322 research outputs found
Spectator detection for the measurement of proton neutron interactions at ANKE
A telescope of three silicon detectors has been installed close to the
internal target position of the ANKE spectrometer, which is situated inside the
ultra-high vacuum of the COSY-Juelich light-ion storage ring. The detection and
identification of slow protons and deuterons emerging from a deuterium
cluster-jet target thus becomes feasible. A good measurement of the energy and
angle of such a spectator proton (p_sp) allows one to identify a reaction as
having taken place on the neutron in the target and then to determine the
kinematical variables of the ion-neutron system on an event-by-event basis over
a range of c.m. energies.
The system has been successfully tested under laboratory conditions. By
measuring the spectator proton in the p d to p_sp d pi^0 reaction in
coincidence with a fast deuteron in the ANKE Forward Detector, values of the p
n to d pi^0 total cross-section have been deduced. Further applications of the
telescope include the determination of the luminosity and beam polarisation
which are required for several experiments.Comment: 16 pages, 9 figure
Medium effects in the production and pi0 gamma decay of omega-mesons in pA collisions in the GeV region
The omega-resonance production and its pi0 gamma decay in p-A reactions close
to threshold is considered within the Intranuclear Cascade (INC) Model. The pi0
gamma invariant mass distribution shows two components which correspond to the
omega decay 'inside' and 'outside' the nucleus, respectively. The 'inside'
component is distorted by medium effects, which introduce a mass shift as well
as collisional broadening for the omega-meson and its decaying pion. The
relative contribution of the 'inside' component is analyzed in detail for
different kinematical conditions and nuclear targets. It is demonstrated that a
measurement of the correlation in azimuthal angle between the pi0 and gamma
momenta allows to separate events related to the 'inside' omega decay from
different sources of background when uncorrelated pi0's and gamma's are
produced.Comment: 24 pages, 11 figure
Pluto: A Monte Carlo Simulation Tool for Hadronic Physics
Pluto is a Monte-Carlo event generator designed for hadronic interactions
from Pion production threshold to intermediate energies of a few GeV per
nucleon, as well as for studies of heavy ion reactions. This report gives an
overview of the design of the package, the included models and the user
interface.Comment: XI International Workshop on Advanced Computing and Analysis
Techniques in Physics Research, April 23-27 2007, Amsterdam, the Netherland
Transition form factors of the N*(1535) as a dynamically generated resonance
We discuss how electromagnetic properties provide useful tests of the nature
of resonances, and we study these properties for the N*(1535) which appears
dynamically generated from the strong interaction of mesons and baryons. Within
this coupled channel chiral unitary approach, we evaluate the A_1/2 and S_1/2
helicity amplitudes as a function of Q^2 for the electromagnetic N*(1535) to
gamma* N transition. Within the same formalism we evaluate the cross section
for the reactions gamma N to eta N. We find a fair agreement for the absolute
values of the transition amplitudes, as well as for the Q^2 dependence of the
amplitudes, within theoretical and experimental uncertainties discussed in the
paper. The ratios obtained between the S_1/2 and A_1/2 for the neutron or
proton states of the N*(1535) are in qualitative agreement with experiment and
there is agreement on the signs. The same occurs for the ratio of cross
sections for the eta photoproduction on neutron and proton targets in the
vicinity of the N*(1535) energy. The global results support the idea of this
resonance as being dynamically generated, hence, largely built up from meson
baryon components. However, the details of the model indicate that an admixture
with a genuine quark state is also demanded that could help obtain a better
agreement with experimental data.Comment: 19 pages, 16 figures, REVTe
Exclusive measurement of coherent eta photoproduction from the deuteron
Coherent photoproduction of eta mesons from the deuteron has been measured
from threshold up to incident photon energies of 750 MeV using the photon
spectrometer TAPS at the tagged photon facility at the Mainz microtron MAMI.
For the first time, differential coherent cross sections have been deduced from
the coincident detection of the eta meson and the recoil deuteron. A missing
energy analysis was used for the suppression of background events so that a
very clean identification of coherent eta-photoproduction was achieved. The
resulting cross sections agree with previous experimental results except for
angles around 90 deg in the photon-deuteron cm-system where they are smaller.
