Temperature controls diel oscillation of the CO2 concentration in a desert soil

The diel dynamic of the CO2 concentration in soils in relation to temperature is not yet fully understood. Air temperature might control the soil CO2 concentration due to thermal convective venting at sites experiencing large temperature differences between the atmosphere and the soil. Therefore, the objective of this study was to determine the soil CO2 concentration and its temporal dynamic in a deep desert soil in relationship to soil and air temperature based on high frequency measurements. For this purpose, CO2 concentration and temperature were measured in six soil depths (ranging from 15 to 185 cm) in a coarse-textured desert soil in the North of Chile every 60 min together with precipitation and air temperature for one year. The mean CO2 concentration calculated across the whole measuring period increased linearly with soil depth from 463 ppm in 15 cm to 1542 ppm in 185 cm depth. We observed a strong diel oscillation of the CO2 concentration that decreased with soil depth and a hysteretic relationship between the topsoil CO2 concentration and both air and soil temperature. The Rayleigh-Darcy number calculated for different times indicates that thermal convective venting of the soil occurred during the night and in the early morning. A small precipitation event (4 mm) increased the CO2 concentrations in 15, 30, and 50 cm depths for several days but did not alter the amplitude of the diel oscillation of the CO2 concentration. The diel oscillation of the CO2 concentration and the hysteretic relationship between soil CO2 concentration and air temperature were likely caused by thermal convection, leading to transport of CO2-rich air from the soil to the atmosphere at night. In conclusion, our results indicate that the soil CO2 concentration can be largely controlled by convection caused by temperature differences, and not only by diffusion. The results have important implications as they provide further evidence that thermal convective venting contributes to gas exchange at sites experiencing large temperature differences between the atmosphere and the soil, which is relevant for soil chemical reactions.

Correlation of Tritium Concentration in Rainwater with Cosmic Rays: Preliminary Results

The Radiochronology Center has been established in 1999 as a member of the Horizontal Laboratories network of the University of Ioannina. Recently it has added to its activities the development of a tritium measurements laboratory as part of the Radiochronology Center. The laboratory is equipped with a super low level background liquid scintillation counter, which is capable to measure very low concentrations of tritium for applications in radioprotection, dating and hydrology.For the aims of the present continuing study rainwater samples are collected monthly. Each sample is distilled and then it is passed through an electrolysis process to increase the tritium concentration. Five mL of the enriched sample are mixed with 15 mL of a scintillation cocktail, specially designed for tritium measurements and its beta activity is measured for 200 min. The LLD of tritium in the samples is estimated 3 Bq/L or 27 TU.Our preliminary results show that, during the measuring period tritium concentration increased with time. The tritium values are correlated with the cosmic ray neutron flux data at ground level, available for Greece in the same period. The measured tritium concentrations in rainwater, which range from 36 ± 8 to 64 ± 8 TU, may be used for local hydrology studies.

On the challenges of precise velocity measurements in vertical convective wall jets

