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"Christensen, T"
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Exploring creativity : evaluative practices in innovation, design and the arts
\"Moeran and Christensen examine evaluative practices in the creative industries by exploring the processes surrounding the conception, design, manufacture, appraisal and use of creative goods. The book describes the editorial choices made by different participants in a 'creative world', as they go about conceiving, composing or designing, performing or making, selling and assessing a range of cultural products. The study draws upon ethnographically rich case studies from companies as varied as Bang and Olufsen, Hugo Boss and Lonely Planet, in order to reveal the broad range of factors guiding and inhibiting creative processes. Some of these constraints are material and technical; others social or defined by aesthetic norms. The authors explore how these various constraints affect creative work and how ultimately they contribute to the development of creativity\"-- Provided by publisher.
Primary cilia as dynamic and diverse signalling hubs in development and disease
by
Pedersen, Lotte B
,
Christensen, Søren T
,
Mill, Pleasantine
in
Cilia
,
Developmental stages
,
Disease
2023
Primary cilia, antenna-like sensory organelles protruding from the surface of most vertebrate cell types, are essential for regulating signalling pathways during development and adult homeostasis. Mutations in genes affecting cilia cause an overlapping spectrum of >30 human diseases and syndromes, the ciliopathies. Given the immense structural and functional diversity of the mammalian cilia repertoire, there is a growing disconnect between patient genotype and associated phenotypes, with variable severity and expressivity characteristic of the ciliopathies as a group. Recent technological developments are rapidly advancing our understanding of the complex mechanisms that control biogenesis and function of primary cilia across a range of cell types and are starting to tackle this diversity. Here, we examine the structural and functional diversity of primary cilia, their dynamic regulation in different cellular and developmental contexts and their disruption in disease.Mutations that affect primary cilia cause ciliopathies with variable severity and expressivity. The diversity of cilia across cell types, tissues and developmental stages enables their function as versatile signalling hubs but may underlie the disconnect between genotype and phenotype. This Review examines the structural and functional diversity of primary cilia, their dynamic regulation in different cellular and developmental contexts and their disruption in disease.
Journal Article
An assessment of the carbon balance of Arctic tundra: comparisons among observations, process models, and atmospheric inversions
2012
Although Arctic tundra has been estimated to cover only 8% of the global land surface, the large and potentially labile carbon pools currently stored in tundra soils have the potential for large emissions of carbon (C) under a warming climate. These emissions as radiatively active greenhouse gases in the form of both CO2 and CH4 could amplify global warming. Given the potential sensitivity of these ecosystems to climate change and the expectation that the Arctic will experience appreciable warming over the next century, it is important to assess whether responses of C exchange in tundra regions are likely to enhance or mitigate warming. In this study we compared analyses of C exchange of Arctic tundra between 1990 and 2006 among observations, regional and global applications of process-based terrestrial biosphere models, and atmospheric inversion models. Syntheses of flux observations and inversion models indicate that the annual exchange of CO2 between Arctic tundra and the atmosphere has large uncertainties that cannot be distinguished from neutral balance. The mean estimate from an ensemble of process-based model simulations suggests that Arctic tundra has acted as a sink for atmospheric CO2 in recent decades, but based on the uncertainty estimates it cannot be determined with confidence whether these ecosystems represent a weak or a strong sink. Tundra was 0.6 °C warmer in the 2000s compared to the 1990s. The central estimates of the observations, process-based models, and inversion models each identify stronger sinks in the 2000s compared with the 1990s. Some of the process models indicate that this occurred because net primary production increased more in response to warming than heterotrophic respiration. Similarly, the observations and the applications of regional process-based models suggest that CH4 emissions from Arctic tundra have increased from the 1990s to 2000s because of the sensitivity of CH4 emissions to warmer temperatures. Based on our analyses of the estimates from observations, process-based models, and inversion models, we estimate that Arctic tundra was a sink for atmospheric CO2 of 110 Tg C yr−1 (uncertainty between a sink of 291 Tg C yr−1 and a source of 80 Tg C yr−1) and a source of CH4 to the atmosphere of 19 Tg C yr−1 (uncertainty between sources of 8 and 29 Tg C yr−1). The suite of analyses conducted in this study indicate that it is important to reduce uncertainties in the observations, process-based models, and inversions in order to better understand the degree to which Arctic tundra is influencing atmospheric CO2 and CH4 concentrations. The reduction of uncertainties can be accomplished through (1) the strategic placement of more CO2 and CH4 monitoring stations to reduce uncertainties in inversions, (2) improved observation networks of ground-based measurements of CO2 and CH4 exchange to understand exchange in response to disturbance and across gradients of climatic and hydrological variability, and (3) the effective transfer of information from enhanced observation networks into process-based models to improve the simulation of CO2 and CH4 exchange from Arctic tundra to the atmosphere.
