Experimental Flux Measurements Research Articles

Demonstration of direct ocean carbon capture using encapsulated solvents

Direct ocean carbon capture (DOC) is an emerging form of negative emissions technology that requires expedited characterization and comparison against more well-established forms of carbon capture. Using microencapsulated solvents for DOC affords large membrane surface areas for carbon dioxide (CO2) in the ocean water to flux across a gas-permeable membrane, and reversible regeneration of the contained solution. The feasibility of using a packed bed of Na2CO3 capsules to extract CO2 from seawater is assessed here through lab-scale experimentation, one-dimensional modeling, and techno-economic assessment (TEA). The experimental flux measurements match the flux predictions of the 1D model, validating the model. Parametric studies with our capsule bed model suggest that for a balance between pressure drop and breakthrough time the optimal capsule diameter is between 400-600μm, the optimal bed porosity is between 0.5-0.7, and the optimal seawater velocity through the bed is 0.10-0.15 m/s. The TEA estimates that the carbon capture cost of a 1 MTonne/year greenfield system using Na2CO3 capsules would be exorbitant: $8,977.14 per tonne of CO2. This work demonstrates the potential of using microencapsulated solvents for direct ocean carbon capture and illustrates a need for further research to reduce system costs.

Quantum chemical calculations of the thermochemistry of tantalum oxyhydroxide species

AbstractTantalum pentoxide and water vapor are predicted to react at elevated temperatures to form TaO(OH)3(g), TaO2(OH)(g), and Ta(OH)5(g). The thermochemistry of these species is calculated with quantum chemistry methods. Geometries and vibrational frequencies are determined from B3LYP DFT methods. Energetics are calculated from high levels of theory—CCSD(T) and larger basis sets for Ta, O, and H. We report the enthalpies of formation at 0 K and 298.15 K, entropy at 298.15 K, and heat capacity. These quantities are used to calculate vapor pressures at 1400‐1800 K and 50% water vapor. TaO(OH)3(g) is found to be the dominant species. The calculated vapor pressure of TaO(OH)3(g) is converted to a vapor flux and compared to previous experimental flux measurements from a flat plate in a slowly flowing H2O/Ar gas and also vapor flux from a steam jet experiment. These “open system” experiments result in lower fluxes that are within 1.12‐17X of the calculated equilibrium fluxes. This suggests that the experimental measurements are near equilibrium or have a small kinetic barrier.

Estimating Metabolic Fluxes Using a Maximum Network Flexibility Paradigm.

MotivationGenome-scale metabolic networks can be modeled in a constraint-based fashion. Reaction stoichiometry combined with flux capacity constraints determine the space of allowable reaction rates. This space is often large and a central challenge in metabolic modeling is finding the biologically most relevant flux distributions. A widely used method is flux balance analysis (FBA), which optimizes a biologically relevant objective such as growth or ATP production. Although FBA has proven to be highly useful for predicting growth and byproduct secretion, it cannot predict the intracellular fluxes under all environmental conditions. Therefore, alternative strategies have been developed to select flux distributions that are in agreement with experimental “omics” data, or by incorporating experimental flux measurements. The latter, unfortunately can only be applied to a limited set of reactions and is currently not feasible at the genome-scale. On the other hand, it has been observed that micro-organisms favor a suboptimal growth rate, possibly in exchange for a more “flexible” metabolic network. Instead of dedicating the internal network state to an optimal growth rate in one condition, a suboptimal growth rate is used, that allows for an easier switch to other nutrient sources. A small decrease in growth rate is exchanged for a relatively large gain in metabolic capability to adapt to changing environmental conditions.ResultsHere, we propose Maximum Metabolic Flexibility (MMF) a computational method that utilizes this observation to find the most probable intracellular flux distributions. By mapping measured flux data from central metabolism to the genome-scale models of Escherichia coli and Saccharomyces cerevisiae we show that i) indeed, most of the measured fluxes agree with a high adaptability of the network, ii) this result can be used to further reduce the space of feasible solutions iii) this reduced space improves the quantitative predictions made by FBA and contains a significantly larger fraction of the measured fluxes compared to the flux space that was reduced by a uniform sampling approach and iv) MMF can be used to select reactions in the network that contribute most to the steady-state flux space. Constraining the selected reactions improves the quantitative predictions of FBA considerably more than adding an equal amount of flux constraints, selected using a more naïve approach. Our method can be applied to any cell type without requiring prior information.AvailabilityMMF is freely available as a MATLAB plugin at: http://cs.ru.nl/~wmegchel/mmf.

Achieving Metabolic Flux Analysis for S. cerevisiae at a Genome-Scale: Challenges, Requirements, and Considerations.

