SEARCH · Engineering Papers

Results for “Drop size distribution”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 307 records · Page 17

All sources NASA NTRS DOE OSTI

NASA NTRS2014

Evaluation of the New Version of the Laser-Optical Disdrometer, OTT Parsivel2

A comparative study of raindrop size distribution measurements has been conducted at NASA's Goddard Space Flight Center where the focus was to evaluate the performance of the upgraded laser-optical OTT Particle Size Velocity (Parsivel2; P2) disdrometer. The experimental setup included a collocated pair of tipping-bucket rain gauges, OTT Parsivel (P1) and P2 disdrometers, and Joss-Waldvogel (JW) disdrometers. Excellent agreement between the two collocated rain gauges enabled their use as a relative reference for event rain totals. A comparison of event total showed that the P2 had a 6%absolute bias with respect to the reference gauges, considerably lower than the P1 and JW disdrometers. Good agreement was also evident between the JW and P2 in hourly raindrop spectra for drop diameters between 0.5 and 4 mm. The P2 drop concentrations mostly increased toward small sizes, and the peak concentrations were mostly observed in the first three measurable size bins. The P1, on the other hand, underestimated small drops and overestimated the large drops, particularly in heavy rain rates. From the analysis performed, it appears that the P2 is an improvement over the P1 model for both drop size and rainfall measurements. P2 mean fall velocities follow accepted terminal fall speed relationships at drop sizes less than 1 mm. As a caveat, the P2 had approximately 1ms21 slower mean fall speed with respect to the terminal fall speed near 1 mm, and the difference between the mean measured and terminal fall speeds reduced with increasing drop size. This caveat was recognized as a software bug by the manufacturer and is currently being investigated.

disdrometers↗

NASA NTRS2005

Small-Scale Drop-Size Variability: Empirical Models for Drop-Size-Dependent Clustering in Clouds

By analyzing aircraft measurements of individual drop sizes in clouds, it has been shown in a companion paper that the probability of finding a drop of radius r at a linear scale l decreases as l(sup D(r)), where 0 less than or equals D(r) less than or equals 1. This paper shows striking examples of the spatial distribution of large cloud drops using models that simulate the observed power laws. In contrast to currently used models that assume homogeneity and a Poisson distribution of cloud drops, these models illustrate strong drop clustering, especially with larger drops. The degree of clustering is determined by the observed exponents D(r). The strong clustering of large drops arises naturally from the observed power-law statistics. This clustering has vital consequences for rain physics, including how fast rain can form. For radiative transfer theory, clustering of large drops enhances their impact on the cloud optical path. The clustering phenomenon also helps explain why remotely sensed cloud drop size is generally larger than that measured in situ.

Marshak, Alexander↗

NASA NTRS1987

Spiky parallel dc electric fields in the aurora

A series of computer simulations is reported on the detailed shape and distribution of the dc electric fields that result when an external potential drop is applied to a plasma with strong low-frequency turbulence. The structures are shown to depend on the size of the potential drop and upon the shape of the ion turbulence. For the type of turbulence expected for current driven electrostatic ion cyclotrron waves the dc fields seen in the simulations are in good agreement with those observed in the aurora.

Rowland, H. L.↗

NASA NTRS1997

The Effect of Rain on Air-Water Gas Exchange

The relationship between gas transfer velocity and rain rate was investigated at NASA's Rain-Sea Interaction Facility (RSIF) using several SF, evasion experiments. During each experiment, a water tank below the rain simulator was supersaturated with SF6, a synthetic gas, and the gas transfer velocities were calculated from the measured decrease in SF6 concentration with time. The results from experiments with IS different rain rates (7 to 10 mm/h) and 1 of 2 drop sizes (2.8 or 4.2 mm diameter) confirm a significant and systematic enhancement of air-water gas exchange by rainfall. The gas transfer velocities derived from our experiment were related to the kinetic energy flux calculated from the rain rate and drop size. The relationship obtained for mono-dropsize rain at the RSIF was extrapolated to natural rain using the kinetic energy flux of natural rain calculated from the Marshall-Palmer raindrop size distribution. Results of laboratory experiments at RSIF were compared to field observations made during a tropical rainstorm in Miami, Florida and show good agreement between laboratory and field data.

