Graphical abstract Highlights ► hASCs were differentiated to Schwann cell-like cells with a mixture of growth factors. ► Differentiated hASCs secreted neurotrophic factors and promoted neurite ...outgrowth. ► hASCs transplanted into nude rats survived and formed myelin on regenerating axons. ► In vitro differentiation improved survival and myelin-forming rates of hASCs in vivo.
We have statistically analyzed data from the European Incoherent Scatter (EISCAT) UHF/VHF radars in Tromsø (69.60°N, 19.20°E), Norway, to reveal how the occurrence of pulsating auroras (PsAs) ...modifies the electron density profile in the ionosphere. By checking five winter seasons' (2007–2012) observations of all‐sky aurora cameras of the National Institute of Polar Research in Tromsø, we have extracted 21 cases of PsA. During these PsA events, either the UHF or VHF radar of EISCAT was operative and the electron density profiles were obtained along the field‐aligned or vertical direction near the zenith. From these electron density measurements, we calculated hmE (E region peak height) and NmE (E region peak density), which are proxies for the energy and flux of the precipitating PsA electrons, respectively. Then, we examined how these two parameters changed during the evolution of 21 PsA events in a statistical fashion. The results can be summarized as follows: (1) hmE is lower (the energy of precipitation electrons is higher) during the periods of PsA than that in the surrounding interval; (2) when NmE is higher (flux of PsA electrons is larger), hmE tends to be lower (precipitation is harder); (3) hmE is lower and NmE is larger in the later magnetic local time; and (4) when the AE index during the preceding substorm is larger, hmE is lower and NmE is larger. These tendencies are discussed in terms of the characteristics of particles and plasma waves in the source of PsA in the magnetosphere. In addition to the statistics of the EISCAT data, we carried out several detailed case studies, in which the altitude profiles of the electron density were derived by separating the On and Off phases of PsA. This allows us to estimate the true altitude profiles of the PsA ionization, which can be used for estimating the characteristic energy of the PsA electrons and better understanding the wave‐particle interaction process in the magnetosphere.
Key Points
Statistical characteristics of ionization during pulsating aurora are derived
Ionization associated with pulsating aurora occurs well below 100 km altitude
Pulsating aurora electrons tend to be harder in the later MLT
On 24 November 2012, an interval of polar cap patches was identified by an all‐sky airglow imager located near the dayside cusp. During the interval, the successive appearance of poleward moving ...auroral forms (PMAFs) was detected, which are known to represent ionospheric manifestations of pulsed magnetic reconnections at the dayside magnetopause. All of the patches observed during the interval appeared from these transient auroral features (i.e., there was a one‐to‐one correspondence between PMAFs and newly created baby patches). This fact strongly suggests that patches can be directly and seamlessly created from a series of PMAFs. The optical intensities of the baby patches were 100–150 R, which is slightly lower than typical patch luminosity on the nightside and may imply that PMAF‐induced patches are generally low density. The generation of such patches could be explained by impact ionization due to soft particle precipitation into PMAFs traces. In spite of the faint signature of the baby patches, two coherent HF radars of the SuperDARN network observed backscatter echoes in the central polar cap, which represented signatures of plasma irregularities associated with the baby patches. These indicate that patches created from PMAFs have the potential to affect the satellite communications environment in the central polar cap region.
Key Points
Simultaneous observations of PMAF and polar cap patches near the cusp
Patches are directly and seamlessly produced from PMAF
PMAF‐generated patches are low density but accompanied by irregularities
A thermospheric wind data set from a Fabry‐Perot interferometer (630 nm) and the ion velocity from a Dynasonde in Tromsø, Norway, was analyzed for nine winter seasons to study the dynamics of the ...thermosphere and F‐region ionosphere at an auroral latitude. This study focused on bifurcation in the zonal component of the neutral wind and ion velocity at midnight and its dependence on the Y component of the interplanetary magnetic field (IMF). Ionospheric plasma convection patterns are evidently imprinted on the thermospheric wind variations as aspects of the westward and eastward accelerations at dusk and late morning, respectively. The zonal wind bifurcates immediately before midnight for IMF By < 0, but for By > 0, it inverts gradually into the postmidnight sector. Neutral wind streams, originating from higher latitudes, may result in the dependence because of anti‐sunward plasma flow distorted in the polar cap.
