Search

The present study aimed to explore the association between parent-children relationship and internet addiction with the mediating effect of self-concept among Chinese adolescents. The Chinese Parent-Children Relationship Diagnostic Test, the Chinese revised edition of Tennessee Self-concept Scale, and the Chinese Internet Addiction Scale were administered to 300 junior and high school students aged 13–18 years (in grades 7–12). Results indicated that parent-children relationship was positively related to self-concept and was negatively related to internet addiction, while self-concept was negatively related to internet addiction among adolescents. Moreover, the association between parent-children relationship and internet addiction was partially mediated by self-concept. Findings of the present study suggested that parent-children relationship exerted not only direct effect but also indirect effect on internet addiction through self-concept. Limitations of the study are considered and implications of the findings for reducing adolescents' internet addiction are discussed. [ABSTRACT FROM AUTHOR]

Rapid developments in the electric industry have promoted an increasing demand for lithium resources. Lithium in salt lake brines has emerged as the main source for industrial lithium extraction, owing to its low cost and extensive reserves. The effective separation of Mg2+ and Li+ is critical to achieving high recovery efficiency and purity of the final lithium product. This paper summarizes Mg2+/Li+ separation materials and methods in the field of lithium recovery from salt lake brines. The review begins with an introduction to the global distribution and demand for lithium resources, followed by a description of the materials used in various separation techniques, including precipitation, adsorption, solvent extraction, nanofiltration membrane, electrodialysis, and electrochemical methods. A comparison, analysis, and outlook of such methods are comprehensively discussed in terms of principles, mechanisms, synthesis/operation, development, and industrial applications. We conclude with a presentation of challenges and insights into the future directions of lithium extraction from salt lake brines. A combination of the advantages of various materials is the most logical step toward developing novel methods for extracting lithium from brines with high separation selectivity, stability, low cost, and environmentally friendly characteristics. [ABSTRACT FROM AUTHOR]

Graphene sheet (GS) is a two-dimensional material with extremely favorable mass sensor properties. In this work, the potential of a nanoscale mass sensor based on individual single layer GS is examined. An atomic-resolution nanomechanical mass sensor is modeled by a fixed supported circular monolayer GS with attached nanoparticles, based on a continuum elastic model and Rayleigh's energy method. We analyze the vibrational properties of the GS used as a mass sensor in detail, and the relationship between the attached mass and the vibrational frequency (frequency shift) of the GS is simulated and discussed using the two models. The sensitivity of vibrational frequency (frequency shift) to both aspect ratio and vibration mode is demonstrated, and comparison of the two models proves their accuracy and that of the simulation of the monolayer GS mass sensor. [ABSTRACT FROM AUTHOR]

Composite masterbatches of polyphenylene sulfide (PPS) with functionalized graphene nanoplatelets (GNPs) were prepared by melt blending via a twin-screw extruder. The structure and morphology of composite masterbatches were characterized by scanning electron microscopy and X-ray diffraction analysis. The PPS/functionalized GNPs composite fibers were then manufactured by a self-made spinning equipment via melt spinning. The oxidation resistance and other properties of PPS composite fibers were also examined. The results showed that the pure PPS fibers exhibited smooth surface, whereas the surface of PPS/functionalized GNPs composite fibers was rough. The addition of functionalized GNPs could be acted as heterogeneous nucleating agents to improve the crystallization and increase the degree of crystallinity. The retention rate of breaking strength of PPS/functionalized GNPs composite fibers could maintain up to 85% after the oxidation treatment. The improvement in the oxidation resistance of PPS/functionalized GNPs composite fibers is the results of comprehensive effects characterized by the X-ray photoelectron spectroscopy analyses. The addition of functionalized GNPs could limit the damage of the C–S group and retard the generation of sulfuryl groups (–SO–) during the oxidation treatment. The chemical combination of the elements sulfur (S) and oxygen (O) could also be restricted, thus weakening the oxidation activity. [ABSTRACT FROM AUTHOR]

