These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

Active microchannel heat exchanger  

Microsoft Academic Search

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

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

2001-01-01

2

Insect gas exchange patterns: a phylogenetic perspective.  

PubMed

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

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

2005-12-01

3

BOREAS TE-12 Leaf Gas Exchange Data  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

4

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

5

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

6

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

Microsoft Academic Search

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

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

2005-01-01

7

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

8

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

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. PMID:25006037

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

2014-01-01

10

BOREAS TE-10 Leaf Gas Exchange Data  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

11

History of respiratory gas exchange.  

PubMed

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

West, John B

2011-07-01

12

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

13

BOREAS TE-11 Leaf Gas Exchange Measurements  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

14

Reversible brain inactivation induces discontinuous gas exchange in cockroaches.  

PubMed

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

Matthews, Philip G D; White, Craig R

2013-06-01

15

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

16

Forced convection modulates gas exchange in cnidarians  

PubMed Central

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

Patterson, Mark R.; Sebens, Kenneth P.

1989-01-01

17

New fiber configuration for intravenous gas exchange.  

PubMed

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

Cattaneo, G F; Reul, H

2005-03-01

18

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. PMID:12430953

Maina, JN

2002-01-01

19

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

20

BOREAS TF-11 SSA-Fen Leaf Gas Exchange Data  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

21

A Role for Altimeter Radars in Gas Exchange Studies  

NASA Astrophysics Data System (ADS)

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 of research has shown the utility of sea surface roughness, represented by the mean square surface slope (mss) due to gravity-capillary scale waves, as a proxy for gas exchange. Normalized backscatter of altimeter radars can be used in scattering models to estimate mss by combining coordinated ship-based measurements of mss with satellite overflights. These coordinated field experiments over the last decade have begun to provide the data necessary to calibrate mss estimates from altimeter radars. Now we have developed this technique into an alternative approach for assessing global gas transfer velocity fields remotely. This paper will trace the evolution of this concept from key laboratory and in situ observations to remote sensing observations and construction of a decade-long time series from the TOPEX and Jason-1 data streams.

Frew, N. M.; Glover, D. M.; McCue, S. J.

2006-07-01

22

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

23

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

Microsoft Academic Search

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

PETER L. LUTZ; ANN BERGEY; MICHAEL BERGEY

1989-01-01

24

Collateral ventilation and gas exchange in emphysema.  

PubMed

Resistance to collateral flow of gas is high in the normal human lung but may be lower in emphysema. However, the contribution of collateral ventilation to gas exchange in emphysema remains unclear. This study evaluates the role and magnitude of collateral ventilation between bronchopulmonary segments in six patients with clinical, functional, and computed tomographic evidence of emphysema, compared with our previous findings in 12 normal subjects. To assess collateral flow, a balloon-tipped catheter with a lumen that opened distal to the balloon was inflated in segmental bronchi during fiberoptic bronchoscopy. Respiratory gas tensions were sampled by mass spectrometer from beyond the occlusion via the catheter lumen. Subjects breathed air until occlusion was established and then switched to 79% helium/21% oxygen. The rate of rise of helium concentration was measured within occluded segments and used as an index of collateral ventilation. The mean (+/- SEM) rate of rise of helium concentration was ten times greater in emphysema patients (9.5 +/- 2.7%/min) compared with normal subjects (0.8 +/- 0.3%/min) (p = 0.009). The mean PO2 within occluded segments was similar in normal subjects and emphysema patients: 45.4 +/- 1.8 mm Hg and 44.8 +/- 3.6 mm Hg, respectively. Mean PCO2 within occluded segments was lower in patients (40.1 +/- 1.9 mm Hg) than in normal subjects (46.4 +/- 1.3 mm Hg), probably due to higher regional ventilation-perfusion ratios in emphysema patients rather than collateral ventilation. In emphysema patients there was a positive correlation between rate of rise of helium concentration and final PO2 within an occluded segment (r = 0.73; p = 0.02).(ABSTRACT TRUNCATED AT 250 WORDS) PMID:8087331

Morrell, N W; Wignall, B K; Biggs, T; Seed, W A

1994-09-01

25

Experimental Investigation on Heat Transfer Characteristics of a Gas-to-Gas Counterflow Microchannel Heat Exchanger  

Microsoft Academic Search

Heat transfer characteristics of a gas-to-gas counterflow microchannel heat exchanger have been experimentally investigated. Temperatures and pressures at inlets and outlets of the heat exchanger have been measured to obtain heat transfer rates and pressure drops. The heat transfer and the pressure drop characteristics are discussed. Since the partition wall of the heat exchanger is thick compared with the microchannel

K. Koyama; Y. Asako

2010-01-01

26

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

E-print Network

Improved helium exchange gas cryostat and sample tube designs for automated gas sampling, California 92093-0244, USA [1] 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

Severinghaus, Jeffrey P.

27

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

28

Hydraulic and thermal design of a gas microchannel heat exchanger  

Microsoft Academic Search

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

Yahui Yang; Juergen J Brandner; Gian Luca Morini

2012-01-01

29

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

30

Gas exchange and ventilation-perfusion relationships in the lung.  

PubMed

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

Petersson, Johan; Glenny, Robb W

2014-10-01

31

Surface gas-exchange processes of snow algae  

PubMed Central

The red-colored chlorophyte Chlamydomonas nivalis is commonly found in summer snowfields. We used a modified Li-Cor gas-exchange system to investigate surface gas-exchange characteristics of snow colonized by this alga, finding rates of CO2 uptake up to 0.3 ?mol m?2?s?1 in dense algal blooms. Experiments varying the irradiance resulted in light curves that resembled those of the leaves of higher plants. Red light was more effective than white and much more effective than green or blue, because of the red astaxanthin that surrounds and masks the algal chloroplasts. Integrating daily course measurements of gas exchange showed CO2 uptake around 2,300 ?mol?m?2?day?1 in heavily colonized patches, indicating that summer snowfields can be surprisingly productive. PMID:12518048

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

2003-01-01

32

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

PubMed Central

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

Anderson, Joseph C.; Hlastala, Michael P.

2011-01-01

33

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

PubMed

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

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

2012-07-01

34

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

35

Ventilation and gas exchange in the mute swan, Cygnus olor.  

PubMed

Ventilation and gas exchange have been continuously measured in the mute swan using pneumotachography and breath to breath analysis of the ventilated gas by mass spectrometry combined with blood gas analysis. The breathing frequency was much lower and the tidal volume much higher than values predicted from allometric relations. The breathing cycles typically showed long end-inspiratory breath holding periods. End-tidal PCO2 and PO2 were above and below respectively typical end-tidal gas tensions reported earlier in birds. A pronounced positive PCO2 difference between end-tidal gas and mixed venous blood was present averaging 9.8 mm Hg. The blood-gas values found in the mute swan fall within a range typical of birds. A very low air convection requirement (13.6 ml . ml-1) and high O2 extraction coefficient (33.0%) indicate a high gas exchange efficiency of the swan lung. The unusually large tidal volumes and the long breath holds succeeding each inspiration are likely contributing factors to the high exchange efficiency. Calculated low values for the blood convection requirement (12.8 ml . ml-1) match the low air convection requirements and result in a ventilation/perfusion ratio near unity (VI/Q=1.06). PMID:6770431

Bech, C; Johansen, K

1980-03-01

36

[The physiology of gas exchange in divers].  

PubMed

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

Rieder, H U

1989-04-01

37

SURFACE ENERGY BALANCE AFFECTS GAS EXCHANGE OF THREE SHRUB SPECIES  

Microsoft Academic Search

We investigated the energy balance of vegetative and nonvegetative surfaces and gas exchange for 3 shrub species growing over each surface. During a 1 -week period, incoming short-wave radiation, surface and soil tempera- ture, and soil heat flux for turf and pine-bark mulch surfaces were gathered. Air temperature and relative humidity at 2 heights over each surface were also measured.

Thayne Montague; Roger Kjelgren; Larry Rupp

38

On Factors Controlling AirWater Gas Exchange in a Large Tidal River  

E-print Network

and estuaries. Here, we present gas transfer velocities measured in the tidal Hudson River with a method widely that wind is the dominant driver of gas exchange in the tidal Hudson River, with negligible contribution variables and gas exchange in tidal inland waters. Keywords Air­water gas exchange . 3 He/SF6 . Hudson River

Ho, David

39

Naphthenic acids inhibit root water transport, gas exchange and leaf growth in aspen (Populus tremuloides) seedlings.  

PubMed

Effects of sodium naphthenates (NAs) on root hydraulic conductivity (Lp) and gas exchange processes were examined in aspen (Populus tremuloides Michx.) seedlings grown in solution culture. Exposure of roots to NAs for 3-5 weeks significantly decreased Lp and stomatal conductance. Root-absorbed NAs also decreased leaf chlorophyll concentration, net photosynthesis and leaf growth. Short-term (< or = 2 h) exposure of excised roots to NAs significantly decreased root water flow (Qv) with a concomitant decline in root respiration. We conclude that NAs metabolically inhibited Lp, likely by affecting water channel activity, and that this inhibition could be responsible for the observed reductions in gas exchange and leaf growth. PMID:12464580

Kamaluddin, M; Zwiazek, Janusz J

2002-12-01

40

WHY DO TOOTHED LEAVES CORRELATE WITH COLD CLIMATES? GAS EXCHANGE AT LEAF MARGINS PROVIDES NEW INSIGHTS  

E-print Network

WHY DO TOOTHED LEAVES CORRELATE WITH COLD CLIMATES? GAS EXCHANGE AT LEAF MARGINS PROVIDES NEW measure the seasonal patterns of leaf-margin photosynthesis and transpiration for 60 woody species from 30 d); second, toothed margins are more active with respect to photosynthesis and transpiration than

Royer, Dana

41

Gas exchange on Mono Lake and Crowley Lake, California  

NASA Astrophysics Data System (ADS)

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

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

1987-12-01

42

Sensible and latent heat transfer in cross-counterflow gas-to-gas heat exchangers  

SciTech Connect

Simultaneous heat and mass transfer during condensation in cross-counterflow gas-to-gas heat exchangers has been analyzed. The coupled heat and mass transfer equations are derived for boundary-layer controlled heat and mass transfer and include longitudinal heat conduction in the exchanger wall. A numerical method of the finite-difference type is applied to the steady-state performance. Temperature and absolute humidity distributions are calculated for exchanger parameters that are typical in air conditioning systems. Temperature and humidity efficiencies together with frosting limits are evaluated for different inlet air conditions.

Holmberg, R.B. (Flakt Evaporator AB, S-551 84 Jonkoping (SE))

1989-02-01

43

BOREAS TE-4 Gas Exchange Data from Boreal Tree Species  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

44

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

E-print Network

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

Paris-Sud XI, Université de

45

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....

46

Gas exchange on Mono Lake and Crowley Lake, California  

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

47

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

Microsoft Academic Search

A conceptual model was tested for explaining environmental and physiological effects on leaf gas exchange in the deciduous dry tropical woodland tree Boswellia papyrifera (Del.) Hochst. For this species we aimed at (i) understanding diurnal patterns in leaf gas exchange, (ii) exploring cause–effect relationships among external environment, internal physiology and leaf gas exchange, and (iii) exploring site differences in leaf

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

2011-01-01

48

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

49

The use of stable isotopes to study ecosystem gas exchange  

Microsoft Academic Search

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

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

2000-01-01

50

Intrapulmonary gas mixing and pulmonary gas exchange in artificially ventilated dogs  

Microsoft Academic Search

To investigate the effect of incomplete gas mixing between tidal air and residual gas on pulmonary gas exchange, anaesthetized dogs were ventilated artificially with breathing patterns with different durations of the post-inspiratory apnoea (ta=0,0.5,1.0 and 2.0 s), where tidal volume, breathing frequency, inspiratory and expiratory flow patterns were kept constant. We determined the alveolar ventilations (V\\u000a$$\\\\dot V$$\\u000a) of

A. C. M. Schrikker; H. Wesenhagen; S. C. M. Luijendijk

1993-01-01

51

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

52

Gas Diodes for Thermoacoustic Self-circulating Heat Exchangers  

NASA Astrophysics Data System (ADS)

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

Swift, Greg; Backhaus, Scott

2006-05-01

53

AIR-WATER GAS EXCHANGE: MECHANISMS GOVERNING THE COMBINED EFFECTS OF WIND AND RAIN ON THE GAS TRANSFER  

E-print Network

AIR-WATER GAS EXCHANGE: MECHANISMS GOVERNING THE COMBINED EFFECTS OF WIND AND RAIN ON THE GAS at the Florida International University for water sample analysis during the Everglades experiment presented here, rain and iv #12;their effects on air-water gas and momentum exchanges. Funding for the Everglades

Luther, Douglas S.

54

PREDICTION OF TOTAL DISSOLVED GAS EXCHANGE AT HYDROPOWER DAMS  

SciTech Connect

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

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

2012-07-01

55

Steady-state canopy gas exchange: system design and operation  

NASA Technical Reports Server (NTRS)

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

Bugbee, B.

1992-01-01

56

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

57

[The variability of respiratory pattern and gas exchange].  

PubMed

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

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

2012-01-01

58

Plant Gas Exchange in Urban Landscapes L. Brooke McDowell and Chris A. Martin  

E-print Network

Plant Gas Exchange in Urban Landscapes L. Brooke McDowell and Chris A. Martin Department of Plant-term monitoring of gas exchange, irrigation practices, and microclimate in urban landscape plants was initiated in 1998 to research this question. Methods Effects of landscape design and land use history on plant gas

Hall, Sharon J.

59

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

Microsoft Academic Search

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

M. J. Davies; G. H. Chaffey

2008-01-01

60

Effect of airway disease on blood gas exchange in racehorses.  

PubMed

Inflammatory Airway Disease (IAD), exercise-induced pulmonary hemorrhage (EIPH), and upper airway obstruction (UAO) are common respiratory tract diseases that can decrease performance. The purpose of this retrospective study was to compare bronchoalveolar lavage fluid cytology and arterial blood gas analysis during a treadmill test by poorly performing racehorses presented to Purdue University. One hundred thirty-two horses with a history of poor performance were included in this study. Ten horses with no history or diagnosis of EIPH, IAD, or UAO served as controls. Horses were evaluated by rhinolaryngoscopy for upper airway abnormalities and underwent a standardized treadmill test, and samples were collected for blood gas analysis. Horses with IAD or EIPH had a more severe exercise-induced hypoxemia, (mean+/-SD; 84.8+/-1.5 and 86.0+/-1.7 mm Hg average Pao2, respectively), than horses in the control group (92.8+/-2.1 mm Hg). The average Pao2 of horses with only UAO (88.3+/-3.3 mm Hg) was not significantly different from control horses. Gas exchanges were the most severely impaired in horses affected with both EIPH and UAO because they exhibited the lowest Pao2 and highest Paco2 values (66.5+/-15.2 and 52.2+/-6.3 mm Hg, respectively). PMID:15715053

Sánchez, A; Couëtil, L L; Ward, M P; Clark, S P

2005-01-01

61

Energy requirements and equipment for continuous processing of raw foods by gas-exchange  

SciTech Connect

Equipment was developed to treat raw foods by gas-exchange in sufficient quantities to supply test samples for extensive laboratory tests. Design constraints were noted and the equipment and its operation described. Energy consumption measurements taken on the operating gas-exchange equipment were used to compare energy consumption in gas-exchange, freezing and canning processes. Energy savings of up to 43 percent were estimated for gas-exchange processing versus canning and freezing in a production to consumer food supply system.

Wheaton, F.W. (Univ. of Maryland, College Park); Kramer, A.; Ehrman, L.

1981-01-01

62

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

63

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

64

Effects of incomplete pulmonary gas exchange on VO2 max.  

PubMed

Recent evidence suggests that heavy exercise may lower the percentage of O2 bound to hemoglobin (%SaO2) by greater than or equal to 5% below resting values in some highly trained endurance athletes. We tested the hypothesis that pulmonary gas exchange limitations may restrict VO2max in highly trained athletes who exhibit exercise-induced hypoxemia. Twenty healthy male volunteers were divided into two groups according to their physical fitness status and the demonstration of exercise-induced reductions in %SaO2 less than or equal to 92%: 1) trained (T), mean VO2max = 56.5 ml.kg-1.min-1 (n = 13) and 2) highly trained (HT) with maximal exercise %SaO2 less than or equal to 92%, mean VO2max = 70.1 ml.kg-1.min-1 (n = 7). Subjects performed two incremental cycle ergometer exercise tests to determine VO2max at sea level under normoxic (21% O2) and mild hyperoxic conditions (26% O2). Mean %SaO2 during maximal exercise was significantly higher (P less than 0.05) during hyperoxia compared with normoxia in both the T group (94.1 vs. 96.1%) and the HT group (90.6 vs. 95.9%). Mean VO2max was significantly elevated (P less than 0.05) during hyperoxia compared with normoxia in the HT group (74.7 vs. 70.1 ml.kg-1.min-1). In contrast, in the T group, no mean difference (P less than 0.05) existed between treatments in VO2max (56.5 vs. 57.1 ml.kg-1.min-1). These data suggest that pulmonary gas exchange may contribute significantly to the limitation of VO2max in highly trained athletes who exhibit exercise-induced reductions in %SaO2 at sea level.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:2745310

Powers, S K; Lawler, J; Dempsey, J A; Dodd, S; Landry, G

1989-06-01

65

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

66

Gas exchange alterations in patients with chronic obstructive lung disease.  

PubMed

In a series of 23 patients with COPD, Wagner et al showed three distinct patterns of VA/Q distributions and a correlation between Burrows' clinical classification and the observed distribution patterns. Using the inert gas method, we studied 51 patients suffering from severe but stable COPD (FEV1 = 0.84 +/- 0.38 L; PaO2 = 58.5 +/- 10.5 mm Hg; PaCo2 = 48 +/- 6 mmHg; Ppa = 22 +/- 8 mmHg) breathing room air in a steady state. The H pattern (high mode of VA in high VA/Q) was found in 24 cases. There was an L pattern (Q mode in low VA/Q units) in nine cases and an HL (high-low) pattern in 16 cases (two patients were assigned another group). The analysis of the distribution data confirmed that VA/Q heterogeneity was the main factor underlying gas exchange disturbances in COPD. The PaO2 of the H subjects was higher than that of both HL (p less than 0.02) and L subjects. The true shunt value in the L group was significantly lower than in the H and HL groups. However, the relationship between clinical or functional aspects and distribution was not direct. The fraction of patients of H, HL, or (H + HL) types was nearly identical in the three clinical groups. The H pattern was found to be predominant in cases of COPD. PMID:3979134

Marthan, R; Castaing, Y; Manier, G; Guenard, H

1985-04-01

67

Compact design improves efficiency and CAPEX -- combining plate heat exchangers and gas-liquid separators for gas processing savings  

SciTech Connect

This paper presents the unique combination of two well proven technologies: a compact large scale welded plate heat exchanger with a gas-liquid separator within the same pressure vessel. Explained are the benefits for raw gas processing on production sites where cost, weight and efficiency are of particular importance. Application of this Combined Heat Exchanger-Separator is presented for various gas processing schemes: Turbo Expander, Mechanical Refrigeration and Joule-Thompson.

Waintraub, L.; Sourp, T. [Proser (France)

1998-12-31

68

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

Microsoft Academic Search

The removal of methyl iodide by adsorption onto silver mordenite was studied using a simulated off-gas from the fuel dissolution step of a nuclear fuel reprocessing plant. The methyl iodide adsorption of partially exchanged silver mordenite was examined for the effects of NO\\/sub x\\/, humidity, filter temperature, and degree of silver exchange. Partially exchanged silver mordenite, in general, achieved significantly

Jubin

1982-01-01

69

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

Microsoft Academic Search

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

Feng Yang; Xiugan Yuan; Guiping Lin

2003-01-01

70

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

71

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

E-print Network

Circadian rhythms constrain leaf and canopy gas exchange in an Amazonian forest Christopher E circadian rhythms constrain the rates of leaf and canopy gas exchange in an Amazonian forest over a day of the day. We attribute these cycles to circadian rhythms that are analogous to ones that have been reported

Goulden, Michael L.

72

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

E-print Network

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

Ahmad, Sajjad

73

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

ERIC Educational Resources Information Center

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

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

2013-01-01

74

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

EPA Science Inventory

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

75

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...

76

Effects of ionomer content on mass transport in gas diffusion electrodes for proton exchange membrane fuel cells  

Microsoft Academic Search

The effect of the ionomer content on the mass transport ability in gas diffusion electrodes of proton exchange membrane fuel cells (PEMFCs) was investigated. The influence of the catalytic activity caused by a change in ionomer content was eliminated by adjusting the amount of the catalyst. The mass transport ability was evaluated by the current of the oxygen reduction reaction

Z Siroma; T Sasakura; K Yasuda; M Azuma; Y Miyazaki

2003-01-01

77

Compact Ceramic Heat Exchangers for Corrosive Waste Gas Applications  

E-print Network

The development of large ceramic heat exchangers is described and performance data given for units installed on steel industry soaking pits in the U.K. Operational experience since 1973 confirms that ceramic heat exchangers capable of operating...

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

1982-01-01

78

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

79

Effects of Ozone on Gas Exchange in Invasive Forest Plants.  

NASA Astrophysics Data System (ADS)

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

Elton, E. E.

2006-12-01

80

Gas exchange impairment and pulmonary densities after cardiac surgery.  

PubMed

In 11 patients with impaired respiratory function after coronary artery revascularization surgery, thoracic computed tomography (TCT) and cardiopulmonary profile were obtained. The patients were haemodynamically stable without clinical or radiological signs of lung oedema. Oxygenation was reduced in all patients (alveolo-arterial PO2-difference (PA-aO2) = 37.3 +/- 10.39 kPa, venous admixture (QVA/QT) = 26.4 +/- 4.4%) during mechanical ventilation with positive end-expiratory pressure (PEEP = 5 cmH2O) (0.5 kPa). TCT-scan analysis revealed considerable amounts of crest-shaped bilateral densities in dependent lung regions. There were no differences between the right and left hemithorax. Atelectatic lung tissues were defined as areas presenting with attenuation values of -200 to +20 Hounsfield Units. The magnitude of non-ventilated areas correlated with QVA/QT (r = 0.875, P < or = 0.01), but not with the duration of either extracorporeal circulation, surgical procedure or general anaesthesia. It is concluded that atelectasis in dependent lung areas contributes to impaired gas exchange after cardiac surgery. PMID:1466218

Hachenberg, T; Brüssel, T; Roos, N; Lenzen, H; Möllhoff, T; Gockel, B; Konertz, W; Wendt, M

1992-11-01

81

Gas in active galactic nuclei  

Microsoft Academic Search

An overview of line-emitting regions in active galactic nuclei (AGN) is presented. Most existing AGN gas line-intensity measurements are accounted for by detailed photoionization models used in conjunction with spectrophotometric observations. The Seyfert 1 galaxy and quasar picture includes gravity as the primary energy source, and a black hole of 1-10 billion solar masses with a radiating accretion disk. None

G. M. MacAlpine

1986-01-01

82

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

83

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

E-print Network

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

84

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

NASA Astrophysics Data System (ADS)

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

Chmielniak, Tadeusz; Czaja, Daniel; Lepszy, Sebastian

2013-12-01

85

Impact of an artificial surfactant release on airsea gas fluxes during Deep Ocean Gas Exchange Experiment II  

E-print Network

; accepted 7 September 2011; published 12 November 2011. [1] During the 2007 UK SOLAS Deep Ocean Gas Exchange physical barrier and through modification of sea surface hydrodynamics and hence turbulent energy transfer

Ho, David

86

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

Microsoft Academic Search

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

Kohei Koyama; Chungpyo Hong; Yutaka Asako

2012-01-01

87

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

Microsoft Academic Search

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

Kohei Koyama; Chungpyo Hong; Yutaka Asako

2011-01-01

88

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

E-print Network

August 2006. [1] The SOLAS Air-Sea Gas Exchange (SAGE) Experiment was conducted in the western Pacific of air-sea gas exchange. Globally, the dominant control of air-sea gas exchange is turbulent energy as the primary source of energy for the atmospheric and oceanic molecular boundary layers have been derived from

Ho, David

89

Simultaneous measurement of acetylene reduction and respiratory gas exchange of attached root nodules.  

PubMed

A method was developed for the simultaneous measurement of acetylene reduction, carbon dioxide evolution and oxygen uptake by individual root nodules of intact nitrogen-fixing plants (Alnus rubra Bong.). The nodules were enclosed in a temperature-controlled leak-tight cuvette. Assay gas mixtures were passed through the cuvette at a constant, known flow rate and gas exchange was measured by the difference between inlet and outlet gas compositions. Gas concentrations were assayed by a combination of an automated gas chromatograph and a programmable electronic integrator. Carbon dioxide and ethylene evolution were determined with a coefficient of variation which was less than 2%, whereas the coefficient of variation for oxygen uptake measurements was less than 5%. Nodules subjected to repeated removal from and reinsertion into the cuvette and to long exposures of 10% v/v acetylene showed no irreversible decline in respiration or acetylene reduction. This system offers long-term stability and freedom from disturbance artifacts plus the ability to monitor continuously, rapidly and specifically the changes in root nodule activity caused by environmental perturbation. PMID:16662496

Winship, L J; Tjepkema, J D

1982-08-01

90

Establishment and activities of the Japan Chemistry Program Exchange  

NASA Astrophysics Data System (ADS)

Recently, many chemists have developed various computer programs for the research of computer chemistry such as computer-aided design of new chemicals or materials. The Japan Chemistry Program Exchange (JCPE) has just started in order to further develop computer chemistry in Japan by making these programs effectively accessible to other chemists who desire to use them. The JCPE will undertake such activities as registration, reference service and distribution of the computer chemistry programs and will contribute to international exchange of these programs. Every chemist who has an interest in this field, regardless of academic or industrial, is asked to be a member of the Exchange.

Tanabe, Kazutoshi

91

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

PubMed

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

Matthews, Philip G D; White, Craig R

2011-09-15

92

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

93

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

SciTech Connect

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

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

1986-08-01

94

Steric Effects in Peptide and Protein Exchange with Activated Disulfides  

PubMed Central

Disulfide exchange is an important bioconjugation tool, enabling chemical modification of peptides and proteins containing free cysteines. We previously reported the synthesis of a macromer bearing an activated disulfide and its incorporation into hydrogels. Despite their ability to diffuse freely into hydrogels, larger proteins were unable to undergo in-gel disulfide exchange. In order to understand this phenomenon, we synthesized four different activated disulfide-bearing model compounds (Mn = 300 Da-10 kDa) and quantified their rate of disulfide exchange with a small peptide (glutathione), a moderate-sized protein (?-lactoglobulin), and a large protein (bovine serum albumin) in four different pH solutions (6.0, 7.0, 7.4, and 8.0) to mimic biological systems. Rate constants of exchange depend significantly on the size and accessibility of the thiolate. pH also significantly affects the rate of reaction, with the faster reactions occurring at higher pH. Surprisingly, little difference in exchange rates is seen between macromolecular disulfides of varying size (Mn = 2 kDa – 10kDa), although all undergo exchange more slowly than their small molecule analogue (MW = 300 g/mol). The maximum exchange efficiencies (% disulfides exchanged after 24 h) are not siginificantly affected by thiol size or pH, but somewhat affected by disulfide size. Therefore, while all three factors investigated (pH, disulfide size and thiolate size) can influence the exchange kinetics and extent of reaction, the size of the thiolate and its accessibility plays the most significant role. PMID:23865598

Kerr, Jason; Schlosser, Jessica L.; Griffin, Donald R.; Wong, Darice Y.; Kasko, Andrea M.

2014-01-01

95

Pulmonary and cutaneous O?gas exchange: a student laboratory exercise in the frog.  

PubMed

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

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

2013-03-01

96

Effects of temperature and altitude on ventilation and gas exchange in chukars ( Alectoris chukar )  

Microsoft Academic Search

The effects of ambient temperature (Ta) on ventilation and gas exchange in chukar partridges (Alectoris chukar) were determined after acclimation to low and high altitute (LA and HA; 340 and 3,800 m, respectively).

