Aortic pulse wave velocity (AoPWV) and augmentation index (AIx) are commonly used measures of large elastic artery stiffness and wave reflection, respectively. Recently, a new cuff-based SphygmoCor ...device (Xcel) has been developed to measure both AoPWV and AIx. We sought to examine the following: (1) the validity of Xcel compared with the well-validated tonometry-based SphygmoCor device (MM3); (2) the intratest and day-to-day reliability of Xcel; (3) the influence of body side (right or left) on Xcel measurements; and (4) the relation of Xcel measurements to carotid artery compliance, distensibility and β-stiffness index. We found that measurements of AoPWV and AIx between Xcel and MM3 were not different (P=0.26 and P=0.43, N=22 and 26, respectively) and were strongly related (r=0.85 and 0.75, P<0.0001), and based on Bland-Altman plots there was good agreement between them. Intra-test (intraclass correlation=0.996 and 0.983, P<0.0001; AoPWV and AIx, N=24 and 26, respectively) and day-to-day reliability (intraclass correlation=0.979 and 0.939, P<0.0001) were high. Xcel AoPWV and AIx on the left versus right body side were not different (P=0.19 and P=0.58, N=14 and 15, respectively) and were highly correlated (r=0.99 and 0.94, P<0.0001). AoPWV and AIx measured with Xcel were positively related with β-stiffness index (r=0.62 and 0.51, P< or = 0.005, N=23 and 24, respectively) and negatively related with distensibility (r = -0.58 and -0.44, P < or = 0.02, N=23 and 24, respectively). In conclusion, Xcel measures of AIx and AoPWV are valid, highly reliable and not affected by body side. Xcel is a useful tool for use in research and the clinic.
This paper presents Magnetospheric Multiscale mission (MMS) observations of the exhaust region in the vicinity of the central reconnection site in Earth's magnetopause current sheet. ...High-time-resolution measurements of field and particle distributions enable us to explore the fine structure of the diffusion region near the X line. Ions are decoupled from the magnetic field throughout the entire current sheet crossing. Electron jets flow downstream from the X line at speeds greater than the E by B drift velocity. At or around the magnetospheric separatrix, large-amplitude electric fields containing field-aligned components accelerate electrons along the magnetic field toward the X line. Near the neutral sheet, crescent-shaped electron distributions appear coincident with (1) an out-of-plane electric field whose polarity is opposite to that of the reconnection electric field and (2) the energy transfer from bulk kinetic to field energy. The observations indicate that MMS passed through the edge of an elongated electron diffusion region (EDR) or the outer EDR in the exhaust region.
Coulomb collisions provide plasma resistivity and diffusion but in many low-density astrophysical plasmas such collisions between particles are extremely rare. Scattering of particles by ...electromagnetic waves can lower the plasma conductivity. Such anomalous resistivity due to wave-particle interactions could be crucial to many processes, including magnetic reconnection. It has been suggested that waves provide both diffusion and resistivity, which can support the reconnection electric field, but this requires direct observation to confirm. Here, we directly quantify anomalous resistivity, viscosity, and cross-field electron diffusion associated with lower hybrid waves using measurements from the four Magnetospheric Multiscale (MMS) spacecraft. We show that anomalous resistivity is approximately balanced by anomalous viscosity, and thus the waves do not contribute to the reconnection electric field. However, the waves do produce an anomalous electron drift and diffusion across the current layer associated with magnetic reconnection. This leads to relaxation of density gradients at timescales of order the ion cyclotron period, and hence modifies the reconnection process.
Electron inflow and outflow velocities during magnetic reconnection at and near the dayside magnetopause are measured using satellites from NASA's Magnetospheric Multiscale (MMS) mission. A case ...study is examined in detail, and three other events with similar behavior are shown, with one of them being a recently published electron‐only reconnection event in the magnetosheath. The measured inflow speeds of 200–400 km/s imply dimensionless reconnection rates of 0.05–0.25 when normalized to the relevant electron Alfvén speed, which are within the range of expectations. The outflow speeds are about 1.5–3 times the inflow speeds, which is consistent with theoretical predictions of the aspect ratio of the inner electron diffusion region. A reconnection rate of 0.04 ± 25% was obtained for the case study event using the reconnection electric field as compared to the 0.12 ± 20% rate determined from the inflow velocity.
Key Points
Electron inflow velocities are determined for reconnection at the magnetopause and in the magnetosheath
For four events inflow velocities of 200–400 km/s imply normalized reconnection rates of 0.05–0.25
Reconnection rates using electron inflow velocities (0.12) and the reconnection electric field (0.04) are compared for one event
Plain Language Summary
When the solar wind impacts the Earth's magnetosphere, an explosive energy conversion process called magnetic reconnection opens the door for solar wind energy to enter the magnetosphere by interconnection of the magnetic fields of the solar wind and of Earth. In this process, magnetic energy is converted to charged‐particle energy. Magnetic reconnection is fairly well understood at large scales and even down to the ion scale. However, the breaking and linking of field lines and the acceleration of electrons occur at much smaller scales, which are only recently being accessed by the NASA Magnetospheric Multiscale mission. This paper analyzes the speed at which electrons flow into and out of reconnection sites. The inflow speeds are crucial because they provide a measurement of the rate at which reconnection proceeds.
