6,905 research outputs found
Interview with Nicholas Christopher, author of Somewhere in the Night: Film Noir and the American City
No full textInterview with Nicholas Christopher, author of Somewhere in the Night: Film Noir and the American Cit
Resurrecting the Author
No full textPresentation of Nicholas Wolterstorff\u27s Paper Resurrecting the Author with time after for questions beginning at 18:00
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Experimental and Numerical Modeling of Seismic Earth Pressures on Retaining Walls with Cohesive Backfills
No full textObservations from recent earthquakes show that all types of retaining structures with non-liquefiable backfills perform very well and there is limited evidence of damage or failures related to seismic earth pressures. Even retaining structures designed only for static loading have performed well during strong ground motions suggesting that special seismic design provisions may not be required in some cases. The objective of this study was to characterize the seismic interaction of backfill-wall systems using experimental and numerical models, with emphasis on cohesive soils, and to review the basic assumptions of current design methods.In the experimental phase of this research, two sets of centrifuge models were conducted at the Center for Geotechnical modeling in UC Davis. The first experiment consisted of a basement wall and a freestanding cantilever wall with level backfill, while the second one consists of a cantilever wall with sloping backfill. The soil used in the experiments was a compacted low plasticity clay. Numerical simulations were performed using FLAC2-D code, featuring non-linear constitutive relationships for the soil and interface elements. The non-linear hysteretic constitutive UBCHYST was used to model the level ground experiment and Mohr-Coulomb with hysteretic damping was used to model the sloping backfill experiment. The simulations captured the most important aspects of the seismic responses, including the ground motion propagation and the dynamic soil-structure interaction. Special attention was given to the treatment of boundary conditions and the selection of the model parameters. The results from the experimental and numerical analysis provide information to guide the designers in selecting seismic design loads on retaining structures with cohesive backfills. The experimental results show that the static and seismic earth pressures increase linearly with depth and that the resultant acts at 0.35H-0.4H, as opposed to 0.5-0.6H assumed in current engineering practice. In addition, the observed seismic loads are a function of the ground motion intensity, the wall type and backfill geometry. In general, the total seismic load can be expressed using Seed and Whitman's (1970) notation as: Pae=Pa+dPae, where Pa is the static load and dPae is the dynamic load increment. While the static load is a function of the backfill strength, previous stress history and compaction method, the dynamic load increment is a function of the free field PGA, the wall displacements, and is relatively independent of cohesion. In level ground, the dynamic load coefficient can be expressed as dKae=1/2gH2(0.68PGAff/g) for basement walls and dKae=1/2gH2(0.42PGAff/g) for cantilever walls; these results are consistent with similar experiments performed in cohesionless soils (Mikola & Sitar, 2013. In the sloping ground experiment the seismic coefficient came out to dKae=1/2gH2(0.7PGAff/g), which is consistent with Okabe's (1926) Coulomb wedge analysis of the problem. However, that slope was stable under gravity loads even without the presence of the retaining wall (FS=1.4). Measured slope displacements were very small and in reasonable good agreement with the predictions made with the Bray and Travasarou (2007) semi-empirical method. The experimental data was not sufficient to determine accurately the point of action of the seismic loads. However, the numerical simulations and Okabe's (1926) limit state theory suggest that the resultant acts between 0.37H-0.40H for typical values of cohesion. While the resultant acts at a point higher than 0.33H with increasing cohesion, the total seismic moment is reduced due to the significant reduction in the total load Pae, particularly for large ground accelerations. The results also show that typical retaining walls designed with a static factor of safety of 1.5 have enough strength capacity to resist ground accelerations up to 0.4g. This observation is consistent with the field performance of retaining walls as documented by Clough and Fragaszy (1977) and the experimental results by al Atik and Sitar (2010) and Geraili and Sitar (2013).The evaluation of earth pressures at the wall-backfill interface continues to be a technical challenge. Identified sources of error in the present study include the behavior of pressure sensors, the geometric and mass asymmetry of the model and the dynamic interaction between the model and the container. While these centrifuge experiments reproduced the basic response of prototype models, ultimately, instrumented full-scale structures are most essential to fully characterize the response of tall walls and deep basements with varieties of backfill
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Constitutive Modeling of Weakly Cemented Sands
No full textAbstractConstitutive Modeling of Weakly Cemented SandsByChukwuebuka NwekeDoctor of Philosophy in Civil and Environmental EngineeringUniversity of California, BerkeleyProfessor Nicholas Sitar, ChairWeakly cemented sands are prominent in nature and can be found in many geologic deposits all over the world. The same is true for loose sand deposits, which conversely, create undesirable conditions for engineering design and execution. The primary difference between weakly cemented sand and loose sand is the presence of cementation, which enhances the mechanical properties and behavioral response of the former. As a result, the ability to replicate this cementation feature and use it to improve loose sand deposits has been (and is currently) an area of intense investigation and research. Traditional ground improvement methods employ the use of Portland cement via jet grouting, deep soil mixing, compaction grouting, and many others. These methods are considered “environmentally