97 research outputs found
Nucleation and growth of precipitates in demixing glass melts in the system NA2O-CAO-SIO2.
As an example of a first order phase transition with conserved order parameter the demixing of glass-forming quasibinary systems has been investigated by in situ measurement of light scattering during heat treatment. The relative supercooling is consistent with theoretical expectations. Using a two stage heat treatment, nucleation and growth are decoupled. Nuclei formed at a nucleation temperature Tn can grow to sizes detectable by light scattering at a higher temperature Tgr, where no more nuclei are formed. Reducing the nucleation time, one at last ends up with an incubation time, the temperature dependence of which is described by an Arrhenius ansatz. For low particle densities, the growth mechanism can be deduced from the initial increase of the scattering intensity. The proportionality of the latter to t5 is characteristic for diffusion controlled growth of spheres in a depleted zone. From extrema in the scattering a definite size is assigned to the aggregate. Then, the number of particles can be deduced from the absolute intensity. For the systems investigated, however, growth time is limited by the occurrence of crystallisation, thus allowing only the determination of relative nucleation rates
Tunneling Mechanism due to Chaos in a Complex Phase Space
We have revealed that the barrier-tunneling process in non-integrable systems
is strongly linked to chaos in complex phase space by investigating a simple
scattering map model. The semiclassical wavefunction reproduces complicated
features of tunneling perfectly and it enables us to solve all the reasons why
those features appear in spite of absence of chaos on the real plane.
Multi-generation structure of manifolds, which is the manifestation of
complex-domain homoclinic entanglement created by complexified classical
dynamics, allows a symbolic coding and it is used as a guiding principle to
extract dominant complex trajectories from all the semiclassical candidates.Comment: 4 pages, RevTeX, 6 figures, to appear in Phys. Rev.
Chaos assisted instanton tunneling in one dimensional perturbed periodic potential
For the system with one-dimensional spatially periodic potential we
demonstrate that small periodic in time perturbation results in appearance of
chaotic instanton solutions. We estimate parameter of local instability, width
of stochastic layer and correlator for perturbed instanton solutions.
Application of the instanton technique enables to calculate the amplitude of
the tunneling, the form of the spectrum and the lower bound for width of the
ground quasienergy zone
Detection and mobility of hafnium in SiO2
High-angle annular dark-field imaging in scanning transmission electron microscopy and x-ray photoelectron spectroscopy were used to investigate thermal SiO2 layers doped with Hf by ion-implantation. Hf was mobile under the focused electron beam in the asimplanted samples. After annealing for 5 min at 1200 °C, clusters of crystalline HfO2 were observed that were a few nm in size and surrounded by residual Hf that had remained trapped in the SiO2. Hf was not mobile under the electron beam in the annealed samples. Further annealing caused an expansion of the SiO2 that was damaged by ionimplantation. Hf rearrangement was confined to the ion beam damaged regions of the SiO2 layer. No diffusion of Hf into the undamaged SiO2 was observed. The implications of the results for complementary metal-oxide-semiconductor transistors with HfO2 gate dielectrics are discussed
Statistical analysis of scars in stadium billiard
In this paper, by using our improved plane wave decomposition method, we
study the scars in the eigenfunctions of the stadium billiard from very low
state to as high as about the one millionth state. In the systematic searching
for scars of various types, we have used the approximate criterion based on the
quantization of the classical action along the unstable periodic orbit
supporting the scar. We have analized the profile of the integrated probability
density along the orbit. We found that the maximal integrated intensity of
different types of scars scales in different way with the , which
confirms qualitatively and quantitatively the existing theories of scars such
as that of Bogomolny (1988) and that of Robnik (1989).Comment: 22 plain Latex pages, 14 EPS figures (Figs. 4-6, 9,10,12 are
included, others (too large) are availabe upon request.) to appear in J.
Phys. A: Math. & Gen. 31 (1998
An efficient Fredholm method for calculation of highly excited states of billiards
A numerically efficient Fredholm formulation of the billiard problem is
presented. The standard solution in the framework of the boundary integral
method in terms of a search for roots of a secular determinant is reviewed
first. We next reformulate the singularity condition in terms of a flow in the
space of an auxiliary one-parameter family of eigenproblems and argue that the
eigenvalues and eigenfunctions are analytic functions within a certain domain.
