In-depth analyses of post-corrosion mechanical properties and architecture of open cell iron foams with hollow struts as absorbable bone scaffolds were carried out. Variations in the architectural ...features of the foams after 14 days of immersion in a Hanks’ solution were investigated using micro-computed tomography and scanning electron microscope images. Finite element Kelvin foam model was developed, and the numerical modeling and experimental results were compared against each other. It was observed that the iron foam samples were mostly corroded in the periphery regions. Except for quasi-elastic gradient, other mechanical properties (i.e. compressive strength, yield strength and energy absorbability) decreased monotonically with immersion time. Presence of adherent corrosion products enhanced the load-bearing capacity of the open cell iron foams at small strains. The finite element prediction for the quasi-elastic response of the 14-day corroded foam was in an agreement with the experimental results. This study highlights the importance of considering corrosion mechanism when designing absorbable scaffolds; this is indispensable to offer desirable mechanical properties in porous materials during degradation in a biological environment.
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•Compressive strength of open cell iron foam decreases monotonically with immersion time.•Adherent corrosion products enhance the load-bearing capacity of the iron foam.•μCT and Kelvin foam CAD model provide a good representation of corroded iron foam.•Kelvin foam model decently predicts the quasi-elastic response of corroded iron foam.
The internal combustion engine used in majority of cars at the present time do not use their fuel input very efficiently. A majority of this energy is dissipated as heat in the exhaust. The related ...problems of global warming and dwindling fossil fuel supplies has led to improving the efficiency of the internal combustion engine being a priority. One method to improve the efficiency is to develop methods to utilise heat in car exhausts that is usually wasted. Two promising technologies that were found to be useful for this purpose were thermoelectric cells (TECs) and heat pipes. Therefore this project involved making a bench type, proof of concept model of power production by thermoelectric cells using heat pipes and hot engine exhaust gases. 8 cells were used and managed to produce 6.03 W when charging the battery. The system operated with a heat to electricity conversion efficiency of 1.43%. The discrepancy between the actual efficiency and the predicted efficiency of 2.31% is most likely due to the cells not operating at their optimum voltage. The predicted efficiency is approximately 1/9 of the Carnot efficiency and the actual efficiency is approximately 1/15 of the Carnot efficiency.
•Car exhaust heat recovery design.•Unique design that utilises heat pipes and thermoelectric cells.•System is solid state and passive.•The electrical power produced was 6.03 W.•The resultant efficiency of the system was 1.43%.
•The design of a plate type power generation unit coupling with solar pond using TECs is proposed.•An open channel power generation unit operates at atmospheric pressure is realised.•The power ...generation unit is able to generate favourable power even at low flow rate.
Solar pond (SP) has been a reliable supply of heat source for heating process that requires temperature <100°C. In this work, the capability of solar pond in generating electricity has been explored experimentally using a plate type power generation unit (PTPGU). The open channel PTPGU was designed and fabricated in order to accommodate the TECs. The heat stored in the lower convective zone (LCZ) is used as the heat source needed for generating electricity by utilising thermoelectric cells (TECs) and thus a combined SP-PTPGU system is proposed. The PTPGU was tested with different hot water temperatures and flow rates. Also, the possibility of performance enhancement utilising copper mesh as insertion is presented. From the testing conducted, the PTPGU is able to generate 35.9W of electricity at the flow rate as low as 5.1 LPM (litre per minute) at the hot water temperature of 81°C. Besides coupling with solar pond, the PTPGU designed can also be coupled with other type of hot water source, such as hot spring.
Objective
Hybrid PET/MRI presents many advantages in comparison with its counterpart PET/CT in terms of improved soft-tissue contrast, decrease in radiation exposure, and truly simultaneous and ...multi-parametric imaging capabilities. However, the lack of well-established methodology for MR-based attenuation correction is hampering further development and wider acceptance of this technology. We assess the impact of ignoring bone attenuation and using different tissue classes for generation of the attenuation map on the accuracy of attenuation correction of PET data.
