150 research outputs found
Effect of polymer fibers on pore pressure development and explosive spalling of ultra-high performance concrete at elevated temperature
No full textThis paper investigated pore pressure development of ultra-high performance concrete (UHPC) included various polymer fibers, i.e., linear low-density polyethylene (LLDPE), ultra-high molecular weight polyethylene (UHMWPE), polypropylene (PP), polyester (PET), and polyamide (PA) fibers. Temperature and pore pressure were measured simultaneously at different depths of UHPC specimens subjected to one-dimensional heating. It was found that the PP and PA fibers prevented spalling of UHPC by enhancing moisture migration, which resulted in the development of pore pressure in the deeper region of the specimens. The moisture migration in UHPC with LLDPE fibers caused spalling of a layer of concrete in a deep region of specimen. UHMWPE fibers did not affect pore pressure development and spalling resistance of UHPC significantly, while with PET fibers, the pore pressure of UHPC raised sharply due to inadequate moisture migration, leading to spalling of a whole layer. Instead of melting polymer fibers and empty channels left, microcracks created by the fibers were responsible for releasing vapor pressure and spalling prevention. Fibers with high thermal expansion between 100 and 200 °C are recommended for spalling prevention of UHPC
Effect of fiber content and fiber length on the dynamic compressive properties of strain-hardening ultra-high performance concrete
No full textStrain-hardening ultra-high performance concrete (SH-UHPC) exhibits excellent mechanical properties at the quasi-static state and becomes a promising material for protective structures exposed to impact or blast threats. But its performance under loads with high magnitude and short duration remains unanswered. The focus of this study is to investigate the dynamic compressive properties of SH-UHPC under high strain rates, which are achieved by split Hopkinson pressure bar (SHPB) tests. SH-UHPC with different fiber contents of 1, 1.5, and 2 vol % and different fiber lengths of 6, 12, and 18 mm are tested. The considered strain rate ranges from 180 s-1 to ~& nbsp;300 s(-1). The results show that SH-UHPC exhibits good impact resistance in terms of integrity. Samples could remain good integrity at a strain rate of 240 s(-1). The key parameters to measure the dynamic properties, i.e. energy absorption, dynamic compressive strength, and dynamic increase factor (DIF) of SH-UHPC show strain rate sensitivity and all of them increase with strain rate. Increasing fiber content leads to a slight improvement of the impact resistance of SH-UHPC while reducing fiber length impairs the impact resistance. Empirical DIF relations of SH-UHPC are firstly proposed in this study
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Dialoguing with the World: Xue Yiwei and His Traveling with Marco Polo
No full textThis essay introduces the author Xue Yiwei and his Traveling with Marco Polo, a creative collection that dialogues with Invisible Cities by the postmodern Italian writer Italo Calvino. While Calvino imagines a young Marco Polo describing the fantastic sights of fifty-five cities to an aging Kublai Khan, Xue Yiwei joins the conversation and provides a meticulous explication of each one of Calvino’s cities. Furthermore, Traveling with Marco Polo expands the imaginary cityscapes to include oblique commentaries on the past, present, and future of China as well as the profound meditation on the city as a microcosm of our world. The result is a daring literary experiment that is representative of Xue’s oeuvre overall: at once giving a powerful literary representation of modern Chinese history while engaging in dialogue with writers from all over the world
New Insights into Materialism and Conspicuous Consumption in China
No full textThis paper provides insights based on recent literature and findings that relate to materialism and conspicuous consumption among Chinese consumers. There is a specific focus on gender related issues and implications on consumer well-being. Our work is intended to assist in both conceptual and hypothesis development for other interested scholars.Peer reviewe
Development and optimization of 3D printable cementitious composites for printing applications
No full text3D concrete printing (3DCP) builds up objectives in a layer-atop-layer manner and has attracted much attention recently due to many advantages, such as customized production, reduced waste, and diminished lead-time of the rapid prototype. A number of works have been conducted in 3DCP in recent years. However, limitations remain in 3DCP, especially in the field of developing consistent and reliable cementitious materials for 3DCP.
