693,969 research outputs found
Topological Charge and the Spectrum of the Fermion Matrix in Lattice-QED_2
We investigate the interplay between topological charge and the spectrum of
the fermion matrix in lattice-QED_2 using analytic methods and Monte Carlo
simulations with dynamical fermions. A new theorem on the spectral
decomposition of the fermion matrix establishes that its real eigenvalues (and
corresponding eigenvectors) play a role similar to the zero eigenvalues (zero
modes) of the Dirac operator in continuous background fields. Using numerical
techniques we concentrate on studying the real part of the spectrum. These
results provide new insights into the behaviour of physical quantities as a
function of the topological charge. In particular we discuss fermion
determinant, effective action and pseudoscalar densities.Comment: 33 pages, 10 eps-figures; reference adde
Non-linear Plasma Wake Growth of Electron Holes
An object's wake in a plasma with small Debye length that drifts
\emph{across} the magnetic field is subject to electrostatic electron
instabilities. Such situations include, for example, the moon in the solar wind
wake and probes in magnetized laboratory plasmas. The instability drive
mechanism can equivalently be considered drift down the potential-energy
gradient or drift up the density-gradient. The gradients arise because the
plasma wake has a region of depressed density and electrostatic potential into
which ions are attracted along the field. The non-linear consequences of the
instability are analysed in this paper. At physical ratios of electron to ion
mass, neither linear nor quasilinear treatment can explain the observation of
large-amplitude perturbations that disrupt the ion streams well before they
become ion-ion unstable. We show here, however, that electron holes, once
formed, continue to grow, driven by the drift mechanism, and if they remain in
the wake may reach a maximum non-linearly stable size, beyond which their
uncontrolled growth disrupts the ions. The hole growth calculations provide a
quantitative prediction of hole profile and size evolution. Hole growth appears
to explain the observations of recent particle-in-cell simulations
Photoferroelectric oxides
Giant photovoltaic effect due to bulk photovoltaic effect observed in
multiferroic BiFeO3 thin films has triggered a renewed interest on
photoferroelectric materials for photovoltaic applications. Tremendous advance
has been done to improve power conversion efficiency (up to up to 8.1%) in
photoferroelectrics via absorption increase using narrow bandgap
ferroelectrics. Other strategies, as it is the more efficient use of
ferroelectric internal electric field, are ongoing. Moreover, as a by-product,
several progress have been also achieved on photostriction that is the
photo-induced deformation phenomenon. Here, we review ongoing and promising
routes to improve ferroelectrics photoresponse
Imaging and quantum efficiency measurement of chromium emitters in diamond
We present direct imaging of the emission pattern of individual
chromium-based single photon emitters in diamond and measure their quantum
efficiency. By imaging the excited state transition dipole intensity
distribution in the back focal plane of high numerical aperture objective, we
determined that the emission dipole is oriented nearly orthogonal to the
diamond-air interface. Employing ion implantation techniques, the emitters were
engineered with various proximities from the diamond-air interface. By
comparing the decay rates from the single chromium emitters at different depths
in the diamond crystal, an average quantum efficiency of 28% was measured.Comment: 11 pages and 4 figure
First Result of Net-Charge Jet-Correlations from STAR
We presented results on azimuthal correlation of net-charge with high
trigger particles. It is found that the net-charge correlation shape is similar
to that of total-charge. On the near-side, the net-charge and total-charge
spectra have similar shape and both are harder than the inclusives. On
the away-side, the correlated spectra are not much harder than the inclusives,
and the net-charge/total-charge ratio increases with and is similar to
the inclusive ratio
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A Raman spectroscopic study of carbon phases in impact melt rocks and breccias from the Gardnos impact structure, Norway
Raman spectroscopy suggests that the C was emplaced in at least two separate episodes into the impactites of the Gardnos impact structure
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