Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Social network analysis for facilitating the innovative water technologies towards more efficient water use in industrial zone
Tran, Trang - \ 2019
Vietnam Journal of Construction 58 (2019)4-2019. - ISSN 0866-8762 - p. 103 - 108.
Social network analysis - industrial zone - water use efficiency - network
Industrial zones (IZs) in Vietnam require a huge quantity of water for production activities to develop society an economy. However, the quality and quantity of IZ-related water resources are depleted and threatened. In order to prevent water scarcity, mismanagement and wasting of water supplies, it is necessary to develop new technologies to increase water use efficiency in the IZs. However, new technologies would be not fit with the existing socio-institutional framework so that the societal aspects could be transformed to facilitate the innovative technologies. This paper aims to analyse the existing actor network for facilitating the innovative water technologies towards more efficient water use in Hiep Phuoc IZ. Using the results from the collected data, Social Network Analysis (SNA) is applied to understand the social structure and dimension of the four networks (policy, economic, societal and research networks) that govern IZ's water flows (Borgatti et al., 2002; Domenech, 2009; Reed et al., 2009; Ashton, 2008; Steveson and Greenberg, 2000). The findings contribute insight to how the actors correlate among the four networks and their roles in facilitating the technological innovation in Hiep Phuoc Industrial Zone in the South of Vietnam.
The implementation of Natura 2000 in forests: A trans- and interdisciplinary assessment of challenges and choices.
Winkel, G. ; Blondet, M. ; Borrass, L. ; Frei, T. ; Geitzenauer, M. ; Gruppe, A. ; Jump, A. ; Koning, J. de; Sotirov, M. ; Weiss, G. ; Winter, S. ; Turnhout, E. - \ 2015
Environmental Science & Policy 52 (2015). - ISSN 1462-9011 - p. 23 - 32.
climate-change - biodiversity conservation - european-union - management - science - policy - network - stand
Natura 2000 is the core of the EU's biodiversity conservation policy. 50% of the overall protected area under Natura 2000 is forest. Yet, comparatively little is known about the implementation of the policy in forests. Building on a rich set of social and natural science data, and an inter- and transdisciplinary discussion process involving scientists from different disciplines as well as EU, national and local stakeholders, this paper identifies five important challenges related to the implementation of Natura 2000 in forests: (1) the balancing of biodiversity conservation and timber production, (2) the integration of conservation (science) and local stakeholders’ demands, (3) climate change, (4) lacking and less effective funding, and (5) conflicts related to other sectoral policies. Subsequently, five possible pathways to tackle these challenges are proposed: (1) a learning approach through better communication and transparency, (2) a pathway emphasizing the role of conservation science in developing management strategies and responding to climate change, (3) an approach of better integrating Europe's citizens in the design and implementation of the policy, (4) an approach highlighting the necessity of an effective funding strategy, and (5) the vision to work towards an integrated European land use and conservation policy. In conclusion, we emphasize, on one hand, the distinct character of the five pathways but, on the other hand, underline that probably all of them need to be followed in order to make the implementation of Natura 2000 in Europe's forests a success story.
The construction of legitimacy in European nature policy: expertise and participation in the service of cost-effectiveness
Turnhout, E. ; Behagel, J.H. ; Ferranti, F. ; Beunen, R. - \ 2015
Environmental Politics 24 (2015)3. - ISSN 0964-4016 - p. 461 - 480.
environmental-policy - ecosystem services - democratic legitimacy - conservation policy - governance - implementation - network - netherlands - science - union
In environmental governance, the European Union draws on norms of effectiveness, decentralisation, and participation to ensure that its policies and regulations are considered legitimate. This article analyses how the construction of legitimacy in European nature policy has changed over time. Although the norms of participation and decentralisation are increasingly evoked to address the needs of stakeholders and member states in the implementation and financing of Natura 2000, the norm of effectiveness continues to dominate the construction of legitimacy. Effectiveness first acquired its meaning in the context of a science-based approach to Natura 2000 to emphasise the importance of achieving its conservation objectives. More recently, it has become increasingly re-articulated as cost-effectiveness, which reflects a growing influence of neoliberal discourse. The article concludes by discussing the implications of the findings for the legitimacy of European environmental governance.
