AbstractThere has been important understanding of the process by which a hypersonic dust impact makes an electrical signal on a spacecraft sensor, leading to a fuller understanding of the physics. Zaslavsky (2015), https://doi.org/10.1002/2014ja020635 showed that the most important signal comes from the charging of the spacecraft, less from charging of an antenna. The present work is an extension of the work of Zaslavsky. An analytical treatment of the physics of a hypersonic dust impact and the mechanism for generating an electrical signal in a sensor, an antenna, is presented. The treatment is compared with observations from STEREO and Parker Solar Probe. A full treatment of this process by simulations seems beyond present computer capabilities, but some parts of the treatment must depend on simulations but other features can be better understood through analytical treatment. Evidence for a somewhat larger contribution from the antenna part of the signal than in previous publications is presented. Importance of electrostatic forces in forming the exiting plasma cloud is emphasized. Electrostatic forces lead to a rapid expansion of the escaping cloud, so that it expands more rapidly than it escapes, and sometimes surrounds one or more antennas. This accounts for the ability of dipole antennas to detect dust impacts. Some progress toward understanding occasional negative charging of an antenna is presented, together with direct evidence of such charging. Use of laboratory measurements of charge to estimate size of spacecraft impacts are shown to be not reliable without further calibration work.
AbstractWhen a tragic accident occurred in November 1962 in the coalmine of Kings Bay Company in Ny‐Ålesund, Svalbard, (78°55´N, 11°56´E) it led to the fall of the labour government that had been ruling Norway since the Second World War. A year later the mine was closed, the infrastructure left unattended, and the community of Ny‐Ålesund evacuated. The Norwegian government was then facing a challenge as it had to establish a new activity in the village in order to keep the sovereignty over the territory. This was in the middle of the Cold War. The Russian population on Svalbard was about twice as large as the Norwegian, while the production of the Russian mines was approximately half the output of the Norwegians. An empty village with well‐developed infrastructure on Svalbard was therefore an enticement for the Soviet Union.
With the identification of two distinct classes of high affinity, physiologically relevant, ligands for PH domains, it appears reasonable to assume that additional specific high affinity ligands for other PH domains will be identified in the future. It is not clear, however, whether each of the 90 proposed PH domains will have its own specific ligand. Possible candidates for specific PH domain ligands include various inositol polyphosphates, phosphorylated membrane components, as well as specific protein sequences containing phosphorylated tyrosine, serine, threonine, or histidine residues. It appears unlikely that the low affinity interactions of phosphoinositides described for several PH domains are physiologically relevant. It is difficult to imagine why such a large and diverse family of PH domains (with just 10-15% sequence identity) would exist in order to bind with a similar low affinity to PtdInsP2-containing membranes. Rather, we suggest that these interactions represent limited binding to noncognate ligands - the physiologically relevant ligands have yet to be identified. It is likely that many, if not all, PH domains have their own high affinity, cell membrane-associated, ligands and operate according to the paradigms described for the PH domains of PLCδ1 and Shc (Figure 2Figure 2A and Figure 2Figure 2B). The structural homology between PH domains might reflect a particularly stable protein scaffold of β sheets that can present variable ligand-binding loops in a manner analogous to that seen in the immunoglobulin superfamily.
The electronic absorption spectrum, susceptibility to fluoride inhibition, redox potential, and substrate turnover of several fungal laccases have been explored as a function of pH. The laccases showed a single spectrally detectable acid-base transition at pH 6-9 and a fluoride inhibition that diminished by increased pH (indicating a competition with hydroxide inhibition). Relatively small changes in the redox potentials (≤0.1 V) of laccase were observed over the pH 2.7-11. Under the catalysis of laccase, the apparent oxidation rates (kcat and kcat/Km) of two nonphenolic substrates, potassium ferrocyanide and 2,2′-azinobis-(3-ethylbenzthiazoline-6-sulfonic acid),decreased monotonically as the pH increased. In contrast, the apparent oxidation rates (kcat and kcat/Km) of three 2,6-dimethoxyphenols (whose pKa values range from 7.0 to 8.7) exhibited bell-shaped pH profiles whose maxima were distinct for each laccase but independent of the substrate. By correlating these pH dependences, it is proposed that the balance of two opposing effects, one generated by the redox potential difference between a reducing substrate and the type 1 copper of laccase (which correlates to the electron transfer rate and is favored for a phenolic substrate by higher pH) and another generated by the binding of a hydroxide anion to the type 2/type 3 coppers of laccase (which inhibits the activity at higher pH), contributes to the pH activity profile of the fungal laccases.
AbstractThe magnetosphere of Saturn is known to be warped into a bowl shape, and the severity of the warping varies with the seasonal tilt of Saturn's spin axis in its orbital plane. This peculiar geometry complicates the analysis of many magnetospheric phenomena, because they are symmetric about the warped magnetodisk equator rather than the spin equator. To reorganize the Cassini data, a new coordinate system is proposed wherein a zA coordinate represents the perpendicular distance above or below the warped surface, and a ρA coordinate represents the arc length along the surface from the origin to where the perpendicular intersects the surface. Using the Cassini spacecraft trajectory, examples show how these disk coordinates (ρA, zA) significantly deviate from the standard spin‐equatorial coordinates (ρ, z), especially outside the orbit of Titan. Another example indicates that fluxes of energetic electrons are well organized in this new system. Supporting information tabulates the disk coordinates as a function of time during the Cassini mission.
AbstractThe near‐Mars space environment has a number of regions and boundaries that have numerous and confusing labels. The whole region is sometimes referred to as the induced Martian magnetosphere and sometimes as the solar wind interaction with Mars. The middle boundary where the shocked solar wind plasma gives way to predominately planetary‐derived plasma has a variety of names. The region below that middle boundary and the top of the ionosphere also does not have a uniformly used name. There are several other regions and boundaries that also have naming confusion. The various terms that are currently used in the literature for these subjects are identified and discussed; regions and boundaries that have well‐settled names are not discussed nor are the details of the physics involved.
AbstractThe number of citations to a refereed journal article from other refereed journal articles is a measure of its impact. Papers, individuals, journals, departments, and institutions are increasingly judged by the impact they have in their disciplines, and citation counts are now a relatively easy (though not necessarily accurate or straightforward) way of attempting to quantify impact. This study examines papers published in the Journal of Geophysical Research—Space Physics in the year 2012 (n = 705) and analyzes the characteristics of high‐citation papers compared to low‐citation papers. We find that high‐citation papers generally have a large number of authors (>5) and cite significantly more articles in the reference section than low‐citation papers. We also examined the gender and country of institution of the first author and found that there is not a statistically significant gender bias, but there are some significant differences in citation statistics between articles based on the country of first‐author institution.
Michael W. Liemohn, Yuming Wang, Alan Rodger
et al.
AbstractThe Editors of the Journal of Geophysical Research Space Physics extend a sincere and heartfelt thank you to the 1,448 scientists that conducted 3,511 manuscript reviews for the journal in calendar year 2017. We deeply appreciate the time and effort that you have devoted to the research community.