Plain Language Summary
The ionosphere is partially ionized plasma, but the particle minority of ions plays an important role in controlling dynamics of the thermosphere. Particle collision is the fundamental process for momentum transfer from ionospheric ions to thermospheric neutral particles. The ionospheric plasma flow pattern at high latitudes depends on the direction of the interplanetary magnetic field (IMF), and the pattern may be projected on the thermospheric wind. However, the dependence is not yet well understood. This study derived statistical experimental features regarding the dependence of the thermospheric wind, analyzing data from an optical interferometer (Fabry‐Perot interferometer) and a radio wave technique (Dynasonde) in Tromsø, Norway. The wind pattern around midnight is different from the ionospheric plasma convection, in accordance with the IMF direction. The zonal wind bifurcates immediately before midnight for IMF By < 0, but for By > 0, it inverts gradually into the postmidnight sector. Neutral wind streams, originating from higher latitudes, may cause the dependence because of anti‐sunward plasma flow distortion in the polar cap. In summary, this study concludes that the zonal wind bifurcation at auroral latitudes is caused by the ion velocity bifurcation, and that advection from the polar cap region affects the wind response time to the ion velocity bifurcation.
Key Points
The thermospheric wind from a Fabry‐Perot interferometer (630 nm) and the ionospheric plasma velocity from a Dynasonde were compared
The zonal wind bifurcates immediately before midnight for interplanetary magnetic field By < 0, but for By > 0, it inverts gradually into the postmidnight sector
The wind bifurcation signature is different from the ion velocity bifurcation, probably due to advection from the polar cap region
Abstract
Pulsating aurorae (PsA) are caused by the intermittent precipitations of magnetospheric electrons (energies of a few keV to a few tens of keV) through wave-particle interactions, thereby ...depositing most of their energy at altitudes ~ 100 km. However, the maximum energy of precipitated electrons and its impacts on the atmosphere are unknown. Herein, we report unique observations by the European Incoherent Scatter (EISCAT) radar showing electron precipitations ranging from a few hundred keV to a few MeV during a PsA associated with a weak geomagnetic storm. Simultaneously, the Arase spacecraft has observed intense whistler-mode chorus waves at the conjugate location along magnetic field lines. A computer simulation based on the EISCAT observations shows immediate catalytic ozone depletion at the mesospheric altitudes. Since PsA occurs frequently, often in daily basis, and extends its impact over large MLT areas, we anticipate that the PsA possesses a significant forcing to the mesospheric ozone chemistry in high latitudes through high energy electron precipitations. Therefore, the generation of PsA results in the depletion of mesospheric ozone through high-energy electron precipitations caused by whistler-mode chorus waves, which are similar to the well-known effect due to solar energetic protons triggered by solar flares.
We have identified for the first time an energy‐time dispersion of precipitating electron flux in a pulsating aurora patch, ranging from 6.7 to 580 keV, through simultaneous in‐situ observations of ...sub‐relativistic electrons of microburst precipitations and lower‐energy electrons using the Loss through Auroral Microburst Pulsation sounding rocket launched from the Poker Flat Research Range in Alaska. Our observations reveal that precipitating electrons with energies of 180–320 keV were observed first, followed by 250–580 keV electrons 0–30 ms later, and finally, after 500–1,000 ms, 6.7–14.6 keV electrons were observed. The identified energy‐time dispersion is consistent with the theoretical estimation that the relativistic electron microbursts are a high‐energy tail of pulsating aurora electrons, which are caused by chorus waves propagating along the field line.
Plain Language Summary
Microbursts, which are bursts of high energy electrons, and pulsating auroras, which periodically blink and caused by the precipitation of low energy electrons, are observed in the Earth's polar ionosphere. The detection time differences of the electrons associated with microbursts and pulsating auroras were detected by a sounding rocket. A possible mechanism for the generation of these precipitations is the interaction of electrons with a particular type of wave, known as “chorus,” which propagates along geomagnetic lines. The observed energy‐time dispersion of the precipitating electrons is quantitatively consistent with theories of electron precipitation based on this interaction.
