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1

Gas exchange and thermoregulatory activity of the muscles in a hypoxic atmosphere  

Microsoft Academic Search

Exposure for 1 h to a hypoxic atmosphere containing 11.4% oxygen lowers the gas exchange and the rectal temperature in rats, but the electrical activity of their muscles remains almost unchanged. In an atmosphere containing 7.4% oxygen, besides a decrease in gas exchange to the same level, depression of the thermoregulatory tone of the muscles and a more marked decrease

A. G. Zhironkin; G. V. Troshikhin

1970-01-01

2

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

PubMed Central

1. This study investigated the effects of 7 weeks of sprint training on gas exchange across the lungs and active skeletal muscle during and following maximal cycling exercise in eight healthy males. 2. Pulmonary oxygen uptake (VO2) and carbon dioxide output (VCO2) were measured before and after training during incremental exercise (n = 8) and during and in recovery from a maximal 30 s sprint exercise bout by breath-by-breath analysis (n = 6). To determine gas exchange by the exercising leg muscles, brachial arterial and femoral venous blood O2 and CO2 contents and lactate concentration were measured at rest, during the final 10 s of exercise and during 10 min of recovery. 3. Training increased (P < 0.05) the maximal incremental exercise values of ventilation (VE, by 15.7 +/- 7.1%), VCO2 (by 9.3 +/- 2.1%) and VO2 (by 15.0 +/- 4.2%). Sprint exercise peak power (3.9 +/- 1.0% increase) and cumulative 30 s work (11.7 +/- 2.8% increase) were increased and fatigue index was reduced (by -9.2 +/- 1.5%) after training (P < 0.05). The highest VE, VCO2 and VO2 values attained during sprint exercise were not significantly changed after training, but a significant (P < 0.05) training effect indicated increased VE (by 19.2 +/- 7.9%), VCO2 (by 9.3 +/- 2.1%) and VO2 (by 12.7 +/- 6.5%), primarily reflecting elevated post-exercise values after training. 4. Arterial O2 and CO2 contents were lower after training, by respective mean differences of 3.4 and 21.9 ml l-1 (P < 0.05), whereas the arteriovenous O2 and CO2 content differences and the respiratory exchange ratio across the leg were unchanged by training. 5. Arterial whole blood lactate concentration and the net lactate release by exercising muscle were unchanged by training. 6. The greater peak pulmonary VO2 and VCO2 with sprint exercise, the increased maximal incremental values, unchanged arterial blood lactate concentration and greater sprint performance all point strongly towards enhanced gas exchange across the lungs and in active muscles after sprint training. Enhanced aerobic metabolism after sprint training may contribute to reduced fatigability during maximal exercise, whilst greater pulmonary CO2 output may improve acid-base control after training. PMID:9218229

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

1997-01-01

3

Activities Exchange  

NSDL National Science Digital Library

The site provides a free, colaborative forum where educators share activities that employ TI technology. This page links to hundreds of math and science activities for K-12, authored by teachers as well as Texas Instruments professionals. Social studies and language arts are also well represented in the list of subjects. Activities can be searched as well by curriculum standard or by textbook connection.

Texas Instruments

2008-01-31

4

Gas exchange and electrical activity of the skeletal musculature of animals in a helium and oxygen medium  

NASA Technical Reports Server (NTRS)

The gas exchange electrical activity of the skeletal musculature (EAM) -- the heat regulating tonus, and the rectal temperature for rats which were kept for one hour in the air, in a helium-oxygen mixture and again in air, were studied. Animals kept in the helium-oxygen atmosphere at room temperature showed a definite increase in the level of gas exchange, an increase of the EAM, and a drop in rectal temperature. Transition to air respiration brought about normalization of almost all the functions. Increasing the temperature by 5 deg (25-27 deg) in comparison with that of air (20-22 deg) led to a small decrease of EAM indices, gas exchange, and body temperature.

Troshikhin, G. V.

1973-01-01

5

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

2001-01-01

6

BOREAS TE-12 Leaf Gas Exchange Data  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

7

GAS EXCHANGE Respiration: An Introduction  

E-print Network

Bohr effect Effect of the proton concentration (pH) on the oxygen affinity of hemoglobin. Carbonic cascade A model of gas exchange in which gas is viewed as flowing through a series of resistances from the environment to the tissues or vice versa. The model is based on the analogy of water flowing down a series

Wood, Spencer

8

Active microchannel heat exchanger  

DOEpatents

The present invention is an active microchannel heat exchanger with an active heat source and with microchannel architecture. The 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 exhaust through the exhaust chamber and by conduction through a containment wall to the working fluid in the heat exchanger chamber thereby raising a temperature of the working fluid. The invention is particularly useful as a liquid fuel vaporizer and/or a steam generator for fuel cell power systems, and as a heat source for sustaining endothermic chemical reactions and initiating exothermic reactions.

Tonkovich, Anna Lee Y. (Pasco, WA) [Pasco, WA; Roberts, Gary L. (West Richland, WA) [West Richland, WA; Call, Charles J. (Pasco, WA) [Pasco, WA; Wegeng, Robert S. (Richland, WA) [Richland, WA; Wang, Yong (Richland, WA) [Richland, WA

2001-01-01

9

[Effects of nitrogen application rate on nitrate reductase activity, nitric oxide content and gas exchange in winter wheat leaves].  

PubMed

In this paper, the effects of different nitrogen application rates on the nitrate reductase (NR) activity, nitric oxide (NO) content and gas exchange parameters in winter wheat (Triticum aestivum L.) leaves from tillering stage to heading stage and on grain yield were studied. The results showed that the photosynthetic rate (P(n)), transpiration rate (T(r)) and instantaneous water use efficiency (IWUE) of leaves as well as the grain yield were increased with increasing nitrogen application rate first but decreased then, with the values of all these parameters reached the highest in treatment N180. The NR activity increased with increasing nitrogen application rate, and there was a significant linear correlation between NR activity and NO content at tillering and jointing stages (R2 > or = 0.68, n = 15). NO content had a quadratic positive correlation with stomatal conductance (G(s)) (R2 > or = 0.43, n = 15). The lower NO content produced by lower NR activity under lower nitrogen application rate promoted the stoma opened, while the higher NO content produced by higher NR activity under higher nitrogen application rate induced the stoma closed. Although the leaf NO content had a quadratic positive correlation with stomatal conductance (R2 > or = 0.36, n = 15), no remarkable correlation was observed between NR activity and NO content at heading stage, suggesting that nitrogen fertilization could not affect leaf NO content through promoting NR activity, and further more, regulate the stomatal action. Under appropriate nitrogen application the leaf NR activity and NO content were lower, G(s), T(r) and IWUE were higher, and thus, the crop had a better drought-resistant ability, higher P(n), and higher grain yield. PMID:17886633

Shangguan, Zhou-Ping

2007-07-01

10

BOREAS TE-5 Leaf Gas Exchange Data  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

11

Effect of Iron Deficiency on Gas Exchange and Catalase and Peroxidase Activity in Citrus  

Microsoft Academic Search

The effects of iron (Fe) deficiency on catalase and peroxidase activity, net photosynthesis (Pn), stomatal conductance (gs), plant water relations, and specific leaf weight, were studied under greenhouse conditions in two sweet orange (C. sinensis) cultivars grafted on sour orange (Citrus aurantium) and Swingle citrumelo (C. paradisi × P. trifoliata). Iron deficiency caused by the absence of Fe in the Hoagland nutrient

Vassilios Chouliaras; Ioannis Therios; Athanassios Molassiotis; Angelos Patakas; Gregorios Diamantidis

2005-01-01

12

A high throughput gas exchange screen for determining rates of photorespiration or regulation of C4 activity.  

PubMed

Large-scale research programmes seeking to characterize the C4 pathway have a requirement for a simple, high throughput screen that quantifies photorespiratory activity in C3 and C4 model systems. At present, approaches rely on model-fitting to assimilatory responses (A/C i curves, PSII quantum yield) or real-time carbon isotope discrimination, which are complicated and time-consuming. Here we present a method, and the associated theory, to determine the effectiveness of the C4 carboxylation, carbon concentration mechanism (CCM) by assessing the responsiveness of V O/V C, the ratio of RuBisCO oxygenase to carboxylase activity, upon transfer to low O2. This determination compares concurrent gas exchange and pulse-modulated chlorophyll fluorescence under ambient and low O2, using widely available equipment. Run time for the procedure can take as little as 6 minutes if plants are pre-adapted. The responsiveness of V O/V C is derived for typical C3 (tobacco, rice, wheat) and C4 (maize, Miscanthus, cleome) plants, and compared with full C3 and C4 model systems. We also undertake sensitivity analyses to determine the impact of R LIGHT (respiration in the light) and the effectiveness of the light saturating pulse used by fluorescence systems. The results show that the method can readily resolve variations in photorespiratory activity between C3 and C4 plants and could be used to rapidly screen large numbers of mutants or transformants in high throughput studies. PMID:25006037

Bellasio, Chandra; Burgess, Steven J; Griffiths, Howard; Hibberd, Julian M

2014-07-01

13

A high throughput gas exchange screen for determining rates of photorespiration or regulation of C4 activity  

PubMed Central

Large-scale research programmes seeking to characterize the C4 pathway have a requirement for a simple, high throughput screen that quantifies photorespiratory activity in C3 and C4 model systems. At present, approaches rely on model-fitting to assimilatory responses (A/C i curves, PSII quantum yield) or real-time carbon isotope discrimination, which are complicated and time-consuming. Here we present a method, and the associated theory, to determine the effectiveness of the C4 carboxylation, carbon concentration mechanism (CCM) by assessing the responsiveness of V O/V C, the ratio of RuBisCO oxygenase to carboxylase activity, upon transfer to low O2. This determination compares concurrent gas exchange and pulse-modulated chlorophyll fluorescence under ambient and low O2, using widely available equipment. Run time for the procedure can take as little as 6 minutes if plants are pre-adapted. The responsiveness of V O/V C is derived for typical C3 (tobacco, rice, wheat) and C4 (maize, Miscanthus, cleome) plants, and compared with full C3 and C4 model systems. We also undertake sensitivity analyses to determine the impact of R LIGHT (respiration in the light) and the effectiveness of the light saturating pulse used by fluorescence systems. The results show that the method can readily resolve variations in photorespiratory activity between C3 and C4 plants and could be used to rapidly screen large numbers of mutants or transformants in high throughput studies. PMID:25006037

Bellasio, Chandra; Burgess, Steven J; Griffiths, Howard

2014-01-01

14

BOREAS TE-10 Leaf Gas Exchange Data  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

15

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.

2002-01-01

16

Exchange energy of an inhomogeneous electron gas  

Microsoft Academic Search

Expressions for the exchange-energy density of an inhomogeneous electron gas are obtained which describe the Hund rule in an atom and a modified Hund rule in a crystal. The expressions are used to analyze the properties of an electron gas in the 3d subshells of various transition metals, including Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu. The

S. A. Beznosiuk; Iu. A. Khon; V. M. Kuznetsov; V. P. Fadin

1977-01-01

17

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.

2012-04-01

18

ANALYSIS AND MODELING OF GAS EXCHANGE PROCESSES IN SCAEVOLA AEMULA  

Technology Transfer Automated Retrieval System (TEKTRAN)

Scaevola aemula is a popular ornamental crop cultivated as a bedding plant or for hanging baskets. We characterized gas exchange properties of S.aemula 'New Wonder' in response to photo synthetically active radiation (PAR), carbon dioxide concentration, and leaf temperature. Net CO2 assimilation ra...

19

COLLISON-ACTIVATED CLEAVAGE OF A PEPTIDE/ANTIOBIOTIC LINKAGE: EVIDENCE FOR GAS-PHASE INTRAMOLECULAR DISULFIDE EXCHANGE  

Technology Transfer Automated Retrieval System (TEKTRAN)

Ceftiofur is a third generation beta-lactam antibiotic widely used in livestock for treatment of infections. Upon administration, ceftiofur is rapidly metabolized to desfuroylceftiofur, an antimicrobially active metabolite that has a free thiol functional group. Previous experiments using electron...

20

Effect of water deficit on leaf phenolic composition, gas exchange, oxidative damage and antioxidant activity of four Greek olive (Olea europaea L.) cultivars.  

PubMed

The olive tree (Olea europaea L.) is often exposed to severe water stress during the summer season. In this study, we determined the changes in total phenol content, oleuropein and hydroxytyrosol in the leaves of four olive cultivars ('Gaidourelia', 'Kalamon', 'Koroneiki' and 'Megaritiki') grown under water deficit conditions for two months. Furthermore, we investigated the photosynthetic performance in terms of gas exchange and chlorophyll a fluorescence, as well as malondialdehyde content and antioxidant activity. One-year-old self-rooted plants were subjected to three irrigation treatments that received a water amount equivalent to 100% (Control, C), 66% (Field Capacity 66%, FC(66)) and 33% (Field Capacity 33%, FC(33)) of field capacity. Measurements were conducted 30 and 60 days after the initiation of the experiment. Net CO(2) assimilation rate, stomatal conductance and F(v)/F(m) ratio decreased only in FC(33) plants. Photosynthetic rate was reduced mainly due to stomatal closure, but damage to PSII also contributed to this decrease. Water stress induced the accumulation of phenolic compounds, especially oleuropein, suggesting their role as antioxidants. Total phenol content increased in FC(33) treatment and oleuropein presented a slight increase in FC(66) and a sharper one in FC(33) treatment. Hydroxytyrosol showed a gradual decrease as water stress progressed. Malondialdehyde (MDA) content increased due to water stress, mostly after 60 days, while antioxidant activity increased for all cultivars in the FC(33) treatment. 'Gaidourelia' could be considered as the most tolerant among the tested cultivars, showing higher phenolic concentration and antioxidant activity and lower lipid peroxidation and photochemical damage after two months of water stress. The results indicated that water stress affected olive tree physiological and biochemical parameters and magnitude of this effect depended on genotype, the degree of water limitation and duration of treatment. However, the severity as well as the duration of water stress might exceed antioxidant capacity, since MDA levels and subsequent oxidative damage increased after two months of water deficit. PMID:22885895

Petridis, Antonios; Therios, Ioannis; Samouris, Georgios; Koundouras, Stefanos; Giannakoula, Anastasia

2012-11-01

21

Does gender affect human pulmonary gas exchange during exercise?  

PubMed Central

Women may experience greater pulmonary gas exchange impairment during exercise than men. To test this we used the multiple inert gas elimination technique to study eight women and seven men matched for age, height and V?O2max (?48 ml kg?1 min?1) during normoxic and hypoxic (inspired PO2= 95 Torr) cycle exercise. Resting lung function was similar between the sexes, except for a lower carbon monoxide diffusing capacity (DLCO) in women (P < 0.05). Arterial PO2,PCO2 and alveolar–arterial O2 difference (A?aDO2) were not significantly different in men and women. Despite a lower diffusing capacity for O2 (DLO2) in women, the ratio DLO2/?Q? (which estimates pulmonary end-capillary diffusion equilibrium) was similar between men and women and estimates of diffusion limitation during hypoxic exercise were not different between the sexes. Ventilation–perfusion inequality (described by the second moment of the perfusion distribution, logSDQ?) increased during both normoxic and hypoxic exercise. Surprisingly, logSDQ? values were slightly lower for women under all conditions (P < 0.05), but this did not significantly affect gas exchange. These data indicate that these active women, despite a lower DLCO and DLO2, do not experience greater exercise-induced abnormalities in gas exchange than men matched for age, height, aerobic capacity and lung size. Possibly fitness level and lung size are more important in determining whether or not pulmonary gas exchange impairment occurs during exercise than sex per se. PMID:14990677

Olfert, I Mark; Balouch, Jamal; Kleinsasser, Axel; Knapp, Amy; Wagner, Harrieth; Wagner, Peter D; Hopkins, Susan R

2004-01-01

22

BOREAS TF-11 SSA-Fen Leaf Gas Exchange Data  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

23

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.

1989-01-01

24

EFFECTS OF TEMPERATURE ON GAS EXCHANGE AND ACIDBASE BALANCE IN THE SEA TURTLE CARETTA CARETTA AT REST AND DURING ROUTINE ACTIVITY  

Microsoft Academic Search

Summary Oxygen consumption, lung ventilation, plasma ion concentrations and osmo- lality, venous blood acid-base status and gas tensions were measured in unrestrained loggerhead sea turtles in sea water at 10, 15, 20 and 30 °C at rest and during routine activity. Moderate activity caused a threefold increase in oxygen consumption, accommodated by a twofold increase in ventilation (the result of

PETER L. LUTZ; ANN BERGEY; MICHAEL BERGEY

1989-01-01

25

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.

2011-03-01

26

Inhomogeneous electron gas at nonzero temperatures: Exchange effects  

Microsoft Academic Search

The exchange energy, exchange potential, and the exchange contribution to the interaction function are evaluated for all nonzero temperatures. These results are the finite temperature versions of the rho13-theory of Kohn-Sham. The applications of the results reported here are indicated. The paramagnetic susceptibility of an interacting electron gas as a function of temperature exhibits an interesting peak structure.

Uday Gupta; A. K. Rajagopal

1980-01-01

27

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

PubMed

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

Lange, O L

1969-03-01

28

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 exchange

Kapitan, Kent S.

2008-01-01

29

Gas exchange and ventilation-perfusion relationships in the lung.  

PubMed

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

Petersson, Johan; Glenny, Robb W

2014-10-01

30

Noble gas constraints on air-sea gas exchange and bubble fluxes  

NASA Astrophysics Data System (ADS)

Air-sea gas exchange is an important part of the biogeochemical cycles of many climatically and biologically relevant gases including CO2, O2, dimethyl sulfide and CH4. Here we use a three year observational time series of five noble gases (He, Ne, Ar, Kr, and Xe) at the Bermuda Atlantic Time series Study (BATS) site in tandem with a one-dimensional upper ocean model to develop an improved parameterization for air-sea gas exchange that explicitly includes separate components for diffusive gas exchange and bubble processes. Based on seasonal timescale noble gas data, this parameterization, which has a 1? uncertainty of ±14% for diffusive gas exchange and ±29% for bubble fluxes, is more tightly constrained than previous parameterizations. Although the magnitude of diffusive gas exchange is within errors of that of Wanninkhof (1992), a commonly used parameterization, we find that bubble-mediated exchange, which is not explicitly included by Wanninkhof (1992) or many other formulations, is significant even for soluble gases. If one uses observed saturation anomalies of Ar (a gas with similar characteristics to O2) and a parameterization of gas exchange to calculate gas exchange fluxes, then the calculated fluxes differ by ˜240% if the parameterization presented here is used compared to using the Wanninkhof (1992) parameterization. If instead one includes the gas exchange parameterization in a model, then the calculated fluxes differ by ˜35% between using this parameterization and that of Wanninkhof (1992). These differences suggest that the bubble component should be explicitly included in a range of marine biogeochemical calculations that incorporate air-sea gas fluxes.

Stanley, Rachel H. R.; Jenkins, William J.; Lott, Dempsey E.; Doney, Scott C.

2009-11-01

31

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

PubMed Central

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

Anderson, Joseph C.; Hlastala, Michael P.

2011-01-01

32

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. PMID:17515731

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

2007-01-01

33

Impacts of winter storms on air-sea gas exchange  

NASA Astrophysics Data System (ADS)

The objective of this study is to investigate air-sea gas exchange during winter storms, using field measurements from Ocean Station Papa in the Northeast Pacific (50°N, 145°W). We show that increasing gas transfer rates are coincident with increasing winds and deepening depth of bubble penetration, and that this process depends on sea state. Wave-breaking is shown to be an important factor in the gas transfer velocity during the peaks of the storms, increasing the flux rates by up to 20%. Gas transfer rates and concentrations can exhibit asymmetry, reflecting a sudden increase with the onset of a storm, and gradual recovery stages.

Zhang, Weiqing; Perrie, Will; Vagle, Svein

2006-07-01

34

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

NASA Technical Reports Server (NTRS)

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

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

1974-01-01

35

Sunlight supply and gas exchange systems in microalgal bioreactor  

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

36

Effect of body position on gas exchange after thoracotomy  

Microsoft Academic Search

To determine the effect of change in body position on gas exchange after thoracotomy, 12 patients with potentially resectable lung tumours were studied before and 24 hours after operation. Measurements of arterial blood gas tension (PaO2, PaCO2), alveolar-arterial oxygen difference (A--adO2), venous admixture effect (Qs\\/Qt percent), and physiological dead space to tidal volume ratio (Vd\\/Vt), were made in the supine,

D Seaton; N L Lapp; W K Morgan

1979-01-01

37

Original article Gas exchange in young Scots pine following  

E-print Network

stem growth, insect ac- tivity also has qualitative effects on physio- logical processes in the treeOriginal article Gas exchange in young Scots pine following pruning of current shoots E Troeng B; A pine shoot beetle attack was simulated by cutting all current shoots in the upper crown of 2 20-yr

Boyer, Edmond

38

ORIGINAL PAPER Impacts of ocean acidification on respiratory gas exchange  

E-print Network

ORIGINAL PAPER Impacts of ocean acidification on respiratory gas exchange and acid­base balance; Orr et al. 2005). Consequently, the effects of ocean acidification on these organisms have been). These unprecedented changes in the marine environment pose potentially dramatic challenges for marine organisms

Grosell, Martin

39

Gas exchange on Mono Lake and Crowley Lake, California  

NASA Astrophysics Data System (ADS)

Gas exchange coefficients have been determined for freshwater Crowley Lake and for saline Mono Lake through the use of a man-made purposefully injected gas, sulfur hexafluoride (SF6). The concentration decreased from an initial value of 40×10-12 mol/L to 4×10-12 mol/L for Mono Lake and from 20×10-12 mol/L to 1×10-12 mol/L for Crowley Lake over a period of 6 weeks. Wind speed records from anemometers on the shore of each lake enabled us to determine the relationship between the gas exchange coefficient k and wind speed u. The average wind speed and average exchange coefficient for the experiment were identical for the two lakes (uav=2.9 m/s, kav=2.5 cm/h), despite a large difference in size and chemical composition. From laboratory experiments and theoretical calculations it is estimated that for wind speeds observed over Mono Lake from July until December 1984 the exchange of CO2 occurred 2-½ times faster than without chemical enhancement. This is a factor of 4 lower than needed to explain the high invasion rate of 14C produced by nuclear bomb tests.

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

1987-12-01

40

Development of corrosion resistant heat exchangers for flue gas desulfurization  

NASA Astrophysics Data System (ADS)

A glass lining as protection against corrosion in flue gas desulfurization plants was developed. Glasses were evaluated under corrosive attack of fluoride-containing acids. The corrosion properties of one-layer and two-layer glass enamels are optimized. Two-layer systems always show better resistance and longer life. The optimized glass linings were tested in a power plant. Manufacturing principles for glass-lined heat exchanger elements are derived. The optimized glasses may be used as protective lining design for heat exchangers or parts of them.

Ernst, E.; Lorentz, R.

1984-12-01

41

Leaf gas exchange and carbohydrate concentrations in Pinus pinaster plants subjected to elevated CO2  

E-print Network

Note Leaf gas exchange and carbohydrate concentrations in Pinus pinaster plants subjected, whereas no significant CO2 effect was observed on the soluble carbohydrate concentration. These compounds. (© Inra/Elsevier, Paris.) elevated [CO2] / drought / leaf gas exchange / carbohydrate / Pinus

Paris-Sud XI, Université de

42

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

EPA Science Inventory

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

43

BOREAS TE-4 Gas Exchange Data from Boreal Tree Species  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

44

Multiple modeling in the study of interaction of hemodynamics and gas exchange  

Microsoft Academic Search

Circulation plays an important rule in gas exchange. Therefore, there is an interaction between circulation and gas exchange. To understand the dynamic effect of these two physiological systems, a computer simulation model of hemodynamics and gas exchange is established in this work. This model includes two physiological systems, namely the respiratory and circulatory systems. It consists of five parts: the

Anqi Qiu; Jing Bai

2001-01-01

45

Gas exchange on Mono Lake and Crowley Lake, California  

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

46

A continuum model for metabolic gas exchange in pear fruit.  

PubMed

Exchange of O(2) and CO(2) 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 O(2) and increased CO(2) levels to extend their commercial storage life, anoxia may occur, eventually leading to physiological disorders. In this manuscript we have developed a mathematical model to predict the internal gas concentrations, including permeation, diffusion, and respiration and fermentation kinetics. Pear fruit has been selected as a case study. The model has been used to perform in silico experiments to evaluate the effect of, for example, fruit size or ambient gas concentration on internal O(2) and CO(2) levels. The model incorporates the actual shape of the fruit and was solved using fluid dynamics software. Environmental conditions such as temperature and gas composition have a large effect on the internal distribution of oxygen and carbon dioxide in fruit. Also, the fruit size has a considerable effect on local metabolic gas concentrations; hence, depending on the size, local anaerobic conditions may result, which eventually may lead to physiological disorders. The model developed in this manuscript is to our knowledge the most comprehensive model to date to simulate gas exchange in plant tissue. It can be used to evaluate the effect of environmental stresses on fruit via in silico experiments and may lead to commercial applications involving long-term storage of fruit under controlled atmospheres. PMID:18369422

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

2008-03-01

47

A Continuum Model for Metabolic Gas Exchange in Pear Fruit  

PubMed Central

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

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

2008-01-01

48

Development of corrosion resistant heat exchangers for flue gas desulfurization  

Microsoft Academic Search

A glass lining as protection against corrosion in flue gas desulfurization plants was developed. Glasses were evaluated under corrosive attack of fluoride-containing acids. The corrosion properties of one-layer and two-layer glass enamels are optimized. Two-layer systems always show better resistance and longer life. The optimized glass linings were tested in a power plant. Manufacturing principles for glass-lined heat exchanger elements

E. Ernst; R. Lorentz

1984-01-01

49

Metabolic rate and respiratory gas-exchange patterns in tenebrionid beetles from the Negev Highlands, Israel.  

PubMed

This study correlates the pattern of external gas exchange with the diel activity of nine species of tenebrionid beetle from the Negev Desert, Israel. The study species are active throughout the summer months when daytime temperatures are high and no rain falls. There were no differences in standard metabolic rate, determined by flow-through respirometry, among the nine species. All the nocturnally active beetles exhibited a form of continuous respiration, whereas the two diurnally active and one crepuscular species exhibited a cyclic form of respiration referred to as the discontinuous gas-exchange cycle (DGC). The DGCs recorded have a long flutter period consisting of miniature ventilations, and 29-48 % of the total CO(2) output occurred during this period. In this study, the flutter period played an important role in the modulation of metabolic rate, in contrast to other studies in which the burst period has been shown to be important. We suggest that the long flutter period is important in reducing respiratory water loss in arid-dwelling arthropods. This study lends support to the hypothesis that discontinuous gas exchange is important in reducing respiratory water loss from beetles that need to minimise dessication because of the high water vapour pressure gradient they experience. If the use of underground burrows were responsible for the evolution of discontinuous gas exchange, then we would expect all nine tenebrionid species to use DGCs since both the nocturnally and diurnally active species bury in the sand during periods of inactivity. We conclude that the activity patterns of the beetles are more important than their habitat associations in designating the type of respiration used. PMID:11914387

Duncan, Frances D; Krasnov, Boris; McMaster, Megan

2002-03-01

50

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

2006-05-01

51

Effect of certain dicarboxylic acid monoesters on growth, chlorophyll content, chlorophyllase and peroxidase activities, and gas-exchange of young maize plants  

Microsoft Academic Search

The effect of some dicarboxylic acid monoesters on growth, chlorophyll content, chlorophyllase (EC 3.1.1.14), and total peroxidase\\u000a (EC 1.11.1.7.) activities was examined in detached and intact leaves of maize (Zea mays) plants grown in a greenhouse. The ?-monomethyl ester of itaconic acid (MEIA) at 1250 ppm had no effect on growth. However,\\u000a application of the monoethyl ester of succinic (MESA)

D. Todorov; V. Alexieva; E. Karanov; D. Velichkov; V. Velikova

1992-01-01

52

Exchange-Correlation Energy Functional Based on the Airy-Gas Reference System  

Microsoft Academic Search

In recent work, generalized gradient approximations (GGA's) have been constructed from the energy density of the Airy gas for exchange but not for correlation. We report the random phase approximation (RPA) conventional correlation energy density of the Airy gas, the simplest edge electron gas, in which the auxiliary noninteracting electrons experience a linear potential. By fitting the Airy-gas RPA exchange-correlation

Lucian A. Constantin; Adrienn Ruzsinszky; John P. Perdew

2009-01-01

53

Effect of crude oil on gas exchange functions of Juncus roemerianus and Spartina alterniflora  

Microsoft Academic Search

The effect of crude oil on gas exchange functions of Juncus roemerianus and Spartina alterniflora, two important U.S. Gulf Coast plant species, were examined. Plants were exposed to petroleum hydrocarbons (Mexican Sour type) mixed with water at 4.4 mL L-1 (2 L m-2). Coating entire leaf with oil resulted in cessation of photosynthetic activity. Partial leaf exposure to oil resulted

S. R. Pezeshki; R. D. Laune

1993-01-01

54

PREDICTION OF TOTAL DISSOLVED GAS EXCHANGE AT HYDROPOWER DAMS  

SciTech Connect

Total dissolved gas (TDG) supersaturation in waters released at hydropower dams can cause gas bubble trauma in fisheries resulting in physical injuries and eyeball protrusion that can lead to mortality. Elevated TDG pressures in hydropower releases are generally caused by the entrainment of air in spillway releases and the subsequent exchange of atmospheric gasses into solution during passage through the stilling basin. The network of dams throughout the Columbia River Basin (CRB) are managed for irrigation, hydropower production, flood control, navigation, and fish passage that frequently result in both voluntary and involuntary spillway releases. These dam operations are constrained by state and federal water quality standards for TDG saturation which balance the benefits of spillway operations designed for Endangered Species Act (ESA)-listed fisheries versus the degradation to water quality as defined by TDG saturation. In the 1970s, the United States Environmental Protection Agency (USEPA), under the federal Clean Water Act (Section 303(d)), established a criterion not to exceed the TDG saturation level of 110% in order to protect freshwater and marine aquatic life. The states of Washington and Oregon have adopted special water quality standards for TDG saturation in the tailrace and forebays of hydropower facilities on the Columbia and Snake Rivers where spillway operations support fish passage objectives. The physical processes that affect TDG exchange at hydropower facilities have been studied throughout the CRB in site-specific studies and routine water quality monitoring programs. These data have been used to quantify the relationship between project operations, structural properties, and TDG exchange. These data have also been used to develop predictive models of TDG exchange to support real-time TDG management decisions. These empirically based predictive models have been developed for specific projects and account for both the fate of spillway and powerhouse flows in the tailrace channel and resultant exchange in route to the next downstream dam. Currently, there exists a need to summarize the general finding from operational and structural TDG abatement programs conducted throughout the CRB and for the development of a generalized prediction model that pools data collected at multiple projects with similar structural attributes. A generalized TDG exchange model can be tuned to specific projects and coupled with water regulation models to allow the formulation of optimal daily water regulation schedules subject to water quality constraints for TDG supersaturation. A generalized TDG exchange model can also be applied to other hydropower dams that affect TDG pressures in tailraces and can be used to develop alternative operational and structural measures to minimize TDG generation. It is proposed to develop a methodology for predicting TDG levels downstream of hydropower facilities with similar structural properties as a function of a set of variables that affect TDG exchange; such as tailwater depth, spill discharge and pattern, project head, and entrainment of powerhouse releases. TDG data from hydropower facilities located throughout the northwest region of the United States will be used to identify relationships between TDG exchange and relevant dependent variables. Data analysis and regression techniques will be used to develop predictive TDG exchange expressions for various structural categories.

Hadjerioua, Boualem [ORNL; Pasha, MD Fayzul K [ORNL; Stewart, Kevin M [ORNL; Bender, Merlynn [Bureau of Reclamation; Schneider, Michael L. [U.S. Army Corps of Engineers

2012-07-01

55

The Effect of Rain on Air-Water Gas Exchange  

NASA Technical Reports Server (NTRS)

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

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

1997-01-01

56

Atmosphere-ocean gas exchange based on radiocarbon data  

NASA Astrophysics Data System (ADS)

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

Byalko, Alexey

2014-05-01

57

Sulfur gas exchange in Sphagnum-dominated wetlands  

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

58

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 www.siumed.edu/medicine/pulm/vqmodeling.htm). 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)

2007-11-19

59

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

PubMed

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

Wagner, Peter D

2015-01-01

60

Inhaled nitric oxide reverses hypoxic pulmonary vasoconstriction without impairing gas exchange  

SciTech Connect

Nitric oxide (NO) is an endogenous endothelium-derived relaxing factor that participates in the regulation of vascular tone. The authors studied the effects of inhaled NO gas on transient hypoxic pulmonary vasoconstriction and normal lungs in mechanically ventilated sheep. They measured hemodynamics and pulmonary gas exchange. For gas exchange measurements they used conventional blood gas analysis and the multiple inert gas elimination technique to estimate ventilation-perfusion heterogeneity. The hypotheses were (1) inhaled NO reverses hypoxic pulmonary vasoconstriction, (2) the hemodynamic effects of inhaled NO are limited to the pulmonary circulation, and (3) inhaled NO does not impair pulmonary gas exchange and may redistribute blood flow to better ventilated areas of the lungs. Hypoxic pulmonary vasoconstriction was induced by using a hypoxic inspiratory gas mixture. The addition of 20 ppm NO to the hypoxic inspiratory gases returned pulmonary arterial pressure to baseline values. Systemic hemodynamics and gas exchange indexes derived from conventional blood gas analysis remained constant. Gas exchange indexes for ventilation-perfusion ratios and gas dispersions improved. The addition of 20 ppm NO to medical air (21% O[sub 2]) had no such significant effects on hemodynamics or pulmonary gas exchange. The findings show that inhaled NO reverses transient hypoxic pulmonary vasoconstriction. The hemodynamic effects of NO are limited to the pulmonary circulation; it does not impair pulmonary gas exchange. Moreover, it redistributes blood flow to better ventilated alveoli. As such, NO has potential in the treatment of lung diseases associated with pulmonary hypertension. 35 refs., 4 figs., 3 tabs.

Pison, U.; Lopez, F.A.; Heidelmeyer, C.F.; Rossaint, R.; Falke, K.J. (Freie Universitaet Berlin (Germany))

1993-03-01

61

Exact-exchange density-functional theory applied to a strongly inhomogeneous electron gas  

Microsoft Academic Search

A recently developed quasi-two-dimensional exact-exchange formalism within the framework of density-functional theory has been applied to a strongly inhomogeneous interacting electron gas. Results are presented for the exchange-hole density at different positions in the system, the exchange-energy density, and the exchange energy per particle. It has been found that the exact exchange hole is strongly nonlocal when evaluated at a

S. Rigamonti; F. A. Reboredo; C. R. Proetto

2003-01-01

62

Understanding Fraudulent Activities in Online Ad Exchanges  

E-print Network

), marketplaces known as "ad exchanges" are employed. These exchanges allow publishers (sellers of ad space) and adver- tisers (buyers of this ad space) to dynamically broker traffic through ad networks to efficiently/seller relationship between those who want to show ads (advertisers, who buy space on Web pages) and those who get

California at Santa Barbara, University of

63

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

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

64

Leaf Water Relations and Maintenance of Gas Exchange in Coffee Cultivars Grown in Drying Soil 1  

PubMed Central

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 (?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 ?L at which turgor loss occurred. Adjustments in ?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 ?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, Frederick C.; Grantz, David A.; Goldstein, Guillermo; Saliendra, Nicanor Z.

1990-01-01

65

Factors controlling sulfur gas exchange in Sphagnum-dominated wetlands  

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

66

Exchange-correlation energy functional based on the Airy-gas reference system  

Microsoft Academic Search

In recent work, generalized gradient approximations (GGA's) have been\\u000aconstructed from the energy density of the Airy gas for exchange but not for\\u000acorrelation. We report the random phase approximation (RPA) conventional\\u000acorrelation energy density of the Airy gas, the simplest edge electron gas, in\\u000awhich the auxiliary noninteracting electrons experience a linear potential. By\\u000afitting the Airy-gas RPA exchange-correlation

Lucian A. Constantin; Adrienn Ruzsinszky; John P. Perdew

2009-01-01

67

Exchange-correlation energy functional based on the Airy-gas reference system  

Microsoft Academic Search

In recent work, generalized gradient approximations (GGAs) have been constructed from the energy density of the Airy gas for exchange but not for correlation. We report the random-phase approximation (RPA) conventional correlation energy density of the Airy gas, the simplest edge electron gas, in which the auxiliary noninteracting electrons experience a linear potential. By fitting the Airy-gas RPA exchange-correlation energy

Lucian A. Constantin; Adrienn Ruzsinszky; John P. Perdew

2009-01-01

68

Respiratory gas exchange of high altitude adapted chick embryos  

NASA Technical Reports Server (NTRS)

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

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

1974-01-01

69

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

2007-03-01

70

Waste heat recovery using heat pipe heat exchanger for heating automobile using exhaust gas  

Microsoft Academic Search

The feasibility of using heat pipe heat exchangers for heating applying automotive exhaust gas is studied and the calculation method is developed. Practical heat pipe heat exchanger is set up for heating HS663, a large bus. Simple experiments are carried out to examine the performance of the heat exchanger. It is shown that the experimental results, which indicate the benefit

Feng Yang; Xiugan Yuan; Guiping Lin

2003-01-01

71

Seasonal Patterns of Acid Metabolism and Gas Exchange in Opuntia basilaris.  

PubMed

Acid metabolism and gas exchange studies were conducted in situ on the cactus Opuntia basilaris Engelm. and Bigel. A pattern of significant seasonal variation was evident. The pattern was controlled by rainfall, which significantly influenced plant water potentials, total gas transfer resistances, and nocturnal organic acid synthesis. In winter and early spring, when plant water stress was mild, stomatal and mesophyll resistances remained low, permitting enhanced nocturnal assimilation of (14)CO(2). The day/night accumulation of acidity was large during these seasons. In summer and fall, plant water stress was moderate, although soil water stress was severe. The nocturnal assimilation of (14)CO(2) was very low during these seasons, even in stems with open stomata, indicating large mesophyll resistances restricting exogenous gas incorporation. The day/night accumulation of acidity was reduced, and a low level of acid metabolism persisted throughout this period. The rapid response to a midsummer rainfall emphasizes the importance of plant water potential as a parameter controlling over-all metabolic activity. The seasonal variations of acid metabolism and gas exchange significantly influenced the efficiency of water use and carbon dioxide assimilation. Periods of maximal efficiency followed rainfall throughout the course of the year. PMID:16658842

Szarek, S R; Ting, I P

1974-07-01

72

Discontinuous Gas Exchange in Insects: A Clarification of Hypotheses and Approaches*  

E-print Network

333 Discontinuous Gas Exchange in Insects: A Clarification of Hypotheses and Approaches* Steven L Accepted 4/25/2005; Electronically Published 2/2/2006 ABSTRACT Many adult and diapausing pupal insects. Introduction Discontinuous gas exchange is often regarded as the quintes- sential characteristic of insect

Ahmad, Sajjad

73

JOINT ACTION OF O3 AND SO2 IN MODIFYING PLANT GAS EXCHANGE  

EPA Science Inventory

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

74

INTRODUCTION Gas exchange in bird eggs occurs across the porous shell and  

E-print Network

consumption. MATERIALS AND METHODS Egg source and incubation Eggs of fertilized White Leghorn chickens (Gallus883 INTRODUCTION Gas exchange in bird eggs occurs across the porous shell and underlying, even in the heavily diffusion-limited respiratory systems of bird eggs, effective gas exchange

Burggren, Warren

75

Gas exchange characteristics of Pinus canariensis needles in a forest stand on Tenerife, Canary Islands  

Microsoft Academic Search

Gas exchange characteristics and chlorophyll fluorescence of the Canarian endemic pine ( Pinus canariensis) were measured during the day for a year in a field stand on Tenerife, Canary Islands, Spain. Diurnal tendencies of gas exchange were variable depending on ambient conditions. In general they paralleled photosynthetic photon flux density with only one peak at midday, except on summer days

Juliane Peters; Domingo Morales; M. Soledad Jiménez

2003-01-01

76

Original article Effect of fungal infection on leaf gas-exchange  

E-print Network

Original article Effect of fungal infection on leaf gas-exchange and chlorophyll fluorescence after excision of the shoot. Leaf gas-exchange and chlorophyll a fluorescence were recorded on plants intensity at any point; Fo, F'o minimum flu- orescence yield in dark-adapted and light-adapted state; Fm, F

Boyer, Edmond

77

A ceramic heat exchanger for exhaust fired gas turbine power cycles  

Microsoft Academic Search

Until recently, combustion of solid fuels such as forest product residues, municipal waste, or coal in gas turbine power cycles has been limited by the corrosive action of the combustion products. A heat exchanger which can operate in this corrosive environment has been developed, making the exhaust fired gas turbine an economically viable power source. This heat exchanger is fabricated

I. G. Most; K. G. Hagen

1977-01-01

78

Effect of nitrogen on root and shoot relations and gas exchange in winter wheat  

Microsoft Academic Search

The seedling growth of two drought-resistant wheat varieties was studied under solution culture in a plant growth chamber. The results showed that the shoot dry weight and leaf gas exchange parameters increased with the increase of nitrogen supply, but decreased when nitrogen supply reached a certain level. The optimum nitrogen concentrations for shoot dry weight and gas exchange were different

Z. P. Shangguan; M. A. Shao; S. J. Ren; L. M. Zhang; Q. Xue

2004-01-01

79

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.

