Early Condensation Research Articles

CXCL12 is required for stirrup-shaped stapes formation during mammalian middle ear development.

The mammalian middle ear comprises a chain of three ossicles-the malleus, incus, and stapes-each of which has a unique morphology for efficiently transmitting sound information. In particular, the stapes, which is attached to the inner ear, is stirrup-shaped with a head and base connected by two crural arches, forming the stapedial foramen, through which the stapedial artery passes. However, how the stapes acquires this critical stirrup shape for association with the stapedial artery during development is not clear. C-X-C motif chemokine ligand 12 (CXCL12) is a chemoattractant essential for cellular movement and angiogenesis. In Cxcl12 -/- embryos, migration of neural crest cells into the prospective middle ear regions and their mesenchymal condensation to form the three ossicles proceed normally in correct alignment with each other and the inner ear. However, in the absence of CXCL12, the stapes loses its stirrup shape and instead exhibits a columnar shape lacking the crural arches and central hole. In addition, although the stapedial artery initially forms during early mesenchymal condensation of the stapes, it degenerates without CXCL12 function. CXCL12 plays an essential role in establishing the stirrup-shaped architecture of the stapes, possibly by maintaining the stapedial foramen and stapedial artery throughout development.

Role of N-Cadherin in a Niche-Mimicking Microenvironment for Chondrogenesis of Mesenchymal Stem Cells In Vitro.

During the development of natural cartilage, mesenchymal condensation is the starting event of chondrogenesis, and mesenchymal stem cells (MSCs) experienced a microenvironment transition from primarily cell-cell interactions to a later stage, where cell-extracellular matrix (ECM) interactions dominate. Although micromass pellet culture has been developed to mimic mesenchymal condensation in vitro, the molecular mechanism remains elusive, and the transition from cell-cell to cell-ECM interactions has been poorly recapitulated. In this study, we first constructed MSC microspheres (MMs) and investigated their chondrogenic differentiation with functional blocking of N-cadherin. The results showed that early cartilage differentiation and cartilage-specific matrix deposition of MSCs in the group with the N-cadherin antibody were significantly postponed. Next, poly(l-lysine) treatment was transiently applied to promote the expression of N-cadherin gene, CDH2, and the treatment-promoted MSC chondrogenesis. Upon one-day culture in MMs with established cell-cell adhesions, collagen hydrogel-encapsulated MMs (CMMs) were constructed to simulate the cell-ECM interactions, and the collagen microenvironment compensated the inhibitory effects from N-cadherin blocking. Surprisingly, chondrogenic-differentiated cell migration, which has important implications in cartilage repair and integration, was found in the CMMs without N-cadherin blocking. In conclusion, our study demonstrated that N-cadherin plays the critical role in early mesenchymal condensation, and the collagen hydrogel provides a supportive microenvironment for late chondrogenic differentiation. Therefore, sequential presentations of cell-cell adhesion and cell-ECM interaction in an engineered microenvironment seem to be a promising strategy to facilitate MSC chondrogenic differentiation.

Subsolar Al/Si and Mg/Si ratios of non-carbonaceous chondrites reveal planetesimal formation during early condensation in the protoplanetary disk

The Al/Si and Mg/Si ratios in non-carbonaceous chondrites are lower than the solar (i.e., CI-chondritic) values, in sharp contrast to the non-CI carbonaceous meteorites and the Earth, which are enriched in refractory elements and have Mg/Si ratios that are solar or larger. We show that the formation of a first generation of planetesimals during the condensation of refractory elements implies the subsequent formation of residual condensates with strongly sub-solar Al/Si and Mg/Si ratios. The mixing of residual condensates with different amounts of material with solar refractory/Si element ratios explains the Al/Si and Mg/Si values of non-carbonaceous chondrites. To match quantitatively the observed ratios, we find that the first-planetesimals should have accreted when the disk temperature was ∼1,330–1,400 K depending on pressure and assuming a solar C/O ratio of the disk. We discuss how this model relates to our current understanding of disk evolution, grain dynamics, and planetesimal formation. We also extend the discussion to moderately volatile elements (e.g., Na), explaining how it may be possible that the depletion of these elements in non-carbonaceous chondrites is correlated with the depletion of refractory elements (e.g., Al). Extending the analysis to Cr, we find evidence for a higher than solar C/O ratio in the protosolar disk's gas when/where condensation from a fractionated gas occurred. Finally, we discuss the possibility that the supra-solar Al/Si and Mg/Si ratios of the Earth are due to the accretion of ∼40% of the mass of our planet from the first-generation of refractory-rich planetesimals.