Atmospheric CO2, d(O2/N2), APO and oxidative ratios from aircraft flask samples over Fyodorovskoye, Western Russia
Laan, S. van der; Laan-Luijkx, I.T. van der; Rödenbeck, C. ; Varlagin, A. ; Shironya, I. ; Neubert, R.E.M. - \ 2014
Atmospheric Environment 97 (2014). - ISSN 1352-2310 - p. 174 - 181.
southern taiga - carbon-cycle - oxygen - o-2/n-2 - siberia - air - climatology - variability - network - tower
We present atmospheric CO2 and d(O2/N2) from flask samples taken on board aircraft over Fyodorovskoye (56°27'N, 32°55'E) at heights of 3000 m and 100 m between 1998 and 2008. The long-term trends for CO2 and d(O2/N2) are similar for both sampling heights, and also similar to observations from marine background station Mace Head (Ireland) and coastal station Lutjewad (the Netherlands). The seasonal CO2 amplitude at 100 m was almost twice as large as at 3000 m and a phase shift in the seasonality of about two weeks between both sampling heights was observed. This indicates a dominant influence on CO2 in the boundary layer from the regional biosphere which is confirmed by analysis of the d(O2/N2) to CO2 oxidative ratio (OR). Together with simulations with the TM3 model, our data suggest that the observed OR of -1.7 ± 0.2 in the free troposphere is mainly driven by exchange processes with the ocean. Within the boundary layer an OR of -0.89 ± 0.12 was observed which supports the results of other recent studies suggesting the commonly used value of -1.1 for biospheric OR is likely too low.
Natura 2000 and climate change—Polarisation, uncertainty, and pragmatism in discourses on forest conservation and management in Europe
Koning, J. de; Winkel, G. ; Sotirov, M. ; Blondet, M. ; Borras, L. ; Ferranti, F. ; Geitzenauer, M. - \ 2014
Environmental Science & Policy 39 (2014). - ISSN 1462-9011 - p. 129 - 138.
change impacts - policy - biodiversity - network - implementation - perspectives - experiences - countries - areas - trees
European forests are a resource that is targeted by several EU environmental and land use policies as forests can be of critical importance to mitigate climate change. At the same time, they are central to the EU's biodiversity policy, and particular the Natura 2000 network of protected areas. Yet, the interlinkage between climate change and biodiversity policy is complex and discursively contested. In this paper, we assess how the debate on climate change adaptation affects forest conservation and management under Natura 2000. Drawing on the concept of argumentative discourse analysis, we present evidence from 213 qualitative interviews with policy stakeholders and practitioners that were conducted at both the European policy level and the local country level in 6 EU member states. Our results demonstrate that the nexus between climate change adaptation and forest conservation policy is conceptualised differently by different stakeholders and practioners at different levels. Three major discourses can be made out (pragmatic discourse, dynamics discourse, threat discourse), which are characterised by a set of partially overlapping story lines. These discourses are employed by four discourse coalitions (environmental, forest users’, expert, and grass root coalition). As a general rule, debates at the European level are more polarised and politicised, while the local debates on climate change and Natura 2000 remain rather vague and are less polarised. This seems to indicate that the link between climate change adaptation and forest conservation is mostly an issue for an abstract high-level policy debate. At this level, climate change is used to influence well-known policies, and to legitimise distinct interests that were already present before the climate change debate has emerged.