2013-01-01

80

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...

81

The combined effect of rain and wind on airwater gas exchange: A feasibility study  

E-print Network

The combined effect of rain and wind on air­water gas exchange: A feasibility study David T. Ho a to examine the combined effects of rain and wind on air­water 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

Ho, David

82

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. PMID:20404161

Woods, H. Arthur; Smith, Jennifer N.

2010-01-01

83

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

NASA Astrophysics Data System (ADS)

Air-sea gas exchange is important to the global partitioning of CO2.Exchange fluxes are products of an air-sea gas concentration difference, ?C, and a gas transfer velocity, kw. The latter is controlled by the rate of turbulent diffusion at the air-sea interface but it cannot be directly measured and has a high uncertainty that is now considered one of the greatest challenges to quantifying net global air-sea CO2 exchange ...(Takahashi et al., 2009). One important control on kw is exerted by sea surface surfactants that arise both naturally from biological processes and through anthropogenic activity. They influence gas exchange in two fundamental ways: as a monolayer physical barrier and through modifying sea surface hydrodynamics and hence turbulent energy transfer. These effects have been demonstrated in the laboratory with artificial surfactants ...(Bock et al., 1999; Goldman et al., 1988) and through purposeful surfactant releases in coastal waters .(.).........().(Brockmann et al., 1982) and in the open ocean (Salter et al., 2011). Suppression of kwin these field experiments was ~5-55%. While changes in both total surfactant concentration and the composition of the natural surfactant pool might be expected to impact kw, the required in-situ studies are lacking. New data collected from the coastal North Sea in 2012-2013 shows significant spatio-temporal variability in the surfactant activity of organic matter within the sea surface microlayer that ranges from 0.07-0.94 mg/L T-X-100 (AC voltammetry). The surfactant activities show a strong winter/summer seasonal bias and general decrease in concentration with increasing distance from the coastline possibly associated with changing terrestrial vs. phytoplankton sources. Gas exchange experiments of this seawater using a novel laboratory tank and gas tracers (CH4 and SF6) demonstrate a 12-45% reduction in kw compared to surfactant-free water. Seasonally there is higher gas exchange suppression in the summer months likely from primary production and spatially there is less suppression of air-sea gas exchange with increasing distance from the shoreline, which is likely due to riverine inputs. REFERENCES Bock, E. J., Hara, T., Frew, N. M., and McGillis, W. R., 1999. Relationship between air-sea gas transfer and short wind waves. Journal of Geophysical Research-Oceans 104, 25821-25831. Brockmann, U. H., Huhnerfuss, H., Kattner, G., Broecker, H. C., and Hentzschel, G., 1982. Artificial surface-films in the sea area near sylt. Limnology and Oceanography 27, 1050-1058. Goldman, J. C., Dennett, M. R., and Frew, N. M., 1988. Surfactant effects on air sea gas-exchange under turbulent conditions. Deep-Sea Research Part a-Oceanographic Research Papers 35, 1953-1970. McKenna, S. P. and McGillis, W. R., 2004. The role of free-surface turbulence and surfactants in air-water gas transfer. International Journal of Heat and Mass Transfer 47, 539-553. Salter, M. E., R. C. Upstill-Goddard, P. D. Nightingale, S. D. Archer, B. Blomquist, D. T. Ho, B. Huebert, P. Schlosser, and M. Yang (2011), Impact of an artificial surfactant release on air-sea gas fluxes during Deep Ocean Gas Exchange Experiment II, J. Geophys. Res., 116, C11016, doi:10.1029/2011JC00702 Takahashi, T., Sutherland, S. C., Wanninkhof, R., Sweeney, C., Feely, R. A., Chipman, D. W., Hales, B., Friederich, G., Chavez, F., Sabine, C., Watson, A., Bakker, D. C. E., Schuster, U., Metzl, N., Yoshikawa-Inoue, H., Ishii, M., Midorikawa, T., Nojiri, Y., Körtzinger, A., Steinhoff, T., Hoppema, M., Olafsson, J., Arnarson, T. S., Tilbrook, B., Johannessen, T., Olsen, A., Bellerby, R., Wong, C. S., Delille, B., Bates, N. R., and de Baar, H. J. W., 2009. Climatological mean and decadal change in surface ocean pCO 2, and net sea-air CO 2 flux over the global oceans. Deep-Sea Research Part II: Topical Studies in Oceanography 56, 554-577.

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

2014-05-01

84

INTERNATIONAL INFORMATION EXCHANGE ACTIVITIES ON DIOXINS  

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...

85

Innovative, counterflow gas/fine solids, direct contact heat exchanger  

NASA Astrophysics Data System (ADS)

The Aerojet Energy Conversion Company has completed the first phase of study for development of a heat exchanger. The heat exchanger, a highly efficient, low cost concept, is a candidate for application in process manufacturing industries such as cement, lime, or glass. The analytical effort was to establish the heat exchanger performance via computer modeling and analysis; the experimental effort was to demonstrate the heat exchanger performance.

Mah, C. S.

1987-10-01

86

POSTING: Technician 5 Heat and Greenhouse gas Exchange The Centre for Earth Observation Science (CEOS) within the Faculty of Environment,  

E-print Network

POSTING: Technician 5 ­ Heat and Greenhouse gas Exchange technician in support of multidisciplinary research on heat and greenhouse gas exchange within marine and estuarine environments of the Arctic and sub

87

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.

2006-12-01

88

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

NASA Astrophysics Data System (ADS)

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

Chmielniak, Tadeusz; Czaja, Daniel; Lepszy, Sebastian

2013-12-01

89

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

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

90

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

PubMed

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

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

2011-07-01

91

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

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

92

Long-term gas exchange characteristics as markers of deterioration in patients with cystic fibrosis  

Microsoft Academic Search

BACKGROUND AND AIM: In patients with cystic fibrosis (CF) the architecture of the developing lungs and the ventilation of lung units are progressively affected, influencing intrapulmonary gas mixing and gas exchange. We examined the long-term course of blood gas measurements in relation to characteristics of lung function and the influence of different CFTR genotype upon this process. METHODS: Serial annual

Richard Kraemer; Philipp Latzin; Isabelle Pramana; Pietro Ballinari; Sabina Gallati; Urs Frey

2009-01-01

93

Relationships between gas exchange adaptation of Sitka x interior spruce genotypes and ribosomal DNA markers.  

PubMed

Adaptive physiological changes were investigated in seven populations of Sitka (Picea sitchensis (Bong.) Carr.) x interior spruce (P. glauca (Moench) Voss x P. engelmannii Parry ex Engelm.) spanning the Nass-Skeena transition zone in British Columbia, Canada. Each population was represented by an Si rDNA index that was calculated from the relative optical densities on a gel autoradiogram of five ribosomal DNA bands characteristic of Sitka spruce and interior spruce. This index estimates the proportion of the genome contributed by interior spruce. Physiological adaptations were assessed by gas exchange parameters measured under both well-watered and drought conditions. Under well-watered conditions, Sitka spruce populations had higher maximal photosynthesis at saturating light and ambient CO(2), higher quantum yield at the light compensation point, and higher dark respiration than interior spruce populations. Sitka spruce populations also reached maximal photosynthesis at lower photosynthetically active radiation and higher CO(2) concentrations, and had higher stomatal densities that resulted in lower stomatal limitations to photosynthesis than interior spruce populations. In contrast, interior spruce populations exhibited greater drought tolerance than Sitka spruce populations. Their gas exchange rates declined at a slower rate in response to drought. They maintained higher gas exchange rates in response to moderate to severe drought (predawn plant water potentials = -1.5 MPa), and their photosynthetic rates recovered faster when they were rewatered after exposure to drought. Comparison of the seven populations indicated that physiological parameters were significantly related to the Si rDNA index. An increase in Si rDNA index was associated with proportional changes in physiological measurements, suggesting that genetic interchange among species with contrasting ecological adaptations can enhance the environmental adaptation of natural populations. PMID:14759881

Fan, S; Grossnickle, S C; Sutton, B C

1997-02-01

94

[Changes in pulmonary hemodynamics, gas exchange and extravascular lung fluid in esophageal resection].  

PubMed

Postoperative convalescence after esophagectomy is frequently complicated by pulmonary insufficiency and a high mortality rate. The literature and our own observations suggest that pathological changes actually begin during the operative procedure; we therefore studied 11 male patients during and after esophageal surgery by monitoring heart rate, systemic and pulmonary arterial pressures, cardiac output, extravascular lung water (EVLW), cardiac index, and systemic (TPR) and pulmonary vascular resistance (PVR). Blood samples were taken for analysis of epinephrine, norepinephrine, serotonin, and arterial and mixed-venous blood gases. The changes were found to be most marked during esophageal resection: PaO2 decreased from 217 to 147 mmHg while PaCO2 increased, i.e. pulmonary gas exchange was disturbed (Fig. 4). PVR (Fig. 3) and mean pulmonary arterial pressure (MPAP) (Fig. 2) increased after esophagectomy. Norepinephrine, but not epinephrine (Fig. 6), increased continuously until the end of the operation. EVLW was slightly elevated at approximately 9 ml/kg body weight before operation and did not change during surgery. Six patients who developed severe pulmonary complications showed lung water retention up to 18 ml/kg body weight on the 4th postoperative day (Fig. 5). Compression of the heart and lungs as well as injury of the vagus nerve during esophagectomy may provoke increased MPAP, PVR, and disorders of pulmonary gas exchange. Furthermore, the non-respiratory function of the lung must be taken into consideration: the lung is known to have clearance activities for various endogenous substances such as norepinephrine, serotonin, some prostaglandins, and bradykinin. Most of these substances may provoke vasoconstriction followed by disturbances of microvascular permeability and gas exchange in the lung.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:3364668

Heinrichs, W; Duda, D; Rothmund, M; Halmágyi, M

1988-02-01

95

Land use and ecosystem level controls of trace gas exchange  

NASA Astrophysics Data System (ADS)

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

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

2003-04-01

96

Failure analysis of heat exchanger tubes of four gas coolers  

Microsoft Academic Search

A Number of leaks occurred on four heat exchangers used on an off-shore platform in the south of Iran. As a result heat exchanger tubes made of Inconel 625 failed after only two years in operation. The failure was caused by pitting corrosion in two contact regions, tubes and baffles as well as in tube sheet and shell contact regions

S. R. Allahkaram; P. Zakersafaee; S. A. M. Haghgoo

2011-01-01

97

Gas exchange and water relations of evergreen and deciduous tropical savanna trees  

E-print Network

Gas exchange and water relations of evergreen and deciduous tropical savanna trees G. Goldstein1 F savannas with pro- nounced wet/dry seasonality and well- drained soils are characterized by the presence

Boyer, Edmond

98

Stomatal behaviour and gas exchange of Sedges ( Carex spp.) under different soil moisture regimes  

NASA Astrophysics Data System (ADS)

Sedges ( Carex spec., Cyperaceae) are important members of different vegetation types in temperate zones nearly all over the world. For this, knowledge of gas exchange and stomata behaviour of sedges is significant for understanding the exchange of water vapour and carbon dioxide between such vegetation types and the atmosphere. The gas exchange of several Carex species was studied in an experimental site of the Botanical Garden Düsseldorf (Germany). Transpiration and netassimilation rates (A), leaf conductances (g) and microclimatic parameters were measured porometrically during two vegetation periods. Patterns of dependence of leaf gas exchange on microclimatic conditions were worked out for different species and culture regimes. The sedges differ in stomatal sensitivity to changing air humidity. Water loss through transpiration is therefore decoupled from evaporation in a species-specific degree. Resulting mathematical models of g and A are presented and the importance of these species-specific differences in modelling and upscaling water vapour, carbon dioxide and trace gas fluxes are pointed out.

Busch, J.; Lösch, R.

99

Heat exchanger design for thermoelectric electricity generation from low temperature flue gas streams  

E-print Network

An air-to-oil heat exchanger was modeled and optimized for use in a system utilizing a thermoelectric generator to convert low grade waste heat in flue gas streams to electricity. The NTU-effectiveness method, exergy, and ...

Latcham, Jacob G. (Jacob Greco)

2009-01-01

100

Quantum Monte Carlo Analysis of Exchange and Correlation in the Strongly Inhomogeneous Electron Gas  

Microsoft Academic Search

We use the variational quantum Monte Carlo method to calculate the density-functional exchange-correlation hole n{sub xc} , the exchange-correlation energy density e{sub xc} , and the total exchange-correlation energy E{sub xc} of several strongly inhomogeneous electron gas systems. We compare our results with the local density approximation and the generalized gradient approximation. It is found that the nonlocal contributions to

Maziar Nekovee; W. M. C. Foulkes; R. J. Needs

2001-01-01

101

A quantum Monte Carlo investigation of exchange and correlation of the inhomogeneous electron gas  

Microsoft Academic Search

The exchange-correlation (XC) energy functional, E_xc, plays a fundamental role in the density functional theory of solids. Using an adiabatic connection procedure, E_xc can be expressed in terms of the non-local exchange-correlation hole surrounding each electron. We devised a new method for sampling the exchange-correlation hole of the inhomogeneous electron gas which is based on combining the above adiabatic connection

Maziar Nekovee; W. M. C. Foulkes; A. J. Williamson; G. Rajagopal; R. J. Needs

1997-01-01

102

Quantum Monte Carlo Analysis of Exchange and Correlation in the Strongly Inhomogeneous Electron Gas  

Microsoft Academic Search

We use the variational quantum Monte Carlo method to calculate the density-functional exchange-correlation hole nxc, the exchange-correlation energy density exc, and the total exchange-correlation energy Exc of several strongly inhomogeneous electron gas systems. We compare our results with the local density approximation and the generalized gradient approximation. It is found that the nonlocal contributions to exc contain an energetically significant

Maziar Nekovee; W. M. Foulkes; R. J. Needs

2001-01-01

103

Europa: Geological activity and surface - subsurface exchange  

NASA Astrophysics Data System (ADS)

Jupiter's moon Europa has a geologically young surface, allowing the possibility of current, ongoing geological activity. We are searching the Galileo database for overlapping images taken during the 5-year mission, and are comparing images using an iterative coregistration technique to look for changes due to geological activity. We will also discuss methods by which such activity could occur on Europa. We are particularly interested in the ability of geological processes to bring surface material down into the subsurface, and to bring subsurface material up to the surface. We are continuing a survey of such processes, including endogenic tectonic and cryovolcanic activity, and exogenic processes such as gardening and impact cratering.

Phillips, C. B.; Cowell, W.

2005-12-01

104

Study of the exchange energy of an inhomogeneous electron gas at a surface  

Microsoft Academic Search

In this work we have studied the exchange energy property of an inhomogeneous electron gas at a jellium surface. The nonlocal surface exchange energy is determined exactly for the accurate set of single-particle wave functions generated within the linear-potential approximation to the effective potential at a surface, and written in terms of a universal function of the field strength. It

C. Q. Ma; V. Sahni

1979-01-01

105

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

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

106

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

PubMed

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

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

2014-12-01

107

THE TRANSIENT RESPONSE OF GAS TURBINE PLANT HEAT EXCHANGERS--REGENERATORS, INTERCOOLERS, PRECOOLERS, AND DUCTING. Technical Report No. 38  

Microsoft Academic Search

Transient response of heat exchangers are investigated. Analog ; solutions are used to supplement some limiting analytical solutions to provide ; fairly complete coverage for the heat exchangers encountered in gas turbine ; plants. Because a gas-flow exists on at least one side of the heat transfer ; surface, these exchangers are characterized by a large wall capacitance effect. ;

A. L. London; F. R. Biancardi; J. W. Mitchell

1958-01-01

108

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

1991-01-01

109

Hydraulically actuated gas exchange valve assembly and engine using same  

DOEpatents

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)

2002-09-03

110

The relationship between leaf water status, gas exchange, and spectral reflectance in cotton leaves  

NASA Technical Reports Server (NTRS)

Measurements of leaf spectral reflectance, the components of water potential, and leaf gas exchanges as a function of leaf water content were made to evaluate the use of NIR reflectance as an indicator of plant water status. Significant correlations were determined between spectral reflectance at 810 nm, 1665 nm, and 2210 nm and leaf relative water content, total water potential, and turgor pressure. However, the slopes of these relationships were relatively shallow and, when evaluated over the range of leaf water contents in which physiological activity occurs (e.g., photosynthesis), had lower r-squared values, and some relationships were not statistically significant. NIR reflectance varied primarily as a function of leaf water content, and not independently as a function of turgor pressure, which is a sensitive indicator of leaf water status. The limitations of this approach to measuring plant water stress are discussed.

Bowman, William D.

1989-01-01

111

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

PubMed Central

The magnitude and timing of oxygenation responses in highly active leg muscle, less active arm muscle, and cerebral tissue, have not been studied with simultaneous alveolar gas exchange measurement during incremental treadmill exercise. Nor is it known, if blood O2 carrying capacity affects the tissue-specific oxygenation responses. Thus, we investigated alveolar gas exchange and tissue (m. vastus lateralis, m. biceps brachii, cerebral cortex) oxygenation during incremental treadmill exercise until volitional fatigue, and their associations with blood O2 carrying capacity in 22 healthy men. Alveolar gas exchange was measured, and near-infrared spectroscopy (NIRS) was used to monitor relative concentration changes in oxy- (?[O2Hb]), 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 O2 carrying capacity [total hemoglobin mass (tHb-mass)] was determined with the CO-rebreathing method. In all tissues, NIPs coincided with AT, whereas RC was followed by NIPs. High tHb-mass associated with leg muscle deoxygenation at peak exercise (e.g., ?[HHb] from baseline walking to peak exercise vs. tHb-mass: r = 0.64, p < 0.01), but not with arm muscle- or cerebral deoxygenation. In conclusion, regional tissue oxygenation was characterized by inflection points, and tissue oxygenation in relation to alveolar gas exchange during incremental treadmill exercise resembled previous findings made during incremental cycling. It was also found out, that O2 delivery to less active m. biceps brachii may be limited by an accelerated increase in ventilation at high running intensities. In addition, high capacity for blood O2 carrying was associated with a high level of m. vastus lateralis deoxygenation at peak exercise. PMID:22934021

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

2012-01-01

112

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

1992-01-01

113

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

2008-01-01

114

Breaking Waves and Gas Exchange On Mechanically Driven Waves  

Microsoft Academic Search

We present experimental results on turbulence and the effects of breaking gravity waves on air-water exchange. The transition from singly connected to multiply connected standing waves is strongly dependent on the wave mode being excited. The excited state dictates the critical power flux into the fluid necessary for breaking waves to occur. Standing waves are excited in a cylindrical tank

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

1999-01-01

115

Compact Ceramic Heat Exchangers for Corrosive Waste Gas Applications  

E-print Network

Frequently the installed cost of metallic h t exchangers can be considerably increased by uch protective and control systems thereby obvia ir~ the initial advantages of reducir~ the recuPfrator costs. There is therefore a stror~ case to be put forward...

Laws, W. R.; Reed, G. R.

1982-01-01

116

Multiple modeling in the study of interaction of hemodynamics and gas exchange.  

PubMed

Circulation plays an important rule in gas exchange. Therefore, there is an interaction between circulation and gas exchange. To understand the dynamic effect of these two physiological systems, a computer simulation model of hemodynamics and gas exchange is established in this work. This model includes two physiological systems, namely the respiratory and circulatory systems. It consists of five parts: the model of gas transport, exchange and storage within the body, the multi-element nonlinear mathematical model of human circulatory system, an alveolar ventilation controller, a cardiac output controller, and a controller of breathing frequency. Model simulations provide results consistent with both dynamic and steady-state responses under hypoxia. Simulation results can reflect the interaction of hemodynamics and gas exchange. Using this model, the changes of pulmonary arterial pressure and right ventricular pressure in high altitude are studied. The optimal mode of breathing extra oxygen using nasal prongs or a facial mask is studied. This model may provide a useful tool to study reaction of hypoxia and the oxygen inhalation mode under hypoxia environments. PMID:11058694

Qiu, A; Bai, J

2001-01-01

117

Platelet sodium/hydrogen exchanger activity in normotensives and hypertensives.  

PubMed

Increased activity of sodium/hydrogen exchange provides a potentially important mechanism for the development of hypertension. The aims of this study were to compare platelet sodium/hydrogen exchanger activity and renal acid-base excretion in normotensives and hypertensives of Caucasian origin. Platelet intracellular pH (pHi) was measured using the fluorescent dye BCECF to monitor intracellular pH. Sodium/hydrogen exchanger activity was estimated from the recovery of pHi clamped to 6.25 with nigericin. Normotensives had supine blood pressures of < 140 and < 90 mmHg; those with essential hypertension had blood pressures > 150/95 mmHg with no known secondary cause. Measurements of platelet pHi and sodium/hydrogen exchanger activity were made on 26 normotensives (ten female, sixteen male) and 25 hypertensives (five female, twenty male). All subjects were on their usual dietary sodium intake. Statistical analysis was by two-way analysis of variance for gender and blood pressure status. Group values are expressed as means+/-SD and a P value of < 0.05 was taken as being statistically significant. There were no significant differences in platelet pHi between the normotensive (n = 26) and the hypertensive (n = 25) group: pHi 7.21+/-0.14 and 7.18+/-0.16, respectively. The pHi recovery after acidification was sodium-dependent and inhibited by N-hexamethylene amiloride. Comparison of kinetic constants showed no significant differences between the normotensive and the hypertensive groups: values for rate constants and initial velocities were 0.24+/-0.04 s(-1), 0.16+/-0.03 dpHi/s for the normotensives and 0.25+/-0.05 s(-1), 0.16+/-0.03 dpHi/s for the hypertensives, respectively; there were also no significant differences in proton fluxes. The inability to find raised platelet sodium/hydrogen exchanger in the hypertensives contrasts with previous observations using other methods for the measurement of this exchanger in platelets and this raises important methodological issues in the assessment of platelet sodium/hydrogen exchanger activity. PMID:10404735

Sagnella, G A; Miller, M A; Khong, T K; MacGregor, G A

1999-05-01

118

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

1978-01-01

119

Exchange and Correlation in the Strongly Inhomogeneous Electron Gas  

Microsoft Academic Search

Density functional theory (DFT) is the most popular quantum-mechanical technique used to study atoms, molecules and solids and the local density approximation (LDA) is the central approximation in practical applications of DFT. Using the variational quantum Monte Carlo method, in combination with a constrained variance minimization technique, we have calculated the central quantities in DFT: the exchange-correlation hole n_xc, the

Maziar Nekovee

2001-01-01

120

Catalytically active mass for the exchange of hydrogen isotopes between streams of gaseous hydrogen and liquid water  

SciTech Connect

For the exchange of hydrogen isotopes between streams of gaseous hydrogen and liquid water, wherein the streams are at a temperature in the range 273 to 573K are brought into contact with one another and a catalytically active mass, an improved catalytically active mass is provided comprising an inherently hydrophotic, porous, polytetrafluoroethylene matrix and partially platinized carbon particles dispersed throughout the whole of the porous polytetrafluoroethylene matrix in the weight ratio of 1:1 to 3:1 of polytetrafluoroethylene to partially platinized high surface area carbon particles. The inherently hydrophobic, porous , polytetrafluoroethylene matrix allows the catalytically active metal to catalyze the hydrogen isotope exchange reaction between hydrogen gas and water vapor in the presence of liquid water while retarding loss of activity of the catalytically active metal by contact of the metal catalyst with liquid water. This catalyzed chemical isotope exchange proceeds simultaneously with isotope exchange from water vapor to liquid water by a noncatalyzed, physical evaporation and condensation exchange reaction. The efficient coupling of these two isotopic transfer steps which results in a rapid overall isotopic exchange between hydrogen and liquid water without a pronounced loss of activity of the catalytically active mass is dependent upon the weight ratio of the catalytically active platinized carbon to the polytetrafluoroethylene matrix being in the above mentioned range of 1:1 to 3:1.

Butler, J.P.; Goodale, J.W.; Hartog, J.D.; Molson, F.W.; Rolston, J.H.

1980-10-14

121

Nonlocal Exchange-Correlation Potential for Inhomogeneous Electron Gas and Quantum Fluids  

Microsoft Academic Search

An exact but formal expression for the exchange-correlation potential muxc(r|n) for an inhomogeneous electron gas at arbitrary temperature is obtained in terms of the quantal direct correlation function (DCF) of the inhomogeneous system. By introducing the effective local density n*(r) and approximating it by the functional Taylor's series around a suitable density to first order, approximate exchange-correlation potentials are derived

Junzo Chihara

1978-01-01

122

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

1978-01-01

123

Recovery of Water from Boiler Flue Gas Using Condensing Heat Exchangers  

SciTech Connect

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

Edward Levy; Harun Bilirgen; John DuPoint

2011-03-31

124

Recovery of Water from Boiler Flue Gas Using Condensing Heat Exchangers  

SciTech Connect

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

Levy, Edward; Bilirgen, Harun; DuPont, John

2011-03-31

125

Heat exchanger design considerations for high temperature gas-cooled reactor (HTGR) plants  

SciTech Connect

Various aspects of the high-temperature heat exchanger conceptual designs for the gas turbine (HTGR-GT) and process heat (HTGR-PH) plants are discussed. Topics include technology background, heat exchanger types, surface geometry, thermal sizing, performance, material selection, mechanical design, fabrication, and the systems-related impact of installation and integration of the units in the prestressed concrete reactor vessel. The impact of future technology developments, such as the utilization of nonmetallic materials and advanced heat exchanger surface geometries and methods of construction, is also discussed.

McDonald, C.F.; Vrable, D.L.; Van Hagan, T.H.; King, J.H.; Spring, A.H.

1980-02-01

126

Quantum Monte Carlo Analysis of Exchange and Correlation in the Strongly Inhomogeneous Electron Gas  

SciTech Connect

We use the variational quantum Monte Carlo method to calculate the density-functional exchange-correlation hole n{sub xc} , the exchange-correlation energy density e{sub xc} , and the total exchange-correlation energy E{sub xc} of several strongly inhomogeneous electron gas systems. We compare our results with the local density approximation and the generalized gradient approximation. It is found that the nonlocal contributions to e{sub xc} contain an energetically significant component, the magnitude, shape, and sign of which are controlled by the Laplacian of the electron density.

Nekovee, Maziar; Foulkes, W. M. C.; Needs, R. J.

2001-07-16

127

Quantum Monte Carlo analysis of exchange and correlation in the strongly inhomogeneous electron gas.  

PubMed

We use the variational quantum Monte Carlo method to calculate the density-functional exchange-correlation hole n(xc), the exchange-correlation energy density e(xc), and the total exchange-correlation energy E(xc) of several strongly inhomogeneous electron gas systems. We compare our results with the local density approximation and the generalized gradient approximation. It is found that the nonlocal contributions to e(xc) contain an energetically significant component, the magnitude, shape, and sign of which are controlled by the Laplacian of the electron density. PMID:11461577

Nekovee, M; Foulkes, W M; Needs, R J

2001-07-16

128

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.

2000-07-19

129

Greenhouse gas exchange in tropical mountain ecosystems in Tanzania  

NASA Astrophysics Data System (ADS)

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

Gerschlauer, Friederike; Kikoti, Imani; Kiese, Ralf

2014-05-01

130

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

131

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.

2013-10-01

132

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

Microsoft Academic Search

We designed a small scale gas loop that can simulate reference operating conditions, that is, a temperature up to 950 deg C and a pressure up to 6 MPa. Main objective of the loop is to screen the candidate process-heat-exchanger designs of a very small capacity of 10 â 20 kW. We arranged the components of a primary gas loop

Hong SungDeok; Oh DongSeok; Lee WonJae; Chang JongHwa

2006-01-01

133

Comparative heat and gas exchange measurements in the Heidelberg Aeolotron, a large annular wind-wave tank  

NASA Astrophysics Data System (ADS)

A comparative study of simultaneous heat and gas exchange measurements was performed in the large annular Heidelberg Air-Sea Interaction Facility, the Aeolotron, under homogeneous water surface conditions. The use of two gas tracers, N2O and C2HF5, resulted not only in gas transfer velocities, but also in the measurement of the Schmidt number exponent n with a precision of ±0.025. The original controlled flux, or active thermographic, technique proposed by Jähne et al. (1989) was applied by heating a large patch at the water surface to measure heat transfer velocities. Heating a large patch, the active thermography technique is laterally homogeneous, and problems of lateral transport effects are avoided. Using the measured Schmidt number exponents, the ratio of the scaled heat transfer velocities to the measured gas transfer velocities is 1.046 ± 0.040, a good agreement within the limits of experimental uncertainties. This indicates the possibility to scale heat transfer velocities measured by active thermography to gas transfer velocities, provided that the Schmidt number exponent is known and that the heated patch is large enough to reach the thermal equilibrium.

Nagel, L.; Krall, K. E.; Jähne, B.

2015-01-01

134

Structural analyses of a constitutively active mutant of exchange protein directly activated by cAMP.  

PubMed

Exchange proteins directly activated by cAMP (EPACs) are important allosteric regulators of cAMP-mediated signal transduction pathways. To understand the molecular mechanism of EPAC activation, we have combined site-directed mutagenesis, X-ray crystallography, and peptide amide hydrogen/deuterium exchange mass spectrometry (DXMS) to probe the structural and conformational dynamics of EPAC2-F435G, a constitutively active EPAC2 mutant. Our study demonstrates that conformational dynamics plays a critical role in cAMP-induced EPAC activation. A glycine mutation at 435 position shifts the equilibrium of conformational dynamics towards the extended active conformation. PMID:23189173

White, Mark A; Li, Sheng; Tsalkova, Tamara; Mei, Fang C; Liu, Tong; Woods, Virgil L; Cheng, Xiaodong

2012-01-01

135

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

PubMed

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

2011-06-01

136

Gas Exchange Properties of Agronomic Crops: A Medley of Experimental Methodology and Results after 25 Years  

Technology Transfer Automated Retrieval System (TEKTRAN)

Alterations in biotic (i.e., water, nitrogen) and abiotic (i.e., light, temperature, [CO2], [O3]) conditions can significantly affect gas exchange properties of agronomic crops. Our objective was to elucidate mechanistic-based ecophysiological response of a broad range of agronomic crops to globa...

137

Respiratory Physiology & Neurobiology 154 (2006) 1829 Discontinuous gas exchange in insects  

E-print Network

Respiratory Physiology & Neurobiology 154 (2006) 18­29 Discontinuous gas exchange in insects, University of Nevada, Las Vegas, NV 89154, USA Accepted 7 April 2006 Abstract Insect respiratory physiology has been studied for many years, and interest in this area of insect biology has become revitalized

Ahmad, Sajjad

138

Cerebral autoregulation and gas exchange studied using a human cardiopulmonary model  

E-print Network

developed a model of the human cardiopulmonary (CP) system, which included the whole body circulatory system Dynamical Systems Group, Rice University, Houston 77005; 2 Baylor College of Medicine, Houston 77005; 3, lung and peripheral tissue gas exchange, and the central nervous system control of arterial pressure

139

A STAGE-BASED STUDY OF DROUGHT RESPONSE IN CRYPTANTHA FLAVA (BORAGINACEAE): GAS EXCHANGE, WATER USE  

E-print Network

A STAGE-BASED STUDY OF DROUGHT RESPONSE IN CRYPTANTHA FLAVA (BORAGINACEAE): GAS EXCHANGE, WATER USE in the frequency of major droughts, yet we know little about the consequences of drought for the demography (Boraginaceae) to determine how plants of different developmental stages respond to drought through changes

Wait, D. Alexander

140

The Multifunctional Fish Gill: Dominant Site of Gas Exchange, Osmoregulation, Acid-Base Regulation, and  

E-print Network

The Multifunctional Fish Gill: Dominant Site of Gas Exchange, Osmoregulation, Acid-Base Regulation, Maine I. Introduction 98 II. Evolutionary Origin and External Structure 98 A. Gills of protovertebrates and modern fishes 98 B. External structure of fish gills 99 III. Internal Structure: Vascular and Neural 109

Evans, David H.

141

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

PubMed

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

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

2014-12-01

142

Hydraulic Properties of Rice and the Response of Gas Exchange to Water Stress1  

E-print Network

Hydraulic Properties of Rice and the Response of Gas Exchange to Water Stress1 Volker Stiller*, H.R.L.) We investigated the role of xylem cavitation, plant hydraulic conductance, and root pressure-specific photosynthetic rate, leaf diffusive conductance, and soil-leaf hydraulic conductance that were associated

Stiller, Volker

143

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

E-print Network

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

Federspiel, William J.

144

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

NASA Technical Reports Server (NTRS)

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

Zorya, L. V.

1980-01-01

145

EFFECT OF GIRDLING ON GAS EXCHANGES AND LEAF MINERAL CONTENT IN THE “INDEPENDENCE” NECTARINE  

Microsoft Academic Search

The aim of this work was to analyze the physiological modifications induced by girdling, and to evaluate their effects on the gas exchanges and mobility of the mineral elements in peach leaves. On 15 trees, sixty 1-yr-old shoots were chosen, thirty of which were girdled (a ring of bark 1 cm thick was removed), and 30 were used as control.

C. Di Vaio; A. Petito; M. Buccheri

2001-01-01

146

Modeling bronchial circulation with application to soluble gas exchange: description and sensitivity analysis  

E-print Network

of ethanol ( blood 1,756 at 37°C) in the airways depends on the blood flow rate from the bronchial that range from low solubility, such as sulfurhexafluo- ride or helium ( blood 0.01), to high solubility; pulmonary circulation; airways GAS EXCHANGE EFFICIENCY is extremely dependent on the blood solubility

George, Steven C.

147

ACCENTUATION OF GAS EXCHANGE GRADIENTS IN FLUSHES OF PONDEROSA PINE EXPOSED TO OZONE  

EPA Science Inventory

Patterns of O3 injury have been positively correlated with leaf age in deciduous trees and needle age-classes in conifers. his study was designed to determine the patterns of gas exchange within and between needle flushes and to determine how O3 affects those patterns. esults wil...

148

Response of shoot growth and gas exchange of Picea abies clones to rain acidity  

E-print Network

Response of shoot growth and gas exchange of Picea abies clones to rain acidity and the addition, particularly the effect of acidity and the addition of a realistic ionic mixture to simulated acidic.0 with a mixture of sulfuric and nitric acids (S02-/NO-weight ratio = 2.4). Ionic concentrations m mg/1were: 4.50 S

Paris-Sud XI, Université de

149

Investigating the Effects of Random Balloon Pulsation on Gas Exchange in a Respiratory Assist Catheter  

E-print Network

Investigating the Effects of Random Balloon Pulsation on Gas Exchange in a Respiratory Assist-fiber membranes wrapped around a pul- sating balloon that increases oxygenation and CO2 removal with increased balloon pulsation. Our current pulsation sys- tem operates with a constant rate of pulsation and delivered

Federspiel, William J.

150

Falling through the cracks: The role of fractures in Earth-atmosphere gas exchange  

E-print Network

by blocking soil pores with water [Riveros-Iregui et al., 2007]. Historically, the process of gas exchange], but enhanced to shallow depths by advective trans- port driven by wind and atmospheric pressure fluctuations enhanced drying was never elucidated. Moreover, it has been observed that salt crust accumulation within

Weisbrod, Noam

151

Gradient Corrections in the Exchange and Correlation Energy of an Inhomogeneous Electron Gas  

Microsoft Academic Search

An exact result is derived for the coefficient Bxc which determines the first gradient corrections to the exchange and correlation energy of an inhomogeneous electron gas. A method of approximation, which is based on the random-phase approximation and is exact at high density, is given for the explicit evaluation of Bxc. Numerical results are also given for the metallic density

M. Rasolt; D. J. W. Geldart

1975-01-01

152

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

NASA Technical Reports Server (NTRS)

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

Corey, Kenneth A.; Wheeler, Raymond M.

1992-01-01

153

Inhibition by light of CO 2 evolution from dark respiration: Comparison of two gas exchange methods  

Microsoft Academic Search

Two approaches to determine the fraction (?) of mitochondrial respiration sustained during illumination by measuring CO2 gas exchange are compared. In single leaves, the respiration rate in the light (`day respiration' rate Rd) is determined as the ordinate of the intersection point of A–ci curves at various photon flux densities and compared with the CO2 evolution rate in darkness (`night

Martin Peisker; Hannelore Apel

2001-01-01

154

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

1999-01-01

155

Gas-exchange patterns of Mediterranean fruit fly Pupae (Diptera: Tephritidae): A tool to forecast developmental stage  

Microsoft Academic Search

The pattern of gas-exchange (COâ emission) was investigated for developing Mediterranean fruit fly (medfly) Ceratitis capitata (Wiedemann) pupae incubated at different temperatures. This study was undertaken to explore the usefulness of gas-exchange systems in the determination of physiological age in developing pupae that are mass produced for sterile insect technique projects. The rate of COâ emission was measured in a

D. Nestel; E. Nemny-Lavy; V. Alchanatis

2007-01-01

156

Development and Evaluation of a Coupled Photosynthesis-Based Gas Exchange Evapotranspiration Model (GEM) for Mesoscale Weather Forecasting Applications  

E-print Network

Development and Evaluation of a Coupled Photosynthesis-Based Gas Exchange Evapotranspiration Model with a photosynthesis-based scheme and still achieve dynamically consistent results. To demonstrate this transformative potential, the authors developed and coupled a photosynthesis, gas exchange­based surface evapotranspiration

Niyogi, Dev

157

Nitrogen nutrition and water stress effects on leaf photosynthetic gas exchange and water use efficiency in winter wheat  

Microsoft Academic Search

The responses of gas exchange and water use efficiency to nitrogen nutrition for winter wheat were investigated under well-watered and drought conditions. The photosynthetic gas exchange parameters of winter wheat are remarkably improved by water and nitrogen nutrition and the regulative capability of nitrogen nutrition is influenced by water status. The effects of nitrogen nutrition on photosynthetic characteristics and on

Z. P. Shangguan; M. A. Shao; J. Dyckmans

2000-01-01

158

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.

2004-01-01

159

Seasonal differences in needle gas exchange between mature branches and seedlings of Pinus ponderosa  

SciTech Connect

In 1990, an interactive study was initiated to understand the differing physiological and morphological response of mature tissue and seedling tissue to stress. The study was conducted at the Air Pollution and Climate Change Exposure Facility in a Pinus ponderosa seed production orchard at the US Forest Service Tree Improvement Center in Chico, CA. The orchard consists of clonal trees and the authors have planted half-sibling seedlings which correspond to the mature clones which were measured. Both the mature trees and seedlings were regularly irrigated and fertilized. The result is that they have minimized the genetic and environmental differences that might otherwise influence the physiological differences between mature and seedling tissue. One of the physiological parameters which was measured was seasonal and diurnal gas exchange using a LICOR 6200. They measured gas exchange in November 1989, March, July, and October 1990. They found that throughout the year, all gas exchange components (eg. photosynthesis, transpiration, stomatal conductance) were significantly greater for seedling tissue. Photosynthetic differences were greater during early October, with diurnal mean rates of 1.1 {mu}mol m{sup {minus}2}s{sup {minus}1} and 0.5 {mu}mol m{sup {minus}2}s{sup {minus}1} for seedling and mature tissue, respectively. Transpiration differences were greater during early October, with diurnal mean rates of 2.2 mmol m{sup {minus}2}2{sup {minus}1} and 1.2 mmol m{sup {minus}2}s{sup {minus}1} for seedling and mature tissue, respectively. Finally, gas exchange differences between seedling and mature tissue were greater for current needles than one-year old needles. The results of this study demonstrate that gas exchange differences between seedling and mature tissue observed in the field may be the result of inherent physiological differences, and not merely genetic and environmental differences.

Houpis, J.L.J.; Anderson, P.D. (Lawrence Livermore National Lab., CA (United States))

1991-05-01

160

The dynamics of gas-surface energy exchange in collisions rare gases with organic surfaces  

NASA Astrophysics Data System (ADS)

This presentation will focus on recent experiments that combine molecular beam scattering techniques with self-assembled monolayers (SAMs) to probe the relative importance of surface mass, atomic-scale roughness, and molecular rigidity in controlling the dynamics of gas-surface energy exchange. Specifically, SAMs of carbonyl-containing alkanethiols on gold are employed to explore the influence of hydrogen-bonding interactions in gas-surface energy exchange and accommodation. H-bonding, COOH-terminated SAMs are found to produce more impulsive scattering and less thermal accommodation than non-H-bonding, ester-terminated monolayers. For carbamate-functionalized SAMs, impulsive scattering decreases and accommodation increases as the H-bonding group is positioned further below the terminal methyl group. These results are beginning to provide some insight into the importance of surface characteristics in determining the outcome of gas-surface collisions on organic thin films.

Day, Scott; Ferguson, Melinda; Morris, John

2004-03-01

161

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. PMID:21224337

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

2011-01-01

162

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

NASA Technical Reports Server (NTRS)

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

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

1974-01-01

163

EXCHANGE  

SciTech Connect

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

Boltz, J.C. (ed.)

