Limits Of Experimental Uncertainty Research Articles

High‐Temperature Deformation of Enstatite‐Olivine Aggregates

AbstractSynthesized polycrystalline samples composed of enstatite and olivine with different volumetric ratios were deformed in compression under anhydrous conditions in a Paterson gas‐medium apparatus at 1150–1300°C, an oxygen fugacity buffered at Ni/NiO, and confining pressures of 300 or 450 MPa (protoenstatite or orthoenstatite fields). Mechanical data suggest a transition from diffusion to dislocation creep with increasing differential stress for all compositions. Microstructural analyses by optical and scanning electron microscopy reveal well‐mixed aggregates and homogeneous deformation. Crystallographic preferred orientations measured by electron backscatter diffraction are consistent with activation of the slip systems (010)[100] and (010)[001] for olivine and (100)[001] and (010)[001] for enstatite, as expected at these conditions. Nonlinear least‐squares fitting to the full data set from each experiment allowed the determination of dislocation creep flow laws for the different mixtures. The stress exponent is 3.5 for all compositions, and the apparent activation energies increase slightly as a function of enstatite volume fraction. Within the limits of experimental uncertainties, all two‐phase aggregates have strengths that lie between the uniform strain rate (Taylor) and the uniform stress (Sachs) bounds calculated using the dislocation creep flow laws for olivine and enstatite. Calculation of the Taylor and Sachs bounds at strain rate and temperature conditions expected in nature (but not extrapolating in pressure) indicates that using the dislocation creep flow law for monomineralic olivine aggregates provides a good estimate of the viscosity of olivine‐orthopyroxene rocks deforming by dislocation creep in the deeper lithosphere and asthenosphere.

Hybrid RPA:DFT Approach for Adsorption on Transition Metal Surfaces: Methane and Ethane on Platinum (111).

The hybrid QM:QM approach is extended to adsorption on transition metal surfaces. The random phase approximation (RPA) as the high-level method is applied to cluster models and, using the subtractive scheme, embedded in periodic models which are treated with density functional theory (DFT) that is the low-level method. The PBE functional, both without dispersion and augmented with the many-body dispersion (MBD), is employed. Adsorption of methane and ethane on the Pt(111) surface is studied. For methane in a 2 × 2 surface cell, the hybrid RPA:PBE and RPA:PBE+MBD results, -14.3 and -16.0 kJ mol-1, respectively, are in close agreement with the periodic RPA value of -13.8 kJ mol-1 at significantly reduced computational cost (factor of ∼50). For methane and ethane, the RPA:PBE results (-14.3 and -17.8 kJ mol-1, respectively) indicate underbinding relative to energies derived from experimental desorption barriers for relevant loadings (-15.6 ± 1.6 and -27.2 ± 2.9 kJ mol-1, respectively), whereas the hybrid RPA:PBE+MBD results (-16.0 and -24.9 kJ mol-1, respectively) agree with the experiment well within experimental uncertainty limits (deviation of -0.4 ± 1.5 and +2.3 ± 2.9 kJ mol-1, respectively). Finding a cluster that adequately and robustly represents the adsorbate at the bulk surface is important for the success of the RPA-based QM:QM scheme for metals.

Predictive radiation heat transfer modeling in fibrous insulation at high temperature

The modeling of heat transfer in fibrous materials is important for designing and improving thermal insulation systems. At high temperatures and low sample density, thermal radiation is expected to be the primary mode of heat transfer in fibrous insulation. Currently, the most common and successful models for modelling heat transfer in insulation at high temperatures require the use of semi-empirical methods. The main limitation of this approach is that the model parameters need to be determined from thermal measurements for each possible material and re-determined if the morphological structure is modified, even for the same material. This paper presents a predictive model for radiation heat transfer based solely on physical and morphological properties. The model was validated using experimental determinations of the effective thermal conductivity in a low-density alumina-based insulation. The model demonstrates good agreement with experimental measurements, and its predictions fall within the experimental uncertainty limits for temperatures between 800 K and 1700 K.

