32,062 research outputs found
Intermittent turbulence and turbulent structures in a linear magnetized plasma
Strongly intermittent turbulence is observed in the shadow of a limiter in
the Large Plasma Device (LAPD) at UCLA [W. Gekelman, H. Pfister, Z. Lucky, J.
Bamber, D. Leneman, and J. Maggs, Rev. Sci. Inst. {\bfseries 62}, 2875 (1991)].
The amplitude probability distribution function (PDF) of the turbulence is
strongly skewed, with density depletion events (or ``holes'') dominant in the
high density region and density enhancement events (or ``blobs'') dominant in
the low density region. Two-dimensional cross-conditional averaging shows that
the blobs are detached, outward-propagating filamentary structures with a clear
dipolar potential while the holes appear to be part of a more extended
turbulent structure. A statistical study of the blobs reveals a typical size of
ten times the ion sound gyroradius and a typical velocity of one tenth the
sound speed.Comment: 12 pages, 4 figures, to appear in Physics of Plasma
Inclusion Polymerization and Doping in Zeolite Channels. Polyaniline
Aniline has been polymerized in the three-dimensional channel system of zeolite Y. The monomer was diffused into zeolites with different levels of acidity from hexane solution. Subsequent admission of peroxydisulfate or iodate from aqueous solution yielded the intrazeolite polymers, as demonstrated by FT-IR, electronic absorption data and recovery of the included polymer. With S2O82-, the intrazeolite products are a function of the proton content of the zeolite. Polymer is only formed when a sufficient supply of protons is present in the zeolite host. When neutral iodate solution is used, no polymer is formed in NaY and acid zeolites, but at low pH aniline polymerizes in all zeolites. The open pore system of the zeolite host can be accessed by base such that the intrazeolite protonated polymer is transformed into the corresponding neutral polymer.
The polymer chains encapsulated in zeolite hosts represent a new class of low- dimensional electronic materials
Experimental study of ion heating and acceleration during magnetic reconnection
Ion heating and acceleration has been studied in the well-characterized reconnection layer of the Magnetic Reconnection Experiment [M. Yamada , Phys. Plasmas 4, 1936 (1997)]. Ion temperature in the layer rises substantially during null-helicity reconnection in which reconnecting field lines are anti-parallel. The plasma outflow is sub-Alfvenic due to a downstream back pressure. An ion energy balance calculation based on the data and including classical viscous heating indicates that ions are heated largely via nonclassical mechanisms. The T-i rise is much smaller during co-helicity reconnection in which field lines reconnect obliquely. This is consistent with a slower reconnection rate and a smaller resistivity enhancement over the Spitzer value. These observations show that nonclassical dissipation mechanisms can play an important role both in heating the ions and in facilitating the reconnection process
Transonic Elastic Model for Wiggly Goto-Nambu String
The hitherto controversial proposition that a ``wiggly" Goto-Nambu cosmic
string can be effectively represented by an elastic string model of exactly
transonic type (with energy density inversely proportional to its tension
) is shown to have a firm mathematical basis.Comment: 8 pages, plain TeX, no figure
Dynamics of cosmic strings and springs; a covariant formulation
A general family of charge-current carrying cosmic string models is
investigated. In the special case of circular configurations in arbitrary
axially symmetric gravitational and electromagnetic backgrounds the dynamics is
determined by simple point particle Hamiltonians. A certain "duality"
transformation relates our results to previous ones, obtained by Carter et.
al., for an infinitely long open stationary string in an arbitrary stationary
background.Comment: 11 pages, Latex, Nordita preprint 93/28
Recent developments in Vorton Theory
This article provides a concise overview of recent theoretical results
concerning the theory of vortons, which are defined to be (centrifugally
supported) equilibrium configurations of (current carrying) cosmic string
loops. Following a presentation of the results of work on the dynamical
evolution of small circular string loops, whose minimum energy states are the
simplest examples of vortons, recent order of magnitude estimates of the
cosmological density of vortons produced in various kinds of theoretical
scenario are briefly summarised.Comment: 6 pages Latex. Contribution to 1996 Cosmology Meeting, Peyresq,
Franc
The Mauna Kea Observatories Near-Infrared Filter Set. I: Defining Optimal 1-5 m Bandpasses
A new MKO-NIR infrared filter set is described, including techniques and
considerations given to designing a new set of bandpasses that are useful at
both mid- and high-altitude sites. These filters offer improved photometric
linearity and in many cases reduced background, as well as preserve good
throughput within the JHKLM atmospheric windows. MKO-NIR filters have already
been deployed with a number of instruments around the world as part of a filter
consortium purchase to reduce the unit cost of filters. Through this effort we
hope to establish, for the first time, a single standard set of infrared
fitlers at as many observatories as possible.Comment: PASP, in press; 32 pages, 11 figures, 3 Table
Fabrication and evaluation of advanced titanium and composite structural panels
Advanced manufacturing methods for titanium and composite material structures are being developed and evaluated. The focus for the manufacturing effort is the fabrication of full-scale structural panels which replace an existing shear panel on the upper wing surface of the NASA YF-12 aircraft. The program involves design, fabrication, ground testing, and Mach 3 flight service of full-scale structural panels and laboratory testing of representative structural element specimens
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