2,444 research outputs found
Polarized Proton Pionic Capture in Deuterium as a Probe of 3N Dynamics
The proton analyzing power Ay in pion production reaction pd --> pi0 3He has
been calculated including one- and two-body meson production mechanisms with a
proper treatment of the three-nucleon dynamics and an accurate solution of the
3N bound-state problem for phenomenological two-nucleon potentials. In the
region around the Delta resonance, the structure of the analyzing power can be
understood once interference effects among amplitudes describing intermediate
Delta N formation in different orbital states are considered along with the
additional interference with the S-wave pion production amplitudes. Then, the
inclusion of three-nucleon dynamics in the initial state produces the structure
of the analyzing power that has been observed experimentally.Comment: 9 pages, 5 figure
Hadronic Decays of Baryons in Point-Form Relativistic Quantum Mechanics
We discuss strong decays of baryon resonances within the concept of
relativistic constituent quark models. In particular, we follow a
Poincare-invariant approach along the point form of relativistic quantum
mechanics. Here, we focus on pionic decay modes of N and Delta resonances. It
is found that the covariant quark-model predictions calculated in the
point-form spectator model in general underestimate the experimental data
considerably. This points to a systematic defect in the used decay operator
and/or the baryon wave functions. From a detailed investigation of the
point-form decay operator it is seen that the requirement of translational
invariance implies effective many-body contributions. Furthermore, one has to
employ a normalization factor in the definition of the decay operator in the
point-form spectator model. Our analysis suggests that this normalization
factor is best chosen consistently with the one used for the electromagnetic
and axial current operators for elastic nucleon form factors.Comment: 8 pages, 6 figures, presented at the "X Convegno su Problemi di
Fisica Nucleare Teorica", Cortona, Italy, 6-9 Oct. 200
Vested Interests and Resistance to Technology Adoption
Employed technologies differ vastly across countries. Within countries many technologies that would obviously improve firms’ efficiency are not adopted. This paper explains these observations by emphasizing that a new technology positively affects workers by lowering prices and increasing their real income, but also negatively by costs of getting acquainted with the new technology. If the costs of adoption for workers exceed the benefits, they will aim at keeping the old technology in place. We formalise the trade-off in a simple OLG model with majority voting. Age groups that lose from adopting resist. Successful resistance blocks adoption and hence lowers growth. Finally, we analyse the effects of tougher competition. Provided that consumption and leisure are relatively good substitutes, tougher competition mitigates resistance and thus favours economic growth as it increases the share of the rent associated with the new technology that is being captured by the workers.technological change;resistance;vested interests;overlapping generations;competition
Test of ID carbon-carbon composite prototype tiles for the SPIDER diagnostic calorimeter
Additional heating will be provided to the thermonuclear fusion experiment ITER by injection of neutral beams from accelerated negative ions. In the SPIDER test facility, under construction at Consorzio RFX in Padova (Italy), the production of negative ions will be studied and optimised. To this purpose the STRIKE (Short-Time Retractable Instrumented Kalorimeter Experiment) diagnostic will be used to characterise the SPIDER beam during short operation (several seconds) and to verify if the beam meets the ITER requirement regarding the maximum allowed beam non-uniformity (below \ub110%). The most important measurements performed by STRIKE are beam uniformity, beamlet divergence and stripping losses. The major components of STRIKE are 16 1D-CFC (Carbon matrix-Carbon Fibre reinforced Composite) tiles, observed at the rear side by a thermal camera. The requirements of the 1D CFC material include a large thermal conductivity along the tile thickness (at least 10 times larger than in the other directions); low specific heat and density; uniform parameters over the tile surface; capability to withstand localised heat loads resulting in steep temperature gradients. So 1D CFC is a very anisotropic and delicate material, not commercially available, and prototypes are being specifically realised. This contribution gives an overview of the tests performed on the CFC prototype tiles, aimed at verifying their thermal behaviour. The spatial uniformity of the parameters and the ratio between the thermal conductivities are assessed by means of a power laser at Consorzio RFX. Dedicated linear and non-linear simulations are carried out to interpret the experiments and to estimate the thermal conductivities; these simulations are described and a comparison of the experimental data with the simulation results is presented
Characterization of nanoporous lanthanide-doped gadolinium gallium garnet powders obtained by propellant synthesis
In the present work we study the nanocrystalline powders of lanthanide-doped
Gd3Ga5O12 (GGG, gadolinium gallium garnet) prepared using propellant synthesis. A series of
GGG samples containing a number of different trivalent lanthanide ions (Tm, Er, Ho, Eu, Sm, Nd,
and Pr) in different quantities (1%, 5%, 10%) were produced. Samples were characterized by X-ray
diffraction (pre- and post calcination) for phase identification and line-broadening analysis, and by
electron microscopy (SEM and TEM) for morphological and nanostructural investigation. Thermal
behavior of the powder was investigated by thermal gravimetric analysis (TGA) and differential
thermal analysis (DTA). The samples have a polycrystalline porous structure. Elemental
microanalysis made by energy dispersive X-ray spectroscopy (EDX) detector attached to TEM and
XRD unit-cell determinations confirmed that the lanthanides ions entered the structure of GGG.
Crystallites have a high degree of disorder
Isoscalar off-shell effects in threshold pion production from pd collisions
We test the presence of pion-nucleon isoscalar off-shell effects in the
reaction around the threshold region. We find that these
effects significantly modify the production cross section and that they may
provide the missing strength needed to reproduce the data at threshold.Comment: 6 pages, REVTeX, twocolumn, including 3 figures (Postscript), uses
psfig, updated and extended versio
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