Laminar burning velocities and Markstein numbers for pure hydrogen and methane/hydrogen/air mixtures at elevated pressures

Spherically expanding flame propagations have been employed to measure flame speeds for H2/CH4/air mixtures over a wide range of H2 fractions (30 %, 50 %, 70 and 100 % hydrogen by volume), at initial temperatures of 303 K and 360 K, and pressures of 0.1, 0.5 and 1.0 MPa. The equivalence ratio (ϕ) was varied from 0.5 to 2.5 for pure hydrogen and from 0.8 to 1.2 for methane/hydrogen mixtures. Experimental laminar burning velocities and Markstein numbers for methane/hydrogen/air mixtures at high pressures, which are crucial for gas turbine applications, are very rare in the literature. Moreover, simulations using three recent chemical kinetic mechanisms (Konnov-2018 detailed reaction, Aramco-2.0-2016 and San Diego Methane detailed mechanism (version 20161214)) were compared against the experimentally derived laminar burning velocities. The maximum laminar burning velocity for 30 % and 50 % H2 occurs at ϕ = 1.1. However, it shifts to ϕ = 1.2 for 70 % H2 and to ϕ = 1.7 for a pure H2 flame. The laminar burning velocities increased with hydrogen fraction and temperature, and decreased with pressure. Unexpected behaviour was recorded for pure H2 flames at low temperature and ϕ = 1.5, 1.7 wherein ul did not decrease when the pressure increased from 0.1 to 0.5 MPa. Although, the measurement uncertainty is large at these conditions, the flame structure analysis showed a minimum decline in the mass fractions of the active species (H, O, and OH) with the rise in the initial pressure. Markstein length (Lb) and Markstein number (Mab and Masr) varied non-monotonically with hydrogen volume fraction, pressure and temperature. There was generally good agreement between simulations and experimentally derived laminar burning velocities, however, for experiments of rich-pure hydrogen at high initial pressures, the level of agreement decreased but remained within the limits of experimental uncertainty.

Numerical investigation of air curtain flows in the doorway of a building using RANS and LES

Air curtains are commonly adopted in building flows to facilitate aerodynamic sealing against the exchange flow that occurs across an open doorway due to the density differences owing to buoyancy. This paper reports numerical simulations of air curtain flows using Reynolds-averaged Navier–Stokes (RANS) and large-eddy simulation (LES) methodologies. Computations are performed for various operating conditions that are described using a deflection modulus (Dm) which ranges from 0 to 1.25. Physically, Dm represents the relative strength of the jet momentum flux compared to the transverse stack effect. The value of this deflection modulus, along with qualitative distribution of buoyancy, demarcates the operating regime of an air curtain into unstable (Dm⪅ 0.1), stable (Dm⪆ 0.2), and strong installation (Dm⪆ 0.6). The quantification of aerodynamic sealing is established using effectiveness, E, which suggests that the optimal operation lies in the stable regime with the poorest performance in the unstable regime. The comparison between various simulation methodologies suggests that 2D RANS computations generally over-predict the effectiveness, whereas both 3D RANS and LES are able to estimate E reasonably well, especially at practical values of Dm. If the employed LES grid is sufficiently fine, the predicted effectiveness falls within the experimental uncertainty limits. Furthermore, we quantify the statistics of turbulence in the flow field using the transport equation of turbulent kinetic energy. This analysis reveals that shear production and turbulent dissipation are dominant processes in the flow. In comparison, the effects of transport terms and buoyancy production are rather small. These quantities are shown to scale well with w3/l where w and l are the characteristic velocity and length scales associated with an air curtain. Visualization of large-scale coherent structures using the Q-criterion depicted the presence of long spanwise vortices in the shear layer with a wide range of scales of motion at higher Dm. These vortical structures break down significantly upon impinging on the wall (floor), resulting in a complex spatiotemporal distribution of vortices.

