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At least 991 records · Page 55Linked to original sources

PubMed2003

Vertical profile of tritium concentration in air during a chronic atmospheric HT release.

The vertical profiles of tritium gas and tritiated water concentrations in air, which would have an influence on the assessment of tritium doses as well as on the environmental monitoring of tritium, were measured in a chronic tritium gas release experiment performed in Canada in 1994. While both of the profiles were rather uniform during the day because of atmospheric mixing, large gradients of the profiles were observed at night. The gradient coefficients of the profiles were derived from the measurements. Correlations were analyzed between the gradient coefficients and meteorological conditions: solar radiation, wind speed, and turbulent diffusivity. It was found that the solar radiation was highly correlated with the gradient coefficients of tritium gas and tritiated water profiles and that the wind speed and turbulent diffusivity showed weaker correlations with those of tritiated water profiles. A one-dimensional tritium transport model was developed to analyze the vertical diffusion of tritiated water re-emitted from the ground into the atmosphere. The model consists of processes of tritium gas deposition to soil including oxidation into tritiated water, reemission of tritiated water, dilution of tritiated water in soil by rain, and vertical diffusion of tritiated water in the atmosphere. The model accurately represents the accumulation of tritiated water in soil water and the time variations and vertical profiles of tritiated water concentrations in air.

Air Pollutants, Radioactive↗

PubMed1976

Influence of atmospheric oxygen concentration on acetylene reduction and efficiency of nitrogen fixation in intact Klebsiella pneumoniae.

Oxygen-limited (N2-fixing) chemostat cultures of Klebsiella pneumoniae supplied with a N-free medium were established by introducing low atmospheric O2 concentrations into the gas supply of anaerobic glucose-limited N2-fixing chemostat cultures; the molar growth yield for glucose and the efficiency of N2 fixation (mug N fixed/mg glucose consumed) were increased (by up to 82%) from the anaerobic values. Acetylene-reducing activity was inhibited reversibly by O2 in samples from O2-limited and anaerobic glucose-limited chemostat cultures. Oxygen uptake rates in samples from these chemostat cultures were similar, but C2-H2-reducing activity in samples from O2-limited chemostat cultures was more tolerant of low atmospheric O2 concentrations, in part because of a higher population density. In the absence of glucose, O2 was required at a low atmospheric concentration for C2H2 reduction in samples from either O2-limited or anaerobic glucose-limited chemostat cultures. The possibility is discussed that ATP generated from oxidative phosphorylation can be used for N2 fixation in K. pneumoniae.

Acetylene↗

PubMed2006

Evolution of discharge structure in capacitive radio-frequency atmospheric microplasmas.

Conventional radio-frequency (rf) nonthermal atmospheric plasmas are generated in a millimeter gap. In this Letter, we present a self-consistent numerical study of rf atmospheric microplasmas in a submillimeter gap comparable to their sheath thickness. It is shown that the narrow electrode gap deforms the discharge structure, ultimately removing the bulk-plasma region and disabling electron trapping. Significantly, these properties permit rf atmospheric microplasmas to operate at very high current densities thus simultaneously achieving higher stability and greater chemical reactivity.

Journal Article↗

PubMed1996

Ammonia Flux between Oilseed Rape Plants and the Atmosphere in Response to Changes in Leaf Temperature, Light Intensity, and Air Humidity (Interactions with Leaf Conductance and Apoplastic NH4+ and H+ Concentrations).

NH3 exchange between oilseed rape (Brassica napus) plants and the atmosphere was examined at realistic ambient NH3 levels under controlled environmental conditions. Different leaf conductances to NH3 diffusion were obtained by changing leaf temperature (10 to 40[deg]C), light intensity (0 to 600 [mu]mol m-2 s-1), and air humidity (20 to 80%), respectively. NH3 adsorption to the cuticle with subsequent NH3 transport through the epidermis had no significant effect on the uptake of atmospheric NH3, even at 80% relative air humidity. NH3 fluxes increased linearly with leaf conductance when light intensities were increased from 0 to 600 [mu]mol m-2 s-1. Increasing leaf temperatures from 10 to 35[deg]C caused an exponential increase in NH3 emission from plants exposed to low ambient NH3 concentrations, indicating that leaf conductance was not the only factor responding to the temperature increase. The exponential relationship between NH3 emission and temperature was closely matched by the temperature dependence of the mole fraction of gaseous NH3 above the leaf apoplast (NH3 compensation point), as calculated on the basis of NH4+ and H+ concentrations in the leaf apoplast at the different leaf temperatures. NH3 fumigation experiments showed that an increase in leaf temperature may cause a plant to switch from being a strong sink for atmospheric NH3 to being a significant NH3 source. In addition to leaf temperature, the size of the NH3 compensation point depended on plant N status and was related to plant ontogeny.

