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Sample records for affecting gas exchange

  1. Ozone affects gas exchange, growth and reproductive development in Brassica campestris (Wisconsin fast plants).

    PubMed

    Black, V J; Stewart, C A; Roberts, J A; Black, C R

    2007-01-01

    Exposure to ozone (O(3)) may affect vegetative and reproductive development, although the consequences for yield depend on the effectiveness of the compensatory processes induced. This study examined the impact on reproductive development of exposing Brassica campestris (Wisconsin Fast Plants) to ozone during vegetative growth. Plants were exposed to 70 ppb ozone for 2 d during late vegetative growth or 10 d spanning most of the vegetative phase. Effects on gas exchange, vegetative growth, reproductive development and seed yield were determined. Impacts on gas exchange and foliar injury were related to pre-exposure stomatal conductance. Exposure for 2 d had no effect on growth or reproductive characteristics, whereas 10-d exposure reduced vegetative growth and reproductive site number on the terminal raceme. Mature seed number and weight per pod and per plant were unaffected because seed abortion was reduced. The observation that mature seed yield per plant was unaffected by exposure during the vegetative phase, despite adverse effects on physiological, vegetative and reproductive processes, shows that indeterminate species such as B. campestris possess sufficient compensatory flexibility to avoid reductions in seed production. PMID:17803646

  2. Ecosystem Warming Affects Vertical Distribution of Leaf Gas Exchange Properties and Water Relations of Spring Wheat

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The vertical distribution of gas exchange and water relations responses to full-season in situ infrared (IR) warming were evaluated for hard red spring wheat (Triticum aestivum L. cv. Yecora Rojo) grown in an open field in a semiarid desert region of the Southwest USA. A Temperature Free-Air Contro...

  3. Vasomotor tone does not affect perfusion heterogeneity and gas exchange in normal primate lungs during normoxia

    NASA Technical Reports Server (NTRS)

    Glenny, R. W.; Robertson, H. T.; Hlastala, M. P.

    2000-01-01

    To determine whether vasoregulation is an important cause of pulmonary perfusion heterogeneity, we measured regional blood flow and gas exchange before and after giving prostacyclin (PGI(2)) to baboons. Four animals were anesthetized with ketamine and mechanically ventilated. Fluorescent microspheres were used to mark regional perfusion before and after PGI(2) infusion. The lungs were subsequently excised, dried inflated, and diced into approximately 2-cm(3) pieces (n = 1,208-1,629 per animal) with the spatial coordinates recorded for each piece. Blood flow to each piece was determined for each condition from the fluorescent signals. Blood flow heterogeneity did not change with PGI(2) infusion. Two other measures of spatial blood flow distribution, the fractal dimension and the spatial correlation, did not change with PGI(2) infusion. Alveolar-arterial O(2) differences did not change with PGI(2) infusion. We conclude that, in normal primate lungs during normoxia, vasomotor tone is not a significant cause of perfusion heterogeneity. Despite the heterogeneous distribution of blood flow, active regulation of regional perfusion is not required for efficient gas exchange.

  4. Gas Exchange of Algae

    PubMed Central

    Ammann, Elizabeth C. B.; Lynch, Victoria H.

    1966-01-01

    Changes in the oxygen partial pressure of air over the range of 8 to 258 mm of Hg did not adversely affect the photosynthetic capacity of Chlorella pyrenoidosa. Gas exchange and growth measurements remained constant for 3-week periods and were similar to air controls (oxygen pressure of 160 mm of Hg). Oxygen partial pressures of 532 and 745 mm of Hg had an adverse effect on algal metabolism. Carbon dioxide consumption was 24% lower in the gas mixture containing oxygen at a pressure 532 mm of Hg than in the air control, and the growth rate was slightly reduced. Oxygen at a partial pressure of 745 mm of Hg decreased the photosynthetic rate 39% and the growth rate 37% over the corresponding rates in air. The lowered metabolic rates remained constant during 14 days of measurements, and the effect was reversible after this time. Substitution of helium or argon for the nitrogen in air had no effect on oxygen production, carbon dioxide consumption, or growth rate for 3-week periods. All measurements were made at a total pressure of 760 mm of Hg, and all gas mixtures were enriched with 2% carbon dioxide. Thus, the physiological functioning and reliability of a photosynthetic gas exchanger should not be adversely affected by: (i) oxygen partial pressures ranging from 8 to 258 mm of Hg; (ii) the use of pure oxygen at reduced total pressure (155 to 258 mm of Hg) unless pressure per se affects photosynthesis, or (iii) the inclusion of helium or argon in the gas environment (up to a partial pressure of 595 mm of Hg). PMID:5927028

  5. The hygric hypothesis does not hold water: abolition of discontinuous gas exchange cycles does not affect water loss in the ant Camponotus vicinus.

    PubMed

    Lighton, John R B; Turner, Robbin J

    2008-02-01

    The discontinuous gas exchange cycle (DGC) of insects and other tracheate arthropods temporally decouples oxygen uptake and carbon dioxide emission and generates powerful concentration gradients for both gas species between the outside world and the tracheal system. Although the DGC is considered an adaptation to reduce respiratory water loss (RWL) - the "hygric hypothesis" - it is absent from many taxa, including xeric ones. The "chthonic hypothesis" states that the DGC originated as an adaptation to gas exchange in hypoxic and hypercapnic, i.e. underground, environments. If that is the case then the DGC is not the ancestral condition, and its expression is not necessarily a requirement for reducing RWL. Here we report a study of water loss rate in the ant Camponotus vicinus, measured while its DGC was slowly eliminated by gradual hypoxia (hypoxic ramp de-DGCing). Metabolic rate remained constant. The DGC ceased at a mean P(O2) of 8.4 kPa. RWL in the absence of DGCs was not affected until P(O2) declined below 3.9 kPa. Below that value, non-DGC spiracular regulation failed, accompanied by a large increase in RWL. Thus, the spiracular control strategy of the DGC is not required for low RWL, even in animals that normally express the DGC. PMID:18245633

  6. Discontinuous gas exchange in insects.

    PubMed

    Quinlan, Michael C; Gibbs, Allen G

    2006-11-01

    Insect respiratory physiology has been studied for many years, and interest in this area of insect biology has become revitalized recently for a number of reasons. Technical advances have greatly improved the precision, accuracy and ease with which gas exchange can be measured in insects. This has made it possible to go beyond classic models such as lepidopteran pupae and examine a far greater diversity of species. One striking result of recent work is the realization that insect gas exchange patterns are much more diverse than formerly recognized. Current work has also benefited from the inclusion of comparative methods that rigorously incorporate phylogenetic, ecological and life history information. We discuss these advances in the context of the classic respiratory pattern of insects, discontinuous gas exchange. This mode of gas exchange was exhaustively described in moth pupae in the 1950s and 1960s. Early workers concluded that discontinuous gas exchange was an adaptation to reduce respiratory water loss. This idea is no longer universally accepted, and several competing hypotheses have been proposed. We discuss the genesis of these alternative hypotheses, and we identify some of the predictions that might be used to test them. We are pleased to report that what was once a mature discipline, in which the broad parameters and adaptive significance of discontinuous gas exchange were thought to be well understood, is now a thriving and vigorous field of research. PMID:16870512

  7. Discontinuous gas-exchange cycle characteristics are differentially affected by hydration state and energy metabolism in gregarious and solitary desert locusts.

    PubMed

    Talal, Stav; Ayali, Amir; Gefen, Eran

    2015-12-01

    The termination of discontinuous gas exchange cycles (DGCs) in severely dehydrated insects casts doubt on the generality of the hygric hypothesis, which posits that DGCs evolved as a water conservation mechanism. We followed DGC characteristics in the two density-dependent phases of the desert locust Schistocerca gregaria throughout exposure to an experimental treatment of combined dehydration and starvation stress, and subsequent rehydration. We hypothesized that, under stressful conditions, the more stress-resistant gregarious locusts would maintain DGCs longer than solitary locusts. However, we found no phase-specific variations in body water content, water loss rates (total and respiratory) or timing of stress-induced abolishment of DGCs. Likewise, locusts of both phases re-employed DGCs after ingesting comparable volumes of water when rehydrated. Despite comparable water management performances, the effect of exposure to stressful experimental conditions on DGC characteristics varied significantly between gregarious and solitary locusts. Interburst duration, which is affected by the ability to buffer CO2, was significantly reduced in dehydrated solitary locusts compared with gregarious locusts. Moreover, despite similar rehydration levels, only gregarious locusts recovered their initial CO2 accumulation capacity, indicating that cycle characteristics are affected by factors other than haemolymph volume. Haemolymph protein measurements and calculated respiratory exchange ratios suggest that catabolism of haemolymph proteins may contribute to a reduced haemolymph buffering capacity, and thus a compromised ability for CO2 accumulation, in solitary locusts. Nevertheless, DGC was lost at similar hydration states in the two phases, suggesting that DGCs are terminated as a result of inadequate oxygen supply to the tissues. PMID:26486365

  8. Gas Exchange of Algae

    PubMed Central

    Ammann, Elizabeth C. B.; Lynch, Victoria H.

    1965-01-01

    Continuously growing cultures of Chlorella pyrenoidosa Starr 252, operating at constant density and under constant environmental conditions, produced uniform photosynthetic quotient (PQ = CO2/O2) and O2 values during 6 months of observations. The PQ for the entire study was 0.90 ± 0.024. The PQ remained constant over a threefold light-intensity change and a threefold change in O2 production (0.90 ± 0.019). At low light intensities, when the rate of respiration approached the rate of photosynthesis, the PQ became extremely variable. Six lamps of widely different spectral-energy distribution produced no significant change in the PQ (0.90 ± 0.025). Oxygen production was directly related to the number of quanta available, irrespective of spectral-energy distribution. Such dependability in producing uniform PQ and O2 values warrants a consideration of algae to maintain a constant gas environment for submarine or spaceship use. Images Fig. 1 PMID:14339260

  9. [Pathophysiology of gas exchange in ARDS].

    PubMed

    Fernández Fernández, R

    2006-11-01

    ARDS is produced in a pulmonary edema picture due to increased vascular patency. In this way, the initial alteration consists in an alveolar occupation due to protein rich edema. This occupation reduces the alveolar surface available for gas exchange, increasing the pulmonary areas with poor or null V/Q ratio. As ARDS progresses, vascular phenomena occur that affect the gas exchange differently, giving rise to heterogeneity in the V/Q ratio. This situation worsens due to the appearance of areas with null ventilation in relationship with the appearance of atelectasis in lung dependent zones. All these factors form the hypoxemia picture refractory to the increase of the inspired oxygen fraction characteristic of this clinical entity. In this article, we make a review of these physiological mechanisms and the effect on the oxygenation of different ventilatory and drug maneuvers. PMID:17129535

  10. Testing the Grandchildren's Received Affection Scale using Affection Exchange Theory.

    PubMed

    Mansson, Daniel H

    2013-04-01

    The purpose of this study was to test the Grandchildren's Received Affection Scale (GRAS) using Affection Exchange Theory (Floyd, 2006). In accordance with Affection Exchange Theory, it was hypothesized that grandchildren's scores on the Trait Affection Received Scale (i.e., the extent to which individuals by nature receive affection) would be related significantly and positively to their reports of received affection from their grandparents (i.e., their scores on the GRAS). Additionally, a research question was asked to explore if grandchildren's received affection from their grandparents is dependent on their grandparent's biological sex or lineage (i.e., maternal vs paternal). Thus, young adult grandchildren (N = 422) completed the GRAS and the Trait Affection Received Scale. The results of zero-order Pearson correlational analyses provided support for the hypothesis, whereas the results of MANOVAs tests only partially support extant grandparent-grandchild theory and research. These findings broaden the scope of Affection Exchange Theory and also bolster the GRAS's utility in future grandparent-grandchild affectionate communication research. PMID:23833883

  11. Breath tests and airway gas exchange.

    PubMed

    Anderson, Joseph C; Hlastala, Michael P

    2007-01-01

    Measuring soluble gas in the exhaled breath is a non-invasive technique used to estimate levels of respiratory, solvent, and metabolic gases. The interpretation of these measurements is based on the assumption that the measured gases exchange in the alveoli. While the respiratory gases have a low blood-solubility and exchange in the alveoli, high blood-soluble gases exchange in the airways. The effect of airway gas exchange on the interpretation of these exhaled breath measurements can be significant. We describe airway gas exchange in relation to exhaled measurements of soluble gases that exchange in the alveoli. The mechanisms of airway gas exchange are reviewed and criteria for determining if a gas exchanges in the airways are provided. The effects of diffusion, perfusion, temperature and breathing maneuver on airway gas exchange and on measurement of exhaled soluble gas are discussed. A method for estimating the impact of airway gas exchange on exhaled breath measurements is presented. We recommend that investigators should carefully control the inspired air conditions and type of exhalation maneuver used in a breath test. Additionally, care should be taken when interpreting breath tests from subjects with pulmonary disease. PMID:16413216

  12. History of respiratory gas exchange.

    PubMed

    West, John B

    2011-07-01

    As early as the 6th century B.C. the Greeks speculated on a substance pneuma that meant breath or soul, and they argued that this was essential for life. An important figure in the 2nd century A.D. was Galen whose school developed an elaborate cardiopulmonary system that influenced scientific thinking for 1400 years. A key concept was that blood was mixed with pneuma from the lung in the left ventricle thus forming vital spirit. It was also believed that blood flowed from the right to the left ventricle of the heart through pores in the interventricular septum but this view was challenged first by the Arab physician Ibn al-Nafis in the 13th century and later by Michael Servetus in the 16th century. The 17th century saw an enormous burgeoning of knowledge about the respiratory gases. First Torricelli explained the origin of atmospheric pressure, and then a group of physiologists in Oxford clarified the properties of inspired gas that were necessary for life. This culminated in the work of Lavoisier who first clearly elucidated the nature of the respiratory gases, oxygen, carbon dioxide and nitrogen. At that time it was thought that oxygen was consumed in the lung itself, and the fact that the actual metabolism took place in peripheral tissues proved to be a very elusive concept. It was not until the late 19th century that the issue was finally settled by Pflüger. In the early 20th century there was a colorful controversy about whether oxygen was secreted by the lung. During and shortly after World War II, momentous strides were made on the understanding of pulmonary gas exchange, particularly the role of ventilation-perfusion inequality. A critical development in the 1960s was the introduction of blood gas electrodes, and these have transformed the management of patients with severe lung disease. PMID:23733651

  13. Insect gas exchange patterns: a phylogenetic perspective.

    PubMed

    Marais, Elrike; Klok, C Jaco; Terblanche, John S; Chown, Steven L

    2005-12-01

    Most investigations of insect gas exchange patterns and the hypotheses proposed to account for their evolution have been based either on small-scale, manipulative experiments, or comparisons of a few closely related species. Despite their potential utility, no explicit, phylogeny-based, broad-scale comparative studies of the evolution of gas exchange in insects have been undertaken. This may be due partly to the preponderance of information for the endopterygotes, and its scarcity for the apterygotes and exopterygotes. Here we undertake such a broad-scale study. Information on gas exchange patterns for the large majority of insects examined to date (eight orders, 99 species) is compiled, and new information on 19 exemplar species from a further ten orders, not previously represented in the literature (Archaeognatha, Zygentoma, Ephemeroptera, Odonata, Mantodea, Mantophasmatodea, Phasmatodea, Dermaptera, Neuroptera, Trichoptera), is provided. These data are then used in a formal, phylogeny-based parsimony analysis of the evolution of gas exchange patterns at the order level. Cyclic gas exchange is likely to be the ancestral gas exchange pattern at rest (recognizing that active individuals typically show continuous gas exchange), and discontinuous gas exchange probably originated independently a minimum of five times in the Insecta. PMID:16339869

  14. Nonpulmonary influences on gas exchange.

    PubMed

    Rodriguez-Roisin, Roberto

    2014-10-01

    There are several determinants governing arterial and mixed venous blood PO2 and PCO2. Ventilation-perfusion imbalance, increased intrapulmonary shunt, and diffusion limitation to oxygen encompass the pulmonary factors. Alternatively, inspired oxygen concentration, overall ventilation, cardiac output, and oxygen consumption (uptake) are contemplated as the four most influential nonpulmonary determinants. All three pulmonary factors plus oxygen uptake cannot be directly modulated, but all the other remaining nonpulmonary determinants are. Inspired oxygen concentration, the amount and pattern of total ventilation, and cardiac output may be, at least in part, relatively well clinically controlled. Arterial PO2 (PaO2) may fall if inspired PO2, overall ventilation, and/or cardiac output decrease, and/or oxygen consumption increases, even though the pulmonary factors remain unchanged. Conversely, if inspired oxygen fraction, ventilation, and/or cardiac output increase, and/or oxygen consumption decreases, PaO2 may improve regardless of the changes operated at the level of the pulmonary determinants. Several pathophysiologic features deserve to be underlined. First, the importance of understanding the role played by mixed venous PO2 as a vital nonpulmonary determinant governing PaO2. Second, the response to 100% oxygen breathing repeatedly exhibits a consistent amount of agreement in the main findings. Third, there is always an interactive interplay between pulmonary and nonpulmonary determinants of PaO2 and arterial PCO2 (PaCO2) in any respiratory disease state following the use of pharmacologic or nonpharmacologic approaches. All in all both PaO2 and PaCO2 become the end-point outcomes of the complex interaction of pulmonary and nonpulmonary factors modulating pulmonary gas exchange. This needs to be unraveled to improve the understanding and management of most acute and chronic respiratory disease states. PMID:25428851

  15. BOREAS TE-12 Leaf Gas Exchange Data

    NASA Technical Reports Server (NTRS)

    Hall, Forrest G. (Editor); Curd, Shelaine (Editor); Arkebauer, Timothy J.; Yang, Litao

    2000-01-01

    The BOREAS TE-12 team collected several data sets in support of its efforts to characterize and interpret information on the reflectance, transmittance, and gas exchange of boreal vegetation. This data set contains measurements of leaf gas exchange conducted in the SSA during the growing seasons of 1994 and 1995 using a portable gas exchange system. The data are stored in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Center (DAAC).

  16. Gas exchange measurements in natural systems

    SciTech Connect

    Broecker, W.S.; Peng, T.H.

    1983-01-01

    Direct knowledge of the rates of gas exchange in lakes and the ocean is based almost entirely on measurements of the isotopes /sup 14/C, /sup 222/Rn and /sup 3/He. The distribution of natural radiocarbon has yielded the average rate of CO/sub 2/ exchange for the ocean and for several closed basin lakes. That of bomb produced radiocarbon has been used in the same systems. The /sup 222/Rn to /sup 226/Ra ratio in open ocean surface water has been used to give local short term gas exchange rates. The radon method generally cannot be used in lakes, rivers, estuaries or shelf areas because of the input of radon from sediments. A few attempts have been made to use the excess /sup 3/He produced by decay of bomb produced tritium in lakes to give gas transfer rates. The uncertainty in the molecular diffusivity of helium and in the diffusivity dependence of the rate of gas transfer holds back the application of this method. A few attempts have been made to enrich the surface waters of small lakes with /sup 226/Ra and /sup 3/H in order to allow the use of the /sup 222/Rn and /sup 3/He methods. While these studies give broadly concordant results, many questions remain unanswered. The wind velocity dependence of gas exchange rate has yet to be established in field studies. The dependence of gas exchange rate on molecular diffusivity also remains in limbo. Finally, the degree of enhancement of CO/sub 2/ exchange through chemical reactions has been only partially explored. 49 references, 2 figures, 2 tables.

  17. Forced convection modulates gas exchange in cnidarians

    PubMed Central

    Patterson, Mark R.; Sebens, Kenneth P.

    1989-01-01

    Boundary layer thickness is a potentially important component of the diffusive pathway for gas exchange in aquatic organisms. The soft coral Alcyonium siderium (Octocorallia) and sea anemone Metridium senile (Actiniaria) exhibit significant increases in respiration with water flow over a range of Reynolds numbers encountered subtidally. A nondimensional mass transfer analysis of the effect of forced convection demonstrates the importance of the state of the organism's boundary layer in regulating metabolism in these invertebrates. Flow-modulated gas exchange may limit secondary productivity in subtidal environments. PMID:16594087

  18. Gas Transfer in Cellularized Collagen-Membrane Gas Exchange Devices

    PubMed Central

    Lo, Justin H.; Bassett, Erik K.; Penson, Elliot J. N.; Hoganson, David M.

    2015-01-01

    Chronic lower respiratory disease is highly prevalent in the United States, and there remains a need for alternatives to lung transplant for patients who progress to end-stage lung disease. Portable or implantable gas oxygenators based on microfluidic technologies can address this need, provided they operate both efficiently and biocompatibly. Incorporating biomimetic materials into such devices can help replicate native gas exchange function and additionally support cellular components. In this work, we have developed microfluidic devices that enable blood gas exchange across ultra-thin collagen membranes (as thin as 2 μm). Endothelial, stromal, and parenchymal cells readily adhere to these membranes, and long-term culture with cellular components results in remodeling, reflected by reduced membrane thickness. Functionally, acellular collagen-membrane lung devices can mediate effective gas exchange up to ∼288 mL/min/m2 of oxygen and ∼685 mL/min/m2 of carbon dioxide, approaching the gas exchange efficiency noted in the native lung. Testing several configurations of lung devices to explore various physical parameters of the device design, we concluded that thinner membranes and longer gas exchange distances result in improved hemoglobin saturation and increases in pO2. However, in the design space tested, these effects are relatively small compared to the improvement in overall oxygen and carbon dioxide transfer by increasing the blood flow rate. Finally, devices cultured with endothelial and parenchymal cells achieved similar gas exchange rates compared with acellular devices. Biomimetic blood oxygenator design opens the possibility of creating portable or implantable microfluidic devices that achieve efficient gas transfer while also maintaining physiologic conditions. PMID:26020102

  19. FACTORS AFFECTING AIR EXCHANGE IN TWO HOUSES

    EPA Science Inventory

    Air exchange rate is critical to determining the relationship between indoor and outdoor concentrations of hazardous pollutants. Approximately 150 air exchange experiments were completed in two residences: a two-story detached house located in Redwood City, CA and a three-story...

  20. Pulmonary ventilation and gas exchange in bronchiectasis

    PubMed Central

    Pande, J. N.; Jain, B. P.; Gupta, R. G.; Guleria, J. S.

    1971-01-01

    The subdivisions of the lung volume, pulmonary mechanics, and resting steady state pulmonary transfer factor were measured in 31 patients with bronchographically proven bronchiectasis. In seven patients the process of gas exchange was further investigated by fractionating the total alveolar-arterial oxygen tension gradient into diffusion, distribution, and true shunt components. A restrictive type of ventilatory defect with varying degrees of airway obstruction was observed in a majority of the patients; the airway obstruction was partially reversed by a bronchodilator. Dynamic compliance was usually decreased and the pulmonary resistance increased. Pulmonary transfer factor was decreased in proportion to the number of segments involved. Vital capacity, maximum breathing capacity, and dynamic compliance bore a less significant correlation with the extent of disease. The degree of airway obstruction, as judged by pulmonary resistance, was independent of the extent of disease. All the patients were hypoxaemic and some had hypercapnia as well. The alveolar-arterial oxygen tension gradient was widened primarily because of distributional abnormalities and, to some extent, by the presence of true right-to-left shunts. The latter amounted to 13·6% of the total cardiac output. Surgical resection of the affected lobe or segments resulted in a further deterioration of all the parameters of pulmonary function tested. PMID:5144652

  1. BOREAS TE-5 Leaf Gas Exchange Data

    NASA Technical Reports Server (NTRS)

    Hall, Forrest G. (Editor); Curd, Shelaine (Editor); Ehleriinger, Jim; Brooks, J. Renee; Flanagan, Larry

    2000-01-01

    The BOREAS TE-5 team collected measurements in the NSA and SSA on gas exchange, gas composition, and tree growth. The leaf photosynthetic gas exchange data were collected in the BOREAS NSA and the SSA from 06-Jun- 1994 to 13-Sep- 1994 using a LI-COR 6200 portable photosynthesis system. The data were collected to compare the photosynthetic capacity, stomata] conductance, and leaf intercellular CO, concentrations among the major tree species at the BOREAS sites. The data are average values from diurnal measurements on the upper canopy foliage (sun leaves). The data are available in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Activity Archive Center (DAAC).

  2. The physiological basis of pulmonary gas exchange: implications for clinical interpretation of arterial blood gases.

    PubMed

    Wagner, Peter D

    2015-01-01

    The field of pulmonary gas exchange is mature, with the basic principles developed more than 60 years ago. Arterial blood gas measurements (tensions and concentrations of O₂ and CO₂) constitute a mainstay of clinical care to assess the degree of pulmonary gas exchange abnormality. However, the factors that dictate arterial blood gas values are often multifactorial and complex, with six different causes of hypoxaemia (inspiratory hypoxia, hypoventilation, ventilation/perfusion inequality, diffusion limitation, shunting and reduced mixed venous oxygenation) contributing variably to the arterial O₂ and CO₂ tension in any given patient. Blood gas values are then usually further affected by the body's abilities to compensate for gas exchange disturbances by three tactics (greater O₂ extraction, increasing ventilation and increasing cardiac output). This article explains the basic principles of gas exchange in health, mechanisms of altered gas exchange in disease, how the body compensates for abnormal gas exchange, and based on these principles, the tools available to interpret blood gas data and, quantitatively, to best understand the physiological state of each patient. This understanding is important because therapeutic intervention to improve abnormal gas exchange in any given patient needs to be based on the particular physiological mechanisms affecting gas exchange in that patient. PMID:25323225

  3. Closed system respirometry may underestimate tissue gas exchange and bias the respiratory exchange ratio (RER).

    PubMed

    Malte, Christian Lind; Nørgaard, Simon; Wang, Tobias

    2016-02-01

    Closed respirometry is a commonly used method to measure gas exchange in animals due to its apparent simplicity. Typically, the rates of O2 uptake and CO2 excretion (VO2 and VCO2, respectively) are assumed to be in steady state, such that the measured rates of gas exchange equal those at tissue level. In other words, the respiratory gas exchange ratio (RER) is assumed to equal the respiratory quotient (RQ). However, because the gas concentrations change progressively during closure, the animal inspires air with a progressively increasing CO2 concentration and decreasing O2 concentration. These changes will eventually affect gas exchange causing the O2 and CO2 stores within the animal to change. Because of the higher solubility/capacitance of CO2 in the tissues of the body, VCO2 will be more affected than VO2, and we hypothesize therefore that RER will become progressively underestimated as closure time is prolonged. This hypothesis was addressed by a combination of experimental studies involving closed respirometry on ball pythons (Python regius) as well as mathematical models of gas exchange. We show that increased closed duration of the respirometer reduces RER by up to 13%, and these findings may explain previous reports of RER values being below 0.7. Our model reveals that the maximally possible reduction in RER is determined by the storage capacity of the body for CO2 (product of size and specific capacitance) relative to the respirometer storage capacity. Furthermore, modeling also shows that pronounced ventilatory and circulatory response to hypercapnia can alleviate the reduction in RER. PMID:26523499

  4. BOREAS TE-10 Leaf Gas Exchange Data

    NASA Technical Reports Server (NTRS)

    Hall, Forrest G. (Editor); Papagno, Andrea (Editor); Middleton, Elizabeth; Sullivan, Joseph

    2000-01-01

    The Boreal Ecosystem-Atmospheric Study (BOREAS) TE-10 (Terrestrial Ecology) team collected several data sets in support of its efforts to characterize and interpret information on the reflectance, transmittance, gas exchange, chlorophyll content, carbon content, hydrogen content, and nitrogen content of boreal vegetation. This data set contains measurements of assimilation, stomatal conductance, transpiration, internal CO2 concentration, and water use efficiency conducted in the Southern Study Area (SSA) during the growing seasons of 1994 and 1996 using a portable gas exchange system. The data are stored in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

  5. BOREAS TE-11 Leaf Gas Exchange Measurements

    NASA Technical Reports Server (NTRS)

    Hall, Forrest G. (Editor); Papagno, Andrea (Editor); Saugier, Bernard; Pontailler, J. Y.

    2000-01-01

    The Boreal Ecosystem-Atmospheric Study (BOREAS) TE-11 (Terrestrial Ecology) team collected several data sets in support of its efforts to characterize and interpret information on the sap flow, gas exchange, and lichen photosynthesis of boreal vegetation and meteorological data of the area studied. This data set contains measurements of assimilation and transpiration conducted at the Old Jack Pine (OJP) site during the growing seasons of 1993 and 1994. The data are stored in ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

  6. High temperature heat exchanger studies for applications to gas turbines

    NASA Astrophysics Data System (ADS)

    Min, June Kee; Jeong, Ji Hwan; Ha, Man Yeong; Kim, Kui Soon

    2009-12-01

    Growing demand for environmentally friendly aero gas-turbine engines with lower emissions and improved specific fuel consumption can be met by incorporating heat exchangers into gas turbines. Relevant researches in such areas as the design of a heat exchanger matrix, materials selection, manufacturing technology, and optimization by a variety of researchers have been reviewed in this paper. Based on results reported in previous studies, potential heat exchanger designs for an aero gas turbine recuperator, intercooler, and cooling-air cooler are suggested.

  7. BOREAS TF-11 SSA-Fen Leaf Gas Exchange Data

    NASA Technical Reports Server (NTRS)

    Arkebauer, Timothy J.; Hall, Forrest G. (Editor); Knapp, David E. (Editor)

    2000-01-01

    The BOREAS TF-11 team gathered a variety of data to complement its tower flux measurements collected at the SSA-Fen site. This data set contains single-leaf gas exchange data from the SSA-Fen site during 1994 and 1995. These leaf gas exchange properties were measured for the dominant vascular plants using portable gas exchange systems. The data are stored in tabular ASCII files.

  8. Gas Exchange with Mass Cultures of Algae

    PubMed Central

    Hannan, P. J.; Patouillet, Constance

    1963-01-01

    The performance of a small photosynthetic gas exchanger is described in which simultaneous measurements of suspension density, O2 production, and CO2 absorption are readily accomplished. The volume of suspension was 6200 ml. With the Sorokin strain of Chlorella pyrenoidosa 7-11-05, this unit produced 4500 cc of O2 per hr at a light intensity of 34,000 ft-c from each of six Quartzline lamps. At any given light intensity, the O2 production was proportional to the rate of CO2 input up to a maximum. The impetus for this study was the consideration of the algal system as a means of oxygen generation in a submarine. Based on the performance of this unit, the power requirement per man for a system having the geometry described would be 52 kw, but reasons are given for the hope that this may be reduced to less than 5 kw. PMID:14063789

  9. Carbon cycling and gas exchange in soils

    SciTech Connect

    Trumbore, S.E.

    1989-01-01

    This thesis summaries three independent projects, each of which describes a method which can be used to study the role of soils in regulating the atmospheric concentrations of CO{sub 2} and other trace gases. The first chapter uses the distribution of natural and bomb produced radiocarbon in fractionated soil organic matter to quantify the turnover of carbon in soils. A comparison of {sup 137}Cs and {sup 14}C in the modern soil profiles indicates that carbon is transported vertically in the soil as dissolved organic material. The remainder of the work reported is concerned with the use of inert trace gases to explore the physical factors which control the seasonal to diel variability in the fluxes of CO{sub 2} and other trace gases from soils. Chapter 2 introduces a method for measuring soil gas exchange rates in situ using sulfur hexafluoride as a purposeful tracer. The measurement method uses standard flux box technology, and includes simultaneous determination of the fluxes and soil atmosphere concentrations of CO{sub 2} and CH{sub 4}. In Chapter 3, the natural tracer {sup 222}Rn is used as an inert analog for exchange both in the soils and forest canopy of the Amazon rain forest.

  10. Greenhouse gas exchange over grazed systems

    NASA Astrophysics Data System (ADS)

    Felber, R.; Ammann, C.; Neftel, A.

    2012-04-01

    Grasslands act as sinks and sources of greenhouse gases (GHG) and are, in conjunction with livestock production systems, responsible for a large share of GHG emissions. Whereas ecosystem scale flux measurements (eddy covariance) are commonly used to investigate CO2 exchange (and is becoming state-of-the-art for other GHGs, too), GHG emissions from agricultural animals are usually investigated on the scale of individual animals. Therefore eddy covariance technique has to be tested for combined systems (i.e. grazed systems). Our project investigates the ability of field scale flux measurements to reliably quantify the contribution of grazing dairy cows to the net exchange of CO2 and CH4. To quantify the contribution of the animals to the net flux the position, movement, and grazing/rumination activity of each cow are recorded. In combination with a detailed footprint analysis of the eddy covariance fluxes, the animal related CO2 and CH4 emissions are derived and compared to standard emission values derived from respiration chambers. The aim of the project is to test the assumption whether field scale CO2 flux measurements adequately include the respiration of grazing cows and to identify potential errors in ecosystem Greenhouse gas budgets.

  11. Annual sea ice. An air-sea gas exchange moderator

    SciTech Connect

    Gosink, T.A.; Kelley, J.J.

    1982-01-01

    Arctic annual sea ice, particularly when it is relatively warm (> -15/sup 0/C) permits significant gas exchange between the sea and air throughout the entire year. Sea ice, particularly annual sea ice, differs from freshwater ice with respect to its permeability to gases. The presence of brine allows for significant air-sea-ice exchange of CO/sub 2/ throughout the winter, which may significantly affect the global carbon dioxide balance. Other trace gases are also noted to be enriched in sea ice, but less is known about their importance to air-sea-interactions at this time. Both physical and biological factors cause and modify evolution of gases from the surface of sea ice. Quantitative and qualitative descriptions of the nature and physical behavior of sea ice with respect to brine and gases are discussed.

  12. Trace Gas Exchange of Biofuel Crops

    NASA Astrophysics Data System (ADS)

    Graus, M.; Warneke, C.; Williams, E. J.; Lerner, B. M.; Gilman, J. B.; Li, R.; Eller, A. S.; Gray, C.; Fierer, N.; Fall, R.; Harley, P. C.; Roberts, J. M.; Yuan, B.; Qian, Y.; Westra, P.; Fryrear, C.; Collins, M.; Whitman, K.; De Gouw, J. A.

    2011-12-01

    In 2010 leaf level gas exchange and VOC fluxes from switchgrass and corn grown at the CSU horticultural farm in Ft Collins (CO) were measured using a PTR-MS coupled to a modified Li6400 cuvette system. Both species are C4 plants with corn currently being the dominant biofuel crop in the USA whilst switchgrass being a promising candidate for cellulosic fuel ethanol production. Amongst the strongest VOC emissions from both plants were methanol, acetic acid, acetaldehyde, acetone and toluene. The switchgrass VOC emissions compare reasonably well with the only published data measured from potted plants in a whole plant enclosure (Eller et al. 2011). VOC emission studies on corn are almost as scarce as those of switchgrass. Considering the acreage of corn grown in the USA every year, VOC flux measurements of this plant species are largely under-represented in the literature. The emission rates that do exist in the literature do not compare well with the numbers found in this study (e.g. Das et al. 2003; 35μg methanol per hour per gram biomass). To investigate the biosphere atmosphere exchange of corn fields in more detail the field campaign BioCORN 2011 was initiated. In summer 2011 an eddy covariance system was set up in a corn field at ARDEC (CSU, Ft Collins, CO) to investigate the energy flux and the trace gas exchange of the US' dominant biofuel crop. Besides energy flux, evapotranspiration and CO2 flux a comprehensive suite of volatile organic compounds and inorganic species (O3, NO, NO2, CO) are measured for virtual disjunct eddy covariance (vDEC) analysis and true eddy covariance (EC) fluxes, respectively. VOCs are monitored by PTR-MS and, for the first time, fluxes of formic acid are measured utilizing NI-CIMS data for vDEC analysis. Besides the EC approach leaf level flux measurements and soil flux measurements are performed using a GC-MS system (TACOH) coupled to a modified Li6400 system and to soil chambers, respectively. Ethanol and methanol are amongst the

  13. PREDICTION OF TOTAL DISSOLVED GAS EXCHANGE AT HYDROPOWER DAMS

    SciTech Connect

    Hadjerioua, Boualem; Pasha, MD Fayzul K; Stewart, Kevin M; Bender, Merlynn; Schneider, Michael L.

    2012-07-01

    Total dissolved gas (TDG) supersaturation in waters released at hydropower dams can cause gas bubble trauma in fisheries resulting in physical injuries and eyeball protrusion that can lead to mortality. Elevated TDG pressures in hydropower releases are generally caused by the entrainment of air in spillway releases and the subsequent exchange of atmospheric gasses into solution during passage through the stilling basin. The network of dams throughout the Columbia River Basin (CRB) are managed for irrigation, hydropower production, flood control, navigation, and fish passage that frequently result in both voluntary and involuntary spillway releases. These dam operations are constrained by state and federal water quality standards for TDG saturation which balance the benefits of spillway operations designed for Endangered Species Act (ESA)-listed fisheries versus the degradation to water quality as defined by TDG saturation. In the 1970s, the United States Environmental Protection Agency (USEPA), under the federal Clean Water Act (Section 303(d)), established a criterion not to exceed the TDG saturation level of 110% in order to protect freshwater and marine aquatic life. The states of Washington and Oregon have adopted special water quality standards for TDG saturation in the tailrace and forebays of hydropower facilities on the Columbia and Snake Rivers where spillway operations support fish passage objectives. The physical processes that affect TDG exchange at hydropower facilities have been studied throughout the CRB in site-specific studies and routine water quality monitoring programs. These data have been used to quantify the relationship between project operations, structural properties, and TDG exchange. These data have also been used to develop predictive models of TDG exchange to support real-time TDG management decisions. These empirically based predictive models have been developed for specific projects and account for both the fate of spillway and

  14. Environmental sensitivity of gas exchange in different-sized trees.

    PubMed

    McDowell, Nate G; Licata, Julian; Bond, Barbara J

    2005-08-01

    The carbon isotope signature (delta13C) of foliar cellulose from sunlit tops of trees typically becomes enriched as trees of the same species in similar environments grow taller, indicative of size-related changes in leaf gas exchange. However, direct measurements of gas exchange in common environmental conditions do not always reveal size-related differences, even when there is a distinct size-related trend in delta13C of the very foliage used for the gas exchange measurements. Since delta13C of foliage predominately reflects gas exchange during spring when carbon is incorporated into leaf cellulose, this implies that gas exchange differences in different-sized trees are most likely to occur in favorable environmental conditions during spring. If gas exchange differs with tree size during wet but not dry conditions, then this further implies that environmental sensitivity of leaf gas exchange varies as a function of tree size. These implications are consistent with theoretical relationships among height, hydraulic conductance and gas exchange. We investigated the environmental sensitivity of gas exchange in different-sized Douglas-fir (Pseudotsuga menziesii) via a detailed process model that specifically incorporates size-related hydraulic conductance [soil-plant-atmosphere (SPA)], and empirical measurements from both wet and dry periods. SPA predicted, and the empirical measurements verified, that differences in gas exchange associated with tree size are greatest in wet and mild environmental conditions and minimal during drought. The results support the hypothesis that annual net carbon assimilation and transpiration of trees are limited by hydraulic capacity as tree size increases, even though at particular points in time there may be no difference in gas exchange between different-sized trees. Maximum net ecosystem exchange occurs in spring in Pacific Northwest forests; therefore, the presence of hydraulic limitations during this period may play a large role

  15. Factors controlling sulfur gas exchange in Sphagnum-dominated wetlands

    NASA Technical Reports Server (NTRS)

    Demello, William Zamboni; Hines, Mark E.; Bayley, Suzanne E.

    1992-01-01

    Atmosphere-peatland exchange of reduced sulfur gases was determined seasonally in fen in NH, and in an artificially-acidified fen at the Experimental Lakes Area (ELA) in Canada. Dimethyl sulfide (DMS) dominated gas fluxes at rates as high as 400 nmol/m(sup -2)hr(sup -1). DMS fluxes measured using enclosures were much higher than those calculated using a stagnant-film model, suggesting that Sphagnum regulated efflux. Temperature controlled diel and seasonal variability in DMS emissions. Use of differing enclosure techniques indicated that vegetated peatlands consume atmospheric carbonyl sulfide. Sulfate amendments caused DMS and methane thiol concentrations in near-surface pore waters to increase rapidly, but fluxes of these gases to the atmosphere were not affected. However, emission data from sites experiencing large differences in rates of sulfate deposition from the atmosphere suggested that chronic elevated sulfate inputs enhance DMS emissions from northern wetlands.

  16. What Affects Clinicians’ Usage of Health Information Exchange?

    PubMed Central

    Rudin, R.; Volk, L.; Simon, S.; Bates, D.

    2011-01-01

    Background The ability to electronically exchange health information among healthcare providers holds enormous promise to improve care coordination and reduce costs. Provider-to-provider data exchange is an explicit goal of the American Recovery and Reinvestment Act of 2009 and may be essential for the long-term success of the Affordable Care Act of 2010. However, little is known about what factors affect clinicians’ usage of health information exchange (HIE) functionality. Objective To identify factors that affect clinicians’ HIE usage - in terms of frequency of contributing data to and accessing data from aggregate patient records - and suggest policies for fostering its usage. Methods We performed a qualitative study using grounded theory by interviewing clinician-users and HIE staff of one operational HIE which supported aggregate patient record functionality. Fifteen clinicians were interviewed for one hour each about what factors affect their HIE usage. Five HIE staff were asked about technology and training issues to provide context. Interviews were recorded, transcribed and analyzed. Recruitment excluded clinicians with little or no familiarity with the HIE and was restricted to one community and a small number of specialties. Results Clinicians were motivated to access the HIE by perceived improvements in care quality and time savings, but their motivation was moderated by an extensive list of factors including gaps in data, workflow issues and usability issues. HIE access intensities varied widely by clinician. Data contribution intensities to the HIE also varied widely and were affected by billing concerns and time constraints. Conclusions Clinicians, EHR and HIE product vendors and trainers should work toward integrating HIE into clinical workflows. Policies should create incentives for HIE organizations to assist clinicians in using HIE, develop measures of HIE contributions and accesses, and create incentives for clinicians to contribute data to

  17. FASTGAS: Fast Gas Sampling for palladium exchange tests

    SciTech Connect

    Malinowski, M.E.; Stewart, K.D.; VerBerkmoes, A.A.

    1991-06-01

    A mass spectrometric technique for measuring the composition of gas flows in rapid H/D exchange reactions in palladium compacts has been developed. This method, called FASTGAS (Fast Gas Sampling)'' has been used at atmospheric pressures and above with a time response of better than 100 ms. The current implementation of the FASTGAS technique is described in detail and examples of its application to palladium hydride exchange tests are given. 12 refs., 10 figs.

  18. Reversible brain inactivation induces discontinuous gas exchange in cockroaches.

    PubMed

    Matthews, Philip G D; White, Craig R

    2013-06-01

    Many insects at rest breathe discontinuously, alternating between brief bouts of gas exchange and extended periods of breath-holding. The association between discontinuous gas exchange cycles (DGCs) and inactivity has long been recognised, leading to speculation that DGCs lie at one end of a continuum of gas exchange patterns, from continuous to discontinuous, linked to metabolic rate (MR). However, the neural hypothesis posits that it is the downregulation of brain activity and a change in the neural control of gas exchange, rather than low MR per se, which is responsible for the emergence of DGCs during inactivity. To test this, Nauphoeta cinerea cockroaches had their brains inactivated by applying a Peltier-chilled cold probe to the head. Once brain temperature fell to 8°C, cockroaches switched from a continuous to a discontinuous breathing pattern. Re-warming the brain abolished the DGC and re-established a continuous breathing pattern. Chilling the brain did not significantly reduce the cockroaches' MR and there was no association between the gas exchange pattern displayed by the insect and its MR. This demonstrates that DGCs can arise due to a decrease in brain activity and a change in the underlying regulation of gas exchange, and are not necessarily a simple consequence of low respiratory demand. PMID:23430991

  19. Peptide Orientation Affects Selectivity in Ion-Exchange Chromatography

    SciTech Connect

    Alpert, Andrew J.; Petritis, Konstantinos; Kangas, Lars J.; Smith, Richard D.; Mechtler, Karl; Mitulovic, Goran; Mohammed, Shabaz; Heck, Albert J.

    2010-06-15

    Here we demonstrate that separation of proteolytic peptides, having the same net charge and one basic residue, is affected by their specific orientation toward the stationary phase in ion-exchange chromatography. In electrostatic repulsion-hydrophilic interaction chromatography (ERLIC) with an anion-exchange material, the C-terminus of the peptides is, on average, oriented toward the stationary phase. In cation exchange, the average peptide orientation is the opposite. Data with synthetic peptides, serving as orientation probes, indicate that in tryptic/Lys-C peptides the C-terminal carboxyl group appears to be in a zwitterionic bond with the side chain of the C-terminal Lys/Arg residue. In effect, the side chain is then less basic than the N-terminus, accounting for the specific orientation of tryptic and Lys-C peptides. Analyses of larger sets of peptides, generated from lysates by either Lys-N, Lys-C, or trypsin, reveal that specific peptide orientation affects the ability of harged side chains, such as phosphate residues, to influence retention. Phosphorylated residues that are remote in the sequence from the binding site affect retention less than those that are closer. When a peptide contains multiple charged sites, then orientation is observed to be less rigid and retention tends to be governed by the peptide’s net charge rather than its sequence. These general observations could be of value in confirming a peptide’s identification and, in particular, phosphosite assignments in proteomics analyses. More generally, orientation accounts for the ability of chromatography to separate peptides of the same compositionbut different sequence.

  20. Peptide Orientation Affects Selectivity in Ion-Exchange Chromatography

    SciTech Connect

    Alpert, Andrew J.; Petritis, Konstantinos; Kangas, Lars J.; Smith, R. D.; Mechtler, Karl; Mitulovic, Goran; Mohammed, Shabaz; Heck, Albert J.

    2010-06-15

    Here we demonstrate that separation of proteolytic peptides, having the same net charge and one basic residue, is affected by their specific orientation toward the stationary phase in ion-exchange chromatography. In electrostatic repulsion-hydrophilic interaction chromatography (ERLIC) with an anion-exchange material, the C-terminus of the peptides is, on average, oriented toward the stationary phase. In cation exchange, the average peptide orientation is the opposite. Data with synthetic peptides, serving as orientation probes, indicate that in tryptic/ Lys-C peptides the C-terminal carboxyl group appears to be in a zwitterionic bond with the side chain of the C-terminal Lys/Arg residue. In effect, the side chain is then less basic than the N-terminus, accounting for the specific orientation of tryptic and Lys-C peptides. Analyses of larger sets of peptides, generated from lysates by either Lys-N, Lys-C, or trypsin, reveal that specific peptide orientation affects the ability of charged side chains, such as phosphate residues, to influence retention. Phosphorylated residues that are remote in the sequence from the binding site affect retention less than those that are closer. When a peptide contains multiple charged sites, then orientation is observed to be less rigid and retention tends to be governed by the peptide’s net charge rather than its sequence. These general observations could be of value in confirming a peptide’s identification and, in particular, phosphosite assignments in proteomics analyses. More generally, orientation accounts for the ability of chromatography to separate peptides of the same composition but different sequence.

  1. Peptide Orientation Affects Selectivity in Ion-Exchange Chromatography

    PubMed Central

    2010-01-01

    Here we demonstrate that separation of proteolytic peptides, having the same net charge and one basic residue, is affected by their specific orientation toward the stationary phase in ion-exchange chromatography. In electrostatic repulsion−hydrophilic interaction chromatography (ERLIC) with an anion-exchange material, the C-terminus of the peptides is, on average, oriented toward the stationary phase. In cation exchange, the average peptide orientation is the opposite. Data with synthetic peptides, serving as orientation probes, indicate that in tryptic/Lys-C peptides the C-terminal carboxyl group appears to be in a zwitterionic bond with the side chain of the C-terminal Lys/Arg residue. In effect, the side chain is then less basic than the N-terminus, accounting for the specific orientation of tryptic and Lys-C peptides. Analyses of larger sets of peptides, generated from lysates by either Lys-N, Lys-C, or trypsin, reveal that specific peptide orientation affects the ability of charged side chains, such as phosphate residues, to influence retention. Phosphorylated residues that are remote in the sequence from the binding site affect retention less than those that are closer. When a peptide contains multiple charged sites, then orientation is observed to be less rigid and retention tends to be governed by the peptide’s net charge rather than its sequence. These general observations could be of value in confirming a peptide’s identification and, in particular, phosphosite assignments in proteomics analyses. More generally, orientation accounts for the ability of chromatography to separate peptides of the same composition but different sequence. PMID:20481592

  2. Prototype Vent Gas Heat Exchanger for Exploration EVA - Performance and Manufacturing Characteristics

    NASA Technical Reports Server (NTRS)

    Jennings, Mallory; Quinn, Gregory; Strange, Jeremy

    2012-01-01

    NASA is developing new portable life support system (PLSS) technologies, which it is demonstrating in an unmanned ground based prototype unit called PLSS 2.0. One set of technologies within the PLSS provides suitable ventilation to an astronaut while on an EVA. A new component within the ventilation gas loop is a liquid-to-gas heat exchanger to transfer excess heat from the gas to the thermal control system's liquid coolant loop. A unique bench top prototype heat exchanger was built and tested for use in PLSS 2.0. The heat exchanger was designed as a counter-flow, compact plate fin type using stainless steel. Its design was based on previous compact heat exchangers manufactured by United Technologies Aerospace Systems, but was half the size of any previous heat exchanger model and one third the size of previous liquid-to-gas heat exchangers. The prototype heat exchanger was less than 40 cubic inches and weighed 2.6 lb. The water side and gas side pressure drops were 0.8 psid and 0.5 inches of water, respectively. Performance of the heat exchanger at the nominal pressure of 4.1 psia was measured at 94%, while a gas inlet pressure of 25 psia resulted in an effectiveness of 84%. These results compared well with the model, which was scaled for the small size. Modeling of certain phenomena that affect performance, such as flow distribution in the headers was particularly difficult due to the small size of the heat exchanger. Data from the tests has confirmed the correction factors that were used in these parts of the model.

  3. Effect of impeller design and spacing on gas exchange in a percutaneous respiratory assist catheter.

    PubMed

    Jeffries, R Garrett; Frankowski, Brian J; Burgreen, Greg W; Federspiel, William J

    2014-12-01

    Providing partial respiratory assistance by removing carbon dioxide (CO2 ) can improve clinical outcomes in patients suffering from acute exacerbations of chronic obstructive pulmonary disease and acute respiratory distress syndrome. An intravenous respiratory assist device with a small (25 Fr) insertion diameter eliminates the complexity and potential complications associated with external blood circuitry and can be inserted by nonspecialized surgeons. The impeller percutaneous respiratory assist catheter (IPRAC) is a highly efficient CO2 removal device for percutaneous insertion to the vena cava via the right jugular or right femoral vein that utilizes an array of impellers rotating within a hollow-fiber membrane bundle to enhance gas exchange. The objective of this study was to evaluate the effects of new impeller designs and impeller spacing on gas exchange in the IPRAC using computational fluid dynamics (CFD) and in vitro deionized water gas exchange testing. A CFD gas exchange and flow model was developed to guide a progressive impeller design process. Six impeller blade geometries were designed and tested in vitro in an IPRAC device with 2- or 10-mm axial spacing and varying numbers of blades (2-5). The maximum CO2 removal efficiency (exchange per unit surface area) achieved was 573 ± 8 mL/min/m(2) (40.1 mL/min absolute). The gas exchange rate was found to be largely independent of blade design and number of blades for the impellers tested but increased significantly (5-10%) with reduced axial spacing allowing for additional shaft impellers (23 vs. 14). CFD gas exchange predictions were within 2-13% of experimental values and accurately predicted the relative improvement with impellers at 2- versus 10-mm axial spacing. The ability of CFD simulation to accurately forecast the effects of influential design parameters suggests it can be used to identify impeller traits that profoundly affect facilitated gas exchange. PMID:24749994

  4. Effect of Impeller Design and Spacing on Gas Exchange in a Percutaneous Respiratory Assist Catheter

    PubMed Central

    Jeffries, R. Garrett; Frankowski, Brian J.; Burgreen, Greg W.; Federspiel, William J.

    2014-01-01

    Providing partial respiratory assistance by removing carbon dioxide (CO2) can improve clinical outcomes in patients suffering from acute exacerbations of chronic obstructive pulmonary disease and acute respiratory distress syndrome. An intravenous respiratory assist device with a small (25 Fr) insertion diameter eliminates the complexity and potential complications associated with external blood circuitry and can be inserted by nonspecialized surgeons. The impeller percutaneous respiratory assist catheter (IPRAC) is a highly efficient CO2 removal device for percutaneous insertion to the vena cava via the right jugular or right femoral vein that utilizes an array of impellers rotating within a hollow-fiber membrane bundle to enhance gas exchange. The objective of this study was to evaluate the effects of new impeller designs and impeller spacing on gas exchange in the IPRAC using computational fluid dynamics (CFD) and in vitro deionized water gas exchange testing. A CFD gas exchange and flow model was developed to guide a progressive impeller design process. Six impeller blade geometries were designed and tested in vitro in an IPRAC device with 2- or 10-mm axial spacing and varying numbers of blades (2–5). The maximum CO2 removal efficiency (exchange per unit surface area) achieved was 573 ± 8 mL/min/m2 (40.1 mL/min absolute). The gas exchange rate was found to be largely independent of blade design and number of blades for the impellers tested but increased significantly (5–10%) with reduced axial spacing allowing for additional shaft impellers (23 vs. 14). CFD gas exchange predictions were within 2–13% of experimental values and accurately predicted the relative improvement with impellers at 2- versus 10-mm axial spacing. The ability of CFD simulation to accurately forecast the effects of influential design parameters suggests it can be used to identify impeller traits that profoundly affect facilitated gas exchange. PMID:24749994

  5. Gas exchange responses to bronchodilators following methacholine challenge in dogs.

    PubMed

    Rodriguez-Roisin, R; Bencowitz, H Z; Ziegler, M G; Wagner, P D

    1984-10-01

    To determine how and why different bronchodilators affect ventilation-perfusion (V/Q) relationships differently in experimental asthma, 10 anesthetized dogs were exposed 3 times each (2-1/2 h apart) to aerosolized 1% methacholine over 3 to 5 min. Mechanical, hemodynamic, gas exchange, and catecholamine concentration measurements were made before challenge, and 10, 20, 30, and 135 min after challenge. Fifteen min after challenge the dogs were exposed to aerosolized epinephrine, isoproterenol, salbutamol, or isotonic saline in random order. The worsened V/Q inequality after isoproterenol paralleled increased cardiac output (QT) and decreased pulmonary vascular resistance (PVR). Because of increased QT, arterial PO2 (PaO2) did not fall in spite of the increased V/Q inequality. After administration of isoproterenol, improvement in air-flow obstruction was always associated with significantly less increase in mean PaO2 and more V/Q inequality than after saline. After epinephrine and salbutamol a similar significant decrease in airflow obstruction was associated with only slightly more V/Q mismatching than after saline. The effects of epinephrine on low V/Q ratio areas, shunt, PaO2, QT, heart rate, and PVR were less and of shorter duration than those of isoproterenol. Salbutamol resulted in changes similar to but more persistent than those induced by epinephrine. All variables approached prechallenge values within 2 h after bronchodilator administration, regardless of agent used. These studies show that in a repeatable canine asthma model, randomized administration of epinephrine, isoproterenol, and salbutamol produce different gas exchange responses in spite of similar improvements in air-flow obstruction.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:6435488

  6. Carbon dioxide control in an open system that measures canopy gas exchanges

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Atmospheric carbon dioxide concentration affects both C3 carbon net assimilation as well as crop water use. Methods for measuring whole canopy gas exchange responses under carbon dioxide enrichment are needed for breeding programs aiming to develop crop cultivars resistant to stresses like drought i...

  7. Non-destructive evaluation of membrane lung gas exchange performance.

    PubMed

    Tallman, R D; Guardia, Z A; Gruber, M A

    1996-12-01

    This paper describes a method of evaluating the gas exchange effectiveness of hollow fiber oxygenators utilizing gas on both sides of the membrane. The goal of the study was to develop an evaluation technique which was accurate, reliable, and did not harm or contaminate a new, sterile oxygenator. Three pediatric oxygenators were tested and compared: the Medtronic Minimax Plus, the Terumo Capiox 320, and the Sorin Masterflo 34 (all with rated blood flows of 2-2.5 L/min). Gas entering the "blood" side was a mixture of CO2, O2, and N2 in a mixture matching typical venous blood partial pressures. The "blood" flows used were 0.5, 1, 1.5, or 2 L/min. Gas entering the gas port had an FiO2 of 0.4 flowing at 0.5, 1, 1.5, 2, 2.5, 3, or 3.5 L/min. Fractional contents of CO2 and O2 at all inlets and outlets were determined using a gas analyzer and converted to partial pressures. Efficacy indices and gas transfer rates were calculated and compared. Of the devices studied, the Masterflo 34 had the highest gas transport rates and effectiveness followed by the Minimax-Plus and the Capiox 320. Reversing the direction of the flow through the "blood" phase of the Minimax-Plus greatly changed its gas exchange effectiveness. The techniques described in this study should allow for a more uniform and consistent evaluation of gas exchange by membrane lungs which can be made inexpensively and relatively quickly. In addition, these methods should allow manufactures to evaluate gas exchange effectiveness and transfer rates of individual units during production as well as reduce the complexity involved when evaluating newly developed oxygenators. PMID:10164050

  8. Gas exchange and ventilation-perfusion relationships in the lung.

    PubMed

    Petersson, Johan; Glenny, Robb W

    2014-10-01

    This review provides an overview of the relationship between ventilation/perfusion ratios and gas exchange in the lung, emphasising basic concepts and relating them to clinical scenarios. For each gas exchanging unit, the alveolar and effluent blood partial pressures of oxygen and carbon dioxide (PO2 and PCO2) are determined by the ratio of alveolar ventilation to blood flow (V'A/Q') for each unit. Shunt and low V'A/Q' regions are two examples of V'A/Q' mismatch and are the most frequent causes of hypoxaemia. Diffusion limitation, hypoventilation and low inspired PO2 cause hypoxaemia, even in the absence of V'A/Q' mismatch. In contrast to other causes, hypoxaemia due to shunt responds poorly to supplemental oxygen. Gas exchanging units with little or no blood flow (high V'A/Q' regions) result in alveolar dead space and increased wasted ventilation, i.e. less efficient carbon dioxide removal. Because of the respiratory drive to maintain a normal arterial PCO2, the most frequent result of wasted ventilation is increased minute ventilation and work of breathing, not hypercapnia. Calculations of alveolar-arterial oxygen tension difference, venous admixture and wasted ventilation provide quantitative estimates of the effect of V'A/Q' mismatch on gas exchange. The types of V'A/Q' mismatch causing impaired gas exchange vary characteristically with different lung diseases. PMID:25063240

  9. Integrated flue gas treatment condensing heat exchanger for pollution control

    SciTech Connect

    Johnson, D.W.; Warchol, J.J.; Schulze, K.H.; Carrigan, J.F.

    1994-12-31

    Condensing heat exchangers recover both sensible and latent heat from flue gases. Using Teflon{reg_sign} to cover the heat exchanger tubes and inside surfaces that are exposed to the flue gas ensures adequate material lifetime in the corrosive environment encountered when the flue gas temperature drops below the acid dew point. A recent design improvement, called the integrated flue gas treatment (IFGT) concept, offers the ability to remove pollutants from the flue gas, as well as recover waste heat. It has been shown to remove SO{sub 2}, SO{sub 3}, particulates, and trace emissions. Babcock and Wilcox (B and W) is undertaking an extensive program to optimize this technology for a variety of flue gas applications. This paper summarizes the current status of IFGT technology and the development activities that are in progress.

  10. Impact of airway gas exchange on the multiple inert gas elimination technique: theory.

    PubMed

    Anderson, Joseph C; Hlastala, Michael P

    2010-03-01

    The multiple inert gas elimination technique (MIGET) provides a method for estimating alveolar gas exchange efficiency. Six soluble inert gases are infused into a peripheral vein. Measurements of these gases in breath, arterial blood, and venous blood are interpreted using a mathematical model of alveolar gas exchange (MIGET model) that neglects airway gas exchange. A mathematical model describing airway and alveolar gas exchange predicts that two of these gases, ether and acetone, exchange primarily within the airways. To determine the effect of airway gas exchange on the MIGET, we selected two additional gases, toluene and m-dichlorobenzene, that have the same blood solubility as ether and acetone and minimize airway gas exchange via their low water solubility. The airway-alveolar gas exchange model simulated the exchange of toluene, m-dichlorobenzene, and the six MIGET gases under multiple conditions of alveolar ventilation-to-perfusion, VA/Q, heterogeneity. We increased the importance of airway gas exchange by changing bronchial blood flow, Qbr. From these simulations, we calculated the excretion and retention of the eight inert gases and divided the results into two groups: (1) the standard MIGET gases which included acetone and ether and (2) the modified MIGET gases which included toluene and m-dichlorobenzene. The MIGET mathematical model predicted distributions of ventilation and perfusion for each grouping of gases and multiple perturbations of VA/Q and Qbr. Using the modified MIGET gases, MIGET predicted a smaller dead space fraction, greater mean VA, greater log(SDVA), and more closely matched the imposed VA distribution than that using the standard MIGET gases. Perfusion distributions were relatively unaffected. PMID:20336837

  11. Impact of Airway Gas Exchange on the Multiple Inert Gas Elimination Technique: Theory

    PubMed Central

    Anderson, Joseph C.; Hlastala, Michael P.

    2011-01-01

    The multiple inert gas elimination technique (MIGET) provides a method for estimating alveolar gas exchange efficiency. Six soluble inert gases are infused into a peripheral vein. Measurements of these gases in breath, arterial blood, and venous blood are interpreted using a mathematical model of alveolar gas exchange (MIGET model) that neglects airway gas exchange. A mathematical model describing airway and alveolar gas exchange predicts that two of these gases, ether and acetone, exchange primarily within the airways. To determine the effect of airway gas exchange on the MIGET, we selected two additional gases, toluene and m-dichlorobenzene, that have the same blood solubility as ether and acetone and minimize airway gas exchange via their low water solubility. The airway-alveolar gas exchange model simulated the exchange of toluene, m-dichlorobenzene, and the six MIGET gases under multiple conditions of alveolar ventilation-to-perfusion, V̇A/Q̇, heterogeneity. We increased the importance of airway gas exchange by changing bronchial blood flow, Q̇br. From these simulations, we calculated the excretion and retention of the eight inert gases and divided the results into two groups: 1) the standard MIGET gases which included acetone and ether and 2) the modified MIGET gases which included toluene and m-dichlorobenzene. The MIGET mathematical model predicted distributions of ventilation and perfusion for each grouping of gases and multiple perturbations of V̇A/Q̇ and Q̇br. Using the modified MIGET gases, MIGET predicted a smaller dead space fraction, greater mean V̇A, greater log(SDVA), and more closely matched the imposed V̇A distribution than that using the standard MIGET gases. Perfusion distributions were relatively unaffected. PMID:20336837

  12. Structure, function and evolution of the gas exchangers: comparative perspectives

    PubMed Central

    Maina, JN

    2002-01-01

    Over the evolutionary continuum, animals have faced similar fundamental challenges of acquiring molecular oxygen for aerobic metabolism. Under limitations and constraints imposed by factors such as phylogeny, behaviour, body size and environment, they have responded differently in founding optimal respiratory structures. A quintessence of the aphorism that ‘necessity is the mother of invention’, gas exchangers have been inaugurated through stiff cost–benefit analyses that have evoked transaction of trade-offs and compromises. Cogent structural–functional correlations occur in constructions of gas exchangers: within and between taxa, morphological complexity and respiratory efficiency increase with metabolic capacities and oxygen needs. Highly active, small endotherms have relatively better-refined gas exchangers compared with large, inactive ectotherms. Respiratory structures have developed from the plain cell membrane of the primeval prokaryotic unicells to complex multifunctional ones ofthe modern Metazoa. Regarding the respiratory medium used to extract oxygen from, animal life has had only two choices – water or air – within the biological range of temperature and pressure the only naturally occurring respirable fluids. In rarer cases, certain animalshave adapted to using both media. Gills (evaginated gas exchangers) are the primordial respiratory organs: they are the archetypal water breathing organs. Lungs (invaginated gas exchangers) are the model air breathing organs. Bimodal (transitional) breathers occupy the water–air interface. Presentation and exposure of external (water/air) and internal (haemolymph/blood) respiratory media, features determined by geometric arrangement of the conduits, are important features for gas exchange efficiency: counter-current, cross-current, uniform pool and infinite pool designs have variably developed. PMID:12430953

  13. Sunlight supply and gas exchange systems in microalgal bioreactor

    NASA Technical Reports Server (NTRS)

    Mori, K.; Ohya, H.; Matsumoto, K.; Furune, H.

    1987-01-01

    The bioreactor with sunlight supply system and gas exchange systems presented has proved feasible in ground tests and shows much promise for space use as a closed ecological life support system device. The chief conclusions concerning the specification of total system needed for a life support system for a man in a space station are the following: (1) Sunlight supply system - compactness and low electrical consumption; (2) Bioreactor system - high density and growth rate of chlorella; and (3) Gas exchange system - enough for O2 production and CO2 assimilation.

  14. [The physiology of gas exchange in divers].

    PubMed

    Rieder, H U

    1989-04-01

    After a short reminder of Boyle's law and the physiology of oxygen and nitrogen, a mathematical model will be discussed (without formulas). Its limitations are shown in relation to the calculation of partial gas pressures in different human organs. Such models are already used in closed circuit anesthesia delivery systems and valuable insights can be obtained by this way, which enable us to calculate better nitrogen decompression tables. PMID:2727653

  15. Automated measurement of respiratory gas exchange by an inert gas dilution technique

    NASA Technical Reports Server (NTRS)

    Sawin, C. F.; Rummel, J. A.; Michel, E. L.

    1974-01-01

    A respiratory gas analyzer (RGA) has been developed wherein a mass spectrometer is the sole transducer required for measurement of respiratory gas exchange. The mass spectrometer maintains all signals in absolute phase relationships, precluding the need to synchronize flow and gas composition as required in other systems. The RGA system was evaluated by comparison with the Douglas bag technique. The RGA system established the feasibility of the inert gas dilution method for measuring breath-by-breath respiratory gas exchange. This breath-by-breath analytical capability permits detailed study of transient respiratory responses to exercise.

  16. Relationship between wind speed and gas exchange over the ocean

    NASA Technical Reports Server (NTRS)

    Wanninkhof, Rik

    1992-01-01

    A quadratic dependence of gas exchange on wind speed is employed to analyze the relationship between gas transfer and wind speed with particular emphasizing variable and/or low wind speeds. The quadratic dependence is fit through gas-transfer velocities over the ocean determined by methods based on the natural C-14 disequilibrium and the bomb C-14 inventory. The variation in the CO2 levels is related to these mechanisms, but the results show that other causes play significant roles. A weaker dependence of gas transfer on wind is suggested for steady winds, and long-term averaged winds demonstrate a stronger dependence in the present model. The chemical enhancement of CO2 exchange is also shown to play a role by increasing CO2 fluxes at low wind speeds.

  17. In calm seas, precipitation drives air-sea gas exchange

    NASA Astrophysics Data System (ADS)

    Schultz, Colin

    2012-05-01

    In a series of experiments run in what resembles a heavily instrumented fish tank, Harrison et al. investigated the interwoven roles of wind and rain on air-sea gas exchange rates. Working with a 42-meterlong, 1-meter-wide, and 1.25-meter-tall experimental pool, the authors were able to control the wind speed, rainfall rate, water circulation speed, and other parameters, which they used to assess the effect of 24 different wind speed-rainfall rate combinations on the gas exchange rate of sulfur hexafuoride, a greenhouse gas. In trials that lasted up to 3 hours, the authors collected water samples from the tank at regular intervals, tracking the concentration of the dissolved gas.

  18. The effect of high temperatures on tropical forest gas exchange.

    NASA Astrophysics Data System (ADS)

    Doughty, C. E.; Goulden, M.; Miller, S.; Da Rocha, H.

    2006-12-01

    Further research is required to understand the sensitivity of tropical forest to climate warming. Previous research has shown that tropical forest photosynthesis decreases and respiration increases at high leaf temperatures and that tree growth is reduced in years with higher average air temperatures (Clark et al 2003). Models indicate that the climate related destruction of the Amazon forest will amplify global warming by 1.5¢ª C, resulting in a mean temperature increase of 5.5¢ª C, as compared with 4¢ª C without this carbon cycle feedback (Cox et al 2000). These studies demonstrate the importance of temperature on tropical forest gas exchange. At the LBA Tapajos km 83 site we determined what controls tropical leaf temperature and how temperature affects photosynthesis and respiration. Sunlit leaves were substantially warmer than air temperatures and this had a negative effect on photosynthesis and stomatal conductance. We used eddy flux data to compare intervals of 10 minute cloudy periods followed by 20 minute sunny periods to see if similar trends could be seen at both the leaf and canopy level. The longer the sunny interval the warmer the canopy became and canopy conductance and CO2 exchange declined correspondingly. As the canopy warmed u* increased which increased turbulence and kept the canopy temperature from rising more. Long light intervals can cause heat stress in tropical forests but due to the very cloudy nature of the tropics such intervals are rare. However, if the tropics become both warmer and less cloudy such heat stress will increase.

  19. Sequential gas delivery provides precise control of alveolar gas exchange.

    PubMed

    Fisher, Joseph A; Iscoe, Steve; Duffin, James

    2016-05-01

    Of the factors determining blood gases, only alveolar ventilation (V˙A) is amenable to manipulation. However, current physiology text books neither describe how breath-by-breath V˙A can be measured, nor how it can be precisely controlled in spontaneously breathing subjects. And such control must be effected independent of minute ventilation (V˙E) and the pattern of breathing. Control of V˙A requires the deliberate partition of inhaled gas between the alveoli and the anatomical deadspace. This distribution is accomplished by sequential gas delivery (SGD): each breath consists of a chosen volume of 'fresh' gas followed by previously exhaled gas. Control of V˙A through SGD is a simple, inexpensive, yet powerful tool with many applications. Here we describe how to implement SGD, how it precisely controls V˙A, and consequently how it controls arterial blood gases. PMID:26840836

  20. [External respiration, pulmonary gas exchange and energy expenditure in weightlessness].

    PubMed

    Kas'ian, I I; Makarov, G F

    1984-01-01

    This paper summarizes the data on external respiration and energy expenditures of men exposed to zero-g for 185 days and to 1/6 g on the lunar surface reported by Soviet and foreign authors. The paper also discusses factors that may be responsible for a higher level of gas exchange processes at reduced g. PMID:6392736

  1. Lung Structure and the Intrinsic Challenges of Gas Exchange.

    PubMed

    Hsia, Connie C W; Hyde, Dallas M; Weibel, Ewald R

    2016-04-01

    Structural and functional complexities of the mammalian lung evolved to meet a unique set of challenges, namely, the provision of efficient delivery of inspired air to all lung units within a confined thoracic space, to build a large gas exchange surface associated with minimal barrier thickness and a microvascular network to accommodate the entire right ventricular cardiac output while withstanding cyclic mechanical stresses that increase several folds from rest to exercise. Intricate regulatory mechanisms at every level ensure that the dynamic capacities of ventilation, perfusion, diffusion, and chemical binding to hemoglobin are commensurate with usual metabolic demands and periodic extreme needs for activity and survival. This article reviews the structural design of mammalian and human lung, its functional challenges, limitations, and potential for adaptation. We discuss (i) the evolutionary origin of alveolar lungs and its advantages and compromises, (ii) structural determinants of alveolar gas exchange, including architecture of conducting bronchovascular trees that converge in gas exchange units, (iii) the challenges of matching ventilation, perfusion, and diffusion and tissue-erythrocyte and thoracopulmonary interactions. The notion of erythrocytes as an integral component of the gas exchanger is emphasized. We further discuss the signals, sources, and limits of structural plasticity of the lung in alveolar hypoxia and following a loss of lung units, and the promise and caveats of interventions aimed at augmenting endogenous adaptive responses. Our objective is to understand how individual components are matched at multiple levels to optimize organ function in the face of physiological demands or pathological constraints. PMID:27065169

  2. Greenhouse Gas Exchange in Small Arctic Thaw Ponds

    NASA Astrophysics Data System (ADS)

    Laurion, I.; Bégin, P. N.; Bouchard, F.; Preskienis, V.

    2014-12-01

    Arctic lakes and ponds can represent up to one quarter of the land surface in permafrost landscapes, particularly in lowland tundra landscapes characterized by ice wedge organic polygons. Thaw ponds can be defined as the aquatic ecosystems associated to thawing of organic soils, either resulting from active layer processes and located above low-center peat polygons (hereafter low-center polygonal or LCP ponds), or resulting from thermokarst slumping above melting ice wedges linked to the accelerated degradation of permafrost (hereafter ice-wedge trough or IWT ponds). These ponds can merge together forming larger water bodies, but with relatively stable shores (hereafter merged polygonal or MPG ponds), and with limnological characteristics similar to LCP ponds. These aquatic systems are very small and shallow, and present a different physical structure than the larger thermokarst lakes, generated after years of development and land subsidence. In a glacier valley on Bylot Island, Nunavut, Canada, thermokarst and kettle lakes together represent 29% of the aquatic area, with a thermal profile resembling those of more standard arctic lakes (mixed epilimnion). The IWT ponds (44% of the area) are stratified for a large fraction of the summer despite their shallowness, while LCP and MPG ponds (27% of the area) show a more homogeneous water column. This will affect gas exchange in these diverse aquatic systems, in addition to their unique microbiota and organic carbon lability that control the production and consumption rates of greenhouse gases. The stratification in IWT ponds generates hypoxic conditions at the bottom, and together with the larger availability of organic carbon, stimulates methanogenesis and limits the mitigating action of methanotrophs. Overall, thaw ponds are largely supersaturated in methane, with IWT ponds dominating the emissions in this landscape (92% of total aquatic emissions estimated for the same valley), and they present large variations in

  3. Respiratory gas exchange using a triaxial alveolar gas diagram.

    PubMed Central

    Fuster, J. F.; Pages, T.; Palacios, L.

    1993-01-01

    A triaxial alveolar gas diagram to depict fractional concentration of oxygen, carbon dioxide and nitrogen is described, in which the R = 1 line is always implicit. Although it is not claimed that this representation leads to new insights into respiratory physiology, a method of plotting on a triaxial coordinate system has been found to be well suited to many applications when a direct display of fractional nitrogen concentration is required. PMID:8303637

  4. Gas Exchange Models for a Flexible Insect Tracheal System.

    PubMed

    Simelane, S M; Abelman, S; Duncan, F D

    2016-06-01

    In this paper two models for movement of respiratory gases in the insect trachea are presented. One model considers the tracheal system as a single flexible compartment while the other model considers the trachea as a single flexible compartment with gas exchange. This work represents an extension of Ben-Tal's work on compartmental gas exchange in human lungs and is applied to the insect tracheal system. The purpose of the work is to study nonlinear phenomena seen in the insect respiratory system. It is assumed that the flow inside the trachea is laminar, and that the air inside the chamber behaves as an ideal gas. Further, with the isothermal assumption, the expressions for the tracheal partial pressures of oxygen and carbon dioxide, rate of volume change, and the rates of change of oxygen concentration and carbon dioxide concentration are derived. The effects of some flow parameters such as diffusion capacities, reaction rates and air concentrations on net flow are studied. Numerical simulations of the tracheal flow characteristics are performed. The models developed provide a mathematical framework to further investigate gas exchange in insects. PMID:27209375

  5. Dynamics of heat, water, and soluble gas exchange in the human airways: 1. A model study.

    PubMed

    Tsu, M E; Babb, A L; Ralph, D D; Hlastala, M P

    1988-01-01

    In order to provide a means for analysis of heat, water, and soluble gas exchange with the airways during tidal ventilation, a one dimensional theoretical model describing heat and water exchange in the respiratory airways has been extended to include soluble gas exchange with the airway mucosa and water exchange with the mucous layer lining the airways. Not only do heat, water, and gas exchange occur simultaneously, but they also interact. Heating and cooling of the airway surface and mucous lining affects both evaporative water and soluble gas exchange. Water evaporation provides a major source of heat exchange. The model-predicted mean airway temperature profiles agree well with literature data for both oral and nasal breathing validating that part of the model. With model parameters giving the best fit to experimental data, the model shows: (a) substantial heat recovery in the upper airways, (b) minimal respiratory heat and water loss, and (c) low average mucous temperatures and maximal increases in mucous thickness. For resting breathing of room air, heat and water conservation appear to be more important than conditioning efficiency. End-tidal expired partial pressures of very soluble gases eliminated by the lungs are predicted to be lower than the alveolar partial pressures due to the absorption of the expired gases by the airway mucosa. The model may be usable for design of experiments to examine mechanisms associated with the local hydration and dehydration dynamics of the mucosal surface, control of bronchial perfusion, triggering of asthma, mucociliary clearance and deposition of inhaled pollutant gases. PMID:3228218

  6. BIODEGRADATION AND GAS-EXCHANGE OF GASEOUS ALKANES IN MODEL ESTUARINE ECOSYSTEMS

    EPA Science Inventory

    Gas exchange-biodegradation experiments conducted in model estuarine ecosystems indicate that the ease of degradation of gaseious normal alkanes increases with chain length. The behavior of gaseous perhalogenated alkanes can be explained by gas exchange alone with no degradation....

