907 research outputs found
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
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)
No classical limit of quantum decay for broad states
Though the classical treatment of spontaneous decay leads to an exponential
decay law, it is well known that this is an approximation of the quantum
mechanical result which is a non-exponential at very small and large times for
narrow states. The non exponential nature at large times is however hard to
establish from experiments. A method to recover the time evolution of unstable
states from a parametrization of the amplitude fitted to data is presented. We
apply the method to a realistic example of a very broad state, the sigma meson
and reveal that an exponential decay is not a valid approximation at any time
for this state. This example derived from experiment, shows the unique nature
of broad resonances
Synthesis of polyesteramides by a new palladium catalyzed carbonylation–polycondensation reaction
This is the published version. Copyright © The Royal Society of Chemistry 2001Alternating polyesteramides are prepared by palladium catalyzed carbonylation–polycondensation reactions of aromatic diiodides and aminohydroxy compounds in the presence of an organic base
Bose-Einstein Condensate Driven by a Kicked Rotor in a Finite Box
We study the effect of different heating rates of a dilute Bose gas confined
in a quasi-1D finite, leaky box. An optical kicked-rotor is used to transfer
energy to the atoms while two repulsive optical beams are used to confine the
atoms. The average energy of the atoms is localized after a large number of
kicks and the system reaches a nonequilibrium steady state. A numerical
simulation of the experimental data suggests that the localization is due to
energetic atoms leaking over the barrier. Our data also indicates a correlation
between collisions and the destruction of the Bose-Einstein condensate
fraction.Comment: 7 pages, 8 figure
Mechanical behavior of polycrystalline ceramics: Brittle fracture of Si C - Si3N4 materials
The results are described of the final stage of the research involving the role of anions in the behavior of magnesium oxide, as well as the continued efforts of the fracture behavior of silicon nitride materials. These efforts, particularly the first, are further sub-divided in subsections describing individual types of behavior of materials
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