Corona-induced graft polymerization for surface modification of porous polyethersulfone membranes

Graft polymerization of acrylic acid (AA) onto porous polyethersulfone (PES) membrane surfaces was developed using corona discharge in atmospheric ambience as an activation process followed by polymerization of AA in aqueous solution. The effects of the corona parameters and graft polymerization conditions on grafting yield (GY) of AA were investigated. The grafting of AA on the PES membranes was confirmed by ATR-FTIR and X-ray photoelectron spectroscopy (XPS) analysis. Porosimetry measurements indicate the average pore diameters and porosities of the modified membranes decrease with the increase of the GY. The hydrophilicity and surface wetting properties of the original and modified membranes were evaluated by observing the dynamic changes of water contact angles. It is found that the grafting of AA occurs not only on the membrane surfaces, but also on the pore walls of the cells inside the membrane. The permeability experiments of protein solution reveal that the grafting of PAA endows the modified membranes with enhanced fluxes and anti-fouling properties. The optimized GY of AA is in the range of 150-200 μg/cm². In addition, the tensile experiments show the corona discharge treatment with the power lower than 150 W yields little damage to the mechanical strength of the membranes.     

δ/γ transformation in non-equilibrium solidified peritectic Fe-Ni alloy

Through phase transformation kinetic analysis and experimental observation, the δ/γ transformation occurring in the non-equilibrium peritectic Fe-4.33at.%Ni alloys was systematically investigated. According to JMA solid-state transformation kinetic theory, the Time-Temperature-Transformation (TTT) curves of the δ/γ transformation in peritectic Fe-Ni alloy were calculated. On this basis, the physical correlation between the δ/γ transformation and the initial undercooling of melt (△T) was elucidated. The results indicate that the change of △T can alter not only the overall δ/γ transformation pathways but also the transformation fraction with respect to each transformation mechanism.     

Observability analysis of navigation system using point-based visual and inertial sensors

A matrix Kalman filter (MKF) has been implemented for a navigation system using point-based visual and inertial sensors. The observability conditions have been proved by the observability rank criterion based on Lie derivatives. The conditions are: (a) at least one degree of rotational freedom is excited and (b) at least three observed points are not collinear where any two points are linearly independent. Experimental results have demonstrated that the proposed algorithm obtains the same accurate as the line-based algorithm.     

Experimental and DFT investigation of surface degradation of polyvinylidene fluoride membrane in alkaline solution

The degradation processes of polyvinylidene fluoride (PVDF) membranes in alkaline solutions were studied using FTIR, FT-Raman, XPS and density functional theory (DFT) simulations. The activation energies for the degradation paths were calculated by LST/QST search methods. The corresponding Gibbs free energies were calculated using a continuum solvation model. The analysis of the spectra indicates the presence of C=C bonds, hydroxyl and carbonyl groups on PVDF membranes. It can be inferred, from DFT calculations, that defluorination is the energetically favorable path, followed by the formation of C=C bonds. The subsequent hydroxylation and carbonyl formation experience higher activation barriers than the formation of C=C bonds. The results indicate that the theoretical calculations are in accordance with the experimental data.     

Phases of supersymmetric gauge theories with flavors

We explore the phases of supersymmetric U(N) gauge theories with fundamental matter that arise as deformations of SQCD by the addition of a superpotential for the adjoint chiral multiplet. As the parameters in the superpotential are varied, the vacua of this theory sweep out various branches, which in some cases have multiple semiclassical limits. In such limits, we recover the vacua of various product gauge group theories, with flavors charged under some group factors. We describe in detail the structure of the vacua in both classical and quantum regimes, and develop general techniques such as an addition and a multiplication map which relate vacua of different gauge theories. We also consider possible indices characterizing different branches and potential relationships with matrix models.     