Journal Article↗

PubMed1973

The Effect of an Oxygen-free Atmosphere on Net Photosynthesis and Transpiration of Barley (Hordeum vulgare L.) and Wheat (Triticum aestivum L.) Leaves.

Stomata of barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.) leaves failed to open in the light and close in the dark or respond to changes in the CO(2) concentration of the atmosphere in either light or dark when the leaves were in an O(2)-free atmosphere. In contrast, the expected responses to environmental changes were found in atmospheres containing 1.5% O(2). It appears that O(2) is necessary for both opening and closing of wheat and barley stomata.

Journal Article↗

PubMed1988

Three Phases of Plant Response to Atmospheric CO(2) Enrichment.

Several years of research on seven different plants (five terrestrial and two aquatic species) suggest that the beneficial effects of atmospheric CO(2) enrichment may be divided into three distinct growth response phases. First is a well-watered optimum-growth-rate phase where a 300 parts per million increase in the CO(2) content of the air generally increases plant productivity by approximately 30%. Next comes a nonlethal water-stressed phase where the same increase in atmospheric CO(2) is more than half again as effective in increasing plant productivity. Finally, there is a water-stressed phase normally indicative of impending death, where atmospheric CO(2) enrichment may actually prevent plants from succumbing to the rigors of the environment and enable them to maintain essential life processes, as life ebbs from corresponding ambient-treatment plants.

Journal Article↗

PubMed2001

Identification of the chemical states of phosphorus in atmospheric aerosols by XANES spectrometry.

Depth selective XAFS spectrometry was applied to determine the chemical states of phosphorus in atmospheric aerosols. Atmospheric aerosols were collected on aluminum foils and polyethylene films using a 4-stage cascade impactor and a 12-stage low pressure Andersen sampler, respectively. Samplings were performed at Uji (urban area) and Sakurajima (near a volcano). We measured X-ray fluorescence yield (XFY) and total electron yield (sample current) simultaneously to obtain the X-ray absorption near edge structure (XANES) spectra of the atmospheric aerosols. X-ray absorption in the vicinities of P K-edges was measured on the beamline BL-11B at the Photon Factory, High Energy Accelerator Research Organization, Tsukuba, Japan. The Sakurajima aerosol samples showed only a P5+ peak and the peak was remarkable in coarse mode. In case of the Uji samples, the P5+ peak was dominant and a slight P3+ peak was detected for sample current measurement.

Journal Article↗

PubMed1993

The urban/rural divide in head and neck cancer--the effect of atmospheric pollution.

Inter-district variations in the incidence of head and neck squamous carcinoma in the period 1978-1987 have been identified from records at the West Midlands Cancer Registry, England. Analysis of the records reflect the national and international trend of higher urban cancer rates compared with neighbouring rural communities. Atmospheric pollution data (mean sulphur dioxide and smoke concentrations) from a national survey are positively correlated with squamous cancer of the larynx and pharynx. The correlation is most significant between laryngeal cancer rates and atmospheric sulphur dioxide levels. The periods 1950-1970 and 1970-1990 have been analysed separately to reflect the reduction in atmospheric pollution that has occurred over these years and thus avoid missing a latent effect that this might have on cancer rates.

Air Pollutants↗

PubMed1976

Hypobaric helium atmospheres for light and electron microscopy of mammalian cells.

The development of electron microscope environmental/hydration chambers (EMC's) for the examination of living biological specimens has necessitated a search for a suitable gaseous environment that is compatible with both electron imaging and cell survival. Helium has a lower electron scattering cross section than air. The effects of hydrated helium and hydrated air atmospheres in an EMC at pressures 50-200 Torr were examined with a JEM 200 transmission electron microscope operated at 200 kV and 22 degrees C. Results showed that whereas 200 Torr of air reduced beam transmission by more than 90% under these conditions, 200 Torr of moist helium only reduced beam transmission by 30%. The effects of sub-atmospheric or hypobaric helium atmospheres on human white blood cells attached to glass coverslips were investigated by phase-contrast light microscopy in a simulated EMC or light microscope environmental chamber (LMC) at ...37 degrees C. gross morphological changes were observed in cells held at pressures of 300 Torr of moist helium for exposure times of 15 min. At pressures below 300 Torr, morphological changes occurred more rapidly as the pressure was reduced. At the lowest pressures tested (60 and 80 Torr) 50% of the cell populations died within 6-7 min. The development of morphological changes produced by hypobaric stress followed a characteristic pattern. The filopodia, or microvilli attaching the cells to the substrate, became withdrawn, with only occasional retraction fibers remaining. Blends appeared around the cell surface and increased in size as hypobaric exposures progressed. Vacuoles, or cler spherical regions, appeared within the cytoplasm and the overall shape of the cells became circular. The cells became flatter during circularization, showing an apparent 2-2-5 X increase in size as they respread on the substrate...

