Evolution Of Core Research Articles

A Long-lived Lunar Magnetic Field Powered by Convection in the Core and a Basal Magma Ocean

An internally generated magnetic field once existed on the Moon. This field reached high intensities (∼10–100 μT, perhaps intermittently) from ∼4.3 to 3.6 Gyr ago and then weakened to ≲5 μT before dissipating by ∼1.9–0.8 Gyr ago. While the Moon’s metallic core could have generated a magnetic field via a dynamo powered by vigorous convection, models of a core dynamo often fail to explain the observed characteristics of the lunar magnetic field. In particular, the core alone may not contain sufficient thermal, chemical, or radiogenic energy to sustain the high-intensity fields for >100 Myr. A recent study by Scheinberg et al. suggested that a dynamo hosted in electrically conductive, molten silicates in a basal magma ocean (BMO) may have produced a strong early field. However, that study did not fully explore the BMO’s coupled evolution with the core. Here we show that a coupled BMO–core dynamo driven primarily by inner core growth can explain the timing and staged decline of the lunar magnetic field. We compute the thermochemical evolution of the lunar core with a 1D parameterized model tied to extant simulations of mantle evolution and BMO solidification. Our models are most sensitive to four parameters: the abundances of sulfur and potassium in the core, the core’s thermal conductivity, and the present-day heat flow across the core–mantle boundary. Our models best match the Moon’s magnetic history if the bulk core contains ∼6.5–8.5 wt% sulfur, in agreement with seismic structure models.

Association of Bun/Cr ratio-based dehydration status with infarct volumes and stroke severity in acute ischemic stroke

BackgroundOnly a few clinical research had previously investigated the dehydration status to predict the evolution of the ischemic core. The aim of this study is to clarify the association between blood urea nitrogen (BUN)/creatinine (Cr)ratio-based dehydration and infarct volume measured using DWI (Diffusion-weighted imaging) at admission in patients with AIS (Acute Ischemic Stroke). MethodsWe retrospectively recruited a total of 203 consecutive patients who were hospitalized through emergency or outpatient services within 72 h of acute ischemic stroke onset between October 2015 and September 2019. Stroke severity was measured by assessing the National Institutes of Health Stroke Scale (NIHSS) on admission. Infarct volume was measured using DWI with MATLAB software. ResultsIn this study, 203 patients who met the study criteria were enrolled. Patients in the dehydration group (Bun/Cr ratio>15) had a higher median NIHSS score (6(IQR:4–10) VS. 5(3−7); P = 0.0015)and larger DWI infarct volume (1.55 ml (IQR:0.51–6.79) VS. (0.37 ml (0.05–1.22); P < 0.001) on admission compared with patients in normal group. Further, a statistically significant correlation was found between DWI infarct volumes and NIHSS score with nonparametric Spearman rank correlation (r = 0.77; P < 0.001). The median NIHSS scores for the DWI infarct volumes quartiles were 3 ml (IQR, 2–4), 5 ml (4−7), 6 ml (5−8), and12 ml (8−17) from lowest to highest. However, the second quartile group did not show any significant correlation with the third quartile group (P = 0.4268). Multivariable linear and logistic regression analyses were used to test dehydration (Bun/Cr ratio>15), representing a predictor of infarct volume and stroke severity. ConclusionBun/Cr ratio-based dehydration is associated with larger volumes of ischemic tissue measured using DWI and worse neurological deficit assessed by the NIHSS score in acute ischemic stroke.

An idealized model for collapse of a molecular core within a filament

ABSTRACT We present an analytic treatment of the self-similar collapse of a uniform density ellipsoid to linear order in the deviations from sphericity. First we obtain a self-consistent closed-form solution for the evolution of an isolated ellipsoid and then impose the effects of an external forcing. This model describes the evolution under gravity of a pre-stellar core of molecular gas embedded in a much larger and lower-density filament. We compare with numerical solutions for the collapse without the limitation of small deviations. These show how the external perturbing force producing the initial deviation from sphericity is eventually surpassed by the anisotropic forces generated by the collapsing ellipsoid itself. This model should be useful in interpreting the way in which environment shapes the evolution of pre-stellar cores.

