Tracer Measurements Research Articles

1916-P: Postprandial Glucagon Metabolism in Healthy Subjects: Use of 13C 15N Glucagon

Glucagon metabolism in humans is poorly understood and is currently under active investigation. We have recently developed a new isotope dilution method using nonradioactive, stable human glucagon (Phe 6 13C9, 15N; Phe 22 13C9, 15N) tracer to measure glucagon fluxes. To estimate postprandial glucagon turnover using this novel technique, we present data from the first 5 healthy subjects (3 males, age 26.2±7.9 years, BMI 25.4±2.6 kg/m2, fasting plasma glucose 4.7±0.2 mM, HbA1c 5.1±0.2 %) done thus far. After IRB approval and informed consent, subjects presented to the clinical research unit in the morning after an overnight fast. A catheter was inserted in a forearm vein for glucagon tracer infusion and another catheter placed in the contralateral hand and the hand kept in a heated box for periodic draws of arterialized venous samples for measurements of glucagon tracer (tandem mass spectrometry), glucagon and glucose concentrations during the study. A mixed meal (75 grams carb, 15% protein, 35% fat; 8 kcal/kg) was ingested at time 0 and the glucagon tracer infusion rate adjusted to mimic the anticipated changes in postprandial circulating glucagon concentrations for 6 hours. Systemic glucagon appearance rate (Ra glucagon) was calculated by the isotope dilution method. Fig 1 shows the Ra glucagon in all subjects. These initial data show that postprandial glucagon turnover can be calculated in humans applying this novel technique. Disclosure F. Ruchi: None. Y.R. Yadav: None. D. Romeres: None. S. Sawleh: None. L.M. Benson: None. K.L. Johnson: None. M. Schiavon: None. C. Dalla Man: Research Support; Self; Sanofi-Aventis Deutschland GmbH. C. Cobelli: None. D.J. McCormick: None. R. Basu: Consultant; Self; GENFIT. Research Support; Self; AstraZeneca. A. Basu: Consultant; Spouse/Partner; GENFIT. Research Support; Spouse/Partner; AstraZeneca. Funding National Institutes of Health (R01DK029953 to R.B.), (R01DK085516 to A.B.), (DK059637, DK020593)

Ventilation in the Arctic Ocean and the Role of Pacific Inflow Deduced From Transient Tracer Measurements

AbstractDuring the seventh Chinese National Arctic Research Expedition, measurements of CFC‐12 and SF6 were used to estimate ventilation time scales and anthropogenic CO2 (Cant) concentrations in the Arctic Ocean and Bering Sea based on the transit time distribution (TTD) method. The profile distribution showed that there was a high CFC tongue entering through the Canada Basin in the intermediate layer (27.6 kg m−3 < σθ < 28 kg m−3), at latitudes between 75 and 85°N, related to the inflow of Atlantic water. The result shows that both intermediate and deep/bottom waters are better ventilated in the Arctic Ocean than in the Bering Sea. The mean age gradient of the Bering Sea Surface Water and Pacific water core of the southwest Canada Basin (24.7 < σθ < 26.2) could be a consequence of intensive mixing and entrainment of the inflow water from the Bering Sea. An expected difference in age between these areas was interpreted to reflect the transit time for the given water layers. Thus, a mean transit time from the Bering Sea (175.2–179.9°E, 59.7–61.6°N) to the western Arctic Ocean (151.6–158°W, 73.1–74.8°N) of 14.6 ± 4.6 years was estimated. The mean Cant column inventory in the upper 2,000 m was higher (~45 mol m−2) in the Arctic Ocean than in the Bering Sea (~25 mol m−2).

