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1

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.

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

1997-01-01

2

Gas Exchange of Algae  

PubMed Central

The oxygen production of a photosynthetic gas exchanger containing Chlorella pyrenoidosa (1% packed cell volume) was measured when various concentrations of carbon dioxide were present within the culture unit. The internal carbon dioxide concentrations were obtained by manipulating the entrance gas concentration and the flow rate. Carbon dioxide percentages were monitored by means of electrodes placed directly in the nutrient medium. The concentration of carbon dioxide in the nutrient medium which produced maximal photosynthesis was in the range of 1.5 to 2.5% by volume. Results were unaffected by either the level of carbon dioxide in the entrance gas or the rate of gas flow. Entrance gases containing 2% carbon dioxide flowing at 320 ml/min, 3% carbon dioxide at 135 ml/min, and 4% carbon dioxide at 55 ml/min yielded optimal carbon dioxide concentrations in the particular unit studied. By using carbon dioxide electrodes implanted directly in the gas exchanger to optimize the carbon dioxide concentration throughout the culture medium, it should be possible to design more efficient large-scale units.

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

1967-01-01

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.

Instruments, Texas

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

Gas Exchange under Environmental Stress.  

National Technical Information Service (NTIS)

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

H. I. Modell M. P. Hlastala

1978-01-01

6

Airway heat and gas exchange  

Microsoft Academic Search

The usual approach to analysis of pulmonary gas exchange deals with the airways as a dead space that does not participate in gas exchange and acts simply as a conduit for the passage of air between the outside environment and the alveoli. In reality, however, inspired air undergoes some change during its trans-airway passage. The relatively cool and dry air

M P Hlastala

1992-01-01

7

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

8

[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

9

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.

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

2014-01-01

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

Leaf anatomy, gas exchange and photosynthetic enzyme activity in Flaveria kochiana  

Microsoft Academic Search

Abstract. Flaveria (Asteraceae) is one of the few genera known to contain both C3 and C4 species, in addition to numerous,biochemically-intermediate species. C3-C4 and C4-like intermediate photosynthesis,have arisen more,than once in different phylogenetic clades of Flaveria. Here, we characterise for the first time the photosynthetic pathway of the recently described species Flaveria kochiana B.L. Turner. We examined leaf anatomy, activity

Erika A. Sudderth; Athena D. McKown; Ferit Kocacinar; Rowan F. Sage

2007-01-01

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

Genetic and environmental influences on gas exchange.  

PubMed

Gas exchange is a critical process required for sufficient tissue perfusion. The environment, genetics, or a combination of the two can affect this process. Various strategies have evolved to overcome the specific gas exchange challenges in different environments and it is clear that some genes are pivotal to the development of gas exchanging organs (e.g. Bmp4). Lower partial pressure of oxygen (hypoxia), reducing the partial pressure gradient, makes gas exchange more challenging and therefore the height to which gas exchangers can travel above sea level is limited. However, some human populations (e.g. Tibetans) and other animals (e.g. Bar-headed goose) have adapted well to profoundly hypoxic conditions, suggesting genetic factors are important. Gas exchange can also be affected by air pollution, including particulate matter and ozone among others, and exposure can lead to cardiopulmonary responses depending on individual susceptibility or preexisting disease, both of which have genetic and environmental components. Diseases that affect gas exchange include, but are not limited to, pulmonary hypertension, chronic obstructive pulmonary disease (COPD), and bronchopulmonary dysplasia. Moreover, different species successfully exchange gases in their specific environment, for example animals that fly or burrow. Under these conditions, common genetic mechanisms, and their interaction with environment, help to maintain, or are detrimental to, gas exchange. PMID:23720259

Howden, Reuben; Kleeberger, Steven R

2012-10-01

14

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

15

A ROLE FOR ALTIMETER RADARS IN GAS EXCHANGE STUDIES  

Microsoft Academic Search

Accurate estimates of air-sea transfer rates of radiatively active gases are needed for studies of regional and global gas cycling and for climate change studies. However, estimates using traditional wind speed - gas transfer velocity parameterizations vary by a factor of 2- 3, contributing significantly to error budgets in global modeling of gas exchange and the carbon cycle. A decade

Nelson M. Frew; David M. Glover; Scott J. McCue

16

Respiratory Gas Exchange by the Avian Embryo.  

National Technical Information Service (NTIS)

The mechanism of gas exchange by an avian embryo is discussed in terms of the embryo's changing metabolic rate, a constant egg shell gas permeability and the changing gas tensions inside the shell. Since gas transport across the shell is by diffusion, equ...

O. D. Wangensteen H. Rahn

1970-01-01

17

Anesthesia and gas exchange in tracheal surgery.  

PubMed

Tracheobronchial surgery constitutes a challenge to the anesthetist because it involves the anatomic structures dedicated to bulk gas transport. Common approaches to airway management and gas exchange for extrathoracic and intrathoracic airway surgery are reviewed, with due regard to less common methods thought crucial for specific procedures. Tracheal surgery, beyond sharing the airways, requires sharing with the surgeon ideas on preoperative assessment, on the impact on gas exchange of induction across compromised airways, and of emergence from anesthesia with airways altered by surgical repair. Mutual understanding is essential to prevent, rapidly identify, and correct imminent loss of airway viability. PMID:24295656

Wiedemann, Klaus; Männle, Clemens

2014-02-01

18

Gas exchange measurements in natural systems  

SciTech Connect

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

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

1983-01-01

19

Gas exchange during exercise in hypoxic ducks.  

PubMed

We quantitatively assessed pulmonary gas exchange in Pekin ducks (Anas platyrhynchos) during running exercise (1.44 km X h-1 at 3 degrees incline) while the ducks spontaneously breathed either air (FIO2 = 0.21) or a hypoxic gas mixture (FIO2 = 0.12). During exercise, oxygen consumption increased 3 times above the resting value in normoxia and 3.6 times above rest in hypoxia. The convection requirement rose 34% and 20% in running normoxic and hypoxic ducks, respectively. The O2 extraction coefficient was the same in resting normoxic and hypoxic ducks (0.19 vs 0.18) and decreased by the same amount under exercise conditions (0.14 vs 0.15). Arterial PO2 was maintained during exercise in normoxia but increased slightly during exercise in hypoxia. Cardiac output increased by 73% and 111% during exercise in normoxic and hypoxic ducks, respectively. Calculations indicate that both the O2-diffusing capacity and the total conductance for O2 of the gas exchange system increased markedly during exercise in normoxia and hypoxia. We conclude that at this level of exercise, there was no apparent limitation to gas exchange in either the normoxic or hypoxic Pekin duck. PMID:3975498

Kiley, J P; Faraci, F M; Fedde, M R

1985-01-01

20

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

PubMed Central

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

Maina, JN

2002-01-01

21

Nitrogen gas exchange in the human knee  

SciTech Connect

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

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

1986-10-01

22

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

23

High temperature heat exchanger studies for applications to gas turbines  

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

24

Kinetics of ¹³CO exchange with ¹²CO in (HMâ(¹²CO)ââ)⁻ and (DMâ(¹²CO)ââ)⁻ (M = Ru or Os): relationship between exchange pathway and catalytic activity in the catalysis of the water gas shift reaction  

Microsoft Academic Search

The roles of the anions (HRuâ(CO)ââ)⁻ and (HOsâ(CO)ââ)⁻ in the catalysis of the water gas shift reaction are investigated. The kinetics of ¹³CO exchange with ¹²CO provides confirmation of the greater activity of the ruthenium based anion.

M. W. Payne; D. L. Leussing; S. G. Shore

1987-01-01

25

Gas Exchange with Mass Cultures of Algae  

PubMed Central

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

Hannan, P. J.; Patouillet, Constance

1963-01-01

26

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

27

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

28

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

NASA Astrophysics Data System (ADS)

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

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

2003-12-01

29

Antioxidant defense and physiological gas-exchange responses in ozone-exposed Pinus taeda L  

Microsoft Academic Search

Controlled-field experiments were utilized to evaluate the exposure-response relationships of the chloroplast ascorbate\\/glutathione hydrogen-peroxide detoxification system and physiological gas-exchange responses in ozone-exposed loblolly pine. Physiological gas-exchange processes included photosynthesis, conductance, transpiration, and intercellular COâ concentration (C{sub i}). Biochemical processes include both enzymatic activities and substrate concentrations. Total concentrations of glutathione and ascorbate were measured in both oxidized and reduced forms.

Fendick

1991-01-01

30

Surface gas-exchange processes of snow algae  

Microsoft Academic Search

The red-colored chlorophyte Chlamydomonas nivalis is commonly found in summer snowfields. We used a modified Li-Cor gas-exchange system to investigate surface gas-exchange characteristics of snow colonized by this alga, finding rates of CO2 uptake up to 0.3 mumol m2·s1 in dense algal blooms. Experiments varying the irradiance resulted in light curves that resembled those of the leaves of higher plants.

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

2003-01-01

31

High temperature heat exchanger studies for applications to gas turbines  

Microsoft Academic Search

Growing demand for environmentally friendly aero gas-turbine engines with lower emissions and improved specific fuel consumption\\u000a can be met by incorporating heat exchangers into gas turbines. Relevant researches in such areas as the design of a heat exchanger\\u000a matrix, materials selection, manufacturing technology, and optimization by a variety of researchers have been reviewed in\\u000a this paper. Based on results reported

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

2009-01-01

32

FASTGAS: Fast Gas Sampling for palladium exchange tests  

SciTech Connect

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

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

1991-06-01

33

Model analysis of intra-acinar gas exchange.  

PubMed

A previously described multibranch-point model, incorporating branching asymmetry within an acinus, has been extended to include gas exchange at the alveolar surface. Using a transport equation for simultaneous convection and diffusion within the gas phase and independent perfusion of all nodes, we obtained steady-state solutions for the temporal and spatial distributions of O2 and CO2 tensions within an acinus during a respiratory cycle. Results for conditions corresponding to both rest and moderate exercise indicated a significant inhomogeneity of gas concentrations within a single acinus. The coefficient of variation of PACO2 at end-inspiration during exercise reached 11.3%. Despite this non-uniformity the computation of a negligible PAO2 - PAO2 difference indicated no impairment in gas exchange. The simulations are consistent with the hypothesis that in the normal lung the whole acinus acts functionally as a gas exchanging unit and ventilation-perfusion inequality has an interacinar basis. PMID:3936144

Paiva, M; Engel, L A

1985-11-01

34

Modeling soluble gas exchange in the airways and alveoli.  

PubMed

A mathematical model of heat, water and soluble gas exchange in the airways and alveoli was used to predict the location of soluble gas exchange in the lung. A previously published model of heat, water and soluble gas exchange in the airways was improved by incorporating anatomical data on the airway wall to better describe the bronchial circulation and expanding the model to include a time varying description of soluble gas concentration in the alveoli. Next, the model was validated using two experimental data sets from the literature: (1) ethanol expirograms and (2) the uptake of seven soluble gases. Then, the model simulated the excretion of ten soluble gases whose blood:air partition coefficient (lambda(b:a)), a measure of blood solubility, ranged over 5 orders of magnitude. We found that gases with lambda(b:a) < 10 exchange almost solely in the alveoli and gases with lambda(b:a) > 100 exchange almost exclusively in the airways. Gases with lambda(b:a) between 10 and 100 have significant interaction with the airways and alveoli. These results suggest that the airways play a larger role in pulmonary gas exchange than previously assumed and may require a reevaluation of pulmonary tests that involve exhaled samples of gases with lambda(b:a) > 10. PMID:14758930

Anderson, Joseph C; Babb, Albert L; Hlastala, Michael P

2003-12-01

35

Neural regulation of discontinuous gas exchange in Periplaneta americana.  

PubMed

Patterns of gas exchange among terrestrial arthropods are highly variable from continuous to discontinuous with discretely partitioned phases. The underlying initiation and co-ordination of these patterns is relatively poorly understood. Here we present a novel method for the simultaneous measurement of central nervous system (CNS) activity of the metathoracic ganglion and VCO(2) in medium to large sized live terrestrial arthropods. Using Periplaneta americana at four oxygen levels (40%, 21%, 10% and 2% at 25 degrees C; n=6 per treatment), we present minimally invasive visualization of nervous output relative to typical resting discontinuous gas exchange (DGE) data for the first time. DGE was maintained when cockroaches were exposed to hyperoxia or moderate hypoxia, but was lost in severe hypoxia. CNS activity was manifested in three signal types: large CNS output coinciding with peak CO(2) production during a burst, moderate CNS output coinciding with CO(2) sawtoothing and fluttering, and minimal CNS activity during the closed phase of DGE in normoxia. Large and moderate CNS outputs were associated with observed abdominal pumping and congruent CO(2) peaks. At 10% oxygen, VCO(2) was significantly elevated during the inter-burst period in association with almost constant moderate CNS output between the periodic large CNS output. At 2% oxygen, DGE and large CNS output are lost to continuous CO(2) release and largely continuous moderate CNS output. As previously reported for this species, a central pattern generator for ventilation in the metathoracic ganglion is supported and we infer the presence of localized oxygen chemoreceptors based on clear CNS response to a change in oxygen tension. PMID:18178217

Woodman, James D; Cooper, Paul D; Haritos, Victoria S

2008-02-01

36

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

37

Respiratory gas exchange in patients with spontaneous pneumothorax  

Microsoft Academic Search

Pulmonary gas exchange was studied in 12 patients with spontaneous pneumothorax by measuring the partial pressure of oxygen and carbon dioxide in arterial blood and expired gas when breathing air and 100% oxygen. The arterial oxygen tension was below 80 mm. Hg in nine patients, and the alveolar-arterial difference in oxygen tension was abnormally large in 10, but the physiological

R. M. Norris; J. G. Jones; J. M. Bishop

1968-01-01

38

Efficient gas exchange between a boreal river and the atmosphere  

NASA Astrophysics Data System (ADS)

largest uncertainties in accurately resolving the role of rivers and streams in carbon cycling stem from difficulties in determining gas exchange between water and the atmosphere. So far, estimates for river-atmosphere gas exchange have lacked direct ecosystem-scale flux measurements not disturbing gas exchange across the air-water interface. We conducted the first direct riverine gas exchange measurements with eddy covariance in tandem with continuous surface water CO2 measurements in a large boreal river for 30 days. Our measured gas transfer velocity was, on average, 20.8 cm h-1, which is clearly higher than the model estimates based on river channel morphology and water velocity, whereas our floating chambers gave comparable values at 17.3 cm h-1. These results demonstrate that present estimates for riverine CO2 emissions are very likely too low. This result is also relevant to any other gases emitted, as their diffusive exchange rates are similarly proportional to gas transfer velocity.

Huotari, Jussi; Haapanala, Sami; Pumpanen, Jukka; Vesala, Timo; Ojala, Anne

2013-11-01

39

Pair Correlations and Exchange Phenomena in the Free Electron Gas  

Microsoft Academic Search

:   We present a rigorous derivation of the formulae of Dirac-Bloch and Wigner-Seitz for the quantum mechanical exchange energy\\u000a and the ‘exchange hole’ of the free electron gas. More precisely we establish that for arbitrary determinantal ground states\\u000a of the underlying finite system of N free electrons in a box, subject to periodic or zero boundary conditions, the formulae are

G. Friesecke

1997-01-01

40

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

41

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

42

The usefulness of submaximal exercise gas exchange to define pulmonary arterial hypertension  

PubMed Central

Background The six-minute walk test is widely utilized to characterize activity tolerance and response to therapy in pulmonary arterial hypertension (PAH), but provides little information about cardiopulmonary pathophysiology. The aim of the present study was to determine whether measures of pulmonary gas exchange during relatively light exercise can be used to differentiate between PAH patients and healthy individuals, and stratify disease severity. Methods 40 PAH patients and 25 matched controls participated in the study. Each individual completed a submaximal exercise test, consisting of 2-min rest, 3-min exercise and 1-min recovery. Ventilation, pulmonary gas exchange, arterial oxygen saturation (SaO2) and heart rate were measured throughout using a simplified gas analysis system. Results A number of gas exchange variables differentiated PAH patients and controls. End-tidal CO2 (PETCO2) and SaO2 were lower in PAH vs. controls (31±7vs.39±3mmHg and 89±5vs95±2%, respectively, p<0.05). By contrast, breathing efficiency (VE/VCO2 ratio) was higher in PAH vs. controls (42±10 vs. 33±5, p<0.05). Additionally, PETCO2 and VE/VCO2 discriminated between different severities of PAH. Conclusions Gas exchange variables obtained during light submaximal exercise differentiated PAH patients from healthy controls and also between different severities of PAH. Submaximal exercise gas exchange may be a useful endpoint measure in a PAH population.

Woods, Paul R; Frantz, Robert P; Taylor, Bryan J; Olson, Thomas P; Johnson, Bruce D

2011-01-01

43

In calm seas, precipitation drives air-sea gas exchange  

NASA Astrophysics Data System (ADS)

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

Schultz, Colin

2012-05-01

44

Relationship between wind speed and gas exchange over the ocean  

NASA Technical Reports Server (NTRS)

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

Wanninkhof, Rik

1992-01-01

45

Gas exchange under water : acclimation of terrestrial plants to submergence  

Microsoft Academic Search

Gas exchange between the plant and the environment is severely hampered when plants are submerged, leading to oxygen and energy deficits. A straightforward way to reduce these shortages of oxygen and carbohydrates would be prolonged photosynthesis under water, but this has received only little attention. This thesis, therefore, aims to investigate in depth the effects of acclimation to submergence on

Liesje Mommer

2005-01-01

46

The new advanced membrane gas exchanger.  

PubMed

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

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

2011-12-01

47

Respiratory gas exchange using a triaxial alveolar gas diagram  

Microsoft Academic Search

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

J F Fuster; T Pages; L Palacios

1993-01-01

48

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....

49

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

PubMed Central

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

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

1996-01-01

50

Using noble gases to constrain gas exchange and biological productivity  

NASA Astrophysics Data System (ADS)

The five noble gases (He, Ne, Ar, Kr, and Xe) are biologically and chemically inert, making them useful oceanographic tracers. Moreover, the noble gases have a wide range of solubilities and diffusivities, and thus respond differently to physical forcing. We present here a one year time-series of the five noble gases and the isotope 3He, measured in the upper 400 m of the Sargasso Sea with monthly resolution at the Bermuda Atlantic Time-series Site (BATS). Two profiles of the noble gases in the entire water column down to 4200 m are presented as well. We combine the upper ocean noble gas time-series data, nutrient, oxygen, and hydrographic data from BATS, and a one-dimensional vertical mixed layer model (a modified Price-Weller-Pinkel model) in order to quantify air-sea gas exchange processes. We use inverse modeling to quantify the magnitude of both diffusive gas exchange and air injection processes. The estimates obtained constrain the seasonal time-scale gas exchange rate to a precision of 6% and the bubble injection fluxes to 15%, valid for wind speeds up to 15 m/sec. The overall results suggest that the Wanninkhof quadratic formulation needs to be adjusted downward by approximately 20%. Additionally, 3He is used as a tracer of upwelling nutrients in order to constrain new production. Nutrients in the upper thermocline are well correlated with 3He, and thus 3He and nitrate measurements, combined with estimates of gas exchange, are used to quantify the input of new nutrients into the mixed layer. 3He measurement are also used in conjunction with tritium and oxygen data in order to calculate apparent oxygen utilization rates (AOUR) and thus to estimate export production.

Stanley, R.; Jenkins, W. J.; Lott, D. E.; Doney, S. C.

2007-12-01

51

Respiratory gas exchange using a triaxial alveolar gas diagram.  

PubMed Central

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

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

1993-01-01

52

Different characteristic of gas exchange between leaf and canopy scale  

NASA Astrophysics Data System (ADS)

The eddy covariance system is a powerful tool for research on carbon and water exchange between the atmosphere and the terrestrial ecosystem on canopy scale, meanwhile gas exchange measurement on leaf scale fosters understanding towards stomata behavior on controlling carbon and water. In this research, coupling relationship of water and carbon were compared on canopy and leaf scale. Canopy scale transpiration was derived from LE (latent heat flux) observed by eddy covariance and simulated soil evaporation by Penman equation validated through bare soil evaporation measurements using micro-lysimeter, canopy scale carbon assimilation was acquired through partitioning NEE (Net Ecosystem Exchange) into GPP (Gross Primary Productivity) and ER (Ecosystem Respiration). And leaf level gas exchange measurements were conducted in order to get transpiration and net carbon assimilation. Results showed that net carbon assimilation rate correlated well with transpiration in a linear manner on canopy scale, similar relationship also exists on leaf scale, however, regression coefficients differ. So carbon and water coupling relationship on canopy scale does not perform the same as that on leaf scale. What's more, when the Ball-Berry model was applied to estimate stomatal conductance for leaf scale and canopy conductance for canopy scale, the prime coefficients of m and b also showed different magnitude, that means Ball-Berry model calibrated on leaf scale was not necessarily applicable on canopy scale. While it is important to get the knowledge filling the gap between the two different scale, especially for upscaling gas exchange measurements from leaf scale to canopy scale. Transpiration and carbon assimilation relationship on leaf and canopy scale Ball-Berry model on leaf and canopy scale

Zhang, Q.; Lei, H.; Yang, D.

2012-12-01

53

Energy Exchange between Weakly Ionized Gas and a Metal Surface  

NASA Astrophysics Data System (ADS)

An attempt to describe heat exchange of low ionized gas with a metal surface has been made with the use of DSMC approach and kinetic Monte-Carlo method. Modeling is adhered to concrete experimental conditions at which thin tungsten wire is placed in plasma and dependence of a heat flow on wire surface temperature, gas pressure, gas nature and a degree of ionization is investigated. As a result of simulation temperature profiles near the wire surface for nitrogen and argon as well as dependence of relative heat flow in a gas/surface system on temperature and degree of ionization with consideration of energy accommodation have been obtained. In the case of nitrogen the chemical charge-transfer reaction is taken into account.

Polikarpov, A. Ph.; Polikarpov, Ph. J.; Borisov, S. F.

2008-12-01

54

Phlebotomy improves Pulmonary Gas Exchange in Chronic Mountain Polycythemia  

Microsoft Academic Search

There is not unanimous agreement in the literature regarding the effects of bleeding on pulmonary gas exchange in polycythemic patients. Spirometry, alveolar-arterial O2 and CO2 tension differences, PaO2 breathing 100% oxygen and carbon monoxide-diffusing capacity were measured before and after 1 week of chronic phlebotomy in 4 chronic mountain polycythemic patients. Studies were carried out at 3,700 m above sea

Julio C. Cruz; Carlos Diaz; Emilio Marticorena; Vilma Hilario

1979-01-01

55

Gas circulation and mass exchange between animal and plant units  

Microsoft Academic Search

To investigate the gas circulation and mass exchange relations among animal, plant and other biological units in the bioregenarative life support system, a closed cultivating system consisting of animal breeding chamber and plant growing chamber was established. This facility is 1.4 m high with the bottom area measuring 1.4 m X 0.8 m. In the animal chamber, silkworms in the

Hong Liu; Ling Tong; Enzhu Hu

2008-01-01

56

Modeling automotive gas-exchange solenoid valve actuators  

Microsoft Academic Search

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

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

2005-01-01

57

Reliability of gas exchange measurements from two different spiroergometry systems.  

PubMed

Reliability of two different spiroergometric systems was investigated by comparing gas exchange measurements from two consecutive identical bicycle ergometer ramp exercise tests which were conducted after an initial habituation trial. Twenty-three healthy subjects (age: 25+/-5 years; weight: 71+/-10 kg; peak oxygen uptake: 55+/-9 ml x min(-1) x kg(-1)) took part in the study. One apparatus was a portable mixing chamber system (MetaMax I, Cortex, Leipzig, Germany), the other one a stationary spiroergometric device measuring in the breath-by-breath mode (MetaLyzer 3B, Cortex). There were no relevant systematic changes in gas exchange measurements and heart rate from test 1 to test 2. Intra-class reliability coefficients were 0.984 (oxygen uptake = VO2), 0.977 (carbon dioxide output = VCO2), and 0.973 (minute ventilation = VE) for the MetaMax I, and 0.969 (VO2), 0.964 (VCO2), and 0.953 (VE) for the MetaLyzer 3B. Bland-Altman plots revealed a slightly smaller variability of MetaLyzer 3B measurements compared to those of MetaMax I. It is concluded that the spiroergometric devices MetaMax I and MetaLyzer 3B represent reliable instruments for exercise testing in sports medical routine and research. This is important to decide if longitudinal changes in gas exchange measurements represent clinically meaningful differences in performance or merely inconsistencies of the measuring tool. PMID:11719895

Meyer, T; Georg, T; Becker, C; Kindermann, W

2001-11-01

58

Hydraulic and thermal design of a gas microchannel heat exchanger  

NASA Astrophysics Data System (ADS)

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

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

2012-05-01

59

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

PubMed

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

Moerbitz, Christian; Hetz, Stefan K

2010-05-01

60

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

NASA Astrophysics Data System (ADS)

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

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

1990-03-01

61

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

62

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

63

Gas exchange and leaf metabolism of irrigated maize at different growth stages  

Microsoft Academic Search

Net ecosystem exchange (NEE), leaf gas exchange and biochemical traits were investigated in an irrigated maize crop grown under Mediterranean conditions. Sub-optimal irrigation water supply determined a drought stress during the early vegetative growth stage (45–49 days after swing) that decreased NEE. Drought, in the late vegetative stage, also caused a reduction of leaf gas exchange. In the latter period,

L. Vitale; C. Arena; P. Carillo; P. Di Tommasi; B. Mesolella; F. Nacca; A. Virzo De Santo; A. Fuggi; V. Magliulo

2011-01-01

64

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

65

Ambulatory gas exchange measurements--current status and future options.  

PubMed

This article summarizes the scientific literature on portable devices used for the measurement of gas exchange during exercise. Firstly, the results from validity investigations are reviewed in terms of accuracy, reliability, and influence of additional weight during field testing. On the basis of these findings, at least two of the most often tested portable devices, MetaMax I/II and K2/K4 b (2), can be regarded as valid, with their results not differing substantially from (stationary) metabolic carts. The second part of the article provides an overview of ambulatory gas exchange applications which have been investigated so far. There is a number of descriptive (cross-sectional) studies that characterize the physiological profiles of different sports. In addition, some diagnostic tests of functional capacity have been validated, and a few investigations have assessed nutritional interventions and their effect on metabolism. Some indicate potential future directions including an evaluation of the efficacy of modifying metabolic pathways during exercise, e. g. by specifically designed training. Also, the extension of descriptive/cross-sectional investigations to typical training sessions will be worthwhile. PMID:15702452

Meyer, T; Davison, R C R; Kindermann, W

2005-02-01

66

Protonated serine octamer cluster: structure elucidation by gas-phase H/D exchange reactions.  

PubMed

The H/D exchange kinetics of the protonated serine octamer was investigated by both flow-tube and FT-ICR experiments. The exchange was observed to be bimodal in agreement with previous observations. Quantitative analysis of the experimental results led to site-specific H/D exchange rate constants on the basis of which the structures of both ion populations were deduced. We observe the two separate conformers exchanging 33 hydrogens each-in an independent manner and at different rates. This result was achieved through a probabilistic algorithm that groups together equivalent hydrogen atoms having equal rate constants. The slower exchanging population A is assigned an all-zwitterionic structure. Its faster exchanging counterpart B is assigned an all-neutral structure. Population A was found to be more stable toward collision-induced activation than population B. All of these findings are consistent with previous experimental results, thus comprising a self-consistent picture of the protonated serine octamer and its gas-phase properties. PMID:16838981

Mazurek, Ulf; Geller, Orit; Lifshitz, Chava; McFarland, Melinda A; Marshall, Alan G; Reuben, Bryan G

2005-03-17

67

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

68

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

69

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

Microsoft Academic Search

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

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

1976-01-01

70

Toward a universal relationship between wind speed and gas exchange: Gas transfer velocities measured with 3He/SF6 during the Southern Ocean Gas Exchange Experiment  

NASA Astrophysics Data System (ADS)

Two 3He/SF6 dual-gas tracer injections were conducted during the Southern Ocean Gas Exchange Experiment (SO GasEx) to determine gas transfer velocities. During the experiment, wind speeds of up to 16.4 m s-1 were encountered. A total of 360 3He and 598 SF6 samples were collected at 40 conductivity-temperature-depth (CTD) rosette casts and two pumped stations. The gas transfer velocity k was calculated from the decrease in the observed 3He/SF6 ratio using three different approaches. Discrete points of wind speed and corresponding k were obtained from the change in 3He/SF6 ratio over three time intervals. The results were also evaluated using an analytical model and a 1-D numerical model. The results from the three approaches agreed within the error of the estimates of about ±13%-15% for Patch 1 and ±4% for Patch 2. Moreover, 3He/SF6 dual-tracer results from SO GasEx are similar to those from other areas in both the coastal and open ocean and are in agreement with existing parameterizations between wind speed and gas exchange. This suggests that wind forcing is the major driver of gas exchange for slightly soluble gases in the ocean and that other known impacts are either intrinsically related to wind or have a small effect (<20% on average) on time scales of the order of days to weeks. The functionality of the wind speed dependence (quadratic or cubic) cannot be unequivocally determined from SO GasEx results.

