The entering behavior of environmental gases into the plastic zone around fatigue crack tips in titanium

Fatigue crack growth tests were performed on titanium in vacuum, a nitrogen gas, inert gases (helium and argon), and air. Fracture surface morphologies were different from each other even if these environments were mild. Microcracks which were parallel to the striations were observed on the fracture surfaces, and the frequency of them increased with the environment becoming active (He<N₂<Air). These results suggest that the environment has some effects on the deformation behavior in the plastic zone at the crack tip. The concentration of nitrogen in the plastic zone around a crack surface tested in nitrogen was analyzed using electron probe microanalysis (EPMA). The concentration of nitrogen in the plastic zone, especially in the cyclic plastic zone, increased significantly. The result indicates that nitrogen may be adsorbed on the fresh surfaces produced at the crack tip during loading and diffuse into the cyclic plastic zone with cyclic dislocation movement. Considering all the results, it can be thought that atoms of environmental gases including argon, as well as nitrogen, have some effects on the chemical composition of the cyclic plastic zone.     

Retinoic acid inhibits cell growth in HPV negative cervical carcinoma cells by induction of insulin-like growth factor binding protein-5 (IGFBP-5) secretion

Retinoids have been demonstrated to inhibit epithelial cell growth and differentiation. We examined the anti-proliferative effects of retinoic acid (RA) in an HPV positive and negative cervical carcinoma cell line. Our findings indicate that HPV-negative C33A cervical carcinoma cells are more sensitive to the growth inhibitory activity of retinoic acid (RA) than are HPV-positive CaSki cervical carcinoma cells. However, conditioned medium from RA-treated C33A cells displayed strong growth inhibitory activity in both C33A and CaSki cells. Since RA has been shown to modulate the expression of insulin-like growth factor binding proteins (IGFBPs) in many cells, we examined RA regulated expression of IGFBPs in medium isolated from RA treated C33A cells. IGFBP-5 was detectable in medium from C33A cells exposed to RA, and addition of purified exogenous IGFBP-5 resulted in growth inhibition of C33A cells. These results indicate that RA exerts it's anti-neoplastic effect in HPV negative cervical carcinoma cells via the overproduction of IGFBP-5.     

Intramural delivery of a specific tyrosine kinase inhibitor with biodegradable stent suppresses the restenotic changes of the coronary artery in pigs in vivo

STUDY OBJECTIVE: Elevated pulmonary vascular resistance is a risk factor in heart transplantation and reversibility of high pulmonary vascular resistance is evaluated preoperatively in potential recipients using i.v. vasodilators or inhaled nitric oxide. Prostacyclin is a potent vasodilator, which when inhaled, has selective pulmonary vasodilatory properties. The aim of this study was to compare the central hemodynamic effects of inhaled prostacyclin with those of inhaled nitric oxide in heart transplant candidates. DESIGN: A pharmacodynamic comparative study. SETTING: Cardiothoracic ICU or laboratory for diagnostic heart catheterization at a university hospital. PATIENTS: Ten heart transplant candidates with elevated pulmonary vascular resistance (>200 dynes x s x cm(-5) and/or a transpulmonary pressure gradient > 10 mm Hg) were included in the study. INTERVENTIONS: Nitric oxide (40 ppm) and aerosolized prostacyclin (10 microg/mL) were administered by inhalation in two subsequent 10-min periods. Hemodynamic measurements preceded and followed inhalation of each agent. MEASUREMENTS AND RESULTS: Both inhaled nitric oxide and inhaled prostacyclin reduced mean pulmonary artery pressure (-7% vs -7%), pulmonary vascular resistance (-43% vs -49%), and the transpulmonary gradient (-44% vs -38%). With inhaled prostacyclin, an 11% increase in cardiac output was observed. Other hemodynamic variables, including the systemic BP, remained unaffected by each of the agents. CONCLUSIONS: Inhaled prostacyclin induces a selective pulmonary vasodilation that is comparable to the effect of inhaled nitric oxide. Major advantages with inhaled prostacyclin are its lack of toxic reactions and easy administration as compared with the potentially toxic nitric oxide requiring more complicated delivery systems.     

Effects of inert gases on fatigue crack growth and their transportation into subsurface regions in titanium

To clarify the effects of inert gases on the fatigue behavior of titanium, fatigue crack growth tests were carried out in pure inert gases and in vacuum. Fatigue crack growth rates increased, and the fracture surface appearance was changed in inert gases, as compared to those in vacuum. The transportation of inert gases into subsurface regions of fracture surfaces was confirmed using Auger electron spectroscopy. This transportation is considered to be due to the reverse slip of slip planes on which inert gas atoms have adsorbed.     

A new life extension method for high cycle fatigue using micro-martensitic transformation in an austenitic stainless steel

Most of the conventional strengthening methods for metals and alloys such as work hardening, precipitation hardening, cause a decrease in ductility and are not very effective for cyclic loading. In this study, a new strengthening method, which is effective for high cycle fatigue, has been developed. The intersections of dislocations in a stainless steel are freezed by very fine martensite particles, which are supposed to suppress dislocation motion at low stress amplitudes. Fatigue life in a high cycle regime increased >60 times, and no decrease in ductility was observed in tensile tests, as compared to a work-hardened stainless steel.     

Nondestructive evaluation of crazes and microcracks on polymers by the elastic-wave transfer function method

The precise study of the relation between microdefects such as crazes or microcracks and the elastic-wave transfer function method (ETFuM) was conducted in acrylonitrile butadiene styrene and acetal homopolymer. The ETFuM is the method of comparing the input elastic wave and the output wave from the specimens, and separating and analysing only the information on the object condition in the specimen from the transfer function in the frequency domain. In order to investigate the formation of crazes or microcracks caused by tensile deformation, transmission electron microscopy and polarization microscopy was used. The variation of transfer function before/after annealing indicated the dependence on the nucleation and growth of crazes or microcracks. The results suggested that ETFuM has potential as a useful method for the analysis of the micromechanism of the deformation process during nondestructive tensile and fatigue tests on polymers.     

Occipitocervical fusion by Luque loop rod instrumentation in Down syndrome

Four children with Down syndrome who had developed atlantoaxial dislocation and myelopathy underwent occipitocervical fusion with Luque loop rod instrumentation and decompressive laminectomy of C1. The postoperative results are presented and the indications discussed. This procedure provides many advantages in the surgical treatment of Down syndrome compared with the conventional procedures, because of the associated mental retardation that makes the postoperative management very complicated.