High Temporal Resolution Measurements Research Articles

Technical note: Long-term probe misalignment and proposed quality control using the heat pulse method for transpiration estimations

Abstract. Transpiration is a crucial component in the hydrological cycle and a key parameter in many disciplines like agriculture, forestry, ecology and hydrology. Sap flow measurements are one of the most widely used approaches to estimate whole-plant transpiration in woody species; this is due to their applicability in different environments and in a variety of species as well as the fact that continuous high temporal resolution measurements of this parameter are possible. Several techniques have been developed and tested under different climatic conditions and using different wood properties. However, the scientific literature also identifies considerable sources of error when using sap flow measurements that need to be accounted for, including probe misalignment, wounding, thermal diffusivity and stem water content. This study aims to explore probe misalignment as a function of time in order to improve measurements during long-term field campaigns (>3 months). The heat ratio method (HRM) was chosen because it can assess low and reverse flows. Sensors were installed in four Pinus halepensis trees for 20 months. The pines were located in a coastal valley in south-eastern Spain (39∘57′45′′ N 1∘8′31′′ W) that is characterised by a Mediterranean climate. We conclude that even small geometrical misalignments in the probe placement can create a significant error in sap flow estimations. Additionally, we propose that new statistical information should be recorded during the measurement period which can subsequently be used as a quality control of the sensor output. The relative standard deviation and slope against time of the averaged v1v2 were used as quality indicators. We conclude that no general time limit can be set regarding the longevity of the sensors, and this threshold should rather be determined from individual performance over time.

Simultaneous 2D filtered Rayleigh scattering thermometry and stereoscopic particle image velocimetry measurements in turbulent non-premixed flames

The current work presents simultaneous high-resolution temperature and three-component velocity measurements taken in a series of turbulent (Re = 10,000, 20,000, and 30,000) piloted, non-premixed jet flames using filtered Rayleigh scattering (FRS) thermometry and stereoscopic particle image velocimetry (sPIV). This manuscript details the experimental approach with a key focus on the experimental protocol and specific challenges unique to simultaneous single-shot FRS/sPIV measurements in turbulent non-premixed flames. Specific areas of discussion include the experimental particle scattering rejection for FRS measurements, elimination of signal “crosstalk” between FRS and PIV channels, tracer particle selection, data processing for noise removal, and spatial resolution for both the temperature and velocity measurements. Sample joint temperature/velocity fields are presented highlighting interactions between the flow turbulence and the temperature fields, and a detailed statistical assessment of the temperature and velocity measurements demonstrates the quantitative nature of the results. Dissipation spectra from the measured temperature and velocity fluctuations are used to assess the true spatial resolution of the measurements. Results indicate that the sPIV measurements are resolved well into the dissipative range and the highest spatial frequencies (smallest dissipative scales) are resolved for the temperature measurements under all flame cases and measurement locations. The current joint FRS/sPIV approach enables the first simultaneous single-shot temperature/velocity imaging in turbulent non-premixed flames.

Convection velocity of temperature fluctuations in a natural convection boundary layer

Measurements of instantaneous temperature are carried out in a natural convection boundary layer (NCBL) developing over a vertical hot plate using a combination of an infra-red sensor, three cold-wire probes and a Resistance Temperature device (RTD). The aim of this study is to establish experimental procedures for high spatial and temporal resolution temperature measurements, and use that information to measure the convective speed of thermal structures in the flow. The evolution of NCBL along the hot plate is compared against existing empirical models. Statistics of mean and fluctuating temperature are in excellent agreement with the previously reported experimental data for a turbulent NCBL. The boundary layer thickness is observed to grow as y0.45, where y is the vertical distance along the heated plate. Separate experiments are conducted by varying the heat input to investigate its effect on convection velocity (Uc) of thermal structures in the flow. It is found that Uc remained nominally constant in the region 0 ≤ x ≤ δT/2 (δT is the thickness of thermal boundary layer) and decreased in a log-linear fashion in the outer region of NCBL. The results of Uc are found to be consistent with the shadowgraph measurements carried out in the same test rig, and the normalised convection velocity, Uc*=UcδTν is found to depend on Rayleigh number as Uc*∝Ra0.82, where ν is the kinematic viscosity of air. Importantly, these experimental observations are in agreement with the three layer model put forth by Wells and Worster (2008).