Ho, David T.; Wanninkhof, Rik; Schlosser, Peter; Ullman, David S.; Hebert, David; Sullivan, Kevin F.

2011-04-01

71

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

72

The effect of high temperatures on tropical forest gas exchange.  

NASA Astrophysics Data System (ADS)

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

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

2006-12-01

73

An Activity Model to Demonstrate Countercurrent Exchange.  

ERIC Educational Resources Information Center

Discusses the scant coverage in high school textbooks of countercurrent exchange for the efficient movement of molecules across biological membranes. Argues that this is one of the most intriguing of the physiological adaptive mechanisms. (DDR)

Benner, D. B.

1998-01-01

74

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

75

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

NASA Astrophysics Data System (ADS)

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

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

2006-10-01

76

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

NASA Astrophysics Data System (ADS)

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

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

1992-07-01

77

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

78

Inner Heliospheric Gas and Dust from Solar Wind Charge Exchange  

NASA Astrophysics Data System (ADS)

The Low Energy Neutral Atom (LENA) imager, launched on the IMAGE spacecraft in March of 2000, detects neutral atoms with energies from 10 eV up to >1 keV. Because LENA has low sensitivity to light and looks directly at the Sun every spin during six months of the year, it has observed a neutral component of the solar wind (NSW) that results when solar wind ions charge exchange with interstellar neutrals, with dust and with the Earth's geocorona [Collier et al., JGR, 106, 24,893, 2001]. We examine long-term variations in the intensity of the counting rate from the solar direction (NSW). Results from year 2001, during which the instrument state remained constant, show a maximum in the count rate between June and July with a long, low count-rate period stretching from mid-November through early March. This annual modulation of solar wind energetic neutral atom flux at the Earth is interpreted as a pronounced variation of the neutral gas column density between the Sun and the Earth with season. This modulation is evidently dominated by interstellar neutral gas and the solar erosion of that gas in the galactic downstream region. It also contains a relatively constant contribution from inner solar system dust and relatively smaller variations produced by solar wind fluctuations and possibly structure in the dust population. The LENA observations place an upper limit on the column density of dust at 1 AU of less than 6x10-19 cm-1. Implications of the LENA data on the interpretation of observations of low frequency electromagnetic waves by Tsurutani et al. [GRL, 21, 633, 1994] will also be considered.

Collier, M. R.; Moore, T. E.; Ogilvie, K. W.; Simpson, D.; Fok, M.; Chornay, D.; Keller, J.; Fuselier, S.; Quinn, J.; Wurz, P.; Wuest, M.; Hsieh, J.; Tsurutani, B.

2002-05-01

79

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 ...

80

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

81

Restriction of prenatal gas exchange impairs memory consolidation in the chick  

Microsoft Academic Search

Our aim was to assess the effects of restricting gas exchange during incubation on postnatal memory formation and growth in the chick. Gas exchange across the eggshell was restricted by covering 50% of the eggshell with an impermeable membrane for 4 or 8 days, commencing at days 14 and 10, respectively, of a 21-day incubation. Memory formation was examined postnatally

Emily J Camm; Marie E Gibbs; Richard Harding

2001-01-01

82

Gas phase hydrogen\\/deuterium exchange of proteins in an ion trap mass spectrometer  

Microsoft Academic Search

Electrospray ionization ion trap mass spectrometry (ESI-ITMS) coupled with gas phase hydrogen\\/deuterium (H\\/D) exchange is demonstrated to be a useful tool to investigate the gas phase conformations of proteins when coupled with a mechanistic understanding of exchange. We have investigated the H\\/D exchange of multiple charge states of lysozyme, cytochrome c, ubiquitin, insulin, thioredoxin and melittin with deuterated methanol in

Sarah E. Evans; Nathan Lueck; Elaine M. Marzluff

2003-01-01

83

Seasonal Patterns of Acid Metabolism and Gas Exchange in Opuntia basilaris1  

PubMed Central

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 14CO2. 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 14CO2 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.

Szarek, Stan R.; Ting, Irwin P.

1974-01-01

84

Market Power, Innovative Activity and Exchange Rate Pass-Through  

Microsoft Academic Search

This paper considers an international oligopoly where firms simultaneously choose both the amount of output produced and the proportion of R&D investment to output. The model captures the links between the exchange rate, market power, innovative activity and price, which are important for the determination of the optimal degree of exchange rate pass-through. It is found that in the long

Sophocles N. Brissimis; Theodora S. Kosma

2005-01-01

85

Gas developments lead Canadian activity  

SciTech Connect

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

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

1998-05-01

86

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

Microsoft Academic Search

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

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

2006-01-01

87

Gas exchange in open-top field chambers—I. Measurement and analysis of atmospheric resistances to gas exchange  

NASA Astrophysics Data System (ADS)

Factors controlling rates of gas exchange between the atmosphere and plants growing in open-top field chambers, commonly used for studying crop responses to air quality, are measured and analysed. Restrictions on gas transfer by incursion through the open top, by air movement from the ventilation fan and by transfer through the leaf boundary layer are described by a resistance analogue. A method of measuring incursion resistance r i, using sulphur hexafluoride is described and applied to chambers of a standard design and of a design with a truncated conical top. There was a well-defined variation of r i with windspeed for the modified design and r i, decreased for a given windspeed as crop height increased. Leaf boundary layer resistance r b was measured in both chamber designs and was analysed as a function of incursion and fan ventilation rate. Values of r b in chambers may be lower than in crop canopies in the field, and possible consequences of this difference are discussed.

Unsworth, M. H.; Heagle, A. S.; Heck, W. W.

88

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...

89

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

SciTech Connect

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

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

1991-09-01

90

Test results from a helium gas-cooled porous metal heat exchanger  

NASA Astrophysics Data System (ADS)

A helium-cooled porous metal heat exchanger was built and tested, which successfully absorbed heat fluxes exceeding all previously tested gas-cooled designs. Helium-cooled plasma-facing components are being evaluated for fusion applications. Helium is a favorable coolant for fusion devices because it is not a plasma contaminant, it is not easily activated, and it is easily removed from the device in the event of a leak. The main drawback of gas coolants is their relatively poor thermal transport properties. This limitation can be removed through use of a highly efficient heat exchanger design. A low flow resistance porous metal heat exchanger design was developed, based on the requirements of the Faraday shield for the International Thermonuclear Experimental Reactor device. High heat flux tests were conducted on two representative test articles at the Plasma Materials Test Facility at Sandia National Laboratories. Absorbed heat fluxes as high as 40 MW/m2 were successfully removed during these tests without failure of the devices. Commercial applications for electronics cooling and other high heat flux applications are being identified.

North, Mark T.; Rosenfeld, John H.; Youchison, Dennis L.

1996-11-01

91

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

92

Molecular gas in active environments  

NASA Astrophysics Data System (ADS)

The question whether or not the initial mass function (IMF) is universal, i.e. the same in all kinds of environments, is subject to intense debate. A number of recent observations have been interpreted as evidence for a nonstandard IMF. Hydrodynamical simulations indicate that the kinetic temperature of the collapsing molecular gas is crucial for the shape of the resulting IMF. Unfortunately, the kinetic temperature of the molecular gas in external galaxies is often not well constrained. We demonstrate the diagnostic power of a selected set of para-formaldehyde lines as tracers of the kinetic temperature as well as the gas density in external galaxies using our non-LTE radiative transfer model. With this new observational tool, we have engaged in characterizing the properties of the dense molecular gas phase in a number of nearby starburst galaxies and near AGN. Our first results suggest the existence of a dense molecular gas phase in these active environments that is significantly warmer than the dust and much warmer than dense molecular gas found in the disk of our own Galaxy.

Mühle, S.; Henkel, C.; de Maio, T.; Seaquist, E. R.

2012-07-01

93

A system to simulate gas exchange in humans to control quality of metabolic measurements  

Microsoft Academic Search

We have developed a gas exchange simulation system (GESS) to assess the quality control in measurements of metabolic gas\\u000a exchange. The GESS simulates human breathing from rest to maximal exercise. It approximates breath-by-breath waveforms, ventilatory\\u000a output, gas concentrations, temperature and humidity during inspiration and expiration. A programmable motion control driving\\u000a two syringes allows the ventilation to be set at any

F. Prieur; T. Busso; J. Castells; R. Bonnefoy; H. Benoit; A. Geyssant; C. Denis

1998-01-01

94

Clinical assessment of gas exchange in mature horses.  

PubMed

There are limited methods of assessing pulmonary function in horses at rest. We developed clinical techniques to measure gas exchange efficiency in horses and evaluated 3 groups of horses that were 1) asymptomatic based on auscultation with rebreathing, transtracheal aspirate cytology, and thoracic radiographs (n = 6), 2) asymptomatic at rest but symptomatic with rebreathing (n = 11) and 3) symptomatic at rest (n = 9). Blood samples were obtained from the transverse facial artery and jugular vein. Maximal end-tidal CO2 tension (PETCO2) was measured by an infrared capnograph through a facemask. Alveolar O2 tension, dead space fraction (V(D)/V(T)), and physiological shunt fraction (Q(S)/Q(T)) were calculated using standard formulae. Arterial O2 tension in Group 1 horses (mean +/-s.d.103+/-3 mmHg) was significantly higher than in Group 2 or Group 3 horses. Q(S)/Q(T) in Group 1 horses (0.37+/-0.98%) was significantly lower than in Group 2 and Group 3 horses. Mean +/-s.d.V(D)/V(T) in Group 1 horses (-18.2+/-3.1) was significantly lower than Group 3 horses but not Group 2 horses. PMID:9758096

Davis, M S; Murray, M J; Donaldson, L L

1998-09-01

95

Gas exchange characteristics of Pinus edulis and Juniperus monosperma  

SciTech Connect

A shift in the relative dominance of Pinus edulis and Juniperus monosperma is associated with a complex elevational gradient in northern new Mexico. The ecophysiological parameters contributing to this dominance pattern were studied by determining the gas exchange characteristics of the two species in response to temperature, light and water stress under controlled conditions. P. edulis has a higher photosynthetic capacity than J. monosperma, and has a tendency to form ecotypes with individuals from mesic sites having higher rates of carbon gain than xeric site individuals. J. monosperma is more drought-tolerant than P. edulis. As soil moisture decreases, zero carbon gain in J. monosperma occurs at a lower predawn leaf water potential (-4.6 MPa) than in P. edulis (-2.2 MPa). There is no significant difference between species in the temperature of peak carbon gain. J. monosperma has a significantly wider temperature optimum than P. edulis with the additional range being at high temperatures. The observed lower elevational limit of P. edulis coincides with its physiological tolerance of water stress as estimated by seasonal leaf carbon gain. Environmental limitations to the distribution of J. monosperma were not found at higher elevations where P. edulis is dominant.

Barnes, F.J.

1987-07-01

96

Gas circulation and mass exchange between animal and plant units  

NASA Astrophysics Data System (ADS)

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

Liu, Hong; Tong, Ling; Hu, Enzhu

97

Gas-Substrate Heat Exchange During Cold-Gas Dynamic Spraying  

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

98

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

99

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

100

On mechanisms of rain-induced air-water gas exchange  

NASA Astrophysics Data System (ADS)

Previous studies have shown that rain significantly enhances the rate of air-water gas exchange. However, even though an empirical correlation between the rain rate or kinetic energy flux (KEF) delivered to the water surface by rain and the gas transfer velocity has been established, the physical mechanisms underlying the gas exchange enhancement remain unexamined. During a series of experiments, the processes behind rain-induced air-water gas exchange were examined at NASA's Rain-Sea Interaction Facility (RSIF). Gas transfer velocities for helium (He), nitrous oxide (N2O), and sulfur hexafluoride (SF6) were determined for 22 rain rates (13.6 to 115.2 mm h-1) and three drop sizes (2.3, 2.8, 4.2 mm). Bubbles generated by the raindrops were characterized using a video-microscope technique, and surface waves were characterized by a capacitance probe. Additionally, rain-generated turbulence was inferred from friction velocities u*w calculated from KEF. Together, these data suggest that rain-induced air-water gas exchange is mainly caused by turbulence-driven exchange processes, with bubbles contributing anywhere from 0 to 20%, depending on rain rate, drop size, and the solubility of the gas tracer. Furthermore, the data confirm that the previously selected variable KEF is the best correlate for rain-induced air-water gas exchange.

Ho, David T.; Asher, William E.; Bliven, Larry F.; Schlosser, Peter; Gordan, Elizabeth L.

2000-10-01

101

Development of gas–solid direct contact heat exchanger by use of axial flow cyclone  

Microsoft Academic Search

A heat exchanger between particulate or granular materials and gas is developed. It makes use of a swirling gas flow similar to the usual cyclone separators but the difference from them is that the swirl making gas is issued into the cyclone chamber with downward axial velocity component. After it turns the flow direction near the bottom of the chamber,

Akihiko Shimizu; Takehiko Yokomine; Tatsuro Nagafuchi

2004-01-01

102

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

103

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

NASA Technical Reports Server (NTRS)

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

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

2013-01-01

104

Irradiance stress responses of gas exchange and antioxidant enzyme contents in pariparoba [ Pothomorphe umbellata (L.) Miq.] plants  

Microsoft Academic Search

We evaluated the growth and development of the medicinal species Pothomorphe umbellata (L.) Miq. under different shade levels (full sun and 30, 50, and 70 % shade, marked as I100, I70, I50, and I30, respectively) and their effects on gas exchange and activities of antioxidant enzymes. Photosynthetically active radiation\\u000a varied from 1 254 µmol m?2 s?1 at I100 to 285

J. A. Marchese; R. S. Mattana; L. C. Ming; F. Broetto; P. F. Vendramini; R. M. Moraes

2008-01-01

105

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

106

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.

107

Linking Employee Development Activity, Social Exchange and Organizational Citizenship Behavior  

ERIC Educational Resources Information Center

The authors examined "perceived beneficiary" of employee development (self, organization) for relationships with employee development activity. Perceived organizational support served as a moderator. The authors conclude that employees may engage in development activities to partly benefit their organization to the extent that a positive exchange…

Pierce, Heather R.; Maurer, Todd J.

2009-01-01

108

STUDY OF BEHAVIOR IN THE HEAT EXCHANGER OF A MIXED GAS JOULE-THOMSON COOLER  

Microsoft Academic Search

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

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

109

Flow characteristics of gas–liquid two-phase flow in plate heat exchanger  

Microsoft Academic Search

In order to clarify the gas–liquid two-phase flow characteristics in a plate heat exchanger, gas–liquid two-phase flows in simulated heat exchangers with a single channel placed in a vertical plane were visualized by a neutron radiography method. Air–water adiabatic two-phase flows and chlorofluorocarbon R141b boiling two-phase flows were visualized, and two-dimensional void fraction distributions were measured from visualized images via

Hitoshi Asano; Nobuyuki Takenaka; Terushige Fujii

2004-01-01

110

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

Microsoft Academic Search

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

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

2006-01-01

111

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

PubMed

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

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

2013-10-15

112

Exploring exchange mechanisms with a cold-atom gas  

NASA Astrophysics Data System (ADS)

Fermionic atoms trapped in a double-well potential are an ideal setting to study fundamental exchange mechanisms. We use exact diagonalization and complementary analytic calculations to demonstrate that two trapped fermions deliver a minimal model of the direct-exchange mechanism. This is an ideal quantum simulator of the Heisenberg antiferromagnet, exposes the competition between covalent and ionic bonding, and can create, manipulate, and detect quantum entanglement. Three trapped atoms form a faithful simulator of the double-exchange mechanism that is the fundamental building block behind many Heisenberg ferromagnets.

Bugnion, P. O.; Conduit, G. J.

2013-07-01

113

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

114

Noninvasive detection of gas exchange rate by near infrared spectroscopy  

NASA Astrophysics Data System (ADS)

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

Xu, Guodong; Mao, Zongzhen; Wang, Bangde

2008-12-01

115

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

NASA Technical Reports Server (NTRS)

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

Jennings, Mallory; Quinn, Gregory; Strange, Jeremy

2012-01-01

116

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

PubMed

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

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

2009-01-01

117

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

PubMed

Over its life, an organism's survival and success are determined by the inventory of vital adaptations that its progenitors have creatively appropriated, devised and harnessed along the evolutionary pathway. Such conserved attributes provide the armamentarium necessary for withstanding the adverse effects of natural selection. Refinements of the designs of the respiratory organs have been critical for survival and phylogenetic advancement of animal life. Gas exchangers have changed in direct response to the respiratory needs of whole organisms in different environmental states and conditions. Nowhere else is the dictum that in biology 'there are no rules but only necessities' more manifest than in the evolutionary biology of the gas exchangers. The constructions have been continually fashioned and refined to meet specific needs. Solutions to common respiratory needs have been typified by profound structural convergence. Over the evolutionary continuum, as shifts in environmental situations occurred, infinitely many designs should theoretically have emerged. Moreover, without specific selective pressures and preference for certain designs, considering that there are only two naturally occurring respirable fluid media (air and water), air-lungs, water-lungs, air-gills and water-gills would have formed to similar extents. Factors such as body size, phylogenetic level of development, respiratory medium utilized and habitats occupied have permutatively prescribed the design of the gas exchangers. The construction of the modern gas exchangers has eventuated through painstaking cost-benefit analysis. Trade-offs and compromises have decreed only a limited number of structurally feasible and functionally competent outcomes. The morphological congruity (analogy) of the gas exchangers indicates that similar selective pressures have compelled the designs. Solutions to metabolic demands for molecular O2 have only differed in details. Passive physical diffusion, for example, is the ubiquitous method of transfer of O2 across biological tissues. Gills, evaginated gas exchangers, were the primordial respiratory organs that evolved for water breathing, whereas lungs (invaginated gas exchangers) developed for terrestrial (air) breathing. Transitional (= bimodal = amphibious) breathing has evolved in animals with specialized organs that extract O2 from both water and air. Lungs are tidally (= bidirectionally) ventilated, while gills are unidirectionally ventilated, a feature that allows the highly efficient counter-current disposition between blood and water. Since animals occupy inconstant environmental milieus and their metabolic states vary, gas exchangers are designed to operate optimally across a spectrum of conditions that range from resting to exercise and even under hypoxia. Inbuilt structural and functional flexibility provides the requisite safety factors that allow adjustments to modest pressures. The fundamental structural features that determine the respiratory function of a gas exchanger are respiratory surface area, thickness of the blood-water/gas (tissue) barrier and volume of the pulmonary capillary blood. The diffusing capacity of a gas exchanger correlates directly with the surface area and inversely with the thickness of the blood-water/gas (tissue) barrier. An extensive surface area is generated in gills by extensive stratification of the gas exchanger and in lungs by profuse internal subdivision. Compartmentalization yields small terminal gas exchange compartments that compel greater commitment of energy to ventilate. The surfactant, a phospholipid lining, reduces the forces of surface tension at the air-water interface. This attenuates the propensity of physical collapse of the minute gas exchange units and minimizes the cost of ventilation. The surfactant characterizes all the gas exchangers derived from the piscine air bladder. In the lower air-breathing vertebrates, such as the lungfishes (Dipnoi), amphibians and certain reptiles, the pneumocytes are not differentiated into type I and II cells, as is the case in t

Maina, J N

2002-01-01

118

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

NASA Technical Reports Server (NTRS)

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

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

1983-01-01

119

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

NASA Astrophysics Data System (ADS)

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

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

1983-09-01

120

Determination of Photosynthesis and Transpiration Using a Flow Through Gas Exchange Chamber.  

National Technical Information Service (NTIS)

Carbon assimilation chambers for measuring gas flux between the atmosphere and a leaf or plant have been used in various forms for many years. Gas exchange systems may be classified into three types: closed, semi-closed, and open. This discussion is limit...

G. E. Kleinkopf A. J. Steen T. L. Hartsock A. Wallace

1971-01-01

121

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

Microsoft Academic Search

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,

John E. Greenleaf; Arup K. SenGupta

2009-01-01

122

Gas-Phase Hydrogen Isotope Exchange in HF + D sub 2 O.  

National Technical Information Service (NTIS)

The gas-phase isotope exchange reaction of HF and D sub 2 O has been studied by flow tube and matrix isolation techniques over a range of concentrations and reaction times. The matrix isolation/FTIR gas sampling and analysis technique proved capable of de...

L. D. Trowbridge

1982-01-01

123

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

124

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

125

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

PubMed

The magnitude and timing of oxygenation responses in highly active leg muscle, less active arm muscle, and cerebral tissue, have not been studied with simultaneous alveolar gas exchange measurement during incremental treadmill exercise. Nor is it known, if blood O(2) carrying capacity affects the tissue-specific oxygenation responses. Thus, we investigated alveolar gas exchange and tissue (m. vastus lateralis, m. biceps brachii, cerebral cortex) oxygenation during incremental treadmill exercise until volitional fatigue, and their associations with blood O(2) carrying capacity in 22 healthy men. Alveolar gas exchange was measured, and near-infrared spectroscopy (NIRS) was used to monitor relative concentration changes in oxy- (?[O(2)Hb]), deoxy- (?[HHb]) and total hemoglobin (?[tHb]), and tissue saturation index (TSI). NIRS inflection points (NIP), reflecting changes in tissue-specific oxygenation, were determined and their coincidence with ventilatory thresholds [anaerobic threshold (AT), respiratory compensation point (RC); V-slope method] was examined. Blood O(2) carrying capacity [total hemoglobin mass (tHb-mass)] was determined with the CO-rebreathing method. In all tissues, NIPs coincided with AT, whereas RC was followed by NIPs. High tHb-mass associated with leg muscle deoxygenation at peak exercise (e.g., ?[HHb] from baseline walking to peak exercise vs. tHb-mass: r = 0.64, p < 0.01), but not with arm muscle- or cerebral deoxygenation. In conclusion, regional tissue oxygenation was characterized by inflection points, and tissue oxygenation in relation to alveolar gas exchange during incremental treadmill exercise resembled previous findings made during incremental cycling. It was also found out, that O(2) delivery to less active m. biceps brachii may be limited by an accelerated increase in ventilation at high running intensities. In addition, high capacity for blood O(2) carrying was associated with a high level of m. vastus lateralis deoxygenation at peak exercise. PMID:22934021

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

2012-01-01

126

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.

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

2012-01-01

127

Gas sensing in microplates with optodes: influence of oxygen exchange between sample, air, and plate material.  

PubMed

Microplates with integrated optical oxygen sensors are a new tool to study metabolic rates and enzyme activities. Precise measurements are possible only if oxygen exchange between the sample and the environment is known. In this study we quantify gas exchange in plastic microplates. Dissolved oxygen was detected using either an oxygen-sensitive film fixed at the bottom of each well or a needle-type sensor. The diffusion of oxygen into wells sealed with different foils, paraffin oil, and paraffin wax, respectively, was quantified. Although foil covers showed the lowest oxygen permeability, they include an inevitable gas phase between sample and sealing and are difficult to manage. The use of oil was found to be critical due to the extensive shaking caused by movement of the plates during measurements in microplate readers. Thus, paraffin wax was the choice material because it avoids convection of the sample and is easy to handle. Furthermore, without shaking, significant gradients in pO2 levels within a single well of a polystyrene microplate covered with paraffin oil were detected with the needle-type sensor. Higher pO2 levels were obtained near the surface of the sample as well as near the wall of the well. A significant diffusion of oxygen through the plastic plate material was found using plates based on polystyrene. Thus, the location of a sensor element within the well has an effect on the measured pO2 level. Using a sensor film fixed on the bottom of a well or using a dissolved pO2-sensitive indicator results in pO2 offset and in apparently lower respiration rates or enzyme activities. Oxygen diffusion through a polystyrene microplate was simulated for measurements without convection--that is, for samples without oxygen diffusion through the cover and for unshaken measurements using permeable sealings. This mathematical model allows for calculation of the correct kinetic parameters. PMID:15772950

Arain, Sarina; Weiss, Svenja; Heinzle, Elmar; John, Gernot T; Krause, Christian; Klimant, Ingo

2005-05-01

128

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

NASA Astrophysics Data System (ADS)

Rain has been shown to significantly enhance the rate of air-water gas exchange in fresh water environments, and the mechanism behind this enhancement has been studied in laboratory experiments. However, in the ocean, the effects of rain are complicated by the potential of causing density stratification at the water surface. Since it is difficult to perform controlled rain-induced gas exchange experiments in the open ocean, we conducted a SF6 evasion experiment in an artificial ocean at Biosphere 2. Our measurements show a rapid depletion of SF6 in the surface layer due to rain enhancement of air-sea gas exchange. However, because vertical mixing is mitigated by stratification, the overall gas exchange rate is lower than that predicted from freshwater laboratory experiments. Physical measurements of various properties of the ocean during the rain events further elucidate the mechanisms behind the observed response. The findings suggest that short and intense rain events may accelerate gas exchange in oceanic environments.

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

2003-04-01

129

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

NASA Astrophysics Data System (ADS)

Rain has been shown to significantly enhance the rate of air-water gas exchange in fresh water environments, and the mechanism behind this enhancement has been studied in laboratory experiments. In the ocean, the effects of rain are complicated by the potential influence of density stratification at the water surface. Since it is difficult to perform controlled rain-induced gas exchange experiments in the open ocean, an SF6 evasion experiment was conducted in the artificial ocean at Biosphere 2. The measurements show a rapid depletion of SF6 in the surface layer due to rain enhancement of air-sea gas exchange, and the gas transfer velocity was similar to that predicted from the relationship established from freshwater laboratory experiments. However, because vertical mixing is reduced by stratification, the overall gas flux is lower than that found during freshwater experiments. Physical measurements of various properties of the ocean during the rain events further elucidate the mechanisms behind the observed response. The findings suggest that short, intense rain events accelerate gas exchange in oceanic environments.

Ho, David T.; Zappa, Christopher J.; McGillis, Wade R.; Bliven, Larry F.; Ward, Brian; Dacey, John W. H.; Schlosser, Peter; Hendricks, Melissa B.

2004-08-01

130

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

131

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

132

Natural course of treated pulmonary embolism. Evaluation by perfusion lung scintigraphy, gas exchange, and chest roentgenogram.  

PubMed

Perfusion lung scintigrams, pulmonary gas exchange data, and chest roentgenograms were obtained in 33 patients during acute embolism and over the following six months in order to assess their clinical usefulness in monitoring the effect of therapy. To this purpose, the measurement of pulmonary gas exchange and the presence of chest x-ray findings were compared with perfusion lung scintigraphic abnormalities both at diagnosis and after 7, 30, and 180 days during treatment. More than 50 percent of the pulmonary arterial tree was obstructed at diagnosis, and a large part of perfusion recovery was complete within the first month. All of the gas exchange parameters were abnormal at diagnosis, and the rate of their improvement was related to that of perfusion recovery. Interestingly, PaO2st (ie, PaO2 corrected for hyperventilation) and VE tended to return to normal during the first month as a consequence of the progressive recovery of perfusion, whereas oxygen and carbon dioxide gradients and physiologic dead space showed the persistence of some abnormalities six months after diagnosis. Significant correlations were observed between the number of ULSs evaluated on the perfusion lung scintigram (and considered an index of the severity of pulmonary embolization) and all of the gas exchange parameters at diagnosis (correlation coefficients averaged from 0.41 to 0.73) and after 7 and 30 days. The enlargement of the right descending pulmonary artery and particularly the "sausage" sign and the Westermark sign were significantly associated with a higher degree of gas exchange impairment and with a more severe embolization. In conclusion, this study demonstrates that perfusion lung scintigraphy has a primary role in monitoring the recovery of patients with pulmonary embolism under treatment. Moreover, the chest roentgenogram may help in this purpose. A second major result is that the simple measurement of some gas exchange parameters may allow the assessment of functional recovery of these patients, thus giving additional information about the effect of therapy. PMID:2106409

Prediletto, R; Paoletti, P; Fornai, E; Perissinotto, A; Petruzzelli, S; Formichi, B; Ruschi, S; Palla, A; Giannella-Neto, A; Giuntini, C

1990-03-01

133

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

PubMed Central

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

Harris, Fred S.; Martin, Craig E.

