413 research outputs found
Biodiversity Impact of Green Roofs and Constructed Wetlands as Progressive Eco-Technologies in Urban Areas
The total amount of sealed surfaces is increasing in many urban areas, which presents a challenge for sewerage systems and wastewater treatment plants when extreme rainfall events occur. One promising solution approach is the application of decentralized eco-technologies for water management such as green roofs and constructed wetlands, which also have the potential to improve urban biodiversity. We review the effects of these two eco-technologies on species richness, abundance and other facets of biodiversity (e.g., functional diversity). We find that while green roofs support fewer species than ground-level habitats and thus are not a substitute for the latter, the increase in green roof structural diversity supports species richness. Species abundance benefits from improved roof conditions (e.g., increased substrate depth). Few studies have investigated the functional diversity of green roofs so far, but the typical traits of green roof species have been identified. The biodiversity of animals in constructed wetlands can be improved by applying animal-aided design rather than by solely considering engineering requirements. For example, flat and barrier-free shore areas, diverse vegetation, and heterogeneous surroundings increase the attractiveness of constructed wetlands for a range of animals. We suggest that by combining and making increasing use of these two eco-technologies in urban areas, biodiversity will benefit
PALP - a User Manual
This article provides a complete user's guide to version 2.1 of the toric
geometry package PALP by Maximilian Kreuzer and others. In particular,
previously undocumented applications such as the program nef.x are discussed in
detail. New features of PALP 2.1 include an extension of the program mori.x
which can now compute Mori cones and intersection rings of arbitrary dimension
and can also take specific triangulations of reflexive polytopes as input.
Furthermore, the program nef.x is enhanced by an option that allows the user to
enter reflexive Gorenstein cones as input. The present documentation is
complemented by a Wiki which is available online.Comment: 71 pages, to appear in "Strings, Gauge Fields, and the Geometry
Behind - The Legacy of Maximilian Kreuzer". PALP Wiki available at
http://palp.itp.tuwien.ac.at/wiki/index.php/Main_Pag
A âSolvent-Freeâ Crystal Structure of [FeN(SiMe3)23] â Synthesis, Structure and Properties
For the synthesis of the ferric bis(trimethylsilyl)amido complex [Fe{N(SiMe3)2}3] literature gives differing synthetic protocols based on crystallization from solution. In this report we present a âsolventâfreeâ structural phase of [Fe{N(SiMe)}] which was isolated by sublimation of the product obtained from the reaction of 2â
eq FeCl with 3â
eq LiN(SiMe) in benzene. It could be characterized by single crystal as well as powder XRD and elemental analysis. However, Fe MöĂbauer spectroscopy suggests a contamination of the main product with an Fe(II) species. Also, a part of the solid reaction byproducts from the reactions in solution were identified by powder XRD and Li MAS NMR which indicate distinct redox side reactions between oxidizing FeCl and reducing LiN(SiMe), a fact which rationalizes the lower than expected yields and the observation of an Fe(II) impurity compound. AC magnetic measurements of [Fe{N(SiMe)}] ave been performed in an extended frequency range up to 10â
s allowing for a more precise evaluation of the magnetic relaxation parameters when compared to previously published measurements
Activity-independent screening of secreted proteins using split GFP
The large-scale industrial production of proteins requires efficient secretion, as provided, for instance, by the Sec system of Gram-positive bacteria. Protein engineering approaches to optimize secretion often involve the screening of large libraries, e.g. comprising a target protein fused to many different signal peptides. Respective high-throughput screening methods are usually based on photometric or fluorimetric assays enabling fast and simple determination of enzymatic activities. Here, we report on an alternative method for quantification of secreted proteins based on the split GFP assay. We analyzed the secretion by Bacillus subtilis of a homologous lipase and a heterologous cutinase by determination of GFP fluorescence and enzyme activity assays. Furthermore, we identified from a signal peptide library a variant of the biotechnologically relevant B. subtilis protein swollenin EXLX1 with up to 5-fold increased secretion. Our results demonstrate that the split GFP assay can be used to monitor secretion of enzymatic and non-enzymatic proteins in B. subtilis in a high-throughput manner
