3,565 research outputs found
Spectacular Role of Electron Correlation in the Hyperfine Interactions in States in Alkaline Earth Ions
The low-lying n(=3,4,5)d states alkaline earth ions are of vital
importance in a number of different physical applications. The hyperfine
structure constants of these states are characterized by unusually strong
electron correlation effects. Relativistic coupled-cluster theory has been
employed to carry out {\it ab initio} calculations of these constants. The role
of the all order core-polarization effects was found to be decisive in
obtaining good agreement of the results of our calculations with accurate
measurements. The present work is an apt demonstration of the power of the
coupled-cluster method to cope with strongly interacting configurations.Comment: Submitted to Physical Review Letters, 3 figures and 5 table
The PI3K pathway regulates endochondral bone growth through control of hypertrophic chondrocyte differentiation
<p>Abstract</p> <p>Background</p> <p>The majority of our bones develop through the process of endochondral ossification that involves chondrocyte proliferation and hypertrophic differentiation in the cartilage growth plate. A large number of growth factors and hormones have been implicated in the regulation of growth plate biology, however, less is known about the intracellular signaling pathways involved. PI3K/Akt has been identified as a major regulator of cellular proliferation, differentiation and death in multiple cell types.</p> <p>Results and Discussion</p> <p>Employing an organ culture system of embryonic mouse tibiae and LY294002, a pharmacological inhibitor of PI3K, we show that inhibition of the pathway results in significant growth reduction, demonstrating that PI3K is required for normal endochondral bone growth <it>in vitro</it>. PI3K inhibition reduces the length of the proliferating and particularly of the hypertrophic zone. Studies with organ cultures and primary chondrocytes in micromass culture show delayed hypertrophic differentiation of chondrocytes and increased apoptosis in the presence of LY294002. Surprisingly, PI3K inhibition had no strong effect on IGF1-induced bone growth, but partially blocked the anabolic effects of C-type natriuretic peptide.</p> <p>Conclusion</p> <p>Our data demonstrate an essential role of PI3K signaling in chondrocyte differentiation and as a consequence of this, in the endochondral bone growth process.</p
Recoil correction to the bound-electron g factor in H-like atoms to all orders in
The nuclear recoil correction to the bound-electron g factor in H-like atoms
is calculated to first order in and to all orders in . The
calculation is performed in the range Z=1-100. A large contribution of terms of
order and higher is found. Even for hydrogen, the higher-order
correction exceeds the term, while for uranium it is above the
leading correction.Comment: 6 pages, 3 tables, 1 figur
Complete two-loop correction to the bound-electron g factor
Within a systematic approach based on the dimensionally regularized
nonrelativistic quantum electrodynamics, we derive the complete result for the
two-loop correction to order for the factor
of an electron bound in an state of a hydrogenlike ion. The results
obtained significantly improve the accuracy of the theoretical predictions for
the hydrogenlike carbon and oxygen ions and influence the value of the electron
mass inferred from factor measurements.Comment: 11 pages, 1 figur
Toward high-precision values of the self energy of non-S states in hydrogen and hydrogen-like ions
The method and status of a study to provide numerical, high-precision values
of the self-energy level shift in hydrogen and hydrogen-like ions is described.
Graphs of the self energy in hydrogen-like ions with nuclear charge number
between 20 and 110 are given for a large number of states. The self-energy is
the largest contribution of Quantum Electrodynamics (QED) to the energy levels
of these atomic systems. These results greatly expand the number of levels for
which the self energy is known with a controlled and high precision.
Applications include the adjustment of the Rydberg constant and atomic
calculations that take into account QED effects.Comment: Minor changes since previous versio
Technical Note: Mesocosm approach to quantify dissolved inorganic carbon percolation fluxes
Dissolved inorganic carbon (DIC) fluxes across the vadose zone are
influenced by a complex interplay of biological, chemical and physical
factors. A novel soil mesocosm system was evaluated as a tool for providing
information on the mechanisms behind DIC percolation to the groundwater from
unplanted soil. Carbon dioxide partial pressure (<i>p</i>CO<sub>2</sub>), alkalinity, soil
moisture and temperature were measured with depth and time, and DIC in the
percolate was quantified using a sodium hydroxide trap. Results showed good
reproducibility between two replicate mesocosms. The <i>p</i>CO<sub>2</sub> varied between
0.2 and 1.1%, and the alkalinity was 0.1â0.6 meq L<sup>â1</sup>. The measured cumulative
effluent DIC flux over the 78-day experimental period was 185â196 mg L<sup>â1</sup> m<sup>â2</sup> and in the same range as estimates derived from
<i>p</i>CO<sub>2</sub> and alkalinity in samples extracted from the side of the mesocosm
column and the drainage flux. Our results indicate that the mesocosm system
is a promising tool for studying DIC percolation fluxes and other
biogeochemical transport processes in unsaturated environments
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