
original coronal hole plasma. This process is a variation on that previously
discussed for two temperature accretion flows by Begelman & Chiueh. Lower
hybrid waves are generated by gyrating minor ions (mainly alpha-particles) and
become significant once strong ion cyclotron heating sets in beyond 1.5 R_sun.
In this way the model avoids conflict with SUMER electron temperature
diagnostic measurements between 1 and 1.5 R_sun. The principal requirement for
such a process to work is the existence of density gradients in the fast solar
wind, with scale length of similar order to the proton inertial length. Similar
size structures have previously been inferred by other authors from radio
scintillation observations and considerations of ion cyclotron wave generation
by global resonant MHD waves.Comment: 32 pages including 11 figures, 4 tables, accepted by Ap
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