Field study of atmospheric boundary layer observation in a hilly Gobi Desert region and comparison with the CALMET/CALPUFF model

Abstract A field campaign consisting of atmospheric boundary layer (ABL) observations and tracer experiments was conducted in September 2016 in a hilly region of the Gobi Desert in northwest China. High-frequency wind shears were observed between 70 and 200 m based on both 100-meter tower data and wind profiles. The ABL observations indicated that sub-layers of different atmospheric stability present within the ABL weakened the vertical transfer of momentum and tracer gas, resulting in low wind speed and high surface concentration. The CALMET model showed thermal heterogeneity to some extent in the temperature fields and mixing height distributions, and large deviations in the friction velocity between the model and observations were noted. The comparison of the CALPUFF model with the tracer measurements indicated a general tendency toward under-prediction of the concentration in the far distance because of wind shears and vertical thermal discontinuity. The results of the SCIPUFF model showed the same trend as those of CALPUFF, and comparisons demonstrated a good consistency of the two models.

A study of the data augmentation strategy for stochastic differential equations

ABSTRACTMultivariate stochastic differential equations (SDEs) are commonly used in many applications. Statistical inference based on discretely observed data requires estimating the transition density, which is unknown for most models. Typically, one would estimate the transition density and use the approximation for statistical inference. However, many estimation methods will fail when the observations are too sparse or when the SDE models have a hierarchical structure. In a Bayesian approach, we explore the posterior distribution of the SDE model parameters. In the Markov Chain Monte Carlo algorithm, we use data augmentation to understand how the approximation of the transition density affects the inference procedure. We give guidelines on balancing the computational demands with the need to provide reliable and accurate posterior inference. Simulations are used to evaluate these guidelines. We demonstrate these methods on the analysis of oceanography tracer measurements.

Using radon to quantify groundwater discharge and methane fluxes to a shallow, tundra lake on the Yukon-Kuskokwim Delta, Alaska

Northern lakes are a source of greenhouse gases to the atmosphere and contribute substantially to the global carbon budget. However, the sources of methane (CH4) to northern lakes are poorly constrained limiting our ability to the assess impacts of future Arctic change. Here we present measurements of the natural groundwater tracer, radon, and CH4 in a shallow lake on the Yukon-Kuskokwim Delta, AK and quantify groundwater discharge rates and fluxes of groundwater-derived CH4. We found that groundwater was significantly enriched (2000%) in radon and CH4 relative to lake water. Using a mass balance approach, we calculated average groundwater fluxes of 1.2 ± 0.6 and 4.3 ± 2.0 cm day−1, respectively as conservative and upper limit estimates. Groundwater CH4 fluxes were 7—24 mmol m−2 day−1 and significantly exceeded diffusive air–water CH4 fluxes (1.3–2.3 mmol m−2 day−1) from the lake to the atmosphere, suggesting that groundwater is an important source of CH4 to Arctic lakes and may drive observed CH4 emissions. Isotopic signatures of CH4 were depleted in groundwaters, consistent with microbial production. Higher methane concentrations in groundwater compared to other high latitude lakes were likely the source of the comparatively higher CH4 diffusive fluxes, as compared to those reported previously in high latitude lakes. These findings indicate that deltaic lakes across warmer permafrost regions may act as important hotspots for CH4 release across Arctic landscapes.

Tracer Measurements in Growing Sea Ice Support Convective Gravity Drainage Parameterizations

AbstractGravity drainage is the dominant process redistributing solutes in growing sea ice. Modeling gravity drainage is therefore necessary to predict physical and biogeochemical variables in sea ice. We evaluate seven gravity drainage parameterizations, spanning the range of approaches in the literature, using tracer measurements in a sea ice growth experiment. Artificial sea ice is grown to around 17 cm thickness in a new experimental facility, the Roland von Glasow air‐sea‐ice chamber. We use NaCl (present in the water initially) and rhodamine (injected into the water after 10 cm of sea ice growth) as independent tracers of brine dynamics. We measure vertical profiles of bulk salinity in situ, as well as bulk salinity and rhodamine in discrete samples taken at the end of the experiment. Convective parameterizations that diagnose gravity drainage using Rayleigh numbers outperform a simpler convective parameterization and diffusive parameterizations when compared to observations. This study is the first to numerically model solutes decoupled from salinity using convective gravity drainage parameterizations. Our results show that (1) convective, Rayleigh number‐based parameterizations are our most accurate and precise tool for predicting sea ice bulk salinity; and (2) these parameterizations can be generalized to brine dynamics parameterizations, and hence can predict the dynamics of any solute in growing sea ice.

