Showing papers by "Technical University of Berlin published in 2013"
Alternatives1, John Innes Centre2, University of Bonn3, University of North Carolina at Chapel Hill4, University of Wisconsin-Madison5, University of Utah6, University of Southern California7, University of Edinburgh8, University of Warwick9, Harvard University10, University College Cork11, University of Queensland12, University of Hertfordshire13, University of Potsdam14, University of California, San Diego15, Goethe University Frankfurt16, University of California, San Francisco17, University of Delaware18, Uppsala University19, Medical University of Vienna20, J. Craig Venter Institute21, University of Hawaii at Manoa22, Leibniz Association23, University of Iowa24, University of Aberdeen25, Georgia Institute of Technology26, University of California, Berkeley27, University of Groningen28, Princeton University29, University of Marburg30, University of Illinois at Urbana–Champaign31, Saarland University32, Norwegian University of Life Sciences33, Massey University34, Toyama Prefectural University35, ETH Zurich36, University of Saskatchewan37, Rutgers University38, Scripps Research Institute39, University of Helsinki40, Texas A&M University41, National Institutes of Health42, Technical University of Berlin43, University of Otago44, University of Cambridge45, University of Alberta46, Michigan State University47, Hofstra University48
TL;DR: This review presents recommended nomenclature for the biosynthesis of ribosomally synthesized and post-translationally modified peptides (RiPPs), a rapidly growing class of natural products.
1,560 citations
TL;DR: In this paper, a state-of-the-art update on the most recent developments concerning the advanced heteroatom doping of carbon that goes beyond nitrogen is given, with respect to their boron-, sulphur-and phosphorus-doping.
Abstract: Heteroatom doped carbon materials represent one of the most prominent families of materials that are used in energy related applications, such as fuel cells, batteries, hydrogen storage or supercapacitors. While doping carbons with nitrogen atoms has experienced great progress throughout the past decades and yielded promising material concepts, also other doping candidates have gained the researchers' interest in the last few years. Boron is already relatively widely studied, and as its electronic situation is contrary to the one of nitrogen, codoping carbons with both heteroatoms can probably create synergistic effects. Sulphur and phosphorus have just recently entered the world of carbon synthesis, but already the first studies published prove their potential, especially as electrocatalysts in the cathodic compartment of fuel cells. Due to their size and their electronegativity being lower than those of carbon, structural distortions and changes of the charge densities are induced in the carbon materials. This article is to give a state of the art update on the most recent developments concerning the advanced heteroatom doping of carbon that goes beyond nitrogen. Doped carbon materials and their applications in energy devices are discussed with respect to their boron-, sulphur- and phosphorus-doping.
1,490 citations
TL;DR: The segregation and leaching mechanisms revealed here highlight the complexity with which shape-selective nanoalloys form and evolve under reactive conditions.
Abstract: Shape-selective monometallic nanocatalysts offer activity benefits based on structural sensitivity and high surface area. In bimetallic nanoalloys with well-defined shape, site-dependent metal surface segregation additionally affects the catalytic activity and stability. However, segregation on shaped alloy nanocatalysts and their atomic-scale evolution is largely unexplored. Exemplified by three octahedral PtxNi1-x alloy nanoparticle electrocatalysts with unique activity for the oxygen reduction reaction at fuel cell cathodes, we reveal an unexpected compositional segregation structure across the {111} facets using aberration-corrected scanning transmission electron microscopy and electron energy-loss spectroscopy. In contrast to theoretical predictions, the pristine PtxNi1-x nano-octahedra feature a Pt-rich frame along their edges and corners, whereas their Ni atoms are preferentially segregated in their {111} facet region. We follow their morphological and compositional evolution in electrochemical environments and correlate this with their exceptional catalytic activity. The octahedra preferentially leach in their facet centres and evolve into 'concave octahedra'. More generally, the segregation and leaching mechanisms revealed here highlight the complexity with which shape-selective nanoalloys form and evolve under reactive conditions.
1,080 citations
TL;DR: In this paper, a facile synthesis of mesoporous g-CN using molecular cooperative assembly between triazine molecules is reported, which is a promising heterogeneous metal-free catalyst for organic photosynthesis, solar energy conversion, and photodegradation of pollutants.
