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At least 307 records · Page 17

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NASA NTRS2001

Differential expression of neuroleukin in osseous tissues and its involvement in mineralization during osteoblast differentiation

Osteoblast differentiation is a multistep process that involves critical spatial and temporal regulation of cellular processes marked by the presence of a large number of differentially expressed molecules. To identify key functional molecules, we used differential messenger RNA (mRNA) display and compared RNA populations isolated from the defined transition phases (proliferation, matrix formation, and mineralization) of the MC3T3-E1 osteoblast-like cell line. Using this approach, a complementary DNA (cDNA) fragment was isolated and identified as neuroleukin (NLK), a multifunctional cytokine also known as autocrine motility factor (AMF), phosphoglucose isomerase (PGI; phosphohexose isomerase [PHI]), and maturation factor (MF). Northern analysis showed NLK temporal expression during MC3T3-E1 cell differentiation with a 3.5-fold increase during matrix formation and mineralization. Immunocytochemical studies revealed the presence of NLK in MC3T3-E1 cells as well as in the surrounding matrix, consistent with a secreted molecule. In contrast, the NLK receptor protein was detected primarily on the cell membrane. In subsequent studies, a high level of NLK expression was identified in osteoblasts and superficial articular chondrocytes in bone of 1-, 4-, and 8-month-old normal mice, as well as in fibroblasts, proliferating chondrocytes, and osteoblasts within a fracture callus. However, NLK was not evident in hypertrophic chondrocytes or osteocytes. In addition, treatment of MC3T3 cells with 6-phosphogluconic acid (6PGA; a NLK inhibitor) resulted in diminishing alkaline phosphatase (ALP) activity and mineralization in MC3T3-E1 cells, especially during the matrix formation stage of differentiating cells. Taken together, these data show specific expression of NLK in discrete populations of bone and cartilage cells and suggest a possible role for this secreted protein in bone development and regeneration.

NASA Discipline Musculoskeletal↗

NASA NTRS1977

Laser induced photoluminiscence studies of primary photochemical production processes of cometary radicals

A tunable vacuum ultraviolet flash lamp was constructed. This unique flash lamp was coupled with a tunable dye laser detector and permits the experimenter to measure the production rates of ground state radicals as a function of wavelength. A new technique for producing fluorescent radicals was discovered. This technique called multiphoton ultraviolet photodissociation is currently being applied to several problems of both cometary and stratospheric interest. It was demonstrated that NO2 will dissociate to produce an excited fragment and the radiation can possibly be used for remote detection of this species.

Jackson, W. M.↗

NASA NTRS1998

Thermal Infrared Remote Sensing for Analysis of Landscape Ecological Processes: Methods and Applications

Thermal Infrared (TIR) remote sensing data can provide important measurements of surface energy fluxes and temperatures, which are integral to understanding landscape processes and responses. One example of this is the successful application of TIR remote sensing data to estimate evapotranspiration and soil moisture, where results from a number of studies suggest that satellite-based measurements from TIR remote sensing data can lead to more accurate regional-scale estimates of daily evapotranspiration. With further refinement in analytical techniques and models, the use of TIR data from airborne and satellite sensors could be very useful for parameterizing surface moisture conditions and developing better simulations of landscape energy exchange over a variety of conditions and space and time scales. Thus, TIR remote sensing data can significantly contribute to the observation, measurement, and analysis of energy balance characteristics (i.e., the fluxes and redistribution of thermal energy within and across the land surface) as an implicit and important aspect of landscape dynamics and landscape functioning. The application of TIR remote sensing data in landscape ecological studies has been limited, however, for several fundamental reasons that relate primarily to the perceived difficulty in use and availability of these data by the landscape ecology community, and from the fragmentation of references on TIR remote sensing throughout the scientific literature. It is our purpose here to provide evidence from work that has employed TIR remote sensing for analysis of landscape characteristics to illustrate how these data can provide important data for the improved measurement of landscape energy response and energy flux relationships. We examine the direct or indirect use of TIR remote sensing data to analyze landscape biophysical characteristics, thereby offering some insight on how these data can be used more robustly to further the understanding and modeling of landscape ecological processes.

