Toluene (C6H5CH3, boiling point of 384 K) is a monocyclic aromatic compound found in transportation fuels, which plays an important role in soot formation during combustion. To understand its combustion and sooting dynamics, an attractive experimental platform is the spherically symmetric droplet flame. In this work, droplet combustion experiments carried out on the International Space Station are reported to study near spherically symmetric burning of untethered or free-floating toluene droplets at atmospheric pressure over a wide range of initial droplet diameters (D-0 similar to 1 to 7 mm). Spherically symmetric burning conditions and one-dimensional gas transport provide a useful environment to reveal the burning characteristics of this complex fuel, including the influence of D-0 on radiative transport, fuel burning rate, and flame extinction. Results showed that droplets burned to completion without experiencing radiative extinction for D-0 < 2.5 mm, while a two-stage burning process was noted for larger droplets: steady combustion with a visible flame, and then radiative extinction, after which the droplets continued to evaporate because of thermal transport from the locally hot ambience. After radiative extinction, wideband and narrowband radiometer measurements indicated no cool flame or low-temperature combustion regimes. Results also showed that the extinction diameter increased with D-0, which is consistent with trends previously reported for other hydrocarbon fuels. The instantaneous droplet burning rate (K) was initially steady as combustion developed and then decreased with time, accompanied by a significant reduction in flame radiance when the flame radiatively extinguished. A scaling analysis by an energy balance at the droplet interface revealed that the estimated flame temperature dropped sharply from approximately 1400 to 560 K shortly after radiative extinction and then gradually decreased toward ambient levels. Finally, an averaged K (K-avg) was obtained for each D-0 in the visible flame regime and correlated by a power law relation K-avg similar to D-0(-n).

This paper describes a sensitivity-based algorithm for extracting the soot volume fraction (SVF, fv) from digital video images of organic liquid droplets burning under conditions that promote spherically symmetric gas transport. The algorithm was applied for the first time to digital video images of n-propylbenzene (nP) droplets with initial diameters (D0) ranging from 2.1 mm to 5.8 mm. The SVF was obtained by measuring the intensity of light along rays-of-interest (ROIs) through a droplet’s center on the images. A “greedy algorithm” was employed to calculate the dynamic Coefficient of Variation to optimize the number of ROIs and thus enhance the repeatability and accuracy of SVF data. These data analysis efforts revealed many new physical insights into the sooting dynamics of a heavily sooty fuel, nP. The results showed that fv increased with time for a given D0, reached a maximum (fv, max), then decreased. Also, fv, max coincided with the measured soot shell location. The actual mass of soot formed as a function of time followed this same trend, increasing first because of fuel pyrolysis and then decreasing because of oxidation. While the peak value of fv, max over the entire duration of a burn (f *v, max) decreased with increasing D0, the maximum mass of soot (ms, max) itself increased linearly with D02.

In this paper we formulate and analyze an elementary model for the extinction of hydrothermal flames in laminar reactive jets experimentally observed in an aqueous environment at pressures exceeding the critical point of water. This work is motivated by experimental studies of the dynamics of hydrothermal flames performed at the high-pressure laboratory of the NASA Glenn Research Center. Guided by experimental observations, we use several simplifying assumptions that allow the derivation of a simple, yet experimentally feasible, mathematical model for the hydrothermal flame extinction. The analysis of the model shows that the principal parameters of the problem determining flame extinction are Damk & ouml;hler number and the injection velocity of the reactive components. In particular, we formulate a sharp condition for the extinction of hydrothermal flames in terms of Damk & ouml;hler number. The results of the present study may assist in the interpretation of existing experimental data and provide guidance for future experiments.

In this paper we formulate and analyze an elementary model for the propagation of advancing autoignition fronts in reactive co-flow fuel/oxidizer jets injected into an aqueous environment at high pressure. This work is motivated by the experimental studies of autoignition of hydrothermal flames performed at the high pressure laboratory of NASA Glenn Research Center. Guided by experimental observations, we use several simplifying assumptions that allow the derivation of a simple, still experimentally feasible, mathematical model for the propagation of advancing ignition fronts. The model consists of a single diffusion-absorption-advection equation posed in an infinite cylindrical domain with a non-linear condition on the boundary of the cylinder and describes the temperature distribution within the jet. This model manifests an interplay of thermal diffusion, advection and volumetric heat loss within a fuel jet which are balanced by the weak chemical reaction on the jet's boundary. We analyze the model by means of asymptotic and numerical techniques and discuss feasible regimes of propagation of advancing ignition fronts. In particular, we show that in the most interesting parametric regime when the advancing ignition front is on the verge of extinction this model reduces to a one dimensional reaction-diffusion equation with bistable non-linearity. We hope that the present study will be helpful for the interpretation of existing experimental data and guiding of future experiments.