Ho, David T.↗

NASA NTRS2003

Characterization of Martian Rock Shape for MER Airbag Drop Tests

Using the Viking and Mars Pathfinder landing sites as a guide, this study assessed rock shapes, sizes and burial so they could be compared with rocks on the test platforms. This work allowed comparison of the severity of the rock distributions on the test platforms with the 3 landing sites and helped guide the rocks used on the test platforms during the final airbag qualification tests.

DiMaggio, E. N.↗

NASA NTRS1999

A TRMM Rainfall Estimation Method Applicable to Land Areas

Methods developed to estimate rain rate on a footprint scale over land with the satellite-borne multispectral dual-polarization Special Sensor Microwave Imager (SSM/1) radiometer have met with limited success. Variability of surface emissivity on land and beam filling are commonly cited as the weaknesses of these methods. On the contrary, we contend a more significant reason for this lack of success is that the information content of spectral and polarization measurements of the SSM/I is limited. because of significant redundancy. As a result, the complex nature and vertical distribution C, of frozen and melting ice particles of different densities, sizes, and shapes cannot resolved satisfactorily. Extinction in the microwave region due to these complex particles can mask the extinction due to rain drops. Because of these reasons, theoretical models that attempt to retrieve rain rate do not succeed on a footprint scale. To illustrate the weakness of these models, as an example we can consider the brightness temperature measurement made by the radiometer in the 85 GHz channel (T85). Models indicate that T85 should be inversely related to the rain rate, because of scattering. However, rain rate derived from 15-minute rain gauges on land indicate that this is not true in a majority of footprints. This is also supported by the ship-borne radar observations of rain in the Tropical Oceans and Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA-COARE) region over the ocean. Based on these observations. we infer that theoretical models that attempt to retrieve rain rate do not succeed on a footprint scale. We do not follow the above path of rain retrieval on a footprint scale. Instead, we depend on the limited ability of the microwave radiometer to detect the presence of rain. This capability is useful to determine the rain area in a mesoscale region. We find in a given rain event that this rain area is closely related to the mesoscale-average rain rate. Based on this observation, in this study we have developed a method to estimate the mesoscale-average rain rate over land utilizing microwave radiometer data. Because of the high degree of geographic and seasonal variability in the nature and intensity of rain, this method requires some tuning with 15-minute rain gauge data on land. After tuning the method, it can be applied to an independent set of rain events that are close in time and space. We find that the mesoscale rain rates retrieved over the period of a month on land with this method shows a correlation of about 0.85 with respect to the surface rain-gauge observations. This mesoscale-average rain rate estimation method can be useful to extend the spatial and temporal coverage of the rainfall data provided by the Precipitation Radar on board the Tropical Rainfall Measuring Mission (TRMM) satellite.

Prabhakara, C.↗

NASA NTRS1999

Comparison of Techniques for Non-Intrusive Fuel Drop Size Measurements in a Subscale Gas Turbine Combustor

In aviation gas turbine combustors, many factors, such as the degree and extent of fuel/air mixing and fuel vaporization achieved prior to combustion, influence the formation of undesirable pollutants. To assist in analyzing the extent of fuel/air mixing, flow visualization techniques have been used to interrogate the fuel distributions during subcomponent tests of lean-burning fuel injectors. Discrimination between liquid and vapor phases of the fuel was determined by comparing planar laser-induced fluorescence (PLIF) images, elastically-scattered light images, and phase/Doppler interferometer measurements. Estimates of Sauter mean diameters are made by ratioing PLIF and Mie scattered intensities for various sprays, and factors affecting the accuracy of these estimates are discussed. Mie calculations of absorption coefficients indicate that the fluorescence intensities of individual droplets are proportional to their surface areas, instead of their volumes, due to the high absorbance of the liquid fuel for the selected excitation wavelengths.