  7. Educational software for illustrating gas-exchange processes in plants

    SciTech Connect

    Wullschleger, S.D.; Hanson, P.J. ); Sage, R.F. )

    1991-05-01

    Simulation models are increasingly being used to describe physiological processes in the plant sciences. These models, while useful for research purposes, also offer tremendous potential for demonstrating a wide array of scientific topics to students. The authors have developed an educational software package, based on currently accepted principles, that illustrates the environmental and biochemical control of plant gas-exchange. Graphic and tabular presentations, coupled with on-screen requests for student input, serve to effectively convey the basic fundamentals of photosynthesis and transpiration, as well as the diurnal patterns of plant gas-exchange in response to fluctuating environmental conditions. More advanced topics focus on the biochemical limitations to photosynthesis imposed by Rubisco activity, electron transport capacity, and the regeneration of inorganic phosphorus. Also included is an exercise that challenges students to call upon the lessons learned in order to optimize carbon assimilation, while minimizing water losses, over a 72-h simulation period.

  8. Design of peripheral airways for efficient gas exchange.

    PubMed

    Weibel, Ewald R; Sapoval, Bernard; Filoche, Marcel

    2005-08-25

    Peripheral airways combine branched tubes for ventilation with the gas exchanging alveoli in the pulmonary acini, defined as the complex of airways supplied by one first order respiratory or transitional bronchiole. In this part, the replenishment of oxygen at the alveolar surface occurs by a combination of convective air flow with diffusion of oxygen in the air. The transition between convection and diffusion depends on the morphometric properties of the airways. The design of the peripheral airways in the acinus of the human lung is described quantitatively on the basis of measurements obtained on casts of the acinar airways. Comparable data for rat and rabbit are also discussed. On the basis of this morphometric information, a typical path model for human acinar airways is derived. These studies also form the basis for advanced modeling studies of gas exchange and ventilation. In particular the problems occurring because of diffusional screening and the design conditions for minimizing this effect are discussed. PMID:15921964

  9. Gas exchange on Mono Lake and Crowley Lake, California

    NASA Technical Reports Server (NTRS)

    Wanninkhof, Rik; Ledwell, James R.; Broecker, Wallace S.

    1987-01-01

    Gas exchange coefficients (k) have been determined for freshwater Crowley Lake and saline Mono Lake through the use of a man-made purposefully injected gas, SF6. The concentration decreased from an initial value of 40 to 4 pmol/L for Mono Lake and from 20 to 1 pmol/L for Crowley lake over a period of 6 wks. Wind-speed (u) records from anemometers on the shore of each lake made it possible to determine the relationship between k and u. The average u and k values for the experiment were identical for the two lakes, despite the large chemical differences. It is estimated that, for the u values observed over Mono Lake from July to December 1984, the exchange of CO2 occurred 2.5 times faster than without chemical enhancement. This is a factor of 4 lower than needed to explain the high invasion rate of C-14 produced by nuclear bomb tests.

  10. The SOLAS air-sea gas exchange experiment (SAGE) 2004

    NASA Astrophysics Data System (ADS)

    Harvey, Mike J.; Law, Cliff S.; Smith, Murray J.; Hall, Julie A.; Abraham, Edward R.; Stevens, Craig L.; Hadfield, Mark G.; Ho, David T.; Ward, Brian; Archer, Stephen D.; Cainey, Jill M.; Currie, Kim I.; Devries, Dawn; Ellwood, Michael J.; Hill, Peter; Jones, Graham B.; Katz, Dave; Kuparinen, Jorma; Macaskill, Burns; Main, William; Marriner, Andrew; McGregor, John; McNeil, Craig; Minnett, Peter J.; Nodder, Scott D.; Peloquin, Jill; Pickmere, Stuart; Pinkerton, Matthew H.; Safi, Karl A.; Thompson, Rona; Walkington, Matthew; Wright, Simon W.; Ziolkowski, Lori A.

    2011-03-01

    The SOLAS air-sea gas exchange experiment (SAGE) was a multiple-objective study investigating gas-transfer processes and the influence of iron fertilisation on biologically driven gas exchange in high-nitrate low-silicic acid low-chlorophyll (HNLSiLC) Sub-Antarctic waters characteristic of the expansive subpolar zone of the southern oceans. This paper provides a general introduction and summary of the main experimental findings. The release site was selected from a pre-voyage desktop study of environmental parameters to be in the south-west Bounty Trough (46.5°S 172.5°E) to the south-east of New Zealand and the experiment was conducted between mid-March and mid-April 2004. In common with other mesoscale iron addition experiments (FeAX's), SAGE was designed as a Lagrangian study, quantifying key biological and physical drivers influencing the air-sea gas exchange processes of CO 2, DMS and other biogenic gases associated with an iron-induced phytoplankton bloom. A dual tracer SF 6/ 3He release enabled quantification of both the lateral evolution of a labelled volume (patch) of ocean and the air-sea tracer exchange at tenths of kilometer scale, in conjunction with the iron fertilisation. Estimates from the dual-tracer experiment found a quadratic dependency of the gas exchange coefficient on windspeed that is widely applicable and describe air-sea gas exchange in strong wind regimes. Within the patch, local and micrometeorological gas exchange process studies (100 m scale) and physical variables such as near-surface turbulence, temperature microstructure at the interface, wave properties and windspeed were quantified to further assist the development of gas exchange models for high-wind environments. There was a significant increase in the photosynthetic competence ( Fv/ Fm) of resident phytoplankton within the first day following iron addition, but in contrast to other FeAX's, rates of net primary production and column-integrated chlorophyll a concentrations had

  11. Reactive oxygen species production and discontinuous gas exchange in insects

    PubMed Central

    Boardman, Leigh; Terblanche, John S.; Hetz, Stefan K.; Marais, Elrike; Chown, Steven L.

    2012-01-01

    While biochemical mechanisms are typically used by animals to reduce oxidative damage, insects are suspected to employ a higher organizational level, discontinuous gas exchange mechanism to do so. Using a combination of real-time, flow-through respirometry and live-cell fluorescence microscopy, we show that spiracular control associated with the discontinuous gas exchange cycle (DGC) in Samia cynthia pupae is related to reactive oxygen species (ROS). Hyperoxia fails to increase mean ROS production, although minima are elevated above normoxic levels. Furthermore, a negative relationship between mean and mean ROS production indicates that higher ROS production is generally associated with lower . Our results, therefore, suggest a possible signalling role for ROS in DGC, rather than supporting the idea that DGC acts to reduce oxidative damage by regulating ROS production. PMID:21865257

  12. Reactive oxygen species production and discontinuous gas exchange in insects.

    PubMed

    Boardman, Leigh; Terblanche, John S; Hetz, Stefan K; Marais, Elrike; Chown, Steven L

    2012-03-01

    While biochemical mechanisms are typically used by animals to reduce oxidative damage, insects are suspected to employ a higher organizational level, discontinuous gas exchange mechanism to do so. Using a combination of real-time, flow-through respirometry and live-cell fluorescence microscopy, we show that spiracular control associated with the discontinuous gas exchange cycle (DGC) in Samia cynthia pupae is related to reactive oxygen species (ROS). Hyperoxia fails to increase mean ROS production, although minima are elevated above normoxic levels. Furthermore, a negative relationship between mean and mean ROS production indicates that higher ROS production is generally associated with lower . Our results, therefore, suggest a possible signalling role for ROS in DGC, rather than supporting the idea that DGC acts to reduce oxidative damage by regulating ROS production. PMID:21865257

  13. Oxygen-induced plasticity in tracheal morphology and discontinuous gas exchange cycles in cockroaches Nauphoeta cinerea.

    PubMed

    Bartrim, Hamish; Matthews, Philip G D; Lemon, Sussan; White, Craig R

    2014-12-01

    The function and mechanism underlying discontinuous gas exchange in terrestrial arthropods continues to be debated. Three adaptive hypotheses have been proposed to explain the evolutionary origin or maintenance of discontinuous gas exchange cycles (DGCs), which may have evolved to reduce respiratory water loss, facilitate gas exchange in high CO2 and low O2 micro-environments, or to ameliorate potential damage as a result of oversupply of O2. None of these hypotheses have unequivocal support, and several non-adaptive hypotheses have also been proposed. In the present study, we reared cockroaches Nauphoeta cinerea in selected levels of O2 throughout development, and examined how this affected growth rate, tracheal morphology and patterns of gas exchange. O2 level in the rearing environment caused significant changes in tracheal morphology and the exhibition of DGCs, but the direction of these effects was inconsistent with all three adaptive hypotheses: water loss was not associated with DGC length, cockroaches grew fastest in hyperoxia, and DGCs exhibited by cockroaches reared in normoxia were shorter than those exhibited by cockroaches reared in hypoxia or hyperoxia. PMID:25378216

  14. Tradeoffs between metabolic rate and spiracular conductance in discontinuous gas exchange of Samia cynthia (Lepidoptera, Saturniidae).

    PubMed

    Moerbitz, Christian; Hetz, Stefan K

    2010-05-01

    The insect tracheal system is a unique respiratory system, designed for maximum oxygen delivery at high metabolic demands, e.g. during activity and at high ambient temperatures. Therefore, large safety margins are required for tracheal and spiracular conductance. Spiracles are the entry to the tracheal system and play an important role in controlling discontinuous gas exchange (DGC) between tracheal system and atmosphere in moth pupae. We investigated the effect of modulated metabolic rate (by changing ambient temperature) and modulated spiracular conductance (by blocking all except one spiracles) on gas exchange patterns in Samia pupae. Both, spiracle blocking and metabolic rates, affected respiratory behavior in Samia cynthia pupae. While animals showed discontinuous gas exchange cycles at lower temperatures with unblocked spiracles, the respiratory patterns were cyclic at higher temperatures, with partly blocked spiracles or a combination of these two factors. The threshold for the transition from a discontinuous (DGC) to a cyclic gas exchange ((cyc)GE) was significantly higher in animals with unblocked spiracles (18.7 nmol g(-1) min(-1) vs. 7.9 nmol g(-1) min(-1)). These findings indicate an important influence of spiracle conductance on the DGC, which may occur mostly in insects showing high spiracular conductances and low metabolic rates. PMID:19682454

  15. A Continuum Model for Metabolic Gas Exchange in Pear Fruit

    PubMed Central

    Ho, Q. Tri; Verboven, Pieter; Verlinden, Bert E.; Lammertyn, Jeroen; Vandewalle, Stefan; Nicolaï, Bart M.

    2008-01-01

    Exchange of O2 and CO2 of plants with their environment is essential for metabolic processes such as photosynthesis and respiration. In some fruits such as pears, which are typically stored under a controlled atmosphere with reduced O2 and increased CO2 levels to extend their commercial storage life, anoxia may occur, eventually leading to physiological disorders. In this manuscript we have developed a mathematical model to predict the internal gas concentrations, including permeation, diffusion, and respiration and fermentation kinetics. Pear fruit has been selected as a case study. The model has been used to perform in silico experiments to evaluate the effect of, for example, fruit size or ambient gas concentration on internal O2 and CO2 levels. The model incorporates the actual shape of the fruit and was solved using fluid dynamics software. Environmental conditions such as temperature and gas composition have a large effect on the internal distribution of oxygen and carbon dioxide in fruit. Also, the fruit size has a considerable effect on local metabolic gas concentrations; hence, depending on the size, local anaerobic conditions may result, which eventually may lead to physiological disorders. The model developed in this manuscript is to our knowledge the most comprehensive model to date to simulate gas exchange in plant tissue. It can be used to evaluate the effect of environmental stresses on fruit via in silico experiments and may lead to commercial applications involving long-term storage of fruit under controlled atmospheres. PMID:18369422

  16. EXCHANGE

    SciTech Connect

    Boltz, J.C.

    1992-09-01

    EXCHANGE is published monthly by the Idaho National Engineering Laboratory (INEL), a multidisciplinary facility operated for the US Department of Energy (DOE). The purpose of EXCHANGE is to inform computer users about about recent changes and innovations in both the mainframe and personal computer environments and how these changes can affect work being performed at DOE facilities.

  17. Gas Diodes for Thermoacoustic Self-circulating Heat Exchangers

    NASA Astrophysics Data System (ADS)

    Swift, Greg; Backhaus, Scott

    2006-05-01

    An asymmetrical constriction in a pipe functions as an imperfect gas diode for acoustic oscillations in the gas in the pipe. One or more gas diodes in a resonant loop of pipe create substantial steady flow, which can carry substantial heat between a remote heat exchanger and a thermoacoustic or Stirling engine or refrigerator; the flow is driven directly by the oscillations in the engine or refrigerator itself. This invention gives Stirling and thermoacoustic devices unprecedented flexibility, and may lead to Stirling engines of unprecedented power. We have built two of these resonant self-circulating heat exchangers, one as a fundamental test bed and the other as a demonstration of practical levels of heat transfer. Measurements of flow and heat transfer are in factor-of-two agreement with either of two simple calculation methods. One calculation method treats the oscillating and steady flows as independent and simply superimposed, except in the gas diodes. The other method accounts for the interaction between the oscillating and steady flow with the quasi-steady approximation. The mutual influence of superimposed turbulent oscillating and steady flows is a theoretical challenge.

  18. Bacterioneuston control of air-water methane exchange determined with a laboratory gas exchange tank

    NASA Astrophysics Data System (ADS)

    Upstill-Goddard, Robert C.; Frost, Thomas; Henry, Gordon R.; Franklin, Mark; Murrell, J. Colin; Owens, Nicholas J. P.

    2003-12-01

    The apparent transfer velocities (kw) of CH4, N2O, and SF6 were determined for gas invasion and evasion in a closed laboratory exchange tank. Tank water (pure Milli-RO® water or artificial seawater prepared in Milli-RO®) and/or tank air gas compositions were adjusted, with monitoring of subsequent gas transfer by gas chromatography. Derived kw was converted to "apparent k600," the value for CO2 in freshwater at 20°C. For CH4, analytical constraints precluded estimating apparent k600 based on tank air measurements. In some experiments we added strains of live methanotrophs. In others we added chemically deactivated methanotrophs, non-CH4 oxidizers (Vibrio), or bacterially associated surfactants, as controls. For all individual controls, apparent k600 estimated from CH4, N2O, or SF6 was indistinguishable. However, invasive estimates always exceeded evasive estimates, implying some control of gas invasion by bubbles. Estimates of apparent k600 differed significantly between methanotroph strains, possibly reflecting species-specific surfactant release. For individual strains during gas invasion, apparent k600 estimated from CH4, N2O, or SF6 was indistinguishable, whereas during gas evasion, k600-CH4 was significantly higher than either k600-N2O or k600-SF6, which were identical. Hence evasive k600-CH4/k600-SF6 was always significantly above unity, whereas invasive k600-CH4/k600-SF6 was not significantly different from unity. Similarly, k600-CH4/k600-SF6 for the controls and k600-N2O/k600-SF6 for all experiments did not differ significantly from unity. Our results are consistent with active metabolic control of CH4 exchange by added methanotrophs in the tank microlayer, giving enhancements of ˜12 ± 10% for k600-CH4. Hence reactive trace gas fluxes determined by conventional tracer methods at sea may be in error, prompting a need for detailed study of the role of the sea surface microlayer in gas exchange.

  19. Impact of phytoplankton-generated surfactants on air-sea gas exchange

    NASA Astrophysics Data System (ADS)

    Frew, Nelson M.; Goldman, Joel C.; Dennett, Mark R.; Johnson, A. Sherwood

    1990-03-01

    The effect of surface-active organic matter generated by seven common species of marine phytoplankton on gas exchange rates under turbulent conditions at the air-water interface was determined. Reductions in oxygen evasion rates ranging from 5 to 50% were observed relative to clean seawater controls. Relative oxygen exchange coefficients (expressed as R = Kw [sample]/Kw [control]) were shown to be sensitive to small changes in total dissolved carbohydrate at concentrations <1 mg C (carbon) L-1 and to asymptotically decrease to a lower limit (R = 55-70%) at concentrations between 2 and 6 mg C L-1. A corresponding relationship was observed in which R decreased with increasing relative surfactant amounts derived from surface pressure-area measurements. However, gas exchange reductions were significant for plankton exudate samples displaying surface pressures ≲1 mN m-1. It thus seems that condensed monolayer films are not a prerequisite for reduced gas exchange and that relatively soluble surfactants derived from phytoplankton can strongly affect the dissipation of near-surface turbulence and lead to changes in the Schmidt number dependency of Kw. Based on detailed analyses of carbohydrate-containing surface-active exudates isolated by solid phase extraction from one of the species, Phaeodactylum tricornutum, it appears that small glucans and heteropolysaccharides associated with proteins and possibly lipids were responsible for the observed reductions in R.

  20. Observational Studies of Parameters Influencing Air-sea Gas Exchange

    NASA Astrophysics Data System (ADS)

    Schimpf, U.; Frew, N. M.; Bock, E. J.; Hara, T.; Garbe, C. S.; Jaehne, B.

    A physically-based modeling of the air-sea gas transfer that can be used to predict the gas transfer rates with sufficient accuracy as a function of micrometeorological parameters is still lacking. State of the art are still simple gas transfer rate/wind speed relationships. Previous measurements from Coastal Ocean Experiment in the Atlantic revealed positive correlations between mean square slope, near surface turbulent dis- sipation, and wind stress. It also demonstrated a strong negative correlation between mean square slope and the fluorescence of surface-enriched colored dissolved organic matter. Using heat as a proxy tracer for gases the exchange process at the air/water interface and the micro turbulence at the water surface can be investigated. The anal- ysis of infrared image sequences allow the determination of the net heat flux at the ocean surface, the temperature gradient across the air/sea interface and thus the heat transfer velocity and gas transfer velocity respectively. Laboratory studies were carried out in the new Heidelberg wind-wave facility AELOTRON. Direct measurements of the Schmidt number exponent were done in conjunction with classical mass balance methods to estimate the transfer velocity. The laboratory results allowed to validate the basic assumptions of the so called controlled flux technique by applying differ- ent tracers for the gas exchange in a large Schmidt number regime. Thus a modeling of the Schmidt number exponent is able to fill the gap between laboratory and field measurements field. Both, the results from the laboratory and the field measurements should be able to give a further understanding of the mechanisms controlling the trans- port processes across the aqueous boundary layer and to relate the forcing functions to parameters measured by remote sensing.

  1. How is Order 636 affecting the gas distribution industry

    SciTech Connect

    Margossian, K.M. )

    1993-12-01

    This paper is part of a six part series on how interstate gas pipelines have been affected by Order 636. These papers are written in an interview format with different individuals representing the pipeline, natural gas, utility, and regulatory side of this new regulation. The issues deal with how it has affected these industries; how the relationships have changed between suppliers, marketers, distributors, etc.; the risks now involved in marketing, shipping, and buying gas products; and new technology developments have resulted to comply with the new regulations. This paper is an interview with Kenneth M. Magossian, president and chief operating officer of Commonwealth Gas Co. and Hopkinton LNG Corp.

  2. The Effect of Rain on Air-Water Gas Exchange

    NASA Technical Reports Server (NTRS)

    Ho, David T.; Bliven, Larry F.; Wanninkhof, Rik; Schlosser, Peter

    1997-01-01

    The relationship between gas transfer velocity and rain rate was investigated at NASA's Rain-Sea Interaction Facility (RSIF) using several SF, evasion experiments. During each experiment, a water tank below the rain simulator was supersaturated with SF6, a synthetic gas, and the gas transfer velocities were calculated from the measured decrease in SF6 concentration with time. The results from experiments with IS different rain rates (7 to 10 mm/h) and 1 of 2 drop sizes (2.8 or 4.2 mm diameter) confirm a significant and systematic enhancement of air-water gas exchange by rainfall. The gas transfer velocities derived from our experiment were related to the kinetic energy flux calculated from the rain rate and drop size. The relationship obtained for mono-dropsize rain at the RSIF was extrapolated to natural rain using the kinetic energy flux of natural rain calculated from the Marshall-Palmer raindrop size distribution. Results of laboratory experiments at RSIF were compared to field observations made during a tropical rainstorm in Miami, Florida and show good agreement between laboratory and field data.

  3. Atmosphere-ocean gas exchange based on radiocarbon data

    NASA Astrophysics Data System (ADS)

    Byalko, Alexey

    2014-05-01

    In recent decades, the intensity of global atmospheric convection has accelerated faster than climate warming; it is possible to judge this process from indirect data. Increasing ocean salinity contrasts provide evidence that evaporation has intensified [1]; sea surface wind velocities and wave heights have increased [2]. The CO2 gas exchange between the atmosphere and ocean must also simultaneously increase. Monthly measurements of atmospheric CO2 concentration have been published since 1958 [3], but directly measuring its fluxes from the atmosphere to the ocean and back is hardly possible. We show they can be reconstructed from 14C isotope concentration data. In the past century, two processes influenced the atmospheric 14C concentration in opposite directions: burning fossil fuels and testing nuclear weapons in the atmosphere. We compare the gas exchange theory with measurements of radiocarbon content in the atmosphere [4—6], which allows assessing the gas exchange quantitatively for the ocean to atmosphere and atmosphere to ocean fluxes separately for period 1960—2010 [7]. References 1. Durack P. J. and Wijffels S. E., J. Climate 23, 4342 (2010). 2. Young I. R., Sieger S., and Babanin A.V., Science 332, 451 (2011). 3. NOAA Earth System Research Laboratory Data: ftp://ftp.cmdl.noaa.gov/ccg/co2/trends/co2_mm_mlo.txt. 4. Nydal R., Lövseth K. // J. Geophys. Res. 1983. V. 88. P. 3579. 5. Levin I., Kromer B. // Radiocarbon. 1997. V. 39. P. 205. 6. Miller J.B., Lehman S.J., Montzka S.A., et al. // J. Geophys. Res. 2012. V. 117. D08302. 7. Byalko A.V. Doklady Physics, 2013. V. 58, 267-271.

  4. Leaf gas exchange characteristics of three neotropical mangrove species in response to varying hydroperiod

    USGS Publications Warehouse

    Krauss, Ken W.; Twilley, Robert R.; Doyle, Thomas W.; Gardiner, Emile S.

    2006-01-01

    We determined how different hydroperiods affected leaf gas exchange characteristics of greenhouse-grown seedlings (2002) and saplings (2003) of the mangrove species Avicennia germinans (L.) Stearn., Laguncularia racemosa (L.) Gaertn. f., and Rhizophora mangle L. Hydroperiod treatments included no flooding (unflooded), intermittent flooding (intermittent), and permanent flooding (flooded). Plants in the intermittent treatment were measured under both flooded and drained states and compared separately. In the greenhouse study, plants of all species maintained different leaf areas in the contrasting hydroperiods during both years. Assimilation–light response curves indicated that the different hydroperiods had little effect on leaf gas exchange characteristics in either seedlings or saplings. However, short-term intermittent flooding for between 6 and 22 days caused a 20% reduction in maximum leaf-level carbon assimilation rate, a 51% lower light requirement to attain 50% of maximum assimilation, and a 38% higher demand from dark respiration. Although interspecific differences were evident for nearly all measured parameters in both years, there was little consistency in ranking of the interspecific responses. Species by hydroperiod interactions were significant only for sapling leaf area. In a field study, R. mangle saplings along the Shark River in the Everglades National Park either demonstrated no significant effect or slight enhancement of carbon assimilation and water-use efficiency while flooded. We obtained little evidence that contrasting hydroperiods affect leaf gas exchange characteristics of mangrove seedlings or saplings over long time intervals; however, intermittent flooding may cause short-term depressions in leaf gas exchange. The resilience of mangrove systems to flooding, as demonstrated in the permanently flooded treatments, will likely promote photosynthetic and morphological adjustment to slight hydroperiod shifts in many settings..

  5. [CO2-gas exchange of mosses following water vapour uptake].

    PubMed

    Lange, O L

    1969-03-01

    The CO2-gas exchange of dry mosses which were exposed to air of high water vapour content has been followed. Some moss species behave as do lichens and aerophilic green algae: they are able to take up enough water vapour to make a rather high photosynthetic activity possible. Other species lack this ability. They need liquid water for reactivation of photosynthesis, as do poikilohydric ferns and phanerogams. In this respect too the mosses are located between the real thallophytes and the cormophytes. From this point of view they are useful objects for studying the relationships between water vapour reactivation, morphological organisation and ecological capability. PMID:24504355

  6. Steady-state canopy gas exchange: system design and operation

    NASA Technical Reports Server (NTRS)

    Bugbee, B.

    1992-01-01

    This paper describes the use of a commercial growth chamber for canopy photosynthesis, respiration, and transpiration measurements. The system was designed to measure transpiration via water vapor fluxes, and the importance of this measurement is discussed. Procedures for continuous measurement of root-zone respiration are described, and new data is presented to dispel myths about sources of water vapor interference in photosynthesis and in the measurement of CO2 by infrared gas analysis. Mitchell (1992) has described the fundamentals of various approaches to measuring photosynthesis. Because our system evolved from experience with other types of single-leaf and canopy gas-exchange systems, it is useful to review advantages and disadvantages of different systems as they apply to various research objectives.

  7. Mechanisms of gas exchange response to lung volume reduction surgery in severe emphysema.

    PubMed

    Cremona, George; Barberà, Joan A; Barbara, Joan A; Melgosa, Teresa; Appendini, Lorenzo; Roca, Josep; Casadio, Caterina; Donner, Claudio F; Rodriguez-Roisin, Roberto; Wagner, Peter D

    2011-04-01

    Lung volume reduction surgery (LVRS) improves lung function, respiratory symptoms, and exercise tolerance in selected patients with chronic obstructive pulmonary disease, who have heterogeneous emphysema. However, the reported effects of LVRS on gas exchange are variable, even when lung function is improved. To clarify how LVRS affects gas exchange in chronic obstructive pulmonary disease, 23 patients were studied before LVRS, 14 of whom were again studied afterwards. We performed measurements of lung mechanics, pulmonary hemodynamics, and ventilation-perfusion (Va/Q) inequality using the multiple inert-gas elimination technique. LVRS improved arterial Po₂ (Pa(O₂)) by a mean of 6 Torr (P = 0.04), with no significant effect on arterial Pco₂ (Pa(CO₂)), but with great variability in both. Lung mechanical properties improved considerably more than did gas exchange. Post-LVRS Pa(O₂) depended mostly on its pre-LVRS value, whereas improvement in Pa(O(2)) was explained mostly by improved Va/Q inequality, with lesser contributions from both increased ventilation and higher mixed venous Po(2). However, no index of lung mechanical properties correlated with Pa(O₂). Conversely, post-LVRS Pa(CO₂) bore no relationship to its pre-LVRS value, whereas changes in Pa(CO₂) were tightly related (r² = 0.96) to variables, reflecting decrease in static lung hyperinflation (intrinsic positive end-expiratory pressure and residual volume/total lung capacity) and increase in airflow potential (tidal volume and maximal inspiratory pressure), but not to Va/Q distribution changes. Individual gas exchange responses to LVRS vary greatly, but can be explained by changes in combinations of determining variables that are different for oxygen and carbon dioxide. PMID:21233341

  8. Measuring gas temperature during spin-exchange optical pumping process

    NASA Astrophysics Data System (ADS)

    Normand, E.; Jiang, C. Y.; Brown, D. R.; Robertson, L.; Crow, L.; Tong, X.

    2016-04-01

    The gas temperature inside a Spin-Exchange Optical Pumping (SEOP) laser-pumping polarized 3He cell has long been a mystery. Different experimental methods were employed to measure this temperature but all were based on either modelling or indirect measurement. To date there has not been any direct experimental measurement of this quantity. Here we present the first direct measurement using neutron transmission to accurately determine the number density of 3He, the temperature is obtained using the ideal gas law. Our result showed a surprisingly high gas temperature of 380°C, compared to the 245°C of the 3He cell wall temperature and 178°C of the optical pumping oven temperature. This experiment result may be used to further investigate the unsolved puzzle of the "X-factor" in the SEOP process which places an upper bound to the 3He polarization that can be achieved. Additional spin relaxation mechanisms might exist due to the high gas temperature, which could explain the origin of the X-factor.

  9. Sulfur gas exchange in Sphagnum-dominated wetlands

    NASA Technical Reports Server (NTRS)

    Hines, Mark E.; Demello, William Zamboni; Porter, Carolyn A.

    1992-01-01

    Sulfur gases are important components of the global cycle of S. They contribute to the acidity of precipitation and they influence global radiation balance and climate. The role of terrestrial sources of biogenic S and their effect on atmospheric chemistry remain as major unanswered questions in our understanding of the natural S cycle. The role of northern wetlands as sources and sinks of gaseous S was investigated by measuring rates of S gas exchange as a function of season, hydrologic conditions, and gradients in trophic status. The effects of inorganic S input on the production and emission of gaseous S were also investigated. Experiments were conducted in wetlands in New Hampshire, particularly a poor fen, fens within the Experimental Lakes Area (ELA) in Ontario, Canada and in freshwater and marine tundra. Emissions were determined using Teflon enclosures, gas cryotrapping methods, and gas chromatography (GC) with flame photometric detection. Dynamic (sweep flow) and static enclosures were employed. Dissolved gases were determined by gas stripping followed by GC.

  10. Optimal allocation of leaf epidermal area for gas exchange.

    PubMed

    de Boer, Hugo J; Price, Charles A; Wagner-Cremer, Friederike; Dekker, Stefan C; Franks, Peter J; Veneklaas, Erik J

    2016-06-01

    A long-standing research focus in phytology has been to understand how plants allocate leaf epidermal space to stomata in order to achieve an economic balance between the plant's carbon needs and water use. Here, we present a quantitative theoretical framework to predict allometric relationships between morphological stomatal traits in relation to leaf gas exchange and the required allocation of epidermal area to stomata. Our theoretical framework was derived from first principles of diffusion and geometry based on the hypothesis that selection for higher anatomical maximum stomatal conductance (gsmax ) involves a trade-off to minimize the fraction of the epidermis that is allocated to stomata. Predicted allometric relationships between stomatal traits were tested with a comprehensive compilation of published and unpublished data on 1057 species from all major clades. In support of our theoretical framework, stomatal traits of this phylogenetically diverse sample reflect spatially optimal allometry that minimizes investment in the allocation of epidermal area when plants evolve towards higher gsmax . Our results specifically highlight that the stomatal morphology of angiosperms evolved along spatially optimal allometric relationships. We propose that the resulting wide range of viable stomatal trait combinations equips angiosperms with developmental and evolutionary flexibility in leaf gas exchange unrivalled by gymnosperms and pteridophytes. PMID:26991124

  11. Assimilate transport in phloem sets conditions for leaf gas exchange.

    PubMed

    Nikinmaa, Eero; Hölttä, Teemu; Hari, Pertti; Kolari, Pasi; Mäkelä, Annikki; Sevanto, Sanna; Vesala, Timo

    2013-03-01

    Carbon uptake and transpiration in plant leaves occurs through stomata that open and close. Stomatal action is usually considered a response to environmental driving factors. Here we show that leaf gas exchange is more strongly related to whole tree level transport of assimilates than previously thought, and that transport of assimilates is a restriction of stomatal opening comparable with hydraulic limitation. Assimilate transport in the phloem requires that osmotic pressure at phloem loading sites in leaves exceeds the drop in hydrostatic pressure that is due to transpiration. Assimilate transport thus competes with transpiration for water. Excess sugar loading, however, may block the assimilate transport because of viscosity build-up in phloem sap. Therefore, for given conditions, there is a stomatal opening that maximizes phloem transport if we assume that sugar loading is proportional to photosynthetic rate. Here we show that such opening produces the observed behaviour of leaf gas exchange. Our approach connects stomatal regulation directly with sink activity, plant structure and soil water availability as they all influence assimilate transport. It produces similar behaviour as the optimal stomatal control approach, but does not require determination of marginal cost of water parameter. PMID:22934921

  12. Daily Social Exchanges and Affect in Middle and Later Adulthood: The Impact of Loneliness and Age

    ERIC Educational Resources Information Center

    Russell, Alissa; Bergeman, C. S.; Scott, Stacey B.

    2012-01-01

    Although daily social exchanges are important for well-being, it is unclear how different types of exchanges affect daily well-being, as well as which factors influence the way in which individuals react to their daily social encounters. The present study included a sample of 705 adults aged 31 to 91, and using Multilevel Modeling analyses…

  13. Direct Energy Exchange Enhancement in Distributed Injection Light Gas Launchers

    SciTech Connect

    Alger, T W; Finucane, R G; Hall, J P; Penetrante, B M; Uphaus, T M

    2000-04-06

    initially contained in the reservoir. This results deserves emphasis: whereas conventional guns apply a few percent of the reservoir pressure to a fast moving projectile, our design is paradoxically capable of applying nearly double the contained pressure. We later confirmed this experimental result analytically and related it to a type of direct energy exchange between unsteady fluid flows. This physical approach was the basis for the German V-1 ''buzz bomb'' of World War II; it has been applied to a limited number of commercial applications. (This work should not be confused with the German WWII distributed injection missile launchers.) Direct fluid-energy exchange has not previously been applied to any gas-launcher technology. As a result of these discoveries, we estimate that a practical, 15 km/s, high-velocity launcher could be built using our direct-energy-exchange, distributed-injection approach. However, the radical nature of the results, the lack of confirming or allied work being carried out anywhere else, and the fact that it would take extensive time and resources to demonstrate targeted performance precluded further development. We plan to submit the results to a refereed journal to ensure that the work will not be lost to the launcher community.

  14. The effects of oxygen induced pulmonary vasoconstriction on bedside measurement of pulmonary gas exchange.

    PubMed

    Weinreich, Ulla M; Thomsen, Lars P; Rees, Stephen E; Rasmussen, Bodil S

    2016-04-01

    In patients with respiratory failure measurements of pulmonary gas exchange are of importance. The bedside automatic lung parameter estimator (ALPE) of pulmonary gas exchange is based on changes in inspired oxygen (FiO2) assuming that these changes do not affect pulmonary circulation. This assumption is investigated in this study. Forty-two out of 65 patients undergoing coronary artery bypass grafting (CABG) had measurements of mean pulmonary arterial pressure (MPAP), cardiac output and pulmonary capillary wedge pressure thus enabling the calculation of pulmonary vascular resistance (PVR) at each FiO2 level. The research version of ALPE was used and FiO2 was step-wise reduced a median of 0.20 and ultimately returned towards baseline values, allowing 6-8 min' steady state period at each of 4-6 levels before recording the oxygen saturation (SpO2). FiO2 reduction led to median decrease in SpO2 from 99 to 92 %, an increase in MPAP of 4 mmHg and an increase in PVR of 36 dyn s cm(-5). Changes were immediately reversed on returning FiO2 towards baseline. In this study changes in MPAP and PVR are small and immediately reversible consistent with small changes in pulmonary gas exchange. This indicates that mild deoxygenation induced pulmonary vasoconstriction does not have significant influences on the ALPE parameters in patients after CABG. PMID:25962614

  15. How do land management practices affect net ecosystem CO2 exchange of an invasive plant infestation?

    NASA Astrophysics Data System (ADS)

    Sonnentag, O.; Detto, M.; Runkle, B.; Kelly, M.; Baldocchi, D. D.

    2009-12-01

    Ecosystem gas and energy exchanges of invasive plant infestations under different land management practices have been subject of few studies and thus little is known. Our goal is to characterize seasonal changes in net ecosystem CO2 exchange (NEE) through the processes of photosynthesis (GEP) and ecosystem respiration (Reco) of a grassland used as pasture yet infested by perennial pepperweed (Lepidium latifolium) in California’s Sacramento-San Joaquin River Delta. We analyze eddy-covariance supported by environmental and canopy-scale hyperspectral reflectance measurements acquired in 2007-2009. Our study covers three summer drought periods with slightly different land management practices. Over the study period the site was subject to year-round grazing, and in 2008 the site was additionally mowed. Specific questions we address are a) how does pepperweed flowering affect GEP, b) does a mowing event affect NEE mainly through GEP or Reco, and c) can the combined effects of phenology and mowing on pepperweed NEE potentially be tracked using routinely applied remote sensing techniques? Preliminary results indicate that pepperweed flowering drastically decreases photosynthetic CO2 uptake due to shading by the dense arrangement of white flowers at the canopy top, causing the infestation to be almost CO2 neutral. In contrast, mowing causes the infestation to act as moderate net CO2 sink, mainly due to increased CO2 uptake during regrowth. We demonstrate that spectral regions other than commonly-used red and near-infrared might be more promising for pepperweed monitoring because of its spectral uniqueness during the flowering phase. Our results have important implications for land-use land-cover (LULC) change studies when biological invasions and their management alter ecosystem structure and functioning but not necessarily the respective LULC class.

  16. DAILY SOCIAL EXCHANGES AND AFFECT IN MIDDLE AND LATER ADULTHOOD: THE IMPACT OF LONELINESS AND AGE*

    PubMed Central

    RUSSELL, ALISSA; BERGEMAN, C. S.; SCOTT, STACEY B.

    2013-01-01

    Although daily social exchanges are important for well-being, it is unclear how different types of exchanges affect daily well-being, as well as which factors influence the way in which individuals react to their daily social encounters. The present study included a sample of 705 adults aged 31 to 91, and using Multilevel Modeling analyses investigated whether loneliness or age moderate the relationship between daily affect and daily social exchanges with family and friends. Results indicated differences between events involving family and those involving friends. Furthermore, lonelier individuals benefitted more from positive events than less lonely adults but were not more negatively reactive to negative events. Moreover, results suggested that older adults’ affect is more independent of both positive and negative social events compared to younger people. Implications are discussed for the importance of daily social exchanges, daily social stress vulnerability, and the influences of loneliness across middle and later adulthood. PMID:22950350

  17. Respiratory gas exchange of high altitude adapted chick embryos

    NASA Technical Reports Server (NTRS)

    Wangensteen, O. D.; Rahn, H.; Burton, R. R.; Smith, A. H.

    1974-01-01

    Study of gas exchange by embryos from chickens acclimatized to an altitude of 3800 m. The oxygen partial pressure and carbon dioxide partial pressure differences across the egg shell were measured and found to be less than the values previously reported for sea-level eggs by about a factor of two. Further measurements of embryonic oxygen consumption and shell conductivity to oxygen indicated that, compared to eggs at sea level, oxygen consumption was reduced by a factor of 0.58 while conductivity to oxygen was increased only by a factor of 1.07 in the high-altitude eggs. These independent measurements predict the change in oxygen partial pressure across the egg shell of the high-altitude eggs to be only 0.54 times that of sea-level eggs; the directly measured factor was 0.53. The authors conclude that at high altitude, a major adaptation of the chick embryo is a reduced metabolism which decreases the change in oxygen partial pressure across the egg shell since its gas conductivity remains essentially unchanged.

  18. Human Regional Pulmonary Gas Exchange with Xenon Polarization Transfer (XTC)

    NASA Astrophysics Data System (ADS)

    Muradian, Iga; Butler, James; Hrovat, Mirko; Topulos, George; Hersman, Elizabeth; Ruset, Iulian; Covrig, Silviu; Frederick, Eric; Ketel, Stephen; Hersman, F. W.; Patz, Samuel

    2007-03-01

    Xenon Transfer Contrast (XTC) is an existing imaging method (Ruppert et al, Magn Reson Med, 51:676-687, 2004) that measures the fraction F of ^129Xe magnetization that diffuses from alveolar gas spaces to septal parenchymal tissue in lungs in a specified exchange time. As previously implemented, XTC is a 2-breath method and has been demonstrated in anesthetized animals. To use XTC in humans and to avoid issues associated with obtaining identical gas volumes on subsequent breath-hold experiments as well as precise image registration in post-processing, a single breath XTC method was developed that acquires three consecutive gradient echo images in an 8s acquisition. We report here initial measurements of the mean and variance of F for 5 normal healthy subjects as well as 7 asymptomatic smokers. The experiments were performed at two lung volumes (˜45 and 65% of TLC). We found that both the mean and variance of F increased with smoking history. In comparison, standard pulmonary function tests such as DLCO FEV1 showed no correlation with smoking history.

  19. How does subsurface characterization affect simulations of hyporheic exchange?

    PubMed

    Ward, Adam S; Gooseff, Michael N; Singha, Kamini

    2013-01-01

    We investigated the role of increasingly well-constrained geologic structures in the subsurface (i.e., subsurface architecture) in predicting streambed flux and hyporheic residence time distribution (RTD) for a headwater stream. Five subsurface realizations with increasingly resolved lithological boundaries were simulated in which model geometries were based on increasing information about flow and transport using soil and geologic maps, surface observations, probing to depth to refusal, seismic refraction, electrical resistivity (ER) imaging of subsurface architecture, and time-lapse ER imaging during a solute tracer study. Particle tracking was used to generate RTDs for each model run. We demonstrate how improved characterization of complex lithological boundaries and calibration of porosity and hydraulic conductivity affect model prediction of hyporheic flow and transport. Models using hydraulic conductivity calibrated using transient ER data yield estimates of streambed flux that are three orders of magnitude larger than uncalibrated models using estimated values for hydraulic conductivity based on values published for nearby hillslopes (10(-4) vs. 10(-7) m(2)/s, respectively). Median residence times for uncalibrated and calibrated models are 10(3) and 10(0) h, respectively. Increasingly well-resolved subsurface architectures yield wider hyporheic RTDs, indicative of more complex hyporheic flowpath networks and potentially important to biogeochemical cycling. The use of ER imaging to monitor solute tracers informs subsurface structure not apparent from other techniques, and helps to define transport properties of the subsurface (i.e., hydraulic conductivity). Results of this study demonstrate the value of geophysical measurements to more realistically simulate flow and transport along hyporheic flowpaths. PMID:22289021

  20. An automated gas exchange tank for determining gas transfer velocities in natural seawater samples

    NASA Astrophysics Data System (ADS)

    Schneider-Zapp, K.; Salter, M. E.; Upstill-Goddard, R. C.

    2014-07-01

    In order to advance understanding of the role of seawater surfactants in the air-sea exchange of climatically active trace gases via suppression of the gas transfer velocity (kw), we constructed a fully automated, closed air-water gas exchange tank and coupled analytical system. The system allows water-side turbulence in the tank to be precisely controlled with an electronically operated baffle. Two coupled gas chromatographs and an integral equilibrator, connected to the tank in a continuous gas-tight system, allow temporal changes in the partial pressures of SF6, CH4 and N2O to be measured simultaneously in the tank water and headspace at multiple turbulence settings, during a typical experimental run of 3.25 h. PC software developed by the authors controls all operations and data acquisition, enabling the optimisation of experimental conditions with high reproducibility. The use of three gases allows three independent estimates of kw for each turbulence setting; these values are subsequently normalised to a constant Schmidt number for direct comparison. The normalised kw estimates show close agreement. Repeated experiments with Milli-Q water demonstrate a typical measurement accuracy of 4% for kw. Experiments with natural seawater show that the system clearly resolves the effects on kw of spatial and temporal trends in natural surfactant activity. The system is an effective tool with which to probe the relationships between kw, surfactant activity and biogeochemical indices of primary productivity, and should assist in providing valuable new insights into the air-sea gas exchange process.

  1. An automated gas exchange tank for determining gas transfer velocities in natural seawater samples

    NASA Astrophysics Data System (ADS)

    Schneider-Zapp, K.; Salter, M. E.; Upstill-Goddard, R. C.

    2014-02-01

    In order to advance understanding of the role of seawater surfactants in the air-sea exchange of climatically active trace gases via suppression of the gas transfer velocity (kw), we constructed a fully automated, closed air-water gas exchange tank and coupled analytical system. The system allows water-side turbulence in the tank to be precisely controlled with an electronically operated baffle. Two coupled gas chromatographs and an integral equilibrator, connected to the tank in a continuous gas-tight system, allow temporal changes in the partial pressures of SF6, CH4 and N2O to be measured simultaneously in the tank water and headspace at multiple turbulence settings, during a typical experimental run of 3.25 h. PC software developed by the authors controls all operations and data acquisition, enabling the optimisation of experimental conditions with high reproducibility. The use of three gases allows three independent estimates of kw for each turbulence setting; these values are subsequently normalised to a constant Schmidt number for direct comparison. The normalised kw estimates show close agreement. Repeated experiments with MilliQ water demonstrate a typical measurement accuracy of 4% for kw. Experiments with natural seawater show that the system clearly resolves the effects on kw of spatial and temporal trends in natural surfactant activity. The system is an effective tool with which to probe the relationships between kw, surfactant activity and biogeochemical indices of primary productivity, and should assist in providing valuable new insights into the air-sea gas exchange process.

  2. Air-water Gas Exchange Rates on a Large Impounded River Measured Using Floating Domes (Poster)

    EPA Science Inventory

    Mass balance models of dissolved gases in rivers typically serve as the basis for whole-system estimates of greenhouse gas emission rates. An important component of these models is the exchange of dissolved gases between air and water. Controls on gas exchange rates (K) have be...

  3. JOINT ACTION OF O3 AND SO2 IN MODIFYING PLANT GAS EXCHANGE

    EPA Science Inventory

    The joint action of O3 and SO2 stress on plants was investigated. Gas exchange measurements of O3, SO2, and H2O vapor were made for garden pea. Plants were grown under controlled environments; O3, SO2, H2O vapor fluxes were evaluated with a whole-plant gas exchange chamber using ...

  4. Pulmonary and Cutaneous O[subscript 2] Gas Exchange: A Student Laboratory Exercise in the Frog

    ERIC Educational Resources Information Center

    Tattersall, Glenn J.; Currie, Suzanne; LeBlanc, Danielle M.

    2013-01-01

    Gas exchange in animals is ultimately diffusion based, generally occurring across dedicated respiratory organs. In many aquatic amphibians, however, multiple modes of gas exchange exist, allowing for the partitioning of O[subscript 2] uptake and CO[subscript 2] excretion between respiratory organs with different efficiencies. For example, due to…

  5. Measuring air-sea gas exchange velocities in a large scale annular wind-wave tank

    NASA Astrophysics Data System (ADS)

    Mesarchaki, E.; Kräuter, C.; Krall, K. E.; Bopp, M.; Helleis, F.; Williams, J.; Jähne, B.

    2014-06-01

    In this study we present gas exchange measurements conducted in a large scale wind-wave tank. Fourteen chemical species spanning a wide range of solubility (dimensionless solubility, α = 0.4 to 5470) and diffusivity (Schmidt number in water, Scw = 594 to 1194) were examined under various turbulent (u10 = 0.8 to 15 m s-1 conditions. Additional experiments were performed under different surfactant modulated (two different concentration levels of Triton X-100) surface states. This paper details the complete methodology, experimental procedure and instrumentation used to derive the total transfer velocity for all examined tracers. The results presented here demonstrate the efficacy of the proposed method, and the derived gas exchange velocities are shown to be comparable to previous investigations. The gas transfer behaviour is exemplified by contrasting two species at the two solubility extremes, namely nitrous oxide (N2O) and methanol (CH3OH). Interestingly, a strong transfer velocity reduction (up to a factor of three) was observed for N2O under a surfactant covered water surface. In contrast, the surfactant affected CH3OH, the high solubility tracer only weakly.

  6. A system for continuous long-term measurement of respiratory gas exchange in ventilated patients.

    PubMed

    Guttmann, J; Krieg, N; Vogel, W M

    1987-01-01

    A system for continuous long-term measurement of respiratory gas exchange in ventilated patients is presented. The method is noninvasive and may be applied in a clinical setting over a period of several days without adversely affecting the patient's wellbeing. The set-up was designed exclusively as a research tool. It registers oxygen uptake and CO2 elimination at 5 min intervals; breath-averaged measurements are carried out every 30 s. Expired minute volume is measured with a pneumotachograph equipped with an automatic drift compensation. A newly developed gas mixer insures that the inspiratory oxygen concentration remains constant. Expired gases are analysed for O2 and CO2 concentrations by mass spectrometer. The effect of the compressible gas volume is eliminated by segregating the inspiratory gas from the expired gas. The basic accuracy of measurement of the method is +/- 2.5% for oxygen uptake and +/- 2.0% for CO2 elimination. This result is based on a comparison of the individual components of the system with standard methods. The system's time constant (t90) for changes in O2 and CO2 concentrations is about 50 s. Based on the results of a case study, we will discuss oxygen uptake, CO2 elimination and the oxygen uptake profile of a patient measured over a period of seven days. PMID:3120837

  7. Risk factors for transient dysfunction of gas exchange after cardiac surgery

    PubMed Central

    Rodrigues, Cristiane Delgado Alves; Moreira, Marcos Mello; Lima, Núbia Maria Freire Vieira; de Figueirêdo, Luciana Castilho; Falcão, Antônio Luis Eiras; Petrucci, Orlando; Dragosavac, Desanka

    2015-01-01

    Objective A retrospective cohort study was preformed aiming to verify the presence of transient dysfunction of gas exchange in the postoperative period of cardiac surgery and determine if this disorder is linked to cardiorespiratory events. Methods We included 942 consecutive patients undergoing cardiac surgery and cardiac procedures who were referred to the Intensive Care Unit between June 2007 and November 2011. Results Fifteen patients had acute respiratory distress syndrome (2%), 199 (27.75%) had mild transient dysfunction of gas exchange, 402 (56.1%) had moderate transient dysfunction of gas exchange, and 39 (5.4%) had severe transient dysfunction of gas exchange. Hypertension and cardiogenic shock were associated with the emergence of moderate transient dysfunction of gas exchange postoperatively (P=0.02 and P=0.019, respectively) and were risk factors for this dysfunction (P=0.0023 and P=0.0017, respectively). Diabetes mellitus was also a risk factor for transient dysfunction of gas exchange (P=0.03). Pneumonia was present in 8.9% of cases and correlated with the presence of moderate transient dysfunction of gas exchange (P=0.001). Severe transient dysfunction of gas exchange was associated with patients who had renal replacement therapy (P=0.0005), hemotherapy (P=0.0001), enteral nutrition (P=0.0012), or cardiac arrhythmia (P=0.0451). Conclusion Preoperative hypertension and cardiogenic shock were associated with the occurrence of postoperative transient dysfunction of gas exchange. The preoperative risk factors included hypertension, cardiogenic shock, and diabetes. Postoperatively, pneumonia, ventilator-associated pneumonia, renal replacement therapy, hemotherapy, and cardiac arrhythmia were associated with the appearance of some degree of transient dysfunction of gas exchange, which was a risk factor for reintubation, pneumonia, ventilator-associated pneumonia, and renal replacement therapy in the postoperative period of cardiac surgery and cardiac

  8. Universal model for water costs of gas exchange by animals and plants

    PubMed Central

    Woods, H. Arthur; Smith, Jennifer N.

    2010-01-01

    For terrestrial animals and plants, a fundamental cost of living is water vapor lost to the atmosphere during exchange of metabolic gases. Here, by bringing together previously developed models for specific taxa, we integrate properties common to all terrestrial gas exchangers into a universal model of water loss. The model predicts that water loss scales to gas exchange with an exponent of 1 and that the amount of water lost per unit of gas exchanged depends on several factors: the surface temperature of the respiratory system near the outside of the organism, the gas consumed (oxygen or carbon dioxide), the steepness of the gradients for gas and vapor, and the transport mode (convective or diffusive). Model predictions were largely confirmed by data on 202 species in five taxa—insects, birds, bird eggs, mammals, and plants—spanning nine orders of magnitude in rate of gas exchange. Discrepancies between model predictions and data seemed to arise from biologically interesting violations of model assumptions, which emphasizes how poorly we understand gas exchange in some taxa. The universal model provides a unified conceptual framework for analyzing exchange-associated water losses across taxa with radically different metabolic and exchange systems. PMID:20404161

  9. Universal model for water costs of gas exchange by animals and plants.

    PubMed

    Woods, H Arthur; Smith, Jennifer N

    2010-05-01

    For terrestrial animals and plants, a fundamental cost of living is water vapor lost to the atmosphere during exchange of metabolic gases. Here, by bringing together previously developed models for specific taxa, we integrate properties common to all terrestrial gas exchangers into a universal model of water loss. The model predicts that water loss scales to gas exchange with an exponent of 1 and that the amount of water lost per unit of gas exchanged depends on several factors: the surface temperature of the respiratory system near the outside of the organism, the gas consumed (oxygen or carbon dioxide), the steepness of the gradients for gas and vapor, and the transport mode (convective or diffusive). Model predictions were largely confirmed by data on 202 species in five taxa--insects, birds, bird eggs, mammals, and plants--spanning nine orders of magnitude in rate of gas exchange. Discrepancies between model predictions and data seemed to arise from biologically interesting violations of model assumptions, which emphasizes how poorly we understand gas exchange in some taxa. The universal model provides a unified conceptual framework for analyzing exchange-associated water losses across taxa with radically different metabolic and exchange systems. PMID:20404161

  10. A Biomimetic Three-Dimensional Gas Exchange Unit for CO 2 Capture

    NASA Astrophysics Data System (ADS)

    Nguyen, Du Thai

    For the capture of CO2 from mixed gas streams, materials for increased gas exchange are necessary. Efficient gas exchange systems already exist in the form of vascularized lung-tissue. Herein we report a fabrication technique for the synthesis of three-dimensional microvascular gas exchange units capable of removing CO2 from flowing gas created using the recently reported Vaporization of a Sacrificial Component (VaSC) technique. We demonstrate the spatiotemporal pattern of CO2 reactivity in the microvascular gas exchange unit using colorimetric, pH sensitive dyes. Control over three-dimensional placement of channels is shown to increase capture efficiencies. A computational finite element model validates and explains the experimental observations.

  11. Ventilation and gas exchange management after cardiac arrest.

    PubMed

    Sutherasan, Yuda; Raimondo, Pasquale; Pelosi, Paolo

    2015-12-01

    For several decades, physicians had integrated several interventions aiming to improve the outcomes in post-cardiac arrest patients. However, the mortality rate after cardiac arrest is still as high as 50%. Post-cardiac arrest syndrome is associated with high morbidity and mortality due to not only poor neurological outcome and cardiovascular failure but also respiratory dysfunction. To minimize ventilator-associated lung injury, protective mechanical ventilation by using low tidal volume ventilation and driving pressure may decrease pulmonary complications and improve survival. Low level of positive end-expiratory pressure (PEEP) can be initiated and titrated with careful cardiac output and respiratory mechanics monitoring. Furthermore, optimizing gas exchange by avoiding hypoxia and hyperoxia as well as maintaining normocarbia may improve neurological and survival outcome. Early multidisciplinary cardiac rehabilitation intervention is recommended. Minimally invasive monitoring techniques, that is, echocardiography, transpulmonary thermodilution method measuring extravascular lung water, as well as transcranial Doppler ultrasound, might be useful to improve appropriate management of post-cardiac arrest patients. PMID:26670813

  12. Gas circulation and mass exchange between animal and plant units

    NASA Astrophysics Data System (ADS)

    Liu, Hong; Tong, Ling; Hu, Enzhu

    To investigate the gas circulation and mass exchange relations among animal, plant and other biological units in the bioregenarative life support system, a closed cultivating system consisting of animal breeding chamber and plant growing chamber was established. This facility is 1.4 m high with the bottom area measuring 1.4 m X 0.8 m. In the animal chamber, silkworms in the multistage instars from the first instar to the third day in the fifth instar were bred; in the plant chamber, lettuce with sharp leaves were grown in a staggered manner. After transferring the silkworms in different instars hatched in the artificial climate box proportionally, utilizing mulberry leaves supplied from the outside of the closed cultivating system to feed the silkworms from the first instar to the third instar; fed the silkworms after the third instar to the third day in the fifth instar with the lettuce leaves grown in the closed facility, meanwhile, took out silkworms' excretion whose amount was in proportion to that of the mulberry leaves input into the facility. Furthermore, the silkworms on the third day in the fifth instar were took out to provide animal protein with high quality for astronauts at certain intervals and the next batch of the silkworms in the first instar were put into the animal chamber. In this cultivating process, the O2 cycle period and CO2 concentration change were investigated, moreover, the transfer and transforming ways of carbon and other elements were determined.

  13. Gas exchange mechanism of orthodeoxia in hepatopulmonary syndrome.

    PubMed

    Gómez, Federico P; Martínez-Pallí, Graciela; Barberà, Joan A; Roca, Josep; Navasa, Miquel; Rodríguez-Roisin, Robert

    2004-09-01

    The mechanism of orthodeoxia (OD), or decreased partial pressure of arterial oxygen (PaO2) from supine to upright, a characteristic feature of hepatopulmonary syndrome (HPS), has never been comprehensively elucidated. We therefore investigated the intrapulmonary (shunt and ventilation-perfusion [VA/Q] mismatching) and extrapulmonary factors governing PaO2 in 20 patients with mild to severe HPS (14 males, 6 females; 50 +/- 3 years old SE) at upright and supine, in random order. We set out a cutoff value for OD, namely a PaO2 decrease > or = 5% or > or = 4 mm Hg (area under the receiver operating characteristic curve, 0.96 each). Compared to supine, 5 patients showed OD (PaO2 change, -11% +/- 2%, -7 +/- 1 mm Hg, P < .05) with further VA/Q worsening (shunt + low VA/Q mode increased from 19% +/- 7% to 21% +/- 7% of cardiac output [QT], P < .05), as opposed to 15 patients who did not (+2% +/- 2%, +1+/- 1 mm Hg) with VA/Q improvement (from 20% +/- 4% to 16% +/- 4% of QT, P < .01). Cardiac output was significantly lower in OD patients in both positions. Changes in extrapulmonary factors at upright, such as increased minute ventilation and decreased QT, were of similar magnitude in both subsets of patients. In conclusion, our data suggest that gas exchange response to OD in HPS points to a more altered pulmonary vascular tone inducing heterogeneous blood flow redistribution to lung zones with prominent intrapulmonary vascular dilatations. PMID:15349905

  14. BOREAS TE-4 Gas Exchange Data from Boreal Tree Species

    NASA Technical Reports Server (NTRS)

    Hall, Forrest G. (Editor); Curd, Shelaine (Editor); Collatz, G. James; Berry, Joseph A.; Gamon, John; Fredeen, Art; Fu, Wei

    2000-01-01

    The BOREAS TE-4 team collected steady-state gas exchange and reflectance data from several species in the BOREAS SSA during 1994 and in the NSA during 1996. Measurements of light, CO2, temperature, and humidity response curves were made by the BOREAS TE-4 team during the summers of 1994 and 1996 using intact attached leaves of boreal forest species located in the BOREAS SSA and NSA. These measurements were conducted to calibrate models used to predict photosynthesis, stomatal conductance, and leaf respiration. The 1994 and 1996 data can be used to construct plots of response functions or for parameterizing models. Parameter values are suitable for application in SiB2 (Sellers et al., 1996) or the leaf model of Collatz et al. (1991), and programs can be obtained from the investigators. The data are stored in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

  15. Effects of wind speed on leaf energy and gas exchange

    NASA Astrophysics Data System (ADS)

    Schymanski, Stanislaus J.; Or, Dani

    2013-04-01

    The common practice of modelling transpiration from plant leaves as an isothermal process (assuming equal leaf and air temperatures) may introduce significant bias into estimates of transpiration rates and energy partitioning. In a recent study (Schymanski et al., 2013, PLOS ONE, in print) we investigated effects of fluctuating irradiance (sunflecks) on leaf thermal regime and transpiration rates using a physically-based leaf model. Results suggest that leaf temperatures may deviate substantially from air temperature, leading to greatly modified transpiration rates compared to isothermal conditions, even under steady-state conditions. The results also highlighted the importance of intrinsic thermal protection imparted by transpiration flux. In this study we consider leaf energy balance to systematically investigate effects of wind speed on plant heat and gas exchange. Surprisingly, under certain conditions increasing wind speeds can result in a decrease in transpiration rates. This is due to the feedbacks between sensible heat flux, leaf temperature and latent heat flux. The model predicts that for high wind velocities the same leaf conductance (for water vapour and carbon dioxide) can be maintained with less evaporative losses. This may have profound implications for estimates of water use efficiency (WUE, the amount of carbon gained by photosynthesis per unit of water lost by transpiration), and the interpretation of changes in "Potential Evaporation" in relation to plant water use.

  16. Ethylene directly inhibits foliar gas exchange in Glycine max

    SciTech Connect

    Gunderson, C.A.; Taylor, G.E. Jr. )

    1991-01-01

    Gas exchange of individual attached leaves of soybean, Glycine max (L,) Merr cv Davis, was monitored during exposure to exogenous ethylene (C{sub 2}H{sub 4}) to test the hypothesis that the effects of C{sub 2}H{sub 4} on net photosynthesis (P{sub n}) and stomatal conductance to H{sub 2}O{sub 4} vapor (g{sub s}) are direct and not mediated by changes in leaf orientation to light. Leaflets were held perpendicular to incident light in a temperature-controlled cuvette throughout a 5.5 hour exposure to 10 microliters per liter C{sub 2}H{sub 4}. Declines in both P{sub N} and g{sub s} were evident within 2 hours and became more pronounced throughout the exposure period. In C{sub 2}H{sub 4} treated plants, P{sub N} and g{sub s} decreased to 80 and 62%, respectively, of the rates in control plants. Because epinastic movement of the leaflets was prohibited by the cuvette, the observed declines in P{sub N} and g{sub s} were a direct effect of C{sub 2}H{sub 4} rather than the result of reduced light interception caused by changing leaf angle.

  17. Land use and ecosystem level controls of trace gas exchange

    NASA Astrophysics Data System (ADS)

    Mosier, A.; Ojima, D.; Parton, W.; Delgrosso, S.

    2003-04-01

    Significant changes in the way land areas are used have taken place over the past 50 years modifying critical biogeochemical cycles. These alterations in biogeochemical cycles have resulted in structural and functional changes within many ecosystems. Human activities are the primary agent of these changes. The conversion of forests to other uses, conversion of agricultural lands to urban development, conversion of range lands to crop lands and conversion from one type of agricultural system to another, have a significant impact on human society through changes in air quality, water quality and food production. One such concern is related to changes in agricultural field management and the impact on atmospheric trace gas concentrations. Water management in rice production can directly impact both methane (CH4) and nitrous oxide (N2O) fluxes and changes from animal waste based fertilization practices to synthetic fertilization can greatly influence N2O, NH3 and NOx emissions are. Regional analysis of these changes in land use and understanding of how these affect biogenic trace gas emissions are the focus of the collaborative research effort developed in the BATREX activity and the associated TRAGnet Data base development. Analysis of environmental and land management characteristics affecting the various process level controls on biogenic trace gas fluxes have been conducted and incorporated in modeling analysis for regional extrapolation. Results from these studies at site level and regional scale will be presented. The focus of these studies has been on agriculture since agricultural systems account for a large share of anthropogenic CH4 and N2O emissions as well as NH3 and NOx fluxes globally. Concurrently, the development of ecosystem level, process-based models such as the DNDC Model and DAYCENT are permitting the numerical evaluation of land management and conversion on trace gas fluxes. The development of the data bases and analyses of the data using such

  18. Breathing hypoxic gas affects the physiology as well as the diving behaviour of tufted ducks.

    PubMed

    Halsey, Lewis G; Butler, Patrick J; Woakes, Anthony J

    2005-01-01

    We measured the effects of exposure to hypoxia (15% and 11% oxygen) and hypercapnia (up to 4.5% carbon dioxide) on rates of respiratory gas exchange both between and during dives in tufted ducks, Aythya fuligula, to investigate to what extent these may explain changes in diving behaviour. As found in previous studies, the ducks decreased dive duration (t(d)) and increased surface duration when diving from a hypoxic or hypercapnic gas mix. In the hypercapnic conditions, oxygen consumption during the dive cycle was not affected. Oxygen uptake between dives was reduced by only 17% when breathing a hypoxic gas mix of 11% oxygen. However, estimates of the rate of oxygen metabolism during the foraging periods of dives decreased nearly threefold in 11% oxygen. Given that tufted ducks normally dive well within their aerobic dive limits and that they significantly reduced their t(d) during hypoxia, it is not at all clear why they make this physiological adjustment. PMID:15778946

  19. Gas-Substrate Heat Exchange During Cold-Gas Dynamic Spraying

    NASA Astrophysics Data System (ADS)

    McDonald, A. G.; Ryabinin, A. N.; Irissou, E.; Legoux, J.-G.

    2013-03-01

    In this study, the temperature distribution of the surfaces of several substrates under an impinging gas jet from a cold spray nozzle was determined. A low-pressure cold-gas dynamic spraying unit was used to generate a jet of hot compressed nitrogen that impinged upon flat substrates. Computer codes based on a finite differences method were used to solve a simplified 2D temperature distribution equation for the substrate to produce nondimensional relationships between the surface temperature and the radius of the impinging fluid jet, the axial velocity of the cold spray nozzle, the substrate thickness, and the heating time. It was found that a single profile of the transient nondimensional maximum surface temperature could be used to estimate the dimensional maximum surface temperature, regardless of the value of the compressed gas temperature. It was found further that, as the thermal conductance of the substrate increased, the maximum surface temperature of the substrate beneath the gas jet decreased. Heat exchange between the substrate and the compressed gas jet during motion of the nozzle to produce heat conduction within the substrate was characterized by the nondimensional Peclét number. It was found that lower Peclét numbers produced higher temperatures within the substrate. The close agreement of the numerical results with the experimental results suggests that the nondimensionalized results may be applied to a wide range of conditions and materials.

  20. Observations on gas exchange and element recycle within a gas-closed algal-mouse system

    NASA Technical Reports Server (NTRS)

    Smernoff, D. T.; Wharton, R. A., Jr.; Averner, M. M.

    1986-01-01

    Life support systems based on bioregeneration rely on the control and manipulation of organisms. Algae are potentially useful for a variety of Closed Ecological Life Support System (CELSS) functions including the revitalization of atmospheres, production of food and for nitrogen fixation. The results of experiments conducted with a gas-closed algal-mouse system designed to investigate gas exchange phenomena under varying algal environmental conditions, and the ability of algae to utilize oxidized mouse solid waste are reported. Inherent instabilities exist between the uptake and release of carbon dioxide (CO2) and oxygen (O2) by the mouse and algae in a gas-closed system. Variations in light intensity and cell density alter the photosynthetic rate of the algae and enable short-term steady-state concentrations of atmospheric CO2 and O2. Different nitrogen sources (urea and nitrate) result in different algal assimilatory quotients (AQ). Combinations of photosynthetic rate and AQ ratio manipulations were examined for their potential in stabilizing atmospheric gas concentrations in the gas-closed algal-mouse system.

  1. Selection of the air heat exchanger operating in a gas turbine air bottoming cycle

    NASA Astrophysics Data System (ADS)

    Chmielniak, Tadeusz; Czaja, Daniel; Lepszy, Sebastian

    2013-12-01

    A gas turbine air bottoming cycle consists of a gas turbine unit and the air turbine part. The air part includes a compressor, air expander and air heat exchanger. The air heat exchanger couples the gas turbine to the air cycle. Due to the low specific heat of air and of the gas turbine exhaust gases, the air heat exchanger features a considerable size. The bigger the air heat exchanger, the higher its effectiveness, which results in the improvement of the efficiency of the gas turbine air bottoming cycle. On the other hand, a device with large dimensions weighs more, which may limit its use in specific locations, such as oil platforms. The thermodynamic calculations of the air heat exchanger and a preliminary selection of the device are presented. The installation used in the calculation process is a plate heat exchanger, which is characterized by a smaller size and lower values of the pressure drop compared to the shell and tube heat exchanger. Structurally, this type of the heat exchanger is quite similar to the gas turbine regenerator. The method on which the calculation procedure may be based for real installations is also presented, which have to satisfy the economic criteria of financial profitability and cost-effectiveness apart from the thermodynamic criteria.

  2. Quantifying air-sea gas exchange using noble gases in a coastal upwelling zone

    NASA Astrophysics Data System (ADS)

    Manning, C. C.; Stanley, R. H. R.; Nicholson, D. P.; Squibb, M. E.

    2016-05-01

    The diffusive and bubble-mediated components of air-sea gas exchange can be quantified separately using time-series measurements of a suite of dissolved inert gases. We have evaluated the performance of four published air-sea gas exchange parameterizations using a five-day time-series of dissolved He, Ne, Ar, Kr, and Xe concentration in Monterey Bay, CA. We constructed a vertical model including surface air-sea gas exchange and vertical diffusion. Diffusivity was measured throughout the cruise from profiles of turbulent microstructure. We corrected the mixed layer gas concentrations for an upwelling event that occurred partway through the cruise. All tested parameterizations gave similar results for Ar, Kr, and Xe; their air-sea fluxes were dominated by diffusive gas exchange during our study. For He and Ne, which are less soluble, and therefore more sensitive to differences in the treatment of bubble-mediated exchange, the parameterizations gave widely different results with respect to the net gas exchange flux and the bubble flux. This study demonstrates the value of using a suite of inert gases, especially the lower solubility ones, to parameterize air-sea gas exchange.

  3. The effect of wind and currents on gas exchange in an estuarine system

    NASA Technical Reports Server (NTRS)

    Broecker, W. S.; Ledwell, J. R.; Bopp, R.

    1987-01-01

    The objectives were to develop a non-volatile tracer to use in gas exchange experiments in laterally unconfined systems and to study applications of deliberate tracers in limnology and oceanography. Progress was made on both fronts but work on the development of the non-volatile tracer proved to be more difficult and labor intensive that anticipated so no field experiments using non-volatile tracers was performed as yet. In the search for a suitable non-volatile tracer for an ocean scale gas exchange experiment a tracer was discovered which does not have the required sensitivity for a large scale experiment, but is very easy to analyze and will be well suited for smaller experiments such as gas exchange determinations on rivers and streams. Sulfur hexafluoride, SF6, was used successfully as a volatile tracer along with tritium as a non-volatile tracer to study gas exchange rates from a primary stream. This is the first gas exchange experiment in which gas exchange rates were determined on a head water stream where significant groundwater input occurs along the reach. In conjunction with SF6, Radon-222 measurements were performed on the groundwater and in the stream. The feasibility of using a combination of SF6 and radon is being studied to determine groundwater inputs and gas exchange of rates in streams with significant groundwater input without using a non-volatile tracer.

  4. Leaf gas exchange in the frankincense tree (Boswellia papyrifera) of African dry woodlands.

    PubMed

    Mengistu, Tefera; Sterck, Frank J; Fetene, Masresha; Tadesse, Wubalem; Bongers, Frans

    2011-07-01

    A conceptual model was tested for explaining environmental and physiological effects on leaf gas exchange in the deciduous dry tropical woodland tree Boswellia papyrifera (Del.) Hochst. For this species we aimed at (i) understanding diurnal patterns in leaf gas exchange, (ii) exploring cause-effect relationships among external environment, internal physiology and leaf gas exchange, and (iii) exploring site differences in leaf gas exchange in response to environmental variables. Diurnal courses in gas exchange, underlying physiological traits and environmental variables were measured for 90 trees on consecutive days at two contrasting areas, one at high and the other at low altitude. Assimilation was highest in the morning and slightly decreased during the day. In contrast, transpiration increased from early morning to midday, mainly in response to an increasing vapor pressure deficit (VPD) and gradual stomatal closure. The leaf water potential varied relatively little and did not influence gas exchange during the measurement period. Our results suggest that the same cause-effect relationships function at contrasting areas. However, leaves at the higher altitude had higher photosynthetic capacity, reflecting acclimation to higher light levels. Trees at both areas nevertheless achieved similar leaf assimilation rates since assimilation was down-regulated by stomatal closure due to the higher VPD at the higher altitude, while it became more light limited at the lower altitude. Gas exchange was thus limited by a high VPD or low light levels during the wet season, despite the ability of the species to acclimate to different conditions. PMID:21849593

  5. A dynamic leaf gas-exchange strategy is conserved in woody plants under changing ambient CO2: evidence from carbon isotope discrimination in paleo and CO2 enrichment studies

    EPA Science Inventory

    Rising atmospheric [CO2], ca, is expected to affect stomatal regulation of leaf gas-exchange of woody plants, thus influencing energy fluxes as well as carbon (C), water and nutrient cycling of forests. Researchers have reported that stomata regulate leaf gas-exchange around &ldq...

  6. The Relationships between Clan Culture, Leader-Member Exchange, and Affective Organizational Commitment

    ERIC Educational Resources Information Center

    Short, Emily Carter

    2013-01-01

    As colleges and universities face the challenge of transitioning to a scheme of funding based on student retention and graduation rates, it is imperative that all variables that can effect enrollment be considered. This study focused on the relationships between clan culture, leader-member exchange, and affective organizational commitment.…

  7. Mother-Toddler Affect Exchanges and Children's Mastery Behaviours during Preschool Years

    ERIC Educational Resources Information Center

    Wang, Jun; Morgan, George A.; Biringen, Zeynep

    2014-01-01

    This study examined the longitudinal relations of mother-child affect exchanges at 18?months with children's mastery motivation at 39?months. Observation and questionnaire data were collected from mother-child dyads when children were 18?months; 43 mothers again rated their children's mastery motivation at 39?months. Results suggested…

  8. Whole Plant and Leaf Steady State Gas Exchange during Ethylene Exposure in Xanthium strumarium L. 1

    PubMed Central

    Woodrow, Lorna; Jiao, Jirong; Tsujita, M. James; Grodzinski, Bernard

    1989-01-01

    The effects of ethylene evolved from ethephon on leaf and whole plant photosynthesis in Xanthium strumarium L. were examined. Ethylene-induced epinasty reduced light interception by the leaves of ethephon treated plants by up to 60%. Gas exchange values of individual, attached leaves under identical assay conditions were not inhibited even after 36 hours of ethylene exposure, although treated leaves required a longer induction period to achieve steady state photosynthesis. The speed of translocation of recently fixed 11C-assimilate movement was not seriously impaired following ethephon treatment; however, a greater proportion of the assimilate was partitioned downward toward the roots. Within 24 hours of ethephon treatment, the whole plant net carbon exchange rate expressed on a per plant basis or a leaf area basis had dropped by 35%. The apparent inhibition of net carbon exchange rate was reversed by physically repositioning the leaves with respect to the light source. Ethylene exposure also inhibited expansion of young leaves which was partially reversed when the leaves were repositioned. The data indicated that ethylene indirectly affected net C gain and plant growth through modification of light interception and altered sink demand without directly inhibiting leaf photosynthesis. Images Figure 1 PMID:16666773

  9. Gas exchange-wind speed relation measured with sulfur hexafluoride on a lake

    NASA Technical Reports Server (NTRS)

    Wanninkhof, R.; Broecker, W. S.; Ledwell, J. R.

    1985-01-01

    Gas-exchange processes control the uptake and release of various gases in natural systems such as oceans, rivers, and lakes. Not much is known about the effect of wind speed on gas exchange in such systems. In the experiment described here, sulfur hexafluoride was dissolved in lake water, and the rate of escape of the gas with wind speed (at wind speeds up to 6 meters per second) was determined over a 1-month period. A sharp change in the wind speed dependence of the gas-exchange coefficient was found at wind speeds of about 2.4 meters per second, in agreement with the results of wind-tunnel studies. However the gas-exchange coefficients at wind speeds above 3 meters per second were smaller than those observed in wind tunnels and are in agreement with earlier lake and ocean results.

  10. Ceramic heat exchangers for gas turbines or turbojets

    NASA Astrophysics Data System (ADS)

    Boudigues, S.; Fabri, J.

    The required performance goals and several proposed designs for SiC heat exchangers for aerospace turbines are presented. Ceramic materials are explored as a means for achieving higher operating temperatures while controlling the weight and cost of the heat exchangers. Thermodynamic analyses and model tests by ONERA have demonstrated the efficacy of introducing a recooling cycle and placing the heat exchangers between stages of the turbine. Sample applications are discussed for small general aviation aircraft and subsonic missiles equipped with single-flux exchangers. A double-flux exchanger is considered for an aircraft capable of Mach 0.8 speed and at least 11 km altitude for cruise. Finally, the results of initial attempts to manufacture SiC honeycomb heat exchangers are detailed.

  11. Prototype Vent Gas Heat Exchanger for Exploration EVA - Performance and Manufacturing Characteristics

    NASA Technical Reports Server (NTRS)

    Quinn, Gregory J.; Strange, Jeremy; Jennings, Mallory

    2013-01-01

    NASA is developing new portable life support system (PLSS) technologies, which it is demonstrating in an unmanned ground based prototype unit called PLSS 2.0. One set of technologies within the PLSS provides suitable ventilation to an astronaut while on an EVA. A new component within the ventilation gas loop is a liquid-to-gas heat exchanger to transfer excess heat from the gas to the thermal control system s liquid coolant loop. A unique bench top prototype heat exchanger was built and tested for use in PLSS 2.0. The heat exchanger was designed as a counter-flow, compact plate fin type using stainless steel. Its design was based on previous compact heat exchangers manufactured by United Technologies Aerospace Systems (UTAS), but was half the size of any previous heat exchanger model and one third the size of previous liquid-to-gas heat exchangers. The prototype heat exchanger was less than 40 cubic inches and weighed 2.57 lb. Performance of the heat exchanger met the requirements and the model predictions. The water side and gas side pressure drops were less 0.8 psid and 0.5 inches of water, respectively, and an effectiveness of 94% was measured at the nominal air side pressure of 4.1 psia.