1991-01-01

134

Evaluation of Local Gas Exchange in a Pulsating Respiratory Support Catheter  

PubMed Central

An intravenous respiratory support catheter, the next generation of artificial lungs, is being developed in our laboratory to potentially support acute respiratory failure or patients with chronic obstructive pulmonary disease with acute exacerbations. A rapidly pulsating 25 ml balloon inside a bundle of hollow fiber membranes facilitates supplemental oxygenation and CO2 removal. In this study, we hypothesized that nonuniform gas exchange in different regions of this fiber bundle was present because of asymmetric balloon collapse and the interaction of longitudinal flow. Four quarter regions and two rings around the central balloon were selectively perfused to evaluate local gas exchange in a 3.18 cm test section using helium as the sweep gas. Quarter region CO2 exchange rates at 400 beats per minute were 156.8 ± 0.8, 162.5 ± 1.8, 157.2 ± 0.2, and 196.6 ± 0.8 ml/min/m² (top, front, bottom, and back, respectively). The back section, adjacent to convex balloon collapse, had 17–20% higher exchange than the other sections caused by higher relative velocities past its stationary fibers. Inner and outer ring maximum pulsation gas exchange rates were 174.4 ± 1.8 and 174.6 ± 0.9 ml/min/m², respectively, showing that fluid flow was equally distributed throughout the fiber bundle.

Eash, Heide J.; Frankowski, Brian J.; Hattler, Brack G.; Federspiel, William J.

2007-01-01

135

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

136

Gas developments lead Canadian activity  

Microsoft Academic Search

Canada has an immense supply of natural gas. The Western Sedimentary Basin of Canada is North America`s largest gas-bearing geologic province and extends from British Columbia on Canada`s west coast, eastward through the provinces of Alberta, Saskatchewan and Manitoba and includes portions of the Northwest Territories and the Yukon. The basin supplies most of Canada`s natural gas with nearly 85%

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

1998-01-01

137

Free-Surface Turbulence and Air-Water Gas Exchange.  

National Technical Information Service (NTIS)

This thesis investigates the physical mechanisms of air-water gas transfer through direct measurements of turbulence at the air-water interface. To enable this study, a new approach to the particle image velocimetry (PIV) technique is developed in order t...

S. P. McKenna

2000-01-01

138

Active heat exchange thermal storage unit with pentaerythritol  

Microsoft Academic Search

A latent thermal energy storage unit with pentaerythritol was developed, and in the storage unit an active heat transfer enhancement was performed. The phase change material, pentaerythritol, was mixed with a hydrocarbon heat transfer oil and this two-phase storage medium was stirred in a shell-coil type heat exchanger. Through the preliminary experiments in a glass vessel, a lab-scale storage unit

Y. Abe; M. Kamimoto; K. Kanari; T. Ozawa; R. Sakamoto; Y. Takahashi

1984-01-01

139

Kinetic model for the vibrational energy exchange in flowing molecular gas mixtures. Ph.D. Thesis  

NASA Technical Reports Server (NTRS)

The present study is concerned with the development of a computational model for the description of the vibrational energy exchange in flowing gas mixtures, taking into account a given number of energy levels for each vibrational degree of freedom. It is possible to select an arbitrary number of energy levels. The presented model uses values in the range from 10 to approximately 40. The distribution of energy with respect to these levels can differ from the equilibrium distribution. The kinetic model developed can be employed for arbitrary gaseous mixtures with an arbitrary number of vibrational degrees of freedom for each type of gas. The application of the model to CO2-H2ON2-O2-He mixtures is discussed. The obtained relations can be utilized in a study of the suitability of radiation-related transitional processes, involving the CO2 molecule, for laser applications. It is found that the computational results provided by the model agree very well with experimental data obtained for a CO2 laser. Possibilities for the activation of a 16-micron and 14-micron laser are considered.

Offenhaeuser, F.

1987-01-01

140

Activated carbon for gas separation and storage  

Microsoft Academic Search

Activated carbons offer a large spectrum of pore structures and surface chemistry for adsorption of gases, which are being used to design practical pressure swing and thermal swing adsorption processes for separation and purification of gas mixtures. The activated carbons are often preferred over the zeolitic adsorbents in a gas separation process because of their relatively moderate strengths of adsorption

S. Sircar; T. C. Golden; M. B. Rao

1996-01-01

141

Greenhouse Gas Exchange and Biogeochemistry of Fertilized Canadian Plantation Forests  

Microsoft Academic Search

Canada's ratification of the Kyoto Protocol in 2002 has raised questions of the role of ecosystem management as a tool to temporarily reduce the net greenhouse gas burden of the forestry industry and potentially generate emission offset credits. We examined growing season methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2) fluxes, soil nutrient chemistry, and microbial biomass and CH4-oxidizing

N. Basiliko; S. J. Grayston; R. Roy; W. W. Mohn; V. Yolova; C. Prescott

2005-01-01

142

Experimental results with a natural gas cogeneration system using a polymer exchange membrane fuel cell  

Microsoft Academic Search

This paper reports experimental results of an investigation of five identical CHP (combined heat and power) units using PEMFC (proton exchange membrane fuel cell) and running on natural gas. The natural gas is reformed locally to produce hydrogen. The net electric power is 4.5kWe and the installations are designed for low temperature heat recovery (6kW at 60°C). The performances of

Mihai Radulescu; Olivier Lottin; Michel Feidt; Christophe Lombard; David Le Noc; Stéphane Le Doze

2006-01-01

143

Two-dimensional transient solutions for crossflow heat exchangers with neither gas mixed  

Microsoft Academic Search

The two-dimensional transient behavior of gas-to-gas crossflow heat exchangers is investigated, solving by analytical methods the thermal balance equations in order to determine the transient distribution of temperatures in the core wall and in both the unmixed gases. Assuming large wall capacitance, the general solutions are deduced by the Laplace transform method and are presented as integrals of modified Besel

G. Spiga; M. Spiga

1987-01-01

144

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

Microsoft Academic Search

Immediate gas changes occurred when untreated Martian surface samples were humidified and\\/or wet by an aqueous nutrient medium in the Viking lander gas exchange experiment. The evolutions of N2, CO2, and Ar are mainly associated with soil surface desorption caused by water vapor, while O2 evolution is primarily associated with decomposition of superoxides inferred to be present on Mars. On

Vance I. Oyama; B. J. Berdahl

1977-01-01

145

Role of nitrogen in transmucosal gas exchange rate in the rat middle ear.  

PubMed

This study investigates the role of nitrogen (N2) in transmucosal gas exchange of the middle ear (ME). We used an experimental rat model to measure gas volume variations in the ME cavity at constant pressure. We disturbed the steady-state gas composition with either air or N2 to measure resulting changes in volume at ambient pressure. Changes in gas volume over time could be characterized by three phases: a primary transient increase with time (phase I), followed by a linear decrease (phase II), and then a gradual decrease (phase III). The mean slope of phase II was -0.128 microl/min (SD 0.023) in the air group (n = 10) and -0.105 microl/min (SD 0.032) in the N2 group (n = 10), but the difference was not significant (P = 0.13), which suggests that the rate of gas loss can be attributed mainly to the same steady-state partial pressure gradient of N2 reached in this phase. Furthermore, a mathematical model was developed analyzing the transmucosal N2 exchange in phase II. The model takes gas diffusion into account, predicting that, in the absence of change in mucosal blood flow rate, gas volume in the ME should show a linear decrease with time after steady-state conditions and gas composition are established. In accordance with the experimental results, the mathematical model also suggested that transmucosal gas absorption of the rat ME during steady-state conditions is governed mainly by diffusive N2 exchange between the ME gas and its mucosal blood circulation. PMID:16840582

Kania, Romain E; Herman, Philippe; Tran Ba Huy, Patrice; Ar, Amos

2006-11-01

146

Turbulence and Wave Breaking Effects on Air-Water Gas Exchange  

Microsoft Academic Search

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

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

2000-01-01

147

Impact of Phytoplankton-Generated Surfactants on Air-Sea Gas Exchange.  

National Technical Information Service (NTIS)

In a recent series of controlled laboratory-based gas exchange experiments we were able to show that oxygen evasion at the air-liquid interface of clean (Sargasso) seawater could be reduced by as much as 50% in the presence of synthetic surfactants and th...

N. M. Frew J. C. Goldman M. R. Dennett A. S. Johnson

1990-01-01

148

Gas diffusion layer for proton exchange membrane fuel cells—A review  

Microsoft Academic Search

Gas diffusion layer (GDL) is one of the critical components acting both as the functional as well as the support structure for membrane–electrode assembly in the proton exchange membrane fuel cell (PEMFC). The role of the GDL is very significant in the H2\\/air PEM fuel cell to make it commercially viable. A bibliometric analysis of the publications on the GDLs

L. Cindrella; A. M. Kannan; J. F. Lin; K. Saminathan; Y. Ho; C. W. Lin; J. Wertz

2009-01-01

149

Variation in gas exchange and water use efficiency patterns among populations of western redcedar  

Microsoft Academic Search

Western redcedar ( Thuja plicata Donn) populations were planted out on a reforestation site and measured, during the summer, to define their gas exchange processes in relation to evaporative demand under non-limiting light and edaphic conditions. These populations came from various locations across a longitudinal transect representing various biogeoclimatic subzones, differing in annual and summer precipitation, in British Columbia, Canada.

Steven C. Grossnickle; Shihe Fan; John H. Russell

2005-01-01

150

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

PubMed

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

Heinrich, Erica; Bradley, Timothy

2014-08-01

151

The hyperoxic switch: assessing respiratory water loss rates in tracheate arthropods with continuous gas exchange  

Microsoft Academic Search

Partitioning the relative contributions of cuticular and respiratory water loss in a tracheate arthropod is relatively easy if it undergoes discontinuous gas exchange cycles or DGCs, leaving its rate of cuticular water loss in primary evidence while its spiracles are closed. Many arthropods are not so obliging and emit CO2 continuously, making cuticular and respiratory water losses difficult or impossible

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

2004-01-01

152

Development of gas diffusion electrodes for low relative humidity proton exchange membrane fuel cells  

Microsoft Academic Search

A series of polyaniline nanofibers (PANFs) were synthesized and incorporated into gas diffusion electrodes (GDE) of proton exchange membrane fuel cells (PEMFC) to improve their performances at low relative humidity (RH) conditions. Three different placements to incorporate the PANFs in the anodes include (1) placing a PANFs layer between catalyst layer (CL) and membrane, (2) coating the CL with PANFs

Y. F. Huang; A. M. Kannan; C. S. Chang; C. W. Lin

2011-01-01

153

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

Microsoft Academic Search

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

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

1998-01-01

154

Effects of Gall Induction by Epiblema Strenuana on Gas Exchange, Nutrients, and Energetics in Parthenium Hysterophorus  

Microsoft Academic Search

Gall induction by arthropods results in a range of morphological and physiological changes in their host plants. We examined changes in gas exchange, nutrients, and energetics related to the presence of stem galls on Parthenium hysterophorus L. (Asteraceae) induced by the moth, Epiblema strenuana Walker (Lepidoptera: Tortricidae). We compared the effects of galls on P. hysterophorus in the rosette (young),

S. K. Florentine; A. Raman; K. Dhileepan

2005-01-01

155

Gas Exchange in the Avocado Leaves Under Water Stress and Recovery  

Microsoft Academic Search

Net photosynthesis, transpirations, water potential, and stomatal resistance were studied in avocado leaves during stress and recovery periods. The changes in leaf gas exchange seemed to be influenced more due to drastic changes in stomatal resistance than the leaf water potential. During the period of development of water stress and its initial recovery, the leaf water potential remained steady at

A. Ramadasan

156

Acclimation of a terrestrial plant to submergence facilitates gas exchange under water  

Microsoft Academic Search

Flooding imposes stress upon terrestrial plants since it severely hampers gas exchange rates between the shoot and the environment. The resulting oxygen deficiency is considered to be the major problem for submerged plants. Oxygen microelectrode studies have, however, shown that aquatic plants maintain relatively high internal oxygen pressures under water, and even may release oxygen via the roots into the

L. Mommer; O. Pedersen; E. J. W. Visser

2004-01-01

157

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...

158

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

SciTech Connect

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

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

1987-06-01

159

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

160

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

161

Effects of Acute through Life-Long Hypoxic Exposure on Exercise Pulmonary Gas Exchange.  

National Technical Information Service (NTIS)

The adequacy, efficiency and control of pulmonary gas exchange during exercise was compared among groups who were exposed for various durations of time to moderate hypoxia (3100 m altitude, PIO2 100 mm Hg). These groups included native lowlanders during a...

H. V. Forster J. A. Dempsey J. S. Thoden M. L. Birnbaum W. G. Reddan

1971-01-01

162

Water removal characteristics of proton exchange membrane fuel cells using a dry gas purging method  

Microsoft Academic Search

Water removal from proton exchange membrane fuel cells (PEMFC) is of great importance to improve start-up ability and mitigate cell degradation when the fuel cell operates at subfreezing temperatures. In this study, we report water removal characteristics under various shut down conditions including a dry gas-purging step. In order to estimate the dehydration level of the electrolyte membrane, the high

Sang-Yeop Lee; Sang-Uk Kim; Hyoung-Juhn Kim; Jong Hyun Jang; In-Hwan Oh; Eun Ae Cho; Seong-Ahn Hong; Jaejun Ko; Tae-Won Lim; Kwan-Young Lee; Tae-Hoon Lim

2008-01-01

163

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

NASA Astrophysics Data System (ADS)

The exchange of carbon dioxide and other trace gases across the air-sea interface plays an important role in global and regional biogeochemical cycles. The gas transfer velocity (k) is thought to be controlled by near- surface turbulence at low to moderate wind speeds and by bubble-mediated processes at higher wind speeds. At low to moderate wind speeds, small-scale waves including microbreaking disrupt the diffusive boundary layer, contribute to mixing at the surface, and enhance exchange. Likewise, at higher wind speeds, large-scale wave breaking, or whitecapping, generates mixing and additionally enhances gas transfer via bubble-mediated exchange. The parameterization for k based on the direct covariance fluxes is shown to have a cubic dependence on wind speed. This result supports the hypothesis that, if bubble mediated exchange is important, the transfer velocity should increase proportionally with whitecap coverage, since whitecap coverage been shown to increase with at least a cubic dependence on wind speed. However, the very large uncertainties under high wind speed conditions limit the universality of this result and the role of breaking waves and bubble modulated transfer. Here, we present results of the combination of turbulence, deep-ocean wave statistics, whitecapping, and CO2 gas exchange measured during the Southern Ocean Gas Exchange Experiment (SO GasEx) with sustained conditions between 10-20 m s-1. Directional ocean wave spectra, significant wave height, peak wave period, and peak wave direction were obtained with a Wave and Surface Current Monitoring System (WaMoS® II). WaMoS® II also has the capability to resolve two-dimensional maps of surface elevation snapshots with the significant advantage of continuous availability of wave data in rough seas. In addition, significant wave height was measured using a laser altimeter as well as a nadir-looking microwave system. Oceanic turbulent kinetic energy dissipation rates were measured using a pulse-coherent Doppler sonar mounted at 2-m depth from a drifting surface buoy. Lastly, wave-breaking statistics and whitecapping coverage are reported using two high-resolution digital cameras from the flying bridge. We present results of process studies that investigate the various models for gas transfer that incorporate turbulence and wave- breaking statistics with the goal of developing a focused parameterization.

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

2008-12-01

164

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

PubMed

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

Terblanche, John S; Chown, Steven L

2010-05-01

165

Estimating air-sea gas exchange in the seasonal sea ice zone  

NASA Astrophysics Data System (ADS)

In the ice-free surface ocean gas exchange is driven, to first order, by turbulent kinetic energy from wind. Temperature changes, wave age, and bubbles, surfactants, and rain also play a role. In the presence of sea ice, the surface area for heat and gas exchange is significantly reduced, potentially mitigating the effect of wind-driven processes in favor of other turbulence production mechanisms. These mechanisms include (1) surface roughening and dissipation by interaction of wind, waves and ice floes (2) buoyancy production near the lead opening (3) convection during brine drainage and (4) ice-water boundary layer turbulence. The contribution of each of these mechanisms is unique, however they share the common quantities of turbulence production and turbulent energy dissipation, (?), which can be related to the gas transfer velocity, k. This study considers the individual turbulence production mechanisms and it attempts to use existing theory and empirical relationships to explore how gas exchange may scale with the fraction of ice-covered ocean surface area. The work demonstrates that the presence of sea ice can simultaneously enhance the magnitude of k and modulate the net gas flux across the air-sea interface.

Loose, B.; McGillis, W. R.

2011-12-01

166

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

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

167

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

168

Predict the temperature distribution in gas-to-gas heat pipe heat exchanger  

NASA Astrophysics Data System (ADS)

A theoretical model has been developed to investigate the thermal performance of a continuous finned circular tubing of an air-to-air thermosyphon-based heat pipe heat exchanger. The model has been used to determine the heat transfer capacity, which expresses the thermal performance of heat pipe heat exchanger. The model predicts the temperature distribution in the flow direction for both evaporator and condenser sections and also the saturation temperature of the heat pipes. The approach used for the present study considers row-by-row heat-transfer in evaporator and condenser sections of the heat pipe heat exchanger.

Azad, E.

2012-07-01

169

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

170

Poly-methyl pentene oxygenators have improved gas exchange capability and reduced transfusion requirements in adult extracorporeal membrane oxygenation.  

PubMed

The performance of poly-methyl pentene (PMP) oxygenators (Medos Hilite 7000LT) was compared with that of silicone membrane (SM) oxygenators (Medtronic 1-4500-2A) for adult extracorporeal membrane oxygenation (ECMO). Forty consecutive patients were selected retrospectively pre- and post-introduction of PMP oxygenators. They were selected according to the dates they received ECMO and were separated into two equal groups with similar backgrounds. The flow path resistance, gas and heat exchange efficiency, consumption of coagulation factors and platelets, blood transfusion requirements, and incidence of clots for each oxygenator type was assessed. Adult PMP oxygenators showed lower blood path resistance than SM oxygenators. However, lower consumption of blood products in these oxygenators was a direct result of their smaller surface area and heparin coated design, reducing contact activation of coagulation factors. These oxygenators are noticeably smaller, require lower priming volumes, and have better gas exchange capability than SM oxygenators. They showed greater stability and preservation of coagulation factors and platelets compared with SM oxygenators. They also had the advantage of a functioning integrated heat exchanger. Using a single PMP oxygenator in the first instance may be adequate for the majority of patients and would significantly reduce red blood cell consumption during ECMO. PMID:15968960

Khoshbin, Espeed; Roberts, Neil; Harvey, Chris; Machin, David; Killer, Hilliary; Peek, Giles J; Sosnowski, Andrzej W; Firmin, Richard K

2005-01-01

171

Submaximal exercise gas exchange is an important prognostic tool to predict adverse outcomes in heart failure  

PubMed Central

Aims Traditionally, VO2peak has been used to determine prognosis in heart failure; however, this measure has limitations. Hence, other exercise and gas exchange parameters measured submaximally, e.g. breathing efficiency (VE/VCO2), end-tidal CO2 (PETCO2), oxygen uptake efficiency slope (OUES), and circulatory power [ systolic blood pressure (SBP)], have been investigated. The aim of this study was to investigate the prognostic relevance of submaximal exercise gas exchange in heart failure patients. Method and results One hundred and thirty-two consecutive heart failure patients (mean age 56 ± 12 years, ejection fraction 29 ± 11%) performed peak treadmill testing. Gas exchange and haemodynamic variables were measured continuously. Gas exchange data obtained from the first 2 min of exercise and at a respiratory exchange ratio (RER) of 0.9 were the measurements of interest. Over a median follow-up period of 62.4 (range 0–114) months, there were 44 endpoints (death or transplant). Univariate analysis demonstrated submaximal predictors of survival, which included VE/VCO2 slope and ratio, PETCO2, OUES, and circulatory power (P? 0.01). When these and additional submaximal variables were included together in the multivariable analysis, the strongest submaximal exercise predictive model (C-statistic 0.75) comprised data from the first stage of exercise (VE and circulatory power) and at an RER of 0.9 (VE/VCO2 ratio). The inclusion of VO2peak and demographic data, with submaximal data (VE/VCO2 ratio at an RER = 0.9), increased the predictiveness of the model (C-statistic 0.78). Conclusion Submaximal exercise measures provide useful prognostic information for predicting survival in heart failure. This form of testing is logistically easier, cheaper, and safer for patients compared with maximal exercise.

Woods, Paul R.; Bailey, Kent R.; Wood, Christina M.; Johnson, Bruce D.

2011-01-01

172

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

173

Accurate homogeneous electron gas exchange-correlation free energy for local spin-density calculations.  

PubMed

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. PMID:24579621

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

2014-02-21

174

H/D exchange of gas phase bradykinin ions in a linear quadrupole ion trap.  

PubMed

The gas phase H/D exchange reaction of bradykinin ions, as well as fragment ions of bradykinin generated through collisions in an orifice skimmer region, have been studied with a linear quadrupole ion trap (LIT) reflectron time-of-flight (rTOF) mass spectrometer system. The reaction in the trap takes only tens of seconds at a pressure of few mTorr of D2O or CD3OD. The exchange rate and hydrogen exchange level are not sensitive to the trapping q value over a broad range, provided q is not close to the stability boundary (q = 0.908). The relative rates and hydrogen exchange levels of protonated and sodiated +1 and +2 ions are similar to those observed previously by others with a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer system. The doubly and triply protonated ions show multimodal isotopic distributions, suggesting the presence of several different conformations. The y fragment ions show greater exchange rates and levels than a or b ions, and when water or ammonia is lost from the fragment ions, no exchange is observed. PMID:12586457

Mao, Dunmin; Douglas, D J

2003-02-01

175

Ultrasonic gas-body activation in Drosophila.  

PubMed

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

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

1983-01-01

176

Poly-Use Multi-Level Sampling Rod to Measure Soil-Gas Exchange in Glacier Forefield Soils  

NASA Astrophysics Data System (ADS)

The forefields of receding glaciers provide unique opportunities to investigate initial microbial processes in the vadose zone and their role in soil formation. Various studies revealed a surprising diversity of microbes and of their strategies to cope with the extreme conditions in this C- and N-limited environment. In the forefield of receding glaciers as well as in developed soils microorganisms are the driving force for the exchange of greenhouse gases between soil and atmosphere. However, in young and developing soils, little is known about soil-gas exchange and the activities of the involved microorganisms. Knowledge of soil-gas composition and gas diffusion at various depths in a soil profile allows for the precise calculation of gas fluxes among different depths within the vadose zone and at the soil-atmosphere boundary. The acquisition of undisturbed soil-gas samples at a high depth-resolution is difficult, and the estimation of soil-gas diffusion coefficients requires knowledge of volumetric water content at the exact location of gas sampling. By using conventional techniques, e.g. the burial of permanent probes, these tasks are virtually impossible to accomplish in a remote glacier forefield dominated by rocks and boulders. We developed a novel poly-use multi-level sampling rod (PULSAR) primarily consisting of two devices: a newly-designed multi-level sampler (MLS) for soil-gas sampling, and a commercially available profile probe (PR2) for non-invasive multi-level water content measurements. These devices fit into the same access tubes (ATs) of 1.1m length, which need to be pre-installed into the soil with the help of a steel rod. We modified the ATs to feature eight 1mm diameter holes each at 20 sampling depths in intervals of 5cm. Our MLS can be inserted into the ATs and allows for the selective extraction of soil-gas from each sampling depth. The interspaces between the sampling depths are sealed by inflatable rubber membranes for the time of sampling. Once soil-gas has been extracted, soil water content can be measured with the PR2 probe at each sampled depth. After gas concentration analysis, knowledge of water content and soil-gas composition at 20 different depths allows for the quantification of depth-resolved soil-gas fluxes and calculation of microbial production and degradation rates in situ with minimal disturbance. The PULSAR concept was applied to investigate greenhouse gas fluxes in the forefields of two receding glaciers on calcareous and siliceous bedrock in the Swiss Alps. We installed a total of 33 ATs distributed among three soil-age groups of approx. 10, 40 and 70 years. Soil-gas sampling and water content measurements were performed twice during the snow-free season. In between sampling, the ATs were sealed with inflatable rubber tubes featuring iButton® temperature loggers. The resulting data will provide valuable insights into the development of gas exchange of these young soils, while illustrating the feasibility of the PULSAR in soils with high skeleton contents.

Nauer, P. A.; Schroth, M. H.; Zeyer, J. A.

2012-12-01

177

The Na+/H+ exchanger present in trout erythrocyte membranes is not responsible for the amiloride-insensitive Na+/Li+ exchange activity.  

PubMed

The protein responsible for the Na+/Li+ exchange activity across the erythrocyte membrane has not been cloned or isolated. It has been suggested that a Na+/H+ exchanger could be responsible for the Na+/Li+ exchange activity across the erythrocyte membrane. Previously, we reported that in the trout erythrocyte, the Li+/H+ exchange activity (mediated by the Na+/H+ exchanger beta NHE) and the Na+/Li+ exchange activity respond differently to cAMP, DMA (dimethyl-amiloride) and O2. We concluded that the DMA insensitive Na+/Li+ exchange activity originates from a different protein. To further examine these findings, we measured Li+ efflux in fibroblasts expressing the beta NHE as the only Na+/H+ exchanger. Moreover, the internal pH of these cells was monitored with a fluorescent probe. Our findings indicate that acidification of fibroblasts expressing the Na+/H+ exchanger beta NHE, induces a Na+ stimulated Li+ efflux activity in trout erythrocytes. This exchange activity, however, is DMA sensitive and therefore differs from the DMA insensitive Na+/Li+ exchange activity. In these fibroblasts no significant DMA insensitive Na+/Li+ exchange activity was found. These results support the hypothesis that the trout erythrocyte Na+/Li+ exchange activity is not mediated by the Na+/H+ exchanger (beta NHE) present in these membranes. PMID:9425603

van Norren, K; Gorissen, R; Borgese, F; Borggreven, J M; De Pont, J J

1997-12-01

178

Interactions between heart rate variability and pulmonary gas exchange efficiency in humans.  

PubMed

The respiratory component of heart rate variability (respiratory sinus arrhythmia, RSA) has been associated with improved pulmonary gas exchange efficiency in humans via the apparent clustering and scattering of heart beats in time with the inspiratory and expiratory phases of alveolar ventilation, respectively. However, since human RSA causes only marginal redistribution of heart beats to inspiration, we tested the hypothesis that any association between RSA amplitude and pulmonary gas exchange efficiency may be indirect. In 11 patients with fixed-rate cardiac pacemakers and 10 healthy control subjects, we recorded R-R intervals, respiratory flow, end-tidal gas tension and the ventilatory equivalents for carbon dioxide and oxygen during 'fast' (0.25 Hz) and 'slow' paced breathing (0.10 Hz). Mean heart rate, mean arterial blood pressure, mean arterial pressure fluctuations, tidal volume, end-tidal CO(2), and were similar between pacemaker and control groups in both the fast and slow breathing conditions. Although pacemaker patients had no RSA and slow breathing was associated with a 2.5-fold RSA amplitude increase in control subjects (39 +/- 21 versus 97 +/- 45 ms, P < 0.001), comparable (main effect for breathing frequency, F(1,19) = 76.54, P < 0.001) and reductions (main effect for breathing frequency, F(1,19) = 23.90, P < 0.001) were observed for both cohorts during slow breathing. In addition, the degree of (r = 0.36, P = 0.32) and reductions (r = 0.29, P = 0.43) from fast to slow breathing were not correlated to the degree of associated RSA amplitude enhancements in control subjects. These findings suggest that the association between RSA amplitude and pulmonary gas exchange efficiency during variable-frequency paced breathing observed in prior human work is not contingent on RSA being present. Therefore, whether RSA serves an intrinsic physiological function in optimizing pulmonary gas exchange efficiency in humans requires further experimental validation. PMID:20382666

Sin, Peter Y W; Webber, Matthew R; Galletly, Duncan C; Ainslie, Philip N; Brown, Stephen J; Willie, Chris K; Sasse, Alexander; Larsen, Peter D; Tzeng, Yu-Chieh

2010-07-01

179

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

180

Regulation and acclimation of leaf gas exchange in a piñon-juniper woodland exposed to three different precipitation regimes.  

