Magnetic reconnection is a key fundamental process in collisionless plasmas that explosively converts magnetic energy to plasma kinetic and thermal energies through a change of magnetic field ...topology in a central electron‐scale region called the electron diffusion region (EDR). Past simulations and observations demonstrated that this process causes efficient energy conversion through the formation of multiple macro‐scale or micro‐scale magnetic islands/flux ropes. However, the coupling of these phenomena on different spatiotemporal scales is still poorly understood. Here, based on a new large‐scale fully kinetic simulation with a realistic, initially fluctuating magnetic field, we demonstrate that macro‐scale evolution of turbulent reconnection involving merging of macro‐scale islands induces repeated, quick formation of new electron‐scale islands within the EDR which soon grow to larger scales. This process causes an efficient cross‐scale energy transfer from electron‐ to larger‐scales, and leads to strong electron energization within the growing islands.
Plain Language Summary
Space above the Earth’s atmosphere is broadly filled with ionized gas, called plasma. Since the density of the space plasma is mostly small enough to neglect the viscosity, the behavior of it is essentially different from neutral viscous fluids. In such a collisionless plasma system, the boundary layer between regions with different electromagnetic field and plasma properties plays a central role in transferring energy. One of the representative energy transfer processes in collisionless plasmas is magnetic reconnection that explosively converts magnetic energy to plasma kinetic energy through the topology change of magnetic field lines across the boundary layer with a large magnetic shear. On the other hand, understanding how the energy transfer between different spatiotemporal scales in turbulence, which has been commonly observed in space, is also a key for understanding the energy transfer physics in collisionless plasmas. In this study, based on a new plasma kinetic simulation of magnetic reconnection newly considering realistic, turbulent magnetic field fluctuations, it is found that during macro‐scale evolution of the background fluctuations, the topology change of the reconnecting field lines occurs at multiple points within the micro‐scale central region of reconnection. This process causes an efficient cross‐scale energy transfer from micro‐ to larger‐scales.
Key Points
2‐1/2 dimensional fully kinetic simulation of turbulent reconnection with a realistic, initially fluctuating magnetic field is performed
Turbulent reconnection involving merging of macro‐scale islands induces repeated micro‐scale island formation in electron diffusion region
During the macro‐scale island merging, the micro‐scale islands grow to larger scales, leading to an efficient cross‐scale energy transfer
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
A method based on electron magnetohydrodynamics (EMHD) for the reconstruction of steady, two‐dimensional plasma and magnetic field structures from data taken by a single spacecraft, first developed ...by Sonnerup et al. (2016), https://doi.org/10.1002/2016ja022430, is extended to accommodate inhomogeneity of the electron density and temperature, electron inertia effects, and guide magnetic field in and around the electron diffusion region (EDR), the central part of the magnetic reconnection region. The new method assumes that the electron density and temperature are constant along, but may vary across, the magnetic field lines. We present two models for the reconstruction of electron streamlines, one of which is not constrained by any specific formula for the electron pressure tensor term in the generalized Ohm's law that is responsible for electron unmagnetization in the EDR, and the other is a modification of the original model to include the inertia and compressibility effects. Benchmark tests using data from fully kinetic simulations show that our new method is applicable to both antiparallel and guide‐field (component) reconnection, and the electron velocity field can be better reconstructed by including the inertia effects. The new EMHD reconstruction technique has been applied to an EDR of magnetotail reconnection encountered by the Magnetospheric Multiscale spacecraft on 11 July 2017, reported by Torbert et al. (2018), https://doi.org/10.1126/science.aat2998 and reconstructed with the original inertia‐less version by Hasegawa et al. (2019), https://doi.org/10.1029/2018ja026051, which demonstrates that the new method better performs in recovering the electric field and electron streamlines than the original version.
