Elucidating the polycyclic aromatic hydrocarbons involved in soot inception.

Polycyclic aromatic hydrocarbons are the main precursors to soot particles in combustion systems. A lack of direct experimental evidence has led to controversial theoretical explanations for the transition from gas-phase species to organic soot clusters. This work focuses on sampling infant soot particles from well-defined flames followed by analysis using state-of-the-art mass spectrometry. We found that PAH molecules present in soot particles are all stabilomers. Kinetic Monte Carlo simulations and thermodynamic stability calculations further identify the detected PAHs as peri-condensed and without aliphatic chains. Van der Waals forces can easily link PAHs of such size and shape to form PAH dimers and larger clusters under the specified flame conditions. Our results provide direct experimental evidence that soot inception is initiated by a physical process under typical flame conditions. This work improves our understanding of aerosol particulates, which has implications for their environmental and climate change impacts.

Is cavitation a truly sensible choice for intensifying photocatalytic oxidation processes? - Implications on phenol degradation using ZnO photocatalysts.

Phenols are recalcitrant compounds that constitute the majority of organic contaminants in industrial wastewaters. Their removal at large scales require a combination of various processes to reach the desired discharge quality. An extensive body of work has already been published in the area of phenol removal from wastewater, however none of them have focussed on a truly 'sensible' approach for coupling advanced oxidation processes (AOPs). Rather, a higher removal efficiency was targeted by unduly complicating the process by combining multiple AOPs. The most influential AOP as the primary method typically driven by the nature of the pollutant should form the basis for a hybrid AOP followed by a complementary AOP to intensify the oxidation process. This strategy is lacking in current literature. We address this knowledge gap directly by systematically identifying the best hybrid process for ZnO mediated photocatalysis of phenol. Either a cavitation mediated pre-treatment of ZnO or cavitation-photocatalysis-peroxide based hybrid AOP was investigated. While the pre-treatment approach led to >25% increase in phenol oxidation compared to bare ZnO photocatalysis, the hydrodynamic cavitation-photocatalysis-peroxide based system was found to have a cavitational yield 5 times higher than its acoustic cavitation counterpart. A new phenomenon known as the 'pseudo staggered effect' was also observed and established in hydrodynamic cavitation mediated photocatalysis-peroxide hybrid process for the first time. While we demonstrated that cavitation is a truly 'sensible' choice to enhance photocatalysis, the nature of the pollutant under investigation must always be the key driver when designing such hybrid AOPs.

Sonoprocessing of oil: Asphaltene declustering behind fine ultrasonic emulsions.

Despite the transition toward carbon-free energy carriers, liquid fossil fuels are expected to occupy an important market share in the future. Therefore, it is crucial to develop innovative technology for better combustion reducing the emissions of pollutants associated with their utilization. Water in oil (w/o) emulsions contribute to greener combustion, increasing carbon efficiency and reducing emissions. Water content, emulsions stability, and droplet size distributions are key parameters in targeting the efficient use of emulsions as combustibles. In particular, for fixed water content, the finer the emulsion, the better its beneficial effect on combustion. In this work, two emulsions, mechanically and ultrasonically generated, were compared. Cryogenic scanning electron microscopy (cryo-SEM) allowed the visualization of water droplets inside the oily matrix. No surfactants were added to the oil, due to its high asphaltenic content. Asphaltene molecular aggregates, namely clusters, act as natural surfactants stabilizing the emulsions by arranging at w/o interface and forming a rigid film. The asphaltenic rigid film is clearly visualized in this work and compared for the two emulsions. The results showed finer water droplets in the ultrasonically generated emulsion, together with a reduction in the thickness of the asphaltenic film. Ultrasonically induced cavitation favored the de-clustering (breakage of intermolecular forces) of asphaltene molecules. Thus, smaller clusters allowed to stabilize smaller water droplets resulting in an ultra-fine emulsion, which improves the combustion performances of the fuel.

Flame Synthesis of Carbon and Metal-Oxide Nanoparticles: Flame Types, Effects of Combustion Parameters on Properties and Measurement Methods.

