179,528 research outputs found
Molecular and nanostructural mechanisms of deformation, strength and toughness of spider silk fibrils
No full textSpider silk is one of the strongest, most extensible and toughest biological materials known, exceeding the properties of many engineered materials including steel. Silks feature a hierarchical architecture where highly organized, densely H-bonded beta-sheet nanocrystals are arranged within a semi-amorphous protein matrix consisting of 31-helices and beta-turn protein structures. By using a bottom-up molecular-based mesoscale model that bridges the scales from Angstroms to hundreds of nanometers, here we show that the specific combination of a crystalline phase and a semi-amorphous matrix is crucial for the unique properties of silks. Specifically, our results reveal that the superior mechanical properties of spider silk can be explained solely by structural effects, where the geometric confinement of beta-sheet nanocrystals combined with highly extensible semi-amorphous domains with a large hidden length is the key to reach great strength and great toughness, despite the dominance of mechanically inferior chemical interactions such as H-bonding. Our model directly shows that semi-amorphous regions unravel first when silk is being stretched, leading to the large extensibility of silk. Conversely, the large-deformation mechanical properties and ultimate tensile strength of silk is controlled by the strength of beta-sheet nanocrystals, which is directly related to their size, where small beta-sheet nanocrystals are crucial to reach outstanding levels of strength and toughness. Our model agrees well with observations in recent experiments, where it was shown that a significant change in the strength and toughness can be achieved solely by tuning the size of beta-sheet nanocrystals. Our findings unveil the material design strategy that enables silks to achieve superior material performance despite simple and inferior constituents, resulting in a new paradigm in materials design where enhanced functionality is not achieved using complex building blocks, but rather through the utilization of simple repetitive constitutive elements arranged in hierarchical structures
V. Dolson, Fred Buehler, and Dave Halsey
No full textPhotograph of three men (L-R: V. Dolson, Fred Buehler, and Dave Halsey) seated on an airplane cart in front of an aircraft that has the text "United States Air Force, Convair, YB-60" along the side. All of the men are wearing suits though Dolson does not have a jacket; Buehler and Halsey are seated on the front of the cart above the words, "Development, 706 No Riders." The plane is parked on the tarmac and other equipment is visible along a fence in the background
Data from range-wide study of migratory connectivity of Vermivora warblers
No full textSee ReadMe.txt for detailed description of files.This collection of files provide data from a range-wide study of the migratory ecology of Vermivora warblers. Data include raw light-level data from geolocators, R code, and associated output. These data can be used to recreate analyses including:
(1) Individual nonbreeding occurrence and population-level nonbreeding overlap
(2) Individual migration routes and spatial distribution of individuals and populations during migrationU.S. Fish and Wildlife ServiceU.S Geological SurveyMinnesota Cooperative Fish and Wildlife Research UnitNational Science FoundationVirginia Department of Game and Inland FisheriesGrace Jones Richardson TrustKramer, Gunnar R; Andersen, David E; Buehler, David A.; Wood, Petra B; Peterson, Sean M; Lehman, Justin A; Aldinger, Kyle R; Bulluck, Lesley P; Harding, Sergio; Jones, John A; Loegering, John P; Smalling, Curtis; Vallender, Rachel; Streby, Henry M. (2018). Data from range-wide study of migratory connectivity of Vermivora warblers. Retrieved from the University Digital Conservancy, https://doi.org/10.13020/D6D97W
Jakob Matthias Buehler: Conservative Missionary and Theologian
No full textThe purpose of the paper is not so much to sketch a history, as to see whether the difficulties Rev. Buehler encountered were a result of his liberalism or conservatism
Evidence of the Most Stretchable Egg Sac Silk Stalk, of the European Spider of the Year Meta menardi
No full textSpider silks display generally strong mechanical properties, even if differences between species and within the same species can be observed. While many different types of silks have been tested, the mechanical properties of stalks of silk taken from the egg sac of the cave spider Meta menardi have not yet been analyzed. Meta menardi has recently been chosen as the “European spider of the year 2012”, from the European Society of Arachnology. Here we report a study where silk stalks were collected directly from several caves in the north-west of Italy. Field emission scanning electron microscope (FESEM) images showed that stalks are made up of a large number of threads, each of them with diameter of 6.03±0.58 µm. The stalks were strained at the constant rate of 2 mm/min, using a tensile testing machine. The observed maximum stress, strain and toughness modulus, defined as the area under the stress-strain curve, are 0.64 GPa, 751% and 130.7 MJ/m[superscript 3], respectively. To the best of our knowledge, such an observed huge elongation has never been reported for egg sac silk stalks and suggests a huge unrolling microscopic mechanism of the macroscopic stalk that, as a continuation of the protective egg sac, is expected to be composed by fibres very densely and randomly packed. The Weibull statistics was used to analyze the results from mechanical testing, and an average value of Weibull modulus (m) is deduced to be in the range of 1.5–1.8 with a Weibull scale parameter (σ[subscript 0]) in the range of 0.33–0.41 GPa, showing a high coefficient of correlation (R[superscript 2] = 0.97).Presidential Early Career Award for Scientists and Engineers (award number N00014-10-1-0562
