30 research outputs found
Differential cross section and recoil polarization measurements for the gamma p to K+ Lambda reaction using CLAS at Jefferson Lab
We present measurements of the differential cross section and Lambda recoil
polarization for the gamma p to K+ Lambda reaction made using the CLAS detector
at Jefferson Lab. These measurements cover the center-of-mass energy range from
1.62 to 2.84 GeV and a wide range of center-of-mass K+ production angles.
Independent analyses were performed using the K+ p pi- and K+ p (missing pi -)
final-state topologies; results from these analyses were found to exhibit good
agreement. These differential cross section measurements show excellent
agreement with previous CLAS and LEPS results and offer increased precision and
a 300 MeV increase in energy coverage. The recoil polarization data agree well
with previous results and offer a large increase in precision and a 500 MeV
extension in energy range. The increased center-of-mass energy range that these
data represent will allow for independent study of non-resonant K+ Lambda
photoproduction mechanisms at all production angles.Comment: 22 pages, 16 figure
Capillary filling with pseudo-potential binary Lattice-Boltzmann model
We present a systematic study of capillary filling for a binary fluid by
using a mesoscopic lattice Boltzmann model for immiscible fluids describing a
diffusive interface moving at a given contact angle with respect to the walls.
The phenomenological way to impose a given contact angle is analysed.
Particular attention is given to the case of complete wetting, that is contact
angle equal to zero. Numerical results yield quantitative agreement with the
theoretical Washburn law, provided that the correct ratio of the dynamic
viscosities between the two fluids is used. Finally, the presence of precursor
films is experienced and it is shown that these films advance in time with a
square-root law but with a different prefactor with respect to the bulk
interface.Comment: 13 pages, 8 figures, accepted for publication on The European journal
of physics
First measurement of direct photoproduction on the proton
We report on the results of the first measurement of exclusive
meson photoproduction on protons for GeV and GeV. Data were collected with the CLAS detector at the Thomas
Jefferson National Accelerator Facility. The resonance was detected via its
decay in the channel by performing a partial wave analysis of the
reaction . Clear evidence of the meson
was found in the interference between and waves at GeV. The -wave differential cross section integrated in the mass range of
the was found to be a factor of 50 smaller than the cross section
for the meson. This is the first time the meson has been
measured in a photoproduction experiment
Partial wave analysis of the reaction gamma p -> p omega$ and the search for nucleon resonances
An event-based partial wave analysis (PWA) of the reaction gamma p -> p omega
has been performed on a high-statistics dataset obtained using the CLAS at
Jefferson Lab for center-of-mass energies from threshold up to 2.4 GeV. This
analysis benefits from access to the world's first high precision spin density
matrix element measurements, available to the event-based PWA through the decay
distribution of omega-> pi+ pi - pi0. The data confirm the dominance of the
t-channel pi0 exchange amplitude in the forward direction. The dominant
resonance contributions are consistent with the previously identified states
F[15](1680) and D[13](1700) near threshold, as well as the G[17](2190) at
higher energies. Suggestive evidence for the presence of a J(P)=5/2(+) state
around 2 GeV, a "missing" state, has also been found. Evidence for other states
is inconclusive
Semi-inclusive pi(0) target and beam-target asymmetries from 6 GeV electron scattering with CLAS
We present precision measurements of the target and beam-target spin
asymmetries from neutral pion electroproduction in deep-inelastic scattering
(DIS) using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. We
scattered 6-GeV, longitudinally polarized electrons off longitudinally
polarized protons in a cryogenic NH target, and extracted double and
single target spin asymmetries for in
multidimensional bins in four-momentum transfer ( GeV),
Bjorken- (), hadron energy fraction (), transverse
pion momentum ( GeV), and azimuthal angle between the
lepton scattering and hadron production planes. We extracted asymmetries as a
function of both and , which provide access to transverse-momentum
distributions of longitudinally polarized quarks. The double spin asymmetries
depend weakly on . The moments are zero within
uncertainties, which is consistent with the expected suppression of the Collins
fragmentation function. The observed moments suggest that quark
gluon correlations are significant at large .Comment: 18 preprint pages, 3 figure
Field-scale dispersal of <i>Aphodius</i> dung beetles (Coleoptera: Scarabaeidae) in response to avermectin treatments on pastured cattle
Very few studies have examined, at the field scale, the potential for faecal residues in the dung of avermectin-treated cattle to affect dung-breeding insects. The current study examined populations of dung beetles (Scarabaeidae: <i>Aphodius</i>) using pitfall traps baited with dung from untreated cattle on 26 fields across eight farms in southwest Scotland. The fields were grazed either by untreated cattle or by cattle treated with an avermectin product, i.e. doramectin or ivermectin. During the two-year study, significantly more beetles were trapped in fields grazed by treated cattle (n=9377 beetles) than in fields where cattle remained untreated (n=2483 beetles). Additional trials showed that beetles preferentially colonised dung of untreated versus doramectin-treated cattle. This may explain the higher captures of beetles in traps baited with dung of untreated cattle, which were located in fields of treated cattle. Given that <i>Aphodius</i> beetles avoided dung of treated cattle in the current study, the potential harmful effects of avermectin residues in cattle dung could be reduced through livestock management practices that maximise the availability of dung from untreated livestock in areas where avermectins are being use
Farming on the edge The nature of traditional farmland in Europe
SIGLEAvailable from British Library Document Supply Centre- DSC:GPC/06878 / BLDSC - British Library Document Supply CentreGBUnited Kingdo
Parent age, lifespan and offspring survival: structured variation in life history in a wild population
1. Understanding the degree to which reproductive success varies with an individualâs age and lifespan, and the degree to which population-level variation mirrors individual-level variation, is central to understanding life-history evolution and the dynamics of age-structured populations. We quantified variation in the survival probability of offspring, one key component of reproductive success and fitness, in relation to parent age and lifespan in a wild population of red-billed choughs (Pyrrhocorax pyrrhocorax).
2. On average across the study population, the first-year survival probability of offspring decreased with increasing parent age and lifespan; offspring of old parents were less likely to survive than offspring of young parents, and offspring of long-lived parents were less likely to survive than offspring of short-lived parents.
3. However, survival did not vary with parent age across offspring produced by groups of parents that ultimately had similar lifespans.
4. Rather, across offspring produced by young parents, offspring survival decreased with increasing parent lifespan; parents that ultimately had long lifespans produced offspring that survived poorly, even when these parents were breeding at young ages.
5. The average decrease in offspring survival with increasing parent age observed across the population therefore reflected the gradual disappearance of short-lived parents that produced offspring that survived well, not age-specific variation in offspring survival within individual parents.
6. The negative correlation between offspring survival and maternal lifespan was strongest when environmental conditions meant that offspring survival was low across the population.
7. These data suggest an environment-dependent trade-off between parent and offspring survival, show consistent individual variation in the resolution of this trade-off that is set early in a parentâs life, and demonstrate that such structured life-history variation can generate spurious evidence of senescence in key fitness components when measured across a populatio