Mark A. Chappell; Theresa L. Bucher

1987-01-01

97

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

E-print Network

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

Latcham, Jacob G. (Jacob Greco)

2009-01-01

98

A trace gas technique for measuring clothing microclimate air exchange rates  

PubMed Central

Crockford, G. W., Crowder, M., and Prestidge, S. P. (1972).Brit. J. industr. Med.,29, 378-386. A trace gas technique for measuring clothing microclimate air exchange rates. The rate at which clothing microclimate air is exchanged for ambient air influences the sensible and insensible heat loss from the microclimate. Factors which influence this air exchange are clothing permeability, wind speed, body movements, clothing design, and fabric properties. The influence of the first four factors has been studied using a trace gas technique for measuring the rate at which microclimate air is exchanged for ambient air. The trace gas technique and the mathematical model describing the loss of the trace gas from the microclimate are described. The technique is shown to have a high resolving power, enabling small changes in the four factors studied to be identified, and as the method is also very quick detailed studies of garment design can be made. Images PMID:4636659

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

1972-01-01

99

Prediction of Gas Generation and Bubble Formation in Crystalline Silicotitanate Ion Exchange Columns  

SciTech Connect

Non-elutable ion exchange technology using crystalline silicotitanate (CST) has been studied at the Savannah River Site (SRS) for removing cesium from SRS soluble radioactive waste. The authors developed a transient model to describe the process of gas generation due to radiolysis and bubble formation in CST ion exchange (IX) columns using the Aspen Custom Modeler (ACM) software package. The model calculates gas concentrations and onset of bubble formation for large CST IX columns. The calculations include cesium loading as a function of time, gas generation as a function of cesium loading, and bubble formation as a function of gas solubility.

Hang, T.

2000-12-19

100

Cyclic gas exchange in the giant burrowing cockroach, Macropanesthia rhinoceros: Effect of oxygen tension and temperature  

Microsoft Academic Search

The giant burrowing cockroach, Macropanesthia rhinoceros, is endemic to north-eastern Australia and excavates a permanent burrow up to 1m deep into soil. Using flow-through respirometry, we investigated gas exchange and water loss at three different oxygen tensions (21%, 10% and 2% at 20°C) and temperatures (10, 20 and 30°C at 21% oxygen). M. rhinoceros employ cyclic gas exchange (CGE) making

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

2007-01-01

101

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

102

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

103

Pulmonary vascular dilatation and diffusion-dependent impairment of gas exchange in liver cirrhosis  

Microsoft Academic Search

To test the hypothesis that diffusion-limitation for oxygen is due to abnormal vascular dilatation and significantly contributes to the arterial hypox- aemia of liver cirrhosis requires an experimental approach that detects both dif- fusion-limitation for oxygen and the presence of abnormal dilatation of pulmonary vessels exposed to alveolar gas. We therefore studied the gas exchange of a 64 year old

A. B. H. Crawford; J. Regnis; L. Laks; P. Donnelly; L. A. Engel; I. H. Young

1995-01-01

104

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

Microsoft Academic Search

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

Dennis D. Baldocchi; Tilden P. Meyers

1991-01-01

105

INFLUENCE OF WETTABILITY ON LIQUID WATER TRANSPORT IN GAS DIFFUSION LAYER OF PROTON EXCHANGE MEMBRANE FUEL  

E-print Network

INFLUENCE OF WETTABILITY ON LIQUID WATER TRANSPORT IN GAS DIFFUSION LAYER OF PROTON EXCHANGE to 3D systems, notably from binarised images of GDLs obtained by X ray microtomography. 1. INTRODUCTION that a detailed understanding of liquid water transport in the gas diffusion layer (GDL) is necessary

Paris-Sud XI, Université de

106

Inhibition and activation of Na/sup +/-Ca/sup 2 +/ exchange activity by quinacrine  

SciTech Connect

Quinacrine either inhibited or stimulated Na-Ca exchange in cardiac sarcolemmal vesicles, depending on the experimental conditions. When present in the assay medium for Na-Ca exchange, quinacrine inhibited both Na/sub i/-dependent Ca/sup 2 +/ uptake (K/sub i/ = 50 ..mu..M) and Na/sub 0/-dependent Ca/sup 2 +/ efflux. Quinacrine's inhibition of Ca/sub 2//sup +/ efflux was attenuated by high concentrations of Na/sup +/. Quinacrine also blocked Na-Na and Ca-Ca exchange activities in the vesicles. The inhibitory effects of quinacrine on Na-Ca exchange activity are qualitatively similar to those reported previously for amiloride derivatives. When Na-loaded vesicles were preincubated with quinacrine and then assayed for Na-Ca exchange in a quinacrine-free medium, stimulation of exchange activity was observed. This stimulation was reversible on the removal of bound quinacrine and involved a reduction in the apparent K/sub m/ for extravesicular Ca/sup 2 +/. Stimulation of exchange activity under these conditions was also observed with the lipophilic cations tetraphenylphosphonium. Since Ca/sup 2 +/, quinacrine and tetraphenylphosphonium all bind strongly to sarcolemmal membranes it is suggested that the observed stimulation of exchange activity involves a local electrostatic effect of the bound cations in accelerating a rate-limiting step in the reaction mechanism for Na-Ca exchange.

de la Pena, P.; Reeves, J.P.

1987-01-01

107

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

NASA Technical Reports Server (NTRS)

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

Bowman, William D.

1989-01-01

108

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

Microsoft Academic Search

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

P. M. Dussinger; J. R. Hartenstine

1992-01-01

109

The state of the photosynthetic apparatus in leaves as analyzed by rapid gas exchange and optical methods: the pH of the chloroplast stroma and activation of enzymes in vivo.  

PubMed

The exchange of CO2 and O2 was measured in leaves using specially constructed equipment capable of responding to rapid transients. Optical measurements provided information on cytochrome f and P 700 oxidation in the light. The following results were obtained: i) The solubilization of CO2 was used to calculate the pH of the chloroplast stroma in darkened leaves. Values ranged from pH 7.8 to pH 8.0 in different C3 plants. ii) Illumination of predarkened leaves of Helianthus annuus L. resulted in three distinct phases of O2 evolution that illustrate the complexity of light activation of the photosynthetic apparatus. A first burst of O2 is attributed to the reduction of electron carriers of the electron-transport chain. While plastoquinone was reduced, cytochrome f was oxidized. Appreciable oxidation of P 700 became possible only during the second O2 burst, which indicates the reduction of the phosphoglycerate pool. Extensive oxidation required the opening of an electron gate on the reducing side of photosystem I. The subsequent slow rise in O2 evolution towards a steady state reflects activation of the Calvin cycle and is the result of CO2 assimilation. iii) Light-dependent CO2 uptake by predarkened leaves occurred in four phases, three of them based on pH changes in the chloroplast stroma. Initial CO2 uptake was small and probably caused by protonation of reduced plastoquinone. In the second phase, which coincided with the reduction of the pool of phosphoglycerate, the initial alkalization of the chloroplast stroma was substantially increased. In the third phase, the stroma alkalization decreased, and the fourth phase was dominated by CO2 assimilation. iv) Respiratory CO2 production was partially suppressed in the light during the second phase of O2 evolution while phosphoglycerate was being reduced. PMID:24212428

Laisk, A; Oja, V; Kiirats, O; Raschke, K; Heber, U

1989-03-01

110

Synergism of Pratylenchus penetrans and Verticillium dahliae Manifested by Reduced Gas Exchange in Potato.  

PubMed

ABSTRACT The effects of solitary and concurrent infection by Pratylenchus pene-trans and Verticillium dahliae on gas exchange of Russet Burbank potato (Solanum tuberosum) were studied in growth chamber experiments. Treatments were P. penetrans at low, medium, and high density; V. dahliae alone at one initial density; the combination of the nematode at these three densities and V. dahliae; and a noninfested control. Gas exchange parameters of leaf cohorts of different ages in the different treatments were repeatedly measured with a Li-Cor LI-6200 portable photosynthesis system. At 45 days after planting, joint infection significantly reduced net photosynthesis, stomatal conductance, and transpiration of 1- to 25-day-old leaf cohorts. Intercellular CO(2) levels were significantly increased by co-infection, especially in older leaves. The synergistic effect of co-infection on gas exchange parameters was greater in the oldest cohort than in the youngest cohort. No consistent effects on leaf gas exchange parameters were observed in plants infected by the nematode or the fungus alone. The relationship between the assimilation rate and stomatal conductance remained linear regardless of solitary or concomitant infection, indicating that stomatal factors are primarily responsible for regulating photosynthesis. The significant reduction of gas exchange in leaves of co-infected plants without reduction in intercellular CO(2) concentrations suggests that nonstomatal factors also play a role when both organisms are present. PMID:18945123

Saeed, I A; Macguidwin, A E; Rouse, D I

1997-04-01

111

The effect of the bain circuit on gas exchange  

Microsoft Academic Search

This is an experimental and theoretical analysis of the Mapleson D (Bain) circuit. A bench model was used to determine the\\u000a effects of breathing rate, tidal volume, and fresh gas flow on the simulated alveolar gas composition when a commercial Bain\\u000a breathing circuit is used. in addition, an effort was made to derive mathematical equations that describe the CO2-profile in

Marc J. Jaeger; Raymond R. Schultetus

1987-01-01

112

Hybrid numerical simulation of large-scale gas-fired tubular heat exchangers  

Microsoft Academic Search

This article presents a hybrid computational fluid dynamics (CFD) modeling approach to the large-scale gas-fired heat exchanger. As the full-grid simulation on this heat exchanger requires impractical computational cost, a simplified “1D + 2D + 3D” hybrid CFD model is developed to reduce the computational cost and make the simulation doable on the common workstations. In this model, the air

Junjie Ji; Yuling Shi; Chunlu Zhang

2011-01-01

113

The impact of ten years at -20°C on gas exchange in five lichen species  

Microsoft Academic Search

Rates of net CO2 exchange in five sympatric species of Umbilicaria were measured after 10 years at-20°C. During that time, the lichens had been at either a high (saturated) or a low (air-dry) water content. The results showed an immediate, return to normal rates of gas exchange for air-dried then frozen U.vellea. Rates returned to normal for air-dried U. deusta

D. W. Larson

1989-01-01

114

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

115

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

NASA Astrophysics Data System (ADS)

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

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

2011-05-01

116

Evaluation of local gas exchange in a pulsating respiratory support catheter.  

PubMed

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 non-uniform 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. PMID:15839440

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

2005-01-01

117

Energy Recovery By Direct Contact Gas-Liquid Heat Exchange  

E-print Network

that the effective heat transfer coefficient may be based on the sensible cooling duty of the non-condensing portion of the gas: Q s = W rr (c g)(t g,in - tg,o.,) = Va (r g - ti) metJn (4) (5)where Correlations for the values of Va, hga and hLa have been based... that the effective heat transfer coefficient may be based on the sensible cooling duty of the non-condensing portion of the gas: Q s = W rr (c g)(t g,in - tg,o.,) = Va (r g - ti) metJn (4) (5)where Correlations for the values of Va, hga and hLa have been based...

Fair, J. R.; Bravo, J. L.

118

Estimating oxygen diffusive conductances of gas-exchange systems: A stereological approach illustrated with the human placenta.  

PubMed

For many organisms, respiratory gas exchange is a vital activity and different types of gas-exchange apparatus have evolved to meet individual needs. They include not only skin, gills, tracheal systems and lungs but also transient structures such as the chorioallantois of avian eggs and the placenta of eutherian mammals. The ability of these structures to allow passage of oxygen by passive diffusion can be expressed as a diffusive conductance (units: cm(3) O2 min(-1) kPa(-1)). Occasionally, the ability to estimate diffusive conductance by physiological techniques is compromised by the difficulty of obtaining O2 partial pressures on opposite sides of the tissue interface between the delivery medium (air, water, blood) and uptake medium (usually blood). An alternative strategy is to estimate a morphometric diffusive conductance by combining stereological estimates of key structural quantities (volumes, surface areas, membrane thicknesses) with complementary physicochemical data (O2-haemoglobin chemical reaction rates and Krogh's permeability coefficients). This approach has proved valuable in a variety of comparative studies on respiratory organs from diverse species. The underlying principles were formulated in pioneering studies on the pulmonary lung but are illustrated here by taking the human placenta as the gas exchanger. PMID:23069190

Mayhew, Terry M

2014-01-01

119

Diode laser absorption spectroscopy for studies of gas exchange in fruits  

NASA Astrophysics Data System (ADS)

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

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

2006-07-01

120

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

NASA Astrophysics Data System (ADS)

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

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

2004-12-01

121

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

PubMed Central

The adaptive significance of discontinuous gas exchange cycles (DGC) in insects is contentious. Based on observations of DGC occurrence in insects of typically large brain size and often socially-complex life history, and spontaneous DGC in decapitated insects, the neural hypothesis for the evolution of DGC was recently proposed. It posits that DGC is a non-adaptive consequence of adaptive down-regulation of brain activity at rest, reverting ventilatory control to pattern-generating circuits in the thoracic ganglia. In line with the predictions of this new hypothesis, we expected a higher likelihood of DGC in the gregarious phase of the desert locust (Schistocerca gregaria, Orthoptera), which is characterized by a larger brain size and increased sensory sensitivity compared with the solitary phase. Furthermore, surgical severing of the neural connections between head and thoracic ganglia was expected to increase DGC prevalence in both phases, and to eliminate phase-dependent variation in gas exchange patterns. Using flow-through respirometry, we measured metabolic rates and gas exchange patterns in locusts at 30°C. In contrast to the predictions of the neural hypothesis, we found no phase-dependent differences in DGC expression. Likewise, surgically severing the descending regulation of thoracic ventilatory control did not increase DGC prevalence in either phase. Moreover, connective-cut solitary locusts abandoned DGC altogether, and employed a typical continuous gas exchange pattern despite maintaining metabolic rate levels of controls. These results are not consistent with the predictions of the neural hypothesis for the evolution of DGC in insects, and instead suggest neural plasticity of ventilatory control. PMID:23555850

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

2013-01-01

122

Neural control of gas exchange patterns in insects: locust density-dependent phases as a test case.  

PubMed

The adaptive significance of discontinuous gas exchange cycles (DGC) in insects is contentious. Based on observations of DGC occurrence in insects of typically large brain size and often socially-complex life history, and spontaneous DGC in decapitated insects, the neural hypothesis for the evolution of DGC was recently proposed. It posits that DGC is a non-adaptive consequence of adaptive down-regulation of brain activity at rest, reverting ventilatory control to pattern-generating circuits in the thoracic ganglia. In line with the predictions of this new hypothesis, we expected a higher likelihood of DGC in the gregarious phase of the desert locust (Schistocerca gregaria, Orthoptera), which is characterized by a larger brain size and increased sensory sensitivity compared with the solitary phase. Furthermore, surgical severing of the neural connections between head and thoracic ganglia was expected to increase DGC prevalence in both phases, and to eliminate phase-dependent variation in gas exchange patterns. Using flow-through respirometry, we measured metabolic rates and gas exchange patterns in locusts at 30°C. In contrast to the predictions of the neural hypothesis, we found no phase-dependent differences in DGC expression. Likewise, surgically severing the descending regulation of thoracic ventilatory control did not increase DGC prevalence in either phase. Moreover, connective-cut solitary locusts abandoned DGC altogether, and employed a typical continuous gas exchange pattern despite maintaining metabolic rate levels of controls. These results are not consistent with the predictions of the neural hypothesis for the evolution of DGC in insects, and instead suggest neural plasticity of ventilatory control. PMID:23555850

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

2013-01-01

123

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

Microsoft Academic Search

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

Hong SungDeok; Oh DongSeok; Lee WonJae; Chang JongHwa

2006-01-01

124

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

125

The effect of surface films on the air–sea gas exchange in the Baltic Sea  

Microsoft Academic Search

Gas exchange experiments were performed with water from a coastal station in the southwestern Baltic Sea in order to investigate the effect of organic films on the gas transfer velocity. Samples were taken on a weekly basis during January to July in 2007 and 2008. Using a 1.5l glass vessel, the evasion of oxygen from the sample into an O2-free

R. Schmidt; B. Schneider

2011-01-01

126

Light heterogeneity and gas exchange dynamics above and within a monodominant Congolese rain forest canopy  

NASA Astrophysics Data System (ADS)

Photosynthetic photon flux density (PPFD; ?mol photosynthetically active photons m-2 s-1) regimes within vegetation canopies are intrinsically heterogeneous in time and space. Because the nature of the PPFD environment within a canopy can affect many aspects of plant ecophysiology, characterizing canopy PPFD dynamics is essential for assessing vegetation regeneration, growth, succession, and trace gas exchange with the atmosphere. Despite the fact that clouds and aerosols are ubiquitous and can dramatically affect the intensity and source direction of the photon flux impinging upon a vegetation canopy, few studies have addressed how various sky conditions affect PPFD regimes and ecophysiology within the canopy. In this dissertation, I address PPFD dynamics above and within a tropical rain forest and the concomitant effects on canopy trace gas exchange with the atmosphere. Each investigation I report centers upon empirical measurements acquired in 42 m tall primary, monodominant Gilbertiodendron dewevrei (Caesalpiniaceae) tropical rain forest located in the Republic of Congo. In Chapter 2, I examine the intensity and temporal frequency of sunflecks at three canopy depths over a 12 day period. In Chapter 3, I analyze a subset of the raw data used in Chapter 2 to investigate how within-canopy PPFD heterogeneity varies with respect to sky diffuse fraction (SDF; diffuse downwelling PPFD/total downwelling PPFD). In Chapter 4, I develop an empirical model to investigate changes in Gilbertiodendron dewevrei canopy- atmosphere exchange of carbon dioxide and isoprene under varying SDF. Model results indicate that net carbon assimilation by this canopy reached maximum rates during periods of intermediate SDF (i.e. partly cloudy/hazy skies). Mean canopy light use efficiency (mole CO2 assimilated/mole of incident photons) during overcast skies was twice as high as during clear periods. The modeled isoprene flux from this canopy exhibited a near-linear decrease with increasing SDF. In sum, quantifying the effects of SDF on canopy functioning may be important for understanding future changes in tropical plant community ecology and the flow of materials between the biosphere and the atmosphere given ever increasing human influences on cloud and haze cover in the tropics.

Vierling, Lee Alexander

1999-10-01

127

The effect of light on stomatal control of gas exchange in Douglas fir ( Pseudotsuga menziesii ) saplings  

Microsoft Academic Search

Attached twigs of young Pseudotsuga menziesii (Mirb.) Franco plants were subjected to variations in irradaince. Stomatal responsiveness to irradiance, measured in an open type gas exchange system, varied seasonally. During the autumn and winter, stomatal conductance was relatively unresponsive to changes in irradiance, but during the summer stomatal conductance decreased in response to reduced irradiance. The summer stomatal response to

Frederick C. Meinzer

1982-01-01

128

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

129

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

E-print Network

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

Paris-Sud XI, Université de

130

Indirect effects of insect herbivory on leaf gas exchange in soybean  

Microsoft Academic Search

Herbivory can affect plant carbon gain directly by removing photosynthetic leaf tissue and indirectly by inducing the production of costly defensive compounds or disrupting the movement of water and nutrients. The indirect effects of herbivory on carbon and water fluxes of soybean leaves were investigated using gas exchange, chlorophyll fluores- cence and thermal imaging. Herbivory by Popillia japon- ica and

MIHAI ALDEA; JASON G. HAMILTON; JOSEPH P. RESTI; ARTHUR R. ZANGERL; MAY R. BERENBAUM; EVAN H. D eLUCIA

2005-01-01

131

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...

132

Gas exchange and water balance of a mistletoe species and its mangrove hosts  

Microsoft Academic Search

The gas exchange and water relations of the hemiparasite Pthirusa maritima and two its mangrove host species, Conocarpus erectus and Coccoloba uvifera, were studied in an intertidal zone of the Venezuelan coast. Carbon uptake and transpiration, leaf osmotic and total water potential, as well as nutrient content in the xylem sap and leaves of mistletoes and hosts were followed through

G. Goldstein; F. Rada; L. Sternberg; J. L. Burguera; M. Burguera; A. Orozco; M. Montilla; O. Zabala; A. Azocar; M. J. Canales; A. Celis

1989-01-01

133

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

E-print Network

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

Stiller, Volker

134

Numerical optimization of a fin-tube gas to liquid heat exchanger  

Microsoft Academic Search

The influence of plate fin, fin tube and protrusion parameters on heat transfer and pressure drop characteristics of a finned tube gas to liquid heat exchanger is examined in this study. The optimization of plate fin, fin tube and protrusion dimensions as well as protrusion locations on plate fin surface is performed numerically using a computational fluid dynamics (CFD) program

Levent Bilir; Zafer ?lken; Aytunç Erek

135

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

136

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

PubMed

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

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

2014-12-01

137

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

E-print Network

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

Ahmad, Sajjad

138

Effects of elevated atmospheric carbon dioxide on gas exchange and growth of white clover  

Microsoft Academic Search

Effects of rising atmospheric CO2 concentrations on gas exchange, growth and productivity were investigated on an important grassland species, Trifolium repens L. cv. Blanca. Pure stands of this species were cultivated over an entire growing season in small acrylic greenhouses with an artificial atmosphere of ±367 or ±620 ppm CO2, respectively. Effects on growth and development were examined in a

I. Nijs; I. Impens; T. Behaeghe

1988-01-01

139

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

E-print Network

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

Federspiel, William J.

140

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

E-print Network

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

Wait, D. Alexander

141

Effects of elevated carbon dioxide on leaf gas exchange and growth of cork-oak  

E-print Network

Short note Effects of elevated carbon dioxide on leaf gas exchange and growth of cork-oak (Quercus) and at elevated (700 ?mol mor-1) concentrations of carbon dioxide. In well-watered conditions, daily max- imum CO2, but no change in root/shoot ratio was observed. Quercus suber / carbon dioxide / photosynthesis

Paris-Sud XI, Université de

142

Gas exchange responses of Chesapeake Bay tidal marsh species under field and laboratory conditions  

Microsoft Academic Search

Laboratory and field gas exchange measurements were made on C3 (Scirpus olneyi Gray) and C4 (Spartina patens (Ait.) Mahl., Distichlis spicata (L.) Green) species from an irregularly flooded tidal marsh on the Chesapeake Bay. Laboratory measurements were made on plants grown from root stocks that were transplanted to a greenhouse and grown under high light and high nutrient conditions. The

T. M. DeJong; B. G. Drake; R. W. Pearcy

1982-01-01

143

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

144

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

Microsoft Academic Search

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

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

2008-01-01

145

High-frequency partial liquid ventilation in respiratory distress syndrome: hemodynamics and gas exchange.  

PubMed

Partial liquid ventilation using conventional ventilatory schemes improves lung function in animal models of respiratory failure. We examined the feasibility of high-frequency partial liquid ventilation in the preterm lamb with respiratory distress syndrome and evaluated its effect on pulmonary and systemic hemodynamics. Seventeen lambs were studied in three groups: high-frequency gas ventilation (Gas group), high-frequency partial liquid ventilation (Liquid group), and high-frequency partial liquid ventilation with hypoxia-hypercarbia (Liquid-Hypoxia group). High-frequency partial liquid ventilation increased oxygenation compared with high-frequency gas ventilation over 5 h (arterial oxygen tension 253 +/- 21.3 vs. 17 +/- 1.8 Torr; P < 0.001). Pulmonary vascular resistance decreased 78% (P < 0.001), pulmonary blood flow increased fivefold (P < 0.001), and aortic pressure was maintained (P < 0.01) in the Liquid group, in contrast to progressive hypoxemia, hypercarbia, and shock in the Gas group. Central venous pressure did not change. The Liquid-Hypoxia group was similar to the Gas group. We conclude that high-frequency partial liquid ventilation improves gas exchange and stabilizes pulmonary and systemic hemodynamics compared with high-frequency gas ventilation. The stabilization appears to be due in large part to improvement in gas exchange. PMID:9451653

Sukumar, M; Bommaraju, M; Fisher, J E; Morin, F C; Papo, M C; Fuhrman, B P; Hernan, L J; Leach, C L

1998-01-01

146

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

E-print Network

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

Niyogi, Dev

147

Early season cuticular conductance and gas exchange in two oaks near the western edge of their range  

Microsoft Academic Search

Seasonal changes in minimum leaf conductance to water vapor (gmin), an estimate of cuticular conductance, and photosynthetic gas exchange in two co-occurring oak species in north-east Kansas (USA) were examined to determine if leaf gas exchange characteristics correlated with differences in tree distribution. Bur oak (Quercus macrocarpa Michx.) is more abundant in mesic gallery forest sites, whereas chinquapin oak (Quercus

Erik P. Hamerlynck; Alan K. Knapp

1996-01-01

148

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

SciTech Connect

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

Jubin, R.T.

1982-01-01

149

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

SciTech Connect

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

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

2004-01-01

150

Gas exchange during high-frequency ventilation in the pigeon (Columba livia).  

PubMed

We studied the effect of high-frequency ventilation (HFV) on the gas exchange of tracheotomized pigeons. The pigeons were artificially ventilated using a piston pump, which alternately connected the pigeons' airways to a constant-flow source. Two-minute periods of HFV were interposed between long periods of normal ventilation. The effect of HFV was assessed by the recorded changes in the PO2, PCO2 and pH of arterial blood and from the changes in the composition of the gas in the interclavicular air sacs. The results showed that HFV can augment gas exchange when the tidal volume (VT) is less than the volume of the anatomical dead space (VD). However, normal arterial gas composition can only be maintained if respiratory frequency is high (greater than 20 Hz). At the normal panting frequency of pigeons (7.8 Hz), gas exchange can thus only be maintained if tidal volume is approximately 125% of the dead space. When panting the VT must be greater than the VD. This finding agrees with the results of recent work showing flush-out- or compound-panting in birds: i.e. if, during panting, VT approaches close to the VD, intermittent interruptions, by taking deeper breaths in order to ensure a supply of fresh air to the lungs, are necessary. PMID:3147570

Bech, C; Johansen, K; Nicol, S

1988-02-01

151

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

152

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

PubMed Central

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

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

2011-01-01

153

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

154

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

155

Laser photoacoustic spectroscopy of biosystems gas exchange with the atmosphere  

NASA Astrophysics Data System (ADS)

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

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

1998-10-01

156

Gas-exchange properties of developing cotton fruit  

SciTech Connect

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

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

1990-05-01

157

Pulmonary gas exchange efficiency during exercise breathing normoxic and hypoxic gas in adults born very preterm with low diffusion capacity.  

PubMed

Adults with a history of very preterm birth (<32 wk gestational age; PRET) have reduced lung function and significantly lower lung diffusion capacity for carbon monoxide (DLCO) relative to individuals born at term (CONT). Low DLCO may predispose PRET to diffusion limitation during exercise, particularly while breathing hypoxic gas because of a reduced O2 driving gradient and pulmonary capillary transit time. We hypothesized that PRET would have significantly worse pulmonary gas exchange efficiency [i.e., increased alveolar-to-arterial Po2 difference (AaDO2)] during exercise breathing room air or hypoxic gas (FiO2 = 0.12) compared with CONT. To test this hypothesis, we compared the AaDO2 in PRET (n = 13) with a clinically mild reduction in DLCO (72 ± 7% of predicted) and CONT (n = 14) with normal DLCO (105 ± 10% of predicted) pre- and during exercise breathing room air and hypoxic gas. Measurements of temperature-corrected arterial blood gases, and direct measure of O2 saturation (SaO2), were made prior to and during exercise at 25, 50, and 75% of peak oxygen consumption (V?o2peak) while breathing room air and hypoxic gas. In addition to DLCO, pulmonary function and exercise capacity were significantly less in PRET. Despite PRET having low DLCO, no differences were observed in the AaDO2 or SaO2 pre- or during exercise breathing room air or hypoxic gas compared with CONT. Although our findings were unexpected, we conclude that reduced pulmonary function and low DLCO resulting from very preterm birth does not cause a measureable reduction in pulmonary gas exchange efficiency. PMID:24970854

Duke, Joseph W; Elliott, Jonathan E; Laurie, Steven S; Beasley, Kara M; Mangum, Tyler S; Hawn, Jerold A; Gladstone, Igor M; Lovering, Andrew T

2014-09-01

158

Effect of body positions on hemodynamics and gas exchange in anesthetized pigs shortly after pneumonectomy.  