Relaxation of Wind Stress Drives the Abrupt Onset of Biological Carbon Uptake in the Kerguelen Bloom: A Multisensor Approach

AbstractWe deployed sensors for physical and biogeochemical measurements on one Eulerian mooring and two Lagrangian biogeochemical Argo floats on the Kerguelen Plateau. High temporal and vertical resolution measurements revealed an abrupt shoaling of both the mixed‐layer depth and mixing‐layer depth. The sudden stratification was concomitant with the start of significant biological activity detected by chlorophyll‐a accumulation, oxygen oversaturation, and dissolved inorganic carbon drawdown. The net community production computed in the mixing‐layer during the onset period of 9 days was 119 ± 7 mmol·m−2·day−1. While it is generally admitted that bloom initiation is mostly driven by the onset of positive heat fluxes, our results suggest that this is not a sufficient condition. Here we report that the decrease in the depth over which wind mixes the upper layer drives the initiation of the bloom. These results suggest that future atmospheric changes in Southern Ocean could impact the phenology of the blooms.

Experimental Study of the Formation of Three-Dimensional Waves from a Two-Dimensional Solitary Wave on Vertically Falling Liquid Films

The decay of a two-dimensional solitary wave into three-dimensional waves in film flow along a vertical plate has been studied using a high-speed laser-induced fluorescence technique that allows high spatial and temporal resolution measurements of the thickness of wave liquid films. It has been shown that the three-dimensional wave packet resulting from the decay of a two-dimensional solitary wave has a strong perturbing effect on the falling film and leads to the formation of rivulets on its surface.

Resolving the relative contributions of cistern and pour flushing to toilet water usage: Measurements from urban test sites in India

A challenge in water reuse for toilet flushing in India and other Asian countries derives from pour flushing practices. It is a common assumption that the amount of pour flushed water used for personal cleansing is small in comparison to the cistern flush volume, however there is a knowledge gap regarding the actual contribution of each water source to the blackwater amount. In this study, digital water meters were used to measure the fraction of water from personal wash tap relative to cistern water that is used for toilet flushing. High temporal resolution measurements were carried in three different urban sites in the city of Coimbatore in the southern Indian state of Tamil Nadu where onsite sanitation treatment prototypes that may provide reclaimed water for cistern flushing are being tested. Data collected over periods of up to 2 months show that the contribution of the cistern flush to the total blackwater volume is low (14–40%). These data highlight an important factor to inform interventions designed around water reuse for flushing in world geographies where personal toilet cleansing by water is the common practice.

Source apportionment of hourly-resolved ambient volatile organic compounds: Influence of temporal resolution

High temporal-resolution VOC concentration data can provide detailed and important temporal variations of VOC species and emission sources, which is not possible when using coarse temporal-resolution data. In this study, we utilized the positive matrix factorization (PMF) model to conduct source apportionment of hourly concentrations of nineteen VOC species and CO measured at the Mong Kok air quality monitoring station, operated by the Hong Kong Environmental Protection Department, from January 2013 to December 2014. The PMF analysis of the hourly dataset (PMF_Hourly) identified five sources, including liquefied petroleum gas (LPG) (contribution of 45%), gasoline exhaust (21%), combustion (20%), biogenic emission (9%), and paint solvents (6%). The diurnal patterns of VOC emissions from identified sources are likely to be affected by the strength of emissions, variation of the planetary boundary layer height, and photochemical reactions. In addition, the PMF analyses of hourly and 24-hour averaged data of the hourly-resolved data (PMF_Hourly and PMF_Daily) were generally comparable, but the time series of VOC emissions from PMF_Hourly could not be well captured by PMF_Daily for two local VOC sources of gasoline exhaust and LPG. This study highlights the benefit of high temporal-resolution measurement data in apportioning VOC sources, hence providing critical information on VOC emission sources (e.g., diurnal variations) for controlling VOC emissions effectively.

High temporal resolution and polarization resolved fluorescence lifetime measurements through stimulated emission

We have implemented polarization-resolved fluorescence lifetime measurement through stimulated emission based pump-probe technique, which promises much higher temporal resolution (∼4 ps) than conventional time-correlated single-photon counting (TCSPC). The depolarization of ATTO 647N fluorescent dye is resolved through anisotropy fluorescence lifetime measurements, with variable time delay introduced between the pump and the probe beams. Importantly, the polarization anisotropy measurement and the corresponding rotational correlation time characterization of the fluorescent dye are carried out at various temperatures. We have also demonstrated the need of high temporal resolution via hetero Förster energy transfer (Hetero-FRET) through the interaction between the gold nanorods (GNRs) and the fluorescent dye ATTO 647N. Notably, our results compare highly favorably with conventional TCSPC method, which is rather limited in temporal resolution, for the above characterization. Additionally, this technique is applicable even under ambient light while being very cost-effective and robust.

