219 research outputs found
Characterization of Strontium Oxide Layers on Silicon for CMOS High-K Gate Stack Scaling
Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7-August 11, 201
A stacking-fault based microscopic model for platelets in diamond
We propose a new microscopic model for the planar defects in
diamond commonly called platelets. This model is based on the formation of a
metastable stacking fault, which can occur because of the ability of carbon to
stabilize in different bonding configurations. In our model the core of the
planar defect is basically a double layer of three-fold coordinated
carbon atoms embedded in the common diamond structure. The properties of
the model were determined using {\it ab initio} total energy calculations. All
significant experimental signatures attributed to the platelets, namely, the
lattice displacement along the direction, the asymmetry between the
and the directions, the infrared absorption peak
, and broad luminescence lines that indicate the introduction of
levels in the band gap, are naturally accounted for in our model. The model is
also very appealing from the point of view of kinetics, since naturally
occurring shearing processes will lead to the formation of the metastable
fault.Comment: 5 pages, 4 figures. Submitted for publication on August 2nd, 200
The prismatic Sigma 3 (10-10) twin bounday in alpha-Al2O3 investigated by density functional theory and transmission electron microscopy
The microscopic structure of a prismatic twin
boundary in \aal2o3 is characterized theoretically by ab-initio
local-density-functional theory, and experimentally by spatial-resolution
electron energy-loss spectroscopy in a scanning transmission electron
microscope (STEM), measuring energy-loss near-edge structures (ELNES) of the
oxygen -ionization edge. Theoretically, two distinct microscopic variants
for this twin interface with low interface energies are derived and analysed.
Experimentally, it is demonstrated that the spatial and energetical resolutions
of present high-performance STEM instruments are insufficient to discriminate
the subtle differences of the two proposed interface variants. It is predicted
that for the currently developed next generation of analytical electron
microscopes the prismatic twin interface will provide a promising benchmark
case to demonstrate the achievement of ELNES with spatial resolution of
individual atom columns
Density functional theory calculations of the carbon ELNES of small diameter armchair and zigzag nanotubes: core-hole, curvature and momentum transfer orientation effects
We perform density functional theory calculations on a series of armchair and
zigzag nanotubes of diameters less than 1nm using the all-electron
Full-Potential(-Linearised)-Augmented-Plane-Wave (FPLAPW) method. Emphasis is
laid on the effects of curvature, the electron beam orientation and the
inclusion of the core-hole on the carbon electron energy loss K-edge. The
electron energy loss near-edge spectra of all the studied tubes show strong
curvature effects compared to that of flat graphene. The curvature induced
hybridisation is shown to have a more drastic effect on the
electronic properties of zigzag tubes than on those of armchair tubes. We show
that the core-hole effect must be accounted for in order to correctly reproduce
electron energy loss measurements. We also find that, the energy loss near edge
spectra of these carbon systems are dominantly dipole selected and that they
can be expressed simply as a proportionality with the local momentum projected
density of states, thus portraying the weak energy dependence of the transition
matrix elements. Compared to graphite, the ELNES of carbon nanotubes show a
reduced anisotropy.Comment: 25 pages, 15 figures, revtex4 submitted for publication to Phys. Rev.
Controlling on-demand gastric acidity in obese subjects: a randomized, controlled trial comparing a single dose of 20Â mg rabeprazole and 20Â mg omeprazole
Excellent outcomes of laparoscopic esophagomyotomy for achalasia in patients older than 60Â years of age
The effectiveness of an esophagomyotomy for dysphagia in elderly patients with achalasia has been questioned. This study was designed to provide an answer.
A total of 162 consecutive patients with achalasia who had a laparoscopic myotomy and Dor fundoplication and who were available for follow-up interview were divided by age: <60Â years (range, 14â59; 118 patients), and â„60Â years (range, 60â93; 44 patients). Primary outcome measures were severity of dysphagia, regurgitation, heartburn, and chest pain before and after the operation as assessed on a four-point Likert scale, and the need for postoperative dilatation or revisional surgery.
Follow-up averaged 64Â months. Older patients had less dysphagia (mean score 3.6 vs. 3.9; PÂ <Â 0.01) and less chest pain (1.0 vs. 1.8; PÂ <Â 0.01). Regurgitation (3.0 vs. 3.2; PÂ =Â not significant (NS)) and heartburn (1.6 vs. 2.0, PÂ =Â NS) were similar. Older patients were no different in degree of esophageal dilation, manometric findings, number of previous pneumatic dilatations, or previous botulinum toxin therapy. None of the older patients had previously had an esophagomyotomy, whereas 14% of younger patients had (PÂ <Â 0.01).
After laparoscopic myotomy, older patients had better relief of dysphagia (mean score 1.0 vs 1.6; PÂ <Â 0.01), less heartburn (0.8 vs. 1.1; PÂ =Â 0.03), and less chest pain (0.2 vs. 0.8, PÂ <Â 0.01). Complication rates were similar. Older patients did not require more postoperative dilatations (22 patients vs. 10 patients; PÂ =Â 0.7) or revisional surgery for recurrent or persistent symptoms (3 vs. 1 patients; PÂ =Â 0.6). Satisfaction scores did not differ, and more than 90% of patients in both groups said in retrospect they would have undergone the procedure if they had known beforehand how it would turn out.
This retrospective review with long follow-up supports laparoscopic esophagomyotomy as first-line therapy in older patients with achalasia. They appeared to benefit even more than younger patients
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