Surface modification and characterization of magnesium hydroxide sulfate hydrate nanowhiskers

In order to enhance the compatibility with plastic polymers, magnesium hydroxide sulfate hydrate (MHSH) nanowhiskers were modified through grafting methyl methacrylate (MMA) on the surface of the nanowhiskers by emulsion polymerization. The influences of the reaction time, MMA monomer content, adding speed of monomer and the reaction temperature on the grafting ratio were investigated. Thermogravimetry (TG), Fourier transform infrared (FT-IR) spectroscopy, X-ray powder diffraction (XRD), scanning electron microscope (SEM), energy-dispersive X-ray (EDX) spectroscopy and surface contact angle measurement were used to characterize the effect of surface modification. The results showed that the MHSH nanowhiskers were uniformly coated by polymethyl methacrylate (PMMA), and a well-defined core-shell hybrid structure of MHSH/PMMA was obtained. The surface contact angle of the hybrid whiskers increased to 87.32° from 12.71° and the whiskers surface was changed from hydrophilic to lipophilic.     

A simple pathway to ordered silica nanopattern from self-assembling of block copolymer containing organic silicon block

Self-assembly of block copolymer is an effective strategy to prepare periodic structures at nanoscale. In this paper an unique and very simple method to prepare inorganic silica nanopattern is demonstrated from self-assembling of poly(styrene-block-dimethylsiloxane) (PS-b-PDMS) on the surface of silicon wafer. To simplify the patterning process, at first we obtain highly ordered PDMS microdomains, which are covered with PS layer by controlling solvent vapor annealing conditions. Following exposure to UV/O₃ irradiation, nanopatterned surface consisting of silicon oxide is fabricated directly via selectively etching PS phase and converting PDMS phase into silicon oxide. As tuning the composition of the block copolymer, hexagonally packing dot and straight stripe pattern can be obtained. Finally, the time evolution from spheres morphology to aligned long cylinders is discussed. These results hold promise for nanolithography and the fabrication of nanodevices.     

Synchronization transition in gap-junction-coupled leech neurons

Real neurons can exhibit various types of firings including tonic spiking, bursting as well as silent state, which are frequently observed in neuronal electrophysiological experiments. More interestingly, it is found that neurons can demonstrate the co-existing mode of stable tonic spiking and bursting, which depends on initial conditions. In this paper, synchronization in gap-junction-coupled neurons with co-existing attractors of spiking and bursting firings is investigated as the coupling strength gets increased. Synchronization transitions can be identified by means of the bifurcation diagram and the correlation coefficient. It is illustrated that the coupled neurons can exhibit different types of synchronization transitions between spiking and bursting when the coupling strength increases. In the course of synchronization transitions, an intermittent synchronization can be observed. These results may be instructive to understand synchronization transitions in neuronal systems.     

Cytotoxic effects and in vitro reversal of multidrug resistance by therapeutic ultrasound in human hepatocarcinoma cell line (HepG2)

Multidrug resistance (MDR) is one of the major obstacles to successful chemotherapy of human malignancies. Although many strategies have been explored to overcome MDR, none of them have been proven to be clinically useful until now. The aim of this study was to investigate whether a novel therapeutic ultrasound (US) approach would have useful effects on the reversal of MDR in cancer cells. Wild-type and MDR phenotype (HepG2/ADM) cells of the human hepatocarcinoma cell line HepG2 were exposed to 0.8 MHz US at an intensity of 0.43 W/cm² for a 9 s exposure (total energy density: 3.87 J/cm²). After US exposure, cell number and viability were counted immediately, and flow cytometry was performed to measure retention of rhodamine 123 and adriamycin in HepG2 and HepG2/MDR cells. Both cell lines were then incubated in suspension with adriamycin, vincristine, etoposide, cisplatin and 5-fluorouracil, respectively, and the MTT assay was used to determine cytotoxicity. The results showed that US exposure could significantly increase the uptake of Rh123 and ADM by HepG2/ADM tumor cells. The resistant index for the chemotherapeutic drugs was significantly lower in the US-exposed HepG2/ADM cells than in those not exposed to US. It was therefore concluded that US exposure could enhance the sensitivity of HepG2/ADM tumor cells to these chemotherapeutic agents, and the functional and structural changes induced by previous US exposure in MDR tumor cells may be responsible for it. However, further study is needed to investigate the mechanism behind US-mediated reversal of MDR.