unfriendly” due to their use of “high-embodied” energy materials. A potential solution may lie in the realm of biocementation where sustainable ground improvement technologies use microbial metabolic activity to activate chemical reactions that inevitably induce precipitation of calcium carbonate, which accumulates at the grain contacts and binds the soil skeleton. These artificial cemented granular materials (biocement or Portland cement), as well as naturally cemented materials often serve as the foundation material or support foundation structures of varying overlying infrastructures. For this reason, there is a need for tools that are capable of assessing the improvements (or enhanced characteristics) of these types of sands, and predicting the performance under varying loading conditions.The focus of this dissertation is to gain a better understanding of the mechanics of cemented and uncemented sands, considering the vast similarities between both states, but highlighting the distinctions that may give insights into how the effects of cementation alter the mechanical properties of sands. Laboratory triaxial tests were used as a means to investigate the mechanical behavior. It was observed that light cementation preserved the characteristics of stress-strain response typical of uncemented sands, while it also significantly enhanced the strength and stiffness for even low levels of cement content. This was attributed to strengthening of the soil fabric that resulted from the formation of “cement bridges” at the interparticle contacts, which induced increased strength in shear and in compression. Furthermore, it was found that the stress-dilatancy theories used in modeling uncemented sands also apply to weakly cemented sands. Specifically, it was shown that the critical state conditions were relatively unaffected by cementation, leaving the dilatancy to harbor most, if not all, of the cementation enhancement effects. Nor-Sand “bounding plasticity” model was employed as the foundation model due to its ability to represent dilation of the material at low confining pressures. As such, attention was placed on enhancing the dilation component of the model via the inclusion of a cementation parameter that is a function of the amount of cement. In addition, the cementation parameter is capable of evolving with accumulated deformation, allowing for the transition from the cemented to uncemented state. The new model, N-We-Ce (Nor-Sand for Weakly Cemented sands) maintains usage of the majority of parameters from the Nor-Sand base model, while adding 4 – 6 new parameters (depending on the type of test data) describing the contribution of cementation to the strength and stiffness of the sand
Heritability and Linkage Analysis of Appendicitis Utilizing Age at Onset
No full textAppendicitis usually afflicts the young, but there is a large tail in the distribution of onset age. The genetics of this disease are still not well understood. A heritability analysis and genome wide linkage analysis of a large twin dataset was undertaken. Treating age of onset of appendicitis as a censored survival trait revealed a heritability of 0.21, and found evidence of linkage to Chromosome 1p37.3. Author(s): Christopher Oldmeadow 1 * | Kerrie Mengersen 2 | Nicholas Martin 3 | David L. Duffy
Nicholas de Monchaux: Local Code / Real Estates
No full textNicholas de Monchaux is an architect and urbanist whose work explores the intersections between nature, technology, and the city. He is the author of Spacesuit: Fashioning Apollo (MIT Press, 2011), an architectural history of the Apollo 11 spacesuit. He is Assistant Professor of Architecture and Urban Design at UC Berkeley. The work of his design studio has been exhibited widely and is currently being featured in the US Pavillion of the 13th Venice Biennale
Nicholas Meyer: 10-31-1979
No full textNicholas Meyer is a screenwriter, producer, director, and author, and a graduate of the University of Iowa. He is the author of the screenplay the Seven Per Cent Solution and co-author of The Black Orchid. He begins the interview by discussing his professional career as both a film writer/director and a novelist. He then talks about how he began writing novels, and discusses the research that goes into his novels. Meyer continues by discussing his movie Time After Time and concludes the interview by listing prominent teachers and writing influences.Archived web contentSUNY BrockportWriters Forum Video
Nicholas Meyer: 10-31-1979
No full textNicholas Meyer is a screenwriter, producer, director, and author, and a graduate of the University of Iowa. He is the author of the screenplay the Seven Per Cent Solution and co-author of The Black Orchid. He begins the interview by discussing his professional career as both a film writer/director and a novelist. He then talks about how he began writing novels, and discusses the research that goes into his novels. Meyer continues by discussing his movie Time After Time and concludes the interview by listing prominent teachers and writing influences.https://digitalcommons.brockport.edu/writers_videos/1022/thumbnail.jp
Interview with Nicholas Wade by Marni Siegel, November 8, 2007
No full textThe interview was a project of the Center for Public Genomics (http://www.genome.duke.edu/centers/cpg/).Nicholas Wade is a science writer for the New York Times and author of several books, including LifeScripts, about genetics and genomics. He also covered the Asilomar Conference for Science magazine.Funded by a grant from the National Human Genome Research Institute and the US Department of Energy (P50 HG003391)
LSE festival Beveridge 2.0 preview: the five giants by Nicholas Timmins
No full textOn Monday 19 February, LSE Festival opened with ‘The Five Giants and the Ministers Who Made a Difference’. Chaired by LSE Director Minouche Shafik, Nicholas Timmins, author of The Five Giants: A Biography of the Welfare State, and Professor Sir Julian Le Grand debated the key UK politicians who really made a difference when it came to Beveridge’s ‘Five Giants’: listen to the podcast here. Ahead of the event, Nicholas Timmins gives insight into the reception and impact of Beveridge’s 1942 report, as well as its enduring significance in today’s global, 21st-century context
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