•A collaborative approach was used to compare water potential measurement methods.•Time of the day (predawn, mid-morning and noon) and mode (stem vs. leaf) were compared.•Discrimination Ratio (DR) ...was used to determine the discrimination ability of each.•Leaf water potential was less discriminant than predawn or stem water potential at any time.
Water potential is considered to be the “gold-standard” measure for plant water status determination. However, there are some discrepancies on how and at what time of the day water potential measurements should be performed in order to obtain meaningful information. The aim of this work is to evaluate the discrimination ability of water potential measurements in grapevines depending on the time of the day and of the measurement procedure (leaf vs. stem). To do so, a meta-analysis was performed using >78,000 measurements of water potential data obtained in field irrigation experiments, provided by 13 research teams working in this subject in Spain. For each measurement day and experiment, Discrimination Ratio (DR) was calculated and used to determine the discrimination ability of each method, and then pooled for comparison. The measurement procedure with the greatest DR can be hypothesised to be the most suitable under the average working conditions. Leaf water potential showed lower DR mean values than predawn or stem water potential. The climatic conditions and the cultivar may affect to the discrimination ability, although the abovementioned trend was always maintained. Leaf water potential in vineyards should therefore be replaced, as a general rule, by either stem or predawn water potential readings, without a clear pre-eminence of the performance of predawn and stem water potential measurements. Building a common dataset and its subsequent meta-analysis has been proved to be an efficient and robust tool to compare plant measurements, and should be implemented for other species and/or measurement procedures.
Spray cross-impingement in a high-pressure chamber (10–30 atm) was studied experimentally, the results being compared to the spray opposed-impingement. The comparison was subsequently extended to the ...spray combustion in a model opposed-piston compression ignition engine. To account for the ambient pressure effects in collision outcomes, a recently proposed pressure-dependent droplet collision model was implemented in the KIVA-3V computer program for simulating the experiments. Compared with the widely used Estrade et al.’s and O’Rourke’s models, the pressure-dependent model produces satisfactory predictions to spray characteristics. The uncertainty of the kinetic energy recovery coefficient, which affects the post-collision characteristics of bouncing droplets, was found to cause insignificant difference in model predictions. In the high-pressure chamber, droplet collisions in cross-impingement occur earlier than those in the opposed-impingement and result in more coalescence, consequently producing larger droplet sizes. With increasing the ambient pressure, the increasing tendency of droplet bouncing diminishes the difference of these two spray impingements. In the model OPCI, the presence of strong swirling flow deflects sprays from impingement and therefore the opposed-impingement shows slightly better combustion performance by producing more spatially uniform droplet distribution. However, the spray cross-impingement enhances droplet collision hence promotes atomization in the absence of swirling flow.
•Recutting the petiole has no significant effect of on Ψleaf values.•Up to 30 s may elapse between sample excision and pressurization without significantly affecting Ψleaf measurements.•Only 10 min ...of equilibration time is necessary for Ψstem measurements.•In most cases, the effect of operator on Ψ determinations was greater than any of the sample preparation methods tested.
Despite the fact that the pressure chamber has been used as a tool to assess vine water status and assist in scheduling vineyard irrigation for more than 30 years, there remains some disagreement in sampling protocol with respect to midday leaf water potential (Ψleaf) and midday stem water potential (Ψstem) determination. Therefore, the primary goal of this study was to test various sampling protocols associated with the measurement of these two variables. Specifically, experiments were conducted to test the effects of (1) re-cutting the petiole prior to placing the leaf in the chamber, (2) time span between sample excision and pressurization, (3) sample equilibration time on Ψstem values, and (4) the effect of operator. Results showed that there was no significant effect of re-cutting the petiole on Ψleaf values. Furthermore, up to 30 s of time span between sample excision and pressurization was acceptable for accurate Ψleaf determinations, as long as the sample was kept shaded during that time. Finally, only 10 min of equilibration time was necessary for accurate Ψstem determination. In most cases, the effect of operator on all Ψ determinations was greater than any of the sample preparation methods tested. This reinforces the need to properly train vineyard technicians in using the pressure chamber. However, improved flexibility in sampling protocol for either Ψleaf or Ψstem determinations may improve efficiency of vine water status monitoring in vineyards, thus reducing labor costs associated with pressure chamber-based irrigation scheduling.
The high-capacity tensiometer and thermocouple psychrometer measure xylem water potential with high accuracy and adequate response time, as demonstrated by simultaneous measurements on sapling stems.