PubMed

Leaf gas-exchange regulation plays a central role in the ability of trees to survive drought, but forecasting the future response of gas exchange to prolonged drought is hampered by our lack of knowledge regarding potential acclimation. To investigate whether leaf gas-exchange rates and sensitivity to drought acclimate to precipitation regimes, we measured the seasonal variations of leaf gas exchange in a mature piñon-juniper Pinus edulis-Juniperus monosperma woodland after 3 years of precipitation manipulation. We compared trees receiving ambient precipitation with those in an irrigated treatment (+30% of ambient precipitation) and a partial rainfall exclusion (-45%). Treatments significantly affected leaf water potential, stomatal conductance and photosynthesis for both isohydric piñon and anisohydric juniper. Leaf gas exchange acclimated to the precipitation regimes in both species. Maximum gas-exchange rates under well-watered conditions, leaf-specific hydraulic conductance and leaf water potential at zero photosynthetic assimilation all decreased with decreasing precipitation. Despite their distinct drought resistance and stomatal regulation strategies, both species experienced hydraulic limitation on leaf gas exchange when precipitation decreased, leading to an intraspecific trade-off between maximum photosynthetic assimilation and resistance of photosynthesis to drought. This response will be most detrimental to the carbon balance of piñon under predicted increases in aridity in the southwestern USA. PMID:23461476

Limousin, Jean-Marc; Bickford, Christopher P; Dickman, Lee T; Pangle, Robert E; Hudson, Patrick J; Boutz, Amanda L; Gehres, Nathan; Osuna, Jessica L; Pockman, William T; McDowell, Nate G

2013-10-01

181

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

NASA Astrophysics Data System (ADS)

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

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

2010-10-01

182

Organic iodine removal from simulated dissolver off-gas systems utilizing silver-exchanged mordenite  

SciTech Connect

The removal of methyl iodide by adsorption onto silver mordenite was studied using a simulated off-gas from the fuel dissolution step of a nuclear fuel reprocessing plant. The adsorption of methyl iodide on silver mordenite was examined for the effect of NO/sub x/, humidity, iodine concentration, filter temperature, silver loadings and filter pretreatment. The highest iodine loading achieved in these tests was 142 mg CH/sub 3/I per g of substrate on fully exchanged zeolite, approximately the same as elemental iodine loadings. A filter using fully exchanged silver mordenite operating at 200/sup 0/C obtained higher iodine loadings than a similar filter operating at 150/sup 0/C. Pretreatment of the sorbent bed with hydrogen rather than dry air, at a temperature of 200/sup 0/C, also improved the loading. Variations in the methyl iodide concentration had minimal effects on the overall loading. Filters exposed to moist air streams attained higher loadings than those in contact with dry air. Partially exchanged silver mordenite achieved higher silver utilizations than the fully exchanged material. The partially exchanged mordenite also achieved higher loadings at 200/sup 0/C than at 250/sup 0/C. The iodine loaded onto these beds was not stripped at 500/sup 0/C by either 4.5% hydrogen or 100% hydrogen; however, the iodine could be removed by air at 500/sup 0/C, and the bed could be reloaded. A study of the regeneration characteristics of fully exchanged silver mordenite indicates limited adsorbent capacity after complete removal of the iodine with 4.5% hydrogen in the regeneration gas stream at 500/sup 0/C. The loss of adsorbent capacity is much higher for silver mordenite regenerated in a stainless steel filter housing than in a glass filter housing.

Jubin, R.T.

1981-01-01

183

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

NASA Astrophysics Data System (ADS)

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

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

2007-03-01

184

Pulsatile blood flow and gas exchange across a cylindrical fiber array.  

PubMed

The pulsatile blood flow and gas transport of oxygen and carbon dioxide through a cylindrical array of microfibers are numerically simulated. Blood is modeled as a homogeneous Casson fluid, and hemoglobin molecules in blood are assumed to be in local equilibrium with oxygen and carbon dioxide. It is shown that flow pulsatility enhances gas transport and the amount of gas exchange is sensitive to the blood flow field across the fibers. The steady Sherwood number dependence on Reynolds number was shown to have a linear relation consistent with experimental findings. For most cases, an enhancement in gas transport is accompanied with an increase in flow resistance. Maximum local shear stress is provided as a possible indicator of thrombosis, and the computed shear stress is shown to be below the threshold value for thrombosis formation for all cases evaluated. PMID:17887893

Chan, Kit Yan; Fujioka, Hideki; Hirshl, Ronald B; Bartlett, Robert H; Grotberg, James B

2007-10-01

185

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

186

Growth and gas exchange response to water shortage of a maize crop on different soil types  

Microsoft Academic Search

The effect of water shortage on growth and gas exchange of maize grown on sandy soil (SS) and clay soil was studied. The lower\\u000a soil water content in the SS during vegetative growth stages did not affect plant height, above-ground biomass, and leaf area\\u000a index (LAI). LAI reduction was observed on the SS during the reproductive stage due to early

Luca Vitale; Paul Di Tommasi; Carmen Arena; Michele Riondino; Annachiara Forte; Angelo Verlotta; Angelo Fierro; Amalia Virzo De Santo; Amodio Fuggi; Vincenzo Magliulo

2009-01-01

187

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

PubMed

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. PMID:16585041

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

2006-07-01

188

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

Microsoft Academic Search

The South African grass, Lehmann lovegrass (Eragrostis lehmanniana), may alter ecosystem processes across extensive semiarid grasslands and savannahs of western North America. We compared\\u000a volumetric soil moisture (?), total and green tissue leaf area index (LAI), ecosystem (i.e. whole-plant and soil), and leaf-level gas exchange of Lehmann\\u000a lovegrass and the native bush muhly (Muhlenbergia porteri) over the 2008 monsoon season

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

2010-01-01

189

Gas exchange responses to constant work rate exercise in chronic cardiac failure.  

PubMed Central

OBJECTIVE--To examine the time course of changes in minute oxygen consumption and other gas exchange variables and heart rate during constant work rate exercise in patients with chronic cardiac failure. DESIGN--Treadmill exercise with on line measurement of gas exchange and a target duration of 10 minutes. SUBJECTS--Seven men in New York Heart Association class II, six in class III, and seven controls. MAIN OUTCOME MEASURES--Gas exchange variables and heart rate were averaged for the final two minutes of exercise. Time constants were calculated for the increase in all variables. RESULTS--Consumption of oxygen at the end of exercise (VO2) was similar in class II patients (mean (95% confidence interval (95% CI) 14.9 (13.6 to 16.1) ml kg-1 min-1), class III patients (13.2 (11.2 to 15.1) ml kg-1 min-1), and controls (13.3 (12.5 to 14.2) ml kg-1 min-1). The patients reached this VO2 more slowly with longer exponential time constants of 0.82 (0.59 to 1.04) min in class II and 1.19 (0.86 to 1.51) min in class III, than the 0.49 (0.35 to 0.64) min in the controls. Time constants of other gas exchange variables and heart rate were also longer in patients. By analysis of covariance, peak VO2 accounted for the between group difference in the time constant for VO2, suggesting that circulatory factors may be an important cause of the delayed kinetics. CONCLUSIONS--A delayed rise in VO2 in response to exercise may be responsible for subnormal values of VO2 early in exercise in patients with chronic cardiac failure.

Riley, M; Porszasz, J; Stanford, C F; Nicholls, D P

1994-01-01

190

Feeding and respiratory gas exchange in the American dog tick, Dermacentor variabilis  

Microsoft Academic Search

This study investigated the effect of blood feeding on respiratory gas exchange in the dog tick Dermacentor variabilis. Adult male and female ticks were fed on bovine hosts from 1 to 11days. Females fed slowly for the first 6days and then rapidly engorged on blood 2–3days prior to dropping from the host. Ticks were removed at daily intervals during feeding,

Laura J. Fielden; Robert M. Jones; Martin Goldberg; Yigal Rechav

1999-01-01

191

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

Microsoft Academic Search

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

Francesco Loreto; Thomas D. Sharkey

1990-01-01

192

Lung compression effects on gas exchange in human breath-hold diving  

Microsoft Academic Search

Lung compression during breath-hold diving reduces gas exchanging surface area. Beyond a critical depth, collapse of all alveoli should result in total pulmonary shunt and a drop in arterial oxygen partial pressure toward the mixed-venous level. The effect of lung collapse on human breath-hold diving capability is analysed using a computational model of the lungs and circulation that simulates oxygen,

John R. Fitz-Clarke

2009-01-01

193

Air-water gas exchange of hexachlorocyclohexanes (HCHs) and the enantiomers of ?-HCH in arctic regions  

Microsoft Academic Search

In the summers of 1993 and 1994, air and water samples were taken in the Bering and Chukchi Seas and on a transect across the polar cap to the Greenland Sea to measure the air-sea gas exchange of hexachlorocyclohexanes (HCHs) and the enantiomers of a-HCH. Atmospheric concentrations of a- and 3,-HCH have decreased threefold or more since the mid-1980s, whereas

Liisa M. Jantunen; Terry Bidleman

1996-01-01

194

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

NASA Technical Reports Server (NTRS)

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

Stuart, T. S.; Gaffron, H.

1972-01-01

195

Gas exchange, chlorophyll fluorescence, and osmotic adjustment in two mango cultivars under drought stress  

Microsoft Academic Search

The responses of photosynthetic gas exchange, chlorophyll fluorescence, content of pigments, main osmolytes, and malondialdehyde\\u000a (MDA) to water-withholding for 15 days and re-hydration in seedlings of two mango cultivars (Mangifera indica L. var. “Choke Anand’ and var. “Khieo Sawoei”) under 50% sunlight and full sunlight were investigated. For both cultivars, the water-witholding resulted\\u000a in progressively decreases in leaf relative water content,

Nabil I. Elsheery; Kun-Fang Cao

2008-01-01

196

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

SciTech Connect

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

SungDeok, Hong; DongSeok, Oh; WonJae, Lee; JongHwa, Chang [Korea Atomic Energy Research Institute, Yuseong-Gu, Daejeon, 305-600 (Korea, Republic of)

2006-07-01

197

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

198

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

199

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

200

Air-sea fluxes from drifting buoys during two recent open-ocean gas exchange experiments  

NASA Astrophysics Data System (ADS)

A summary (progress report) of measurements from Air-Sea Interaction Spar (ASIS) buoys during the 2007 Deep Ocean Gas Exchange Experiment (DOGEE) and 2008 Southern Ocean Gas Exchange experiment (SO Gasex) is presented. Flux instrumentation consisted of a sonic anemometer, measuring temperature and the velocity components, and an open-path gas analyzer, LI-7500, measuring carbon dioxide and water vapor. Exchange-coefficients used in bulk-formulas, such as the Dalton and Stanton number are calculated. SAMI sensors mounted on the buoy measured the partial pressure of CO2 in the water. In combination with the vertical CO2 flux and mean CO2 values measured by the LI-7500 the transfer velocity of CO2 is evaluated. A specially designed outrigger attached to the ASIS structure enabled measurements of small waves. Wave lengths of the order of 20 cm could be resolved. This allows for a unique study of the relation between the transfer velocity and the mean square slope of the short waves.

Drennan, W.; Sahlee, E.; Degrandpre, M.

2008-12-01

201

Oxygen transport during exercise in large mammals. II. Oxygen uptake by the pulmonary gas exchanger.  

PubMed

Because the maximal rate of O2 consumption (VO2max) of the horse is 2.6 times larger than that of steers of equal size, we wondered whether their pulmonary gas exchanger is proportionately larger. Three Standardbred racehorses [body mass (Mb) = 447 kg] and three domestic steers (Mb = 474 kg) whose cardiovascular function at VO2max had been thoroughly studied (Jones et al. J. Appl. Physiol. 67: 862-870, 1989) were used to study their lungs by morphometry. The basic morphometric parameters were similar in both species. The nearly 2 times larger lung volumes of the horses caused the gas exchange surfaces and capillary blood volume to be 1.6 to 1.8 times larger. Morphometric pulmonary diffusing capacity was 2 times larger in the horse than in the steer; the 2.6-fold greater rate of O2 uptake thus required the alveolar-capillary PO2 difference to be 1.3 times larger in the horse than in the steer. Combining physiological and morphometric data, we calculated capillary transit time at VO2max to be 0.4-0.5 s. Bohr integration showed capillary blood to be equilibrated with alveolar air after 75 and 58% of transit time in horses and steers, respectively; horses maintain a smaller degree of redundancy in their pulmonary gas exchanger. PMID:2793687

Constantinopol, M; Jones, J H; Weibel, E R; Taylor, C R; Lindholm, A; Karas, R H

1989-08-01

202

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

PubMed

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

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

2011-08-01

203

Emphysema following vitrectomy with fluid-gas exchange: description of a rare complication  

PubMed Central

Purpose To report a case of subcutaneous emphysema involving the orbit, mediastinum, and face after pars plana vitrectomy with fluid–gas exchange. Methods Case report of a 55-year-old man who presented with bilateral eyelid and face edema and dysphagia in the immediate postoperative period after pars plana vitrectomy. Orbital and chest computed tomographies were performed, revealing emphysema of the orbit and soft tissue of the face, extending from the neck to the upper chest. Results The patient with a retinal detachment in the right eye underwent 23-gauge vitrectomy surgery with fluid–gas exchange and an implantation of silicone oil. The patient had a previous history of facial trauma for more than 20 years with an orbital fracture. After surgery, the patient developed emphysema of the orbit, soft tissue of the face and upper chest. Systemic prophylactic antibiotics associated with antibiotics and steroid drops performed a satisfactory evolution. Conclusion The fluid–gas exchange during pars plana vitrectomy in patients with orbital fracture can lead to emphysema of the face, chest, and soft tissue.

Damasceno, Eduardo F; Damasceno, Nadyr; Horowitz, Soraya; Rodrigues, Marcio Mortera

2014-01-01

204

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.

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

2010-01-01

205

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

NASA Astrophysics Data System (ADS)

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

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

2000-03-01

206

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

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

207

Gas-phase H\\/D exchange and collision cross sections of hemoglobin monomers, dimers, and tetramers  

Microsoft Academic Search

The conformations of gas-phase ions of hemoglobin, and its dimer and monomer subunits have been studied with H\\/D exchange\\u000a and cross section measurements. During the H\\/D exchange measurements, tetramers undergo slow dissociation to dimers, and dimers\\u000a to monomers, but this did not prevent drawing conclusions about the relative exchange levels of monomers, dimers, and tetramers.\\u000a Assembly of the monomers into

P. John Wright; D. J. Douglas

2009-01-01

208

Effects of air current speed on gas exchange in plant leaves and plant canopies  

NASA Astrophysics Data System (ADS)

To obtain basic data on adequate air circulation to enhance plant growth in a closed plant culture system in a controlled ecological life support system (CELSS), an investigation was made of the effects of the air current speed ranging from 0.01 to 1.0 m s-1 on photosynthesis and transpiration in sweetpotato leaves and photosynthesis in tomato seedlings canopies. The gas exchange rates in leaves and canopies were determined by using a chamber method with an infrared gas analyzer. The net photosynthetic rate and the transpiration rate increased significantly as the air current speeds increased from 0.01 to 0.2 m s-1. The transpiration rate increased gradually at air current speeds ranging from 0.2 to 1.0 m s-1 while the net photosynthetic rate was almost constant at air current speeds ranging from 0.5 to 1.0 m s-1. The increase in the net photosynthetic and transpiration rates were strongly dependent on decreased boundary-layer resistances against gas diffusion. The net photosynthetic rate of the plant canopy was doubled by an increased air current speed from 0.1 to 1.0 m s-1 above the plant canopy. The results demonstrate the importance of air movement around plants for enhancing the gas exchange in the leaf, especially in plant canopies in the CELSS.

Kitaya, Y.; Tsuruyama, J.; Shibuya, T.; Yoshida, M.; Kiyota, M.

209

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

NASA Technical Reports Server (NTRS)

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

Stalder, Jackson R; Spies, Ray J , Jr

1948-01-01

210

EFFECT OF LEAF ANATOMY ON HYPOSTOMATOUS LEAF GAS EXCHANGE: A THEORETICAL STUDY WITH THE 2DLEAF MODEL  

Microsoft Academic Search

PACHEPSKY L. B. and ACOCK B. Effect of leaf anatomy on hypostomatous leaf gas exchange: A theoretical study with the 2DLEAF model. BIOTRONICS 27, 1-14, 1998. The two-dimensional model of leaf gas exchange, 2DLEAF, which accounts for leaf intercellular structure, was used to study the effect of leaf anatomy on the photosynthesis and transpiration rates of hypostomatous Cg plants. The

L. B. P ACHEPSKYI; B. ACOCK

211

Ventilation-perfusion heterogeneity and gas exchange variables in acute pulmonary embolism evaluated by two different computerized techniques  

Microsoft Academic Search

Summary  The mechanisms by which the disturbances of gas exchange develop in human pulmonary embolism are unknown. We investigated\\u000a whether the inequality of ventilation-perfusion ratio is associated with the abnormalities of pulmonary gas exchange as evaluated\\u000a by two different computerized techniques. We measured the alveolar to arterial gradients of oxygen and carbon dioxide by means\\u000a of a computer based system with

R. Prediletto; B. Formichi; E. Begliomini; E. Fornai; G. Viegi; S. Ruschi; P. Paoletti; A. N. Giannella; A. Santolicandro; C. Giuntini

1988-01-01

212

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

213

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

NASA Technical Reports Server (NTRS)

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

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

1977-01-01

214

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.

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

2011-01-01

215

A Multivariable Index for Grading Exercise Gas Exchange Severity in Patients with Pulmonary Arterial Hypertension and Heart Failure  

PubMed Central

Patients with pulmonary arterial hypertension (PAH) and heart failure (HF) display many abnormalities in respiratory gas exchange. These abnormalities are accentuated with exercise and track with disease severity. However, use of gas exchange measures in day-to-day clinical practice is limited by several issues, including the large number of variables available and difficulty in data interpretation. Moreover, maximal exercise testing has limitations in clinical populations due to their complexity, patient anxiety and variability in protocols and cost. Therefore, a multivariable gas exchange index (MVI) that integrates key gas exchange variables obtained during submaximal exercise into a severity score that ranges from normal to severe-very-severe is proposed. To demonstrate the usefulness of this index, we applied this to 2 groups (PAH, n = 42 and HF, n = 47) as well as to age matched healthy controls (n = 25). We demonstrate that this score tracks WHO classification and right ventricular systolic pressure in PAH (r = 0.53 and 0.73, P ? 0.01) and NYHA and cardiac index in HF (r = 0.49 and 0.74, P ? 0.01). This index demonstrates a stronger relationship than any single gas exchange variable alone. In conclusion, MVI obtained from light, submaximal exercise gas exchange is a useful approach to simplify data interpretation in PAH and HF populations.

Kim, Chul-Ho; Anderson, Steve; MacCarter, Dean; Johnson, Bruce

2012-01-01

216

The Gas Exchange of Hydrogen-adapted Algae as Followed by Mass Spectrometry 1  

PubMed Central

A mass spectrometer inlet and an oxygen electrode in the same vessel allowed the continuous recording of the gases exchanged (H2, CO2, O2) by hydrogenase-containing anaerobically adapted Scenedesmus obliquus strain D3 (Gaffron) and Chlorella fusca Shihira et Krauss (= pyrenoidosa) 211-15. A light intensity which produces more photosynthetic oxygen than the cells can re-reduce to water leads to de-adaptation and the substitution of normal photosynthesis for photoreduction. The sequence of these metabolic events was recorded in a matter of a few minutes. Upon exposure of these adapted algae to light, an evolution of hydrogen lasting up to 60 seconds preceded any other light-dependent gas exchange. In the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea, this initial hydrogen production was inhibited approximately 50%, pointing to a contribution of electrons by photosystem II. At very low hydrogen tensions (0.1 microliter per milliliter), a balance between light-induced production and absorption of hydrogen was observed in normal, unpoisoned algae. Addition of either glucose or inhibitors of phosphorylation increased the release of hydrogen in the light very considerably. When the light was turned off the algae consumed the remaining amount of hydrogen, only to release it again upon illumination. This reversible hydrogen exchange persisted even when any concomitant carbon dioxide exchange had been abolished.

Stuart, Tim S.; Gaffron, Hans

1972-01-01

217

The Gas Exchange of Hydrogen-adapted Algae as Followed by Mass Spectrometry.  

PubMed

A mass spectrometer inlet and an oxygen electrode in the same vessel allowed the continuous recording of the gases exchanged (H(2), CO(2), O(2)) by hydrogenase-containing anaerobically adapted Scenedesmus obliquus strain D(3) (Gaffron) and Chlorella fusca Shihira et Krauss (= pyrenoidosa) 211-15. A light intensity which produces more photosynthetic oxygen than the cells can re-reduce to water leads to de-adaptation and the substitution of normal photosynthesis for photoreduction. The sequence of these metabolic events was recorded in a matter of a few minutes. Upon exposure of these adapted algae to light, an evolution of hydrogen lasting up to 60 seconds preceded any other light-dependent gas exchange. In the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea, this initial hydrogen production was inhibited approximately 50%, pointing to a contribution of electrons by photosystem II. At very low hydrogen tensions (0.1 microliter per milliliter), a balance between light-induced production and absorption of hydrogen was observed in normal, unpoisoned algae. Addition of either glucose or inhibitors of phosphorylation increased the release of hydrogen in the light very considerably. When the light was turned off the algae consumed the remaining amount of hydrogen, only to release it again upon illumination. This reversible hydrogen exchange persisted even when any concomitant carbon dioxide exchange had been abolished. PMID:16658108

Stuart, T S; Gaffron, H

1972-07-01

218

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

PubMed

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

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

2013-02-01

219

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

220

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

SciTech Connect

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

Miller, F.E.

1992-06-23

221

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

NASA Astrophysics Data System (ADS)

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

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

1987-06-01

222

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

NASA Technical Reports Server (NTRS)

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

Olson, Douglas A.; Glover, Michael P.

1990-01-01

223

Integration of Daily Inundation Extent Estimates into an Ecosystem-Atmosphere Gas Exchange Model  

NASA Astrophysics Data System (ADS)

Soil moisture and the spatial extent of soil saturation, transient inundation, and wetland ecosystems are key determinants of greenhouse gas (GHG, e.g., methane) emissions from the land surface to the atmosphere. We are investigating how near-daily surface water and soil moisture observations from NASA's planned Soil Moisture Active-Passive (SMAP) mission can be integrated into an ecosystem-atmosphere gas exchange model to improve its estimates of GHG fluxes. SMAP, to be launched in 2014, will combine 1- to 3-km resolution synthetic aperture radar (SAR), 40-km-resolution L-band radiometry, and 3-day revisit period to make a novel dataset expected to provide inundation and soil moisture estimates superior to alternative methods at that temporal-spatial scale. We are testing the potential impact of this new data source using the Dynamic Land Surface Ecosystem Model (DLEM). DLEM quantifies regional fluxes of methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) given atmospheric forcing data, with soil saturation as a prognostic variable. We have developed a new combined SMAP-DLEM model for North America with ~9-km grid cell size and a time-varying subgrid land cover fraction scheme that allows soil moisture, inundation, and wetlands extent to be externally prescribed from remote sensing observations. The model is designed to use SMAP-like ~9-km inundation fraction inputs as an external forcing term in addition to daily meteorological inputs. We will present results of studies aimed toward validating and optimizing the SMAP-DLEM model when external inundation extent forcing data are available. To emulate SMAP observations, a daily inundation fraction dataset has been derived for 2008 using data from NASA's Advanced Microwave Scanning Radiometer-EOS (AMSR-E). This dataset was mapped to the DLEM 9-km grid using a downscaling and data-merging algorithm that estimates the spatial extent of water cover at the resolution of digital elevation models (e.g., 30-100 m). The downscaling approach enables subgrid water cover fraction to be classified according to the permanent land cover types being inundated. We present results comparing DLEM methane fluxes from the baseline model configuration (i.e., lacking daily variation in wetlands extent) and new configurations that use daily inundation extent forcing data. We discuss sources of SMAP inundation mapping uncertainties and how errors can be mitigated to minimize their propagation into DLEM GHG flux estimates.

Galantowicz, J.; Samanta, A.; Tian, H.

2012-12-01

224

Gas exchange characteristics, metabolic rate and water loss of the Heelwalker, Karoophasma biedouwensis (Mantophasmatodea: Austrophasmatidae).  

PubMed

This study presents the first physiological information for a member of the wingless Mantophasmatodea, or Heelwalkers. This species shows cyclic gas exchange with no evidence of a Flutter period (more typical of discontinuous gas exchange in insects) and no indication that the spiracles are fully occluded during quiescent metabolism. Standard metabolic rate at 20 degrees C was 21.32+/-2.73 microl CO(2)h(-1) (mean+/-S.E.), with a Q(10) (10-25 degrees C) of 1.7. Increases in V()CO(2) associated with variation in mass and with trial temperature were modulated by an increase in burst period volume and a decline in cycle frequency. Total water loss rate, determined by infrared gas analysis, was 0.876+/-0.08 mg H(2)Oh(-1) (range 0.602-1.577, n=11) whilst cuticular water loss rate, estimated by linear regression of total water loss rate and metabolic rate, was 0.618+/-0.09 mg H(2)Oh(-1) (range 0.341-1.363, n=11). Respiratory water loss rate was therefore no more than 29% of the total rate of water loss. Both total water loss rate and estimated cuticular water loss rate were significantly repeatable, with intraclass correlation coefficients of 0.745 and 0.553, respectively. PMID:16466738

Chown, S L; Marais, E; Picker, M D; Terblanche, J S

2006-05-01

225

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

226

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

227

Using Riverboat-Mounted Eddy Covariance for Direct Measurements of Air-water Gas Exchange in Amazonia  

NASA Astrophysics Data System (ADS)

Gas evasion from Amazonian rivers and lakes to the atmosphere has been estimated to play an important role in the regional budget of carbon dioxide (Richey et al., 2002) and the global budget of methane (Melack et al., 2004). These flux estimates were calculated by combining remote sensing estimates of inundation area with water-side concentration gradients and gas transfer rates (piston velocities) estimated primarily from floating chamber measurements (footprint ~1 m2). The uncertainty in these fluxes was large, attributed primarily to uncertainty in the gas exchange parameterization. Direct measurements of the gas exchange coefficient are needed to improve the parameterizations in these environments, and therefore reduce the uncertainty in fluxes. The micrometeorological technique of eddy covariance is attractive since it is a direct measurement of gas exchange that samples over a much larger area than floating chambers, and is amenable to use from a moving platform. We present eddy covariance carbon dioxide exchange measurements made using a small riverboat in rivers and lakes in the central Amazon near Santarem, Para, Brazil. Water-side carbon dioxide concentration was measured in situ, and the gas exchange coefficient was calculated. We found the piston velocity at a site on the Amazon River to be similar to existing ocean-based parameterizations, whereas the piston velocity at a site on the Tapajos River was roughly a factor 5 higher. We hypothesize that the enhanced gas exchange at the Tapajos site was due to a shallow upwind fetch. Our results demonstrate the feasibility of boat-based eddy covariance on these rivers, and also the utility of a mobile platform to investigate spatial variability of gas exchange.

Miller, S. D.; Freitas, H.; Read, E.; Goulden, M. L.; Rocha, H.

2007-12-01

228

Forest Canopy-Atmosphere Gas Exchange Rates in the Tapajos National Forest, Para, Brazil, Determined by Radon-222 Measurements  

NASA Astrophysics Data System (ADS)

Continuous canopy air and soil-air flux measurements of radon-222 have been combined to quantify canopy-atmosphere gas exchange rates and canopy air residence times in Amazonian old growth and selectively logged forests in the Tapajos National Forest near Santarém, Pará, Brazil, as part of the LBA project led by Brazil. Radon canopy air and soil flux measurements, when fully integrated with LBA studies led by other investigators including tower eddy covariance fluxes, forest canopy gas inventories and soil gas fluxes can provide independent quantification of gas production, consumption and within the canopy plus net canopy-atmosphere fluxes. Canopy and above-canopy air radon activities at up to ten tower elevations at forest sites decrease systematically with height above the soil surface. Diel radon activity variations in the Tapajos forest canopy at both sites are characterized by dual maxima peaking near approximately 0900 and 1730 local time that occur respectively as a result of nocturnal stratification and late afternoon stratification during the early evening transition. Radon inventories within the lower 10m of the forest canopy typically range by over 200 percent over a diel cycle. Soil-air radon fluxes were determined using portable radon fluxometers capable of repeated thirty-minute flux measurements on soil collars installed around the tower sites. Radon flux divergence within the forest canopy can be utilized to quantitatively determine the net rates and canopy vertical distribution of CO2 or methane and other trace gas production and consumption processes when combined with their soil flux and canopy profile measurements. The combined canopy and soil flux radon data also yields canopy air residence times throughout the diel cycle.