Quattrochi, Dale A.↗

DOE OSTI2025

Regulation of sarcomere formation and function in the healthy heart requires a titin intronic enhancer

Heterozygous truncating variants in the sarcomere protein titin (TTN) are the most common genetic cause of heart failure. To understand mechanisms that regulate abundant cardiomyocyte (CM) TTN expression, we characterized highly conserved intron 1 sequences that exhibited dynamic changes in chromatin accessibility during differentiation of human CMs from induced pluripotent stem cells (hiPSC-CMs). Homozygous deletion of these sequences in mice caused embryonic lethality, whereas heterozygous mice showed an allele-specific reduction in Ttn expression. A 296 bp fragment of this element, denoted E1, was sufficient to drive expression of a reporter gene in hiPSC-CMs. Deletion of E1 downregulated TTN expression, impaired sarcomerogenesis, and decreased contractility in hiPSC-CMs. Site-directed mutagenesis of predicted binding sites of NK2 homeobox 5 (NKX2-5) and myocyte enhancer factor 2 (MEF2) within E1 abolished its transcriptional activity. In embryonic mice expressing E1 reporter gene constructs, we validated in vivo cardiac-specific activity of E1 and the requirement for NKX2-5- and MEF2-binding sequences. Moreover, isogenic hiPSC-CMs containing a rare E1 variant in the predicted MEF2-binding motif that was identified in a patient with unexplained dilated cardiomyopathy (DCM) showed reduced TTN expression. Together, these discoveries define an essential, functional enhancer that regulates TTN expression. Manipulation of this element may advance therapeutic strategies to treat DCM caused by TTN haploinsufficiency.

Kim, Yuri↗

DOE OSTI2025

Light-Driven C(sp 3 )–C(sp 3 ) Bond Functionalizations Enabled by the PCET Activation of Alcohol O–H Bonds

Methods that enable the selective functionalization of C–C bonds offer unique opportunities for the skeletal diversification of complex molecules and provide access to unique structures without the need for de novo synthesis. While considerable advances have been made in transition-metal-based approaches, much recent work has focused on alternative strategies for C–C bond cleavage enabled by transient free radicals. In particular, alkoxy radicals derived from simple alcohols are known to significantly destabilize adjacent C–C bonds, enabling spontaneous cleavage to eject a carbon-centered radical and afford carbonyl products via β-fragmentation. Here, while this reactivity has long been recognized, its applications in synthesis have been limited, in part, by the challenges associated with generating the key alkoxy radical intermediates.

Alcohols↗

NASA NTRS2001

Impact of dilution on microbial community structure and functional potential: comparison of numerical simulations and batch culture experiments

A series of microcosm experiments was performed using serial dilutions of a sewage microbial community to inoculate a set of batch cultures in sterile sewage. After inoculation, the dilution-defined communities were allowed to regrow for several days and a number of community attributes were measured in the regrown assemblages. Based upon a set of numerical simulations, community structure was expected to differ along the dilution gradient; the greatest differences in structure were anticipated between the undiluted-low-dilution communities and the communities regrown from the very dilute (more than 10(-4)) inocula. Furthermore, some differences were expected among the lower-dilution treatments (e.g., between undiluted and 10(-1)) depending upon the evenness of the original community. In general, each of the procedures used to examine the experimental community structures separated the communities into at least two, often three, distinct groups. The groupings were consistent with the simulated dilution of a mixture of organisms with a very uneven distribution. Significant differences in community structure were detected with genetic (amplified fragment length polymorphism and terminal restriction fragment length polymorphism), physiological (community level physiological profiling), and culture-based (colony morphology on R2A agar) measurements. Along with differences in community structure, differences in community size (acridine orange direct counting), composition (ratio of sewage medium counts to R2A counts, monitoring of each colony morphology across the treatments), and metabolic redundancy (i.e., generalist versus specialist) were also observed, suggesting that the differences in structure and diversity of communities maintained in the same environment can be manifested as differences in community organization and function.