Systems-level modeling of mycobacterial metabolism for the identification of new (multi-)drug targets
Rienksma, R.A. ; Suarez Diez, M. ; Spina, L. ; Schaap, P.J. ; Martins dos Santos, V.A.P. - \ 2014
Seminars in Immunology 26 (2014)6. - ISSN 1044-5323 - p. 610 - 622.
constraint-based models - escherichia-coli - cholesterol-metabolism - global reconstruction - tuberculosis - growth - network - biosynthesis - insights - biology
Systems-level metabolic network reconstructions and the derived constraint-based (CB) mathematical models are efficient tools to explore bacterial metabolism. Approximately one-fourth of the Mycobacterium tuberculosis (Mtb) genome contains genes that encode proteins directly involved in its metabolism. These represent potential drug targets that can be systematically probed with CB models through the prediction of genes essential (or the combination thereof) for the pathogen to grow. However, gene essentiality depends on the growth conditions and, so far, no in vitro model precisely mimics the host at the different stages of mycobacterial infection, limiting model predictions. These limitations can be circumvented by combining expression data from in vivo samples with a validated CB model, creating an accurate description of pathogen metabolism in the host. To this end, we present here a thoroughly curated and extended genome-scale CB metabolic model of Mtb quantitatively validated using 13C measurements. We describe some of the efforts made in integrating CB models and high-throughput data to generate condition specific models, and we will discuss challenges ahead. This knowledge and the framework herein presented will enable to identify potential new drug targets, and will foster the development of optimal therapeutic strategies.
Tracking C and N dynamics and stabilization in soil amended with wheat residue and its correponding bioethanol by-product: a 13C/15C study
Cayuela, M.L. ; Kuikman, P.J. ; Bakker, R.R.C. ; Groenigen, J.W. van - \ 2014
Global change biology Bioenergy 6 (2014)5. - ISSN 1757-1693 - p. 499 - 508.
organic-matter - macroaggregate dynamics - carbon sequestration - microbial biomass - removal - network - quality - impact - inputs
Removing agricultural cellulosic residues from fields for the production of ‘second generation biofuels'has the potential to profoundly alter C and N cycling in soil, increasing the risk of soil organic matter depletion and favoring soil–atmosphere gaseous exchanges. However, these negative impacts could potentially be offset by amending the soil with the solid by-product which is generated during bioethanol production. In a 100 days laboratory study, we investigated the fate of C and N after soil amendment with doubly labeled (13C, 15N) wheat residue (WR) and the corresponding bioethanol by-product (i.e. nonfermentable wheat residue NFWR) with and without extra N addition. Substituting WR with the corresponding amount of recovered bioethanol by-product partially compensated the C losses of full crop residue removal. When the equivalent amount of C was added as WR and NFWR, NFWR-derived C was found in significantly higher proportion in macroaggregates in soil (17.0 vs. 8.9%) after 100 days. Addition of both WR and NFWR reduced soil organic C (SOC) mineralization, i.e. it caused a negative priming effect in soil. However, this pattern was reversed when extra N was added. Both WR and NFWR increased the proportion of soil water-stable macroaggregates from 16% (in control) to 20–24% (in the different treatments). The results suggest that the more recalcitrant compounds derived from bioethanol production may stabilize more strongly and persist within the protected fractions of SOM pools. Our study demonstrates that NFWR, compared with WR application, neither increased N2O emissions nor had a negative impact on aggregate formation in the midterm. This demonstrates that NFWR has potential for replenishing SOC stocks
Shifting nature conservation approaches in Natura 2000 and the implications for the roles of stakeholders
Ferranti, F. ; Turnhout, E. ; Beunen, R. ; Behagel, J.H. - \ 2014
Journal of Environmental Planning and Management 57 (2014)11. - ISSN 0964-0568 - p. 1642 - 1657.
policy - participation - governance - implementation - netherlands - empowerment - ecosystem - network - power
This paper analyses Natura 2000 as a shifting configuration of different approaches to nature conservation and discusses the consequences of these shifts for the roles of the stakeholders affected by this policy. Natura 2000 started with a technocratic approach that privileged conservation experts and marginalised socio-economic stakeholders. Over time, this approach has been complemented with participatory and economic approaches that offered scope for the inclusion of land users and business actors. However, the analysis also shows that the selective inclusion of economic values and stakeholders in the Natura 2000 framework risks marginalising other important socio-environmental actors.
