Buckling behavior of ternary one-dimensional van der Waals heterostructures.

One-dimensional van der Waals heterostructures (1D vdWHs) may suffer from external compression when applied in field-effect, light-emitting and photovoltaic devices. Ternary 1D vdWHs were recently reported to be successfully synthesized (Xianget al2020Science367, 537). In present work, the buckling behavior of ternary 1D vdWH consisting of an inner carbon nanotube, a middle boron nitride nanotube and an outer molybdenum disulfide nanotube is extensively investigated by using molecular dynamics simulations. We find that the composite can effectively enhance the capability of axial compression of the inner nanotubes. The 1D vdWH gradually loses its stability under uniaxial compression and the critical stress of buckling decreases as the temperature increases. Slenderness ratioαof 4.8 ≤α≤ 7.2 has a slight influence on the strength and stability of ternary 1D vdWH under axial compression. To obtain a 1D vdWH with best compressive stability and strength, there is an optimal diameter existing for any specific length. Our work provides guidance for the design of 1D vdWH with desired compressive stability.

Analogous Diamondene Nanotube Structure Prediction Based on Molecular Dynamics and First-Principle Calculations.

A concentric twin tube (CTT) can be built by placing a carbon nanotube (CNT) in another identical CNT. Different from diamondene nanotubes, a stable CTT has no inter-shell covalent bond. As a prestressed double-walled nanotube, CTT has a lower structural stability at a finite temperature. According to the molecular dynamics and first-principle calculations, (a) CTTs have three types of relaxed configurations. In a type III CTT, the inner tube buckles to produce a V-shaped cross-section, and the outer tube may be convex or concave. (b) The minimal radii of relaxed zigzag and armchair CTTs with concave outer tubes were found. (c) After relaxation, the circumferences and areas of the two tubes in a type III CTT are different from those of the corresponding ideal CNT. The area change rate (A-CR) and circumference change rate (C-CR) of the outer tube are the first-order Gaussian function of the radius of the ideal CNT (which forms the CTT), and tends to be 73.3% of A-CR or 95.3% of C-CR, respectively. For the inner tube of a CTT, the A-CR is between 29.3% and 37.0%, and the C-CR is close to 95.8%. (d) The temperature slightly influences the findings given above.

Friction induced structural transformations of water monolayers at graphene/Cu interfaces.

Tribological and structural properties of water monolayers confined at interfaces between graphene and Cu substrates at cryogenic and room temperatures are extensively studied using molecular dynamics simulations and first-principles calculations. The frictions caused by the sliding of graphene sheets and increasing temperature will reduce the interfacial density of water molecules and lead to structural transformations of water monolayers and direct contacts of graphene with the underlying Cu substrates. Such changes in water structures give rise to higher friction forces and shear strengths at the graphene/Cu interfaces. Depending on the water coverage density and temperature, the motions of graphene on monolayer water covered Cu exhibit stick-slip and continuous slipping behaviors. The strong association of friction characteristics with structural transformations of water molecules could be used to unveil interfacial information of graphene on water adsorbed metal surfaces.

Thermal stability of a free nanotube from single-layer black phosphorus.

Similar to a carbon nanotube fabricated from a graphene sheet, a black phosphorus nanotube (BPNT) can also be theoretically produced by curling rectangular single-layer black phosphorus (SLBP). In the present study, the effect of the thermal vibration of atoms on the failure of a BPNT is investigated using molecular dynamics simulations. Two types of double-shell BPNTs obtained by curling the SLBP along its armchair/pucker and zigzag directions respectively are involved in simulation. At finite temperature, a bond on the outer shell of the tube is under tension due to both the curvature of the tube and the serious thermal vibration of the atoms. As the length of a bond with such elongation approaches its critical value, i.e. 0.279 nm, or the smallest distance between two nonbonding phosphorus atoms is over 0.389 nm caused by a great variation of the bond angle, the tube fails quickly. The critical stable states of either an armchair or a zigzag BPNT at finite temperature are calculated and compared. To achieve a stable BPNT with high robustness, the tube should have a higher radius or should work at a lower temperature. Only when the BPNT has structural stability does it have the potential application as a nanowire in a future nano electro-mechanical system.

[Tight junction protein expression of gastric mucosa and its significance in children with Helicobacter pylori infection].

