Observations on the desiccation and cracking of clay layers

Waterways and lakes in low-lying delta areas require regular dredging for maintenance. Often these sediments are placed on land, where they are allowed to ripen through a combination of drainage, consolidation and evaporation. When cracks develop during desiccation, the physical response of the soil is affected by changes in the overall strength, stiffness and permeability of the material. To better identify how cracks form and propagate, a series of tests was carried out in a controlled laboratory environment on samples of drying clay slurries under different initial and boundary conditions. The outcomes of this study indicate that the results from laboratory small scale models must be carefully analyzed, as they depend on the area and the thickness of the sample. However, common features from the different tests can be identified, which are mostly related to the intrinsic behavior of the material. For instance, the water content at which cracks initiate depends mostly on the drying rate and not only on the initial water content. Typically for the clayey soil investigated, the cracking water content is well above the shrinkage limit and in some instances even above the liquid limit. Cracks can form anywhere a defect is encountered, but it was observed that they propagate in horizontal directions below the soil surface. On the soil surface they tend to intersect with each other perpendicularly, suggesting that they are dominated by a tensile stress regime. Shear stresses also influence the response, but mainly near the boundaries of the samples, due to the interface friction

Voorstel bouwstenen nieuwe weidevogelpakketten agrarisch natuurbeheer in een notendop : wat regelen we in Nederland, wat in Brussel?

In opdracht van directie Kennis van het ministerie van LNV is een voorstel ontwikkeld voor bouwstenen voor nieuwe pakketten weidevogelbeheer. De doelstellingen worden per gebiedsplan vastgesteld. De verantwoordelijkheid hiervoor ligt bij provincies en Rijk, die daarvoor desgewenst een gebiedscommissie in het leven kunnen roepen. Het minimum dat altijd (in alle gebiedsplannen) geldt is: 35 bp /100 ha, bestaande uit één of meer van de volgende soorten: Grutto, Tureluur, Watersnip, Kemphaan, Slobeend, Zomertaling, Veldleeuwerik, Wulp, Kluut, Krakeend, Kuifeend, Wintertaling, Graspieper, Gele kwikstaart, Kievit, Scholekster. Per gebied kan deze doelstelling nader worden gefocust op één of meerdere van bovengenoemde soorten en/of naar boven worden bijgestel

The Skill Assumption -Over-Reliance on Perception Skills in Hazard Assessment

In the analysis of human performance and human error, considerable attention is given to the cognitive processes of actors involved in error or success scenarios. Even with awareness of hindsight bias, it takes effort to understand the actions of agents in later inspection of error scenarios. One such topic of heated discussion was the perceived poor performance of pilots in the two 737 MAX MCAS-related crashes in applying the “memory item” checklist pertaining to a runaway trim. In this paper, we argue that it is not so much the reproduction of the checklist that was lacking in these scenarios, but the trigger for even starting the checklist. Not only trim run-away problems, but several other issues likewise require an instant reaction from pilots, designated as “memory items”. Rasmussen’s simplifed schematic for the “skill, rule and knowledge” taxonomy already provides the tools for properly analyzing this. The skill to provide the triggers for these reactions relies on pattern extraction from the available sensory input, and, importantly, it can only be learned in a valid training context. It is argued that re-appraisal of these items is needed, addressing explicitly the validity of the training environments that enable pilots to learn the required pattern recognition skills

Van regels naar ondernemersverantwoordelijkheid : belemmeringen door wet- en regelgeving voor de plantaardige sectoren

Dit rapport over belemmeringen door wet- en regelgeving voor de plantaardige sectoren is gebaseerd op een onderzoek bij ongeveer 850 ondernemers. Uit het rapport van blijkt dat deze ondernemers nog veel knelpunten ervaren in de vorm van belemmerende regelgeving. Die variëren van algemene klachten over de veelheid aan regels tot specifieke onderdelen van de mestregels, regels voor gewasbescherming, arbo-wetgeving en bestemmingsplannen. Het onderzoek vormt in die zin een bevestiging van signalen die ik ook langs andere weg ontvang. De waarde van het rapport zit vooral in het feit dat belemmeringen en aanbevelingen in de breedte in kaart zijn gebracht

Transport of <i>Sporosarcina pasteurii</i> in sandstone and its significance for subsurface engineering technologies