1992-09-01

164

Accurate Homogeneous Electron Gas Exchange-Correlation Free Energy for Local Spin-Density Calculations  

NASA Astrophysics Data System (ADS)

An accurate analytical parametrization for the exchange-correlation free energy of the homogeneous electron gas, including interpolation for partial spin polarization, is derived via thermodynamic analysis of recent restricted path integral Monte Carlo (RPIMC) data. This parametrization constitutes the local spin density approximation (LSDA) for the exchange-correlation functional in density functional theory. The new finite-temperature LSDA reproduces the RPIMC data well, satisfies the correct high-density and low- and high-T asymptotic limits, and is well behaved beyond the range of the RPIMC data, suggestive of broad utility.

Karasiev, Valentin V.; Sjostrom, Travis; Dufty, James; Trickey, S. B.

2014-02-01

165

Gas exchange in Paulownia species growing under different soil moisture conditions in the field.  

PubMed

In order to evaluate their responses to drought, we determined the photosynthetic activity water potential, stomatal conductance, transpiration, water use efficiency photosynthetic photon flux density and leaf temperature of Paulownia imperialis, P. fortunei and P. elongata in three different soil moisture conditions in the field. Our results showed that P. imperialis had greater photosynthesis (8.86 micromol CO2 m(-2) s(-1)) and instantaneous water use efficiency (0.79 micromol CO2 mmol H2O(-1)) than either P. elongata (8.20 micromol CO2 m(-2) s(-1) and 0.71 micromol CO2 mmol H2O(-1)) or P. fortunei (3.26 micromol CO2 m(-2) s(-1) and 0.07 micromol CO2 mmol H2O(-1)). The rapid growth of Paulownia did not appear to be correlated with photosynthetic rates. Paulownia fortunei showed more transpiration (48.78 mmol H2O m(-2) s(-1)) and stomatal conductance (840 mmol m(-2) s(-1)) than P. imperialis (20 mmol H2O m(-2) s(-1) and 540 mmol m(-2) s(-1)) and P. elongata (20 mmol H2O m(-2) s(-1) and 410 mmol m(-2) s(-1)), which allowed these two Paulownia species to increase their tolerance to low soil moisture, and maintain higher water use efficiency under these conditions. According to our physiological gas exchange field tests, Paulownia imperialis does appear to be capable of successful growth in semiarid zones. PMID:21186726

Llano-Sotelo, J M; Alcaraz-Melendez, L; Castellanos Villegas, A E

2010-07-01

166

Rapid hydraulic recovery in Eucalyptus pauciflora after drought: linkages between stem hydraulics and leaf gas exchange.  

PubMed

In woody plants, photosynthetic capacity is closely linked to rates at which the plant hydraulic system can supply water to the leaf surface. Drought-induced embolism can cause sharp declines in xylem hydraulic conductivity that coincide with stomatal closure and reduced photosynthesis. Recovery of photosynthetic capacity after drought is dependent on restored xylem function, although few data exist to elucidate this coordination. We examined the dynamics of leaf gas exchange and xylem function in Eucalyptus pauciflora seedlings exposed to a cycle of severe water stress and recovery after re-watering. Stomatal closure and leaf turgor loss occurred at water potentials that delayed the extensive spread of embolism through the stem xylem. Stem hydraulic conductance recovered to control levels within 6?h after re-watering despite a severe drought treatment, suggesting an active mechanism embolism repair. However, stomatal conductance did not recover after 10?d of re-watering, effecting tighter control of transpiration post drought. The dynamics of recovery suggest that a combination of hydraulic and non-hydraulic factors influenced stomatal behaviour post drought. PMID:23937187

Martorell, Sebastià; Diaz-Espejo, Antonio; Medrano, Hipólito; Ball, Marilyn C; Choat, Brendan

2014-03-01

167

Gas Exchange and Phytoluminography of Single Red Kidney Bean Leaves during Periods of Induced Stomatal Oscillations  

PubMed Central

This report examines the capabilities of a new approach to the study of gas exchange and electron transport properties of single, intact leaves. The method combines conventional aspects of analysis with an image intensification system that records the spatial distribution of delayed light emission (DLE) over single leaf surfaces. The combined system was used to investigate physiological perturbations induced by exposure of single leaves of Phaseolus vulgaris cv `California Light Red' to a combination of SO2 (0.5 microliters per liter) and ozone (0.1 microliters per liter). Exposure of one-half of a leaf to this combination induced DLE and stomatal oscillations, but only in the half of the leaf exposed to the combined gases. Examination of phytoluminographs taken during these oscillations revealed distinct leaf patches where the greatest changes in DLE intensity occurred. This phenomenon is interpreted to be evidence that control of stomatal activity of intact plant leaves occurs within discrete leaf areas defined within the vascular network. Images Fig. 6 PMID:16662989

Ellenson, James L.; Raba, Richard M.

1983-01-01

168

Cryogenic Heat-Exchanger Design for Freeze-out Removal of Carbon Dioxide from Landfill Gas  

NASA Astrophysics Data System (ADS)

A cryogenic heat exchanger to remove carbon dioxide from landfill gas (LFG) is proposed and designed for applications to LNG production in distributed-scale. Since the major components of LFG are methane and carbon dioxide, CO2 removal is a significant pre-process in the liquefaction systems. A new and simple approach is proposed to directly remove carbon dioxide as frost on the surface wall along the cooling passage in a liquefying heat exchanger and to install two identical heat exchangers in parallel for alternative switching. As a first step of feasibility study, combined heat and mass transfer analysis is performed on the freeze-out process of CO2 in a counterflow heat exchanger, where CH4-CO2 mixture is cooled below its frost temperature in thermal contact with cold refrigerant. Engineering correlations for the analogy of heat and mass transfer are incorporated into numerical heat exchanger analysis with detailed fluid properties. The developed analytical model is used to estimate the distribution of CO2 accumulation and the required heat exchanger size with latent thermal load for the cryogenic CO2 removal in various operating conditions.

Chang, Ho-Myung; Chung, Myung Jin; Park, Seong Bum

169

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

NASA Astrophysics Data System (ADS)

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

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

2008-09-01

170

Gas-exchange properties of developing cotton fruit  

SciTech Connect

Field studies were conducted to document the photosynthetic and respiratory properties of cotton (Gossypium hirsutum L.) fruit during ontogeny. Dark respiration by the developing boll averaged {minus}18.7 {mu}mol per meter squared per second for the first six days after anthesis and gradually declined to less than 16% of this value after 40 days. Diurnal patterns of respiration were age dependent and closely correlated with stomatal conductance of the capsule wall. Stomata of young fruit were highly responsive to diurnal signals but lost this capacity with increasing age. Radio-labeled carbon dioxide injected into the fruit was rapidly assimilated by the outer capsule wall in the light, while fiber and seed fixed significant carbon-14 activity in both the light and dark. These data indicate that cotton fruit are sites of carbon dioxide evolution, but also serve a role in the reassimilation of carbon dioxide and thereby, function as important sources of assimilate for reproductive development.

Wullschleger, S.D.; Oosterhuis, D.M. (Univ. of Arkansas, Fayetteville (USA))

1990-05-01

171

Dust and gas in active galaxies  

NASA Astrophysics Data System (ADS)

There are strong evidences which favour the existence of dust in active galaxies. Understanding the way in which dust interacts with the radiation and influences the physical conditions of the gas is crucial if we want to learn about the nature of the central active nucleus and about the physical conditions of the ISM in such galaxies. Not taking into account such effects may lead us towards misleading interpretations. Many intriguing questions concerns to the nature and the existence of dust in active galaxies: for instance, under which conditions does the very hard ionizing continuum of an AGN allows the survival of dust grains? Is the composition and size distribution of the dust the same as in our local interstellar medium? How is dust distributed compared to the gas which is at least in part highly ionized by the central AGN? Does dust also exist in radio galaxies at very high redshifts? The work developed in this thesis tries to find answers to some of these questions, through a detailed theoretical and observational research of the mechanisms which control the interaction of dust with the radiation and with the ions. The observable effects of the dust on the emission line spectrum are also analyzed in detail. The final goal has been to give clues about more general questions: origin of the emitting gas, ionization mechanisms, geometry, connection between low and high redshift active galaxies or the validity of the unification scenario. This thesis tries, in summary, to provide a clearer understanding of active galaxies in general.

Villar-Martin, Montserrat

172

The Effect of Thermal Convection on Earth-Atmosphere CO2 Gas Exchange in Aggregated Soil  

NASA Astrophysics Data System (ADS)

Gas transport in soils and surface-atmosphere gas exchange are important processes that affect different aspects of soil science such as soil aeration, nutrient bio-availability, sorption kinetics, soil and groundwater pollution and soil remediation. Diffusion and convection are the two main mechanisms that affect gas transport, fate and emissions in the soils and in the upper vadose zone. In this work we studied CO2 soil-atmosphere gas exchange under both day-time and night-time conditions, focusing on the impact of thermal convection (TCV) during the night. Experiments were performed in a climate-controlled laboratory. One meter long columns were packed with matrix of different grain size (sand, gravel and soil aggregates). Air with 2000 ppm CO2 was injected into the bottom of the columns and CO2 concentration within the columns was continuously monitored by an Infra Red Gas Analyzer. Two scenarios were compared for each soil: (1) isothermal conditions, representing day time conditions; and (2) thermal gradient conditions, i.e., atmosphere colder than the soil, representing night time conditions. Our results show that under isothermal conditions, diffusion is the major mechanism for surface-atmosphere gas exchange for all grain sizes; while under night time conditions the prevailing mechanism is dependent on the air permeability of the matrix: for sand and gravel it is diffusion, and for soil aggregates it is TCV. Calculated CO2 flux for the soil aggregates column shows that the TCV flux was three orders of magnitude higher than the diffusive flux.

Ganot, Y.; Weisbrod, N.; Dragila, M. I.

2011-12-01

173

Adsorbed natural gas storage with activated carbon  

SciTech Connect

Despite technical advances to reduce air pollution emissions, motor vehicles still account for 30 to 70% emissions of all urban air pollutants. The Clean Air Act Amendments of 1990 require 100 cities in the United States to reduce the amount of their smog within 5 to 15 years. Hence, auto emissions, the major cause of smog, must be reduced 30 to 60% by 1998. Natural gas con be combusted with less pollutant emissions. Adsorbed natural gas (ANG) uses adsorbents and operates with a low storage pressure which results in lower capital costs and maintenance. This paper describes the production of an activated carbon adsorbent produced from an Illinois coal for ANG.

Sun, Jian; Brady, T.A.; Rood, M.J. [Univ. of Illinois, Urbana, IL (United States)] [and others

1996-12-31

174

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

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

175

Short-range exchange-correlation energy of a uniform electron gas with modified electron-electron interaction  

E-print Network

-correlation energy of the uniform electron gas to the inhomogeneous system of interest. Actually, it is been realized-correlation energy of the uniform electron gas must not be transferred to inhomogeneous systems. Guided by the sameShort-range exchange-correlation energy of a uniform electron gas with modified electron-electron

Paris-Sud XI, Université de

176

Exact-exchange density-functional theory applied to a strongly inhomogeneous electron gas  

Microsoft Academic Search

A recently developed quasi two-dimensional exact-exchange formalism within\\u000athe framework of Density Functional Theory has been applied to a strongly\\u000ainhomogeneous interacting electron gas, and the results were compared with\\u000astate-of-the-art Variational Quantum Monte Carlo (VMC) numerical simulations\\u000afor a three-dimensional electron gas under a strong external potential. The VMC\\u000aresults, extremely demanding from the computational point of view, could

S. Rigamonti; F. A. Reboredo; C. R. Proetto

2003-01-01

177

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

USGS Publications Warehouse

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

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

2014-01-01

178

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

179

Impairment of gas exchange and structure in birch leaves ( Betula pendula ) caused by low ozone concentrations  

Microsoft Academic Search

Injury caused by low O3 concentrations (0, 0.05, 0.075, 0.1 µl 1-1) was analyzed in the epidermis and mesophyll of fully developed birch leaves by gas exchange experiments and low-temperature SEM: (I) after leaf formation in O3-free and ozonated air, and (II) after transferring control plants into ozonated air. In control leaves, autumnal senescence also was studied in O3-free air

Rainer Matyssek; Madeleine S. Giinthardt-Goerg; Theodor Keller; Christoph Scheidegger

1991-01-01

180

Gas Exchange and Water Use Efficiency of Three Native Tree Species in Hunshandak Sandland of China  

Microsoft Academic Search

Only three tree species, i.e. Ulmus pumila, Malus baccata, and Prunus padus, are distributed in Hunshandak Sandland (HS) in Inner Mongolia, China. Field studies of gas exchange and chlorophyll (Chl)\\u000a fluorescence of these three tree species were conducted in three arid periods of growth season 2002. Net photosynthetic rate\\u000a (P\\u000a N), transpiration rate (E), stomatal conductance (g\\u000a s), and Fv\\/Fm

Y. G. Li; G. M. Jiang; S. L. Niu; M. Z. Liu; Y. Peng; S. L. Yu; L. M. Gao

2003-01-01

181

Factors affecting the performances of sprayed chromium carbide coatings for gas-cooled reactor heat exchangers  

Microsoft Academic Search

The paper discusses some important factors to be considered for using sprayed coatings in gas-cooled reactor heat exchangers. These factors include (a) high-temperature gaseous corresion, (b) thermal stability of coatings, (c) metallurgical compatibility between the coating and substrate, and (d) effects of the coating on the mechanical properties of the substrate alloy. The coatings evaluated were CrâCâ--NiCr and CrââCâ--NiCr applied

G. Lai

1979-01-01

182

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

USGS Publications Warehouse

We determined how different hydroperiods affected leaf gas exchange characteristics of greenhouse-grown seedlings (2002) and saplings (2003) of the mangrove species Avicennia germinans (L.) Stearn., Laguncularia racemosa (L.) Gaertn. f., and Rhizophora mangle L. Hydroperiod treatments included no flooding (unflooded), intermittent flooding (intermittent), and permanent flooding (flooded). Plants in the intermittent treatment were measured under both flooded and drained states and compared separately. In the greenhouse study, plants of all species maintained different leaf areas in the contrasting hydroperiods during both years. Assimilation-light response curves indicated that the different hydroperiods had little effect on leaf gas exchange characteristics in either seedlings or saplings. However, short-term intermittent flooding for between 6 and 22 days caused a 20% reduction in maximum leaf-level carbon assimilation rate, a 51% lower light requirement to attain 50% of maximum assimilation, and a 38% higher demand from dark respiration. Although interspecific differences were evident for nearly all measured parameters in both years, there was little consistency in ranking of the interspecific responses. Species by hydroperiod interactions were significant only for sapling leaf area. In a field study, R. mangle saplings along the Shark River in the Everglades National Park either demonstrated no significant effect or slight enhancement of carbon assimilation and water-use efficiency while flooded. We obtained little evidence that contrasting hydroperiods affect leaf gas exchange characteristics of mangrove seedlings or saplings over long time intervals; however, intermittent flooding may cause short-term depressions in leaf gas exchange. The resilience of mangrove systems to flooding, as demonstrated in the permanently flooded treatments, will likely promote photosynthetic and morphological adjustment to slight hydroperiod shifts in many settings. ?? 2006 Heron Publishing.

Krauss, K.W.; Twilley, R.R.; Doyle, T.W.; Gardiner, E.S.

2006-01-01

183

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

2007-01-01

184

Detection of disturbances in pulmonary gas exchanges during exercise from arterialized earlobe P O 2  

Microsoft Academic Search

Blood sampling from the arterialized earlobe is widely used in clinical exercise testing but Fajac et al. (1998) (Eur. Respir. J. 11, 712–715) have shown that arterialized PO2(PcCO2) is not a valid surrogate for PaO2. In the present study, in order to detect disturbances in pulmonary gas exchanges during clinical exercise testing from the alveolar-arterial gradient of PO2 (P[Ai­a]O2), a

Bernard Aguilaniu; Jocelyne Maitre; Samia Diab; Hélène Perrault; François Péronnet

2011-01-01

185

Effects of the Prone Position on Respiratory Mechanics and Gas Exchange during Acute Lung Injury  

Microsoft Academic Search

We studied 16 patients with acute lung injury receiving volume-controlled ventilation to assess the relationships between gas exchange and respiratory mechanics before, during, and after 2 h in the prone position. We measured the end-expiratory lung volume (EELV, helium dilution), the total respi- ratory system (Cst,rs), the lung (Cst,L) and the thoracoabdominal cage (Cst,w) compliances (end- inspiratory occlusion technique and

PAOLO PELOSI; DANIELA TUBIOLO; DANIELE MASCHERONI; PIERLUIGI VICARDI; STEFANIA CROTTI; FRANCO VALENZA; LUCIANO GATTINONI

1998-01-01

186

Exact-Exchange Density Functional Theory applied to a strongly inhomogeneous electron gas  

Microsoft Academic Search

A recently developed quasi two-dimensional exact-exchange formalism within the framework of Density Functional Theory has been applied to a strongly inhomogeneous interacting electron gas, and the results compared with state-of-the-art Variational Quantum Monte Carlo (VMC) numerical simulations for the same system. These latter results, extremely demanding from the computational point of view, could be considered as a benchmark for the

Santiago Rigamonti; Fernando A. Reboredo; Cesar R. Proetto

2003-01-01

187

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

Microsoft Academic Search

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

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

2010-01-01

188

Exchange and correlation energy of an inhomogeneous electron gas at metallic densities  

Microsoft Academic Search

A convenient expression is derived for the coefficient, Bxc(n), which determines the first gradient corrections to the exchange and correlation energy of an inhomogeneous electron gas. The result is exact to all orders in e2 and is expressed in terms of a single-particle propagator. The lowest-order contributions to Bxc are evaluated without the simplifying high-density approximation. The formal structure of

D. J. W. Geldart; M. Rasolt

1976-01-01

189

Exact Dynamical Exchange-Correlation Kernel of a Weakly Inhomogeneous Electron Gas  

Microsoft Academic Search

The dynamical exchange-correlation kernel fxc of a nonuniform electron gas is an essential input for the time-dependent density-functional theory of electronic systems. The long-wavelength behavior of this kernel is known to be of the form fxc=alpha\\/q2 where q is the wave vector and alpha is a frequency-dependent coefficient. We show that in the limit of weak nonuniformity the coefficient alpha

V. U. Nazarov; G. Vignale; Y.-C. Chang

2009-01-01

190

Enhanced gas-phase hydrogen-deuterium exchange of oligonucleotide and protein ions stored in an external multipole ion reservoir.  

PubMed

Rapid gas-phase hydrogen-deuterium (H-D) exchange from D(2)O and ND(3) into oligonucleotide and protein ions was achieved during storage in a hexapole ion reservoir. Deuterated gas is introduced through a capillary line that discharges directly into the low-pressure region of the reservoir. Following exchange, the degree of H-D exchange is determined using Fourier transform ion cyclotron resonance mass spectrometry. Gas-phase H-D exchange experiments can be conducted more than 100 times faster than observed using conventional in-cell exchange protocols that require lower gas pressures and additional pump-down periods. The short experimental times facilitate the quantitation of the number of labile hydrogens for less reactive proteins and structured oligonucleotides. For ubiquitin, we observe approximately 65 H-D exchanges after 20 s. Exchange rates of > 250 hydrogens s(-1) are observed for oligonucleotide ions when D(2)O or ND(3) is admitted directly into the external ion reservoir owing to the high local pressure in the hexapole. Partially deuterated oligonucleotide ions have been fragmented in the reservoir using infrared multiphoton dissociation (IRMPD). The resulting fragment ions show that exchange predominates at charged sites on the 5'- and 3'-ends of the oligonucleotide, whereas exchange is slower in the core. This hardware configuration is independent of the mass detector and should be compatible with other mass spectrometric platforms including quadrupole ion trap and time-of-flight mass spectrometers. PMID:10633235

Hofstadler, S A; Sannes-Lowery, K A; Griffey, R H

2000-01-01

191

Modulating the light environment with the peach ‘asymmetric orchard’: effects on gas exchange performances, photoprotection, and photoinhibition  

PubMed Central

The productivity of fruit trees is a linear function of the light intercepted, although the relationship is less tight when greater than 50% of available light is intercepted. This paper investigates the management of light energy in peach using the measurement of whole-tree light interception and gas exchange, along with the absorbed energy partitioning at the leaf level by concurrent measurements of gas exchange and chlorophyll fluorescence. These measurements were performed on trees of a custom-built ‘asymmetric’ orchard. Whole-tree gas exchange for north–south, vertical canopies (C) was similar to that for canopies intercepting the highest irradiance in the morning hours (W), but trees receiving the highest irradiance in the afternoon (E) had the highest net photosynthesis and transpiration while maintaining a water use efficiency (WUE) comparable to the other treatments. In the W trees, 29% and 8% more photosystems were damaged than in C and E trees, respectively. The quenching partitioning revealed that the non-photochemical quenching (NPQ) played the most important role in excess energy dissipation, but it was not fully active at low irradiance, possibly due to a sub-optimal trans-thylakoid ?pH. The non-net carboxylative mechanisms (NC) appeared to be the main photoprotective mechanisms at low irradiance levels and, probably, they could facilitate the establishment of a trans-thylakoid ?pH more appropriate for NPQ. These findings support the conclusion that irradiance impinging on leaves may be excessive and can cause photodamage, whose repair requires energy in the form of carbohydrates that are thereby diverted from tree growth and productivity. PMID:20124356

Losciale, Pasquale; Chow, Wah Soon; Corelli Grappadelli, Luca

2010-01-01

192

Modulating the light environment with the peach 'asymmetric orchard': effects on gas exchange performances, photoprotection, and photoinhibition.  

PubMed

The productivity of fruit trees is a linear function of the light intercepted, although the relationship is less tight when greater than 50% of available light is intercepted. This paper investigates the management of light energy in peach using the measurement of whole-tree light interception and gas exchange, along with the absorbed energy partitioning at the leaf level by concurrent measurements of gas exchange and chlorophyll fluorescence. These measurements were performed on trees of a custom-built 'asymmetric' orchard. Whole-tree gas exchange for north-south, vertical canopies (C) was similar to that for canopies intercepting the highest irradiance in the morning hours (W), but trees receiving the highest irradiance in the afternoon (E) had the highest net photosynthesis and transpiration while maintaining a water use efficiency (WUE) comparable to the other treatments. In the W trees, 29% and 8% more photosystems were damaged than in C and E trees, respectively. The quenching partitioning revealed that the non-photochemical quenching (NPQ) played the most important role in excess energy dissipation, but it was not fully active at low irradiance, possibly due to a sub-optimal trans-thylakoid DeltapH. The non-net carboxylative mechanisms (NC) appeared to be the main photoprotective mechanisms at low irradiance levels and, probably, they could facilitate the establishment of a trans-thylakoid DeltapH more appropriate for NPQ. These findings support the conclusion that irradiance impinging on leaves may be excessive and can cause photodamage, whose repair requires energy in the form of carbohydrates that are thereby diverted from tree growth and productivity. PMID:20124356

Losciale, Pasquale; Chow, Wah Soon; Corelli Grappadelli, Luca

2010-02-01

193

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. PMID:17114276

Franks, Peter J.; Farquhar, Graham D.

2007-01-01

194

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

PubMed

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

2007-01-01

195

Breathe softly, beetle: continuous gas exchange, water loss and the role of the subelytral space in the tenebrionid beetle, Eleodes obscura.  

PubMed

Flightless, diurnal tenebrionid beetles are commonly found in deserts. They possess a curious morphological adaptation, the subelytral cavity (an air space beneath the fused elytra) the function of which is not completely understood. In the tenebrionid beetle Eleodes obscura, we measured abdominal movements within the subelytral cavity, and the activity of the pygidial cleft (which seals or unseals the subelytral cavity), simultaneously with total CO2 release rate and water loss rate. First, we found that E. obscura has the lowest cuticular permeability measured in flow-through respirometry in an insect (0.90 microg H2O cm(-2) Torr(-1) h(-1)). Second, it does not exhibit a discontinuous gas exchange cycle. Third, we describe the temporal coupling between gas exchange, water loss, subelytral space volume, and the capacity of the subelytral space to exchange gases with its surroundings as indicated by pygidial cleft state. Fourth, we suggest possible mechanisms that may reduce respiratory water loss rates in E. obscura. Finally, we suggest that E. obscura cannot exchange respiratory gases discontinuously because of a morphological constraint (small tracheal or spiracular conductance). This "conductance constraint hypothesis" may help to explain the otherwise puzzling phylogenetic patterns of continuous vs. discontinuous gas exchange observed in tracheate arthropods. PMID:17936295

Schilman, Pablo E; Kaiser, Alexander; Lighton, John R B

2008-01-01

196

Plant Water Use Efficiency over Geological Time – Evolution of Leaf Stomata Configurations Affecting Plant Gas Exchange  

PubMed Central

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

2013-01-01

197

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

SciTech Connect

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

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

2000-07-13

198

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

PubMed

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

2012-08-01

199

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.

200

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

NASA Astrophysics Data System (ADS)

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

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

201

Effect of a patent foramen ovale on pulmonary gas exchange efficiency at rest and during exercise  

PubMed Central

The prevalence of a patent foramen ovale (PFO) is ?30%, and this source of right-to-left shunt could result in greater pulmonary gas exchange impairment at rest and during exercise. The aim of this work was to determine if individuals with an asymptomatic PFO (PFO+) have greater pulmonary gas exchange inefficiency at rest and during exercise than subjects without a PFO (PFO?). Separated by 1 h of rest, 8 PFO+ and 8 PFO? subjects performed two incremental cycle ergometer exercise tests to voluntary exhaustion while breathing either room air or hypoxic gas [fraction of inspired O2 (FiO2) = 0.12]. Using echocardiography, we detected small, intermittent boluses of saline contrast bubbles entering directly into the left atrium within 3 heart beats at rest and during both exercise conditions in PFO+. These findings suggest a qualitatively small intracardiac shunt at rest and during exercise in PFO+. The alveolar-to-arterial oxygen difference (AaDo2) was significantly (P < 0.05) different between PFO+ and PFO? in normoxia (5.9 ± 5.1 vs. 0.5 ± 3.5 mmHg) and hypoxia (10.1 ± 5.9 vs. 4.1 ± 3.1 mmHg) at rest, but not during exercise. However, arterial oxygen saturation was significantly different between PFO+ and PFO? at peak exercise in normoxia (94.3 ± 0.9 vs. 95.8 ± 1.0%) as a result of a significant difference in esophageal temperature (38.4 ± 0.3 vs. 38.0 ± 0.3°C). An asymptomatic PFO contributes to pulmonary gas exchange inefficiency at rest but not during exercise in healthy humans and therefore does not explain intersubject variability in the AaDo2 at maximal exercise. PMID:21372097

Lovering, Andrew T.; Stickland, Michael K.; Amann, Markus; O'Brien, Matthew J.; Hokanson, John S.

2011-01-01

202

Effects of perfluorocarbon associated high frequency oscillatory ventilation on hemodynamics and gas exchange in the newborn piglets with respiratory distress.  

PubMed Central

We sought to know whether there is a further improvement in gas exchange when partial liquid ventilation (PLV) is added to high-frequency oscillatory ventilation (HFOV) in a piglet model of saline lavage-induced acute lung injury. Seven 7-9 day-old newborn piglets of mixed strain were treated with repeated saline lavage to achieve a uniform degree of acute lung injury. Then, HFOV were applied to the subject. Four animals received two consecutive doses (15 mL/kg) of perfluorodecalin at 30-min interval (PFC+HFOV group). The other three animals remained on HFOV alone (HFOV-only group). Repetitive lung lavage led to a significant acute aggravation in both gas exchange and hemodynamic parameters. Subsequent application of HFOV produced a significant rapid recovery in both gas exchange and hemodynamic parameters to near baseline levels. During and after perfluorodecalin dosing, there were no significant changes in gas exchange or hemodynamic parameters over time in both groups, and no significant differences in gas exchange or hemodynamic parameters between groups. We concluded that the addition of 30 mL/kg of perfluorodecalin to HFOV showed no detrimental effect on hemodynamics, but did not produce a significant improvement in gas exchange over a three-hour period. PMID:14555817

Choi, Chang Won; Koh, Sun Young; Chang, Yun Sil; Park, Won Soon

2003-01-01

203

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

2012-12-01

204

Polarization exchange in colliding photon beams in an atomic gas medium  

NASA Astrophysics Data System (ADS)

Photon-photon interactions mediated by an atomic gas can effect efficient polarization exchanges between two beams, leaving the medium exactly in its initial state. In, e.g., hydrogen, the distance required for macroscopic exchange is of the order of one-tenth the distance in which the ordinary nonlinear index of refraction would induce a phase change of ?. Several examples are worked out that show the variety of behaviors that can result, depending on the initial respective polarizations stated and the angle between the beams. Of particular interest are initial conditions in which there is no exchange at a mean-field level, conventionally believed to apply when the number of photons N is large. Then the full theory leads both to large exchange and to large entanglement between the beams. Our most solid results indicate that one would have to wait a time proportional to log[N] to see this effect, but there are some indications that this behavior can be circumvented.

Sawyer, R. F.

2014-05-01

205

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

1995-08-01

206

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

207

Gas to particle conversion-gas exchange technique for direct analysis of metal carbonyl gas by inductively coupled plasma mass spectrometry.  

PubMed

A novel gas to particle conversion-gas exchange technique for the direct analysis of metal carbonyl gas by inductively coupled plasma mass spectrometry (ICPMS) was proposed and demonstrated in the present study. The technique is based on a transfer of gas into particle, which can be directly analyzed by ICPMS. Particles from metal carbonyl gases such as Cr(CO)6, Mo(CO)6, and W(CO)6 are formed by reaction with ozone (O3) and ammonium (NH3) gases within a newly developed gas to particle conversion device (GPD). The reaction mechanism of the gas to particle conversion is based on either oxidation of metal carbonyl gas by O3 or agglomeration of metal oxide with ammonium nitrate (NH4NO3) which is generated by the reaction of O3 and NH3. To separate the reaction gases (remaining O3 and NH3) from the formed particles, a previously reported gas exchange device (GED) was used and the in argon stabilized analyte particles were directly introduced and measured by ICPMS. This new technique provided limits of detection (LOD) of 0.15 pL L(-1) (0.32 ng m(-3)), 0.02 pL L(-1) (0.07 ng m(-3)), and 0.01 pL L(-1) (0.07 ng m(-3)) for Cr(CO)6, Mo(CO)6, and W(CO)6, respectively, which were 4-5 orders of magnitude lower than those conventional applied for detecting these gases, e.g., gas chromatography with electron captured detector (GC-ECD) as well as Fourier transform-infrared spectroscopy (FT-IR). The achieved LODs were also similar or slightly better than those for ICPMS coupled to GC. Since the gas to particle conversion technique can achieve the direct measurement of metal carbonyl gases as well as the removal of reaction and ambient gases from metal carbonyl gases, the technique is considered to be well suited to monitor gas quality in semiconductor industry, engine exhaust gases, and or waste incineration products. PMID:25247610

Nishiguchi, Kohei; Utani, Keisuke; Gunther, Detlef; Ohata, Masaki

2014-10-21

208

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

209

Function of the nucleotide exchange activity of vav1 in T cell development and activation.  

PubMed

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 and protein kinase D1, and cell polarization. Thus, in T cells, the GEF activity of Vav1 is essential for some, but not all, of its functions. PMID:20009105

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

2009-01-01

210

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. PMID:20009105

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

2012-01-01

211

[Gas exchange features of Ambrosia artemisiifolia leaves and fruits and their correlations with soil heavy metals].  

PubMed

Ambrosia artemisiifolia can survive well in the habitats of heavy human disturbance and partial soil pollution. Weather its photosynthetic features benefit their survival is worthwhile to concern. With a refuse dump in Changchun City (43 degrees 50'N, 125 degrees 23'E) as study site, this paper analyzed the contents of soil Cu, Pb, Zn, Mn, Cr, Co, Ni, Cd, As, Sb and Hg at ten plots, and measured in situ the gas exchange in A. artemisiifolia leaves and young fruits. The results showed that the study site was slightly contaminated by Ni, but the contents of other soil heavy metals were approached to or substantially lower than their threshold values. The net photosynthetic rate of leaves ranged from 1.88 to 9.41 micromol x m(-2) x s(-1), while that of young fruits could be up to 2. 81 micromol x m(-2) s(-1). Averagely, the respiration rate, stomatal conductance, photosynthetic rate, and water utilization efficiency of leaves were 1.81 micromol x m(-2) x s(-1), 75.7 mmol x m(-2) x s(-1), 6.05 micromol x m(-2) x s(-1), and 4.72 micromol CO2 x mmol(-1) H2O, being 5.26, 0.64, 1.31 and 1.69 times as much as those of young fruits, respectively, indicating that the respiratory and photosynthetic capacities and water use efficiency of A. artemisiifolia young fruits were equivalent to or higher than those of its leaves. Many test heavy metals, such as Cu, Pb, Zn, Cd, As, Sb and Hg, had no significant effects on the gas exchange features of leaves and fruits, but there were significant correlations of Ni and Cr with the stomatal conductance and water use efficiency of leaves and young fruits, Cr with the gross photosynthesis of leaves, and As with the stomatal conductance of young fruits, suggesting that a majority of test soil heavy metals had no direct effects on the gas exchange in A. artemisiifolia leaves and fruits, but soil Ni, Cr and As with the contents approached to or substantially lower than the threshold values could affect the gas exchange features of A. artemisiifolia. PMID:17330473

Zu, Yuangang; Wang, Wenjie; Chen, Huafeng; Yang, Fengjian; Zhang, Zhonghua

2006-12-01

212

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

NASA Astrophysics Data System (ADS)

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

Zhuchenko, S. V.

2014-11-01

213

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

1999-01-01

214

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

1996-01-01

215

Na /H Exchange Activity in the Plasma Membrane of Arabidopsis1  

E-print Network

localizes to the plasma membrane of leaves and roots. To characterize the transport activity of this protein, purified plasma membrane vesicles were isolated from leaves of Arabidopsis. Na /H exchange activity provide a framework for future studies into the regulation of the plant plasma membrane Na /H exchanger

Schumaker, Karen

216

Flue gas carbon dioxide sequestration during water softening with ion-exchange fibers  

SciTech Connect

This study examines the use of ion-exchange fibers (IX fibers) to permanently sequester carbon dioxide present in flue gas into an aqueous phase as calcium or magnesium alkalinity while concurrently softening hard water. The only process inputs besides carbon dioxide (or flue gas) are snowmelt (or rainwater); no other chemicals are required for the regeneration of the IX fibers. Importantly, the process is not energy intensive and carbon dioxide does not need to be compressed to excessive pressures (>150 psi) for efficient use. Sources of carbon dioxide do not require concentration and, therefore, the use of raw flue gas (similar to 17% CO{sub 2}) is feasible with the rate of sequestration governed only by the partial pressure of carbon dioxide. While valid for flue gas obtained from any combustion process (e.g., coal, oil, natural gas, etc.), emissions from oil or gas combustion may be more appropriate for use in the described process due to the absence of mercury and particulates. It should also be noted that the presence of sulfur dioxide in flue gas would not adversely affect the process and may even enhance regeneration efficiency. The only product of the proposed process is an environmentally benign regenerant stream containing calcium and/or magnesium alkalinity. The unique property of IX fibers that makes the proposed process both environmentally sustainable and economically feasible is amenability to efficient regeneration with carbon dioxide and harvested snowmelt. Low intraparticle diffusional resistance is the underlying reason why IX fibers are amenable to efficient regeneration using snowmelt sparged with carbon dioxide; 95% calcium recovery was attained at a CO{sub 2} partial pressure of 6.8 atm. The energy balance for a typical electric utility shows that up to 1% of carbon dioxide emitted during combustion would be sequestered in the softening process.

Greenleaf, J.E.; SenGupta, A.K. [Lafayette College, Easton, PA (United States). Dept. of Civil & Environmental Engineering

2009-06-15

217

Exact dynamical exchange-correlation kernel of a weakly inhomogeneous electron gas.  

PubMed

The dynamical exchange-correlation kernel f{xc} of a nonuniform electron gas is an essential input for the time-dependent density-functional theory of electronic systems. The long-wavelength behavior of this kernel is known to be of the form f{xc}=alpha/q{2} where q is the wave vector and alpha is a frequency-dependent coefficient. We show that in the limit of weak nonuniformity the coefficient alpha has a simple and exact expression in terms of the ground-state density and the frequency-dependent kernel of a uniform electron gas at the average density. We present an approximate evaluation of this expression for Si and discuss its implications for the theory of excitonic effects. PMID:19392197

Nazarov, V U; Vignale, G; Chang, Y-C

2009-03-20

218

Carbon nano-chain and carbon nano-fibers based gas diffusion layers for proton exchange membrane fuel cells  

Microsoft Academic Search

Gas diffusion layers (GDL) for proton exchange membrane fuel cell have been developed using a partially ordered graphitized nano-carbon chain (Pureblack® carbon) and carbon nano-fibers. The GDL samples’ characteristics such as, surface morphology, surface energy, bubble-point pressure and pore size distribution were characterized using electron microscope, inverse gas chromatograph, gas permeability and mercury porosimetry, respectively. Fuel cell performance of the

Arunachala M. Kannan; Lakshmi Munukutla

2007-01-01

219

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

PubMed

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

2013-01-16

220

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

NASA Astrophysics Data System (ADS)

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

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

221

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

PubMed

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

2007-01-01

222

Fluorescence Quenching and Gas Exchange in a Water Stressed C3 Plant, Digitalis lanata  

PubMed Central

A leaf cuvette has been adapted for use with a pulse-modulation fluorometer and an open gas exchange system. Leaf water potential (?) was decreased by withholding watering from Digitalis lanata EHRH. plants. At different stages of water deficiency the photochemical (qQ) and nonphotochemical (qE) fluorescence quenching was determined during the transition between darkness and light-induced steady state photosynthesis of the attached leaves. In addition, the steady state CO2 and H2O gas exchange was recorded. Following a decrease of leaf water potential with increasing water deficiency, the transition of photochemical quenching was almost unaffected, whereas nonphotochemical quenching increased. This is indicative of an enhanced thylakoid membrane energization during the transition and is interpreted as a partial inhibition of either the ATP generating or the ATP consuming reaction sequences. Complete reversion of the stress induced changes was achieved within 6 hours after rewatering. In contrast to the variations during transition, the final steady state values of qQ and qE remained unchanged over the entire stress range from ?0.7 to ?2.5 megapascals. From these results we conclude that, once established, electron transport via photosystem II and the transmembrane proton gradient remain unaffected by water stress. These data are indicative of a protective mechanism against photoinhibition during stress, when net CO2 uptake is limited. PMID:16665875

Stuhlfauth, Thomas; Sültemeyer, Dieter F.; Weinz, Stefanie; Fock, Heinrich P.

1988-01-01

223

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

SciTech Connect

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

Samuelson, L.; Seiler, J. (Virginia Polytechnic Inst., Blacksburg (United States))

1991-05-01

224

Supramaximal exercise after training-induced hypervolemia. I. Gas exchange and acid-base balance.  

PubMed

The effect of an exercise-induced reduction in blood O2-carrying capacity on ventilatory gas exchange and acid-base balance during supramaximal exercise was studied in six males [peak O2 consumption (VO2peak), 3.98 +/- 0.49 l/min]. Three consecutive days of supramaximal exercise resulted in a preexercise reduction of hemoglobin concentration from 15.8 to 14.0 g/dl (P less than 0.05). During exercise (120% VO2peak) performed intermittently (1 min work to 4 min rest); a small but significant (P less than 0.05) increase was found for both O2 consumption (VO2) (l X min) and heart rate (beats/min) on day 2 of the training. On day 3, VO2 (l/min) was reduced 3.2% (P less than 0.05) over day 1 values. No changes were found in CO2 output and minute ventilation during exercise between training days. Similarly, short-term training failed to significantly alter the changes in arterialized blood PCO2, pH, and [HCO-3] observed during exercise. It is concluded that hypervolemia-induced reductions in O2-carrying capacity in the order of 10-11% cause minimal impairment to gas exchange and acid-base balance during supramaximal non-steady-state exercise. PMID:3597267

Green, H J; Hughson, R L; Thomson, J A; Sharratt, M T

1987-05-01

225

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.

2010-12-01

226

Alveolar ventilation to perfusion heterogeneity and diffusion impairment in a mathematical model of gas exchange  

NASA Technical Reports Server (NTRS)

This study describes a two-compartment model of pulmonary gas exchange in which alveolar ventilation to perfusion (VA/Q) heterogeneity and impairment of pulmonary diffusing capacity (D) are simultaneously taken into account. The mathematical model uses as input data measurements usually obtained in the lung function laboratory. It consists of two compartments and an anatomical shunt. Each compartment receives fractions of alveolar ventilation and blood flow. Mass balance equations and integration of Fick's law of diffusion are used to compute alveolar and blood O2 and CO2 values compatible with input O2 uptake and CO2 elimination. Two applications are presented. The first is a method to partition O2 and CO2 alveolar-arterial gradients into VA/Q and D components. The technique is evaluated in data of patients with chronic obstructive pulmonary disease (COPD). The second is a theoretical analysis of the effects of blood flow variation in alveolar and blood O2 partial pressures. The results show the importance of simultaneous consideration of D to estimate VA/Q heterogeneity in patients with diffusion impairment. This factor plays an increasing role in gas alveolar-arterial gradients as severity of COPD increases. Association of VA/Q heterogeneity and D may produce an increase of O2 arterial pressure with decreasing QT which would not be observed if only D were considered. We conclude that the presented computer model is a useful tool for description and interpretation of data from COPD patients and for performing theoretical analysis of variables involved in the gas exchange process.

