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Hibernation and gas exchange.  


Hibernation in endotherms and ectotherms is characterized by an energy-conserving metabolic depression due to low body temperatures and poorly understood temperature-independent mechanisms. Rates of gas exchange are correspondly reduced. In hibernating mammals, ventilation falls even more than metabolic rate leading to a relative respiratory acidosis that may contribute to metabolic depression. Breathing in some mammals becomes episodic and in some small mammals significant apneic gas exchange may occur by passive diffusion via airways or skin. In ectothermic vertebrates, extrapulmonary gas exchange predominates and in reptiles and amphibians hibernating underwater accounts for all gas exchange. In aerated water diffusive exchange permits amphibians and many species of turtles to remain fully aerobic, but hypoxic conditions can challenge many of these animals. Oxygen uptake into blood in both endotherms and ectotherms is enhanced by increased affinity of hemoglobin for O? at low temperature. Regulation of gas exchange in hibernating mammals is predominately linked to CO?/pH, and in episodic breathers, control is principally directed at the duration of the apneic period. Control in submerged hibernating ectotherms is poorly understood, although skin-diffusing capacity may increase under hypoxic conditions. In aerated water blood pH of frogs and turtles either adheres to alphastat regulation (pH ?8.0) or may even exhibit respiratory alkalosis. Arousal in hibernating mammals leads to restoration of euthermic temperature, metabolic rate, and gas exchange and occurs periodically even as ambient temperatures remain low, whereas body temperature, metabolic rate, and gas exchange of hibernating ectotherms are tightly linked to ambient temperature. PMID:23737179

Milsom, William K; Jackson, Donald C



Activities Exchange  

NSDL National Science Digital Library

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Instruments, Texas



Gas Exchange under Environmental Stress.  

National Technical Information Service (NTIS)

The purpose of this project was threefold: (1) to assemble available information concerning the effects of various environmental factors such as altitude, acceleration, and breathing gas composition on gas exchange, (2) to initiate a mathematical simulati...

H. I. Modell M. P. Hlastala



Active microchannel heat exchanger  

Microsoft Academic Search

The present invention is an active microchannel heat exchanger with an active heat source and with microchannel architecture. The active microchannel heat exchanger has (a) an exothermic reaction chamber; (b) an exhaust chamber; and (c) a heat exchanger chamber in thermal contact with the exhaust chamber, wherein (d) heat from the exothermic reaction chamber is convected by an exothermic reaction

Anna Lee Y. Tonkovich; Gary L. Roberts; Charles J. Call; Robert S. Wegeng; Yong Wang



Southern Ocean Gas Exchange Experiment  

NASA Astrophysics Data System (ADS)

The Southern Ocean Gas Exchange Experiment (SO GasEx) is the third in a series of US-led open ocean process studies aimed at quantifying air-sea gas exchange. SO GasEx took place in the Atlantic sector of the Southern Ocean near South Georgia Island from February 29 to April 12, 2008. The main objectives of the experiment are to 1) improve quantification of the gas transfer velocity in a high wind and wave environment; and 2) determine whether there are unique controls on the gas transfer velocity in this significant CO2 sink region. An important goal of these efforts is to improve the quantification of gas transfer velocities on regional scales so that more accurate global air-sea CO2 fluxes can be determined. A systematic approach was followed during the cruise and will be continued after the cruise to accomplish this goal: 1) Perform direct flux measurements to obtain short-term estimates of local gas transfer velocities; 2) Combine integrated measurements of gas transfer velocities using 3He/SF6 dual tracer technique with short-term estimates and water column budgets; 3) Understand the mechanisms controlling ocean mixed layer pCO2 on short time and space scales; 4) Elucidate the forcing functions controlling gas transfer; and 5) Relate forcing functions to parameters that can be detected by remote sensing.

Ho, D. T.; Sabine, C. L.



Activation Energies for Carbon Acid/D2 Exchange Over a Solid Base Catalyst. Correlation with Gas Phase Acidities.  

National Technical Information Service (NTIS)

Thermally activated Magnesium oxide has been employed as a highly basic solid catalyst for carrying out CH/D2 exchange in hydrocarbons. A series of benzylic, aromatic, and alkane C-H bonds were studied. Reaction rates at various temperatures yielded activ...

M. Fazlul K. J. Klabunde



SAFE gas turbine cycle primary heat exchangers  

NASA Astrophysics Data System (ADS)

Los Alamos National Laboratory and Marshall Space Flight Center are jointly developing two modular heat pipe heat exchangers, collectively named FIGMENT (Fission Inert Gas Metal Exchanger for Non-nuclear Testing). The FIGMENT heat exchangers are designed to transfer power from the SAFE nuclear reactor cores to gas turbine energy converters. A stainless steel prototype heat exchanger will be built during 2002 in preparation for the construction of a larger refractory metal version. Two promising FIGMENT stainless steel heat exchanger concepts are reviewed here. .

Reid, Robert S.; Kapernick, Richard J.



Breath tests and airway gas exchange  

Microsoft Academic Search

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

Joseph C. Anderson; Michael P. Hlastala


Reversible brain inactivation induces discontinuous gas exchange in cockroaches.  


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

Matthews, Philip G D; White, Craig R



Greenhouse gas exchange over grazed systems  

NASA Astrophysics Data System (ADS)

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.

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



Gas exchange measurements in natural systems  

SciTech Connect

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.

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



Forced convection modulates gas exchange in cnidarians  

PubMed Central

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.

Patterson, Mark R.; Sebens, Kenneth P.



Breath-by-breath alveolar gas exchange.  


A method is described for breath-by-breath measurement of alveolar gas exchange corrected for changes of lung gas stores. In practice, the subject inspires from a spirometer, and each expired tidal volume is collected into a rubber bag placed inside a rigid box connected to the same spirometer. During the inspiration following any given expiration the bag is emptied by a vacuum pump. A computer monitors inspiratory and expiratory tidal volumes, drives four solenoid valves allowing appropriate operation of the system, and memorizes end-tidal gas fractions as well as mixed expired gas composition analyzed by mass spectrometer. Thus all variables for calculating alveolar gas exchange, based on the theory developed by Auchincloss et al. (J. Appl. Physiol. 21: 810-818, 1966), are obtained on a single-breath basis. Mean resting and steady-state exercise gas exchange data are equal to those obtained by conventional open-circuit measurements. Breathing rates up to 30 X min-1 can be followed. The breath-to-breath variability of O2 uptake at the alveolar level is less (25-35%) than that measured at the mouth as the difference between the inspired and expired volumes, both at rest and during exercise up to 0.7 of maximum O2 consumption. PMID:6618950

Giezendanner, D; Cerretelli, P; Di Prampero, P E



New fiber configuration for intravenous gas exchange.  


Implantation of a membrane oxygenator (IO) into the vena cava for blood oxygenation in patients with acute lung failure has been researched for the last 25 years. Compared to the extra corporeal blood oxygenation, where blood is handled outside the body, IO doesn't present tubes, housings or heat exchangers, thus reducing considerably blood contact surface and setting priming volume to zero. Otherwise, restricted space in the vena cava and unadvantageous blood flow conditions represent so far a limitation for sufficient gas exchange. A new fiber configuration for intravenous use is being developed, which increases the implantable fiber surface and enhances gas exchange due to the increased blood convection. This is made possible by new fiber bundles, which are free to slide on a catheter and after implantation assume a twisted shape characterized by high homogeneity and fiber density. PMID:15818547

Cattaneo, G F; Reul, H



[Advanced development of blood-gas exchanger].  


In order to simplify the technique of extracorporeal membrane oxygenation (ECMO) and apply extracorporeal life support ( ECLS) broadly for assisting the treatment of severe respiratory failure patients, we have developed a blood-gas exchanger (BGE) with the characteristics of small volume and simple structure. The exchange between blood and gas of BGE adopts cross-flowing model; blood flows along the outer hollow fiber and gas flows in the inner hollow fiber with the reverse direction of blood flowing. The interface of blood flow in and out was designed as the internal spiral, and the caliber of BGE is matched with the blood interface of dialysis. Thus it may successfully make single-use spiral connectors link up mutually in the extracorporeal blood circulation of dialysis, may help clinical operations become safe, convenient and easily-controlled, and may simplify the technique of EGMO. PMID:19166210

Sun, Xin; Zhang, Wenliang; Wu, Qi; Du, Zhongzhen



Nitrogen gas exchange in the human knee  

SciTech Connect

Human decompression sickness is presumed to result from excess inert gas in the body when ambient pressure is reduced. Although the most common symptom is pain in the skeletal joints, no direct study of nitrogen exchange in this region has been undertaken. For this study, nitrogen tagged with radioactive 13N was prepared in a linear accelerator. Nine human subjects rebreathed this gas from a closed circuit for 30 min, then completed a 40- to 100-min washout period breathing room air. The isotope 13N was monitored continuously in the subject's knee during the entire period using positron detectors. After correction for isotope decay (half-life = 9.96 min), the concentration in most knees continued to rise for at least 30 min into the washout period. Various causes of this unexpected result are discussed, the most likely of which is an extensive redistribution of gas within avascular knee tissues.

Weathersby, P.K.; Meyer, P.; Flynn, E.T.; Homer, L.D.; Survanshi, S.



Gas exchange of six tree species from Central Amazonian floodplains  

Microsoft Academic Search

In Central Amazonian floodplain forests, trees are subjected to periodical flood- ing. The gas exchange behaviour of six tree species with different growth strategies was com- pared between the non-flooded and flooded period. Photosynthetic assimilation and quantum yields were 20-50% lower in the flooded period in non-pioneers, and 10-20% lower in pioneers. The photosynthetic activities reported here appear to be



The performance of a new gas to gas heat exchanger with strip fin  

Microsoft Academic Search

A compact gas to gas heat exchanger needs large heat transfer areas on both fluid sides. This can be realised by adding secondary surfaces. The secondary surfaces are plate fin, strip fin, and louvered fin, etc. The fins extend the heat transfer surfaces and promote turbulence.This paper presents a gas to gas heat exchanger with strip fins. The heat exchanger

J. Wang; G. G. Hirs; P. Rollmann



Imaging regional PAO2 and gas exchange.  


Several methods allow regional gas exchange to be inferred from imaging of regional ventilation and perfusion (V/Q) ratios. Each method measures slightly different aspects of gas exchange and has inherent advantages and drawbacks that are reviewed. Single photon emission computed tomography can provide regional measure of ventilation and perfusion from which regional V/Q ratios can be derived. PET methods using inhaled or intravenously administered nitrogen-13 provide imaging of both regional blood flow, shunt, and ventilation. Electric impedance tomography has recently been refined to allow simultaneous measurements of both regional ventilation and blood flow. MRI methods utilizing hyperpolarized helium-3 or xenon-129 are currently being refined and have been used to estimate local PaO(2) in both humans and animals. Microsphere methods are included in this review as they provide measurements of regional ventilation and perfusion in animals. One of their advantages is their greater spatial resolution than most imaging methods and the ability to use them as gold standards against which new imaging methods can be tested. In general, the reviewed methods differ in characteristics such as spatial resolution, possibility of repeated measurements, radiation exposure, availability, expensiveness, and their current stage of development. PMID:22604886

Petersson, Johan; Glenny, Robb W



Carbon cycling and gas exchange in soils  

SciTech Connect

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.

Trumbore, S.E.



Eccentric exercise-induced muscle damage dissociates the lactate and gas exchange thresholds  

Microsoft Academic Search

We tested the hypothesis that exercise-induced muscle damage would increase the ventilatory ([Vdot]E) response to incremental\\/ramp cycle exercise (lower the gas exchange threshold) without altering the blood lactate profile, thereby dissociating the gas exchange and lactate thresholds. Ten physically active men completed maximal incremental cycle tests before (pre) and 48 h after (post) performing eccentric exercise comprising 100 squats. Pulmonary gas

Rosemary C. Davies; Ann V. Rowlands; David C. Poole; Andrew M. Jones; Roger G. Eston



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

NASA Astrophysics Data System (ADS)

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 only doubled relative to the unfertilised surrounding waters by the end of the experiment. After 15 days and four iron additions totalling 1.1 ton Fe 2+, this was a very modest response compared to other mesoscale iron enrichment experiments. An investigation of the factors limiting bloom development considered co-limitation by light and other nutrients, the phytoplankton seed-stock and grazing regulation. Whilst incident light levels and the initial Si:N ratio were the lowest recorded in all FeAXs to date, there was only a small seed-stock of diatoms (less than 1% of biomass) and the main response to iron addition was by the picophytoplankton. A high rate of dilution of the fertilised patch relative to phytoplankton growth rate, the greater than expected depth of the surface mixed layer and microzooplankton grazing were all considered as factors that prevented significant biomass accumulation. In line with the limited response, the enhanced biological draw-down of pCO 2 was small and masked by a general increase in pCO 2 due to mixing with higher pCO 2 waters. The DMS precursor DMSP was kept in check through grazing activity and in contrast to most FeAX's dissolved dimethylsulfide (DMS) concentration declined through the experiment. SAGE is an important low-end member in the range of responses to iron addition in FeAX's. In the context of iron fertilisation as a geoengineering tool for atmospheric CO 2 removal, SAGE has clearly demonstrated that a significant proportion of the low iron ocean may not produce a phytoplankton bloom in response to iron addition.

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.



Parameterization of Gas Exchange from the Southern Ocean Gas Exchange Experiment  

NASA Astrophysics Data System (ADS)

Momentum, mass and heat are transferred across the air-sea interface mediating the biogeochemical cycling processes that facilitates life on earth. A particular relevant process is the carbon transfer between atmosphere and ocean via the exchange of CO2. A micrometeorological approach is taken in order to parameterize the gas transfer velocity (k) under a variety of atmospheric and oceanic conditions due to wind speeds ranging up to 20 m/s. The fluxes of CO2, momentum and heat are calculated via the direct covariance method (eddy correlation) and analyzed over a wide range of atmospheric forcing conditions. This process captures the physical variability in the transfer velocity and its dependents on turbulent transport and air-sea exchange. Different atmospheric variables are analyzed in order to capture the atmospheric conditions ruling the gas transfer. Particular attention is given to the relation of (k) and wind speed where we explore whether the exchange is best modeled by a linear, quadratic or cubic wind speed relationship for gas transfer velocity at high winds. GASEX 08 data set is complemented with data from GASEX 98 and GASEX 01, which provides a wind velocity range between 4 and up to 20 m/s, generating a solid data ensemble from which an empirical parameterization for (k) is developed.

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



Gas turbine power plant having a heat exchanger  

Microsoft Academic Search

A gas turbine power plant, such as a gas turbine engine for a motor vehicle, having a gas turbine, a combustor for producing hot gas to drive the turbine, and an air compressor for furnishing compressed air to the combustor are described. A heat exchanger, such as a rotary regenerator or a cross-flow recuperator, is located between the air compressor

J. Huller; W. Krockow



Gas exchange between the forest and the atmosphere  

SciTech Connect

Forest gas exchange is discussed in terms of the processes that control the rate of exchange with the atmosphere. Examples are presented to show how vegetative uptake control is varied for gases with different characteristics. The prediction of uptake for large areas and over long periods of time is discussed in terms of quantitative models of the gas exchange processes. Finally, remote sensing is suggested as a means of obtaining the parameters needed to make the model predictions. 46 refs., 6 figs.

Murphy, C.E. Jr.



Analysis of factors affecting gas exchange in intravascular blood gas exchanger.  


A mathematical model of an intravascular hollow-fiber gas-exchange device, called IVOX, has been developed using a Krogh cylinder-like approach with a repeating unit structure comprised of a single fiber with gas flowing through its lumen surrounded by a coaxial cylinder of blood flowing in the opposite direction. Species mass balances on O2 and CO2 result in a nonlinear coupled set of convective-diffusion parabolic partial differential equations that are solved numerically using an alternating-direction implicit finite-difference method. Computed results indicated the presence of a large resistance to gas transport on the external (blood) side of the hollow-fiber exchanger. Increasing gas flow through the device favored CO2 removal from but not O2 addition to blood. Increasing blood flow over the device favored both CO2 removal as well as O2 addition. The rate of CO2 removal increased linearly with the transmural PCO2 gradient imposed across the device. The effect of fiber crimping on blood phase mass transfer resistance was evaluated indirectly by varying species blood diffusivity. Computed results indicated that CO2 excretion by IVOX can be significantly enhanced with improved bulk mixing of vena caval blood around the IVOX fibers. PMID:7836191

Niranjan, S C; Clark, J W; San, K Y; Zwischenberger, J B; Bidani, A



Circadian rhythms constrain leaf and canopy gas exchange in an Amazonian forest  

NASA Astrophysics Data System (ADS)

We used a controlled-environment leaf gas-exchange system and the micrometeorological technique eddy covariance to determine whether circadian rhythms constrain the rates of leaf and canopy gas exchange in an Amazonian forest over a day. When exposed to continuous and constant light for 20 to 48 hours leaves of eleven of seventeen species reduced their photosynthetic rates and closed their stomata during the normally dark period and resumed active gas exchange during the normally light period. Similarly, the rate of whole-forest CO2 uptake at a predetermined irradiance declined during the late afternoon and early morning and increased during the middle of the day. We attribute these cycles to circadian rhythms that are analogous to ones that have been reported for herbaceous plants in the laboratory. The importance of endogenous gas exchange rhythms presents a previously unrecognized challenge for efforts to both interpret and model land-atmosphere energy and mass exchange.

Doughty, Christopher E.; Goulden, Michael L.; Miller, Scott D.; da Rocha, Humberto R.



The SOLAS air–sea gas exchange experiment (SAGE) 2004  

Microsoft Academic Search

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

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



Heat transfer characteristics of a gas-to-gas heat exchanger using heat pipes  

Microsoft Academic Search

The heat transfer characteristics of a gas-to-gas heat exchanger employing heat pipes as the heat transfer elements were examined. Experimental data obtained on the heat exchanger containing 66 finned heat pipes were compared with the values calculated by using various empirical and theoretical equations. A basic design procedure for gas-to-gas heat exchangers using heat pipes was then established. The results

Y. Wakiyama; K. Harada; S. Inoue; J. Fujita; H. Suematsu



Gas exchange characteristics of the tropical mangrove, Pelliciera rhizophoreae  

Microsoft Academic Search

Photosynthetic characteristics were investigated in the geographically isolated and restricted mangrove species, P.rhizophoreae. Gas exchange measurements were made on two to seven years old hydroponically grown plants maintained in 10%, 50% and 100% seawater. CO2 exchange in the 50% and 100% seawater treatments was reduced by 10% and 26%, respectively, compared to the 10% seawater treatment. CO2 response curves indicated

G. Naidoo; D. J. von Willert



Bacterioneuston control of airwater methane exchange determined with a laboratory gas exchange tank  

Microsoft Academic Search

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 MilliRO water or artificial seawater prepared in MilliRO) 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

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



The gas turbine heat exchanger in the fluidized bed combustor  

Microsoft Academic Search

In a current research and development program a coal-fired atmospheric fluidized bed combustor is being designed to supply the heat to a closed cycle gas turbine cogeneration system. The major technical effort is directed towards the design of the in-bed heat exchanger, which is required to operate near bed temperature. This high temperature (850° C) exposes the heat exchanger tubes

C. F. Holt; A. A. Boiarski; H. E. Carlton



Spin-exchange optical pumping of noble-gas nuclei  

Microsoft Academic Search

Spin-exchange optical pumping of mixtures of alkali-metal vapors and noble gases can be used to efficiently polarize the nuclei of the noble-gas atoms. Liters of noble gases at standard temperature and pressure and with nuclear spin polarizations of several tens of percent are now used in many applications. The authors describe the basic phenomena that govern the spin-exchange process and

Thad G. Walker; William Happer



Surface gas-exchange processes of snow algae  

PubMed Central

The red-colored chlorophyte Chlamydomonas nivalis is commonly found in summer snowfields. We used a modified Li-Cor gas-exchange system to investigate surface gas-exchange characteristics of snow colonized by this alga, finding rates of CO2 uptake up to 0.3 ?mol m?2?s?1 in dense algal blooms. Experiments varying the irradiance resulted in light curves that resembled those of the leaves of higher plants. Red light was more effective than white and much more effective than green or blue, because of the red astaxanthin that surrounds and masks the algal chloroplasts. Integrating daily course measurements of gas exchange showed CO2 uptake around 2,300 ?mol?m?2?day?1 in heavily colonized patches, indicating that summer snowfields can be surprisingly productive.

Williams, William E.; Gorton, Holly L.; Vogelmann, Thomas C.



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

PubMed Central

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.

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



[The physiology of gas exchange in divers].  


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

Rieder, H U



Gas exchange between humans and multibiological life support system  

Microsoft Academic Search

To establish a Bioregenerative Life Support System (BLSS) in lunar or Mars bases in the future, manned stimulation experiments including several kinds of creatures are needed to be conducted first. Gas exchange relation, element transfer and transformation principles, etc. between humans and the multibiological system composed of plants, animals, microalgae and so on must be investigated in order to place

Ling Tong; Dawei Hu; Hong Liu; Ming Li; Yuming Fu; Boyang Jia; Fangzhou Du; Enzhu Hu



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


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

Kas'ian, I I; Makarov, G F


Gas exchange in the incubation mounds of megapode birds  

Microsoft Academic Search

The brush turkey (Alectura lathami) and mallee fowl (Leipoa ocellata) are megapode birds that incubate their eggs by burying them in mounds. Respiratory gas exchange between the buried eggs and the atmosphere occurs mainly by diffusion through about 60 cm of decomposing forest litter (brush turkey) or sand (mallee fowl).

Roger S. Seymour; David Vleck; Carol M. Vleck



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

Microsoft Academic Search

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

Christian Moerbitz; Stefan K. Hetz



Effects of temperature on gas exchange characteristics in leaves of Lonicera Japonica Thunb effects of temperature on gas exchange  

Microsoft Academic Search

The temperature which affects plant growth and development, is an important ecological factor. In the present study, we mainly aimed to study the effects of temperature on gas exchange characteristics in the leaves of Lonicera Japonica Thunb., The results showed that light elevated temperature had no significant effects on the photosynthesis of L. japonica (Lonicera Japonica), which was well indicated

Zhouli Liu; Wei Chen; Lian Jia; Xingyuan He



The new advanced membrane gas exchanger.  


Current membrane oxygenators are constructed for patients with a body surface under 2.2 m(2). If the body surface exceeds 2.5 m(2), commercially available devices may not allow adequate oxygenation during cardiopulmonary bypass. To address this, a hollow-fiber oxygenator with an enlarged contact surface of 1.81 m(2) was tested. In an experimental set-up, six calves of mean weight 85.4 ± 3 kg were connected to cardiopulmonary bypass. They were randomly assigned to a standard oxygenator (n = 3; ADMIRAL, Euroset, Medola, Italy) with a surface of 1.35 m(2) or to an enlarged surface oxygenator (n = 3; AMG, Euroset). Blood samples were taken before bypass, after 10 min on bypass, and after 1, 2, 5 and 6 h of perfusion. Analysis of variance was used for repeated measurements. The mean flow rate was 6.5 l/min for 6 h. The total oxygen transfer at 6 h was significantly higher in the high-surface group (P < 0.05). Blood trauma, evaluated by plasma hemoglobin and lactate dehydrogenase levels, did not detect any significant hemolysis. Thrombocytes and white blood cell count profiles showed no significant differences between the two groups at 6 h of perfusion (P = 0.06 and 0.80, respectively). At the end of testing, no clot deposition was found in the oxygenator, and there was no evidence of peripheral emboli. The results suggest that the new oxygenator allows very good gas transfer and may be used for patients with a large body surface area. PMID:21835847

Berdajs, Denis A; de Stefano, Eleonora; Delay, Dominique; Ferrari, Enrico; Horisberger, Judith; Ditmar, Quntin; von Segesser, Ludwig K




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....


A mathematical model of pulmonary gas exchange under inflammatory stress  

PubMed Central

During a severe local or systemic inflammatory response, immune mediators target lung tissue. This process may lead to acute lung injury and impaired diffusion of gas molecules. Although several mathematical models of gas exchange have been described, none simulate acute lung injury following inflammatory stress. In view of recent laboratory and clinical progress in the understanding of the pathophysiology of acute lung injury, such a mathematical model would be useful. We first derived a partial differential equations model of gas exchange on a small physiological unit of the lung (325 alveoli), which we refer to as a respiratory unit (RU). We next developed a simple model of the acute inflammatory response and implemented its effects within a RU, creating a single RU model. Linking multiple RUs with various ventilation/perfusion ratios and taking into account pulmonary venous blood remixing yielded our lung-scale model. Using the lung-scale model, we explored the predicted effects of inflammation on ventilation/perfusion distribution and the resulting pulmonary venous partial pressure oxygen level during systemic inflammatory stresses. This model represents a first step towards the development of anatomically faithful models of gas exchange and ventilation under a broad range of local and systemic inflammatory stimuli resulting in acute lung injury, such as infection and mechanical strain of lung tissue.

Reynolds, Angela; Ermentrout, G. Bard; Clermont, Gilles



Peritoneal ventilation in rabbits: augmentation of gas exchange with cisapride.  

PubMed Central

BACKGROUND: Peritoneal ventilation has been shown to be effective in achieving extrapulmonary oxygenation and carbon dioxide elimination in an animal model of severe adult respiratory distress syndrome (ARDS). Cisapride is a "prokinetic" agent (increases gastric emptying), that may increase the splanchnic circulation and thus favourably affect gas exchange in peritoneal ventilation. METHODS: Using Doppler ultrasound the effect of cisapride on the portal venous circulation was examined in eight spontaneously breathing rabbits and the effect of cisapride on gas exchange in five rabbits spontaneously breathing room air was compared with that of a control group who did not receive cisapride. Its effect on gas exchange in five rabbits with ARDS being treated with mechanical lung and peritoneal ventilation was compared with that of a control group, and its effect on gas exchange in five rabbits with ARDS treated with conventional ventilation was also compared with that of a control group. RESULTS: Enteral administration of cisapride increased portal venous blood velocity, as measured ultrasonographically, by a mean of 188% one hour after receiving the drug. In rabbits with ARDS being treated with both peritoneal ventilation and mechanical ventilation to the lungs, those receiving cisapride had arterial oxygen tensions 1.5-3 times that of controls. Cisapride had no effect on arterial blood gas tensions in rabbits who were spontaneously breathing room air, nor in rabbits with ARDS who received only conventional mechanical lung ventilation. CONCLUSIONS: Cisapride increases arterial oxygenation in rabbits with severe ARDS treated with peritoneal ventilation, probably due to its ability to increase splanchnic circulation. It should be considered as an adjuvant medication to peritoneal ventilation.

Barr, J.; Lushkov, G.; Strauss, S.; Gurevitch, S.; Lahat, E.; Bistritzer, T.; Klin, B.; Eshel, G.



Standard and exercise metabolism and the dynamics of gas exchange in the giant red velvet mite, Dinothrombium magnificum  

Microsoft Academic Search

Although many adult insects and adult, unfed ticks are known to exchange respiratory gases discontinuously, the respiratory physiology of other tracheate arthropods is almost unknown. In this paper we present data to test hypotheses on the gas exchange dynamics, standard metabolic rate (SMR, as a function of body mass and temperature) and activity metabolism of the giant red velvet mite

John R. B. Lighton; Frances D. Duncan



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

Microsoft Academic Search

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

T. Mengistu; F. J. Sterck; M. Fetene; W. Tadesse; F. Bongers



Respiratory gas exchange using a triaxial alveolar gas diagram.  

PubMed Central

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.

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



The use of stable isotopes to study ecosystem gas exchange  

Microsoft Academic Search

Stable isotopes are a powerful research tool in environmental sciences and their use in ecosystem research is increasing.\\u000a In this review we introduce and discuss the relevant details underlying the use of carbon and oxygen isotopic compositions\\u000a in ecosystem gas exchange research. The current use and potential developments of stable isotope measurements together with\\u000a concentration and flux measurements of CO2

D. Yakir; L. da S. L. Sternberg



Gas exchange strategy in the Nile crocodile: a morphometric study  

Microsoft Academic Search

The respiratory surface area (SAR) per kilogram body mass (MB), the harmonic mean thickness of the air-blood barrier (thtR) in the gas exchange tissue, and the anatomical diffusion factor (ADF=SAR\\/thtR per MB) were calculated for four juvenile Nile crocodiles. The ADF of three small specimens (mean MB=3.59 kg) was 625 cm2·µm-1·kg-1. The values varied considerably among individuals and were similar

S. F. Perry



Modeling automotive gas-exchange solenoid valve actuators  

Microsoft Academic Search

We develop a finite-element analysis (FEA) model to describe transient and static operation of gas-exchange valves. Such valves, directly controlled by solenoids, are a promising method for enhancing automotive engine efficiency. The FEA model is validated by experimental testing on an actual automotive prototype valve. We show that a nonlinear lumped-parameter model that uses FEA results also closely matches experimental

Ryan R. Chladny; Charles Robert Koch; Alan F. Lynch



Carbon dioxide absorption and gas exchange during pelvic laparoscopy  

Microsoft Academic Search

Twelve ASA physical status I-II patients undergoing pelvic laparoscopy for infertility were enrolled in a study to quantify\\u000a the effects of CO2 insufflation and the Trendelenburg position on CO2 elimination and pulmonary gas exchange, and to determine the minute ventilation required to maintain normocapnia during CO2 insufflation. Measurements of O2 uptake (VO2), CO2 elimination (VCO2), minute ventilation (Ve), FlO2, and

P. L. Tan; T. L. Lee; W. A. Tweed



Hydraulic and thermal design of a gas microchannel heat exchanger  

NASA Astrophysics Data System (ADS)

In this paper investigations on the design of a gas flow microchannel heat exchanger are described in terms of hydrodynamic and thermal aspects. The optimal choice for thermal conductivity of the solid material is discussed by analysis of its influences on the thermal performance of a micro heat exchanger. Two numerical models are built by means of a commercial CFD code (Fluent). The simulation results provide the distribution of mass flow rate, inlet pressure and pressure loss, outlet pressure and pressure loss, subjected to various feeding pressure values. Based on the thermal and hydrodynamic analysis, a micro heat exchanger made of polymer (PEEK) is designed and manufactured for flow and heat transfer measurements in air flows. Sensors are integrated into the micro heat exchanger in order to measure the local pressure and temperature in an accurate way. Finally, combined with numerical simulation, an operating range is suggested for the present micro heat exchanger in order to guarantee uniform flow distribution and best thermal and hydraulic performances.

Yang, Yahui; Brandner, Juergen J.; Morini, Gian Luca



Gas Diodes for Thermoacoustic Self-circulating Heat Exchangers  

NASA Astrophysics Data System (ADS)

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.

Swift, Greg; Backhaus, Scott



Gas exchange in man during combined +Gz acceleration and exercise.  


Gravity and acceleration from head to foot (+Gz) handicap gas exchange by shifting blood from thorax to dependent veins and creating a ventilation/perfusion (V/Q) mismatch in the lung. At 1 G leg exercise improves V/Q matching. Gas exchange was measured in six subjects +1, +2, and +3 Gz during rest and two levels of exercise, either unloaded pedaling or 600 kpm/min. The VO2 for pedaling was clearly related to G level, but work efficiency was unaffected. Acceleration lowered resting Pao2 while raising VE/VO2, HR, AaDo2, VD, and VD/VT. Unloaded pedaling returned VE/VO2 and HR toward their 1-G values. In contrast, at 3 G each increase in VO2 caused a fall in Pao2 and a rise in AaDo2. The VD showed no further change with exercise, while VD/VT decreased at all G levels. It thus appears that only some of the effects of acceleration are counteracted by exercise, probably by the peripheral muscle pump. Any accompanying rise in VO2 adds to the stress of acceleration, due to limitations on gas transport. PMID:931869

Nunneley, S A



Gas supersaturation in the surface ocean: The roles of heat flux, gas exchange, and bubbles  

Microsoft Academic Search

In this paper, a one-dimensional model of mixed layer dynamics is used to examine the roles of heat flux, gas exchange, and bubble processes in producing nitrogen and argon gas supersaturation in the surface subtropical Pacific ocean at U.S. JGOFS Station ALOHA during 1989–1990. The N2\\/Ar ratio is measured within a high degree of accuracy by mass spectrometry, and the

Rebecca Schudlich; Steven Emerson



Improved helium exchange gas cryostat and sample tube designs for automated gas sampling and cryopumping  

Microsoft Academic Search

In order to eliminate the use of liquid helium for the extraction of atmospheric gases from polar ice cores, two units of a redesigned top load helium exchange gas cryostat were built and tested. The cryostats feature the shortest and largest diameter sample wells built to date, a base temperature below 7 Kelvin, and a sample well without baffles. The

P. R. Buerki; Brian C. Jackson; Tim Schilling; Terry Rufer; Jeffrey P. Severinghaus



Teaching pulmonary gas exchange physiology using computer modeling  

NSDL National Science Digital Library

Students often have difficulty understanding the relationship of O2 consumption, CO2 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 that is web based and allows the student to vary multiple factors simultaneously and observe the final effect on the arterial blood gas composition (available at In this article, the underlying mathematics of the computer model is presented, as is the teaching strategy. The simulation is applied to a typical clinical case drawn from the intensive care unit to demonstrate the interdependence of the above factors as well as the less-appreciated importance of the Bohr and Haldane effects in clinical pulmonary medicine. The use of a computer to vary the many interacting factors involved in the arterial blood gas composition appeals to today's students and demonstrates the importance of basic physiology to the actual practice of medicine.

Kent S Kapitan (Southern Ilinois University Pulmonary Medicine)



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

Microsoft Academic Search

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

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



[The variability of respiratory pattern and gas exchange].  


It is known, that spectral analysis of heart rate and respiratory variability allows to find out the very low frequency (VLF) rhythm. However it is not known, it is necessary to carry this rhythm to what type of wave processes. The purpose of the present researches was to study the respiratory variability and the variability of gas exchange parameters. 10 healthy subjects have been surveyed. The pneumogramms within 30 minutes spent record, and then a method "breath-by-breath" within 30 minutes registered gas exchange parameters (Ve--lung ventilation, V(O2) -O2 consumption and other parameters). Fast Fourier transform method has found out two groups of the basic peaks. The first--in a range 0.2-0.3 Hz (a time cycle--3-5 s), that corresponds respiratory frequency which size at subjects varied from 12 to 20 per minute. The second--in a range 0.002-0.0075 Hz, that corresponds VLF diapason (a time cycle--1-3.5 minutes). At the analysis pneumogramms rhythms in the same ranges have been established. The carried out researches allow to draw a conclusion on steady character of wave process in a VLF-range. It can be carried to quasi-periodic oscillations type. First oscillator or respiratory frequency it is formed by means of mechanisms of chemoreception. Considering, that V(O2) and V(CO2) are function energy exchange, it is possible to believe, what exactly energy demand define the second oscillator. PMID:22679801

Grishin, O V; Grishin, V G; Kovalenko, Iu V


Direct Energy Exchange Enhancement in Distributed Injection Light Gas Launchers  

SciTech Connect

It is not widely acknowledged or appreciated that conventional, two-stage light-gas launchers do not efficiently apply their high breech pressures to the design intent: accelerating the projectile. Our objective in this project was to carry out the analysis, design, construction, and testing of a new class of launchers that will address this limitation. Our particular application is to expand the pressure range of the conventional, two-stage gas launcher to overlap and validate the pressure regimes previously attainable only with shock waves generated by nuclear explosions, lasers, or multistage conventional explosions. That is, these launchers would have the capability to conduct--in a laboratory setting--high-velocity-impact, equation-of-state (EOS) measurements at up to 2-TPa (20 Mbar) pressure levels in high-Z materials. Our design entailed a new class of distributed-injection, gas-dynamic launchers that are designed to use a boat-tail projectile to overcome the fundamental gas-expansion phenomena known as escape velocity (the Riemann limit). Our program included analytical, numerical, and experimental studies of the fast gas release flow technique that is central to the success of our approach. The analyses led us to believe that, in a typical configuration, the pressure will be effectively applied to the projectile in a time short relative to its few-microsecond traverse time; the experimental program we conducted during FY1999 supported these estimates. In addition, our program revealed dramatic increased efficiency in this process that was previously unknown to the launcher community. The most fundamental practical restrictions on the performance of any gas launcher are the ability of the launcher to (1) contain pressure in a reservoir, and (2) effectively apply that pressure to the base of a moving projectile. Our gas-release test-fixture experiments showed that our design was capable of applying nearly twice the pressure to the projectile that is 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.

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



Development and demonstration of improved gas to gas heat pipe heat exchangers for the recovery of residual heat. Final report  

Microsoft Academic Search

A new form of heat exchanger has been developed with the following characteristics: (1) compact modular construction: the modules are built up to provide the final exchanger face area as required by the available exhaust gas stream; (2) the above construction allows in situ dismantling of the heat exchanger for cleaning in case of internal fouling; (3) in order that

M. J. Davies; G. H. Chaffey



The search for life on Mars: Viking 1976 gas changes as indicators of biological activity  

Microsoft Academic Search

Gas compositional changes in the headspace of the Viking Biology Gas Exchange Experiment can originate from biological activity as well as redox chamical reactions, sorption and desorption phenomena, acid-base reactions, and trapped gas release. Biological phenomena are differentiated from the nonbiological gas changes by their dynamical qualities, notably by the ability of the M4 medium to sustain biological activity. Medium

V. I. Oyama; B. J. Berdahl; G. C. Carle; M. E. Lehwalt; H. S. Ginoza



The effect of high temperatures on tropical forest gas exchange.  

NASA Astrophysics Data System (ADS)

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.

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



Leaf water relations and maintenance of gas exchange in coffee cultivars grown in drying soil.  


Plant water status, leaf tissue pressure-volume relationships, and photosynthetic gas exchange were monitored in five coffee (Coffea arabica L.) cultivars growing in drying soil in the field. There were large differences among cultivars in the rates at which leaf water potential (Psi(L)) and gas exchange activity declined when irrigation was discontinued. Pressure-volume curve analysis indicated that increased leaf water deficits in droughted plants led to reductions in bulk leaf elasticity, osmotic potential, and in the Psi(L) at which turgor loss occurred. Adjustments in Psi(L) at zero turgor were not sufficient to prevent loss or near loss of turgor in three of five cultivars at the lowest values of midday Psi(L) attained. Maintenance of protoplasmic volume was more pronounced than maintenance of turgor as soil drying progressed. Changes in assimilation and stomatal conductance were largely independent of changes in bulk leaf turgor, but were associated with changes in relative symplast volume. It is suggested that osmotic and elastic adjustment contributed to maintenance of gas exchange in droughted coffee leaves probably through their effects on symplast volume rather than turgor. PMID:16667916

Meinzer, F C; Grantz, D A; Goldstein, G; Saliendra, N Z



Improved helium exchange gas cryostat and sample tube designs for automated gas sampling and cryopumping  

NASA Astrophysics Data System (ADS)

In order to eliminate the use of liquid helium for the extraction of atmospheric gases from polar ice cores, two units of a redesigned top load helium exchange gas cryostat were built and tested. The cryostats feature the shortest and largest diameter sample wells built to date, a base temperature below 7 Kelvin, and a sample well without baffles. The cryostats allowed shortening the length and thus increasing the gas pressure inside our sample tubes by 58% and increasing the amount of sample ending up in the mass spectrometer by 4.4%. The cryostats can either be used as mobile stand-alone units for manual gas processing lines or integrated into a fully automated vacuum extraction and gas analysis line. For the latter application the cryostat was equipped with a custom-designed automated changeover system.

Buerki, P. R.; Jackson, Brian C.; Schilling, Tim; Rufer, Terry; Severinghaus, Jeffrey P.