PubMed

Positional changes are thought to affect hemodynamics, respiratory mechanics, and gas exchange after pneumonectomy. The objective of this study was to compare hemodynamic and respiratory parameters and gas exchange in different positions before and after pneumonectomy. Twenty pigs were anesthetized and mechanically ventilated. Seven received right-side pneumonectomy, seven received left-side pneumonectomy, and six were anesthetized but did not receive surgery and served as controls. Hemodynamic and respiratory parameters and blood gas values were measured in different positions (supine and right and left lateral decubitus). Minute mechanical ventilation was controlled throughout. Pneumonectomy resulted in significant reductions in MAP, accompanied by significant decreases in cardiac index, stroke volume index, global ejection fraction, and global end-diastolic volume index. Mean pulmonary arterial pressure and pulmonary vascular resistance index increased. PaCO2, airway resistance, and peak airway pressure increased, whereas PaO2 and lung compliance decreased. Hemodynamic and respiratory parameters and gas exchange were also significantly affected by changes in position with pneumonectomy. Mean arterial pressure, cardiac index, stroke volume index, global ejection fraction, and global end-diastolic volume index were significantly lower in the supine than in the right or left lateral decubitus position. PaO2 was significantly higher in a lateral position, with the remaining lung uppermost. Our findings suggest that avoiding the supine positioning after pneumonectomy may facilitate improvements in hemodynamics and a decreased risk of hypoxemia. The optimal position for gas exchange after pneumonectomy is a lateral position, with the remaining lung in the uppermost position. PMID:20220567

Lan, Chou-Chin; Chang, Chia-Yu; Peng, Chung-Kan; Wu, Chin-Pyng; Huang, Kun-Lun; Lee, Shih-Chun; Chang, Hung

2010-11-01

159

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

PubMed

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

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

2014-03-01

160

Gas exchange efficiency of an oxygenator with integrated pulsatile displacement blood pump for neonatal patients.  

PubMed

Oxygenators have been used in neonatal extracorporeal membrane oxygenation (ECMO) since the 1970s. The need to develop a more effective oxygenator for this patient cohort exists due to their size and blood volume limitations. This study sought to validate the next design iteration of a novel oxygenator for neonatal ECMO with an integrated pulsatile displacement pump, thereby superseding an additional blood pump. Pulsating blood flow within the oxygenator is generated by synchronized active air flow expansion and contraction of integrated silicone pump tubes and hose pinching valves located at the oxygenator inlet and outlet. The current redesign improved upon previous prototypes by optimizing silicone pump tube distribution within the oxygenator fiber bundle; introduction of an oval shaped inner fiber bundle core, and housing; and a higher fiber packing density, all of which in combination reduced the priming volume by about 50% (50 to 27 mL and 41 to 20 mL, respectively). Gas exchange efficiency was tested for two new oxygenators manufactured with different fiber materials: one with coating and one with smaller pore size, both capable of long-term use (OXYPLUS® and CELGARD®). Results demonstrated that the oxygen transfer for both oxygenators was 5.3-24.7 mlO2/min for blood flow ranges of 100-500 mlblood/min. Carbon dioxide transfer for both oxygenators was 3.7-26.3 mlCO2/min for the same blood flow range. These preliminary results validated the oxygenator redesign by demonstrating an increase in packing density and thus in gas transfer, an increase in pumping capacity and a reduction in priming volume. PMID:24634337

Schlanstein, Peter C; Borchardt, Ralf; Mager, Ilona; Schmitz-Rode, Thomas; Steinseifer, Ulrich; Arens, Jutta

2014-01-01

161

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

162

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

163

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

SciTech Connect

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

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

1991-05-01

164

Prediction of Gas Exchange Rate Using Microwave Backscatter From the Ocean Surface  

NASA Astrophysics Data System (ADS)

Radar backscatter from the surface of the ocean is proving to be useful in establishing a relationship between sea surface roughness and gas transfer velocity. This is possible because radar wavelengths fall in the same centimetric range as surface waves that promote near surface turbulence that drives gas exchange. We have established two algorithms that link a field-based relationship between gas transfer velocity and mean square slope of the capillary wave field to a relationship between mean square slope and radar backscatter. The first algorithm exploits specular scattering of altimeter microwave pulses by the sea surface. The second algorithm involves Bragg scattering of microwave signals from a scatterometer. We will briefly review these algorithms, their uses and drawbacks, and insights they provide about the global distribution of gas transfer velocity.

Glover, D. M.; Frew, N. M.; Caruso, M. J.; McCue, S. J.

2004-12-01

165

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

166

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

167

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

168

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

Microsoft Academic Search

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

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

2007-01-01

169

Can Gas-Exchange Characteristics help Explain the Invasive Success of Lythrum salicaria ?  

Microsoft Academic Search

Since its introduction to North America, Lythrum salicaria (L.) (purple loosestrife) has become invasive in marshy and riparian habitats. We compared gas-exchange responses to external\\u000a CO2 partial pressure and light, as well as related leaf structural and biochemical characteristics, of L. salicaria with those of co-occurring native Asclepias syriaca (common milkweed) and Solidago graminifolia (lance-leaved goldenrod) along a pond bank

Jennifer M. Nagel; Kevin L. Griffin

2004-01-01

170

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

171

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

Microsoft Academic Search

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

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

2003-01-01

172

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

173

DOI: 10.1002/chem.201002135 High Gas Sorption and Metal-Ion Exchange of Microporous MetalOrganic  

E-print Network

DOI: 10.1002/chem.201002135 High Gas Sorption and Metal-Ion Exchange of Microporous Metal of their potential ap- plications in gas storage, gas separation, catalysis, and fabri- cation of nanoparticles.[1 by the creation of open metal sites, through syn- thesis of catenated frameworks, and by imbedding metal

Paik Suh, Myunghyun

174

Noninvasive determination of anaerobic threshold by monitoring the %SpO2 changes and respiratory gas exchange.  

PubMed

The purpose of this study was to determine the validity of noninvasive anaerobic threshold (AT) estimation using %SpO2 (arterial oxyhemoglobin saturation) changes and respiratory gas exchanges. Fifteen active, healthy males performed 2 graded exercise tests on a motor-driven treadmill in 2 separated sessions. Respiratory gas exchanges and heart rate (HR), lactate concentration, and %SpO2 were measured continuously throughout the test. Anaerobic threshold was determined based on blood lactate concentration (lactate-AT), %SpO2 changes (%SpO2-AT), respiratory exchange ratio (RER-AT), V-slope method (V-slope-AT), and ventilatory equivalent for O2 (EqO2-AT). Blood lactate measuring was considered as gold standard assessment of AT and was applied to confirm the validity of other noninvasive methods. The mean O2 corresponding to lactate-AT, %SpO2-AT, RER-AT, V-slope -AT, and EqO2-AT were 2176.6 +/- 206.4, 1909.5 +/- 221.4, 2141.2 +/- 245.6, 1933.7 +/- 216.4, and 1975 +/- 232.4, respectively. Intraclass correlation coefficient (ICC) analysis indicates a significant correlation between 4 noninvasive methods and the criterion method. Blond-Altman plots showed the good agreement between O2 corresponding to AT in each method and lactate-AT (95% confidence interval (CI). Our results indicate that a noninvasive and easy procedure of monitoring the %SpO2 is a valid method for estimation of AT. Also, in the present study, the respiratory exchange ratio (RER) method seemed to be the best respiratory index for noninvasive estimation of anaerobic threshold, and the heart rate corresponding to AT predicted by this method can be used by coaches and athletes to define training zones. PMID:19855338

Nikooie, Roohollah; Gharakhanlo, Reza; Rajabi, Hamid; Bahraminegad, Morteza; Ghafari, Ali

2009-10-01

175

Activation-triggered subunit exchange between CaMKII holoenzymes facilitates the spread of kinase activity  

PubMed Central

The activation of the dodecameric Ca2+/calmodulin dependent kinase II (CaMKII) holoenzyme is critical for memory formation. We now report that CaMKII has a remarkable property, which is that activation of the holoenzyme triggers the exchange of subunits between holoenzymes, including unactivated ones, enabling the calcium-independent phosphorylation of new subunits. We show, using a single-molecule TIRF microscopy technique, that the exchange process is triggered by the activation of CaMKII, and that exchange is modulated by phosphorylation of two residues in the calmodulin-binding segment, Thr 305 and Thr 306. Based on these results, and on the analysis of molecular dynamics simulations, we suggest that the phosphorylated regulatory segment of CaMKII interacts with the central hub of the holoenzyme and weakens its integrity, thereby promoting exchange. Our results have implications for an earlier idea that subunit exchange in CaMKII may have relevance for information storage resulting from brief coincident stimuli during neuronal signaling. DOI: http://dx.doi.org/10.7554/eLife.01610.001 PMID:24473075

Stratton, Margaret; Lee, Il-Hyung; Bhattacharyya, Moitrayee; Christensen, Sune M; Chao, Luke H; Schulman, Howard; Groves, Jay T; Kuriyan, John

2014-01-01

176

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

177

Effects of elevated atmospheric carbon dioxide on gas exchange and growth of white clover.  

PubMed

Effects of rising atmospheric CO2 concentrations on gas exchange, growth and productivity were investigated on an important grassland species, Trifolium repens L. cv. Blanca. Pure stands of this species were cultivated over an entire growing season in small acrylic greenhouses with an artificial atmosphere of ±367 or ±620 ppm CO2, respectively. Effects on growth and development were examined in a functional growth analysis, while consequences for gas exchange were determined by photosynthesis and transpiration measurements on canopy level. The stands were regularly clipped for production assessment. Canopies grown at high CO2 levels showed an average increase in productivity of almost 75%. Growth analysis indicated development of a larger foliage area as the major cause, particularly in the first days of regrowth after cutting. The growth advantage that began in this stage was maintained or bettered during the following weeks. The difference between gas exchange measurements expressed per unit leaf area and per unit ground area suggested that changes in net photosynthesis and respiration did not contribute to the increase in total yield. Transpiration declined under high CO2 if expressed on a leaf area basis but total canopy transpiration was at least as large as in ambient CO2 due to the larger leaf area. Water-use efficiency calculations on the summer data indicated a 35% improvement with a doubling of CO2 concentration. PMID:24430861

Nijs, I; Impens, I; Behaeghe, T

1988-02-01

178

Influence of Vesicular Arbuscular Mycorrhizae and Leaf Age on Net Gas Exchange of Citrus Leaves 1  

PubMed Central

The purpose of this study was to test the hypothesis that vesicular arbuscular mycorrhizal (VAM) fungi affect net assimilation of CO2 (A) of different-aged citrus leaves independent of mineral nutrition effects of mycorrhizae. Citrus aurantium L., sour orange plants were grown for 6 months in a sandy soil low in phosphorus that was either infested with the VAM fungus, Glomus intraradices Schenck & Smith, or fertilized with additional phosphorus and left nonmycorrhizal (NM). Net CO2 assimilation, stomatal conductance, water use efficiency, and mineral nutrient status for expanding, recently expanded, and mature leaves were evaluated as well as plant size and relative growth rate of leaves. Nutrient status and net gas exchange varied with leaf age. G. intraradices-inoculated plants had well-established colonization (79% of root length) and were comparable in relative growth rate and size at final harvest with NM plants. Leaf mineral concentrations were generally the same for VAM and NM plants except for nitrogen. Although leaf nitrogen was apparently sufficient for high rates of A, VAM plants did have higher nitrogen concentrations than NM at the time of gas exchange measurements. G. intraradices had no effect on A, stomatal conductance, or water use efficiency, irrespective of leaf age. These results show that well-established VAM colonization does not affect net gas exchange of citrus plants that are comparable in size, growth rate, and nutritional status with NM plants. PMID:16667848

Syvertsen, James P.; Graham, James H.

1990-01-01

179

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

180

Preservation of fresh solid foods by gas exchange. Final report of Phase I  

SciTech Connect

GASPAK is a new system for preserving fresh, solid foods through gas-exchange methods. Its objective is to stabilize or at least significantly extend like-fresh, high-quality shelf-life at ambient and/or chilled temperatures. This is a brief, comprehensive final report of Phase I of a projected three-phase GASPAK project carried out by the University of Maryland. Work to date indicates that through gas exchange procedures the like-fresh quality of peeled and sliced apples and potatoes can be maintained for extended periods. This was determined through gas exchange processing in a device engineered specifically for the purpose and by laboratory tests. From an energy consumption standpoint, it was determined that for more acid (less than ph 4.6) foods at least, the energy cost for the process itself is about one-fourth that required for canning or freezing. It was also determined that total energy costs from harvest to the consumer are approximately half those for canning or freezing.

Not Available

1980-09-30

181

Effects of local gas diffusion layer gas permeability variations on spatial proton exchange membrane fuel cells performance  

NASA Astrophysics Data System (ADS)

The effects of local gas diffusion layer (GDL) gas permeability variation and its location on spatial and overall proton exchange membrane fuel cell (PEMFC) performance were studied using a segmented cell approach. Variations in the physical and chemical parameters of the main membrane electrode assembly's (MEA) components (e.g., the membrane, electrode, and GDL) are considered defects and might negatively affect fuel cell performance. An artificial GDL defect was introduced by exchanging a standard (or intact) cathode GDL at one segment (segment 4 or 9) with a defective GDL. The standard and defective cathode GDLs had different through-plane gas permeabilities, while values were similar for in-plane permeability and some other structural parameters. The effects from a defective GDL were observed at a high current. Introducing a highly permeable GDL as a defect increased local performance due to a decrease in mass-transfer overpotential. For a defective GDL with lower permeability than the standard GDL, a local performance decrease was observed because mass-transfer losses increased. Simultaneously, downstream segment performance improved, which might be due to changes in water management. Defect localization at the cell outlet resulted in the detection of the defect at a lower current density compared with localization at the cell inlet. Spatial polarization curves (VI) and electrochemical impedance spectroscopy (EIS) facilitated detection and localization of GDL defects. Thus it was demonstrated that the local GDL anomalies are detectable by the segmented cell system.

Reshetenko, Tatyana V.; St-Pierre, Jean; Rocheleau, Richard

2013-11-01

182

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

PubMed Central

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

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

2010-01-01

183

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

PubMed

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

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

2010-02-01

184

Ion exchange using poorly activated supports, an easy way for purification of large proteins  

Microsoft Academic Search

Ion-exchange chromatography using commercial ionic supports is a commonly used technique for protein purification. However, selective adsorption of a target protein from a given extract onto commercial ion exchangers seems to be quite complex since they are designed to adsorb the maximum percentage of proteins with the opposite charge. In this paper, ion-exchanger supports with different activation degrees (from 1

Benevides C. C. Pessela; Roberto Munilla; Lorena Betancor; Manuel Fuentes; Alfonso V. Carrascosa; Alejandro Vian; Roberto Fernandez-Lafuente; Jose M. Guisán

2004-01-01

185

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

186

Excess radiocarbon constraints on air-sea gas exchange and the uptake of CO2 by the oceans  

Microsoft Academic Search

We re-assess the constraints that estimates of the global ocean excess radiocarbon inventory (IE) place on air-sea gas exchange. We find that the gas exchange scaling parameter aq cannot be constrained by IE alone. Non-negligible biases in different global wind speed data sets require a careful adaptation of aq to the wind field chosen. Furthermore, aq depends on the spatial

T. Naegler; P. Ciais; K. Rodgers; I. Levin

2006-01-01

187

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

Microsoft Academic Search

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

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

2005-01-01

188

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

PubMed Central

Background Gas exchange between the middle ear and adjacent compartments determines the trajectory of middle ear pressure change. Little information is available regarding the permeability of the tympanic membrane (TM) to physiological gases. Objective Determine in vivo if the human TM is permeable to O2 and CO2 at physiologic transTM pressure gradients. Methods An ear canal (EC) probe (ECP) constructed from a custom-fitted acrylic body, a glass capillary tube enclosing an oil meniscus to maintain ambient ECP+EC pressure and a silica glass microtube linked to a mass spectrometer (MS) for measuring gas composition was hermetically sealed within one ear canal of 15 adults. ECP+EC volume was measured and gas samples taken at 10 minute intervals for 1 hour. 1:100,000 epinephrine was applied topically to the ipsilateral TM to decrease blood flow and the experiment repeated. The MS recorded ECP+EC pressures of O2 (32 AMU) and CO2 (44 AMU) were regressed on time and the slope divided by the predicted transTM partial-pressure gradients to yield estimates of transTM O2 and CO2 conductance. Results Consistent with expectation for transTM gas exchange, ECP+EC O2 decreased and CO2 increased during the experiments. TransTM CO2 exchange was faster after application of the epinephrine suggesting an effect of perfusion on that estimate. The ratio of O2/CO2 conductances was approximately 5 which is not consistent with the TM acting primarily as a water or lipid barrier to diffusion. Conclusion The human TM is permeable to CO2 and O2 at physiologic pressure gradients. PMID:18728916

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

2009-01-01

189

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

NASA Astrophysics Data System (ADS)

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

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

190

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

USGS Publications Warehouse

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

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

2013-01-01

191

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

NASA Technical Reports Server (NTRS)

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

Gedeon, Louis

1959-01-01

192

Dust and gas in active galaxies  

E-print Network

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.

M. Villar-Martin

1996-05-21

193

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

194

Fluoride inhibits root water transport and affects leaf expansion and gas exchange in aspen (Populus tremuloides) seedlings.  

PubMed

The effects of sodium fluoride (0.3, 5 and 10 mM NaF) on root hydraulic conductivity, and gas exchange processes were examined in aspen (Populus tremuloides Michx.) seedlings grown in solution culture. A long-term exposure of roots to NaF significantly decreased root hydraulic conductivity (Lp) and stomatal conductance ( gs). Root absorbed NaF significantly affected electrolyte leakage in leaf tissues and substantially restricted leaf expansion. NaF did not significantly affect leaf chlorophyll contents but decreased net photosynthesis (Pn). A short-term exposure of excised roots to 5 mM NaF and KF significantly decreased root water flow (Qv) with a concomitant decline in root respiration and reduced gs when applied through intact roots or excised stems. The same molar concentration of NaCl also decreased Qv and gs in intact seedlings, but to a lesser extent than NaF or KF, and did not significantly affect root respiration. The results suggest that fluoride metabolically inhibited Qv or Lp, probably by affecting water channel activity. We suggest that the metabolic inhibition of Lp by root-absorbed fluoride affected gas exchange and leaf expansion in aspen seedlings. PMID:12654037

Kamaluddin, Mohammed; Zwiazek, Janusz J.

2003-03-01

195

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

196

Polarization exchange in colliding photon beams in a medium of an atomic gas  

E-print Network

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

R. F. Sawyer

2014-02-20

197

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

SciTech Connect

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

Kim, W. [Department of Physics, Kyungpook National University Daegu, 702-701 (Korea, Republic of); Korea Basic Science Institute (Korea, Republic of); Stepanyan, S. S.; Kim, A.; Jung, Y.; Woo, S.; Yurov, M.; Jang, J. [Department of Physics, Kyungpook National University Daegu, 702-701 (Korea, Republic of)

2009-08-04

198

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

199

Making Activated Carbon for Storing Gas  

NASA Technical Reports Server (NTRS)

Solid disks of microporous activated carbon, produced by a method that enables optimization of pore structure, have been investigated as means of storing gas (especially hydrogen for use as a fuel) at relatively low pressure through adsorption on pore surfaces. For hydrogen and other gases of practical interest, a narrow distribution of pore sizes <2 nm is preferable. The present method is a variant of a previously patented method of cyclic chemisorption and desorption in which a piece of carbon is alternately (1) heated to the lower of two elevated temperatures in air or other oxidizing gas, causing the formation of stable carbon/oxygen surface complexes; then (2) heated to the higher of the two elevated temperatures in flowing helium or other inert gas, causing the desorption of the surface complexes in the form of carbon monoxide. In the present method, pore structure is optimized partly by heating to a temperature of 1,100 C during carbonization. Another aspect of the method exploits the finding that for each gas-storage pressure, gas-storage capacity can be maximized by burning off a specific proportion (typically between 10 and 20 weight percent) of the carbon during the cyclic chemisorption/desorption process.

Wojtowicz, Marek A.; Serio, Michael A.; Suuberg, Eric M.

2005-01-01

200

DIRECTIONAL ASYMMETRY IN THE MEASURED N2O TIME-CONSTANT FOR MIDDLE EAR TRANSMUCOSAL GAS EXCHANGE  

PubMed Central

Simple, two-compartment models of transmucosal gas exchange for the middle ear (ME) are useful for describing ME pressure behavior under a variety of conditions. The most well developed exchange models require input of an experimentally determined, lumped-parameter, exchange-constant for each represented gas species. Evidences from past studies suggest that the value of the exchange-constant for inert gases is specific to the direction of the extant pressure-gradient, an unexpected result. In this study, the N2O transmucosal exchange-constant (time-constant) for 16 ears of 8 monkeys was measured for positive and negative ME-blood N2O gradients using previously published methods. The results showed that the two time-constant measures were highly correlated, but that the ME-blood time-constant was approximately 13 times greater than the blood-ME time-constant. This directional effect depends on the value of a gradient-ratio (arterial-venous/arterial-ME) included as a parameter in the time-constant for perfusion-limited gas exchange. All values of that ratio not equal to 1 introduce directional asymmetry into the measured time-constant. The significance of this phenomenon to current models and as a lead to the development of more complex, distributed models of transmucosal gas exchange is discussed. PMID:17305281

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

2011-01-01

201

Sexual dimorphism in the architecture of the lung's gas-exchange region.  

PubMed Central

The lung's only vital function is to provide sufficient gas-exchange surface area (Sa) to meet the organism's needs for oxygen uptake (VO2) and carbon dioxide elimination. A direct linear relation between Sa and VO2 and an inverse linear relation between the size of the lung's gas-exchange units and the species mass-specific VO2 are strongly conserved across species. Within species, Sa increases in response to prolonged (weeks) elevation of VO2. We now report sex-dependent deviations from these relationships that seem to anticipate the need for increased gas-exchange capacity engendered in females by the metabolic demands of pregnancy and lactation. We found that although VO2 almost doubled in rats during pregnancy and lactation, Sa was the same in age-matched virgin, pregnant, and lactating females. However, at the onset of sexual maturity, virgin female rats and mice had higher mass-specific Sa than males of the same species although mass-specific VO2 was identical, within species, in both sexes. In addition, even though mass-specific VO2 was identical in males and females, alveoli were 30% and 50% smaller in female rats and mice, respectively, than males of the same species. We suggest the greater mass-specific Sa and smaller alveoli in females in spite of identical mass-specific VO2 as males were selected for evolutionarily; they help females meet the metabolic demands of reproduction without adding to the energy demands of these periods a requirement to form additional lung. Images Fig. 1 PMID:7862643

Massaro, G D; Mortola, J P; Massaro, D

1995-01-01

202

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

PubMed Central

The guanine nucleotide exchange factor (GEF) Vav1 is essential for transducing T cell antigen receptor (TCR) signals and therefore plays a critical role in the development and activation of T cells. It has been presumed that the GEF activity of Vav1 is important for its function; however, there has been no direct demonstration of this. Here, we generated mice expressing enzymatically inactive, but normally folded, Vav1 protein. Analysis of these mice showed that the GEF activity of Vav1 was necessary for the selection of thymocytes and for the optimal activation of T cells, including signal transduction to Rac1, Akt, and integrins. In contrast, the GEF activity of Vav1 was not required for TCR-induced calcium flux, activation of extracellular signal–regulated kinase (ERK) and protein kinase D1 (PKD1), and cell polarization. Thus, in T cells, the GEF activity of Vav1 is essential for some, but not all, of its functions. PMID:20009105

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

2012-01-01

203

Nesting behaviour influences species-specific gas exchange across avian eggshells  

PubMed Central

Carefully controlled gas exchange across the eggshell is essential for the development of the avian embryo. Water vapour conductance (GH2O) across the shell, typically measured as mass loss during incubation, has been demonstrated to optimally ensure the healthy development of the embryo while avoiding desiccation. Accordingly, eggs exposed to sub-optimal gas exchange have reduced hatching success. We tested the association between eggshell GH2O and putative life-history correlates of adult birds, ecological nest parameters and physical characteristics of the egg itself to investigate how variation in GH2O has evolved to maintain optimal water loss across a diverse set of nest environments. We measured gas exchange through eggshell fragments in 151 British breeding bird species and fitted phylogenetically controlled, general linear models to test the relationship between GH2O and potential predictor parameters of each species. Of our 17 life-history traits, only two were retained in the final model: wet-incubating parent and nest type. Eggs of species where the parent habitually returned to the nest with wet plumage had significantly higher GH2O than those of parents that returned to the nest with dry plumage. Eggs of species nesting in ground burrows, cliffs and arboreal cups had significantly higher GH2O than those of species nesting on the ground in open nests or cups, in tree cavities and in shallow arboreal nests. Phylogenetic signal (measured as Pagel's ?) was intermediate in magnitude, suggesting that differences observed in the GH2O are dependent upon a combination of shared ancestry and species-specific life history and ecological traits. Although these data are correlational by nature, they are consistent with the hypothesis that parents constrained to return to the nest with wet plumage will increase the humidity of the nest environment, and the eggs of these species have evolved a higher GH2O to overcome this constraint and still achieve optimal water loss during incubation. We also suggest that eggs laid in cup nests and burrows may require a higher GH2O to overcome the increased humidity as a result from the confined nest microclimate lacking air movements through the nest. Taken together, these comparative data imply that species-specific levels of gas exchange across avian eggshells are variable and evolve in response to ecological and physical variation resulting from parental and nesting behaviours. PMID:25232199

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

2014-01-01

204

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

PubMed

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

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

2006-12-01

205

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

206

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

NASA Astrophysics Data System (ADS)

In land plants, the carbon fluxes are closely associated with those of water. The loss of water from leaves pulls water from soil in plants. High transpiration relative to compensating water flux from soil increases the tension of water column that may lead to its rupture and catastrophic dysfunction of the xylem if the transpiration rate is not regulated. Modification of the size of stomatal openings in leaves regulates the interconnected fluxes of water and carbon. Stomatal regulation of transpiration has direct influence also on the carbon transport from source leaves to sinks. Under given conditions, the water tension of xylem in leaves is linearly related to stomatal conductance while the assimilation rate, which is linked to the loading capacity, has saturating relationship with stomatal conductance. High sugar loading at source could compensate for the high water tension in xylem resulting from eg. high transpiration. However, excessive loading rate of the most commonly transported sugar, sucrose, causes rapid viscosity build up that effectively blocks the phloem transport. Assimilate transport from the shoot is a clear requirement for continuous photosynthetic production in leaves. Without transport the storage capacity of the leaves would be rapidly exhausted and accumulation of excess sugars in leaves lead to downregulation of photosynthesis. In this presentation we study the stomatal response to environment and its linkage to xylem and phloem tranport with dynamic model. We hypothesize that stomatal reaction to environment would maintain maximal assimilate transport in phloem under those conditions. We added to the xylem phloem transport model stomatal control of leaf gas-exchange, light and CO2 concentration dependent photosynthesis rate and carbon storage in leaf. For each time step we varied the stomatal conductance and selected the sollution that maximised the transport of assimilates in phloem. Our hypothesis reproduced realistically stomatal response to main environmental drivers and it reproduced the measured variation in leaf gas exchange both during daily variation of light, temperature and vapor pressure deficit and also during gradually developing drought. During the normal soil water availability the modeled results were identical to those that the optimal stomatal control of gas exchange would give. However, this new approach could also predict directly how soil drying is influencing the gas-exchange and also feed-forward response of stomatal conductance that has not been possible previously. Although maximising sugar transport from leaves to sink tissues as such is not mechansitic explanation to the actual control of stomata, the approach gives new possibilities to evaluate the impact of number of plant processes and environmental variables on tree production.

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

2009-04-01

207

Active heat exchange system development for latent heat thermal energy storage  

Microsoft Academic Search

Active heat exchange concepts for use with thermal energy storage systems in the temperature range of 250 C to 350 C, using the heat of fusion of molten salts for storing thermal energy are described. Salt mixtures that freeze and melt in appropriate ranges are identified and are evaluated for physico-chemical, economic, corrosive and safety characteristics. Eight active heat exchange

R. T. Lefrois; G. R. Knowles; A. K. Mathur; J. Budimir

1979-01-01

208

Design and optimization of a non-TEMA type tubular recuperative heat exchanger used in a regenerative gas turbine cycle  

Microsoft Academic Search

A special non-TEMA type tubular recuperative heat exchanger used as a regenerator of a gas turbine cycle is considered for multi-criteria optimization. It is assumed that the recuperator is designed for an existing gas turbine cycle to be retrofitted. Three scenarios for optimization of the proposed system have been considered. In one scenario, the objective is minimizing the cost of

Hoseyn Sayyaadi; Hamid Reza Aminian

2010-01-01

209

ABOUT DISTRIBUTION OF LINEAR WAVES TO THE DAMP POROUS ENVIRONMENTS SATURATED BY GAS IN VIEW OF INTERPHASE HEAT EXCHANGE  

Microsoft Academic Search

In work the system of the differential equations describing process of distribution of acoustic waves in the damp porous environment sated by gas in two-high-speed approach is offered. The dispersive parity considering interphase forces of interaction and processes of a thermal exchange between a skeleton of the porous environment, is received by a liquid and gas. The account of influence

V. L. Dmitriev; S. V. Volodin

2007-01-01

210

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

PubMed

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

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

2014-10-21

211

Oxygenation during perfluorocarbon associated gas exchange in normal and abnormal lungs.  