Non-NASA Center↗

DOE OSTI2025

Mass spectrometry structural analysis of intrinsically disordered phosphoproteins

Phosphorylation is a ubiquitous protein modification that is known to play important roles in many biological phenomena including cell signaling, the opening and closing of membrane protein channels, and even triggering of amyloid protein aggregation. Despite the effects phosphorylation has on protein function, the impact phosphorylation has on the structure of proteins is not well understood. Here, to determine how phosphorylation affects the structure of proteins, top-down mass spectrometry (TD-MS) and ion mobility-mass spectrometry (IM-MS) were performed on various phosphorylated proteins and their dephosphorylated proteoforms. TD-MS with collision- and electron-based fragmentation techniques was utilized to locate phosphorylation sites on the intrinsically disordered amyloid proteins β-casein and α-synuclein. TD-MS also provided evidence that alkaline phosphatase dephosphorylates β-casein from the N-terminus to the C-terminus. Furthermore, IM-MS of common phosphorylated proteins such as β-casein, α-casein, ovalbumin, and phosvitin indicates that phosphorylation promotes compaction of protein structure in denaturing as well as native conditions. Increases in abundance of more compact conformers are also observed when the disease related amyloid protein α-synuclein is phosphorylated at serine 129. We interpret the increased abundance of more compact conformers when proteins are phosphorylated as evidence that salt bridges form between negatively charged phosphates and positively charged residues, which alters protein structure. Salt bridge formation due to phosphorylation could be a mechanism for regulating protein function and be responsible for many of the phenomena observed in nature.

Amyloid proteins↗

DOE OSTI2026

Small-𝑥 Factorization in the Target Fragmentation Region

We consider the differential cross-section for single-inclusive jet production with transverse momentum 𝑃 ⊥ in deep inelastic scattering at small Bjorken 𝑥 Bj , mediated by a virtual photon with virtuality 𝑄 2 . Unlike most studies at small 𝑥, which focus on particle production in the current fragmentation region, we investigate the kinematic regime where the jet is produced in the target fragmentation hemisphere of the Breit frame, and with 𝑃 ⊥ ≪ 𝑄. For a longitudinally polarized photon, we demonstrate that this cross section is not power suppressed in 𝑃 ⊥ /𝑄 and we derive a factorized expression in terms of extended quark and gluon jet fracture functions. Our formula, valid at next-to-leading order in 𝛼 𝑠 at small 𝑥, is akin to the Altarelli-Martinelli identity for the longitudinal DIS structure function. Numerical estimates show that the extended quark jet fracture function is the most sensitive to saturation effects in large nuclei.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

NASA NTRS1990

An analysis of CCD images of the coma of Comet Halley

The analysis of selected CCD images of the coma of comet P/Halley is presented. The images were taken using specially designed filters that isolate regions of a comet's spectrum such that only sunlight which has been scattered by the dust in the coma is recorded. The modeling analysis objective is to make use of the skills developed in the development of Monte Carlo particle trajectory models for the distributions of gas species in cometary comae and to use those models as a basis for a new dust coma model. This model will include a self-consistant picture of the time-dependent dusty-gas dynamics of the inner coma and the three-dimensional time-dependent trajectories of the dust particles under the influence of solar gravity and solar radiation pressure in the outer coma. The model is intended to be used as a tool to analyze selected images from the two sets of CCD images with the hope that it will help the understanding of the effects of a number of important processes on the spatial morphology of the observed dust coma. The processes of importance to the observed dust coma include: (1) the dust particle size distribution function; (2) the terminal velocities of various sized dust particles in the inner coma; (3) the radiation scattering properties of dust particles, which are important both in terms of the observe scattered radiation and the radiation pressure acceleration on dust particles; (4) the fragmentation and/or vaporization of dust particles; and (5) the relative importance of CHON and silicate dust particles as they contribute both to the dusty-gasdynamics in the inner coma (that produce the dust particle terminal velocities) and to the observed spatial morphology on the outer dust coma.

Combi, Michael↗

NASA NTRS1992

Analysis of CCD images of the coma of comet P/Halley

The modeling analysis objective of this project is to make use of the skill acquired in the development of Monte Carlo particle trajectory models for the distributions of gas species in cometary comae as a basis for a new dust coma model. This model will include a self-consistent picture of the time-dependent dusty-gas dynamics of the inner coma and the three-dimensional time-dependent trajectories of the dust particles under the influence of solar gravity and solar radiation pressure in the outer coma. Our purpose is to use this model as a tool to analyze selected images from two sets of data of the comet P/Halley with the hope that we can help to understand the effects of a number of important processes on the spatial morphology of the observed dust coma. The study will proceed much in the same way as our study of the spatially extended hydrogen coma where we were able to understand the spatial morphology of the Lyman-alpha coma in terms of the partial thermalization of the hot H atoms produced by the photodissociation of cometary H2O and OH. The processes of importance to the observed dust coma include: (1) the dust particle size distribution function; (2) the terminal velocities of various sized dust particles in the inner coma; (3) the radiation scattering properties of dust particles, which are important both in terms of the observed scattered radiation and the radiation pressure acceleration on dust particles; (4) the fragmentation and/or vaporization of dust particles; (5) the relative importance of CHON and silicate dust particles as they contribute both to the dusty-gas dynamics in the inner coma (that produce the dust particle terminal velocities) and to the observed spatial morphology of the outer dust coma; and (6) the time and direction dependence of the source of dust.