Dynamic measurement precision assessment has been achieved for a differential circle measurement application. Differential circle diameter measurement, in image analysis, typically requires fitting a circle model that optimizes for image distortions, defects or occlusions. The differential task occurs when precise measurements of diameter change are required given object size variation with time. An automated system was designed to provide diameter measurements and associated measurement precision of images of a fuel droplet undergoing combustion in zero gravity for the FLEX-2 dataset. An image gradient-based, least-squares boundary point fitting method to a circle or ellipse model is used for diameter measurement. The presence of soot aggregates poses significant challenges for diameter measurements when it occludes part of the droplet boundary. The precision of the diameter measurements depends upon the image quality. Using synthetic image simulations that model the soot behavior, we developed a model based on image quality measures that assesses the measurement precision for each individual diameter measurement. Thus, diameter measurements with precision assessments were made available for follow-up scientific analysis. The algorithm's success rate for measurable runs was 98%. In cases of limited occlusion, a measurement precision of ±0.2 pixels for the FLEX-2 dataset was achieved.

This paper reports an image analysis approach using a newly-developed open-source program to extract quantitative measurements of soot volume fraction (SVF) from digital video images of burning n-heptane droplets. The automated program developed in this work can analyze images of fixed and untethered droplets to quantify sooting dynamics. The images analyzed in the program were taken from experiments carried out in the Multiuser Droplet Combustion Apparatus (MDCA) onboard the International Space Station (ISS). In these experiments, video imaging of burning droplets was obtained using backlighting by a laser diode with a wavelength of 653 nm. The light was collimated before it passed through the droplet and soot-containing region, after which the light was then attenuated and projected onto the camera's sensors. This technique facilitates the measurements of SVF based on the principles of the full field light extinction method (FFLEM). The measurements provide quantitative data that reveal the sooting dynamics of liquid fuels during droplet combustion processes.The analyses of a soot-attenuating image (ISS n-heptane, untethered droplet) at an instant during the burning show that the SVF distribution has a peak at the soot shell location. It then decreases due to soot oxidation when the location is further away from the burning droplet. Regarding temporal effects on the maximum SVF (SVFmax), results show that SVFmax first increases after the burning is initiated until a peak value is reached, after which SVFmax decreases. The SVFmax values identified in this study for n-heptane are quantitatively consistent with previously reported values for fiber-supported droplets and are reached relatively early in the burning history. n- Heptane images are also analyzed to show the effects of initial droplet sizes on the maximum soot volume fraction. Results show that SVFmax decreases with increasing initial droplet size, which is consistent with visual observations of less soot formed and dimmer flame brightness as Do increases.

Hydrothermal flames are formed in supercritical water in the presence of a fuel and an oxidant (usually air or oxygen). Integrating hydrothermal flames as the heat source for supercritical water oxidation helps to minimize the reaction time (to milliseconds), improve the reaction kinetics and reduce the chances of corrosion and reactor plugging. This review outlines state-of-the-art research on hydrothermal flames including the impacts of process parameters on flame ignition. The ignition and sustainability of hydrothermal flames are dependent on several factors such as the type of fuel and its concentration, type of oxidant (air and oxygen) as well as the temperatures and flow rate of the feed and oxidant. The article describes some novel applications of hydrothermal flames for clean energy production, geothermal energy recovery, deep well spallation, wastewater treatment, degradation of recalcitrant nitrogen-containing compounds and heavy oil upgrading. Finally, the challenges and future perspectives of hydrothermal flame applications are discussed. This review also highlights some technical considerations relating to hydrothermal flames such as the choice of organic solvent and its characteristics, preheating, ignition mechanism, flame stability and propagation, advanced reactor configurations, mixing with subcritical and supercritical components, recirculation zones, cooling mechanisms, corrosion and salt precipitation.

Experimental observations of two-stage autoignition dynamics of fiber-supported normal dodecane droplets in air under normal gravity are presented for a range of pressures and temperatures. High-speed shadowgraph imaging of the autoignition process reveals cool-flame and hot-flame front-formation and propagation dynamics. During two-stage ignition, a cool-flame kernel is first formed below the droplet; it then propagates toward the droplet along the fuel-vapor plume, and subsequently a hot-flame kernel is established behind the cool-flame front which rapidly expands, engulfing the droplet and establishing the classical diffusion flame. Results for the cool-flame and hot-flame kernel locations and their propagation speeds are presented for a range of ambient pressures, varying between normal atmospheric pressure and super-critical pressures and temperatures.