Carbon and metal-oxide nanoparticles (NP) are currently synthesized worldwide for various applications in the solar-energy, optical, pharmaceutical, and biomedical industries, among many others. Gas phase methods comprise flame synthesis and flame spray pyrolysis (FSP), which provide high efficiency, low cost, and the possibility of large-scale applications. The variation of combustion operation parameters exerts significant effects on the properties of the NPs. An analysis of the latest research results relevant to NP flame synthesis can provide new insight into the optimization of these methods and the development of these techniques for a large scale. This review offers insight into the current status of flame synthesis for carbon and metal-oxide NPs-specifically containing analysis and comparison of the most common carbon and metal-oxide NP production techniques. The burner configurations used at the laboratory scale and large scale are also discussed, followed by the assessment of the influence of combustion parameters on the properties of NPs. Finally, the features of the measurement techniques applied for determining NP properties were described.

Study of the Effect of Research Octane Number on the Auto-Ignition of Lubricant Oil Surrogates (n-Hexadecane).

Engine oil is considered one of the sources for pre-ignition in downsized boosted direct injection spark-ignited engines. When interacting with fuel sprayed in the combustion chamber, engine oil forms an ignitable mixture and can cause an ignition event before firing the spark plug. Because high research octane number (RON) fuels are difficult to auto-ignite and tend to suppress the knock in an internal combustion engine, studying their interaction with engine oil is essential. Hence, in the current study, a suitable lubricant oil surrogate, namely, n-hexadecane, is mixed with iso-octane and n-heptane at different concentrations to investigate the auto-ignition behavior at elevated pressures. Five sets of fuels (PRF0, PRF20, PRF50, PRF80, and PRF100) were prepared to get a wide range of RONs and blended with n-hexadecane at 15, 25, 35, and 45% mixture concentrations (vol %). These experiments were conducted in a constant volume combustion chamber, keeping the initial temperature constant at 300 °C. A single droplet of the mixture was suspended on a thermocouple bead to record the droplet's lifetime temperature. It was observed that hexadecane mixed with PRF0, PRF20, PRF50, and PRF80 showed similar auto-ignition behaviors. The time of ignition (TI) for these mixtures initially increased until 25% concentration of the fuel in n-hexadecane, and further addition of fuels to 35% and higher concentrations showed a gradual decrease in TI. Ignition of mixtures with 35% and 45% fuel concentrations is attributed to n-heptane, as its low temperature chemistry is the dominant factor in its high reactivity compared to iso-octane. TI increased with the increasing concentration of PRF100 mixtures in hexadecane, unlike other PRF fuels tested in this study. This is because iso-octane is a high RON fuel with a higher auto-ignition temperature, making it challenging to auto-ignite.

Gas-to-Liquid Phase Transition of PAH at Flame Temperatures.

Significant evidence has shown that soot can be formed from polycyclic aromatic hydrocarbon (PAH) in combustion environments, but the transition of high molecular PAH from the gas phase to soot in a liquid or solid state remains unclear. In this study, the relationships between the boiling points of various planar PAHs and their thermodynamic properties are systematically investigated, to find a satisfactory marker for the phase transition event. Temperature-dependent thermodynamic properties, including entropy, specific heat capacity, enthalpy, and Gibbs free energy, are simultaneously calculated for PAHs, using density functional theory and three composite compound methods. Comparison of the results indicates that the individual G3 method, plus an atomization reaction approach, produces the most accurate thermochemistry parameters. Compared to entropy, enthalpy, and Gibbs free energy, the specific heat capacity at 298 K is found to be a better marker for the boiling point of PAHs due to the observed linear correlation, predictable characteristics, and fidelity of accuracy as a function of temperature. The correlation equation Y = 10.996X + 122.111 is proposed (where Y is the boiling temperature (K) and X is Cp at 298 K (cal/K/mol)). The standard deviation is as low as 16.7 K when comparing the calculated boiling points and experimentally determined values for 25 different aromatic species ranging from benzene to ovalene (C32H14). The effects of carbon number, structural arrangement, and partial pressure on the boiling point of large planar PAH are discussed. The results reveal that the carbon number in large planar PAH is the dominant factor determining its boiling points. It is shown that PAHs containing about 60-65 carbon atoms are likely to exist as liquids in flames, although the partial pressure of such species is very low.

An Investigation of the Relationship Between COMLEX-USA Licensure Examination Performance and State Licensing Board Disciplinary Actions.

