Single-stage Test Research Articles

Influence of Dilution and Effusion Flows in Generating Variable Inlet Profiles for a High-Pressure Turbine

Abstract The elevated flow temperatures and pressures exiting gas turbine combustors affect the efficiency and durability of the high-pressure turbine stage. Understanding the effects that result from the upstream dilution and effusion flow interaction in creating the combustor exit profiles is important to advancing gas turbines. Understanding how common combustor features, such as dilution jets and effusion cooling, interact based on computational predictions guided the design of a non-reacting profile simulator capable of producing a wide range of non-uniform temperature profiles representative of those entering high-pressure turbines. The mechanical design of a new simulator device, which will be experimentally tested in the future, is presented in this paper along with computational predictions of flow and thermal fields. The simulator was designed for modular installation into the Steady Thermal Aero Research Turbine (START), which is a continuous-duration, steady-state turbine facility that houses a single-stage test turbine. Features of the simulator included interchangeable liner panels with multiple rows of dilution jets and wall effusion cooling to study various hole diameters and patterns. The dilution jets generate elevated turbulence intensities and tailor the temperature profiles in the radial and circumferential directions. The air mass flow distribution and source flow temperatures are independently controlled. To aid in the simulator design, computational fluid dynamics (CFD) simulations using Reynolds-averaged Navier–Stokes modeling were conducted with a two-level Design of Experiments (DOE) approach to determine a number of engine-representative target profiles with temperature shapes that are mid-radius peaked, outer-diameter peaked, inner-diameter peaked, and uniform. A sensitivity analysis of the CFD DOE results determined which factors significantly affected the profile shape so that the target profiles could be produced. The analysis indicated that the main contributor to the temperature profile shape at near-wall vane radial span locations of 0–15% and 85–100% was the injection temperature of the effusion flow. The main contributor at radial span locations of 15–40% and 60–85% was the injection temperature of the third-row dilution jets, and at the mid-radius location of 40–60% vane radial span, the main contributor was the diameter of the first-row dilution holes.

Recent test experiences with applying multiple unshrouded impellers in a single-shaft compressor

The use of unshrouded impellers to increase the pressure ratio and volume reduction achieved in low mole weight, single-shaft compressor applications is discussed. The aerodynamic and mechanical implications of using multiple unshrouded impellers in series is also addressed. Test results will show that with proper management of impeller tip gaps good aerodynamic performance can be achieved with three unshrouded impellers in a single process section. The development effort also leveraged a knowledge-based impeller design system to provide new impeller designs that were optimized as a function of Mach number to provide a 30% axially shorter section without compromising aerodynamic performance. The shorter axial stages in the first section pushed the rotor natural frequency 20% higher, enabling faster rotor tip speeds. Test results from a single-stage test rig and from a full-size prototype testing are provided and generally show good agreement.

Application and comparison of multistage triaxial compression test procedures on reconstituted Ankara clay

The ability to conduct conventional triaxial compression tests on multiple identical specimens is restricted by available sample quantity, sample homogeneity, as well as testing duration. Multistage triaxial testing is an alternative method to tackle these issues by using a single specimen sheared under different confining stresses to attain the strength parameters. Although there are widely accepted procedures to decide when to stop each shearing stage and proceed to the next stress level, the applicability of these procedures on different soil types is still a question. This study examines the applicability of combinations of two multistage triaxial testing procedures (Rational Procedure and Minimum Slope) under two different deviator stress conditions (Sustained or Cyclic) during confining stress increase. The outcome is compared to conventional triaxial test results for undrained and drained shearing of reconstituted specimens of high-plasticity Ankara Clay. Out of the four options, the rational procedure with cyclic deviator loading and minimum slope with cyclic deviatoric loading conditions, are found to give the most accurate strength parameters in reference to single-stage test results. The maximum number of the shearing-reconsolidation sequences applicable before strength loss is also investigated for each multistage triaxial testing procedure.