...Abstract
The pressure chamber, the most popular method used to measure xylem water potential, is a discontinuous and destructive technique and is therefore not suitable for automated monitoring. Continuous non-destructive monitoring could until very recently be achieved only by use of the thermocouple psychrometer (TP). Here we present the high-capacity tensiometer (HCT) as an alternative method for continuous non-destructive monitoring. This provided us with a unique chance to cross-validate the two instruments by installing them simultaneously on the same sapling stem. The HCT and the TP showed excellent agreement for xylem water potential less than –0.5 MPa. Response to day/night cycles and watering was remarkably in phase, indicating excellent response time of both instruments despite substantially different working principles. For xylem water potential greater than –0.5 MPa, the discrepancies sometimes observed between the HCT and TP were mainly attributed to the kaolin paste used to establish contact between the xylem and the HCT, which becomes hydraulically poorly conductive in this range of water potential once dried beyond its air-entry value and subsequently re-wetted. Notwithstanding this limitation, which can be overcome by selecting a clay paste with higher air-entry value, the HCT has been shown to represent a valid alternative to the TP.
The relationship between leaf water potential, soil water potential, and transpiration depends on soil and plant hydraulics and stomata regulation. Recent concepts of stomatal response to soil drying ...relate stomatal regulation to plant hydraulics, neglecting the loss of soil hydraulic conductance around the roots. Our objective was to measure the effect of soil drying on the soil-plant hydraulic conductance of maize and to test whether stomatal regulation avoids a loss of soil-plant hydraulic conductance in drying soils. We combined a root pressure chamber, in which the soil-root system is pressurized to maintain the leaf xylem at atmospheric pressure, with sap flow sensors to measure transpiration rate. The method provides accurate and high temporal resolution measurements of the relationship between transpiration rate and xylem leaf water potential. A simple soil-plant hydraulic model describing the flow of water across the soil, root, and xylem was used to simulate the relationship between leaf water potential and transpiration rate. The experiments were carried out with 5-week-old maize grown in cylinders of 9 cm diameter and 30 cm height filled with silty soil. The measurements were performed at four different soil water contents (WC). The results showed that the relationship between transpiration and leaf water potential was linear in wet soils, but as the soil dried, the xylem tension increased, and nonlinearities were observed at high transpiration rates. Nonlinearity in the relationship between transpiration and leaf water potential indicated a decrease in the soil-plant hydraulic conductance, which was explained by the loss of hydraulic conductivity around the roots. The hydraulic model well reproduced the observed leaf water potential. Parallel experiments performed with plants not being pressurized showed that plants closed stomata when the soil-plant hydraulic conductance decreased, maintaining the linearity between leaf water potential and transpiration rate. We conclude that stomata closure during soil drying is caused by the loss of soil hydraulic conductivity in a predictable way.
The fast development of deep-ocean engineering equipment requires more deep-ocean pressure chambers (DOPCs) with a large inner diameter and ultra-high-pressure (UHP). Using the pre-stressed ...wire-wound (PSWW) concept, cold isostatic pressing (CIP) chambers have become a new concept of DOPCs, which can provide 100% performance of materials in theory. This paper aims to provide a comprehensive design process for a practical metal-made CIP chamber. First, the generalized design equations are derived by considering the fact that the cylinder and wire have different Young's moduli and Poisson's ratios. Second, to verify the theory and the reliability of the CIP chamber, the authors proposed a series of FEA models based on ANSYS Mechanical, including a two-dimensional (2D) model with the thermal strain method (TSM) and a three-dimensional (3D) model with the direct method (DM). The relative errors of the pre-stress coefficient range from 0.17% to 5%. Finally, the crack growth path is predicted by using ANSYS's Separating Morphing and Adaptive Remeshing Technology (SMART) algorithm, and the fatigue life is evaluated by using the unified fatigue life prediction (UFLP) method developed by the authors' group. This paper provides a more valuable basis to the design of DOPCs as well as to the similar pressure vessels than the previous work.
With long-term missions to Mars and beyond that would not allow resupply, a self-sustaining Bioregenerative Life Support System (BLSS) is essential. Algae are promising candidates for BLSS due to ...their completely edible biomass, fast growth rates and ease of handling. Extremophilic algae such as snow algae and halophilic algae may also be especially suited for a BLSS because of their ability to grow under extreme conditions. However, as indicated from over 50 prior space studies examining algal growth, little is known about the growth of algae at close to Mars-relevant pressures. Here, we explored the potential for five algae species to produce oxygen and food under low-pressure conditions relevant to Mars. These included
Chloromonas brevispina
,
Kremastochrysopsis austriaca
,
Dunaliella salina
,
Chlorella vulgaris
, and
Spirulina plantensis
. The cultures were grown in duplicate in a low-pressure growth chamber at 670 ± 20 mbar, 330 ± 20 mbar, 160 ± 20 mbar, and 80 ± 2.5 mbar pressures under continuous light exposure (62–70 μmol m
–2
s
–1
). The atmosphere was evacuated and purged with CO
2
after sampling each week. Growth experiments showed that
D. salina, C. brevispina
, and
C. vulgaris
were the best candidates to be used for BLSS at low pressure. The highest carrying capacities for each species under low pressure conditions were achieved by
D. salina
at 160 mbar (30.0 ± 4.6 × 10
5
cells/ml), followed by
C. brevispina
at 330 mbar (19.8 ± 0.9 × 10
5
cells/ml) and
C. vulgaris
at 160 mbar (13.0 ± 1.5 × 10
5
cells/ml).