In this paper we derive a simple, still experimentally feasible, model for propagation of traveling fronts of ignition which were recently observed in experimental studies of autoignition of co-flow reactive jets at high pressure. We obtain a closed form analytical solution for this model and present a detailed analysis of this solution. We also present a qualitative comparison of the model predictions with available experimental data.

This study reports an experimental and numerical investigation of droplet combustion of a miscible nheptane/iso-octane mixture at a fixed mixture fraction (equi-volume) for initial diameters (D-o) in the range of 0.8 mm <= D-o < 5 mm. This range encompasses burning transitions from hot flame (HF) combustion to the cool flame (CF) regime where radiative extinction can occur. The simulations assume spherically symmetric gas transport which was promoted in the experiments by a low gravity environment and relatively stationary droplets. Unsupported or free-floating droplets were deployed and ignited in a sealed chamber on the International Space Station to provide a low gravity condition and to accommodate the anticipated long droplet burning times (tens of seconds) for the droplet sizes investigated. The simulations incorporated multistep combustion kinetics with an embedded low temperature kinetic mechanism, non-luminous flame radiation, a model for phase equilibrium of the mixture, variable properties, unsteady gas and liquid transport, and species diffusion in the liquid. The results showed no evidence of preferential vaporization because of the close boiling points of n-heptane and iso-octane. For D-o < 3 mm, the mixture droplets remained in the initial HF burning regime. For larger D-o, a transition to extinction like behavior occurred. Measured flame radiances confirmed the importance of radiation as a controlling mechanism for driving radiative extinction and transitioning to CF burning. Radiative extinction diameters exhibited a linear relationship with D-o which agreed very well with simulations. Mixture radiative extinction diameters were also consistent with literature values for n-decane, n-heptane, and iso-octane. Simulated droplet and flame diameters, burning rates, and flame radiances were also in good agreement with experiments. (C) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Experimental data and detailed numerical modelling are presented on the burning characteristics of a model gasoline/biofuel mixture consisting of n-heptane and iso-butanol. A droplet burning in an environment that minimises the influence of buoyant and forced convective flows in the standard atmosphere is used to promote one-dimensional gas transport to facilitate numerical modelling of the droplet burning process. The numerical model includes a detailed combustion kinetic mechanism, unsteady gas and liquid transport, multicomponent diffusion inside the droplet, variable properties, and non-luminous radiative heat transfer from the flame. The numerical simulation was validated by experimental measurements in the standard atmosphere which showed good agreement with the evolutions of droplet and flame diameters. The iso-butanol concentration had a strong effect on formation of particulates. Above ~20% (volume) iso-butanol, flame luminosity was significantly diminished anddecreased with increasing iso-butanol concentration, while CO2 emissions as a representative greenhouse gas were not strongly influenced by the iso-butanol loading. The soot shell was located near a 1350 K isotherm for concentrations up to 20% (volume) iso-butanol, suggesting this value as a possible soot inception temperature for the mixture droplet. The combustion rate decreased with increasing iso-butanol concentration which was attributed to iso-butanol's higher liquid density. No evidence of a low temperature burning regime, or of extinction, was found (in experiments and simulations) for the small droplet sizes investigated.

Background Modern medicine is rapidly moving towards a data-driven paradigm based on comprehensive multimodal health assessments. Integrated analysis of data from different modalities has the potential of uncovering novel biomarkers and disease signatures. Methods We collected 1385 data features from diverse modalities, including metabolome, microbiome, genetics, and advanced imaging, from 1253 individuals and from a longitudinal validation cohort of 1083 individuals. We utilized a combination of unsupervised machine learning methods to identify multimodal biomarker signatures of health and disease risk. Results Our method identified a set of cardiometabolic biomarkers that goes beyond standard clinical biomarkers. Stratification of individuals based on the signatures of these biomarkers identified distinct subsets of individuals with similar health statuses. Subset membership was a better predictor for diabetes than established clinical biomarkers such as glucose, insulin resistance, and body mass index. The novel biomarkers in the diabetes signature included 1-stearoyl-2-dihomo-linolenoyl-GPC and 1-(1-enyl-palmitoyl)-2-oleoyl-GPC. Another metabolite, cinnamoylglycine, was identified as a potential biomarker for both gut microbiome health and lean mass percentage. We identified potential early signatures for hypertension and a poor metabolic health outcome. Additionally, we found novel associations between a uremic toxin, p-cresol sulfate, and the abundance of the microbiome genera Intestinimonas and an unclassified genus in the Erysipelotrichaceae family. Conclusions Our methodology and results demonstrate the potential of multimodal data integration, from the identification of novel biomarker signatures to a data-driven stratification of individuals into disease subtypes and stages-an essential step towards personalized, preventative health risk assessment.