Recent advances in 13C-Metabolic flux analysis (13C-MFA) have increased its capability to accurately resolve fluxes using a genome-scale model with narrow confidence intervals without pre-judging the activity or inactivity of alternate metabolic pathways. However, the necessary precautions, computational challenges, and minimum data requirements for successful analysis remain poorly established. This review aims to establish the necessary guidelines for performing 13C-MFA at the genome-scale for a compartmentalized eukaryotic system such as yeast in terms of model and data requirements, while addressing key issues such as statistical analysis and network complexity. We describe the various approaches used to simplify the genome-scale model in the absence of sufficient experimental flux measurements, the availability and generation of reaction atom mapping information, and the experimental flux and metabolite labeling distribution measurements to ensure statistical validity of the obtained flux distribution. Organism-specific challenges such as the impact of compartmentalization of metabolism, variability of biomass composition, and the cell-cycle dependence of metabolism are discussed. Identification of errors arising from incorrect gene annotation and suggested alternate routes using MFA are also highlighted.

Investigating profile stiffness and critical gradients in shaped TCV discharges using local gyrokinetic simulations of turbulent transport

The experimental observation made on the TCV tokamak of a significant confinement improvement in plasmas with negative triangularity (δ < 0) compared to those with standard positive triangularity has been interpreted in terms of different degrees of profile stiffness (Sauter et al 2014 Phys. Plasmas 21 055906) and/or different critical gradients. Employing the Eulerian gyrokinetic code GENE (Jenko et al 2000 Phys. Plasmas 7 1904), profile stiffness and critical gradients are studied under TCV relevant conditions. For the considered experimental discharges, trapped electron modes (TEMs) and electron temperature gradient (ETG) modes are the dominant microinstabilities, with the latter providing a significant contribution to the non-linear electron heat fluxes near the plasma edge. Two series of simulations with different levels of realism are performed, addressing the question of profile stiffness at various radial locations. Retaining finite collisionality, impurities and electromagnetic effects, as well as the physical electron-to-ion mass ratio are all necessary in order to approach the experimental flux measurements. However, flux-tube simulations are unable to fully reproduce the TCV results, pointing towards the need to carry out radially nonlocal (global) simulations, i.e. retaining finite machine size effects, in a future study. Some conclusions about the effect of triangularity can nevertheless be drawn based on the flux-tube results. In particular, the importance of considering the sensitivity to both temperature and density gradient is shown. The flux tube results show an increase of the critical gradients towards the edge, further enhanced when δ < 0, and they also appear to indicate a reduction of profile stiffness towards plasma edge.

An Analytical Approach of Magnetic Diffusion in a Plate Under Time-Varying Flux Excitation

A new analytical computation of magnetic flux distribution and eddy currents is proposed in this paper. Equations are set down for a plate subjected to a time-varying flux excitation. This method consists of using Neumann's boundary conditions in the flux-density diffusion equation to consider the instantaneous variations of the imposed flux waveform. The diffusion equation is solved by separation of variables and Duhamel's theorem. Different cases of imposed magnetic flux are studied: sinusoidal flux, flux ramp, and arbitrary time-varying flux. This new analytical method is a complement of the classical approach (with Dirichlet's boundary conditions) where induction at boundary needs to be corrected to fit the instantaneous total flux. In this paper, a distinctive method allows to compute the instantaneous distributions and corresponding losses directly from the experimental flux measurements on electromagnetic devices. The analytical expressions of magnetic flux density and eddy current distributions are explicitly given. The comparison between analytical and finite-element simulation results shows the validity of the new analytical method.

Pore structure characterization of asymmetric membranes: Non-destructive characterization of porosity and tortuosity

Internal concentration polarization (ICP) in osmotic processes is largely influenced by the porous structure of the support layer of the membrane. Recent publications on osmotic separations have described a ‘structural parameter’, S (function of the thickness, tortuosity, and porosity of the support layer), that represents the support layer's contribution to the overall mass transfer resistance during osmosis. To date, S has only been calculated as a fitted parameter in a model that requires experimental flux measurements. Such a method is inaccurate since the models fail to account for all of the different mass transfer phenomena. An alternative is to characterize the thickness, tortuosity, and porosity independently and thus calculate the actual value of the structural parameter. However, for soft materials like porous membranes, no standard methods have been established for measuring porosity and tortuosity. In this study, we propose the use of X-ray microscopy (XRM) for determining the structural parameter of thin film composite (TFC) membrane support layers. The S value could be calculated from the XRM images and was compared to the results obtained from more conventional mercury intrusion porosimetry as well as an existing model used with empirical data. Substantial differences between the values obtained from the different techniques indicated the need to revise the traditional approaches of characterizing membrane structures.