We identify the electron diffusion region (EDR) of a guide field dayside reconnection site encountered by the Magnetospheric Multiscale (MMS) mission and estimate the terms in generalized Ohm's law ...that controlled energy conversion near the X‐point. MMS crossed the moderate‐shear (∼130°) magnetopause southward of the exact X‐point. MMS likely entered the magnetopause far from the X‐point, outside the EDR, as the size of the reconnection layer was less than but comparable to the magnetosheath proton gyroradius, and also as anisotropic gyrotropic “outflow” crescent electron distributions were observed. MMS then approached the X‐point, where all four spacecraft simultaneously observed signatures of the EDR, for example, an intense out‐of‐plane electron current, moderate electron agyrotropy, intense electron anisotropy, nonideal electric fields, and nonideal energy conversion. We find that the electric field associated with the nonideal energy conversion is (a) well described by the sum of the electron inertial and pressure divergence terms in generalized Ohms law though (b) the pressure divergence term dominates the inertial term by roughly a factor of 5:1, (c) both the gyrotropic and agyrotropic pressure forces contribute to energy conversion at the X‐point, and (d) both out‐of‐the‐reconnection‐plane gradients (∂/∂M) and in‐plane (∂/∂L,N) in the pressure tensor contribute to energy conversion near the X‐point. This indicates that this EDR had some electron‐scale structure in the out‐of‐plane direction during the time when (and at the location where) the reconnection site was observed.
Key Points
We analyze MMS data measured during a slow crossing of the density‐asymmetric magnetopause
Ion and electron dynamics are consistent with a normal crossing of an inner diffusion region
J→·E→′ appeared to result from in and out‐of‐plane gradients of gyrotropic and agyrotropic electron pressure tensor
Using MMS high‐resolution measurements, we present the first observation of fast electron jet (Ve ~2,000 km/s) at a dipolarization front (DF) in the magnetotail plasma sheet. This jet, with scale ...comparable to the DF thickness (~ 0.9 di), is primarily in the tangential plane to the DF current sheet and mainly undergoes the E × B drift motion; it contributes significantly to the current system at the DF, including a localized ring‐current that can modify the DF topology. Associated with this fast jet, we observed a persistent normal electric field, strong lower hybrid drift waves, and strong energy conversion at the DF. Such strong energy conversion is primarily attributed to the electron‐jet‐driven current (E ⋅ je ≈ 2 E ⋅ ji), rather than the ion current suggested in previous studies.
Key Points
For the first time, fast electron jet is observed at dipolarization front
This jet is responsible for current and energy conversion at dipolarization front
Quantitatively, the partition of energy conversion is E ⋅ je ≈ 2 E ⋅ ji
We present in‐depth analysis of three southward‐moving meso‐scale (ion‐to magnetohydrodynamic‐scale) flux transfer events (FTEs) and subsequent crossing of a reconnecting magnetopause current sheet ...(MPCS), which were observed on 8 December 2015 by the Magnetospheric Multiscale spacecraft in the subsolar region under southward and duskward magnetosheath magnetic field conditions. We aim to understand the generation mechanism of ion‐scale magnetic flux ropes (ISFRs) and to reveal causal relationship among magnetic field structures, electromagnetic energy conversion, and kinetic processes in magnetic reconnection layers. Results from magnetic field reconstruction methods are consistent with a flux rope with a length of about one ion inertial length growing from an electron‐scale current sheet (ECS) in the MPCS, supporting the idea that ISFRs can be generated through secondary reconnection in an ECS. Grad‐Shafranov reconstruction applied to the three FTEs shows that the FTEs had axial orientations similar to that of the ISFR. This suggests that these FTEs also formed through the same secondary reconnection process, rather than multiple X‐line reconnection at spatially separated locations. Four‐spacecraft observations of electron pitch‐angle distributions and energy conversion rate j·E′=j·E+ve×B $\mathbf{j}\cdot {\mathbf{E}}^{\prime }=\mathbf{j}\cdot \left(\mathbf{E}+{\mathbf{v}}_{\mathrm{e}}\times \mathbf{B}\right)$ suggest that the ISFR had three‐dimensional magnetic topology and secondary reconnection was patchy or bursty. Previously reported positive and negative values of j·E′ $\mathbf{j}\cdot {\mathbf{E}}^{\prime }$, with magnitudes much larger than expected for typical MP reconnection, were seen in both magnetosheath and magnetospheric separatrix regions of the ISFR. Many of them coexisted with bi‐directional electron beams and intense electric field fluctuations around the electron gyrofrequency, consistent with their origin in separatrix activities.
