Polytetrafluoroethylene (PTFE) has been widely applied as a biomaterial owing to its good stability and bioinertness. A PDA/TiO2 composite film was prepared on the surface of PTFE substrate through polydopamine (PDA) assisted in-situ co-deposition, so that the hydrophilicity and cellular responses could be improved. It was found that the film consists of PDA and TiO2. The content of TiO2 in the film can be controlled through the amount of TiO2 sol added in the deposition solution. The film is bonded to the substrate strongly. The shear strength reaches 23.5 MPa. Fibroblasts and osteoblasts are seeded on the surface of the modified substrate, and one-day cell adhesion and three-day proliferation experiments show that the cellular response of the modified substrate are significantly improved. Such deposition method is simple and easy, exhibiting wide potential in surface modification of PTFE for biomedical application.
The novel tubular carbon membranes produced from natural materials are, for the first time, reported. The novelty of this idea is to use natural rattans as precursors for making carbon membranes to address the challenges of cellulose polymers. The rattan precursors were carbonized to present evenly distributed channels inside the tubular carbon membranes. Each channel has an inner diameter of 2 x 10(-4) m with a dense-selective inner layer and a porous outer layer. Future work on selection of suitable rattans, proper pre-treatment, carbon structure tailoring can be conducted to open a new research field of carbon membranes/materials.
Gear eccentricity, one of the most common defects of gear systems, affects not only dynamic behavior but also mesh stiffness. Accurate mesh stiffness under defect conditions is vital for the dynamic simulation and fault diagnosis of gear systems. Hence, the timevarying mesh stiffness affected by gear eccentricity, which is commonly neglected in most studies, is incorporated in the proposed twostage spur gear dynamic model and calculated by a novel gear mesh model with an improved potential energy method. The effects of mesh stiffness with and without gear eccentricity on the gear system are compared on the basis of the constructed dynamic model. The influences of gear eccentricity on dynamic transverse and torsional responses, as well as dynamic transmission errors, are also quantitatively studied. Some helpful analytical results are then presented.
Novel nanocomposites for dielectric applications based on a polypropylene (PP) blend filled with nanosilica are developed in the frame of the European `GRIDABLE' project. A systematic study of the influence of surface modification of the nanosilica on the dielectric properties of the PP/silica blend was performed. The main goal of this investigation was to modify the chemical composition of the silica surface, which is expected to improve the charge trapping properties of the nanocomposites. For the modification of the silica surface, a "green" approach was utilized: a dry silanization method, which is performed without the need of a solvent. Eight different silanes were investigated in this study, which are categorized into three different groups: I) Aliphatic silanes with a different number of alkoxy groups II) Hydrocarbon silanes containing delocalized electron clouds III) Polar silanes containing hetero elements (nitrogen, sulfur or oxygen) The results of the thermogravimetric analysis (TGA) show higher weight loss of the modified silicas in comparison to the unmodified one. This indicates that the dry process is an effective method to perform silica surface modification using alkoxysilanes. The charge trapping properties were studied by Thermally Stimulated Depolarization Current (TSDC) measurements. The obtained TSDC results show that the trap density peak is not significantly shifted in temperature when the silica is modified with functional groups elementally similar to the polymer matrix. However, their incorporation influences the traps density and suppress the deeper traps occurring near the range of the melting temperature of PP. When the silica surface is modified with a precursor containing a hetero element, it has an effect on both, trap level depth as well as density. Depending on the type of the hetero element (sulfur, nitrogen, oxygen), the trap depth shifted to higher temperatures, and the trap density decreased to significantly lower levels. Nitrogen appears to have the strongest effect on the charge trap properties. All these first stage of results show that incorporation of modified nanosilica into a PP matrix seems to be a promising approach to tailor its electric properties. Further development of these composites would lead to benefits for high-voltage cable and capacitors applications.
Magnetic fluid seal is the most important and mature application of magnetic fluid. Usually, gravity is ignored when analysing the performance of magnetic fluid seal and designing magnetic fluid sealing devices. With the expansion of magnetic fluid seal applications, gravity could seriously affect the performance of magnetic fluid seal, especially when the "O" ring diameter of magnetic fluid and sealing gap are both large. In this paper, the influence of gravity on the anti-pressure ability of magnetic fluid seal is theoretically analysed and proven by the experiments. The results show that magnetic fluid seal has a limit size that is directly proportional to the magnetic field gradient in the sealing gap and is inversely proportional to the ratio of magnetic fluid density to the magnetization. If the diameter of the magnetic fluid "O" rings, whose centre axis is perpendicular to the direction of gravity, is far smaller than the limit size, the influence of gravity on the anti-pressure ability of magnetic fluid seal can be neglected. However, if the size is close to or greater than the limit size, gravity would lead to a drop in the anti-pressure ability of magnetic fluid seal.