Five-Brane Superpotentials and Heterotic/F-theory Duality
Under heterotic/F-theory duality it was argued that a wide class of heterotic
five-branes is mapped into the geometry of an F-theory compactification
manifold. In four-dimensional compactifications this identifies a five-brane
wrapped on a curve in the base of an elliptically fibered Calabi-Yau threefold
with a specific F-theory Calabi-Yau fourfold containing the blow-up of the
five-brane curve. We argue that this duality can be reformulated by first
constructing a non-Calabi-Yau heterotic threefold by blowing up the curve of
the five-brane into a divisor with five-brane flux. Employing
heterotic/F-theory duality this leads us to the construction of a Calabi-Yau
fourfold and four-form flux. Moreover, we obtain an explicit map between the
five-brane superpotential and an F-theory flux superpotential. The map of the
open-closed deformation problem of a five-brane in a compact Calabi-Yau
threefold into a deformation problem of complex structures on a dual Calabi-Yau
fourfold with four-form flux provides a powerful tool to explicitly compute the
five-brane superpotential.Comment: 43 pages, v2: minor correction
G_4 flux, chiral matter and singularity resolution in F-theory compactifications
We construct a set of chirality inducing G_4-fluxes in global F-theory
compactifications on Calabi-Yau four-folds. Special emphasis is put on models
with gauge group SU(5) x U(1)_X relevant in the context of F-theory GUT model
building, which are described in terms of a U(1)-restricted Tate model. In this
type of constructions, the G_4-flux arises in a manner completely analogous to
the U(1)_X gauge potential. We describe in detail the resolution by blow-up of
the various singularities responsible for the U(1)_X factor and the standard
SU(5) gauge group and match the result with techniques applied in the context
of toric geometry. This provides an explicit identification of the structure of
the resolved fibre over the matter curves and over the enhancement points
relevant for Yukawa couplings. The U(1)_X flux induces a chiral matter
spectrum. We compute the chiral index both of SU(5) charged matter and of SU(5)
singlets charged only under U(1)_X localised on curves which are not contained
in the SU(5) locus. We furthermore discuss global consistency conditions such
as D3-tadpole cancellation, D-term supersymmetry and Freed-Witten quantisation.
The U(1)_X gauge flux is a global extension of a class of split spectral cover
bundles. It constitutes an essential ingredient in the construction of globally
defined F-theory compactifications with chiral matter. We exemplify this in a
three-generation SU(5) x U(1)_X model whose flux satisfies all of the above
global consistency conditions. We also extend our results to chiral fluxes in
models without U(1) restriction.Comment: 53 pages, 2 figures; v2: details on Freed-Witten quantisation
condition included, typos correcte
Consistent Device Simulation Model Describing Perovskite Solar Cells in Steady-State, Transient, and Frequency Domain
A variety of experiments on vacuum-deposited methylammonium lead iodide perovskite solar cells are presented, including JV curves with different scan rates, light intensity-dependent open-circuit voltage, impedance spectra, intensity-modulated photocurrent spectra, transient photocurrents, and transient voltage step responses. All these experimental data sets are successfully reproduced by a charge drift-diffusion simulation model incorporating mobile ions and charge traps using a single set of parameters. While previous modeling studies focused on a single experimental technique, we combine steady-state, transient, and frequency-domain simulations and measurements. Our study is an important step toward quantitative simulation of perovskite solar cells, leading to a deeper understanding of the physical effects in these materials. The analysis of the transient current upon voltage turn-on in the dark reveals that the charge injection properties of the interfaces are triggered by the accumulation of mobile ionic defects. We show that the current rise of voltage step experiments allow for conclusions about the recombination at the interface. Whether one or two mobile ionic species are used in the model has only a minor influence on the observed effects. A delayed current rise observed upon reversing the bias from +3 to -3 V in the dark cannot be reproduced yet by our drift-diffusion model. We speculate that a reversible chemical reaction of mobile ions with the contact material may be the cause of this effect, thus requiring a future model extension. A parameter variation is performed in order to understand the performance-limiting factors of the device under investigation
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