Numerical and Experimental Investigation of Residual Stress and Bond Strength in Friction Surface Cladding Process

The bond strength is an essential property of cladded products, which are produced by deposition processes such as friction surface cladding (FSC). Friction and severe plastic deformation of the deposited material cause the process to take place at elevated temperatures, and inhomogeneous cooling after the deposition process can lead to the formation of residual stresses that influence the remaining bond strength. A novel simulation method for the evaluation of the residual stress distribution in clad layer and substrate after the cladding of AA6060 onto an AA2024 substrate is proposed in this study. The effect of residual stresses on the bond strength was correlated with data gathered from 3-point bending tests aimed at the determination of the mechanical properties at the clad layer–substrate interface. The results show that on the one side, the occurrence of a higher compressive residual stress magnitude increases the bond strength, but on the other side, this relationship is not always true for average tool temperature, tool rotating speed, normal force, and tool tilt angle. Therefore, it is necessary to investigate the effect of average tool temperature, tool rotating speed, normal force, and tool tilt angle parameters on the residual stress to find the best process window for carrying out the process to have optimal bond strength.</p

Space environmental effects on polymer composites: Research needs and opportunities

The long-term performance of polymer-based composites in the space environment is discussed. Both thermoset and thermoplastic matrix composites are included in this discussion. Previous efforts on the space environmental effects on composites are briefly reviewed. Focus of this review is placed on the effects of hygrothermal stresses, atomic oxygen, ultraviolet (UV), and space debris/micrometeoroid impacts along with the potential synergism. Potential approaches to estimating the residual strength of polymer composites after exposure to atomic oxygen erosion or space debris/micrometeoroid impact are evaluated. New ground-based data are then utilized to illustrate the effects of atomic oxygen and thermal cycling on the failure behavior of polymer composites. Finally, research needs, challenges, and opportunities in the field of space environmental effects on composite materials are highlighted

Effective connectivity reveals strategy differences in an expert calculator

Mathematical reasoning is a core component of cognition and the study of experts defines the upper limits of human cognitive abilities, which is why we are fascinated by peak performers, such as chess masters and mental calculators. Here, we investigated the neural bases of calendrical skills, i.e. the ability to rapidly identify the weekday of a particular date, in a gifted mental calculator who does not fall in the autistic spectrum, using functional MRI. Graph-based mapping of effective connectivity, but not univariate analysis, revealed distinct anatomical location of “cortical hubs” supporting the processing of well-practiced close dates and less-practiced remote dates: the former engaged predominantly occipital and medial temporal areas, whereas the latter were associated mainly with prefrontal, orbitofrontal and anterior cingulate connectivity. These results point to the effect of extensive practice on the development of expertise and long term working memory, and demonstrate the role of frontal networks in supporting performance on less practiced calculations, which incur additional processing demands. Through the example of calendrical skills, our results demonstrate that the ability to perform complex calculations is initially supported by extensive attentional and strategic resources, which, as expertise develops, are gradually replaced by access to long term working memory for familiar material

Analytical, numerical, and experimental investigation of a Luneburg lens system for directional cloaking

In this study, the design of a directional cloaking based on the Luneburg lens system is proposed and its operating principle is experimentally verified. The cloaking concept is analytically investigated via geometrical optics and numerically realized with the help of the finite-difference time-domain method. In order to benefit from its unique focusing and/or collimating characteristics of light, the Luneburg lens is used. We show that by the proper combination of Luneburg lenses in an array form, incident light bypasses the region between junctions of the lenses, i.e., the "dark zone." Hence, direct interaction of an object with propagating light is prevented if one places the object to be cloaked inside that dark zone. This effect is used for hiding an object which is made of a perfectly electric conductor material. In order to design an implementable cloaking device, the Luneburg lens is discretized into a photonic crystal structure having gradually varying air cylindrical holes in a dielectric material by using Maxwell Garnett effective medium approximations. Experimental verifications of the designed cloaking structure are performed at microwave frequencies of around 8 GHz. The proposed structure is fabricated by three-dimensional printing of dielectric polylactide material and a brass metallic alloy is utilized in place of the perfectly electric conductor material in microwave experiments. Good agreement between numerical and experimental results is found. © 2019 American Physical Society