PURPOSE: Passing the Comprehensive Osteopathic Medical Licensing Examination of the United States (COMLEX-USA) serves as a licensing requirement, yet there is limited understanding between this high-stakes exam and performance outcomes. This study examined the relationship between COMLEX-USA scores and disciplinary actions received by osteopathic physicians. METHOD: Data for osteopathic physicians (N = 26,383) who graduated from medical school between 2004 and 2013 were analyzed using multinomial logistic regression to assess the relationship between COMLEX-USA scores and placement into one of 3 disciplinary action categories relative to no action received, controlling for years in practice and gender. RESULTS: Less than 1% of physicians in this study (n = 187) had a disciplinary action(s). Controlling for all COMLEX-USA levels, years in practice, and gender, higher Level 3 scores were associated with significant decreased odds for all action categories: revoked licensed (odds ratio [OR] = 0.51, 95% confidence interval [CI] 0.36, 0.72; P < .001), imposed limitations to practice (OR = 0.59, 95% CI 0.41, 0.84; P < .01), and other action imposed (OR = 0.48, 95% CI 0.33, 0.69; P < .001), relative to not receiving an action. In these same models, higher Level 2 Performance Evaluation Biomedical/Biomechanical Domain scores decreased the odds for an action that revoked a license (OR = 0.75, 95% CI 0.58, 0.98; P < .05) and imposed limitations to practice (OR = 0.64, 95% CI 0.49, 0.84; P < .001). CONCLUSIONS: These findings provide evidence that the COMLEX-USA delivers useful information regarding the likelihood of a practitioner receiving state board disciplinary actions.

Parents' observed responses to children's emotional distress: Relations with social competence in preschool.

Although affective interactions in the family are important for development, home observational data are sparse. We replicated and extended one such study, Roberts & Strayer (1987, Developmental Psychology, 23, 415). Interactions in 33 two-parent families (mean child age = 4.8 years; 48% girls) were observed for four evenings, from suppertime until the child settled for the night. Parents completed the Child Rearing Practices Q-sort. Peer interactions and friendship networks in preschool were observed over four days. Teachers and observers completed the Preschool Behavior Q-Sort. Based on Q-rated peer competence and aggression, three expected groups of children were identified, one of them high on both aggression and peer competence. Although socially active and accepted by peers, they were, compared with other children, less cooperative with adults, less prosocial with peers, more impulsive, less achievement oriented, less purposive, and less happy (mean η2  = .52). Parenting, especially observed impatience, threats, and use of force when children were emotionally distressed, showed important differences across groups.

Theoretical Study of PAH Growth by Phenylacetylene Addition.

Although there was significant advancement on polycyclic aromatic hydrocarbon (PAH) formation, current mechanisms are still limited in providing an integrated and accurate scheme of PAH yield in combustion conditions; thus, a more detailed and comprehensive understanding is necessary. This work provides a systematic investigation of PAH growth by phenylacetylene addition. A combination of the density functional theory (DFT/B3LYP/6-311+G(d,p)) and the complete basis set method (CBS-QB3) is utilized to calculate the potential energy surfaces. The reaction system is initiated by the H elimination reaction of phenylacetylene + H → o-ethynylphenyl + H2, and then, the addition reaction of phenylacetylene and o-ethynylphenyl can produce PAHs with one, two, three, and four rings. The temperature- and pressure-dependent reaction rate coefficients are calculated via a combination of conventional transition state theory (TST) and Rice-Ramsperger-Kassel-Marcus (RRKM) theory with solving the master equation in the temperature range of 500-2500 K and at the pressure range of 0.01-10 atm. There are 263 species and 65 reactions in this reaction system. It shows that the rate constants of this reaction system are highly temperature-dependent and slightly sensitive to the pressure at temperatures lower than 1300 K. To evaluate the yield distributions of various PAH products in the whole reaction network, a closed 0-D batch reactor model in Chemkin is used to calculate the C6H5C2H-C2H2-H-Ar reaction system. The results showed that the prevailing products of this system are three-ring PAHs with side chain structures. Compared with the traditional HACA pathways, the investigated reaction system presents higher efficiency in large PAH formations, which could subsequently promote the formation of soot particles. The phenylacetylene and o-ethynylphenyl reaction network emphasizes the importance of species with side chains, and it enriches current PAH growth pathways aside from the addition of small species such as C2H2.

Tracer-free laser-induced grating spectroscopy using a pulse burst laser at 100 kHz.

This work shows the first application of a burst laser for laser-induced grating spectroscopy (LIGS) diagnostics. High repetition rate (100 kHz) LIGS is performed in non reacting and reacting flows using the fundamental harmonic of a Nd:YAG pulse-burst laser as pump. In the first part of the paper, we demonstrate the first time-resolved, high repetition rate electrostrictive LIGS measurements in a sinusoidally-modulated helium jet, allowed by the highly energetic pulses delivered by the burst laser (around 130 mJ per pulse). In the second part of the paper, we perform thermal LIGS measurements in a premixed laminar methane/air flame. Thermal gratings are generated in the flame products from the water vapour, which weakly absorbs 1064 nm light. Thus, this work demonstrates the potential of seeding-free high repetition rate LIGS as a technique to detect and time-resolve the instantaneous speed of sound, temperature, and composition in unsteady flow processes.

