A trapped surface in the higher-dimensional self-similar Vaidya spacetime

We investigate a trapped surface and naked singularity in a $D$-dimensional Vaidya spacetime with a self-similar mass function. A trapped surface is defined as a closed spacelike $(D-2)$-surface which has negative both null expansions. There is no trapped surface in the Minkowski spacetime. However, in a four-dimensional self-similar Vaidya spacetime, Bengtsson and Senovilla considered non-spherical trapped surfaces and showed that a trapped surface can penetrate into a flat region, if and only if the mass function rises fast enough [I. Bengtsson and J. M. M. Senovilla, Phys. Rev. D \textbf{79}, 024027 (2009).]. We apply this result to a $D$-dimensional spacetime motivated by the context of large extra dimensions or TeV-scale gravity. In this paper, similarly to Bengtsson and Senovilla's study, we match four types of $(D-2)$-surfaces and show that a trapped surface extended into the flat region can be constructed in the $D$-dimensional Vaidya spacetime, if the increasing rate of the mass function is greater than 0.4628. Moreover, we show that the maximum radius of the trapped surface constructed here approaches the Schwarzschild-Tangherlini radius in the large $D$ limit. Also, we show that there is no naked singularity, if the spacetime has the trapped surface constructed here.Comment: 13 pages, 5 figure

Why Don't We Have a Covariant Superstring Field Theory?

This talk deals with the old problem of formulatingn a covariant quantum theory of superstrings, ``covariant'' here meaning having manifest Lorentz symmetry and supersymmetry. The advantages and disadvantages of several quantization methods are reviewed. Special emphasis is put on the approaches using twistorial variables, and the algebraic structures of these. Some unsolved problems are identified.Comment: 5 pages, Goteborg-ITP-94-24, plain te

Consistent couplings between fields with a gauge freedom and deformations of the master equation

The antibracket in BRST theory is known to define a map $\rm{H^p \times H^q \longrightarrow H^{p+q+1}}$ associating with two equivalence classes of BRST invariant observables of respective ghost number p and q an equivalence class of BRST invariant observables of ghost number p+q+1. It is shown that this map is trivial in the space of all functionals, i.e., that its image contains only the zeroth class. However it is generically non trivial in the space of local functionals. Implications of this result for the problem of consistent interactions among fields with a gauge freedom are then drawn. It is shown that the obstructions to constructing such interactions lie precisely in the image of the antibracket map and are accordingly inexistent if one does not insist on locality. However consistent local interactions are severely constrained. The example of the Chern-Simons theory is considered. It is proved that the only consistent, local, Lorentz covariant interactions for the abelian models are exhausted by the non-abelian Chern-Simons extensions.Comment: 14 pages LaTeX file, ULB-PMIF-93/0

Adsorption and diffusion of H2O molecule on the Be(0001) surface: A density-functional theory study

Using first-principles calculations, we systematically study the adsorption behavior of a single molecular H$_{2}$O on the Be(0001) surface. We find that the favored molecular adsorption site is the top site with an adsorption energy of about 0.3 eV, together with the detailed electronic structure analysis, suggesting a weak binding strength of the H$_{2}$O/Be(0001) surface. The adsorption interaction is mainly contributed by the overlapping between the $s$ and $p_{z}$ states of the top-layer Be atom and the molecular orbitals 1$b_{1}$ and 3$a_{1}$ of H$_{2}$O. The activation energy for H$_{2}$O diffusion on the surface is about 0.3 eV. Meanwhile, our study indicates that no dissociation state exists for the H$_{2}$O/Be(0001) surface.Comment: 10 pages, 4 figure

Urban natur

Uppsatsen undersöker hur design av grönområden skulle kunna se ut om de gjordes med målen att skapa värden för biologisk mångfald och tillgängliggöra naturupplevelser för människor i staden, med ett designförslag av en befintlig park i Malmö som fallstudie. I växande städer är förtätning en strategi för att minska städers utbredning och konsumtion av omgivande landområden vilket innebär en allvarlig påverkan på biologisk mångfald. Förtätningen av städer sker ofta på bekostnad av urbana grönområden och urban natur. Samtidigt finns en tradition i utformningen av urbana parker och grönområden som innebär låga värden för biologisk mångfald och naturupplevelser. Genom en litteraturstudie, observationsstudie och designförslag av Ögårdsparken i Malmö, samt observationsstudie av parker i Berlin och läsning av skötselbeskrivningar för Berlins grönområden diskuterar uppsatsen på vilka sätt urbana grönområden skulle kunna designas och förvaltas med målet biologisk mångfald och att skapa naturupplevelser, och varför det är viktigt i en urbaniserad värld.The thesis explores the possibility of creating design of urban green areas and parks with the aim to achieve biodiversity and access to nature experiences in the city, with a design proposal for an existing park in Malmö as showcase. In growing cities densification is a strategy to limit cities expansion and consumption of surrounding land , with serious loss of biodiversity as a consequence. The densification of cities often results in loss of urban green areas and urban nature. At the same time there is an existing tradition in design of urban green areas and parks, that means lack of values for biodiversity and nature experience. Through a literature review, observational study and design proposal Ögårdsparken in Malmö , and an observational study of parks in Berlin and a reading of the official management- documents of Berlins green areas, the thesis discuss in what ways urban green spaces could be designed and managed with the goal to create values for biodiversity and access off experiences of nature, and why this is important in an urbanized world

A standardised method for measuring in situ denitrification in shallow aquifers: numerical validation and measurements in riparian wetlands

A tracer test to examine in situ denitrification in shallow groundwater by a piezometer with a packer system used bromide as a tracer of dilution and acetylene (10%) to block the denitrification process at the nitrous oxide stage. During the test, dissolved oxygen, nitrate (NO3-), bromide (Br-), nitrous oxide (N2O) and dissolved organic carbon (DOC) were measured. To calibrate the experimental method, comparison with numerical simulations of the groundwater transfer were carried out, taking into account the environmental characteristics. The method was tested by measurements undertaken in different environmental conditions (geology, land use and hydrology) in two riparian wetlands. Denitrification rates measured by this method ranged from 5.7 10-6 g N-NO3-L-1 h-1 to 1.97 10-3 g N-NO3-L-1 h-1 The method is applicable in shallow aquifers with a permeability from 10-2 to 10-4m s-1

Development of Collembolans after coversion towards organic farming

In Northern Germany, a diverse and complex experimental farm of the Federal Agricultural Research Centre (FAL) was set-up in 2001 covering all main aspects of organic farming. Previously, the 600 ha farm had been managed conventionally. Adjacent conventional farms were used as reference. The aim of this project was to study collembolans, microbial biomass and soil organic carbon in six organically farmed fields managed as a crop rotation of six different crops compared with an adjacent conventionally managed field. We hypothesised that the specific management in organic farming promotes soil biota. Soil samples were taken during the growing season in 2004. Collembolan abundances and microbial biomass were lower under organic management, but, generally, collembolan diversity was higher in organically farmed fields combined with a shifting in the dominance structure of the species. This result reveals that, even after three years, the soil biota is still changing with management conversion