219 research outputs found
Genetic and oceanographic tools reveal high population connectivity and diversity in the endangered pen shell Pinna nobilis
For marine meta-populations with source-sink dynamics knowledge about genetic connectivity
is important to conserve biodiversity and design marine protected areas (MPAs). We evaluate
connectivity of a Mediterranean sessile species, Pinna nobilis. To address a large geographical scale,
partial sequences of cytochrome oxidase I (COI, 590 bp) were used to evaluate phylogeographical
patterns in the Western Mediterranean, and in the whole basin using overlapping sequences from
the literature (243 bp). Additionally, we combined (1) larval trajectories based on oceanographic
currents and early life-history traits and (2) 10 highly polymorphic microsatellite loci collected in the
Western Mediterranean. COI results provided evidence for high diversity and low inter-population
differentiation. Microsatellite genotypes showed increasing genetic differentiation with oceanographic
transport time (isolation by oceanographic distance (IBD) set by marine currents). Genetic
differentiation was detected between Banyuls and Murcia and between Murcia and Mallorca. However,
no genetic break was detected between the Balearic populations and the mainland. Migration rates
together with numerical Lagrangian simulations showed that (i) the Ebro Delta is a larval source for
the Balearic populations (ii) Alicante is a sink population, accumulating allelic diversity from nearby
populations. The inferred connectivity can be applied in the development of MPA networks in the
Western MediterraneanProject MEDEICG funded by the Spanish Ministry of Economy and Competitiveness (CTM2009-07013)IEH was supported by Ramon y Cajal Fellowship RYC2014-14970Spanish Ministry of Economy, Industry and Competitiveness IFCT Investigator Programme-Career Development (IF/00998/2014)MGW and AHE was supported by FCT fellowships SFRH/BPD/63703/2009 and SFRH/BPD/107878/2015National Science Foundation (OCE-1419450)CCMAR team via excellence research line EXCL/AAG-GLO/0661/2012Ciencias del Ma
Precision Measurement of the Proton and Deuteron Spin Structure Functions g\u3csub\u3e2\u3c/sub\u3e and Asymmetries A\u3csub\u3e2\u3c/sub\u3e
We have measured the spin struction functions g2(p) and g(2)(d) and the virtual photon asymmetries A(2)(p) and A(2)(d) over the kinetmatic range 0.02 less than or equal to x less than or equal to 0.8 and 0.7 less than or equal to Q2 less than or equal to 20 GeV2 by scattering 29.1 and 32.3 GeV longitudinally polarized electrons from transversely polarized NH3 and (LiD)-Li-6 targets. Our measured g2 approximately follows the twist-2 Wandzura-Wilczek calculation. The twist-3 reduced matrix elements d(2)(p) and d(2)(n) are less than two standard deviations from zero. The data are inconsistent with the Burkhardt-Cottingham sum rule if there is no pathological behavior as x --\u3e 0. The Efremov-Leader-Teryaev integral is consistent with zero within our measured kinematic range. The absolute value of A2 is significantly smaller than the A2 \u3c √ R(1 +A1)/2 limit
Scaling of the F_2 structure function in nuclei and quark distributions at x>1
We present new data on electron scattering from a range of nuclei taken in
Hall C at Jefferson Lab. For heavy nuclei, we observe a rapid falloff in the
cross section for , which is sensitive to short range contributions to the
nuclear wave-function, and in deep inelastic scattering corresponds to probing
extremely high momentum quarks. This result agrees with higher energy muon
scattering measurements, but is in sharp contrast to neutrino scattering
measurements which suggested a dramatic enhancement in the distribution of the
`super-fast' quarks probed at x>1. The falloff at x>1 is noticeably stronger in
^2H and ^3He, but nearly identical for all heavier nuclei.Comment: 5 pages, 4 figures, to be submitted to physical revie
Study of the A(e,e') Reaction on H, H, C, Al, Cu and Au
Cross sections for the p()n process on H, H, C,
Al, Cu and Au targets were measured at the Thomas
Jefferson National Accelerator Facility (Jefferson Lab) in order to extract the
nuclear transparencies. Data were taken for four-momentum transfers ranging
from =1.1 to 4.8 GeV for a fixed center of mass energy of =2.14
