243 research outputs found
Neutral interstellar He parameters in front of the heliosphere 1994--2007
Analysis of IBEX measurements of neutral interstellar He flux brought the
inflow velocity vector different from the results of earlier analysis of
observations from GAS/Ulysses. Recapitulation of results on the helium inflow
direction from the past ~40 years suggested that the inflow direction may be
changing with time. We reanalyze the old Ulysses data and reprocess them to
increase the accuracy of the instrument pointing to investigate if the GAS
observations support the hypothesis that the interstellar helium inflow
direction is changing. We employ a similar analysis method as in the analysis
of the IBEX data. We seek a parameter set that minimizes reduced chi-squared,
using the Warsaw Test Particle Model for the interstellar He flux at Ulysses
with a state of the art model of neutral He ionization in the heliosphere, and
precisely reproducing the observation conditions. We also propose a
supplementary method of constraining the parameters based on cross-correlations
of parameters obtained from analysis of carefully selected subsets of data. We
find that the ecliptic longitude and speed of interstellar He are in a very
good agreement with the values reported in the original GAS analysis. We find,
however, that the temperature is markedly higher. The 3-seasons optimum
parameter set is lambda = 255.3, beta = 6, v = 26.0 km/s, T = 7500 K. We find
no evidence that it is varying with time, but the uncertainty range is larger
than originally reported. The originally-derived parameters of interstellar He
from GAS are in good agreement with presently derived, except for the
temperature, which seems to be appreciably higher, in good agreement with
interstellar absorption line results. While the results of the present analysis
are in marginal agreement with the earlier reported results from IBEX, the most
likely values from the two analyses differ for reasons that are still not
understood.Comment: submitted for publication in Astronomy & Astrophysic
A turbulence-driven model for heating and acceleration of the fast wind in coronal holes
A model is presented for generation of fast solar wind in coronal holes,
relying on heating that is dominated by turbulent dissipation of MHD
fluctuations transported upwards in the solar atmosphere. Scale-separated
transport equations include large-scale fields, transverse Alfvenic
fluctuations, and a small compressive dissipation due to parallel shears near
the transition region. The model accounts for proton temperature, density, wind
speed, and fluctuation amplitude as observed in remote sensing and in situ
satellite data.Comment: accepted for publication in ApJ
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
Warm Compressor system Overview and status of the PIP-II cryogenic system
The Proton Improvement Plan-II (PIP-II) is a major upgrade to the Fermilab
accelerator complex, featuring a new 800-MeV Superconducting Radio-Frequency
(SRF) linear accelerator (Linac) powering the accelerator complex to provide
the world's most intense high-energy neutrino beam. The PIP-II Linac consists
of 23 SRF cryomodules operating at 2 K, 5 K, and 40 K temperature levels
supplied by a single helium cryoplant providing 2.5 kW of cooling capacity at
2.0 K. The PIP-II cryogenic system consists of two major systems: a helium
cryogenic plant and a cryogenic distribution system. The cryogenic plant
includes a refrigerator cold box, a warm compressor system, and helium storage,
recovery, and purification systems. The cryogenic distribution system includes
a distribution box, intermediate transfer line, and a tunnel transfer line
consisting of modular bayonet cans which supply and return cryogens to the
cryomodules. A turnaround can is located at the end of the Linac to turnaround
cryogenic flows. This paper describes the layout, design, and current status of
the PIP-II cryogenic system.Comment: 2023 Cryogenic Engineering Conference and International Cryogenic
Materials Conference (CEC/ICMC
Stereoscopic Polar Plume Reconstructions from Stereo/Secchi Images
We present stereoscopic reconstructions of the location and inclination of
polar plumes of two data sets based on the two simultaneously recorded images
taken by the EUVI telescopes in the SECCHI instrument package onboard the
\emph{STEREO (Solar TErrestrial RElations Observatory)} spacecraft. The ten
plumes investigated show a superradial expansion in the coronal hole in 3D
which is consistent with the 2D results. Their deviations from the local
meridian planes are rather small with an average of . By
comparing the reconstructed plumes with a dipole field with its axis along the
solar rotation axis, it is found that plumes are inclined more horizontally
than the dipole field. The lower the latitude is, the larger is the deviation
from the dipole field. The relationship between plumes and bright points has
been investigated and they are not always associated. For the first data set,
based on the 3D height of plumes and the electron density derived from
SUMER/\emph{SOHO} Si {\sc viii} line pair, we found that electron densities
along the plumes decrease with height above the solar surface. The temperature
obtained from the density scale height is 1.6 to 1.8 times larger than the
temperature obtained from Mg {\sc ix} line ratios. We attribute this
discrepancy to a deviation of the electron and the ion temperatures. Finally,
we have found that the outflow speeds studied in the O {\sc vi} line in the
plumes corrected by the angle between the line of sight and the plume
orientation are quite small with a maximum of 10 . It is
unlikely that plumes are a dominant contributor to the fast solar wind.Comment: 25 pages, 13 figure
Molecular subtyping of bladder cancer using Kohonen self-organizing maps
