Explore the vast range of titles available.

Recently, the tribological characteristics of rubber elastomers have attracted widespread attention of researchers due to its destructive character and its high frequency of occurrence. However, most experiments were performed by using relatively smooth mating surfaces and did not consider the effect of the surface roughness of the harder counter surface, which could be important in practical applications. This study is devoted to investigate the effect of surface roughness on friction and wear behaviour of elastomer. Various kinds of rough mating surfaces with different surface roughness from R a  = 0.5 to R a  = 0.003 on the steel plates were attained, and the reciprocating sliding tests were performed on a NBR pin against a steel plate. The friction coefficients obtained when the rubber slid against the different textured surfaces were analysed and compared. The morphologies of the NBR worn surface were examined by using scanning electron microscopy. On the basis, the optimal surface roughness values of the metal counterpart are proposed for the rubber sliding against the metal. In addition, Stribeck-like curves are obtained and their characteristics are discussed. A series of experimental results are presented to examine the effect of surface roughness on the Stribeck curves. The results show that surface roughness had a significant effect on the lubrication regime and tribological behaviours of the NBR. Overall, the rougher the surface of the counterpart is, the more easily the friction pairs enter into the ML regime. The surface damage of rubber depends on coupling action of surface roughness of the harder counter surface and lubrication regime. The knowledge gained herein provides a better understanding for the tribological characteristics of rubber elastomers associated with surface roughness, and it is useful to reduce sealant wear and lengthen their service life.

Background/Aims: Human leukocyte antigen-G (HLA-G) plays an important role in inhibiting natural killer (NK) cell function and promoting immune escape. However, the specific mechanism of HLA-G on NK in gastric cancer (GC) remains not well understood. This study investigated the expression of HLA-G in GC and the role of HLA-G-effected NK cells in GC progression. Methods: HLA-G expression in GC tissues obtained from 49 patients with GC was analyzed by immunohistochemistry and western blot. The number of tumor-infiltrating NK cells and the expression of their surface receptors were analyzed by immunohistochemistry and flow cytometry, respectively. The effect of HLA-G on NK cell proliferation was examined by Cell Counting Kit-8 (CCK8) assay. LDH release assay was used to evaluate the effect of HLA-G on the cytotoxic activity of NK cells, and the levels of IFN-γ and TNF-α in the co-cultured supernatant were detected by ELISA. Mice bearing a xenograft tumor model were used to examine the effect of HLA-G on the anti-tumor effect of NK cells. Results: HLA-G positive expression was detected in most of the GC tissues, and was correlated with the adverse prognosis of the disease. The expression of HLA-G was negatively associated with the number of tumor-infiltrating NK cells. Furthermore, GC cell lines with overexpressed HLA-G revealed their ability to inhibit the cell proliferation and cytotoxic activity of NK-92MI cells, and reduce the secretion of IFN-γ and TNF-α through immunoglobulin-like transcript 2 (ILT2). Finally, this in vivo experiment was able to prove that HLA-G can inhibit the anti-tumor effect of NK cells through ILT2. Conclusion: The expression of HLA-G was strongly correlated with the adverse prognosis of GC. The reason may be that it inhibits the proliferation and cytotoxic activity of infiltrating NK cells through ILT2.

A thermo-hydrodynamic model was introduced by considering fluid film phase change to analyze the stability of a spiral groove mechanical seal under high speeds. The Reynolds equation, energy equation and heat conduction equation were solved using the finite difference method. Two kinds of phase state stability criteria and fluid film temperature or pressure distributions in each phase state were studied. Different phase states of fluid film and phase state stability of such a spiral groove mechanical seal under variable operating and geometry conditions were analyzed. The results show that vapor mass fraction volume ratio vs sealed fluid temperature (κ-Tf) curve and film pressure coefficient versus sealed fluid temperature (Km-Tf) curve can be used as phase state stability criteria which can predict the range of instability, stability and quasi-stability of a spiral groove mechanical seal. But the Km-Tf curve is more suitable for practical engineering applications. It is found that a significant change in pressure distribution will bring about instability of a spiral groove mechanical seal. The sudden change of film pressure distribution usually occurs when the leakage flow medium in the interface is in the transition phase from quasi-liquid to quasi-vapor where κλ=0 = κ0<λ<1 and κλ=1 = 0. Optimized design of a spiral groove mechanical seal will improve its stability during the phase change from liquid phase state to vapor phase state.

The supercritical carbon dioxide (SCO2) Brayton cycle system is an energy conversion system with great potential, and its efficiency can be improved significantly by using low-leakage dry gas seals in SCO2 compressors and gas turbines. However, the high-pressure and high-speed conditions of a SCO2 dry gas seal make the impact of turbulence not negligible. In this paper, the influences of flow state on flow field distribution and sealing performance of a SCO2 dry gas seal are studied, the criteria for determining the overall flow state into the sealing gap are proposed. Explicit expressions of the flow factor for flow state determination are obtained based on the artificial neural network algorithm. The results show that turbulent flow is easy to occur in a SCO2 dry gas seal, leading to a remarkable error in predicting sealing performance using a laminar flow model. When employing a laminar flow model, there is a large error on opening force in the transition regions between turbulent and transitional flows, and a large error on leakage rate at high inlet pressure and close to the critical temperature compared to those obtained by using a turbulent flow model. In addition, the flow state judgment method proposed in this paper can accurately determine the overall flow state of a SCO2 dry gas seal under different operating conditions.