Martens, C. S.; Shay, T. J.; Mendlovitz, H. P.; Moura, J. S.; Lima, R. L.; Sampaio, I. G.; Moraes, O. L.; Woodward, W. S.; Crill, P. M.

2004-12-01

229

Surviving floods: leaf gas films improve O? and CO? exchange, root aeration, and growth of completely submerged rice.  

PubMed

When completely submerged, the leaves of some species retain a surface gas film. Leaf gas films on submerged plants have recently been termed 'plant plastrons', analogous with the plastrons of aquatic insects. In aquatic insects, surface gas layers (i.e. plastrons) enlarge the gas-water interface to promote O? uptake when under water; however, the function of leaf gas films has rarely been considered. The present study demonstrates that gas films on leaves of completely submerged rice facilitate entry of O? from floodwaters when in darkness and CO? entry when in light. O? microprofiles showed that the improved gas exchange was not caused by differences in diffusive boundary layers adjacent to submerged leaves with or without gas films; instead, reduced resistance to gas exchange was probably due to the enlarged water-gas interface (cf. aquatic insects). When gas films were removed artificially, underwater net photosynthesis declined to only 20% of the rate with gas films present, such that, after 7 days of complete submergence, tissue sugar levels declined, and both shoot and root growth were reduced. Internal aeration of roots in anoxic medium, when shoots were in aerobic floodwater in darkness or when in light, was improved considerably when leaf gas films were present. Thus, leaf gas films contribute to the submergence tolerance of rice, in addition to those traits already recognized, such as the shoot-elongation response, aerenchyma and metabolic adjustments to O? deficiency and oxidative stress. PMID:19077169

Pedersen, Ole; Rich, Sarah Meghan; Colmer, Timothy David

2009-04-01

230

The role of catecholamines in memory impairment in chicks following reduced gas exchange in ovo.  

PubMed

We have shown previously that reducing gas exchange to chick embryos by half wrapping eggs with an impermeable membrane from either days 14-18 (W14-18) or days 10-18 (W10-18) of the 21 day incubation results in post-hatch memory deficits. In the W10-18 chicks, short-term memory following training is impaired, whereas in the W14-18 chicks, memory is intact for 30 min but does not consolidate into long-term storage. The reduction in gas exchange caused by half wrapping eggs resulted in alterations in hematocrit, O2 and CO2 tensions suggesting that the embryos are hypoxic and hypercapnic. Our aim was to test the hypothesis that increases in circulating levels of catecholamines in ovo, as a result of hypoxia, lead to a disturbance of the central noradrenergic pathways resulting in cognitive impairment. Noradrenaline is critical for memory consolidation and a disturbance during development could compromise cognitive ability. In the present study, plasma noradrenaline levels were significantly elevated compared with control levels 2 days after hatch in W14-18 chicks. There was also a decrease in tissue noradrenaline concentration in the anterior forebrain in both W14-18 and W10-18 chicks. The differential ability of centrally administered beta2- and beta3-adrenoceptor agonists to overcome the memory deficit post-training, suggests altered responsiveness of central beta2-adrenoceptors to noradrenaline in W14-18 chicks. By comparing the W10-18 and W14-18 chicks with those from eggs wrapped from W10-14 we show that it is the timing of the prenatal hypoxia, rather than its duration, that determines the nature of cognitive dysfunction. We conclude that prenatal hypoxia induced by restriction of gas exchange can disrupt or alter central noradrenergic transmission causing cognitive impairment. PMID:15381283

Camm, E J; Harding, R; Lambert, G W; Gibbs, M E

2004-01-01

231

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

NASA Astrophysics Data System (ADS)

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

Fahr, H. J.

2003-06-01

232

Echangeur Ceramique Gaz-Gaz en Carbure de Silicium: Prototype Deuxieme Generation. Essais et Synthese (Ceramic Silicon Carbide Gas/Gas Exchanger: Prototype of Second Generation).  

National Technical Information Service (NTIS)

The project is concerned with the development of a ceramic (SiC) gas/gas heat exchanger module that can be operated up to 1200 C. The present study has addressed: thermal and thermo-mechanical design of a second generation design; construction of a protot...

M. Cellier S. Galant G. Martinez C. Morillon J. C. Mulet

1986-01-01

233

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

PubMed

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

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

2011-10-14

234

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

SciTech Connect

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

Not Available

1983-01-01

235

Exchange-correlation energy for the three-dimensional homogeneous electron gas at arbitrary temperature  

NASA Astrophysics Data System (ADS)

We fit finite-temperature path integral Monte Carlo calculations of the exchange-correlation energy of the 3D finite-temperature homogeneous electron gas in the warm-dense regime [rs?(3/4?n)1/3aB-1<40 and ??T/TF>0.0625]. In doing so, we construct a Padé approximant which collapses to Debye-Hückel theory in the high-temperature, low-density limit. Likewise, the zero-temperature limit matches the numerical results of ground-state quantum Monte Carlo, as well as analytical results in the high-density limit.

Brown, Ethan W.; DuBois, Jonathan L.; Holzmann, Markus; Ceperley, David M.

2013-08-01

236

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

237

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

238

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

Microsoft Academic Search

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

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

2011-01-01

239

Aqueous turbulence structure immediately adjacent to the air - water interface and interfacial gas exchange  

NASA Astrophysics Data System (ADS)

Air-sea interaction and the interfacial exchange of gas across the air-water interface are of great importance in coupled atmospheric-oceanic environmental systems. Aqueous turbulence structure immediately adjacent to the air-water interface is the combined result of wind, surface waves, currents and other environmental forces and plays a key role in energy budgets, gas fluxes and hence the global climate system. However, the quantification of turbulence structure sufficiently close to the air-water interface is extremely difficult. The physical relationship between interfacial gas exchange and near surface turbulence remains insufficiently investigated. This dissertation aims to measure turbulence in situ in a complex environmental forcing system on Lake Michigan and to reveal the relationship between turbulent statistics and the CO2 flux across the air-water interface. The major objective of this dissertation is to investigate the physical control of the interfacial gas exchange and to provide a universal parameterization of gas transfer velocity from environmental factors, as well as to propose a mechanistic model for the global CO2 flux that can be applied in three dimensional climate-ocean models. Firstly, this dissertation presents an advanced measurement instrument, an in situ free floating Particle Image Velocimetry (FPIV) system, designed and developed to investigate the small scale turbulence structure immediately below the air-water interface. Description of hardware components, design of the system, measurement theory, data analysis procedure and estimation of measurement error were provided. Secondly, with the FPIV system, statistics of small scale turbulence immediately below the air-water interface were investigated under a variety of environmental conditions. One dimensional wave-number spectrum and structure function sufficiently close to the water surface were examined. The vertical profiles of turbulent dissipation rate were intensively studied. Comparison between the turbulence structures measured during the wind wave initiation period and those obtained during the growing period was presented. Significant wave effects on near surface turbulence were found. A universal scaling law was proposed to parameterize turbulent dissipation rate immediately below the air-water interface with friction velocity, significant wave height and wave age. Finally, the gas transfer velocity was measured with a floating chamber (FC) system, along with simultaneously FPIV measurements. Turbulent dissipation rate both at the interface and at a short distance away from the interface (~ 10 cm) were analyzed and used to examine the small scale eddy model. The model coefficient was found to be dependent on the level of turbulence, instead of being a constant. An empirical relationship between the model coefficient and turbulent dissipation rate was provided, which improved the accuracy of the gas transfer velocity estimation by more than 100% for data acquired. Other data from the literature also supported this empirical relation. Furthermore, the relationship between model coefficient and turbulent Reynolds number was also investigated. In addition to physical control of gas exchange, the disturbance on near surface hydrodynamics by the FC was also discussed. Turbulent dissipation rates are enhanced at the short distance away from the interface, while the surface dissipation rates do not change significantly.

Wang, Binbin

240

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

NASA Astrophysics Data System (ADS)

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

Iwabuchi, K.; Kurata, K.

241

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

SciTech Connect

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

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

1992-01-01

242

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

PubMed Central

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

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

1989-01-01

243

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

PubMed

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

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

2009-07-01

244

Models for estimating the change-point in gas exchange data.  

PubMed

In subjects undertaking an incremental exercise test to exhaustion, the onset of metabolic acidosis can be detected by an increased rate of carbon dioxide output (VCO2) relative to the rate of increase of oxygen uptake (VO2). To locate the change-point (the gas exchange threshold) in such subjects, a two-line regression model relating these two quantities has been used, where the location of the change-point is unknown. We argue that statistical models where the change-point is set on time (rather than VO2) are more appropriate. This is because VO2 is not monotone in time. We use novel statistical methodology of hidden Markov models to demonstrate the existence of the change-point. We use time series models, to estimate the position of the change-point. In these models distributions other than the multivariate normal are considered. For some subjects, the variance of VCO2 increases with time because of increasing ventilation and this is also modelled. The results are illustrated using gas exchange data on three healthy subjects who performed a 20 W min(-1) workrate ramp test. PMID:15712721

Kelly, G E; Lindsey, J K; Thin, A G

2004-12-01

245

Dry deposition and soil-air gas exchange of polychlorinated biphenyls (PCBs) in an industrial area.  

PubMed

Ambient air and dry deposition, and soil samples were collected at the Aliaga industrial site in Izmir, Turkey. Atmospheric total (particle+gas) Sigma(41)-PCB concentrations were higher in summer (3370+/-1617 pg m(-3), average+SD) than in winter (1164+/-618 pg m(-3)), probably due to increased volatilization with temperature. Average particulate Sigma(41)-PCBs dry deposition fluxes were 349+/-183 and 469+/-328 ng m(-2) day(-1) in summer and winter, respectively. Overall average particulate deposition velocity was 5.5+/-3.5 cm s(-1). The spatial distribution of Sigma(41)-PCB soil concentrations (n=48) showed that the iron-steel plants, ship dismantling facilities, refinery and petrochemicals complex are the major sources in the area. Calculated air-soil exchange fluxes indicated that the contaminated soil is a secondary source to the atmosphere for lighter PCBs and as a sink for heavier ones. Comparable magnitude of gas exchange and dry particle deposition fluxes indicated that both mechanisms are equally important for PCB movement between air and soil in Aliaga. PMID:18640753

Bozlaker, Ayse; Odabasi, Mustafa; Muezzinoglu, Aysen

2008-12-01

246

Air water gas exchange of ?-hexachlorocyclohexane enantiomers in the South Atlantic Ocean and Antarctica  

NASA Astrophysics Data System (ADS)

Between November 1997 and February 1998, air and water samples were collected on the African side of the South Atlantic Ocean to Antarctica, on board the S.A. Agulhas, to determine the spatial distribution of ?-hexachlorocyclohexane ( ?-HCH) and the net direction of air/water gas exchange. The ?-HCH concentrations in air and surface water were much lower than in Arctic regions, consistent with the historically lower usage of technical HCH in the Southern Hemisphere. The water/air fugacity ratios of ?-HCH were ?1.0, indicating steady state or net deposition conditions. The ?-HCH in water was enantioselectively metabolized, with resulting enantiomer fractions (EFs) that differed from the racemic (0.500) value of the technical product. The EFs decreased from >0.500 at the lower latitudes to <0.500 farther south, indicating preferential loss of (-) ?-HCH or (+) ?-HCH in different ocean regions. EFs in the air boundary layer reflected those in surface water, showing the bidirectional nature of gas exchange.

Jantunen, Liisa M.; Kylin, Henrik; Bidleman, Terry F.

2004-11-01

247

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

PubMed

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

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

2014-05-01

248

Dissolution without disappearing: multicomponent gas exchange for CO2 bubbles in a microfluidic channel.  

PubMed

We studied the dissolution dynamics of CO2 gas bubbles in a microfluidic channel, both experimentally and theoretically. In the experiments, spherical CO2 bubbles in a flow of a solution of sodium dodecyl sulfate (SDS) first shrink rapidly before attaining an equilibrium size. In the rapid dissolution regime, the time to obtain a new equilibrium is 30 ms regardless of SDS concentration, and the equilibrium radius achieved varies with the SDS concentration. To explain the lack of complete dissolution, we interpret the results by considering the effects of other gases (O2, N2) that are already dissolved in the aqueous phase, and we develop a multicomponent dissolution model that includes the effect of surface tension and the liquid pressure drop along the channel. Solutions of the model for a stationary gas bubble show good agreement with the experimental results, which lead to our conclusion that the equilibrium regime is obtained by gas exchange between the bubbles and liquid phase. Also, our observations from experiments and model calculations suggest that SDS molecules on the gas-liquid interface form a diffusion barrier, which controls the dissolution behaviour and the eventual equilibrium radius of the bubble. PMID:24874437

Shim, Suin; Wan, Jiandi; Hilgenfeldt, Sascha; Panchal, Prathamesh D; Stone, Howard A

2014-06-17

249

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

250

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

NASA Astrophysics Data System (ADS)

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

Ukhov, Alexander; Borisov, Sergey; Porodnov, Boris

2011-05-01

251

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

252

The influence of sea ice cover on air-sea gas exchange estimated with radon-222 profiles  

NASA Astrophysics Data System (ADS)

gas exchange plays a key role in the cycling of greenhouse and other biogeochemically important gases. Although air-sea gas transfer is expected to change as a consequence of the rapid decline in summer Arctic sea ice cover, little is known about the effect of sea ice cover on gas exchange fluxes, especially in the marginal ice zone. During the Polarstern expedition ARK-XXVI/3 (TransArc, August/September 2011) to the central Arctic Ocean, we compared 222Rn/226Ra ratios in the upper 50 m of 14 ice-covered and 4 ice-free stations. At three of the ice-free stations, we find 222Rn-based gas transfer coefficients in good agreement with expectation based on published relationships between gas transfer and wind speed over open water when accounting for wind history from wind reanalysis data. We hypothesize that the low gas transfer rate at the fourth station results from reduced fetch due to the proximity of the ice edge, or lateral exchange across the front at the ice edge by restratification. No significant radon deficit could be observed at the ice-covered stations. At these stations, the average gas transfer velocity was less than 0.1 m/d (97.5% confidence), compared to 0.5-2.2 m/d expected for open water. Our results show that air-sea gas exchange in an ice-covered ocean is reduced by at least an order of magnitude compared to open water. In contrast to previous studies, we show that in partially ice-covered regions, gas exchange is lower than expected based on a linear scaling to percent ice cover.

Rutgers van der Loeff, Michiel M.; Cassar, Nicolas; Nicolaus, Marcel; Rabe, Benjamin; Stimac, Ingrid

2014-05-01

253

Observations of Volatile Organic Compounds (VOC) from the Remote North Atlantic: Preliminary Results from the High-Wind Gas-Exchange Study (HiWinGS)  

NASA Astrophysics Data System (ADS)

Marine biogenic volatile organic compounds (BVOCs) can play a controlling role in setting the oxidative capacity of the marine boundary layer, secondary organic aerosol production rates and the chemistry of the upper ocean. Models suggest a wide range of significance for these reactive trace gases driven largely by local biophysical controls. This variability remains poorly constrained by observations, particularly from open-ocean regions. Here, we report preliminary BVOC mixing ratios and direct flux measurements from the High-Wind Gas Exchange Study (HiWinGS). This research cruise targeted regions of enhanced trace gas exchange, driven by elevated biological activity and strong surface winds in the remote North Atlantic during Fall of 2013. A custom-built chemical-ionization time-of-flight mass spectrometer was deployed to capture full mass spectra at high resolution (10 Hz) with demonstrated sensitivity (>10^2 Hz/pptv) to a wide range of BVOC species such as dimethylsulfide, isoprene, monoterpenes and alkylamines.

Kim, M.; Bertram, T. H.

2013-12-01

254

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

255

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.

Makanya, Andrew N; Mortola, Jacopo P

2007-01-01

256

Gas exchange in wetlands with emergent vegetation: The effects of wind and thermal convection at the air-water interface  

NASA Astrophysics Data System (ADS)

Methane, carbon dioxide, and oxygen are exchanged between wetlands and the atmosphere through multiple pathways. One of these pathways, the hydrodynamic transport of dissolved gas through the surface water, is often underestimated in importance. We constructed a model wetland in the laboratory with artificial emergent plants to investigate the mechanisms and magnitude of this transport. We measured gas transfer velocities, which characterize the near-surface stirring driving air-water gas transfer, while varying two stirring processes important to gas exchange in other aquatic environments: wind and thermal convection. To isolate the effects of thermal convection, we identified a semiempirical model for the gas transfer velocity as a function of surface heat loss. The laboratory results indicate that thermal convection will be the dominant mechanism of air-water gas exchange in marshes with emergent vegetation. Thermal convection yielded peak gas transfer velocities of 1 cm h-1. Because of the sheltering of the water surface by emergent vegetation, gas transfer velocities for wind-driven stirring alone are likely to exceed this value only in extreme cases.

Poindexter, Cristina M.; Variano, Evan A.

2013-07-01

257

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

PubMed

The hygric hypothesis postulates that insect discontinuous gas exchange cycles (DGCs) are an adaptation that reduces respiratory water loss (RWL), but evidence is lacking for reduction of water loss by insects expressing DGCs under normal ecological conditions. Larvae of Erynnis propertius (Lepidoptera: Hesperiidae) naturally switch between DGCs and continuous gas exchange (CGE), allowing flow-through respirometry comparisons of water loss between the two modes. Water loss was lower during DGCs than CGE, both between individuals using different patterns and within individuals using both patterns. The hygric cost of gas exchange (water loss associated with carbon dioxide release) and the contribution of respiratory to total water loss were lower during DGCs. Metabolic rate did not differ between DGCs and CGE. Thus, DGCs reduce RWL in E. propertius, which is consistent with the suggestion that water loss reduction could account for the evolutionary origin and/or maintenance of DGCs in insects. PMID:19923135

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

2010-04-23

258

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

NASA Astrophysics Data System (ADS)

The formaldehyde, tracer gas, and water vapor transfer rates in two enthalpy exchangers were measured. The first exchanger uses a cross flow fabricated from a treated paper. The core of the second heat exchanger is a rotating heat wheel coated with lithium chloride. To reduce the transfer of gases by air leakage each core was installed in a specially fabricated case. Only 5% to 8% of the two tracer gases and 7% to 15% of the formaldehyde injected into the exhaust airstream was transferred to the supply airstream. Therefore, formaldehyde transfer between airstreams by processes other than air leakage does not seriously compromise the performance of these enthalpy exchangers. Theoretical calculations indicate, however, that the transfer of water vapor between airstreams in enthalpy exchangers can significantly diminish their ability to lower indoor formaldehyde concentrations because of the positive coupling between indoor humidity and the emission rates of formaldehyde from building materials.

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

1984-07-01

259

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

260

Total parenteral nutrition in the newborn infant: energy substrates and respiratory gas exchange.  

PubMed

The hypothesis that a high-fat parenteral regimen was beneficial for respiratory gas exchanges, in comparison with a high-glucose regimen, was tested in a paired crossover design. Ten parenterally fed newborn infants with no respiratory problems received two 5-day isoenergetic and isonitrogenous regimens that differed in their nonprotein source of energy; the level of fat intake (low fat (LF) 1 gm.kg-1.day-1; high fat (HF) 3 gm.kg-1.day-1) varied inversely with that of glucose. Continuous transcutaneous PO2 (tcPO2) and PCO2 (tcPCO2), respiratory gas exchange (indirect calorimetry), and plasma arachidonate metabolites were measured at the end of each regimen. Oxygen consumption and resting energy expenditure were not affected by modification of the source of energy. However, carbon dioxide production (VCO2) was higher during LF than during HF (6.9 +/- 0.2 vs 6.2 +/- 0.1 ml.kg-1.min-1; p less than 0.01), as was the respiratory quotient (1.08 +/- 0.02 vs 0.96 +/- 0.02; p less than 0.001). Despite the differences in VCO2, the tcPCO2 was not affected, suggesting adequate pulmonary compensation during LF, as documented by the higher minute ventilation (160 +/- 7 vs 142 +/- 5 ml.kg-1.min-1; p less than 0.01). The lower tcPO2 during the HF regimen (73.8 +/- 2.8 vs 68.8 +/- 2.6 mm Hg; p less than 0.015) indicated a disturbance at the alveolocapillary level induced by the lipid emulsion. No differences were found in circulating levels of prostaglandins and thromboxanes. The substitution of glucose for lipid did not modify fat storage (2.1 +/- 0.3 vs 2.1 +/- 0.3 gm.kg-1.day-1). We conclude that the supposed beneficial effect of a fat emulsion on respiratory gas exchange is questionable. PMID:1898751

Piedboeuf, B; Chessex, P; Hazan, J; Pineault, M; Lavoie, J C

1991-01-01

261

Casting Granular Ion Exchange Resins with Medium-Active Waste in Cement.  

National Technical Information Service (NTIS)

Medium active waste from nuclear power stations in Sweden is trapped in granular ion exchange resins. The resin is mixed with cement paste and cast in a concrete shell which is cubic and has an edge dimension of 1.2 m. In some cases the ion exchange cemen...

O. Beijer

1980-01-01

262

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

263

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

264

Activation of AMP-activated protein kinase revealed by hydrogen/deuterium exchange mass spectrometry.  

PubMed

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 with 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 the 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 F; Hoth, Lise R; Magyar, Rachelle; Pascal, Bruce D; Chalmers, Michael J; Busby, Scott A; Kurumbail, Ravi G; Griffin, Patrick R

2013-11-01

265

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

266

Assessing Gibberellins Oxidase Activity by Anion Exchange/Hydrophobic Polymer Monolithic Capillary Liquid Chromatography-Mass Spectrometry  

PubMed Central

Bioactive gibberellins (GAs) play a key regulatory role in plant growth and development. In the biosynthesis of GAs, GA3-oxidase catalyzes the final step to produce bioactive GAs. Thus, the evaluation of GA3-oxidase activity is critical for elucidating the regulation mechanism of plant growth controlled by GAs. However, assessing catalytic activity of endogenous GA3-oxidase remains challenging. In the current study, we developed a capillary liquid chromatography – mass spectrometry (cLC-MS) method for the sensitive assay of in-vitro recombinant or endogenous GA3-oxidase by analyzing the catalytic substrates and products of GA3-oxidase (GA1, GA4, GA9, GA20). An anion exchange/hydrophobic poly([2-(methacryloyloxy)ethyl]trimethylammonium-co-divinylbenzene-co-ethylene glycol dimethacrylate)(META-co-DVB-co-EDMA) monolithic column was successfully prepared for the separation of all target GAs. The limits of detection (LODs, Signal/Noise?=?3) of GAs were in the range of 0.62–0.90 fmol. We determined the kinetic parameters (Km) of recombinant GA3-oxidase in Escherichia coli (E. coli) cell lysates, which is consistent with previous reports. Furthermore, by using isotope labeled substrates, we successfully evaluated the activity of endogenous GA3-oxidase that converts GA9 to GA4 in four types of plant samples, which is, to the best of our knowledge, the first report for the quantification of the activity of endogenous GA3-oxidase in plant. Taken together, the method developed here provides a good solution for the evaluation of endogenous GA3-oxidase activity in plant, which may promote the in-depth study of the growth regulation mechanism governed by GAs in plant physiology.

Liu, Jiu-Feng; Wu, Yan; Feng, Yu-Qi; Yuan, Bi-Feng

2013-01-01

267

Assessing gibberellins oxidase activity by anion exchange/hydrophobic polymer monolithic capillary liquid chromatography-mass spectrometry.  

PubMed

Bioactive gibberellins (GAs) play a key regulatory role in plant growth and development. In the biosynthesis of GAs, GA3-oxidase catalyzes the final step to produce bioactive GAs. Thus, the evaluation of GA3-oxidase activity is critical for elucidating the regulation mechanism of plant growth controlled by GAs. However, assessing catalytic activity of endogenous GA3-oxidase remains challenging. In the current study, we developed a capillary liquid chromatography--mass spectrometry (cLC-MS) method for the sensitive assay of in-vitro recombinant or endogenous GA3-oxidase by analyzing the catalytic substrates and products of GA3-oxidase (GA1, GA4, GA9, GA20). An anion exchange/hydrophobic poly([2-(methacryloyloxy)ethyl]trimethylammonium-co-divinylbenzene-co-ethylene glycol dimethacrylate)(META-co-DVB-co-EDMA) monolithic column was successfully prepared for the separation of all target GAs. The limits of detection (LODs, Signal/Noise = 3) of GAs were in the range of 0.62-0.90 fmol. We determined the kinetic parameters (K m) of recombinant GA3-oxidase in Escherichia coli (E. coli) cell lysates, which is consistent with previous reports. Furthermore, by using isotope labeled substrates, we successfully evaluated the activity of endogenous GA3-oxidase that converts GA9 to GA4 in four types of plant samples, which is, to the best of our knowledge, the first report for the quantification of the activity of endogenous GA3-oxidase in plant. Taken together, the method developed here provides a good solution for the evaluation of endogenous GA3-oxidase activity in plant, which may promote the in-depth study of the growth regulation mechanism governed by GAs in plant physiology. PMID:23922762

Chen, Ming-Luan; Su, Xin; Xiong, Wei; Liu, Jiu-Feng; Wu, Yan; Feng, Yu-Qi; Yuan, Bi-Feng

2013-01-01

268

A study on the transport process in gas diffusion layer of proton exchange membrane fuel cells  

NASA Astrophysics Data System (ADS)

Gas diffusion layer (GDL) plays a great important role in proton exchange membrane fuel cell (PEMFC). Water transport mechanism in GDL is still not clear. In the present study, an ex-situ transparent setup is built to visualize the transport phenomena and to measure the threshold pressure of water in GDL at different temperatures. It is found that the relationship between the breakthrough pressure and the temperature is nearly linear (i.e. the pressure decreases linearly with the increase of temperature). To avoid the problems faced by the continuum models, the pore network model is developed to simulate the liquid water transport through the carbon paper. A uniform pressure boundary condition is used in simulation and the results are similar to the ones obtained in the experiment. The reason is that the contact angle and surface tension coefficient of water in GDLs change accordingly with the change of temperature.

Tan, Zetao; Jia, Li; Zhang, Zhuqian

2011-10-01

269

Pt loaded carbon aerogel catalyst for catalytic exchange reactions between water and hydrogen gas  

NASA Astrophysics Data System (ADS)

We report development and characterization of platinum doped carbon aerogel catalyst for catalytic exchange reactions between water and hydrogen gas. The carbon aerogel with uniformly dispersed platinum nanoparticles was prepared by adding platinum precursor during the sol-gel process. Thereafter colloidal PTFE was mixed with the platinum doped carbon aerogel powder and coated on Dixon rings to obtain hydrophobic catalyst with required mechanical strength. Detailed studies have been carried out to observe the effect of physical characteristics of the catalyst powder (surface area and pore size of aerogels, Pt cluster size and its valence state etc) and the different coating parameters (PTFE to Pt-CA ratio and Pt loading on Dixon ring) on volume transfer rate (Ky.a) for H/D reaction. Ky.a values of ~0.8 m3 (STP).s-1. m-3 were obtained for Pt loading of 7% and Pt cluster size of 3 nm at atmospheric pressure.

Singh, Rashmi; Singh, Ashish; Kohli, D. K.; Singh, M. K.; Gupta, P. K.

2013-06-01

270

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

NASA Astrophysics Data System (ADS)

The hypothesis that predawn midlatitude storms are triggered by a soil humidification process is examined. A freeze/thaw model of the process is evaluated in the Viking Gas Exchange experiments conducted on Mars. The humidification-driven desorption and desiccation state of Martian soil samples are analyzed. The periodic humidification of equatorial regolith soil is studied in terms of pore space pressure during desorption events and soil diffusivity; the thermal properties of the regolith surface layer are modeled using the program of Clifford (1984). Consideration is given to the diurnal and seasonal cycles of the humidification process, the permanent, low-albedo features in the midlatitudes, and the production of H2SO4 and HCl aerosols.

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

1986-10-01

271

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

272

Ventilation-perfusion heterogeneity and gas exchange variables in acute pulmonary embolism evaluated by two different computerized techniques.  

