High-frequency pressure variations in the vicinity of a surface CO2 flux chamber

2003 ◽  
Vol 114 (3-4) ◽  
pp. 245-250 ◽  
Author(s):  
E Takle
Keyword(s):  
High Frequency ◽  
Co2 Flux ◽  
Flux Chamber

scholarly journals Automatic high-frequency measurements of full soil greenhouse gas fluxes in a tropical forest

2018 ◽  
Author(s):  
Elodie Alice Courtois ◽  
Clément Stahl ◽  
Benoit Burban ◽  
Joke Van den Berge ◽  
Daniel Berveiller ◽  
...  
Keyword(s):  
High Frequency ◽  
Co2 Flux ◽  
Appropriate Technology ◽  
Flux Chamber ◽  
Soil Co2 Flux ◽  
Reliable Estimation ◽  
Closure Time ◽  
N2o Fluxes ◽  
Ch4 And N2o ◽  
Carbon Dioxide Co2

Abstract. Measuring in situ soil fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) continuously at high frequency requires appropriate technology. We tested the combination of a commercial automated soil CO2 flux chamber system (LI-8100A) with a CH4 and N2O analyzer (Picarro G2308) in a tropical rainforest for 4 months. A chamber closure time of 2 minutes was sufficient for a reliable estimation of CO2 and CH4 fluxes (100 % and 98.5 % of fluxes were above Minimum Detectable Flux – MDF, respectively). This closure time was generally not suitable for a reliable estimation of the low N2O fluxes in this ecosystem but was sufficient for detecting rare major peak events. A closure time of 25 minutes was more appropriate for reliable estimation of most N2O fluxes (85.6 % of measured fluxes are above MDF ± 0.002 nmol m−2 s−1). Our study highlights the importance of adjusted closure time for each gas.

scholarly journals Automatic high-frequency measurements of full soil greenhouse gas fluxes in a tropical forest

2019 ◽  
Vol 16 (3) ◽  
pp. 785-796 ◽  
Author(s):  
Elodie Alice Courtois ◽  
Clément Stahl ◽  
Benoit Burban ◽  
Joke Van den Berge ◽  
Daniel Berveiller ◽  
...  
Keyword(s):  
High Frequency ◽  
Co2 Flux ◽  
Appropriate Technology ◽  
Flux Chamber ◽  
Soil Co2 Flux ◽  
Reliable Estimation ◽  
Closure Time ◽  
N2o Fluxes ◽  
Ch4 And N2o ◽  
Carbon Dioxide Co2

Abstract. Measuring in situ soil fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) continuously at high frequency requires appropriate technology. We tested the combination of a commercial automated soil CO2 flux chamber system (LI-8100A) with a CH4 and N2O analyzer (Picarro G2308) in a tropical rainforest for 4 months. A chamber closure time of 2 min was sufficient for a reliable estimation of CO2 and CH4 fluxes (100 % and 98.5 % of fluxes were above minimum detectable flux – MDF, respectively). This closure time was generally not suitable for a reliable estimation of the low N2O fluxes in this ecosystem but was sufficient for detecting rare major peak events. A closure time of 25 min was more appropriate for reliable estimation of most N2O fluxes (85.6 % of measured fluxes are above MDF ± 0.002 nmol m−2 s−1). Our study highlights the importance of adjusted closure time for each gas.

scholarly journals The current state of CO2 flux chamber studies in the Arctic tundra

2017 ◽  
Vol 42 (2) ◽  
pp. 162-184 ◽  
Author(s):  
Anna-Maria Virkkala ◽  
Tarmo Virtanen ◽  
Aleksi Lehtonen ◽  
Janne Rinne ◽  
Miska Luoto
Keyword(s):  
Carbon Balance ◽  
Ecosystem Respiration ◽  
Vegetation Type ◽  
Gross Primary Production ◽  
Co2 Flux ◽  
Arctic Tundra ◽  
The Arctic ◽  
Environmental Drivers ◽  
Soil Conditions ◽  
Flux Chamber

The Arctic tundra plays an important role in the carbon cycle as it stores 50% of global soil organic carbon reservoirs. The processes (fluxes) regulating these stocks are predicted to change due to direct and indirect effects of climate change. Understanding the current and future carbon balance calls for a summary of the level of knowledge regarding chamber-derived carbon dioxide (CO2) flux studies. Here, we describe progress from recently (2000–2016) published studies of growing-season CO2 flux chamber measurements, namely GPP (gross primary production), ER (ecosystem respiration), and NEE (net ecosystem exchange), in the tundra region. We review the study areas and designs along with the explanatory environmental drivers used. Most of the studies were conducted in Alaska and Fennoscandia, and we stress the need for measuring fluxes in other tundra regions, particularly in more extreme climatic, productivity, and soil conditions. Soil respiration and other greenhouse gas measurements were seldom included in the studies. Although most of the environmental drivers of CO2 fluxes have been relatively well investigated (such as the effect of vegetation type and soil microclimate on fluxes), soil nutrients, other greenhouse gases and disturbance regimes require more research as they might define the future carbon balance. Particular attention should be paid to the effects of shrubification, geomorphology, and other disturbance effects such as fire events, and disease and herbivore outbreaks. An improved conceptual framework and understanding of underlying processes of biosphere–atmosphere CO2 exchange will provide more information on carbon cycling in the tundra.

