188,055 research outputs found
Compositional changes on GaN surfaces under low-energy ion bombardment studied by synchrotron-based spectroscopies
We have investigated compositional changes on GaNsurfaces under Ar-ion bombardment using synchrotron-based high-resolution x-rayphotoemission (PES) and near-edge x-ray absorption fine structure(NEXAFS)spectroscopy. The low-energy ion bombardment of GaN produces a Ga-rich surface layer which transforms into a metallic Ga layer at higher bombarding energies. At the same time, the photoemissionspectra around N 1s core levels reveal the presence of both uncoordinated nitrogen and nitrogen interstitials, which we have analyzed in more details by x-rayabsorption measurements at N K edge. We have demonstrated that PES and NEXAFS provide a powerful combination for studying the compositional changes on GaNsurfaces. A mechanism for the relocation and loss of nitrogen during ion bombardment in agreement with some recent experimental and theoretical studies of defect formation in GaN has been proposed.P.N.K.D. is grateful for the financial
support of the Australian Research Council
Lattice Calculation of Quarkonium Decay Matrix Elements
We calculate the NRQCD matrix elements for the decays of the lowest-lying S-
and P-wave states of charmonium and bottomonium in quenched lattice QCD. We
also compute the one-loop relations between the lattice and continuum matrix
elements.Comment: 10 pages, LaTeX. Talk presented at the Quarkonium Physics Workshop,
University of Illinois, Chicago, June 13-15, 199
Quantum network architecture of tight-binding models with substitution sequences
We study a two-spin quantum Turing architecture, in which discrete local
rotations \alpha_m of the Turing head spin alternate with quantum controlled
NOT-operations. Substitution sequences are known to underlie aperiodic
structures. We show that parameter inputs \alpha_m described by such sequences
can lead here to a quantum dynamics, intermediate between the regular and the
chaotic variant. Exponential parameter sensitivity characterizing chaotic
quantum Turing machines turns out to be an adequate criterion for induced
quantum chaos in a quantum network.Comment: Accepted for publication in J. mod. Optics [Proc. Workshop
"Entanglement and Decoherence", Gargnano (Italy), Sept 1999], 3 figure
The thermopower as a fingerprint of the Kondo breakdown quantum critical point
We propose that the thermoelectric power distinguishes two competing
scenarios for quantum phase transitions in heavy fermions : the
spin-density-wave (SDW) theory and breakdown of the Kondo effect. In the Kondo
breakdown scenario, the Seebeck coefficient turns out to collapse from the
temperature scale , associated with quantum fluctuations of the Fermi
surface reconfiguration. This feature differs radically from the physics of the
SDW theory, where no reconstruction of the Fermi surface occurs, and can be
considered as the hallmark of the Kondo breakdown theory. We test these ideas,
upon experimental results for YbRhSi
Modeling of fluidized bed silicon deposition process
The model is intended for use as a means of improving fluidized bed reactor design and for the formulation of the research program in support of the contracts of Silicon Material Task for the development of the fluidized bed silicon deposition process. A computer program derived from the simple modeling is also described. Results of some sample calculations using the computer program are shown
Glassy dynamics of partially pinned fluids: an alternative mode-coupling approach
We use a simple mode-coupling approach to investigate glassy dynamics of
partially pinned fluid systems. Our approach is different from the
mode-coupling theory developed by Krakoviack [Phys. Rev. Lett. 94, 065703
(2005), Phys. Rev. E 84, 050501(R) (2011)]. In contrast to Krakoviack's theory,
our approach predicts a random pinning glass transition scenario that is
qualitatively the same as the scenario obtained using a mean-field analysis of
the spherical p-spin model and a mean-field version of the random first-order
transition theory. We use our approach to calculate quantities which are often
considered to be indicators of growing dynamic correlations and static
point-to-set correlations. We find that the so-called static overlap is
dominated by the simple, low pinning fraction contribution. Thus, at least for
randomly pinned fluid systems, only a careful quantitative analysis of
simulation results can reveal genuine, many-body point-to-set correlations
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