Electrostatic enhancement of heat transfer in a gas-to-gas heat exchanger  

NASA Astrophysics Data System (ADS)

This is the final report on the last phase of a four-year GRI-sponsored experimental effort on heat transfer enhancement in gas-to-gas heat exchangers utilizing the electrostatic (or electrohydrodynamic, EHD) technique. The feasibility of the technique and the role of various controlling parameters for basic pipe flows and in a double-pipe heat exchanger were addressed in the first three phases of the project. In the current, and last, phase the feasibility of the electrostatic technique as a compound heat transfer augmentation methodology and its use in multi-tube heat exchangers was investigated. The compound enhancement experiments were performed on a commercially available finned tube by performing experiments on a micro-finned tube in the presence of electric field. Next, to address some of the practical problems that may be associated with the EHD technique, a multi-tube shell-and-tube heat exchanger was designed, fabricated, and experimentally tested. It is demonstrated that the EHD effect when used in conjunction with a low-fin or enhanced tube can yield additional enhancements to the already enhanced configuration as much as 80 percent in the present experiments technique.

Ohadi, M. M.; Ansari, A. I.



Electrostatic enhancement of heat transfer in gas-to-gas heat exchangers  

NASA Astrophysics Data System (ADS)

Basic study of electrohydrodynamic (EHD) enhancement of heat transfer in heat exchangers was the subject of an investigation. The author's efforts over the three-year project time period can be categorized into three consecutive phases. In phase 1, EHD heat transfer enhancements and pressure drop characteristics for conventional pipe flows as a function of electric field potential, field polarity, number of electrodes (single or double configuration), and flow regime (Reynolds number ranging from fully laminar to fully turbulent conditions) were studied. Study of heat transfer enhancements and pressure drop characteristics in a shell-and-tube, gas-to-gas heat exchanger were performed in Phase 2 of the project. To address the applicability of the EHD technique under operating conditions of gas-fired equipment, the role of various working fluid properties were studied in Phase 3 of the project. Specifically, effects of working fluid humidity, temperature, pressure, and impurity level on the magnitude and nature of the EHD heat transfer enhancements were studied. A maximum of 322 percent heat transfer enhancement with only 112 percent increase in pressure drops was achieved under simultaneous excitation of the tube and shell sides of the heat exchanger in the study. With optimized electric and flow field parameters, much higher enhancements can be expected.

Ohadi, M. M.



32 CFR 643.112 - Army exchange activities.  

Code of Federal Regulations, 2013 CFR

...2013-07-01 2013-07-01 false Army exchange activities. 643.112 Section...Defense (Continued) DEPARTMENT OF THE ARMY (CONTINUED) REAL PROPERTY REAL ESTATE...Authority of Commanders § 643.112 Army exchange activities. Use of space...



Liquid–gas heat exchanger for household refrigerator  

Microsoft Academic Search

This paper considers the influence of heat exchangers to the efficiency of a household refrigerating system. A steady state mathematical model is used to compare three most commonly used heat exchanger designs. For each design, an optimal inner diameter of the heat exchanger, subject to the compressor's capacity and the heat exchanger's length is found. The influence of operating conditions,

V. Dagilis; L. Vaitkus; A. Bal?ius



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

NASA Astrophysics Data System (ADS)

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.

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



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...


Influence of rain on air-sea gas exchange: Lessons from a model ocean  

Microsoft Academic Search

Rain has been shown to significantly enhance the rate of air-water gas exchange in fresh water environments, and the mechanism behind this enhancement has been studied in laboratory experiments. However, in the ocean, the effects of rain are complicated by the potential of causing density stratification at the water surface. Since it is difficult to perform controlled rain-induced gas exchange

D. T. Ho; C. Zappa; W. R. McGillis; L. F. Bliven; B. Ward; J. W. H. Dacey; P. Schlosser; M. B. Hendricks



In situ evaluation of air-sea gas exchange parameterizations using novel conservative and volatile tracers  

Microsoft Academic Search

Measurements of air-sea gas exchange rates are reported from two deliberate tracer experiments in the southern North Sea during February 1992 and 1993. A conservative tracer, spores of the bacterium Bacillus globigii var. Niger, was used for the first time in an in situ air-sea gas exchange experiment. This nonvolatile tracer is used to correct for dispersive dilution of the

Philip D. Nightingale; Gill Malin; Cliff S. Law; Andrew J. Watson; Peter S. Liss; Malcolm I. Liddicoat; Jacqueline Boutin; Robert C. Upstill-Goddard




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 ...


Leaf gas exchange of cassava as affected by quality of planting material and water stress  

Microsoft Academic Search

Field trial was conducted to study the effects of quality of planting material and prolonged water stress on leaf gas exchange of the cassava (Manihot esculenta Crantz) cultivar M Col 1684. Nutrient contents of planting material affected rootlet formation, but not leaf gas exchange. Net photosynthetic rate (PN), stomatal conductance (gs), and intercellular CO2 concentration (Ci) were significantly reduced by

M. G. Cayón; M. A. El-Sharkawy; L. F. Cadavid



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

ERIC Educational Resources Information Center

|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…

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



New designs of heat exchangers for natural gas liquefying and separating plants  

Microsoft Academic Search

The special operational features of heat exchangers of natural gas liquefying and separating plants are shown. A new design\\u000a of coil heat exchanger having tubes finned with round wire with a statically uniform structure is described. The technical\\u000a specifications of heat exchangers finned with wire having annular intensifiers and of conventional coil flat-tube heat exchanger\\u000a are compared.

O. K. Krasnikova; O. M. Popov; V. N. Udut



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

PubMed Central

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.

Woods, H. Arthur; Smith, Jennifer N.



Tritium labelled nucleotides: Heterogeneous metal catalyzed exchange labelling of ATP with tritium gas  

SciTech Connect

Adenosine 5{prime} triphosphate (ATP) in aqueous solution has been labeled by exchange with tritium gas in the presence of palladium oxide catalyst. Comparison with our experiments using Pd/BaSO{sub 4} as the catalyst shows that we have obtained product with higher specific activity and improved chemical purity. {sup 3}H NMR spectroscopy of the tritiated ATP shows labelling in both the C-8 and C-2 positions, and the integral ratio of these positions was found to vary from 3:1 to 1:1 under different reaction conditions. 5 refs., 1 fig., 2 tabs.

Jaiswal, D.K. (Defence Research and Development Establishment, Gwalior (India)); Morimoto, H.; Williams, P.G.; Wemmer, D.E. (Lawrence Berkeley Lab., CA (United States))



Hot gas heat exchanger fired from the fluidized bed wood combustor  

Microsoft Academic Search

An atmospheric fluidized-bed combustor hot gas heat exchanger system has operated in Green Bay, WI since the spring of 1983. The system burns 50% moisture wood residue, and provides nearly 100 MM BTU\\/hour of clean process air at 100 deg. F. for a paper dryer. The gas-to-air heat exchanger receives hot, dirty exhaust gas at 1800 deg. F. directly from



Liquid-Metal-Gas Heat Exchanger for HTGR Type Reactors.  

National Technical Information Service (NTIS)

The aim of this study is to investigate the heat transfer characteristics of a liquid metal heat exchanger (HE) for a helium-cooled high temperature reactor. A tube-type heat exchanger is considered as well as two direct exchangers: a bubble-type heat exc...

G. Werth



Effects of wind speed on leaf energy and gas exchange  

NASA Astrophysics Data System (ADS)

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.

Schymanski, Stanislaus J.; Or, Dani



Effects of Ozone on Gas Exchange in Invasive Forest Plants.  

NASA Astrophysics Data System (ADS)

Evaluations of invasive plant biology have failed to investigate the relationship between leaf structure and effects of ozone among closely related native and non-native plants. When exposed to toxic pollutants plants with lower stomatal density and lower stomatal conductance might experience reduced exposure and consequently be more competitive. To test for systematic differences between invasive and native species, experiments assessed the stomatal density and stomatal conductance of nine non-native invasive species and thirteen native species. Field sites, used for forest surveys, centered on three urban areas including sites with differing ozone levels (low 0-60 ppb, medium 80-99 ppb, high 111-125+ ppb). Three sites were selected within each of the three urban areas, and surveys were taken at each of the nine sites determining the native and non-native plant composition. The low level sites had greater densities of native plants than the high ozone level sites. Leaf impressions revealed a significantly higher (t = 14.13, p < 0.0001) stomatal density for the natives, and a LI-COR 1600 showed significantly higher (Fndf,ddf = 12.88, p = 0.0004) stomatal conductance for native plants. Dissimilar gas-exchange capacities are likely to be linked to the observed differences in plant composition among study sites. The importance of addressing air and biotic pollution grows every year as human health, agriculture, and ecosystem function are negatively affected in new areas.

Elton, E. E.



IAEA activities in Gas-cooled Reactor technology development  

SciTech Connect

The International Atomic Energy Agency (IAEA) has the charter to ``foster the exchange of scientific and technical information``, and ``encourage and assist research on, and development and practical application of, atomic energy for peaceful uses throughout the world``. This paper describes the Agency`s activities in Gas-cooled Reactor (GCR) technology development.

Cleveland, J. [Oak Ridge National Lab., TN (United States); Kupitz, J. [International Atomic Energy Agency, Vienna (Austria)



IAEA activities in Gas-cooled Reactor technology development  

SciTech Connect

The International Atomic Energy Agency (IAEA) has the charter to foster the exchange of scientific and technical information'', and encourage and assist research on, and development and practical application of, atomic energy for peaceful uses throughout the world''. This paper describes the Agency's activities in Gas-cooled Reactor (GCR) technology development.

Cleveland, J. (Oak Ridge National Lab., TN (United States)); Kupitz, J. (International Atomic Energy Agency, Vienna (Austria))



Gas developments lead Canadian activity  

SciTech Connect

Canada has an immense supply of natural gas. The Western Sedimentary Basin of Canada is North America`s largest gas-bearing geologic province and extends from British Columbia on Canada`s west coast, eastward through the provinces of Alberta, Saskatchewan and Manitoba and includes portions of the Northwest Territories and the Yukon. The basin supplies most of Canada`s natural gas with nearly 85% of it coming from Alberta. The production of natural gas supplies from conventional fields continues to increase. Major gas discoveries, made in the frontier and offshore regions, are going to be developed as well over time, as the economics and the markets dictate. Furthermore, Canada`s relatively unexplored Arctic and offshore basins, which promise excellent geological potential, will be developed at some point in the future. The paper discusses gas exploration and drilling activities, market access, the future of Canadian natural gas, how price challenges development of heavy oil and tar sands, and extending life of oil fields.

Riahi, M.L.; Perdue, J.M.; Kunkel, B.




EPA Science Inventory

A project promoting the exchange of information on polychlorinated dibenzo-p-dioxins and related chemicals has been initiated on an international basis. The project is being conducted under the auspices of the Committee on the Challenges of Modern Society of the North Atlantic Tr...


Gas-Substrate Heat Exchange During Cold-Gas Dynamic Spraying  

NASA Astrophysics Data System (ADS)

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.

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



Effect of Partition Wall on Heat Transfer Characteristics of a Gas-to-Gas Counterflow Microchannel Heat Exchanger  

Microsoft Academic Search

The effect of a partition wall on heat transfer characteristics of a two-stream gas-to-gas counterflow microchannel heat exchanger has been numerically investigated. The flow passages of the microchannel heat exchanger are plane channels of 100 ?m in height and 20 mm in length. The material of the partition wall is assumed to be stainless steel. The computations were performed for

Kohei Koyama; Chungpyo Hong; Yutaka Asako



Simultaneous Measurement of Acetylene Reduction and Respiratory Gas Exchange of Attached Root Nodules 1  

PubMed Central

A method was developed for the simultaneous measurement of acetylene reduction, carbon dioxide evolution and oxygen uptake by individual root nodules of intact nitrogen-fixing plants (Alnus rubra Bong.). The nodules were enclosed in a temperature-controlled leak-tight cuvette. Assay gas mixtures were passed through the cuvette at a constant, known flow rate and gas exchange was measured by the difference between inlet and outlet gas compositions. Gas concentrations were assayed by a combination of an automated gas chromatograph and a programmable electronic integrator. Carbon dioxide and ethylene evolution were determined with a coefficient of variation which was less than 2%, whereas the coefficient of variation for oxygen uptake measurements was less than 5%. Nodules subjected to repeated removal from and reinsertion into the cuvette and to long exposures of 10% v/v acetylene showed no irreversible decline in respiration or acetylene reduction. This system offers long-term stability and freedom from disturbance artifacts plus the ability to monitor continuously, rapidly and specifically the changes in root nodule activity caused by environmental perturbation.

Winship, Lawrence J.; Tjepkema, John D.



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


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

Matthews, Philip G D; White, Craig R



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

SciTech Connect

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.

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



Interaction of Anti-G Measures and Chest Wall Mechanics in Determining Gas Exchange.  

National Technical Information Service (NTIS)

During the last twelve months, progress has been made in three experimental areas: (1) determination that right ventricular blood provides an accurate mixed venous blood sample in the canine; (2) investigation of gas exchange during repeated canine +Gz ex...

H. I. Modell



Ventilation, Lung Volumes, and Gas Exchange During Lower Body Negative Pressure.  

National Technical Information Service (NTIS)

Ventilation, lung volumes, and gas exchange were measured in six normal subjects before, during, and following the application of -40 mm Hg lower body negative pressure (LBNP). Mean arterial pressure was unchanged by LBNP, but heart rate increased signifi...

A. R. Dowell P. G. Schmid D. O. Nutter K. N. Sullivan



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


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

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



A trace gas technique for measuring clothing microclimate air exchange rates  

PubMed Central

Crockford, G. W., Crowder, M., and Prestidge, S. P. (1972).Brit. J. industr. Med.,29, 378-386. A trace gas technique for measuring clothing microclimate air exchange rates. The rate at which clothing microclimate air is exchanged for ambient air influences the sensible and insensible heat loss from the microclimate. Factors which influence this air exchange are clothing permeability, wind speed, body movements, clothing design, and fabric properties. The influence of the first four factors has been studied using a trace gas technique for measuring the rate at which microclimate air is exchanged for ambient air. The trace gas technique and the mathematical model describing the loss of the trace gas from the microclimate are described. The technique is shown to have a high resolving power, enabling small changes in the four factors studied to be identified, and as the method is also very quick detailed studies of garment design can be made. Images

Crockford, G. W.; Crowder, M.; Prestidge, S. P.



Skyrmions in electron gas with nonlocal exchange in a strong magnetic field  

Microsoft Academic Search

The energy and action for skyrmions in two-dimensional electron gas with nonlocal exchange have been calculated. The energy\\u000a of positively charged skyrmions is considerably lower than the energy of negatively charged skyrmions and does not contain\\u000a an exchange contribution. The action has been calculated taking into account collective skyrmion null modes.

S. V. Iordanskii; S. G. Plyasunov; V. I. Falko



Trace Gas Dynamics in Snow and Their Role in Snow-Atmosphere Surface Exchanges (Invited)  

Microsoft Academic Search

The strength and persistence of stable atmospheric conditions above snow cover exemplifies the influence of surface fluxes on atmospheric composition and chemistry. Recent research has also shown that gases inside the snowpack exchange rapidly with air above the surface. Consequently, chemical transformations in the snowpack can have a determining effect on gas exchanges and atmospheric chemistry over snow. Our snow

D. Helmig; R. E. Honrath; B. A. van Dam; L. J. Kramer; L. Ganzeveld; B. Seok; P. V. Doskey; H. Jacques



Impact of leaf physiology on gas exchange in a Japanese evergreen broad-leaved forest  

Microsoft Academic Search

We used a multi-layer model to analyse the impact of leaf physiology on the diurnal, seasonal, and inter-annual fluctuations in gas exchange in a warm-temperate evergreen broad-leaved forest in Japan. The influences of physiological parameters at the single leaf scale on the canopy scale gas exchange were investigated, including normalised dark respiration rate, Rnleaf25, normalised maximum carboxylation rate, Vcmax25, and

Yoshiko Kosugi; Satoru Takanashi; Naoko Matsuo; Katsunori Tanaka; Hiroki Tanaka



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


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

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




Microsoft Academic Search

The object of the investigation is a mixed gas Joule-Thomson (J-T) cooler. A computa- tional model was developed, which makes it possible to investigate the steady state behavior of the refrigerant in the heat exchanger of a mixed gas J-T system. The calculations show that the temperature distribution as well as the pressure distribution in the heat exchanger channels depends

A. Alexeev; A. Thiel; Ch. Haberstroh; H. Quack


Characterization of air-sea gas exchange processes and dissolved gas/ice interactions using noble gases  

NASA Astrophysics Data System (ADS)

In order to constrain the processes controlling the cycles of biogeochemically important gases such as O2 and CO2, and thereby infer rates of biological activity in the upper ocean or the uptake of radiatively important ``greenhouse'' gases, the noble gases are used to characterize and quantify the physical processes affecting the dissolved gases in aquatic environments. The processes of vertical mixing, gas exchange, air injection, and radiative heating are investigated using a 2 year time-series of the noble gases, temperature, and meteorological data from Station S near Bermuda, coupled with a 1-dimensional upper ocean mixing model to simulate the physical processes in the upper ocean. The rate of vertical mixing that best simulates the thermal cycle is 1.1 +/- 0.1 × 10-4 m s-1. The gas exchange rate required to simulate the data is consistent with the formulation of Wanninkhof (1992) to +/-40%, while the formulation of Liss and Merlivat (1986) must be increased by a factor of 1.7 +/- 0.6. The air injection rate is consistent with the formulation of Monahan and Torgersen (1991) using an air entrainment velocity of 3 +/- 1 cm s-1. Gas flux from bubbles is dominated on yearly time-scales by larger bubbles that do not dissolve completely, while the bubble flux is dominated by complete dissolution of bubbles in the winter at Bermuda. In order to obtain a high-frequency time-series of the noble gases to better parameterize the gas flux from bubbles, a moorable, sequential noble gas sampler was developed. Preliminary results indicate that the sampler is capable of obtaining the necessary data. Dissolved gas concentrations can be significantly modified by ice formation and melting, and due to the solubility of He and Ne in ice, the noble gases are shown to be unique tracers of these interactions. A three-phase equilibrium partitioning model was constructed to quantify these interactions in perennially ice-covered Lake Fryxell, and this work was extended to oceanic environments. Preliminary surveys indicate that the noble gases may provide useful and unique information about interactions between water and ice. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.)

Hood, Eda Maria


Vertical variation in leaf gas exchange parameters for a Southeast Asian tropical rainforest in Peninsular Malaysia.  


Vertical variation in leaf gas exchange characteristics of trees grown in a lowland dipterocarp forest in Peninsular Malaysia was investigated. Maximum net photosynthetic rate, stomatal conductance, and electron transport rate of leaves at the upper canopy, lower canopy, and forest floor were studied in situ with saturated condition photosynthetic photon flux density. The dark respiration rate of leaves at the various heights was also studied. Relationships among gas exchange characteristics, and also with nitrogen content per unit leaf area and leaf dry matter per area were clearly detected, forming general equations representing the vertical profile of several important parameters related to gas exchange. Numerical analysis revealed that the vertical distribution of gas exchange parameters was well determined showing both larger carbon gain for the whole canopy and at the same time positive carbon gain for the leaves of the lowest layer. For correct estimation of gas exchange at both leaf and canopy scales using multi-layer models, it is essential to consider the vertical distribution of gas exchange parameters with proper scaling coefficients. PMID:22644315

Kosugi, Yoshiko; Takanashi, Satoru; Yokoyama, Naoto; Philip, Elizabeth; Kamakura, Mai



Platelet sodium-hydrogen exchanger activity and left ventricular mass  

Microsoft Academic Search

Introduction: The sodium-hydrogen exchanger (NHE) is integral to the processes that facilitate cell growth and may contribute to the development of left ventricular hypertrophy. The aim of this study was to examine the relationship between platelet sodium-hydrogen exchanger activity and left ventricular mass index (LVMI).Methods: Twenty male untreated Caucasians (mean age ± s.d.: 48 ± 13; body mass index: 29

TK Khong; GA Sagnella; ND Markandu; MA Miller; CG Missouris; GA MacGregor; TK Khong MRCP



Detection of oligonucleotide gas-phase conformers: H\\/D exchange and ion mobility as complementary techniques  

Microsoft Academic Search

Gas-phase hydrogen\\/deuterium exchange of small oligonucleotides (dTG, dC6 and C6) with CD3OD was performed in the second hexapole of a Fourier transform ion-cyclotron resonance (FTICR) mass spectrometer. Ion activation\\u000a experiments were conducted by accelerating the ions at the entrance of the H\\/D exchange cell under conditions promoting exclusively\\u000a collisional isomerization. These experiments allowed us to assess the presence of several

Dorothée Balbeur; Joëlle Widart; Bernard Leyh; Laetitia Cravello; Edwin De Pauw



Effects of respiratory rate and tidal volume on gas exchange in total liquid ventilation.  


Using a rabbit model of total liquid ventilation (TLV), and in a corresponding theoretical model, we compared nine tidal volume-respiratory rate combinations to identify a ventilator strategy to maximize gas exchange, while avoiding choked flow, during TLV. Nine different ventilation strategies were tested in each animal (n = 12): low [LR = 2.5 breath/min (bpm)], medium (MR = 5 bpm), or high (HR = 7.5 bpm) respiratory rates were combined with a low (LV = 10 ml/kg), medium (MV = 15 ml/kg), or high (HV = 20 ml/kg) tidal volumes. Blood gases and partial pressures, perfluorocarbon gas content, and airway pressures were measured for each combination. Choked flow occurred in all high respiratory rate-high volume animals, 71% of high respiratory rate-medium volume (HRMV) animals, and 50% of medium respiratory rate-high volume (MRHV) animals but in no other combinations. Medium respiratory rate-medium volume (MRMV) resulted in the highest gas exchange of the combinations that did not induce choke. The HRMV and MRHV animals that did not choke had similar or higher gas exchange than MRMV. The theory predicted this behavior, along with spatial and temporal variations in alveolar gas partial pressures. Of the combinations that did not induce choked flow, MRMV provided the highest gas exchange. Alveolar gas transport is diffusion dominated and rapid during gas ventilation but is convection dominated and slow during TLV. Consequently, the usual alveolar gas equation is not applicable for TLV. PMID:19506467

Bull, Joseph L; Tredici, Stefano; Fujioka, Hideki; Komori, Eisaku; Grotberg, James B; Hirschl, Ronald B


Prediction of Total Dissolved Gas Exchange at Hydropower Dams, Report.  

National Technical Information Service (NTIS)

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 ge...

B. Hadjerioua F. K. Pasha K. Stewart M. D. Bender M. L. Schneider



Linking employee development activity, social exchange and organizational citizenship behavior  

Microsoft Academic Search

The authors examined ‘perceived beneficiary’ of employee development (self, organization) for relationships with employee development activity. Perceived organizational support served as a moderator. The authors conclude that employees may engage in development activities to partly benefit their organization to the extent that a positive exchange relationship exists. Correlational data also show that development behavior is related to organizational citizenship behavior,

Heather R. Pierce; Todd J. Maurer



Trace gas exchange above the floor of a deciduous forest: 1. Evaporation and CO2 efflux  

Microsoft Academic Search

The eddy correlation method has great potential for directly measuring trace gas fluxes at the floor of a forest canopy, but a thorough validation study has not been yet conducted. Another appeal of the eddy correlation method is its ability to study processes that regulate and modulate gas exchange between the soil\\/litter complex and the atmosphere that cannot be probed

Dennis D. Baldocchi; Tilden P. Meyers



Development of a novel box-shaped shake flask with efficient gas exchange capacity  

Microsoft Academic Search

A novel box-shaped shake flask with membrane filters fitted in its upper sides was developed for efficient gas exchange. During rotation, the liquid flow inside the flask is broken up at the four angles of the flask, while membrane filters in opposite sides serve alternately as gas inlet and outlet ports, depending on the direction in which the flask is

Isao Kato; Hideo Tanaka



Fuel cell with polymer electrolyte: calculation of overall characteristics of oxygen cathode with account for processes of gas, vapor, and heat exchange  

Microsoft Academic Search

Computer simulation was performed for the processes occurring in the basic elements of the cathode (active layer, gas-diffusion\\u000a layer) and bipolar plate of a fuel cell with Nafion as electrolyte and a platinum catalyst. Current generation in the active\\u000a layer was considered together with the heat exchange processes (release of the heat formed in the active layer through the\\u000a gas-diffusion

Yu. G. Chirkov; V. I. Rostokin



The effect of prolonged submaximal exercise on gas exchange kinetics and ventilation during heavy exercise in humans  

Microsoft Academic Search

This study compared ventilation, gas exchange (oxygen uptake, V?O2) and the surface electromyogram (EMG) activity of four major lower limb muscles during heavy exercise before (Pre-Ex) and\\u000a after (Post-Ex) a sustained 90-min cycling exercise at 60% V?O2peak. The 90-min exercise was incorporated under the hypothesis that sustained exercise would alter substrate availability in\\u000a the second exercise bout causing differences in

Stephane Perrey; Robin Candau; Jean-Denis Rouillon; Richard L. Hughson



Hydraulically actuated gas exchange valve assembly and engine using same  


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.

Carroll, Thomas S. (Peoria, IL); Taylor, Gregory O. (Hinsdale, IL)



The effect of rain on air-water gas exchange  

Microsoft Academic Search

The relationship between gas transfer velocity and rain rate was investigated at NASA's Rain-Sea Interaction Facility (RSIF) using several SF6 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

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



Nonequilibrium membranes : exchanges and active transport  

Microsoft Academic Search

Many function of the biological systems (cells and internal organelles such as mitochondria, ) depends directly on the structure of the biological membranes since they serve to separate and protect a cell or an organelle from its surrounding environment. Cell membranes play a role essential to the life in a variety of biological processes like passive and active transport, recognition,

Phillippe Girard


Facilitated separation of a select gas through an ion exchange membrane  

Microsoft Academic Search

Suitable for separating COâ, HâS, olefins, etc., from a gas mixture, GE's selective purification process uses an ion-exchange membrane that has specific mobile counter-ions electrostatically retained in it. These counter-ions react reversibly with the specific gas molecules to be separated. Besides being highly selective, the membrane facilitates gas transport across it, thus accomplishing a separation superior to that of other

S. G. Kimura; W. J. Ward; S. L. Matson



Gas Separation Using Ion Exchange Membranes: Final Report.  

National Technical Information Service (NTIS)

The objectives of this project were twofold. The primary objective was to demonstrate the concept of using reactive ion exchange membranes (IEMs) containing organic amines for the separation of CO sub 2 and H sub 2 S from coal gasification product gases. ...

J. D. Way R. D. Noble L. A. Powers



A Continuum Model for Metabolic Gas Exchange in Pear Fruit  

Microsoft Academic Search

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

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



Gas turbine heat exchanger in the fluidized bed combustor  

Microsoft Academic Search

Design guidelines for an in-bed heat exchanger that is exposed to high temperatures (850C) and sulfidation are given based on research results. The combustor was designed to use a high sulfur coal of approximately 4 percent sulfur. Limestone or dolomite additions neutralize the sulfur action to a certain extent. Results of series of measurements of oxygen partial pressure at various

C. F. Holt; A. A. Boiarski; H. E. Carlton




Microsoft Academic Search

A corroded heat exchanger failing after only a few years of service has been investigated. Critical species causing corrosion were identified. These are sulfuric acid generated by oxidation of SO2 to SO3 and dissolution in water and nitric acid by dissolution of NO2 in water. Corrosion products hydrolyse during service to a significant extent. By a calculation of burning of

G. Mori; H. Zitter


Development of residential gas-fired furnaces using heat pipe heat exchangers. Final report, July 1988-February 1992  

SciTech Connect

The principal objective of the heat pipe heat exchanger development program was to design, fabricate, and demonstrate the performance of heat pipe heat exchangers for gas-fired residential furnaces that improved upon the previously marketed heat pipe furnace.

Dussinger, P.M.; Hartenstine, J.R.



Development of Residential Gas-Fired Furnaces Using Heat Pipe Heat Exchangers. Final Report, July 1988-February 1992.  

National Technical Information Service (NTIS)

The principal objective of the heat pipe heat exchanger development program was to design, fabricate, and demonstrate the performance of heat pipe heat exchangers for gas-fired residential furnaces that improved upon the previously marketed heat pipe furn...

P. M. Dussinger J. R. Hartenstine



Development of residential gas-fired furnaces using heat pipe heat exchangers. Final report, July 1988February 1992  

Microsoft Academic Search

The principal objective of the heat pipe heat exchanger development program was to design, fabricate, and demonstrate the performance of heat pipe heat exchangers for gas-fired residential furnaces that improved upon the previously marketed heat pipe furnace.

P. M. Dussinger; J. R. Hartenstine



In situ evaluation of air-sea gas exchange parameterizations using novel conservative and volatile tracers  

NASA Astrophysics Data System (ADS)

Measurements of air-sea gas exchange rates are reported from two deliberate tracer experiments in the southern North Sea during February 1992 and 1993. A conservative tracer, spores of the bacterium Bacillus globigii var. Niger, was used for the first time in an in situ air-sea gas exchange experiment. This nonvolatile tracer is used to correct for dispersive dilution of the volatile tracers and allows three estimations of the transfer velocity for the same time period. The first estimation of the power dependence of gas transfer on molecular diffusivity in the marine environment is reported. This allows the impact of bubbles on estimates of the transfer velocity derived from changes in the helium/sulphur hexafluoride ratio to be assessed. Data from earlier dual tracer experiments are reinterpreted, and findings suggest that results from all dual tracer experiments are mutually consistent. The complete data set is used to test published parameterizations of gas transfer with wind speed. A gas ex- change relationship that shows a dependence on wind speed intermediate between those ofLiss and Merlivat [1986] and Wanninkhof [1992] is found to be optimal. The dual tracer data are shown to be reasonably consistent with global estimates of gas exchange based on the uptake of natural and bomb-derived radiocarbon. The degree of scatter in the data when plotted against wind speed suggests that parameters not scaling with wind speed are also influencing gas exchange rates.

Nightingale, Philip D.; Malin, Gill; Law, Cliff S.; Watson, Andrew J.; Liss, Peter S.; Liddicoat, Malcolm I.; Boutin, Jacqueline; Upstill-Goddard, Robert C.



Teaching Pulmonary Gas Exchange Physiology Using Computer Modeling  

ERIC Educational Resources Information Center

|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

Kapitan, Kent S.



Relationship Between Wind Speed and Gas Exchange Over the Ocean  

Microsoft Academic Search

Relationships between wind speed and gas transfer, combined with knowledge of the partial pressure difference of CO2 across the air-sea interface, are frequently used to determine the CO2 flux between the ocean and the atmosphere. Little attention has been paid to the influence of variability in wind speed on the calculated gas transfer velocities and the possibility of chemical enhancement

Rik Wanninkhof



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

Microsoft Academic Search

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

J. I. Gitelson; Yu. N. Okladnikov



Alveolar gas exchange and tissue oxygenation during incremental treadmill exercise, and their associations with blood O(2) carrying capacity.  


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 O(2) 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 O(2) 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- (?[O(2)Hb]), deoxy- (?[HHb]) and total hemoglobin (?[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 O(2) 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., ?[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 O(2) 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 O(2) carrying was associated with a high level of m. vastus lateralis deoxygenation at peak exercise. PMID:22934021

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



Low Net Community Production from Oxygen/Argon Mass Balance during the Southern Ocean Gas Exchange Experiment  

NASA Astrophysics Data System (ADS)

Mass balance techniques using oxygen/argon ratios can yield high quality estimates of net community production. By ratioing with argon, the oxygen signal is corrected for physical influences such as bubble- mediated gas exchange and temperature change. We made near-continuous observations of dissolved oxygen/argon ratios and absolute oxygen concentrations in surface seawater pumped into the ship during the Southern Ocean Gas Exchange Experiment (SO GasEx). This experiment focused on an area to the east of the southern tip of South America during March and April 2008. Oxygen was measured by optode and calibrated with Winkler titrations. Oxygen/argon ratios were measured using a quadrupole mass spectrometer with a membrane equilibrator inlet. Ratios were standardized by comparison with air values and further calibrated by discrete measurements made by high-accuracy sector mass spectrometry. Repeated Winkler measurements of oxygen concentrations in water collected from Niskin bottles and the underway system confirmed the absence of heterotrophic activity in the ship's seawater lines. Spatial surveys showed significant variability in net community production around the study area. Preliminary estimates of productivity in the 3He/SF6 tracer patches laid down for the gas exchange experiment suggested that the first tracer patch had small but measurable rates of net community production but that the second tracer patch was characterized by net respiration or recent upwelling.

Hamme, R. C.; Cassar, N.



High temperature active heat exchanger research for latent heat storage  

Microsoft Academic Search

An active heat exchange method in a latent heat (salt) thermal energy storage system that prevents a low conductivity solid salt layer from forming on heat transfer surfaces was developed. An evaluation of suitable media with melting points in the temperature range of interest (250 to 400 C) limited the candidates to molten salts from the chloride, hydroxide and nitrate

J. Alario; R. Haslett



Temperature and water regulation of gas exchange of Opuntia polyacantha  

Microsoft Academic Search

Opuntia polyacantha was collected from the shortgrass prairie in Colorado. Carbon dioxide and water vapor exchange was monitored in plants pretreated and analyzed under cool temperatures (20\\/15°C) and warm temperatures (35\\/15°C). Well watered plants under a 35\\/15 thermoperiod supported the fixation of atmospheric CO2 during the night, early morning, and late afternoon. Plants under a 20\\/15 thermoperiod exhibited CO2 uptake

B. Clifford Gerwick; George J. Williams



Gas exchanges between galaxies and IGM (Rodrigues+, 2012)  

NASA Astrophysics Data System (ADS)

The galaxies presented in this paper are a subsample of Rodrigues et al. (2008A&A...492..371R) which have available archival Hubble Space Telescope (HST) data. The imaging is used to measure their gas radius and to derive their gas fraction. The targets have been gathered from the IMAGES-FORS2 survey, a representative sample drawn from both spectroscopic and MJ selection criteria (see Rodrigues et al., 2008A&A...492..371R). (2 data files).

Rodrigues, M.; Puech, M.; Hammer, F.; Rothberg, B.; Flores, H.




Microsoft Academic Search

A compartmental-population balance model is presented for describing heat transfer in gas-solid flu- idized bed heat exchangers, modelling the particle-particle and particle-surface heat transfers by colli- sions. The results of numerical experimentation, obtained by means of a second order moment equation model indicate that the model can be used efficiently for analysing fluidized bed heat exchangers recover- ing heat either



Nonlocal approximation to the exchange potential and kinetic energy of an inhomogeneous electron gas  

Microsoft Academic Search

A nonlocal approximation to the exchange energy and the exchange potential of an inhomogeneous electron gas is presented that is based on the conservation of the main characteristics of the correct Fermi hole. Tested for atoms, it gives better results than the local-density approximation. A new kinetic-energy functional in the Hartree-Fock approximation is also derived that depends explicitly on the

J. A. Alonso; L. A. Girifalco



Gas-Chromatographic Identification of UrinaryCarbohydrates Isolatedby AnionExchange Chromatography  

Microsoft Academic Search

More than 40 chromatographic peaks representing carbohydrates have been separated from human urine by a carbohydrate analyzer that makes use of anion-exchange chromatography. Ten of these separated carbo- hydrates have been identified by gas chromatography of their trimethyl- silyl derivatives, which were formed by reaction with N-trimethylsilylimid- azole. The borate buffer from the anion-exchange separation was removed from the samples

W. C. Buttsand; R. L. Jolley


Fluctuation scaling of quotation activities in the foreign exchange market  

NASA Astrophysics Data System (ADS)

We study the scaling behavior of quotation activities for various currency pairs in the foreign exchange market. The components’ centrality is estimated from multiple time series and visualized as a currency pair network. The power-law relationship between a mean of quotation activity and its standard deviation for each currency pair is found. The scaling exponent ? and the ratio between common and specific fluctuations ? increase with the length of the observation time window ?t. The result means that although for ?t=1(min), the market dynamics are governed by specific processes, and at a longer time scale ?t>100(min) the common information flow becomes more important. We point out that quotation activities are not independently Poissonian for ?t=1(min), and temporally or mutually correlated activities of quotations can happen even at this time scale. A stochastic model for the foreign exchange market based on a bipartite graph representation is proposed.

Sato, Aki-Hiro; Nishimura, Maiko; Ho?yst, Janusz A.



Gas generation and bubble formation model for crystalline silicotitanate ion exchange columns  

SciTech Connect

The authors developed a transient model to describe the process of gas generation due to radiolysis and bubble formation in crystalline silicotitanate (CST) ion exchange (IX) columns using the Aspen Custom Modeler (ACM) software package. The model calculates gas concentrations and onset of bubble formation for large CST IX columns. The calculations include cesium loading as a function of time, gas generation as a function of cesium loading, and bubble formation as a function of gas solubility. This report summarizes the model development and predictions.

Hang, T.



Near and Far Scale Gas Exchange Associated with Natural Marine Hydrocarbon Seeps  

NASA Astrophysics Data System (ADS)

The Coal Oil Point seep field, Santa Barbara Channel, CA, USA is one of the world's most intense areas of natural marine hydrocarbon seepage. Oil and gas is emitted from seafloor vents, which occur mostly in water depths between 20 and 70 m over an area of about 3 km2. Detailed measurements of bubble composition, dissolved gas concentrations, seepage rates, and plume dynamics have been conducted over the last decade. Within rising bubble plumes, methane, carbon dioxide, and heavier hydrocarbons are lost while nitrogen and oxygen are gained due to bubble-seawater gas exchange. Dissolved methane concentrations are more than 4 orders of magnitude greater than atmospheric equilibrium concentrations in the water, which surrounds and rises with the bubbles. Strong upwelling flows (typically >40cm/s) were observed and bubble rise times are on the order of 1 minute (depending on water depth and upwelling flow), demonstrating the rapid exchange of gases within the bubble plume. Dissolved hydrocarbon plumes were mapped more than 20 km down current of the seep field. Surface mapping of the plume reveal that gas concentrations vary with current velocity (determined with the CODAR network). The influence of the far field air-water gas exchange is being examined in detail with Lagrangian experiments, where the water mass has been followed using surface drifters and dual gas (sulfur hexafluoride-He-3) tracer experiments. Preliminary results suggest gas loss is reduced by the oil slicks, which also drift down current from the seep field.

Clark, J. F.; Mau, S.; Valentine, D. L.; Ohlmann, J. C.; Washburn, L.; Leifer, I.



Gamma radiation effect on gas production in anion exchange resins  

NASA Astrophysics Data System (ADS)

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.

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



Dynamic modeling of active solar thermal systems with heat exchangers  

SciTech Connect

The successful design of cost-effective controllers for active solar energy systems requires the use of simulation models to predict the distributed dynamic thermal response of each system component. Such models have been developed for the collector and transport. However, the effects of distributed heat exchanger dynamics in the modeling of solar energy system dynamic performance have often been neglected due to model complexity. A dynamic distributed parameter heat exchanger model suitable for solar energy applications is presented. An exact transcendental transform solution is derived for this model. Analytical methods are used to obtain a rational approximate transform solution for counter flow operation which is capable of accepting arbitrary inputs. An error analysis of this approximate transform solution is presented. The exact and approximate transform solutions are in close agreement for a range of heat exchanger characteristics common in solar energy applications. The approximate heat exchanger model solution is incorporated into a simulation capable of estimating the distributed short-term dynamics and long-term thermal performance of an active solar energy system. A graphical presentation of simulation results is given.

Konyk, S. Jr.



Trace gas exchanges and convective transports over the Amazonian rain forest  

NASA Astrophysics Data System (ADS)

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 to estimate 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. The level of convective activity and the closely coupled Hadley and Walker circulations over the Amazon basin and its associated trace chemistry suggest the importance of this region to the global atmosphere.