Vidal Melo, M. F.; Loeppky, J. A.; Caprihan, A.; Luft, U. C.

1993-01-01

227

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

PubMed

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

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

2014-10-01

228

The structural design of the bat wing web and its possible role in gas exchange  

PubMed Central

The structure of the skin in the epauletted fruit bat (Epomophorus wahlbergi) wing and body trunk was studied with a view to understanding possible adaptations for gas metabolism and thermoregulation. In addition, gas exchange measurements were performed using a respirometer designed for the purpose. The body skin had an epidermis, a dermis with hair follicles and sweat glands and a fat-laden hypodermis. In contrast, the wing web skin was made up of a thin bilayered epidermis separated by a connective tissue core with collagen and elastic fibres and was devoid of hair follicles and sweat glands. The wings spanned 18–24 cm each, with about 753 cm2 of surface exposed to air. The body skin epidermis was thick (61 ± 3 µm, SEM), the stratum corneum alone taking a third of it (21 ± 3 µm). In contrast, the wing web skin epidermis was thinner at 9.8 ± 0.7 µm, with a stratum corneum measuring 4.1 ± 0.3 µm (41%). The wing capillaries in the wing web skin ran in the middle of the connective tissue core, with a resultant surface-capillary diffusion distance of 26.8 ± 3.2 µm. The rate of oxygen consumption (V?O2) of the wings alone and of the whole animal measured under light anaesthesia at ambient temperatures of 24 ºC and 33 ºC, averaged 6% and 10% of the total, respectively. Rate of carbon dioxide production had similar values. The membrane diffusing capacity for the wing web was estimated to be 0.019 ml O2 min?1 mmHg?1. We conclude that in Epomophorus wahlbergi, the wing web has structural modifications that permit a substantial contribution to the total gas exchange. PMID:17971117

Makanya, Andrew N; Mortola, Jacopo P

2007-01-01

229

Activation of Na +,H + exchanger produces vasoconstriction of renal resistance vessels  

Microsoft Academic Search

To evaluate the influence of the sodium\\/proton exchanger (Na+,H+ exchanger) on the constriction of rat resistance vessels and on the iliac artery, the isometric vasoconstrictions of renal resistance vessels and strips from iliac artery derived from Wistar-Kyoto rats were measured using a vessel myograph. The Na+,H+ exchanger was activated by intracellular acidification using propionic acid. Cytosolic pH (pHi) and cytosolic

Martin Tepel; Joachim Jankowski; Christian Ruess; Martin Steinmetz; Marcus van der Giet; Walter Zidek

1998-01-01

230

Gas turbine engine active clearance control  

NASA Technical Reports Server (NTRS)

Method for controlling the clearance between rotating and stationary components of a gas turbine engine are disclosed. Techniques for achieving close correspondence between the radial position of rotor blade tips and the circumscribing outer air seals are disclosed. In one embodiment turbine case temperature modifying air is provided in flow rate, pressure and temperature varied as a function of engine operating condition. The modifying air is scheduled from a modulating and mixing valve supplied with dual source compressor air. One source supplies relatively low pressure, low temperature air and the other source supplies relatively high pressure, high temperature air. After the air has been used for the active clearance control (cooling the high pressure turbine case) it is then used for cooling the structure that supports the outer air seal and other high pressure turbine component parts.

Deveau, Paul J. (Inventor); Greenberg, Paul B. (Inventor); Paolillo, Roger E. (Inventor)

1985-01-01

231

Activation of AMP-activated protein kinase revealed by hydrogen/deuterium exchange Mass Spectrometry  

PubMed Central

Summary AMP-Activated protein kinase (AMPK) monitors cellular energy, regulates genes involved in ATP synthesis and consumption, and is allosterically activated by nucleotides and synthetic ligands. Analysis of the intact enzyme by hydrogen/deuterium exchange mass spectrometry reveals conformational perturbations of AMPK in response to binding of nucleotides, cyclodextrin and a synthetic small molecule activator, A769662. Results from this analysis clearly show that binding of AMP leads to conformational changes primarily in the ? subunit of AMPK and subtle changes in the ? and ? subunits. In contrast, A769662 causes profound conformational changes in the glycogen binding module of the ? subunit and in the kinase domain of the ? subunit suggesting that the molecular binding site of latter resides between the ? and ? subunits. The distinct short and long-range perturbations induced upon binding of AMP and A769662 suggest fundamentally different molecular mechanisms for activation of AMPK by these two ligands. PMID:24076403

Landgraf, Rachelle R.; Goswami, Devrishi; Rajamohan, Francis; Harris, Melissa S.; Calabrese, Matthew; Hoth, Lise R.; Magyar, Rachelle; Pascal, Bruce D.; Chalmers, Michael J.; Busby, Scott A.; Kurumbail, Ravi; Griffin, Patrick R.

2013-01-01

232

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 78..mu..m, and oxygen mass balance calculations resulted in an average of 38..mu..m. Given a boundary layer thickness on the order of 50..mu..m, 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.

1987-01-01

233

On-line stable isotope gas exchange reveals an inducible but leaky carbon concentrating mechanism in Nannochloropsis salina.  

PubMed

Carbon concentrating mechanisms (CCMs) are common among microalgae, but their regulation and even existence in some of the most promising biofuel production strains is poorly understood. This is partly because screening for new strains does not commonly include assessment of CCM function or regulation despite its fundamental role in primary carbon metabolism. In addition, the inducible nature of many microalgal CCMs means that environmental conditions should be considered when assessing CCM function and its potential impact on biofuels. In this study, we address the effect of environmental conditions by combining novel, high frequency, on-line (13)CO2 gas exchange screen with microscope-based lipid characterization to assess CCM function in Nannochloropsis salina and its interaction with lipid production. Regulation of CCM function was explored by changing the concentration of CO2 provided to continuous cultures in airlift bioreactors where cell density was kept constant across conditions by controlling the rate of media supply. Our isotopic gas exchange results were consistent with N. salina having an inducible "pump-leak" style CCM similar to that of Nannochloropsis gaditana. Though cells grew faster at high CO2 and had higher rates of net CO2 uptake, we did not observe significant differences in lipid content between conditions. Since the rate of CO2 supply was much higher for the high CO2 conditions, we calculated that growing cells bubbled with low CO2 is about 40 % more efficient for carbon capture than bubbling with high CO2. We attribute this higher efficiency to the activity of a CCM under low CO2 conditions. PMID:24844569

Hanson, David T; Collins, Aaron M; Jones, Howland D T; Roesgen, John; Lopez-Nieves, Samuel; Timlin, Jerilyn A

2014-09-01

234

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

NASA Technical Reports Server (NTRS)

Concepts of a Closed Ecological Life Support System (CELSS) anticipate the use of photosynthetic organisms (higher plants and algae) for air revitalization. The rates of production and uptake of carbon dioxide and oxygen between the crew and the photosynthetic organisms are mismatched. An algal system used for gas exchange only will have the difficulty of an accumulation or depletion of these gases beyond physiologically tolerable limits (in a closed system the mismatch between assimilatory quotient (AQ) and respiratory quotient (RQ) is balanced by the operation of the waste processor). The results are given of a study designed to test the feasibility of using environmental manipulations to maintain physiologically appropriate atmospheres for algae and mice in a gas closed system. Specifically, the atmosphere behavior of this system is considered with algae grown on nitrate or urea and at different light intensities and optical densities. Manipulation of both allow operation of the system in a gas stable manner. Operation of such a system in a CELSS may be useful for reduction of buffer sizes, as a backup system for higher plant air revitalization and to supply extra oxygen to the waste processor or during crew changes.

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

1987-01-01

235

Characterization techniques for gas diffusion layers for proton exchange membrane fuel cells - A review  

NASA Astrophysics Data System (ADS)

The gas diffusion layer (GDL) in a proton exchange membrane fuel cell (PEMFC) is one of the functional components that provide a support structure for gas and water transport. The GDL plays a crucial role when the oxidant is air, especially when the fuel cell operates in the higher current density region. There has been an exponential growth in research and development because the PEMFC has the potential to become the future energy source for automotive applications. In order to serve in this capacity, the GDL requires due innovative analysis and characterization toward performance and durability. It is possible to achieve the optimum fuel cell performance only by understanding the characteristics of GDLs such as structure, pore size, porosity, gas permeability, wettability, thermal and electrical conductivities, surface morphology and water management. This review attempts to bring together the characterization techniques for the essential properties of the GDLs as handy tools for R&D institutions. Topics are categorized based on the ex-situ and in-situ characterization techniques of GDLs along with related modeling and simulation. Recently reported techniques used for accelerated durability evaluation of the GDLs are also consolidated within the ex-situ and in-situ methods.

Arvay, A.; Yli-Rantala, E.; Liu, C.-H.; Peng, X.-H.; Koski, P.; Cindrella, L.; Kauranen, P.; Wilde, P. M.; Kannan, A. M.

2012-09-01

236

Structural basis of Rad53 kinase activation by dimerization and activation segment exchange.  

PubMed

The protein kinase Rad53 is a key regulator of the DNA damage checkpoint in budding yeast. Its human ortholog, CHEK2, is mutated in familial breast cancer and mediates apoptosis in response to genotoxic stress. Autophosphorylation of Rad53 at residue Thr354 located in the kinase activation segment is essential for Rad53 activation. In this study, we assessed the requirement of kinase domain dimerization and the exchange of its activation segment during the Rad53 activation process. We solved the crystal structure of Rad53 in its dimeric form and found that disruption of the observed head-to-tail, face-to-face dimer structure decreased Rad53 autophosphorylation on Thr354 in vitro and impaired Rad53 function in vivo. Moreover, we provide critical functional evidence that Rad53 trans-autophosphorylation may involve the interkinase domain exchange of helix ?EF via an invariant salt bridge. These findings suggest a mechanism of autophosphorylation that may be broadly applicable to other protein kinases. PMID:24815189

Wybenga-Groot, Leanne E; Ho, Cynthia S; Sweeney, Frédéric D; Ceccarelli, Derek F; McGlade, C Jane; Durocher, Daniel; Sicheri, Frank

2014-09-01

237

The death domain of Rab3 guanine nucleotide exchange protein in GDP/GTP exchange activity in living cells.  

PubMed Central

Rab3 GTPases regulate exocytosis of neurons, endocrine and exocrine cells. In the present paper, we report a system to measure the guanine nucleotide status of Rab3 proteins in living cells. The assay is based on the ability of the Rab3 interacting molecule RIM to extract selectively the GTP-bound form of Rab3. Using this system, we found that approx. 20% of wild-type Rab3A, -B, -C or -D transfected in the insulin-secreting cell line HIT-T15 is in the GTP-bound conformation. The pool of activated Rab3 is decreased under conditions that stimulate exocytosis or by co-expression of the Rab3 GTPase-activating protein. In contrast, co-expression of Mss4 or Rab3-GEP (guanine nucleotide exchange protein) increases by approx. 3-fold the GTP-bound pool of Rab3 isoforms. Rab3-GEP is very similar to MADD, a death domain-containing protein that associates with the type 1 tumour necrosis factor receptor. We observed that the death domain of Rab3-GEP is involved in intramolecular interactions and that deletions or mutations that affect this domain of the protein impair the nucleotide exchange activity towards Rab3. We propose that the death domain of Rab3-GEP acts as a molecular switch and co-ordinates multiple functions of the protein by exchanging its binding partners. PMID:11853534

Coppola, Thierry; Perret-Menoud, Véronique; Gattesco, Sonia; Magnin, Sarah; Pombo, Isabel; Blank, Ulrich; Regazzi, Romano

2002-01-01

238

A numerical modelling of gas exchange mechanisms between air and turbulent water with an aquarium chemical reaction  

NASA Astrophysics Data System (ADS)

This paper proposes a new numerical modelling to examine environmental chemodynamics of a gaseous material exchanged between the air and turbulent water phases across a gas-liquid interface, followed by an aquarium chemical reaction. This study uses an extended concept of a two-compartment model, and assumes two physicochemical substeps to approximate the gas exchange processes. The first substep is the gas-liquid equilibrium between the air and water phases, A(g)?A(aq), with Henry's law constant H. The second is a first-order irreversible chemical reaction in turbulent water, A(aq)+H2O?B(aq)+H+ with a chemical reaction rate ?A. A direct numerical simulation (DNS) technique has been employed to obtain details of the gas exchange mechanisms and the chemical reaction in the water compartment, while zero velocity and uniform concentration of A is considered in the air compartment. The study uses the different Schmidt numbers between 1 and 8, and six nondimensional chemical reaction rates between 10(?0) to 101 at a fixed Reynolds number. It focuses on the effects of the Schmidt number and the chemical reaction rate on fundamental mechanisms of the gas exchange processes across the interface.

Nagaosa, Ryuichi S.

2014-01-01

239

Reprint of: A numerical modelling of gas exchange mechanisms between air and turbulent water with an aquarium chemical reaction  

NASA Astrophysics Data System (ADS)

This paper proposes a new numerical modelling to examine environmental chemodynamics of a gaseous material exchanged between the air and turbulent water phases across a gas-liquid interface, followed by an aquarium chemical reaction. This study uses an extended concept of a two-compartment model, and assumes two physicochemical substeps to approximate the gas exchange processes. The first substep is the gas-liquid equilibrium between the air and water phases, A(g)?A(aq), with Henry's law constant H. The second is a first-order irreversible chemical reaction in turbulent water, A(aq)+H2O?B(aq)+H+ with a chemical reaction rate ?A. A direct numerical simulation (DNS) technique has been employed to obtain details of the gas exchange mechanisms and the chemical reaction in the water compartment, while zero velocity and uniform concentration of A is considered in the air compartment. The study uses the different Schmidt numbers between 1 and 8, and six nondimensional chemical reaction rates between 10(?0) to 101 at a fixed Reynolds number. It focuses on the effects of the Schmidt number and the chemical reaction rate on fundamental mechanisms of the gas exchange processes across the interface.

Nagaosa, Ryuichi S.

2014-08-01

240

Gas exchange: large surface and thin barrier determine pulmonary diffusing capacity.  

PubMed

The lung is characterized by its diffusing capacity for oxygen, DLO2, which is estimated from morphometric information as a theoretical capacity. It is determined by the large gas exchange surface, the thin tissue barrier, and the amount of capillary blood. The question is asked whether DLO2 could be a limiting factor for O2 uptake in heavy exercise, particularly in athletes with their 50% higher O2 demand. This is answered by studying the relation between DLO2 and maximal O2 consumption in different sedentary and athletic mammals, comparing horse and cow, dog and goat, and, finally, the most athletic mammal, the pronghorn antelope of the Rocky Mountains. It is concluded that in athletic species the lung is just sufficient to satisfy the O2 needs and can therefore be a limiting factor for aerobic work. PMID:10394805

Weibel, E R

1999-06-01

241

Modulation of Cl-/OH- exchange activity in Caco-2 cells by nitric oxide.  

PubMed

The present studies were undertaken to determine the direct effects of nitric oxide (NO) released from an exogenous donor, S-nitroso-N-acetyl pencillamine (SNAP) on Cl-/OH- exchange activity in human Caco-2 cells. Our results demonstrate that NO inhibits Cl-/OH- exchange activity in Caco-2 cells via cGMP-dependent protein kinases G (PKG) and C (PKC) signal-transduction pathways. Our data in support of this conclusion can be outlined as follows: 1) incubation of Caco-2 cells with SNAP (500 microM) for 30 min resulted in approximately 50% inhibition of DIDS-sensitive 36Cl uptake; 2) soluble guanylate cyclase inhibitors Ly-83583 and (1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one significantly blocked the inhibition of Cl-/OH- exchange activity by SNAP; 3) addition of 8-bromo-cGMP (8-BrcGMP) mimicked the effects of SNAP; 4) specific PKG inhibitor KT-5823 significantly inhibited the decrease in Cl-/OH- exchange activity in response to either SNAP or 8-BrcGMP; 5) Cl-/OH-exchange activity in Caco-2 cells in response to SNAP was not altered in the presence of protein kinase A (PKA) inhibitor (Rp-cAMPS), demonstrating that the PKA pathway was not involved; 6) the effect of NO on Cl-/OH- exchange activity was mediated by PKC, because each of the two PKC inhibitors chelerythrine chloride and calphostin C blocked the SNAP-mediated inhibition of Cl-/OH- exchange activity; 7) SO/OH- exchange in Caco-2 cells was unaffected by SNAP. Our results suggest that NO-induced inhibition of Cl-/OH- exchange may play an important role in the pathophysiology of diarrhea associated with inflammatory bowel diseases. PMID:12181176

Saksena, Seema; Gill, Ravinder K; Syed, Irfan A; Tyagi, Sangeeta; Alrefai, Waddah A; Ramaswamy, K; Dudeja, Pradeep K

2002-09-01

242

Air-sea exchange and gas-particle partitioning of polycyclic aromatic hydrocarbons in the Mediterranean  

NASA Astrophysics Data System (ADS)

Polycyclic aromatic hydrocarbon (PAH) concentration in air of the central and eastern Mediterranean in summer 2010 was 1.45 (0.30-3.25) ng m-3 (sum of 25 PAHs), with 8 (1-17)% in the particulate phase, almost exclusively associated with particles < 0.25 ?m. The total deposition flux of particulate PAHs was 0.3-0.5 ? g m-2 yr-1. The diffusive air-sea exchange fluxes of fluoranthene and pyrene were mostly found net-depositional or close to phase equilibrium, while retene was net-volatilisational in a large sea region. Regional fire activity records in combination with box model simulations suggest that seasonal depositional input of retene from biomass burning into the surface waters during summer is followed by an annual reversal of air-sea exchange, while interannual variability is dominated by the variability of the fire season. One-third of primary retene sources to the sea region in the period 2005-2010 returned to the atmosphere as secondary emissions from surface seawaters. It is concluded that future negative emission trends or interannual variability of regional sources may trigger the sea to become a secondary PAH source through reversal of diffusive air-sea exchange. Capsule: In late summer the seawater surface in the Mediterranean has turned into a temporary secondary source of PAH, obviously related to biomass burning in the region.

Mulder, M. D.; Heil, A.; Kuku?ka, P.; Klánová, J.; Kuta, J.; Prokeš, R.; Sprovieri, F.; Lammel, G.

2014-09-01

243

Isotope exchange reaction between 235UF5 nanoparticles and 238UF6 gas  

NASA Astrophysics Data System (ADS)

The equilibrium in the isotope exchange reaction between 235U-enriched UF5 nanoparticles and natural UF6 gas was experimentally investigated. From the relationship between the isotopic fraction of UF6 gas at equilibrium and the specific surface area of the UF5 nanoparticles, it was experimentally demonstrated for the first time that all UF5 molecules on the outermost layer of the particles participated in the reaction until the isotopic fraction of UF5 on the outermost layer became equal to that of the UF6 gas. A fast rate process during the early period of the reaction and a subsequent slow rate process were quantitatively observed. These facts contradict the previously reported assumption not supported by experimental evidence that the UF5 molecules in the underlying layer of the particle participate in the reaction. A new model based on our experimental findings was proposed. Our model suggests that there are two kinds of molecules on the outermost layer with different reactivities and all UF5 molecules on the outermost layer contribute to the reaction. The rate equations were derived from the proposed model and analytically solved. The time dependency of the isotopic fraction of the UF6 gas and UF5 particles was expressed by three kinetic parameters such as the rate constant of the high reactivity molecule, ks, the rate constant of the low reactivity molecule, ks', and the fraction of high reactivity molecules on the outermost layer, ?. Our model reproduced well all the experimental data determined in the present study with ks=5.5×10-20 cm3/(s molecules), ks'=4.5×10-22 cm3/(s molecules), and ?=0.078.

Kuga, Yoshikazu; Takeuchi, Kazuo

1998-03-01

244

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) 1.kg-1.min-1) were evaluated. Intrapulmonary gas distribution was assessed from regional 133Xe clearances. In dogs lying supine, CO2 elimination was more efficient with endobronchial insufflation than with tracheal insufflation, but the alveolar-arterial O2 partial pressure difference was larger during CFV than during CMV, regardless of the type of insufflation. By contrast, endobronchial insufflation maintained both arterial PCO2 and alveolar-arterial O2 partial pressure difference at significantly lower levels in dogs lying prone than in dogs lying supine. In dogs lying supine, the dependent lung was preferentially ventilated during CMV but not during CFV. In dogs lying prone, gas distribution was uniform with both modes of ventilation. The alveolar-arterial O2 partial pressure difference during CFV in dogs lying supine was negatively correlated with the reduced ventilation of the dependent lung, which suggests that increased ventilation-perfusion mismatching was responsible for the increase in alveolar-arterial O2 partial pressure difference. The more efficient oxygenation during CFV in dogs lying prone suggests a more efficient matching of ventilation to perfusion, presumably because the distribution of blood flow is also nearly uniform.

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

1988-05-01

245

Joint Action of O3 and SO2 in Modifying Plant Gas Exchange 1  

PubMed Central

The joint action of O3 and SO2 stress on plants was investigated by determining the quantitative relationship between air pollutant fluxes and effects on stomatal conductance. Gas exchange measurements of O3, SO2, and H2O vapor were made for Pisum sativum L. (garden pea). Plants were grown under controlled environments, and O3, SO2, and H2O vapor fluxes were evaluated with a whole-plant gas exchange chamber using the mass-balance approach. Maximum O3 and SO2 fluxes per unit area (2 sided) into leaves averaged 8 nanomoles per square meter per second with exposure to either O3 or SO2 at 0.1 microliters per liter. Internal fluxes of either O3 or SO2 were reduced by up to 50% during exposure to combined versus individual pollutants; the greatest reduction occurred with simultaneous versus sequential combinations of the pollutants. Stomatal conductance to H2O was substantially altered by the pollutant exposures, with O3 molecules twice as effective as SO2 molecules in inducing stomatal closure. Stomatal conductance was related to the integrated dose of pollutants. The regression equations relating integrated dose to stomatal conductance were similar with O3 alone, O3 plus added SO2, and O3 plus SO2 simultaneously; i.e. a dose of 100 micromoles per square meter produced a 39 to 45% reduction in conductance over nonexposed plants. With SO2 alone, or SO2 plus added O3, a dose of 100 micromoles per square meter produced a 20 to 25% reduction in conductance. When O3 was present at the start of the exposure, then stomatal response resembled that for O3 more than the response for SO2. This study indicated that stomatal responses with combinations of O3 and SO2 are not dependent solely on the integrated dose of pollutants, but suggests that a metabolic synergistic effect exists. PMID:16665041

Olszyk, David M.; Tingey, David T.

1986-01-01

246

A computational study of an HCCI engine with direct injection during gas exchange  

SciTech Connect

We present a new probability density function (PDF)-based computational model to simulate a homogeneous charge compression ignition (HCCI) engine with direct injection (DI) during gas exchange. This stochastic reactor model (SRM) accounts for the engine breathing process in addition to the closed-volume HCCI engine operation. A weighted-particle Monte Carlo method is used to solve the resulting PDF transport equation. While simulating the gas exchange, it is necessary to add a large number of stochastic particles to the ensemble due to the intake air and EGR streams as well as fuel injection, resulting in increased computational expense. Therefore, in this work we apply a down-sampling technique to reduce the number of stochastic particles, while conserving the statistical properties of the ensemble. In this method some of the most important statistical moments (e.g., concentration of the main chemical species and enthalpy) are conserved exactly, while other moments are conserved in a statistical sense. Detailed analysis demonstrates that the statistical error associated with the down-sampling algorithm is more sensitive to the number of particles than to the number of conserved species for the given operating conditions. For a full-cycle simulation this down-sampling procedure was observed to reduce the computational time by a factor of 8 as compared to the simulation without this strategy, while still maintaining the error within an acceptable limit. Following the detailed numerical investigation, the model, intended for volatile fuels only, is applied to simulate a two-stroke, naturally aspirated HCCI engine fueled with isooctane. The in-cylinder pressure and CO emissions predicted by the model agree reasonably well with the measured profiles. In addition, the new model is applied to estimate the influence of engine operating parameters such as the relative air-fuel ratio and early direct injection timing on HCCI combustion and emissions. The qualitative trends observed in the parametric variation study match well with experimental data in literature. (author)

Su, Haiyun; Vikhansky, Alexander; Mosbach, Sebastian; Kraft, Markus [Department of Chemical Engineering, University of Cambridge, Cambridge CB2 3RA (United Kingdom); Bhave, Amit [Reaction Engineering Solutions Ltd., 61 Canterbury Street, Cambridge CB4 3QG (United Kingdom); Kim, Kyoung-Oh; Kobayashi, Tatsuo [Higashifuji Technical Center, Toyota Motor Corporation, Mishuku 1200, Susono, Shizuoka 480-1193 (Japan); Mauss, Fabian [Division of Combustion Physics, Lund Institute of Technology, Box 118, S-22100 Lund (Sweden)

2006-10-15

247

Effects of the prone position on respiratory mechanics and gas exchange during acute lung injury.  

PubMed

We studied 16 patients with acute lung injury receiving volume-controlled ventilation to assess the relationships between gas exchange and respiratory mechanics before, during, and after 2 h in the prone position. We measured the end-expiratory lung volume (EELV, helium dilution), the total respiratory system (Cst,rs), the lung (Cst,L) and the thoracoabdominal cage (Cst,w) compliances (end-inspiratory occlusion technique and esophageal balloon), the hemodynamics, and gas exchange. In the prone position, PaO2 increased from 103.2 +/- 23.8 to 129.3 +/- 32.9 mm Hg (p < 0.05) without significant changes of Cst,rs and EELV. However, Cst,w decreased from 204.8 +/- 97.4 to 135.9 +/- 52.5 ml/cm H2O (p < 0.01) and the decrease was correlated with the oxygenation increase (r = 0.62, p < 0.05). Furthermore, the greater the baseline supine Cst,w, the greater its decrease in the prone position (r = 0.82, p < 0.01). Consequently, the oxygenation changes in the prone position were predictable from baseline supine Cst,w (r = 0.80, p < 0.01). Returning to the supine position, Cst,rs increased compared with baseline (42.3 +/- 14.4 versus 38.4 +/- 13.7 ml/cm H2O; p < 0.01), mainly because of the lung component (57.5 +/- 25.1 versus 52.4 +/- 23.3 ml/cm H2O; p < 0.01). Thus, (1) baseline Cst,w and its changes may play a role in determining the oxygenation response in the prone position; (2) the prone position improves Cst,rs and Cst,L when the supine position is resumed. PMID:9476848

Pelosi, P; Tubiolo, D; Mascheroni, D; Vicardi, P; Crotti, S; Valenza, F; Gattinoni, L

1998-02-01

248

Anaerobic metabolism, gas exchange, and acid-base balance during hypoxic exposure in the channel catfish,Ictalurus punctatus  

Microsoft Academic Search

Gill ventilation, blood gas and acid-base values, Mo,, Mc.02 and the gas exchange ratio have been measured before, during, and after exposure to hypoxia in the channel catfish, Zctalurus punctatus. Z.punctatus maintains M,,, at control levels to a PI,, as low as 60 mm Hg, through a profound branchial hyperventilation. Concomitantly, however, a lactic acidosis usually develops, indicating a significant

Warren W. Burggren; James N. Cameron

1980-01-01

249

Influence of preparation method on the catalytic properties of acid-activated tetramethylammonium-exchanged clays  

Microsoft Academic Search

Two montmorillonites STx-1 (Texas) and SWy-2 (Wyoming) were first activated with different amounts of 12M HCl and then exchanged with a fixed amount of 1M tetramethylammonium (TMA+) chloride solution (H\\/TMA samples) at room temperature. TMA+-exchanged samples and then acid activated (TMA\\/H samples) were also prepared to evaluate the resistance to displacement of TMA+ by protons. The surface area and the

Alexander Moronta; Victor Ferrer; Jorlens Quero; Geomar Arteaga; Eduardo Choren

2002-01-01

250

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.

251

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

PubMed Central

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 129Xe 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 129Xe 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 129Xe distributions in the same breath. These images were normalized and divided to calculate “129Xe gas-transfer” maps. We hypothesized that, for healthy volunteers, 129Xe gas-transfer maps would retain the previously observed posture-dependent gradients. This was tested in nine subjects: when the subjects were supine, 129Xe 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 129Xe 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 129Xe MR imaging yields 129Xe 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

2013-01-01

252

Gas exchange and heart rate in the harbour porpoise, Phocoena phocoena.  

PubMed

The respiratory physiology, heart rates and metabolic rates of two captive juvenile male harbour porpoises (both 28 kg) were measured using a rapid-response respiratory gas analysis system in the laboratory. Breath-hold durations in the laboratory (12 +/- 0.3 s, mean +/- SEM) were shorter than field observations, although a few breath-holds of over 40 s were recorded. The mean percentage time spent submerged was 89 +/- 0.4%. Relative to similarly-sized terrestrial mammals, the respiratory frequency was low (4.9 +/- 0.19 breaths.min-1) but with high tidal volumes (1.1 +/- 0.011), enabling a comparatively high minute rate of gas exchange. Oxygen consumption under these experimental conditions (247 +/- 13.8 ml O2.min-1) was 1.9-fold higher than predicted by standard scaling relations. These data together with an estimate of the total oxygen stores predicted an aerobic dive limit of 5.4 min. The peak end-tidal O2 values were related to the length of the previous breath-hold, demonstrating the increased oxygen uptake from the lung for the longer dives. Blood oxygen capacity was 23.5 +/- 1.0 ml.100 ml-1, and the oxygen affinity was high, enabling rapid oxygen loading during ventilation. PMID:10707319

Reed, J Z; Chambers, C; Hunter, C J; Lockyer, C; Kastelein, R; Fedak, M A; Boutilier, R G

2000-02-01

253

[Extracorporeal gas exchange--an alternative to ventilation of the premature newborn infant with respiratory insufficiency].  

PubMed

In spite of improvements in its prophylaxis and therapy the membrane syndrome is still one of the main causes of morbidity and mortality in newborns. In many perinatal centers in the United States extracorporeal gas exchange via an artificial lung is the ultimate step in therapy for this group of patients today. As a result of our own research work we are able to introduce an extracorporeal circulation system which is especially suited to the particular situation of the immature newborn and which enables a complete immobilization of the lung to avoid baro-trauma with alveolar oxygen diffusion and CO2-removal through the membrane lung. Using appropriate dimensions the system can be housed in a newborn incubator. With low total resistance the perfusion in the newborn is performed via an arterio-venous shunt of the umbilical vessels alternatively with and without a mechanical pump. We tested this perfusion system on premature lambs with a gestational age of 128 to 130 days. During a test period of from 6 to 8 hours at a low blood flow rate (200 ml/min) we achieved a sufficient CO2-removal via the membrane lung with enough oxygen supply through the non-ventilated lung. By means of suitable materials, and using CO2 gas priming procedure and employing prostacyclin analogons to inhibit thrombocyte aggregation, it was possible to lower the heparine dosage to a minimum. PMID:6591629

Schmidt, S; Dudenhausen, J W; Langner, K; Laiblin, C; Saling, E

1984-01-01

254

Trace gas exchanges and convective transports over the Amazonian rain forest  

NASA Technical Reports Server (NTRS)

The NASA Amazon Boundary Layer Experiment (ABLE 2A) based in Manaus, Brazil, in July and August 1985, is used to examine meteorological processes responsible for the vertical and horizontal transport of biogenic and anthropogenic trace gases generated over the Amazon basin. Direct sampling of the surrounding environment of deep convective clouds shows marked changes in the vertical distribution of the lower and midtroposphere concentration of O3 and such surface-derived species as CO, CO2, and NO. Thermodynamic observations, together with two-dimensional cloud model simulations, confirm vertical transports within the convection and provide a basis for an estimation of the magnitude and efficiency of cloud upward and downward exchanges. A distinction is drawn between local changes due to convective updrafts and downdrafts and convective overturning as a net result of the storm processes. Marked variability is seen in trace gas concentrations along horizontal flight paths in the vicinity of the convection. Interpretation of simultaneously measured thermodynamic quantities and trace gas concentrations provide the information to infer the presence and direction of atmospheric transports and/or the presence of anthropogenic influences.

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

1988-01-01

255

Effect of stratified inequality of blood flow on gas exchange in liquid-filled lungs.  

NASA Technical Reports Server (NTRS)

This investigation set out to answer two questions: (1) are the distal alveoli in the terminal lung units less well perfused than the proximal alveoli, i.e., is there stratification of blood flow; and (2) if so, does this enhance gas exchange in the presence of stratified inequality of ventilation. Excised dog lungs were ventilated with saline and perfused with blood. Following single inspirations of xenon 133 in saline and various periods of breath holding, the expired xenon concentration against volume was measured and it confirmed marked stratified inequality of ventilation under these conditions. By measuring the rate of depletion of xenon from alveoli during a period of blood flow, we showed that the alveoli which emptied at the end of expiration had 16% less blood flow than those exhaling earlier. However, by measuring the xenon concentration in pulmonary venous blood, we found that about 10% less tracer was transferred from the alveoli into the blood when the inspired xenon was stratified within the respiratory zone. Thus while stratification of blood flow was confirmed, it was shown to impair rather than enhance the efficiency of gas transfer.

West, J. B.; Maloney, J. E.; Castle, B. L.

1972-01-01

256

Gas exchange measurements within a magnetic environment: validation of a new system.  

PubMed

Although simultaneous measurements of pulmonary oxygen uptake (VO2) and Phosphorus-31 magnetic resonance spectroscopy ((31)P MRS) is attractive to investigate muscular metabolism during exercise, the superconducting magnet requires the design of specific gas exchange analyser (GEA). Thus, this study aimed to assess the validity of a commercial GEA system (ZAN600) compatible with (31)P MRS measurements. Using nonmagnetic pneumotachograph and prolonged sampling line (from 2m, control condition, to 6.5m) did not alter the proper synchronisation between flow and gas concentration signals. Also, end-expiratory fraction of O2 (FETO2) and CO(2) (FETCO2), and finally the values of steady-state ventilation (V(E)), carbon dioxide production (VCO2) and VO2 kinetics during moderate knee-extension exercise were not significantly different between 2m and 6.5m conditions and between 6.5m condition inside and outside the magnet. These results showed that a prolonged sampling line used inside the superconducting magnet did not affect the accuracy of VO2 measurements of a commercial GEA system; the latter appears suitable for simultaneous measurements of VO2 and (31)P MRS. PMID:22366154

Bringard, Aurélien; Layec, Gwenael; Micallef, Jean-Paul; Bendahan, David; Perrey, Stéphane

2012-06-15

257

Activation of catalysts for synthesizing methanol from synthesis gas  

DOEpatents

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)

1985-01-01

258

Increasing the pump-up rate to polarize 3He gas using spin-exchange optical pumping method  

NASA Astrophysics Data System (ADS)

In recent years, polarized 3He gas has increasingly been used as neutron polarizers and polarization analyzers. Two of the leading methods to polarize the 3He gas are the spin-exchange optical pumping (SEOP) method and the meta-stable exchange optical pumping (MEOP) method. At present, the SEOP setup is comparatively compact due to the fact that it does not require the sophisticated compressor system used in the MEOP method. The temperature and the laser power available determine the speed, at which the SEOP method polarizes the 3He gas. For the quantity of gas typically used in neutron scattering work, this speed is independent of the quantity of the gas required, whereas the polarizing time using the MEOP method is proportional to the quantity of gas required. Currently, using the SEOP method to polarize several bar-liters of 3He to 70% polarization would require 20-40 h. This is an order of magnitude longer than the MEOP method for the same quantity of gas and polarization. It would therefore be advantageous to speed up the SEOP process. In this article, we analyze the requirements for temperature, laser power, and the type of alkali used in order to shorten the time required to polarize 3He gas using the SEOP method.

Lee, Wai Tung; Tong, Xin; Rich, Dennis; Liu, Yun; Fleenor, Michael; Ismaili, Akbar; Pierce, Joshua; Hagen, Mark; Dadras, Jonny; Robertson, J. Lee

2009-09-01

259

Design of Plant Gas Exchange Experiments in a Variable Pressure Growth Chamber  

NASA Technical Reports Server (NTRS)

Sustainable human presence in extreme environments such as lunar and martian bases will require bioregenerative components to human life support systems where plants are used for generation of oxygen, food, and water. Reduced atmospheric pressures will be used to minimize mass and engineering requirements. Few studies have assessed the metabolic and developmental responses of plants to reduced pressure and varied oxygen atmospheres. The first tests of hypobaric pressures on plant gas exchange and biomass production at the Johnson Space Center will be initiated in January 1996 in the Variable Pressure Growth Chamber (VPGC), a large, closed plant growth chamber rated for 10.2 psi. Experiments were designed and protocols detailed for two complete growouts each of lettuce and wheat to generate a general database for human life support requirements and to answer questions about plant growth processes in reduced pressure and varied oxygen environments. The central objective of crop growth studies in the VPGC is to determine the influence of reduced pressure and reduced oxygen on the rates of photosynthesis, dark respiration, evapotranspiration and biomass production of lettuce and wheat. Due to the constraint of one experimental unit, internal controls, called pressure transients, will be used to evaluate rates of CO2 uptake, O2 evolution, and H2O generation. Pressure transients will give interpretive power to the results of repeated growouts at both reduced and ambient pressures. Other experiments involve the generation of response functions to partial pressures of O2 and CO2 and to light intensity. Protocol for determining and calculating rates of gas exchange have been detailed. In order to build these databases and implement the necessary treatment combinations in short time periods, specific requirements for gas injections and removals have been defined. A set of system capability checks will include determination of leakage rates conducted prior to the actual crop growouts. Schedules of experimental events for lettuce and wheat are outlined and include replications in time of diurnal routines, pressure transients, variable pO2, pO2/pCO2 ratio, and light intensity responses.

Corey, Kenneth A.

1996-01-01

260

Effect of soil temperature on stem sap flow, shoot gas exchange and water potential of Picea engelmannii (Parry) during snowmelt  

Microsoft Academic Search

The effect of cold soils on stem sap flow, shoot gas exchange and water potential of Picea engelmannii (Parry) was investigated during the snowmelt period in the Medicine Bow Mountains, Wyoming, USA. Shoot net photosynthetic rates were higher in young trees (1.5–1.8 m in height) growing in cold soils (2 concentrations. Midday through afternoon shoot water potentials of trees in

T. A. Day; E. H. DeLucia; W. K. Smith

1990-01-01

261

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

2010-01-01

262

Asymmetrical effects of mesophyll conductance on fundamental photosynthetic parameters and their relationships estimated from leaf gas exchange measurements  

Technology Transfer Automated Retrieval System (TEKTRAN)

Most previous analyses of leaf gas exchange measurements assumed an infinite value of mesophyll conductance (gm) and thus equaled CO2 partial pressures in the substomatal cavity and chloroplast. Yet an increasing number of studies have recognized that gm is finite and there is a drawdown of CO2 part...

263

Gas exchange of four arctic and alpine tundra plant species in relation to atmospheric and soil moisture stress  

Microsoft Academic Search

Gas exchange measurements of two arctic tundra plants, Dupontia fischeri and Carex aquatilis, and two alpine tundra species, Deschampsia caespitosa and Geum rossii, were conducted under a range of atmospheric and soil moisture stress conditions to determine if photosynthetic adaptations to water stress may play a role in the local distributions of these species. Under low soil moisture stress, the

Douglas A. Johnson; Martyn M. Caldwell

1975-01-01

264

Interactive effects of salinity and water stress on growth, leaf water relations, and gas exchange in amaranth (Amaranthus spp.)  

Microsoft Academic Search

Amaranth (Amaranthus spp.) is a promising vegetable species often grown under semi?arid conditions prone to both drought and salinity. This study was initiated to evaluate the effects of water and salinity stresses, both individually and in combination, on plant growth\\/leaf water relations and gas exchange of two amaranth genotypes— Amaranthus tricolor and A. cruentus. Plants were grown in a greenhouse

E. N. Omami; P. S. Hammes

2006-01-01

265

Transpiration efficiency over an annual cycle, leaf gas exchange and wood carbon isotope ratio of three tropical tree species  

E-print Network

Transpiration efficiency over an annual cycle, leaf gas exchange and wood carbon isotope ratio. Cumulative transpiration was determined by repeatedly weighing the pots with a pallet truck scale. Dry matter that leaf-level processes largely determined variation among the three tropical tree species in whole

Bermingham, Eldredge

266

Blood lactate concentrations are mildly affected by mobile gas exchange measurements.  

