Dimensional Effects on Densities of States and Interactions in Nanostructures

We consider electrons in the presence of interfaces with different effective electron mass, and electromagnetic fields in the presence of a high-permittivity interface in bulk material. The equations of motion for these dimensionally hybrid systems yield analytic expressions for Green’s functions and electromagnetic potentials that interpolate between the two-dimensional logarithmic potential at short distance, and the three-dimensional r−1 potential at large distance. This also yields results for electron densities of states which interpolate between the well-known two-dimensional and three-dimensional formulas. The transition length scales for interfaces of thickness L are found to be of order Lm/2m* for an interface in which electrons move with effective mass m*, and for a dielectric thin film with permittivity in a bulk of permittivity . We can easily test the merits of the formalism by comparing the calculated electromagnetic potential with the infinite series solutions from image charges. This confirms that the dimensionally hybrid models are excellent approximations for distances r ≳ L/2

Hierarchical model fitting to 2D and 3D data

©2006 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.We propose a method for interactively generating a model-based reconstruction of a scene from a set of images. The method facilitates the fitting of multiple object models to the data in a manner that provides the best overall fit to the image set. This requires that models are not fit independently, but rather collectively, each potentially impacting upon the fit of the other.A. van den Hengel, A. Dick, T. Thormahlen, B. Ward, P. H. S. Tor

Sympathetic Cooling of Mixed Species Two-Ion Crystals for Precision Spectroscopy

Sympathetic cooling of trapped ions has become an indispensable tool for quantum information processing and precision spectroscopy. In the simplest situation a single Doppler-cooled ion sympathetically cools another ion which typically has a different mass. We analytically investigate the effect of the mass ratio of such an ion crystal on the achievable temperature limit in the presence of external heating. As an example, we show that cooling of a single Al+ with Be+, Mg+ and Ca+ ions provides similar results for heating rates typically observed in ion traps, whereas cooling ions with a larger mass perform worse. Furthermore, we present numerical simulation results of the rethermalisation dynamics after a background gas collision for the Al+/Ca+ crystal for different cooling laser configurations.Comment: Made Graphics black & white print compatible, clarified abstract and summar

Hot new directions for quasi-Monte Carlo research in step with applications

This article provides an overview of some interfaces between the theory of quasi-Monte Carlo (QMC) methods and applications. We summarize three QMC theoretical settings: first order QMC methods in the unit cube $[0,1]^s$ and in $\mathbb{R}^s$, and higher order QMC methods in the unit cube. One important feature is that their error bounds can be independent of the dimension $s$ under appropriate conditions on the function spaces. Another important feature is that good parameters for these QMC methods can be obtained by fast efficient algorithms even when $s$ is large. We outline three different applications and explain how they can tap into the different QMC theory. We also discuss three cost saving strategies that can be combined with QMC in these applications. Many of these recent QMC theory and methods are developed not in isolation, but in close connection with applications

Sputter Crater Contour Mapping with Multilayered Films

Multilayered films composed of alternating 200 Å Al and 267 Å Al203 layers are made by physical vapor deposition. Twenty-two pairs of these films are deposited on a polished Si wafer. Ion beam sputtering is used to form craters in the multilayered film. When a crater is viewed or photographed in situ by scanning electron microscopy, the Al2O3 layers appear bright and the Al layers appear dark. In the scanning electron microscope (SEM) the Al2O3 layers have a high secondary electron yield compared to Al. In secondary ion mass spectrometry (SIMS), using Cs+ as the ion beam, imaging with O- produces an image with Al2O3 layers appearing white and with Al layers appearing dark. Scanning Auger microscopy (SAM) imaging of oxygen produces the same result. In all cases, the alternating bright and dark layers along the wall of the sputter crater form a contour map. The width of each bright band represents a change of depth corresponding to the thickness of the Al2O3 layer and similarly for the dark Al bands. Therefore, the operator of a SEM, SAM or SIMS unit can determine the depth as well as the shape of a sputter crater in situ by using a multilayered film. The main requirement is that the films be smooth on a scale that is small compared to the thickness of each layer and that alternate films have high contrast in the imaging process

Analytic Approximations for Three Neutrino Oscillation Parameters and Probabilities in Matter

The corrections to neutrino mixing parameters in the presence of matter of constant density are calculated systematically as series expansions in terms of the mass hierarchy \dm{21}/\dm{31}. The parameter mapping obtained is then used to find simple, but nevertheless accurate formulas for oscillation probabibilities in matter including CP-effects. Expressions with one to one correspondence to the vacuum case are derived, which are valid for neutrino energies above the solar resonance energy. Two applications are given to show that these results are a useful and powerful tool for analytical studies of neutrino beams passing through the Earth mantle or core: First, the ``disentanglement problem'' of matter and CP-effects in the CP-asymmetry is discussed and second, estimations of the statistical sensitivity to the CP-terms of the oscillation probabilities in neutrino factory experiments are presented.Comment: 17 pages, 3 figure

Searches for Stable Strangelets in Ordinary Matter: Overview and a Recent Example

Our knowledge on the possible existence in nature of stable exotic particles depends solely upon experimental observation. Guided by this general principle and motivated by theoretical hypotheses on the existence of stable particles of strange quark matter, a variety of experimental searches have been performed. We provide an introduction to the theoretical hypotheses, an overview of the past searches, and a more detailed description of a recent search for helium-like strangelets in the Earth's atmosphere using a sensitive laser spectroscopy method

On spontaneous scalarization

We study in the physical frame the phenomenon of spontaneous scalarization that occurs in scalar-tensor theories of gravity for compact objects. We discuss the fact that the phenomenon occurs exactly in the regime where the Newtonian analysis indicates it should not. Finally we discuss the way the phenomenon depends on the equation of state used to describe the nuclear matter.Comment: 41 pages, RevTex, 10 ps figures, submitted to Phys. Rev.