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1.
Cereb Cortex ; 33(5): 2260-2272, 2023 02 20.
Article in English | MEDLINE | ID: mdl-35641153

ABSTRACT

Attention and reading are essential skills for successful schooling and in adult life. While previous studies have documented that attention development supports reading acquisition, whether and how learning to read may improve attention among school-age children and the brain structural and functional development that may be involved remain unknown. In this prospective longitudinal study, we examined bidirectional and longitudinal predictions between attention and reading development and the neural mediators of attention and reading development among school-age children using cross-lagged panel modeling. The results showed that better baseline reading performance significantly predicted better attention performance one year later after controlling for baseline attention performance. In contrast, after controlling for baseline reading performance, attention did not significantly predict reading performance one year later, while more attention problems also significantly predicted worse reading performance. Both the increasing gray matter volume of the left middle frontal gyrus and the increasing connectivity between the left middle frontal gyrus and the ventral attention network mediated the above significant longitudinal predictions. This study, directly revealed that reading skills may predict the development of important cognitive functions, such as attention, in school-age children. Therefore, learning to read is not only a challenge for school-age children but is also an important way to optimize attention and brain development.


Subject(s)
Brain , Reading , Child , Adult , Humans , Longitudinal Studies , Prospective Studies , Frontal Lobe , Magnetic Resonance Imaging
2.
Cereb Cortex ; 33(9): 5251-5263, 2023 04 25.
Article in English | MEDLINE | ID: mdl-36320154

ABSTRACT

The default mode network (DMN) is a workspace for convergence of internal and external information. The frontal parietal network (FPN) is indispensable to executive functioning. Yet, how they interplay to support cognitive development remains elusive. Using longitudinal developmental fMRI with an n-back paradigm, we show a heterogeneity of maturational changes in multivoxel activity and network connectivity among DMN and FPN nodes in 528 children and 103 young adults. Compared with adults, children exhibited prominent longitudinal improvement but still inferior behavioral performance, which paired with less pronounced DMN deactivation and weaker FPN activation in children, but stronger DMN coupling with FPN regions. Children's DMN reached an adult-like level earlier than FPN at both multivoxel activity pattern and intranetwork connectivity levels. Intrinsic DMN-FPN internetwork coupling in children mediated the relationship between age and working memory-related functional coupling of these networks, with posterior cingulate cortex (PCC)-dorsolateral prefrontal cortex (DLPFC) coupling emerging as most prominent pathway. Coupling of PCC-DLPFC may further work together with task-invoked activity in PCC to account for longitudinal improvement in behavioral performance in children. Our findings suggest that the DMN provides a scaffolding effect in support of an immature FPN that is critical for the development of executive functions in children.


Subject(s)
Cognition , Default Mode Network , Young Adult , Child , Humans , Executive Function/physiology , Memory, Short-Term/physiology , Frontal Lobe , Magnetic Resonance Imaging , Brain Mapping , Brain/physiology , Nerve Net/physiology
3.
Cereb Cortex ; 32(5): 1024-1039, 2022 02 19.
Article in English | MEDLINE | ID: mdl-34378030

ABSTRACT

Functional brain networks require dynamic reconfiguration to support flexible cognitive function. However, the developmental principles shaping brain network dynamics remain poorly understood. Here, we report the longitudinal development of large-scale brain network dynamics during childhood and adolescence, and its connection with gene expression profiles. Using a multilayer network model, we show the temporally varying modular architecture of child brain networks, with higher network switching primarily in the association cortex and lower switching in the primary regions. This topographical profile exhibits progressive maturation, which manifests as reduced modular dynamics, particularly in the transmodal (e.g., default-mode and frontoparietal) and sensorimotor regions. These developmental refinements mediate age-related enhancements of global network segregation and are linked with the expression profiles of genes associated with the enrichment of ion transport and nucleobase-containing compound transport. These results highlight a progressive stabilization of brain dynamics, which expand our understanding of the neural mechanisms that underlie cognitive development.