Zaller, Michelle↗

NASA NTRS2000

GCSS Cirrus Parcel Model Comparison Project

The Cirrus Parcel Model Comparison Project, a project of GCSS Working Group on Cirrus Cloud Systems (WG2), involves the systematic comparison of current models of ice crystal nucleation and growth for specified, typical, cirrus cloud environments. The goal of this project is to document and understand the factors resulting in significant inter-model differences. The intent is to foment research leading to model improvement and validation. In Phase 1 of the project reported here, simulated cirrus cloud microphysical properties are compared for situations of "warm" (-40 C) and "cold" (-60 C) cirrus subject to updrafts of 4, 20 and 100 cm/s, respectively. Five models participated. These models employ explicit microphysical schemes wherein the size distribution of each class of particles (aerosols and ice crystals) is resolved into bins. Simulations are made including both homogeneous and heterogeneous ice nucleation mechanisms. A single initial aerosol population of sulfuric acid particles is prescribed for all simulations. To isolate the treatment of the homogeneous freezing (of haze drops) nucleation process, the heterogeneous nucleation mechanism is disabled for a second parallel set of simulations. Qualitative agreement is found for the homogeneous-nucleation-only simulations, e.g., the number density of nucleated ice crystals increases with the strength of the prescribed updraft. However, non-negligible quantitative differences are found. Detailed analysis reveals that the homogeneous nucleation formulation, aerosol size, ice crystal growth rate (particularly the deposition coefficient), and water vapor uptake rate are critical components that lead to differences in predicted microphysics. Systematic bias exists between results based on a modified classical theory approach and models using an effective freezing temperature approach to the treatment of nucleation. Each approach is constrained by critical freezing data from laboratory studies, but each includes assumptions that can only be justified by further laboratory data. Consequently, it is not yet clear if the two approaches can be made consistent. Large haze particles may deviate considerably from equilibrium size in moderate to strong updrafts (20-100 cm/s) at -60 C when the commonly invoked equilibrium assumption is lifted. The resulting difference in particle-size-dependent solution concentration of haze particles may significantly affect the ice nucleation rate during the initial nucleation interval. The uptake rate for water vapor excess by ice crystals is another key component regulating the total number of nucleated ice crystals. This rate, the product of ice number concentration and ice crystal diffusional growth rate, which is sensitive to the deposition coefficient when ice particles are small, partially controls the peak nucleation rate achieved in an air parcel and the duration of the active nucleation time period. The effects of heterogeneous nucleation are most pronounced in weak updraft situations. Vapor competition by the nucleated (heterogeneous) ice crystals limits the achieved ice supersaturation and thus suppresses the contribution of homogeneous nucleation. Correspondingly, ice crystal number density is markedly reduced. Definitive laboratory and atmospheric benchmark data are needed for the heterogeneous nucleation process. Inter-model differences are correspondingly greater than in the case of the homogeneous nucleation process acting alone.

Lin, Ruei-Fong↗

NASA NTRS2001

Doppler and Reflectivity Measurements at Two Closely-Spaced Frequencies

Spaceborne and airborne radars are limited with a respect to the mass and size of the instrument and the power available to operate it. As a consequence, dual-wavelength radars that require separate antennas and power amplifiers are expensive and often impractical. However, if the frequency difference can be reduced so that a single antenna and the same radio-frequency subsystem can be used for both frequencies, dual- wavelength Doppler measurements can be made with a radar of about the same size and mass as its single-frequency counterpart. In the first part of the paper we present calculations of the reflectivity factor differences as functions of the center frequency from 10 to 35 GHz and for frequency differences between -10% and 10% of the center frequency. The results indicate that differential-frequency operation at Ka-band frequencies (26.5 - 40 GHz) provides relatively strong differential signals if the frequencies can be separated by at least 5%. Unlike lower frequency operation, the differential signals at Ka-band (both reflectivity and Doppler) are directly related to the median mass diameter. An important feature of the differential mean Doppler is that it depends only on the drop-size dependent part of the radial velocity. In principle, the mean and mean differential Doppler data from a nadir-looking platform can be used to infer vertical air motion and characteristics of the particle size distribution. To test the instrument concept, the ER-2 Doppler radar was modified for differential frequency operation. Measurements by the modified radar, operating at frequencies of 9.1 GHz and 10 GHz, were made using an 8 degree zenith-pointing offset parabolic antenna. Simultaneous data were taken with an optical rain gauge and an impact disdrometer. Measured and DSD-estimated values of the differential dBZ mean Doppler are presented.

