A compact and stable eddy covariance set-up for methane measurements using off-axis integrated cavity output spectroscopy

A Fast Methane Analyzer (FMA) is assessed for its applicability in a closed path eddy covariance field set-up in a peat meadow. The FMA uses off-axis integrated cavity output spectroscopy combined with a highly specific narrow band laser for the detection of CH<sub>4</sub> and strongly reflective mirrors to obtain a laser path length of 2–20×10<sup>3</sup> m. Statistical testing and a calibration experiment showed high precision (7.8×10<sup>−3</sup> ppb) and accuracy (<0.30%) of the instrument, while no drift was observed. The instrument response time was determined to be 0.10 s. In the field set-up, the FMA is attached to a scroll pump and combined with a 3-axis ultrasonic anemometer and an open path infrared gas analyzer for measurements of carbon dioxide and water vapour. The power-spectra and co-spectra of the instruments were satisfactory for 10 Hz sampling rates. <br><br> Due to erroneous measurements, spikes and periods of low turbulence the data series consisted for 26% of gaps. Observed CH<sub>4</sub> fluxes consisted mainly of emission, showed a diurnal cycle, but were rather variable over. The average CH<sub>4</sub> emission was 29.7 nmol m<sup>−2</sup> s<sup>−1</sup>, while the typical maximum CH<sub>4</sub> emission was approximately 80.0 nmol m<sup>−2</sup> s<sup>−1</sup> and the typical minimum flux was approximately 0.0 nmol m<sup>−2</sup> s<sup>−1</sup>. The correspondence of the measurements with flux chamber measurements in the footprint was good and the observed CH<sub>4</sub> emission rates were comparable with eddy covariance CH<sub>4</sub> measurements in other peat areas. <br><br> Additionally, three measurement techniques with lower sampling frequencies were simulated, which might give the possibility to measure CH<sub>4</sub> fluxes without an external pump and save energy. Disjunct eddy covariance appeared to be the most reliable substitute for 10 Hz eddy covariance, while relaxed eddy accumulation gave reliable estimates of the fluxes over periods in the order of days or weeks

The full greenhouse gas balance of an abandoned peat meadow

International audienceGlobally, peat lands are considered to be a sink of CO2, but a source when drained. Additionally, wet peat lands are thought to emit considerable amounts of CH4 and N2O. Hitherto, reliable and integrated estimates of emissions and emission factors for this type of area have been lacking and the effects of wetland restoration on methane emissions have been poorly quantified. In this paper we estimate the full GHG balance of a restored natural peat land by determining the fluxes of CO2, CH4 and N2O through atmosphere and water, while accounting for the different GWP's. This site is an abandoned agricultural peat meadow, which has been converted into a wetland nature reserve ten years ago by raising the water level. GHG fluxes were measured continuously with an eddy-correlation system (CO2) and flux chamber measurements (CH4 and N2O). Meteorological and hydrological measurements were done as well. With growing seasons of respectively 192 and 155 days, the net annual CO2 uptake was 276±61 g C m?2 for 2004 and 311±58 g C m?2 for 2005. Ecosystem respiration was estimated as 887±668 g C m?2 for 2004 and 866±666 g C m?2 for 2005. CH4 fluxes from water, saturated land and relatively dry land varied: total annual CH4 fluxes are 10.4±19.2 g C m?2 yr?1, 101 g C m?2 yr?1±30 and 37.3±10.9 g C m?2 yr?1, respectively, and a annual weighed total CH4 emission of 31.27±20.44 g C m?2 yr?1. N2O fluxes were too low to be of significance. The carbon-balance consists for the largest part of CO2 uptake, CO2 respiration and CH4 emission from wet land and water. CO2 emission has decreased significantly as result of the raised water table, while CH4 fluxes have increased. In global warming potentials the area is a very small sink of 71 g CO2-equiv m?2 (over a 100-year period)

Development of the clinical learning evaluation questionnaire for undergraduate clinical education: Factor structure, validity, and reliability study