Solute transport in heterogeneous model porous media under different flow rates: Experimental and modelling study

The present paper focuses on solute transport behaviour in a Model Heterogeneous Porous Medium (MHPM) under different flow rates. We report tracer experiments under stationary hydraulic conditions, with 7 different stationary flow rates spanning two orders of magnitude. Several replicates are carried out on several MHPMs, allowing for a sound statistical assessment of experimental imprecision. The experimental BreakThrough Curves (BTCs) exhibit a dual transport mode in agreement with previously-reported field scale experiments. This dual transport mode is shown to be flow-rate independent under a suitable variable change, with the BTCs superposing in the limit of experimental uncertainty. The experiment is modelled using a classical Multi-Region Advection-Dispersion (MRAD) model with only two mobile regions. We present a flow rate independent reformulation of the MRAD model that allows both water and solute continuity to be preserved during the calibration process. Assuming a linear dependence of the dispersion and exchange coefficients on the flow rate is shown to yield satisfactory model behaviour. This confirms the linearity of the dispersion coefficient with respect to the flow rate, often suggested in the literature, over a wide range of flow conditions.

A round-robin approach provides a detailed assessment of biomolecular small-angle scattering data reproducibility and yields consensus curves for benchmarking.

Through an expansive international effort that involved data collection on 12 small-angle X-ray scattering (SAXS) and four small-angle neutron scattering (SANS) instruments, 171 SAXS and 76 SANS measurements for five proteins (ribonuclease A, lysozyme, xylanase, urate oxidase and xylose isomerase) were acquired. From these data, the solvent-subtracted protein scattering profiles were shown to be reproducible, with the caveat that an additive constant adjustment was required to account for small errors in solvent subtraction. Further, the major features of the obtained consensus SAXS data over the q measurement range 0-1 Å-1 are consistent with theoretical prediction. The inherently lower statistical precision for SANS limited the reliably measured q-range to <0.5 Å-1, but within the limits of experimental uncertainties the major features of the consensus SANS data were also consistent with prediction for all five proteins measured in H2O and in D2O. Thus, a foundation set of consensus SAS profiles has been obtained for benchmarking scattering-profile prediction from atomic coordinates. Additionally, two sets of SAXS data measured at different facilities to q > 2.2 Å-1 showed good mutual agreement, affirming that this region has interpretable features for structural modelling. SAS measurements with inline size-exclusion chromatography (SEC) proved to be generally superior for eliminating sample heterogeneity, but with unavoidable sample dilution during column elution, while batch SAS data collected at higher concentrations and for longer times provided superior statistical precision. Careful merging of data measured using inline SEC and batch modes, or low- and high-concentration data from batch measurements, was successful in eliminating small amounts of aggregate or interparticle interference from the scattering while providing improved statistical precision overall for the benchmarking data set.

Low -parametric equation for calculating the viscosity coefficient of nitrogen in liquid, gas and fluid states

The formulation for the viscosity coefficient of nitrogen is obtained. In the developed equation the dependence of the residua viscosity of various states of substance on the internal energy density is used. The new correlation represents the viscosity of nitrogen at temperatures from 70 K to 1000 K and pressures of up to 50 MPa within the limits of experimental uncertainties.

Slot-die-coating operability windows for polymer electrolyte membrane fuel cell cathode catalyst layers