Key Points
A sounding rocket observed simultaneously precipitating sub‐relativistic electron microbursts and pulsating auroral electrons
250–580 keV electron precipitations were detected 0–30 ms after 180–320 keV electron precipitations in a single auroral patch
The energy dispersion of observed electrons is consistent with the theory that they are due to chorus waves propagating to higher latitudes
The brightness of aurorae in Earth's polar region often beats with periods ranging from sub-second to a few tens of a second. Past observations showed that the beat of the aurora is composed of a ...superposition of two independent periodicities that co-exist hierarchically. However, the origin of such multiple time-scale beats in aurora remains poorly understood due to a lack of measurements with sufficiently high temporal resolution. By coordinating experiments using ultrafast auroral imagers deployed in the Arctic with the newly-launched magnetospheric satellite Arase, we succeeded in identifying an excellent agreement between the beats in aurorae and intensity modulations of natural electromagnetic waves in space called "chorus". In particular, sub-second scintillations of aurorae are precisely controlled by fine-scale chirping rhythms in chorus. The observation of this striking correlation demonstrates that resonant interaction between energetic electrons and chorus waves in magnetospheres orchestrates the complex behavior of aurora on Earth and other magnetized planets.
Background and aims: In the present study, we describe a newly developed microchip‐based analytical system to evaluate white thrombus formation (WTF). Efficacies of various antithrombotic agents were ...compared under different flow conditions. Methods: Whole blood containing corn trypsin inhibitor was perfused over a microchip coated with collagen and tissue thromboplastin at the lower and higher shear rates of 240 and 600 s−1, and WTF process inside the microchip was quantified by monitoring a flow pressure. Parameters of T10 (time to 10 kPa), T10–80 (time from 10 to 80 kPa) and OT (occlusion time; time to 80 kPa) were used to evaluate the onset and the growth rate of WTF, and the capillary occlusion, respectively. Results: After perfusion was started, white thrombus composed of activated platelets and fibrin was formed on the coated surface. Thrombus gradually increased in size and eventually occluded the capillary. Among anticoagulants, heparin (0.5–1.0 U mL−1) potently prolonged T10 at both shear rates, whereas low molecular weight heparin (1.0–2.0 IU mL−1) inhibited the growth of WTF at the lower shear rate. Among antiplatelet agents, abciximab (1–2 μg mL−1) significantly reduced the size and number of thrombi, which was additively enhanced in the presence of heparin (0.5 U mL−1). OS‐1 (specific GPIbα‐antagonist) prevented the complete capillary occlusion. Conclusion: The novel monitoring system of WTF may be useful in preclinical and clinical evaluations of different types of antithrombotic strategies, and their effects in combination.
On the equatorward side of the dayside cusp there often appear diffuse auroras. In this paper, we report north‐south aligned discrete aurora events and show the spatial relationships between the ...auroras and the plasma flow. Several events of the north‐south aligned discrete auroral structures were identified using an all‐sky imager at Longyearbyen, Svalbard, during the recovery of a moderately disturbed period on 8 December 2013. During a brief interval of the moderately disturbed period, the cusp shifted to higher latitudes; as a result, the field‐aligned beam of the EISCAT Svalbard Radar (ESR) passed through the northern portion of the north‐south aligned auroral structures. Simultaneous observations from the all‐sky imager and ESR reveal that enhancements in ion temperature (caused by fast ion flow) occurred near the eastward and westward boundaries of the north‐south aligned auroral structures. However, within the region of the most enhanced aurora, the ion temperature enhancements were moderately suppressed. These features indicate that the ion flow slows down in the region of electron precipitation responsible for north‐south aligned auroral structures. We can quantitatively interpret the slowdown of the flow as the reduction of the electric field due to the polarization effect in the north‐south aligned region of the increased Pedersen conductivity. It thus appears that the magnetospheric source of the north‐south aligned discrete auroras is a limited area embedded in the region of plasma flow toward the dayside magnetopause.
Key Points
First simultaneous observations of north‐south aligned discrete auroras equatorward of the cusp from an all‐sky imager and EISCAT are presented
A decrease in the elevated ion temperature is coincident with the north‐south aligned aurora
The plasma flow slows in the middle of the east‐west dimension of the north‐south aligned aurora
A search for dark matter using an underground single-phase liquid xenon detector was conducted at the Kamioka Observatory in Japan, particularly for Weakly Interacting Massive Particles (WIMPs). We ...have used 705.9 live days of data in a fiducial volume containing 97kg of liquid xenon at the center of the detector. The event rate in the fiducial volume after the data reduction was (4.2±0.2)×10−3day−1kg−1keVee−1 at 5keVee, with a signal efficiency of 20%. All the remaining events are consistent with our background evaluation, mostly of the “mis-reconstructed events” originated from 210Pb in the copper plates lining the detector's inner surface. The obtained upper limit on a spin-independent WIMP-nucleon cross section was 2.2×10−44cm2 for a WIMP mass of 60GeV/c2 at the 90% confidence level, which was the most stringent limit among results from single-phase liquid xenon detectors.
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