Subject(s)
Brain , Magnetic Resonance Imaging , Adolescent , Brain Mapping , Cerebral Cortex , Child , Cognition , Humans , Magnetic Resonance Imaging/methods , Neural Pathways
4.
J Am Chem Soc ; 142(51): 21522-21529, 2020 12 23.
Article in English | MEDLINE | ID: mdl-33301680

ABSTRACT

Adhesive materials that are resistant to low temperatures have wide applications in daily life, scientific research, and industry. Currently, the overwhelming majority of low-temperature-resistant adhesives are traditional polymer systems. In this study, a new strategy was developed to obtain strong and long-lasting adhesion effects from low-molecular-weight adhesives at low temperatures. The introduction of water molecules and the formation of hydrogen bonds not only triggered supramolecular polymerization but also endowed the water-involved copolymer with low-temperature resistance. The water content of the polymeric supramolecular system played a crucial role in exhibiting adhesion behavior at low temperatures. Good adhesion performance was obtained in extremely low-temperature environments, including liquid nitrogen.

5.
J Am Chem Soc ; 142(11): 5371-5379, 2020 03 18.
Article in English | MEDLINE | ID: mdl-32092262

ABSTRACT

Modern functional adhesives have attracted considerable attention due to their reversible adhesion capacities and stimuli-responsive adhesion behavior. However, for modern functional adhesives, polymeric structures were highly necessary to realize adhesion behaviors. Supramolecular adhesives from low-molecular-weight monomers were rarely recognized. Compared with polymeric adhesive materials, it remains challenging for supramolecualr adhesive materials to realize tough adhesion on wet surfaces or even under water. In this study, a new supramolecular adhesive consisting of low-molecular-weight monomers was successfully designed and prepared. Strong and long-term adhesion performance was realized on various surfaces, with a maximum adhesion strength of 4.174 MPa. This supramolecular adhesive exhibits tough and stable adhesion properties in high-moisture and underwater environments (including seawater). Long-term underwater adhesion tests display the potential application of low-molecular-weight adhesive as a marine adhesive.

6.
Zhongguo Gu Shang ; 37(1): 57-60, 2024 Jan 25.
Article in Zh | MEDLINE | ID: mdl-38286452

ABSTRACT

OBJECTIVE: To compare the biomechanical stability of three cross-bridge headless compression screws and locking plates in the fixation of Mason type Ⅲ radial head fractures by finite element method. METHODS: Using reverse modeling technology, the radial CT data and internal fixation data of a healthy 25-year-old male were imported into the relevant software. Three-dimensional finite element model of 3 cross-bridge headless compression screws and locking plates for MasonⅢ radial head fractures were established, and the radial head was loaded with 100 N axial loading. The maximum displacement, maximum Von Mises stress and stress distribution of the two groups were compared. RESULTS: The maximum displacements of the three cross-bridge screws group and locking plate group were 0.069 mm and 0.087 mm respectively, and the Von Mises stress peaks were 18.59 MPa and 31.85 MPa respectively. The stress distribution of the three screws group was more uniform. CONCLUSION: Both internal fixation methods can provide good fixation effect. CoMPared with the locking plate fixation method, the 3 cross-bridge headless compression screws fixation is more stable and the stress distribution is more uniform.


Subject(s)
Fractures, Comminuted , Radial Head and Neck Fractures , Radius Fractures , Male , Humans , Adult , Finite Element Analysis , Bone Screws , Biomechanical Phenomena , Radius Fractures/surgery , Fracture Fixation, Internal/methods , Bone Plates
7.
Nat Commun ; 15(1): 4265, 2024 May 20.
Article in English | MEDLINE | ID: mdl-38769305