Topological mirror symmetry with fluxes

Motivated by SU(3) structure compactifications, we show explicitly how to construct half--flat topological mirrors to Calabi--Yau manifolds with NS fluxes. Units of flux are exchanged with torsion factors in the cohomology of the mirror; this is the topological complement of previous differential--geometric mirror rules. The construction modifies explicit SYZ fibrations for compact Calabi--Yaus. The results are of independent interest for SU(3) compactifications. For example one can exhibit explicitly which massive forms should be used for Kaluza--Klein reduction, proving previous conjectures. Formality shows that these forms carry no topological information; this is also confirmed by infrared limits and old classification theorems.Comment: 35 pages, 5 figure

Very frequent physical aggression and vocalizations in nursing home residents with dementia

Objectives: We investigated the 2-week prevalence and correlates of very frequent physical aggression (PA) and vocalizations in nursing home (NH)-residents with dementia. Method/Design: This cross-sectional study used combined data of 2074 NH-residents from four studies, collected from 119 dementia special care units in 26 Dutch NH. Very frequent PA was defined as scoring 6 or 7 on the items ‘hitting’, pushing’, ‘biting’ and ‘kicking’ of the Cohen Mansfield Agitation Inventory; very frequent vocalizations as scoring 6 or 7 on ‘screaming’ and ‘making strange noises’. We compared NH-residents with very frequent PA or vocalizations with residents with less frequent PA or vocalizations, assessing correlates using univariate and multivariate multilevel logistic regression analyses. Results: We found a 2-week prevalence of 2.2% (95% confidence interval (CI): 1.63–2.89) of very frequent PA and 11.5% of very frequent vocalizations (95% CI: 10.23–12.98). Very frequent PA was only associated with apathy (odds ratio (OR)=1.93, 95% CI: 1.04–3.61). Correlates of very frequent vocalizations were age (OR = 0.97, 95% CI: 0.951–0.998), dementia severity (overall p-value 0.020), antipsychotic drug use (OR = 1.56, 95% CI: 1.08–2.26), antiepileptic drug use (OR = 2.75, 95% CI: 1.34–5.68) and euphoria (OR = 2.01, 95% CI: 1.22–3.31). Conclusion: Characteristics of NH-residents with very frequent PA or very frequent vocalizations differ from those of NH-residents with less frequent PA or vocalizations. Frontal lobe damage, boredom, pain and/or external factors may explain several of the found associations, but further research is necessary. Our findings may contribute to better care for these residents and thereby to improving their quality of life

The value of reasons for encounter in early detection of colorectal cancer

BACKGROUND: Symptoms with a high predictive power for colorectal cancer (CRC) do not exist. OBJECTIVE: To explore the predictive value of patients' reason for encounter (RFE) in the two years prior to the diagnosis of CRC. METHODS: A retrospective nested case-control study using prospectively collected data from electronic records in general practice over 20 years. Matching was done based on age (within two years), gender and practice. The positive likelihood ratios (LR+) and odds ratios (OR) were calculated for RFE between cases and controls in the two years before the index date. RESULTS: We identified 184 CRC cases and matched 366 controls. Six RFEs had significant LR + and ORs for CRC, which may have high predictive power. These RFEs are part of four chapters in the International Classification of Primary Care (ICPC) that include tiredness (significant at 3-6 months prior to the diagnosis; LR+ 2.6 and OR 3.07; and from 0 to 3 months prior to the diagnosis; LR+ 2.0 and OR 2.36), anaemia (significant at three months before diagnosis; LR+ 9.8 and OR 16.54), abdominal pain, rectal bleeding and constipation (significant at 3-6 months before diagnosis; LR+ 3.0 and OR 3.33; 3 months prior to the diagnosis LR+ 8.0 and OR 18.10) and weight loss (significant at three months before diagnosis; LR+ 14.9 and OR 14.53). CONCLUSION: Data capture and organization in ICPC permits study of the predictive value of RFE for CRC in primary care

A Smooth Interface Method for Simulating Liquid Crystal Colloid Dispersions

A new method is presented for mesoscopic simulations of particle dispersions in liquid crystal solvents. It allows efficient first-principle simulations of the dispersions involving many particles with many-body interactions mediated by the solvents. Demonstrations have been performed for the aggregation of colloid dispersions in two-dimensional nematic and smectic-C* solvents neglecting hydrodynamic effects, which will be taken into account in the near future.Comment: 13 pages, 4 figure