Interplay of Turbulence and Proton-Microinstability Growth in Space Plasmas

Both kinetic instabilities and strong turbulence have potential to impact the behavior of space plasmas. To assess effects of these two processes we compare results from a 3 dimensional particle-in-cell (PIC) simulation of collisionless plasma turbulence against observations by the MMS spacecraft in the terrestrial magnetosheath and by the Wind spacecraft in the solar wind. The simulation develops coherent structures and anisotropic ion velocity distributions that can drive micro-instabilities. Temperature-anisotropy driven instability growth rates are compared with inverse nonlinear turbulence time scales. Large growth rates occur near coherent structures; nevertheless linear growth rates are, on average, substantially less than the corresponding nonlinear rates. This result casts some doubt on the usual basis for employing linear instability theory, and raises questions as to why the linear theory appears to work in limiting plasma excursions in anisotropy and plasma beta.Comment: Under revie

Statistics of Energy Dissipation rate at reconnection sites

Magnetic reconnection is considered to play a central role in dissipating turbulent energy in plasmas. Traditionally, the Ohmic dissipation measure ($\mathbf{j}.\mathbf{E}$) has been used to identify the dissipation region and calculate the dissipation rates in reconnection sites. However, recent works have shown that the pressure-strain rate may be a more appropriate measure of dissipation. We consider large-scale reconnection in the Earth\u27s magnetopause, small-scale reconnection in the Earth\u27s magnetosheath, and the electron-only reconnection sites recently observed by MMS in the magnetosheath. We carry out a statistical survey of the pressure-strain rates and the Ohmic dissipation measure at these different reconnection sites, in order to better understand the nature of energy conversion in reconnection

Development of a Genus Specific Primer Set for Detection of Leishmania Parasites by Polymerase Chain Reaction

We have compared the sequences of a major class of kinetoplast DNA (kDNA) minicircle (pLURkE3) of Laishmunia strain UR6 with other minicircle sequences from different Leishmaniu species. Alignment of these sequences allowed the selection of a pair of oligonucleotides suitable as primers in polymerase chain reaction (PCR) which is specific for Leishmania parasites. PCR with this genus-specific primer set is capable of detecting 1 femtogram of kDNA. These primers have been tested with kDNAs from both old world and new world Leishmania species. The results indicate that the primers may be suitable for detection of any kind of leishmaniasis

Energy transfer and proton-electron heating in turbulent plasmas

Despite decades of study of high-temperature weakly-collisional plasmas, a complete understanding of how energy is transferred between particles and fields remains elusive. Two major questions in this regard are how fluid-scale energy transfer rates, associated with turbulence, connect with kinetic-scale dissipation, and what controls the fraction of dissipation on different charged species. Although the rate of cascade has long been recognized as a limiting factor in the heating rate at kinetic scale, no study has reported direct evidence correlating the heating rate with MHD-scale cascade rates. Using kinetic simulations and in-situ spacecraft data, we show the connection between the fluid-scale energy flux and the total energy dissipated at kinetic scales. The proton versus electron heating is controlled by the ratio of non-linear time scale to the proton-cyclotron time and increases with the total dissipation rate. These results advance a key step toward understanding dissipation of turbulent energy in collisionless plasmas

Relaxation of the Turbulent Magnetosheath

The large-scale phenomena that involve plasmas can be adequately described by using magnetohydrodynamics equations. Such a set of equations consists of several nonlinear terms that are responsible for driving the energy contained in the large-scale eddies to small scales through the so-called energy cascade. A turbulent state is a state in which the nonlinear terms are of the order of (or greater) than the linear terms. It has been shown that space plasma turbulence (e.g., described by three-dimensional magnetohydrodynamics) tends to relax toward equilibrium states that minimize the energy; these states, in principle, are considered global. However, turbulence can locally relax toward such equilibrium states, creating patches where the magnitude of the nonlinear terms is reduced and the energy cascade impaired. Boundaries between such patches are expected to have a stronger unimpaired cascade. We argue that this “cellularization” of turbulence can happen in strongly turbulent environments (large fluctuations\u27 amplitude) such as the Earth\u27s magnetosheath, as we demonstrate here by analysis of MMS observations