236 research outputs found
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
A multi-phase biogeochemical model for mitigating earthquake-induced liquefaction via microbially induced desaturation and calcium carbonate precipitation
A next-generation biogeochemical model was developed to
explore the impact of the native water source on microbially induced
desaturation and precipitation (MIDP) via denitrification. MIDP is a
non-disruptive, nature-based ground improvement technique that offers the
promise of cost-effective mitigation of earthquake-induced soil liquefaction
under and adjacent to existing structures. MIDP leverages native soil
bacteria to reduce the potential for liquefaction triggering in the short
term through biogenic gas generation (treatment completed within hours to
days) and over the longer term through calcium carbonate precipitation
(treatment completed in weeks to months). This next-generation
biogeochemical model expands earlier modeling to consider multi-phase
speciation, bacterial competition, inhibition, and precipitation. The
biogeochemical model was used to explore the impact of varying treatment
recipes on MIDP products and by-products in a natural seawater environment.
The case study presented herein demonstrates the importance of optimizing
treatment recipes to minimize unwanted by-products (e.g., H2S
production) or incomplete denitrification (e.g., nitrate and nitrite
accumulation).</p
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Evaluation of materials for retention of sodium and core debris in reactor systems. Annual progress report, September 1977-December 1978. [LMFBR]
This report considers some of the consequences of a hypothetical core disruptive accident in a nuclear reactor. The interactions expected between molten core debris, liquid sodium, and materials that might be employed in an ex-vessel sacrificial-bed or in the reactor building are discussed. Experimental work performed for NRC by Sandia Laboratories and Hanford Engineering Development Laboratory on the interactions between liquid sodium and basalt concrete is reviewed. Studies of molten steel interactions with concrete at Sandia Laboratories and molten UO/sub 2/ interactions with concrete at The Aerospace Corporation are also discussed. The potential of MgO for use in core containment is discussed and refractory materials other than MgO are reviewed. Finally, results from earlier experiments with molten core debris and various materials performed at The Aerospace Corporation are presented
Geolocators lead to better measures of timing and renesting in black-tailed godwits and reveal the bias of traditional observational methods
Long-term population studies can identify changes in population dynamics over time. However, to realize meaningful conclusions, these studies rely on accurate measurements of individual traits and population characteristics. Here, we evaluate the accuracy of the observational methods used to measure reproductive traits in individually marked black-tailed godwits (Limosa limosa limosa). By comparing estimates from traditional methods with data obtained from light-level geolocators, we provide an accurate estimate of the likelihood of renesting in godwits and the repeatability of the lay dates of first clutches. From 2012 to 2018, we used periods of shading recorded on the light-level geolocators carried by 68 individual godwits to document their nesting behaviour. We then compared these estimates to those simultaneously obtained by our long-term observational study. We found that among recaptured geolocator-carrying godwits, all birds renested after a failed first clutch, regardless of the date of nest loss or the number of days already spent incubating. We also found that 43% of these godwits laid a second replacement clutch after a failed first replacement, and that 21% of these godwits renested after a hatched first clutch. However, the observational study correctly identified only 3% of the replacement clutches produced by geolocator-carrying individuals and designated as first clutches a number of nests that were actually replacement clutches. Additionally, on the basis of the observational study, the repeatability of lay date was 0.24 (95% CI 0.17-0.31), whereas it was 0.54 (95% CI 0.28-0.75) using geolocator-carrying individuals. We use examples from our own and other godwit studies to illustrate how the biases in our observational study discovered here may have affected the outcome of demographic estimates, individual-level comparisons, and the design, implementation and evaluation of conservation practices. These examples emphasize the importance of improving and validating field methodologies and show how the addition of new tools can be transformational
Management of adult-onset Still's disease:evidence- and consensus-based recommendations by experts