The brassinosteroid insensitive1-like3 signalosome complex regulates Arabidopsis root development
Fàbregas, N. ; Li, N. ; Boeren, S. ; Nash, T.E. ; Goshe, M.B. ; Clouse, S.D. ; Vries, S.C. de; Caño-Delgado, A.I. - \ 2013
The Plant Cell 25 (2013)9. - ISSN 1040-4651 - p. 3377 - 3388.
receptor kinase bri1 - signaling pathways - statistical-model - plasma-membrane - gene-expression - transduction - growth - identification - thaliana - network
Brassinosteroid (BR) hormones are primarily perceived at the cell surface by the leucine-rich repeat receptor-like kinase brassinosteroid insensitive1 (BRI1). In Arabidopsis thaliana, BRI1 has two close homologs, BRI1-LIKE1 (BRL1) and BRL3, respectively, which are expressed in the vascular tissues and regulate shoot vascular development. Here, we identify novel components of the BRL3 receptor complex in planta by immunoprecipitation and mass spectrometry analysis. Whereas BRI1 associated kinase1 (BAK1) and several other known BRI1 interactors coimmunoprecipitated with BRL3, no evidence was found of a direct interaction between BRI1 and BRL3. In addition, we confirmed that BAK1 interacts with the BRL1 receptor by coimmunoprecipitation and fluorescence microscopy analysis. Importantly, genetic analysis of brl1 brl3 bak1-3 triple mutants revealed that BAK1, BRL1, and BRL3 signaling modulate root growth and development by contributing to the cellular activities of provascular and quiescent center cells. This provides functional relevance to the observed protein-protein interactions of the BRL3 signalosome. Overall, our study demonstrates that cell-specific BR receptor complexes can be assembled to perform different cellular activities during plant root growth, while highlighting that immunoprecipitation of leucine-rich repeat receptor kinases in plants is a powerful approach for unveiling signaling mechanisms with cellular resolution in plant development
Contested delineations: planning, law, and the governance of protected areas
Beunen, R. ; Assche, K. van - \ 2013
Environment and Planning A 45 (2013)6. - ISSN 0308-518X - p. 1285 - 1301.
nature conservation - policy - implementation - experiences - systems - network
In this paper we reflect on the relationship between planning and law. We analyse the Dutch interpretation and implementation of the European Union Habitats and Birds Directives by investigating the practices of delineation of protected areas. These directives provide a legislative framework for the designation of protected sites as well as for decision making about social and economic activities that might have negative effects on the conservation objectives. The formal boundaries of the protected area can have legal, political, and economic consequences and are therefore the subject of much debate. Using Niklas Luhmann’s social systems theory, we analyse the debates concerning delineation and the potential for planning to reduce tensions and balance interests. It is argued that the irreducible differences between the economic, political, and legal perspectives, in combination with the Dutch path of a legalistic interpretation of EU directives, have produced a situation in which the role of planning is reduced and new forms of planning are hard to implement.
Predictive modelling of complex agronomic and biological systems
Keurentjes, J.J.B. ; Molenaar, J. ; Zwaan, B.J. - \ 2013
Plant, Cell & Environment 36 (2013)9. - ISSN 0140-7791 - p. 1700 - 1710.
quantitative trait loci - root-growth - escherichia-coli - network - crop - arabidopsis - metabolism - cell - genomics - reveal
Biological systems are tremendously complex in their functioning and regulation. Studying the multifaceted behaviour and describing the performance of such complexity has challenged the scientific community for years. The reduction of real-world intricacy into simple descriptive models has therefore convinced many researchers of the usefulness of introducing mathematics into biological sciences. Predictive modelling takes such an approach another step further in that it takes advantage of existing knowledge to project the performance of a system in alternating scenarios. The ever growing amounts of available data generated by assessing biological systems at increasingly higher detail provide unique opportunities for future modelling and experiment design. Here we aim to provide an overview of the progress made in modelling over time and the currently prevalent approaches for iterative modelling cycles in modern biology. We will further argue for the importance of versatility in modelling approaches, including parameter estimation, model reduction and network reconstruction. Finally, we will discuss the difficulties in overcoming the mathematical interpretation of in vivo complexity and address some of the future challenges lying ahead
Shared Protein Complex Subunits Contribute to Explaining Disrupted Co-occurrence
Schneider, A. ; Seidl, M.F. ; Snel, B. - \ 2013
PLoS Computational Biology 9 (2013)7. - ISSN 1553-734X
functional modules - evolution - identification - duplication - eukaryotes - network - yeast
The gene composition of present-day genomes has been shaped by a complicated evolutionary history, resulting in diverse distributions of genes across genomes. The pattern of presence and absence of a gene in different genomes is called its phylogenetic profile. It has been shown that proteins whose encoding genes have highly similar profiles tend to be functionally related: As these genes were gained and lost together, their encoded proteins can probably only perform their full function if both are present. However, a large proportion of genes encoding interacting proteins do not have matching profiles. In this study, we analysed one possible reason for this, namely that phylogenetic profiles can be affected by multi-functional proteins such as shared subunits of two or more protein complexes. We found that by considering triplets of proteins, of which one protein is multi-functional, a large fraction of disturbed co-occurrence patterns can be explained.