This paper presents a series of small-scale physical model tests, using transparent soil and particle image velocimetry technique. The soil displacements, anchor load and displacement responses were measured directly from the tests. Based on the results, the anchor's ultimate uplift load, impact area within the surrounding soil and failure mechanism of the anchor system were studied. Furthermore, numerical investigation was also carried out to study the effect of shoulder sizes on the ultimate uplift bearing capacity. It was observed that the fracture surface formed at the shoulder was convex and bullet-shaped. The analysis of results showed that the ultimate uplift bearing capacity of end bearing anchors was affected by enlargement diameter (D), shaft diameter (d) and enlargement segment length (L), especially with the enlargement shoulder dimension (D − d). The model tests and numerical simulation results were compared with equations from the British and Chinese standards. When (D − d)/L ≥ 0.2, Chinese standard was more suitable, and when (D − d)/L < 0.2, British standard performed better. Finally, the effect of varying shoulder sizes and enlargement lengths were discussed, and some suggestions for better design of end bearing anchor were proposed to improve the anchorage efficiency. [ABSTRACT FROM AUTHOR]

Background: Diabetic retinopathy (DR) is a serious microvascular complication of diabetes and remains the leading cause of blindness in adults. Retinal inflammation is playing a crucial role in the development of DR, and targeting inflammatory mediators is a promising strategy for controlling DR. Here, we investigated compound Chinese medicine Luo Tong formula (LTF) alleviated retinal inflammatory responses in a STZ-induced diabetic rat model. Methods: Sprague–Dawley rats were divided into four groups: control, streptozotocin-induced diabetic, LTF-treated diabetic, and calcium dobesilate (CaD)-treated diabetic rats. Blood samples were collected for blood glucose examination. Hematoxylin–eosin and periodic acid-Schiff staining were conducted for light microscopy observations. Retinal cell apoptosis was detected using the TUNEL assay. Proteins expression was quantified by Western blotting and/or immunohistochemistry, and gene expression was assessed by real-time PCR. Results: Diabetic rats showed significant increases in the expression of tumor necrosis factor α (TNF-α), interleukin-1β (IL-1β), monocyte chemotactic protein-1 (MCP-1), intercellular adhesion molecule-1 (ICAM-1), nuclear factor-κB (NF-κB), and the phospho-p38 mitogen-activated protein kinase (p-p38-MAPK)/p38 MAPK ratio compared to control rats. LTF treatment significantly improved both retinal and pancreatic pathological injury, LTF treatment also inhibited inducible the p-p38 MAPK/p38 MAPK ratio and NF-κB activation and decreased the subsequent induction of the retinal expression of proinflammatory mediators TNF-α, IL-1β, MCP-1 and ICAM-1 compared to diabetic rats. LTF also exhibited a protective effect on islet function. Conclusions: LTF before the onset of DR can alleviate retinal pathological injury, LTF may play an anti-inflammatory role by inhibiting p38-MAPK and then inhibiting NF-κB pathway. But further studies are needed to confirm this conclusion. Trial registration This is an animal experiment, trial registration is not necessary. [ABSTRACT FROM AUTHOR]

Background: Diabetic kidney disease (DKD) is the main cause of end-stage kidney disease and has become a heavy economic and social burden due to its high prevalence and morbidity. The most effective strategy is that patients with DKD should be diagnosed and treated early. Preliminary studies showed that the Chinese herbal Tangshen Formula (TSF) may delay the progression of DKD, reducing microalbuminuria and macroalbuminuria and improving renal function. We designed a randomized, double-blind, placebo-controlled trial to evaluate the efficacy of TSF in patients with DKD.Methods/design: This trial is a 13-center, randomized, double-blind, placebo-controlled study. A total of 632 participants will be randomized in a 1:1 ratio to an experiment group (TSF plus losartan) and a control group (placebo plus losartan). The trial cycle will last 24 weeks. The primary outcome will be the change in the urine microalbumin-creatinine ratio from baseline to week 24. The secondary outcome will be the change in the rate of progression to the clinical proteinuria period after intervention, the rate of urine microalbumin negative conversion, the rate of normal urinary microalbumin, the doubling rate of the baseline creatinine value and the glomerular filtration rate between the two groups. Safety in medication will also be evaluated.Discussion: We hypothesize that patients with type 2 diabetes in the early stage of DKD will benefit from TSF. If successful, this study will provide evidence-based recommendations for clinicians.Trial Registration: ClinicalTrials.gov, NCT03009864. Registered January 2017. [ABSTRACT FROM AUTHOR]