Combi, Michael R.↗

NASA NTRS1999

The Effects of Gravity on the Circadian Timing System

All vertebrates have a physiological control system that regulates the timing of the rhythms of their daily life. Dysfunction of this system, the circadian timing system (CTS), adversely affects an organism's ability to respond to environmental challenges and has been linked to physiological and psychological disorders. Exposure to altered gravitational environments (the microgravity of space and hyperdynamic environments produced via centrifugation) produces changes in both the functioning of the CTS and the rhythmic variables it controls. The earliest record of primate rhythms in a spaceflight environment come from Biosatellite III. The subject, a pig-tailed macaque, showed a loss of synchronization of the body temperature rhythm and a fragmented sleep-wake cycle. Alterations in the rhythm of body temperature were also seen in rhesus macaques flown on COSMOS 1514. Squirrel monkeys exposed to chronic centrifugation showed an initial decrease in the amplitude and mean of their body temperature and activity rhythms. In a microgravity environment, Squirrel monkeys on Spacelab-3 showed a reduction in the mean and amplitude of their feeding rhythms. Since 1992 we have had the opportunity to participate on three US/Russian sponsored biosatellite missions on which a total of six juvenile male rhesus macaques were flown. These animals uniformly exhibited delays in the phasing of their temperature rhythms, but not their heart rate or activity rhythms during spaceflight. There was also a tendency for changes in waveform mean and amplitude. These data suggest that the spaceflight environment may have a differential effect on the different oscillators controlling different rhythmic variables. Ongoing studies are examining the effects of +G on the CTS. The long-term presence of humans in space highlights the need for effective countermeasures to gravitational effects on the CTS.

Fuller, Charles A.↗

NASA NTRS2002

Immunoglobulin Fc gamma receptor promotes immunoglobulin uptake, immunoglobulin-mediated calcium increase, and neurotransmitter release in motor neurons

Receptors for the Fc portion of immunoglobulin G (IgG; FcgammaRs) facilitate IgG uptake by effector cells as well as cellular responses initiated by IgG binding. In earlier studies, we demonstrated that amyotrophic lateral sclerosis (ALS) patient IgG can be taken up by motor neuron terminals and transported retrogradely to the cell body and can alter the function of neuromuscular synapses, such as increasing intracellular calcium and spontaneous transmitter release from motor axon terminals after passive transfer. In the present study, we examined whether FcgammaR-mediated processes can contribute to these effects of ALS patient immunoglobulins. F(ab')(2) fragments (which lack the Fc portion) of ALS patient IgG were not taken up by motor axon terminals and were not retrogradely transported. Furthermore, in a genetically modified mouse lacking the gamma subunit of the FcR, the uptake of whole ALS IgG and its ability to enhance intracellular calcium and acetylcholine release were markedly attenuated. These data suggest that FcgammaRs appear to participate in IgG uptake into motor neurons as well as IgG-mediated increases in intracellular calcium and acetylcholine release from motor axon terminals. Copyright 2002 Wiley-Liss, Inc.

Non-NASA Center↗

NASA NTRSDate not supplied

Constraints on triple oxygen isotope kinetics

The general assumption that systems are in equilibrium is convenient, but imperfect. Instead, the partial or full expression of kinetic reaction steps may need to be determined. Using an isotope fractionation Monte-Carlo model under the harmonic approximation (Figure 1 envelopes), we find the range of kinetic isotope effects (i.e., resulting from unidirectional chemical reactions) contains and exceeds the range of accessible equilibrium isotope effects. For the 16O-17O-18O system, accessible kinetic isotope effects can yield Δ′17O variations as large 0.8‰ from a single kinetic fractionation step. Reactions that yield the largest deviations from equilibrium are those with the largest molecular mass difference between decomposition fragments, typically the two products, such as a gas and solid generated from the thermal decomposition of an initial solid. For example, previously published experiments on the thermal decomposition of calcite (CaCO3) and dehydroxylation of brucite (Mg(OH)2) are matched by density functional theory models of each kinetic isotope effect, thus revealing their origin in mass-dependent reaction. Beyond oxygen, our approach applies to any system with more than two isotopes.

