318 research outputs found
Numerical simulation of ram extrusion in short-fiber-reinforced fresh cementitious composites
This is the author's accepted manuscript. The final published article is available from the link below. First published in JoMMS in 4(10), 2009, published by Mathematical Sciences Publishers.A series of ram extrusion tests was carried out on a short-fiber-reinforced, semisolid, fresh cementitious composite. An elastoviscoplastic constitutive model is proposed for the extrudable fresh cementitious composite. It features the associative flow rule, a nonlinear strain rate-hardening law, and the von Mises yield criterion. The model is then implemented in ANSYS/LS-DYNA explicit finite element code.
Various ram extrusion processes of the fresh cementitious composite were simulated. It has been found that the extrusion load versus imposed displacement predictions agree well with the experimental results. The fresh paste flow, through the die entry and the die-land, is then interpreted in light of the evolution of the deformation and distribution of state variables, mainly based on numerical results and the ram extrusion mechanism.
The effects of extrusion ratio and extrusion velocity on extrusion load are also investigated, based on the mechanical properties of the fresh cementitious composite. The study indicates that the numerical procedure established, together with the constitutive model proposed, is applicable for describing ram extrusion of short-fiber-reinforced fresh cementitious composites, which might provide a numerical rheometric tool from which ram extrusion of elastoviscoplastic paste-like materials can be examined and quantified.Hong Kong Research Grant Council and China Ministry of Science and Technology
Current View on Hematopoiesis and Beyond
Hematopoietic stem cells (HSCs) have the ability to self-renew and give rise to all lineages of blood cells while remain the capacity of regenerative in hematopoiesis. As the only stem cell type in routine clinical use, HSCs can be isolated from bone marrow, peripheral blood and umbilical cord blood. Stem cells transplantation is mainly used in HSCs while the trans-differentiation ability broadens the research of HSCs in regenerative medicine. Here, we focus on the current view on hematopoiesis and beyond and summarize the clinical application and the regulation of the fate of HSCs. We intend to outline recent advances in the human HSCs research area and review the characteristic of HSCs from definition through development to their clinical applications and future prospect
Extracellular Matrix Enhances Therapeutic Effects of Stem Cells in Regenerative Medicine
Stem cell therapy is a promising option for regenerative of injured or diseased tissues. However, the extremely low survival and engraftment of transplanted cells and the obviously inadequate recruitment and activation of the endogenous resident stem cells are the major challenges for stem cell therapy. Fortunately, recent progresses show that extracellular matrix (ECM) could not only act as a spatial and mechanical scaffold to enhance cell viability but also provide a supportive niche for engraftment or accelerating stem cell differentiation. These findings provide a new approach for increasing the efficiency of stem cell therapy and may lead to substantial changes in cell administration. In order to take a giant stride forward in stem cell therapy, we need to know much more about how the ECM affects cell behaviours. In this chapter, we provide an overview of the influence of ECM on regulating stem cell maintenance and differentiation. Moreover, the enhancement of supportive microenvironment function of natural or synthetic ECMs in stem cell therapy is discussed
Manufacturing cement-based materials and building products via extrusion: From laboratory to factory
Manufacturing is critical to the economies of the UK and many other countries in the rest of the world. However, manufacturing of cement-based materials and building products predominantly remains based on old batch processing such as casting and pressing technologies and this may limit the applications and performance of the materials and products formed. In this paper, research is reported on transforming manufacturing of precast cement-based materials and building products from in batches to continuous processes via extrusion. Techniques used for producing plastic products are transferred into manufacturing cement-based building products like flat and corrugated sheet tiles, down pipes, door/window frames, door panels, solid wall/facade panels, honeycomb wall/facade panels etc. at laboratory and factory scales. In combination with sustainable cementitious materials with low carbon and low energy as matrix, this enables sustainable building products with key characteristics required by the 21st century can be manufactured via extrusion. The cement-based building products extrusion technique has been successfully transferred to industry. For instance, fibre reinforced cement-based partition wall panels, with a honeycomb cross section as large as 600 mm wide and 90 mm high, have been produced by a continuous extrusion process in a precast concrete products factory in Hangzhou, China.European Commission Seventh Framework Programme, (grant agreement no. 262954) and from the Hong Kong Research Grants Council through grants 6091/00E, 6226/01E, 6273/03E and 6167/06
