Spatial aspects of the design and targeting of agricultural development strategies:

Two increasingly shared perspectives within the international development community are that (a) geography matters, and (b) many government interventions would be more successful if they were better targeted. This paper unites these two notions by exploring the opportunities for, and benefits of, bringing an explicitly spatial dimension to the tasks of formulating and evaluating agricultural development strategies. We first review the lingua franca of land fragility and find it lacking in its capacity to describe the dynamic interface between the biophysical and socioeconomic factors that help shape rural development options. Subsequently, we propose a two-phased approach. First, development strategy options are characterized to identify the desirable ranges of conditions that would most favor successful strategy implementation. Second, those conditions exhibiting important spatial dependency – such as agricultural potential, population density, and access to infrastructure and markets – are matched against a similarly characterized, spatially-referenced (GIS) database. This process generates both spatial (map) and tabular representations of strategy-specific development domains. An important benefit of a spatial (GIS) framework is that it provides a powerful means of organizing and integrating a very diverse range of disciplinary and data inputs. At a more conceptual level we propose that it is the characterization of location, not the narrowly-focused characterization of land, that is more properly the focus of attention from a development perspective. The paper includes appropriate examples of spatial analysis using data from East Africa and Burkina Faso, and concludes with an appendix describing and interpreting regional climate and soil data for Sub-Saharan Africa that was directly relevant to our original goal.Spatial analysis (Statistics), Agricultural development., Burkina Faso., Africa, Sub-Saharan.,

The role of tropical forests in supporting biodiversity and hydrological integrity: a synoptic overview

Conservation of high-biodiversity tropical forests is sometimes justified on the basis of assumed hydrological benefits - in particular, the reduction of flooding hazards for downstream floodplain populations. However, the"far-field"link between deforestation and distant flooding has been difficult to demonstrate empirically. This simulation study assesses the relationship between forest cover and hydrology for all river basins intersecting the world's tropical forest biomes. The study develops a consistent set of pan-tropical land cover maps gridded at one-half degree latitude and longitude. It integrates these data with existing global biogeophysical data. The study applies the Water Balance Model - a coarse-scale process-based hydrological model - to assess the impact of land cover changes on runoff. It quantifies the impacts of forest conversion on biodiversity and hydrology for two scenarios - historical forest conversion and the potential future conversion of the most threatened remaining tropical forests. A worst-case scenario of complete conversion of the most threatened of the remaining forested areas would mean the loss of another three million km2 of tropical forests. Increased annual yield from the conversion of threatened tropical forests would be less than 5 percent of contemporary yield in aggregate. However, about 100 million people - 80 million of them in floodplains - would experience increases of more than 25 percent in annual water flows. This might be associated with commensurate increases in peak flows, though further analysis would be necessary to gauge the impact on flooding. The study highlights basins in Southeast Asia, southern China, and Latin America that warrant further study.Wetlands,Forestry,Climate Change,Drylands&Desertification,Earth Sciences&GIS

Directly probing thin film morphology - optoelectronic property relationships in organic and hybrid solar cells

Solution processable organic semiconductors offer a promising route towards low-cost solar photovoltaics. The performance of these devices is critically dependent on the morphology of the thin film active layer and is very sensitive to both the chemical structure and deposition conditions of the materials. In this thesis a range of complementary techniques are used to characterise the morphology, particularly resonant Raman spectroscopy and atomic force microscopy, in addition to analysis of the device performance. By comparing these results we are able to fulfil the aim of this project, which was to elucidate the fundamental relationships between the thin film morphology and photovoltaic performance for a range of organic and hybrid solar cells. For polymer/polymer blends we consider the impacts of nanowire formation, molecular weight, and thermal annealing on the thin film molecular order. By controlling the interactions between the two polymers we are able to increase the charge carrier mobilities by several orders of magnitude, resulting in reduced bimolecular recombination and enhanced device efficiency. For the hybrid polymer/inorganic devices that we consider, we identify an interfacial region of disordered polymer, which can be partly controlled but not fully overcome. We suggest that this represents an intrinsic limitation, which should be addressed by considering alternative routes to interface formation. Donor-acceptor copolymers are an important class of materials showing promising optoelectronic properties for polymer/fullerene solar cells. We consider how various chemical modifications including fluorination, side chain branching, and heavy atom substitution affect the molecular properties and thin film morphology. In particular, we consider the nature of the electronic absorption transitions of diketopyrrolopyrrole-based copolymers and find that the low energy transition is localised on the diketopyrrolopyrrole unit and is very stable to photodegradation, whereas the high energy transition couples more strongly to the donor unit, which is more vulnerable to photooxidation.Open Acces

Genomic signatures of heterokaryosis in the oomycete pathogen Bremia lactucae.

