Pluto's Interaction With Energetic Heliospheric Ions Kollmann, P.; Hill, M. E.; Allen, R. C. ...
Journal of geophysical research. Space physics,
September 2019, 2019-09-00, 20190901, Letnik:
124, Številka:
9
Journal Article
Recenzirano
Odprti dostop
Pluto energies of a few kiloelectron volts and suprathermal ions with tens of kiloelectron volts and above. We measure this population using the Pluto Energetic Particle Spectrometer Science ...Investigation (PEPSSI) instrument on board the New Horizons spacecraft that flew by Pluto in 2015. Even though the measured ions have gyroradii larger than the size of Pluto and the cross section of its magnetosphere, we find that the boundary of the magnetosphere is depleting the energetic ion intensities by about an order of magnitude close to Pluto. The intensity is increasing exponentially with distance to Pluto and reaches nominal levels of the interplanetary medium at about 190RP distance. Inside the wake of Pluto, we observe oscillations of the ion intensities with a periodicity of about 0.2 hr. We show that these can be quantitatively explained by the electric field of an ultralow‐frequency wave and discuss possible physical drivers for such a field. We find no evidence for the presence of plutogenic ions in the considered energy range.
Plain Language Summary
Space around Pluto is not entirely empty but filled with solar wind plasma and ions that originate from interstellar space and are pushed outward by the solar wind. All planetary bodies interact with their surrounding medium. In the case of a magnetized body like Earth, this interaction is strong and creates a magnetosphere. Unmagnetized bodies like that of the dwarf planet Pluto have a much weaker interaction. What makes Pluto special is that it is far outside in our solar system and therefore embedded in relatively high intensities of interstellar ions. When New Horizons passed Pluto and measured the distribution of these ions, we found that Pluto is forming a wake in the interstellar ion flow. It is more difficult to deflect the motion of the relatively fast‐moving interstellar ions than it is to deflect the lower‐energy solar wind. Therefore, it was not obvious that we would observe this. Even Pluto's wake is not entirely empty because some interstellar ions do manage to enter. Another finding was that a wave is propagating within the tenuous medium of the wake. This wave modulates the ion intensities resembling a sound wave propagating through air and modulating the gas density.
Key Points
Pluto forms a wake for energetic heliospheric ions
Waves cause ion intensity oscillations in the wake
Crystallographic slip planes in body centered cubic (BCC) metals are not fully understood. In polycrystals, there are additional confounding effects from grain interactions. This paper describes an ...experimental investigation into the effects of grain orientation and neighbors on elastic–plastic strain accumulation. In situ strain fields were obtained by performing digital image correlation (DIC) on images from a scanning electron microscope (SEM) and from optical microscopy. These strain fields were statistically compared to the grain structure measured by electron backscatter diffraction (EBSD). Spearman rank correlations were performed between effective strain and six microstructural factors including four Schmid factors associated with the 〈111〉 slip direction, grain size, and Taylor factor. Modest correlations (∼10%) were found for a polycrystal tension specimen.
The influence of grain neighbors was first investigated by re-correlating the polycrystal data using clusters of similarly-oriented grains identified by low grain boundary misorientation angles. Second, the experiment was repeated on a tantalum oligocrystal, with through-thickness grains. Much larger correlation coefficients were found in this multicrystal due to the dearth of grain neighbors and subsurface microstructure. Finally, a slip trace analysis indicated (in agreement with statistical correlations) that macroscopic slip often occurs on {110}〈111〉 slip systems and sometimes by pencil glide on maximum resolved shear stress planes (MRSSP). These results suggest that Schmid factors are suitable for room temperature, quasistatic, tensile deformation in tantalum as long as grain neighbor effects are accounted for.
Hydrogen Peroxide on the Surface of Europa Carlson, R. W.; Anderson, M. S.; Johnson, R. E. ...
Science (American Association for the Advancement of Science),
03/1999, Letnik:
283, Številka:
5410
Journal Article
Recenzirano
Spatially resolved infrared and ultraviolet wavelength spectra of Europa's leading, anti-jovian quadrant observed from the Galileo spacecraft show absorption features resulting from hydrogen ...peroxide. Comparisons with laboratory measurements indicate surface hydrogen peroxide concentrations of about 0.13 percent, by number, relative to water ice. The inferred abundance is consistent with radiolytic production of hydrogen peroxide by intense energetic particle bombardment and demonstrates that Europa's surface chemistry is dominated by radiolysis.