The thermochemical properties of the ethanol hydrothermal flame (30%-v ethanol-water solution), established in air co-flow under supercritical water conditions, are measured by a quantitative Raman diagnostic technique. The unique spectroscopic features of the chemical compounds are revealed to aid understanding of the fuel decomposition and oxidation process in supercritical phase. A point-wise fiber-optic probe is designed to resolve the needle-like thin flame and identify the spatial profiles - across the flame thickness and over the height of the visible flame - of the combustion species at different fuel/air ratios and airflow rates. An attempt is made to analyze the steep thermal gradients in the primary reaction zone near the fuel nozzle by estimating thermodynamic temperatures from the measured fluid density. The test cell was held at conditions above the critical point of water, at a nominal pressure of 25 MPa and a nominal temperature of 723K (450 degrees C). The flames were over ventilated with an excess air:fuel ratio between two and five times stoichiometric. Depending upon the air:fuel ratio non-sooting blue flames or yellow sooting flames are observed. The results of the Raman diagnostic provide temperature and species profiles that will prove useful for validating numerical models using an idealized laboratory hydrothermal flame. The Raman diagnostic results are augmented with imaging from two orthogonal camera views: a backlit shadow-graphic image of the co-flow jet and a color image of the flame. Published by Elsevier B.V.

Genome sequencing has established clinical utility for rare disease diagnosis. While increasing numbers of individuals have undergone elective genome sequencing, a comprehensive study surveying genome-wide disease-associated genes in adults with deep phenotyping has not been reported. Here we report the results of a 3-y precision medicine study with a goal to integrate whole-genome sequencing with deep phenotyping. A cohort of 1,190 adult participants (402 female [33.8%]; mean age, 54 y [range 20 to 89+]; 70.6% European) had whole-genome sequencing, and were deeply phenotyped using metabolomics, advanced imaging, and clinical laboratory tests in addition to family/medical history. Of 1,190 adults, 206 (17.3%) had at least 1 genetic variant with pathogenic (P) or likely pathogenic (LP) assessment that suggests a predisposition of genetic risk. A multidisciplinary clinical team reviewed all reportable findings for the assessment of genotype and phenotype associations, and 137 (11.5%) had genotype and phenotype associations. A high percentage of genotype and phenotype associations (>75%) was observed for dyslipidemia (n = 24), cardiomyopathy, arrhythmia, and other cardiac diseases (n = 42), and diabetes and endocrine diseases (n = 17). A lack of genotype and phenotype associations, a potential burden for patient care, was observed in 69 (5.8%) individuals with P/LP variants. Genomics and metabolomics associations identified 61 (5.1%) heterozygotes with phenotype manifestations affecting serum metabolite levels in amino acid, lipid and cofactor, and vitamin pathways. Our descriptive analysis provides results on the integration of whole-genome sequencing and deep phenotyping for clinical assessments in adults.

A series of microgravity investigations have been formulated to be performed in the DECLIC and DECLIC-Evo on board the International Space Station to provide a better understanding of fundamental processes that take place in water solutions at near-critical conditions. These investigations rely on the design heritage of an earlier fundamental physics study that explored the nearcritical behavior of pure water and for which the High Temperature Insert (HTI) was originally designed and built. The experiments also have the overarching goal of providing some of the scientific underpinnings for future advances in supercritical water oxidation (SCWO) technologies. SCWO technology is one of NASAs candidate technologies for waste management and resource reclamation for extraterrestrial missions. However, during typical SCWO reactions, inorganic salts present in the reactant stream will precipitate and coat reactor surfaces and control mechanisms, often severely impacting the systems performance. The first of the considered experiments, the Supercritical Water Mixture (SCWM) experiment, is a phenomenological study to provide observations of the phase separation and transport mechanisms of salt precipitate of a dilute solution of Na2SO4 (aq) 0.5%-w at 0-g. In the absence of gravity a unique window for observation of a variety of near-critical physical phenomena is made possible. Observations of this dilute solution have shown striking differences from pure water in its incipient boiling processes, trans-critical phase partitioning, and density stratification as influenced by an overlay of concentration and temperature gradients. A subsequent experiment, SCWM-2, is planned that will expand on the science obtained in SCWM, using the same High Temperature Insert (HTI), which is to be refurbished and filled with a different test solution. A third microgravity experiment, SCWO-D, will then allow for observations of autoignition and stabilization of hydrothermal flames in supercritical water. This final experiment will require a significant insert redesign to accommodate a flow system and a properly designed test cell for observations of small hydrothermal flames without quenching. Additionally, significant ground development work is underway in support of the science associated with the generation and stabilization of hydrothermal flames. The science team at the University of Bordeaux is developing the micro-fluidic devices to support the miniaturized infrastructure for the flow system. The science team at NASA Glenn Research Center is currently developing the science behind the autoignition and stabilization of hydrothermal flames. Preliminary findings of the SCWM experiment and progress in the development of the SCWM-2 and SCWO-D experiments will be discussed in this work.

