Infrastructure Engineering - Research Publications
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Measuring physical activity during pregnancy
BACKGROUND: Currently, little is known about physical activity patterns in pregnancy with prior estimates predominantly based on subjective assessment measures that are prone to error. Given the increasing obesity rates and the importance of physical activity in pregnancy, we evaluated the relationship and agreement between subjective and objective physical activity assessment tools to inform researchers and clinicians on optimal assessment of physical activity in pregnancy. METHODS: 48 pregnant women between 26-28 weeks gestation were recruited. The Yamax pedometer and Actigraph accelerometer were worn for 5-7 days under free living conditions and thereafter the International Physical Activity Questionnaire (IPAQ) was completed. IPAQ and pedometer estimates of activity were compared to the more robust and accurate accelerometer data. RESULTS: Of 48 women recruited, 30 women completed the study (mean age: 33.6 ± 4.7 years; mean BMI: 31.2 ± 5.1 kg/m(2)) and 18 were excluded (failure to wear [n = 8] and incomplete data [n = 10]). The accelerometer and pedometer correlated significantly on estimation of daily steps (ρ = 0.69, p < 0.01) and had good absolute agreement with low systematic error (mean difference: 505 ± 1498 steps/day). Accelerometer and IPAQ estimates of total, light and moderate Metabolic Equivalent minutes/day (MET min(-1) day(-1)) were not significantly correlated and there was poor absolute agreement. Relative to the accelerometer, the IPAQ under predicted daily total METs (105.76 ± 259.13 min(-1) day(-1)) and light METs (255.55 ± 128.41 min(-1) day(-1)) and over predicted moderate METs (-112.25 ± 166.41 min(-1) day(-1)). CONCLUSION: Compared with the accelerometer, the pedometer appears to provide a reliable estimate of physical activity in pregnancy, whereas the subjective IPAQ measure performed less accurately in this setting. Future research measuring activity in pregnancy should optimally encompass objective measures of physical activity. TRIAL REGISTRATION: Australian New Zealand Clinical Trial Registry Number: ACTRN12608000233325. Registered 7/5/2008.
Using Crowdsourced Trajectories for Automated OSM Data Entry Approach
The concept of crowdsourcing is nowadays extensively used to refer to the collection of data and the generation of information by large groups of users/contributors. OpenStreetMap (OSM) is a very successful example of a crowd-sourced geospatial data project. Unfortunately, it is often the case that OSM contributor inputs (including geometry and attribute data inserts, deletions and updates) have been found to be inaccurate, incomplete, inconsistent or vague. This is due to several reasons which include: (1) many contributors with little experience or training in mapping and Geographic Information Systems (GIS); (2) not enough contributors familiar with the areas being mapped; (3) contributors having different interpretations of the attributes (tags) for specific features; (4) different levels of enthusiasm between mappers resulting in different number of tags for similar features and (5) the user-friendliness of the online user-interface where the underlying map can be viewed and edited. This paper suggests an automatic mechanism, which uses raw spatial data (trajectories of movements contributed by contributors to OSM) to minimise the uncertainty and impact of the above-mentioned issues. This approach takes the raw trajectory datasets as input and analyses them using data mining techniques. In addition, we extract some patterns and rules about the geometry and attributes of the recognised features for the purpose of insertion or editing of features in the OSM database. The underlying idea is that certain characteristics of user trajectories are directly linked to the geometry and the attributes of geographic features. Using these rules successfully results in the generation of new features with higher spatial quality which are subsequently automatically inserted into the OSM database.
Experimental and numerical investigation of mechanical properties on novel modular connections with superimposed beams
The use of lightweight modular construction becomes increasing popular all around the world today. The benefits of off-site prefabrication include consistent quality, shorter construction time, eco-friendly function which are being realized in both residential and commercial building construction. The connection of modular building plays a critical role in ensuring the stability, robustness and seismic resistance of buildings. However, conventional connection design for modular buildings (e.g. blind flange gaskets, on-site welding or open large access holes) ignores the potentiation of composite effect on the stability of the modular buildings. This study presents a novel modular connection configuration (i.e. Type A modular connection) for connecting modular units to columns in both vertical and horizontal directions by an in-build component. The proposed connection can bring the floor beam of upper units and ceiling beam of bottom units into an integrated system with the advantages of easy installation without on-site welding. The mechanical behavior of modular connection was firstly experimentally investigated. An experimentally validated numerical model was then developed to further investigate the mechanical and deformation behavior of the joint. The results show that the proposed novel connection could allow the twins beam to rotate identically. In addition, they demonstrate that the twin beams’ flexural stiffness ratio and gap between in-build component and column are two critical factors that govern the continuity of the overall joint.
