WC-CoCr coatings on cast iron discs were prepared with different surface roughness and submitted to dry sliding wear tests against a commercial friction material using a pin-on-disc configuration. ...The effect of roughness on the friction and wear of the tribological system was evaluated. The pin wear rate increases with the coating roughness and becomes very high for an arithmetic average roughness, Ra, in excess of 1 μm. In contrast, the friction coefficient was found to increase as roughness decreased. The discs wear was anyway negligible. The experimental results were explained considering the characteristics of the friction layer that forms during sliding at the interface of the mating bodies in dependence of the initial roughness of the coatings. It is shown that the friction layer plays an important role in determining the relative contribution of the abrasive and adhesive interactions and, thereby, the resulting friction and wear behavior of the tribological system.
•Using the as-sprayed coated disc, wear is extremely severe and friction is low.•Decreasing surface roughness, wear decreases and friction increases.•The friction layer is mainly made by particles originating from the friction material.•Decreasing the surface roughness, W in the friction layer also increases.
The tribological behavior of a commercial semi-metallic friction material dry sliding against an uncoated cast iron disc and HVOF coated discs at room temperature and at 300 °C has been investigated. ...Two types of coatings were investigated, based on Cr3C2-NiCr and WC-CoCr systems. The tests were carried out using a pin-on-disc apparatus. The characteristics of the friction layer that forms on the worn surfaces of the friction material (the pin) and on the counterface disc were analyzed and correlated with the friction and wear behavior of the couplings. At room temperature, quite a long initial stage was observed, required to form a compact friction layer and to achieve a constant average friction coefficient. At 300 °C, steady-state conditions are attained almost from the beginning of the test. The wear rates of the friction materials are mild at room temperature and close to severe at 300 °C because of the thermal softening of the friction material. The wear rates of the coated discs are always negligible, since the contact temperature is not sufficiently high to induce a softening or an oxidative damage of the coatings. Although referring to rather simplified testing conditions, the results obtained in this study provide useful indications on the possibility of using HVOF coatings in braking systems to reduce not only their wear but also, most importantly, the release of particulate matter in the environment.
•Wear of coated discs is always negligible.•Wear of pins is mild at RT and increases very much at 300 °C.•At 300 °C, the formation of a wide and thick friction layer is observed.•At 300 °C, steady-state conditions for friction and wear were reached soon.
•We investigated whether dynamic visual cues modifies the perceived visual vertical.•Parabolic motions implying Gravity vector orientations affected the perceived visual vertical.•The ability to ...estimate time-to-contact in an interception task was influenced by motion orientation.•These effect changed with the body tilt of the participant.
Observers typically present a strong bias in estimating the orientation of a visual bar when their body is tilted >60° in the roll plane and in the absence of visual background information. Known as the A-effect, this phenomenon likely results from the under-compensation of body tilt. Static visual cues can reduce such bias in the perceived vertical. Yet, it is unknown whether dynamic visual cues would be also effective. Here we presented projectile motions of a visual target along parabolic trajectories with different orientations relative to physical gravity. The aim of the experiment was twofold: First, we assessed whether the projectile motions could bias the estimation of the perceived orientation of a visual bar, measured with a classical subjective visual vertical (SVV) task. Second, we evaluated whether the ability to estimate time-to-contact of the visual target in an interception task was influenced by the orientation of these parabolic trajectories. Two groups of participants performed the experiment, either with their head and body tilted 90° along the roll plane or in an upright position. We found that the perceived orientation of the visual bar in the SVV task was affected by the orientation of the parabolic trajectories. This result was present in the tilted but not in the upright participants. In the interception task, the timing error increased linearly as a function of the orientation of the parabola. These results support the hypothesis that a gravity vector estimated from dynamic visual stimuli contributes to the subjective visual vertical.
In psychophysics, researchers usually apply a two-level model for the analysis of the behavior of the single subject and the population. This classical model has two main disadvantages. First, the ...second level of the analysis discards information on trial repetitions and subject-specific variability. Second, the model does not easily allow assessing the goodness of fit. As an alternative to this classical approach, here we propose the Generalized Linear Mixed Model (GLMM). The GLMM separately estimates the variability of fixed and random effects, it has a higher statistical power, and it allows an easier assessment of the goodness of fit compared with the classical two-level model. GLMMs have been frequently used in many disciplines since the 1990s; however, they have been rarely applied in psychophysics. Furthermore, to our knowledge, the issue of estimating the point-of-subjective-equivalence (PSE) within the GLMM framework has never been addressed. Therefore the article has two purposes: It provides a brief introduction to the usage of the GLMM in psychophysics, and it evaluates two different methods to estimate the PSE and its variability within the GLMM framework. We compare the performance of the GLMM and the classical two-level model on published experimental data and simulated data. We report that the estimated values of the parameters were similar between the two models and Type I errors were below the confidence level in both models. However, the GLMM has a higher statistical power than the two-level model. Moreover, one can easily compare the fit of different GLMMs according to different criteria. In conclusion, we argue that the GLMM can be a useful method in psychophysics.