Roll-to-roll (R2R) slot-die coating of polymer electrolyte membrane fuel cell (PEMFC) catalyst layers represents a scalable deposition method for producing 10–20 m2·min−1 of catalyst-coated gas diffusion layers (GDLs). This high-throughput production technique will help lower the cost of PEMFC catalyst layers. The uniformity of the wet layer applied by slot die deposition is affected by process parameters such as substrate speed, vacuum pressure applied at the upstream meniscus, gap between the slot die lips and substrate, ink rheology, and other ink and substrate properties. The set of conditions for producing a defect-free coating with a dilute ink typically requires little to no upstream vacuum pressure, so suitable operating conditions can be found easily through trial and error and operator intuition. However, the higher viscosity of more concentrated inks dramatically shifts the range of settings that result in a homogeneous coating to higher vacuum levels, which are harder to find through hit or miss. A predictive model showing the range of operable conditions decreases material wastage inherent in experimentally searching for suitable parameters. In this study, the defect-free coating parameter window is explored experimentally and theoretically for two concentrations of PEFC cathode inks. Both a full capillary hydrodynamic model and a computationally cheaper viscocapillary model successfully predict the experimentally determined coating window within the experimental and model uncertainty limits for inks with 5.3 wt% and 12.0 wt% solids ink while maintaining the 0.1 mgPt·cm−2Pt areal loading target. This paper demonstrates a viable pathway for meeting the $30/kWnet ultimate cost target of the United States Department of Energy (U.S. DOE) Hydrogen Fuel Cells Technologies Office (HFTO). The concentrated ink lowers the thermal energy and capital expenditure (CapEx) budget of the coating process by decreasing the amount of time, energy, and floorspace required for drying the coating.

Gamma-ray attenuation behaviors of hematite doped polymer composites

The studies for protection from gamma radiation have gained speed in recent years. Researchers are in search of a new material without toxic effects such as lead (Pb) and its derivatives. In this study, the polymer composites having different ratios of hematite (25, 50, 75 and 100%) were prepared. To determine the gamma radiation attenuation characteristics of the prepared composites, some gamma-ray radiation attenuation parameters such as transmission factor, mass and linear attenuation coefficients, half and tenth value layers, mean free path, effective atomic number and electron density, energy absorption build-up factor and exposure build-up factor were obtained. The experimental measurements were performed using an HPGe detector and eight different radioactive sources. The photon energies emitted from these sources range from 59.5 keV to 1408.0 keV. The obtained experimental results were compared with the theoretical ones and small differences were observed among them within the limits of experimental uncertainty. It was observed that the mass attenuation coefficients of prepared composites doped with 25%, 50%, 75% and 100% hematite in the range of 59.5–1408.0 keV photon energy were changed between 0.3301–0.0551, 0.4254–0.0545, 0.4943–0.0540 and 0.5461–0.0537 cm2 g−1, respectively. It was reported that the hematite (100%) polymer composite sample is a better gamma radiation shielding material than other prepared composites.

Equations of State to Describe Isothermal Compression of Certain Molecular Nitro Compound Crystals

An approach to constructing semiempirical equations of state of molecular crystals of nitro compounds is suggested allowing one to describe isothermal compression of the crystal of triaminotrinitrobenzene (1,3,5-triamino-2,4,6- trinitrobenzene) by the familiar modulus of three-dimensional compression and sublimation heat of the crystal obtained from experiments not related to isothermal compression. A comparative analysis of experimental data on isothermal compression of the molecular crystal of triaminotrinitrobenzene and calculations by the proposed equation of state have shown that the experimental and calculated values of pressure are within the limits of experimental uncertainty.

Nonadditivity Analysis

We introduce the statistics behind a novel type of SAR analysis named "nonadditivity analysis". On the basis of all pairs of matched pairs within a given data set, the approach analyzes whether the same transformations between related molecules have the same effect, i.e., whether they are additive. Assuming that the experimental uncertainty is normally distributed, the additivities can be analyzed with statistical rigor and sets of compounds can be found that show significant nonadditivity. Nonadditivity analysis can not only detect nonadditivity, potential SAR outliers, and sets of key compounds but also allow estimating an upper limit of the experimental uncertainty in the data set. We demonstrate how complex SAR features that inform medicinal chemistry can be found in large SAR data sets. Finally, we show how the upper limit of experimental uncertainty for a given biochemical assay can be estimated without the need for repeated measurements of the same protein-ligand system.

Interpretation of results from the competitive Biacore procedure for characterizing immunochemical interactions in solution.

