Magnetic reconnection is the underlying process that releases impulsively an enormous amount of magnetic energy in solar flares , flares on strongly magnetized neutron stars and substorms in the ...Earth's magnetosphere. Studies of energy release during solar flares, in particular, indicate that up to 50% of the released energy is carried by accelerated 20-100 keV suprathermal electrons. How so many electrons can gain so much energy during reconnection has been a long-standing question. A recent theoretical study suggests that volume-filling contracting magnetic islands formed during reconnection can produce a large number of energetic electrons. Here we report the first evidence of the link between energetic electrons and magnetic islands during reconnection in the Earth's magnetosphere. The results indicate that energetic electron fluxes peak at sites of compressed density within islands, which imposes a new constraint on theories of electron acceleration.
The poly(A) tail enhances translation and transcript stability, and tail length is under dynamic control during cell state transitions. Tail regulation plays essential roles in translational timing ...and fertilization in early development, but poly(A) tail dynamics have not been fully explored in post-embryonic systems. Here, we examined the landscape and impact of tail length control during macrophage activation. Upon activation, more than 1500 mRNAs, including proinflammatory genes, underwent distinctive changes in tail lengths. Increases in tail length correlated with mRNA levels regardless of transcriptional activity, and many mRNAs that underwent tail extension encode proteins necessary for immune function and post-transcriptional regulation. Strikingly, we found that
ZFP36
, whose protein product destabilizes target transcripts, undergoes tail extension. Our analyses indicate that many mRNAs undergoing tail lengthening are, in turn, degraded by elevated levels of ZFP36, constituting a post-transcriptional feedback loop that ensures transient regulation of transcripts integral to macrophage activation. Taken together, this study establishes the complexity, relevance, and widespread nature of poly(A) tail dynamics, and the resulting post-transcriptional regulation during macrophage activation.
Microbial exposure during development can elicit long-lasting effects on the health of an individual. However, how microbial exposure in early life leads to permanent changes in the immune system is ...unknown. Here, we show that the microbial environment alters the set point for immune susceptibility by altering the developmental architecture of the CD8+ T cell compartment. In particular, early microbial exposure results in the preferential expansion of highly responsive fetal-derived CD8+ T cells that persist into adulthood and provide the host with enhanced immune protection against intracellular pathogens. Interestingly, microbial education of fetal-derived CD8+ T cells occurs during thymic development rather than in the periphery and involves the acquisition of a more effector-like epigenetic program. Collectively, our results provide a conceptual framework for understanding how microbial colonization in early life leads to lifelong changes in the immune system.
Strong interplanetary shock interactions with the Earth's magnetosphere have great impacts on energetic particle dynamics in the magnetosphere. An interplanetary shock on 7 November 2004 (with the ...maximum solar wind dynamic pressure of ∼70 nPa) was observed by the Cluster constellation to induce significant ULF waves in the plasmasphere boundary, and energetic electrons (up to 2 MeV) were almost simultaneously accelerated when the interplanetary shock impinged upon the magnetosphere. In this paper, the relationship between the energetic electron bursts and the large shock‐induced ULF waves is studied. It is shown that the energetic electrons could be accelerated and decelerated by the observed ULF wave electric fields, and the distinct wave number of the poloidal and toroidal waves at different locations also indicates the different energy ranges of electrons resonating with these waves. For comparison, a rather weak interplanetary shock on 30 August 2001 (dynamic pressure ∼2.7 nPa) is also investigated. It is found that interplanetary shocks or solar wind pressure pulses with even small dynamic pressure change can have a nonnegligible role in the radiation belt dynamics.
Energetic electrons in an earthward reconnection outflow region have been observed by Cluster/Research with Adaptive Particle Imaging Detectors. We found a good correlation between the energetic ...electron enhancement and a normal magnetic field (Bz) enhancement within a 0.25‐s time resolution. The large normal magnetic field is thought to be associated with magnetic reconnection because the negative/positive Bz reversal observed during the fast proton tailward/earthward flow reversal is a good indicator of magnetic reconnection. Using the four‐spacecraft Cluster, we can clearly see that this large positive Bz structure propagates in the earthward direction. Furthermore, we find that the energy spectrum of the energetic electrons becomes harder toward the downstream region. A negative Bz enhancement is also observed. The intensity of energetic electron enhancement associated with the negative Bz enhancement is weaker than that associated with the positive one. To discuss the temporal and spatial profile of energetic electron acceleration in the magnetic reconnection region, we determined the spacecraft position in the temporally evolving magnetic structures of reconnection. Our observation clearly indicates second‐step acceleration, in addition to X line acceleration, of energetic electrons in the downstream reconnection outflow region.
Baryonic matter in geospace is almost exclusively in a plasma state, with protons (H
+) and to some extent ionized helium (He) and oxygen (O) being the dominant ion species. But also other heavier ...ion species and even molecular ions are present in geospace. The Research with Adaptive Particle Imaging Detectors (RAPID) on board the Cluster satellites can identify and characterize some of these ions by utilizing their measured time of flight and energy. Usually, the measurements are then assigned into three discrete species channels; protons (H
+), helium (He), and a common channel for carbon, nitrogen, and oxygen (CNO), each with flux, energy, and angular information. But RAPID also has a Direct Event (DE) diagnostic mode in which the full time of flight and energy information for a limited number of incident particles are stored. With knowledge about energy losses in the various detector parts, it is then possible to derive the atomic mass of the incident particle. In this paper we report on results from a study of Cluster DE events during the years 2001–2018, with a particular emphasis of iron (Fe) ions. We show that suprathermal Fe ions can be found all over geospace covered by Cluster, and that the time variation is consistent with modulation by geomagnetic disturbances and solar activity. We do not find any clear correlations between detection of suprathermal Fe and meteor showers or sputtering off the moon.