Study of subcritical and supercritical gas adsorption behavior in different nanopore systems in shale using lattice Boltzmann method

Adsorption has been studied for decades in either petroleum or chemical industry. However, the detailed adsorption behavior is yet not well understood in nanoporous media with complex pore structures and surface properties, especially for subcritical gases when capillary condensation might occur. Shale (mudrock) has complex pore systems as a result of heterogeneous mineralogy and diagenesis, and interparticle (interP) and intraparticle (intraP) pores are two main components. Understanding gas adsorption and phase transition behavior in different pore systems is essential for petrophysical characterization, reserve estimation and production forecast. In this study, we use lattice Boltzmann method (LBM) to study nitrogen (subcritical) and methane (supercritical) adsorption behavior in reconstructed shale nanopore systems. The model accounts for the van der Walls (vdW) forces between fluid molecules by incorporating a modified pseudopotential model based on Peng-Robinson equation of state (PR-EOS). Rock-fluid interaction is also considered by introducing phenomenological surface forces, which take two different forms for subcritical and supercritical gases respectively. The correlation between parameters defined in LBM and physical properties (i.e. density, pressure, isosteric heat of adsorption) is established systematically. Using the developed model, we observe quantitative agreement between LBM and lattice density functional theory (LDFT)/experimental data in terms of adsorption isotherms and density distributions. We then compare adsorption behavior in two ‘model’ interP and intraP pore systems and a synthesized polyethylene porous medium with more complex pore shapes. We observe three adsorption stages for subcritical gas adsorption: a) early capillary condensation near grain contacts or sharp corners, forming isolated pendular rings or fluid clusters; b) growing, merging, and spreading of the isolated condensed phase, forming circular gas/liquid meniscus; c) the condensed phase becomes fully-connected across the geometry, leaving isolated gas bubbles. We observe a signature behavior for the adsorption isotherm of intraP pore system, where a stepped feature occurs around relative pressure of 0.8, and the adsorption uptake for the polyethylene porous medium is bounded by the upper and lower limits given by the interP and intraP pore systems. On the other hand, we find that supercritical methane adsorption in mesoporous media is less sensitive to pore shape, but rather controlled by the specific surface area. The existence of micropores also affects the adsorption uptake.

Early stage condensation frosting characteristics on plain and nano Al2O3-epoxy mixture-coated brass

Early stage condensation frosting on plain and nano Al2O3-epoxy mixture-coated brass were experimentally investigated. The contact angles of water on the plain and coated brass were 95.8° ± 80.8° and 135.5° ± 80.5° respectively. Surface temperature of both samples ranged from −7.4 °C ± 1.6 °C to −21.3 °C ± 0.3 °C. Dropwise condensation, crystal growth and early frost layer growth were observed. Effects of surface temperature and hydrophobicity on nucleation, crystal growth and crystal shape were examined. It is found that the critical nucleation size of the condensed droplet varies with surface hydrophobicity at different surface temperatures. The crystallization is remarkably postponed using the present coating. The crystal height does not increase until t = 1924 s ± 180 s at Tsurf = −7.4 °C ± 1.6 °C, t = 422 s ± 57 s at Tsurf = −15.0 °C ± 1.2 °C, and t = 73 s ± 12 s at Tsurf = −21.3 °C ± 0.3 °C on the coated brass, compared with t = 39 s ± 5.1 s, t = 30 s ± 2.4 s and t = 14 s ± 3.3 s respectively on the plain brass. Besides, three types of crystal shapes are captured, including the column clumping, stacked stellar plates and dendrites. A stronger dendritical pattern is built at a lower surface temperature. However, no obvious dependency of the crystal shape on the surface hydrophobicity is detected. Moreover, the crystal height growth rate is quantitatively analyzed. The maximum growth rate of crystal height, which corresponds to the moment when the sensible heat removal rate equals to the latent heat release rate, increases with decreasing surface temperature, and is achieved sooner at a lower surface temperature or on the surface with higher hydrophobicity.

