The scalable preparation of high-quality and low-cost two-dimensional (2D) materials is critical to achieving their potential applications in various fields. Chemical vapor deposition (CVD) method is considered the most promising method for producing ultrathin 2D materials and has continued to develop in recent years. First-principles calculations have provided important theoretical guidance for the CVD synthesis of 2D materials, and have played an increasingly important role in the field of material synthesis in recent years.In this review, we present recent advances in the growth mechanism of 2D materials, focusing on the theoretical research progress of four typical 2D materials: graphene, hexagonal boron nitride (hBN), transition metal dichalcogenide (TMDC), and phosphorene. Several aspects of the growth process are discussed in detail, including the decomposition of precursors, nucleation, growth kinetics, domain shape, and epitaxial and alignment of 2D crystals. Based on the understanding of these atomic-scale growth processes, strategies toward the wafer-scale growth of continuous and homogeneous 2D thin films are proposed and confirmed by experiments. In the final section, we summarize future challenges and opportunities in the computational studies of the growth mechanism of 2D materials.
In this paper, a metamaterial absorber is proposed, which is constructed by graphene rings and a gold film separated by an ultrathin S i O 2 layer. The feature of this absorber is that the absorption bands can be adjusted either by applying external electric fields or by rotating the polarization angles of the incident electromagnetic waves. The calculation results show that the continuous tunable or two- to multi-band absorptions can be realized by the above two methods. Through equivalent medium theory and impedance-matching condition, the anisotropic absorption mechanism of this absorber is explained. Moreover, the simple specific design makes the absorption bands able to be further tuned by adjusting various parameters, such as the geometry sizes and relaxation times of graphene rings. Our results indicate that the absorber has great adjustability and great potential application in filtering, terahertz signal detection, signal parameter estimation, smart sensing, tunable absorbers, and cloaking.
Background: Rotator cuff pathology is a common cause of pain and shoulder dysfunction. Several nonoperative treatment modalities have been developed for rotator cuff lesions, but their relative efficacy is not well-established. Purpose/Hypothesis: The purpose of this systematic review and meta-analysis was to evaluate the efficacy and safety of sodium hyaluronate (SH) in the treatment of patients with rotator cuff lesions. It was hypothesized that SH would be found to be more effective than other nonoperative regimens. Study Design: Systematic review; Level of evidence, 3. Methods: We searched various databases to identify eligible studies that evaluated the effects of SH on the pain and shoulder dysfunction attributed to rotator cuff lesions. Outcome measures were pain visual analog scale (VAS) score; Constant score; University of California, Los Angeles (UCLA) score; satisfaction rate; complications; and factors affecting the pain VAS score. Outcomes were reported as weighted mean difference (WMD) or risk ratio. Results: A total of 9 studies were identified for data analysis. Compared with patients treated with other nonoperative treatments (controls), those treated with SH had significantly improved pain VAS scores at 1 week (WMD = −0.95; 95% CI, −1.75 to −0.16; P = .019), 2 weeks (WMD = −1.05; 95% CI, −2.07 to −0.03; P = .044), 3 weeks (WMD = −1.49; 95% CI, −2.88 to −0.11; P = .035), and 4 weeks (WMD = −2.12; 95% CI, −4.05 to −0.19; P = .031). The Constant score was significantly improved in the SH group versus controls at 2 weeks (WMD = 3.25; 95% CI, 2.36 to 4.13; P < .001), 3 months (WMD = 20.28; 95% CI, 0.54 to 40.03; P = .044), and 6 months (WMD = 5.58; 95% CI, 0.94 to 10.21; P = .018). The UCLA score and satisfaction rate did not differ significantly between the 2 groups. No complications associated with SH were reported in the included studies. Metaregression analysis showed that, except for study design (coefficient = −1.64; 95% CI, −2.64 to −0.63; P = .002), none of the variables (sample size, tear type, control treatments) significantly predicted the difference in VAS pain score between SH and other treatments. Conclusion: The present meta-analysis demonstrated that SH was effective in treating patients with rotator cuff lesions.
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