scholarly journals Fractal Dimension Analysis Applied to Soil CO2 Fluxes in Campotosto’s Seismic Area, Central Italy

Geosciences ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 233
Author(s):  
Simone D’Incecco ◽  
Piero Di Carlo ◽  
Eleonora Aruffo ◽  
Nikolaos Chatzisavvas ◽  
Ermioni Petraki ◽  
...  
Keyword(s):  
Fractal Dimension ◽  
Central Italy ◽  
Fractal Dimensions ◽  
Co2 Flux ◽  
Co2 Fluxes ◽  
Soil Co2 ◽  
Flux Chamber ◽  
Dimension Analysis ◽  
Fractal Dimension Analysis ◽  
Seismic Area

This article reports fractal dimension analysis applied to soil CO2 fluxes measured in an Italian seismic area. The work was carried out with the use of a calibrated flux chamber unit. The fractal dimension (FD) from isotropic variograms was used as a method to understand related scale-dependent phenomena. The aim was to investigate the spatial variability of CO2 flux measurements in four directions (horizontal, vertical, 45° and 135° directions) related to different distances between the measuring points and from a fault. High fractal dimension values were found (2.5 ≤ FD ≤ 3.0). These imply strong anti-persistent behavior near to and far from the fault. Lower fractal dimensions were addressed at longer distances from the fault.

scholarly journals Impact of forest floor fire on soil carbon sequestration of Pinus roxburghii forest in Langtang National Park, Nepal

2018 ◽  
Vol 30 ◽  
pp. 148-163
Author(s):  
Biva Aryal ◽  
Bishnu Prasad Bhattarai ◽  
Mohan Pandey ◽  
Anjana Giri
Keyword(s):  
Carbon Sequestration ◽  
Organic Carbon ◽  
Soil Carbon ◽  
High Frequency ◽  
Forest Floor ◽  
National Park ◽  
Carbon Stock ◽  
Co2 Flux ◽  
Significant Difference ◽  
One Way Anova

Forest floor fires are known to be significantly important in carbon sequestration in soil. The present study investigated the total soil carbon stock (charcoal+soil organic carbon) andCO2 flux from four different depths (0-2, 2-10, 10-30 and >30cm) in fired and unfired forest of P. roxburghii from Langtang National Park, Nepal. The aim of this study was to test the impact of forest floor fire on soil carbon sequestration. We measured total carbon stock in soil of unfired and fired sites of different intensities namely: high frequency and high intensity, high frequency and moderate intensity and high frequency and low intensity. There was significant difference (P=0.00) of the soil organic carbon between the sites and different soil depths tested by one-way ANOVA. Similarly, one-way ANOVA test showed that soil charcoal stock was significantly different (P=0.00) at different soil depths. The value of CO2 flux was increased with increasing volumetric water content and decreasing soil temperature. One-way ANOVA showed significant difference (P=0.00) of volumetric water content, soil temperature and CO2 flux between the sites. In high frequency and medium intensity site, high amount of carbon sequestrated in soil suggested that fire of medium intensity mitigates high CO2 from the atmosphere.

scholarly journals Development and validation of inexpensive, automated, dynamic flux chambers

2014 ◽  
Vol 7 (7) ◽  
pp. 6877-6915
Author(s):  
B. B. Almand-Hunter ◽  
J. T. Walker ◽  
N. P. Masson ◽  
L. Hafford ◽  
M. P. Hannigan
Keyword(s):  
Eddy Covariance ◽  
Co2 Flux ◽  
Atmospheric Pollutants ◽  
Flux Chamber ◽  
Area Index ◽  
Chapel Hill ◽  
Eddy Covariance System ◽  
Flux Chambers ◽  
Multiple Species ◽  
Development And Validation

Abstract. We developed and validated an automated, inexpensive, and continuous multiple-species gas-flux monitoring system that can provide data for a variety of relevant atmospheric pollutants, including O3, CO2, and NOx. Validation consisted of conducting concurrent gas-phase dry-deposition experiments, using both dynamic flux chambers and an eddy-covariance system, in a grassy clearing in the Duke Forest (Chapel Hill, NC). Experiments were carried out in June and September, under a variety of meteorological conditions. Ozone-deposition measurements from the two methods matched very well (4–10% difference in mean flux rate) when the leaf-area index (LAI) inside the chambers was representative of the average LAI in the field. The dynamic flux chambers can be considered an accurate measurement system under these conditions. CO2 measurements were conducted for one 20 h period, and the flux chamber captured the diurnal trend in CO2 flux well, although the quantity of the data was not sufficient to validate chamber performance. Flux-chamber NOx measurements could be calculated when ambient NOx concentrations were above 1 ppb. Unfortunately, the eddy-covariance system for measuring NOx was not available during this field campaign, so comparisons cannot be made. NOx fluxes were in a reasonable range for the field site.