Impermeability and interfacial bonding strength of TiO2-graphene modified epoxy resin coated OPC concrete
In this study, a novel TiO2-graphene modified epoxy resin employed as coatings for ordinary Portland cement (OPC) concrete was for the first time fabricated with three different dosages. It was found that the TiO2-graphene could be dispersed homogeneously in the epoxy resin matrix without reducing interfacial bonding strengths between coatings and OPC concrete substrates. Moreover, with the aid of certain dosages of TiO2-graphene nanofiller (0.3 % and 0.5 %), both the impermeability towards water and chloride of the OPC concrete reflected by capillary sorptivity and chloride penetration respectively was greatly improved compared to the pure epoxy resin coated concrete or concrete substrate without coatings. In contrast, 1.0 % dosage led to higher water and chloride permeability than the concrete coated by pure epoxy resin coating. Thus, within the range of considered dosages, it seems that 0.5 % dosage achieved the best coating performance evidenced by the lowest capillary sorptivity and chloride permeability, overcoming the disadvantages of 0.3 % (not enough) and 1.0 % (noticeable agglomerations). In addition, TiO2-graphene addition seems to have no significant impact on the gas permeability of the epoxy resin coated OPC concrete. Overall, the cost-effective fabrication method and improved impermeability of OPC concrete coated by the epoxy resin which is enhanced by the TiO2-graphene nano-composite create more opportunities for epoxy resin being utilised as surface coatings for cementitious binders.
Preparation of TiO2/epoxy resin composite and its effect on mechanical and bonding properties of OPC mortars
Bisphenol A-type epoxy resin reinforced by TiO2 with different dosages (0, 1%, 3%, 5%) was for the first time used as a polymeric admixture to prepare ordinary Portland cement (OPC) mortars in this study. Tensile strength of the TiO2/epoxy resin composite, and flowability, compressive strength and flexural strength as well as the bonding strength of OPC mortars were measured. Scanning electron microscopy (SEM) was also carried out to observe the interfacial transition zone (ITZ) between sand and OPC paste, and the bonding interfacial transition zone (BITZ) between OPC mortar (either modified by the epoxy resin or not) and a substrate material. Results showed the tensile strength of the TiO2/epoxy resin composite was enhanced to a greater extent with a higher content of TiO2 nanoparticles. A lower flowability of mortar samples when modified by the epoxy resin was observed compared to the pure OPC counterpart. The compressive, flexural strength, flexural toughness indicated by the flexural-to-compressive strength ratio and bonding strengths of TiO2/epoxy resin-modified mortars quantified by the interface tensile strength were noted to be the highest for mortars modified by the epoxy resin containing 5% TiO2. For interface tensile strength, it was found that the increment was 7.3% and 14.6% for the mortar specimen modified by the epoxy resin with 5% TiO2 compared to the mortar modified by the same amount of epoxy resin but without TiO2 and the control with no epoxy resin respectively. SEM results showed that both ITZ and BITZ were denser when epoxy resin was added into the OPC mortar systems, leading to an improved flexural toughness and bonding strength. Several enhancing mechanisms are proposed including epoxy resin bridging effect, pore-filling effect, claw-like adhesion and delayed water loss and rigid TiO2 particles with good adhesion towards epoxy resin polymer molecules.
Study of soil expansion characteristics in rainfall-induced red-bed shallow landslides: Microscopic and macroscopic perspectives
(Public Library of Science (PLoS), 2021)
The main cause of rainfall-induced red-bed shallow landslides is the tendency of red-bed weathered soil to expand when it meets water. However, studies on the expansion mechanism of expansive soil have not considered the effects of hydration and particle orientation. In this study, the hydration force of soil was determined according to the electric double-layer theory, the particle direction of soil was determined by analyzing images of soil obtained by scanning electron microscopy, and, finally, a microscopic model of the electrical double layer of red-bed weathered expansive soil was established in which the hydration force and soil-particle orientation were taken into account. The results showed that the expansion of red-bed weathered expansive soil is the result of hydration forces and repulsive forces in the electric double layer. The grain orientation of the soil strongly influenced the microscopic model. The unloading expansion rate of red-bed weathered expansive soil decreased with an increase in cation concentration and a decrease in pH value. It increased with an increase in the hydration cation radius. These experiments indicate the reliability of the microscopic model and provide a theoretical basis for the prevention and control of rainfall-induced red-bed shallow landslides.
The investigation of bone fracture healing under intramembranous and endochondral ossification.
(Elsevier BV, 2021-06)
After trauma, fractured bone starts healing directly through bone union or indirectly through callus formation process. Intramembranous and endochondral ossification are two commonly known mechanisms of indirect healing. The present study investigated the bone fracture healing under intramembranous and endochondral ossification by developing theoretical models in conjunction with performing a series of animal experiments. Using experimentally determined mean bone densities in sheep tibia stabilized by the Locking Compression Plate (LCP) fixation system, the research outcomes showed that intramembranous and endochondral ossification can be described by Hill Function with two unique sets of function parameters in mechanical stimuli mediated fracture healing. Two different thresholds exist within the range of mechanical simulation index which could trigger significant intramembranous and endochondral ossification, with a relatively higher bone formation rate of endochondral ossification than that of intramembranous ossification. Furthermore, the increase of flexibility of the LCP system and the use of titanium LCP could potentially promote uniform bone formation across the fracture gap, ultimately better healing outcomes.