PubMed

Perfluorocarbon-associated gas exchange (PAGE) has been proposed for the treatment of lung diseases characterized by high alveolar surface tension. Perflubron (perfluorooctyl bromide, LiquiVent, Alliance Pharmaceutical Corp.) is a high purity medical grade perfluorocarbon suitable for PAGE. We studied PAGE using perflubron in normal piglets and in animal models of pulmonary disease (meconium aspiration syndrome, oleic acid infusion and gastric acid aspiration as models of ARDS, and neonatal respiratory distress syndrome). All animals were studied under anesthesia. PAGE was instituted by intratracheal instillation of a volume of perflubron (generally 30 ml/kg) that approximates a normal functional residual capacity of the lung. Arterial blood gases were measured at 15 minute intervals. FiO2 during PAGE was 1.0. In normal piglets, PaO2 fell from 543 torr (during conventional gas breathing) to 363 torr (during PAGE). However, in models of lung disease, PAGE significantly enhanced PaO2. PMID:7849947

Hernan, L J; Fuhrman, B P; Papo, M C; Leach, C L; Thompson, A E; Nesti, F D; Salman, N; Steinhorn, D M; Novotny, W; Paczan, P

1994-01-01

212

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

213

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

PubMed

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 (11)C-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. PMID:16666773

Woodrow, L; Jiao, J; Tsujita, M J; Grodzinski, B

1989-05-01

214

Mass exchange in gas desorption from finely dispersed liquid particles in an a near-wall two-phase jet  

SciTech Connect

This work deals with the experimental investigation of the mass exchange between finely dispersed liquid particles and a gas flow. We investigate mass transfer in the desorption process of a slightly water-soluble carbonic acid gas from the liquid particle surface at wide variations of the rate parameters for both gas and liquid phase. These data may be further used in the analysis of heat and mass transfer processes in near-wall two-phase flows.

Lebedev, V.P.; Terekhov, V.I.; Shishkin, N.E. [Institute of Thermophysics, Novosibirsk (Russian Federation)

1995-11-01

215

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

Microsoft Academic Search

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

Arunachala M. Kannan; Lakshmi Munukutla

2007-01-01

216

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

217

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

PubMed Central

In patients with fibrotic idiopathic interstitial pneumonia (f-IIP), the diffusing capacity for carbon monoxide (DLCO) has been used to predict abnormal gas exchange in the lung. However, abnormal values for arterial blood gases during exercise are likely to be the most sensitive manifestations of lung disease. The aim of this study was to compare DLCO, resting PaO2, P(A-a)O2 at cardiopulmonary exercise testing peak, and oxygen desaturation during a 6-min walk test (6MWT). Results were obtained in 121 patients with idiopathic pulmonary fibrosis (IPF, n = 88) and fibrotic nonspecific interstitial pneumonias (NSIP, n = 33). All but 3 patients (97.5%) had low DLCO values (35?mmHg) and 100 (83%) demonstrated significant oxygen desaturation during 6MWT (>4%). Interestingly 27 patients had low DLCO and normal P(A-a)O2, peak and/or no desaturation during the 6MWT. The 3 patients with normal DLCO also had normal PaO2, normal P(A-a)O2, peak, and normal oxygen saturation during 6MWT. Our results demonstrate that in fibrotic IIP, DLCO better defines impairment of pulmonary gas exchange than resting PaO2, exercise P(A-a)O2, peak, or 6MWT SpO2. PMID:22900170

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

2012-01-01

218

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

NASA Astrophysics Data System (ADS)

Recent work near the Arctic treeline has revealed that an increasing number of white spruce are showing negative growth responses to rising air temperatures. Researchers have speculated that these negative responders are experiencing warm temperature-induced drought stress. Measurements of white spruce needle gas exchange near the Arctic treeline are rare and, to our knowledge, measurements of whole canopy gas exchange have not been made. In this study, we measured sap flow to estimate whole canopy transpiration at hourly intervals for the entire growing seasons of 2010 and 2011 in white spruce growing on a riverside terrace, in a hillslope forest and at the treeline. We used weekly measurements of needle-scale photosynthesis, transpiration and needle ?13C to estimate water use efficiency at each site. We then applied these estimates of water use efficiency to our sap flow data in order to estimate hourly whole canopy photosynthesis at each site for the two growing seasons. Our results show evidence of stomatal control when the atmospheric vapor pressure deficit exceeds approximately 1.0 kPa, but no evidence of complete stomatal closure. Trees growing on the riverside terrace, where soils are relatively warm and dry, are more efficient in their water use, have greater leaf area and assimilate more carbon per unit basal diameter than trees in the forest and at the treeline. We found that the month of September, after growth has almost completely ceased, can be an important time for carbon uptake in white spruce near the Arctic treeline.

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

2011-12-01

219

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

NASA Astrophysics Data System (ADS)

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

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

220

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

221

Ionized gas in active molecular cloud cores  

NASA Astrophysics Data System (ADS)

The star-forming regions NGC 2071, CRL 961, S106 IR, and S87, contain compact continuum radio sources. It is hypothesized that powerful stellar winds generate the radio emission in S106 IR and CRL 961, in view of their miniscule 5-GHz angular size, strong 4.05 micron Br-alpha H-recombination line, and proximity to the centers of expanding molecular or ionized gas. All of the objects studied are sufficiently hot and active to produce ionizing radiation and/or powerful stellar winds. The disruption of the star-forming molecular cloud is in progress. The direct observation of high velocity molecular and ionized gas shows that energetic mass outflow is a major process associated with the birth and early life of the stars studied.

Bally, J.; Predmore, R.

1983-02-01

222

Pulmonary vascular dilatation and diffusion-dependent impairment of gas exchange in liver cirrhosis.  

PubMed

To test the hypothesis that diffusion-limitation for oxygen is due to abnormal vascular dilatation and significantly contributes to the arterial hypoxaemia of liver cirrhosis requires an experimental approach that detects both diffusion-limitation for oxygen and the presence of abnormal dilatation of pulmonary vessels exposed to alveolar gas. We therefore studied the gas exchange of a 64 year old man with alcoholic liver cirrhosis and severe resting arterial hypoxaemia (arterial oxygen tension (Pa,O2) 7.5 kPa) whilst breathing air and 100% O2 using conventional blood gas (CBG) analysis, the multiple inert gas elimination technique (MIGET) and whole body scintigraphy (WBS) following the i.v. administration of radiolabelled boli of macroaggregates with a minimum diameter of 15 microM. During air breathing, there was a consistently positive difference between the arterial oxygen tension predicted by MIGET and that actually measured (P-M Pa,O2, average 0.9 kPa). During O2 breathing, P-M Pa,O2 became negative, (average -12.2 kPa), and shunt estimated by the O2 method (% of Q') was consistently less than that measured by MIGET. Whereas both O2 method and MIGET estimates of shunt never exceeded 25%, the WBS shunt was 40%, indicating that a substantial fraction of cardiac output flowed through abnormally dilated pulmonary vessels, some of which were exposed to alveolar gas and, hence, participated in gas exchange. Although our observations pertain to one subject, we believe they provide the most convincing in vivo evidence to date that abnormal dilatation of interalveolar vessels may, per se, result in a significant diffusion impairment for O2. Furthermore, in view of the consistently negative P-M Pa,O2 observed during oxygen breathing, we speculate that such abnormal vascular dilatation may also have produced a significant diffusive impairment of one or more of the less soluble inert gases used in the MIGET analysis. PMID:8666095

Crawford, A B; Regnis, J; Laks, L; Donnelly, P; Engel, L A; Young, I H

1995-12-01

223

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

224

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

225

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

PubMed

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

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

2014-10-01

226

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

227

Dielectric function of the electron gas with dynamical-exchange decoupling. II. Discussion and results  

NASA Astrophysics Data System (ADS)

By making the dynamical-exchange decoupling in the equation of motion for the Wigner distribution function, exchange effects in the dielectric function of the homogeneous electron gas were, in an earlier derivation, described by a frequency-dependent local-field correction G(q,?). In paper I, details were provided how the sixfold integral for G(q,?) can be reduced analytically into a double integral, adapted for numerical purposes. In this paper, the consequences of dynamical-exchange effects are studied, and the theory is tested for its internal consistency. The evaluation of the pair correlation function g(r) at the origin from both the static limit and the high-frequency limit of the frequency-dependent local-field correction G(q,?) leads to the same value g(0)=12, in contrast to other theories where, from both limits, different results are obtained. Also, the compressibility, calculated from the dielectric function including exchange, agrees with the Hartree-Fock result. Furthermore, it is shown that the high-frequency limit of G(q,?) satisfies the general properties implied by the third-frequency-moment sum rule, resulting again in g(0)=12 and leading to the Hartree-Fock ground-state energy. This consistency between the static and high-frequency behavior of G(q,?) cannot be fulfilled by any static approximation to G(q,?), because an adequate treatment of dynamical-exchange effects involves excited states that are consistent with the Hartree-Fock ground state. In the static limit, G(q,?) exhibits a relatively sharp peak near q=2kF. This peak induces an instability of the homogeneous electron gas, quite similar to and in the same density range as the instability of the spin susceptibility discussed by Hamann and Overhauser. For rs>=10.6, a supplementary instability relative to charge-density deformations occurs. The frequency dependence of G(q,?) is examined, and numerical values for ReG(q,?) and ImG(q,?) are presented. The real part of the dielectric function and the imaginary part of the inverse dielectric function are plotted for several densities in the metallic range. Compared to the random-phase approximation (RPA), the frequencies of the maxima in the structure factor obtained in the present work (i.e., with dynamical-exchange decoupling) are shifted to lower frequencies. The plasmon dispersion is considerably closer to recent experimental data in aluminium than with RPA. Finally, it turns out that the inclusion of frequency-dependent exchange effects results in the natural occurrence of spin- and charge-density waves. These are the dynamical extension of the instability relative to magnetic perturbations, found in the static limit at low densities.

Brosens, F.; Devreese, J. T.; Lemmens, L. F.

1980-02-01

228

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

229

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

PubMed

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

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

2005-07-01

230

Active heat exchange system development for latent heat thermal energy storage  

Microsoft Academic Search

Alternative mechanizations of active heat exchange concepts were analyzed for use with heat of fusion Phase Change Materials (PCM's) in the temperature range of 250 C to 350 C for solar and conventional power plant applications. Over 24 heat exchange concepts were reviewed, and eight were selected for detailed assessment. Two candidates were chosen for small-scale experimentation: a coated tube

R. T. Lefrois; A. K. Mathur

1980-01-01

231

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

232

Effect of gas diffusion layer and membrane properties in an annular proton exchange membrane fuel cell  

NASA Astrophysics Data System (ADS)

A complete three-dimensional and single phase computational dynamics model for annular proton exchange membrane (PEM) fuel cell is used to investigate the effect of changing gas diffusion layer and membrane properties on the performances, current density and gas concentration. The proposed model is a full cell model, which includes all the parts of the PEM fuel cell, flow channels, gas diffusion electrodes, catalyst layers and the membrane. Coupled transport and electrochemical kinetics equations are solved in a single domain; therefore no interfacial boundary condition is required at the internal boundaries between cell components. This computational fluid dynamics code is used as the direct problem solver, which is used to simulate the two-dimensional mass, momentum and species transport phenomena as well as the electron- and proton-transfer process taking place in a PEMFC that cannot be investigated experimentally. The results show that by increasing the thickness and decreasing the porosity of GDL the performance of the cell enhances that it is different with planner PEM fuel cell. Also the results show that by decreasing the thickness of the membrane the performance of the cell increases.

Khazaee, I.; Ghazikhani, M.; Esfahani, M. Nasr

2012-01-01

233

Effective diffusivity of gas diffusion layer in proton exchange membrane fuel cells  

NASA Astrophysics Data System (ADS)

In gas diffusion layers (GDLs) of proton exchange membrane fuel cells (PEMFCs), effective gas diffusivity is a key parameter to be determined and engineered. Existing theoretical models of effective diffusivity are limited to one-dimensional (1D) regular fiber arrays. Numerical simulations were carried out to simulate gas diffusion through more realistic fibrous materials like GDLs, in which fibers are randomly distributed in a two-dimensional (2D) plane or three-dimensional (3D) space, but they could not fully reveal the underlying mechanisms. In this paper, we propose an analytical model to predict the effective diffusivities of 1D, 2D and 3D randomly distributed fiber assembles. The present model is established by extending the model of 1D regular fiber alignments to 1D random fiber arrangements through Voronoi Tessellation method, and using the 1D local diffusivities to determine the 2D and 3D diffusivities based on mixing rules. The predicted effective diffusivities agree well with experimental results and numerical data. With the new model, the influences of porosity, fiber distribution, and fiber orientation are analyzed in this study.

Shou, Dahua; Fan, Jintu; Ding, Feng

2013-03-01

234

The Response of Foliar Gas Exchange to Exogenously Applied Ethylene 1  

PubMed Central

The responsiveness to ethylene of net photosynthesis and stomatal conductance to water vapor in intact plants was investigated in 13 herbaceous species representing seven plant families. Exposures were conducted in an open, whole-plant exposure system providing controlled levels of irradiance, air temperature, CO2, relative humidity, and ethylene concentration. Net photosynthesis and stomatal conductance to water vapor in units of moles per square meter per second were measured on recently expanded leaves in control and ethylene-treated plants using a remotely operated single-leaf cuvette. The ethylene concentration was either 0 or 210 micromoles per cubic meter and was maintained for 4 hours. Species varied substantially in the response of their foliar gas exchange to ethylene. In 7 of the 13 species, net photosynthesis was inhibited statistically by 4 hours of ethylene exposure. As a function of the rate in control plants, the responses were most pronounced and statistically significant in Arachis hypogaea (?51.1%), Gossypium hirsutum (?31.7%), Glycine max (?24.8%), Cucurbita pepo (?20.4%), Phaseolus vulgaris (?18.4%), Setaria viridis (?17.5%), and Raphanus sativus (?4.4%). Whereas the responsiveness of net photosynthesis to ethylene among the 13 species showed no specific taxonomic associations, the responsiveness was positively correlated with the intrinsic rate of net photosynthesis. Stomatal conductance to water vapor after 4 hours of ethylene exposure declined statistically in 6 of the 13 species. As a function of control rates, the most marked and statistically significant responses of stomatal conductance were in Glycine max (?53.6%), Gossypium hirsutum (?51.2%), Arachis hypogaea (?42.7%), Phaseolus vulgaris (?38.6%), Raphanus sativus (?26.8%), and Solanum tuberosum (?23.4%). Although ethylene-induced changes in net photosynthesis and stomatal conductance were positively correlated, there were species-specific exceptions in which net photosynthesis declined after 4 hours of exposure without a concurrent change in stomatal conductance, stomatal conductance declined without a change in net photosynthesis, and the decline in stomatal conductance substantially exceeded the corresponding decline in net photosynthesis. Thus, the responsiveness to ethylene of net photosynthesis and stomatal conductance to water vapor were not consistently synchronous or equivalent among the 13 species. It is concluded that foliar gas exchange is responsive to exogenously applied ethylene in many plant species. The sensitivity of foliar gas exchange to ethylene may play a role in general plant response to environmental stress in which one of the physiological sites of action for endogenously produced stress ethylene in the leaf is the plant's photosynthetic capacity and/or stomatal conductance to water vapor. PMID:16665086

Taylor, George E.; Gunderson, Carla A.

1986-01-01

235

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. PMID:23922762

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

2013-01-01

236

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

237

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

Federal Register 2010, 2011, 2012, 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 proposed production...

2013-09-27

238

Theoretical and experimental insights into effects of wind on leaf heat and gas exchange  

NASA Astrophysics Data System (ADS)

Transpiration and heat exchange by plant leaves are coupled physiological processes of significant importance for surface-climate interactions and ecohydrology. The common practice of modelling transpiration as an isothermal process (assuming equal leaf and air temperatures) may introduce significant bias into estimates of transpiration rates and water use efficiency (WUE, the amount of carbon gained by photosynthesis per unit of water lost by transpiration). In contrast, explicit consideration of stomatal and leaf boundary layer resistances in series and the leaf energy balance in a physically-based model led to some surprising results, such as suppressed transpiration rates for increasing wind speed at constant stomatal conductance. The model predicts that for high wind velocities, the same leaf conductance (for water vapour and carbon dioxide) can be maintained with less evaporative losses. If this leaf-scale effect is consistent across most leaves, it may have profound implications for canopy-scale water use efficiency under globally decreasing wind speeds. This presentation reports the results of a systematic study of the effect of wind speed on leaf heat and gas exchange rates and introduces a novel experimental design to verify the modelling results using an insulated wind tunnel and artificial leaves with defined pore geometries, allowing to measure leaf-scale latent and sensible heat fluxes independently. First experimental results and new insights will be highlighted.

Schymanski, Stanislaus J.; Or, Dani

2014-05-01

239

77 FR 37941 - Order Granting a Limited Exemption From Exchange Act Rule 10b-17 to Certain Actively Managed...  

Federal Register 2010, 2011, 2012, 2013

...Limited Exemption From Exchange Act Rule 10b-17 to Certain Actively Managed Exchange-Traded Funds Pursuant to Exchange Act Rule 10b-17(b)(2) June 19, 2012. By letter dated...issue an exemption from Rule 10b-17 under the Securities Exchange Act of...

2012-06-25

240

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

241

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

242

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

PubMed Central

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

Olszyk, David M.; Tingey, David T.

1986-01-01

243

Acute effects of upright position on gas exchange in patients with acute respiratory distress syndrome.  

PubMed

Patients with acute respiratory distress syndrome (ARDS) have dorsal atelectasis of the lungs. This is probably caused by several mechanisms: compression on dependent lung zones, purulent secretions in alveoli, and upward shift of the diaphragm. An upright position (UP) of the patient (the whole body in a straight line at 40 to 45 degrees) can theoretically ameliorate these mechanisms. The objective was to evaluate whether there was an improvement of gas exchange during UP of ARDS patients and to evaluate the hemodynamic effects. A prospective interventional study was performed in the surgical and medical ICUs and the burn unit of the Ghent University Hospital, a tertiary care center. Included were ARDS patients with onset of ARDS within 48 hours before start of the study. Patients were excluded when there was hemodynamic instability or when the PaO2/FiO2 ratio deteriorated during the 2 hours preceding UP. After a 2-hour observation period in a semirecumbent position, patients were put in UP for 12 hours. Respiration and hemodynamic data were recorded at the start and end of the 2-hour observation period, and after 1, 4, and 12 hours in UP. Eighteen patients were included in the study. There was a significant increase of the PaO2/FiO2 ratio during UP (P < .001). Except for the need for volume resuscitation in 5 patients (27.8%), there was no significant change in the hemodynamic profile of the patients. Upright positioning of patients with ARDS, a relatively simple maneuver, resulted in an improvement of gas exchange and was tolerated hemodynamically relatively well during a 12-hour observation period. PMID:15665259

Hoste, Eric A J; Roosens, Carl D V K; Bracke, Steven; Decruyenaere, Johan M A; Benoit, Dominique D; Vandewoude, Koenraad H D K; Colardyn, Francis A

2005-01-01

244

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

PubMed Central

Background Past in vivo studies in humans showed that the tympanic membrane (TM) is permeable to physiological gases. Animal studies show that transTM CO2 conductance is increased by TM pathology. Objective Determine if transTM CO2 exchange in humans is affected by atrophic and sclerotic pathologies. Methods An ear canal (EC) probe (ECP) constructed from a custom-fitted acrylic body, a glass capillary tube enclosing an oil meniscus to maintain ambient ECP+EC pressure and a silica glass microtube linked to a mass spectrometer (MS) for measuring gas composition was hermetically sealed within the ear canal of the test ear. ECP+EC volume was measured and gas samples taken at 10 minute intervals for 1 hour. The fractional CO2 pressure measured in the ECP+EC for each sample was regressed on time and the slope of the function multiplied by the ECP+EC volume and divided by the estimated transTM CO2 gradient at the start of the experiment to yield transTM CO2 conductance (uL/min/Pa). Data were complete for 15 normal, 13 sclerotic and 9 atrophic TMs. Results The average (±std) transTM CO2 conductances were 1.76×10?4 ± 7.27×10?5, 2.26×10?4 ± 1.5×10?4 and 2.36×10?4 ± 1.14×10?4 uL/min/Pa/TM for the normal, sclerotic and atrophic TMs, respectively. A pairwise comparison of data for the normal and atrophic TMs under the directional hypothesis of a greater CO2 exchange rate for thinner TMs approached statistical significance (P=.07). A similar pairwise comparison for the sclerotic and normal TMs did not approach statistical significance (P=.28) Conclusion The effect of TM pathologies on CO2 conductance is limited. PMID:20809264

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

2011-01-01

245

Gas exchange by intratracheal insufflation in a ventilatory failure dog model.  

PubMed Central

Respiratory insufficiency patients who need only partial ventilatory support are, nevertheless, intubated and connected to a respirator. In search of a partial respiratory assistance method we evaluated the gas exchange, mechanisms, and hemodynamic effects of intratracheal insufflation (ITI) via a narrow (0.2-cm) catheter. The effects of flow rate (0.05-0.2 liter/min per kg), catheter tip position (carina, bronchus, and trachea), and superimposed chest vibration at 22 Hz were studied in seven anesthetized and partially paralyzed dogs. ITI in the carina induced CO2 removal (VCO2) of 48 +/- 16 ml/min in the periods between breaths, which was 39% of the control VCO2. CO2 removal rates between breaths with ITI in a bronchus and in the trachea were 63 and 28% of control, respectively (P < 0.05). ITI at 0.15-0.2 liter/min per kg augmented total VCO2 by > 50% over control (P < 0.05) and decreased PaCO2 by 10% (P < 0.05) despite a 28% fall in VE and 32% lower work of breathing (P < 0.05). Adding vibration to ITI at 0.15 liter/min per kg induced VCO2 of 162 +/- 34 ml/min, which was significantly greater than control, while PaCO2 fell from 69 +/- 24 to 47 +/- 6 mmHg (P < 0.05), despite complete cessation of spontaneous breathing. ITI with or without vibration did not cause any hemodynamic changes, except for a fall in the shunt fraction from 14.6 +/- 9.9% to 5.8 +/- 2.8% with vibration. Thus, ITI at low flow rates can support respiration with no hemodynamic side effects. Adding chest vibration further enhances gas exchange and can provide total ventilation. Images PMID:1469093

Gavriely, N; Eckmann, D; Grotberg, J B

1992-01-01

246

Carbon gas exchange at a southern Rocky Mountain wetland, 1996-1998  

USGS Publications Warehouse

Carbon dioxide (CO2) and methane (CH4) exchange between the atmosphere and a subalpine wetland located in Rocky Mountain National Park, Colorado, at 3200 m elevation were measured during 1996-1998. Respiration, net CO2 flux, and CH4 flux were measured using the closed chamber method during snow-free periods and using gas diffusion calculations during snow-covered periods. The ranges of measured flux were 1.2-526 mmol CO2 m-2 d-1 (respiration), -1056-100 mmol CO2 m-2 d-1 (net CO2 exchange), and 0.1-36.8 mmol CH4 m-2 d-1 (a positive value represents efflux to the atmosphere). Respiration and CH4 emission were significantly correlated with 5 cm soil temperature. Annual respiration and CH4 emission were modeled by applying the flux-temperature relationships to a continuous soil temperature record during 1996-1998. Gross photosynthesis was modeled using a hyperbolic equation relating gross photosynthesis, photon flux density, and soil temperature. Modeled annual flux estimates indicate that the wetland was a net source of carbon gas to the atmosphere each of the three years: 8.9 mol C m-2 yr-1 in 1996, 9.5 mol C m-2 yr-1 in 1997, and 9.6 mol C m-2 yr-1 in 1998. This contrasts with the long-term carbon accumulation of ???0.7 mol m-2 yr-1 determined from 14C analyses of a peat core collected from the wetland.

Wickland, K.P.; Striegl, R.G.; Mast, M.A.; Clow, D.W.

2001-01-01

247

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

248

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

PubMed

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

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

1998-02-01

249

New audit guidelines for oil- and gas-producing activities  

Microsoft Academic Search

During 1981, the Accounting Standards Executive Committee (AccSEC) declared the necessity of audit guidance for engagements involving oil and gas producing activities. The task of developing audit guidelines was assigned to the Oil and Gas Committee of AccSEC. After approximately two years of deliberations, a draft of a proposed audit guide on audits of oil and gas producing activities was

T. R. Weirich; R. E. Jr. Blatz

1984-01-01

250

The loading capacity of selected cation exchange resins and activated carbons for gold-thiourea complex  

Microsoft Academic Search

The loading capacities of several types of cation exchange resin and activated carbon for gold-thiourea complex has been evaluated. The maximum loading capacity after 96 hours at ambient temperature (22°C) ranged from 189 to 243 kg Au\\/t for the cation exchange resins and 159 to 208 kg Au\\/t for the activated carbons. These values are higher than the capacity values

R. Mensah-Biney; K. J. Reid; M. T. Hepworth

1995-01-01

251

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

PubMed Central

Pulmonary hemodynamics and gas exchange were studied in four physicians during 72 hr acclimatization to 12,470 ft. Pulmonary catheters were left in three subjects for 72 hr. Resting mean pulmonary arterial pressure (P??P?) rose progressively during the first 24 hr from 10.3 ±1.0 to 21.1 ±4.0 torr and remained at this level. During this same 24 hr period cardiac output increased from 7.1 ±1.4 to 8.4 ±2.0 liters/min and total pulmonary resistance rose from 122 ±16 to 209 ±40 dynes·sec/cm-5. Excercise at 60 w after 24 hr of hypoxia increased P??P? to 28.8 ±5.1 torr and decreased total pulmonary resistance to 155 ±25. Shunt fractions were 11 ±3.8% after 24 hr at altitude and fell to 7 ±0% after 72 hr. Alveolar to arterial O2 difference (P(A-a)O2) breathing oxygen fell from 116 ±10.8 to 92 ±33.3 torr during the same period of acclimatization, whereas dead space to tidal volume ratio (VD/VT) rose from 33 ±4.0% to 40 ±5.3% and P(A-a)O2 breathing ambient air rose from 8 ±2.6 to 11 ±3.0 torr. Inspiratory static lung compliance decreased significantly from a control of 176 ±8 to 141 ±8 ml/cm H2O after 72 hr of hypoxia. After 4-7 days at altitude, further deterioration in gas exchange was observed after a 5 mile, 1800 ft climb to the summit (14,255 ft) and return. P(A-a)O2 on air rose from 2.5 ±2.1 just before starting, to 16.3 ±2.8 at the summit (rested), and was still 9.0 ±2.2 several hours after returning. The O2-breathing values paralleled these, whereas dead space appeared to fall. We speculate that the hypoxic pulmonary hypertension which develops over 24 hr in some way may be responsible for a reduction of compliance and deterioration in oxygen exchange efficiency, possibly representing a sub-clinical form of pulmonary edema of high altitude. The increased alveolar to arterial O2 difference induced by hypoxic exercise persists for several hours of hypoxic rest. PMID:5547278

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

1971-01-01

252

Lack of Agreement Between Gas Exchange Variables Measured by Two Metabolic Systems  

PubMed Central

The purpose of this study was to assess the agreement and consistency between gas exchange variables measured by two online metabolic systems during an incremental exercise test. After obtaining local ethics approval and informed consent, 15 healthy subjects performed an incremental exercise test to volitional fatigue using the Bruce protocol. The Innocor (Innovision, Denmark) and CardiO2 (Medical Graphics, USA) systems were placed in series, with the Innocor mouthpiece attached to the pneumotach of the CardiO2. Metabolic data were analysed during the last 30 seconds of each stage and at peak exercise. There were non- significant differences (p > 0.05) between the two systems in estimation of oxygen consumption (VO2) and in minute ventilation (VE). Mean Cronbach’s alpha for VO2 and VE were 0.88 and 0.92. The Bland-Altman analysis revealed that limits of agreement were -0.52 to 0.55 l.min-1 for VO2, and -8.74 to 10.66 l.min-1 for VE. Carbon dioxide production (VCO2) and consequently respiratory exchange ratio (RER) measured by the Innocor were significantly lower (p < 0.05) through all stages. The CardiO2 measured fraction of expired carbon dioxide (FeCO2) significantly higher (p < 0.05). The limits of agreement for VO2 and VE are wide and unacceptable in cardio-pulmonary exercise testing. The Innocor reported VCO2 systematically lower. Therefore the Innocor and CardiO2 metabolic systems cannot be used interchangeably without affecting the diagnosis of an individual patient. Results from the present study support previous suggestion that considerable care is needed when comparing metabolic data obtained from different automated metabolic systems. Key pointsThere is general concern regarding the limited knowledge available about the accuracy of a number of commercially available systems.Demonstrated limits of agreement between key gas exchange variables (oxygen consumption and minute ventilation) as measured by the two metabolic systems were wide and unacceptable in cardio-pulmonary exercise testing.Considerable care is needed when comparing metabolic data obtained from different automated metabolic systems. PMID:24150129

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

2008-01-01

253

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.

