1,296 research outputs found
Possible eta-mesic 3He states within the finite rank approximation
We extend the method of time delay proposed by Eisenbud and Wigner, to search
for unstable states formed by eta mesons and the 3He nucleus. Using few body
equations to describe eta-3He elastic scattering, we predict resonances and
unstable bound states within different models of the eta-N interaction. The
eta-3He states predicted within this novel approach are in agreement with the
recent claim of the evidence of eta-mesic 3He made by the TAPS collaboration.Comment: 10 pages LaTex, 3 figure
Small eta-N scattering lengths favour eta-d and eta-alpha states
Unstable states of the eta meson and the 3He nucleus predicted using the time
delay method were found to be in agreement with a recent claim of eta-mesic 3He
states made by the TAPS collaboration. Here, we extend this method to a
speculative study of the unstable states occurring in the eta-d and eta-4He
elastic scattering. The T-matrix for eta-4He scattering is evaluated within the
Finite Rank Approximation (FRA) of few body equations. For the evaluation of
time delay in the eta-d case, we use a parameterization of an existing Faddeev
calculation and compare the results with those obtained from FRA. With an eta-N
scattering length, fm, we find an eta-d unstable
bound state around -16 MeV, within the Faddeev calculation. A similar state
within the FRA is found for a low value of , namely, fm. The existence of an eta-4He unstable bound state close to
threshold is hinted by fm, but is ruled out by
large scattering lengths.Comment: 21 pages, LaTex, 7 Figure
Analyses of quasi-isotropic composite plates under quasi-static point loads simulating low-velocity impact phenomena
In thin composite laminates, the first level of visible damage occurs in the back face and is called back face spalling. A plate-membrane coupling model, and a finite element model to analyze the large deformation behavior of eight-ply quasi-isotropic circular composite plates under impact type point loads are developed. The back face spalling phenomenon in thin composite plates is explained by using the plate-membrane coupling model and the finite element model in conjunction with the fracture mechanics principles. The experimental results verifying these models are presented. Several conclusions concerning the deformation behavior are reached and discussed in detail
Mechanical behavior of polycrystalline ceramics: Brittle fracture of SiC-Si3N4 materials
The first study area involved magnesium oxide and the role of anion impurities, while the second area was directed toward slow crack growth in silicon nitride-silicon carbide ceramics. The oxide program involved development of fabrication techniques for anion doped materials and evaluation of the role of these anions in the hot pressing response, grain boundary diffusion of nickel doped material, grain boundary microhardness, and grain growth
Short Range Interactions in the Hydrogen Atom
In calculating the energy corrections to the hydrogen levels we can identify
two different types of modifications of the Coulomb potential , with one
of them being the standard quantum electrodynamics corrections, ,
satisfying over the whole range of
the radial variable . The other possible addition to is a potential
arising due to the finite size of the atomic nucleus and as a matter of fact,
can be larger than in a very short range. We focus here on the latter
and show that the electric potential of the proton displays some undesirable
features. Among others, the energy content of the electric field associated
with this potential is very close to the threshold of pair production.
We contrast this large electric field of the Maxwell theory with one emerging
from the non-linear Euler-Heisenberg theory and show how in this theory the
short range electric field becomes smaller and is well below the pair
production threshold
Kinetics of hydroformylation of 1-octene in ionic liquid-organic biphasic media using rhodium sulfoxantphos catalyst
Biphasic hydroformylation of 1-octene was performed using rhodium sulfoxantphos catalyst dissolved in [BuPy][BF4] ionic liquid. Preliminary experiments proved this system to retain the catalytic complex within the ionic liquid phase and to maintain a high selectivity towards the linear aldehyde (n:iso ratio of 30) over several cycles. Process parameter investigation showed a first order dependence of the initial rate with respect to the catalyst and 1-octene concentrations, but a more complex behavior with respect to hydrogen (fractional order) and carbon monoxide partial pressures (inhibition at high pressures). Different mathematical models were selected based on the trends observed and evaluated for data fitting. Also, rate models were derived from a proposed mechanism, using Christiansen matrix approach. To calculate concentrations of substrates in the catalytic phase as required by this kinetic modeling, solubility measurements were preformed for the gases (pressure drop technique), as well as for 1-octene and n-nonanal (thermogravimetry analysis)
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