This and the companion paper present a constitutive model for granular materials with evolving contact structure and contact forces, where the contact structure and contact forces are characterised by some statistics of grain-scale entities such as contact normals and contact forces. And these statistics are actually the fabric or force terms in the stress-force-fabric (SFF) equation. The stress-strain response is obtained by inserting the predicted fabric or force terms from evolution equations into the SFF equation. Discrete element modelling is used to verify the slightly modified SFF equation and also to obtain the data of how the contact structure and contact forces evolve in various loading paths. It is demonstrated that a normalised contact force is a better measure of the contact forces in polydisperse granular assemblies and strong contacts should be contacts with larger normalised contact forces. The modified SFF equation is shown to predict the stress accurately. The constitutive equations regarding the response of the contact structure and contact forces are presented and they along with the SFF equation form a constitutive model, which is found capable of capturing the observed phenomena correctly and predicting the mechanical response in various loading conditions. The model is shown to be an extension to the hypoplastic models with more state variables.
This and the companion paper present a constitutive model for granular materials with evolving contact structure and contact forces, where the contact structure and contact forces are characterised by some statistics of grain-scale entities such as contact normals and contact forces. And these statistics are actually the fabric or force terms in the stress-force-fabric (SFF) equation. The stress-strain response is obtained by inserting the predicted fabric or force terms from evolution equations into the SFF equation. In the model, the critical state is characterised by two fitting equations and three critical state parameters. A semi-mechanistic analysis is conducted about the change of the contact number and the obtained results are combined with observed phenomena in DEM virtual experiments to give the constitutive equations for the fabric terms. The change of fabric anisotropy is related to the strain rate, current fabric anisotropy and also contact forces. The change of coordination number is induced by two terms related to volumetric and shear deformations, and also an additional term related to the change of fabric anisotropy. The constitutive equations regarding the force terms are also proposed. All the fabric or force terms are modelled to tend toward their critial state value, which agrees with Li and Dafalias's (J Eng Mech 138(3):263-275, 2012. 10.1061/(ASCE)EM.1943-7889.0000324) basic philosophy in their evolution equation for the fabric tensor. These equations along with the SFF equation form a constitutive model.
Novel nanocomposites for dielectric applications-based polypropylene/poly(ethylene-co-octene) (PP/POE) blends filled with nano silica are developed in the framework of the European 'GRIDABLE' project. A tailor-made low-pressure-plasma reactor was applied in this study for an organic surface modification of silica. Acetylene gas was used as the monomer for plasma polymerization in order to deposit a hydrocarbon layer onto the silica surface. The aim of this modification is to increase the compatibility between silica and the PP/POE blends matrix in order to improve the dispersion of the filler in the polymer matrix and to suppress the space charge accumulation by altering the charge trapping properties of these silica/PP/POE blends composites. The conditions for the deposition of the acetylene plasma-polymer onto the silica surface were optimized by analyzing the modification in terms of weight loss by thermogravimetry (TGA). X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray fluorescence spectroscopy (EDX) measurements confirmed the presence of hydrocarbon compounds on the silica surface after plasma modification. The acetylene plasma modified silica with the highest deposition level was selected to be incorporated into the PP/POE blends matrix. X-ray diffraction (XRD) showed that there is no new crystal phase formation in the PP/POE blends nanocomposites after addition of the acetylene plasma modified silica. Differential scanning calorimetry results (DSC) show two melting peaks and two crystallization peaks of the PP/POE blends nanocomposites corresponding to the PP and POE domains. The improved dispersion of the silica after acetylene plasma modification in the PP/POE blends matrix was shown by means of SEM-EDX mapping. Thermally stimulated depolarization current (TSDC) measurements confirm that addition of the acetylene plasma modified silica affects the charge trapping density and decreases the amount of injected charges into PP/POE blends nanocomposites. This work shows that acetylene plasma modification of the silica surface is a promising route to tune charge trapping properties of PP/POE blend-based nanocomposites.
Given the scheduling model of bike-sharing, we consider the problem of hitting a set of n axis-parallel line segments in R2 by a square or an -circle (and two squares, or two -circles) whose center(s) must lie on some line segment(s) such that the (maximum) edge length of the square(s) is minimized. Under a different tree model, we consider (virtual) hitting circles whose centers must lie on some tree edges with similar minmax-objectives (with the distance between a center to a target segment being the shortest path length between them). To be more specific, we consider the cases when one needs to compute one (and two) centers on some edge(s) of a tree with m edges, where n target segments must be hit, and the objective is to minimize the maximum path length from the target segments to the nearer center(s). We give three linear-time algorithms and an O(n2logn) algorithm for the four problems in consideration.
