754 research outputs found
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The heliospheric magnetic field
The heliospheric magnetic field (HMF) is the extension of the coronal magnetic field carried out into the solar system by the solar wind. It is the means by which the Sun interacts with planetary magnetospheres and channels charged particles propagating through the heliosphere. As the HMF remains rooted at the solar photosphere as the Sun rotates, the large-scale HMF traces out an Archimedean spiral. This pattern is distorted by the interaction of fast and slow solar wind streams, as well as the interplanetary manifestations of transient solar eruptions called coronal mass ejections. On the smaller scale, the HMF exhibits an array of waves, discontinuities, and turbulence, which give hints to the solar wind formation process. This review aims to summarise observations and theory of the small- and large-scale structure of the HMF. Solar-cycle and cycle-to-cycle evolution of the HMF is discussed in terms of recent spacecraft observations and pre-spaceage proxies for the HMF in geomagnetic and galactic cosmic ray records
The evolution of inverted magnetic fields through the inner heliosphere
Local inversions are often observed in the heliospheric magnetic field (HMF), but their origins and evolution are not yet fully understood.Parker Solar Probe has recently observed rapid, AlfvĂ©nic, HMF inversions in the inner heliosphere, known as âswitchbacksâ, which have been interpreted as the possible remnants of coronal jets. It has also been suggested that inverted HMF may be produced by near-Sun interchange reconnection; a key process in mechanisms proposed for slow solar wind release. These cases suggest that the source of inverted HMF is near the Sun, and it follows that these inversions would gradually decay and straighten as they propagate out through the heliosphere. Alternatively, HMF inversions could form during solar wind transit, through phenomena such velocity shears, draping over ejecta, or waves and turbulence. Such processes are expected to lead to a qualitatively radial evolution of inverted HMF structures. Using Helios measurements spanning 0.3â1 AU, we examine the occurrence rate of inverted HMF, as well as other magnetic field morphologies, as a function of radial distance r, and find that it continually increases. This trend may be explained by inverted HMF observed between 0.3â1 AU being primarily driven by one or more of the above in-transit processes, rather than created at the Sun. We make suggestions as to the relative importance of these different processes based on the evolution of the magnetic field properties associated with inverted HMF. We also explore alternative explanations outside of our suggested driving processes which may lead to the observed trend
Robust Machine Learning Applied to Astronomical Datasets I: Star-Galaxy Classification of the SDSS DR3 Using Decision Trees
We provide classifications for all 143 million non-repeat photometric objects
in the Third Data Release of the Sloan Digital Sky Survey (SDSS) using decision
trees trained on 477,068 objects with SDSS spectroscopic data. We demonstrate
that these star/galaxy classifications are expected to be reliable for
approximately 22 million objects with r < ~20. The general machine learning
environment Data-to-Knowledge and supercomputing resources enabled extensive
investigation of the decision tree parameter space. This work presents the
first public release of objects classified in this way for an entire SDSS data
release. The objects are classified as either galaxy, star or nsng (neither
star nor galaxy), with an associated probability for each class. To demonstrate
how to effectively make use of these classifications, we perform several
important tests. First, we detail selection criteria within the probability
space defined by the three classes to extract samples of stars and galaxies to
a given completeness and efficiency. Second, we investigate the efficacy of the
classifications and the effect of extrapolating from the spectroscopic regime
by performing blind tests on objects in the SDSS, 2dF Galaxy Redshift and 2dF
QSO Redshift (2QZ) surveys. Given the photometric limits of our spectroscopic
training data, we effectively begin to extrapolate past our star-galaxy
training set at r ~ 18. By comparing the number counts of our training sample
with the classified sources, however, we find that our efficiencies appear to
remain robust to r ~ 20. As a result, we expect our classifications to be
accurate for 900,000 galaxies and 6.7 million stars, and remain robust via
extrapolation for a total of 8.0 million galaxies and 13.9 million stars.
