Hierarchical image segmentation based on similarity of NDVI time series

Although a variety of hierarchical image segmentation procedures for remote sensing imagery have been published, none of them specifically integrates remote sensing time series in spatial or hierarchical segmentation concepts. However, this integration is important for the analysis of ecosystems which are hierarchical in nature, with different ecological processes occurring at different spatial and temporal scales. Therefore, the objective of this paper is to introduce a multi-temporal hierarchical image segmentation (MTHIS) methodology to generate a hierarchical set of segments based on spatial similarity of remote sensing time series. MTHIS employs the similarity of the fast Fourier transform (FFT) components of multi-seasonal time series to group pixels with similar temporal behavior into hierarchical segments at different scales. Use of the FFT allows the distinction between noise and vegetation related signals and increases the computational efficiency. The MTHIS methodology is demonstrated on the area of South Africa in an MTHIS protocol for Normalized Difference Vegetation Index (NDVI) time series. Firstly, the FFT components that express the major spatio-temporal variation in the NDVI time series, the average and annual term, are selected and the segmentation is performed based on these components. Secondly, the results are visualized by means of a boundary stability image that confirms the accuracy of the algorithm to spatially group pixels at different scale levels. Finally, the segmentation optimum is determined based on discrepancy measures which illustrate the correspondence of the applied MTHIS output with landcover-landuse maps describing the actual vegetation. In future research, MTHIS can be used to analyze the spatial and hierarchical structure of any type of remote sensing time series and their relation to ecosystem processes.     

On the assessment of economic risk: factorial design versus Monte Carlo methods

The feasibility of large investment projects (such as gas transmission and power system projects) has many aspects. Usually, this problem cannot be modeled as a single optimization problem; instead, the multiple aspects (demand, supply, prices, investment costs) are modeled separately. Each aspect may require a large, nonlinear submodel. The results of such a submodel can often be summarized by one or a few variables, which combine all the submodel's information; for example, total demand is the sum of the demand per customer type, each type being modeled separately. Traditionally, the feasibility of the investment project is then judged by combining the results of the various submodels for the ‘base case’ values of all model inputs.This base case information, however, is not sufficient for the decision makers; they also like to know the economic risk they are taking. To assess this risk on the project level (Hertz, D. B., Risk analysis in capital investment. Harvard Business Review, 1964, 95–106) developed a method known as risk analysis. This method is based on the estimated probability distribution of a project's net present value (NPV). This distribution is obtained by introducing distributions for the model inputs. The project's economic risk is then. expressed as the probability of a negative NPV exceeding a critical value (say) α. Nowadays this approach is becoming popular, because many software packages (such as @RISK and Crystal Ball) facilitate such a risk analysis. Although Hertz's risk analysis is appealing, it has a number of theoretical and practical flaws, which may lead to wrong conclusions. These flaws are discussed in this paper.From a modelling point of view, Hertz's risk analysis is similar to analysing the technological or operational risk of an investment. However, economic risk and technological risk are different concepts that require different analyses. In this paper these differences are discussed and it is shown that Hertz's risk analysis does not measure what is normally meant by a project's economic risk. Furthermore, the information requirements for the application of risk analysis to large investment projects are formidable; this makes the results of Hertz's investment analysis unreliable. Less information is required by sensitivity analysis based on the statistical design of experiments (such as 2^k−P designs); this analysis is more robust, and leads to results that better satisfy the information needs of decision makers.     

Refined Epistemic Entrenchment

Epistemic entrenchment, as presented by Gärdenfors and Makinson (1988) and Gärdenfors (1988), is a formalisation of the intuition that, when forced to choose between two beliefs, an agent will giveup the less entrenched one. While their formalisation satisfactorilycaptures the intuitive notion of the entrenchment of beliefs in a number ofaspects, the requirement that all wffs be comparable has drawn criticismfrom various quarters. We define a set of refined versions of theirentrenchment orderings that are not subject to the same criticism, andinvestigate the relationship between the refined entrenched orderings,the entrenchment orderings of Gärdenfors and Makinson, and AGM theorycontraction (Alchourrón et al., 1985). To conclude, we compare refinedentrenchment with two related approaches to epistemic entrenchment.     

Investigation of the Failure Mechanism of HTPB/AP/Al Propellant by In‐situ Uniaxial Tensile Experimentation in SEM

The failure mechanism of a propellant consisting of hydroxyl terminated poly‐butadiene filled with ammonium perchlorate and aluminum (HTPB/AP/Al) was determined by performing in‐situ uniaxial tensile tests in a scanning electron microscope (SEM). The experimental test plan contained uniaxial tensile test experiments performed at room temperature (25 °C) at three different strain rates (30, 150 and 750 μm min⁻¹). The in‐situ images and in‐situ videos collected by the SEM were correlated with the stress‐strain diagrams created with the tensile experiments, in order to relate the failure mechanism to the features found in the stress‐strain diagram. No significant strain rate dependency of the failure mechanism was observed when working with strain rates up to 750 μm min⁻¹ and working at room temperature. The stress‐strain diagram showed indications of existing cracks and voids opening up prior to the creation of new cracks and/or voids in the sample, debonding of binder with AP particles as well as nucleation and coalescence of voids. On the fracture surfaces of the samples, it was apparent that the binder cleanly separated from the large AP particles but had a better bond with the aluminum particles. However, a difference in the appearance of a short drawing phase in the stress‐strain diagram of the propellant is observed at different strain rates. The presented results clearly demonstrate the major advantage of the combination of microscopic tensile tests with microscopic observations, linking the stress‐strain behavior to the mechanical deformation processes taking place in these propellant samples at the microscopic level.     