Definition of new stopping criteria for the characterization of permanent deformation of granular materials

In the characterization of the plastic deformation of granular materials for pavement use, it is possible to identify different behaviors throughout the load application in the triaxial equipment. In certain stress pairs, some soils may present very small accumulated deformation variations, reaching accommodation, not requiring the application of thousands of load cycles, as suggested in the Brazilian approach. In this sense, a preliminary assessment of this type of behavior can save time and resources in paving works. Therefore, the objective of this paper is to analyze the applicability of shakedown classification criteria for soils from a sampling region and to determine the effect of prior disruption in single-stage testing, in case of accommodation. For this purpose, 58 tests were analyzed for 7 soils, applying 9 stress pairs and 150,000 load cycles at a frequency of 2 Hz. The rutting calculation in a pavement section suggested that, for soils whose total deformation was less than 2 mm, stopping the procedure after about 30,000 cycles would generate approximately 0.1 mm variations compared to the values obtained at 150,000 cycles. Realizing that the criteria available in the literature would not be adequate for Brazilian standards and soils, Decision Tree models were used, based on ranges of vertical strain rate values at different intervals prior to 10,000 cycles. The results demonstrated that the algorithm was able to accurately predict the occurrence of Type A tests, with no false positives observed for the other plastic accommodation ranges. Thus, the application of the proposed methods in combination can provide significant economy and optimize the design and construction of Brazilian road pavements.

On Dynamics of Flow past a Stage Axial Air Turbine

The air flow inside a single-stage test turbine is studied experimentally using the Particle Image Velocimetry technique. The measurements were performed at the axial-tangential plane just behind the rotor at the middle blade radius. The large vortical structures are identified in the shear layers between the blade wakes and channel jet. The phase-locked structures topology of random dynamical structures in the flow behind the stage are to be analysed using the Proper Orthogonal Decomposition method.

Analysis of the Influence of System Parameters on Launch Performance of Electromagnetic Induction Coil Launcher

The influence of electromagnetic induction coil launcher (EICL) system parameters on the launch performance was analyzed, and a method for measuring the launch performance of an EICL system with a muzzle velocity and energy conversion efficiency was proposed. The EICL system mainly includes a pulse power supply and launcher. The parameters of the pulse power supply mainly include the discharge voltage and the capacitance value of the capacitor bank. The structural parameters of the launcher mainly include the bore size of the launcher, the air gap length between the armature and the drive coil, the length and width of the drive coil, and the trigger position of the armature. Change in single or multiple parameters in the launch system will influence the launch performance. The influence of single or multiple parameters on the launch performance was summarized, and the physical law as analyzed. The influence law of the EICL system parameters on the launch performance was obtained, which lays a theoretical foundation for the optimization design of EICL. Finally, experimental verification was carried out by a single-stage test platform.

Experimental investigation into the cyclic behaviour of geogrid enhanced base layer aggregate through large-diameter triaxial tests

The base layer is constructed of coarse-grain soils, usually reinforced by geogrid. In the study, a large-diameter cyclic triaxial testing system was employed to study the cyclic behaviour of geogrid enhanced soil, especially the long-term deformation behaviour. The multi-stage cyclic loading test was performed to determine the shakedown behaviour of soil enhanced by different geogrid layers under different cyclic loading amplitudes. Then, single-stage tests with one cyclic loading amplitude in plastic creep range and the other in the incremental range were performed on soils enhanced by different geogrid layers. Test results indicated that the effect of geogrid on the long-term deformation of soil is dependent on the shakedown response of soil: the enhancement effect was observed to be much more significant for specimens that exhibit the incremental collapse response than those that exhibit the plastic creep response. Besides, the resilient modulus was found limited affected by the geogrid layer, irrespectively the specimen that exhibits plastic creep or incremental collapse. Furthermore, the reinforcement mechanism was discussed in detail from the consistent/inconsistent deformation of soil and geogrid, which benefits geogrid design and construction.

Submaximal Walking Tests: A Review of Clinical Use

ABSTRACT Though graded exercise testing is the gold standard for assessing cardiorespiratory fitness, submaximal exercise testing is also useful to assess cardiorespiratory status and functional capacity when maximal testing is not feasible. Submaximal walking tests are advantageous as they have less risk, lower cost, require less time and equipment, and walking is a familiar activity that is easy to do in most environments. A number of submaximal walking tests exist for both overground and treadmill walking. Regression equations to predict V̇o2max values based on walking time, distance, and other variables that influence exercise tolerance have been developed for some submaximal tests, including the Rockport Fitness Walking Test and the Single-Stage Treadmill Walk Test. The 6-Minute Walk Test is a common test used in clinical populations to predict prognosis and assess change in functional capacity after intervention. Determining which submaximal walking test to use depends on purpose and setting, subject characteristics, equipment availability, space, and time. This review will provide clinicians with an overview of submaximal walking test protocols and provide reference equations and minimal clinically important difference values to interpret results.