Abstract: Graphitic carbon nitride (g-CN) is a promising heterogeneous metal-free catalyst for organic photosynthesis, solar energy conversion, and photodegradation of pollutants. Its catalytic performance is easily adjustable by modifying texture, optical, and electronic properties via nanocasting, doping, and copolymerization. However, simultaneous optimization has yet to be achieved. Here, a facile synthesis of mesoporous g-CN using molecular cooperative assembly between triazine molecules is reported. Flower-like, layered spherical aggregates of melamine cyanuric acid complex (MCA) are formed by precipitation from equimolecular mixtures in dimethyl sulfoxide (DMSO). Thermal polycondensation of MCA under nitrogen at 550 °C produces mesoporous hollow spheres comprised of tri-s-triazine based g-CN nanosheets (MCA-CN) with the composition of C3N4.14H1.98. The layered structure succeeded from MCA induces stronger optical absorption, widens the bandgap by 0.16 eV, and increases the lifetime of photoexcited charge carriers by twice compared to that of the bulk g-CN, while the chemical structure remains similar to that of the bulk g-CN. As a result of these simultaneous modifications, the photodegradation kinetics of rhodamine B on the catalyst surface can be improved by 10 times.
691 citations
TL;DR: In this paper, the authors explore the resilience domain, which is important in the field of supply chain management; they investigate the effects relational competencies have for resilience and the effect resilience, in turn, has on a supply chain's s customer value.
Abstract: Purpose – The purpose of this research is to explore the resilience domain, which is important in the field of supply chain management; it investigates the effects relational competencies have for resilience and the effect resilience, in turn, has on a supply chain ' s customer value. Design/methodology/approach – The research is empirical in nature and employs a confirmatory approach that builds on the relational view as a primary theoretical foundation. It utilizes survey data collected from manufacturing firms from three countries, which is analyzed using structural equation modeling. Findings – It is found that communicative and cooperative relationships have a positive effect on resilience, while integration does not have a significant effect. It is also found that improved resilience, obtained by investing in agility and robustness, enhances a supply chain ' s customer value. Practical implications – Some findings contrast the expectations derived from theory. Particularly, practitioners can learn t...
620 citations
TL;DR: In this article, the impacts of biochar (BC) and hydrochar (HTC) on water retention characteristics (WRC) as well as on the wettability of sandy soils, using lab and field studies.
586 citations
TL;DR: In this article, a deep multi-task artificial neural network is used to predict multiple electronic ground and excited-state properties, such as atomization energy, polarizability, frontier orbital eigenvalues, ionization potential, electron affinity and excitation energies.
Abstract: The combination of modern scientific computing with electronic structure theory can lead to an unprecedented amount of data amenable to intelligent data analysis for the identification of meaningful, novel and predictive structure?property relationships. Such relationships enable high-throughput screening for relevant properties in an exponentially growing pool of virtual compounds that are synthetically accessible. Here, we present a machine learning model, trained on a database of ab initio calculation results for thousands of organic molecules, that simultaneously predicts multiple electronic ground- and excited-state properties. The properties include atomization energy, polarizability, frontier orbital eigenvalues, ionization potential, electron affinity and excitation energies. The machine learning model is based on a deep multi-task artificial neural network, exploiting the underlying correlations between various molecular properties. The input is identical to ab initio methods, i.e.?nuclear charges and Cartesian coordinates of all atoms. For small organic molecules, the accuracy of such a ?quantum machine? is similar, and sometimes superior, to modern quantum-chemical methods?at negligible computational cost.
488 citations
TL;DR: In this paper, a deep multi-task artificial neural network is used to predict multiple electronic ground-and excited-state properties, such as atomization energy, polarizability, frontier orbital eigenvalues, ionization potential, electron affinity, and excitation energies.