Reduction in lumen area is associated with the δ18O exchange between sugars and source water during cellulose synthesis

High temporal resolution measurements of wood anatomy and the isotopic composition in tree-rings have the potential to enhance our interpretation of climate variability, but the sources of variation within the growing season are still not well understood. Here we test the response of wood anatomical features in Pinus ponderosa and Pseudotsuga menziesii, including cell-wall thickness (CWT) and lumen area (LA), along with the oxygen isotopic composition of α-cellulose (δ18 Ocell ) to shifts in relative humidity (RH) in two treatments, one from high-low RH and the second one form low-high RH. We observed a significant decrease in LA and a small increase in CWT within the experimental growing season in both treatments. The measured δ18 Ocell along the ring was responsive to RH variations in both treatments. However, estimated δ18 Ocell did not agree with measured δ18 Ocell when the proportion of exchangeable oxygen during cellulose synthesis (Pex ) was kept constant. We found that Pex increased throughout the ring as LA decreased. Based on this varying Pex within an annual ring, we propose a targeted sampling strategy for different hydroclimate signals: earlier season cellulose is a better recorder of RH while late-season cellulose is a better recorder of the source water.

Mixing Rates and Bottom Drag in Bering Strait

AbstractThree shipboard survey lines were occupied in Bering Strait during autumn of 2015, where high-resolution measurements of temperature, salinity, velocity, and turbulent dissipation rates were collected. These first-reported turbulence measurements in Bering Strait show that dissipation rates here are high even during calm winds. High turbulence in the strait has important implications for the modification of water properties during transit from the Pacific Ocean to the Arctic Ocean. Measured diffusivities averaging 2 × 10−2 m2 s−1 are capable of causing watermass property changes of 0.1°C and 0.1 psu during the ~1–2-day transit through the narrowest part of the strait. We estimate friction velocity using both the dissipation and profile methods and find a bottom drag coefficient of 2.3 (±0.4) × 10−3. This result is smaller than values typically used to estimate bottom stress in the region and may improve predictions of transport variability through Bering Strait.

High-Resolution, In Situ Monitoring of Stable Isotopes of Water Revealed Insight into Hydrological Response Behavior

High temporal resolution (20-min intervals) measurements of stable isotopes from groundwater, stream water and precipitation were investigated to understand the hydrological response behavior and control of precipitation and antecedent wetness conditions on runoff generation. Data of 20 precipitation events were collected by a self-sufficient mobile system for in situ measurements over four months in the Schwingbach Environmental Observatory (SEO, temperate climate), Germany. Isotopic hydrograph separation indicated that more than 79% of the runoff consisted of pre-event water. Short response times of maximum event water fractions in stream water and groundwater revealed that shallow subsurface flow pathways rapidly delivered water to the stream. Macropore and soil pipe networks along relatively flat areas in stream banks were likely relevant pathways for the rapid transmission of water. Event water contribution increased with increasing precipitation amount. Pre-event water contribution was moderately affected by precipitation, whereas, the antecedent wetness conditions were not strong enough to influence pre-event water contribution. The response time was controlled by mean precipitation intensity. A two-phase system was identified, at which the response times of stream water and groundwater decreased after reaching a threshold of mean precipitation intensity of 0.5 mm h−1. Our results suggest that high temporal resolution measurements of stable isotopes of multiple water sources combined with hydrometrics improve the understanding of the hydrological response behavior and runoff generation mechanisms.

