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Abstract With drastic fossil fuel depletion and environmental deterioration concerns, a move towards a more sustainable bioenergy-based economy is essential. Lately, the application of microwave (MW) irradiation for waste processing has been attracting interest globally. MW-assisted heating possesses several advantages such as the provision of high microwave energy into dielectric materials with deeper penetration for internal heat generation, showing beneficial features in improving the heating rate and reducing the reaction time. Consequently, the most recent literature regarding the applications of MW-assisted heating for biomass pretreatment as well as biofuel and bioenergy production was reviewed and consolidated in this study. An impressive increase in the product yield and improvement of the product properties are reported, with the use of MW-assisted heating in several conversion routes to produce biofuels. Despite being a promising technology for biofuel production, some major fundamental data of MW-assisted heating have not been comprehensively identified. Therefore, the feasibility of this technology for large-scale implementation is still subpar. Understanding the interaction between the feedstock and the microwave electromagnetic field, and the optimization of several operational and mechanical parameters are the two main keystones that would propel the industrialization of MW heating in the near future. This provides key insights leading to increased feasibility and more advanced application of MW heating.

Wood biomass is turned into industrial fuel through chipping. The efficiency of chipping depends on many factors, including chipper knife wear. Chipper knife wear was determined through a long-term follow-up study, conducted at a waste wood recycling yard. Knife wear determined a sharp drop of productivity (>20%) and a severe decay in product quality. Dry sharpening with a grinder mitigated this effect, but it could not replace proper wet sharpening. Increasing the frequency of wet sharpening sessions determined a moderate increase of knife depreciation cost, but it could drastically enhance machine performance and reduce biomass processing cost. Since benefits largely exceed costs, increasing the frequency of wet sharpening sessions may be an effective measure for reducing overall chipping cost. If the main goal of a chipper operator is to increase productivity and/or decrease fuel consumption, then managing knife wear should be a primary target. (C) 2014 Elsevier Ltd. All rights reserved.

The growing interest in forest biomass has made chipping increasingly popular all across Europe. Many operators have equipped for the purpose, but the large variety of working conditions found in the European forests makes it difficult to correctly estimate the productivity of each specific operation, leading to uncertainty in crucial decisions, such as: operation scheduling, price setting, machinery selection and acquisition. In 2001, the Italian National Council for Research (CNR) and the University of California (UC) developed a spreadsheet freeware capable of returning reliable estimates of chipping productivity and cost, on the basis of user-defined input data. The model is still available from the CNR website and is the object of frequent downloading and inquiries. Such model contains a set of predictive equations derived from the results of 102 field trials, conducted with 30 different machines, under a range of working conditions. In order to facilitate comparison with other estimates and to achieve methodological transparency, the equations are assembled into a simple Microsoft Excel workbook, and the costs are calculated with standard costing methods currently used in Forest and Agricultural Engineering. Since then CNR has continued to work on the subject, with the goal of updating and refining the model. Such work has included 45 validation tests and a separate study on the delay (idle) time typical for different chipping operation layouts. The study was concluded in 2009 and confirms that the model developed by CNR can provide reliable estimates of chipper productivity under a range of operational conditions. Authors believe that such a model can assist European foresters in keeping ahead with the growing biomass sector, thus helping them to seize an important business opportunity.

Decreasing nutrient losses from excessive synthetic fertilizer inputs is the direct and valid way to address low nutrient use efficiency and the related environmental consequences. Here, we established a comprehensive database of nitrogen (N), phosphorus (P), and carbon (C) losses from rice paddy fields in China, which we used to evaluate fertilization-induced losses and the impact of environmental factors, and to mitigate losses by adopting alternative fertilization options and setting input thresholds. Our results showed that most N-loss pathways had exponential increases with additional N input. In average, 23.8% of the N applied was lost via NH3 (16.1%), N2O (0.3%), leaching (4.8%), and runoff (2.6%). Total P loss was approximately 2.7% of the input, composed of leaching (1.3%) and runoff (1.4%). C lost as CH4 accounted for 4.9% of the organic C input. A relative importance analysis indicated that climate or soil variation rather than fertilizer rate was the dominant factor driving N and P leaching, and CH4 emissions. Based on the sensitivity of multiple N-loss pathways to N fertilization, we propose upper thresholds for N inputs of 142–191 kg N ha−1 across four rice types, which would avoid dramatic increases in N losses. Compared to conventional chemical fertilization, alternative fertilization options had diverse performances: enhanced-efficiency N fertilizer reduced N loss rate by 7.8 percent points and the global warming potential (GWP, considering N2O and CH4 emissions) by 28.8%; combined manure and chemical N fertilizer reduced N loss rate by 9.0 percent points but increased the GWP by 56.9%; straw return had no effect on total N loss but almost doubled the GWP. Using nutrient sources most appropriate to site-specific conditions is demonstrated as a robust way to decrease nutrient losses. Setting nutrient input thresholds would also contribute to the mitigation of environmental pollution, especially in regions with poor fertilization recommendation systems.