Physical and physiological benefits of small sided recreational handball in untrained males: relationship of body fat with aerobic capacity

Background and Study Aim. Exercise and Recreation play major role in promotion of health and fitness. Recreational exercise or sports can be useful in physically inactive population. The aim of study was to investigate the effect of recreational handball on body fat percent, VO2max, blood pressure and resting heart rate. Another purpose to find relationship between VO2max and body fat percentage.
 Material and Methods. Twenty-four students were randomized into intervention (n=14) and control group (n=10). The intervention group was asked to play recreational handball for 12 weeks. Handball training was held twice a week for 30 minutes duration. The Control group performed their normal routine. Aerobic capacity measured using single-stage treadmill test. Body fat was measured with Omron Body Fat Analyzer. T-test was employed to find a significant difference in the two groups. For the relationship in aerobic capacity and body fat, Pearson Product Moment Correlation was used.
 Results. We found significant difference in body percent (t22 = 2.031, P = 0.054). No significant difference was seen in aerobic capacity (t22 = 1.578, P = 0.129), systolic blood pressure (t22 = -1.637, P = 0.116), diastolic blood pressure (t22 = -1.562, P = 0.133) and resting heart rate (t22 = 1.620, P = 0.120). Significant relationship was established between body percent and aerobic capacity (r= -5.23, n=14, p= 0.055) in the intervention group.
 Conclusions. It can be concluded that recreational handball was useful in eliciting good response with respect to reduction of body fat in intervention group. However, recreation handball sessions were not effective in reducing blood pressure, resting heart and aerobic capacity among untrained males. A significant relationship was observed in VO2max and percent body fat.

Loading History Effect on Stress Relaxation of Rock Joints

In this study, a data analysis method for the relaxation test was proposed under step loading by conducting creep and stress relaxation tests of dentate discontinuity poured by cement mortar using biaxial creep machine under step loading and single-stage loading. First, a superposition method for the stress relaxation curve was deduced based on the data processing method of creep test by considering the effect of loading history on the relaxation curve and the characteristic of relaxation was analyzed. Second, this superposition method was verified by testing data under step loading and single-stage loading. Finally, this paper indicate the accurate way for the processing of relaxation test data under step loading. The results show that under the same stress level, the values of relaxation curve after the superposition are different from that under the single-stage loading test. Furthermore, the relaxation curves in the step loading test under different stress levels are similar to those in single-stage loading under the same stress level. Furthermore, creep deformation increase monotonically during the creep, but stress do not exhibit such a trend during relaxation, which is inconsistent with the Boltzmann superposition principle. The relaxation curve in the step loading test under different shear stress could reflect the relaxation properties of the single-stage loading test under the same shear stress, and unlike the data processing method of step loading creep test, superimposition is not needed.

Effect of Suction and Confining Pressure on Shear Strength and Dilatancy of Highly Compacted Silty Sand: Single-Stage versus Multistage Triaxial Testing

Abstract Evaluating short- and long-term performance of engineered earthen structures and slopes requires proper understanding of the behavior of compacted and highly compacted soils. However, limited studies exist in the literature of unsaturated soil mechanics experimentally testing highly compacted soils, which often possess complex shear strength and dilatancy characteristics. The main objective of this study is to investigate the effect of suction and confining pressure on shear strength and dilatancy of a highly compacted silty sand through multistage and single-stage triaxial testing. Multistage triaxial testing offers a time and cost efficient approach that can reasonably represent field conditions where soils experience fluctuations in external loading conditions (e.g., flood loading/unloading). This article presents the results of consolidated drained multistage and single-stage triaxial tests on highly compacted silty sand under saturated and unsaturated conditions. Soil specimens were isotropically consolidated at a constant matric suction of 0 (saturated), 20, 50, and 95 kPa under net confining pressures of 50, 100, and 200 kPa. Unsaturated specimens consistently exhibited higher shear strength in multistage and single-stage tests compared to saturated specimens. Peak state lines for all unsaturated tests were plotted and found to be near parallel to the saturated peak state line. All tested specimens exhibited dilatancy following a small initial contraction. Although the dilatancy during shearing in multistage tests was comparable to that in the single-stage tests, the cumulative volumetric strain resulted in a net increase in the specimen volume in the case of unsaturated tests, and a net decrease in the case of saturated tests. This difference in volumetric strain behavior resulted in a lower peak shear strength of the saturated specimens tested using multistage testing compared to single stage but a higher peak shear strength in the case of the unsaturated specimens.

