Anisotropic interfacial properties of monolayer C2N field effect transistors.

Monolayer C2N is promising for next-generation electronic and optoelectronic applications due to its appropriate band gap and high carrier efficiency. However, relative studies have been held back due to the lack of high-quality electrode contacts. Here, we comprehensively study the electronic and transport properties of monolayer C2N with a series of electrode materials (Al, Ti, Ni, Cu, Ag, Pt, V2C, Cr2C and graphene) by using the nonequilibrium Green's function (NEGF) method combined with density functional theory (DFT). The monolayer C2N forms Ohmic contacts with the Ti/Cu/Ag electrode material in both armchair and zigzag directions, whereas Ohmic contact is only formed in the zigzag direction of the C2N-Al field effect transistor. However, the C2N-Ni, -Pt, -V2C, -Mo2C, -graphene contact systems form n-type Schottky contacts in either the armchair or zigzag direction owing to the relatively strong Fermi level pinning (the pinning factor S = 0.32 in the armchair direction and S = 0.26 in the zigzag direction). By insertion of BN or graphene between the C2N and Pt electrode in the armchair direction of contact systems, the Fermi level pinning can be effectively weakened due to the suppression of metal-induced gap states. Conspicuously, an Ohmic contact is realized in the C2N field effect transistors with the BN-Pt electrode, suggesting a possible approach to fabricating high-performance devices. Our study is conducive to selecting appropriate electrode materials for C2N-based field effect transistors.

Pervasive Ohmic contacts of monolayer 4-hT2 graphdiyne transistors.

Monolayer (ML) graphdiyne, a two-dimensional semiconductor with appropriate band gap and high carrier mobility, is a promising candidate for channel material in field effect transistors (FETs). Using density functional theory combined with non-equilibrium Green's function method, we systematically investigate the contact and transport properties of graphdiyne FETs with various electrodes, including metals (Cu, Au, Ni, Al and Ag) and MXenes (Cr2C, Ta2C and V2C). Strong interaction can be found between ML graphdiyne and the Cu, Ni and MXenes electrodes with indistinguishable band structure of ML graphdiyne, while weak or medium interaction exists in the contacts of ML graphdiyne and the Au, Al and Ag electrodes where the band structure of ML graphdiyne remains intact. Despite the different contact interactions, Ohmic contacts are generated with all considered electrode materials owing to the weak Fermi level pinning of graphdiyne. The linear I-V characteristic curve verifies the Ohmic contact between Au electrode and graphdiyne ultimately. The theoretically calculated Schottky barrier heights of graphdiyne with Cu electrode are consistent with the available experimental data. Our calculation suggests that graphdiyne is an excellent channel material of FETs forming desired Ohmic contacts with wide-ranging electrodes and thus is promising to fabricate high performance FETs.

[Effect of different orthodontic techniques on alveolar bone changes in the upper incisor area of patients with periodontitis].

PURPOSE: To explore the effects of different orthodontic techniques on the changes of alveolar bone density, height and gingival crevicular fluid (GCF) bleeding in upper incisor in patients with periodontitis. METHODS: Twenty-three patients with moderate periodontitis who underwent orthodontic treatment from January 2016 to December 2019 in the Department of Stomatology of Jiangxi Pingxiang People's Hospital were divided into experimentalexperimental group(n=12) and control group(n=11). Patients in the experimental group were treated with bracket-less invisible appliance, while patients in the control group were treated with conventional lip-side fixed appliance. Changes of gingival crevicular hemorrhage index, probing depth, alveolar bone height and bone density in the incisor area were compared between the two groups before and after treatment. Statistical analysis was performed on data using SPSS 22.0 software package. RESULTS: After treatment, the bone mineral density of the upper incisor alveolar crest (L1) of the two groups decreased, and the rate of decrease in the experimental group was significantly less than that in the control group (P<0.05). The bone density at the apical point of the anatomical root of the control group at 1 mm (L3) was also significantly reduced, but there was no significant change in the experimental group. There was no significant change in the alveolar bone height of the upper incisor area between the two groups before and after treatment (P>0.05). Root resorption of the upper incisors in the experimental group was significantly lower than that in the control group(P<0.05). After treatment, the probing depth and GCF bleeding index of the two groups decreased, and the change in the experimental group was significantly greater than that in the control group(P<0.05). CONCLUSIONS: Bracket-free invisible appliance for periodontitis is more conducive to the restoration of alveolar bone mineral density in the upper incisor than the conventional lip-side fixed appliance, and both of which have the same effect on bone height and are safe and effective orthodontic treatment.