Abstract: The combination of modern scientific computing with electronic structure theory can lead to an unprecedented amount of data amenable to intelligent data analysis for the identification of meaningful, novel, and predictive structure-property relationships. Such relationships enable high-throughput screening for relevant properties in an exponentially growing pool of virtual compounds that are synthetically accessible. Here, we present a machine learning (ML) model, trained on a data base of \textit{ab initio} calculation results for thousands of organic molecules, that simultaneously predicts multiple electronic ground- and excited-state properties. The properties include atomization energy, polarizability, frontier orbital eigenvalues, ionization potential, electron affinity, and excitation energies. The ML model is based on a deep multi-task artificial neural network, exploiting underlying correlations between various molecular properties. The input is identical to \emph{ab initio} methods, \emph{i.e.} nuclear charges and Cartesian coordinates of all atoms. For small organic molecules the accuracy of such a "Quantum Machine" is similar, and sometimes superior, to modern quantum-chemical methods---at negligible computational cost.
456 citations
TL;DR: In this paper, the authors propose a new measure System LCOE as the sum of generation and integration costs per unit of variable renewable energy generation (VRE) for evaluating variable renewables like wind and solar power.
Abstract: Levelized costs of electricity (LCOE) are a common metric for comparing power generating technologies. However, there is qualified criticism particularly towards evaluating variable renewables like wind and solar power based on LCOE because it ignores integration costs that occur at the system level. In this paper we propose a new measure System LCOE as the sum of generation and integration costs per unit of VRE. For this purpose we develop a conclusive definition of integration costs. Furthermore we decompose integration costs into different cost components and draw conclusions for integration options like transmission grids and energy storage. System LCOE are quantified from a power system model and a literature review. We find that at moderate wind shares (~20%) integration costs can be in the same range as generation costs of wind power and conventional plants. Integration costs further increase with growing wind shares. We conclude that integration costs can become an economic barrier to deploying VRE at high shares. This implies that an economic evaluation of VRE must not neglect integration costs. A pure LCOE comparison would significantly underestimate the costs of VRE at high shares. System LCOE give a framework of how to consistently account for integration costs and thus guide policy makers and system planers in designing a cost-efficient power system.
450 citations
TL;DR: Elements of work environment are associated with intention to leave the nursing profession but differ between countries, indicating the importance of national contexts in explaining and preventing nurses' intention to left their profession.
418 citations
TL;DR: In this article, the authors explore the utilization of two methods, namely coding and qualitative content analysis, for the first steps in the data analysis process, namely "cleaning" and organizing qualitative data.
Abstract: Qualitative research aimed at "mechanismic" explanations poses specific challenges to qualitative data analysis because it must integrate existing theory with patterns identified in the data. We explore the utilization of two methods—coding and qualitative content analysis—for the first steps in the data analysis process, namely "cleaning" and organizing qualitative data. Both methods produce an information base that is structured by categories and can be used in the subsequent search for patterns in the data and integration of these patterns into a systematic, theoretically embedded explanation. Used as a stand-alone method outside the grounded theory approach, coding leads to an indexed text, i.e. both the original text and the index (the system of codes describing the content of text segments) are subjected to further analysis. Qualitative content analysis extracts the relevant information, i.e. separates it from the original text, and processes only this information. We suggest that qualitative content analysis has advantages compared to coding whenever the research question is embedded in prior theory and can be answered without processing knowledge about the form of statements and their position in the text, which usually is the case in the search for "mechanismic" explanations. Coding outperforms qualitative content analysis in research that needs this information in later stages of the analysis, e.g. the exploration of meaning or the study of the construction of narratives.
TL;DR: A multi-organ-chip capable of maintaining 3D tissues derived from cell lines, primary cells and biopsies of various human organs is presented, providing a potential new tool for systemic substance testing.
Abstract: Current in vitro and animal tests for drug development are failing to emulate the systemic organ complexity of the human body and, therefore, to accurately predict drug toxicity. In this study, we present a multi-organ-chip capable of maintaining 3D tissues derived from cell lines, primary cells and biopsies of various human organs. We designed a multi-organ-chip with co-cultures of human artificial liver microtissues and skin biopsies, each a 1/100 000 of the biomass of their original human organ counterparts, and have successfully proven its long-term performance. The system supports two different culture modes: i) tissue exposed to the fluid flow, or ii) tissue shielded from the underlying fluid flow by standard Transwell® cultures. Crosstalk between the two tissues was observed in 14-day co-cultures exposed to fluid flow. Applying the same culture mode, liver microtissues showed sensitivity at different molecular levels to the toxic substance troglitazone during a 6-day exposure. Finally, an astonishingly stable long-term performance of the Transwell®-based co-cultures could be observed over a 28-day period. This mode facilitates exposure of skin at the air–liquid interface. Thus, we provide here a potential new tool for systemic substance testing.