  12. Flat-plate, gas-to-gas heat exchanger recovers 1. 5 million Btu/hr from perlite production

    SciTech Connect

    Hench, R.; Hodel, A.E.; Regan, J.T.

    1986-08-01

    Calshake, a mineral shake shingle manufacturer in Irwindale, CA started having problems with a carbon steel, gas-to-gas process heat exchanger when the plant changed their perlite popping process from a three shift to a two shift operation. The first evidence of trouble was a loss of air volume throughput. Then the heat transfer efficiency of the stationary flatplate heat exchanger was reduced. The economy of the operation continued to diminish as fans drawing gases through the exchanger had to work harder. Finally the plant was forced to shut down the processing line. Calshake replaced the single, 20' long carbon steel, flat-plate heat exchanger with two, 10' long, modular, stainless steel units from the same manufacturer. The new exchangers were installed vertically in series to provide basically the same 20' long heat transfer surface. The flow path on the hot side was made continuous. The flow path on the cold side was interrupted by a duct joining the top and bottom units. Counterflow conditions were maintained just as they were in the original unit. The flat-plate, gas-to-gas heat exchanger recovers 1.5 million Btu/hr from perlite production. The new exchanger gives nearly twice the recovery of the system it replaced. Since installation in August 1985 it has required only minor maintenance (total downtime of 9 hours) and has performed above expectations.

  13. Pulmonary and cutaneous O₂gas exchange: a student laboratory exercise in the frog.

    PubMed

    Tattersall, Glenn J; Currie, Suzanne; LeBlanc, Danielle M

    2013-03-01

    Gas exchange in animals is ultimately diffusion based, generally occurring across dedicated respiratory organs. In many aquatic amphibians, however, multiple modes of gas exchange exist, allowing for the partitioning of O2 uptake and CO2 excretion between respiratory organs with different efficiencies. For example, due to the physical properties of O2 being vastly different between air and water phases, the lung and skin play disproportionately important roles in O2 uptake. Many aquatic frogs are renowned for their cutaneous gas exchange capacity, where often the majority of CO2 is excreted across the skin. Furthermore, the roles of these gas exchange organs change with the animal's behavior. Under diving conditions, most of the frog's gas exchange needs must be met by the skin. In this article, we describe an interactive undergraduate laboratory that allows a class of students to share equipment while assessing pulmonary and cutaneous respiration in frogs provided with an air/water choice and under enforced dive conditions. Concepts explored in this laboratory exercise include animal energetics, diving reflex, pulmonary and cutaneous gas exchange processes, diffusion-based gas flux, and O2 debt. PMID:23471257

  14. Discontinuous gas exchange exhibition is a heritable trait in speckled cockroaches Nauphoeta cinerea.

    PubMed

    Schimpf, N G; Matthews, P G D; White, C R

    2013-07-01

    The regulation of insect respiratory gas exchange has long been an area of interest. In particular, the reason why insects from at least five orders exhibit patterns of gas exchange that include regular periods of spiracular closure has been the source of much controversy. Three adaptive hypotheses propose that these discontinuous gas-exchange cycles (DGCs) evolved to either limit water loss across respiratory surfaces, facilitate gas exchange in underground environments or to limit oxidative damage. It is possible that DGCs evolved independently multiple times and for different reasons, but for DGCs to be a plausible target for natural selection, they must be heritable and confer a fitness benefit. In a previous study of cockroaches Nauphoeta cinerea, we demonstrated that DGCs are repeatable and extend survival under food and water restriction. Here, we show for the first time that DGCs are heritable, suggesting that they are a plausible target for natural selection. PMID:23662792

  15. [Prone position: effect on gas exchange and functional capacity for exercise in patients with pulmonary hypertension].

    PubMed

    Bastidas-L, Andrea Carolina; Colina-Chourio, José A; Guevara, Jesnel M; Nunez, Alexis

    2015-03-01

    The objective of this investigation was to evaluate gas exchange and cardiopulmonary functional behavior in patients with pulmonary hypertension (PH) before, during and after the change to a prone position. Thirty patients with PH and alterations in gas exchange were included in the study. Gas exchange measurements were performed in four stages: at the baseline supine position and after 30, 120 and 240 minutes in prone position. Also, the patients were evaluated by the six minutes walking test (6MWT) after 30 days in prone position during night's sleep. After four hours in prone position, all patients showed an increase of PaO2 and arterial saturation of oxygen (SaO2), with a decrease of intrapulmonary shunts, improving the gas exchange and therefore the physiological demand imposed by exercise in patients with PH. PMID:25920183

  16. Tuning a High Transmission Ion Guide to Prevent Gas-Phase Proton Exchange During H/D Exchange MS Analysis.

    PubMed

    Guttman, Miklos; Wales, Thomas E; Whittington, Dale; Engen, John R; Brown, Jeffery M; Lee, Kelly K

    2016-04-01

    Hydrogen/deuterium exchange (HDX) mass spectrometry (MS) for protein structural analysis has been adopted for many purposes, including biopharmaceutical development. One of the benefits of examining amide proton exchange by mass spectrometry is that it can readily resolve different exchange regimes, as evidenced by either binomial or bimodal isotope patterns. By careful analysis of the isotope pattern during exchange, more insight can be obtained on protein behavior in solution. However, one must be sure that any observed bimodal isotope patterns are not artifacts of analysis and are reflective of the true behavior in solution. Sample carryover and certain stationary phases are known as potential sources of bimodal artifacts. Here, we describe an additional undocumented source of deuterium loss resulting in artificial bimodal patterns for certain highly charged peptides. We demonstrate that this phenomenon is predominantly due to gas-phase proton exchange between peptides and bulk solvent within the initial stages of high-transmission conjoined ion guides. Minor adjustments of the ion guide settings, as reported here, eliminate the phenomenon without sacrificing signal intensity. Such gas-phase deuterium loss should be appreciated for all HDX-MS studies using such ion optics, even for routine studies not focused on interpreting bimodal spectra. Graphical Abstract ᅟ. PMID:26810432

  17. Tuning a High Transmission Ion Guide to Prevent Gas-Phase Proton Exchange During H/D Exchange MS Analysis

    NASA Astrophysics Data System (ADS)

    Guttman, Miklos; Wales, Thomas E.; Whittington, Dale; Engen, John R.; Brown, Jeffery M.; Lee, Kelly K.

    2016-04-01

    Hydrogen/deuterium exchange (HDX) mass spectrometry (MS) for protein structural analysis has been adopted for many purposes, including biopharmaceutical development. One of the benefits of examining amide proton exchange by mass spectrometry is that it can readily resolve different exchange regimes, as evidenced by either binomial or bimodal isotope patterns. By careful analysis of the isotope pattern during exchange, more insight can be obtained on protein behavior in solution. However, one must be sure that any observed bimodal isotope patterns are not artifacts of analysis and are reflective of the true behavior in solution. Sample carryover and certain stationary phases are known as potential sources of bimodal artifacts. Here, we describe an additional undocumented source of deuterium loss resulting in artificial bimodal patterns for certain highly charged peptides. We demonstrate that this phenomenon is predominantly due to gas-phase proton exchange between peptides and bulk solvent within the initial stages of high-transmission conjoined ion guides. Minor adjustments of the ion guide settings, as reported here, eliminate the phenomenon without sacrificing signal intensity. Such gas-phase deuterium loss should be appreciated for all HDX-MS studies using such ion optics, even for routine studies not focused on interpreting bimodal spectra.

  18. Gas exchange patterns and water loss rates in the Table Mountain cockroach, Aptera fusca (Blattodea: Blaberidae).

    PubMed

    Groenewald, Berlizé; Bazelet, Corinna S; Potter, C Paige; Terblanche, John S

    2013-10-15

    The importance of metabolic rate and/or spiracle modulation for saving respiratory water is contentious. One major explanation for gas exchange pattern variation in terrestrial insects is to effect a respiratory water loss (RWL) saving. To test this, we measured the rates of CO2 and H2O release ( and , respectively) in a previously unstudied, mesic cockroach, Aptera fusca, and compared gas exchange and water loss parameters among the major gas exchange patterns (continuous, cyclic, discontinuous gas exchange) at a range of temperatures. Mean , and per unit did not differ among the gas exchange patterns at all temperatures (P>0.09). There was no significant association between temperature and gas exchange pattern type (P=0.63). Percentage of RWL (relative to total water loss) was typically low (9.79±1.84%) and did not differ significantly among gas exchange patterns at 15°C (P=0.26). The method of estimation had a large impact on the percentage of RWL, and of the three techniques investigated (traditional, regression and hyperoxic switch), the traditional method generally performed best. In many respects, A. fusca has typical gas exchange for what might be expected from other insects studied to date (e.g. , , RWL and cuticular water loss). However, we found for A. fusca that expressed as a function of metabolic rate was significantly higher than the expected consensus relationship for insects, suggesting it is under considerable pressure to save water. Despite this, we found no consistent evidence supporting the conclusion that transitions in pattern type yield reductions in RWL in this mesic cockroach. PMID:23821716

  19. A hierarchy of factors influence discontinuous gas exchange in the grasshopper Paracinema tricolor (Orthoptera: Acrididae).

    PubMed

    Groenewald, Berlizé; Chown, Steven L; Terblanche, John S

    2014-10-01

    The evolutionary origin and maintenance of discontinuous gas exchange (DGE) in tracheate arthropods are poorly understood and highly controversial. We investigated prioritization of abiotic factors in the gas exchange control cascade by examining oxygen, water and haemolymph pH regulation in the grasshopper Paracinema tricolor. Using a full-factorial design, grasshoppers were acclimated to hypoxic or hyperoxic (5% O2, 40% O2) gas conditions, or dehydrated or hydrated, whereafter their CO2 release was measured under a range of O2 and relative humidity (RH) conditions (5%, 21%, 40% O2 and 5%, 60%, 90% RH). DGE was significantly less common in grasshoppers acclimated to dehydrating conditions compared with the other acclimations (hypoxia, 98%; hyperoxia, 100%; hydrated, 100%; dehydrated, 67%). Acclimation to dehydrating conditions resulted in a significant decrease in haemolymph pH from 7.0±0.3 to 6.6±0.1 (mean ± s.d., P=0.018) and also significantly increased the open (O)-phase duration under 5% O2 treatment conditions (5% O2, 44.1±29.3 min; 40% O2, 15.8±8.0 min; 5% RH, 17.8±1.3 min; 60% RH, 24.0±9.7 min; 90% RH, 20.6±8.9 min). The observed acidosis could potentially explain the extension of the O-phase under low RH conditions, when it would perhaps seem more useful to reduce the O-phase to lower respiratory water loss. The results confirm that DGE occurrence and modulation are affected by multiple abiotic factors. A hierarchical framework for abiotic factors influencing DGE is proposed in which the following stressors are prioritized in decreasing order of importance: oxygen supply, CO2 excretion and pH modulation, oxidative damage protection and water savings. PMID:25063854

  20. Noninvasive detection of gas exchange rate by near infrared spectroscopy

    NASA Astrophysics Data System (ADS)

    Xu, Guodong; Mao, Zongzhen; Wang, Bangde

    2008-12-01

    In order to study the relationship among the oxygen concentration in skeletal muscle tissues and the heart rate (HR), oxygen uptake (VO2), respiratory exchange ratio (RER) during incremental running exercises on a treadmill, a near-infrared spectroscopy muscle oxygen monitor system is employed to measure the relative change in muscle oxygenation, with the heart rate, oxygen uptake, production of carbon dioxide (VCO2) and respiratory exchange ratio are recorded synchronously. The results indicate parameters mentioned above present regular changes during the incremental exercise. High correlations are discovered between relative change of oxy-hemoglobin concentration and heart rate, oxygen uptake, respiratory exchange ratio at the significance level (P=0.01). This research might introduce a new measurement technology and/or a novel biological monitoring parameter to the evaluation of physical function status, control the training intensity, estimation of the effectiveness of exercise. Keywords: near-infrared spectroscopy; muscle oxygen concentration; heart rate; oxygen uptake; respiratory exchange ratio.

  1. Leader-member exchange and affective organizational commitment: the contribution of supervisor's organizational embodiment.

    PubMed

    Eisenberger, Robert; Karagonlar, Gokhan; Stinglhamber, Florence; Neves, Pedro; Becker, Thomas E; Gonzalez-Morales, M Gloria; Steiger-Mueller, Meta

    2010-11-01

    In order to account for wide variation in the relationship between leader-member exchange and employees' affective organizational commitment, we propose a concept termed supervisor's organizational embodiment (SOE), which involves the extent to which employees identify their supervisor with the organization. With samples of 251 social service employees in the United States (Study 1) and 346 employees in multiple Portuguese organizations (Study 2), we found that as SOE increased, the association between leader-member exchange and affective organizational commitment became greater. This interaction carried through to in-role and extra-role performance. With regard to antecedents, we found in Study 1 that supervisor's self-reported identification with the organization increased supervisor's expression of positive statements about the organization, which in turn increased subordinates' SOE. PMID:20718516

  2. Almitrine has no effect on gas exchange after bilateral carotid body resection in severe chronic airflow obstruction.

    PubMed

    De Backer, W; Vermeire, P; Bogaert, E; Janssens, E; Van Maele, R

    1985-01-01

    Using a double-blind cross-over design, a single dose of 100 mg almitrine bismesylate and placebo were administered orally to eight patients with chronic airflow obstruction having undergone bilateral carotid body resection (BCBR) up to two years earlier to alleviate their extreme dyspnoea. In an open study, two other patients have been given almitrine before and three weeks after BCBR. In all patients, arterial blood gases, ventilation and breathing patterns, neuromuscular drive and hypoxic responsiveness have been studied before and three hours after drug administration. Almitrine failed to improve gas exchange in the patients with BCBR, nor did it affect ventilation, ventilatory or hypoxic drive. In the patients studied before and after BCBR, almitrine only improved gas exchange significantly before BCBR. It is concluded that in man almitrine acts solely as a peripheral chemoreceptor agonist and that the well-documented improvement in V/Q relationship is mediated through carotid body stimulation. PMID:3904873

  3. Lagrangian evolution of DMS during the Southern Ocean gas exchange experiment: The effects of vertical mixing and biological community shift

    NASA Astrophysics Data System (ADS)

    Yang, M.; Archer, S. D.; Blomquist, B. W.; Ho, D. T.; Lance, V. P.; Torres, R. J.

    2013-12-01

    Concentrations of dimethylsulfide (DMS) and its precursor dimethylsulfoniopropionate (DMSP) are highly variable in time and space. What is driving the variability in DMS(P), and can those variability be explained by physical processes and changes in the biological community? During the Southern Ocean Gas Exchange Experiment (SO GasEx) in the austral fall of 2008, two 3He/SF6 labeled patches were created in the surface water. SF6 and DMS were surveyed continuously in a Lagrangian framework, while direct measurements of air-sea exchange further constrained the gas budgets. Turbulent diffusivity at the base of the mixed layer was estimated from SF6 profiles and used to calculate the vertical fluxes of DMS and nutrients. Increasing mixed layer nutrient concentrations due to mixing were associated with a shift in the phytoplankton community structure, which in turned likely affected the sulfur dynamics on timescales of days. DMS concentration as well as air-sea DMS flux appeared to be decoupled from the DMSP concentration, possibly due to grazing and bacterial DMS production. Contrary to expectations, in an environment with high winds and modest productivity, physical processes (air-sea exchange, photochemistry, vertical mixing) only accounted for a small fraction of DMS loss from the surface water. Among the DMS sinks, inferred biological consumption most likely dominated during SO GasEx.

  4. Hydraulically actuated gas exchange valve assembly and engine using same

    DOEpatents

    Carroll, Thomas S.; Taylor, Gregory O.

    2002-09-03

    An engine comprises a housing that defines a hollow piston cavity that is separated from a gas passage by a valve seat. The housing further defines a biasing hydraulic cavity and a control hydraulic cavity. A gas valve member is also included in the engine and is movable relative to the valve seat between an open position at which the hollow piston cavity is open to the gas passage and a closed position in which the hollow piston cavity is blocked from the gas passage. The gas valve member includes a ring mounted on a valve piece and a retainer positioned between the ring and the valve piece. A closing hydraulic surface is included on the gas valve member and is exposed to liquid pressure in the biasing hydraulic cavity.

  5. Respiratory dynamics of discontinuous gas exchange in the tracheal system of the desert locust, Schistocerca gregaria.

    PubMed

    Groenewald, Berlizé; Hetz, Stefan K; Chown, Steven L; Terblanche, John S

    2012-07-01

    Gas exchange dynamics in insects is of fundamental importance to understanding evolved variation in breathing patterns, such as discontinuous gas exchange cycles (DGCs). Most insects do not rely solely on diffusion for the exchange of respiratory gases but may also make use of respiratory movements (active ventilation) to supplement gas exchange at rest. However, their temporal dynamics have not been widely investigated. Here, intratracheal pressure, V(CO2) and body movements of the desert locust Schistocerca gregaria were measured simultaneously during the DGC and revealed several important aspects of gas exchange dynamics. First, S. gregaria employs two different ventilatory strategies, one involving dorso-ventral contractions and the other longitudinal telescoping movements. Second, although a true spiracular closed (C)-phase of the DGC could be identified by means of subatmospheric intratracheal pressure recordings, some CO(2) continued to be released. Third, strong pumping actions do not necessarily lead to CO(2) release and could be used to ensure mixing of gases in the closed tracheal system, or enhance water vapour reabsorption into the haemolymph from fluid-filled tracheole tips by increasing the hydrostatic pressure or forcing fluid into the haemocoel. Finally, this work showed that the C-phase of the DGC can occur at any pressure. These results provide further insights into the mechanistic basis of insect gas exchange. PMID:22675191

  6. Free volume and gas permeation in ion-exchanged forms of the Nafion® membrane

    NASA Astrophysics Data System (ADS)

    Mohamed, Hamdy F. M.; Kobayashi, Y.; Kuroda, C. S.; Ohira, A.

    2010-04-01

    Variations of free volume and gas permeability of the Nafion® membrane upon ion-exchange of H+ with Cs+ or Pt2+ was studied as a function of temperature. Free volume was quantified using the positron annihilation lifetime technique. Our results showed that the free volume (VFV,Ps) of the dried membrane is enlarged by thermal expansion. It was found that the ion-exchange significantly expands the free volume and at the same time decreases the permeabilities of O2 and H2. Good linear correlations between the logarithm of permeabilities of O2 and H2 at different temperatures and 1/VFV,Ps for the ion-exchanged forms of Nafion® in the dried state suggest an important role played by the free volume in gas permeation. Considerable downward deviation of the correlations for the ion-exchanged ionomers from the H+-form suggested the importance of polymer stiffening in gas permeation.

  7. High effectiveness liquid droplet/gas heat exchanger for space power applications

    NASA Technical Reports Server (NTRS)

    Bruckner, A. P.; Mattick, A. T.

    1983-01-01

    A high-effectiveness liquid droplet/gas heat exchanger (LDHX) concept for thermal management in space is described. Heat is transferred by direct contact between fine droplets (approximately 100-300 microns in diameter) of a suitable low vapor pressure liquid and an inert working gas. Complete separation of the droplet and gas media in the zero-g environment is accomplished by configuring the LDHX as a vortex chamber.The large heat transfer area presented by the small droplets permits heat exchanger effectiveness of 0.9-0.95 in a compact, lightweight geometry which avoids many of the limitations of conventional plate and fin or tube and shell heat exchangers, such as their tendency toward single point failure. The application of the LDHX in a high temperature Brayton cycle is discussed to illustrate the performance and operational characteristics of this new heat exchanger concept.

  8. High effectiveness liquid droplet/gas heat exchanger for space power applications

    NASA Technical Reports Server (NTRS)

    Bruckner, A. P.; Mattick, A. T.

    1983-01-01

    A high-effectiveness liquid droplet/gas heat exchanger (LDHX) concept for thermal management in space is described. Heat is transferred by direct contact between fine droplets (approx. 100 to 300 micron diameter) of a suitable low vapor pressure liquid and an inert working gas. Complete separation of the droplet and gas media in the zero-g environment is accomplished by configuring the LDHX as a vortex chamber. The large heat transfer area presented by the small droplets permits heat exchanger effectiveness of 0.9 to 0.95 in a compact, lightweight geometry which avoids many of the limitations of conventional plate and fin or tube and shell heat exchangers, such as their tendency toward single point failure. The application of the LDHX in a high temperature Bryaton cycle is discussed to illustrate the performance and operational characteristics of this heat exchanger concept.

  9. Radiation from Large Gas Volumes and Heat Exchange in Steam Boiler Furnaces

    SciTech Connect

    Makarov, A. N.

    2015-09-15

    Radiation from large cylindrical gas volumes is studied as a means of simulating the flare in steam boiler furnaces. Calculations of heat exchange in a furnace by the zonal method and by simulation of the flare with cylindrical gas volumes are described. The latter method is more accurate and yields more reliable information on heat transfer processes taking place in furnaces.

  10. Teaching Pulmonary Gas Exchange Physiology Using Computer Modeling

    ERIC Educational Resources Information Center

    Kapitan, Kent S.

    2008-01-01

    Students often have difficulty understanding the relationship of O[subscript 2] consumption, CO[subscript 2] production, cardiac output, and distribution of ventilation-perfusion ratios in the lung to the final arterial blood gas composition. To overcome this difficulty, I have developed an interactive computer simulation of pulmonary gas exchange…

  11. Homeostatic maintenance of ponderosa pine gas exchange in response to stand density changes.

    PubMed

    McDowell, Nate G; Adams, Henry D; Bailey, John D; Hess, Marcey; Kolb, Thomas E

    2006-06-01

    Homeostatic maintenance of gas exchange optimizes carbon gain per water loss. Homeostasis is regulated by short-term physiological and long-term structural mechanisms, both of which may respond to changes in resource availability associated with competition. Therefore, stand density regulation via silvicultural manipulations may facilitate growth and survival through mechanisms operating at both short and long timescales. We investigated the responses of ponderosa pine (Pinus ponderosa) to stand basal area manipulations in Arizona, USA. Stand basal area was manipulated to seven replicated levels in 1962 and was maintained for four decades by decadal thinning. We measured basal area increment (BAI) to assess the response and sustainability of wood growth, carbon isotope discrimination (A) inferred from annual rings to assess the response of crown gas exchange, and ratios of leaf area to sapwood area (A(l):A(s)) to assess longer term structural acclimation. Basal area treatments increased soil water potential (r2 = 0.99) but did not affect photosynthetic capacity. BAI increased within two years of thinning, and the 40-year mean BAI was negatively correlated with stand basal area (r2 = 0.98). delta was negatively correlated with stand basal area for years 5 through 12 after thinning (r2 = 0.90). However, delta was relatively invariant with basal area for the period 13-40 years after initial thinning despite maintenance of treatment basal areas via repeated decadal thinnings. Independent gas exchange measurements verified that the ratio of photosynthesis to stomatal conductance was invariant with basal area, but absolute values of both were elevated at lower basal areas. A(l):A(s) was negatively correlated with basal area (r2 = 0.93). We hypothesize that increased A(l):A(s) is a homeostatic response to increased water availability that maximizes water-use efficiency and whole-tree carbon uptake. Elevated A(l):A(s) of trees at low basal areas was associated with greater

  12. Fundamental structural aspects and features in the bioengineering of the gas exchangers: comparative perspectives.

    PubMed

    Maina, J N

    2002-01-01

    Over its life, an organism's survival and success are determined by the inventory of vital adaptations that its progenitors have creatively appropriated, devised and harnessed along the evolutionary pathway. Such conserved attributes provide the armamentarium necessary for withstanding the adverse effects of natural selection. Refinements of the designs of the respiratory organs have been critical for survival and phylogenetic advancement of animal life. Gas exchangers have changed in direct response to the respiratory needs of whole organisms in different environmental states and conditions. Nowhere else is the dictum that in biology 'there are no rules but only necessities' more manifest than in the evolutionary biology of the gas exchangers. The constructions have been continually fashioned and refined to meet specific needs. Solutions to common respiratory needs have been typified by profound structural convergence. Over the evolutionary continuum, as shifts in environmental situations occurred, infinitely many designs should theoretically have emerged. Moreover, without specific selective pressures and preference for certain designs, considering that there are only two naturally occurring respirable fluid media (air and water), air-lungs, water-lungs, air-gills and water-gills would have formed to similar extents. Factors such as body size, phylogenetic level of development, respiratory medium utilized and habitats occupied have permutatively prescribed the design of the gas exchangers. The construction of the modern gas exchangers has eventuated through painstaking cost-benefit analysis. Trade-offs and compromises have decreed only a limited number of structurally feasible and functionally competent outcomes. The morphological congruity (analogy) of the gas exchangers indicates that similar selective pressures have compelled the designs. Solutions to metabolic demands for molecular O2 have only differed in details. Passive physical diffusion, for example, is

  13. The role of bubbles during air-sea gas exchange

    NASA Astrophysics Data System (ADS)

    Emerson, Steven; Bushinsky, Seth

    2016-06-01

    The potential for using the air-sea exchange rate of oxygen as a tracer for net community biological production in the ocean is greatly enhanced by recent accuracy improvements for in situ measurements of oxygen on unmanned platforms. A limiting factor for determining the exchange process is evaluating the air-sea flux contributed by bubble processes produced by breaking waves, particularly during winter months under high winds. Highly accurate measurements of noble gases (Ne, Ar & Kr) and nitrogen, N2, in seawater are tracers of the importance of bubble process in the surface mixed layer. We use measured distributions of these gases in the ventilated thermocline of the North Pacific and an annual time series of N2 in the surface ocean of the NE Subarctic Pacific to evaluate four different air-water exchange models chosen to represent the range of model interpretation of bubble processes. We find that models must have an explicit bubble mechanism to reproduce concentrations of insoluble atmospheric gases, but there are periods when they all depart from observations. The recent model of Liang et al. (2013) stems from a highly resolved model of bubble plumes and categorizes bubble mechanisms into those that are small enough to collapse and larger ones that exchange gases before they resurface, both of which are necessary to explain the data.

  14. 40 CFR 60.5375 - What standards apply to gas well affected facilities?

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 7 2013-07-01 2013-07-01 false What standards apply to gas well... Performance for Crude Oil and Natural Gas Production, Transmission and Distribution § 60.5375 What standards apply to gas well affected facilities? If you are the owner or operator of a gas well affected...

  15. 40 CFR 60.5375 - What standards apply to gas well affected facilities?

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 7 2014-07-01 2014-07-01 false What standards apply to gas well... Performance for Crude Oil and Natural Gas Production, Transmission and Distribution § 60.5375 What standards apply to gas well affected facilities? If you are the owner or operator of a gas well affected...

  16. More than just CO2: Multiple trace gas exchange measurements at a temperate mountain grassland

    NASA Astrophysics Data System (ADS)

    Wohlfahrt, Georg; Hammerle, Albin; Hörtnagl, Lukas; Bamberger, Ines; Hansel, Armin

    2015-04-01

    Ecosystems exchange a large number of different trace gases to/from the atmosphere, however the vast majority of FLUXNET sites quantifies only the fluxes of carbon dioxide and when assessing the carbon or greenhouse gas balance neglect other carbon or greenhouse gas fluxes. This causes an overestimation of the role of carbon dioxid exchange for the ecosystem carbon and greenhouse gas balance, the magnitude of which is largely unconstrained Here we use the eddy covariance method (and variants thereof) with a large variety of analytical methods to quantify the exchange of multiple trace gases to/from a mountain grassland, partly for a time period of over a decade. The monitored trace gas fluxes cover: carbon dioxide, methane, nitrous oxide, carbon monoxide and several volatile organic compounds. The main result of our study is that carbon dioxide is the major contributor to the gaseous carbon and greenhouse gas budget at this temperate mountain grassland, which however may be significantly modulated by other trace gases may, at least during some years. Differences between source and sink periods for the different trace gases and the underlying drivers are discussed and annual budgets, for some compounds covering multiple years up to decades, are presented. We conclude that multiple trace gas flux measurements help to elucidate the importance of the exchange of carbon dioxide for the ecosystem carbon and greenhouse gas budget.

  17. Discontinuous gas exchange, water loss, and metabolism in Protaetia cretica (Cetoniinae, Scarabaeidae).

    PubMed

    Matthews, Philip G D; White, Craig R

    2012-01-01

    Insects are at high risk of desiccation because of their small size, high surface-area-to-volume ratio, and air-filled tracheal system that ramifies throughout their bodies to transport O(2) and CO(2) to and from respiring cells. Although the tracheal system offers a high-conductance pathway for the movement of respiratory gases, it has the unintended consequence of allowing respiratory transpiration to the atmosphere. When resting, many species exchange respiratory gases discontinuously, and an early hypothesis for the origin of these discontinuous gas exchange cycles (DGCs) is that they serve to reduce respiratory water loss. In this study, we test this "hygric" hypothesis by comparing rates of CO(2) exchange and water loss among flower beetles Protaetia cretica (Cetoniinae, Scarabaeidae) breathing either continuously or discontinuously. We show that, consistent with the expectations of the hygric hypothesis, rates of total water loss are higher during continuous gas exchange than during discontinuous gas exchange and that the ratio of respiratory water loss to CO(2) exchange is lower during discontinuous gas exchange. This conclusion is in agreement with other studies of beetles and cockroaches that also support the hygric hypothesis. However, this result does not exclude other adaptive hypotheses supported by work on ants and moth pupae. This ambiguity may arise because there are multiple independent evolutionary origins of DGCs and no single adaptive function underlying their genesis. Alternatively, the observed reduction in water loss during DGCs may be a side effect of a nonadaptive gas exchange pattern that is elicited during periods of inactivity. PMID:22418709

  18. A meta-analysis of leaf gas exchange and water status responses to drought

    PubMed Central

    Yan, Weiming; Zhong, Yangquanwei; Shangguan, Zhouping

    2016-01-01

    Drought is considered to be one of the most devastating natural hazards, and it is predicted to become increasingly frequent and severe in the future. Understanding the plant gas exchange and water status response to drought is very important with regard to future climate change. We conducted a meta-analysis based on studies of plants worldwide and aimed to determine the changes in gas exchange and water status under different drought intensities (mild, moderate and severe), different photosynthetic pathways (C3 and C4) and growth forms (herbs, shrubs, trees and lianas). Our results were as follows: 1) drought negatively impacted gas exchange and water status, and stomatal conductance (gs) decreased more than other physiological traits and declined to the greatest extent in shrubs and C3 plants. Furthermore, C4 plants had an advantage compared to C3 plants under the same drought conditions. 2) The decrease in gs mainly reduced the transpiration rate (Tr), and gs could explain 55% of the decrease in the photosynthesis (A) and 74% of the decline in Tr. 3). Finally, gas exchange showed a close relationship with the leaf water status. Our study provides comprehensive information about the changes in plant gas exchange and water status under drought. PMID:26868055

  19. A meta-analysis of leaf gas exchange and water status responses to drought.

    PubMed

    Yan, Weiming; Zhong, Yangquanwei; Shangguan, Zhouping

    2016-01-01

    Drought is considered to be one of the most devastating natural hazards, and it is predicted to become increasingly frequent and severe in the future. Understanding the plant gas exchange and water status response to drought is very important with regard to future climate change. We conducted a meta-analysis based on studies of plants worldwide and aimed to determine the changes in gas exchange and water status under different drought intensities (mild, moderate and severe), different photosynthetic pathways (C3 and C4) and growth forms (herbs, shrubs, trees and lianas). Our results were as follows: 1) drought negatively impacted gas exchange and water status, and stomatal conductance (gs) decreased more than other physiological traits and declined to the greatest extent in shrubs and C3 plants. Furthermore, C4 plants had an advantage compared to C3 plants under the same drought conditions. 2) The decrease in gs mainly reduced the transpiration rate (Tr), and gs could explain 55% of the decrease in the photosynthesis (A) and 74% of the decline in Tr. 3). Finally, gas exchange showed a close relationship with the leaf water status. Our study provides comprehensive information about the changes in plant gas exchange and water status under drought. PMID:26868055

  20. Evaluation of Fiber Bundle Rotation for Enhancing Gas Exchange in a Respiratory Assist Catheter

    PubMed Central

    Eash, Heide J.; Mihelc, Kevin M.; Frankowski, Brain J.; Hattler, Brack G.; Federspiel, William J.

    2007-01-01

    Supplemental oxygenation and carbon dioxide removal through an intravenous respiratory assist catheter can be used as a means of treating patients with acute respiratory failure. We are beginning development efforts toward a new respiratory assist catheter with an insertional size <25F, which can be inserted percutaneously. In this study, we evaluated fiber bundle rotation as an improved mechanism for active mixing and enhanced gas exchange in intravenous respiratory assist catheters. Using a simple test apparatus of a rotating densely packed bundle of hollow fiber membranes, water and blood gas exchange levels were evaluated at various rotation speeds in a mock vena cava. At 12,000 RPM, maximum CO2 gas exchange rates were 449 and 523 mL/min per m², water and blood, respectively, but the rate of increase with increasing rotation rate diminished beyond 7500 RPM. These levels of gas exchange efficiency are two‐ to threefold greater than achieved in our previous respiratory catheters using balloon pulsation for active mixing. In preliminary hemolysis tests, which monitored plasma‐free hemoglobin levels in vitro over a period of 6 hours, we established that the rotating fiber bundle per se did not cause significant blood hemolysis compared with an intra‐aortic balloon pump. Accordingly, fiber bundle rotation appears to be a potential mechanism for increasing gas exchange and reducing insertional size in respiratory catheters. PMID:17515731

  1. Alveolar gas exchange and tissue oxygenation during incremental treadmill exercise, and their associations with blood O2 carrying capacity

    PubMed Central

    Rissanen, Antti-Pekka E.; Tikkanen, Heikki O.; Koponen, Anne S.; Aho, Jyrki M.; Hägglund, Harriet; Lindholm, Harri; Peltonen, Juha E.

    2012-01-01

    The magnitude and timing of oxygenation responses in highly active leg muscle, less active arm muscle, and cerebral tissue, have not been studied with simultaneous alveolar gas exchange measurement during incremental treadmill exercise. Nor is it known, if blood O2 carrying capacity affects the tissue-specific oxygenation responses. Thus, we investigated alveolar gas exchange and tissue (m. vastus lateralis, m. biceps brachii, cerebral cortex) oxygenation during incremental treadmill exercise until volitional fatigue, and their associations with blood O2 carrying capacity in 22 healthy men. Alveolar gas exchange was measured, and near-infrared spectroscopy (NIRS) was used to monitor relative concentration changes in oxy- (Δ[O2Hb]), deoxy- (Δ[HHb]) and total hemoglobin (Δ[tHb]), and tissue saturation index (TSI). NIRS inflection points (NIP), reflecting changes in tissue-specific oxygenation, were determined and their coincidence with ventilatory thresholds [anaerobic threshold (AT), respiratory compensation point (RC); V-slope method] was examined. Blood O2 carrying capacity [total hemoglobin mass (tHb-mass)] was determined with the CO-rebreathing method. In all tissues, NIPs coincided with AT, whereas RC was followed by NIPs. High tHb-mass associated with leg muscle deoxygenation at peak exercise (e.g., Δ[HHb] from baseline walking to peak exercise vs. tHb-mass: r = 0.64, p < 0.01), but not with arm muscle- or cerebral deoxygenation. In conclusion, regional tissue oxygenation was characterized by inflection points, and tissue oxygenation in relation to alveolar gas exchange during incremental treadmill exercise resembled previous findings made during incremental cycling. It was also found out, that O2 delivery to less active m. biceps brachii may be limited by an accelerated increase in ventilation at high running intensities. In addition, high capacity for blood O2 carrying was associated with a high level of m. vastus lateralis deoxygenation at peak exercise

  2. Greenhouse gas exchange in tropical mountain ecosystems in Tanzania

    NASA Astrophysics Data System (ADS)

    Gerschlauer, Friederike; Kikoti, Imani; Kiese, Ralf

    2014-05-01

    Tropical mountain ecosystems with their mostly immense biodiversity are important regions for natural resources but also for agricultural production. Their supportive ecosystem processes are particularly vulnerable to the combined impacts of global warming and the conversion of natural to human-modified landscapes. Data of impacts of climate and land use change on soil-atmosphere interactions due to GHG (CO2, CH4, and N2O) exchange from these ecosystems are still scarce, in particular for Africa. Tropical forest soils are underestimated as sinks for atmospheric CH4 with regard to worldwide GHG budgets (Werner et al. 2007, J GEOPHYS RES Vol. 112). Even though these soils are an important source for the atmospheric N2O budget, N2O emissions from tropical forest ecosystems are still poorly characterized (Castaldi et al. 2013, Biogeosciences 10). To obtain an insight of GHG balances of selected ecosystems soil-atmosphere exchange of N2O, CH4 and CO2 was investigated along the southern slope of Mt. Kilimanjaro, Tanzania. We will present results for tropical forests in three different altitudes (lower montane, Ocotea, and Podocarpus forest), home garden (extensive agro-forestry), and coffee plantation (intensive agro-forestry). Therefore we used a combined approach consisting of a laboratory parameterization experiment (3 temperature and 2 moisture levels) and in situ static chamber measurements for GHG exchange. Field measurements were conducted during different hygric seasons throughout two years. Seasonal variation of temperature and especially of soil moisture across the different ecosystems resulted in distinct differences in GHG exchange. In addition environmental parameters like soil bulk density and substrate availability varying in space strongly influenced the GHG fluxes within sites. The results from parameterization experiments and in situ measurements show that natural forest ecosystems and extensive land use had higher uptakes of CH4. For the investigated

  3. Discontinuous gas exchange in insects: is it all in their heads?

    PubMed

    Matthews, Philip G D; White, Craig R

    2011-01-01

    Some insects display an intermittent pattern of gas exchange while at rest, often going hours between breaths. These discontinuous gas exchange cycles (DGCs) are known to have evolved independently within five insect orders, but their possible adaptive benefit and evolutionary origin remain an enigma. Current research is primarily concerned with testing three adaptive hypotheses: that DGCs originally evolved or are currently maintained to (1) limit respiratory water loss, (2) enhance gas exchange in subterranean environments, or (3) limit oxidative damage. These adaptive explanations fail to unite a range of apparently contradictory observations regarding the insects that display DGCs and the conditions under which they occur. Here we argue that DGCs are explained by circadian, developmental, or artificially induced reductions in brain activity. We conclude that this pattern results from the thoracic and abdominal ganglia regulating ventilation in the absence of control from higher neural centers, and it is indicative of a sleeplike state. PMID:21087153

  4. Recovery of Water from Boiler Flue Gas Using Condensing Heat Exchangers

    SciTech Connect

    Edward Levy; Harun Bilirgen; John DuPoint

    2011-03-31

    Most of the water used in a thermoelectric power plant is used for cooling, and DOE has been focusing on possible techniques to reduce the amount of fresh water needed for cooling. DOE has also been placing emphasis on recovery of usable water from sources not generally considered, such as mine water, water produced from oil and gas extraction, and water contained in boiler flue gas. This report deals with development of condensing heat exchanger technology for recovering moisture from flue gas from coal-fired power plants. The report describes: (1) An expanded data base on water and acid condensation characteristics of condensing heat exchangers in coal-fired units. This data base was generated by performing slip stream tests at a power plant with high sulfur bituminous coal and a wet FGD scrubber and at a power plant firing high-moisture, low rank coals. (2) Data on typical concentrations of HCl, HNO{sub 3} and H{sub 2}SO{sub 4} in low temperature condensed flue gas moisture, and mercury capture efficiencies as functions of process conditions in power plant field tests. (3) Theoretical predictions for sulfuric acid concentrations on tube surfaces at temperatures above the water vapor dewpoint temperature and below the sulfuric acid dew point temperature. (4) Data on corrosion rates of candidate heat exchanger tube materials for the different regions of the heat exchanger system as functions of acid concentration and temperature. (5) Data on effectiveness of acid traps in reducing sulfuric acid concentrations in a heat exchanger tube bundle. (6) Condensed flue gas water treatment needs and costs. (7) Condensing heat exchanger designs and installed capital costs for full-scale applications, both for installation immediately downstream of an ESP or baghouse and for installation downstream of a wet SO{sub 2} scrubber. (8) Results of cost-benefit studies of condensing heat exchangers.

  5. Recovery of Water from Boiler Flue Gas Using Condensing Heat Exchangers

    SciTech Connect

    Levy, Edward; Bilirgen, Harun; DuPont, John

    2011-03-31

    Most of the water used in a thermoelectric power plant is used for cooling, and DOE has been focusing on possible techniques to reduce the amount of fresh water needed for cooling. DOE has also been placing emphasis on recovery of usable water from sources not generally considered, such as mine water, water produced from oil and gas extraction, and water contained in boiler flue gas. This report deals with development of condensing heat exchanger technology for recovering moisture from flue gas from coal-fired power plants. The report describes: • An expanded data base on water and acid condensation characteristics of condensing heat exchangers in coal-fired units. This data base was generated by performing slip stream tests at a power plant with high sulfur bituminous coal and a wet FGD scrubber and at a power plant firing highmoisture, low rank coals. • Data on typical concentrations of HCl, HNO{sub 3} and H{sub 2}SO{sub 4} in low temperature condensed flue gas moisture, and mercury capture efficiencies as functions of process conditions in power plant field tests. • Theoretical predictions for sulfuric acid concentrations on tube surfaces at temperatures above the water vapor dewpoint temperature and below the sulfuric acid dew point temperature. • Data on corrosion rates of candidate heat exchanger tube materials for the different regions of the heat exchanger system as functions of acid concentration and temperature. • Data on effectiveness of acid traps in reducing sulfuric acid concentrations in a heat exchanger tube bundle. • Condensed flue gas water treatment needs and costs. • Condensing heat exchanger designs and installed capital costs for full-scale applications, both for installation immediately downstream of an ESP or baghouse and for installation downstream of a wet SO{sub 2} scrubber. • Results of cost-benefit studies of condensing heat exchangers.

  6. Gamma radiation effect on gas production in anion exchange resins

    NASA Astrophysics Data System (ADS)

    Traboulsi, A.; Labed, V.; Dauvois, V.; Dupuy, N.; Rebufa, C.

    2013-10-01

    Radiation-induced decomposition of Amberlite IRA400 anion exchange resin in hydroxide form by gamma radiolysis has been studied at various doses in different atmospheres (anaerobic, anaerobic with liquid water, and aerobic). The effect of these parameters on the degradation of ion exchange resins is rarely investigated in the literature. We focused on the radiolysis gases produced by resin degradation. When the resin was irradiated under anaerobic conditions with liquid water, the liquid phase over the resin was also analyzed to identify any possible water-soluble products released by degradation of the resin. The main products released are trimethylamine (TMA), molecular hydrogen (H2g) and carbon dioxide (CO2g). TMA and H2g are produced in all the irradiation atmospheres. However, TMA was in gaseous form under anaerobic and aerobic conditions and in aqueous form in presence of liquid water. In the latter conditions, TMAaq was associated with aqueous dimethylamine (DMAaq), monomethylamine (MMAaq) and ammonia (NH). CO2g is formed in the presence of oxygen due to oxidation of organic compounds present in the system, in particular the degradation products such as TMAg.

  7. A computational model of insect discontinuous gas exchange: A two-sensor, control systems approach.

    PubMed

    Grieshaber, Beverley J; Terblanche, John S

    2015-06-01

    The insect gas exchange system is characterised by branching air-filled tubes (tracheae/tracheoles) and valve-like structures in their outer integument (spiracles) which allow for a periodic gas exchange pattern known as the discontinuous gas exchange cycle (DGC). The DGC facilitates the temporal decoupling of whole animal gas exchange from cellular respiration rates and may confer several physiological benefits, which are nevertheless highly controversial (primarily reduction of cellular oxidative damage and/or respiratory water saving). The intrinsic and extrinsic factors influencing DGCs are the focus of extensive ongoing research and little consensus has been reached on the evolutionary genesis or mechanistic costs and benefits of the pattern. Despite several hypotheses and much experimental and evolutionary biology research, a mechanistic physical model, which captures various key elements of the DGC pattern, is currently lacking. Here, we present a biologically realistic computational, two-sensor DGC model (pH/carbon dioxide and oxygen setpoints) for an Orthopteran gas exchange system, and show computationally for the first time that a control system of two interacting feedback loops is capable of generating a full DGC pattern with outputs which are physiologically realistic, quantitatively matching experimental results found in this taxonomic model elsewhere. A finite-element mathematical approach is employed and various trigger sets are considered. Parameter sensitivity analyses suggest that various aspects of insect DGC are adequately captured in this model. In particular, with physiologically relevant input parameters, the full DGC pattern is induced; and the phase durations, endotracheal carbon dioxide partial pressure ranges, and pH fluctuations which arise are physically realistic. The model results support the emergent property hypothesis for the existence of DGC, and indicate that asymmetric loading and off-loading (hysteresis) in one of the sensor

  8. Correlation between CAM-Cycling and Photosynthetic Gas Exchange in Five Species of Talinum (Portulacaceae) 1

    PubMed Central

    Harris, Fred S.; Martin, Craig E.

    1991-01-01

    Photosynthetic gas exchange and malic acid fluctuations were monitored in 69 well-watered plants from five morphologically similar species of Talinum in an investigation of the ecophysiological significance of the Crassulacean acid metabolism (CAM)-cycling mode of photosynthesis. Unlike CAM, atmospheric CO2 uptake in CAM-cycling occurs exclusively during the day; at night, the stomata are closed and respiratory CO2 is recaptured to form malic acid. All species showed similar patterns of day-night gas exchange and overnight malic acid accumulation, confirming the presence of CAM-cycling. Species averages for gas exchange parameters and malic acid fluctuation were significantly different such that the species with the highest daytime gas exchange had the lowest malic acid accumulation and vice versa. Also, daytime CO2 exchange and transpiration were negatively correlated with overnight malic acid fluctuation for all individuals examined together, as well as within one species. This suggests that malic acid may effect reductions in both atmospheric CO2 uptake and transpiration during the day. No significant correlation between malic acid fluctuation and water-use efficiency was found, although a nonsignificant trend of increasing water-use efficiency with increasing malic acid fluctuation was observed among species averages. This study provides evidence that CO2 recycling via malic acid is negatively correlated with daytime transpirational water losses in well-watered plants. Thus, CAM-cycling could be important for survival in the thin, frequently desiccated soils of rock outcrops on which these plants occur. PMID:16668307

  9. Gas exchange and pulmonary hypertension following acute pulmonary thromboembolism: has the emperor got some new clothes yet?

    PubMed Central

    2014-01-01

    Abstract Patients present with a wide range of hypoxemia after acute pulmonary thromboembolism (APTE). Recent studies using fluorescent microspheres demonstrated that the scattering of regional blood flows after APTE, created by the embolic obstruction unique in each patient, significantly worsened regional ventilation/perfusion (V/Q) heterogeneity and explained the variability in gas exchange. Furthermore, earlier investigators suggested the roles of released vasoactive mediators in affecting pulmonary hypertension after APTE, but their quantification remained challenging. The latest study reported that mechanical obstruction by clots accounted for most of the increase in pulmonary vascular resistance, but that endothelin-mediated vasoconstriction also persisted at significant level during the early phase. PMID:25006441

  10. Gas exchange and pulmonary hypertension following acute pulmonary thromboembolism: has the emperor got some new clothes yet?

    PubMed

    Tsang, John Y C; Hogg, James C

    2014-06-01

    Patients present with a wide range of hypoxemia after acute pulmonary thromboembolism (APTE). Recent studies using fluorescent microspheres demonstrated that the scattering of regional blood flows after APTE, created by the embolic obstruction unique in each patient, significantly worsened regional ventilation/perfusion (V/Q) heterogeneity and explained the variability in gas exchange. Furthermore, earlier investigators suggested the roles of released vasoactive mediators in affecting pulmonary hypertension after APTE, but their quantification remained challenging. The latest study reported that mechanical obstruction by clots accounted for most of the increase in pulmonary vascular resistance, but that endothelin-mediated vasoconstriction also persisted at significant level during the early phase. PMID:25006441

  11. The use of aviation gas-liquid heat exchangers employing heat pipes

    NASA Astrophysics Data System (ADS)

    Baranov, Iu. F.; Lokai, N. V.; Khananov, R. I.

    The possibility of using gas-liquid heat-pipe exchangers in different systems of aviation engines is examined, and methods for calculating the characteristics of such heat exchangers are discussed. A program developed for calculating the static and dynamic characteristics of heat-pipe exchangers is described. The program, which consists of 13 modules, uses the finite difference method. The program includes modules for calculating the gravitational characteristics of heat pipes with and without a capillary structure; the vapor parameters are calculated in the one-dimensional formulation for the viscous and inertial components with allowance for compressibility.

  12. Nanocomposite exchange-spring magnet synthesized by gas phase method: From isotropic to anisotropic

    NASA Astrophysics Data System (ADS)

    Liu, Xiaoqi; He, Shihai; Qiu, Jiao-Ming; Wang, Jian-Ping

    2011-05-01

    The fabrication of anisotropic nanocomposite exchange-spring magnets is demonstrated experimentally by using a gas-phase nanoparticle deposition technique. High resolution transmission electron microscopy images prove the experimental easy-axis definition of embedded hard magnetic nanoparticles in soft magnetic matrix. Exchange coupling between the hard and soft phases is confirmed by measuring recoil loops and δ M-H curve of the anisotropic FePt/Fe0.8Ni0.2 nanocomposite. The magnetic energy product for the anisotropic exchange-spring magnet is 224% higher than the isotropic case.

  13. Allometric scaling of discontinuous gas exchange patterns in the locust Locusta migratoria throughout ontogeny.

    PubMed

    Snelling, Edward P; Matthews, Philip G D; Seymour, Roger S

    2012-10-01

    The discontinuous gas exchange cycle (DGC) is a three-phase breathing pattern displayed by many insects at rest. The pattern consists of an extended breath-hold period (closed phase), followed by a sequence of rapid gas exchange pulses (flutter phase), and then a period in which respiratory gases move freely between insect and environment (open phase). This study measured CO(2) emission in resting locusts Locusta migratoria throughout ontogeny, in normoxia (21 kPa P(O2)), hypoxia (7 kPa P(O2)) and hyperoxia (40 kPa P(O2)), to determine whether body mass and ambient O(2) affect DGC phase duration. In normoxia, mean CO(2) production rate scales with body mass (M(b); g) according to the allometric power equation , closed phase duration (C; min) scales with body mass according to the equation C=8.0M(b)(0.38±0.29), closed+flutter period (C+F; min) scales with body mass according to the equation C+F=26.6M (0.20±0.25)(b) and open phase duration (O; min) scales with body mass according to the equation O=13.3M(b) (0.23±0.18). Hypoxia results in a shorter C phase and longer O phase across all life stages, whereas hyperoxia elicits shorter C, C+F and O phases across all life stages. The tendency for larger locusts to exhibit longer C and C+F phases might arise if the positive allometric scaling of locust tracheal volume prolongs the time taken to reach the minimum O(2) and maximum CO(2) set-points that determine the duration of these respective periods, whereas an increasingly protracted O phase could reflect the additional time required for larger locusts to expel CO(2) through a relatively longer tracheal pathway. Observed changes in phase duration under hypoxia possibly serve to maximise O(2) uptake from the environment, whereas the response of the DGC to hyperoxia is difficult to explain, but could be affected by elevated levels of reactive oxygen species. PMID:22735346

  14. Relationship between gas exchange, wind speed, and radar backscatter in a large wind-wave tank

    NASA Technical Reports Server (NTRS)

    Wanninkhof, Richard H.; Bliven, L. F.

    1991-01-01

    The relationships between the gas exchange, wind speed, friction velocity, and radar backscatter from the water surface was investigated using data obtained in a large water tank in the Delft (Netherlands) wind-wave tunnel, filled with water supersaturated with SF6, N2O, and CH4. Results indicate that the gas-transfer velocities of these substances were related to the wind speed with a power law dependence. Microwave backscatter from water surface was found to be related to gas transfer velocities by a relationship in the form k(gas) = a 10 exp (b A0), where k is the gas transfer velocity for the particular gas, the values of a and b are obtained from a least squares fit of the average backscatter cross section and gas transfer at 80 m, and A0 is the directional (azimuthal) averaged return.

  15. Charge exchange of laser-produced ions in a pulsed gas jet

    NASA Astrophysics Data System (ADS)

    Shaikhislamov, I. F.; Ponomarenko, A. G.; Antonov, V. M.; Boyarintsev, E. L.; Posukh, V. G.; Melekhov, A. V.

    2007-10-01

    Results of an experiment on the interaction of laser-produced plasma with a pulsed gas jet are reported. A resonant charge-exchange pumping of the n=3 level of the C3+ ion was observed. A spatial structure of the region of intensive interaction was obtained by a short time imaging of filtered plasma radiation. According to independent probe measurements, the interaction was realized at densities of ions and gas particles in excess of 1016 cm-3. The obtained data provide a prospect for future experiments on laser gain in the EUV spectral range based on charge-exchange pumping of the C5+ ion.

  16. Diode laser absorption spectroscopy for studies of gas exchange in fruits

    NASA Astrophysics Data System (ADS)

    Persson, L.; Gao, H.; Sjöholm, M.; Svanberg, S.

    2006-07-01

    Gas exchange in fruits, in particular oxygen transport in apples, was studied non-intrusively using wavelength modulation diode laser absorption spectroscopy at about 761 nm, applied to the strongly scattering intact fruit structure. The applicability of the technique was demonstrated by studies of the influence of the skin to regulate the internal oxygen balance and of cling film in modifying it by observing the response of the signal from the internal oxygen gas to a transient change in the ambient gas concentration. Applications within controlled atmosphere fruit storage and modified atmosphere packaging are discussed. The results suggest that the technique could be applied to studies of a large number of problems concerning gas exchange in foods and in food packaging.

  17. Reduced soil wettability can affect greenhouse gas fluxes

    NASA Astrophysics Data System (ADS)

    Urbanek, Emilia; Qassem, Khalid

    2015-04-01

    Soil moisture is known to be an important factor affecting the carbon (C) dynamics in soils including decomposition of organic matter and exchange of gases like CO2 and CH4 between the soil and the atmosphere. Most studies and process models looking at the soil C dynamics assume, however, that soils are easily wettable and water is relatively uniformly distributed within the soil pores. Most soils, however, do not wet spontaneously when dry or moderately moist, but instead exhibit some degree of soil water repellency (i.e. hydrophobicity), which can restrict infiltration and conductivity of water for weeks or months. This is world-wide occurring phenomenon which affects all soil textural types but is particularly common under permanent vegetation e.g. forest, grass and shrub vegetation. Soil water repellency is most profound during drier seasons, when the soil moisture content is relatively low. Although prolonged contact with water can gradually decrease water repellency, some soils do not recover to being completely wettable even after very wet winter months or substantial rainfall events. It has been recognized that with the predicted climatic changes the phenomenon of soil water repellency will become even more pronounced and severe, additionally it may occur in the areas and climatic zones where the effect have not been currently recognized. One of the main implications of soil water repellency is restricted water infiltration and reduced conductivity, which results in reduced soil water availability for plants and soil biota, even after prolonged periods of rainfall. As the process of C mineralization and consequently CO2 efflux from soil is driven by the accessibility of organic matter to decomposing organisms, which in turn is directly dependent on (i) soil moisture and (ii) soil temperature it is, therefore hypothesised that carbon decomposition and CO2 efflux in water repellent soils will also be affected when soil in the water repellent state. The CO2

  18. Gas exchange as monitored in mixed venous and arterial blood during experimental cardiopulmonary resuscitation.

    PubMed

    Wiklund, L; Jorfeldt, L; Stjernström, H; Rubertsson, S

    1992-07-01

    Nineteen anaesthetized piglets were investigated. After catheterization and a stabilization period, ventricular fibrillation was induced with a transthoracic DC shock, after which a 10-min period of cardiopulmonary resuscitation (CPR) took place. CPR included manual chest compression and mechanical ventilation with pure oxygen. After 1 min of CPR, an infusion of alkaline buffer was begun and completed within 5 min. A total of 50 mmol of either sodium bicarbonate (n = 6) or tris buffer mixture (n = 7) were given. These two groups were compared with a third control group (n = 6) receiving the same volume of normal saline. After 8 min of CPR all animals were given 0.5 mg adrenaline i.v., and after 10 min DC shocks were used to revert the heart back to normal sinus rhythm. Our results demonstrate that blood flow and not ventilation is the limiting factor for the efficient disposal of CO2 during CPR. This also applied when the demand for CO2 transport was increased by administration of sodium bicarbonate. The respiratory exchange ratio increased 1.9-fold, indicating that the transport of carbon dioxide was less affected than that of oxygen. The estimated alveolo-arterial oxygen tension difference, shunt, and overall ventilation/perfusion ratio increased, creating an inverse hyperbolic relationship between arterial PCO2 and PO2. The difference between mixed venous and arterial PCO2 correlated well to the mixed venous PCO2, implying more efficient pulmonary elimination of PCO2 when the mixed venous PCO2 was high. Pulmonary gas exchange during CPR appears to be independent of alkaline buffer therapy in the form of sodium bicarbonate or tris buffer mixture.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:1632165

  19. Effects of stomata clustering on leaf gas exchange.

    PubMed

    Lehmann, Peter; Or, Dani

    2015-09-01

    A general theoretical framework for quantifying the stomatal clustering effects on leaf gaseous diffusive conductance was developed and tested. The theory accounts for stomatal spacing and interactions among 'gaseous concentration shells'. The theory was tested using the unique measurements of Dow et al. (2014) that have shown lower leaf diffusive conductance for a genotype of Arabidopsis thaliana with clustered stomata relative to uniformly distributed stomata of similar size and density. The model accounts for gaseous diffusion: through stomatal pores; via concentration shells forming at pore apertures that vary with stomata spacing and are thus altered by clustering; and across the adjacent air boundary layer. Analytical approximations were derived and validated using a numerical model for 3D diffusion equation. Stomata clustering increases the interactions among concentration shells resulting in larger diffusive resistance that may reduce fluxes by 5-15%. A similar reduction in conductance was found for clusters formed by networks of veins. The study resolves ambiguities found in the literature concerning stomata end-corrections and stomatal shape, and provides a new stomata density threshold for diffusive interactions of overlapping vapor shells. The predicted reduction in gaseous exchange due to clustering, suggests that guard cell function is impaired, limiting stomatal aperture opening. PMID:25967110

  20. Influence of Waves, Whitecaps, and Turbulence on the Gas Transfer during the Southern Ocean Gas Exchange Experiment

    NASA Astrophysics Data System (ADS)

    Zappa, C. J.; Cifuentes-Lorenzen, A.; Edson, J. B.; McGillis, W. R.; Bariteau, L.; Fairall, C. W.

    2008-12-01

    The exchange of carbon dioxide and other trace gases across the air-sea interface plays an important role in global and regional biogeochemical cycles. The gas transfer velocity (k) is thought to be controlled by near- surface turbulence at low to moderate wind speeds and by bubble-mediated processes at higher wind speeds. At low to moderate wind speeds, small-scale waves including microbreaking disrupt the diffusive boundary layer, contribute to mixing at the surface, and enhance exchange. Likewise, at higher wind speeds, large-scale wave breaking, or whitecapping, generates mixing and additionally enhances gas transfer via bubble-mediated exchange. The parameterization for k based on the direct covariance fluxes is shown to have a cubic dependence on wind speed. This result supports the hypothesis that, if bubble mediated exchange is important, the transfer velocity should increase proportionally with whitecap coverage, since whitecap coverage been shown to increase with at least a cubic dependence on wind speed. However, the very large uncertainties under high wind speed conditions limit the universality of this result and the role of breaking waves and bubble modulated transfer. Here, we present results of the combination of turbulence, deep-ocean wave statistics, whitecapping, and CO2 gas exchange measured during the Southern Ocean Gas Exchange Experiment (SO GasEx) with sustained conditions between 10-20 m s-1. Directional ocean wave spectra, significant wave height, peak wave period, and peak wave direction were obtained with a Wave and Surface Current Monitoring System (WaMoS® II). WaMoS® II also has the capability to resolve two-dimensional maps of surface elevation snapshots with the significant advantage of continuous availability of wave data in rough seas. In addition, significant wave height was measured using a laser altimeter as well as a nadir-looking microwave system. Oceanic turbulent kinetic energy dissipation rates were measured using a pulse

  1. Gas Exchange Characteristics of the Sorghum-Striga Host-Parasite Association

    PubMed Central

    Press, Malcolm C.; Tuohy, Janet M.; Stewart, George R.

    1987-01-01

    Gas exchange characteristics are reported for both members of the sorghum-Striga host-parasite association. Both Striga hermonthica (Del.) Benth and Striga asiatica (L.) Kuntze had transpiration rates considerably in excess of those of sorghum (Sorghum bicolor (L.) Moench, cv CSH1). Stomatal conductance in both Striga spp. showed little response to periods of darkness and moderate water stress. Low rates of net CO2 fixation and high rates of dark respiration led to no net daily (24 hours) C gain, and Striga would appear to be reliant on its host for photosynthate. Infection of sorghum plants with either S. hermonthica or S. asiatica reduced host photosynthetic capacity. Infected sorghum plants were also more prone to water stress, but reduced rates of CO2 fixation could not be accounted for in terms of lower stomatal conductance. Lower stomatal conductances were associated with an increase in water use efficiency (WUE) in uninfected sorghum; however, Striga-infected sorghum plants had lower WUE than those of uninfected plants. We suggest that Striga exerts a specific effect on processes affecting C acquisition in sorghum leaves. The water relations of S. hermonthica and S. asiatica are not characteristic of plants growing in semiarid environments and are more likely to reflect the nature of the parasitic life-style. Despite transfer of water and solutes from host to parasite, the reduction in C fixation observed in infected sorghum plants appears to be the major determinant of growth reductions observed in sorghum supporting Striga. PMID:16665527

  2. Modeling the influence of the pulmonary pressure-volume curve on gas exchange.

    PubMed

    Smith, Bram; Rees, Stephen; Tvorup, Jan; Christensen, Casper; Andreassen, Steen

    2005-01-01

    Current models of lung mechanics and gas exchange act independently to simulate variations in pressure-volume (PV) and ventilation-perfusion (V/Q) properties in the lungs respectively. However, changes in ventilator pressures can cause alveoli recruitment, collapse or over-distension causing V/Q changes in the lungs that are unaccounted for in these models. A compartmental model of the lungs is presented that is based on a physiological interpretation of lung function and simulates each alveolus individually. By combining this model with currently available lung mechanics and gas exchange models, the effect of changing ventilator settings on gas exchange could be simulated. The model is shown to simulate experimentally measured static PV data from an ARDS patient with an accuracy equivalent to that achieved by the sigmoid function. It could enable quantification of variations in V/Q in the lungs and also gives estimates of other physiological lung properties such as lung density and alveoli compliance. The alveoli model offers a physiologically relevant method of simulating the PV relationship in the lungs and its influence of gas exchange. PMID:17282708

  3. Carbon dioxide control in an open system that measures canopy gas exchanges

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Atmospheric carbon dioxide concentration ([CO2]) effects both C3 net assimilation (A) as well as crop water use. Methods for measuring whole canopy gas exchange responses under [CO2] enrichment are needed for breeding programs aiming to develop crop cultivars resistant to stresses like drought in a...

  4. Gas exchange and water relations responses of spring wheat to full-season infrared warming

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Gas exchange and water relations responses to full-season in situ infrared (IR) warming were evaluated for hard red spring wheat (Triticum aestivum L. cv. Yecora Rojo) grown in an open field in a semi-arid desert region of the Southwest USA. A Temperature Free-Air Controlled Enhancement (T-FACE) ap...

  5. Gas exchange in NASA's biomass production chamber - A preprototype closed human life support system

    NASA Technical Reports Server (NTRS)

    Corey, Kenneth A.; Wheeler, Raymond M.

    1992-01-01

    The unique capabilities of the NASA biomass production chamber for monitoring and evaluating gas exchange rates are examined. Special emphasis is given to results with wheat and soybeans. The potential of the chamber as a preprototype of a closed human life support system is considered.

  6. Deficit irrigation: Arriving at the crop water stress index via gas exchange measurements

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Plant gas exchange provides a highly sensitive measure of the degree of drought stress. Canopy temperature (Tc) provides a much easier to acquire indication of crop water deficit that has been used in irrigation scheduling systems, but interpretation of this measurement has proven difficult. Our goa...

  7. Quantifying biases in non-steady state chamber measurements of soil-atmosphere gas exchange

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Limitations of non-steady state (NSS) chamber methods for determining soil-to-atmosphere trace gas exchange rates have been recognized for several decades. Of these limitations, the so-called “chamber effect” is one of the most challenging to overcome. The chamber effect can be defined as the inhere...

  8. Effect of nitric oxide inhalation on gas exchange in acute severe pneumonia.

    PubMed

    Gómez, Federico P; Amado, Veronica M; Roca, Josep; Torres, Antoni; Nicolas, Josep M; Rodriguez-Roisin, Robert; Barberà, Joan A

    2013-06-15

    Inhaled nitric oxide (NO) causes selective pulmonary vasodilatation and may improve gas exchange. The study was aimed to evaluate the acute effects of inhaled NO on pulmonary gas exchange in severe unilateral pneumonia, where hypoxemia results from increased intrapulmonary shunt. We studied 8 patients without preexisting lung disease (59±18 yr; 4M/4F) with early unilateral severe pneumonia and respiratory failure. Pulmonary and systemic hemodynamics and gas exchange, including ventilation-perfusion (V;A/Q;) distributions, were measured at baseline and while breathing 5 and 40 parts per million (ppm) of NO. Inhaled NO caused a dose-dependent fall in pulmonary vascular resistance (by 12% and 21%, with 5 and 40ppm, respectively; p<0.01, each) and improvement of PaO2 (by 25% and 23%; p<0.05, each), owing to the reduction of intrapulmonary shunt (by 23% and 27%; p<0.05, each), without changes in the amount of perfusion to low V;A/Q; ratio alveolar units. Patients with greater baseline intrapulmonary shunt exhibited greater improvement in arterial oxygenation (r(2)=0.55, p<0.05). We conclude that low doses of inhaled NO improve pulmonary gas exchange in acute severe pneumonia. PMID:23537586

  9. Field Evaluation of Open System Chambers for Measuring Whole Canopy Gas Exchanges

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The ability to monitor whole canopy CO2 and H2O fluxes of crop plants in the field is needed for many research efforts ranging from plant breeding to the study of Climate Change effects on crops. Four portable, transparent, open system chambers for measuring canopy gas exchanges were field tested on...

  10. Impaired gas exchange: accuracy of defining characteristics in children with acute respiratory infection1

    PubMed Central

    Pascoal, Lívia Maia; Lopes, Marcos Venícios de Oliveira; Chaves, Daniel Bruno Resende; Beltrão, Beatriz Amorim; da Silva, Viviane Martins; Monteiro, Flávia Paula Magalhães

    2015-01-01

    OBJECTIVE: to analyze the accuracy of the defining characteristics of the Impaired gas exchange nursing diagnosis in children with acute respiratory infection. METHOD: open prospective cohort study conducted with 136 children monitored for a consecutive period of at least six days and not more than ten days. An instrument based on the defining characteristics of the Impaired gas exchange diagnosis and on literature addressing pulmonary assessment was used to collect data. The accuracy means of all the defining characteristics under study were computed. RESULTS: the Impaired gas exchange diagnosis was present in 42.6% of the children in the first assessment. Hypoxemia was the characteristic that presented the best measures of accuracy. Abnormal breathing presented high sensitivity, while restlessness, cyanosis, and abnormal skin color showed high specificity. All the characteristics presented negative predictive values of 70% and cyanosis stood out by its high positive predictive value. CONCLUSION: hypoxemia was the defining characteristic that presented the best predictive ability to determine Impaired gas exchange. Studies of this nature enable nurses to minimize variability in clinical situations presented by the patient and to identify more precisely the nursing diagnosis that represents the patient's true clinical condition. PMID:26155010

  11. Effect of local disturbance of bronchial patency on the circulation and gas exchange in the lungs

    SciTech Connect

    Putov, N.V.; Danilov, D.N.; Lebedeva, E.S.; Chermenskii, Yu.V.

    1987-06-01

    The purpose of this paper was to obtain proof that alveolar hypoxia develops in the presence of local bronchial obstruction and to establish the role of the latter in disturbances of pulmonary circulation and gas exchange. Experiments were conducted on male mongrel dogs. Albumin microspheres labelled with technetium 99m were injected intravenously to trace the distribution and loss of blood flow.

  12. Changes in gas exchange, tissue respiration and glycolysis in rats during hypokinesia

    NASA Technical Reports Server (NTRS)

    Zorya, L. V.

    1980-01-01

    The results of an experiment which studied changes in oxygen balance under conditions of hypokinesia in rats is presented. The effect of the stress during hypokinesia is expressed most clearly in the changes of general gas exchange, and in the intensity of liver and myocardial tissue respiration.

  13. Gas Exchange and Water Relations Responses of Spring Wheat to Full-Season Infrared Warming

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Gas exchange and water relations were evaluated under full-season in situ infrared (IR) warming for hard red spring wheat (Triticum aestivum L. cv. Yecora Rojo) grown in an open field in a semiarid desert region of the southwest USA. A temperature free-air controlled enhancement (T-FACE) apparatus u...

  14. Temperature-dependent variation in gas exchange patterns and spiracular control in Rhodnius prolixus.

    PubMed

    Heinrich, Erica; Bradley, Timothy

    2014-08-01

    Insects display an array of respiratory behaviors, including the use of discontinuous gas exchange. This pattern is characterized by periods of spiracular closure, micro-openings (flutter), and complete openings during which the majority of gas exchange takes place. A current model of insect spiracular control suggests that spiracles are controlled by two interacting feedback loops, which produce the discontinuous pattern. The flutter period is thought to be initiated by a critically low partial pressure of oxygen, while the open period is initiated by a critically high CO2 threshold. The goal of our study was to test this control model under conditions of feeding-induced or temperature-induced changes in metabolic rate. We manipulated the metabolic rate of the insect Rhodnius prolixus using two discrete mechanisms: (1) feeding the insects a bloodmeal or (2) exposing them to a range of temperatures (18-38°C). Examining the variation in the gas exchange patterns produced by insects in each of these treatments allowed us to determine whether spiracular control is sensitive to metabolic rate and/or temperature. We found that increases in temperature caused significant decreases in open phase burst volumes and premature abandonment of discontinuous gas exchange cycles. These effects were not observed in fed individuals maintained at a single temperature despite their higher metabolic rates. Our results indicate that some part of the spiracular control mechanism is temperature sensitive, suggesting a possible role for pH in CO2 sensing. PMID:25079894

  15. Leaf gas exchange traits of domestic and exotic tree species in Cambodia

    NASA Astrophysics Data System (ADS)

    Miyazawa, Y.; Tateishi, M.; Kumagai, T.; Otsuki, K.

    2009-12-01

    In forests under the management by community villagers, exotic tree species with rapid growth rate are introduced in wide range of Cambodia. To evaluate the influence of the introduction on the forest gas exchange and water budget, we investigated the leaf gas exchange traits of two domestic (Dipterocarpus obtusifolius and Shorea roxburghii) and exotic tree species (Acasia auriculiformis and Eucalyptus camadilansis). We sampled shoots of each species and measured the leaf gas exchange traits (photosynthetic rates under different CO2 concentrations, transpiration rate and stomatal conductance) (6 leaves x 3 trees x 4 species). We carried out this measurement at 2 months intervals for a year from the beginning of rainy season and compared the obtained traits among species. Light saturated rate of net photosynthesis was higher in E. camadilansis but did not differ among other species both in rainy and dry seasons. Seasonal patter in photosynthetic traits was not obvious. Each species changed stomatal conductance in response to changes in environmental conditions. The response was more sensitive than reported values. In this presentation, we show details about the basic information about the leaf-level gas exchange traits, which are required to run soil- vegetation - atmosphere transfer model.

  16. Guest Molecule Exchange Kinetics for the 2012 Ignik Sikumi Gas Hydrate Field Trial

    SciTech Connect

    White, Mark D.; Lee, Won Suk

    2014-05-14

    A commercially viable technology for producing methane from natural gas hydrate reservoirs remains elusive. Short-term depressurization field tests have demonstrated the potential for producing natural gas via dissociation of the clathrate structure, but the long-term performance of the depressurization technology ultimately requires a heat source to sustain the dissociation. A decade of laboratory experiments and theoretical studies have demonstrated the exchange of pure CO2 and N2-CO2 mixtures with CH4 in sI gas hydrates, yielding critical information about molecular mechanisms, recoveries, and exchange kinetics. Findings indicated the potential for producing natural gas with little to no production of water and rapid exchange kinetics, generating sufficient interest in the guest-molecule exchange technology for a field test. In 2012 the U.S. DOE/NETL, ConocoPhillips Company, and Japan Oil, Gas and Metals National Corporation jointly sponsored the first field trial of injecting a mixture of N2-CO2 into a CH4-hydrate bearing formation beneath the permafrost on the Alaska North Slope. Known as the Ignik Sikumi #1 Gas Hydrate Field Trial, this experiment involved three stages: 1) the injection of a N2-CO2 mixture into a targeted hydrate-bearing layer, 2) a 4-day pressurized soaking period, and 3) a sustained depressurization and fluid production period. Data collected during the three stages of the field trial were made available after an extensive quality check. These data included continuous temperature and pressure logs, injected and recovered fluid compositions and volumes. The Ignik Sikumi #1 data set is extensive, but contains no direct evidence of the guest-molecule exchange process. This investigation is directed at using numerical simulation to provide an interpretation of the collected data. A numerical simulator, STOMP-HYDT-KE, was recently completed that solves conservation equations for energy, water, mobile fluid guest molecules, and hydrate guest

  17. How does the Porosity of Interstellar Ice Affect Chemical Complexity and Deuteration Exchange?

    NASA Astrophysics Data System (ADS)

    Fraser, Helen Jane; Noble, Jennifer; Hill, Catherine Rachel; Bowron, Daniel; Youngs, Tristan; Loerting, Thomas; Mitteldorfer, Christian; Millar, James; Elkind, Pavel; Cousan, Stephane; Lui, Yuan; Ojamae, Lars

    2015-08-01

    The porosity of interstellar water ice, Amorphous Solid Water (ASW), greatly enhances the ability of ice to uptake, then release small gas adsorbates. This provides the strongest evidence that interstellar ices must be porous, accounting for the differences between predicted and observed gas-phase abundances, and provides a mechanism to enhance reagent diversity for complex chemistry in the ice. However, no dangling OH (d-OH) bond features, to-date associated with ice porosity, have been reported in interstellar ice spectra, so some conclude that interstellar ices must be non-porous, given that the d-OH spectra disappear in laboratory studies when ASW is energetically processed. But are d-OH features and gas-uptake reliable experimental measures of ice porosity? Here we combine fundamental studies of ASW with observational data to determine ASW porosity and understand its role in the chemical evolution of interstellar ices.We show upper-limit detections of d-OH in observational spectra towards a handful of sources (Fraser et al (2015)). Laboratory experiments on selective irradiation of d-OH features (Noble et al (2013), (2014)), combined with quantum chemical calculations (Lui et al (2015)), show that the d-OH bonds probe the density of defect sites in the surface and sub-surface structure. Consequently surfaces with d-OH bonds are significantly more reactive and therefore promote chemical complexity across extra-terrestrial regions where they are found, but do not reflect ice porosity.Our neutron scattering data show that ASW ices actually contain cylindrical pores of around 10 Å diameter (Mitteldorfer et al (2014)). The pore collapse process can only be initiated by long range molecular diffusion at T > 121 K, and follows complex kinetics (Hill et al (2015a); such effects can be reproduced by molecular dynamics simulations of ASW ice-heating (Elkind et al (2015): Miller et al (2015)), and are directly linked to deuteration exchange. We explain the implications

  18. A study of gas-surface energy exchange processes: Final report

    SciTech Connect

    Kunc, J.A.; Shemansky, D.E.

    1985-01-01

    The objective of this theoretical research program was to study the fundamental characteristics of gas-surface energy exchange reactions. The interaction process refers to low density conditions in the gas component and therefore has general application to a number of disparate disciplines, including the maintenance of clean high vacuum systems for research in subjects such as fusion reactions, and many other important areas in engineering and technology. The approach to the calculations is to construct accurate theoretical models of the solid structure on a microscopic scale, and account for the aggregate gas-surface physical interaction using Monte Carlo techniques. 18 refs., 5 figs.

  19. Hybrid heat exchange for the compression capture of CO2 from recirculated flue gas

    SciTech Connect

    Oryshchyn, Danylo B.; Ochs, Thomas L.; Summers, Cathy A.

    2004-01-01

    An approach proposed for removal of CO2 from flue gas cools and compresses a portion of a recirculated flue-gas stream, condensing its volatile materials for capture. Recirculating the flue gas concentrates SOx, H2O and CO2 while dramatically reducing N2 and NOx, enabling this approach, which uses readily available industrial components. A hybrid system of indirect and direct-contact heat exchange performs heat and mass transfer for pollutant removal and energy recovery. Computer modeling and experimentation combine to investigate the thermodynamics, heat and mass transfer, chemistry and engineering design of this integrated pollutant removal (IPR) system.

  20. The Gas Exchange Experiment for life detection - The Viking Mars Lander.

    NASA Technical Reports Server (NTRS)

    Oyama, V. I.