The developmental trajectory of human skeletal myogenesis and the transition between progenitor and stem cell states are unclear. We used single-cell RNA sequencing to profile human skeletal muscle tissues from embryonic, fetal, and postnatal stages. In silico, we identified myogenic as well as other cell types and constructed a "roadmap" of human skeletal muscle ontogeny across development. In a similar fashion, we also profiled the heterogeneous cell cultures generated from multiple human pluripotent stem cell (hPSC) myogenic differentiation protocols and mapped hPSC-derived myogenic progenitors to an embryonic-to-fetal transition period. We found differentially enriched biological processes and discovered co-regulated gene networks and transcription factors present at distinct myogenic stages. This work serves as a resource for advancing our knowledge of human myogenesis. It also provides a tool for a better understanding of hPSC-derived myogenic progenitors for translational applications in skeletal muscle-based regenerative medicine.

Hydrothermal flame is produced in an aqueous environment beyond the thermodynamic critical properties of water. It is an interface developed at the contact of oxidant and fuel in supercritical water and depends on the operating parameters. In-situ diffusion-limited hydrothermal flames were generated in a novel supercritical flame reactor designed by the National Aeronautics and Space Administration (NASA) at Glenn Research Center to investigate the impacts of oxidant flow rate and temperature on flame ignition and stabilization. The reactor system comprises of n-propanol as fuel and air as the oxidant. Two-dimensional simulation studies were performed to interpret different thermal events occurring during the process. Temperatures inside the reactor were recorded at different times to determine the onset and propagation of hydrothermal flames. Temperature profiles obtained via simulations were compared with the experimental data at near-critical temperatures (380 degrees C and 20.5 MPa). The study of oxidant flow rate on ignition and temperature profile at near-critical and supercritical conditions (400 degrees C and 22.5 MPa) was conducted by varying the air flow rate ranging from 0.5 to 3 mLis. A flow rate of 1.5 mLis was found to be optimal with the spontaneous ignition of hydrothermal flames. The effect of inertial and buoyant forces on hydrothermal flames was qualitatively explained using the non-dimensional Reynolds and Froude numbers. The ignition delay times of hydrothermal flames for near-critical and supercritical reactor conditions for different flow rates are reported. Ignition mechanism and impact of the oxidant characteristics during supercritical water oxidation were inferred using a two-dimensional simulation model for n-propanol-air. (C) 2019 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Results on the autoignition and stabilization of ethanol hydrothermal fames in a Supercritical Water Oxidation (SCWO) reactor operating at constant pressure are reported. The flames are observed as luminous reaction zones occurring in supercritical water; i.e., water at conditions above its critical point (approximately 22 MPa and 374 °C). A co-flow injector is used to inject fuel (inner flow), comprising an aqueous solution ranging from 20 %-v to 50 %-v ethanol, and air (annular flow) into a reactor filled with supercritical water at approximately 24.3 MPa and 425 °C. Results show hydrothermal fames are autoignited and form diffusion flames which exhibit laminar and/or turbulent features depending upon flow conditions. Two orthogonal camera views are used; one providing a backlit shadowgraphic image of the co-flow jet and the other providing color images of the flame. In addition, spectroscopic measurements of flame emissions in the UV and visible spectrum are discussed.

Sequence variation data of the human proteome can be used to analyze 3D protein structures to derive functional insights. We used genetic variant data from nearly 140,000 individuals to analyze 3D positional conservation in 4,715 proteins and 3,951 homology models using 860,292 missense and 465,886 synonymous variants. Sixty percent of protein structures harbor at least one intolerant 3D site as defined by significant depletion of observed over expected missense variation. Structural intolerance data correlated with deep mutational scanning functional readouts for PPARG, MAPK1/ERK2, UBE2I, SUMO1, PTEN, CALM1, CALM2, and TPK1 and with shallow mutagenesis data for 1,026 proteins. The 3D structural intolerance analysis revealed different features for ligand binding pockets and orthosteric and allosteric sites. Large-scale data on human genetic variation support a definition of functional 3D sites proteome-wide.