Plain Language Summary
Magnetic reconnection is a physical process that converts magnetic energy to plasma energy by changing the topology of magnetic field lines. Reconnection occurring at the outer boundary of planetary magnetospheres, called the magnetopause, is key to the entry of solar wind mass and energy into planetary magnetospheres. Reconnection occurring in the nightside portion of the magnetospheres is also key to fast release of magnetic energy during substorms or sudden auroral brightening. However, space plasma and magnetic field in those reconnection regions are invisible to any remote sensing instruments currently available, and should be measured in situ by spacecraft to understand details of the reconnection process. In the present study, we have improved a method for analyzing data from such in‐situ measurements, which can visualize two‐dimensional magnetic field and electron streamline structures in the central part of the reconnection region. The newly developed method allows spatial variations of the electron density and temperature, effects of finite electron mass, and not strictly antiparallel magnetic field configurations in the reconnection region, as commonly observed at the magnetopause, and thus has more applicability. Tests of the method using numerical simulation results and application to actual spacecraft observations demonstrate a better performance than earlier ones.
Key Points
Method to reconstruct two‐dimensional plasma and field structures from spacecraft data based on compressible electron magnetohydrodynamics
The new method accommodates nonuniform density/temperature, finite electron inertia, and guide magnetic field in the reconnection region
The new method successfully benchmarked by use of fully kinetic simulation results and applied to a magnetotail reconnection event
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
We examine a Dipolarization Front (DF) event with an embedded electron diffusion region (EDR), observed by the Magnetospheric Multiscale (MMS) spacecraft on 08 September 2018 at 14:51:30 UT in the ...Earth's magnetotail by applying multi‐scale multipoint analysis methods. In order to study the large‐scale context of this DF, we use conjunction observations of the Cluster spacecraft together with MMS. A polynomial magnetic field reconstruction technique is applied to MMS data to characterize the embedded electron current sheet including its velocity and the X‐line exhaust opening angle. Our results show that the MMS and Cluster spacecraft were located in two counter‐rotating vortex flows, and such flows may distort a flux tube in a way that the local magnetic shear angle is increased and localized magnetic reconnection may be triggered. Using multi‐point data from MMS we further show that the local normalized reconnection rate is in the range of R ∼ 0.16 to 0.18. We find a highly asymmetric electron in‐ and outflow structure, consistent with previous simulations on strong guide‐field reconnection events. This study shows that magnetic reconnection may not only take place at large‐scale stable magnetopause or magnetotail current sheets but also in transient localized current sheets, produced as a consequence of the interaction between the fast Earthward flows and the Earth's dipole field.
Plain Language Summary
Magnetic Reconnection is a key energy conversion process, where magnetic energy is converted into kinetic energy of plasma particles. During this process the magnetic field topology changes and the plasma particles decouple from the magnetic field in the so‐called diffusion region and get accelerated, forming a fast outflow jet. Over the last decades, hints arise that reconnection can take place at many different places in the magnetosphere and also very locally and intermittently. Fast plasma flows in the Magnetotail, moving toward the Earth, are assumed to be a consequence of magnetic reconnection, and are often accompanied by dipolar‐shaped magnetic flux bundles, embedded into them. The leading edges of such flux bundles are called dipolarization fronts (DF). In this work, we investigate a DF event, which hosts a diffusion region. First, we study the large‐scale characteristics of the DF, by utilizing data from both the Magnetospheric Multiscale (MMS) and the Cluster mission, that observe different regions of the event almost simultaneously. Second, we performed a 3D magnetic field reconstruction technique and compared the results to MMS data, to investigate the event on small scales.
