165 research outputs found
Testing a model of antecedents and consequences of defensive pessimism and self-handicapping in school physical education
There has been very limited research on the use of self-worth protection strategies in the achievement context of school physical education (PE). Thus, this study aimed to examine some antecedents and consequences of defensive pessimism and self-handicapping. The sample comprised 534 (females n = 275; males n = 259) British pupils recruited from two schools who responded to established questionnaires. Results of structural equation modelling analysis indicated that self-handicapping and defensive pessimism were positively predicted by fear of failure and negatively predicted by competence valuation. In addition, defensive pessimism was negatively predicted by physical self-concept. In turn, defensive pessimism negatively predicted enjoyment in PE and intentions to participate in future optional PE programs. Self-handicapping did not predict enjoyment or intentions. Results from multi-sample structural equation modelling showed the specified model to be largely invariant across males and females. The findings indicate that although both strategies aim to protect one’s self-worth, some of their antecedents and consequences in PE may differ
New mechanism of cluster-field evaporation in rf breakdown
Using a simple field evaporation model and molecular dynamics simulations of nanoscale copper tip evolution in a high electric field gradient typical for linacs, we have studied a new mechanism for rf-field evaporation. The mechanism consists of simultaneous (collective) field evaporation of a large group of tip atoms in high-gradient fields. Thus, evaporation of large clusters is energetically more favorable when compared with the conventional, ‘‘one-by-one’’ mechanism. The studied mechanism could also be considered a new mechanism for the triggering of rf-vacuum breakdown. This paper discusses the mechanism and the experimental data available for electric field evaporation of field emission microscopy tips
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Natural low Z coatings for fusion reactors
Coating the walls of a vacuum chamber with Be or some other low Z material has been proposed as a possible solution to the problem of high Z impurities in plasmas. The properties of any coating will be highly dependent on (1) the nature of plasma impurity deposition on walls, and (2) radiation-induced solute segregation. The latter process can spontaneously produce low Z coatings in some alloys and drastically alter metallic interdiffusion in a reactor environment. We have studied the required parameters of coatings (thickness, composition, purity, etc.) and possible means of in situ deposition. We present results of a preliminary survey of coatings, substrates, and deposition methods whih are most compatible with reactor operation. We also outline experiments presently underway which will measure the stability of coatings in a radiation environment
Sheath parameters for non-Debye plasmas: simulations and arc damage
This paper describes the surface environment of the dense plasma arcs that
damage rf accelerators, tokamaks and other high gradient structures. We
simulate the dense, non-ideal plasma sheath near a metallic surface using
Molecular Dynamics (MD) to evaluate sheaths in the non-Debye region for high
density, low temperature plasmas. We use direct two-component MD simulations
where the interactions between all electrons and ions are computed explicitly.
We find that the non-Debye sheath can be extrapolated from the Debye sheath
parameters with small corrections. We find that these parameters are roughly
consistent with previous PIC code estimates, pointing to densities in the range
. The high surface fields implied by these
results could produce field emission that would short the sheath and cause an
instability in the time evolution of the arc, and this mechanism could limit
the maximum density and surface field in the arc. These results also provide a
way of understanding how the "burn voltage" of an arc is generated, and the
relation between self sputtering and the burn voltage, while not well
understood, seems to be closely correlated. Using these results, and equating
surface tension and plasma pressure, it is possible to infer a range of plasma
densities and sheath potentials from SEM images of arc damage. We find that the
high density plasma these results imply and the level of plasma pressure they
would produce is consistent with arc damage on a scale 100 nm or less, in
examples where the liquid metal would cool before this structure would be lost.
We find that the sub-micron component of arc damage, the burn voltage, and
fluctuations in the visible light production of arcs may be the most direct
indicators of the parameters of the dense plasma arc, and the most useful
diagnostics of the mechanisms limiting gradients in accelerators.Comment: 8 pages, 16 figure
Muon Colliders
Muon Colliders have unique technical and physics advantages and disadvantages
when compared with both hadron and electron machines. They should thus be
regarded as complementary. Parameters are given of 4 TeV and 0.5 TeV high
luminosity \mumu colliders, and of a 0.5 TeV lower luminosity demonstration
machine. We discuss the various systems in such muon colliders, starting from
the proton accelerator needed to generate the muons and proceeding through muon
cooling, acceleration and storage in a collider ring. Problems of detector
background are also discussed.Comment: 28 pages, with 12 postscript figures. To be published Proceedings of
the 9th Advanced ICFA Beam Dynamics Workshop, AIP Pres
Demersal fishes associated with Lophelia pertusa coral and hard-substrate biotopes on the continental slope, northern Gulf of Mexico
The demersal fish fauna of Lophelia pertusa (Linnaeus, 1758) coral reefs and associated hard-bottom biotopes was investigated at two depth horizons in the northern Gulf of Mexico using a manned submersible and remote sampling. The Viosca Knoll fauna consisted of at least 53 demersal fish species, 37 of which were documented by submersible video. On the 325 m horizon, dominant taxa determined from frame-by-frame video analysis included Stromateidae, Serranidae, Trachichthyidae, Congridae, Scorpaenidae, and Gadiformes. On the 500 m horizon, large mobile visual macrocarnivores of families Stromateidae and Serranidae dropped out, while a zeiform microcarnivore assumed importance on reef “Thicket” biotope, and the open-slope taxa Macrouridae and Squalidae gained in importance. The most consistent faunal groups at both depths included sit-and-wait and hover-and-wait strategists (Scorpaenidae, Congridae, Trachichthyidae), along with generalized mesocarnivores (Gadiformes). The specialized microcarnivore, Grammicolepis brachiusculus Poey, 1873, appears to be highly associated with Lophelia reefs. The coral “Thicket” biotope was extensively developed on the 500 m site, but fish abundance was low with only 95 fish per hectare. In contrast to Lophelia reefs from the eastern the North Atlantic, the coral “Rubble” biotope was essentially absent. This study represents the first quantitative analysis of fishes associated with Lophelia reefs in the Gulf of Mexico, and generally in the western North Atlantic
Status of Muon Collider Research and Development and Future Plans
The status of the research on muon colliders is discussed and plans are
outlined for future theoretical and experimental studies. Besides continued
work on the parameters of a 3-4 and 0.5 TeV center-of-mass (CoM) energy
collider, many studies are now concentrating on a machine near 0.1 TeV (CoM)
that could be a factory for the s-channel production of Higgs particles. We
discuss the research on the various components in such muon colliders, starting
from the proton accelerator needed to generate pions from a heavy-Z target and
proceeding through the phase rotation and decay ()
channel, muon cooling, acceleration, storage in a collider ring and the
collider detector. We also present theoretical and experimental R & D plans for
the next several years that should lead to a better understanding of the design
and feasibility issues for all of the components. This report is an update of
the progress on the R & D since the Feasibility Study of Muon Colliders
presented at the Snowmass'96 Workshop [R. B. Palmer, A. Sessler and A.
Tollestrup, Proceedings of the 1996 DPF/DPB Summer Study on High-Energy Physics
(Stanford Linear Accelerator Center, Menlo Park, CA, 1997)].Comment: 95 pages, 75 figures. Submitted to Physical Review Special Topics,
Accelerators and Beam
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