The Microstructure of Steatite (Protoenstatite)

1985 ◽  
Vol 43 ◽  
pp. 236-237
Author(s):  
W. E. Lee ◽  
A. H. Heuer
Keyword(s):  
High Frequency ◽  
Glass Ceramics ◽  
Magnesium Silicate ◽  
Beam Current ◽  
Glassy Matrix ◽  
Angle Of Incidence ◽  
X Ray ◽  
Mechanical And Electrical Properties ◽  
Argon Ions ◽  
High Temperature Polymorph

IntroductionTraditional steatite ceramics, made by firing (vitrifying) hydrous magnesium silicate, have long been used as insulators for high frequency applications due to their excellent mechanical and electrical properties. Early x-ray and optical analysis of steatites showed that they were composed largely of protoenstatite (MgSiO3) in a glassy matrix. Recent studies of enstatite-containing glass ceramics have revived interest in the polymorphism of enstatite. Three polymorphs exist, two with orthorhombic and one with monoclinic symmetry (ortho, proto and clino enstatite, respectively). Steatite ceramics are of particular interest a they contain the normally unstable high-temperature polymorph, protoenstatite.Experimental3mm diameter discs cut from steatite rods (∼10” long and 0.5” dia.) were ground, polished, dimpled, and ion-thinned to electron transparency using 6KV Argon ions at a beam current of 1 x 10-3 A and a 12° angle of incidence. The discs were coated with carbon prior to TEM examination to minimize charging effects.

Simulations of high-resolution images of amorphous silicon films

1986 ◽  
Vol 44 ◽  
pp. 544-545
Author(s):  
G. Y. Fan ◽  
J. M. Cowley
Keyword(s):  
Electron Microscope ◽  
High Frequency ◽  
Fourier Transformation ◽  
Amorphous Materials ◽  
Low Frequency ◽  
Chromatic Aberration ◽  
Structure Information ◽  
Frequency Components ◽  
High Resolution Images ◽  
Spatial Frequency Spectrum

It is well known that the structure information on the specimen is not always faithfully transferred through the electron microscope. Firstly, the spatial frequency spectrum is modulated by the transfer function (TF) at the focal plane. Secondly, the spectrum suffers high frequency cut-off by the aperture (or effectively damping terms such as chromatic aberration). While these do not have essential effect on imaging crystal periodicity as long as the low order Bragg spots are inside the aperture, although the contrast may be reversed, they may change the appearance of images of amorphous materials completely. Because the spectrum of amorphous materials is continuous, modulation of it emphasizes some components while weakening others. Especially the cut-off of high frequency components, which contribute to amorphous image just as strongly as low frequency components can have a fundamental effect. This can be illustrated through computer simulation. Imaging of a whitenoise object with an electron microscope without TF limitation gives Fig. 1a, which is obtained by Fourier transformation of a constant amplitude combined with random phases generated by computer.

SEM image sharpness analysis

1996 ◽  
Vol 54 ◽  
pp. 142-143
Author(s):  
M. T. Postek ◽  
A. E. Vladar
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Quantitative Information ◽  
Primary Electron ◽  
Image Sharpness ◽  
Critical Dimensions ◽  
Sem Image ◽  
Frequency Changes ◽  
Electron Microscopes ◽  
Scanning Electron

Fully automated or semi-automated scanning electron microscopes (SEM) are now commonly used in semiconductor production and other forms of manufacturing. The industry requires that an automated instrument must be routinely capable of 5 nm resolution (or better) at 1.0 kV accelerating voltage for the measurement of nominal 0.25-0.35 micrometer semiconductor critical dimensions. Testing and proving that the instrument is performing at this level on a day-by-day basis is an industry need and concern which has been the object of a study at NIST and the fundamentals and results are discussed in this paper.In scanning electron microscopy, two of the most important instrument parameters are the size and shape of the primary electron beam and any image taken in a scanning electron microscope is the result of the sample and electron probe interaction. The low frequency changes in the video signal, collected from the sample, contains information about the larger features and the high frequency changes carry information of finer details. The sharper the image, the larger the number of high frequency components making up that image. Fast Fourier Transform (FFT) analysis of an SEM image can be employed to provide qualitiative and ultimately quantitative information regarding the SEM image quality.

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