Biomedical subjects

D Vrinceanu

Publications and source records attributed to D Vrinceanu.

5 recordsLinked to original sources

PubMed2005

Molecular-dynamics simulations of cold antihydrogen formation in strongly magnetized plasmas.

Employing a high-order symplectic integrator and an adaptive time-step algorithm, we perform molecular-dynamics simulations of antihydrogen formation, in a cold plasma confined by a strong magnetic field, over time scales of microseconds. Sufficient positron-antiproton recombination events occur to allow a statistical analysis for various properties of the formed antihydrogen atoms. Giant-dipole states are formed in the initial stage of recombination. In addition to neutral atoms, we also observe antihydrogen positive ions (H(+)), in which two positrons simultaneously bind to an antiproton.

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PubMed2004

Strongly magnetized antihydrogen and its field ionization.

Internal orbits of experimentally analyzed antihydrogen (H) atoms depend as much on an external magnetic field as on the Coulomb force. A circular "guiding center atom" model is used to understand their field ionization. This useful model, assumed in the theory of three-body H recombination so far, ignores the important coupling between internal and center-of-mass motion. A conserved pseudomomentum, effective potential, saddle point analysis, and numerical simulation show where the simple model is valid and classify the features of the general case, including "giant dipole states."

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PubMed2001

Exchange forces in dispersion relations investigated using circuit relations.

We propose a novel method to compute in an exact manner the left-hand cut discontinuity of the electron-atom partial wave scattering amplitude in the complex energy plane within the static exchange approximation. Zero energy dispersion relations for electron-hydrogen scattering are computed numerically for illustration.

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PubMed2000

Classical stark mixing at ultralow collision energies

Exact solutions of the time-dependent classical equations are obtained for the full array of angular momentum mixing transitions nl-->nl(') in atomic hydrogen induced by collisions with charged particles at ultralow energies. A novel classical expression for the transition probability P(l(')l) is presented. The exact classical results for P(l(')l)(alpha) as a function of l,l(') and the Stark parameter alpha agree exceptionally well with (exact) quantal results. They complement the quantal results by revealing essential characteristics which remain obscured in the quantal treatment.

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PubMed2000

Quantal-classical correspondence impulse theory

The quantal impulse cross section is derived in a novel form appropriate for direct classical correspondence. The classical impulse cross section is then uniquely defined and yields the first general classical expression for nl-n(')l(') collisional transitions. The derived cross sections satisfy the optical theorem and detailed balance. Direct connection with the classical binary encounter approximation is also firmly established. The unified method introduced is general in its application to various collision and recombination processes and enables new directions of enquiry to be pursued quite succinctly.

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