Atmospheric CO2, d(O2/N2) and d13CO2 measurements at Jungfraujoch, Switzerland: results from a flask sampling intercomparison program
Laan-Luijkx, I.T. van der; Laan, S. van der; Uglietti, C. ; Schibig, M.F. ; Neubert, R.E.M. ; Meijer, H.A.J. ; Brand, W.A. ; Jordan, A. ; Richter, J.M. ; Rothe, M. ; Leuenberger, M.C. - \ 2013
Atmospheric Measurement Techniques 6 (2013). - ISSN 1867-1381 - p. 1805 - 1815.
isotope-ratio - mass-spectrometry - greenhouse gases - carbon sinks - air samples - tall tower - oxygen - network - o-2 - delta-c-13
We present results from an intercomparison program of CO2, d(O2/N2) and d13CO2 measurements from atmospheric flask samples. Flask samples are collected on a bi-weekly basis at the High Altitude Research Station Jungfraujoch in Switzerland for three European laboratories: the University of Bern, Switzerland, the University of Groningen, the Netherlands and the Max Planck Institute for Biogeochemistry in Jena, Germany. Almost 4 years of measurements of CO2, d(O2/N2) and d13CO2 are compared in this paper to assess the measurement compatibility of the three laboratories. While the average difference for the CO2 measurements between the laboratories in Bern and Jena meets the required compatibility goal as defined by the World Meteorological Organization, the standard deviation of the average differences between all laboratories is not within the required goal. However, the obtained annual trend and seasonalities are the same within their estimated uncertainties. For d(O2/N2) significant differences are observed between the three laboratories. The comparison for d13CO2 yields the least compatible results and the required goals are not met between the three laboratories. Our study shows the importance of regular intercomparison exercises to identify potential biases between laboratories and the need to improve the quality of atmospheric measurements
EURRECA—Framework for Aligning Micronutrient Recommendations
Veer, P. van 't; Grammatikaki, E. ; Matthys, C. ; Raats, M.M. ; Contor, L. - \ 2013
Critical Reviews in Food Science and Nutrition 53 (2013)10. - ISSN 1040-8398 - p. 988 - 998.
nutrition - requirements - challenges - phenotype - alignment - evaluate - biology - network - europe - health
There is currently no standard approach for deriving micronutrient recommendations, and large variations exist across Europe, causing confusion among consumers, food producers, and policy makers. More aligned information could influence dietary behaviors and potentially lead to a healthier population. Funded by the European Commission, EURRECA (EURopean micronutrient RECommendations Aligned) has developed methods and applications to guide Nutrient Recommendation Setting Bodies through the process of setting micronutrient reference values. The EURRECA approach is crystallized into its framework that outlines a standard process for deriving and using dietary reference values for micronutrients in a transparent, systematic, and scientific way. The 9 activities of the framework can be clustered into four stages (i) defining the problem, (ii) monitoring and evaluating, (iii) deriving dietary reference values, and (iv) using dietary reference values in policy making. The EURRECA framework should not be interpreted as a prescriptive description of a linear process, but as a structured guide for checking that all issues essential for deriving requirements have at least been considered.