Comparison study of judged clinical skills competence from standard setting ratings generated under different administration conditions.

When the safety of the public is at stake, it is particularly relevant for licensing and credentialing exam agencies to use defensible standard setting methods to categorize candidates into competence categories (e.g., pass/fail). The aim of this study was to gather evidence to support change to the Comprehensive Osteopathic Medical Licensing-USA Level 2-Performance Evaluation standard setting design and administrative process. Twenty-two video recordings of candidates assessed for clinical competence were randomly selected from the 2014-2015 Humanistic domain test score distribution ranging from the highest to lowest quintile of performance. Nineteen panelists convened at the same site to receive training and practice prior to generating judgments of qualified or not qualified performance to each of the twenty videos. At the end of training, one panel remained onsite to complete their judgments and the second panel was released and given 1 week to observe the same twenty videos and complete their judgments offsite. The two one-sided test procedure established equivalence between panel group means at the 0.05 confidence level, controlling for rater errors within each panel group. From a practical cost-effective and administrative resource perspective, results from this study suggest it is possible to diverge from typical panel groups, who are sequestered the entire time onsite, to larger numbers of panelists who can make their judgments offsite with little impact on judged samples of qualified performance. Standard setting designs having panelists train together and then allowing those to provide judgments yields equivalent ratings and, ultimately, similar cut scores.

Soot, organics, and ultrafine ash from air- and oxy-fired coal combustion.

Pulverized bituminous coal was burned in a 10W externally heated entrained flow furnace under air-combustion and three oxy-combustion inlet oxygen conditions (28, 32, and 36%). Experiments were designed to produce flames with practically relevant stoichiometric ratios (SR=1.2-1.4) and constant residence times (2.3s). Size-classified fly ash samples were collected, and measurements focused on the soot, elemental carbon (EC), and organic carbon (OC) composition of the total and ultrafine (<0.6µm) fly ash. Results indicate that although the total fly ash carbon, as measured by loss on ignition, was always acceptably low (<2%) with all three oxycombustion conditions lower than air-combustion, the ultrafine fly ash for both air-fired and oxy-fired combustion conditions consists primarily of carbonaceous material (50-95%). Carbonaceous components on particles <0.6µm measured by a thermal optical method showed that large fractions (52-93%) consisted of OC rather than EC, as expected. This observation was supported by thermogravimetric analysis indicating that for the air, 28% oxy, and 32% oxy conditions, 14-71% of this material may be OC volatilizing between 100 and 550°C with the remaining 29-86% being EC/soot. However, for the 36% oxy condition, OC may comprise over 90% of the ultrafine carbon with a much smaller EC/soot contribution. These data were interpreted by considering the effects of oxy-combustion on flame attachment, ignition delay, and soot oxidation of a bituminous coal, and the effects of these processes on OC and EC emissions. Flame aerodynamics and inlet oxidant composition may influence emissions of organic hazardous air pollutants (HAPs) from a bituminous coal. During oxy-coal combustion, judicious control of inlet oxygen concentration and placement may be used to minimize organic HAP and soot emissions.

Multisite evaluation of a monoclonal IMMULITE erythropoietin immunoassay.

BACKGROUND: Erythropoietin (EPO) measurements are useful in diagnosing anemias and polycythemias. We conducted a multisite evaluation of a monoclonal IMMULITE® EPO immunoassay.(1) DESIGN AND METHODS: The IMMULITE EPO assay is a solid-phase enzyme-labeled chemiluminescent immunometric assay. Method comparison to the Beckman ACCESS 2 assay using clinically characterized samples and reproducibility studies were conducted at three external independent laboratories. Internal evaluation conducted at Siemens included comparison of IMMULITE® 2000 and IMMULITE® 1000 assays to the ACCESS 2 assay; imprecision; linearity; limit of blank (LoB), limit of detection (LoD), and functional sensitivity; potential interference and cross-reactants; and reference interval determination. RESULTS: External method comparison gave Deming regression of (IMMULITE 2000)=0.96(ACCESS 2)+2.57IU/L, r=0.98 (n=217). Reproducibility ranged from 6.1% to 16.2%. Internal method comparisons gave Deming regressions of (IMMULITE 2000)=1.09(ACCESS 2)-3.51IU/L, r=0.98 and (IMMULITE 1000)=0.95(ACCESS 2)+0.52IU/L, r=0.95. Total imprecision ranged from 6.4% to 10.3% and linearity was confirmed from 3.5 to 562IU/L. LoB, LoD, and functional sensitivity were 0.5, 1.0, and 1.5IU/L, respectively. The assay was highly specific for EPO. Nonparametric reference interval was 4.3 to 29.0IU/L (n=170). CONCLUSIONS: The monoclonal IMMULITE EPO assay showed acceptable performance for EPO measurement.

