High-resolution Regime Research Articles

Multiple Description Quantization Via Gram–Schmidt Orthogonalization

The multiple description (MD) problem has received considerable attention as a model of information transmission over unreliable channels. A general framework for designing efficient multiple description quantization schemes is proposed in this paper. We provide a systematic treatment of the El Gamal-Cover (EGC) achievable MD rate-distortion region, and show that any point in the EGC region can be achieved via a successive quantization scheme along with quantization splitting. For the quadratic Gaussian case, the proposed scheme has an intrinsic connection with the Gram-Schmidt orthogonalization, which implies that the whole Gaussian MD rate-distortion region is achievable with a sequential dithered lattice-based quantization scheme as the dimension of the (optimal) lattice quantizers becomes large. Moreover, this scheme is shown to be universal for all i.i.d. smooth sources with performance no worse than that for an i.i.d. Gaussian source with the same variance and asymptotically optimal at high resolution. A class of low-complexity MD scalar quantizers in the proposed general framework also is constructed and is illustrated geometrically; the performance is analyzed in the high resolution regime, which exhibits a noticeable improvement over the existing MD scalar quantization schemes.

In situ High-Resolution Electron Microscopy

The strength of in situ electron microscopy lies in its ability to observe directly material changes which are pertinent to bulk processes. The most rigorous experiments employ a purpose-built specimen holder to simulate specific testing conditions (e.g. heating, cooling, straining, environment), with the associated microstructural changes deduced from appropriate micrographs, diffraction patterns or video-recordings. The influence of the electron microscope itself must always be taken into account (e.g. thin-foil specimen, large electron flux, high electron energy). However when artifacts are overcome, remarkable insight into the mechanisms of the behavior of solids can be achieved. The purpose of this article is to review our work in extending this capability into the high-resolution regime, so that atomic reactions can be followed. In the right circumstances this allows straightforward interpretation of atomic-scale phenomena.Our studies have employed a Philips EM430ST, 300 kV transmission electron microscope (TEM) with about 0.2 nm resolution. To-date we have carried out only heating experiments, utilizing the standard side-entry, single-tilt specimen holder (model number PW 6592), mainly on reactions at semiconductor interfaces. The zone axis orientation necessary for high-resolution TEM is obtained by careful sectioning of the substrate crystals and judicious positioning in the heating holder. The imaging conditions (including drift) can be optimized at a temperature slightly below that required for the changes of interest, so that recording can be initiated immediately on ramping up.

Inelastic X-ray scattering with synchrotron radiation: The scientific case, current experiments and projects

When applying inelastic X-ray scattering in condensed matter physics, one can distinguish three regimes with very different requirements on primary energy, magnitude of energy- and momentum-transfer, and energy resolution: the Compton regime (measurement of electron momentum distribution), the characteristic energy loss regime (information about collective and individual excitations of electron systems), and the high energy resolution regime (phonon-like excitations). For each regime, the experimental requirements are defined, current experiments are described, and, for the benefit of future projects, optimized combinations of insertion devices, monochromators and analyzers are searched for.