An Optimal Algorithm for Tiling the Plane with a Translated Polyomino

We give a $O(n)$-time algorithm for determining whether translations of a polyomino with $n$ edges can tile the plane. The algorithm is also a $O(n)$-time algorithm for enumerating all such tilings that are also regular, and we prove that at most $\Theta(n)$ such tilings exist.Comment: In proceedings of ISAAC 201

On the Number of Facets of Three-Dimensional Dirichlet Stereohedra III: Full Cubic Groups

We are interested in the maximum possible number of facets that Dirichlet stereohedra for three-dimensional crystallographic groups can have. The problem for non-cubic groups was studied in previous papers by D. Bochis and the second author (Discrete Comput. Geom. 25:3 (2001), 419-444, and Beitr. Algebra Geom., 47:1 (2006), 89-120). This paper deals with ''full'' cubic groups, while ''quarter'' cubic groups are left for a subsequent paper. Here, ''full'' and ''quarter'' refers to the recent classification of three-dimensional crystallographic groups by Conway, Delgado-Friedrichs, Huson and Thurston (math.MG/9911185, Beitr. Algebra Geom. 42.2 (2001), 475-507). Our main result in this paper is that Dirichlet stereohedra for any of the 27 full groups cannot have more than 25 facets. We also find stereohedra with 17 facets for one of these groups.Comment: 28 pages, 12 figures. Changes from v1: apart of some editing (mostly at the end of the introduction) and addition of references, an appendix has been added, which analyzes the case where the base point does not have trivial stabilize

Experimental application of sum rules for electron energy loss magnetic chiral dichroism

We present a derivation of the orbital and spin sum rules for magnetic circular dichroic spectra measured by electron energy loss spectroscopy in a transmission electron microscope. These sum rules are obtained from the differential cross section calculated for symmetric positions in the diffraction pattern. Orbital and spin magnetic moments are expressed explicitly in terms of experimental spectra and dynamical diffraction coefficients. We estimate the ratio of spin to orbital magnetic moments and discuss first experimental results for the Fe L_{2,3} edge.Comment: 11 pages, 2 figure

Long term stability and infectivity of herpesviruses in water

For viruses to utilize environmental vectors (hard surfaces, soil, water) for transmission, physical and chemical stability is a prerequisite. There are many factors including pH, salinity, temperature, and turbidity that are known to contribute to the ability of viruses to persist in water. Equine herpesvirus type-1 (EHV-1) is a pathogenic alphaherpesvirus associated with domestic horses and wild equids. EHV-1 and recombinants of EHV-1 and EHV-9 are able to cause infections in non-equid animal species, particularly in captive settings. Many of the captive non-equid mammals are not naturally sympatric with equids and do not share enclosures, however, in many cases water sources may overlap. Similarly, in the wild, equids encounter many species at waterholes in times of seasonal drought. Therefore, we hypothesized that EHV-1 is stable in water and that water may act as a vector for EHV-1. In order to establish the conditions promoting or hindering EHV-1 longevity, infectivity and genomic stability in water; we exposed EHV-1 to varied water environments (pH, salinity, temperature, and turbidity) in controlled experiments over 21 days. The presence and infectivity of the virus was confirmed by both qPCR and cell culture experiments. Our results show that EHV-1 remains stable and infectious under many conditions in water for up to three weeks

Line defects in epitaxial silicon films grown at 560 C

We present an investigation of line defects in epitaxially grown silicon layers using Secco defect etching and transmission electron microscopy TEM . 1 m thick layers were deposited onto Si 100 wafers at a substrate temperature of 560 C using electron cyclotron resonance chemical vapour deposition ECRCVD . Defect etching reveals a variety of etch pits related to extended defects. A detailed analysis of the orientations and shapes of etch pits related to line defects is carried out. Using this information it is then possible to assign different types of etch pits to line defects observed by TEM. The investigations show, that one type of defect are extended dislocations parallel to lt;112 gt;, while the direction of two other types are lt;110 gt; as well as lt;314 gt;, a direction uncommon for line defects in silico

Nonlinear interaction of charged particles with a free electron gas beyond the random-phase approximation

A nonlinear description of the interaction of charged particles penetrating a solid has become of basic importance in the interpretation of a variety of physical phenomena. Here we develop a many-body theoretical approach to the quadratic decay rate, energy loss, and wake potential of charged particles moving in an interacting free electron gas. Explicit expressions for these quantities are obtained either within the random-phase approximation (RPA) or with full inclusion of short-range exchange and correlation effects. The Z^3 correction to the energy loss of ions is evaluated beyond RPA, in the limit of low velocities.Comment: 5 pages, 2 figures To appear in Phys. Rev.

Minkowski-type and Alexandrov-type theorems for polyhedral herissons

Classical H.Minkowski theorems on existence and uniqueness of convex polyhedra with prescribed directions and areas of faces as well as the well-known generalization of H.Minkowski uniqueness theorem due to A.D.Alexandrov are extended to a class of nonconvex polyhedra which are called polyhedral herissons and may be described as polyhedra with injective spherical image.Comment: 19 pages, 8 figures, LaTeX 2.0

The Big Society and the Conjunction of Crises: Justifying Welfare Reform and Undermining Social Housing

The idea of the “Big Society” can be seen as culmination of a long-standing debate about the regulation of welfare. Situating the concept within governance theory, the article considers how the UK coalition government has justified a radical restructuring of welfare provision, and considers its implications for housing provision. Although drawing on earlier modernization processes, the article contends that the genesis for welfare reform was based on an analysis that the government was forced to respond to a unique conjunction of crises: in morality, the state, ideology and economics. The government has therefore embarked upon a programme, which has served to undermine the legitimacy of the social housing sector (most notably in England), with detrimental consequences for residents and raising significant dilemmas for those working in the housing sector