    1972-01-01

    The Gas Exchange Experiment of the Viking mission accepts a sample of Martian soil, incubates this soil with nutrient medium, and periodically samples the enclosed atmosphere over this soil for the gases H2, N2, O2, Kr, and CO2. These gases are analyzed by an automated gas chromatograph, and the data are transmitted to earth. The design of the experiment and the qualitative and quantitative changes, if any, of gas composition should allow conclusions to be made on the presence of life on Mars. Data and theory substantiating this approach are presented.

  1. Effects of flow rate and temperature on cyclic gas exchange in tsetse flies (Diptera, Glossinidae).

    PubMed

    Terblanche, John S; Chown, Steven L

    2010-05-01

    Air flow rates may confound the investigation and classification of insect gas exchange patterns. Here we report the effects of flow rates (50, 100, 200, 400 ml min(-1)) on gas exchange patterns in wild-caught Glossina morsitans morsitans from Zambia. At rest, G. m. morsitans generally showed continuous or cyclic gas exchange (CGE) but no evidence of discontinuous gas exchange (DGE). Flow rates had little influence on the ability to detect CGE in tsetse, at least in the present experimental setup and under these laboratory conditions. Importantly, faster flow rates resulted in similar gas exchange patterns to those identified at lower flower rates suggesting that G. m. morsitans did not show DGE which had been incorrectly identified as CGE at lower flow rates. While CGE cycle frequency was significantly different among the four flow rates (p<0.05), the direction of effects was inconsistent. Indeed, inter-individual variation in CGE cycle frequency exceeded flow rate treatment variation. Using a laboratory colony of closely related, similar-sized G. morsitans centralis we subsequently investigated the effects of temperature, gender and feeding status on CGE pattern variation since these factors can influence insect metabolic rates. At 100 ml min(-1) CGE was typical of G. m. centralis at rest, although it was significantly more common in females than in males (57% vs. 43% of 14 individuals tested per gender). In either sex, temperature (20, 24, 28 and 32 degrees C) had little influence on the number of individuals showing CGE. However, increases in metabolic rate with temperature were modulated largely by increases in burst volume and cycle frequency. This is unusual among insects showing CGE or DGE patterns because increases in metabolic rate are usually modulated by increases in frequency, but either no change or a decline in burst volume. PMID:20399350

  2. Potassium concentration effect on growth, gas exchange and mineral accumulation in potatoes

    NASA Technical Reports Server (NTRS)

    Cao, W.; Tibbitts, T. W.

    1991-01-01

    This study was conducted to evaluate the responses of potatoes to six K solution concentrations maintained with a flow-through nutrient film system. Potato plants were grown for 42 days in sloping shallow trays containing a 1 cm layer of quartz gravel with a continuous flow of 4 ml min-1 of nutrient solutions having K concentrations of 0.10, 0.55, 1.59, 3.16, 6.44, 9.77 meq L-1. Plant leaf area, total and tuber dry weights were reduced over 25% at 0.10 meq L-1 of K and over 17% at 9.77 meq L-1 of K compared to concentrations of 0.55, 1.59, 3.16 and 6.44 meq L-1 of K. Gas exchange measurements on leaflets in situ after 39 days of growth demonstrated no significant differences among different K treatments in CO2 assimilation rate, stomatal conductance, intercellular CO2 concentration, and transpiration. Further measurements made only on plants grown at 0.10, 1.59, 6.44 meq L-1 of K showed similar responses of CO2 assimilation rate to different intercellular CO2 concentrations. This suggested that the photosynthetic systems were not affected by different K nutrition. The leaves of plants accumulated about 60% less K at 0.10 meq L-1 of K than at higher K concentrations. However, Ca and Mg levels in the leaves were higher at 0.10 meq L-1 of K than at higher K concentrations. This indicates that low K nutrition not only reduced plant growth, but also affected nutrient balance between major cations.

  3. Potassium concentration effect on growth, gas exchange and mineral accumulation in potatoes.

    PubMed

    Cao, W; Tibbitts, T W

    1991-01-01

    This study was conducted to evaluate the responses of potatoes to six K solution concentrations maintained with a flow-through nutrient film system. Potato plants were grown for 42 days in sloping shallow trays containing a 1 cm layer of quartz gravel with a continuous flow of 4 ml min-1 of nutrient solutions having K concentrations of 0.10, 0.55, 1.59, 3.16, 6.44, 9.77 meq L-1. Plant leaf area, total and tuber dry weights were reduced over 25% at 0.10 meq L-1 of K and over 17% at 9.77 meq L-1 of K compared to concentrations of 0.55, 1.59, 3.16 and 6.44 meq L-1 of K. Gas exchange measurements on leaflets in situ after 39 days of growth demonstrated no significant differences among different K treatments in CO2 assimilation rate, stomatal conductance, intercellular CO2 concentration, and transpiration. Further measurements made only on plants grown at 0.10, 1.59, 6.44 meq L-1 of K showed similar responses of CO2 assimilation rate to different intercellular CO2 concentrations. This suggested that the photosynthetic systems were not affected by different K nutrition. The leaves of plants accumulated about 60% less K at 0.10 meq L-1 of K than at higher K concentrations. However, Ca and Mg levels in the leaves were higher at 0.10 meq L-1 of K than at higher K concentrations. This indicates that low K nutrition not only reduced plant growth, but also affected nutrient balance between major cations. PMID:11538369

  4. A three-dimensional multiscale model for gas exchange in fruit.

    PubMed

    Ho, Quang Tri; Verboven, Pieter; Verlinden, Bert E; Herremans, Els; Wevers, Martine; Carmeliet, Jan; Nicolaï, Bart M

    2011-03-01

    Respiration of bulky plant organs such as roots, tubers, stems, seeds, and fruit depends very much on oxygen (O2) availability and often follows a Michaelis-Menten-like response. A multiscale model is presented to calculate gas exchange in plants using the microscale geometry of the tissue, or vice versa, local concentrations in the cells from macroscopic gas concentration profiles. This approach provides a computationally feasible and accurate analysis of cell metabolism in any plant organ during hypoxia and anoxia. The predicted O2 and carbon dioxide (CO2) partial pressure profiles compared very well with experimental data, thereby validating the multiscale model. The important microscale geometrical features are the shape, size, and three-dimensional connectivity of cells and air spaces. It was demonstrated that the gas-exchange properties of the cell wall and cell membrane have little effect on the cellular gas exchange of apple (Malus×domestica) parenchyma tissue. The analysis clearly confirmed that cells are an additional route for CO2 transport, while for O2 the intercellular spaces are the main diffusion route. The simulation results also showed that the local gas concentration gradients were steeper in the cells than in the surrounding air spaces. Therefore, to analyze the cellular metabolism under hypoxic and anoxic conditions, the microscale model is required to calculate the correct intracellular concentrations. Understanding the O2 response of plants and plant organs thus not only requires knowledge of external conditions, dimensions, gas-exchange properties of the tissues, and cellular respiration kinetics but also of microstructure. PMID:21224337

  5. Analysis of effect of the solubility on gas exchange in nonhomogeneous lungs

    NASA Technical Reports Server (NTRS)

    Colburn, W. E., Jr.; Evans, J. W.; West, J. B.

    1974-01-01

    A comparison is made of the gas exchange in nonhomogeneous lung models and in homogeneous lung models with the same total blood flow and ventilation. It is shown that the ratio of the rate of gas transfer of the inhomogeneous lung model over the rate of gas transfer of the homogeneous lung model as a function of gas solubility always has the qualitative features for gases with linear dissociation curves. This ratio is 1 for a gas with zero solubility and decreases to a single minimum. It subsequently rises to approach 1 as the solubility tends to infinity. The early portion of the graph of this function is convex, then after a single inflection point it is concave.

  6. Plant mineral nutrition, gas exchange and photosynthesis in space: A review

    NASA Astrophysics Data System (ADS)

    Wolff, S. A.; Coelho, L. H.; Zabrodina, M.; Brinckmann, E.; Kittang, A.-I.

    2013-02-01

    Successful growth and development of higher plants in space rely on adequate availability and uptake of water and nutrients, and efficient energy distribution through photosynthesis and gas exchange. In the present review, literature has been reviewed to assemble the relevant knowledge within space plant research for future planetary missions. Focus has been on fractional gravity, space radiation, magnetic fields and ultimately a combined effect of these factors on gas exchange, photosynthesis and transport of water and solutes. Reduced gravity prevents buoyancy driven thermal convection in the physical environment around the plant and alters transport and exchange of gases and liquids between the plant and its surroundings. In space experiments, indications of root zone hypoxia have frequently been reported, but studies on the influences of the space environment on plant nutrition and water transport are limited or inconclusive. Some studies indicate that uptake of potassium is elevated when plants are grown under microgravity conditions. Based on the current knowledge, gas exchange, metabolism and photosynthesis seem to work properly in space when plants are provided with a well stirred atmosphere and grown at moderate light levels. Effects of space radiation on plant metabolism, however, have not been studied so far in orbit. Ground experiments indicated that shielding from the Earth's magnetic field alters plant gas exchange and metabolism, though more studies are required to understand the effects of magnetic fields on plant growth. It has been shown that plants can grow and reproduce in the space environment and adapt to space conditions. However, the influences of the space environment may result in a long term effect over multiple generations or have an impact on the plants' role as food and part of a regenerative life support system. Suggestions for future plant biology research in space are discussed.

  7. Treadmill chamber for studies of respiratory gas exchange in the rat during exercise.

    PubMed

    Ardévol, A; Adán, C; Fernández-López, J A; Pérez, J; Corts, J L; Binagui, D; Remesar, X; Alemany, M

    1995-05-01

    A treadmill for studying gas exchange in small mammals during exercise is presented. The system consists of a motor-driven running mat enclosed in a gastight chamber that receives a measured flow of air from a compressed air cylinder. The gas flow and temperature, pressure and instantaneous gas composition of the chamber (oxygen, carbon dioxide and water) are measured continuously and the data are computed to include the effects on chamber atmosphere of the rat activity, either running or at rest. The system is completed with a shock delivery grid that stimulates the rat to run. The calculations are based on the changes in the composition of the gas in the chamber (constantly stirred by a small electric fan) induced by the rat instead of relying on the alterations induced in the outflowing gas. The consumption of oxygen, and production of carbon dioxide and water by the rat are computed in real time, giving a very fast response to physiological change induced by exercise. The chamber is custom-made from an aluminium block and a plexiglass lid; all other components are available commercially. The system, as described, allows for a detailed analysis of respiratory gas (and water) exchange by rats under varying exercise conditions, there is practically no time lag between changes in respiratory gases and the detection of these changes, and the buffering effect of the chamber size is practically eliminated because of the calculation approach used. PMID:9338089

  8. Modeled natural and excess radiocarbon: Sensitivities to the gas exchange formulation and ocean transport strength

    NASA Astrophysics Data System (ADS)

    Müller, S. A.; Joos, F.; Plattner, G.-K.; Edwards, N. R.; Stocker, T. F.

    2008-09-01

    Observation-based surface ocean Δ14C distributions and regional inventories for excess, bomb-produced radiocarbon are compared with results of two ocean models of intermediate complexity. By applying current descriptions of the air-sea gas exchange the models produce similar column inventories for excess 14C among all basins. This result is robust across a wide range of transport parameter settings, but inconsistent with data-based inventories. In the absence of evidence of fundamentally different gas exchange mechanisms in the North Atlantic than in the other basins, we infer regional North Atlantic 14C inventories which are considerably smaller than previous estimates. The results further suggest that the gas exchange velocity field should be reduced by (19 ± 16)%, which corresponds to a global mean air-sea gas transfer rate for CO2 in seawater of 17.1 ± 3.3 cm h-1, to find good agreement of simulated quantities with a range of data-based metrics.

  9. A Comparative Data-Based Modeling Study on Respiratory CO2 Gas Exchange during Mechanical Ventilation

    PubMed Central

    Kim, Chang-Sei; Ansermino, J. Mark; Hahn, Jin-Oh

    2016-01-01

    The goal of this study is to derive a minimally complex but credible model of respiratory CO2 gas exchange that may be used in systematic design and pilot testing of closed-loop end-tidal CO2 controllers in mechanical ventilation. We first derived a candidate model that captures the essential mechanisms involved in the respiratory CO2 gas exchange process. Then, we simplified the candidate model to derive two lower-order candidate models. We compared these candidate models for predictive capability and reliability using experimental data collected from 25 pediatric subjects undergoing dynamically varying mechanical ventilation during surgical procedures. A two-compartment model equipped with transport delay to account for CO2 delivery between the lungs and the tissues showed modest but statistically significant improvement in predictive capability over the same model without transport delay. Aggregating the lungs and the tissues into a single compartment further degraded the predictive fidelity of the model. In addition, the model equipped with transport delay demonstrated superior reliability to the one without transport delay. Further, the respiratory parameters derived from the model equipped with transport delay, but not the one without transport delay, were physiologically plausible. The results suggest that gas transport between the lungs and the tissues must be taken into account to accurately reproduce the respiratory CO2 gas exchange process under conditions of wide-ranging and dynamically varying mechanical ventilation conditions. PMID:26870728

  10. Leaf gas exchange and nutrient use efficiency help explain the distribution of two Neotropical mangroves under contrasting flooding and salinity

    USGS Publications Warehouse

    Cardona-Olarte, Pablo; Krauss, Ken W.; Twilley, Robert R.

    2013-01-01

    Rhizophora mangle and Laguncularia racemosa co-occur along many intertidal floodplains in the Neotropics. Their patterns of dominance shift along various gradients, coincident with salinity, soil fertility, and tidal flooding. We used leaf gas exchange metrics to investigate the strategies of these two species in mixed culture to simulate competition under different salinity concentrations and hydroperiods. Semidiurnal tidal and permanent flooding hydroperiods at two constant salinity regimes (10 g L−1 and 40 g L−1) were simulated over 10 months. Assimilation (A), stomatal conductance (gw), intercellular CO2 concentration (Ci), instantaneous photosynthetic water use efficiency (PWUE), and photosynthetic nitrogen use efficiency (PNUE) were determined at the leaf level for both species over two time periods. Rhizophora mangle had significantly higher PWUE than did L. racemosa seedlings at low salinities; however, L. racemosa had higher PNUE and stomatal conductance and gw, accordingly, had greater intercellular CO2 (calculated) during measurements. Both species maintained similar capacities for assimilation at 10 and 40 g L−1 salinity and during both permanent and tidal hydroperiod treatments. Hydroperiod alone had no detectable effect on leaf gas exchange. However, PWUE increased and PNUE decreased for both species at 40 g L−1 salinity compared to 10 g L−1. At 40 g L−1 salinity, PNUE was higher for L. racemosa than R. mangle with tidal flooding. These treatments indicated that salinity influences gas exchange efficiency, might affect how gases are apportioned intercellularly, and accentuates different strategies for distributing leaf nitrogen to photosynthesis for these two species while growing competitively.

  11. Land use affects the net ecosystem CO2 exchange and its components in mountain grasslands

    PubMed Central

    Schmitt, M.; Bahn, M.; Wohlfahrt, G.; Tappeiner, U.; Cernusca, A.

    2011-01-01

    Changes in land use and management have been strongly affecting mountain grassland, however, their effects on the net ecosystem exchange of CO2 (NEE) and its components have not yet been well documented. We analysed chamber-based estimates of NEE, gross primary productivity (GPP), ecosystem respiration (R) and light use efficiency (LUE) of six mountain grasslands differing in land use and management, and thus site fertility, for the growing seasons of 2002 to 2008. The main findings of the study are that: (1) land use and management affected seasonal NEE, GPP and R, which all decreased from managed to unmanaged grasslands; (2) these changes were explained by differences in leaf area index (LAI), biomass and leaf-area-independent changes that were likely related to photosynthetic physiology; (3) diurnal variations of NEE were primarily controlled by photosynthetically active photon flux density and soil and air temperature; seasonal variations were associated with changes in LAI; (4) parameters of light response curves were generally closely related to each other, and the ratio of R at a reference temperature/ maximum GPP was nearly constant across the sites; (5) similarly to our study, maximum GPP and R for other grasslands on the globe decreased with decreasing land use intensity, while their ratio remained remarkably constant. We conclude that decreasing intensity of management and, in particular, abandonment of mountain grassland lead to a decrease in NEE and its component processes. While GPP and R are generally closely coupled during most of the growing season, GPP is more immediately and strongly affected by land management (mowing, grazing) and season. This suggests that management and growing season length, as well as their possible future changes, may play an important role for the annual C balance of mountain grassland. PMID:23293657

  12. Volatile Exchange between Undamaged Plants - a New Mechanism Affecting Insect Orientation in Intercropping

    PubMed Central

    Ninkovic, Velemir; Dahlin, Iris; Vucetic, Andja; Petrovic-Obradovic, Olivera; Glinwood, Robert; Webster, Ben

    2013-01-01

    Changes in plant volatile emission can be induced by exposure to volatiles from neighbouring insect-attacked plants. However, plants are also exposed to volatiles from unattacked neighbours, and the consequences of this have not been explored. We investigated whether volatile exchange between undamaged plants affects volatile emission and plant-insect interaction. Consistently greater quantities of two terpenoids were found in the headspace of potato previously exposed to volatiles from undamaged onion plants identified by mass spectrometry. Using live plants and synthetic blends mimicking exposed and unexposed potato, we tested the olfactory response of winged aphids, Myzus persicae. The altered potato volatile profile deterred aphids in laboratory experiments. Further, we show that growing potato together with onion in the field reduces the abundance of winged, host-seeking aphids. Our study broadens the ecological significance of the phenomenon; volatiles carry not only information on whether or not neighbouring plants are under attack, but also information on the emitter plants themselves. In this way responding plants could obtain information on whether the neighbouring plant is a competitive threat and can accordingly adjust their growth towards it. We interpret this as a response in the process of adaptation towards neighbouring plants. Furthermore, these physiological changes in the responding plants have significant ecological impact, as behaviour of aphids was affected. Since herbivore host plants are potentially under constant exposure to these volatiles, our study has major implications for the understanding of how mechanisms within plant communities affect insects. This knowledge could be used to improve plant protection and increase scientific understanding of communication between plants and its impact on other organisms. PMID:23922710

  13. Nax loci affect SOS1-like Na+/H+ exchanger expression and activity in wheat

    PubMed Central

    Zhu, Min; Shabala, Lana; Cuin, Tracey A; Huang, Xin; Zhou, Meixue; Munns, Rana; Shabala, Sergey

    2016-01-01

    Salinity stress tolerance in durum wheat is strongly associated with a plant’s ability to control Na+ delivery to the shoot. Two loci, termed Nax1 and Nax2, were recently identified as being critical for this process and the sodium transporters HKT1;4 and HKT1;5 were identified as the respective candidate genes. These transporters retrieve Na+ from the xylem, thus limiting the rates of Na+ transport from the root to the shoot. In this work, we show that the Nax loci also affect activity and expression levels of the SOS1-like Na+/H+ exchanger in both root cortical and stelar tissues. Net Na+ efflux measured in isolated steles from salt-treated plants, using the non-invasive ion flux measuring MIFE technique, decreased in the sequence: Tamaroi (parental line)>Nax1=Nax2>Nax1:Nax2 lines. This efflux was sensitive to amiloride (a known inhibitor of the Na+/H+ exchanger) and was mirrored by net H+ flux changes. TdSOS1 relative transcript levels were 6–10-fold lower in Nax lines compared with Tamaroi. Thus, it appears that Nax loci confer two highly complementary mechanisms, both of which contribute towards reducing the xylem Na+ content. One enhances the retrieval of Na+ back into the root stele via HKT1;4 or HKT1;5, whilst the other reduces the rate of Na+ loading into the xylem via SOS1. It is suggested that such duality plays an important adaptive role with greater versatility for responding to a changing environment and controlling Na+ delivery to the shoot. PMID:26585227

  14. Nax loci affect SOS1-like Na+/H+ exchanger expression and activity in wheat.

    PubMed

    Zhu, Min; Shabala, Lana; Cuin, Tracey A; Huang, Xin; Zhou, Meixue; Munns, Rana; Shabala, Sergey

    2016-02-01

    Salinity stress tolerance in durum wheat is strongly associated with a plant's ability to control Na(+) delivery to the shoot. Two loci, termed Nax1 and Nax2, were recently identified as being critical for this process and the sodium transporters HKT1;4 and HKT1;5 were identified as the respective candidate genes. These transporters retrieve Na(+) from the xylem, thus limiting the rates of Na(+) transport from the root to the shoot. In this work, we show that the Nax loci also affect activity and expression levels of the SOS1-like Na(+)/H(+) exchanger in both root cortical and stelar tissues. Net Na(+) efflux measured in isolated steles from salt-treated plants, using the non-invasive ion flux measuring MIFE technique, decreased in the sequence: Tamaroi (parental line)>Nax1=Nax2>Nax1:Nax2 lines. This efflux was sensitive to amiloride (a known inhibitor of the Na(+)/H(+) exchanger) and was mirrored by net H(+) flux changes. TdSOS1 relative transcript levels were 6-10-fold lower in Nax lines compared with Tamaroi. Thus, it appears that Nax loci confer two highly complementary mechanisms, both of which contribute towards reducing the xylem Na(+) content. One enhances the retrieval of Na(+) back into the root stele via HKT1;4 or HKT1;5, whilst the other reduces the rate of Na(+) loading into the xylem via SOS1. It is suggested that such duality plays an important adaptive role with greater versatility for responding to a changing environment and controlling Na(+) delivery to the shoot. PMID:26585227

  15. Field experiments yield new insights into gas exchange and excess air formation in natural porous media

    NASA Astrophysics Data System (ADS)

    Klump, Stephan; Tomonaga, Yama; Kienzler, Peter; Kinzelbach, Wolfgang; Baumann, Thomas; Imboden, Dieter M.; Kipfer, Rolf

    2007-03-01

    Gas exchange between seepage water and soil air within the unsaturated and quasi-saturated zones is fundamentally different from gas exchange between water and gas across a free boundary layer, e.g., in lakes or rivers. In addition to the atmospheric equilibrium fraction, most groundwater samples contain an excess of dissolved atmospheric gases which is called "excess air". Excess air in groundwater is not only of crucial importance for the interpretation of gaseous environmental tracer data, but also for other aspects of groundwater hydrology, e.g., for oxygen availability in bio-remediation and in connection with changes in transport dynamics caused by the presence of entrapped air bubbles. Whereas atmospheric solubility equilibrium is controlled mainly by local soil temperature, the excess air component is characterized by the (hydrostatic) pressure acting on entrapped air bubbles within the quasi-saturated zone. Here we present the results of preliminary field experiments in which we investigated gas exchange and excess air formation in natural porous media. The experimental data suggest that the formation of excess air depends significantly on soil properties and on infiltration mechanisms. Excess air was produced by the partial dissolution of entrapped air bubbles during a sprinkling experiment in fine-grained sediments, whereas similar experiments conducted in coarse sand and gravel did not lead to the formation of excess air in the infiltrating water. Furthermore, the experiments revealed that the noble gas temperatures determined from noble gases dissolved in seepage water at different depths are identical to the corresponding in situ soil temperatures. This finding is important for all applications of noble gases as a paleotemperature indicator in groundwater since these applications are always based on the assumption that the noble gas temperature is identical to the (past) soil temperature.

  16. 30 CFR 250.120 - How does injecting, storing, or treating gas affect my royalty payments?

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 2 2010-07-01 2010-07-01 false How does injecting, storing, or treating gas... Performance Standards § 250.120 How does injecting, storing, or treating gas affect my royalty payments? (a... and treat it at an off-lease or off-unit location, you must pay royalties when the gas is...

  17. Operation of an experimental algal gas exchanger for use in a CELSS

    NASA Technical Reports Server (NTRS)

    Smernoff, David T.; Wharton, Robert A., Jr.; Averner, Maurice M.

    1987-01-01

    Concepts of a CELSS anticipate the use of photosynthetic organisms for air revitalization. The rates of production and uptake of carbon dioxide and oxygen between the crew and the photosynthetic organisms are mismatched. An algal system used for gas exchange only will have the difficulty of an accumulation or depletion of these gases beyond physiologically tolerable limits. The results of a study designed to test the feasibility of using environmental manipulations to maintain physiologically appropriate atmospheres for algae (Chlorella pyrenoidosa) and mice (Mus musculus strain DW/J) in a gas-closed system is reported. Specifically, the atmosphere behavior of this system with Chlorella grown on nitrate or urea and at different light intensities and optical densities is considered. Manipulation of both the photosynthetic rate and the assimilatory quotient of the alga has been found to reduce the mismatch of gas requirements and allow operation of the system in a gas-stable manner.

  18. Experimental investigation of a reticulated porous alumina heat exchanger for high temperature gas heat recovery

    SciTech Connect

    Banerjee, A; Chandran, RB; Davidson, JH

    2015-01-22

    The present study presents an experimental study of a prototype counter-flow heat exchanger designed to recover sensible heat from inert and reactive gases flowing through a high temperature solar reactor for splitting CO2. The tube-in-tube heat exchanger is comprised of two concentric alumina tubes, each filled with reticulated porous alumina with a nominal porosity of 80% and pore density of 5 pores per inch (ppi). The RPC provides high heat transfer surface area per unit volume (917 m(-1)) with low pressure drop. Measurements include the permeability, inertial coefficient, overall heat transfer coefficient, effectiveness and pressure drop. For laminar flow and an inlet gas temperature of 1240 K, the overall heat transfer coefficients are 36-41 W m(-2) K-1. The measured performance is in good agreement with a prior CFD model of the heat exchanger. (C) 2014 Elsevier Ltd. All rights reserved.

  19. Air-water gas exchange and CO2 flux in a mangrove-dominated estuary

    USGS Publications Warehouse

    Ho, David T.; Ferrón, Sara; Engel, Victor C.; Larsen, Laurel G.; Barr, Jordan G.

    2014-01-01

    Mangrove forests are highly productive ecosystems, but the fate of mangrove-derived carbon remains uncertain. Part of that uncertainty stems from the fact that gas transfer velocities in mangrove-surrounded waters are not well determined, leading to uncertainty in air-water CO2 fluxes. Two SF6 tracer release experiments were conducted to determine gas transfer velocities (k(600) = 8.3 ± 0.4 and 8.1 ± 0.6 cm h−1), along with simultaneous measurements of pCO2 to determine the air-water CO2 fluxes from Shark River, Florida (232.11 ± 23.69 and 171.13 ± 20.28 mmol C m−2 d−1), an estuary within the largest contiguous mangrove forest in North America. The gas transfer velocity results are consistent with turbulent kinetic energy dissipation measurements, indicating a higher rate of turbulence and gas exchange than predicted by commonly used wind speed/gas exchange parameterizations. The results have important implications for carbon fluxes in mangrove ecosystems.

  20. Design of a Small Scale High Temperature Gas Loop for Process Heat Exchanger Design Tests

    SciTech Connect

    SungDeok, Hong; DongSeok, Oh; WonJae, Lee; JongHwa, Chang

    2006-07-01

    We designed a small scale gas loop that can simulate reference operating conditions, that is, a temperature up to 950 deg C and a pressure up to 6 MPa. Main objective of the loop is to screen the candidate process-heat-exchanger designs of a very small capacity of 10 {approx} 20 kW. We arranged the components of a primary gas loop and a secondary SO{sub 3} loop. Design requirements are prepared for the safe design of a main heater, a hot-gas-duct and a process heat exchanger that avoid a risk of a failure owing to thermal stresses, a flow-induced vibration or an acoustic vibration in both nitrogen and helium mediums. In the primary and secondary loops, the hot-gas-ducts are internally insulated by a ceramic fiber insulation material to protect the pressure housing from high gas temperatures. We determined a total pressure loss of the primary loop to be 66 kPa and the minimum outer diameter of the loop pressure pipe to be 90 mm at a hot location that will prevent a thermal failure. Very toxic SO{sub 3} secondary loop is needed a scrubber and a SO{sub 3} collector for safety and preventing a contamination of the environment. (authors)

  1. Air-water gas exchange and CO2 flux in a mangrove-dominated estuary

    NASA Astrophysics Data System (ADS)

    Ho, David T.; Ferrón, Sara; Engel, Victor C.; Larsen, Laurel G.; Barr, Jordan G.

    2014-01-01

    forests are highly productive ecosystems, but the fate of mangrove-derived carbon remains uncertain. Part of that uncertainty stems from the fact that gas transfer velocities in mangrove-surrounded waters are not well determined, leading to uncertainty in air-water CO2 fluxes. Two SF6 tracer release experiments were conducted to determine gas transfer velocities (k(600) = 8.3 ± 0.4 and 8.1 ± 0.6 cm h-1), along with simultaneous measurements of pCO2 to determine the air-water CO2 fluxes from Shark River, Florida (232.11 ± 23.69 and 171.13 ± 20.28 mmol C m-2 d-1), an estuary within the largest contiguous mangrove forest in North America. The gas transfer velocity results are consistent with turbulent kinetic energy dissipation measurements, indicating a higher rate of turbulence and gas exchange than predicted by commonly used wind speed/gas exchange parameterizations. The results have important implications for carbon fluxes in mangrove ecosystems.

  2. A two-dimensional microscale model of gas exchange during photosynthesis in maize (Zea mays L.) leaves.

    PubMed

    Retta, Moges; Ho, Quang Tri; Yin, Xinyou; Verboven, Pieter; Berghuijs, Herman N C; Struik, Paul C; Nicolaï, Bart M

    2016-05-01

    CO2 exchange in leaves of maize (Zea mays L.) was examined using a microscale model of combined gas diffusion and C4 photosynthesis kinetics at the leaf tissue level. Based on a generalized scheme of photosynthesis in NADP-malic enzyme type C4 plants, the model accounted for CO2 diffusion in a leaf tissue, CO2 hydration and assimilation in mesophyll cells, CO2 release from decarboxylation of C4 acids, CO2 fixation in bundle sheath cells and CO2 retro-diffusion from bundle sheath cells. The transport equations were solved over a realistic 2-D geometry of the Kranz anatomy obtained from light microscopy images. The predicted responses of photosynthesis rate to changes in ambient CO2 and irradiance compared well with those obtained from gas exchange measurements. A sensitivity analysis showed that the CO2 permeability of the mesophyll-bundle sheath and airspace-mesophyll interfaces strongly affected the rate of photosynthesis and bundle sheath conductance. Carbonic anhydrase influenced the rate of photosynthesis, especially at low intercellular CO2 levels. In addition, the suberin layer at the exposed surface of the bundle sheath cells was found beneficial in reducing the retro-diffusion. The model may serve as a tool to investigate CO2 diffusion further in relation to the Kranz anatomy in C4 plants. PMID:26993234

  3. Impaired Gas Exchange at Birth and Risk of Intellectual Disability and Autism: A Meta-Analysis

    ERIC Educational Resources Information Center

    Modabbernia, Amirhossein; Mollon, Josephine; Boffetta, Paolo; Reichenberg, Abraham

    2016-01-01

    We conducted meta-analyses of 67 studies on the association between neonatal proxies of impaired gas exchange and intellectual disability (ID) or autism spectrum disorders (ASD). Neonatal acidosis was associated with an odds ratio (OR) of 3.55 [95% confidence interval (95% CI) 2.23-5.49] for ID and an OR of 1.10 (95% CI 0.91-1.31) for ASD.…

  4. The gas exchange of hydrogen-adapted algae as followed by mass spectrometry.

    NASA Technical Reports Server (NTRS)

    Stuart, T. S.; Gaffron, H.

    1972-01-01

    The combination of a mass spectrometer inlet and an oxygen electrode in the same vessel permitted continuous recording of the gas exchange of hydrogenase-containing anaerobically adapted algae. In contrast to conventional manometry, the present method made it possible to discern the simultaneous course of reactions involving O2, CO2, and H2. The experiments strongly support the idea of a balance between the photoproduction and photoutilization of H2.

  5. Gas exchange

    MedlinePlus Videos and Cool Tools

    ... lungs to the bloodstream, and the elimination of carbon dioxide from the bloodstream to the lungs. It ... membrane with the capillaries in which oxygen and carbon dioxide move freely between the respiratory system and ...

  6. Gas exchange

    MedlinePlus

    ... lungs to the bloodstream, and the elimination of carbon dioxide from the bloodstream to the lungs. It occurs ... membrane with the capillaries in which oxygen and carbon dioxide move freely between the respiratory system and the ...

  7. Are carbon and nitrogen exchange between fungi and the orchid Goodyera repens affected by irradiance?

    PubMed Central

    Liebel, Heiko T.; Bidartondo, Martin I.; Gebauer, Gerhard

    2015-01-01

    Background and Aims The green orchid Goodyera repens has been shown to transfer carbon to its mycorrhizal partner, and this flux may therefore be affected by light availability. This study aimed to test whether the C and N exchange between plant and fungus is dependent on light availability, and in addition addressed the question of whether flowering and/or fruiting individuals of G. repens compensate for changes in leaf chlorophyll concentration with changes in C and N flows from fungus to plant. Methods The natural abundances of stable isotopes of plant C and N were used to infer changes in fluxes between orchid and fungus across natural gradients of irradiance at five sites. Mycorrhizal fungi in the roots of G. repens were identified by molecular analyses. Chlorophyll concentrations in the leaves of the orchid and of reference plants were measured directly in the field. Key Results Leaf δ13C values of G. repens responded to changes in light availability in a similar manner to autotrophic reference plants, and different mycorrhizal fungal associations also did not affect the isotope abundance patterns of the orchid. Flowering/fruiting individuals had lower leaf total N and chlorophyll concentrations, which is most probably explained by N investments to form flowers, seeds and shoot. Conclusions The results indicate that mycorrhizal physiology is relatively fixed in G. repens, and changes in the amount and direction of C flow between plant and fungus were not observed to depend on light availability. The orchid may instead react to low-light sites through increased clonal growth. The orchid does not compensate for low leaf total N and chlorophyll concentrations by using a 13C- and 15N-enriched fungal source. PMID:25538109

  8. Host suitability and gas exchange response of grapevines to potato leafhopper (Hemiptera: Cicadellidae).

    PubMed

    Lamp, William O; Miranda, Daniel; Culler, Lauren E; Alexander, Laurie C

    2011-08-01

    Although potato leafhopper, Empoasca fabae (Harris) (Hemiptera: Cicadellidae), is highly polyphagous, classic host studies do not recognize grapevines (Vitis spp.), as suitable hosts. Recently, injury has been reported and reproduction documented within grape vineyards, suggesting a host expansion for the leafhopper. To document this apparent expansion in host use, we determined whether grape plants were suitable hosts for potato leafhopper reproduction, measured the consequence of feeding injury on gas exchange rates of grape leaves, and compared the susceptibility to feeding injury among cultivars. We found that potato leafhopper adults survived equally well on grape (Vitis vinifera L.), alfalfa (Medicago sativa L.), and fava bean (Vicia faba L.). The total number of offspring was greater on fava bean but did not differ between alfalfa and grape. Injury to grapevines was assessed by measuring gas exchange responses of leaves in field cages and in greenhouse tests. We found marginally significant declines in photosynthesis and transpiration rates in the field (9.6 and 13.2%, respectively), and much stronger effects in greenhouse tests (ranging between 22 and 52%). Our results verify that Vitis is a suitable host, and that potato leafhopper is capable of injuring its gas exchange physiology. We discuss possible explanations for the host expansion, and its potential to damage commercial grapevines. PMID:21882698

  9. BOREAS TE-9 In Situ Diurnal Gas Exchange of NAS Boreal Forest Stands

    NASA Technical Reports Server (NTRS)

    Hall, Forrest G. (Editor); Curd, Shelaine (Editor); Margolis, Hank; Coyea, Marie; Dang, Qinglai

    2000-01-01

    The BOREAS TE-9 team collected several data sets related to chemical and photosynthetic properties of leaves in boreal forest tree species. The purpose of the BOREAS TE-09 study was threefold: 1) to provide in situ gas exchange data that will be used to validate models of photosynthetic responses to light, temperature, and carbon dioxide (CO2); 2) to compare the photosynthetic responses of different tree crown levels (upper and lower); and 3) to characterize the diurnal water potential curves for these sites to get an indication of the extent to which soil moisture supply to leaves might be limiting photosynthesis. The gas exchange data of the BOREAS NSA were collected to characterize diurnal gas exchange and water potential of two canopy levels of five boreal canopy cover types: young jack pine, old jack pine, old aspen, lowland old black spruce, and upland black spruce. These data were collected between 27-May-1994 and 17-Sep-1994. The data are provided in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

  10. Plantecophys - An R Package for Analysing and Modelling Leaf Gas Exchange Data

    PubMed Central

    Duursma, Remko A.

    2015-01-01

    Here I present the R package 'plantecophys', a toolkit to analyse and model leaf gas exchange data. Measurements of leaf photosynthesis and transpiration are routinely collected with portable gas exchange instruments, and analysed with a few key models. These models include the Farquhar-von Caemmerer-Berry (FvCB) model of leaf photosynthesis, the Ball-Berry models of stomatal conductance, and the coupled leaf gas exchange model which combines the supply and demand functions for CO2 in the leaf. The 'plantecophys' R package includes functions for fitting these models to measurements, as well as simulating from the fitted models to aid in interpreting experimental data. Here I describe the functionality and implementation of the new package, and give some examples of its use. I briefly describe functions for fitting the FvCB model of photosynthesis to measurements of photosynthesis-CO2 response curves ('A-Ci curves'), fitting Ball-Berry type models, modelling C3 photosynthesis with the coupled photosynthesis-stomatal conductance model, modelling C4 photosynthesis, numerical solution of optimal stomatal behaviour, and energy balance calculations using the Penman-Monteith equation. This open-source package makes technically challenging calculations easily accessible for many users and is freely available on CRAN. PMID:26581080

  11. Plantecophys--An R Package for Analysing and Modelling Leaf Gas Exchange Data.

    PubMed

    Duursma, Remko A

    2015-01-01

    Here I present the R package 'plantecophys', a toolkit to analyse and model leaf gas exchange data. Measurements of leaf photosynthesis and transpiration are routinely collected with portable gas exchange instruments, and analysed with a few key models. These models include the Farquhar-von Caemmerer-Berry (FvCB) model of leaf photosynthesis, the Ball-Berry models of stomatal conductance, and the coupled leaf gas exchange model which combines the supply and demand functions for CO2 in the leaf. The 'plantecophys' R package includes functions for fitting these models to measurements, as well as simulating from the fitted models to aid in interpreting experimental data. Here I describe the functionality and implementation of the new package, and give some examples of its use. I briefly describe functions for fitting the FvCB model of photosynthesis to measurements of photosynthesis-CO2 response curves ('A-Ci curves'), fitting Ball-Berry type models, modelling C3 photosynthesis with the coupled photosynthesis-stomatal conductance model, modelling C4 photosynthesis, numerical solution of optimal stomatal behaviour, and energy balance calculations using the Penman-Monteith equation. This open-source package makes technically challenging calculations easily accessible for many users and is freely available on CRAN. PMID:26581080

  12. Respiratory and cuticular water loss in insects with continuous gas exchange: comparison across five ant species.

    PubMed

    Schilman, Pablo E; Lighton, John R B; Holway, David A

    2005-12-01

    Respiratory water loss (RWL) in insects showing continuous emission of CO(2) is poorly studied because few methodologies can measure it. Comparisons of RWL between insects showing continuous and discontinuous gas exchange cycles (DGC) are therefore difficult. We used two recently developed methodologies (the hyperoxic switch and correlation between water-loss and CO(2) emission rates) to compare cuticular permeabilities and rates of RWL in five species of ants, the Argentine ant (Linepithema humile) and four common native ant competitors. Our results showed that RWL in groups of ants with moderate levels of activity and continuous gas exchange were similar across the two measurement methods, and were similar to published values on insects showing the DGC. Furthermore, ants exposed to anoxia increased their total water loss rates by 50-150%. These results suggest that spiracular control under continuous gas exchange can be as effective as the DGC in reducing RWL. Finally, the mesic-adapted Argentine ant showed significantly higher rates of water loss and cuticular permeability compared to four ant species native to dry environments. Physiological limitations may therefore be responsible for restricting the distribution of this invasive species in seasonally dry environments. PMID:16154585

  13. [A comparative study of external respiration, gas exchange and circulation during static and dynamic muscular loads].

    PubMed

    Bubeev, Iu A; Khomenko, M N; Poliukhovich, V V; Remizov, Iu I

    1995-01-01

    Indices of external breathing, gas exchange, and circulation were studied during bicycle ergometry and static ergometry of 19 healthy male volunteers which were stopped at critical levels of heart rate, arterial pressure, ECG or subjective fatigue. The bicycle workload maximum averaged 210 Watts, the static ergometric, 224 kg/s. Both types of exercises were characterized by unidirectional shifting of the external breathing and gas exchange indices; however, they were less pronounced at static loads. Arterial pressure and resistance of the peripheral vessels were the only indices of the array the dynamics of which complied with and even exceeded that during bicycling. In contrast to the dynamic muscular load, the maximal dynamics of gas exchange and external breathing during static ergometric workload was observed in the rehabilitation period following restoration of muscle blood flow; this must be taken into account in interpretation of test results. It is concluded that high information virtues of the static ergometric test in the context of predicting aerobatic load tolerance, and similarity of dynamics in the period of rehabilitation hold much promise for using the tests with static muscular loading in aviation and space medicine. PMID:8664858

  14. Gas exchange pattern transitions in the workers of the harvester termite.

    PubMed

    Inder, Isabelle M; Duncan, Frances D

    2015-04-01

    The evolutionary genesis and the current adaptive significance of the use of the discontinuous gas exchange cycle (DGC) for respiration by insects is the subject of intense debate. Years of research have resulted in several leading hypotheses, one of which is the emergent-property hypothesis. This hypothesis states that DGC is an emergent property or consequence of interactions between the O2 and CO2 set points that regulate spiracular function, i.e. opening and closing. Workers of the harvester termite, Hodotermes mossambicus were selected as a model to test this hypothesis. The respiratory patterns of major workers, investigated using flow-through respirometry, were obtained at 100% relative humidity (RH) under varying temperature to evaluate the assumptions of the emergent-property hypothesis. Metabolic rate, measured as VCO2 increased significantly after 15 °C. As VCO2 increased in response to increasing temperature and activity, the gas exchange pattern displayed by workers transitioned to a continuous gas exchange. A true DGC, defined as showing all three phases and a coefficient of variation value close to 2, was not expressed under the experimental conditions. The conclusion drawn from this study of termite workers is that changes in respiratory patterns are most likely an emergent property of the insects' nervous and respiratory system. PMID:25770978

  15. The effects of temperature on the gas exchange cycle in Agathemera crassa.

    PubMed

    Thienel, Mariana; Canals, Mauricio; Bozinovic, Francisco; Veloso, Claudio

    2015-05-01

    Insects exhibit three patterns of gas exchange: continuous (CoGE), cyclic (CGE) and discontinuous (DGE). In this work, we present the first record of a DGE in Phasmatodea and its transition to CGE and to CoGE through a thermal gradient. The rate of CO2 production (VCO2) at 10, 20 and 30°C was examined in adults of Agathemera crassa, a high-Andean phasmid of central Chile. Carbon dioxide release was recorded during 24 h with L:D cycle of 12:12 h in order to record both rest and activity periods. At rest, A. crassa showed three patterns of gas exchange, highlighting the use of DGE preferably at 10°C. As the temperature increased, the CoGE pattern was more frequent being the only pattern observed in all individuals at 30°C. During activity, patterns changed to CoGE with a significant increase in VCO2. Our results support the idea that gas exchange patterns in insects are not distinct but correspond to a continuum of responses addressed by metabolic demand and where DGE can be expressed only under an absolute state of rest. Our results support the idea that the presence of the DGE may be underestimated in other insect taxa because they may have been measured under conditions where this pattern not necessarily can be expressed. PMID:25624164

  16. Mapping intercellular CO2 mole fraction (Ci) in rosa rubiginosa leaves fed with abscisic acid by using chlorophyll fluorescence imaging. Significance Of ci estimated from leaf gas exchange

    PubMed

    Meyer; Genty

    1998-03-01

    Imaging of photochemical yield of photosystem II (PSII) computed from leaf chlorophyll fluorescence images and gas-exchange measurements were performed on Rosa rubiginosa leaflets during abscisic acid (ABA) addition. In air ABA induced a decrease of both the net CO2 assimilation (An) and the stomatal water vapor conductance (gs). After ABA treatment, imaging in transient nonphotorespiratory conditions (0.1% O2) revealed a heterogeneous decrease of PSII photochemical yield. This decline was fully reversed by a transient high CO2 concentration (7400 mol mol-1) in the leaf atmosphere. It was concluded that ABA primarily affected An by decreasing the CO2 supply at ribulose-1,5-bisphosphate carboxylase/oxygenase. Therefore, the An versus intercellular mole fraction (Ci) relationship was assumed not to be affected by ABA, and images of Ci and gs were constructed from images of PSII photochemical yield under nonphotorespiratory conditions. The distribution of gs remained unimodal following ABA treatment. A comparison of calculations of Ci from images and gas exchange in ABA-treated leaves showed that the overestimation of Ci estimated from gas exchange was only partly due to heterogeneity. This overestimation was also attributed to the cuticular transpiration, which largely affects the calculation of the leaf conductance to CO2, when leaf conductance to water is low. PMID:9501127

  17. Evaluation of Gas Disengaging Equipment Supporting a Crystalline Silicotitanate Ion-Exchange Column System

    SciTech Connect

    Spencer, B.B.

    2001-04-12

    The objective of this experimental program was to evaluate the effectiveness of gas-disengaging equipment (GDE) to separate gas from the liquid effluent of CST ion-exchange columns. The GDE designed for this evaluation supports four fundamental separation methods: (1) passive settling, (2) gas sparging to strip entrained gas or gas bubbles, (3) subatmospheric pressure separation, and (4) injection of ultrasonic waves to induce coalescence of bubbles with attendant settling. These methods may be used separately or in combination, provided that the selections are not mutually exclusive (e.g., passive settling and gas sparging are mutually exclusive by definition). The method using ultrasonic waves is limited because the acoustic actuator cannot be used on a continuous basis; only intermittent bursts are recommended to prevent overheating and subsequent failure. Each separation method was evaluated to determine which, if any, would be suitable for application to CST ion-exchange columns. The GDE supports two general modes of column operation. In one mode, the GDE operates at an elevated pressure and the feed pump must push fluid through the series of columns. In the other mode, operation proceeds in a vented condition and an interstage pump is required to reelevate the liquid pressure to feed the downstream column. In the third mode, the GDE may be bypassed to obtain base-line data in the absence of gas removal. Again, the feed pump must overcome the frictional losses and elevation differences associated with both columns. The efficiency/effectiveness of the GDE is based on the fraction of undissolved gas removed in the unit and on the size of the gas bubbles carried into and out of the unit with the liquid stream. Optimization of combinations of the fundamental separation methods is beyond the scope of the tests reported here. Pressure drop (caused by resistance to flow) in the second column was measured since increases can be used as an indirect indicator of gas

  18. Surfactant control of gas transfer velocity along an offshore coastal transect: results from a laboratory gas exchange tank

    NASA Astrophysics Data System (ADS)

    Pereira, R.; Schneider-Zapp, K.; Upstill-Goddard, R. C.

    2016-07-01

    Understanding the physical and biogeochemical controls of air-sea gas exchange is necessary for establishing biogeochemical models for predicting regional- and global-scale trace gas fluxes and feedbacks. To this end we report the results of experiments designed to constrain the effect of surfactants in the sea surface microlayer (SML) on the gas transfer velocity (kw; cm h-1), seasonally (2012-2013) along a 20 km coastal transect (North East UK). We measured total surfactant activity (SA), chromophoric dissolved organic matter (CDOM) and chlorophyll a (Chl a) in the SML and in sub-surface water (SSW) and we evaluated corresponding kw values using a custom-designed air-sea gas exchange tank. Temporal SA variability exceeded its spatial variability. Overall, SA varied 5-fold between all samples (0.08 to 0.38 mg L-1 T-X-100), being highest in the SML during summer. SML SA enrichment factors (EFs) relative to SSW were ˜ 1.0 to 1.9, except for two values (0.75; 0.89: February 2013). The range in corresponding k660 (kw for CO2 in seawater at 20 °C) was 6.8 to 22.0 cm h-1. The film factor R660 (the ratio of k660 for seawater to k660 for "clean", i.e. surfactant-free, laboratory water) was strongly correlated with SML SA (r ≥ 0.70, p ≤ 0.002, each n = 16). High SML SA typically corresponded to k660 suppressions ˜ 14 to 51 % relative to clean laboratory water, highlighting strong spatiotemporal gradients in gas exchange due to varying surfactant in these coastal waters. Such variability should be taken account of when evaluating marine trace gas sources and sinks. Total CDOM absorbance (250 to 450 nm), the CDOM spectral slope ratio (SR = S275 - 295/S350 - 400), the 250 : 365 nm CDOM absorption ratio (E2 : E3), and Chl a all indicated spatial and temporal signals in the quantity and composition of organic matter in the SML and SSW. This prompts us to hypothesise that spatiotemporal variation in R660 and its relationship with SA is a consequence of compositional

  19. Exergy destruction analysis of a vortices generator in a gas liquid finned tube heat exchanger: an experimental study

    NASA Astrophysics Data System (ADS)

    Ghazikhani, M.; Khazaee, I.; Monazzam, S. M. S.; Takdehghan, H.

    2016-01-01

    In the present work, the effect of using different shapes of vortices generator (VG) on a gas liquid finned heat exchanger is investigated experimentally with irreversibility analysis. In this project the ambient air with mass flow rates of 0.047-0.072 kg/s is forced across the finned tube heat exchanger. Hot water with constant flow rate of 240 L/h is circulated inside heat exchanger tubes with inlet temperature range of 45-73 °C. The tests are carried out on the flat finned heat exchanger and then repeated on the VG finned heat exchanger. The results show that using the vortex generator can decrease the ratio of air side irreversibility to heat transfer (ASIHR) of the heat exchanger. Also the results show that the IASIHR is >1.05 for all air mass flow rates, which means that ASIHR for the initial heat exchanger is higher than 5 % greater than that of improved heat exchanger.

  20. Effect of Sediment Gas Voids and Ebullition on Benthic Solute Exchange.

    PubMed

    Flury, Sabine; Glud, Ronnie N; Premke, Katrin; McGinnis, Daniel F

    2015-09-01

    The presence of free gas in sediments and ebullition events can enhance the pore water transport and solute exchange across the sediment-water interface. However, we experimentally and theoretically document that the presence of free gas in sediments can counteract this enhancement effect. The apparent diffusivities (Da) of Rhodamine WT and bromide in sediments containing 8-18% gas (Da,YE) were suppressed by 7-39% compared to the control (no gas) sediments (Da,C). The measured ratios of Da,YE:Da,C were well within the range of ratios predicted by a theoretical soil model for gas-bearing soils. Whereas gas voids in sediments reduce the Da for soluble species, they represent a shortcut for low-soluble species such as methane and oxygen. Therefore, the presence of even minor amounts of gas can increase the fluxes of low-soluble species (i.e., gases) by several factors, while simultaneously suppressing fluxes of dissolved species. PMID:26214174

  1. Laser gas analyzers for studying kinetics of gas exchange between vegetation biosystems and atmosphere

    NASA Astrophysics Data System (ADS)

    Ageev, B. G.; Kapitanov, V. A.; Ponomarev, Yu. N.; Vasiliev, V. A.; Karapuzikov, A. I.; Sherstov, I. V.

    2006-11-01

    Specifications and examples of application of laser gas-analyzers of near- and mid-infrared ranges for diagnostics of greenhouse gases (CO II, C IIH 4, and CH 4) emission by vegetation biosystems both under standard conditions and under impacts of natural and anthropogenic stresses are considered in the report. The gas-analyzer complex includes: 1) gas-analyzer with a multipass absorption cell based on the frequency-tunable diode laser (1600-1650 nm) for measuring sub-background methane concentrations (<= 20 ppbV); 2) gas-analyzer based on the wave-guide CO II-laser equipped with the intracavity acoustic detector capable of fast frequency scanning in the 9 and 10 μm generation bands and having the ethylene-sensitivity better than 1 ppbV. The technology of measurements of gas emission by plant stripped leaves and coniferous needles is described and the measurements of CO II and CH 4 emissions are presented.

  2. Laser gas-analyzers for studying kinetics of gas-exchange between vegetation biosystems and atmosphere

    NASA Astrophysics Data System (ADS)

    Ageev, B. G.; Kapitanov, V. A.; Ponomarev, Yu. N.; Vasiliev, V. A.; Karapuzikov, A. I.; Sherstov, I. V.

    2006-12-01

    Specifications and examples of application of laser gas-analyzers of near- and mid-infrared ranges for diagnostics of greenhouse gases (C0 II, C IIH 4, and CH 4) emission by vegetation biosystems both under standard conditions and under impacts of natural and anthropogenic stresses are considered in the report. The gas-analyzer complex includes: 1) gas-analyzer with a multipass absorption cell based on the frequency-tunable diode laser (1600-1 650 nm) for measuring sub-background methane concentrations (<=20 ppbV); 2) gas-analyzer based on the wave-guide C0 II-laser equipped with the intracavity acoustic detector capable of fast frequency scanning in the 9 and 10 μm generation bands and having the ethylene-sensitivity better than 1 ppbV. The technology of measurements of gas emission by plant stripped leaves and coniferous needles is described and the measurements of CO II and CH 4 emissions are presented.

  3. Measurement of void volume of a fuel rod and the exchange of occluded gases from mixed carbide fuel with filling gas helium

    NASA Astrophysics Data System (ADS)

    Rao, G. A. Rama; Kukarni, S. G.; Venugoopal, V.; Manchanda, V. K.; Goswami, G. L.

    1995-02-01

    The presence of gaseous impurities in the filling gas of a fuel pin is detriental to the thermal performance of a nuclear reactor fuel. The composition of the filling gas does not remain constant throughout the life of the fuel pin. The gas exchange phenomena that occur between the cover gas and impurity gases affect the fuel performance more severely in (U, Pu)O 2 fuel pin due to its inherently poor thermal conductivity than in advanced fuels such as mixed carbides and nitrides. In the present study the exchange phenomenon of the occluded gases present in our Fast Breeder Test Reactor (FBTR) fuel pellets [(U 0.30, Pu 0.70)C with 6500 ppm o] with the cover gas helium was observed as a function of time and temperature. Quantitative analysis of the released gases namely H 2, O 2 + Ar, N 2, CH 4 and CO was carried out at subambient pressure by gas chromatography. The void volume of the fuel element is determined experimentally by gas equilibration with known volume.

  4. The Role of Snow Cover on Surface Trace Gas Exchanges at Toolik Lake, AK

    NASA Astrophysics Data System (ADS)

    Helmig, D.; Obrist, D.; Moore, C.; Van Dam, B.; Jacques, H.; Molnar, T.; Williams, M. W.; Kramer, L. J.; Doskey, P. V.; Fain, X.

    2014-12-01

    Snow has a profound influence on the emission and deposition of atmospheric trace gases in the arctic environment. Processes that play a role in modulating gas exchanges include biological, soil biogeochemical, snow chemical, and snow physical processes. Environmental conditions underneath the snow are relatively stable throughout the winter period. Above the snow surface, variations in temperature, radiation, and wind exert a wide range of influences on snowpack gas chemistry, gas exchanges at the snow-air interface, and chemical interactions between the interstitial snowpack air and vegetation and soil below the snowpack. This presentation will present an overview of experimental approaches for continuous, all winter-long experiments conducted at a permafrost site at the Long-Term Ecological Research (LTER) station at Toolik Lake on the north slope of the Brooks Range, Alaska. These studies include observations of carbon dioxide and the reactive gases ozone, nitrogen oxides, and gaseous elemental mercury. Parameterizations developed from these measurements are used for improving descriptions of trace gas budgets and their feedbacks on climate and associated snow cover changes in the Arctic and seasonally snow-covered midlatitude environments.

  5. Canopy photosynthesis and transpiration in microgravity: gas exchange measurements aboard Mir.

    PubMed

    Monje, O; Bingham, G E; Carman, J G; Campbell, W F; Salisbury, F B; Eames, B K; Sytchev, V; Levinskikh, M A; Podolsky, I

    2000-01-01

    The SVET Greenhouse on-board the Orbital Station Mir was used to measure canopy photosynthesis and transpiration rates for the first time in space. During the Greenhouse IIB experiment on Mir (June-January 1997), carbon and water vapor fluxes from two wheat (cv. Superdwarf) canopies were measured using the US developed Gas Exchange Measurement System (GEMS). Gas analyzers capable of resolving CO2 concentration differences of 5 micromoles mol-1 against a background of 0.9% CO2, are necessary to measure photosynthetic and respiratory rates on Mir. The ability of the GEMS gas analyzers to measure these CO2 concentration differences was determined during extensive ground calibrations. Similarly, the sensitivity of the analyzers to water vapor was sufficient to accurately measure canopy evapotranspiration. Evapotranspiration, which accounted for over 90% of the water added to the root zone, was estimated using gas exchange and used to estimate substrate moisture content. This paper presents canopy photosynthesis and transpiration data during the peak vegetative phase of development in microgravity. PMID:11543166

  6. Sodic Soil Properties and Sunflower Growth as Affected by Byproducts of Flue Gas Desulfurization

    PubMed Central

    Wang, Jinman; Bai, Zhongke; Yang, Peiling

    2012-01-01

    The main component of the byproducts of flue gas desulfurization (BFGD) is CaSO4, which can be used to improve sodic soils. The effects of BFGD on sodic soil properties and sunflower growth were studied in a pot experiment. The experiment consisted of eight treatments, at four BFGD rates (0, 7.5, 15 and 22.5 t ha−1) and two leaching levels (750 and 1200 m3 ha−1). The germination rate and yield of the sunflower increased, and the exchangeable sodium percentage (ESP), pH and total dissolved salts (TDS) in the soils decreased after the byproducts were applied. Excessive BFGD also affected sunflower germination and growth, and leaching improved reclamation efficiency. The physical and chemical properties of the reclaimed soils were best when the byproducts were applied at 7.5 t ha−1 and water was supplied at 1200 m3·ha−1. Under these conditions, the soil pH, ESP, and TDS decreased from 9.2, 63.5 and 0.65% to 7.8, 2.8 and 0.06%, and the germination rate and yield per sunflower reached 90% and 36.4 g, respectively. Salinity should be controlled by leaching when sodic soils are reclaimed with BFGD as sunflower growth is very sensitive to salinity during its seedling stage. PMID:23285042

  7. Sodic soil properties and sunflower growth as affected by byproducts of flue gas desulfurization.

    PubMed

    Wang, Jinman; Bai, Zhongke; Yang, Peiling

    2012-01-01

    The main component of the byproducts of flue gas desulfurization (BFGD) is CaSO(4), which can be used to improve sodic soils. The effects of BFGD on sodic soil properties and sunflower growth were studied in a pot experiment. The experiment consisted of eight treatments, at four BFGD rates (0, 7.5, 15 and 22.5 t ha(-1)) and two leaching levels (750 and 1200 m(3) ha(-1)). The germination rate and yield of the sunflower increased, and the exchangeable sodium percentage (ESP), pH and total dissolved salts (TDS) in the soils decreased after the byproducts were applied. Excessive BFGD also affected sunflower germination and growth, and leaching improved reclamation efficiency. The physical and chemical properties of the reclaimed soils were best when the byproducts were applied at 7.5 t ha(-1) and water was supplied at 1200 m(3)·ha(-1). Under these conditions, the soil pH, ESP, and TDS decreased from 9.2, 63.5 and 0.65% to 7.8, 2.8 and 0.06%, and the germination rate and yield per sunflower reached 90% and 36.4 g, respectively. Salinity should be controlled by leaching when sodic soils are reclaimed with BFGD as sunflower growth is very sensitive to salinity during its seedling stage. PMID:23285042

  8. The Viking gas exchange experiment results from Chryse and Utopia surface samples

    NASA Technical Reports Server (NTRS)

    Oyama, V. I.; Berdahl, B. J.

    1977-01-01

    Immediate gas changes occurred when untreated Martian surface samples were humidified and/or wet by an aqueous nutrient medium in the Viking lander gas exchange experiment. The evolutions of N2, CO2, and Ar are mainly associated with soil surface desorption caused by water vapor, while O2 evolution is primarily associated with decomposition of superoxides inferred to be present on Mars. On recharges with fresh nutrient and test gas, only CO2 was given off, and its rate of evolution decreased with each recharge. This CO2 evolution is thought to come from the oxidation of organics present in the nutrient by gamma Fe2O3 in the surface samples. Atmospheric analyses were also performed at both sites. The mean atmospheric composition from four analyses is N2, 2.3%; O2, not greater than 0.15%; Ar, 1.5% and CO2, 96.2%.

  9. Polarized {sup 3}He gas compression system using metastability-exchange optical pumping

    SciTech Connect

    Hussey, D.S.; Rich, D.R.; Belov, A.S.; Tong, X.; Yang, H.; Bailey, C.; Keith, C.D.; Hartfield, J.; Hall, G.D.R.; Black, T.C.; Snow, W.M.; Gentile, T.R.; Chen, W.C.; Jones, G.L.; Wildman, E.

    2005-05-15

    Dense samples (10-100 bar cm) of nuclear spin polarized {sup 3}He are utilized in high energy physics, neutron scattering, atomic physics, and magnetic resonance imaging. Metastability exchange optical pumping can rapidly produce high {sup 3}He polarizations ({approx_equal}80%) at low pressures (few mbar). We describe a polarized {sup 3}He gas compressor system which accepts 0.26 bar l h{sup -1} of {sup 3}He gas polarized to 70% by a 4 W neodymium doped lanthanum magnesium hexaluminate (Nd:LMA) laser and compresses it into a 5 bar cm target with final polarization of 55%. The spin relaxation rates of the system's components have been measured using nuclear magnetic resonance and a model of the {sup 3}He polarization loss based on the measured relaxation rates and the gas flow is in agreement with a {sup 3}He polarization measurement using neutron transmission.

  10. Polarized 3He gas compression system using metastability-exchange optical pumping

    NASA Astrophysics Data System (ADS)

    Hussey, D. S.; Rich, D. R.; Belov, A. S.; Tong, X.; Yang, H.; Bailey, C.; Keith, C. D.; Hartfield, J.; Hall, G. D. R.; Black, T. C.; Snow, W. M.; Gentile, T. R.; Chen, W. C.; Jones, G. L.; Wildman, E.

    2005-05-01

    Dense samples (10-100barcm) of nuclear spin polarized He3 are utilized in high energy physics, neutron scattering, atomic physics, and magnetic resonance imaging. Metastability exchange optical pumping can rapidly produce high He3 polarizations (≈80%) at low pressures (few mbar). We describe a polarized He3 gas compressor system which accepts 0.26barlh-1 of He3 gas polarized to 70% by a 4W neodymium doped lanthanum magnesium hexaluminate (Nd:LMA) laser and compresses it into a 5barcm target with final polarization of 55%. The spin relaxation rates of the system's components have been measured using nuclear magnetic resonance and a model of the He3 polarization loss based on the measured relaxation rates and the gas flow is in agreement with a He3 polarization measurement using neutron transmission.

  11. Dynamics of Exchange at Gas-Zeolite Interfaces 1: Pure Component n-Butane and Isobutane

    SciTech Connect

    CHANDROSS,MICHAEL E.; WEBB III,EDMUND B.; GREST,GARY S.; MARTIN,MARCUS G.; THOMPSON,AIDAN P.; ROTH,M.W.

    2000-07-13

    The authors present the results of molecular dynamics simulations of n-butane and isobutane in silicalite. They begin with a comparison of the bulk adsorption and diffusion properties for two different parameterizations of the interaction potential between the hydrocarbon species, both of which have been shown to reproduce experimental gas-liquid coexistence curves. They examine diffusion as a function of the loading of the zeolite, as well as the temperature dependence of the diffusion constant at loading and for infinite dilution. They continue with simulations in which interfaces are formed between single component gases and the zeolite. After reaching equilibrium, they examine the dynamics of exchange between the bulk gas and the zeolite. Finally, they calculate the permeability of the zeolite for n-butane and isobutane as a function of pressure. Their simulations are performed for a number of different gas temperatures and pressures, covering a wide range of state points.

  12. The sexual erotic market as an analytical framework for understanding erotic-affective exchanges in interracial sexually intimate and affective relationships.

    PubMed

    Vigoya, Mara Viveros

    2015-01-01

    This paper examines the way in which erotic-affective exchanges in interracial relationships have been analysed in Latin America. It considers how race, gender and class operate within a market of values such that erotic, affective and economic status are shaped by racial, gender and class hierarchies. In this paper I analyse historical and social arrangements that embody the region's political economy of race and sex. Such a perspective allows me to address the simultaneous co-existence of socio-racial exclusion and inclusion and the repressive and productive effects of power, attraction and anxiety as aspects of lived experiences in relation to sexuality. From there, I outline an analytical framework that references an erotic or pleasure-based market in which capital and other resources are exchanged from a structural perspective stressing relationship alliances. I conclude by identifying the scope and limits of such an approach. PMID:25431884

  13. Surfactant control of air-sea gas exchange across contrasting biogeochemical regimes

    NASA Astrophysics Data System (ADS)

    Pereira, Ryan; Schneider-Zapp, Klaus; Upstill-Goddard, Robert

    2014-05-01

    Air-sea gas exchange is important to the global partitioning of CO2.Exchange fluxes are products of an air-sea gas concentration difference, ΔC, and a gas transfer velocity, kw. The latter is controlled by the rate of turbulent diffusion at the air-sea interface but it cannot be directly measured and has a high uncertainty that is now considered one of the greatest challenges to quantifying net global air-sea CO2 exchange ...(Takahashi et al., 2009). One important control on kw is exerted by sea surface surfactants that arise both naturally from biological processes and through anthropogenic activity. They influence gas exchange in two fundamental ways: as a monolayer physical barrier and through modifying sea surface hydrodynamics and hence turbulent energy transfer. These effects have been demonstrated in the laboratory with artificial surfactants ...(Bock et al., 1999; Goldman et al., 1988) and through purposeful surfactant releases in coastal waters .(.).........().(Brockmann et al., 1982) and in the open ocean (Salter et al., 2011). Suppression of kwin these field experiments was ~5-55%. While changes in both total surfactant concentration and the composition of the natural surfactant pool might be expected to impact kw, the required in-situ studies are lacking. New data collected from the coastal North Sea in 2012-2013 shows significant spatio-temporal variability in the surfactant activity of organic matter within the sea surface microlayer that ranges from 0.07-0.94 mg/L T-X-100 (AC voltammetry). The surfactant activities show a strong winter/summer seasonal bias and general decrease in concentration with increasing distance from the coastline possibly associated with changing terrestrial vs. phytoplankton sources. Gas exchange experiments of this seawater using a novel laboratory tank and gas tracers (CH4 and SF6) demonstrate a 12-45% reduction in kw compared to surfactant-free water. Seasonally there is higher gas exchange suppression in the summer

  14. Justice at the millennium, a decade later: a meta-analytic test of social exchange and affect-based perspectives.

    PubMed

    Colquitt, Jason A; Scott, Brent A; Rodell, Jessica B; Long, David M; Zapata, Cindy P; Conlon, Donald E; Wesson, Michael J

    2013-03-01

    Although a flurry of meta-analyses summarized the justice literature at the turn of the millennium, interest in the topic has surged in the decade since. In particular, the past decade has witnessed the rise of social exchange theory as the dominant lens for examining reactions to justice, and the emergence of affect as a complementary lens for understanding such reactions. The purpose of this meta-analytic review was to test direct, mediating, and moderating hypotheses that were inspired by those 2 perspectives, to gauge their adequacy as theoretical guides for justice research. Drawing on a review of 493 independent samples, our findings revealed a number of insights that were not included in prior meta-analyses. With respect to social exchange theory, our results revealed that the significant relationships between justice and both task performance and citizenship behavior were mediated by indicators of social exchange quality (trust, organizational commitment, perceived organizational support, and leader-member exchange), though such mediation was not apparent for counterproductive behavior. The strength of those relationships did not vary according to whether the focus of the justice matched the target of the performance behavior, contrary to popular assumptions in the literature, or according to whether justice was referenced to a specific event or a more general entity. With respect to affect, our results showed that justice-performance relationships were mediated by positive and negative affect, with the relevant affect dimension varying across justice and performance variables. Our discussion of these findings focuses on the merit in integrating the social exchange and affect lenses in future research. PMID:23458336

  15. A mass balance method for non-intrusive measurements of surface-air trace gas exchange

    NASA Astrophysics Data System (ADS)

    Denmead, O. T.; Harper, L. A.; Freney, J. R.; Griffith, D. W. T.; Leuning, R.; Sharpe, R. R.

    A mass balance method is described for calculating gas production from a surface or volume source in a small test plot from measurements of differences in the horizontal fluxes of the gas across upwind and downwind boundaries. It employs a square plot, 24 m×24 m, with measurements of gas concentration at four heights (up to 3.5 m) along each of the four boundaries. Gas concentrations are multiplied by the appropriate vector winds to yield the horizontal fluxes at each height on each boundary. The difference between these fluxes integrated over downwind and upwind boundaries represents production. Illustrations of the method, which involve exchanges of methane and carbon dioxide, are drawn from experiments with landfills, pastures and grazing animals. Tests included calculation of recovery rates from known gas releases and comparisons with a conventional micrometeorological approach and a backward dispersion model. The method performed satisfactorily in all cases. Its sensitivity for measuring exchanges of CO 2, CH 4 and N 2O in various scenarios was examined. As employed by us, the mass balance method can suffer from errors arising from the large number of gas analyses required for a flux determination, and becomes unreliable when there are light winds and variable wind directions. On the other hand, it is non-disturbing, has a simple theoretical basis, is independent of atmospheric stability or the shape of the wind profile, and is appropriate for flux measurement in situations where conventional micrometeorological methods can not be used, e.g. for small plots, elevated point sources, and heterogeneous surface sources.

  16. Leaf-level gas exchange and scaling-up of forest understory carbon fixation rates with a ``patch-scale'' canopy model

    NASA Astrophysics Data System (ADS)

    Wedler, M.; Geyer, R.; Heindl, B.; Hahn, S.; Tenhunen, J. D.

    1996-03-01

    During the Hartheim experiment (HartX) 1992, conducted in the Upper Rhine Valley, Germany, we estimated water vapor flux from the understory by several methods as reported in Wedler et al. (this issue). We also examined the photosynthetic gas exchange of the dominant understory species Brachypodium pinnatum, Carex alba, and Carex flacca at the leaf level with an CO2/H2O porometer. A mechanisticallybased leaf gas exchange model was parameterized for these understory species and validated via the measured diurnal courses of carbon dioxide exchange. Leaf CO2 gas exchange was scaled-up to patch- and then to stand-level utilizing the leaf gas exchange model as a component of the canopy light interception/energy balance model GAS-FLUX, and by further considering variation in vegetation “patch-type” distribution, patch-specific spatial structure, patch-type leaf area index, and microclimate beneath the tree canopy. At patch-level, C. alba exhibited the lowest net CO2 uptake of ca. 75 mmol m-2 d-1 due to a low leaf-level photosynthetic capacity, whereas net CO2 fixation of B. pinnatum- and C. flacca-patches was approx. 178 and 184 mmol m-2 d-1, respectively. Highest CO2 uptake was estimated for mixed patches where B. pinnatum grew together with the sedge species C. alba or C. flacca. Scaling-up of leaf gas exchange to stand level resulted in an estimated average rate of total CO2 fixation by the graminoid understory patches of approximately 93 mmol m-2 d-1 during the HartX period. The conservative gas exchange behavior of C. alba at Hartheim and its apparent success in space capture seems to affect overall functioning of this pine forest ecosystem by limiting understory CO2 uptake. The CO2 uptake by the understory is approximately 20% of stand total CO2 uptake. CO2 uptake fluxes mirror the relative differences in water loss from the understory and crown layer during the HartX period. Comparative measurements indicate that understory vegetation in spruce and pine

  17. Peach water relations, gas exchange, growth and shoot mortality under water deficit in semi-arid weather conditions.

    PubMed

    Rahmati, Mitra; Davarynejad, Gholam Hossein; Génard, Michel; Bannayan, Mohammad; Azizi, Majid; Vercambre, Gilles

    2015-01-01

    In this study the sensitivity of peach tree (Prunus persica L.) to three water stress levels from mid-pit hardening until harvest was assessed. Seasonal patterns of shoot and fruit growth, gas exchange (leaf photosynthesis, stomatal conductance and transpiration) as well as carbon (C) storage/mobilization were evaluated in relation to plant water status. A simple C balance model was also developed to investigate sink-source relationship in relation to plant water status at the tree level. The C source was estimated through the leaf area dynamics and leaf photosynthesis rate along the season. The C sink was estimated for maintenance respiration and growth of shoots and fruits. Water stress significantly reduced gas exchange, and fruit, and shoot growth, but increased fruit dry matter concentration. Growth was more affected by water deficit than photosynthesis, and shoot growth was more sensitive to water deficit than fruit growth. Reduction of shoot growth was associated with a decrease of shoot elongation, emergence, and high shoot mortality. Water scarcity affected tree C assimilation due to two interacting factors: (i) reduction in leaf photosynthesis (-23% and -50% under moderate (MS) and severe (SS) water stress compared to low (LS) stress during growth season) and (ii) reduction in total leaf area (-57% and -79% under MS and SS compared to LS at harvest). Our field data analysis suggested a Ψstem threshold of -1.5 MPa below which daily net C gain became negative, i.e. C assimilation became lower than C needed for respiration and growth. Negative C balance under MS and SS associated with decline of trunk carbohydrate reserves--may have led to drought-induced vegetative mortality. PMID:25830350

  18. Peach Water Relations, Gas Exchange, Growth and Shoot Mortality under Water Deficit in Semi-Arid Weather Conditions

    PubMed Central

    Rahmati, Mitra; Davarynejad, Gholam Hossein; Génard, Michel; Bannayan, Mohammad; Azizi, Majid; Vercambre, Gilles

    2015-01-01

    In this study the sensitivity of peach tree (Prunus persica L.) to three water stress levels from mid-pit hardening until harvest was assessed. Seasonal patterns of shoot and fruit growth, gas exchange (leaf photosynthesis, stomatal conductance and transpiration) as well as carbon (C) storage/mobilization were evaluated in relation to plant water status. A simple C balance model was also developed to investigate sink-source relationship in relation to plant water status at the tree level. The C source was estimated through the leaf area dynamics and leaf photosynthesis rate along the season. The C sink was estimated for maintenance respiration and growth of shoots and fruits. Water stress significantly reduced gas exchange, and fruit, and shoot growth, but increased fruit dry matter concentration. Growth was more affected by water deficit than photosynthesis, and shoot growth was more sensitive to water deficit than fruit growth. Reduction of shoot growth was associated with a decrease of shoot elongation, emergence, and high shoot mortality. Water scarcity affected tree C assimilation due to two interacting factors: (i) reduction in leaf photosynthesis (-23% and -50% under moderate (MS) and severe (SS) water stress compared to low (LS) stress during growth season) and (ii) reduction in total leaf area (-57% and -79% under MS and SS compared to LS at harvest). Our field data analysis suggested a Ψstem threshold of -1.5 MPa below which daily net C gain became negative, i.e. C assimilation became lower than C needed for respiration and growth. Negative C balance under MS and SS associated with decline of trunk carbohydrate reserves – may have led to drought-induced vegetative mortality. PMID:25830350

  19. Gas exchange and low temperature resistance in two tropical high mountain tree species from the Venezuelan Andes

    NASA Astrophysics Data System (ADS)

    Cavieres, Lohengrin A.; Rada, Fermín; Azócar, Aura; García-Núñez, Carlos; Cabrera, Hernán M.

    2000-05-01

    Temperature may determine altitudinal tree distribution in different ways: affecting survival through freezing temperatures or by a negative carbon balance produced by lower photosynthetic rates. We studied gas exchange and supercooling capacity in a timberline and a treeline species ( Podocarpus oleifolius and Espeletia neriifolia, respectively) in order to determine if their altitudinal limits are related to carbon balance, freezing temperature damage, or both. Leaf gas exchange, leaf temperature-net photosynthesis curves and leaf temperature at which ice formation occurred were measured at two sites along an altitudinal gradient. Mean CO 2 assimilation rates for E. neriifolia were 3.4 and 1.3 μmol·m -2·s -1, at 2 400 and 3 200 m, respectively. Mean night respiration was 2.2 and 0.9 μmol·m -2·s -1 for this species at 2 400 and 3 200 m, respectively. Mean assimilation rates for P. oleifolius were 3.8 and 2.2 μmol·m -2·s -1 at 2 550 and 3 200 m, respectively. Night respiration was 0.8 μmol·m -2·s -1 for both altitudes. E. neriifolia showed similar optimum temperatures for photosynthesis at both altitudes, while a decrease was observed in P. oleifolius.E. neriifolia and P. oleifolius presented supercooling capacities of -6.5 and -3.0 °C, respectively. For E. neriifolia, freezing resistance mechanisms are sufficient to reach higher altitudes; however, other environmental factors such as cloudiness may be affecting its carbon balance. P. oleifolius does not reach higher elevations because it does not have the freezing resistance mechanisms.