GeV. The ratio of and was extracted from the measured
cross sections for H, H, C and Cu targets at = 2.15
and 4.0 GeV allowing for additional studies of the reaction mechanism. The
experimental setup and the analysis of the data are described in detail
including systematic studies needed to obtain the results. The results for the
nuclear transparency and the differential cross sections as a function of the
pion momentum at the different values of are presented. Global features
of the data are discussed and the data are compared with the results of model
calculations for the p()n reaction from nuclear targets.Comment: 28 pages, 19 figures, submited to PR
Transverse momentum dependence of semi-inclusive pion production
Cross sections for semi-inclusive electroproduction of charged pions
() from both proton and deuteron targets were measured for
, GeV, , and GeV. For
GeV, we find the azimuthal dependence to be small, as expected
theoretically. For both and , the dependence from the
deuteron is found to be slightly weaker than from the proton. In the context of
a simple model, this implies that the initial transverse momenta width of
quarks is larger than for quarks and, contrary to expectations, the
transverse momentum width of the favored fragmentation function is larger than
the unfavored one.Comment: 15 pages, 4 figures. Fit form changed to include Cahn effect Minor
revisions. Added one new figur
New measurements of high-momentum nucleons and short-range structures in nuclei
We present new measurements of electron scattering from high-momentum
nucleons in nuclei. These data allow an improved determination of the strength
of two-nucleon correlations for several nuclei, including light nuclei where
clustering effects can, for the first time, be examined. The data also include
the kinematic region where three-nucleon correlations are expected to dominate.Comment: 5 pages, 3 figures. Results from JLab E02-01
Scaling study of the pion electroproduction cross sections and the pion form factor
The H()n cross section was measured for a range of
four-momentum transfer up to =3.91 GeV at values of the invariant
mass, , above the resonance region. The -dependence of the longitudinal
component is consistent with the -scaling prediction for hard exclusive
processes. This suggests that perturbative QCD concepts are applicable at
rather low values of . Pion form factor results, while consistent with the
-scaling prediction, are inconsistent in magnitude with perturbative QCD
calculations. The extraction of Generalized Parton Distributions from hard
exclusive processes assumes the dominance of the longitudinal term. However,
transverse contributions to the cross section are still significant at
=3.91 GeV.Comment: 6 pages, 3 figure
Measurement of Nuclear Transparency for the A(e,e' pi^+) Reaction
We have measured the nuclear transparency of the A(e,e' pi^+) process in
^{2}H,^{12}C, ^{27}Al, ^{63}Cu and ^{197}Au targets. These measurements were
performed at the Jefferson Laboratory over a four momentum transfer squared
range Q^2 = 1.1 - 4.7 (GeV/c)^2. The nuclear transparency was extracted as the
super-ratio of from data to a model of
pion-electroproduction from nuclei without pi-N final state interactions. The
Q^2 and atomic number dependence of the nuclear transparency both show
deviations from traditional nuclear physics expectations, and are consistent
with calculations that include the quantum chromodynamical phenomenon of color
transparency.Comment: 5 pages, 3 figs Changes to figure 2 and 3 (error band updated and
theory curves updated
The Onset of Quark-Hadron Duality in Pion Electroproduction
A large data set of charged-pion electroproduction from both hydrogen and
deuterium targets has been obtained spanning the low-energy residual-mass
region. These data conclusively show the onset of the quark-hadron duality
phenomenon, as predicted for high-energy hadron electroproduction. We construct
several ratios from these data to exhibit the relation of this phenomenon to
the high-energy factorization ansatz of electron-quark scattering and
subsequent quark-to- pion production mechanisms.Comment: 11 pages, 3 figures, accepted in Phys. Rev. Lett. Tables adde
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