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A series of novel phenylethynyl-endcapped polyimide oligomers were prepared by polycondensation of an aromatic diamine mixture of 1,3-bis(4-aminophenoxy) benzene (1,3,4-APB) and 3,4'-oxydianiline (3,4'-ODA) with different aromatic dianhydrides including 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 4,4'-(hexafluoro isopropylidene)diphthalic anhydride (6FDA), 4,4'-oxydiphthalic anhydride (ODPA), and 4,4'-[2,2,2-trifluoro-1-(3',5'-bis-(trifluoro-methyl)phenyl)ethylidene]-diphthalic anhydride (9FDA) in the presence of 4-phenyl-ethynylaniline (PEA) as endcapping agent in aprotic solvent at elevated temperature. The chemical structures, thermal behavior, and melt rheological properties of the synthesized polyimide oligomers were investigated. Experimental results indicated that the fluorinated polyimide oligomers derived from 6FDA (PI-2) and 9FDA (PI-4) are amorphous solid resins and exhibited lower melt viscosities than those prepared from the unfluorinated aromatic dianhydrides such as BPDA and ODPA. The BPDA-based polyimide oligomers with a molar ratio of 1,3,4-APB/3,4'-ODA = 50:50 (PI-5) showed lower melt viscosity than those derived from a mixture of 1,3,4-APB and 3,4'-ODA with molar ratios of 75:25 and 100:0, respectively. In addition, the melt viscosity of the polyimide oligomers increased obviously with increasing of the polymer calculated molecular weights. POLYM. ENG. SCI., 48:918-924, 2008. © 2008 Society of Plastics Engineers, INTRODUCTION High temperature/high performance polyimides have been widely used in aerospace and microelectronic industries, e.g. as matrices for high performance composites, as thin films and coatings for microelectronic application, as [...]

In order to improve the tribological properties of aluminum alloys, the finite element method was used to simulate the bearing capacity of the lubricant film between the friction pairs of three different textures, such as square pit array, strip groove array and the combined texture array of pits and strip grooves. The influence of different texture sizes on the bearing capacity of oil film was explored. Simulation results show that the lubricant film on combined texture array of pits and strip grooves has the best bearing capacity. The texture array of square pits and strip grooves with regular morphology were prepared on the surface of aluminum alloy specimens by pulsed Nd: YAC laser. The friction properties of combined texture array specimens were tested by the CFT-I high-speed reciprocating friction and wear tester to study the effect of texture geometry on the tribological properties between the contact surfaces of friction pairs. The morphologies of the wear surface of the specimens were observed by the microscopy system. The test results show that compared with the non-textured surface, the average friction coefficient of the combined texture surface is significantly reduced, and the fluctuation range of friction coefficient is small. The specimen with texture size of 80 µm shows the lowest friction coefficient. The variation regulations of wear mark depth on matrix surface by test and the lift coefficient of lubricating oil by simulation are similar, which provides a certain theoretical basis for the design of micro-texture parameters. [ABSTRACT FROM AUTHOR]

A general technique describing the pulse shape and temporal width of Q-switched lasers is presented. It was possible to obtain characteristic equations for the pulse shape of Q-switched lasers and identify some definitions for calculation of pulse symmetry properties and pulse width.

Hypoxia is a remarkable trait of the tumor microenvironment (TME). When facing selective pressure, tumor cells show various adaptive characteristics, such as changes in the expression of cancer hallmarks (increased proliferation, suppressed apoptosis, immune evasion, and so on) and more frequent cell communication. Because of the adaptation of cancer cells to hypoxia, exploring the association between cell communication mediators and hypoxia has become increasingly important. Exosomes are important information carriers in cell-to-cell communication. Abundant evidence has proven that hypoxia effects in the TME are mediated by exosomes, with the occasional formation of feedback loops. In this review, we equally focus on the biogenesis and heterogeneity of cancer-derived exosomes and their functions under hypoxia and describe the known and potential mechanism ascribed to exosomes and hypoxia. Notably, we call attention to the size change of hypoxic cancer cell-derived exosomes, a characteristic long neglected, and propose some possible effects of this size change. Finally, jointly considering recent developments in the understanding of exosomes and tumors, we describe noteworthy problems in this field that urgently need to be solved for better research and clinical application. [ABSTRACT FROM AUTHOR]

Objective: Distal‐less homeobox 6 (DLX6) has been reported to play important roles in the development of craniofacial structures, inner ear, limb, and brain. We found in our previous investigation that DLX6 was significantly highly expressed in oral cancer tissues in The Cancer Genome Atlas database. This study aimed to explore its roles and regulation mechanism in oral squamous cell carcinoma. Materials and methods: We analyzed the expression of DLX6 and its association with overall survival in OSCC by real‐time quantitative PCR. Besides, clone formation, proliferation, and apoptosis were detected after knocking down DLX6 and microarray analysis was performed to explore the possible regulatory mechanism. Results: DLX6 was overexpressed in oral cancer tissues and was associated with advance tumor stage and poor prognosis. In vitro studies have shown that DLX6 promotes proliferation and inhibits cell apoptosis in oral cancer cells. Microarray analysis along with Western blotting results indicated that DLX6 significantly associated with malignant tumors and may regulate OSCC cells proliferation through EGFR‐CCND1 axis. Conclusion: DLX6 promotes cell proliferation and suppresses cell apoptosis in oral cancer cells. EGFR‐CCND1 pathway might be the potential mechanism participating in the regulating axis. [ABSTRACT FROM AUTHOR]