Low body mass index and dyslipidemia in dialysis patients linked to elevated plasma fibroblast growth factor 23.

BACKGROUND: Fibroblast growth factor 23 (FGF23) has been associated with death in dialysis patients. Since FGF23 shares structural features with FGF19 subfamily members that exert hormonal control of fat mass, we hypothesized that high circulating FGF23 concentrations would be associated with the development of a uremic lipid profile and lower body mass index (BMI). METHODS: This study was conducted among 654 patients receiving chronic hemodialysis. C-terminal FGF23 concentrations were measured in stored plasma samples. Linear regression was used to examine the cross-sectional associations of plasma FGF23 concentrations with BMI, total cholesterol (TC), low-density lipoprotein-cholesterol (LDL-C), high-density lipoprotein-cholesterol (HDL-C) and triglycerides. Cox proportional hazard models were used to examine the association between FGF23 concentrations and all-cause mortality. RESULTS: Participants had a mean age of 60 ± 11 years and a median (IQR) FGF23 concentration of 4,212 (1,411-13,816) RU/ml. An increase per SD in log10 FGF23 was associated with lower BMI (ß = -1.11; p = 0.008), TC (ß = -6.46; p = 0.02), LDL-C (ß = -4.73; p = 0.04) and HDL-C (ß = -2.14; p = 0.03); after adjusting for age, gender, race, cardiovascular risk factors, serum albumin, markers of mineral metabolism, and use of lipid-lowering drugs. The association of FGF23 with death was attenuated after adjustment for HDL-C (HR of highest quartile 1.53, 95% CI 1.06-2.20 compared to lowest quartile). CONCLUSION: These results indicate that higher plasma FGF23 levels are associated with lower BMI and dyslipidemia in dialysis patients. The association between FGF23 and death may be mediated through unexplored metabolic risk factors unrelated to mineral metabolism.

Measurement of thyroglobulin by liquid chromatography-tandem mass spectrometry in serum and plasma in the presence of antithyroglobulin autoantibodies.

BACKGROUND: Measurement of serum thyroglobulin (Tg) is used to monitor patients after treatment for differentiated thyroid carcinoma (TC). Difficulty in using Tg as a biomarker of the recurrence of TC in many patients stems from the presence of endogenous anti-Tg autoantibodies (Tg-AAbs), which can interfere with immunoassays (IAs) and cause false-negative results. METHODS: We enriched Tg from serum samples using rabbit polyclonal anti-Tg antiserum and protein precipitation. Unrelated proteins were partially depleted in the process. Enriched proteins were then denatured, reduced, and digested with trypsin after the addition of a winged internal standard peptide. A Tg-specific tryptic peptide was purified by immunoaffinity extraction and analyzed by 2-dimensional LC-MS/MS. Instrument cycle time was 6.5 min per sample. RESULTS: The lower limit of quantification was 0.5 ng/mL (0.76 fmol/mL dimer). Total imprecision of triplicate measurements in serum samples over 5 days was <10%. Comparison with a commercial IA using serum samples free of Tg-AAb (n = 73) showed Deming regression, IA = 1.00 * LC-MS/MS - 2.35, r = 0.982, standard error of the estimate (S(y|x)) = 9.52. In a set of Tg-AAb-positive samples that tested negative for Tg using IA (n = 71), concentrations determined by LC-MS/MS were ≥0.5 ng/mL in 23% of samples (median 1.2, range 0.7-11 ng/mL). CONCLUSIONS: The introduced method has acceptable performance characteristics for use in clinical diagnostic applications. The most substantial disagreement between methods was observed in Tg-AAb-positive samples with concentrations <2 ng/mL (determined with LC-MS/MS). The affinity-assisted enrichment strategy used for Tg in this method should be applicable to other biomarkers that have endogenous autoantibodies.