Lettuce downy mildew caused by Bremia lactucae is the most important disease of lettuce globally. This oomycete is highly variable and rapidly overcomes resistance genes and fungicides. The use of multiple read types results in a high-quality, near-chromosome-scale, consensus assembly. Flow cytometry plus resequencing of 30 field isolates, 37 sexual offspring, and 19 asexual derivatives from single multinucleate sporangia demonstrates a high incidence of heterokaryosis in B. lactucae. Heterokaryosis has phenotypic consequences on fitness that may include an increased sporulation rate and qualitative differences in virulence. Therefore, selection should be considered as acting on a population of nuclei within coenocytic mycelia. This provides evolutionary flexibility to the pathogen enabling rapid adaptation to different repertoires of host resistance genes and other challenges. The advantages of asexual persistence of heterokaryons may have been one of the drivers of selection that resulted in the loss of uninucleate zoospores in multiple downy mildews

Curvature-enhanced localised emission from dark states in wrinkled monolayer WSe2 at room temperature

Localised emission from defect states in monolayer transition metal dichalcogenides is of great interest for optoelectronic and quantum device applications. Recent progress towards high temperature localised emission relies on the application of strain to induce highly confined excitonic states. Here we propose an alternative paradigm based on curvature, rather than in-plane stretching, achieved through free-standing wrinkles of monolayer tungsten diselenide (WSe2). We probe these nanostructures using tip-enhanced optical spectroscopy to reveal the spatial localisation of out-of-plane polarised emission from the WSe2 wrinkles. Based on the photoluminescence and Raman scattering signatures resolved with nanoscale spatial resolution, we propose the existence of a manifold of spin-forbidden excitonic states that are activated by the local curvature of the WSe2. We are able to access these dark states through the out-of-plane polarised surface plasmon polariton resulting in enhanced strongly localised emission at room temperature, which is of potential interest for quantum technologies and photonic devices

High prevalence of self-reported undiagnosed HIV despite high coverage of HIV testing : a cross-sectional population based sero-survey in South Africa

CITATION: Kranzer, K. et al. 2011. High prevalence of self-reported undiagnosed HIV despite high coverage of HIV testing : a cross-sectional population based sero-survey in South Africa. PLoS ONE, 6(9): e25244, doi:10.1371/journal.pone.0025244.The original publication is available at http://journals.plos.org/plosoneObjectives To measure HIV prevalence and uptake of HIV counseling and testing (HCT) in a peri-urban South African community. To assess predictors for previous HIV testing and the association between the yield of previously undiagnosed HIV and time of last negative HIV test Methods A random sample of 10% of the adult population (≥15 years) were invited to attend a mobile HCT service. Study procedures included a questionnaire, HIV testing and CD4 counts. Predictors for previous testing were determined using a binominal model. Results 1,144 (88.0%) of 1,300 randomly selected individuals participated in the study. 71.0% (68.3–73.6) had previously had an HIV test and 37.5% (34.6–40.5) had tested in the past 12 months. Men, migrants and older (>35 years) and younger (<20 years) individuals were less likely to have had a previous HIV test. Overall HIV prevalence was 22.7 (20.3–25.3) with peak prevalence of 41.8% (35.8–47.8) in women aged 25.1–35 years and 37.5% (26.7–48.3) in men aged 25.1–45 years. Prevalence of previously undiagnosed HIV was 10.3% (8.5–12.1) overall and 4.5% (2.3–6.6), 8.0% (CI 3.9–12.0) and 20.0% (13.2–26.8) in individuals who had their most recent HIV test within 1, 1–2 and more than 2 years prior to the survey. Conclusion The high burden of undiagnosed HIV in individuals who had recently tested underscores the importance of frequent repeat testing at least annually. The high prevalence of previously undiagnosed HIV in individuals reporting a negative test in the 12 months preceding the survey indicates a very high incidence. Innovative prevention strategies are needed.http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0025244Publisher's versio

Development of time-resolved photoluminescence microscopy of semiconductor materials and devices using a compressed sensing approach

Charge carrier lifetime is a key property of semiconductor materials for photonic applications. One of the most established methods for measuring lifetimes is time-resolved photoluminescence (TRPL), which is typically performed as a single-point measurement. In this paper, we demonstrate a new time-correlated single photon counting method (TCSPC) for TRPL microscopy, for which spatial information can be achieved without requiring point-by-point scanning through the use of a compressed sensing (CS) approach. This enables image acquisition with a single pixel detector for mapping the lifetime of semiconductors with high repeatability. The methodology for signal acquisition and image reconstruction was developed and tested through simulations. Effects of noise levels on the reliability and quality of image reconstruction were investigated. Finally, the method was implemented experimentally to demonstrate a proof-of-concept CS TCSPC imaging system for acquiring TRPL maps of semiconductor materials and devices. TRPL imaging results of a semiconductor device acquired using a CS approach are presented and compared with results of TRPL mapping of the same excitation area measured through a point-by-point method. The feasibility of the methodology is demonstrated, the benefits and challenges of the experimental prototype system are presented and discussed