254

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

255

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

Microsoft Academic Search

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

Warren W. Burggren; James N. Cameron

1980-01-01

256

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

257

Trace gas exchanges and convective transports over the Amazonian rain forest  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

258

High Frequency Nasal Ventilation for 21 Days Maintains Gas Exchange with Lower Respiratory Pressures and Promotes Alveolarization in Preterm Lambs  

PubMed Central

Background Short-term high-frequency nasal ventilation (HFNV) of preterm neonates provides acceptable gas exchange compared to endotracheal intubation and intermittent mandatory ventilation (IMV). Whether long-term HFNV will provide acceptable gas exchange is unknown. We hypothesized that HFNV for up to 21d would lead to acceptable gas exchange at lower inspired oxygen (O2) levels and airway pressures compared to intubation and IMV. Methods Preterm lambs were exposed to antenatal steroids, and treated with perinatal surfactant and postnatal caffeine. Lambs were intubated and resuscitated by IMV. At ~3h of age, half of the lambs were switched to non-invasive HFNV. Support was for 3d or 21d. By design, PaO2 and PaCO2 were not different between groups. Results At 3d (n=5) and 21d (n=4) of HFNV, fractional inspired O2 (FiO2), peak inspiratory pressure, mean airway, intra-tracheal, and positive end-expiratory pressures, oxygenation index, and Alveolar-arterial gradient were significantly lower than matched periods of intubation and IMV. PaO2/FiO2 ratio was significantly higher at 3d and 21d of HFNV compared to matched intubation and IMV. HFNV led to better alveolarization at 3d and 21d. Conclusion Long-term HFNV provides acceptable gas exchange at lower inspired O2 levels and respiratory pressures compared to intubation and IMV. PMID:24378898

Null, Donald M.; Alvord, Jeremy; Leavitt, Wendy; Wint, Albert; Dahl, Mar Janna; Presson, Angela P.; Lane, Robert H.; DiGeronimo, Robert J.; Yoder, Bradley A.; Albertine, Kurt H.

2014-01-01

259

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

E-print Network

Transpiration efficiency over an annual cycle, leaf gas exchange and wood carbon isotope ratio; published online August 6, 2009 Summary Variation in transpiration efficiency (TE) and its relationship. Cumulative transpiration was determined by repeatedly weighing the pots with a pallet truck scale. Dry matter

Bermingham, Eldredge

260

Importance of air movement for promoting gas and heat exchanges between plants and atmosphere under controlled environments  

Microsoft Academic Search

The effects of the air velocity less than 1.3 m s?1on net photosynthetic rates, transpiration rates and water use efficiencies of plant seedlings canopies and single leaves were assessed. Control of air movement is important to enhance gas exchange between plants and the ambient air, and would consequently be important to promote plant growth. The suppression of the transpiration rate

Yoshiaki Kitaya

261

Nonsteady-state methods of measuring heat exchange between a layer of lumpy material and a gas flow  

Microsoft Academic Search

In a previous work of Bekmuradov and Baum (1975) the problem of heat exchange between a hot gas and a layer of particles was solved with allowance for finite cross section of the layer, the effect of channel walls, and turbulent mixing of the flow for various boundary conditions at the channel wall. The present paper describes some applications of

O. Bekmuradov; V. A. Baum

1977-01-01

262

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

Microsoft Academic Search

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

Rajani S Modiyani

2010-01-01

263

Use of transcutaneous oxygen and carbon dioxide tensions for assessing indices of gas exchange during exercise testing  

Microsoft Academic Search

The slow response characteristics of the combined transcutaneous electrode have been viewed as a major disadvantage when compared with other types of non-invasive assessment of gas exchange during exercise testing. We have previously shown that by using the highest recommended temperature of 45°C to reduce response times, and combining this with an exercise protocol of gradual work load increments, that

R CARTER; S. W BANHAM

2000-01-01

264

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

Microsoft Academic Search

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

ORLANDO DIAZ; RAQUEL IGLESIA; MIQUEL FERRER; ELISABETH ZAVALA; CRISTINA SANTOS; PETER D. WAGNER; JOSEP ROCA; ROBERT RODRIGUEZ-ROISIN

265

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

Microsoft Academic Search

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

Douglas A. Johnson; Martyn M. Caldwell

1975-01-01

266

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

267

FORMALDEHYDE AND TRACER GAS TRANSFER BETWEEN AIRSTREAMS IN ENTHALPY-TYPE AIR-TO-AIR HEAT EXCHANGERS  

SciTech Connect

Enthalpy exchangers are frequently employed to transfer heat and water between the supply and exhaust airstreams of mechanical ventilation systems. Concern has been expressed that some indoor-generated air pollutants, especially formaldehyde, may be transferred between airstreams by this type of heat exchanger and, thus, returned to the indoor space. This paper describes an experimental study in which the formaldehyde, tracer gas, and water vapor transfer rates in two enthalpy exchangers were measured. The first exchanger uses a crossflow core fabricated from a treated paper. The core of the second heat exchanger is a rotating heat wheel coated with lithium chloride. To reduce the transfer of gases by air leakage each core was installed in a specially fabricated case. Only 5% to 8% of the two tracer gases and 7% to 15% of the formaldehyde injected into the exhaust airstream was transferred to the supply airstream. Therefore, formaldehyde transfer between airstreams by processes other than air leakage does not seriously compromise the performance of these enthalpy exchangers. Theoretical calculations indicate, however, that the transfer of water vapor between airstreams in enthalpy exchangers can significantly diminish their ability to lower indoor formaldehyde concentrations because of the positive coupling between indoor humidity and the emission rates of formaldehyde from building materials.

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

1984-07-01

268

Investigating onychophoran gas exchange and water balance as a means to inform current controversies in arthropod physiology.  

PubMed

Several controversies currently dominate the fields of arthropod metabolic rate, gas exchange and water balance, including the extent to which modulation of gas exchange reduces water loss, the origins of discontinuous gas exchange, the relationship between metabolic rate and life-history strategies, and the causes of Palaeozoic gigantism. In all of these areas, repeated calls have been made for the investigation of groups that might most inform the debates, especially of taxa in key phylogenetic positions. Here we respond to this call by investigating metabolic rate, respiratory water loss and critical oxygen partial pressure (Pc) in the onychophoran Peripatopsis capensis, a member of a group basal to the arthropods, and by synthesizing the available data on the Onychophora. The rate of carbon dioxide release (VCO2) at 20 degrees C in P. capensis is 0.043 ml CO2 h(-1), in keeping with other onychophoran species; suggesting that low metabolic rates in some arthropod groups are derived. Continuous gas exchange suggests that more complex gas exchange patterns are also derived. Total water loss in P. capensis is 57 mg H2O h(-1) at 20 degrees C, similar to modern estimates for another onychophoran species. High relative respiratory water loss rates ( approximately 34%; estimated using a regression technique) suggest that the basal condition in arthropods may be a high respiratory water loss rate. Relatively high Pc values (5-10% O2) suggest that substantial safety margins in insects are also a derived condition. Curling behaviour in P. capensis appears to be a strategy to lower energetic costs when resting, and the concomitant depression of water loss is a proximate consequence of this behaviour. PMID:18805813

Clusella-Trullas, Susana; Chown, Steven L

2008-10-01

269

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

PubMed

The South African grass, Lehmann lovegrass (Eragrostis lehmanniana), may alter ecosystem processes across extensive semiarid grasslands and savannahs of western North America. We compared volumetric soil moisture (theta), total and green tissue leaf area index (LAI), ecosystem (i.e. whole-plant and soil), and leaf-level gas exchange of Lehmann lovegrass and the native bush muhly (Muhlenbergia porteri) over the 2008 monsoon season in a semiarid savanna in southern Arizona, USA, to see if these were consistent with high productivity associated with lovegrass invasive success. theta across 0-5 and 0-25 cm was higher while evapotranspiration (ET) was similar between lovegrass and bush muhly plots, except shortly after rainfall, when ET was 32-81% higher in lovegrass plots. Lehmann lovegrass had lower, quickly developing LAI with greater leaf proportions than bush muhly. When early season theta was high, net ecosystem CO(2) exchange (NEE) was similar, but as storm frequency and theta declined, NEE was more negative in lovegrass (-0.69 to -3.00 micromol m(-2) s(-1)) than bush muhly (+1.75 to -1.55 micromol m(-2) s(-1)). Ecosystem respiration (R (eco)) responded quickly to monsoon onset and late-season rains, and was lower in lovegrass (2.44-3.74 micromol m(-2) s(-1)) than bush muhly (3.60-5.3 micromol m(-2) s(-1)) across the season. Gross ecosystem photosynthesis (GEP) was greater in Lehmann lovegrass, concurrent with higher leaf-level photosynthesis and stomatal conductance. We conclude that canopy structure facilitates higher theta under Lehmann lovegrass, reducing phenological constraints and stomatal limitations to whole-plant carbon uptake through the short summer monsoon growing season. PMID:20063168

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

2010-07-01

270

Respiratory gas exchange and physiological demands during a fire fighter evaluation circuit in men and women.  

PubMed

We examined the oxygen uptake (VO2) and carbon dioxide output (VCO2) during completion of a circuit developed for testing fire fighters and related performance time to laboratory measures of fitness. Twenty-two healthy university students (ten women) were trained in the tasks then performed the circuit as quickly as possible. Breath-by-breath gas exchange and heart rate were continuously measured with a portable system. Median circuit time was 6:13 (min:s, 25-75% = 5:46-6:42) for men and 7:25 (25-75% = 6:49-10:21) for 8 women finishers (P = 0.023), and VO2 averaged 68 and 64% VO2max for the men and women during the circuit. Both men and women had high respiratory exchange ratios (>1.0) suggesting marked anaerobic energy contribution. Physiological variables associated with circuit time were assessed by backward stepwise regression yielding a significant model that included only peak work rate during arm cranking exercise as a function of circuit completion time across men and women combined (P < 0.001). For men, but especially for women, the time required for the simulated victim drag (68.2 kg mannequin) was positively correlated with total time to complete the other circuit elements (r = 0.51, r = 0.96 respectively). The simple correlation between circuit time and VO2max (mL/kg/min) revealed poor relationships for men (r = -0.37, P > 0.05) and women (r = 0.20, P > 0.05). These data demonstrated that upper body fitness as reflected by peak work rate during arm cranking correlated with total circuit time for the men and women in our population sample. PMID:18204853

Harvey, D G; Kraemer, J L; Sharratt, M T; Hughson, R L

2008-05-01

271

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

SciTech Connect

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

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

2007-03-15

272

Structural Basis for Rab GTPase Activation by VPS9 Domain Exchange Factors  

SciTech Connect

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

Delprato,A.; Lambright, D.

2007-01-01

273

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

PubMed

Gas exchanges of whole canopy can be studied by covering entire plants with a chamber and using portable infrared gas analyzers (IRGAs) to measure CO2 and H2O exchanged with the air blown through the chamber enclosure. The control of temperature rise inside the chamber, which should be kept low, and the accurate measurement of the air flow are two crucial aspects for realistic and precise estimation of photosynthesis and transpiration. An automated open-system plant chamber (clear flexible balloon enclosure) for small plants was developed to ameliorate such a technique. The temperature rise is here predicted by heat balance analysis inside the chamber. The analysis shows that when as much as 500 W m2 of solar radiation is converted to sensible heat, a flow rate of 0.98 mol s(-1) (approximately = 20 L s(-1)) of air blown into a cylinder-shaped enclosure (0.8 m high, 0.5 m wide) is adequate to limit temperature increase to 2 K. An improved calibration for the measurement of the chamber airflow was obtained by combining the use of a Pitot tube anemometer with the classical CO2 injection approach. The concentration increase due to the injection of CO2 at a known rate into the chamber was predicted by the air flow calculated from the "Pitot" air velocity. The turbulent regime of air assured that a single-point Pitot measurement was enough for a good estimation (slope = 0.99; R2 = 0.999) of the actual air flow. The open-system chamber was tested on potted sunflower (Helianthus annuus, L.) and maize (Zea mays, L.) plants under variable solar radiation, temperature, and air humidity during the daytime. As expected, similar rates of maximal leaf-area based photosynthesis (about 40 micromol m(-2) s(-1)) were observed in the two species confirming the reliability of our system. The consistency of data also resulted from the typical relationships observed between photosynthetic rate and light. PMID:16570620

Alterio, Giovanni; Giorio, Pasquale; Sorrentino, Giuseppe

2006-03-15

274

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

275

Design of compact intermediate heat exchangers for gas cooled fast reactors  

E-print Network

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

Gezelius, Knut, 1978-

2004-01-01

276

Multidimensional Separations of Ubiquitin Conformers in the Gas Phase: Relating Ion Cross Sections to H/D Exchange Measurements  

PubMed Central

Investigating gas-phase structures of protein ions can lead to an improved understanding of intramolecular forces that play an important role in protein folding. Both hydrogen/deuterium (H/D) exchange and ion mobility spectrometry provide insight into the structures and stabilities of different gas-phase conformers, but how best to relate the results from these two methods has been hotly debated. Here, high-field asymmetric waveform ion mobility spectrometry (FAIMS) is combined with Fourier-transform ion cyclotron resonance mass spectrometry (FT/ICR MS) and is used to directly relate ubiquitin ion cross sections and H/D exchange extents. Multiple conformers can be identified using both methods. For the 9+ charge state of ubiquitin, two conformers (or unresolved populations of conformers) that have cross sections differing by 10% are resolved by FAIMS, but only one conformer is apparent using H/D exchange at short times. For the 12+ charge state, two conformers (or conformer populations) have cross sections differing by <1%, yet H/D exchange of these conformers differ significantly (6 versus 25 exchanges). These and other results show that ubiquitin ion collisional cross sections and H/D exchange distributions are not strongly correlated and that factors other than surface accessibility appear to play a significant role in determining rates and extents of H/D exchange. Conformers that are not resolved by one method could be resolved by the other, indicating that these two methods are highly complementary and that more conformations can be resolved with this combination of methods than by either method alone. PMID:16023362

Robinson, Errol W.; Williams, Evan R.

2009-01-01

277

Modeling of an aerobic bioprocess based on gas exchange and dynamics: a novel approach.  

PubMed

Monitoring of the biological degradation of a substrate by microorganisms is a key issue, especially in the soil bioremediation area. Respiration measurement is the easiest way to obtain online information on the biological activity. Nevertheless, it is indirectly related to substrate consumption and microbial growth. To be able to link these phenomena, a robust and descriptive model has been developed. Both biological and gas/liquid transfer dynamics must be taken into account to link the online measurement with the actual biological respiration. For that, experimental evolution of the respiratory ouotient (RQ) during a biodegradation has been compared against general biodegradation knowledge. To obtain a reliable model, practical and structural sensitivity analyses have been conducted. The model can describe the evolution of both online measurable and non-measurable states. It also gives a new definition of the apparent RQ, measured in the gas phase, compared to the actual biological RQ. PMID:24658795

Lemaire, Cyril; Schoefs, Olivier; Lamy, Edvina; Pauss, André; Mottelet, Stéphane

2014-09-01

278

Effect of cardiac output on gas exchange in one-lung atelectasis.  

PubMed

To evaluate the effect of administration of dobutamine on gas exchange in patients with one-lung atelectasis during pneumonectomy, ten patients with normal pulmonary function and localized carcinoma of the lung were studied during pulmonary resection. With each patient in the lateral decubitus position, hemodynamic profiles and oxygen transport data were recorded before and after administration of dobutamine at 5 micrograms/kg/min. Patients were ventilated with one-lung anesthesia and administration of 100 percent oxygen. With infusion of dobutamine, the heart rate, cardiac index, and LVSWI significantly increased. Mean arterial pressure increased while PAP fell. Systemic and pulmonary vascular resistance also declined. Arterial oxygenization and delivery improved, while oxygen uptake was unchanged. Pulmonary shunt fraction was significantly reduced. While the mechanism for shunt reduction in our patients is unclear, operative factors may include pulmonary vasodilation with dobutamine inhibition of HPV. The negative impact of reduced HPV may have been lessened by gravitational distribution of blood flow and dobutamine-mediated reduction in PAP in our patients. PMID:2331907

Mathru, M; Dries, D J; Kanuri, D; Blakeman, B; Rao, T

1990-05-01

279

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

NASA Technical Reports Server (NTRS)

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

Olson, D. A.

1991-01-01

280

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

PubMed Central

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

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

1987-01-01

281

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

282

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

283

Changes in gas exchange kinetics with training in patients with spinal cord injury.  

PubMed

We examined the ability of patients with spinal cord injury to undergo adaptations to chronic exercise training (cycle ergometry) invoked by functional electrical stimulation (FES) of the legs. Nine such patients performed incremental and constant work rate exercise before and after exercise training. Exercise sessions averaged 2.1 +/- 0.4/wk, and consisted of 30 min/session of continuous FES recumbent cycling with increasing work rate as tolerated. Peak VO2 and peak work rate significantly improved with training. Peak VO2 was significantly correlated with peak heart rate both before and after training (r = 0.97 pre and 0.85 post, P < 0.01 for both). The time course of the VO2, VCO2 and VE responses to constant-load exercise (unloaded cycling) and in recovery (mean response time MRT) were very long prior to training, and became significantly faster following training. However, there was no correlation between percentage improvement in either MRTon or MRToff for VO2 and the percentage increase in peak VO2. Exercise tolerance in these patients with spinal cord injury appears to be a direct function of the ability to increase heart rate. Further, exercise training can elicit significant improvements in both exercise tolerance and in gas exchange kinetics, even when performed only twice per week. However, these improvements may be accomplished by different mechanisms. PMID:8897377

Barstow, T J; Scremin, A M; Mutton, D L; Kunkel, C F; Cagle, T G; Whipp, B J

1996-10-01

284

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

PubMed

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

Yamamoto, Y

1999-01-01

285

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

286

Regulation of Tiam1 nucleotide exchange activity by pleckstrin domain binding ligands.  

PubMed

Rho family GTPases play roles in cytoskeletal organization and cellular transformation. Tiam1 is a member of the Dbl family of guanine nucleotide exchange factors that activate Rho family GTPases. These exchange factors have in common a catalytic Dbl homology and adjacent pleckstrin homology domain. Previous structural studies suggest that the pleckstrin domain, a putative phosphoinositide-binding site, may serve a regulatory function. We identified ascorbyl stearate as a compound that binds to the pleckstrin domain of p120 Ras GTPase-activating protein. Furthermore, ascorbyl stearate appears to be a general pleckstrin domain ligand, perhaps by mimicking an endogenous amphiphilic ligand. Tiam1 nucleotide exchange activity was greatly stimulated by ascorbyl stearate. Certain phosphoinositides also stimulated Tiam1 activity but were less potent than ascorbyl stearate. Tiam1 contains an additional N-terminal pleckstrin domain, but only the C-terminal pleckstrin domain was required for activation. Our results suggest that the pleckstrin domains of Dbl-type proteins may not only be involved in subcellular localization but may also directly regulate the nucleotide exchange activity of an associated Dbl homology domain. In addition, this paper introduces ascorbyl stearate as a pleckstrin domain ligand that can modulate the activity of certain pleckstrin domain-containing proteins. PMID:10835422

Crompton, A M; Foley, L H; Wood, A; Roscoe, W; Stokoe, D; McCormick, F; Symons, M; Bollag, G

2000-08-18

287

Corrosive resistant heat exchanger  

DOEpatents

A corrosive and errosive resistant heat exchanger which recovers heat from a contaminated heat stream. The heat exchanger utilizes a boundary layer of innocuous gas, which is continuously replenished, to protect the heat exchanger surface from the hot contaminated gas. The innocuous gas is conveyed through ducts or perforations in the heat exchanger wall. Heat from the heat stream is transferred by radiation to the heat exchanger wall. Heat is removed from the outer heat exchanger wall by a heat recovery medium.

Richlen, Scott L. (Annandale, VA)

1989-01-01

288

Contact Activation of Blood Plasma and Factor XII by Ion-exchange Resins  

PubMed Central

Sepharose ion-exchange particles bearing strong Lewis acid/base functional groups (sulfopropyl, carboxymethyl, quarternary ammonium, dimethyl aminoethyl, and iminodiacetic acid) exhibiting high plasma protein adsorbent capacities are shown to be more efficient activators of blood factor XII in neat-buffer solution than either hydrophilic clean-glass particles or hydrophobic octyl sepharose particles ( FXII?surfaceactivatorFXIIa; a.k.a autoactivation, where FXII is the zymogen and FXIIa is a procoagulant protease). In sharp contrast to the clean-glass standard of comparison, ion-exchange activators are shown to be inefficient activators of blood plasma coagulation. These contrasting activation properties are proposed to be due to the moderating effect of plasma-protein adsorption on plasma coagulation. Efficient adsorption of blood plasma proteins unrelated to the coagulation cascade impedes FXII contacts with ion-exchange particles immersed in plasma, reducing autoactivation, and causing sluggish plasma coagulation. By contrast, plasma proteins do not adsorb to hydrophilic clean glass and efficient autoactivation leads directly to efficient activation of plasma coagulation. It is also shown that competitive-protein adsorption can displace FXIIa adsorbed to the surface of ion-exchange resins. As a consequence of highly-efficient autoactivation and FXIIa displacement by plasma proteins, ion-exchange particles are slightly more efficient activators of plasma coagulation than hydrophobic octyl sepharose particles that do not bear strong Lewis acid/base surface functionalities but to which plasma proteins adsorb efficiently. Plasma proteins thus play a dual role in moderating contact activation of the plasma coagulation cascade. The principal role is impeding FXII contact with activating surfaces but this same effect can displace FXIIa from an activating surface into solution where the protease can potentiate subsequent steps of the plasma coagulation cascade. PMID:21982294

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

2011-01-01

289

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

290

Active heat exchange system development for latent heat thermal energy storage  

NASA Astrophysics Data System (ADS)

Five tasks to select, design, fabricate, test and evaluate candidate active heat exchanger modules for future applications to solar and conventional utility power plants were discussed. Alternative mechanizations of active heat exchange concepts were analyzed for use with heat of fusion phase change materials (PCMs) in the temperature range of 250 to 350 C. Twenty-six heat exchange concepts were reviewed, and eight were selected for detailed assessment. Two candidates were selected for small-scale experimentation: a coated tube and shell heat exchanger and a direct contact reflux boiler. A dilute eutectic mixture of sodium nitrate and sodium hydroxide was selected as the PCM from over 50 candidate inorganic salt mixtures. Based on a salt screening process, eight major component salts were selected initially for further evaluation. The most attractive major components in the temperature range of 250 to 350 C appeared to be NaNO3, NaNO2, and NaOH. Sketches of the two active heat exchange concepts selected for test are given.

Lefrois, R. T.; Mathur, A. K.

1980-04-01

291

Active heat exchange system development for latent heat thermal energy storage  

NASA Technical Reports Server (NTRS)

Five tasks to select, design, fabricate, test and evaluate candidate active heat exchanger modules for future applications to solar and conventional utility power plants were discussed. Alternative mechanizations of active heat exchange concepts were analyzed for use with heat of fusion phase change materials (PCMs) in the temperature range of 250 to 350 C. Twenty-six heat exchange concepts were reviewed, and eight were selected for detailed assessment. Two candidates were selected for small-scale experimentation: a coated tube and shell heat exchanger and a direct contact reflux boiler. A dilute eutectic mixture of sodium nitrate and sodium hydroxide was selected as the PCM from over 50 candidate inorganic salt mixtures. Based on a salt screening process, eight major component salts were selected initially for further evaluation. The most attractive major components in the temperature range of 250 to 350 C appeared to be NaNO3, NaNO2, and NaOH. Sketches of the two active heat exchange concepts selected for test are given.

Lefrois, R. T.; Mathur, A. K.

1980-01-01

292

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

293

Effects of experimental warming on phenology, growth and gas exchange of treeline birch ( Betula utilis ) saplings, Eastern Tibetan Plateau, China  

Microsoft Academic Search

Mountain birch (Betula utilis) is the most important treeline species in alpine forests of southwestern China. In order to understand the effects of future\\u000a warming on treeline birch, this study was conducted to examine the effects of experimental warming on leaf phenology, growth\\u000a and gas exchange of B. utilis saplings using the open top chamber (OTC) method in a treeline

Zhenfeng Xu; Tingxing Hu; Yuanbin Zhang

294

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

Microsoft Academic Search

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

Rossano Massai; Damiano Remorini; Massimiliano Tattini

2004-01-01

295

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

296

Response to drought and salt stress of lemon ‘Fino 49’ under field conditions: Water relations, osmotic adjustment and gas exchange  

Microsoft Academic Search

Drought and salinity are two of the most important factors limiting the lemon yield in south-eastern Spain. The effects of drought and salt stress, applied independently, on water relations, osmotic adjustment and gas exchange in the highest evapotranspiration period were studied to compare the tolerance and adaptive mechanisms of 13-year-old ‘Fino 49’ lemon trees, in immature and mature leaves. The

J. G. Pérez-Pérez; J. M. Robles; J. C. Tovar

2009-01-01

297

Leaf Water Relations and Net Gas Exchange Responses of Salinized Carrizo Citrange Seedlings during Drought Stress and Recovery  

Microsoft Academic Search

† Background and Aims Since salinity and drought stress can occur together, an assessment was made of their interacting effects on leaf water relations, osmotic adjustment and net gas exchange in seedlings of the relatively chloride-sensitive Carrizo citrange, Citrus sinensisPoncirus trifoliata. † Methods Plants were fertilized with nutrient solution with or without additional 100 mM NaCl (salt and no-salt treatments).

J. G. P EREZ-PEREZ; J. P. S YV; E RT S E N; P. B OTIA; F. GA RC IA-SANCHEZ

2007-01-01

298

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

299

Diurnal gas exchange characteristics and water use efficiency of three salt-secreting mangroves at low and high salinities  

Microsoft Academic Search

Continuous measurements of gas exchange characteristics were made on two to nine year old hydroponically grown Avicennia germinans (L.) Stearn, Aegialitis annulata R. Br. and Aegiceras corniculatum (L.) Blanco maintained at 50 or 500 mol m-3 NaCl. In Avicennia germinans and Aegialitis annulata, CO2 assimilation rates were initially higher at 500 mol m-3 NaCl and decreased gradually towards the end

G. Naidoo; D. J. Willert

1995-01-01

300

Bronchodilator effect on ventilatory, pulmonary gas exchange, and heart rate kinetics during high-intensity exercise in COPD  

Microsoft Academic Search

Respiratory mechanical abnormalities in patients with chronic obstructive pulmonary disease (COPD) may impair cardiodynamic\\u000a responses and convective oxygen delivery during exercise, resulting in slower ventilatory, pulmonary gas exchange (PGE), and\\u000a heart rate (HR) kinetics compared with normal. We reasoned that bronchodilators and the attendant reduction of operating lung\\u000a volumes should accelerate ventilatory, PGE, and HR kinetics in the transition from

Pierantonio Laveneziana; Paolo Palange; Josuel Ora; Dario Martolini; Denis E. O’Donnell

2009-01-01

301

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

302

The Effect of Experimentally Induced Root Mortality on Trace Gas Exchange  

NASA Astrophysics Data System (ADS)

Soil-atmosphere exchange of carbon dioxide (CO2), nitric oxide (NO), nitrous oxide (N2O) and methane (CH4) was measured following a root exclusion experiment in the Tapajos National Forest near Santarem, Para, Brazil. The sampling period (June 4 - August 14, 2000) coincided with the beginning of the dry season. The experiment was set up as a randomized complete block design with 5 pairs of 2.5 x 2.5 m plots in both sand and clay soils. Trenches were dug around one plot in each pair for screen installation. Trace gas fluxes were measured weekly for ten weeks following the trenching. Duplicate flux measurements were made for each of the trenched and non-trenched plots. Enclosures made of 0.25 m diameter PVC pipe were placed on a base imbedded in the soil. Dynamic measurements using a portable backpack system equipped with an NO2 chemiluminescent detector for NO and an infrared gas analyzer for CO2 were completed in the field. CH4 and N2O fluxes were measured through a static enclosure method. Syringe samples of the enclosure headspace were analyzed by GC-FID (CH4) and ECD (N2O) the following day. Daily average fluxes ranged between -0.01 and 60.3 ng-N cm-2 hr-1 for N2O. NO fluxes ranged between 0.58 and 8.74 ng-N cm-2 hr-1. CH4 fluxes varied between net consumption and production from -1.73 to 0.912 mg m-2 d-1. Soil respiration ranged from 1.34 to 5.12 umoles CO2 m-2 s-1. Significant differences were seen between trenched and non-trenched plots in both clay and sand soils for N2O emissions only. Hourly field standardization of the NO2 chemiluminescent analyzer resulted in lower variability than the traditional method of standardization which is completed at the beginning and end of the measurement day. Frequent field standardization of the analyzer is necessary to reduce measurement error due to intra-day variability.