Flexible films with electromagnetic interference (EMI) shielding properties can be effective in reducing electromagnetic interference and radiation problems in everyday environments. However, maintaining the durability of shielding materials in harsh environments is another important challenge. Herein, a "sandwich-structured" EMI shielding film with high thermal stability and high toughness was prepared by electrospinning technology. The sandwich film consisted of two identical layers of silver nanowire-polyimide (AgNW-PI) nanofiber mats and a highly conductive layer of Ti3C2Tx MXene nanosheets. The AgNW-PI/MXene/AgNW-PI films obtained after hot pressing have excellent mechanical properties and EMI shielding performances (3885.6 dB cm–1), and they have long-term serviceability in harsh environments. In addition, the unique sandwich structure gives these materials low thermal conductivity (32.77 mW m–1 k–1) and superior flame retardant properties. This work provides a feasible strategy for the preparation of flexible multifunctional EMI shielding films, which have the potential to be widely applied in harsh environments. [ABSTRACT FROM AUTHOR]

Calcium hydroxide was used as a swelling agent and grinding aid to grind together with cellulose raw materials to prepare microfibrillated cellulose (MFC). Carbon dioxide was introduced to obtain MFC coated with calcium carbonate (CMFC). The effect of calcium hydroxide dosage on the fibrillation process of cellulose materials and the characteristics of MFCs and CMFCs were studied. Results show that when the dosage of calcium hydroxide was 5 % (based on cellulose materials), calcium hydroxide could be completely dissolved in water and had a swelling effect on cellulose materials. When the dosage reached 10 %, undissolved calcium hydroxide particles could serve as grinding media to assist in the fibrillation of cellulose materials. When the dosage exceeded 50 %, the auxiliary grinding effect of calcium hydroxide was more obvious. After accelerated carbonation, the generated calcium carbonate nanoparticles were coated on the surface of MFC, which increased its viscosity and decreased water retention value. The presence of calcium carbonate also facilitated the concentration, redispersion, and drying of MFC. The pretreatment, mechanical fibrillation, and accelerated carbonation were carried out in the same equipment without the need for heating or washing. Therefore, this study provides a in situ and one step method for the preparation of MFC. [ABSTRACT FROM AUTHOR]

Background: Tumor cells are known to release large numbers of exosomes containing active substances that participate in cancer progression. Abnormally expressed long noncoding RNAs (lncRNAs) have been confirmed to regulate multiple processes associated with tumor progression. However, the mechanism by which lncRNAs affect exosome secretion remains unclear. Methods: The underlying mechanisms of long noncoding RNA LINC00511 (LINC00511) regulation of multivesicular body (MVB) trafficking, exosome secretion, invadopodia formation, and tumor invasion were determined through gene set enrichment analysis (GSEA), immunoblotting, nanoparticle tracking analysis, confocal colocalization analysis, electron microscopy, and invasion experiments. Results: We revealed that the tumorigenesis process is associated with a significant increase in vesicle secretion in hepatocellular carcinoma (HCC). Additionally, LINC00511 was significantly more highly expressed in HCC tissues and is related to vesicle trafficking and MVB distribution. We also found that in addition to the formation of invadopodia in HCC progression, abnormal LINC00511 induces invadopodia formation in HCC cells by regulating the colocalization of vesicle associated membrane protein 7 (VAMP7) and synaptosome associated protein 23 (SNAP23) to induce the invadopodia formation, which are key secretion sites for MVBs and control exosome secretion. Finally, we revealed that LINC0051-induced invadopodia and exosome secretion were involved in tumor progression. Conclusions: Our experiments revealed novel findings on the relationship between LINC00511 dysregulation in HCC and invadopodia production and exosome secretion. This is a novel mechanism by which LINC00511 regulates invadopodia biogenesis and exosome secretion to further promote cancer progression. [ABSTRACT FROM AUTHOR]

The co‑carbonization of refined coal tar pitch (RCTP) and brominated industrial methyl naphthalene (BIMNP) employing benzoyl chloride (BC) as a catalyst has been explored to create an isotropic spinnable pitch for carbon fibers with notable tensile strength. BIMNP is derived from industrial methyl naphthalene (IMNP) via photo-bromination assisted by visible light using N-bromosuccinimide (NBS) as a brominating agent. This research investigates the impact of the mass ratio of RCTP and BIMNP on the composition, molecular structure, and thermophysical characteristics of the co‑carbonized pitch. A tentative elucidation of the co‑carbonization mechanism involving RCTP, BIMNP, and BC is presented. Adjusting the NBS-to-IMNP mass ratio leads to the complete conversion of 1-methylnaphthalene (1-MNP) and 2-methylnaphthalene (2-MNP) in IMNP into 1-bromomethylnaphthalene (1-BMNP) and 2-bromomethylnaphthalene (2-BMNP), respectively. The co‑carbonized pitch exhibits enhanced pitch production, increased thermal stability, and improved spinnability compared to pitch synthesized via thermal polycondensation. The resulting carbon fibers experience a rise in tensile strength by 947 MPa and an increase in Young's modulus by 41.3 GPa as BIMNP content varies from 10% to 30%. Using BIMNP as a co‑carbonization agent offers a promising avenue for producing pitch-based carbon fibers meeting automotive industry requirements. [Display omitted] • Industrial methylnaphthalene was selectively brominated by N-bromosuccinimide under visible light irradiation. • Isotropic pitches were synthesized by co-carbonization of coal tar pitch and brominated industrial methylnaphthalene. • The co-carbonized pitch exhibits an increased pitch yield and enhanced polycondensation degree. • The structure of methylene-bridged aromatic rings enhances the spinnability of the co-carbonized pitch. • The prepared carbon fibers exhibit a tensile strength of 2283 MPa and a Young's modulus of 94.3 GPa. [ABSTRACT FROM AUTHOR]