Garstang, Michael; Scala, John; Greco, Steve; Harriss, Robert; Beck, Sherwin; Browell, Edward; Sachse, Glen; Gregory, Gerald; Hill, Gerald; Simpson, Joanne; Tao, Wei-Kuo; Torres, Arnold



Parameterization of Leaf-Level Gas Exchange for Plant Functional Groups From Amazonian Seasonal Tropical Rain Forest  

NASA Astrophysics Data System (ADS)

Plant communities exert strong influence over the magnitude of carbon and water cycling through ecosystems by controlling photosynthetic gas exchange and respiratory processes. Leaf-level gas exchange fluxes result from a combination of physiological properties, such as carboxylation capacity, respiration rates and hydraulic conductivity, interacting with environmental drivers such as water and light availability, leaf-to-air vapor pressure deficit, and temperature. Carbon balance models concerned with ecosystem-scale responses have as a common feature the description of eco-physiological properties of vegetation. Here we focus on the parameterization of ecophysiological gas-exchange properties of plant functional groups from a pristine Amazonian seasonally dry tropical rain forest ecosystem (FLONA-Tapajós, Santarém, PA, Brazil). The parameters were specific leaf weight, leaf nitrogen content, leaf carbon isotope ratio, maximum photosynthetic assimilation rate, photosynthetic carboxylation capacity, dark respiration rates, and stomatal conductance to water vapor. Our plant functional groupings were lianas at the top of the canopy, trees at the top of the canopy, mid-canopy trees and undestory trees. Within the functional groups, we found no evidence that leaves acclimated to seasonal changes in precipitation. However, there were life-form dependent distinctions when a combination of parameters was included. Top-canopy lianas were statistically different from top-canopy trees for leaf carbon isotope ratio, maximum photosynthetic assimilation rate, and stomatal conductance to water vapor, suggesting that lianas are more conservative in the use of water, causing a stomatal limitation on photosynthetic assimilation. Top-canopy, mid canopy and understory groupings were distinct for specific leaf weight, leaf nitrogen content, leaf carbon isotope ratio, maximum photosynthetic assimilation rate, and photosynthetic carboxylation capacity. The recognition that plant functional groups have distinct impacts on ecosystem-scale gas exchange can increase the accuracy of process-based carbon balance models where structure is known and when logging activities are incorporated into production models.

Domingues, T. F.; Berry, J. A.; Ometto, J. P.; Martinelli, L. A.; Ehleringer, J. R.



Neural Control of Gas Exchange Patterns in Insects: Locust Density-Dependent Phases as a Test Case  

PubMed Central

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.

Berman, Tali S.; Ayali, Amir; Gefen, Eran



Temperature effects on lung and blood gases in Bufo paracnemis: consequences of bimodal gas exchange  

Microsoft Academic Search

The arterial pH decreases with rising body temperature in ectothermic vertebrates. We report on how this regulation was achieved in relation to bimodal respiration in the toad Bufo paracnemis. Gas exchange was measured for the lung and also for the whole body (skin and lung). In addition, lung gas pressures (PLO2 and PLCO2) and arterial blood gases (pH and PO2)

T. Wang; A. S. Abe; M. L. Glass



Respiratory gas exchange in the assessment of patients with impaired ventricular function  

Microsoft Academic Search

Respiratory gas exchange on exercise was evaluated as a non-invasive method of assessing patients with heart failure. Twenty four men (age 28-72) with symptomatic chronic stable heart failure (New York Heart Association class II-III) and ten controls aged 36-70 were studied. During treadmill exercise oxygen consumption and carbon dioxide production were measured continuously by analysis of mixed expired gas with

D P Lipkin; J Perrins; P A Poole-Wilson



Air-Sea Gas Exchange Measured with 3He/SF6 during SO GasEx  

NASA Astrophysics Data System (ADS)

Two 3He/SF6 dual gas tracer experiment were conducted during the Southern Ocean Gas Exchange Experiment (SO GasEx) to determine gas transfer velocities, k(600). During the experiment, wind speeds of up to 19.5 m/s were encountered. A total of 361 3He and 609 SF6 samples were taken at 40 CTD casts and 2 pumped stations. k(600) was calculated from the decrease in the observed 3He/SF6 ratio, assuming that dispersion is a first order process. The results are compared to those of previous 3He/SF6 dual tracer experiment in the coastal and open ocean, and with commonly used parameterizations between wind speed and gas transfer velocity.

Ho, D. T.; Wanninkhof, R.; Schlosser, P.; Sullivan, K. F.



Reactant gas flow fields in advanced PEM (Proton Exchange Membrane) fuel cell designs. [Proton exchange membranes- Flow in gas channels  

SciTech Connect

A mathematical model of the two-phase flow in a fuel cell gas channel is developed and used to predict the mass, momentum, and thermal distributions of a multi-component gas and liquid water mixture on the cathode side. Regions were flooding may occur are demonstrated by using the model evaluated with various operating conditions typical of fuel cell operations. Conditions where dry, saturated, and two-phase flows are introduced into the channel are demonstrated and the results compared. These results show the distribution of water and heat in the channel which may be used to design better flow channels.

Kimble, M.C.; Vanderborgh, N.E.



Formaldehyde and tracer gas transfer between airstreams in enthalpy-type air-to-air heat exchangers  

Microsoft Academic Search

The formaldehyde, tracer gas, and water vapor transfer rates in two enthalpy exchangers were measured. The first exchanger uses a cross flow 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

W. J. Fisk; B. S. Pedersen; D. Hekmat; R. E. Chant; H. Kaboli



Gas phase RNA and DNA ions 2. Conformational dependence of the gas-phase H\\/D exchange of nucleotide-5?-monophosphates  

Microsoft Academic Search

The conformational dependence of the gas-phase hydrogen\\/deuterium (H\\/D) exchange of nucleotide-5-monophosphate anions with\\u000a the H\\/D exchange reagent D2S is reported here. The electrospray-generated [M ? H]? anions of adenosine-5?-monophosphate, adenosine-5?-carboxylic acid, ribitol-5-phosphate, and 2-deoxy-ribitol-5-phosphate\\u000a were reacted with D2S in the gas phase. Their reactivity (adenosine-5?-monophosphate exchanged 2 of 5 labile hydrogens, adenosine-5?-carboxylic\\u000a acid exchanged 1 of 4, ribitol-5-phosphate exchanged 2

Michael A. Freitas; Alan G. Marshall



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...


Assessment of saltwater intrusion impact on gas exchange behavior of Louisiana Gulf Coast wetland species  

Microsoft Academic Search

A review of gas exchange responses of wetland plants to salinity is presented for several species representative of different wetland habitats extending along water level and salinity gradients in the Louisiana Gulf Coast, U.S.A. The information was synthesized from earlier plant physiological response studies. Vegetation examined represent a broad range of sensitivity to salt, including brackish marsh, freshwater marsh, and

S. R. Pezeshki; R. D. DeLaune



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

NASA Astrophysics Data System (ADS)

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.

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



Program Plan for Development of Hot Dirty-Gas Heat Exchangers for Coal-Gasification Systems.  

National Technical Information Service (NTIS)

This report deals with the heat exchanger applications, and its scope includes a broad range of gasification systems, such as the generic models for entrained-flow, moving-bed, and fluidized-bed gasifiers. The major application of hot dirty-gas heat excha...

E. L. Churnetski



Multicomponent transport in porous electrodes of proton exchange membrane fuel cells using the interdigitated gas distributors  

Microsoft Academic Search

Hydrodynamics of gases in the cathode of a proton exchange membrane fuel cell that is contacted to an interdigitated gas distributor are investigated using a steady-state multicomponent transport model. The model describes the two-dimensional flow patterns and the distributions of the gaseous species in the porous electrode and predicts the current density generated t the electrode and membrane interface as

Jung Seok Yi; T. van Nguyen



Effects of two successive maximal exercise tests on pulmonary gas exchange in athletes  

Microsoft Academic Search

Pulmonary extravascular water accumulation may be involved in exercise-induced hypoxaemia in highly aerobically trained athletes. We hypothesized that if such an alteration were present in elite athletes performing a maximal exercise test, the impairment of gas exchange would be worse during a second exercise test following the first one. Eight male athletes performed two incremental exercise tests separated by a

Corinne F. Caillaud; Florence M. Anselme; Christian G. Prefaut



Effects of pneumoperitoneum on intraoperative pulmonary mechanics and gas exchange during laparoscopic gastric bypass  

Microsoft Academic Search

Background: Hypercarbia and elevated intraabdominal pressure resulting from carbon dioxide (CO 2) pneumoperitoneum can adversely affect respiratory mechanics. This study examined the changes in mechanical ventilation, CO 2 homeostasis, and pulmonary gas exchange in morbidly obese patients undergoing a laparoscopic or open gastric bypass (GBP) procedure. Methods: In this study, 58 patients with a body mass index (BMI) of 40

N. T. Nguyen; J. T. Anderson; M. Budd; N. W. Fleming; H. S. Ho; J. Jahr; C. M. Stevens; B. M. Wolfe



Gas exchange characteristics of Typha latifolia L. from nine sites across North America  

Microsoft Academic Search

Gas exchange characteristics were measured in the field for nine populations of Typha latifolia L. from Florida to Minnesota in North America. These populations spanned a substantial gradient in growing season length and environmental conditions. The purpose of this study was to assess geographic variability in stomatal conductance (gst) in T. latifolia populations, as well as to identify key environmental

Alan K. Knapp; Joseph B. Yavitt



Carbon dynamics and greenhouse gas exchanges in an age-sequence of temperate pine forests  

Microsoft Academic Search

Forest ecosystems play an important role in the global carbon (C) cycle by exchanging large amounts of carbon dioxide (CO2) with the atmosphere. Their potential to act as significant sink for atmospheric CO2 has been recognized and is relevant to current efforts in reducing atmospheric CO2 concentrations. Besides the most important greenhouse gas CO 2, forests also emit and consume

Matthias Peichl



Correlated patterns of tracheal compression and convective gas exchange in a carabid beetle  

Microsoft Academic Search

SUMMARY Rhythmic tracheal compression is a prominent feature of internal dynamics in multiple orders of insects. During compression parts of the tracheal system collapse, effecting a large change in volume, but the ultimate physiological significance of this phenomenon in gas exchange has not been determined. Possible functions of this mechanism include to convectively transport air within or out of the

John J. Socha; Wah-Keat Lee; Jon F. Harrison; James S. Waters; Kamel Fezzaa; Mark W. Westneat



Adenosine 5'-monophosphate in asthma: gas exchange and sputum cellular responses  

Microsoft Academic Search

Adenosine 59-monophosphate (AMP) bronchoprovocation reproduces the lung function abnormalities that occur spontaneously during acute asthma and detects peripheral airway inflammation better than direct bronchoconstrictive agents. Pulmonary gas exchange disturbances may reflect changes in small airways related to airway inflammation rather than bronchoconstriction alone. The present authors investigated whether AMP induced a greater imbalance in the ventilation\\/ perfusion ratio than methacholine

H. A. Manrique; F. P. Gomez; P. A. Munoz; A. M. Pena; J. A. Barbera; J. Roca; R. Rodriguez-Roisin



The efficacy of pulmonary thromboendarterectomy on long-term gas exchange  

Microsoft Academic Search

It has not been delineated in detail how pulmonary thromboen- darterectomy (PTE) affects gas exchange through long-term follow-up. In Japan, this surgery has been undertaken in a limited number of institutions, and the results of PTE have not been well publicized. A total of 25 patients were operated on during the period from 1985 to 1996 at our institution, and

N. Tanabe; O. Okada; Y. Nakagawa; M. Masuda; K. Kato; N. Nakajima; T. Kuriyama



Heartbeat and body movement: roles in gas exchange in Galleria mellonella L. (Lepidoptera: Pyralidae) pupae  

Microsoft Academic Search

The objective of the present article is to analyse the role of heartbeat and body movements in respiratory function in Galleria mellonella L. (Lepidoptera: Pyralidae) pupae with clear gas exchange cycles. We did not find any direct evidence of co-ordination between heartbeat and respiration or body movements and respiration. Cyclic CO2 output was independent of abdominal movements and heart pulsations

U Tartes; A Kuusik; A Vanatoa



The Gas Exchange of Animals Exposed to 100% Oxygen at Atmospheric Pressure.  

National Technical Information Service (NTIS)

Rats were exposed to 100% oxygen at near atmospheric pressure for times long enough to cause death or for 100 hours. The gas exchange was estimated from summations of carbon dioxide removed from the environmental system and oxygen added to it and from the...

G. H. Kydd



Pigments and Gas Exchange Characteristics in Leaves of Chlorophyll Mutants of Pisum sativum  

Microsoft Academic Search

Quantitative and qualitative characteristics of pigment composition and gas exchange were studied in chlorophyll mutants of pea, Pisum sativum L.: chlorotica 2004 and 2014. The mutant 2004 had light-green color, whereas the mutant 2014 has yellow-green leaves and stems; they contained about 80 and 50% of chlorophyll, respectively, compared to the initial line. cv. Torsdag. Leaves of the mutant 2004

V. G. Ladygin; A. A. Kosobryukhov; O. B. Vaishlya



Water relations and gas exchange of Acer saccharum seedlings in contrasting natural light and water regimes  

Microsoft Academic Search

Summary Field measurements were made of leaf photosynthesis (A), stomata1 conductance (g) and leaf water relations for sugar maple (Acer saccharum Marsh.) seedlings growing in a forest understory, small gap or large clearing habitat in southwestern Wisconsin, USA. Predawn water status, leaf gas exchange and plasticity in field and laboratory water relations characteristics were compared among contrasting light environments in



Lack of agreement between gas exchange variables measured by two metabolic systems  

Microsoft Academic Search

The purpose of this study was to assess the agreement and con- sistency between gas exchange variables measured by two online metabolic systems during an incremental exercise test. After obtaining local ethics approval and informed consent, 15 healthy subjects performed an incremental exercise test to voli- tional fatigue using the Bruce protocol. The Innocor (Innovision, Denmark) and CardiO2 (Medical Graphics,

Djordje G. Jakovljevic; David Nunan; Gay Donovan; Lynette D. Hodges; Gavin R. H. Sandercock; David A. Brodie



CO2 gas exchange and ocean acidification studies in the coastal Gulf of Maine  

Microsoft Academic Search

The University of New Hampshire is studying CO2 gas exchange, ocean acidification, air-sea dynamics, and associated biological processes in the western Gulf of Maine. Three buoys and shipboard cruises have provided data to support these studies. The first, a CO2 monitoring buoy, is deployed jointly with NOAA's Pacific Marine Environmental Laboratory and has been moored in 70 m of water

James Irish; Douglas Vandemark; Shawn Shellito; Joseph Salisbury; Amanda Plagge; Kevin Hanley; Marc Emond



Turbulence and Wave Breaking Effects on Air-Water Gas Exchange  

Microsoft Academic Search

We present an experimental characterization of the effects of turbulence and breaking gravity waves on air-water gas exchange in standing waves. We identify two regimes that govern aeration rates: turbulent transport when no wave breaking occurs and bubble dominated transport when wave breaking occurs. In both regimes, we correlate the qualitative changes in the aeration rate with corresponding changes in

Evelyn J. Boettcher; Jay Fineberg; Daniel P. Lathrop



Multisystem corrosion monitoring in a condensing flue gas heat exchanger, Phase 2  

Microsoft Academic Search

This report describes the second stage of an investigation of heat exchanger tube corrosion in a cyclic reheat test facility at the Scholz Steam Plant of the Gulf Power Company. Continuous electrochemical corrosion monitoring equipment was installed in a flue gas slipstream in order to investigate attack on tube welds and high corrosion rates at certain other locations that had

D. M. Farrell; W. M. Cox



The Effects of Body Mass on Lung Volumes, Respiratory Mechanics, and Gas Exchange During General Anesthesia  

Microsoft Academic Search

We investigated the effects of body mass index (BMI) on functional residual capacity (FRC), respiratory me- chanics (compliance and resistance), gas exchange, and the inspiratory mechanical work done per liter of venti- lation during general anesthesia. We used the esopha- geal balloon technique, together with rapid airway oc- clusion during constant inspiratory flow, to partition the mechanics of the respiratory

Paolo Pelosi; Massimo Croci; Irene Ravagnan; Stefano Tredici; Alessia Pedoto; Alfredo Lissoni; Luciano Gattinoni



Is the sheet-flow design a ‘frozen core’ (a Bauplan) of the gas exchangers?  

Microsoft Academic Search

The sheet-flow design is ubiquitous in the respiratory microvascular systems of the modern gas exchangers. The blood percolates through a maze of narrow microvascular channels spreading out into a thin film, a “sheet”. The design has been convergently conceived through remarkably different evolutionary strategies. Endothelial cells, e.g. connect parallel epithelial cells in the fish gills and reptilian lungs; epithelial cells

J. N Maina




Microsoft Academic Search

Summary Lung and gill performance in gas exchange have been evaluated in eight species of air-breathing crabs with two different lung circulatory designs, those with portal systems and smooth lung linings, and those without portal systems and with invaginated and evaginated lung linings. In all species, the lungs were extremely effective in oxygen uptake whilst the performance of the gills




Response-time enhancement of a clinical gas analyzer facilitates measurement of breath-by-breath gas exchange.  


Tidal ventilation gas-exchange models in respiratory physiology and medicine not only require solution of mass balance equations breath-by-breath but also may require within-breath measurements, which are instantaneous functions of time. This demands a degree of temporal resolution and fidelity of integration of gas flow and concentration signals that cannot be provided by most clinical gas analyzers because of their slow response times. We have characterized the step responses of the Datex Ultima (Datex Instrumentation, Helsinki, Finland) gas analyzer to oxygen, carbon dioxide, and nitrous oxide in terms of a Gompertz four-parameter sigmoidal function. By inversion of this function, we were able to reduce the rise times for all these gases almost fivefold, and, by its application to real on-line respiratory gas signals, it is possible to achieve a performance comparable to the fastest mass spectrometers. With the use of this technique, measurements required for non-steady-state and tidal gas-exchange models can be made easily and reliably in the clinical setting. PMID:10926641

Farmery, A D; Hahn, C E



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

NASA Astrophysics Data System (ADS)

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-coherent Doppler sonar mounted at 2-m depth from a drifting surface buoy. Lastly, wave-breaking statistics and whitecapping coverage are reported using two high-resolution digital cameras from the flying bridge. We present results of process studies that investigate the various models for gas transfer that incorporate turbulence and wave- breaking statistics with the goal of developing a focused parameterization.

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



Microgravity does not alter plant stand gas exchange of wheat at moderate light levels and saturating CO 2 concentration  

Microsoft Academic Search

Plant stand gas exchange was measured nondestructively in microgravity during the Photosynthesis Experiment Subsystem Testing and Operations experiment conducted onboard the International Space Station. Rates of evapotranspiration and photosynthesis measured in space were compared with ground controls to determine if microgravity directly affects whole-stand gas exchange of Triticum aestivum. During six 21-day experiment cycles, evapotranspiration was determined continuously from water

O. Monje; G. Stutte; D. Chapman



Activated carbon for gas phase arsenic capture  

Microsoft Academic Search

Investigation of activated carbon as a multifunctional sorbent for trace metal capture is the focus of this study. In addition to mercury and halides, selenium and arsenic represent two of the most volatile trace species that remain in gas phase in substantial amounts. In this work, fundamental sorption characteristics of the activated carbon for arsenic removal from the gas phase

R. Jadhav; H. Gupta; S. Misro; R. Agnihotri; L. S. Fan



Organic iodine removal from simulated dissolver off-gas streams using partially exchanged silver mordenite  

SciTech Connect

The removal of methyl iodide by adsorption onto silver mordenite was studied using a simulated off-gas from the fuel dissolution step of a nuclear fuel reprocessing plant. The methyl iodide adsorption of partially exchanged silver mordenite was examined for the effects of NO/sub x/, humidity, filter temperature, and degree of silver exchange. Partially exchanged silver mordenite, in general, achieved significantly higher silver utilizations than the fully exchanged material. Silver utilizations of > 95% were achieved, assuming the formation of AgI. The experimental results indicate that CH/sub 3/I loadings increase proportionally with silver loading up to 5 wt % silver and then appear to level off. Tests conducted to determine the effect of temperature on the loading showed higher loadings at 200/sup 0/C than at either 150 or 250/sup 0/C. The presence of NO, NO/sub 2/, and H/sub 2/O vapor showed negligible effects on the loading of CH/sub 3/I. In contrast to iodine loaded onto fully exchanged silver mordenite, the iodine loaded onto the partially exchanged silver mordenite could not be stripped by either 4.5% hydrogen or 100% hydrogen at temperatures up to 500/sup 0/C. A study of the regeneration characteristics of fully exchanged silver mordenite indicates a decreased adsorbent capacity after complete removal of the iodine with 4.5% hydrogen in the regeneration gas stream at 500/sup 0/C. The loss of adsorbent capacity was much higher for silver mordenite regenerated in a stainless steel filter housing than in a glass filter housing. A cost evaluation for the use of the partially exchanged silver mordenite shows that the cost of the silver mordenite on a once-through basis is < $10/h of operation for a 0.5-t/d reprocessing plant.

Jubin, R.T.



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

SciTech Connect

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.

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



High capacity Na+/H+ exchange activity in mineralizing osteoblasts.  


Osteoblasts synthesize bone in polarized groups of cells sealed by tight junctions. Large amounts of acid are produced as bone mineral is precipitated. We addressed the mechanism by which cells manage this acid load by measuring intracellular pH (pHi) in non-transformed osteoblasts in response to weak acid or bicarbonate loading. Basal pHi in mineralizing osteoblasts was ? 7.3 and decreased by ? 1.4 units upon replacing extracellular Na(+) with N-methyl-D-glucamine. Loading with 40 mM acetic or propionic acids, in normal extracellular Na(+), caused only mild cytosolic acidification. In contrast, in Na(+) -free solutions, weak acids reduced pHi dramatically. After Na(+) reintroduction, pHi recovered rapidly, in keeping with Na(+) /H(+) exchanger (NHE) activity. Sodium-dependent pHi recovery from weak acid loading was inhibited by amiloride with the Ki consistent with NHEs. NHE1 and NHE6 were expressed strongly, and expression was upregulated highly, by mineralization, in human osteoblasts. Antibody labeling of mouse bone showed NHE1 on basolateral surfaces of all osteoblasts. NHE6 occurred on basolateral surfaces of osteoblasts mainly in areas of mineralization. Conversely, elevated HCO?3- alkalinized osteoblasts, and pH recovered in medium containing Cl(-), with or without Na(+), in keeping with Na(+) -independent Cl(-) /HCO?3- exchange. The exchanger AE2 also occurred on the basolateral surface of osteoblasts, consistent with Cl(-) /HCO?3- exchange for elimination of metabolic carbonate. Overexpression of NHE6 or knockdown of NHE1 in MG63 human osteosarcoma cells confirmed roles of NHE1 and NHE6 in maintaining pHi. We conclude that in mineralizing osteoblasts, slightly basic basal pHi is maintained, and external acid load is dissipated, by high-capacity Na(+) /H(+) exchange via NHE1 and NHE6. PMID:21413028

Liu, Li; Schlesinger, Paul H; Slack, Nicole M; Friedman, Peter A; Blair, Harry C



Nonlinear interaction between rain- and wind-induced air-water gas exchange  

NASA Astrophysics Data System (ADS)

The combined effects of rain and wind on air-water gas exchange were investigated with a series of experiments conducted at University of Delaware's Air-Sea Interaction Laboratory (ASIL). During this study, the third ASIL Wind and Rain Experiment (WRX 3), a combination of three rain rates and eight wind speeds were executed using aqueous mass balances of SF6 to determine gas transfer velocities, k(600). In addition, measurements of wave properties, currents, and turbulence were obtained. Study results show that rain and wind effects combine nonlinearly to enhance air-water gas exchange. Also, rainfall appears to contribute significantly to the total air-water gas flux at low wind speeds, while at higher speeds rain effects appear to be negligible. We find that the range of conditions over which the rain effects are important is well defined by the ratio of rain kinetic energy flux to that of the wind. A nonlinear parameterization of k(600) for the combined effects of rain and wind is proposed. We extend this parameterization to field conditions and obtain the approximate rain rate and wind speed conditions where rain is expected to have a significant effect on air-sea gas exchange. Low wind speed-high rain rate regions such as the tropics are regions where rain is expected to play a significant role.

Harrison, E. L.; Veron, F.; Ho, D. T.; Reid, M. C.; Orton, P.; McGillis, W. R.



Charge exchange of multiply charged laser plasma ions with rare-gas jet atoms  

SciTech Connect

The interaction of a gas jet (He, Ne, Xe) with the incident laser plasma from a solid target [B, (CH{sub 2}){sub n}, (CF{sub 4}){sub n}] removed by {approx}1 cm is investigated. Line spectra arising from the charge exchange of multiply charged plasma ions with rare-gas atoms are recorded in the multiply charged ions-gas interaction region. The ratios between the partial cross sections of the charge exchange with the production of these ions in excited states are determined from the relative intensities of the Balmer series transitions in BV and CVI ions. These results are compared with theoretical data. (interaction of laser radiation with matter. laser plasma)

Beigman, I L; Levashov, V E; Mednikov, K N; Pirozhkov, A S; Ragozin, E N; Tolstikhina, I Yu [P.N. Lebedev Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation)



Heat exchangers and thermal energy storage concepts for the off-gas heat of steelmaking devices  

NASA Astrophysics Data System (ADS)

The fluctuating thermal emissions of electric arc furnaces require energy storage systems to provide downstream consumers with a continuous amount of thermal energy or electricity. Heat recovery systems based on thermal energy storage are presented. A comparison of different thermal energy storage systems has been performed. For the purpose, suitable heat exchangers for the off-gas heat have been developed. Dynamic process simulations of the heat recovery plants were necessary to check the feasibility of the systems and consider the non-steady-state off-gas emissions of the steelmaking devices. The implementation of a pilot plant into an existing off-gas duct of an electric arc furnace was required to check the real behavior of the heat exchanger and determine suitable materials in view of corrosion issues. The pilot plant is presented in this paper.

Steinparzer, T.; Haider, M.; Fleischanderl, A.; Hampel, A.; Enickl, G.; Zauner, F.



Evaluation of Residence Time for Rock Gas-Atmospheric Exchange for a Fractured Tuff at Yucca Mountain, Nevada  

NASA Astrophysics Data System (ADS)

Rock gas in the TCw (Tiva Canyon member of the Paintbrush Tuff), the uppermost fractured tuff unit at Yucca Mountain, is subject to substantial advective transport, arising from a combination of barometric pumping, thermosyphon effects, and wind pumping. The exchange of rock gas with the atmosphere induced by these mechanisms is of interest for its potential to remove water vapor from the unit and thus reduce infiltration to underlying rocks, which are proposed as a nuclear waste repository horizon. Measurements of gas-phase CFC (chlorofluorocarbon) concentrations and 14CO2 activities provide a means for evaluating such exchange. Box models may be invoked to determine the residence time for each gas species, based on the assumptions of complete gas-phase mixing and of instantaneous equilibration of the somewhat soluble gases with residual rock moisture. Residence times for selected gas species pairs may be used with their known or estimated Kw's (gas-liquid partitioning coefficients) to determine both the residence time for air and for the effective water saturation of the fractured porous medium. For the analyses, residence times for the CFCs CCl3F, CCl2F2, and C2Cl3F3 and for 14CO2 were determined using box models and historical concentrations in the atmosphere. Kw's for the CFCs were computed from published equations, and Kw for 14CO2 was estimated from an assumed dissolved inorganic content of the pore water. Computed residence times, which include effects of differing Kw's for the different species, were 2.6 to 4 years for the CFCs and about 70 years for 14CO2. Based on analyses for various species pairs, the residence time of air in the TCw ranged from 1.6 to 3.0 years, with a mean value of 2.5 years. This residence time allows for a vapor loss of only about 0.02 mm/yr, which would have little effect on infiltration through the unit. Estimates of the effective liquid saturation ranged from 0.3 to 0.8, with a mean value of 0.55, which is only somewhat less than the water saturation (typically about 0.8, but ranging from 0.3 to 0.9) determined for the porous rock matrix from cores. These analyses indicate that a substantial fraction of water in the rock matrix, as well as that in the fractures, participates in gas-water exchange, even during relatively rapid advective gas transport.

Weeks, E. P.; Thorstenson, D. C.



High temperature active heat exchanger research for latent heat storage  

NASA Astrophysics Data System (ADS)

An active heat exchange method in a latent heat (salt) thermal energy storage system that prevents a low conductivity solid salt layer from forming on heat transfer surfaces was developed. An evaluation of suitable media with melting points in the temperature range of interest (250 to 400 C) limited the candidates to molten salts from the chloride, hydroxide and nitrate families, based on high storage capacity, good corrosion characteristics and availability in large quantities at reasonable cost. The specific salt recommended for laboratory tests was a choride eutectic (20.5KCL o 24.5NaCL o 55.MgCl2% by wt.), with a nominal melting point of 385 C. Various active heat exchange concepts were given a technical and economic comparison to a passive tube shell design for a reference application (300 MW sub t for 6 hours). Test hardware was then built for the most promising concept: a direct contact heat exchanger in which molten salt droplets are injected into a cooler counter flowing stream of liquid metal carrier fluid (lead/Bismuth).

Alario, J.; Haslett, R.



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


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

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



A Three-Dimensional Multiscale Model for Gas Exchange in Fruit1[C][W][OA  

PubMed Central

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.

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



Combined Effects of Wind and Rain on Air-Water Gas Exchange  

NASA Astrophysics Data System (ADS)

In constraining local and global carbon cycle budgets, it is important to know the air-water gas transfer velocity (k). Historically, k has been parameterized by wind speed or rain rate separately, and pilot experiments in the laboratory with wind and rain suggested that these parameterizations may be linearly additive (Ho et al., 2007). Here we present results from a series of experiments completed at the University of Delaware’s Air-Sea Interaction Laboratory (ASIL) that aim to study the combined effect of wind and rain on air-water gas exchange. Experimental conditions included 11 wind speeds and 6 rain rates, where gas transfer velocity, turbulent kinetic energy, and bubble size and density were measured. Our results indicate that these effects are not linearly additive, particularly at higher wind speeds (approximately 19 m/s). At these higher wind speeds wind contributes significantly more to the total kinetic energy flux than the rain. These results corroborate findings at the ASIL from 2008 (Harrison et al., in prep). Here, we further examine changes in turbulence due to wind and rain and bubble production due to rain at the air-water interface to elucidate the nonlinear effects of wind and rain on air-water gas exchange. References Harrison, E., et al. (in prep), The combined effect of rain and wind on air-water gas exchange. Ho, D. T., et al. (2007), The combined effect of rain and wind on air-water gas exchange: A feasibility study, Journal of Marine Systems, 66(1-4), 150-160.

Eggleston, S.; Harrison, E.; Ho, D. T.; Veron, F.



Electrostatic enhancement of heat transfer in a gas-to-gas heat exchanger. Final report, July 1991-June 1992  

SciTech Connect

This is the final report on the last phase of a four-year GRI-sponsored experimental effort on heat transfer enhancement in gas-to-gas heat exchangers utilizing the electrostatic (or electrohydrodynamic, EHD) technique. The feasibility of the technique and the role of various controlling parameters for basic pipe flows and in a double-pipe heat exchanger were addressed in the first three phases of the project. In the current, and last, phase the feasibility of the electrostatic technique as a compound heat transfer augmentation methodology and its use in multi-tube heat exchangers was investigated. The compound enhancement experiments were performed on a commercially available finned tube by performing experiments on a micro-finned tube in the presence of electric field. Next, to address some of the practical problems that may be associated with the EHD technique, a multi-tube shell-and-tube heat exchanger was designed, fabricated, and experimentally tested. It is demonstrated that the EHD effect when used in conjunction with a low-fin or enhanced tube can yield additional enhancements to the already enhanced configuration as much as 80% in the present experiments technique.

Ohadi, M.M.; Ansari, A.I.



Isomeric Differentiation of Green Tea Catechins using Gas-Phase Hydrogen/Deuterium Exchange Reactions  

PubMed Central

Hydrogen/deuterium exchange reactions in a quadrupole ion trap mass spectrometer are used to differentiate galloylated catechin stereoisomers (catechin gallate and epicatechin gallate; gallocatechin gallate and epigallocatechin gallate) and the non-galloylated analogs (catechin and epicatechin, gallocatechin and epigallocatechin). Significant differences in the hydrogen/deuterium exchange behavior of the four pairs of deprotonated catechin stereoisomers are observed upon reaction with D2O. Interestingly, the non-galloylated catechins undergo H/D exchange to a much greater extent than the galloylated species, incorporating deuterium at both aromatic/allylic and active phenolic sites. Non-galloylated catechin isomers are virtually indistinguishable by their H/D exchange kinetics over a wide range of reaction times (0.05 to 10 s). Our experimental results are explained using high-level ab initio calculations to elucidate the subtle structural variations in the catechin stereoisomers that lead to their differing H/D exchange kinetics.

Niemeyer, Emily D.; Brodbelt, Jennifer S.



Soil-atmosphere trace gas exchange in semiarid and arid zones.  


A review is presented on trace gas exchange of CH4, CO, N2O, and NOx arising from agriculture and natural sources in the world's semiarid and arid zones due to soil processes. These gases are important contributors to the radiative forcing and the chemistry of the atmosphere. Quantitative information is summarized from the available studies. Between 5 and 40% of the global soil-atmosphere exchange for these gases (CH4, CO, N2O, and NOx) may occur in semiarid and arid zones, but for each of these gases there are fewer than a dozen studies to support the individual estimates, and these are from a limited number of locations. Significant differences in the biophysical and chemical processes controlling these trace gas exchanges are identified through the comparison of semiarid and arid zones with the moist temperate or wet/dry savanna land regions. Therefore, there is a poorly quantified understanding of the contribution of these regions to the global trace gas cycles and atmospheric chemistry. More importantly, there is a poor understanding of the feedback between these exchanges, global change, and regional land use and air pollution issues. A set of research issues is presented. PMID:18396546

Galbally, Ian E; Kirstine, Wayne V; Meyer, C P Mick; Wang, Ying Ping


Xenon Anesthesia Improves Respiratory Gas Exchanges in Morbidly Obese Patients  

PubMed Central

Background. Xenon-in-oxygen is a high density gas mixture and may improve PaO2/FiO2 ratio in morbidly obese patients uniforming distribution of ventilation during anesthesia. Methods. We compared xenon versus sevoflurane anesthesia in twenty adult morbidly obese patients (BMI > 35) candidate for roux-en-Y laparoscopic gastric bypass and assessed PaO2/FiO2 ratio at baseline, at 15?min from induction of anaesthesia and every 60?min during surgery. Differences in intraoperative and postoperative data including heart rate, systolic and diastolic pressure, oxygen saturation, plateau pressure, eyes opening and extubation time, Aldrete score on arrival to the PACU were compared by the Mann-Whitney test and were considered as secondary aims. Moreover the occurrence of side effects and postoperative analgesic demand were assessed. Results. In xenon group PaO2-FiO2 ratio was significantly higher after 60?min and 120?min from induction of anesthesia; heart rate and overall remifentanil consumption were lower; the eyes opening time and the extubation time were shorter; morphine consumption at 72?hours was lower; postoperative nausea was more common. Conclusions. Xenon anesthesia improved PaO2/FiO2 ratio and maintained its distinctive rapid recovery times and cardiovascular stability. A reduction of opioid consumption during and after surgery and an increased incidence of PONV were also observed in xenon group.

Abramo, Antonio; Di Salvo, Claudio; Foltran, Francesca; Forfori, Francesco; Anselmino, Marco; Giunta, Francesco



Pulmonary carbonic anhydrase in vertebrate gas exchange organs  

Microsoft Academic Search

Carbonic anhydrase (CA) catalyzes the interconversion of CO2 and HCO3?. Intracellular (extravascular) and intravascular (extracellular) CA has been identified and localized in the lungs of reptiles and mammals. Less information is known, however, on the presence of intravascular CA in the lungs of amphibians and avians. In the present study, perfusion studies were used to compare the catalytic activity of

Erich K. Stabenau; Thomas Heming



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

NASA Astrophysics Data System (ADS)

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.

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



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


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 Po? (Pa(O?)) by a mean of 6 Torr (P = 0.04), with no significant effect on arterial Pco? (Pa(CO?)), but with great variability in both. Lung mechanical properties improved considerably more than did gas exchange. Post-LVRS Pa(O?) 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(O?). Conversely, post-LVRS Pa(CO?) bore no relationship to its pre-LVRS value, whereas changes in Pa(CO?) 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

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



Laser photoacoustic spectroscopy of biosystems gas exchange with the atmosphere  

NASA Astrophysics Data System (ADS)

A response of plants to stress action is characterized by an activation of the respiration process. The CO2 evolution by some plants exposed to elevated concentration of pollutants and pressure decrease is studied using a photoacoustic spectrometer with a CO2 laser. The measurements show a considerable CO2 evolution by all kinds of the test plants. The quantity of CO2 emitted by pea seedlings at 8 kPa, for example, exceeds the control one by about 20 times (24 h after the exposure start). The exposure of pea seedlings to C2H4 and O3 at various concentrations also increases CO2 evolution: the 48-h exposure of test plants to C2H4 (at 0.01 ppm) increases CO2 evolution by approximately 100% with respect to the control plants.

Ageev, B. G.; Ponomarev, Y. N.; Sapozhnikova, V. A.



A test of the oxidative damage hypothesis for discontinuous gas exchange in the locust Locusta migratoria.  


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

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



Experimental and numerical analyses of finned cross flow heat exchangers efficiency under non-uniform gas inlet flow conditions  

NASA Astrophysics Data System (ADS)

The work deals with experimental and numerical thermodynamic analyses of cross-flow finned tube heat exchangers of the gas-liquid type. The aim of the work is to determine an impact of the gas non-uniform inlet on the heat exchangers performance. The measurements have been carried out on a special testing rig and own numerical code has been used for numerical simulations. Analysis of the experimental and numerical results has shown that the range of the non-uniform air inlet to the considered heat exchangers may be significant and it can significantly affect the heat exchanger efficiency.

Bury, Tomasz; Sk?adzie?, Jan; Widziewicz, Katarzyna



Temperature and body mass-related variation in cyclic gas exchange characteristics and metabolic rate of seven weevil species: Broader implications  

Microsoft Academic Search

The influence of temperature on metabolic rate and characteristics of the gas exchange patterns of flightless, sub-Antarctic Ectemnorhinus-group species from Heard and Marion islands was investigated. All of the species showed cyclic gas exchange with no Flutter period, indicating that these species are not characterized by discontinuous gas exchange cycles. Metabolic rate estimates were substantially lower in this study than

C. J. Klok; S. L. Chown



Gas exchange in NASA's biomass production chamber: a preprototype closed human life support system.  


An important aspect of environmental control in a life-support system is the monitoring and regulation of atmospheric gases (Sager et al. 1988) at concentrations required for the maintenance of all life forms. It will be necessary to know the rates of CO2 use, oxygen evolution, and water flux through evapotranspiration by a crop stand under various environmental conditions, so that appropriate designs and control systems for maintaining mass balances of those gases can be achieved for a full range of environmental regimes. Mass budgets of gases will also enable evaluation of crop health by monitoring directly the rates of gas exchange and indirectly the rate of accumulation of dry matter, based on rates of carbon dioxide use. This article focuses on the unique capabilities of the NASA biomass production chamber for monitoring and evaluating gas exchange rates, with special emphasis on results with wheat and soybean, two candidate species identified by NASA for CELSS. PMID:11537404

Corey, K A; Wheeler, R M


Leaf gas exchange and ABA accumulation in Phaseolus vulgaris genotypes of contrasting drought tolerance  

SciTech Connect

Drought tolerance mechanisms in Phaseolus vulgaris (Pv) are still largely unknown. Gas exchange responses and ABA accumulation were monitored in Pv genotypes differing in their drought adaptation. Higher rates of photosynthesis were observed under well-watered conditions in drought sensitive genotypes. Water stress caused a significant reduction in leaf water potential and photosynthetic rates regardless of drought adaptation. Higher photosynthetic rates were maintained under stress conditions in one drought tolerant genotype. Interestingly water stress caused significant ABA accumulation only in this genotype. Root ABA levels were similar among genotypes and were not modified by water stress. Endogenous levels of free ABA in leaves and roots did not correlated with gas exchange response to water stress. These results differ from previous reports on genotypic variation in ABA accumulation under water stress.

Bertrand, A.; Castonguay, Y.; Nadeau, P. (Agriculture Canada, Ste-Foy, Quebec (Canada))



Ultrasonic gas-body activation in Drosophila.  


