Effects of Nonuniform Fiber Geometries on the Microstructural Fracture Behavior of Ceramic Matrix Composites

Microstructural fracture behavior of a ceramic matrix composite (CMC) with nonuniformly distributed fibers is studied in the presentation. A comprehensive numerical analysis package to study the effect of nonuniform fiber dimensions and locations on the microstructural fracture behavior is developed. The package starts with an optimization algorithm for generating representative volume element (RVE) models that are statistically equivalent to experimental measurements. Experimentally measured statistical data are used as constraints while the optimization algorithm is running. Virtual springs are utilized between any adjacent fibers to nonuniformly distribute the coated fibers in the RVE model. The virtual spring with the optimization algorithm can efficiently generate multiple RVEs that are statistically identical to each other. Smeared crack approach (SCA) is implemented to consider the fracture behavior of the CMC material in a mesh-objective manner. The RVEs are subjected to tension as well as the shear loading conditions. SCA is capable of predicting different fracture patterns, uniquely defined by not only the fiber arrangement but also the specific loading type. In addition, global stress-strain curves show that the microstructural fracture behavior of the RVEs is highly dependent on the fiber distributions

Prediction of the Chemical Composition and Fermentation Parameters of Fresh Coarse Italian Ryegrass Haylage Using Near Infrared Spectroscopy

Italian ryegrass (Lolium multiflorum) is an annual forage grass species which is widely cultivated in South Korea. It grows extensively in the southern part of the country and is an important component of winter forage for livestock. Each year, in Korea, over one million hectares of Italian ryegrass is converted to round bale haylage. Quality control is an important field in forage utilization research and marketing, and involves the estimation of forage nutrient content. Wet chemistry is the traditional method used to analyze the nutrient content of forage. However, this technique is often destructive, expensive, and time consuming, and it is not suitable for real-time feedstuff analysis. Near infrared spectroscopy (NIRS), on the other hand, is an alternative technique that has several major advantages over traditional methods. The analysis of silage nutrient content, using NIR, conventionally includes the drying and milling of samples. However, these processes can lead to reduction of volatile acids, which are important components of silage. NIRS can be affected by spectral regions, drying and grinding methods, particle size, packing density and the temperature of samples (Reeves and Blosser, 1991). In order to obtain accurate NIRS results, sample preparation, and the measurement conditions of the calibration set and predicted samples, need to match. The objectives of this study were to (1) assess the usefulness of NIRS in determining the nutritional composition and fermentative parameters of fresh coarse samples of Italian ryegrass haylage, (2) assess the predictive value of various NIRS calibration models, and (3) explore cost-effective and time saving methods for forage quality estimation, in field populations

Comparative Pharmacokinetics of Orbifloxacin Following a Single Intravenous or Oral Administration to Healthy and Diabetic Rats

The single-dose disposition kinetics of orbifloxacin was determined in clinically healthy and diabetic rats  after intravenous or oral administration of 5 mg/kg body weight. Orbifloxacin concentrations were determined  by HPLC with fluorescence detection. The HPLC method was sensitive, specific and repeatable. A  systemic bioavailability of 99.1% and 108 %, and a Cmax of 6.55 } 1.09 μg /mL and 8.63 } 1.09 μg /mL were  observed in healthy and diabetic rats, respectively. The terminal half-life after intravenous and oral administration  was 4.17 } 0.38 h and 4.03 } 0.41 h for healthy and 2.31 } 0.34 h and 3.03 } 0.28 h for diabetic  rats. Orbifloxacin was cleared more rapidly in diabetic rats (0.15 } 0.01 L/kg.h) than healthy group (0.11 }  0.01 L/kg.h), with longer mean resident time (MRT) values observed in the latter. Other kinetic parameters  were almost the same between the healthy and diabetic groups. This investigation revealed that a dose of 5  mg/kg orbifloxacin can be safely and effectively used to combat infections in rats of either group associated  with susceptible bacteria.

Acoustic metamaterial exhibiting four different sign combinations of density and modulus

We fabricated a double negative acoustic metamaterial which consisted of Helmholtz resonators and membranes. Experimental data on the transmission and dispersion relation are presented. The system exhibits three frequencies where the acoustic state makes sharp transitions from density negative ({\rho} -NG) to double negative (DNG), modulus negative (B-NG), and double positive (DPS) in sequence with the frequency. We observed a wide range of negative refractive index from -0.06 to -3.7 relative to air, which will allow for new acoustic transformation techniques.Comment: 5 pages, 4 figures, submitted to Physical Review Letter