This thesis proposes a holistic approach to develop consistent and reliable 3D printable cementitious materials for large-scale printing applications. Three levels are included in the conceptualized methodology. Rheology control serves as a vital factor at the lowest level to ensure that material fresh properties can satisfy the printing requirement in terms of buildability, pumpability, setting control and shape retention capability. Afterwards, material design are the critical factors at the intermedium level to ensure that hardened properties of printed materials are suitable for structural or non-structural applications. Hardened properties are focused on compressive and flexure performance in this thesis. Process design focuses on the optimization of printing parameters for better material distribution and interlayer properties. Finally, integration of building information modeling (BIM) and architecture with 3DCP is expected to promote automatic construction fabrication for digitalized products at the third level. Due to time constraint of this PhD study, this thesis focused on the first two levels and the third level is discussed in the section on future work.
The first level study focused on the influence of various factors on material rheological properties. Firstly, empirical models are constructed to predict the rheological properties based on material constituents and chemical admixtures. Secondly, theoretical models are developed to link rheological properties with printability in terms of buildability, which was validated by a new testing method proposed in this study. Thirdly, a class of rapid hardening materials, magnesia phosphate cement-based materials, is also developed.
The second level study characterized the hardened properties of developed printable materials. Three different types of printable materials were investigated, i.e. plain cementitious materials, fiber reinforced cementitious materials, and rapid hardening cementitious materials, respectively. The hardened properties were studied in terms of compressive and flexural strength.Doctor of Philosoph
Surface patterning atop poly(methyl methacrylate)
No full textShape memory polymers (SMPs), which are featured by the shape memory effect, belong to a new class of materials that have become popular recently due to their potential applications in fields related to engineering and medicine. Microlens have a wild utilization in many fields, such as, engineering, medicine, robotic, etc. Especially artificial compound eyes have many advantages, such as, a large field of view (FOV), high sensitivity, small volume, and 3D imaging etc. As reported in the literature, fabrication of microlens arrays atop poly(methyl methacrylate) (PMMA) is in a two-step manner, indentation and then followed by immersing into ethanol. Cross-section, 3D profile scanning and projection (optical property) of the obtained microlenses are characterized. In this project, three types of microlens arrays were fabricated. One was fabricated with the same size atop a PMMA plate from same sized indents. As tested, these microlenses have the same focus length. The second sample was manufactured with different sized microlens arrays atop the same kind of PMMA plate. In the third sample, microlens arrays were produced atop a curved PMMA sample. Surface scanning experiment and projection experiment were conducted to test the optical properties of these microlens arrays.Master of Science (Precision Engineering
Exploring Causal Factors Influencing Enterprise Architecture Failure
No full textOrganizations have adopted Enterprise Architecture (EA) for managing their IT-landscape and ensuring coherence among projects and activities. There is much work about approaches, methods, and tools for EA based on the assumption that their use will create business value. However, the failure of many EA efforts results in the need to investigate the factors influencing EA failure in practice. In this paper, we used a literature review to identify ten EA failure factors. Then we employed the grey-DEMATEL method to explore and analyze the influence of the ten EA failure factors based on the input of five EA experts. The result shows that failure factors are not in isolation, and they can be divided into either causal or effect factors. The factors do not have equal importance but differ in the levels of influence. For the causal factors, the ranking from most to least important is the inability to handle complexity, lack of proven EA methodology, lack of EA knowledge, lack of communication, and lack of tools. For the effect factors, the factors are a lack of support, too high effort, lack of motivation, parallel processes, and unused artifacts. We recommend practitioners to pay more attention to the five causal factors in their EA efforts. Further research is needed to generalize the findings, to understand the dependencies among factors, and to take into account situational dependency of EA failure.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Information and Communication Technolog
Site-Specific Ground Motions for Dynamic Analyses in Regions of Lower Seismicity
No full text© 2022 Yiwei HUSite-specific dynamic analyses of structures have many advantages over traditional code spectrum procedures in regions of lower seismicity. The prime reason is that the site-specific response spectra and accelerograms are more realistic representations of earthquake actions for a structure located on a unique construction site. Developing site-specific ground motions requires a comprehensive understanding of regional seismic hazard analyses, soil condition analyses and site response analyses. Guidelines or facilities for performing site-specific dynamic analyses in accordance with the design code are unavailable to engineering practitioners in Australia.