This paper presents a study on the natural vibration of circular double-layer graphene sheets (DLGSs) using circular plate theory. The circular DLGSs are assumed to be coupled together through the carbon-carbon van der Waals (vdW) force between their two layers. An analytical solution of coupled governing equations is proposed to predict the natural frequencies of circular DLGSs. The vibration behaviors in circular DLGSs are found to have an in-phase mode (IPM) associated with the classical natural frequency, and an anti-phase mode (APM) owing to the influence of the vdW interaction. The natural frequencies of the IPM are independent of vdW interactions between adjacent layers, while those of the APM depend on the vdW interaction, and are larger. Based on the exact solution, the influences of wavenumbers (m, n) on the natural frequencies of simply supported circular DLGSs are also investigated in detail. [ABSTRACT FROM AUTHOR]

Graphene nanoribbons (GNRs) are potential nanomaterial electromechanical oscillators because of their outstanding mechanical and electronic properties. Double-layer GNRs (DLGNRs), which are two-layer finite-wide counterparts of crystalline graphene sheets coupled to each other via van der Waals interaction forces, present two kinds of vibrational modes in flexural wave propagation. These two modes are defined as the in-phase mode and anti-phase mode. In this study, based on the nonlocal Timoshenko beam theory and Winkler spring model, the wave propagation characteristics of DLGNRs embedded in an elastic matrix are investigated by dividing the vibrational mode into the in-phase mode and anti-phase mode. This will provide more accurate guidance for the application of DLGNRs. When the nonlocal effects and elastic matrix are considered, three critical frequencies are found. These are defined as the cutoff, escape, and low-cutoff frequencies. Moreover, the results show that the wave propagation characteristics of embedded DLGNRs are significantly influenced by nonlocal parameters and the Winkler foundation modulus. [ABSTRACT FROM AUTHOR]

An elastic continuum mechanics model is presented to study the elastic buckling of single- and double-walled carbon nanotubes (CNTs) subjected to hydrostatic pressure. It is shown that a pressure-induced instability can occur in CNTs when a circle cross-section of the CNTs is destroyed. In this paper, we investigate the effects of deformation modes and dimension of CNTs on their mechanical stability. The results show that the critical pressure depends largely on the buckling mode, the diameter and aspect ratio of CNTs. The critical pressure of the single-walled CNTs (SWCNTs) with a diameter 1.3 nm is about 1.6 GPa, which is in excellent agreement the results reported in the relative literatures. The critical pressure of the double-walled nanotubes (DWCNTs) with a diameter of 2.2 nm will increase by 26%, compared with that of an identical diameter SWCNT. [ABSTRACT FROM AUTHOR]

Vibration characteristics of double-walled carbon nanotubes (DWCNTs) with conveying fluid are analyzed based on the Euler–Bernoulli beam theory and using the wave propagation approach. The DWCNTs are considered as two nanotube shells coupled through the van der Waals interaction between them. The influences of internal moving fluids, such as flow velocity and mass density of fluids, on the vibration frequency of DWCNTs and the DWCNTs embedded in an elastic matrix are investigated in detail. The effect of matrix surrounding carbon nanotubes is considered as a spring element defined by the Winkler model. In this paper, we consider the double-walled nanotubes with an inner diameter of 2.2 nm and an outer diameter of 3.0 nm. According to this analysis, the numerical results indicate that the vibration frequency for the first mode (mode 1) reduces to zero at a critical flow velocity in the case of higher flow velocity, which coincides with the previous study based on a single beam model. The critical flow velocity is largely affected by the fluid properties and the vibration modes. [ABSTRACT FROM AUTHOR]

