12,129 research outputs found
Notes on drift theory
It is shown that there is a simpler way to derive the average guiding center drift of a distribution of particles than via the so-called single particle analysis. Based on this derivation it is shown that the entire drift formalism can be considerably simplified, and that results for low order anisotropies are more generally valid than is usually appreciated. This drift analysis leads to a natural alternative derivation of the drift velocity along a neutral sheet
Direct comparison of the performance of CZT detectors contacted with various metals
Cadmium Zinc Telluride (CZT) achieves excellent spatial resolution and good
energy resolution over the broad energy range from several keV into the MeV
energy range. In this paper we present the results of a systematic study of the
performance of CZT detectors manufacturered by Orbotech (before IMARAD)
depending on surface preparation, contact materials and contact deposition. The
standard Orbotech detectors have the dimension of 2.0 x 2.0 x 0.5 cm. They have
a pixellated In anode with 8 x 8 pixels and a monolithic In cathode. Using the
same CZT substrates several times, we have made a direct comparison of the
performance of different contact materials by replacing the cathode and/or the
anode contacts with several high-workfunction metals. We present the
performance of the detectors and conclude with an overview over our ongoing
detector optimization.Comment: 8 pages, 5 figures, to appear in the proceedings of the conference
5922, "Hard X-Ray and Gamma-Ray Detector Physics VII" on the "Optics &
Photonics 2005" SPIE Symposium, July 31- August 4, 2005, San Diego, C
Importance of appropriate selection environments for breeding maize adapted to organic farming systems
Organic farming systems, characterized by special attention to soil fertility, recycling techniques and low external inputs, gained increased significance in recent years. As a consequence, there is a growing demand for varieties adapted to organic and/or low input farming. The objectives of the present study were to (i) compare the testcross performance of segregating maize (Zea mays) populations under established organic (OF) and conventional farming (CF) systems, (ii) determine quantitative genetic parameters decisive for the selection response under OF vs CF conditions, and (iii) draw conclusions for breeding new varieties optimally adapted to OF. Testcross performance of four different material groups of preselected lines (90 lines per group) derived from early European breeding material was assessed under OF and CF in three different geographic regions in Germany in 2008. Grain yields under OF were 3 to 18% lower than under CF in the individual experiments depending on the test region and, to a lesser extent, on the genetic material. On average, grain dry matter yield under OF was 1077 g m-2 compared to 1186 g m-2 under CF. Phenotypic correlations between OF and CF were small or moderate for grain yield in each of the four material groups (0.22 to 0.45), while strong and highly significant correlations were found for dry matter content (0.89 to 0.94). Genotypes with top grain yields under OF often did not show this superiority under CF and vice versa. Despite considerable heterogeneity of the OF test sites, the heritability for grain yield was in the same order of magnitude under OF and CF. It is concluded that test sites managed by OF are indispensable for making maximum progress in developing maize varieties for these conditions
Evolution of a coherent array of Bose-Einstein Condensates in a magnetic trap
We investigate the evolution process of the interference pattern for a
coherent array of Bose-Einstein condensates in a magnetic trap after the
optical lattices are switched off. It is shown that there is a decay and
revival of the density oscillation for the condensates confined in the magnetic
trap. We find that, due to the confinement of the magnetic trap, the
interference effect is much stronger than that of the experiment induced by
Pedri et al. (Phys. Rev. Lett, {\bf 87}, 220401), where the magnetic trap is
switched off too. The interaction correction to the interference effect is also
discussed for the density distribution of the central peak.Comment: RevTex, 17 pages,9 figures. E-mail: [email protected]
Mutual Event Observations of Io's Sodium Corona
We have measured the column density profile of Io's sodium corona using 10 mutual eclipses between the Galilean satellites. This approach circumvents the problem of spatially resolving Io's corona directly from Io's bright continuum in the presence of atmospheric seeing and telescopic scattering. The primary goal is to investigate the spatial and temporal variations of Io's corona. Spectra from the Keck Observatory and McDonald Observatory from 1997 reveal a corona that is only approximately spherically symmetric around Io. Comparing the globally averaged radial sodium column density profile in the corona with profiles measured in 1991 and 1985, we find that there has been no significant variation. However, there appears to be a previously undetected asymmetry: the corona above Io's sub-Jupiter hemisphere is consistently more dense than above the anti-Jupiter hemisphere
The effect of fruit maturity and storage duration on friction discolouration of Packham's Triumph and Doyenne du Comice pears
The original publication is available at http://www.actahort.org/books/671/671_53.htmFriction discolouration (FD) is causing the South African pear industry
multi-million rand losses due to blemished fruit being rejected for the export market
and being sold locally. The occurrence of FD was studied over two seasons using
âPackhamâs Triumphâ and âDoyenne du Comiceâ (Pyrus communis) fruit. The
influence of fruit maturity and storage duration were investigated by harvesting
over three maturities and storing fruit for up to three months. FD was induced using
a modified laboratory shaker that was shown to closely mimic pack line damage.