Dysregulated expression of long non-coding RNAs (lncRNAs) has been reported in many types of cancers, indicating that it has important regulatory roles in human cancer biology. Recently, lncRNA urothelial cancer-associated 1 (UCA1) was shown to be dysregulated in many cancer types, but the detailed mechanisms remain largely unknown. In our study, we found that upregulated UCA1 is associated with poor prognosis in gastric cancer patients. Further experiments revealed that UCA1 knockdown significantly repressed the proliferation and migration both in vitro and in vivo. Moreover, RNA sequencing (RNA-seq) analysis revealed that UCA1 knockdown preferentially affected genes that are linked to cell proliferation, cell cycle, and cell migration. Mechanistically, UCA1 promotes cell proliferation progression through repressing p21 and Sprouty RTK signaling antagonist 1 (SPRY1) expression by binding to EZH2. We found that UCA1 could mediate the trimethylation of H3K27 in promoters of p21 and SPRY1. To our knowledge, this is the first report showing the global gene profile of downstream targets of UCA1 in the progression of gastric cancer. Collectively, our data reveal the important roles of UCA1 in gastric cancer (GC) oncogenesis.
This study explored the effects of NaCl on volatile fatty acid (VFA) production from food waste by acidogenic fermentation. The production and composition of VFAs, and the microbial community in acidogenic fermentation were investigated at four different NaCl concentrations: 10, 30, 50, and 70 g/L, and at 0 g/L (control). The highest VFA production was 0.542 g/g dry weight of food waste at 10 g/L NaCl, and about 23% lower but still high at 70 g/L NaCl. Interestingly, as NaCl concentration increased, the residence time of lactic acid in the reactor increased, and the maximum production also increased. The type of acidogenic fermentation also changed from butyric acid to propionic acid as the NaCl concentration increased. Microbial community analysis showed that a large number of propionibacteria were present at the end of fermentation, indicating their high tolerance to NaCl.
This review highlights recent developments and future perspectives on CO2 capture from power plants and energy-intensive industries to reduce CO2 emissions. Different types of membrane materials for CO2 capture were reviewed in terms of material performance, energy efficiency, and cost. With regard to gas separation membrane technology, only three types of membranes have been demonstrated at pilot scale. Therefore, this work paid particular attention to recent development of membrane materials such as fixed-site-carrier membranes and ultrathin nanocomposite membranes. The required high-performance membranes with CO2 permeance of 3m(3)(STP)/(m(2)hbar) and high CO2/N-2 selectivity (>40) were identified as the future direction of material development. Moreover, novel energy-efficient process development for CO2 capture in power plant and process industry are discussed; the MTR patented air sweeping process is considered one of the most energy-efficient processes for post-combustion CO2 capture. In the last part, CO2/CH4 selectivity of >30 was pointed out to be the requirement of energy-efficient membrane system for CO2 removal from natural gas and biogas. Finally, significant improvements on membrane material performance, module, and process efficiency are still needed for membrane technology to be competitive in CO2 capture.
Biomethane, produced by biogas upgrading, has a great potential to replace part of the fossil fuel natural gas, and may be injected into a gas grid or used as compressed biomethane as vehicle fuel. The state-ofthe-art technologies for biogas upgrading in the European region are water scrubbing, pressure swing adsorption and chemical absorption, however, high performance carbon membranes may also have a great potential in this application. In this work, cellulose-derived hollow fiber carbon membranes were tested for CO2/CH4 separation at moderate pressures (5-20 bar), and a CO2/CH4 permeance selectivity >60 was obtained. The developed membranes were evaluated for biogas upgrading in a 1000 m(3)(STP)/h biogas plant based on HYSYS simulation and cost estimation. The results indicated that carbon membranes can be a promising candidate for biogas upgrading with a low processing cost of 0.078 $/m(3) at the feed pressure of 8.5 bar. Increased membrane performance can further reduce the cost. Moreover, a carbon membrane system can be very cost-effective for upgrading of biogas in small-scale plants of around 350 m(3)(STP)/h. (C) 2018 Elsevier Ltd. All rights reserved.
For the use in packer elements for oil exploration, rubber materials are required that can withstand high mechanical loads, high temperatures, and aggressive chemical media. To fulfill these demands, we designed composites of hydrogenated acrylonitrile butadiene rubber filled with both carbon black and short cut aramid fibers. Scanning electron micrographs indicate a strong connection between the resorcinol formaldehyde latex fiber coating and the peroxide-cured rubber matrix. During the preparation of the test specimens, especially care was taken to obtain samples with very well-defined fiber orientations. We studied the effect of fiber anisotropy on the hardness and on the mechanical properties under uniaxial elongation and cyclic compression at room temperature and 150 degrees C. The strongest reinforcing effect is observed when the fibers are oriented along the main direction of deformation. For tensile test, this is the case, as expected, for fibers oriented parallel to elongation. For compression tests on cylindrical specimens, we find that the fiber orientation perpendicular to compression direction is most effective. At 20-40% strain, tensile tests exhibit a pronounced yield stress which is likely the result of the loss of adhesion between the rubber matrix and the fibers. Repeated loading and unloading compression tests reveal a considerable stress softening effect between the first and second cycle for fiber-filled composites. At 150 degrees C, the rubber composites soften considerably, but small amounts of fiber still induce a significant reinforcement. POLYM. COMPOS., 39:3212-3226, 2018. (c) 2017 Society of Plastics Engineers