PubMed

We sought to investigate the effects of wearing a mobile respiratory gas analysis system during a treadmill test on blood lactate (bLa) concentrations and commonly applied bLa thresholds. A total of 16 recreational athletes (31±3 years, VO2max: 58±6?ml?·?min(-1)?·?kg(-1)) performed one multistage treadmill test with and one without gas exchange measurements (GEM and noGEM). The whole bLa curve, the lactate threshold (LT), the individual anaerobic thresholds according to Stegmann (IATSt) and Dickhuth (IATDi), and a fixed bLa concentration of 4?mmol???l(-1) (OBLA) were evaluated. The bLa curve was shifted slightly leftward in GEM compared to noGEM (P<0.05), whereas the heart rate response was not different between conditions (P=0.89). There was no difference between GEM and noGEM for LT (2.61±0.34 vs. 2.64±0.39?m?·?s(-1), P=0.49) and IATSt (3.47±0.42 vs. 3.55±0.47?m?·?s(-1), P=0.12). However, IATDi (3.57±0.39 vs. 3.66±0.44?m?·?s(-1), P<0.01) and OBLA (3.85±0.46 vs. 3.96±0.47?m?·?s(-1), P<0.01) occurred at slower running velocities in GEM. The bLa response to treadmill tests is mildly affected by wearing a mobile gas analysis system. This also applies to bLa thresholds located at higher exercise intensities. While the magnitude of the effects is of little importance for recreational athletes, it might be relevant for elite athletes and scientific studies. PMID:24258472

Scharhag-Rosenberger, F; Wochatz, M; Otto, C; Cassel, M; Mayer, F; Scharhag, J

2014-06-01

267

Quantifying the measurement errors in a LI-6400 gas exchange system and their effects on the parameterization of Farquhar et al. model for C3 leaves  

Technology Transfer Automated Retrieval System (TEKTRAN)

The LI-6400 gas exchange system (Li-Cor, Inc, Lincoln, NE, USA) has been widely used for the measurement of net gas exchanges and calibration/parameterization of leaf models. Measurement errors due to diffusive leakages of water vapor and carbon dioxide between inside and outside of the leaf chamber...

268

Toxicodynamics of rigid polystyrene microparticles on pulmonary gas exchange in mice: Implications for microemboli-based drug delivery systems  

SciTech Connect

The toxicodynamic relationship between the number and size of pulmonary microemboli resulting from uniformly sized, rigid polystyrene microparticles (MPs) administered intravenously and their potential effects on pulmonary gas exchange were investigated. CD-1 male mice (6–8 weeks) were intravenously administered 10, 25 and 45 ?m diameter MPs. Oxygen hemoglobin saturation in the blood (SpO{sub 2}) was measured non-invasively using a pulse oximeter while varying inhaled oxygen concentration (F{sub I}O{sub 2}). The resulting data were fit to a physiologically based non-linear mathematical model that estimates 2 parameters: ventilation–perfusion ratio (V{sub A}/Q) and shunt (percentage of deoxygenated blood returning to systemic circulation). The number of MPs administered prior to a statistically significant reduction in normalized V{sub A}/Q was dependent on particle size. MP doses that resulted in a significant reduction in normalized V{sub A}/Q one day post-treatment were 4000, 40,000 and 550,000 MPs/g for 45, 25 and 10 ?m MPs, respectively. The model estimated V{sub A}/Q and shunt returned to baseline levels 7 days post-treatment. Measuring SpO{sub 2} alone was not sufficient to observe changes in gas exchange; however, when combined with model-derived V{sub A}/Q and shunt early reversible toxicity from pulmonary microemboli was detected suggesting that the model and physical measurements are both required for assessing toxicity. Moreover, it appears that the MP load required to alter gas exchange in a mouse prior to lethality is significantly higher than the anticipated required MP dose for effective drug delivery. Overall, the current results indicate that the microemboli-based approach for targeted pulmonary drug delivery is potentially safe and should be further explored. -- Highlights: ? Murine pulmonary gas exchange after microembolization was non-invasively studied. ? A physiologically based model quantified impairment of pulmonary gas exchange. ? Number and size of microemboli determine severity of impaired gas exchange. ? Pulmonary gas exchange returns to baseline within 7 days.

Kutscher, H.L. [Department of Pharmaceutics, Ernest Mario School of Pharmacy, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 (United States)] [Department of Pharmaceutics, Ernest Mario School of Pharmacy, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 (United States); Gao, D.; Li, S. [Department of Pharmaceutics, Ernest Mario School of Pharmacy, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 (United States) [Department of Pharmaceutics, Ernest Mario School of Pharmacy, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 (United States); UMDNJ-Rutgers CounterACT Research Center of Excellence, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 (United States); Massa, C.B.; Cervelli, J. [Department of Pharmacology and Toxicology, Ernest Mario School of Pharmacy, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 (United States)] [Department of Pharmacology and Toxicology, Ernest Mario School of Pharmacy, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 (United States); Deshmukh, M. [Department of Pharmaceutics, Ernest Mario School of Pharmacy, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 (United States) [Department of Pharmaceutics, Ernest Mario School of Pharmacy, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 (United States); UMDNJ-Rutgers CounterACT Research Center of Excellence, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 (United States); Joseph, L.B.; Laskin, D.L. [UMDNJ-Rutgers CounterACT Research Center of Excellence, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 (United States) [UMDNJ-Rutgers CounterACT Research Center of Excellence, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 (United States); Department of Pharmacology and Toxicology, Ernest Mario School of Pharmacy, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 (United States); Sinko, P.J., E-mail: sinko@rci.rutgers.edu [Department of Pharmaceutics, Ernest Mario School of Pharmacy, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 (United States); UMDNJ-Rutgers CounterACT Research Center of Excellence, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 (United States)

2013-01-15

269

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

NASA Astrophysics Data System (ADS)

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 hypersonic propulsion systems. The numerical codes developed by ONERA for the modeling of heat exchanger thermodynamics are evaluated.

Avran, Patrick; Bernard, Pierre

270

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.

2009-10-01

271

Gas-exchange patterns of Mediterranean fruit fly Pupae (Diptera: Tephritidae): A tool to forecast developmental stage  

SciTech Connect

The pattern of gas-exchange (CO{sub 2} emission) was investigated for developing Mediterranean fruit fly (medfly) Ceratitis capitata (Wiedemann) pupae incubated at different temperatures. This study was undertaken to explore the usefulness of gas-exchange systems in the determination of physiological age in developing pupae that are mass produced for sterile insect technique projects. The rate of CO{sub 2} emission was measured in a closed flow-through system connected to commercial infrared gas analysis equipment. Metabolic activity (rate of CO{sub 2} emission) was related to pupal eye-color, which is the current technique used to determine physiological age. Eye-color was characterized digitally with 3 variables (Hue, Saturation and Intensity), and color separated by discriminant analysis. The rate of CO{sub 2} emission throughout pupal development followed a U-shape, with high levels of emission during pupariation, pupal transformation and final pharate adult stages. Temperature affected the development time of pupae, but not the basic CO{sub 2} emission patterns during development. In all temperatures, rates of CO{sub 2} emission 1 and 2 d before adult emergence were very similar. After mid larval-adult transition (e.g., phanerocephalic pupa), digital eye-color was significantly correlated with CO{sub 2} emission. Results support the suggestion that gas-exchange should be explored further as a system to determine pupal physiological age in mass production of fruit flies. (author) [Spanish] En el presente estudio se investigaron los patrones de intercambio gaseoso (emision de CO{sub 2}) en pupas de la mosca de las frutas del Mediterraneo (Ceratitis capitata Wiedemann) incubadas a diferentes temperaturas. El estudio fue realizado con la finalidad de explorar la utilizacion de sistemas de intercambio gaseoso en la determinacion de la edad fisiologica de pupas durante su produccion masiva en proyectos de mosca esteril. La proporcion de emision de CO{sub 2} fue medido en un sistema cerrado de 'flujo a traves del sistema' conectado a un detector infrarrojo de gases. La actividad metabolica de la pupa (emision de CO{sub 2}) fue contrastado al color del ojo de la pupa en desarrollo, que constituye la actual tecnica de determinacion de la edad fisiologica. El color de ojos en pupa fue determinado digitalmente, usando tres variables (Tendencia, Saturacion e Intensidad). Los colores fueron separados utilizando el analisis discriminatorio. Los patrones de emision de CO{sub 2} durante el desarrollo de la pupa sugieren una tendencia de U: una alta actividad metabolica durante la fase inicial de pupacion y transformacion y durante la fase final del adulto. La temperatura de incubacion afecto el tiempo de desarrollo pero no el patron basico de actividad metabolica. La proporcion de emision de CO{sub 2} uno y dos dias antes de la emergencia del adulto fue muy similar para pupas mantenidas en las diversas temperaturas. El color digital del ojo de la pupa se correlaciono significativamente con los patrones de emision de CO{sub 2} detectados a partir de la fase media de la transformacion de larva a adulto. Los resultados soportan la utilizacion de sistemas de intercambio gaseoso como un sistema auxiliar para la determinacion de la edad fisiologica en cria masiva de moscas de la fruta. (author)

Nestel, D.; Nemny-Lavy, E. [Department of Entomology, Institute of Plant Protection, Agricultural Research Organization, Volcani Center, P.O. Box 6, 50250 Beit-Dagan (Israel); Alchanatis, V. [Department of Sensing, Information and Mechanization, Institute of Agricultural Engineering, Agricultural Research Organization, Volcani Center, P.O. Box 6, 50250 Beit-Dagan (Israel)

2007-03-15

272

Effect of azathioprine on Na(+)/H(+) exchanger activity in dendritic cells.  

PubMed

Azathioprine is a powerful immunosuppressive drug, which is partially effective by interfering with the maturation and function of dendritic cells (DCs), antigen-presenting cells linking innate and adaptive immunity. DCs are stimulated by bacterial lipopolysaccharides (LPS), which trigger the formation of reactive oxygen species (ROS), paralleled by activation of the Na(+)/H(+) exchanger. The carrier is involved in the regulation of cytosolic pH, cell volume and migration. The present study explored whether azathioprine influences Na(+)/H(+) exchanger activity in DCs. DCs were isolated from murine bone marrow, cytosolic pH (pH(i)) was estimated utilizing 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF-AM) fluorescence, Na(+)/H(+) exchanger activity from the Na(+)-dependent realkalinization following an ammonium pulse, cell volume from forward scatter in FACS analysis, ROS production from 2',7'-dichlorodihydrofluorescein diacetate (DCFDA) fluorescence, TNF? release utilizing ELISA, and migration utilizing transwell migration assays. Exposure of DCs to lipopolysaccharide (LPS, 1 ?g/ml) led to a transient increase of Na(+)/H(+) exchanger activity, an effect paralleled by ROS formation, increased cell volume, TNF? production and stimulated migration. Azathioprine (10 ?M) did not significantly alter the Na(+)/H(+) exchanger activity, cell volume and ROS formation prior to LPS exposure but significantly blunted the LPS-induced stimulation of Na(+)/H(+) exchanger activity, ROS formation, cell swelling, TNF? production and cell migration. In conclusion, azathioprine interferes with the activation of dendritic cell Na(+)/H(+) exchanger by bacterial lipopolysaccharides, an effect likely participating in the anti-inflammatory action of the drug. PMID:22508060

Bhandaru, Madhuri; Pasham, Venkanna; Yang, Wenting; Bobbala, Diwakar; Rotte, Anand; Lang, Florian

2012-01-01

273

Greenhouse gas exchange in grasslands: impacts of climate, intensity of management and other factors  

NASA Astrophysics Data System (ADS)

Grasslands occupy some 40% of the terrestrial land surface. They are generally categorised as natural (occurring mainly in those regions where the rainfall is too low to support forest ecosystems), semi-natural (where management, mainly by grazing, has changed the vegetation composition), and artificial (where forests have been cleared to create new pasture land). The soils of the natural and semi-natural grasslands constitute a large reservoir of carbon, and make a substantial contribution to the soil sink for atmospheric CH_4. The conversion of much of the natural temperate grassland to arable agriculture, e.g. in North America and Europe, resulted in a considerable decrease in soil organic carbon, and its release to the atmosphere as CO_2 has made a substantial contribution to the total atmospheric concentration of this gas. The associated increase in cycling of soil N (released from the organic matter) will have contributed to N_2O emissions, and land disturbance and fertilisation has resulted in a depletion of the soil CH_4 sink. Conversion of tropical forests to pastures has also been a major source of CO_2, and these pastures show elevated emissions of N_2O for some years after conversion. Seasonally flooded tropical grasslands are a significant source of CH_4 emissions. Consideration of grassland ecosystems in their entirety, in relation to GHG exchange, necessitates the inclusion of CH_4 production by fauna - domesticated livestock and wild herbivores, as well as some species of termites - in the overall assessment. Stocking rates on pasture land have increased, and the total CH_4 emissions likewise. The relationship between animal production and CH_4 emissions is dependent on the nutritional quality of the vegetation, as well as on animal numbers. In both temperate and tropical regions, increased N inputs as synthetic fertilisers and manures (and increased N deposition) are producing possibly a more-than-linear response in terms of emissions of N_2O. In several Western European countries, very high rates of N application to both grazed grassland and to grass crops grown for winter feed have made these lands the principal source of N_2O. It has been estimated that 40% of global emissions of NO, a precursor of tropospheric ozone, come from grasslands and savannas. Global warming is expected to bring about substantial changes in the overall greenhouse gas exchange of grasslands, with a net loss of soil C as CO_2, and possibly enhanced N_2O emissions. Increased rainfall is predicted for some regions, and this can also be expected to give rise to increases in N_2O.

Smith, K. A.

2003-04-01

274

Trace gas exchange and the validity of similarity theory in the roughness sublayer above forests  

NASA Astrophysics Data System (ADS)

This thesis is an investigation of (1) methane (CH4) and nitrous oxide (N2O) exchange above a boreal aspen (Populus tremuloides) stand near Prince Albert, Saskatchewan, and (2) the similarity theory upon which the flux measurements were based. Although CH4 and N2O play significant roles in the atmosphere, estimates of their global source and sink strengths are only poorly constrained. Boreal ecosystems are a priority trace gas research area, and the CH4 and N2O exchanges were measured as part of the Boreal Ecosystem-Atmosphere Study (BOREAS). The fluxes were determined micrometeorologically using laser-based Trace Gas Analysis Systems (TGAS). Between April and September, 1994, a mean net CH4 emission of 15.7 ± 2.8 ng m-2 s-1 was measured from a tower above the aspen stand. The CH4 emissions peaked in late summer, and the CH4 flux and soil temperature correlated with r2 = 0.70. In contrast, CH4 uptake was recorded near the tower base. Overall, it appears that CH4 emissions from anoxic patches located throughout the above-canopy footprint overwhelmed uptake from drier areas to yield a net emission of CH4. The mean N2O emission of 1.4 ± 0.7 ng m-2 s-1 was attributable to low soil nitrate (NO3/sp-) and ammonium (NH4+) availability. The small CH4 and N2O fluxes required that they be determined using a flux-gradient approach based upon similarity theory. However, similarity theory has been reported to severely underestimate scalar fluxes in the roughness sublayer above forests. Accordingly, the validity of similarity theory was investigated above a mixed deciduous forest at Camp Borden, Ontario, between July and October 1995. The TGAS used in the research enabled a higher resolution measurement than has been previously possible in similarity theory investigations. Between 1.9 and 2.2 canopy heights (hc), the mean enhancement factor (the ratio of independent fluxes to similarity theory values) was 1.15 ± 0.07. Closer to the canopy (1.2 to 1.4 hc), mean enhancement factors of 1.61 ± 0.10 and 1.82 ± 0.11 were measured, before and after leaf senescence, respectively. Overall, it appears that similarity theory can be used within the roughness sublayer of forests with a greater confidence than previously has been believed.

Simpson, Isobel Jane

1997-11-01

275

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.

2013-04-01

276

Design of compact intermediate heat exchangers for gas cooled fast reactors  

E-print Network

Two aspects of an intermediate heat exchanger (IHX) for GFR service have been investigated: (1) the intrinsic characteristics of the proposed compact printed circuit heat exchanger (PCHE); and (2) a specific design optimizing ...

Gezelius, Knut, 1978-

2004-01-01

277

Innovative, counterflow gas/fine solids, direct contact heat exchanger: Final report  

SciTech Connect

The Aerojet Energy Conversion Company has completed the first phase of study for development of a heat exchanger. The heat exchanger, a highly efficient, low cost concept, is a candidate for application in process manufacturing industries such as cement, lime, or glass. The analytical effort was to establish the heat exchanger performance via computer modeling and analysis; the experimental effort was to demonstrate the heat exchanger performance.

Mah, C.S.

1987-10-01

278

Responses of sap flow, leaf gas exchange and growth of hybrid aspen to elevated atmospheric humidity under field conditions  

PubMed Central

An increase in average air temperature and frequency of rain events is predicted for higher latitudes by the end of the 21st century, accompanied by a probable rise in air humidity. We currently lack knowledge on how forest trees acclimate to rising air humidity in temperate climates. We analysed the leaf gas exchange, sap flow and growth characteristics of hybrid aspen (Populus tremula × P. tremuloides) trees growing at ambient and artificially elevated air humidity in an experimental forest plantation situated in the hemiboreal vegetation zone. Humidification manipulation did not affect the photosynthetic capacity of plants, but did affect stomatal responses: trees growing at elevated air humidity had higher stomatal conductance at saturating photosynthetically active radiation (gs sat) and lower intrinsic water-use efficiency (IWUE). Reduced stomatal limitation of photosynthesis in trees grown at elevated air humidity allowed slightly higher net photosynthesis and relative current-year height increments than in trees at ambient air humidity. Tree responses suggest a mitigating effect of higher air humidity on trees under mild water stress. At the same time, trees at higher air humidity demonstrated a reduced sensitivity of IWUE to factors inducing stomatal closure and a steeper decline in canopy conductance in response to water deficit, implying higher dehydration risk. Despite the mitigating impact of increased air humidity under moderate drought, a future rise in atmospheric humidity at high latitudes may be disadvantageous for trees during weather extremes and represents a potential threat in hemiboreal forest ecosystems. PMID:24887000

Niglas, Aigar; Kupper, Priit; Tullus, Arvo; Sellin, Arne

2014-01-01

279

Responses of sap flow, leaf gas exchange and growth of hybrid aspen to elevated atmospheric humidity under field conditions.  

PubMed

An increase in average air temperature and frequency of rain events is predicted for higher latitudes by the end of the 21st century, accompanied by a probable rise in air humidity. We currently lack knowledge on how forest trees acclimate to rising air humidity in temperate climates. We analysed the leaf gas exchange, sap flow and growth characteristics of hybrid aspen (Populus tremula × P. tremuloides) trees growing at ambient and artificially elevated air humidity in an experimental forest plantation situated in the hemiboreal vegetation zone. Humidification manipulation did not affect the photosynthetic capacity of plants, but did affect stomatal responses: trees growing at elevated air humidity had higher stomatal conductance at saturating photosynthetically active radiation (gs sat) and lower intrinsic water-use efficiency (IWUE). Reduced stomatal limitation of photosynthesis in trees grown at elevated air humidity allowed slightly higher net photosynthesis and relative current-year height increments than in trees at ambient air humidity. Tree responses suggest a mitigating effect of higher air humidity on trees under mild water stress. At the same time, trees at higher air humidity demonstrated a reduced sensitivity of IWUE to factors inducing stomatal closure and a steeper decline in canopy conductance in response to water deficit, implying higher dehydration risk. Despite the mitigating impact of increased air humidity under moderate drought, a future rise in atmospheric humidity at high latitudes may be disadvantageous for trees during weather extremes and represents a potential threat in hemiboreal forest ecosystems. PMID:24887000

Niglas, Aigar; Kupper, Priit; Tullus, Arvo; Sellin, Arne

2014-01-01

280

Heat transfer in a compact heat exchanger containing rectangular channels and using helium gas  

NASA Technical Reports Server (NTRS)

Development of a National Aerospace Plane (NASP), which will fly at hypersonic speeds, require novel cooling techniques to manage the anticipated high heat fluxes on various components. A compact heat exchanger was constructed consisting of 12 parallel, rectangular channels in a flat piece of commercially pure nickel. The channel specimen was radiatively heated on the top side at heat fluxes of up to 77 W/sq cm, insulated on the back side, and cooled with helium gas flowing in the channels at 3.5 to 7.0 MPa and Reynolds numbers of 1400 to 28,000. The measured friction factor was lower than that of the accepted correlation for fully developed turbulent flow, although the uncertainty was high due to uncertainty in the channel height and a high ratio of dynamic pressure to pressure drop. The measured Nusselt number, when modified to account for differences in fluid properties between the wall and the cooling fluid, agreed with past correlations for fully developed turbulent flow in channels. Flow nonuniformity from channel-to-channel was as high as 12 pct above and 19 pct below the mean flow.

Olson, D. A.

1991-01-01

281

Ex-situ characterisation of gas diffusion layers for proton exchange membrane fuel cells  

NASA Astrophysics Data System (ADS)

This paper presents the first part of a complete ex-situ characterisation of a wide range of commercial Gas Diffusion Layers (GDLs) used in low temperature and high temperature Proton Exchange Membrane (PEM) fuel cells. Physical and electrical characteristics of the GDLs are reported. The results show that the substrate structure has a significant effect on the mechanical and electrical properties of the GDL. Moreover, the Micro Porous Layer (MPL) structure determines the roughness of the surface, and affects the permeability and porosity of the GDL. It was found that the substrate treatment with PTFE affects the GDL characteristics; PTFE loading increases the GDLs hydrophobicity and permeability, however, decreases its overall porosity and resistivity. Adding a MPL to the substrate, results in a decrease in porosity and permeability and an increase in resistivity. The contact resistance of the GDL and the bipolar plate increases when the GDL thickness and PTFE loading are increased. This technical paper shows a close relationship between GDL materials and their physical characteristics and highlights the importance of optimising GDLs for fuel cell applications.

El-kharouf, Ahmad; Mason, Thomas J.; Brett, Dan J. L.; Pollet, Bruno G.

2012-11-01

282

UV-B impairs growth and gas exchange in grapevines grown in high altitude.  

PubMed

We previously demonstrated that solar ultraviolet-B (UV-B) radiation levels in high altitude vineyards improve berry quality in Vitis vinifera cv. Malbec, but also reduce berry size and yield, possibly as a consequence of increased oxidative damage and growth reductions (lower photosynthesis). The defense mechanisms toward UV-B signal and/or evoked damage promote production of antioxidant secondary metabolites instead of primary metabolites. Purportedly, the UV-B effects will depend on tissues developmental stage and interplay with other environmental conditions, especially stressful situations. In this work, grapevines were exposed to high solar UV-B (+UV-B) and reduced (by filtering) UV-B (-UV-B) treatments during three consecutive seasons, and the effects of UV-B, developmental stages and seasons on the physiology were studied, i.e. growth, tissues morphology, photosynthesis, photoprotective pigments, proline content and antioxidant capacity of leaves. The +UV-B reduced photosynthesis and stomatal conductance, mainly through limitation in gas exchange, reducing plant's leaf area, net carbon fixation and growth. The +UV-B augmented leaf thickness, and also the amounts of photoprotective pigments and proline, thereby increasing the antioxidant capacity of leaves. The defense mechanisms triggered by + UV-B reduced lipid peroxidation, but they were insufficient to protect the photosynthetic pigments per leaf dry weight basis. The +UV-B effects depend on tissues developmental stage and interplay with other environmental conditions such as total radiation and air temperatures. PMID:23167433

Berli, Federico J; Alonso, Rodrigo; Bressan-Smith, Ricardo; Bottini, Rubén

2013-09-01

283

Leaf Gas Exchange and Chlorophyll a Fluorescence in Maize Leaves Infected with Stenocarpella macrospora.  

PubMed

ABSTRACT This study investigated the effect of macrospora leaf spot (MLS), caused by Stenocarpella macrospora, on photosynthetic gas exchange parameters and chlorophyll a fluorescence parameters determined in leaves of plants from two maize cultivars ('ECVSCS155' and 'HIB 32R48H') susceptible and highly susceptible, respectively, to S. macrospora. MLS severity was significantly lower in the leaves of plants from ECVSCS155 relative to the leaves of plants from HIB 32R48H. In both cultivars, net CO2 assimilation rate, stomatal conductance, and transpiration rate significantly decreased, while the internal to ambient CO2 concentration ratio increased in inoculated plants relative to noninoculated plants. The initial fluorescence and nonphotochemical quenching significantly increased in inoculated plants of ECVSCS155 and HIB 32R48H, respectively, relative to noninoculated plants. The maximum fluorescence, maximum PSII quantum efficiency, coefficient for photochemical quenching, and electron transport rate significantly decreased in inoculated plants relative to noninoculated plants. For both cultivars, concentrations of total chlorophyll (Chl) (a + b) and carotenoids and the Chl a/b ratio significantly decreased in inoculated plants relative to noninoculated plants. In conclusion, the results from the present study demonstrate, for the first time, that photosynthesis in the leaves of maize plants is dramatically affected during the infection process of S. macrospora, and impacts are primarily associated with limitations of a diffusive and biochemical nature. PMID:25014681

Bermúdez-Cardona, Maria Bianney; Filho, João Américo Wordell; Rodrigues, Fabrício Ávila

2015-01-01

284

Leaf Gas Exchange and Chlorophyll a Fluorescence Imaging of Rice Leaves Infected with Monographella albescens.  

PubMed

This study was intended to analyze the photosynthetic performance of rice leaf blades infected with Monographella albescens by combining chlorophyll (Chl) a fluorescence images with gas exchange and photosynthetic pigment pools. The net CO2 assimilation rate, stomatal conductance, transpiration rate, total Chl and carotenoid pools, and Chl a/b ratio all decreased but the internal CO2 concentration increased in the inoculated plants compared with their noninoculated counterparts. The first detectable changes in the images of Chl a fluorescence from the leaves of inoculated plants were already evident at 24 h after inoculation (hai) and increased dramatically as the leaf scald lesions expanded. However, these changes were negligible for the photosystem II photochemical efficiency (Fv/Fm) at 24 hai, in contrast to other Chl fluorescence traits such as the photochemical quenching coefficient, yield of photochemistry, and yield for dissipation by downregulation; which, therefore, were much more sensitive than the Fv/Fm ratio in assessing the early stages of fungal infection. It was also demonstrated that M. albescens was able to impair the photosynthetic process in both symptomatic and asymptomatic leaf areas. Overall, it was proven that Chl a fluorescence imaging is an excellent tool to describe the loss of functionality of the photosynthetic apparatus occurring in rice leaves upon infection by M. albescens. PMID:25163009

Tatagiba, Sandro Dan; DaMatta, Fábio Murilo; Rodrigues, Fabrício Ávila

2015-02-01

285

Relationships between lung computed tomographic density, gas exchange, and PEEP in acute respiratory failure.  

PubMed

Twenty-two patients with acute respiratory failure underwent lung computed tomography (CT) and physiological measurements at 5, 10, and 15 cm H2O positive end-expiratory pressure (PEEP) to investigate the relationship between morphology and function. Lung densities were primarily concentrated in the dependent regions. From the frequency distribution of CT numbers (difference in x-ray attenuation between water and lung) and lung gas volume measurements the authors obtained a quantitative estimate of normally inflated, poorly inflated, and non-inflated lung tissue weight. This estimated average lung weight was increased twofold above normal and excess lung weight correlated with the mean pulmonary artery pressure (P less than 0.01). Venous admixture correlated with the non-inflated tissue mass (P less than 0.01). Increasing PEEP caused progressive clearing of radiographic densities and increased the mass of normally inflated tissue (anatomic recruitment), while reducing venous admixture. The cardiac index decreased after increasing PEEP while oxygen delivery was unchanged. The authors conclude that CT scan lung density and oxygen exchange efficiency are correlated; the main effect of augmenting PEEP is to recruit perfused alveolar units that were previously collapsed. PMID:3057937

Gattinoni, L; Pesenti, A; Bombino, M; Baglioni, S; Rivolta, M; Rossi, F; Rossi, G; Fumagalli, R; Marcolin, R; Mascheroni, D

1988-12-01

286

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

PubMed

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

2013-03-01

287

Neutral Gas in Starbursts and Active Galactic Nuclei  

NASA Astrophysics Data System (ADS)

High angular resolution decimetric observations of neutral gas in active galactic nuclei and starburst galaxies are reviewed. The neutral gas is mostly observed via atomic hydrogen absorption, or via maser emission from the hydroxyl radical (OH). The role of these observations in investigating the properties of neutral gas associated with the proposed dusty torus in AGN is discussed, together with the dynamical constraints to the mass of possible black holes in starburst galaxies.

Pedlar, Alan

288

Neutral Gas in Starbursts and Active Galactic Nuclei  

NASA Astrophysics Data System (ADS)

High angular resolution decimetric observations of neutral gas in active galactic nuclei and starburst galaxies are reviewed. The neutral gas is mostly observed via atomic hydrogen absorption, or via maser emission from the hydroxyl radical (OH). The role of these observations in investigating the properties of neutral gas associated with the proposed dusty torus in AGN is discussed, together with the dynamical constraints to the mass of possible black holes in starburst galaxies.

Pedlar, Alan

2005-01-01

289

Hypersonic flow code validation activity: Real gas flows  

NASA Technical Reports Server (NTRS)

Validation activities and facility types are discussed for six different flow codes: (1) perfect gas; (2) real gas; (3) nozzle/plume; (4) combustion; (5) thermochemical nonequilibrium; and (6) boundary layer and transition. All data and results are presented in viewgraph format.

Deiwert, George S.

1987-01-01

290

Effect of wind and currents on gas exchange in an estuarine system. Final technical report, 1 August 1986-31 July 1987  

SciTech Connect

The objectives were to develop a non-volatile tracer to use in gas exchange experiments in laterally unconfined systems and to study applications of deliberate tracers in limnology and oceanography. Progress was made on both fronts but work on the development of the non-volatile tracer proved to be more difficult and labor intensive that anticipated so no field experiments using non-volatile tracers was performed as yet. In the search for a suitable non-volatile tracer for an ocean scale gas exchange experiment a tracer was discovered which does not have the required sensitivity for a large scale experiment, but is very easy to analyze and will be well suited for smaller experiments such as gas exchange determinations on rivers and streams. Sulfur hexafluoride, SF/sub 6/, was used successfully as a volatile tracer along with tritium as a non-volatile tracer to study gas exchange rates from a primary stream. This is the first gas exchange experiment in which gas exchange rates were determined on a head water stream where significant groundwater input occurs along the reach. In conjunction with SF/sub 6/, Radon-222 measurements were performed on the groundwater and in the stream. The feasibility of using a combination of SF/sub 6/ and radon is being studied to determine groundwater inputs and gas exchange of rates in streams with significant groundwater input without using a non-volatile tracer.

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

1987-11-01

291

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

1998-01-01

292

Ion-exchange sorption and preparative chromatography of biologically active materials  

SciTech Connect

This book presents information on the following topics: the problems of fine physico-chemical biotechnology; types of highly permeable network polyelectrolytes; methods for studying the permeability and porosity of network polyelectrolytes; the conformation state and flexibility of the structural elements of network polyelectrolytes; ion-exchange processes without the sorption of physiologically active substances; ion exchange, hydration, and swelling; nucleosides, nucleotides, alkaloids, sulfonamides, and miscellaneous physiologically active subtances; sharp front formation for the exchange of ions with the same valences; standard quasi-equilibrium frontal chromatography on ionites; sorption kinetics in ionites with structural heterogeneity; experimental investigations of the diffusivities of organic and physiologically active ions in ionite beads; and increasing the efficiency of low-pressure chromatography by using surface-layer and bidispersed ionites.

Samsonov, G.V.

1986-01-01

293

Current activity in the exchange of environmental data between the United States and the Russian Federation  

NASA Astrophysics Data System (ADS)

In November, 2008 data exchange coordinators from NOAA, Roshydromet, Oak Ridge National Laboratory (ORNL), the National Center for Atmospheric Research (NCAR), and the National Snow and Ice Data Center (NSIDC) met at the All Russian Institute for Hydrometeorological Information (RIHMI) in Obninsk, Russia to renew data exchange and research protocols, and to update existing data exchanges between the United States and Russia, many of which have been occurring since the 1970s. The coordinators also discussed the development of new data sets, the exchange of International Polar Year (IPY) data, the rescue of historical data from deteriorating media, and the conduct of joint research activities in support of data collection, compilation, and analyses. In addition to detailing new bilateral data exchanges and joint U.S.- Russian research activities, this paper provides an overview of the status of a number of environmental data sets presently available to researchers that are either directly exchanged between the United States and the Russian Federation or to which both the U.S. and Russia provide data.

Shein, K. A.; Sterin, A. M.; Shaimardanov, M. Z.; Kaiser, D. P.; Worley, S. J.; Barry, R. G.; Fetterer, F. M.; Diamond, H. J.

2008-12-01

294

The greenhouse gas exchange responses of methane and nitrous oxide to forest change in Europe  

NASA Astrophysics Data System (ADS)

Climate change and air pollution, interact with altering forest management and land-use change to produce short and long-term changes to forest in Europe. The impact of these changes on the forest greenhouse gas (GHG) balance is currently difficult to predict. To improve the mechanistic understanding of the ongoing changes, we studied the response of GHG (N2O, CH4) exchange from forest soils at twelve experimental or natural gradient forest sites, representing anticipated future forest change. The experimental manipulations one or more per site included nitrogen (N) addition (4 sites), changes of climate (temperature, 1 site; precipitation, 2 sites), soil hydrology (3 sites), harvest intensity (1 site), wood ash fertilization (1 site), pH gradient in peat (1 site) and afforestation of cropland (1 site). In most of the investigated treatments N2O emissions increased by 7 ± 3 (range 0-30) ?g N2O-N m-2 h-1 across all treatments on mineral soils, but by up to 10 times the mineral soil maximum on an acidic organic soil. Soil moisture together with mineral soil C/N ratio and pH were found to significantly influence N2O emissions across all treatments. Emissions increased with N availability and decreased with soil C/N ratio, especially in interaction with increased soil moisture. High pH reduced the formation of N2O, even under otherwise favourable soil conditions. Oxidation (uptake) of CH4 was reduced from 16 ± 2 to 4 ± 6 ?g CH4-C m-2 h-1 by the investigated treatments. The CH4 exchange was significantly influenced by soil moisture and soil C/N ratio across all treatments, and CH4 emissions occurred only in wet or water-saturated conditions. For most of the investigated forest manipulations or natural gradients, the response of both N2O and CH4 fluxes was towards reducing the overall GHG forest sink. The most resilient forests were dry Mediterranean forests, as well as forests with high soil C/N ratio or high soil pH. Mitigation strategies may focus on (i) sustainable management of wet forest areas and forested peat lands, (ii) continuous forest cover management, (iii) reducing atmospheric N input and, thus, N availability, and (iv) improving neutralisation capacity of acid soils (e.g. wood ash application).

Gundersen, P.; Christiansen, J. R.; Alberti, G.; Brüggemann, N.; Castaldi, S.; Gasche, R.; Kitzler, B.; Klemedtsson, L.; Lobo-do-Vale, R.; Moldan, F.; Rütting, T.; Schleppi, P.; Weslien, P.; Zechmeister-Boltenstern, S.

2012-05-01

295

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. PMID:21982294

Yeh, Chyi-Huey Josh; Dimachkie, Ziad O.; Golas, Avantika; Cheng, Alice; Parhi, Purnendu; Vogler, Erwin A.

2011-01-01

296

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

PubMed

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

1976-01-01

297

Corrosive resistant heat exchanger  

DOEpatents

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)

1989-01-01

298

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

1998-01-01

299

A general model of forest ecosystem processes for regional applications I. Hydrologic balance, canopy gas exchange and primary production processes  

Microsoft Academic Search

Running, S.W. and Coughlan, J.C., 1988. A general model of forest ecosystem processes for regional applications. I. Hydrologic balance, canopy gas exchange and primary production processes. Ecol. Modelling, 42: 125-154. An ecosystem process model is described that calculates the carbon, water and nitrogen cycles through a forest ecosystem. The model, FOREST-BGC, treats canopy interception and evaporation, transpiration, photosynthesis, growth and

STEVEN W. RUNNING; JOSEPH C. COUGHLAN

1988-01-01

300

Seasonal photosynthetic gas exchange and water-use efficiency in a constitutive CAM plant, the giant saguaro cactus ( Carnegiea gigantea )  

Microsoft Academic Search

Crassulacean acid metabolism (CAM) and the capacity to store large quantities of water are thought to confer high water use\\u000a efficiency (WUE) and survival of succulent plants in warm desert environments. Yet the highly variable precipitation, temperature\\u000a and humidity conditions in these environments likely have unique impacts on underlying processes regulating photosynthetic\\u000a gas exchange and WUE, limiting our ability to

Dustin R. Bronson; Nathan B. English; David L. Dettman; David G. Williams

301

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

1984-01-01

302

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

ALLAN H. DEVOL; PAUL D. QUAY; JEFFREY E. RICHEY; LUIZ A. MARTINELLI

1987-01-01

303

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.

RICHARD B. FLAGLER; JOHN E. LOCK; CHRISTINE G. ELSIK

304

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

1995-01-01

305

Relationships between gas exchange and carbon isotope discrimination of Sitka x interior spruce introgressive genotypes and ribosomal DNA markers.  

PubMed

Effects of hybridization on physiological performance were investigated in seven natural introgressive populations and one F(1) population of Sitka (Picea sitchensis (Bong.) Carr.) x interior spruce (P. glauca (Moench) Voss. x P. engelmannii Parry ex Engelm.). Each population was represented by a Sitka-interior spruce ribosomal DNA (Si rDNA) index that was calculated from the relative abundance of species-specific DNA polymorphisms. Gas exchange parameters were measured under well-watered conditions on current-year needle tissues, which were also analyzed for carbon isotope discrimination. Sitka spruce populations had higher gas exchange rates (net photosynthesis, stomatal conductance to water vapor), but lower carbon isotope discrimination values than interior spruce populations. The natural hybrid populations had intermediate values of these parameters consistent with their Si rDNA index. The F(1) population had gas exchange parameters resembling those of Sitka spruce populations, but its carbon isotope discrimination was skewed toward that of interior spruce populations. These results confirmed previous findings that physiological performance of introgressive hybrid spruce populations varied as their DNA constitution changed. PMID:12651325

Fan, Shihe; Grossnickle, Steven C.; Sutton, Ben C. S.

1999-08-01

306

Effect of Adding a Regenerator to Kornhauser's MIT "Two-Space" (Gas-Spring+Heat Exchanger) Test Rig  

NASA Technical Reports Server (NTRS)

This study employed entropy-based second law post-processing analysis to characterize the various thermodynamic losses inside a 3-space solution domain (gas spring+heat exchanger+regenerator) operating under conditions of oscillating pressure and oscillating flow. The 3- space solution domain is adapted from the 2-space solution domain (gas spring+heat exchanger) in Kornhauser's MIT test rig by modifying the heat exchanger space to include a porous regenerator system. A thermal nonequilibrium model which assumes that the regenerator porous matrix and gas average temperatures can differ by several degrees at a given axial location and time during the cycle is employed. An important and primary objective of this study is the development and application of a thermodynamic loss post-processor to characterize the major thermodynamic losses inside the 3-space model. It is anticipated that the experience gained from thermodynamic loss analysis of the simple 3-space model can be extrapolated to more complex systems like the Stirling engine. It is hoped that successful development of loss post-processors will facilitate the improvement of the optimization capability of Stirling engine analysis codes through better understanding of the heat transfer and power losses. It is also anticipated that the incorporation of a successful thermal nonequilibrium model of the regenerator in Stirling engine CFD analysis codes, will improve our ability to accurately model Stirling regenerators relative to current multidimensional thermal-equilibrium porous media models.

Ebiana, Asuquo B.; Gidugu, Praveen

2008-01-01

307

Analytic exchange integral for coupled cluster theory in the homogeneous electron gas  

NASA Astrophysics Data System (ADS)

A six-dimensional integral occurring in the description of the ground state of the homogeneous electron gas was calculated analytically. This formula, together with the one of a previous work [G.G. Hoffman, Phys. Rev. B 45 (1992) 8730], reduces from seven to one the dimension of the numerical integrations to be performed in the RPA+RPAEX approximation for the correlation energy [R.F. Bishop, K.H. Lührmann, Phys. Rev. B 26 (1982) 5523]. Program summaryTitle of program: qexm2em1 Catalogue identifier:ADXJ_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADXJ_v1_0 Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Distribution format: tar.gz Computers: Created using a PC, but can be run on UNIX machines Operating system under which the program has been tested: Linux Programming language used: Mathematica 4.0 (due to versions incompatibility the program does not work with more recent versions like Mathematica 5.1) Memory required to execute with typical data: 151 Mb Number of processors used: 1 Has this code been vectorized or parallelized? no No. of lines in distributed program, including test data, etc.: 13 415 Number of bytes in distributed program, including test data, etc.: 102 988 Nature of the physical problem: The program gives an analytical derivation of a six-dimensional exchange integral involved in the calculation of the correlation energy of the electron gas. Method of solution: Changes of variables were gradually introduced in order to decrease the dimensionality of the integral, and eventually an analytical expression was obtained. Restrictions on the complexity of the program: The present version of the program has been designed only for calculating only one integral. Though, the method can be used for other cylindrically-symmetric integrals. Typical running times: file formula.nb: less than 1 s; qexm2em1.nb: 02 mn 02 s; qexm2em1qinf2AA.nb: 09 mn 42 s; qexm2em1qinf2BB.nb: 08 mn 05 s; qexm2em1qinf2AB.nb: 00 mn 43 s; qexm2em1qsup2.nb: 23 mn 26 s on 1 GHz machine.