  20. An Experimental Investigation of an Exhaust-gas-to-air Heat Exchanger for Use on Jet-stack-equipped Engines

    NASA Technical Reports Server (NTRS)

    Stalder, Jackson R; Spies, Ray J , Jr

    1948-01-01

    Tests were made to determine the loss in exhaust-jet thrust and engine power resulting from the insertion of an exhaust-gas-to-air heat exchanger in a jet-type exhaust stack of an aircraft engine. The thermal performance of the heat exchanger was also determined.

  1. Air/sea DMS gas transfer in the North Atlantic: evidence for limited interfacial gas exchange at high wind speed

    NASA Astrophysics Data System (ADS)

    Bell, T. G.; De Bruyn, W.; Miller, S. D.; Ward, B.; Christensen, K.; Saltzman, E. S.

    2013-05-01

    Shipboard measurements of eddy covariance DMS air/sea fluxes and seawater concentration were carried out in the North Atlantic bloom region in June/July 2011. Gas transfer coefficients (k660) show a linear dependence on mean horizontal wind speed at wind speeds up to 11 m s-1. At higher wind speeds the relationship between k660 and wind speed weakens. At high winds, measured DMS fluxes were lower than predicted based on the linear relationship between wind speed and interfacial stress extrapolated from low to intermediate wind speeds. In contrast, the transfer coefficient for sensible heat did not exhibit this effect. The apparent suppression of air/sea gas flux at higher wind speeds appears to be related to sea state, as determined from shipboard wave measurements. These observations are consistent with the idea that long waves suppress near surface water side turbulence, and decrease interfacial gas transfer. This effect may be more easily observed for DMS than for less soluble gases, such as CO2, because the air/sea exchange of DMS is controlled by interfacial rather than bubble-mediated gas transfer under high wind speed conditions.

  2. Experimental Investigation of Gas-Side Performance of a Compact Finned-Tube Heat Exchanger

    NASA Technical Reports Server (NTRS)

    Gedeon, Louis

    1959-01-01

    Heat-transfer and pressure-drop data were obtained experimentally for the gas side of a liquid-metal to air, compact finned-tube heat exchanger. The heat exchanger was fabricated from 0.185-inch Inconel tubing in an inline array. The fins were made of 310 stainless-steel- clad copper with a total thickness of 0.010 inch, and the fin pitch was 15.3 fins per inch. The liquid used as the heating medium was sodium. The heat-exchanger inlet gas temperature was varied from 5100 to 1260 R by burning JP fuel for airflow rates of 0.4 to 10.5 pounds per second corresponding to an approximate Reynolds number range of 300 to 9000. The sodium inlet temperature was held at 1400 R with the exception of a few runs taken at 1700 and 1960 R. The maximum ratio of surface temperature to air bulk temperature was 1.45. Friction-factor data with heat transfer were best represented by a single line when the density and viscosity of Reynolds number were evaluated at the average film temperature. At the lower Reynolds numbers reported, the friction data with heat transfer plotted slightly above the friction data without heat transfer. The density of the friction factor was calculated at the average bulk temperature. Heat-transfer results of this investigation were correlated by evaluating the physical properties of air (specific heat, viscosity, and thermal conductivity) at the film temperature.

  3. The impact of lower sea-ice extent on Arctic greenhouse-gas exchange

    USGS Publications Warehouse

    Parmentier, Frans-Jan W.; Christensen, Torben R.; Sørensen, Lise Lotte; Rysgaard, Søren; McGuire, A. David; Miller, Paul A.; Walker, Donald A.

    2013-01-01

    In September 2012, Arctic sea-ice extent plummeted to a new record low: two times lower than the 1979–2000 average. Often, record lows in sea-ice cover are hailed as an example of climate change impacts in the Arctic. Less apparent, however, are the implications of reduced sea-ice cover in the Arctic Ocean for marine–atmosphere CO2 exchange. Sea-ice decline has been connected to increasing air temperatures at high latitudes. Temperature is a key controlling factor in the terrestrial exchange of CO2 and methane, and therefore the greenhouse-gas balance of the Arctic. Despite the large potential for feedbacks, many studies do not connect the diminishing sea-ice extent with changes in the interaction of the marine and terrestrial Arctic with the atmosphere. In this Review, we assess how current understanding of the Arctic Ocean and high-latitude ecosystems can be used to predict the impact of a lower sea-ice cover on Arctic greenhouse-gas exchange.

  4. Hypoxia and hypercarbia in endophagous insects: Larval position in the plant gas exchange network is key.

    PubMed

    Pincebourde, Sylvain; Casas, Jérôme

    2016-01-01

    Gas composition is an important component of any micro-environment. Insects, as the vast majority of living organisms, depend on O2 and CO2 concentrations in the air they breathe. Low O2 (hypoxia), and high CO2 (hypercarbia) levels can have a dramatic effect. For phytophagous insects that live within plant tissues (endophagous lifestyle), gas is exchanged between ambient air and the atmosphere within the insect habitat. The insect larva contributes to the modification of this environment by expiring CO2. Yet, knowledge on the gas exchange network in endophagous insects remains sparse. Our study identified mechanisms that modulate gas composition in the habitat of endophagous insects. Our aim was to show that the mere position of the insect larva within plant tissues could be used as a proxy for estimating risk of occurrence of hypoxia and hypercarbia, despite the widely diverse life history traits of these organisms. We developed a conceptual framework for a gas diffusion network determining gas composition in endophagous insect habitats. We applied this framework to mines, galls and insect tunnels (borers) by integrating the numerous obstacles along O2 and CO2 pathways. The nature and the direction of gas transfers depended on the physical structure of the insect habitat, the photosynthesis activity as well as stomatal behavior in plant tissues. We identified the insect larva position within the gas diffusion network as a predictor of risk exposure to hypoxia and hypercarbia. We ranked endophagous insect habitats in terms of risk of exposure to hypoxia and/or hypercarbia, from the more to the less risky as cambium mines>borer tunnels≫galls>bark mines>mines in aquatic plants>upper and lower surface mines. Furthermore, we showed that the photosynthetically active tissues likely assimilate larval CO2 produced. In addition, temperature of the microhabitat and atmospheric CO2 alter gas composition in the insect habitat. We predict that (i) hypoxia indirectly favors

  5. Stability of Intercellular Exchange of Biochemical Substances Affected by Variability of Environmental Parameters

    NASA Astrophysics Data System (ADS)

    Mihailović, Dragutin T.; Budinčević, Mirko; Balaž, Igor; Mihailović, Anja

    Communication between cells is realized by exchange of biochemical substances. Due to internal organization of living systems and variability of external parameters, the exchange is heavily influenced by perturbations of various parameters at almost all stages of the process. Since communication is one of essential processes for functioning of living systems it is of interest to investigate conditions for its stability. Using previously developed simplified model of bacterial communication in a form of coupled difference logistic equations we investigate stability of exchange of signaling molecules under variability of internal and external parameters.

  6. Direct analysis of ultra-trace semiconductor gas by inductively coupled plasma mass spectrometry coupled with gas to particle conversion-gas exchange technique.

    PubMed

    Ohata, Masaki; Sakurai, Hiromu; Nishiguchi, Kohei; Utani, Keisuke; Günther, Detlef

    2015-09-01

    An inductively coupled plasma mass spectrometry (ICPMS) coupled with gas to particle conversion-gas exchange technique was applied to the direct analysis of ultra-trace semiconductor gas in ambient air. The ultra-trace semiconductor gases such as arsine (AsH3) and phosphine (PH3) were converted to particles by reaction with ozone (O3) and ammonia (NH3) gases within a gas to particle conversion device (GPD). The converted particles were directly introduced and measured by ICPMS through a gas exchange device (GED), which could penetrate the particles as well as exchange to Ar from either non-reacted gases such as an air or remaining gases of O3 and NH3. The particle size distribution of converted particles was measured by scanning mobility particle sizer (SMPS) and the results supported the elucidation of particle agglomeration between the particle converted from semiconductor gas and the particle of ammonium nitrate (NH4NO3) which was produced as major particle in GPD. Stable time-resolved signals from AsH3 and PH3 in air were obtained by GPD-GED-ICPMS with continuous gas introduction; however, the slightly larger fluctuation, which could be due to the ionization fluctuation of particles in ICP, was observed compared to that of metal carbonyl gas in Ar introduced directly into ICPMS. The linear regression lines were obtained and the limits of detection (LODs) of 1.5 pL L(-1) and 2.4 nL L(-1) for AsH3 and PH3, respectively, were estimated. Since these LODs revealed sufficiently lower values than the measurement concentrations required from semiconductor industry such as 0.5 nL L(-1) and 30 nL L(-1) for AsH3 and PH3, respectively, the GPD-GED-ICPMS could be useful for direct and high sensitive analysis of ultra-trace semiconductor gas in air. PMID:26388365

  7. Uncertainties in gas exchange parameterization during the SAGE dual-tracer experiment

    NASA Astrophysics Data System (ADS)

    Smith, Murray J.; Ho, David T.; Law, Cliff S.; McGregor, John; Popinet, Stéphane; Schlosser, Peter

    2011-03-01

    A dual tracer experiment was carried out during the SAGE experiment using the inert tracers SF 6 and 3He, in order to determine the gas transfer velocity, k, at high wind speeds in the Southern Ocean. Wind speed/gas exchange parameterization is characterised by significant variability and we examine the major measurement uncertainties that contribute to that scatter. Correction for the airflow distortion over the research vessel, as determined by computational fluid dynamics (CFD) modelling, had the effect of increasing the calculated value of k by 30%. On the short time scales of such experiments, the spatial variability of the wind field resulted in differences between ship and satellite QuikSCAT winds, which produced significant differences in transfer velocity. With such variability between wind estimates, the comparison between gas exchange parameterizations from diverse experiments should clearly be made on the basis of the same wind product. Uncertainty in mixed layer depth of ˜10% arose from mixed layer deepening at high wind speed and limited resolution of vertical sampling. However the assumption of equal mixing of the two tracers is borne out by the experiment. Two dual tracer releases were carried out during SAGE, and showed no significant difference in transfer velocities using QuikSCAT winds, despite the differences in wind history. In the SAGE experiment, duration limitation on the development of waves was shown to be an important factor for Southern Ocean waves, despite the presence of long fetches.

  8. High temperature corrosion of advanced ceramic materials for hot gas filters and heat exchangers. Final report

    SciTech Connect

    Kupp, E.R.; Trubelja, K.E.; Spear, K.E.; Tressler, R.E.

    1995-08-01

    Experimental corrosion studies of hot gas filter materials and heat exchanger materials in oxidizing combustion environments have been initiated. Filter materials from 3M Co. and DuPont Lanxide Composites Inc. are being tested over a range of temperatures, times and gas flows. It has been demonstrated that morphological and phase changes due to corrosive effects occur after exposure of these materials to a simulated coal combustion environment for relatively short periods of time (10-50 hours). Heat exchanger tubes from DuPont Lanxide Composite Inc. were cut and infiltrated with Cr by heating in a Cr{sub 2}O{sub 3} powder bed. This resulted in continuous Cr-rich layers with thicknesses ranging from 20 to 250 {mu}m. The Cr-free and the Cr-infiltrated specimens were reacted with the molten Illinois No. 6 slag for 2 and 20 h at 1260{degrees}C, and the reaction layers examined with SEM and EDX. In the Cr-free specimens, the segregation of Fe and the precipitation of Fe{sub 2}O{sub 3} were detected near the liquid/gas interface, but no evidence of corrosion was present. In the Cr-infiltrate specimens, corrosion was evident, since a rearrangement and segregation of the Cr-rich grains occurred toward the surface of the molten slag. In addition, evidence of the diffusion of major quantities of Fe was observed from the liquid slag into the Cr-rich layer formed by infiltration.

  9. Control of discontinuous gas exchange in Samia cynthia: effects of atmospheric oxygen, carbon dioxide and moisture.

    PubMed

    Terblanche, John S; Marais, Elrike; Hetz, Stefan K; Chown, Steven L

    2008-10-01

    The evolution of discontinuous gas exchange (DGE) in insects is highly controversial. Adaptive hypotheses which have obtained experimental support include a water savings mechanism for living in dry environments (hygric hypothesis), a reduction in oxidative damage due to a high-performance oxygen delivery system (oxidative damage hypothesis), and the need for steep intratracheal partial pressure gradients to exchange gases under the hypercapnic and/or hypoxic conditions potentially encountered in subterranean environments (chthonic hypothesis). However, few experimental studies have simultaneously assessed multiple competing hypotheses within a strong inference framework. Here, we present such a study at the species level for a diapausing moth pupa, Samia cynthia. Switching gas conditions from controlled normoxic, normocapnic and intermediate humidity to either high or low oxygen, high or low moisture, elevated carbon dioxide, or some combination of these, revealed that DGE was abandoned under all conditions except high oxygen, and high or low gas moisture levels. Thus, support is found for the oxidative damage hypothesis when scored as maintenance of DGE. Modulation of DGE under either dry or hyperoxic conditions suggested strong support for the oxidative damage hypothesis and some limited support for the hygric hypothesis. Therefore, this study demonstrates that the DGE can be maintained and modulated in response to several environmental variables. Further investigation is required using a strong-inference, experimental approach across a range of species from different habitats to determine how widespread the support for the oxidative damage hypothesis might be. PMID:18840661

  10. Gas exchange and dive characteristics of the free-swimming backswimmer Anisops deanei.

    PubMed

    Jones, Karl K; Snelling, Edward P; Watson, Amy P; Seymour, Roger S

    2015-11-01

    Many aquatic insects utilise air bubbles on the surface of their bodies to supply O2 while they dive. The bubbles can simply store O2, as in the case of an 'air store', or they can act as a physical 'gas gill', extracting O2 from the water. Backswimmers of the genus Anisops augment their air store with O2 from haemoglobin cells located in the abdomen. The O2 release from the haemoglobin helps stabilise bubble volume, enabling backswimmers to remain near neutrally buoyant for a period of the dive. It is generally assumed that the backswimmer air store does not act as a gas gill and that gas exchange with the water is negligible. This study combines measurements of dive characteristics under different exotic gases (N2, He, SF6, CO) with mathematical modelling, to show that the air store of the backswimmer Anisops deanei does exchange gases with the water. Our results indicate that approximately 20% of O2 consumed during a dive is obtained directly from the water. Oxygen from the water complements that released from the haemoglobin, extending the period of near-neutral buoyancy and increasing dive duration. PMID:26538177

  11. Optical Pumping Spin Exchange {sup 3}He Gas Cells for Magnetic Resonance Imaging

    SciTech Connect

    Kim, W.; Stepanyan, S. S.; Kim, A.; Jung, Y.; Woo, S.; Yurov, M.; Jang, J.

    2009-08-04

    We present a device for spin-exchange optical pumping system to produce large quantities of polarized noble gases for Magnetic Resonance Imaging (MRI). A method and design of apparatus for pumping the polarization of noble gases is described. The method and apparatus enable production, storage and usage of hyperpolarized noble gases for different purposes, including Magnetic Resonance Imaging of human and animal subjects. Magnetic imaging agents breathed into lungs can be observed by the radio waves of the MRI scanner and report back physical and functional information about lung's health and desease. The technique known as spin exchange optical pumping is used. Nuclear magnetic resonance is implemented to measure the polarization of hyperpolarized gas. The cells prepared and sealed under high vacuum after handling Alkali metals into the cell and filling with the {sup 3}He-N{sub 2} mixture. The cells could be refilled. The {sup 3}He reaches around 50% polarization in 5-15 hours.

  12. Exchange-correlations in a dilute quasi-two-dimensional electron gas at finite temperature

    NASA Astrophysics Data System (ADS)

    Bhukal, Nisha; Moudgil, R. K.

    2012-06-01

    We have studied the extent to which temperature and finite transversal confinement can influence the exchange-correlations in a dilute two-dimensional electron gas as realized in a narrow GaAs-based single quantum well. The correlations are treated within the self-consistent mean-field theory of Singwi et al. Numerical results are presented for the local-field correction factor at experimentally realized electron densities and temperature, choosing a harmonic confinement model. We find that the local-field correction factor, which is a direct measure of exchange-correlation correction to the bare Coulomb interaction potential, becomes less (at least over the currently accessible wave vector region to experiments) with increasing T/TF and/or decreasing confinement; TF is the Fermi temperature. These findings are expected to be useful in the theoretical understanding of dynamical excitation spectra and transport properties of a two-dimensional electron system.

  13. Heat transfer in a compact tubular heat exchanger with helium gas at 3.5 MPa

    NASA Technical Reports Server (NTRS)

    Olson, Douglas A.; Glover, Michael P.

    1990-01-01

    A compact heat exchanger was constructed consisting of circular tubes in parallel brazed to a grooved base plate. This tube specimen heat exchanger was tested in an apparatus which radiatively heated the specimen on one side at a heat flux of up to 54 W/sq cm, and cooled the specimen with helium gas at 3.5 MPa and Reynolds numbers of 3000 to 35,000. The measured friction factor of the tube specimen was lower than that of a circular tube with fully developed turbulent flow, although the uncertainty was high due to entrance and exit losses. The measured Nusselt number, when modified to account for differences in fluid properties between the wall and the cooling fluid, agreed with past correlations for fully developed turbulent flow in circular tubes.

  14. A modified photo- and magnetoacoustic multigas analyzer applied in gas exchange measurements.

    PubMed

    Clemensen, P; Christensen, P; Norsk, P; Grønlund, J

    1994-06-01

    The feasibility of replacing a conventional mass spectrometer (MS) with a specially modified multicomponent (O2, CO2, Freon 22, and SF6) acoustic infrared and paramagnetic (IR/PM) gas analyzer in inert gas-rebreathing and metabolic gas exchange measurements has been investigated. Rebreathing variables were determined simultaneously with the MS and IR/PM analyzers in duplicate measurements at rest and during submaximal exercise in 10 subjects. The differences (means +/- SD, IR/PM - MS) were 0.028 +/- 0.048 liters [functional residual capacity (FRC)], 0.18 +/- 0.38 l/min [cardiac output (Qc)], -0.006 +/- 0.030 l/min [O2 consumption (VO2)], and -33 +/- 108 ml [combined lung tissue and capillary blood volume (Vti,c)]. The coefficients of variation on repeated estimates were 5.8% (FRC), 5.4% (Qc), 6.2% (VO2), and 17% (Vti,c) with the IR/PM analyzer and 5.9% (FRC), 4.2% (Qc), 5.0% (VO2), and 9.8% (Vti,c) with the MS. The differences (IR/PM - MS) obtained in mixed-expirate measurements were -0.006 +/- 0.020 l/min (VO2) and 0.020 +/- 0.021 l/min (CO2 production). Breath-by-breath estimates of VO2 and CO2 production with the IR/PM analyzer were, on average, 2.4 and 4.4% higher than the MS estimates, respectively. Our results demonstrate that the IR/PM gas analyzer, when appropriately modified, can substitute for a complex MS in a variety of noninvasive pulmonary gas exchange measurements. PMID:7928918

  15. Estimating gas exchange of CO2 and CH4 between headwater systems and the atmosphere in Southwest Sweden

    NASA Astrophysics Data System (ADS)

    Somlai, Celia; Natchimuthu, Sivakiruthika; Bastviken, David; Lorke, Andreas

    2015-04-01

    Quantifying the role of inland water systems in terms of carbon sinks and sources and their connection to the terrestrial ecosystems and landscapes is fundamental for improving the balance approach of regional and global carbon budgets. Recent research showed that freshwater bodies emit significant amounts of CO2 and CH4 into the atmosphere. The extent of the emissions from small streams and headwaters, however, remains uncertain due to a limited availability of data. Studies have shown that headwater systems receive most of the terrestrial organic carbon, have the highest dissolved CO2 concentration and the highest gas exchange velocities and cover the largest fractional surface area within fluvial networks. The gas exchange between inland waters and the atmosphere is controlled by two factors: the difference between the dissolved gas concentration and its atmospheric equilibrium concentration, and the gas exchange velocity. The direct measurement of the dissolved gas concentration of greenhouse gases can be measured straightforwardly, for example, by gas chromatography from headspace extraction of water sample. In contrast, direct measurement of gas exchange velocity is more complex and time consuming, as simultaneous measurements with a volatile and nonvolatile inert tracer gas are needed. Here we analyze measurements of gas exchange velocities, concentrations and fluxes of dissolved CO2 and CH4, as well as loads of total organic and inorganic carbon in 10 reaches in headwater streams in Southwest Sweden. We compare the gas exchange velocities measured directly through tracer injections with those estimated through various empirical approaches, which are based on modelled and measured current velocity, stream depth and slope. Furthermore, we estimate the resulting uncertainties of the flux estimates. We also present different time series of dissolved CO2, CH4 and O2 concentration, water temperature, barometric pressure, electro conductivity, and pH values

  16. Operation of an ADR using helium exchange gas as a substitute for a failed heat switch

    NASA Astrophysics Data System (ADS)

    Shirron, P.; DiPirro, M.; Kimball, M.; Sneiderman, G.; Porter, F. S.; Kilbourne, C.; Kelley, R.; Fujimoto, R.; Yoshida, S.; Takei, Y.; Mitsuda, K.

    2014-11-01

    The Soft X-ray Spectrometer (SXS) is one of four instruments on the Japanese Astro-H mission, which is currently planned for launch in late 2015. The SXS will perform imaging spectroscopy in the soft X-ray band (0.3-12 keV) using a 6 × 6 pixel array of microcalorimeters cooled to 50 mK. The detectors are cooled by a 3-stage adiabatic demagnetization refrigerator (ADR) that rejects heat to either a superfluid helium tank (at 1.2 K) or to a 4.5 K Joule-Thomson (JT) cryocooler. Four gas-gap heat switches are used in the assembly to manage heat flow between the ADR stages and the heat sinks. The engineering model (EM) ADR was assembled and performance tested at NASA/GSFC in November 2011, and subsequently installed in the EM dewar at Sumitomo Heavy Industries, Japan. During the first cooldown in July 2012, a failure of the heat switch that linked the two colder stages of the ADR to the helium tank was observed. Operation of the ADR requires some mechanism for thermally linking the salt pills to the heat sink, and then thermally isolating them. With the failed heat switch unable to perform this function, an alternate plan was devised which used carefully controlled amounts of exchange gas in the dewar's guard vacuum to facilitate heat exchange. The process was successfully demonstrated in November 2012, allowing the ADR to cool the detectors to 50 mK for hold times in excess of 10 h. This paper describes the exchange-gas-assisted recycling process, and the strategies used to avoid helium contamination of the detectors at low temperature.

  17. Operation of an ADR Using Helium Exchange Gas as a Substitute for a Failed Heat Switch

    NASA Technical Reports Server (NTRS)

    Shirron, P.; DiPirro, M.; Kimball, M.; Sneiderman, G.; Porter, F. S.; Kilbourne, C.; Kelley, R.; Fujimoto, R.; Yoshida, S.; Takei, Y.; Mitsuda, K.

    2014-01-01

    The Soft X-ray Spectrometer (SXS) is one of four instruments on the Japanese Astro-H mission, which is currently planned for launch in late 2015. The SXS will perform imaging spectroscopy in the soft X-ray band (0.3-12 keV) using a 6 6 pixel array of microcalorimeters cooled to 50 mK. The detectors are cooled by a 3-stage adiabatic demagnetization refrigerator (ADR) that rejects heat to either a superfluid helium tank (at 1.2 K) or to a 4.5 K Joule-Thomson (JT) cryocooler. Four gas-gap heat switches are used in the assembly to manage heat flow between the ADR stages and the heat sinks. The engineering model (EM) ADR was assembled and performance tested at NASA/GSFC in November 2011, and subsequently installed in the EM dewar at Sumitomo Heavy Industries, Japan. During the first cooldown in July 2012, a failure of the heat switch that linked the two colder stages of the ADR to the helium tank was observed. Operation of the ADR requires some mechanism for thermally linking the salt pills to the heat sink, and then thermally isolating them. With the failed heat switch unable to perform this function, an alternate plan was devised which used carefully controlled amounts of exchange gas in the dewar's guard vacuum to facilitate heat exchange. The process was successfully demonstrated in November 2012, allowing the ADR to cool the detectors to 50 mK for hold times in excess of 10 h. This paper describes the exchange-gas-assisted recycling process, and the strategies used to avoid helium contamination of the detectors at low temperature.

  18. Evaluation of a new weaning index based on ventilatory endurance and the efficiency of gas exchange.

    PubMed

    Jabour, E R; Rabil, D M; Truwit, J D; Rochester, D F

    1991-09-01

    We hypothesized that the ventilatory capacity needed to wean from mechanical ventilation (mv) depends on two variables: ventilatory endurance and the efficiency of gas exchange. We also hypothesized that these variables could be assessed from data readily available at the bedside, including tidal volume (VT) on mv and during spontaneous breathing (sb), ventilator peak inspiratory pressure (Ppk), and patient negative inspiratory pressure (NIP). Ventilatory endurance was evaluated using a modified pressure-time index: PTI = TI/Ttot x Pbreath/NIP, where Pbreath = Ppk x VTsb/VTmv. Defining VE40 as the minute ventilation needed to bring PaCO2 to 40 mm Hg, the efficiency of gas exchange was evaluated by calculating VE40/VTsb = (VE x PaCO2)mv/VTsb x 40. Because high levels of inspiratory effort might cause patients to reduce VTsb and thereby compromise CO2 elimination, we devised a weaning index (WI) that combines ventilatory endurance and the efficiency of gas exchange: WI = PTI x (VE40/VTsb). The study population comprised 38 patients with chronic obstructive pulmonary disease, adult respiratory distress syndrome, pneumonia, neuromuscular disease, and miscellaneous other conditions. They had been mechanically ventilated more than 3 days and were considered by clinical criteria to be ready for weaning. Of 46 weaning trials, 19 were successful, 2 were partially successful, and 25 failed. PTI and VE40/VTsb were higher in patients who failed (p less than 0.05), but neither variable alone had sufficient sensitivity or specificity to predict the outcome of weaning trials accurately.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:1892291

  19. Regulation of gas exchange and haemolymph pH in the cockroach Nauphoeta cinerea.

    PubMed

    Matthews, Philip G D; White, Craig R

    2011-09-15

    Ventilatory control of internal CO(2) plays an important role in regulating extracellular acid-base balance in terrestrial animals. While this phenomenon is well understood among vertebrates, the role that respiration plays in the acid-base balance of insects is in need of much further study. To measure changes in insect haemolymph pH, we implanted micro pH optodes into the haemocoel of cockroaches (Nauphoeta cinerea). They were then exposed to normoxic, hypoxic, hyperoxic and hypercapnic atmospheres while their haemolymph pH, VCO(2) and abdominal ventilation frequency were measured simultaneously. Intratracheal O(2) levels were also measured in separate experiments. It was found that cockroaches breathing continuously control their ventilation to defend a haemolymph pH of 7.3, except under conditions where hypoxia (<10% O(2)) induces hyperventilation, or where ambient hypercapnia is in excess of haemolymph (>1% CO(2)). In contrast, intratracheal O(2) levels fluctuated widely, but on average remained above 15% in normoxic (21% O(2)) atmospheres. Decapitation caused the cockroaches to display discontinuous gas exchange cycles (DGCs). The alternating periods of ventilation and apnoea during DGCs caused haemolymph pH to fluctuate by 0.11 units. Exposure to hypoxia caused haemolymph pH to increase and initiated brief bouts of spiracular opening prior to the active ventilation phase. The spontaneous occurrence of DGCs in decapitated cockroaches indicates that central pattern generators in the thoracic and abdominal ganglia generate the periodic gas exchange pattern in the absence of control from the cephalic ganglion. This pattern continues to maintain gas exchange, but with less precision. PMID:21865519

  20. Anchoring and support system of pulmonary gas-exchange tissue in four bird species.

    PubMed

    Klika, E; Scheuermann, D W; De Groodt-Lasseel, M H; Bazantova, I; Switka, A

    1997-01-01

    Avian air capillaries are delicate structures compared to the mammalian pulmonary alveolus. A transmission and scanning electron microscopic study was carried out on several species of birds with the aim of determining the support structures of the avian gas-exchange mantle. Lung tissue of two bird species belonging to strong flying birds (pigeon and barn owl) and two relatively flightless species (domestic fowl and quail) was subjected to standard processing for transmission and scanning electron microscopy after intratracheal inflation. Twisted profiles of lipoproteinaceous trilaminar substance as specific secretory product of avian squamous respiratory cells can be seen in the cell body and cytoplasmic extensions that are wedged between the blood capillaries, partly surrounding them. The intracytoplasmatically located trilaminar complexes form a three-dimensional intricate spiderweb-like system between the blood capillaries and air capillaries, which presumably function as an anchoring and support structure of the gas-exchange tissue. This system is strengthened by retinacula--pairs of attenuated parallel processes of squamous respiratory cells that project to the airway lumen--expanding and bridging the opposite side of air capillaries. The trilaminar substance is discharged in the form of a 15-nm-thick acellular lining layer which is uniquely adapted to the extremely thin respiratory epithelium. The trilaminar substance arises in the cytoplasm of squamous respiratory cells from profiles of granular and smooth endoplasmic reticulum. The integrity and stability of the gas-exchange tissue is likely to be guaranteed by a specific arrangement of the squamous respiratory cells, in which the trilaminar substance plays a paramount role. This general pattern can be observed in strong flying bird species as in the relatively flightless birds. PMID:9522895

  1. 40 CFR 60.5415 - How do I demonstrate continuous compliance with the standards for my gas well affected facility...

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ..., my storage vessel affected facility, and my affected facilities at onshore natural gas processing... Oil and Natural Gas Production, Transmission and Distribution § 60.5415 How do I demonstrate... affected facility, my storage vessel affected facility, and my affected facilities at onshore natural...

  2. 40 CFR 60.5415 - How do I demonstrate continuous compliance with the standards for my gas well affected facility...

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ..., my storage vessel affected facility, and my affected facilities at onshore natural gas processing... Oil and Natural Gas Production, Transmission and Distribution § 60.5415 How do I demonstrate... affected facility, my storage vessel affected facility, and my affected facilities at onshore natural...

  3. Ozone gas affects the physical and chemical properties of wheat (Triticum aestivum L.) starch

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Ozone can oxidize hydroxyl groups present at C2, C3, and C6 positions on the starch molecule and affect its physicochemical properties. In this experiment, bread wheat flour and isolated wheat starch were treated with ozone gas (1,500 ppm, gas flow rate 2.5 L/minutes) for 45 minutes and 30 minutes, ...

  4. Preliminary findings of the Viking gas exchange experiment and a model for Martian surface chemistry

    NASA Technical Reports Server (NTRS)

    Oyama, V. I.; Berdahl, B. J.; Carle, G. C.

    1977-01-01

    Earlier results reported from the Viking Lander-1 experiment are reexamined and interpreted in terms of a model of the Martian soil surface morphology and chemistry. Major events in the gas exchange experiment (GEX) first cycle are tabulated and data are presented on the sample processing and transport environments experienced by the soil samples. Oxygen and CO2 evolved from humidified Martian soil in GEX and slight changes in N2 present are investigated. A soil model involving iron oxide coating on silicate material is entertained to yield a mechanistic explanation of the experimental findings, and invocation of biotic processes is eschewed.

  5. Electronic excitations of slow ions in a free electron gas metal: evidence for charge exchange effects.

    PubMed

    Primetzhofer, D; Rund, S; Roth, D; Goebl, D; Bauer, P

    2011-10-14

    Electronic energy loss of light ions transmitted through nanometer films of Al has been studied at very low ion velocities. For hydrogen, the electronic stopping power S is found to be perfectly proportional to velocity, as expected for a free electron gas. For He, the same is anticipated, but S shows a transition between two distinct regimes, in both of which S is velocity proportional-however, with remarkably different slopes. This finding can be explained as a consequence of charge exchange in close encounters between He and Al atoms, which represents an additional energy loss channel. PMID:22107378

  6. Guard cell biochemistry: response to environmental stimuli causing changes in gas exchange. Progress report

    SciTech Connect

    Not Available

    1983-01-01

    A progress report covering several interrelated studies on the biochemistry and metabolism of leaf guard cells is presented. Subjects covered are: (1) abscisic acid and the control of stomatal aperture size; (2) real-time, direct measurements of NAD(P)H in microdroplets; (3) electron transport through the PSII reaction center in guard cells; (4) organic anion/acid fluctuations as a general phenomena; (5) histological compartmentation of metabolic functions; (6) construction of a gas exchange system; and (7) guard cell protoplast isolation. (DT)

  7. Numerical simulation of gas dynamics and heat exchange tasks in fuel assemblies of the nuclear reactors

    SciTech Connect

    Zhuchenko, S. V.

    2014-11-12

    This report presents a PC-based program for solution gas dynamics and heat exchange mathematical tasks in fuel assemblies of the fast-neutron nuclear reactors. A fuel assembly consisting of bulk heat-generating elements, which are integrated together by the system of supply and pressure manifolds, is examined. Spherical heat-generating microelements, which contain nuclear fuel, are pulled into the heat-generating elements. Gaseous coolant proceed from supply manifolds to heat-generating elements, where it withdraws the nuclear reaction heat and assembles in pressure manifolds.

  8. Stomatal control of gas-exchange is related to assimilate transport from leaves

    NASA Astrophysics Data System (ADS)

    Nikinmaa, E.; Holtta, T.; Sevanto, S.; Makela, A.; Hari, P.; Vesala, T.

    2009-04-01

    In land plants, the carbon fluxes are closely associated with those of water. The loss of water from leaves pulls water from soil in plants. High transpiration relative to compensating water flux from soil increases the tension of water column that may lead to its rupture and catastrophic dysfunction of the xylem if the transpiration rate is not regulated. Modification of the size of stomatal openings in leaves regulates the interconnected fluxes of water and carbon. Stomatal regulation of transpiration has direct influence also on the carbon transport from source leaves to sinks. Under given conditions, the water tension of xylem in leaves is linearly related to stomatal conductance while the assimilation rate, which is linked to the loading capacity, has saturating relationship with stomatal conductance. High sugar loading at source could compensate for the high water tension in xylem resulting from eg. high transpiration. However, excessive loading rate of the most commonly transported sugar, sucrose, causes rapid viscosity build up that effectively blocks the phloem transport. Assimilate transport from the shoot is a clear requirement for continuous photosynthetic production in leaves. Without transport the storage capacity of the leaves would be rapidly exhausted and accumulation of excess sugars in leaves lead to downregulation of photosynthesis. In this presentation we study the stomatal response to environment and its linkage to xylem and phloem tranport with dynamic model. We hypothesize that stomatal reaction to environment would maintain maximal assimilate transport in phloem under those conditions. We added to the xylem phloem transport model stomatal control of leaf gas-exchange, light and CO2 concentration dependent photosynthesis rate and carbon storage in leaf. For each time step we varied the stomatal conductance and selected the sollution that maximised the transport of assimilates in phloem. Our hypothesis reproduced realistically stomatal

  9. Gas exchange in the Pee Dee River based on /sup 222/Rn evasion

    SciTech Connect

    Moore, W.S.; Elsinger, R.J.

    1983-06-01

    Excess /sup 222/Rn concentrations decrease downstream in the fresh water section of the Pee Dee River. Ground water is the primary source of the excess /sup 222/Rn to the River. Using the radon concentration gradients determined during four sampling periods, gas exchange rates based on the stagnant film model are calculated. Stagnant film thicknesses range from 19 ..mu..m to 48 ..mu..m and mass transfer coefficients range from 2.1 m/d to 4.1 m/d.

  10. Nesting behaviour influences species-specific gas exchange across avian eggshells

    PubMed Central

    Portugal, Steven J.; Maurer, Golo; Thomas, Gavin H.; Hauber, Mark E.; Grim, Tomáš; Cassey, Phillip

    2014-01-01

    Carefully controlled gas exchange across the eggshell is essential for the development of the avian embryo. Water vapour conductance (GH2O) across the shell, typically measured as mass loss during incubation, has been demonstrated to optimally ensure the healthy development of the embryo while avoiding desiccation. Accordingly, eggs exposed to sub-optimal gas exchange have reduced hatching success. We tested the association between eggshell GH2O and putative life-history correlates of adult birds, ecological nest parameters and physical characteristics of the egg itself to investigate how variation in GH2O has evolved to maintain optimal water loss across a diverse set of nest environments. We measured gas exchange through eggshell fragments in 151 British breeding bird species and fitted phylogenetically controlled, general linear models to test the relationship between GH2O and potential predictor parameters of each species. Of our 17 life-history traits, only two were retained in the final model: wet-incubating parent and nest type. Eggs of species where the parent habitually returned to the nest with wet plumage had significantly higher GH2O than those of parents that returned to the nest with dry plumage. Eggs of species nesting in ground burrows, cliffs and arboreal cups had significantly higher GH2O than those of species nesting on the ground in open nests or cups, in tree cavities and in shallow arboreal nests. Phylogenetic signal (measured as Pagel's λ) was intermediate in magnitude, suggesting that differences observed in the GH2O are dependent upon a combination of shared ancestry and species-specific life history and ecological traits. Although these data are correlational by nature, they are consistent with the hypothesis that parents constrained to return to the nest with wet plumage will increase the humidity of the nest environment, and the eggs of these species have evolved a higher GH2O to overcome this constraint and still achieve optimal water

  11. Factors affecting ground-water exchange and catchment size for Florida lakes in mantled karst terrain

    USGS Publications Warehouse

    Lee, Terrie Mackin

    2002-01-01

    In the mantled karst terrain of Florida, the size of the catchment delivering ground-water inflow to lakes is often considerably smaller than the topographically defined drainage basin. The size is determined by a balance of factors that act individually to enhance or diminish the hydraulic connection between the lake and the adjacent surficial aquifer, as well as the hydraulic connection between the surficial aquifer and the deeper limestone aquifer. Factors affecting ground-water exchange and the size of the ground-water catchment for lakes in mantled karst terrain were examined by: (1) reviewing the physical and hydrogeological characteristics of 14 Florida lake basins with available ground-water inflow estimates, and (2) simulating ground-water flow in hypothetical lake basins. Variably-saturated flow modeling was used to simulate a range of physical and hydrogeologic factors observed at the 14 lake basins. These factors included: recharge rate to the surficial aquifer, thickness of the unsaturated zone, size of the topographically defined basin, depth of the lake, thickness of the surficial aquifer, hydraulic conductivity of the geologic units, the location and size of karst subsidence features beneath and onshore of the lake, and the head in the Upper Floridan aquifer. Catchment size and the magnitude of ground-water inflow increased with increases in recharge rate to the surficial aquifer, the size of the topographically defined basin, hydraulic conductivity in the surficial aquifer, the degree of confinement of the deeper Upper Floridan aquifer, and the head in the Upper Floridan aquifer. The catchment size and magnitude of ground-water inflow increased with decreases in the number and size of karst subsidence features in the basin, and the thickness of the unsaturated zone near the lake. Model results, although qualitative, provided insights into: (1) the types of lake basins in mantled karst terrain that have the potential to generate small and large

  12. The charge-exchange induced coupling between plasma-gas counterflows in the heliosheath

    NASA Astrophysics Data System (ADS)

    Fahr, H. J.

    2003-06-01

    Many hydrodynamic models have been presented which give similar views of the interaction of the solar wind plasma bubble with the counterstreaming partially ionized interstellar medium. In the more recent of these models it is taken into account that the solar and interstellar hydrodynamic flows of neutral atoms and protons are coupled by mass-, momentum-, and energy-exchange terms due to charge exchange processes. We shall reinvestigate the theoretical basis of this coupling here by use of a simplified description of the heliospheric interface and describe the main physics of the H-atom penetration through the more or less standing well-known plasma wall ahead of the heliopause. Thereby we can show that the type of charge exchange coupling terms used in up-to-now hydrodynamic treatments unavoidably leads to an O-type critical point at the sonic point of the H-atom flow, thus not allowing for a continuation of the integration of the hydrodynamic set of differential equations. The remedy for this problem is given by a more accurate formulation of the momentum exchange term for quasi-and sub-sonic H-atom flows. With a refined momentum exchange term derived from basic kinetic Boltzmann principles, we instead arrive at a characteristic equation with an X-type critical point, allowing for a continuous solution from supersonic to subsonic flow conditions. This necessitates that the often treated problem of the propagation of inter-stellar H-atoms through the heliosheath has to be solved using these newly derived, differently effective plasma - gas friction forces. Substantially different results are to be expected from this context for the filtration efficiency of the heliospheric interface.

  13. Gas separation using ion exchange membranes for producing hydrogen from synthesis gas

    SciTech Connect

    Pellegrino, J.J.; Giarratano, P.J.

    1992-01-01

    The main goal of this project is to demonstrate the use of facilitated transport membranes to separate gases resulting from the formation of H{sub 2}, specifically C0{sub 2} and H{sub 2}S from CO and H{sub 2}. As part of this goal a field test is performed at a producing natural gas plant (Carter Creek Chevron Natural Gas Plant, Evanston, WY) to evaluate the performance and long term stability of candidate membranes. Laboratory work at the National Institute of Standard and Technology (NIST) leads and parallels the field tests. Through a series of tests in the WIST laboratory and at the Chevron/Carter Creek test rig, the investigators are establishing the apparent separation and productivity capabilities of polymer membranes imbibed with various solvents and chemical carriers. In some samples the membranes are also subjected to solvent-swelling heat treatment (gel-treatment). The polymer material is polyperfluorosufonic acid (PFSA-Nafion). The chemical carriers, e.g. methyldiethanolamine (EDA) and ethylenediamine (EDA) enhance the transport and selectivity of the membrane. They may be in solution with H{sub 2}0, glycerol, ethylene glycol, and n-methylpyrrolidone (NMP). Nafion 117 (NE117) is a commercial film, 200 microns thick, which is available from DuPont Co. A developmental polymer film, Nafion 111 (NE111) 30--40 microns thick was made available by the DuPont Co.

  14. The hydrology of northern peatlands as affected by biogenic gas: Current developments and research needs

    USGS Publications Warehouse

    Rosenberry, D.O.; Glaser, P.H.; Siegel, D.I.

    2006-01-01

    Recent research indicates that accumulation and release of biogenic gas from northern peatlands may substantially affect future climate. Sudden release of free-phase gas bubbles into the atmosphere may preclude the conversion of methane to carbon dioxide in the uppermost oxic layer of the peat, resulting in greater contribution of methane to the atmosphere than is currently estimated. The hydrology of these peatlands also affects and is affected by this process, especially when gas is released suddenly and episodically. Indirect hydrological evidence indicates that ebullitive gas releases are relatively frequent in some peatlands and time-averaged rates may be significantly greater than diffusive releases. Estimates of free-phase gas contained in peat have ranged from 0 to nearly 20% of the peat volume. Abrupt changes in the volume of gas may alter hydraulic gradients and movement of water and solutes in peat, which in turn could alter composition and fluxes of the gas. Peat surfaces also move vertically and horizontally in response to accumulation and release of free-phase gas. Future research should address the distribution, temporal variability, and relative significance of ebullition in peatlands and the consequent hydrological responses to these gas-emission events. Copyright ?? 2006 John Wiley & Sons, Ltd.

  15. Gas exchange dependency on diffusion coefficient: direct /sup 222/Rn and /sup 3/He comparisons in a small lake

    SciTech Connect

    Torgersen, T.; Mathieu, G.; Hesslein, R.H.; Broecker, W.S.

    1982-01-20

    A direct field comparison was conducted to determine the dependency of gas exchange coefficient (k/sub x/) on the diffusion coefficient (D/sub x/). The study also sought to confirm the enhanced vertical exchange properties of limnocorrals and similar enclosures. Gas exchange coefficients for /sup 222/Rn and /sup 3/He were determined in a small northern Ontario lake, using a /sup 226/Ra and /sup 3/H spike to gain the necessary precision. The results indicate that the gas exchange coefficient is functionally dependent on the diffusion coefficient raised to the 1.22/sub -35//sup + > 12/ power (k/sub x/ = f(D/sub x//sup 1.22)), clearly supporting the stagnant film model of gas exchange. Limnocorrals were found to have gas exchange rates up to 1.7 times higher than the whole lake in spite of the observation of more calm surface conditions in the corral than in the open lake. 33 references, 6 figures, 8 tables.

  16. Oxygen exchange at gas/oxide interfaces: how the apparent activation energy of the surface exchange coefficient depends on the kinetic regime.

    PubMed

    Fielitz, Peter; Borchardt, Günter

    2016-08-10

    In the dedicated literature the oxygen surface exchange coefficient KO and the equilibrium oxygen exchange rate [Fraktur R] are considered to be directly proportional to each other regardless of the experimental circumstances. Recent experimental observations, however, contradict the consequences of this assumption. Most surprising is the finding that the apparent activation energy of KO depends dramatically on the kinetic regime in which it has been determined, i.e. surface exchange controlled vs. mixed or diffusion controlled. This work demonstrates how the diffusion boundary condition at the gas/solid interface inevitably entails a correlation between the oxygen surface exchange coefficient KO and the oxygen self-diffusion coefficient DO in the bulk ("on top" of the correlation between KO and [Fraktur R] for the pure surface exchange regime). The model can thus quantitatively explain the range of apparent activation energies measured in the different regimes: in the surface exchange regime the apparent activation energy only contains the contribution of the equilibrium exchange rate, whereas in the mixed or in the diffusion controlled regime the contribution of the oxygen self-diffusivity has also to be taken into account, which may yield significantly higher apparent activation energies and simultaneously quantifies the correlation KO ∝ DO(1/2) observed for a large number of oxides in the mixed or diffusion controlled regime, respectively. PMID:27460608

  17. Do volcanic emissions affect carbon gas fluxes in peatlands?

    NASA Astrophysics Data System (ADS)

    Harrison, Nicola; Delmelle, Pierre; Toet, Sylvia; Gauci, Vincent; Ineson, Phil

    2010-05-01

    Recently, a link has been suggested between volcanic deposition of SO4 and the suppression of CH4 emissions in northern peatlands (Gauci et al., 2008). This link stems from the widely accepted idea that acid rain SO4 additions to peatlands can cause a shift in microbial communities as SO4 reducing bacteria out-compete methanogens for substrates, which results in a suppression of CH4 emission. However, volcanic emissions contain besides S other chemically reactive species that are potentially harmful to the environment. In particular, gaseous and particulate F emissions from volcanoes constitute a steady or intermittent source of F emission and deposition into the environment both close to the source and within fallout range of large eruptions. The objective of this study was to investigate the effect of volcanic depositions of SO4, both alone and in combination with F, on CH4 emission in peatlands. Peat mesocosms collected from Pennine uplands in the UK were treated with weekly pulses of Na2SO4 and NaF over 20 weeks in doses of 74 kg SO4/ ha and 13.5 and 135 kg F /ha. CH4 emissions were measured at regular intervals by taking headspace samples, which were analysed by GC-FID. CO2 fluxes were also measured using a portable Infra Red Gas Analyser (IRGA). No significant differences in CH4 and CO2 emissions were observed for any of the treatments when compared to the controls, which had only received deionised water. These findings are in contrast with previous studies where SO4 reduces CH4 emission in peatlands. The reason for this is unclear but may be due to the heterogeneous nature of peat soils. An alternative explanation relates to the previous history of the soils used in the mesocosms which are known to have been previously exposed to large volumes of anthropogenic S pollution. This may have caused microbial communities to evolve and become acclimatised to high levels of S addition. In either case, the assumption that CH4 suppression in peatlands occurs upon

  18. Differences in gas exchange contribute to habitat differentiation in Iberian columbines from contrasting light and water environments.

    PubMed

    Jaime, R; Serichol, C; Alcántara, J M; Rey, P J

    2014-03-01

    During photosynthesis, respiration and transpiration, gas exchange occurs via the stomata and so plants face a trade-off between maximising photosynthesis while minimising transpiration (expressed as water use efficiency, WUE). The ability to cope with this trade-off and regulate photosynthetic rate and stomatal conductance may be related to niche differentiation between closely related species. The present study explored this as a possible mechanism for habitat differentiation in Iberian columbines. The roles of irradiance and water stress were assessed to determine niche differentiation among Iberian columbines via distinct gas exchange processes. Photosynthesis-irradiance curves (P-I curves) were obtained for four taxa, and common garden experiments were conducted to examine plant responses to water and irradiance stress, by measuring instantaneous gas exchange and plant performance. Gas exchange was also measured in ten individuals using two to four field populations per taxon. The taxa had different P-I curves and gas exchange in the field. At the species level, water stress and irradiance explained habitat differentiation. Within each species, a combination of irradiance and water stress explained the between-subspecies habitat differentiation. Despite differences in stomatal conductance and CO2 assimilation, taxa did not have different WUE under field conditions, which suggests that the environment equally modifies photosynthesis and transpiration. The P-I curves, gas exchange in the field and plant responses to experimental water and irradiance stresses support the hypothesis that habitat differentiation is associated with differences among taxa in tolerance to abiotic stress mediated by distinct gas exchange responses. PMID:23957244

  19. Heat exchange effects on the performance of a clearance-sealed piston prover for gas flow measurements

    NASA Astrophysics Data System (ADS)

    Kutin, J.; Bobovnik, G.; Bajsić, I.

    2015-12-01

    This paper deals with heat exchange effects in a compact, high-speed, clearance-sealed version of a piston prover for gas flow measurements that has the temperature measurements limited to the time-averaged temperature of the gas flow. A lumped-element mathematical model is used to study the physical background of the heat exchange effects. Experimental testing is performed to validate the theoretical results, estimate the required temperature homogeneity in the piston prover and propose a modified measurement model that considers the heat exchange effects. These effects are almost linearly related to the temperature difference between the gas flow into the piston prover and the cylinder wall, with the sensitivity coefficient being dependent on the measured flow rate. The piston-prover configuration with the gas temperature sensor in the mixed inlet /outlet flow is found to be advantageous in comparison to a measurement of the inlet temperature.

  20. Short-term and long-term effects of low total pressure on gas exchange rates of spinach.

    PubMed

    Iwabuchi, K; Kurata, K

    2003-01-01

    In this study, spinach plants were grown under atmospheric and low pressure conditions with constant O2 and CO2 partial pressures, and the effects of low total pressure on gas exchange rates were investigated. CO2 assimilation and transpiration rates of spinach grown under atmospheric pressure increased after short-term exposure to low total pressure due to the enhancement of leaf conductance. However, gas exchange rates of plants grown at 25 kPa total pressure were not greater than those grown at atmospheric pressure. Stomatal pore length and width were significantly smaller in leaves grown at low total pressure. This result suggested that gas exchange rates of plants grown under low total pressure were not stimulated even with the enhancement of gas diffusion because the stomatal size and stomatal aperture decreased. PMID:12580188

  1. Consistency of gas exchange of man and plants in a closed ecological system: lines of attack on the problem.

    PubMed

    Gitelson, J I; Okladnikov YuN

    1996-01-01

    Gas exchange between man and plants in a closed ecological system based on atmosphere regeneration by plant photosynthesis is made consistent by attaining the equilibrium of human CO2 discharge and the productivity of the gas consuming bioregenerator. In this case the gas exchange might be, however, qualitatively disturbed from the equilibrium in terms of oxygen making it accumulate or decrease continuously in the air of the system. Gas exchange equilibrium in terms of O2 was attained in long-term experiments by equality of the human respiration coefficient and the plant assimilation coefficient. Varying the ratio of these parameters it is possible to control the oxygen concentration in the atmosphere to be reclaimed. PMID:11538965

  2. Short-term and long-term effects of low total pressure on gas exchange rates of spinach

    NASA Astrophysics Data System (ADS)

    Iwabuchi, K.; Kurata, K.

    In this study, spinach plants were grown under atmospheric and low pressure conditions with constant O2 and CO2 partial pressures, and the effects of low total pressure on gas exchange rates were investigated. CO2 assimilation and transpiration rates of spinach grown under atmospheric pressure increased after short-term exposure to low total pressure due to the enhancement of leaf conductance. However, gas exchange rates of plants grown at 25 kPa total pressure were not greater than those grown at atmospheric pressure. Stomatal pore length and width were significantly smaller in leaves grown at low total pressure. This result suggested that gas exchange rates of plants grown under low total pressure were not stimulated even with the enhancement of gas diffusion because the stomatal size and stomatal aperture decreased.

  3. Surface Chemical Composition Effect on Internal Gas Flow and Molecular Heat Exchange in a Gas-Solids System

    NASA Astrophysics Data System (ADS)

    Ukhov, Alexander; Borisov, Sergey; Porodnov, Boris

    2011-05-01

    On the basis of classical knowledge about movement of atoms and lattice theory of F. Goodman and G. Wachman the program modeling helium atom interaction with a three-dimensional crystal tungsten lattice taking into account partial surface covering by chemisorbed oxygen atoms is developed. An efficiency of molecular heat exchange of helium for pure and partially chemisorbed tungsten surface is calculated for different temperatures. Similar model of the surface and procedure of calculations have been applied for description of free-molecular gas flow in long cylindrical channel with clean and fully chemisorbed metal surface. Within the limits of the developed approach the results of calculations for both problems agree well with available experiments with surface contamination control.

  4. Seasonal patterns and control of gas exchange in local populations of the Mediterranean evergreen shrub Pistacia lentiscus L.

    NASA Astrophysics Data System (ADS)

    Flexas, Jaume; Gulías, Javier; Jonasson, Sven; Medrano, Hipólito; Mus, Mauricio

    2001-02-01

    We examined temporal and spatial variations in net photosynthesis, stomatal conductance, intrinsic water-use efficiency, sub-stomatal CO 2 concentration, apparent carboxylation efficiency and chlorophyll fluorescence in the Mediterranean shrub Pistacia lentiscus. The study was done at the extremes of a precipitation and temperature gradient on the coast and in the mountains of Mallorca, Spain, with gas exchange measurements at different times of the year, and combined measurements of gas exchange and chlorophyll fluorescence in a controlled experiment. The objectives were to relate annual variation in photosynthetic functions to environmentally induced constraints and to quantify to which extent local differences in climate can affect photosynthesis in shrub populations. In the mountain population, net photosynthesis peaked in spring and autumn, when water was abundant and temperature was moderately high. It was reduced in winter paralleling reduced carboxylation efficiency. Photosynthesis was at the annual minimum in summer at both sites due to drought-induced stomata closure combined with impaired function of the Calvin cycle. The coastal population maintained high photosynthesis in mid winter but had a pronounced decline in spring, and the summer decline lasted longer than in the mountains. Integrated over the seasons, net photosynthesis was about 25 % lower in the coastal than in the mountain population, in spite of maintained high mid winter photosynthesis. Hence, the reduction at the coast was mainly due to early onset of drought in spring and a long period of summer drought, showing that local climatic differences can cause pronounced spatial differences in plant carbon balance. As a consequence, similar differences probably also occur as a function of year-to-year variability of precipitation patterns and temperatures.

  5. Dynamics of leaf gas exchange, chlorophyll fluorescence and stem diameter changes during freezing and thawing of Scots pine seedlings.

    PubMed

    Lindfors, Lauri; Hölttä, Teemu; Lintunen, Anna; Porcar-Castell, Albert; Nikinmaa, Eero; Juurola, Eija

    2015-12-01

    Boreal trees experience repeated freeze-thaw cycles annually. While freezing has been extensively studied in trees, the dynamic responses occurring during the freezing and thawing remain poorly understood. At freezing and thawing, rapid changes take place in the water relations of living cells in needles and in stem. While freezing is mostly limited to extracellular spaces, living cells dehydrate, shrink and their osmotic concentration increases. We studied how the freezing-thawing dynamics reflected on leaf gas exchange, chlorophyll fluorescence and xylem and living bark diameter changes of Scots pine (Pinus sylvestris L.) saplings in controlled experiments. Photosynthetic rate quickly declined following ice nucleation and extracellular freezing in xylem and needles, almost parallel to a rapid shrinking of xylem diameter, while that of living bark followed with a slightly longer delay. While xylem and living bark diameters responded well to decreasing temperature and water potential of ice, the relationship was less consistent in the case of increasing temperature. Xylem showed strong temporal swelling at thawing suggesting water movement from bark. After thawing xylem diameter recovered to a pre-freezing level but living bark remained shrunk. We found that freezing affected photosynthesis at multiple levels. The distinct dynamics of photosynthetic rate and stomatal conductance reveals that the decreased photosynthetic rate reflects impaired dark reactions rather than stomatal closure. Freezing also inhibited the capacity of the light reactions to dissipate excess energy as heat, via non-photochemical quenching, whereas photochemical quenching of excitation energy decreased gradually with temperature in agreement with the gas exchange data. PMID:26423334

  6. Open-circuit gas exchange analysis in the non-steady-state.

    PubMed

    Hughson, R L; Kowalchuk, J M; Prime, W M; Green, H J

    1980-03-01

    The serial measurement of oxygen uptake (VO2) of four subjects was calculated during the transition from rest to constant-load cycle ergometer work using an open-circuit gas exchange analysis system. In calculating VO2, the mixed expired gas concentrations were matched with the ventilatory volume by various delay factors. A delay factor equivalent to the passing of 20 L of expired ventilation through the mixing chamber yielded results which were most similar to the VO2 obtained by a computerized breath-by-breath analysis. Previous checks of the response of the system to changes in calibrating gas mixtures had indicated that it was necessary to pass approximately 20-25 L of gas through the system before a plateau response was observed. This volume remained relatively constant, independent of flow rate. It is proposed that an understanding of the response characteristics of an open circuit system will enable the accurate calculation of VO2 over short time intervals in the non-steady-state. PMID:7389042

  7. Operation of an experimental algal gas exchanger for use in a CELSS

    NASA Astrophysics Data System (ADS)

    Smernoff, David T.; Wharton, Robert A.; Averner, Maurice M.

    Concepts of a CELSS anticipate the use of photosynthetic organisms (higher plants and algae) for air revitalization. The rates of production and uptake of carbon dioxide and oxygen between the crew and the photosynthetic organisms are mismatched. An aglal system used for gas exchange only will have the difficulty of an accumulation or depletion of these gases beyond physiologically tolerable limits (in a materially closed system the mismatch between assimilatory quotient (AQ) and respiratory quotient (RQ) will be balanced by the operation of the waste processor). We report the results of a study designed to test the feasibility of using environmental manipulations to maintain physiologically appropriate atmospheres for algae (Chlorella pyrenoidosa) and mice (Mus musculus strain DW/J) in a gas-closed system. Specifically, we consider the atmosphere behavior of this system with Chlorella grown on nitrate or urea and at different light intensities and optical densities. Manipulation of both the photosynthetic rate and AQ of the alga has been found to reduce the mismatch of gas requirements and allow operation of the system in a gas-stable manner. Operation of such a system in a CELSS may be useful for reduction of buffer sizes, as a backup system for higher plant air revitalization and to supply extra oxygen to the waste processor or during crew changes. In addition, mass balance for components of the system (mouse, algae and a waste processor) are presented.

  8. Wind driven vertical transport in a vegetated, wetland water column with air-water gas exchange

    NASA Astrophysics Data System (ADS)

    Poindexter, C.; Variano, E. A.

    2010-12-01

    Flow around arrays of cylinders at low and intermediate Reynolds numbers has been studied numerically, analytically and experimentally. Early results demonstrated that at flow around randomly oriented cylinders exhibits reduced turbulent length scales and reduced diffusivity when compared to similarly forced, unimpeded flows (Nepf 1999). While horizontal dispersion in flows through cylinder arrays has received considerable research attention, the case of vertical dispersion of reactive constituents has not. This case is relevant to the vertical transfer of dissolved gases in wetlands with emergent vegetation. We present results showing that the presence of vegetation can significantly enhance vertical transport, including gas transfer across the air-water interface. Specifically, we study a wind-sheared air-water interface in which randomly arrayed cylinders represent emergent vegetation. Wind is one of several processes that may govern physical dispersion of dissolved gases in wetlands. Wind represents the dominant force for gas transfer across the air-water interface in the ocean. Empirical relationships between wind and the gas transfer coefficient, k, have been used to estimate spatial variability of CO2 exchange across the worlds’ oceans. Because wetlands with emergent vegetation are different from oceans, different model of wind effects is needed. We investigated the vertical transport of dissolved oxygen in a scaled wetland model built inside a laboratory tank equipped with an open-ended wind tunnel. Plastic tubing immersed in water to a depth of approximately 40 cm represented emergent vegetation of cylindrical form such as hard-stem bulrush (Schoenoplectus acutus). After partially removing the oxygen from the tank water via reaction with sodium sulfite, we used an optical probe to measure dissolved oxygen at mid-depth as the tank water re-equilibrated with the air above. We used dissolved oxygen time-series for a range of mean wind speeds to estimate the

  9. Enhanced pulmonary and active skeletal muscle gas exchange during intense exercise after sprint training in men.

    PubMed Central

    McKenna, M J; Heigenhauser, G J; McKelvie, R S; Obminski, G; MacDougall, J D; Jones, N L

    1997-01-01

    1. This study investigated the effects of 7 weeks of sprint training on gas exchange across the lungs and active skeletal muscle during and following maximal cycling exercise in eight healthy males. 2. Pulmonary oxygen uptake (VO2) and carbon dioxide output (VCO2) were measured before and after training during incremental exercise (n = 8) and during and in recovery from a maximal 30 s sprint exercise bout by breath-by-breath analysis (n = 6). To determine gas exchange by the exercising leg muscles, brachial arterial and femoral venous blood O2 and CO2 contents and lactate concentration were measured at rest, during the final 10 s of exercise and during 10 min of recovery. 3. Training increased (P < 0.05) the maximal incremental exercise values of ventilation (VE, by 15.7 +/- 7.1%), VCO2 (by 9.3 +/- 2.1%) and VO2 (by 15.0 +/- 4.2%). Sprint exercise peak power (3.9 +/- 1.0% increase) and cumulative 30 s work (11.7 +/- 2.8% increase) were increased and fatigue index was reduced (by -9.2 +/- 1.5%) after training (P < 0.05). The highest VE, VCO2 and VO2 values attained during sprint exercise were not significantly changed after training, but a significant (P < 0.05) training effect indicated increased VE (by 19.2 +/- 7.9%), VCO2 (by 9.3 +/- 2.1%) and VO2 (by 12.7 +/- 6.5%), primarily reflecting elevated post-exercise values after training. 4. Arterial O2 and CO2 contents were lower after training, by respective mean differences of 3.4 and 21.9 ml l-1 (P < 0.05), whereas the arteriovenous O2 and CO2 content differences and the respiratory exchange ratio across the leg were unchanged by training. 5. Arterial whole blood lactate concentration and the net lactate release by exercising muscle were unchanged by training. 6. The greater peak pulmonary VO2 and VCO2 with sprint exercise, the increased maximal incremental values, unchanged arterial blood lactate concentration and greater sprint performance all point strongly towards enhanced gas exchange across the lungs and in

  10. Novel shell device for gas exchange in an operculate land snail.

    PubMed

    Páll-Gergely, Barna; Naggs, Fred; Asami, Takahiro

    2016-07-01

    The operculum of terrestrial snails tightly seals the shell aperture providing protection from predators and body-water loss. To allow respiration with a closed operculum, operculate land snails repeatedly evolved shell devices such as tubes or channels that open to the air. In all Asian members of the Alycaeidae, an externally closed tube lies along the suture behind the aperture that possesses a small internal opening into the last whorl at the tube's anterior end. However, this structure presents a paradox: how is gas exchanged through an externally closed tube? Here we show that many microtunnels open into the tube and run beneath radial ribs along the growth line of the last whorl in Alycaeus conformis These tunnels open to the outside of the shell surface near the umbilicus. Examination under high magnification revealed that the outermost shell layer forms these tunnels only in the whorl range beneath the sutural tube. Each tunnel (ca 16 µm diameter) is far narrower than any known metazoan parasite. These findings support our hypothesis that the externally closed sutural tube functions with microtunnels as a specialized apparatus for predator-free gas exchange with minimal water loss when the operculum seals the aperture. PMID:27405378

  11. Pulmonary gas exchange during dialysis in patients with obstructive lung disease.

    PubMed

    Pitcher, W D; Diamond, S M; Henrich, W L

    1989-11-01

    Hypoxemia occurs during routine hemodialysis and may contribute to morbidity, but its cause is not well understood. We reasoned that patients with COPD would be more vulnerable to abnormalities in gas exchange with dialysis. Thus, to investigate the cause of dialysis-related hypoxemia, we measured gas exchange in a group of stable dialysis patients with normal pulmonary function (n = 6) and a group of dialysis patients with COPD (n = 6). Measurements were made predialysis, at 1 h, and postdialysis with both acetate and bicarbonate dialysates. Acetate dialysis decreased PaO2 in normal and COPD patients at 1 h and postdialysis. Acetate-induced hypoxemia was associated with reduced respiratory CO2 excretion and hypoventilation but PaCO2 did not change. This decrease in CO2 excretion resulted from CO2 fixation during acetate metabolism and modest CO2 loss across the dialyzer. Hypoxemia occurred only postdialysis with bicarbonate dialysate in normal and COPD patients. An increased P(A-a)O2 occurred postdialysis with both dialysates, and was most consistently observed in the COPD patients. In summary, at least two mechanisms contribute to dialysis hypoxemia. With acetate dialysate, alveolar hypoventilation from CO2 unloading occurs at 1 h and postdialysis due to acetate metabolism. However, abnormalities in ventilation/perfusion contribute to postdialysis hypoxemia observed with both dialysates. In addition, the decrement in PaO2 associated with dialysis is similar in normal and COPD patients, although preexisting COPD makes postdialysis changes more apparent. PMID:2805844

  12. Red spruce gas exchange in response to light, temperature, CO sub 2 and water stress

    SciTech Connect

    Samuelson, L.; Seiler, J. )

    1991-05-01

    The objective of this research was to examine the gas exchange responses of native red spruce seedlings to light, temperature and CO{sub 2} in combination with water stress to determine how red spruce physiologically responds to water stress. Gas exchange responses were examined under well-watered conditions and at an average leaf water potential of {minus}1.6 MPa. Net photosynthesis (Pnet) and leaf conductance (gl) were on average 35% and 53% lower, respectively, during water stress. The nature of the response of Pnet and gl to temperature and CO{sub 2} was similar to the well-watered response. Pnet was lower with water stress at high irradiances only. Water use efficiency was greater during water stress at 15C but not at 25 and 35C. No change in osmotic potential during water stress was observed. The response of red spruce physiology to varying light, temperature and CO{sub 2} does not appear to be greatly modified by water stress.

  13. Effects of stomatal delays on the economics of leaf gas exchange under intermittent light regimes.

    PubMed

    Vico, Giulia; Manzoni, Stefano; Palmroth, Sari; Katul, Gabriel

    2011-11-01

    • Understory plants are subjected to highly intermittent light availability and their leaf gas exchanges are mediated by delayed responses of stomata and leaf biochemistry to light fluctuations. In this article, the patterns in stomatal delays across biomes and plant functional types were studied and their effects on leaf carbon gains and water losses were quantified. • A database of more than 60 published datasets on stomatal responses to light fluctuations was assembled. To interpret these experimental observations, a leaf gas exchange model was developed and coupled to a novel formulation of stomatal movement energetics. The model was used to test whether stomatal delays optimize light capture for photosynthesis, whilst limiting transpiration and carbon costs for stomatal movement. • The data analysis showed that stomatal opening and closing delays occurred over a limited range of values and were strongly correlated. Plant functional type and climate were the most important drivers of stomatal delays, with faster responses in graminoids and species from dry climates. • Although perfectly tracking stomata would maximize photosynthesis and minimize transpiration at the expense of large opening costs, the observed combinations of opening and closure times appeared to be consistent with a near-optimal balance of carbon gain, water loss and movement costs. PMID:21851359

  14. Ventilation and gas exchange in two turtles: Podocnemis unifilis and Phrynops geoffroanus (Testudines: Pleurodira).

    PubMed

    Cordeiro, Tábata E F; Abe, Augusto S; Klein, Wilfried

    2016-04-01

    Turtles (Testudines) have two major taxa, Pleurodira and Cryptodira. To date, only limited data are available regarding the respiratory physiology of pleurodirans. To begin to address this, we studied ventilation and gas exchange in Podocnemis unifilis and Phrynops geoffroanus. Breathing pattern in both species could be described as episodic with breathing episodes separated by large non-ventilatory periods. We measured duration of inspiration and expiration, breathing frequency, duration of the non-ventilatory period (time between episodes), tidal volume, and oxygen consumption when breathing normoxia, hypoxia and hypercarbia at 25°C. In both species hypercarbia caused a greater increase in ventilation compared to hypoxia, increasing both breathing frequency and tidal volume. Minute ventilation and oxygen consumption in P. geoffroanus were the lowest described so far in testudines, indicating either extra-pulmonary gas exchange or a significantly lower metabolism. Oxidative costs of breathing, estimated using the regression method, was the highest described so far for any reptile. Further studies are necessary to better understand respiratory physiology in Phrynops and Podocnemis species. PMID:25534144

  15. Chlorophyll, anthocyanin, and gas exchange changes assessed by spectroradiometry in Fragaria chiloensis under salt stress.

    PubMed

    Garriga, Miguel; Retamales, Jorge B; Romero-Bravo, Sebastián; Caligari, Peter D S; Lobos, Gustavo A

    2014-05-01

    Chlorophyll and anthocyanin contents provide a valuable indicator of the status of a plant's physiology, but to be more widely utilized it needs to be assessed easily and non-destructively. This is particularly evident in terms of assessing and exploiting germplasm for plant-breeding programs. We report, for the first time, experiments with Fragaria chiloensis (L.) Duch. and the estimation of the effects of response to salinity stress (0, 30, and 60 mmol NaCl/L) in terms of these pigments content and gas exchange. It is shown that both pigments (which interestingly, themselves show a high correlation) give a good indication of stress response. Both pigments can be accurately predicted using spectral reflectance indices (SRI); however, the accuracy of the predictions was slightly improved using multilinear regression analysis models and genetic algorithm analysis. Specifically for chlorophyll content, unlike other species, the use of published SRI gave better indications of stress response than Normalized Difference Vegetation Index. The effect of salt on gas exchange is only evident at the highest concentration and some SRI gave better prediction performance than the known Photochemical Reflectance Index. This information will therefore be useful for identifying tolerant genotypes to salt stress for incorporation in breeding programs. PMID:24618024

  16. Canopy gas exchange of white spruce in contrasting habitats near the Arctic treeline in northwest Alaska

    NASA Astrophysics Data System (ADS)

    Sullivan, P.; Mcnown, R. W.; Sveinbjornsson, B.

    2011-12-01

    Recent work near the Arctic treeline has revealed that an increasing number of white spruce are showing negative growth responses to rising air temperatures. Researchers have speculated that these negative responders are experiencing warm temperature-induced drought stress. Measurements of white spruce needle gas exchange near the Arctic treeline are rare and, to our knowledge, measurements of whole canopy gas exchange have not been made. In this study, we measured sap flow to estimate whole canopy transpiration at hourly intervals for the entire growing seasons of 2010 and 2011 in white spruce growing on a riverside terrace, in a hillslope forest and at the treeline. We used weekly measurements of needle-scale photosynthesis, transpiration and needle δ13C to estimate water use efficiency at each site. We then applied these estimates of water use efficiency to our sap flow data in order to estimate hourly whole canopy photosynthesis at each site for the two growing seasons. Our results show evidence of stomatal control when the atmospheric vapor pressure deficit exceeds approximately 1.0 kPa, but no evidence of complete stomatal closure. Trees growing on the riverside terrace, where soils are relatively warm and dry, are more efficient in their water use, have greater leaf area and assimilate more carbon per unit basal diameter than trees in the forest and at the treeline. We found that the month of September, after growth has almost completely ceased, can be an important time for carbon uptake in white spruce near the Arctic treeline.

  17. Differences in gas exchange between severities of chronic obstructive pulmonary disease.

    PubMed

    Thirapatarapong, Wilawan; Armstrong, Hilary F; Thomashow, Byron M; Bartels, Matthew N

    2013-03-01

    Impaired ventilation on cardiopulmonary exercise test (CPET) is seen in patients with chronic obstructive pulmonary disease (COPD). However, evaluation of the differences of abnormal gas exchange in COPD according to GOLD severity criteria is limited. A retrospective review was performed on all COPD patients referred for CPET at our center between 1998 and 2010. There were 548 patients compared according to GOLD severity. GOLD groups were significantly different from each other in regards to pressure of end-tidal carbon dioxide ( [Formula: see text] ) with progressively higher [Formula: see text] with increasing GOLD severity. Ratio of minute ventilation to carbon dioxide production ( [Formula: see text] ) and exercise capacity as measured by and [Formula: see text] % and work rate in watts% was inversely proportional to GOLD severity. Breathing reserve, minute ventilation, and tidal volume at peak exercise were significantly decreased with increasing disease severity between GOLD groups. We concluded that gas exchange is distinctive among different GOLD severity groups; specifically, GOLD 3 and 4 have a significantly higher [Formula: see text] and a significantly lower [Formula: see text] than GOLD 2. PMID:23318702

  18. Surfactant therapy restores gas exchange in lung injury due to paraquat intoxication in rats.

    PubMed

    So, K L; de Buijzer, E; Gommers, D; Kaisers, U; van Genderen, P J; Lachmann, B

    1998-08-01

    Paraquat is a weed killer which causes often fatal lung damage in humans and other animals. There is evidence that the pulmonary surfactant system is involved in the pathophysiology of respiratory failure after paraquat intoxication and, therefore, the possible therapeutic effect of intratracheal surfactant administration on gas exchange in rats with progressive lung injury induced by paraquat poisoning was studied. In one group of rats, the time course of the development of lung injury due to paraquat intoxication was characterized. In a second group of rats, 72 h after paraquat intoxication, the animals underwent mechanical ventilation and only those animals in which the arterial oxygen tension/inspiratory oxygen fraction (Pa,O2/FI,O2) decreased to below 20 kPa (150 mmHg) received exogenous surfactant (200 mg x kg(-1) body weight). Within 3 days the rats in group 1 developed progressive respiratory failure, demonstrated not only by impaired gas exchange and lung mechanics but also by increased minimal surface tension and increased protein concentration in bronchoalveolar lavage fluid. In group 2, intratracheal surfactant administration increased Pa,O2/FI,O2 significantly within 5 min (14.4+/-2.4 kPa (108+/-18 mmHg)) to (55.2+/-53 kPa (414+/-40 mmHg)) and sustained this level for at least 2 h. It is concluded that intratracheal surfactant administration is a promising approach in the treatment of severe respiratory failure caused by paraquat poisoning. PMID:9727775

  19. Effects of beta-adrenergic blockade on ventilation and gas exchange during incremental exercise.

    PubMed

    Dodd, S; Powers, S; O'Malley, N; Brooks, E; Sommers, H

    1988-08-01

    Controversy exists concerning the effects of acute beta-adrenergic blockade on ventilation during exercise. Hence, the purpose of this study was to determine the effects of acute beta blockade on ventilation and gas exchange during incremental exercise. Nine male subjects underwent incremental exercise on a cycle ergometer (30 W.min-1) to exhaustion, with one trial being performed 60 min after the subject ingested propranolol hydrochloride (Inderal 1 mg.kg-1 BW) while the second test served as control. The treatment order was counterbalanced to preclude any ordering effect on the results, and 1 week separated the tests. Ventilation and gas exchange were monitored by open circuit techniques. No difference (p greater than 0.05) existed in VE, % Hb sat, VCO2, ventilatory threshold, and VE/VCO2 between treatments at the same exercise stage. VO2max was lowered from 3.82 to 3.26 l.min-1 (p less than 0.05) and HRmax was reduced from 190 to 150 bpm (p less than 0.05) as a result of beta blockade. These data suggested that acute beta blockade had no effect on exercise ventilation, but decreased HRmax at comparable work rates. In addition, VO2max and exercise time to exhaustion were hindered, probably due to beta blockade limitation of HRmax, and, thus, oxygen transport. PMID:3178619

  20. High temperature corrosion of advanced ceramic materials for hot-gas filters and heat exchangers

    SciTech Connect

    Kupp, E.R.; Trubelja, M.F.; Spear, K.E.; Tressler, R.E.

    1995-08-01

    Experimental corrosion studies of hot gas filter materials and heat exchanger materials in oxidizing combustion environments have been initiated. Filter materials from 3M Co. and DuPont Lanxide Composites Inc. are being tested over a range of temperatures, times and gas flows. It has been demonstrated that morphological and phase changes due to corrosive effects occur after exposure of the 3M material to a combustion environment for as little as 25 hours at 800{degrees}C. The study of heat exchanger materials has focused on enhancing the corrosion resistance of DuPont Lanxide Dimox{trademark} composite tubes by adding chromium to its surfaces by (1) heat treatments in a Cr{sub 2}O{sub 3} powder bed, or (2) infiltrating surface porosity with molten chromium nitrate. Each process is followed by a surface homogenization at 1500{degrees}C. The powder bed method has been most successful, producing continuous Cr-rich layers with thicknesses ranging from 20 to 250 {mu}m. As-received and Cr-modified DuPont Lanxide Dimox{trademark} samples will be reacted with commonly encountered coal-ash slags to determine the Cr effects on corrosion resistance.