The development of microbially mediated technologies for subsurface remediation and rock engineering is steadily increasing; however, we are lacking experimental data and models to predict bacterial movement through rock matrices. Here, breakthrough curves (BTCs) were obtained to quantify the transport of the ureolytic bacterium, Sporosarcina pasteurii, through sandstone cores, as a function of core length (1.8–7.5 cm), bacterial density (4 × 10&lt;sup&gt;6&lt;/sup&gt; to 9 × 10&lt;sup&gt;7&lt;/sup&gt; cells/ml) and flow rate (5.8–17.5 m/s). &lt;i&gt;S. pasteurii&lt;/i&gt; was easily immobilised within the homogeneous sandstone matrix (&gt;80%) in comparison to a packed sand column (&lt;20%; under similar experimental conditions), and percentage recovery decreased almost linearly with increasing rock core length. Moreover, a decrease in bacterial density or flow rate enhanced bacterial retention. A numerical model based on 1D advection dispersion models used for unconsolidated sand was fitted to the BTC data obtained here for sandstone. Good agreement between data and model was obtained at shorter rock core lengths (&lt;4 cm), suggesting that physicochemical filtration processes are similar in homogeneous packed sand and sandstones at these lengths. Discrepancies were, however observed at longer core lengths and with varying flow rates, indicating that the attributes of consolidated rock might impact bacterial transport progressively more with increasing core length. Implications of these results on microbial mineralisation technologies currently being developed for sealing fluid paths in subsurface environment is discussed

Agricultural innovation platforms in West Africa: How does strategic institutional entrepreneurship unfold in different value chain contexts?

Inspired by Innovation System theory, donors promote Innovation Platforms (IP) to enhance collaboration for development. However, the question arises whether this is the best approach to facilitate change. The article presents the experience of an action-research programme (2009-2013) on the value of IPs for creating institutional change for the benefit of smallholders, in various value chain contexts in West Africa. We analyse the cases from a dialectic perspective on institutional entrepreneurship. Results show: the open IP approach, with some clear principles and in-depth analysis of the antagonistic context, enabled the initiator-cum-facilitators to create a reasonably effective IP coalition that endorsed broker activities fit for the context. In a mature value chain, it was possible to mobilise incumbent actors, who perceived a mutual benefit in enhancing smallholder development. In the other cases, IPs were started at lower administrative levels, building discursive legitimacy and -appeal to mobilise smallholders and higher level authorities for institutional change. We note a researcher-initiated open IP approach is able to induce strategic action in-situ, but the approach has its limitation: In the time given, IPs could neither build a cooperative smallholder movement, nor interest private export companies to invest in smallholders; nor tackle misaligned political interests

Systematic screening for COVID-19 associated invasive aspergillosis in ICU patients by culture and PCR on tracheal aspirate

Background A high prevalence of COVID-19 associated pulmonary aspergillosis (CAPA) has been reported, though histopathological evidence is frequently lacking. To assess the clinical significance of Aspergillus species in respiratory samples of mechanically ventilated COVID-19 patients, we implemented routine screening for Aspergillus in tracheal aspirate (TA).Patients/methods From all adult COVID-19 patients admitted to the intensive care unit (ICU), TA samples were collected twice a week for Aspergillus screening by PCR and or culture. Bronchoalveolar lavage (BAL) sampling was performed in patients with a positive screening result if possible. Clinical information was obtained from the electronic patient record and patients were categorised according to the recently published consensus case definition for CAPA.Results Our study population consisted of 63 predominantly (73%) male patients, with a median age of 62 years and total median ICU stay of 18 days. Aspergillus species were present in TA screening samples from 15 patients (24%), and probable CAPA was diagnosed in 11 (17%) patients. Triazole resistance was detected in one patient (14%). Concordance between TA and BAL was 86%, and all TA culture positives were confirmed in BAL. We were able to withhold treatment in three of fifteen patients with positive screening (20%) but negative BAL results.Conclusions Positive culture, molecular detection and or antigen detection of Aspergillus species do not equal infection. Until we understand the clinical relevance of Aspergillus species detected in respiratory samples of COVID-19 patients, minimal-invasive screening by TA is a feasible method to monitor patients. Positive screening results should be an indication to perform a BAL to rule out upper airway colonisation.Perioperative Medicine: Efficacy, Safety and Outcome (Anesthesiology/Intensive Care