Metastable phases in HxLi1-xTaO3 waveguide layers and pure LiTaO3

The formation of high-temperature phases in low-doped H:LiTaO₃ waveguide layers in Z-cut LiTaO₃ has been observed both by refractive-index and IR-spectra measurements. This permits us to correlate the index jumps to the changes of the OH bonds in the crystal lattice. Reversible phase transitions were detected in the temperature interval T=50–200 °C over a wide range of hydrogen content including as-grown LiTaO₃. The high-temperature phases are metastable close to room temperature. This was demonstrated by tracing the time evolution of the refractive-index change. It was shown that the high-temperature phases are responsible for the long-term refractive-index instabilities in both H:LiTaO₃ waveguides and virgin LiTaO₃. Received: 7 May 2001 / Revised version: 10 August 2001 / Published online: 30 October 2001     

Multistability of Spiking Regimes in a Model of a Laser with Delayed-Feedback

Radiophysics and Quantum Electronics - We use the methods of asymptotic analysis to obtain finite-dimensional maps, whose dynamics determines the dynamics of relaxation oscillations in a laser...     

GROWTH AND SPECTROSCOPIC INVESTIGATIONS OF Na2W2O7 SINGLE CRYSTALS DOPED WITH CERIUM AND CHROMIUM IONS

Journal of Structural Chemistry - Alkaline tungstate crystals are promising scintillation materials for rare events search, especially for WIMP investigations. Na2W2O7 single crystals doped with...     

Discussion

Abstract

Visualization is increasingly being recognized as an effective and efficient way not only to communicate patterns in scientific data, but to discover them as well. In the low dimensions of everyday experience, the human ability to find meaningful order in noisy data may never be matched by automatons. So the introduction of a useful visualization procedure, as provided here by Furnas and Buja, is indeed a welcome development. They show that low-dimensional patterns extracted by a combined projection and section operation (a prosection) can imply the existence of similar higher-dimensional structure. In exploratory or inductive data analyses, then, prosections could be used to generate hypotheses about relationships between sampled variables. However, the familiar curse of dimensionality may confine their practical application to point clouds of only moderate dimension.     

Solving the controllability problem for a nonlinear three-dimensional system

The controllability problem is solved for a nonlinear system of three differential equations that simulates aerated biological wastewater treatment using the thermal metabolism of thermophilic aerobic bacteria. Properties of the phase variables of such a system, bounded and continuable to a given segment, are established. The corresponding attainability set is parameterized by the switching instants of piecewise-constant controls. Parameterization helps reduce the controllability problem for the relevant system to finite dimensional conditional minimization of the auxiliary function. The results from numerical calculations for the solution to the initial problem are given.     

Nanoscale peculiarities of the thermally stimulated surface autosegregation of covalent crystals: Gallium arsenide

Nanoscale changes in the morphology and elemental composition of cleavage surfaces of gallium arsenide crystals, which arise due to thermally stimulated surface autosegregation, are investigated in detail and systematized. It is shown that, depending on the annealing conditions (temperature, duration, and evacuation), gallium arsenide dissociates, forming submicron nonstoichiometric layers on the surface or local phases of arsenic, gallium, and gallium oxide. The mechanism and nature of autosegregation are determined by the competing processes of arsenic sublimation and its surface diffusion with an activation energy of ～31 kJ/mol. The migration of arsenic atoms is described with the help of a crystallochemical model. The nanomorphology of the surface phases includes arsenic and gallium nanoparticles with sizes of 10-200 nm, their agglomerates, and gallium oxide nano- and microcrystallites combined in plate- and chainlike configurations.     

X-Ray fluorescence analysis using synchrotron radiation of manganese minerals from marine and lake bottom sediments

We perform X-ray fluorescence analysis of ferromanganese crusts from regions of the Okhotsk and Bering Seas and the Lake Miassovo (Southern Urals) with different geological structures using synchrotron radiation combined with X-ray diffraction and infrared spectroscopy (SR XRF). The consistency of the minor element composition to the structural patterns of manganese minerals of investigated samples is demonstrated.     

Link distance and shortest path problems in the plane

This paper describes algorithms to compute Voronoi diagrams, shortest path maps, the Hausdorff distance, and the Fréchet distance in the plane with polygonal obstacles. The underlying distance measures for these algorithms are either shortest path distances or link distances. The link distance between a pair of points is the minimum number of edges needed to connect the two points with a polygonal path that avoids a set of obstacles. The motivation for minimizing the number of edges on a path comes from robotic motions and wireless communications because turns are more difficult in these settings than straight movements.Link-based Voronoi diagrams are different from traditional Voronoi diagrams because a query point in the interior of a Voronoi face can have multiple nearest sites. Our site-based Voronoi diagram ensures that all points in a face have the same set of nearest sites. Our distance-based Voronoi diagram ensures that all points in a face have the same distance to a nearest site.The shortest path maps in this paper support queries from any source point on a fixed line segment. This is a middle-ground approach because traditional shortest path maps typically support queries from either a fixed point or from all possible points in the plane.The Hausdorff distance and Fréchet distance are fundamental similarity metrics for shape matching. This paper shows how to compute new variations of these metrics using shortest paths or link-based paths that avoid polygonal obstacles in the plane.     

Titania nanotubes,nanorods and nanopowder in the carbon monoxide oxidation process

Nanotubes, nanorods and nanopowders of hydrated titanium dioxide were studied with respect to their catalytic activity in a model reaction of CO oxidation. It was found that it is the nanotubular form characterized by distorted layered structure that demonstrates outstanding results in catalysis compared to all other forms.