Search

Pulmonary atresia with ventricular septal defect and major aortopulmonary collateral arteries (MAPCAs) is a relatively rare and complex form of congenital heart disease. Unifocalization of MAPCAs has been advocated by some groups for the treatment of this condition. The purpose of this study was to assess the midterm fate of unifocalized MAPCAs in a cohort of patients with retroesophageal MAPCAs. This was a retrospective review of 37 patients who underwent a unifocalization procedure. All patients in this study had 1 or more retroesophageal MAPCAs, and detailed mapping of the MAPCAs was made based on a combination of the cardiac catheterization and surgical findings. The 37 patients had a total of 166 MAPCAs, or 4.5 MAPCAs per patient. One hundred twenty-nine (78%) MAPCAs were unifocalized, whereas 37 (22%) were ligated because they were dual supply. Median follow-up was 69 months. At follow-up cardiac catheterization, evaluation of the 129 unifocalized MAPCAs demonstrated that 123 (95%) had antegrade flow, whereas 6 were occluded. For the 123 MAPCAs with antegrade flow, 97 (80%) were widely patent, whereas 26 were stenotic. Thirteen of the 37 patients have subsequently undergone reintervention on MAPCAs that were determined to be stenotic following unifocalization. Seven of these patients had mild disease and had complete resolution with balloon (n = 5) or surgical revision (n = 2). Six patients with moderate or severe disease underwent surgical revision with confirmed resolution in 4 of 6. The data demonstrate that the majority of unifocalized MAPCAs remain widely patent following unifocalization. However, one-quarter of unifocalized MAPCAs develop stenoses or occlusion. These results suggest the fate for most unifocalized MAPCAs is favorable but highlight the need for close vigilance. Midterm fate of unifocalized MAPCAs. Ninety-five percent of unifocalized MAPCAs had antegrade flow at follow-up evaluation. Of these, 80% were widely patent, whereas 20% had some degree of stenosis. Reinterventions on MAPCAs with stenoses were 100% successful. [Display omitted] [ABSTRACT FROM AUTHOR]

Pulmonary artery stents are widely deployed in patients with stenoses in the branch pulmonary arteries. However, stents do not address more peripheral sites of stenosis and invariably develop in-stent restenosis. The purpose of this study was to review our experience with pulmonary artery reconstruction after failed pulmonary artery stents. This was a retrospective study of 56 patients who underwent pulmonary artery reconstruction after failed pulmonary artery stents. These patients had undergone a median of 2 (range, 0-5) previous surgical procedures and 2 (range, 1-4) pulmonary artery stents. The median age at stent surgery was 5 (range, 0.3-23.6) years. The majority of stents (79%) were completely removed and patch augmented. The minority of stents (21%) were felt to be unremovable and thus were split longitudinally and reconstructed using a pulmonary artery homograft. There was 1 (1.8%) operative mortality. The mean pulmonary artery-to-aortic pressure ratio decreased from a preoperative value of 0.91 ± 0.21 to a postoperative value of 0.31 ± 0.07 (P <.001). The median hospital length of stay was 10 days. The median duration of follow-up was 1.8 years. There has been no midterm mortality. Six patients have undergone balloon dilation postoperatively for residual pulmonary artery stenosis. Pulmonary artery reconstruction resulted in a significant decrease in pulmonary artery-to-aortic pressure ratios. The subsequent need for reintervention on the pulmonary arteries has been relatively low (11% to date). These results suggest that patients with pulmonary artery stents can be successfully treated with surgical reconstruction. [ABSTRACT FROM AUTHOR]

The use of plastic pipes within water distribution systems is viewed as a highly effective means to reduce our unsustainable levels of leakage. However, attention is required to understand the complex behaviour of leaks that do occur in this viscoelastic pipeline material. Results from a novel experimental investigation into the dynamic leakage behaviour of longitudinal slits in MDPE pipe are presented in this paper, reporting on the relationship between pressure head, leak flow-rate, leak area and material strain. The results show the significant time dependent leak behaviour, also highlighting the correlation between measured strain and area. [ABSTRACT FROM AUTHOR]