Diesel Spray Liquid Length Imaging at High Pressure

Engine efficiency and emissions depend on the fuel atomization and dispersion. The fuel atomization and dispersion depend heavily on the ambient pressure and temperature. In this work, to study Diesel sprays in engine conditions, an electrically heated, constant-volume, pressurized vessel was designed and manufactured. The controlling electronics and software were developed and tested to ensure safe and precise operation. A commercial Bosch six-hole automotive Diesel injector was used. The spray spatial and temporal development were studied. In the literature, spray liquid length and cone angle are extensively used to quantify fuel dispersion. In this work, these parameters were quantified using a high-speed shadowgraph technique. Models were derived to describe the temporal evolution of the liquid core. Such models can be used to predict the Diesel spray behaviour and the engine performance.

Spiral structure and massive star formation in the hub-filament-system G326.27-0.49

ABSTRACT Hub-filament systems (HFSs) are potential sites of formation of star clusters and high mass stars. To understand the HFSs and to provide observational constraints on current theories that attempt to explain star formation globally, we report a study of the region associated with G326.27-0.49 using infrared data of dust continuum and newly obtained observations on molecular tracers using the APEX (Atacama Pathfinder EXperiment) telescope. We use the spectroscopic observations to identify velocity-coherent structures (filaments and clumps) and study their properties at a resolution of 0.4 pc. The region contains two main velocity components: first component shows four filaments between −63 and −55 km s−1 forming a spiral structure converging in a hub, the second filamentary component at ∼−72 km s−1 harbours a massive young stellar object (YSO) and possibly interacts with the hub. The clumps harbouring the three main YSOs in the region are massive (187–535 M⊙), have luminosities consistent with B-type stars, have central densities of ∼106 cm−3, and drive large outflows. Majority of the velocity-coherent clumps in the region shows virial parameters between 2 and 7, which considering the detection of protostars implies collapse to be gradual. We conclude that the region consists of a network of filaments through which mass accretes (∼10−4 M⊙ yr−1) onto the hub. The hub and some of the ends of filaments appear to be undergoing collapse to form new stars. This study identifies a target region for future high-resolution studies that would probe the link between the core and filament evolution.

The emergence of a core–periphery structure in evolving multilayer network

The application of the evolutionary game method to studying dynamics on multilayer networks is a current hot issue. However, most current evolutionary game models do not consider some constraints affecting the development of the relationship structure in a multilayer network. Therefore, this paper proposes a new model to explain the emergence and evolution of core and periphery structures in a multilayer network. Our model includes the direct costs of maintaining interactions between players in the game model. We also introduce the ability to end disadvantageous interactions (a defective neighbor that does not bring benefits is disconnected). Third, when establishing new relationships, a player establishes a relationship with another based on the estimate (trust) that this player will cooperate. The simulation results show that a core of densely connected cooperative players gradually emerges, isolating defectors on the periphery and gaining additional advantages. The proposed model contributes to understanding the emergence and development of the core–periphery structure in a multilayered network with a core formed either between players in the same layers or between players from other layers (across layers).

Microstructure and Crystallization Kinetics of Silica-Based Ceramic Cores with Enhanced High-Temperature Property.

Silica-based ceramic cores play key roles in the casting of aeroengine blades, but they are highly limited by the poor high-temperature mechanical property. Here, fused mullite (FM) and sintered mullite (SM) powders were modified in silica-based ceramic cores, and the microstructure evolution and crystallization kinetics of ceramic cores depending on mullite types were studied. The ceramic cores with FM showed a dense microstructure and superior mechanical properties compared to those with SM. The ceramic cores with 10 wt.% of FM showed a crystallization activation energy of 1119.5 kJ/mol and a crystallization exponent of 1.74, and the values of 938.4 kJ/mol and 1.86 as SM were employed; the decreased crystallization activation energy and the elevated crystallization exponent by SM suggested that the excess impurities of alkali oxides and alkaline-earth oxides significantly promoted the crystallization of cristobalite. Even though the ceramic cores with mullite powders decreased slightly in the room-temperature mechanical property, their high-temperature flexure strength and creep deformation resistance were enhanced. The ceramic cores with 10 wt.% of FM showed excellent comprehensive performance, with linear shrinkage of 0.69%, room-temperature strength of 18.9 MPa, and high-temperature strength of 15.5 MPa, which satisfied the demands for hollow-blade casting.