For the transition of our energy supply towards a higher share of renewables, thermal energy storage (TES) systems are, besides electric batteries and chemical energy storage systems, one promising solution to overcome the volatile nature of renewable energy sources. For the most efficient operation, the liquid storage material in the tank should be stratified by its temperature-dependent density. As a result, the cold fluid remains at the bottom, and the heated fluid rises to the top (Alva et al. (2018)). Typically steel tanks are used for TES, and thus, the wall material has a thermal diffusivity that is one to two orders of magnitudehigher than that of the storage fluid. Consequently, the tank’s sidewalls work as a thermal bridge between the stratified layers. In recent studies, the authors have shown that the resulting heat flux induces two counterdirected, convective wall jets near the sidewalls of the tank, which increase mixing of the stratification and thus lowers the exergy content and the storage efficiency (Otto et al. (2019, 2020)). Using a model experiment of a TES, the entire vertical extent of the detected wall jets is investigated. Hence, the typical flow structures of vertical, natural convection under the influence of non-zero temperature gradients in the ambient fluid can be analyzed, which can help to improve storage tanks in the future. The velocity in the region of the wall jets is measured via 2d particle-image velocimetry (PIV) in a rectangular model experiment of 750mm height on a base area of 375mm×375mm made from polycarbonate. The jets evolve on the surface of an aluminum plate simulating the storage tank’s sidewall. The measuring system consists of four cameras with a resolution of 2160×2560 pixels combined with objective lenses with 100mm focal length capturing the raw images in a plane perpendicular to the aluminum wall. A Nd:YAG laser with a wavelength of 532nm illuminates the measuring plane. Simultaneously using up to four cameras adjacent to each other and stitching their resulting vector fields, the vertical extent of the field of view increases from 38mm up to 140mm. Despite this, the field of view is still much smaller than the vertical extent of the model experiment, so that seven consecutive runs are performed to cover the entire height. Disturbing reflections of the laser light sheet on the aluminum wall are eliminated using optical filters for the cameras that are opaque for the green laser light in combination with fluorescently (Rhodamine B) dyed PMMA tracer particles with a diameter between 1–20μm. The particles emit light at a wavelength of 610nm (orange light) and can therefore be detected through the cameras’ filters. During four separate measuring periods, where each lasts for two minutes, double frame images are captured with a time difference of 19.981 ms (maximum possible value) at a measuring frequency of 7 Hz. Figure 1 shows a schematic of the camera setup next to the model experiment and the measurement and evaluation procedure to finally receive one time-averaged velocity field per measuring period of the full height of the experiment. The raw data evaluation process starts with calculating the vector fields of all cameras used at a certain measuring position and stitching them to one flow field of this position. Since the wall jets’ horizontal extents are with 2–7mm relatively small and they show high velocity gradients, the raw images are evaluated in both single-frame and double-frame mode. With a velocity threshold that corresponds to a pixel displacement of 1/4 of the interrogation window size and the time difference of the single-frames, the resulting vector fields are masked and merged into one final vector field. This vector field consists of high velocities evaluated in double-frame mode and low velocities evaluated in single-frame mode (see Figure 2) thus minimizing the relative error. The algorithm used in this work is similar to the multi-frame PIV approach introduced by Hain and K¨ahler (2007). Figure 3 shows the time-averaged results of the first measuring period for each of the seven measuring positions in height.

Immunization against Gonadotropin-Releasing Hormone in Female Beef Calves to Avoid Pregnancy at Time of Slaughter

Precocious puberty in beef heifers can result in unwanted pregnancies due to accidental breeding by farm bulls. Inbreeding, premature calving followed by dystocia and a high stillbirth rate or slaughtering of pregnant heifers are the consequences of this behaviour. The aim of the study was to postpone puberty by using Improvac®, an anti-GnRH vaccine. Therefore, n = 25 calves were twice vaccinated, once at the age of 5 and then at 6.5 months. n = 24 calves served as unvaccinated case controls. The onset of puberty was assigned if progesterone analysis in the blood exceeded 1 ng/mL. Progesterone values were excluded if the corresponding serum cortisol levels were ≥60 nmol/L. Our target was met, as in the vaccinated group none of the calves exceeded a progesterone value >1 ng/mL until the scheduled age of slaughter at 11 months and only 12.5% of the animals exceeded a progesterone value of 1 ng/mL over the whole measuring period (>400 days) compared with 56.5% of the calves in the control group. In conclusion, the favourable results from our study using the vaccine Improvac® represent an animal-friendly, non-invasive and reliable way to avoid early pregnancy in heifers as well as the slaughter of pregnant cattle.

Atmospheric influences on water stable isotopes in Antarctic water vapor and surface snow – implications for ice core interpretation

<p>In Austral summer 2017/18 daily surface snow samples were taken (weather allowing) at two depths, 0-1cm and 6-7cm, at Neumayer III Station, Dronning Maud Land DML, Antarctica. Stable isotope ratios (18O, D, d-excess) of the snow samples were analysed in the AWI isotope lab. In parallel, water vapor stable isotopes were measured continuously on a routine base with a Picarro cavity ring-down spectroscope analyser (CRDS). Neumayer III is also a full meteorological observatory measuring all important meteorological variables including upper-air data. Meteorological data were directly compared to both snow and vapor isotope data. The corresponding synoptic situations were analysed using data from AMPS (Antarctic Mesoscale Prediction System), which employs WRF (Weather Research and Forecasting Model), a mesoscale atmospheric model that has been successfully used in earlier studies in DML. AMPS is run operationally at NCAR for Antarctic weather forecasting, particularly for flight operations of the US Antarctic Program (USAP). Additionally, back-trajectory calculations to investigate moisture sources and transport were carried out using FLEXPART, an open-source Lagrangian particle dispersion model. Due to logistical problems, the measuring period during the expedition was too short for statistical analysis, thus we focus on case studies here. In particular, periods with no precipitation were investigated, since earlier studies in Greenland have shown that the interaction of snow surface and atmosphere is important for the stable isotope ratio in the snow, thus in later ice cores that are used to derive paleo temperatures. A better understanding of the highly complex relationship between water vapor stable isotopes and meteorological conditions (including moisture source and transport) as well as the interaction between surface snow and water vapor is necessary for a correct paleoclimatic interpretation of ice cores.</p>