Gutlé, Claudine

2006-05-01

308

Influence of exercise modality on agreement between gas exchange and heart rate variability thresholds.  

PubMed

The main purpose of this study was to investigate the level of agreement between the gas exchange threshold (GET) and heart rate variability threshold (HRVT) during maximal cardiopulmonary exercise testing (CPET) using three different exercise modalities. A further aim was to establish whether there was a 1:1 relationship between the percentage heart rate reserve (%HRR) and percentage oxygen uptake reserve (%VO2 R) at intensities corresponding to GET and HRVT. Sixteen apparently healthy men 17 to 28 years of age performed three maximal CPETs (cycling, walking, and running). Mean heart rate and VO2 at GET and HRVT were 16 bpm (P<0.001) and 5.2 mL · kg(-1) · min(-1) (P=0.001) higher in running than cycling, but no significant differences were observed between running and walking, or cycling and walking (P>0.05). There was a strong relationship between GET and HRVT, with R2 ranging from 0.69 to 0.90. A 1:1 relationship between %HRR and % VO2 R was not observed at GET and HRVT. The %HRR was higher during cycling (GET mean difference=7%; HRVT mean difference=11%; both P<0.001), walking (GET mean difference=13%; HRVT mean difference=13%; both P<0.001), or running (GET mean difference=11%; HRVT mean difference=10%; both P<0.001). Therefore, using HRVT to prescribe aerobic exercise intensity appears to be valid. However, to assume a 1:1 relationship between %HRR and % VO2 R at HRVT would probably result in overestimation of the energy expenditure during the bout of exercise. PMID:25003546

Cunha, F A; Montenegro, R A; Midgley, A W; Vasconcellos, F; Soares, P P; Farinatti, P

2014-08-01

309

Effects of elevated CO(2) on chloroplast components, gas exchange and growth of oak and cherry.  

PubMed

Specific chloroplast proteins, gas exchange and dry matter production in oak (Quercus robur L.) seedlings and clonal cherry (Prunus avium L. x pseudocerasus Lind.) plants were measured during 19 months of growth in climate-controlled greenhouses at ambient (350 vpm) or elevated (700 vpm) CO(2). In both species, the elevated CO(2) treatment increased the PPFD saturated-rate of photosynthesis and dry matter production. After two months at elevated CO(2), Prunus plants showed significant increases in leaf (55%) and stem (61%) dry mass but not in root dry mass. However, this initial stimulation was not sustained: treatment differences in net assimilation rate (A) and plant dry mass were less after 10 months of growth than after 2 months of growth, suggesting acclimation of A to elevated CO(2) in Prunus. In contrast, after 10 months of growth at elevated CO(2), leaf dry mass of Quercus increased (130%) along with shoot (356%) and root (219%) dry mass, and A was also twice that of plants grown and measured at ambient CO(2). The amounts of Rubisco and the thylakoid-bound protein cytochrome f were higher in Quercus plants grown for 19 months in elevated CO(2) than in control plants, whereas in Prunus there was less Rubisco in plants grown for 19 months in elevated CO(2) than in control plants. Exposure to elevated CO(2) for 10 months resulted in increased mean leaf area in both species and increased abaxial stomatal density in Quercus. There was no change in leaf epidermal cell size in either species in response to the elevated CO(2) treatment. The lack of acclimation of photosynthesis in oak grown at elevated CO(2) is discussed in relation to the production and allocation of dry matter. We propose that differences in carbohydrate utilization underlie the differing long-term CO(2) responses of the two species. PMID:14759855

Atkinson, C J; Taylor, J M; Wilkins, D; Besford, R T

1997-05-01

310

Influence of exercise modality on agreement between gas exchange and heart rate variability thresholds  

PubMed Central

The main purpose of this study was to investigate the level of agreement between the gas exchange threshold (GET) and heart rate variability threshold (HRVT) during maximal cardiopulmonary exercise testing (CPET) using three different exercise modalities. A further aim was to establish whether there was a 1:1 relationship between the percentage heart rate reserve (%HRR) and percentage oxygen uptake reserve (%V?O2?R) at intensities corresponding to GET and HRVT. Sixteen apparently healthy men 17 to 28 years of age performed three maximal CPETs (cycling, walking, and running). Mean heart rate and V?O2 at GET and HRVT were 16 bpm (P<0.001) and 5.2 mL·kg-1·min-1 (P=0.001) higher in running than cycling, but no significant differences were observed between running and walking, or cycling and walking (P>0.05). There was a strong relationship between GET and HRVT, with R2 ranging from 0.69 to 0.90. A 1:1 relationship between %HRR and %V?O2?R was not observed at GET and HRVT. The %HRR was higher during cycling (GET mean difference=7%; HRVT mean difference=11%; both P<0.001), walking (GET mean difference=13%; HRVT mean difference=13%; both P<0.001), or running (GET mean difference=11%; HRVT mean difference=10%; both P<0.001). Therefore, using HRVT to prescribe aerobic exercise intensity appears to be valid. However, to assume a 1:1 relationship between %HRR and %V?O2?R at HRVT would probably result in overestimation of the energy expenditure during the bout of exercise. PMID:25003546

Cunha, F.A.; Montenegro, R.A.; Midgley, A.W.; Vasconcellos, F.; Soares, P.P.; Farinatti, P.

2014-01-01

311

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

NASA Technical Reports Server (NTRS)

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

Cao, W.; Tibbitts, T. W.

1991-01-01

312

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

2010-09-01

313

Molecular gas in water megamaser active galaxies  

E-print Network

We have searched for molecular gas towards the nucleus of four galaxies known to harbor a water vapor megamaser. CO(1-->0) emission of NGC 2639 and NGC 5506 was strong enough to allow us to map their inner regions. Weak emission from Mrk 1210 was detected and Mrk 1 was not detected at all. We report the tentative detection of the CO(2-->1) line in NGC 5506. After this work, 12 of the 18 known galaxies harboring a water vapor megamaser have been observed in CO.

F. Raluy; P. Planesas; L. Colina

1998-03-25

314

Reduced sodium-proton exchange activity in lymphocytes from transgenic rats.  

PubMed

We investigated sodium-proton (Na(+)-H+) exchange activity in transgenic TGR(mRen-2)27 rats, a strain showing fulminant hypertension after the mouse Ren-2d renin gene has been integrated into its genome, in age-matched normotensive Sprague-Dawley (SD) rats, in spontaneously hypertensive rats (SHR) from the Münster strain, and in normotensive Wistar-Kyoto (WKY) rats. From each strain Na(+)-H+ exchange activity was determined in lymphocytes using the pH-sensitive fluorescent dye 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein acetoxymethyl ester (BCECF-AM) by measuring the recovery rate of cytosolic pH (pHi) after intracellular acidification. Resting pHi was not significantly different in transgenic rats (n = 10) compared with SD rats (n = 10) (7.305 +/- 0.038 versus 7.337 +/- 0.031; mean +/- SEM), but resting pHi was significantly lower in lymphocytes from SHR (n = 12) compared with their normotensive WKY counterparts (n = 12) (7.232 +/- 0.030 versus 7.377 +/- 0.022; P < .01). Na(+)-H+ exchange activity was significantly lower in lymphocytes from transgenic rats compared with SD rats (5.102 +/- 0.561 versus 7.385 +/- 0.491 x 10(-3) dpHi/s; P < .01), whereas Na(+)-H+ exchange was significantly enhanced in lymphocytes from SHR compared with WKY rats (5.564 +/- 0.432 versus 3.921 +/- 0.433 x 10(-3) dpHi/s; P < .05). The apparent half-maximal activation of Na(+)-H+ exchange was not significantly different in the strains tested. The present study indicates that hypertension in transgenic rats is not related to Na(+)-H+ exchange overactivity. PMID:8082942

Tepel, M; Klaus, T; Laukemper, S; Zidek, W

1994-09-01

315

Erythropoietin-induced Neuroprotection Requires Cystine Glutamate Exchanger Activity  

PubMed Central

Erythropoietin (Epo) has been used for many years in neonates for the treatment of anemia of prematurity. Epo has also been proposed for treatment of neonatal brain injury, as mounting evidence suggests neuroprotective properties for Epo. However, Epo’s neuroprotective mechanism of action is poorly understood. In this study we hypothesized that Epo may confer neuroprotection by enhancing cellular redox defense brought about by cellular glutathione (GSH). This was examined in cultures of differentiated cortical neural stem cells and using the B104 cell line as model systems. Our data shows that Epo causes a time- and dose-dependent increase in expression and activity of system Xc?, the transporter responsible for uptake of cystine for the production of glutathione. Cystine uptake increases 3–5 fold in differentiated neural stem cells and B104 cells treated with Epo. Exposure of cells to 100?M kainate suppressed cellular GSH and caused excitotoxicity, but GSH levels and cell viability was completely restored by Epo in the continued presence of kainate. This rescue effect of Epo vanished if system Xc? was inhibited pharmacologically using S4-CPG in the presence of Epo leading to marked cell death of B104 cells and cultured mouse cortical neural stem cells. This could also be achieved using xCT siRNA to decrease xCT expression. This data suggests that system Xc? activity and protein expression are positively regulated by Epo directly explaining its neuroprotective effect. PMID:20102705

Sims, Brian; Clarke, Melinda; Njah, Wilfred; Hopkins, E’lana Shuford; Sontheimer, Harald

2010-01-01

316

Rapid intravenous infusion of 20 ml/kg saline does not impair resting pulmonary gas exchange in the healthy human lung  

PubMed Central

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 (V??a/Q??) inequality as opposed to a diffusive impairment in O2 exchange. Seven males (26 ± 3 yr; FEV1: 110 ± 16% predicted.) performed spirometry and had V??a/Q?? mismatch measured using the multiple inert gas elimination technique, before and after 20 ml/kg iv of normal saline delivered in ?30 min. Infusion increased thoracic fluid content from transthoracic impedance by 12% (P < 0.0001) and left FVC unchanged but reduced expiratory flows (FEF25–75 falling from 5.1 ± 0.4 to 4.2 ± 0.4 l/s, P < 0.05). However, V??a/Q?? mismatch as measured by the log standard deviation of the ventilation (LogSDV??) and perfusion (LogSDQ??) distributions remained unchanged; LogSDV??: 0.40 ± 0.03 pre, 0.38 ± 0.04 post, NS; LogSDQ??: 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 V??a/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 V??a 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

Olfert, I. Mark; Arai, Tatsuya J.; Wagner, Peter D.; Hopkins, Susan R.

2010-01-01

317

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. PMID:19921790

Rand, Kasper D.; Pringle, Steven D.; Murphy, James P.; Fadgen, Keith E.; Brown, Jeff; Engen, John R.

2009-01-01

318

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.

2012-01-01

319

Final Report on Regional Exchange Activities During the October 1976-February 1977 Planning Phase.  

ERIC Educational Resources Information Center

This report describes in detail the Central Midwest Regional Educational Laboratory's (CEMREL) activities during the October 1976-February 1977 planning phase of the nationwide R & D Exchange (RDX) program sponsored by the National Institute of Education. Basically, CEMREL's task during the planning period was to develop plans for the creation and…

CEMREL, Inc., St. Louis, MO.

320

ARSENIC REMOVAL FROM DRINKING WATER BY ION EXCHANGE AND ACTIVATED ALUMINA PLANTS  

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...

321

Feasibility study on the applicability of a diffusion-welded compact intermediate heat exchanger to next-generation high temperature gas-cooled reactor  

Microsoft Academic Search

The development of an intermediate heat exchanger (IHX) transferring high temperature heat to a process heat application is of prime importance for a next-generation high temperature gas-cooled reactor (HTGR). The IHX needs high structural integrity and reliability over 900°C for a long duration. A plate fin type compact heat exchanger (PFCHX) has a large heat transfer area per heat exchanger

Takeshi Takeda; Kazuhiko Kunitomi; Tetsuji Horie; Katsuo Iwata

1997-01-01

322

Selective inhibition of the Na + \\/H + exchanger type 3 activates CO 2 \\/H + -sensitive medullary neurones  

Microsoft Academic Search

Hypercapnia as well as lowered intracellular pH (pHi) increase the bioelectric activity of CO2\\/H+-sensitive neurones (VLNcs) of the ventrolateral medulla oblongata. Here we describe that immunoreactive Na+\\/H+ exchanger (NHE3) is present in ventrolateral neurones from medullary organotypic cultures (obex level). To test whether VLNcs\\u000a can be acidified and thereby activated by inhibition of NHE3, we used the novel high-affinity NHE3-inhibitors

Martin Wiemann; Jan-Robert Schwark; Udo Bonnet; Hans Willi Jansen; Sergio Grinstein; Robert E. Baker; Hans-Jochen Lang; Klaus Wirth; Dieter Bingmann

1999-01-01

323

You can use a mobile device to access your Exchange account. On this page you will find the settings ActiveSync/Exchange to set up your Blackberry mobile devices.  

E-print Network

Overview: You can use a mobile device to access your Exchange account. On this page you will find the settings ActiveSync/Exchange to set up your Blackberry mobile devices. If you set up an Exchange and task data! Use these settings to access your Exchange e-mail on a Blackberry mobile device: Username

Qiu, Weigang

324

You can use a mobile device to access your Exchange account. On this page you will find the settings ActiveSync/Exchange to set up your Windows mobile devices.  

E-print Network

Overview: You can use a mobile device to access your Exchange account. On this page you will find the settings ActiveSync/Exchange to set up your Windows mobile devices. If you set up an Exchange and task data! Use these settings to access your Exchange e-mail on a Windows mobile device: Username

Qiu, Weigang

325

The role of the sea-surface microlayer in the air-sea gas exchange of organochlorine compounds.  

PubMed

Simultaneous measurements of organochlorine compounds (OCs) in seawater, the sea-surface microlayer and the atmosphere were conducted in June-July 2004 in the coastal marine environment of Singapore. Together, these measurements represent the first data on the flux of OCs between the ocean and atmosphere reported in the scientific literature that take into account the implication of the sea surface microlayer (SML) as a controlling boundary layer for the exchange of OCs. The average fluxes of SigmaPCBs and SigmaHCHs were 127.5 and -32.8 ng m(-2) day(-1) respectively using a modified two-layer model (negative flux indicates adsorption by the ocean). The average fluxes using a conventional approach, ignoring the SML as boundary layer (classical two-layer model), were 67.2 and -43.1 ng m(-2) day(-1) for SigmaPCBs and SigmaHCHs, respectively. However, the maximum difference in the flux calculation between the two approaches was up to 15-fold for individual compounds at high enrichment in the SML. It is shown that the SML plays an important role in the control of air-sea gas exchange of OCs, particular under a low prevailing wind regime and with an enrichment of OCs in the SML. The physical and chemical properties of OCs are critical factors in the control of the air-sea gas exchange process, and the effect of the SML on this process is more significant for more hydrophobic OCs. PMID:16806403

Wurl, Oliver; Karuppiah, Subramanian; Obbard, Jeffrey Philip

2006-10-01

326

Lunar activity from recent gas release.  

PubMed

Samples of material returned from the Moon have established that widespread lunar volcanism ceased about 3.2 Gyr ago. Crater statistics and degradation models indicate that last-gasp eruptions of thin basalt flows continued until less than 1.0 Gyr ago, but the Moon is now considered to be unaffected by internal processes today, other than weak tidally driven moonquakes and young fault systems. It is therefore widely assumed that only impact craters have reshaped the lunar landscape over the past billion years. Here we report that patches of the lunar regolith in the Ina structure were recently removed. The preservation state of relief, the number of superimposed small craters, and the 'freshness' (spectral maturity) of the regolith together indicate that features within this structure must be as young as 10 Myr, and perhaps are still forming today. We propose that these features result from recent, episodic out-gassing from deep within the Moon. Such out-gassing probably contributed to the radiogenic gases detected during past lunar missions. Future monitoring (including Earth-based observations) should reveal the composition of the gas, yielding important clues to volatiles archived at great depth over the past 4-4.5 Gyr. PMID:17093445

Schultz, Peter H; Staid, Matthew I; Pieters, Carlé M

2006-11-01

327

Dynamic C and N stocks - key factors controlling the C gas exchange of maize in a heterogenous peatland  

NASA Astrophysics Data System (ADS)

Drainage and cultivation of fen peatlands creates complex small-scale mosaics of soils with extremely variable soil organic carbon (SOC) stocks and groundwater-level (GWL). To date, it remains unclear if such sites are sources or sinks for greenhouse gases like CO2 and CH4, especially if used for cropland. As individual control factors like GWL fail to account for this complexity, holistic approaches combining gas fluxes with the underlying processes are required to understand the carbon (C) gas exchange of drained fens. It can be assumed that the stocks of SOC and N located above the variable GWL - defined as dynamic C and N stocks - play a key role in the regulation of plant- and microbially mediated C gas fluxes of these soils. To test this assumption, the present study analysed the C gas exchange (gross primary production - GPP, ecosystem respiration - Reco, net ecosystem exchange - NEE, CH4) of maize using manual chambers for four years. The study sites were located near Paulinenaue, Germany. Here we selected three soils, which represent the full gradient in pedogenesis, GWL and SOC stocks (0-1 m) of the fen peatland: (a) Haplic Arenosol (AR; 8 kg C m-2); (b) Mollic Gleysol (GL; 38 kg C m-2); and (c) Hemic Histosol (HS; 87 kg C m-2). Daily GWL data was used to calculate dynamic SOC (SOCdyn) and N (Ndyn) stocks. Average annual NEE differed considerably among sites, ranging from 47 ± 30 g C m-2 a-1 at AR to -305 ± 123 g C m-2 a-1 at GL and -127 ± 212 g C m-2 a-1 at HS. While static SOC and N stocks showed no significant effect on C fluxes, SOCdyn and Ndyn and their interaction with GWL strongly influenced the C gas exchange, particularly NEE and the GPP:Reco ratio. Moreover, based on nonlinear regression analysis, 86% of NEE variability was explained by GWL and SOCdyn. The observed high relevance of dynamic SOC and N stocks in the aerobic zone for plant and soil gas exchange likely originates from the effects of GWL-dependent N availability on C formation and transformation processes in the plant-soil system, which promote CO2 input via GPP more than CO2 emission via Reco. The process-oriented approach of dynamic C and N stocks is a promising, potentially generalizable method for system-oriented investigations of the C gas exchange of groundwater-influenced soils and could be expanded to other nutrients and soil characteristics. However, in order to assess the climate impact of arable sites on drained peatlands, it is always necessary to consider the entire range of groundwater-influenced mineral and organic soils and their respective areal extent within the soil landscape.

Pohl, M.; Hoffmann, M.; Hagemann, U.; Giebels, M.; Albiac Borraz, E.; Sommer, M.; Augustin, J.

2014-11-01

328

Probing the mechanisms and dynamics of gas phase hydrogen-deuterium exchange reactions of sodiated polyglycines.  

PubMed

The rate constants for H-D exchange reactions of sodiated polyglycines (GnNa(+), n = 2-8) and polyalanines (AnNa(+), n = 2, 3 and 5) with ND3 have been measured in the cell of an FT-ICR mass spectrometer. All peptides except G2Na(+) are found to undergo three exchange reactions, all of which are consecutive with no sign of multiple exchanges within a single collision event. This information has been used to construct full mechanistic scenarios with the help of detailed quantum chemical calculations of the possible reaction paths for H-D exchange. The first exchange is always located at the C terminus however with different mechanisms depending upon whether the peptide termini can (larger peptides) or cannot (smaller peptides) interact directly without strong energy penalty. The most favourable mechanisms for the second and third exchanges of the N terminus protons, are found to be different from those for the first for all peptide sizes. The peptide distortions that are necessary in order for some of these reactions to occur are made possible by the energy reservoir provided by the favorable interaction of the peptide ion with ND3. Their occurrence and variety preclude any general relationship between H-D exchange kinetics and the most stable ion structures. There is however a break at G7Na(+) in the kinetics trend, with a first exchange rate which is much smaller than for all other peptide sizes. This break can be directly related to a different structural type in which the C terminus is neither free nor close to the N terminus. PMID:25573245

McMahon, T B; Ohanessian, G

2015-01-28

329

Fast exhaust channel optical absorption method and apparatus to study the gas exchange in large diesel engines  

NASA Astrophysics Data System (ADS)

An optical absorption spectroscopic method and apparatus with shorter than 1 ms response time have been used to study the gas exchange processes in realistic conditions for a single cylinder of a large diesel engine. The method is based on measuring the differential line-of-sight optical uv absorption of the exhaust-gas-contained SO2 as a function of time in the exhaust port area just after the exhaust valves. The optical absorption by SO2 is determined from light transmission measurements at 280 and 340 nm performed through optical probes installed into the exhaust channel wall. The method has been applied to a continuously fired, large, medium speed production-line-type diesel engine with 990 kW rated power. The test engine was operated with standard light fuel oil (MDO Termoshell) and with light fuel oil treated with a sulfur additive {Di-Tert-Butyldisulfid [(CH3)3C]2S2}. The latter was to improve the optical absorption signals without increasing the fouling of the exhaust channel optical probes as in the case of heavier fuel oil qualities. In the reported case of a four-stroke diesel engine measurement results show that the method can provide time-resolved information of the SO2 density in the exhaust channel and thus give information on the single-cylinder gas exchange. During the inlet and exhaust valve overlap period the moment of fresh air entering into the measurement volume can be detected. If independent exhaust gas temperature and pressure data are available, the absorption measurements can readily be used for determining the burnt gas fraction in the exhaust channel. In this work the possibility of using the optical absorption measurement to determine the instaneous exhaust gas temperature was studied. Based on known fuel properties and conventional averaged SO2 measurements from the exhaust channel a known concentration of SO2 was assumed in the exhaust gas after the exhaust valves opening and before the inlet and exhaust valves overlap period. Together with an exhaust gas pressure measurement the optical absorption signal was used to determine the instaneous exhaust gas temperature. Due to the minimal modifications needed by the engine for optical access, and continuously fired operation with relevant power levels and realistic fuel qualities, this measurement method, with some further development, can be useful to obtain time-resolved data from the exhaust channel of real production-line-type diesel engines.

Vattulainen, J.; Hernberg, R.; Hattar, C.; Gros, S.

1998-01-01

330

Effect of acetazolamide on gas exchange and acid-base control after maximal exercise.  

PubMed

To investigate the interactions between the systems that contribute to acid-base homeostasis after severe exercise, we studied the effects of carbonic anhydrase inhibition on exchange of strong ions and CO2 in six subjects after 30 s of maximal isokinetic cycling exercise. Each subject exercised on two randomly assigned occasions, a control (CON) condition and 30 min after intravenous injection of 1,000 mg acetazolamide (ACZ) to inhibit blood carbonic anhydrase activity. Leg muscle power output was similar in the two conditions; peak O2 uptake (VO2) after exercise was lower in ACZ (2,119 +/- 274 ml/min) than in CON (2,687 +/- 113, P less than 0.05); peak CO2 production (VCO2) was also lower (2,197 +/- 241 in ACZ vs. 3,237 +/- 87 in CON, P less than 0.05) and was accompanied by an increase in the recovery half-time from 1.7 min in CON to 2.3 min in ACZ. Whereas end-tidal PCO2 was lower in ACZ than in CON, arterial PCO2 (PaCO2) was higher, and a large negative end-tidal-to-arterial difference (less than or equal to 20 Torr) was present in ACZ on recovery. In ACZ, postexercise increases in arterial plasma [Na+] and [K+] were greater but [La-] was lower. Arteriovenous differences across the forearm showed a greater uptake of La- and Cl- in CON than in ACZ. Carbonic anhydrase inhibition with ACZ, in addition to impairing equilibration of the CO2 system to the acid-base challenge of exercise, was accompanied by changes in equilibration of strong inorganic ions. A lowered plasma [La-] was not accompanied by greater uptake of La- by inactive muscle. PMID:1537726

Kowalchuk, J M; Heigenhauser, G J; Sutton, J R; Jones, N L

1992-01-01

331

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. PMID:20530115

Gagnon, Kenneth B; Delpire, Eric

2010-01-01

332

Effect of N-acetylcysteine on gas exchange after methacholine challenge and isoprenaline inhalation in the dog.  

PubMed

N-acetylcysteine (NAC) has antioxidant and possibly mucolytic properties. To determine whether NAC could be of benefit in acute bronchoconstriction induced by methacholine, 12 of 24 anaesthetized dogs (group 1) received NAC i.v. (loading dose 150 mg.kg-1, then 20 mg.kg-1.hr-1). The other 12 (group 2) received diluent. Nebulized methacholine (1%) was then inhaled until arterial oxygen tension (PaO2) fell to a mean of 5.5 kPa, after which isoprenaline 0.5% was inhaled in six dogs of each group to reverse bronchoconstriction. Over the next 3 h we measured total lung resistance, functional residual capacity (FRC), haemodynamic variables, and pulmonary gas exchange for respiratory and inert gases. After methacholine challenge, lung resistance increased and then fell similarly for both groups, but PaO2 was higher in the NAC group (by 0.6-1.9 kPa) throughout the observation period. The ventilation-perfusion distribution measured by inert gas elimination also showed less abnormality in the NAC treated dogs over this time. Mucus was visible during post-mortem in the large airways in about half of the dogs in both groups, with no significant differences between them. These results show that NAC produces a measurable improvement in gas exchange following methacholine challenge (both with and without subsequent isoprenaline therapy) by mechanisms that remain to be determined. PMID:2659384

Ueno, O; Lee, L N; Wagner, P D

1989-03-01

333

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

NASA Astrophysics Data System (ADS)

In this study we present gas-exchange measurements conducted in a large-scale wind-wave tank. Fourteen chemical species spanning a wide range of solubility (dimensionless solubility, ? = 0.4 to 5470) and diffusivity (Schmidt number in water, Scw = 594 to 1194) were examined under various turbulent (u10 = 0.73 to 13.2 m s-1) conditions. Additional experiments were performed under different surfactant modulated (two different concentration levels of Triton X-100) surface states. This paper details the complete methodology, experimental procedure and instrumentation used to derive the total transfer velocity for all examined tracers. The results presented here demonstrate the efficacy of the proposed method, and the derived gas-exchange velocities are shown to be comparable to previous investigations. The gas transfer behaviour is exemplified by contrasting two species at the two solubility extremes, namely nitrous oxide (N2O) and methanol (CH3OH). Interestingly, a strong transfer velocity reduction (up to a factor of 3) was observed for the relatively insoluble N2O under a surfactant covered water surface. In contrast, the surfactant effect for CH3OH, the high solubility tracer, was significantly weaker.

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

2015-01-01

334

Trace gas exchange above the floor of a deciduous forest. 1. Evaporation and CO sub 2 efflux  

SciTech Connect

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 with chambers. In this paper, the authors report on eddy correlation measurements of water vapor, sensible heat, and carbon dioxide exchange that were made at the floor of a deciduous forest. The validity of the eddy correlation method to measure the emission of water vapor and CO{sub 2} from a deciduous forest floor is demonstrated by the ability to close the surface energy budget during periods that meet the requirements of the technique. Water vapor fluxes from a dry forest floor are strongly influenced by large-scale turbulent events that penetrate deep into the canopy. The frequency of these turbulent events prevents equilibrium evaporation rates from being achieved because the dynamic time constant for water vapor exchange is longer. Consequently, maximal evaporation rates are capped to rates defined by the product of the driving potential of the atmosphere and the surface conductance. On the other hand, evaporation from a wet forest floor proceeds at rates reaching or exceeding equilibrium evaporation and are highly correlated with static pressure fluctuations. CO{sub 2} efflux rates are governed by litter and soil temperature, as expected. But the authors also find a significant correlation between static pressure fluctuations and soil/litter CO{sub 2} exchange rates.

Baldocchi, D.D.; Meyers, T.P. (NOAA Atmospheric Turbulence and Diffusion Division, Oak Ridge, TN (USA))

1991-04-20

335

Association between carbonyl sulfide uptake and (18)? during gas exchange in C(3) and C(4) leaves.  

PubMed

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

2011-09-01

336

Association between Carbonyl Sulfide Uptake and 18? during Gas Exchange in C3 and C4 Leaves1[OA  

PubMed Central

Carbonyl sulfide (COS) and C18OO exchange by leaves provide potentially powerful tracers of biosphere-atmosphere CO2 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 C3 and C4 plants, hypothesizing that the rates of COS and C18OO exchange by leaves respond in parallel to environmental and biological drivers. Using CA-deficient antisense lines of C4 and C3 plants, COS uptake was essentially eliminated and discrimination against C18OO 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 CO2 assimilation rates, As/Ac, normalized to their respective ambient concentrations), which reflected the effects of stomatal conductance on both COS and C18OO exchange. Unexpectedly, a decoupling between As and 18? was observed in comparing C4 and C3 plants, with a large decrease in 18? but no parallel reduction in As in the former. This could be explained by C4 plants having higher COS concentrations at the CA site (maintaining high As with reduced CA) and a high phosphoenolpyruvate carboxylase/CA activity ratio (reducing 18O exchange efficiency between CO2 and water, but not As). Similar As but higher Ac in C4 versus C3 plants resulted in lower LRU values in the former (1.16 ± 0.20 and 1.82 ± 0.18 for C4 and C3, 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

2011-01-01

337

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

USGS Publications Warehouse

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

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

2013-01-01

338

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

PubMed

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 receiving carbon-filtered (CF) air, and four receiving non-filtered (NF) air. Significant variation in gas exchange (F > 12.7, P < 0.001) was detected among species with average net photosynthesis and average stomatal conductance differing by a factor of two. Species also varied significantly in foliar injury for those leaves for which we measured gas exchange (F = 39.6, P < 0.001). Fraxinus excelsior, M. nigra, P. avium, P. serotina, R. cathartica, and V. lantana showed more injury than A. pseudoplatanus, B. pendula, C. avellana, and Fagus sylvatica. Plants grown in CF chambers had significantly higher net photosynthesis (A) and stomatal conductance to water vapor (gwv), and lower foliar injury than plants grown in NF chambers and AA plots; interactions between species and ozone treatments were significant for all variables (F > or = 2.2, P < 0.05) except gwv (F = 0.7, P > 0.1). Although A and gwv decreased and foliar injury increased with leaf age, the magnitude of these changes was lower for plants grown in CF chambers than for plants grown in NF chambers and AA plots. Neither ozone uptake threshold (r = 0.26, P > 0.20) nor whole-plant injury (r = -0.15, P > 0.41) was significantly correlated with stomatal conductance across these species. It appears that the relationships between stomatal conductance and foliar injury are species-specific and interactions between physiology and environments and leaf biochemical processes must be considered in determining species sensitivity to ambient ozone exposures. PMID:11383335

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

2001-01-01

339

Toxicodynamics of rigid polystyrene microparticles on pulmonary gas exchange in mice: implications for microemboli-based drug delivery systems.  

PubMed

The toxicodynamic relationship between the number and size of pulmonary microemboli resulting from uniformly sized, rigid polystyrene microparticles (MPs) administered intravenously and their potential effects on pulmonary gas exchange were investigated. CD-1 male mice (6-8 weeks) were intravenously administered 10, 25 and 45 ?m diameter MPs. Oxygen hemoglobin saturation in the blood (SpO(2)) was measured non-invasively using a pulse oximeter while varying inhaled oxygen concentration (F(I)O(2)). The resulting data were fit to a physiologically based non-linear mathematical model that estimates 2 parameters: ventilation-perfusion ratio (V(A)/Q) and shunt (percentage of deoxygenated blood returning to systemic circulation). The number of MPs administered prior to a statistically significant reduction in normalized V(A)/Q was dependent on particle size. MP doses that resulted in a significant reduction in normalized V(A)/Q one day post-treatment were 4000, 40,000 and 550,000 MPs/g for 45, 25 and 10 ?m MPs, respectively. The model estimated V(A)/Q and shunt returned to baseline levels 7 days post-treatment. Measuring SpO(2) alone was not sufficient to observe changes in gas exchange; however, when combined with model-derived V(A)/Q and shunt early reversible toxicity from pulmonary microemboli was detected suggesting that the model and physical measurements are both required for assessing toxicity. Moreover, it appears that the MP load required to alter gas exchange in a mouse prior to lethality is significantly higher than the anticipated required MP dose for effective drug delivery. Overall, the current results indicate that the microemboli-based approach for targeted pulmonary drug delivery is potentially safe and should be further explored. PMID:23142466

Kutscher, H L; Gao, D; Li, S; Massa, C B; Cervelli, J; Deshmukh, M; Joseph, L B; Laskin, D L; Sinko, P J

2013-01-15

340

On the correlation between air-sea heat flux and abiotically induced oxygen gas exchange in a circulation model of the North Atlantic  

Microsoft Academic Search

The assumption that abiotic air-sea gas exchange is, via the temperature dependence of the gas' solubility, proportional to the surface heat flux is often used to distinguish between physically and biotically inferred oxygen fluxes across the sea surface. We quantitatively investigate its validity in the context of an eddy-permitting circulation model that contains an abiotic oxygen compartment. In the model,

H. Dietze; A. Oschlies

2005-01-01

341

Induction and stability of somaclonal variation in growth, leaf phenotype and gas exchange characteristics of poplar regenerated from callus culture.  

PubMed

Populus trichocarpa Torr. and Grey x P. balsamifera L. TT32 lines were regenerated from calli that had been maintained under differing in vitro conditions for sixteen months. In the final months, calli were maintained with one of six concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D, 0.1, 0.2, 0.3, 0.4, 0.5 or 0.6 mg l(-1))and regenerated with 0.25, 0.50 or 1.0 mg l(-1) benzylaminopurine (BA). Regenerant lines were obtained from 15 of these 18 treatments. The spectrum of variation in several morphological, physiological and leaf gas exchange traits was evaluated in the primary regenerants in 1986, and in their secondary vegetative propagules in the two subsequent years, in relation to differences in the original culture conditions. The results indicate that somoclonal variation was induced largely as a result of prolonged culture in the presence of 2,4-D, but that the terminal maintenance and regeneration phases also induced changes in the regenerants. Qualitative differences among the regenerant lines were detected by the end of 1986. For most traits, these differences were statistically confirmed within the 3-year period. The treatment lines ultimately diverged sufficiently to produce lines showing general performance that was either above or below that of the original TT32 clone. An early visible indicator of this divergence was variation in leaf shape (leaf length/width ratio), which could be related to 2,4-D-BA interactions in the final stages of culture. Graphic illustration of the independent effects of either 2,4-D or BA on stem height and gas exchange parameters suggested an inverse relationship with BA concentration and a complex interaction with 2,4-D. Significant correlations were detected between gas exchange parameters and morphological characteristics representing leaf form and stem development. Overall, the results indicate the presence of somaclonal lines that offer potential for the selective improvement of growth using morphological and gas exchange parameters as screening tools. PMID:14967629

Saieed, N T; Douglas, G C; Fry, D J

1994-01-01

342

Biology and air-sea gas exchange controls on the distribution of carbon isotope ratios (?13C) in the ocean  

NASA Astrophysics Data System (ADS)

Analysis of observations and sensitivity experiments with a new three-dimensional global model of stable carbon isotope cycling elucidate processes that control the distribution of ?13C of dissolved inorganic carbon (DIC) in the contemporary and preindustrial ocean. Biological fractionation and the sinking of isotopically light ?13C organic matter from the surface into the interior ocean leads to low ?13CDIC values at depths and in high latitude surface waters and high values in the upper ocean at low latitudes with maxima in the subtropics. Air-sea gas exchange has two effects. First, it acts to reduce the spatial gradients created by biology. Second, the associated temperature-dependent fractionation tends to increase (decrease) ?13CDIC values of colder (warmer) water, which generates gradients that oppose those arising from biology. Our model results suggest that both effects are similarly important in influencing surface and interior ?13CDIC distributions. However, since air-sea gas exchange is slow in the modern ocean, the biological effect dominates spatial ?13CDIC gradients both in the interior and at the surface, in contrast to conclusions from some previous studies. Calcium carbonate cycling, pH dependency of fractionation during air-sea gas exchange, and kinetic fractionation have minor effects on ?13CDIC. Accumulation of isotopically light carbon from anthropogenic fossil fuel burning has decreased the spatial variability of surface and deep ?13CDIC since the industrial revolution in our model simulations. Analysis of a new synthesis of ?13CDIC measurements from years 1990 to 2005 is used to quantify preformed and remineralized contributions as well as the effects of biology and air-sea gas exchange. The model reproduces major features of the observed large-scale distribution of ?13CDIC as well as the individual contributions and effects. Residual misfits are documented and analyzed. Simulated surface and subsurface ?13CDIC are influenced by details of the ecosystem model formulation. For example, inclusion of a simple parameterization of iron limitation of phytoplankton growth rates and temperature-dependent zooplankton grazing rates improves the agreement with ?13CDIC observations and satellite estimates of phytoplankton growth rates and biomass, suggesting that ?13C can also be a useful test of ecosystem models.

Schmittner, A.; Gruber, N.; Mix, A. C.; Key, R. M.; Tagliabue, A.; Westberry, T. K.

2013-09-01

343

Influence of Buried Hydrogen-Bonding Groups within Monolayer Films on Gas-Surface Energy Exchange and Accommodation  

NASA Astrophysics Data System (ADS)

Self-assembled monolayers (SAMs) of carbonyl-containing alkanethiols on gold are employed to explore the influence of hydrogen-bonding interactions on gas-surface energy exchange and accommodation. H-bonding, COOH-terminated SAMs are found to produce more impulsive scattering and less thermal accommodation than non-H-bonding, COOCH3-terminated monolayers. For carbamate-functionalized SAMs of the form Au/S(CH2)16OCONH(CH2)n-1CH3, impulsive scattering decreases and accommodation increases as the H-bonding group is positioned farther below the terminal CH3.

Ferguson, M. K.; Lohr, J. R.; Day, B. S.; Morris, J. R.

2004-02-01

344

Electron self-exchange activation parameters of diethyl sulfide and tetrahydrothiophene  

PubMed Central

Summary Electron transfer between the title compounds and their radical cations, which were generated by photoinduced electron transfer from the sulfides to excited 2,4,6-triphenylpyrylium cations, was investigated by time-resolved measurements of chemically induced dynamic nuclear polarization (CIDNP) in acetonitrile. The strongly negative activation entropies provide evidence for an associative–dissociative electron exchange involving dimeric radical cations. Despite this mechanistic complication, the free energies of activation were found to be well reproduced by the Marcus theory of electron transfer, with the activation barrier still dominated by solvent reorganization. PMID:23946842

Vogtherr, Martin

2013-01-01

345

O2 activation by binuclear Cu sites: Noncoupled versus exchange coupled reaction mechanisms  

NASA Astrophysics Data System (ADS)

Binuclear Cu proteins play vital roles in O2 binding and activation in biology and can be classified into coupled and noncoupled binuclear sites based on the magnetic interaction between the two Cu centers. Coupled binuclear Cu proteins include hemocyanin, tyrosinase, and catechol oxidase. These proteins have two Cu centers strongly magnetically coupled through direct bridging ligands that provide a mechanism for the 2-electron reduction of O2 to a µ-2:2 side-on peroxide bridged species. This side-on bridged peroxo-CuII2 species is activated for electrophilic attack on the phenolic ring of substrates. Noncoupled binuclear Cu proteins include peptidylglycine -hydroxylating monooxygenase and dopamine -monooxygenase. These proteins have binuclear Cu active sites that are distant, that exhibit no exchange interaction, and that activate O2 at a single Cu center to generate a reactive CuII/O2 species for H-atom abstraction from the C-H bond of substrates. O2 intermediates in the coupled binuclear Cu enzymes can be trapped and studied spectroscopically. Possible intermediates in noncoupled binuclear Cu proteins can be defined through correlation to mononuclear CuII/O2 model complexes. The different intermediates in these two classes of binuclear Cu proteins exhibit different reactivities that correlate with their different electronic structures and exchange coupling interactions between the binuclear Cu centers. These studies provide insight into the role of exchange coupling between the Cu centers in their reaction mechanisms.

Chen, Peng; Solomon, Edward I.

