671 research outputs found
Peculiar Features of the Interaction Potential between Hydrogen and Antihydrogen at Intermediate Separations
We evaluate the interaction potential between a hydrogen and an antihydrogen
using the second-order perturbation theory within the framework of the
four-body system in a separable two-body basis. We find that the H-Hbar
interaction potential possesses the peculiar features of a shallow local
minimum located around interatomic separations of r ~ 6 a.u. and a barrier
rising at r~5 a.u. Additional theoretical and experimental investigations on
the nature of these peculiar features will be of great interest.Comment: 13 pages, 6 figure
Growth Hormone (GH)-Releasing Peptide Stimulation of GH Release from Human Somatotroph Adenoma Cells: Interaction with GH-Releasing Hormone, Thyrotropin- Releasing Hormone, and Octreotide.
The synthetic hexapeptide GH-releasing peptide (GHRP; His-D-Trp-Ala-Trp-D-Phe-Lys-NH2) specifically stimulates GH secretion in humans in vivo and in animals in vitro and in vivo via a still unknown receptor and mechanism. To determine the effect of GHRP on human somatotroph cells in vitro, we stimulated cell cultures derived from 12 different human somatotroph adenomas with GHRP alone and in combination with GH-releasing hormone (GHRH), TRH, and the somatostatin analog octreotide. GH secretion of all 12 adenoma cultures could be stimulated with GHRP, whereas GHRH was active only in 6 adenoma cultures. In GHRH-responsive cell cultures, simultaneous application of GHRH and GHRP had an additive effect on GH secretion. TRH stimulated GH release in 4 of 7 adenoma cultures; in TRH-responsive cell cultures there was also an additive effect of GHRP and TRH on GH secretion. In 5 of 9 adenoma cultures investigated, octreotide inhibited basal GH secretion. In these cell cultures, GHRP-induced GH release was suppressed by octreotide. In 5 of 5 cases, the protein kinase-C inhibitor phloretin partly inhibited GHRP-stimulated GH release, but not basal GH secretion. In summary, GH secretion was stimulated by GHRP in all somatotroph adenomas investigated, indicating that its unknown receptor and signaling pathway are expressed more consistently in somatotroph adenoma cells than those for GHRH, TRH, and somatostatin. Our data give further evidence that GHRP-stimulated GH secretion is mediated by a receptor different from that for GHRH or TRH, respectively, and that protein kinase-C is involved in the signal transduction pathway. Because human somatotroph adenoma cell cultures respond differently to various neuropeptides (GHRH, TRH, somatostatin, and others), they provide a model for further investigation of the mechanism of action of GHRP-induced GH secretion
Variational calculations for the hydrogen-antihydrogen system with a mass-scaled Born-Oppenheimer potential
The problem of proton-antiproton motion in the --
system is investigated by means of the variational method. We introduce a
modified nuclear interaction through mass-scaling of the Born-Oppenheimer
potential. This improved treatment of the interaction includes the nondivergent
part of the otherwise divergent adiabatic correction and shows the correct
threshold behavior.
Using this potential we calculate the vibrational energy levels with angular
momentum 0 and 1 and the corresponding nuclear wave functions, as well as the
S-wave scattering length. We obtain a full set of all bound states together
with a large number of discretized continuum states that might be utilized in
variational four-body calculations. The results of our calculations gives an
indication of resonance states in the hydrogen-antihydrogen system
Surfaces immersed in su(N+1) Lie algebras obtained from the CP^N sigma models
We study some geometrical aspects of two dimensional orientable surfaces
arrising from the study of CP^N sigma models. To this aim we employ an
identification of R^(N(N+2)) with the Lie algebra su(N+1) by means of which we
construct a generalized Weierstrass formula for immersion of such surfaces. The
structural elements of the surface like its moving frame, the Gauss-Weingarten
and the Gauss-Codazzi-Ricci equations are expressed in terms of the solution of
the CP^N model defining it. Further, the first and second fundamental forms,
the Gaussian curvature, the mean curvature vector, the Willmore functional and
the topological charge of surfaces are expressed in terms of this solution. We
present detailed implementation of these results for surfaces immersed in su(2)
and su(3) Lie algebras.Comment: 32 pages, 1 figure; changes: major revision of presentation,
clarifications adde
Large dimension Configuration Interaction calculations of positron binding to the group II atoms
The Configuration Interaction (CI) method is applied to the calculation of
the structures of a number of positron binding systems, including e+Be, e+Mg,
e+Ca and e+Sr. These calculations were carried out in orbital spaces containing
about 200 electron and 200 positron orbitals up to l = 12. Despite the very
large dimensions, the binding energy and annihilation rate converge slowly with
l, and the final values do contain an appreciable correction obtained by
extrapolating the calculation to the l to infinity limit. The binding energies
were 0.00317 hartree for e+Be, 0.0170 hartree for e+Mg, 0.0189 hartree for
e+Ca, and 0.0131 hartree for e+Sr.Comment: 13 pages, no figs, revtex format, Submitted to PhysRev
Calculation of the positron bound state with the copper atom
A new relativistic method for calculation of positron binding to atoms is
presented. The method combines a configuration interaction treatment of the
valence electron and the positron with a many-body perturbation theory
description of their interaction with the atomic core. We apply this method to
positron binding by the copper atom and obtain the binding energy of 170 meV (+
- 10%). To check the accuracy of the method we use a similar approach to
calculate the negative copper ion. The calculated electron affinity is 1.218
eV, in good agreement with the experimental value of 1.236 eV. The problem of
convergence of positron-atom bound state calculations is investigated, and
means to improve it are discussed. The relativistic character of the method and
its satisfactory convergence make it a suitable tool for heavier atoms.Comment: 15 pages, 5 figures, RevTe
Multipositronic systems
The stability of Coulombic systems containing positrons are investigated by
the stochastic variational method. The existence of several new exotic atoms
are predicted, including HPse+, LiPs2e+, or (H-,Ps2). Similar systems
(replacing the positrons by holes) might be observed in semiconductors.Comment: Phys. Rev. Lett., in pres
Resonant Phenomena in Antihydrogen-Hydrogen Scattering
We present a treatment of cold hydrogen-antihydrogen collisions based on the
asymptotic properties of atom-antiatom interactions. We derive general formulas
for the elastic and inelastic cross sections and for the scattering lengths and
analyze their sensitivity to the parameters characterizing the inelasticity of
the collision process. Given the inelasticity, we obtain bounds for the complex
scattering length. We investigate the influence of strong nuclear forces and
the isotope effects in and collisions
and demonstrate enhancement of these effects due to the presence of the
near-threshold narrow () states. The
values of the elastic and inelastic cross-sections with simultaneous account of
rearrangement and strong forces are presented. General expressions for the
(complex) energies of the near-threshold states are
obtained.Comment: 26 pages 7 figure
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