ABSTRACT

The advancement of contemporary adhesives is often limited by the balancing act between cohesion and interfacial adhesion strength. This study explores an approach to overcome this trade-off by utilizing the spontaneous polymerization of a protic ionic liquid-based monomer obtained through the neutralization of 2-acrylamide-2-methyl propane sulfonic acid and hydroxylamine. The initiator-free polymerization process is carried out through a gradual increase in monomer concentration in aqueous solutions caused by solvent evaporation upon heating, which results in the in-situ formation of a tough and thin adhesive layer with a highly entangled polymeric network and an intimate interface contact between the adhesive and substrate. The abundance of internal and external non-covalent interactions also contributes to both cohesion and interfacial adhesion. Consequently, the produced protic poly(ionic liquid)s exhibit considerable adhesion strength on a variety of substrates. This method also allows for the creation of advanced adhesive composites with electrical conductivity or visualized sensing functionality by incorporating commercially available fillers into the ionic liquid adhesive. This study provides a strategy for creating high-performance ionic liquid-based adhesives and highlights the importance of in-situ polymerization for constructing adhesive composites.

8.
Adv Mater ; : e2403039, 2024 May 28.
Article in English | MEDLINE | ID: mdl-38805574

ABSTRACT

The resistance of adhesives to organic solvents is of paramount importance in diverse industries. Unfortunately, many currently available adhesives exhibit either weak intermolecular chain interactions, resulting in insufficient resistance to organic solvents, or possess a permanent covalent crosslinked network, impeding recyclability. This study introduces an innovative approach to address this challenge by formulating zwitterionic poly(ionic liquid) (ZPIL) derivatives with robust dipole-dipole interactions, incorporating sulfonic anions and imidazolium cations. Due to its unique dynamic and electrostatic self-crosslinking structure, the ZPIL exhibits significant adhesion to various substrates and demonstrates excellent recyclability even after multiple adhesion tests. Significantly, ZPIL exhibits exceptional adhesion stability across diverse nonpolar and polar organic solvents, including ionic liquids, distinguishing itself from nonionic polymers and conventional poly(ionic liquid)s. Its adhesive performance remains minimally affected even after prolonged exposure to soaking conditions. The study presents a promising solution for the design of highly organic solvent-resistant materials for plastics, coatings, and adhesives.

9.
Beijing Da Xue Xue Bao Yi Xue Ban ; 45(6): 928-32, 2013 Dec 18.
Article in Zh | MEDLINE | ID: mdl-24343076

ABSTRACT

OBJECTIVE: To analyze the impact of passing items above the roof level in the gross motor subtest of Peabody development motor scales (PDMS-2) on its assessment results. METHODS: In the subtests of PDMS-2, 124 children from 1.2 to 71 months were administered. Except for the original scoring method, a new scoring method which includes passing items above the ceiling were developed. The standard scores and quotients of the two scoring methods were compared using the independent-samples t test. RESULTS: Only one child could pass the items above the ceiling in the stationary subtest, 19 children in the locomotion subtest, and 17 children in the visual-motor integration subtest. When the scores of these passing items were included in the raw scores, the total raw scores got the added points of 1-12, the standard scores added 0-1 points and the motor quotients added 0-3 points. The diagnostic classification was changed only in two children. There was no significant difference between those two methods about motor quotients or standard scores in the specific subtest (P>0.05). CONCLUSION: The passing items above a ceiling of PDMS-2 isn't a rare situation. It usually takes place in the locomotion subtest and visual-motor integration subtest. Including these passing items into the scoring system will not make significant difference in the standard scores of the subtests or the developmental motor quotients (DMQ), which supports the original setting of a ceiling established by upassing 3 items in a row. However, putting the passing items above the ceiling into the raw score will improve tracking of children's developmental trajectory and intervention effects.