PubMed

The mechanisms by which the disturbances of gas exchange develop in human pulmonary embolism are unknown. We investigated whether the inequality of ventilation-perfusion ratio is associated with the abnormalities of pulmonary gas exchange as evaluated by two different computerized techniques. We measured the alveolar to arterial gradients of oxygen and carbon dioxide by means of a computer based system with a mass spectrometer and the ventilation-perfusion distributions by the multiple inert gas technique in 5 patients with acute pulmonary embolism. In these subjects there was a marked ventilation-perfusion inhomogeneity, as detected from inert gases and this finding was in agreement with the impairment of the alveolar to arterial gradients and of their derived indexes. Consideration on the responsible mechanisms for the disturbances of gas exchange are also reported. In conclusion these two computerized techniques provide a useful assessment of the ventilation-perfusion relationships in order to explain the disturbances of gas exchange in critically ill patients. PMID:3071566

Prediletto, R; Formichi, B; Begliomini, E; Fornai, E; Viegi, G; Ruschi, S; Paoletti, P; Giannella, A N; Santolicandro, A; Giuntini, C

1988-01-01

273

Continuously Infusing Hyperpolarized 129Xe into Flowing Aqueous Solutions Using Hydrophobic Gas Exchange Membranes  

PubMed Central

Hyperpolarized (HP) 129Xe yields high signal intensities in magnetic resonance (MR) and, through its large chemical shift range of ?300 ppm, provides detailed information about the local chemical environment. To exploit these properties in aqueous solutions and living tissues requires the development of methods for efficiently dissolving HP 129Xe over an extended time period. To this end, we have used commercially available gas exchange modules to continuously infuse concentrated HP 129Xe into flowing liquids, including rat whole blood, for periods as long as one hour, and have demonstrated the feasibility of dissolved-phase MR imaging with sub-millimeter resolution within minutes. These modules, which exchange gases using hydrophobic microporous polymer membranes, are compatible with a variety of liquids and are suitable for infusing HP 129Xe into the bloodstream in vivo. Additionally, we have developed a detailed mathematical model of the infused HP 129Xe signal dynamics that should be useful in designing improved infusion systems that yield even higher dissolved HP 129Xe signal intensities.

Cleveland, Zackary I.; Moller, Harald E.; Hedlund, Laurence W.; Driehuys, Bastiaan

2009-01-01

274

Glyphosate effects on carbon assimilation and gas exchange in sugar beet leaves.  

PubMed

The mechanism responsible for the inhibition of net carbon exchange (NCE) which was reported previously (DR Geiger et al. 1986 Plant Physiol 82: 468-472) was investigated by applying glyphosate [N-(phosphonomethyl)glycine] to exporting leaves of sugar beet (Beta vulgaris L.). Leaf internal CO(2) concentration (C(i)) remained constant despite decreases in stomatal conductance and NCE following glyphosate treatment, indicating that the cause of the inhibition was a slowing of carbon assimilation rather than decreased conductance of CO(2). Throughout a range of CO(2) concentrations, NCE rate at a given C(i) declined gradually, with the time-series of response curves remaining parallel. Gas exchange measurements revealed that disruption of chloroplast carbon metabolism was an early and important factor in mediating these glyphosate effects, perhaps by slowing the rate of ribulose bisphosphate regeneration. An increase in the CO(2) compensation point accompanied the decrease in NCE and this increase was hastened by stepwise lowering of the ambient CO(2) concentration. Eventually the CO(2) compensation point approached the CO(2) level of air and the difference between internal and external CO(2) concentrations decreased. In control and in glyphosate-treated plants, both carbon assimilation and photorespiration at atmospheric CO(2) level were inhibited to a similar extent of air level of O(2). Maintaining leaves in low O(2) concentration did not prevent the decline in NCE rate. PMID:16665703

Geiger, D R; Tucci, M A; Serviates, J C

1987-10-01

275

Gas exchange of two CAM species of the genus Cissus (vitaceae) differing in morphological features.  

PubMed

Pattern and magnitude of stem gas exchange were studied under controlled conditions on two CAM species of the genus Cissus differing in morphological features. In the cactus-like liana Cissus quadrangularis, at water vapour deficit of the air (VPD) lower than 400 mPa Pa(-1) during daytime, under 24/16°C and 27/16°C temperature regime, CO2 uptake occurred during daytime and nighttime but night fixation was responsible for 74 and 77% respectively of the CO2 fixed during the whole diurnal cycle; the contribution of night fixation increased up to 84% at VPD of 590 mPa Pa(-1) under 27/15°C. In Cissus sp., a slightly succulent xerophytic liana with mesophytic deciduous leaves, at 27°C day temperature and VPD of 520-540 mPa Pa(-1), under both 12 and 16°C night temperature, CO2 uptake occurred exclusively during the night; however at lower day temperatures (18-20°C) and lower VPD (169-269 mPa Pa(-1)) substantial CO2 uptake was observed in the light. Transpiration was higher in Cissus sp. than in Cissus quadrangularis under all of the conditions applied; moreover night transpiration in Cissus sp. contributed more to total day transpiration as compared with Cissus quadrangularis. The results support the opinion that the nocturnal gas exchange has a preeminent role in Cissus sp. as compared with Cissus quadrangularis. Indeed under conditions which enhance evaporative demand even well-watered plants of Cissus sp. resort totally to night fixation. In contrast Cissus quadrangularis which shows a larger resistance to water loss and possesses an abundant water storing parenchyma as compared with Cissus sp. resorts totally to night CO2 fixation only under drought stress. PMID:24435781

De Santo, A V; Fioretto, A; Bartoli, G; Alfani, A

1987-01-01

276

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.

Olszyk, David M.; Tingey, David T.

1986-01-01

277

C3-C 4 intermediate photosynthetic characteristics of cassava (Manihot esculenta Crantz) : I. Gas exchange.  

PubMed

The gas exchange characteristics of cassava were compared with one C3 species, common bean, and two C4 species, maize and amaranthus. Cassava leaf photorespiration, about 12% of maximum net photosynthesis in normal air, and the CO2 release in CO2-free air under intense light were lower than the values typically reported for C3 species. The CO2 compensation point of whole leaves (25 cm(3) CO2m(-3)) was intermediate between C3 and C4 species values.Gas exchange was restricted to either the upper or lower surface of amphistomatous leaves by covering one side of the leaf with silicone grease. The CO2 compensation point of the upper leaf surface was less than 6 cm(3) CO2m(-3) and the CO2 release into CO2-free air in the light was essentially zero. On the lower leaf surface considerable CO2 release occurred in both the light and the dark.The hypothesis presented to explain these results is the existence of an efficient CO2 recycling mechanism in the palisade layer in the upper half of the leaf. In the light of recent data (presented in the second paper of this series) indicating that cassava produces C4 acids as primary products of photosynthesis, it is proposed that this hypothesis is consistent with the possible existence of the C4 photosynthetic pathway in the palisade layer of cassava leaves.The results and hypothesis are discussed in relation to the crop's adaptation to the environmental conditions where it is normally grown. The implications of variation in anatomical features such as stomatal distribution on both surfaces of the leaf are analyzed with a view to enhancing the potential productivity of cassava under stress conditions. PMID:24435689

El-Sharkawy, M A; Cock, J H

1987-01-01

278

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

279

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

280

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

Microsoft Academic Search

A vertically oriented solid-to-gas direct-contact heat exchanger (DCHX) has been proposed for heat recovery in high temperature plants that process finely divided solids. The flows are countercurrent, with the inlet gas flow entering on the centerline and swirling strongly. Swirling enhances heat transfer and centrifuges the solid particles from the center to the wall in order to minimize entrainment and

K. J. Bell; B. Arman

1991-01-01

281

ANALYSIS OF A GAS-PARTICLE DIRECT-CONTACT HEAT EXCHANGER WITH TWO-PHASE RADIATION EFFECT  

Microsoft Academic Search

A direct-contact heat exchange using particle-suspended gas as a heat transfer medium is analyzed with an extended emphasis on the radiation, i.e., considering the radiation by both gas and particles. While the Runge-Kutta method is used for a numerical analysis of the momentum and energy equations, the finite volume method is utilized to solve the radiative transfer equation. The present

Joe Hyun Park; Seung Wook Back; Se Jin Kwon

1998-01-01

282

Technical review of DOE activities in the eastern gas shales  

Microsoft Academic Search

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

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

1980-01-01

283

Composition change of uranium perchlorates with organic ligands upon mechanochemical activation of exchange processes  

NASA Astrophysics Data System (ADS)

Results of studies on the effect of mechanochemical activation of ligand exchange processes in uranyl perchlorate-dimethylsulfoxide are presented. Spectroscopic data show that mechanical activation of the exchange process in this system results in the replacement of H2O in the first coordination sphere of uranyl UO{2/2+} by DMSO to form nanocrystals with a defined ligand sphere. Possible factors governing the noted features are considered.

Zazhogin, A. P.; Zazhogin, A. A.; Komyak, A. I.; Umreiko, D. S.

2008-03-01

284

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

285

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.

286

Air-water gas exchange of organochlorine compounds in Lake Baikal, Russia  

SciTech Connect

Air and surface water samples were collected at Lake Baikal, Russia, during June 1991 to determine concentrations of organochlorine pesticides and polychlorinated biphenyl (PCB) congeners. These data were combined with Henry`s law constants to estimate the gas flux rate across the air-water interface of each compound class. Air samples were collected at Lake Baikal and from nearby Irkutsk. Water samples were collected from three mid-lake stations and at the mouth of two major tributaries. Average air concentrations of chlorinated bornanes (14 pg m{sup -3}), chlordanes (4.9 pg m{sup -3}), and hexachlorobenzene (HCB) (194 pg m{sup -3}) were similar to global backgound of Arctic levels. However, air concentrations of hexachlorocyclohexanes (HCHs), DDTs, and PCBs were closer to those observed in the Great Lakes region. Significantly higher levels of these three compound classes in air over Irkutsk suggests that regional atmospheric transport and deposition may be an important source of these persistent compounds to Lake Baikal. Air-water gas exchange calculations resulted in net depositional flux values for {alpha}-HCH, {gamma}-HCH, DDTs, and chlorinated bornanes at 112, 23, 3.6, and 2.4 ng m{sup -2} d{sup -1}, respectively. The total net flux of 22 PCB congeners, chlordanes, and HCB was from water to air (volatilization) at 47, 1.8, and 32 ng m{sup -2} d{sup -1}, respectively. 50 refs., 7 figs., 5 tabs.

McConnell, L.L. [USDA, Beltsville, MD (United States)] [USDA, Beltsville, MD (United States); Kucklick, J.R. [National Marine Fisheries Service, Charleston, SC (United States)] [National Marine Fisheries Service, Charleston, SC (United States); Bidleman, T.F. [Univ. of South Carolina, Columbia, SC (United States)] [Univ. of South Carolina, Columbia, SC (United States); Ivanov, G.P. [Limnological Inst., Irkutsk (Russian Federation)] [Limnological Inst., Irkutsk (Russian Federation); Chernyak, S.M. [Inst. of Fisheries, Moscow (Russian Federation)] [Inst. of Fisheries, Moscow (Russian Federation)

1996-10-01

287

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

288

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

289

The probiotic Lactobacillus acidophilus stimulates chloride/hydroxyl exchange activity in human intestinal epithelial cells.  

PubMed

Probiotics are viable nonpathogenic microorganisms that are considered to confer health benefits to the host. Recent studies indicated that some Lactobacillus species function as probiotics and have been used as alternative treatments for diarrhea, which occurs due to increased secretion, decreased absorption, or both. However, the direct effects of probiotics on intestinal electrolyte absorption are not known. Therefore, we examined the effects of Lactobacillus on luminal chloride/hydroxyl (Cl(-)/OH(-)) exchange activity in human intestinal epithelial cells. Postconfluent Caco-2 cells were treated with the Lactobacillus species Lactobacillus acidophilus (LA), Lactobacillus casei, Lactobacillus plantarum, or Lactobacillus rhamnosus (LR) for 3 h at a multiplicity of infection of 50. Cl(-)/OH(-) exchange activity was measured as 4,4'-diisothiocyanostilbene-2, 2'-disulfonic acid-sensitive (36)Cl uptake in base-loaded cells. Treatment with live, but not heat-killed, LA and LR significantly increased Cl(-)/OH(-) exchange activity (approximately 50%), whereas other species were ineffective. Similarly, the conditioned medium (supernatant) of live LA increased Cl(-)/OH(-) exchange. The ability of LA or its conditioned culture medium to enhance Cl(-)/OH(-) exchange activity was blocked by PI-3 kinase inhibition but was unaffected by inhibition of mitogen-activated protein kinases. Corresponding to the increased Cl(-)/OH(-) exchange activity, LA treatment increased the surface expression of the apical anion exchanger, SLC26A3 [Down Regulated in Adenoma (DRA)]. The increased DRA membrane localization might contribute to the increased Cl(-) absorption by LA. Our results suggest that LA secretes soluble effector molecule(s) into the culture medium that stimulate apical Cl(-)/OH(-) exchange activity via phosphatidylinositol-3 kinase mediated mechanism. PMID:18567760

Borthakur, Alip; Gill, Ravinder K; Tyagi, Sangeeta; Koutsouris, Athanasia; Alrefai, Waddah A; Hecht, Gail A; Ramaswamy, Krishnamurthy; Dudeja, Pradeep K

2008-07-01

290

Photosynthetic gas exchange, chlorophyll fluorescence and some associated metabolic changes in cowpea ( Vigna unguiculata) during water stress and recovery  

Microsoft Academic Search

The responses of photosynthetic gas exchange and chlorophyll fluorescence along with changes in carbohydrate and proline levels were studied in cowpea (Vigna unguiculata) during water stress and recovery. Three experiments were conducted under greenhouse and laboratory conditions. Decreased CO2 assimilation rates during water stress were largely dependent on stomatal closure, which reduced available internal CO2 and restricted water loss through

R. P. Souza; E. C. Machado; J. A. B. Silva; A. M. M. A. Lagôa; J. A. G. Silveira

2004-01-01

291

Growth, gas exchange, and root respiration of Quercus rubra seedlings exposed to low root zone temperatures in solution culture  

Microsoft Academic Search

Spring planting is standard operational practice in the Central Hardwood Region, though little is known about potential impacts of low root temperature (RT) common during spring on establishment success of temperate deciduous forest tree species. The effects of low RT on growth, gas exchange, and root respiration following winter dormancy were studied in 1-year-old northern red oak (Quercus rubra L.)

Kent G. Apostol; Douglass F. Jacobs; Barrett C. Wilson; K. Francis Salifu; R. Kasten Dumroese

2007-01-01

292

The effects of pressurization rate on breathing pattern, work of breathing, gas exchange and patient comfort in pressure support ventilation  

Microsoft Academic Search

The aim of this study was to investigate the effects of different pressurization rates during pressure support ventilation on breathing pattern, work of breathing, gas exchange and patient comfort in patients with acute lung injury. The pressurization rate modifies the initial pressure ramp by changing the initial peak flow rate: the increase in pressurization rate is associated with a decrease

D. Chiumello; P. Pelosi; M. Croci; L. M. Bigatello; L. Gattinoni

2001-01-01

293

Effects of short term high frequency negative pressure ventilation on gas exchange using the Hayek oscillator in normal subjects  

Microsoft Academic Search

BACKGROUND--The Hayek oscillator is a negative pressure cuirass that can operate at a range of frequencies to provide ventilation, and is a technique which could potentially be used on a general ward. This study examined the effect of different frequencies and different ranges of inspiratory and expiratory pressures on gas exchange, respiratory rate, and blood pressure in normal subjects. METHODS--Eight

F M Hardinge; R J Davies; J R Stradling

1995-01-01

294

Growth and gas exchange responses of Brazilian pepper ( Schinus terebinthifolius ) and native South Florida species to salinity  

Microsoft Academic Search

Schinus terebinthifolius Raddi ( Schinus) is an invasive exotic species widely found in disturbed and native communities of Florida. This species has been shown to displace native species as well as alter community structure and function. The purpose of this study was to determine if the growth and gas exchange patterns of Schinus, under differing salinity conditions, were different from

Sharon M. L. Ewe; Leonel da Silveira Lobo Sternberg

2005-01-01

295

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

296

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, V?O2max: 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

297

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

298

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

SciTech Connect

In conventional flue gas heat recovery systems, the fouling by fly ashes and the related problems such as corrosion and cleaning are known to be major drawbacks. To overcome these problems, a single-riser no-distributor-fluidized-bed heat exchanger is devised and studied. Fouling and cleaning tests are performed for a uniquely designed fluidized bed-type heat exchanger to demonstrate the effect of particles on the fouling reduction and heat transfer enhancement. The tested heat exchanger model (1 m high and 54 mm internal diameter) is a gas-to-water type and composed of a main vertical tube and four auxiliary tubes through which particles circulate and transfer heat. Through the present study, the fouling on the heat transfer surface could successfully be simulated by controlling air-to-fuel ratios rather than introducing particles through an external feeder, which produced soft deposit layers with 1 to 1.5 mm thickness on the inside pipe wall. Flue gas temperature at the inlet of heat exchanger was maintained at 450{sup o}C at the gas volume rate of 0.738 to 0.768 CMM (0.0123 to 0.0128 m{sup 3}/sec). From the analyses of the measured data, heat transfer performances of the heat exchanger before and after fouling and with and without particles were evaluated. Results showed that soft deposits were easily removed by introducing glass bead particles, and also heat transfer performance increased two times by the particle circulation. In addition, it was found that this type of heat exchanger had high potential to recover heat of waste gases from furnaces, boilers, and incinerators effectively and to reduce fouling related problems.

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

2008-07-01

299

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

PubMed

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

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

2013-04-01

300

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

Microsoft Academic Search

The presence of gaseous impurities in the filling gas of a fuel pin is detriental to the thermal performance of a nuclear reactor fuel. The composition of the filling gas does not remain constant throughout the life of the fuel pin. The gas exchange phenomena that occur between the cover gas and impurity gases affect the fuel performance more severely

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

1995-01-01

301

Pulmonary Perfusion and Xenon Gas Exchange in Rats: MR Imaging with Intravenous Injection of Hyperpolarized 129Xe1  

PubMed Central

Purpose: To develop and demonstrate a method for regional evaluation of pulmonary perfusion and gas exchange based on intravenous injection of hyperpolarized xenon 129 (129Xe) and subsequent magnetic resonance (MR) imaging of the gas-phase 129Xe emerging in the alveolar airspaces. Materials and Methods: Five Fischer 344 rats that weighed 200—425 g were prepared for imaging according to an institutional animal care and use committee—approved protocol. Rats were ventilated, and a 3-F catheter was placed in the jugular (n = 1) or a 24-gauge catheter in the tail (n = 4) vein. Imaging and spectroscopy of gas-phase 129Xe were performed after injecting 5 mL of half-normal saline saturated with 129Xe hyperpolarized to 12%. Corresponding ventilation images were obtained during conventional inhalation delivery of hyperpolarized 129Xe. Results: Injections of 129Xe-saturated saline were well tolerated and produced a strong gas-phase 129Xe signal in the airspaces that resulted from 129Xe transport through the pulmonary circulation and diffusion across the blood-gas barrier. After a single injection, the emerging 129Xe gas could be detected separately from 129Xe remaining in the blood and was imaged with an in-plane resolution of 1 × 1 mm and a signal-to-noise ratio of 25. Images in one rat revealed a matched ventilation-perfusion deficit, while images in another rat showed that xenon gas exchange was temporarily impaired after saline overload, with recovery of function 1 hour later. Conclusion: MR imaging of gas-phase 129Xe emerging in the pulmonary airspaces after intravenous injection has the potential to become a sensitive and minimally invasive new tool for regional evaluation of pulmonary perfusion and gas exchange. Supplemental material: http://radiology.rsnajnls.org/cgi/content/full/2513081550/DC1

Driehuys, Bastiaan; Moller, Harald E.; Cleveland, Zackary I.; Pollaro, James; Hedlund, Laurence W.

2009-01-01

302

Gas exchange measurements, what can they tell us about the underlying limitations to photosynthesis? Procedures and sources of error.  

PubMed

The principles, equipment and procedures for measuring leaf and canopy gas exchange have been described previously as has chlorophyll fluorescence. Simultaneous measurement of the responses of leaf gas exchange and modulated chlorophyll fluorescence to light and CO2 concentration now provide a means to determine a wide range of key biochemical and biophysical limitations on photo synthesis in vivo. Here the mathematical frameworks and practical procedures for determining these parameters in vivo are consolidated. Leaf CO2 uptake (A) versus intercellular CO2 concentration (Ci) curves may now be routinely obtained from commercial gas exchange systems. The potential pitfalls, and means to avoid these, are examined. Calculation of in vivo maximum rates of ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase (Rubisco) carboxylation (Vc,max), electron transport driving regeneration of RuBP (Jmax), and triose-phosphate utilization (VTPU) are explained; these three parameters are now widely assumed to represent the major limitations to light-saturated photosynthesis. Precision in determining these in intact leaves is improved by the simultaneous measurement of electron transport via modulated chlorophyll fluorescence. The A/Ci response also provides a simple practical method for quantifying the limitation that stomata impose on CO2 assimilation. Determining the rate of photorespiratory release of oxygen (Rl) has previously only been possible by isotopic methods, now, by combining gas exchange and fluorescence measurements, Rl may be determined simply and routinely in the field. The physical diffusion of CO2 from the intercellular air space to the site of Rubisco in C3 leaves has long been suspected of being a limitation on photosynthesis, but it has commonly been ignored because of the lack of a practical method for its determination. Again combining gas exchange and fluorescence provides a means to determine mesophyll conductance. This method is described and provides insights into the magnitude and basis of this limitation. PMID:14512377

Long, S P; Bernacchi, C J

2003-11-01

303

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

304

Kombiniertes Gas- und Dampfturbinenkraftwerk mit Kohlevergasung. Komponentenentwicklungsprogramm fuer Rohgas-/Reingaswaermetauscher. Schlussbericht. (Combined-cycle power plant with integrated coal-gasification. Development program for raw gas/clean gas heat exchanger. Final report).  

National Technical Information Service (NTIS)

Within the scope of a development program for components of a combined cycle power plant with integrated coal gasification the operational behaviour of a raw gas - clean gas heat exchanger (RRWT), mounted in the PRENFLO-testing plant, was subjected to tho...

W. Emsperger W. Ganzer J. Kellner

1990-01-01

305

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

PubMed Central

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

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

2013-01-01

306

Measurements of Physical and Gas Exchanges between the Atmosphere and Surface at the Tiksi Hydrometeorological Observatory  

NASA Astrophysics Data System (ADS)

In recent years a number of Arctic stations have installed micro-meteorological towers in recognition of the need to explicitly quantify the detailed exchanges between the surface and the atmosphere. One of the newer installations is a 20 meter tower in Tiksi, Russia that is located at 71.58N, 128.92E in the Russian Far East. The Tiksi tower is equipped with temperature, humidity and wind sensors at several levels (allowing the calculation of turbulent heat fluxes and fine scale characterization of the near-surface boundary layer) and H2O/CO2 sensors, It is located in near proximity to measurements of incoming and outgoing solar radiation (allowing energy balance calculations), and CH4 sensors, surface O3 measurements (allowing detection of ozone depletion events), and ancillary measurements of snow depth and permafrost active layer temperature profiles. An integrated analysis will look at the variability of these physical and chemical exchanges and variations over one annual cycle with an emphasis on detecting connections and linkages. This network of measurements supports the International Arctic Systems for Observing the Atmosphere (www.iasoa.org) and Global Cryosphere Watch (http://globalcryospherewatch.org/)

Uttal, T.; Grachev, A. A.; Makshtas, A. P.; Repina, I.; Persson, O. P.; Laurila, T. J.; Crepinsek, S.

2013-12-01

307

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

308

Structural and spatial determinants regulating TC21 activation by RasGRF family nucleotide exchange factors.  

PubMed

RasGRF family guanine nucleotide exchange factors (GEFs) promote guanosine diphosphate (GDP)/guanosine triphosphate (GTP) exchange on several Ras GTPases, including H-Ras and TC21. Although the mechanisms controlling RasGRF function as an H-Ras exchange factor are relatively well characterized, little is known about how TC21 activation is regulated. Here, we have studied the structural and spatial requirements involved in RasGRF 1/2 exchange activity on TC21. We show that RasGRF GEFs can activate TC21 in all of its sublocalizations except at the Golgi complex. We also demonstrate that TC21 susceptibility to activation by RasGRF GEFs depends on its posttranslational modifications: farnesylated TC21 can be activated by both RasGRF1 and RasGRF2, whereas geranylgeranylated TC21 is unresponsive to RasGRF2. Importantly, we show that RasGRF GEFs ability to catalyze exchange on farnesylated TC21 resides in its pleckstrin homology 1 domain, by a mechanism independent of localization and of its ability to associate to membranes. Finally, our data indicate that Cdc42-GDP can inhibit TC21 activation by RasGRF GEFs, demonstrating that Cdc42 negatively affects the functions of RasGRF GEFs irrespective of the GTPase being targeted. PMID:19692568

Calvo, Fernando; Crespo, Piero

2009-10-01

309

[Changes in pulmonary gas exchange in chronic obstructive bronchopneumopathies and their modifications induced by therapy].  

PubMed

In order to assess the mechanisms of gas exchange disturbances (i.e. to what extent shunting and diffusion impairment contribute to hypoxemia) in chronic obstructive pulmonary disease (COPD) and respiratory failure, ventilation-perfusion relationships (V/Q) by the multiple inert gas elimination technique were obtained in 16 patients with respiratory failure breakthrough. In 6 instances the study was repeated after long-term treatment with the aim to analyze V/Q changes after therapy. Initially, patients showed severe hypoxemia and hypercapnia and they presented signs of marked bronchoconstriction. A great dispersion of V and Q distribution was present as indicated by the marked increase of the second moment of V and Q distributions. Interestingly, few patients presented a unimodal distribution of both V and Q, whereas most-patients had bimodal distributions where the ventilation was distributed in a mode such that high V/Q areas were present between 10 and 100 of V/Q ratio and blood flow was displaced leftward or toward lower V/Q values. No correlations were found between V and Q distribution and clinical types A or B of COPD. Significant relationships were found between measured and calculated arterial PO2 (r = 0.90, p less than 0.001) and between measured PO2 and the sum of the fractional perfusion to regions with V/Q ratio less than 0.1, suggesting that V/Q inequality and shunting, instead of the impairment of diffusion equilibration, can account for all the hypoxemia. Finally, the reduced inhomogeneity of ventilation after treatment, especially in the fraction located in high V/Q regions is mostly related to some functional and reversible damages in COPD. PMID:2739533

Prediletto, R; Formichi, B; Bertolaccini, P

1989-01-01

310

Facile oxygen exchange by cobalt cluster oxide ions with water- sup 18 O in the gas phase  

SciTech Connect

In an attempt to understand dissociative chemisorption on transition-metal clusters, the potential of water-{sup 18}O was investigated as a probe of metal cluster oxide character since oxygen exchange with water has been observed on metal oxide surfaces. Observations of facile oxygen exchange suggested that water-{sup 18}O may be employed as a sensitive probe for oxide character in transition-metal clusters in complexes. This technique should prove to be a powerful and nondestructive method for probing the structure of complex transition-metal cluster ions in the gas phase. 30 refs.

Klassen, J.J.; Jacobson, D.B. (North Dakota State Univ., Fargo (USA))

1989-05-31

311

What can be Learned from X-ray Spectroscopy Concerning Hot Gas in Local Bubble and Charge Exchange Processes?  

NASA Technical Reports Server (NTRS)

What can be learned from x-ray spectroscopy in observing hot gas in local bubble and charge exchange processes depends on spectral resolution, instrumental grasp, instrumental energy band, signal-to-nose, field of view, angular resolution and observatory location. Early attempts at x-ray spectroscopy include ROSAT; more recently, astronomers have used diffuse x-ray spectrometers, XMM Newton, sounding rocket calorimeters, and Suzaku. Future observations are expected with calorimeters on the Spectrum Roentgen Gamma mission, and the Solar Wind Charge Exchange (SWCX). The Geospheric SWCX may provide remote sensing of the solar wind and magnetosheath and remote observations of solar CMEs moving outward from the sun.

