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When spacecraft (s/c) missions probe plasma structures (PSs) the relative location of the s/c with respect to the PS is unknown. This information is, however, needed to measure the geometrical features of the PS (orientation and thickness) and to understand the physical processes underlying the PS dynamics. Methods to determine the s/c location exist, but they need strong assumptions to be satisfied (stationarity and special spatial dependencies). The number of cases for which these assumptions are likely to be valid for the entire PS seems to be limited, and even weak departures from these hypotheses may affect the results. For a quasi‐1‐D geometry in particular, the determination of the velocity component along the two quasi‐invariant directions is very inaccurate and the assumption of strict stationarity may lead these quantities to diverge. In this paper we present new methods to compute the s/c trajectory through a PS, without a priori assumption on its spatial geometry, and able to work even in the presence of weak nonstationarities. The methods are tested both on artificial and real data, the latter provided by the Magnetospheric Multiscale mission probing the Earth's magnetopause. The 1‐D and 2‐D trajectories of the Magnetospheric Multiscale are found that can be used as an initial step for future reconstruction studies. Advanced minimization procedures to optimize the results are discussed. Key Points: The spatiotemporal difference method is extended to determine nonmonodimensional spacecraft trajectoriesTwo new methods are developed for this determination: the single and the multivariate fit methods; they are compared to previous onesA gradient‐directed Monte Carlo approach is applied to optimize the results; the spacecraft path and magnetopause thickness are so computed [ABSTRACT FROM AUTHOR]

Abstract: We explore the structure of the magnetopause using a crossing observed by the Magnetospheric Multiscale (MMS) spacecraft on 16 October 2015. Several methods (minimum variance analysis, BV method, and constant velocity analysis) are first applied to compute the normal to the magnetopause considered as a whole. The different results obtained are not identical, and we show that the whole boundary is not stationary and not planar, so that basic assumptions of these methods are not well satisfied. We then analyze more finely the internal structure for investigating the departures from planarity. Using the basic mathematical definition of what is a one‐dimensional physical problem, we introduce a new single spacecraft method, called LNA (local normal analysis) for determining the varying normal, and we compare the results so obtained with those coming from the multispacecraft minimum directional derivative (MDD) tool developed by Shi et al. (2005). This last method gives the dimensionality of the magnetic variations from multipoint measurements and also allows estimating the direction of the local normal when the variations are locally 1‐D. This study shows that the magnetopause does include approximate one‐dimensional substructures but also two‐ and three‐dimensional structures. It also shows that the dimensionality of the magnetic variations can differ from the variations of other fields so that, at some places, the magnetic field can have a 1‐D structure although all the plasma variations do not verify the properties of a global one‐dimensional problem. A generalization of the MDD tool is proposed. [ABSTRACT FROM AUTHOR]

The turbulence developing inside Kelvin-Helmholtz vortices has been studied using a two-fluid numerical simulation. From an initial large-scale velocity shear, the nonlinear evolution of the instability leads to the formation of a region inside the initial vortex characterized by small-scale fluctuations and structures. The magnetic energy spectrum is compatible with a Kolmogorov-like power-law decay, followed by a steeper power-law below proton scales, in agreement with other studies. The magnetic field increments show non-Gaussian distributions with increasing tails going towards smaller scales, consistent with presence of intermittency. The strong magnetic field fluctuations populating the tails of the distributions have been identified as current sheets by using the Partial Variance of the Increments (PVI) method. The strongest current sheets (largest PVI) appear around proton scales and below. By selecting several of such current sheets, it has been found that most of them are consistent with ongoing magnetic reconnection. The detailed study of one reconnecting current sheet as crossed by a virtual spacecraft is also presented. Inflow and outflow regions have been identified and the reconnection rate has been estimated. The observation of reconnection rates higher than typical fast rate ~0:1 suggests that reconnection in turbulent plasma can be faster than laminar reconnection. This study indicates that intermittency and reconnecting current sheets are important ingredients of turbulence within Kelvin-Helmholtz vortices and that reconnection can play an important role for energy dissipation therein. [ABSTRACT FROM AUTHOR]

The problem of particle diffusion in position space, as a consequence of electromagnetic fluctuations is addressed. Numerical results obtained with a self-consistent hybrid code are presented, and a method to calculate diffusion coefficient in the direction perpendicular to the mean magnetic field is proposed. The diffusion is estimated for two different types of fluctuations. The first type (resulting from an agyrotropic initial setting) is stationary, wide band white noise, and associated to Gaussian probability distribution function for the magnetic fluctuations. The second type (resulting from a Kelvin-Helmholtz instability) is non-stationary, with a power-law spectrum, and a non-Gaussian probability distribution function. The results of the study allow revisiting the question of loading particles of solar wind origin in the Earth magnetosphere. [ABSTRACT FROM AUTHOR]

Discusses the separation of Earth's intrinsic dipolar magnetic field from the ambient magnetosheath field by the magnetopause, a thin current-carrying plasma surface layer. Observation of net change in the field across the plasma boundary; Illustration of the magnetic field behavior; Addition of magnetic field to the geomagnetic field inward of the magnetopause.

