Bradford Scholars is the University of Bradford online research archive. Access is free to anyone interested in research being conducted at Bradford. In the repository you will find a range of materials from journal articles and conference papers to research reports and theses.
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Bond Performance between Corroded Steel and Recycled Aggregate Concrete Incorporating Nano SilicaThe current research project mainly aims to investigate the corrosion resistance and bond performance of steel reinforced recycled aggregate concrete incorporating nano-silica under both normal and corrosive environmental conditions. The experimental part includes testing of 180 pull-out specimens prepared from 12 different mixtures. The main parameters studied were the amount of recycled aggregate (RCA) (i.e. 0%, 25%, 50% and 100%), nano silica (1.5% and 3%), steel embedment length as well as steel bar diameter (12 and 20mm). Different levels of corrosion were electrochemically induced by applying impressed voltage technique for 2, 5, 10 and 15 days. The experimental observations mainly focused on the corrosion level in addition to the ultimate bond, failure modes and slips occurred. Experimental results showed that the bond performance between un-corroded steel and recycled aggregate concrete slightly reduced, while a significant degradation was observed after being exposed to corrosive conditions, in comparison to normal concrete. On the other hand, the use of nano silica (NS) showed a reasonable bond enhancement with both normal and RCA concretes under normal conditions. However, much better influence in terms of bond and corrosion resistance was observed under advancing levels of corrosion exposure, reflecting the improvement in corrosion resistance. Therefore, NS was superbly effective in recovering the poor performance in bond for RCA concretes. More efficiency was reported with RCA concretes compared to the conventional concrete. The bond resistance slightly with a small amount of corrosion (almost 2% weight loss), then a significant bond degradation occurs with further corrosion. The influence of specific surface area and amount of nano silica on the performance of concrete with different water/binder (w/b) ratios has been also studied, using 63 different mixtures produced with three different types of colloidal NS having various surface areas and particle sizes. The results showed that the performance of concrete is heavily influenced by changing the surface area of nano silica. Amongst the three used types of nano silica, NS with SSA of 250 m2 /g achieved the highest enhancement rate in terms of compressive strength, water absorption and microstructure analysis, followed by NS with SSA of 500 m2/g, whilst NS with SSA of 51.4 m2 /g was less advantageous for all mixtures. The optimum nano silica ratio in concrete is affected by its particle size as well as water to binder ratio. The feasibility of the impact-echo method for identifying the corrosion was evaluated and compared to the corrosion obtained by mass loss method. The results showed that the impact-echo testing can be effectively used to qualitatively detect the damage caused by corrosion in reinforced concrete structures. A significant difference in the dominant frequencies response was observed after exposure to the high and moderate levels of corrosion, whilst no clear trend was observed at the initial stage of corrosion. Artificial neural network models were also developed to predict bond strength for corroded/uncorroded steel bars in concrete using the main influencing parameters (i.e., concrete strength, concrete cover, bar diameter, embedment length and corrosion rate). The developed models were able to predict the bond strength with a high level of accuracy, which was confirmed by conducting a parametric study.
The Construction of Care in Computed Tomography. Exploring Care from the Perspective of Patients and RadiographersPurpose: Patient centred care and the ‘patient voice’ are core components of UK healthcare policy and practice guidance. This study explores how care is perceived and experienced within the high technology environment of CT. Methods and Materials: A two-phase approach of Critical Discourse Analysis (CDA) and adapted Grounded Theory (GT) methodology using semi structured interviews, was used to obtain primary data from CT radiographers and patients. Recruitment and data collection were performed at a 1200 bed teaching hospital over a 6-month period. Results: The radiographer patient relationship and the radiographer’s role in providing care within CT are complex and multifaceted. Both patients and radiographer’s perceive CT imaging to be an integral part of the overall patient care and treatment pathway. As such, the act of being imaged is perceived as a care process and while image acquisition is recognised as a task orientated and technical process, the human element of providing care is cognitive, dynamic and responsive to individual need. Importantly, patient confidence in the care received was influenced by the radiographer’s ability to build a trusting relationship and display technical competence and this in turn facilitated active compliance resulting in a technically accurate examination. Despite previous literature suggesting that the technical environment created a barrier to patient care, patients within this study confirmed that radiographers provide care commensurate to the nursing ideals represented by the 6C’s (Care; Compassion; Competence; Communication; Courage; Commitment). Conclusions: A co-constructed model of care encompassing both technical components and patient-centeredness has been identified. This model promotes a new vision of patient centred care based on care perceptions within the high technology environment of CT.
