Influence of surface roughness on the color of dental-resin composites

This study deals with the influence of surface roughness on the color of resin composites. Ten resin composites (microfilled, hybrid, and microhybrid) were each polished with 500-grit, 1 200-grit, 2 000-grit, and 4 000-grit SiC papers. The roughness parameter (R _a) was measured using a Plμ confocal microscope, and field-emission scanning electron microscope (Fe-SEM) images were used to investigate filler morphology. Color was measured using a spectroradiometer and a D65 standard illuminant (geometry diffuse/0° specular component excluded (SCE) mode). Surface roughness decreased with grit number and was not influenced by filler size or size distribution. A significant influence of R _a on lightness (L*) was found. Lightness increased with decreases in roughness, except for specimens that underwent polishing procedure 4 (PP4; 500-grit, 1 200-grit, 2 000-grit, and 4 000-grit SiC papers consecutively). Generally, it was found that surface roughness influenced the color of resin composites. The composites that underwent PP1 (500-grit SiC paper) exhibited significant differences in chroma (C*), hue (h°), and lightness (L*) compared to composites that underwent PP3 (500-grit, 1 200-grit, and 2 000-grit SiC papers consecutively) and PP4. Color difference (ΔE*) between the polishing procedures was within acceptability thresholds in dentistry.     

The relationship between homework and the academic progress of children in Spain during compulsory elementary education: A twin fixed-effects approach

Homework has traditionally been considered positive for students’ academic achievement, to the extent that it makes children more responsible while learning. Nevertheless, making students do a large amount of homework has been one of the most criticised practices in recent years. Parental associations have long held the view that Spanish elementary school pupils spend too much time on homework. This situation is so alarming that it has recently caused a ‘homework strike’, which has been supported by many children's parents. Furthermore, being assigned an excessive amount of homework is a serious problem which extends well beyond Spain. In light of this context, this article aims to provide new evidence on the relationship between homework and academic performance. To carry out this research, rich longitudinal census data, together with a twin fixed-effects approach and value-added models, have been used. In this way, we can control for variables that are the same within twins, allowing us to generate a better understanding of the association between homework time and primary children's academic achievement. Our main finding is that homework is not associated with young people's academic achievement (at least within this specific country context).     

Positive Aging Beyond “Success”: Towards a More Inclusive Perspective of High Level Functioning in Old Age

Successful aging is the ability to maintain low probability of disease and disability, high cognitive and physical functioning, and active engagement with life (Rowe &; Kahn, 1999 Rowe, J. W. &; Kahn, R. L. (1999). Successful aging. New York, NY: Dell Pub. [Google Scholar]). These criteria allow for a minority of people to be classified as being “successful” and overlook the importance of psychological variables in balancing the weight of disease. A total of 1322 seniors (55 + years) were classified on their overall functioning according to core domains (health, psychological, cognitive, biobehavioural, social, personality). Findings support the idea that a broader perspective of aging outcomes, rather than success criteria, may better reflect reality.     

The indigenous worldview of Yupiaq culture: Its scientific nature and relevance to the practice and teaching of science

Is science an invention of European thought, or have legitimate scientific bodies of knowledge and scientific ways of thinking emerged separately in other cultures? Can indigenous knowledge systems contribute to contemporary science teaching? Here we describe evidence from the Yupiaq culture in southwestern Alaska which demonstrates a body of scientific knowledge and epistemology that differs from that of Western science. We contend that drawing from Yupiaq culture, knowledge, and epistemology can provide not only a more culturally relevant frame of reference for teaching science concepts to Yupiaq students, but also a potentially valuable context for more effectively addressing many of the recommendations of U.S. science education reform initiatives. © 1998 John Wiley & Sons, Inc. J Res Sci Teach 35: 133–144, 1998.     

Activity optimization method in SPECT： A comparison with ROC analysisActivity optimization method in SPECT： A comparison with ROC analysis

A discriminant method for optimizing activity in nuclear medicine studies is validated by comparison with ROC （received operating characteristic）-curves. The method is tested in 21 single photon emission computerized tomography （SPECT）, performed with a cardiac phantom. Three different lesions （Lb L2 and L3） were placed in the myocardium-wall by pairs fbr each SPECT. Three activities （84, 37 or 18.5 MBq） of 99mTc were used as background. Linear discriminant analysis was used to select the parameters that characterize image quality among the measured variables in the images [（Background-to-Lesion （B/Li） and Signal-to-Noise （S/N） ratios）]. Two clusters with different image quality （P=0.021 ） were obtained. The ratios B/Lj, B/L2 and B/L3 are the parameters used to construct the function with 100% of cases correctly classified into the clusters. The value of 37 MBq was the lowest tested activity for which good results for the B/Li ratios were obtained. The result coincides with the applied ROC-analysis （r=0.89）.     

Real time observer and control scheme for a wind turbine system based on a high order sliding modes

The introduction of advanced control algorithms may improve considerably the efficiency of wind turbine systems. This work proposes a high order sliding mode (HOSM) control scheme based on the super twisting algorithm for regulating the wind turbine speed in order to obtain the maximum power from the wind. A robust aerodynamic torque observer, also based on the super twisting algorithm, is included in the control scheme in order to avoid the use of wind speed sensors. The presented robust control scheme ensures good performance under system uncertainties avoiding the chattering problem, which may appear in traditional sliding mode control schemes. The stability analysis of the proposed HOSM observer is provided by means of the Lyapunov stability theory. Experimental results show that the proposed control scheme, based on HOSM controller and observer, provides good performance and that this scheme is robust with respect to system uncertainties and external disturbances.     

High-gain fractional disturbance observer control of uncertain dynamical systems

Disturbance observer-based control allows to compensate unknown inputs, however, in most cases, requiring their integer-order differentiability. In this paper, a novel disturbance observer-based state feedback controller is proposed to compensate a more general class of fractional-, but not necessarily integer-order, differentiable unknown inputs. The proposed fractional PI-like structure yields precise conditions for feedback gain tuning. Remarkably, the resulting controller rejects non-differentiable disturbances with a smooth controller, guaranteeing robustness, an outstanding features for tracking tasks, under a prescribed practical stability regimen. A comparison to a fractional sliding mode observer is conducted via simulations to highlight the reliability of the proposed scheme.