The different levels of description of fluid media [e.g., magnetohydrodynamics (MHD), Hall-magnetohydrodynamics, bi-fluid,...] are commonly known under the form of Newtonian systems of equations. Nevertheless, this form proves to be ill-suited to derive a fully analytical weak turbulence theory of these media, due to the well-known complexity of the calculations implied. For such studies, therefore, a more appropriate mathematical frame needs to be found and this is shown to be the Hamiltonian formalism, even though it can often appear difficult to handle. The goal of this paper is to look for Hamiltonian formulations for the different levels of the fluid description of a plasma using the variational principle. Starting from the bi-fluid system, it is shown that such a formulation can be obtained by combining the Lagrangians already used for describing: (i) the motion of a charged particle in an electromagnetic field; (ii) the evolution of an electromagnetic field in presence of sources; (iii) the motion of a neutral fluid (Clebsch variables). The equivalence of the obtained description in terms of the generalized-Clebsch variables to the familiar Newtonian formulation is discussed. It is shown that each solution of the Hamiltonian system is also a solution for the Newtonian one, but that the converse is not true. The origin and the implication of this restriction are discussed. Reducing the Hamiltonian formulation obtained for the bi-fluid system to lower orders of the fluid approximations is then shown to be mandatory when one tries to obtain analytical results for linear waves and nonlinear wave-wave couplings. It is shown that this goal can be reached in two steps. The first one leads to a "reduced bi-fluid" system, which is identical to the bi-fluid one when the displacement current is neglected but the electron inertia is still working. The number of linear modes then goes down from six to three. The second step, leading to the Hall-MHD system, consists... [ABSTRACT FROM AUTHOR]

We show the first three dimensional (3D) dispersion relations and k spectra of magnetic turbulence in the solar wind at subproton scales. We used the Cluster data with short separations and applied the k-filtering technique to the frequency range where the transition to subproton scales occurs. We show that the cascade is carried by highly oblique kinetic Alfvén waves with ω(plas) ≤ 0.1ω(ci) down to k(⊥) ρ(i)∼2. Each k spectrum in the direction perpendicular to B0 shows two scaling ranges separated by a breakpoint (in the interval [0.4,1]k(⊥)ρ(i): a Kolmogorov scaling k(⊥)⁻¹ⁱ⁷ followed by a steeper scaling ∼k(⊥)⁻⁴ⁱ⁵. We conjecture that the turbulence undergoes a transition range, where part of the energy is dissipated into proton heating via Landau damping and the remaining energy cascades down to electron scales where electron Landau damping may predominate.

Here we report the first three-dimensional spatial spectrum of the low frequency magnetic turbulence obtained from the four Cluster spacecraft in the terrestrial magnetosheath close to the magnetopause. We show that the turbulence is compressible and dominated by mirror structures, its energy is injected at a large scale kp approximately 0.3 (l approximately 2000 km) via a mirror instability well predicted by linear theory, and cascades nonlinearly and unexpectedly up to kp approximately 3.5 (l approximately 150 km), revealing a new power law in the inertial range not predicted by any turbulence theory, and its strong anisotropy is controlled by the static magnetic field and the magnetopause normal.

An improved method is described for the purification of the alpha-subunit of tryptophan synthase from Escherichia coli. The standard manganese chloride and acid-precipitation steps have been replaced by rapid and efficient chromatographic procedures. Indoleethanol phosphate, indoleprapanol phosphate and indolebutanol phosphate have been synthesized. They are not cleaved by tryptophan synthase and are strictly competitive inhibitors versus indoleglycerol phosphate. The inhibition constant decreases as the number of methylene groups in the side chain increases. This may reflect an improved accommodation of the indole and phosphate moienerated by binding indole, indoleglycerol phosphate and indolepropanol phosphate to the alpha-subunit are very similar. This reflects the transfer of the indole moiety to an hydrophobic environment within the active center. The binding of indolepropanol phosphate to the alpha2beta2-complex perturbs the spectrum of pyridoxal 5'-phosphate located in the beta2-subunit. This demonstrates direct or indirect interactions between the component active sites. Bind studies by spectrophotometric titration and equilibrium dialysis with indolepropanol [32P]phosphate show that there is only one binding site per equivalent of alpha-subunit. Complex formation with the beta2-subunit increases the affinity of the alpha-subunit for indolepropanol phosphate, It is a general consequence of protein-protein interaction in this system.

Continuous exposure to 100% oxygen at atmospheric pressure for two weeks causes significant alterations in the growth of the lung and the body of newborn mice. These changes can be divided into three phases. The initial phase, which lasts 96 hours, is characterized by inhibition of lung DNA synthesis, diminished total lung DNA, and a decrease in the ratio of lung DNA to body weight. The intermediate phase from 96 to 144 hours is characterized by a sharp increase in mortality, a plateau in body weight, and a minimal lung DNA/body weight ratio. During this period, however, surviving animals show a reversal of the inhibition of DNA synthesis and thus an increase in total lung DNA. The third phase, occurring after 144 hours, is characterized by a continued increase in DNA synthesis and total lung DNA, a gain in body weight, a return of the lung DNA/body weight ratio to control levels, and a sharp decline in mortality. The survival rate of 54% in newborn mice over two weeks contrasts with the near total mortality reported for adult experimental animals similarly exposed. The reversal of the inhibition of lung DNA synthesis in surviving mice suggests either that some newborn animals are inherently resistant to pulmonary oxygen toxicity or that they develop, during a critical exposure period, an adaptive process necessary for their survival.