Oxygen isotopes↗

DOE OSTI2025

Bottom-Up Simulation, Reconstruction, and Quantification of Macromolecule Sequences from Experimental Polymerizations

Motivated by the canonical sequence–structure–function paradigm, tools to characterize chemical patterning in natural biomacromolecules, from proteins to nucleic acids, have grown exponentially in recent years. However, analogous strategies for synthetic macromolecules remain in nascent stages, complicated by sequence polydispersity and analytical limitations. To address this, we have developed a comprehensive and open-source Python package, PRISM (polymer rate insights and sequence modeling), an end-to-end workflow that provides a path from experimental kinetics measurements to quantitative and qualitative metrics for describing chemical patterning in stochastic polymers. First, a numerical integration strategy was constructed to simulate and fit experimental data from reversible addition–fragmentation chain transfer (RAFT) polymerization kinetics, enabling the facile estimation of relevant reactivity ratios. These ratios were then used in a mechanism-specific stochastic kinetic simulation strategy to simulate sequence ensembles corresponding to model systems spanning experimental copolymers, classes of statistical polymers (e.g., alternating, block, and gradient), and multiblock copolymers. Lastly, inspired by sequence homology metrics from bioinformatics, we introduce visualization strategies and quantitative metrics to facilitate comparisons of different sequence ensembles. As the sequence–structure–function paradigm becomes increasingly central in de novo design of synthetic macromolecules, this toolkit provides a first step toward accurate and representative sequence description and featurization.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2024

Engineering a tumor-selective prodrug T-cell engager bispecific antibody for safer immunotherapy

T-cell engaging (TCE) bispecific antibodies are potent drugs that trigger the immune system to eliminate cancer cells, but administration can be accompanied by toxic side effects that limit dosing. TCEs function by binding to cell surface receptors on T cells, frequently CD3, with one arm of the bispecific antibody while the other arm binds to cell surface antigens on cancer cells. On-target, off-tumor toxicity can arise when the target antigen is also present on healthy cells. The toxicity of TCEs may be ameliorated through the use of pro-drug forms of the TCE, which are not fully functional until recruited to the tumor microenvironment. This can be accomplished by masking the anti-CD3 arm of the TCE with an autoinhibitory motif that is released by tumor-enriched proteases. Here, we solve the crystal structure of the antigen-binding fragment of a novel anti-CD3 antibody, E10, in complex with its epitope from CD3 and use this information to engineer a masked form of the antibody that can activate by the tumor-enriched protease matrix metalloproteinase 2 (MMP-2). We demonstrate with binding experiments and in vitro T-cell activation and killing assays that our designed prodrug TCE is capable of tumor-selective T-cell activity that is dependent upon MMP-2. Furthermore, we demonstrate that a similar masking strategy can be used to create a pro-drug form of the frequently used anti-CD3 antibody SP34. This study showcases an approach to developing immune-modulating therapeutics that prioritizes safety and has the potential to advance cancer immunotherapy treatment strategies.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2026