Environmental effects of star-forming cores on mass accretion rate

ABSTRACT We calculate the evolution of cloud cores embedded in different envelopes to investigate environmental effects on the mass accretion rate on to protostars. As the initial state, we neglect the magnetic field and cloud rotation, and adopt star-forming cores composed of two parts: a centrally condensed core and an outer envelope. The inner core has a critical Bonnor–Ebert density profile and is enclosed by the outer envelope. We prepare 15 star-forming cores with different outer envelope densities and gravitational radii, within which the gas flows into the collapsing core, and calculate their evolution until ∼2 × 105 yr after protostar formation. The mass accretion rate decreases as the core is depleted when the outer envelope density is low. In contrast, the mass accretion rate is temporarily enhanced when the outer envelope density is high and the resultant protostellar mass exceeds the initial mass of the centrally condensed core. Some recent observations indicate that the mass of pre-stellar cores is too small to reproduce the stellar mass distribution. Our simulations show that the mass inflow from outside the core contributes greatly to protostellar mass growth when the core is embedded in a high-density envelope, which could explain the recent observations.

The “New Core Paradox”: Challenges and Potential Solutions

AbstractThe “new core paradox” suggests that the persistence of the geomagnetic field over nearly all of Earth history is in conflict with the core being highly thermally conductive, which makes convection and dynamo action in the core much harder prior to the nucleation of the inner core. Here we revisit this issue by exploring the influence of six important parameters on core evolution: upper/lower mantle viscosity ratio, core thermal conductivity, core radiogenic heat rate, mantle radiogenic heating rate, central core melting temperature, and initial core‐mantle boundary (CMB) temperature. Each parameter is systematically explored by the model, which couples mantle energy and core energy‐entropy evolution. A model is “successful” if the correct present‐day inner core size is achieved and the dynamo remains alive, as implied by the paleomagnetic record. In agreement with previous studies, we do not find successful thermal evolutions using nominal parameters, which includes a core thermal conductivity of 70 Wm−1K−1, zero core radioactivity, and an initial CMB temperature of 5,000 K. The dynamo can be kept alive by assuming an unrealistically low thermal conductivity of 20 Wm−1K−1 or an unrealistically high core radioactive heat flow of 3 TW at present‐day, which are considered “unsuccessful” models. We identify a third scenario to keep the dynamo alive by assuming a hot initial CMB temperature of ∼6,000 K and a central core liquidus of ∼5,550 K. These temperatures are on the extreme end of typical estimates, but should not be ruled out and deserve further scrutiny.

Miocene-Holocene paleoenvironmental changes in the Tinto River estuary (SW Spain) evidenced by sedimentology, geochemistry and fauna

This paper investigates the paleoenvironmental evolution of a long core extracted in a small cove located in the Tinto-Odiel estuary (SW Spain). The inferred reconstruction is supported by sedimentological, geochemical, paleontological data and dating. Seven phases have been identified, with the transit from Late Neogene marine environments to a subrecent freshwater pond and a final anthropic filling. On the basis of these data, this area was flooded during the maximum of the MIS-1 transgression (6.5-5.2 cal. kyr BP), with the temporary presence of a subtidal channel with phanerogam meadows. During this evolution, three geochemical peaks have been detected, which correspond to 1) the first evidence of mining activities (~4.5 cal. kyr BP), 2) an interval of intensive mining (1850-1960) and 3) an industrial period (1966-1985), affected by the dumping of highly polluting waste into this estuary.

Earth's Paleomagnetic Field and its Changes Through Time

Paleomagnetic data is the only way to access the behavior of the geomagnetic field of internal origin through geological time. Therefore, the complete description of the paleosecular variation (PSV) is fundamental for unraveling the evolution of the Earth's core. Modeling of PSV relies on observing the fluctuations in the direction and intensity of the field on the surface, the evaluation of the paleomagnetic data dispersion in different times and situations of low and high reversal rates, the kinematics of the virtual poles during reversals, and other aspects. Magneto-cyclostratigraphy is a powerful tool to constrain the age of sedimentary formations, and the recognition of patterns of magnetic variation represents a breakthrough in the development of cyclostratigraphy. This paper reviews some of the contributions to the subject of the Laboratory of Paleomagnetism at Instituto de Astronomia, Geofísica e Ciências Atmosféricas the University of São Paulo.

