1,089 research outputs found
Alarm initiated activities: Matching formats to tasks
No full textThis paper addresses the selection of visual alarm formats for different 'alarm initiated activities'. The activities under examination were alarm handling tasks. Seven such tasks have been identified, namely: observe, accept, analyse, investigate, correct, monitor and reset. One of the most important stages is the initial analysis of the alarm information as this determines the subsequent manner in which the information is processed. It was hypothesised that the format in which the information is presented will determine the success of the alarm handling task, hence the proposal to match formats to tasks. The findings suggest that text-based formats are best suited to tasks requiring time-based reasoning, mimic formats are best suited to tasks requiring spatial location and annunciator formats are best suited to tasks requiring recognition of spatial patterns. The importance of considering both reaction time and accuracy of response in consideration of task match was also noted. In summary, it is suggested that care needs to be taken to determine the appropriateness of the medium for any given task and the demands it places on the human operator
A comparison of structured and unstructured navigation through a CBT package
No full textThe advent of hypertext has opened up new possibilities in computer-based training. The design of courseware without any predetermined structure could make the designer's task easier, and allow greater flexibility for the trainee to structure the learning environment to suit their own learning style, This investigation was concerned with the exploration of performance differences in structured and unstructured training environments. In the structured condition, subjects encountered presequenced training and practice modules. For the unstructured condition, subjects determined their own sequence of modules. It was proposed that performance may be better in the unstructured condition. The findings indicate that this depends upon individual differences in cognitive style, some styles seemingly better at exploiting the unstructured learning environment than others
Commenting on the commentators: What would Bartlett have made of the future past?
No full textThis Article does not have an abstract
Alarms in human supervisory control: a human factors perspective
No full textThis paper presents a human factors perspective of alarm handling. This is done by first considering what defines an alarm, and how a number of perspectives contribute towards the definition. The nature of alarms and incidents are discussed, then the problems with, and the reduction of, alarms are considered. Finally, a model of alarm handling is presented to demonstrate how a human factors approach might contribute to an improved understanding of the operator's task
Segmenting Mechanomyography Measures of Muscle Activity Phases Using Inertial Data
No full textThis dataset contains the data used in our manuscript titled "Segmenting Mechanomyography Measures of Muscle Activity Phases Using Inertial Data". Data structure is explained in the README.txt file located at the top-level of the dataset. Manuscript title in the README.txt file and contained in the title of the zip file are of a previous working title. Please contact corresponding author Richard B. Woodward for any questions.</span
Mixed-Mode Fatigue Disbond on Metallic Bonded Joints
No full textAerospace structures have been long dealing with the safety versus weight issue. Lighter airplanes are cheaper to operate, however, they may face a safety issue because of the reduced fatigue life. Consequently, a heavier/safer structure is designed. Adhesive bonding is a joining technique that offers potential for improvement in the fatigue behavior of a structure, resulting in reduced weight. However, predicting the fatigue behavior of a bonded joint for its use in a damage tolerance design philosophy still remains a problem with no satisfactory solution. Often, the joint is subjected to a combination of peeling and shearing stresses. Hence, one of the most important factors influencing the fatigue behavior of an adhesively bonded joint is the Mode Ratio. The objective of this investigation was to study of the Mode Ratio on the fatigue behavior of a bonded joint. First, the fatigue disbond mechanisms were investigated throughout the entire Mode Ratio range and compared to fatigue delamination mechanisms. After the mechanisms were identifed, a parameter related to the mechanisms was chosen as similitude in the Paris relation and the Mixed-Mode fatigue disbond model was developed. Later, the model was evaluated on a different adhesive and on a condition of variable Mode Ratio. The fatigue disbond mechanisms study identified the local principal stress as the driving force for the micro-crack formation and growth, and the Mode Ratio was identified as the controlling parameter for coalescence between the micro-cracks. Based on these findings, a parameter directly related to the principal stress was proposed as a similitude parameter. Additionally, a linear interpolation between Mode I and Mode II parameters of the Paris relation was proposed to predict the Mixed-Mode fatigue behavior. Thus, the model predicts the fatigue behavior for the entire Mode Ratio range using only pure Mode I and pure Mode II as inputs. The evaluation of this model revealed that it presents good predictions for Mode Ratios in the range of 0% to 50% and conservative predictions in the range of 50% to 100%. The model also seems to be valid in a variable Mode Ratio condition. The limitations and shortcomings of the model along with the limitations of using a damage tolerance philosophy on adhesive bonding were discussed. Despite these issues, the model is an improvement over the models available in the literature because it captures some of the phenomena involved in the Mixed-Mode fatigue disbond. Additionally, the model also reduces the amount of empirical data required for its implementation.Aerospace Structures and MaterialsAerospace Engineerin