Journal Article
Future scenarios and life cycle assessment: systematic review and recommendations
2021
PurposeFuture scenarios and life cycle assessment (LCA) are powerful tools that can provide early sustainability assessments of novel products, technologies and systems. The combination of the two methods involves practical and conceptual challenges, but formal guidance and consensus on a rigorous approach are currently missing. This study provides a comprehensive overview of how different topic areas use future scenarios and LCA in order to identify useful methods and approaches, and to provide overall recommendations.MethodsThis study carried out a systematic literature review that involved searching for peer-reviewed articles on Web of Science, Scopus and Science Direct, utilising a rigorous set of keywords for future scenarios and for LCA. We identified 514 suitable peer-reviewed articles that were systematically analysed according to pre-defined sets of characteristics for the combined modelling of future scenarios and LCA.Results and discussionThe numbers of studies combining future scenarios and LCA increase every year and in all of the 15 topic areas identified. This combination is highly complex, due to different sequences in the modelling between future scenarios and LCA, the use of additional models and topic area-specific challenges. We identify and classify studies according to three archetypal modelling sequences: input, output and hybrid. More than 100 studies provide methods and approaches for combining future scenarios and LCA, but existing recommendations are specific to topic areas and for modelling sequences, and consensus is still missing. The efficacy of many studies is hampered by lack of quality. Only half of the articles complied with the LCA ISO standards, and only one quarter demonstrated consistent knowledge of future scenario theory. We observed inconsistent use of terminology and a considerable lack of clarity in the descriptions of methodological choices, assumptions and time frames.Conclusions and RecommendationsThe combined use of future scenarios and LCA requires formal guidance, in order to increase clarity and communicability. Guidance should provide unambiguous definitions, identify minimum quality requirements and produce mandatory descriptions of modelling choices. The goal and scope of future scenarios and LCA should be in accordance, and quality should be ensured both for the future scenarios and the LCA. In particular, future scenarios should always be developed contextually, to ensure effective assessment of the problem at hand. Guidance should also allow for maintaining current modelling complexity and topic area differences. We provide recommendations from the reference literature on terminology, future scenario development and the combined use of future scenarios and LCA that may already constitute preliminary guidance in the field. Information collected and recommendations provided will assist in a more balanced development of the combined use of future scenarios and LCA in view of the urgent challenges of sustainable development.
Journal Article
Numerical and experimental study of mechanisms responsible for turbulent secondary flows in boundary layer flows over spanwise heterogeneous roughness
by
Barros, Julio M.
,
Awasthi, Ankit
,
Anderson, William
in
Atmospheric boundary layer
,
Bed forms
,
Bedforms
2015
We study the dynamics of turbulent boundary layer flow over a heterogeneous topography composed of roughness patches exhibiting relatively high and low correlation in the streamwise and spanwise directions, respectively (i.e. the roughness appears as streamwise-aligned ‘strips’). It has been reported that such roughness induces a spanwise-wall normal mean secondary flow in the form of mean streamwise vorticity associated with counter-rotating boundary-layer-scale circulations. Here, we demonstrate that this mean secondary flow is Prandtl’s secondary flow of the second kind, both driven and sustained by spatial gradients in the Reynolds-stress components, which cause a subsequent imbalance between production and dissipation of turbulent kinetic energy that necessitates secondary advective velocities. In reaching this conclusion, we study (i) secondary circulations due to spatial gradients of turbulent kinetic energy, and (ii) the production budgets of mean streamwise vorticity by gradients of the Reynolds stresses. We attribute the secondary flow phenomena to extreme peaks of surface stress on the relatively high-roughness regions and associated elevated turbulence production in the fluid immediately above. An optimized state is attained by entrainment of fluid exhibiting the lowest turbulent stresses – from above – and subsequent lateral ejection in order to preserve conservation of mass.
