Meteorite collection inventories show that many related meteorite groups have very different numerical abundances (e.g., lunar versus Martian meteorites; Eagle Station pallasites versus main‐group pallasites; eucrites versus diogenites; ungrouped Antarctic irons versus ungrouped non‐Antarctic irons; carbonaceous chondrite‐related (CC) iron meteorites versus noncarbonaceous chondrite‐related (NC) iron meteorites). The number of members of individual meteorite groups reflects the entire history of these rocks from excavation on their parent bodies to recovery on Earth. These numbers are functions of six main selection factors: (1) volume of the parent‐body source region, (2) depth of this source region, (3) time spent in interplanetary space, (4) friability of meteoroids in space and during transit through the Earth's atmosphere, (5) susceptibility of meteorite finds to terrestrial weathering, and (6) post‐fall biases resulting from geography, demography, and preferences by meteorite collectors and analysts. The numerical ratio of lunar/Martian meteorites (~1.8) results from several factors including the Moon's proximity, the short transit time of lunar meteoroids through interplanetary space, the lower crustal depth from which lunar meteorites were excavated, the lower energy required to launch samples off the Moon than off Mars, and the lower porosity and higher mechanical strength of lunar meteorites. The dunite shortage among asteroidal meteorites may have resulted from the deeply buried olivine‐rich meteoroids being ejected hundreds of millions of years ago at the same time as pallasites and irons; however, the dunitic meteoroids (with their lower mechanical strength) would have eroded in interplanetary space on much shorter time scales than their metal‐rich fellow travelers.

Background: Presbyopia is often overlooked in refractive error distribution analysis. This article employs multivariate analysis to address this gap, enhancing understanding of means, outliers and variations through graphical data presentation. Aim: To analyse the distribution of near-corrective optical additions for presbyopic patients over 2 years at a rural optometry clinic. Setting: The study was conducted at Sekororo District Hospital, South Africa. Methods: Non-cycloplegic near-refractive error data for presbyopic patients who visited the clinic at the district hospital from January 2018 to December 2019 were extracted from the hospital’s records. The records were randomly divided into two groups for 2018 and 2019. Meridional plots and stereo-pair scatter plots were used to analyse the refractive states for the right (OD) and left (OS) eyes. Results: In the 2018 sample, the clinical means for OD and OS were +1.33 ‒0.32 × 90 and +2.01 ‒0.37 × 77, respectively. Similarly, for the 2019 sample, the clinical means for OD and OS were +2.01 ‒0.32 × 82 and +1.82 ‒0.18 × 95, respectively. The data were not normally distributed, and outliers were present. Sample variances were spherical rather than astigmatic. Conclusion: Deviation from the normality showed that the data for OD and OS were mainly mildly positively skewed. Much of the variation in the refractive state was spherical (the stigmatic) irrespective of the laterality. Contribution: The article makes a valuable contribution to the current understanding of multivariate analysis, in academic training including optometry fraternity, as it pertains to the refractive state of the eyes in a rural optometry clinic.

About 17% of L6 chondrites (15/87) show significant reduction features in BSE images in thin section. Because some thin sections of these meteorites do not show reduction features, this percentage is a lower limit. Reduction features include: (1) 4-5-mu m-thick BSE-dark reduction rims on olivine and orthopyroxene grains and along fracture boundaries in these grains, (2) 4-12-mu m-thick dark bands (probably poorly crystalline pyrrhotite) at the margins and along fractures in troilite grains, and (3) 2-5-mu m-thick dark rinds of kamacite around some taenite grains. Only one of 70 L-group chondrites (1.4%) of lower petrologic type exhibits minor reduction. The L6 chondrites showing major reduction have Ar-40/Ar-39 plateau ages ranging from 156 +/- 1 Ma for Guangnan to 4543 +/- 3 Ma for Thamaniyat Ajras. Reduction occurred after silicate, sulfide, and metal grains had attained their present sizes during parent-body thermal metamorphism (and had been fractured by parent-body collisions). The precise plateau age of Thamaniyat Ajras probably marks the timing of the L6 reduction event. It seems likely the reductant was a low-viscosity fluid, plausibly CO, derived from oxidation of poorly graphitized and amorphous carbon within fine-grained matrix. Water-ice that had accreted to the L-chondrite asteroid was heated and mobilized during metamorphism, causing oxidation. After peak metamorphism, similar to 75% of the water had been used up or lost; the remaining water facilitated continuing graphite oxidation so that, after this point, overall reduction effects exceeded those of oxidation. L chondrites of lower petrologic type were less affected by reduction due to their lower metamorphic temperatures.