Investigation of Fluid-Injection-Induced Coal Stiffness Alteration using a Single-Core Multistage Triaxial Test

Nonlinear stress-strain behavior and failure envelopes are critical rock mechanical data for gas reservoir evaluation and development, especially when the basic rock properties are measured under actual reservoir conditions that include pore pressure. For coalbed methane (CBM) reservoirs, the mechanical properties of coal may be different under actual reservoir conditions because the in situ coal is fluid saturated. Multistage triaxial testing of coal can generate a full failure envelope using a single core instead of a set of destructive core tests—as is the case with single stage testing. This multistage technique is necessary because of the scarcity of actual reservoir specimens. Consequently, in this study, a series of multistage triaxial compression tests on a fluid-saturated coal specimen was conducted to determine the mechanical properties of reservoir coal formations as a function of confining stress and fluid compositions and pressures. An oven-dried coal core 50 mm in diameter and 100 mm in length was prepared. Different fluids were employed in the test, including the non-sorbing gas He and sorbing gases, such as N2, CH4 and CO2, and also H2O. Coal sorption behavior was investigated during the triaxial compression test, and the peak stresses under various pore pressures and confining pressure conditions were measured. In addition, the competition between the fluid-density-induced hardening and adsorption-induced softening of the coal core is discussed. The coal strength under gas-saturated conditions was sensitive to the confining pressure. The coal under a higher confining pressure exhibited a stiffer response and the peak load increased with higher confining pressure. Strength weakening due to gas adsorption was observed for N2, CH4, CO2, and water injection. Both CH4 and CO2 had a strong influence on coal stiffness alteration mainly because the higher adsorption capacity of coal for them. Stress-strain relationships behaved in a non-linear when a sorbing-gas was involved. The softening effect of CO2 injection was complicated by a CO2 phase change at higher pressure conditions. This study is applicable to a wide range of engineering applications, including reservoir stress response, permeability evolution, hydraulic fractures, coal mining, and borehole stability, and fault slipping.

The Effects of Pulp Rheology on Gravity Gold Recovery in Free Milling Gold Ore of the Tarkwaian Systems of Ghana

ABSTRACT Gravity gold characterization provides a comprehensive understanding on the effect of mineralogy, particle size, and liberation on gravity concentrator performance. This is of significant economic importance for gold ores with a high amount of coarse gold particles. In this study, the effect of pulp rheology on gravity recoverable gold (GRG) was investigated using a single-stage GRG test on paleoplacer gold deposits of the Tarkwaian system of Ghana. The elemental and mineralogical composition of the gold ore was characterized using ICP-MS, XRD, and QEMSCAN analyses. Bench-scale gravity concentration was performed on the gold ore at varying clay contents (in the range of 5–30 wt.%) using Lab Knelson concentrator in the absence and presence of NaOH (2.5 kg/t) and CaO (2.5 kg/t). The mineralogical analysis showed the ore is oxidized and comprised 88% Quartz, 8% muscovite mica, 2% hematite, and 2% kaolinite. Liberation and association analyses showed 58% of the gold particles were liberated, 1% formed binary with quartz, and 41% formed complex aggregates with other mineral phases. The gravity concentration of the ore without clay material yielded 51% Au recovery (11.2 g/t) at the grind size of 80% passing 106 µm. Partial replacement of the ore with clay material at 5%, 10%, 15%, 20%, and 30% decreased gold recovery from 51% to 25.7%, 12.7%, 8.8%, 5.1%, and 1.5%, respectively. Subsequent conditioning of the slurry with NaOH improved gold recovery due to possible improvement in slurry rheology. However, the addition of CaO decreased gold recovery due to an increase in slurry viscosity.