They are compared to various model calculations.Comment: 4 pages, 4 figure
Justifications-on-demand as a device to promote shifts of attention associated with relational thinking in elementary arithmetic
Student responses to arithmetical questions that can be solved by using arithmetical structure can serve to reveal the extent and nature of relational, as opposed to computational thinking. Here, student responses to probes which require them to justify-on-demand are analysed using a conceptual framework which highlights distinctions between different forms of attention. We analyse a number of actions observed in students in terms of forms of attention and shifts between them: in the short-term (in the moment), medium-term (over several tasks), and long-term (over a year). The main factors conditioning studentsÂŽ attention and its movement are identified and some didactical consequences are proposed
Autocrine and Paracrine Secretion of Vascular Endothelial Growth Factor in the Pre-Hypoxic Diabetic Retina
Vascular endothelial growth factor (VEGF) is well established as the main agent responsible for vascular leakage and angiogenesis in the diabetic retina. While VEGF can have positive effects on hyperglycemia stressed retinal tissues, it also plays a role in events progressing to the oxygen- stressed, i.e. hypoxic, diabetic retina. Some VEGF makes its way to the retina from systemic sources and some is produced locally within the eye. Hyperglycemia, oxidants, inflammation, and advanced glycation end-products are all stimulants to VEGF production, both in the hypoxic and the pre-hypoxic retina. Endothelial cells, pericytes, MĂŒller cells, microglia, astrocytes, retinal pigment epithelium and neurons have all been known to produce VEGF at some point in retinal development or in disease. Excessive VEGF production in the early diabetic retina can lead to retinal exposure or mechanisms which exacerbate further damage. While MĂŒller cells are likely the most significant producer of VEGF in the pre-hypoxic retina, other VEGF producing cells may also play a role due to their proximity to vessels or neurons. Study of the release of VEGF by retinal cells in hyperglycemia conditions, may help identify targets for early treatment and prevent the serious consequences of diabetic retinopathy
Structure, bonding and morphology of hydrothermally synthesised xonotlite
The authors have systematically investigated the role of synthesis conditions upon the structure and morphology of xonotlite. Starting with a mechanochemically prepared, semicrystalline phase with Ca/Si=1, the authors have prepared a series of xonotlite samples hydrothermally, at temperatures between 200 and 250 degrees C. Analysis in each case was by X-ray photoelectron spectroscopy, environmental scanning electron microscopy and X-ray diffraction. The authorsâ use of a much lower water/solid ratio has indirectly confirmed the âthrough solutionâ mechanism of xonotlite formation, where silicate dissolution is a key precursor of xonotlite formation. Concerning the role of temperature, too low a temperature (~200 degrees C) fails to yield xonotlite or leads to increased number of structural defects in the silicate chains of xonotlite and too high a temperature (>250 degrees C) leads to degradation of the xonotlite structure, through leaching of interchain calcium. Synthesis duration meanwhile leads to increased silicate polymerisation due to diminishing of the defects in the silicate chains and more perfect crystal morphologies
Evidence of kaon nuclear and Coulomb potential effects on soft K+ production from nuclei
The ratio of forward K+ production on copper, silver and gold targets to that
on carbon has been measured at proton beam energies between 1.5 and 2.3 GeV as
a function of the kaon momentum p_K using the ANKE spectrometer at
COSY-Juelich. The strong suppression in the ratios observed for p_K<200-250
MeV/c can be ascribed to a combination of Coulomb and nuclear repulsion in the
K+A system. This opens a new way to investigate the interaction of K+-mesons in
the nuclear medium. Our data are consistent with a K+A nuclear potential of
V_K~20 MeV at low kaon momenta and normal nuclear density. Given the
sensitivity of the data to the kaon potential, the current experimental
precision might allow one to determine V_K to better than 3 MeV.Comment: 9 pages, 3 figures; changed conten
Inclusive K^+ meson production in proton-nucleus interactions
The production of K^+ mesons in pA (A = D, C, Cu, Ag, Au) collisions has been
investigated at the COoler SYnchrotron COSY-J\"ulich for beam energies T_p =
1.0 - 2.3 GeV. Double differential inclusive pC cross sections at forward
angles theta < 12 degrees as well as the target-mass dependence of the K^+
momentum spectra have been measured with the ANKE spectrometer. Far below the
free NN threshold at T_{NN}=1.58 GeV the spectra reveal a high degree of
collectivity in the target nucleus. From the target-mass dependence of the
cross sections at higher energies, the repulsive in-medium potential of K^+
mesons can be deduced. Using pN cross-section parameterisations from literature
and our measured pD data we derive a cross-section ratio of sigma(pn -> K^+ X)
/ sigma(pp -> K^+ X) ~ (3-4).Comment: Accepted for publication in EPJ A; 17 pages, 10 figures, 11 table
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