Fumitoshi Sato

Mechanical properties of polycrystalline Ti3SiC2 at ambient and elevated temperatures

Abstract Dense polycrystalline Ti 3 SiC 2 samples were fabricated by reactively hot-isostatic pressing (HIPing) a mixture of elemental Ti, Si and C powders. The mechanical properties, including load–strain response, bending strength, fracture toughness and crack propagation, were investigated from ambient temperature to 1573 K. Non-linear stress–strain responses were observed in the polycrystalline Ti 3 SiC 2 materials at ambient temperature. It is conceivable that the inelastic deformation is attributable to micro-deformations that consist of slip between micro-lamellae within individual grains and the formation of microcracks between grains. The polycrystalline Ti 3 SiC 2 exhibited a brittle-to-ductile transition at about 1473 K; above this the Ti 3 SiC 2 samples deformed plastically and exhibited high strains (>1.5%), whereas below 1373 K only limited inelastic deformation was observed prior to fracture. The mode I fracture toughness, K IC , was measured by the single-edge notched beam (SENB) method to be 4.52 MPa m 1/2 at ambient temperature. Both fracture strength and fracture toughness decrease only slightly with increasing temperature up to 1273 K, above which they decrease more rapidly and reach half of their room-temperature values by 1473 K.

Normalization of impaired coronary circulation in hypertrophied rat hearts.

We tested the hypothesis that impaired coronary autoregulation, decreased flow reserve, and diminished reactive hyperemic response in hypertrophied hearts with coronary arterial hypertension may be reversible after relief of pressure overload. In 4-week ascending aortic banded rats, in vivo peak systolic left ventricular pressure increased to 178 +/- 8 mm Hg (103 +/- 6 mm Hg in sham-operated control group). This increased pressure produced myocardial hypertrophy, and the left ventricular weight/body weight ratio was 46% above that of the control group. After the rats were killed, the coronary perfusion pressure-flow relations were obtained during resting conditions and maximal vasodilation after a 40-second period of ischemia in beating but nonworking isolated hearts perfused with Tyrodes solution with bovine red blood cells and albumin. In hearts from control rats, coronary autoregulation (i.e., a slight decrease in flow with reduction of pressure) was observed in the range of 50-100 mm Hg of perfusion pressure. A pronounced reactive hyperemic response was observed: a peak flow/resting flow ratio of 2.9 +/- 0.1 and a repayment ratio of 1.7 +/- 0.2 at 100 mm Hg of perfusion pressure. In hearts of banded rats the resting pressure-flow relation was rectilinear in the range of 25-175 mm Hg of perfusion pressure. Flow reserve and the time of reactive hyperemia to one half peak flow decreased at 50, 100, and 150 mm Hg of perfusion pressure compared with values in control rat hearts. Four weeks after debanding, peak systolic left ventricular pressure and cardiac hypertrophy had normalized. The impaired autoregulation, decreased flow reserve, and diminished reactive hyperemic response had completely reversed.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of age on coronary circulation after imposition of pressure-overload in rats.

We examined the effects of pressure overload on coronary circulation in young adult (7 months old) and old rats (18 months old). Four weeks after the ascending aorta was banded, in vivo left ventricular pressure was measured to estimate the degree of pressure load. In the two age groups, similar increases in peak left ventricular pressure were observed (113 ±7 mm Hg in sham-operated rats versus 160 ±11 mm Hg in banded rats of the young adult group; 103 ±7 mm Hg in sham-operated rats versus 156±11 mm Hg in banded rats of the old group). After isolating the hearts, they were perfused with Tyrodes solution containing bovine red blood cells and albumin. Resting coronary perfusion pressure-flow relations and reactive hyperemic response after a 40-second ischemia were obtained under beating but nonworking conditions. In young adult banded rats, significant myocardial hypertrophy was observed at the organ level (124% of controls in left ventricular dry weight/body weight ratio; 119% in left ventricular dry weight/tibial length ratio) and at the cell level. Minimal coronary vascular resistance obtained by the perfusion pressure-peak flow relation during reactive hyperemia increased to 150% of controls, and coronary flow reserve decreased significantly. In contrast, myocardial hypertrophy was not observed at the organ or cell level in old banded rats. However, minimal coronary vascular resistance increased, and flow reserve decreased significantly. Thus, pressure overload with coronary arterial hypertension caused abnormalities of the coronary circulation in old subjects even in the absence of myocardial hypertrophy. These coronary vascular changes as well as diminished hypertrophic response may explain the high incidence of heart failure or ischemic episodes during chronic hemodynamic stress in aged patients.

Grain Diameter and Coercivity of Fe, Ni, and Co Metals

The relationship between coercivity and grain diameter was investigated for pure Fe, Ni and Co metals. The grain diameter of samples was varied between 200Å and 5 ¿m by preparing sputtered films and rapidly quenched ribbons. The coercivity in all cases was roughly proportional to the sixth power of the grain diameter below a certain diameter (200Å, 400Å and 300Å for Fe, Ni and Co respectively), and was proportional to the reciprocal of the grain diameter at larger values. This behavior can be satisfactorily explained in terms of the random anisotropy model proposed by Herzer and Alben et al.

