549 research outputs found
Mediation, translation and local ecologies: understanding the impact of policy levers on FE colleges
This article reports the views of managers and tutors on the role of policy âleversâ on teaching, learning, and inclusion in colleges of Further Education (FE) in our research project, âThe impact of policy on learning and inclusion in the Learning and Skills Sector (LSS)â.i Using data from five research visits conducted over two years in eight FE learning sites, we explore the processes by which colleges âmediateâ and âtranslateâ national policy levers and how this affects their ability to respond to local need. The paper tentatively develops three related concepts/metaphors to explain the complexity of the policy/college interface â âthe process of mediationâ, âacts of translationâ and âlocal ecologiesâ. We found that policy levers interacted with a complex set of national, local and institutional factors as colleges responded to pressures from the external environment and turned these into internal plans, systems and practices. We conclude by suggesting that national policy-makers, who design national policy levers, may not be fully aware of these complexities and we make the case for the benefits of greater local control over policy levers, where these interactions are better understood
Instability Heating of Sympathetically-Cooled Ions in a Linear Paul Trap
Sympathetic laser cooling of ions stored within a linear-geometry, radio
frequency, electric-quadrupole trap has been investigated using computational
and theoretical techniques. The simulation, which allows 5 sample ions to
interact with 35 laser-cooled atomic ions, revealed an instability heating
mechanism, which can prevent ions below a certain critical mass from being
sympathetically cooled. This critical mass can however be varied by changing
the trapping field parameters thus allowing ions with a very large range of
masses to be sympathetically cooled using a single ion species. A theoretical
explanation of this instability heating mechanism is presented which predicts
that the cooling-heating boundary in trapping parameter space is a line of
constant (ion trap stability coefficient), a result supported by the
computational results. The threshold value of depends on the masses of
the interacting ions. A functional form of this dependence is given
Polarization Correlation Measurements of Electron Impact Excitation of Hs2pd at 54.4 eV
First direct measurements are reported of the linear reduced Stokes parameters P1,P2 for H(2p)
excited by electron impact at the benchmark energy of 54.4 eV. The results differ significantly from
previous values deduced from angular correlation measurements which are in serious conflict with all
sophisticated theoretical approaches. Our results support the trend of theoretical predictions for P2
and confirm that its value is negative at electron scattering angles above 100±, as predicted by theory
Polarization Correlation Measurements of Electron Impact Excitation of Hs2pd at 54.4 eV
First direct measurements are reported of the linear reduced Stokes parameters P1,P2 for H(2p)
excited by electron impact at the benchmark energy of 54.4 eV. The results differ significantly from
previous values deduced from angular correlation measurements which are in serious conflict with all
sophisticated theoretical approaches. Our results support the trend of theoretical predictions for P2
and confirm that its value is negative at electron scattering angles above 100±, as predicted by theory
Three Dimensional Annihilation Imaging of Antiprotons in a Penning Trap
We demonstrate three-dimensional annihilation imaging of antiprotons trapped
in a Penning trap. Exploiting unusual feature of antiparticles, we investigate
a previously unexplored regime in particle transport; the proximity of the trap
wall. Particle loss on the wall, the final step of radial transport, is
observed to be highly non-uniform, both radially and azimuthally. These
observations have considerable implications for the production and detection of
antihydrogen atoms.Comment: Invited Talk at NNP03, Workshop on Non-Neutral Plasmas, 200
Positron plasma diagnostics and temperature control for antihydrogen production
Production of antihydrogen atoms by mixing antiprotons with a cold, confined,
positron plasma depends critically on parameters such as the plasma density and
temperature. We discuss non-destructive measurements, based on a novel,
real-time analysis of excited, low-order plasma modes, that provide
comprehensive characterization of the positron plasma in the ATHENA
antihydrogen apparatus. The plasma length, radius, density, and total particle
number are obtained. Measurement and control of plasma temperature variations,
and the application to antihydrogen production experiments are discussed.Comment: 5 pages, 4 figures, to be published in Phys. Rev. Let
Centrifugal separation and equilibration dynamics in an electron-antiproton plasma
Charges in cold, multiple-species, non-neutral plasmas separate radially by
mass, forming centrifugally-separated states. Here, we report the first
detailed measurements of such states in an electron-antiproton plasma, and the
first observations of the separation dynamics in any centrifugally-separated
system. While the observed equilibrium states are expected and in agreement
with theory, the equilibration time is approximately constant over a wide range
of parameters, a surprising and as yet unexplained result. Electron-antiproton
plasmas play a crucial role in antihydrogen trapping experiments
ATHENA -- First Production of Cold Antihydrogen and Beyond
Atomic systems of antiparticles are the laboratories of choice for tests of
CPT symmetry with antimatter. The ATHENA experiment was the first to report the
production of copious amounts of cold antihydrogen in 2002. This article
reviews some of the insights that have since been gained concerning the
antihydrogen production process as well as the external and internal properties
of the produced anti-atoms. Furthermore, the implications of those results on
future prospects of symmetry tests with antimatter are discussed.Comment: Proc. of the Third Meeting on CPT and Lorentz Symmetry, Bloomington
(Indiana), USA, August 2004, edited by V. A. Kostelecky (World Scientific,
Singapore). 10 pages, 5 figures, 1 table. Author affiliations cor
Cold-Antimatter Physics
The CPT theorem and the Weak Equivalence Principle are foundational
principles on which the standard description of the fundamental interactions is
based. The validity of such basic principles should be tested using the largest
possible sample of physical systems. Cold neutral antimatter (low-energy
antihydrogen atoms) could be a tool for testing the CPT symmetry with high
precision and for a direct measurement of the gravitational acceleration of
antimatter. After several years of experimental efforts, the production of
low-energy antihydrogen through the recombination of antiprotons and positrons
is a well-established experimental reality. An overview of the ATHENA
experiment at CERN will be given and the main experimental results on
antihydrogen formation will be reviewed.Comment: Proceedings of the XLIII International Meeting on Nuclear Physics,
Bormio (Italy), March 13-20 (2005). 10 pages, 4 figures, 1 tabl
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