Polyphenol oxidase (PPO) activity and total phenolics (TP) content were also
evaluated. âDoyenne du Comiceâ was more prone to FD than âPackhamâs Triumphâ.
Harvest maturity significantly influenced FD susceptibility, with the middle picking
maturity generally giving higher FD ratings. Increasing storage duration generally
increased FD ratings, although not consistently. PPO activity was not influenced by
harvest maturity, but was influenced by storage duration. In âPackhamâs Triumphâ,
the TP content was not affected by harvest maturity or storage duration, whereas
both these factors significantly influenced TP content in âDoyenne du Comiceâ.
Susceptibility to development of FD symptoms is not easily linked to either PPO
activity or TP content, and seasonal differences in susceptibility make prediction of
possible levels of FD very difficult
Atomic Bose-Fermi mixtures in an optical lattice
A mixture of ultracold bosons and fermions placed in an optical lattice
constitutes a novel kind of quantum gas, and leads to phenomena, which so far
have been discussed neither in atomic physics, nor in condensed matter physics.
We discuss the phase diagram at low temperatures, and in the limit of strong
atom-atom interactions, and predict the existence of quantum phases that
involve pairing of fermions with one or more bosons, or, respectively, bosonic
holes. The resulting composite fermions may form, depending on the system
parameters, a normal Fermi liquid, a density wave, a superfluid liquid, or an
insulator with fermionic domains. We discuss the feasibility for observing such
phases in current experiments.Comment: 4 pages, 1 eps figure, misprints correcte
Indirect Self-Modulation Instability Measurement Concept for the AWAKE Proton Beam
AWAKE, the Advanced Proton-Driven Plasma Wakefield Acceleration Experiment,
is a proof-of-principle R&D experiment at CERN using a 400 GeV/c proton beam
from the CERN SPS (longitudinal beam size sigma_z = 12 cm) which will be sent
into a 10 m long plasma section with a nominal density of approx. 7x10^14
atoms/cm3 (plasma wavelength lambda_p = 1.2mm). In this paper we show that by
measuring the time integrated transverse profile of the proton bunch at two
locations downstream of the AWAKE plasma, information about the occurrence of
the self-modulation instability (SMI) can be inferred. In particular we show
that measuring defocused protons with an angle of 1 mrad corresponds to having
electric fields in the order of GV/m and fully developed self-modulation of the
proton bunch. Additionally, by measuring the defocused beam edge of the
self-modulated bunch, information about the growth rate of the instability can
be extracted. If hosing instability occurs, it could be detected by measuring a
non-uniform defocused beam shape with changing radius. Using a 1 mm thick
Chromox scintillation screen for imaging of the self-modulated proton bunch, an
edge resolution of 0.6 mm and hence a SMI saturation point resolution of 1.2 m
can be achieved.Comment: 4 pages, 4 figures, EAAC conference proceeding
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