32 research outputs found
Fast Computation of Voigt Functions via Fourier Transforms
This work presents a method of computing Voigt functions and their
derivatives, to high accuracy, on a uniform grid. It is based on an adaptation
of Fourier-transform based convolution. The relative error of the result
decreases as the fourth power of the computational effort. Because of its use
of highly vectorizable operations for its core, it can be implemented very
efficiently in scripting language environments which provide fast vector
libraries. The availability of the derivatives makes it suitable as a function
generator for non-linear fitting procedures.Comment: 8 pages, 1 figur
A probability-conserving cross-section biasing mechanism for variance reduction in Monte Carlo particle transport calculations
In Monte Carlo particle transport codes, it is often important to adjust
reaction cross sections to reduce the variance of calculations of relatively
rare events, in a technique known as non-analogous Monte Carlo. We present the
theory and sample code for a Geant4 process which allows the cross section of a
G4VDiscreteProcess to be scaled, while adjusting track weights so as to
mitigate the effects of altered primary beam depletion induced by the cross
section change. This makes it possible to increase the cross section of nuclear
reactions by factors exceeding 10^4 (in appropriate cases), without distorting
the results of energy deposition calculations or coincidence rates. The
procedure is also valid for bias factors less than unity, which is useful, for
example, in problems that involve computation of particle penetration deep into
a target, such as occurs in atmospheric showers or in shielding
Enhanced adhesion of films to semiconductors or metals by high energy bombardment
Films (12) of a metal such as gold or other non-insulator materials are firmly bonded to other non-insulators such as semiconductor substrates (10), suitably silicon or gallium arsenide by irradiating the interface with high energy ions. The process results in improved adhesion without excessive doping and provides a low resistance contact to the semiconductor. Thick layers can be bonded by depositing or doping the interfacial surfaces with fissionable elements or alpha emitters. The process can be utilized to apply very small, low resistance electrodes (78) to light-emitting solid state laser diodes (60) to form a laser device 70
Device-Orientation Effects on Multiple-Bit Upset in 65-nm SRAMs
Heavy ion irradiations have been performed: a) SEU varies little with angle of ion incidence b) MBU depend on the device orientation. The MBU response depends on the well orientation of the device. MRED simulation of an omni-directional GEO environment shows the MBU response to be a combination of response from different orientations. Testing and simulation must account for multiple orientations