Magmatic iron-meteorite parent bodies are the earliest planetesimals in the Solar System, and they preserve information about conditions and planet-forming processes in the solar nebula. In this study, we include comprehensive elemental compositions and fractional-crystallization modeling for iron meteorites from the cores of five differentiated asteroids from the inner Solar System. Together with previous results of metallic cores from the outer Solar System, we conclude that asteroidal cores from the outer Solar System have smaller sizes, elevated siderophile-element abundances, and simpler crystallization processes than those from the inner Solar System. These differences are related to the formation locations of the parent asteroids because the solar protoplanetary disk varied in redox conditions, elemental distributions, and dynamics at different heliocentric distances. Using highly siderophile-element data from iron meteorites, we reconstruct the distribution of calcium-aluminum-rich inclusions (CAIs) across the protoplanetary disk within the first million years of Solar-System history. CAIs, the first solids to condense in the Solar System, formed close to the Sun. They were, however, concentrated within the outer disk and depleted within the inner disk. Future models of the structure and evolution of the protoplanetary disk should account for this distribution pattern of CAIs.

Complex interelement trends among magmatic IIIF iron meteorites are difficult to explain by fractional crystallization and have raised uncertainty about their genetic relationships. Nucleosynthetic Mo isotope anomalies provide a powerful tool to assess if individual IIIF irons are related to each other. However, while trace element data are available for all nine IIIF irons, Mo isotopic data are limited to three samples. We present Mo isotopic data for all but one IIIF irons that help assess the genetic relationships among these irons, together with new Mo and W isotopic data for Fitzwater Pass (classified IIIF), and the Zinder pallasite (for which a cogenetic link with IIIF irons has been proposed). After correction for cosmic-ray exposure, the Mo isotopic compositions of the IIIF irons are identical within uncertainty and confirm their belonging to carbonaceous chondrite (CC)-type meteorites. The mean Mo isotopic composition of group IIIF overlaps those groups IIF and IID, but a common parent body for these groups is ruled out based on distinct trace element systematics. The new Mo isotopic data do not argue against a single parent body for the IIIF irons, and suggest a close genetic link among these samples. In contrast, Fitzwater Pass has distinct Mo and W isotopic compositions, identical to those of some non-magmatic IAB irons. The Mo and W isotope data for Zinder indicate that this meteorite is not related to IIIF irons, but belongs to the non-carbonaceous (NC) type and has the same Mo and W isotopic composition as main-group pallasites.

Background: Non-cycloplegic subjective refraction (NCSR) is useful to measure refractive errors with active ocular accommodation.Aim: This study aimed to compare annual NCSR distributions between January 2018 and December 2019.Setting: The study was conducted in the Optometry Clinic at Sekororo Hospital in Limpopo province, South Africa.Methods: Data, extracted retrospectively from the clinical archive, were randomly stratified into two strata (2018 and 2019) for analysis. Stereo-pair scatter plots and polar plots of variance were used to better understand the samples concerned.Results: Clinic patients were mostly females of African descent. Mean ages and standard deviations (± SD) for the 2018 and 2019 samples were similar (48.35 ± 20.86 years and 46.22 ± 20.36 years, respectively). For the 2018 sample, the clinical means for NCSR for the right and left eyes, respectively, were similar (R −0.44 ‒0.15 × 86 and L ‒0.46 ‒0.16 × 75) and similar for the 2019 samples (R ‒0.38 ‒0.17 × 77 and L ‒0.14 ‒0.05 × 99). Samples were not normally distributed and outliers were present, although uncommon. Sample variances were mainly spherical rather than astigmatic.Conclusion: Non-cycloplegic subjective refractions were mostly classified as mild ([−2: 2 D]) compound myopic astigmatism. Severe myopia (|6 D|) and hyperopia were uncommon.Contribution: This article adds to current scientific knowledge of multivariate methods for the analysis of refractive states, especially when applied within rural environments. Such multivariate methods are ideally suited for the analysis of distributions of refractive state.

Type II chondrules have higher oxidation states than type I chondrules; in ordinary chondrites (OC), type II chondrules tend to be larger, richer in bulk Fe, and have higher densities than type I chondrules. Magnesian type IA chondrules tend to be richer in O-16 than type II chondrules. Because the aerodynamic behavior of a particle is a function of the product of its size and density, type I and type II chondrules (or their precursors) were partly separated in the ordinary chondrite zone of the solar nebula prior to the accretion of OC parent asteroids. LL chondrites acquired a chondrule population with the highest type II/type I ratios, L chondrites acquired chondrules with an intermediate ratio, and H chondrites acquired chondrules with the lowest type II/type I ratios. This contributed to the observed differences among OC groups in oxidation state and O-isotopic composition: in going from H to L to LL, mean oxidation state increases and mean Delta O-17 values increase. Higher oxidation is marked by increases in the FeO contents of olivine, low-Ca pyroxene, chromite, and ilmenite; increases in the TiO2 content of chromite; and increases in the Co content of kamacite.