Meneghini, Robert↗

NASA NTRS1999

Optical Imaging of Flow Pattern and Phantom

Time-resolved optical imaging technique has been used to image the spatial distribution of small droplets and jet sprays in a highly scattering environment. The snake and ballistic components of the transmitted pulse are less scattered, and contain direct information about the sample to facilitate image formation as opposed to the diffusive components which are due to multiple collisions as a light pulse propagates through a scattering medium. In a time-gated imaging scheme, these early-arriving, image-bearing components of the incident pulse are selected by opening a gate for an ultrashort period of time and a shadowgram image is detected. Using a single shot cooled CCD camera system, the formation of water droplets is monitored as a function of time. Picosecond time-gated image of drop in scattering cells, spray droplets as a function of let speed and gas pressure, and model calcification samples consisted of calcium carbonate particles of irregular shapes ranging in size from 0. 1 to 1.5 mm affixed to a microscope slide have been measured. Formation produced by an impinging jet will be further monitored using a CCD with 1 kHz framing illuminated with pulsed light. The desired image resolution of the fuel droplets is on the 20 pm scale using early light through a highly scattering medium. A 10(exp -6)m displacement from a jet spray with a flow speed of 100 m/sec introduced by the ns grating pulse used in the imaging is negligible. Early ballistic/snake light imaging offers nondestructive and noninvasive method to observe the spatial distribution of hidden objects inside a highly scattering environment for space, biomedical, and materials applications. In this paper, the techniques we will present are time-resolved K-F transillumination imaging and time-gated scattered light imaging. With a large dynamic range and high resolution, time-gated early light imaging has the potential for improving rocket/aircraft design by determining jets shape and particle sizes. Refinements to these techniques may enable drop size measurements in the highly scattering, optically dense region of multi-element rocket injectors. These types of measurements should greatly enhance the design of stable, and higher performing rocket engines.

Galland, Pierre A.↗

NASA NTRS2024

A Break In the Size-Stellar Mass Relation: Evidence for Quenching and Feedback in Dwarf Galaxies

Mapping stars and gas in nearby galaxies is fundamental for understanding their growth and the impact of their environment. This issue is addressed by comparing the stellar ‘edges’ of galaxies D stellar, defined as the outermost diameter where in situ star formation significantly drops, with the gaseous distribution parameterized by the neutral atomic hydrogen diameter measured at 1M⊙/pc2,DHI. By sampling a broad HI mass range 105M⊙< MHI<1011M⊙, we find several dwarf galaxies withMHI<109M⊙from the field and Fornax Cluster which are distinguished by D stellar>> DHI. For the cluster dwarfs, the average HI surface density near D stellar is∼0.3M⊙/pc2, reflecting the impact of quenching and outside-in gas removal from ram pressure and tidal interactions. In comparison, D stellar/DHI ranges between 0.5–2 in dwarf field galaxies, consistent with the expectations from stellar feedback. Only more massive disk galaxies in the field can thus be characterized by the common assumption that D stellar≲DHI. We discover a break in the D stellar−M⋆relation atm break∼4×108M⊙that potentially differentiates the low mass regime where the influence of stellar feedback and environmental processes more prominently regulates the sizes of nearby galaxies. Our results highlight the importance of combining deep optical and HI imaging for understanding galaxy evolution.

Scaling relations↗

NASA NTRS2011

Evaluation of the New Version of the Laser-Optical Disdrometer, Parsivel

Disdrometer based hydrometeor size distribution measurements have a wide range of application in radar meteorology among other disciplines. The low-cost laser optical disdrometer which became commercially available in 2005 opened a new era to study the variability of the hydrometeor size distribution. The pixel and footprint scale variability of the ground and spaceborne radar remote sensing of precipitation, respectively, has been investigated through a network of Parsivel disdrometers. At the same timE, the cross comparison of impact-type, two-dimensional video and laser-optical disdrometers highlighted the relative strengths and weaknesses of each type of disdrometer. The Parsivel instrument tended to underestimate the number of small drops less than 0.8 mm in diameter quite severely, while the size of drops larger than 2.0 mm in diameter were overestimated at heavy rain quite frequently. Through a close collaboration with the manufacturer, these shortcomings were attributed to the inexpensive laser device. The manufacturer has just released a beta version of Parsivel2. The preliminary comparisons with old and new versions of Parsivel, impact type disdrometer and rain gauges showed a noticeable improvement of the Parsivel at both small and large drop end. This presentation will demonstrate the evaluation of the new unit and its potential impact on radar rainfall relations, including polarimetric and high frequency radar rainfall.