OBJECTIVE: To understand the junction protein expression of gastric mucosa including occlusal proteins (occludin), closed protein-4 (claudin-4), zonula occluden-1(ZO-1), epithelial cadherin (E-cadherin), and ß ring protein (ß-catenin) and the clinical significance in children with Helicobacter pylori (Hp) infection. METHOD: Seventy patients in whom gastric endoscopy was performed because of nausea, vomiting, abdominal pain, bloating, acid reflux, melena, and other gastrointestinal symptoms were enrolled in this study from Dec. 2010 to Apr. 2013 in our hospital. Informed consent was signed by their parents, and the study was in accordance with the principles of medical ethics. Hp positivity was confirmed if both respiratory urea test (RUT) and Hp were positive by gastric mucosal pathology. Gastric mucosal samples from 70 patients were enrolled in this study, 23 of them were Hp negative, 47 of them were Hp positive (24 cases without peptic ulcer, 23 cases with peptic ulcer). The mRNA levels and protein expression of tight junction protein of gastric mucosa were measured by RT-PCR and Western blot respectively. The location and semi quantitative content of E-cadherin and ß-catenin in gastric mucosa were detected by immunohistochemical staining method. RESULT: The mRNA level of E-cadherin, ß-catenin, ZO-1 in the Hp positive group regardless of peptic ulcer was significantly lower than that in the Hp negative group. Hp positive without peptic ulcer group were 0.0008, 0.0040, 0.0014, respectively; Hp positive with peptic ulcer group were 0.0010, 0.0090, 0.0013, respectively; Hp negative group were 0.0137, 0.0423, 0.0198, respectively (F values were 36.956, 39.893, 38.962, respectively, all P<0.05). The expression of claudin-4 mRNA in Hp positive group with peptic ulcer increased significantly, the difference among Hp positive group with peptic ulcer, Hp positive group without peptic ulcer and Hp negative group was statistically significant (0.1438 vs. 0.0926 vs. 0.0789) (F value was 11.964, P<0.05), while the difference of occludin mRNA levels among the three groups was not statistically significant.Immunohistochemistry results showed that the score of E-cadherin, ß-catenin positive cell in the Hp positive patients were also significantly lower than that in the Hp negative group (t values were 3.981 and 2.340, all P<0.05, respectively). Western blot results showed that the protein levels of ß-catenin in Hp positive group with peptic ulcer were significantly lower than that in Hp negative group, while the protein levels of E-cadherin in Hp positive patients regardless of peptic ulcer were decreased significantly in Hp negative group. CONCLUSION: Our results revealed that the tight junction protein E-cadherin, ß-catenin, ZO-1 expression of gastric mucosa were decreased in children with Hp infection, while claudin-4 expression was increased in Hp positive patients with peptic ulcer, suggesting that damage to gastric epithelial barrier function may be the main pathogenesis of Hp associated gastric diseases in children.

Genetic variation of Helicobacter pylori in the oral cavity and stomach detected using thymine adenine cloning in children with chronic gastritis.

OBJECTIVES: To investigate the DNA sequence variations of Helicobacter pylori in the oral cavities and stomachs of children with chronic gastritis. METHODS: Dental plaques and gargle on 235 patients were obtained before gastroscopy. Gastric H. pylori infection was diagnosed using rapid urease test or Giemsa staining. H. pylori 16S rDNA and CagA gene were analyzed using PCR methods. Thymine adenine cloning-based sequencing was performed in patients with CagA gene positive from oral cavities. The sequence alignments and V1 variable region were evaluated by comparison with the sequence of the standard H. pylori 26695 strain. RESULTS: Totally, 46 out of the 235 patients were positive for gastric H. pylori infection. Of the 46 patients, 26 cases had amplified H. pylori 16S rDNA in both oral (plaque and gargle) and gastric samples. Of the 26 cases, 12 patients (46.1%) were positive for the H. pylori CagA gene in the oral samples, which was significantly lower than that in the gastric mucosa (80.8%; P = 0.010). The homology of the complete sequence alignment ranged from 74.0% to 92.1% in the oral and gastric samples. The V1 region alleles (positions 75-99) had 7-22 polymorphisms (homology from 12.0% to 72.0%) in 11 patients between the oral and gastric samples, but had 100% homology in 1 patient. CONCLUSIONS: Our study found that distinct H. pylori strains exist in the oral cavities of children, but we would not support the hypothesis that H. pylori in the oral cavities is an important reservoir of gastric H. pylori infections in children.

The role of the 5-hydroxytryptamine pathway in reflux-induced esophageal mucosal injury in rats.

BACKGROUND: Dysfunction of the 5-hydroxytryptamine (5-HT) signaling pathway can lead to gastrointestinal motility and secretion abnormalities and to visceral hypersensitivity. The aim of this study is to investigate the role of 5-HT in reflux-induced esophageal mucosal injury. METHODS: Fifty 8-week-old male Sprague-Dawley (SD) rats were randomly divided into a gastroesophageal reflux (GER) model group (30 rats) and a sham surgery control group (20 rats). Four weeks after surgery, the esophageal mucosa was collected for histological evaluation, 5-HT concentrations, and 5-HT selective reuptake transporter (SERT) mRNA and 5-HT4 receptor (5-HT4R) protein expressions. RESULTS: Twenty-seven rats in the GER model group survived, and three rats died. Histologically, in the GER model group, 20 rats had reflux esophagitis (RE group), and 7 rats had non-erosive reflux disease (NERD group). The 5-HT levels in the esophageal tissue from the RE group were significantly higher than those from the control and NERD groups. Both the RE and NERD groups showed significant increases in SERT mRNA expression of the esophageal mucosa than that of the controls, and the SERT mRNA level in the RE group was significantly higher than that in the NERD group. The 5-HT4R protein level of the esophageal mucosa in the RE group was significantly lower than that in the controls and the NERD group. CONCLUSIONS: We conclude that a 5-HT signaling pathway disorder could be a major factor in the pathogenesis of GER and RE.

[Application of clinical pathways in children with Rotavirus enteritis].

OBJECTIVE: Clinical pathways are standardized, multidisciplinary, integrated management plans. This study aimed to evaluate the efficacy of clinical pathways in children with Rotavirus enteritis. METHODS: Seventy-one children with Rotavirus enteritis were treated according to the clinical pathways. Seventy-five children with Rotavirus enteritis who received routine therapy and nursing interventions served as the control group. The clinical efficacies were compared between the two groups. RESULTS: The average hospitalization duration was shortened, the hospitalization costs were reduced and the parents' satisfaction rate increased in the observed group compared with the control group (P<0.05). CONCLUSIONS: The use of clinical pathways may decrease the hospitalization duration and costs and improve the quality of nursing care and the parents' satisfaction rate in children with Rotavirus enteritis.