Fabrication of three-dimensional microdisk resonators in calcium fluoride by femtosecond laser micromachining

We report on fabrication of on-chip calcium fluoride (CaF2) microdisk resonators using water-assisted femtosecond laser micromachining. Focused ion beam (FIB) milling is used to create ultra-smooth sidewalls. The quality (Q)-factors of the fabricated microresonators are measured to be 4.2x10^4 at wavelengths near 1550 nm. The Q factor is mainly limited by the scattering from the bottom surface of the disk whose roughness remains high due to the femtosecond laser micromachining process. This technique facilitates formation of on-chip microresonators on various kinds of bulk crystalline materials, which can benefit a wide range of applications such as nonlinear optics, quantum optics, and chip-level integration of photonic devices.Comment: 7 pages, 3 figure

Characterization of Soybean Protein Adhesives Modified by Xanthan Gum

The aim of this study was to provide a basis for the preparation of medical adhesives from soybean protein sources. Soybean protein (SP) adhesives mixed with different concentrations of xanthan gum (XG) were prepared. Their adhesive features were evaluated by physicochemical parameters and an in vitro bone adhesion assay. The results showed that the maximal adhesion strength was achieved in 5% SP adhesive with 0.5% XG addition, which was 2.6-fold higher than the SP alone. The addition of XG significantly increased the hydrogen bond and viscosity, as well as increased the β-sheet content but decreased the α-helix content in the second structure of protein. X-ray diffraction data showed significant interactions between SP molecules and XG. Scanning electron microscopy observations showed that the surface of SP adhesive modified by XG was more viscous and compact, which were favorable for the adhesion between the adhesive and bone. In summary, XG modification caused an increase in the hydrogen bonding and zero-shear viscosity of SP adhesives, leading to a significant increase in the bond strength of SP adhesives onto porcine bones

Response of Three Kinds of Detoxifying Enzymes from Odontotermes formosanus (Shiraki) to the Stress Caused by Serratia marcescens Bizio (SM1)

Subterranean termite Odontotermes formosanus (Shiraki) (Blattodea: Isoptera: Termitidae), is a pest species found in forests and dams. Serratia marcescens Bizio (SM1) has a potential pathogenic effect on O. formosanus. However, the response of detoxifying enzymes to exposure by S. marcescens in O. formosanus has not been studied. In the present work, 20 detoxifying enzyme genes, including 6 glutathione S-transferases (GSTs), 5 UDP glycosyltransferases (UGTs) and 9 Cytochrome P450s (CYPs), were identified from the O. formosanus transcriptome dataset by bioinformatics analysis. Furthermore, the effects of SM1 infection on the transcription levels of detoxifying enzyme genes (GSTs, UGTs and CYPs) in O. formosanus were determined. The results showed that the expression of all detoxifying enzyme gene, except one GST, in O. formosanus were altered in response to the infection by SM1. The response of GSTs, UGTs and CYPs to SM1 in O. formosanus suggested that they may play an important role in the defense against bacterial infection such as SM1, and implies that termites have evolved a complex immune response to potential pathogens

Computational diagnostics for flame acceleration and transition to detonation in a hydrogen/air mixture

A new computational diagnostic method for pressure-induced compressibility is proposed by projecting its local contribution to the chemical explosive mode (CEM) in the chemical explosive mode analysis (CEMA) framework. The new method is validated for the study of detonation development during the deflagration-to-detonation transition (DDT) process. The flame characteristics are identified through the quantification of individual CEM contributions of chemical reaction, diffusion, and pressure-induced compressibility. Numerical simulations are performed to investigate the DDT processes in a stoichiometric hydrogen-air mixture. A Godunov algorithm, fifth-order in space, and third-order in time are used to solve the fully compressible Navier-Stokes equations on a dynamically adapting mesh. A single-step, calibrated chemical diffusive model (CDM) described by Arrhenius kinetics is used for energy release and conservation between the fuel and the product. The new diagnostic method is first applied to one-dimensional (1D) canonical flame configurations followed by two-dimensional (2D) simulations of DDT in an obstructed channel where different detonation initiation scenarios are examined using the new CEMA projection formulation. Detailed examinations of the idealized configuration of detonation initiation through shock focusing mechanism at a flame front are also studied using the new formulation. A comparison of the currently proposed CEMA projection and the original formulation by the authors suggests that including the pressure-induced compressibility is essential for the use of CEMA in DDT process. The results also show that the new formulation of CEMA projection can successively capture the detonation initiation through either a gradient mechanism or a direct initiation mechanism, and therefore can be used as an effective local analytical tool for the computational diagnostics of detonation initiation in a DDT process. It was found that detonation development is characterized by a strong contribution of chemistry role to the CEM which is pivotal to the initiation of detonation. The role of compressibility is found enhanced at the edge of the detonation front where diffusion was found to have minimal effects on detonation development

Effect of activation energy on detonation re-initiation behaviors in hydrogen-air mixtures

Two-dimensional simulations of a detonation propagating over a semi-cylinder in a channel filled with a stoichiometric hydrogen-air mixture are presented. A full set of Navier-Stokes equations is solved using a third-order WENO algorithm with HLLC flux, coupled with a calibrated, single-step chemical diffusive model (CDM). Simulation results using five different effective activation energies $\mathcal{E}=$ 4, 6, 10, 12 and 14 are presented featuring four distinct detonation attenuation regimes, including unattenuated detonation transmission ($\mathcal{E}=$ 4), critical detonation re-initiation ($\mathcal{E}=$ 6, and 10), cycled detonation re-initiation ($\mathcal{E}=$ 12), and complete quenching ($\mathcal{E}=$ 14). The degree of cell irregularity and the intensity of triple points are found positively correlated with the effective activation energy. With a low effective activation energy ($\mathcal{E}=$ 4), the CDM captures a regular cellular pattern, and the cellular structure remains intact as it propagates over the obstacle. With intermediate effective activation energies ($\mathcal{E}=$ 6, and 10), the detonation cell size increases and the cell structures become less regular with emerging multi-level cell structures. Here, a critical detonation re-initiation event is captured, where a strong transverse detonation wave forms following the Mach shock reflection, and eventually leads to a steady detonation propagation. At high effective activation energy ($\mathcal{E}=$ 12), the initial transverse detonations fail to produce a self-sustained detonation wave and multiple ignition and quenching events are found before the final establishment of the detonation wave