Rigorous consideration of the consequences of antibody bivalence in the published competitive kinetic procedure for quantifying the solution characteristics of an antigen-antibody interaction in solution has rendered redundant the practice of substituting the Fab fragment for the antibody to ensure validity of the analysis of results in terms of theory developed for a univalent analyte. Although the quantitative expressions differ for univalent and bivalent analytes, the additional contribution arising from bivalence is likely to be well within the limits of experimental uncertainty in the measured binding constant.

In-situ Raman spectroscopy analysis of the interface between ceria-containing SOFC anode and stabilized zirconia electrolyte

The combined experimental approach for in-situ Raman spectroscopy of the inner “anode|electrolyte” interfaces in solid oxide fuel cells under current load was examined in a case study centered on the behavior of gadolinia-doped ceria (GDC) interlayers between cermet anodes and stabilized zirconia membrane. The Raman spectra of ceria at 850 °C were found sensitive enough with respect to the variations of anodic current and fuel gas mixture composition, which induce oxygen nonstoichiometry changes in GDC. Linear dependence of the Raman peak area on the open-circuit voltage makes it possible to estimate local overpotentials at the GDC interlayer|electrolyte interface under current load. The calculated local overpotentials exhibit a Tafel-like dependence on the current density, and are essentially independent on the hydrogen and water vapor partial pressures within the limits of experimental uncertainties. The relevant rate-determining mechanism may be associated with ion transfer via the GDC|zirconia interface, whilst the contributions of exchange-related processes involving gaseous phase are less significant in this interfacial zone.

Electron effective mass in Sn-doped monoclinic single crystal β-gallium oxide determined by mid-infrared optical Hall effect

The isotropic average conduction band minimum electron effective mass in Sn-doped monoclinic single crystal β-Ga2O3 is experimentally determined by the mid-infrared optical Hall effect to be (0.284 ± 0.013)m0 combining investigations on (010) and (2¯01) surface cuts. This result falls within the broad range of values predicted by theoretical calculations for undoped β-Ga2O3. The result is also comparable to recent density functional calculations using the Gaussian-attenuation-Perdew-Burke-Ernzerhof hybrid density functional, which predict an average effective mass of 0.267m0. Within our uncertainty limits, we detect no anisotropy for the electron effective mass, which is consistent with most previous theoretical calculations. We discuss upper limits for possible anisotropy of the electron effective mass parameter from our experimental uncertainty limits, and we compare our findings with recent theoretical results.

Sublimation enthalpies of 9 substituted acetanilides at 298 K estimated by solution calorimetry approach

In this work a solution calorimetry approach was applied for determination of the sublimation enthalpies of 9 substituted acetanilides. The solution enthalpies of acetanilide and 9 its derivatives in acetonitrile were measured and solvation enthalpies were calculated by a group-additivity scheme. Additivity of solvation enthalpy due to influence of the substituent on the acidity of the proton of NHCOCH3-group and OH-group was checked with the use of IR-spectroscopy. The sublimation enthalpies obtained from the solution calorimetry approach were compared to the available literature data. In most cases convergence within the limits of experimental uncertainty was demonstrated.

Infrared dielectric functions, phonon modes, and free-charge carrier properties of high-Al-content AlxGa1−xN alloys determined by mid infrared spectroscopic ellipsometry and optical Hall effect

We report on the analysis of a combined mid-infrared spectroscopic ellipsometry and mid-infrared optical Hall effect investigation of wurtzite structure c-plane oriented, crack-free, single crystalline, and high-Al-content AlxGa1−xN layers on 4H-SiC. For high-Al-content AlxGa1−xN, a two mode behavior is observed for both transverse and longitudinal branches of the infrared-active modes with E1 symmetry, while a single mode behavior is found for the longitudinal modes with A1(LO) symmetry. We report their mode dependencies on the Al content. We determine and discuss static and high frequency dielectric constants depending on x. From the analysis of the optical Hall effect data, we determine the effective mass parameter in high-Al-content AlxGa1−xN alloys and its composition dependence. Within the experimental uncertainty limits, the effective mass parameters are found isotropic, which depend linearly on the Al content. The combination of all data permits the quantification of the free electron density N and mobility parameters μ.