Cytoplasm↗

PubMed1996

Childhood asthma and atmospheric conditions.

Bronchial asthma is the most common chronic respiratory illness in childhood. It is characterized by paroxysmal bronchospastic periods. There are many studies giving reasons to explain the bronchospasm periods. One of the reasons, atmospheric conditions, is effective in creating a clinical picture of asthmatic patients. In the present study, the correlation between atmospheric conditions and asthmatic symptoms in children was investigated using peak expiratory flow rate (PEFR) as the respiratory function test. Twenty-one children with bronchial asthma were monitored in the study. They were followed as outpatients of the Ege University Medical Faculty, Department of Pediatric Allergy and Pneumotology, between November 1993 and June 1994. Atmospheric conditions were recorded from the local meteorology center. Complaints and the PEFR of children were compared with the meteorological data. Asthmatic symptoms were increased by low temperatures in all asthmatic children. An increase was detected in the extrinsic group by relative humidity and ratio of cloud, but in the intrinsic group only by relative humidity.

Adolescent↗

PubMed2005

Sensing an atmosphere of ease: a tentative theory of supportive care settings.

Nightingale saw the art of nursing as providing an environment in which patients were offered the best conditions for nature to act upon them. However, we still have limited research-based understandings of care settings experienced as supportive by patients, significant others and staff. The aim of this study was to construct a theoretical understanding of processes contributing to supportive care settings. The authors used grounded theory design and the constant comparative method to analyse theoretically sampled interview and observational data from three different contexts of care. The tentative theory conceptualizes supportive care settings as sensing an atmosphere of ease, and five categories were recognized: experiencing welcoming; recognizing oneself in the environment; creating and maintaining social relations; experiencing a willingness to serve; and experiencing safety. Having one's expectations of the environment exceeded was a mediating factor in sensing an atmosphere of ease. Sensing an atmosphere of ease facilitated experiences of being able to locate oneself in familiar and safe surroundings; being able to follow one's own rhythm; being seen, acknowledged and cared about; and having possibilities of benefiting from beauty and contacts with others.

Adult↗

PubMed1995

Fate of Aeromonas and Yersinia on modified-atmosphere-packaged (MAP) cod and trout.

The growth/survival of Aeromonas spp. and Yersinia enterocolitica on cod and trout stored in two modified atmospheres at 0 degrees, 5 degrees and 12 degrees C was compared with that on aerobically stored fish. Both organisms grew on aerobically stored fish at all three temperatures. Growth on the modified-atmosphere-stored fish was never greater and was generally markedly less than on aerobically stored fish. This reduction in growth was greater in the higher carbon dioxide-containing atmosphere and at the lower temperature(s).

Aeromonas↗

PubMed2004

Atmospheric contamination during ultrasonic scaling.

OBJECTIVE: The aim of this study was to determine the microbial atmospheric contamination during initial periodontal treatment using a piezoelectric ultrasonic scaler in combination with either high-volume evacuation (HVE) or conventional dental suction (CDS). METHODS: The study included 17 treatment sessions, consisting of a 40-min episode of continuous plaque and calculus removal using an ultrasonic unit (EMS). The treatment sessions were carried out in six patients with generalized adult periodontitis and ranged from two to four sessions per patient according to their needs. The use of HVE and CDS was randomly assigned over the sessions within each patient. Before each treatment, the operating room was not used for 15 h. To measure baseline microbial air pollution two Petri dishes containing blood agar were exposed for 10 min to the air. At the start of each treatment session, two Petri dishes were exposed for 5 min at a distance of 40 cm from the mouth of the patients. After 20 min, this procedure was repeated. At a distance of 150 cm, two Petri dishes were exposed for 20 min followed by exposure of two new Petri dishes for the rest of the session. The plates were cultured aerobically and anaerobically for 3 and 7 days, respectively. RESULTS: The mean colony forming units (CFU) before treatment never exceeded 0.6 colonies per plate. At 40 cm, the mean CFU, when considering a period of 40 min, was 8.0 for HVE and 17.0 for CDS. The mean CFU at 150 cm during this period was 8.1 with HVE and 10.3 with the CDS. With reference to the Air Microbial Index the operatory atmosphere was considered to be in a good condition during 40 min of continuous use of the ultrasonic scaler in combination with both HVE and CDS. CONCLUSION: Within the restrictions of this study, only limited atmospheric microbial contamination is produced when using a piezoelectric ultrasonic scaler.

Adult↗

PubMed1994

The influence of endotoxin upon middle ear fibroblasts cultured in normal middle ear gas and atmospheric air.

