Global modelling of H2 mixing ratios and isotopic compositions with the TM5 model

The isotopic composition of molecular hydrogen (H2) contains independent information for constraining the global H2 budget. To explore this, we have implemented hydrogen sources and sinks, including their isotopic composition, into the global chemistry transport model TM5. For the first time, a global model now includes a simplified but explicit isotope reaction scheme for the photochemical production of H2. We present a comparison of modelled results for the H2 mixing ratio and isotope composition with available measurements on the seasonal to inter annual time scales for the years 2001–2007. The base model results agree well with observations for H2 mixing ratios. For dD[H2], modelled values are slightly lower than measurements. A detailed sensitivity study is performed to identify the most important parameters for modelling the isotopic composition of H2. The results show that on the global scale, the discrepancy between model and measurements can be closed by adjusting the default values of the isotope effects in deposition, photochemistry and the stratosphere-troposphere exchange within the known range of uncertainty. However, the available isotope data do not provide sufficient information to uniquely constrain the global isotope budget. Therefore, additional studies focussing on the isotopic composition near the tropopause and on the isotope effects in the photochemistry and deposition are recommended

Independent predictors of breast malignancy in screen-detected microcalcifications: biopsy results in 2545 cases

Background: Mammographic microcalcifications are associated with many benign lesions, ductal carcinoma in situ (DCIS) and invasive cancer. Careful assessment criteria are required to minimise benign biopsies while optimising cancer diagnosis. We wished to evaluate the assessment outcomes of microcalcifications biopsied in the setting of population-based breast cancer screening. Methods: Between January 1992 and December 2007, cases biopsied in which microcalcifications were the only imaging abnormality were included. Patient demographics, imaging features and final histology were subjected to statistical analysis to determine independent predictors of malignancy. Results: In all, 2545 lesions, with a mean diameter of 21.8 mm (s.d. 23.8 mm) and observed in patients with a mean age of 57.7 years (s.d. 8.4 years), were included. Using the grading system adopted by the RANZCR, the grade was 3 in 47.7%; 4 in 28.3% and 5 in 24.0%. After assessment, 1220 lesions (47.9%) were malignant (809 DCIS only, 411 DCIS with invasive cancer) and 1325 (52.1%) were non-malignant, including 122 (4.8%) premalignant lesions (lobular carcinoma in situ, atypical lobular hyperplasia and atypical ductal hyperplasia). Only 30.9% of the DCIS was of low grade. Mammographic extent of microcalcifications >15 mm, imaging grade, their pattern of distribution, presence of a palpable mass and detection after the first screening episode showed significant univariate associations with malignancy. On multivariate modeling imaging grade, mammographic extent of microcalcifications >15 mm, palpable mass and screening episode were retained as independent predictors of malignancy. Radiological grade had the largest effect with lesions of grade 4 and 5 being 2.2 and 3.3 times more likely to be malignant, respectively, than grade 3 lesions. Conclusion: The radiological grading scheme used throughout Australia and parts of Europe is validated as a useful system of stratifying microcalcifications into groups with significantly different risks of malignancy. Biopsy assessment of appropriately selected microcalcifications is an effective method of detecting invasive breast cancer and DCIS, particularly of non-low-grade subtypes.G Farshid, T Sullivan, P Downey, P G Gill, and S Pieters

A consistent molecular hydrogen isotope chemistry scheme based on an independent bond approximation

The isotopic composition of molecular hydrogen (H<sub>2</sub>) produced by photochemical oxidation of methane (CH<sub>4</sub>) and Volatile Organic Compounds (VOCs) is a key quantity in the global isotope budget of (H<sub>2</sub>). The many individual reaction steps involved complicate its investigation. Here we present a simplified structure-activity approach to assign isotope effects to the individual elementary reaction steps in the oxidation sequence of CH<sub>4</sub> and some other VOCs. The approach builds on and extends the work by Gerst and Quay (2001) and Feilberg et al. (2007b). The description is generalized and allows the application, in principle, also to other compounds. The idea is that the C-H and C-D bonds – seen as reactive sites – have similar relative reaction probabilities in isotopically substituted, but otherwise identical molecules. The limitations of this approach are discussed for the reaction CH<sub>4</sub>+Cl. The same approach is applied to VOCs, which are important precursors of H<sub>2</sub> that need to be included into models. Unfortunately, quantitative information on VOC isotope effects and source isotope signatures is very limited and the isotope scheme at this time is limited to a strongly parameterized statistical approach, which neglects kinetic isotope effects. Using these concepts we implement a full hydrogen isotope scheme in a chemical box model and carry out a sensitivity study to identify those reaction steps and conditions that are most critical for the isotope composition of the final H<sub>2</sub> product. The reaction scheme is directly applicable in global chemistry models, which can thus include the isotope pathway of H<sub>2</sub> produced from CH<sub>4</sub> and VOCs in a consistent way

Emission ratio and isotopic signatures of molecular hydrogen emissions from tropical biomass burning