Besides providing information on elementary properties of objects, like texture, roughness, and softness, the sense of touch is also important in building a representation of object movement and the ...movement of our hands. Neural and behavioral studies shed light on the mechanisms and limits of our sense of touch in the perception of texture and motion, and of its role in the control of movement of our hands. The interplay between the geometrical and mechanical properties of the touched objects, such as shape and texture, the movement of the hand exploring the object, and the motion felt by touch, will be discussed in this article. Interestingly, the interaction between motion and textures can generate perceptual illusions in touch. For example, the orientation and the spacing of the texture elements on a static surface induces the illusion of surface motion when we move our hand on it or can elicit the perception of a curved trajectory during sliding, straight hand movements. In this work we present a multiperspective view that encompasses both the perceptual and the motor aspects, as well as the response of peripheral and central nerve structures, to analyze and better understand the complex mechanisms underpinning the tactile representation of texture and motion. Such a better understanding of the spatiotemporal features of the tactile stimulus can reveal novel transdisciplinary applications in neuroscience and haptics.
Metabolic dysfunction-associated fatty liver disease (MAFLD) represents a new inclusive definition of the whole spectrum of liver diseases associated to metabolic disorders. The main objective of ...this study was to compare patients with MAFLD and non-MAFLD with hepatocellular carcinoma (HCC) included in a nationally representative cohort.
We analysed 6882 consecutive patients with HCC enrolled from 2002 to 2019 by 23 Italian Liver Cancer centres to compare epidemiological and future trends in three subgroups: pure, single aetiology MAFLD (S-MAFLD); mixed aetiology MAFLD (metabolic and others, M-MAFLD); and non-MAFLD HCC.
MAFLD was diagnosed in the majority of patients with HCC (68.4%). The proportion of both total MAFLD and S-MAFLD HCC significantly increased over time (from 50.4% and 3.6% in 2002-2003, to 77.3% and 28.9% in 2018-2019, respectively, p<0.001). In Italy S-MAFLD HCC is expected to overcome M-MAFLD HCC in about 6 years. Patients with S-MAFLD HCC were older, more frequently men and less frequently cirrhotic with clinically relevant portal hypertension and a surveillance-related diagnosis. They had more frequently large tumours and extrahepatic metastases. After weighting, and compared with patients with non-MAFLD, S-MAFLD and M-MAFLD HCC showed a significantly lower overall (p=0.026, p=0.004) and HCC-related (p<0.001, for both) risk of death. Patients with S-MAFLD HCC showed a significantly higher risk of non-HCC-related death (p=0.006).
The prevalence of MAFLD HCC in Italy is rapidly increasing to cover the majority of patients with HCC. Despite a less favourable cancer stage at diagnosis, patients with MAFLD HCC have a lower risk of HCC-related death, suggesting reduced cancer aggressiveness.
In the previous work, we reported that tactile information (tactile slip) during finger sliding and reaching actions over a textured surface contributes to the control of the hand movement. More ...specifically, we observed a significant bias in the motion trajectories, which was explained by the tactile estimate accounted by the tactile flow model-i.e. a perceived motion direction always perpendicular to the ridge orientation, and its integration with the muscular-skeletal proprioceptive cues. However, to which extent this observed behavior also depends on the reaction force exerted by the surface ridges on the finger pad during the dynamic interaction still represents a largely unexplored research question. If not properly addressed, this point could rise the alternative explanation that the systematic bias is determined by the insufficient compensation of the reaction force by participants. In this article, we investigate the role of the lateral component of the reaction force on the surface plane ( lateral force ) in texture-related motion bias. We asked participants to slide their finger straight on a lubricated ridged plate towards a target goal displayed in a virtual reality environment. They exerted two different levels of normal force, which produced two different levels of lateral force during the finger interaction with the ridges. The effect of ridge orientation was found to be larger for the high compared to the low force level. However, also in the latter case, we still observed the same biased trajectories reported in our previous work, despite the negligible value of the lateral force. This supports our hypothesis that the motor bias arises from the integration of the tactile motion estimate, biased by the texture, and the other proprioceptive cues.
Whenever we move the hand across a surface, tactile signals provide information about the relative velocity between the skin and the surface. If the system were able to integrate the tactile velocity ...information over time, cutaneous touch may provide an estimate of the relative displacement between the hand and the surface. Here, we asked whether humans are able to form a reliable representation of the motion path from tactile cues only, integrating motion information over time. In order to address this issue, we conducted three experiments using tactile motion and asked participants (1) to estimate the length of a simulated triangle, (2) to reproduce the shape of a simulated triangular path, and (3) to estimate the angle between two-line segments. Participants were able to accurately indicate the length of the path, whereas the perceived direction was affected by a direction bias (inward bias). The response pattern was thus qualitatively similar to the ones reported in classical path integration studies involving locomotion. However, we explain the directional biases as the result of a tactile motion aftereffect.
In contrast with the anisotropies in spatial and motion vision, anisotropies in the perception of motion duration have not been investigated to our knowledge. Here, we addressed this issue by asking ...observers to judge the duration of motion of a target accelerating over a fixed length path in one of different directions. Observers watched either a pictorial or a quasi-blank scene, while being upright or tilted by 45° relative to the monitor and Earth's gravity. Finally, observers were upright and we tilted the scene by 45°. We found systematic anisotropies in the precision of the responses, the performance being better for downward motion than for upward motion relative to the scene both when the observer and the scene were upright and when either the observer or the scene were tilted by 45°, although tilting decreased the size of the effect. We argue that implicit knowledge about gravity force is incorporated in the neural mechanisms computing elapsed time. Furthermore, the results suggest that the effects of a virtual gravity can be represented with respect to a vertical direction concordant with the visual scene orientation and discordant with the direction of Earth's gravity.
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