Mechanisms of nonstoichiometry in HfN_1-<i>x</i>

Density functional theory is used to calculate defect structures that can accommodate nonstoichiometry in hafnium nitride: HfN1-x, 0 ≤ X ≤ 0.25. It is predicted that a mechanism assuming simple distributions of nitrogen vacancies can accurately describe the variation in the experimentally observed lattice parameter with respect to the nitrogen nonstoichiometry. Although the lattice parameter changes are remarkably small across the whole nonstoichiometry range, the variations in the bulk modulus are much greater

Population Growth and Other Statistics of Middle-sized Irish Towns. General Research Series Paper No. 85, April 1976

The basic aim of the study is the presentation of tables of comparative statistical data relating to 97 towns with population 5OO-1O,OOO in 1971 and analyses of such data. The exclusion of the four County Boroughs and Dun Laoghaire together with twelve other large towns and all small towns and villages, was to impart a degree of homogeneity to the inquiry, as regards function of town. The 97 towns range from Mullingar, the largest with a population of 9,245 to Cootehill with 1,542

Models and Strategies for Variants of the Job Shop Scheduling Problem

Recently, a variety of constraint programming and Boolean satisfiability approaches to scheduling problems have been introduced. They have in common the use of relatively simple propagation mechanisms and an adaptive way to focus on the most constrained part of the problem. In some cases, these methods compare favorably to more classical constraint programming methods relying on propagation algorithms for global unary or cumulative resource constraints and dedicated search heuristics. In particular, we described an approach that combines restarting, with a generic adaptive heuristic and solution guided branching on a simple model based on a decomposition of disjunctive constraints. In this paper, we introduce an adaptation of this technique for an important subclass of job shop scheduling problems (JSPs), where the objective function involves minimization of earliness/tardiness costs. We further show that our technique can be improved by adding domain specific information for one variant of the JSP (involving time lag constraints). In particular we introduce a dedicated greedy heuristic, and an improved model for the case where the maximal time lag is 0 (also referred to as no-wait JSPs).Comment: Principles and Practice of Constraint Programming - CP 2011, Perugia : Italy (2011

Oxygen diffusion in Sr_0.75Y_0.25CoO_2.625: a molecular dynamics study

Oxygen diffusion in Sr0.75Y0.25CoO2.625 is investigated using molecular dynamics simulations in conjunction with an established set of Born model potentials. We predict an activation energy of diffusion for 1.56 eV in the temperature range of 1000-1400 K. We observe extensive disordering of the oxygen ions over a subset of lattice sites. Furthermore, oxygen ion diffusion both in the a-b plane and along the c axis requires the same set of rate-limiting ion hops. It is predicted that oxygen transport in Sr0.75Y0.25CoO2.625 is therefore isotropic

The sub-millimeter properties of broad absorption line quasars

We have carried out the first systematic survey of the sub-millimeter properties of broad absorption line (BAL) quasars. 30 BAL quasars drawn from a homogeneously selected sample from the Sloan Digital Sky Survey at redshifts 2<z<2.6 were observed with the SCUBA array at the JCMT to a typical rms sensitivity of 2.5 mJy. Eight quasars were detected at > 2 sigma significance, four of which are at > 3 sigma significance. The far-infrared luminosities of these quasars are > 10^{13} L_solar. There is no correlation of sub-millimeter flux with either the strength of the broad absorption feature or with absolute magnitude in our sample. We compare the sub-millimeter flux distribution of the BAL quasar sample with that of a sample of quasars which do not show BAL features in their optical spectra and find that the two are indistinguishable. BAL quasars do not have higher sub-millimeter luminosities than non-BAL quasars. These findings are consistent with the hypothesis that all quasars would contain a BAL if viewed along a certain line-of-sight. The data are inconsistent with a model in which the BAL phenomenon indicates a special evolutionary stage which co-incides with a large dust mass in the host galaxy and a high sub-millimeter luminosity. Our work provides constraints on alternative evolutionary explanations of BAL quasars.Comment: 8 pages, 2 figures, ApJ, in pres

