1,023 research outputs found
Reply to "Comment on "Some implications of the quantum nature of laser fields for quantum computations''''
In this revised reply to quant-ph/0211165, I address the question of the
validity of my results in greater detail, by comparing my predictions to those
of the Silberfarb-Deutsch model, and I deal at greater length with the beam
area paradox. As before, I conclude that my previous results are an
(order-of-magnitude) accurate estimate of the error probability introduced in
quantum logical operations by the quantum nature of the laser field. While this
error will typically (for a paraxial beam) be smaller than the total error due
to spontaneous emission, a unified treatment of both effects reveals that they
lead to formally similar constraints on the minimum number of photons per pulse
required to perform an operation with a given accuracy; these constraints agree
with those I have derived elsewhere.Comment: A reply to quant-ph/0211165. Added more calculations and discussion,
removed some flippanc
Outbreak of encephalitic listeriosis in red-legged partridges (Alectoris rufa)
An outbreak of neurological disease was investigated in red-legged partridges between 8 and 28 days of age. Clinical signs included torticollis, head tilt and incoordination and over an initial eight day period approximately 30–40 fatalities occurred per day. No significant gross post mortem findings were detected. Histopathological examination of the brain and bacterial cultures followed by partial sequencing confirmed a diagnosis of encephalitis due to Listeria monocytogenes. Further isolates were obtained from follow-up carcasses, environmental samples and pooled tissue samples of newly imported day-old chicks prior to placement on farm. These isolates had the same antibiotic resistance pattern as the isolate of the initial post mortem submission and belonged to the same fluorescent amplified fragment length polymorphism (fAFLP) subtype. This suggested that the isolates were very closely related or identical and that the pathogen had entered the farm with the imported day-old chicks, resulting in disease manifestation in partridges between 8 and 28 days of age. Reports of outbreaks of encephalitic listeriosis in avian species are rare and this is to the best of our knowledge the first reported outbreak in red-legged partridges
The transition between hole-pairs and four-hole clusters in four-leg tJ ladders
Holes weakly doped into a four-leg \tj ladder bind in pairs. At dopings
exceeding a critical doping of four hole clusters are
observed to form in DMRG calculations. The symmetry of the ground state
wavefunction does not change and we are able to reproduce this behavior
qualitatively with an effective bosonic model in which the four-leg ladder is
represented as two coupled two-leg ladders and hole-pairs are mapped on hard
core bosons moving along and between these ladders. At lower dopings,
, a one dimensional bosonic representation for hole-pairs
works and allows us to calculate accurately the Luttinger liquid parameter
\krho, which takes the universal value \krho=1 as half-filling is
approached
Spin Gap Fixed Points in the Double Chain Problem
Applying the bosonization procedure to weakly coupled Hubbard chains we
discuss the fixed points of the renormalization group flow where all spin
excitations are gapful and a singlet pairing becomes the dominant instability.Comment: 15 pages, TeX, C Version 3.
Short-range repulsion and isospin dependence in the KN system
The short-range properties of the KN interaction are studied within the
meson-exchange model of the Juelich group. Specifically, dynamical explanations
for the phenomenological short-range repulsion, required in this model for
achieving agreement with the empirical KN data, are explored. Evidence is found
that contributions from the exchange of a heavy scalar-isovector meson
(a_0(980)) as well as from genuine quark-gluon exchange processes are needed.
Taking both mechanisms into account a satisfactory description of the KN phase
shifts can be obtained without resorting to phenomenological pieces.Comment: 26 pages, 5 figure
Excited B mesons from the lattice
We determine the energies of the excited states of a heavy-light meson
, with a static heavy quark and light quark with mass approximately
that of the strange quark from both quenched lattices and with dynamical
fermions. We are able to explore the energies of orbital excitations up to L=3,
the spin-orbit splitting up to L=2 and the first radial excitation. These mesons will be very narrow if their mass is less than 5775 MeV -- the
threshold. We investigate this in detail and present evidence that the
scalar meson (L=1) will be very narrow and that as many as 6
excited states will have energies close to the threshold and should also
be relatively narrow.Comment: 17 pages, 6 ps figure
The discontinuous nature of chromospheric activity evolution
Chromospheric activity has been thought to decay smoothly with time and,
hence, to be a viable age indicator. Measurements in solar type stars in open
clusters seem to point to a different conclusion: chromospheric activity
undergoes a fast transition from Hyades level to that of the Sun after about 1
Gyr of main--sequence lifetime and any decaying trend before or after this
transition must be much less significant than the short term variations.Comment: 6 pages, 1 figure, to be published in Astrophysics and Space Scienc
Kaon-Nucleon Scattering Amplitudes and Z-Enhancements from Quark Born Diagrams
We derive closed form kaon-nucleon scattering amplitudes using the ``quark
Born diagram" formalism, which describes the scattering as a single interaction
(here the OGE spin-spin term) followed by quark line rearrangement. The low
energy I=0 and I=1 S-wave KN phase shifts are in reasonably good agreement with
experiment given conventional quark model parameters. For Gev
however the I=1 elastic phase shift is larger than predicted by Gaussian
wavefunctions, and we suggest possible reasons for this discrepancy. Equivalent
low energy KN potentials for S-wave scattering are also derived. Finally we
consider OGE forces in the related channels K, KN and K,
and determine which have attractive interactions and might therefore exhibit
strong threshold enhancements or ``Z-molecule" meson-baryon bound states.
We find that the minimum-spin, minimum-isospin channels and two additional
K channels are most conducive to the formation of bound states.
Related interesting topics for future experimental and theoretical studies of
KN interactions are also discussed.Comment: 34 pages, figures available from the authors, revte
Strong Decays of Strange Quarkonia
In this paper we evaluate strong decay amplitudes and partial widths of
strange mesons (strangeonia and kaonia) in the 3P0 decay model. We give
numerical results for all energetically allowed open-flavor two-body decay
modes of all nsbar and ssbar strange mesons in the 1S, 2S, 3S, 1P, 2P, 1D and
1F multiplets, comprising strong decays of a total of 43 resonances into 525
two-body modes, with 891 numerically evaluated amplitudes. This set of
resonances includes all strange qqbar states with allowed strong decays
expected in the quark model up to ca. 2.2 GeV. We use standard nonrelativistic
quark model SHO wavefunctions to evaluate these amplitudes, and quote numerical
results for all amplitudes present in each decay mode. We also discuss the
status of the associated experimental candidates, and note which states and
decay modes would be especially interesting for future experimental study at
hadronic, e+e- and photoproduction facilities. These results should also be
useful in distinguishing conventional quark model mesons from exotica such as
glueballs and hybrids through their strong decays.Comment: 69 pages, 5 figures, 39 table
Dimerization and Incommensurate Spiral Spin Correlations in the Zigzag Spin Chain: Analogies to the Kondo Lattice
Using the density matrix renormalization group and a bosonization approach,
we study a spin-1/2 antiferromagnetic Heisenberg chain with near-neighbor
coupling and frustrating second-neighbor coupling , particularly in
the limit . This system exhibits both dimerization and
incommensurate spiral spin correlations. We argue that this system is closely
related to a doped, spin-gapped phase of the one-dimensional Kondo lattice.Comment: 18 pages, with 13 embedded encapsulated Postscript figures, uses
epsf.sty. Corrects a misstatement about the pitch angle, and contains
additional reference
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