Characterisation of atmospheric pollution near an industrial site with a biogas production and combustion plant in southern Italy

Although biogas production can have some benefits, there is a research gap on potential influence of biogas plant emissions on local air quality, thus an accurate and comprehensive evaluation of impacts of this technology is needed. This study deals with this issue by means of a characterisation of air pollution near an industrial area including a biogas production (from biomass) and combustion plant located in South Italy. The methodology consists in advanced statistical analysis on concentration of gaseous pollutants, particles concentration and size distribution in number and mass, and PM2.5 chemical composition. High-temporal resolution measurements, supported by ancillary meteorological parameters, and source apportionment of PM2.5 using Positive Matrix Factorization (PMF) receptor model, are performed. The integrated approach provides the emissive picture consisting in different anthropogenic sources (i.e. traffic, biomass burning, and industrial facilities) with particular focus on biogas plant emissions. Results showed that CO and nitrogen oxides were influenced by vehicular traffic and biomass combustion, however, a contribution of the plant to NO was observed. SO2 was influenced mainly by transport from the industrial zone, but a second local contribution compatible with the emissions of the biogas plant was detected. Number particle concentrations were analysed in four size ranges: nanoparticles (D < 0.05 μm), ultrafine particles (D < 0.3 μm), accumulation (0.3 < D < 1 μm) and coarse particles (D > 1 μm). Nanoparticles and ultrafine particles were mainly influenced by vehicular traffic and biomass burning, instead, a contribution of the plant was individuated in the accumulation mode. PMF5 identified the contribution of six sources: crustal (14.7% ± 2.1% of measured PM2.5); marine aerosol (aged) (12.9% ± 2.3%); biomass burning (32.8% ± 1.4%); secondary sulphate (19.7% ± 2.4%); primary industrial emissions (5.4% ± 2.3%); traffic and secondary nitrate (17.0% ± 3.9%). The plant is likely to contribute to both sources, the industrial and the traffic plus secondary nitrate.

A kinetic method for measuring agonist efficacy and ligand bias using high resolution biosensors and a kinetic data analysis framework

The kinetics/dynamics of signaling are of increasing value for G-protein-coupled receptor therapeutic development, including spatiotemporal signaling and the kinetic context of biased agonism. Effective application of signaling kinetics to developing new therapeutics requires reliable kinetic assays and an analysis framework to extract kinetic pharmacological parameters. Here we describe a platform for measuring arrestin recruitment kinetics to GPCRs using a high quantum yield, genetically encoded fluorescent biosensor, and a data analysis framework to quantify the recruitment kinetics. The sensor enabled high temporal resolution measurement of arrestin recruitment to the angiotensin AT1 and vasopressin V2 receptors. The analysis quantified the initial rate of arrestin recruitment (kτ), a biologically-meaningful kinetic drug efficacy parameter, by fitting time course data using routine curve-fitting methods. Biased agonism was assessed by comparing kτ values for arrestin recruitment with those for Gq signaling via the AT1 receptor. The kτ ratio values were in good agreement with bias estimates from existing methods. This platform potentially improves and simplifies assessment of biased agonism because the same assay modality is used to compare pathways (potentially in the same cells), the analysis method is parsimonious and intuitive, and kinetic context is factored into the bias measurement.

Sensor Array Enables Accurate Profiling of Produced Fluids During Drillstem Tests

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 29749, “Determining Produced-Fluid Properties for Accurate Production Profiling During a Drillstem Test Using Thermal-Imaging Technology,” by David Lavery and David Fyfe, Metrol, and Abu Rashid Hasan, SPE, Texas A&amp;M University, prepared for the 2019 Offshore Technology Conference Brasil, Rio de Janeiro, 29–31 October. Copyright 2019 Offshore Technology Conference. Reproduced by permission. This paper describes the use of a downhole temperature-sensor array during a commingled drillstem test (DST) to determine the density of produced fluids accurately. In a typical DST that uses only downhole pressure gauges, any fluid contacts between the pressure gauges would be missed and the produced-fluid density calculated would be erroneous. The complete paper demonstrates the importance of taking fluid properties into account when determining the zonal flow-rate contributions using the mass-enthalpy method. Introduction Downhole temperature-sensor-array data provide accurate fluid contact depths during buildup periods of the DST that typically cannot be observed in pressure gradients. Determination of these fluid contacts permits the calculation of individual produced-fluid densities. In a case study described in the complete paper, the deepest perforated zone produced a fluid with a higher density than that seen in shallower perforated intervals. The higher density of the produced brine caused the wellbore fluids to slug during the flow periods with a measurable response in pressure and temperature data. If this difference in the fluid properties is not taken into account, zonal-allocation flow rate will be in error because it relies on density and specific heat capacity. Qualitative assessment of the temperature-array data identified producing zones and clearly highlighted different fluid interfaces in detail that would remain hidden if the pressure gauges were relied upon solely. High-Resolution Temperature Measurement During DST Operations The deployment of the downhole temperature-sensor array during DSTs provides an in-depth look into reservoir characteristics that go beyond traditional downhole pressure-gauge measurements. The temperature sensors, contained within steel tubing and clamped to the outside of the tubing-conveyed perforating guns, cover the three perforated intervals in this case study. Two temperature sensor arrays were run, each with a sensor spacing of 0.6 m and offset with an effective sensor spacing of 0.3 m. Throughout the DST, the readings from the temperature sensor arrays were recorded on downhole memory devices at 1-minute intervals. The temperature measurement covered the entire perforated interval. High-resolution pressure gauges are placed above and below the perforated interval and above and below the tester valve. Using an acoustic communication system, real-time temperature and pressure data were available during the DST so that observations across the entire test could be made. Zonal Allocation of Produced Reservoir Fluids From Mass-Enthalpy Balance The mass-enthalpy method of calculating zonal contributions relies on intervals higher in the wellbore producing at a lower temperature than deeper producing intervals. The higher- temperature contributions from the deepest producing intervals will flow up the wellbore while losing some heat to the colder wellbore. The rate of cooling is dependent on the flow velocity. The shallower producing intervals contribute at a lower temperature than the mixture and will cool down the mixture. This method is detailed in the complete paper.