TL;DR: In this article, a new metric System LCOE that accounts for integration and generation costs is proposed to evaluate variable renewables like wind and solar PV (photovoltaics) power.
TL;DR: This simultaneous XRD-XES study shows that the PS II crystals are intact during measurements at the LCLS, not only with respect to the structure of PS II, but also with regard to the electronic structure of the highly radiation-sensitive Mn4CaO5 cluster, opening new directions for future dynamics studies.
Abstract: Intense femtosecond x-ray pulses produced at the Linac Coherent Light Source (LCLS) were used for simultaneous x-ray diffraction (XRD) and x-ray emission spectroscopy (XES) of microcrystals of photosystem II (PS II) at room temperature. This method probes the overall protein structure and the electronic structure of the Mn4CaO5 cluster in the oxygen-evolving complex of PS II. XRD data are presented from both the dark state (S1) and the first illuminated state (S2) of PS II. Our simultaneous XRD-XES study shows that the PS II crystals are intact during our measurements at the LCLS, not only with respect to the structure of PS II, but also with regard to the electronic structure of the highly radiation-sensitive Mn4CaO5 cluster, opening new directions for future dynamics studies.
TL;DR: In this paper, the authors use a hybrid method for estimating the carbon footprint of cities and other human settlements in the UK explicitly linking global supply chains to local consumption activities and associated lifestyles.
Abstract: A growing body of literature discusses the CO2 emissions of cities. Still, little is known about emission patterns across density gradients from remote rural places to highly urbanized areas, the drivers behind those emission patterns and the global emissions triggered by consumption in human settlements—referred to here as the carbon footprint. In this letter we use a hybrid method for estimating the carbon footprints of cities and other human settlements in the UK explicitly linking global supply chains to local consumption activities and associated lifestyles. This analysis comprises all areas in the UK, whether rural or urban. We compare our consumption-based results with extended territorial CO2 emission estimates and analyse the driving forces that determine the carbon footprint of human settlements in the UK. Our results show that 90% of the human settlements in the UK are net importers of CO2 emissions. Consumption-based CO2 emissions are much more homogeneous than extended territorial emissions. Both the highest and lowest carbon footprints can be found in urban areas, but the carbon footprint is consistently higher relative to extended territorial CO2 emissions in urban as opposed to rural settlement types. The impact of high or low density living remains limited; instead, carbon footprints can be comparatively high or low across density gradients depending on the location-specific socio-demographic, infrastructural and geographic characteristics of the area under consideration. We show that the carbon footprint of cities and other human settlements in the UK is mainly determined by socio-economic rather than geographic and infrastructural drivers at the spatial aggregation of our analysis. It increases with growing income, education and car ownership as well as decreasing household size. Income is not more important than most other socio-economic determinants of the carbon footprint. Possibly, the relationship between lifestyles and infrastructure only impacts carbon footprints significantly at higher spatial granularity.
TL;DR: It is found that, depending on the coupling strength and range, different multichimera states arise in a transition from classical chimera states, which cannot be observed in simple phase-oscillator models.
Abstract: Systems of nonlocally coupled oscillators can exhibit complex spatio-temporal patterns, called chimera states, which consist of coexisting domains of spatially coherent (synchronized) and incoherent dynamics. We report on a novel form of these states, found in a widely used model of a limit-cycle oscillator if one goes beyond the limit of weak coupling typical for phase oscillators. Then patches of synchronized dynamics appear within the incoherent domain giving rise to a multichimera state. We find that, depending on the coupling strength and range, different multi-chimeras arise in a transition from classical chimera states. The additional spatial modulation is due to strong coupling interaction and thus cannot be observed in simple phase-oscillator models.
TL;DR: In this article, a review of recent developments in the exploration of the structure and composition of multimetallic core-shell nanoparticles is presented, addressing current achievements and challenges in the preparation as well as microscopic and spectroscopic characterization of coreshell nanocatalysts.
