Fatigue crack growth and fracture toughness properties of 304 stainless steel pipe for LNG transmission

The fatigue crack growth rate and fracture toughness tests of type 304 stainless steel were studied over a temperature range of −162°C to room temperature. Girth weld metal specimens were fabricated using a combination of gas-tungsten-arc-welding and shielded-metal-arc-welding. The seam weld metal was made with submerged arc welding. Fatigue crack growth rate tests were conducted using compact tension specimens in accordance with ASTM E647. Fracture toughness was evaluated through CTOD tests with three point bend specimens. The CTOD values were affected by crack orientation with respect to the rolling direction, but orientation had no influence on fatigue crack growth rates. The fatigue crack growth rates and the CTOD values decreased with decreasing test temperature.     

Cellular Defensive Mechanisms of Tea Polyphenols: Structure-Activity Relationship

Tea is particularly rich in polyphenols, including catechins and theaflavins, thearubigins, flavonols, and phenolic acids, which are believed to contribute to the health benefits of tea. The health-promoting effects of tea polyphenols are believed to be related to their cellular defensive properties. This review is intended to briefly summarize the relationship between the chemical structures of tea polyphenols and their biological activities. Tea polyphenols appear as direct antioxidants by scavenging reactive oxygen/nitrogen species; chelating transition metals; and inhibiting lipid, protein, and DNA oxidations. They also act directly by suppressing “pro-oxidant” enzymes, inducing endogenous antioxidants, and cooperating with vitamins. Moreover, tea polyphenols regulate cellular signaling transduction pathways, importantly contributing to the prevention of chronic diseases and the promotion of physiological functions. Apparently, the features in the chemical structures of tea polyphenols are closely associated with their antioxidant potentials.     

Antioxidant and Hepatoprotective Effects of Procyanidins from Wild Grape (Vitis amurensis) Seeds in Ethanol-Induced Cells and Rats

In the present study, we characterized the antioxidant and hepatoprotective mechanisms underlying of wild grape seed procyanidins (WGP) against oxidative stress damage in ethanol-treated HepG2 cell and Sprague-Dawley (SD)-rat models. In HepG2 cells, WGP not only diminished the ethanol (EtOH, 100 mM)-induced reactive oxygen species (ROS) formation and cytochrome P450 2E1 (CYP2E1) expression, but also renovated both the activity and expression of antioxidant enzymes including catalase, superoxide dismutase, and glutathione peroxidase. Additionally, to investigate the hepatoprotective effect of WGP, rats were orally administered 10 or 50 mg/kg WGP once daily for seven days prior to the single oral administration of EtOH (6 g/kg). The results show that WGP administration decreased the EtOH-induced augment of the levels of serum aspartate transaminase and alanine transaminase as well as serum alcohol and acetaldehyde. WGP treatment upregulated the activities and protein levels of hepatic alcohol dehydrogenase, aldehyde dehydrogenase, and antioxidant enzymes but downregulated the protein expression level of liver CYP2E1 in EtOH-treated rats. Moreover, the decreased phosphorylation levels of mitogen activated protein kinases (MAPKs) by ethanol were induced in both HepG2 cell and rat models. Overall, pretreatment of WGP displayed the protective activity against EtOH-mediated toxicity through the regulation of antioxidant enzymes and alcohol metabolism systems via MAPKs pathways.     

Crack-initiation toughness and crack-arrest toughness in advanced 9 pct Ni steel welds containing local brittle zones

The present study investigates the influence of local brittle zones (LBZs) on the fracture resistance of the heat-affected zones (HAZs) in quenched, lamellarized, and tempered (QLT) 9 pct Ni steel weld joints. The results of Charpy impact tests using simulated coarse-grained, heat-affected zone (CGHAZ) specimens show that the intercritically reheated (IC) CGHAZ and unaltered (UA) CGHAZ are the primary and secondary LBZs, respectively, of the steel at cryogenic temperature. Compact crack arrest (CCA) tests and crack-tip opening displacement (CTOD) tests were conducted at a liquefied natural gas (LNG) temperature to measure the variations in crack-arrest toughness and crack-initiation toughness along the distance from the fusion line (FL) within the actual HAZ. While CTOD tests show a decrease in toughness when approaching the FL, i.e., the regions containing LBZs, the crack-arrest-toughness values are found to be higher than those in the regions near the base materials. This is due to the fact that the crack-arrest toughness is governed by the fraction of microstructures surrounding LBZs instead of the LBZs themselves. By direct comparison of the brittle-crack-arrest toughness (K _a ) with the brittle-crack-initiation toughness (K _c ), this investigation has determined that, with regard to crack-arrest behavior, the LBZs of QLT-9 pct Ni steel do not limit the practical safety performance of the weld joints in LNG storage tanks.     

Prediction of macromolecular transport through the deformable porous media of an artery wall by pore theory

To determine the transport properties of macromolecules in the media of an artery wall deformed inhomogeneously by the transmural pressure, we combine a simple mechano-hydraulic model based on a two parameter strain-dependent permeability function, which was developed by Klanchar and Tarbell [1987], with a pore theory. The combined theory allows us to calculate the spatial distributions of porosity, solute partition, pore radius and macromolecuiar solute concentration in the media and their dependence on the transmural pressure. The predictions from the pore theory are in good agreement with experimental measurements of sucrose space, albumin space and albumin concentration profiles in the media of rabbit aortas at transmural pressures of 70 and 180 mmHg. The prediction indicates that albumin transport through the aortic media is dominated by convection rather than diffusion. It is further demonstrated that the transport properties of planar tissue samples, which are often used inin vitro experimentais, may be quile different from those of intact vessels in their natural cylindrical configuration because of the variation in tissue deformation. Using the pore theory we are also able to calculate the interstitial shear stress associated with transmural volume flow which may act on the smooth muscle cells residing in the media and find it to be on the order of several dyne/cm². This level of shear stress will stimulate endothelial cells and may also affect smooth muscle cells.     

