84,789 research outputs found
Ultraviolet photonic crystal laser
We fabricated two dimensional photonic crystal structures in zinc oxide films
with focused ion beam etching. Lasing is realized in the near ultraviolet
frequency at room temperature under optical pumping. From the measurement of
lasing frequency and spatial profile of the lasing modes, as well as the
photonic band structure calculation, we conclude that lasing occurs in the
strongly localized defect modes near the edges of photonic band gap. These
defect modes originate from the structure disorder unintentionally introduced
during the fabrication process.Comment: 4 pages, 4 figure
Slow Atomic Motion in Zr-Ti-Cu-Ni-Be Metallic Glasses Studied by NMR
Nuclear magnetic resonance is used for the first time to detect slow atomic motion in metallic glasses, specifically, Be motion in Zr-Ti-Cu-Ni-Be bulk metallic glasses. The observations are not consistent with the vacancy-assisted and interstitial diffusion mechanisms and favor the spread-out free volume fluctuation mechanism for Be diffusion. Comparison with the results of Be diffusion measured by elastic backscattering the NMR results also indicates that the energy barriers for short- and long-range Be motion are the same
An extended finite element method with smooth nodal stress
The enrichment formulation of double-interpolation finite element method
(DFEM) is developed in this paper. DFEM is first proposed by Zheng \emph{et al}
(2011) and it requires two stages of interpolation to construct the trial
function. The first stage of interpolation is the same as the standard finite
element interpolation. Then the interpolation is reproduced by an additional
procedure using the nodal values and nodal gradients which are derived from the
first stage as interpolants. The re-constructed trial functions are now able to
produce continuous nodal gradients, smooth nodal stress without post-processing
and higher order basis without increasing the total degrees of freedom. Several
benchmark numerical examples are performed to investigate accuracy and
efficiency of DFEM and enriched DFEM. When compared with standard FEM,
super-convergence rate and better accuracy are obtained by DFEM. For the
numerical simulation of crack propagation, better accuracy is obtained in the
evaluation of displacement norm, energy norm and the stress intensity factor
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