302,686 research outputs found
Fourth Order Gradient Symplectic Integrator Methods for Solving the Time-Dependent Schr\"odinger Equation
We show that the method of splitting the operator
to fourth order with purely positive coefficients produces excellent algorithms
for solving the time-dependent Schr\"odinger equation. These algorithms require
knowing the potential and the gradient of the potential. One 4th order
algorithm only requires four Fast Fourier Transformations per iteration. In a
one dimensional scattering problem, the 4th order error coefficients of these
new algorithms are roughly 500 times smaller than fourth order algorithms with
negative coefficient, such as those based on the traditional Ruth-Forest
symplectic integrator. These algorithms can produce converged results of
conventional second or fourth order algorithms using time steps 5 to 10 times
as large. Iterating these positive coefficient algorithms to 6th order also
produced better converged algorithms than iterating the Ruth-Forest algorithm
to 6th order or using Yoshida's 6th order algorithm A directly.Comment: 11 pages, 2 figures, submitted to J. Chem. Phy
Waveguide cooling system
An improved system is described for cooling high power waveguides by the use of cooling ducts extending along the waveguide, which minimizes hot spots at the flanges where waveguide sections are connected together. The cooling duct extends along substantially the full length of the waveguide section, and each flange at the end of the section has a through hole with an inner end connected to the duct and an opposite end that can be aligned with a flange hole in another waveguide section. Earth flange is formed with a drainage groove in its face, between the through hole and the waveguide conduit to prevent leakage of cooling fluid into the waveguide. The ducts have narrowed sections immediately adjacent to the flanges to provide room for the installation of fasteners closely around the waveguide channel
Multiple Quantum Well AlGaAs Nanowires
This letter reports on the growth, structure and luminescent properties of
individual multiple quantum well (MQW) AlGaAs nanowires (NWs). The composition
modulations (MQWs) are obtained by alternating the elemental flux of Al and Ga
during the molecular beam epitaxy growth of the AlGaAs wire on GaAs (111)B
substrates. Transmission electron microscopy and energy dispersive X-ray
spectroscopy performed on individual NWs are consistent with a configuration
composed of conical segments stacked along the NW axis. Micro-photoluminescence
measurements and confocal microscopy showed enhanced light emission from the
MQW NWs as compared to non-segmented NWs due to carrier confinement and
sidewall passivation
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