Emulating the early phases of human tooth development in vitro

Functional in vitro models emulating the physiological processes of human organ formation are invaluable for future research and the development of regenerative therapies. Here, a developmentally inspired approach is pursued to reproduce fundamental steps of human tooth organogenesis in vitro using human dental pulp cells. Similar to the in vivo situation of tooth initiating mesenchymal condensation, a 3D self-organizing culture was pursued resulting in an organoid of the size of a human tooth germ with odontogenic marker expression. Furthermore, the model is capable of epithelial invagination into the condensed mesenchyme, mimicking the reciprocal tissue interactions of human tooth development. Comprehensive transcriptome analysis revealed activation of well-studied as well as rather less investigated signaling pathways implicated in human tooth organogenesis, such as the Notch signaling. Early condensation in vitro revealed a shift to the TGFß signal transduction pathway and a decreased RhoA small GTPase activity, connected to the remodeling of the cytoskeleton and actin-mediated mechanotransduction. Therefore, this in vitro model of tooth development provides a valuable model to study basic human developmental mechanisms.

Characteristics of Tire Wear Particles Generated by a Tire Simulator under Various Driving Conditions

Physicochemical properties of pure tire wear particles (TWPs) were investigated in a laboratory. A tire simulator installed in an enclosing chamber was employed to eliminate artifacts caused by interfering particles during the generation and measurement of TWPs. TWP particulate matter (PM2.5 and PM10) was correlated with tire speed ( r > 0.94) and load ( r > 0.99). Their mass size distributions showed that TWP mode diameters ranged between 3 and 4 μm (unimodal). Tire wear caused by slip events resulted in an increase in the number concentration (ca. 8.4 × 105 cm-3) of particles (mainly ultrafine particles (UFPs)) at low PM2.5 and PM10 values (1 and 2 μg m-3, respectively). During braking events, UFPs were emitted at an early stage, with an increase in number concentration (up to 1.1 × 107 cm-3); a high mass concentration (3.6 mg m-3) was observed at a later stage via the coagulation of early emitted UFPs and condensation. On the basis of morphology and elemental composition, TWPs generally had elongated (micrometer-scale) and round/irregular (submicrometer-scale) shapes and they were classified into C/Si-rich, heavy metal-containing, S-containing, and mineral-containing particles. This study determined that TWP emissions can vary with changes in driving condition.

SFMBT2 positively regulates SOX9 and chondrocyte proliferation.

SRY‑box9(SOX9) is the master regulator of the chondrocyte phenotype, which is essential for differentiating chondrogenic mesenchymal condensations into chondrocytes, and is involved in regulating every stage of chondrocyte differentiation. SOX9 deletion in chondrocytes at the late stages of cartilage development results in decreased chondrocyte proliferation; inhibited expression of cartilage matrix genes, including Indian hedgehog and the downstream parathyroid hormone‑related protein; and premature conversion of proliferating chondrocytes into hypertrophic chondrocytes, which mineralize their matrix prematurely. Therefore, SOX9 is considered vital for the majority of phases of chondrocyte lineage, from early condensations to the differentiation of proliferating chondrocytes, leading to chondrocyte hypertrophy. It has been reported that SOX9 expression is decreased in osteoarthritis(OA) cartilage. Regeneration or repair of cartilage degradation in OA remains a challenge. Previous studies have indicated that overexpression of SOX9 can promote cartilage repair and can be used as a potential therapeutic agentat the early stages of human OA. The present study identified Scm‑like with four malignant brain tumor domains2(SFMBT2) as a novel regulator of SOX9 expression in human chondrocytes. Our previous study revealed that SFMBT2 is negatively regulated in OA cartilage, and decreased levels of SFMBT2 contribute to the catabolic phenotype of chondrocytes. The present study detected increased expression levels of SFMBT2 in early cartilage development and during the early phases of chondrogenesis. Overexpression of SFMBT2 in C28/I2 cells upregulated SOX9 expression in a dose‑dependent manner. Furthermore, SFMBT2 positively regulated C28/I2 cell proliferation and restored the decreased levels of SOX9 in chondrocytes following tumor necrosis factor‑α treatment. Additional studies may reveal novel insights into the molecular mechanism involved and the potential role of SFMBT2 in cartilage repair and OA management.

