a b s t r a c tInhaled aerosol dose models play critical roles in medicine, the regulation of air pollutants and basic research. The models fall into several categories: traditional, computational fluid dynamical (CFD), physiologically based pharmacokinetic (PBPK), empirical, semi-empirical, and "reference". Each type of model has its strengths and weaknesses, so multiple models are commonly used for practical applications. Aerosol dose models combine information on aerosol behavior and the anatomy and physiology of exposed human and laboratory animal subjects. Similar models are used for in-vitro studies. Several notable advances have been made in aerosol dose modeling in the past 80 years. The pioneers include Walter Findeisen, who in 1935 published the first traditional model and established the structure of modern models. His model combined aerosol behavior with simplified respiratory tract structures. Ewald Weibel established morphometric techniques for the lung in 1963 that are still used to develop data for modeling today. Advances in scanning techniques have similarly contributed to the knowledge of respiratory tract structure and its use in aerosol dose modeling. Several scientists and research groups have developed and advanced traditional, CFD, and PBPK models. Current issues under study include understanding individual and species differences; examining localized particle deposition; modeling non-ideal aerosols and nanoparticle behavior; linking the regions of the respiratory tract airways from nasal-oral to alveolar; and developing sophisticated supporting software. Although a complete history of inhaled aerosol dose modeling is far too extensive to cover here, selected highlights are described in this paper.

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Previous studies (1-9) have suggested that peripheral human T cells can be divided into two mutually exclusive functional subsets by the two monoclonal antibodies, OKT8 and OKT4. The OKT8+ subset does not provide helper activity but contains cells capable of suppressing B cell differentiation . Importantly, the suppression observed with OKT8+ cells requires the presence of radiosensitive OKT4 + cells . Potent helper activity is found in a radiosensitive OKT4' subset . Irradiated OKT4+ cells also induced B cell differentiation, but only at high ratios of T cells to B cells . In our previous studies (7), we also found that the addition of graded numbers of radiosensitive OKT4 + cells to B cells eventually decreased the net helper activity observed . These experiments raised the possibility that precursors of suppressor cells may be contained within the OKT4 + population .The current study was undertaken to further investigate the functional heterogeneity within the OKT4+ population. In particular, we asked whether OKT4 + cells could be induced to differentiate into immunoregulatory cells capable of suppressing B cell differentiation . In the experiments reported here, we observed that although in vitro pokeweed mitogen (PWM) -activated' OKT4+ cells can function as radioresistant helper cells, these activated OKT4+ cells could also exert potent feedback suppression . This suppression mediated by activated OKT4+ cells required the presence of radiosensitive cells contained within the resting OKT4 + population. These data emphasize the potential role of interactions of T cell subsets contained exclusively within the OKT4 + population in the immunoregulation of B cell differentiation . Volume 154 August 1981 459-467 Materials and MethodsLymphocyte Preparation and Isolation ofHuman T and B Cells . Fresh peripheral blood lymphocytes were isolated from consenting healthy human volunteers by Ficoll-Hypaque density gradient centrifugation . Highly enriched population of T and B cells were then isolated by methods previously described in detail (10) . In brief, human mononuclear cells were washed in minimum essential medium (Grand Island Biological Co ., Grand Island, N . Y .) containing 5% fetal calf serum (FCS ; Microbiological Associates, Bethesda, Md .) and then separated into surface Ig* Supported in part by grants AI-14969 and AI-11524 from the National Institutes of Health, and by The Robert Wood Johnson, Jr . Charitable Trust and The Arthritis Foundation .'Abbreviations used in this paper: C, complement ; E+ , E rosette positive ; FCS, fetal calf serum ; PFC, plaqueforming cells ; PWM, pokeweed mitogen. J . Exp . MED .

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Well-characterized purified water was exposed for 6 h to pulsed low-frequency weak electromagnetic fields. After various time periods, nondegassed and degassed water samples were analyzed by static light scattering. Just after electromagnetic exposure (day 0), a reduction of over 20% in the maximum light scattering intensity at 488 nm wavelength in both nondegassed and degassed samples was observed. By contrast, on day 12 the difference was observed only in nondegassed water samples. The latter effect was attributed to the different geometries of the containers combined with the basic origin of the whole phenomenon due to gas bubbles present in water. By the use of dynamic light scattering, the bubble mean diameter was estimated to be around 300 nm. Our results suggest that the electromagnetic exposure acts on gas nanobubbles present in water and emphasizes the role of the gas/liquid interface. The possibility that exposure to electromagnetic fields disturbs the ionic double layer that contributes to bubble stabilization in water is discussed.

Abstract. Wastewater sludges are used in agriculture as soil amendment and fertilizer, with regard to their organic matter and nutrient content. However, availability of nitrogen and phosphorus from sludge-amended soils and their transfer in runoff may lead to eutrophication of downstream surface water. The aim of this study is to establish and compare the effect of two different sludges on these transfers: an anaerobically digested and thermically stabilised sludge (Seine-Aval treatment plant, sludge no. 1), and a limed sludge (Saint-Quentin treatment plant, sludge no. 2). Experiments were performed on 12 sloping micro-plots (1 m × 1 m) submitted to sludge spreading and controlled rainfall simulation. Runoff water was sampled and analysed for concentrations in nitrogen species and phosphorus. Results show that spreading of sludge no. 1 increased both ammonium nitrogen (mean of 1.1 mg L −1 N-NH 4 vs. 0.2 mg L −1 N-NH 4 for control micro-plots) and particulate phosphorus concentrations (mean of 2 mg L −1 P vs. 1.1 mg L −1 P for control micro-plots) in runoff water. On the other hand, sludge no. 2 did not induce any significant effect on nutrient concentrations in runoff. These results are related to chemical composition and physical treatment of sludges. This study underlines the existence of a short-term risk of nutrient mobilisation by runoff after sludge spreading on soil, and the need to check precisely the impact of this practice on water quality.

Clinical studies suggest that Helicobacter pylori may play a role in the pathogenesis of gastroduodenal ulcers in man but direct evidence of mucosal injury by this microorganism is still lacking. Paf-acether (paf) causes a number of disorders including ischaemic bowel necrosis and gastroduodenal ulceration. Since paf is produced by Escherichia coli, we investigated whether it could be synthesised by H pylori. Five H pylori isolates were coliected from antral biopsy specimens from patients with gastritis and duodenal ulcer and cultured with selective antibiotics. Colonies obtained from both blood agar and brucella broth medium were used. Paf was determined by platelet aggregation assay after ethanolic extraction and subsequent purification by high performance liquid chromatography. Paf was detected in H pylon in blood agar plates (680 (390) pg paf/lx 101 organisms) but not in bacteria cultured on brucelia broth medium. Supplementation of the latter medium with lyso paf and acetylCoA, two paf precursors present in high amounts in the mammalian intestine, induced paf production in three of five isolates. The platelet aggregating material extracted from H pylori exhibited biological and physiochemical characteristics identical to those of paf released from eukaryotic cells. These findings suggest that H pylori may add to the local production of paf in inflamed gastric mucosa.