C. brevispina, D. salina
, and
C. vulgaris
all also displayed substantial growth at the lowest tested pressure of 80 mbar reaching concentrations of 43.4 ± 2.5 × 10
4
, 15.8 ± 1.3 × 10
4
, and 57.1 ± 4.5 × 10
4
cells per ml, respectively. These results indicate that these species are promising candidates for the development of a Mars-based BLSS using low pressure (∼200–300 mbar) greenhouses and inflatable structures that have already been conceptualized and designed.
The simultaneous reduction of fuel consumption and pollutant emissions such as Nitrogen oxides (NOx) and soot remains the primary goal of modern engine development. In this context, Low Temperature ...Combustion (LTC) concepts are considered promising approaches. The so-called Reactivity Controlled Compression Ignition (RCCI) combustion process is one of these LTC concepts. RCCI combustion with two differently reactive fuels enables highly efficient combustion while reducing NOx and soot raw emissions compared to conventional combustion processes. RCCI combustion is significantly affected by the thermodynamical conditions in the combustion chamber (i.e., pressure and temperature), by the injection parameters (i.e., injection duration, timing, and offset), and by the reactivity of the fuels. It is very important to understand how these parameters affect the mixture formation in RCCI combustion and consequently the engine efficiency and emissions.
This paper therefore focuses on the analysis of RCCI mixture formation and combustion. To this end, optical fuel injection investigations were performed in a High Pressure Chamber (HPC) under steady-state conditions to gain in-depth insights into the fuel spray propagation and mixture formation of the differently reactive fuels. Ethanol (low reactivity fuel) and diesel (high reactivity fuel) were used in the study. The results from the optical investigations showed that RCCI combustion is very sensitive to the chamber temperature and that a small increase in temperature change leads to a significant reduction in the Ignition Delay (ID) and results in early combustion. The reactivity gradients and concentrations are governed by the injection timing and duration of the low and high reactivity fuels, and also the offset between them. It was found that with increased chamber pressure, the Liquid Penetration Length (LPL) and the ID decrease. However, there is no impact on the Gaseous Penetration Length (GPL). The results from the optical HPC investigations were used to calibrate the spray model for the numerical simulations of RCCI combustion. The calibrated spray models agree well with the experimental data regarding LPL and GPL for ethanol and diesel fuel, indicating that they are well calibrated.
•RCCI combustion in the High Pressure Chamber (HPC) was successfully achieved for diesel and ethanol fuel.•The optical studies showed that RCCI combustion is very sensitive to changes in the chamber temperature.•Variations in injection duration and injection offset have a significant effect on the reactivity of mixture inside the HPC.•The LPL and GPL data from the numerical 3D-CFD simulations matches well with the experimental data form HPC.
Laser-induced breakdown spectroscopy (LIBS) has been proven to be an attractive technique for in situ oceanic applications. However, when applying LIBS into deep-sea, the pressure effect caused by ...different ocean depths is inescapable and could have great influence on the LIBS signals. In this work, spectral characteristics of underwater LIBS were investigated as a function of pressure in the range of 0.1-45 MPa. A high-pressure chamber built in the laboratory was used to simulate the high-pressure deep-sea environment. Optimal laser energy and detection delay were first determined under different pressure conditions and were shown to be independent of the external pressure. The increase in pressure has a significant impact both on the peak intensity and line broadening of the observed spectra. The peak intensity of Na, Li and K lines increases with the increasing pressure until a maximum intensity is reached at 12.5 MPa. Above this value, the peak intensity decreases gradually up to 45 MPa. For Ca line, the maximum intensity was observed at 30 MPa. The line broadening keeps constant at low pressures from 0.1-10 MPa, while it increases linearly at higher pressures, indicating a higher electron density caused by the compression effect of the high external pressure. We also compared the spectral data obtained from the high-pressure chamber and from the field sea trials, and the good consistency between the laboratory data and sea-trial data suggested the key role of pressure effect on underwater LIBS signals for practical deep-sea applications.
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