The role of gas bodies in the interaction of Drosophila eggs and larvae with ultrasonic fields has been studied (1) by direct microscopic examination, (2) by observation of gas body activation during sonation with a special microscope, (3) by direct measurement of the volume fraction of gas in eggs and (4) through the absorption of ultrasound. All approaches provide support for the postulate that these organisms contain a rich distribution of gas bodies which play a dominant role in the acoustic properties of eggs and are the most probable site of action for ultrasonic biological effects on these organisms. PMID:6428019

Carstensen, E L; Child, S Z; Lam, S; Miller, D L; Nyborg, W L


Modeling and simulation of main cryogenic heat exchanger in a base-load liquefied natural gas plant  

Microsoft Academic Search

Recent growth in world-wide consumption of natural gas highlights its immense importance as a source of primary energy. Liquefied natural gas (LNG) is the most economic way to transport natural gas over long distances. Main Cryogenic Heat Exchanger (MCHE) is a very critical equipment in an energy intensive LNG plant. To that end, modeling MCHE is the inevitable first step

MM Faruque Hasan; Iftekhar A Karimi; Hassan Alfadala; Henk Grootjans



A gas-exchange study of photosynthesis and isoprene emission in Quercus rubra L  

Microsoft Academic Search

We have investigated the signals which affect the rate of isoprene emission from photosynthesizing leaves of red oak (Quercus rubra L.) using analytical gas-exchange techniques, chlorophyll-fluorescence measurements, and inhibitor feeding. Isoprene emission\\u000a increased with increasing photon flux density at low CO2 but much less so at high CO2 partial pressure. Photosynthetic CO2 assimilation exhibited the opposite behavior. In CO2-free air,

Francesco Loreto; Thomas D. Sharkey



Calculator-assisted measurements of photosynthetic, respiration and photorespiration rates in a closed gas exchange system  

Microsoft Academic Search

A closed gas exchange system has been designed for connection to the Hewlett-Packard programmable calculator controlled data\\u000a acquisition system to provide a complete process of measuring and control. The system enables routine measurements of photosynthetic\\u000a and dark respiration rates at different irradiances and different carbon dioxide and oxygen concentrations and leaf temperatures,\\u000a and also a simple and rapid automatic control

M. Kaše; J. ?atský



The combined effect of rain and wind on air–water gas exchange: A feasibility study  

Microsoft Academic Search

A series of experiments were conducted at University of Delaware's Air–Sea Interaction Laboratory to examine the combined effects of rain and wind on air–water gas exchange. During this study, ASIL WRX I, a combination of 3 rain rates and 4 wind speeds were used, for a total of 12 different environmental conditions. The SF6 evasion method was used to determine

David T. Ho; Fabrice Veron; Emily Harrison; Larry F. Bliven; Nicholas Scott; Wade R. McGillis



The effect of nitrogen deficiency on leaf gas exchange and chlorophyll fluorescence parameters in sunflower  

Microsoft Academic Search

Fully expanded leaves of sunflower (Helianthus annuus L.) growing with either complete or nitrogen-deficient nutrition solution were analysed for gas exchange and chlorophyll fluoresence after 24 days from the transplanting. Under N-stress the decline in photosynthesis and the rise in stomatal conductance determined at light saturation level were accompanied by an increase of the intercellular CO2 concentration (about +60%). This

Stefania Ciompi; Elisa Gentili; Lucia Guidi; Gian Franco Soldatini



Constraining global air-sea gas exchange for CO2 with recent bomb 14C measurements  

Microsoft Academic Search

The 14CO2 released into the stratosphere during bomb testing in the early 1960s provides a global constraint on air-sea gas exchange of soluble atmospheric gases like CO2. Using the most complete database of dissolved inorganic radiocarbon, DI14C, available to date and a suite of ocean general circulation models in an inverse mode we recalculate the ocean inventory of bomb-produced DI14C

Colm Sweeney; Emanuel Gloor; Andrew R. Jacobson; Robert M. Key; Galen McKinley; Jorge L. Sarmiento; Rik Wanninkhof



Gas exchange at extreme altitude: results from the British 40th Anniversary Everest Expedition  

Microsoft Academic Search

Gas exchange at high extreme altitude: results from the British 40th Anniversary Everest Expedition. A.J. Peacock, P.L. Jones. ©ERS Journals Ltd 1997. ABSTRACT: Since Messner and Habeler climbed to the summit of Mount Everest (8,848 m) without oxygen in 1978, there has been controversy between scientists trying to explain this feat. Field studies have suggested better respiratory perfor- mance than

A. J. Peacock; P. L. Jones



Effect of infusion and withdrawl of glucose and insulin on gas exchange in injured ventilated patients  

Microsoft Academic Search

Purpose: To evaluate the effect induced on gas exchange and on urea excretion by glucose and insulin infusion in injured patients. The magnitude and time necessary for the full development of the metabolic effect were investigated.Methods: Six injured patients were investigated. During the first 24 hours, the fasting period, patients received 1 mg\\/kg?min of glucose; during the second 24 hours,

Danilo Radrizzani; Gaetano Iapichino; Angelo Colombo; Daniela Codazzi; Giovanni Pasetti; Giulio Ronzoni; Monica Savioli



Hemodynamics and gas exchange during carbon dioxide insufflation for totally endoscopic coronary artery bypass grafting  

Microsoft Academic Search

Background. In addition to single-lung ventilation (SLV), positive-pressure CO2 insufflation is mandatory for totally endoscopic coronary artery bypass grafting. Studies on the effects of unilateral CO2 insufflation on hemodynamics produced controversial results, and bilateral insufflation has not been studied to our knowledge. The present study sought to investigate hemodynamics and gas exchange during unilateral and bilateral CO2 insufflation in patients

Christian Byhahn; Stephan Mierdl; Dirk Meininger; Gerhard Wimmer-Greinecker; Georg Matheis; Klaus Westphal



Sildenafil citrate, bronchopulmonary dysplasia and disordered pulmonary gas exchange: any benefits?  

Microsoft Academic Search

Objective:The objective of this study is to determine the effects that sildenafil citrate has on gas exchange in infants with bronchopulmonary dysplasia (BPD)-associated pulmonary hypertension (PH).Study Design:A retrospective review was performed from 2005 to 2009. Infants treated with sildenafil citrate for greater than 48 h were included. Standard patient data was collected, including echocardiogram, inspired oxygen and systemic blood pressure,

M Nyp; T Sandritter; N Poppinga; C Simon; W E Truog



Changes in optimal distribution of heat exchanger area between the evaporator and suction gas heat exchanger when replacing R22 with R407C  

Microsoft Academic Search

An investigation was made on whether the optimal distribution of heat exchanger area between the evaporator and the suction gas heat exchanger, at a given cost, will change when R22 is replaced with the non-azeotropic mixture R407C. A comprehensive computer program was used to simulate a refrigeration plant, originally designed for R22, where the tube-and-shell evaporator is of dry-expansion type.

Cecilia Gabrielii; Lennart Vamling



The Mechanical Diversity of Stomata and Its Significance in Gas-Exchange Control[OA  

PubMed Central

Given that stomatal movement is ultimately a mechanical process and that stomata are morphologically and mechanically diverse, we explored the influence of stomatal mechanical diversity on leaf gas exchange and considered some of the constraints. Mechanical measurements were conducted on the guard cells of four different species exhibiting different stomatal morphologies, including three variants on the classical “kidney” form and one “dumb-bell” type; this information, together with gas-exchange measurements, was used to model and compare their respective operational characteristics. Based on evidence from scanning electron microscope images of cryo-sectioned leaves that were sampled under full sun and high humidity and from pressure probe measurements of the stomatal aperture versus guard cell turgor relationship at maximum and zero epidermal turgor, it was concluded that maximum stomatal apertures (and maximum leaf diffusive conductance) could not be obtained in at least one of the species (the grass Triticum aestivum) without a substantial reduction in subsidiary cell osmotic (and hence turgor) pressure during stomatal opening to overcome the large mechanical advantage of subsidiary cells. A mechanism for this is proposed, with a corollary being greatly accelerated stomatal opening and closure. Gas-exchange measurements on T. aestivum revealed the capability of very rapid stomatal movements, which may be explained by the unique morphology and mechanics of its dumb-bell-shaped stomata coupled with “see-sawing” of osmotic and turgor pressure between guard and subsidiary cells during stomatal opening or closure. Such properties might underlie the success of grasses.

Franks, Peter J.; Farquhar, Graham D.



The mechanical diversity of stomata and its significance in gas-exchange control.  


Given that stomatal movement is ultimately a mechanical process and that stomata are morphologically and mechanically diverse, we explored the influence of stomatal mechanical diversity on leaf gas exchange and considered some of the constraints. Mechanical measurements were conducted on the guard cells of four different species exhibiting different stomatal morphologies, including three variants on the classical "kidney" form and one "dumb-bell" type; this information, together with gas-exchange measurements, was used to model and compare their respective operational characteristics. Based on evidence from scanning electron microscope images of cryo-sectioned leaves that were sampled under full sun and high humidity and from pressure probe measurements of the stomatal aperture versus guard cell turgor relationship at maximum and zero epidermal turgor, it was concluded that maximum stomatal apertures (and maximum leaf diffusive conductance) could not be obtained in at least one of the species (the grass Triticum aestivum) without a substantial reduction in subsidiary cell osmotic (and hence turgor) pressure during stomatal opening to overcome the large mechanical advantage of subsidiary cells. A mechanism for this is proposed, with a corollary being greatly accelerated stomatal opening and closure. Gas-exchange measurements on T. aestivum revealed the capability of very rapid stomatal movements, which may be explained by the unique morphology and mechanics of its dumb-bell-shaped stomata coupled with "see-sawing" of osmotic and turgor pressure between guard and subsidiary cells during stomatal opening or closure. Such properties might underlie the success of grasses. PMID:17114276

Franks, Peter J; Farquhar, Graham D



Cyclic gas-exchange in the Chilean red cricket: inter-individual variation and thermal dependence.  


One of the most puzzling features of respiration in insects is cyclic gas exchange (CGE, the extreme form of discontinuous gas exchange-cycles, DGC), a periodic respiratory pattern that appeared independently several times in the evolution of arthropods. Although it is a striking feature of insects and some non-insect species, to date there is no clear knowledge of how widespread it is, or its adaptive significance. Here we show for the first time that a cricket (Cratomelus armatus) from the Stenopelmatidae family exhibits CGE. C. armatus shows a conspicuous, convective O-phase, with significantly repeatable ventilatory period and O-phase duration (intraclass correlation coefficients of 0.51 and 0.74, respectively). Also, C. armatus exhibits high variation in the CGE patterns, ranging from continuous to highly periodic records, sometimes including the classic F-phase. No record went to zero and we found significant (inverse) effects of ambient temperature on O-phase duration but not on the ventilatory period. Average VCO2 and O-phase amplitude (i.e. mean VCO2 of the peaks) increased with temperature whereas the amplitude of the interburst did not change significantly with ambient temperature. C. armatus is a species that lives below ground in humid forests, so our results support the chthonic-hygric hypothesis (i.e. facilitation of gas exchange under hypoxic and hypercapnic conditions, minimizing evaporative water loss), although this assertion needs to be confirmed statistically by a strong inference approach. PMID:17267652

Nespolo, Roberto F; Artacho, Paulina; Castañeda, Luis E



Respiration and Gas Exchange in Stem Tissue of Opuntia basilaris1  

PubMed Central

Respiration and gas exchange in the light were studied manometrically with tissue slices from stem material of Opuntia basilaris Engelm. and Bigel. Dark respiration rates were greater in young stems than in mature stems. The timing of the experiment in the day/night cycle influences the magnitude and pattern of respiration and gas exchange in the light. Net dark respiration has a temperature optimum between 35 and 40 C, and is maintained at 60% of the control rate in tissue equilibrated with experimental osmotic potentials of ?25 bars. Net gas exchange in the light is regulated by the titratable acidity of the tissue and by the tissue temperature. Increased rates of net CO2 evolution and net O2 consumption occur in the light with high levels of titratable acidity and high temperatures. An efflux of CO2 and influx of O2 occur following light/dark transitions. These patterns are reversed following dark/light transitions. Similar results were demonstrated at 15, 25, and 35 C, and are interpreted as a mechanism of adaptation to desert environments.

Szarek, Stan R.; Ting, Irwin P.



Use of Noninvasive Gas Exchange to Track Pulmonary Vascular Responses to Exercise in Heart Failure  

PubMed Central

We determined whether a non-invasive gas exchange based estimate of pulmonary vascular (PV) capacitance [PVCAP = stroke volume (SV) × pulmonary arterial pressure (Ppa)] (GXCAP) tracked the PV response to exercise in heart-failure (HF) patients. Pulmonary wedge pressure (Ppw), Ppa, PV resistance (PVR), and gas exchange were measured simultaneously during cycle exercise in 42 HF patients undergoing right-heart catheterization. During exercise, PETCO2 and VE/VCO2 were related to each other (r = ?0.93, P < 0.01) and similarly related to mean Ppa (mPpa) (r = ?0.39 and 0.36; P < 0.05); PETCO2 was subsequently used as a metric of mPpa. Oxygen pulse (O2 pulse) tracked the SV response to exercise (r = 0.91, P < 0.01). Thus, GXCAP was calculated as O2 pulse × PETCO2. During exercise, invasively determined PVCAP and non-invasive GXCAP were related (r = 0.86, P < 0.01), and GXCAP correlated with mPpa and PVR (r = ?0.46 and ?0.54; P < 0.01). In conclusion, noninvasive gas exchange measures may represent a simple way to track the PV response to exercise in HF.

Taylor, Bryan J.; Olson, Thomas P.; Chul-Ho-Kim; MacCarter, Dean; Johnson, Bruce D.



Alveolar recruitment strategy during cardiopulmonary bypass does not improve postoperative gas exchange and lung function.  


Pulmonary dysfunction with impairment of lung function and oxygenation is one of the most serious problems in the early postoperative period after cardiac surgery. In this study we investigated the effect of alveolar recruitment strategy during cardiopulmonary bypass on postoperative gas exchange and lung function. This prospective randomized study included 32 patients undergoing elective myocardial revascularization with cardiopulmonary bypass. In 16 patients 5 cm H(2)O of positive end-expiratory pressure was applied after intubation and maintained until extubation (Group I). In the other 16 patients (group II) a positive end expiratory pressure (PEEP) of 5 cm H(2)O was maintained as well but was increased to 14 cm H(2)O every 20 min for 2 min during cross clamp. Measurements were taken preoperatively, before skin incision, before and after (3, 24, 48 h) cardiopulmonary bypass and before discharge (6th postoperative day). Postoperative gas exchange, extravascular lung water and lung function showed no significant difference between the groups. Postoperative pulmonary function variables were lower in both groups compared to baseline values. In patients with normal preoperative pulmonary function, application of an alveolar recruitment strategy during cardiopulmonary bypass does not improve postoperative gas exchange and lung function after cardiac surgery. PMID:19259813

Scherer, Mirela; Dettmer, Sebastian; Meininger, Dirk; Deschka, Heinz; Geyer, Galina; Regulla, Caroline; Moritz, Anton



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

NASA Astrophysics Data System (ADS)

Specifications and examples of application of laser gas-analyzers of near- and mid-infrared ranges for diagnostics of greenhouse gases (CO2, C2H4, and CH4) 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 CO2-laser equipped with the intracavity acoustic detector capable of fast frequency scanning in the 9 and 10 ?m 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 CO2 and CH4 emissions are presented.

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



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

NASA Astrophysics Data System (ADS)

Specifications and examples of application of laser gas-analyzers of near- and mid-infrared ranges for diagnostics of greenhouse gases (C02, C2H4, and CH4) 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 C02-laser equipped with the intracavity acoustic detector capable of fast frequency scanning in the 9 and 10 ?m 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 CO2 and CH4 emissions are presented.

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



Accuracy of Gas Exchange Monitoring During Noninvasive Ventilation: An In Vitro Metabolic Simulation.  


Background: Gas exchange monitoring by indirect calorimetry (IC) during noninvasive ventilation (NIV) is desirable but currently not available. Leaks around the mask preclude reliable measurements of carbon dioxide production (VCO2) and oxygen consumption (VO2) in this population. We aimed to examine the impact of system leaks and gas flows on the accuracy of gas exchange measurements during NIV using an in vitro metabolic simulation. Materials and Methods: We examined the agreement between VCO2 and VO2 measurements by IC (using a novel canopy device) and reference values generated during an in vitro metabolic simulation of NIV at room air. The flow rate of gas sampled by the IC device (VIC) was set relative to the output flow of the ventilator (VVENT) to obtain a range of sample factors (SF = VIC/VVENT). Linear regression was used to determine the effect of SF on the accuracy of the system. Results: An acceptable agreement between measured and reference values was observed, with mean bias (limits of agreement) of -3.3% (-6.9% to 0.3%) and -10.6% (-14.9% to -6.4%) for VCO2 and VO2, respectively. An SF of 1.25 was associated with the highest accuracy of measurement. VO2 measurement accuracy deteriorated with system leak and at SF >1.25 and was linearly related to sample dilution by ambient air entrainment. Conclusions: A novel canopy device with titration of IC sample flow in relation to the ventilator flow allowed in vitro gas exchange measurements during simulated NIV with acceptable accuracy. This model needs to be tested in clinical settings. PMID:23542337

Smallwood, Craig D; Mehta, Nilesh M



Carbon Isotope Discrimination, Gas Exchange, and Growth of Sugarcane Cultivars under Salinity.  


Physiological features associated with differential resistance to salinity were evaluated in two sugarcane (Saccharum spp. hybrid) cultivars over an 8-week period during which greenhouse-grown plants were drip-irrigated with water or with NaCI solutions of 2, 4, 8, or 12 decisiemens (dS) m-1 electrical conductivity (EC). The CO2 assimilation rate (A), stomatal conductance (g), and shoot growth rate (SGR) began to decline as EC of the irrigation solution increased above 2 dS m-1. A, g, and SGR of a salinity-resistant cultivar (H69-8235) were consistently higher than those of a salinity-susceptible cultivar (H65-7052) at all levels of salinity and declined less sharply with increasing salinity. Carbon isotope discrimination ([delta]) in tissue obtained from the uppermost fully expanded leaf increased with salinity and with time elapsed from the beginning of the experiment, but [delta] was consistently lower in the resistant than in the susceptible cultivar at all levels of salinity. Gas-exchange measurements suggested that variation in [delta] was attributable largely to variation in bundle sheath leakiness to CO2 ([phi]). Salinity-induced increases in [phi] appeared to be caused by a reduction in C3 pathway activity relative to C4 pathway activity rather than by physical changes in the permeability of the bundle sheath to CO2. A strong correlation between [delta] and A, g, and SGR permitted these to be predicted from [delta] regardless of the cultivar and salinity level. [delta] thus provided an integrated measure of several components of physiological performance and response. PMID:12232101

Meinzer, F. C.; Plaut, Z.; Saliendra, N. Z.



Laboratory Measurements of Oxygen Gas Release from Basaltic Minerals Exposed to UV- Radiation: Implications for the Viking Gas Exchange Experiments  

NASA Astrophysics Data System (ADS)

The biology experiments onboard the Viking Landers determined that the Martian soils at Chryse and Utopia Planitia contain an unknown chemical compound of a highly oxidizing nature. The Gas Exchange Experiments (GEx) demonstrated that the humidification of a 1-cc Martian soil sample resulted in the production of as much as 790 nanomoles of oxygen gas. Yen et al. (2000) have provided experimental evidence that superoxide radicals can be generated on plagioclase feldspar (labradorite) grain surfaces by exposure to ultraviolet (UV) light in the presence of oxygen gas. Adsorbed superoxide radicals are thought to react readily with water vapor, and produce oxygen gas in quantities sufficient to explain the Viking GEx results. Direct evidence for the formation of oxygen gas, however, was not provided in the experiments of Yen et al (2000). Accordingly, the motivation of this study is to determine whether superoxide radicals adsorbed on labradorite surfaces are capable of producing oxygen gas upon exposure to water vapor. We have constructed an experimental apparatus that is capable of monitoring oxygen gas release from basaltic mineral powders that have been exposed to UV-radiation under Martian atmospheric pressure conditions. The apparatus consists of a stainless-steel vacuum chamber with a UV- transparent window where sample radiation exposures are performed. The vacuum chamber has multiple valved ports for injection of gases and water vapor. The vacuum chamber is connected via a precision leak valve to a quadrupole mass spectrometer, which measures changes in the composition of the headspace gases over our mineral samples. We will report on the results of our experiments, which are aimed at detecting and quantifying oxygen gas release from UV-exposed basaltic mineral samples using this new experimental facility. These results will further constrain whether superoxide ions adsorbed on mineral surfaces provide a viable explanation for the Viking GEx results, which have been of considerable controversy in the roughly three decades since the measurements were first made.

Hurowitz, J. A.; Yen, A. S.



Correlation between solution and gas-phase protein conformation: H/D exchange, IRMPD, and ESI FT-ICR MS  

NASA Astrophysics Data System (ADS)

Infrared multiphoton dissociation (IRMPD) of the hydrogen/deuterium (H/D) exchanged 12+ charge state of gas-phase bovine ubiquitin was performed on a Fourier transform ion cyclotron resonance mass spectrometer. The H/D exchange of the 12+ charge state revealed two distinct isotopic distributions indicating the presence of at least two distinct conformations of the 12+ charge state. Following H/D exchange, IRMPD was used to dissociate the conformations. The fragments clearly showed little or no deuterium scrambling as evidenced by a nonstatistical distribution of deuterium incorporation. Analysis of the deuterium incorporation for the five most abundant fragment ions indicated a slow exchanging region of the fast exchanging conformation that corresponds to a stable (beta) - sheet observed by NMR in alcoholic solutions. The data suggest that protection of the amide hydrogens in the (beta) -sheet may result in the observed slow exchange rate and provides further evidence for the retention of secondary structure in gas phase.

Freitas, Michael A.; Hendrickson, Christopher L.; Marshall, Alan G.



Fouling Reduction Characteristics of a No-Distributor-Fluidized-Bed Heat Exchanger for Flue Gas Heat Recovery  

Microsoft Academic Search

Heat exchangers and heat exchanger networks are extensively used for the purpose of recovering energy. 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

Y. D. Jun; K. B. Lee; S. Z. Islam; S. B. Ko



Regulation of sodium-calcium exchanger activity by creatine kinase.  


It has been shown that in rat heart NCX1 exists in a macromolecular -complex including PKA, PKA-anchoring protein, PKC, and phosphatases PP1 and PP2A. In addition, several lines of evidence suggest that the interactions of the exchanger with other molecules are closely associated with its function in regulation of [Ca(2+)](i). NCX contains a large intracellular loop (NCXIL) that is responsible for regulating NCX activity. We used the yeast two-hybrid method to screen a human heart cDNA library and found that the C-terminal region of sarcomeric mitochondrial creatine kinase (sMiCK) interacted with NCX1IL. Among the four creatine kinase (CK) isozymes, both sMiCK and the muscle-type cytosolic creatine kinase (CKM) co-immunoprecipitated with NCX1. Both sMiCK and CKM were able to produce a recovery in the decreased NCX1 activity that was lost under energy-compromised conditions. This regulation is mediated through a putative PKC phosphorylation site of sMiCK and CKM. The catalytic activity of sMiCK and CKM is not required for their regulation of NCX1 activity. Our results suggest a novel mechanism for the regulation of NCX1 activity and a novel role for CK. PMID:23224878

Yang, Ya-Chi; Kao, Lung-Sen



Plant water use efficiency over geological time - evolution of leaf stomata configurations affecting plant gas exchange.  


Plant gas exchange is a key process shaping global hydrological and carbon cycles and is often characterized by plant water use efficiency (WUE - the ratio of CO2 gain to water vapor loss). Plant fossil record suggests that plant adaptation to changing atmospheric CO2 involved correlated evolution of stomata density (d) and size (s), and related maximal aperture, amax . We interpreted the fossil record of s and d correlated evolution during the Phanerozoic to quantify impacts on gas conductance affecting plant transpiration, E, and CO2 uptake, A, independently, and consequently, on plant WUE. A shift in stomata configuration from large s-low d to small s-high d in response to decreasing atmospheric CO2 resulted in large changes in plant gas exchange characteristics. The relationships between gas conductance, gws , A and E and maximal relative transpiring leaf area, (amax ?d), exhibited hysteretic-like behavior. The new WUE trend derived from independent estimates of A and E differs from established WUE-CO2 trends for atmospheric CO2 concentrations exceeding 1,200 ppm. In contrast with a nearly-linear decrease in WUE with decreasing CO2 obtained by standard methods, the newly estimated WUE trend exhibits remarkably stable values for an extended geologic period during which atmospheric CO2 dropped from 3,500 to 1,200 ppm. Pending additional tests, the findings may affect projected impacts of increased atmospheric CO2 on components of the global hydrological cycle. PMID:23844085

Assouline, Shmuel; Or, Dani



Canopy Photosynthesis and Transpiration in Micro-Gravity: Gas Exchange Measurements Aboard MIR  

NASA Astrophysics Data System (ADS)

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 ?mol 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

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


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


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

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



Numerical evaluation of static-chamber measurements of soil-atmosphere gas exchange: Identification of physical processes  

Microsoft Academic Search

The exchange of gases between soil and atmosphere is an important process that affects atmospheric chemistry and therefore climate. The static-chamber method is the most commonly used technique for estimating the rate of that exchange. We examined the method under hypothetical field conditions where diffusion was the only mechanism for gas transport and the atmosphere outside the chamber was maintained

Richard W. Healy; Robert G. Striegl; Thomas F. Russell; Gordon L. Hutchinson; Gerald P. Livingston



Seasonal trends in reduced leaf gas exchange and ozone-induced foliar injury in three ozone sensitive woody plant species  

Microsoft Academic Search

Seasonal trends in leaf gas exchange and ozone-induced visible foliar injury were investigated for three ozone sensitive woody plant species. Seedlings of Populus nigra L., Viburnum lantana L., and Fraxinus excelsior L. were grown in charcoal-filtered chambers, non-filtered chambers and open plots. Injury assessments and leaf gas exchange measurements were conducted from June to October during 2002. All species developed

K. Novak; M. Schaub; J. Fuhrer; J. M. Skelly; C. Hug; W. Landolt; P. Bleuler; N. Kräuchi



Leaf gas exchange in a clonal eucalypt plantation as related to soil moisture, leaf water potential and microclimate variables  

Microsoft Academic Search

In order to determine how environmental and physiological factors affect leaf gas exchange in a 9-year-old clonal eucalypt\\u000a plantation (Eucalyptus grandis Hill ex. Maiden hybrids) in the State of Espirito Santo, Brazil, the diurnal patterns of predawn leaf water potential (?pd), and leaf gas exchange were monitored from November 1995 to August 1996. Soil water content (?) and microclimatic variables

Marcelo S. Mielke; Marco A. Oliva; Nairam F. de Barros; Ricardo M. Penchel; Carlos A. Martinez; Sebastião da Fonseca; Auro C. de Almeida



In Vivo Measurement of O2 and CO2 Gas Exchange Across the Human Tympanic Membrane  

PubMed Central

Background Gas exchange between the middle ear and adjacent compartments determines the trajectory of middle ear pressure change. Little information is available regarding the permeability of the tympanic membrane (TM) to physiological gases. Objective Determine in vivo if the human TM is permeable to O2 and CO2 at physiologic transTM pressure gradients. Methods An ear canal (EC) probe (ECP) constructed from a custom-fitted acrylic body, a glass capillary tube enclosing an oil meniscus to maintain ambient ECP+EC pressure and a silica glass microtube linked to a mass spectrometer (MS) for measuring gas composition was hermetically sealed within one ear canal of 15 adults. ECP+EC volume was measured and gas samples taken at 10 minute intervals for 1 hour. 1:100,000 epinephrine was applied topically to the ipsilateral TM to decrease blood flow and the experiment repeated. The MS recorded ECP+EC pressures of O2 (32 AMU) and CO2 (44 AMU) were regressed on time and the slope divided by the predicted transTM partial-pressure gradients to yield estimates of transTM O2 and CO2 conductance. Results Consistent with expectation for transTM gas exchange, ECP+EC O2 decreased and CO2 increased during the experiments. TransTM CO2 exchange was faster after application of the epinephrine suggesting an effect of perfusion on that estimate. The ratio of O2/CO2 conductances was approximately 5 which is not consistent with the TM acting primarily as a water or lipid barrier to diffusion. Conclusion The human TM is permeable to CO2 and O2 at physiologic pressure gradients.

Yuksel, Sansak; Swarts, J. Douglas; Banks, Julianne; Seroky, James T.; Doyle, William J.



Heat and Moisture Exchange in a Permafrost Active Layer, Churchill, Manitoba  

Microsoft Academic Search

This thesis examines heat and moisture exchanges in the active layer of wet tundra soils during freeze-back and thaw. Measurements of rainfall, snow depth, air and soil temperature, soil moisture, and frost heave were recorded daily. Net radiation, soil heat exchange from soil solids and soil moisture, and soil latent heat exchange were calculated. It was determined that soil moisture

Linda Carol Jordan



Effect of multi-stream heat exchanger on performance of natural gas liquefaction with mixed refrigerant  

NASA Astrophysics Data System (ADS)

A thermodynamic study is carried out to investigate the effect of multi-stream heat exchanger on the performance of natural gas (NG) liquefaction with mixed refrigerant (MR). A cold stream (low-pressure MR) is in thermal contact with opposite flow of two hot streams (high-pressure MR and NG feed) at the same time. In typical process simulation with commercial software (such as Aspen HYSYS®), the liquefaction performance is estimated with a method of minimum temperature approach, simply assuming that two hot streams have the same temperature. In this study, local energy balance equations are rigorously solved with temperature-dependent properties of MR and NG feed, and are linked to the thermodynamic cycle analysis. The figure of merit (FOM) is quantitatively examined in terms of UA (the product of overall heat transfer coefficient and heat exchange area) between respective streams. In a single-stage MR process, it is concluded that the temperature profile from HYSYS is difficult to realize in practice, and the FOM value from HYSYS is an over-estimate, but can be closely achieved with a proper heat-exchanger design. It is also demonstrated that there exists a unique optimal ratio in three UA's, and no direct heat exchanger between hot streams is recommended.

Chang, Ho-Myung; Lim, Hye Su; Choe, Kun Hyung



Glyphosate effects on gas exchange and chlorophyll fluorescence responses of two Lolium perenne L. biotypes with differential herbicide sensitivity.  


Despite the extensive use of glyphosate, how it alters the physiology and metabolism of plants is still unclear. Photosynthesis is not regarded to be a primary inhibitory target of glyphosate, but it has been reported to be affected by this herbicide. The aim of the current research was to determine the effects of glyphosate on the light and dark reactions of photosynthesis by comparing glyphosate-susceptible and glyphosate-resistant Lolium perenne biotypes. After glyphosate treatment, accumulation of reduced carbohydrates occurred before a decrease in gas exchange. Stomatal conductance and CO(2) assimilation were reduced earlier than chlorophyll fluorescence and the amount of chlorophyll in susceptible plants. In the glyphosate-resistant biotype, stomatal conductance was the only parameter slightly affected only 5 days post-application. In susceptible plants, the initial glyphosate effects on gas exchange could be a response to a feedback regulation of photosynthesis. Since the herbicide affects actively growing tissues regardless of the inhibition of photosynthesis, the demand of assimilates decreased and consequently induced an accumulation of carbohydrates in leaves. We concluded that stomatal conductance could be a very sensitive parameter to assess both the susceptibility/resistance to glyphosate before the phytotoxic symptoms become evident. PMID:22738865

Yanniccari, Marcos; Tambussi, Eduardo; Istilart, Carolina; Castro, Ana María



Investigation of gas exchange processes in peat bog ecosystems by means of innovative Raman gas spectroscopy.  


Highly sensitive Raman gas spectroscopy is introduced for simultaneous real time analysis of O(2), CO(2), CH(4), and N(2) in order to elucidate the dynamics of greenhouse gases evolving from climate-sensitive ecosystems. The concentrations and fluxes of this suite of biogenic gases were quantified in the head space of a water-saturated, raised peat bog ecotron. The intact peat bog, exhibiting various degradation stages of peat and sphagnum moss, was exposed to various light regimes in order to determine important ecosystem parameters such as the maximum photosynthesis rate of the sphagnum as well as the extent of soil and plant respiration. Miniaturized Raman gas spectroscopy was proven to be an extremely versatile analytical technique that allows for onsite multigas analysis in high temporal resolution. Therefore it is an urgently needed tool for elucidation of complex biochemical processes especially in climate-sensitive ecosystems and consequently for the estimation of climate-relevant gas budgets. PMID:23320649

Frosch, Torsten; Keiner, Robert; Michalzik, Beate; Fischer, Bernhard; Popp, Jürgen



Biogenic emissions and CO 2 gas exchange investigated on four Mediterranean shrubs  

NASA Astrophysics Data System (ADS)

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, ?-pinene and ?-pinene for rosemary and ?-pinene, linalool and ?-pinene + sabinene for pistachio. Total monoterpene emission rates standardized to 30°C of 1.84 ± 0.24 and 0.35 ± 0.04 ?g Cg -1 dw h -1 were found for rosemary and pistachio, respectively (on a leaf dry weight basis). Myrtle emitted 22.2 ± 4.9 ?g C g -1 dw h -1 at standard conditions (30°C, PAR 1000 ?mol photons m -2 s -1 as isoprene and erica 5.61 ?g 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.

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.


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

NASA Astrophysics Data System (ADS)

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.

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



Activated carbon for gas phase arsenic capture  

SciTech Connect

Investigation of activated carbon as a multifunctional sorbent for trace metal capture is the focus of this study. In addition to mercury and halides, selenium and arsenic represent two of the most volatile trace species that remain in gas phase in substantial amounts. In this work, fundamental sorption characteristics of the activated carbon for arsenic removal from the gas phase are investigated. Activated carbons with different structural properties are studied for their usefulness in removing arsenic species from flue gas. Arsenic oxide (As{sub 2}O{sub 3}) is used as the source of arsenic. Preliminary sorption studies indicate that arsenic removal occurs by physical adsorption, with increased capture by carbons with higher surface areas.

Jadhav, R.; Gupta, H.; Misro, S.; Agnihotri, R.; Fan, L.S.



Simulation of gas phase diffusion on fouling and deposition in heat exchange systems  

NASA Astrophysics Data System (ADS)

Results of numerical predictions on the distributions of velocity, temperature, and species concentration above a simulated heat exchange system surface in the form of a flat plate with a leading edge are presented. Two-dimensional results show that the mass transfer increases with lower Schmidt and Reynolds number values. Under turbulent conditions, deposition is found to be higher than that for the corresponding laminar counterpart for a given species in the hot gas stream, and the rate of mass transfer is more sensitive to temperature gradients. Experimental results show good agreement with predictions from the two-dimensional code and from a three-dimensional code, except in the region close to the leading edge above the simulated heat exchanger.

Gupta, A. K.; Lilley, D. G.; Esmaili, H.; Ong, L. H.



Precooling heat exchange arrangement integral with mounting structure fairing of gas turbine engine  

SciTech Connect

This patent describes a gas turbine engine including a core engine, a casing surrounding the core engine and defining an annular cooling compartment, and outer annular nacelle spaced radially outward from the casing and defining therebetween an annular fan duct, and an engine mounting structure extending radially between and interconnecting the nacelle and the casing, a precooling heat exchange arrangement. It comprises a hollow fairing mounted on a forward side of the mounting structure across the main air flow through the fan duct, means for routing a source of high pressure hot bleed air to the fairing; at least one heat exchanger mounted in the fairing and including a heat transfer structure having an interior connected in communication with the routing means; and an air flow control mechanism in communication with and mounted to the fairing.

Miller, F.E.



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

SciTech Connect

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.

Kupp, E.R.; Trubelja, K.E.; Spear, K.E.; Tressler, R.E. [Pennsylvania State Univ., University Park, PA (United States). Dept. of Materials Science and Engineering



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

NASA Astrophysics Data System (ADS)

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.

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




PubMed Central

Simple, two-compartment models of transmucosal gas exchange for the middle ear (ME) are useful for describing ME pressure behavior under a variety of conditions. The most well developed exchange models require input of an experimentally determined, lumped-parameter, exchange-constant for each represented gas species. Evidences from past studies suggest that the value of the exchange-constant for inert gases is specific to the direction of the extant pressure-gradient, an unexpected result. In this study, the N2O transmucosal exchange-constant (time-constant) for 16 ears of 8 monkeys was measured for positive and negative ME-blood N2O gradients using previously published methods. The results showed that the two time-constant measures were highly correlated, but that the ME-blood time-constant was approximately 13 times greater than the blood-ME time-constant. This directional effect depends on the value of a gradient-ratio (arterial-venous/arterial-ME) included as a parameter in the time-constant for perfusion-limited gas exchange. All values of that ratio not equal to 1 introduce directional asymmetry into the measured time-constant. The significance of this phenomenon to current models and as a lead to the development of more complex, distributed models of transmucosal gas exchange is discussed.

Doyle, William J.; Yuksel, Sancak; Banks, Juliane; Alper, Cuneyt M.



Novel Components of an Active Mitochondrial K+/H+ Exchange*  

PubMed Central

Defects of the mitochondrial K+/H+ exchanger (KHE) result in increased matrix K+ content, swelling, and autophagic decay of the organelle. We have previously identified the yeast Mdm38 and its human homologue LETM1, the candidate gene for seizures in Wolf-Hirschhorn syndrome, as essential components of the KHE. In a genome-wide screen for multicopy suppressors of the pet? (reduced growth on nonfermentable substrate) phenotype of mdm38? mutants, we now characterized the mitochondrial carriers PIC2 and MRS3 as moderate suppressors and MRS7 and YDL183c as strong suppressors. Like Mdm38p, Mrs7p and Ydl183cp are mitochondrial inner membrane proteins and constituents of ?500-kDa protein complexes. Triple mutant strains (mdm38? mrs7? ydl183c?) exhibit a remarkably stronger pet? phenotype than mdm38? and a general growth reduction. They totally lack KHE activity, show a dramatic drop of mitochondrial membrane potential, and heavy fragmentation of mitochondria and vacuoles. Nigericin, an ionophore with KHE activity, fully restores growth of the triple mutant, indicating that loss of KHE activity is the underlying cause of its phenotype. Mdm38p or overexpression of Mrs7p, Ydl183cp, or LETM1 in the triple mutant rescues growth and KHE activity. A LETM1 human homologue, HCCR-1/LETMD1, described as an oncogene, partially suppresses the yeast triple mutant phenotype. Based on these results, we propose that Ydl183p and the Mdm38p homologues Mrs7p, LETM1, and HCCR-1 are involved in the formation of an active KHE system.