Key Points
We present the first observations of (Fe
+/Fe
N+) from the Cluster mission
Suprathermal Fe is detected in all regions traversed by Cluster
Time variations and likely sources of the observed Fe ions are investigated
We study acceleration of energetic electrons in an earthward plasma jet due to magnetic reconnection in the Earth magnetotail for one case observed by Cluster. The case has been selected based on the ...presence of high fluxes of energetic electrons, Cluster being in the burst mode and Cluster separation being around 1,000 km that is optimal for studies of ion scale physics. We show that two characteristic acceleration mechanisms are operating during this event. First, significant acceleration is achieved inside the magnetic flux pile‐up of the jet, the acceleration mechanism being consistent with betatron acceleration. Second, strong energetic electron acceleration occurs in magnetic flux rope like structure forming in front of the magnetic flux pile‐up region. Energetic electrons inside the magnetic flux rope are accelerated predominantly in the field‐aligned direction and the acceleration can be due to Fermi acceleration in a contracting flux rope.
Key Points
Detailed study of energetic electron acceleration in the braking region of earthward propagating reconnection jet
Large electron acceleration in the magnetic flux pile‐up region and in a magnetic flux rope in front of the jet
The largest energetic electron fluxes are inside the flux rope, probably due to Fermi acceleration process
We performed a genome-wide association scan in 1461 patients with bipolar (BP) 1 disorder, 2008 controls drawn from the Systematic Treatment Enhancement Program for Bipolar Disorder and the ...University College London sample collections with successful genotyping for 372,193 single nucleotide polymorphisms (SNPs). Our strongest single SNP results are found in myosin5B (MYO5B; P=1.66 x 10(-7)) and tetraspanin-8 (TSPAN8; P=6.11 x 10(-7)). Haplotype analysis further supported single SNP results highlighting MYO5B, TSPAN8 and the epidermal growth factor receptor (MYO5B; P=2.04 x 10(-8), TSPAN8; P=7.57 x 10(-7) and EGFR; P=8.36 x 10(-8)). For replication, we genotyped 304 SNPs in family-based NIMH samples (n=409 trios) and University of Edinburgh case-control samples (n=365 cases, 351 controls) that did not provide independent replication after correction for multiple testing. A comparison of our strongest associations with the genome-wide scan of 1868 patients with BP disorder and 2938 controls who completed the scan as part of the Wellcome Trust Case-Control Consortium indicates concordant signals for SNPs within the voltage-dependent calcium channel, L-type, alpha 1C subunit (CACNA1C) gene. Given the heritability of BP disorder, the lack of agreement between studies emphasizes that susceptibility alleles are likely to be modest in effect size and require even larger samples for detection.
The pitch angle distribution (PAD) of suprathermal electrons can have both spatial and temporal evolution in the magnetotail and theoretically can be an indication of electron energization/cooling ...processes there. So far, the spatial evolution of PAD has been well studied, leaving the temporal evolution as an open question. To reveal the temporal evolution of electron PAD, spacecraft should monitor the same flux tube for a relatively long period, which is not easy in the dynamic magnetotail. In this study, we present such an observation by Cluster spacecraft in the magnetotail behind a dipolarization front (DF). We find that the PAD of suprathermal electrons can evolve from pancake type to butterfly type during <4 s and then to cigar type during <8 s. During this process, the flow velocity is nearly zero and the plasma entropy is constant, meaning that the evolution is temporal. We interpret such temporal evolution using the betatron cooling process, which is driven by quasi‐adiabatic expansion of flux tubes, and the magnetic mirror effect, which possibly exists behind the DF as well.
Key Points
Rapid temporal evolution of PAD of suprathermal electrons was observed behind DF
PAD evolves from pancake to butterfly then to cigar quasi‐adiabatically during <12 s
The evolution may stem from betatron cooling and magnetic mirror effect
We examine the pitch angle distribution (PAD) of suprathermal electrons (>40 keV) inside the flux pileup regions (FPRs) that are located behind the dipolarization fronts (DFs), in order to better ...understand the particle energization mechanisms operating therein. The 303 earthward‐propagating DFs observed during 9 years (2001–2009) by Cluster 1 have been analyzed and divided into two groups according to the differential fluxes of the >40 keV electrons inside the FPR. One group, characterized by the low flux (F < 500/cm2 · s · sr · keV), consists of 153 events and corresponds to a broad distribution of IMF Bz components. The other group, characterized by the high flux (F ≥ 500/cm2 · s · sr · keV), consists of 150 events and corresponds to southward IMF Bzcomponents. Only the high‐flux group is considered to investigate the PAD of the >40 keV electrons as the low‐flux situation may lead to large uncertainties in computing the anisotropy factor that is defined asA = F⊥/F∥ − 1 for F⊥ > F∥, and A = −F∥/F⊥ + 1 for F⊥ < F∥. We find that, among the 150 events, 46 events have isotropic distribution (|A| ≤ 0.5); 60 events have perpendicular distribution (A > 0.5), and 44 events have field‐aligned distribution inside the FPR (A < −0.5). The perpendicular distribution appears mainly inside the growing FPR, where the flow velocity is increasing and the local flux tube is compressed. The field‐aligned distribution occurs mainly inside the decaying FPR, where the flow velocity is decreasing and the local flux tube is expanding. Inside the steady FPR, we observed primarily the isotropic distribution of suprathermal electrons. This statistical result confirms the previous case study and gives an overview of the PAD of suprathermal electrons behind DFs.
Key Points
One hundred fifty hot flux pileup regions (FPRs) are examined
Perpendicular PAD in growing FPR; field‐aligned PAD in decaying FPR
Maximum flux is well correlated with the Bz peak at the DF
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