Dust motion and possibility of dust growth in a growing circumstellar disk

ABSTRACT We calculate the evolution of a star-forming cloud core using a three-dimensional resistive magnetohydrodynamics simulation, treating dust grains as Lagrangian particles, to investigate the dust motion in the early star formation stage. We prepare six different-sized set of dust particles in the range ad = 0.01–$1000\, \mu$m, where ad is the dust grain size. In a gravitationally collapsing cloud, a circumstellar disk forms around a protostar and drives a protostellar outflow. Almost all the small dust grains (ad ≲ 10–$100\, \mu$m) initially distributed in the region θ0 ≲ 45° are ejected from the center by the outflow, where θ0 is the initial zenith angle relative to the rotation axis, whereas only a small number of the large dust grains ($a_{\rm d} \gtrsim 100\, \mu$m) distributed in the region are ejected. All other grains fall onto either the protostar or disk without being ejected by the outflow. Regardless of the dust grain size, the behavior of the dust motion is divided into two trends after dust particles settle into the circumstellar disk. The dust grains reaching the inner disk region from the upper envelope preferentially fall onto the protostar, while those reaching the outer disk region or disk outer edge from the envelope can survive without an inward radial drift. These surviving grains can induce dust growth. Thus, we expect that the outer disk regions could be a favored place of planet formation.

The Himalayan Collisional Orogeny: A Metamorphic Perspective

AbstractThis paper introduces how crustal thickening controls the growth of the Himalaya by summarizing the P‐T‐t evolution of the Himalayan metamorphic core. The Himalayan orogeny was divided into three stages. Stage 60–40 Ma: The Himalayan crust thickened to ∼40 km through Barrovian‐type metamorphism (15–25 °C/km), and the Himalaya rose from &lt;0 to ∼1000 m. Stage 40–16 Ma: The crust gradually thickened to 60–70 km, resulting in abundant high‐grade metamorphism and anatexis (peak‐P, 15–25 °C/km; peak‐T, &gt;30 °C/km). The three sub‐sheets in the Himalayan metamorphic core extruded southward sequentially through imbricate thrusts of the Eo‐Himalayan thrust, High Himalayan thrust, and Main Central thrust, and the Himalaya rose to ≥5,000 m. Stage 16–0 Ma: the mountain roots underwent localized delamination, causing asthenospheric upwelling and overprinting of the lower crust by ultra‐high‐temperature metamorphism (30–50 °C/km), and the Himalaya reached the present elevation of ∼6,000 m. Underplating and imbricate thrusting dominated the Himalaya' growth and topographic rise, conforming to the critical taper wedge model. Localized delamination of mountain roots facilitated further topographic rise. Future Himalayan metamorphic studies should focus on extreme metamorphism and major collisional events, contact metamorphism and rare metal mineralization, metamorphic decarbonation and the carbon cycle in collisional belts.

Differences in chemical evolution between isolated and embedded prestellar cores

ABSTRACT Models of prestellar cores often assume that the cores are isolated from their environment – material outside the core boundary plays no role in the subsequent evolution. This is unlikely to be the case in reality, where cores are located within hierarchically substructured molecular clouds. We investigate the dynamical and chemical evolution of prestellar cores, modelled as Bonnor–Ebert spheres, and show that the density of the ambient medium has a large impact on the resulting chemical properties of the cores. Models embedded in high-density, low-temperature surroundings have greatly enhanced abundances of several molecules, such as CO and CS, compared to models with more diffuse surroundings, corresponding to relatively isolated cores. The predicted intensities and profile shapes of molecular lines are also affected. The density of the ambient medium has a stronger effect on the chemical evolution than whether the cores are initially in or out of equilibrium. This suggests that the impact of environment cannot be neglected when modelling chemistry in prestellar cores; the results of these models are highly sensitive to the assumptions made about the core surroundings.