  1. Oxygen convective uptakes in gas exchange cycles in early diapause pupae of Pieris brassicae.

    PubMed

    Jõgar, Katrin; Kuusik, Aare; Ploomi, Angela; Metspalu, Luule; Williams, Ingrid; Hiiesaar, Külli; Kivimägi, Irja; Mänd, Marika; Tasa, Tea; Luik, Anne

    2011-09-01

    Oxygen convective uptakes in gas exchange cycles were directly recorded in early diapause pupae of Pieris brassicae L. (Lepidoptera; Pieridae) by means of O2 coulometric respirometry. This method was combined with flow-through CO2 respirometry, the two systems being switchable one to the other. During recording with both systems, measurements were also taken with infrared actography. The pupae displayed short discontinuous gas exchange cycles lasting 40-70 min. No true C phase was found by flow-through measurements; instead, flutter opening of the spiracles with discrete convective O2 uptakes began shortly after the O phase whereas CO2 release was suppressed by the inward directed passive suction ventilation. The F phase was characterized by a series of small CO2 bursts (flutter events). Between these bursts, novel sub-phase `miniflutter' was observed, which consisted of six to 10 miniature inspirations without any CO2 emission. During the flow-through measurements, oxygen convective uptakes were indirectly recorded by the infrared actograph as sudden extensions (lengthening) of the abdominal segments at each spiracular microopening. PMID:21832124

  2. Retrospective analysis of lung function abnormalities of Bhopal gas tragedy affected population

    PubMed Central

    De, Sajal

    2012-01-01

    Background & objectives: A large numbers of subjects were exposed to the aerosol of methyl isocyanate (MIC) during Bhopal gas disaster and lung was one of the most commonly affected organs. The aim of the present study was to analyze retrospectively the lung function abnormalities among the surviving MIC exposed population (gas victims) and to compare it with the non-MIC exposed (non gas exposed) population. Methods: The spirometry data of both gas victims and non gas exposed population who attended the Bhopal Memorial Hospital & Research Centre for evaluation of their respiratory complaints from August 2001 to December 2009, were retrospectively evaluated and compared. Results: A total 4782 gas victims and 1190 non gas exposed individuals performed spirometry during the study period. Among the gas victims, obstructive pattern was the commonest (50.8%) spirometric abnormality followed by restrictive pattern (13.3%). The increased relative risk of developing restrictive abnormality among gas victims was observed in 20-29 yr age group only (adjusted relative risk: 2.94, P<0.001). Male gas victims were more affected by severe airflow obstruction than females and the overall increased relative risk (1.33 to 1.45, P<0.001) of developing obstructive pattern among gas victims was observed. Interpretation & conclusions: The present study showed that the relative risk for pulmonary function abnormalities in gas victims was significantly more among those who were young at the time of disaster. Increased smoking habit among gas victims might have played an additive effect on predominance of obstructive pattern in spirometry. PMID:22446861

  3. Nitrogen and phosphorus leaching as affected by gypsum amendment and exchangeable calcium and magnesium

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The movement of N and P from the soil by leaching contributes to losses from agricultural land and represents an important environmental and human health concern. The objective of this study was to evaluate the effect of gypsum amendment and the resultant impact of different levels of exchangeable C...

  4. The influence of sea ice cover on air-sea gas exchange estimated with radon-222 profiles

    NASA Astrophysics Data System (ADS)

    Rutgers van der Loeff, Michiel M.; Cassar, Nicolas; Nicolaus, Marcel; Rabe, Benjamin; Stimac, Ingrid

    2014-05-01

    Air-sea gas exchange plays a key role in the cycling of greenhouse and other biogeochemically important gases. Although air-sea gas transfer is expected to change as a consequence of the rapid decline in summer Arctic sea ice cover, little is known about the effect of sea ice cover on gas exchange fluxes, especially in the marginal ice zone. During the Polarstern expedition ARK-XXVI/3 (TransArc, August/September 2011) to the central Arctic Ocean, we compared 222Rn/226Ra ratios in the upper 50 m of 14 ice-covered and 4 ice-free stations. At three of the ice-free stations, we find 222Rn-based gas transfer coefficients in good agreement with expectation based on published relationships between gas transfer and wind speed over open water when accounting for wind history from wind reanalysis data. We hypothesize that the low gas transfer rate at the fourth station results from reduced fetch due to the proximity of the ice edge, or lateral exchange across the front at the ice edge by restratification. No significant radon deficit could be observed at the ice-covered stations. At these stations, the average gas transfer velocity was less than 0.1 m/d (97.5% confidence), compared to 0.5-2.2 m/d expected for open water. Our results show that air-sea gas exchange in an ice-covered ocean is reduced by at least an order of magnitude compared to open water. In contrast to previous studies, we show that in partially ice-covered regions, gas exchange is lower than expected based on a linear scaling to percent ice cover.

  5. Quantitative variation in water-use efficiency across water regimes and its relationship with circadian, vegetative, reproductive, and leaf gas-exchange traits.

    PubMed

    Edwards, Christine E; Ewers, Brent E; McClung, C Robertson; Lou, Ping; Weinig, Cynthia

    2012-05-01

    Drought limits light harvesting, resulting in lower plant growth and reproduction. One trait important for plant drought response is water-use efficiency (WUE). We investigated (1) how the joint genetic architecture of WUE, reproductive characters, and vegetative traits changed across drought and well-watered conditions, (2) whether traits with distinct developmental bases (e.g. leaf gas exchange versus reproduction) differed in the environmental sensitivity of their genetic architecture, and (3) whether quantitative variation in circadian period was related to drought response in Brassica rapa. Overall, WUE increased in drought, primarily because stomatal conductance, and thus water loss, declined more than carbon fixation. Genotypes with the highest WUE in drought expressed the lowest WUE in well-watered conditions, and had the largest vegetative and floral organs in both treatments. Thus, large changes in WUE enabled some genotypes to approach vegetative and reproductive trait optima across environments. The genetic architecture differed for gas-exchange and vegetative traits across drought and well-watered conditions, but not for floral traits. Correlations between circadian and leaf gas-exchange traits were significant but did not vary across treatments, indicating that circadian period affects physiological function regardless of water availability. These results suggest that WUE is important for drought tolerance in Brassica rapa and that artificial selection for increased WUE in drought will not result in maladaptive expression of other traits that are correlated with WUE. PMID:22319207

  6. Near-surface physics during convection affecting air-water gas transfer

    NASA Astrophysics Data System (ADS)

    Fredriksson, S. T.; Arneborg, L.; Nilsson, H.; Handler, R. A.

    2016-05-01

    The gas flux at the water surface is affected by physical processes including turbulence from wind shear, microscale wave breaking, large-scale breaking, and convection due to heat loss at the surface. The main route in the parameterizations of the gas flux has been to use the wind speed as a proxy for the gas flux velocity, indirectly taking into account the dependency of the wind shear and the wave processes. The interest in the contributions from convection processes has increased as the gas flux from inland waters (with typically lower wind and sheltered conditions) now is believed to play a substantial role in the air-water gas flux budget. The gas flux is enhanced by convection through the mixing of the mixed layer as well as by decreasing the diffusive boundary layer thickness. The direct numerical simulations performed in this study are shown to be a valuable tool to enhance the understanding of this flow configuration often present in nature.

  7. Alveolar ventilation to perfusion heterogeneity and diffusion impairment in a mathematical model of gas exchange

    NASA Technical Reports Server (NTRS)

    Vidal Melo, M. F.; Loeppky, J. A.; Caprihan, A.; Luft, U. C.

    1993-01-01

    This study describes a two-compartment model of pulmonary gas exchange in which alveolar ventilation to perfusion (VA/Q) heterogeneity and impairment of pulmonary diffusing capacity (D) are simultaneously taken into account. The mathematical model uses as input data measurements usually obtained in the lung function laboratory. It consists of two compartments and an anatomical shunt. Each compartment receives fractions of alveolar ventilation and blood flow. Mass balance equations and integration of Fick's law of diffusion are used to compute alveolar and blood O2 and CO2 values compatible with input O2 uptake and CO2 elimination. Two applications are presented. The first is a method to partition O2 and CO2 alveolar-arterial gradients into VA/Q and D components. The technique is evaluated in data of patients with chronic obstructive pulmonary disease (COPD). The second is a theoretical analysis of the effects of blood flow variation in alveolar and blood O2 partial pressures. The results show the importance of simultaneous consideration of D to estimate VA/Q heterogeneity in patients with diffusion impairment. This factor plays an increasing role in gas alveolar-arterial gradients as severity of COPD increases. Association of VA/Q heterogeneity and D may produce an increase of O2 arterial pressure with decreasing QT which would not be observed if only D were considered. We conclude that the presented computer model is a useful tool for description and interpretation of data from COPD patients and for performing theoretical analysis of variables involved in the gas exchange process.

  8. Responses of sap flow, leaf gas exchange and growth of hybrid aspen to elevated atmospheric humidity under field conditions

    PubMed Central

    Niglas, Aigar; Kupper, Priit; Tullus, Arvo; Sellin, Arne

    2014-01-01

    An increase in average air temperature and frequency of rain events is predicted for higher latitudes by the end of the 21st century, accompanied by a probable rise in air humidity. We currently lack knowledge on how forest trees acclimate to rising air humidity in temperate climates. We analysed the leaf gas exchange, sap flow and growth characteristics of hybrid aspen (Populus tremula × P. tremuloides) trees growing at ambient and artificially elevated air humidity in an experimental forest plantation situated in the hemiboreal vegetation zone. Humidification manipulation did not affect the photosynthetic capacity of plants, but did affect stomatal responses: trees growing at elevated air humidity had higher stomatal conductance at saturating photosynthetically active radiation (gs sat) and lower intrinsic water-use efficiency (IWUE). Reduced stomatal limitation of photosynthesis in trees grown at elevated air humidity allowed slightly higher net photosynthesis and relative current-year height increments than in trees at ambient air humidity. Tree responses suggest a mitigating effect of higher air humidity on trees under mild water stress. At the same time, trees at higher air humidity demonstrated a reduced sensitivity of IWUE to factors inducing stomatal closure and a steeper decline in canopy conductance in response to water deficit, implying higher dehydration risk. Despite the mitigating impact of increased air humidity under moderate drought, a future rise in atmospheric humidity at high latitudes may be disadvantageous for trees during weather extremes and represents a potential threat in hemiboreal forest ecosystems. PMID:24887000

  9. Responses of sap flow, leaf gas exchange and growth of hybrid aspen to elevated atmospheric humidity under field conditions.

    PubMed

    Niglas, Aigar; Kupper, Priit; Tullus, Arvo; Sellin, Arne

    2014-01-01

    An increase in average air temperature and frequency of rain events is predicted for higher latitudes by the end of the 21st century, accompanied by a probable rise in air humidity. We currently lack knowledge on how forest trees acclimate to rising air humidity in temperate climates. We analysed the leaf gas exchange, sap flow and growth characteristics of hybrid aspen (Populus tremula × P. tremuloides) trees growing at ambient and artificially elevated air humidity in an experimental forest plantation situated in the hemiboreal vegetation zone. Humidification manipulation did not affect the photosynthetic capacity of plants, but did affect stomatal responses: trees growing at elevated air humidity had higher stomatal conductance at saturating photosynthetically active radiation (gs sat) and lower intrinsic water-use efficiency (IWUE). Reduced stomatal limitation of photosynthesis in trees grown at elevated air humidity allowed slightly higher net photosynthesis and relative current-year height increments than in trees at ambient air humidity. Tree responses suggest a mitigating effect of higher air humidity on trees under mild water stress. At the same time, trees at higher air humidity demonstrated a reduced sensitivity of IWUE to factors inducing stomatal closure and a steeper decline in canopy conductance in response to water deficit, implying higher dehydration risk. Despite the mitigating impact of increased air humidity under moderate drought, a future rise in atmospheric humidity at high latitudes may be disadvantageous for trees during weather extremes and represents a potential threat in hemiboreal forest ecosystems. PMID:24887000

  10. Gas exchange in wetlands with emergent vegetation: The effects of wind and thermal convection at the air-water interface

    NASA Astrophysics Data System (ADS)

    Poindexter, Cristina M.; Variano, Evan A.

    2013-07-01

    Methane, carbon dioxide, and oxygen are exchanged between wetlands and the atmosphere through multiple pathways. One of these pathways, the hydrodynamic transport of dissolved gas through the surface water, is often underestimated in importance. We constructed a model wetland in the laboratory with artificial emergent plants to investigate the mechanisms and magnitude of this transport. We measured gas transfer velocities, which characterize the near-surface stirring driving air-water gas transfer, while varying two stirring processes important to gas exchange in other aquatic environments: wind and thermal convection. To isolate the effects of thermal convection, we identified a semiempirical model for the gas transfer velocity as a function of surface heat loss. The laboratory results indicate that thermal convection will be the dominant mechanism of air-water gas exchange in marshes with emergent vegetation. Thermal convection yielded peak gas transfer velocities of 1 cm h-1. Because of the sheltering of the water surface by emergent vegetation, gas transfer velocities for wind-driven stirring alone are likely to exceed this value only in extreme cases.

  11. Effect of Alterations in Mechanical Ventilator Settings on Pulmonary Gas Exchange in Hyaline Membrane Disease

    PubMed Central

    Reynolds, E. O. R.

    1971-01-01

    The effect of altering peak airway pressure, respiratory frequency, and inspiration: expiration ratio on arterial blood gas tensions, blood pressure, and calculated right-to-left shunt was investigated in 6 infants undergoing mechanical ventilation for hyaline membrane disease with a Bennet ventilator. The use of a very long inspiratory phase resulted in a large increase in Pao2 and fall in right-to-left shunt without affecting mean arterial blood pressure. ImagesFIG. 1FIG. 4 PMID:5576023

  12. A tonoplast Glu/Asp/GABA exchanger that affects tomato fruit amino acid composition.

    PubMed

    Snowden, Christopher J; Thomas, Benjamin; Baxter, Charles J; Smith, J Andrew C; Sweetlove, Lee J

    2015-03-01

    Vacuolar accumulation of acidic metabolites is an important aspect of tomato fruit flavour and nutritional quality. The amino acids Asp and Glu accumulate to high concentrations during ripening, while γ-aminobutyrate (GABA) shows an approximately stoichiometric decline. Given that GABA can be catabolised to form Glu and subsequently Asp, and the requirement for the fruit to maintain osmotic homeostasis during ripening, we hypothesised the existence of a tonoplast transporter that exports GABA from the vacuole in exchange for import of either Asp or Glu. We show here that the tomato vacuolar membrane possesses such a transport property: transport of Glu across isolated tonoplast vesicle membranes was trans-stimulated in counterexchange mode by GABA, Glu and Asp. We identified SlCAT9 as a candidate protein for this exchanger using quantitative proteomics of a tonoplast-enriched membrane fraction. Transient expression of a SlCAT9-YFP fusion in tobacco confirmed a tonoplast localisation. The function of the protein was examined by overexpression of SlCAT9 in transgenic tomato plants. Tonoplast vesicles isolated from transgenic plants showed higher rates of Glu and GABA transport than wild-type (WT) only when assayed in counterexchange mode with Glu, Asp, or GABA. Moreover, there were substantial increases in the content of all three cognate amino acids in ripe fruit from the transgenic plants. We conclude that SlCAT9 is a tonoplast Glu/Asp/GABA exchanger that strongly influences the accumulation of these amino acids during fruit development. PMID:25602029

  13. How choices in exchange design for states could affect insurance premiums and levels of coverage.

    PubMed

    Blavin, Fredric; Blumberg, Linda J; Buettgens, Matthew; Holahan, John; McMorrow, Stacey

    2012-02-01

    The Affordable Care Act gives states the option to create health insurance exchanges from which individuals and small employers can purchase health insurance. States have considerable flexibility in how they design and implement these exchanges. We analyze several key design options being considered, using the Urban Institute's Health Insurance Policy Simulation Model: creating separate versus merged small-group and nongroup markets, eliminating age rating in these markets, removing the small-employer credit, and setting the maximum number of employees for firms in the small-group market at 50 versus 100 workers. Among our findings are that merging the small-group and nongroup markets would result in 1.7 million more people nationwide participating in the exchanges and, because of greater affordability of nongroup coverage, approximately 1.0 million more people being insured than if the risk pools were not merged. The various options generate relatively small differences in overall coverage and cost, although some, such as reducing age rating bands, would result in higher costs for some people while lowering costs for others. These cost effects would be most apparent among people who purchase coverage without federal subsidies. On the whole, we conclude that states can make these design choices based on local support and preferences without dramatic repercussions for overall coverage and cost outcomes. PMID:22323158

  14. Operation of an experimental algal gas exchanger for use in a CELSS

    NASA Technical Reports Server (NTRS)

    Smernoff, David T.; Wharton, Robert A., Jr.; Averner, Maurice M.

    1987-01-01

    Concepts of a Closed Ecological Life Support System (CELSS) anticipate the use of photosynthetic organisms (higher plants and algae) for air revitalization. The rates of production and uptake of carbon dioxide and oxygen between the crew and the photosynthetic organisms are mismatched. An algal system used for gas exchange only will have the difficulty of an accumulation or depletion of these gases beyond physiologically tolerable limits (in a closed system the mismatch between assimilatory quotient (AQ) and respiratory quotient (RQ) is balanced by the operation of the waste processor). The results are given of a study designed to test the feasibility of using environmental manipulations to maintain physiologically appropriate atmospheres for algae and mice in a gas closed system. Specifically, the atmosphere behavior of this system is considered with algae grown on nitrate or urea and at different light intensities and optical densities. Manipulation of both allow operation of the system in a gas stable manner. Operation of such a system in a CELSS may be useful for reduction of buffer sizes, as a backup system for higher plant air revitalization and to supply extra oxygen to the waste processor or during crew changes.

  15. Gas cells for 3He hyperpolarized via spin-exchange optical pumping

    NASA Astrophysics Data System (ADS)

    Kim, W.; Stepanyan, S. S.; Kim, A.; Tan, J. A.; Woo, S.

    2016-01-01

    We present a device for the production of hyperpolarized 3He, which is widely used in spinrelated nuclear physics research. Spin-exchange optical pumping (SEOP) is employed to polarize 3He enclosed in a circular borosilicate glass cell suitable not only for the production of polarized gas but also for its storage. The portable glass cell can, thus, be transported to any other research facility. The glass cell can be refilled several times. Special attention is given to the preparation and the filling of the cell to minimize the impurities on its walls and in the gas. We employ glass tubes with shorter lengths and larger diameters in the gas-filling system to achieve the improvement in the air flow necessary to obtain purer polarized 3He samples. The cell is prepared, and after it has been filled with rubidium (Rb) and 3He-N2 mixture, it is sealed under high vacuum conditions. The cell containing the mixture is exposed to circularly-polarized laser light with a wavelength of 795 nm at temperatures of 180 - 220 °C for SEOP. The polarization of 3He is measured via nuclear magnetic resonance (NMR). We obtained 40% polarized 3He in less than 15 hours and 50% in about 25 hours. The longitudinal relaxation time T 1 of the polarized 3He we measured was about 58 hours.

  16. Intra-individual variation allows an explicit test of the hygric hypothesis for discontinuous gas exchange in insects

    PubMed Central

    Williams, Caroline M.; Pelini, Shannon L.; Hellmann, Jessica J.; Sinclair, Brent J.

    2010-01-01

    The hygric hypothesis postulates that insect discontinuous gas exchange cycles (DGCs) are an adaptation that reduces respiratory water loss (RWL), but evidence is lacking for reduction of water loss by insects expressing DGCs under normal ecological conditions. Larvae of Erynnis propertius (Lepidoptera: Hesperiidae) naturally switch between DGCs and continuous gas exchange (CGE), allowing flow-through respirometry comparisons of water loss between the two modes. Water loss was lower during DGCs than CGE, both between individuals using different patterns and within individuals using both patterns. The hygric cost of gas exchange (water loss associated with carbon dioxide release) and the contribution of respiratory to total water loss were lower during DGCs. Metabolic rate did not differ between DGCs and CGE. Thus, DGCs reduce RWL in E. propertius, which is consistent with the suggestion that water loss reduction could account for the evolutionary origin and/or maintenance of DGCs in insects. PMID:19923135

  17. Intra-individual variation allows an explicit test of the hygric hypothesis for discontinuous gas exchange in insects.

    PubMed

    Williams, Caroline M; Pelini, Shannon L; Hellmann, Jessica J; Sinclair, Brent J

    2010-04-23

    The hygric hypothesis postulates that insect discontinuous gas exchange cycles (DGCs) are an adaptation that reduces respiratory water loss (RWL), but evidence is lacking for reduction of water loss by insects expressing DGCs under normal ecological conditions. Larvae of Erynnis propertius (Lepidoptera: Hesperiidae) naturally switch between DGCs and continuous gas exchange (CGE), allowing flow-through respirometry comparisons of water loss between the two modes. Water loss was lower during DGCs than CGE, both between individuals using different patterns and within individuals using both patterns. The hygric cost of gas exchange (water loss associated with carbon dioxide release) and the contribution of respiratory to total water loss were lower during DGCs. Metabolic rate did not differ between DGCs and CGE. Thus, DGCs reduce RWL in E. propertius, which is consistent with the suggestion that water loss reduction could account for the evolutionary origin and/or maintenance of DGCs in insects. PMID:19923135

  18. Investigation of the gas-phase hydrogen/deuterium exchange behavior of aromatic dicarboxylic acids in a quadrupole ion trap

    NASA Astrophysics Data System (ADS)

    Chipuk, Joseph E.; Brodbelt, Jennifer S.

    2007-11-01

    Gas-phase hydrogen/deuterium (H/D) exchange reactions of four deprotonated aromatic dicarboxylic acids (phthalic acid, isophthalic acid, terephthalic acid and 2,6-naphthalic acid) with D2O were performed in a quadrupole ion trap mass spectrometer. Experimental results showed significant differences in the rate and extent of exchange when the relative position of the carboxylic acid groups varied. Spontaneous and near complete exchange of one aromatic hydrogen atom occurred when the carboxylic acid groups were in the meta-position, whereas no additional exchange was observed for either the ortho- or para-isomers or for the structurally similar naphthalic acid. Computational investigations support the participation of several possible exchange mechanisms with the contribution of each relying heavily on the relative orientation of the acid moieties. A relay mechanism that bridges the deprotonation site and the labile hydrogen site appears to be responsible for the H/D exchange of not only the labile hydrogen atom of isophthalic acid, but also for the formation of a stable carbanion and corresponding subsequent exchange of one aromatic hydrogen atom. The impact of hydrogen bonding on the relay mechanism is demonstrated by the reaction of phthalic acid as the extent and rate of reaction are greatly retarded by the favorable interaction of the two carboxylic acid groups. Finally, a flip-flop mechanism is likely responsible for the exchange of both terephthalic acid and 2,6-naphthalic acid where the reactive sites are too remote for exchange via relay.

  19. Nonlocal energy-optimized kernel: Recovering second-order exchange in the homogeneous electron gas

    NASA Astrophysics Data System (ADS)

    Bates, Jefferson E.; Laricchia, Savio; Ruzsinszky, Adrienn

    2016-01-01

    In order to remedy some of the shortcomings of the random phase approximation (RPA) within adiabatic connection fluctuation-dissipation (ACFD) density functional theory, we introduce a short-ranged, exchange-like kernel that is one-electron self-correlation free and exact for two-electron systems in the high-density limit. By tuning a free parameter in our model to recover an exact limit of the homogeneous electron gas correlation energy, we obtain a nonlocal, energy-optimized kernel that reduces the errors of RPA for both homogeneous and inhomogeneous solids. Using wave-vector symmetrization for the kernel, we also implement RPA renormalized perturbation theory for extended systems, and demonstrate its capability to describe the dominant correlation effects with a low-order expansion in both metallic and nonmetallic systems. The comparison of ACFD structural properties with experiment is also shown to be limited by the choice of norm-conserving pseudopotential.

  20. The relationship between leaf water status, gas exchange, and spectral reflectance in cotton leaves

    NASA Technical Reports Server (NTRS)

    Bowman, William D.

    1989-01-01

    Measurements of leaf spectral reflectance, the components of water potential, and leaf gas exchanges as a function of leaf water content were made to evaluate the use of NIR reflectance as an indicator of plant water status. Significant correlations were determined between spectral reflectance at 810 nm, 1665 nm, and 2210 nm and leaf relative water content, total water potential, and turgor pressure. However, the slopes of these relationships were relatively shallow and, when evaluated over the range of leaf water contents in which physiological activity occurs (e.g., photosynthesis), had lower r-squared values, and some relationships were not statistically significant. NIR reflectance varied primarily as a function of leaf water content, and not independently as a function of turgor pressure, which is a sensitive indicator of leaf water status. The limitations of this approach to measuring plant water stress are discussed.

  1. Accurate exchange-correlation energies for the warm dense electron gas

    NASA Astrophysics Data System (ADS)

    Malone, Fionn; Blunt, Nicholas; Shepherd, James; Lee, Derek; Spencer, James; Foulkes, Matthew

    The accurate treatment of matter at high temperatures and densities is of increasing importance to many fields in physics and chemistry, with applications ranging from planetary physics to inertial confinement fusion and plasmonic catalysis. Faithfully including the effects of temperature in density functional theory simulations of warm dense matter requires accurate results for the uniform electron gas (UEG) across the whole temperature-density plane. While accurate ground state quantum Monte Carlo data have existed for over 30 years, there remains significant disagreement between results obtained using different path integral Monte Carlo methods at finite temperature. To resolve this disagreement, we use the systematically improvable density matrix quantum Monte Carlo method to calculate the exchange-correlation energy of the UEG. We also demonstrate how the evaluation of free energies emerges naturally from our method.

  2. Differential leaf gas exchange responses to salinity and drought in the mangrove tree Avicecennia germinans (Avicenniaceae).

    PubMed

    Sobrado, M A

    2006-06-01

    Leaf gas exchange was assessed in Avicennia germinans L. grown under different NaCl concentrations (0-40 per thousand), after salt-relief, and then during drought. Stomatal conductance (gs) and net photosynthetic rate (Pn) decreased with increasing NaCl concentration, and intrinsic water use efficiency (Pn / gs) increased. Under desalinization Pn / gs declined. Thus, gs did not change in plants grown at low NaCl concentration (10 per thousand), but increased up to 30-32% at higher NaCl concentration (20-40 per thousand). However, Pn was only slightly enhanced (10-15%). Under drought, Pn decreased by as much as 46% in plants grown at low NaCl concentration (10 per thousand) and by 22% at high NaCl concentration (40 per thousand). Thus, Pn / gs decreased and water use efficiency was lower during drought compared to estimates prior to salt-relief. PMID:18494307

  3. Injection of dust into the Martian atmosphere - Evidence from the Viking Gas Exchange experiment

    NASA Technical Reports Server (NTRS)

    Huguenin, R. L.; Harris, S. L.; Carter, R.

    1986-01-01

    The hypothesis that predawn midlatitude storms are triggered by a soil humidification process is examined. A freeze/thaw model of the process is evaluated in the Viking Gas Exchange experiments conducted on Mars. The humidification-driven desorption and desiccation state of Martian soil samples are analyzed. The periodic humidification of equatorial regolith soil is studied in terms of pore space pressure during desorption events and soil diffusivity; the thermal properties of the regolith surface layer are modeled using the program of Clifford (1984). Consideration is given to the diurnal and seasonal cycles of the humidification process, the permanent, low-albedo features in the midlatitudes, and the production of H2SO4 and HCl aerosols.

  4. The closed spiracle phase of discontinuous gas exchange predicts diving duration in the grasshopper Paracinema tricolor.

    PubMed

    Gudowska, Agnieszka; Boardman, Leigh; Terblanche, John S

    2016-08-15

    The discontinuous gas exchange (DGE) pattern of respiration shown by many arthropods includes periods of spiracle closure (C-phase) and is largely thought to serve as a physiological adaptation to restrict water loss in terrestrial environments. One major challenge to this hypothesis is to explain the presence of DGE in insects in moist environments. Here, we show a novel ecological correlate of the C-phase, namely, diving behaviour in mesic Paracinema tricolor grasshoppers. Notably, maximal dive duration is positively correlated with C-phase length, even after accounting for mass scaling and absolute metabolic rate. Here, we propose that an additional advantage of DGE may be conferred by allowing the tracheal system to act as a sealed underwater oxygen reservoir. Spiracle closure may facilitate underwater submersion, which, in turn, may contribute to predator avoidance, the survival of accidental immersion or periodic flooding and the exploitation of underwater resources. PMID:27296045

  5. Protein structural dynamics at the gas/water interface examined by hydrogen exchange mass spectrometry.

    PubMed

    Xiao, Yiming; Konermann, Lars

    2015-08-01

    Gas/water interfaces (such as air bubbles or foam) are detrimental to the stability of proteins, often causing aggregation. This represents a potential problem for industrial processes, for example, the production and handling of protein drugs. Proteins possess surfactant-like properties, resulting in a high affinity for gas/water interfaces. The tendency of previously buried nonpolar residues to maximize contact with the gas phase can cause significant structural distortion. Most earlier studies in this area employed spectroscopic tools that could only provide limited information. Here we use hydrogen/deuterium exchange (HDX) mass spectrometry (MS) for probing the conformational dynamics of the model protein myoglobin (Mb) in the presence of N(2) bubbles. HDX/MS relies on the principle that unfolded and/or highly dynamic regions undergo faster deuteration than tightly folded segments. In bubble-free solution Mb displays EX2 behavior, reflecting the occurrence of short-lived excursions to partially unfolded conformers. A dramatically different behavior is seen in the presence of N(2) bubbles; EX2 dynamics still take place, but in addition the protein shows EX1 behavior. The latter results from interconversion of the native state with conformers that are globally unfolded and long-lived. These unfolded species likely correspond to Mb that is adsorbed to the surface of gas bubbles. N(2) sparging also induces aggregation. To explain the observed behavior we propose a simple model, that is, "semi-unfolded" ↔ "native" ↔ "globally unfolded" → "aggregated". This model quantitatively reproduces the experimentally observed kinetics. To the best of our knowledge, the current study marks the first exploration of surface denaturation phenomena by HDX/MS. PMID:25761782

  6. Gas exchange and intrapulmonary distribution of ventilation during continuous-flow ventilation

    SciTech Connect

    Vettermann, J.; Brusasco, V.; Rehder, K.

    1988-05-01

    In 12 anesthetized paralyzed dogs, pulmonary gas exchange and intrapulmonary inspired gas distribution were compared between continuous-flow ventilation (CFV) and conventional mechanical ventilation (CMV). Nine dogs were studied while they were lying supine, and three dogs were studied while they were lying prone. A single-lumen catheter for tracheal insufflation and a double-lumen catheter for bilateral endobronchial insufflation (inspired O2 fraction = 0.4; inspired minute ventilation = 1.7 +/- 0.3 (SD) 1.kg-1.min-1) were evaluated. Intrapulmonary gas distribution was assessed from regional 133Xe clearances. In dogs lying supine, CO2 elimination was more efficient with endobronchial insufflation than with tracheal insufflation, but the alveolar-arterial O2 partial pressure difference was larger during CFV than during CMV, regardless of the type of insufflation. By contrast, endobronchial insufflation maintained both arterial PCO2 and alveolar-arterial O2 partial pressure difference at significantly lower levels in dogs lying prone than in dogs lying supine. In dogs lying supine, the dependent lung was preferentially ventilated during CMV but not during CFV. In dogs lying prone, gas distribution was uniform with both modes of ventilation. The alveolar-arterial O2 partial pressure difference during CFV in dogs lying supine was negatively correlated with the reduced ventilation of the dependent lung, which suggests that increased ventilation-perfusion mismatching was responsible for the increase in alveolar-arterial O2 partial pressure difference. The more efficient oxygenation during CFV in dogs lying prone suggests a more efficient matching of ventilation to perfusion, presumably because the distribution of blood flow is also nearly uniform.

  7. Protein structural dynamics at the gas/water interface examined by hydrogen exchange mass spectrometry

    PubMed Central

    Xiao, Yiming; Konermann, Lars

    2015-01-01

    Gas/water interfaces (such as air bubbles or foam) are detrimental to the stability of proteins, often causing aggregation. This represents a potential problem for industrial processes, for example, the production and handling of protein drugs. Proteins possess surfactant-like properties, resulting in a high affinity for gas/water interfaces. The tendency of previously buried nonpolar residues to maximize contact with the gas phase can cause significant structural distortion. Most earlier studies in this area employed spectroscopic tools that could only provide limited information. Here we use hydrogen/deuterium exchange (HDX) mass spectrometry (MS) for probing the conformational dynamics of the model protein myoglobin (Mb) in the presence of N2 bubbles. HDX/MS relies on the principle that unfolded and/or highly dynamic regions undergo faster deuteration than tightly folded segments. In bubble-free solution Mb displays EX2 behavior, reflecting the occurrence of short-lived excursions to partially unfolded conformers. A dramatically different behavior is seen in the presence of N2 bubbles; EX2 dynamics still take place, but in addition the protein shows EX1 behavior. The latter results from interconversion of the native state with conformers that are globally unfolded and long-lived. These unfolded species likely correspond to Mb that is adsorbed to the surface of gas bubbles. N2 sparging also induces aggregation. To explain the observed behavior we propose a simple model, that is, “semi-unfolded” ↔ “native” ↔ “globally unfolded” → “aggregated”. This model quantitatively reproduces the experimentally observed kinetics. To the best of our knowledge, the current study marks the first exploration of surface denaturation phenomena by HDX/MS. PMID:25761782

  8. Theories on the nature of the coupling between ventilation and gas exchange during exercise.

    PubMed

    Haouzi, Philippe

    2006-04-28

    For over a century of creative research, many theories on the possible mechanisms controlling respiration during exercise have been developed and discussed. One of the most enduring questions is certainly related to the mechanisms that can prevent P(a)(CO(2)) rising when CO(2) production increases. As multiple systems and structures are capable of increasing ventilation (V (E)), not all the mechanisms controlling respiration can provide a proper answer to this question. Indeed, exercise is a complex physiological condition combining motor activity with a change in metabolic rate. The most intriguing aspect of exercise is that when the changes in metabolism are dissociated from the motor and locomotor activity, the strategy 'chosen' by the respiratory control system is to follow the metabolic rate (or more precisely factors temporally associated with the pulmonary gas exchange rate) regardless of the motor act. The strategy used by the respiratory system during exercise therefore appears to select from among various sources of information the most relevant to follow the rate at which CO(2) is ultimately exchanged by the lungs. Yet, the nature of the signal(s) which prevents CO(2)/H(+) disturbance during exercise is the fundamental question addressed by this simple observation and remains to be clarified. This review illustrates the attempts of many physiologists to collect experimental evidence for theories which could provide satisfactory mechanisms accounting for the matching between ventilation and the rate at which CO(2) leaves the tissues and is exchanged at the lungs. More recent models based on somatic information of circulatory origin are presented and discussed. PMID:16412707

  9. Continuously Infusing Hyperpolarized 129Xe into Flowing Aqueous Solutions Using Hydrophobic Gas Exchange Membranes

    PubMed Central

    Cleveland, Zackary I.; Möller, Harald E.; Hedlund, Laurence W.; Driehuys, Bastiaan

    2009-01-01

    Hyperpolarized (HP) 129Xe yields high signal intensities in magnetic resonance (MR) and, through its large chemical shift range of ∼300 ppm, provides detailed information about the local chemical environment. To exploit these properties in aqueous solutions and living tissues requires the development of methods for efficiently dissolving HP 129Xe over an extended time period. To this end, we have used commercially available gas exchange modules to continuously infuse concentrated HP 129Xe into flowing liquids, including rat whole blood, for periods as long as one hour, and have demonstrated the feasibility of dissolved-phase MR imaging with sub-millimeter resolution within minutes. These modules, which exchange gases using hydrophobic microporous polymer membranes, are compatible with a variety of liquids and are suitable for infusing HP 129Xe into the bloodstream in vivo. Additionally, we have developed a detailed mathematical model of the infused HP 129Xe signal dynamics that should be useful in designing improved infusion systems that yield even higher dissolved HP 129Xe signal intensities. PMID:19702286

  10. Isotopic exchange during derivatization of platelet activating factor for gas chromatography-mass spectrometry

    SciTech Connect

    Haroldsen, P.E.; Gaskell, S.J.; Weintraub, S.T.; Pinckard, R.N. )

    1991-04-01

    One approach to the quantitative analysis of platelet activating factor (PAF, 1-O-alkyl-2-acetyl-sn-glycerol-3-phosphocholine; also referred to as AGEPC, alkyl glyceryl ether phosphocholine) is hydrolytic removal of the phosphocholine group and conversion to an electron-capturing derivative for gas chromatography-negative ion mass spectrometry. (2H3)Acetyl-AGEPC has been commonly employed as an internal standard. When 1-hexadecyl-2-(2H3)acetyl glycerol (obtained by enzymatic hydrolysis of (2H3)-C16:0 AGEPC) is treated with pentafluorobenzoyl chloride at 120 degrees C, the resulting 3-pentafluorobenzoate derivative shows extensive loss of the deuterium label. This exchange is evidently acid-catalyzed since derivatization of 1-hexadecyl-2-acetyl glycerol under the same conditions in the presence of a trace of 2HCl results in the incorporation of up to three deuterium atoms. Isotope exchange can be avoided if the reaction is carried out at low temperature in the presence of base. Direct derivatization of (2H3)-C16:0 AGEPC by treatment with pentafluorobenzoyl chloride or heptafluorobutyric anhydride also results in loss of the deuterium label. The use of (13C2)-C16:0 AGEPC as an internal standard is recommended for rigorous quantitative analysis.

  11. Theoretical and experimental insights into effects of wind on leaf heat and gas exchange

    NASA Astrophysics Data System (ADS)

    Schymanski, Stanislaus J.; Or, Dani

    2014-05-01

    Transpiration and heat exchange by plant leaves are coupled physiological processes of significant importance for surface-climate interactions and ecohydrology. The common practice of modelling transpiration as an isothermal process (assuming equal leaf and air temperatures) may introduce significant bias into estimates of transpiration rates and water use efficiency (WUE, the amount of carbon gained by photosynthesis per unit of water lost by transpiration). In contrast, explicit consideration of stomatal and leaf boundary layer resistances in series and the leaf energy balance in a physically-based model led to some surprising results, such as suppressed transpiration rates for increasing wind speed at constant stomatal conductance. The model predicts that for high wind velocities, the same leaf conductance (for water vapour and carbon dioxide) can be maintained with less evaporative losses. If this leaf-scale effect is consistent across most leaves, it may have profound implications for canopy-scale water use efficiency under globally decreasing wind speeds. This presentation reports the results of a systematic study of the effect of wind speed on leaf heat and gas exchange rates and introduces a novel experimental design to verify the modelling results using an insulated wind tunnel and artificial leaves with defined pore geometries, allowing to measure leaf-scale latent and sensible heat fluxes independently. First experimental results and new insights will be highlighted.

  12. Whole-Plant Gas Exchange and Reductive Biosynthesis in White Lupin1

    PubMed Central

    Cen, Yan-Ping; Turpin, David H.; Layzell, David B.

    2001-01-01

    Simultaneous measurements of CO2 (CER) and O2 (OER) exchange in roots and shoots of vegetative white lupin (Lupinus albus) were used to calculate the flow of reducing power to the synthesis of biomass that was more reduced per unit of carbon than carbohydrate. On a whole-plant basis, the diverted reductant utilization rate (DRUR which is: 4 × [CER + OER]) of shoot tissue was consistently higher than that of roots, and values obtained in the light were greater than those in the dark. An analysis of the biomass being synthesized over a 24-h period provided an estimate of whole-plant DRUR (3.5 mmol e− plant−1 d−1), which was similar to that measured by gas exchange (3.2 mmol e− plant−1 d−1). Given that nitrate reduction to ammonia makes up about 74% of whole-plant DRUR, root nitrate reduction in white lupin was estimated to account for less than 43% of whole-plant nitrate reduction. The approach developed here should offer a powerful tool for the noninvasive study of metabolic regulation in intact plants or plant organs. PMID:11500554

  13. Water loss and gas exchange by eggs of Manduca sexta: trading off costs and benefits.

    PubMed

    Woods, H Arthur

    2010-05-01

    Like all terrestrial organisms, insect eggs face a tradeoff between exchanging metabolic gases (O(2) and CO(2)) and conserving water. Here I summarize the physiology underlying this tradeoff and the ecological contexts in which it may be important. The ideas are illustrated primarily by work from my laboratory on eggs of the sphingid moth Manduca sexta. In particular, I discuss: (1) dynamic changes in metabolic demand and water loss during development; and (2) how the eggshell layers and embryonic tracheal system control the traffic of gases between the embryo and its environment. Subsequently, I identify three areas with interesting but unresolved issues: (1) what eggs actually experience in their microclimates, focusing particularly on the leaf microclimates relevant to eggs of M. sexta; (2) how egg experience influences whether or not hatchling larvae succeed in establishing feeding sites on host plants; and (3) whether Hetz and Bradley's [Hetz, S.K., Bradley, T.J., 2005. Insects breathe discontinuously to avoid oxygen toxicity. Nature 433, 516-519] oxygen toxicity hypothesis for discontinuous gas-exchange cycles applies to insect eggs. PMID:19573530

  14. Gas sensing in microplates with optodes: influence of oxygen exchange between sample, air, and plate material.

    PubMed

    Arain, Sarina; Weiss, Svenja; Heinzle, Elmar; John, Gernot T; Krause, Christian; Klimant, Ingo

    2005-05-01

    Microplates with integrated optical oxygen sensors are a new tool to study metabolic rates and enzyme activities. Precise measurements are possible only if oxygen exchange between the sample and the environment is known. In this study we quantify gas exchange in plastic microplates. Dissolved oxygen was detected using either an oxygen-sensitive film fixed at the bottom of each well or a needle-type sensor. The diffusion of oxygen into wells sealed with different foils, paraffin oil, and paraffin wax, respectively, was quantified. Although foil covers showed the lowest oxygen permeability, they include an inevitable gas phase between sample and sealing and are difficult to manage. The use of oil was found to be critical due to the extensive shaking caused by movement of the plates during measurements in microplate readers. Thus, paraffin wax was the choice material because it avoids convection of the sample and is easy to handle. Furthermore, without shaking, significant gradients in pO2 levels within a single well of a polystyrene microplate covered with paraffin oil were detected with the needle-type sensor. Higher pO2 levels were obtained near the surface of the sample as well as near the wall of the well. A significant diffusion of oxygen through the plastic plate material was found using plates based on polystyrene. Thus, the location of a sensor element within the well has an effect on the measured pO2 level. Using a sensor film fixed on the bottom of a well or using a dissolved pO2-sensitive indicator results in pO2 offset and in apparently lower respiration rates or enzyme activities. Oxygen diffusion through a polystyrene microplate was simulated for measurements without convection--that is, for samples without oxygen diffusion through the cover and for unshaken measurements using permeable sealings. This mathematical model allows for calculation of the correct kinetic parameters. PMID:15772950

  15. High temperature corrosion of advanced ceramic materials for hot gas filters and heat exchangers

    SciTech Connect

    Crossland, C.E.; Shelleman, D.L.; Spear, K.E.

    1996-08-01

    A vertical flow-through furnace has been built to study the effect of corrosion on the morphology and mechanical properties of ceramic hot gas filters. Sections of 3M Type 203 and DuPont Lanxide SiC-SiC filter tubes were sealed at one end and suspended in the furnace while being subjected to a simulated coal combustion environment at 870{degrees}C. X-ray diffraction and electron microscopy is used to identify phase and morphology changes due to corrosion while burst testing determines the loss of mechanical strength after exposure to the combustion gases. Additionally, a thermodynamic database of gaseous silicon compounds is currently being established so that calculations can be made to predict important products of the reaction of the environment with the ceramics. These thermodynamic calculations provide useful information concerning the regimes where the ceramic may be degraded by material vaporization. To verify the durability and predict lifetime performance of ceramic heat exchangers in coal combustion environments, long-term exposure testing of stressed (internally pressurized) tubes must be performed in actual coal combustion environments. The authors have designed a system that will internally pressurize 2 inch OD by 48 inch long ceramic heat exchanger tubes to a maximum pressure of 200 psi while exposing the outer surface of the tubes to coal combustion gas at the Combustion and Environmental Research Facility (CERF) at the Pittsburgh Energy and Technology Center. Water-cooled, internal o-ring pressure seals were designed to accommodate the existing 6 inch by 6 inch access panels of the CERF. Tubes will be exposed for up to a maximum of 500 hours at temperatures of 2500 and 2600{degrees}F with an internal pressure of 200 psi. If the tubes survive, their retained strength will be measured using the high temperature tube burst test facility at Penn State University. Fractographic analysis will be performed to identify the failure source(s) for the tubes.

  16. Carbon gas exchange at a southern Rocky Mountain wetland, 1996-1998

    USGS Publications Warehouse

    Wickland, K.P.; Striegl, R.G.; Mast, M.A.; Clow, D.W.

    2001-01-01

    Carbon dioxide (CO2) and methane (CH4) exchange between the atmosphere and a subalpine wetland located in Rocky Mountain National Park, Colorado, at 3200 m elevation were measured during 1996-1998. Respiration, net CO2 flux, and CH4 flux were measured using the closed chamber method during snow-free periods and using gas diffusion calculations during snow-covered periods. The ranges of measured flux were 1.2-526 mmol CO2 m-2 d-1 (respiration), -1056-100 mmol CO2 m-2 d-1 (net CO2 exchange), and 0.1-36.8 mmol CH4 m-2 d-1 (a positive value represents efflux to the atmosphere). Respiration and CH4 emission were significantly correlated with 5 cm soil temperature. Annual respiration and CH4 emission were modeled by applying the flux-temperature relationships to a continuous soil temperature record during 1996-1998. Gross photosynthesis was modeled using a hyperbolic equation relating gross photosynthesis, photon flux density, and soil temperature. Modeled annual flux estimates indicate that the wetland was a net source of carbon gas to the atmosphere each of the three years: 8.9 mol C m-2 yr-1 in 1996, 9.5 mol C m-2 yr-1 in 1997, and 9.6 mol C m-2 yr-1 in 1998. This contrasts with the long-term carbon accumulation of ???0.7 mol m-2 yr-1 determined from 14C analyses of a peat core collected from the wetland.

  17. Gas exchange in disease: asthma, chronic obstructive pulmonary disease, cystic fibrosis, and interstitial lung disease.

    PubMed

    Young, Iven H; Bye, Peter T P

    2011-04-01

    Ventilation-perfusion (VA/Q) inequality is the underlying abnormality determining hypoxemia and hypercapnia in lung diseases. Hypoxemia in asthma is characterized by the presence of low VA/Q units, which persist despite improvement in airway function after an attack. This hypoxemia is generally attenuated by compensatory redistribution of blood flow mediated by hypoxic vasoconstriction and changes in cardiac output, however, mediator release and bronchodilator therapy may cause deterioration. Patients with chronic obstructive pulmonary disease have more complex patterns of VA/Q inequality, which appear more fixed, and changes in blood flow and ventilation have less benefit in improving gas exchange efficiency. The inability of ventilation to match increasing cardiac output limits exercise capacity as the disease progresses. Deteriorating hypoxemia during exacerbations reflects the falling mixed venous oxygen tension from increased respiratory muscle activity, which is not compensated by any redistribution of VA/Q ratios. Shunt is not a feature of any of these diseases. Patients with cystic fibrosis (CF) have no substantial shunt when managed according to modern treatment regimens. Interstitial lung diseases demonstrate impaired oxygen diffusion across the alveolar-capillary barrier, particularly during exercise, although VA/Q inequality still accounts for most of the gas exchange abnormality. Hypoxemia may limit exercise capacity in these diseases and in CF. Persistent hypercapnic respiratory failure is a feature of advancing chronic obstructive pulmonary disease and CF, closely associated with sleep disordered breathing, which is not a prominent feature of the other diseases. Better understanding of the mechanisms of hypercapnic respiratory failure, and of the detailed mechanisms controlling the distribution of ventilation and blood flow in the lung, are high priorities for future research. PMID:23737199

  18. Gas exchange by intratracheal insufflation in a ventilatory failure dog model.

    PubMed Central

    Gavriely, N; Eckmann, D; Grotberg, J B

    1992-01-01

    Respiratory insufficiency patients who need only partial ventilatory support are, nevertheless, intubated and connected to a respirator. In search of a partial respiratory assistance method we evaluated the gas exchange, mechanisms, and hemodynamic effects of intratracheal insufflation (ITI) via a narrow (0.2-cm) catheter. The effects of flow rate (0.05-0.2 liter/min per kg), catheter tip position (carina, bronchus, and trachea), and superimposed chest vibration at 22 Hz were studied in seven anesthetized and partially paralyzed dogs. ITI in the carina induced CO2 removal (VCO2) of 48 +/- 16 ml/min in the periods between breaths, which was 39% of the control VCO2. CO2 removal rates between breaths with ITI in a bronchus and in the trachea were 63 and 28% of control, respectively (P < 0.05). ITI at 0.15-0.2 liter/min per kg augmented total VCO2 by > 50% over control (P < 0.05) and decreased PaCO2 by 10% (P < 0.05) despite a 28% fall in VE and 32% lower work of breathing (P < 0.05). Adding vibration to ITI at 0.15 liter/min per kg induced VCO2 of 162 +/- 34 ml/min, which was significantly greater than control, while PaCO2 fell from 69 +/- 24 to 47 +/- 6 mmHg (P < 0.05), despite complete cessation of spontaneous breathing. ITI with or without vibration did not cause any hemodynamic changes, except for a fall in the shunt fraction from 14.6 +/- 9.9% to 5.8 +/- 2.8% with vibration. Thus, ITI at low flow rates can support respiration with no hemodynamic side effects. Adding chest vibration further enhances gas exchange and can provide total ventilation. Images PMID:1469093

  19. Functional differences between the arteries perfusing gas exchange and nutritional membranes in the late chicken embryo.

    PubMed

    Mohammed, Riazudin; Cavallaro, Giacomo; Kessels, Carolina G A; Villamor, Eduardo

    2015-10-01

    The chicken extraembryonic arterial system comprises the allantoic arteries, which irrigate the gas exchange organ (the chorioallantoic membrane, CAM) and the yolk sac (YS) artery, which irrigates the nutritional organ (the YS membrane). We compared, using wire myography, the reactivity of allantoic and YS arteries from 19-day chicken embryos (total incubation 21 days). The contractions induced by KCl, the adrenergic agonists norepinephrine (NE, nonselective), phenylephrine (α1), and oxymetazoline (α2), electric field stimulation (EFS), serotonin, U46619 (TP receptor agonist), and endothelin (ET)-1 and the relaxations induced by acetylcholine (ACh), sodium nitroprusside (SNP, NO donor), forskolin (adenylate cyclase activator), and isoproterenol (β-adrenergic agonist) were investigated. Extraembryonic allantoic arteries did not show α-adrenergic-mediated contraction (either elicited by exogenous agonists or EFS) or ACh-induced (endothelium-dependent) relaxation, whereas these responses were present in YS arteries. Interestingly, the intraembryonic segment of the allantoic artery showed EFS- and α-adrenergic-induced contraction and ACh-mediated relaxation. Moreover, glyoxylic acid staining showed the presence of catecholamine-containing nerves in the YS and the intraembryonic allantoic artery, but not in the extraembryonic allantoic artery. Isoproterenol- and forskolin-induced relaxation and ET-1-induced contraction were higher in YS than in allantoic arteries, whereas serotonin- and U46619-induced contraction and SNP-induced relaxation did not significantly differ between the two arteries. In conclusion, our study demonstrates a different pattern of reactivity in the arteries perfusing the gas exchange and the nutritional membranes of the chicken embryo. PMID:26119481

  20. Joint Action of O3 and SO2 in Modifying Plant Gas Exchange 1

    PubMed Central

    Olszyk, David M.; Tingey, David T.

    1986-01-01

    The joint action of O3 and SO2 stress on plants was investigated by determining the quantitative relationship between air pollutant fluxes and effects on stomatal conductance. Gas exchange measurements of O3, SO2, and H2O vapor were made for Pisum sativum L. (garden pea). Plants were grown under controlled environments, and O3, SO2, and H2O vapor fluxes were evaluated with a whole-plant gas exchange chamber using the mass-balance approach. Maximum O3 and SO2 fluxes per unit area (2 sided) into leaves averaged 8 nanomoles per square meter per second with exposure to either O3 or SO2 at 0.1 microliters per liter. Internal fluxes of either O3 or SO2 were reduced by up to 50% during exposure to combined versus individual pollutants; the greatest reduction occurred with simultaneous versus sequential combinations of the pollutants. Stomatal conductance to H2O was substantially altered by the pollutant exposures, with O3 molecules twice as effective as SO2 molecules in inducing stomatal closure. Stomatal conductance was related to the integrated dose of pollutants. The regression equations relating integrated dose to stomatal conductance were similar with O3 alone, O3 plus added SO2, and O3 plus SO2 simultaneously; i.e. a dose of 100 micromoles per square meter produced a 39 to 45% reduction in conductance over nonexposed plants. With SO2 alone, or SO2 plus added O3, a dose of 100 micromoles per square meter produced a 20 to 25% reduction in conductance. When O3 was present at the start of the exposure, then stomatal response resembled that for O3 more than the response for SO2. This study indicated that stomatal responses with combinations of O3 and SO2 are not dependent solely on the integrated dose of pollutants, but suggests that a metabolic synergistic effect exists. PMID:16665041

  1. A computational study of an HCCI engine with direct injection during gas exchange

    SciTech Connect

    Su, Haiyun; Vikhansky, Alexander; Mosbach, Sebastian; Kraft, Markus; Bhave, Amit; Kim, Kyoung-Oh; Kobayashi, Tatsuo; Mauss, Fabian

    2006-10-15

    We present a new probability density function (PDF)-based computational model to simulate a homogeneous charge compression ignition (HCCI) engine with direct injection (DI) during gas exchange. This stochastic reactor model (SRM) accounts for the engine breathing process in addition to the closed-volume HCCI engine operation. A weighted-particle Monte Carlo method is used to solve the resulting PDF transport equation. While simulating the gas exchange, it is necessary to add a large number of stochastic particles to the ensemble due to the intake air and EGR streams as well as fuel injection, resulting in increased computational expense. Therefore, in this work we apply a down-sampling technique to reduce the number of stochastic particles, while conserving the statistical properties of the ensemble. In this method some of the most important statistical moments (e.g., concentration of the main chemical species and enthalpy) are conserved exactly, while other moments are conserved in a statistical sense. Detailed analysis demonstrates that the statistical error associated with the down-sampling algorithm is more sensitive to the number of particles than to the number of conserved species for the given operating conditions. For a full-cycle simulation this down-sampling procedure was observed to reduce the computational time by a factor of 8 as compared to the simulation without this strategy, while still maintaining the error within an acceptable limit. Following the detailed numerical investigation, the model, intended for volatile fuels only, is applied to simulate a two-stroke, naturally aspirated HCCI engine fueled with isooctane. The in-cylinder pressure and CO emissions predicted by the model agree reasonably well with the measured profiles. In addition, the new model is applied to estimate the influence of engine operating parameters such as the relative air-fuel ratio and early direct injection timing on HCCI combustion and emissions. The qualitative trends

  2. Reprint of: A numerical modelling of gas exchange mechanisms between air and turbulent water with an aquarium chemical reaction

    NASA Astrophysics Data System (ADS)

    Nagaosa, Ryuichi S.

    2014-08-01

    This paper proposes a new numerical modelling to examine environmental chemodynamics of a gaseous material exchanged between the air and turbulent water phases across a gas-liquid interface, followed by an aquarium chemical reaction. This study uses an extended concept of a two-compartment model, and assumes two physicochemical substeps to approximate the gas exchange processes. The first substep is the gas-liquid equilibrium between the air and water phases, A(g)⇌A(aq), with Henry's law constant H. The second is a first-order irreversible chemical reaction in turbulent water, A(aq)+H2O→B(aq)+H+ with a chemical reaction rate κA. A direct numerical simulation (DNS) technique has been employed to obtain details of the gas exchange mechanisms and the chemical reaction in the water compartment, while zero velocity and uniform concentration of A is considered in the air compartment. The study uses the different Schmidt numbers between 1 and 8, and six nondimensional chemical reaction rates between 10(≈0) to 101 at a fixed Reynolds number. It focuses on the effects of the Schmidt number and the chemical reaction rate on fundamental mechanisms of the gas exchange processes across the interface.

  3. A numerical modelling of gas exchange mechanisms between air and turbulent water with an aquarium chemical reaction

    NASA Astrophysics Data System (ADS)

    Nagaosa, Ryuichi S.

    2014-01-01

    This paper proposes a new numerical modelling to examine environmental chemodynamics of a gaseous material exchanged between the air and turbulent water phases across a gas-liquid interface, followed by an aquarium chemical reaction. This study uses an extended concept of a two-compartment model, and assumes two physicochemical substeps to approximate the gas exchange processes. The first substep is the gas-liquid equilibrium between the air and water phases, A(g)⇌A(aq), with Henry's law constant H. The second is a first-order irreversible chemical reaction in turbulent water, A(aq)+H2O→B(aq)+H+ with a chemical reaction rate κA. A direct numerical simulation (DNS) technique has been employed to obtain details of the gas exchange mechanisms and the chemical reaction in the water compartment, while zero velocity and uniform concentration of A is considered in the air compartment. The study uses the different Schmidt numbers between 1 and 8, and six nondimensional chemical reaction rates between 10(≈0) to 101 at a fixed Reynolds number. It focuses on the effects of the Schmidt number and the chemical reaction rate on fundamental mechanisms of the gas exchange processes across the interface.

  4. Underwater photosynthesis and respiration in leaves of submerged wetland plants: gas films improve CO2 and O2 exchange.

    PubMed

    Colmer, Timothy David; Pedersen, Ole

    2008-01-01

    Many wetland plants have gas films on submerged leaf surfaces. We tested the hypotheses that leaf gas films enhance CO(2) uptake for net photosynthesis (P(N)) during light periods, and enhance O(2) uptake for respiration during dark periods. Leaves of four wetland species that form gas films, and two species that do not, were used. Gas films were also experimentally removed by brushing with 0.05% (v/v) Triton X. Net O(2) production in light, or O(2) consumption in darkness, was measured at various CO(2) and O(2) concentrations. When gas films were removed, O(2) uptake in darkness was already diffusion-limited at 20.6 kPa (critical O(2) pressure for respiration, COP(R)>/= 284 mmol O(2) m(-3)), whereas for some leaves with gas films, O(2) uptake declined only at approx. 4 kPa (COP(R) 54 mmol O(2) m(-3)). Gas films also improved CO(2) uptake so that, during light periods, underwater P(N) was enhanced up to sixfold. Gas films on submerged leaves enable continued gas exchange via stomata and thus bypassing of cuticle resistance, enhancing exchange of O(2) and CO(2) with the surrounding water, and therefore underwater P(N) and respiration. PMID:18086222

  5. Gas exchange rates across the sediment-water and air-water interfaces in south San Francisco Bay

    USGS Publications Warehouse

    Hartman, Blayne; Hammond, Douglas E.

    1984-01-01

    Radon 222 concentrations in the water and sedimentary columns and radon exchange rates across the sediment-water and air-water interfaces have been measured in a section of south San Francisco Bay. Two independent methods have been used to determine sediment-water exchange rates, and the annual averages of these methods agree within the uncertainty of the determinations, about 20%. The annual average of benthic fluxes from shoal areas is nearly a factor of 2 greater than fluxes from the channel areas. Fluxes from the shoal and channel areas exceed those expected from simple molecular diffusion by factors of 4 and 2, respectively, apparently due to macrofaunal irrigation. Values of the gas transfer coefficient for radon exchange across the air-water interface were determined by constructing a radon mass balance for the water column and by direct measurement using floating chambers. The chamber method appears to yield results which are too high. Transfer coefficients computed using the mass balance method range from 0.4 m/day to 1.8 m/day, with a 6-year average of 1.0 m/day. Gas exchange is linearly dependent upon wind speed over a wind speed range of 3.2–6.4 m/s, but shows no dependence upon current velocity. Gas transfer coefficients predicted from an empirical relationship between gas exchange rates and wind speed observed in lakes and the oceans are within 30% of the coefficients determined from the radon mass balance and are considerably more accurate than coefficients predicted from theoretical gas exchange models.

  6. Gas-exchange patterns of Mediterranean fruit fly Pupae (Diptera: Tephritidae): A tool to forecast developmental stage

    SciTech Connect

    Nestel, D.; Nemny-Lavy, E.; Alchanatis, V.

    2007-03-15

    The pattern of gas-exchange (CO{sub 2} emission) was investigated for developing Mediterranean fruit fly (medfly) Ceratitis capitata (Wiedemann) pupae incubated at different temperatures. This study was undertaken to explore the usefulness of gas-exchange systems in the determination of physiological age in developing pupae that are mass produced for sterile insect technique projects. The rate of CO{sub 2} emission was measured in a closed flow-through system connected to commercial infrared gas analysis equipment. Metabolic activity (rate of CO{sub 2} emission) was related to pupal eye-color, which is the current technique used to determine physiological age. Eye-color was characterized digitally with 3 variables (Hue, Saturation and Intensity), and color separated by discriminant analysis. The rate of CO{sub 2} emission throughout pupal development followed a U-shape, with high levels of emission during pupariation, pupal transformation and final pharate adult stages. Temperature affected the development time of pupae, but not the basic CO{sub 2} emission patterns during development. In all temperatures, rates of CO{sub 2} emission 1 and 2 d before adult emergence were very similar. After mid larval-adult transition (e.g., phanerocephalic pupa), digital eye-color was significantly correlated with CO{sub 2} emission. Results support the suggestion that gas-exchange should be explored further as a system to determine pupal physiological age in mass production of fruit flies. (author) [Spanish] En el presente estudio se investigaron los patrones de intercambio gaseoso (emision de CO{sub 2}) en pupas de la mosca de las frutas del Mediterraneo (Ceratitis capitata Wiedemann) incubadas a diferentes temperaturas. El estudio fue realizado con la finalidad de explorar la utilizacion de sistemas de intercambio gaseoso en la determinacion de la edad fisiologica de pupas durante su produccion masiva en proyectos de mosca esteril. La proporcion de emision de CO{sub 2} fue

  7. The impact of epicuticular wax on gas-exchange and photoinhibition in Leucadendron lanigerum (Proteaceae)

    NASA Astrophysics Data System (ADS)

    Mohammadian, Mansour A.; Watling, Jennifer R.; Hill, Robert S.

    2007-01-01

    This study investigated the seasonal modification of wax deposition, and the impact of epicuticular wax on gas-exchange as well as photoinhibition in Leucadendron lanigerum, a species from the Proteaceae family with wax-covered leaf surfaces and the stomata also partially occluded by wax. The results of this study demonstrated that the deposition of epicuticular wax in L. lanigerum is dependent on the age of the leaf as well as the season, and generation and regeneration of wax occur mostly in spring while transformation and also degeneration of wax crystals occur in winter. Epicuticular waxes decreased cuticular water loss, but had little impact on leaf reflectance. The temperature of leaves without wax was lower than that of wax-covered leaves, indicating that the rate of transpiration impacted more on leaf temperature than reflectance of light in the PAR range in L. lanigerum. The wax coverage at the entrance of stomata in L. lanigerum increased resistance to gas diffusion and as a consequence decreased stomatal conductance, transpiration and photosynthesis. Also, the results indicated that epicuticular waxes do help prevent photodamage in L. lanigerum, and so this property could benefit plants living in arid environments with high solar radiation.

  8. The Role of Interfacial Molecular Structure and Hydrogen-Bonding in Gas-Surface Energy Exchange

    NASA Astrophysics Data System (ADS)

    Day, Scott; Fergusion, Melinda; Morris, John

    2004-03-01

    Atomic-beam scattering experiments using n-alkanethiol and w-functionalized alkanethiol self-assembled monolayers (SAMs) on gold are employed to explore the dynamics of gas-surface energy exchange in collisions with model organic surfaces. The studies are performed by directing a nearly monoenergetic beam of 80 kJ/mol Ar atoms onto a particular SAM at an incident angle of 30° with respect to the surface normal and recording the time-of-flight distributions for the atoms as they scatter from the surface at a final angle of 30°. Among the monolayers studied, long-chain methyl-terminated SAMs are found to be the most effective at dissipating the translational energy of impinging atoms. For alkanethiols with greater than seven total carbon atoms, we find that, for specular scattering conditions, over 80the incident energy is transferred to the surface and that over 60with the surface before scattering back into the gas phase. In contrast to methyl-terminated monolayers, SAMs constructed from hydrogen-bonding alkanethiols exhibit characteristics of more rigid collision partners. The Ar atoms transfer about 77with only 43equilibrium before recoiling. Further comparisons of mixed hydroxyl- and methyl-terminated SAMs and alkene-terminated SAMs suggest that intramonolayer hydrogen bonding of terminal functional groups may play an important role in determining the extent of energy transfer and thermalization.

  9. Trace gas exchanges and convective transports over the Amazonian rain forest

    NASA Technical Reports Server (NTRS)

    Garstang, Michael; Harriss, Robert; Beck, Sherwin; Browell, Edward; Sachse, Glen; Gregory, Gerald; Hill, Gerald; Simpson, Joanne; Tao, Wei-Kuo; Torres, Arnold

    1988-01-01

    The NASA Amazon Boundary Layer Experiment (ABLE 2A) based in Manaus, Brazil, in July and August 1985, is used to examine meteorological processes responsible for the vertical and horizontal transport of biogenic and anthropogenic trace gases generated over the Amazon basin. Direct sampling of the surrounding environment of deep convective clouds shows marked changes in the vertical distribution of the lower and midtroposphere concentration of O3 and such surface-derived species as CO, CO2, and NO. Thermodynamic observations, together with two-dimensional cloud model simulations, confirm vertical transports within the convection and provide a basis for an estimation of the magnitude and efficiency of cloud upward and downward exchanges. A distinction is drawn between local changes due to convective updrafts and downdrafts and convective overturning as a net result of the storm processes. Marked variability is seen in trace gas concentrations along horizontal flight paths in the vicinity of the convection. Interpretation of simultaneously measured thermodynamic quantities and trace gas concentrations provide the information to infer the presence and direction of atmospheric transports and/or the presence of anthropogenic influences.

  10. Kinetic model for the vibrational energy exchange in flowing molecular gas mixtures. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Offenhaeuser, F.

    1987-01-01

    The present study is concerned with the development of a computational model for the description of the vibrational energy exchange in flowing gas mixtures, taking into account a given number of energy levels for each vibrational degree of freedom. It is possible to select an arbitrary number of energy levels. The presented model uses values in the range from 10 to approximately 40. The distribution of energy with respect to these levels can differ from the equilibrium distribution. The kinetic model developed can be employed for arbitrary gaseous mixtures with an arbitrary number of vibrational degrees of freedom for each type of gas. The application of the model to CO2-H2ON2-O2-He mixtures is discussed. The obtained relations can be utilized in a study of the suitability of radiation-related transitional processes, involving the CO2 molecule, for laser applications. It is found that the computational results provided by the model agree very well with experimental data obtained for a CO2 laser. Possibilities for the activation of a 16-micron and 14-micron laser are considered.

  11. Bubble Continuous Positive Airway Pressure Enhances Lung Volume and Gas Exchange in Preterm Lambs

    PubMed Central

    Pillow, J. Jane; Hillman, Noah; Moss, Timothy J. M.; Polglase, Graeme; Bold, Geoff; Beaumont, Chris; Ikegami, Machiko; Jobe, Alan H.

    2007-01-01

    Rationale: The technique used to provide continuous positive airway pressure (CPAP) to the newborn may influence lung function and breathing efficiency. Objectives: To compare differences in gas exchange physiology and lung injury resulting from treatment of respiratory distress with either bubble or constant pressure CPAP and to determine if the applied flow influences short-term outcomes. Methods: Lambs (133 d gestation; term is 150 d) born via cesarean section were weighed, intubated, and treated with CPAP for 3 hours. Two groups were treated with 8 L/minute applied flow using the bubble (n = 12) or the constant pressure (n = 12) technique. A third group (n = 10) received the bubble method with 12 L/minute bias flow. Measurements at study completion included arterial blood gases, oxygraphy, capnography, tidal flow, multiple breath washout, lung mechanics, static pressure–volume curves, and bronchoalveolar lavage fluid protein. Measurements and Main Results: Birth weight and arterial gas variables at 15 minutes were comparable. Flow (8 or 12 L/min) did not influence the 3-hour outcomes in the bubble group. Bubble technique was associated with a higher pH, PaO2, oxygen uptake, and area under the flow–volume curve, and a decreased alveolar protein, respiratory quotient, PaCO2, and ventilation inhomogeneity compared with the constant pressure group. Conclusions: Compared with constant pressure technique, bubble CPAP promotes enhanced airway patency during treatment of acute postnatal respiratory disease in preterm lambs and may offer protection against lung injury. PMID:17431223

  12. Effect of stratified inequality of blood flow on gas exchange in liquid-filled lungs.

    NASA Technical Reports Server (NTRS)

    West, J. B.; Maloney, J. E.; Castle, B. L.

    1972-01-01

    This investigation set out to answer two questions: (1) are the distal alveoli in the terminal lung units less well perfused than the proximal alveoli, i.e., is there stratification of blood flow; and (2) if so, does this enhance gas exchange in the presence of stratified inequality of ventilation. Excised dog lungs were ventilated with saline and perfused with blood. Following single inspirations of xenon 133 in saline and various periods of breath holding, the expired xenon concentration against volume was measured and it confirmed marked stratified inequality of ventilation under these conditions. By measuring the rate of depletion of xenon from alveoli during a period of blood flow, we showed that the alveoli which emptied at the end of expiration had 16% less blood flow than those exhaling earlier. However, by measuring the xenon concentration in pulmonary venous blood, we found that about 10% less tracer was transferred from the alveoli into the blood when the inspired xenon was stratified within the respiratory zone. Thus while stratification of blood flow was confirmed, it was shown to impair rather than enhance the efficiency of gas transfer.

  13. State policies affecting natural gas consumption (Notice of inquiry issued on August 14, 1992)

    SciTech Connect

    Lemon, R.; Kamphuis-Zatopa, W.

    1993-03-25

    On August 14, 1992, the United States Department of Energy issued a Request for Comments Concerning State Policies Affecting Natural Gas Consumption. This Notice of (NOI) noted the increasing significance of the role played by states and sought to gain better understanding of how state policies impact the gas industry. The general trend toward a. more competitive marketplace for natural gas, as well as recent regulatory and legislative changes at the Federal level, are driving State regulatory agencies to reevaluate how they regulate natural gas. State action is having a significant impact on the use of natural gas for generating electricity, as well as affecting the cost-effective trade-off between conservation expenditures and gas use. Additionally, fuel choice has an impact upon the environment and national energy security. In light of these dimensions, the Department of Energy initiated this study of State regulation. The goals of this NOI are: (1) help DOE better understand the impact of State policies on the efficient use of gas; (2) increase the awareness of the natural gas industry and Federal and State officials to the important role of State policies and regulations; (3) create an improved forum for dialogue on State and Federal natural gas issues; and, (4) develop a consensus on an analytical agenda that would be most helpful in addressing the regulatory challenges faced by the States. Ninety-seven parties filed comments, and of these ninety-seven, fifteen parties filed reply comments. Appendix One lists these parties. This report briefly syntheses the comments received. The goal is to assist parties to judging the extent of consensus on the problems posed and the remedies suggested, aid in identifying future analytical analyses, and assist parties in assessing differences in strategies and regulatory philosophies which shape these issues and their resolution.

  14. Mechanisms underlying gas exchange alterations in an experimental model of pulmonary embolism.

    PubMed

    Ferreira, J H T; Terzi, R G G; Paschoal, I A; Silva, W A; Moraes, A C; Moreira, M M

    2006-09-01

    The aim of the present study was to determine the ventilation/perfusion ratio that contributes to hypoxemia in pulmonary embolism by analyzing blood gases and volumetric capnography in a model of experimental acute pulmonary embolism. Pulmonary embolization with autologous blood clots was induced in seven pigs weighing 24.00 +/- 0.6 kg, anesthetized and mechanically ventilated. Significant changes occurred from baseline to 20 min after embolization, such as reduction in oxygen partial pressures in arterial blood (from 87.71 +/- 8.64 to 39.14 +/- 6.77 mmHg) and alveolar air (from 92.97 +/- 2.14 to 63.91 +/- 8.27 mmHg). The effective alveolar ventilation exhibited a significant reduction (from 199.62 +/- 42.01 to 84.34 +/- 44.13) consistent with the fall in alveolar gas volume that effectively participated in gas exchange. The relation between the alveolar ventilation that effectively participated in gas exchange and cardiac output (V Aeff/Q ratio) also presented a significant reduction after embolization (from 0.96 +/- 0.34 to 0.33 +/- 0.17 fraction). The carbon dioxide partial pressure increased significantly in arterial blood (from 37.51 +/- 1.71 to 60.76 +/- 6.62 mmHg), but decreased significantly in exhaled air at the end of the respiratory cycle (from 35.57 +/- 1.22 to 23.15 +/- 8.24 mmHg). Exhaled air at the end of the respiratory cycle returned to baseline values 40 min after embolism. The arterial to alveolar carbon dioxide gradient increased significantly (from 1.94 +/- 1.36 to 37.61 +/- 12.79 mmHg), as also did the calculated alveolar (from 56.38 +/- 22.47 to 178.09 +/- 37.46 mL) and physiological (from 0.37 +/- 0.05 to 0.75 +/- 0.10 fraction) dead spaces. Based on our data, we conclude that the severe arterial hypoxemia observed in this experimental model may be attributed to the reduction of the V Aeff/Q ratio. We were also able to demonstrate that V Aeff/Q progressively improves after embolization, a fact attributed to the alveolar ventilation

  15. Design of Plant Gas Exchange Experiments in a Variable Pressure Growth Chamber

    NASA Technical Reports Server (NTRS)

    Corey, Kenneth A.

    1996-01-01

    Sustainable human presence in extreme environments such as lunar and martian bases will require bioregenerative components to human life support systems where plants are used for generation of oxygen, food, and water. Reduced atmospheric pressures will be used to minimize mass and engineering requirements. Few studies have assessed the metabolic and developmental responses of plants to reduced pressure and varied oxygen atmospheres. The first tests of hypobaric pressures on plant gas exchange and biomass production at the Johnson Space Center will be initiated in January 1996 in the Variable Pressure Growth Chamber (VPGC), a large, closed plant growth chamber rated for 10.2 psi. Experiments were designed and protocols detailed for two complete growouts each of lettuce and wheat to generate a general database for human life support requirements and to answer questions about plant growth processes in reduced pressure and varied oxygen environments. The central objective of crop growth studies in the VPGC is to determine the influence of reduced pressure and reduced oxygen on the rates of photosynthesis, dark respiration, evapotranspiration and biomass production of lettuce and wheat. Due to the constraint of one experimental unit, internal controls, called pressure transients, will be used to evaluate rates of CO2 uptake, O2 evolution, and H2O generation. Pressure transients will give interpretive power to the results of repeated growouts at both reduced and ambient pressures. Other experiments involve the generation of response functions to partial pressures of O2 and CO2 and to light intensity. Protocol for determining and calculating rates of gas exchange have been detailed. In order to build these databases and implement the necessary treatment combinations in short time periods, specific requirements for gas injections and removals have been defined. A set of system capability checks will include determination of leakage rates conducted prior to the actual crop

  16. Overview of U.S. Legislation and Regulations Affecting Offshore Natural Gas and Oil Activity

    EIA Publications

    2005-01-01

    This article presents a summary of the legislative and regulatory regime that affects natural gas and oil exploration and production in offshore regions of the United States. It discusses the role and importance of these areas as well as the competing interests surrounding ownership, production, exploration and conservation.

  17. Pulmonary gas exchange is not impaired 24 h after extravehicular activity.

    PubMed

    Prisk, G Kim; Fine, Janelle M; Cooper, Trevor K; West, John B

    2005-12-01

    Extravehicular activity (EVA) during spaceflight involves a significant decompression stress. Previous studies have shown an increase in the inhomogeneity of ventilation-perfusion ratio (VA/Q) after some underwater dives, presumably through the embolic effects of venous gas microemboli in the lung. Ground-based chamber studies simulating EVA have shown that venous gas microemboli occur in a large percentage of the subjects undergoing decompression, despite the use of prebreathe protocols to reduce dissolved N(2) in the tissues. We studied eight crewmembers (7 male, 1 female) of the International Space Station who performed 15 EVAs (initial cabin pressure 748 mmHg, final suit pressure either approximately 295 or approximately 220 mmHg depending on the suit used) and who followed the denitrogenation procedures approved for EVA from the International Space Station. The intrabreath VA/Q slope was calculated from the alveolar Po(2) and Pco(2) in a prolonged exhalation maneuver on the day after EVA and compared with measurements made in microgravity on days well separated from the EVA. There were no significant changes in intrabreath VA/Q slope as a result of EVA, although there was a slight increase in metabolic rate and ventilation (approximately 9%) on the day after EVA. Vital capacity and other measures of pulmonary function were largely unaltered by EVA. Because measurements could only be performed on the day after EVA because of logistical constraints, we were unable to determine an acute effect of EVA on VA/Q inequality. The results suggest that current denitrogenation protocols do not result in any major lasting alteration to gas exchange in the lung. PMID:16123205

  18. Effects of ozone on growth, yield and leaf gas exchange rates of two Bangladeshi cultivars of wheat (Triticum aestivum L.).