Abstract: Pt-based core–shell nanoparticles have emerged as a promising generation of highly active electrocatalysts to accelerate the sluggish kinetics of oxygen reduction reaction (ORR) in fuel cell systems. Their electronic and structural properties can be easily tailored by modifying the Pt shell thickness, core composition, diameter, and shape; this results in significant improvements of activity and durability over state-of-the-art pure Pt catalysts. Prompted by the relevance of efficient and robust ORR catalysts for electrochemical energy conversion, this Perspective reviews several concepts and selected recent developments in the exploration of the structure and composition of core–shell nanoparticles. Addressing current achievements and challenges in the preparation as well as microscopic and spectroscopic characterization of core–shell nanocatalysts, a concise account of our understanding is provided on how the surface and subsurface structure of multimetallic core–shell nanoparticles affect their reactiv...
TL;DR: In this article, a novel covalent triazine framework (CTF-0) was prepared by trimerization of 1,3,5-tricyanobenzene in molten ZnCl2.
Abstract: A novel covalent triazine framework (CTF-0) was prepared by trimerization of 1,3,5-tricyanobenzene in molten ZnCl2. The monomer/ZnCl2 ratio, the reaction time, and temperature significantly influence the structure and porosity of such networks. XRD measurements revealed that crystalline frameworks can be formed with surface areas around 500 m2·g–1 and high CO2 uptakes. Increasing the reaction temperature yielded an amorphous material with an enlarged surface area of 2000 m2·g–1. This material showed good catalytic activity for CO2 cycloaddition.
TL;DR: NLEVP serves both to illustrate the tremendous variety of applications of nonlinear eigenvalue problems and to provide representative problems for testing, tuning, and benchmarking of algorithms and codes.
Abstract: We present a collection of 52 nonlinear eigenvalue problems in the form of a MATLAB toolbox. The collection contains problems from models of real-life applications as well as ones constructed specifically to have particular properties. A classification is given of polynomial eigenvalue problems according to their structural properties. Identifiers based on these and other properties can be used to extract particular types of problems from the collection. A brief description of each problem is given. NLEVP serves both to illustrate the tremendous variety of applications of nonlinear eigenvalue problems and to provide representative problems for testing, tuning, and benchmarking of algorithms and codes.
TL;DR: This Perspective provides a concise overview of various cationic and neutral silicon-, boron-, and aluminum-based Lewis acids that have been identified to facilitate the heterolytic fluoride abstraction from aliphatic fluorides.
Abstract: The significant benefits of fluorinated compounds have inspired the development of diverse techniques for the activation and subsequent (de)functionalization of rather inert C–F bonds. Although substantial progress has been made in the selective activation of C(sp2)–F bonds employing transition metal complexes, protocols that address nonactivated C(sp3)–F bonds are much less established. In this regard, the use of strong main-group Lewis acids has emerged as a powerful tool to selectively activate C(sp3)–F bonds in saturated fluorocarbons. This Perspective provides a concise overview of various cationic and neutral silicon-, boron-, and aluminum-based Lewis acids that have been identified to facilitate the heterolytic fluoride abstraction from aliphatic fluorides. The potential of these Lewis acids in hydrodefluorination as well as defluorinative C–F bond functionalization reactions is highlighted. Emphasis is placed on the underlying mechanistic principles to provide a systematic classification of the in...
Qantas1, École Polytechnique Fédérale de Lausanne2, École Polytechnique3, Technical University of Berlin4, ETH Zurich5, PE International6, National Institute of Advanced Industrial Science and Technology7, Institut national de la recherche agronomique8, Chalmers University of Technology9, University of California, Santa Barbara10, Commonwealth Scientific and Industrial Research Organisation11, Radboud University Nijmegen12
TL;DR: In this paper, the authors reviewed a multitude of methods and indicators for freshwater use potentially applicable in life cycle assessment and identified the key elements to build a scientific consensus for operational characterization methods for LCA.