Air temperature controls diel oscillation of the CO2 concentration in a desert soil

<p>The factors that control the soil CO<sub>2</sub> concentration are not yet well understood.<strong> </strong>Therefore, the objective of this study was to explore what factors control the soil CO<sub>2</sub> concentration and its dynamic in a desert soil. For this purpose, CO<sub>2</sub> concentration and temperature were measured in six soil depths (ranging from 15 to 185 cm) in a deeply weathered, coarse-textured desert soil in the North of Chile at high frequency (every 60 minutes) together with precipitation and air temperature for one year. The mean CO<sub>2</sub> concentration calculated across the whole measuring period increased linearly with soil depth from 463 ppm in 15 cm to 1542 ppm in 185 cm soil depth. We observed a diel oscillation of the CO<sub>2</sub> concentration that decreased with soil depth and a hysteretic relationship between the topsoil CO<sub>2</sub> concentration and both air and soil temperature. A small precipitation event increased the CO<sub>2 </sub>concentrations in 15, 30, and 50 cm soil depths for several days but did not alter the amplitude of the diel oscillation of the CO<sub>2</sub> concentration. The diel oscillation was very likely caused by strong differences between the soil and the air temperature at night, in particular in summer, causing transport of topsoil air to the atmosphere by thermal convection. Our results have important implications as they show that the soil CO<sub>2</sub> concentration can be controlled by air temperature through thermal convection, rather than by soil temperature, and that the hysteretic relationship between soil CO<sub>2</sub> concentration and temperature can be caused by physical factors alone.</p><p> </p>

Developing an Automated Gas Sampling Chamber for Measuring Variations in CO2 Exchange in a Maize Ecosystem at Night

The measurement of net ecosystem exchange (NEE) of field maize at a plot-sized scale is of great significance for assessing carbon emissions. Chamber methods remain the sole approach for measuring NEE at a plot-sized scale. However, traditional chamber methods are disadvantaged by their high labor intensity, significant resultant changes in microclimate, and significant impact on the physiology of crops. Therefore, an automated portable chamber with an air humidity control system to determinate the nighttime variation of NEE in field maize was developed. The chamber system can automatically open and close the chamber, and regularly collect gas in the chamber for laboratory analysis. Furthermore, a humidity control system was created to control the air humidity of the chamber. Chamber performance test results show that the maximum difference between the temperature and humidity outside and inside the chamber was 0.457 °C and 5.6%, respectively, during the NEE measuring period. Inside the chamber, the leaf temperature fluctuation range and the maximum relative change of the maize leaf respiration rate were −0.3 to 0.3 °C and 23.2015%, respectively. We verified a series of measurements of NEE using the dynamic and static closed chamber methods. The results show a good common point between the two measurement methods (N = 10, R2 = 0.986; and mean difference: ΔCO2 = 0.079 μmol m−2s−1). This automated chamber was found to be useful for reducing the labor requirement and improving the time resolution of NEE monitoring. In the future, the relationship between the humidity control system and chamber volume can be studied to control the microclimate change more accurately.

Cerebral and peripheral muscle oxygenation and perfusion: Course in moderate and late preterm neonates during the first day after birth

AimTo investigate the ratio of cerebral tissue oxygenation index (cTOI) to peripheral muscle tissue oxygenation index (pTOI) measured by near-infrared spectroscopy (NIRS) in cardio-circulatory stable preterm neonates without signs of inflammation/infection on the first day after birth.MethodsObservational study analysing secondary outcome parameters of the ‘Avoiding Hypotension in Preterm Neonates (AHIP)’ trial (ClinicalTrials.gov identifier: NCT01910467). Preterm neonates, who had cTOI and pTOI measurements during 24 h after birth, were included. In each neonate the mean of the cTOI/pTOI-ratio, cTOI, pTOI and routine monitoring parameters were calculated for each hour and for the 24-h measuring period. Courses of all measured parameters were analysed.ResultsEighty-seven stable preterm neonates (33.1 [32.1–34.1] weeks of gestation) were included. The mean value over the 24-h measuring period for the cTOI/pTOI-ratio was 0.96 ± 0.02, for cTOI 70.1 ± 1.4 and for pTOI 73.4 ± 0.9. Routine monitoring parameters were in the normal ranges over 24 h. The courses of the cTOI/pTOI-ratio and cTOI showed significantly lower values from hour 5 to 15 compared to the first hours after birth. Heart rate decreased significantly over time, whereas mean arterial blood pressure increased significantly. pTOI, arterial oxygen saturation and body temperature showed no significant change over time.ConclusionWe are the first to report on cTOI/pTOI-ratios for cardio-circulatory stable preterm neonates over a 24-h period after birth, showing significantly lower values from hour 5 to 15 compared to the first hours after birth.