Multifunctional Filter Membranes Based on Self-Assembled Core-Shell Biodegradable Nanofibers for Persistent Electrostatic Filtration through the Triboelectric Effect.

The massive production of polymer-based respiratory masks during the COVID-19 pandemic has rekindled the issue of environmental pollution from nonrecyclable plastic waste. To mitigate this problem, conventional filters should be redesigned with improved filtration performance over the entire operational life while also being naturally degradable at the end. Herein, we developed a functional and biodegradable polymeric filter membrane consisting of a polybutylene adipate terephthalate (PBAT) matrix blended with cetyltrimethylammonium bromide (CTAB) and montmorillonite (MMT) clay, whose surface properties have been modified through cation exchange reactions for good miscibility with PBAT in an organic solvent. Particularly, the spontaneous evolution of a partial core-shell structure (i.e., PBAT core encased by CTAB-MMT shell) during the electrospinning process amplified the triboelectric effect as well as the antibacterial/antiviral activity that was not observed in naive PBAT. Unlike the conventional face mask filter that relies on the electrostatic adsorption mechanism, which deteriorates over time and/or due to external environmental factors, the PBAT@CTAB-MMT nanofiber membrane (NFM)-based filter continuously retains electrostatic charges on the surface due to the triboelectric effect of CTAB-MMT. As a result, the PBAT@CTAB-MMT NFM-based filter showed high filtration efficiencies (98.3%, PM0.3) even at a low differential pressure of 40 Pa or less over its lifetime. Altogether, we not only propose an effective and practical solution to improve the performance of filter membranes while minimizing their environmental footprint but also provide valuable insight into the synergetic functionalities of organic-inorganic hybrid materials for applications beyond filter membranes.

Electrical resistivity of the Fe–Si–S ternary system: implications for timing of thermal convection shutdown in the lunar core

The composition of the lunar core has been suggested to be Fe-rich with varying amounts of lighter elements, such as Si and S. Presence of Si and S affects electrical and thermal transport properties and thus influences core thermal processes and evolution. Paleomagnetic observations constrain a high intensity magnetic field that ceases shortly after formation of the moon (~ 3.5–4.2 Ga year ago), and thermal convection in the core may contribute to generation of this field. In this study, the electrical resistivity of Fe-14 wt% Si-3 wt% S was measured in both solid and molten states at pressures up to 5 GPa and thermal conductivity was calculated via the Wiedemann–Franz Law from the electrical measurements. The results were used to estimate the adiabatic conductive heat flux of a molten Fe-14 wt% Si-3 wt% S lunar core and compared to a Fe-2-17 wt% Si lunar core, which showed that thermal convection of either core composition shuts down within the duration of the high intensity magnetic field: (1) 3.17–3.72 Ga year ago for a Fe-14 wt% Si-3 wt% S core; and (ii) 3.38–3.86 Ga years ago for a Fe-2-17 wt% Si core. Results favouring compatibility of these core compositions with paleomagnetic observations are strongly dependent on the temperature of the core-mantle boundary and time-dependent mantle-side heat flux.

Ammonia characterisation of dense cores in the Rosette Molecular Cloud

Context. The Rosette molecular cloud complex is a well-known Galactic star-forming region with a morphology pointing towards triggered star formation. The distribution of its young stellar population and the gas properties point to the possibility that star formation is globally triggered in the region. Aims. We focus on the characterisation of the most massive pre- and protostellar cores distributed throughout the molecular cloud in order to understand the star formation processes in the region. Methods. We observed a sample of 33 dense cores, identified in Herschel continuum maps, with the Effelsberg 100-m telescope. Using NH3 (1,1) and (2,2) measurements, we characterise the dense core population, computing rotational and gas kinetic temperatures and NH3 column density with multiple methods. We also estimated the gas pressure ratio and virial parameters to examine the stability of the cores. Using results from Berschel data, we examined possible correlations between gas and dust parameters. Results. Ammonia emission is detected towards 31 out of the 33 selected targets. We estimate kinetic temperatures to be between 12 and 20 K, and column densities within the 1014−2 × 1015 cm−2 range in the selected targets. Our virial analysis suggests that most sources are likely to be gravitationally bound, while the line widths are dominated by non-thermal motions. Our results are compatible with large-scale dust temperature maps suggesting that the temperature decreases and column density increases with distance from NGC 2244 except for the densest protoclusters. We also identify a small spatial shift between the ammonia and dust peaks in the regions most exposed to irradiation from the nearby NGC 2244 stellar cluster. However, we find no trends in terms of core evolution with spatial location, in the prestellar to protostellar core abundance ratio, or the virial parameter. Conclusions. Star formation is more likely based on the primordial structure of the cloud in spite of the impact of irradiation from the nearby cluster, NGC 2244. The physical parameters from the NH3 measurements suggest gas properties in between those of low- and high-mass star-forming regions, suggesting that the Rosette molecular cloud could host ongoing intermediate-mass star formation, and is unlikely to form high-mass stars.