Varner, R. K.; Keller, M.; Robertson, J. R.; Dias, J. D.; Silva, H.; Crill, P. M.; McGroddy, M.; Silver, W. L.

2002-12-01

303

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. PMID:11154355

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

2001-01-01

304

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

305

Erythropoietin-induced Neuroprotection Requires Cystine Glutamate Exchanger Activity  

PubMed Central

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

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

2010-01-01

306

Effects of long-term low atmospheric pressure on gas exchange and growth of lettuce  

NASA Astrophysics Data System (ADS)

The objectives of this research were to determine photosynthesis, evapotranspiration and growth of lettuce at long-term low atmospheric pressure. Lettuce ( Lactuca sativa L . cv. Youmaicai) plants were grown at 40 kPa total pressure (8.4 kPa p) or 101 kPa total pressure (20.9 kPa p) from seed to harvest for 35 days. Germination rate of lettuce seeds decreased by 7.6% at low pressure, although this was not significant. There was no significant difference in crop photosynthetic rate between hypobaria and ambient pressure during the 35-day study. The crop evapotranspiration rate was significantly lower at low pressure than that at ambient pressure from 20 to 30 days after planting (DAP), but it had no significant difference before 20 DAP or after 30 DAP. The growth cycle of lettuce plants at low pressure was delayed. At low pressure, lettuce leaves were curly at the seedling stage and this disappeared gradually as the plants grew. Ambient lettuce plants were yellow and had an epinastic growth at harvest. The shoot height, leaf number, leaf length and shoot/root ratio were lower at low pressure than those at ambient pressure, while leaf area and root growth increased. Total biomass of lettuce plants grown at two pressures had no significant difference. Ethylene production at low pressure decreased significantly by 38.8% compared with ambient pressure. There was no significant difference in microelements, nutritional phytochemicals and nitrate concentrations at the two treatments. This research shows that lettuce can be grown at long-term low pressure (40 kPa) without significant adverse effects on seed germination, gas exchange and plant growth. Furthermore, ethylene release was reduced in hypobaria.

Tang, Yongkang; Guo, Shuangsheng; Dong, Wenping; Qin, Lifeng; Ai, Weidang; Lin, Shan

2010-09-01

307

Effect of mean airway pressure on gas exchange during high-frequency oscillatory ventilation.  

PubMed

We studied the effect of mean airway pressure (Paw) on gas exchange during high-frequency oscillatory ventilation in 14 adult rabbits before and after pulmonary saline lavage. Sinusoidal volume changes were delivered through a tracheostomy at 16 Hz, a tidal volume of 1 or 2 ml/kg, and inspired O2 fraction of 0.5. Arterial PO2 and PCO2 (PaO2, PaCO2), lung volume change, and venous admixture were measured at Paw from 5 to 25 cmH2O after either deflation from total lung capacity or inflation from relaxation volume (Vr). The rabbits were lavaged with saline until PaO2 was less than 70 Torr, and all measurements were repeated. Lung volume change was measured in a pressure plethysmograph. Raising Paw from 5 to 25 cmH2O increased lung volume by 48-50 ml above Vr in both healthy and lavaged rabbits. Before lavage, PaO2 was relatively insensitive to changes in Paw, but after lavage PaO2 increased with Paw from 42.8 +/- 7.8 to 137.3 +/- 18.3 (SE) Torr (P less than 0.001). PaCO2 was insensitive to Paw change before and after lavage. At each Paw after lavage, lung volume was larger, venous admixture smaller, and PaO2 higher after deflation from total lung capacity than after inflation from Vr. This study shows that the effect of increased Paw on PaO2 is mediated through an increase in lung volume. In saline-lavaged lungs, equal distending pressures do not necessarily imply equal lung volumes and thus do not imply equal PaO2. PMID:2022562

Boynton, B R; Villanueva, D; Hammond, M D; Vreeland, P N; Buckley, B; Frantz, I D

1991-02-01

308

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

PubMed Central

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

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

2014-01-01

309

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

PubMed

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

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

2014-08-01

310

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

311

Active heat exchange system development for latent heat thermal energy storage  

NASA Technical Reports Server (NTRS)

Active heat exchange concepts for use with thermal energy storage systems in the temperature range of 250 C to 350 C, using the heat of fusion of molten salts for storing thermal energy are described. Salt mixtures that freeze and melt in appropriate ranges are identified and are evaluated for physico-chemical, economic, corrosive and safety characteristics. Eight active heat exchange concepts for heat transfer during solidification are conceived and conceptually designed for use with selected storage media. The concepts are analyzed for their scalability, maintenance, safety, technological development and costs. A model for estimating and scaling storage system costs is developed and is used for economic evaluation of salt mixtures and heat exchange concepts for a large scale application. The importance of comparing salts and heat exchange concepts on a total system cost basis, rather than the component cost basis alone, is pointed out. The heat exchange concepts were sized and compared for 6.5 MPa/281 C steam conditions and a 1000 MW(t) heat rate for six hours. A cost sensitivity analysis for other design conditions is also carried out.

Lefrois, R. T.; Knowles, G. R.; Mathur, A. K.; Budimir, J.

1979-01-01

312

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

Microsoft Academic Search

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

H. Z. Liu; X. F. Lu

2010-01-01

313

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...

314

An Activity Theory Exegesis on Conflict and Contradictions in Networked Discussions and Feedback Exchanges  

ERIC Educational Resources Information Center

The goal of this study was to investigate the culturally afforded contradictions that ten advanced English as a Second Language (ESL) learner encountered when they posted their paper topics and exchanged feedback strategies online and contextualized some of these strategies to draft their papers. Using Cultural-Historical Activity Theory (CHAT),…

Hadjistassou, Stella K.

2012-01-01

315

H Exchange Reveals a Mechanism of Thrombin Activation Julia R. Koeppe and Elizabeth A. Komives*  

E-print Network

Amide H/2 H Exchange Reveals a Mechanism of Thrombin Activation Julia R. Koeppe and Elizabeth A: Thrombin is a dual action serine protease in the blood clotting cascade. Similar to other clotting factors, thrombin is mainly present in the blood in a zymogen form, prothrombin. Although the two cleavage events

Komives, Elizabeth A.

316

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...

317

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

Microsoft Academic Search

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

Takeshi Takeda; Kazuhiko Kunitomi; Tetsuji Horie; Katsuo Iwata

1997-01-01

318

Evolution of volatile substances from strongly basic anion-exchangers into the gas phase  

SciTech Connect

The purpose of this work was chemical evaluation, from the sanitary standpoint, of strongly basic anion-exchangers and of polyacrylonitrile fibers filled with them, in relation to their use for purification of air intended for human respiration. The carbonate forms of granulated anion-exchange resins AV-17-8 and AV-29-10P and fibers filled with them were investigated. Amines were determined spectrophotometrically. It is determined that the sanitary chemical characteristics of PAN fibers filled with strongly basic anion-exchangers of the polymerization type make them suitable for removing substances which have no destructive effects on the resins from air.

Ryabikina, L.G.; Afanas'eva, E.K.; Vulkih, A.I.; Yakovlev, A.I.

1985-05-10

319

An on-demand microfluidic hydrogen generator with self-regulated gas generation and self-circulated reactant exchange with a rechargeable reservoir  

Microsoft Academic Search

This article introduces an on-demand microfluidic hydrogen generator that can be integrated with a micro-proton exchange membrane\\u000a (PEM) fuel cell. The catalytic reaction, reactant circulation, gas\\/liquid separation, and autonomous control functionalities\\u000a are all integrated into a single microfluidic device. It generates hydrated hydrogen gas from an aqueous ammonia borane solution\\u000a which is circulated and exchanged between the microfluidic reactor and

L. Zhu; N. Kroodsma; J. Yeom; J. L. Haan; M. A. Shannon; D. D. Meng

320

Taxation of oil and gas activities in Spain  

SciTech Connect

Special tax norms in Spain deal with the exploration, drilling, production, and distribution of oil and gas companies that set them apart from the activities of other companies doing business. A review of the Corporation Tax, Turnover Tax, and taxes related to exploration, provincial and local tax exemptions, importations, withholding obligations, and other activities concludes that the oil and gas industries benefit more than they would under the general tax system. 33 references.

Anton, F.L.

1984-09-01

321

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

322

Studying the aerodynamic parameters characterizing motion of gas suspension in a countercurrent cyclone heat exchanger  

Microsoft Academic Search

The physical pattern of flow in a countercurrent cyclone heat exchanger obtained from experiments carried out on a small-scale model of it is presented. Self-oscillation behavior of a toroidal vortex occurring in the apparatus was experimentally observed. A possibility of reducing the quantity of large particles of solid materials 0.07-0.15 mm in size entrained from a countercurrent cyclone heat exchanger

P. A. Kovgan; M. G. Abuov

2009-01-01

323

Studying the aerodynamic parameters characterizing motion of gas suspension in a countercurrent cyclone heat exchanger  

Microsoft Academic Search

The physical pattern of flow in a countercurrent cyclone heat exchanger obtained from experiments carried out on a small-scale\\u000a model of it is presented. Self-oscillation behavior of a toroidal vortex occurring in the apparatus was experimentally observed.\\u000a A possibility of reducing the quantity of large particles of solid materials 0.07–0.15 mm in size entrained from a countercurrent\\u000a cyclone heat exchanger

P. A. Kovgan; M. G. Abuov

2009-01-01

324

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

Microsoft Academic Search

\\u000a A new type scaling-up scheme of CFB boiler that takes separator as center and furnaces are laid around was put forward in\\u000a this paper. In the recycle system, a new type heat exchanger device with double outlets was designed for this disposal scheme.\\u000a As we know, the external heat exchanger is very important for the CFB, which be able no

H. Z. Liu; X. F. Lu

325

Measuring the hydrogen/deuterium exchange of proteins at high spatial resolution by mass spectrometry: overcoming gas-phase hydrogen/deuterium scrambling.  

PubMed

Conspectus Proteins are dynamic molecules that exhibit conformational flexibility to function properly. Well-known examples of this are allosteric regulation of protein activity and ligand-induced conformational changes in protein receptors. Detailed knowledge of the conformational properties of proteins is therefore pertinent to both basic and applied research, including drug development, since the majority of drugs target protein receptors and a growing number of drugs introduced to the market are therapeutic peptides or proteins. X-ray crystallography provides a static picture at atomic resolution of the lowest-energy structure of the native ensemble. There is a growing need for sensitive analytical tools to explore all of the significant molecular structures in the conformational landscape of proteins. Hydrogen/deuterium exchange monitored by mass spectrometry (HDX-MS) has recently emerged as a powerful method for characterizing protein conformational dynamics. The basis of this method is the fact that backbone amides in stable hydrogen-bonded structures (e.g., ?-helices and ?-sheets) are protected against exchange with the aqueous solvent. All protein structures are dynamic, however, and eventually all of the protecting hydrogen bonds will transiently break as the protein-according to thermodynamic principles-cycles through partially unfolded states that correspond to excited free energy levels. As a result, all of the backbone amides will eventually become temporarily solvent-exposed and exchange-competent over time. Consequently, a folded protein in D2O will gradually incorporate deuterium into its backbone amides, and the kinetics of the process can be readily monitored by mass spectrometry. The deuterium uptake kinetics for the intact protein (global exchange kinetics) represents the sum of the exchange kinetics for the individual backbone amides. Local exchange kinetics is typically achieved by using pepsin digestion under quench conditions (i.e., under cold acidic conditions where the amide hydrogen exchange rate is slowed by many orders of magnitude). The ability to localize the individual deuterated residues (the spatial resolution) is determined by the size (typically ?7-15 residues) and the number of peptic peptides. These peptides provide a relatively coarse-grained picture of the protein dynamics. A fundamental understanding of the relationship between protein function/dysfunction and conformational dynamics requires in many cases higher resolution and ultimately single-residue resolution. In this Account, we summarize our efforts to achieve single-residue deuterium levels in proteins by electron-based or laser-induced gas-phase fragmentation methods. A crucial analytical requirement for this approach is that the pattern of deuterium labeling from solution is retained in the gas-phase fragment ions. It is therefore essential to control and minimize any occurrence of gas-phase randomization of the solution deuterium label (H/D scrambling) during the MS experiment. For this purpose, we have developed model peptide probes to accurately measure the onset and extent of H/D scrambling. Our analytical procedures to control the occurrence of H/D scrambling are detailed along with the physical parameters that induce it during MS analysis. In light of the growing use of gas-phase dissociation experiments to measure the HDX of proteins in order to obtain a detailed characterization and understanding of the dynamic conformations and interactions of proteins at the molecular level, we discuss the perspectives and challenges of future high-resolution HDX-MS methodology. PMID:25171396

Rand, Kasper D; Zehl, Martin; Jørgensen, Thomas J D

2014-10-21

326

Amide H/2H exchange reveals a mechanism of thrombin activation.  

PubMed

Thrombin is a dual action serine protease in the blood clotting cascade. Similar to other clotting factors, thrombin is mainly present in the blood in a zymogen form, prothrombin. Although the two cleavage events required to activate thrombin are well-known, little is known about why the thrombin precursors are inactive proteases. Although prothrombin is much larger than thrombin, prethrombin-2, which contains all of the same amino acids as thrombin, but has not yet been cleaved between Arg320 and Ile321, remains inactive. Crystal structures of both prethrombin-2 and thrombin are available and show almost no differences in the active site conformations. Slight differences were, however, seen in the loops surrounding the active site, which are larger in thrombin than in most other trypsin-like proteases, and have been shown to be important for substrate specificity. To explore whether the dynamics of the active site loops were different in the various zymogen forms of thrombin, we employed amide H/(2)H exchange experiments to compare the exchange rates of regions of thrombin with the same regions of prothrombin, prethrombin-2, and meizothrombin. Many of the surface loops showed less exchange in the zymogen forms, including the large loop corresponding to anion binding exosite 1. Conversely, the autolysis loop and sodium-binding site exchanged more readily in the zymogen forms. Prothrombin and prethrombin-2 gave nearly identical results while meizothrombin in some regions more closely resembled active thrombin. Thus, cleavage of the Arg320-Ile321 peptide bond is the key to formation of the active enzyme, which involves increased dynamics of the substrate-binding loops and decreased dynamics of the catalytic site. PMID:16784223

Koeppe, Julia R; Komives, Elizabeth A

2006-06-27

327

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

328

Gas Adsorption by Activated and Impregnated Carbons.  

National Technical Information Service (NTIS)

HCN/H2O mixed vapor isotherms were measured on BPL activated and ASC whetlerite carbons maintaining an essentially constant relative water pressure and varying the relative HCN pressure. Chemisorption data on ASC whetlerite showed water vapor retention va...

G. B. Freeman, P. J. Reucroft

1977-01-01

329

Osmotic activation of a Na(+)-dependent Cl-/HCO3- exchanger.  

PubMed

In many systems, osmotically induced cell shrinkage activates the Na+/H+ exchanger. To assess the role of H(+)-extruding transporters in the response to osmotic shrinkage in vascular smooth muscle (VSM) and Chinese hamster ovary (CHO) cells, intracellular pH (pHi) was measured with 2',7'-bis(carboxy-ethyl)-5(6)- carboxyfluorescein-acetoxymethyl ester (BCECF-AM) after exposing cells to hypertonic medium. In nominally HCO(3-)-free medium, addition of 200 mM sucrose caused pHi to increase 0.33 pH unit on average in VSM cells but only 0.13 pH unit in CHO cells. Permeant solutes failed to increase pHi significantly. Cytochalasin B (1-20 microM), colchicine (1-10 microM), Ca2+ removal, and downregulation of protein kinase C activity did not affect osmotic activation of H+ extrusion in either cell type. Additional work was carried out to determine why osmotic activation of H+ extrusion was less in CHO than in VSM cells. In CHO cells, the osmotically induced delta pHi was only weakly sensitive to amiloride, suggesting that osmotic forces may activate an H+ transport system other than Na+/H+ exchange. In the presence of 10 mM HCO3-, osmotically induced delta pHi decreased by 60% in VSM cells but increased by 50% in CHO cells compared with the delta pHi in HCO(3-)-free medium. Lastly, removal of extracellular Cl- did not affect osmotically induced delta pHi in VSM cells but completely abolished the response in CHO cells. We conclude that in VSM cells osmotically induced changes in pHi are mediated by Na+/H+ exchange, whereas in CHO cells they are most likely mediated by a Na(+)-dependent Cl-/HCO3- exchanger. PMID:7840143

Reusch, H P; Lowe, J; Ives, H E

1995-01-01

330

Kinetic approach to evaluate the energy and entropy of activation for the exchange of alkaline earth metal ions on tin(IV) tungstate cation exchanger  

SciTech Connect

A new approach based on the Nernst-Planck equations has been applied to study the reaction kinetics on the surface of tin(IV) tungstate for the Mg(II)-H(I), Ca(II)-H(I), Sr(II)-H(I) and Ba(II)-H(I) exchanges under the conditions favouring a particle diffusion phenomenon. On the basis of these studies the various physical parameters such as the effective diffusion coefficients, activation energies and entropies of activation have been evaluated which give some informations regarding the mechanism of ion-exchange on the surface of inorganic materials. 25 references, 3 figures, 3 tables.

Varshney, K.G.; Khan, A.A.; Varshney, K.; Agrawal, S.

1984-01-01

331

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

PubMed

Gas exchange and ozone-induced foliar injury were intensively measured during a 6-day period in mid-August 1998 on leaves of Acer pseudoplatanus, Betula pendula, Corylus avellana, Fagus sylvatica, Fraxinus excelsior, Morus nigra, Prunus avium, Prunus serotina, Rhamnus cathartica, and Viburnum lantana at a forest nursery site in Canton Ticino, Switzerland. Plants were grown in four open plots (AA), four open-top chambers receiving carbon-filtered (CF) air, and four receiving non-filtered (NF) air. Significant variation in gas exchange (F > 12.7, P < 0.001) was detected among species with average net photosynthesis and average stomatal conductance differing by a factor of two. Species also varied significantly in foliar injury for those leaves for which we measured gas exchange (F = 39.6, P < 0.001). Fraxinus excelsior, M. nigra, P. avium, P. serotina, R. cathartica, and V. lantana showed more injury than A. pseudoplatanus, B. pendula, C. avellana, and Fagus sylvatica. Plants grown in CF chambers had significantly higher net photosynthesis (A) and stomatal conductance to water vapor (gwv), and lower foliar injury than plants grown in NF chambers and AA plots; interactions between species and ozone treatments were significant for all variables (F > or = 2.2, P < 0.05) except gwv (F = 0.7, P > 0.1). Although A and gwv decreased and foliar injury increased with leaf age, the magnitude of these changes was lower for plants grown in CF chambers than for plants grown in NF chambers and AA plots. Neither ozone uptake threshold (r = 0.26, P > 0.20) nor whole-plant injury (r = -0.15, P > 0.41) was significantly correlated with stomatal conductance across these species. It appears that the relationships between stomatal conductance and foliar injury are species-specific and interactions between physiology and environments and leaf biochemical processes must be considered in determining species sensitivity to ambient ozone exposures. PMID:11383335

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

2001-01-01

332

Electron self-exchange activation parameters of diethyl sulfide and tetrahydrothiophene.  

PubMed

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

Goez, Martin; Vogtherr, Martin

2013-01-01

333

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.

334

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. PMID:25006441

2014-01-01

335

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

336

Influence of Saline Irrigation on Growth, Ion Accumulation and Partitioning, and Leaf Gas Exchange of Carrot (Daucus carota L.)  

PubMed Central

Like those of many horticultural crop species, the growth and leaf gas exchange responses of carrot (Daucus carota L.) to salinity are poorly understood. In this study ion accumulation in root tissues (periderm, xylem and phloem tissues) and in leaves of different ages was assessed for carrot plants grown in the field with a low level of salinity (5·8 mm Na+ and 7·5 mm Cl–) and in a glasshouse with salinity ranging from 1–80 mm. At low levels of salinity (1–7·5 mm), in both the field and glasshouse, carrot leaves accumulated high concentrations of Cl– (140–200 mm); these appear to be the result of a high affinity for Cl– uptake and a low retention of Cl– in the root system. However, Cl– uptake is under tight control, with an 80?fold increase in external salinity resulting in only a 1·5?fold change in the Cl– concentration of the shoot and no increase in the Cl– concentration of the root xylem tissue. In contrast to Cl–, shoot Na+ concentrations were comparatively low (30–40 mm) but increased by seven?fold when salinity was increased by 80?fold. Growth over the 56?d treatment period in the glasshouse was insensitive to salinity less than 20 mm, but at higher concentrations the yield of carrot tap roots declined by 7 % for each 10 mm increase in salinity. At low levels of salinity the accumulation of high concentrations of Cl– (150 mm) in carrot laminae did not appear to limit leaf gas exchange. However, photosynthesis and stomatal conductance were reduced by 38 and 53 %, respectively, for plants grown at a salinity of 80 mm compared with those grown at 1 mm. Salinity?induced reductions in both pi and carbon isotope discrimination (?) were small (2·5 Pa and 1·4 ‰, respectively, at 80 mm) indicating that the reduction in photosynthesis was only marginally influenced by CO2 supply. At a salinity of 80 mm the photosynthetic capacity was reduced, with a 30 % reduction in the CO2?saturated rate of photosynthesis (Amax) and a 40 % reduction in both the apparent rate of RuBP?carboxylase?limited CO2 fixation (Vcmax) and the electron transport rate limiting RuBP regeneration (Jmax). This study has shown that carrot growth and leaf gas exchange are insensitive to the high leaf Cl– concentrations that occur at low levels (1–7 mm) of salinity. However, growth is limited at salinity levels above 20 mm and leaf gas exchange is limited at salinity levels above 8 mm. PMID:12451027

GIBBERD, MARK R.; TURNER, NEIL C.; STOREY, RICHARD

2002-01-01

337

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

E-print Network

the settings ActiveSync/Exchange to set up your Android mobile devices. If you set up an Exchange/ActiveSync account on your Android device, the information you sync includes e-mail messages, calendars, contacts and task data! Use these settings to access your Exchange e-mail on an Android mobile device: Username

Qiu, Weigang

338

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

E-print Network

the settings ActiveSync/Exchange to set up your Apple mobile devices. If you set up an Exchange/ActiveSync account on your Apple device, the information you sync includes e-mail messages, calendars, contacts and task data! Use these settings to access your Exchange e-mail on an Apple mobile device: Username

Qiu, Weigang

339

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

340

Gas exchange and ventilation during dormancy in the tegu lizard tupinambis merianae  

PubMed

The tegu lizard Tupinambis merianae exhibits an episodic ventilatory pattern when dormant at 17 degrees C but a uniform ventilatory pattern when dormant at 25 degrees C. At 17 degrees C, ventilatory episodes were composed of 1-22 breaths interspaced by non-ventilatory periods lasting 1.8-26 min. Dormancy at the higher body temperature was accompanied by higher rates of O(2) consumption and ventilation. The increase in ventilation was due only to increases in breathing frequency with no change observed in tidal volume. The air convection requirement for O(2) did not differ at the two body temperatures. The respiratory quotient was 0.8 at 17 degrees C and 1.0 at 25 degrees C. We found no consistent relationship between expired gas composition and the start/end of the ventilatory period during episodic breathing at 17 degrees C. However, following non-ventilatory periods of increasing duration, there was an increase in the pulmonary O(2) extraction that was not coupled to an equivalent increase in elimination of CO(2) from the lungs. None of the changes in the variables studied could alone explain the initiation/termination of episodic ventilation in the tegus, suggesting that breathing episodes are shaped by a complex interaction between many variables. The estimated oxidative cost of breathing in dormant tegus at 17 degrees C was equivalent to 52.3 % of the total metabolic rate, indicating that breathing is the most costly activity during dormancy. PMID:10574745

de Andrade DV; Abe

1999-12-01

341

Soil-atmosphere greenhouse-gas exchange in a bioretention system  

NASA Astrophysics Data System (ADS)

Bioretention systems are a popular green-technology for the management of urban stormwater runoff in many countries. They typically consist of a trench filled with a highly permeable soil medium that supports vegetation; runoff is diverted to bioretention systems and, by percolating through the filter medium, is subjected to a number of treatment processes. Nitrogen (N) is one of the key pollutants targeted by bioretention systems, which are able to reduce N concentrations considerably from inflow to outflow. To increase N removal, a saturated zone at the bottom of the filter medium is often artificially generated, to both enhance the denitrification process and increase the water available to the vegetation between inflow events. Although studies on the N-removal performance of bioretention systems are widely available in the literature, less is known about the exchange of greenhouse gases (GHG), especially nitrous oxide (N2O), between the bioretention systems and the atmosphere. Here, we present an experimental pilot study to measure N2O and CO2 soil emissions in a bioretention system installed on the Clayton Campus of Monash University in Melbourne, Australia. The bioretention system is divided into three cells, each 15 m2; the system as a whole receives water run-off from 4500 m2 of impervious car park. We monitored two cells with mostly sandy-loam vegetated with native sedges (mainly Carex Appressa and Lomandra Longifolia), one with and one without a saturated zone. Three manual flux chambers were installed in both cells. Gas flux samples were taken twice a week at about 11 am between the 2nd of March and the 18th of May 2011 (late summer and fall). Since October 2010, air-phase soil CO2 concentration profiles were measured continuously using solid-state infrared CO2 transmitters (GMT-221 model, Vaisala, Finland), along with soil moisture and soil temperature. Preliminary analysis of the chamber data (March only) showed that N2O fluxes were in general below 50 ?g N/ (m2 h) with occasional pulse emissions > 150 ?g N /(m2 h) after recent inflow events. Fluxes from the cell with the saturated zone were consistently higher than those from the cell without a saturated zone. CO2 fluxes were comparable between the two cells, and usually between 50 and 200 mg C/(m2 h) whilst temperatures ranged between 12 and 26 degrees Celsius through this late summer/autumn period. Results from the entire data-set (March-May) will be presented along with an investigation of the relationship between these fluxes and other environmental and soil variables, such as soil nitrate and ammonium content and soil redox potential. Seasonal fluctuations and the effect of random inflow pulses will be also assessed and discussed. The results from this pilot study are useful to provide direct quantification of the GHG emissions associated with urban bioretention systems, which are one of the most used green infrastructures to manage stormwater runoff.

Daly, E.; Chan, H.; Beringer, J.; Livesley, S. J.

2011-12-01

342

Development of heat exchangers for reheating scrubbed flue gas in a pilot plant  

NASA Astrophysics Data System (ADS)

Application of some reheating systems in flue gas desulphurization plants was studied. The following problems are examined: the influence of solid impurities in gas on the heat transfer coefficient, the different operational conditions to test clearing of the heat transfer surface, the rate of corrosion, and the partial gas recirculation. Measurements to increase the heat transfer coefficient and removing of liquid drops are suggested. Measurement techniques, insulation and prevention of leakage are discussed.