Based on this analytic behavior we present a numerical algorithm to compute a
range of billiard eigenvalues and associated eigenvectors by only two
diagonalizations.Comment: 15 pages, 10 figures; included systematic study of accuracy with 2
new figures, movie to Fig. 4,
http://www.quantumchaos.de/Media/0703030media.av
Fresnel filtering in lasing emission from scarred modes of wave-chaotic optical resonators
We study lasing emission from asymmetric resonant cavity (ARC) GaN
micro-lasers. By comparing far-field intensity patterns with images of the
micro-laser we find that the lasing modes are concentrated on three-bounce
unstable periodic ray orbits, i.e. the modes are scarred. The high-intensity
emission directions of these scarred modes are completely different from those
predicted by applying Snell's law to the ray orbit. This effect is due to the
process of ``Fresnel filtering'' which occurs when a beam of finite angular
spread is incident at the critical angle for total internal reflection.Comment: 4 pages, 3 figures (eps), RevTeX 3.1, submitted to Phys. Rev. Lett;
corrected a minor (transcription) erro
Localization of Eigenfunctions in the Stadium Billiard
We present a systematic survey of scarring and symmetry effects in the
stadium billiard. The localization of individual eigenfunctions in Husimi phase
space is studied first, and it is demonstrated that on average there is more
localization than can be accounted for on the basis of random-matrix theory,
even after removal of bouncing-ball states and visible scars. A major point of
the paper is that symmetry considerations, including parity and time-reversal
symmetries, enter to influence the total amount of localization. The properties
of the local density of states spectrum are also investigated, as a function of
phase space location. Aside from the bouncing-ball region of phase space,
excess localization of the spectrum is found on short periodic orbits and along
certain symmetry-related lines; the origin of all these sources of localization
is discussed quantitatively and comparison is made with analytical predictions.
Scarring is observed to be present in all the energy ranges considered. In
light of these results the excess localization in individual eigenstates is
interpreted as being primarily due to symmetry effects; another source of
excess localization, scarring by multiple unstable periodic orbits, is smaller
by a factor of .Comment: 31 pages, including 10 figure
Structure and Sodium Ion Dynamics in Sodium Strontium Silicate Investigated by Multinuclear Solid-State NMR
© 2016 American Chemical Society.The high oxide ion conductivity of the proposed sodium strontium silicate ion conductors Sr0.55Na0.45SiO2.775 (>10-2 S·cm-1 at 525 °C) and its unusual alkali metal substitution strategy have been extensively questioned in the literature. Here, we present a comprehensive understanding of the structure of this material using a combination of XRD and multinuclear 17O, 23Na, and 29Si solid-state NMR spectroscopy data and a detailed investigation of the Na ion dynamics by high temperature 23Na NMR line shape analysis and relaxation rates measurements. Both 23Na and 29Si NMR spectra demonstrate the absence of Na doping in strontium silicate SrSiO3 and the presence of an amorphous phase identified as Na2O·2SiO2 glass as the Na-containing product. Devitrification at 800 °C yields crystallization of the Na2O·2SiO2 glass into the known crystalline α-Na2Si2O5 phase which was positively identified by its XRD pattern and the extensive and clear 17O, 23Na, and 29Si NMR fingerprints. High temperature 23Na NMR reveals that the Na ions are mobile in the Na2O·2SiO2 amorphous component below its glass transition temperature (âŒ450 °C). In contrast, 23Na NMR data obtained on the crystalline α-Na2Si2O5 shows limited Na dynamics below âŒ650 °C, and this result explains the large discrepancy in the conductivity observed in the literature which strongly depends on the thermal history of the Sr0.55Na0.45SiO2.775 material. These insights demonstrate that the high conductivity observed in Sr0.55Na0.45SiO2.775 is due to Na conduction in the Na2O·2SiO2 glass, and this motivates the quest for the discovery of low temperature fast ion conductors in noncrystalline solids
Dynamical Tunneling in Mixed Systems
We study quantum-mechanical tunneling in mixed dynamical systems between
symmetry-related phase space tori separated by a chaotic layer. Considering
e.g. the annular billiard we decompose tunneling-related energy splittings and
shifts into sums over paths in phase space. We show that tunneling transport is
dominated by chaos-assisted paths that tunnel into and out of the chaotic layer
via the ``beach'' regions sandwiched between the regular islands and the
chaotic sea. Level splittings are shown to fluctuate on two scales as functions
of energy or an external parameter: they display a dense sequence of peaks due
to resonances with states supported by the chaotic sea, overlaid on top of slow
modulations arising from resonances with states supported by the ``beaches''.
We obtain analytic expressions which enable us to assess the relative
importance of tunneling amplitudes into the chaotic sea vs. its internal
transport properties. Finally, we average over the statistics of the chaotic
region, and derive the asymptotic tail of the splitting distribution function
under rather general assumptions concerning the fluctuation properties of
chaotic states.Comment: 28 pages, Latex, 16 EPS figure
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