Secure and Prepared Newsletter, February 10, 2012, Vol. 8, no. 3

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Distorted-wave calculation of cross sections for inner-shell ionization by electron and positron impact

The relativistic distorted-wave Born approximation is used to calculate differential and total cross sections for inner shell ionization of neutral atoms by electron and positron impact. The target atom is described within the independent-electron approximation using the self-consistent Dirac-Fock-Slater potential. The distorting potential for the projectile is also set equal to the Dirac-Fock-Slater potential. For electrons, this guarantees orthogonality of all the orbitals involved and simplifies the calculation of exchange T-matrix elements. The interaction between the projectile and the target electrons is assumed to reduce to the instantaneous Coulomb interaction. The adopted numerical algorithm allows the calculation of differential and total cross sections for projectiles with kinetic energies ranging from the ionization threshold up to about ten times this value. Algorithm accuracy and stability are demonstrated by comparing differential cross sections calculated by our code with the distorting potential set to zero with equivalent results generated by a more robust code that uses the conventional plane-wave Born approximation. Sample calculation results are presented for ionization of K- and L-shells of various elements and compared with the available experimental data.

Secure and Prepared Newsletter, February 24, 2012, Vol. 8, no. 4

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Secure and Prepared Newsletter, March 9, 2012, Vol. 8, no. 5

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Secure and Prepared Newsletter, March 23, 2012, Vol. 8, no. 6

A bi-weekly newsletter for those involved in the fields of homeland security and/or emergency management

Microscopic origin of exchange bias in core/shell nanoparticles

We report the results of Monte Carlo simulations with the aim to clarify the microscopic origin of exchange bias in the magnetization hysteresis loops of a model of individual core/shell nanoparticles. Increase of the exchange coupling across the core/shell interface leads to an enhancement of exchange bias and to an increasing asymmetry between the two branches of the loops which is due to different reversal mechanisms. A detailed study of the magnetic order of the interfacial spins shows compelling evidence that the existence of a net magnetization due to uncompensated spins at the shell interface is responsible for both phenomena and allows to quantify the loop shifts directly in terms of microscopic parameters with striking agreement with the macroscopic observed values.

Secure and Prepared Newsletter, April 6, 2012, Vol. 8, no. 7

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Secure and Prepared Newsletter, May 8, 2012, Vol. 8, no. 8

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Secure and Prepared Newsletter, May 15, 2012, Vol. 8, no. 9

A bi-weekly newsletter for those involved in the fields of homeland security and/or emergency management

Secure and Prepared Newsletter, June 1, 2012, Vol. 8, no. 10

A bi-weekly newsletter for those involved in the fields of homeland security and/or emergency management

Secure and Prepared Newsletter, June 15, 2012, Vol. 8, no. 11

A bi-weekly newsletter for those involved in the fields of homeland security and/or emergency management

Secure and Prepared Newsletter, June 19, 2012, Vol. 8, no. 12

A bi-weekly newsletter for those involved in the fields of homeland security and/or emergency management

Secure and Prepared Newsletter, July 13, 2012, Vol. 8, no. 13

A bi-weekly newsletter for those involved in the fields of homeland security and/or emergency management

Secure and Prepared Newsletter, July 27, 2012, Vol. 8, no. 13

A bi-weekly newsletter for those involved in the fields of homeland security and/or emergency management