Optimal Design for Vibration Mitigation of a Planar Parallel Mechanism for a Fast Automatic Machine

This work studies a planar parallel mechanism installed on a fast-operating automatic machine. In particular, the mechanism design is optimized to mitigate experimentally-observed vibrations. The latter are a frequent issue in mechanisms operating at high speeds, since they may lead to low-quality products and, ultimately, to permanent damage to the goods that are processed. In order to identify the vibration cause, several possible factors are explored, such as resonance phenomena, elastic deformations of the components, and joint deformations under operation loads. Then, two design optimization are performed, which result in a significant improvement in the vibrational behaviour, with oscillations being strongly reduced in comparison to the initial design

Processing of hybrid laminates integrating ZrB2/SiC and SiC layers

Tape casting technique was used to develop hybrid laminates constituting by SiC and ZrB2-SiC layers; the main aim is obtaining a structure which integrate the unique properties of these materials and potentially extent their application temperature range. Multilayer with ZrB2-SiC layers stacked in between SiC ones were successfully processed. Thin cracks propagated in the composite layers without affecting SiC ones; their formation was due to residual stresses developed in the two materials because of the differences in their shrinkage and coefficients of thermal expansion. However, these cracks did not significantly affect the material properties: relative density, elastic modulus and flexural strength of hybrid laminates was indeed only slightly lower than those of laminates made up of layers with the same composition

Magnetostatic bias in multilayer microwires: theory and experiments

The hysteresis curves of multilayer microwires consisting of a soft magnetic nucleus, intermediate non-magnetic layers, and an external hard magnetic layer are investigated. The magnetostatic interaction between magnetic layers is proved to give rise to an antiferromagnetic-like coupling resulting in a magnetostatic bias in the hysteresis curves of the soft nucleus. This magnetostatic biasing effect is investigated in terms of the microwire geometry. The experimental results are interpreted considering an analytical model taking into account the magnetostatic interaction between the magnetic layers.Comment: 6 pages, 7 figure

Burden and associated factors for caregivers of the elderly in a developing country

The elderly population in South Asia is growing. In Pakistan trained caregivers are scarce and culturally not acceptable. This study assessed the level of stress experienced by caregivers of the elderly and determined the association of care giving burden with different characteristics of the elderly. A cross-sectional, questionnaire based study was conducted using nonprobability purposive sampling. All consenting participants aged 60 years and above needing help with at least one activity of daily living or two instrumental activities of daily living were included. 350 participants were assessed for perceived care giver burden. Care providers were mostly female (68.9%). Half (50.3%) of the caregivers had a positive score on a perceived care burden scale. Financial impact had a strong correlation (0.79) with perceived caregiver burden. Higher dependency levels of a physical and cognitive nature posed greater burden on caregivers. Behavioural issues of the elderly such as verbal abuse and difficulty sleeping were predictors of a higher caregiver burden. Caregiver burden is a significant issue for those caring for elderly family members in Karachi, Pakistan

Effect of stocking density and protein/fat ratio of the diet on growth of Dover sole (Solea solea)

250 soles (30g initial weight) were randomly placed in 12 experimental tanks at the Discizia's aquaculture marine station. They were reared at 2 different stocking densities (2.3 and 1.3kg/m2 corresponding to 40% and 25% of the bottom surface area covered by fish) and fed on 2 diets with different protein/fat ratio (50% and 54% crude protein and 21% and 18% total lipid, respectively for diets A and B) with triplicate tanks per treatment. The trial lasted 120 days. Fish stocked at the lower density resulted in significantly higher weight gain than fish reared at 2.3 kg/m2 (29.0±7.3 g vs 20.3±8.0g; P<0.01) with a specific growth rate (SGR) of 0.54±0.09 and 0.42±0.13, respectively. Feed conversion rate (FCR) was improved at the lower density (1.8 vs 2.4, P<0.01). The chemical composition of the test diets significantly affected the growth performance of sole. Diet B led to a higher final weight (59.7 vs 50.8g; P<0.01) and better feed utilisation (FCR: 1.8 vs 2.4, P<0.01). These results confirm the necessity to ensure an adequate space for the growing sole and suggest the need for high protein diets to meet sole's requirements

Optimization of selective laser sintering process conditions using stable sintering region approach