Measurement of convective heat transfer coefficients in a randomly packed bed of silica gel particles using IHTP analysis

The purpose of this research is to determine the convective heat transfer coefficient (ht) for airflow through two randomly packed beds of microporous silica gel particles of nearly uniform diameter (i.e., for the average diameter of 1.60 and 2.58mm). The experimental test facility was developed to induce a transient step change in the inlet uniform airflow while the temperature was measured at several locations within the silica gel beds (x/L=0.29, 0.48, 0.69). The transient test data were simulated numerically using the volume averaging method for air flow through a homogeneous packed bed of particles for a range of Reynolds numbers (40<Redh<100). The convective heat transfer coefficient was determined by using the numerical inverse method to minimize the difference between the simulated and experimental temperature profiles. The sensitivity analysis stated that the thermocouple placed at the middle of the test section (x/L=0.48) had the highest sensitivity during the first 400s of transient testing. Using the ht values obtained by the inverse calculations, a good agreement is obtained within the experimental uncertainty limits for the experimental and numerical temperature temporal profiles at different locations within the beds; but the agreement is best using the transient temperature data at x/L=0.48. Based on the ht values, a new correlation between Nusselt number and Reynolds number is presented with lower uncertainty (the maximum uncertainty of ±30%) compared to the correlations in the literatures. It was found that the proposed correlation is in agreement with the data in literature within their uncertainty bounds.

Comparative heat and gas exchange measurements in the Heidelberg Aeolotron, a large annular wind-wave tank

Abstract. A comparative study of simultaneous heat and gas exchange measurements was performed in the large annular Heidelberg Air–Sea Interaction Facility, the Aeolotron, under homogeneous water surface conditions. The use of two gas tracers, N2O and C2HF5, resulted not only in gas transfer velocities, but also in the measurement of the Schmidt number exponent n with a precision of ±0.025. The original controlled flux, or active thermographic, technique proposed by Jähne et al. (1989) was applied by heating a large patch at the water surface to measure heat transfer velocities. Heating a large patch, the active thermography technique is laterally homogeneous, and problems of lateral transport effects are avoided. Using the measured Schmidt number exponents, the ratio of the scaled heat transfer velocities to the measured gas transfer velocities is 1.046 ± 0.040, a good agreement within the limits of experimental uncertainties. This indicates the possibility to scale heat transfer velocities measured by active thermography to gas transfer velocities, provided that the Schmidt number exponent is known and that the heated patch is large enough to reach the thermal equilibrium.

Solute transport in periodical heterogeneous porous media: Importance of observation scale and experimental sampling

Summary This paper focuses on the effects of the observation scale and sampling on the dispersion of tracers in periodical heterogeneous porous media. A Model Heterogeneous Porous Medium (MHPM) with a high degree of heterogeneity was built. It consists of a preferential flow path surrounded by glass beads. 44 tracer experiments were carried out on several series of periodic MHPM to investigate the effect of the observation scale on solute dispersion. Each series was replicated several times, allowing for a statistical description of the unit transfer function of the MHPM. No significant trend was found for the dispersion coefficient as a function of the size of the MHPM. However, given the variability of the breakthrough curves from one experiment replicate to another, under-sampling might easily lead to conclude that the dispersion coefficient is variable with distance. Depending on the samples used, it would be as easy to (wrongly) detect an increasing trend as to detect a decreasing one. A confidence interval analysis of the experimental breakthrough curves in the Laplace space shows that (i) there exists a model with scale independent parameters that can describe the experimental breakthrough curves within the limits of experimental uncertainty, (ii) this model is not the advection–dispersion (AD) model, (iii) the modelling error of the AD model decreases with the number of periods, (iv) the size of the Reference Elementary Volume for the dispersion coefficient is between 10 and 20 periods. The effects of sampling prove to override those of scaling. This, with the invalidity of the AD model, leads to question attempts to calibrate and/or identify trends in the dispersion coefficient at intermediate scales from a limited number of experiment replicates.