Zotova, Ludmila; Aleschko, Markus; Sponder, Gerhard; Baumgartner, Roland; Reipert, Siegfried; Prinz, Monika; Schweyen, Rudolf J.; Nowikovsky, Karin



Effects of water stress on the gas exchange, the activities of some enzymes of carbon and nitrogen metabolism, and on the pool sizes of some organic acids in maize leaves  

Microsoft Academic Search

Water-stressed maize (Zea mays L.) leaves showed a large decrease in leaf conductance during photosynthesis. Net CO2 uptake and evaporation declined fast at mild stress (?=?0.6 to ?1.0 MPa) and slower at more severe stress (?=?1.0 to -1.2 MPa), whereas the CO2 concentration in the intercellular spaces (Ci) did not drop to the CO2 compensation point. The activities of the

Thomas W. Becker; Heinrich P. Fock



Modeling the effects of temperature and relative humidity on gas exchange of prickly pear cactus ( Opuntia spp.) stems  

Microsoft Academic Search

A model to estimate gas profile of modified atmosphere packaged (MAP) prickly pear cactus stems was developed and calibrated. The model describes the transient gas exchange taking in consideration the effect of temperature (T) and relative humidity (RH) on film permeability (FPgas), respiration rate (Rx) and tissue permeance (TPgas). A closed system was used for respiration measurement, generating conditions of

Juan Carlos Guevara-Arauza; Elhadi M. Yahia; Luis Cedeño; L. M. M. Tijskens



Transient Simulation and Experimental Verification of Gas-Steam and Liquid-Steam, Shell, and Tube Type Heat Exchangers  

Microsoft Academic Search

The condensing steam heaters dynamically modeled in this work are shell and tube type heat exchangers with the condensing steam on the shell side. Two variations of the model are developed, one for heating a gas stream where the thermal mass of the gas is very small, and one for heating a liquid stream where the thermal mass of the

K. J. Daniel; A. W. Crapo; D. H. Brown



Upper ocean state estimation in the Southern Ocean Gas Exchange Experiment region using the four-dimensional variational technique  

Microsoft Academic Search

A prototypical ocean circulation model, and associated 4-D variational data assimilation system, is configured in support of the Southern Ocean Gas Exchange Experiment (Southern Ocean GasEx). The regional circulation model has 4 km horizontal resolution and 5 m vertical resolution in the upper ocean. In situ temperature and salinity observations and remotely sensed, gridded sea surface temperature and sea surface

S. Dwivedi; T. W. N. Haine; C. E. Del Castillo



Breath-to-breath “noise” in the ventilatory and gas exchange responses of children to exercise  

Microsoft Academic Search

The purposes of this investigation were to quantify the noise component of child breath-by-breath data, investigate the major\\u000a determinants of the breath-to-breath noise, and to characterise the noise statistically. Twenty-four healthy children (12\\u000a males and 12 females) of mean (SD) age 13.1 (0.3) years completed 25?min of steady-state cycle ergometry at an exercise intensity\\u000a of 50?W. Ventilatory and gas exchange

C. R. Potter; D. J. Childs; W. Houghton; N. Armstrong



Peripheral endothelial dysfunction is associated with gas exchange inefficiency in smokers  

Microsoft Academic Search

Aims  To assess the cross-sectional association between exercise capacity, gas exchange efficiency and endothelial function, as\\u000a measured by flow-mediated dilation (FMD) and nitroglycerin-mediated dilation (NMD) of the brachial artery, in a large-scale\\u000a population-based survey.\\u000a \\u000a \\u000a \\u000a \\u000a 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.

Sven Gläser; Anne Obst; Christian F Opitz; Marcus Dörr; Stephan B Felix; Klaus Empen; Henry Völzke; Ralf Ewert; Christoph Schäper; Beate Koch



V? O 2peak and the gas-exchange anaerobic threshold during incremental arm cranking in able-bodied and paraplegic men  

Microsoft Academic Search

Resting energy expenditure, peak oxygen uptake (V?O2peak) and the gas-exchange anaerobic threshold (Than) were measured during incremental arm cranking (15?W?·?min?1) in six able-bodied (AB) and six paraplegic (P) subjects. Only male subjects with traumatic spinal cord injuries in the area\\u000a of the 10–12th thoracic segment were included in the P group. All AB and P subjects were physically active. Mean

Donald A. Schneider; Darlene A. Sedlock; Elizabeth Gass; Greg Gass



Feasibility study for an advanced coal fired heat exchanger/gas turbine topping cycle for a high efficiency power plant  

SciTech Connect

The overall objective of this project is to prove the feasibility of AFR's concepts for a high efficiency coal-fired generating plant using the REACH/Exchanger concept to power an externally fired gas turbine. It will provide a design of an advanced technology furnace/heat exchanger combination in which a ceramic heat exchanger is aerodynamically protected from the corrosive particle laden coal combustion products. The heat exchanger is fired by radiative and convective heat transfer from a moderately clean fuel stream and by radiative heat transfer from the flame of a much larger uncleaned fuel stream. In principle, 35% of the energy will be provided by the former and 65% by the later. The fluid mechanics in the furnace/heat exchanger are controlled so that the flow of the combustion products, from the moderately clean fuel stream, sweeps past the heat exchanger to prevent the contact of coal particles with the uncleaned stream.

Solomon, P.R.; Zhao, Yuxin; Pines, D.S.



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

NASA Astrophysics Data System (ADS)

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.

Iwabuchi, K.; Kurata, K.


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


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

Gitelson, J I; Okladnikov YuN



Measurements of air-sea gas exchange at high wind speeds in the Southern Ocean: Implications for global parameterizations  

Microsoft Academic Search

The SOLAS Air-Sea Gas Exchange (SAGE) Experiment was conducted in the western Pacific sector of the Southern Ocean. During SAGE, gas transfer velocities were determined using the 3He\\/SF6 dual gas tracer technique, and results were obtained at higher wind speeds (16.0 m s-1) than in previous open ocean dual tracer experiments. The results clearly reveal a quadratic relationship between wind

David T. Ho; Cliff S. Law; Murray J. Smith; Peter Schlosser; Mike Harvey; Peter Hill



Measurements of air-sea gas exchange at high wind speeds in the Southern Ocean: Implications for global parameterizations  

Microsoft Academic Search

The SOLAS Air-Sea Gas Exchange (SAGE) Experiment was conducted in the western Pacific sector of the Southern Ocean. During SAGE, gas transfer velocities were determined using the 3He\\/SF6 dual gas tracer technique, and results were obtained at higher wind speeds (16.0 m s?1) than in previous open ocean dual tracer experiments. The results clearly reveal a quadratic relationship between wind

David T. Ho; Cliff S. Law; Murray J. Smith; Peter Schlosser; Mike Harvey; Peter Hill



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

PubMed Central

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

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



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

SciTech Connect

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.

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



Do We Need Exercise Tests to Detect Gas Exchange Impairment in Fibrotic Idiopathic Interstitial Pneumonias?  

PubMed Central

In patients with fibrotic idiopathic interstitial pneumonia (f-IIP), the diffusing capacity for carbon monoxide (DLCO) has been used to predict abnormal gas exchange in the lung. However, abnormal values for arterial blood gases during exercise are likely to be the most sensitive manifestations of lung disease. The aim of this study was to compare DLCO, resting PaO2, P(A-a)O2 at cardiopulmonary exercise testing peak, and oxygen desaturation during a 6-min walk test (6MWT). Results were obtained in 121 patients with idiopathic pulmonary fibrosis (IPF, n = 88) and fibrotic nonspecific interstitial pneumonias (NSIP, n = 33). All but 3 patients (97.5%) had low DLCO values (35?mmHg) and 100 (83%) demonstrated significant oxygen desaturation during 6MWT (>4%). Interestingly 27 patients had low DLCO and normal P(A-a)O2, peak and/or no desaturation during the 6MWT. The 3 patients with normal DLCO also had normal PaO2, normal P(A-a)O2, peak, and normal oxygen saturation during 6MWT. Our results demonstrate that in fibrotic IIP, DLCO better defines impairment of pulmonary gas exchange than resting PaO2, exercise P(A-a)O2, peak, or 6MWT SpO2.

Wallaert, Benoit; Wemeau-Stervinou, Lidwine; Salleron, Julia; Tillie-Leblond, Isabelle; Perez, Thierry



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


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

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



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


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

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



Effects of tree height on branch hydraulics, leaf structure and gas exchange in California redwoods.  


We examined changes in branch hydraulic, leaf structure and gas exchange properties in coast redwood (Sequoia sempervirens) and giant sequoia (Sequoiadendron giganteum) trees of different sizes. Leaf-specific hydraulic conductivity (k(L)) increased with height in S. sempervirens but not in S. giganteum, while xylem cavitation resistance increased with height in both species. Despite hydraulic adjustments, leaf mass per unit area (LMA) and leaf carbon isotope ratios (delta(13)C) increased, and maximum mass-based stomatal conductance (g(mass)) and photosynthesis (A(mass)) decreased with height in both species. As a result, both A(mass) and g(mass) were negatively correlated with branch hydraulic properties in S. sempervirens and uncorrelated in S. giganteum. In addition, A(mass) and g(mass) were negatively correlated with LMA in both species, which we attributed to the effects of decreasing leaf internal CO(2) conductance (g(i)). Species-level differences in wood density, LMA and area-based gas exchange capacity constrained other structural and physiological properties, with S. sempervirens exhibiting increased branch water transport efficiency and S. giganteum exhibiting increased leaf-level water-use efficiency with increasing height. Our results reveal different adaptive strategies for the two redwoods that help them compensate for constraints associated with growing taller, and reflect contrasting environmental conditions each species faces in its native habitat. PMID:19210642

Ambrose, Anthony R; Sillett, Stephen C; Dawson, Todd E



Air-water gas exchange of organochlorine pesticides in Taihu Lake, China.  


Previous research in the Taihu Lake Region (TLR) of China found high levels of atmospheric organochlorine pesticides (OCPs). To understand the sources and the environmental behaviors of these OCPs in the TLR, research on air-water gas exchange was performed in 2004. Hexachlorocyclohexanes (HCHs), DDT related compounds (DDTs), cis-chlordane (CC), trans-chlordane (TC), heptachlor (HEPT), and alpha-endosulfan in both air and water samples were analyzed, and air-water gas exchange fluxes of these compounds were calculated. The net volatilization flux of alpha-HCH was 58 ng m(-2) day(-1), suggesting that the residue of technical HCH in the lake sediment might have been an important source of alpha-HCH to the air of this region after the ban of technical HCH two decades ago. The main components of technical chlordane, TC, CC, and HEPT, each had net volatilization fluxes >230 ng m(-2) day(-1), suggesting that waste discharge from manufacturing plants in the upper region was the main source of chlordane to the lake. Unlike alpha-HCH and chlordane, o,p'-DDT and alpha-endosulfan had net deposition fluxes, suggesting that these compounds were transported through the atmosphere from land sources and then deposited into the lake. The correlation between air concentrations and ambient air temperature indicated that the current sources of o,p'-DDT and alpha-endosulfan were from land; alpha-HCH and chlordane were mainly from the lake. PMID:18409615

Qiu, Xinghua; Zhu, Tong; Wang, Feng; Hu, Jianxin



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

NASA Astrophysics Data System (ADS)

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 gas transfer coefficient, k, for both a vegetated condition and a control condition (no cylinders). The presence of cylinders in the tank substantially increased the rate of the gas transfer. For the highest wind speed, the gas transfer coefficient was several times higher when cylinders were present compared to when they were not. The gas transfer coefficient for the vegetated condition also proved sensitive to wind speed, increasing markedly with increasing mean wind speeds. Profiles of dissolved oxygen revealed well-mixed conditions in the bulk water column following prolonged air-flow above the water surface, suggesting application of the thin-film model is appropriate. The enhanced gas exchange observed might be explained by increased turbulent kinetic energy within the water column and the anisotropy of the cylinder array, which constrains horizontal motions more than vertical motions. Improved understanding of gas exchange in vegetated water columns may be of particularly use to investigations of carbon fluxes and soil accretion in wetlands. Reference: Nepf, H. (1999), Drag, turbulence, and diffusion in flow through emergent vegetation, Water Resour. Res., 35(2), 479-489.

Poindexter, C.; Variano, E. A.



Reduction of molecular gas diffusion through gaskets in leaf gas exchange cuvettes by leaf-mediated pores.  


There is an ongoing debate on how to correct leaf gas exchange measurements for the unavoidable diffusion leakage that occurs when measurements are done in non-ambient CO(2) concentrations. In this study, we present a theory on how the CO(2) diffusion gradient over the gasket is affected by leaf-mediated pores (LMP) and how LMP reduce diffusive exchange across the gaskets. Recent discussions have so far neglected the processes in the quasi-laminar boundary layer around the gasket. Counter intuitively, LMP reduce the leakage through gaskets, which can be explained by assuming that the boundary layer at the exterior of the cuvette is enriched with air from the inside of the cuvette. The effect can thus be reduced by reducing the boundary layer thickness. The theory clarifies conflicting results from earlier studies. We developed leaf adaptor frames that eliminate LMP during measurements on delicate plant material such as grass leaves with circular cross section, and the effectiveness is shown with respiration measurements on a harp of Deschampsia flexuosa leaves. We conclude that the best solution for measurements with portable photosynthesis systems is to avoid LMP rather than trying to correct for the effects. PMID:23320654

Boesgaard, Kristine S; Mikkelsen, Teis N; Ro-Poulsen, Helge; Ibrom, Andreas



SP-100 inert gas act activation  

SciTech Connect

As part of the SP-100 test program at the US Department of Energy Field Office, Richland, there are plans to test the SP-100 space reactor in a vacuum in the test facility shown in Figure 1. The vacuum vessel will be in an inert gas atmosphere in the reactor experiment (RX) cell. The upper assembly (UA)/pump cells will also be inerted. The objective is to determine whether the radioactivity levels in the facility exhaust are within permissible levels. This radioactivity comes from leakage of activation products from the inert gas cells into the facility ventilation exhaust stream. The specific activities were calculated for the activation products from the combinations of inert gases that were considered for this facility, for a range of leakage rates, and for leakage from the UA/pump cells into the RX cell, and results are detailed in this report.

Wilcox, A.D.



Extraction of extracellular polymers from activated sludge using a cation exchange resin  

Microsoft Academic Search

The extraction of water soluble extracellular polymeric substances (EPS) from activated sludge was investigated. The extraction procedure was based upon cation exchange using a cation exchange resin (CER). Activated sludge from two different types of treatment plants responded very similarly to the extraction procedure. The EPS yield was enhanced by increasing the stirring intensity, the amounts of CER added and

Bo Frølund; Rikke Palmgren; Kristian Keiding; Per Halkjær Nielsen



Reference Laboratory for Radon Gas Activity Concentration Measurements at PSI.  

National Technical Information Service (NTIS)

Active or passive radon gas measuring instruments are exposed during intercomparison exercises in the radon chamber of the Reference Laboratory for Radon Gas Concentration Measurements at Paul Scherrer Institut: The traceability of radon gas measurements ...

C. Schuler



Observation of zwitterion formation in the gas-phase H\\/D-exchange with CH 3 OD: Solution-phase structures in the gas phase  

Microsoft Academic Search

Infrared spectroscopy of gas-phase singly deuterated [Trp+K]+ (formed by H\\/D exchange with CH3OD) shows that some (?20%) kinetically stable zwitterionic (ZW) conformer is formed, based on the diagnostic antisymmetric\\u000a CO stretch of the deprotonated carboxylate moiety, ?as(CO2?), at 1680 cm?1. A majority of the deuterated [Trp+K]+ is found to be in the charge solvation (CS) conformation, with deuterium exchange occurring

Nick C. Polfer; Robert C. Dunbar; Jos Oomens



Function of the Nucleotide Exchange Activity of Vav1 in T cell Development and Activation*  

PubMed Central

The guanine nucleotide exchange factor (GEF) Vav1 is essential for transducing T cell antigen receptor (TCR) signals and therefore plays a critical role in the development and activation of T cells. It has been presumed that the GEF activity of Vav1 is important for its function; however, there has been no direct demonstration of this. Here, we generated mice expressing enzymatically inactive, but normally folded, Vav1 protein. Analysis of these mice showed that the GEF activity of Vav1 was necessary for the selection of thymocytes and for the optimal activation of T cells, including signal transduction to Rac1, Akt, and integrins. In contrast, the GEF activity of Vav1 was not required for TCR-induced calcium flux, activation of extracellular signal–regulated kinase (ERK) and protein kinase D1 (PKD1), and cell polarization. Thus, in T cells, the GEF activity of Vav1 is essential for some, but not all, of its functions.

Saveliev, Alexander; Vanes, Lesley; Ksionda, Olga; Rapley, Jonathan; Smerdon, Stephen J.; Rittinger, Katrin; Tybulewicz, Victor L. J.



Active Heat Exchange System Development for Latent Heat Thermal Energy Storage.  

National Technical Information Service (NTIS)

The results of Contract DEN 3-38, Active Heat Exchanger System Development for Latent Heat Thermal Energy Storage Systems are documented. The overall project consisted of five tasks to select, design, fabricate, test and evaluate candidate active heat exc...

R. T. LeFrois A. K. Mathur



Seasonal trends in reduced leaf gas exchange and ozone-induced foliar injury in three ozone sensitive woody plant species.  


Seasonal trends in leaf gas exchange and ozone-induced visible foliar injury were investigated for three ozone sensitive woody plant species. Seedlings of Populus nigra L., Viburnum lantana L., and Fraxinus excelsior L. were grown in charcoal-filtered chambers, non-filtered chambers and open plots. Injury assessments and leaf gas exchange measurements were conducted from June to October during 2002. All species developed typical ozone-induced foliar injury. For plants exposed to non-filtered air as compared to the charcoal-filtered air, mean net photosynthesis was reduced by 25%, 21%, and 18% and mean stomatal conductance was reduced by 25%, 16%, and 8% for P. nigra, V. lantana, and F. excelsior, respectively. The timing and severity of the reductions in leaf gas exchange were species specific and corresponded to the onset of visible foliar injury. PMID:15809106

Novak, K; Schaub, M; Fuhrer, J; Skelly, J M; Hug, C; Landolt, W; Bleuler, P; Kräuchi, N



Intra-individual variation allows an explicit test of the hygric hypothesis for discontinuous gas exchange in insects  

PubMed Central

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.

Williams, Caroline M.; Pelini, Shannon L.; Hellmann, Jessica J.; Sinclair, Brent J.



Formaldehyde and tracer gas transfer between airstreams in enthalpy-type air-to-air heat exchangers  

SciTech Connect

An experimental study is described in which the formaldehyde, tracer gas, and water vapor transfer rates in two enthalpy exchangers were measured. The first exchanger uses a cross-flow 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.

Fisk, W.J.; Pedersen, B.S.; Hekmat, D.; Chant, R.E.; Kaboli, H.



Leaf Gas Exchange in Relict Spruce-Fir Cloud Forests of the Southern Appalachian Mountains, USA.  

NASA Astrophysics Data System (ADS)

The relict spruce-fir (Picea rubens Sarg. - Abies fraseri (Pursh) Poir.) forests of the southern Appalachian mountains are found only on high altitude mountain tops that receive copious precipitation (>2000 mm annually) and experience frequent cloud immersion (~65% of the total growth season days). Cloud deposition accounts for up to 50% of the annual water budget for these high-elevation forests. Two sites in North Carolina were established to investigate the influences of cloudiness and cloud immersion on leaf gas exchange and water relations of Fraser fir: Mt. Mitchell (2028 m elevation) and Roan Mtn., NC (1890 m elevation). It was hypothesized that the cool, moist, and cloudy conditions at these sites would exert a strong influence on leaf carbon and water fluxes. Water status was high throughout all hours on measurement days, with xylem water potential always >-1.75 MPa and soil water content always >0.1 m3 m-3. Leaves were wet frequently (>60% of all hours) due to cloud immersion and nightly dewfall, which did not appear to limit photosynthesis, but may influence stomatal response and transpiration. Maximum photosynthesis (Amax) was about 15 umol CO2 m-2 s-1, and saturated at sunlight levels between 400-500 umol m-2 s-1. Maximum leaf conductance (gmax) and transpiration (Emax) were 0.31 mol m-2 s-1 and 3.9 mmol m-2 s-1, respectively, and were strongly associated with LAVD. At both sites, conductance and transpiration decreased exponentially as LAVD increased, with 50-75% reduction between 0-0.5 kPa. Mean instantaneous water use efficiency on clear days was 3.5 umol CO2 m-2 s-1/mmol H2O m-2 s-1 across all transpiration fluxes, but increased on cloudy and cloud-immersed days (range of 2.3 - 6.0 umol CO2 m-2 s-1/mmol H2O m-2 s-1) as transpiration increased. Leaf gas exchange appeared tightly coupled to the response of conductance to LAVD which maintained high water status, even at the relatively low LAVD of these cloud forests. Thus, the cloudy, humid environment of these refugial forests appears to exert a strong influence on leaf gas exchange and water relations of these montane species. Because global climate change is predicted to increase regional cloud ceiling levels, more research on cloud impacts on carbon gain and water relations is needed to predict the future survival of these relic forests.

Reinhardt, K.; Smith, W. K.



The Response of Foliar Gas Exchange to Exogenously Applied Ethylene 1  

PubMed Central

The responsiveness to ethylene of net photosynthesis and stomatal conductance to water vapor in intact plants was investigated in 13 herbaceous species representing seven plant families. Exposures were conducted in an open, whole-plant exposure system providing controlled levels of irradiance, air temperature, CO2, relative humidity, and ethylene concentration. Net photosynthesis and stomatal conductance to water vapor in units of moles per square meter per second were measured on recently expanded leaves in control and ethylene-treated plants using a remotely operated single-leaf cuvette. The ethylene concentration was either 0 or 210 micromoles per cubic meter and was maintained for 4 hours. Species varied substantially in the response of their foliar gas exchange to ethylene. In 7 of the 13 species, net photosynthesis was inhibited statistically by 4 hours of ethylene exposure. As a function of the rate in control plants, the responses were most pronounced and statistically significant in Arachis hypogaea (?51.1%), Gossypium hirsutum (?31.7%), Glycine max (?24.8%), Cucurbita pepo (?20.4%), Phaseolus vulgaris (?18.4%), Setaria viridis (?17.5%), and Raphanus sativus (?4.4%). Whereas the responsiveness of net photosynthesis to ethylene among the 13 species showed no specific taxonomic associations, the responsiveness was positively correlated with the intrinsic rate of net photosynthesis. Stomatal conductance to water vapor after 4 hours of ethylene exposure declined statistically in 6 of the 13 species. As a function of control rates, the most marked and statistically significant responses of stomatal conductance were in Glycine max (?53.6%), Gossypium hirsutum (?51.2%), Arachis hypogaea (?42.7%), Phaseolus vulgaris (?38.6%), Raphanus sativus (?26.8%), and Solanum tuberosum (?23.4%). Although ethylene-induced changes in net photosynthesis and stomatal conductance were positively correlated, there were species-specific exceptions in which net photosynthesis declined after 4 hours of exposure without a concurrent change in stomatal conductance, stomatal conductance declined without a change in net photosynthesis, and the decline in stomatal conductance substantially exceeded the corresponding decline in net photosynthesis. Thus, the responsiveness to ethylene of net photosynthesis and stomatal conductance to water vapor were not consistently synchronous or equivalent among the 13 species. It is concluded that foliar gas exchange is responsive to exogenously applied ethylene in many plant species. The sensitivity of foliar gas exchange to ethylene may play a role in general plant response to environmental stress in which one of the physiological sites of action for endogenously produced stress ethylene in the leaf is the plant's photosynthetic capacity and/or stomatal conductance to water vapor.

Taylor, George E.; Gunderson, Carla A.



Influence of structure of sulfonated cation exchange resins on their catalytic activity in alkylation of phenol by olefins  

SciTech Connect

The catalytic activity of the resins was evaluated from results obtained in alkylation of phenol by n-nonene and n-decene. The contents of olefins, phenol, sec-alkyl phenyl ethers, o- and p-sec-alkylphenols, and dialkylphenols in the alkylated products were determined by gas-liquid chromatography. The effect rate constant of alkylation was calculated on the basis of a second order equation. The influence of pore characteristics of sulfonated cation exchange resins was generalized on their catalytic selectivity. Optimal activity and selectivity of catalytic action in the alkylation of phenol by higher olefins were exhibited by macroporous cation exchange resins of the KU-23(10/60) type.

Korenev, K.D.; Belov, P.S.; Zavadovskaya, A.S.; Kapustin, P.P.; Kozyreva, G.I.; Uvarova, E.A.; Zavorotnyi, V.A.



Lithium activates mammalian Na + \\/H + exchangers: isoform specificity and inhibition by genistein  

Microsoft Academic Search

Replacement of external NaCl with LiCl induced cytoplasmic alkalinization in CCL-39 cells and rat L6 myoblasts expressing the endogenous Na+\\/H+ exchanger isoform NHE1. This Li+-induced alkalinization is due to activation of the Na+\\/H+ exchanger because it was completely inhibited by 100 µM ethylisopropylamiloride (apparent Kd=1 µM) and because it did not occur in exchanger-deficient PS120 cells. The effect of Li+

Yoko Kobayashi; Tianxiang Pang; Takahiro Iwamoto; Shigeo Wakabayashi; Munekazu Shigekawa



Role of gas exchange in the inorganic carbon, oxygen, and /sup 222/Rn budgets of the Amazon River  

SciTech Connect

Dissolved oxygen, /sup 222/Rn, pCO/sub 2/, alkalinity, respiration rate, and discharge have been measured at eight mainstem and seven tributary stations during February-March 1984 in a 1700-km stretch of the Amazon River between Vargem Grande and Obidos in Brazil. Air-water gas exchange rates were estimated two ways: measurements of the flux of /sup 222/Rn int floating domes yielded an average boundary layer thickness of, and oxygen mass balance calculations resulted in an average of Given a boundary layer thickness on the order of, CO/sub 2/ loss to the atmosphere in the entire reach would have been 37.4 kmol s/sup -1/, which is about equal to the total tributary dissolved inorganic carbon (DIC) input and is about half of the total fluvial DIC input to the section. Thus, CO/sub 2/ evasion is a major component of Amazon River DIC balance. Because gas exchange within the section was rapid relative to water travel time through the section, a quasi-steady state was maintained between respiratory input and evasion of CO/sub 2/. Dissolved /sup 222/Rn activities in the mainstem varied from 3.5 to 8.3 dpm liter/sup -1/ and were always highly supersaturated with respect to the atmosphere. Dissolved radon was also not supported by decay of /sup 222/Ra in the mainstem. A /sup 222/Rn mass balance indicated that direct groundwater input into this stretch of the Amazon mainstem probably accounted for no more than 1% of water discharge.

Devol, A.H.; Quay, P.D.; Richey, J.E.; Martinelli, L.A.



Application of a laboratory gas exchange chamber for assessment of in situ mercury emissions  

NASA Astrophysics Data System (ADS)

The potential for the use of a laboratory gas exchange system to estimate of mercury emissions from naturally and anthropogenically mercury-enriched areas was assessed by comparison of mercury fluxes measured from the same substrate in situ and in the laboratory. In general, mercury emissions measured with the laboratory chamber for daytime conditions were of the same magnitude as mean mercury emissions measured in situ with field chambers. Mercury emissions measured with both the field chamber and laboratory chamber were lower than those measured with micrometeorological methods. Within the controlled experimental regime of the laboratory chamber, data were developed that demonstrated that substrate mercury concentrations and light are important parameters in controlling mercury emissions. However, with light and other parameters interacting with the soil, the correlation between mercury fluxes and substrate mercury concentrations declined. Mercury emissions from a variety of substrates in the dark were ˜25% of those emissions measured in the light at the same soil surface temperature.

Gustin, M. Sexauer; Rasmussen, P.; Edwards, G.; Schroeder, W.; Kemp, J.



Injection of dust into the Martian atmosphere - Evidence from the Viking Gas Exchange experiment  

NASA Astrophysics Data System (ADS)

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.

Huguenin, R. L.; Harris, S. L.; Carter, R.



Time-dependent effective potential and exchange kernel of homogeneous electron gas  

NASA Astrophysics Data System (ADS)

By minimizing the difference between the left- and the right-hand sides of the many-body time-dependent Schrödinger equation with the Slater-determinant wave function, we derive a nonadiabatic and self-interaction-free time-dependent single-particle effective potential, which is the generalization to the time-dependent case of the so-called localized Hartree-Fock potential. The new potential can be efficiently used within the framework of the time-dependent density-functional theory as we demonstrate by the evaluation of the wave vector and frequency-dependent exchange kernel fxh(q,?) of the homogeneous electron gas. This is found to be nonsingular and causal, and it satisfies the positiveness of the dissipation, in contrast to the earlier known kernel from the first-order perturbation theory, which makes our fxh promising for applications.

Nazarov, V. U.



Differential leaf gas exchange responses to salinity and drought in the mangrove tree Avicecennia germinans (Avicenniaceae).  


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

Sobrado, M A



Antiadiabatic limit of the exchange-correlation kernels of an inhomogeneous electron gas  

NASA Astrophysics Data System (ADS)

We express the high-frequency (antiadiabatic) limit of the exchange-correlation (xc) kernels of an inhomogeneous electron gas in terms of the following equilibrium properties: the ground-state density, the xc kinetic stress tensor, the pair-correlation function and the ground-state xc potential. Of these quantities, the first three are amenable to exact evaluation by quantum Monte Carlo methods while the last can be obtained from the inversion of the Kohn-Sham equation for the ground-state orbitals. The exact scalar kernel, in this limit, is found to be of very long range in space, at variance with the kernel that is used in the standard local density approximation. The antiadiabatic xc kernels will be useful in calculations of excitation energies by time-dependent density-functional theory in atoms, molecules, and solids, and provide a solid basis for interpolation between the low- and high-frequency limits of the xc kernels.

Nazarov, V. U.; Tokatly, I. V.; Pittalis, S.; Vignale, G.



Horizontal and vertical distributions of colored dissolved organic matter during the Southern Ocean Gas Exchange Experiment  

NASA Astrophysics Data System (ADS)

Field and remote sensing measurements of colored dissolved organic matter (CDOM) were acquired in the Southern Ocean during the 2008 Gas Exchange experiment. Values of CDOM absorption coefficient at 440 nm (ag440) ranged from ˜0.02 to ˜0.06 m-1. In general, CDOM was higher in the region sampled during this study than in other regions of the Southern Ocean. CDOM showed an inverse correlation with salinity, and the spectral slope parameter S varied directly with salinity. These relationships, water circulation patterns, and characteristics of South Georgia Island suggested that runoff was a source of CDOM in the study site. Analysis of seasonal variability of ag440 using ocean color imagery of areas away from the effect of South Georgia Island showed seasonal fluctuations between ˜0.02 to ˜0.03 m-1. CDOM production models showed that in situ production could also account for seasonal changes in CDOM.

Del Castillo, Carlos E.; Miller, Richard L.



Isotope exchange for gas-phase acetic acid and ethanol at aqueous interfaces: A study of surface reactions  

SciTech Connect

Isotope exchange for deuterated gas-phase acetic acid and ethanol in contact with water (H{sub 2}O) droplets was studied using a droplet train apparatus. In these experiments, the gas-phase species interacts with liquid droplets and the loss of the species is monitored. The loss of the species may be due to the entry of the molecules into the bulk or to a reaction of the species at the gas-liquid interface, in this case isotope exchange. Studies were conducted as a function of pH in the range 0--14, droplet temperature in the range 291--263 K and gas-liquid interaction time in the range 2--15 ms. For deuterated acetic acid the isotope exchange probability with water molecules at the interface is near unity. On the other hand, isotope exchange probability for ethanol with surface water molecules at the interface is near unity. On the other hand, isotope exchange probability for ethanol with surface water molecules at pH 7 is much smaller, ranging from 0.033 at 263 K to 0.051 at 291 K. Ethanol isotope exchange is both acid and base catalyzed. The exchange probability therefore increases both toward low and high pH and levels off to a plateau at pH 2 and 12, respectively. The maximum value of the isotope exchange probability at the plateau is significant less than 1. It ranges between 0.14 and 0.18 with no clear trend in temperature. Results are explained in terms of a kinetic model in which it is assumed that the surface-adsorbed ethanol molecules are distributed between two distinct forms: a weakly adsorbed state and a partially solvated state. Only the partially solvated molecules can interact with the near-surface ions in the interior of the liquid. A finite rate of entering the partially solvated state is responsible for the observed plateaus in isotope exchange at high and low pH. Parameters describing the gas uptake and isotope exchange processes are examined using two models to describe the surface species: surface nucleation and Gibbs surface excess.

Shi, Q.; Li, Y.Q.; Davidovits, P. [Boston Coll., Chestnut Hill, MA (United States); Jayne, J.T.; Worsnop, D.R.; Mozurkewich, M.; Kolb, C.E. [Aerodyne Research, Inc., Billerica, MA (United States). Center for Aerosol and Cloud Chemistry



Relationships between carbonyl sulfide (COS) and CO2 during leaf gas exchange.  


*Carbonyl sulfide (COS) exchange in C(3) leaves is linked to that of CO(2), providing a basis for the use of COS as a powerful tracer of gross CO(2) fluxes between plants and the atmosphere, a critical element in understanding the response of the land biosphere to global change. *Here, we carried out controlled leaf-scale gas-exchange measurements of COS and CO(2) in representative C(3) plants under a range of light intensities, relative humidities and temperatures, CO(2) and COS concentrations, and following abscisic acid treatments. *No 'respiration-like' emission of COS or detectable compensation point, and no cross-inhibition effects between COS and CO(2) were observed. The mean ratio of COS to CO(2) assimilation flux rates, A(s)/A(c), was c. 1.4 pmol micromol(-1) and the leaf relative uptake (assimilation normalized to ambient concentrations, (A(s)/A(c))(C(a)(c)/C(a)(s))) was 1.6-1.7 across species and conditions, with significant deviations under certain conditions. Stomatal conductance was enhanced by increasing COS, which was possibly mediated by hydrogen sulfide (H(2)S) produced from COS hydrolysis, and a correlation was observed between A(s) and leaf discrimination against C(18)OO. *The results provide systematic and quantitative information necessary for the use of COS in photosynthesis and carbon-cycle research on the physiological to global scales. PMID:20298480

Stimler, Keren; Montzka, Stephen A; Berry, Joseph A; Rudich, Yinon; Yakir, Dan



Water loss and gas exchange by eggs of Manduca sexta: trading off costs and benefits.  


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

Woods, H Arthur



Whole-Plant Gas Exchange and Reductive Biosynthesis in White Lupin1  

PubMed Central

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.

Cen, Yan-Ping; Turpin, David H.; Layzell, David B.



Sesuvium portulacastrum maintains adequate gas exchange, pigment composition, and thylakoid proteins under moderate and high salinity.  


Cuttings of Sesuvium portulacastrum L. (Aizoaceae) were taken from plants cultivated under severe saline conditions. The obtained seedlings were grown on sand and irrigated with nutrient solution over 5 weeks under no (0 mM NaCl), moderate (200 mM NaCl), or high (400 mM NaCl) salinity conditions. A follow-up of gas exchange was performed weekly and pigment levels and patterns of fully expanded leaves were determined after 3 and 5 weeks of treatment. At the end of the 5-week period, immunoblot analysis of the main polypeptides of photosystem I and II was performed with the aim to investigate salt-induced variations in photosystem composition. Net CO2 assimilation rate (Pn) increased under salinity up to 3 weeks of treatment then decreased to reach the value of 0mM-treated plants at the end of the experiment. For stomatal conductance (gs) and intercellular CO2 concentration (Ci), the opposite occurred. These results were concomitant with an increase in practically all pigment levels, mainly under high salinity, with the exception of zeaxanthin. The de-epoxidation index (DEPS index) was much lower under saline than non-saline conditions in the 3rd week, indicating light stress in 0mM-treated plants. At the end of the experiment, this index showed much lower values with no significant differences between treatments, which coincided with no significant differences in gas exchange as well. Protein amounts of D1, CP47, and CP43 did not show noticeable variations with salt treatment, whereas LHCII underwent a slight but significant decrease (-15%) at the highest NaCl concentration. LHCI polypeptides were unaffected by the salt treatments, where conversely, the highest concentration induced a significant decrease in PsaA/B amount (-18%). PMID:20619928

Rabhi, Mokded; Giuntini, Deborah; Castagna, Antonella; Remorini, Damiano; Baldan, Barbara; Smaoui, Abderrazak; Abdelly, Chedly; Ranieri, Annamaria



CO2 Gas Exchange Across the Human Tympanic Membrane is not Appreciably Affected by Pathology  

PubMed Central

Background Past in vivo studies in humans showed that the tympanic membrane (TM) is permeable to physiological gases. Animal studies show that transTM CO2 conductance is increased by TM pathology. Objective Determine if transTM CO2 exchange in humans is affected by atrophic and sclerotic pathologies. Methods An ear canal (EC) probe (ECP) constructed from a custom-fitted acrylic body, a glass capillary tube enclosing an oil meniscus to maintain ambient ECP+EC pressure and a silica glass microtube linked to a mass spectrometer (MS) for measuring gas composition was hermetically sealed within the ear canal of the test ear. ECP+EC volume was measured and gas samples taken at 10 minute intervals for 1 hour. The fractional CO2 pressure measured in the ECP+EC for each sample was regressed on time and the slope of the function multiplied by the ECP+EC volume and divided by the estimated transTM CO2 gradient at the start of the experiment to yield transTM CO2 conductance (uL/min/Pa). Data were complete for 15 normal, 13 sclerotic and 9 atrophic TMs. Results The average (±std) transTM CO2 conductances were 1.76×10?4 ± 7.27×10?5, 2.26×10?4 ± 1.5×10?4 and 2.36×10?4 ± 1.14×10?4 uL/min/Pa/TM for the normal, sclerotic and atrophic TMs, respectively. A pairwise comparison of data for the normal and atrophic TMs under the directional hypothesis of a greater CO2 exchange rate for thinner TMs approached statistical significance (P=.07). A similar pairwise comparison for the sclerotic and normal TMs did not approach statistical significance (P=.28) Conclusion The effect of TM pathologies on CO2 conductance is limited.

Yuksel, Sancak; Swarts, J. Douglas; Banks, Julianne; Doyle, William J.



Gas exchange and intrapulmonary distribution of ventilation during continuous-flow ventilation  

SciTech Connect

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) 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.

Vettermann, J.; Brusasco, V.; Rehder, K.



CO2 gas exchange of benthic microalgae during exposure to air: a technique for the rapid assessment of primary production  

Microsoft Academic Search

A method of measuring CO2gas exchange (caused, for example, by microalgal photosynthesis on emersed tidal mudflats) using open flow IR gas analyzers is described. The analyzers are integrated in a conventional portable photosynthesis system (LI-6400, LI-COR, Nebraska, USA), which allows manipulation and automatic recording of environmental parameters at the field site. Special bottomless measuring chambers are placed directly on the

Dirk Schories; Ulf Mehlig



Multidimensional separations of ubiquitin conformers in the gas phase: Relating ion cross sections to H\\/D exchange measurements  

Microsoft Academic Search

Investigating gas-phase structures of protein ions can lead to an improved understanding of intramolecular forces that play\\u000a an important role in protein folding. Both hydrogen\\/deuterium (H\\/D) exchange and ion mobility spectrometry provide insight\\u000a into the structures and stabilities of different gas-phase conformers, but how best to relate the results from these two methods\\u000a has been hotly debated. Here, high-field asymmetric

Errol W. Robinson; Evan R. Williams



Routine activation analysis with an automatic ion-exchange apparatus  

Microsoft Academic Search

Summary The application of the automatic ion-exchange apparatus by Samsahl, to the determination of trace elements in biological, medical and environmental samples, is described. By this method it is possible to analyse for up to about 40 trace elements in various materials. Because of the large number of elements determined by this device, a flux-monitor irradiation method is applied for

Peter Schramel



Pulmonary Artery Pressure and Alveolar Gas Exchange in Man during Acclimatization to 12,470 ft  

PubMed Central

Pulmonary hemodynamics and gas exchange were studied in four physicians during 72 hr acclimatization to 12,470 ft. Pulmonary catheters were left in three subjects for 72 hr. Resting mean pulmonary arterial pressure (P??P?) rose progressively during the first 24 hr from 10.3 ±1.0 to 21.1 ±4.0 torr and remained at this level. During this same 24 hr period cardiac output increased from 7.1 ±1.4 to 8.4 ±2.0 liters/min and total pulmonary resistance rose from 122 ±16 to 209 ±40 dynes·sec/cm-5. Excercise at 60 w after 24 hr of hypoxia increased P??P? to 28.8 ±5.1 torr and decreased total pulmonary resistance to 155 ±25. Shunt fractions were 11 ±3.8% after 24 hr at altitude and fell to 7 ±0% after 72 hr. Alveolar to arterial O2 difference (P(A-a)O2) breathing oxygen fell from 116 ±10.8 to 92 ±33.3 torr during the same period of acclimatization, whereas dead space to tidal volume ratio (VD/VT) rose from 33 ±4.0% to 40 ±5.3% and P(A-a)O2 breathing ambient air rose from 8 ±2.6 to 11 ±3.0 torr. Inspiratory static lung compliance decreased significantly from a control of 176 ±8 to 141 ±8 ml/cm H2O after 72 hr of hypoxia. After 4-7 days at altitude, further deterioration in gas exchange was observed after a 5 mile, 1800 ft climb to the summit (14,255 ft) and return. P(A-a)O2 on air rose from 2.5 ±2.1 just before starting, to 16.3 ±2.8 at the summit (rested), and was still 9.0 ±2.2 several hours after returning. The O2-breathing values paralleled these, whereas dead space appeared to fall. We speculate that the hypoxic pulmonary hypertension which develops over 24 hr in some way may be responsible for a reduction of compliance and deterioration in oxygen exchange efficiency, possibly representing a sub-clinical form of pulmonary edema of high altitude. The increased alveolar to arterial O2 difference induced by hypoxic exercise persists for several hours of hypoxic rest.