Association between Apolipoprotein E polymorphism and myocardial infarction risk: A systematic review and meta-analysis.

Published data regarding the association between Apolipoprotein E (ApoE) genetic variation and myocardial infarction (MI) risk were not always consistent. Therefore, the current meta-analysis was conducted to derive a more precise estimation of the association between ApoE polymorphism and MI risk. PubMed and Web of Science were searched to identify relevant studies. Summary odds ratio (ORs) and 95% confidence intervals (CIs) were calculated using random-effect or fixed-effect models based on the heterogeneity of included studies. All the tests were performed using Stata 11.0. A total of 22 eligible studies were identified in this meta-analysis. The results show that ApoE ε2 and ε4 alleles were associated with MI risk. The study suggests that there is close association between ApoE polymorphism and MI risk. It shows that ApoE ε2 allele is a protective factor of MI, while ε4 allele is a risk factor of MI, especially in Caucasian and Asian population. Nevertheless, well-designed, unbiased and larger sample size studies are required to confirm the results.

[Effect of parathyroid hormone related protein on proliferation of human osteoblast-like cell under tension force].

OBJECTIVE: To investigate the effect of parathyroid hormone related protein (PTHrP) on proliferation of human osteoblasts (MG-63) under the circumstance of tension force in vitro. METHODS: An apparatus was designed and fabricated by which force was loaded onto the cultured cells in vitro. Reverse transcription-polymerase chain reaction (RT-PCR) was used for measuring the expression of PTHrP mRNA and c-fos mRNA. The effect of tension force and different PTHrP dose(0, 0.01, 0.1, 1 nmol/L) on the proliferation of human osteoblasts were examined using flow cytometry. RESULTS: Various forces of the mechanical stretching exerted different influences on the intensities of the mRNA' expression. The strain of 12% induced the most remarkable mRNA' expression. The mitogenesis happened in the group with tension force (12%) combined with PTHrP was more active than that in the group with PTHrP or tension' force only. Tension force combined with PTHrP induced significantly more c-fos mRNA than that of tension force only. CONCLUSION: The mechanical stretching can inevitably influence the expression of PTHrP mRNA. The most active mitogenesis happened in the group with tension force combined with PTHrP. The effect may be related with the signaling pathways of c-fos.

[Effect of continuously compressive pressure on the expression of RANKL mRNA in human periodontal ligament cells in vitro].

OBJECTIVE: To determine the effect of continuously compressive pressure (CCP) on the expression of receptor activator of nuclear factor kappa B ligand (RANKL) in human periodontal ligament cells (HPDLCs) and to investigate the role of RANKL in alveolar bone rebuilding during orthodontic tooth movement. METHODS: The primary HPDLCs were isolated from human periodontal ligament by explanting enzymatic digestion with trypsin and collagenase to establish a pressure model. Top-bottom axial pressures (1, 2, and 3 g/cm(2)) were laid on HPDLCs for 0.5, 1.5, 6, 12, 24, and 48 h, respectively. The RANKL expression was identified by the reverse transcription-polymerase chain reaction (RT-PCR) at the mRNA level. RESULTS: The expression of RANKL mRNA significantly increased in a time-dependent manner (P<0.01), so did the value of pressure, especially in the 2 g/cm(2) group (P<0.05). CONCLUSION: CCP can up-regulate the expression of RANKL mRNA in human periodontal ligament cells.