Snowden, Steve

2007-01-01

312

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

PubMed Central

We investigated the role of xylem cavitation, plant hydraulic conductance, and root pressure in the response of rice (Oryza sativa) gas exchange to water stress. In the field (Philippines), the percentage loss of xylem conductivity (PLC) from cavitation exceeded 60% in leaves even in watered controls. The PLC versus leaf water potential relationship indicated diurnal refilling of cavitated xylem. The leaf water potential causing 50 PLC (P50) was –1.6 MPa and did not differ between upland versus lowland rice varieties. Greenhouse-grown varieties (Utah) were more resistant to cavitation with a 50 PLC of –1.9 MPa but also showed no difference between varieties. Six-day droughts caused concomitant reductions in leaf-specific photosynthetic rate, leaf diffusive conductance, and soil-leaf hydraulic conductance that were associated with cavitation-inducing water potentials and the disappearance of nightly root pressure. The return of root pressure after drought was associated with the complete recovery of leaf diffusive conductance, leaf-specific photosynthetic rate, and soil-leaf hydraulic conductance. Root pressure after the 6-d drought (61.2 ± 8.8 kPa) was stimulated 7-fold compared with well-watered plants before drought (8.5 ± 3.8 kPa). The results indicate: (a) that xylem cavitation plays a major role in the reduction of plant hydraulic conductance during drought, and (b) that rice can readily reverse cavitation, possibly aided by nocturnal root pressure.

Stiller, Volker; Lafitte, H. Renee; Sperry, John S.

2003-01-01

313

Plant size, not age, regulates growth and gas exchange in grafted Scots pine trees.  

PubMed

We studied the effect of scion donor-tree age on the physiology and growth of 6- to 7-year-old grafted Scots pine (Pinus sylvestris L.) trees (4 and 5 years after grafting). Physiological measurements included photosynthethetic rate, stomatal conductance, transpiration, whole plant hydraulic conductance, needle nitrogen concentration and carbon isotope composition. Growth measurements included total and component biomasses, relative growth rates and growth efficiency. Scion donor trees ranged in age from 36 to 269 years at the time of grafting. Hydraulic conductance was measured gravimetrically, applying the Ohm's law analogy, and directly, with a high-pressure flow meter. We found no effect of scion donor-tree age on any of the variables measured. There was, however, great variation within scion donor-tree age groups, which was related to the size of the grafted trees. Differences in size may have been caused by variable initial grafting success, but there was no indication that grafting success and age were related. At the stem level, hydraulic conductance scaled with total leaf area so that total conductance per unit leaf area did not vary with crown size. However, leaf specific hydraulic conductance (gravimetric), transpiration, photosynthesis and stomatal conductance declined with increasing total tree leaf area and needle width. We hypothesize that needle width is inversely related to mesophyll conductance. We conclude that canopy and needle size and not scion donor-tree age determined gas exchange in our grafted trees. PMID:17169908

Vanderklein, D; Martínez-Vilalta, J; Lee, S; Mencuccini, M

2007-01-01

314

The importance of cutaneous gas exchange during aerial and aquatic respiration in galaxiids.  

PubMed

The Canterbury mudfish Neochanna burrowsius was found to be a pseudo-aestivating galaxiid with a low metabolic rate and significant cutaneous oxygen uptake (c. 43%) in both air and water. Another galaxiid, inanga Galaxias maculatus, had a higher metabolic rate in both media but the proportion of oxygen uptake met by cutaneous respiration rose significantly from 38 to 63% when the fish were exposed to air. Besides its important role in oxygen uptake, the skin of both species also contributed significantly to excretion of carbon dioxide in air, indicating the critical role of the integument as a respiratory tissue. In air, G. maculatus may increase cutaneous gas exchange to meet metabolic demands owing to the reduced utility of the gills, but as emersed G. maculatus were only able to maintain metabolic rates at c. 67% of that measured in water, this strategy probably only permits short-term survival. By contrast, the low and unchanging metabolic rate in water and air in N. burrowsius is a feature that may facilitate tolerance of long periods of emersion in the desiccating environments they inhabit. PMID:24417441

Urbina, M A; Meredith, A S; Glover, C N; Forster, M E

2014-03-01

315

Decline of hexachlorocyclohexane in the Arctic atmosphere and reversal of air-sea gas exchange  

NASA Astrophysics Data System (ADS)

Hexachlorocyclohexanes (HCHs) are the most abundant organochlorine pesticides in the arctic atmosphere and ocean surface water. A compilation of measurements made between 1979-93 from stations in the Canadian and Norwegian Arctic and from cruises in the Bering and Chukchi seas indicates that atmospheric concentrations of ?-HCH have declined significantly (p < 0.01), with a time for 50% decrease of about 4 y in summer-fall and 6 y in winter-spring. The 1992-93 levels of about 100 pg m-3 are 2-4 fold lower than values in the mid-1980s. The trend in ?-HCH is less pronounced, but a decrease is also suggested from measurements in the Canadian Arctic and the Bering-Chukchi seas. HCHs in ocean surface water have remained relatively constant since the early 1980s. The decline in atmospheric ?-HCH has reversed the net direction of air-sea gas exchange to the point where some northern waters are now sources of the pesticide to the atmosphere instead of sinks.

Bidleman, T. F.; Jantunen, L. M.; Falconer, R. L.; Barrie, L. A.; Fellin, P.

1995-02-01

316

Advantages of the gas-exchange approach to microbiological studies. Memorandum report 1983-1985  

SciTech Connect

Studies of the effects of various chemical or physical stimuli on the growth rates of microorganisms generally involve some measure of biomass. In the case of algae, one might measure the cell number, the chlorophyll concentration, the fluorescence, or the wet weight of the culture as a function of time. Each such measurement requires a sampling of the culture which could be a disturbing factor in the system being measured. Another disadvantage of these traditional measurements is that the times required for significant change to take place in the culture might be hours or days; furthermore, growth rate measurements calculated from the data must be based on the assumption that during the time between measurements the growth rate was constant. This report describes another approach to the problem. It consists simply of monitoring the O/sub 2/ or CO/sub 2/ concentration of an air stream passing through the system (the gas exchange method), and it has several distinct advantages: 1) there is no need to take samples of the culture, 2) each measurement is a rate measurement and indicates the performance of the culture at that very moment, and 3) transitory changes in growth rates are readily detected. Examples are given of studies made previously with this method at NRL. Also the possible value of these methods in a study of the corrosion susceptibility of alloys is described.

Hannan, P.J.; Jones, D.S.

1986-04-03

317

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.

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

2014-01-01

318

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

319

Study of the Behavior of Inorganic Ion Exchangers in the Treatment of Medium Active Effluents. Pt. 5. The Encapsulation of Inorganic Ion Exchangers in Cement.  

National Technical Information Service (NTIS)

This report describes some results obtained for a generic program of work for the Department of the Environment on the potential application of inorganic ion exchangers for the treatment of medium active effluents. The results from a preliminary investiga...

G. W. Beaven J. E. Cross E. W. Hooper

1988-01-01

320

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

321

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

322

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

323

Influence of understory greenness on trace gas and energy exchange in forested ecosystems  

NASA Astrophysics Data System (ADS)

Forested ecosystems are important sources and sinks of carbon, water, and energy - affecting land surface - atmosphere interactions at multiple scales. Understanding how forested ecosystems will respond to climate change is critical for quantifying how they will feedback with the climate system. Addressing this need is challenging in forested ecosystems because of their complex structure and composition, both vertically and horizontally. Here we highlight the different functioning of the main overstory canopy and the more seasonal understory. Both the overstory and the understory contribute differently to the exchange of carbon, water and energy with the atmosphere. Both eddy covariance measurements and remotely sensed products can provide ecosystem-scale estimates of trace gas and energy flux, but the contribution of the understory to these estimates remains relatively unexplored. In this study, we aim to address the contribution of the understory to ecosystem-scale carbon uptake. Specifically, we ask the following questions: (1) how big is the contribution of the understory to ecosystem carbon uptake?; (2) at what times of year is the understory contribution important?; (3) does the eddy covariance carbon uptake signal (NEE-) reflect the greening up dynamics of the understory?; (4) is the greening up dynamics of the understory captured in our remotely-sensed products?; and (5) can remotely-sensed vegetation products such as MODIS-derived NDVI and EVI accurately reflect ecosystem-scale carbon uptake dynamics? To address these questions, we use three years of eddy covariance data from two similar subalpine mixed-conifer ecosystems within the Jemez River Basin - Santa Catalina Mountain Critical Zone Observatory (JRB-SCM CZO). The mixed-conifer site at the JRB is at roughly 3000 m and has substantial understory, while the mixed-conifer ecosystem of the SCM is at roughly 2500 m has very minimal understory. Within the footprint of the eddy covariance towers at both sites, three time-lapse digital cameras (phenocams) take hourly images of the understory from which a greenness index (Ig) is calculated. We show that daily NEE- and Ig are generally synchronized, suggesting that the understory may substantially contribute to ecosystem-scale carbon uptake. However, while remotely-sensed vegetation indices and Ig are synched at certain times throughout the study period, often they are not. For instance, in 2010 NDVI remains higher for a longer period than does Ig. This suggests that relying solely on remotely-sensed products may lead to an overestimation of carbon sequestration by these ecosystems. We argue the contribution of the understory to ecosystem-scale carbon, water, and energy exchange with the atmosphere is important and therefore critical to understanding how climate change will alter their feedback with the climate system.

Swetish, J.; Papuga, S. A.; Litvak, M. E.; Barron-Gafford, G. A.; Mitra, B.

2012-12-01

324

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

NASA Astrophysics Data System (ADS)

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

Mayo, Michael; Pfeifer, Peter; Gheorghiu, Stefan

2008-03-01

325

Extremely low flow tracheal gas insufflation of helium-oxygen mixture improves gas exchange in a rabbit model of piston-type high-frequency oscillatory ventilation.  

PubMed

OBJECTIVE: The purpose of this study was to show the effects of the tra gas insufflation (TGI) technique on gas exchange using helium-oxygen mixtures during high-frequency oscillatory ventilation (HFOV). We hypothesized that a helium-oxygen mixture delivered into the trachea using the TGI technique (0.3 L/min) would enhance gas exchange during HFOV. METHOD: Three rabbits were prepared and ventilated by HFOV with carrier 70% helium/oxygen or 70% nitrogen/oxygen gas mixture with TGI in a crossover study. Changing the gas mixture from nitrogen70% to helium70% and back was performed three times per animal with constant ventilation parameters. RESULTS: Compared with the nitrogen-oxygen mixture, the helium-oxygen mixture of TGI reduced PaCO2 by 7.6 mmHg (p < 0.01) and improved PaO2 by 14 mmHg (p < 0.01). Amplitude during TGI was significantly lower with the helium-oxygen mixture than with the nitrogen-oxygen mixture (p < 0.01) and did not significantly affect mean airway pressure. CONCLUSION: This study demonstrated that a helium-oxygen mixture delivered into the trachea using the TGI technique would enhance CO2 elimination and improve oxygenation during HFOV. PMID:23566050

Baba, Atsushi; Nakamura, Tomohiko; Aikawa, Tetsuya; Koike, Kenichi

2013-04-01

326

Relationship of water status to vegetative growth and leaf gas exchange of peach (Prunus persica) trees on different rootstocks.  

PubMed

We investigated relationships between tree water status, vegetative growth and leaf gas exchange of peach trees growing on different rootstocks under field conditions. Tree water status was manipulated by partially covering (0, approximately 30 and approximately 60%) the tree canopies on individual days and then evaluating the effects of tree water status on vegetative growth and leaf gas exchange. Early morning stem water potentials were approximately -0.4 MPa for trees in all treatments, but mean midday values ranged from -1.1 to -1.7 MPa depending on rootstock and canopy coverage treatment. Relative shoot extension growth rate, leaf conductance, transpiration rate and net CO2 exchange rate differed significantly among trees in the different rootstocks and canopy coverage treatments. Shoot extension growth rate, leaf conductance, leaf transpiration rate and leaf net CO2 exchange rate were linearly correlated with midday stem water potential. These relationships were independent of the rootstock and canopy coverage treatments, indicating that tree water relations are probably directly involved in the mechanism that imparts vegetative growth control by selected peach rootstocks. PMID:16815835

Solari, Luis I; Johnson, Scott; DeJong, Theodore M

2006-10-01

327

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

Microsoft Academic Search

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

Carles Castell; Jaume Terradas; John D. Tenhunen

1994-01-01

328

Simultaneous analysis of cocaine, benzoylecgonine, methylecgonine, and ecgonine in plasma using an exchange resin and gas chromatography-mass spectrometry  

Microsoft Academic Search

A gas chromatographic-mass spectrometric method is described for the simultaneous analysis of cocaine and the hydrolytic products benzoylecgonine, methylecgonine and ecgonine from plasma (0.25–2 ?g\\/ml). Isopropylecgonine was incorporated as an internal standard. Samples were extracted using a sulfonate cation exchange resin, then derivatized with pentafluoropropionic anhydride and pentafluoropropanol. Analytical separations were on a dimethylsilicone capillary column using a temperature program,

C. C. Okeke; J. E. Wynn; K. S. Patrick

1994-01-01

329

Three-dimensional transient numerical simulation for gas exchange process in a four-stroke motorcycle engine  

Microsoft Academic Search

Three-dimensional transient numerical simulation of gas exchange process in a four-stroke motorcycle engine with a semi-spherical\\u000a combustion chamber with two tilt valves was studied. Combination of the grid re-meshing method and the snapper technique made\\u000a the valves move smoothly. The flow structure and pattern in a complete engine cycle were described in detail. Tumble ratios\\u000a around thex-axis andy-axis were analyzed.

Wang Chun-fa; Chen Guo-hua; Luo Ma-ji; Yang Wan-li

2005-01-01

330

Three-dimensional transient numerical simulation for gas exchange process in a four-stroke motorcycle engine  

Microsoft Academic Search

Three-dimensional transient numerical simulation of gas exchange process in a four-stroke motorcycle engine with a semi-spherical combustion chamber with two tilt valves was studied. Combination of the grid re-meshing method and the snapper technique made the valves move smoothly. The flow structure and pattern in a complete engine cycle were described in detail. Tumble ratios around the x-axis and y-axis

WANG Chun-fa; CHEN Guo-hua; LUO Ma-ji; YANG Wan-li

2005-01-01

331

Study of polyaniline doped with trifluoromethane sulfonic acid in gas-diffusion electrodes for proton-exchange membrane fuel cells  

Microsoft Academic Search

Polytetrafluoroethylene (PTFE)-bonded gas-diffusion electrodes (GDEs), modified with polyaniline as an electron and proton conductor in the catalyst layer, are prepared and evaluated for use in proton-exchange membrane fuel cells (PEMFCs). Polyaniline is coated on the GDE by electropolymerization of aniline and trifluoromethane sulfonic acid as the proton-conductive monomer. The electrodes are characterized by cyclic voltammetry, current–potential measurements, electrochemical impedance spectroscopy,

Hussein Gharibi; Mohammad Zhiani; Ali Akbar Entezami; Rasol Abdullah Mirzaie; Mehdi Kheirmand; Karim Kakaei

2006-01-01

332

Forest Canopy-Atmosphere Gas Exchange Rates in the Tapajos National Forest, Para, Brazil, Determined by Radon222 Measurements  

Microsoft Academic Search

Continuous canopy air and soil-air flux measurements of radon-222 have been combined to quantify canopy-atmosphere gas exchange rates and canopy air residence times in Amazonian old growth and selectively logged forests in the Tapajos National Forest near Santarém, Pará, Brazil, as part of the LBA project led by Brazil. Radon canopy air and soil flux measurements, when fully integrated with

C. S. Martens; T. J. Shay; H. P. Mendlovitz; J. S. Moura; R. L. Lima; I. G. Sampaio; O. L. Moraes; W. S. Woodward; P. M. Crill

2004-01-01

333

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

Microsoft Academic Search

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

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

1990-01-01

334

Limitations of photosynthesis in Phaseolus vulgaris under drought stress: gas exchange, chlorophyll fluorescence and Calvin cycle enzymes  

Microsoft Academic Search

In this article, the effects of drought stress (DS) on gas exchange, chlorophyll (Chl) a fluorescence and Calvin cycle enzymes in Phaseolus vulgaris are evaluated. Three-week-old plants were exposed to DS by receiving only so much water every evening to ensure 30% field\\u000a capacity water content overnight. After three days under these conditions, we observed that DS induced a decline

M. C. Dias; W. Brüggemann

2010-01-01

335

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

336

Use of a combined oxygen and carbon dioxide transcutaneous electrode in the estimation of gas exchange during exercise.  

PubMed Central

BACKGROUND--Accurate and reliable measurement of gas exchange during exercise has traditionally involved arterial cannulation. Non-invasive devices to estimate arterial oxygen (O2) and carbon dioxide (CO2) tensions are now available. A method has been devised and evaluated for measuring gas exchange during exercise with a combined transcutaneous O2 and CO2 electrode. METHODS--Symptom limited exercise tests were carried out in 24 patients reporting effort intolerance and breathlessness. Exercise testing was performed by bicycle ergometry with a specifically designed protocol involving gradual two minute workload increments. Arterial O2 and CO2 tensions were measured at rest and during exercise by direct blood sampling from an indwelling arterial cannula and a combined transcutaneous electrode heated to 45 degrees C. The transcutaneous system was calibrated against values obtained by direct arterial sampling before each test. RESULTS--In all tests the trend of gas exchange measured by the transcutaneous system was true to the trend measured from direct arterial sampling. In the 140 measurements the mean difference between the O2 tensions estimated by direct sampling and the transcutaneous method was 0.08 kPa (0.62 mm Hg, limits of agreement 4.42 and -3.38 mm Hg). The mean difference between the methods for CO2 was 0.02 kPa (0.22 mm Hg, limits of agreement 2.20 and -1.70 mm Hg). There was no morbidity associated with the use of the transcutaneous electrode heated to 45 degrees C. CONCLUSIONS--A combined transcutaneous O2 and CO2 electrode heated to 45 degrees C can be used to provide a reliable estimate of gas exchange during gradual incremental exercise in adults.

Sridhar, M K; Carter, R; Moran, F; Banham, S W

1993-01-01

337

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

338

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

339

Air-water gas exchange and evidence for metabolism of hexachlorocyclohexanes in Resolute Bay, N.W.T  

Microsoft Academic Search

Paired air and water samples were collected at Resolute Bay (74°N, 95°W) in summer 1992 to estimate the direction of gas exchange of hexachlorocyelohexanes (HCHs) and investigate possible loss processes in the water column. Average concentrations of ?-HCH and ?-HCH in ocean surface water were 4.7 ± 0.9 and 0.44 ± 0.11 ng\\/l, respectively. These ?- and ?-HCH levels are

R. L. Falconer; T. F. Bidleman; D. J. Gregor

1995-01-01

340

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

341

Effects of Nitrogen Deficiency on Gas Exchange, Chlorophyll Fluorescence, and Antioxidant Enzymes in Leaves of Rice Plants  

Microsoft Academic Search

Gas exchange, chlorophyll (Chl) fluorescence, and contents of photosynthetic pigments, soluble proteins (ribulose-1,5-bisphosphate carboxylase\\/oxygenase, RuBPCO), and antioxidant enzymes were characterized in the fully expanded 6th leaves in rice seedlings grown on either complete (CK) or on nitrogen-deficient nutrient (N-deficiency) solutions during a 20-chase period. Compared with the control plants, the lower photosynthetic capacity at saturation irradiance (Pmax) was accompanied by

Z.-A. Huang; D.-A. Jiang; Y. Yang; J.-W. Sun; S.-H. Jin

2004-01-01

342

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

Microsoft Academic Search

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

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

2001-01-01

343

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

NASA Astrophysics Data System (ADS)

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

Bell, K. J.; Arman, B.

1991-06-01

344

Basic characteristics of heat-exchanger-type steam reformer heated by high-temperature helium gas (2). Analysis by simulation model (2)  

NASA Astrophysics Data System (ADS)

A computer-simulation model was developed to analyze the basic characteristics of a heat-exchanger-type steam-methane reformer, which is the key component to produce hydrogen using the nuclear process heat from a high-temperature gas-cooled reactor. This model is based on the one-dimensional one taking account of heat transfer and reaction kinetics. In a previous report, the analytical model and the solution procedure are described, and an example of calculation results were shown compared with the experimental data. This report describes simulation results of the dependencies of the characteristic quantities such as heat flux, reaction rates, and hydrogen production rate in the reformer tube on selected parameters, namely, the operating conditions (inlet gas temperatures, pressure, and flow rates), the activities of the catalyst, the heat-transfer rate and the dimensions of the reaction tube.

Okuyama, K.

1987-02-01

345

Effects of orally administered activated charcoal on intestinal gas.  

PubMed

The effectiveness of activated charcoal in treating intestinal gas, following a gas producing meal, was compared with a placebo. Both the number of flatus events and breath hydrogen levels were measured. These experiments showed that orally administered activated charcoal was effective in preventing the large increase in the number of flatus events and increased breath hydrogen concentrations that normally occur following a gas-producing meal. PMID:7015846

Hall, R G; Thompson, H; Strother, A

1981-03-01

346

Comparison of Gas Exchange and Bioassay Determinations of the Ammonia Compensation Point in Luzula sylvatica (Huds.) Gaud.1  

PubMed Central

Determinations of the NH3 compensation point for the understory plant of semi-natural woodlands Luzula sylvatica (Huds.) Gaud. were carried out by measurements of gas exchange and by calculation from the NH4+ concentration and pH of extracts of the foliar apoplast. Compensation points determined by gas exchange measurements were among the lowest yet reported (0.51–1.10 ?g NH3 m?3) and those calculated from apoplast extracts were lower than any yet reported (0.017–0.54 ?g NH3 m?3). Those determined by gas exchange were consistently found to be between 2 and 30 times higher than those determined from apoplast extracts. Consideration of possible causes of this discrepancy, which is not confined to this investigation, showed that all likely errors would result in an increase in the discrepancy, or were insufficient to account for observed differences. It is suggested that spatial variability of pH and NH4+ concentration within the foliar apoplast represents the most promising line for further investigation. It is also shown that the foliar apoplast of L. sylvatica is sufficiently buffered to eliminate the need for correction of H+ concentration for dilution during extraction, but that it is necessary to correct the NH4+ concentration of apoplast extracts for dilution.

Hill, Paul W.; Raven, John A.; Loubet, Benjamin; Fowler, David; Sutton, Mark A.

2001-01-01

347

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

348

Ventilatory and gas exchange responses under spontaneous and fixed breathing modes during arm exercise.  

PubMed

To evaluate the difference of ventilatory and gas exchange response differences between arm and leg exercise, six healthy young men underwent ramp exercise testing at a rate of 15 W.min-1 on a cycle ergometer separately under either spontaneous (SPNT) or fixed (FIX) breathing modes, respectively. Controlled breathing was defined as a breathing frequency (fb; 30 breaths.min-1) which was neither equal to, nor a multiple of, cranking frequency (50 rev.min-1) to prevent coupling of locomotion and respiratory movement, i.e., so-called locomotor-respiratory coupling (LRC). Breath-by-breath oxygen uptake (VO2), ventilation (VE), CO2 output (VCO2), tidal volume (VT), fb and end-tidal PCO2 (PETCO2) were determined using a computerized metabolic cart. Arm exercise engendered a higher level of VO2 at each work rate than leg exercise under both FIX and SPNT conditions. However, FIX did not notably affect the VO2 response during either arm or leg exercise at each work rate compared to SPNT. During SPNT a significantly higher fb and lower PETCO2 during arm exercise was found compared with leg exercise up to a fb of 30 breaths.min-1 while VE and VT were nearly the same. During fixed breathing when fb was fixed at a higher rate than during SPNT, a significantly lower PETCO2 was observed during both exercise modes. These results suggest that: 1) FIX breathing does not affect the VO2 response during either arm or leg exercise even when non-synchronization between limb locomotion movement and breathing rate was adopted; 2) at a fb of 30 breaths.min-1 FIX breathing induced a hyperventilation resulting in a lower PETCO2 which was not associated with the metabolic rate during either arm or leg exercise, showing that VE during only leg exercise under the FIX condition was significantly higher than under the SPNT condition. PMID:12491821

Itoh, Masahiro; Fukuoka, Yoshiyuki; Endo, Masako; Kagawa, Harumi; Araki, Haruo; Nishi, Katsuhide

2002-09-01

349

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

350

Plasma volume expansion in canine pneumococcal pneumonia: its effects on respiratory gas exchange and pneumonia size.  

PubMed

Patients with pneumococcal pneumonia are often given fluids intravenously for hydration and maintenance of circulating blood volume. We studied the effects of plasma volume expansion on respiratory gas exchange and pneumonia size in a canine model of lobar pneumonia. Seven ventilated anesthetized dogs (Group T) with left lower lobe pneumococcal pneumonia were infused with dextran 75 in 0.9% saline solution to increase the pulmonary capillary wedge pressure to 10 mmHg for 3 h. These were compared with 7 control dogs (Group C) with left lower lobe pneumonia. Measurements of cardiac output, intrapulmonary shunt (QS/QT), and lobar distribution of perfusion were taken at baseline (B), immediately after volume infusion (V), and 3 h later (F); similar intervals were used in control animals. In Group T, QS/QT increased significantly from 24% at B to 34% at F. Part of this increase in QS/QT occurred immediately after volume infusion (29% at V) and was associated with the concomitant increase in cardiac output (4.7 L/min at B to 10.6 L/min at F). In Group C, there were no changes in cardiac output or QS/QT. At autopsy, mean wet weight for both lower lobes in Group T were greater than in Group C. Accordingly, small elevations in pulmonary capillary wedge pressure associated with fluid administration caused large increases in lobar wet weights. At least in part, these increases represented transudation of plasma and crystalloid into alveolar spaces and suggested large increases in extravascular lung liquid flux from inflamed vessels in infected lung. PMID:6807159

Cooligan, T; Light, R B; Wood, L D; Mink, S N

1982-07-01

351

The chemical precipitation of nickel on ion exchangers and active carbons  

NASA Astrophysics Data System (ADS)

The chemical precipitation of nickel in the form of poorly soluble precipitates in ion exchanger matrices and on active carbons from solutions of nickel chloride and chemical nickel plating electrolytes was studied. The sorption of nickel ions from a solution of nickel chloride occurs most effectively on Purolite D24002 macroporous chelate forming ion exchanger, KU-23-15/100 sulfo cation exchanger, and KU-2-8 gel sulfo cation exchanger. Nickel enters sulfo cation exchangers in the form of counterions, and is adsorbed on Purolite D24002 largely because of complex formation. The subsequent precipitation of nickel in the solid state in matrix pores liberates ionogenic centers, which allows repeated sorption cycles to be performed. After three chemical precipitation cycles under static conditions, the amount of nickel is higher by 170-250% than the ion exchange capacity of the sorbents. The electrolyte of chemical nickel plating contains nickel predominantly in the form of negatively charged and neutral complexes with glycine, which cannot form bonds with the matrices under study. It is therefore reasonable to perform sorption at decreased solution pH values.

Khorol'Skaya, S. V.; Zolotukhina, E. V.; Polyanskii, L. N.; Peshkov, S. V.; Kravchenko, T. A.; Krysanov, V. A.

2010-12-01

352

Theory of Spin Exchange between Optically Pumped Rubidium and Foreign Gas Nuclei  

Microsoft Academic Search

Cross sections for spin exchange between alkali valence electrons and foreign nuclei in collisions of atomic Rb with atomic He, Ne, Kr, and molecular hydrogen are calculated. It is concluded that while classical dipolar hyperfine interactions are negligible, scalar interaction strengths are greatly magnified as a result of electron exchange. Specifically, it is shown that cross sections associated with the

R. M. Herman

1965-01-01

353

Analysis of a liquid\\/gas direct contact heat exchanger concept  

Microsoft Academic Search

The performance of spray heat exchangers employing uniform drop generators is analyzed using a computer simulation of the air\\/water counterflow direct contact heat exchanger for the cases of heat transfer from water to air, and from air to water. The effect of air temperature and humidity on water cooling is demonstrated. For the case of air cooling, the dry bulb

R. O. Warrington; R. L. Mussulman

1983-01-01

354

Effects of boron deficiency on major metabolites, key enzymes and gas exchange in leaves and roots of Citrus sinensis seedlings.  