Physiologically based pharmacokinetic model outputs depend on dissolution data and their input: Case examples glibenclamide and dipyridamole

A plethora of dissolution tests exists for oral dosage forms, with variations in selection of the dissolution medium, the hydrodynamics and the dissolution equipment. This work aimed at determining the influence of media composition, the type of dissolution test and the method for entering the data into a PBPK model on the ability to simulate the in vivo plasma profile of an immediate release formulation.Using two rDCS IIa substances, glibenclamide and dipyridamole, housed in immediate-release formulations as model dosage forms, dissolution tests were performed in USP apparatus II with the biorelevant media FaSSGF, FaSSIF V1, V2 and V3 using both single-stage and two-stage test designs. The results were then integrated into the PBPK software SimcypⓇ either as the observed release profile (dissolution rate model, DRM) or using a semi-mechanistic model (diffusion layer model, DLM) and compared with in vivo plasma profiles.The selection of the FaSSIF version did not appear to have any relevant influence on the dissolution of the weakly basic dipyridamole, while the weakly acidic glibenclamide was sensitive to the difference in pH between FaSSIF V1, V2 and FaSSIF V3. Since both compounds have pKa values close to the pH of biorelevant media representing conditions in the small intestine, these results may be specific to compounds with similar ionization behavior. Single-stage and two-stage testing led to equivalent simulations for glibenclamide. Only results from the single-stage test in FaSSGF led to a close simulation of the pharmacokinetic profile of dipyridamole when data were inputted using the DRM, while simulations from two-stage testing were most similar to the observed pharmacokinetic profile when DLM with selection of a dynamic pH profile in the small intestine was selected as the data input method. These results emphasize the importance of data input to the simulation results.

An Investigation on Failure Behaviour of a Porous Sandstone Using Single-Stage and Multi-stage True Triaxial Stress Tests

The deformational characteristics of a set of synthetic sandstones when subjected to true triaxial stress conditions were investigated in this study. The experimental results showed that the lateral stress anisotropy (σ2 ≠ σ3) significantly affected the rock’s compressive strength, elastic modulus, inelastic deformation, dilatancy and failure mode. By increasing the intermediate principal stress (σ2) over quasi-isotropic conditions (σ2 = σ3), the measured compressive strength increased more than twice in some cases, and the onset of dilatancy was suppressed to more than 80% of the peak stress. The obtained failure stresses were examined against a Mogi-type true triaxial criterion and indicated a good fit to the empirical model. Furthermore, multistage-true triaxial tests were carried out on the sandstones, and their results were compared against the single-stage test data to examine the suitability of this testing method for evaluation of the σ2 impact on the rock’s mechanical properties. Over the course of each multistage-true triaxial test, a sample was loaded to several levels of intermediate principal stress, while the minimum stress was held constant. Comparing the results of the multistage-true triaxial tests on the synthetic sandstones with the equivalent single-stage true triaxial measurements revealed noticeable differences between the resultant rock strengths and elastic properties. The findings of these tests are discussed and the potential mechanisms responsible for the observed disagreements are explained in this paper.

Asymptotic versus exact methods in the analysis of contingency tables: Evidence-based practical recommendations

Controversy over the validity of significance tests in the analysis of contingency tables is motivated by the disagreement between asymptotic and exact p values and its dependence on the magnitude of expected frequencies. Variants of Pearson's X2 statistic and their asymptotic distributions were proposed to overcome the difficulties, but several approaches also exist to conduct exact tests. This paper shows that discrepant asymptotic and exact results may or may not occur whether expected frequencies are large or small: Eventual inaccuracy of asymptotic p values is instead caused by idiosyncrasies of the discrete distribution of X2. More importantly, discrepancies are also artificially created by the hypergeometric sampling model used to perform exact tests. Exact computations under the alternative full-multinomial or product-multinomial models require eliminating nuisance parameters and we propose a novel method that integrates them out. The resultant exact distributions are very accurately approximated by the asymptotic distribution, which eliminates concerns about the accuracy of the latter. We also discuss that the two-stage approach that tests for significance of residuals conditional on a significant X2 test is inadvisable and that an alternative single-stage test preserves Type-I error rates and further eliminates concerns about asymptotic accuracy.

Vortices inside a single-stage axial air turbine captured by Particle Image Velocimetry

Particle Image Velocimetry (PIV) is an experimental method of fluid research resulting into a spatially resolved two-dimensional velocity field. We measured the velocity inside a single-stage axial test turbine at the Czech Aerospace Research Centre. We studied the axial × tangential plane just behind the rotor wheel at the tip radius under three regimes: underloaded, designed and overloaded ones. We found individual vortices in the instantaneous snapshots and we analyze their properties statistically.