Prospective multicenter evaluation of the Beckman Coulter Prostate Health Index using WHO calibration.

PURPOSE: Reported prostate specific antigen values may differ substantially among assays using Hybritech® or WHO standardization. The Beckman Coulter® Prostate Health Index and [-2]proPSA are newly approved serum markers associated with prostate cancer risk and aggressiveness. We studied the influence of assay standardization on these markers. MATERIALS AND METHODS: Prostate specific antigen, percent free prostate specific antigen and [-2]proPSA were measured using Hybritech calibration in 892 men from a prospective, multicenter study undergoing prostate biopsy. We calculated the Prostate Health Index using the equation, ([-2]proPSA/free prostate specific antigen) × PSA. Index performance characteristics for prostate cancer detection were then determined using recalculated WHO calibration prostate specific antigen values. RESULTS: The median Prostate Health Index was significantly higher in men with prostate cancer than in those with negative biopsies using WHO values (47.4 vs 39.8, p <0.001). The index offered improved discrimination of prostate cancer detection on biopsy (AUC 0.704) compared to percent free or total prostate specific antigen using the WHO calibration. CONCLUSIONS: The Prostate Health Index can be calculated using Hybritech or WHO standardized assays. It significantly improved prediction of the biopsy outcome over that of percent free or prostate specific antigen alone.

Performance characteristics of the ARCHITECT Galectin-3 assay.

OBJECTIVES: Galectin-3 is an emerging biomarker that is commonly increased in patients with heart failure and/or patients at risk for cardiovascular disease. We evaluated the Galectin-3 assay on the Abbott ARCHITECT i1000(SR) and ARCHITECT i2000(SR) at 2 testing sites. DESIGN AND METHODS: Imprecision (%CV), interference, limits of blank (LoB), detection (LoD), and quantitation (LoQ), linearity, method comparison to an ELISA method, comparisons between plasma and serum, and reference intervals were evaluated. Imprecision was performed based on two runs of duplicate testing conducted daily. Verification of LoB, LoD, and LoQ was performed according to Clinical and Laboratory Standards Institute guidelines. Linearity was evaluated by making 5 dilutions of a high patient EDTA plasma pool with a low patient pool. Reference intervals were established using EDTA plasma collected from self-reported healthy volunteers. A second lot of reagent was used at one site for method comparison and imprecision studies. RESULTS: Total CV's were ≤6.0%. A positive interference was observed for hemolyzed samples over 2.0 g/L hemolysate. The LoB ranged from 0.1 to 0.3 ng/mL, the LoD from 1.4 to 2.1 ng/mL and the LoQ from 3.0 to 3.3 ng/mL. Linearity studies had slopes and correlation coefficients equal to 1.0. Comparison of the i1000(SR) and i2000(SR) to the ELISA method demonstrated slopes of 1.0 to 1.2 and correlation coefficients of 0.93 to 0.97. The 97.5th percentile of the reference interval was 18.7 and 17.9 ng/mL for the i1000(SR) and i2000(SR), respectively. CONCLUSIONS: The Abbott Galectin-3 assay demonstrated acceptable analytical performance on both the ARCHITECT i1000(SR) and ARCHITECT i2000(SR).

Investigation of standardized patient ratings of humanistic competence on a medical licensure examination using Many-Facet Rasch Measurement and generalizability theory.

Humanistic doctor-patient interaction has been measured for eight years using the Global Patient Assessment (GPA) tool in the national osteopathic clinical skills medical licensure examination. Standardized patients (SPs) apply the GPA tool to rate examinees' competence on doctor-patient communication, interpersonal skills, and professionalism. Many-Facet Rasch Measurement was employed to evaluate the overall functioning of the GPA rating scale and to estimate measurement errors associated with characteristics of SP raters and medical case presentations. Generalizability theory was applied to investigate variance components corresponding to each facet of interest. For the 2010-2011 testing cycle, 50,090 SP ratings were analyzed. Although SP raters varied in leniency/stringency of rating, SPs differentiated the six GPA aspects in difficulty, and utilized a reasonable range of the 9-point scale. Reliability indices resulted in sufficient examinee separation, 0.94, from the Rasch model and sufficient dependability from the generalizability analysis for raw scores, 0.83, and transformed Rasch scores, 0.97. Results indicate that medical students' humanistic competence can be reliably measured through the GPA tool in the simulated environment. These measurement models supplement other means of observation and quality control with valuable information about the psychometric quality of SP ratings of humanistic competence.