Analysis of temperature trends and urban heat island in Madrid

<p>The temperature in the cities is affected by both global climate change and local changes due to human activities and the different land use compared to rural surroundings. These local changes, which modify the surface energy budget in urban areas, include the replacement of the natural surfaces by buildings and pavements and the heat of anthropogenic origin (heating, air conditioning, traffic). Madrid city (Spain) has a current population of near 3.3 million people and a larger metropolitan area reaching around 6.5 million people. Hence, it is affected by the phenomenon called urban heat island (UHI), which indicates that a higher temperature is found in the city compared with the surrounding rural areas. UHI is defined as the temperature difference between the urban observatory and the rural one and especially affects the minimum temperatures since urban areas cool down to a lesser extent than the neighbouring rural sites. Moreover, the intensity of the UHI is modulated by the meteorological conditions (wind, cloudiness, surface pressure, precipitation), highly associated with different synoptic situations. In this work, we use the Madrid-Retiro meteorological station as the urban one, which has regular and homogeneous data from the beginning of XX century; and the station at Barajas airport (12 km from the city centre) as well as other stations out of Madrid city (but within a range of 20 km from the city centre) as the rural stations. They all have a common measuring period from 1961 until present. The main objectives of the work are: 1) to identify temperature trends in the meteorological stations (both urban and rural); 2) to evaluate the intensity of the UHI for the different rural stations; 3) to apply a systematic and objective algorithm to classify each day in different categories (related to synoptic situation) that produce a different degree of UHI intensity; and, 4) to evaluate possible trends in the UHI intensity.</p>

Investigations on the permeability of MgO concrete with 5-1-8 phase at the GV2-drift-sealing in the Teutschenthal mine

<p>For underground storage facilities and future HAW repositories, a secure closure is indispensable. Within the scope of two consecutive research projects, three closure elements were installed in large-scale tests at the Teutschenthal mine in the Carnallitit Mountains between 2006 and 2008. Special mention should be made here of the large-scale test 2 (“GV2”), which was produced from MgO concrete with the 5-1-8 binder phase. This structure was made using the dry-mix shotcrete procedure. The low temperature development during the setting of the shotcrete was very advantageous. The 10.25 m long structure, with a height and width of 3.55 m each, consists of 104 concreting sections with an average layer thickness of 9.9 cm. It was of interest whether the concreting section boundaries (“BAG”) influence the permeability (negatively). The structure is equipped with pressure transmitters and TDR sensors in three measuring levels. After completion of the structure and injections in the contact area, the integral system permeability was 2*10<sup>‑16</sup> m². Liquid pressurization via pressure chamber was carried out on the test structure after a maturing period of about 10 years. After 8 years, the permeability with gas and with solution was determined in boreholes and on drill cores, especially with regard to the development over time. The determined in-situ gas permeability is on average 2.7*10<sup>‑19</sup> m², on compact concrete (without BAGs) on average 2.0*10<sup>-20</sup> m². Test areas containing BAGs showed a higher permeability of maximum three orders of magnitude in some measurements. The solution permeability was determined both with a saturated NaCl solution and with a NaCl-saturated solution containing MgCl<sub>2</sub> and is between 1.0*10<sup>‑20</sup> m² and 9.0*10<sup>‑20</sup> m², whereby this decreases by half a power of ten over the measurement period of 600 days. In further integral injection tests in 4.5 m and 4.8 m long boreholes, a significant decrease in permeability over time was also observed. From an initial 2*10<sup>‑15</sup> m² and 4*10<sup>‑16</sup> m², respectively, the integral permeability decreased to <10<sup>‑19</sup> m² over a measuring period of 2.5 years. The reason for this decrease is the reduction of pore space due to the recrystallization of MgO and the transformation of the metastable 5-1-8 phase to the long-term stable 3-1-8 phase due to the increase in volume that takes place when the solution is added. Potential weak points or defects at the technically determined concrete section boundaries, therefore, do not represent weak zones in the structure in the long term due to this self-healing effect.</p><p>This paper reports on the large-scale experiment GV2 made of MgO concrete with 5-1-8 phase and the comprehensive permeability and strength investigations in drillings and on drill cores. The test results are the precondition for a modeling of the long-term behaviour of MgO-concrete.</p>