Abstract: Water distribution systems typically contain large numbers of pipes joining sources of supply to consumers; in addition they include a number of ancillary devices such as pumping stations, valves, storage reservoirs and surge suppression devices. These ancillaries and potential flow control points create systems with complex, varied dynamic conditions. Presented here are the results of a field monitoring case study that evidences propagation of transients within complex distribution system. The outcomes test the common assumption that damping and dissipation of transient occurs due to system complexity while travelling through a network. Ultimately such work improves understanding of dynamic pressure behaviors in complex networks which may help assess vulnerability to transients. [Copyright &y& Elsevier]

Abstract: It has been hypothesised that negative transient pressures may result in ingress of contaminated groundwater through leakage orifices. This paper presents results of contaminant ingress tests from a novel laboratory facility at the University of Sheffield. An engineered leak surrounded by porous media was subjected to a pressure transient resulting from the rapid closure of an upstream valve. It has been shown that a pollutant originating externally was drawn in and transported to the end of the pipe loop. Thus this paper presents the first fully representative results of contaminant ingress. [Copyright &y& Elsevier]

Abstract: A method of characteristics-based computational model of a straight reservoir/pipe/valve system was created as a very simple rep- resentation of a small residential water distribution system. The model was used to assess transient modelling and analysis errors which occur due to demand aggregation and uncertainty. The effect of aggregating demand from the small network of residences was investigated and found to be most significant when the number and distribution of the demands was randomly varied. The inclusion of service connection pipes was also investigated; in this case leading to a higher peak head and a phase-shift in the head oscillations, which increased over time; this demonstrates the importance of modelling complete systems with high levels of accuracy. [Copyright &y& Elsevier]

Abstract: An active control strategy for vibration control of structures using ATMDs is proposed. The control strategy incorporates the minimax criteria for shaping the frequency response function (FRF) of the structure–TMD system and the bang–bang control law with a control force applied to a TMD. In the control scheme, the control law using bang–bang control is obtained by minimising the time derivative of a Lyapunov function of the open-loop structural system [Wu Z, Soong TT. Modified bang–bang control law for structural control implementation. Journal of Engineering Mechanics 1996;122(8):771–7] and is used to control the ATMD. In addition, the corresponding FRF for the coupled structure–ATMD system is reshaped by changing the tuning parameter of the TMD (when there is no control force applied), such that peaks in the FRF of the structure are equal in magnitude. When the active control is ineffective or is turned off, the damper system acts as a passive TMD. The proposed strategy is compared to another conventional control strategy, the Linear Quadratic Controller (LQC) applied to the structure–TMD system and the advantages are highlighted. The system is examined under harmonic and random excitations. [Copyright &y& Elsevier]

Abstract: The result of experimental and numerical study that was undertaken to determine the performance characteristics of viscous flow turbines is presented. It is anticipated that these devices may find use in applications such as small power sources for electronic appliances and micro-combined heat and power applications. In the numerical work that was carried out to broaden the experimental results, commercial CFD solver Fluent 6.2 was used while accompanying software, Gambit 3.2, was used for performing the necessary pre-processing. The results of the experimental study indicate that the adiabatic efficiency of these machines is around 25%. The main reasons for the low efficiency have been identified to be, parasitic losses in the bearing, viscous losses in the end walls, and other dissipative losses in the plenum chamber that also significantly contribute to the low efficiencies of these devices. If these parasitic losses can be minimised the turbine could potentially operate with an adiabatic expansion efficiency close to the theoretical limit of around 40%. [Copyright &y& Elsevier]

Abstract: Mars is a compelling astrobiological target, and a human mission would provide an opportunity to collect immense amounts of scientific data. Exploration alone, however, cannot justify the increased risk. Instead, three factors drive a human mission: economics, education, and exploration. A human mission has a unique potential to inspire the next generation of young people to enter critically needed science and engineering disciplines. A mission is economically feasible, and the research and development program put in place for a human mission would propel growth in related high-technology industries. The main hurdles are human physiological responses to 1–2 years of radiation and microgravity exposure. However, enabling technologies are sufficiently mature in these areas that they can be developed within a few decade timescale. Hence, the decision of whether or not to undertake a human mission to Mars is a political decision, and thus, educational and economic benefits are the crucial factors. [Copyright &y& Elsevier]