    PubMed

    Akhtar, Nahid; Yamaguchi, Masahiro; Inada, Hidetoshi; Hoshino, Daiki; Kondo, Taisuke; Izuta, Takeshi

    2010-05-01

    To clarify the effects of O(3) on crop plants cultivated in Bangladesh, two Bangladeshi wheat cultivars (Sufi and Bijoy) were grown in plastic boxes filled with Andisol and exposed daily to charcoal-filtered air or O(3) at 60 and 100 nl l(-1) (10:00-17:00) from 13 March to 4 June 2008. The whole-plant dry mass and grain yield per plant of the two cultivars at the final harvest were significantly reduced by the exposure to O(3). Although there was no significant effect of O(3) on stomatal diffusive conductance to H(2)O of flag leaf, net photosynthetic rate of the leaf was significantly reduced by the exposure to O(3.) The sensitivity of growth, yield, yield components and leaf gas exchange rates to O(3) was not significantly different between the two cultivars. The results obtained in the present study suggest that ambient levels of O(3) may detrimentally affect wheat production in Bangladesh. PMID:19962222

  19. High Frequency Nasal Ventilation for 21 Days Maintains Gas Exchange with Lower Respiratory Pressures and Promotes Alveolarization in Preterm Lambs

    PubMed Central

    Null, Donald M.; Alvord, Jeremy; Leavitt, Wendy; Wint, Albert; Dahl, Mar Janna; Presson, Angela P.; Lane, Robert H.; DiGeronimo, Robert J.; Yoder, Bradley A.; Albertine, Kurt H.

    2014-01-01

    Background Short-term high-frequency nasal ventilation (HFNV) of preterm neonates provides acceptable gas exchange compared to endotracheal intubation and intermittent mandatory ventilation (IMV). Whether long-term HFNV will provide acceptable gas exchange is unknown. We hypothesized that HFNV for up to 21d would lead to acceptable gas exchange at lower inspired oxygen (O2) levels and airway pressures compared to intubation and IMV. Methods Preterm lambs were exposed to antenatal steroids, and treated with perinatal surfactant and postnatal caffeine. Lambs were intubated and resuscitated by IMV. At ~3h of age, half of the lambs were switched to non-invasive HFNV. Support was for 3d or 21d. By design, PaO2 and PaCO2 were not different between groups. Results At 3d (n=5) and 21d (n=4) of HFNV, fractional inspired O2 (FiO2), peak inspiratory pressure, mean airway, intra-tracheal, and positive end-expiratory pressures, oxygenation index, and Alveolar-arterial gradient were significantly lower than matched periods of intubation and IMV. PaO2/FiO2 ratio was significantly higher at 3d and 21d of HFNV compared to matched intubation and IMV. HFNV led to better alveolarization at 3d and 21d. Conclusion Long-term HFNV provides acceptable gas exchange at lower inspired O2 levels and respiratory pressures compared to intubation and IMV. PMID:24378898

  20. Asymmetrical effects of mesophyll conductance on fundamental photosynthetic parameters and their relationships estimated from leaf gas exchange measurements

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Most previous analyses of leaf gas exchange measurements assumed an infinite value of mesophyll conductance (gm) and thus equaled CO2 partial pressures in the substomatal cavity and chloroplast. Yet an increasing number of studies have recognized that gm is finite and there is a drawdown of CO2 part...

  1. Canopy gas exchange and water use efficiency of 'Empire' apple in response to particle film, irrigation, and microclimatic factors

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This study examined the interaction between a reflective particle film and water use efficiency (WUE) response of irrigated and non-irrigated apple trees over a wide range of environmental conditions. The objectives were to measure the specific gas exchange and WUE response of 'Empire' apple treate...

  2. Weak coordination among petiole, leaf, vein, and gas-exchange traits across 41 Australian angiosperm species and its possible implications

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Background and Aims Close coordination between leaf gas exchange and maximal hydraulic supply has been reported across diverse plant life-forms. However, recent reports suggest that this relationship may become weak or break down completely within the angiosperms. Methods To examine this possi...

  3. Toxicodynamics of rigid polystyrene microparticles on pulmonary gas exchange in mice: Implications for microemboli-based drug delivery systems

    SciTech Connect

    Kutscher, H.L.; Gao, D.; Li, S.; Massa, C.B.; Cervelli, J.; Deshmukh, M.; Joseph, L.B.; Laskin, D.L.; Sinko, P.J.

    2013-01-15

    The toxicodynamic relationship between the number and size of pulmonary microemboli resulting from uniformly sized, rigid polystyrene microparticles (MPs) administered intravenously and their potential effects on pulmonary gas exchange were investigated. CD-1 male mice (6–8 weeks) were intravenously administered 10, 25 and 45 μm diameter MPs. Oxygen hemoglobin saturation in the blood (SpO{sub 2}) was measured non-invasively using a pulse oximeter while varying inhaled oxygen concentration (F{sub I}O{sub 2}). The resulting data were fit to a physiologically based non-linear mathematical model that estimates 2 parameters: ventilation–perfusion ratio (V{sub A}/Q) and shunt (percentage of deoxygenated blood returning to systemic circulation). The number of MPs administered prior to a statistically significant reduction in normalized V{sub A}/Q was dependent on particle size. MP doses that resulted in a significant reduction in normalized V{sub A}/Q one day post-treatment were 4000, 40,000 and 550,000 MPs/g for 45, 25 and 10 μm MPs, respectively. The model estimated V{sub A}/Q and shunt returned to baseline levels 7 days post-treatment. Measuring SpO{sub 2} alone was not sufficient to observe changes in gas exchange; however, when combined with model-derived V{sub A}/Q and shunt early reversible toxicity from pulmonary microemboli was detected suggesting that the model and physical measurements are both required for assessing toxicity. Moreover, it appears that the MP load required to alter gas exchange in a mouse prior to lethality is significantly higher than the anticipated required MP dose for effective drug delivery. Overall, the current results indicate that the microemboli-based approach for targeted pulmonary drug delivery is potentially safe and should be further explored. -- Highlights: ► Murine pulmonary gas exchange after microembolization was non-invasively studied. ► A physiologically based model quantified impairment of pulmonary gas exchange.

  4. Fouling reduction characteristics of a no-distributor-fluidized-bed heat exchanger for flue gas heat recovery

    SciTech Connect

    Jun, Y.D.; Lee, K.B.; Islam, S.Z.; Ko, S.B.

    2008-07-01

    In conventional flue gas heat recovery systems, the fouling by fly ashes and the related problems such as corrosion and cleaning are known to be major drawbacks. To overcome these problems, a single-riser no-distributor-fluidized-bed heat exchanger is devised and studied. Fouling and cleaning tests are performed for a uniquely designed fluidized bed-type heat exchanger to demonstrate the effect of particles on the fouling reduction and heat transfer enhancement. The tested heat exchanger model (1 m high and 54 mm internal diameter) is a gas-to-water type and composed of a main vertical tube and four auxiliary tubes through which particles circulate and transfer heat. Through the present study, the fouling on the heat transfer surface could successfully be simulated by controlling air-to-fuel ratios rather than introducing particles through an external feeder, which produced soft deposit layers with 1 to 1.5 mm thickness on the inside pipe wall. Flue gas temperature at the inlet of heat exchanger was maintained at 450{sup o}C at the gas volume rate of 0.738 to 0.768 CMM (0.0123 to 0.0128 m{sup 3}/sec). From the analyses of the measured data, heat transfer performances of the heat exchanger before and after fouling and with and without particles were evaluated. Results showed that soft deposits were easily removed by introducing glass bead particles, and also heat transfer performance increased two times by the particle circulation. In addition, it was found that this type of heat exchanger had high potential to recover heat of waste gases from furnaces, boilers, and incinerators effectively and to reduce fouling related problems.

  5. Nitrogen supply modulates the effect of changes in drying-rewetting frequency on soil C and N cycling and greenhouse gas exchange.

    PubMed

    Morillas, Lourdes; Durán, Jorge; Rodríguez, Alexandra; Roales, Javier; Gallardo, Antonio; Lovett, Gary M; Groffman, Peter M

    2015-10-01

    Climate change and atmospheric nitrogen (N) deposition are two of the most important global change drivers. However, the interactions of these drivers have not been well studied. We aimed to assess how the combined effect of soil N additions and more frequent soil drying-rewetting events affects carbon (C) and N cycling, soil:atmosphere greenhouse gas (GHG) exchange, and functional microbial diversity. We manipulated the frequency of soil drying-rewetting events in soils from ambient and N-treated plots in a temperate forest and calculated the Orwin & Wardle Resistance index to compare the response of the different treatments. Increases in drying-rewetting cycles led to reductions in soil NO3- levels, potential net nitrification rate, and soil : atmosphere GHG exchange, and increases in NH4+ and total soil inorganic N levels. N-treated soils were more resistant to changes in the frequency of drying-rewetting cycles, and this resistance was stronger for C- than for N-related variables. Both the long-term N addition and the drying-rewetting treatment altered the functionality of the soil microbial population and its functional diversity. Our results suggest that increasing the frequency of drying-rewetting cycles can affect the ability of soil to cycle C and N and soil : atmosphere GHG exchange and that the response to this increase is modulated by soil N enrichment. PMID:25916277

  6. The Exchange Relationship between Work-Family Enrichment and Affective Commitment: the Moderating Role of Gender.

    PubMed

    Marques, António Manuel; Chambel, Maria José; Pinto, Inês

    2015-01-01

    Workers' perception that their job experience enriches their family life has been considered a mechanism that explains their positive attitudes toward the organization where they work. However, because women and men live their work and family differently, gender may condition this relationship between the work-family enrichment and workers' attitudes. With a sample of 1885 workers from one Portuguese bank, with 802 women, the current study investigated the relationship between work-family enrichment and organizational affective commitment as well as the role of sex as a moderator of this relationship. The hypotheses were tested by using regression analysis. The results indicated that the perception held by workers that their work enriches their family is positively correlated with their affective commitment toward the organization. Furthermore, the data revealed that this relationship is stronger for women than for men. Study results have implications for management, particularly for human resource management, enhancing their knowledge about the relationship of work-family enrichment and workers' affective commitment toward organization. PMID:26037591

  7. Quantifying the measurement errors in a LI-6400 gas exchange system and their effects on the parameterization of Farquhar et al. model for C3 leaves

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The LI-6400 gas exchange system (Li-Cor, Inc, Lincoln, NE, USA) has been widely used for the measurement of net gas exchanges and calibration/parameterization of leaf models. Measurement errors due to diffusive leakages of water vapor and carbon dioxide between inside and outside of the leaf chamber...

  8. Investigating onychophoran gas exchange and water balance as a means to inform current controversies in arthropod physiology.

    PubMed

    Clusella-Trullas, Susana; Chown, Steven L

    2008-10-01

    Several controversies currently dominate the fields of arthropod metabolic rate, gas exchange and water balance, including the extent to which modulation of gas exchange reduces water loss, the origins of discontinuous gas exchange, the relationship between metabolic rate and life-history strategies, and the causes of Palaeozoic gigantism. In all of these areas, repeated calls have been made for the investigation of groups that might most inform the debates, especially of taxa in key phylogenetic positions. Here we respond to this call by investigating metabolic rate, respiratory water loss and critical oxygen partial pressure (Pc) in the onychophoran Peripatopsis capensis, a member of a group basal to the arthropods, and by synthesizing the available data on the Onychophora. The rate of carbon dioxide release (VCO2) at 20 degrees C in P. capensis is 0.043 ml CO2 h(-1), in keeping with other onychophoran species; suggesting that low metabolic rates in some arthropod groups are derived. Continuous gas exchange suggests that more complex gas exchange patterns are also derived. Total water loss in P. capensis is 57 mg H2O h(-1) at 20 degrees C, similar to modern estimates for another onychophoran species. High relative respiratory water loss rates ( approximately 34%; estimated using a regression technique) suggest that the basal condition in arthropods may be a high respiratory water loss rate. Relatively high Pc values (5-10% O2) suggest that substantial safety margins in insects are also a derived condition. Curling behaviour in P. capensis appears to be a strategy to lower energetic costs when resting, and the concomitant depression of water loss is a proximate consequence of this behaviour. PMID:18805813

  9. Gas exchange measurements, what can they tell us about the underlying limitations to photosynthesis? Procedures and sources of error.

    PubMed

    Long, S P; Bernacchi, C J

    2003-11-01

    The principles, equipment and procedures for measuring leaf and canopy gas exchange have been described previously as has chlorophyll fluorescence. Simultaneous measurement of the responses of leaf gas exchange and modulated chlorophyll fluorescence to light and CO2 concentration now provide a means to determine a wide range of key biochemical and biophysical limitations on photo synthesis in vivo. Here the mathematical frameworks and practical procedures for determining these parameters in vivo are consolidated. Leaf CO2 uptake (A) versus intercellular CO2 concentration (Ci) curves may now be routinely obtained from commercial gas exchange systems. The potential pitfalls, and means to avoid these, are examined. Calculation of in vivo maximum rates of ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase (Rubisco) carboxylation (Vc,max), electron transport driving regeneration of RuBP (Jmax), and triose-phosphate utilization (VTPU) are explained; these three parameters are now widely assumed to represent the major limitations to light-saturated photosynthesis. Precision in determining these in intact leaves is improved by the simultaneous measurement of electron transport via modulated chlorophyll fluorescence. The A/Ci response also provides a simple practical method for quantifying the limitation that stomata impose on CO2 assimilation. Determining the rate of photorespiratory release of oxygen (Rl) has previously only been possible by isotopic methods, now, by combining gas exchange and fluorescence measurements, Rl may be determined simply and routinely in the field. The physical diffusion of CO2 from the intercellular air space to the site of Rubisco in C3 leaves has long been suspected of being a limitation on photosynthesis, but it has commonly been ignored because of the lack of a practical method for its determination. Again combining gas exchange and fluorescence provides a means to determine mesophyll conductance. This method is described and provides

  10. Performance analysis of three nanofluids in liquid to gas and liquid to liquid heat exchangers

    NASA Astrophysics Data System (ADS)

    Ray, Dustin R.

    One purpose of this research was to analyze the thermal and fluid dynamic performance of nanofluids in an automotive radiator (liquid to gas). Detailed computations were performed on an automotive radiator using three different nanofluids containing aluminum oxide, copper oxide and silicon dioxide nanoparticles dispersed in the base fluid, 60:40 ethylene glycol and water (EG/W) by mass. The computational scheme adopted was the effectiveness-Number of Transfer Unit (epsilon-NTU) method encoded in Matlab. The computational scheme was validated by comparing the predicted results with that of the base fluid reported by other researchers. Then, the scheme was adapted to compute the performance of nanofluids. Results show that a dilute 1% volumetric concentration of nanoparticles can have substantial savings in the pumping power or surface area of the heat exchanger, while transferring the same amount of heat as the base fluid. The second purpose of this research was to carry out experimental and theoretical studies for a plate heat exchanger (PHE). A benchmark test was performed with the minichannel PHE to validate the test apparatus with water. Next, using a 0.5% aluminum oxide nanoparticle concentration dispersed in EG/W preliminary correlations for the Nusselt number and the friction factor for nanofluid flow in a PHE were derived. Then, a theoretical study was conducted to compare the performance of three nanofluids comprised of aluminum oxide, copper oxide and silicon dioxide nanoparticles in EG/W. This theoretical analysis was conducted using the epsilon-NTU method. The operational parameters were set by the active thermal control system currently under design by NASA. The analysis showed that for a dilute particle volumetric concentration of 1%, all the nanofluids showed improvements in their performance over the base fluid by reducing the pumping power and surface area of the PHE.

  11. Growing season ecosystem and leaf-level gas exchange of an exotic and native semiarid bunchgrass.

    PubMed

    Hamerlynck, Erik P; Scott, Russell L; Moran, M Susan; Keefer, Timothy O; Huxman, Travis E

    2010-07-01

    The South African grass, Lehmann lovegrass (Eragrostis lehmanniana), may alter ecosystem processes across extensive semiarid grasslands and savannahs of western North America. We compared volumetric soil moisture (theta), total and green tissue leaf area index (LAI), ecosystem (i.e. whole-plant and soil), and leaf-level gas exchange of Lehmann lovegrass and the native bush muhly (Muhlenbergia porteri) over the 2008 monsoon season in a semiarid savanna in southern Arizona, USA, to see if these were consistent with high productivity associated with lovegrass invasive success. theta across 0-5 and 0-25 cm was higher while evapotranspiration (ET) was similar between lovegrass and bush muhly plots, except shortly after rainfall, when ET was 32-81% higher in lovegrass plots. Lehmann lovegrass had lower, quickly developing LAI with greater leaf proportions than bush muhly. When early season theta was high, net ecosystem CO(2) exchange (NEE) was similar, but as storm frequency and theta declined, NEE was more negative in lovegrass (-0.69 to -3.00 micromol m(-2) s(-1)) than bush muhly (+1.75 to -1.55 micromol m(-2) s(-1)). Ecosystem respiration (R (eco)) responded quickly to monsoon onset and late-season rains, and was lower in lovegrass (2.44-3.74 micromol m(-2) s(-1)) than bush muhly (3.60-5.3 micromol m(-2) s(-1)) across the season. Gross ecosystem photosynthesis (GEP) was greater in Lehmann lovegrass, concurrent with higher leaf-level photosynthesis and stomatal conductance. We conclude that canopy structure facilitates higher theta under Lehmann lovegrass, reducing phenological constraints and stomatal limitations to whole-plant carbon uptake through the short summer monsoon growing season. PMID:20063168

  12. FORMALDEHYDE AND TRACER GAS TRANSFER BETWEEN AIRSTREAMS IN ENTHALPY-TYPE AIR-TO-AIR HEAT EXCHANGERS

    SciTech Connect

    Fisk, W. J.; Pedersen, B. S.; Hekmat, D.; Chant, R. E.; Kaboli, H.

    1984-07-01

    Enthalpy exchangers are frequently employed to transfer heat and water between the supply and exhaust airstreams of mechanical ventilation systems. Concern has been expressed that some indoor-generated air pollutants, especially formaldehyde, may be transferred between airstreams by this type of heat exchanger and, thus, returned to the indoor space. This paper describes an experimental study in which the formaldehyde, tracer gas, and water vapor transfer rates in two enthalpy exchangers were measured. The first exchanger uses a crossflow core fabricated from a treated paper. The core of the second heat exchanger is a rotating heat wheel coated with lithium chloride. To reduce the transfer of gases by air leakage each core was installed in a specially fabricated case. Only 5% to 8% of the two tracer gases and 7% to 15% of the formaldehyde injected into the exhaust airstream was transferred to the supply airstream. Therefore, formaldehyde transfer between airstreams by processes other than air leakage does not seriously compromise the performance of these enthalpy exchangers. Theoretical calculations indicate, however, that the transfer of water vapor between airstreams in enthalpy exchangers can significantly diminish their ability to lower indoor formaldehyde concentrations because of the positive coupling between indoor humidity and the emission rates of formaldehyde from building materials.

  13. Experimental Analyses of the Major Parameters Affecting the Intensity of Outbursts of Coal and Gas

    PubMed Central

    Nie, W.; Peng, S. J.; Xu, J.; Liu, L. R.; Wang, G.; Geng, J. B.

    2014-01-01

    With an increase in mining depth and production, the intensity and frequency of outburst of coal and gas have a tendency to increase. Estimating the intensity of outbursts of coal and gas plays an important role because of its relation with the risk value. In this paper, we described the semiquantitative relations between major parameters and intensity of outburst based on physical experiments. The results showed increment of geostress simulated by horizontal load (from 1.4, 2.4, 3.2, to 3.4 MPa) or vertical load (from 2, 3, 3.6, to 4 MPa) improved the relative intensity rate (3.763–7.403% and 1.273–7.99%); the increment of porosity (from 1.57, 2.51, 3, to 3.6%) improved the relative intensity rate from 3.8 to 13.8%; the increment of gas pressure (from 0, 0.5, 0.65, 0.72, 1, to 1.5 Mpa) induced the relative intensity rate to decrease from 38.22 to 0%; the increment of water content (from 0, 2, 4, to 8%) caused the relative intensity rate to drop from 5.425 to 0.5%. Furthermore, sensitivity and range analysis evaluates coupled factors affecting the relative intensity. In addition, the distinction with initiation of outburst of coal and gas affected by these parameters is discussed by the relative threshold of gas content rate. PMID:25162042

  14. Pulmonary gas exchange and its determinants during sustained microgravity on Spacelabs SLS-1 and SLS-2.

    PubMed

    Prisk, G K; Elliott, A R; Guy, H J; Kosonen, J M; West, J B

    1995-10-01

    We measured resting pulmonary gas exchange in eight subjects exposed to 9 or 14 days of microgravity (microG) during two Spacelab flights. Compared with preflight standing measurements, microG resulted in a significant reduction in tidal volume (15%) but an increase in respiratory frequency (9%). The increased frequency was caused chiefly by a reduction in expiratory time (10%), with a smaller decrease in inspiratory time (4%). Anatomic dead space (VDa) in microG was between preflight standing and supine values, consistent with the known changes in functional residual capacity. Physiological dead space (VDB) decreased in microG, and alveolar dead space (VDB-VDa) was significantly less in microG than in preflight standing (-30%) or supine (-15%), consistent with a more uniform topographic distribution of blood flow. The net result was that, although total ventilation fell, alveolar ventilation was unchanged in microG compared with standing in normal gravity (1 G). Expired vital capacity was increased (6%) compared with standing but only after the first few days of exposure to microG. There were no significant changes in O2 uptake, CO2 output, or end-tidal PO2 in microG compared with standing in 1 G. End-tidal PCO2 was unchanged on the 9-day flight but increased by 4.5 Torr on the 14-day flight where the PCO2 of the spacecraft atmosphere increased by 1-3 Torr. Cardiogenic oscillations in expired O2 and CO2 demonstrated the presence of residual ventilation-perfusion ratio (VA/Q) inequality. In addition, the change in intrabreath VA/Q during phase III of a long expiration was the same in microG as in preflight standing, indicating persisting VA/Q inequality and suggesting that during this portion of a prolonged exhalation the inequality in 1 G was not predominantly on a gravitationally induced topographic basis. However, the changes in PCO2 and VA/Q at the end of expiration after airway closure were consistent with a more uniform topographic distribution of gas

  15. Open-system chamber for measurements of gas exchanges at plant level.

    PubMed

    Alterio, Giovanni; Giorio, Pasquale; Sorrentino, Giuseppe

    2006-03-15

    Gas exchanges of whole canopy can be studied by covering entire plants with a chamber and using portable infrared gas analyzers (IRGAs) to measure CO2 and H2O exchanged with the air blown through the chamber enclosure. The control of temperature rise inside the chamber, which should be kept low, and the accurate measurement of the air flow are two crucial aspects for realistic and precise estimation of photosynthesis and transpiration. An automated open-system plant chamber (clear flexible balloon enclosure) for small plants was developed to ameliorate such a technique. The temperature rise is here predicted by heat balance analysis inside the chamber. The analysis shows that when as much as 500 W m2 of solar radiation is converted to sensible heat, a flow rate of 0.98 mol s(-1) (approximately = 20 L s(-1)) of air blown into a cylinder-shaped enclosure (0.8 m high, 0.5 m wide) is adequate to limit temperature increase to 2 K. An improved calibration for the measurement of the chamber airflow was obtained by combining the use of a Pitot tube anemometer with the classical CO2 injection approach. The concentration increase due to the injection of CO2 at a known rate into the chamber was predicted by the air flow calculated from the "Pitot" air velocity. The turbulent regime of air assured that a single-point Pitot measurement was enough for a good estimation (slope = 0.99; R2 = 0.999) of the actual air flow. The open-system chamber was tested on potted sunflower (Helianthus annuus, L.) and maize (Zea mays, L.) plants under variable solar radiation, temperature, and air humidity during the daytime. As expected, similar rates of maximal leaf-area based photosynthesis (about 40 micromol m(-2) s(-1)) were observed in the two species confirming the reliability of our system. The consistency of data also resulted from the typical relationships observed between photosynthetic rate and light. PMID:16570620

  16. Gas exchange characteristics of wheat stands grown in a closed, controlled environment.

    PubMed

    Wheeler, R M; Corey, K A; Sager, J C; Knott, W M

    1993-01-01

    Information on gas exchange of crop stands grown in controlled environments is limited, but is vital for assessing the use of crops for human life-support in closed habitats envisioned for space. Two studies were conducted to measure gas exchange of wheat stands (Triticum aestivum L. cv. Yecora Rojo) grown from planting to maturity in a large (20 m2 canopy area), closed growth chamber. Daily rates of dark-period respiration and net photosynthesis of the stand were calculated from rates of CO2 build-up during dark cycles and subsequent CO2 drawdown in the light (i.e., a closed-system approach). Lighting was provided as a 20-h photoperiod by high-pressure sodium lamps, with canopy-level photosynthetic photon flux density (PPFD) ranging from 500 to 800 micromoles m-2 s-1 as canopy height increased. Net photosynthesis rates peaked near 27 micromoles CO2 m-2 s-1 at 25 d after planting, which corresponded closely with stand closure, and then declined slowly with age. Similarly, dark-period respiration rates peaked near 14 micromoles CO2 m-2 s-1 at 25 d and then gradually declined with age. Responses to short-term changes in irradiance after canopy closure indicated the stand light compensation point for photosynthesis to be near 200 micromoles m-2 s-1 PPFD. Tests in which CO2 concentration was raised to approximately 2000 micromoles mol-1 and then allowed to draw down to a compensation point showed that net photosynthesis was nearly saturated at > 1000 micromoles mol-1; below approximately 500 micromoles mol-1, net photosynthesis rates dropped sharply with decreasing CO2. The CO2 compensation point for photosynthesis occurred near 50 micromoles mol-1. Short-term (24 h) temperature tests showed net photosynthesis at 20 degrees C > or = 16 degrees C > 24 degrees C, while dark-period respiration at 24 degrees C > 20 degrees C > 16 degrees C. Rates of stand evapotranspiration peaked near Day 25 and remained relatively constant until about Day 75, after which rates declined

  17. Greenhouse gas exchange in grasslands: impacts of climate, intensity of management and other factors

    NASA Astrophysics Data System (ADS)

    Smith, K. A.

    2003-04-01

    Grasslands occupy some 40% of the terrestrial land surface. They are generally categorised as natural (occurring mainly in those regions where the rainfall is too low to support forest ecosystems), semi-natural (where management, mainly by grazing, has changed the vegetation composition), and artificial (where forests have been cleared to create new pasture land). The soils of the natural and semi-natural grasslands constitute a large reservoir of carbon, and make a substantial contribution to the soil sink for atmospheric CH_4. The conversion of much of the natural temperate grassland to arable agriculture, e.g. in North America and Europe, resulted in a considerable decrease in soil organic carbon, and its release to the atmosphere as CO_2 has made a substantial contribution to the total atmospheric concentration of this gas. The associated increase in cycling of soil N (released from the organic matter) will have contributed to N_2O emissions, and land disturbance and fertilisation has resulted in a depletion of the soil CH_4 sink. Conversion of tropical forests to pastures has also been a major source of CO_2, and these pastures show elevated emissions of N_2O for some years after conversion. Seasonally flooded tropical grasslands are a significant source of CH_4 emissions. Consideration of grassland ecosystems in their entirety, in relation to GHG exchange, necessitates the inclusion of CH_4 production by fauna - domesticated livestock and wild herbivores, as well as some species of termites - in the overall assessment. Stocking rates on pasture land have increased, and the total CH_4 emissions likewise. The relationship between animal production and CH_4 emissions is dependent on the nutritional quality of the vegetation, as well as on animal numbers. In both temperate and tropical regions, increased N inputs as synthetic fertilisers and manures (and increased N deposition) are producing possibly a more-than-linear response in terms of emissions of N_2O. In

  18. Review of the findings of the Ignik Sikumi CO2-CH4 gas hydrate exchange field trial

    SciTech Connect

    Anderson, Brian J.; Boswell, Ray; Collett, Tim S.; Farrell, Helen; Ohtsuka, Satoshi; White, Mark D.

    2014-08-01

    The Ignik Sikumi Gas Hydrate Exchange Field Trial was conducted by ConocoPhillips in partnership with the U.S. Department of Energy, the Japan Oil, Gas, and Metals National Corporation, and the U.S. Geological Survey within the Prudhoe Bay Unit on the Alaska North Slope (ANS) during 2011 and 2012. The 2011 field program included drilling the vertical test well and performing extensive wireline logging through a thick section of gas-hydrate-bearing sand reservoirs that provided substantial new insight into the nature of ANS gas hydrate occurrences. The 2012 field program involved an extended, scientific field trial conducted within a single vertical well (“huff-and-puff” design) through three primary operational phases: 1) injection of a gaseous phase mixture of CO2, N2, and chemical tracers; 2) flowback conducted at down-hole pressures above the stability threshold for native CH4-hydrate, and 3) extended (30-days) flowback at pressures below the stability threshold of native CH4-hydrate. Ignik Sikumi represents the first field investigation of gas hydrate response to chemical injection, and the longest-duration field reservoir response experiment yet conducted. Full descriptions of the operations and data collected have been fully reported by ConocoPhillips and are available to the science community. The 2011 field program indicated the presence of free water within the gas hydrate reservoir, a finding with significant implications to the design of the exchange trial – most notably the use of a mixed gas injectant. While this decision resulted in a complex chemical environment within the reservoir that greatly tests current experimental and modeling capabilities – without such a mixture, it is apparent that injection could not have been achieved. While interpretation of the field data are continuing, the primary scientific findings and implications of the program are: 1) gas hydrate destabilizing is self-limiting, dispelling any notion of the potential for

  19. A dynamic leaf gas-exchange strategy is conserved in woody plants under changing ambient CO2 : evidence from carbon isotope discrimination in paleo and CO2 enrichment studies.

    PubMed

    Voelker, Steven L; Brooks, J Renée; Meinzer, Frederick C; Anderson, Rebecca; Bader, Martin K-F; Battipaglia, Giovanna; Becklin, Katie M; Beerling, David; Bert, Didier; Betancourt, Julio L; Dawson, Todd E; Domec, Jean-Christophe; Guyette, Richard P; Körner, Christian; Leavitt, Steven W; Linder, Sune; Marshall, John D; Mildner, Manuel; Ogée, Jérôme; Panyushkina, Irina; Plumpton, Heather J; Pregitzer, Kurt S; Saurer, Matthias; Smith, Andrew R; Siegwolf, Rolf T W; Stambaugh, Michael C; Talhelm, Alan F; Tardif, Jacques C; Van de Water, Peter K; Ward, Joy K; Wingate, Lisa

    2016-02-01

    Rising atmospheric [CO2 ], ca , is expected to affect stomatal regulation of leaf gas-exchange of woody plants, thus influencing energy fluxes as well as carbon (C), water, and nutrient cycling of forests. Researchers have proposed various strategies for stomatal regulation of leaf gas-exchange that include maintaining a constant leaf internal [CO2 ], ci , a constant drawdown in CO2 (ca  - ci ), and a constant ci /ca . These strategies can result in drastically different consequences for leaf gas-exchange. The accuracy of Earth systems models depends in part on assumptions about generalizable patterns in leaf gas-exchange responses to varying ca . The concept of optimal stomatal behavior, exemplified by woody plants shifting along a continuum of these strategies, provides a unifying framework for understanding leaf gas-exchange responses to ca . To assess leaf gas-exchange regulation strategies, we analyzed patterns in ci inferred from studies reporting C stable isotope ratios (δ(13) C) or photosynthetic discrimination (∆) in woody angiosperms and gymnosperms that grew across a range of ca spanning at least 100 ppm. Our results suggest that much of the ca -induced changes in ci /ca occurred across ca spanning 200 to 400 ppm. These patterns imply that ca  - ci will eventually approach a constant level at high ca because assimilation rates will reach a maximum and stomatal conductance of each species should be constrained to some minimum level. These analyses are not consistent with canalization toward any single strategy, particularly maintaining a constant ci . Rather, the results are consistent with the existence of a broadly conserved pattern of stomatal optimization in woody angiosperms and gymnosperms. This results in trees being profligate water users at low ca , when additional water loss is small for each unit of C gain, and increasingly water-conservative at high ca , when photosystems are saturated and water loss is large for each unit C gain

  20. How do increasing background concentrations of tropospheric ozone affect peatland plant growth and carbon gas exchange?

    NASA Astrophysics Data System (ADS)

    Williamson, Jennifer L.; Mills, Gina; Hayes, Felicity; Jones, Timothy; Freeman, Chris

    2016-02-01

    In this study we have demonstrated that plants originating from upland peat bogs are sensitive to increasing background concentrations of ozone. Peatland mesocosms from an upland peat bog in North Wales, UK were exposed to eight levels of elevated background ozone in solardomes for 4 months from May to August, with 24 h mean ozone concentrations ranging from 16 to 94 ppb and cumulative AOT024hr ranging from 45.98 ppm h to 259.63 ppm h. Our results show that plant senescence increased with increasing exposure to ozone, although there was no significant effect of increasing ozone on plant biomass. Assessments of carbon dioxide and methane fluxes from the mesocosms suggests that there was no change in carbon dioxide fluxes over the 4 month exposure period but that methane fluxes increased as cumulative ozone exposure increased to a maximum AOT 024hr of approximately 120 ppm h and then decreased as cumulative ozone exposure increased further.

  1. Pulmonary gas exchange in Andean natives with excessive polycythemia--effect of hemodilution.

    PubMed

    Manier, G; Guenard, H; Castaing, Y; Varene, N; Vargas, E

    1988-11-01

    Pulmonary gas exchange in Andean natives (n = 8) with excessive high-altitude (3,600-4,200 m) polycythemia (hematocrit 65.1 +/- 6.6%) and hypoxemia (arterial PO2 45.6 +/- 5.6 Torr) in the absence of pulmonary or cardiovascular disease was investigated both before and after isovolemic hemodilution by use of the inert gas elimination technique. The investigations were carried out in La Paz, Bolivia (3,650 m, 500 mmHg barometric pressure). Before hemodilution, a low ventilation-perfusion (VA/Q) mode (VA/Q less than 0.1) without true shunt accounted for 11.6 +/- 5.5% of the total blood flow and was mainly responsible for the hypoxemia. The hypoventilation with a low mixed venous PO2 value may have contributed to the observed hypoxemia in the absence of an impairment in alveolar capillary diffusion. After hemodilution, cardiac output and ventilation increased from 5.5 +/- 1.2 to 6.9 +/- 1.2 l/min and from 8.5 +/- 1.4 to 9.6 +/- 1.3 l/min, respectively, although arterial and venous PO2 remained constant. VA/Q mismatching fell slightly but significantly. The hypoxemia observed in subjects suffering from high-altitude excessive polycythemia was attributed to an increased in blood flow perfusing poorly ventilated areas, but without true intra- or extrapulmonary shunt. Hypoventilation as well as a low mixed venous PO2 value may also have contributed to the observed hypoxemia. PMID:3209554

  2. Carbon exchange between ecosystems and atmosphere in the Czech Republic is affected by climate factors.

    PubMed

    Marek, Michal V; Janouš, Dalibor; Taufarová, Klára; Havránková, Kateřina; Pavelka, Marian; Kaplan, Věroslav; Marková, Irena

    2011-05-01

    By comparing five ecosystem types in the Czech Republic over several years, we recorded the highest carbon sequestration potential in an evergreen Norway spruce forest (100%) and an agroecosystem (65%), followed by European beech forest (25%) and a wetland ecosystem (20%). Because of a massive ecosystem respiration, the final carbon gain of the grassland was negative. Climate was shown to be an important factor of carbon uptake by ecosystems: by varying the growing season length (a 22-d longer season in 2005 than in 2007 increased carbon sink by 13%) or by the effect of short- term synoptic situations (e.g. summer hot and dry days reduced net carbon storage by 58% relative to hot and wet days). Carbon uptake is strongly affected by the ontogeny and a production strategy which is demonstrated by the comparison of seasonal course of carbon uptake between coniferous (Norway spruce) and deciduous (European beech) stands. PMID:21345558

  3. Scaling of stomatal size and density optimizes allocation of leaf epidermal space for gas exchange in angiosperms

    NASA Astrophysics Data System (ADS)

    de Boer, Hugo Jan; Price, Charles A.; Wagner-Cremer, Friederike; Dekker, Stefan C.; Franks, Peter J.; Veneklaas, Erik J.

    2015-04-01

    Stomata on plant leaves are key traits in the regulation of terrestrial fluxes of water and carbon. The basic morphology of stomata consists of a diffusion pore and two guard cells that regulate the exchange of CO2 and water vapour between the leaf interior and the atmosphere. This morphology is common to nearly all land plants, yet stomatal size (defined as the area of the guard cell pair) and stomatal density (the number of stomata per unit area) range over three orders of magnitude across species. Evolution of stomatal sizes and densities is driven by selection pressure on the anatomical maximum stomatal conductance (gsmax), which determines the operational range of leaf gas exchange. Despite the importance of stomata traits for regulating leaf gas exchange, a quantitative understanding of the relation between adaptation of gsmax and the underlying co-evolution of stomatal sizes and densities is still lacking. Here we develop a theoretical framework for a scaling relationship between stomatal sizes and densities within the constraints set by the allocation of epidermal space and stomatal gas exchange. Our theory predicts an optimal scaling relationship that maximizes gsmax and minimizes epidermal space allocation to stomata. We test whether stomatal sizes and densities reflect this optimal scaling with a global compilation of stomatal trait data on 923 species reflecting most major clades. Our results show optimal scaling between stomatal sizes and densities across all species in the compiled data set. Our results also show optimal stomatal scaling across angiosperm species, but not across gymnosperm and fern species. We propose that the evolutionary flexibility of angiosperms to adjust stomatal sizes underlies their optimal allocation of leaf epidermal space to gas exchange.

  4. The importance of cutaneous gas exchange during aerial and aquatic respiration in galaxiids.

    PubMed

    Urbina, M A; Meredith, A S; Glover, C N; Forster, M E

    2014-03-01

    The Canterbury mudfish Neochanna burrowsius was found to be a pseudo-aestivating galaxiid with a low metabolic rate and significant cutaneous oxygen uptake (c. 43%) in both air and water. Another galaxiid, inanga Galaxias maculatus, had a higher metabolic rate in both media but the proportion of oxygen uptake met by cutaneous respiration rose significantly from 38 to 63% when the fish were exposed to air. Besides its important role in oxygen uptake, the skin of both species also contributed significantly to excretion of carbon dioxide in air, indicating the critical role of the integument as a respiratory tissue. In air, G. maculatus may increase cutaneous gas exchange to meet metabolic demands owing to the reduced utility of the gills, but as emersed G. maculatus were only able to maintain metabolic rates at c. 67% of that measured in water, this strategy probably only permits short-term survival. By contrast, the low and unchanging metabolic rate in water and air in N. burrowsius is a feature that may facilitate tolerance of long periods of emersion in the desiccating environments they inhabit. PMID:24417441

  5. Characterization of photosynthetic gas exchange in leaves under simulated adaxial and abaxial surfaces alternant irradiation.

    PubMed

    Zhang, Zi-Shan; Li, Yu-Ting; Gao, Hui-Yuan; Yang, Cheng; Meng, Qing-Wei

    2016-01-01

    Previous investigations on photosynthesis have been performed on leaves irradiated from the adaxial surface. However, leaves usually sway because of wind. This action results in the alternating exposure of both the adaxial and abaxial surfaces to bright sunlight. To simulate adaxial and abaxial surfaces alternant irradiation (ad-ab-alt irradiation), the adaxial or abaxial surface of leaves were exposed to light regimes that fluctuated between 100 and 1,000 μmol m(-2) s(-1). Compared with constant adaxial irradiation, simulated ad-ab-alt irradiation suppressed net photosynthetic rate (Pn) and transpiration (E) but not water use efficiency. These suppressions were aggravated by an increase in alternant frequency of the light intensity. When leaves were transferred from constant light to simulated ad-ab-alt irradiation, the maximum Pn and E during the high light period decreased, but the rate of photosynthetic induction during this period remained constant. The sensitivity of photosynthetic gas exchange to simulated ad-ab-alt irradiation was lower on abaxial surface than adaxial surface. Under simulated ad-ab-alt irradiation, higher Pn and E were measured on abaxial surface compared with adaxial surface. Therefore, bifacial leaves can fix more carbon than leaves with two "sun-leaf-like" surfaces under ad-ab-alt irradiation. Photosynthetic research should be conducted under dynamic conditions that better mimic nature. PMID:27377989

  6. Effect of Dichlorphenamide on Gas Exchange and CSF Acid-Base State in Chronic Respiratory Failure

    PubMed Central

    Naimark, Arnold; Cherniack, Reuben M.

    1966-01-01

    Dichlorphenamide was administered to 13 patients with chronic respiratory failure, and the effects on gas exchange at rest and during exercise and on the acid-base state of CSF were observed. The ventilation for a given level of CO2 production was increased both at rest and during exercise, resulting in an increased arterial Po2 and decreased Pco2. The ventilatory stimulation paralleled the development of a metabolic acidosis but was not associated with tissue CO2 accumulation. Indeed, CSF Pco2 and the oxygenated mixed venous (rebreathing) Pco2 fell by the same amount as arterial Pco2. The level of CO2 elimination after two minutes of exercise was as great for a given work load after dichlorphenamide as before. These findings do not support the view that the drug impairs CO2 transport from tissues either at rest or during exercise. They are most consistent with the view that the primary locus of action of dichlorphenamide in therapeutic doses is the kidney. The metabolic acidosis which results is likely the basis of the respiratory stimulatin, perhaps by its effects on the CSF H2CO3-HCO3 - system. Inhibition of carbonic anhydrase in the red cell and choroid plexus are probably unimportant effects. ImagesFig. 4 PMID:5901159

  7. Decline of hexachlorocyclohexane in the Arctic atmosphere and reversal of air-sea gas exchange

    NASA Astrophysics Data System (ADS)

    Bidleman, T. F.; Jantunen, L. M.; Falconer, R. L.; Barrie, L. A.; Fellin, P.

    1995-02-01

    Hexachlorocyclohexanes (HCHs) are the most abundant organochlorine pesticides in the arctic atmosphere and ocean surface water. A compilation of measurements made between 1979-93 from stations in the Canadian and Norwegian Arctic and from cruises in the Bering and Chukchi seas indicates that atmospheric concentrations of α-HCH have declined significantly (p < 0.01), with a time for 50% decrease of about 4 y in summer-fall and 6 y in winter-spring. The 1992-93 levels of about 100 pg m-3 are 2-4 fold lower than values in the mid-1980s. The trend in γ-HCH is less pronounced, but a decrease is also suggested from measurements in the Canadian Arctic and the Bering-Chukchi seas. HCHs in ocean surface water have remained relatively constant since the early 1980s. The decline in atmospheric α-HCH has reversed the net direction of air-sea gas exchange to the point where some northern waters are now sources of the pesticide to the atmosphere instead of sinks.

  8. Gas exchange and leaf anatomy of a C3-CAM hybrid, Yucca gloriosa (Asparagaceae).

    PubMed

    Heyduk, Karolina; Burrell, Nia; Lalani, Falak; Leebens-Mack, Jim

    2016-03-01

    While the majority of plants use the typical C3 carbon metabolic pathway, ~6% of angiosperms have adapted to carbon limitation as a result of water stress by employing a modified form of photosynthesis known as Crassulacean acid metabolism (CAM). CAM plants concentrate carbon in the cells by temporally separating atmospheric carbon acquisition from fixation into carbohydrates. CAM has been studied for decades, but the evolutionary progression from C3 to CAM remains obscure. In order to better understand the morphological and physiological characteristics associated with CAM photosynthesis, phenotypic variation was assessed in Yucca aloifolia, a CAM species, Yucca filamentosa, a C3 species, and Yucca gloriosa, a hybrid species derived from these two yuccas exhibiting intermediate C3-CAM characteristics. Gas exchange, titratable leaf acidity, and leaf anatomical traits of all three species were assayed in a common garden under well-watered and drought-stressed conditions. Yucca gloriosa showed intermediate phenotypes for nearly all traits measured, including the ability to acquire carbon at night. Using the variation found among individuals of all three species, correlations between traits were assessed to better understand how leaf anatomy and CAM physiology are related. Yucca gloriosa may be constrained by a number of traits which prevent it from using CAM to as high a degree as Y. aloifolia. The intermediate nature of Y. gloriosa makes it a promising system in which to study the evolution of CAM. PMID:26717954

  9. Effect of Salinity on Leaf Gas Exchange in Two Populations of a C4 Nonhalophyte 1

    PubMed Central

    Bowman, William D.

    1987-01-01

    Gas exchange measurements were made on plants from two natural populations differing in salt tolerance of Andropogon glomeratus, a C4 nonhalophyte, to examine the effect of salinity on components responsible for differences in photosynthetic capacity. Net CO2 uptake and stomatal conductance decreased with increasing salinity in both populations, but to a greater extent in the inland (nontolerant) population. The intercellular CO2 concentrations increased with increasing salinity in the inland population, but decreased in the marsh (tolerant) population. Water use efficiency decreased as salinity increased in the inland population, and remained unchanged in the marsh population. Carboxylation efficiency decreased and CO2 compensation points increased with increasing salinity in both populations, but to a lesser extent in the marsh population. Carboxylation efficiencies were higher with 2% relative to 21% atmospheric O2 in salt stressed plants, suggesting that a decrease in the carboxylation:oxygenation ratio of ribulose 1,5-bisphosphate carboxylase/oxygenase was partly responsible for the decrease in photosynthetic capacity. Populational differences in photosynthetic capacity were the result of greater salinity-induced changes in carboxylation efficiency in the inland population, and not due to differences in the stomatal limitation to CO2 diffusion. PMID:16665802

  10. Characterization of photosynthetic gas exchange in leaves under simulated adaxial and abaxial surfaces alternant irradiation

    PubMed Central

    Zhang, Zi-Shan; Li, Yu-Ting; Gao, Hui-Yuan; Yang, Cheng; Meng, Qing-Wei

    2016-01-01

    Previous investigations on photosynthesis have been performed on leaves irradiated from the adaxial surface. However, leaves usually sway because of wind. This action results in the alternating exposure of both the adaxial and abaxial surfaces to bright sunlight. To simulate adaxial and abaxial surfaces alternant irradiation (ad-ab-alt irradiation), the adaxial or abaxial surface of leaves were exposed to light regimes that fluctuated between 100 and 1,000 μmol m−2 s−1. Compared with constant adaxial irradiation, simulated ad-ab-alt irradiation suppressed net photosynthetic rate (Pn) and transpiration (E) but not water use efficiency. These suppressions were aggravated by an increase in alternant frequency of the light intensity. When leaves were transferred from constant light to simulated ad-ab-alt irradiation, the maximum Pn and E during the high light period decreased, but the rate of photosynthetic induction during this period remained constant. The sensitivity of photosynthetic gas exchange to simulated ad-ab-alt irradiation was lower on abaxial surface than adaxial surface. Under simulated ad-ab-alt irradiation, higher Pn and E were measured on abaxial surface compared with adaxial surface. Therefore, bifacial leaves can fix more carbon than leaves with two “sun-leaf-like” surfaces under ad-ab-alt irradiation. Photosynthetic research should be conducted under dynamic conditions that better mimic nature. PMID:27377989

  11. Gas exchange and leaf anatomy of a C3–CAM hybrid, Yucca gloriosa (Asparagaceae)

    PubMed Central

    Heyduk, Karolina; Burrell, Nia; Lalani, Falak; Leebens-Mack, Jim

    2016-01-01

    While the majority of plants use the typical C3 carbon metabolic pathway, ~6% of angiosperms have adapted to carbon limitation as a result of water stress by employing a modified form of photosynthesis known as Crassulacean acid metabolism (CAM). CAM plants concentrate carbon in the cells by temporally separating atmospheric carbon acquisition from fixation into carbohydrates. CAM has been studied for decades, but the evolutionary progression from C3 to CAM remains obscure. In order to better understand the morphological and physiological characteristics associated with CAM photosynthesis, phenotypic variation was assessed in Yucca aloifolia, a CAM species, Yucca filamentosa, a C3 species, and Yucca gloriosa, a hybrid species derived from these two yuccas exhibiting intermediate C3–CAM characteristics. Gas exchange, titratable leaf acidity, and leaf anatomical traits of all three species were assayed in a common garden under well-watered and drought-stressed conditions. Yucca gloriosa showed intermediate phenotypes for nearly all traits measured, including the ability to acquire carbon at night. Using the variation found among individuals of all three species, correlations between traits were assessed to better understand how leaf anatomy and CAM physiology are related. Yucca gloriosa may be constrained by a number of traits which prevent it from using CAM to as high a degree as Y. aloifolia. The intermediate nature of Y. gloriosa makes it a promising system in which to study the evolution of CAM. PMID:26717954

  12. Peripheral endothelial dysfunction is associated with gas exchange inefficiency in smokers

    PubMed Central

    2011-01-01

    Aims To assess the cross-sectional association between exercise capacity, gas exchange efficiency and endothelial function, as measured by flow-mediated dilation (FMD) and nitroglycerin-mediated dilation (NMD) of the brachial artery, in a large-scale population-based survey. Methods The study population was comprised of 1416 volunteers 25 to 85 years old. Oxygen uptake at anaerobic threshold (VO2@AT), peak exercise (peakVO2) and ventilatory efficiency (VE vs. VCO2 slope and VE/VCO2@AT) were assessed on a breath-by-breath basis during incremental symptom-limited cardiopulmonary exercise. FMD and NMD measurements at rest were performed using standardised ultrasound techniques. Results Multivariable logistic regression analyses revealed a significant association between FMD and ventilatory efficiency in current smokers but not in ex-smokers or non-smokers. There was no association between FMD and VO2@AT or peak VO2. In current smokers, for each one millimetre decrement in FMD, VE/VCO2@AT improved by -3.6 (95% CI -6.8, -0.4) in the overall population [VE vs. VCO2 slope -3.9 (-7.1, -0.6)]. These results remained robust after adjusting for all major influencing factors. Neither exercise capacity nor ventilatory efficiency was significantly associated with NMD. Conclusion In current smokers, FMD is significantly associated with ventilatory efficiency. This result may be interpreted as a potential clinical link between smoking and early pulmonary vasculopathy due to smoking. PMID:21518441

  13. Plant size, not age, regulates growth and gas exchange in grafted Scots pine trees.

    PubMed

    Vanderklein, D; Martínez-Vilalta, J; Lee, S; Mencuccini, M

    2007-01-01

    We studied the effect of scion donor-tree age on the physiology and growth of 6- to 7-year-old grafted Scots pine (Pinus sylvestris L.) trees (4 and 5 years after grafting). Physiological measurements included photosynthethetic rate, stomatal conductance, transpiration, whole plant hydraulic conductance, needle nitrogen concentration and carbon isotope composition. Growth measurements included total and component biomasses, relative growth rates and growth efficiency. Scion donor trees ranged in age from 36 to 269 years at the time of grafting. Hydraulic conductance was measured gravimetrically, applying the Ohm's law analogy, and directly, with a high-pressure flow meter. We found no effect of scion donor-tree age on any of the variables measured. There was, however, great variation within scion donor-tree age groups, which was related to the size of the grafted trees. Differences in size may have been caused by variable initial grafting success, but there was no indication that grafting success and age were related. At the stem level, hydraulic conductance scaled with total leaf area so that total conductance per unit leaf area did not vary with crown size. However, leaf specific hydraulic conductance (gravimetric), transpiration, photosynthesis and stomatal conductance declined with increasing total tree leaf area and needle width. We hypothesize that needle width is inversely related to mesophyll conductance. We conclude that canopy and needle size and not scion donor-tree age determined gas exchange in our grafted trees. PMID:17169908

  14. Heat transfer in a compact heat exchanger containing rectangular channels and using helium gas

    NASA Technical Reports Server (NTRS)

    Olson, D. A.

    1991-01-01

    Development of a National Aerospace Plane (NASP), which will fly at hypersonic speeds, require novel cooling techniques to manage the anticipated high heat fluxes on various components. A compact heat exchanger was constructed consisting of 12 parallel, rectangular channels in a flat piece of commercially pure nickel. The channel specimen was radiatively heated on the top side at heat fluxes of up to 77 W/sq cm, insulated on the back side, and cooled with helium gas flowing in the channels at 3.5 to 7.0 MPa and Reynolds numbers of 1400 to 28,000. The measured friction factor was lower than that of the accepted correlation for fully developed turbulent flow, although the uncertainty was high due to uncertainty in the channel height and a high ratio of dynamic pressure to pressure drop. The measured Nusselt number, when modified to account for differences in fluid properties between the wall and the cooling fluid, agreed with past correlations for fully developed turbulent flow in channels. Flow nonuniformity from channel-to-channel was as high as 12 pct above and 19 pct below the mean flow.

  15. Proton exchange membrane micro fuel cells on 3D porous silicon gas diffusion layers

    NASA Astrophysics Data System (ADS)

    Kouassi, S.; Gautier, G.; Thery, J.; Desplobain, S.; Borella, M.; Ventura, L.; Laurent, J.-Y.

    2012-10-01

    Since the 90's, porous silicon has been studied and implemented in many devices, especially in MEMS technology. In this article, we present a new approach to build miniaturized proton exchange membrane micro-fuel cells using porous silicon as a hydrogen diffusion layer. In particular, we propose an innovative process to build micro fuel cells from a “corrugated iron like” 3D structured porous silicon substrates. This structure is able to increase up to 40% the cell area keeping a constant footprint on the silicon wafer. We propose here a process route to perform electrochemically 3D porous gas diffusion layers and to deposit fuel cell active layers on such substrates. The prototype peak power performance was measured to be 90 mW cm-2 in a “breathing configuration” at room temperature. These performances are less than expected if we compare with a reference 2D micro fuel cell. Actually, the active layer deposition processes are not fully optimized but this prototype demonstrates the feasibility of these 3D devices.

  16. Advantages of the gas-exchange approach to microbiological studies. Memorandum report 1983-1985

    SciTech Connect

    Hannan, P.J.; Jones, D.S.

    1986-04-03

    Studies of the effects of various chemical or physical stimuli on the growth rates of microorganisms generally involve some measure of biomass. In the case of algae, one might measure the cell number, the chlorophyll concentration, the fluorescence, or the wet weight of the culture as a function of time. Each such measurement requires a sampling of the culture which could be a disturbing factor in the system being measured. Another disadvantage of these traditional measurements is that the times required for significant change to take place in the culture might be hours or days; furthermore, growth rate measurements calculated from the data must be based on the assumption that during the time between measurements the growth rate was constant. This report describes another approach to the problem. It consists simply of monitoring the O/sub 2/ or CO/sub 2/ concentration of an air stream passing through the system (the gas exchange method), and it has several distinct advantages: 1) there is no need to take samples of the culture, 2) each measurement is a rate measurement and indicates the performance of the culture at that very moment, and 3) transitory changes in growth rates are readily detected. Examples are given of studies made previously with this method at NRL. Also the possible value of these methods in a study of the corrosion susceptibility of alloys is described.

  17. A test of the oxidative damage hypothesis for discontinuous gas exchange in the locust Locusta migratoria.

    PubMed

    Matthews, Philip G D; Snelling, Edward P; Seymour, Roger S; White, Craig R

    2012-08-23

    The discontinuous gas exchange cycle (DGC) is a breathing pattern displayed by many insects, characterized by periodic breath-holding and intermittently low tracheal O(2) levels. It has been hypothesized that the adaptive value of DGCs is to reduce oxidative damage, with low tracheal O(2) partial pressures (PO(2) ≈ 2-5 kPa) occurring to reduce the production of oxygen free radicals. If this is so, insects displaying DGCs should continue to actively defend a low tracheal PO(2) even when breathing higher than atmospheric levels of oxygen (hyperoxia). This behaviour has been observed in moth pupae exposed to ambient PO(2) up to 50 kPa. To test this observation in adult insects, we implanted fibre-optic oxygen optodes within the tracheal systems of adult migratory locusts Locusta migratoria exposed to normoxia, hypoxia and hyperoxia. In normoxic and hypoxic atmospheres, the minimum tracheal PO(2) that occurred during DGCs varied between 3.4 and 1.2 kPa. In hyperoxia up to 40.5 kPa, the minimum tracheal PO(2) achieved during a DGC exceeded 30 kPa, increasing with ambient levels. These results are consistent with a respiratory control mechanism that functions to satisfy O(2) requirements by maintaining PO(2) above a critical level, not defend against high levels of O(2). PMID:22491761

  18. Leaf gas exchange performance and the lethal water potential of five European species during drought.

    PubMed

    Li, Shan; Feifel, Marion; Karimi, Zohreh; Schuldt, Bernhard; Choat, Brendan; Jansen, Steven

    2016-02-01

    Establishing physiological thresholds to drought-induced mortality in a range of plant species is crucial in understanding how plants respond to severe drought. Here, five common European tree species were selected (Acer campestre L., Acer pseudoplatanus L., Carpinus betulus L., Corylus avellana L. and Fraxinus excelsior L.) to study their hydraulic thresholds to mortality. Photosynthetic parameters during desiccation and the recovery of leaf gas exchange after rewatering were measured. Stem vulnerability curves and leaf pressure-volume curves were investigated to understand the hydraulic coordination of stem and leaf tissue traits. Stem and root samples from well-watered and severely drought-stressed plants of two species were observed using transmission electron microscopy to visualize mortality of cambial cells. The lethal water potential (ψlethal) correlated with stem P99 (i.e., the xylem water potential at 99% loss of hydraulic conductivity, PLC). However, several plants that were stressed beyond the water potential at 100% PLC showed complete recovery during the next spring, which suggests that the ψlethal values were underestimated. Moreover, we observed a 1 : 1 relationship between the xylem water potential at the onset of embolism and stomatal closure, confirming hydraulic coordination between leaf and stem tissues. Finally, ultrastructural changes in the cytoplasm of cambium tissue and mortality of cambial cells are proposed to provide an alternative approach to investigate the point of no return associated with plant death. PMID:26614785

  19. Multidimensional Separations of Ubiquitin Conformers in the Gas Phase: Relating Ion Cross Sections to H/D Exchange Measurements

    PubMed Central

    Robinson, Errol W.; Williams, Evan R.

    2009-01-01

    Investigating gas-phase structures of protein ions can lead to an improved understanding of intramolecular forces that play an important role in protein folding. Both hydrogen/deuterium (H/D) exchange and ion mobility spectrometry provide insight into the structures and stabilities of different gas-phase conformers, but how best to relate the results from these two methods has been hotly debated. Here, high-field asymmetric waveform ion mobility spectrometry (FAIMS) is combined with Fourier-transform ion cyclotron resonance mass spectrometry (FT/ICR MS) and is used to directly relate ubiquitin ion cross sections and H/D exchange extents. Multiple conformers can be identified using both methods. For the 9+ charge state of ubiquitin, two conformers (or unresolved populations of conformers) that have cross sections differing by 10% are resolved by FAIMS, but only one conformer is apparent using H/D exchange at short times. For the 12+ charge state, two conformers (or conformer populations) have cross sections differing by <1%, yet H/D exchange of these conformers differ significantly (6 versus 25 exchanges). These and other results show that ubiquitin ion collisional cross sections and H/D exchange distributions are not strongly correlated and that factors other than surface accessibility appear to play a significant role in determining rates and extents of H/D exchange. Conformers that are not resolved by one method could be resolved by the other, indicating that these two methods are highly complementary and that more conformations can be resolved with this combination of methods than by either method alone. PMID:16023362

  20. What can be Learned from X-ray Spectroscopy Concerning Hot Gas in Local Bubble and Charge Exchange Processes?

    NASA Technical Reports Server (NTRS)

    Snowden, Steve

    2007-01-01

    What can be learned from x-ray spectroscopy in observing hot gas in local bubble and charge exchange processes depends on spectral resolution, instrumental grasp, instrumental energy band, signal-to-nose, field of view, angular resolution and observatory location. Early attempts at x-ray spectroscopy include ROSAT; more recently, astronomers have used diffuse x-ray spectrometers, XMM Newton, sounding rocket calorimeters, and Suzaku. Future observations are expected with calorimeters on the Spectrum Roentgen Gamma mission, and the Solar Wind Charge Exchange (SWCX). The Geospheric SWCX may provide remote sensing of the solar wind and magnetosheath and remote observations of solar CMEs moving outward from the sun.

  1. Mass-spectrometric determination of O2 and CO 2 gas exchange in illuminated higher-plant cells : Evidence for light-inhibition of substrate decarboxylations.

    PubMed

    Avelange, M H; Thiéry, J M; Sarrey, F; Gans, P; Rébeillé, F

    1991-01-01

    In order to estimate photosynthetic and respiratory rates in illuminated photoautotrophic cells of carnation (Dianthus caryophyllus L.), simultaneous measurements of CO2 and O2 gas exchange were performed using (18)O2, (13)CO2 and a mass-spectrometry technique. This method allowed the determination, and thus the comparison, of unidirectional fluxes of O2 and CO2. In optimum photosynthetic conditions (i.e. in the presence of high light and a saturating level of CO2), the rate of CO2 influx represented 75±5% of the rate of gross O2 evolution. After a dark-to-light transition, the rate of CO2 efflux was inhibited by 50% whereas the O2-uptake rate was little affected. The effect of a recycling of respiratory CO2 through photosynthesis on the exchange of CO2 gas was investigated using a mathematical model. The confliction of the experimental data with the simulated gas-exchange rates strongly supported the view that CO2 recycling was a minor event in these cells and could not be responsible for the observed inhibition of CO2 efflux. On the basis of this assumption it was concluded that illumination of carnation cells resulted in a decrease of substrate decarboxylations, and that CO2 efflux and O2 uptake were not as tightly coupled in the light as in the dark. Furthermore, it could be calculated from the rate of gross photosynthesis that the chloroplastic electron-transport chain produced enough ATP in the light to account for the measured CO2-uptake rate without involving cyclic transfer of electrons around PS I or mitochondrial supplementation. PMID:24193614

  2. 40 CFR 60.5400 - What equipment leak standards apply to affected facilities at an onshore natural gas processing...

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... affected facilities at an onshore natural gas processing plant? 60.5400 Section 60.5400 Protection of... NEW STATIONARY SOURCES Standards of Performance for Crude Oil and Natural Gas Production, Transmission... natural gas processing plant? This section applies to the group of all equipment, except...

  3. 40 CFR 60.5400 - What equipment leak standards apply to affected facilities at an onshore natural gas processing...

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... affected facilities at an onshore natural gas processing plant? 60.5400 Section 60.5400 Protection of... NEW STATIONARY SOURCES Standards of Performance for Crude Oil and Natural Gas Production, Transmission... natural gas processing plant? This section applies to the group of all equipment, except...

  4. Optimization of heat and mass transfers in counterflow corrugated-plate liquid-gas exchangers used in a greenhouse dehumidifier

    NASA Astrophysics Data System (ADS)

    Bentounes, N.; Jaffrin, A.

    1998-09-01

    Heat and mass transfers occuring in a counterflow direct contact liquid-gas exchanger determine the performance of a new greenhouse air dehumidifier designed at INRA. This prototype uses triethylene glycol (TEG) as the desiccant fluid which extracts water vapor from the air. The regeneration of the TEG desiccant fluid is then performed by direct contact with combustion gas from a high efficiency boiler equipped with a condensor. The heat and mass transfers between the thin film of diluted TEG and the hot gas were simulated by a model which uses correlation formula from the literature specifically relevant to the present cross-corrugated plates geometry. A simple set of analytical solutions is first derived, which explains why some possible processes can clearly be far from optimal. Then, more exact numerical calculations confirm that some undesirable water recondensations on the upper part of the exchanger were limiting the performance of this prototype. More suitable conditions were defined for the process, which lead to a new design of the apparatus. In this second prototype, a gas-gas exchanger provides dryer and cooler gas to the basis of the regenerators, while a warmer TEG is fed on the top. A whole range of operating conditions was experimented and measured parameters were compared with numerical simulations of this new configuration: recondensation did not occur any more. As a consequence, this second prototype was able to concentrate the desiccant fluid at the desired rate of 20 kg H_{2O}/hour, under temperature and humidity conditions which correspond to the dehumidification of a 1000 m2 greenhouse heated at night during the winter season.

  5. Influence of current velocity and wind speed on air-water gas exchange in a mangrove estuary

    NASA Astrophysics Data System (ADS)

    Ho, David T.; Coffineau, Nathalie; Hickman, Benjamin; Chow, Nicholas; Koffman, Tobias; Schlosser, Peter

    2016-04-01

    Knowledge of air-water gas transfer velocities and water residence times is necessary to study the fate of mangrove derived carbon exported into surrounding estuaries and ultimately to determine carbon balances in mangrove ecosystems. For the first time, the 3He/SF6 dual tracer technique, which has been proven to be a powerful tool to determine gas transfer velocities in the ocean, is applied to Shark River, an estuary situated in the largest contiguous mangrove forest in North America. The mean gas transfer velocity was 3.3 ± 0.2 cm h-1 during the experiment, with a water residence time of 16.5 ± 2.0 days. We propose a gas exchange parameterization that takes into account the major sources of turbulence in the estuary (i.e., bottom generated shear and wind stress).

  6. Involvement of Plant Growth Substances in the Alteration of Leaf Gas Exchange of Flooded Tomato Plants 1

    PubMed Central

    Bradford, Kent J.

    1983-01-01

    Ethylene, abscisic acid, and cytokinins were tested for their ability to either induce or prevent the changes which occur in gas exchange characteristics of tomato (Lycopersicon esculentum Mill. cv. Rheinlands Ruhm) leaves during short-term soil flooding. Ethylene, which increases in the shoots of flooded plants, had no effect on stomatal conductance or photosynthetic capacity of drained plants. Abscisic acid, which also accumulates in the shoots of flooded plants, could reproduce the stomatal behavior of flooded plants when sprayed on the leaves of drained plants. However, photosynthetic capacity of drained plants was unaffected by abscisic acid sprays. Cytokinin export from the roots to the shoots declines in flooded plants. Spray applications of benzyladenine increased stomatal conductance in both flooded and drained plants. In addition, the decline in photosynthetic capacity during flooding was largely prevented by supplementary cytokinin applications. The possible involvement of these growth substances in modifying leaf gas exchange during flooding is discussed. PMID:16663243

  7. Current developments affecting future availability of oil and gas in the free world

    SciTech Connect

    Borg, I.Y.

    1981-03-17

    This review focuses on developments during the last 18 months likely to affect the availability of oil and gas in coming decades. These developments include new discoveries (Hibernia, Beaufort Sea, Ivory Coast, the Western and Eastern Overthrust Belts, and the Gulf of Suez). They also include new energy policies of both producer and consumer nations that will ultimately affect supply. New policies and a rapidly increasing domestic demand may stabilize Mexico's exports at their present level, even if production reaches 4 to 5 million barrels per day (b/d). Canada's new policy toward foreign oil companies operating within her borders may well stifle exploration and investment in both oil and tar sand deposits. OPEC contract and pricing schemes are profoundly altering distribution systems and markets. OPEC plans to allocate oil arbitrarily in times of shortage could disrupt the industrial world. Inability to reassign oil contracted for from OPEC nations is forcing buyers to increase storage capacity. The oil inventories reported are not equivalent to availability, since 50 to 90% is essentially unavailable. Thus, stock equivalent to 110 days of imports may include only a few weeks of primary usable stocks. Only Sweden and South Africa have federally owned oil reserves that could meet demand for periods of months or years. Natural gas from the USSR will probably comprise 30% of Western Europe's total supply in the 1990s, if plans to import gas from the Yamal Peninsula come to fruition. Soviet gas is seen as an acceptable alternative to undependable OPEC oil supplies and similarly unreliable gas supplies from North Africa. However, the proposed, increased dependency on the USSR may add a new dimension to Soviet and Western European politics.

  8. Ion-exchange and hydrophobic interactions affecting selectivity for neutral and charged solutes on three structurally similar agglomerated ion-exchange and mixed-mode stationary phases.

    PubMed

    Kazarian, Artaches A; Taylor, Mark R; Haddad, Paul R; Nesterenko, Pavel N; Paull, Brett

    2013-11-25

    The nature and extent of mixed-mode retention mechanisms evident for three structurally related, agglomerated, particle-based stationary phases were evaluated. These three agglomerated phases were Thermo Fisher ScientificIon PacAS11-HC - strong anion exchange, Thermo Fisher Scientific IonPac CS10--strong cation-exchange PS-DVB, and the Thermo Fisher Scientific Acclaim Trinity P1silica-based substrate, which is commercially marketed as a mixed-mode stationary phase. All studied phases can exhibit zwitterionic and hydrophobic properties, which contribute to the retention of charged organic analytes. A systematic approach was devised to investigate the relative ion-exchange capacities and hydrophobicities for each of the three phases, together with the effect of eluent pH upon selectivity, using a specifically selected range of anionic, cationic and neutral aromatic compounds. Investigation of the strong anion-exchange column and the Trinity P1 mixed-mode substrate, in relation to ion-exchange capacity and pH effects, demonstrated similar retention behaviour for both the anionic and ampholytic solutes, as expected from the structurally related phases. Further evaluation revealed that the ion-exchange selectivity of the mixed-mode phase exhibited properties similar to that of the strong anion-exchange column, with secondary cation-exchange selectivity, albeit with medium to high anion-exchange and cation-exchange capacities, allowing selective retention for each of the anionic, cationic and ampholytic solutes. Observed mixed-mode retention upon the examined phases was found to be a sum of anion- and cation-exchange interactions, secondary ion-exchange and hydrophobic interactions, with possible additional hydrogen bonding. Hydrophobic evaluation of the three phases revealed logP values of 0.38-0.48, suggesting low to medium hydrophobicity. These stationary phases were also benchmarked against traditional reversed-phase substrates namely, octadecylsilica YMC-Pac Pro C18

  9. The Effects of N Nutrition on the Water Relations and Gas Exchange Characteristics of Wheat (Triticum aestivum L.) 1

    PubMed Central

    Morgan, Jack A.

    1986-01-01

    The purpose of this study was to characterize leaf photosynthetic and stomatal responses of wheat (Triticum aestivum L.) plants grown under two N-nutritional regimes. High- and low-N regimes were imposed on growth-chamber-grown plants by fertilizing with nutrient solutions containing 12 or 1 millimolar nitrogen, respectively. Gas-exchange measurements indicated not only greater photosynthetic capacity of high-N plants under well-watered conditions, but also a greater sensitivity of CO2 exchange rate and leaf conductance to CO2 and leaf water potential compared to low-N plants. Increased sensitivity of high-N plants was associated with greater tissue elasticity, lower values of leaf osmotic pressure and greater aboveground biomass. These N-nutritional-related changes resulted in greater desiccation (lowered relative water content) of high-N plants as leaf water potential fell, and were implicated as being important in causing greater sensitivity of high-N leaf gas exchange to reductions in water potential. Water use efficiency of leaves, calculated as CO2 exchange rate/transpiration, increased from 9.1 to 13 millimoles per mole and 7.9 to 9.1 millimoles per mole for high- and low-N plants as water became limiting. Stomatal oscillations were commonly observed in the low-N treatment at low leaf water potentials and ambient CO2 concentrations, but disappeared as CO2 was lowered and stomata opened. PMID:16664606

  10. The Effect of Experimentally Induced Root Mortality on Trace Gas Exchange

    NASA Astrophysics Data System (ADS)

    Varner, R. K.; Keller, M.; Robertson, J. R.; Dias, J. D.; Silva, H.; Crill, P. M.; McGroddy, M.; Silver, W. L.

    2002-12-01

    Soil-atmosphere exchange of carbon dioxide (CO2), nitric oxide (NO), nitrous oxide (N2O) and methane (CH4) was measured following a root exclusion experiment in the Tapajos National Forest near Santarem, Para, Brazil. The sampling period (June 4 - August 14, 2000) coincided with the beginning of the dry season. The experiment was set up as a randomized complete block design with 5 pairs of 2.5 x 2.5 m plots in both sand and clay soils. Trenches were dug around one plot in each pair for screen installation. Trace gas fluxes were measured weekly for ten weeks following the trenching. Duplicate flux measurements were made for each of the trenched and non-trenched plots. Enclosures made of 0.25 m diameter PVC pipe were placed on a base imbedded in the soil. Dynamic measurements using a portable backpack system equipped with an NO2 chemiluminescent detector for NO and an infrared gas analyzer for CO2 were completed in the field. CH4 and N2O fluxes were measured through a static enclosure method. Syringe samples of the enclosure headspace were analyzed by GC-FID (CH4) and ECD (N2O) the following day. Daily average fluxes ranged between -0.01 and 60.3 ng-N cm-2 hr-1 for N2O. NO fluxes ranged between 0.58 and 8.74 ng-N cm-2 hr-1. CH4 fluxes varied between net consumption and production from -1.73 to 0.912 mg m-2 d-1. Soil respiration ranged from 1.34 to 5.12 umoles CO2 m-2 s-1. Significant differences were seen between trenched and non-trenched plots in both clay and sand soils for N2O emissions only. Hourly field standardization of the NO2 chemiluminescent analyzer resulted in lower variability than the traditional method of standardization which is completed at the beginning and end of the measurement day. Frequent field standardization of the analyzer is necessary to reduce measurement error due to intra-day variability.

  11. Weak coordination among petiole, leaf, vein, and gas-exchange traits across Australian angiosperm species and its possible implications.

    PubMed

    Gleason, Sean M; Blackman, Chris J; Chang, Yvonne; Cook, Alicia M; Laws, Claire A; Westoby, Mark

    2016-01-01

    Close coordination between leaf gas exchange and maximal hydraulic supply has been reported across diverse plant life forms. However, it has also been suggested that this relationship may become weak or break down completely within the angiosperms. We examined coordination between hydraulic, leaf vein, and gas-exchange traits across a diverse group of 35 evergreen Australian angiosperms, spanning a large range in leaf structure and habitat. Leaf-specific conductance was calculated from petiole vessel anatomy and was also measured directly using the rehydration technique. Leaf vein density (thought to be a determinant of gas exchange rate), maximal stomatal conductance, and net CO 2 assimilation rate were also measured for most species (n = 19-35). Vein density was not correlated with leaf-specific conductance (either calculated or measured), stomatal conductance, nor maximal net CO 2 assimilation, with r (2) values ranging from 0.00 to 0.11, P values from 0.909 to 0.102, and n values from 19 to 35 in all cases. Leaf-specific conductance calculated from petiole anatomy was weakly correlated with maximal stomatal conductance (r (2) = 0.16; P = 0.022; n = 32), whereas the direct measurement of leaf-specific conductance was weakly correlated with net maximal CO 2 assimilation (r (2) = 0.21; P = 0.005; n = 35). Calculated leaf-specific conductance, xylem ultrastructure, and leaf vein density do not appear to be reliable proxy traits for assessing differences in rates of gas exchange or growth across diverse sets of evergreen angiosperms. PMID:26811791

  12. Neural control of gas exchange patterns in insects: locust density-dependent phases as a test case.

    PubMed

    Berman, Tali S; Ayali, Amir; Gefen, Eran

    2013-01-01

    The adaptive significance of discontinuous gas exchange cycles (DGC) in insects is contentious. Based on observations of DGC occurrence in insects of typically large brain size and often socially-complex life history, and spontaneous DGC in decapitated insects, the neural hypothesis for the evolution of DGC was recently proposed. It posits that DGC is a non-adaptive consequence of adaptive down-regulation of brain activity at rest, reverting ventilatory control to pattern-generating circuits in the thoracic ganglia. In line with the predictions of this new hypothesis, we expected a higher likelihood of DGC in the gregarious phase of the desert locust (Schistocerca gregaria, Orthoptera), which is characterized by a larger brain size and increased sensory sensitivity compared with the solitary phase. Furthermore, surgical severing of the neural connections between head and thoracic ganglia was expected to increase DGC prevalence in both phases, and to eliminate phase-dependent variation in gas exchange patterns. Using flow-through respirometry, we measured metabolic rates and gas exchange patterns in locusts at 30°C. In contrast to the predictions of the neural hypothesis, we found no phase-dependent differences in DGC expression. Likewise, surgically severing the descending regulation of thoracic ventilatory control did not increase DGC prevalence in either phase. Moreover, connective-cut solitary locusts abandoned DGC altogether, and employed a typical continuous gas exchange pattern despite maintaining metabolic rate levels of controls. These results are not consistent with the predictions of the neural hypothesis for the evolution of DGC in insects, and instead suggest neural plasticity of ventilatory control. PMID:23555850

  13. Pulmonary gas exchange in cystic fibrosis: basal status and the effect of i.v. antibiotics and inhaled amiloride.

    PubMed

    Lagerstrand, L; Hjelte, L; Jorulf, H

    1999-09-01

    In order to evaluate the degree and type of gas exchange impairment in cystic fibrosis, ventilation/perfusion relationships in ten patients (mean age 26 yrs, mean Shwachman score 86) were examined. Pulmonary gas exchange was studied using the multiple inert gas elimination technique. High-resolution computed tomography (HRCT) and spirometry, including diffusing capacity, were performed after each gas exchange study for comparison. Examinations were done before and after home i.v. antibiotic treatment (HIVAT, 14 days) and after inhaled amiloride and placebo (14 days), in crossover fashion, clinical status after HIVAT serving as the baseline for the crossover study. Before HIVAT, the mean residual volume was 182% of the predicted value, the mean vital capacity 72% pred and the mean forced expiratory volume in one second 53% pred (p<0.001). The dispersion of pulmonary blood flow at different ventilation/perfusion ratios (V'/Q') ((logarithmic SD of the perfusion distribution (log SDQ)), used as an index for gas exchange impairment, was increased to a mean of 0.72. No linear correlation was seen between ventilation/perfusion inequality, spirometry and HRCT (p>0.05). After HIVAT, log SDQ was significantly improved to 0.66 (p<0.05). After placebo, but not after amiloride, log SDQ, arterial oxygen tension, alveolar-arterial oxygen tension difference and maximal expiratory flows when 50% and 25% of the forced vital capacity tension remain to be exhaled were significantly worse (p<0.05, respectively). Areas with a low V'/Q' were significantly lower after amiloride compared to after the placebo period (p<0.05). Moderate ventilation/perfusion inequality was present in the majority of the studied cystic fibrosis patients. The degree of ventilation/perfusion inequality cannot be estimated from spirometry or high-resolution computed tomography. The low proportion of low ventilation/perfusion ratios indicates that the regular treatment directed towards mucus plugging of small

  14. Pulmonary gas exchange during histamine-induced bronchoconstriction in asthmatic subjects.

    PubMed

    Burke, T V; Küng, M; Burki, N K

    1989-10-01

    Bronchial provocation for testing airway hyperreactivity is now well-established. However, the effects of histamine-induced bronchoconstriction on pulmonary gas exchange in man have not been systematically studied. We empirically noted marked decreases in PaO2 in some asthmatic subjects following induced bronchoconstriction. Nine subjects with mild, stable asthma were studied, each on two separate days. The first determined the dose of inhaled histamine necessary to decrease FEV1 by 20 percent and the relationship to lung volume and to pulmonary resistance by the interrupter technique (Rint). On the second day arterial blood gases, ventilation, Rint, and the anatomic (VDan) and physiologic (VDphys) dead spaces were measured simultaneously. There was a significant (p less than 0.05), profound fall in PaO2 (mean, -21.8 mm Hg) and in P(A-a)O2 (mean +14.7 mm Hg) within 5 min after bronchoconstriction, associated with a significant (p less than 0.05) increase in respiratory frequency (mean +5.1 min-1); and decrease in tidal volume (mean, -0.3 L). The ratio VDphys/VT increased significantly (p less than 0.05; mean change, +0.08) even though VDan and VDphys did not. Bronchoconstriction induced the broadening of ventilation (V)/perfusion (Q) ratios, with, most likely, an increase in areas of high V/Q. Histamine-induced bronchoconstriction in mild asthma results in a marked fall in PaO2 due to induced V/Q inequality. Therefore, histamine airway challenge should be used with caution in patients with any preexisting hypoxemia. PMID:2791669

  15. Biogenic emissions and CO 2 gas exchange investigated on four Mediterranean shrubs

    NASA Astrophysics Data System (ADS)

    Hansen, U.; van Eijk, J.; Bertin, N.; Staudt, M.; Kotzias, D.; Seufert, G.; Fugit, J.-L.; Torres, L.; Cecinato, A.; Brancaleoni, E.; Ciccioli, P.; Bomboi, T.