Michalak, S.

1982-09-01

343

A comparative study of adsorption of perfluorooctane sulfonate (PFOS) onto granular activated carbon, ion-exchange polymers and non-ion-exchange polymers.  

PubMed

Perfluorooctane sulfonate (PFOS) is the latest chemical categorized as persistent organic pollutants (POPs). PFOS appears in the environmental water and tap water in ng L(-1) level. The process of adsorption has been identified as an effective technique to eliminate PFOS in water. Three non-ion-exchange polymers (DowV493, DowL493 and AmbXAD4), two ion-exchange polymers (DowMarathonA and AmbIRA400) and one granular activated carbon (GAC) (Filtersorb400) were tested with regard to their sorption kinetics and isotherms at low PFOS concentrations (100-1000 ng L(-1) equilibrium concentrations). The sorption capacities at 1 microg L(-1) equilibrium concentration decreased in the following order: ion-exchange polymers>non-ion-exchange polymers > GAC, but at further low equilibrium concentration (100 ng L(-1)) non-ion-exchange polymers showed higher adsorption capacity than other adsorbents. In the case of sorption kinetics, GAC and ion-exchange polymers reached the equilibrium concentration within 4 h and AmbXAD4 within 10 h. DowV493 and DowL493 took more than 80 h to reach equilibrium concentration. AmbIRA400 was identified as the best filter material to eliminate PFOS at equilibrium concentration > 1000 ng L(-1). Considering both adsorption isotherms and adsorption kinetics, AmbXAD4 and DowMarathonA were recommended to eliminate PFOS at ng L(-1) equilibrium concentration. PMID:20546842

Senevirathna, S T M L D; Tanaka, S; Fujii, S; Kunacheva, C; Harada, H; Shivakoti, B R; Okamoto, R

2010-07-01

344

Determination of activated sludge biological activity using model corrected CO 2 off-gas data  

Microsoft Academic Search

Carbon dioxide (CO2) online off-gas monitoring is useful to detect changes in biological activity for activated sludge systems especially under limited oxygen conditions like under simultaneous nitrification–denitrification (SND) where respirometric measurements are not applicable. So far, the influence of the bicarbonate system on the liquid–gas transfer of CO2 prevented the wider use of off-gas CO2 for monitoring purposes in wastewater

Norbert Weissenbacher; Katharina Lenz; Susanne N. Mahnik; Bernhard Wett; Maria Fuerhacker

2007-01-01

345

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

Microsoft Academic Search

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

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

1989-01-01

346

Experimental study of work exchange with a granular gas: the viewpoint of the Fluctuation Theorem.  

E-print Network

is that of Feitosa and Menon [4]. In a 2D vibrated granular material, they mea- sured by video tracking the momentum of the fluctuations of energy flux between a granular gas and a small driven harmonic oscillator. The DC-motor driving-response), is performed by means of a driven harmonic oscillator coupled to the gran- ular gas. The Fluctuation Theorem

347

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, instead of the typical high-energy neutral beam. This diagnostic, named gas puff CXRS (GP-CXRS), is used to measure ion density, velocity, and temperature in the tokamak edge/pedestal region with excellent signal-background ratios, and has a number of advantages to conventional beam-based CXRS systems. Here we develop the physics basis for GP-CXRS, including the neutral transport, the charge-exchange process at low energies, and effects of energy-dependent rate coefficients on the measurements. The GP-CXRS hardware setup is described on two separate tokamaks, Alcator C-Mod and ASDEX Upgrade. Measured spectra and profiles are also presented. Profile comparisons of GP-CXRS and a beam based CXRS system show good agreement. Emphasis is given throughout to describing guiding principles for users interested in applying the GP-CXRS diagnostic technique.

Churchill, R. M.; Theiler, C.; Lipschultz, B. [MIT Plasma Science and Fusion Center, Cambridge, Massachusetts 02139 (United States)] [MIT Plasma Science and Fusion Center, Cambridge, Massachusetts 02139 (United States); Dux, R.; Pütterich, T.; Viezzer, E. [Max-Planck-Institut für Plasmaphysik, EURATOM Association, Boltzmannstrasse 2, D-85748 Garching (Germany)] [Max-Planck-Institut für Plasmaphysik, EURATOM Association, Boltzmannstrasse 2, D-85748 Garching (Germany); Collaboration: Alcator C-Mod Team; ASDEX Upgrade Team

2013-09-15

348

Functional exchange of components between light-activated photoreceptor phosphodiesterase and hormone-activated adenylate cyclase systems  

SciTech Connect

Previous studies have noted profound similarities between the regulation of light-activated (3',5'-cyclic-nucleotide 5'-nucleotidohydrolase, EC 3.1.4.17) in retinal rods and hormone-activated adenylate cyclase (ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1) in a variety of tissues. We report ere the functional exchange of components isolated from the photoreceptor system, which displayed predicted functional characteristics when incubated with recipient adenylate cyclase systems from rat cerebral cortical and hypothalamic synaptic membranes and frog erythrocyte ghosts. We demonstrate functional exchange of photoreceptor components at each of three loci: the hormone receptor, the GTP-binding protein (GBP), and the catalytic moiety of adenylate cyclase. Illuminated (but not unilluminated) rhodopsin was found to mimic the hormone-receptor complex, causing GTP-dependent activation of adenylate cyclase. The photoreceptor GBP complexed with guanosine 5'-(..beta..,..gamma..)imidotriphosphate (p(NH)ppG) produced a marked activation of recipient adenylate cyclase systems. Much smaller activation was observed when GBP was not complexed with p(NH)ppG. A heat-stable photoreceptor phosphodiesterase inhibitor reduced both basal and Mn/sup 2 +/-activated adenylate cyclase activites and this inhibition was reversed by photoreceptor GBPp(NH)ppG. These data demonstrate a remarkable functional compatibility between subunits of both systems and furthermore imply that specialized peptide domains responsible for protein-protein interactions are highly conserved.

Bitensky, M.W.; Wheeler, M.A.; Rasenick, M.M.; Yamazaki, A.; Stein, P.J.; Halliday, K.R.; Wheeler, G.L.

1982-06-01

349

Active heat exchange system development for latent heat thermal energy storage  

NASA Technical Reports Server (NTRS)

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

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

1980-01-01

350

Use of transcutaneous oxygen and carbon dioxide tensions for assessing indices of gas exchange during exercise testing.  

PubMed

The slow response characteristics of the combined transcutaneous electrode have been viewed as a major disadvantage when compared with other types of non-invasive assessment of gas exchange during exercise testing. We have previously shown that by using the highest recommended temperature of 45 degrees C to reduce response times, and combining this with an exercise protocol of gradual work load increments, that this allows changes in arterial blood gases to be closely followed by transcutaneous values. In the present study we have validated the use of a transcutaneous electrode for estimation of alveolar-arterial oxygen gradient (AaO2) and dead space to tidal volume ratio (V(D)/V(T)) during exercise, against values calculated from direct arterial blood gas analysis. One hundred measurements were made in 20 patients with various cardiopulmonary disorders who underwent exercise testing. Exercise testing was performed by bicycle ergometry with a specific protocol involving gradual work load increments at 2 min intervals. Transcutaneous gas tensions were measured by a heated combined O2 and CO2 electrode. Arterial blood was sampled at the midpoint of each stage of exercise and transcutaneous tensions noted at the end of each stage. The mean difference of the AaO2 gradient calculated from blood gas tensions obtained by the two methods was 0.14 kPa. The limits of agreement were -0.26 and 0.63 kPa. The same values for V(D)/V(T) calculated from gas tensions measured by the two methods were: mean difference 0001; limits of agreement -0.0242 and 0.0252. For both these parameters there was an even scatter around the mean value on Bland and Altman analysis. The findings of this study suggest that estimation of parameters of gas exchange using transcutaneous values during exercise testing is reliable, provided the electrode is heated to a slightly higher temperature than usual and the work load increments are gradual, allowing for the latency in the response time of the system. This system allows the assessment of the contribution of ventilation/perfusion inequality to breathlessness on exertion in patients, provided an initial arterial or ear lobe capillary sample is obtained for calibration purposes. This technique is particularly valuable in patients undergoing repeat exercise tests as it circumvents the need for arterial cannulation. PMID:10845433

Carter, R; Banham, S W

2000-04-01

351

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

SciTech Connect

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

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

1994-06-01

352

Pyk2 activation is integral to acid stimulation of sodium/hydrogen exchanger 3  

PubMed Central

The present study examines the role of Pyk2 in acid regulation of sodium/hydrogen exchanger 3 (NHE3) activity in OKP cells, a kidney proximal tubule epithelial cell line. Incubation of OKP cells in acid media caused a transient increase in Pyk2 phosphorylation that peaked at 30 seconds and increased Pyk2/c-Src binding at 90 seconds. Pyk2 isolated by immunoprecipitation and studied in a cell-free system was activated and phosphorylated at acidic pH. Acid activation of Pyk2 (a) was specific for Pyk2 in that acid did not activate focal adhesion kinase, (b) required calcium, and (c) was associated with increased affinity for ATP. Transfection of OKP cells with dominant-negative pyk2K457A or small interfering pyk2 duplex RNA blocked acid activation of NHE3, while neither had an effect on glucocorticoid activation of NHE3. In addition, pyk2K457A blocked acid activation of c-Src kinase, which is also required for acid regulation of NHE3. The present results demonstrate that Pyk2 is directly activated by acidic pH and that Pyk2 activation is required for acid activation of c-Src kinase and NHE3. Given that partially purified Pyk2 can be activated by acid in a cell-free system, Pyk2 may serve as the pH sensor that initiates the acid-regulated signaling cascade involved in NHE3 regulation. PMID:15599403

Li, Shaoying; Sato, Soichiro; Yang, Xiaojing; Preisig, Patricia A.; Alpern, Robert J.

2004-01-01

353

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

NASA Astrophysics Data System (ADS)

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

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

1997-01-01

354

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

NASA Astrophysics Data System (ADS)

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

1997-01-01

355

Ideas Exchange: "How Important Is Activity in Young Children (Preschool) to a Lifetime of Physical Activity?"  

ERIC Educational Resources Information Center

This article presents the opinions of several professionals who were asked: "How important is activity in young children (preschool) to a lifetime of physical activity?" These professionals point out the importance of physical activity to young children.

Hushman, GLenn; Morrison, Jaime; Mally, Kristi; McCall, Renee; Corso, Marjorie; Kamla, Jim; Magnotta, John; Chase, Melissa A.; Garrahy, Deborah A.; Lorenzi, David G.; Barnd, Sue

2009-01-01

356

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

PubMed Central

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

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

1994-01-01

357

Disease Progress Based on Effects of Verticillium dahliae and Pratylenchus penetrans on Gas Exchange in Russet Burbank Potato.  

PubMed

ABSTRACT The interactive effects of concomitant infection by the nematode Pratylenchus penetrans and the fungus Verticillium dahliae on symptom expression in Russet Burbank potato was studied in growth chamber experiments. Treatments were P. penetrans at three initial densities, V. dahliae at one inoculum density, the combination of the nematode at these three densities and the fungus, and a noninfested control. Gas exchange was measured nondestructively in leaf cohorts of different ages, one to three times weekly, with a LI-COR portable photosynthesis system. The single-pathogen treatments had no effect on assimilation or transpiration rates, but joint infection had a significant impact. In concomitant infection, photosynthesis was impaired more than transpiration, so estimates of leaf health were based on carbon assimilation rates only. Reductions in assimilation rate were apparent before the onset of visual symptoms. Assimilation rates decreased as much as 44% in the top, and newest, leaves of concomitantly infected plants, compared to rates in control plants. Even so, the health of newly produced leaves did not become progressively worse through time. With light use efficiency less than 0.20 mol of CO(2) fixed per mol of photosynthetically active radiation used as the criterion for disease incidence, disease progressed acropetally from the oldest to the youngest leaves. In plants infected with P. penetrans (0.8 nematodes per cm(3) of soil) in combination with V. dahliae, all leaves in cohorts 1 and 2 were symptomatic by 45 days after planting, and leaves in cohorts 3 to 6 became symptomatic at weekly intervals thereafter. For the control and single-pathogen treatments, the first time that light use efficiency fell below 0.20 in all leaves in cohort 1 was 71 days after planting. Concomitant infection reduced leaf life span by about 3 weeks. Both visual and physiological symptom expression were invariant to differences in initial nematode inoculum densities ranging from 0.8 to 2.5 nematodes per cm(3) of soil in one experiment and from 1.3 to 4.1 nematodes per cm(3) of soil in a second experiment. PMID:18945124

Saeed, I A; Macguidwin, A E; Rouse, D I

1997-04-01

358

Time-cycled inverse ratio ventilation does not improve gas exchange during anaesthesia  

Microsoft Academic Search

Inverse ratio ventilation (IRV) has been reported to improve oxygenation at lower peak airway pressures in patients with respiratory\\u000a failure. Therefore we hypothesised that IRV might also improve oxygen exchange during anaesthesia. Conventional ratio ventilation\\u000a (CRV) and IRV were compared in 24 low-risk surgical patients who were paralysed and whose lungs were ventilated with air\\/02 by a non-rebreathing circuit and

W. A. Tweed; T. L. Lee

1991-01-01

359

Two-phase gas-liquid flow characteristics inside a plate heat exchanger  

SciTech Connect

In the present study, the air-water two-phase flow characteristics including flow pattern and pressure drop inside a plate heat exchanger are experimentally investigated. A plate heat exchanger with single pass under the condition of counter flow is operated for the experiment. Three stainless steel commercial plates with a corrugated sinusoidal shape of unsymmetrical chevron angles of 55 and 10 are utilized for the pressure drop measurement. A transparent plate having the same configuration as the stainless steel plates is cast and used as a cover plate in order to observe the flow pattern inside the plate heat exchanger. The air-water mixture flow which is used as a cold stream is tested in vertical downward and upward flow. The results from the present experiment show that the annular-liquid bridge flow pattern appeared in both upward and downward flows. However, the bubbly flow pattern and the slug flow pattern are only found in upward flow and downward flow, respectively. The variation of the water and air velocity has a significant effect on the two-phase pressure drop. Based on the present data, a two-phase multiplier correlation is proposed for practical application. (author)

Nilpueng, Kitti [Department of Mechanical Engineering, South East Asia University, Bangkok 10160 (Thailand); Wongwises, Somchai [Fluid Mechanics, Thermal Engineering and Multiphase Flow Research Lab (FUTURE), Department of Mechanical Engineering, King Mongkut's University of Technology Thonburi, Bangmod, Bangkok 10140 (Thailand)

2010-11-15

360

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

PubMed

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

Hawkins, Justin L

2014-03-01

361

Splitting of H3–H4 tetramers at transcriptionally active genes undergoing dynamic histone exchange  

PubMed Central

Nucleosome deposition occurs on newly synthesized DNA during DNA replication and on transcriptionally active genes via nucleosome-remodeling complexes recruited by activator proteins and elongating RNA polymerase II. It has been long believed that histone deposition involves stable H3–H4 tetramers, such that newly deposited nucleosomes do not contain H3 and H4 molecules with their associated histone modifications from preexisting nucleosomes. However, biochemical analyses and recent experiments in mammalian cells have raised the idea that preexisting H3–H4 tetramers might split into dimers, resulting in mixed nucleosomes composed of “old” and “new” histones. It is unknown to what extent different genomic loci might utilize such a mechanism and under which circumstances. Here, we address whether tetramer splitting occurs in a locus-specific manner by using sequential chromatin immunoprecipitation of mononucleosomes from yeast cells containing two differentially tagged versions of H3 that are expressed “old” and “new” histones. At many genomic loci, we observe little or no nucleosomal cooccupancy of old and new H3, indicating that tetramer splitting is generally infrequent. However, cooccupancy is detected at highly active genes, which have a high rate of histone exchange. Thus, DNA replication largely results in nucleosomes bearing exclusively old or new H3–H4, thereby precluding the acquisition of new histone modifications based on preexisting modifications within the same nucleosome. In contrast, tetramer splitting, dimer exchange, and nucleosomes with mixed H3–H4 tetramers occur at highly active genes, presumably linked to rapid histone exchange associated with robust transcription. PMID:21220302

Katan-Khaykovich, Yael; Struhl, Kevin

2011-01-01

362

Expression profile of genes regulated by activity of the Na-H exchanger NHE1  

PubMed Central

Background In mammalian cells changes in intracellular pH (pHi), which are predominantly controlled by activity of plasma membrane ion exchangers, regulate a diverse range of normal and pathological cellular processes. How changes in pHi affect distinct cellular processes has primarily been determined by evaluating protein activities and we know little about how pHi regulates gene expression. Results A global profile of genes regulated in mammalian fibroblasts by decreased pHi induced by impaired activity of the plasma membrane Na-H exchanger NHE1 was characterized by using cDNA microarrays. Analysis of selected genes by quantitative RT-PCR, TaqMan, and immunoblot analyses confirmed results obtained from cDNA arrays. Consistent with established roles of pHi and NHE1 activity in cell proliferation and oncogenic transformation, grouping regulated genes into functional categories and biological pathways indicated a predominant number of genes with altered expression were associated with growth factor signaling, oncogenesis, and cell cycle progression. Conclusion A comprehensive analysis of genes selectively regulated by pHi provides insight on candidate targets that might mediate established effects of pHi on a number of normal and pathological cell functions. PMID:15257760

Putney, Luanna K; Barber, Diane L

2004-01-01

363

Note on the CO 2 air-sea gas exchange at high temperatures  

NASA Astrophysics Data System (ADS)

The temperature dependency of ocean-atmosphere gas transfer velocities is commonly estimated in terms of Schmidt numbers, i.e. the ratio of kinematic viscosity to diffusivity. In numerical models least square regressions are used to fit the limited number of experimentally derived Schmidt numbers to a function of temperature. For CO 2 a well established fit can be found in the literature. This fit constitutes an integral part in standardized carbon cycle simulation projects (e.g. C4MIP, OC4MIP, Friedlingstein et al., 2006). However, the fit is valid only in the range where diffusivity measurements exist, i.e., from 0 to about 30 °C. In many climate warming simulations like e.g. the MPI contribution to the fourth Intergovernmental Panel on Climate Change Assessment Report (IPCC AR 4), sea surface temperatures largely exceed the validated range and approach or even reach the range, where the standard fits leave the physically meaningful range. Thus, this paper underlines the demand for new measurements of seawater diffusivities for CO 2 and other trace gases especially for the temperature range >30 °C. In this paper we provide improved fits for the temperature dependence of the Schmidt number. For carbon dioxide our fit is compared to the established fit under identical climate change simulations carried out with the 3D-carbon cycle model HAMOCC. We find that in many tropical and subtropical high temperature regions the established fit leads to unrealistically short adaption times of the surface water pCO 2 to altered atmospheric pCO 2. In regions where the local oceanic pCO 2 is not primarily controlled by the atmospheric boundary pCO 2 but by other processes such as biological activity, the atmosphere ocean pCO 2 gradient is clearly underestimated when using the established fit. The effect on global oceanic carbon uptake in a greenhouse world is rather small and the potential climate feedback introduced by this bias seems to be negligible. However, the bias will clearly gain in significance the more regions warm up to over 30 °C. On a regional scale, especially in coastal regions at low latitudes, the effect is not negligible and a different steady state is approached.

Gröger, Matthias; Mikolajewicz, Uwe

364

Collateral ventilation and gas exchange during airway occlusion in the normal human lung.  

PubMed

The effectiveness of collateral ventilation in maintaining alveolar gas tensions in obstructed lung segments was investigated using fiberoptic bronchoscopy to place an occluding catheter-tip balloon in selected lobar and segmental bronchi in supine normal human subjects. Gas tensions from beyond the occlusion were measured with a respiratory mass spectrometer. Collateral ventilation is known to be minimal between lobes; therefore, values measured in obstructed lobes provide a control. No significant difference was found between the partial pressures of oxygen or carbon dioxide measured in obstructed lobes and in obstructed segments. In both cases respiratory gas tensions approached reported values for mixed venous levels. The time taken to attain a steady state of gas composition in the obstructed lung was rapid (approximately 50 s), and it was no different for lobes and segments. In addition, collateral ventilation was assessed by measuring the amount of helium reaching occluded lobes and segments when subjects breathed a mixture of 21% oxygen and 79% helium. The rate of rise in helium concentration was less than 1%/min in both lobes and segments, a figure that may be explained by delivery of helium in recirculated blood rather than by collateral ventilation. We conclude that intersegmental collateral ventilation has a negligible role in the maintenance of alveolar gas tensions in supine normal humans during tidal breathing. PMID:8442584

Morrell, N W; Roberts, C M; Biggs, T; Seed, W A

1993-03-01

365

High Resolution CH4 Emissions and Dissolved CH4 Measurements Elucidate Surface Gas Exchange Processes in Toolik Lake, Arctic Alaska  

NASA Astrophysics Data System (ADS)

Approximately 14% of the Alaskan North Slope is covered in lakes of various sizes and depths. Diffusive carbon emissions (CH4 and CO2) from these lakes offset the tundra sink by ~20 %, but the offset would substantially increase if ebullitive CH4 emissions were also considered. Ultimately, arctic lake CH4 emissions are not insignificant in the global CH4 budget and their contribution is bound to increase due to impacts from climate change. Here we present high resolution CH4 emission data as measured via eddy covariance and a Los Gatos gas analyzer during the ice free period from Toolik Lake, a deep (20 m) Arctic lake located on the Alaskan North Slope, over the last few summers. Emissions are relatively low (< 25 mg CH4 m-2 d-1) with little variation over the summer. Diurnal variations regularly occur, however, with up to 3 times higher fluxes at night. Gas exchange is a relatively difficult process to estimate, but is normally done so as the product of the CH4 gradient across the air-water interface and the gas transfer velocity, k. Typically, k is determined based on the turbulence on the water side of the interface, which is most commonly approximated by wind speed; however, it has become increasingly apparent that this assumption does not remain valid across all water bodies. Dissolved CH4 profiles in Toolik revealed a subsurface peak in CH4 at the thermocline of up to 3 times as much CH4 as in the surface water. We hypothesize that convective mixing at night due to cooling surface waters brings the subsurface CH4 to the surface and causes the higher night fluxes. In addition to high resolution flux emission estimates, we also acquired high resolution data for dissolved CH4 in surface waters of Toolik Lake during the last two summers using a CH4 equilibrator system connected to a Los Gatos gas analyzer. Thus, having both the flux and the CH4 gradient across the air-water interface measured directly, we can calculate k and investigate the processes influencing CH4 gas exchange in this lake. Preliminary results indicate that there are two regimes in wind speed that impact k - one at low wind speeds up to ~5 m s-1 and another at higher wind speeds (max ~10 m s-1). The differential wind speeds during night and day may compound the effect of convective mixing and cause the diurnal variation in observed fluxes.

Del Sontro, T.; Sollberger, S.; Kling, G. W.; Shaver, G. R.; Eugster, W.

2013-12-01

366

Optical Breath Gas Sensor for Extravehicular Activity Application.  

National Technical Information Service (NTIS)

The function of the infrared gas transducer used during extravehicular activity in the current space suit is to measure and report the concentration of carbon dioxide (CO2) in the ventilation loop. The next generation portable life support system (PLSS) r...

A. B. Vakhtin, C. Chullen, E. A. Falconi, J. S. Pilgrim, M. E. Casias, S. McMillin, W. R. Wood

2013-01-01

367

Regeneration of spent powdered activated carbon saturated with inorganic ions by cavitation united with ion exchange method.  

PubMed

Using ion exchange resin as transfer media, regenerate powdered activated carbon (PAC) adsorbed inorganic ions by cavitation to enhance the transfer; we studied how the regeneration time and the mass ratio of resin and PAC influence the regeneration rate respectively through re-adsorption. The result showed that the effective regeneration of PAC saturated with inorganic ions was above 90% using ion exchange resin as media and transfer carrier, the quantity of PAC did not reduced but activated in the process. PMID:25084579

Li, Gang; Gao, Hong; Li, Yansheng; Yang, Huixin

2011-06-01

368

Toward the Active Control of Heat Transfer in the Hot Gas Path of Gas Turbines  

NASA Technical Reports Server (NTRS)

The work at NASA this summer has focused on assisting the Professor's project, namely "Toward the Active Control of Heat Transfer in the Hot Gas Path of Gas Turbines." The mode of controlling the Heat Transfer that the project focuses on is film cooling. Film cooling is used in high temperature regions of a gas turbine and extends the life of the components exposed to these extreme temperatures. A "cool" jet of air is injected along the surface of the blade and this layer of cool air shields the blade from the high temperatures. Cool is a relative term. The hot gas path temperatures reach on the order of 1500 to 2000 K. The "coo" air is on the order of 700 to 1000 K. This cooler air is bled off of an appropriate compressor stage. The next parameter of interest is the jet s position and orientation in the flow-field.

Oertling, Jeremiah E.

2003-01-01

369

Local Area Water Removal Analysis of a Proton Exchange Membrane Fuel Cell under Gas Purge Conditions  

PubMed Central

In this study, local area water content distribution under various gas purging conditions are experimentally analyzed for the first time. The local high frequency resistance (HFR) is measured using novel micro sensors. The results reveal that the liquid water removal rate in a membrane electrode assembly (MEA) is non-uniform. In the under-the-channel area, the removal of liquid water is governed by both convective and diffusive flux of the through-plane drying. Thus, almost all of the liquid water is removed within 30 s of purging with gas. However, liquid water that is stored in the under-the-rib area is not easy to remove during 1 min of gas purging. Therefore, the re-hydration of the membrane by internal diffusive flux is faster than that in the under-the-channel area. Consequently, local fuel starvation and membrane degradation can degrade the performance of a fuel cell that is started from cold. PMID:22368495

Lee, Chi-Yuan; Lee, Yu-Ming; Lee, Shuo-Jen

2012-01-01

370

Single Channel Testing for Characterization of the Direct Gas Cooled Reactor and the SAFE-100 Heat Exchanger  

NASA Astrophysics Data System (ADS)

Experiments have been designed to characterize the coolant gas flow in two space reactor concepts that are currently under investigation by NASA Marshall Space Flight Center and Los Alamos National Laboratory: the direct-drive gas-cooled reactor (DDG) and the SAFE-100 heatpipe-cooled reactor (HPR). For the DDG concept, initial tests have been completed to measure pressure drop versus flow rate for a prototypic core flow channel, with gas exiting to atmospheric pressure conditions. The experimental results of the completed DDG tests presented in this paper validate the predicted results to within a reasonable margin of error. These tests have resulted in a re-design of the flow annulus to reduce the pressure drop. Subsequent tests will be conducted with the re-designed flow channel and with the outlet pressure held at 150 psi (1 MPa). Design of a similar test for a nominal flow channel in the HPR heat exchanger (HPR-HX) has been completed and hardware is currently being assembled for testing this channel at 150 psi. When completed, these test programs will provide the data necessary to validate calculated flow performance for these reactor concepts (pressure drop and film temperature rise).

Bragg-Sitton, S. M.; Kapernick, R.; Godfroy, T. J.

2004-02-01

371

Active heat exchange system development for latent heat thermal energy storage  

NASA Astrophysics Data System (ADS)

Alternative mechanizations of active heat exchange concepts were analyzed for use with heat of fusion Phase Change Materials (PCM's) in the temperature range of 250 C to 350 C for solar and conventional power plant applications. Over 24 heat exchange concepts were reviewed, and eight were selected for detailed assessment. Two candidates were chosen for small-scale experimentation: a coated tube and shell that exchanger, and a direct contact reflux boiler. A dilute eutectic mixture of sodium nitrate and sodium hydroxide was selected as the PCM from over fifty inorganic salt mixtures investigated. Preliminary experiments with various tube coatings indicated that a nickel or chrome plating of Teflon or Ryton coating had promise of being successful. An electroless nickel plating was selected for further testing. A series of tests with nickel-plated heat transfer tubes showed that the solidifying sodium nitrate adhered to the tubes and the experiment failed to meet the required discharge heat transfer rate of 10 kW(t). Testing of the reflux boiler is under way.

Lefrois, R. T.