Information‐Based Machine Learning for Tracer Signature Prediction in Karstic Environments

AbstractKarstic groundwater systems are often investigated by a combination of environmental or artificial tracers. One of the major downsides of tracer‐based methods is the limited availability of tracer measurements, especially in data sparse regions. This study presents an approach to systematically evaluate the information content of the available data, to interpret predictions of tracer concentration from machine learning algorithms, and to compare different machine learning algorithms to obtain an objective assessment of their applicability for predicting environmental tracers. There is a large variety of machine learning approaches, but no clear rules exist on which of them to use for this specific problem. In this study, we formulated a framework to choose the appropriate algorithm for this purpose. We compared four different well‐established machine learning algorithms (Support Vector Machines, Extreme Learning Machines, Decision Trees, and Artificial Neural Networks) in seven different karst springs in France for their capability to predict tracer concentrations, in this case SO42− and NO3−, from discharge. Our study reveals that the machine learning algorithms are able to predict some characteristics of the tracer concentration, but not the whole variance, which is caused by the limited information content in the discharge data. Nevertheless, discharge is often the only information available for a catchment, so the ability to predict at least some characteristics of the tracer concentrations from discharge time series to fill, for example, gaps or increase the database for consecutive analyses is a helpful application of machine learning in data sparse regions or for historic databases.

Surface Reaeration in Tropical Headwater Streams: the Dissolution Rate of a Soluble Floating Probe as a New Variable for Reaeration Coefficient Prediction

The reaeration coefficient (Ka20) is one of the main indicators of dissolved O2 movement to and from aquatic systems via the atmosphere. Direct gas tracer measurements, physical models, and models of O2 dynamics have been used for Ka20 estimation, especially in temperate aquatic ecosystems, with fewer examples in their tropical counterparts. Here we investigate a less commonly employed soluble floating probe (SFP) method, based on the dissolution rate of a soluble solid (VS20) as an auxiliary variable for Ka20 estimation. Our objectives were to test the SFP method for estimating Ka20, validate such estimates through the traditional gas tracer method, and develop empirical models for Ka20 prediction using VS20 and additional physical variables. Five reaches (with lengths from 20 to 250 m) of four tropical headwater streams were selected, and their main physical, hydrological, and hydraulic variables were measured in eight sampling periods. The gas tracer (using NaCl and SF6 tracers) and the SFP (spherical format made with oxalic acid dihydrate) methods were carried out in each reach. The Ka20 values ​​ranged from 16.94 to 373.79 days− 1 and the VS20 ranged from 0.079 to 0.778 mm min− 1. We observed a significant linear relationship between Ka20 and VS20. The best model (R2 = 0.78) combined the variables depth, Froude number, and VS20. Our study highlighted that models developed for temperate aquatic systems can underestimate Ka20 in tropical streams, bringing uncertainties for modeling metabolic rates, self-depuration capacity, or any other processes that depend on reaeration.

Urban Tracer Dispersion and Infiltration into Buildings Over a 2-km Scale

Field experiments were undertaken in the summer of 2015 in Manchester, UK, to investigate the dispersion behaviour and infiltration into buildings of gas-phase pollutants over horizontal distances of 1–5 km. Inert cyclic perfluorocarbon tracers were released for 15 min at either one or three release points and samples taken in locations indoors and outdoors up to 2 km downwind. Background measurements of these cyclic perfluorocarbons range between 5.6 and 12.6 parts per quadrillion (ppq). On most occasions, tracer concentrations are higher on the sixth floor than at ground level. Tracer concentrations persist in the least well-ventilated rooms after concentrations return to background levels outdoors. The highest tracer concentrations, 329 ppq above background, occur at dawn on 23 July from a sixth-floor sampling position during thermally stable conditions. At low wind speeds, tracer is detected upwind of the prevailing wind direction; on 24 July, tracer is detected to the north-west of the release point for north-north-east wind direction. A simple street network model does not predict tracer concentrations at low wind speeds over the km scales in this investigation due to tracer likely escaping the urban canopy. Predictions from a simple correlation model overestimate concentrations originating from distant sources, which is believed to be due to infiltration into buildings along the journey from source to receptor. A Gaussian plume model predicts the highest tracer concentrations for most receptor points on 23 July when the lowest Obukhov length of – 26 m was measured, agreeing with tracer measurements.

