Quantum-mechanical analysis of effect of alloying elements on ε-martensite start temperature of steels.

With regard to the transformation mechanism of austenitic high manganese steel, the prediction of the ε-martensite start temperature is a critical consideration in alloy design. Evaluation of the ε-martensite start temperature makes it possible to predict the microstructure and to understand the phase transformation occurring during deformation. Here we use the quantum mechanical calculation of random alloys to understand the physics for ε-martensitic transformation in steels. We could find the linear relationship between the measured ε-martensite start temperatures and the crystal structure stability for various compositions. We also could estimate the effect of several alloying elements. It is expected that the effect of decreasing the temperatures for the same amount of alloying elements addition will be larger moving farther from Group VIII. By creating a free-energy model that reflects the temperature effect, we were able to calculate the average driving force required for the ε-martensitic transformations.

An adjustable superior oblique tendon spacer with the use of nonabsorbable suture.

PURPOSE: Philip Knapp described a method, sometimes referred to as the "chicken suture,"of securing a loose nonabsorbable suture to the cut ends of the superior oblique tendon to facilitate future reversal. The purpose of this study is to describe a modification of Knapp's technique to achieve partial, reversible, and intraoperatively adjustable superior oblique weakening. METHODS: The superior oblique tendon was exposed, 2 polyester nonabsorbable sutures were placed 4 mm apart, and the tendon was cut. With the use of a slip knot, the cut ends of the tendon were separated by 2 to 8 mm. Tendon separation was adjusted intraoperatively according to the exaggerated traction test and, in some cases, fundus torsion. Medical records of all patients who underwent surgery with this technique were reviewed and the outcomes tabulated. RESULTS: Twelve patients (16 eyes) were treated for superior oblique overaction and 3 patients (3 eyes) for Brown syndrome. Follow-up was 2 to 46 months (mean, 17 months). Mean superior oblique overaction improved from +1.3 before surgery to +0.3 after surgery, mean A pattern improved from 20 PD to 2 PD, and fundus intorsion improved from +1.2 to +0.3. In Brown syndrome, the mean elevation in adduction improved from -3.8 to -1.0. One patient from each group developed an overcorrection. None of the patients developed recurrence. The patients with Brown syndrome continued to improve over a 1-year period. CONCLUSIONS: The superior oblique tendon suture spacer is effective, intraoperatively adjustable, and technically easier to perform than a silicone expander procedure. This technique should be considered as an alternative for patients requiring superior oblique weakening.

Ocular findings after bone marrow transplantation in a pediatric population.

PURPOSE: With the increasing use of bone marrow transplantation (BMT) in children to treat diseases of the hematopoietic system, ocular complications have been recognized in greater numbers. The authors performed a retrospective study to determine the prevalence and types of ocular abnormalities in a pediatric population following BMT. DESIGN: Retrospective noncomparative study. PARTICIPANTS: One hundred and four consecutive pediatric patients with aplastic anemia and various hematologic malignancies who required BMT. INTERVENTION: Bone marrow transplantation. MAIN OUTCOME MEASURES: Visual acuity and slit-lamp biomicroscopic and funduscopic examinations. RESULTS: Ocular changes developed in 51% of patients. The most frequent findings included dry eye syndrome (12.5%), cataract (23.0%), and posterior segment complications (13.5%). A final visual acuity of 20/40 or better was achieved in 95.7% of eyes. CONCLUSIONS: Pediatric patients can develop severe and potentially vision-threatening complications following BMT. Despite the high incidence of anterior and posterior segment abnormalities, ocular symptoms were generally mild and the majority of patients retained excellent visual function. Factors associated with ocular complications included the underlying disease, total body irradiation, systemic chemotherapy, graft-versus-host disease, and immunosuppression. Familiarity with these risk factors and potential complications in pediatric patients is important for successful treatment.

Evaluation of retinal susceptibility to light damage in pigmented rats supplemented with beta-carotene.

The present study evaluated the influence of beta-carotene supplementation on the susceptibility of the retina to light damage. Long-Evans pigmented rats were supplemented with beta-carotene by either dietary or intraperitoneal administration, and beta-carotene levels in plasma, liver and retina were determined by high performance liquid chromatography. Other animals from each group were exposed to ultraviolet-A light at a dose of 8.1 J/cm2 in their right eye only, and photoreceptor cell losses determined by light microscopic morphometry. In supplemented animals, beta-carotene levels increased markedly in the liver, and were elevated from non-detectable to detectable in the plasma and retina, relative to nonsupplemented controls. In each tissue, beta-carotene levels were found to be higher in animals receiving intraperitoneal supplementation as compared to dietary. Beta-carotene supplementation by either route did not protect the retina against photoreceptor cell loss measured at two weeks following UVA exposure. Preliminary observations indicated that beta-carotene supplementation decreased the incidence of light-induced retinal pigment epithelium destruction.