Design of Magnesium Phosphate Cement Based Composite for High Performance Bipolar Plate of Fuel Cells
In this work, we report a comprehensive study on a magnesium phosphate cement (MPC) based composite as the construction material for high performance bipolar plates of fuel cells. MPC with partial replacement of fly ash was employed as the binding matrix. Some carbon-based materials, such as graphite, carbon black, carbon fiber, and multi-walled carbon nanotubes were used to construct the conductive phase. A simple hot-press process was applied to produce the composite. The formula and the structure of the composite was modified and adjusted to optimize the properties of the composite to meet the US DOE 2015 technical targets, including the introducing of a reinforcement support. Finally, all the technical targets such as electrical conductivity (\u3e100 S cm-1), the flexural strength (\u3e25 MPa), the corrosion resistance ( \u3c 1 ÎŒA cm-2), and gas permeability ( \u3c 10-5 cm3 (s cm2)-1) were achieved as well as low cost ( \u3c 5 $ per kW). The optimized formula and the detailed procedures to fabricate the MPC based composite were concluded
Evaluating the robustness of selfâconsolidating concrete: an approach to the mix design procedure
This paper aimed to develop a method to analyze and rank selfâconsolidating concrete (SCC) according to its robustness, considering isolated and simultaneous variations in its main components, like water (±6%) and cement content (ÎC±), in three matrices with binder to aggregate ratio (rich, intermediate and poor). In the experimental campaign, only water variations (±6%) were considered, and the cement content variations were considered in the analytical method. The method regarded the behavior of SCC in fresh and hardened states and turned out to be potentially useful to the academic community and the industry. The simple additive weighting method was used for that reason, which is probably the most adopted among methods for decisions with multiple variables due to its simplicity. Among the families studied, the poor mixture presented the lowest robustness with variation in water content due to the higher initial w/c ratio. However, for the condition ÎC±, the poor mixture achieved the secondâbest robustness index. The rich mixture behaved differently as it was ranked second for ±6% of water and the worst for ÎC± due to slumpâflow and segregation results. The intermediate matrix presented the highest robustness in both conditions analyzed, water (±6%), and cement content (ÎC±)
STW-MD: A Novel Spatio-Temporal Weighting and Multi-Step Decision Tree Method for Considering Spatial Heterogeneity in Brain Gene Expression Data
Motivation: Gene expression during brain development or abnormal development
is a biological process that is highly dynamic in spatio and temporal. Due to
the lack of comprehensive integration of spatial and temporal dimensions of
brain gene expression data, previous studies have mainly focused on individual
brain regions or a certain developmental stage. Our motivation is to address
this gap by incorporating spatio-temporal information to gain a more complete
understanding of the mechanisms underlying brain development or disorders
associated with abnormal brain development, such as Alzheimer's disease (AD),
and to identify potential determinants of response.
Results: In this study, we propose a novel two-step framework based on
spatial-temporal information weighting and multi-step decision trees. This
framework can effectively exploit the spatial similarity and temporal
dependence between different stages and different brain regions, and facilitate
differential gene analysis in brain regions with high heterogeneity. We focus
on two datasets: the AD dataset, which includes gene expression data from
early, middle, and late stages, and the brain development dataset, spanning
fetal development to adulthood. Our findings highlight the advantages of the
proposed framework in discovering gene classes and elucidating their impact on
brain development and AD progression across diverse brain regions and stages.
These findings align with existing studies and provide insights into the
processes of normal and abnormal brain development.
Availability: The code of STW-MD is available at
https://github.com/tsnm1/STW-MD.Comment: 11 pages, 6 figure
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