The aim of this study is to calculate realistic dose distributions that include the continuous deformation of organs and continuous motion of machine using 4D Monte Carlo methods for both volumetric ...modulated arc therapy and helical tomotherapy treatments. As part of a previous study, we presented a method to perform position-probability-sampled Monte Carlo dose calculations in the BEAMnrc and DOSXZYnrc user codes of EGSnrc. In this study, the DOSXYZnrc user code was further modified to account for the continuous intra-fraction deformation of the patient geometry. We implemented in the user code a method to update the transport grid densities as a function of time and map the energy deposited in the time dependent transport grid back to a reference grid. We provide information on the measurements performed to validate the implementation of this method and present an example of the application of the method for lung stereotactic treatments with intra-fraction motion. The results show that breathing motion is properly addressed with the internal target volume method for the cases studied.
Expression of microRNAs (miRs) has been shown to be altered in many solid tumours and is being explored in melanoma. The malignant potential of some melanocytic lesions is difficult to predict. We ...hypothesised that characterisation of miR expression in borderline melanocytic proliferations would lead to the identification of a molecular profile that could be used with known prognostic factors to differentiate lesions with high malignant potential.
The miR expression profile of melanocytic lesions (benign naevi, malignant melanoma and borderline melanocytic tumours) was evaluated by real-time PCR.
PCR analysis revealed primary cutaneous melanomas had an 8.6-fold overexpression of miR-21 and a 7.5-fold overexpression of miR-155 compared with benign naevi (P<0.0001). In situ hybridisation confirmed these results. miR-21 and miR-155 were significantly overexpressed within borderline lesions (P=0.0011 and P=0.0048, respectively). When borderline lesions were categorised by mitotic activity and Breslow thickness, miR-21 was associated with mitotic activity and miR-155 was associated with thickness (P<0.025). Among 14 patients with borderline lesions who underwent sentinel lymph node biopsy (SLNB), positive SLNB was associated with increased miR-21 and miR-155 in the primary lesion compared with lesions with a negative SLNB.
MicroRNA expression profiles can be used to characterise atypical melanocytic lesions.
Annexins are a multigene family in most plant species and are suggested to play a role in a wide variety of essential cellular processes. In
Arabidopsis thaliana there are eight different annexins (
...AnnAt1-8), which range from 29% to 83% in deduced amino acid sequence identity. As a first step toward clarifying the individual functions of these annexins, in this study we have used quantitative real time reverse transcription PCR to assess their differential expression in different tissues or after different stimuli. We determined which annexins are expressed during germination and early seedling growth by assaying annexin expression levels in dry and germinating seeds and in 7-day-old light-grown seedlings. Our results indicate that transcripts for all eight annexins are present in germinating seeds and that transcript levels for all the annexins increase by 7 days of normal growth. We assayed transcript levels in dark grown roots, cotyledons, and hypocotyls and found that the relative abundance of each annexin varied in these dark-grown tissues. We also examined the effects of red and far red light treatments on annexin expression in 5.5-day-old etiolated seedlings. Light treatments significantly altered transcript levels in hypocotyls and cotyledons for only two members of the gene family. Finally, we monitored annexin expression changes in response to a variety of abiotic stresses. We found that the expression of most of the
Arabidopsis annexin genes is differentially regulated by exposure to salt, drought, and high- and low-temperature conditions, indicating a likely role for members of this gene family in stress responses.
Medulloblastoma is a malignant childhood brain tumor arising from the developing cerebellum. In Sonic Hedgehog (SHH) subgroup medulloblastoma, aberrant activation of SHH signaling causes increased ...proliferation of granule neuron progenitors (GNPs), and predisposes these cells to tumorigenesis. A second, cooperating genetic hit is often required to push these hyperplastic cells to malignancy and confer mutation-specific characteristics associated with oncogenic signaling. Somatic loss-of-function mutations of the transcriptional corepressor
are recurrent and enriched in SHH medulloblastoma. To investigate
as a putative tumor suppressor, we used a genetically engineered mouse model to delete exons 9/10 of
(
) in GNPs during development. This mutation leads to reduced expression of C-terminally truncated BCOR (BCOR
). While
alone did not promote tumorigenesis or affect GNP differentiation,
combined with loss of the SHH receptor gene
resulted in fully penetrant medulloblastomas. In
;
tumors, the growth factor gene
was aberrantly up-regulated, and ectopic
overexpression was sufficient to drive tumorigenesis in
GNPs. BCOR directly regulates
, likely through the PRC1.1 complex; the repressive histone mark H2AK119Ub is decreased at the
promoter in
;
tumors. Overall, our data suggests that BCOR-PRC1.1 disruption leads to
overexpression, which transforms preneoplastic cells to malignant tumors.
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