Background: Teaching and learning of clinical skills for undergraduate medical students usually takes place during the clinical clerkship. Therefore, it is of vital importance to ensure the effectiveness of the rotations within this clerkship. The aims of this study were to develop an instrument that measures the effectiveness of the clinical learning environment, to determine its factor structure, and to find first evidence for the reliability and validity of the total scale and the different factors. Methods. The Clinical Learning Evaluation Questionnaire (CLEQ) is an instrument, consisting of 40 items, which have been developed after consideration of the results of a qualitative study that investigated the important factors influencing clinical learning, both from the perspective of students, as well as teachers. Results of relevant literature that investigated this issue were also incorporated in the CLEQ. This instrument was administered to a sample of students (N = 182) from three medical colleges in Riyadh city, the capital of Saudi Arabia. The factor structure of the CLEQ (Principal component analysis, Oblimin rotation) and reliability of the factor scales (Cronbach's α) were determined. Hypotheses concerning the correlations between the different factors were tested to investigate their convergent and divergent validity. Results: One hundred and nine questionnaires were returned. The factor analysis yielded six factors: F1 Cases (8 items), F2 Authenticity of clinical experience (8 items), F3 Supervision (8 items), F4 Organization of the doctor-patient encounter (4 items), F5 Motivation to learn (5 items), and F6 Self awareness (4 items). The overall internal consistency (α) of the CLEQ was 0.88, and the reliabilities (Cronbach's α) of the six factors varied from.60 to.86. Hypotheses concerning the correlations between the different factors were partly confirmed, which supported the convergent validity of the factors, but not their divergent validity. Significant differences were found between the scores of the students of the three different schools on the factors Supervision and Organization of patient-doctor encounter. Conclusions: The results of this study demonstrated that CLEQ is a multidimensional and reliable instrument. It can be utilized as an evaluation tool for clinical teaching activities, both by educators as well as students. Further research is needed into the validity of the CLEQ

Longer growing seasons do not increase net carbon uptake in Northeastern Siberian tundra

With global warming, snowmelt is occurring earlier and growing seasons are becoming longer around the Arctic. It has been suggested that this would lead to more uptake of carbon due to a lengthening of the period in which plants photosynthesize. To investigate this suggestion, 8 consecutive years of eddy covariance measurements at a northeastern Siberian graminoid tundra site were investigated for patterns in net ecosystem exchange, gross primary production (GPP) and ecosystem respiration (Reco). While GPP showed no clear increase with longer growing seasons, it was significantly increased in warmer summers. Due to these warmer temperatures however, the increase in uptake was mostly offset by an increase in Reco. Therefore, overall variability in net carbon uptake was low, and no relationship with growing season length was found. Furthermore, the highest net uptake of carbon occurred with the shortest and the coldest growing season. Low uptake of carbon mostly occurred with longer or warmer growing seasons. We thus conclude that the net carbon uptake of this ecosystem is more likely to decrease rather than to increase under a warmer climate. These results contradict previous research that has showed more net carbon uptake with longer growing seasons. We hypothesize that this difference is due to site-specific differences, such as climate type and soil, and that changes in the carbon cycle with longer growing seasons will not be uniform around the Arcti

The growing season greenhouse gas balance of a continental tundra site in the Indigirka lowlands, NE Siberia.

Carbon dioxide and methane fluxes were measured at a tundra site near Chokurdakh, in the lowlands of the Indigirka river in north-east Siberia. This site is one of the few stations on Russian tundra and it is different from most other tundra flux stations in its continentality. A suite of methods was applied to determine the fluxes of NEE, GPP, <i>R</i><sub>eco</sub> and methane, including eddy covariance, chambers and leaf cuvettes. Net carbon dioxide fluxes were high compared with other tundra sites, with NEE=−92 g C m<sup>−2</sup> yr<sup>−1</sup>, which is composed of an <i>R</i><sub>eco</sub>=+141 g C m<sup>−2</sup> yr<sup>−1</sup> and GPP=−232 g C m<sup>−2</sup> yr<sup>−1</sup>. This large carbon dioxide sink may be explained by the continental climate, that is reflected in low winter soil temperatures (−14°C), reducing the respiration rates, and short, relatively warm summers, stimulating high photosynthesis rates. Interannual variability in GPP was dominated by the frequency of light limitation (<i>R<sub>g</sub></i><200 W m<sup>−2</sup>), whereas <i>R</i><sub>eco</sub> depends most directly on soil temperature and time in the growing season, which serves as a proxy of the combined effects of active layer depth, leaf area index, soil moisture and substrate availability. The methane flux, in units of global warming potential, was +28 g C-CO<sub>2</sub>e m<sup>−2</sup> yr<sup>−1</sup>, so that the greenhouse gas balance was −64 g C-CO<sub>2</sub>e m<sup>−2</sup> yr<sup>−1</sup>. Methane fluxes depended only slightly on soil temperature and were highly sensitive to hydrological conditions and vegetation composition

