Appearance of the Single Gyroid Network Phase in Nuclear Pasta Matter

Nuclear matter under the conditions of a supernova explosion unfolds into a rich variety of spatially structured phases, called nuclear pasta. We investigate the role of periodic network-like structures with negatively curved interfaces in nuclear pasta structures, by static and dynamic Hartree-Fock simulations in periodic lattices. As the most prominent result, we identify for the first time the {\it single gyroid} network structure of cubic chiral $I4_123$ symmetry, a well known configuration in nanostructured soft-matter systems, both as a dynamical state and as a cooled static solution. Single gyroid structures form spontaneously in the course of the dynamical simulations. Most of them are isomeric states. The very small energy differences to the ground state indicate its relevance for structures in nuclear pasta.Comment: 7 pages, 4 figure

Structure of steps on As-passivated Si(111): Ab initio calculations and scanning tunneling microscopy

The structures of terrace steps on As-covered Si(111) are examined using ab initio calculations. In scanning tunneling microscope (STM) images, two orientations of steps are found to terminate As-covered Si islands after annealing: [11 (2) over bar] and [(11) over bar2]. Total energy calculations and simulations of STM images yield detailed information on the atomic structures of the steps: In the lowest-energy configuration for both orientations, surplus As atoms replace any exposed Si atoms at the steps. The As atoms rearrange to establish a threefold coordination. For [11 (2) over bar] steps the atom positions of the relaxed configuration are very close to the ideal bulk positions, but for [(11) over bar2] steps the terminating As atoms form dimers in front of the steps. The different atomic structures of the two step orientations clearly show up in the simulated STM images for negative bias (occupied states imaged), the STM images for positive bias (unoccupied states) are much less distinctive. All features of existing experimental positive-bias STM images can be explained by an analysis of the electronic local density of states. With the calculated step energies we construct a phase diagram for the equilibrium shape of As-covered islands. In the accessible range of As chemical potentials between As bulk and As-4 molecules, we expect either triangular islands terminated by [11 (2) over bar] steps or hexagons with long edges of [11 (2) over bar] orientation and short ones with [(11) over bar2] orientation

Generation of multi-modal dialogue for a net environment

In this paper an architecture and special purpose markup language for simulated affective face-to-face communication is presented. In systems based on this architecture, users will be able to watch embodied conversational agents interact with each other in virtual locations on the internet. The markup language, or Rich Representation Language (RRL), has been designed to provide an integrated representation of speech, gesture, posture and facial animation

Metal-Ferroelectric-Metal heterostructures with Schottky contacts I. Influence of the ferroelectric properties

A model for Metal-Ferroelectric-Metal structures with Schottky contacts is proposed. The model adapts the general theories of metal-semiconductor rectifying contacts for the particular case of metal-ferroelectric contact by introducing: the ferroelectric polarization as a sheet of surface charge located at a finite distance from the electrode interface; a deep trapping level of high concentration; the static and dynamic values of the dielectric constant. Consequences of the proposed model on relevant quantities of the Schottky contact such as built-in voltage, charge density and depletion width, as well as on the interpretation of the current-voltage and capacitance-voltage characteristics are discussed in detail.Comment: 14 pages with 4 figures, manuscript under revision at Journal of Applied Physics for more than 1 year (submitted May 2004, first revision September 2004, second revision May 2005

Comparison of Measured and Calculated Specific Resistances of Pd/Pt Interfaces

We compare specific resistances (AR equals area A times resistance R) of sputtered Pd/Pt interfaces measured in two different ways with no-free-parameter calculations. One way gives 2AR(Pd/Pt) of 0.29 (0.03) fohm-m(2) and the other 0.17 (0.13) fohm-m(2). From these we derive a best estimate of 2AR(Pd/Pt) of 0.28 (0.06) fohm-m(2), which overlaps with no-free-parameter calculations: 2AR(predicted) of 0.30 (0.04) fohm-m(2) for flat, perfect interfaces, or 0.33 (0.04) fohm-m(2) for interfaces composed of 2 monolayers of a 50percent-50percent PdPt alloy. These results support three prior examples of agreement between calculations and measurements for pairs of metals having the same crystal structure and the same lattice parameter to within 1 percent. We also estimate the spin-flipping probability at Pd/Pt interfaces as 0.13 (0.08).Comment: 3 pages, 3 figures, submitted for publication New version has corrected value of delta(Pd/Pt

Seeking Sustainability: COSA preliminary analysis of sustainability initiatives in the coffee sector

The growing economic value and consumer popularity of sustainability standards inevitably raise questions about the extent to which their structure and dynamics actually address many environmental, economic and public welfare issues. The Committee on Sustainable Assessment (COSA) was formed, in part, to develop a scientifically credible framework capable of assessing the impacts associated with the adoption of sustainability initiatives. This paper examines the pilot phase of vetting and testing the COSA method, an innovative management tool used to gather and analyze data using economic, environmental and social metrics.sustainability initiatives, standards, organic, fair trade, Rainforest, social, environmental, economic certification

Artifacts with uneven sampling of red noise

The vast majority of sampling systems operate in a standard way: at each tick of a fixed-frequency master clock a digitizer reads out a voltage that corresponds to the value of some physical quantity and translates it into a bit pattern that is either transmitted, stored, or processed right away. Thus signal sampling at evenly spaced time intervals is the rule: however this is not always the case, and uneven sampling is sometimes unavoidable. While periodic or quasi-periodic uneven sampling of a deterministic signal can reasonably be expected to produce artifacts, it is much less obvious that the same happens with noise: here I show that this is indeed the case only for long-memory noise processes, i.e., power-law noises $1/f^\alpha$ with $\alpha > 2$. The resulting artifacts are usually a nuisance although they can be eliminated with a proper processing of the signal samples, but they could also be turned to advantage and used to encode information.Comment: 5 figure