EFFECT OF PVA AND GELATIN ADDITIVES ON BARIUM SULFATE PRECIPITATION IN AN MSMPR REACTOR

The effect of high molecular weight additives (PVA and gelatin) on barium sulfate precipitation in an MSMPR reactor is investigated. The impeller speed is varied from 0 to 1200 rpm and the additive concentration in the bulk solution is increased up to 5.0 g/1. As the additive concentration is increased, the particle growth rate decreases and the nucleation rate increases. However, the particle morphology is not changed by the additives. The experimental results are explained qualitatively by supposing that the additive is adsorbed on the particle surface and inhibits the mass transfer to the surface.

To explain the additive effect quantitatively a diffusion limitation model is developed. The diffusion limitation model predicts the effects of additives over the entire range of additive concentrations and impeller speeds set in the experiments. The model predicts very high supersaturation levels in the reactor which is consistent with a mass transfer controlled particle growth. Furthermore, the model results are consistent with simple theories of polymer adsorption and diffusion in polymer solutions     

Layer-by-layer assembly of thin film oxygen barrier

Thin films of sodium montmorillonite clay and cationic polyacrylamide were grown on a polyethylene terephthalate film using layer-by-layer assembly. After 30 clay–polymer layers are deposited, with a thickness of 571 nm, the resulting transparent film has an oxygen transmission rate (OTR) below the detection limit of commercial instrumentation (< 0.005 cc/m²/day/atm). This low OTR, which is unprecedented for a clay-filled polymer composite, is believed to be due to a brick wall nanostructure comprised of completely exfoliated clay in polymeric mortar. With an optical transparency greater than 90% and potential for microwaveability, this thin composite is a good candidate for foil replacement in food packaging and may also be useful for flexible electronics packaging.     

Is it possible to synthesize cubic aluminum nitride by the carbothermal reduction and nitridation method?

In order to investigate whether it is possible to synthesize cubic AlN (c-AlN) by the carbothermal reduction and nitridation method, the products obtained by calcining a (hydroxo)(suberato)Al(III) complex under a flow of nitrogen in the temperature range of 1200–1600 °C were characterized by XRD and ²⁷Al magic-angle spinning (MAS) NMR spectroscopy. The products consisted of wurtzite AlN (w-AlN), γ-Al₂O₃, α-Al₂O₃ and γ-aluminum oxynitride (γ-AlON). The two materials γ-AlON and c-AlN, which have very similar XRD patterns each other, were differentiated by their ²⁷Al MAS NMR spectra. The ²⁷Al MAS NMR spectra of the products showed no peak at the chemical shift of c-AlN, which was estimated by the correlation between the ²⁷Al chemical shifts of AlX (X = P, As and Sb) in the cubic phase with the reciprocal of their band gaps. These results indicate that it is impossible to synthesize metastable c-AlN by the CRN method because of very high reaction temperature.     

Antioxidant Properties of Flavone C-Glycosides from Atractylodes japonica Leaves in Human Low-density Lipoprotein Oxidation

ABSTRACT: Three antioxidant flavone C -glucosides, isoorientin, vitexin, and isovitexin, were identified for the 1st time from Atractylodes japonica leaves by an activity-guided fractionation with various analytical techniques including column chromatography, high-performance liquid chromatography (HPLC), fast atom bombardment mass spectrometry (FAB-MS), and nuclear magnetic resonance (NMR). Hydroxyl and superoxide anion radicals scavenging activities of these compounds were examined using electron spin resonance (ESR). Inhibitory activities of these compounds on human low-density lipoprotein (LDL) oxidation were evaluated by malondialdehyde (MDA) and thiobarbituric acid-reactive substances (TBARS), both representing intermediates of lipid peroxidation. These flavone C -glucosides displayed about 50% of scavenging activity against hydroxyl radicals at the concentrations below 10 μ M . The superoxide dismutase (SOD)-equivalent activities of isoorientin, vitexin, and isovitexin at 1 m M were 31.37, 2.71, and 2.63 unit/mL, respectively. Isoorientin at 1 μ M exhibited over 60% inhibition of MDA formed during copper-mediated human LDL oxidation. Amounts of free MDA in LDL treated with isoorientin, vitexin, isovitexin, and control were 20.06, 40.73, 34.08, and 48.03 n M /mg protein, respectively. These compounds also prolonged the lag phase time of the conjugated diene formation. There was a positive correlation between the free radical scavenging activities and the inhibitory effects on the LDL oxidation of these compounds. These results suggest that the flavone C -glucosides isolated from the leaves of A japonica possess beneficial antioxidant properties against free radicals as well as LDL oxidation.     

Change of ginsenoside composition in red ginseng processed with citric acid

The purpose of this research was to investigate the composition of ginsenosides and to identify the chemical structures of ginsenosides generated from red ginseng by citric acid pre-treatment (RGC). The amount and the composition of ginsenosides in red ginseng (RG) and RGC were determined by high performance liquid chromatography (HPLC) analysis. The content of Rg₃, a well-known bioactive ginsenoside in RGC increased significantly (p<0.05) over 2 fold (0.411 mg/g) when compared with RG (0.186 mg/g). Moreover, the structures of 5 novel ginsenosides in RGC were investigated by liquid chromatography/mass spectrometry (LC/MS/MS) analysis. Three peaks were completely fragmentized from their mother ions to aglycones and suggested to be less polar ginsenosides Rk₃/Rh₄, Rk₁, and Rg₅. This study suggested that by processing red ginseng with citric acid it is possible to enhance the yield of both ginsenoside Rg₃ and less polar ginsenosides.