Alfvèn波与慢激波的相互作用

本文分析了斜入射波矢与背景磁场和激波法线共面时,一维小幅度Alfvèn波干扰下,慢激波的稳定性问题;论证了Alfvèn波在慢激波上的射线反射和折射规律;并就日冕慢激波情形进行了具体的数值计算。结果表明,除非上游法向流速接近上游法向Alfvèn波波速,在上述斜入射的Alfvèn波干扰下,慢激波总是稳定的。日冕慢激波是这种稳定性的一个例子;日冕慢激波的存在,能使起源于日冕向行星际空间传播（不管它起源于日冕慢激波之内或外）的Alfvèn波的法向能流密度增大。     

Greedy or needy? Land use and climate impacts of food in 2050 under different livestock futures

Both supply and demand side changes are necessary to achieve a sustainable food system. However, the weight accorded to these depends on one’s view of what the priority goals are for the food system and the extent to which production systems versus consumption patterns are open to change. Some stakeholders see the problem as one of ‘not enough food’ and focus on the need to sustainably increase supply, while others consider the resource demanding and ‘greedy’ consumption patterns of the Western world as the main problem and emphasize the need to shift diets. In this study global land use and greenhouse gas emissions are estimated for a set of scenarios, building on four ‘livestock futures’ reflecting these different perspectives. These scenarios are: further intensification of livestock systems; a transition to plant-based eating; a move towards artificial meat and dairy; and a future in which livestock production is restricted to the use of ‘ecological leftovers’ i.e. grass from pastures, food waste and food and agricultural byproducts. Two dietary variants for each scenario are modelled: 1) a projected diet following current trends and 2) a healthy diet with more fruits and vegetables and fewer animal products, vegetable oils and sugar. Livestock production in all scenarios (except the baseline scenario) was assumed to intensify to current levels of intensive production in North-Western Europe. For each scenario, several variant assumptions about yield increases and waste reductions were modelled. Results show that without improvements in crop productivity or reductions on today’s waste levels available cropland will only suffice if production of all protein currently supplied by animal foods is replaced by (hypothetical) artificial variants not requiring any land. With livestock intensities corresponding to current ones in North-Western Europe and with yield gaps closed by 50% and waste reduced by 50%, available cropland will suffice for all scenarios that include a reduction of animal products and/or a transition to poultry or aquaculture. However, in the scenario based on an extrapolation of current consumption patterns (animal product amounts and types consumed in proportions corresponding to the current average consumption in different world regions) and with livestock production based on feed from cropland, available cropland will not be enough. The scenario that makes use of pastures for ruminant production and food waste for pigs, uses considerably less cropland and could provide 40–56 kg per capita per year of red meat. However, such a livestock future would not reduce GHG emissions from agriculture on current levels. This study confirms previous research that to achieve a sustainable food future, action is needed on all fronts; improved supply and reduced demand and waste.     

The global environmental paw print of pet food

Global pet ownership, especially of cats and dogs, is rising with income growth, and so too are the environmental impacts associated with their food. The global extent of these impacts has not been quantified, and existing national assessments are potentially biased due to the way in which they account for the relative impacts of constituent animal by-products (ABPs). ABPs typically have lower value than other animal products (i.e. meat, milk and eggs), but are nevertheless associated with non-negligible environmental impacts. Here we present the first global environmental impact assessment of pet food. The approach is novel in applying an economic value allocation approach to the impact of ABPs and other animal products to represent better the environmental burden. We find annual global dry pet food production is associated with 56–151 Mt CO₂ equivalent emissions (1.1%−2.9% of global agricultural emissions), 41–58 Mha agricultural land-use (0.8–1.2% of global agricultural land use) and 5–11 km³ freshwater use (0.2–0.4% of water extraction of agriculture). These impacts are equivalent to an environmental footprint of around twicethe UK land area, and would make greenhouse gas emission from pet food around the 60th highest emitting country, or equivalent to total emissions from countries such as Mozambique or the Philippines. These results indicate that rising pet food demand should be included in the broader global debate about food system sustainability.     

Variation in low food access areas due to data source inaccuracies

Several spatial measures of community food access identifying so called “food deserts” have been developed based on geospatial information and commercially-available, secondary data listings of food retail outlets. It is not known how data inaccuracies influence the designation of Census tracts as areas of low access. This study replicated the U.S. Department of Agriculture Economic Research Service (USDA ERS) food desert measure and the Centers for Disease Control and Prevention (CDC) non-healthier food retail tract measure in two secondary data sources (InfoUSA and Dun & Bradstreet) and reference data from an eight-county field census covering 169 Census tracts in South Carolina. For the USDA ERS food deserts measure accuracy statistics for secondary data sources were 94% concordance, 50–65% sensitivity, and 60–64% positive predictive value (PPV). Based on the CDC non-healthier food retail tracts both secondary data demonstrated 88–91% concordance, 80–86% sensitivity and 78–82% PPV. While inaccuracies in secondary data sources used to identify low food access areas may be acceptable for large-scale surveillance, verification with field work is advisable for local community efforts aimed at identifying and improving food access.     