Insights into the Evaporation Kinetics of Indomethacin Solutions

AbstractEvaporation rates play a key role in evaporation crystallization and the drying of crystal products. Raman analysis was used to study the effect of the evaporation rate on the polymorphs of indomethacin at room temperature. The studied solvents were highly volatile ethanol, acetone, and ethyl acetate. The approach was based on a mass transfer model of evaporation, and experimental flux measurements were used for model evaluation. Evaporation rates from porous carriers were also investigated. The studied mesoporous silicon microparticles can be used in oral dosage forms of poorly soluble active pharmaceutical ingredients. Evaporation rates of dimethyl sulfoxide from a pure solvent, from indomethacin solutions, and from solutions containing microparticles were measured at 100 °C. An evaporation rate model of porous particles was used and the predicted results were compared with the experimental results obtained.

Comparison between elementary flux modes analysis and 13C-metabolic fluxes measured in bacterial and plant cells

Background13C metabolic flux analysis is one of the pertinent ways to compare two or more physiological states. From a more theoretical standpoint, the structural properties of metabolic networks can be analysed to explore feasible metabolic behaviours and to define the boundaries of steady state flux distributions. Elementary flux mode analysis is one of the most efficient methods for performing this analysis. In this context, recent approaches have tended to compare experimental flux measurements with topological network analysis.ResultsMetabolic networks describing the main pathways of central carbon metabolism were set up for a bacteria species (Corynebacterium glutamicum) and a plant species (Brassica napus) for which experimental flux maps were available. The structural properties of each network were then studied using the concept of elementary flux modes. To do this, coefficients of flux efficiency were calculated for each reaction within the networks by using selected sets of elementary flux modes. Then the relative differences - reflecting the change of substrate i.e. a sugar source for C. glutamicum and a nitrogen source for B. napus - of both flux efficiency and flux measured experimentally were compared. For both organisms, there is a clear relationship between these parameters, thus indicating that the network structure described by the elementary flux modes had captured a significant part of the metabolic activity in both biological systems. In B. napus, the extension of the elementary flux mode analysis to an enlarged metabolic network still resulted in a clear relationship between the change in the coefficients and that of the measured fluxes. Nevertheless, the limitations of the method to fit some particular fluxes are discussed.ConclusionThis consistency between EFM analysis and experimental flux measurements, validated on two metabolic systems allows us to conclude that elementary flux mode analysis could be a useful tool to complement 13C metabolic flux analysis, by allowing the prediction of changes in internal fluxes before carbon labelling experiments.

Experimental flux measurements on a network scale

Metabolic flux is a fundamental property of living organisms. In recent years, methods for measuring metabolic flux in plants on a network scale have evolved further. One major challenge in studying flux in plants is the complexity of the plant’s metabolism. In particular, in the presence of parallel pathways in multiple cellular compartments, the core of plant central metabolism constitutes a complex network. Hence, a common problem with the reliability of the contemporary results of 13C-Metabolic Flux Analysis in plants is the substantial reduction in complexity that must be included in the simulated networks; this omission partly is due to limitations in computational simulations. Here, I discuss recent emerging strategies that will better address these shortcomings.

Integrated Energy and Flux Balance Based Multiobjective Framework for Large-Scale Metabolic Networks

Flux balance analysis (FBA) provides a framework for the estimation of intracellular fluxes and energy balance analysis (EBA) ensures the thermodynamic feasibility of the computed optimal fluxes. Previously, these techniques have been used to obtain optimal fluxes that maximize a single objective. Because mammalian systems perform various functions, a multi-objective approach is needed when seeking optimal flux distributions in such systems. For example, hepatocytes perform several metabolic functions at various levels depending on environmental conditions; furthermore, there is a potential benefit to enhance some of these functions for applications such as bioartificial liver (BAL) support devices. Herein we developed a multi-objective optimization approach that couples the normalized Normal Constraint (NC) with both FBA and EBA to obtain multi-objective Pareto-optimal solutions. We investigated the Pareto frontiers in gluconeogenic and glycolytic hepatocytes for various combinations of liver-specific objectives (albumin synthesis, glutathione synthesis, NADPH synthesis, ATP generation, and urea secretion). Next, we evaluated the impact of experimental flux measurements on the Pareto frontiers. We found that measurements induce dramatic changes in Pareto frontiers and further constrain the network fluxes. This multi-objective optimality analysis may help explain certain features of the metabolic control of hepatocytes, which is relevant to the response to hepatocytes and liver to various physiological stimuli and disease states.

