1,638 research outputs found
Shear Alfven wave continuous spectrum within magnetic islands
The radial structure of the continuous spectrum of shear Alfven waves is
calculated in this paper within the separatrix of a magnetic island.
Geometrical effects due to the noncircularity of the flux surface's cross
section are retained to all orders. On the other hand, we keep only curvature
effects responsible for the beta-induced gap in the low-frequency part of the
continuous spectrum. Modes with different helicity from that of the magnetic
island are considered. The main result is that, inside a magnetic island, there
is a continuous spectrum very similar to that of tokamak plasmas, where a
generalized safety factor q can be defined and where a wide frequency gap is
formed, analogous to the ellipticity induced Alfven eigenmode gap in tokamaks.
The presence of this gap is due to the strong eccentricity of the island cross
section. The importance of the existence of such a gap is recognized in
potentially hosting magnetic-island induced Alfven eigenmodes (MiAE). Due to
the frequency dependence of the shear Alfven wave continuum on the
magnetic-island size, the possibility of utilizing MiAE frequency scalings as a
novel magnetic-island diagnostic is also discussed
2D continuous spectrum of shear Alfven waves in the presence of a magnetic island
The radial structure of the continuous spectrum of shear Alfven modes is
calculated in the presence of a magnetic island in tokamak plasmas. Modes with
the same helicity of the magnetic island are considered in a slab model
approximation. In this framework, with an appropriate rotation of the
coordinates the problem reduces to 2 dimensions. Geometrical effects due to the
shape of the flux surface's cross section are retained to all orders. On the
other hand, we keep only curvature effects responsible of the beta induced gap
in the low-frequency part of the continuous spectrum. New continuum
accumulation points are found at the O-point of the magnetic island. The
beta-induced Alfven Eigenmodes (BAE) continuum accumulation point is found to
be positioned at the separatrix flux surface. The most remarkable result is the
nonlinear modification of the BAE continuum accumulation point frequency
Distinct sensory representations of wind and near-field sound in the Drosophila brain
Behavioural responses to wind are thought to have a critical role in controlling the dispersal and population genetics of wild Drosophila species^(1, 2), as well as their navigation in flight^3, but their underlying neurobiological basis is unknown. We show that Drosophila melanogaster, like wild-caught Drosophila strains^4, exhibits robust wind-induced suppression of locomotion in response to air currents delivered at speeds normally encountered in nature^(1, 2). Here we identify wind-sensitive neurons in Johnston's organ, an antennal mechanosensory structure previously implicated in near-field sound detection (reviewed in refs 5 and 6). Using enhancer trap lines targeted to different subsets of Johnston's organ neurons^7, and a genetically encoded calcium indicator^8, we show that wind and near-field sound (courtship song) activate distinct populations of Johnston's organ neurons, which project to different regions of the antennal and mechanosensory motor centre in the central brain. Selective genetic ablation of wind-sensitive Johnston's organ neurons in the antenna abolishes wind-induced suppression of locomotion behaviour, without impairing hearing. Moreover, different neuronal subsets within the wind-sensitive population respond to different directions of arista deflection caused by air flow and project to different regions of the antennal and mechanosensory motor centre, providing a rudimentary map of wind direction in the brain. Importantly, sound- and wind-sensitive Johnston's organ neurons exhibit different intrinsic response properties: the former are phasically activated by small, bi-directional, displacements of the aristae, whereas the latter are tonically activated by unidirectional, static deflections of larger magnitude. These different intrinsic properties are well suited to the detection of oscillatory pulses of near-field sound and laminar air flow, respectively. These data identify wind-sensitive neurons in Johnston's organ, a structure that has been primarily associated with hearing, and reveal how the brain can distinguish different types of air particle movements using a common sensory organ
Development of an experiment-based robust design paradigm for multiple quality characteristics using physical programming
The well-known quality improvement methodology, robust design, is a powerful and cost-effective technique for building quality into the design of products and processes. Although several approaches to robust design have been proposed in the literature, little attention has been given to the development of a flexible robust design model. Specifically, flexibility is needed in order to consider multiple quality characteristics simultaneously, just as customers do when judging products, and to capture design preferences with a reasonable degree of accuracy. Physical programming, a relatively new optimization technique, is an effective tool that can be used to transform design preferences into specific weighted objectives. In this paper, we extend the basic concept of physical programming to robust design by establishing the links of experimental design and response surface methodology to address designers’ preferences in a multiresponse robust design paradigm. A numerical example is used to show the proposed procedure and the results obtained are validated through a sensitivity study
University of San Diego Softball Media Guide 2009
40 pages : illustrations, portraits ; 21.5 x 28 cmhttps://digital.sandiego.edu/amg-softball/1019/thumbnail.jp
University of San Diego Softball Media Guide 2007
32 pages : illustrations, portraits ; 21.5 x 28 cmhttps://digital.sandiego.edu/amg-softball/1017/thumbnail.jp
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