Effect of initial water flooding on the performance of polymer flooding for heavy oil production

In the domain of heavy to extra heavy oil production, viscous polymer may be injected after water injection (tertiary mode), or as an alternative (secondary mode) to improve the sweep efficiency and increase oil recovery. To prepare field implementation, nine polymer injection experiments in heavy oil have been performed at core scale, to assess key modelling parameters in both situations. Among this consistent set of experiments, two have been performed on reconstituted cylindrical sandpacks in field-like conditions, and seven on consolidated Bentheimer sandstone in laboratory conditions. All experiments target the same oil viscosity, between 2000 cP and 7000 cP, and the viscosity of Partially Hydrolyzed Polyacrylamide solutions (HPAM 3630) ranges from 60 cP to 80 cP. Water and polymer front propagation are studied using X-ray and tracer measurements. The new experimental results presented here for water flood and polymer flood experiments are compared with experiments described in previous papers. The effects of geometry, viscosity ratio, injection sequence on recoveries, and history match parameters are investigated. Relative permeabilities of the water flood experiment are in line with previous experiments in linear geometry. Initial water floods led to recoveries of 15–30% after one Pore Volume Injected (PVI), a variation influenced by boundary conditions, viscosity, and velocities. The secondary polymer flood in consolidated sandstone confirms less stable displacement than tertiary floods in same conditions. Comparison of secondary and tertiary polymer floods history matching parameters suggests two mechanisms. First, hysteresis effect during oil bank mobilization stabilizes the tertiary polymer front; secondly, the propagation of polymer at higher oil saturation leads to lower adsorption during secondary experiment, generating a lower Residual Resistance Factor (RRF), close to unity. Finally, this paper discusses the use of the relative permeabilities and polymer properties estimated using Darcy equation for field simulation, depending on water distribution at polymer injection start-up.

The Tumor Metabolic Microenvironment: Lessons from Lactate.

The extracellular milieu of tumors is generally assumed to be immunosuppressive due in part to metabolic factors. Here, we review methods for probing the tumor metabolic microenvironment. In parallel, we consider the resulting available evidence, with a focus on lactate, which is the most strongly increased metabolite in bulk tumors. Limited microenvironment concentration measurements suggest depletion of glucose and modest accumulation of lactate (less than 2-fold). Isotope tracer measurements show rapid lactate exchange between the tumor and circulation. Such exchange is catalyzed by MCT transporters, which cotransport lactate and protons (H+). Rapid lactate exchange seems at odds with tumor lactate accumulation. We propose a potential resolution to this paradox. Because of the high pH of tumor cells relative to the microenvironment, H+-coupled transport by MCTs tends to drive lactate from the interstitium into tumor cells. Accordingly, lactate may accumulate preferentially in tumor cells, not the microenvironment. Thus, although they are likely subject to other immunosuppressive metabolic factors, tumor immune cells may not experience a high lactate environment. The lack of clarity regarding microenvironmental lactate highlights the general need for careful metabolite measurements in the tumor extracellular milieu.