Objectives: Adult-onset Still's disease (AOSD) is a rare condition characterized by fevers, rash, and arthralgia/arthritis; most doctors treating AOSD in the Netherlands treat <5 patients per year. Currently, there is no internationally accepted treatment guideline for AOSD. The objectives of this study were to conduct a Delphi panel aimed at reaching consensus about diagnostic and treatment strategies for patients with AOSD and to use the outcomes as a basis for a treatment algorithm. Methods: The Delphi panel brought together 18 AOSD experts: rheumatologists, internists and paediatricians. The Delphi process consisted of three rounds. In the first two rounds, online lists of questions and statements were completed. In the third round, final statements were discussed during a virtual meeting and a final vote took place. Consensus threshold was set at 80%. Two targeted literature searches were performed identifying the level of evidence of the consensus-based statements. Results: Consensus was reached on 29 statements, including statements related to diagnosis and diagnostic tests, definition of response and remission, the therapy, the use of methotrexate and tapering of treatment. The panel consented on reduction of the use of glucocorticoids to avoid side effects, and preferred the use of biologics over conventional treatment. The role of IL-1 and IL-6 blocking agents was considered important in the treatment of AOSD. Conclusion:Â In this Delphi panel, a high level of consensus was achieved on recommendations for diagnosis and therapy of AOSD that can serve as a basis for a treatment guideline.</p
Management of adult-onset Still's disease:evidence- and consensus-based recommendations by experts
Objectives: Adult-onset Still's disease (AOSD) is a rare condition characterized by fevers, rash, and arthralgia/arthritis; most doctors treating AOSD in the Netherlands treat <5 patients per year. Currently, there is no internationally accepted treatment guideline for AOSD. The objectives of this study were to conduct a Delphi panel aimed at reaching consensus about diagnostic and treatment strategies for patients with AOSD and to use the outcomes as a basis for a treatment algorithm. Methods: The Delphi panel brought together 18 AOSD experts: rheumatologists, internists and paediatricians. The Delphi process consisted of three rounds. In the first two rounds, online lists of questions and statements were completed. In the third round, final statements were discussed during a virtual meeting and a final vote took place. Consensus threshold was set at 80%. Two targeted literature searches were performed identifying the level of evidence of the consensus-based statements. Results: Consensus was reached on 29 statements, including statements related to diagnosis and diagnostic tests, definition of response and remission, the therapy, the use of methotrexate and tapering of treatment. The panel consented on reduction of the use of glucocorticoids to avoid side effects, and preferred the use of biologics over conventional treatment. The role of IL-1 and IL-6 blocking agents was considered important in the treatment of AOSD. Conclusion:Â In this Delphi panel, a high level of consensus was achieved on recommendations for diagnosis and therapy of AOSD that can serve as a basis for a treatment guideline.</p
A Dutch consensus statement on the diagnosis and treatment of ANCA-associated vasculitis
INTRODUCTION: Despite the availability of several guidelines on the diagnosis and treatment of antineutrophil cytoplasmic antibody-associated vasculitis (AAV), clinical routine practice will only improve when an implementation strategy is in place to support clinical decision making and adequate implementation of guidelines. We describe here an initiative to establish national and multidisciplinary consensus on broad aspects of the diagnosis and treatment of AAV relevant to daily clinical practice in the Netherlands. METHODS: A multidisciplinary working group of physicians in the Netherlands with expertise on AAV addressed the broad spectrum of diagnosis, terminology, and immunosuppressive and non-immunosuppressive treatment, including an algorithm for AAV patients. Based on recommendations from (inter)national guidelines, national consensus was established using a Delphi-based method during a conference in conjunction with a nationally distributed online consensus survey. Cut-off for consensus was 70% (dis)agreement. RESULTS: Ninety-eight professionals were involved in the Delphi procedure to assess consensus on 50 statements regarding diagnosis, treatment, and organisation of care for AAV patients. Consensus was achieved for 37/50 statements (74%) in different domains of diagnosis and treatment of AAV including consensus on the treatment algorithm for AAV. CONCLUSION: We present a national, multidisciplinary consensus on a diagnostic strategy and treatment algorithm for AAV patients as part of the implementation of (inter)national guideline-derived recommendations in the Netherlands. Future studies will focus on evaluating local implementation of treatment protocols for AAV, and assessments of current and future clinical practice variation in the care for AAV patients in the Netherlands
Simulation of Front Instabilities in Density-Driven Flow, Using a Reactive Transport Model for Biogrout Combined with a Randomly Distributed Permeability Field
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