Asymmetric Vertical Integration
No full textWe examine vertical backward integration in a reducedform model of successive oligopolies. Our key findings are: (i) There may be asymmetric equilibria where some firms integrate and others remain separated, even if firms are symmetric initially; (ii) Efficient firms are more likely to integrate vertically. As a result, integrated firms also tend to have a large market share. The driving force behind these findings are demand/mark-up complementarities in the product market. We also identify countervailing forces resulting from strong vertical foreclosure, upstream sales and endogenous acquisition costs.successive oligopolies, vertical integration, effciency, foreclosure
Data and code supporting: Exposure to risk factors experienced during migration is not associated with recent Vermivora warbler population trends
No full textCode, data, and spatial layers. See readme file for description of files.Data and code supporting the publication "Exposure to risk-factors experienced during migration is not associated with recent Vermivora warbler population trends".Funding for this research was provided by the U.S. Fish and Wildlife Service and the U.S. Geological Survey through Research Work Order 98 at the U.S. Geological Survey, Minnesota Cooperative Fish and Wildlife Research Unit, and by the National Science Foundation through Postdoctoral Research Fellowship 1202729. Additional funding was provided by the University of Toledo College of Graduate Studies through a Graduate Dean’s Fellowship, the Virginia Department of Wildlife Resources and the Grace Jones Richardson Trust.Kramer, Gunnar R; Andersen, David E; Buehler, David A; Wood, Petra B; Peterson, Sean M; Lehman, Justin A; Aldinger, Kyle R; Bulluck, Lesley P; Harding, Sergio; Jones, John A; Loegering, John P; Smalling, Curtis; Vallender, Rachel; Streby, Henry M. (2023). Data and code supporting: Exposure to risk factors experienced during migration is not associated with recent Vermivora warbler population trends. Retrieved from the University Digital Conservancy, https://doi.org/10.13020/1dap-6d14
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Letter to the editor: naltrexone sustained-release/bupropion sustained-release for the management of obesity: review of the data to date
No full textAnna M Buehler Hospital Alemao Oswaldo Cruz, Institute of Health Education and Sciences, Sao Paulo, BrazilI read with great interest the systematic review by Caixàs et al1 on the effect of naltrexone sustained-release/bupropion sustained-release (NB) for the management of obesity. By comprehensively appraising five recent clinical trials, the authors concluded that the naltrexone/bupropion combination might represent an important new therapeutic option for the management of obesity, with a weight reduction effect that is similar to other drugs approved for the treatment of obesity.View original paper by Caixàs and colleagues
Flaw-tolerance in silk fibrils explains strength, extensibility and toughness of spider silk
No full textSilk is an ancient but remarkably strong, extensible and tough material made from simple protein building blocks. Earlier work has shown that the particular molecular geometry of silk with a composite of semi-amorphous and nanocrystalline beta-sheet protein domains provides the structural basis for its characteristic softening-stiffening behavior and remarkable strength at the nanoscale. Yet, an open question remains as to how these nanoscale properties are upscaled so effectively to create strong, extensible and tough silk fibers. Here we discover that the geometric confinement of fibrils to ≈50-100 nm width and arranged in bundles to form larger-scale silk fibers, is the key to explaining the upscaling of the mechanical properties of silk from the atomistic scale upwards. We find that under this geometric confinement, hundreds of thousands of protein domains unfold simultaneously and thereby act synergistically to resist deformation and failure, providing access to enhanced large-scale strength, extensibility and toughness. Moreover, since the material is in a flaw-tolerant state under this geometric confinement, structural inhomogeneities such as cavities or tears that typically act as stress concentrators do not compromise the material performance. Indeed, experimental work showed that the diameter of silk fibrils that make up larger-scale silk fibers are on the order of 20-100 nm, in agreement with our findings. The exploitation of this mechanism in engineering design enables the synthesis of hierarchical fiber materials for superior performance despite limited and inferior building blocks
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