1,983 research outputs found
Analytical study of electrostatic ion beam traps
The use of electrostatic ion beam traps require to set many potentials on the
electrodes (ten in our case), making the tuning much more difficult than with
quadrupole traps. In order to obtain the best trapping conditions, an
analytical formula giving the electrostatic potential inside the trap is
required. In this paper, we present a general method to calculate the
analytical expression of the electrostatic potential in any axisymmetric set of
electrodes. We use conformal mapping to simplify the geometry of the boundary.
The calculation is then performed in a space of simple geometry. We show that
this method, providing excellent accuracy, allows to obtain the potential on
the axis as an analytic function of the potentials applied to the electrodes,
thus leading to fast, accurate and efficient calculations. We conclude by
presenting stability maps depending on the potentials that enabled us to find
the good trapping conditions for oxygen 4+ at much higher energies than what
has been achieved until now.Comment: 9 page
Relativistic transition wavelenghts and probabilities for spectral lines of Ne II
Transition wavelengths and probabilities for several 2p4 3p - 2p4 3s and 2p4
3d - 2p4 3p lines in fuorine-like neon ion (NeII) have been calculated within
the multiconfiguration Dirac-Fock (MCDF) method with quantum electrodynamics
(QED) corrections. The results are compared with all existing experimental and
theoretical data
Formality and Star Products
These notes, based on the mini-course given at the PQR2003 Euroschool held in
Brussels in 2003, aim to review Kontsevich's formality theorem together with
his formula for the star product on a given Poisson manifold. A brief
introduction to the employed mathematical tools and physical motivations is
also given.Comment: 49 pages, 9 figures; proceedings of the PQR2003 Euroschool. Version 2
has minor correction
Minimum energy paths for conformational changes of viral capsids
In this work we study how a viral capsid can change conformation using
techniques of Large Deviations Theory for stochastic differential equations.
The viral capsid is a model of a complex system in which many units - the
proteins forming the capsomers - interact by weak forces to form a structure
with exceptional mechanical resistance. The destabilization of such a structure
is interesting both per se, since it is related either to infection or
maturation processes, and because it yields insights into the stability of
complex structures in which the constitutive elements interact by weak
attractive forces. We focus here on a simplified model of a dodecahederal viral
capsid, and assume that the capsomers are rigid plaquettes with one degree of
freedom each. We compute the most probable transition path from the closed
capsid to the final configuration using minimum energy paths, and discuss the
stability of intermediate states.Comment: 27 pages, 4 figures. New version, to appear in Physical Review
Atomic Energy Levels with QED and Contribution of the Screened Self-Energy
We present an introduction to the principles behind atomic energy level
calculations with Quantum Electrodynamics (QED) and the two-time Green's
function method; this method allows one to calculate an effective Hamiltonian
that contains all QED effects and that can be used to predict QED Lamb shifts
of degenerate, quasidegenerate and isolated atomic levels.Comment: 4 pages, 6 figures, summary of a talk given at the QED2000 Conference
held in Trieste, Italy in Oct. 200
Degrees of freedom effect on fragmentation in tandem mass spectrometry of singly charged supramolecular aggregates of sodium sulfonates
The characteristic collision energy (CCE) to obtain 50% fragmentation of positively and negatively single charged non-covalent clusters has been measured. CCE was found to increase linearly with the degrees of freedom (DoF) of the precursor ion, analogously to that observed for synthetic polymers. This suggests that fragmentation behavior (e.g. energy randomization) in covalent molecules and clusters are similar. Analysis of the slope of CCE with molecular size (DoF) indicates that activation energy of fragmentation of these clusters (loss of a monomer unit) is similar to that of the lowest energy fragmentation of protonated leucine-enkephalin. Positively and negatively charged aggregates behave similarly, but the slope of the CCE vs DoF plot is steeper for positive ions, suggesting that these are more stable than their negative counterparts
Hyperfine Quenching of the Level in Zn-like Ions
In this paper, we used the multiconfiguration Dirac-Fock method to compute
with high precision the influence of the hyperfine interaction on the
level lifetime in Zn-like ions for stable and some
quasi-stable isotopes of nonzero nuclear spin between Z=30 and Z=92. The
influence of this interaction on the separation energy is also calculated for the same ions
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