Subject(s)
Child Development/physiology , Motor Skills/physiology , Child, Preschool , Female , Humans , Infant , Male , Neuropsychological Tests , Retrospective Studies
10.
Polymers (Basel) ; 15(11)2023 Jun 04.
Article in English | MEDLINE | ID: mdl-37299375

ABSTRACT

To improve the wear resistance of polyimide (PI), surface modification was developed. In this study, the tribological properties of graphene (GN), graphene oxide (GO), and KH550-grafted graphene oxide (K5-GO) modified PI were evaluated by molecular dynamics (MD) at the atomic level. The findings indicated that the addition of nanomaterials can significantly enhance the friction performance of PI. The friction coefficient of PI composites decreased from 0.253 to 0.232, 0.136, and 0.079 after coating GN, GO and K5-GO, respectively. Among them, the K5-GO/PI exhibited the best surface wear resistance. Importantly, the mechanism behind the modification of PI was thoroughly revealed by observing the wear state, analyzing the changes of interfacial interactions, interfacial temperature, and relative concentration.

11.
Micromachines (Basel) ; 14(3)2023 Mar 07.
Article in English | MEDLINE | ID: mdl-36985023

ABSTRACT

The thermal conductivity, mechanical, and tribological properties of polyimide (PI) composites filled by copper (Cu), carbon nanotube (CNT), graphene nanosheet (GNS), or combination were investigated by molecular dynamics simulation (MD). The simulated results suggested that Cu can improve thermal stability and thermal conductivity, but it reduces mechanical properties and tribological properties. CNT and GNS significantly improved the thermal and tribological properties at low content, but they decreased the properties at high content. In this study, the modification mechanism, friction, and wear mechanism of different fillers on polyimide were revealed by observing the frictional interface evolution process from the atomic scale, extracting the atomic relative concentration, the temperature and velocity distribution at the friction interface, and other microscopic information.

12.
Dev Psychol ; 59(11): 2050-2064, 2023 Nov.
Article in English | MEDLINE | ID: mdl-37768598

ABSTRACT

This study examined the longitudinal associations of various executive function components with subsequent psychiatric problems in Chinese school-age children. Data from 1,639 children (44.36% girls) ages 6-13 years were drawn from the Children School Functions and Brain Development project. Executive function components were assessed by the cancellation test, the Corsi test, and the Wisconsin Card Sorting Test. Psychiatric problems were determined by parent report. All assessments were administered twice, separated by a 1-year interval. Cross-lagged panel models showed that cognitive flexibility and general psychiatric problems (general p) mutually predicted each other. Worse inhibitory control at baseline significantly predicted more externalizing problems 1 year later, regardless of age, while externalizing problems did not significantly predict inhibitory control 1 year later. Working memory at baseline did not significantly predict internalizing problems and vice versa. These findings demonstrate that better inhibitory control may help to prevent or reduce externalizing problems in Chinese school-age children and that higher cognitive flexibility may help to mitigate general psychiatric problems. (PsycInfo Database Record (c) 2023 APA, all rights reserved).


Subject(s)
Child Behavior Disorders , Executive Function , Female , Humans , Child , Male , Longitudinal Studies , Child Behavior Disorders/psychology , Memory, Short-Term
13.
Int J Numer Method Biomed Eng ; 39(10): e3691, 2023 10.
Article in English | MEDLINE | ID: mdl-36799066

ABSTRACT

Orthokeratology (OK) is becoming a mainstream modality for myopia correction and control, but its underlying mechanism is not yet fully understood. In this study, the biomechanical response of cornea under the OK lens was investigated to further understand the mechanism of OK therapy. Numerical models of the cornea and OK lens with different corneal refractive powers and myopia degrees were established to analyze features and differences of the spatial displacement and stress distribution in different areas of the anterior corneal surface by finite element method. Displacement distributions on the anterior cornea surface with refractive powers of 39.5, 43, 46 D, and myopia degrees of -1.0, -3.0, -6.0 D demonstrate similar deformation trends and nearly rotationally symmetrical attributes of different corneal parameters. Displacement of mid-peripheral cornea was significantly high compared with that of the central and peripheral cornea, peaking at ~2.4 mm off the corneal apex. The stress increased with the increase in myopia degrees and was significantly large for the myopia degrees of -6.0 D at S1; the stress at S2 and S6 was low and stable and did not differ much at S3; the stress at S4 and S5, however, was extremely high. In summary, simulation result of orthokeratology can effectively evaluate the performance of OK lens and it properly associates with the differential map of the corneal topography. The base curve of the OK lens may also play a role in mid-peripheral corneal steepening. The design around the OK lens' alignment curve needs to be optimized.