SAXS instruments with slit collimation: investigation of resolution and flux

Six small-angle X-ray cameras with block collimation systems were simulated, namely the original Kratky camera, a high-flux version of the Kratky camera, a SAXSess (Anton Parr) camera with a focusing mirror in a linear collimation setup and in a pin-hole setup, as well as a similar camera with a parallelizing mirror in a linear and a pin-hole setup. Their performance was examined using Monte Carlo ray-tracing. The Kratky and the SAXSess camera gave resolutions of 64–65 nm, the high-flux Kratky camera gave a resolution of 44 nm, and the camera with parallelizing mirror gave a resolution of 32 nm. The flux of the camera with parallelizing mirror was 1.47 times higher than for the SAXSess camera, and 18.6 times the flux of the Kratky camera. On changing the alignment, the camera with parallelizing mirror exhibited the best performance up to a resolution of 44 nm; the SAXSess camera was better for higher resolutions. Experimental flux measurements agree if no collimation system is added. Measurements of beam profiles and flux including collimation systems show only qualitative agreement because of user-dependent factors during alignment.

Effects of Oil and Grease on the Vaporization of Organic Compounds from Contaminated Sediments

Contaminated sediments, which contain hazardous compounds such as polynuclear aromatic hydrocarbons (PAHs), are dredged and stored in confined disposal facilities (CDFs). Exposure of the sediment to air results in volatilization of contaminants. Many of the field sediments also contain substantial amounts of oil and grease. An uncontaminated sediment from a local lake (University Lake, Baton Rouge) was spiked with motor oil and PAHs. The air emission flux of three compounds (dibenzofuran, phenanthrene, and pyrene) from the oily sediment was compared to that from the same sediment without oil. The oil content of the sediment was 2.3%, and it had a moisture content of 6.5% to provide 100% pore air relative humidity. Experiments were also conducted with another moisture content of 55% in the sediment. Experiments were performed in dynamic flux chambers in the laboratory. The experimental flux measurements for all three compounds were lowered substantially in the presence of the oil in the sediment. At the end of the experiment, the sediment was cored to obtain the sediment concentration profiles. A mathematical model was constructed based on the hypothesis that the oil served as an additional compartment for the partitioning of the chemicals, and did not contribute an additional layer of resistance to mass transfer resistance from sediments. The comparison of experimental data and the model simulations showed that this hypothesis was true for sediments used in this study, where the oil was immobile.

Can yeast glycolysis be understood in terms of in vitro kinetics of the constituent enzymes? Testing biochemistry.

This paper examines whether the in vivo behavior of yeast glycolysis can be understood in terms of the in vitro kinetic properties of the constituent enzymes. In nongrowing, anaerobic, compressed Saccharomyces cerevisiae the values of the kinetic parameters of most glycolytic enzymes were determined. For the other enzymes appropriate literature values were collected. By inserting these values into a kinetic model for glycolysis, fluxes and metabolites were calculated. Under the same conditions fluxes and metabolite levels were measured. In our first model, branch reactions were ignored. This model failed to reach the stable steady state that was observed in the experimental flux measurements. Introduction of branches towards trehalose, glycogen, glycerol and succinate did allow such a steady state. The predictions of this branched model were compared with the empirical behavior. Half of the enzymes matched their predicted flux in vivo within a factor of 2. For the other enzymes it was calculated what deviation between in vivo and in vitro kinetic characteristics could explain the discrepancy between in vitro rate and in vivo flux.

Measurement of diffusive and surface transport resistances for deuterium in palladium-coated zirconium membranes

Palladium-coated zirconium membranes are attractive choices for low pressure, high temperature hydrogen and hydrogen isotope extractions, e.g. from fission and fusion coolant fluids. Oxidizing the exiting hydrogen to water (oxidative extraction) is a good way of providing very low downstream hydrogen pressures that are sometimes needed to drive the extraction. We present here experimental data and a theoretical treatment of deuterium transport through Zr-Pd membranes at temperatures of 600–700 K and upstream deuterium pressures of 2.7 × 10−2 to 6.7 × 10−4 Pa. We also present a new technique for analyzing experimental flux measurements for calculating the effective permeation and sticking coefficients during such experiments. At very low pressures, transport is limited by molecular adsorption on the palladium surface; the sticking coefficient for this adsorption is log σ = −0.676 − 0.0021(T − 273). At higher upstream pressures, permeability in zirconium limits transport; PZr = 2.00 × 10−6 exp (59/T) ± 40% mol/msPa12. These permeability values are slightly higher than predicted. We find no evidence for additional transport resistance caused by zirconium surface oxidation, or from Zr-Pd interface effects. Membranes were used for several months without showing signs of deterioration.