An experimental and numerical study of fracture coalescence in pre-cracked specimens under uniaxial compression

This study presents crack initiation, propagation and coalescence at or near pre-existing open cracks or flaws in a specimen under uniaxial compression. The flaw geometry in the specimen was a combination of a horizontal flaw and an inclined flaw underneath. This flaw geometry is different from those reported in the previous studies, where a pair of parallel flaws was used. Three materials were used, PMMA (Poly Methyl MethAcrylate), Diastone (types of molded gypsum), and Hwangdeung granite. Crack initiation and propagation showed similar and different patterns depending on the material. In PMMA, tensile cracks initiated at the flaw tips and propagated to the tip of the other flaw in the bridge area. The cracks then coalesced at a point of the inclined flaw, which is affected by the flaw inclination angle. For Diastone and Hwangdeung granite, tensile cracks were observed followed by the initiation of shear cracks. Coalescence occurred mainly through the tensile cracks or tensile and shear cracks. Crack coalescence was classified according to the crack coalescence types of parallel flaws for overlapping flaw geometry in the past works. In addition, crack initiation and coalescence stresses in the double-flawed specimens were analyzed and compared with those in the single-flawed specimen. Numerical simulations using PFC^2D (Particle Flow Code in two dimensions) based on the DEM (Discrete Element Method) were carried out and showed a good agreement with the experimental results in the coalescence characteristics in Hwangdeung granite. These experimental and numerical results are expected to improve the understanding of the characteristics of cracking and crack coalescence and can be used to analyze the stability of rock and rock structures, such as the excavated underground openings or slopes, tunneling construction, where pre-existing cracks or fractures play a crucial role in the overall integrity of such structures.     

Single‐mode distributed feedback laser operation with no dependence on the morphology of the gain medium

Organic distributed feedback (DFB) lasers can be useful photonic tools for biological applications where the roles of organic materials are important, because highly coherent single mode emission with broad tuning range can be obtained. However, the formulaic structures of organic lasers, and the uses of gain media as resonators themselves, are not suitable for inducing laser emission from irregular shaped gain media, such as dye‐staining cells and tissues. Here, we report a reusable photonic template comprising an exceedingly thin and discrete titanium dioxide (TiO₂) layer on a one‐dimensional (1D) quartz grating to induce single mode DFB lasing from a variety of states of optical gain media. Using the same template, the external gain media of optically thick and thin casted film, liquid, and a free‐standing thick film reveal single mode lasing with reliable performance. Numerical simulations demonstrate that the 25‐nm thick TiO₂ disconnected grating lines support a spatially confined DFB mode in the vertical direction, even under no index difference between superstrate and substrate. Additionally, not using the typical waveguide gain layer promises high sensitivity and detection limit in refractometric sensing. These results suggest that the photonic structure may serve as a versatile sensing platform for bioapplications.     

Bio-photonic detection method for morphological analysis of anthracnose disease and physiological disorders of Diospyros kaki

Optical Review - The pathological and physiological defects in various types of fruits lead to large amounts of economical waste. It is well recognized that internal fruit defects due to...     

Optical encryption of gray-level image using on-axis and 2-f digital holography with two-step phase-shifting method

In this paper we propose an encryption/decryption technique of gray-level image information using an on-axis 2-f digital holographic optical encrypting system with two-step phase-shifting method. This technique reduces the number of holograms in phase-shifting digital holography and minimizes the setup of the encryption system more than multistep phase-shifting technique. We are able to get the complete decrypted image by controlling the K-ratio which is defined as the reference beam intensity versus the object beam intensity. We remove the DC-term of the phase-shifting digital hologram to reconstruct and decrypt the original image information. Simulation results show that the proposed method can be used for encryption and decryption of a 256 gray-level image. Also, the result shows some errors of the decrypted image according to K-ratio.     

An efficient synthesis of valienamine via ring-closing metathesis

An efficient synthesis of valienamine is described. Valienamine was synthesized starting from commercially available 2,3,4,6-tetra-O-benzyl-D-glucose in nine steps, using ring-closing metathesis of (4S,5S,6S)-4,5,6-tribenzyloxy-7-(benzyloxymethyl)octa-1,7-dien-3-ol as a key step.     

