Electric fields and surface charges induced by ELF magnetic fields

A method is described for evaluating electric fields induced by ELF magnetic fields into electrically inhomogeneous, low-conductivity (less than 5 S/m) structures. It is applied to cylinders and spheres, and numerical results are given for electrical properties that are representative of some tissues, or of cells embedded either in saline solution or a tissue matrix. Surface currents on spherical cell boundaries are estimated and compared with thermal noise due to ion motion.     

Predictive value of minor anomalies: II. Use in cohort studies to identify teratogens

Cohort studies of putative human teratogens can identify the full spectrum of phenotypic effects, including both major malformations and minor anomalies. Cohort studies which include the much more common minor anomalies make it possible to use a relatively small number of exposed and unexposed infants to identify an increase in the frequency of malformations. We evaluated this use of minor anomalies in a cohort study of newborn infants who had been exposed in utero to three putative teratogens: insulin-dependent diabetes mellitus in the mother and the use of the anticonvulsant phenytoin and exogenous sex hormones by the mother. In addition, the reproducibility of identifying minor anomalies was tested by comparing the results of examinations by two independent observers of 444 unexposed infants. The frequency of minor anomalies was increased among infants of diabetic mothers. However, the reproducibility of identifying minor anomalies was poor. We conclude that the examination of teratogen-exposed infants for minor anomalies cannot be used in epidemiologic studies of putative teratogens unless special efforts are made to maximize consistency in the identification of these features.     

Germination of Phyllosticta ampelicidaPycnidiospores: Prerequisite of Adhesion to the Substratum and the Relationship of Substratum Wettability

Pycnidiospores of Phyllosticta ampelicida, the causal agent of black rot of grape, were found to germinate only on substrata on which they were firmly attached. Such surfaces were poorly wettable and had advancing contact angles (straight thetaa) formed by a water drop of >80°, e.g., grape leaf, polystyrene, Teflon, polycarbonate, collodion, and glass treated with the silanes n-octadecyltrichlorosilane, dimethyldichlorosilane, or diphenyldichlorosilane. When pycnidiospores were deposited on more wettable surfaces they did not attach firmly and did not germinate. Such highly wettable surfaces had straight thetaa 相似文献   

Extracting useful data from imperfect monitoring schemes: endangered butterflies at San Bruno Mountain,San Mateo County,California (1982–2000) and implications for habitat management

Managers surveyed for sensitive butterfly species in the San Bruno Mountain Habitat Conservation Plan area between 1982 and 2000 using an opportunistic “wandering transect” method. To extract as much valuable information as possible from the data collected by this method we analyzed patterns of surveys and butterfly presence and absence within 250 m square cells gridded across the area within a Geographic Information System. While estimates of butterfly abundance were not possible, the data could be tested for trends in butterfly occupancy. For those cells surveyed during at least 10 years, no trends in the total number of occupied cells was evident for either Callippe silverspot or mission blue butterfly. There were cells, however, that showed positive or negative trends (P < 0.20) in occupancy for each species (Callippe silverspot: 14 positive, 15 negative, 6 cells occupied all years; mission blue butterfly: 40 positive, 40 negative, 2 cells occupied all years). We conclude that for the period 1982–2000 the population of each species was stable in overall total distribution, but indicate geographic areas of concern for each, specifically the edges of the northeast ridge for Callippe silverspot butterfly and the northwest of the study area for mission blue butterfly. Vegetation composition analysis using orthophotography with field corroboration indicates that those areas with declines in occupancy for these species experienced native coastal scrub succession and a corresponding loss in grassland butterfly habitat, while positive trending and stable cells had stable grassland proportions. Habitat managers at San Bruno Mountain should therefore incorporate programs for protecting grassland butterfly habitat not only from invasive weeds but also from succession to native coastal scrub. This approach illustrates the feasibility of using occupancy as an indicator to track butterfly status in a protected area even when suboptimal data collection methods are used, but the difficulties of using these data also reinforces the need for managers to devise monitoring schemes appropriate for their objectives before implementing them.     

Quantification of phagocytosis in human neutrophils by flow cytometry.

Phagocytosis represents a central element of the host response to microbial invasion. We describe a flow cytometric method for measuring the kinetics of phagocytosis of two bacteria by human polymorphonuclear leukocytes (PMNs). Over a 60-min period, isolated human PMNs were exposed to Staphylococcus aureus (rapidly phagocytosed) and Klebsiella pneumoniae (slowly phagocytosed). This method distinguished adherent from ingested bacteria by quenching fluorescein isothiocyanate-labeled extracellular bacteria with ethidium bromide. This further allowed the exclusion of dead, highly permeable, and subsequently bright-red fluorescent PMNs. Our experiments with two different bacteria, various PMN-to-bacteria ratios (1:1, 1:10, 1:100), and different individuals proved that 1) flow cytometric analysis is accurate and useful for characterizing phagocytosis, 2) adherent bacteria can be distinguished from ingested bacteria after quenching with ethidium bromide, and that 3) phagocytosis kinetics of two bacteria with different onsets of phagocytosis can be determined by flow cytometry and the assessment of a score that quantifies phagocytosis.