Methodology for improving reliability of river discharge measurements

Programs to monitor water characteristics are undertaken to identify any possible water pollution of a river. To compute reliable water pollution loads, accurate river discharge and pollutant/tracer concentrations are required. When pollutants/tracers are measured with sufficient precision, the accuracy of river discharge measurements becomes the most critical parameter of the pollutant load computation, as well as the largest error source. The absence of permanent measuring equipment in many rivers is a common difficulty for the implementation of monitoring programs. Alternatively, quick measurement methods which are low in cost and reliability (e.g. floats) are often employed to get an estimate of river discharges, when there are budgetary and time restrictions. In this paper, an original technique, mainly for use in ungauged rivers, is proposed for correcting river discharge measurements which have low levels of accuracy; this in turn would correct pollutant concentrations. A nonlinear optimization problem is developed based on water volume and pollutant mass conservation principles for river balance nodes, taking into consideration non-measurable latent quantities. Parallel measurements of discharge and tracers for representative cross-sections of a river and its tributaries are required. The measurement conditions should refer to the steady-state hydraulic conditions usually prevailing in the flow under consideration. In order to test the reliability of the method, a virtual river example is built, defining the real values of water characteristics and generating measurement sets via Monte-Carlo simulations combining random and systematic errors. For more than 92% of the generated measurement sets, the proposed technique results in a successful and acceptable correction for the total of the measured cross-sections. Finally, the method is applied to a real river and the measurements are corrected successfully.

Analytic reconstruction of a two-dimensional velocity field from an observed diffusive scalar

Inverting an evolving diffusive scalar field to reconstruct the underlying velocity field is an underdetermined problem. Here we show, however, that for two-dimensional incompressible flows, this inverse problem can still be uniquely solved if high-resolution tracer measurements, as well as velocity measurements along a curve transverse to the instantaneous scalar contours, are available. Such measurements enable solving a system of partial differential equations for the velocity components by the method of characteristics. If the value of the scalar diffusivity is known, then knowledge of just one velocity component along a transverse initial curve is sufficient. These conclusions extend to the shallow-water equations and to flows with spatially dependent diffusivity. We illustrate our results on velocity reconstruction from tracer fields for planar Navier–Stokes flows and for a barotropic ocean circulation model. We also discuss the use of the proposed velocity reconstruction in oceanographic applications to extend localized velocity measurements to larger spatial domains with the help of remotely sensed scalar fields.

Sensitivity of a continuous hot-melt extrusion and strand pelletization line to control actions and composition variation

The purpose of this work was to develop a robust hot-melt extrusion and strand pelletization process for manufacturing pellets with an immediate release (IR) of a poorly water-soluble active pharmaceutical ingredient (API), nimodipine. The robustness of pharmaceutical continuous manufacturing processes and of its control strategy is vital for competitiveness to traditional batch-manufacturing. Therefore, first the sensitivity of product quality, process stability, and process monitoring tools to i) parameter changes due to control actions and ii) typical process deviations, i.e., feeding errors, was investigated in a design of experiments (DoE). Thereby, die melt pressure was found to be highly sensitive to composition deviations, i.e. a limiting factor for process stability. Especially critical were deviations to increased HPMC content, since it behaved as a filler in the melt. Pelletization, or pellet size and size distribution respectively, were found to be sensitive to an increased throughput, due to the resulting insufficient strand cooling before the pelletizer. API dissolution in contrast, was found to be robust across the entire investigated range of formulation and process settings. Second, a design space for the production of IR pellets for subsequent tableting was established, and finally, a technical control strategy was developed to ensure a robust process. Near-infrared (NIR) spectroscopy was applied to monitor API content and the sensitivity of the residence time distribution (RTD) was investigated by means of tracer measurements. NIR-based API content monitoring and RTD models for material tracking were found to be at risk after processing melt with high HPMC content, due to a lack of purging by less viscous formulation compositions.

Associations between Aerobic Capacity, Hepatic Bile Acid Synthesis and Fecal Bile Acid Concentration in Humans