Nanoscale Phase Measurement for the Shale Challenge: Multicomponent Fluids in Multiscale Volumes.

Hydrocarbon recovery from shale reservoirs provides an increasing share of world energy. These resources are multicomponent fluid mixtures within multiscale geometries, and understanding their associated phase-change thermodynamics presents an array of challenges for experimentalists, theorists, operators, and policy makers. Here, we quantify hydrocarbon mixture phase behavior via direct imaging of connected channels spanning 4 orders of magnitude (10 nm to 10 μm) with supporting density functional theory. The methane/propane mixture dew point shifts, with early condensation of heavy components in nanopores because of a combination of capillarity and competitive surface adsorption. The bubble point in nanoconfinement is found to be deeply suppressed (∼3-fold), to below the bulk dew point of the original mixture, because of the exchange of mixture components with larger connected volumes. The trapping of the heaviest components of hydrocarbon mixtures within the smallest connected pores has implications for shale operations, reserve estimation, and ultimately energy security.

Interpretation of Nuclear-Magnetic-Resonance Response to Hydrocarbons: Application to Miscible Enhanced-Oil-Recovery Experiments in Shales

Summary Estimation of total reserves in shale/gas and shale/oil reservoirs is challenging but critical. Different logging tools and core-evaluation procedures are used to address this challenge. Nuclear magnetic resonance (NMR) plays a vital role in understanding fluid content, rock/fluid interaction, and determination of pore-body-size distributions. Hydrocarbon (HC)-hosting pore systems in shale includes both organic and inorganic pores. Recoverable HCs include bitumen and light HCs. Their relative fractions are strongly dependent on thermal maturity. Regardless of detailed chemical characterization, “bitumen” is simply defined on the basis of mobility in this study. The apparent mobility of HCs depends on fluid composition, solubility, and reservoir temperature. Historically, NMR laboratory-calibration measurements (nominally, 2-MHz) on core are conducted at room temperature (25–35°C). This study highlights the importance of running NMR tests at reservoir temperature. Experiments were performed for both bulk fluids and fluid-saturated rock samples. The results show that, at a specific temperature, NMR responds only to the fraction of HCs present in the liquid phase. For routine NMR measurement, at 31°C, only the relaxation signals of compounds more volatile than C17 are acquired. Thus, the C17+ fraction would be invisible to NMR at room temperature, but perhaps not at reservoir temperature. This is critical to the interpretation of NMR log response within the early oil and condensate windows, in which C17+ can be a major fraction. Thus, engineers can underestimate movable HCs by using routine core data as a basis for interpretation. On the basis of NMR experiments for several oil samples, we observed that the T1–T2 distributions depend on the overall composition of total HCs and effective mobilities. The results also show that, in the case when both light and heavy HC fractions coexist in a single phase, they do not appear as different clusters in a T1–T2 distribution map. NMR parameters were used to monitor the amount, composition, and effective mobility of remaining HCs after each injection and discharging cycle, during miscible enhanced-oil-recovery (EOR) huff ’n’ puff experiments on Eagle Ford samples.

Character definition and tempus optimum in comparative chondrocranial research

AbstractHere, we define a research program using primordial skull characters for broad scale phylogenetic comparisons, particularly for amniotes. There are many chondrocranium descriptions in the literature, encompassing many clades of vertebrates. The definition of a comparable “tempus optimum” for fully formed chondrocrania, as developed herein, will enable discrete character definition in the sense of phylogenetic systematics. The “tempus optimum” is a time period in which the nose region shows full chondrification and the basicranium has not yet changed in its anatomy by ossification processes. For studies on heterochrony, changes in the developmental timing through evolution, the available data in the literature are insufficient. Anatomical standardizations, traceable methodological approaches and clear definitions of comparable developmental stages are needed. Moreover, for profound homology assertions of chondrocranial structures, ontogeny needs to be traced from early mesenchymal condensation, through several stages of cartilage development, up to postnatal stages, in which ossifications are already present. A holistic observation, including hard and soft tissue anatomy, is of paramount importance to generate hypotheses of homology with much explanatory power and to derive conclusions on functional morphology. For that, traditional histological methodology is needed. We exemplify the suggested approach in two case studies on the disputed laterosphenoid in turtles and crocodiles and on the homology of pila antotica in a pleurodire turtle, and, using here defined criteria, we formulate hypotheses on their homology.

