999 research outputs found
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
Subthreshold K+ production in deuteron and alpha induced nuclear reactions
Double differential cross sections have been measured for pi+ and K+ emitted
around midraidity in d+A and He+A collisions at a beam kinetic energy of 1.15
GeV/nucleon. The total pi+ yield increases by a factor of about 2 when using an
alpha projectile instead of a deuteron whereas the K+ yield increases by a
factor of about 4. According to transport calculations, the K+ enhancement
depends both on the number of hadron-hadron collisions and on the energy
available in those collisions: their center-of-mass energy increases with
increasing number of projectile nucleons
\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.
Nocturnal sleep duration trajectories in early childhood and school performance at age 10 years
Summary
Sleep plays a fundamental role in brain development and resultant functions. The aim was to verify whether nocturnal sleep duration during early childhood has long-term associations with academic achievement at age 10?years. The present study is part of the Quebec Longitudinal Study of Child Development, a representative cohort of infants born in 1997?1998 in the province of Quebec, Canada. Children with known neurological conditions were excluded from this cohort. Four trajectories of parent-reported nocturnal sleep duration at ages 2.5, 3, 4, 5 and 6?years were determined using a SAS procedure named PROC TRAJ. Sleep duration at age 10?years was also reported. Teachers provided data on academic performance when the children were age 10?years. These data were available for 910 children (430 boys, 480 girls; 96.6% Caucasians). Univariate and multivariable logistic regressions were performed using SPSS. Children who slept less than 8?hr per night at 2.5?years but normalized later on (Traj1) had three?five times the odds of having grades below the class average in reading, writing, mathematics and science compared with children who slept sufficiently (Traj3?4: 10?11?hr per night). Children who slept about 9?hr per night throughout childhood (Traj2) had two?three times the odds of being below the class average in mathematics and science. Sleep duration at age 10?years was not correlated with the academic performance. These results point to the presence of a very important early period during which sufficient sleep is needed to fine-tune the functions necessary for academic achievement later on
Cumulant expansion for studying damped quantum solitons
The quantum statistics of damped optical solitons is studied using
cumulant-expansion techniques. The effect of absorption is described in terms
of ordinary Markovian relaxation theory, by coupling the optical field to a
continuum of reservoir modes. After introduction of local bosonic field
operators and spatial discretization pseudo-Fokker-Planck equations for
multidimensional s-parameterized phase-space functions are derived. These
partial differential equations are equivalent to an infinite set of ordinary
differential equations for the cumulants of the phase-space functions.
Introducing an appropriate truncation condition, the resulting finite set of
cumulant evolution equations can be solved numerically. Solutions are presented
in Gaussian approximation and the quantum noise is calculated, with special
emphasis on squeezing and the recently measured spectral photon-number
correlations [Spaelter et al., Phys. Rev. Lett. 81, 786 (1998)].Comment: 17 pages, 13 figures, revtex, psfig, multicols, published in
Phys.Rev.
SEARCH FOR NARROW ISOVECTOR DIBARYONS CLOSE TO LOW MASSES THRESHOLD
For masses larger than 2 MN + MĎ€, narrow peaks in two proton invariant (missing) masses spectra : Mpp (Mx) are now well established. The existence of such narrow peaks is not so unquestionable below 2 MN + MĎ€. Tensor analyzing power T20 of the invariant mass Mpp has been studied using the p ([MATH], pp) reaction. Depending on the assumption done for background substraction -a hole or an oscillation may appear at Mpp = 1941 MeV. Additional data are under analysis and will improve the statistics
Enhancing Optical Up-Conversion Through Electrodynamic Coupling with Ancillary Chromophores
In lanthanide-based optical materials, control over the relevant operating characteristics–for example transmission wavelength, phase and quantum efficiency–is generally achieved through the modification of parameters such as dopant/host combination, chromophore concentration and lattice structure. An alternative avenue for the control of optical response is through the introduction of secondary, codoped chromophores. Here, such secondary centers act as mediators, commonly bridging the transfer of energy between primary absorbers of externally sourced optical input and other sites of frequency-converted emission. Utilizing theoretical models based on experimentally feasible, three-dimensional crystal lattice structures; a fully quantized theoretical framework provides insights into the locally modified mechanisms that can be implemented within such systems. This leads to a discussion of how such effects might be deployed to either enhance, or potentially diminish, the efficiency of frequency up-conversion
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