Methods
This work was performed using simulation studies based on the XCAT phantom and clinical input data. For the latter, PET and CT images of patients were used as input for the analytic simulation model using realistic activity distributions where CT-based attenuation correction was utilized as reference for comparison. For both phantom and clinical studies, the reference attenuation map was classified into various numbers of tissue classes to produce three (air, soft tissue and lung), four (air, lungs, soft tissue and cortical bones) and five (air, lungs, soft tissue, cortical bones and spongeous bones) class attenuation maps.
Results
The phantom studies demonstrated that ignoring bone increases the relative error by up to 6.8 % in the body and up to 31.0 % for bony regions. Likewise, the simulated clinical studies showed that the mean relative error reached 15 % for lesions located in the body and 30.7 % for lesions located in bones, when neglecting bones. These results demonstrate an underestimation of about 30 % of tracer uptake when neglecting bone, which in turn imposes substantial loss of quantitative accuracy for PET images produced by hybrid PET/MRI systems.
Conclusion
Considering bones in the attenuation map will considerably improve the accuracy of MR-guided attenuation correction in hybrid PET/MR to enable quantitative PET imaging on hybrid PET/MR technologies.
•Heat extraction from gradient and heat storage zones of SGSP were evaluated.•An in-pond heat exchanger covering the pond wall (NCZ and LCZ) was used.•Experiments were carried out using each heat ...exchanger or both at the same time.•Instantaneous efficiency increases with LHE regardless the weather conditions.•Simultaneous HE delivers the same quantity of energy but at lower flow rate.
In this study, heat extraction from both the gradient and heat storage zones of a salinity-gradient solar pond (SGSP) has been evaluated. For this purpose, an experimental solar pond pilot plant was constructed in 2009 in Barcelona (Spain). The structure of the pond is a cylindrical tank of 3-m height and 8m diameter with a total area of 50m2. The main objective was to evaluate a heat-extraction system from the SGSP designed to enhance the system efficiency under different conditions. Thus, an in-pond heat exchanger covering all of the lateral wall area of the pond was installed, and its performance was compared with the traditional in-pond heat exchanger situated on the bottom of the pond. Heat extraction experiments were performed using both heat exchangers individually or both at the same time. The study covers the experiments performed at three different seasonal temperature conditions: winter (December), summer (July) and autumn (October and November). The variations of the temperature inside the pond during the heat extraction were measured and analyzed. The results demonstrated that the efficiency of the pond increases when the heat is removed from the lateral heat exchanger alone compared to either using the bottom heat exchanger or using both heat exchangers simultaneously.
Modeling the behavior of groundwater levels is necessary to implement sustainable groundwater resource management. Groundwater is a non-linear and complex system, which can be modeled by data-driven ...models. This study evaluates the performances of data-driven models, support vector machine regression (SVR) and artificial neural network (ANN), for forecasting groundwater levels of confined and unconfined systems at 1-, 2-, and 3-month ahead. This is the first time that confined and unconfined aquifers have been compared using data-driven models. In addition, to identify the optimal input combination, a hybrid gamma test (GT) and genetic algorithm (GA) was used. The coefficient of correlation (
R
), Mean Absolute Error (MAE), root mean squared error (RMSE), Nash–Sutcliffe efficiency (NSE), and developed discrepancy ratio (DDR) were applied to evaluate the SVR and ANN models. Results showed that the SVR and ANN models were more accurate for the unconfined system than the confined system for forecasts up to 3-month ahead. In both hydrogeological systems for 1-month ahead, the models performed better than for 2- and 3-month ahead forecasts, and the accuracy of the models decreased as the months ahead increased. The SVR model performed better than the ANN model for 1-, 2-, and 3-month ahead groundwater-level forecasting. The SVR model could be successfully used in predicting monthly groundwater in confined and unconfined systems.
