1,789 research outputs found
Comparison of eta and eta' production in the pp -> pp eta(eta') reactions near threshold
The total cross section of the pp -> pp eta' reaction has been measured at
two energies near threshold by detecting the final protons in a magnetic
spectrometer. The values obtained are about a factor of 70 less than for the
corresponding eta production, in good agreement with the predictions of a
one-pion-exchange model.Comment: 10 pages, Latex with 3 eps figure
Possible Indication of Narrow Baryonic Resonances Produced in the 1720-1790 MeV Mass Region
Signals of two narrow structures at M=1747 MeV and 1772 MeV were observed in
the invariant masses M_{pX} and M_{\pi^{+}X} of the pp->ppX and pp->p\pi^{+}X
reactions respectively. Many tests were made to see if these structures could
have been produced by experimental artefacts. Their small widths and the
stability of the extracted masses lead us to conclude that these structures are
genuine and may correspond to new exotic baryons. Several attempts to identify
them, including the possible "missing baryons" approach, are discussed.Comment: 17 pages including 8 figures and 3 tables. ReVte
Near-Threshold Production of omega Mesons in the pp -> pp omega Reaction
The total cross section for omega production in the pp -> pp omega reaction
has been measured at five c.m. excess energies from 3.8 to 30 MeV. The energy
dependence is easily understood in terms of a strong proton-proton final state
interaction combined with a smearing over the width of the state. The ratio of
near-threshold phi and omega production is consistent with the predictions of a
one-pion-exchange model and the degree of violation of the OZI rule is similar
to that found in the pi-p -> n omega/phi reactions.Comment: Report in LaTeX2e. 12 pages with 2 eps figure
\pi N and \eta p deexcitation channels of the N^* and \Delta baryonic resonances between 1470 and 1680 MeV
Two reactions, pp->ppX and pp->p\pi^+X, are used to study the 1.47<M<1.68 GeV
baryonic mass range. Three different final states are considered in the
invariant masses: N^* or \Delta^+, p\pi^0, and p\eta. The last two channels are
defined by software cuts applied to the missing mass of the first reaction.
Several narrow structures are extracted with widths \sigma(\Gamma) varying
between 3 and 9 MeV. Some structures are observed in one channel but not in
others. Such nonobservation may be due either to the spectrometer momenta
limits or to the physics (e.g. no such disintegration channel is allowed from
the narrow state considered).
We tentatively conclude that the broad Particle Data Group (PDG) baryonic
resonances N(1520)D13, N(1535)S11, Delta(1600)P33, and N(1675)D15 are
collective states built from several narrow and weakly excited resonances, each
having a (much) smaller width than the one reported by PDG.Comment: 29 pages, plus 50 (.png) figures Will be published in a slightly
reduced size in Phys. Rev.
PDF model based on Langevin equation for polydispersed two-phase flows applied to a bluff-body gas-solid flow,
The aim of the paper is to discuss the main characteristics of a complete
theoretical and numerical model for turbulent polydispersed two-phase flows,
pointing out some specific issues. The theoretical details of the model have
already been presented [Minier and Peirano, Physics Reports, Vol. 352/1-3, 2001
]. Consequently, the present work is mainly focused on complementary aspects,
that are often overlooked and that require particular attention. In particular,
the following points are analysed : the necessity to add an extra term in the
equation for the velocity of the fluid seen in the case of twoway coupling, the
theoretical and numerical evaluations of particle averages and the fulfilment
of the particle mass-continuity constraint. The theoretical model is developed
within the PDF formalism. The important-physical choice of the state vector
variables is first discussed and the model is then expressed as a stochastic
differential equation (SDE) written in continuous time (Langevin equations) for
the velocity of the fluid seen. The interests and limitations of Langevin
equations, compared to the single-phase case, are reviewed. From the numerical
point of view, the model corresponds to an hybrid Eulerian/Lagrangian approach
where the fluid and particle phases are simulated by different methods.
