2,929 research outputs found
Basal-plane metallography of deformed pyrolytic carbon
Cleavage technique is recommended over the normal polishing technique in preparing pyrolytic carbon for metallographic examination of basal-plane surfaces. After careful removal of torn basal-plane fragments and other cleavage debris with cellulose tape, the true structure is clearly revealed
Composite Skyrme Model with Vector Mesons
We study the composite Skyrme model, proposed by Cheung and G\"{u}rsey,
introducing vector mesons in a chiral Lagrangian. We calculate the static
properties of baryons and compare with results obtained from models without
vector mesons.Comment: LaTeX, 9 pages, 3 figures, to be published in Phys. Rev.
alpha^2 corrections to parapositronium decay: a detailed description
We present details of our recent calculation of alpha^2 corrections to the
parapositronium decay into two photons. These corrections are rather small and
our final result for the parapositronium lifetime agrees well with the most
recent measurement. Implications for orthopositronium decays are briefly
discussed.Comment: 18 pages, late
The "recoil" correction of order to hyperfine splitting of positronium ground state
The "recoil" correction of order to the hyperfine splitting of
positronium ground state was found. The formalism employed is based on the
noncovariant perturbation theory in QED. Equation for two-particle component of
full (many-body) wave function is used, in which effective Hamiltonian depends
on the energy of a system. The effective Hamiltonian is not restricted to the
nonrelativistic region, so there is no need in any regularization. To evaluate
integrals over loop momenta, they are divided into "hard" and "soft" parts,
coming from large and small momenta respectively. Soft contributions were found
analytically, and hard ones are evaluated by numerical integration. Some soft
terms due to the retardation cancel each other. To calculate the "hard"
contributions, a great number of noncovariant graphs is replaced by only a few
covariant ones. The hard contribution was found in two ways. The first way is
to evaluate contributions of separate graphs, using the Coulomb gauge. The
second one is to calculate full hard contribution as a whole using the Feynman
gauge. The final result for the "recoil" correction is 0.381(6) m\al^6 and
agrees with those of previous papers. Diagram-to-diagram comparison with the
revised results of Adkins&Sapirstein was done. All the results agree, so the
"recoil" correction is now firmly established. This means a considerable
disagreement with the experimental data.Comment: 28 pages, latex including latex figure
Skyrmions and domain walls in (2+1) dimensions
We study classical solutions of the vector O(3) sigma model in (2+1)
dimensions, spontaneously broken to O(2)xZ2. The model possesses Skyrmion-type
solutions as well as stable domain walls which connect different vacua. We show
that different types of waves can propagate on the wall, including waves
carrying a topological charge. The domain wall can also absorb Skyrmions and,
under appropriate initial conditions, it is possible to emit a Skyrmion from
the wall.Comment: plain tex : 15 pages, 21 Postscript figures, uses epsf.te
Interactions of B = 4 Skyrmions
It is known that the interactions of single Skyrmions are asymptotically
described by a Yukawa dipole potential. Less is known about the interactions of
solutions of the Skyrme model with higher baryon number. In this paper, it is
shown that Yukawa multipole theory can be more generally applied to Skyrmion
interactions, and in particular to the long-range dominant interactions of the
B = 4 solution of the Skyrme model, which models the alpha-particle. A method
that gives the quadrupole nature of the interaction a more intuitive meaning in
the pion field colour picture is demonstrated. Numerical methods are employed
to find the precise strength of quadrupole and octupole interactions. The
results are applied to the B = 8 and B = 12 solutions and to the Skyrme
crystal.Comment: 21 pages, 11 figure
On the quantization of SU(3)-skyrmions
The quantization condition derived previously for SU(2) solitons quantized
with SU(3)-collective coordinates is generalized for SU(3) skyrmions with
strangeness content different from zero. Quantization of the dipole-type
configuration with large strangeness content found recently is considered as an
example.Comment: 7 pages, 2 figures (available by request
Ulta-slow relaxation in discontinuous-film based electron glasses
We present field effect measurements on discontinuous 2D thin films which are
composed of a sub monolayer of nano-grains of Au, Ni, Ag or Al. Like other
electron glasses these systems exhibit slow conductance relaxation and memory
effects. However, unlike other systems, the discontinuous films exhibit a
dramatic slowing down of the dynamics below a characteristic temperature .
is typically between 10-50K and is sample dependent. For the
sample exhibits a few other peculiar features such as repeatable conductance
fluctuations in millimeter size samples. We suggest that the enhanced system
sluggishness is related to the current carrying network becoming very dilute in
discontinuous films so that the system contains many parts which are
electrically very weakly connected and the transport is dominated by very few
weak links. This enables studying the glassy properties of the sample as it
transitions from a macroscopic sample to a mesocopic sample, hence, the results
provide new insight on the underlying physics of electron glasses.Comment: 4 pages, 4 figure
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