Kinetics of the acid-catalyzed hydrolysis of tetraethoxysilane (TEOS) by 29Si NMR spectroscopy and mathematical modeling

Tetraethoxysilane (TEOS) is widely used to synthesize siliceous material by the sol–gel process. However, there is still some disagreement about the nature of the limiting step in the hydrolysis and condensation reactions. The goal of this research was to measure the variation in the concentration of intermediates formed in the acid-catalyzed hydrolysis by 29Si NMR spectroscopy, to model the reactions, and to obtain the rate constants and the activation energy for the hydrolysis and early condensation steps. We studied the kinetics of TEOS between pH 3.8 and 4.4, and four temperature values in the range of 277.2–313.2 K, with a TEOS:ethanol:water molar ratio of 1:30:20. Both hydrolysis and the condensation rate speeded up with the temperature and the concentration of oxonium ions. The kinetic constants for hydrolysis reactions increased in each step kh1 < kh2 < kh3 < kh4, but the condensation rate was lower for dimer formation than for the formation of the fully hydrolyzed Si(OH)4. The system was described according to 13 parameters: six of them for the kinetic constants estimated at 298.2 K, six to the activation energies, and one to the equilibrium constant for the fourth hydrolysis. The mathematical model shows a steady increase in the activation energy from 34.5 kJ mol−1 for the first hydrolysis to 39.2 kJ mol−1 in the last step. The activation energy for the condensation reaction from Si(OH)4 was ca. 10 kJ mol−1 higher than the largest activation energy in the hydrolytic reactions. The decrease in the net positive charge on the Si atom contributes to the protonation of the ethoxy group and makes it a better leaving group.

Chondritic Mn/Na ratio and limited post-nebular volatile loss of the Earth

The depletion pattern of volatile elements on Earth and other differentiated terrestrial bodies provides a unique insight as to the nature and origin of planetary building blocks. The processes responsible for the depletion of volatile elements range from the early incomplete condensation in the solar nebula to the late de-volatilization induced by heating and impacting during planetary accretion after the dispersion of the H2-rich nebular gas. Furthermore, as many volatile elements are also siderophile (metal-loving), it is often difficult to deconvolve the effect of volatility from core formation. With the notable exception of the Earth, all the differentiated terrestrial bodies for which we have samples have non-chondritic Mn/Na ratios, taken as a signature of post-nebular volatilization. The bulk silicate Earth (BSE) is unique in that its Mn/Na ratio is chondritic, which points to a nebular origin for the depletion; unless the Mn/Na in the BSE is not that of the bulk Earth (BE), and has been affected by core formation through the partitioning of Mn in Earth's core. Here we quantify the metal–silicate partitioning behavior of Mn at deep magma ocean pressure and temperature conditions directly applicable to core formation. The experiments show that Mn becomes more siderophile with increasing pressure and temperature. Modeling the partitioning of Mn during core formation by combining our results with previous data at lower P–T conditions, we show that the core likely contains a significant fraction (20 to 35%) of Earth's Mn budget. However, we show that the derived Mn/Na value of the bulk Earth still lies on the volatile-depleted end of a trend defined by chondritic meteorites in a Mn/Na vs Mn/Mg plot, which tend to higher Mn/Na with increasing volatile depletion. This suggests that the material that formed the Earth recorded similar chemical fractionation processes for moderately volatile elements as chondrites in the solar nebula, and experienced limited post nebular volatilization.

High-density human mesenchymal stem cell rings with spatiotemporally-controlled morphogen presentation as building blocks for engineering bone diaphyseal tissue.