Kronenberg, Richard S.; Safar, Peter; Lee, Joseph; Wright, Fred; Noble, William; Wahrenbrock, Eric; Hickey, Robert; Nemoto, Edwin; Severinghaus, John W.



Comparison of Radon-222 and satellite-wind-based estimates of gas exchange in the Eastern Tropical South Pacific ocean  

NASA Astrophysics Data System (ADS)

The rate of atmosphere-ocean gas exchange remains a key uncertainty in oceanic in situ dissolved trace gas budgets, including CO2 fluxes and net oxygen production based on oxygen supersaturation and using oxygen triple isotopes to constrain gross productivity. Excellent gas exchange parameterization algorithms based on sea-surface wind speeds exist, but the uncertainty of wind-based piston velocities often exceeds 30%. We present gas exchange rates at stations in the Eastern Tropical South Pacific calculated using the radon-222 deficit method, which is sensitive to gas exchange on timescales ranging up to weeks, the typical residence time of O2, N2, and Ar in the oceanic mixed layer. Our study area encompassed the oceanic box bounded by 10-20° S and 80-100°W. We compare these results to gas exchange rates based on parameterizations of wind speeds retrieved from the ASCAT satellite and from shipboard winds. Average satellite wind speeds ranged from 4-8 m/s and predicted piston velocities ranged from 1-6 m/d. These results are compared with piston velocities calculated from a 1-D, steady state two-box radon model (mixed layer and thermocline) fit to 7-12 radon analyses collected from the upper 150 m. Radium-226 was also measured on upper ocean water following ingrowth of radon. This study involved extensive measurement of bottle and board blanks to ascertain Ra values. Preliminary analyses of radon results predict a range in piston velocity of 1-5 m/d, similar to the range predicted from 30 day average wind velocity. However, the correlation between radon- and wind speed-based piston velocities for individual stations is quite poor. Additional work is in progress to consider more sophisticated strategies for calculating effective wind speed, based on incorporating its temporal variability prior to collection of the radon profiles.

Berelson, W.; Yeung, L. Y.; Hammond, D. E.; Wolfe, C. I.; Rollins, N.; Prokopenko, M. G.



Technical Note: A simple method for air-sea gas exchange measurements in mesocosms and its application in carbon budgeting  

NASA Astrophysics Data System (ADS)

Mesocosms as large experimental units provide the opportunity to perform elemental mass balance calculations, e.g. to derive net biological turnover rates. However, the system is in most cases not closed at the water surface and gases exchange with the atmosphere. Previous attempts to budget carbon pools in mesocosms relied on educated guesses concerning the exchange of CO2 with the atmosphere. Here, we present a simple method for precise determination of air-sea gas exchange in mesocosms using N2O as a deliberate tracer. Beside the application for carbon budgeting, transfer velocities can be used to calculate exchange rates of any gas of known concentration, e.g. to calculate aquatic production rates of climate relevant trace gases. Using an arctic KOSMOS (Kiel Off Shore Mesocosms for future Ocean Simulation) experiment as an exemplary dataset, it is shown that the presented method improves accuracy of carbon budget estimates substantially. Methodology of manipulation, measurement, data processing and conversion to CO2 fluxes are explained. A theoretical discussion of prerequisites for precise gas exchange measurements provides a guideline for the applicability of the method under various experimental conditions.

Czerny, J.; Schulz, K. G.; Ludwig, A.; Riebesell, U.



High temperature heat exchangers for gas turbines and future hypersonic air breathing propulsion  

Microsoft Academic Search

After surveying the results of ONERA's investigations to date of metallic and ceramic heat exchangers applicable to automotive and aircraft powerplants, which are primarily of finned-tube counterflow configuration, attention is given to the influence of heat-exchanger effectiveness on fuel consumption and exchanger dimensions and weight. Emphasis is placed on the results of studies of cryogenic heat exchangers used by airbreathing

Patrick Avran; Pierre Bernard



Bubble Continuous Positive Airway Pressure Enhances Lung Volume and Gas Exchange in Preterm Lambs  

PubMed Central

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.

Pillow, J. Jane; Hillman, Noah; Moss, Timothy J. M.; Polglase, Graeme; Bold, Geoff; Beaumont, Chris; Ikegami, Machiko; Jobe, Alan H.



In Vivo Gas Exchange Measurement of the Site and Dynamics of Nitrate Reduction in Soybean1  

PubMed Central

A gas analysis system was built to study the relationship between the reductant cost of NO3? assimilation and the measured rate of CO2 and O2 exchange in roots, leaves, and stems+ petioles of soybean (Glycine max L. Merr. cv Maple glen) plants. The measurements were used to calculate the diverted reductant utilization rate (DRUR = 4*[measured rate of CO2 + measured rate of O2], in moles of high-energy electron [e?] per gram per hour) in plants in the presence (N+) and absence (N?) of NO3?. The differences in DRUR between the N+ and N? treatments provided a measure of the NO3?-coupled DRUR of 25-d-old plants, whereas a 15NO3?-enriched nutrient solution was used to obtain an independent measure of the rate of NO3? assimilation. The measured reductant cost for the whole plant was 9.6 e? per N assimilated, a value within the theoretical range of four to 10 e? per N assimilated. The results predicted that shoots accounted for about 55% of the whole-plant NO3? assimilation over the entire day, with shoots dominating in the light, and roots in the dark. The gas analysis approach described here holds promise as a powerful, noninvasive tool to study the regulation of NO3? assimilation in plant tissue.

Cen, Yan-Ping; Layzell, David B.



Effect of water and salt stresses on the growth, gas exchange and water relations in Argyranthemum coronopifolium plants  

Microsoft Academic Search

Plants of Argyranthemum coronopifolium were submitted to water stress (preconditioned by watering every 3 days, two dry–wet cycles were imposed) and salt stress (15 days of exposure to 140 mm NaCl followed by a recovery period of 11 days), independently. Effects of water and salt stresses on gas exchange, water relations and growth parameters were investigated in order to know

F. De Herralde; C. Biel; R. Savé; M. A. Morales; A. Torrecillas; J. J. Alarcón; M. J. Sánchez-Blanco



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...


Aerosol size distribution and aerosol water content measurements during Atlantic Stratocumulus Transition Experiment\\/Marine Aerosol and Gas Exchange  

Microsoft Academic Search

Aerosol size distribution data measured during the June 1992 Marine Aerosol and Gas Exchange experiment are analyzed to investigate the characteristics of fine marine aerosol particles measured over the North Atlantic near the Azores Islands. Measured aerosol size distribution data were corrected using the corrected size calibration data based on the optical properties of particles being measured. The corrected size

Y. Kim; H. Sievering; J. Boatman; D. Wellman; A. Pszenny



Effects of Noninvasive Ventilation on Pulmonary Gas Exchange and Hemodynamics during Acute Hypercapnic Exacerbations of Chronic Obstructive Pulmonary Disease  

Microsoft Academic Search

Noninvasive positive pressure ventilation (NIPPV) can replace tracheal intubation in acute exacerba- tions of chronic obstructive pulmonary disease (COPD) with severe hypercapnic respiratory failure. However, the underlying mechanisms by which NIPPV improves pulmonary gas exchange are not known. We studied 10 male COPD patients (68 6 8 (SD) yr) with acute severe hypercapnic respira- tory failure within 36 h after



Leaf Abscisic Acid Accumulation in Response To Substrate Water Content: Linking Leaf Gas Exchange Regulation with Leaf Abscisic Acid Concentration  

Microsoft Academic Search

ADDITIONAL INDEX WORDS. stomatal conductance, drought tolerance, genotype variation ABSTRACT. Quantitative differences in leaf abscisic acid (ABAL) among four cultivars of red maple (Acer rubrum L.) and one freeman maple (Acer ×freemanii E. Murray) cultivar were investigated. This study tested the hypothesis that ABAL concentration can be used to compare the effects of water stress on the gas exchange response

William L. Bauerle; William W. Inman; Jerry B. Dudley



Effects of Head-Out Immersion at 19.18 Ata on Pulmonary Gas Exchange in Man.  

National Technical Information Service (NTIS)

Pulmonary gas exchange was studied during the performance of graded exercise in two normal male subjects breathing a mixture of helium and oxygen PIO2=167-172 mm Hg. while immersed to the chin in water at a simulated depth of 600 ft (19.18 Ata.) When comp...

E. T. Flynn H. A. Saltzman J. K. Summitt



A Photosynthesis - Based Gas Exchange Evapotranspiration Model (GEM) Coupled With A Soil - Atmosphere System For Environmental Applications  

Microsoft Academic Search

Recent advances in vegetation models have developed explicit relations for modeling photosynthesis and stomatal conductance and hence the variations in the surface evapotranspiration. These photosynthesis or carbon assimilation based stomatal models have been successfully employed at leaf scale and climate studies. We developed and couple a gas exchange based surface evapotranspiration model (GEM) as a land surface \\/ SVAT scheme

D. S. Niyogi; K. Alapaty; S. Raman



Leaf gas exchange responses of 13 prairie grassland species to elevated CO2 and increased nitrogen supply  

Microsoft Academic Search

Summary • Leaf gas exchange responses to elevated CO 2 and N are presented for 13 perennial species, representing four functional groups: C 3 grasses, C 4 grasses, legumes, and nonleguminous forbs. Understanding how CO 2 and N effects interact is important to predict plant community response to global change. • Plants were field-grown in monoculture under current ambient and

Tali D. Lee; Mark G. Tjoelker; David S. Ellsworth; Peter B. Reich



The impact of prolonged flood-irrigation on leaf gas exchange in mature pecans in an orchard setting  

Microsoft Academic Search

Woody perennials subjected to root oxygen-stress often respond with varying levels of reduced assimilation and leaf gas exchange. Yet in most of these studies, seedlings grown in pots were subjected to experimental conditions that rarely exist in nature for mature trees. To determine if flooding mature orchard-grown pecan (Carya illinoiensis (Wangh) K. Koch) results in a similar depressed photosynthetic rate

J. C. Kallestad; T. W. Sammis; J. G. Mexal; V. Gutschick


Responses of hardwood regeneration to fire in mesic forest openings. II. Leaf gas exchange, nitrogen concentration, and water status  

Microsoft Academic Search

The physiological responses of tree regeneration to fire were studied in openings in a mesic hardwood forest. Gas exchange, nitrogen concentration, and water potential were monitored on foliage of burned and nonburned regeneration of northern red oak (Quercus rubra L.), white ash (Fraxinus americana L.), and sugar maple (Acer saccharum Marsh.) following spring fires in 1989 and 1990. Fire led

Eric L. Kruger; Peter B. Reich



Effect of intake valve closure timing on effective compression ratio and gas exchange process of a modern diesel engine  

Microsoft Academic Search

Advanced combustion strategies including premixed charge compression ignition (PCCI) and lifted flame combustion are promising strategies for meeting increasingly stringent emissions regulations and improving fuel efficiency in next generation powertrains. In order to promote and implement these strategies closed-loop control of the gas exchange process and combustion is critical. Variable valve actuation (VVA) can play a key role in determining

Rajani S Modiyani



Iloprost Improves Gas Exchange and Exercise Tolerance in Patients with Pulmonary Hypertension and Chronic Obstructive Pulmonary Disease  

Microsoft Academic Search

Background: Nonselective systemic vasodilators worsen ventilation perfusion (V\\/Q) matching and gas exchange in patients with chronic obstructive pulmonary disease (COPD). Inhaled iloprost has the potential to act preferentially in ventilated regions of the lung, thereby reducing pulmonary hypertension (PH) while alveolar ventilation is still maintained. Objectives: To investigate the acute effects of inhaled iloprost on V\\/Q matching in patients with

Tarek A. Dernaika; Mikel Beavin; Gary T. Kinasewitz



Probing the regional distribution of pulmonary gas exchange through single-breath gas- and dissolved-phase 129Xe MR imaging.  


Although some central aspects of pulmonary function (ventilation and perfusion) are known to be heterogeneous, the distribution of diffusive gas exchange remains poorly characterized. A solution is offered by hyperpolarized (129)Xe magnetic resonance (MR) imaging, because this gas can be separately detected in the lung's air spaces and dissolved in its tissues. Early dissolved-phase (129)Xe images exhibited intensity gradients that favored the dependent lung. To quantitatively corroborate this finding, we developed an interleaved, three-dimensional radial sequence to image the gaseous and dissolved (129)Xe distributions in the same breath. These images were normalized and divided to calculate "(129)Xe gas-transfer" maps. We hypothesized that, for healthy volunteers, (129)Xe gas-transfer maps would retain the previously observed posture-dependent gradients. This was tested in nine subjects: when the subjects were supine, (129)Xe gas transfer exhibited a posterior-anterior gradient of -2.00 ± 0.74%/cm; when the subjects were prone, the gradient reversed to 1.94 ± 1.14%/cm (P < 0.001). The (129)Xe gas-transfer maps also exhibited significant heterogeneity, as measured by the coefficient of variation, that correlated with subject total lung capacity (r = 0.77, P = 0.015). Gas-transfer intensity varied nonmonotonically with slice position and increased in slices proximal to the main pulmonary arteries. Despite substantial heterogeneity, the mean gas transfer for all subjects was 1.00 ± 0.01 while supine and 1.01 ± 0.01 while prone (P = 0.25), indicating good "matching" between gas- and dissolved-phase distributions. This study demonstrates that single-breath gas- and dissolved-phase (129)Xe MR imaging yields (129)Xe gas-transfer maps that are sensitive to altered gas exchange caused by differences in lung inflation and posture. PMID:23845983

Kaushik, S Sivaram; Freeman, Matthew S; Cleveland, Zackary I; Davies, John; Stiles, Jane; Virgincar, Rohan S; Robertson, Scott H; He, Mu; Kelly, Kevin T; Foster, W Michael; McAdams, H Page; Driehuys, Bastiaan



Ventilatory Support by Continuous Positive Airway Pressure Breathing Improves Gas Exchange as Compared with Partial Ventilatory Support with Airway Pressure Release Ventilation  

Microsoft Academic Search

In acute lung injury, airway pressure release ventilation (APRV) with superimposed spontaneous breathing im- proves gas exchange compared with controlled me- chanical ventilation. However, the release of airway pressure below the continuous positive airway pres- sure (CPAP) level may provoke lung collapse. There- fore, we compared gas exchange and hemodynamics using a crossover design in nine pigs with oleic acid-

Peter Neumann



Short-term impacts of nutrient manipulations on leaf gas exchange and biomass partitioning in contrasting 2-year-old Pinus taeda clones during seedling establishment  

Microsoft Academic Search

We conducted a 1-year greenhouse experiment to assess the impact of nutrient manipulations on seedling growth, biomass partitioning, and leaf gas exchange between two fast growing Pinus taeda clones that differed in growth efficiency. After 1 year we observed significant treatment and treatment by clone effects on growth, biomass partitioning, and gas exchange parameters. Fertilization increased total seedling biomass 18%

Michael C. Tyree; John R. Seiler; Chris A. Maier



Fouling reduction characteristics of a no-distributor-fluidized-bed heat exchanger for flue gas heat recovery  

SciTech Connect

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.

Jun, Y.D.; Lee, K.B.; Islam, S.Z.; Ko, S.B. [Kongju National University, Kong Ju (Republic of Korea). Dept. for Mechanical Engineering



Fluid dynamic energy exchanger  

Microsoft Academic Search

A gas-to-gas energy exchanger utilizing a commutator repetitively diverts a jet of a first pressurized gas between an energy exchange conduit and an exhaust outlet. Upon entering the energy exchange conduit, the first gas creates a pressure wave which traverses the conduit at sonic velocity and, in so doing, compresses a second gas in the conduit. The now pressurized second



Water-gas exchange of organochlorine pesticides at Lake Chaohu, a large Chinese lake.  


Organochlorine pesticides (OCPs), a potential threat to ecosystems and human health, are still widely residual in the environment. The residual levels of OCPs in the water and gas phase were monitored in Lake Chaohu, a large Chinese lake, from March 2010 to February 2011. Nineteen types of OCPs were detected in the water with a total concentration of 7.27 ± 3.32 ng/l. Aldrin, DDTs and HCHs were the major OCPs in the water, accounting for 38.3%, 28.9% and 23.6% of the total, respectively. The highest mean concentration (12.32 ng/l) in the water was found in September, while the lowest (1.74 ng/l) was found in November. Twenty types of gaseous OCPs were detected in the atmosphere with a total concentration of 542.0 ± 636.5 pg/m(3). Endosulfan, DDTs and chlordane were the major gaseous OCPs in the atmosphere, accounting for 48.9%, 22.5% and 14.4% of the total, respectively. The mean concentration of gaseous OCPs was significantly higher in summer than in winter. o,p'-DDE was the main metabolite of DDT in both the water and gas phase. Of the HCHs, 52.3% existed as ?-HCH in the water, while ?-HCH (37.9%) and ?-HCH (30.9%) were dominant isomers in the gas phase. The average fluxes were -21.11, -3.30, -152.41, -35.50 and -1314.15 ng/(m(2) day) for ?-HCH, ?-HCH, HCB, DDT and DDE, respectively. The water-gas exchanges of the five types of OCPs indicate that water was the main potential source of gaseous OCPs in the atmosphere. A sensitivity analysis indicated that the water-gas flux of ?-HCH, ?-HCH and DDT is more vulnerable than that of HCB and DDE to the variation of the parameters. The possible source of the HCHs in the water was from the historical usage of lindane; however, that in the air was mainly from the recent usage of lindane. The technical DDT and dicofol might be the source of DDTs in the water and air. PMID:23238597

Ouyang, Hui-Ling; He, Wei; Qin, Ning; Kong, Xiang-Zhen; Liu, Wen-Xiu; He, Qi-Shuang; Yang, Chen; Jiang, Yu-Jiao; Wang, Qing-Mei; Yang, Bin; Xu, Fu-Liu



Gas-phase hydrogen/deuterium exchange of dinucleotides and 5'-monophosphate dinucleotides in a quadrupole ion trap  

NASA Astrophysics Data System (ADS)

Gas-phase hydrogen/deuterium (H/D) exchange reactions of four deprotonated dinucleotides (dAA, dAG, dGA, dGG) and their 5'-monophosphate analogs (5'-dAA, 5'-dAG, 5'-dGA, 5'-dGG) with D2O were performed in a quadrupole ion trap mass spectrometer. Significant differences in the rates and extents of exchange were found when the 5'-hydroxyl group of the dinucleotides was replaced by a phosphate functionality. Extensive and nucleobase-dependent exchange occurred for the deprotonated 5'-monophosphate dinucleotides, whereas the dinucleotides all exhibited essentially the same limited exchange. Results for the isomeric 5'-monophosphates, 5'-dAG and 5'-dGA, were remarkably different, indicating that the H/D exchange reaction was sequence dependent. An elaborate array of computations was performed to investigate the gas-phase structures of the ions individually and also as participants in ion-molecule complexes with D2O. Integration of the experimental and theoretical results supports a relay exchange mechanism and suggests that the exchange behavior depends highly on the identity and sequence of the nucleobases as well as their ability to interact with the deprotonation site. Finally, a shuttling mechanism is proposed to possibly account for the bimodal H/D exchange behavior observed for deprotonated 5'P-dGA. In this case, hydrogen bonding between the nucleobases in concert with interaction from the deuterating agent creates an ion-molecule complex in which hydrogen and deuterium atoms may be shuttled amongst the hydrogen-bonded participants.

Chipuk, Joseph E.; Brodbelt, Jennifer S.



Technical review of DOE activities in the eastern gas shales  

Microsoft Academic Search

US Department of Energy activities in the eastern gas shales are directed at deetermining the geologic character and magnitude of the Devonian age shale gas resource and toward increasing production of natural gas. Geologic evaluations of the collected formation characterization data are essentially complete to determine basin limits and stratigraphic intervals as potential gas sources. With these developments, large areas

C. A. Komar; A. E. Hunt; A. B. Yost



Triennial Central Bank Survey of Foreign Exchange and Derivatives Market Activity 1998  

NSDL National Science Digital Library

The Central Bank Survey of Foreign Exchange and Derivatives Market Activity 1998 is a triennial statistical publication by the Bank for International Settlements (BIS) (reviewed in the March 7, 1997 Scout Report). The survey reports on foreign exchange and OTC derivative activities in 43 countries, and an 83-page statistical annex provides spot, outright forward, foreign exchange swap, and total turnover figures by country for the month of April 1998. Links to central bank and monetary authority data home pages as well as a discussion of main findings are also available on-site.


Growing season ecosystem and leaf-level gas exchange of an exotic and native semiarid bunchgrass.  


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

Hamerlynck, Erik P; Scott, Russell L; Moran, M Susan; Keefer, Timothy O; Huxman, Travis E



Carbon source/sink function of a subtropical, eutrophic lake determined from an overall mass balance and a gas exchange and carbon burial balance.  


Although studies on carbon burial in lake sediments have shown that lakes are disproportionately important carbon sinks, many studies on gaseous carbon exchange across the water-air interface have demonstrated that lakes are supersaturated with CO(2) and CH(4) causing a net release of CO(2) and CH(4) to the atmosphere. In order to more accurately estimate the net carbon source/sink function of lake ecosystems, a more comprehensive carbon budget is needed, especially for gaseous carbon exchange across the water-air interface. Using two methods, overall mass balance and gas exchange and carbon burial balance, we assessed the carbon source/sink function of Lake Donghu, a subtropical, eutrophic lake, from April 2003 to March 2004. With the overall mass balance calculations, total carbon input was 14 905 t, total carbon output was 4950 t, and net carbon budget was +9955 t, suggesting that Lake Donghu was a great carbon sink. For the gas exchange and carbon burial balance, gaseous carbon (CO(2) and CH(4)) emission across the water-air interface totaled 752 t while carbon burial in the lake sediment was 9477 t. The ratio of carbon emission into the atmosphere to carbon burial into the sediment was only 0.08. This low ratio indicates that Lake Donghu is a great carbon sink. Results showed good agreement between the two methods with both showing Lake Donghu to be a great carbon sink. This results from the high primary production of Lake Donghu, substantive allochthonous carbon inputs and intensive anthropogenic activity. Gaseous carbon emission accounted for about 15% of the total carbon output, indicating that the total output would be underestimated without including gaseous carbon exchange. PMID:17664033

Yang, Hong; Xing, Yangping; Xie, Ping; Ni, Leyi; Rong, Kewen



Reduced thrombocyte adhesion to endothelialized poly 4-methyl-1-pentene gas exchange membranes—a first step toward bioartificial lung development.  


Polymeric materials used in biomedical devices, bioartificial organs, or for the fabrication of tissue engineering scaffolds should completely prevent the activation of the coagulation system and subsequent clot formation. Surface endothelialization is considered an important tool to optimize the blood compatibility of synthetic materials, as a functional endothelial cell layer on an artificial material may help control hemostasis and, therefore, provide a solution to improve the biocompatibility of these materials. Here we report on the endothelialization of poly 4-methyl-1-pentene (PMP) gas exchange membranes using human cord blood-derived late outgrowth endothelial colony forming cells. We achieved complete endothelialization of PMP membranes; and when seeded and cultivated on the membrane, cord blood-derived late outgrowth endothelial colony forming cells maintained both endothelial characteristics and functionality. Endothelialization resulted in significantly lower platelet adhesion and activation compared with unseeded membranes. Of importance, the endothelial layer had no major impact on gas permeability of PMP membranes. This study is a first promising step toward the development of a biofunctionalized surface for the use in gas exchange devices with blood contacting surfaces and a straightforward approach toward a long-term bio-hybrid lung replacement system. PMID:20486793

Hess, Christian; Wiegmann, Bettina; Maurer, Andreas N; Fischer, Philipp; Möller, Lena; Martin, Ulrich; Hilfiker, Andres; Haverich, Axel; Fischer, Stefan



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


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

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



Gas exchange characteristics of wheat stands grown in a closed, controlled environment.  


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 slowly. Results from these tests will be used to model the use of plants for CO2 removal, O2 production, and water evaporation for controlled ecological life support systems proposed for extraterrestrial environments. PMID:11538198

Wheeler, R M; Corey, K A; Sager, J C; Knott, W M


Open-system chamber for measurements of gas exchanges at plant level.  


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

Alterio, Giovanni; Giorio, Pasquale; Sorrentino, Giuseppe



Water relations and gas exchange of Acer saccharum seedlings in contrasting natural light and water regimes.  


Field measurements were made of leaf photosynthesis (A), stomatal conductance (g) and leaf water relations for sugar maple (Acer saccharum Marsh.) seedlings growing in a forest understory, small gap or large clearing habitat in southwestern Wisconsin, USA. Predawn water status, leaf gas exchange and plasticity in field and laboratory water relations characteristics were compared among contrasting light environments in a wet year (1987) and a dry year (1988) to evaluate possible interactions between light and water availability in these habitats. Leaf water potentials (Psi(leaf)) at predawn and midday were lower for clearing than gap or understory seedlings. Acclimation of tissue osmotic potentials to light environment was observed among habitats but did not occur within any of the habitats in response to prolonged drought. During a summer drought in 1988, decreases in daily maximum g (g(max)) and maximum A (A(max)) in clearing seedlings were correlated with predawn Psi(leaf), which reached a seasonal minimum of -2.0 MPa. Under well-watered conditions, diurnal fluctuations in Psi(leaf) of up to 2.0 MPa in clearing seedlings occurred along with large midday depressions of A and g. In a wet year, strong stomatal responses to leaf-to-air vapor pressure difference (VPD) in sunny habitats were observed over nine diurnal courses of gas exchange measurements on seedlings in a gap and a clearing. Increasing stomatal limitations to photosynthesis appeared to be responsible for the reduction in A at high VPD for clearing seedlings. In understory seedlings, however, low water-use efficiency and development of leaf water deficits in sunflecks was related to reduced stomatal limitations to photosynthesis relative to seedlings in sunny habitats. Predawn Psi(leaf) and VPD appear to be important factors limiting carbon assimilation in sugar maple seedlings in light-saturating irradiances, primarily through stomatal closure. The overall results are consistent with the idea that sugar maple seedlings exhibit "conservative" water use patterns and have low drought tolerance. Leaf water relations and patterns of water use should be considered in studies of acclimation and species photosynthetic performance in contrasting light environments. PMID:14969871

Ellsworth, D S; Reich, P B



Alveolar Gas Exchange and Pulmonary Functions in Patients with Type II Diabetes Mellitus  

PubMed Central

Background: The incidence of diabetes is increasing tremendously throughout the world especially in the developing countries. This disease affects various organs like eyes, nerves, kidneys and the heart. In this study, we investigated whether lungs are also one of the target organs of diabetes mellitus or not. Aim: To assess the pulmonary function parameters including alveolar gas exchange in patients with Type 2 Diabetes mellitus and to find the influence of hyperglycaemia and duration of diabetes. Methodology: This cross sectional study involved 30 type II diabetic patients of age 30-60 years attending the diabetic outpatient department of SRM Medical College & Research Centre and 30 age and sex matched non-diabetic subjects as controls. The glycated haemoglobin (HbA1c) levels, fasting and post prandial blood glucose levels, pulmonary function parameters such as Forced Vital Capacity (FVC), Forced Expiratory Volume in 1 second (FEV1), Forced Expiratory Volume Percentage (FEV1 /FVC), Peak Expiratory Flow Rate (PEFR), Forced Expiratory Flow (25 – 75%), Peak Inspiratory flow ( PIF), Forced Inspiratory Vital Capacity ( FIVC), Total Lung Capacity ( TLC),Diffusing capacity of lung for carbon monoxide( DLCO) were measured for all the participants using Easyone Pro computerised spirometer. DLCO was measured by single breath Carbon Monoxide (CO) diffusion test. The alveolar membrane permeability was assessed by evaluating the ratio of DLCO to Alveolar Ventilation (VA). Results: The pulmonary function parameters FVC, FEV1, PEFR, PIF, FIVC, TLC , DLCO and DLCO/VA were significantly low (p<0.05) in patients with type II diabetes mellitus when compared to control group. The DLCO and DLCO/VA were significantly lower (p<0.05) in patients with poor glycemic control(HbA1c > 7). Conclusion: We conclude that the pulmonary function parameters like FVC, FEV1, PEFR, PIF, FIVC, TLC and alveolar gas exchange were significantly reduced in patients with type II diabetes. The patients with Type II diabetes mellitus had a restrictive pattern of respiratory abnormality. The patients with poor glycaemic control( HbA1c > 7) had reduced alveolar diffusion which was not dependent on the duration of diabetes. The impaired respiratory function may give way for the development of pulmonary complications. Spirometry can be used as a screening tool among diabetics as an early preventive measure.

S, Anandhalakshmi; S, Manikandan; P, Ganeshkumar; C, Ramachandran



The Impact of a Lower Sea Ice Extent on Arctic Greenhouse Gas Exchange  

NASA Astrophysics Data System (ADS)

Arctic sea ice extent hit a new record low in September 2012, when it fell to a level about two times lower than the 1979-2000 average. Record low sea ice extents such as these are often hailed as an obvious example of the impact of climate change on the Arctic. Less obvious, however, are the further implications of a lower sea ice extent on Arctic greenhouse gas exchange. For example, a reduction in sea ice, in consort with a lower snow cover, has been connected to higher surface temperatures in the terrestrial part of the Arctic (Screen et al., 2012). These higher temperatures and longer growing seasons have the potential to alter the CO2 balance of Arctic tundra through enhanced photosynthesis and respiration, as well as the magnitude of methane emissions. In fact, large changes are already observed in terrestrial ecosystems (Post et al., 2009), and concerns have been raised of large releases of carbon through permafrost thaw (Schuur et al., 2011). While these changes in the greenhouse gas balance of the terrestrial Arctic are described in numerous studies, a connection with a decline in sea ice extent is nonetheless seldom made. In addition to these changes on land, a lower sea ice extent also has a direct effect on the exchange of greenhouse gases between the ocean and the atmosphere. For example, due to sea ice retreat, more ocean surface remains in contact with the atmosphere, and this has been suggested to increase the oceanic uptake of CO2 (Bates et al., 2006). However, the sustainability of this increased uptake is uncertain (Cai et al., 2010), and carbon fluxes related directly to the sea ice itself add much uncertainty to the oceanic uptake of CO2 (Nomura et al., 2006; Rysgaard et al., 2007). Furthermore, significant emissions of methane from the Arctic Ocean have been observed (Kort et al., 2012; Shakhova et al., 2010), but the consequence of a lower sea ice extent thereon is still unclear. Overall, the decline in sea ice that has been seen in recent years has the potential to influence greenhouse gas exchange across terrestrial ecosystems and the Arctic Ocean, but the overall impact remains unclear. In this study, we therefore try to reduce this uncertainty by addressing the influence of the decline in sea ice extent on all affected greenhouse gas fluxes in the high latitudes. Also, we will address the need for more research, on the ocean and on the land, to understand the impact of a lower sea ice extent on Arctic greenhouse gas exchange. References: Bates, N. R., Moran, S. B., Hansell, D. A. and Mathis, J. T.: An increasing CO2 sink in the Arctic Ocean due to sea-ice loss, Geophys. Res. Lett., 33, L23609, doi:10.1029/2006GL027028, 2006. Cai, W.-J., Chen, L., Chen, B., Gao, Z., Lee, S. H., Chen, J., Pierrot, D., Sullivan, K., Wang, Y., Hu, X., Huang, W.-J., et al.: Decrease in the CO2 Uptake Capacity in an Ice-Free Arctic Ocean Basin, Science, 329(5991), 556-559, doi:10.1126/science.1189338, 2010. Kort, E. A., Wofsy, S. C., Daube, B. C., Diao, M., Elkins, J. W., Gao, R. S., Hintsa, E. J., Hurst, D. F., Jimenez, R., Moore, F. L., Spackman, J. R., et al.: Atmospheric observations of Arctic Ocean methane emissions up to 82 degrees north, Nature Geosci., 5(5), 318-321, doi:10.1038/NGEO1452, 2012. Nomura, D., Yoshikawa-Inoue, H. and Toyota, T.: The effect of sea-ice growth on air-sea CO2 flux in a tank experiment, vol. 58, pp. 418-426. 2006. Post, E., Forchhammer, M. C., Bret-Harte, M. S., Callaghan, T. V., Christensen, T. R., Elberling, B., Fox, A. D., Gilg, O., Hik, D. S., Høye, T. T., Ims, R. A., et al.: Ecological Dynamics Across the Arctic Associated with Recent Climate Change, Science, 325(5946), 1355-1358, doi:10.1126/science.1173113, 2009. Rysgaard, S., Glud, R. N., Sejr, M. K., Bendtsen, J. and Christensen, P. B.: Inorganic carbon transport during sea ice growth and decay: A carbon pump in polar seas, J. Geophys. Res., 112, C03016, doi:10.1029/2006JC003572, 2007. Schuur, E. A. G., Abbott, B. and Network, P. C.: High risk of permafrost thaw, Nature, 480(7375), 32-33, 2011. Screen, J. A., Deser, C. and

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



Corrosive resistant heat exchanger  


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.

Richlen, Scott L. (Annandale, VA)



Arterial blood gases, acid-base balance, and lactate and gas exchange variables during hypoxic exercise.  


To determine the effect of hypoxia on lactate threshold (LT), onset of blood lactate accumulation (OBLA), and gas exchange threshold (GET), the lactate level together with VO2, VCO2, VE, and acid-base status in arterial blood from 12 female distance runners performing a progressive incremental treadmill test under the condition of hypoxic gas inhalation (HC: FIO2 is 16.0% in N2) compared with normoxic conditions (NC: FIO2 is 20.9%; i.e., air) were examined. During exercise, HC shifted LT, GET, and OBLA to a lower VO2 by 12.5%, 12.9%, and 9.3%, respectively. The GET during hypoxic exercise was well correlated with LT (GET = 0.973LT + 0.04; expressed in VO2 l.min-1). The close reciprocal changes in arterial blood lactate and bicarbonate (HCO3-) were observed during hypoxic as well as normoxic exercise. These findings provide evidence for the cause and effect relationship between LT and GET, even in hypoxic exercise. During submaximal exercise below the LT, PaCO2 and HCO3- slightly increased both in NC and HC with pH remaining unchanged. However, during exercise above the LT, the PaCO2, HCO3-, and pH all decreased with pH decreasing more markedly during hypoxia. In conclusion, this study demonstrated a clear increase in arterial lactate during hypoxic exercise above the LT. Both the LT and GET are shifted to a lower work rate by hypoxia in the same manner with the correlation between them remaining high, supporting the cause and effect relationship of these two parameters. PMID:2514152

Yoshida, T; Udo, M; Chida, M; Makiguchi, K; Ichioka, M; Muraoka, I



Gas exchange function through the middle ear mucosa in piglets: comparative study of normal and inflamed ears.  


The gas exchange function through the middle ear (ME) mucosa was investigated by comparing normal and inflamed ears in an animal model. Piglets were examined (n = 15) because their tympanic bulla closely resembles the human mastoid air cell system. Four untreated ears served as controls. Eleven ears were injected with glycerin into the tympanic bulla to induce inflammation and were studied as inflamed ears. Two respiratory conditions, spontaneous respiration and hyperventilation by a ventilator, were alternated repeatedly. ME pressure was measured intermittently by a tympanometer and blood gas was measured simultaneously. In all four normal ears, both ME pressure and carbon dioxide (CO2) partial pressure in the blood decreased in parallel following alternation of the respiratory conditions from spontaneous respiration to hyperventilation, while both pressure levels increased in parallel when respiration was changed from hyperventilation to spontaneous respiration. This result indicates that there is a gas exchange between the ME and the blood through the mucosa. However, ME pressure change in inflamed ears was limited, though the change in CO2 partial pressure in the blood was the same as that in normal ears. There was a significant difference in the degree of ME pressure change occurring in normal ears compared to that in inflamed ears, suggesting that inflammation of the mucosa reduced gas exchange function in the ME. PMID:10219389

Yamamoto, Y



Effect of Dichlorphenamide on Gas Exchange and CSF Acid-Base State in Chronic Respiratory Failure  

PubMed Central

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

Naimark, Arnold; Cherniack, Reuben M.



Extracorporeal gas exchange in acute lung injury: step by step towards expanded indications?  


Extracorporeal membrane oxygenation (ECMO) is widely accepted as a rescue therapy in patients with acute life-threatening hypoxemia in the course of severe acute respiratory distress syndrome (ARDS). However, possible side effects and complications are considered to limit beneficial outcome effects. Therefore, widening indications with the aim of reducing ventilator induced lung injury (VILI) is still controversial. Consequently, technological progress is an important strategy. Miniaturized ECMO systems are believed to simplify handling and reduce side effects and complications. Mueller and co-workers evaluated such a small-sized device in 60 patients with severe ARDS. They accomplished both the treatment of severe hypoxemia and reduction of VILI, demonstrating feasibility, a moderate rate of severe complications, and a 45% intensive care survival rate. Although neither randomized nor controlled, this study should encourage others to implement such systems in clinical practice. From a strategic perspective, this is another small but useful step towards implementing extracorporeal gas exchange for the prevention of VILI. It is already common sense that the prevention of acute life-threatening hypoxemia usually outweighs the risks of this technique. The next step should be to prove that prevention of life-threatening VILI balances the risks too. PMID:20236482

Dembinski, Rolf; Kuhlen, Ralf



Extracorporeal gas exchange in acute lung injury: step by step towards expanded indications?  

PubMed Central

Extracorporeal membrane oxygenation (ECMO) is widely accepted as a rescue therapy in patients with acute life-threatening hypoxemia in the course of severe acute respiratory distress syndrome (ARDS). However, possible side effects and complications are considered to limit beneficial outcome effects. Therefore, widening indications with the aim of reducing ventilator induced lung injury (VILI) is still controversial. Consequently, technological progress is an important strategy. Miniaturized ECMO systems are believed to simplify handling and reduce side effects and complications. Mueller and co-workers evaluated such a small-sized device in 60 patients with severe ARDS. They accomplished both the treatment of severe hypoxemia and reduction of VILI, demonstrating feasibility, a moderate rate of severe complications, and a 45% intensive care survival rate. Although neither randomized nor controlled, this study should encourage others to implement such systems in clinical practice. From a strategic perspective, this is another small but useful step towards implementing extracorporeal gas exchange for the prevention of VILI. It is already common sense that the prevention of acute life-threatening hypoxemia usually outweighs the risks of this technique. The next step should be to prove that prevention of life-threatening VILI balances the risks too.



Heterogeneity of gas exchange rates over the leaf surface in tobacco: an effect of hydraulic architecture?  


Spatial heterogeneity of gas exchange rates in the leaves of Nicotiana tabacum L. (tobacco) was investigated. Leaf conductance to water vapour was higher (by about 18%) at the apical regions of leaves than at the basal ones. Local, small-scale measurements of pressure-volume (PV) parameters and water status (performed with a dewpoint hygrometer) revealed that bulk leaf water potential, osmotic potential, turgor pressure and bulk modulus of elasticity were not significantly different in the leaf apex or base. Hydraulic measurements showed that the apical regions of the leaf blade were about 30% more conductive than the basal regions. Such differences were explained by analogous differences in terms of venation patterns. In fact, vein density turned out to be higher (by about 13%) near the leaf apex with respect to the leaf base. On the contrary, stomatal density was the same both in the apical and basal leaf portions. Our data suggest that spatial stomatal heterogeneity may arise from heterogenous distribution of local hydraulic resistances and would be addressed to maintaining local water potential above critical values, possibly triggering vein cavitation. PMID:18284586

Nardini, Andrea; Gortan, Emmanuelle; Ramani, Matteo; Salleo, Sebastiano



Gasotransmitters are emerging as new guard cell signaling molecules and regulators of leaf gas exchange.  