Tokay, Ali↗

NASA NTRSDate not supplied

High Energy Hydroforming Friction Stir Welded 2050 Al-Li Blanks for Aerospace Domes and Cones

Friction stir welded (FSW) aluminum blanks offer larger preform sizes than available from the mill in single width plates. Large blanks made from aerospace-grade aluminum alloys are essential for making large domes and cones for launch vehicles and crew vehicles. Previous research efforts have demonstrated >5m FSW blanks can be formed into large domes or cones using spin forming, but the subsequent solution heat treatment consistently led to abnormal grain growth (AGG). The AGG phenomenon occurs because the FSW blanks must be spin formed in the -O annealed temper to withstand the high strain process without cracking. Subsequently, the solution heat treatment process leads to the onset of AGG, whereby a small number of grains grow much larger than the surrounding matrix. Ultimately, the large grains and bimodal grain-size distribution leads to unacceptable ductility in the short-transverse direction of the part. Alternatively, explosive hydroforming is a nascent process that can be applied to large and thick aerospace-grade aluminum alloy blanks in the -T3 temper and only require a post-forming artificial aging process to a -T8. Avoiding the solution heat treatment (SHT) process mitigates AGG, and also eliminates the need for very rare drop-furnace quench baths that can accommodate a part size larger than 5m in diameter. This presentation summarizes a Lockheed Martin-led effort that demonstrated explosive hydroforming of a 1.9m diameter, 39mm thick 2050 aluminum lithium FSW blank. Details will be provided on the process flow, mechanical properties, and metallographic analyses. This work was performed in partnership with NASA Langley Research Center (LaRC) under a NASA Announcement of Collaboration Opportunities program.

Friction stir welded blank↗

NASA NTRS2000

The Cirrus Parcel Model Comparison Project

The cirrus Parcel Model Comparison Project involves the systematic comparison of current models of ice crystal nucleation and growth for specified, typical, cirrus cloud environments. In Phase 1 of the project reported here, simulated cirrus cloud microphysical properties are compared for situations of "warm" (-40 C) and "cold" (-60 C) cirrus subject to updrafts of 4, 20 and 100 centimeters per second, respectively. Five models are participating in the project. These models employ explicit microphysical schemes wherein the size distribution of each class of particles (aerosols and ice crystals) is resolved into bins. Simulations are made including both homogeneous and heterogeneous ice nucleation mechanisms. A single initial aerosol population of sulfuric acid particles is prescribed for all simulations. To isolate the treatment of the homogeneous freezing (of haze drops) nucleation process, the heterogeneous nucleation mechanism is disabled for a second parallel set of simulations. Qualitative agreement is found amongst the models for the homogeneous-nucleation-only simulations, e.g., the number density of nucleated ice crystals increases with the strength of the prescribed updraft. However, non-negligible quantitative differences are found. Systematic bias exists between results of a model based on a modified classical theory approach and models using an effective freezing temperature approach to the treatment of nucleation. Each approach is constrained by critical freezing data from laboratory studies. This information is necessary, but not sufficient, to construct consistent formulae for the two approaches. Large haze particles may deviate considerably from equilibrium size in moderate to strong updrafts (20-100 centimeters per second) at -60 C when the commonly invoked equilibrium assumption is lifted. The resulting difference in particle-size-dependent solution concentration of haze particles may significantly affect the ice nucleation rate during the initial nucleation interval. The uptake rate for water vapor excess by ice crystals is another key component regulating the total number of nucleated ice crystals. This rate, the product of ice number concentration and ice crystal diffusional growth rate, partially controls the peak nucleation rate achieved in an air parcel and the duration of the active nucleation time period.

Lin, Ruei-Fong↗

NASA NTRS1989

Denitrification in the Antarctic stratosphere

Rapid loss of ozone over Antarctica in spring requires that the abundance of gaseous nitric acid be very low. Precipitation of particulate nitric acid has been assumed to occur in association with large ice crystals, requiring significant removal of H2O and temperatures well below the frost point. However, stratospheric clouds exhibit a bimodal size distribution in the Antarctic atmosphere, with most of the nitrate concentrated in particles with radii of 1 micron or greater. It is argued here that the bimodal size distribution sets the stage for efficient denitrification, with nitrate particles either falling on their own or serving as nuclei for the condensation of ice. Denitrification can therefore occur without significant dehydration, and it is unnecessary for temperatures to drop significantly below the frost point.