Overcoming the false-minima problem in direct methods: Structure determination of the packaging enzyme P4 from bacteriophage φ13

The problems encountered during the phasing and structure determination of the packaging enzyme P4 from bacteriophage φ13 using the anomalous signal from selenium in a single-wavelength anomalous dispersion experiment (SAD) are described. The oligomeric state of P4 in the virus is a hexamer (with sixfold rotational symmetry) and it crystallizes in space group C2, with four hexamers in the crystallographic asymmetric unit. Current state-of-the-art ab initio phasing software yielded solutions consisting of 96 atoms arranged as sixfold symmetric clusters of Se atoms. However, although these solutions showed high correlation coefficients indicative that the substructure had been solved, the resulting phases produced uninterpretable electron-density maps. Only after further analysis were correct solutions found (also of 96 atoms), leading to the eventual identification of the positions of 120 Se atoms. Here, it is demonstrated how the difficulties in finding a correct phase solution arise from an intricate false-minima problem. © 2005 International Union of Crystallography - all rights reserved

The space physics environment data analysis system (SPEDAS)

With the advent of the Heliophysics/Geospace System Observatory (H/GSO), a complement of multi-spacecraft missions and ground-based observatories to study the space environment, data retrieval, analysis, and visualization of space physics data can be daunting. The Space Physics Environment Data Analysis System (SPEDAS), a grass-roots software development platform (www.spedas.org), is now officially supported by NASA Heliophysics as part of its data environment infrastructure. It serves more than a dozen space missions and ground observatories and can integrate the full complement of past and upcoming space physics missions with minimal resources, following clear, simple, and well-proven guidelines. Free, modular and configurable to the needs of individual missions, it works in both command-line (ideal for experienced users) and Graphical User Interface (GUI) mode (reducing the learning curve for first-time users). Both options have “crib-sheets,” user-command sequences in ASCII format that can facilitate record-and-repeat actions, especially for complex operations and plotting. Crib-sheets enhance scientific interactions, as users can move rapidly and accurately from exchanges of technical information on data processing to efficient discussions regarding data interpretation and science. SPEDAS can readily query and ingest all International Solar Terrestrial Physics (ISTP)-compatible products from the Space Physics Data Facility (SPDF), enabling access to a vast collection of historic and current mission data. The planned incorporation of Heliophysics Application Programmer’s Interface (HAPI) standards will facilitate data ingestion from distributed datasets that adhere to these standards. Although SPEDAS is currently Interactive Data Language (IDL)-based (and interfaces to Java-based tools such as Autoplot), efforts are under-way to expand it further to work with python (first as an interface tool and potentially even receiving an under-the-hood replacement). We review the SPEDAS development history, goals, and current implementation. We explain its “modes of use” with examples geared for users and outline its technical implementation and requirements with software developers in mind. We also describe SPEDAS personnel and software management, interfaces with other organizations, resources and support structure available to the community, and future development plans.Published versio

Microwave Absorption of Surface-State Electrons on Liquid 3^3He

We have investigated the intersubband transitions of surface state electrons (SSE) on liquid $^3$He induced by microwave radiation at temperatures from 1.1 K down to 0.01 K. Above 0.4 K, the transition linewidth is proportional to the density of $^3$He vapor atoms. This proportionality is explained well by Ando's theory, in which the linewidth is determined by the electron - vapor atom scattering. However, the linewidth is larger than the calculation by a factor of 2.1. This discrepancy strongly suggests that the theory underestimates the electron - vapor atom scattering rate. At lower temperatures, the absorption spectrum splits into several peaks. The multiple peak structure is partly attributed to the spatial inhomogeneity of the static holding electric field perpendicular to the electron sheet.Comment: 15 pages, 7 figures, submitted to J. Phys. Soc. Jp