Specialized guard cells modulate plant gas exchange through the regulation of stomatal aperture. The size of the stomatal pore is a direct function of the volume of the guard cells. The transport of solutes across channels in plasma membrane is a crucial process in the maintenance of guard cell water status. The fine tuned regulation of that transport requires an integrated convergence of multiple endogenous and exogenous signals perceived at both the cellular and the whole plant level. Gasotransmitters are novel signaling molecules with key functions in guard cell physiology. Three gasotransmitters, nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H(2)S) are involved in guard cell regulatory processes. These molecules are endogenously produced by plant cells and are part of the guard cells responses to drought stress conditions through ABA-dependent pathways. In this review, we summarize the current knowledge of gasotransmitters as versatile molecules interacting with different components of guard cell signaling network and propose them as players in new paradigms to study ABA-independent guard cell responses to water deficit. PMID:23352403

García-Mata, Carlos; Lamattina, Lorenzo



Shoot development, chlorophyll, gas exchange and carbohydrates in lychee seedlings (Litchi chinensis).  


Shoot growth, chlorophyll concentrations, gas exchange and starch concentrations were studied in lychee (Litchi chinensis Sonn.) seedlings of cultivar "Wai Chee" grown in a heated greenhouse at Nambour in subtropical Australia (27 degrees S). We also examined the effects of shoot defoliation and root pruning on leaf expansion. Shoot growth showed a rhythmic cycle under constant greenhouse conditions, with a mean duration of flushing of 20 days and an interval of 10 days over three cycles. Shoots and leaves expanded in a sigmoidal pattern to about 80 mm and 500 cm(2), respectively, for each flush. Starch concentrations of the lower stem and roots decreased as the young red leaves expanded, and increased as the fully expanded leaves turned dark green. Chlorophyll concentrations and net CO(2) assimilation rate were highest in the fully expanded dark green leaves. Removing 50% of the area of each fully expanded leaf had little effect on the expansion of younger leaves, but total biomass of defoliated plants was only 60% of that of controls. In contrast, removing half the roots just before bud swelling reduced final leaf area by 80%. We conclude that the young shoot has relatively low rates of photoassimilation until the leaves are fully expanded and dark green, and depends on assimilates from elsewhere in the plant. During leaf expansion, translocation of assimilates to the shoot occurred at the expense of the roots. PMID:12204851

Hieke, S; Menzel, C M; Lüdders, P



Effect of Salinity on Leaf Gas Exchange in Two Populations of a C4 Nonhalophyte 1  

PubMed Central

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.

Bowman, William D.



Body size-independent safety margins for gas exchange across grasshopper species.  


Why is maximal insect body size relatively small compared to that of vertebrates? Possibly insect body size is limited by the capacity of the tracheal respiratory system to delivery oxygen down longer and longer tracheae to the tissues. If so, one possible outcome would be that larger insect species would have a smaller safety margin for oxygen delivery (higher critical P(O2), P(c)). We tested this idea by exposing inactive adult grasshoppers of a range of species and body sizes (0.07-6.4 g) to progressively lower oxygen atmospheres and measuring their ventilation frequency and their ability to maintain metabolic rate (indexed by CO(2) emission rate). We analyzed effects of body size on these parameters by simple linear regressions, as well as methods to control for phylogenetic relatedness among species. We found interspecific variation in P(c), but P(c) did not significantly correlate with body mass (average P(c) across all species = 4 kPa). Maximal tracheal system conductance scaled approximately with mass(0.7), and estimated ventilation in hypoxia (ventilatory frequency x tidal volume) scaled directly with mass, suggesting that convection is the major mechanism of gas exchange in all these species. These comparative data strengthen the growing body of evidence that body size does not affect the safety margin for oxygen delivery in insects. PMID:17371927

Greenlee, Kendra J; Nebeker, Christina; Harrison, Jon F



Stable carbon isotope discrimination, photosynthetic gas exchange, and growth differences among western larch families.  


Photosynthetic gas exchange, stable carbon isotope discrimination (Delta), height and diameter were compared among five open-pollinated families of 12-year-old western larch trees growing in a common garden in Moscow, Idaho, USA. Statistically significant variation was detected among the families in the two growth traits, Delta and stomatal conductance to water vapor (g) (P /= 0.203). Water-use efficiency was strongly correlated with Delta (r = -0.95, P < 0.01). Neither growth trait was correlated with A (r 0.93) and height was not significantly correlated with Delta (r = -0.75, P = 0.15). Tree diameter and Delta were significantly correlated (r = -0.92, P = 0.03). These results were strongly influenced by a single family. Both the variation in Delta and correlation trends between Delta and the growth traits height and diameter suggest the possibility of selecting for high water-use efficiency with the potential for simultaneous gains in height and diameter growth. PMID:14967688

Zhang, J; Fins, L; Marshall, J D



Structural Basis for Rab GTPase Activation by VPS9 Domain Exchange Factors  

SciTech Connect

RABEX-5 and other exchange factors with VPS9 domains regulate endocytic trafficking through activation of the Rab family GTPases RAB5, RAB21 and RAB22. Here we report the crystal structure of the RABEX-5 catalytic core in complex with nucleotide-free RAB21, a key intermediate in the exchange reaction pathway. The structure reveals how VPS9 domain exchange factors recognize Rab GTPase substrates, accelerate GDP release and stabilize the nucleotide-free conformation. We further identify an autoinhibitory element in a predicted amphipathic helix located near the C terminus of the VPS9 domain. The autoinhibitory element overlaps with the binding site for the multivalent effector RABAPTIN-5 and potently suppresses the exchange activity of RABEX-5. Autoinhibition can be partially reversed by mutation of conserved residues on the nonpolar face of the predicted amphipathic helix or by assembly of the complex with RABAPTIN-5.

Delprato,A.; Lambright, D.



Dynamics of Gas Exchange through the Fractal Architecture of the Human Lung, Modeled as an Exactly Solvable Hierarchical Tree  

NASA Astrophysics Data System (ADS)

The acinar airways lie at the periphery of the human lung and are responsible for the transfer of oxygen from air to the blood during respiration. This transfer occurs by the diffusion-reaction of oxygen over the irregular surface of the alveolar membranes lining the acinar airways. We present an exactly solvable diffusion-reaction model on a hierarchically branched tree, allowing a quantitative prediction of the oxygen current over the entire system of acinar airways responsible for the gas exchange. We discuss the effect of diffusional screening, which is strongly coupled to oxygen transport in the human lung. We show that the oxygen current is insensitive to a loss of permeability of the alveolar membranes over a wide range of permeabilities, similar to a ``constant-current source'' in an electric network. Such fault tolerance has been observed in other treatments of the gas exchange in the lung and is obtained here as a fully analytical result.

Mayo, Michael; Pfeifer, Peter; Gheorghiu, Stefan



Effect of fominoben-HCl on circulation, pulmonary gas exchange and acid-base balance at rest and during exercise.  


The effect of 3'-chloro-2'-[N-methyl-N[(morpholino-carbonyl)methyl]aminomethyl]benzanilide-hydrochloride (forminoben-HCl, Noleptan) on pulse rates and blood pressures, ventilation and gas exchange, and acid base balance was studied in eleven patients aged 31 to 72 years at rest and during a standardised excercise. Mean systolic and diastolic blood pressures decreased at rest before and 10 min after work as well as during work. Mean alveolar ventilation was reduced by 9% at rest and was unchanged during work. No changes occurred in mean alveolar-arterial oxygen differences or in mean anatomical right-to-left shunt. In a few individual patients with grossly impaired intrapulmonary gas exchange, however, an improvement with regard to alveolar ventilation in relation to oxygen uptake and the alveolar-arterial oxygen tension difference could be demonstrated. PMID:134718

Koch, G



Renal brush-border Na/sup +/-H/sup +/ exchange activity in the aging rat  

SciTech Connect

Amiloride-sensitive Na/sup +/-H/sup +/ exchange activity in brush-border membrane vesicles isolated from male rat proximal tubules was decreased in the senescent rat (24 mo) compared with the young adult (6 mo). There was no significant loss in Na/sup +/-H/sup +/ exchange activity in the kidneys of animals between 6 and 18 mo of age. Amiloride-insensitive /sup 22/Na/sup +/ uptake and the rate of pH gradient dissipation were not altered during aging. The decrease in sodium-dependent (/sup 32/P) phosphate transport preceded the decline in Na/sup +/-H/sup +/ exchange activity by at least 6 mo. Sodium-dependent D-(/sup 3/H) glucose transport was not significantly altered during aging. Thus various renal plasma membrane transport functions were affected differently in the aging rat. The decrease in Na/sup +/-H/sup +/ exchange activity during aging contrasted with the increase in exchange activity reported previously in acute ablation models of chronic renal failure.

Kinsella, J.L.; Sacktor, B.



Direct-contact heat exchanger for swirling countercurrent flow of hot gas and finely divided solids: A parametric study  

SciTech Connect

A vertically oriented solid-to-gas direct-contact heat exchanger (DCHX) has been proposed for heat recovery in high-temperature plants that process finely divided solids. The flows are countercurrent, with the inlet gas flow entering on the centerline and swirling strongly. Swirling enhances heat transfer and centrifuges the solid particles from the center to the wall in order to minimize entrainment and permit gravity separation. A computer program was written to calculate particle trajectories and heat-transfer rates (and, therefore, temperature profiles) for gas and solid phases. The flow model considers interactions between the particles and the flow field of the gas. The results of the computer program showed that the introduction of swirl significantly reduced the vertical distance required to achieve a given thermal efficiency. The countercurrent flow arrangement achieves high thermal efficiency in one contacting stage, unlike existing cocurrent suspension preheater systems, which require four or five stages. The practical application of this design to the cement industry appears unlikely, because very low gas velocities and correspondingly large areas of cross-sectional flow are required to prevent elutriation of the 74-{mu}m particles required for the chemical reactions. The computer program can be modified for spray-dryer applications by the addition of mass-transfer terms and a spray-formation model. In addition, the concept of a swirling flow heat exchanger may be applicable to other processes in which larger and heavier particles are used. 17 refs., 9 figs., 4 tabs.

Bell, K.J.; Arman, B.



Water relations, gas exchange, and growth of resprouts and mature plant shoots of Arbutus unedo L. and Quercus ilex L  

Microsoft Academic Search

Resprout and mature plant shoot growth, leaf water status and gas exchange behavior, tissue nutrient content, flowering, and production were studied for co-occurring shallow-rooted (Arbutus unedo L.) and deeprooted (Quercus ilex L.) Mediterranean tree species at the Collserola Natural Park in Northeast Spain Resprouts showed higher growth rates than mature plant shoots. During fall, no differences in eco-physiological performance of

Carles Castell; Jaume Terradas; John D. Tenhunen



Leaf-level and whole-plant gas exchange characteristics of shortleaf pine exposed to ozone and simulated acid rain  

Microsoft Academic Search

Field-grown shortleaf pine (Pinus echinata Mill.) seedlings were exposed to ozone (0s) and simulated acid rain @AR) in open-top chambers over three growing seasons. Ranges of 03 and SAR spanned ambient levels found in the southern USA. Effects of 0s on leaf-level and whole-plant gas exchange were characterized for a single measurement period immediately before the third summer of exposure.



Gas exchange, water relations and osmotic adjustment in two scion\\/rootstock combinations of Prunus under various salinity concentrations  

Microsoft Academic Search

Growth, gas exchange and water relations have been studied on hydroponically grown peach (cv. Armking) plants, grafted on GF677 (Arm\\/GF) and Mr.S.2\\/5 (Arm\\/MrS), exposed to 0, 40, 80 and 120 mM NaCl concentration, over a four-week period. Plant performance was also evaluated during a subsequent four-week period of relief from stress, by supplying the plants with a complete nutrient solution.

Rossano Massai; Damiano Remorini; Massimiliano Tattini



The Effect of Drought and Vapour Pressure Deficit on Gas Exchange of Young Kiwifruit ( Actinidia deliciosa var. deliciosa ) Vines  

Microsoft Academic Search

To evaluate the effect of drought and vapour pressure deficit (VPD) on stomatal behaviour and gas exchange parameters, young kiwifruit vines (Actinidia deliciosavar.deliciosacv. Hayward) were exposed to alternating periods of drought and drought-relief over two growing seasons. Vines were grown either in the field or in containers. Stomatal conductance of fully-expanded leaves rapidly decreased as pre-dawn leaf water potential was




Control of photosynthesis in leaves as revealed by rapid gas exchange and measurements of the assimilatory force F A  

Microsoft Academic Search

The rapid transients of CO2 gas exchange have been measured in leaves ofHelianthus annuus L. In parallel experiments the assimilatory force FA, which is the product of the phosphorylation potential and the redox ratio NADPH\\/NADP, has been calculated from measured\\u000a ratios of dihydroxyacetone phosphate to phosphoglycerate in the chloroplast stroma and in leaves. The following results were\\u000a obtained: (i) When

K. Siebke; A. Laisk; V. Oja; O. Kiirats; K. Raschke; U. Heber



Role of gas exchange in the inorganic carbon, oxygen, and ²²²Rn budgets of the Amazon River  

Microsoft Academic Search

Dissolved oxygen, ²²²Rn, pCOâ, alkalinity, respiration rate, and discharge have been measured at eight mainstem and seven tributary stations during February-March 1984 in a 1700-km stretch of the Amazon River between Vargem Grande and Obidos in Brazil. Air-water gas exchange rates were estimated two ways: measurements of the flux of ²²²Rn int floating domes yielded an average boundary layer thickness




Effects of branch position on water relations and gas exchange of European larch trees in an alpine community  

Microsoft Academic Search

Water relations and gas exchange were studied in the crowns of small European larch (Larix decidua Mill.) trees with respect to branch position. The upper-crown branches showed significantly higher branch sap flux rate (F\\u000a la) and branch conductance (g\\u000a b) compared to the lower crown (Pg\\u000a l), transpiration rate (E) and net photosynthesis (A), averaged for different ranges of atmospheric

Priit Kupper; Arne Sellin; John Tenhunen; Markus Schmidt; Märt Rahi



Effects of sodium sulfate and sodium bicarbonate on the growth, gas exchange and mineral composition of lettuce  

Microsoft Academic Search

The responses of two butterhead lettuce (Lactuca sativa L.) cultivars ‘P’ and ‘L-2’ were investigated under Na2SO4 and NaHCO3 salinity stress. The influences of salinity on gas exchange and distribution of mineral composition in plants were determined. The salinity treatments were applied through a nutrient solution containing 0, 20, 40 and 60mM Na2SO4 or 0, 2.5, 5 and 7.5mM NaHCO3.

Zhilong Bie; Tadashi Ito; Yutaka Shinohara



Heat Exchanger Design for the 30 kA Gas Cooled Current Leads in the ENEA 12 T CICC Facility  

Microsoft Academic Search

The preliminary design of the heat exchanger part for the pair of 30 kA hybrid current leads that will be installed in the ENEA 12 T CICC facility is presented. To limit the overall length and the amount of cooling gas to be employed, a hybrid re- sistive\\/HTS configuration has been conceived. Regarding the resis- tive part, a screw-like solution

G. M. Polli; L. Affinito; A. della Corte



Novel single-layer gas diffusion layer based on PTFE\\/carbon black composite for proton exchange membrane fuel cell  

Microsoft Academic Search

A series of poly(tetrafluoroethylene)\\/carbon black composite-based single-layer gas diffusion layers (PTFE\\/CB-GDLs) for proton exchange membrane fuel cell (PEMFC) was successfully prepared from carbon black and un-sintered PTFE, which included powder resin and colloidal dispersion, by a simple inexpensive method. The scanning electron micrographs of PTFE\\/CB-GDLs indicated that the PTFE resins were homogeneously dispersed in the carbon black matrix and showed

Y. W. Chen-Yang; T. F. Hung; J. Huang; F. L. Yang



Interactive effect of elevated temperature and O 3 on antioxidant capacity and gas exchange in Betula pendula saplings  

Microsoft Academic Search

We studied the effects of slightly elevated temperature (T), O3 concentration (O3) and their combination (T + O3) on the antioxidant defense, gas exchange and total leaf area of Betula pendula saplings in field conditions. During the second year of the experiment, T enhanced the total leaf area, net photosynthesis (P\\u000a n) and maximum capacity of carboxylation, redox state of ascorbate and

Johanna Riikonen; Maarit Mäenpää; Marjo Alavillamo; Tarja Silfver; Elina Oksanen



Gas exchange across an air-water interface: experimental results and modeling of bubble contribution to transfer  

Microsoft Academic Search

Gas exchange experiments have been performed in a wind-water tunnel filled with fresh water or seawater. Transfer velocities have been measured for nitrous oxide and argon in a range of wind speeds extending from 3 m\\/s to 14 m\\/s. The air-liquid interface was covered either with only normally developed wind waves or with mechanically generated waves in addition. For u<9

Liliane Merlivat; Laurent Memery




Microsoft Academic Search

As a potential phytoremediation system for phytoextraction of chromium (Cr), we evaluated the influence of the arbuscular mycorrhizal fungus Glomus intraradices on leaf tissue elemental composition, growth and gas exchange of sunflower (Helianthus annuus L.). Sunflower seedlings were either inoculated with mycorrhizal fungi (AM) or non-inoculated (Non-AM) and then exposed to two Cr species: {12?mmol of trivalent cation (Cr) [Cr(III)

F. T. Davies Jr; J. D. Puryear; R. J. Newton; J. N. Egilla; J. A. Saraiva Grossi



Analysis of differences in field performance of vegetatively and seed-propagated Eucalyptus varieties I: survival and leaf gas exchange  

Microsoft Academic Search

The aim of this study was to compare survival rates and leaf gas exchange of micro- and macro-propagated Eucalyptus grandis × E. nitens, and seed-propagated E. grandis and E. nitens, at a site in Hilton, KwaZulu-Natal, South Africa, where the conditions were suitable for cold-tolerant hybrid eucalypts. Fourteen months after planting, 50% of micropropagated E. grandis × E. nitens had

M EO Mokotedi; M P Watt; N W Pammenter



Variation of gas exchange within native plant species of Switzerland and relationships with ozone injury: an open-top experiment  

Microsoft Academic Search

Gas exchange and ozone-induced foliar injury were intensively measured during a 6-day period in mid-August 1998 on leaves of Acer pseudoplatanus, Betula pendula, Corylus avellana, Fagus sylvatica, Fraxinus excelsior, Morus nigra, Prunus avium, Prunus serotina, Rhamnus cathartica, and Viburnum lantana at a forest nursery site in Canton Ticino, Switzerland. Plants were grown in four open plots (AA), four open-top chambers

J Zhang; J. A Ferdinand; D. J Vanderheyden; J. M Skelly; J. L Innes



The relationship between steady-state gas exchange of bean leaves and the levels of carbon-reduction-cycle intermediates  

Microsoft Academic Search

The relationship between the gas-exchange characteristics of attached leaves of Phaseolus vulgaris L. and the pool sizes of several carbon-reduction-cycle intermediates was examined. After determining the rate of CO2 assimilation at known intercellular CO2 pressure, O2 pressure and light, the leaf was rapidly killed (2, photosynthesis appeared RuBP-saturated at low CO2 pressure and RuBP-limited at high CO2 pressure. In 21

Murray R. Badger; Thomas D. Sharkey; Susanne von Caemmerer



Leaf Gas Exchange and Chlorophyll Fluorescence Parameters in Phaseolus Vulgaris as Affected by Nitrogen and Phosphorus Deficiency  

Microsoft Academic Search

The effects of N and P deficiency, isolated or in combination, on leaf gas exchange and fast chlorophyll (Chl) fluorescence\\u000a emission were studied in common bean cv. Negrito. 10-d-old plants grown in aerated nutrient solution were supplied with high\\u000a N (HN, 7.5 mol m?3) or low N (LN, 0.5 mol m?3), and also with high P (HP, 0.5 mol m?3)

J. D. Lima; P. R. Mosquim; F. M. Da Matta



Gas Exchange, Membrane Permeability, and Ion Uptake in Two Species of Indian Jujube Differing in Salt Tolerance  

Microsoft Academic Search

Effect of NaCl (electrical conductivity of 0, 5, 10, 15, and 20 dS m-1) on growth, gas exchange, and ion uptake in two Ziziphus species (Z. rotundifolia and Z. nummularia) differing in salt tolerance was studied. At 30 and 45 d after first leaf initiation, the dry mass of shoot and leaves, and rates of net photosynthesis (PN) and transpiration

N. K. Gupta; S. K. Meena; S. Gupta; S. K. Khandelwal



Large tidal volume ventilation improves pulmonary gas exchange during lower abdominal surgery in Trendelenburg’s position  

Microsoft Academic Search

Impaired pulmonary gas exchange is a common complication of general anaesthesia. Periodic hyperinflation of the lungs and\\u000a large tidal volume ventilation were the first preventive measures to be widely embraced, but their effectiveness in clinical\\u000a practice has never been clearly established by controlled clinical studies. To assess their effects in high-risk patients\\u000a we studied 24 adults having lower abdominal gynaecological

W. A. Tweed; W. T. Phua; K. Y. Chong; E. Lim; T. L. Lee



Ozone oxidation of sulfur in sea-salt aerosol particles during the Azores Marine Aerosol and Gas Exchange experiment  

Microsoft Academic Search

Sea-salt aerosol particles in the lowest tens of meters above the ocean are, typically, more than three-fourths water on a volume basis. Calculations herein indicate that aqueous-phase conversion of sulfur dioxide dissolved in the water associated with sea-salt particles (sea-salt aerosol water) supported the production of 2-8 nmolm-3 of non-sea-salt sulfate (nssSO=4) during the Marine Aerosol and Gas Exchange (MAGE)

H. Sievering; E. Gorman; T. Ley; A. Pszenny; M. Springer-Young; J. Boatman; Y. Kim; C. Nagamoto; D. Wellman



Long chain versus medium chain lipids in patients with ARDS: effects on pulmonary haemodynamics and gas exchange  

Microsoft Academic Search

Objective: To compare pulmonary haemodynamic and gas exchange alterations in septic patients with ARDS receiving long-chain triglycerides\\u000a (LCT) versus medium-chain triglycerides (MCT). Design: Prospective, randomised, clinical study. Setting: Surgical ICU patients in a University Hospital. Patients: Twenty-one septic patients with ARDS were randomly assigned to receive 50 % of their non-protein caloric requirements as\\u000a either 20 % LCT (group 1,

V. Smirniotis; G. Kostopanagiotou; J. Vassiliou; N. Arkadopoulos; P. Vassiliou; A. Datsis; E. Kourias



Gas exchange during a soil drying cycle in seedlings of four black walnut (Juglans nigra L.) families.  


Photosynthetic and stomatal responses to a soil drying cycle were examined in half-sib seedlings of four walnut (Juglans nigra L.) families. Well-watered seedlings of an Iowa seed source had significantly higher rates of net photosynthesis than seedlings from New York or Michigan sources. This superior photosynthetic potential was associated with both greater stomatal conductance and mesophyll capacity for CO(2) fixation. In a drying soil, net photosynthesis and leaf conductance to water vapor of all families declined substantially, even under mild water stress. These responses were more strongly related to soil water status, as estimated by predawn leaf water potential, than to leaf water potential at the time of gas exchange measurement. There were no differences among families in the pattern of gas exchange response to developing water stress; however, families differed in capacity for recovery of gas exchange from water stress following rehydration. Sensitivity of photosynthesis of black walnut seedlings to water stress may be associated with poor growth and survival of this species in xeric habitats. PMID:14972845

Parker, W C; Pallardy, S G



Effects of long-term low atmospheric pressure on gas exchange and growth of lettuce  

NASA Astrophysics Data System (ADS)

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.

Tang, Yongkang; Guo, Shuangsheng; Dong, Wenping; Qin, Lifeng; Ai, Weidang; Lin, Shan



Effect of mean airway pressure on gas exchange during high-frequency oscillatory ventilation.  


We studied the effect of mean airway pressure (Paw) on gas exchange during high-frequency oscillatory ventilation in 14 adult rabbits before and after pulmonary saline lavage. Sinusoidal volume changes were delivered through a tracheostomy at 16 Hz, a tidal volume of 1 or 2 ml/kg, and inspired O2 fraction of 0.5. Arterial PO2 and PCO2 (PaO2, PaCO2), lung volume change, and venous admixture were measured at Paw from 5 to 25 cmH2O after either deflation from total lung capacity or inflation from relaxation volume (Vr). The rabbits were lavaged with saline until PaO2 was less than 70 Torr, and all measurements were repeated. Lung volume change was measured in a pressure plethysmograph. Raising Paw from 5 to 25 cmH2O increased lung volume by 48-50 ml above Vr in both healthy and lavaged rabbits. Before lavage, PaO2 was relatively insensitive to changes in Paw, but after lavage PaO2 increased with Paw from 42.8 +/- 7.8 to 137.3 +/- 18.3 (SE) Torr (P less than 0.001). PaCO2 was insensitive to Paw change before and after lavage. At each Paw after lavage, lung volume was larger, venous admixture smaller, and PaO2 higher after deflation from total lung capacity than after inflation from Vr. This study shows that the effect of increased Paw on PaO2 is mediated through an increase in lung volume. In saline-lavaged lungs, equal distending pressures do not necessarily imply equal lung volumes and thus do not imply equal PaO2. PMID:2022562

Boynton, B R; Villanueva, D; Hammond, M D; Vreeland, P N; Buckley, B; Frantz, I D



Combined Low Temperature-High Light Effects on Gas Exchange Properties of Jojoba Leaves 1  

PubMed Central

Jojoba (Simmondsia chinensis [Link] Schneider) is an important crop in desert climates. A relatively high frequency of periods of chilling and high photon flux density (PFD) in this environment makes photoinhibition likely, resulting in a reduction of assimilation capacity in overwintering leaves. This could explain the low net photosynthesis found in shoots from the field (4-6 micromoles per square meter per second) when compared to greenhouse grown plants (12-15 micromoles per square meter per second). The responses of photosynthesis and stomatal conductance to changes in absorbed PFD and in substomatal partial pressure of CO2 were measured on jojoba leaves recovering from chilling temperature (4°C) in high or low PFD. No measurable gas exchange was found immediately after chilling in either high or low PFD. For leaves chilled in low PFD, the original quantum yield was restored after 24 hours. The time course of recovery from chilling in high PFD was much longer. Quantum yield recovered to 60% of its original value in 72 hours but failed to recover fully after 1 week. Measurements of PSII chlorophyll fluorescence at 77 K showed that the reduced quantum yield was caused by photoinhibition. The ratio of variable to maximal fluorescence fell from a control level of 0.82 to 0.41 after the photoinhibitory treatment and recovery was slow. We also found a large increase in net assimilation rate and little closure of stomata as CO2 was increased from ambient partial pressure of 35 to 85 pascals. For plants grown in full light, the increase in net assimilation rate was 100%. The photosynthetic response at high CO2 concentration may constitute an ecological advantage of jojoba as a crop in the future.

Loreto, Francesco; Bongi, Guido



Particle Populations in the Southern Ocean During the Southern Ocean Gas Exchange Experiment  

NASA Astrophysics Data System (ADS)

The particle size distribution conveys information about the size and number of phytoplankton, non-algal particles, and potentially bubbles suspended in the water column. Here, we present measurements with the LISST-100X (Sequoia Scientific) of in-situ, non-disturbed suspended particle size distributions made during the Southern Ocean Gas Exchange experiment. Measurements were obtained in the open ocean Southern Atlantic sector of the Southern Ocean and in waters surrounding South Georgia Island. The resulting slope of the particle size distribution is estimated for particles ranging from 6-250 ?m assuming a Jungian or power law distribution. Data from vertical profiles conducted within the water column will be presented. Slopes of the particle size distribution (PSD) vary from 3.31 to 3.96 within the range of theoretical values. The PSD slopes showed three statistically distinct areas corresponding to the two patch locations and the waters near South Georgia Island. In the waters surrounding South Georgia Island, the PSD slope was steeper than that in the open ocean sector indicating an increased prevalence of smaller particles. The particle volume concentrations ranged from 13 to 639 ?l/L. The lowest particle volume concentrations occurred in the waters near South Georgia Island. The mixed layer showed higher particle volume concentrations for particle sizes below 50 microns compared to deeper waters. For particle sizes above 50 microns, there was no significant difference in the particle volume concentrations between the mixed layer and deeper waters. The relationship between the PSD slope and chlorophyll concentration is compared with data collected from other regions of the world's oceans. Overall, the relationship follows an inverse correlation where increasing chlorophyll concentration corresponds to a decrease in the particle size distribution slope.

Buonassissi, C. J.; Dierssen, H.



Response of gas exchange to water stress in seedlings of woody angiosperms.  


Responses of net photosynthesis (A), leaf conductance to water vapor (g(wv)) and instantaneous water use efficiency (WUE) to decreasing leaf and soil water potentials (Psi(l), Psi(s)) were studied in three-month-old white oak (Quercus alba L.), post oak (Q. stellata Wangenh.), sugar maple (Acer saccharum Marsh.), and black walnut (Juglans nigra L.) seedlings. Quercus seedlings had the highest A and g(wv) when plants were well watered. As the soil was allowed to dry, both A and g(wv) decreased; however, trace amounts of A were observed at a Psi(l) as low as -2.9 MPa in Q. stellata and -2.6 MPa in Q. alba and A. saccharum. Photosynthesis was not measurable at Psi(l) lower than -2.2 MPa in J. nigra and water stress-induced leaflet senescence was observed in this species. Within each species, g(wv) showed a similar relationship to soil and leaf Psi, but the response to Psi(l) was shifted to more negative values by 1.2 to 1.6 MPa. As Psi(s) declined below -1 MPa, the difference between soil and leaf Psi diminished because of the suppression of transpiration. There was no indication that Psi(s) had a more direct influence on g(wv) than did Psi(l). Water use efficiency showed an initial increase as the soil dried, followed by a decline under severe water stress. Water use efficiency was highest in J. nigra, intermediate in Quercus species and lowest in A. saccharum. There was an evident relationship between gas exchange characteristics and natural distribution in these species, with the more xeric species showing higher A and g(wv) under both well-watered and water-stressed conditions. There was no trend toward increased efficiency of water use in the more xeric species. PMID:14972892

Ni, B R; Pallardy, S G



Effects of diffuse radiation on canopy gas exchange processes in a forest ecosystem  

NASA Astrophysics Data System (ADS)

Forest ecosystems across the globe show an increase in ecosystem carbon uptake efficiency under conditions with high fraction of diffuse radiation. Here, we combine eddy covariance flux measurements at a deciduous temperate forest in central Germany with canopy-scale modeling using the biophysical multilayer model CANVEG to investigate the impact of diffuse radiation on various canopy gas exchange processes and to elucidate the underlying mechanisms. Increasing diffuse radiation enhances canopy photosynthesis by redistributing the solar radiation load from light saturated sunlit leaves to nonsaturated shade leaves. Interactions with atmospheric vapor pressure deficit and reduced leaf respiration are only of minor importance to canopy photosynthesis. The response strength of carbon uptake to diffuse radiation depends on canopy characteristics such as leaf area index and leaf optical properties. Our model computations shows that both canopy photosynthesis and transpiration increase initially with diffuse fraction, but decrease after an optimum at a diffuse fraction of 0.45 due to reduction in global radiation. The initial increase in canopy photosynthesis exceeds the increase in transpiration, leading to a rise in water-use-efficiency. Our model predicts an increase in carbon isotope discrimination with water-use-efficiency resulting from differences in the leaf-to-air vapor pressure gradient and atmospheric vapor pressure deficit. This finding is in contrast to those predicted with simple big-leaf models that do not explicitly calculate leaf energy balance. At an annual scale, we estimate a decrease in annual carbon uptake for a potential increase in diffuse fraction, since diffuse fraction was beyond the optimum for 61% of the data.

Knohl, Alexander; Baldocchi, Dennis D.



Evaluation of an apparatus for continuous monitoring of gas exchange in mechanically ventilated patients.  


Indirect calorimetry has been integrated with a commercially available ventilator, permitting continuous monitoring of energy expenditure and respiratory quotient. This equipment, the ventilator Erica, the Engström metabolic computer EMC and the carbon dioxide analyzer Eliza (Gambro Engström AB, Sweden) was evaluated in laboratory tests and in critically ill patients. In the laboratory evaluation, the variability in FIO2 was less than 0.05% at FIO2 less than 0.47. The linearity error of the oxygen sensor and the CO2 analyzer was less than 0.06%. The variability of the oxygen sensor was 0.01% O2 and of the CO2 analyzer 0.04% CO2. The CO2 analyzer was sensitive to oxygen concentration and underestimated CO2 concentration by 3.3% at FIO2 = 0.5 if calibrated on room air. The pneumotachometer was oxygen dependent and overestimated inspired volume by 5.5% at 100% O2, if calibrated on room air, and was negligibly affected by changes in minute volume or PEEP within the physiological range for adults. In the patient evaluation, 15 measurements of gas exchange were performed in 9 critically ill patients and the results were compared with data obtained simultaneously by the Scholander technique or mass spectrometry. The standard deviation of the mean difference in comparison with the reference methods was 9.4% for O2 uptake, 6.6% for CO2 elimination, 12.5% for respiratory quotient and 3.9% for minute volume. Paired t-test analysis showed no systematic difference between the various methods. It is concluded that the EMC has an accuracy sufficient for clinical use and represents a commercially available technique of potential clinical value. PMID:3836285

Carlsson, M; Forsberg, E; Thörne, A; Nordenström, J; Hedenstierna, G



Interionic and intermolecular interactions in ion-exchange and sorption systems involving physiologically active substances  

SciTech Connect

This paper reviews the results obtained by studying the sorption of physiologically active substances (PAS) of different types such as, amino acids, nucleotides and melanoidins on ion exchangers and non-ionogenic sorbents. The review is mainly focused upon the mechanisms of interaction of PAS molecules in the sorbent phase. The contribution of ion-ionic, ion-molecular and intermolecular interactions to the overall sorption effect is discussed. The results of studying ion-exchange isothermal supersaturation of amino acid solutions on anion exchangers are reported and discussed. The mechanisms of aging of ion-exchange materials in the course of recovery of PAS from fermentation broths and hydrolysates are proposed. 48 refs.

Selemenev, V.F.; Chikin, G.A.; Khokhlov, V.J.



Balloons and Bottles: Activities on Air-Sea Heat Exchange.  

ERIC Educational Resources Information Center

|Presents an activity designed to demonstrate how heating and cooling an air mass affects its temperature, volume, density, and pressure. Illustrates how thermal energy can cause atmospheric motion such as expansion, contraction, and winds. (Author/WRM)|

Murphree, Tom



Balloons and Bottles: Activities on Air-Sea Heat Exchange.  

ERIC Educational Resources Information Center

Presents an activity designed to demonstrate how heating and cooling an air mass affects its temperature, volume, density, and pressure. Illustrates how thermal energy can cause atmospheric motion such as expansion, contraction, and winds. (Author/WRM)

Murphree, Tom



Contact Activation of Blood Plasma and Factor XII by Ion-exchange Resins  

PubMed Central

Sepharose ion-exchange particles bearing strong Lewis acid/base functional groups (sulfopropyl, carboxymethyl, quarternary ammonium, dimethyl aminoethyl, and iminodiacetic acid) exhibiting high plasma protein adsorbent capacities are shown to be more efficient activators of blood factor XII in neat-buffer solution than either hydrophilic clean-glass particles or hydrophobic octyl sepharose particles ( FXII?surfaceactivatorFXIIa; a.k.a autoactivation, where FXII is the zymogen and FXIIa is a procoagulant protease). In sharp contrast to the clean-glass standard of comparison, ion-exchange activators are shown to be inefficient activators of blood plasma coagulation. These contrasting activation properties are proposed to be due to the moderating effect of plasma-protein adsorption on plasma coagulation. Efficient adsorption of blood plasma proteins unrelated to the coagulation cascade impedes FXII contacts with ion-exchange particles immersed in plasma, reducing autoactivation, and causing sluggish plasma coagulation. By contrast, plasma proteins do not adsorb to hydrophilic clean glass and efficient autoactivation leads directly to efficient activation of plasma coagulation. It is also shown that competitive-protein adsorption can displace FXIIa adsorbed to the surface of ion-exchange resins. As a consequence of highly-efficient autoactivation and FXIIa displacement by plasma proteins, ion-exchange particles are slightly more efficient activators of plasma coagulation than hydrophobic octyl sepharose particles that do not bear strong Lewis acid/base surface functionalities but to which plasma proteins adsorb efficiently. Plasma proteins thus play a dual role in moderating contact activation of the plasma coagulation cascade. The principal role is impeding FXII contact with activating surfaces but this same effect can displace FXIIa from an activating surface into solution where the protease can potentiate subsequent steps of the plasma coagulation cascade.

Yeh, Chyi-Huey Josh; Dimachkie, Ziad O.; Golas, Avantika; Cheng, Alice; Parhi, Purnendu; Vogler, Erwin A.



Program plan for development of hot dirty-gas heat exchangers for coal-gasification systems. [Entrained-flow, moving bed, and fluidized-bed gasifiers  

Microsoft Academic Search

This report deals with the heat exchanger applications, and its scope includes a broad range of gasification systems, such as the generic models for entrained-flow, moving-bed, and fluidized-bed gasifiers. The major application of hot dirty-gas heat exchangers is in the area of heat recovery for improved gasifier efficiency. The inlet temperature requirements for these heat exchangers varies from approx. 650




Indirect-Fired, Biomass-Fueled, Combined-Cycle, Gas Turbine Power Plant Using a Ceramic Heat Exchanger. Volume I. Conceptual Plant Design and Analysis. Final Report.  

National Technical Information Service (NTIS)

A new technology for a wood-fueled electrical generation plant was evaluated. The proposed plant utilizes an indirectly fired gas turbine (IFGT) using a ceramic heat exchanger for high efficiency, due to its high temperature capability. The proposed plant...



Effects of orally administered activated charcoal on intestinal gas.  


The effectiveness of activated charcoal in treating intestinal gas, following a gas producing meal, was compared with a placebo. Both the number of flatus events and breath hydrogen levels were measured. These experiments showed that orally administered activated charcoal was effective in preventing the large increase in the number of flatus events and increased breath hydrogen concentrations that normally occur following a gas-producing meal. PMID:7015846

Hall, R G; Thompson, H; Strother, A



Gas-phase hydrogen/deuterium exchange in a travelling wave ion guide for the examination of protein conformations  

PubMed Central

Accumulating evidence suggests that solution-phase conformations of small globular proteins and large molecular protein assemblies can be preserved for milliseconds after electrospray ionization. Thus, the study of proteins in the gas-phase on this time-scale is highly desirable. Here we demonstrate that a travelling wave ion guide (TWIG) of a Synapt mass spectrometer offers a highly suitable environment for rapid and efficient gas-phase hydrogen/deuterium exchange (HDX). Gaseous ND3 was introduced into either the source TWIG or the TWIG located just after the ion mobility cell, such that ions underwent HDX as they passed through the ND3 on the way to the time-of-flight analyzer. The extent of deuterium labeling could be controlled by varying the quantity of ND3 or the speed of the travelling wave. The gas-phase HDX of model peptides corresponded to labeling of primarily fast exchanging sites due to the short labeling times (ranging from 0.1 to 10 ms). In addition to peptides, gas-phase HDX of ubiquitin, cytochrome c, lysozyme and apomyoglobin were examined. We conclude that HDX of protein ions in a TWIG is highly sensitive to protein conformation, enables the detection of conformers present on sub-milliseconds timescales and can readily be combined with ion mobility spectrometry.

Rand, Kasper D.; Pringle, Steven D.; Murphy, James P.; Fadgen, Keith E.; Brown, Jeff; Engen, John R.



Landfill gas activity in New York State  

Microsoft Academic Search

Landfill gas (LFG) recovery in New York State today ranks second to California with eight NYS projects in various stages of development. A research project begun in 1977 at NYC's Fresh Kills landfill on Staten Island catalyzed initial interest in LFG recovery in the state. This four-phase project included determining optimum gas withdrawal rates and recovery well spacings; using raw




Activation of catalysts for synthesizing methanol from synthesis gas  


A method for activating a methanol synthesis catalyst is disclosed. In this method, the catalyst is slurried in an inert liquid and is activated by a reducing gas stream. The activation step occurs in-situ. That is, it is conducted in the same reactor as is the subsequent step of synthesizing methanol from a methanol gas stream catalyzed by the activated catalyst still dispersed in a slurry.

