6,576 research outputs found
A luminosity monitor for the A4 parity violation experiment at MAMI
A water Cherenkov luminosity monitor system with associated electronics has
been developed for the A4 parity violation experiment at MAMI. The detector
system measures the luminosity of the hydrogen target hit by the MAMI electron
beam and monitors the stability of the liquid hydrogen target. Both is required
for the precise study of the count rate asymmetries in the scattering of
longitudinally polarized electrons on unpolarized protons. Any helicity
correlated fluctuation of the target density leads to false asymmetries. The
performance of the luminosity monitor, investigated in about 2000 hours with
electron beam, and the results of its application in the A4 experiment are
presented.Comment: 22 pages, 12 figures, submitted to NIM
Inertial waves and modes excited by the libration of a rotating cube
We report experimental measurements of the flow in a cubic container
submitted to a longitudinal libration, i.e. a rotation modulated in time.
Velocity fields in a vertical and a horizontal plane are measured in the
librating frame using a corotating particle image velocimetry system. When the
libration frequency is smaller than twice the mean rotation rate
, inertial waves can propagate in the interior of the fluid. At
arbitrary excitation frequencies , the oscillating flow
shows two contributions: (i) a basic flow induced by the libration motion, and
(ii) inertial wave beams propagating obliquely upward and downward from the
horizontal edges of the cube. In addition to these two contributions, inertial
modes may also be excited at some specific resonant frequencies. We
characterize in particular the resonance of the mode of lowest order compatible
with the symmetries of the forcing, noted [2,1,+]. By comparing the measured
flow fields to the expected inviscid inertial modes computed numerically
[L.R.M. Maas, Fluid Dyn. Res. \textbf{33}, 373 (2003)], we show that only a
subset of inertial modes, matching the symmetries of the forcing, can be
excited by the libration.Comment: Phys. Fluids (in press
Network Structure Explains the Impact of Attitudes on Voting Decisions
Attitudes can have a profound impact on socially relevant behaviours, such as
voting. However, this effect is not uniform across situations or individuals,
and it is at present difficult to predict whether attitudes will predict
behaviour in any given circumstance. Using a network model, we demonstrate that
(a) more strongly connected attitude networks have a stronger impact on
behaviour, and (b) within any given attitude network, the most central attitude
elements have the strongest impact. We test these hypotheses using data on
voting and attitudes toward presidential candidates in the US presidential
elections from 1980 to 2012. These analyses confirm that the predictive value
of attitude networks depends almost entirely on their level of connectivity,
with more central attitude elements having stronger impact. The impact of
attitudes on voting behaviour can thus be reliably determined before elections
take place by using network analyses.Comment: Final version published in Scientific Report
Color-superconductivity in the strong-coupling regime of Landau gauge QCD
The chirally unbroken and the superconducting 2SC and CFL phases are
investigated in the chiral limit within a Dyson-Schwinger approach for the
quark propagator in QCD. The hierarchy of Green's functions is truncated such
that at vanishing density known results for the vacuum and at asymptotically
high densities the corresponding weak-coupling expressions are recovered. The
anomalous dimensions of the gap functions are analytically calculated. Based on
the quark propagator the phase structure is studied, and results for the gap
functions, occupation numbers, coherence lengths and pressure differences are
given and compared with the corresponding expressions in the weak-coupling
regime. At moderate chemical potentials the quasiparticle pairing gaps are
several times larger than the extrapolated weak-coupling results.Comment: 14 pages, 9 figures; v2: one reference adde
Revision of Oxandra (Annonaceae)
A taxonomic revision is given of the Neotropical genus Oxandra (Annonaceae). Within the genus 27 species are recognized, 4 of which are new to science. Most of the species are occurring in tropical South America, whereas a few (6) are found in Mexico and Central America and two in the West Indies (Greater and Lesser Antilles). A key to all species is provided. The treatment includes chapters about the history of the genus and morphology. All species are fully described, including full synonymy, notes on distribution and ecology, field observations (when available), vernacular names (when given), and mostly short notes about relationships of the species concerned. For each species a distribution map is made. At the end of the revision a complete list of vernacular names is included.Peer reviewe
Observations on the vertical structure of tidal and inertial currents in the central North Sea
Tidal and inertial current ellipses, measured at several locations and depths in the central North Sea during a number of monthly periods in 1980, 1981 and 1982, are decomposed into counterrotating, circular components to which Ekman dynamics are applied to determine Ekman layer depths and vertical phase differences, from which are inferred overall values of the eddy viscosity and drag coefficient. Stratification effects produce an additional vertical phase shift of the anticyclonic rotary component, indicative of an inverse proportionality of the eddy viscosity to the vertical density gradient. From the time variations of the Ekman layer depths of the semidiurnal tidal components, as well as from the vertical structure of the inertial current component, we infer variations in the relative vorticity of the low-frequency flow
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