Subject(s)
Myopia , Orthokeratologic Procedures , Humans , Finite Element Analysis , Refraction, Ocular , Orthokeratologic Procedures/methods , Cornea , Myopia/therapy
14.
J Hazard Mater ; 448: 130821, 2023 04 15.
Article in English | MEDLINE | ID: mdl-36709736

ABSTRACT

Lignin, the most abundant source of renewable aromatic compounds derived from natural lignocellulosic biomass, has great potential for various applications as green materials due to its abundant active groups. However, it is still challenging to quickly construct green polymers with a certain crystallinity by utilizing lignin as a building block. Herein, new green lignin-based covalent organic polymers (LIGOPD-COPs) were one-pot fabricated with water as the reaction solvent and natural lignin as the raw material. Furthermore, by using paraformaldehyde as a protector and modulator, the LIGOPD-COPs prepared under optimized conditions displayed better crystallinity than reported lignin-based polymers, demonstrating the feasibility of preparing lignin-based polymers with improved crystallinity. The improved crystallinity confers LIGOPD-COPs with enhanced application performance, which was demonstrated by their excellent performances in sample treatment of non-targeted food safety analysis. Under optimized conditions, phytochromes, the main interfering matrices, were almost completely removed from different phytochromes-rich vegetables by LIGOPD-COPs, accompanied by "full recovery" of 90 chemical hazards. Green, low-cost, and reusable properties, together with improved crystallinity, will accelerate the industrialization and marketization of lignin-based COPs, and promote their applications in many fields.


Subject(s)
Lignin , Polymers , Lignin/chemistry , Polymers/chemistry , Biomass , Water , Solvents
15.
Dev Cogn Neurosci ; 63: 101296, 2023 10.
Article in English | MEDLINE | ID: mdl-37690374

ABSTRACT

Predicting the risk for general psychopathology (the p factor) requires the examination of multiple factors ranging from brain to cognitive skills. While an increasing number of findings have reported the roles of the cerebral cortex and executive functions, it is much less clear whether and how the cerebellum and cognitive flexibility (a core component of executive function) may be associated with the risk for general psychopathology. Based on the data from more than 400 children aged 6-12 in the Children School Functions and Brain Development (CBD) Project, this study examined whether the left cerebellar lobule VIIb and its connectivity within the cerebellum may prospectively predict the risk for general psychopathology one year later and whether cognitive flexibility may mediate such predictions in school-age children. The reduced gray matter volume in the left cerebellar lobule VIIb and the increased connectivity of this region to the left cerebellar lobule VI prospectively predicted the risk for general psychopathology and was partially mediated by worse cognitive flexibility. Deficits in cognitive flexibility may play an important role in linking cerebellar structure and function to the risk for general psychopathology.


Subject(s)
Cerebellum , Mental Disorders , Humans , Child , Cerebellum/pathology , Cerebral Cortex , Brain , Cognition , Mental Disorders/pathology , Magnetic Resonance Imaging
16.
CNS Neurosci Ther ; 29(11): 3528-3548, 2023 11.
Article in English | MEDLINE | ID: mdl-37287420

