Lunar base CELSS: A bioregenerative approach

During the twenty-first century, human habitation of a self-sustaining lunar base could become a reality. To achieve this goal, the occupants will have to have food, water, and an adequate atmosphere within a carefully designed environment. Advanced technology will be employed to support terrestrial life-sustaining processes on the Moon. One approach to a life support system based on food production, waste management and utilization, and product synthesis is outlined. Inputs include an atmosphere, water, plants, biodegradable substrates, and manufacutured materials such as fiberglass containment vessels from lunar resources. Outputs include purification of air and water, food, and hydrogen (H2) generated from methane (CH4). Important criteria are as follows: (1) minimize resupply from Earth; and (2) recycle as efficiently as possible

Coherent and incoherent atomic scattering: Formalism and application to pionium interacting with matter

The experimental determination of the lifetime of pionium provides a very important test on chiral perturbation theory. This quantity is determined in the DIRAC experiment at CERN. In the analysis of this experiment, the breakup probabilities of of pionium in matter are needed to high accuracy as a theoretical input. We study in detail the influence of the target electrons. They contribute through screening and incoherent effects. We use Dirac-Hartree- Fock-Slater wavefunctions in order to determine the corresponding form factors. We find that the inner-shell electrons contribute less than the weakly bound outer electrons. Furthermore, we establish a more rigorous estimate for the magnitude of the contributions form the transverse current (magnetic terms thus far neglected in the calculations).Comment: Journal of Physics B: Atomic, Molecular and Optical Physics; (accepted; 22 pages, 6 figures, 26 references) Revised version: more detailed description of DIRAC experiment; failure of simplest models for incoherent scattering demonstrated by example

Ecological equivalence: a realistic assumption for niche theory as a testable alternative to neutral theory

Hubbell's 2001 neutral theory unifies biodiversity and biogeography by modelling steady-state distributions of species richness and abundances across spatio-temporal scales. Accurate predictions have issued from its core premise that all species have identical vital rates. Yet no ecologist believes that species are identical in reality. Here I explain this paradox in terms of the ecological equivalence that species must achieve at their coexistence equilibrium, defined by zero net fitness for all regardless of intrinsic differences between them. I show that the distinction of realised from intrinsic vital rates is crucial to evaluating community resilience. An analysis of competitive interactions reveals how zero-sum patterns of abundance emerge for species with contrasting life-history traits as for identical species. I develop a stochastic model to simulate community assembly from a random drift of invasions sustaining the dynamics of recruitment following deaths and extinctions. Species are allocated identical intrinsic vital rates for neutral dynamics, or random intrinsic vital rates and competitive abilities for niche dynamics either on a continuous scale or between dominant-fugitive extremes. Resulting communities have steady-state distributions of the same type for more or less extremely differentiated species as for identical species. All produce negatively skewed log-normal distributions of species abundance, zero-sum relationships of total abundance to area, and Arrhenius relationships of species to area. Intrinsically identical species nevertheless support fewer total individuals, because their densities impact as strongly on each other as on themselves. Truly neutral communities have measurably lower abundance/area and higher species/abundance ratios. Neutral scenarios can be parameterized as null hypotheses for testing competitive release, which is a sure signal of niche dynamics. Ignoring the true strength of interactions between and within species risks a substantial misrepresentation of community resilience to habitat los

The effects of individual nonheritable variation on fitness estimation and coexistence

Demographic theory and data have emphasized that non-heritable variation in individual frailty enables selection within cohorts, affecting the dynamics of a population while being invisible to its evolution. Here we include the component of individual variation in longevity or viability which is non-heritable in simple bacterial growth models and explore its ecological and evolutionary impacts. First, we find that this variation produces consistent trends in longevity differences between bacterial genotypes when measured across stress gradients. Given that direct measurements of longevity are inevitably biased due to the presence of this variation and ongoing selection, we propose the use of the trend itself for obtaining more exact inferences of genotypic fitness. Second, we show how species or strain coexistence can be enabled by non36 heritable variation in longevity or viability. These general conclusions are likely to extend beyond bacterial systems