Effects of duration of pressure overload on the reversibility of impaired coronary autoregulation in rats

The aim of this study was to determine the effects of duration of pressure overload on the reversibility of impaired coronary autoregulation in hypertropied hearts. The experiments were performed on 38 anesthetized male Wistar rats aged 6 to 8 weeks. The ascending aorta was banded for 4 or 10 weeks, then in some rats the bands were removed for 4 weeks. We estimated coronary hemodynamics in a model consisting of isolated non-working hearts perfused with Tyrodes solution containing bovine red blood cells and serum albumin. Myocardial mass increased significantly in 4 and 10-week banded groups compared to controls. Four weeks after debanding in 4- and 10-week banded groups, the value returned to that of controls. Autoregulation gain was significantly lower in banded groups than in controls in the range between 50 and 100 mmHg of coronary perfusion pressure. Although the gain normalized in the debanded group after 4 weeks of banding, the value in the debanded groups after 10 weeks of banding remained less than zero between 25 and 150 mmHg of perfusion pressure. In transient flow response to a stepwise increase of perfusion pressure within the autoregulatory range, promptly increased flow was followed by more rapid and greater decrease in controls than in banded groups. The flow response regressed in the debanded group after 4 weeks of banding, while it remained unchanged in the debanded group after 10 weeks of banding. Thus, duration of pressure overload alters the regression of impaired coronary autoregulation in cardiac hypertrophy.

Soft Magnetic Properties of Fe-Co/ZnO Multilayer Films

The dependence of the soft magnetic properties of sputtered Fe-Co/ZnO multilayer films on the film thickness and composition has been investigated. The coercivity decreases with decreasing average crystal grain size D, particularly in the range from 9~17 nm, for all multilayer films except Co/ZnO. A coercivity Hc = 160 A/m and effective permeability ¿e (10 MHz) = 800 were obtained for Fe/ZnO and 24wt% Co-bal.Fe/ZnO multilayer films with D = 2~3 nm.

Excitonic properties of Cd1−xMnxTe quantum wells grown by molecular beam epitaxy

Abstract Time-resolved photoluminescence has been studied in molecular beam epitaxy grown Cd 1− x Mn x Te/Cd 1− y Mg y Te and CdTe/Cd 1− x Mn x Te single and multiple quantum wells. The excitonic properties were investigated at several temperatures and magnetic fields. The dynamics of the exciton magnetic polaron are greatly influenced by the quantum confinement of the excitons in the single quantum wells. The formation of a spin superlattice structure was realized in Cd 0.95 Mn 0.05 Te/Cd 0.95 Mg 0.05 Te multi-quantum wells under an external magnetic field.

Magnetic Properties of Fe-Co-Ti Thin Films

Sputtered (Fe<inf>100-y</inf>Co<inf>Y</inf>)<inf>100-X</inf>Ti<inf>X</inf> (0¿X¿5, 23¿Y¿53) films were studied with emphasis on the dependence of the soft magnetic properties on composition, annealing temperature and film thickness. After annealing at 823K for 3600 s, the permeability of the film system had a maximum of 1650 at (Fe<inf>69</inf>Co<inf>31</inf>)<inf>97</inf>Ti<inf>3</inf>. The corresponding saturation magnetic flux density was 2.2 T. When the lattice constant of Fe-Co film expands by about 0.2%, the permeability reaches a maximum; when the film thickness reaches 1357 nm, the permeability decreases to 500. The permeability of an (Fe<inf>69</inf>Co<inf>31</inf>)<inf>97</inf>Ti<inf>3</inf>/ZnO multi-layer film annealed at 773K for 3600 s is 1100; this is about twice the permeability of a single-layer film.

Grain Diameter and Magnetic Properties of Rapidly Quenched Fe-M-Si-Ge (M=Ti, V, Zr, Nb, Ta) and Fe-Hf-Cu Alloys

The grain diameters and magnetic properties of rapidly quenched Fe-M-Si-Ge (M=Ti, V, Zr, Nb, Ta) and Fe-Hf-Cu alloy ribbons were investigated. The grain size of Fe-Ta-Si-Ge alloys decreases rapidly from 2700 Å to about 400 Å with the addition of up to 3 at% Ta. The coercivity increases rapidly from 2.3 to 30 Oe with increasing Ta content. For the Fe-M-Si-Ge alloy systems, the decrease in grain diameter and increase in coercivity with the addition of M rank in the order Ta, Nb, Zr, Ti, V. The grain diameter of Fe-Hf-Cu alloys decreases to about 600 Å as the Hf content is increased to 4 to 6 at%. The coercivity increases to about 20 Oe with increasing Hf content. The coercivity of these rapidly quenched Fe-base alloys is roughly proportional to the reciprocal of the grain diameter.

Anti-atherogenicity in women does not prevent restenosis after balloon angioplasty

SummaryTo test the hypothesis that antiatherogenicity in women exerts beneficial effects to prevent restenosis formation after coronary angioplasty, we studied 493 men (988 lesions) and 81 women (159 lesions), aged 40–60 years, who had undergone successful balloon angioplasty and had follow-up angiography, 4.9±4.1 months later. We compared the extent of restenosis between men and women, and between pre- and post-menopausal women, which was assessed by a categorical definition of restenosis (more than 50% diameter stenosis at follow-up) and by percent diameter measured immediately after angioplasty and at follow-up. Hypertension was more frequent in women and a significantly lower percentage of women smoked. In women, the levels of total cholesterol and low-density lipoprotein cholesterol were higher. The location of dilated lesions, frequency of angioplasty for lesions with chronic total occlusion, and frequency of emergency angioplasty in patients with unstable angina or acute myocardial infarction were similar in men and women. Restenosis formation, estimated by the categorical definition or percent diameter, did not differ between men and women, or between pre- and post-menopausal women. Menopausal status or sex was not an independent predictor of restenosis by multivariate analysis. Thus, the benefit of anti-atherogenicity in women does not play an important role in preventing restenosis after coronary angioplasty.