ABSTRACT

AIMS: Increasing evidence indicates that major neurodevelopmental disorders have potential links to abnormal cerebellar development. However, the developmental trajectories of cerebellar subregions from childhood to adolescence are lacking, and it is not clear how emotional and behavioral problems affect them. We aim to map the developmental trajectories of gray matter volume (GMV), cortical thickness (CT), and surface area (SA) in cerebellar subregions from childhood to adolescence and examine how emotional and behavioral problems change the cerebellar development trajectory in a longitudinal cohort study. METHOD: This population-based longitudinal cohort study used data on a representative sample of 695 children. Emotional and behavioral problems were assessed at baseline and at three annual follow-ups with the Strengths and Difficulties Questionnaire (SDQ). RESULTS: Using an innovative automated image segmentation technique, we quantified the GMV, CT, and SA of the whole cerebellum and 24 subdivisions (lobules I-VI, VIIB, VIIIA&B, and IX-X plus crus I-II) with 1319 MRI scans from a large longitudinal sample of 695 subjects aged 6-15 years and mapped their developmental trajectories. We also examined sex differences and found that boys showed more linear growth, while girls showed more nonlinear growth. Boys and girls showed nonlinear growth in the cerebellar subregions; however, girls reached the peak earlier than boys. Further analysis found that emotional and behavioral problems modulated cerebellar development. Specifically, emotional symptoms impede the expansion of the SA of the cerebellar cortex, and no gender differences; conduct problems lead to inadequate cerebellar GMV development only in girls, but not boys; hyperactivity/inattention delays the development of cerebellar GMV and SA, with left cerebellar GMV, right VIIIA GMV and SA in boys and left V GMV and SA in girls; peer problems disrupt CT growth and SA expansion, resulting in delayed GMV development, with bilateral IV, right X CT in boys and right Crus I GMV, left V SA in girls; and prosocial behavior problems impede the expansion of the SA and lead to excessive CT growth, with bilateral IV, V, right VI CT, left cerebellum SA in boys and right Crus I GMV in girls. CONCLUSIONS: This study maps the developmental trajectories of GMV, CT, and SA in cerebellar subregions from childhood to adolescence. In addition, we provide the first evidence for how emotional and behavioral problems affect the dynamic development of GMV, CT, and SA in the cerebellum, which provides an important basis and guidance for the prevention and intervention of cognitive and emotional behavioral problems in the future.


Subject(s)
Gray Matter , Problem Behavior , Humans , Child , Male , Female , Adolescent , Gray Matter/diagnostic imaging , Longitudinal Studies , Emotions , Cohort Studies , Magnetic Resonance Imaging/methods
17.
Food Res Int ; 159: 111599, 2022 09.
Article in English | MEDLINE | ID: mdl-35940762

ABSTRACT

Although collagen is widely used as an emulsifier in the food industry, its emulsifying properties are strongly influenced by processing conditions. This research investigated the effects of NaCl on the emulsifying properties of type I collagen after heating. Before heating, the solubility, emulsifying activity index (EAI), emulsifying stability index (ESI), and viscosity of type I collagen initially increased after adding NaCl (0.2 M), after which decreased with increasing NaCl concentration (0.4 M and 0.6 M) due to salt-in effect and the salt-out effects of the protein. While after heating (90℃, 30 min), the collagen became more soluble, with improved EAI and ESI, viscosity, and reduced particle size in response to increasing NaCl concentrations. It was found that NaCl increased the EAI of type I collagen twice after heating, and the EAI reached its maximum at 0.6 M NaCl concentration. We concluded that the improved emulsifying properties may due to thermal denaturation of the protein, resulting in an unfolded and disordered structure with increase of hydrogen bonds with water, rupture of disulfide bonds, and exposure of hydrophobic groups, leading to the increase of adsorption at the oil/water interface. Meanwhile, the Raman spectra analysis and Atomic Force Microscope (AFM) images showed that unfolding of the collagen triple helix was gradually destroyed after NaCl addition and heating, with emulsifying properties improved. The specific outcomes of present study can be adapted towards the requirements to improve the quality of emulsified meat products in the food industry.