2004-09-01

346

Multi-scale Analysis of Methane Gas Hydrate Formation and Dissociation via Point Source Thermal Stimulation and Carbon Dioxide Exchange  

NASA Astrophysics Data System (ADS)

The formation and dissociation of methane gas hydrate was investigated over a range of laboratory scale systems with sample volumes of 1.3 cm 3, 0.059 m3 and 0.141 m3. Three unique hydrate apparatuses were used to study a point source thermal dissociation method in which gas production profiles and cumulative efficiencies were found to be dependent on the initial hydrate saturation and the degree of thermal stimulation. Hydrate growth was observed to develop in a non-homogeneous manner with hydrate distribution displaying strong apparatus specific behavior. Heterogeneous hydrate distribution contributed to the production efficiencies of point source thermal stimulation and is an essential parameter when evaluating a gas hydrate reservoir. Thermal stimulation was applied to sediments with initial pore space hydrate saturations ranging from 10% to 80% producing maximum cumulative thermal production efficiencies ranging from 57% to 90%. Production performance was improved with higher initial hydrate saturation; increasing the initial hydrate saturation from 20% to 35% on the small scale system raised peak cumulative efficiencies from 57-63% to 70-74%. Increasing hydrate saturation from 10% to 30% in the medium scale system increased peak cumulative efficiencies from 83% to 90%. During thermal stimulation experiments in both the medium and large scale reactors a flow recirculation pattern developed within the pore space following an initially conduction dominated heat transfer regime. The outward propagation of the heat front from the heating element resulted in increased permeability and the release of mobile water and gas phases as the hydrate underwent dissociation. This change in flow parameters facilitated convection cells within the reactor causing increased heat transfer away from the heating element while displaying a strong upward bias. The flow development detected within the medium scale system was confirmed via history matching of numerical simulation with experimental data. Increased hydrate saturation and increased heating rate lead to a more intense flow development. Thermal stimulation methane production has been coupled with the simultaneous injection of gaseous carbon dioxide as method of enhancing gas production rates while providing a means for long term storage of carbon dioxide in the hydrate phase. The exchange process was investigated at low and high gas injection rates under conditions of both low and high thermal stimulation applied to a 50% hydrate saturated quartz sand pack. The amount of carbon dioxide stored in the hydrate phased was greatest for the low injection-high heating condition sequestering 69 moles, and lowest for the high injection- low heating condition sequestering 13 moles. The gas exchange is improved with longer contact time between gas phase carbon dioxide and hydrate phase methane, this condition is optimized at low carbon dioxide injection rates. The availability of free water for formation of carbon dioxide is enhanced with the higher heating rates. Thus it is possible to tune the gas production rates and carbon dioxide storage potential by manipulating heating rates and gas injection rates to achieve the desired ratio between methane produced and carbon dioxide sequestered. Understanding the transition period and flow development within the pore fluid mixture should play a large role in determining the optimum placement and geometry of heating and exchange systems on industrial scale hydrate production scenarios. In addition to the optimization of thermal stimulation heating location, the profile and degree of heating rate can be tuned in order to maximize gas collection and minimize excessive heating of unproductive sediment matrix after it has been exhausted of methane hydrate. The production efficiency produced across the three experimental scales averaged between 80 and 90% and appears to be independent of scale. The scale up of this method for industrial scale production should pay close attention to the distribution of heat during thermal stimulation as a result of the

Fitzgerald, Garrett Christopher

347

Amide hydrogen/deuterium exchange & MALDI-TOF mass spectrometry analysis of Pak2 activation.  

PubMed

Amide hydrogen/deuterium exchange (H/D exchange) coupled with mass spectrometry has been widely used to analyze the interface of protein-protein interactions, protein conformational changes, protein dynamics and protein-ligand interactions. H/D exchange on the backbone amide positions has been utilized to measure the deuteration rates of the micro-regions in a protein by mass spectrometry(1,2,3). The resolution of this method depends on pepsin digestion of the deuterated protein of interest into peptides that normally range from 3-20 residues. Although the resolution of H/D exchange measured by mass spectrometry is lower than the single residue resolution measured by the Heteronuclear Single Quantum Coherence (HSQC) method of NMR, the mass spectrometry measurement in H/D exchange is not restricted by the size of the protein(4). H/D exchange is carried out in an aqueous solution which maintains protein conformation. We provide a method that utilizes the MALDI-TOF for detection(2), instead of a HPLC/ESI (electrospray ionization)-MS system(5,6). The MALDI-TOF provides accurate mass intensity data for the peptides of the digested protein, in this case protein kinase Pak2 (also called ?-Pak). Proteolysis of Pak 2 is carried out in an offline pepsin digestion. This alternative method, when the user does not have access to a HPLC and pepsin column connected to mass spectrometry, or when the pepsin column on HPLC does not result in an optimal digestion map, for example, the heavily disulfide-bonded secreted Phospholipase A(2;) (sPLA(2;)). Utilizing this method, we successfully monitored changes in the deuteration level during activation of Pak2 by caspase 3 cleavage and autophosphorylation(7,8,9). PMID:22143461

Hsu, Yuan-Hao; Traugh, Jolinda A

2011-01-01

348

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.

2011-12-01

349

Activated gas nitriding of 17-4 PH stainless steel  

Microsoft Academic Search

Results of the investigation of nitrided precipitation-hardened steel 17-4 PH surface have been presented. The layers have been created as a result of the gas nitriding process in a partly dissociated ammonia. Hydrogen chloride admixture to ammonia was used as a steel surface activator. The influence of the steel heat treatment before nitriding on the diffusive process has been considered.

P. Kochma?ski; J. Nowacki

2006-01-01

350

Membrane androgen receptor sensitive Na+/H+ exchanger activity in prostate cancer cells.  

PubMed

Membrane androgen receptors (mAR) are expressed in several tumors. mAR activation by testosterone albumin conjugates (TAC) suppresses tumor growth and migration. mAR signaling involves phosphoinositide-3-kinase (PI3K) and Rho-associated protein kinase (ROCK). PI3K stimulates serum- and glucocorticoid-inducible kinase SGK1, which in turn activates Na(+)/H(+)-exchangers (NHE). In prostate cancer cells cytosolic pH (pHi) was determined utilizing 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein-fluorescence and NHE-activity utilizing Na(+)-dependent cytosolic realkalinization following an ammonium pulse. TAC (100 nM) significantly increased pHi and NHE-activity, effects abrogated by NHE1-inhibitor cariporide (10 ?M), SGK1-inhibitors EMD638683 (50 ?M) and GSK650349 (10 ?M) and ROCK-inhibitors Y-27632 (10 ?M) and fasudil (100 ?M). TAC treatment rapidly and significantly increased cell volume and actin polymerization, effects abolished in the presence of cariporide. Thus, mAR-activation activates cariporide-sensitive Na(+)/H(+)-exchangers, an effect requiring SGK1 and ROCK activity. PMID:24607544

Chatterjee, Soumya; Schmidt, Sebastian; Pouli, Stella; Honisch, Sabina; Alkahtani, Saad; Stournaras, Christos; Lang, Florian

2014-05-01

351

Particle-phase dry deposition and air-soil gas-exchange of polybrominated diphenyl ethers (PBDEs) in Izmir, Turkey.  

PubMed

The particle-phase dry deposition and soil-air gas-exchange of polybrominated diphenyl ethers (PBDEs) were measured in Izmir, Turkey. Relative contributions of different deposition mechanisms (dry particle, dry gas, and wet deposition) were also determined. BDE-209 was the dominating congener in all types of samples (air, deposition, and soil). Average dry deposition fluxes of total PBDEs (sigma7PBDE) for suburban and urban sites were 67.6 and 128.8 ng m(-2) day(-1), respectively. Particulate dry deposition velocities ranged from 11.5 (BDE-28) to 3.9 cm s(-1) (BDE-209) for suburban sites and 7.8 (BDE-28) to 2.8 cm s(-1) (BDE-154) for urban sites with an overall average of 5.8 +/- 3.7 cm s(-1). The highest sigma7PBDE concentration (2.84 x 10(6) ng kg(-1) dry wt) was found around an electronic factory among the 13 soil samples collected from different sites. The concentration in a bag filter dust from a steel plant was also high (2.05 x 10(5) ng kg(-1)), indicating that these industries are significant PBDE sources. Calculated net soil-air gas exchange flux of sigma7PBDE ranged from 11.8 (urban) to 23.4 (industrial) ng m(-2) day(-1) in summer, while in winter it ranged from 3.2 (urban) to 11.6 (suburban) ng m(-2) day(-1). All congeners were deposited at all three sites in winter and summer. It was estimated that the wet deposition also contributes significantly to the total PBDE deposition to soil. Dry particle, wet, and gas deposition contribute 60, 32, and 8%, respectively, to annual PBDE flux to the suburban soil. PMID:17711213

Cetin, Banu; Odabasi, Mustafa

2007-07-15

352

Variation in eggshell characteristics and gas exchange of montane and lowland coot eggs  

Microsoft Academic Search

This study determined how structural features of the eggshells of coots (Fulica americana) laid at 4150 m in the Peruvian Andes differed from those at sea level in Peru and California and how these features affected exchange of water vapor, O2, and CO2. While barometric pressure at 4150 m was reduced to 60% of that at sea level, the conductance

Cynthia Carey; Fabiola Leon-Velarde; Olga Dunin-Borkowski; Theresa L. Bucher; Grimaneza de la Torre; Daniel Espinoza; Carlos Monge

1989-01-01

353

Exchange Energy as Functional of Electronic Density from Hartree-Fock Theory of Inhomogeneous Electron Gas  

Microsoft Academic Search

In a previous paper, the validity of gradient corrections to the Dirac-Slater exchange energy was discussed within the density functional theory, for a local potential. This local potential, by definition, generated the exact charge density in the (infinite) system considered. The present work considers the full Hartree-Fock theory within the same density functional framework. In particular, using a perturbation expansion

A. M. Beattie; J. C. Stoddart; N. H. March

1971-01-01

354

Exchange-correlation correction to the dielectric function of the inhomogeneous electron gas  

Microsoft Academic Search

Exchange-correlation (XC) and band structure corrections to the dielectric matrix are investigated simultaneously within the framework of non-local density functional theory. The XC correction is calculated in the weighted density approximation and band structure effects are taken into account in second order in the pseudopotential. Particular attention is devoted to the question of whether or not the minimum in the

M. Taut

1992-01-01

355

Description of exchange and correlation in the strongly inhomogeneous electron gas using a nonlocal density functional  

Microsoft Academic Search

We present exchange-correlation energy densities exc, total energies Exc, and holes, calculated for strongly inhomogeneous electron gases using the nonlocal weighted density approximation. The results closely resemble variational Monte Carlo simulations performed recently [Phys. Rev. Lett. 87, 036401 (2001)], demonstrating the effectiveness of a nonlocal density functional description.

Philip P. Rushton; David J. Tozer; Stewart J. Clark

2002-01-01

356

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.

2005-01-01

357

Gas-phase hydrogen/deuterium exchange of 5'- and 3'-mononucleotides in a quadrupole ion trap: exploring the role of conformation and system energy.  

PubMed

Gas-phase hydrogen/deuterium (H/D) exchange reactions for deprotonated 2'-deoxy-5'-monophosphate and 2'-deoxy-3'-monophosphate nucleotides with D(2)O were performed in a quadrupole ion trap mass spectrometer. To augment these experiments, molecular modeling was also conducted to identify likely deprotonation sites and potential gas-phase conformations of the anions. A majority of the 5'-monophosphates exchanged extensively with several of the compounds completely incorporating deuterium in place of their labile hydrogen atoms. In contrast, most of the 3'-monophosphate isomers exchanged relatively few hydrogen atoms, even though the rate of the first two exchanges was greater than observed for the 5'-monophosphates. Mononucleotides that failed to incorporate more than two deuterium atoms under default reaction conditions were often found to exchange more extensively when reactions were performed under higher energy conditions. Integration of the experimental and theoretical results supports the use of a relay exchange mechanism and suggests that the exchange behavior depends highly on the identity and orientation of the nucleobase and the position and flexibility of the deprotonated phosphate moiety. These observations also highlight the importance of the distance between the various participating groups in addition to their gas-phase acidity and basicity. PMID:17289398

Chipuk, Joseph E; Brodbelt, Jennifer S

2007-04-01

358

Simulation of the heat exchange between the supersonic flow and the stationary body in a gas centrifuge  

NASA Astrophysics Data System (ADS)

We have made comparative calculations of the heat exchange in the subpersonic flow of gaseous UF6 around the stationary cylindrical body inside the rotating rotor of the gas centrifuge. It has been revealed that the integral heat flux from the gas to the body calculated with the use of the ANSYS-CFX program complex from the viewpoint of the continuum model is much smaller than the heat flow calculated by the Monte Carlo method of direct statistical simulation. Estimates show that under the conditions being considered the boundary layer on the surface of the body has no time to be formed and has a thickness of the order of the mean free path of the gas molecules and, therefore, the use of the methods of continuum mechanics in this region is incorrect. On the contrary, the method of direct statistical simulation permits taking into account the interaction of gas molecules directly with the surface of the streamline body and obtaining more correct results.

Zvonarev, K. V.; Seleznev, V. D.; Tokmantsev, V. I.; Abramov, Yu. V.

2012-11-01

359

Leaf gas exchange and chlorophyll a fluorescence in wheat plants supplied with silicon and infected with Pyricularia oryzae.  

PubMed

This study investigated the effect of silicon (Si) on the photosynthetic gas exchange parameters (net CO2 assimilation rate [A], stomatal conductance to water vapor [gs], internal CO2 concentration [Ci], and transpiration rate [E]) and chlorophyll fluorescence a parameters (maximum quantum quenching [Fv/Fm and Fv'/Fm'], photochemical [qP] and nonphotochemical [NPQ] quenching coefficients, and electron transport rate [ETR]) in wheat plants grown in a nutrient solution containing 0 mM (-Si) or 2 mM (+Si) Si and noninoculated or inoculated with Pyricularia oryzae. Blast severity decreased due to higher foliar Si concentration. For the inoculated +Si plants, A, gs, and E were significantly higher in contrast to the inoculated -Si plants. For the inoculated +Si plants, significant differences of Fv/Fm between the -Si and +Si plants occurred at 48, 96, and 120 h after inoculation (hai) and at 72, 96, and 120 hai for Fv'/Fm'. The Fv/Fm and Fv'/Fm', in addition to total chlorophyll concentration (a + b) and the chlorophyll a/b ratio, significantly decreased in the -Si plants compared with the +Si plants. Significant differences between the -Si and +Si inoculated plants occurred for qP, NPQ, and ETR. The supply of Si contributed to decrease blast severity in addition to improving gas exchange performance and causing less dysfunction at the photochemical level. PMID:24047250

Perez, Carlos Eduardo Aucique; Rodrigues, Fabrício Ávila; Moreira, Wiler Ribas; DaMatta, Fábio Murilo

2014-02-01

360

Nitrogen nutrition and water stress effects on leaf photosynthetic gas exchange and water use efficiency in winter wheat.  

PubMed

The responses of gas exchange and water use efficiency to nitrogen nutrition for winter wheat were investigated under well-watered and drought conditions. The photosynthetic gas exchange parameters of winter wheat are remarkably improved by water and nitrogen nutrition and the regulative capability of nitrogen nutrition is influenced by water status. The effects of nitrogen nutrition on photosynthetic characteristics and on the limited factors to photosynthesis are not identical under different water status. Intrinsic water use efficiency (WUE(i)) of the plants at the high-N nutrition was decreased by a larger value than that of the plants in the low-N treatment due to a larger decrease in photosynthetic rate than in transpiration rate. Carbon isotope composition of plant material (delta(p)) is increased by the increase of drought intensity. The delta(p) at a given level of C(i)/C(a) is reduced by nitrogen deficiency. Leaf carbon isotope discrimination (Delta) is increased by the increase of nitrogen nutrition and decreased by the increase of drought intensity. Transpirational water use efficiency (WUE(t)) is negatively correlated with Delta in both nitrogen supply treatments and increased with the nitrogen supply. PMID:10996367

Shangguan; Shao; Dyckmans

2000-10-01

361

Influence of stratification in near-surface water layer on intensity of gas exchange between atmosphere and water  

NASA Astrophysics Data System (ADS)

Little is known concerning the influence of the temperature field in the near-water layer on gas exchange between the atmosphere and water. During periods of calm the transfer of oxygen from the air to water is sometimes impeded and large numbers of fish may die. A laboratory experiment was carried out in glass thermostated containers, in each of which the temperature was maintained with great accuracy. One was heated to 39 to 40 C; another was cooled to 12 to 13 C; a third was kept at ambient temperature. In each case the aeration coefficient and rate of mass transfer were computed. Air and water temperatures were varied to determine temperature gradients in the near-water and near-surface layers. A copper constantan thermocouple was used in measuring temperatures above and below the interface. The influence of petroleum films on the rate of mass transfer was also determined. The rate of evaporation at different temperatures was ascertained. The greatest influence was observed in experiments with cooled air. It was found that temperature stratification in the near-surface water layer exerts a considerable influence on water-air gas exchange. In certain cases a petroleum film increases the temperature gradient and causes an even greater decrease in mass transfer rate.

Brekhovskikh, V. F.; Bratkov, V. I.

1986-07-01

362

[Methanogenic activity and methanogen diversity in marine gas field sediments].  

PubMed

Methanogens play an important role in marine sediments, which are related to methane production and methane hydrate deposits. Methanogenic activity of marine gas field sediments was investigated using substrates that methanogens usually used as carbon sources. H2/CO2, methanol, methylamines and trimethylamines could support the growth and methane production of gas field sediments. 16S rRNA gene sequence analysis indicated that the predominant methanogens in the enrichment cultures were related to known cultured methanogens in the family Methanosarcinaceae of the order Methanosarcinales and the family Methanomicrobiales of the order Methanomicrobiales, with genera Methanococcoides, Methanogenium and Methanosarcina as major methanogens. PMID:25158513

Tian, Qi; Wang, Jia; Fan, Xiao-Lei; Luo, Sheng-Jun; Guo, Rong-Bo; Qiu, Yan-Ling

2014-06-01

363

Effects of experimentally-warmed tundra on diurnal gas exchange in Salix-, Carex, and Eriophorum in a high-arctic lowland oasis  

SciTech Connect

Gas exchange was measured for the willow Salix arctica and two sede species. Carex qauatilus stans and Eriophorum angustifolium triste, at Alexandra Fiord, Ellesmere Island (78[degrees]52'N) in an experiment designed to stimulate climate change. The tundra was warmed using passive, open-topped experimental chambers that raised daily mean temperatures approx. 2[degrees] over two seasons. The chambers are part of the International Tundra Experiment (ITEX), the objective of which is to assess potential impacts of global warming on tundra plant communities. Salix arctica was measured in dry tundra and on adjacent wet meadow hummocks. The sedges were measured on hummocks and in hollows in the wet meadow only. Gas exchange was measured every four hours for 48 hours for each species. For S arctica, experimental warming had no effect in the dry tundra, but appeared to depress net assimilation (NA) in the wet meadow. Gas exchange parameters were slightly higher overall in the dry tundra for this species. For the sedges, the warming treatment had no major effect, although it caused some reduction of NA for Eriophorum on the hummocks. Gas exchange parameters were generally higher for Carex than for Eriophorum. No regular diurnal patterns of gas exchange were observed for any species.

Jones, M.H.; MacDonald, S.E. (Univ. of Alberta, Edmonton (Canada)); Henry, G.H.R. (Univ. of British Columbia, Vancouver, BC (Canada))

1994-06-01

364

Gas Exchange and Carbon Partitioning in the Leaves of Celery (Apium graveolens L.) at Various Levels of Root Zone Salinity.  

PubMed Central

Both mannitol and sucrose (Suc) are primary photosynthetic products in celery (Apium graveolens L.). In other biological systems mannitol has been shown to serve as a compatible solute or osmoprotectant involved in stress tolerance. Although mannitol, like Suc, is translocated and serves as a reserve carbohydrate in celery, its role in stress tolerance has yet to be resolved. Mature celery plants exposed to low (25 mM NaCl), intermediate (100 mM NaCl), and high (300 mM NaCl) salinities displayed substantial salt tolerance. Shoot fresh weight was increased at low NaCl concentrations when compared with controls, and growth continued, although at slower rates, even after prolonged exposure to high salinities. Gas-exchange analyses showed that low NaCl levels had little or no effect on photosynthetic carbon assimilation (A), but at intermediate levels decreases in stomatal conductance limited A, and at the highest NaCl levels carboxylation capacity (as measured by analyses of the CO2 assimilation response to changing internal CO2 partial pressures) and electron transport (as indicated by fluorescence measurements) were the apparent prevailing limits to A. Increasing salinities up to 300 mM, however, increased mannitol accumulation and decreased Suc and starch pools in leaf tissues, e.g. the ratio of mannitol to Suc increased almost 10-fold. These changes were due in part to shifts in photosynthetic carbon partitioning (as measured by 14C labeling) from Suc into mannitol. Salt treatments increased the activity of mannose-6-phosphate reductase (M6PR), a key enzyme in mannitol biosynthesis, 6-fold in young leaves and 2-fold in fully expanded, mature leaves, but increases in M6PR protein were not apparent in the older leaves. Mannitol biosynthetic capacity (as measured by labeling rates) was maintained despite salt treatment, and relative partitioning into mannitol consequently increased despite decreased photosynthetic capacity. The results support a suggested role for mannitol accumulation in adaptation to and tolerance of salinity stress. PMID:12232328

Everard, J. D.; Gucci, R.; Kann, S. C.; Flore, J. A.; Loescher, W. H.

1994-01-01

365

Stomata size and spatial pattern effects on leaf gas exchange - a quantitative assessment of plant evolutionary choices  

NASA Astrophysics Data System (ADS)

Land plants developed a dynamically gas-permeable layer at their leaf surfaces to allow CO2 uptake for photosynthesis while controlling water vapor loss through numerous adjustable openings (stomata) in the impervious leaf epidermis. Details of stomata structure, density and function may vary greatly among different plant families and respond to local environmental conditions, yet they share basic traits in dynamically controlling gaseous exchange rates by varying stomata apertures. We implement a pore scale gas diffusion model to quantitatively interpret the functionality of different combinations of stomata size and pattern on leaf gas exchange and thermal management based on data from fossil records and contemporary data sets. Considering all available data we draw several general conclusions concerning stomata design considerations: (1) the sizes and densities of stomata in the available fossil record leaves were designed to evaporate at rates in the range 0.75?e/e0 ?0.99 (relative to free water evaporation); (2) examination of evaporation curves show that for a given stomata size, the density (jointly defining the leaf evaporating area when fully open) was chosen to enable a high sensitivity in reducing evaporation rate with incremental stomatal closure, nevertheless, results show the design includes safety margins to account for different wind conditions (boundary layer thickness); (3) scaled for mean vapor flux, the size of stomata plays a minor role in the uniformity of leaf thermal field for a given stomata density. These principles enable rationale assessment of plant response to raising CO2, and provide a physical framework for considering the consequences of different stomata patterns (patchy) on leaf gas exchange (and thermal regime). In contrast with present quantitative description of traits and functionality of these dynamic covers in terms of gaseous diffusion resistance (or conductance), where stomata size, density and spatial pattern are lumped into a single effective resistance parameter, the present approach enables derivation of nuanced insights and offers predictive capabilities that link changes in stomata structure and geometrical attributes to quantifying environmental influences and feedbacks on leaf structure and function.

Or, Dani; Assouline, Shmuel; Aminzadeh, Milad; Haghighi, Erfan; Schymanski, Stan; Lehmann, Peter

2014-05-01

366

The mechanics of motorised momentum exchange tethers when applied to active debris removal from LEO  

NASA Astrophysics Data System (ADS)

The concept of momentum exchange when applied to space tethers for propulsion is well established, and a considerable body of literature now exists on the on-orbit modelling, the dynamics, and also the control of a large range of tether system applications. The authors consider here a new application for the Motorised Momentum Exchange Tether by highlighting three key stages of development leading to a conceptualisation that can subsequently be developed into a technology for Active Debris Removal. The paper starts with a study of the on-orbit mechanics of a full sized motorised tether in which it is shown that a laden and therefore highly massasymmetrical tether can still be forced to spin, and certainly to librate, thereby confirming its possible usefulness for active debris removal (ADR). The second part of the paper concentrates on the modelling of the centripetal deployment of a symmetrical MMET in order to get it initialized for debris removal operations, and the third and final part of the paper provides an entry into scale modelling for low cost mission design and testing. It is shown that the motorised momentum exchange tether offers a potential solution to the removal of large pieces of orbital debris, and that dynamic methodologies can be implemented to in order to optimise the emergent design.

Caldecott, Ralph; Kamarulzaman, Dayangku N. S.; Kirrane, James P.; Cartmell, Matthew P.; Ganilova, Olga A.

2014-12-01

367

Active heat exchange system development for latent heat thermal energy storage  

NASA Technical Reports Server (NTRS)

Various active heat exchange concepts were identified from among three generic categories: scrapers, agitators/vibrators and slurries. The more practical ones were given a more detailed technical evaluation and an economic comparison with a passive tube-shell design for a reference application (300 MW sub t storage for 6 hours). Two concepts were selected for hardware development: (1) a direct contact heat exchanger in which molten salt droplets are injected into a cooler counterflowing stream of liquid metal carrier fluid, and (2) a rotating drum scraper in which molten salt is sprayed onto the circumference of a rotating drum, which contains the fluid salt is sprayed onto the circumference of a rotating drum, which contains the fluid heat sink in an internal annulus near the surface. A fixed scraper blade removes the solidified salt from the surface which was nickel plated to decrease adhesion forces. In addition to improving performance by providing a nearly constant transfer rate during discharge, these active heat exchanger concepts were estimated to cost at least 25% less than the passive tube-shell design.

Alario, J.; Kosson, R.; Haslett, R.

1980-01-01

368

Excretion-retention data of steady state gas exchange in tidal breathing  

Microsoft Academic Search

The aim of this study is to investigate the steady state gas transfer properties of the lungs. These properties can be derived from excretion-retention (E-R) data of inert tracer gases that are infused intravenously.E=PE\\/Pv andR=Pa\\/Pv, wherePE,Pa andPv represent the partial pressures of the tracer gases in mixed expired gas, arterial blood and mixed venous blood, respectively. In this paper, special

Aart Zwart; Sybrand C. M. Luijendijk; Wouter R. de Vries

1986-01-01

369

Element exchange in a water- and gas-closed biological Life Support System.  

PubMed

Liquid human wastes and household water used for nutrition of wheat made possible to realize 24% closure for the mineral exchange in an experiment with a 2-component version of "Bios-3" life support system (LSS) Input-output balances of revealed, that elements (primarily trace elements) within the system. The structural materials (steel, titanium), expanded clay aggregate, and catalytic furnace catalysts. By the end of experiment, the permanent nutrient solution, plants, and the human diet gradually built up Ni, Cr, Al, Fe, V, Zn, Cu, and Mo. Thorough selection and pretreatment of materials can substantially reduce this accumulation. To enhance closure of the mineral exchange involves processing of human-metabolic wastes and inedible biomes inside LSS. An efficient method to oxidize wastes by hydrogen peroxide icon a quartz reactor at the temperature of 80 degrees C controlled electromagnetic field is proposed. PMID:11542588

Gribovskaya, I V; Kudenko YuA; Gitelson, J I

1997-01-01

370

Element exchange in a water-and gas-closed biological life support system  

NASA Astrophysics Data System (ADS)

Liquid human wastes and household water used for nutrition of wheat made possible to realize 24% closure for the mineral exchange in an experiment with a 2-component version of ``Bios-3'' life support system (LSS) Input-output balances of revealed, that elements (primarily trace elements) within the system. The structural materials (steel, titanium), expanded clay aggregate, and catalytic furnace catalysts. By the end of experiment, the permanent nutrient solution, plants, and the human diet gradually built up Ni, Cr, Al, Fe, V, Zn, Cu, and Mo. Thorough selection and pretreatment of materials can substantially reduce this accumulation. To enhance closure of the mineral exchange involves processing of human- metabolic wastes and inedible biomes inside LSS. An efficient method to oxidize wastes by hydrogen peroxide in a quartz reactor at the temperature of 80 degC controlled electromagnetic field is proposed.

Gribovskaya, I. V.; Kudenko, Yu. A.; Gitelson, J. I.

1997-01-01

371

Element exchange in a water-and gas-closed biological life support system  

NASA Astrophysics Data System (ADS)

Liquid human wastes and household water used for nutrition of wheat made possible to realize 24% closure for the mineral exchange in an experiment with a 2-component version of ``Bios-3'' life support system (LSS) Input-output balances of revealed, that elements (primarily trace elements) within the system. The structural materials (steel, titanium), expanded clay aggregate, and catalytic furnace catalysts. By the end of experiment, the permanent nutrient solution, plants, and the human diet gradually built up Ni, Cr, Al, Fe, V, Zn, Cu, and Mo. Thorough selection and pretreatment of materials can substantially reduce this accumulation. To enhance closure of the mineral exchange involves processing of human- metabolic wastes and inedible biomes inside LSS. An efficient method to oxidize wastes by hydrogen peroxide in a quartz reactor at the temperature of 80°C controlled electromagnetic field is proposed.

1997-01-01

372

Effect of Ozone Exposure on Seasonal Gas Exchange of Five Western Conifers 1  

Microsoft Academic Search

Five species of western conifers (Pinus ponderosa, Abies concolor, Pseudotsuga menziesii, Abies lasiocarpa, and Picea engelmannii) were exposed, in two standard open-top exposure chambers per treatment, to charcoal-filtered air and a simulated diurnal ozone exposure profile (120 d sum of 136 ppm-h) to test their relative sensitivity. CO 2 exchange rate (CER), stomatal conductance (gs), and total leaf nitrogen of

Nancy E. Grulke; Paul R. Miller; Theodor D. Leininger

373

Low energy of activation for amide hydrogen exchange reactions in proteins supports a local unfolding model.  

PubMed

Hydrogen exchange reactions of amides in hen egg white lysozyme that are pH dependent and have a low energy of activation have been shown to be in accordance with a reaction mechanism in two steps, an equilibrium step and an exchange step. These results are not in agreement with the model, proposed by C.K. Woodward & B.D. Hilton, known as the penetration model. Therefore our results suggest that this model should be revised. The amide hydrogen/deuterium exchange rates in hen egg white lysozyme were measured at 4 degrees C, 10 degrees C, 15 degrees C and 25 degrees C at pH 7.0 by 1H nuclear magnetic resonance spectroscopy. Activation energies of the exchange reactions in the range from 20 kJ mol-1 to 333 kJ mol-1 were obtained for 32 of the 129 residues in the protein. The amides of lysozyme studied here could be divided into two groups, one group of amides are characterized by an observed amide exchange rate (ko) in the range 10(-4) to 10(-6) s-1, an equilibrium constant k1/k2 close to 10(-5), a low energy of activation (20 to 50 kJ mol-1) and a distance less than 6 A from solvent. The other group of amides are characterized by a ko less than 10(-6) s-1, a k1/k2 close to 10(-7), higher energies of activation (40 to 330 kJ mol-1) and a distance more than 4 A from solvent. In terms of structure the amides of the last group are from the core of the protein. They are typically involved in a hydrogen bond and form part of the secondary structure either as interior alpha-helices or central strands of beta-sheets. The first group consists of amides that are in the shell of the protein between the core and the surface. These amides are typically hydrogen bonded and involved in secondary structure such as external alpha-helices or outer strands of beta-sheets and turns. PMID:8230202

Thomsen, N K; Poulsen, F M

1993-11-01

374

Membrane oxygenator heat exchanger failure detected by unique blood gas findings.  

PubMed

Failure of components integrated into the cardiopulmonary bypass circuit, although rare, can bring about catastrophic results. One of these components is the heat exchanger of the membrane oxygenator. In this compartment, unsterile water from the heater cooler device is separated from the sterile blood by stainless steel, aluminum, or by polyurethane. These areas are glued or welded to keep the two compartments separate, maintaining sterility of the blood. Although quality control testing is performed by the manufacturer at the factory level, transport presents the real possibility for damage. Because of this, each manufacturer has included in the instructions for use a testing procedure for testing the integrity of the heat exchanger component. Water is circulated through the heat exchanger before priming and a visible check is made of the oxygenator bundle to check for leaks. If none are apparent, then priming of the oxygenator is performed. In this particular case, this procedure was not useful in detecting communication between the water and blood chambers of the oxygenator. PMID:24779125

Hawkins, Justin L

2014-03-01

375

Generation of biologically active substances in a natural gas flame  

SciTech Connect

Samples of gaseous and solid species taken from the central axis of a 1 megawatt heat-input natural gas flame were tested in vitro for mutagenic activity and teratogenic potential. Mutagenicity was determined by a Salmonella typhimurium forward mutation assay. Potential teratogenicity was indicated by the ability of samples to interfere with the attachment of mammalian cells to a lectin coated surface. Both the mutagenic and anti-attachment activities were found to peak in samples originating from the flame regions where the total polyaromatic compound (PAC) species concentration reached a maximum, indicating a strong correlation between PAC presence in the samples and biological activity. Additional anti-attachment activity was found close to the injection nozzle. No biologically active material was detected beyond the luminous portion of the flame.

Braun, A.G.; Pakzaban, P.; Toqan, M.A.; Beer, J.M.

1987-06-01

376

Generation of biologically active substances in a natural gas flame.  

PubMed

Samples of gaseous and solid species taken from the central axis of a 1 megawatt heat-input natural gas flame were tested in vitro for mutagenic activity and teratogenic potential. Mutagenicity was determined by a Salmonella typhimurium forward mutation assay. Potential teratogenicity was indicated by the ability of samples to interfere with the attachment of mammalian cells to a lectin coated surface. Both the mutagenic and anti-attachment activities were found to peak in samples originating from the flame regions where the total polyaromatic compound (PAC) species concentration reached a maximum, indicating a strong correlation between PAC presence in the samples and biological activity. Additional anti-attachment activity was found close to the injection nozzle. No biologically active material was detected beyond the luminous portion of the flame. PMID:3622438

Braun, A G; Pakzaban, P; Toqan, M A; Beér, J M

1987-06-01

377

Na+-H+ exchange activity in rat hepatocytes: role in regulation of intracellular pH.  

PubMed

Amiloride-sensitive Na+-H+ exchange has been identified in basolateral membrane vesicles from rat liver, but little is currently known about its regulation or its role in maintenance of resting intracellular pH (pHi) in intact hepatocytes. We have assessed Na+-H+ exchange activity in isolated or cultured rat hepatocytes in nominally HCO3- free solution under basal conditions and after intracellular acidification by an NH4Cl pulse by measuring 1) pHi, using the pH-sensitive dye 2',7'-bis(carboxyethyl)-5(6)-carboxy fluorescein, 2) net H+ efflux by pH-stat titration, and 3) amiloride-inhibitable 22Na uptake. Under resting conditions, Na+-H+ exchange did not contribute measurably to Na+ uptake and accounted for less than 20% of net H+ efflux. Hepatocyte pHi averaged 7.07 +/- 0.03, significantly above H+ electrochemical equilibrium (6.92 +/- 0.08) determined using an electrogenic proton ionophore. Transient removal of extracellular Na+ or exposure to amiloride reversibly lowered pHi by 0.09 +/- 0.01 and 0.12 +/- 0.03 pH units, respectively, within 5-10 min. After intracellular acidification by an NH4Cl pulse, Na+ uptake rate increased about twofold, the increase being entirely amiloride inhibitable. Net H+ efflux increased about threefold, and 70% of the increase was amiloride inhibitable. Recovery of pHi after an NH4Cl pulse was reversibly blocked by exposure to amiloride or removal of Na+. Na+-H+ exchange activity (calculated from the rate of change in pHi and intracellular buffering capacity) was inversely related to pHi and was estimated to approach zero at pHi 7.25-7.50.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:2536240

Renner, E L; Lake, J R; Persico, M; Scharschmidt, B F

1989-01-01

378

Solution and Gas-Phase H/D Exchange of Protein-Small-Molecule Complexes: Cex and Its Inhibitors  

NASA Astrophysics Data System (ADS)

The properties of noncovalent complexes of the enzyme exo-1,4-?-D-glycanase ("Cex") with three aza-sugar inhibitors, deoxynojirimycin (X2DNJ), isofagomine lactam (X2IL), and isofagomine (X2IF), have been studied with solution and gas-phase hydrogen deuterium exchange (H/Dx) and measurements of collision cross sections of gas-phase ions. In solution, complexes have lower H/Dx levels than free Cex because binding the inhibitors blocks some sites from H/Dx and reduces fluctuations of the protein. In mass spectra of complexes, abundant Cex ions are seen, which mostly are formed by dissociation of complexes in the ion sampling interface. Both complex ions and Cex ions formed from a solution containing complexes have lower cross sections than Cex ions from a solution of Cex alone. This suggests the Cex ions formed by dissociation "remember" their solution conformations. For a given charge, ions of the complexes have greater gas-phase H/Dx levels than ions of Cex. Unlike cross sections, H/Dx levels of the complexes do not correlate with the relative gas-phase binding strengths measured by MS/MS. Cex ions from solutions with or without inhibitors, which have different cross sections, show the same H/Dx level after 15 s, indicating the ions may fold or unfold on the seconds time scale of the H/Dx experiment. Thus, cross sections show that complexes have more compact conformations than free protein ions on the time scale of ca. 1 ms. The gas-phase H/Dx measurements show that at least some complexes retain different conformations from the Cex ions on a time scale of seconds.

Kang, Yang; Terrier, Peran; Ding, Chuanfan; Douglas, D. J.

2012-01-01

379

Atmospheric Impacts of Marcellus Shale Gas Activities in Southwestern Pennsylvania  

NASA Astrophysics Data System (ADS)

Pittsburgh and the surrounding regions of southwestern Pennsylvania are subject to intensive natural gas exploration, drilling, and extraction associated with the Marcellus Shale formation. Gas extraction from the shale formation uses techniques of horizontal drilling followed by hydraulic fracturing. There are significant concerns about air pollutant emissions from the development and production of shale gas, especially methane emissions. We have deployed a mobile monitoring unit to investigate the atmospheric impacts of Marcellus Shale gas activities. The mobile sampling platform is a van with an on-board generator, a high-resolution GPS unit, cameras, and instrumentation for measuring methane, criteria gases (SO2, NOx, CO, O3), PM size distributions (scanning mobility particle sizer), black carbon mass (multi-angle absorption photometer), particle-bound polycyclic aromatic hydrocarbons, volatile organic compounds (gas chromatograph with flame ionization detection), and meteorological data. A major advantage of the mobile sampling unit over traditional, stationary monitors is that it allows us to rapidly visit a variety of sites. Sampling at multiple sites allows us to characterize the spatial variability of pollutant concentrations related to Marcellus activity, particularly methane. Data collected from the mobile sampling unit are combined with GIS techniques and dispersion models to map pollutants related to Marcellus Shale operations. The Marcellus Shale gas activities are a major and variable source of methane. The background methane concentration in Pittsburgh is 2.1 +/- 0.2 ppm. However, two southwestern Pennsylvania counties with the highest density of Marcellus Shale wells, Washington and Greene Counties, have many areas of elevated methane concentration. Approximately 11% of the sampled sites in Washington County and nearly 50% of the sampled sites in Greene County have elevated (>2.3 ppm) methane concentrations, compared to 1.5% of sites with elevated methane in counties with minimal Marcellus activity (Allegheny and Butler counties). Methane concentrations in areas with large numbers of active well sites can reach as high as 20 ppm (~10 times background), and are highly spatially variable. Areas with elevated methane concentrations also exhibited higher ratios of 13CH4/12CH4, consistent with a thermogenic source of the excess methane.

Presto, A. A.; Lipsky, E. M.; Saleh, R.; Donahue, N. M.; Robinson, A. L.

2012-12-01

380

Somatostatin inhibits the Na+/H+ exchange activity of rat hepatocytes in short term primary culture.  

PubMed

Activation of the Na+/H+ exchanger is associated with cell growth and differentiation. Our study has tested whether somatostatin-14 (SS-14), which is a potent inhibitor of liver regeneration, has an inhibitory effect on the Na+/H+ exchange (NHE-1) of rat hepatocytes. We treated hepatocytes with SS-14 prior and after cell culture. NHE-1 activity of short term cultured hepatocytes was estimated with the recovery rate of pHi after 9 min. acid-loading in a sodium free buffer. Cultured with SS-14 (100 nM) inhibited significantly the pHi recovery rate of hepatocytes, dpHi/dt and set point were significantly decreased in the presence of SS-14 in comparison to controls. The resting pHi of hepatocytes was not affected in the presence of SS-14. In contrast, addition of SS-14 after cell culture had no effect on the pHi recovery rate of hepatocytes. Therefore the inhibitory action of SS-14 on NHE-1 activity of rat hepatocytes appears to depend on the presence of the hormone in the early steps of the process of cell growth/adhesion. Inhibition of SS-14 on NHE-1 activity seems to mediate, at least in part, its inhibition on liver regeneration. PMID:10643967

Ye, W Z; Mathieu, S; Marteau, C

1999-12-01

381

First laboratory study of air-sea gas exchange at hurricane wind speeds  

NASA Astrophysics Data System (ADS)

In a pilot study conducted in October and November 2011, air-sea gas transfer velocities of the two sparingly soluble trace gases hexafluorobenzene and 1,4-difluorobenzene were measured in the unique high-speed wind-wave tank at Kyoto University, Japan. This air-sea interaction facility is capable of producing hurricane strength wind speeds of up to u10 =67 m s-1. This constitutes the first lab study of gas transfer at such high wind speeds. The measured transfer velocities k600 spanned two orders of magnitude, lying between 11 cm h-1 and 1180 cm h-1 with the latter being the highest ever measured wind-induced gas transfer velocity. The measured gas transfer velocities are in agreement with the only available data set at hurricane wind speeds (McNeil and D'Asaro, 2007). The disproportionately large increase of the transfer velocities found at highest wind speeds indicates a new regime of air-sea gas transfer, which is characterized by strong wave breaking, enhanced turbulence and bubble cloud entrainment.

