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This report describes the combined use of a virtual impactor and an electrical classifier to produce fibrous aerosols with narrow distributions of fiber diameter and length. These aerosols are useful for calibrating fiber monitors, studying fiber charging mechanisms, and conducting fiber inhalation toxicological studies. Four types of man-made fibers, including carbon fibers, X7484 glass fibers, X7999 glass fibers, and MMVF10 glass fibers, were selected for this study. The first three types of fibers are monodisperse in diameter [count median diameter (CMD) = 1.8-3.8 μm; geometric standard deviation (GSD) = 1.1–1.2] and polydisperse in length [count median length (CML) = 16.5–35.8 μm; GSD = 1.6–2.1], whereas the MMVF10 glass fibers are polydisperse in diameter (CMD = 1.1 μm; GSD = 1.8) and length (CML = 16.1 μm; GSD = 2.4). To classify each of the first three fiber types by size, a one-stage virtual impactor was used to reduce the nonfibrous debris. An electrical classifier containing a unipolar-ion charger and a differential mobility analyzer was used to classify fibers by length. Results showed that the longer fibers were classified by increasing the total flow rate or decreasing the analyzer voltage in the electrical classifier. Most classified fibers had narrow length distributions with GSDs Results from this study demonstrated that the combined use of a virtual impactor and an electrical classifier produced micrometer-sized (in diameter) fibrous aerosols with narrow size distributions in both diameter and length. In addition, combining the use of these two devices has a potential to classify irregularly shaped particles into different monodisperse fractions for aerosol production and size determination.

The infrared optical properties arising from fundamental and intersubband absorption in III–V and II–VI semiconductor superlattices (SL) are calculated using a superlattice representation formalism. The SL electronic structure at finite wavevector K is obtained from the known K = 0 solutions using SL K· p theory. The theoretical fundamental absorption curves for HgTe/HgCdTe SL are in excellent agreement with recent experimental data. Intersubband absorption between the lowest conduction subbands Cl and C2 is large in both the thick and thin barrier limit, and of potential technological importance.

Visual word recognition begins with the preconscious encoding of semantic, orthographic, phonological, and graphic information. The methods used for exploring these issues are described, as well as the available data. These data sources are then used for activating lexical entries (memory codes), and it appears that the integration of these diverse types of information into a unified percept occurs when a lexical entry is assigned to the display.

Exposure to {alpha}-particles emitted by radon progeny appears to be the second-leading cause of lung cancer mortality. However, individual susceptibility to the carcinogenic effects of {alpha}-particles remains poorly characterized. Variation in susceptibility to cancer produced by certian classes of DNA-damaging chemicals is suspected to involve differences in metabolic activation and detoxication. Susceptibility to {alpha}-particle-induced cancer may involve variations in capacity or opportunity to repair DNA damage. Subtle variations in DNA repair capacity would more likely explain radon-related lung cancer susceptibility. The p53 tumor suppressor protein accumulates as a cellular response to DNA damage from ionizing radiation and regulates arrest in the G{sub 1} portion of the cell cycle. Arrest in G{sub 1} portion of the cell cycle. While upstream regulation of p53 protein stability is poorly understood, variations in the ability to accumulate p53 following DNA damage represent potential variations in lung cancer susceptibility related to radon progeny. Further, transcription of the cell-cycle regulatory gene Cip1 is regulated by p53 and increases following ionizing radiation. Therefore, variations in the expression of Cip1 following {alpha}-particle exposure may also be a susceptibility factor in radon-related lung cancers. The purpose of the present investigation was to measure p53 and Cip1 protein induction followingmore » {alpha}-particle exposure of fibroblast lines from nine individuals to determine if there were significant variations. The expression of Cip1 protein indicates the differences in response are biologically relevant.« less

Our studies have shown that endotoxin intratracheally instilled into the rat lung induces proliferation of alveolar type II cells. In that study, the alveolar type II cells. In that study, the alveolar type II cell hyperplasia occurred 2 d after instillation of endotoxin and persisted for a further 2 d. After hyperplasia, the lung remodeled and returned to a normal state within 24-48 h. Understanding the mechanisms involved in the remodeling process of this transient hyperplasia may be useful to identify molecular changes that are altered in neoplasia. The purpose of the present study was to corroborate induction of epithelial cell hyperplasia by endotoxin and to delineate mechanisms involved in tissue remodeling after endotoxin-induced alveolar type II cell hyperplasia. In conclusion, immonostaining with cyclin D1 and cytokeratin shows that endotoxin induced epithelial cell proliferation and resulted in hyperplasia in the lung which persisted through 4 d post-instillation.

One role of the p53 tumor suppressor protein has been recently revealed. Kastan, M.B. reported that p53 protein accumulates in cells exposed to ionizing radiation. The accumulation of p53 protein is in response to DNA damage, most importantly double-strand breaks, that results from exposure to ionizing radiation. The rise in cellular p53 levels is necessary for an arrest in the G{sub 1} phase of the cell cycle to provide additional time for DNA repair. The p53 response has also been demonstrated to enhance PCNA-dependent repair. p53 is thus an important regulator of the cellular response to DNA-damaging radiation. From this data, it can be concluded that the magnitude of the p53 response is not dependent on the phase of culture growth.

