Additive manufacturing of metal-bonded grinding tools

Grinding tools with superabrasive grains can be manufactured from different bond materials. In several industrial applications, metallic bond systems are used. In general, these show good grain retention and offer a high thermal conductivity, when compared to the other widely used bond types such as vitrified and resin bonds. One drawback of the metallic bond is the lack of pores in the grinding layer. This is caused by the manufacturing processes that are typically used, like brazing or hot pressing. These generally produce very dense layers. The high density and low porosity lead to comparatively little space for the transport of lubricant, coolant, and chips. One approach to eliminate this disadvantage is to introduce cavities into the grinding layer, using the laser powder bed fusion technique (LPBF). In order to evaluate the general suitability of LPBF in combination with the bond material and diamond grains, grinding layer samples with a nickel-titanium bond were produced. The abrasive behavior of these samples was tested in scratch tests on cemented carbide to verify the applicability as grinding tools. While the diamond grains in the powder mixture are not part of the fusion process, they also did not interfere with the manufacturing process, and the scratch tests showed promising abrasive capabilities. The grinding layer itself withstood the process forces, and no grain breakout could be observed. This indicates that the grain retention forces are high enough for the grinding process and that NiTi has a high potential as a bonding material for the manufacturing of grinding tools via LPBF

Assessing measurement equivalence of the Danish and Dutch Four-Dimensional Symptom Questionnaire using differential item and test functioning analysis

Aims: The Dutch Four-Dimensional Symptom Questionnaire (4DSQ) measures distress, depression, anxiety and somatisation, facilitating the distinction between stress-related problems and psychiatric disorder in primary and occupational health care. The aim of the study was to examine the measurement equivalence across the Danish and Dutch 4DSQ. Methods: Danish 4DSQ data were obtained from a cohort of Danish citizens on sick leave for mental-health problems. Dutch 4DSQ data were obtained from a cohort of Dutch employees on sick leave and a cohort of general practice attenders suspected of having mental-health problems. The study samples were matched on age and sex. The 4DSQ scales were assessed for essential unidimensionality using confirmatory factor analysis. Measurement equivalence of the 4DSQ across the groups was assessed using differential item and test functioning (DIF and DTF) analysis. Results: The study groups each consisted of 1363 people (63% female, Mage=42 years). The 4DSQ scales proved essentially unidimensional. DIF was detected in 20 items. In terms of Cohen’s effect size, DIF was mostly small or moderate. In terms of effect size, the mean effect on the scale score (DTF) was negligible. Nevertheless, it is recommended to adjust some of the cut-off points for two Danish 4DSQ scales to retain the meaning of these cut-off points in Dutch respondents. Conclusions: The Danish version of the 4DSQ measures the same constructs as the original Dutch questionnaire. Twenty items functioned differently in Danish respondents than in Dutch respondents, but this had only a small impact on the scale scores

Aerobic Exercise Improves Cognitive Functioning in People With Schizophrenia: A Systematic Review and Meta-Analysis

Cognitive deficits are pervasive among people with schizophrenia and treatment options are limited. There has been an increased interest in the neurocognitive benefits of exercise, but a comprehensive evaluation of studies to date is lacking. We therefore conducted a meta-analysis of all controlled trials investigating the cognitive outcomes of exercise interventions in schizophrenia. Studies were identified from a systematic search across major electronic databases from inception to April 2016. Meta-analyses were used to calculate pooled effect sizes (Hedges g) and 95% CIs. We identified 10 eligible trials with cognitive outcome data for 385 patients with schizophrenia. Exercise significantly improved global cognition (g = 0.33, 95% CI = 0.13-0.53, P = .001) with no statistical heterogeneity (I2 = 0%). The effect size in the 7 studies which were randomized controlled trials was g = 0.43 (P < .001). Meta-regression analyses indicated that greater amounts of exercise are associated with larger improvements in global cognition (β = .005, P = .065). Interventions which were supervised by physical activity professionals were also more effective (g = 0.47, P < .001). Exercise significantly improved the cognitive domains of working memory (g = 0.39, P = .024, N = 7, n = 282), social cognition (g = 0.71, P = .002, N = 3, n = 81), and attention/vigilance (g = 0.66, P = .005, N = 3, n = 104). Effects on processing speed, verbal memory, visual memory and reasoning and problem solving were not significant. This meta-analysis provides evidence that exercise can improve cognitive functioning among people with schizophrenia, particularly from interventions using higher dosages of exercise. Given the challenges in improving cognition, and the wider health benefits of exercise, a greater focus on providing supervised exercise to people with schizophrenia is needed