[Abridged]Comment: 27 pages, 12 figures, to be published in ApJ, uses emulateapj.cl
A Never-ending Story: From the History of Swiss Graphic Design to Swiss Graphic Design Histories
Incidence of physician-diagnosed osteoarthritis among active duty United States military service members
The article of record as published may be found at http://dx.DOI.org/10.1002/art.30498To examine the incidence of osteoarthritis
and the influence of demographic and occupational
factors associated with this condition among
active duty US service members between 1999 and 2008
The Interaction of Neuraminidase and Hemagglutinin Mutations in Influenza Virus in Resistance to 4-Guanidino-Neu5Ac2en
AbstractWe have previously described a 4-guanidino-Neu5Ac2en (zanamivir)-resistant neuraminidase (NA) variant G70C4-G, with an active site mutation Glu 119 to Gly. This variant has been found to also harbor a hemagglutinin (HA) mutation in the receptor binding site, Ser 186 to Phe. Examination of early passages of the G70C4-G virus revealed that this HA mutation had arisen by the first passage. From a subsequent passage two transient variants were isolated which had each acquired a different second HA mutation, Ser 165 to Asn and Lys 222 to Thr. Both were highly drug resistant and drug dependent and their ability to adsorb to and penetrate cells was decreased. Comparison of drug sensitivities between the variant, with the additional HA mutation at Ser 165, and viruses with either mutation alone revealed that these two HA mutations acted synergistically to increase resistance. To determine the contribution to resistance of each of the NA and HA mutations in G70C4-G, the NA mutation was separated from the HA mutation by reassorting. The NA mutation and the HA mutation each conferred low-level resistance to zanamivir, while the two mutations interacted synergistically in the double mutant to give higher resistancein vitro.Infectivity was not adversely affected in the double mutant and while there was a small decrease in sensitivity to zanamivir in the mouse model, there was no detectable resistance to zanamivir in the ferret model
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Sitting and Supine Esophageal Pressures in Overweight and Obese Subjects Authors
Esophageal pressure can be used to approximate pleural pressure and might be clinically useful, particularly in the obese e.g to guide mechanical ventilator settings in critical illness. However, mediastinal artifact (the difference between true pleural pressure and esophageal pressure) may limit acceptance of the measurement, and reproducibility of esophageal pressure measurements remains unknown. Therefore, we aimed to assess the effect of body posture on esophageal pressure in a cohort of obese but healthy subjects, some of whom had multiple measurements, to address the clinical robustness of esophageal manometry. Twenty-five overweight and obese subjects (BMI>25kg/m2) and 11 control lean subjects (BMI<25kg/m2) underwent esophageal manometry with pressures measured seated and supine. Twenty overweight and obese subjects had measurements repeated after ~1-2 weeks. Anthropometric data and sitting and supine spirometry were recorded. The average end-expiratory esophageal pressures sitting and supine were greater in the overweight and obese group than the lean group (sitting â0.1±2.1 vs. â3.3±1.2cmH2O, supine 9.3±3.3 vs. 6.9±2.8cmH2O, respectively). The mean differences between repeated measurements were small (â0.3 ± 1.7cmH2O sitting and â0.1 ± 1.5cmH2O supine). Esophageal pressures correlated with a number of anthropometric and spirometric variables. In conclusion, esophageal pressures are slightly greater in overweight and obese subjects than lean subjects; but changes with position are similar in both groups. These data indicate that mediastinal weight and postural effects on esophageal pressure are within a clinically acceptable range, and suggest that esophageal manometry can be used to inform clinical decision making across wide range of body types
Southern Ocean GLOBEC moored array and automated weather station data report
Southern Ocean GLOBal ocean ECosystemsAs part of the U.S. Southern Ocean GLOBEC program, moored time series measurements of
temperature, conductivity (salinity), pressure, velocity, and acoustic backscatter were made from
March 2001 to March 2003 in and near Marguerite Bay, located on the Antarctic Peninsula western
shelf. To monitor surface forcing during the moored array observations, two automatic weather
stations (AWSs) were deployed on islands in Marguerite Bay and time series of wind, air temperature,
pressure, and relative humidity were collected from May 2001 through March 2003. This
report describes the individual moorings, their locations and local bathymetry, the instrumentation
used and measurement depths, calibration and data processing steps taken to produce final time
series, and basic plots of the final time series. The AWS data acquisition and processing are also
described and basic plots of the final meteorological time series presented. Directions are given
about how to access the raw and processed moored and AWS data via the SO GLOBEC website
(http://globec.whoi.edu/jg/dir/globec/soglobec/).Funding was provided by the National Science Foundation under contract number OPP-99-10092
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