Supramolecular spangling, crocheting, and knitting of functionalized pyrene molecules on a silver surface

Pyrenes, as photoactive polycyclic aromatic hydrocarbons (PAHs), represent promising modules for the bottom-up assembly of functional nanostructures. Here, we introduce the synthesis of a family of pyrene derivatives peripherally functionalized with pyridin-4-ylethynyl termini and comprehensively characterize their self-assembly abilities on a smooth Ag(111) support by scanning tunneling microscopy. By deliberate selection of number and geometric positioning of the pyridyl-terminated substituents, two-dimensional arrays, one-dimensional coordination chains, and chiral, porous kagomé-type networks can be tailored. A comparison to phenyl-functionalized reference pyrenes, not supporting the self-assembly of ordered structures at low coverage, highlights the role of the pyridyl moieties for supramolecular crocheting and knitting. Furthermore, we demonstrate the selective spangling of pores in the two-dimensional pyrene assemblies by a distinct number of iodine atoms as guests by atomically resolved imaging and complementary X-ray photoelectron spectroscopy

Urban agriculture: a global analysis of the space constraint to meet urban vegetable demand

Urban agriculture (UA) has been drawing a lot of attention recently for several reasons: the majority of the world population has shifted from living in rural to urban areas; the environmental impact of agriculture is a matter of rising concern; and food insecurity, especially the accessibility of food, remains a major challenge. UA has often been proposed as a solution to some of these issues, for example by producing food in places where population density is highest, reducing transportation costs, connecting people directly to food systems and using urban areas efficiently. However, to date no study has examined how much food could actually be produced in urban areas at the global scale. Here we use a simple approach, based on different global-scale datasets, to assess to what extent UA is constrained by the existing amount of urban space. Our results suggest that UA would require roughly one third of the total global urban area to meet the global vegetable consumption of urban dwellers. This estimate does not consider how much urban area may actually be suitable and available for UA, which likely varies substantially around the world and according to the type of UA performed. Further, this global average value masks variations of more than two orders of magnitude among individual countries. The variations in the space required across countries derive mostly from variations in urban population density, and much less from variations in yields or per capita consumption. Overall, the space required is regrettably the highest where UA is most needed, i.e., in more food insecure countries. We also show that smaller urban clusters (i.e., <100 km2 each) together represent about two thirds of the global urban extent; thus UA discourse and policies should not focus on large cities exclusively, but should also target smaller urban areas that offer the greatest potential in terms of physical space

Organic Agriculture

Consumers are increasingly aware of the health- and safety-related implications of the food which they can buy in the market. At the same time, households have become more aware of their environmental responsibilities. Regarding the production of food, a crucial and multifunctional role is played by agriculture. The way vegetables, fruits, and other crops are grown and how livestock is raised has an impact on the environment and landscape. Operations performed by farmers, such as water management, can be dangerous for the soil and the whole ecosystem. Consequently, there is a search for natural ways of sustaining the impact of agriculture on the environment. In this context, one of the most popular ideas is organic agriculture. In the literature on the subject, there are many concepts that some authors consider to be synonymous even as others argue that these terms are not interchangeable. There is, for example, "organic agriculture," "alternative agriculture," "sustainable agriculture," "ecological agriculture," "biological agriculture," "niche farming," "community-supported agriculture," and "integrated pest management." Very often, techniques and products related to organic agriculture are described by marketing experts with the use of abbreviations such as "bio" and "eco." Products with such markings and labels are increasingly popular in stores that often give them separate shelves for their sale. Despite the higher price compared to conventional products, they are increasingly sought by consumers. The entry examines the various impacts of organic agriculture with a view to these trends

Spintronics: Fundamentals and applications

Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. This article reviews the current status of this subject, including both recent advances and well-established results. The primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport in semiconductors and metals. Spin transport differs from charge transport in that spin is a nonconserved quantity in solids due to spin-orbit and hyperfine coupling. The authors discuss in detail spin decoherence mechanisms in metals and semiconductors. Various theories of spin injection and spin-polarized transport are applied to hybrid structures relevant to spin-based devices and fundamental studies of materials properties. Experimental work is reviewed with the emphasis on projected applications, in which external electric and magnetic fields and illumination by light will be used to control spin and charge dynamics to create new functionalities not feasible or ineffective with conventional electronics.Comment: invited review, 36 figures, 900+ references; minor stylistic changes from the published versio

Exchanging knowledge to improve organic arable farming: an evaluation of knowledge exchange tools with farmer groups across Europe

Organic farming is knowledge intensive. To support farmers in improving yields and organic agriculture systems, there is a need to improve how knowledge is shared. There is an established culture of sharing ideas, successes and failures in farming. The internet and information technologies open up new opportunities for knowledge exchange involving farmers, researchers, advisors and other practitioners. The OK-Net Arable brought together practitioners from regional Farmer Innovation Groups across Europe in a multi-actor project to explore how online knowledge exchange could be improved. Feedback from the groups was obtained for 35 ‘tools’, defined as end-user materials, such as technical guides, videos and websites informing about practices in organic agriculture. The groups also selected one practice to test on farms, sharing their experiences with others through workshops, exchange visits and through videos

The greenhouse gas impacts of converting food production in England and Wales to organic methods

Agriculture is a major contributor to global greenhouse gas (GHG) emissions and must feature in efforts to reduce emissions. Organic farming might contribute to this through decreased use of farm inputs and increased soil carbon sequestration, but it might also exacerbate emissions through greater food production elsewhere to make up for lower organic yields. To date there has been no rigorous assessment of this potential at national scales. Here we assess the consequences for net GHG emissions of a 100% shift to organic food production in England and Wales using life-cycle assessment. We predict major shortfalls in production of most agricultural products against a conventional baseline. Direct GHG emissions are reduced with organic farming, but when increased overseas land use to compensate for shortfalls in domestic supply are factored in, net emissions are greater. Enhanced soil carbon sequestration could offset only a small part of the higher overseas emissions