A planetary scientist recounts an audacious mission to retrieve mineral samples from space

Background: Uniform Patient Fee Scheme (UPFS) refers to the healthcare subsidy levels provided by public hospitals in South Africa. Such subsidies indirectly reflect socio-economic factors and thus potentially might impact upon distributions of refractive error.Aim: To investigate refractive errors based on the UPFS-classified records of patients consulted at an Optometry Clinic between January 2018 and December 2019. This will provide frequencies and other measures, possibly providing preliminary estimates of prevalences for the wider population for the region concerned.Setting: The study was conducted at Sekororo Hospital in Limpopo province.Methods: Data for UPFS and refractive errors (via subjective refraction) were collected retrospectively based on the archived clinical records. Statistics and Data Analysis (Stata) software was used to analyse data.Results: For H0 in the right eyes means (± s.d.) for myopia, hyperopia, and astigmatism were −2.04 ± 2.60, 1.38 ± 1.72, and −1.07 ± 0.64, respectively. For H0 (left eyes): Myopia (−2.04 ± 2.09), hyperopia (1.47 ± 1.73), and astigmatism (−1.04 ± 0.64). For H1 (right eyes): Myopia (−1.79 ± 1.50), hyperopia (1.06 ± 0.72), and astigmatism (−1.14 ± 0.81). For H1 (left eyes): myopia (−1.71 ± 1.46), hyperopia (1.24 ± 0.91), and astigmatism (−1.71 ± 0.74). (No records were found for H2, H3, or private patients.)Conclusion: Hyperopia and astigmatism were the most common in H0 records while myopia was the most common in H1.Contribution: Various authorities and others in South Africa might use this data and results for National Health Insurance planning policies and implementation purposes.

Background: Refractive errors are common eye disorders affecting people of all age groups worldwide.Aim: To determine the prevalence and determinants of refractive errors among patients attending a rural-based optometry clinic from January 2018 to December 2019.Setting: The study was conducted at Sekororo District Hospital in Mopani District of Limpopo Province, South Africa.Methods: A retrospective cross-sectional study comprising two stratified random samples (2018 and 2019) was conducted based on the clinical records of patients who consulted the clinic. Data were analysed with Statistics or Data Analysis software, STATA ed. 15. Determinants of refractive errors were identified using regression analysis and reported as odds ratios with 95% confidence intervals (CI).Results: In the 2018 sample, the prevalence of myopia, hyperopia and astigmatism in the right eyes was 10% (95% CI: 7.0–14.2), 7.5% (95% CI: 4.5–1.3) and 43.4% (95% CI: 37.6–49.3), respectively. Left eyes had myopia 16.1% (95% CI: 12.2–21.0), hyperopia 7.5% (95% CI: 4.5–1.3) and astigmatism 40.1% (95% CI: 34.5–46.0). For the 2019 sample, the prevalence of myopia in right eyes was 13.3% (95% CI: 9.5–18.3), hyperopia 3.8% (95% CI: 2.0–7.3) and astigmatism 33.8% (95% CI: 28.0–40.1). Left eyes had myopia 17.5% (95% CI: 13.1–23.0), hyperopia 8.1% (95% CI: 5.2–12.4) and astigmatism 26.9% (95% CI: 21.6–33.0).Conclusion: Across the samples (2018 and 2019) and to laterality (right and left eyes), myopia prevalence ranged from 10% to 17.5% while hyperopia ranged from 3.8% to 8.1%. Astigmatism was most prevalent (ranging from 26.9% to 43.4%).Contribution: This article provides useful information about the prevalence of REs in the district hospital setting. The Department of Health Authority may use the results for policy decisions.

A planetary scientist recounts an audacious mission to retrieve mineral samples from space