Last Glacial Maximum Microblade Production at Shizitan 29 and its Implications for North China Pressure Technology

ABSTRACT A techno-functional approach applied to the lithics of the Late Upper Palaeolithic Shizitan 29 site allows the identification of previously unrecognized technical features of microblade pressure production and new behavioral understanding of its evolution beginning ca. 26,000 cal b.p. These technical features may relate to the evolution of so-called boat-shaped cores, including the development of two blade scar sequences and the 8-like contour of the striking platform (likely related to fixing cores in a holding device). Counter to traditional typological lithic analyses centered on final core morphologies, we seek to identify technical objectives related to the required pressure production. In doing so, we argue that earlier semi-conical cores may have maximized the exploitation of the core volume, while subsequent boat-shaped cores developed to maximize the efficiency of the production of straight profile, regular blades. This allowed microblades to become a critical adaptation for final Pleistocene hunter-gatherers in northern East Asia.

CCMOC: A new view of the Earth's outer core through the global coda correlation wavefield

Increasing seismic evidence has accumulated, suggesting that the Earth's outer core consists of distinct zones of low P-wave velocities in the top and bottom regions relative to the Preliminary Reference Earth Model (PREM). Seismically detected low velocities in the outer core could be linked with the stratification, essential for understanding the geodynamo and thermochemical evolution of the liquid core. However, a consistent globally-averaged radial structure of the outer core has not been obtained due to the incomplete coverage of sampling body waves. To remedy this problem, we explore the seismic structure of Earth's outer core by employing a new theoretical and observational concept termed coda correlation wavefield. We construct the global correlogram in the 15–50 s period range by stacking cross-correlations of the long-duration coda waves from the selected ten large earthquakes. We then assemble a dataset of prominent correlation features from the global correlogram that are sensitive to the outer core. The waveforms of these features are fit by computing synthetic correlograms through various outer core models. The obtained optimal model displays P-wave velocities in both the outer core's top and bottom, consistent with Coda Correlation Reference Earth Model (CCREM) and reduced relative to PREM. The P-wave velocity is ∼1% lower in the core's top than that in PREM, and the slow anomaly gradually approaches zero at about 800 km below the core-mantle boundary. The low seismic velocities in the top of the outer core could likely imply the formation of a thermal and/or compositional stratification.

Role of Spin-Orbit Coupling in High-Order Harmonic Generation Revealed by Supercycle Rydberg Trajectories.

High-harmonic generation is typically thought of as a sub-laser-cycle process, with the electron's excursion in the continuum lasting a fraction of the optical cycle. However, it was recently suggested that long-lived Rydberg states can play a particularly important role in high harmonic generation by atoms driven by the combination of the counterrotating circularly polarized fundamental light field and its second harmonic. Here we report direct experimental evidence of very long and stable Rydberg trajectories contributing to high-harmonic generation in such fields. We track their dynamics inside the laser pulse using the spin-orbit evolution in the ionic core, utilizing the spin-orbit Larmor clock. We confirm their effect on harmonic emission both via microscopic simulations and by showing how this radiation can lead to a well-collimated macroscopic far-field signal. Our observations contrast sharply with the general view that long-lived Rydberg orbits should generate negligible contribution to the macroscopic far-field high harmonic response of the medium.