A review on the size-dependent bulking, vibration and, wave propagation of nanostructures.

Size effect is a typical characteristic of micro-/nano-materials, which can contribute to a variety of size-dependent behaviors, phenomena, and properties, such as stiffness softening, deformation springback, etc. The intrinsic causes of size effects are micro-structural properties of materials, and the sensitivity of microstructural properties of materials is closely related to the smallest structural unit of the crystal, crystal defects and geometric dimensions, and is heavily influenced by the material's field conditions. The modeling method based on non-local theory and gradient theory in the model is not only consistent with experimental and molecular dynamics simulation results, but also provides a solid explanation for the size effect underlying 'softening' and 'hardening' behaviors. Taking this as a basic point, this paper further considers the real working environment of materials, and systematically reviews the static and dynamic mechanical behavior cases of various nano-structures, mainly involving bulking, vibration and wave propagation of micro-beams and plates under different theories. A description and discussion of the differences in mechanical properties resulting from size effects under various theoretical frameworks and three key bottleneck problems are provided: the selection of kernel functions, the determination of size parameters, and the physical meaning of boundary conditions at higher orders. A summary is provided of the possible avenues and potentials for size effect models in future research. Many studies have shown that size parameters have a significant impact on the mechanical behavior of micro-/nano-structures, and these effects will increase as the size of the structure decreases. Nevertheless, different theories have varying scopes of application and size effects, and further research is needed to develop a unified size-dependent theory with universal applicability. A major focus of this paper is on the size effect of micro-/nano-structures, as well as provides the necessary data support to resolve the bottleneck problem associated with the size effect in the processing and manufacturing industries, and realizes the design and optimization of micro-scale parts based on their size.

Effects of Moderate-to-Vigorous Acute Exercise on Conscious Perception and Visual Awareness.

Background: the effect of acute exercise on cognition covers almost all stages of information processing, but few studies have focused on visual awareness. Reports on the appearance of faint speed-changes in the perception of stimuli were used as an index for visual awareness. Visual awareness was assessed after exercise or rest. Aside from the detection of speed-changes, speed-change discrimination was added as an index of perception. Results: the results showed that reports on the appearance of faint speed-changes were affected by acute aerobic exercise. The d' index was higher after exercise. The hit rate for speed-change detection was marginally significantly higher after exercise than after the sedentary test condition. Analysis of the results obtained for the discrimination task showed that discrimination speed was boosted only when subjects were aware of the speed-change. Importantly, neither false alarm rate nor response bias was affected by exercise. Conclusions: acute moderate- to vigorous-intensity aerobic exercise improved subjects' awareness of speed changes. In addition, there was a perceptual advantage due to exercise.

Use of fNIRS to Characterize the Neural Mechanism of Inter-Individual Rhythmic Movement Coordination.

Background: Inter-individual rhythmic movement coordination plays an important role in daily life, particularly in competitive sports. Behaviorally, it is more challenging to coordinate alternating movements than symmetrical movements. The neural activity underlying these different movement coordination modes remains to be clarified, particularly considering complex inter-individual coordination differences. Methods: To further test the neural basis of inter-individual rhythmic movement coordination, a revised experimental paradigm of inter-individual coordination was adopted. Participants were asked to perform symmetric, alternate, or single movements (swinging the lower part of the leg) in the same rhythm. A multi-channel, continuous wave, functional near-infrared spectral (fNIRS) imaging instrument was used to monitor hemodynamic activity while 40 volunteers (9 male pairs and 11 female pairs) performed the task. Multivariate analyses of variance were conducted to compare mean oxy-hemoglobin concentration ([HbO]) across experimental conditions. Results: A significant three-way interaction (leg-swing condition × ROI × laterality) on mean [HbO] was observed. Post hoc analysis revealed a significant main effect of leg-swing condition only in brain regions of interest [right inferior parietal lobule (IPL)] contralateral to movement execution. Activation in brain regions of interest [right inferior parietal lobule (IPL)] was much stronger in alternate mode compared with symmetric or single modes, and the differences between symmetric and single mode were not statistically significant. This result suggests that the alternate mode of movement coordination was more likely to be supported by the IPL region than the other modes. Conclusion: The present findings provide neural evidence relevant to the theory of self-organization of movement coordination, in which an alternating movement mode appeared to be a more demanding condition than symmetrical movement.

The Relationship between Biological Motion-Based Visual Consciousness and Attention: An Electroencephalograph Study.

