Superelastic effect in polycrystalline ferrous alloys.

In superelastic alloys, large deformation can revert to a memorized shape after removing the stress. However, the stress increases with increasing temperature, which limits the practical use over a wide temperature range. Polycrystalline Fe-Mn-Al-Ni shape memory alloys show a small temperature dependence of the superelastic stress because of a small transformation entropy change brought about by a magnetic contribution to the Gibbs energies. For one alloy composition, the superelastic stress varies by 0.53 megapascal/°C over a temperature range from -196 to 240°C.

Cobalt-base high-temperature alloys.

We have identified cobalt-base superalloys showing a high-temperature strength greater than those of conventional nickel-base superalloys. The cobalt-base alloys are strengthened by a ternary compound with the L1(2) structure, gamma' Co3(Al,W), which precipitates in the disordered gamma face-centered cubic cobalt matrix with high coherency and with high melting points. We also identified a ternary compound, gamma' Ir3(Al,W), with the L1(2) structure, which suggests that the Co-Ir-Al-W-base systems with gamma+gamma' (Co,Ir)3(Al,W) structures offer great promise as candidates for next-generation high-temperature materials.

Formation of immiscible alloy powders with egg-type microstructure.

The egg-type core microstructure where one alloy encases another has previously been obtained during experiments in space. Working with copper-iron base alloys prepared by conventional gas atomization, we were able to obtain this microstructure under gravity conditions. The minor liquid phase always formed the core of the egg, and it sometimes also formed a shell layer. The origin of the formation of this core microstructure can be explained by Marangoni motion on the basis of the temperature dependence of the interfacial energy, which shows that this type of powder can be formed even if the cooling rate is very high.

[Quantitative assessment of macular appearance with a scanning laser ophthalmoscope in aging or diabetic retinopathy patients].

PURPOSE: Changes in the macula caused by aging or diabetic retinopathy were studied with scanning laser ophthalmoscope (SLO). METHODS: SLO imaging of the macula was done with argon blue, argon green, helium neon, and diode lasers, and the images were recorded on s-VHS video tape. In this study, we examined 29 patients (58 eyes) with no retinal organic change as controls, 8 diabetic patients (16 eyes) without retinopathy, 8 patients (16 eyes) with simple diabetic retinopathy, and 6 patients (12 eyes) with preproliferative diabetic retinopathy. RESULTS: As age increased, the dark area of the macula was enlarged in the argon blue and argon green images. In diabetic patients, the dark area of the macula in patients in their 30 s and 40 s with retinopathy was larger than in diabetic patients without retinopathy (p < 0.05). The dark area of the macula in preproliferative diabetic retinopathy was larger than in patients in their no diabetic retinopathy or simple diabetic retinopathy (p < 0.05). In the 50 s and 60 s, the dark area of the macula in preproliferative diabetic retinopathy was larger than in the controls or in patients with no diabetic retinopathy (p < 0.05). CONCLUSION: The macular dark area became enlarged with aging. In diabetic patients, the dark area of the macula was enlarged in diabetic patients without retinopathy or with progression in diabetic retinopathy stage. Therefore, quantitative assessment of macular appearance with SLO can be used as a new clinical index.

Magnetic resonance imaging in acute optic neuropathy by sphenoidal mucocele.

A 45-year-old man suffered sudden visual loss with Marcus-Gunn pupil and a central scotoma in the right eye as evaluated by visual field examination. The patient's right visual acuity was 0.02 (0.08 x -4.5 D). T1-weighted magnetic resonance imaging (MRI) demonstrated a cystic lesion of high intensity in the right sphenoid sinus. Short T1 inversion recovery (STIR) images presented a cystic lesion of high intensity in the right sphenoid sinus. In addition, a ring-shaped high intensity signal was seen surrounding the right optic nerve. Post-contrast fat suppression T1-weighted images did not demonstrate any enhancement within the right optic nerve. After intranasal sphenoidectomy, good recovery of the right visual acuity was noted. On subsequent MRI, the cystic lesion in the sphenoid sinus disappeared. Also, the ring of high intensity surrounding the right optic nerve became unclear. It was thought that the ring of hyperintensity seen on the STIR images demonstrated cerebrospinal fluid in the dilated perioptic subarachnoid space. Therefore, these MRI findings suggested that the acute visual loss resulted from a disturbed blood supply to the optic nerve due to compression by the sphenoidal mucocele, and not due to an inflammatory process.