Efficiency characterisation of multi-port antennas

A simple radiation efficiency metric is introduced to include the effects of non-ideal source/receiver impedances. The features of this parameter are highlighted and its compact formula is derived. The notion of mean matching efficiency is established. Simulations prove that this matching efficiency is quite useful in a quick estimation of diversity performance of multi-port antennas in rich isotropic multipath environments

Multi-port matching efficiency in antenna systems with cascaded networks

A general compact formula for multi-port matching efficiency in the presence of an arbitrary number of cascaded networks is introduced. A comparison between the decoupling efficiency and multi-port matching efficiency is presented. Similarly, a compact formula for decoupling efficiency in a cascaded chain is provided. The presented compact formulas are quite advantageous for optimization of radiation efficiencies by designing a proper matching network

Binary effect of palm oil fuel ash and eggshell waste powder on heat of hydration for mortar

The effects of mortar containing palm oil fuel ash and eggshell waste powder on heat of hydration was investigated. This study covers the basic properties like the chemical composition of raw materials and the hydration temperature for binary mortar. Malaysia is one of the world’s largest palm oil producers. Palm oil fuel ash (POFA) is a product of the combustion of palm oil waste which is not used and usually disposed of in landfills. The use of eggs in the food industry also generate waste egg shells that can be transform into powder namely eggshell waste powder (ESP). The development in construction technology has contributed to research in producing various methods and materials that provide advantages in the construction field. One of the technologies is to investigate the effectiveness of OPC replacement with appropriate waste materials. In this research, POFA and ESP was used as ingredients to replace a proportion of OPC in the mortar thereby reducing the use of OPC. POFA used in this study were in forms of ground POFA (GPOFA) and unground POFA (UPOFA). GPOFA and ESP are ground to achieve a similar size as OPC while UPOFA was used in its original size. The total percentages replacement of POFA and OPC was 20% by weight with the different level replacements of 4%, 8%, 12%, 16% and 20%. The design of mortar mix proportion made up of three groups, A, B and C. Group A is the control mortar that is OPC only. Group B is the mortar that contains OPC, POFA and ESP. Meanwhile, a third group C, consisting of a mixture of OPC, GPOFA and ESP. The mix proportion used for hydration temperature determination was chosen from the previous study which identified the strength of mortar compression. The optimum compressive strength of each group is chosen to obtain the mortar hydration temperature. For determination of mortar hydration temperature, plywood with size 300 mm x 300 mm x 450 mm cube was used as the exterior mold. It was packed with 76 mm thick polystyrene acting as the insulator. Polyvinyl chloride (PVC) pipe with diameter of 150 mm and a height of 300 mm is used to fill the mortar mix. A thermocouple (Type K) was inserted into the center of each box and was connected to a data logger system. Temperature rises due to heat of hydration in all mixes were recorded for 5 days. The results revealed that the replacement of OPC with binary materials is beneficial, particularly for mass mortar where thermal cracking due to excessive heat rise is of great concern

Stress-Strain Predictions of Semisolid Al-Mg-Mn Alloys During Direct Chill Casting: Effects of Microstructure and Process Variables

The occurrence of hot tearing during the industrial direct chill (DC) casting process results in significant quality issues and a reduction in productivity. In order to investigate their occurrence, a new semisolid constitutive law (Phillion et al.) for AA5182 that takes into account cooling rate, grain size, and porosity has been incorporated within a DC casting finite element process model for round billets. A hot tearing index was calculated from the semisolid strain predictions from the model. This hot tearing index, along with semisolid stress-strain predictions from the model, was used to perform a sensitivity analysis on the relative effects of microstructural features (e.g., grain size, coalescence temperature) as well as process parameters (e.g., casting speed) on hot tearing. It was found that grain refinement plays an important role in the formation of hot cracks. In addition, the combination of slow casting speeds and a low temperature for mechanical coalescence was found to improve hot tearing resistance

Care of Mechanical Ventilated Patients in General Ward: Nurses Perspective

Aim: This study aimed to explore the care of mechanically ventilated patients in general wards from the nurses' perspective.Methodology: A cross-sectional descriptive study using a self administered questionnaire was given to the nurses with a purposive convenient sampling method in adult patients from medical, surgical and isolation units in studied hospital in KSA. Results: 149 participants from general units represents various years of experiences shared their perception on the knowledge and competencies (M= 3.38±.62) the support they received (M= 2.41±.78), their satisfaction and confidence (M= 2.86±.81) and the resources provided (M= 2.44 ±.69) for caring MV patients in their general unit revealed the total mean in each categories were in the state of either neutral or disagree with the items given. The participants admitted that the found themselves are competent in performing suctioning with aseptic technique and ability to identify the possible complications confidently. However the participant concluded that it was inadequate support for them, staffing ratio, equipment and facilities was inappropriate which leads to dissatisfaction and less confident in caring for MV patients.Conclusion: This study concludes that caring for patients in general ward causing dissatisfaction among the staff and place patients in risk. Hospital administration needs to ensure that general ward nurses are trained accordingly, provide adequate staffing ratio, and prepare the physical environment and suitable equipment to care for MV patients in general ward

Coupling effects on richness threshold of multi-port antennas in multipath environments

This paper investigates convergence in diversity gain of multi-port antennas in non-rich multipath environments. It is shown that diversity gain convergence is faster in the presence of strong coupling. In this situation, richness threshold is also smaller. Furthermore, by linking convergence in diversity gain to convergence in antenna ports\u27 correlations, the role of pattern diversity caused by coupling is highlighted. A range of variation for correlations is defined whose upper bound is used to quantify pattern diversity. The lower bound for this range is the corresponding spatial correlation in a rich multipath environment

The effects of microstructural features and process parameters on the hottearing in direct chill cast aluminum alloys

Hot tearing is an irreversible failure that occurs above the the solidus temperature of an alloy during casting, in the presence of a liquid phase. These cracks possess serious quality implications in industrial direct chill (DC) casting process. During solidification, thermal stresses are induced due to the heterogeneous temperature distribution, which causes variations in thermal strain and may result in cracks if these stresses are large enough. In order to investigate the occurrence of hot tears in DC casting, a DC casting finite element process model for round billets was incorporated with (1) a new semi-solid constitutive law for aluminum alloy AA5182 that takes into account cooling rate, grain size and porosity, and (2) a model for cooling rate induced grain size variation. A hot tearing index was calculated from the semi-solid strain predictions from the model. This hot tearing index, along with semi-solid stress predictions from the model, was used to link hot tearing with microstructural features (i.e. grain size and coalescence temperature) as well as process parameters (e.g. casting speed). It was found that grain refinement plays an important role in the formation of hot cracks. In addition, lower assumed coalescence temperature and slow casting speeds were found to improve hot tearing resistance. In addition to simulation of DC casting, experimental studies on an as cast AA5182 ingot (DC cast) were made in terms of grain size, chemical composition and solidification kinetics. Samples for these experiments were collected from the steady state region of the ingot. The results of these experimental investigations show that, (1) grain size increases from surface to centre of the ingot, (2) there is considerable macrosegregation of the alloying elements along the cross section of the ingot, and (3) the solidification kinetics vary as a function of both position and cooling rates. These experimental observations influence the hot tearing susceptibility of the DC cast product. Thus, for the process model to be more accurate in predicting hot tears, inclusion of these factors, along with an improved model for grain size variation is suggested.Applied Science, Faculty ofEngineering, School of (Okanagan)Graduat