The primary objective of this thesis is to develop a computationally effective method to generate response spectra and accelerograms for site-specific dynamic analysis in intraplate regions of lower seismicity, with a focus on the Southeastern Australia (SEA) region. Based on the proposed method, this thesis provides suites of ground motions in compliance with the Australian standard for direct engineering applications.
The conditional mean spectrum (CMS) methodology was first reviewed and its challenges for application in intraplate regions were overcome by employing a diversity of ground motion prediction expressions (GMPEs) and the uniform seismicity model. Three different schemes using a weighted averaging of candidate GMPEs were adopted, and a comparison of predictions demonstrated only minor differences confirming the robustness of the modelling.
The constructed CMS were targeted for sourcing ground motions to define seismic hazard at the bedrock level. The bedrock motions were amplified through soil column models to simulate site amplification effects. Subsoil information retrieved from multiple borehole records from the same site was sampled to construct soil column models to achieve conservative estimations of soil amplification ratio at the fundamental period of vibration of the structure to account for resonance. The sampling process involves closed-form expressions for determining the shear strain profile in a soil column considering degradation in the shear modulus of the soil in seismic conditions.
The applications of resultant site-specific response spectra and accelerograms, following a ground motion selection scheme proposed by the author, were demonstrated with nonlinear time history analysis for structural design and multiple stripe analysis for risk assessment.
This thesis is concluded with three outcomes: (1) a ground motion database for site-specific seismic design based on twenty sites that typify subsoil profiles in SEA, (2) an online program at https://quakeadvice.org/ for generating ground motions with user-defined borehole information, and (3) suites of ground motions for risk assessment of structures following the multiple stripe analysis method
UGent-T2K at the 2nd DialDoc Shared Task: A Retrieval-Focused Dialog System Grounded in Multiple Documents
No full textThis research received funding from the Flemish Government under the "Onderzoeksprogramma Artificiele Intelligentie (AI) Vlaanderen" programme. The first author was supported by China Scholarship Council (201806020194). We thank the anonymous reviewers whose comments helped to improve our work
Dynamics and folding of single two-stranded coiled-coil peptides studied by fluorescent energy transfer confocal microscopy
No full textWe report single-molecule measurements on the folding and unfolding conformational equilibrium distributions and dynamics of a disulfide crosslinked version of the two-stranded coiled coil from GCN4. The peptide has a fluorescent donor and acceptor at the N termini of its two chains and a Cys disulfide near its C terminus. Thus, folding brings the two N termini of the two chains close together, resulting in an enhancement of fluorescent resonant energy transfer. End-to-end distance distributions have thus been characterized under conditions where the peptide is nearly fully folded (0 M urea), unfolded (7.4 M urea), and in dynamic exchange between folded and unfolded states (3.0 M urea). The distributions have been compared for the peptide freely diffusing in solution and deposited onto aminopropyl silanized glass. As the urea concentration is increased, the mean end-to-end distance shifts to longer distances both in free solution and on the modified surface. The widths of these distributions indicate that the molecules are undergoing millisecond conformational fluctuations. Under all three conditions, these fluctuations gave nonexponential correlations on 1- to 100-ms time scale. A component of the correlation decay that was sensitive to the concentration of urea corresponded to that measured by bulk relaxation kinetics. Thetrajectories provided effective intramolecular diffusion coefficients as a function of the end-to-end distances for the folded and unfolded states. Single-molecule folding studies provide information concerning the distributions of conformational states in the folded, unfolded, and dynamically interconverting states.Author manuscript. Published in final edited form as: Proc Natl Acad Sci U S A. 2000 November 21; 97(24): 13021-13026.The final published version of this article is located at: http://www.pnas.org/cgi/reprint/97/24/13021NIH GM54616; to William F. DeGradoNIH GM12592; to Robin M. HochstrasserNIH GM48130; to William F. Degrado and Robin M. HochstrasserThis work was supported by GM54616 (to W.F.D.), GM12592 (to R.M.H.) and GM48130 (to W.F.D. and R.M.H.) with instrumentation developed under RR01348. D.S.T. was supported by National Institutes of Health Grant NRSA F32-GM18589.Also available in PubMed Central. PMCID:PMC2717
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