ABSTRACT
Thermal conductive polymer composites are satisfying for thermal management of electronic devices. However, how to choose the sizes of thermal conductive fillers to get a high thermal conductivity of composites are still clueless and poor filler size matching will also affect the processability of the composites. Closest packing model was used to guide multiscale thermal conductive particles filling silicone rubber in this work. A highest thermal conductivity of 1.381 W·m-1·K-1 at filler loading of 50 vol % was determined among nine comparing formulations. The fillers with small particle size filled the interspaces of fillers with large particle size to form more complete thermal conduction paths and heat dissipation was increased. The apparent densities and rheological tests further verified the effectiveness of closest packing model. This study provides theoretical guidance for thermal conductive polymer composites to achieve high thermal conductivity and good processability, which has an important practical application.
ABSTRACT
Drug resistance inhibits the efficacy of doxorubicin in gastric cancer. Phosphatidylinositol 3,4,5-trisphosphate RAC exchanger 2a (P-REX2a) activates the phosphatidylinositol-3-kinase (PI3K)/protein kinase B (Akt) signaling pathway by binding to and inactivating phosphatase and tensin homolog (PTEN), which functions as a tumor promoter in a number of types of cancer. However, there is no research concerning the association between P-REX2a expression and drug resistance in gastric cancer. In the present study, the expression of P-REX2a in clinical gastric cancer tissues was detected, and the mechanism of doxorubicin resistance in the gastric cancer cell line SGC7901 was investigated. Using reverse transcription-quantitative polymerase chain reaction and western blotting, it was demonstrated that the mRNA and protein expression of P-REX2a was increased in gastric cancer tissues. MTT assays were also used to determine proliferation, and proliferation was revealed to be reduced following transfection of P-REX2a small interfering (si)RNA. When the cells were treated with 0.3 µM doxorubicin for 24 h, the rate of apoptosis in the siRNA-transfected groups significantly increased and no marked changes in of PTEN and Akt expression were observed. By contrast, the activity of PTEN increased, and the expression of p-Akt (S473) decreased in the P-REX2a siRNA-transfected group compared with the control. The detection of PTEN enzymatic activity in the present study was based on phosphatidylinositol-3,4,5-trisphosphate. Therefore, it was concluded that P-REX2a may participate in the generation of resistance to doxorubicin in gastric cancer, and this may be associated with the upregulation of the PI3K/Akt signaling pathway via inactivation of PTEN.
ABSTRACT
OBJECTIVES: To summarize and appraise the available literature regarding the use of the 14C-urea breath test in the diagnosis of Helicobacter pylori infections in adult patients with dyspepsia and to calculate pooled diagnostic accuracy measures. METHODS: We systematically searched the PubMed, EMBASE, Cochrane Library, Chinese Journals Full-text (CNKI) and CBMDisc databases to identify published data regarding the sensitivity, specificity, and other measures of diagnostic accuracy of the 14C-urea breath test in the diagnosis of Helicobacter pylori infections in adult patients with dyspeptic symptoms. Risk of bias was assessed using the QUADAS (Quality Assessment of Diagnostic Accuracy Studies)-2 tool. Statistical analyses were performed using Meta-Disc 1.4 software and STATA. RESULTS: Eighteen studies met the inclusion criteria. Pooled results indicated that the 14C-urea breath test showed a diagnostic sensitivity of 0.96 (95% CI 0.95 to 0.96) and specificity of 0.93 (95% CI 0.91 to 0.94). The positive like ratio (PLR) was 12.27 (95% CI 8.17 to 18.44), the negative like ratio (NLR) was 0.05 (95% CI 0.04 to 0.07), and the area under the curve was 0.985. The DOR was 294.95 (95% CI 178.37 to 487.70). The 14C-urea breath test showed sufficient sensitivity and specificity for diagnosing Helicobacter pylori infection, but unexplained heterogeneity after meta-regression and several subgroup analyses remained. CONCLUSIONS: The UBT has high accuracy for diagnosing H. pylori infections in adult patients with dyspepsia. However, the reliability of these diagnostic meta-analytic estimates is limited by significant heterogeneity due to unknown factors.
