CBED and LACBED: characterization of antiphase boundaries.

Convergent-beam electron diffraction (CBED) and large-angle convergent-beam electron diffraction (LACBED) techniques are well adapted to the characterization of several types of crystal defects. In fact, dislocations, grain boundaries and stacking faults have already been successfully characterized with these methods. In the present paper, we describe the CBED and LACBED characterization of another type of crystal defect showing a special interest in materials science: antiphase boundaries (APBs). The first part of the paper is devoted to the determination of the effects of antiphase boundaries on CBED and LACBED patterns that could be expected from a theoretical point of view. It indicates that the superlattice excess lines present on these patterns are split into two lines with equal intensity when the incident beam is located on an APB. In the second part, we experimentally test these theoretical predictions on a specimen showing two different known types of antiphase boundaries. In a third part we indicate how these methods could be used to identify unknown APBs in a specimen. Finally, the advantages and disadvantages of both methods for the characterization of antiphase boundaries are discussed.

Blood trace metals in military recruits.

Whole blood samples obtained from 2,000 military recruits were analyzed for cadmium, copper, lead, and zinc by atomic absorption spectroscopy. Whole blood copper levels were symmetrically distributed and those for cadmium, lead, and zinc were positively skewed. Average whole blood levels for copper and zinc were generally comparable to published values, but cadmium and lead values were somewhat higher, suggesting possible absorption of trace metals from containers during storage. Average cadmium and zinc levels were similar among blacks and whites, whereas average copper and lead levels were significantly higher in blacks. Cigarette smokers had higher copper levels than nonsmokers. Cadmium and zinc whole blood levels varied inversely with educational attainment. Copper, lead, and zinc levels varied by place of residence, suggesting the influence of dietary or other factors. Future studies characterizing trace metal body burdens or relating trace metals to diseases must carefully measure such pertinent attributes as age, sex, race or ethnic group, smoking habits, diet, and environmental exposure.

Rocky Mountain spotted fever (tick-borne typhus) in South Carolina: an educational program and tick/rickettsial survey in 1973 and 1974.

Because the incidence of spotted fever is increasing in South Carolina, campaigns were carried out in 1973 and 1974 to provide the public and medical practitioners, through pamphlets and news media, with information about spotted fever and the ticks which transmit the causative agent, Rickettsia rickettsii. People were also invited to save and submit live ticks removed from vegetation, animals and humans, for examination by the hemolymph test. A total of 1,186 ticks consisting of 987 Dermacentor variabilis, 103 Rhipicephalus sanguineus, and 96 Amblyomma americanum were examined. Rickettsiae identified by direct immunofluorescence as members of the spotted fever group were detected in 49 (4.9%) of the D. variabilis, and 16 (16.6%) of the A. americanum ticks. Two hundred and twenty (199 D. variabilis, 17 A. americanum, and 4 R. sanguineus) were recorded as having been attached to 199 persons. Nine of these ticks (8 D. variabilis, and 1 A. americanum) were hemolymph test-positive for spotted fever-group rickettsiae. Infected ticks originated from each of the three major South Carolina biogeographic regions, namely Piedmont, Sandhill, and Coastal Plain. Since education is the first and most important step in preventing spotted fever, educational programs and tick examination services similar to those decribed, are suggested for other states with high spotted fever incidence.

DDT uptake and metabolism by a marine diatom.

CONCLUSION: Cylindrotheca closterium, Reimann and Lewin, was capable of absorbing and concentrating DDT above the level in seawater. DDT was metabolized by this organism only to DDE.