Krall, K. E.; Jähne, B.

2014-04-01

382

Effects of nitrogen quenching gas on spin-exchange optical pumping of {sup 3}He  

SciTech Connect

We consider the degree of conservation of nuclear spin polarization in the process of optical pumping under typical spin-exchange optical pumping conditions. Previous analyses have assumed that negligible nuclear spin precession occurs during the brief periods of time in which the alkali-metal atoms are in the excited state after absorbing photons and before undergoing quenching collisions with nitrogen molecules. We include excited-state hyperfine interactions, electronic spin relaxation in collisions with He and N{sub 2}, spontaneous emission, quenching collisions, and a simplified treatment of radiation trapping.

Lancor, B.; Walker, T. G. [Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)

2010-10-15

383

Exact Dynamical Exchange-Correlation Kernel of a Weakly Inhomogeneous Electron Gas  

Microsoft Academic Search

The dynamical exchange-correlation kernel $f_{xc}$ of a non-uniform electron\\u000agas is an essential input for the time-dependent density functional theory of\\u000aelectronic systems. The long-wavelength behavior of this kernel is known to be\\u000aof the form $f_{xc}= \\\\alpha\\/q^2$ where $q$ is the wave vector and $\\\\alpha$ is a\\u000afrequency-dependent coefficient. We show that in the limit of weak\\u000anon-uniformity the

V. U. Nazarov; G. Vignale; Y.-C. Chang

2009-01-01

384

Increased sarcolemmal Na+/H+ exchange activity in hypertrophied myocytes from dogs with chronic atrioventricular block  

PubMed Central

Dogs with compensated biventricular hypertrophy due to chronic atrioventricular block (cAVB), are more susceptible to develop drug-induced Torsade-de-Pointes arrhythmias and sudden cardiac death. It has been suggested that the increased Na+ influx in hypertrophied cAVB ventricular myocytes contribute to these lethal arrhythmias. The increased Na+ influx was not mediated by Na+ channels, in fact the Na+ current proved reduced in cAVB myocytes. Here we tested the hypothesis that increased activity of the Na+/H+ exchanger type 1 (NHE-1), commonly observed in hypertrophic hearts, causes the elevated Na+ influx. Cardiac acid-base transport was studied with a pH-sensitive fluorescent dye in ventricular myocytes isolated from control and hypertrophied cAVB hearts; the H+ equivalent flux through NHE-1, Na+-HCO?3 cotransport (NBC), Cl?/OH? exchange (CHE), and Cl?/HCO?3 exchange (AE) were determined and normalized per liter cell water and corrected for surface-to-volume ratio. In cAVB, sarcolemmal NHE-1 flux was increased by 65 ± 6.3% in the pHi interval 6.3–7.2 and NBC, AE, and CHE fluxes remained unchanged. Accordingly, at steady-state intracellular pH the total sarcolemmal Na+ influx by NHE-1 + NBC increased from 8.5 ± 1.5 amol/?m2/min in normal myocytes to 15 ± 2.4 amol/?m2/min in hypertrophied cAVB myocytes. We conclude that compensated cardiac hypertrophy in cAVB dogs is accompanied with an increased sarcolemmal NHE-1 activity. This in conjunction with unchanged activity of the other acid-base transporters will raise the intracellular Na+ in hypertrophied cAVB myocytes. PMID:24324438

van Borren, Marcel M. G. J.; Vos, Marc A.; Houtman, Marien J. C.; Antoons, Gudrun; Ravesloot, Jan H.

2013-01-01

385

Seasonal and diurnal gas exchange differences in ozone-sensitive common milkweed (Asclepias syriaca L.) in relation to ozone uptake.  

PubMed

Stomatal conductance and net photosynthesis of common milkweed (Asclepias syriaca L.) plants in two different soil moisture regimes were directly quantified and subsequently modeled over an entire growing season. Direct measurements captured the dynamic response of stomatal conductance to changing environmental conditions throughout the day, as well as declining gas exchange and carbon assimilation throughout the growth period beyond an early summer maximum. This phenomenon was observed in plants grown both with and without supplemental soil moisture, the latter of which should theoretically mitigate against harmful physiological effects caused by exposure to ozone. Seasonally declining rates of stomatal conductance were found to be substantial and incorporated into models, making them less susceptible to the overestimations of effective exposure that are an inherent source of error in ozone exposure indices. The species-specific evidence presented here supports the integration of dynamic physiological processes into flux-based modeling approaches for the prediction of ozone injury in vegetation. PMID:17655989

Bergweiler, Chris; Manning, William J; Chevone, Boris I

2008-03-01

386

Hydrolysis and ion exchange of titania nanoparticles towards large-scale titania and titanate nanobelts for gas sensing applications  

NASA Astrophysics Data System (ADS)

One-dimensional titanate and titania nanostructures are prepared by hydrothermal method from titania nanoparticles precursor via hydrolysis and ion exchange processes. The formation mechanism and the reaction process of the nanobelts are elucidated. The effects of the NaOH concentration, HCl leaching duration and the calcination temperature on the morphology and chemical composition of the produced nanobelts are investigated. Na+ ions of the titanate nanobelts can be effectively removed by longer acid leaching and neutralization process and transformed into metastable hydrogen titanate compound. A hybrid hydrogen titanate and anatase titania nanobelts can be obtained under dehydration process of 500 °C. The nanobelts are produced in gram quantities and easily made into nanostructure paper for the bulk study on their electrical and sensing properties. The sensing properties of the nanobelts sheet are tested and exhibited response to H2 gas.

Bela, Somaiah; Weng Wong, Andrew See; Ho, Ghim Wei

2010-01-01

387

Influence of saline irrigation on growth, ion accumulation and partitioning, and leaf gas exchange of carrot (Daucus carota L.).  

PubMed

Like those of many horticultural crop species, the growth and leaf gas exchange responses of carrot (Daucus carota L.) to salinity are poorly understood. In this study ion accumulation in root tissues (periderm, xylem and phloem tissues) and in leaves of different ages was assessed for carrot plants grown in the field with a low level of salinity (5.8 mM Na(+) and 7.5 mM Cl(-)) and in a glasshouse with salinity ranging from 1-80 mM. At low levels of salinity (1-7.5 mM), in both the field and glasshouse, carrot leaves accumulated high concentrations of Cl(-) (140-200 mM); these appear to be the result of a high affinity for Cl(-) uptake and a low retention of Cl(-) in the root system. However, Cl(-) uptake is under tight control, with an 80-fold increase in external salinity resulting in only a 1.5-fold change in the Cl(-) concentration of the shoot and no increase in the Cl(-) concentration of the root xylem tissue. In contrast to Cl(-), shoot Na(+) concentrations were comparatively low (30-40 mM) but increased by seven-fold when salinity was increased by 80-fold. Growth over the 56-d treatment period in the glasshouse was insensitive to salinity less than 20 mM, but at higher concentrations the yield of carrot tap roots declined by 7 % for each 10 mM increase in salinity. At low levels of salinity the accumulation of high concentrations of Cl(-) (150 mM) in carrot laminae did not appear to limit leaf gas exchange. However, photosynthesis and stomatal conductance were reduced by 38 and 53 %, respectively, for plants grown at a salinity of 80 mM compared with those grown at 1 mM. Salinity-induced reductions in both p(i) and carbon isotope discrimination (delta) were small (2.5 Pa and 1.4 per thousand, respectively, at 80 mM) indicating that the reduction in photosynthesis was only marginally influenced by CO(2) supply. At a salinity of 80 mM the photosynthetic capacity was reduced, with a 30 % reduction in the CO(2)-saturated rate of photosynthesis (A(max)) and a 40 % reduction in both the apparent rate of RuBP-carboxylase-limited CO(2) fixation (V(cmax)) and the electron transport rate limiting RuBP regeneration (J(max)). This study has shown that carrot growth and leaf gas exchange are insensitive to the high leaf Cl(-) concentrations that occur at low levels (1-7 mM) of salinity. However, growth is limited at salinity levels above 20 mM and leaf gas exchange is limited at salinity levels above 8 mM. PMID:12451027

Gibberd, Mark R; Turner, Neil C; Storey, Richard

2002-12-01

388

An inhibitor of Na(+)/Ca(2+) exchange blocks activation of insect olfactory receptors.  

PubMed

Earlier we showed that the Na(+)/Ca(2+) exchanger inhibitor, KB-R7943, potently blocks the odor-evoked activity of lobster olfactory receptor neurons. Here we extend that finding to recombinant mosquito olfactory receptors stably expressed in HEK cells. Using whole-cell and outside-out patch clamping and calcium imaging, we demonstrate that KB-R7943 blocks both the odorant-gated current and the odorant-evoked calcium signal from two different OR complexes from the malaria vector mosquito, Anopheles gambiae, AgOr48+AgOrco and AgOr65+AgOrco. Both heteromeric and homomeric (Orco alone) OR complexes were susceptible to KB-R7943 blockade when activated by VUAA1, an agonist that targets the Orco channel subunit, suggesting the Orco subunit may be the target of the drug's action. KB-R7943 represents a valuable tool to further investigate the functional properties of arthropod olfactory receptors and raises the interesting specter that activation of these ionotropic receptors is directly or indirectly linked to a Na(+)/Ca(2+) exchanger, thereby providing a template for drug design potentially allowing improved control of insect pests and disease vectors. PMID:24996179

Bobkov, Y; Corey, E; Ache, B

2014-07-25

389

Catalytic Ester–Amide Exchange Using Group (IV) Metal Alkoxide–Activator Complexes  

PubMed Central

A process for preparation of amides from unactivated esters and amines has been developed using a catalytic system comprised of group (IV) metal alkoxides in conjunction with additives including 1-hydroxy-7-azabenzotriazole (HOAt). In general, ester–amide exchange proceeds using a variety of structurally diverse esters and amines without azeotropic reflux to remove the alcohol byproduct. Initial mechanistic studies on the Zr(Ot-Bu)4–HOAt system revealed that the active catalyst is a novel, dimeric zirconium complex as determined by X-ray crystallography. PMID:16011366

Han, Chong; Lee, Jonathan P.; Lobkovsky, Emil; Porco, John A.

2005-01-01

390

Radon 222 tracing of soil and forest canopy trace gas exchange in an open canopy boreal forest  

NASA Technical Reports Server (NTRS)

A set of continuous, high-resolution atmospheric radon (Rn-222) concentration time series and radon soil flux measurements were acquired during the summer of 1990 at a micrometeorological tower site 13 km northwest of Schefferville, Quebec, Canada. The tower was located in a dry upland, open-canopy lichen-spruce woodland. For the period July 23 to August 1, 1990, the mean radon soil flux was 41.1 +/- 4.8 Bq m(exp -2)/h. Radon surface flux from the two end-member forest floor cover types (lichen mat and bare soil) were 38.8 +/- 5.1 and 61.8 +/- 15.6 Bq m(exp -2)/h, respectively. Average total forest canopy resistances computed using a simple 'flux box' model for radon exchange between the forest canopy and the overlying atmosphere range from 0.47 +/- 0.24 s cm(exp -1) to 2.65 +/- 1.61 cm(exp -1) for daytime hours (0900-1700 LT) and from 3.44 +/- 0.91 s cm(exp -1) to 10.55 +/- 7.16 s cm(exp -1) for nighttime hours (2000-0600) for the period July 23 to August 6, 1990. Continuous radon profiling of canopy atmospheres is a suitable approach for determining rates of biosphere/atmosphere trace gas exchange for remote field sites where daily equipment maintenance is not possible. where daily equipment maintenance is not possible.

Ussler, William, III; Chanton, Jeffrey P.; Kelley, Cheryl A.; Martens, Christopher S.

1994-01-01

391

[Flue gas desulfurization by a novel biomass activated carbon].  

PubMed

A novel biomass columnar activated carbon was prepared from walnut shell and pyrolusite was added as a catalyst. The activated carbon prepared was used for flue gas desulphurization in a fixed-bed reactor with 16 g of activated carbon. The impact of operating parameters such as SO2 inlet concentration, space velocity, bed temperature, moisture content and O2 concentration on the desulfurization efficiency of activated carbon was investigated. The results showed that both the breakthrough sulfur capacity and breakthrough time of activated carbon decreased with the increase of SO2 inlet concentration within the range of 0.1% -0.3%. The breakthrough sulfur capacity deceased with the increase of space velocity, with optimal space velocity of 600 h(-1). The optimal bed temperature was 80 degrees C, and the desulfurization efficiency can be reduced if the temperature continue to increase. The presence of moisture and oxygen greatly promoted the adsorption of SO2 onto the activated carbon. The best moisture content was 10%. When the oxygen concentrations were between 10% and 13%, the desulfurization performance of activated carbon was the highest. Under the optimal operating conditions, the sulfur capacity of activated carbon was 252 mg x g(-1), and the breakthrough time was up to 26 h when the SO2 inlet concentration was 0.2%. PMID:23798152

Liu, Jie-Ling; Tang, Zheng-Guang; Chen, Jie; Jiang, Wen-Ju; Jiang, Xia

2013-04-01

392

Elevated atmospheric carbon dioxide effects on soybean and sorghum gas exchange in conventional and no-tillage systems.  

PubMed

Increasing atmospheric CO(2) concentration has led to concerns about potential effects on production agriculture. In the fall of 1997, a study was initiated to compare the response of two crop management systems (conventional tillage and no-tillage) to elevated CO(2). The study used a split-plot design replicated three times with two management systems as main plots and two atmospheric CO(2) levels (ambient and twice ambient) as split plots using open-top chambers on a Decatur silt loam soil (clayey, kaolinitic, thermic Rhodic Paleudults). The conventional system was a grain sorghum [Sorghum bicolor (L.) Moench.] and soybean [Glycine max (L.) Merr.] rotation with winter fallow and spring tillage practices. In the no-tillage system, sorghum and soybean were rotated, and three cover crops were used [crimson clover (Trifolium incarnatum L.), sunn hemp (Crotalaria juncea L.), and wheat (Triticum aestivum L.)]. Over multiple growing seasons, the effect of management and CO(2) concentration on leaf-level gas exchange during row crop (soybean in 1999, 2001, and 2003; sorghum in 2000, 2002, and 2004) reproductive growth were evaluated. Treatment effects were fairly consistent across years. In general, higher photosynthetic rates were observed under CO(2) enrichment (more so with soybean) regardless of residue management practice. Elevated CO(2) led to decreases in stomatal conductance and transpiration, which resulted in increased water use efficiency. The effects of management system on gas exchange measurements were infrequently significant, as were interactions of CO(2) and management. These results suggest that better soil moisture conservation and high rates of photosynthesis can occur in both tillage systems in CO(2)-enriched environments during reproductive growth. PMID:20176833

Prior, S A; Runion, G B; Rogers, H H; Arriaga, F J

2010-01-01

393

Ammonia-Activated Mesoporous Carbon Membranes for Gas Separations  

SciTech Connect

Porous carbon membranes, which generally show improved chemical and thermal stability compared to polymer membranes, have been used in gas separations for many years. In this work, we show that the post-synthesis ammonia treatment of porous carbon at elevated temperature can improve the permeance and selectivity of these membranes for the separation of carbon dioxide and hydrocarbons from permanent gases. Hierarchically structured porous carbon membranes were exposed to ammonia gas at temperatures ranging from 850 C to 950 C for up to 10 min and the N{sub 2}, CO{sub 2}, and C{sub 3}H{sub 6} permeances were measured for these different membranes. Higher treatment temperatures and longer exposure times resulted in higher gas permeance values. In addition, CO{sub 2}/N{sub 2} and C{sub 3}H{sub 6}/N{sub 2} selectivities increased by a factor of 2 as the treatment temperature and time increased up to a temperature and time of 900 C, 10 min. Higher temperatures showed increased permeance but decreased selectivity indicating excess pore activation. Nitrogen adsorption measurements show that the ammonia treatment increased the porosity of the membrane while elemental analysis revealed the presence of nitrogen-containing surface functionalities in the treated carbon membranes. Thus, ammonia treatment at high temperature provides a controlled method to introduce both added microporosity and surface functionality to enhance gas separations performance of porous carbon membranes.

Mahurin, Shannon Mark [ORNL; Lee, Jeseung [ORNL; Wang, Xiqing [ORNL; Dai, Sheng [ORNL

2011-01-01

394

Application of crop gas exchange and transpiration data obtained with CEEF to global change problem  

NASA Astrophysics Data System (ADS)

In order to predict carbon sequestration of vegetation with the future rise in atmospheric CO 2 concentration, [CO 2] and temperature, long term effects of high [CO 2] and high temperature on responses of both photosynthesis and transpiration of plants as a whole community to environmental parameters need to be elucidated. Especially in the last decade, many studies on photosynthetic acclimation to elevated [CO 2] at gene, cell, tissue or leaf level for only vegetative growth phase ( i.e. before formation of reproductive organs) have been conducted all over the world. However, CO 2 acclimation studies at population or community level for a whole growing season are thus far very rare. Data obtained from repeatable experiments at population or community level for a whole growing season are necessary for modeling carbon sequestration of a plant community. On the other hand, in order to stabilize material circulation in the artificial ecological system of Closed Ecology Experiment Facilities (CEEF), it is necessary to predict material exchange rates in the biological systems. In particular, the material exchange rate in higher plant systems is highly variable during growth periods and there is a strong dependence on environmental conditions. For this reason, dependencies of both CO 2 exchange rate and transpiration rate of three rice populations grown from seed under differing conditions of [CO 2] and day/night air temperature (350 ?L CO 2 L -1, 24/17°C (population A); 700 ?L CO 2 L -1, 24/17°C (population B) and 700 ?L CO 2 L -1, 26/19°C (population C)) upon PPFD, leaf temperature and [CO 2] were investigated every two weeks during whole growing season. Growth of leaf lamina, leaf sheath, panicle and root was also compared. From this experiment, it was elucidated that acclimation of instantaneous photosynthetic response of rice population to [CO 2] occurs in vegetative phase through changes in ratio of leaf area to whole plant dry weight, LAR. But, in reproductive growth phase ( i.e. after initiation of panicle formation), the difference between photosynthetic response to [CO 2] of population A and that of population B decreased. Although LAR of population C was almost always less than that of population A, there was no difference between the photosynthetic response to [CO 2] of population A at 24°C and that of population C at 26°C for its whole growth period. These results are useful to make a model to predict carbon sequestration of rice community, which is an important type of vegetation especially in Asia in future global environmental change.

Tako, Y.; Arai, R.; Otsubo, K.; Nitta, K.

395

Integrin-mediated Membrane Blebbing Is Dependent on Sodium-Proton Exchanger 1 and Sodium-Calcium Exchanger 1 Activity*  

PubMed Central

Integrin signaling and membrane blebbing modulate cell adhesion, spreading, and migration. However, the relationship between integrin signaling and membrane blebbing is unclear. Here, we show that an integrin-ligand interaction induces both membrane blebbing and changes in membrane permeability. Sodium-proton exchanger 1 (NHE1) and sodium-calcium exchanger 1 (NCX1) are membrane proteins located on the bleb membrane. Inhibition of NHE1 disrupts membrane blebbing and decreases changes in membrane permeability. However, inhibition of NCX1 enhances cell blebbing; cells become swollen because of NHE1 induced intracellular sodium accumulation. Our study found that NHE1 induced sodium influx is a driving force for membrane bleb growth, while sodium efflux (and calcium influx) induced by NCX1 in a reverse mode results in membrane bleb retraction. Together, these findings reveal a novel function for NHE1 and NCX1 in membrane blebbing and permeability, and establish a link between membrane blebbing and integrin signaling. PMID:22270364

Yi, Yung-Hsiang; Chang, Yu-Sun; Lin, Chi-Hung; Lew, Tien-Shen; Tang, Chih-Yung; Tseng, Wei-Lien; Tseng, Ching-Ping; Lo, Szecheng J.

2012-01-01

396

Deletion of the anion exchanger Slc26a4 (pendrin) decreases apical Cl(-)/HCO3(-) exchanger activity and impairs bicarbonate secretion in kidney collecting duct.  

PubMed

The anion exchanger Pendrin, which is encoded by SLC26A4 (human)/Slc26a4 (mouse) gene, is localized on the apical membrane of non-acid-secreting intercalated (IC) cells in the kidney cortical collecting duct (CCD). To examine its role in the mediation of bicarbonate secretion in vivo and the apical Cl(-)/HCO(3)(-) exchanger in the kidney CCD, mice with genetic deletion of pendrin were generated. The mutant mice show the complete absence of pendrin expression in their kidneys as assessed by Northern blot hybridization, Western blot, and immunofluorescence labeling. Pendrin knockout (KO) mice display significantly acidic urine at baseline [pH 5.20 in KO vs. 6.01 in wild type (WT); P < 0.0001] along with elevated serum HCO(3)(-) concentration (27.4 vs. 24 meq/l in KO vs. WT, respectively; P < 0.02), consistent with decreased bicarbonate secretion in vivo. The urine chloride excretion was comparable in WT and KO mice. For functional studies, CCDs were microperfused and IC cells were identified by their ability to trap the pH fluorescent dye BCECF. The apical Cl(-)/HCO(3)(-) exchanger activity in B-IC and non-A, non-B-IC cells, as assessed by intracellular pH monitoring, was significantly reduced in pendrin-null mice. The basolateral Cl(-)/HCO(3)(-) exchanger activity in A-IC cells and in non-A, non-B-IC cells, was not different in pendrin KO mice relative to WT animals. Urine NH(4)(+) (ammonium) excretion increased significantly, consistent with increased trapping of NH(3) in the collecting duct in pendrin KO mice. We conclude that Slc26a4 (pendrin) deletion impairs the secretion of bicarbonate in vivo and reduces apical Cl(-)/HCO(3)(-) exchanger activity in B-IC and non-A, non-B-IC cells in CCD. Additional apical Cl(-)/HCO(3)(-) exchanger(s) is (are) present in the CCD. PMID:20375274

Amlal, Hassane; Petrovic, Snezana; Xu, Jie; Wang, Zhaohui; Sun, Xuming; Barone, Sharon; Soleimani, Manoocher

2010-07-01

397

Food production and gas exchange system using blue-green alga (Spirulina) for CELSS  

NASA Astrophysics Data System (ADS)

In order to reduce the cultivation area required for the growth of higher plants in space adoption of algae, which have a higher photosynthetic ability, seems very suitable for obtaining oxygen and food as a useful source of high quality protein. The preliminary cultivation experiment for determining optimum cultivation conditions and for obtaining the critical design parameters of the cultivator itself has been conducted. Spirulina was cultivated in the 6-liter medium containing a sodium hydrogen carbonate solution and a cultivation temperature controlled using a thermostat. Generated oxygen gas was separated using a polypropyrene porous hollow fiber membrane module. Through this experiment, oxygen gas (at a concentration of more than 46%) at a rate of 100 ~ 150 ml per minute could be obtained.

Oguchi, Mitsuo; Otsubo, Koji; Nitta, Keiji; Hatayama, Shigeki

398

Food production and gas exchange system using blue-green alga (spirulina) for CELSS  

NASA Technical Reports Server (NTRS)

In order to reduce the cultivation area required for the growth of higher plants in space adoption of algae, which have a higher photosynthetic ability, seems very suitable for obtaining oxygen and food as a useful source of high quality protein. The preliminary cultivation experiment for determining optimum cultivation conditions and for obtaining the critical design parameters of the cultivator itself was conducted. Spirulina was cultivated in the 6 liter medium containing a sodium hydrogen carbonate solution and a cultivation temperature controlled using a thermostat. Generated oxygen gas was separated using a polypropyrene porous hollow fiber membrane module. Through this experiment, oxygen gas (at a concentration of more than 46 percent) at a rate of 100 to approx. 150 ml per minute could be obtained.

Oguchi, Mitsuo; Otsubo, Koji; Nitta, Keiji; Hatayama, Shigeki

1987-01-01

399

The effects of breaking waves on dual-tracer gas exchange experiments  

SciTech Connect

Quantification of air-sea gas fluxes is important in understanding the global ocean carbon cycle, determining the effect of biologically produced gases on remote marine tropospheric aerosol production, and measuring the atmospheric lifetimes of trace gases. Direct measurement of the flux, F, of a sparingly soluble gas through the air-sea interface is extremely difficult in general, and F is often calculated as F = k{sub L}{delta}C where k{sub L} is the transfer velocity of the gas and AC is its air-sea concentration difference. In the absence of bubbles, k{sub L} is a function of the near-surface aqueous-phase turbulence and the molecular diffusivity of the gas. Although direct measurement of {delta}C is relatively simple, oceanic measurements of k{sub L} are problematical. Because of this, k{sub L} is usually estimated from empirical parameterizations for k{sub L} in terms of wind speed, U. The linear relation between F and k{sub L} at a constant {delta}C implies that the accuracy of the parameterization of k{sub L} in terms of U is critical in calculating F. This is especially true when U is large, since experiments in wind tunnels, lakes, and the ocean suggest that k{sub L} increases quadratically with U (Wanninkhof, 1992). With the exact functional form of the relation between U and k{sub L} not definitively known at present, estimation of k{sub L} at high U could be inaccurate. This problem could be resolved with further oceanic measurements of k{sub L} at high U. However, increases in U are also associated with increases in the frequency of wave breaking. Whitecaps are known to generate bubble plumes, and these bubbles could have a significant effect on the measurement of k{sub L}.

Asher, W. [Pacific Northwest Lab., Sequim, WA (United States); Wanninkhof, R. [National Oceanic and Atomospheric Administration/Atlantic Oceanographic and Meterological Lab., Miami, FL (United States)

1995-07-01

400

Land use change and the impact on greenhouse gas exchange in north Australian savanna soils  

Microsoft Academic Search

Savanna ecosystems are subject to accelerating land use change as human demand for food and forest products increases. Land use change has been shown to both increase and decrease greenhouse gas fluxes from savannas and considerable uncertainty exists about the non-CO2 fluxes from the soil. We measured methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2) over a complete wet-dry

S. P. P. Grover; S. J. Livesley; L. B. Hutley; H. Jamali; B. Fest; J. Beringer; K. Butterbach-Bahl; S. K. Arndt

2011-01-01

401

Hydraulic Performance and Gas Behavior of a Tall Crystalline Silicotitanate Ion-Exchange Column  

SciTech Connect

Crystalline silicotitanate (CST) sorbent is one of several technologies being evaluated by the Savannah River Site (SRS) for removing cesium from high-level tank-waste supernatant. As currently envisioned, three large 5-ft-diam, 20-ft-high ion-exchange columns will be operated in series at a superficial velocity of 4.1 cm/min. The CST will be subjected to a high radiation field from the sorbed cesium. The tests described in this work were conducted to evaluate column hydraulics, to identify changes in the CST particles during operation, to explore how radiolytic gases generated during operation behave, and to demonstrate sluicing of CST into and out of columns.

Welch, T.D.; Anderson, K.K.; Bostick, D.A.; Dillow, T.A.; Getting, M.W.; Hunt, R.D.; Lenarduzzi, R.; Mattus, A.J.; Taylor, P.A.; Wilmarth, W.R.

2000-02-01

402

Evolution and development of gas exchange structures in Mammalia: the placenta and the lung.  

PubMed

Appropriate oxygen supply is crucial for organisms. Here we examine the evolution of structures associated with the delivery of oxygen in the pre- and postnatal phases in mammals. There is an enormous structural and functional variability in the placenta that has facilitated the evolution of specialized reproductive strategies, such as precociality. In particular the cell layers separating fetal and maternal blood differ markedly: a non-invasive epitheliochorial placenta, which increases the diffusion distance, represents a derived state in ungulates. Rodents and their relatives have an invasive haemochorial placental type as optimum for the diffusion distance. In contrast, lung development is highly conserved and differences in the lungs of neonates can be explained by different developmental rates. Monotremes and marsupials have altricial stages with lungs at the early saccular phase, whereas newborn eutherians have lungs at the late saccular or alveolar phase. In conclusion, the evolution of exchange structures in the pre- and postnatal periods does not follow similar principles. PMID:20083237

Mess, Andrea M; Ferner, Kirsten J

2010-08-31

403

Viking gas exchange reaction - Simulation on UV-irradiated manganese dioxide substrate  

NASA Technical Reports Server (NTRS)

The exchange of O2 for H2O, analogous to that recorded on Mars by the Viking GEX experiment, has been observed on humidifying powdered beta-MnO2 (pyrolusite) which had been irradiated by UV in a humidified analog of the Martian atmosphere. Pyrolusite irradiated in a dry atmosphere did not release O2 on humidification. The XPS spectra of Mn and O of the reactive pyrolusite were shifted toward higher binding energies during UV irradiation. These shifts are consistent with the creation of a surface layer of a Mn(V) or Mn(VI) compound. The destruction of such a layer on humidification could account for the observed O2 release. Although manganese has not been identified in the Martian regolith, the upper limit of the Mn concentration is sufficiently high that O2 release from pyrolusite could have been responsible for the results of the Viking GEX experiment.

Blackburn, T. R.; Holland, H. D.; Ceasar, G. P.

1979-01-01

404

Dust and ionized gas in active radio elliptical galaxies  

NASA Technical Reports Server (NTRS)

The authors present broad and narrow bandwidth imaging of three southern elliptical galaxies which have flat-spectrum active radio cores (NGC 1052, IC 1459 and NGC 6958). All three contain dust and extended low excitation optical line emission, particularly extensive in the case of NGC 1052 which has a large H alpha + (NII) luminosity. Both NGC 1052 and IC 1459 have a spiral morphology in emission-line images. All three display independent strong evidence that a merger or infall event has recently occurred, i.e., extensive and infalling HI gas in NGC 1052, a counter-rotating core in IC 1459 and Malin-Carter shells in NGC 6958. This infall event is the most likely origin for the emission-line gas and dust, and the authors are currently investigating possible excitation mechanisms (Sparks et al. 1990).

Forbes, D. A.; Sparks, W. B.; Macchetto, F. D.

1990-01-01

405

Exchange and Redistribution Dynamics of the Cytoskeleton of the Active Zone Molecule Bassoon  

PubMed Central

Presynaptic sites typically appear as varicosities (boutons) distributed along axons. Ultrastructurally, presynaptic boutons lack obvious physical barriers that separate them from the axon proper. Yet activity-related and constitutive dynamics continuously promote the “reshuffling” of presynaptic components and even their dispersal into flanking axonal segments. How presynaptic sites manage to maintain their organization and individual characteristics over long durations is thus unclear. Conceivably, presynaptic tenacity might depend on the active zone (AZ), an electron-dense specialization of the presynaptic membrane, and particularly, on the cytoskeletal matrix associated with the AZ (CAZ) that could act as a relatively stable “core scaffold” that conserves and dictates presynaptic organization. At present, however, little is known on the molecular dynamics of CAZ molecules and thus, the factual basis for this hypothesis remains unclear. To examine the stability of the CAZ, we studied the molecular dynamics of the major CAZ molecule Bassoon in cultured hippocampal neurons. Fluorescence recovery after photobleaching (FRAP) and Photoactivation (FRAPA) experiments revealed that exchange rates of GFP and PAGFP-tagged Bassoon at individual presynaptic sites are very low (? > 8hr). Exchange rates varied between boutons, and were only slightly accelerated by stimulation. Interestingly, photoactivation experiments revealed that Bassoon lost from one synapse was occasionally assimilated into neighboring presynaptic sites. Our findings thus indicate that Bassoon is engaged in relatively stable associations within the CAZ and thus support the notion that the CAZ or some of its components might constitute a relatively stable presynaptic core scaffold. PMID:19144835

Tsuriel, Shlomo; Fisher, Arava; Wittenmayer, Nina; Dresbach, Thomas; Garner, Craig C.; Ziv, Noam E.

2009-01-01

406

Activation of microglia depends on Na+/H+ exchange-mediated H+ homeostasis  

PubMed Central

H+ extrusion is important for sustained NADPH oxidase activation following “respiratory” burst in macrophage/microglia activation. In this study, we investigated the role of Na+/H+ exchanger isoform 1 (NHE-1) in activation of microglia following lipopolysaccharide (LPS) or oxygen and glucose deprivation (OGD/REOX) exposure. NHE-1 functioned in maintaining basal pHi of immortalized M4T.4 microglia or mouse primary microglia. Pharmacological inhibition of NHE-1 activity with the potent inhibitor cariporide (HOE 642) abolished pHi regulation in microglia under basal conditions. Activation of microglia either by LPS, phorbol myristate acetate (PMA), or OGD/REOX accelerated pHi regulation and caused pHi elevation, which was accompanied with an increase in [Na+]i and [Ca2+]i as well as production of superoxide anion and cytokines. Interestingly, inhibition of NHE-1 not only abolished pHi regulation but also reduced production of superoxide anion as well as expression of cytokines and inducible nitric oxide synthase. Taken together, these results reveal that there was a concurrent activation of NHE-1 in microglia in response to proinflammatory stimuli. The study suggests that NHE-1 functions to maintain microglial pHi homeostasis allowing for sustained NADPH oxidase function and “respiratory” burst. PMID:21068326

Liu, Yan; Kintner, Douglas B.; Chanana, Vishal; Algharabli, Jehad; Chen, Xinzhi; Gao, Yanqin; Chen, Jun; Ferrazzano, Peter; Olson, Julie K.; Sun, Dandan

2010-01-01

407

PARP1 orchestrates variant histone exchange in signal-mediated transcriptional activation  

PubMed Central

Transcriptional activation is accompanied by multiple molecular events that remodel the local chromatin environment in promoter regions. These molecular events are often orchestrated in response to the activation of signalling pathways, as exemplified by the response of immediate early genes such as FOS to ERK MAP kinase signalling. Here, we demonstrate that inducible NFI recruitment permits PARP1 binding to the FOS promoter by a mutually reinforcing loop. PARP1 and its poly(ADP-ribosyl)ation activity are required for maintaining FOS activation kinetics. We also show that the histone variant H2A.Z associates with the FOS promoter and acts in a transcription-suppressive manner. However, in response to ERK pathway signalling, H2A.Z is replaced by H2A; PARP1 activity is required to promote this exchange. Thus, our work has revealed an additional facet of PARP1 function in promoting dynamic remodelling of promoter-associated nucleosomes to allow transcriptional activation in response to cellular signalling. PMID:24145797

O'Donnell, Amanda; Yang, Shen-Hsi; Sharrocks, Andrew D

2013-01-01

408

Gas exchange and heart rate in the harbour porpoise, Phocoena phocoena  

Microsoft Academic Search

The respiratory physiology, heart rates and metabolic rates of two captive juvenile male harbour porpoises (both 28?kg) were\\u000a measured using a rapid-response respiratory gas analysis system in the laboratory. Breath-hold durations in the laboratory\\u000a (12?±?0.3?s, mean?±?SEM) were shorter than field observations, although a few breath-holds of over 40?s were recorded. The\\u000a mean percentage time spent submerged was 89?±?0.4%. Relative to

J. Z. Reed; C. Chambers; C. J. Hunter; C. Lockyer; R. Kastelein; M. A. Fedak; R. G. Boutilier

2000-01-01

409

Land use change and the impact on greenhouse gas exchange in north Australian savanna soils  

NASA Astrophysics Data System (ADS)

Savanna ecosystems are subject to accelerating land use change as human demand for food and forest products increases. Land use change has been shown to both increase and decrease greenhouse gas fluxes from savannas and considerable uncertainty exists about the non-CO2 fluxes from the soil. We measured methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2) over a complete wet-dry seasonal cycle at three replicated sites of each of three land uses: savanna, young pasture and old pasture (converted from savanna 5-7 and 25-30 yr ago, respectively) in the Douglas Daly region of northern Australia. The effect of break of season rains at the end of the dry season was investigated with two irrigation experiments. Land use change from savanna to pasture increased net greenhouse gas fluxes from the soil. Pasture sites were a weaker sink for CH4 than savanna sites and, under wet conditions, old pastures turned from being sinks to a significant source of CH4. Nitrous oxide emissions were generally very low, in the range of 0 to 5 ?g N2O-N m-2 h-1, and under dry conditions soil uptake of N2O was apparent. Break of season rains produced a small, short lived pulse of N2O up to 20 ?g N2O-N m-2 h-1, most evident in pasture soil. Annual cumulative soil CO2 fluxes increased after clearing, with savanna (14.6 t CO2-C ha-1 yr-1) having the lowest fluxes compared to old pasture (18.5 t CO2-C ha-1 yr-1) and young pasture (20.0 t CO2-C ha-1 yr-1). Clearing savanna increased soil-based greenhouse gas emissions from 53 to ~70 t CO2-equivalents, a 30% increase dominated by an increase in soil CO2 emissions and shift from soil CH4 sink to source. Seasonal variation was clearly driven by soil water content, supporting the emerging view that soil water content is a more important driver of soil gas fluxes than soil temperature in tropical ecosystems where temperature varies little among seasons.

Grover, S. P. P.; Livesley, S. J.; Hutley, L. B.; Jamali, H.; Fest, B.; Beringer, J.; Butterbach-Bahl, K.; Arndt, S. K.

2011-09-01

410

Land use change and the impact on greenhouse gas exchange in north Australian savanna soils  

NASA Astrophysics Data System (ADS)

Savanna ecosystems are subjected to accelerating land use change as human demand for food and forest products increases. Land use change has been shown to both increase and decrease greenhouse gas fluxes from savannas and considerable uncertainty exists about the non-CO2 fluxes from the soil. We measured methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2) over a complete wet-dry seasonal cycle at three replicate sites of each of three land uses: savanna, young pasture and old pasture (converted from savanna 5-7 and 25-30 yr ago, respectively) in the Douglas Daly region of Northern Australia. The effect of break of season rains at the end of the dry season was investigated with two irrigation experiments. Land use change from savanna to pasture increased net greenhouse gas fluxes from the soil. Pasture sites were a weaker sink for CH4 than savanna sites and, under wet conditions, old pastures turned from being sinks to a significant source of CH4. Nitrous oxide emissions were generally very low, in the range of 0 to 5 ?g N2O-N m-2 h-1, and under dry conditions soil uptake of N2O was apparent. Break of season rains produced a small, short lived pulse of N2O up to 20 ?g N2O-N m-2 h-1, most evident in pasture soil. Annual cumulative soil CO2 fluxes increased after clearing, with savanna (14.6 t CO2-C ha-1 yr-1) having the lowest fluxes compared to old pasture (18.5 t CO2-C ha-1 yr-1) and young pasture (20.0 t CO2-C ha-1 yr-1). Clearing savanna increased soil-based greenhouse gas emissions from 53 to ∼ 70 t CO2-equivalents, a 30% increase dominated by an increase in soil CO2 emissions and shift from soil CH4 sink to source. Seasonal variation was clearly driven by soil water content, supporting the emerging view that soil water content is a more important driver of soil gas fluxes than soil temperature in tropical ecosystems where temperature varies little among seasons.

Grover, S. P. P.; Livesley, S. J.; Hutley, L. B.; Jamali, H.; Fest, B.; Beringer, J.; Butterbach-Bahl, K.; Arndt, S. K.

2012-01-01

411

Anti-adiabatic limit of the exchange-correlation kernels of an inhomogeneous electron gas  

Microsoft Academic Search

We express the high-frequency (anti-adiabatic) limit of the\\u000aexchange-correlation kernels of an inhomogeneous electron gas in terms of the\\u000afollowing equilibrium properties: the ground-state density, the kinetic stress\\u000atensor, the pair-correlation function, and the ground-state\\u000aexchange-correlation potential. Of these quantities, the first three are\\u000aamenable to exact evaluation by Quantum Monte Carlo methods, while the last can\\u000abe obtained from

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

2010-01-01

412

Induction of CO 2 -gas exchange and electron transport: comparison of dynamic and steady-state responses in Fagus sylvatica leaves  

Microsoft Academic Search

Photosynthetic induction was followed in a juvenile understorey beech (Fagus sylvatica L.) in a shaded habitat which was temporarily exposed to direct sunlight passing through a gap in the canopy. Simultaneous in situ measurements of leaf gas exchange and chlorophyll fluorescence were carried out and a steady-state light response curve of photosynthesis was recorded. The measured dynamic carbon gain was

Michael Schulte; Christian Offer; Ute Hansen

2003-01-01

413

Drought-induced defoliation and long periods of near-zero gas exchange play a key role in accentuating metabolic decline of  

E-print Network

Drought-induced defoliation and long periods of near-zero gas exchange play a key role, Pinus sylvestris, sap flow, stomatal conductance, tree mortality, water potential. Summary Drought in Scots pine (Pinus sylvestris). We hypothesize that defoliated individuals are more sensitive to drought

Mencuccini, Maurizio

414

What Is the Effect of Enteral Nutrition with a Raised Fat or Carbohydrate Content on Gas Exchange and Metabolism of Critically ill Patients with Acute Respiratory Failure?  

Microsoft Academic Search

SummaryObjective: Qualitative and quantitative description of gas exchange and metabolism of critically ill patients with complete enteral feeding on two formula diets with a different percentage of fat and carbohydrates. In particular, the study investigated whether carbon dioxide formation can be reduced and the burden on pulmonary ventilation can be lightened by reducing the proportion of carbohydrate. Design: Prospective, randomized

W. Höltermann; P. Lukasewitz; M. Krämer; M. van Wickern; L. Leuchter; H. Lennartz

1997-01-01