Journal Article
Experimental evidence of amplitude modulation in permeable-wall turbulence
by
Blois, Gianluca
,
Kim, Taehoon
,
Christensen, Kenneth T.
in
Amplitude
,
Amplitude modulation
,
Bed roughness
2020
The dynamic interplay between surface and subsurface flow in the presence of a permeable boundary was investigated using low and high frame-rate particle-image velocimetry measurements in a refractive-index-matching flow environment. Two idealized permeable wall models were considered. Both models contained five layers of cubically packed spheres, but one exhibited a smooth interface with the flow, while the other embodied a hemispherical surface topography. The relationship between the large-scale turbulent motions overlying the permeable walls and the small-scale turbulence just above, and within, the walls was explored using instantaneous and statistical analyses. Although previous studies have indirectly identified the potential existence of amplitude modulation in permeable-wall turbulence (a phenomenon identified in impermeable-wall turbulence whereby the outer large scales modulate the intensity of the near-wall, small-scale turbulence), the present effort provides direct evidence of its existence in flow over both permeable walls considered. The spatio-temporal signatures of amplitude modulation were also characterized using conditional averaging based on zero-crossing events. This analysis highlights the connection between large-scale regions of high/low streamwise momentum in the surface flow, downwelling/upwelling across the permeable interface and enhancement/suppression of small-scale turbulence, respectively, just above and within the permeable walls. The presence of bed roughness is found to intensify the strength and penetration of flow into the permeable bed modulated by large-scale structures in the surface flow, and linked to possible roughness-formed channelling effects and shedding of smaller-scale flow structures from the roughness elements.
Journal Article
Expert assessment of future vulnerability of the global peatland carbon sink
2021
The carbon balance of peatlands is predicted to shift from a sink to a source this century. However, peatland ecosystems are still omitted from the main Earth system models that are used for future climate change projections, and they are not considered in integrated assessment models that are used in impact and mitigation studies. By using evidence synthesized from the literature and an expert elicitation, we define and quantify the leading drivers of change that have impacted peatland carbon stocks during the Holocene and predict their effect during this century and in the far future. We also identify uncertainties and knowledge gaps in the scientific community and provide insight towards better integration of peatlands into modelling frameworks. Given the importance of the contribution by peatlands to the global carbon cycle, this study shows that peatland science is a critical research area and that we still have a long way to go to fully understand the peatland–carbon–climate nexus.Peatlands are impacted by climate and land-use changes, with feedback to warming by acting as either sources or sinks of carbon. Expert elicitation combined with literature review reveals key drivers of change that alter peatland carbon dynamics, with implications for improving models.
Journal Article
Soil texture analysis revisited: Removal of organic matter matters more than ever
by
Jensen, Johannes Lund
,
Schjønning, Per
,
Christensen, Bent T.
in
Aluminum Silicates - analysis
,
Barley
,
Biology and Life Sciences
2017
Exact estimates of soil clay (<2 μm) and silt (2-20 μm) contents are crucial as these size fractions impact key soil functions, and as pedotransfer concepts based on clay and silt contents are becoming increasingly abundant. We examined the effect of removing soil organic matter (SOM) by H2O2 before soil dispersion and determination of clay and silt. Soil samples with gradients in SOM were retrieved from three long-term field experiments each with uniform soil mineralogy and texture. For soils with less than 2 g C 100 g-1 minerals, clay estimates were little affected by SOM. Above this threshold, underestimation of clay increased dramatically with increasing SOM content. Silt contents were systematically overestimated when SOM was not removed; no lower SOM threshold was found for silt, but the overestimation was more pronounced for finer textured soils. When exact estimates of soil particles <20 μm are needed, SOM should always be removed before soil dispersion.
Journal Article
Multiple Ecosystem Effects of Extreme Weather Events in the Arctic
by
Scheller, J.
,
Abermann, J.
,
Murphy, M. J.
in
Annual precipitation
,
Arctic region
,
Biomedical and Life Sciences
2021
The Arctic is getting warmer and wetter. Here, we document two independent examples of how associated extreme precipitation patterns have severe implications for high Arctic ecosystems. The events stand out in a 23-year record of continuous observations of a wide range of ecosystem parameters and act as an early indication of conditions projected to increase in the future. In NE Greenland, August 2015, one-quarter of the average annual precipitation fell during a 9-day intensive rain event. This ranked number one for daily sums during the 1996–2018 period and caused a strong and prolonged reduction in solar radiation decreasing CO₂ uptake in the order of 18–23 g C m⁻², a reduction comparable to typical annual C budgets in Arctic tundra. In a different type of event, but also due to changed weather patterns, an extreme snow melt season in 2018 triggered a dramatic gully thermokarst causing rapid transformation in ecosystem functioning from consistent annual ecosystem CO₂ uptake and low methane exchange to highly elevated methane release, net source of CO₂, and substantial export of organic carbon downstream as riverine and coastal input. In addition to climate warming alone, more frequent occurrence of extreme weather patterns will have large implications for otherwise undisturbed tundra ecosystems including their element transport and carbon interactions with the atmosphere and ocean.
Journal Article