Comment on Fossil-fuel constraints on global warming by A. Zecca and L. Chiari [Energy Policy 38 (2010) 1–3]

Zecca and Chiari (2010) have sought to challenge the findings of Nel and Cooper (2009), who argued that the impending peak and decline of fossil fuel production will most likely lead to a lower emissions trajectory than the majority of scenarios offered by the IPCC. Zecca and Chiari used their own model to produce a higher projection of atmospheric CO₂ concentration, drawing on the conclusions of Archer (2005) to do so.     

Self-healing capacity of Mullite-Yb2SiO5 environmental barrier coating material with embedded Ti2AlC MAX phase particles

Repetitive heating and cooling cycles inevitably cause crack damage of hot gas components of gas turbine engines, such as blades and vanes. In this study the self-healing capacity is investigated of mullite + ytterbium monosilicate (Yb₂SiO₅) as EBC material with Ti₂AlC MAX phase particles embedded as a crack-healing agent. The effect of Ti₂AlC in the EBC was compared with the self-healing ability of the mullite + Yb₂SiO₅ material. After introducing cracks by Vickers indentation on the surface of each sample, crack healing was realized by controlling the temperature and time during the post-heat-treatment process. For the mullite + Yb₂SiO₅ composite with Ti₂AlC particles, crack healing occurred at 1000 °C, while in the case of the mullite + Yb₂SiO₅ composite without Ti₂AlC, a sustained temperature of 1300 °C or higher was required. Compared with the healing of the mullite + Yb₂SiO₅ composite by the formation of a eutectic phase, the addition of Ti₂AlC promoted healing via the oxidation of Ti and Al. Notably, the surface formation of a ternary oxide of Ti–Yb–O was confirmed, which completely covered the damage area. Consequently, the addition of a Ti₂AlC MAX phase to the EBC composite resulted in a complete strength recovery, while the mullite + Yb₂SiO₅ composite without Ti₂AlC showed a strength recovery of about 80%. Furthermore, by analyzing the indentation load–displacement curve to indicate the role of Ti₂AlC, the addition of Ti₂AlC improved both the hardness and stiffness of the composite.     

Advanced water treatment with manganese oxide for the removal of 17alpha-ethynylestradiol (EE2)

Municipal wastewater is supposed to be one of the most important sources of endocrine-disrupting compounds (EDCs) in water. Therefore, advanced treatments and cost-efficient techniques should be developed to prevent the spread of this type of pollution into the environment. In this view, experiments were conducted in which the removal of 17alpha-ethynylestradiol (EE2), a synthetic and persistent estrogen, from water was monitored in three upstream bioreactors (UBRs), filled with, respectively, sand, granulated activated carbon (GAC) and MnO(2) granules. Tap water, spiked with 15,000ngEE2/L was filtered through the reactors with a hydraulic retention time of approximately 1h. The removal of EE2 in the sand, GAC and MnO(2) reactors was, respectively, 17.3%,>99.8% and 81.7%. The removal in the GAC reactor was mainly due to adsorption. The MnO(2) reactor, however, removed significantly more EE2 than could be predicted from its adsorption capacity, probably thanks to its catalytic properties. These catalytic properties could make it a cost-efficient technique for the removal of EE2, but further research at more environmentally relevant concentrations is needed.     

Anaerobic treatment of wastes containing methanol and higher alcohols

Experiments have been performed to ascertain the feasibility of anaerobic digestion for the treatment of an alcoholic waste (i.e. fusel oil), consisting of approx. 50% methanol and 50% higher alcohols. Batch experiments as well as continuous experiments have been conducted. The continuous experiments have been carried out using the “Upflow Anaerobic Sludge Blanket” (UASB-) process. As inoculum a sugar beet waste grown and highly settleable and active anaerobic sludge (SBA-sludge) has been used. The SBA-sludge was shown to be superior to digested sewage sludge as seed material for an anaerobic treatment process, because—although it in fact is adapted to the fermentation of volatile fatty acids (VFA)—it does not have any significant difficulty with respect to the methanogenesis of the alcohols present in the fusel oil waste. The breakdown of higher alcohols starts immediately and that of methanol within a few days, depending on the initial load applied. In the UASB-experiments sludge loads up to 0.6 kg COD·kg VSS⁻¹·day⁻¹ could already be well accommodated within 1 week, so that within this period a space load could be handled as high as 20 kg COD·m⁻³·day⁻¹, simply by supplying the reactor with approx. 30 kg SBA-VSS·m⁻³ averaged over the total reactor volume.Contrary to recent findings of Smith & Mah (Appl. envir. Microbial. 36, 870–879, 1978), which were obtained with a pure culture of Methanosarcina barkeri, the sludge is capable of fermenting VFA and methanol rapidly and simultaneously, provided the conditions for VFA and methanol fermentation are favourable. However, as in previous experiments with aqueous solutions of methanol (Lettinga et al., Water Res. 13, 725–737, 1979), we observed that the digestion process can easily become upset, especially with respect to the degradation of VFA. Once again indications have been obtained that one or more trace elements are of eminent importance with respect to the stability of the process. At present the operation of a stable anaerobic treatment process for methanolic wastes cannot be guaranteed.