Dataset on effects of learning curve models on clean energy technology cost developments
This dataset includes input data to estimate learning-by-doing (LbD) and learning-by-researching (LbR) rates for onshore wind and solar PV in the United States. Using different learning curve approaches the simulated technology cost developments are also presented. Coefficient of determination (R square) and Root Mean Square Error (RMSE) were applied for quantification of the agreement between simulated and observed technology costs.
Toward identifying the critical mass in spatial two-sided markets
(Sage Publications, 2020-11-01)
Unlike their nonspatial counterparts, spatial multi-sided platforms are matchmaking platforms with an additional layer of complexity: their customers expect to meet in space, not only virtually. This additional challenge will be studied in this paper in the context of a two-sided ride-sharing platform, which serves drivers and passengers. As with any two-sided platform, there is an interdependence between both groups of customers: More drivers are more attractive for passengers, and vice versa. This interdependence creates the old chicken-and-egg problem, only that here drivers and passengers need to be matched not for a virtual transaction, but by their ability to meet physically and travel jointly. We argue, and illustrate by simulations, that in spatial multi-sided markets there is not a single critical mass frontier that needs to be reached in order to make the system self-sustained (as in nonspatial markets), and that this frontier is varying from one location to the next, depending on the density and distribution of the demand and supply over space and time. Identification of the critical mass frontier will allow for better evaluation of implementation policies and regulations.
Wayfinding and navigation research for sustainable transport
(University of Maine, 2020)
Spatial information science contributes to the foundations of sustainable transport development. This article focuses especially on the role that research on human wayfinding and navigation plays when it comes to designing digital connectivity and autonomy in urban transport.
Investigation of role of cartilage surface polymer brush border in lubrication of biological joints
(Springer Science and Business Media LLC, 2021)
Although experimental evidence has suggested that the polymer brush border (PBB) on the cartilage surface is important in regulating fluid permeability in the contact gap, the current theoretical understanding of joint lubrication is still limited. To address this research gap, a multiscale cartilage contact model that includes PBB, in particular its effect on the fluid permeability of the contact gap, is developed in this study. Microscale modeling is employed to estimate the permeability of the contact gap. This permeability is classified into two categories: For a gap size > 1 µm, the flow resistance is assumed to be dominated by the cartilage roughness; for gap size < 1 µm, flow resistance is assumed to be dominated by the surface polymers extending beyond the collagen network of the articular cartilage. For gap sizes of less than 1 µm, the gap permeability decreases exponentially with increasing aggrecan concentration, whereas the aggrecan concentration varies inversely with the gap size. Subsequently, the gap permeability is employed in a macroscale cartilage contact model, in which both the contact gap space and articular cartilage are modeled as two interacting poroelastic systems. The fluid exchange between these two media is achieved by imposing pressure and normal flux continuity boundary conditions. The model results suggest that PBB can substantially enhance cartilage lubrication by increasing the gap fluid load support (e.g., by 26 times after a 20-min indentation compared with the test model without a PBB). Additionally, the fluid flow resistance of PBB sustains the cartilage interstitial fluid pressure for a relatively long period, and hence reduces the vertical deformation of the tissue. Furthermore, it can be inferred that a reduction in the PBB thickness impairs cartilage lubrication ability.
Fast Checking of Drift Demand in Multi-Storey Buildings with Asymmetry
(MDPI AG, 2020)
Buildings possessing an asymmetrical arrangement of structural elements are torsionally unbalanced and can be vulnerable in a seismic event. Building codes of practices typically recommend the use of three-dimensional dynamic analysis to determine the seismic demands of a multi-storey building. Whilst most design practices are well equipped with commercial software for undertaking such analyses, designers often find it difficult to verify results. Much of the published technical articles present findings for buildings based on an idealised single-storey model. As a result of challenges in dealing with real multi-storey buildings, there has been very limited uptake of research findings in design practices. This article presents a three-tiered approach of estimating the displacement behaviour of the building in term of 3D/2D displacement ratio. The estimate can be used for verifying results reported from a computer package conveniently. The quick method provides predictions of the 3D/2D ratio and only requires the gross plan dimensions of the building to be known. The refined method requires knowledge of the torsional stiffness properties to be known, whereas the detailed method requires the eccentricity properties to be known as well. The proposed methodology is robust and reliable, as is demonstrated by case studies undertaken on six real multi-storey buildings.