Plain Language Summary
Magnetic reconnection is a physical process that converts magnetic energy into plasma energy by changing the connectivity of magnetic field lines from one region to another. Magnetic reconnection at the outer boundary of planetary magnetospheres, known as the magnetopause (MP), is key to the entry of solar wind plasma and energy into the magnetospheres that forms the basis for space weather phenomena in the magnetospheres. MP reconnection often occurs in a transient or patchy manner, forming magnetic flux ropes (FRs) with helical field lines of various sizes. They may become an important pathway for fast coupling between the solar wind and magnetosphere. However, the generation mechanism of a subclass of FRs, relatively small “ion‐scale” FRs, is poorly understood. Computer simulations show that they are formed in thin and elongated current sheets of single active reconnection site, but this scenario has not been confirmed by observations. Our observations based on NASA's Magnetospheric Multiscale mission show that ion‐scale FR can form in a thin current sheet of single ongoing reconnection site at Earth's MP. The observed FR showed signatures of complex field line connectivity and localized conversion from electromagnetic to electron energy and vice versa, indicating complex MP dynamics.
Key Points
Ion‐scale magnetic flux rope (ISFR) can be generated from reconnecting electron‐scale current sheet at the subsolar magnetopause (MP)
Preceding mesoscale flux ropes had axial directions akin to that of the ISFR in the MP, suggesting the same generation mechanism
The ISFR had complex magnetic topology with three‐dimensional effects and involved patchy, intense energy conversion in separatrix regions
This paper reports on Magnetospheric Multiscale observations of whistler mode chorus and higher‐frequency electrostatic waves near and within a reconnection diffusion region on 23 November 2016. The ...diffusion region is bounded by crescent‐shaped electron distributions and associated dissipation just upstream of the X‐line and by magnetic field‐aligned currents and electric fields leading to dissipation near the electron stagnation point. Measurements were made southward of the X‐line as determined by southward directed ion and electron jets. We show that electrostatic wave generation is due to magnetosheath electron beams formed by the electron jets as they interact with a cold background plasma and more energetic population of magnetospheric electrons. On the magnetosphere side of the X‐line the electron beams are accompanied by a strong perpendicular electron temperature anisotropy, which is shown to be the source of an observed rising‐tone whistler mode chorus event. We show that the apex of the chorus event and the onset of electrostatic waves coincide with the opening of magnetic field lines at the electron stagnation point.
Key Points
Whistler mode chorus and higher‐frequency electrostatic waves were observed in the vicinity of a reconnection diffusion region at the dayside magnetopause
The location of the Earthward boundary of chorus and electrostatic waves coincides with the opening of magnetic field lines via reconnection
The causes of whistler mode chorus and electrostatic waves are shown to be electron temperature anisotropy and beam‐plasma interactions, respectively
Aims: The purpose of this study was to search for a novel quorum sensing inhibitor and analyse its inhibitory activity.
Methods and Results: Quorum sensing inhibition was monitored using the Tn‐5 ...mutant, Chromobacterium violaceum CV026. Vanilla beans (Vanilla planifolia Andrews) were extracted using 75% (v/v) aqueous methanol and added to C. violaceum CV026 cultures. Inhibitory activity was measured by quantifying violacein production using a spectrophotometer. The results have revealed that vanilla extract significantly reduced violacein production in a concentration‐dependent manner, indicating inhibition of quorum sensing.
Conclusions: Vanilla, a widely used spice and flavour, can inhibit bacterial quorum sensing.
Significance and Impact of the Study: The results suggest that the intake of vanilla‐containing food materials might promote human health by inhibiting quorum sensing and preventing bacterial pathogenesis. Further studies are required to isolate specific substances from vanilla extract acting as quorum sensing inhibitors.
Data from the NASA Magnetospheric Multiscale mission are used to investigate asymmetric magnetic reconnection at the dayside boundary between the Earth's magnetosphere and the solar wind. ...High‐resolution measurements of plasmas and fields are used to identify highly localized (~15 electron Debye lengths) standing wave structures with large electric field amplitudes (up to 100 mV/m). These wave structures are associated with spatially oscillatory energy conversion, which appears as alternatingly positive and negative values of J · E. For small guide magnetic fields the wave structures occur in the electron stagnation region at the magnetosphere edge of the electron diffusion region. For larger guide fields the structures also occur near the reconnection X‐line. This difference is explained in terms of channels for the out‐of‐plane current (agyrotropic electrons at the stagnation point and guide field‐aligned electrons at the X‐line).
Key Points
Energy conversion is highly localized within asymmetric reconnection electron diffusion regions
Oscillatory reconnection electric fields show characteristics of both spatial structures and propagating waves that are consistent with standing oblique quasi‐electrostatic whistlers
Both positive and negative values of J · E result from uniform current and oscillating electric fields
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