Abstract: In recent years, several methods have been developed which propose different freshwater use inventory schemes and impact assessment characterization models considering various cause–effect chain relationships. This work reviewed a multitude of methods and indicators for freshwater use potentially applicable in life cycle assessment (LCA). This review is used as a basis to identify the key elements to build a scientific consensus for operational characterization methods for LCA. This evaluation builds on the criteria and procedure developed within the International Reference Life Cycle Data System Handbook and has been adapted for the purpose of this project. It therefore includes (1) description of relevant cause–effect chains, (2) definition of criteria to evaluate the existing methods, (3) development of sub-criteria specific to freshwater use, and (4) description and review of existing methods addressing freshwater in LCA. No single method is available which comprehensively describes all potential impacts derived from freshwater use. However, this review highlights several key findings to design a characterization method encompassing all the impact pathways of the assessment of freshwater use and consumption in life cycle assessment framework as the following: (1) in most of databases and methods, consistent freshwater balances are not reported either because output is not considered or because polluted freshwater is recalculated based on a critical dilution approach; (2) at the midpoint level, most methods are related to water scarcity index and correspond to the methodological choice of an indicator simplified in terms of the number of parameters (scarcity) and freshwater uses (freshwater consumption or freshwater withdrawal) considered. More comprehensive scarcity indices distinguish different freshwater types and functionalities. (3) At the endpoint level, several methods already exist which report results in units compatible with traditional human health and ecosystem quality damage and cover various cause–effect chains, e.g., the decrease of terrestrial biodiversity due to freshwater consumption. (4) Midpoint and endpoint indicators have various levels of spatial differentiation, i.e., generic factors with no differentiation at all, or country, watershed, and grid cell differentiation. Existing databases should be (1) completed with input and output freshwater flow differentiated according to water types based on its origin (surface water, groundwater, and precipitation water stored as soil moisture), (2) regionalized, and (3) if possible, characterized with a set of quality parameters. The assessment of impacts related to freshwater use is possible by assembling methods in a comprehensive methodology to characterize each use adequately.
TL;DR: In this article, the influence of processing techniques such as microwaving, boiling, roasting and vacuuming on the red beet was investigated and the impact of processing was evaluated on the basis of belatains content and antioxidant activity of the processed samples.
TL;DR: The approach enables the characterization of the cooperative properties and photocatalytic activities of low-dimensional g-CN materials in hydrogen evolution reactions from water under visible light.
Abstract: Simple organic cooperative assembly of triazine molecules leads to three-dimensional macroscopic assemblies of low-dimensional graphitic carbon nitrides (g-CNs), for example, nanoparticles, nanotubes, and nanosheets. The approach enables the characterization of the cooperative properties and photocatalytic activities of low-dimensional g-CN materials in hydrogen evolution reactions from water under visible light.
TL;DR: In this article, the design and use of microporous polymers for pre-and post-combustion capture of CO2 is discussed, and strategies for enhancing CO2 uptakes including increasing surface area, chemical functionalization to provide high-enthalpy binding sites and the potential for pore size tuning.
Abstract: We review the design and use of microporous polymers for pre- and post-combustion capture of CO2. Microporous organic polymers are promising candidates for CO2 capture materials. They have good physicochemical stabilities and high surface areas. Ultrahigh-surface-area microporous organic polymers could find use in pre-combustion capture, while networks with lower surface areas but higher heats of sorption for CO2 might be more relevant for lower pressure, post-combustion capture. We discuss strategies for enhancing CO2 uptakes including increasing surface area, chemical functionalization to provide high-enthalpy binding sites and the potential for pore size tuning. © 2013 Society of Chemical Industry
TL;DR: The history of metallic foams and the key innovations that have led to the variety of processing methods known today are reviewed in this article, where it is evident that the idea of foaming metals is very old and that most of the techniques used today have been proposed already in the 1950s.
Abstract: The history of metallic foams and the key innovations that have led to the variety of processing methods known today are reviewed. It is evident that the idea of foaming metals is very old and that most of the techniques used today have been proposed already in the 1950s. The most important milestones in the development of foaming technologies and the some of the attempts to commercialise metal foams are reviewed.
TL;DR: Mixed-valent amorphous MnOx catalysts suitable for photochemical and electrochemical water oxidation are prepared by treatment of nanostructured catalytically inactive MnO precursors with (NH4)2Ce(NO3)6 solution for 15 min under vigorous stirring as discussed by the authors.
Abstract: Mixed-valent amorphous MnOx catalysts suitable for photochemical and electrochemical water oxidation are prepared by treatment of nanostructured catalytically inactive MnO precursors with (NH4)2Ce(NO3)6 solution for 15 min under vigorous stirring.