As part of a program to study the effects of inhaled fibers, we characterized the capacity of various fibers to initiate hydroxyl radical (.OH) formation from hydrogen peroxide in a non-cellular system. We studied five natural fibers (erionite, crocidolite, amosite, anthophyllite and chrysotile) and two man-made fibers (JM code 100 glass fibers and glass wool). The fibers were incubated for 5 min at 37 degrees C with hydrogen peroxide and salicylic acid in pH 7.0 aqueous solutions. The salicylate reacted with any .OH formed in these mixtures to produce stable addition products. The amount of .OH addition products formed during the incubations was determined by the salicylate assay which uses HPLC with electrochemical detection. Erionite, JM code 100 and glass wool were the most effective initiators of .OH formation, followed, in order, by crocidolite, amosite and chrysotile. When the capacity of the natural fibers to initiate .OH formation was plotted versus either the values for tumor rates of rats that received pleural inoculations of fibers or the literature values for the human mesothelioma mortality rates, positive correlations (r2 > or = 0.896) were found. Similar correlations with man-made fibers were not found. No positive correlation could be made between .OH formation capacity versus the tumor rates of rats that received peritoneal injections of either type of fibers.

In assessing the health evidence concerning man-made mineral fibers, the chemical composition, surface activity, durability, and size of fibers have to be taken into account. Special-purpose fine glass fibers need to be separated from the insulation wools (glass, rock, and slag wool). The epidemiological evidence is sufficient to conclude that there has been no mesothelioma risk to workers producing or using glass wool, rock wool, or slag wool. The epidemiological studies have been large and powerful, and they show no evidence of a cause-effect relationship between lung cancer and exposure to glass wool, rock wool, or slag wool fibers. There is some evidence of a small cancer hazard attached to the manufacturing process in slag wool plants 20 to 50 years ago, when asbestos was used in some products and other carcinogenic substances were present. However, this hazard is not associated with any index of exposure to slag wool itself. Animal inhalation studies of ordinary insulation wools also show that there is no evidence of hazard associated with exposure to these relatively coarse, soluble fibers. The evidence of carcinogenicity is limited to experiments with special-purpose fine durable glass fibers or experimental fibers, and only when these fibers are injected directly into the pleural or peritoneal cavity. Multiple chronic inhalation studies of these same special-purpose fine glass fibers have not produced evidence of carcinogenicity. It is suggested that the present IARC evaluation of the carcinogenic risk of insulation wools should be revised to Category 3: not classifiable as to carcinogenicity to humans.

Measurements of choroidal blood flow have been made in 34 anaesthetized rabbits by monitoring the clearance of 85-Krypton from the eye. Systemic blood pressure, blood gases and pH were monitored simultaneously and only flow rates within a narrow physiological range of these parameters are presented. In general, the clearance curves contained four exponential components. The physical explanation of these different components is discussed.

The effect of total acute ischaemia on the structure of the rabbit retina has been studied by raising the intraocular pressure above systemic systolic blood pressure for varying periods. The retina as a tissue was readily affected by ischaemia with the individual cells exhibiting varying tolerances to ischaemia. The visual cells were the most vulnerable with changes evident after short periods of ischaemia. The retinal pigment epithelium and the Muller cells were the least susceptible to ischaemic insults with the inner retina exhibiting an intermediate tolerance.

Albino rabbits were given tranexamic acid orally (0.5 g/day) for up to 10 months. This dose (seven times the maximu recommended dose for humans) produced no detectable changes in the ultrastructure of the retina or its function (measured by electroretinography); this was in contrast to a previous report on retinal damage in dogs following long-term oral administration of tranexamic acid.

An angiosarcoma developed in the superior mediastinum of a 50-year-old white woman. The ultrastructural appearance and the significance of Factor VIII-related antigen within the neoplastic cells are discussed.

A significant reduction in the number of phagosomes in the cells of the normal peripheral retinal pigment epithelium occurs as compared to the cells of the central region. In spite of this numerical difference the distribution of the various phagosome stages remained similar in the two locations. The tissue examined immediately after the various periods of ischaemia appeared similar to the control tissue in respect of the numbers and distribution of the phagosome stages. Recovery from short periods of ischaemia was associated with up to a three-fold increase in the initial stages of the phagocytic process. These changes were more marked in the peripheral retina and also with longer periods of recovery.

Measurements of choroidal blood flow have been made in 12 anaesthetized rabbits by monitoring the clearance of radioactive krypton from the eye. Arterial PCO2 was increased by introducing carbon dioxide into the inhalation mixture and blood flow measured at increased levels of PaCO3. Hypercapnia produced an increase in flow over a range of PaCO2 of 15–60 mmHg except in one group of animals in which the initial flow values at low PaCO3 were high and without previously determined control values.

Long-term anaesthesia (5–6 hr) involving a halothane/nitrous oxide and oxygen mixture in rabbits is shown to be accompanied by degenerative changes which are most marked in the visual cells and pigment epithelium. These changes included extensive vacuolation and rounding up of the smooth endoplasmic reticulum in the pigment epithelium, while distortion of the Golgi apparatus, nuclear pyknosis and outer segment disruption occurred in the visual cells. The causes of these pathological changes are speculative, but may be the result of hypotension, reduction in oxygen consumption, hypoxia or a direct toxic effect of the anaesthetic.

The retinal fine structure after long-term anaesthesia involving the administration of 40% urethane alone or a 0·5% halothane/nitrous oxide-oxygen mixture with injection of suxamethonium chloride and phencyclidine was investigated. No changes in ultrastructure were noticed in contrast to changes previously reported for the long-term use of a 0·5–2·5% halothane/nitrous oxide-oxygen mixture. The two former anaesthetics are considered suitable for experiments in rabbits involving the evaluation of retinal fine structure after long periods of anaesthesia. The question of a possible retino-toxic effect of halothane is raised.