Blum, David B. (108 Tall Oaks Dr., Wayne, NJ 07470); Gelbein, Abraham P. (45 Headley Rd., Morristown, NJ 07960)



Rapid intravenous infusion of 20 ml/kg saline does not impair resting pulmonary gas exchange in the healthy human lung.  


Rapid infusion of intravenous saline, a model of pulmonary interstitial edema, alters the distribution of pulmonary perfusion, raises pulmonary capillary blood volume, and increases bronchial wall thickness in humans. We hypothesized that infusion would disrupt pulmonary gas exchange by increasing ventilation/perfusion ((.)VA/(.)Q) inequality as opposed to a diffusive impairment in O2 exchange. Seven males (26 +/- 3 yr; FEV1: 110 +/- 16% predicted.) performed spirometry and had (.)VA/(.)Q mismatch measured using the multiple inert gas elimination technique, before and after 20 ml/kg iv of normal saline delivered in approximately 30 min. Infusion increased thoracic fluid content from transthoracic impedance by 12% (P < 0.0001) and left FVC unchanged but reduced expiratory flows (FEF(25-75) falling from 5.1 +/- 0.4 to 4.2 +/- 0.4 l/s, P < 0.05). However, (.)VA/(.)Q mismatch as measured by the log standard deviation of the ventilation (LogSD(.)V) and perfusion (LogSD(.)Q) distributions remained unchanged; LogSD(.)V: 0.40 +/- 0.03 pre, 0.38 +/- 0.04 post, NS; LogSD(.)Q: 0.38 +/- 0.03 pre, 0.37 +/- 0.03 post, NS. There was no significant change in arterial PO2 (99 +/- 2 pre, 99 +/- 3 mmHg post, NS) but arterial PCO2 was decreased (38.7 +/- 0.6 pre, 36.8 +/- 1.2 mmHg post, P < 0.05). Thus, infusion compressed small airways and caused a mild degree of hyperventilation. There was no evidence for a diffusive limitation to O2 exchange, with the measured-predicted alveolar-arterial oxygen partial pressure difference being unaltered by infusion at FIO2 = 0.125 (4.3 +/- 1.0 pre, 5.2 +/- 1.0 post, NS). After infusion, the fraction of perfusion going to areas with (.)VA/(.)Q < 1 was increased when a subject breathed a hyperoxic gas mixture [0.72 +/- 0.06 (FIO2 = 0.21), 0.80 +/- 0.06 (FIO2 = 0.30), P < 0.05] with similar effects on ventilation in the face of unchanged (.)VA and (.)Q. These results suggest active control of blood flow to regions of decreased ventilation during air breathing, thus minimizing the gas exchange consequences. PMID:19910335

Prisk, G Kim; Olfert, I Mark; Arai, Tatsuya J; Wagner, Peter D; Hopkins, Susan R



Activation of Rho GTPases by DOCK Exchange Factors Is Mediated by a Nucleotide Sensor  

Microsoft Academic Search

Activation of Rho guanosine triphosphatases (GTPases) to the guanine triphosphate (GTP)-bound state is a critical event in their regulation of the cytoskeleton and cell signaling. Members of the DOCK family of guanine nucleotide exchange factors (GEFs) are important activators of Rho GTPases, but the mechanism of activation by their catalytic DHR2 domain is unknown. Through structural analysis of DOCK9-Cdc42 complexes,

Jing Yang; Ziguo Zhang; S. Mark Roe; Christopher J. Marshall; David Barford



Gas-exchange characteristics, leaf water potential and chlorophyll a fluorescence in oil palm ( Elaeis guineensis Jacq.) seedlings under water stress and recovery  

Microsoft Academic Search

The gas-exchange characteristics, leaf water potential and chlorophyll (Chl) a fluorescence of oil palm (Elaeis guineensis Jacq.) seedlings subjected to water stress and recovery were investigated in a greenhouse experiment. At 24 days after imposition\\u000a of stress, leaf water potential in water-stressed seedlings was doubled compared to that of control and there was a drastic\\u000a decline in gas-exchange parameters viz.

K. Suresh; C. Nagamani; K. Ramachandrudu; R. K. Mathur



A review of gas-phase H/D exchange experiments: the protonated arginine dimer and bradykinin nonapeptide systems  

NASA Astrophysics Data System (ADS)

Some recent gas-phase H/D exchange experiments are discussed. These experiments are carried out using an electrospray ionization-fast flow tube technique. Some of the goals are: (1) deducing site-specific rate constants; (2) learning about conformers and isomers of biomolecules; (3) understanding H/D exchange mechanisms. The experimental technique, and its advantages and disadvantages are reviewed, by comparison with other methods such as FT-ICR. The different methods of analyzing the data are described including a newly developed algorithm for extracting site-specific rate constants. The examples of bradykinin (singly and doubly protonated) and the proton bound dimer of arginine are discussed in some detail. Both systems are known to exist as gas-phase salt-bridge structures in which two arginines are protonated and a carboxyl group is deprotonated yielding an ion-zwitterion configuration: + - +. Some internal inconsistencies between H/D exchange results for ND3 with the two systems are pointed out.

Lifshitz, C.



Gas turbine activities of Mitsubishi Heavy Industries  

SciTech Connect

Mitsubishi Heavy Industries, Ltd. (MHI), has been researching, developing, designing, manufacturing, and constructing power plants, including gas turbines, for such various applications as combined cycle power generation, repowering and cogeneration. The output range of MHI-manufactured gas turbines covers 6 to 150 MW (60 Hz) or 6 to 230 MW (50 Hz). A brief review of the following gas turbine models is given here: MF-61, MF-111A, MF-111B, MF-221, MW-251, MW-501, MW-701, MW-701DA, 501F, and 701F. 3 figs., 1 tab.




Effects of Lung Volume Reduction Surgery on Gas Exchange and Breathing Pattern During Maximum Exercise  

PubMed Central

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 (V?e), tidal volume (Vt), carbon dioxide output (V?co2), 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 V?e (32.8 vs 29.6 L/min, respectively; p = 0.001), V?co2, (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 V?co2 (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.

Criner, Gerard J.; Belt, Patricia; Sternberg, Alice L.; Mosenifar, Zab; Make, Barry J.; Utz, James P.; Sciurba, Frank



Effects of light availability on leaf gas exchange and expansion in lychee (Litchi chinensis).  


Effects of photosynthetic photon flux density (PPFD) on leaf gas exchange of lychee (Litchi chinensis Sonn.) were studied in field-grown "Kwai May Pink" and "Salathiel" orchard trees and young potted "Kwai May Pink" plants during summer in subtropical Queensland (27 degrees S). Variations in PPFD were achieved by shading the trees or plants 1 h before measurement at 0800 h. In a second experiment, potted seedlings of "Kwai May Pink" were grown in a heated greenhouse in 20% of full sun (equivalent to maximum noon PPFD of 200 micromol m(-2)xs(-1)) and their growth over three flush cycles was compared with seedlings grown in full sun (1080 micromol m(-2)xs(-1)). Young potted plants of "Kwai May Pink" were also grown outdoors in artificial shade that provided 20, 40, 70 or 100% of full sun (equivalent to maximum PPFDs of 500, 900, 1400 and 2000 micromol m(-2)xs(-1)) and measured for shoot extension and leaf area development over one flush cycle. Net CO2 assimilation increased asymptotically in response to increasing PPFD in both orchard trees and young potted plants. Maximum rates of CO2 assimilation (11.9 +/- 0.5 versus 6.3 +/- 0.2 micromol CO2 m(-2) s(-1)), dark respiration (1.7 +/- 0.3 versus 0.6 +/- 0.2 micromol CO2 m(-2) s(-1)), quantum yield (0.042 +/- 0.005 versus 0.027 +/- 0.003 mol CO2 mol(-1)) and light saturation point (1155 versus 959 micromol m(-2) s(-1)) were higher in orchard trees than in young potted plants. In potted seedlings grown in a heated greenhouse, shoots and leaves exposed to full sun expanded in a sigmoidal pattern to 69 +/- 12 mm and 497 +/- 105 cm(2) for each flush, compared with 27 +/- 7 mm and 189 +/- 88 cm(2) in shaded seedlings. Shaded seedlings were smaller and had higher shoot:root ratios (3.7 versus 3.1) than seedlings grown in full sun. In the potted plants grown outdoors in 20, 40, 70 or 100% of full sun, final leaf area per shoot was 44 +/- 1, 143 +/- 3, 251 +/- 7 and 362 +/- 8 cm(2), respectively. Shoots were also shorter in plants grown in shade than in plants grown in full sun (66 +/- 5 mm versus 101 +/- 2 mm). Photosynthesis in individual leaves of lychee appeared to be saturated at about half full sun, whereas maximum leaf expansion occurred at higher PPFDs. We conclude that lychee plants can persist as seedlings on the forest floor, but require high PPFDs for optimum growth. PMID:12464578

Hieke, S; Menzel, C M; Lüdders, P



A Comparison of the Effects of Chilling on Leaf Gas Exchange in Pea (Pisum sativum L.) and Cucumber (Cucumis sativus L.) 1  

PubMed Central

The effects of chilling on the photosynthesis of a chilling-resistant species, pea (Pisum sativum L. cv Alaska) and a chilling-sensitive species, cucumber (Cucumis sativus L. cv Ashley) were compared in order to determine the differences in the photosynthetic chilling sensitivity of these two species. For these experiments, plants were chilled (5°C) for different lengths of time in the dark or light. Following a 1 hour recovery period at 25°C, photosynthetic activity was measured by gas exchange (CO2 uptake and H2O release), quantum yield, and induced chlorophyll fluorescence. The results show that pea photosynthesis was largely unaffected by two consecutive nights of chilling in the dark, or by chilling during a complete light and dark cycle (15 hours/9 hours). Cucumber gas exchange was reduced by one night of chilling, but its quantum yield and variable fluorescence were unaffected by dark chilling. However, chilling cucumber in the light led to reduced CO2 fixation, increased internal leaf CO2 concentration, decreased quantum yield, and loss of variable fluorescence. These results indicate that chilling temperatures in conjunction with light damaged the light reactions of photosynthesis, while chilling in the dark did not.

Peeler, Thomas C.; Naylor, Aubrey W.



An Activity Theory Exegesis on Conflict and Contradictions in Networked Discussions and Feedback Exchanges  

ERIC Educational Resources Information Center

|The goal of this study was to investigate the culturally afforded contradictions that ten advanced English as a Second Language (ESL) learner encountered when they posted their paper topics and exchanged feedback strategies online and contextualized some of these strategies to draft their papers. Using Cultural-Historical Activity Theory (CHAT),…

Hadjistassou, Stella K.



Electrochemical Ion-Exchange for Medium Active Liquid Waste Treatment. Progress Report 1987.  

National Technical Information Service (NTIS)

A non-active 0.1 m/sup 3//h electrochemical ion-exchange (EIX) treatment plant has been successfully commissioned using 0.2 x 1 m electrodes fabricated from mixed Amberlite CG50/IRC84 by a mould route. At 50% design throughout, DFs of 20,000 were observed...

A. D. Turner N. J. Bridger A. R. Junkison



Diabetes induces Na\\/H exchange activity and hypertrophy of rat mesenteric but not basilar arteries  

Microsoft Academic Search

Experimental hyperglycemia produces a marked hypertrophic response in rat mesenteric arteries, accompanied by activation of Na\\/H exchange (NHE) in medial smooth muscle. This study asked if other vascular beds are similarly affected by examining the hypertrophic and NHE response of the basilar artery. Sections of mesenteric and basilar arteries from adult rats were analysed by standard morphometric techniques at 1

Rodney J. Dilley; Caroline A. Farrelly; Terri J. Allen; Karin Jandeleit-Dahm; Mark E. Cooper; Grant Morahan; Peter J. Little



Active heat exchange system development for latent heat thermal energy storage  

Microsoft Academic Search

The selection and evaluation phase of a program to develop active heat exchange concepts for latent heat thermal energy storage systems applicable to the utility industry is described. An evaluation of suitable storage media with melting points in the temperature range of interest (250 to 400°C) limited the candidates to molten salts from the chloride, hydroxide and nitrate families, based

J. Alario; R. Kosson; R. Haslett



Mechanistic study of the low temperature activity of transition metal exchanged zeolite SCR catalysts  

Microsoft Academic Search

Reactor activity measurements and FTIR spectroscopy were applied to study the transient and steady state behavior of Cu and Fe exchanged zeolite catalysts for the selective catalytic reduction (SCR) of nitrogen oxides (NOx) with NH3 at 200°C. Different surface NOx adsorption complexes were observed on the two catalysts. IR bands assigned to surface nitrate\\/nitrite groups were apparent on the Cu

Joseph M. Fedeyko; Bin Chen; Hai-Ying Chen




EPA Science Inventory

This report documents a long term performance study of two ion exchange (IE) and two activated alumina (AA) treatment plants to remove arsenic from drinking water. Performance information was collected on these systems that are located in the northeast for one full year. The stud...


Greenhouse gas exchange in West African savanna ecosystems - how important are emissions from termite mounds?  

NASA Astrophysics Data System (ADS)

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 ?g CH4-C m-2 h-1 as well as CH4 emission up to 300 ?g 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 ?g 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 ?g 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 0.4% to total soil N2O, CH4 and CO2 emissions, respectively.

Brümmer, C.; Brüggemann, N.



Ccpg1, a Novel Scaffold Protein That Regulates the Activity of the Rho Guanine Nucleotide Exchange Factor Dbs  

Microsoft Academic Search

Dbs is a Rho-specific guanine nucleotide exchange factor (RhoGEF) with in vitro exchange activity specific for RhoA and Cdc42. Like many RhoGEF family members, the in vivo exchange activity of Dbs is restricted in a cell-specific manner. Here we report the characterization of a novel scaffold protein (designated cell cycle progression protein 1 (Ccpg1)) that interacts with Dbs and modulates

Elena V. Kostenko; Oyenike O. Olabisi; Sutapa Sahay; Pedro L. Rodriguez; Ian P. Whitehead



Hydrogel loaded active layer in pressure tolerant gas diffusion electrodes  

SciTech Connect

This patent describes an electrochemical cell. It comprises a gas diffusion electrode comprising an electronically conductive and electrochemically active porous body defining respective mutually exclusive gas and electrolyte contacting surfaces, with a substantially gas impermeable material filling at least a portion of the pore volume of the body so as to prevent gas passage therethrough, the material comprising an electrolyte-insoluble, ionomeric ionically conductive hydrophilic hydrogel formed by coprecipitation between at least first and second precursor polymers, a counter electrode spaced from the gas diffusion electrode; a first compartment having a liquid electrolyte contained therein, the liquid electrolyte being in contact with the counter electrode, the liquid electrolyte also being in contact with the electrolyte contacting surface of the gas diffusion electrode, wherein the electrolyte is an alkaline aqueous electrolyte; a second compartment having a gas therein, the gas in the second compartment being in contact with the gas contacting surface of the gas diffusion electrode but not in contact with the electrolyte contacting surface of the gas diffusion electrode; and, circuit connections between the gas diffusion electrode and the counter electrode.

Hossain, M.S.; Gordon, A.Z.; Yaeger, E.B.; Tryk, D.A.



Anti-Inflammatory Activity of Human IgG4 Antibodies by Dynamic Fab Arm Exchange  

Microsoft Academic Search

Antibodies play a central role in immunity by forming an interface with the innate immune system and, typically, mediate proinflammatory activity. We describe a novel posttranslational modification that leads to anti-inflammatory activity of antibodies of immunoglobulin G, isotype 4 (IgG4). IgG4 antibodies are dynamic molecules that exchange Fab arms by swapping a heavy chain and attached light chain (half-molecule) with

Marijn van der Neut Kolfschoten; Janine Schuurman; Mario Losen; Wim K. Bleeker; Pilar Martínez-Martínez; Ellen Vermeulen; Tamara H. den Bleker; Luus Wiegman; Tom Vink; Lucien A. Aarden; Marc H. De Baets; Rob C. Aalberse; Paul W. H. I. Parren



Molecular gas in nearby active galactic nuclei  

NASA Astrophysics Data System (ADS)

This thesis describes the distributions, physical conditions, and kinematics of the molecular gas in eight nearby galaxies whose Seyfert and LINER nuclei display broad H? emission. We have mapped these systems at a linear resolution of ~100 pc in the CO(2-1) rotational transition, as well as at lower resolution in the CO(1-0) line, using the Owens Valley Radio Observatory millimeter array. Subsequent kinematical modelling allows us to improve on this angular resolution by exploiting our high effective velocity resolution; we simultaneously determine the radial emissivity profile of each line and the velocity field which the gas traces. Analysis of the molecular emission from individual objects reveals (1)massive concentrations of molecular gas at small galactocentric radii; (2)a pattern of high excitation at small radius, implied by variation in the ratio of CO(2-1) to CO(1-0) integrated intensities, which we attribute in part to the external heating of molecular clouds by energetic photons; (3)a high occurrence of nonaxisymmetric structures within 500 pc of the nucleus, including four gas bars; (4)evidence for episodic mass inflow along stellar bars outside 500 pc; and (5)apparent redirection of radio jets and ionizing photons from the nucleus by the molecular gas which they encounter. Our most striking discoveries are a dynamically decoupled secondary bar in the nucleus of NGC 7479, a mean integrated intensity ratio >1.85 in the nucleus of NGC 2681, and a warped molecular disk in the nucleus of NGC 1068.

Baker, Andrew Jordan



Gas exchange and photosynthetic water use efficiency in response to light, CO2 concentration and temperature in Vicia faba.  


Light and temperature-response curves and their resulting coefficients, obtained within ecophysiological characterization of gas exchanges at the leaf level, may represent useful criteria for breeding and cultivar selection and required tools for simulation models aimed at the prediction of potential plant behaviour in response to environmental conditions. Leaf-scale gas exchanges, by means of an IRGA open-flow system, were measured in response to light intensity (8 levels from 0 up to 2000 micromol m(-2) s(-1)), CO(2) concentrations (ambient-350 micromol mol(-1) and short-term enriched-700 micromol mol(-1)) and air temperature (from 7 up to 35 degrees C) on three Vicia faba L. genotypes, each representing one of the three cultivated groups: major, equina and minor. The net assimilation rate response to light intensity was well described by an exponential rise to max function. The short-term CO(2) enrichment markedly increased the values of light response curve parameters such as maximum photosynthetic rate (+80%), light saturation point (+40%) and quantum yield (+30%), while less homogenous behaviour was reported for dark respiration and light compensation point. For each light intensity level, the major and minor genotypes studied showed assimilation rates at least a 30% higher than equina. The positive effects of short-term CO(2) enrichment on photosynthetic water use efficiency (WUE) indicate a relevant advantage in doubling CO(2) concentration. In the major and minor genotypes studied, similar assimilation rates, but different WUE were observed. The optimum leaf temperature for assimilation process, calculated through a polynomial function, was 26-27 degrees C and no relevant limitations were observed in the range between 21 and 32 degrees C. Analysis at the single leaf level provided both rapid information on the variations in gas exchange in response to environmental factors and selection criteria for the screening of genotypes. PMID:18155805

Avola, Giovanni; Cavallaro, Valeria; Patanè, Cristina; Riggi, Ezio



Vertical gradients in photosynthetic gas exchange characteristics and refixation of respired CO(2) within boreal forest canopies.  


We compared vertical gradients in leaf gas exchange, CO(2) concentrations, and refixation of respired CO(2) in stands of Populus tremuloides Michx., Pinus banksiana Lamb. and Picea mariana (Mill.) B.S.P. at the northern and southern boundaries of the central Canadian boreal forest. Midsummer gas exchange rates in Populus tremuloides were over twice those of the two conifer species, and Pinus banksiana rates were greater than Picea mariana rates. Gas exchange differences among the species were attributed to variation in leaf nitrogen concentration. Despite these differences, ratios of intercellular CO(2) to ambient CO(2) (c(i)/c(a)) were similar among species, indicating a common balance between photosynthesis and stomatal conductance in boreal trees. At night, CO(2) concentrations were high and vertically stratified within the canopy, with maximum concentrations near the soil surface. Daytime CO(2) gradients were reduced and concentrations throughout the canopy were similar to the CO(2) concentration in the well-mixed atmosphere above the canopy space. Photosynthesis had a diurnal pattern opposite to the CO(2) profile, with the highest rates of photosynthesis occurring when CO(2) concentrations and gradients were lowest. After accounting for this diurnal interaction, we determined that photosynthesizing leaves in the understory experienced greater daily CO(2) concentrations than leaves at the top of the canopy. These elevated CO(2) concentrations were the result of plant and soil respiration. We estimated that understory leaves in the Picea mariana and Pinus banksiana stands gained approximately 5 to 6% of their carbon from respired CO(2). PMID:14759908

Brooks, J R; Flanagan, L B; Varney, G T; Ehleringer, J R



Association between carbonyl sulfide uptake and (18)? during gas exchange in C(3) and C(4) leaves.  


Carbonyl sulfide (COS) and C(18)OO exchange by leaves provide potentially powerful tracers of biosphere-atmosphere CO(2) exchange, and both are assumed to depend on carbonic anhydrase (CA) activity and conductance along the diffusive pathway in leaves. We investigated these links using C(3) and C(4) plants, hypothesizing that the rates of COS and C(18)OO exchange by leaves respond in parallel to environmental and biological drivers. Using CA-deficient antisense lines of C(4) and C(3) plants, COS uptake was essentially eliminated and discrimination against C(18)OO exchange ((18)?) greatly reduced, demonstrating CA's key role in both processes. (18)? showed a positive linear correlation with leaf relative uptake (LRU; ratio of COS to CO(2) assimilation rates, A(s)/A(c), normalized to their respective ambient concentrations), which reflected the effects of stomatal conductance on both COS and C(18)OO exchange. Unexpectedly, a decoupling between A(s) and (18)? was observed in comparing C(4) and C(3) plants, with a large decrease in (18)? but no parallel reduction in A(s) in the former. This could be explained by C(4) plants having higher COS concentrations at the CA site (maintaining high A(s) with reduced CA) and a high phosphoenolpyruvate carboxylase/CA activity ratio (reducing (18)O exchange efficiency between CO(2) and water, but not A(s)). Similar A(s) but higher A(c) in C(4) versus C(3) plants resulted in lower LRU values in the former (1.16 ± 0.20 and 1.82 ± 0.18 for C(4) and C(3), respectively). LRU was, however, relatively constant in both plant types across a wide range of conditions, except low light (<191 ?mol photon m(-2) s(-1)). PMID:21715674

Stimler, Keren; Berry, Joseph A; Montzka, Steve A; Yakir, Dan



Feasibility study for an advanced coal fired heat exchanger\\/gas turbine topping cycle for a high efficiency power plant. Final report  

Microsoft Academic Search

Significant improvements in efficiency for the conversion of coal into electricity can be achieved by cycles which employ a high temperature gas turbine topping cycle. The objective of this project is the development of an externally fired gas turbine system. The project computationally tested a new concept for a High Temperature Advanced Furnace (HITAF) and high temperature heat exchanger with

P. R. Solomon; Y. Zhao; D. Pines; R. C. Buggeln; S. J. Shamroth



Leaf gas exchange of understory spruce-fir saplings in relict cloud forests, southern Appalachian Mountains, USA.  


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 cloud impacts on carbon gain and water relations is needed to predict future impacts on these relict forests. PMID:17938120

Reinhardt, Keith; Smith, William K



Argon-Hydrogen Shielding Gas Mixtures for Activating Flux-Assisted Gas Tungsten Arc Welding  

Microsoft Academic Search

Using activating flux for gas tungsten arc welding (GTAW) to improve penetration capability is a well-established technique.\\u000a Argon is an inert gas and the one most widely used as a shielding gas for GTAW. For the most austenitic stainless steels,\\u000a pure argon does not provide adequate weld penetration. Argon–hydrogen mixtures give a more even heat input to the workpiece,\\u000a increasing

Her-Yueh Huang



Microbial activities in soil near natural gas leaks  

Microsoft Academic Search

From the present experiments it may be concluded that in the surroundings of natural gas leaks, methane, ethane and possibly some other components of the natural gas are oxidized by microbial activities as long as oxygen is available. This is demonstrated by an increased oxygen consumption and carbon dioxide production, as well as by increased numbers of different types of

A. D. Adamse; J. Hoeks; J. A. M. Bont; J. F. Kessel



Pacific Gas and Electric Company - Biomass energy activities  

Microsoft Academic Search

Pacific Gas and Electric activities in utilizing biomass for the production of gas and electricity are reviewed. Research is centering on quantifying the available resource, identifying viable conversion systems, determining the economics, and defining limiting factors such as balances between competing alternatives and institutional restraints. A feasibility study for a pyrolysis plant for producing syngas from San Francisco solid waste

M. J. Blanchet; B. M. Jenkins; J. G. Meyer; P. Maciel; R. F. Goldstein



Feasibility study for an advanced coal fired heat exchanger/gas turbine topping cycle for a high efficiency power plant. Technical report, September 10, 1992--December 31, 1992  

SciTech Connect

The overall objective of this project is to prove the feasibility of AFR`s concepts for a high efficiency coal-fired generating plant using the REACH/Exchanger concept to power an externally fired gas turbine. It will provide a design of an advanced technology furnace/heat exchanger combination in which a ceramic heat exchanger is aerodynamically protected from the corrosive particle laden coal combustion products. The heat exchanger is fired by radiative and convective heat transfer from a moderately clean fuel stream and by radiative heat transfer from the flame of a much larger uncleaned fuel stream. In principle, 35% of the energy will be provided by the former and 65% by the later. The fluid mechanics in the furnace/heat exchanger are controlled so that the flow of the combustion products, from the moderately clean fuel stream, sweeps past the heat exchanger to prevent the contact of coal particles with the uncleaned stream.

Solomon, P.R.; Zhao, Yuxin; Pines, D.S.



Soil-atmosphere greenhouse-gas exchange in a bioretention system  

NASA Astrophysics Data System (ADS)

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 ?g N/ (m2 h) with occasional pulse emissions > 150 ?g N /(m2 h) after recent inflow events. Fluxes from the cell with the saturated zone were consistently higher than those from the cell without a saturated zone. CO2 fluxes were comparable between the two cells, and usually between 50 and 200 mg C/(m2 h) whilst temperatures ranged between 12 and 26 degrees Celsius through this late summer/autumn period. Results from the entire data-set (March-May) will be presented along with an investigation of the relationship between these fluxes and other environmental and soil variables, such as soil nitrate and ammonium content and soil redox potential. Seasonal fluctuations and the effect of random inflow pulses will be also assessed and discussed. The results from this pilot study are useful to provide direct quantification of the GHG emissions associated with urban bioretention systems, which are one of the most used green infrastructures to manage stormwater runoff.

Daly, E.; Chan, H.; Beringer, J.; Livesley, S. J.



Development of heat exchangers for reheating scrubbed flue gas in a pilot plant  

NASA Astrophysics Data System (ADS)

Application of some reheating systems in flue gas desulphurization plants was studied. The following problems are examined: the influence of solid impurities in gas on the heat transfer coefficient, the different operational conditions to test clearing of the heat transfer surface, the rate of corrosion, and the partial gas recirculation. Measurements to increase the heat transfer coefficient and removing of liquid drops are suggested. Measurement techniques, insulation and prevention of leakage are discussed.

Michalak, S.



Molecular determinants of hyperosmotically activated NKCC1-mediated K+/K+ exchange  

PubMed Central

Na+ ?K+ ?2Cl? cotransport (NKCC) mediates the movement of two Cl? ions for one Na+ and one K+ ion. Under isosmotic conditions or with activation of the kinases SPAK/WNK4, the NKCC1-mediated Cl? uptake in Xenopus laevis oocytes, as measured using 36Cl, is twice the value of K+ uptake, as determined using 86Rb. Under hyperosmotic conditions, there is a significant activation of the bumetanide-sensitive K+ uptake with only a minimal increase in bumetanide-sensitive Cl? uptake. This suggests that when stimulated by hypertonicity, the cotransporter mediates K+/K+ and Cl?/Cl? exchange. Although significant stimulation of K+/K+ exchange was observed with NKCC1, a significantly smaller hyperosmotic stimulatory effect was observed with NKCC2. In order to identify the molecular determinant(s) of this NKCC1-specific activation, we created chimeras of the mouse NKCC1 and the rat NKCC2. Swapping the regulatory amino termini of the cotransporters neither conferred activation to NKCC2 nor prevented activation of NKCC1. Using unique restrictions sites, we created additional chimeric molecules and determined that the first intracellular loop between membrane-spanning domains one and two and the second extracellular loop between membrane-spanning domains three and four of NKCC1 are necessary components of the hyperosmotic stimulation of K+/K+ exchange.

Gagnon, Kenneth B; Delpire, Eric



Removal of NOx from Flue Gas by Reburning with Plasma Activated Natural Gas: Review and Economics  

Microsoft Academic Search

By initiating chain reactions that consume NOx, CHi radicals play an important role in natural gas reburning. In conventional reburning, most of the methane is consumed in reactions with oxygen to form CO, and does not produce CHi- radicals as intermediate products, which limits NO reduction efficiency. Activating natural gas externally to the boiler may generate a mixture of CHi




Effect of low dose fentanyl-droperidol administration on respiratory drive, respiratory pattern and gas exchange in ASA 1 spontaneously breathing patients.  


The aim of this study was to investigate the short term effects of low doses of fentanyl and droperidol on central respiratory drive, gas exchanges, respiratory pattern and inspiratory impedance of the respiratory system in a group of ASA 1 patients. Fourteen ASA 1 patients scheduled for minor surgery or endoscopic procedures were enrolled in the study, thirty minutes before the intervention. During spontaneous breathing of air we evaluated, by recording airflow, airway opening pressure and volume, the following variables: Respiratory Rate (RR), Tidal Volume (TV), Total respiratory cycle, Inspiratory and Expiratory Time (Ti, Te), mean inspiratory flow, P0.1, pH, PaO2 and PaCO2. After obtaining basal measurements, droperidol and fentanyl were injected and the above mentioned variables evaluated at 5 min (T1), 10 min (T2), 15 min (T3) intervals. Arterial blood was age, sampled at T3 for blood gas evaluation. The administration of droperidol (0.1 mg/kg) and fentanyl (0.002 mg/kg) significantly reduced P0.1 and Tidal Volume comparing basal with T1 and, T2 values. The other variables did not significantly modify. Two patients showed transient respiratory rhythm abnormalities in the first 180 sec following the administration of droperidol+fentanyl. Our results suggest that, in ASA 1 patients, droperidol+fentanyl preoperative administration, has no significant effects on respiratory pattern, respiratory impedance and gas exchanges: however also at low doses, the association of droperidol+fentanyl can reduce the respiratory center activity, expressed as P0.1, with a consequent reduction in Tidal Volume. PMID:9259872

Pierdominici, S; Conti, G; Scalise, T; Lappa, A; Cristaldi, A; Pelaia, P; Sarcinelli, L



Leaf gas exchange and oxidative stress in sorghum plants supplied with silicon and infected by Colletotrichum sublineolum.  


Considering the economic importance of anthracnose, caused by Colletotrichum sublineolum, and silicon (Si) to enhance sorghum resistance against this disease, this study aimed to investigate the effect of this element on leaf gas exchange and also the antioxidative system when infected by C. sublineolum. Plants from sorghum line CMSXS142 (BR 009 [Tx623] - Texas), growing in hydroponic culture with (+Si, 2 mM) or without (-Si) Si, were inoculated with C. sublineolum. Disease severity was assessed at 2, 4, 6, 8, and 10 days after inoculation (dai) and data were used to calculate the area under anthracnose progress curve (AUAPC). Further, the net carbon assimilation rate (A), stomatal conductance to water vapor (g(s)), internal-to-ambient CO? concentration ratio (C(i)/C(a)), and transpiration rate (E); the activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR); the electrolyte leakage (EL), and the concentrations of hydrogen peroxide (H?O?) and malondialdehyde (MDA) were determined. The AUAPC was reduced by 86% for the +Si plants compared with the -Si plants. The values of A, g(s), and E were lower upon inoculation of -Si plants in contrast to inoculated +Si plants with decreases of 31 and 60% for A, 34 and 61% for g(s), and 27 and 57% for E, respectively, at 4 and 8 dai. For the noninoculated plants, there was no significant difference between the -Si and +Si treatments for the values of A, g(s), and E. The C(i)/C(a) ratio was similar between the -Si and +Si treatments, regardless of the pathogen inoculation. The activities of SOD, CAT, APX, and GR tended to be higher in the +Si plants compared with the -Si plants upon inoculation with C. sublineolum. The EL significantly increased for -Si plants compared with +Si plants. The MDA concentration significantly increased by 31 and 38% at 4 and 8 dai, respectively, for the -Si plants compared with the +Si plants. Based on these results, Si may have a positive effect on sorghum physiology when infected by C. sublineolum through the maintenance of carbon fixation and also by enhancing the antioxidant system, which resulted in an increase in reactive oxygen species scavenging and, ultimately, reduced damage to the cell membranes. PMID:22671024

Resende, Renata Sousa; Rodrigues, Fabrício Ávila; Cavatte, Paulo Cezar; Martins, Samuel Cordeiro Vitor; Moreira, Wiler Ribas; Chaves, Agnaldo Rodrigues Melo; Damatta, Fábio Murilo



In Vivo MR Imaging of Pulmonary Perfusion and Gas Exchange in Rats via Continuous Extracorporeal Infusion of Hyperpolarized 129Xe  

PubMed Central

Background Hyperpolarized (HP) 129Xe magnetic resonance imaging (MRI) permits high resolution, regional visualization of pulmonary ventilation. Additionally, its reasonably high solubility (>10%) and large chemical shift range (>200 ppm) in tissues allow HP 129Xe to serve as a regional probe of pulmonary perfusion and gas transport, when introduced directly into the vasculature. In earlier work, vascular delivery was accomplished in rats by first dissolving HP 129Xe in a biologically compatible carrier solution, injecting the solution into the vasculature, and then detecting HP 129Xe as it emerged into the alveolar airspaces. Although easily implemented, this approach was constrained by the tolerable injection volume and the duration of the HP 129Xe signal. Methods and Principal Findings Here, we overcome the volume and temporal constraints imposed by injection, by using hydrophobic, microporous, gas-exchange membranes to directly and continuously infuse 129Xe into the arterial blood of live rats with an extracorporeal (EC) circuit. The resulting gas-phase 129Xe signal is sufficient to generate diffusive gas exchange- and pulmonary perfusion-dependent, 3D MR images with a nominal resolution of 2×2×2 mm3. We also show that the 129Xe signal dynamics during EC infusion are well described by an analytical model that incorporates both mass transport into the blood and longitudinal relaxation. Conclusions Extracorporeal infusion of HP 129Xe enables rapid, 3D MR imaging of rat lungs and, when combined with ventilation imaging, will permit spatially resolved studies of the ventilation-perfusion ratio in small animals. Moreover, EC infusion should allow 129Xe to be delivered elsewhere in the body and make possible functional and molecular imaging approaches that are currently not feasible using inhaled HP 129Xe.

Cleveland, Zackary I.; Moller, Harald E.; Hedlund, Laurence W.; Nouls, John C.; Freeman, Matthew S.; Qi, Yi; Driehuys, Bastiaan



A Heat Exchanger Process for Removal of H{sub2}S Gas  

SciTech Connect

A heat exchanger process has been developed for the removal of H{sub 2}S and other noncondensable gases from geothermal steam. The process utilizes a heat exchanger to condense water from geothermal steam while allowing H{sub 2}S and other noncondensable gases to pass through in the vapor phase. The condensed water is evaporated to form a clean steam from which over 90 percent of the H{sub 2}S and other noncondensable gases have been removed. Some of the important advantages of the heat exchanger process are shown in Table 1. The system can be located upstream of a power plant turbine which eliminates much of the potential for corrosion, as well as the requirement for removing H{sub 2}S from water collected in the main condenser. Since almost all noncondensables are removed, much less steam is needed for air ejector operation. The heat exchanger process is simple: it has no chemical addition requirements or sludge by-products and utilizes standard equipment found in many power plant applications. The regular power plant operators and maintenance crews can easily understand and run the system with minimal attention. Capital and operating costs are competitive with those for currently available H{sub 2}S-abatement technology, although significant economic advantages over downstream abatement processes may result due to the use of clean steam in the turbines.

Coury, Glenn E.; Babione, Robert A.; Gosik, Robert J.



Deuterium Exchange in Ethyl Acetoacetate: An Undergraduate GC-MS [Gas Chromatography-Mass Spectroscopy] Experiment  

ERIC Educational Resources Information Center

|The role of ethanol O-d in nullifying the deuterolysis may be demonstrated by determining that transesterification of methyl acetoacetate of the ethyl ester occurs as well as deuterium exchange of the five acetoacetate hydrogens. The significant acidity of the methylene protons in the acetoacetate group, the efficacy of base catalysis, the role…

Heinson, C. D.; Williams, J. M.; Tinnerman, W. N.; Malloy, T. B.



Effect of Langmuir cells on bubble dissolution and air-sea gas exchange  

Microsoft Academic Search

Gases are exchanged between the atmosphere and ocean by diffusion through the sea surface and by dissolution of air bubbles injected by breaking wind waves. Langmuir cells enhance the contribution from bubbles by keeping them under water for longer thus increasing their dissolution. We determine the importance of Langmuir cells by using a bubble model to calculate the amount of

David Chiba; Burkard Baschek



Deuterium Exchange in Ethyl Acetoacetate: An Undergraduate GC-MS [Gas Chromatography-Mass Spectroscopy] Experiment  

ERIC Educational Resources Information Center

The role of ethanol O-d in nullifying the deuterolysis may be demonstrated by determining that transesterification of methyl acetoacetate of the ethyl ester occurs as well as deuterium exchange of the five acetoacetate hydrogens. The significant acidity of the methylene protons in the acetoacetate group, the efficacy of base catalysis, the role of…

Heinson, C. D.; Williams, J. M.; Tinnerman, W. N.; Malloy, T. B.



The Energy Budget at the Earth'S Surface: Effects Of Air Turbulence Upon Gas Exchange from Soil.  

National Technical Information Service (NTIS)

An instrument to measure the rate of gas movement from beneath the surface of soil or other porous media was constructed. Subsequent measured rates of gas movement from beneath surface coverings of coarse and fine gravel, very coarse and medium sand, Chen...

B. A. Kimball E. R. Lemon



Complete respiratory support with AVCO2R and CPAP-mimic ventilation for total gas exchange in sheep.  


The altered respiratory mechanics in patients with chronic obstructive pulmonary disease (COPD) present unique challenges with regard to treatment during an acute exacerbation that often leads to respiratory support with mechanical ventilation. Alternative therapies are badly needed to reduce morbidity and mortality associated with mechanical ventilator use. We hypothesized that arteriovenous carbon dioxide removal (AVCO(2)R) coupled with continuous positive airway pressure (CPAP) would achieve total gas exchange eliminating the need for intubation/mechanical ventilation, thus reducing baro/volutrauma. This hypothesis was tested in six adult sedated apneic sheep with AVCO(2)R administered through a simple arteriovenous (AV) shunt for CO(2) removal. Because it is impractical to apply a CPAP mask to conscious sheep, the CPAP was mimicked in intubated/sedated sheep by positive end-expiratory pressure (PEEP) of 5-10 mmH(2)O with negligible ventilation. The AVCO(2)R and CPAP-mimic maintained Pa(o)(2) and Pa(co)(2) in the normal physiological ranges. The CO(2) removal was 120-150 ml/min through AVCO(2)R with AV blood flow of 1.1-1.5 L/min. A high fraction of inspired oxygen percentage (Fi(o)(2)) level (89 ± 3%) was required to achieve 40 ± 7% O(2) in the small bronchus. Thus, AVCO(2)R and CPAP-mimic achieved total gas exchange in anesthetized sheep and may be a potential option for acute COPD exacerbation in humans. PMID:22370686

Hayes, Don; Zwischenberger, Joseph B; Zhou, Xiaoqin; Liu, Xiaojun; Lynch, James E; Ballard-Croft, Cherry; Wang, Dongfang