5,303 research outputs found
Excited heavy tetraquarks with hidden charm
The masses of the excited heavy tetraquarks with hidden charm are calculated
within the relativistic diquark-antidiquark picture. The dynamics of the light
quark in a heavy-light diquark is treated completely relativistically. The
diquark structure is taken into account by calculating the diquark-gluon form
factor. New experimental data on charmonium-like states above open charm
threshold are discussed. The obtained results indicate that X(3872), Y(4260),
Y(4360), Z(4248), Z(4433) and Y(4660) could be tetraquark states with hidden
charm.Comment: 11 page
Interpretation of x-ray-absorption dichroism experiments
A rule is derived to use x-ray magnetic circular dichroism spectra to extract the magnetic moment of the conduction-band states with j= l -1/2 separately from those with j= l + 1/2 as a function of energy. This quantity is straightforward to determine from the electronic band structure. The rule is illustrated with an application to pure iron and to the random substitutional alloy Fe_{80}CO_{20}
Symmetric Versus Nonsymmetric Structure of the Phosphorus Vacancy on InP(110)
The atomic and electronic structure of positively charged P vacancies on
InP(110) surfaces is determined by combining scanning tunneling microscopy,
photoelectron spectroscopy, and density-functional theory calculations. The
vacancy exhibits a nonsymmetric rebonded atomic configuration with a charge
transfer level 0.75+-0.1 eV above the valence band maximum. The scanning
tunneling microscopy (STM) images show only a time average of two degenerate
geometries, due to a thermal flip motion between the mirror configurations.
This leads to an apparently symmetric STM image, although the ground state
atomic structure is nonsymmetric.Comment: 5 pages including 3 figures. related publications can be found at
http://www.fhi-berlin.mpg.de/th/paper.htm
Sulfur and Methionine Supplementation With Soybean Meal and Urea for Feedlot Lambs
Some experiments have shown that the sulfur containing amino acids are the first limiting ones where urea furnishes a major part of the dietary nitrogren. Rumen microorganisms can synthesize the sulfur containing amino acids when there is an adequate level of sulfur in the diet The objectives of the experiments reported herein were to compare diets using soybean meal or urea as the supplemental protein for growing and finishing lambs and to test the value of an added methionine and various levels and sources of supplemental sulfur
Zeranol or Diethylstilbestrol Implants for Feedlot Lambs
Less research has been conducted with lambs than with cattle where zeranol has been compared to a control group and to a DES-implanted group. With the removal of DES as an additive to the feed or as an implant, there is more interest in possible substitue products. While response of feedlot lambs to DES is of no practical concern at present, results from zeranol in comparison to DES give a more thorough evaluation of the product than studies with a comparison to only a control group. Two such experiments have been completed and are reported herein
Moving boundary approximation for curved streamer ionization fronts: Solvability analysis
The minimal density model for negative streamer ionization fronts is
investigated. An earlier moving boundary approximation for this model consisted
of a "kinetic undercooling" type boundary condition in a Laplacian growth
problem of Hele-Shaw type. Here we derive a curvature correction to the moving
boundary approximation that resembles surface tension. The calculation is based
on solvability analysis with unconventional features, namely, there are three
relevant zero modes of the adjoint operator, one of them diverging;
furthermore, the inner/outer matching ahead of the front has to be performed on
a line rather than on an extended region; and the whole calculation can be
performed analytically. The analysis reveals a relation between the fields
ahead and behind a slowly evolving curved front, the curvature and the
generated conductivity. This relation forces us to give up the ideal
conductivity approximation, and we suggest to replace it by a constant
conductivity approximation. This implies that the electric potential in the
streamer interior is no longer constant but solves a Laplace equation; this
leads to a Muskat-type problem.Comment: 22 pages, 6 figure
Turbulent Cooling Flows in Molecular Clouds
We propose that inward, subsonic flows arise from the local dissipation of
turbulent motions in molecular clouds. Such "turbulent cooling flows" may
account for recent observations of spatially extended inward motions towards
dense cores. These pressure-driven flows may arise from various types of
turbulence and dissipation mechanisms. For the example of MHD waves and
turbulence damped by ion-neutral friction, sustained cooling flow requires that
the outer gas be sufficiently turbulent, that the inner gas have marginal
field-neutral coupling, and that this coupling decrease sufficiently rapidly
with increasing density. These conditions are most likely met at the transition
between outer regions ionized primarily by UV photons and inner regions ionized
primarily by cosmic rays. If so, turbulent cooling flows can help form dense
cores, with speeds faster than expected for ambipolar diffusion. Such motions
could reduce the time needed for dense core formation and could precede and
enhance the motions of star-forming gravitational infall.Comment: To appear ApJL, Nov.10, 4 ApJ style pages, Postscrip
Pion condensation in quark matter with finite baryon density
The phase structure of the Nambu -- Jona-Lasinio model at zero temperature
and in the presence of baryon- and isospin chemical potentials is investigated.
It is shown that in the chiral limit and for a wide range of model parameters
there exist two different phases with pion condensation. In the first, ordinary
phase, quarks are gapped particles. In the second, gapless pion condensation
phase, there is no energy cost for creating only - or both and
quarks, and the density of baryons is nonzero.Comment: 7 pages, 6 figures; two references adde
Observation and theoretical description of the pure Fano-effect in the valence-band photo-emission of ferromagnets
The pure Fano-effect in angle-integrated valence-band photo-emission of
ferromagnets has been observed for the first time. A contribution of the
intrinsic spin polarization to the spin polarization of the photo-electrons has
been avoided by an appropriate choice of the experimental parameters. The
theoretical description of the resulting spectra reveals a complete analogy to
the Fano-effect observed before for paramagnetic transition metals. While the
theoretical photo-current and spin difference spectra are found in good
quantitative agreement with experiment in the case of Fe and Co only a
qualitative agreement could be achieved in the case of Ni by calculations on
the basis of plain local spin density approximation (LSDA). Agreement with
experimental data could be improved in this case in a very substantial way by a
treatment of correlation effects on the basis of dynamical mean field theory
(DMFT).Comment: 11 pages, 3 figures accepted by PR
Analysis of Two-Body Decays of Charmed Baryons Using the Quark-Diagram Scheme
We give a general formulation of the quark-diagram scheme for the nonleptonic
weak decays of baryons. We apply it to all the decays of the antitriplet and
sextet charmed baryons and express their decay amplitudes in terms of the
quark-diagram amplitudes. We have also given parametrizations for the effects
of final-state interactions. For SU(3) violation effects, we only parametrize
those in the horizontal -loop quark diagrams whose contributions are solely
due to SU(3)-violation effects. In the absence of all these effects, there are
many relations among various decay modes. Some of the relations are valid even
in the presence of final-state interactions when each decay amplitude in the
relation contains only a single phase shift. All these relations provide useful
frameworks to compare with future experiments and to find out the effects of
final-state interactions and SU(3) symmetry violations.Comment: 28 pages, 20 Tables in landscape form, 4 figures. Main changes are:
(i) some errors in the Tables and in the relations between the quark-diagram
amplitudes of this paper and those of Ref.[10] are corrected, (ii)
improvements are made in the presentation so that comparisons with previous
works and what have been done to include SU(3) breaking and final-state
interactions are more clearly stated; to appear in the Physical Review
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