The optimization of process parameters represents one of the major drawbacks of selective laser sintering (SLS) technology since it is largely empirical and based on performing a series of trial-and-error builds. This approach is time con-suming, costly, and it ignores the properties of starting powders. This paper provides new results into the prediction of processing conditions starting from the material properties. The stable sintering region (SSR) approach has been applied to two different polymer-based powders: a polyamide 12 filled with chopped carbon fibers and polypropylene. This study shows that the laser exposure parameters suitable for successful sintering are in a range that is significantly smaller than the SSR. For both powders, the best combination of mechanical properties, dimensional accuracy, and porosity level are in fact, achieved by using laser energy density values placed in the middle of the SSR

Selective Laser Sintering versus Multi Jet Fusion: A Comprehensive Comparison Study Based on the Properties of Glass Beads-Reinforced Polyamide 12

Selective laser sintering (SLS) and multi jet fusion (MJF) are the most widespreadpowder bed fusion additive manufacturing techniques for fabricating polymericparts since they offer great designflexibility, productivity, and geometricalaccuracy. However, these technologies differ in the thermal energy source usedto melt the powders as well as the innovative use of printing agents featured inthe latter one to promote material consolidation and to avoid thermal bleeding atthe part contours. The use of a single powder made of glass beads-reinforcedpolyamide 12 (PA12/GB) for the fabrication of MJF and SLS samples makespossible a systematic comparison of the printed parts properties. A thoughtfulanalysis of the microstructure and mechanical properties of the samples revealsdifferences and peculiarities between the two technologies. SLS exhibits lowerporosity and higher mechanical performances when the parts are printed alongthe build plane thanks to the powerful heating ensured by the laser. In contrast,MJF samples show higher mechanical isotropy with greatflexural and tensilebehavior for vertically oriented parts. The role of glass beads in the materialbehavior is defined by their mechanical properties, meaning higher rigidity andlower strength compared to neat PA12, and fracture mechanism

How ethnic are African parties really? Evidence from Francophone Africa

Though African party systems are said to be ethnic, there is little evidence for this claim. The few empirical studies rarely rely on individual data and are biased in favour of Anglophone Africa. This paper looks at four Francophone countries, drawing on representative survey polls. Results reveal that ethnicity matters, but that its impact is generally rather weak and differs with regard to party systems and individual parties. ‘Ethnic parties’ in the strict sense are virtually absent. In particular, the voters’ location seems more important than ethnic affiliation. Other determinants such as regional ties, elite strategies, cross-cutting cleavages, and rational preferences deserve more attention in the future study of voting behaviour in Africa

Is digital cognitive behavioural therapy for insomnia effective in treating sub-threshold insomnia: A pilot RCT

Objective/Background: CBT for insomnia (CBT-I) is useful for many. It is currently unknown if those with sub-threshold insomnia also benefit. Here we assessed whether CBT-I is both feasible and acceptable in participants with sub-threshold insomnia. The primary aims were to evaluate participation rates and treatment acceptability, and to establish an effect size for symptom improvement. Patients/Methods: A total of 199 female participants (Mage 20 ± 5 years) took part. Following baseline assessments, participants were randomly allocated to either a 6-week digital CBT-I intervention or a 6-week session control group receiving puzzles. Additional assessments were performed 3-weeks, 6-weeks, and 6-months later. Results: Participation in each survey wave did not differ between the groups (ps > .140), though adherence to weekly tasks was lower in the CBT-I group, p = .02. Treatment acceptability was high (M (SD) = 33.61 (4.82), range 6 – 42). The CBT-I group showed greater improvement in insomnia symptoms at the end of the intervention compared to the control group (p = .013, d = 0.42), with significant variation in outcome (M = 4.69, SD = 5.41). Sub-threshold participants showed a similar pattern of results, whilst those meeting insomnia criteria showed a smaller between-group difference. CBT-I led to improvements in anxiety, paranoia and perceived stress between baseline and end of intervention. Changes in insomnia symptoms were mediated by cognitions about sleep and somatic pre-sleep arousal. Conclusions: CBT-I provides a benefit even in sub-threshold insomnia. CBT-I may be useful as an early preventative intervention to tackle sleep problems before they manifest as chronic insomnia