Retrieval and validation of global, direct, and diffuse irradiance derived from SEVIRI satellite observations
Greuell, J.W. ; Meirink, J.F. ; Wang, P. - \ 2013
Journal of Geophysical Research: Atmospheres 118 (2013)5. - ISSN 2169-897X - p. 2340 - 2361.
surface solar irradiance - liquid water path - cloud properties - alpine region - cm-saf - models - climatology - network
This paper discusses Surface Insolation under Clear and Cloudy skies derived from SEVIRI imagery (SICCS), a physics-based, empirically adjusted algorithm developed for estimation of surface solar irradiance from satellite data. Its most important input are a cloud mask product and cloud properties derived from Meteosat/Spinning Enhanced Visible and Infrared Imager (SEVIRI) observations. These observations set the characteristics of the output, namely, a temporal resolution of 15¿min, a nadir spatial resolution of 3 × 3 km2, the period from January 2004 until at least November 2012, and the domain equal to most of the Meteosat disc. SICCS computes global, direct, and diffuse irradiance separately. Direct irradiance for cloudy skies is estimated with an empirical method. Hourly means retrieved with SICCS were validated with data from eight Baseline Surface Radiation Network stations for the year 2006. We found median values of the station biases of +6¿W/m2 (+5%) for direct irradiance, +1¿W/m2 (+1%) for diffuse irradiance, and +7¿W/m2 (+2%) for global irradiance. Replacing the three-hourly aerosol optical thickness input by monthly means introduces considerable additional biases in the clear-sky direct (-6%) and diffuse (+26%) irradiances. The performance of SICCS does not degrade when snow covers the surface. Biases do not vary with cloud optical thickness and cloud particle radius. However, the bias in global transmissivity tends to decrease with increasing cloud heterogeneity, and the bias in direct transmissivity is a function of the solar zenith angle. We discuss why satellite retrieval of surface solar irradiance is relatively successful
Gene Ontology consistent protein function prediction: the FALCON algorithm applied to six eukaryotic genomes
Kourmpetis, Y.A.I. ; Dijk, A.D.J. van; Braak, C.J.F. ter - \ 2013
Algorithms for Molecular Biology 8 (2013)1. - ISSN 1748-7188
arabidopsis-thaliana - integration - annotation - regression - network - classification - association - terms - tool
Gene Ontology (GO) is a hierarchical vocabulary for the description of biological functions and locations, often employed by computational methods for protein function prediction. Due to the structure of GO, function predictions can be self- contradictory. For example, a protein may be predicted to belong to a detailed functional class, but not in a broader class that, due to the vocabulary structure, includes the predicted one.We present a novel discrete optimization algorithm called Functional Annotation with Labeling CONsistency (FALCON) that resolves such contradictions. The GO is modeled as a discrete Bayesian Network. For any given input of GO term membership probabilities, the algorithm returns the most probable GO term assignments that are in accordance with the Gene Ontology structure. The optimization is done using the Differential Evolution algorithm. Performance is evaluated on simulated and also real data from Arabidopsis thaliana showing improvement compared to related approaches. We finally applied the FALCON algorithm to obtain genome-wide function predictions for six eukaryotic species based on data provided by the CAFA (Critical Assessment of Function Annotation) project
A large-scale evaluation of computational protein function prediction
Radivojac, P. ; Clark, W.T. ; Oron, T.R. ; Schnoes, A.M. ; Wittkop, T. ; Kourmpetis, Y.A.I. ; Dijk, A.D.J. van; Friedberg, I. - \ 2013
Nature Methods : techniques for life scientists and chemists 10 (2013). - ISSN 1548-7091 - p. 221 - 227.
gene ontology - sequence - rna - annotation - database - network - genomes - gold
Automated annotation of protein function is challenging. As the number of sequenced genomes rapidly grows, the overwhelming majority of protein products can only be annotated computationally. If computational predictions are to be relied upon, it is crucial that the accuracy of these methods be high. Here we report the results from the first large-scale community-based critical assessment of protein function annotation (CAFA) experiment. Fifty-four methods representing the state of the art for protein function prediction were evaluated on a target set of 866 proteins from 11 organisms. Two findings stand out: (i) today's best protein function prediction algorithms substantially outperform widely used first-generation methods, with large gains on all types of targets; and (ii) although the top methods perform well enough to guide experiments, there is considerable need for improvement of currently available tools.