High aerobic capacity protects against a wide range of metabolic diseases and associates with changes in liver metabolism including enhanced mitochondrial function, although mechanisms remain unknown. Bile acids are now seen as active players in metabolic regulation. We have previously found that rodents with high aerobic capacity potentially have the ability to divert excess acetyl‐CoA away from de novo lipogenesis and toward bile acid synthesis and fecal excretion. To determine if the fitness‐bile acid association manifests in humans, in a preliminary study we tested the hypothesis that female subjects screened for high aerobic fitness (Hi‐Fit, n=10) (VO2peak>45 ml/kg/min) also have increased hepatic bile acid synthesis and fecal excretion compared to those matched for age and body mass with low aerobic fitness (Lo‐Fit, n=10) (VO2peak<35 ml/kg/min). Diet intake, activity level, stool, and blood were measured at baseline before receiving a 1 week standardized, weight‐maintaining eucaloric diet. After the 1week standardized diet, stool and blood were again measured, and an Oral Glucose Tolerance Test (OGTT) was performed. Hi‐fit women tended to have higher bile acid synthesis via measured serum 7α‐hydroxy‐4‐cholesten‐3‐one (C4), a clinically proven surrogate of bile acid production, both during fasting (p≈0.16) and following the OGTT (p≈0.06). However, no significant differences in circulating or fecal bile acid concentrations were found. Future research should consider using direct tracer measurements of bile acid synthesis and excretion, and the utilization of 24 hr+ fecal bile acid measures to quantify total production and excretion.Support or Funding InformationUSDA‐Agricultural Research Service Project 6026‐51000‐010‐05SThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Sparse Reconstruction of Glucose Fluxes Using Continuous Glucose Monitors

A new technique for estimating postprandial glucose flux profiles without the use of glucose tracers is proposed. A sparse vector space representation is first found for the space of plausible glucose flux profiles using sparse encoding. A Lasso formulation is then used to estimate the glucose fluxes that combines (1) known patient model parameters; (2) the vector space of plausible glucose flux profiles; (3) continuous glucose monitor measurements taken during the meal; (4) amount of insulin injected; (5) amount of meal carbohydrates; and (6) an estimate of the initial conditions. Three glucose fluxes are then estimated, namely; glucose rate of appearance from the intestine; endogenous glucose production from the liver; insulin dependent glucose utilization; and other important state variables. The simulation results show that the technique is capable of estimating the glucose fluxes with high accuracy, even for complex meal scenarios. The experimental results indicate that the technique is capable of reproducing the triple tracer measurements for three T1DM undergoing the triple tracer protocol while estimating the missing measurements for a certain model parameter selection.

Quantifying new water fractions and transit time distributions using ensemble hydrograph separation: theory and benchmark tests

Abstract. Decades of hydrograph separation studies have estimated the proportions of recent precipitation in streamflow using end-member mixing of chemical or isotopic tracers. Here I propose an ensemble approach to hydrograph separation that uses regressions between tracer fluctuations in precipitation and discharge to estimate the average fraction of new water (e.g., same-day or same-week precipitation) in streamflow across an ensemble of time steps. The points comprising this ensemble can be selected to isolate conditions of particular interest, making it possible to study how the new water fraction varies as a function of catchment and storm characteristics. Even when new water fractions are highly variable over time, one can show mathematically (and confirm with benchmark tests) that ensemble hydrograph separation will accurately estimate their average. Because ensemble hydrograph separation is based on correlations between tracer fluctuations rather than on tracer mass balances, it does not require that the end-member signatures are constant over time, or that all the end-members are sampled or even known, and it is relatively unaffected by evaporative isotopic fractionation. Ensemble hydrograph separation can also be extended to a multiple regression that estimates the average (or “marginal”) transit time distribution (TTD) directly from observational data. This approach can estimate both “backward” transit time distributions (the fraction of streamflow that originated as rainfall at different lag times) and “forward” transit time distributions (the fraction of rainfall that will become future streamflow at different lag times), with and without volume-weighting, up to a user-determined maximum time lag. The approach makes no assumption about the shapes of the transit time distributions, nor does it assume that they are time-invariant, and it does not require continuous time series of tracer measurements. Benchmark tests with a nonlinear, nonstationary catchment model confirm that ensemble hydrograph separation reliably quantifies both new water fractions and transit time distributions across widely varying catchment behaviors, using either daily or weekly tracer concentrations as input. Numerical experiments with the benchmark model also illustrate how ensemble hydrograph separation can be used to quantify the effects of rainfall intensity, flow regime, and antecedent wetness on new water fractions and transit time distributions.