Strengthening the core,improving access: Bringing healthy food downtown via a farmers' market move

Diet-related diseases are a major public health concern, and food environment research explores how built environmental interventions can address nutritional inequalities. Yet other, more direct intervention approaches may also yield positive benefits for residents living in food deserts. This paper presents a case study of a farmers' market move and its effects on healthy food accessibility and customer characteristics in a community with many food deserts. 844 surveys collected in 2011 and 2015 determine customer purchasing patterns and demographics at the Flint (Michigan) Farmers' Market. The market move has meant improved healthy food accessibility for mobility-constrained and low-income residents throughout the region. Counter to past research suggesting that farmers' markets tend to serve higher income groups, socioeconomically disadvantaged people constitute a major consumer demographic at Flint's market. The results of this research have broad utility for communities seeking to ameliorate the challenges of bringing healthy food to isolated food deserts by demonstrating that positioning healthy food in a prominent, central location will attract residents from such neighborhoods while engaging a broad clientele.     

Zoning in: The contributions of buyam–sellams to constructing Cameroon’s wild food zone

Studies of forests in Africa employ the term zone to denote a particular type of forested area. This limited usage speaks to a need for human geographers to pay more attention to elaborating and engaging with the concept of the zone. This article shows why human geography should pay the ‘zone’ more attention. Using Cameroon’s humid forest zone (HFZ) as a case study, the article focuses on how conceptual elaboration of the ‘zone’ can inform analyses of the food product trade in Cameroon. This trade is organized around various types of buyers and sellers (or buyam–sellam in pidgin), and offers a wide variety of wild products to Cameroon’s urban food consumers, including fruits and vegetables, game meat, condiments, medicinal plants, and fibers. Drawing on fieldwork surveys, interviews and focus groups in twenty-four markets of 203 buyam–sellams and 197 of their customers during the wet and dry seasons, this article analyzes narratives about Cameroon’s wild food zone. It ultimately shows what scholarly attention to the ‘zone’ offers in this case that other spatial concepts do not.     

Repoliticising and scaling-up ethical consumption: Lessons from public procurement for school meals in Brazil

Ethical consumption is a vibrant field of research but suffers from both empirical and conceptual biases. Empirically, too much of the data is gathered in the global North, often framing a false binary in which consumption spaces are located in the global North while production takes place in the global South. Conceptually, there is a growing demand for researchers to move away from an emphasis on the individual consumer and instead focus on collective agency and structural change. This paper offers contributions to both of these frontiers of research. It reports on data on ethical consumption and public procurement, collected through the first ever large scale representative survey on procurement criteria and 16 focus groups in Brazil. It concretises these debates by focusing specifically on the pioneering Brazilian school meals policy which supports both “family farms” and organic modes of production at a massive scale, in providing meals to 43 million Brazilian children. Lessons learnt from the study include, firstly, the potential for successfully scaling up ethical consumption through public procurement; secondly, the way in which such scaling-up forces the public debate to engage with food production and consumption at a systemic level; and thirdly, how the systems-level debate leads to a repoliticisation of the discussion of the cultural, social, economic and environmental role of food and farming. The focus group discussions showed a high degree of support for the school meals policy, including from affluent citizens whose children would not benefit from the scheme. Surveys also showed strong support from Brazilian citizens for using environmental and social criteria in public procurement.     

The anticipatory governance of sustainability transformations: Hybrid approaches and dominant perspectives

Anticipation methods and tools are increasingly used to try to imagine and govern transformations towards more sustainable futures across different policy domains and sectors. But there is a lack of research into the steering effects of anticipation on present-day governance choices, especially in the face of urgently needed sustainability transformations. This paper seeks to understand how different perspectives on anticipatory governance connect to attempts to guide policy and action toward transformative change. We analyze perspectives on anticipatory governance in a global network of food system foresight practitioners (Foresight4Food) – using a workshop, interviews, and a survey as our sources of data. We connect frameworks on anticipatory governance and on transformation to analyse different perspectives on the future and their implications for actions in the present to transform food systems and offer new insights for theory and practice. In the global Foresight4Food network, we find that most foresight practitioners use hybrid approaches to anticipatory governance that combine fundamentally different assumptions about the future. We also find that despite these diverse food futures, anticipation processes predominantly produce recommendations that follow more prediction-oriented forms of strategic planning in order to mitigate future risks. We further demonstrate that much anticipation for transformation uses the language on deep uncertainty and deliberative action without fully taking its consequences on board. Thus, opportunities for transforming future food systems are missed due to these implicit assumptions that dominate the anticipatory governance of food systems. Our combined framework helps researchers and practitioners to be more reflexive of how assumptions about key human systems such as food system futures shape what is prioritized/marginalized and included/excluded in actions to transform such systems.     

Religious values and family upbringing as antecedents of food waste avoidance

Consumer intention to avoid food waste is determined by various socio-demographic and psychographic/psychological factors. While many of these factors have been well studied, some remain under-researched. This is the case for religious values and family upbringing that may represent strong antecedents of personal norms towards food waste avoidance. This study tests the role of these factors on a sample (n = 566) of consumers in Poland, a society with strong religious traditions and family ties. The results indicate that religious values play an important role in family upbringing which, by influencing personal social and environmental motives, mediates the effect on personal norms to avoid food waste. This suggests that religious leaders should be engaged in the design of food waste prevention campaigns specifically targeting parents. This is to trigger a cross-generational spillover effect whereby family morals on food waste avoidance are transferred from parents to children and reinforced by religious values.