Salawitch, R. J.↗

NASA NTRS2018

MMS Examination of FTEs at the Earth's Subsolar Magnetopause

Determining the magnetic field structure, electric currents, and plasma distributions within flux transfer event (FTE)-type flux ropes is critical to the understanding of their origin, evolution, and dynamics. Here the Magnetospheric Multiscale mission's high-resolution magnetic field and plasma measurements are used to identify FTEs in the vicinity of the subsolar magnetopause. The constant-alpha flux rope model is used to identify quasi-force free flux ropes and to infer the size, the core magnetic field strength, the magnetic flux content, and the spacecraft trajectories through these structures. Our statistical analysis determines a mean diameter of 1,700 ± 400 km (~30 ± 9 d(sub i)) and an average magnetic flux content of 100 ± 30 kWb for the quasi-force free FTEs at the Earth's subsolar magnetopause which are smaller than values reported by Cluster at high latitudes. These observed nonlinear size and magnetic flux content distributions of FTEs appear consistent with the plasmoid instability theory, which relies on the merging of neighboring, small-scale FTEs to generate larger structures. The ratio of the perpendicular to parallel components of current density, R(sub J), indicates that our FTEs are magnetically force-free, defined as R(sub J) < 1, in their core regions (<0.6 R(sub flux rope)). Plasma density is shown to be larger in smaller, newly formed FTEs and dropping with increasing FTE size. It is also shown that parallel ion velocity dominates inside FTEs with largest plasma density. Field-aligned flow facilitates the evacuation of plasma inside newly formed FTEs, while their core magnetic field strengthens with increasing FTE size.

Akhavan-Tafti, M.↗

NASA NTRS2009

Spatial and Temporal Extrapolation of Disdrometer Size Distributions Based on a Lagrangian Trajectory Model of Falling Rain

Methodologies to improve disdrometer processing, loosely based on mathematical techniques common to the field of particle flow and fluid mechanics, are examined and tested. The inclusion of advection and vertical wind field estimates appear to produce significantly improved results in a Lagrangian hydrometeor trajectory model, in spite of very strict assumptions of noninteracting hydrometeors, constant vertical air velocity, and time independent advection during the scan time interval. Wind field data can be extracted from each radar elevation scan by plotting and analyzing reflectivity contours over the disdrometer site and by collecting the radar radial velocity data to obtain estimates of advection. Specific regions of disdrometer spectra (drop size versus time) often exhibit strong gravitational sorting signatures, from which estimates of vertical velocity can be extracted. These independent wind field estimates become inputs and initial conditions to the Lagrangian trajectory simulation of falling hydrometeors.

Lane, John E.↗

NASA NTRS1997

Combustion of PTFE: The Effects of Gravity and Pigmentation on Ultrafine Particle Generation

Ultrafine particles generated during polymer thermodegradation are a major health hazard, owing to their unique pathway of processing in the lung. This hazard in manned spacecraft is poorly understood, because the particulate products of polymer thermodegradation are generated under low gravity conditions. Particulate generated from the degradation of PolyTetraFluoroEthylene (PTFE), insulation coating for 20 AWG copper wire (representative of spacecraft application) under intense ohmic heating were studied in terrestrial gravity and microgravity. Microgravity tests were done in a 1.2-second drop tower at the Colorado School of Mines (CSM). Thermophoretic sampling was used for particulate collection. Transmission Electron Microscopy (TEM) and Scanning Transmission Electron Microscopy (STEM) were used to examine the smoke particulates. Image software was used to calculate particle size distribution. In addition to gravity, the color of PTFE insulation has an overwhelming effect on size, shape and morphology of the particulate. Nanometer-sized primary particles were found in all cases, and aggregation and size distribution was dependent on both color and gravity; higher aggregation occurred in low gravity. Particulates from white, black, red and yellow colored PTFE insulations were studied. Elemental analysis of the particulates shows the presence of inorganic pigments.

McKinnon, J. Thomas↗