Modified Hydrotalcites as Smart Additives for Improved Corrosion Protection of Reinforced Concrete
No full textCorrosion of reinforcing steel is a major culprit to durability and serviceability of concrete structures. This problem is highly relevant for civil engineering structures in the transport sector, such as bridges, tunnels, harbour quays and parking structures. The dominant aggressive external influence is the chloride load from de-icing salts or sea water, penetrating the concrete and destroying the natural (high pH) passivation of the steel. The direct and indirect costs of reinforcement corrosion are substantial, as it entails additional repair, rehabilitation, and monitoring activities to ensure the safety, functionality and aesthetics of concrete structures and components. In addition, many repairs have a short working life, necessitating repeated repairs within the use life. Consequently, the construction industry is in need of improving the corrosion protection of reinforcing steel, preferably by low-cost measures. Presently available corrosion preventive measures are either too costly or technically too complicated to be applied on a wide scale. Stainless steel reinforcement is 5 or 10 times more expensive than reinforcing (carbon) steel. Cathodic prevention and protection may be effective but both are a special niche expertise and are thus not applied on a wide scale. Coatings on the concrete surface normally do not last long enough (10-20 years), which causes a maintenance cycle of its own. Corrosion inhibitors seem to be attractive owing to their low cost and the ease and flexibility of application. However, there are conflicting opinions about the reliability of the inhibitors for corrosion protection in concrete in terms of long-term efficiency; some are toxic, such as nitrites. A possible promising solution to overcome this problem is the encapsulation/immobilization of desired inhibitors within the molecular structure of a host compound. The immobilized inhibitor then can be slowly released in a controllable way by an external stimulus (e.g. chloride ions) and therefore provide a relatively long-term corrosion protection. Owing to the unique fine tunable molecular structure and high anionic exchange capacity, modified hydrotalcites (MHTs) have the potential to be used for the immobilization of a desired inhibitor. Hydrotalcite is one representative of large mineral group of Layered Double Hydroxides (LDHs), in general formula [MII1-x MIIIx (OH)2]x+ [(An-x/n)]x-·mH2O, where MII and MIII are di- and trivalent metals respectively, and An- is an interlayer charge-balancing anion with valence n. The x value is in the range 0.20-0.33. Although the most common anion found in naturally occurring hydrotalcites is carbonate, in practice however, there is no significant restriction to the nature of the interlayer charge-balancing anions. The MHT structure can accommodate various cations in the hydroxide layers with varying MII/MIII ratios as well as a wide range of anionic species in the interlayer regions. Within the MHT family, a class of materials with emerging importance is that constituted by MHTs intercalated with organic species. In addition, increasing awareness of the health and ecological risks has drawn much attention to amino acid-based inhibitors because they are nontoxic, environmentally friendly, relatively cheap and easy to produce with higher purity. Therefore, the marriage of the two kinds of materials is expected to not only offer an improved inhibiting effect than using the inhibitor alone but also to impose less impact on environment. Recently a study on the application of amino acid modified hydrotalcites in cementitious materials has formed the basis of a patent (WIPO Patent, WO 2011/065825 A1). However, its scale was relatively small and further work was considered necessary by the applicants and their organisations. In this research, four different types of sodium salts of amino acids (i.e., Glycine, 6-aminocaproic acid, 11-aminoundecanoic acid, and p-aminobenzoic acid) were proposed as potential candidates for the modification of hydrotalcite. Sodium nitrite was also chosen as a modification candidate for comparison purposes due to its well-recognized inhibition performance in concrete. Based on the anti-corrosion performance evaluation in chloride contaminated simulated concrete pore solution (Chapter 3), sodium nitrite, sodium salt of p-aminobenzoic acid (pAB) and sodium salt of 11-aminoundecanoic acid (11AUA) were selected as the most promising candidate modifiers for synthesis of MHT. Subsequently, six MHTs (two Mg/Al atomic ratios of 2.2 and 2.7, which were denoted as 2 and 3 respectively) were synthesized through the modification of two commercially available carbonate Mg-Al hydrotalcites PURAL® MG 63 HT (Mg/Al atomic ratio 2.2) and PURAL® MG 70 HT (Mg/Al atomic ratio is 2.7) by NaNO2, pAB and 11AUA (Chapter 4). They were characterized by means of X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Thermogravimetry (TG), Differential scanning calorimetry (DSC) and relevant elemental analysis. The ion exchange characteristics of the six synthesized MHTs and their anti-corrosion performance were investigated in chloride-rich simulated concrete pore solution (Chapter 5). The results showed that ion exchange occurred between free chloride ions in the simulated concrete pore solution and the inhibitive anions intercalated in MHT, thereby reducing the free chloride concentration which is equivalent to increased binding of chloride in mortar/concrete. Moreover, the simultaneously released anions, in particular -pAB, were found to exhibit a notable inhibiting effect and caused shifting of the corrosion initiation of steel to a higher chloride concentration level. This evidence manifested the dual role protecting function that MHT (in particular, Mg(2)Al-pAB) offers to the steel: capturing chlorides as a chloride scavenger and providing of a beneficial release of corrosion inhibitors in parallel as an inhibitor reservoir further protecting reinforcing steel from corrosion. The effects of two MHTs, i.e., Mg(2)Al-NO2 and Mg(2)Al-pAB, were investigated in both plain and reinforced mortar specimens with a focus on their interaction with chloride ions in plain mortar (Chapter 6) and in reinforced mortar, mainly focusing on their inhibition influence on corrosion of the reinforcing steel (Chapter 7). In plain mortar, the two MHTs were incorporated at two dosage levels replacing 5% and 10% mass of cement. A testing programme including workability test, strength test, porosity test, and rapid chloride migration and diffusion test was employed to investigate the effect of the two MHTs on chloride penetration in mortar. The results indicated that the incorporation of Mg(2)Al-pAB at 5% dosage in mortar produced a notably improved chloride diffusion resistance with no remarkably negative influence on the development of mechanical strength and workability of fresh mortar, which therefore validated that the Mg(2)Al-pAB could be a promising alternative in hindering the chloride transport in mortar when an appropriate mixing dosage is adopted. In reinforced mortar, the two MHTs were applied in two different ways: (1) as one of the mixing components in bulk mortar at two dosage levels replacing 5% and 10% mass of cement; (2) as a surface coating on the reinforcing steel in a cement paste replacing 20% of the cement mass. Three test methods including electrically accelerated chloride migration, cyclic wetting-drying and natural chloride diffusion test based on chloride exposure were adopted to custom designed reinforced mortar specimen. Although no corrosion was detected after 30 weeks natural diffusion testing, the results obtained from accelerated chloride migration and cyclic wetting-drying test revealed that when an appropriate mixing dosage is adopted and applied in a proper way, the application of MHT either incorporation of a small amount (in particular, Mg(2)Al-pAB to replace 5% weight of cement) in mortar or as a surface coating of the reinforcing steel (Mg(2)Al-pAB or Mg(2)Al-NO2 to replace 20% weight of cement in paste) resulted in delayed corrosion initiation and increased chloride threshold responsible for initiating corrosion. The effects on service life of structures in chloride contaminated environment is estimated, which shows a significant improvement. In general, the research work presented in this thesis met the expectations and goals formulated at the start of the project. As the first exploration on a wider scale into the application of MHT in cementitious materials for corrosion protection purposes, a new type of smart concrete additive based on amino acid modified hydrotalcites (in particular Mg(2)Al-pAB) aiming to combat chloride-induced corrosion has been developed and documented. The results demonstrated that by using such a material, a longer service life of reinforced mortar/concrete structures can be expected. While realizing that more research is still needed for maximizing the beneficial effect of MHT as a functional additive of cementitious materials, some recommendations for further research are given in the last chapter of this thesis (Chapter 8). MHT has a very rich interlayer chemistry and can participate in anion exchange reactions with great facility. Therefore, the scope of application for MHT with combination of different kinds of host metal hydroxides and various interlayer anions with desired specific function in cement-based materials could be significantly expanded. For example, a controlled release formulation based on MHT can be made by encapsulation/immobilization of a desired functional compound within the layered molecular structure of hydrotalcites. This functional compound could be a superplasticizer, a shrinkage reducer, an ASR inhibiting compound, an air-entraining agent, a pore solution viscosity adjuster, a setting accelerator/retarder and probably other any concrete property adjusters. In this respect, we are confident that future work on applications of new types of smart functional concrete additives based on MHTs will expand rapidly and contribute greatly to the effort of searching for effective measures to improve the durability or other properties of reinforced concrete.Structural EngineeringCivil Engineering and Geoscience
- …