    In order to investigate the impact of plant physiology on emissions of biogenic volatile organic compounds monoterpene emission rates from Rosmarinus officinalis (L.) and Pistacia lentiscus (L.) and isoprene emission rates from Erica arborea (L.) and Myrtus communis (L.) were determined. The study, an activity in the framework of BEMA (Biogenic Emissions in the Mediterranean Area), was carried out in May 1994 at Castelporziano near Rome in Italy, using a dynamic enclosure technique combined with recording CO 2 gas exchange, temperature and irradiance data. The monoterpenes dominating the emission pattern were 1,8-cineol, α-pinene and β-pinene for rosemary and α-pinene, linalool and β-pinene + sabinene for pistachio. Total monoterpene emission rates standardized to 30°C of 1.84 ± 0.24 and 0.35 ± 0.04 μg Cg -1 dw h -1 were found for rosemary and pistachio, respectively (on a leaf dry weight basis). Myrtle emitted 22.2 ± 4.9 μg C g -1 dw h -1 at standard conditions (30°C, PAR 1000 μmol photons m -2 s -1 as isoprene and erica 5.61 μg C g -1 dw h -1 The carbon loss due to terpenoid emissions per photosynthetically carbon uptake was about 0.01-0.1% for the monoterpene emitters. The isoprene emitting shrubs lost 0-0.9% of the assimilated carbon. The rapid induction of emissions in the sun after temporary shading indicates that isoprene emissions were closely linked to photosynthesis. A higher proportion of the assimilated carbon was lost as isoprene under conditions of high light and temperature compared to the morning and evening hours.

  16. Vital capacity, respiratory muscle strength, and pulmonary gas exchange during long-duration exposure to microgravity.

    PubMed

    Prisk, G Kim; Fine, Janelle M; Cooper, Trevor K; West, John B

    2006-08-01

    Extended exposure to microgravity (microG) is known to reduce strength in weight-bearing muscles and was also reported to reduce respiratory muscle strength. Short- duration exposure to microG reduces vital capacity (VC), a surrogate measure for respiratory muscle strength, for the first few days, with little change in O2 uptake, ventilation, or end-tidal partial pressures. Accordingly we measured VC, maximum inspiratory and expiratory pressures, and indexes of pulmonary gas exchange in 10 normal subjects (9 men, 1 woman, 39-52 yr) who lived on the International Space Station for 130-196 days in a normoxic, normobaric atmosphere. Subjects were studied four times in the standing and supine postures preflight at sea level at 1 G, approximately monthly in microG, and multiple times postflight. VC in microG was essentially unchanged compared with preflight standing [5.28 +/- 0.08 liters (mean +/- SE), n = 187; 5.24 +/- 0.09, n = 117, respectively; P = 0.03] and considerably greater than that measured supine in 1G (4.96 +/- 0.10, n = 114, P < 0.001). There was a trend for VC to decrease after the first 2 mo of microG, but there were no changes postflight. Maximum respiratory pressures in microG were generally intermediate to those standing and supine in 1G, and importantly they showed no decrease with time spent in microG. O2 uptake and CO2 production were reduced (approximately 12%) in extended microG, but inhomogeneity in the lung was not different compared with short-duration exposure to microG. The results show that VC is essentially unchanged and respiratory muscle strength is maintained during extended exposure to microG, and metabolic rate is reduced. PMID:16601306

  17. Influence of exercise modality on agreement between gas exchange and heart rate variability thresholds

    PubMed Central

    Cunha, F.A.; Montenegro, R.A.; Midgley, A.W.; Vasconcellos, F.; Soares, P.P.; Farinatti, P.

    2014-01-01

    The main purpose of this study was to investigate the level of agreement between the gas exchange threshold (GET) and heart rate variability threshold (HRVT) during maximal cardiopulmonary exercise testing (CPET) using three different exercise modalities. A further aim was to establish whether there was a 1:1 relationship between the percentage heart rate reserve (%HRR) and percentage oxygen uptake reserve (%V˙O2 R) at intensities corresponding to GET and HRVT. Sixteen apparently healthy men 17 to 28 years of age performed three maximal CPETs (cycling, walking, and running). Mean heart rate and V˙O2 at GET and HRVT were 16 bpm (P<0.001) and 5.2 mL·kg-1·min-1 (P=0.001) higher in running than cycling, but no significant differences were observed between running and walking, or cycling and walking (P>0.05). There was a strong relationship between GET and HRVT, with R2 ranging from 0.69 to 0.90. A 1:1 relationship between %HRR and %V˙O2 R was not observed at GET and HRVT. The %HRR was higher during cycling (GET mean difference=7%; HRVT mean difference=11%; both P<0.001), walking (GET mean difference=13%; HRVT mean difference=13%; both P<0.001), or running (GET mean difference=11%; HRVT mean difference=10%; both P<0.001). Therefore, using HRVT to prescribe aerobic exercise intensity appears to be valid. However, to assume a 1:1 relationship between %HRR and %V˙O2 R at HRVT would probably result in overestimation of the energy expenditure during the bout of exercise. PMID:25003546

  18. Physiological impact of patent foramen ovale on pulmonary gas exchange, ventilatory acclimatization, and thermoregulation.

    PubMed

    Lovering, Andrew T; Elliott, Jonathan E; Davis, James T

    2016-08-01

    The foramen ovale, which is part of the normal fetal cardiopulmonary circulation, fails to close after birth in ∼35% of the population and represents a potential source of right-to-left shunt. Despite the prevalence of patent foramen ovale (PFO) in the general population, cardiopulmonary, exercise, thermoregulatory, and altitude physiologists may have underestimated the potential effect of this shunted blood flow on normal physiological processes in otherwise healthy humans. Because this shunted blood bypasses the respiratory system, it would not participate in either gas exchange or respiratory system cooling and may have impacts on other physiological processes that remain undetermined. The consequences of this shunted blood flow in PFO-positive (PFO+) subjects can potentially have a significant, and negative, impact on the alveolar-to-arterial oxygen difference (AaDO2), ventilatory acclimatization to high altitude and respiratory system cooling with PFO+ subjects having a wider AaDO2 at rest, during exercise after acclimatization, blunted ventilatory acclimatization, and a higher core body temperature (∼0.4(°)C) at rest and during exercise. There is also an association of PFO with high-altitude pulmonary edema and acute mountain sickness. These effects on physiological processes are likely dependent on both the presence and size of the PFO, with small PFOs not likely to have significant/measureable effects. The PFO can be an important determinant of normal physiological processes and should be considered a potential confounder to the interpretation of former and future data, particularly in small data sets where a significant number of PFO+ subjects could be present and significantly impact the measured outcomes. PMID:27418686

  19. Measuring infant metabolism: design and testing of a miniature gas exchange monitor.

    PubMed

    Heiss, K; Hirschl, R; Cilley, R; Wesley, J; Hultquist, K; Fazzalari, F; Bartlett, R

    1988-06-01

    A compact closed-circuit gas exchange monitor (GEM) was built for measurement of oxygen consumption (VO2) in ventilated infants. The GEM includes a ventilator-driven slave bellows, a CO2 scrubber, one-way valves to ensure unidirectional flow, and tubing to complete the small-volume low-compliance system, which fits easily between the ventilator (VENT) and the endotracheal tube (ETT). Oxygen consumption is measured by volume loss from a spirometer attached by a one-way valve. Pressure is monitored at the airway, and the VENT is adjusted to attain the desired pressure pattern. The system was leak tested by placing a 3-kg weight on the spirometer bell (continuous positive airway pressure = 20 cm H2O) and then ventilating with peak inspiratory pressures (PIP) of 60 cm H2O without leak. Bench testing for accuracy of volume loss was checked by ventilating the device into another calibrated spirometer and achieving equal volumes. First, four rabbits were studied to determine the range of ventilator backup rates (BUR = 0 to 60), inspiratory times (IT = .2 to .6 seconds), and airway pressures (up to 40/8 cm H2O) attainable by this device. Then six fasted rabbits weighing 2.2 to 4.0 kg were anesthetized with a ketamine-rompun mixture, underwent tracheostomy, and were placed on a pressure VENT. The BUR was set at 20/min and the IT at .5 seconds. The GEM was placed between the VENT and the ETT, and the PIP was adjusted to maintain PaCO2 between 30 and 40 torr, eliminating spontaneous respiration. Oxygen consumption was measured at five-minute intervals for one hour.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:3418473

  20. Effects of long-term low atmospheric pressure on gas exchange and growth of lettuce

    NASA Astrophysics Data System (ADS)

    Tang, Yongkang; Guo, Shuangsheng; Dong, Wenping; Qin, Lifeng; Ai, Weidang; Lin, Shan

    2010-09-01

    The objectives of this research were to determine photosynthesis, evapotranspiration and growth of lettuce at long-term low atmospheric pressure. Lettuce ( Lactuca sativa L . cv. Youmaicai) plants were grown at 40 kPa total pressure (8.4 kPa p) or 101 kPa total pressure (20.9 kPa p) from seed to harvest for 35 days. Germination rate of lettuce seeds decreased by 7.6% at low pressure, although this was not significant. There was no significant difference in crop photosynthetic rate between hypobaria and ambient pressure during the 35-day study. The crop evapotranspiration rate was significantly lower at low pressure than that at ambient pressure from 20 to 30 days after planting (DAP), but it had no significant difference before 20 DAP or after 30 DAP. The growth cycle of lettuce plants at low pressure was delayed. At low pressure, lettuce leaves were curly at the seedling stage and this disappeared gradually as the plants grew. Ambient lettuce plants were yellow and had an epinastic growth at harvest. The shoot height, leaf number, leaf length and shoot/root ratio were lower at low pressure than those at ambient pressure, while leaf area and root growth increased. Total biomass of lettuce plants grown at two pressures had no significant difference. Ethylene production at low pressure decreased significantly by 38.8% compared with ambient pressure. There was no significant difference in microelements, nutritional phytochemicals and nitrate concentrations at the two treatments. This research shows that lettuce can be grown at long-term low pressure (40 kPa) without significant adverse effects on seed germination, gas exchange and plant growth. Furthermore, ethylene release was reduced in hypobaria.

  1. Corrosive resistant heat exchanger

    DOEpatents

    Richlen, Scott L.

    1989-01-01

    A corrosive and errosive resistant heat exchanger which recovers heat from a contaminated heat stream. The heat exchanger utilizes a boundary layer of innocuous gas, which is continuously replenished, to protect the heat exchanger surface from the hot contaminated gas. The innocuous gas is conveyed through ducts or perforations in the heat exchanger wall. Heat from the heat stream is transferred by radiation to the heat exchanger wall. Heat is removed from the outer heat exchanger wall by a heat recovery medium.

  2. Interruption to cutaneous gas exchange is not a likely mechanism of WNS-associated death in bats.

    PubMed

    Carey, Charleve S; Boyles, Justin G

    2015-07-01

    Pseudogymnoascus destructans is the causative fungal agent of white-nose syndrome (WNS), an emerging fungal-borne epizootic. WNS is responsible for a catastrophic decline of hibernating bats in North America, yet we have limited understanding of the physiological interactions between pathogen and host. Pseudogymnoascus destructans severely damages wings and tail membranes, by causing dryness that leads to whole sections crumbling off. Four possible mechanisms have been proposed by which infection could lead to dehydration; in this study, we tested one: P. destructans infection could cause disruption to passive gas-exchange pathways across the wing membranes, thereby causing a compensatory increase in water-intensive pulmonary respiration. We hypothesized that total evaporative water loss would be greater when passive gas exchange was inhibited. We found that bats did not lose more water when passive pathways were blocked. This study provides evidence against the proposed proximal mechanism that disruption to passive gas exchange causes dehydration and death to WNS-infected bats. PMID:25944919

  3. An Excel tool for deriving key photosynthetic parameters from combined gas exchange and chlorophyll fluorescence: theory and practice.

    PubMed

    Bellasio, Chandra; Beerling, David J; Griffiths, Howard

    2016-06-01

    Combined photosynthetic gas exchange and modulated fluorometres are widely used to evaluate physiological characteristics associated with phenotypic and genotypic variation, whether in response to genetic manipulation or resource limitation in natural vegetation or crops. After describing relatively simple experimental procedures, we present the theoretical background to the derivation of photosynthetic parameters, and provide a freely available Excel-based fitting tool (EFT) that will be of use to specialists and non-specialists alike. We use data acquired in concurrent variable fluorescence-gas exchange experiments, where A/Ci and light-response curves have been measured under ambient and low oxygen. From these data, the EFT derives light respiration, initial PSII (photosystem II) photochemical yield, initial quantum yield for CO2 fixation, fraction of incident light harvested by PSII, initial quantum yield for electron transport, electron transport rate, rate of photorespiration, stomatal limitation, Rubisco (ribulose 1·5-bisphosphate carboxylase/oxygenase) rate of carboxylation and oxygenation, Rubisco specificity factor, mesophyll conductance to CO2 diffusion, light and CO2 compensation point, Rubisco apparent Michaelis-Menten constant, and Rubisco CO2 -saturated carboxylation rate. As an example, a complete analysis of gas exchange data on tobacco plants is provided. We also discuss potential measurement problems and pitfalls, and suggest how such empirical data could subsequently be used to parameterize predictive photosynthetic models. PMID:25923517

  4. Deriving C4 photosynthetic parameters from combined gas exchange and chlorophyll fluorescence using an Excel tool: theory and practice.

    PubMed

    Bellasio, Chandra; Beerling, David J; Griffiths, Howard

    2016-06-01

    The higher photosynthetic potential of C4 plants has led to extensive research over the past 50 years, including C4 -dominated natural biomes, crops such as maize, or for evaluating the transfer of C4 traits into C3 lineages. Photosynthetic gas exchange can be measured in air or in a 2% Oxygen mixture using readily available commercial gas exchange and modulated PSII fluorescence systems. Interpretation of these data, however, requires an understanding (or the development) of various modelling approaches, which limit the use by non-specialists. In this paper we present an accessible summary of the theory behind the analysis and derivation of C4 photosynthetic parameters, and provide a freely available Excel Fitting Tool (EFT), making rigorous C4 data analysis accessible to a broader audience. Outputs include those defining C4 photochemical and biochemical efficiency, the rate of photorespiration, bundle sheath conductance to CO2 diffusion and the in vivo biochemical constants for PEP carboxylase. The EFT compares several methodological variants proposed by different investigators, allowing users to choose the level of complexity required to interpret data. We provide a complete analysis of gas exchange data on maize (as a model C4 organism and key global crop) to illustrate the approaches, their analysis and interpretation. © 2015 John Wiley & Sons Ltd. PMID:26286697

  5. Effect of Adding a Regenerator to Kornhauser's MIT "Two-Space" (Gas-Spring+Heat Exchanger) Test Rig

    NASA Technical Reports Server (NTRS)

    Ebiana, Asuquo B.; Gidugu, Praveen

    2008-01-01

    This study employed entropy-based second law post-processing analysis to characterize the various thermodynamic losses inside a 3-space solution domain (gas spring+heat exchanger+regenerator) operating under conditions of oscillating pressure and oscillating flow. The 3- space solution domain is adapted from the 2-space solution domain (gas spring+heat exchanger) in Kornhauser's MIT test rig by modifying the heat exchanger space to include a porous regenerator system. A thermal nonequilibrium model which assumes that the regenerator porous matrix and gas average temperatures can differ by several degrees at a given axial location and time during the cycle is employed. An important and primary objective of this study is the development and application of a thermodynamic loss post-processor to characterize the major thermodynamic losses inside the 3-space model. It is anticipated that the experience gained from thermodynamic loss analysis of the simple 3-space model can be extrapolated to more complex systems like the Stirling engine. It is hoped that successful development of loss post-processors will facilitate the improvement of the optimization capability of Stirling engine analysis codes through better understanding of the heat transfer and power losses. It is also anticipated that the incorporation of a successful thermal nonequilibrium model of the regenerator in Stirling engine CFD analysis codes, will improve our ability to accurately model Stirling regenerators relative to current multidimensional thermal-equilibrium porous media models.

  6. Estimating oxygen diffusive conductances of gas-exchange systems: A stereological approach illustrated with the human placenta.

    PubMed

    Mayhew, Terry M

    2014-01-01

    For many organisms, respiratory gas exchange is a vital activity and different types of gas-exchange apparatus have evolved to meet individual needs. They include not only skin, gills, tracheal systems and lungs but also transient structures such as the chorioallantois of avian eggs and the placenta of eutherian mammals. The ability of these structures to allow passage of oxygen by passive diffusion can be expressed as a diffusive conductance (units: cm(3) O2 min(-1) kPa(-1)). Occasionally, the ability to estimate diffusive conductance by physiological techniques is compromised by the difficulty of obtaining O2 partial pressures on opposite sides of the tissue interface between the delivery medium (air, water, blood) and uptake medium (usually blood). An alternative strategy is to estimate a morphometric diffusive conductance by combining stereological estimates of key structural quantities (volumes, surface areas, membrane thicknesses) with complementary physicochemical data (O2-haemoglobin chemical reaction rates and Krogh's permeability coefficients). This approach has proved valuable in a variety of comparative studies on respiratory organs from diverse species. The underlying principles were formulated in pioneering studies on the pulmonary lung but are illustrated here by taking the human placenta as the gas exchanger. PMID:23069190

  7. CO 2 and H 2O gas exchange of a triticale field: I. Leaf level porometry and upscaling to canopy level

    NASA Astrophysics Data System (ADS)

    Busch, J.; Lösch, R.; Meixner, F. X.; Ammann, C.

    1996-05-01

    Within the frame of an extended field experiment the CO 2 and H 2O gas exchange between a triticale field and the atmosphere was measured during the period between heading and harvest in the summer of 1995. Diurnal courses of H 2O loss, CO 2 gain and leaf conductance were obtained together with microclimatic parameters for leaves of different insertion levels. Patterns of dependence of leaf gas exchange on microclimatic conditions were determined. Based on the results of porometric measurements and crop structural parameters (LAI) gas exchange was scaled up to canopy level.

  8. Poly-Use Multi-Level Sampling Rod to Measure Soil-Gas Exchange in Glacier Forefield Soils

    NASA Astrophysics Data System (ADS)

    Nauer, P. A.; Schroth, M. H.; Zeyer, J. A.

    2012-12-01

    The forefields of receding glaciers provide unique opportunities to investigate initial microbial processes in the vadose zone and their role in soil formation. Various studies revealed a surprising diversity of microbes and of their strategies to cope with the extreme conditions in this C- and N-limited environment. In the forefield of receding glaciers as well as in developed soils microorganisms are the driving force for the exchange of greenhouse gases between soil and atmosphere. However, in young and developing soils, little is known about soil-gas exchange and the activities of the involved microorganisms. Knowledge of soil-gas composition and gas diffusion at various depths in a soil profile allows for the precise calculation of gas fluxes among different depths within the vadose zone and at the soil-atmosphere boundary. The acquisition of undisturbed soil-gas samples at a high depth-resolution is difficult, and the estimation of soil-gas diffusion coefficients requires knowledge of volumetric water content at the exact location of gas sampling. By using conventional techniques, e.g. the burial of permanent probes, these tasks are virtually impossible to accomplish in a remote glacier forefield dominated by rocks and boulders. We developed a novel poly-use multi-level sampling rod (PULSAR) primarily consisting of two devices: a newly-designed multi-level sampler (MLS) for soil-gas sampling, and a commercially available profile probe (PR2) for non-invasive multi-level water content measurements. These devices fit into the same access tubes (ATs) of 1.1m length, which need to be pre-installed into the soil with the help of a steel rod. We modified the ATs to feature eight 1mm diameter holes each at 20 sampling depths in intervals of 5cm. Our MLS can be inserted into the ATs and allows for the selective extraction of soil-gas from each sampling depth. The interspaces between the sampling depths are sealed by inflatable rubber membranes for the time of sampling

  9. Modelling non-steady-state isotope enrichment of leaf water in a gas-exchange cuvette environment.

    PubMed

    Song, Xin; Simonin, Kevin A; Loucos, Karen E; Barbour, Margaret M

    2015-12-01

    The combined use of a gas-exchange system and laser-based isotope measurement is a tool of growing interest in plant ecophysiological studies, owing to its relevance for assessing isotopic variability in leaf water and/or transpiration under non-steady-state (NSS) conditions. However, the current Farquhar & Cernusak (F&C) NSS leaf water model, originally developed for open-field scenarios, is unsuited for use in a gas-exchange cuvette environment where isotope composition of water vapour (δv ) is intrinsically linked to that of transpiration (δE ). Here, we modified the F&C model to make it directly compatible with the δv -δE dynamic characteristic of a typical cuvette setting. The resultant new model suggests a role of 'net-flux' (rather than 'gross-flux' as suggested by the original F&C model)-based leaf water turnover rate in controlling the time constant (τ) for the approach to steady sate. The validity of the new model was subsequently confirmed in a cuvette experiment involving cotton leaves, for which we demonstrated close agreement between τ values predicted from the model and those measured from NSS variations in isotope enrichment of transpiration. Hence, we recommend that our new model be incorporated into future isotope studies involving a cuvette condition where the transpiration flux directly influences δv . There is an increasing popularity among plant ecophysiologists to use a gas-exchange system coupled to laser-based isotope measurement for investigating non-steady state (NSS) isotopic variability in leaf water (and/or transpiration); however, the current Farquhar & Cernusak (F&C) NSS leaf water model is unsuited for use in a gas-exchange cuvette environment due to its implicit assumption of isotope composition of water vapor (δv ) being constant and independent of that of transpiration (δE ). In the present study, we modified the F&C model to make it compatible with the dynamic relationship between δv and δE as is typically associated

  10. Ecosystem CO2/H2O fluxes are explained by hydraulically limited gas exchange during tree mortality from spruce bark beetles

    NASA Astrophysics Data System (ADS)

    Frank, John M.; Massman, William J.; Ewers, Brent E.; Huckaby, Laurie S.; Negrón, José F.

    2014-06-01

    Disturbances are increasing globally due to anthropogenic changes in land use and climate. This study determines whether a disturbance that affects the physiology of individual trees can be used to predict the response of the ecosystem by weighing two competing hypothesis at annual time scales: (a) changes in ecosystem fluxes are proportional to observable patterns of mortality or (b) to explain ecosystem fluxes the physiology of dying trees must also be incorporated. We evaluate these hypotheses by analyzing 6 years of eddy covariance flux data collected throughout the progression of a spruce beetle (Dendroctonus rufipennis) epidemic in a Wyoming Engelmann spruce (Picea engelmannii)-subalpine fir (Abies lasiocarpa) forest and testing for changes in canopy conductance (gc), evapotranspiration (ET), and net ecosystem exchange (NEE) of CO2. We predict from these hypotheses that (a) gc, ET, and NEE all diminish (decrease in absolute magnitude) as trees die or (b) that (1) gc and ET decline as trees are attacked (hydraulic failure from beetle-associated blue-stain fungi) and (2) NEE diminishes both as trees are attacked (restricted gas exchange) and when they die. Ecosystem fluxes declined as the outbreak progressed and the epidemic was best described as two phases: (I) hydraulic failure caused restricted gc, ET (28 ± 4% decline, Bayesian posterior mean ± standard deviation), and gas exchange (NEE diminished 13 ± 6%) and (II) trees died (NEE diminished 51 ± 3% with minimal further change in ET to 36 ± 4%). These results support hypothesis b and suggest that model predictions of ecosystem fluxes following massive disturbances must be modified to account for changes in tree physiological controls and not simply observed mortality.

  11. Leaf gas exchange and carbohydrates in tropical trees differing in successional status in two light environments in central Amazonia.

    PubMed

    Marenco, R A; de C Gonçalves, J F; Vieira, G

    2001-12-01

    Monoculture and mixed stands of mahogany (Swietenia macrophylla King) and tonka bean (Dipteryx odorata Willd.) trees were established on degraded land in central Amazonia to compare leaf gas exchange parameters between plants grown in sunlight in an open field and in shade beneath a balsa wood (Ochroma pyramidale Cav.) canopy. Shading increased specific leaf area by about 50% in both species. Shading reduced height and diameter growth of S. macrophylla, whereas it increased these parameters for D. odorata. Light-saturated photosynthesis (Amax), stomatal conductance (gs) and transpiration (E) were higher in S. macrophylla than in D. odorata. In S. macrophylla, Amax was higher in sun leaves (12.9 +/- 0.9 micromol m-2 s-1) than in shade leaves (10.2 +/- 1.0 micromol m-2 s-1), whereas light environment had no significant effect on Amax of D. odorata. In both species, CO2-saturated photosynthesis (Apot) was higher in sun leaves (22 +/- 1.4 micromol m-2 s-1) than in shade leaves (17-20 +/- 0.8 micromol m-2 s-1). Stomatal conductance and E increased in sun leaves of S. macrophylla by 45 and 38%, respectively, whereas light environment did not affect gs and E of D. odorata. Photorespiration rates (Pr) varied from 28 to 36% of net photosynthesis (A) at ambient atmospheric CO2 concentration (Ca) but declined to around 7% of A at higher Ca. Leaf dark respiration (Rd) and the CO2 compensation point (Gamma) were lower in shade-grown plants than in open-grown plants. Compared with shade-grown plants, total nonstructural carbohydrate (TNC) concentrations increased by 56% in S. macrophylla and by 30% in D. odorata in the open field. Leaf nitrogen (NL) concentrations were higher in open-grown plants than in shade-grown plants of both species, and TNC and NL concentrations were negatively correlated (r = -0.77). High TNC accumulation in S. macrophylla in the open field suggests that photosynthesis is unlikely to be growth-limiting at this site. We conclude that photosynthetic

  12. Experimental and Numerical Investigation of Guest Molecule Exchange Kinetics based on the 2012 Ignik Sikumi Gas Hydrate Field Trial

    NASA Astrophysics Data System (ADS)

    Ruprecht Yonkofski, C. M.; Horner, J.; White, M. D.

    2015-12-01

    In 2012 the U.S. DOE/NETL, ConocoPhillips Company, and Japan Oil, Gas and Metals National Corporation jointly sponsored the first field trial of injecting a mixture of N2-CO2 into a CH4-hydrate bearing formation beneath the permafrost on the Alaska North Slope. Known as the Ignik Sikumi #1 Gas Hydrate Field Trial, this experiment involved three stages: 1) the injection of a N2-CO2 mixture into a targeted hydrate-bearing layer, 2) a 4-day pressurized soaking period, and 3) a sustained depressurization and fluid production period. Data collected during the three stages of the field trial were made available after a thorough quality check. The Ignik Sikumi #1 data set is extensive, but contains no direct evidence of the guest-molecule exchange process. This study uses numerical simulation to provide an interpretation of the CH4/CO2/N2 guest molecule exchange process that occurred at Ignik Sikumi #1. Simulations were further informed by experimental observations. The goal of the scoping experiments was to understand kinetic exchange rates and develop parameters for use in Iġnik Sikumi history match simulations. The experimental procedure involves two main stages: 1) the formation of CH4 hydrate in a consolidated sand column at 750 psi and 2°C and 2) flow-through of a 77.5/22.5 N2/CO2 molar ratio gas mixture across the column. Experiments were run both above and below the hydrate stability zone in order to observe exchange behavior across varying conditions. The numerical simulator, STOMP-HYDT-KE, was then used to match experimental results, specifically fitting kinetic behavior. Once this behavior is understood, it can be applied to field scale models based on Ignik Sikumi #1.

  13. Carbon nano-chain and carbon nano-fibers based gas diffusion layers for proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Kannan, Arunachala M.; Munukutla, Lakshmi

    Gas diffusion layers (GDL) for proton exchange membrane fuel cell have been developed using a partially ordered graphitized nano-carbon chain (Pureblack ® carbon) and carbon nano-fibers. The GDL samples' characteristics such as, surface morphology, surface energy, bubble-point pressure and pore size distribution were characterized using electron microscope, inverse gas chromatograph, gas permeability and mercury porosimetry, respectively. Fuel cell performance of the GDLs was evaluated using single cell with hydrogen/air at ambient pressure, 70 °C and 100% RH. The GDLs with combination of vapor grown carbon nano-fibers with Pureblack carbon showed significant improvement in mechanical robustness as well as fuel cell performance. The micro-porous layer of the GDLs as seen under scanning electron microscope showed excellent surface morphology showing the reinforcement with nano-fibers and the surface homogeneity without any cracks.

  14. Factors affecting the chemical exchange saturation transfer of Creatine as assessed by 11.7 T MRI.

    PubMed

    Saito, Shigeyoshi; Mori, Yuki; Tanki, Nobuyoshi; Yoshioka, Yoshichika; Murase, Kenya

    2015-01-01

    Chemical exchange saturation transfer (CEST) is a new contrast enhancement approach for imaging exogenous or endogenous substances such as creatine (Cr), amide protons, and glutamate in the human body. An increase in field strength is beneficial for CEST imaging because of the increased chemical shift and longer longitudinal relaxation time (T1). In high-field magnetic resonance imaging (MRI), establishing and evaluating the CEST effect is important for optimizing the magnetization transfer (MT) saturation radio frequency (RF) pulses. In this study, the CEST effect on Cr was evaluated at different concentrations in pH phantoms by appropriately selecting MT saturation RF pulses using 11.7 T MRI. The results showed that the CEST efficiency increased gradually with increasing applied saturation RF pulse power and that it was affected by the number of saturation RF pulses and their bandwidths. However, spillover effects were observed with higher saturation RF pulse powers. In conclusion, we successfully performed in vitro Cr CEST imaging under optimized conditions of MT saturation RF pulses. PMID:25477238

  15. Placental Hypoxia Developed During Preeclampsia Induces Telocytes Apoptosis in Chorionic Villi Affecting The Maternal-Fetus Metabolic Exchange.

    PubMed

    Bosco, Cleofina Becerra; Díaz, Eugenia Guerra; Gutierrez, Rodrigo Rojas; González, Jaime Montero; Parra-Cordero, Mauro; Rodrigo, Ramón Salinas; Barja, Pilar Yañez

    2016-01-01

    Telocytes (TC) are a new type of stromal cells initially found and studied in digestive and extra- digestive organs. These cells have a small cell body with 2 to 5 thin and extremely long cytoplasmic prolongations named telopodes. In recent years, TC have also been described in placental chorionic villi, located in a strategical position between the smooth muscle cells from fetal vessels and the myofibroblasts in the stromal villi. Unlike other organs, the placenta is not innervated and considering the strategic location of TC is has been postulated that TC function would be related to signal transduction mechanisms involved in the regulation of the fetal vessels blood flow, as well as in the shortening/lengthening of the chorionic villi, providing the necessary rhythmicity to the process of maternal/fetal metabolic exchange. Preeclampsia (PE) is a systemic syndrome that affects 4%-6% of pregnancies worldwide. It is characterized by a placental state of ischemia-hypoxia which triggers an oxidative stress stage with the concomitant production of reactive oxygen species (ROS) leading to an increase in the degree of placental apoptosis. Placental vascular tone is regulated by the vasodilator nitric oxide (NO) and, in PE cases, NO is diverted towards the formation of peroxynitrite, a powerful oxidative agent whose activity leads to an increase of placental apoptosis degree that compromises TC and myofibroblasts, a key feature we would like to emphasize in this work. PMID:25643124

  16. How do leader-member exchange quality and differentiation affect performance in teams? An integrated multilevel dual process model.

    PubMed

    Li, Alex Ning; Liao, Hui

    2014-09-01

    Integrating leader-member exchange (LMX) research with role engagement theory (Kahn, 1990) and role system theory (Katz & Kahn, 1978), we propose a multilevel, dual process model to understand the mechanisms through which LMX quality at the individual level and LMX differentiation at the team level simultaneously affect individual and team performance. With regard to LMX differentiation, we introduce a new configural approach focusing on the pattern of LMX differentiation to complement the traditional approach focusing on the degree of LMX differentiation. Results based on multiphase, multisource data from 375 employees of 82 teams revealed that, at the individual level, LMX quality positively contributed to customer-rated employee performance through enhancing employee role engagement. At the team level, LMX differentiation exerted negative influence on teams' financial performance through disrupting team coordination. In particular, teams with the bimodal form of LMX configuration (i.e., teams that split into 2 LMX-based subgroups with comparable size) suffered most in team performance because they experienced greatest difficulty in coordinating members' activities. Furthermore, LMX differentiation strengthened the relationship between LMX quality and role engagement, and team coordination strengthened the relationship between role engagement and employee performance. Theoretical and practical implications of the findings are discussed. PMID:25000359

  17. Mass transport in gas diffusion layers of proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Martinez, Michael J.

    This dissertation describes fundamental properties of gas diffusion media (GDM) and their relationship to the mass transport in proton exchange membrane fuel cells (PEMFCs). First, the accuracy of solving the multi-component equations for PEMFC by using a computational fluid dynamics (CFD) technique is examined. This technique uses an approximated multi-component (AMC) model with a correction term that guarantees the overall mass balance. Accuracy is assessed by comparing the species concentrations computed with the Maxwell-Stefan and the AMC model. This comparison is important because the structure of some CFD programs does not permit the direct use of the Maxwell-Stefan equations. Here, it is shown that the maximum error between the two models is less than 5%. Second, the ratio of tortuosity to porosity, known as the MacMullin number, is reported for different carbon cloth and carbon paper GDM. This analysis show that only carbon cloths GDM follow the commonly accepted Bruggeman equation and that carbon paper GDM have a different relationship between the tortuosity and the porosity. These differences are discussed in terms of path length created by the orientation of fibers of each GDM. Third, data for the hydrophilic and hydrophobic pore size distributions (PSD) are presented for two types of GDM used in PEMFCs. The data were obtained by using two common measurement methods, intrusion porosimetry (IP) and the method of standard porosimetry (MSP). The use of multiple working fluids to access hydrophilic and hydrophobic pores is discussed as well as the limitations associated with structural changes of the GDM during the tests. The differences in interpretations of the data between the two methods for both GDM have significant implications relative to the distribution of hydrophilic and hydrophobic pores that control liquid water transport. Finally, a two-phase mass-transport-only model (MTOM) that incorporates the tortuosity and the PSD data described above is

  18. Gas exchange characteristics of Populus trichocarpa, Populus deltoides and Populus trichocarpa x P. deltoides clones.

    PubMed

    Bassman, J H; Zwier, J C

    1991-03-01

    Responses of net photosynthesis, dark respiration, photorespiration, transpiration, and stomatal conductance to irradiance, temperature, leaf-to-air vapor density difference (VDD), and plant water stress were examined in two Populus trichocarpa clones (one from a moist, coastal climate in western Washington and one from a dry, continental climate in eastern Washington), one P. deltoides clone, and two P. trichocarpa x P. deltoides clones. Light saturation of photosynthesis in greenhouse-grown trees occurred at about 800 micromol m(-2) s(-1) for P. deltoides, P. trichocarpa x P. deltoides, and the eastern Washington ecotype of P. trichocarpa, but at about 600 micromol m(-2) s(-1) for the western Washington ecotype of P. trichocarpa. Average net photosynthesis (at saturating irradiance and the optimum temperature of 25 degrees C) was 20.7, 18.8, 18.2 and 13.4 micromol CO(2) m(-2) s(-1) for P. deltoides, P. trichocarpa x P. deltoides, and the eastern and western Washington clones of P. trichocarpa, respectively. In all clones, net photosynthesis decreased about 14% as VDD increased from 3 to 18 g H(2)O m(-3). Stomatal conductance decreased sharply with decreasing xylem pressure potential (XPP) in all clones except the western Washington clone of P. trichocarpa. Stomata in this clone were insensitive to changes in XPP and did not control water loss. Complete stomatal closure (stomatal conductance < 0.05 cm s(-1)) occurred at about -2.0 MPa in the eastern Washington clone of P. trichocarpa and around -1.25 MPa in the P. deltoides and P. trichocarpa x P. deltoides clones. Transpiration rates were highest in the P. trichocarpa x P. deltoides clone and lowest in the western Washington clone of P. trichocarpa. The P. deltoides clone and eastern Washington clone of P. trichocarpa had the highest water use efficiency (WUE) and the western Washington clone of P. trichocarpa had the lowest WUE. The hybrids were intermediate. It was concluded that: (1) gas exchange

  19. Effects of drought on leaf gas exchange in an eastern broadleaf deciduous forest

    NASA Astrophysics Data System (ADS)

    Roman, D. T.; Brzostek, E. R.; Dragoni, D.; Rahman, A. F.; Novick, K. A.; Phillips, R.

    2013-12-01

    Understanding plant physiological adaptations to drought is critical for predicting changes in ecosystem productivity that result from climate variability and future climate change. From 2011-2013, southern Indiana experienced a late growing season drought in 2011, a severe early season drought in 2012, and a wet growing season in 2013 characterized by an absence of water stress with frequent precipitation and milder temperatures. The 2012 drought was unique due to the severity and early onset drought conditions (compared to the more frequent late season drought) and was characterized by a Palmer Drought severity index below -4 and precipitation totals from May - July that were 70% less than the long-term (2000 - 2010) mean. During the 2012 drought, an 11% decline in net ecosystem productivity relative to the long-term mean was observed at the AmeriFlux tower in Morgan Monroe State Forest despite a growing season that started ~25 days earlier. Thus, the objective of this study is to evaluate species-specific contributions to the canopy-scale response to inter-annual variability in water stress. We investigated differences between tree species in their response to climate variability using weekly leaf gas exchange and leaf water potential measurements during the growing seasons of 2011-2013. We used this unique dataset, collected at the top of the canopy with a 25 m boom lift, to evaluate changes in leaf water status and maximum assimilation capacity in the drought versus non-drought years. The leaf-level physiology of oak (Quercus) species appears to be less sensitive to drought than other species (tulip poplar [Liriodendron tulipifera], sassafras [Sassafras albidum] and sugar maple [Acer saccharum]). Preliminary data shows mean canopy leaf water potential for oaks was 30.5% more negative in May-July 2012 versus the same time period in 2013. During these same periods the rate of C assimilation in oaks was reduced by only 3%, whereas other species were reduced by

  20. Effects of Lung Volume Reduction Surgery on Gas Exchange and Breathing Pattern During Maximum Exercise

    PubMed Central

    Criner, Gerard J.; Belt, Patricia; Sternberg, Alice L.; Mosenifar, Zab; Make, Barry J.; Utz, James P.; Sciurba, Frank

    2009-01-01

    Background: The National Emphysema Treatment Trial studied lung volume reduction surgery (LVRS) for its effects on gas exchange, breathing pattern, and dyspnea during exercise in severe emphysema. Methods: Exercise testing was performed at baseline, and 6, 12, and 24 months. Minute ventilation (V̇e), tidal volume (Vt), carbon dioxide output (V̇co2), dyspnea rating, and workload were recorded at rest, 3 min of unloaded pedaling, and maximum exercise. Pao2, Paco2, pH, fraction of expired carbon dioxide, and bicarbonate were also collected in some subjects at these time points and each minute of testing. There were 1,218 patients enrolled in the study (mean [± SD] age, 66.6 ± 6.1 years; mean, 61%; mean FEV1, 0.77 ± 0.24 L), with 238 patients participating in this substudy (mean age, 66.1 ± 6.8 years; mean, 67%; mean FEV1, 0.78 ± 0.25 L). Results: At 6 months, LVRS patients had higher maximum V̇e (32.8 vs 29.6 L/min, respectively; p = 0.001), V̇co2, (0.923 vs 0.820 L/min, respectively; p = 0.0003), Vt (1.18 vs 1.07 L, respectively; p = 0.001), heart rate (124 vs 121 beats/min, respectively; p = 0.02), and workload (49.3 vs 45.1 W, respectively; p = 0.04), but less breathlessness (as measured by Borg dyspnea scale score) [4.4 vs 5.2, respectively; p = 0.0001] and exercise ventilatory limitation (49.5% vs 71.9%, respectively; p = 0.001) than medical patients. LVRS patients with upper-lobe emphysema showed a downward shift in Paco2 vs V̇co2 (p = 0.001). During exercise, LVRS patients breathed slower and deeper at 6 months (p = 0.01) and 12 months (p = 0.006), with reduced dead space at 6 months (p = 0.007) and 24 months (p = 0.006). Twelve months after patients underwent LVRS, dyspnea was less in patients with upper-lobe emphysema (p = 0.001) and non–upper-lobe emphysema (p = 0.007). Conclusion: During exercise following LVRS, patients with severe emphysema improve carbon dioxide elimination and dead space, breathe slower and deeper, and report less dyspnea

  1. Soil-atmosphere trace gas exchange from tropical oil palm plantations on peat

    NASA Astrophysics Data System (ADS)

    Arn Teh, Yit; Manning, Frances; Zin Zawawi, Norliyana; Hill, Timothy; Chocholek, Melanie; Khoon Kho, Lip

    2015-04-01

    Oil palm is the largest agricultural crop in the tropics, accounting for 13 % of all tropical land cover. Due to its large areal extent, oil palm cultivation may have important implications not only for terrestrial stores of C and N, but may also impact regional and global exchanges of material and energy, including fluxes of trace gases and water vapor. In particular, recent expansion of oil palm into tropical peatlands has raised concerns over enhanced soil C emissions from degradation of peat, and elevated N-gas fluxes linked to N fertilizer application. Here we report our preliminary findings on soil carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) fluxes from a long-term, multi-scale project investigating the C, N and greenhouse gas (GHG) dynamics of oil palm ecosystems established on peat soils in Sarawak, Malaysian Borneo. Flux chamber measurements indicate that soil CO2, CH4 and N2O fluxes averaged 20.0 ± 16.0 Mg CO2-C ha-1 yr-1, 37.4 ± 29.9 kg CH4-C ha-1 yr-1 and 4.7 ± 4.2 g N2O-N ha-1 yr-1, respectively. Soil CO2 fluxes were on par with other drained tropical peatlands; whereas CH4 fluxes exceeded observations from similar study sites elsewhere. Nitrous oxide fluxes were in a similar range to fluxes from other drained tropical peatlands, but lower than emissions from mineral-soil plantations by up to three orders of magnitude. Fluxes of soil CO2 and N2O were spatially stratified, and contingent upon the distribution of plants, deposited harvest residues, and soil moisture. Soil CO2 fluxes were most heavily influenced by the distribution of palms and their roots. On average, autotrophic (root) respiration accounted for approximately 78 % of total soil CO2 flux, and total soil respiration declined steeply away from palms; e.g. soil CO2 fluxes in the immediate 1 m radius around palms were up to 6 times greater than fluxes in inter-palm spaces due to higher densities of roots. Placement of harvest residues played an important - but secondary

  2. Greenhouse gas exchange in West African savanna ecosystems - how important are emissions from termite mounds?

    NASA Astrophysics Data System (ADS)

    Brümmer, C.; Brüggemann, N.

    2012-04-01

    Savannas cover large areas of the Earth's surface and play an important role in global carbon and nitrogen cycling. In this study, we present the soil-atmosphere exchange of N2O, CH4, and CO2 during two field campaigns throughout the growing seasons 2005 and 2006 at a natural savanna site that was not subject to human disturbances except for annual burning, and four agricultural sites planted with sorghum (n=2), cotton and peanut in Burkina Faso. The annual N2O emission of the nature reserve site amounted to 0.52 kg N2O-N ha-1 yr-1 in 2005 and to 0.67 kg N2O-N ha-1 yr-1 in 2006, whereas the calculated average annual N2O release of the crop sites was only 0.19 and 0.20 kg N2O-N ha-1 yr-1 in 2005 and 2006, respectively. As a result of a temporal up-scaling approach, a lower bound of annual N2O release could be given for two fertilized sorghum plots, that is, 0.83 kg N2O-N ha-1 yr-1 for a highly fertilized plot and 0.44 kg N2O-N ha-1 yr-1 for a moderately fertilized plot. During the rainy season both CH4 uptake in the range of up to 20 μg CH4-C m-2 h-1 as well as CH4 emission up to 300 μg CH4-C m-2 h-1 were observed at the nature reserve site, which was on average a CH4 source of 87.4 and 30.8 μg CH4-C m-2 h-1 in 2005 and 2006, respectively. All crop sites were on average weak CH4 sinks without significant seasonal variation. Uptake rates ranged between 2.5 and 8.7 μg CH4-C m-2 h-1. Occasionally very low net CH4 emission was observed after heavy rainfall events. Mean annual CH4 rates could be estimated to 2.48 kg CH4-C ha-1 yr-1 and -0.68 kg CH4-C ha-1 yr-1 for the nature reserve site and the crop sites, respectively. Trace gas emissions from termite (Cubitermes fungifaber) mounds that were almost exclusively found at the nature reserve were one order of magnitude higher for N2O and CO2, and two orders of magnitude higher for CH4 than soil emissions of the respective trace gas. Termite N2O, CH4 and CO2 release at the nature reserve contributed only 3.2%, 8.1% and

  3. Water emergence from the land region and water-sidewall interactions in Proton Exchange Membrane Fuel Cell gas channels with microgrooves

    NASA Astrophysics Data System (ADS)

    Shah, Mihir M.; Kandlikar, Satish G.

    2015-11-01

    Liquid water produced in a Proton Exchange Membrane Fuel Cell (PEMFC) can adversely affect the fuel cell performance in two ways: (a) reduction in surface area available for reactant transport at the channel-gas diffusion layer (GDL) interface, and (b) increase in two-phase pressure drop in channels leading to flow maldistribution and increased pumping power. Further, the channels blocked by water reduce reactant availability at reaction sites. Most of the earlier water transport studies were focused on water droplet formation on the gas diffusion layer (GDL) in the channel and its removal from the gas flow without considering the sidewall interactions. In an actual fuel cell, water under the land emerges in the channel and fills the corner, drawing in additional water from the GDL surface. The present work explores water droplet-sidewall interactions and the transport of water from the corner region. Transverse micro-grooves are introduced on the sidewalls and their effect on water removal from the corner region, flow patterns, area coverage ratio and pressure drop are investigated. The micro-grooves are also seen to introduce a wetting regime that facilitates removal of water at the channel exit without causing blockage at the manifold region.

  4. Treating cattle with antibiotics affects greenhouse gas emissions, and microbiota in dung and dung beetles.

    PubMed

    Hammer, Tobin J; Fierer, Noah; Hardwick, Bess; Simojoki, Asko; Slade, Eleanor; Taponen, Juhani; Viljanen, Heidi; Roslin, Tomas

    2016-05-25

    Antibiotics are routinely used to improve livestock health and growth. However, this practice may have unintended environmental impacts mediated by interactions among the wide range of micro- and macroorganisms found in agroecosystems. For example, antibiotics may alter microbial emissions of greenhouse gases by affecting livestock gut microbiota. Furthermore, antibiotics may affect the microbiota of non-target animals that rely on dung, such as dung beetles, and the ecosystem services they provide. To examine these interactions, we treated cattle with a commonly used broad-spectrum antibiotic and assessed downstream effects on microbiota in dung and dung beetles, greenhouse gas fluxes from dung, and beetle size, survival and reproduction. We found that antibiotic treatment restructured microbiota in dung beetles, which harboured a microbial community distinct from those in the dung they were consuming. The antibiotic effect on beetle microbiota was not associated with smaller size or lower numbers. Unexpectedly, antibiotic treatment raised methane fluxes from dung, possibly by altering the interactions between methanogenic archaea and bacteria in rumen and dung environments. Our findings that antibiotics restructure dung beetle microbiota and modify greenhouse gas emissions from dung indicate that antibiotic treatment may have unintended, cascading ecological effects that extend beyond the target animal. PMID:27226475

  5. Dynamic C and N stocks - key factors controlling the C gas exchange of maize in a heterogenous peatland

    NASA Astrophysics Data System (ADS)

    Pohl, M.; Hoffmann, M.; Hagemann, U.; Giebels, M.; Albiac Borraz, E.; Sommer, M.; Augustin, J.

    2014-11-01

    Drainage and cultivation of fen peatlands creates complex small-scale mosaics of soils with extremely variable soil organic carbon (SOC) stocks and groundwater-level (GWL). To date, it remains unclear if such sites are sources or sinks for greenhouse gases like CO2 and CH4, especially if used for cropland. As individual control factors like GWL fail to account for this complexity, holistic approaches combining gas fluxes with the underlying processes are required to understand the carbon (C) gas exchange of drained fens. It can be assumed that the stocks of SOC and N located above the variable GWL - defined as dynamic C and N stocks - play a key role in the regulation of plant- and microbially mediated C gas fluxes of these soils. To test this assumption, the present study analysed the C gas exchange (gross primary production - GPP, ecosystem respiration - Reco, net ecosystem exchange - NEE, CH4) of maize using manual chambers for four years. The study sites were located near Paulinenaue, Germany. Here we selected three soils, which represent the full gradient in pedogenesis, GWL and SOC stocks (0-1 m) of the fen peatland: (a) Haplic Arenosol (AR; 8 kg C m-2); (b) Mollic Gleysol (GL; 38 kg C m-2); and (c) Hemic Histosol (HS; 87 kg C m-2). Daily GWL data was used to calculate dynamic SOC (SOCdyn) and N (Ndyn) stocks. Average annual NEE differed considerably among sites, ranging from 47 ± 30 g C m-2 a-1 at AR to -305 ± 123 g C m-2 a-1 at GL and -127 ± 212 g C m-2 a-1 at HS. While static SOC and N stocks showed no significant effect on C fluxes, SOCdyn and Ndyn and their interaction with GWL strongly influenced the C gas exchange, particularly NEE and the GPP:Reco ratio. Moreover, based on nonlinear regression analysis, 86% of NEE variability was explained by GWL and SOCdyn. The observed high relevance of dynamic SOC and N stocks in the aerobic zone for plant and soil gas exchange likely originates from the effects of GWL-dependent N availability on C formation and

  6. Gas exchange in seawater with special emphasis on open-cycle ocean thermal energy conversion

    SciTech Connect

    Zapka, M.J.

    1988-01-01

    This study examined gas-transfer characteristics of seawater. Special emphasis is on gas-transfer processes in connection with Open-Cycle Ocean Thermal Energy Conversion (OC-OTEC) applications. Experiments probed the mechanism regulating gas transfer in bubbles and in a packed column. In order to compare gas transfer in seawater with extensively documented transfer characteristics of fresh water, all tests were conducted using both seawater and fresh water in the same experimental setting. Ten main findings are listed and briefly discussed. With appropriate system conditions, an approximately 85% removal of dissolved gas from the OC-OTEC feed stream appears to be feasible.

  7. Effect of N-acetylcysteine on gas exchange after methacholine challenge and isoprenaline inhalation in the dog.

    PubMed

    Ueno, O; Lee, L N; Wagner, P D

    1989-03-01

    N-acetylcysteine (NAC) has antioxidant and possibly mucolytic properties. To determine whether NAC could be of benefit in acute bronchoconstriction induced by methacholine, 12 of 24 anaesthetized dogs (group 1) received NAC i.v. (loading dose 150 mg.kg-1, then 20 mg.kg-1.hr-1). The other 12 (group 2) received diluent. Nebulized methacholine (1%) was then inhaled until arterial oxygen tension (PaO2) fell to a mean of 5.5 kPa, after which isoprenaline 0.5% was inhaled in six dogs of each group to reverse bronchoconstriction. Over the next 3 h we measured total lung resistance, functional residual capacity (FRC), haemodynamic variables, and pulmonary gas exchange for respiratory and inert gases. After methacholine challenge, lung resistance increased and then fell similarly for both groups, but PaO2 was higher in the NAC group (by 0.6-1.9 kPa) throughout the observation period. The ventilation-perfusion distribution measured by inert gas elimination also showed less abnormality in the NAC treated dogs over this time. Mucus was visible during post-mortem in the large airways in about half of the dogs in both groups, with no significant differences between them. These results show that NAC produces a measurable improvement in gas exchange following methacholine challenge (both with and without subsequent isoprenaline therapy) by mechanisms that remain to be determined. PMID:2659384

  8. Measuring air-sea gas-exchange velocities in a large-scale annular wind-wave tank

    NASA Astrophysics Data System (ADS)

    Mesarchaki, E.; Kräuter, C.; Krall, K. E.; Bopp, M.; Helleis, F.; Williams, J.; Jähne, B.

    2015-01-01

    In this study we present gas-exchange measurements conducted in a large-scale wind-wave tank. Fourteen chemical species spanning a wide range of solubility (dimensionless solubility, α = 0.4 to 5470) and diffusivity (Schmidt number in water, Scw = 594 to 1194) were examined under various turbulent (u10 = 0.73 to 13.2 m s-1) conditions. Additional experiments were performed under different surfactant modulated (two different concentration levels of Triton X-100) surface states. This paper details the complete methodology, experimental procedure and instrumentation used to derive the total transfer velocity for all examined tracers. The results presented here demonstrate the efficacy of the proposed method, and the derived gas-exchange velocities are shown to be comparable to previous investigations. The gas transfer behaviour is exemplified by contrasting two species at the two solubility extremes, namely nitrous oxide (N2O) and methanol (CH3OH). Interestingly, a strong transfer velocity reduction (up to a factor of 3) was observed for the relatively insoluble N2O under a surfactant covered water surface. In contrast, the surfactant effect for CH3OH, the high solubility tracer, was significantly weaker.

  9. Does nitrogen gas bubbled through a low density polymer gel dosimeter solution affect the polymerization process?

    PubMed Central

    Shahbazi-Gahrouei, Daryoush; Gholami, Mehrdad; Pourfallah, Tayyeb Allahverdi; Keshtkar, Mohammad

    2015-01-01

    Background: On account of the lower electron density in the lung tissue, the dose distribution in the lung cannot be verified with the existing polymer gel dosimeters. Thus, the aims of this study are to make a low density polymer gel dosimeter and investigate the effect of nitrogen gas bubbles on the R2 responses and its homogeneity. Materials and Methods: Two different types of low density polymer gel dosimeters were prepared according to a composition proposed by De Deene, with some modifications. In the first type, no nitrogen gas was perfused through the gel solution and water. In the second type, to expel the dissolved oxygen, nitrogen gas was perfused through the water and gel solution. The post-irradiation times in the gels were 24 and 5 hours, respectively, with and without perfusion of nitrogen gas through the water and gel solution. Results: In the first type of gel, there was a linear correlation between the doses and R2 responses from 0 to 12 Gy. The fabricated gel had a higher dynamic range than the other low density polymer gel dosimeter; but its background R2 response was higher. In the second type, no difference in R2 response was seen in the dose ranges from 0 to 18 Gy. Both gels had a mass density between 0.35 and 0.45 g.cm-3 and CT values of about -650 to -750 Hounsfield units. Conclusion: It appeared that reactions between gelatin-free radicals and monomers, due to an increase in the gel temperature during rotation in the household mixer, led to a higher R2-background response. In the second type of gel, it seemed that the collapse of the nitrogen bubbles was the main factor that affected the R2-responses. PMID:26015914

  10. Dynamic C and N stocks - key factors controlling the C gas exchange of maize in heterogenous peatland

    NASA Astrophysics Data System (ADS)

    Pohl, M.; Hoffmann, M.; Hagemann, U.; Giebels, M.; Albiac Borraz, E.; Sommer, M.; Augustin, J.

    2015-05-01

    The drainage and cultivation of fen peatlands create complex small-scale mosaics of soils with extremely variable soil organic carbon (SOC) stocks and groundwater levels (GWLs). To date, the significance of such sites as sources or sinks for greenhouse gases such as CO2 and CH4 is still unclear, especially if the sites are used for cropland. As individual control factors such as GWL fail to account for this complexity, holistic approaches combining gas fluxes with the underlying processes are required to understand the carbon (C) gas exchange of drained fens. It can be assumed that the stocks of SOC and N located above the variable GWL - defined as dynamic C and N stocks - play a key role in the regulation of the plant- and microbially mediated CO2 fluxes in these soils and, inversely, for CH4. To test this assumption, the present study analysed the C gas exchange (gross primary production - GPP; ecosystem respiration - Reco; net ecosystem exchange - NEE; CH4) of maize using manual chambers for 4 years. The study sites were located near Paulinenaue, Germany, where we selected three soil types representing the full gradient of GWL and SOC stocks (0-1 m) of the landscape: (a) Haplic Arenosol (AR; 8 kg C m-2); (b) Mollic Gleysol (GL; 38 kg C m-2); and (c) Hemic Histosol (HS; 87 kg C m-2). Daily GWL data were used to calculate dynamic SOC (SOCdyn) and N (Ndyn) stocks. Average annual NEE differed considerably among sites, ranging from 47 ± 30 g C m-2 yr-1 in AR to -305 ± 123 g C m-2 yr-1 in GL and -127 ± 212 g C m-2 yr-1 in HS. While static SOC and N stocks showed no significant effect on C fluxes, SOCdyn and Ndyn and their interaction with GWL strongly influenced the C gas exchange, particularly NEE and the GPP : Reco ratio. Moreover, based on nonlinear regression analysis, 86% of NEE variability was explained by GWL and SOCdyn. The observed high relevance of dynamic SOC and N stocks in the aerobic zone for plant and soil gas exchange likely originates from the

  11. Usefulness of Decrease in Oxygen Uptake Efficiency to Identify Gas Exchange Abnormality in Patients with Idiopathic Pulmonary Arterial Hypertension

    PubMed Central

    Yang, Wenlan; Guo, Jian; Zhang, Yan; Sapkota, Rikesh; Kushwaha, Shailendra Prasad; Gong, Sugang; Sun, Xingguo; Liu, Jinming

    2014-01-01

    Background Decline in oxygen uptake efficiency (OUE), especially during exercise, is found in patients with chronic heart failure. In this study we aimed to test the validity and usefulness of OUE in evaluating gas exchange abnormality of patients with idiopathic pulmonary arterial hypertension (IPAH). Methods We retrospectively investigated the cardiopulmonary exercise test (CPET) with gas exchange measurements in 32 patients with confirmed IPAH. All patients also had resting hemodynamic measurements and pulmonary function test (PFT). Sixteen healthy subjects, matched by age, sex, and body size were used as controls, also had CPET and PFT measurements. Results In IPAH patients, the magnitude of absolute and percentage of predicted (%pred) oxygen uptake efficiency slope (OUES) and oxygen uptake efficiency plateau (OUEP), as well as several other CPET parameters, were strikingly worse than healthy subjects (P<0.0001). Pattern of changes in OUE in patients is similar to that in controls, In IPAH patients, OUE values at rest, warming up, anaerobic threshold and peak exercise were all significantly lower than in normal (P<0.0001). OUEP%pred, better than OUES%pred, correlated significantly with New York Heart Association (NYHA) functional Class (r = −0.724, P<0.005), Total Pulmonary Vascular Resistance (TPVR) (r = −0.694, P<0.005), diffusing capacity for carbon monoxide (DLCO) (r = 0.577, P<0.05), and the lowest ventilation versus CO2 output ratio during exercise (LowestV˙E/V˙CO2) (r = −0.902, P<0.0001). In addition, the coefficient of variation (COV) of OUEP was lower (20.9%) markedly than OUES (34.3%) (P<0.0001). Conclusions In patients with IPAH, OUES and OUEP are both significantly lower than the healthy subjects. OUEP is a better physiological parameter than OUES in evaluating the gas exchange abnormality of patients with IPAH. PMID:24905576

  12. Toxicodynamics of rigid polystyrene microparticles on pulmonary gas exchange in mice: implications for microemboli-based drug delivery systems.

    PubMed

    Kutscher, H L; Gao, D; Li, S; Massa, C B; Cervelli, J; Deshmukh, M; Joseph, L B; Laskin, D L; Sinko, P J

    2013-01-15

    The toxicodynamic relationship between the number and size of pulmonary microemboli resulting from uniformly sized, rigid polystyrene microparticles (MPs) administered intravenously and their potential effects on pulmonary gas exchange were investigated. CD-1 male mice (6-8 weeks) were intravenously administered 10, 25 and 45 μm diameter MPs. Oxygen hemoglobin saturation in the blood (SpO(2)) was measured non-invasively using a pulse oximeter while varying inhaled oxygen concentration (F(I)O(2)). The resulting data were fit to a physiologically based non-linear mathematical model that estimates 2 parameters: ventilation-perfusion ratio (V(A)/Q) and shunt (percentage of deoxygenated blood returning to systemic circulation). The number of MPs administered prior to a statistically significant reduction in normalized V(A)/Q was dependent on particle size. MP doses that resulted in a significant reduction in normalized V(A)/Q one day post-treatment were 4000, 40,000 and 550,000 MPs/g for 45, 25 and 10 μm MPs, respectively. The model estimated V(A)/Q and shunt returned to baseline levels 7 days post-treatment. Measuring SpO(2) alone was not sufficient to observe changes in gas exchange; however, when combined with model-derived V(A)/Q and shunt early reversible toxicity from pulmonary microemboli was detected suggesting that the model and physical measurements are both required for assessing toxicity. Moreover, it appears that the MP load required to alter gas exchange in a mouse prior to lethality is significantly higher than the anticipated required MP dose for effective drug delivery. Overall, the current results indicate that the microemboli-based approach for targeted pulmonary drug delivery is potentially safe and should be further explored. PMID:23142466

  13. Does low gas permeability of rigid-shelled gekkotan eggs affect embryonic development?

    PubMed

    Andrews, Robin M; Thompson, Michael B; Greene, Virginia W

    2013-06-01

    Parchment-shelled eggs are characteristic of most squamates, including the basal clades of gekkotan lizards. The majority of gekkotan lizards, however, produce rigid-shelled eggs that are highly impermeable to gas exchange; eggs are laid in dry sites and experience a net loss of water during incubation. We tested the hypothesis that the 1,000-fold lower rate of oxygen diffusion through the shells of rigid- compared to parchment-shelled eggs imposes a physiological cost on development. To do this, we contrasted species with rigid and with parchment shells with regards to (1) rates of embryonic metabolism and (2) rates and patterns of development of the yolk sac and chorioallantois, the vascularized extra-embryonic membranes that transport oxygen to embryonic tissues. Metabolic rates of embryos from the rigid-shelled eggs of Gehyra variegata did not differ from those of the parchment-shelled eggs of Oedura lesueurii. Moreover, maximum metabolic rates of gekkotans with rigid shells did not differ from those of gekkotan or scincid lizards with parchment shells. In contrast, the yolk sac covered more of the surface area of the egg at oviposition, and the chorioallantois reached its full extent earlier for the species with rigid shelled eggs (Chondrodactylus turneri, G. variegata) than for the species with parchment-shelled eggs (Eublepharis macularius, O. lesueurii). Differences in the temporal patterns of yolk sac and chorioallantois development would thus serve to compensate for low rates of oxygen diffusion through rigid shells of gekkotans. PMID:23495191

  14. Soil-Gas Identification of Environmental Factors Affecting CO2 Concentrations Beneath a Playa Wetland: Implications for Soil-Gas Monitoring at Carbon Storage Sites

    NASA Astrophysics Data System (ADS)

    Romanak, K.; Bennett, P.

    2009-12-01

    Strategies for identifying and interpreting the effects of environmental factors on near-surface CO2 concentrations are essential to developing accurate monitoring protocols at carbon storage sites. Based on the results of a three-year study of a natural analogue we present, 1) a method for using soil-gas to identify near-surface CO2 cycling, and 2) a framework for developing monitoring protocols and site evaluation for near-surface monitoring. Near-surface CO2 production, consumption, and re-distribution was observed in the vadose-zone of a highly CO2-reactive playa wetland in the Texas High Plains. Atmospheric conditions, organic and inorganic soil carbon, subsurface pressure, water flux, and surface and groundwater chemistry were compared to real-time background measurements of CO2, CH4, O2+Ar, and N2 from depths up to 45 feet. Carbon isotopes and spatially and temporally variable concentrations of CO2 ≤ 17%, CH4 ≤ 2%, and O2 from 21-0% indicate CO2 and CH4 are produced by microbes. Molar gas ratios of O2 and CO2 distinguish between oxidation of organic matter (CH2O + O2 → CO2 + H2O), CH4 oxidation (CH4 + 2O2 → CO2 + 2H2O), and potentially acetate fermentation (CH3COOH → CH4 + CO2). O2 consumption and distribution is regulated by water flux that supplies dissolved organics to microbes at depth and regulates oxygen supply by blocking vertical permeability and atmospheric gas exchange. A surface flux experiment indicates that when playa floors are dry, subsurface wetting fronts from rain events or previous ponding periods block vertical permeability resulting in surface flux measurements that do not represent subsurface conditions. Samples with CO2+O2 < 21% and N2 > 78% identify dissolution of CO2 and carbonate minerals into recharging groundwater resulting in loss of pore pressure and chemically-induced advection of atmosphere into pores. Inverse geochemical reaction modeling (PHREEQC) of playa surface water and perched groundwater in high PCO2 zones

  15. Leaf gas exchange of understory spruce-fir saplings in relict cloud forests, southern Appalachian Mountains, USA.

    PubMed

    Reinhardt, Keith; Smith, William K

    2008-01-01

    The southern Appalachian spruce-fir (Picea rubens Sarg. and Abies fraseri (Pursh) Poir.) forest is found only on high altitude mountain tops that receive copious precipitation ( > 2000 mm year(-1)) and experience frequent cloud immersion. These high-elevation, temperate rain forests are immersed in clouds on approximately 65% of the total growth season days and for 30-40% of a typical summer day, and cloud deposition accounts for up to 50% of their annual water budget. We investigated environmental influences on understory leaf gas exchange and water relations at two sites: Mt. Mitchell, NC (MM; 35 degrees 45'53'' N, 82 degrees 15'53'' W, 2028 m elevation) and Whitetop Mtn., VA (WT; 36 degrees 38'19'' N, 81 degrees 36'19'' W, 1685 m elevation). We hypothesized that the cool, moist and cloudy conditions at these sites exert a strong influence on leaf gas exchange. Maximum photosynthesis (A(max)) varied between 1.6 and 4.0 micromol CO(2) m(-2) s(-1) for both spruce and fir and saturated at irradiances between approximately 200 and 400 micromol m(-2) s(-1) at both sites. Leaf conductance (g) ranged between 0.05 and 0.25 mol m(-2) s(-1) at MM and between 0.15 and 0.40 mol m(-2) s(-1) at WT and was strongly associated with leaf-to-air vapor pressure difference (LAVD). At both sites, g decreased exponentially as LAVD increased, with an 80-90% reduction in g between 0 and 0.5 kPa. Predawn leaf water potentials remained between -0.25 and -0.5 MPa for the entire summer, whereas late afternoon values declined to between -1.25 and -1.75 MPa by late summer. Thus, leaf gas exchange appeared tightly coupled to the response of g to LAVD, which maintained high water status, even at the relatively low LAVD of these cloud forests. Moreover, the cloudy, humid environment of these refugial forests appears to exert a strong influence on tree leaf gas exchange and water relations. Because global climate change is predicted to increase regional cloud ceiling levels, more research on

  16. Multiscale study of bacterial growth: Experiments and model to understand the impact of gas exchange on global growth

    NASA Astrophysics Data System (ADS)

    Lalanne-Aulet, David; Piacentini, Adalberto; Guillot, Pierre; Marchal, Philippe; Moreau, Gilles; Colin, Annie

    2015-11-01

    Using a millifluidics and macroscale setup, we study quantitatively the impact of gas exchange on bacterial growth. In millifluidic environments, the permeability of the incubator materials allows an unlimited oxygen supply by diffusion. Moreover, the efficiency of diffusion at small scales makes the supply instantaneous in comparison with the cell division time. In hermetic closed vials, the amount of available oxygen is low. The growth curve has the same trend but is quantitatively different from the millifluidic situation. The analysis of all the data allows us to write a quantitative modeling enabling us to capture the entire growth process.

  17. Effect of anisotropic exchange interactions and short-range phenomena on superfluidity in a homogeneous dipolar Fermi gas

    NASA Astrophysics Data System (ADS)

    Corro, I.; Martin, A. M.

    2016-08-01

    We develop a simple numerical method that allows us to calculate the BCS superfluid transition temperature Tc precisely for any interaction potential. We apply it to a polarized, ultracold Fermi gas with long-range, anisotropic, dipolar interactions and include the effects of anisotropic exchange interactions. We pay particular attention to the short-range behavior of dipolar gases and reexamine current renormalization methods. In particular, we find that dimerization of both atoms and molecules significantly hampers the formation of a superfluid. The end result is that at high density or interaction strengths, we find Tc is orders of magnitude lower than previous calculations.

  18. Soil-atmosphere greenhouse-gas exchange in a bioretention system

    NASA Astrophysics Data System (ADS)

    Daly, E.; Chan, H.; Beringer, J.; Livesley, S. J.

    2011-12-01

    Bioretention systems are a popular green-technology for the management of urban stormwater runoff in many countries. They typically consist of a trench filled with a highly permeable soil medium that supports vegetation; runoff is diverted to bioretention systems and, by percolating through the filter medium, is subjected to a number of treatment processes. Nitrogen (N) is one of the key pollutants targeted by bioretention systems, which are able to reduce N concentrations considerably from inflow to outflow. To increase N removal, a saturated zone at the bottom of the filter medium is often artificially generated, to both enhance the denitrification process and increase the water available to the vegetation between inflow events. Although studies on the N-removal performance of bioretention systems are widely available in the literature, less is known about the exchange of greenhouse gases (GHG), especially nitrous oxide (N2O), between the bioretention systems and the atmosphere. Here, we present an experimental pilot study to measure N2O and CO2 soil emissions in a bioretention system installed on the Clayton Campus of Monash University in Melbourne, Australia. The bioretention system is divided into three cells, each 15 m2; the system as a whole receives water run-off from 4500 m2 of impervious car park. We monitored two cells with mostly sandy-loam vegetated with native sedges (mainly Carex Appressa and Lomandra Longifolia), one with and one without a saturated zone. Three manual flux chambers were installed in both cells. Gas flux samples were taken twice a week at about 11 am between the 2nd of March and the 18th of May 2011 (late summer and fall). Since October 2010, air-phase soil CO2 concentration profiles were measured continuously using solid-state infrared CO2 transmitters (GMT-221 model, Vaisala, Finland), along with soil moisture and soil temperature. Preliminary analysis of the chamber data (March only) showed that N2O fluxes were in general below 50

  19. Oxygen-limited thermal tolerance is seen in a plastron-breathing insect and can be induced in a bimodal gas exchanger.

    PubMed

    Verberk, Wilco C E P; Bilton, David T

    2015-07-01

    Thermal tolerance has been hypothesized to result from a mismatch between oxygen supply and demand. However, the generality of this hypothesis has been challenged by studies on various animal groups, including air-breathing adult insects. Recently, comparisons across taxa have suggested that differences in gas exchange mechanisms could reconcile the discrepancies found in previous studies. Here, we test this suggestion by comparing the behaviour of related insect taxa with different gas exchange mechanisms, with and without access to air. We demonstrate oxygen-limited thermal tolerance in air-breathing adults of the plastron-exchanging water bug Aphelocheirus aestivalis. Ilyocoris cimicoides, a related, bimodal gas exchanger, did not exhibit such oxygen-limited thermal tolerance and relied increasingly on aerial gas exchange with warming. Intriguingly, however, when denied access to air, oxygen-limited thermal tolerance could also be induced in this species. Patterns in oxygen-limited thermal tolerance were found to be consistent across life-history stages in these insects, with nymphs employing the same gas exchange mechanisms as adults. These results advance our understanding of oxygen limitation at high temperatures; differences in the degree of respiratory control appear to modulate the importance of oxygen in setting tolerance limits. PMID:25964420

  20. Oxygen-limited thermal tolerance is seen in a plastron-breathing insect and can be induced in a bimodal gas exchanger

    PubMed Central

    Verberk, Wilco C. E. P.; Bilton, David T.

    2015-01-01

    ABSTRACT Thermal tolerance has been hypothesized to result from a mismatch between oxygen supply and demand. However, the generality of this hypothesis has been challenged by studies on various animal groups, including air-breathing adult insects. Recently, comparisons across taxa have suggested that differences in gas exchange mechanisms could reconcile the discrepancies found in previous studies. Here, we test this suggestion by comparing the behaviour of related insect taxa with different gas exchange mechanisms, with and without access to air. We demonstrate oxygen-limited thermal tolerance in air-breathing adults of the plastron-exchanging water bug Aphelocheirus aestivalis. Ilyocoris cimicoides, a related, bimodal gas exchanger, did not exhibit such oxygen-limited thermal tolerance and relied increasingly on aerial gas exchange with warming. Intriguingly, however, when denied access to air, oxygen-limited thermal tolerance could also be induced in this species. Patterns in oxygen-limited thermal tolerance were found to be consistent across life-history stages in these insects, with nymphs employing the same gas exchange mechanisms as adults. These results advance our understanding of oxygen limitation at high temperatures; differences in the degree of respiratory control appear to modulate the importance of oxygen in setting tolerance limits. PMID:25964420

  1. Gas magnetometer

    DOEpatents

    Walker, Thad Gilbert; Lancor, Brian Robert; Wyllie, Robert

    2016-05-03

    Measurement of a precessional rate of a gas, such as an alkali gas, in a magnetic field is made by promoting a non-uniform precession of the gas in which substantially no net magnetic field affects the gas during a majority of the precession cycle. This allows sensitive gases that would be subject to spin-exchange collision de-phasing to be effectively used for extremely sensitive measurements in the presence of an environmental magnetic field such as the Earth's magnetic field.

  2. Effect of through-plane polytetrafluoroethylene distribution in gas diffusion layers on performance of proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Ito, Hiroshi; Iwamura, Takuya; Someya, Satoshi; Munakata, Tetsuo; Nakano, Akihiro; Heo, Yun; Ishida, Masayoshi; Nakajima, Hironori; Kitahara, Tatsumi

    2016-02-01

    This experimental study identifies the effect of through-plane polytetrafluoroethylene (PTFE) distribution in gas diffusion backing (GDB) on the performance of proton exchange membrane fuel cells (PEMFC). PTFE-drying under vacuum pressure created a relatively uniform PTFE distribution in GDB compared to drying under atmospheric pressure. Carbon paper samples with different PTFE distributions due to the difference in drying conditions were prepared and used for the cathode gas diffusion layer (GDL) of PEMFCs. Also investigated is the effect of MPL application on the performance for those samples. The current density (i) - voltage (V) characteristics of these PEMFCs measured under high relative humidity conditions clearly showed that, with or without MPL, the cell using the GDL with PTFE dried under vacuum condition showed better performance than that dried under atmospheric condition. It is suggested that this improved performance is caused by the efficient transport of liquid water through the GDB due to the uniform distribution of PTFE.

  3. Bilinear and biquadratic interlayer