Kohonen self-organizing maps (SOMs) are unsupervised Artificial Neural Networks (ANNs) that are good for low-density data visualization. They easily deal with complex and nonlinear relationships between variables. We evaluated molecular events that characterize high- and low-grade BC pathways in the tumors from 104 patients. We compared the ability of statistical clustering with a SOM to stratify tumors according to the risk of progression to more advanced disease. In univariable analysis, tumor stage (log rank P = 0.006) and grade (P < 0.001), HPV DNA (P < 0.004), Chromosome 9 loss (P = 0.04) and the A148T polymorphism (rs 3731249) in CDKN2A (P = 0.02) were associated with progression. Multivariable analysis of these parameters identified that tumor grade (Cox regression, P = 0.001, OR.2.9 (95% CI 1.6–5.2)) and the presence of HPV DNA (P = 0.017, OR 3.8 (95% CI 1.3–11.4)) were the only independent predictors of progression. Unsupervised hierarchical clustering grouped the tumors into discreet branches but did not stratify according to progression free survival (log rank P = 0.39). These genetic variables were presented to SOM input neurons. SOMs are suitable for complex data integration, allow easy visualization of outcomes, and may stratify BC progression more robustly than hierarchical clustering
Simulating Heliospheric and Solar Particle Diffusion using the Parker Spiral Geometry
Cosmic Ray transport in curved background magnetic fields is investigated
using numerical Monte-Carlo simulation techniques. Special emphasis is laid on
the Solar system, where the curvature of the magnetic field can be described in
terms of the Parker spiral. Using such geometries, parallel and perpendicular
diffusion coefficients have to be re-defined using the arc length of the field
lines as the parallel displacement and the distance between field lines as the
perpendicular displacement. Furthermore, the turbulent magnetic field is
incorporated using a WKB approach for the field strength. Using a test-particle
simulation, the diffusion coefficients are then calculated by averaging over a
large number of particles starting at the same radial distance from the Sun and
over a large number of turbulence realizations, thus enabling one to infer the
effects due to the curvature of the magnetic fields and associated drift
motions.Comment: accepted for publication at Journal of Geophysical Research - Space
Physic
Propagation of an Earth-directed coronal mass ejection in three dimensions
Solar coronal mass ejections (CMEs) are the most significant drivers of
adverse space weather at Earth, but the physics governing their propagation
through the heliosphere is not well understood. While stereoscopic imaging of
CMEs with the Solar Terrestrial Relations Observatory (STEREO) has provided
some insight into their three-dimensional (3D) propagation, the mechanisms
governing their evolution remain unclear due to difficulties in reconstructing
their true 3D structure. Here we use a new elliptical tie-pointing technique to
reconstruct a full CME front in 3D, enabling us to quantify its deflected
trajectory from high latitudes along the ecliptic, and measure its increasing
angular width and propagation from 2-46 solar radii (approximately 0.2 AU).
Beyond 7 solar radii, we show that its motion is determined by an aerodynamic
drag in the solar wind and, using our reconstruction as input for a 3D
magnetohydrodynamic simulation, we determine an accurate arrival time at the
Lagrangian L1 point near Earth.Comment: 5 figures, 2 supplementary movie
First results on Martian carbon monoxide from Herschel/HIFI observations
We report on the initial analysis of Herschel/HIFI carbon monoxide (CO)
observations of the Martian atmosphere performed between 11 and 16 April 2010.
We selected the (7-6) rotational transitions of the isotopes ^{13}CO at 771 GHz
and C^{18}O at 768 GHz in order to retrieve the mean vertical profile of
temperature and the mean volume mixing ratio of carbon monoxide. The derived
temperature profile agrees within less than 5 K with general circulation model
(GCM) predictions up to an altitude of 45 km, however, show about 12-15 K lower
values at 60 km. The CO mixing ratio was determined as 980 \pm 150 ppm, in
agreement with the 900 ppm derived from Herschel/SPIRE observations in November
2009.Comment: Accepted for publication in Astronomy and Astrophysics (special issue
on HIFI first results); minor changes to match published versio
Can the Solar Wind be Driven by Magnetic Reconnection in the Sun's Magnetic Carpet?
The physical processes that heat the solar corona and accelerate the solar
wind remain unknown after many years of study. Some have suggested that the
wind is driven by waves and turbulence in open magnetic flux tubes, and others
have suggested that plasma is injected into the open tubes by magnetic
reconnection with closed loops. In order to test the latter idea, we developed
Monte Carlo simulations of the photospheric "magnetic carpet" and extrapolated
the time-varying coronal field. These models were constructed for a range of
different magnetic flux imbalance ratios. Completely balanced models represent
quiet regions on the Sun and source regions of slow solar wind streams. Highly
imbalanced models represent coronal holes and source regions of fast wind
streams. The models agree with observed emergence rates, surface flux
densities, and number distributions of magnetic elements. Despite having no
imposed supergranular motions, a realistic network of magnetic "funnels"
appeared spontaneously. We computed the rate at which closed field lines open
up (i.e., recycling times for open flux), and we estimated the energy flux
released in reconnection events involving the opening up of closed flux tubes.
For quiet regions and mixed-polarity coronal holes, these energy fluxes were
found to be much lower than required to accelerate the solar wind. For the most
imbalanced coronal holes, the energy fluxes may be large enough to power the
solar wind, but the recycling times are far longer than the time it takes the
solar wind to accelerate into the low corona. Thus, it is unlikely that either
the slow or fast solar wind is driven by reconnection and loop-opening
processes in the magnetic carpet.Comment: 25 pages (emulateapj style), 13 figures, ApJ, in pres
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