Otitis media represents a continuum of inflammatory stages frequently in association with bacteria and/or endotoxin. Furthermore, the disease is often treated with insertion of ventilation tubes, which causes hyperoxia relative to the physiological state in the tympanic cavity. The present study was undertaken to quantitate the interaction between endotoxin and relative hyperoxia in cultures of rabbit middle ear fibroblasts incubated in normal middle ear gas and atmospheric air, respectively. Growth was monitored by determination of DNA, cell protein and cell division. The synthetic activity was estimated by collagen production. The antioxidant defense was determined by measuring the intra-and extracellular concentrations of superoxide dismutase (SOD). The results demonstrated that hyperoxia significantly impaired the growth of middle ear fibroblasts, which was compensated for by addition of endotoxin stimulating the growth. The collagen synthesis increased significantly in atmospheric air with a synergistic effect of endotoxin. Hyperoxia induced intracellular SOD formation, while endotoxin tended to reduce the synthesis. Finally, exposure to atmospheric air caused significantly larger amounts of reducing agents extracellularly in cultures without endotoxin compared to endotoxin incubated cultures. It is suggested that endotoxin possess both synergistic and antagonistic potential as regards the effects of relative hyperoxia, and that the interaction between endotoxin and hyperoxia may be an important factor in otitis media.

Animals↗

PubMed1992

Atmospheric sun protection factor on clear days: its observed dependence on solar zenith angle and its relevance to the shadow rule for sun protection.

Global irradiances measured in seven 5-nm bands of UV-B at Rockville, MD (39.1 degrees N, 77.1 degrees W) on 28 clear days near the summer solstice are convoluted with the erythemal action spectrum of human skin to determine dose rates at various hours of the day. These rates are averaged with respect to solar zenith angle to obtain the diurnal variation of mean dose rate and of the Sun Protection Factor (SPF) of the atmosphere (reciprocal of the normalized atmospheric transmissivity) on a typical clear summer day in Rockville. At a 45 degrees zenith angle the atmospheric SPF is computed to be 2.7 and increases rapidly to greater than 7 at 60 degrees. Dose rates are integrated with respect to time to obtain estimates of mean doses for various periods during clear days at Rockville in mid summer and near the autumnal equinox. In mid summer the effective erythemal UV-B exposure during the period when the solar zenith angle is less than 45 degrees is about five times greater than that during the remainder of the day. These observations provide scientific basis for a shadow rule for solar UV-B protection: when shadows are shorter than objects casting them, sunburn is much more likely than at other times.

Humans↗

PubMed2001

On atmospheric loss of oxygen ions from earth through magnetospheric processes.

In Earth's environment, the observed polar outflow rate for O(+) ions, the main source of oxygen above gravitational escape energy, corresponds to the loss of approximately 18% of the present-day atmospheric oxygen over 3 billion years. However, part of this apparent loss can actually be returned to the atmosphere. Examining loss rates of four escape routes with high-altitude spacecraft observations, we show that the total oxygen loss rate inferred from current knowledge is about one order of magnitude smaller than the polar O(+) outflow rate. This disagreement suggests that there may be a substantial return flux from the magnetosphere to the low-latitude ionosphere. Then the net oxygen loss over 3 billion years drops to approximately 2% of the current atmospheric oxygen content.

Journal Article↗

PubMed2003

White-light filaments for atmospheric analysis.

Most long-path remote spectroscopic studies of the atmosphere rely on ambient light or narrow-band lasers. High-power femtosecond laser pulses have been found to propagate in the atmosphere as dynamically self-guided filaments that emit in a continuum from the ultraviolet to the infrared. This white light exhibits a directional behavior with enhanced backward scattering and was detected from an altitude of more than 20 kilometers. This light source opens the way to white-light and nonlinear light detection and ranging applications for atmospheric trace-gas remote sensing or remote identification of aerosols. Air ionization inside the filaments also opens promising perspectives for laser-induced condensation and lightning control. The mobile femtosecond-terawatt laser system, Teramobile, has been constructed to study these applications.

Journal Article↗

PubMed2005

Rapid formation of sulfuric acid particles at near-atmospheric conditions.

We investigated the formation of new particles in a laboratory study, starting from H2SO4 produced in situ through the reaction of OH radicals with SO2. Newly formed particles were observed for H2SO4 concentrations above 7 x 10(6) per cubic centimeter. At 293 kelvin, a rough estimate yielded a nucleation rate of 0.3 to 0.4 particles per cubic centimeter per second for approximately 10(7) particles per cubic centimeter of H2SO4 (particle size >/= 3 nanometers). These findings are in agreement with observations from the atmosphere. The results demonstrate that under laboratory conditions similar to the atmosphere, particle formation occurs at atmospheric H2SO4 concentration levels.

Journal Article↗