Performing failure in conservation policy: The implementation of European Union directives in the Netherlands
Beunen, R. ; Assche, K.A.M. van; Duineveld, M. - \ 2013
Land Use Policy 31 (2013). - ISSN 0264-8377 - p. 280 - 288.
natura 2000 - danube delta - performativity - governance - management - participation - experiences - narratives - politics - network
We investigate the impact of performances of failure in nature conservation by means of a detailed reconstruction of the implementation of European Union conservation directives in the Netherlands. We distinguish performance and performativity, whereby the latter is the reality-effect of discourses affecting policy, and partly the result of deliberate performance. It is argued that the implementation history in the Netherlands reveals that even long-standing traditions of deliberation and spatial planning can be disrupted as an unintended consequence of international policy implementation. What was intended as a tool to promote long-term planning for nature conservation can in effect undermine both nature conservation and long-term planning. Only a high degree of reflexivity in the planning system can diminish the chances of misconceiving the spaces for negotiation and deliberation that are left open by the EU directives. Otherwise, a combination of unexpected events and unreflected routine responses will in all likelihood produce results highly diverging from the initial ambitions.
Structures, stresses, and fluctuations in the delayed failure of colloidal gel
Lindstrom, S.B. ; Kodger, T.E. ; Sprakel, J.H.B. ; Weitz, D.A. - \ 2012
Soft Matter 8 (2012)13. - ISSN 1744-683X - p. 3657 - 3664.
fracture - force - suspensions - particles - adhesion - lifetime - strength - network - fluid - bonds
Sample-spanning networks of aggregated colloidal particles have a finite stiffness and deform elastically when subjected to a small shear stress. After some period of creep, these gels ultimately suffer catastrophic failure. This delayed yielding is governed by the association and dissociation dynamics of interparticle bonds and the strand structure of the gel. We derive a model which connects the kinetics of the colloids to the erosion of the strand structure and ultimately to macroscopic failure. Importantly, this model relates time-to-failure of the gel to an applied static stress. Model predictions are in quantitative agreement with experiments. It is predicted that the strand structure, characterized by its mesh size and strand coarseness, has a significant impact on delay time. Decreasing the mesh size or increasing the strand thickness makes colloidal gels more resilient to delayed yielding. The quench and flow history of gels modifies their microstructures. Our experiments show that a slow quenching increases the delay time due to the coarsening of the strands; by contrast, preshear reduces the delay time, which we explain by the increased mesh size as a result of shear-induced fracture of strands.
Tuning of Collagen Triple-Helix Stability in Recombinant Telechelic Polymers
Silva, C.I. da; Skrzeszewska, P.J. ; Golinska, M.D. ; Werten, M.W.T. ; Eggink, G. ; Wolf, F.A. de - \ 2012
Biomacromolecules 13 (2012)5. - ISSN 1525-7797 - p. 1250 - 1258.
triblock copolymers - stabilization - hydrogels - gelatin - gels - hydroxylation - proteins - kinetics - network - water
The melting properties of various triblock copolymers with random coil middle blocks (100–800 amino acids) and triple helix-forming (Pro-Gly-Pro)n end blocks (n = 6–16) were compared. These gelatin-like molecules were produced as secreted proteins by recombinant yeast. The investigated series shows that the melting temperature (Tm) can be genetically engineered to specific values within a very wide range by varying the length of the end block. Elongation of the end blocks also increased the stability of the helices under mechanical stress. The length-dependent melting free energy and Tm of the (Pro-Gly-Pro)n helix appear to be comparable for these telechelic polymers and for free (Pro-Gly-Pro)n peptides. Accordingly, the Tm of the polymers appeared to be tunable independently of the nature of the investigated non-cross-linking middle blocks. The flexibility of design and the amounts in which these nonanimal biopolymers can be produced (g/L range) create many possibilities for eventual medical application.
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