The repercussions of climate change will be felt in various ways throughout both natural and human systems in Sub-Saharan Africa. Climate change projections for this region point to a warming trend, particularly in the inland subtropics; frequent occurrence of extreme heat events; increasing aridity; and changes in rainfall—with a particularly pronounced decline in southern Africa and an increase in East Africa. The region could also experience as much as one meter of sea-level rise by the end of this century under a 4 °C warming scenario. Sub-Saharan Africa’s already high rates of undernutrition and infectious disease can be expected to increase compared to a scenario without climate change. Particularly vulnerable to these climatic changes are the rainfed agricultural systems on which the livelihoods of a large proportion of the region’s population currently depend. As agricultural livelihoods become more precarious, the rate of rural–urban migration may be expected to grow, adding to the already significant urbanization trend in the region. The movement of people into informal settlements may expose them to a variety of risks different but no less serious than those faced in their place of origin, including outbreaks of infectious disease, flash flooding and food price increases. Impacts across sectors are likely to amplify the overall effect but remain little understood.

This paper serves as an introduction to this special issue on new developments in urban transportation planning. The papers in this issue highlight how physical mobility is still an essential priority for urban life, but that there are associated costs in the terms of environmental impacts, quality of life and economic performance of cities. Four features of the emerging urban transportation field are identified. The first defining feature is that it is a discipline in the midst of a paradigmatic transition. Second is its overarching aim of achieving sustainable urban mobility as part of a broader effort towards enhancing quality of life in cities. The third feature is the emphasis on collaboration, integration and exchange with other professions and policy sectors. The last distinctive feature is the recognition that urban transportation planning is a communication-oriented activity.

Feedbacks between land carbon pools and climate provide one of the largest sources of uncertainty in our predictions of global climate. Estimates of the sensitivity of the terrestrial carbon budget to climate anomalies in the tropics and the identification of the mechanisms responsible for feedback effects remain uncertain. The Amazon basin stores a vast amount of carbon, and has experienced increasingly higher temperatures and more frequent floods and droughts over the past two decades. Here we report seasonal and annual carbon balances across the Amazon basin, based on carbon dioxide and carbon monoxide measurements for the anomalously dry and wet years 2010 and 2011, respectively. We find that the Amazon basin lost 0.48 ± 0.18 petagrams of carbon per year (Pg C yr(-1)) during the dry year but was carbon neutral (0.06 ± 0.1 Pg C yr(-1)) during the wet year. Taking into account carbon losses from fire by using carbon monoxide measurements, we derived the basin net biome exchange (that is, the carbon flux between the non-burned forest and the atmosphere) revealing that during the dry year, vegetation was carbon neutral. During the wet year, vegetation was a net carbon sink of 0.25 ± 0.14 Pg C yr(-1), which is roughly consistent with the mean long-term intact-forest biomass sink of 0.39 ± 0.10 Pg C yr(-1) previously estimated from forest censuses. Observations from Amazonian forest plots suggest the suppression of photosynthesis during drought as the primary cause for the 2010 sink neutralization. Overall, our results suggest that moisture has an important role in determining the Amazonian carbon balance. If the recent trend of increasing precipitation extremes persists, the Amazon may become an increasing carbon source as a result of both emissions from fires and the suppression of net biome exchange by drought.

Better prediction of turbulent airflow around urban trees is necessary because it impacts urban pollutant dispersion, outdoor thermal comfort, energy efficiency, pedestrian-level comfort and urban heat island mitigation. A major challenge is how to obtain an accurate numerical model of the turbulent flow field around trees and an improved parameterization of the turbulent momentum deficit using the drag coefficient (Cd). To address this challenge, we use wind tunnel tests and real trees to measure Cd for four common subtropical tree species: Ficus microcarpa, Mangifera indica, Michelia alba and Bauhinia blakeana. The results show that the Cd of the four trees ranges from 0.523 to 0.932, and that the negative relationship between Cd and wind speed (U) can be expressed by the exponential formula Cd=a*U−b. A three-dimensional model of wind modification by trees is proposed, and its accuracy is verified with wind tunnel measurements. With precise Cd and model, the predictability of the influence of trees on urban wind in subtropical areas is enhanced (root mean square error RMSE ranging from 2.89 m/s to 0.45 m/s). Future development and applications of the numerical model will help provide useful guidelines for urban landscape management and sustainable urban planning in terms of urban ventilation.