1980-03-01

372

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 the processes that control the distribution of ?13C in the contemporary and preindustrial ocean. Biological fractionation dominates the distribution of ?13CDIC of dissolved inorganic carbon (DIC) due to the sinking of isotopically light ?13C organic matter from the surface into the interior ocean. This process leads to low ?13CDIC values at dephs 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 provides an important secondary influence due to 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, air-sea gas exchange is slow, so biological effect dominate spatial ?13CDIC gradients both in the interior and at the surface, in constrast to conclusions from some previous studies. Analysis of a new synthesis of ?13CDIC measurements from years 1990 to 2005 is used to quantify preformed (?13Cpre) and remineralized (?13Crem) contributions as well as the effects of biology (??13Cbio) and air-sea gas exchange (?13C*). The model reproduces major features of the observed large-scale distribution of ?13CDIC, ?13Cpre, ?13Crem, ?13C*, and ??13Cbio. 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.

2013-05-01

373

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

PubMed

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

Bobkov, Y; Corey, E; Ache, B

2014-07-25

374

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

E-print Network

.1152/physrev.00050.2003.--The fish gill is a multipurpose organ that, in addition to providing for aquatic gas of aquatic respiration. Aerial- breathing species may use the gill, swim bladder, or other accessory, University of Florida, Gainesville, Florida; Department of Cellular and Molecular Physiology, Yale University

Evans, David H.

375

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

Microsoft Academic Search

The removal of methyl iodide by absorption onto silver mordenite was studied using a simulated off-gas from the fuel dissolution step of a nuclear fuel reprocessing plant. The methyl iodide absorption of silver mordenite was examined for the effects of NO\\/sub x\\/, humidity, iodine concentration, filter temperature, and filter pretreatment. The highest iodine loading achieved in these tests has been

Jubin

1980-01-01

376

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

Microsoft Academic Search

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

Jubin

1981-01-01

377

Radiative heat exchange in the combustion chamber of an MHD electric power plant using methane gas  

Microsoft Academic Search

A method is proposed for calculating radiative thermal fluxes on the wall of the combustion chamber of an MHD electric power plant operating with methane gas. The calculations are performed on the basis of spectral characteristics of the molecular components of the combustion products and ionizing potassium impurity, with allowance for multiple reflection of radiation from the wall of the

L. M. Biberman; M. B. Zhelezniak; A. Kh. Mnatsakanian; A. G. Rotinov; S. A. Tager

1980-01-01

378

Recovery of Water from Boiler Flue Gas Using Condensing Heat Exchangers  

Microsoft Academic Search

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

Edward Levy; Harun Bilirgen; John DuPoint

2011-01-01

379

Determination of activated sludge biological activity using model corrected CO2 off-gas data.  

PubMed

Carbon dioxide (CO(2)) online off-gas monitoring is useful to detect changes in biological activity for activated sludge systems especially under limited oxygen conditions like under simultaneous nitrification-denitrification (SND) where respirometric measurements are not applicable. So far, the influence of the bicarbonate system on the liquid-gas transfer of CO(2) prevented the wider use of off-gas CO(2) for monitoring purposes in wastewater treatment. The objective of the paper is to demonstrate a practical method to correct measured off-gas CO(2) as an indicator of biological activity by taking into account pH shifts (resulting in CO(2) release or retention) and changes in influent alkalinity. The simple model is based on the physicochemical system of the bicarbonate/CO(2) equilibrium and the liquid-gas mass transfer for aerated systems. Standard on-line measurements (pH, temperature, flow rates) and periodical alkalinity titration serve as input data to estimate the influence of the carbonate system on the CO(2) off-gas concentrations measured on-line. For a particular plant the CO(2) mass transfer coefficients are derived from measurements compared to the theoretical calculation from oxygen mass transfer. The model estimates the biological carbon dioxide production rate (CPR; heterotrophic activity) by the correction of the measured carbon dioxide transfer rate (CTR; C-flux by the off-gas) with the calculated inorganic carbon dioxide transfer rate (r(F)) considering bicarbonate consumption (autotrophic activity). PMID:17292940

Weissenbacher, Norbert; Lenz, Katharina; Mahnik, Susanne N; Wett, Bernhard; Fuerhacker, Maria

2007-04-01

380

[The effects of the pause at the end of inspiration on gas exchange and hemodynamics during artificial ventilation].  

PubMed

We have studied the effects of an inspiratory pause (PI) during artificial ventilation in 13 patients in acute respiratory insufficiency. The effects on gas exchange, haemodynamics and distribution of ventilation were observed. During the period of study the total volume, the inspiration/expiration ratio and the inspired oxygen concentration were all maintained constant. With the inspiratory pause arterial oxygenation has not changed significantly, whereas it did change favourably with PEEP. The physiological dead space (VD/VT) was reduced in proportion to the duration of the inspiratory pause. These results suggest that the inspiratory pause triggers regional modification of the ventilation/perfusion ratio, favouring a reduction of the VD/VT ratio. However, this improvement of the VD/VT ratio does not seem to influence the oxygenation or the total distribution of ventilation in this type of patient. PMID:332285

Suter, P M; Jevic, M G; Hemmer, M; Gemperle, M

1977-09-01

381

Developmental Changes in Photosynthetic Gas Exchange in the Polyol-Synthesizing Species, Apium graveolens L. (Celery) 1  

PubMed Central

Developmental changes in photosynthetic gas exchange were investigated in the mannitol synthesizing plant celery (Apium graveolens L. `Giant Pascal'). Greenhouse-grown plants had unusually high photosynthetic rates for a C3 plant, but consistent with field productivity data reported elsewhere for this plant. In most respects, celery exhibited typical C3 photosynthetic characteristics; light saturation occurred at 600 micromoles photons per square meter per second, with a broad temperature optimum, peaking at 26°C. At 2% O2, photosynthesis was enhanced 15 to 25% compared to rates at 21% O2. However, celery had low CO2 compensation points, averaging 7 to 20 microliters per liter throughout the canopy. Conventional mechanisms for concentrating CO2 were not detectable. PMID:16665012

Fox, Theodore C.; Kennedy, Robert A.; Loescher, Wayne H.

1986-01-01

382

Effect of drought stress on gas exchange in channel millet (Echinochloa turneriana) and pearl millet (Pennisetum americanum)  

SciTech Connect

Gas exchange measurements were made on well-watered and droughted plants of the drought resistant pearl millet and of channel millet, a potential new crop for semi-arid regions. Photosynthesis and water use efficiency were similar for controls of both species at atmospheric CO{sub 2} levels and were reduced similarly by drought in both species. The CO{sub 2} saturated rate and the carboxylation efficiency were lowered by drought in both species, while stomatal limitation was increased by drought. Autoradiograms indicated that photosynthesis occurs evenly over the surface of well-watered control leaves of both species, but not in leaves of droughted plants. This could result in an overestimate of the effect of nonstomatal inhibition of photosynthesis by drought.

Conover, D.G.; Sovonick-Dunford, S. (Univ. of Cincinnati, OH (USA))

1990-05-01

383

Equilibrium distribution of gas molecules adsorbed on an active surface  

SciTech Connect

We evaluate the exact equilibrium distribution of gas molecules adsorbed on an active surface with an infinite number of attachment sites. Our result is a Poisson distribution having mean X={mu}PP{sub s}/P{sub e}, with {mu} the mean gas density, P{sub s} the sticking probability, P{sub e} the evaporation probability in a time interval {tau}, and P Smoluchowski's exit probability in time interval {tau} for the surface in question. We then solve for the case of a finite number of attachment sites using the mean field approximation, recovering the Langmuir isotherm in this case. (c) 2000 The American Physical Society.

Adler, Stephen L. [Institute for Advanced Study, Princeton, New Jersey 08540 (United States)] [Institute for Advanced Study, Princeton, New Jersey 08540 (United States); Mitra, Indrajit [Department of Physics, Jadwin Hall, Princeton, New Jersey 08544 (United States)] [Department of Physics, Jadwin Hall, Princeton, New Jersey 08544 (United States)

2000-09-01

384

Parameterization of a coupled CO2 and H2O gas exchange model at the leaf scale of Populus euphratica  

NASA Astrophysics Data System (ADS)

The following two models were combined to simultaneously predict CO2 and H2O gas exchange at the leaf scale of Populus euphratica: a Farquhar et al. type biochemical sub-model of photosynthesis (Farquhar et al., 1980) and a Ball et al. type stomatal conductance sub-model (Ball et al., 1987). The photosynthesis parameters [including maximum carboxylation rate allowed by ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) carboxylation rate (Vcmax), potential light-saturated electron transport rate (Jmax), triose phosphate utilization (TPU) and day respiration (Rd)] were determined by using the genetic algorithm (GA) method based on A/Ci data. Values of Vcmax and Jmax standardized at 25 °C were 75.09±1.36 (mean ± standard error), 117.27±2.47, respectively. The stomatal conductance sub-model was calibrated independently. Prediction of net photosynthesis by the coupled model agreed well with the validation data, but the model tended to underestimate transpiration rates. Overall, the combined model generally captured the diurnal patterns of CO2 and H2O exchange resulting from variation in temperature and irradiation.

Zhu, G. F.; Li, X.; Su, Y. H.; Huang, C. L.

2010-03-01

385

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

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

386

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

PubMed

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

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

2010-01-01

387

Metastability exchange optical pumping of 3He gas up to hundreds of millibars at 4.7 Tesla  

NASA Astrophysics Data System (ADS)

Metastability exchange optical pumping (MEOP) is experimentally investigated in 3He at 4.7 T, at room temperature and for gas pressures ranging from 1 to 267 mbar. The 23S-23P transition at 1083 nm is used for optical pumping and for detection of the laser-induced orientation of 3He atoms in the rf discharge plasma. The collisional broadening rate is measured (12.0 ± 0.4 MHz mbar-1 FHWM) and taken into account for accurate absorption-based measurements of both nuclear polarization in the ground state and atom number density in the metastable 23S state. The results lay the ground for a comprehensive assessment of the efficiency of MEOP, by comparison with achievements at lower field (1 mT-2 T) over an extended range of operating conditions. Stronger hyperfine decoupling in the optically pumped 23S state is observed to systematically lead to slower build-up of 3He orientation in the ground state, as expected. The nuclear polarizations obtained at 4.7 T still decrease at high pressure but in a less dramatic way than observed at 2 T in the same sealed glass cells. To date, thanks to the linear increase in gas density, they correspond to the highest nuclear magnetizations achieved by MEOP in pure 3He gas. The improved efficiency puts less demanding requirements for compression stages in polarized gas production systems and makes high-field MEOP particularly attractive for magnetic resonance imaging of the lungs, for instance.

Nikiel-Osuchowska, Anna; Collier, Guilhem; G?owacz, Bartosz; Pa?asz, Tadeusz; Olejniczak, Zbigniew; W?glarz, W?adys?aw P.; Tastevin, Geneviève; Nacher, Pierre-Jean; Dohnalik, Tomasz

2013-09-01

388

Viking gas exchange reaction - Simulation on UV-irradiated manganese dioxide substrate  

NASA Technical Reports Server (NTRS)

The exchange of O2 for H2O, analogous to that recorded on Mars by the Viking GEX experiment, has been observed on humidifying powdered beta-MnO2 (pyrolusite) which had been irradiated by UV in a humidified analog of the Martian atmosphere. Pyrolusite irradiated in a dry atmosphere did not release O2 on humidification. The XPS spectra of Mn and O of the reactive pyrolusite were shifted toward higher binding energies during UV irradiation. These shifts are consistent with the creation of a surface layer of a Mn(V) or Mn(VI) compound. The destruction of such a layer on humidification could account for the observed O2 release. Although manganese has not been identified in the Martian regolith, the upper limit of the Mn concentration is sufficiently high that O2 release from pyrolusite could have been responsible for the results of the Viking GEX experiment.

Blackburn, T. R.; Holland, H. D.; Ceasar, G. P.

1979-01-01

389

Food production and gas exchange system using blue-green alga (Spirulina) for CELSS  

NASA Astrophysics Data System (ADS)

In order to reduce the cultivation area required for the growth of higher plants in space adoption of algae, which have a higher photosynthetic ability, seems very suitable for obtaining oxygen and food as a useful source of high quality protein. The preliminary cultivation experiment for determining optimum cultivation conditions and for obtaining the critical design parameters of the cultivator itself has been conducted. Spirulina was cultivated in the 6-liter medium containing a sodium hydrogen carbonate solution and a cultivation temperature controlled using a thermostat. Generated oxygen gas was separated using a polypropyrene porous hollow fiber membrane module. Through this experiment, oxygen gas (at a concentration of more than 46%) at a rate of 100 ~ 150 ml per minute could be obtained.

Oguchi, Mitsuo; Otsubo, Koji; Nitta, Keiji; Hatayama, Shigeki

390

The effects of breaking waves on dual-tracer gas exchange experiments  

SciTech Connect

Quantification of air-sea gas fluxes is important in understanding the global ocean carbon cycle, determining the effect of biologically produced gases on remote marine tropospheric aerosol production, and measuring the atmospheric lifetimes of trace gases. Direct measurement of the flux, F, of a sparingly soluble gas through the air-sea interface is extremely difficult in general, and F is often calculated as F = k{sub L}{delta}C where k{sub L} is the transfer velocity of the gas and AC is its air-sea concentration difference. In the absence of bubbles, k{sub L} is a function of the near-surface aqueous-phase turbulence and the molecular diffusivity of the gas. Although direct measurement of {delta}C is relatively simple, oceanic measurements of k{sub L} are problematical. Because of this, k{sub L} is usually estimated from empirical parameterizations for k{sub L} in terms of wind speed, U. The linear relation between F and k{sub L} at a constant {delta}C implies that the accuracy of the parameterization of k{sub L} in terms of U is critical in calculating F. This is especially true when U is large, since experiments in wind tunnels, lakes, and the ocean suggest that k{sub L} increases quadratically with U (Wanninkhof, 1992). With the exact functional form of the relation between U and k{sub L} not definitively known at present, estimation of k{sub L} at high U could be inaccurate. This problem could be resolved with further oceanic measurements of k{sub L} at high U. However, increases in U are also associated with increases in the frequency of wave breaking. Whitecaps are known to generate bubble plumes, and these bubbles could have a significant effect on the measurement of k{sub L}.

Asher, W. [Pacific Northwest Lab., Sequim, WA (United States); Wanninkhof, R. [National Oceanic and Atomospheric Administration/Atlantic Oceanographic and Meterological Lab., Miami, FL (United States)

1995-07-01

391

Temperature-Dependent Halogen-Exchange Activity Studies of Zeolite-Derived Aluminum Trifluoride  

SciTech Connect

A high-surface-area (190 m{sup 2}/g) amorphous aluminum trifluoride material ('plasma-AlF{sub 3}') was synthesized by plasma decomposition of zeolite, and its structural and reactivity properties were investigated. High-resolution transmission electron microscopy of plasma-AlF{sub 3} indicates morphological features on the nanometer-scale, whereas temperature-programmed X-ray diffraction is used to determine the phase-transition temperatures of plasma-AlF{sub 3} to {beta}- and {alpha}-AlF{sub 3}. Halogen-exchange reactivity is studied by temperature-programmed reaction (TPR) techniques using the dismutation of CCl{sub 2}F{sub 2} as a model reaction. Plasma-AlF{sub 3} is found to possess an unexpected low-temperature (>315 C) activity not observed with the well-known halogen-exchange catalyst {beta}-AlF{sub 3}. Supporting TPR studies on aluminum trifluoride hydrates are performed to correlate this new activity with an amorphous AlF{sub 3} structure, and a simple Lewis acid model is presented to explain the reactivity data.

Hajime,E.; Delattre, J.; Stacy, A.

2007-01-01

392

Activation of microglia depends on Na+/H+ exchange-mediated H+ homeostasis  

PubMed Central

H+ extrusion is important for sustained NADPH oxidase activation following “respiratory” burst in macrophage/microglia activation. In this study, we investigated the role of Na+/H+ exchanger isoform 1 (NHE-1) in activation of microglia following lipopolysaccharide (LPS) or oxygen and glucose deprivation (OGD/REOX) exposure. NHE-1 functioned in maintaining basal pHi of immortalized M4T.4 microglia or mouse primary microglia. Pharmacological inhibition of NHE-1 activity with the potent inhibitor cariporide (HOE 642) abolished pHi regulation in microglia under basal conditions. Activation of microglia either by LPS, phorbol myristate acetate (PMA), or OGD/REOX accelerated pHi regulation and caused pHi elevation, which was accompanied with an increase in [Na+]i and [Ca2+]i as well as production of superoxide anion and cytokines. Interestingly, inhibition of NHE-1 not only abolished pHi regulation but also reduced production of superoxide anion as well as expression of cytokines and inducible nitric oxide synthase. Taken together, these results reveal that there was a concurrent activation of NHE-1 in microglia in response to proinflammatory stimuli. The study suggests that NHE-1 functions to maintain microglial pHi homeostasis allowing for sustained NADPH oxidase function and “respiratory” burst. PMID:21068326

Liu, Yan; Kintner, Douglas B.; Chanana, Vishal; Algharabli, Jehad; Chen, Xinzhi; Gao, Yanqin; Chen, Jun; Ferrazzano, Peter; Olson, Julie K.; Sun, Dandan

2010-01-01

393

Mathematical modeling of the "plant community -soil-like substrate -gas exchange with the human" closed ecosystem  

NASA Astrophysics Data System (ADS)

A mathematical model of the "plant community -soil-like substrate -gas exchange with the human" experimental biological life support system (BLSS) has been constructed to predict its functioning and estimate feasibility of controlling it. The mathematical model consists of three compartments -two `phytotron' models (with wheat and radish) and the `mycotron' model (for mushrooms). The following components are included in the model: edible mushrooms (mushroom fruit bodies and mycelium); wheat; radish; straw (processed by mycelium); dead organic matter in the phytotron (separately for the wheat unit and for the radish unit); worms; worms' coprolites; vermicompost used as a soil-like substrate (SLS); bacterial microflora; min-eral nitrogen, phosphorus and iron; products of the system intended for humans (wheat grains, radish roots and mushroom fruit bodies); oxygen and carbon dioxide. Under continuous gas exchange, the mass exchange between the compartments occurs at the harvesting time. The conveyor character of the closed ecosystem functioning has been taken into account -the num-ber of culture age groups can be regulated (in experiments -4 and 8 age groups). The conveyor cycle duration can be regulated as well. The module is designed for the food and gas exchange requirements of 1/30 of a virtually present human. Aim of model analysis is determination of investigation direction in real experimental BLSS. The model allows doing dynamic calcu-lations of closure coefficient based on the main elements taken into account in the model and evaluating all dynamic components of the system under different conditions and modes of its operation, especially under the conditions that can hardly be created experimentally. One of the sustainability conditions can be long-duration functioning of the system under the light-ing that is far from the optimum. The mathematical model of the system can demonstrate variants of its sustainable functioning or ruin under various critical conditions probable for the LSS. An example is loss of part of green plant biomass. Model calculations have been done for different variants of loss of wheat biomass. We estimated the ability of the model to predict the optimal number of age groups in the LSS plant conveyor. This is an essential parameter, because if the number is too low, the total mass of the system components will vary and if it is too high, the system will be too complicated and costly. A high value of this parameter can also be interpreted as approximation to biosphere models. Dynamics of closure coefficient for the nitrogen and carbon loops was investigated for different variants of the BLSS. The system with biological utilization of the wheat straw has the highest closure coefficient, reaching 0.96, and can be used as a prototype of the BLSS of a new generation, with an essentially closed material cycling.

Barkhatov, Yuri; Gubanov, Vladimir; Tikhomirov, Alexander A.; Degermendzhy, Andrey G.

394

Active Combustion Control for Aircraft Gas Turbine Engines  

NASA Technical Reports Server (NTRS)

Lean-burning combustors are susceptible to combustion instabilities. Additionally, due to non-uniformities in the fuel-air mixing and in the combustion process, there typically exist hot areas in the combustor exit plane. These hot areas limit the operating temperature at the turbine inlet and thus constrain performance and efficiency. Finally, it is necessary to optimize the fuel-air ratio and flame temperature throughout the combustor to minimize the production of pollutants. In recent years, there has been considerable activity addressing Active Combustion Control. NASA Glenn Research Center's Active Combustion Control Technology effort aims to demonstrate active control in a realistic environment relevant to aircraft engines. Analysis and experiments are tied to aircraft gas turbine combustors. Considerable progress has been shown in demonstrating technologies for Combustion Instability Control, Pattern Factor Control, and Emissions Minimizing Control. Future plans are to advance the maturity of active combustion control technology to eventual demonstration in an engine environment.

DeLaat, John C.; Breisacher, Kevin J.; Saus, Joseph R.; Paxson, Daniel E.

2000-01-01

395

Study of the structure of the air and blood capillaries of the gas exchange tissue of the avian lung by serial section three-dimensional reconstruction.  

PubMed

We have previously reconstructed the gas exchange tissue of the adult muscovy duck, Cairina moschata using a method of manually aligning sections and tracing the contours of the components of the gas exchange tissue. This reconstruction method demonstrated that the air capillaries are comprised of an expanded globular part interconnected by narrow air channels. The blood capillaries completely surround the air capillaries forming an anastomosing meshwork of short segments. However, the resulting reconstruction was limited in scope because of the laborious process of tracing the profiles of each component through the sequence of micrographs. We have now reconstructed a larger proportion of the exchange tissue by using a cross-correlation based alignment strategy and have demonstrated that the staining intensity of each of the exchange tissue components is sufficiently different to allow them to be identified by simple filtering and thresholding. The resulting reconstructions sample a much larger proportion of the exchange tissue and demonstrate the heterogeneity of structures from different locations in the parabronchus. We have shown that a sheet-flow-type arrangement of blood capillaries surrounds the infundibulum; this represents an unexpected functional convergence with the arrangement of blood capillaries surrounding the mammalian alveoli. It is feasible, using this reconstruction strategy, to analyse the exchange tissue of a large number of avian species in order to determine structural correlates of function. The resulting reconstructions could be analysed in order to determine the basis of the functional efficiency and rigidity of the avian lung. PMID:18387043

Woodward, J D; Maina, J N

2008-04-01

396

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

Microsoft Academic Search

The respiratory physiology, heart rates and metabolic rates of two captive juvenile male harbour porpoises (both 28?kg) were\\u000a measured using a rapid-response respiratory gas analysis system in the laboratory. Breath-hold durations in the laboratory\\u000a (12?±?0.3?s, mean?±?SEM) were shorter than field observations, although a few breath-holds of over 40?s were recorded. The\\u000a mean percentage time spent submerged was 89?±?0.4%. Relative to

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

2000-01-01

397

An in vitro study of gas exchanges in cultures of Phymatotrichum omnivorum (Shear) Duggar  

E-print Network

tored period1cally to determine the CO2, 02, N2 and ethylene concentrations. Observations were made to determine whether the fungus produced strands and sclerotia and the gas concentrations in the flasks dur1ng the process. Air samples taken from... stages of the experiment was so high that it inh1bited the growth of the fungus by not allowing the formation of matuz'e strands and scle:. 'otia? Nitrogen levels ell slo;;ly during the couz se of the experiment. The decrease in nitrogen is probably...

Hill, Thomas Fielding

2012-06-07

398

Respiration and gas exchange during recovery from exercise in the American alligator.  

PubMed

Low respiratory exchange ratios (R) occur in reptiles. In crocodilians they have been attributed to the loss of respiratory CO2 into the urine and to the immediate exercise-history of an animal. In this study, expired ventilation (V(E)), oxygen consumption (V(O2)), and carbon dioxide excretion (V(CO2)) were measured during recovery from treadmill-exercise in the American alligator. Both V(O2) and V(CO2) decreased exponentially during recovery, but the decrease of V(CO2) was greater than that of V(O2). By 55 min into recovery R fell to 0.3 +/- 0.02 (mean +/- S.E.M). These low values of R may be partially attributable to hyperventilation that occurred during exercise. These data suggest that both hyperventilation during exercise and a metabolic acidosis deplete blood bicarbonate stores, contributing to a low R during recovery. We propose that the right to left cardiac shunt could facilitate restoration of these alkaline reserves and blood pH. PMID:10786647

Farmer, C G; Carrier, D R

2000-03-01

399

Uncertainties in Air Exchange using Continuous-Injection, Long-Term Sampling Tracer-Gas Methods  

SciTech Connect

The PerFluorocarbon Tracer (PFT) method is a low-cost approach commonly used for measuring air exchange in buildings using tracer gases. It is a specific application of the more general Continuous-Injection, Long-Term Sampling (CILTS) method. The technique is widely used but there has been little work on understanding the uncertainties (both precision and bias) associated with its use, particularly given that it is typically deployed by untrained or lightly trained people to minimize experimental costs. In this article we will conduct a first-principles error analysis to estimate the uncertainties and then compare that analysis to CILTS measurements that were over-sampled, through the use of multiple tracers and emitter and sampler distribution patterns, in three houses. We find that the CILTS method can have an overall uncertainty of 10-15percent in ideal circumstances, but that even in highly controlled field experiments done by trained experimenters expected uncertainties are about 20percent. In addition, there are many field conditions (such as open windows) where CILTS is not likely to provide any quantitative data. Even avoiding the worst situations of assumption violations CILTS should be considered as having a something like a ?factor of two? uncertainty for the broad field trials that it is typically used in. We provide guidance on how to deploy CILTS and design the experiment to minimize uncertainties.

Sherman, Max H.; Walker, Iain S.; Lunden, Melissa M.

2013-12-01

400

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

SciTech Connect

The removal of methyl iodide by absorption onto silver mordenite was studied using a simulated off-gas from the fuel dissolution step of a nuclear fuel reprocessing plant. The methyl iodide absorption of silver mordenite was examined for the effects of NO/sub x/, humidity, iodine concentration, filter temperature, and filter pretreatment. The highest iodine loading achieved in these tests has been 34 mg CH/sub 3/I per g of substrate, approximately five times less than the elemental iodine loadings. Results indicate that a filter operating at a temperature of 150/sup 0/C obtained higher iodine loadings than a similar filter operating at 100/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. A study of the regeneration characteristics of silver mordenite indicates limited adsorbent capacity after complete removal of the iodine with 4% hydrogen in the regeneration gas stream at 500/sup 0/C. 9 figures.

Jubin, R.T.

1980-01-01

401

Closed and continuous algae cultivation system for food production and gas exchange in CELSS  

NASA Astrophysics Data System (ADS)

In CELSS (Controlled Ecological Life Support System), utilization of photosynthetic algae is an effective means for obtaining food and oxygen at the same time. We have chosen Spirulina, a blue-green alga, and have studied possibilities of algae utilization. We have developed an advanced algae cultivation system, which is able to produce algae continuously in a closed condition. Major features of the new system are as follows. o (1)In order to maintain homogeneous culture conditions, the cultivator was designed so as to cause a swirl on medium circulation. (2)Oxygen gas separation and carbon dioxide supply are conducted by a newly designed membrane module. (3)Algae mass and medium are separated by a specially designed harvester. (4)Cultivation conditions, such as pH, temperature, algae growth rate, light intensity and quanlity of generated oxygen gas are controlled by a computer system and the data are automatically recorded. This equipment is a primary model for ground experiments in order to obtain some design data for space use. A feasibility of algae cultivation in a closed condition is discussed on the basis of data obtained by use of this new system.

Oguchi, Mitsuo; Otsubo, Koji; Nitta, Keiji; Shimada, Atsuhiro; Fujii, Shigeo; Koyano, Takashi; Miki, Keizaburo

402

Response of Sugarcane to Calcium Silicate on Yield, Gas Exchange Characteristics, Leaf Nutrient Concentrations, and Soil Properties in Two Different Soils  

Microsoft Academic Search

Silicon (Si), applied as calcium silicate (Ca-silicate), was evaluated for effects on yield; yield-contributing parameters in sugarcane, such as chlorophyll content, gas exchange characteristics, moisture content, and leaf nutrient concentrations; and soil fertility in the greenhouse in two different soil types. Seven levels of Si (0 20, 40, 60, 80, 120, and 150 g pot) were tested by applying them

S. M. Bokhtiar; Hai-Rong Huang; Yang-Rui Li

2012-01-01

403

Reconstruction of atmospheric CO 2 during the early middle Eocene by application of a gas exchange model to fossil plants from the Messel Formation, Germany  

Microsoft Academic Search

In this study, atmospheric CO2 during the early middle Eocene (~ 47Ma) is reconstructed using fossil plants from the Messel Formation close to Darmstadt, Germany. CO2 concentration is calculated using a mechanistic model of gas exchange which optimizes CO2 uptake by photosynthesis against water vapor loss by transpiration, a strategy that is commonly realized in land plants. Input data for

M. Grein; W. Konrad; V. Wilde; T. Utescher; A. Roth-Nebelsick

2011-01-01

404