Transpiration Reduction in Maize (Zea mays L) in Response to Soil Drying.

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.

Retrieval of cloud top properties from advanced geostationary satellite imager measurements based on machine learning algorithms

The cloud-top height (CTH) product derived from passive satellite instrument measurements is often used to make climate data records (CDR). CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) provides CTH parameters with high accuracy, but with limited temporal-spatial resolution. Recently, the Advanced Himawari Imager (AHI) onboard Japanese Himawari-8/-9, provides high temporal (every 10 min) and high spatial (2 km at nadir) resolution measurements with 16 spectral bands. This paper reports on a study to derive the CTH from combined AHI and CALIPSO using advanced machine learning (ML) algorithms with better accuracy than that from the traditional physical (TRA) algorithms. We find significant CTH improvements (1.54–2.72 km for mean absolute error, MAE) from four different machine learning algorithms (original MAE from TRA method is about 3.24 km based on CALIPSO data validation), particularly in high and optically thin clouds. In addition, we also develop a joint algorithm to combine optimal machine learning and traditional physical (TRA) algorithms of CTH to further reduce MAE to 1.53 km and enhance the layered accuracy (CTH < 18 km). While the ML-based algorithm improves CTH retrieval over the TRA algorithm, the lower or higher clouds still exhibit relatively large uncertainty. Combining both methods provides the better CTH than either alone. The combined approach could be used to process data from advanced geostationary imagers for climate and weather applications.

Evaluation of Second-Hand Exposure to Electronic Cigarette Vaping under a Real Scenario: Measurements of Ultrafine Particle Number Concentration and Size Distribution and Comparison with Traditional Tobacco Smoke.

The present study aims to evaluate the impact of e-cig second-hand aerosol on indoor air quality in terms of ultrafine particles (UFPs) and potential inhalation exposure levels of passive bystanders. E-cig second-hand aerosol characteristics in terms of UFPs number concentration and size distribution exhaled by two volunteers vaping 15 different e-liquids inside a 49 m3 room and comparison with tobacco smoke are discussed. High temporal resolution measurements were performed under natural ventilation conditions to simulate a realistic exposure scenario. Results showed a systematic increase in UFPs number concentration (part cm−3) related to a 20-min vaping session (from 6.56 × 103 to 4.01 × 104 part cm−3), although this was one up to two order of magnitude lower than that produced by one tobacco cigarette consumption (from 1.12 × 105 to 1.46 × 105 part cm−3). E-cig second-hand aerosol size distribution exhibits a bimodal behavior with modes at 10.8 and 29.4 nm in contrast with the unimodal typical size distribution of tobacco smoke with peak mode at 100 nm. In the size range 6–26 nm, particles concentration in e-cig second-hand aerosol were from 2- (Dp = 25.5 nm) to 3800-fold (Dp = 9.31 nm) higher than in tobacco smoke highlighting that particles exhaled by users and potentially inhaled by bystanders are nano-sized with high penetration capacity into human airways.