Emerging biomimetic tissue engineering strategies aim to partially recapitulate fundamental events that transpire during embryonic skeletal development; namely, cellular self-organization and targeted morphogenetic pathway activation. Here, we describe self-assembled, scaffold-free human mesenchymal stem cell (hMSC) rings featuring microparticle-mediated presentation of transforming growth factor-β1 (TGF-β1) and bone morphogenetic protein-2 (BMP-2). We tested the hypothesis that spatiotemporally-controlled dual presentation of TGF-β1 and BMP-2 is superior in modulating in vitro endochondral ossification of high-density cellular constructs compared to single morphogen delivery. hMSC rings were engineered by seeding cells with microparticles presenting (1) TGF-β1, (2) BMP-2, or (3) TGF-β1 + BMP-2 in custom agarose wells to facilitate self-assembly within 2 d, followed by horizontal culture on glass tubes for 5 weeks. At day 2, hMSC rings across groups revealed homogenous cellular organization mimetic of early mesenchymal condensation with no evidence of new matrix or mineral deposition. Significant early chondrogenic and osteogenic priming occurred with TGF-β1 + BMP-2 presentation compared to single morphogen-loaded groups. By week 5, TGF-β1-loaded hMSC rings had undergone chondrogenesis, while presentation of BMP-2 alone or in conjunction with TGF-β1 stimulated chondrogenesis, chondrocyte hypertrophy, and osteogenesis indicative of endochondral ossification. Importantly, tissue mineralization was most compelling with TGF-β1 + BMP-2 loading. Lastly, hMSC ring 'building blocks' were shown to efficiently fuse into tubes within 6 d post self-assembly. The resulting tubular tissue units exhibited structural integrity, highlighting the translational potential of this advanced biomimetic technology for potential early implantation in long bone defects.

Spatio-temporal expression patterns of Wnt signaling pathway during the development of temporomandibular condylar cartilage

There is a growing body of evidence supporting the involvement of the Wnt signaling pathway in various aspects of skeletal and joint development; however, it is unclear whether it is involved in the process of temporomandibular joint development. In order to clarify this issue, we examined the spatio-temporal distribution of mRNAs and proteins of the Wnt family during the formation of the mandibular condylar cartilage at the prenatal and postnatal stages. An in situ hybridization test revealed no mRNAs of β-catenin and Axin2 during early mesenchymal condensation; the ligands surveyed in this study (including Wnt-4, 5a, and 9a) were clearly detected at various ranges of expression, mainly in the condylar blastema and later distinct cartilaginous layers. Apart from β-catenin and Axin2, the Wnt family members surveyed in this study, including Lef-1, were found to be immunopositive during early chondrogenesis in the condylar cartilage at E14.5. After distinct chondrocyte layers were identified within the cartilage at E16.5, the expression of the Wnt signaling members was different and mainly restricted to proliferating cells and mineralized hypertrophic chondrocytes. In the adult mandibular condylar cartilage, the Wnt-4 mRNA, as well as the Wnt-4 and Wnt-9a proteins, was not observed. Our findings demonstrated that the Wnt signaling pathway was associated with the development of mandibular condylar cartilage.

The behavior of osmium and other siderophile elements during impacts: Insights from the Ries impact structure and central European tektites

Impact processes are natural phenomena that contribute to a variety of physico–chemical mechanisms over an extreme range of shock pressures and temperatures, otherwise seldomly achieved in the Earth’s crust through other processes. Under these extreme conditions with transient temperatures and pressures ≥3000K and ≥100GPa, followed by their rapid decrease, the behavior of elements has remained poorly understood. Distal glassy ejecta (tektites) were produced in early phases of contact between the Earth’s surface and an impacting body. Here we provide evidence for a complex behavior of Os and other highly siderophile elements (HSE; Ir, Ru, Pt, Pd, and Re) during tektite production related to a hyper-velocity impact that formed the Ries structure in Germany. Instead of simple mixing between the surface materials, which are thought to form the major source of central European tektites (moldavites), and impactor matter, the patterns of HSE contents and 187Re/188Os – 187Os/188Os ratios in moldavites, target sediments and impact-related breccias (suevites) can be explained by several sequential and/or contemporary processes. These involve (i) evaporative loss of partially oxidized HSE from the overheated tektite melt, (ii) mixing of target-derived and impactor-derived HSE vapor (plasma) phases, and (iii) early (high-temperature) condensation of a part of the mixed vapor phase back to silicate melt droplets. An almost complete loss of terrestrial Os from the tektite melt and its replacement with extra-terrestrial Os are indicated by low 187Os/188Os ratios in tektites (<0.163) relative to precursor materials (>0.69). This is paralleled by a co-variation between Os and Ni contents in tektites but not in suevites formed later in the impact process.