In this study, we identify a biomass-burning signal in molecular hydrogen (H₂) over the Amazonian tropical rainforest. To quantify this signal, we measure the mixing ratios of H₂ and several other species as well as the H₂ isotopic composition in air samples that were collected in the BARCA (Balanço Atmosférico Regional de Carbono na Amazônia) aircraft campaign during the dry season. We derive a relative H₂ emission ratio with respect to carbon monoxide (CO) of 0.31 ± 0.04 ppb ppb⁻¹ and an isotopic source signature of −280 ± 41‰ in the air masses influenced by tropical biomass burning. In order to retrieve a clear source signal that is not influenced by the soil uptake of H₂, we exclude samples from the atmospheric boundary layer. This procedure is supported by data from a global chemistry transport model. The ΔH₂ / ΔCO emission ratio is significantly lower than some earlier estimates for the tropical rainforest. In addition, our results confirm the lower values of the previously conflicting estimates of the H₂ isotopic source signature from biomass burning. These values for the emission ratio and isotopic source signatures of H₂ from tropical biomass burning can be used in future bottom-up and top-down approaches aiming to constrain the strength of the biomass-burning source for H₂. Hitherto, these two quantities relied only on combustion experiments or on statistical relations, since no direct signal had been obtained from in-situ observations

COMET: a Lagrangian transport model for greenhouse gas emission estimation ? forward model technique and performance for methane

International audienceThe Lagrangian transport model COMET has been developed to evaluate emission estimates based on atmospheric concentration observations. This paper describes the model and its application in modelling the methane concentrations at the European stations Cabauw and Macehead. The COMET model captures in most cases both synoptic and diurnal variations of the concentrations as a function of time and in absolute size quite well. The explained variability by COMET of the mixed layer concentration for Cabauw varies from 50% to 84%; for all hourly observations in 2002 the explained variability is 71% with a RMSE of 112 ppb. The explained variability for Macehead is 48%. The most important model parameters were tested for their influence on model performance, but in general the model is not very sensitive to variations within acceptable limits. For a regionally and locally polluted continental site the COMET model shows only a small bias and a moderate random error, and therefore is considered to capture the influence of the sources on the concentration variations quite well. It is therefore concluded that inverse methods and more specifically the COMET model is suitable to be applied in deriving independent estimates of greenhouse gas emissions using Source-Receptor relationships

Powering sub-Saharan Africa’s urban revolution: An energy transitions approach

This paper develops a geographic understanding of urban energy transitions in subSaharan African towns and cities. In doing so this paper seeks to critically reflect on the value and limits of urban transitions analysis as a framework for understanding energy networks beyond the largely integrated systems across the Global North. We explore how these potentials and deficits can be addressed by examining promising developments across a series of debates in urban studies that can help sensitise this approach to energyscapes in the African context. By reviewing urban transi- tions analysis through these debates the paper offers four important contributions to expand existing ways of understanding energy transition. These include the particular urbanisation dynamics of African towns ands cities, the need to locate the urban across energy regimes, the agencies of various intermediaries and urban actors and the contested politics inherent in the governing of energy networks. In the conclusion we reflect on the specific directions that have emerged from the paper in relation to our contributions, offering a geographically informed framework that allows us to better examine the challenges and specificities of transition across these rapidly growing urban regions

Hydrogen Epoch of Reionization Array (HERA)

The Hydrogen Epoch of Reionization Array (HERA) is a staged experiment to measure 21 cm emission from the primordial intergalactic medium (IGM) throughout cosmic reionization ($z=6-12$), and to explore earlier epochs of our Cosmic Dawn ($z\sim30$). During these epochs, early stars and black holes heated and ionized the IGM, introducing fluctuations in 21 cm emission. HERA is designed to characterize the evolution of the 21 cm power spectrum to constrain the timing and morphology of reionization, the properties of the first galaxies, the evolution of large-scale structure, and the early sources of heating. The full HERA instrument will be a 350-element interferometer in South Africa consisting of 14-m parabolic dishes observing from 50 to 250 MHz. Currently, 19 dishes have been deployed on site and the next 18 are under construction. HERA has been designated as an SKA Precursor instrument. In this paper, we summarize HERA's scientific context and provide forecasts for its key science results. After reviewing the current state of the art in foreground mitigation, we use the delay-spectrum technique to motivate high-level performance requirements for the HERA instrument. Next, we present the HERA instrument design, along with the subsystem specifications that ensure that HERA meets its performance requirements. Finally, we summarize the schedule and status of the project. We conclude by suggesting that, given the realities of foreground contamination, current-generation 21 cm instruments are approaching their sensitivity limits. HERA is designed to bring both the sensitivity and the precision to deliver its primary science on the basis of proven foreground filtering techniques, while developing new subtraction techniques to unlock new capabilities. The result will be a major step toward realizing the widely recognized scientific potential of 21 cm cosmology.Comment: 26 pages, 24 figures, 2 table

Preliminary results on electrophoretic and immunoelectrophoretic fractionation of bovine muscle extract

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Tomato: a crop species amenable to improvement by cellular and molecular methods

Tomato is a crop plant with a relatively small DNA content per haploid genome and a well developed genetics. Plant regeneration from explants and protoplasts is feasable which led to the development of efficient transformation procedures. In view of the current data, the isolation of useful mutants at the cellular level probably will be of limited value in the genetic improvement of tomato. Protoplast fusion may lead to novel combinations of organelle and nuclear DNA (cybrids), whereas this technique also provides a means of introducing genetic information from alien species into tomato. Important developments have come from molecular approaches. Following the construction of an RFLP map, these RFLP markers can be used in tomato to tag quantitative traits bred in from related species. Both RFLP's and transposons are in the process of being used to clone desired genes for which no gene products are known. Cloned genes can be introduced and potentially improve specific properties of tomato especially those controlled by single genes. Recent results suggest that, in principle, phenotypic mutants can be created for cloned and characterized genes and will prove their value in further improving the cultivated tomato.