Radiation belt electron acceleration during periods of low plasma density

<p>Electrons in the Van Allen radiation belts can have energies in excess of 7 MeV. We present a unique way of analyzing phase space density data which demonstrates that local acceleration is capable of heating electrons up to 7 MeV. The Van Allen Probes mission not only provided unique measurements of ultra-relativistic radiation belt electrons, but also simultaneous observations of plasma waves that allowed for the routine inference of total plasma number density. Based on long-term observations, we show that the underlying plasma density has a controlling effect over local acceleration to ultra-relativistic energies, which occurs only when the plasma number density drops down to very low values (~10 cm<sup>-3</sup>). The VERB-2D model is used to simulate ultra-relativistic electron acceleration during an event which exhibits an extreme cold plasma depletion. The results show that a reduced electron plasma density allows chorus waves to efficiently resonate with electrons up to ultra-relativistic energies, producing enhancements from 100s of keV up to >7 MeV via local diffusive acceleration. We analyse statistically the observed chorus wave power during ultra-relativistic enhancement events, considering the contribution from both upper and lower band chorus waves. The PINE density model allows for the investigation of global magnetospheric density changes. We analyze the how the global cold plasma density changes during ultra-relativistic enhancement events and compare to in-situ point measurements of the plasma density.</p>

Gyroresonant wave-particle interactions with chorus waves during extreme depletions of plasma density in the Van Allen radiation belts

The Van Allen Probes mission provides unique measurements of the most energetic radiation belt electrons at ultrarelativistic energies. Simultaneous observations of plasma waves allow for the routine inference of total plasma number density, a parameter that is very difficult to measure directly. On the basis of long-term observations in 2015, we show that the underlying plasma density has a controlling effect over acceleration to ultrarelativistic energies, which occurs only when the plasma number density drops down to very low values (~10 cm–3). Such low density creates preferential conditions for local diffusive acceleration of electrons from hundreds of kilo–electron volts up to >7 MeV. While previous models could not reproduce the local acceleration of electrons to such high energies, here we complement the observations with a numerical model to show that the conditions of extreme cold plasma depletion result in acceleration up to >7 MeV.

Long Non-coding RNA ST8SIA6-AS1 Promotes Lung Adenocarcinoma Progression Through Sponging miR-125a-3p

Emerging evidence suggests that long non-coding RNA (lncRNA) plays a critical role in human disease progression. Recently, a novel lncRNA ST8SIA6-AS1 was shown as an important driver in various cancer types. Nevertheless, its contribution to lung adenocarcinoma (LUAD) remains undocumented. Herein, we found that ST8SIA6-AS1 was frequently overexpressed in LUAD cell lines, tissues, and plasma. Depletion of ST8SIA6-AS1 significantly inhibited LUAD cell proliferation and invasion in vitro and tumor growth in vivo. In term of mechanism, ST8SIA6-AS1 was transcriptionally repressed by tumor suppressor p53, and ST8SIA6-AS1 was mainly located in the cytoplasm and could abundantly sponge miR-125a-3p to increase nicotinamide N-methyltransferase (NNMT) expression, thereby facilitating LUAD malignant progression. Clinically, high ST8SIA6-AS1 was positively correlated with larger tumor size, lymph node metastasis, and later TNM stage. Moreover, ST8SIA6-AS1 was identified as an excellent indicator for MM diagnosis and prognosis. Collectively, our data demonstrate that ST8SIA6-AS1 is a carcinogenic lncRNA in LUAD, and targeting the axis of ST8SIA6-AS1/miR-125a-3p/NNMT may be a promising treatment for LUAD patients.

Plasma and magnetic-field structures near the Martian induced magnetosphere boundary

The interaction between the solar wind and the Martian induced magnetosphere can lead to the formation of various regions with different plasma and magnetic-field characteristics. In this paper, these structures are investigated based on the plasma and magnetic-field measurements from Mars Atmosphere and Volatile EvolutioN (MAVEN). We find that the structures upstream of Mars are similar to those around Earth: both have a bow shock, magnetosheath, magnetopause, and a magnetosphere or induced magnetosphere. The inner part of Martian magnetosheath is called a plasma depletion region (PDR), similar to the plasma depletion layer upstream of the Earth’s magnetopause, in which the magnetosheath magnetic fields are piled up and the magnetosheath plasmas (including ions and electrons) are partially depleted. Several cases of PDRs are examined in detail. The hotter plasmas in PDRs are squeezed out along the enhanced magnetic field, resulting in the decrease of the plasma beta, the plasma density, and the ion temperature. The boundary between the magnetosheath and the induced magnetosphere is called the magnetopause, which can be identified as a magnetohydrodynamic discontinuity, either tangential discontinuity (TD) or rotational discontinuity, where the magnetic field changes its orientation. Tangential discontinuities with an insignificant normal component (BN ≈ 0) of the magnetic field are the focus of this study. This discontinuity separates the magnetosheath H+ ions from the heavy ions (e.g. O+, O2+) in the induced magnetosphere. Inside a TD, ions from both sides are mixed. There are 3332 boundary crossings by MAVEN in 2015, 1075 cases of which are identified as the TD (including the potential TD). Tangential discontinuities at Mars are at higher locations in the southern hemisphere and have an average thickness of ~200 km, mostly ranging from 50 to 400 km. The sample of TD is a decreasing function of θ (θ is the magnetic field rotation angle on the two sides of the TD). The PDRs in front of TDs are thicker in the northern hemisphere. From the sub-solar point to the Mars tail, PDR thickness increases and the proton number density and temperature decrease.