Constitutive Behaviour and Formability of Pre-aged AA7075 Sheet in a Warm Forming Process

Warm constitutive and formability characterization of a high strength aluminum alloy (AA7075) was performed for a range of pre-aged (i.e. under-aged) tempers, strain rates and temperatures. The pre-aging processes were composed of a solution treatment process and a natural aging period of 2 days, followed by aging at temperatures of 80, 100 and 120 C for durations of 1, 2, and 4 hours. The peak-aged T6 temper condition was also considered for comparison purposes. Warm constitutive characterization was performed at strain rates of 0.01, 0.1, and 1 s-1, and temperatures of 150, 175 and 200 C. Room temperature and warm formability tests were performed using a Nakazima [1] tooling geometry with a plane strain specimen for the same temperatures, considering a range of tooling stroke rates from 0.5-63 mm/s. The formability results were assessed utilizing limit strains based on the ISO 12004-2:2008 [2] necking detection method, as well as the measured dome heights at failure. In addition, the effect of heating rate prior to elevated temperature constitutive and formability testing was considered. The room temperature constitutive results revealed that the pre-aged tempers exhibit superior work hardening response and elongation compared to the peak-aged T6 temper. However, serrated flow, attributed to PLC effects, was observed in the flow response of the tempers with reduced/insufficient pre-aging schedules (e.g. 1 hour at 80 and 100 C pre-age schedules). This behaviour induced a negative strain rate sensitivity and reduced the repeatability of the tensile flow response and room temperature formability limits. In response to elevated temperature deformation, the T6 tensile samples exhibited clear thermal softening effects. This response, however, was accompanied by early onset of diffuse necking, although the elevated temperature strain rate sensitivity is high which results in increased elongation to failure. The pre-aged tempers, in contrast, also responded positively to the thermal softening effect and exhibited a delay in the onset of diffuse necking, compared to T6. Interestingly, the elevated temperature strain rate sensitivity of the pre-aged tempers was quite low compared to the T6 samples, part of which is attributed to aging during the lower rate (longer duration) tensile tests. The room temperature formability results revealed improvements in forming limits with the pre-aged tempers, as compared to the peak-aged T6 temper. At elevated temperatures, thermal softening resulted in higher forming limits for all evaluated tempers, with the T6 temper at 200 C having the highest limit strain, closely followed by the 100 C 4 hour and 80 C 4 hour aged tempers formed at 175 C. Interestingly, the high limit strain exhibited by the warm formed T6 temper was not fully reflected in its limit dome height, since the early onset of diffuse necking prevented a globally uniform strain distribution along the surface of the specimen. In contrast, the pre-aged tempers in contrast resulted in superior dome height limits, which is attributed to their higher extent of work hardening prior to onset of diffuse necking. Both the tensile elongation and forming limit strains were shown to decrease with test speed. Further, the faster heating rates considered in this study resulted in mildly superior forming limits, since the extent of pre-aging during heating to the warm forming temperatures was reduced. A limited study on the hardness of the warm formed specimens before and after a paint bake cycle (PBC) revealed a notable increase in hardness values in response to the PBC for all tested conditions. Interestingly, the T6 temper exhibited a mild drop in hardness following warm forming, however, the loss in hardness was largely recovered after the PBC, which may be due to retrogression and re-aging effects. For the range of initial tempers and forming conditions considered herein, the specimens heat-treated at 100 C for 4 hours, and warm formed at 175 C (utilizing the rapid heating method) resulted in one of the best overall performances. This process route (evaluated at the slow forming speeds of 1 mm/s) resulted in an increase of approximately 42% in dome height (from 19 to 27 mm), and 77% in major limit strain (from 14.5 to 25.7%), compared to the room temperature limits of the T6 temper. Moreover, the repeatability of this process route proved to be superior compared to the majority of the other under-aged processing routes. In addition, the hardness values of this pre-aged temper, following warm forming and a paint bake cycle (PBC) were within 97% of the as-received T6 temper. Finally, a numerical model was devised, using the Hockett-Sherby [3] constitutive model to fit the warm tensile data. The numerical simulations demonstrated accurate predictions for the tensile experiments and fair predictions for the warm forming experiments

Enzymatic Removal of Diclofenac and Aceclofenac from Synthetic Wastewater by Soybean Peroxidase

Pharmaceutical medications that are a class of emerging contaminants have been detected in wastewater treatment facilities\u27 influent and effluent, and they have reached water sources in amounts ranging from ng/L to ug/L. They threaten the environment and non-target life. Soybean peroxidase (SBP)-catalyzed process was studied to remove two non-steroidal anti-inflammatory drugs (NSAIDS) diclofenac and aceclofenac through enzymatic oxidation from synthetic wastewater. SBP can be extracted from soybean hulls, a by-product of the soybean industry. First, the experiments studied the viability of SBP-catalyzed removal on these two compounds, then the operational parameters including pH, the molar ratio between hydrogen peroxide and substrate and minimum effective enzyme concentration were optimized. The first-order rate constant and half-life of each substrate were also determined under the established optimum conditions. The results demonstrated SBP is robust enzyme to achieve more than 95% removal efficiency for both compounds. Finally, possible oligomerization products of enzymatic treatment were characterized by mass spectrometric analysis and showed formation of tetramer

