L-Histidine tetrafluoroborate: a solution-grown semiorganic crystal for nonlinear frequency conversion.

The crystal structure, refractive indices, and phase-matching conditions for a new nonlinear optical material, L-histidine tetrafluoroborate (HFB), are reported. HFB grows readily, displays favorable mechanical characteristics, and has adequate birefringence to permit phase-matched parametric processes over much of its transparency range (250 nm to 1300 nm). The phase-matching loci and angular sensitivity for second-harmonic generation of 1064-nm light in single crystals of HFB were measured. The effective nonlinearity for HFB is comparable with that of beta-barium borate (~2 pm/V), and its angular sensitivity [delta(Deltak)/deltatheta] is somewhat smaller.

Second-harmonic generation in zinc tris(thiourea) sulfate.

The linear and second-order nonlinear optical properties of single-crystal zinc tris(thiourea) sulfate, or ZTS, are determined. The deduced nonlinear coefficients are |d(31)| = 0.31, |d(32)| = 0.35, and |d(33)| = 0.23 pm/V compared with a |d(14)| value of 0.39 pm/V for potassium dihydrogen phosphate. Because it exhibits a low angular sensitivity (deltaDeltak/deltatheta), ZTS may prove useful for type-II second-harmonic generation from 1.06 to 1.027 microm. We present the phase-matching measurement data for ZTS and compare the calculated frequency conversion efficiency for ZTS with that of several other well-characterized materials.

Femoral head collapse associated with anorexia nervosa in a 20-year-old ballet dancer.

Femoral head collapse occurred in a 20-year-old ballet dancer with anorexia nervosa. The patient developed anorexia nervosa at the age of 11 years and had short stature. The condition never resolved, and she developed pain and stiffness in the right hip at the age of 18 years, with documentation of femoral head collapse on roentgenograms a year later. The patient had delayed pubertal maturation with a bone age of 13 years, primary amenorrhea, and hypoestrogenism. Evaluation for metabolic bone disease was negative, and dual-photon absorptiometry showed significantly decreased bone mass with a bone biopsy revealing only diffuse osteoporosis. Possible etiologic mechanisms of osteonecrosis including repetitive microtrauma and various factors predisposing to femoral head collapse in young women required further investigation.

Scoliosis and fractures in young ballet dancers. Relation to delayed menarche and secondary amenorrhea.

In a survey of 75 dancers (mean age, 24.3 years) in four professional ballet companies, we found that the prevalence of scoliosis was 24 percent and that it rose with increases in age at menarche. Fifteen of 18 dancers (83 percent) with scoliosis had had a delayed menarche (14 years or older), as compared with 31 of 57 dancers (54 percent) without scoliosis (P less than 0.04). The dancers with scoliosis had a slightly higher prevalence of secondary amenorrhea (44 percent vs. 31 percent), the mean (+/- SD) duration of their amenorrhea was longer (11.4 +/- 18.3 vs. 4.1 +/- 7.4 months; P less than 0.05), and they scored higher on a questionnaire that assessed anorectic behavior. The incidence of fractures was 61 percent (46 of 75 dancers), and it rose with increasing age at menarche. Sixty-nine percent of the fractures that were described were stress fractures (mostly in the metatarsals), and their occurrence had an even stronger correlation with increased age at menarche. The incidence of secondary amenorrhea was twice as high among the dancers with stress fractures (P less than 0.01), and its duration was longer (P less than 0.05). In 7 of 10 dancers in whom endocrine studies were performed, the amenorrheic intervals were marked by prolonged hypoestrogenism. These data suggest that a delay in menarche and prolonged intervals of amenorrhea that reflect prolonged hypoestrogenism may predispose ballet dancers to scoliosis and stress fractures.

The supporting structures and layers on the medial side of the knee: an anatomical analysis.

The goal of this study was to delineate the consistent anatomical structures in the medial side of the knee and to determine their relationship to one another. One hundred and fifty-four fresh human knee joints were dissected. A three-layered pattern was found in which ligaments could be consistently placed. We have made suggestions regarding the nomenclature of these structures. The limits of of the so-called capsule and its significance as a stabilizer of the knee joint were examined. Only minor variations in the over-all anatomical pattern were found.