Investigation of Integrated Decoupling Methods for MIMO Antenna Systems. Design, Modelling and Implementation of MIMO Antenna Systems for Different Spectrum Applications with High Port-to-Port Isolation Using Different Decoupling TechniquesMultiple-Input-Multiple-Output (MIMO) antenna technology refers to an antenna with multiple radiators at both transmitter and receiver ends. It is designed to increase the data rate in wireless communication systems by achieving multiple channels occupying the same bandwidth in a multipath environment. The main drawback associated with this technology is the coupling between the radiating elements. A MIMO antenna system merely acts as an antenna array if the coupling between the radiating elements is high. For this reason, strong decoupling between the radiating elements should be achieved, in order to utilize the benefits of MIMO technology. The main objectives of this thesis are to investigate and implement several printed MIMO antenna geometries with integrated decoupling approaches for WLAN, WiMAX, and 5G applications. The characteristics of MIMO antenna performance have been reported in terms of scattering parameters, envelope correlation coefficient (ECC), total active reflection coefficient (TARC), channel capacity loss (CCL), diversity gain (DG), antenna efficiency, antenna peak gain and antenna radiation patterns. Three new 2×2 MIMO array antennas are proposed, covering dual and multiple spectrum bandwidths for WLAN (2.4/5.2/5.8 GHz) and WiMAX (3.5 GHz) applications. These designs employ a combination of DGS and neutralization line methods to reduce the coupling caused by the surface current in the ground plane and between the radiating antenna elements. The minimum achieved isolation between the MIMO antennas is found to be better than 15 dB and in some bands exceeds 30 dB. The matching impedance is improved and the correlation coefficient values achieved for all three antennas are very low. In addition, the diversity gains over all spectrum bands are very close to the ideal value (DG = 10 dB). The forth proposed MIMO antenna is a compact dual-band MIMO antenna operating at WLAN bands (2.4/5.2/5.8 GHz). The antenna structure consists of two concentric double square rings radiating elements printed symmetrically. A new method is applied which combines the defected ground structure (DGS) decoupling method with five parasitic elements to reduce the coupling between the radiating antennas in the two required bands. A metamaterial-based isolation enhancement structure is investigated in the fifth proposed MIMO antenna design. This MIMO antenna consists of two dual-band arc-shaped radiating elements working in WLAN and Sub-6 GHz 5th generation (5G) bands. The antenna placement and orientation decoupling method is applied to improve the isolation in the second band while four split-ring resonators (SRRs) are added between the radiating elements to enhance the isolation in the first band. All the designs presented in this thesis have been fabricated and measured, with the simulated and measured results agreeing well in most cases.
Gate-opening criterion for generating dam-break flow in non-rectangular wet bed channelsA sudden dam failure is usually simulated by the rapid removal of a gate in laboratory tests and numerical simulations. The gate-opening time is often determined according to the Lauber and Hager instantaneous collapse criterion (referred to as Lauber-Hager criterion) established for a rectangular open channel with a dry bed. However, this criterion is not suitable for non-rectangular channels or initial wet-bed conditions. In this study, the effect of the gate-opening time on the wave evolution is investigated by using the large eddy simulation (LES) model. The instantaneous dam break, namely the dam break without a gate, is simulated for comparison. A gate-opening criterion for generating dam-break flow in non-rectangular wet bed channel is proposed in this study, which can be used as an extension of the Lauber-Hager criterion and provides a more comprehensive and reasonable estimate of the gate opening time.
Element failure probability of soil slope under consideration of random groundwater levelThe instability of soil slopes is directly related to both the shear parameters of the soil material and the groundwater, which usually causes some uncertainty. In this study, a novel method, the element failure probability method (EFP), is proposed to analyse the failure of soil slopes. Based on the upper bound theory, finite element discretization, and the stochastic programming theory, an upper bound stochastic programming model is established by simultaneously considering the randomness of shear parameters and groundwater level to analyse the reliability of slopes. The model is then solved by using the Monte-Carlo method based on the random shear parameters and groundwater levels. Finally, a formula is derived for the element failure probability (EFP) based on the safety factors and velocity fields of the upper bound method. The probability of a slope failure can be calculated by using the safety factor, and the distribution of failure regions in space can be determined by using the location information of the element. The proposed method is validated by using a classic example. This study has theoretical value for further research attempting to advance the application of plastic limit analysis to analyse slope reliability.