Net ecosystem exchange of carbon dioxide and water of far eastern Siberian Larch (Larix cajanderii) on permafrost.

Observations of the net ecosystem exchange of water and CO₂ were made during two seasons in 2000 and 2001 above a Larch forest in Far East Siberia (Yakutsk). The measurements were obtained by eddy correlation. There is a very sharply pronounced growing season of 100 days when the forest is leaved. Maximum half hourly uptake rates are 18 &micro;mol m^-2 s^-1; maximum respiration rates are 5 &micro;mol m^-2 s^-1. Net annual sequestration of carbon was estimated at 160 gCm^-2 in 2001. Applying no correction for low friction velocities added 60 g C m^-2. The net carbon exchange of the forest was extremely sensitive to small changes in weather that may switch the forest easily from a sink to a source, even in summer. June was the month with highest uptake in 2001. <P style='line-height: 20px;'> The average evaporation rate of the forest approached 1.46 mm day^-1 during the growing season, with peak values of 3 mm day^-1 with an estimated annual evaporation of 213 mm, closely approaching the average annual rainfall amount. 2001 was a drier year than 2000 and this is reflected in lower evaporation rates in 2001 than in 2000. <P style='line-height: 20px;'> The surface conductance of the forest shows a marked response to increasing atmospheric humidity deficits. This affects the CO₂ uptake and evaporation in a different manner, with the CO₂ uptake being more affected. There appears to be no change in the relation between surface conductance and net ecosystem uptake normalized by the atmospheric humidity deficit at the monthly time scale. The response to atmospheric humidity deficit is an efficient mechanism to prevent severe water loss during the short intense growing season. The associated cost to the sequestration of carbon may be another explanation for the slow growth of these forests in this environment

The effect of deep learning reconstruction on abdominal CT densitometry and image quality: a systematic review and meta-analysis

Objective To determine the difference in CT values and image quality of abdominal CT images reconstructed by filtered back-projection (FBP), hybrid iterative reconstruction (IR), and deep learning reconstruction (DLR). Methods PubMed and Embase were systematically searched for articles regarding CT densitometry in the abdomen and the image reconstruction techniques FBP, hybrid IR, and DLR. Mean differences in CT values between reconstruction techniques were analyzed. A comparison between signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of FBP, hybrid IR, and DLR was made. A comparison of diagnostic confidence between hybrid IR and DLR was made. Results Sixteen articles were included, six being suitable for meta-analysis. In the liver, the mean difference between hybrid IR and DLR was - 0.633 HU (p = 0.483, SD +/- 0.902 HU). In the spleen, the mean difference between hybrid IR and DLR was - 0.099 HU (p = 0.925, SD +/- 1.061 HU). In the pancreas, the mean difference between hybrid IR and DLR was - 1.372 HU (p = 0.353, SD +/- 1.476 HU). In 14 articles, CNR was described. In all cases, DLR showed a significantly higher CNR. In 9 articles, SNR was described. In all cases but one, DLR showed a significantly higher SNR. In all cases, DLR showed a significantly higher diagnostic confidence. Conclusions There were no significant differences in CT values reconstructed by FBP, hybrid IR, and DLR in abdominal organs. This shows that these reconstruction techniques are consistent in reconstructing CT values. DLR images showed a significantly higher SNR and CNR, compared to FBP and hybrid IR.Cardiovascular Aspects of Radiolog