For the purpose of prolonging the service life for rubber sealing elements, the frictional behavior of acrylonitrile–butadiene rubber (NBR) surface by dielectric barrier discharge plasma treatments was investigated in this paper. Surface microstructure and chemical composition were measured by atomic force microscopy, field-emission scanning electron microscopy, and X-ray photoelectron spectroscopy, respectively. Water contact angles of the modified rubber surface were also measured to evaluate the correlation between surface wettability and tribological properties. The results show that plasma treatments can improve the properties of the NBR against friction and wear effectively, the surface microstructure and roughness of plasma-modified NBR surface had an important influence on the surface tribological behavior, and the wear depth first decreased and then increased along with the change of plasma treatment time. It was found that the wettability of the modified surface was gradually improved, which was mainly due to the change of the chemical composition after the treatment. This study suggests that the plasma treatment could effectively improve the tribological properties of the NBR surface, and also provides information for developing wear-resistant NBR for industrial applications.

Mutations in RAD51 gene are believed to be associated with elevated breast cancer risk. However, several case-control studies focusing on the association between RAD51 135G>C and breast cancer risk failed to achieve consensus. To clarify the effect of RAD51 135G>C polymorphism on breast cancer, a meta-analysis was performed. By searching PubMed and EMBASE, a total of 14 case-control studies, containing 12,183 cases and 10,183 controls, were included. The strength of association between RAD51 135G>C polymorphism and breast cancer risk was assessed by odds ratio (OR) with the corresponding 95% confidence interval (95% CI). When all the eligible studies were pooled into the meta-analysis, an elevated cancer risk was revealed in additive model (OR, 1.34; 95% CI, 1.01-1.78; P = 0.044) and recessive model (OR, 1.37; 95% CI, 1.03-1.82; P = 0.032). In subgroup analyses by ethnicity, BRCA1/2 mutation status, and family history, a significant association was found only among BRCA2 mutation carriers (additive model: OR, 4.92; 95% CI, 1.11-21.83; P = 0.036; recessive model: OR, 4.88; 95% CI, 1.10-21.67; P = 0.037). Sensitivity analysis did not perturb the results. In conclusion, this meta-analysis suggests that RAD51 variant 135C homozygote is associated with elevated breast cancer risk among BRCA2 mutation carriers.

Background and objectives Robotic surgery is positioned at the cutting edge of minimally invasive management of colorectal cancer. We performed a meta-analysis of data from randomized controlled trials (RCTs) and non-RCTs (NRCTs) that compared the clinicopathological outcomes of robotic-assisted colorectal surgery (RACS) with those of laparoscopic-assisted colorectal surgery (LACS). Inferences on the feasibility and the relative safety and efficacy have been drawn. Methods A literature search for relevant studies was performed on MEDLINE, Ovid, Embase, Cochrane Library, and Web of Science databases. Inter-group differences in the standardized mean differences and relative risk were assessed. Operation times, conversion rates to open surgery, estimated blood loss (EBL), early postoperative morbidity, and length of hospital stay (LHS) were compared. Oncologic outcomes assessed were number of lymph nodes harvested and lengths of proximal and distal resection margins. Results Twenty-four studies (2 RCTs and 22 NRCTs [5 prospective plus 17 retrospective]) with a total of 3318 patients were included. Of these, 1466 (44.18 %) patients underwent RACS and 1852 (55.82 %) underwent LACS. Conversion rates, EBL and LHS were significantly lower, while the operation times and total costs were similar between RACS and LACS. Complication rates and oncological accuracy of resection showed no significant difference. Conclusion Based on this meta-analysis, RACS appears to be a promising surgical approach with its safety and efficacy comparable to that of LACS in patients undergoing colorectal surgery. Further studies are required to evaluate the long-term cost-efficiency as well as the functional and oncologic outcomes of RACS.

The Elastomeric O-ring seal as a common reciprocating rod seal has been widely used in the aviation hydraulic system for preventing the hydraulic oil from contaminating the environment. When the hydraulic actuator is in the working process, the O-ring seal operates inherently in an unsteady operating condition. Therefore, an isothermal transient soft elastohydrodynamic mixed lubrication model that takes account of the effects of surface roughness and cavitation is implemented in this paper to predict the entire history of the seal performance, which is consisted of coupled fluid mechanics, contact mechanics and deformation analyses. The effects of the surface roughness of seals under different fluid viscosity are also discussed. The analysis results show that there is a critical rms roughness for the seal, below which the seal meets with zero leakage per cycle, but above which the seal will be in the leakage state. In addition, the critical roughness of seal surface is increases with the increasing fluid viscosity.