Efeito do fósforo na formação da simbiose micorrízica vesicular-arbuscular

The effect of phosphorus (P) on formation of the vesicular-arbuscular mycorrhizal (VAM) symbiosis was examined. Using a sand-hydroponic culture chamber, increasing P levels were supplied lo soybean (Glycine max L. Merrill) seedlings. It was found that indirect supply of P up to 600 mM did not affect the germination of Glomus mosseae chlamydospores in the rhizosphere. Similar results were found for germination of either G. mosseae or Gigaspora margarita spores in the rhizosphere of soybean growing in soil amended with increasing P levels. These data suggest that P controls VAM formation at some stage after spore germination in the rhizosphere has occurred. Increasing P supply to the soil enhanced carbon exchange rate, sugar content of the roots and decreased sugars in the root exudates. Bioassays using root extracts from plants supplied with different P levels showed differential effects on germination of G. mosseae and G. margarita spores in vitro. Extracts from plants well supplied with P had high levels of sugars and inhibited spore germination. It was proposed that P controls root colonization through its effect on host carbon metabolism. In addition, the relationship between P availability and plant growth response to mycorrhizal formation is discussed.Foi examinado o efeito do fósforo (P) na formação da simbiose micorrízica vesicular-arbuscular (MVA). Com uso de uma câmara de crescimento do tipo hidropônica, foram fornecidos níveis crescentes de P a plântulas de soja (Glycine max L. Merrill). O fornecimento de P até 600 mM não teve efeito na germinação de clamidósporos de Glomus mosseae na rizosfera. Isto sugere que P controla a formação da simbiose MVA em algum estágio depois que a germinação dos esporos tenha ocorrido. A adição ao solo de pequenas doses de P aumentou a taxa fotossintética e o teor de açúcares nas raízes da soja. Bioensaios usando extratos de raízes de plantas adubadas com diferentes níveis de P mostraram efeitos diferenciados sobre a germinação de esporos de G. mosseae e Gigaspora margarita in vitro. Extratos de plantas bem supridas em P tiveram teores mais elevados de açúcares e mostraram efeito inibitório na germinação dos esporos. Estes dados permitem a formulação da hipótese de que o P controla o grau de colonização das raízes pelos fungos endomicorrízicos através de seu efeito no metabolismo de carboidrato da planta hospedeira. A relação entre a disponibilidade de P no solo e a resposta em crescimento da soja devido a micorrização é, igualmente, discutida

Microfluidics: From Crystallization to Serial Time-Resolved Crystallography

Capturing protein structural dynamics in real-time has tremendous potential in elucidating biological functions and providing information for structure-based drug design. While time-resolved structure determination has long been considered inaccessible for a vast majority of protein targets, serial methods for crystallography have remarkable potential in facilitating such analyses. Here, we review the impact of microfluidic technologies on protein crystal growth and X-ray diffraction analysis. In particular, we focus on applications of microfluidics for use in serial crystallography experiments for the time-resolved determination of protein structural dynamics

Pareto versus lognormal: a maximum entropy test

It is commonly found that distributions that seem to be lognormal over a broad range change to a power-law (Pareto) distribution for the last few percentiles. The distributions of many physical, natural, and social events (earthquake size, species abundance, income and wealth, as well as file, city, and firm sizes) display this structure. We present a test for the occurrence of power-law tails in statistical distributions based on maximum entropy. This methodology allows one to identify the true data-generating processes even in the case when it is neither lognormal nor Pareto. The maximum entropy approach is then compared with other widely used methods and applied to different levels of aggregation of complex systems. Our results provide support for the theory that distributions with lognormal body and Pareto tail can be generated as mixtures of lognormally distributed units

On the Absorption of X-rays in the Interstellar Medium

We present an improved model for the absorption of X-rays in the ISM intended for use with data from future X-ray missions with larger effective areas and increased energy resolution such as Chandra and XMM, in the energy range above 100eV. Compared to previous work, our formalism includes recent updates to the photoionization cross section and revised abundances of the interstellar medium, as well as a treatment of interstellar grains and the H2molecule. We review the theoretical and observational motivations behind these updates and provide a subroutine for the X-ray spectral analysis program XSPEC that incorporates our model.Comment: ApJ, in press, for associated software see http://astro.uni-tuebingen.de/nh

A simple analytical method for heterogeneity corrections in low dose rate prostate brachytherapy

In low energy brachytherapy, the presence of tissue heterogeneities contributes significantly to the discrepancies observed between treatment plan and delivered dose. In this work, we present a simplified analytical dose calculation algorithm for heterogeneous tissue. We compare it with Monte Carlo computations and assess its suitability for integration in clinical treatment planning systems. The algorithm, named as RayStretch, is based on the classic equivalent path length method and TG-43 reference data. Analytical and Monte Carlo dose calculations using Penelope2008 are compared for a benchmark case: a prostate patient with calcifications. The results show a remarkable agreement between simulation and algorithm, the latter having, in addition, a high calculation speed. The proposed analytical model is compatible with clinical real-time treatment planning systems based on TG-43 consensus datasets for improving dose calculation and treatment quality in heterogeneous tissue. Moreover, the algorithm is applicable for any type of heterogeneities