Modeling of the frequency effect on fatigue crack propagation in PMMA

The frequency-dependent fatigue crack growth behavior in PMMA was investigated experimentally and modeled theoretically. The fatigue tests were conducted using single-edge-crack specimens and tension-tension sinusoidal loads. Three load frequencies were considered, i.e. 0.1, 1 and 10 Hz. The theoretical model was developed based upon the fatigue crack growth in viscoelastic media. It was found that the use of the strain intensity factor is suitable for accounting for the frequency-dependent fatigue behavior in PMMA.     

Prediction of the stress—strain curve of a short-fibre reinforced thermoplastic

Analytical work has been performed to predict the stress—strain curve of a carbon fibre reinforced polyamide 66. A typical stress—strain curve of this composite consists of three stages. Beyond the first linear stage the change of slope of the curve is attributed to the initiation and extension of cracks at fibre ends. Several theoretical models have been developed to take into account the development of cracks at various loading levels. Fibre volume-fraction, aspect ratio and orientation as well as fibre and matrix elastic properties and interface energies are the major parameters considered. The theoretical predictions are in close agreement with the experimental data.     

Parallel developmental trajectories of sensation seeking and regular substance use in adolescents.

This study applied piecewise latent growth modeling to longitudinal survey data from 2 different samples of adolescents (N=1,002 and N=1,206) to examine the hypothesis that development of sensation seeking in middle school would predict development of substance use (cigarettes, alcohol, and marijuana) in middle school and high school. Results showed that sensation seeking had strong predictive value for both concurrent and distal marijuana and alcohol use in both samples; however, initial level of sensation seeking predicted initial level of cigarette use during high school in 1 sample only. White participants scored consistently higher on both initial level and rate of increase in sensation seeking than did participants of other ethnicities. Advantages of this methodology are discussed in the context of substance use research. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Admitting cold water into steam filled pipes without water hammer due to steam bubble collapse

Water hammer due to steam bubble collapse when cold water is admitted to vertical upward flowing, vertical downward flowing, and nominally horizontal pipes has been studied both experimentally and analytically. The work in horizontal pipes included a study of the effect of a slight downward inclination, a slight upward inclination, and the length of the pipe on the initiation of water hammer. Stability maps showing the combinations of filling velocities and liquid subcooling that cause water hammer and those which do not for each flow geometry were obtained from experiments. Analytical models were developed to predict those stability boundaries in the stability maps. All these models were tested with experimental data. Based on the verified models, a step-by-step approach for each flow geometry is presented for plant engineers and designers to follow in avoiding water hammer induced by steam bubble collapse.     

Solid-state urea biosensor based on the differential method

In this paper, the solid-state urea biosensor was successfully fabricated based on the differential method, which contains three parts: the SnO/sub 2//ITO glass electrode used as the pseudoreference electrode; the SnO/sub 2//ITO glass electrode used as the contrast electrode; and the urease/SnO/sub 2//ITO glass electrode used as the enzyme electrode. Correspondingly, this solid-state urea biosensor was fabricated based on the SnO/sub 2//ITO glass electrode, whose simple fabrication process reduces the cost of fabricating the solid-state biosensor. Additionally, as revealed in the experimental results, the solid-state urea biosensor has good sensing characteristics between 5 and 80 mg/dl. After fabricating a successful solid-state urea biosensor, an array sensing system was designed to enhance the precision of the solid-state urea biosensor, which comprises four parts: the biosensor system, the input buffer circuit, the differential circuit, and the weighted sum circuit. As indicated in the experimental results of the array sensing system, the sensing characteristic of the array sensing system is similar to the mean sensing characteristic from four solid-state biosensors. Therefore, the sensing signal of the solid-state urea biosensor can be averaged using the array sensing system. In summary, this study successfully investigated a solid-state urea biosensor and designed an array sensing system to increase the precision of solid-state urea biosensors.     

Acute effects of N-methyl-N'-nitro-N-nitrosoguanidine on canine gastric mucosa

The electrophysiological effects of the chemical gastric carcinogen N-methyl-N'-nitro-N-nitrosoquanidine (MNNG) were determined in an in vivo chambered canine stomach and in an in vitro canine gastric mucosal preparation. In the in vivo stomach, the topical application of 2.5 mg MNNG/ml decreased the transmural electrical potential difference, and the systemic blood pressure was essentially unchanged. In the in vitro preparation, exposure of the mucosal side of the isolated canine gastric mucosa to 0.25 and 2.5 mg MNNG/ml for 1 hour sequentially or exposure of the serosal side to 2.5 mg MNNG/ml for 2 hours inhibited net Na+ and Cl- fluxes. With longer duration, the undirectional fluxes of Na+ and Cl- increased, indicating an increase in permeability. These findings suggested that inhibition of active transport in the gastric mucosa may have an important function in the gastric carcinogenicity of MNNG.