Novel molecular drug carrier: encapsulation of oxaliplatin in cucurbit[7]uril and its effects on stability and reactivity of the drug

Oxaliplatin forms a stable 1:1 inclusion complex with cucurbit[7]uril as indicated by NMR, mass spectrometry, isothermal titration calorimetry and X-ray crystallography. The encapsulation of the drug results in a large enhancement in stability, a moderate decrease in reactivity toward guanosine but a much larger decrease in reactivity toward L-methionine, which suggests the encapsulation not only increases the stability of the drug but also may reduce unwanted side effects caused by protein binding of the platinum drug. A preliminary in vitro assay using various tumor cell lines reveals that the encapsulation results in a decrease in the antitumor activity of oxaliplatin.     

Magnetic properties of monodisperse NiHx nanoparticles and comparison to those of monodisperse Ni nanoparticles

We produced, for the first time, monodisperse NiH(x) nanoparticles with particle diameters of 7.0 nm and investigated their magnetic properties. We also produced monodisperse Ni nanoparticles with nearly the same particle diameters as those of NiH(x) nanoparticles as a comparison. The magnetic properties of NiH(x) nanoparticles were quite different from those of Ni nanoparticles. We observed two compositional phases in NiH(x) nanoparticles, similar to bulk material: one is the nearly pure Ni phase with the blocking temperature (T(B)) of 11 K and the other is the hydride phase. We observed T(B) of 40 K in Ni nanoparticles.     

Synthesis of novel amorphous boron carbonitride ceramics from the borazine derivative copolymer via hydroboration

A preceramic polymer for boron carbonitride was synthesized for the first time by the hydroboration of borazine derivatives, B-triethynyl, N-trimethyl borazine and borazine, without a catalyst. A homogeneous, amorphous boron carbonitride ceramic was prepared by the thermolysis of a hydroborated copolymer in an argon atmosphere.     

Selective inhibition of bovine plasma amine oxidase by homopropargylamine, a new inactivator motif

Propargylic and activated allylic amines are known to inactivate the quinone-dependent plasma amine oxidases, possibly through active-site modification by the alpha,beta-unsaturated aldehyde turnover products. Although homopropargylamine (1-amino-3-butyne, 1) is a nonobvious candidate as a mechanism-based inhibitor, 1 was found to be an unusually potent time- and concentration-dependent irreversible inactivator of bovine plasma amine oxidase (BPAO), exhibiting a 30 min IC(50) of 2.9 microM at 30 degrees C ([BPAO] = 1.2 microM). Preserved cofactor redox activity of the denatured inactivated enzyme indicates that inactivation by 1 involves either a cofactor modification that reverses upon enzyme denaturation or a modification of an active-site residue. Because inactivation by 1 may involve enzyme alkylation by the reactive 2,3-butadienal (3) tautomer of the 3-butynal turnover product of 1, aldehyde 3 was prepared and was found to inactivate BPAO, but only at high concentration. In addition, whereas inhibition by 3 was blunted by the presence of mercaptoethanol, no such protection was observed against 1. The amine whose turnover should lead directly to 3 was prepared (1-amino-2,3-butadiene, 4) and was found to be an even more potent inactivator of BPAO than 1, exhibiting a 5 min IC(50) of 1.25 microM. Rat liver mitochondrial monoamine oxidase was also inactivated by 4, as expected, but only very weakly by 1. Potential mechanisms explaining the selective inhibition of BPAO by 1 are discussed.     

Microscopic verification of topological electron-vortex binding in the lowest Landau-level crystal state

When two-dimensional electrons are subjected to a very strong magnetic field, they are believed to form a triangular crystal. By a direct comparison with the exact wave function, we demonstrate that this crystal is not a simple Hartree-Fock crystal of electrons but an inherently quantum mechanical crystal characterized by a nonperturbative binding of quantized vortices to electrons. It is suggested that this has qualitative consequences for experiment.