TL;DR: A facile atmosphere-controlled acid leaching technique to control the formation of nanoporosity in Pt-Ni bimetallic nanoparticles is presented and it is suggested that catalytic stability could further improve by controlling the particle size below ca.
Abstract: Nanoporosity is a frequently reported phenomenon in bimetallic particle ensembles used as electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells. It is generally considered a favorable characteristic, because it increases the catalytically active surface area. However, the effect of nanoporosity on the intrinsic activity and stability of a nanoparticle electrocatalyst has remained unclear. Here, we present a facile atmosphere-controlled acid leaching technique to control the formation of nanoporosity in Pt-Ni bimetallic nanoparticles. By statistical analysis of particle size, composition, nanoporosity, and atomic-scale core-shell fine structures before and after electrochemical stability test, we uncover that nanoporosity formation in particles larger than ca. 10 nm is intrinsically tied to a drastic dissolution of Ni and, as a result of this, a rapid drop in intrinsic catalytic activity during ORR testing, translating into severe catalyst performance degradation. In contrast, O2-free acid leaching enabled the suppression of nanoporosity resulting in more solid core-shell particle architectures with thin Pt-enriched shells; surprisingly, such particles maintained high intrinsic activity and improved catalytic durability under otherwise identical ORR tests. On the basis of these findings, we suggest that catalytic stability could further improve by controlling the particle size below ca. 10 nm to avoid nanoporosity. Our findings provide an explanation for the degradation of bimetallic particle ensembles and show an easy to implement pathway toward more durable fuel cell cathode catalysts.
TL;DR: The role of artists, cultural producers and creative milieux in urban social movements is discussed in this article, with reference to the hypothesis made by David Harvey in Spaces of Capital about the increasing mobilization of cultural producers in oppositional movements.
Abstract: In cities across the globe there is mounting evidence of growing mobilization by members of the so-called ‘creative class’ in urban social movements, defending particular urban spaces and influencing urban development. This essay discusses the meaning of such developments with reference to the hypothesis made by David Harvey in Spaces of Capital about the increasing mobilization of cultural producers in oppositional movements in an era of wholesale instrumentalization of culture and ‘creativity’ in contemporary processes of capitalist urbanization. After briefly reviewing recent scholarly contributions on the transformations of urban social movements, as well as Harvey's hypothesis about the potential role of cultural producers in mobilizations for the construction of ‘spaces of hope’, the essay describes two specific urban protests that have occurred in Berlin and Hamburg in recent years: the fight for Berlin's waterfront in the Media Spree area, and the conflict centred on the Gangeviertel in Hamburg. In both protests artists, cultural producers and creative milieux have played a prominent role. The essay analyses the composition, agenda, contribution and contradictions of the coalitions behind the protests, discussing whether such movements represent the seeds of new types of coalitions with a wide-ranging agenda for urban change. The essay finally proposes a future research agenda on the role of artists, cultural producers and the ‘creative class’ in urban social movements across the globe.
TL;DR: Current practices and developments in the mapping of ESS values are identified, their spatial scope, rational and ESS focus differ widely and guidelines and recommendations are provided for future applications and research.
Abstract: Mapping of ecosystem services’ (ESS) values means valuing ESS in monetary terms across a relatively large geographical area and assessing how values vary across space. Thereby, mapping of ESS values reveals additional information as compared to traditional site-specific ESS valuation, which is beneficial for designing land use policies for maintaining ESS supply. Since the well-known article by Costanza et al. (1997), who mapped global ESS values, the number of publications mapping ESS values has grown exponentially, with almost 60% being published after 2007. Within this paper, we analyse and review articles that map ESS values. Our findings show that methodologies, in particular how spatial variations of ESS values are estimated, their spatial scope, rational and ESS focus differ widely. Still, most case studies rely on relatively simplistic approaches using land use/cover data as a proxy for ESS supply and its values. However, a tendency exists towards more sophisticated methodologies using the ESS models and value functions, which integrate a variety of spatial variables and which are validated against primary data. Based on our findings, we identify current practices and developments in the mapping of EES values and provide guidelines and recommendations for future applications and research.