A new function of graphene oxide emerges: inactivating phytopathogenic bacterium Xanthomonas oryzae pv. Oryzae

The main goal of the present work is to examine the effect of graphene layers on the structural and dynamical properties of polymer systems. We study hybrid poly(methyl methacrylate) (PMMA)/graphene interfacial systems, through detailed atomistic molecular dynamics simulations. In order to characterize the interface, various properties related to density, structure and dynamics of polymer chains are calculated, as a function of the distance from the substrate. A series of different hybrid systems, with width ranging between 2.60 and 13.35 nm, are being modeled. In addition, we compare the properties of the macromolecular chains to the properties of the corresponding bulk system at the same temperature. We observe a strong effect of graphene layers on both structure and dynamics of the PMMA chains. Furthermore, the PMMA/graphene interface is characterized by different length scales, depending on the actual property we probe: density of PMMA polymer chains is larger than the bulk value, for polymer chains close to graphene layers up to distances of about 1.0–1.5 nm. Chain conformations are perturbed for distances up to about 2–3 radius of gyration from graphene. Segmental dynamics of PMMA is much slower close to the solid layers up to about 2–3 nm. Finally, terminal-chain dynamics is slower, compared to the bulk one, up to distances of about 5–7 radius of gyration.     

Image segmentation using adaptive loopy belief propagation

Loopy belief propagation (LBP) algorithm over pairwise-connected Markov random fields (MRFs) has become widely used for low-level vision problems. However, Pairwise MRF is often insufficient to capture the statistics of natural images well, and LBP is still extremely slow for application on an MRF with large discrete label space. To solve these problems, the present study proposes a new segmentation algorithm based on adaptive LBP. The proposed algorithm utilizes local region information to construct a local region model, as well as a local interaction region MRF model for image segmentation. The adaptive LBP algorithm maximizes the global probability of the proposed MRF model, which employs two very important strategies, namely, “message self-convergence” and “adaptive label pruning”. Message self-convergence can improve the reliability of a pixel in choosing a label in local region, and label pruning can dismiss impossible labels for every pixel. Thus, the most reliable information messages transfer through the LBP algorithm. The experimental results show that the proposed algorithm not only obtains more accurate segmentation results but also greater speed.     

Cladding-ring-equivalent effective index method for analyzing the propagation characteristics of multi-cladding photonic crystal fibers

Cladding-ring-equivalent effective index method (CREEIM) is proposed to analyze the propagation characteristics in the multi-cladding photonic crystal fibers (MCPCFs). The effective indices and dispersions of the step index two and three-cladding structures are calculated with the Sellmeier formula. The accuracy of CREEIM is competitive to the results calculated by the multipole method (MPM). With different structure parameters, the differences between two methods are evaluated with the relative error R_E of effective index and relative difference R_D of dispersion. This method is also used to analyze the mode cut-off and nonlinear characteristics in the three-cladding structure PCFs by calculating the mode effective index n_eff instead of complex mode field distribution.     

Bias voltage dependence of inverted magnetoresistance on the annealing temperature in MgO-based magnetic tunnel junctions

MgO-based magnetic tunnel junctions (MTJs) with a layer sequence Ir₂₂Mn₇₈ or Fe₅₀Mn₅₀ (10 nm)/CoFe (2 nm)/Ru (0.85 nm)/CoFeB (0.5?t<2 nm)/MgO (2.5 nm)/CoFeB (3 nm) have been fabricated. The bias voltage dependence of tunneling magnetoresistance (TMR) is given as a function of the annealing temperature for these MTJs, which shows the TMR ratio changes its sign from inverted to normal at a critical bias voltage (V_C) when an unbalanced synthetic antiferromagnetic stack CoFe/Ru/CoFeB is used. V_Cs change with the thickness of the pinned CoFeB and annealing temperature, which implies one can achieve different V_Cs by artificial control. The asymmetric V_C values suggest that a strong density-of-states modification occurs at bottom oxide/ferromagnet interface.     

Saturation field direction dependence of domain structures in NiFe elements

The domain structures in NiFe elements were studied by magnetic force microscopy measurement and micromagnetic modeling. The remanent states in the elements were dependent on the direction of the saturation field. The “S” and “U” states were observed at remanence by applying the saturation field at different directions. The “S” and “U” states are metastable: magnetic force microscopy tip field-induced switching from the “S” and “U” states to the flux closure configuration was observed.     

Self-consistent treatment of spin and magnetization dynamic effect in spin transfer switching

The effect of itinerant spin moment (m) dynamic in spin transfer switching has been ignored in most previous theoretical studies of the magnetization (M) dynamics. Thus in this paper, we proposed a more refined micromagnetic model of spin transfer switching that takes into account in a self-consistent manner of the coupled m and M dynamics. The numerical results obtained from this model further shed insight on the switching profiles of m and M, both of which show particular sensitivity to parameters such as the anisotropy field, the spin torque field, and the initial deviation between m and M.     

Spontaneously generated walking X-shaped light bullets

In quadratic nonlinear media with normal dispersion and nonvanishing group velocity mismatch between fundamental wave and second-harmonic pulses, the wave packets of two harmonics can be locked together in propagation in the form of walking X-shaped light bullets. The output wave packets are developed into X-shaped light bullets with significant group delay time due to mutual dragging and significant shifting in spatiotemporal spectrum due to delayed nonlinear phase shift. We also show that spontaneously generated phase-front tilting can balance the dragging force induced by group velocity mismatch and lead to zero-velocity walking X-shaped light bullets.     

Three-dimension direct writing TiO<Subscript>2</Subscript> crystalline patterns in Bi-free glass using femtosecond laser

Crystalline TiO₂ was induced three dimensionally inside Bi-free glass sample by an 800 nm, 250-kHz femtosecond laser irradiation. Micro-Raman spectra analysis indicated that the laser-induced crystals in the focal point of the laser beam were monophase TiO₂ rutile. Continuous crystalline lines were written through moving the focal point of the laser beam inside the glass. The results demonstrate that this technique is a convenient method to engrave three-dimensional patterns of crystals for fabricating integrated optical devices in transparent materials.