Cyclic and postcyclic behaviour of silts and silty sands from the Indo Gangetic Plain

The Indo Gangetic Plain (IGP) that lies on the verge of subduction zone of Indian and Eurasian plate is a seismically active, densely populated region with deep soil deposits. A number of critical structures such as rail and highway bridges and nuclear power plants are being built in the region to cater to the large population of the region, and hence the characterization of deep soil deposits in this region are important. In the present study undisturbed soil samples (UDS) from a site in the IGP plane are examined for static, cyclic, and post-cyclic behaviour. The soils tested have fines content varying from about 20% to 80%, and the fines are non-plastic in nature. The modulus reduction and damping ratio of soil at small, medium and large strain range is examined with the UDS by carrying out bender element, resonant column, and cyclic triaxial tests, respectively. Post cyclic behaviour of non-plastic silty soils is also examined with single stage and multistage cyclic triaxial testing. It is observed that the post-cyclic shear strength increases with increase in the non-plastic fines in the soil. The history of cyclic loading preceding the post cyclic tests is found to influence the tangent modulus observed in post cyclic tests. A site specific calibration parameter is proposed to predict pore pressure response using the energy based Green Mitchel Polito (GMP) pore pressure model.

Investigation of shear strength of interface between roadbase and geosynthetics using large-scale single-stage and multi-stage direct shear test

The application of geosynthetics in the road pavement industry as a reinforcement has increased dramatically in recent years. Geosynthetic inclusions can significantly: (i) increase the bearing capacity of the pavement, (ii) prolong the road service life, (iii) reduce maintenance costs, iv) diminish unfavourable large vertical and lateral pavement deformations; and (v) prevent reflective cracking and reduce crack propagation. Although considerable research has been carried out on the interfaces between soils and geosynthetics through large-scale direct shear testing, there is a lack of research in the interfaces between roadbase materials and geosynthetics in pavement engineering. The main innovation of this paper is to investigate the shear strength behaviour of the interfaces existing in a geosynthetic-reinforced pavement. One interface is existing between roadbase and geosynthetic reinforcement for base reinforcement; another one is existing between roadbase and subgrade with geosynthetic reinforcement for subgrade stabilisation. Therefore, a series of laboratory, large-scale direct shear tests was carried out on roadbase materials with and without the inclusion of geosynthetics, under applied normal stresses of 25, 50, 75 or 100 kPa, representing the magnitude of the overburden pressure in the pavement. In addition, theoretical interpretations are developed to back up the experimental results, and to quantify the contribution of different shear strength components mobilised along the interface between roadbase materials and geogrids. Finally, the applicability of multi-stage, large-scale direct shear box testing is assessed by comparing the results obtained with those from conventional single-stage tests obtained in the present experimental study.

The Comparison of Aerodynamic Performance Data Acquired From Thermal Measurements and a Torquemeter on a Compressor Impeller

Full-thermal heat-soak of machinery is vital for acquiring accurate aerodynamic performance data, but this process often requires significant testing time to allow all facility components to reach a steady-state temperature. Even still, there is the potential for heat loss in a well-insulated facility, and this can lead to inaccurate results. The implementation of a torquemeter to calculate performance metrics, such as isentropic efficiency, has two potential advantages: (1) the method is not susceptible to effects due to thermal heat loss in the facility, and (2) a torquemeter directly measures actual torque, and thus work, input, which eliminates the need to fully heat-soak to measure the actual enthalpy rise of the gas. This paper presents a comparison of aerodynamic performance metrics calculated both from data acquired with thermal measurements as well as from a torquemeter. These tests were conducted over five speedlines for a shrouded impeller in the Southwest Research Institute Single Stage Test Rig facility. Isentropic efficiency calculated from the torquemeter was approximately 1–2 efficiency points lower than the isentropic efficiency based on thermal measurements. This corresponds to approximately 0.5–1 °C in heat loss in the discharge collector and piping. Furthermore, observations from three full-thermal heat-soak points indicate the significant difference in time required to reach steady-state performance within measurement uncertainty tolerances between the torque-based and thermal-based methods. This comparison, while largely suspected, has not yet been studied in previous publications.