H, L, and LL chondrites all exhibit positive correlations between mean shock stage and petrologic type. At a given shock energy, hot samples exhibit more intense shock features than cold samples. After the ordinary-chondrite (OC) parent asteroids were collisionally disrupted, jumbled, and gravitationally reassembled, the correlations between mean shock stage and petrologic type may have resulted from stochastic collisions into material of different temperatures that were randomly distributed in the near-surface regions of the rubble-pile asteroids. Late-stage processes including shock events and post-shock annealing affected the preexisting correlations to only minor degrees. This model, combined with literature data, permits the following scenario: Each principal OC asteroid initially had an onion-shell structure with deeply buried type 6 materials cooling slowly, yielding young closure ages in Pb-phosphate data. The OC bodies were disrupted at similar to 60 Ma, locking in the Pb-phosphate record of the onion-shell structure. The H-chondrite parent body was collisionally disrupted somewhat later than the L or LL bodies and was thus somewhat cooler at the time of disruption. In the OC asteroidal rubble piles, materials of different petrologic types cooled at similar rates through similar to 500 degrees C, precluding a correlation between petrologic type and metallographic cooling rate. Shortly after rubble-pile formation, materials of higher petrologic types remained hotter than materials of lower petrologic types. The hotter materials recorded more intense shock features from the common meteoroid flux, leading to positive correlations in each OC asteroid between petrologic type and mean shock stage. The cooler H-chondrite materials manifested a lower range in mean shock stage.

In general, barred olivine (BO) chondrules formed from completely melted precursors. Among BO chondrules in unequilibrated ordinary chondrites, there are significant positive correlations among chondrule diameter, bar thickness, and rim thickness. In the nebula, smaller BO precursor droplets cooled faster than larger droplets (due to their higher surface area/volume ratios) and grew thinner bars and rims. There is a bimodal distribution in the olivine FeO content in BO chondrules, with a hiatus between 11 and 19 wt% FeO. The ratio of (FeO rich)/(FeO poor) BO chondrules decreases from 12.0 in H to 1.6 in L to 1.3 in LL. This is the opposite of the case for porphyritic chondrules: the mean (FeO rich)/(FeO poor) modal ratio increases from 0.8 in H to 1.8 in L to 2.8 in LL. During H chondrite agglomeration, most precursor dustballs were small with low bulk FeO/(FeO + MgO) ratios and moderately high melting temperatures. The energy available for chondrule melting from flash heating was relatively low, capable of completely melting many ferroan dusty precursors (to form FeO-rich BO chondrules), but incapable of completely melting many magnesian dusty precursors (to form FeO-poor BO chondrules). When L and LL chondrites agglomerated somewhat later, significant proportions of precursor dustballs were relatively large and had moderately high bulk FeO/(FeO + MgO) ratios. The energy available from flash heating was higher, capable of completely melting higher proportions of magnesian dusty precursors to form FeO-poor BO chondrules. These differences may have resulted from an increase in the amplitude of lightning discharges in the nebula caused by enhanced charge separation.

The two most abundant igneous rocks in the Earth’s crust are of basaltic and granitic composition. There are intrusive and extrusive varieties of each: fine-grained extrusive basalt and coarse-grained intrusive gabbro; fine-grained extrusive rhyolite and coarse-grained intrusive granite. Basalts and gabbros have the same composition and differ only in grain size; the same is true for rhyolite and granite. The coarser grains in the intrusive rocks indicate slow cooling in large magma chambers with small surface/volume ratios. Rocks located at the Earth’s surface are subject to mechanical and chemical weathering. The rate of weathering is a function of the rock’s surface/volume ratio: under identical conditions, large rocks weather slowly, small rocks weather rapidly.

Among the six differentiated bodies of substantial size in the inner Solar System, the largest body (and the one with the smallest surface/volume ratio) is the Earth, where volcanoes erupt every day; the smallest body is the asteroid Vesta, which has been cold for 4.5 billion years. Larger incoming meteoroids (with their small surface/volume ratios) are affected less by atmospheric drag than small meteoroids. Due to their size, small objects are affected to a greater extent by elemental diffusion than large objects—this process is observable in chondrules and cosmic spherules.

The UCLA Cosmochemistry Database was initiated as part of a data-rescue and -storage project aimed at archiving a variety of cosmochemical data acquired at University of California, Los Angeles (UCLA). The data collection includes elemental compositions of extraterrestrial materials analyzed by UCLA cosmochemists over the last five decades. The analytical techniques include atomic absorption spectrometry (AAS) and neutron activation analysis (NAA) at UCLA. The data collection is stored on the Astromaterials Data System (Astromat). We provide both interactive tables and downloadable datasheets for users to access all data. The UCLA Cosmochemistry Database archives cosmochemical data that are essential tools for increasing our understanding of the nature and origin of extraterrestrial materials. Future studies can reference the data collection in the examination, analysis, and classification of newly acquired extraterrestrial samples.

Because surface area increases as the square of length and volume increases as the cube, the surface/volume ratio is high for small objects and low for large objects. Small objects have lots of surface area and relatively little volume; large objects have lots of volume and relatively little surface area.

This book explains that diffusion, osmosis, dissolution, evaporation, and heat loss all affect small bodies due to their high surface/volume ratios