Recently accumulative roll bonding has been used as a novel method to produce particle reinforced metal matrix composites. In this study, aluminum matrix composite reinforced by submicron particulate ...alumina was successfully produced and the effects of number of ARB cycles and the amount of alumina content on the microstructure and mechanical properties of composites were investigated. According to the results of tensile tests, it is shown that the yield and tensile strengths of the composite are increased with the number of ARB cycles. Scanning electron microscopy (SEM) reveals that particles have a random and uniform distribution in the matrix by the ARB cycles and a strong mechanical bonding takes place at the interface of particle-matrix. It is also found that the tensile strength of the composite, as a function of alumina content, has a maximum value at 2vol.%, which is 5.1 times higher than that of the annealed aluminum.
•NEMD simulation conducted to examine the thermal behavior of porous graphene.•Effect of topology, orientation and elongation of pores in porous graphene investigated.•NEMD is appropriate for thermal ...simulations with characteristic length lower than 50 nm.•This paper sheds lights on thermal applications of architecture nanomaterials.
Tuning thermal conductivity of porous graphenes has attracted much interest in the thermal management of nanoelectronics devices due to the promising multifunctional properties of engineered nanomaterials. To explore the potential of tuning thermal properties of monolayer porous graphenes in multiple scales, non-equilibrium molecular dynamics (NEMD) and finite element method (FEM) are implemented to manipulate their thermal conductivity and temperature distribution by the engineering of pore topology. Results indicate that the thermal conductivity of porous graphenes can be significantly lower than a pristine graphene. The thermal conductivity reduction is attributed to phonon scattering at the boundaries of defects described by the phonon density of states analysis. It is found that the thermal conductivity and the temperature distribution of a porous graphene can be desirably tuned by the simultaneous engineering of relative density, pore topology, and pore orientation. Then, the effect of unit cell periodicity on the thermal conductivity of periodic porous graphenes, called phononic graphene or graphene metamaterial, is explored. Finally, comparing the results of continuum mechanics approach through the implementation of FEM and NEMD simulation presents the advantages of NEMD for predicting the thermal conductivity of engineered porous graphenes with characteristic length of lower than 50 nm.
•An experimental solar pond integrating solar collectors is presented.•Heat extraction/supply experiments are performed using heat exchangers.•Solar collectors increases efficiency of solar pond ...during the cold season.•Large amount of heat extracted allows a greater storage capacity of the solar pond.
In this study, an experimental investigation of the performance of a salinity gradient solar pond (SGSP) integrating solar collectors is presented. The SGSP is located in Barcelona (Spain) and has a cylindrical tank 3 m in height and 8 m in diameter with a total area of 50 m2. For this purpose, four solar thermal collectors (10 m2) are integrated, as an external source of heat, with the solar pond pilot plant in order to increase the storage capacity and its overall efficiency. The aim of this study is to evaluate heat extraction and heat supply processes from and to the SGSP under different seasonal conditions. Two in-pond heat exchangers are used, a conventional one situated on the bottom of the pond and a second one covering the lateral wall area of the pond. Heat extraction and supply experiments are performed using both heat exchangers individually or both at the same time. The experiments are conducted under two different seasonal temperature conditions: winter (February and March) and summer (July). The variations of the temperature inside the pond during the heat extraction/supply tests are monitored and analyzed. The results have indicated that the use of solar collectors as an extra source of heat for the solar pond led to a 50% increase in the daily efficiency during the cold season tests, while heat extraction only appeared as the best option during the warm season tests. Higher daily efficiency and heat supply results can only be obtained if large amounts of heat are extracted, otherwise, the daily efficiency of the solar pond could decrease. Finally, the solar collectors can be considered a good alternative for avoiding a significant decrease in solar pond temperatures (especially during the cold season), which would not only result in a significant energy storage efficiency improvement but also increase the capacity of the solar pond to supply heat to an external application.
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