Speech air flow with and without face masks

Face masks slow exhaled air flow and sequester exhaled particles. There are many types of face masks on the market today, each having widely varying fits, filtering, and air redirection characteristics. While particle filtration and flow resistance from masks has been well studied, their effects on speech air flow has not. We built a schlieren system and recorded speech air flow with 14 different face masks, comparing it to mask-less speech. All of the face masks reduced air flow from speech, but some allowed air flow features to reach further than 40 cm from a speaker’s lips and nose within a few seconds, and all the face masks allowed some air to escape above the nose. Evidence from available literature shows that distancing and ventilation in higher-risk indoor environment provide more benefit than wearing a face mask. Our own research shows all the masks we tested provide some additional benefit of restricting air flow from a speaker. However, well-fitted mask specifically designed for the purpose of preventing the spread of disease reduce air flow the most. Future research will study the effects of face masks on speech communication in order to facilitate cost/benefit analysis of mask usage in various environments

Anxiety and cognitive bias in children and young people who stutter

Psychologists recognise various forms of anxiety, such as generalized anxiety disorder, separation anxiety and social phobia. People who stutter are at risk of elevated levels of anxiety, especially social phobia. Recent research has suggested that anxiety may be caused and maintained by cognitive biases such as preferentially allocating attention towards threat stimuli. These biases can be re-trained using cognitive bias modification with resulting improvements in levels of anxiety. In the present study, we measured different forms of anxiety and attentional bias for faces among 8-18 year olds attending the Michael Palin Centre for treatment for stuttering. The clients and their parent(s) completed the child and parent versions, respectively, of the Screen for Childhood Anxiety Related Emotional Disorders (SCARED), which provides an overall anxiety score and sub-scores, with clinical cut-offs, for generalized anxiety disorder, separation anxiety, social phobia, school avoidance and panic. The clients also performed a computerised measure of attentional bias for faces, using schematic stimuli. Levels of anxiety were higher than in the general population, and prevalence increased with age. There was a significant correlation between SCARED scores produced by clients and their parents. Socially anxious participants showed a bias towards sad faces

How Do Long Term Crop Rotations Influence Weed Populations: Exploring the Impacts of More than 50 Years of Crop Management in Serbia

Crop rotation is known as an eco-friendlier approach, as provides diversification in crop management systems, modifies intensive pressure on the agricultural ecosystem, utilizes various soil horizons, and prevents the establishment of specific pests and weeds. We set out here a study on the farms that have been managed over 50 years of specific continuous crop management programs. The experimental treatments were in a different management system: monoculture of maize, winter wheat, and soybean, 2-year crop rotation (winter wheat–maize) with and without chemical fertilizer, and 3-year crop rotation (winter wheat–soybean–maize) with and without chemical fertilizer and manure. We took soil samples six times from 2014 to 2017 prior to sowing and after harvesting each year. Weed seeds were extracted from soils and identified and counted by species. We, upon the data of a long term experiment of crop rotation, could conclude that crop rotations with more crops in the sequence are significantly effective in maintaining weed populations, a low-input crop production could reach a constant low population below an important damaging density, and therefore will be a more sustainable crop production while chemical fertilizers would change the soil’s chemical and structure and imbalance the plant population diversity and manures with high weed seed infestations have the potential to totally eradicate crop rotation effects, Therefore, clean manures or compost are highly recommended

Biased Saccadic Responses to Emotional Stimuli in Anxiety: An Antisaccade Study.

Research suggests that anxiety is maintained by an attentional bias to threat, and a growing base of evidence suggests that anxiety may additionally be associated with the deficient attentional processing of positive stimuli. The present study sought to examine whether such anxiety-linked attentional biases were associated with either stimulus driven or attentional control mechanisms of attentional selectivity. High and low trait anxious participants completed an emotional variant of an antisaccade task, in which they were required to prosaccade towards, or antisaccade away from a positive, neutral or threat stimulus, while eye movements were recorded. While low anxious participants were found to be slower to saccade in response to positive stimuli, irrespectively of whether a pro- or antisaccade was required, such a bias was absent in high anxious individuals. Analysis of erroneous antisaccades further revealed at trend level, that anxiety was associated with reduced peak velocity in response to threat. The findings suggest that anxiety is associated with the aberrant processing of positive stimuli, and greater compensatory efforts in the inhibition of threat. The findings further highlight the relevance of considering saccade peak velocity in the assessment of anxiety-linked attentional processing

High Visual Working Memory Capacity in Trait Social Anxiety

Working memory capacity is one of the most important cognitive functions influencing individual traits, such as attentional control, fluid intelligence, and also psychopathological traits. Previous research suggests that anxiety is associated with impaired cognitive function, and studies have shown low verbal working memory capacity in individuals with high trait anxiety. However, the relationship between trait anxiety and visual working memory capacity is still unclear. Considering that people allocate visual attention more widely to detect danger under threat, visual working memory capacity might be higher in anxious people. In the present study, we show that visual working memory capacity increases as trait social anxiety increases by using a change detection task. When the demand to inhibit distractors increased, however, high visual working memory capacity diminished in individuals with social anxiety, and instead, impaired filtering of distractors was predicted by trait social anxiety. State anxiety was not correlated with visual working memory capacity. These results indicate that socially anxious people could potentially hold a large amount of information in working memory. However, because of an impaired cognitive function, they could not inhibit goal-irrelevant distractors and their performance decreased under highly demanding conditions