Effect of Acetic Acid on the Pitting Corrosion of 2Cr12MoV Turbine Steel in Early Condensates Containing Chloride Ions

Effect of Acetic Acid on the Pitting Corrosion of 2Cr12MoV Turbine Steel in Early Condensates Containing Chloride Ions

In situ isotopic studies of the U-depleted Allende CAI Curious Marie: Pre-accretionary alteration and the co-existence of 26Al and 36Cl in the early solar nebula

The isotopic composition of oxygen as well as 26Al-26Mg and 36Cl-36S systematics were studied in Curious Marie, an aqueously altered Allende CAI characterized by a Group II REE pattern and a large 235U excess produced by the decay of short-lived 247Cm. Oxygen isotopic compositions in the secondary minerals of Curious Marie follow a mass-dependent fractionation line with a relatively homogenous depletion in 16O (Δ17O of −8‰) compared to unaltered minerals of CAI components. Both Mg and S show large excesses of radiogenic isotopes (26Mg∗ and 36S∗) that are uniformly distributed within the CAI, independent of parent/daughter ratio. A model initial 26Al/27Al ratio [(6.2±0.9)×10−5], calculated using the bulk Al/Mg ratio and the uniform δ26Mg∗∼+43‰, is similar to the canonical initial solar system value within error. The exceptionally high bulk Al/Mg ratio of this CAI (∼95) compared to other inclusions is presumably due to Mg mobilization by fluids. Therefore, the model initial 26Al/27Al ratio of this CAI implies not only the early condensation of the CAI precursor but also that aqueous alteration occurred early, when 26Al was still at or near the canonical value. This alteration event is most likely responsible for the U depletion in Curious Marie and occurred at most 50kyr after CAI formation, leading to a revised estimate of the early solar system 247Cm/235U ratio of (5.6±0.3)×10−5. The Mg isotopic composition in Curious Marie was subsequently homogenized by closed-system thermal processing without contamination by chondritic Mg. The large, homogeneous 36S excesses (Δ36S∗∼+97‰) detected in the secondary phases of Curious Marie are attributed to 36Cl decay (t1/2=0.3Myr) that was introduced by Cl-rich fluids during the aqueous alteration event that led to sodalite formation. A model 36Cl/35Cl ratio of (2.3±0.6)×10−5 is calculated at the time of aqueous alteration, translating into an initial 36Cl/35Cl ratio of ∼1.7–3×10−5 at solar system birth. The Mg and S radiogenic excesses suggest that 26Al and 36Cl co-existed in the early solar nebula, raising the possibility that, in addition to an irradiation origin, 36Cl could have also been derived from a stellar source.

Corrosion Behavior of 2Cr12MoV Turbine Steel in Early Condensate in the Presence of Acetic Acid

Corrosion Behavior of 2Cr12MoV Turbine Steel in Early Condensate in the Presence of Acetic Acid

Neutron-captures in Low Mass Stars and the Early Solar System Record of Short-lived Radioactivities

Noticeable improvements were recently introduced in the modelling of n-capture nucleosynthesis in the advanced evolutionary stages of giant stars (Asymptotic Giant Branch, or AGB, stars). Two such improvements are closely linked together and concern the introduction of non-parameterized, physical models for extended mixing processes and the adoption of accurate reaction rates for H- and He-burning reactions, including the one for the main neutron source 13 C(α,n) 16 O. These improvements profited of a longstanding collaboration between stellar physicists and C. Spitaleri’s team and of his seminal work both as a leader in the Nuclear Astrophysics scenario and as a talent-scout in the recruitment of young researchers in the field. We present an example of the innovative results that can be obtained thanks to the novelties introduced, by estimating the contributions from a nearby AGB star to the synthesis of short-lived (t 1/2 ≤ 10 Myr) radioactive nuclei which were alive in early Solar System condensates. We find that the scenario indicating an AGB star as the source of such radioactivities, discussed for many years by researchers in this field, appears now to be no longer viable, when the mentioned improvements of AGB models and nuclear parameters are considered.