100 Years of Progress in Ocean Observing Systems

AbstractThe history of over 100 years of observing the ocean is reviewed. The evolution of particular classes of ocean measurements (e.g., shipboard hydrography, moorings, and drifting floats) are summarized along with some of the discoveries and dynamical understanding they made possible. By the 1970s, isolated and “expedition” observational approaches were evolving into experimental campaigns that covered large ocean areas and addressed multiscale phenomena using diverse instrumental suites and associated modeling and analysis teams. The Mid-Ocean Dynamics Experiment (MODE) addressed mesoscale “eddies” and their interaction with larger-scale currents using new ocean modeling and experiment design techniques and a suite of developing observational methods. Following MODE, new instrument networks were established to study processes that dominated ocean behavior in different regions. The Tropical Ocean Global Atmosphere program gathered multiyear time series in the tropical Pacific to understand, and eventually predict, evolution of coupled ocean–atmosphere phenomena like El Niño–Southern Oscillation (ENSO). The World Ocean Circulation Experiment (WOCE) sought to quantify ocean transport throughout the global ocean using temperature, salinity, and other tracer measurements along with fewer direct velocity measurements with floats and moorings. Western and eastern boundary currents attracted comprehensive measurements, and various coastal regions, each with its unique scientific and societally important phenomena, became home to regional observing systems. Today, the trend toward networked observing arrays of many instrument types continues to be a productive way to understand and predict large-scale ocean phenomena.

Combining a thermal tracer with a transport model to estimate shallow flow velocities

For a long time, tracer techniques based on dyes, salts and more recently heat have been used to estimate shallow flow velocities. Traditionally, flow velocity estimation using tracers would consist of tracking the movement of the leading edge or the centroid of the tracer with the flow. An alternative methodology uses an analytical solution of an advection–dispersion transport equation as the mathematical foundation for measuring shallow water flow velocity from tracer measurements. The main goal of the present study was to ascertain whether this alternative numerical methodology can be used with temperature data from thermal tracer measurements. Salt and thermal tracer techniques were applied simultaneously by injecting a double tracer of salted-heated water into different shallow flows simulated in a laboratory hydraulic flume. Simulated flows combined different bed surfaces (smooth acrylic sheet, rough sand board and synthetic grass carpet), flow discharges (from 47 to 1239 ml s-1) and bed slopes (0.8, 4.4 and 13.2%), resulting in a wide range of hydraulic conditions. Velocities determined with the abovementioned methodology were compared with those estimated by measuring the tracers’ leading edge and centroid and with mean flow velocity calculated using discharge/depth measurements. Results from combining this alternative numerical methodology with thermal tracer data were similar to results from the salt tracer. Also, the proposed alternative numerical methodology predicted the mean flow velocity calculated from discharge/depth measurements better than the measurements of the leading edge and centroid of the tracers.

Determination of the activity and half-life of 227Th

Liquid scintillation samples with 227Th were prepared a few hours after the separation of the progeny. During the measurements, 227Th and its daughters are not in radioactive equilibrium.The counting efficiencies of the individual radionuclides of the decay chain differ from each other and the activity of an individual progeny relative to the activity of 227Th varies with time. Hence, the overall counting efficiency varies with time as well.The counting efficiency εT227h++ of 227Th and its progeny was determined by means of the CIEMAT/NIST efficiency tracing method. The free parameter is derived from the quench-indicating parameter, SQP(E), and from 3H tracer measurements. This makes it possible to compute the efficiency εT227h++ as a function of time. The individual efficiencies of all progeny are to be combined, taking correction factors and activity ratios into account. Thereby, a new, time-dependent correction, namely for the decay during the measurements, is applied.With this method, activity results are obtained that are stable over a long period of time. A least-squares method yields the time of the chemical separation as well as the 227Th half-life, which was also obtained by means of measurements in an ionization chamber. The weighted mean of the two methods (CIEMAT/NIST efficiency tracing and measurements in ionization chambers) was found to be T1/2 = 18.681(9) d.