PubMed

Boron (B) deficiency is a widespread problem in many crops, including Citrus. The effects of B-deficiency on gas exchange, carbohydrates, organic acids, amino acids, total soluble proteins and phenolics, and the activities of key enzymes involved in organic acid and amino acid metabolism in 'Xuegan' [Citrus sinensis (L.) Osbeck] leaves and roots were investigated. Boron-deficient leaves displayed excessive accumulation of nonstructural carbohydrates and much lower CO2 assimilation, demonstrating feedback inhibition of photosynthesis. Dark respiration, concentrations of most organic acids [i.e., malate, citrate, oxaloacetate (OAA), pyruvate and phosphoenolpyruvate] and activities of enzymes [i.e., phosphoenolpyruvate carboxylase (PEPC), NAD-malate dehydrogenase, NAD-malic enzyme (NAD-ME), NADP-ME, pyruvate kinase (PK), phosphoenolpyruvate phosphatase (PEPP), citrate synthase (CS), aconitase (ACO), NADP-isocitrate dehydrogenase (NADP-IDH) and hexokinase] involved in glycolysis, the tricarboxylic acid (TCA) cycle and the anapleurotic reaction were higher in B-deficient leaves than in controls. Also, total free amino acid (TFAA) concentration and related enzyme [i.e., NADH-dependent glutamate 2-oxoglutarate aminotransferase (NADH-GOGAT) and glutamate OAA transaminase (GOT)] activities were enhanced in B-deficient leaves. By contrast, respiration, concentrations of nonstructural carbohydrates and three organic acids (malate, citrate and pyruvate), and activities of most enzymes [i.e., PEPC, NADP-ME, PK, PEPP, CS, ACO, NAD-isocitrate dehydrogenase, NADP-IDH and hexokinase] involved in glycolysis, the TCA cycle and the anapleurotic reaction, as well as concentration of TFAA and activities of related enzymes (i.e., nitrate reductase, NADH-GOGAT, glutamate pyruvate transaminase and glutamine synthetase) were lower in B-deficient roots than in controls. Interestingly, leaf and root concentration of total phenolics increased, whereas that of total soluble protein decreased, in response to B-deficiency. In conclusion, respiration, organic acid (i.e., glycolysis and the TCA cycle) metabolism, the anapleurotic pathway and amino acid biosynthesis were upregulated in B-deficient leaves with excessive accumulation of carbohydrates to 'consume' the excessive carbon available, but downregulated in B-deficient roots with less accumulation of carbohydrates to maintain the net carbon balance. PMID:24957048

Lu, Yi-Bin; Yang, Lin-Tong; Li, Yan; Xu, Jing; Liao, Tian-Tai; Chen, Yan-Bin; Chen, Li-Song

2014-06-01

355

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

PubMed

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

356

Gas-phase hydrogen/deuterium exchange in a travelling wave ion guide for the examination of protein conformations  

PubMed Central

Accumulating evidence suggests that solution-phase conformations of small globular proteins and large molecular protein assemblies can be preserved for milliseconds after electrospray ionization. Thus, the study of proteins in the gas-phase on this time-scale is highly desirable. Here we demonstrate that a travelling wave ion guide (TWIG) of a Synapt mass spectrometer offers a highly suitable environment for rapid and efficient gas-phase hydrogen/deuterium exchange (HDX). Gaseous ND3 was introduced into either the source TWIG or the TWIG located just after the ion mobility cell, such that ions underwent HDX as they passed through the ND3 on the way to the time-of-flight analyzer. The extent of deuterium labeling could be controlled by varying the quantity of ND3 or the speed of the travelling wave. The gas-phase HDX of model peptides corresponded to labeling of primarily fast exchanging sites due to the short labeling times (ranging from 0.1 to 10 ms). In addition to peptides, gas-phase HDX of ubiquitin, cytochrome c, lysozyme and apomyoglobin were examined. We conclude that HDX of protein ions in a TWIG is highly sensitive to protein conformation, enables the detection of conformers present on sub-milliseconds timescales and can readily be combined with ion mobility spectrometry.

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

2009-01-01

357

ARSENIC REMOVAL BY FULL SCALE ION EXCHANGE AND ACTIVATED ALUMINA TREATMENT  

EPA Science Inventory

This presentation discusses the results of a one year performance evaluation study of two ion exchange plants and two activated alumina plants that were designed and operated for the removal of arsenic from well water. All the plants were shown to be capable of reducing arsenic l...

358

ARSENIC REMOVAL FROM DRINKING WATER BY ACTIVATED ALUMINA AND ANION EXCHANGE TREATMENT  

EPA Science Inventory

This paper discusses the results of a one year performance evaluation study of two full scale ion exchange plants and two full scale activated alumina plant that were designed and operated for the removal of arsenic from well water. All the plants were shown to be capable of red...

359

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...

360

Gas-phase H/D exchange of the protonated serine octamer cluster: "Ion ping pong" of populations A and B  

NASA Astrophysics Data System (ADS)

The stability of protonated serine octamer clusters was investigated by forward and reverse H/D exchange in the gas phase. The existence of two independent populations with different overall exchange rate constants and different stabilities toward collision-induced dissociation was confirmed.

Mazurek, Ulf; Engeser, Marianne; Lifshitz, Chava

2006-03-01

361

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

362

Cardiac Na+\\/Ca2+ exchange activity in patients with end-stage heart failure  

Microsoft Academic Search

Objective: The aim of the present study was to investigate the functional activity and expression of the sarcolemmal Na+\\/Ca*+-ex- changer in the failing human heart. Methods: Left ventricular samples were taken from eleven patients with end-stage heart failure and six organ donors (normal controls). The Na+\\/Ca'+-exchanger activity was assessed by measuring Na+ gradient-induced 45Ca2+ transport into sarcolemmal vesicles of quantitatively

Hans Reinecke; Roland Studer; Roland Vetter; Jiirgen Holtz; Helmut Drexler

363

Mass transport in gas diffusion layers of proton exchange membrane fuel cells  

NASA Astrophysics Data System (ADS)

This dissertation describes fundamental properties of gas diffusion media (GDM) and their relationship to the mass transport in proton exchange membrane fuel cells (PEMFCs). First, the accuracy of solving the multi-component equations for PEMFC by using a computational fluid dynamics (CFD) technique is examined. This technique uses an approximated multi-component (AMC) model with a correction term that guarantees the overall mass balance. Accuracy is assessed by comparing the species concentrations computed with the Maxwell-Stefan and the AMC model. This comparison is important because the structure of some CFD programs does not permit the direct use of the Maxwell-Stefan equations. Here, it is shown that the maximum error between the two models is less than 5%. Second, the ratio of tortuosity to porosity, known as the MacMullin number, is reported for different carbon cloth and carbon paper GDM. This analysis show that only carbon cloths GDM follow the commonly accepted Bruggeman equation and that carbon paper GDM have a different relationship between the tortuosity and the porosity. These differences are discussed in terms of path length created by the orientation of fibers of each GDM. Third, data for the hydrophilic and hydrophobic pore size distributions (PSD) are presented for two types of GDM used in PEMFCs. The data were obtained by using two common measurement methods, intrusion porosimetry (IP) and the method of standard porosimetry (MSP). The use of multiple working fluids to access hydrophilic and hydrophobic pores is discussed as well as the limitations associated with structural changes of the GDM during the tests. The differences in interpretations of the data between the two methods for both GDM have significant implications relative to the distribution of hydrophilic and hydrophobic pores that control liquid water transport. Finally, a two-phase mass-transport-only model (MTOM) that incorporates the tortuosity and the PSD data described above is presented. The model provides an understanding of the effect of PSD in the water transport by decoupling it from other factors. The MTOM shows that differences in GDM structure produce significant differences in the liquid saturation.

Martinez, Michael J.

364

Regulation of activity and apical targeting of the Cl-/HCO3- exchanger in rat hepatocytes.  

PubMed Central

To test the hypothesis that rat hepatocyte canalicular Cl-/HCO3- exchange activity might be regulated by HCO3- or protein kinase-induced changes in the apical targeting of vesicles, isolated rat hepatocytes were cultured in the presence or absence of HCO3-/CO2.Cl-/HCO3- exchange activity increased in cells cultured in the presence of HCO3-/CO2 or when stimulated by dibutyryl cAMP. Both of these effects were blocked by either colchicine or the protein kinase C agonist phorbol 12,13-dibutyrate. Fluorescence and confocal microscopy, respectively, revealed increased pericanalicular-apical membrane localization of two canalicular markers, peanut agglutinin and a 110-kDa canalicular ecto-ATPase, when hepatocyte couplets were preincubated in HCO3-/CO2-containing medium, an effect that was again blocked by colchicine. Dibutyryl cAMP also stimulated canalicular localization of the 110-kDa protein. These findings suggest that hepatocyte Cl-/HCO3- exchange activity is regulated by HCO3-/CO2 and by protein kinase A and protein kinase C agonists through microtubule-dependent targeting of vesicles containing this exchanger to the canalicular domain. Images Fig. 3

Benedetti, A; Strazzabosco, M; Ng, O C; Boyer, J L

1994-01-01

365

A Comparison of the Effects of Chilling on Leaf Gas Exchange in Pea (Pisum sativum L.) and Cucumber (Cucumis sativus L.) 1  

PubMed Central

The effects of chilling on the photosynthesis of a chilling-resistant species, pea (Pisum sativum L. cv Alaska) and a chilling-sensitive species, cucumber (Cucumis sativus L. cv Ashley) were compared in order to determine the differences in the photosynthetic chilling sensitivity of these two species. For these experiments, plants were chilled (5°C) for different lengths of time in the dark or light. Following a 1 hour recovery period at 25°C, photosynthetic activity was measured by gas exchange (CO2 uptake and H2O release), quantum yield, and induced chlorophyll fluorescence. The results show that pea photosynthesis was largely unaffected by two consecutive nights of chilling in the dark, or by chilling during a complete light and dark cycle (15 hours/9 hours). Cucumber gas exchange was reduced by one night of chilling, but its quantum yield and variable fluorescence were unaffected by dark chilling. However, chilling cucumber in the light led to reduced CO2 fixation, increased internal leaf CO2 concentration, decreased quantum yield, and loss of variable fluorescence. These results indicate that chilling temperatures in conjunction with light damaged the light reactions of photosynthesis, while chilling in the dark did not.

Peeler, Thomas C.; Naylor, Aubrey W.

1988-01-01

366

Variations in water status, gas exchange, and growth in Rosmarinus officinalis plants infected with Glomus deserticola under drought conditions.  

PubMed

The influence of the arbuscular mycorrhizal fungus Glomus deserticola on the water relations, gas exchange parameters, and vegetative growth of Rosmarinus officinalis plants under water stress was studied. Plants were grown with and without the mycorrhizal fungus under glasshouse conditions and subjected to water stress by withholding irrigation water for 14 days. Along the experimental period, a significant effect of the fungus on the plant growth was observed, and under water stress, mycorrhizal plants showed an increase in aerial and root biomass compared to non-mycorrhizal plants. The decrease in the soil water potential generated a decrease in leaf water potential (psi(l)) and stem water potential (psi(x)) of mycorrhizal and non-mycorrhizal plants, with this decrease being lower in mycorrhizal water-stressed plants. Mycorrhization also had positive effects on the root hydraulic conductivity (Lp) of water stressed plants. Furthermore, mycorrhizal-stressed plants showed a more important decrease in osmotic potential at full turgor (psi(os)) than did non-mycorrhizal-stressed plants, indicating the capacity of osmotic adjustment. Mycorrhizal infection also improved photosynthetic activity (Pn) and stomatal conductance (g(s)) in plants under water stress compared to the non-mycorrhizal-stressed plants. A similar behaviour was observed in the photochemical efficiency of PSII (Fv/Fm) with this parameter being lower in non-mycorrhizal plants than in mycorrhizal plants under water stress conditions. In the same way, under water restriction, mycorrhizal plants showed higher values of chlorophyll content than did non-mycorrhizal plants. Thus, the results obtained indicated that the mycorrhizal symbiosis had a beneficial effect on the water status and growth of Rosmarinus officinalis plants under water-stress conditions. PMID:15266714

Sánchez-Blanco, Ma Jesús; Ferrández, Trinitario; Morales, Ma Angeles; Morte, Asunción; Alarcón, Juan José

2004-06-01

367

Sustainable production of acrylic Acid: alkali-ion exchanged Beta zeolite for gas-phase dehydration of lactic Acid.  

PubMed

Gas-phase dehydration of lactic acid (LA) to acrylic acid (AA) was investigated over alkali-exchanged ? zeolite (Mx Na1-x ?, M=Li(+) , K(+) , Rb(+) , or Cs(+) ) of different exchange degrees (x). The reaction was conducted under varying conditions to understand the catalyst selectivity for AA production and trends of byproduct formation. The nature and exchange degree of M(+) were found to be critical for the acid-base properties and catalytic performance of the exchanged zeolite. Kx Na1-x ? of x=0.94 appeared to be the best performing catalyst whereas Lix Na1-x ? and Na? were the poorest in terms of AA selectivity and yield. The AA yield as high as 61?mol?% (selectivity: 64?mol?%) could be obtained under optimized reaction conditions for up to 8?h over the best performing K0.94 Na0.06 ?. The acid and base properties of the catalysts were probed, respectively by temperature-programmed desorption (TPD) of adsorbed NH3 and CO2 , and were related to the electrostatic potentials of the alkali ions in the zeolite, which provided a basis for the discussion of the acid-base catalysis for sustainable AA formation from LA. PMID:24903259

Yan, Bo; Tao, Li-Zhi; Liang, Yu; Xu, Bo-Qing

2014-06-01

368

Adsorption of natural gas and biogas components on activated carbon  

Microsoft Academic Search

Experimental results are presented for the adsorption equilibria of methane, ethane, propane, butane, carbon dioxide, and nitrogen, as well as natural gas odorants tert-butyl mercaptan and tetrahydrothiophene, on an activated carbon with the desirable characteristics for use in a guard bed for adsorbed natural gas storage, but that can also be applied for separation of biogas components, such as carbon

Isabel A. A. C. Esteves; Marta S. S. Lopes; Pedro M. C. Nunes; José P. B. Mota

2008-01-01

369

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

370

Molecular determinants of hyperosmotically activated NKCC1-mediated K+/K+ exchange  

PubMed Central

Na+ ?K+ ?2Cl? cotransport (NKCC) mediates the movement of two Cl? ions for one Na+ and one K+ ion. Under isosmotic conditions or with activation of the kinases SPAK/WNK4, the NKCC1-mediated Cl? uptake in Xenopus laevis oocytes, as measured using 36Cl, is twice the value of K+ uptake, as determined using 86Rb. Under hyperosmotic conditions, there is a significant activation of the bumetanide-sensitive K+ uptake with only a minimal increase in bumetanide-sensitive Cl? uptake. This suggests that when stimulated by hypertonicity, the cotransporter mediates K+/K+ and Cl?/Cl? exchange. Although significant stimulation of K+/K+ exchange was observed with NKCC1, a significantly smaller hyperosmotic stimulatory effect was observed with NKCC2. In order to identify the molecular determinant(s) of this NKCC1-specific activation, we created chimeras of the mouse NKCC1 and the rat NKCC2. Swapping the regulatory amino termini of the cotransporters neither conferred activation to NKCC2 nor prevented activation of NKCC1. Using unique restrictions sites, we created additional chimeric molecules and determined that the first intracellular loop between membrane-spanning domains one and two and the second extracellular loop between membrane-spanning domains three and four of NKCC1 are necessary components of the hyperosmotic stimulation of K+/K+ exchange.

Gagnon, Kenneth B; Delpire, Eric

2010-01-01

371

Activated Gas Reactions with Silicone and Epoxy Resins.  

National Technical Information Service (NTIS)

Activated gas plasma technology is widely used for the low temperature ashing of organic materials, for cleaning and etching organic and inorganic materials, and for increasing the surface energy of polymeric materials in preparation for bonding. While so...

N. J. DeLollis

1978-01-01

372

Hexachlorocyclohexanes (HCHs) in the Canadian Archipelago. 2. Air-water gas exchange of alpha- and gamma-HCH.  

PubMed

Air and water were sampled in the Canadian Archipelago during summer on the Tundra Northwest 1999 (TNW-99) expedition and air was sampled at Resolute Bay (RB), Nunavut, to determine the gas exchange of alpha- and gamma-hexachlorocyclohexanes (HCHs) and the enantiomers of alpha-HCH. Air concentrations of sigmaHCH during TNW-99 and at RB were similar, averaging 55 and 53 pg m(-3), respectively. The net gas exchange direction was volatilization for alpha-HCH and near equilibrium or deposition for gamma-HCH, whereas actual fluxes depended on the fraction of open water. Enantiomer fractions, EF = (+)/[(+) + (-)] of alpha-HCH in air sampled from shipboard were significantly correlated to those in surface water for events with >90% open water, but were closer to racemic and not correlated to EFs in water for events with 0-50% open water. Levels of alpha-HCH in air at RB averaged 37 +/- 9 pg m(-3) from June to early July, and EFs were close to racemic (0.496 +/- 0.004). In mid-July the ice pack broke up around RB. From this point through August, air concentrations increased significantly to 53 +/- 5 pg m(-3), and the mean EF decreased significantly to 0.483 +/- 0.009. Air concentrations of gamma-HCH at RB did not differ significantly before (8.0 +/- 3.7 pg m(-3)) and after (6.6 +/- 0.76 pg m(-3)) ice breakup. Results show that alpha-HCH enantiomers are sensitive tracers for following the impact of ice cover loss on gas exchange in the Arctic. PMID:18284148

Jantunen, Liisa M; Helm, Paul A; Kylin, Henrik; Bidleman, Terry F

2008-01-15

373

Usefulness of Decrease in Oxygen Uptake Efficiency to Identify Gas Exchange Abnormality in Patients with Idiopathic Pulmonary Arterial Hypertension  

PubMed Central

Background Decline in oxygen uptake efficiency (OUE), especially during exercise, is found in patients with chronic heart failure. In this study we aimed to test the validity and usefulness of OUE in evaluating gas exchange abnormality of patients with idiopathic pulmonary arterial hypertension (IPAH). Methods We retrospectively investigated the cardiopulmonary exercise test (CPET) with gas exchange measurements in 32 patients with confirmed IPAH. All patients also had resting hemodynamic measurements and pulmonary function test (PFT). Sixteen healthy subjects, matched by age, sex, and body size were used as controls, also had CPET and PFT measurements. Results In IPAH patients, the magnitude of absolute and percentage of predicted (%pred) oxygen uptake efficiency slope (OUES) and oxygen uptake efficiency plateau (OUEP), as well as several other CPET parameters, were strikingly worse than healthy subjects (P<0.0001). Pattern of changes in OUE in patients is similar to that in controls, In IPAH patients, OUE values at rest, warming up, anaerobic threshold and peak exercise were all significantly lower than in normal (P<0.0001). OUEP%pred, better than OUES%pred, correlated significantly with New York Heart Association (NYHA) functional Class (r?=??0.724, P<0.005), Total Pulmonary Vascular Resistance (TPVR) (r?=??0.694, P<0.005), diffusing capacity for carbon monoxide (DLCO) (r?=?0.577, P<0.05), and the lowest ventilation versus CO2 output ratio during exercise (LowestV?E/V?CO2) (r?=??0.902, P<0.0001). In addition, the coefficient of variation (COV) of OUEP was lower (20.9%) markedly than OUES (34.3%) (P<0.0001). Conclusions In patients with IPAH, OUES and OUEP are both significantly lower than the healthy subjects. OUEP is a better physiological parameter than OUES in evaluating the gas exchange abnormality of patients with IPAH.

Yang, Wenlan; Guo, Jian; Zhang, Yan; Sapkota, Rikesh; Kushwaha, Shailendra Prasad; Gong, Sugang; Sun, Xingguo; Liu, Jinming

2014-01-01

374

Toxicodynamics of Rigid Polystyrene Microparticles on Pulmonary Gas Exchange in Mice: Implications for Microemboli-based Drug Delivery Systems  

PubMed Central

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 was investigated. CD-1 male mice (6–8 wk) were intravenously administered 10, 25 and 45 ?m diameter MPs. Oxygen hemoglobin saturation in the blood (SpO2) was measured non-invasively using a pulse oximeter while varying inhaled oxygen concentration (FIO2). Resulting data were fit to a physiologically based non-linear mathematical model that estimates 2 parameters: ventilation-perfusion ratio (VA/Q) and shunt (percentage of deoxygenated blood returning to systemic circulation). The number of MPs administered prior to a statistically significant reduction in normalized VA/Q was dependent on particle size. MP doses that resulted in a significant reduction in normalized VA/Q one day post-treatment were 4,000, 40,000 and 550,000 MPs/g for 45, 25 and 10 ?m MPs, respectively. The model estimated VA/Q and shunt returned to baseline levels 7 days post-treatment. Measuring SpO2 alone was not sufficient to observe changes in gas exchange; however, when combined with model-derived VA/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.

Kutscher, HL.; Gao, D.; Li, S.; Massa, CB.; Cervelli, J.; Deshmukh, M.; Joseph, LB.; Laskin, DL.; Sinko, PJ.

2013-01-01

375

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

376

Experimental Research on Gas-Solid Flow in an External Heat Exchanger with Double Outlets  

NASA Astrophysics Data System (ADS)

A new type scaling-up scheme of CFB boiler that takes separator as center and furnaces are laid around was put forward in this paper. In the recycle system, a new type heat exchanger device with double outlets was designed for this disposal scheme. As we know, the external heat exchanger is very important for the CFB, which be able no only to adjust the steam temperature, but also to adjust the bed temperature. In this paper, through the adjustment of air speed in different room of the heat exchanger, the adjusting performance of the new type heat exchanger was analyzed. Moreover, the test of the pressure in the whole recycle system was analyzed. The pressure balance system of the circulating circuit with this new arrangement scheme was realized. Through this test research, the main conclusions were got as follows: The external heat exchanger, which has two recycled solid outlets, could run flexibly and stably and could successfully discharge the materials from the standpipe into either of the furnaces. This test device has a good pressure and material balance system.

Liu, H. Z.; Lu, X. F.

377

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

378

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

PubMed Central

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

2014-01-01

379

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

380

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

381

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

382

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

383

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.

Vogtherr, Martin

2013-01-01

384

78 FR 59650 - Subzone 9F, Authorization of Production Activity, The Gas Company, LLC dba Hawai'i Gas...  

Federal Register 2010, 2011, 2012, 2013

...Zones Board [B-53-2013] Subzone 9F, Authorization of Production Activity, The Gas Company, LLC dba Hawai'i Gas, (Synthetic Natural Gas), Kapolei, Hawaii On May 22, 2013, The Gas Company, LLC dba Hawai'i Gas submitted a notification of...

2013-09-27

385

Gas-chromatographic assay for heme oxygenase activity  

SciTech Connect

The authors have developed an improved assay for microsomal heme oxygenase activity, based on the enzymic release of CO from the ..cap alpha..-methene bridge of hemin and the quantitation of CO by gas chromatography. The detection limit for heme oxygenase activity was approximately 1 nmol/h per milligram of microsomal protein. Gas-chromatographic assays of heme oxygenase activities in rat tissues correlated well (r = 0.94) with results by a spectrophotometric assay based on bilirubin production. Heme oxygenase activity was increased 10-fold in kidney microsomes and threefold in liver microsomes from rats killed 17 h after subcutaneous injection of NiCl/sub 2/ (0.5 mmol/kg body wt.). These findings illustrate the efficacy of the gas-chromatographic assay for measuring xenobiotic effects on heme oxygenase activity.

Sunderman, F.W. Jr.; Downs, J.R.; Reid, M.C.; Bibeau, L.M.

1982-01-01

386

In Vivo MR Imaging of Pulmonary Perfusion and Gas Exchange in Rats via Continuous Extracorporeal Infusion of Hyperpolarized 129Xe  

PubMed Central

Background Hyperpolarized (HP) 129Xe magnetic resonance imaging (MRI) permits high resolution, regional visualization of pulmonary ventilation. Additionally, its reasonably high solubility (>10%) and large chemical shift range (>200 ppm) in tissues allow HP 129Xe to serve as a regional probe of pulmonary perfusion and gas transport, when introduced directly into the vasculature. In earlier work, vascular delivery was accomplished in rats by first dissolving HP 129Xe in a biologically compatible carrier solution, injecting the solution into the vasculature, and then detecting HP 129Xe as it emerged into the alveolar airspaces. Although easily implemented, this approach was constrained by the tolerable injection volume and the duration of the HP 129Xe signal. Methods and Principal Findings Here, we overcome the volume and temporal constraints imposed by injection, by using hydrophobic, microporous, gas-exchange membranes to directly and continuously infuse 129Xe into the arterial blood of live rats with an extracorporeal (EC) circuit. The resulting gas-phase 129Xe signal is sufficient to generate diffusive gas exchange- and pulmonary perfusion-dependent, 3D MR images with a nominal resolution of 2×2×2 mm3. We also show that the 129Xe signal dynamics during EC infusion are well described by an analytical model that incorporates both mass transport into the blood and longitudinal relaxation. Conclusions Extracorporeal infusion of HP 129Xe enables rapid, 3D MR imaging of rat lungs and, when combined with ventilation imaging, will permit spatially resolved studies of the ventilation-perfusion ratio in small animals. Moreover, EC infusion should allow 129Xe to be delivered elsewhere in the body and make possible functional and molecular imaging approaches that are currently not feasible using inhaled HP 129Xe.

Cleveland, Zackary I.; Moller, Harald E.; Hedlund, Laurence W.; Nouls, John C.; Freeman, Matthew S.; Qi, Yi; Driehuys, Bastiaan

2012-01-01

387

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

388

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

389

Activation of Na-Ca exchange current by photolysis of "caged calcium".  

PubMed Central

Intracellular photorelease of Ca2+ from "caged calcium" (DM-nitrophen) was used to investigate the Ca(2+)-activated currents in ventricular myocytes isolated from guinea pig hearts. The patch-clamp technique was applied in the whole-cell configuration to measure membrane current and to dialyze the cytosol with a pipette solution containing the caged compound. In the presence of inhibitors for Ca2+, K+, and Na+ channels, concentration jumps of [Ca2+]i induced a rapidly activating inward Na-Ca exchange current which then decayed slowly (tau approximately 500 ms). The initial peak of the inward current and the time-course of current decay were voltage-dependent, and no reversal of the current direction was found between -100 and +100 mV. The observed shallow voltage dependence can be described in terms of the movement of an apparently fractional elementary charge (+0.44e-) across an energy barrier located symmetrically in the electrical field of the membrane. The currents were dependent on extracellular Na+ with a half-maximal activation at 73 mM and a Hill coefficient of 2.8. No change of membrane conductance was activated by the Ca2+ concentration jump when extracellular Na+ was completely replaced by Li+ or N-methyl-D-glucamine (NMG) or when the Na-Ca exchange was inhibited by extracellular Ni2+, La3+, or dichlorobenzamil (DCB). The velocity of relengthening after a twitch induced by photorelease of Ca2+ was only reduced drastically when both the sarcoplasmic reticulum and the Na-Ca exchange were inhibited suggesting that all other Ca2+ removing mechanisms have a low transport capacity under these conditions. In conclusion, we have used a novel approach to study Na-Ca exchange activity with photolysis of "caged" calcium. We found that in guinea pig heart muscle cells the Na-Ca exchange is a potent mechanism for Ca2+ extrusion, is weakly voltage-dependent (118 mV for e-fold change) and can be studied without contamination with other Ca(2+)-activated currents.

Niggli, E; Lederer, W J

1993-01-01

390

Gas Adsorption by Activated and Impregnated Carbons.  

National Technical Information Service (NTIS)

An assembly has been constructed for measuring equilibrium absorption isotherms on activated and impregnated carbons. The pumping system, pressure-measuring devices and microbalance assembly have been tested. Construction of the fume hood exhaust and filt...

P. J. Reucroft C. T. Chiou

1975-01-01

391

Air-sea dimethylsulfide (DMS) gas transfer in the North Atlantic: evidence for limited interfacial gas exchange at high wind speed  

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

392

Ras-Activated Endocytosis Is Mediated by the Rab5 Guanine Nucleotide Exchange Activity of RIN1  

Microsoft Academic Search

RIN1 was originally identified by its ability to inhibit activated Ras and likely participates in multiple signaling pathways because it binds c-ABL and 14-3-3 proteins, in addition to Ras. RIN1 also contains a region homologous to the catalytic domain of Vps9p-like Rab guanine nucleotide exchange factors (GEFs). Here, we show that this region is necessary and sufficient for RIN1 interaction

Gregory G. Tall; M. Alejandro Barbieri; Philip D. Stahl; Bruce F. Horazdovsky

2001-01-01

393

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

394

Development of the gas puff charge exchange recombination spectroscopy (GP-CXRS) technique for ion measurements in the plasma edge  

SciTech Connect

A novel charge-exchange recombination spectroscopy (CXRS) diagnostic method is presented, which uses a simple thermal gas puff for its donor neutral source,