1,340 research outputs found
Quartz crystal microbalance use in biological studies
Design, development, and applications of quartz crystal microbalance are discussed. Two types of crystals are used. One serves as reference and other senses changes in mass. Specific application to study of bacterial spores is described
Phi meson production in near threshold proton-nucleus collisions
The cross section for production of Phi mesons in proton-nucleus reactions is
calculated as a function of the target mass. The decay width of the Phi meson
is affected by the change of the masses of the Phi, K+ and K- mesons in the
medium. A strong attractive K- potential leads to a measurable change of the
behavior of the cross section as a function of of the target mass. Comparison
between the kaon and electron decay modes are made.Comment: 4 pages, 1figure, new figure, new reference
Transport analysis of in-medium hadron effects in pA and AA collisions
The production and decay of vector mesons () in pA and AA
reactions is studied with particular emphasis on their in-medium spectral
functions. It is explored within transport calculations if hadronic in-medium
decays like or might provide complementary
information to their dilepton () decays. Whereas the
signal from the -meson is found to be strongly distorted by pion
rescattering, the -meson Dalitz decay to appears
promising even for more heavy nuclei in and pA reactions.
Furthermore, the influence of nucleon and kaon/antikaon potentials on the
yields and spectra in pA collisions is calculated and compared to the
recent data from the ANKE Collaboration.Comment: 3 pages, LaTeX, 3 postscript figures; contribution to QNP2002,
Juelich, June 10-14, 200
Time dependence of Bragg forward scattering and self-seeding of hard x-ray free-electron lasers
Free-electron lasers (FELs) can now generate temporally short, high power
x-ray pulses of unprecedented brightness, even though their longitudinal
coherence is relatively poor. The longitudinal coherence can be potentially
improved by employing narrow bandwidth x-ray crystal optics, in which case one
must also understand how the crystal affects the field profile in time and
space. We frame the dynamical theory of x-ray diffraction as a set of coupled
waves in order to derive analytic expressions for the spatiotemporal response
of Bragg scattering from temporally short incident pulses. We compute the
profiles of both the reflected and forward scattered x-ray pulses, showing that
the time delay of the wave is linked to its transverse spatial shift
through the simple relationship , where
is the grazing angle of incidence to the diffracting planes. Finally,
we apply our findings to obtain an analytic description of Bragg forward
scattering relevant to monochromatically seed hard x-ray FELs.Comment: 11 pages, 6 figure
Pressure as a Source of Gravity
The active mass density in Einstein's theory of gravitation in the analog of
Poisson's equation in a local inertial system is proportional to .
Here is the density of energy and its pressure for a perfect fluid.
By using exact solutions of Einstein's field equations in the static case we
study whether the pressure term contributes towards the mass
Spatiotemporal Response of Crystals in X-ray Bragg Diffraction
The spatiotemporal response of crystals in x-ray Bragg diffraction resulting
from excitation by an ultra-short, laterally confined x-ray pulse is studied
theoretically. The theory presents an extension of the analysis in symmetric
reflection geometry [1] to the generic case, which includes Bragg diffraction
both in reflection (Bragg) and transmission (Laue) asymmetric scattering
geometries. The spatiotemporal response is presented as a product of a
crystal-intrinsic plane wave spatiotemporal response function and an envelope
function defined by the crystal-independent transverse profile of the incident
beam and the scattering geometry. The diffracted wavefields exhibit amplitude
modulation perpendicular to the propagation direction due to both angular
dispersion and the dispersion due to Bragg's law. The characteristic measure of
the spatiotemporal response is expressed in terms of a few parameters: the
extinction length, crystal thickness, Bragg angle, asymmetry angle, and the
speed of light. Applications to self-seeding of hard x-ray free electron lasers
are discussed, with particular emphasis on the relative advantages of using
either the Bragg or Laue scattering geometries. Intensity front inclination in
asymmetric diffraction can be used to make snapshots of ultra-fast processes
with femtosecond resolution
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