Shape evolution in neutron-rich odd-even 105–109 Nb isotopes

Background: Neutron-rich nuclei around 𝑍 ≈ 40 are well known for exhibiting multiple shape transitions. Here, this region shows one of the sharpest shape transitions in the nuclear chart, evolving from a spherical vibrator at 𝑁 = 58 to a strongly deformed prolate shape at 𝑁 = 60. The largest deformations are observed for 38 Sr and 40 Zr . This abrupt shape transition disappears at 𝑍 = 36 and below, where a shape transition from spherical to oblate nuclei is predicted. On the other hand, for 𝑍 ≥ 42 and 𝑁 ≥ 60, the shape is known to evolve from axial to triaxial. While the even-𝑍 nuclei in this region have already been extensively studied, new insights can be gained from the studies of odd-𝑍 isotopes for a better understanding of the underlying mechanisms driving these phenomena. Purpose: The 41 Nb nuclei lie at the boundary between axially deformed Zr and triaxially deformed Mo nuclei. This work investigates the nuclear structure of very neutron-rich Nb nuclei up to 𝑁 = 68. The goal is to understand how the nuclear shape evolves as a function of isospin in this isotopic chain and provide new insights into the emergence of triaxial deformation. Methods: The structure of the neutron-rich Nb isotopes was investigated using state-of-the-art high-resolution 𝛾-ray spectroscopy of fission fragments produced via two different fission reactions. The use of 9 Be ⁢( 238 U, 𝑓) inverse kinematics, with a detection system comprising AGATA, EXOGAM, and VAMOS++, enabled the measurement of prompt and delayed 𝛾 rays from isotopically identified fission fragments, and 𝛾−𝛾−𝛾−𝛾 highfold data were obtained from a spontaneous fission source of 252 Cf using the Gammasphere array. Results: The level scheme of 105 Nb has been significantly extended, with the addition of two negative-parity bands observed for the first time. A new level scheme is proposed for 107 Nb, which is not in agreement with an earlier measurement, and new levels and transitions have been added to the very neutron-rich 109 Nb. The degree of triaxiality of the new bands is discussed on the basis of signature splitting analysis. The recently reported level scheme of 99 Nb has been revised. Conclusions: This systematic study on the Nb isotopic chain, compared to Zr and Mo, indicates that while the ground-state band exhibits a triaxial deformation, attributed to a proton hole coupled to a triaxially deformed Mo core, the negative-parity bands, based on isomeric bandheads, display an axially symmetric deformed structure, similar to that observed in the Zr isotopes, revealing the existence of a shape coexistence in the neutron-rich Nb nuclei.

Abushawish, M. [Université Claude-Bernard Lyon 1 (↗

NASA NTRS1976

Calculations of the Electron Energy Distribution Function in a Uranium Plasma by Analytic and Monte Carlo Techniques

Electron energy distribution functions were calculated in a U235 plasma at 1 atmosphere for various plasma temperatures and neutron fluxes. The distributions are assumed to be a summation of a high energy tail and a Maxwellian distribution. The sources of energetic electrons considered are the fission-fragment induced ionization of uranium and the electron induced ionization of uranium. The calculation of the high energy tail is reduced to an electron slowing down calculation, from the most energetic source to the energy where the electron is assumed to be incorporated into the Maxwellian distribution. The pertinent collisional processes are electron-electron scattering and electron induced ionization and excitation of uranium. Two distinct methods were employed in the calculation of the distributions. One method is based upon the assumption of continuous slowing and yields a distribution inversely proportional to the stopping power. An iteration scheme is utilized to include the secondary electron avalanche. In the other method, a governing equation is derived without assuming continuous electron slowing. This equation is solved by a Monte Carlo technique.

Bathke, C. G.↗

NASA NTRS1993

Particle-Gas Dynamics in the Midplane of a Protoplanetary Nebula

In this paper, we study the stage of planetary formation during which the particulate material is still dispersed as centimeter-to-meter sized primordial aggregates. During this stage, particles are able to settle toward the midplane into a layer of mass density comparable to or much greater than that of the gas. Nonlinear, coupled interactions between the particles and the nebula gas become significant and ultimately determine the vertical profiles of the particle density and the mean velocities of the particles and the nearby gas. This is the environment in which the earliest planetesimals probably form. Our numerical models rely on the Reynolds averaged Navier-Stokes equations for the gas and particles and are fully viscous and turbulent (and, for the particles. compressible). Our turbulence modeling uses a Prandtl local shear parametrization, validated by laboratory experiments. We have developed a new model for particle diffusion involving the profile of the nebula gas turbulence and the particle Schmidt number, which is a function of particle size and density. We model a cool, quiescent nebula at 1 AU (280 K) and 10 AU (90 K) and a higher temperature stage (1000 K) at 1 AU. Our main results include: (a) rapid accretion of planetesimals by gravitationally unstable fragmentation on an orbital time scale (the 'Goldreich-Ward instability') is unlikely to occur until objects have already accreted by some other process to the mass of the largest known meteorite samples, if at all; (b) from 'seeds' as small as 10 m, growth of 10- to 100-km planetesimals can proceed rapidly by drift-augmented accretion in the particle-rich midplane with orbital decay of about 1% for the growing planetesimals; (c) outward transport of vapor and small entrained chips can account for significant radial compositional and mineralogical mixing in primitive meteorite parent bodies. Other implications may be drawn concerning particle random collisional velocities and the time scales of midplane turbulence.

Cuzzi, Jeffrey N.↗