Key Points
A thin current sheet inside a dipolarization front, embedded in a diverging flow is analyzed using a polynomial reconstruction technique
Transient reconnection event is detected in a high magnetic shear region, where the magnetic field is deflected due to duskward fast plasma flow
The reconstructed current sheet has a guide field of ∼1.8 the reconnecting component with normalized reconnection rate between 0.16 and 0.18
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Thermal probe with double function of thermocouples and Langmuir probe has been developed, and the initial data observed in far-SOL in QUEST is obtained. Heat flux of megawatt per square meters ...related to energetic electrons and sonic plasma flow in far-SOL have been observed in the current rump-up phase although no high power inductive force like ohmic winding is applied. The heat flux and the flow are suppressed after the current is built up. In the quasi-steady state, plasma current starts and keeps sawtooth-like oscillation with 20Hz frequency. The heat flux and the flow in far-SOL have clear responses to the oscillation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Objective To investigate the performance of screening rectal cultures obtained 2 weeks before transrectal prostate biopsy to detect fluoroquinolone-resistant organisms and again at transrectal ...prostate biopsy. Materials and Methods After institutional review board approval for observational study, we obtained a rectal culture on patients identified for a prostate biopsy but before antibiotic prophylaxis from September 12, 2011 to April 23, 2012. The specimen was cultured onto MacConkey agar with and without 1 μg/mL ciprofloxacin. We then obtained a second rectal culture immediately before prostate biopsy after 24 hours of ciprofloxacin prophylaxis. All cultures were blinded to the practitioner until the end of the study. Results Of 108 patients enrolled, 58 patients had both rectal cultures for comparison. The median time duration between cultures was 14 (6-119) days. There were 54 of 58 concordant pairs (93%), which included 47 negative cultures and 7 positive cultures; 2 patients (3%) who were culture negative from the first screening culture became positive at biopsy. Sensitivity, specificity, negative, positive predictive values, and area under the operator curve were 95.9%, 77.8%, 95.9%, 77.8%, and 0.868, respectively. When Pseudomonas spp. are removed from the analysis, the area under the curve is increased to 0.927. Conclusion Screening rectal cultures 2 weeks before prostate biopsy has favorable test performance, suggesting screening cultures give an accurate estimate of fluoroquinolone-resistant colonization.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Non-inductive plasma current start-up experiments were performed using the lower hybrid wave (LHW) on the TST-2 spherical tokamak. The density limit, observed in previous experiments using the ...outboard-launch antenna, disappeared after changing the plasma condition in the scrape-off layer, and the plasma current reached about 20 kA. In order to improve the LHW power deposition in the plasma core through an up-shift of the parallel wavenumber during the first pass through the plasma, a new top-launch antenna was designed, fabricated and installed. The plasma current ramp-up to 12 kA was achieved using the top-launch antenna alone in a preliminary experiment. Ray-tracing calculations using the measured plasma parameters showed a large up-shift during the first pass, satisfying the strong electron Landau damping condition in the plasma core.
Low refractive index silicon oxide films were deposited using atmospheric-pressure He/SiH
4/CO
2 plasma excited by a 150-MHz very high-frequency power. Significant increase in deposition rate at room ...temperature could prevent the formation of dense SiO
2 network, decreasing refractive index of the resulting film effectively. As a result, a silicon oxide film with the lowest refractive index,
n
=
1.24 at 632.8
nm, was obtained with a very high deposition rate of 235
nm/s. The reflectance and transmittance spectra showed that the low refractive index film functioned as a quarter-wave anti-reflection coating of a glass substrate.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Objectives
Hyperforin, a phloroglucinol derivative of St. John's Wort, has been identified as the major molecule responsible for this plant's products anti‐depressant effects. It can be expected that ...exposure to St. John's Wort during pregnancy occurs with some frequency although embryotoxic or teratogenic effects of St. John's Wort and hyperforin have not yet been experimentally examined in detail. In this study, to determine any embryotoxic effects of hyperforin, we have attempted to determine whether hyperforin affects growth and survival processes of employing mouse embryonic stem (mES) cells (representing embryonic tissue) and fibroblasts (representing adult tissues).
Materials and methods
We used a modified embryonic stem cell test, which has been validated as an in vitro developmental toxicity protocol, mES cells, to assess embryotoxic potential of chemicals under investigation.
Results
We have identified that high concentrations of hyperforin inhibited mouse ES cell population growth and induced apoptosis in fibroblasts. Under our cell culture conditions, ES cells mainly differentiated into cardiomyocytes, although various other cell types were also produced. In this condition, hyperforin affected ES cell differentiation into cardiomyocytes in a dose‐dependent manner. Analysis of tissue‐specific marker expression also revealed that hyperforin at high concentrations partially inhibited ES cell differentiation into mesodermal and endodermal lineages.
Conclusions
Hyperforin is currently used in the clinic as a safe and effective antidepressant. Our data indicate that at typical dosages it has only a low risk of embryotoxicity; ingestion of large amounts of hyperforin by pregnant women, however, may pose embryotoxic and teratogenic risks.
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BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, SIK, UILJ, UKNU, UL, UM, UPUK
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