40,727 research outputs found
A Grassmann representation of the Hubble parameter
The Riccati equation for the Hubble parameter H of barotropic FRW cosmologies
in conformal time for \kappa \neq 0 spatial geometries and in comoving time for
the \kappa =0 geometry, respectively, is generalized to odd Grassmannian time
parameters. We obtain a system of simple differential equations for the four
supercomponents (two of even type and two of odd type) of the Hubble superfield
function {\cal H} that is explicitly solved. The second even Hubble component
does not have an evolution governed by general relativity although there are
effects of the latter upon itComment: 4 pages, no figure
Canonically Transformed Detectors Applied to the Classical Inverse Scattering Problem
The concept of measurement in classical scattering is interpreted as an
overlap of a particle packet with some area in phase space that describes the
detector. Considering that usually we record the passage of particles at some
point in space, a common detector is described e.g. for one-dimensional systems
as a narrow strip in phase space. We generalize this concept allowing this
strip to be transformed by some, possibly non-linear, canonical transformation,
introducing thus a canonically transformed detector. We show such detectors to
be useful in the context of the inverse scattering problem in situations where
recently discovered scattering echoes could not be seen without their help.
More relevant applications in quantum systems are suggested.Comment: 8 pages, 15 figures. Better figures can be found in the original
article, wich can be found in
http://www.sm.luth.se/~norbert/home_journal/electronic/v12s1.html Related
movies can be found in www.cicc.unam.mx/~mau
Helico-conical optical beams self-heal
An optical beam is said to be self-healing when, distorted by an obstacle,
the beam corrects itself upon propagation. In this letter, we show through
experiments supported by numerical simulations, that Helico-conical optical
beams (HCOBs) self-heal. We observe the strong resilience of these beams with
different types of obstructions, and relate this to the characteristics of
their transverse energy flow.Comment: 4 pages, 5 figure
How does breakup influence the total fusion of Li at the Coulomb barrier?
Total (complete + incomplete) fusion excitation functions of Li on
Co and Bi targets around the Coulomb barrier are obtained using
a new continuum discretized coupled channel (CDCC) method of calculating
fusion. The relative importance of breakup and bound-state structure effects on
total fusion is particularly investigated. The effect of breakup on fusion can
be observed in the total fusion excitation function. The breakup enhances the
total fusion at energies just around the barrier, whereas it hardly affects the
total fusion at energies well above the barrier. The difference between the
experimental total fusion cross sections for Li on Co is notably
caused by breakup, but this is not the case for the Bi target.Comment: 9 pages, 9 figures, Submitted to Phys. Rev.
Raman response of Stage-1 graphite intercalation compounds revisited
We present a detailed in-situ Raman analysis of stage-1 KC8, CaC6, and LiC6
graphite intercalation compounds (GIC) to unravel their intrinsic finger print.
Four main components were found between 1200 cm-1 and 1700 cm-1, and each of
them were assigned to a corresponding vibrational mode. From a detailed line
shape analysis of the intrinsic Fano-lines of the G- and D-line response we
precisely determine the position ({\omega}ph), line width ({\Gamma}ph) and
asymmetry (q) from each component. The comparison to the theoretical calculated
line width and position of each component allow us to extract the
electron-phonon coupling constant of these compounds. A coupling constant
{\lambda}ph < 0.06 was obtained. This highlights that Raman active modes alone
are not sufficient to explain the superconductivity within the electron-phonon
coupling mechanism in CaC6 and KC8.Comment: 6 pages, 3 figures, 2 table
Differential Astrometry over 15 degrees
We observed the pair of radio sources 1150+812 and 1803+784 in November 1993
with a VLBI array, simultaneously recording at 8.4 and 2.3 GHz. We determined
the angular separation between the two sources with submilliarcsecond accuracy
by using differential techniques. This result demonstrates the feasibility of
high precision differential astrometry for radio sources separated in the sky
by almost 15 degrees, and opens the avenue to its application to larger samples
of radio sources.Comment: 6 pages, latex2e, 2 figures, To appear in the proceedings of the
EVN/JIVE Symposium No. 4, New Astronomy Reviews (eds. Garret, M. Campbell,
R., and Gurvits, L.
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