Important aspects of the Monte Carlo particle/mesh numerical method are
emphasised. Finally, the complete model is validated and its performance is
assessed by simulating a bluff-body case with an important recirculation zone
and in which two-way coupling is noticeable.Comment: 23 pages, 10 figure
Unmasking features of the auto-epitope essential for β(1)-adrenoceptor activation by autoantibodies in chronic heart failure
AIMS: Chronic heart failure (CHF) can be caused by autoantibodies stimulating the heart via binding to first and/or second extracellular loops of cardiac β(1)-adrenoceptors. Allosteric receptor activation depends on conformational features of the autoantibody binding site. Elucidating these features will pave the way for the development of specific diagnostics and therapeutics. Our aim was (i) to fine-map the conformational epitope within the second extracellular loop of the human β(1)-adrenoceptor (β(1) EC(II)) that is targeted by stimulating β(1)-receptor (auto)antibodies and (ii) to generate competitive cyclopeptide inhibitors of allosteric receptor activation, which faithfully conserve the conformational auto-epitope. METHODS AND RESULTS: Non-conserved amino acids within the β(1) ECII loop (compared with the amino acids constituting the ECII loop of the β(2)-adrenoceptor) were one by one replaced with alanine; potential intra-loop disulfide bridges were probed by cysteine-serine exchanges. Effects on antibody binding and allosteric receptor activation were assessed (i) by (auto)antibody neutralization using cyclopeptides mimicking β(1) ECII ± the above replacements, and (ii) by (auto)antibody stimulation of human β(1)-adrenoceptors bearing corresponding point mutations. With the use of stimulating β(1)-receptor (auto)antibodies raised in mice, rats, or rabbits and isolated from exemplary dilated cardiomyopathy patients, our series of experiments unmasked two features of the β(1) ECII loop essential for (auto)antibody binding and allosteric receptor activation: (i) the NDPK(211-214) motif and (ii) the intra-loop disulfide bond C(209)↔C(215). Of note, aberrant intra-loop disulfide bond C(209)↔C(216) almost fully disrupted the functional auto-epitope in cyclopeptides. CONCLUSIONS: The conformational auto-epitope targeted by cardio-pathogenic β(1)-receptor autoantibodies is faithfully conserved in cyclopeptide homologues of the β(1) EC(II) loop bearing the NDPK(211-214) motif and the C(209)↔C(215) bridge while lacking cysteine C(216). Such molecules provide promising tools for novel diagnostic and therapeutic approaches in β(1)-autoantibody-positive CHF
Eta-Helium Quasi-Bound States
The cross section and tensor analysing power t_20 of the d\vec{d}->eta 4He
reaction have been measured at six c.m. momenta, 10 < p(eta) < 90 MeV/c. The
threshold value of t_20 is consistent with 1/\sqrt{2}, which follows from
parity conservation and Bose symmetry. The much slower momentum variation
observed for the reaction amplitude, as compared to that for the analogous
pd->eta 3He case, suggests strongly the existence of a quasi-bound state in the
eta-4He system and optical model fits indicate that this probably also the case
for eta-3He.Comment: LaTeX, uses elsart.sty, 10 pages, 3 Postscript figures, Submitted to
Physics Letters
Acceleration of heavy and light particles in turbulence: comparison between experiments and direct numerical simulations
We compare experimental data and numerical simulations for the dynamics of
inertial particles with finite density in turbulence. In the experiment,
bubbles and solid particles are optically tracked in a turbulent flow of water
using an Extended Laser Doppler Velocimetry technique. The probability density
functions (PDF) of particle accelerations and their auto-correlation in time
are computed. Numerical results are obtained from a direct numerical simulation
in which a suspension of passive pointwise particles is tracked, with the same
finite density and the same response time as in the experiment. We observe a
good agreement for both the variance of acceleration and the autocorrelation
timescale of the dynamics; small discrepancies on the shape of the acceleration
PDF are observed. We discuss the effects induced by the finite size of the
particles, not taken into account in the present numerical simulations.Comment: 7 pages, 4 figure
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