Carbon nanotubes may hold scientific promise in nanotechnology as nanopipes conveying fluid. In this paper, the wave propagation in double-walled carbon nanotubes (DWCNTs) conveying fluid is studied based on the Euler–Bernoulli beam theory. The influences of internal moving fluids, such as flow velocity and mass density of fluids, on the sound wave propagation of DWCNTs or the DWCNTs embedded in an elastic matrix are investigated in detail. The DWCNTs are considered as a two-shell model coupled together through the van der Waals interaction between two adjacent nanotubes. According to the proposed theoretical approach, the results indicate that fluid flow through carbon nanotubes affects the wave speed and the critical frequency in the carbon nanotubes. The amplitude ratios of the inner to outer nanotubes are largely affected by the fluid velocity and density when the vibrational frequency in nanotubes is larger than 1.5 Hz. The theoretical investigation may give a useful reference for potential application and design of nanoelectronics and nanodevices. [ABSTRACT FROM AUTHOR]

We present an approach for efficient, accurate calculations of the elastic wave properties of three-dimensional periodic solid-solid media with cubic lattice structures based on the principle that the elastic wave should be uniform when averaged over length scales much larger than the size of the scatterers. Utilizing the fact that the media has the same pure mode properties as natural crystal with the corresponding lattice structure, we derive formulas for effective velocities propagating along and normal to the lattice axis, from which three independent effective elastic moduli are calculated, respectively. Effective velocities propagating along any directions can be calculated with this method, which captures the multiple scattering and the structure of the periodic medium. The results agree well with those calculated directly from the slope of the corresponding bands near the Γ point of the first Brillouin zone and are in good agreement with previous isotropic theory at high-symmetry directions. [ABSTRACT FROM AUTHOR]

Wave propagation approach of single- and double-walled carbon nanotubes conveying fluid is presented through the use of the continuum mechanics. A simplified Flügge shell equations are proposed as the governing equations of motion for carbon nanotubes studied here. For the double-walled nanotubes, the deflection of nested tubes is considered to be coupled through the van der Waals interaction between two adjacent nanotubes. Effects of filled fluid property and nanotube diameter on the wave propagation are investigated and analyzed based on the proposed elastic continuum model. The theoretical investigation may give a useful reference for potential design and application of nanoelectronics and nanodevices. [ABSTRACT FROM AUTHOR]

• A data-driven prognostic approach is proposed for bearing health management. • A novel health indicator (HI) to fuse similarity-based multi-scale features is proposed. • Grasshopper optimization algorithm is integrated to adaptively tune hyperparameters. • The proposed prognostic approach is with high accuracy and generalizability. Remaining useful life (RUL) prediction plays a crucial role in bearing health management which can guarantee the rotating machinery systems' safety and reliability. This paper promotes the capability of bearing health management by proposing a novel data-driven prognostic approach. The proposed methodology reveals the underlying deterioration progression by constructing a new health indicator (HI) that fuses distribution-similarity-based multi-scale features. More specifically, a graph named WDgram, to represent the distribution similarity between the analyzed signal and healthy reference at different frequency scales, is developed first using the 1/3-binary tree structure and Wasserstein distance (WD). Then the high-dimensional multi-scale features are fused by the multiobjective grasshopper optimization algorithm (MOGOA) to optimize the HI's monotonicity, robustness, and tenability. By taking advantage of the WDgram and MOGOA, the novel HI is able to thoroughly reveal the underlying degradation characteristics and alleviate random fluctuations which frequently decrease the accuracy of RUL estimation. Subsequently, a gated recurrent unit network, incorporated with the grasshopper optimization algorithm (GOA) to adaptively determine some hyperparameters, is established with high predictive accuracy and generalizability. Experimental validation is conducted to prove the effectiveness of the proposed method. High accuracy and generalizability can be obtained by the proposed method, demonstrating its substantial advantages in health management for rotating machinery systems. [ABSTRACT FROM AUTHOR]