No abstract

Free-and bound-exciton luminescences of GaN epitaxial layers grown by a sublimation technique on 6H-SiC substrates were investigated using time-integrated and time-resolved photoluminescence measurements at low temperatures. Lifetimes were determined for the donor-bound exciton at 3.4722 eV and for two acceptor-bound excitons with energies of 3.4672 eV and 3.459 eV. On the basis of our results we obtain an upper limit of the free-exciton oscillator strength of 0.0046 for GaN. Luminescences between 3.29 eV and 3.37 eV are identified as due to excitons deeply bound to centers located near the substrate-epilayer interface. Free excitons are captured by these centers within 20 ps.

The objective of the study was to determine the incidence rate of osteoporotic fractures among elderly women who had long-term postmenopausal estrogen replacement therapy (ERT) and to compare this with the incidence rate in women who had not used estrogen. In a previous retrospective cohort study based on medical record review in 1982, we showed that long-term ERT was associated with lower incidence of wrist and vertebral fractures. We have extended our follow-up of 490 women by adding a mean 8 years to the observation period, which more than triples the number of osteoporotic fractures. At the Kaiser Permanente Medical Center, San Francisco, a large health maintenance organization, a review of computer pharmacy records from 1968 through 1971 identified 245 postmenopausal women; all had begun estrogen within 3 years of menopause and had used estrogen for at least 5 years. From the same pharmacy records, 245 age-matched postmenopausal non-users were identified. Among estrogen users, mean length of use was 17.0 years, mean follow-up after treatment was 7.3 years and mean dose of conjugated oral estrogen was 0.9 mg daily. We found statistically significant reduction in the incidence of wrist and vertebral fractures in users compared with non-users. The age-adjusted incidence ratios (95% confidence intervals for wrist fractures were 0.55 (0.32-0.92) and for vertebral fractures were 0.57 (0.41-0.80). These results were not statistically significantly altered after adjustment for age of menopause, body mass index and smoking. It is concluded that long-term ERT confers statistically significant protection against wrist and vertebral fractures.

A double antibody enzyme-linked immunosorbent assay (ELISA) was developed to quantitate circulating immune complexed IgA (IgA IC) in human serum. The serum panel for this study consisted of normal blood donors, benign surgery (BS), head and neck cancer (HN), nasopharyngeal carcinoma (NPC), lung cancer (LC), and colon cancer (CC) patients. Immune complexes (IC) were isolated from these sera by precipitation with 3.5% polyethylene glycol (PEG), washed and then redissolved in 0.1 M phosphate-buffered saline pH 7.2. The amount of IgA IC present were then quantified using the double antibody IgA ELISA. This assay was found to be both sensitive (26.0 ng/ml) and reproducible (intra-assay coefficient of variation 4.0%). The mean IgA IC for each cancer group tested (HN = 11.38 +/- 12.54 micrograms/ml; NPC = 13.36 +/- 17.56 micrograms/ml; LC = 17.39 +/- 13.04 micrograms/ml; CC = 26.50 +/- 4.60 micrograms/ml) were significantly elevated (P = 0.001) over both the normals (5.12 +/- 4.09 micrograms/ml) and the benign surgery controls (5.92 +/- 5.04 micrograms/ml). In addition to providing a new tumor marker the presence of high levels of IgA IC in cancer patients could provide a source of tumor-specific antibody as well as antigen and provide reagents to study immune regulation in cancer patients.

A double antibody enzyme immunoassay was used to measure serum ferritin levels in several different control and tumor-bearing populations collected from two institutions. The control groups consisted of normal volunteers, smokers, and Latter Day Saints. No statistically significant differences were noted in ferritin levels between pairs of these groups. Differences were noted among the normal groups when separated on the basis of age and sex, with higher ferritin levels in individuals older than 32 years of age and in men. By one-way analysis of variance, most control groups and subgroups were shown to have significantly lower levels (P < 0.05) than the head and neck cancer group, with the exception of male smokers, who had levels comparable to male head and neck cancer patients. Serum ferritin levels were higher in head and neck cancer patients than in controls; however, there was no difference when compared with patients with other types of solid malignancies or when considering the anatomic site of the head and neck lesion. Ferritin levels were significantly (P < 0.05) higher in patients with advanced (Stages 111 and IV) cancer than in those individuals with Stage I or I1 cancer. In patients with no evidence of clinical disease 5 years after treatment, the ferritin level had essentially returned to normal. In a group of head and neck cancer patients followed longitudinally, a significant decline in ferritin levels (P < 0.05) was seen by 5 months after the completion of successful treatment. Furthermore, ferritin levels showed a tendency to increase or remain at high levels in patients with a poor prognosis and to decrease in those patients with a favorable prognosis, giving support to the contention that ferritin may prove to be a valuable tumor marker in head and neck cancer. Cancer 57:305-311, 1986. URING THE COURSE of tumor development, quan-D titative changes occur in the level of a variety of substances in serum. Such substances are collectively referred to as tumor markers or biochemical serum markers, and these can be classified as belonging to one of several major groups. Examples include oncofetal proteins (car-cinoembryonic antigen [CEA], alpha-fetoprotein [AFP]), hormones (adrenocorticotropin, chorionic gonadotropin, calcitonin), enzymes (prostatic acid phosphatase), or serum proteins (beta-2 microglobulin, fenitin). Many of these markers are elevated in diseases other than cancer, and are therefore considered nonspecific, but have been From the