High temporal resolution measurements of ammonia emissions following different nitrogen application rates from a rice field in the Taihu Lake Region of China

Ammonia emission is one of the dominant pathways of nitrogen fertilizer loss from rice fields in China. It is difficult to measure ammonia emissions by high-frequency sampling with the chamber methods widely used in China, which is of great significance for investigating the environmental effects on the ammonia emissions. The chamber methods also can not accurately determine the ammonia emissions. In this study, the backward Lagrangian stochastic dispersion model, with ammonia concentrations continuously measured by the open-path tunable diode laser absorption spectroscopy technique, was used to determine ammonia emissions from a rice field after fertilizer application at excessive (270 kg N ha−1) and appropriate (210 kg N ha−1) rates in the Taihu Lake Region of China. High temporal resolution measurements of ammonia emissions revealed that high intraday fluctuations of ammonia emissions were significantly affected by the meteorological conditions. Multiple regression analysis showed a dominant solar radiation dependence of intraday ammonia emission cycles, especially during the rice panicle formation stage. The NH4+-N concentrations of the surface water of the rice field were found to be the decisive factor that influenced interday dynamics of ammonia emissions. Accurate quantifications of ammonia emissions indicated that the total ammonia losses under appropriate nitrogen application rate were 27.4 kg N ha−1 during the rice tillering stage and 11.2 kg N ha−1 during the panicle formation stage, which were 29.4% and 17.0% less than those under traditional excessive nitrogen application rate used by the local farmers, respectively. The ammonia loss proportions during the rice panicle formation stage were significantly lower than those of the tillering stage, which might be due to different nitrogen application rates and environmental effects during the two stages. This study indicated that the open-path tunable diode laser absorption spectroscopy technique could facilitate the investigation of high temporal resolution dynamic of ammonia emissions from farmland and the environmental influence on the ammonia emissions.

Thermal imaging as a noninvasive technique for analyzing circadian rhythms in plants.

Endogenous (˜24 circadian) rhythms control an enormously diverse range of processes in plants and are, increasingly, the target of studies aimed at understanding plant performance. Although in the previous few decades most plant circadian research has focused on Arabidopsis, there is a pressing need for low-cost, high-throughput tools for analyzing rhythms in a wider variety of species. The present contribution investigates using circadian temperature oscillations as a novel marker for assaying plant circadian rhythms. A thermal imaging platform was set up to measure diel and circadian rhythms in different plant species, in wild-type and circadian mutant plants, and in leaves and flowers. Results from the thermal imaging technique were compared with those from other established circadian assay techniques. All of the dicot and monocot species examined showed robust circadian rhythms of leaf surface temperature; the effects of circadian mutations on thermocycles were similar to those reported using other techniques. In Petunia×atkinsiana plants circadian oscillations were observed in both leaves and flowers. Thermal imaging is an extremely useful technique for analyzing circadian rhythms in plants. It is predicted that the ability to make very high temporal resolution measurements may facilitate the discovery of novel aspects of circadian control.

An NMR-based investigation of pore water freezing process in sandstone

Understanding the freezing pattern of pore water is the basis for revealing the mechanisms of frost damage in porous rocks. We employed low-field nuclear magnetic resonance method, aided by high-resolution temperature measurements, to investigate the pore water freezing process of in sandstone. Samples were prepared with nine degrees of initial saturation (20% to 100% at 10% intervals). The results indicate the following: 1) pore water in fully-saturated sandstone consists of bound water, capillary water and bulk water. Bound water forms the majority (76%), followed by capillary water (14%) and bulk water (10%). 2) A significant amount of pore water remains unfrozen at −20 °C, which is basically bound water. 3) Supercooling of pore water is distinct in samples with saturation degrees ≧70%. 4) The exotherm of rock temperature declines as the saturation degree decreases, it becomes undetectable in samples with saturation degrees ˂70%. Following further investigation of the variation of each fraction of pore water fully-saturatedduring freezing, we suggest that: 1) The entire freezing process can be broadly divided into four stages: supercooling, repid-freezing stage, stable-freezing and ceasing of freezing. 2) Small pores preferentially freeze before larger ones during the rapid-freezing stage. 3) The initial saturation degree significantly influences the pore water freezing process by determining the fraction of pore water. This study sheds new light on the pore water freezing pattern in sandstone, providing novel ideas for the analysis of frost damage mechanisms in porous rocks.