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Experimental study of lower-hybrid drift turbulence in a reconnecting current sheet (2002)

Carter, T. A. ; Yamada, M. ; Ji, H. ; [et al.]

[S.l.] : American Institute of Physics (AIP)

Physics of Plasmas 9 (2002), S. 3272-3288

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ISSN: 1089-7674

Source: AIP Digital Archive

Topics: Physics

Notes: The role of turbulence in the process of magnetic reconnection has been the subject of a great deal of study and debate in the theoretical literature. At issue in this debate is whether turbulence is essential for fast magnetic reconnection to occur in collisionless current sheets. Some theories claim it is necessary in order to provide anomalous resistivity, while others present a laminar fast reconnection mechanism based on the Hall term in the generalized Ohm's law. In this work, a thorough study of electrostatic potential fluctuations in the current sheet of the magnetic reconnection experiment (MRX) [Yamada et al., Phys. Plasmas 4, 1936 (1997)] was performed in order to ascertain the importance of turbulence in a laboratory reconnection experiment. Using amplified floating Langmuir probes, broadband fluctuations in the lower hybrid frequency range (fLH∼5–15 MHz) were measured which arise with the formation of the current sheet in MRX. The frequency spectrum, spatial amplitude profile, and spatial correlation characteristics of the measured turbulence were examined carefully, finding consistency with theories of the lower-hybrid drift instability (LHDI). The LHDI and its role in magnetic reconnection has been studied theoretically for decades, but this work represents the first detection and detailed study of the LHDI in a laboratory current sheet. The observation of the LHDI in MRX has provided the unique opportunity to uncover the role of this instability in collisionless reconnection. It was found that: (1) the LHDI fluctuations are confined to the low-beta edge of current sheets in MRX; (2) the LHDI amplitude does not correlate well in time or space with the reconnection electric field, which is directly related to the rate of reconnection; and (3) significant LHDI amplitude persists in high-collisionality current sheets where the reconnection rate is classical. These findings suggest that the measured LHDI fluctuations do not play an essential role in determining the reconnection rate in MRX. © 2002 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.1494433

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Feasibility of ex vivo gene therapy for neurological disorders using the new retroviral vector GCDNsap packaged in the vesicular stomatitis virus G protein (2002)

Suzuki, A. ; Obi, K. ; Urabe, T. ; [et al.]

Oxford, UK : Blackwell Science Ltd

Journal of neurochemistry 82 (2002), S. 0

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ISSN: 1471-4159

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Medicine

Notes: Neuronal progenitor cells (NPC) are particularly suited as the target population for genetic and cellular therapy of neurological disorders such as Parkinson's disease or stroke. However, genetic modification of these cells using retroviral vectors remains a great challenge because of the low transduction rate and the need for fetal calf serum (FCS) during the transduction process that induces the cell differentiation to mature neurons. To overcome these problems, we developed a new retrovirus production system in which the simplified retroviral vector GCDNsap engineered to be resistant to denovo methylation was packaged in the vesicular stomatitis virus G protein (VSV-G), concentrated by centrifugation, and resuspended in serum-free medium (StemPro-34 SFM). In transduction experiments using enhanced green fluorescent protein (EGFP) as a marker, the concentrated FCS-free virus supernatant infected NPC at a high rate, while maintaining the ability of these cells to self-renew and differentiate in vitro. When such cells were grafted into mouse brains, EGFP-expressing NPC were detected in the region around the injection site at 8 weeks post transplantation. These findings suggest that the gene transfer system described here may provide a useful tool to genetically modify NPC for treatments of neurological disorders.