Understanding and predicting the intentions of others through limb movements are vital to social interaction. The processing of biological motion is unique from the processing of motion of inanimate objects. Presently, there is controversy over whether visual consciousness of biological motion is regulated by visual attention. In addition, the neural mechanisms involved in biological motion-related visual awareness are not known. In the current study, the relationship between visual awareness (aware vs unaware), represented by a point-light walker and biological-motion-based attention, manipulated by a difference in congruence (congruent, incongruent) between the direction of a pre-cue and that of biological motion was explored. The neural mechanisms involved in processing the stimuli were explored through electroencephalography. Both early (50-150 ms, 100-200 ms, and 174-226 ms after target presentation) and late (350-550 ms after target presentation) awareness-related neural processings were observed during a biological motion-based congruency task. Early processing was localized to occipital-parietal regions, such as the left postcentral gyrus, the left middle occipital gyrus, and the right precentral gyrus. In the 174-226-ms window, the activity in the occipital region was gradually replaced by activity in the parietal and frontal regions. Late processing was localized to frontal-parietal regions, such as the right dorsal superior frontal gyrus, the left medial superior frontal gyrus, and the occipito-temporal regions. Congruency-related processing occurred in the 246-260-ms window and was localized to the right superior occipital gyrus. In summary, due to its complexity, biological motion awareness has a unique neural basis.

Selective Effects of Postural Control on Spatial vs. Nonspatial Working Memory: A Functional Near-Infrared Spectral Imaging Study.

Background: Previous evidence suggests that postural control processing may be more related to spatial working memory (SWM) than to nonspatial working memory (NWM). Methodological discrepancies between spatial and nonspatial cognitive tasks have made direct comparisons between the two systems difficult. Methods: To explore the neural mechanisms of SWM and NWM relative to that of postural control, participants were subjected a cognitive-posture dual-task paradigm, consisting of a 3-back letter working memory (WM) task, using physically identical stimuli with spatial and nonspatial components memorized in different sessions, and a standing balance task with a tandem stance. Additionally, there were two control sessions: a single-postural control session wherein participants pressed mouse buttons at random while standing; and a single-cognitive task control session wherein subjects completed a WM task while seated. The subjects underwent functional near-infrared spectral imaging (fNIRS) during task performance, wherein oxygenated hemoglobin concentration ([HbO]) was measured in frontal and parietal regions. Results: Postural control reduced discernment in the SWM task significantly, but did not affect NWM task performance. fNIRS showed that postural control had a significant tendency to decrease the [HbO] in the frontal-parietal network of the left hemisphere when participants completed the SWM task. No posture-associated differences in [HbO] were observed in NWM-related areas during NWM task performance. Behavioral and fNIRS data demonstrated that postural control had a selective interaction with SWM. Specifically, postural control reduced SWM discrimination and SWM-related brain activity (frontal-parietal network), but not NWM discrimination or NWM-related brain activity. Furthermore, the multiple linear regression analysis showed that SWM, but not NWM, was an important predictor of postural control. These results suggest that postural control may share more cognitive resources with SWM than with NWM.

Dissociable Electroencephalograph Correlates of Visual Awareness and Feature-Based Attention.

Background: The relationship between awareness and attention is complex and controversial. A growing body of literature has shown that the neural bases of consciousness and endogenous attention (voluntary attention) are independent. The important role of exogenous attention (reflexive attention) on conscious experience has been noted in several studies. However, exogenous attention can also modulate subliminal processing, suggesting independence between the two processes. The question of whether visual awareness and exogenous attention rely on independent mechanisms under certain circumstances remains unanswered. Methods: In the current study, electroencephalograph recordings were conducted using 64 channels from 16 subjects while subjects attempted to detect faint speed changes of colored rotating dots. Awareness and attention were manipulated throughout trials in order to test whether exogenous attention and visual awareness rely on independent mechanisms. Results: Neural activity related to consciousness was recorded in the following cue-locked time-windows (event related potential, cluster- based permutation test): 0-50, 150-200, and 750-800 ms. With a more liberal threshold, the inferior occipital lobe was found to be the source of awareness-related activity in the 0-50 ms range. In the later 150-200 ms range, activity in the fusiform and post-central gyrus was related to awareness. Awareness-related activation in the later 750-800 ms range was more widely distributed. This awareness-related activation pattern was quite different from that of attention. Attention-related neural activity was emphasized in the 750-800 ms time window and the main source of attention-related activity was localized to the right angular gyrus. These results suggest that exogenous attention and visual consciousness correspond to different and relatively independent neural mechanisms and are distinct processes under certain conditions.