No abstract

The purpose of this study is to quantitatively estimate the shielding and susceptibility effects of commonly used metallic stents on MR signal. Two experiments were performed using a 3D gradient echo sequence with short TE to image a stent phantom: 1) short TR and high flip angle (contrast enhanced MRA parameters), and 2) long TR (TR ӷ T 1 ) and low flip angle. The factor characterizing susceptibility effects was estimated from the signal phase of the first experiment, and then the factor characterizing the shielding effects was derived from the second experiment. Susceptibility induced signal loss was negligible (<1%) for nonstainless-steel (nitinol, platinum, and cobalt-alloy) stents and totally destructive (100%) for the stainless steel stent. Signal loss due to RF shielding was 31-62% for nitinol stents, 14 -50% for platinum stents, 50 -77% for the cobalt-alloy stents (undetermined for the stainless steel stent), varied with stent orientation, diameter, and wall geometry. In summary, stents made of nitinol, platinum, and cobalt-

The influence of changes in crystallographic texture on the Hall-Petch (H-P) relationship for a Mg alloy was investigated. First, the texture variations were facilitated by changing the uniaxial tensile loading orientation with respect to the normal direction of the rolled Mg plate. With a strong plane texture of the as-received material, the initial dominant deformation mechanisms were systematically varied from the basal slip, prismatic slip to extension twinning as well as combinations thereof. Second, different grain sizes were produced for each loading orientation through isochronal annealing at various temperatures up to 773K while closely monitoring grain size and texture distributions. The experimental results are presented for the grain growth kinetics during annealing; changes in yielding behavior as a function of grain size and initial texture; and H-P relationship as a function of the texture. Moreover, the effects of changes in texture and dominant deformation mechanism on H-P parameters; namely, friction stress, , and strength coefficient, , will be discussed. Finally, H-P relationships for each individual deformation mode including basal, prismatic, and pyramidal slips as well as extension twin will be identified.

No abstract

No abstract

No abstract

No abstract

The correlation between K + -Na + diffusion coefficient and mechanical properties of chemically tempered and hybrid tempered (chemically tempered subsequent to thermally tempered) aluminosilicate glass are investigated. Firstly, the potassium ion concentration profiles are experimentally measured and the diffusion coefficient is calculated according to the Boltzmann-Matano approach. Secondly, the flexure strength and Weibull modulus are determined using a combined experimental (coaxial double ring) and finite element analysis method. The results indicate that the flexural strength decreases with the diffusion coefficient of the air side for both types of glass samples while there is no significant relationship between diffusion coefficient and Weibull modulus. Diffusion coefficient on air side shows a higher value than that of the tin side. With the same diffusion coefficient, the flexural strength of chemically tempered glasses are found to be higher than that for hybrid tempered glasses. The effect of diffusion coefficient on modulus of rupture (MOR) for hybrid tempered glass is more remarkable. These results would be useful in designing the strength of glass and guiding the strengthening process by chemical or hybrid tempering.