Subject(s)
Hot Temperature , Sodium Chloride , Collagen Type I , Emulsifying Agents/chemistry , Emulsions/chemistry , Proteins
18.
Neurosci Bull ; 38(6): 607-621, 2022 Jun.
Article in English | MEDLINE | ID: mdl-35092576

ABSTRACT

School-age children are in a specific development stage corresponding to juvenility, when the white matter of the brain experiences ongoing maturation. Diffusion-weighted magnetic resonance imaging (DWI), especially diffusion tensor imaging (DTI), is extensively used to characterize the maturation by assessing white matter properties in vivo. In the analysis of DWI data, spatial normalization is crucial for conducting inter-subject analyses or linking the individual space with the reference space. Using tensor-based registration with an appropriate diffusion tensor template presents high accuracy regarding spatial normalization. However, there is a lack of a standardized diffusion tensor template dedicated to school-age children with ongoing brain development. Here, we established the school-age children diffusion tensor (SACT) template by optimizing tensor reorientation on high-quality DTI data from a large sample of cognitively normal participants aged 6-12 years. With an age-balanced design, the SACT template represented the entire age range well by showing high similarity to the age-specific templates. Compared with the tensor template of adults, the SACT template revealed significantly higher spatial normalization accuracy and inter-subject coherence upon evaluation of subjects in two different datasets of school-age children. A practical application regarding the age associations with the normalized DTI-derived data was conducted to further compare the SACT template and the adult template. Although similar spatial patterns were found, the SACT template showed significant effects on the distributions of the statistical results, which may be related to the performance of spatial normalization. Looking forward, the SACT template could contribute to future studies of white matter development in both healthy and clinical populations. The SACT template is publicly available now ( https://figshare.com/articles/dataset/SACT_template/14071283 ).


Subject(s)
Diffusion Tensor Imaging , White Matter , Adult , Brain/diagnostic imaging , Brain/pathology , Brain Mapping/methods , Child , Diffusion Magnetic Resonance Imaging/methods , Diffusion Tensor Imaging/methods , Humans , White Matter/diagnostic imaging
19.
Front Psychol ; 12: 644623, 2021.
Article in English | MEDLINE | ID: mdl-34149528

ABSTRACT

Recent research in the underlying structure of pathological Internet use (PIU) has produced considerable debate among academics, in which a new "person-centered" approach of studying PIU has recently gathered support but produced mixed results. This study used the latent profile analysis (LPA) to estimate the types of PIU in a large sample of college students (n = 1,400, aged 17-25 years). Participants provided information on demographics, PIU, and Internet behavior preferences. The adolescent pathological Internet use (APIU), which served as the basis of LPA, was used for searching subgroups that represent participants with PIU. LPA identified the PIU classes, and regressions identified the psychological predictors of class membership. Participants were classified into pathological users, pathological-tendency users, preferential users, and ordinary Internet users. In comparison with pathological Internet users, lower Internet gaming and communication preference were associated with pathological-tendency users, preferential users, and ordinary Internet users. The distinct types of college students belong to each PIU class, suggesting that individual differences may be incorporated into the prevention efforts.

20.
Rev Sci Instrum ; 92(5): 055002, 2021 May 01.
Article in English | MEDLINE | ID: mdl-34243259

ABSTRACT

Friction materials form a critical component of piezoelectric actuators, and wear of the material affects output and service life of the actuator. This paper examines the influence of polyimide (PI) composites when used as a friction material on the performance of a legged piezoelectric bending actuator. We design and manufacture demountable shoe soles, made of a novel PI-based friction material, for an actuator. A Coulomb friction model is also established to determine the behavior resulting from contact-induced friction between the surface and the actuator. Reciprocating wear tests involving an insulation rubber pad against phosphor bronze and PI composites as friction materials yielded average friction coefficients of 0.21 and 0.28, respectively. We also found that PI composites have higher wear resistance than phosphor bronze, with a specific wear rate of 1.36 × 10-4 mm3/N m. The results of experiments and simulations indicate that the shoe soles made of PI composites reduced the actuator's driving frequency and vibrational amplitude, but they did not affect the principle of locomotion of the actuator. Furthermore, the operational stability of the actuator improved by 46.8% by using the demountable shoe soles made of PI composites, albeit at the cost of its velocity and load capacity. This work has guiding significance for the design and selection of friction materials for piezoelectric actuators.

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