2,145 research outputs found
Deuteron properties from muonic atom spectroscopy
Leading order () finite size corrections in muonic deuterium are
evaluated within a few body formalism for the system in muonic
deuterium and found to be sensitive to the input of the deuteron wave function.
We show that this sensitivity, taken along with the precise deuteron charge
radius determined from muonic atom spectroscopy can be used to determine the
elusive deuteron D-state probability, , for a given model of the
nucleon-nucleon (NN) potential. The radius calculated with a of 4.3\% in
the chiral NN models and about 5.7\% in the high precision NN potentials is
favoured most by the data.Comment: 14 pages, 2 figure
On Quasibound N* Nuclei
The possibility for the existence of unstable bound states of the S11 nucleon
resonance N(1535) and nuclei is investigated. These quasibound states are
speculated to be closely related to the existence of the quasibound states of
the eta mesons and nuclei. Within a simple model for the N N interaction
involving a pion and eta meson exchange, N-nucleus potentials for N*-He
and N*-Mg are evaluated and found to be of a Woods-Saxon like form which
supports two to three bound states. In case of N*-He, one state bound by
only a few keV and another by 4 MeV is found. The results are however quite
sensitive to the N N and N N vertex parameters. A rough
estimate of the width of these states, based on the mean free path of the
exchanged mesons in the nuclei leads to very broad states with 80
and 110 MeV for N*-He and N*-Mg respectively.Comment: Presented at the Jagiellonian Symposium on Fundamental and Applied
Subatomic Physics, Cracow, Poland, June 2015; to be published in Acta Physica
Polonica B (2016
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
Perovskite oxides: Oxygen electrocatalysis and bulk structure
Perovskite type oxides were considered for use as oxygen reduction and generation electrocatalysts in alkaline electrolytes. Perovskite stability and electrocatalytic activity are studied along with possible relationships of the latter with the bulk solid state properties. A series of compounds of the type LaFe(x)Ni1(-x)O3 was used as a model system to gain information on the possible relationships between surface catalytic activity and bulk structure. Hydrogen peroxide decomposition rate constants were measured for these compounds. Ex situ Mossbauer effect spectroscopy (MES), and magnetic susceptibility measurements were used to study the solid state properties. X ray photoelectron spectroscopy (XPS) was used to examine the surface. MES has indicated the presence of a paramagnetic to magnetically ordered phase transition for values of x between 0.4 and 0.5. A correlation was found between the values of the MES isomer shift and the catalytic activity for peroxide decomposition. Thus, the catalytic activity can be correlated to the d-electron density for the transition metal cations
Stretched exponential relaxation for growing interfaces in quenched disordered media
We study the relaxation for growing interfaces in quenched disordered media.
We use a directed percolation depinning model introduced by Tang and Leschhorn
for 1+1-dimensions. We define the two-time autocorrelation function of the
interface height C(t',t) and its Fourier transform. These functions depend on
the difference of times t-t' for long enough times, this is the steady-state
regime. We find a two-step relaxation decay in this regime. The long time tail
can be fitted by a stretched exponential relaxation function. The relaxation
time is proportional to the characteristic distance of the clusters of pinning
cells in the direction parallel to the interface and it diverges as a power
law. The two-step relaxation is lost at a given wave length of the Fourier
transform, which is proportional to the characteristic distance of the clusters
of pinning cells in the direction perpendicular to the interface. The stretched
exponential relaxation is caused by the existence of clusters of pinning cells
and it is a direct consequence of the quenched noise.Comment: 4 pages and 5 figures. Submitted (5/2002) to Phys. Rev.
Lorentz Contracted Proton
The proton charge and magnetization density distributions can be related to
the well known Sachs electromagnetic form factors
through Fourier transforms, only in the Breit frame. The Breit frame however
moves with relativistic velocities in the Lab and a Lorentz boost must be
applied to the form factors before extracting the static properties of the
proton from the corresponding densities. Apart from this, the Fourier transform
relating the densities and form factors is inherently a non-relativistic
expression. We show that the relativistic corrections to it can be obtained by
extending the standard Breit equation to higher orders in its
expansion. We find that the inclusion of the above corrections reduces the size
of the proton determined from electron proton scattering data. Indeed the
central value of the latest proton radius of fm as determined
from e-p scattering changes to fm after applying corrections.Comment: 15 page
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