1,431 research outputs found
Grounding Evaluation Capacity Development in Systems Theory
While “systemic thinking” is popular in the context of capacity development and evaluation, there is currently a lack of understanding about the benefits to employing systems theory in evaluation capacity development. Systems theory provides a useful orientation to the work involved in complex systems (e.g. national evaluation systems). This article illustrates how evaluation capacity development practitioners can use systems theory as a conceptual tool to gain a better understanding of the functional aspects and interrelationships present within a given evaluation system. Specifically, the systems theory perspective can help elucidate the reasons for the success or failure of a given evaluation capacity development program or activity. With the goal of motivating evaluation capacity development practitioners to use systems theory in their work, this article presents a systems theory framework for evaluation capacity development and offers practical examples of how it can be adopted
The RFOFO Ionization Cooling Ring for Muons
Practical ionization cooling rings could lead to lower cost or improved
performance in neutrino factory or muon collider designs. The ring modeled here
uses realistic three-dimensional fields. The performance of the ring compares
favorably with the linear cooling channel used in the second US Neutrino
Factory Study. The normalized 6D emittance of an ideal ring is decreased by a
factor of approximately 240, compared with a factor of only 15 for the linear
channel. We also examine such \textit{real-world} effects as windows on the
absorbers and rf cavities and leaving empty lattice cells for injection and
extraction. For realistic conditions the ring decreases the normalized 6D
emittance by a factor of 49.Comment: 27 pages, 18 figures and 5 tables. Submitted to Phys. Rev. ST-A
A low power photoemission source for electrons on liquid helium
Electrons on the surface of liquid helium are a widely studied system that
may also provide a promising method to implement a quantum computer. One
experimental challenge in these studies is to generate electrons on the helium
surface in a reliable manner without heating the cryo-system. An electron
source relying on photoemission from a zinc film has been previously described
using a high power continuous light source that heated the low temperature
system. This work has been reproduced more compactly by using a low power
pulsed lamp that avoids any heating. About 5e3 electrons are collected on 1
cm^2 of helium surface for every pulse of light. A time-resolved experiment
suggests that electrons are either emitted over or tunnel through the 1eV
barrier formed by the thin superfluid helium film on the zinc surface. No
evidence of trapping or bubble formation is seen.Comment: 9 pages, 3 figures, submitted to J. Low Temp. Phy
Electron transport in a quasi-one dimensional channel on suspended helium films
Quasi-one dimensional electron systems have been created using a suspended
helium film on a structured substrate. The electron mobility along the channel
is calculated by taking into account the essential scattering processes of
electrons by helium atoms in the vapor phase, ripplons, and surface defects of
the film substrate. It is shown that the last scattering mechanism may dominate
the electron mobility in the low temperature limit changing drastically the
temperature dependence of the mobility in comparison with that controlled by
the electron-ripplon scattering.Comment: 4 pages, 1 figur
Proton acceleration by irradiation of isolated spheres with an intense laser pulse
We report on experiments irradiating isolated plastic spheres with a peak laser intensity of 2-3 x 10(20) W cm(-2). With a laser focal spot size of 10 mu m full width half maximum (FWHM) the sphere diameter was varied between 520 nm and 19.3 mu m. Maximum proton energies of similar to 25 MeV are achieved for targets matching the focal spot size of 10 mu m in diameter or being slightly smaller. For smaller spheres the kinetic energy distributions of protons become nonmonotonic, indicating a change in the accelerating mechanism from ambipolar expansion towards a regime dominated by effects caused by Coulomb repulsion of ions. The energy conversion efficiency from laser energy to proton kinetic energy is optimized when the target diameter matches the laser focal spot size with efficiencies reaching the percent level. The change of proton acceleration efficiency with target size can be attributed to the reduced cross-sectional overlap of subfocus targets with the laser. Reported experimental observations are in line with 3D3V particle in cell simulations. They make use of well-defined targets and point out pathways for future applications and experiments.DFG via the Cluster of Excellence Munich-Centre for Advanced Photonics (MAP) Transregio SFB TR18NNSA DE-NA0002008Super-MUC pr48meIvo CermakCGC Instruments in design and realization of the Paul trap systemIMPRS-APSLMUexcellent Junior Research FundDAAD|ToIFEEuropean Union's Horizon research and innovation programme 633053Physic
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