Evolution Of Core Research Articles

Effects of stellar feedback on cores in STARFORGE

Stars form in dense cores within molecular clouds, and newly formed stars influence their natal environments. How stellar feedback impacts core properties and evolution has been the subject of extensive investigation. We performed a hierarchical clustering (dendrogram) analysis of a STARFORGE (STAR FORmation in Gaseous Environments) simulation, modelling a giant molecular cloud to identify gas overdensities (cores) and study changes in their radius, mass, velocity dispersion, and virial parameter with respect to stellar feedback. We binned these cores on the basis of the fraction of gas affected by protostellar outflows, stellar winds, and supernovae and analysed the property distributions for each feedback bin. We find that cores that experience more feedback influence are smaller. Feedback notably enhances the velocity dispersion and virial parameter of the cores, more so than it reduces their radius. This is also evident in the linewidth–size relation, according to which cores in higher-feedback bins exhibit higher velocities than their similarly sized pristine counterparts. We conclude that stellar feedback mechanisms, which impart momentum to the molecular cloud, simultaneously compress and disperse the dense molecular gas.

Numerical challenges in modeling gravothermal collapse in Self-Interacting Dark Matter halos

When dark matter has a large cross section for self scattering, halos can undergo a process known as gravothermal core collapse, where the inner core rapidly increases in density and temperature.To date, several methods have been used to implement Self-Interacting Dark Matter (SIDM) in N-body codes, but there has been no systematic study of these different methods or their accuracy in the core-collapse phase. In this paper, we compare three different numerical implementations of SIDM, including the standard methods from the GIZMO and Arepo codes, by simulating idealized dwarf halos undergoing significant dark matter self interactions (σ/m = 50 cm2/g).When simulating these halos, we also vary the massresolution, time-stepping criteria, and gravitational force-softening scheme. The various SIDM methods lead to distinct differences in a halo's evolution during the core-collapse phase, as each results in spurious scattering rate differences and energy gains/losses.The use of adaptive force softening for gravity can lead to numerical heating that artificially accelerates core collapse, while an insufficiently small simulation time step can cause core evolution to stall or completely reverse. Additionally, particle numbers must be large enough to ensure that the simulated halos are not sensitive to noise in the initial conditions. Even for the highest-resolution simulations tested in this study (106 particles per halo), we find that variations of order 10% in collapse time are still present.The results of this work underscore the sensitivity of SIDM modeling on the choice of numerical implementation and motivate a careful study of how these results generalize to halos in a cosmological context.

The ADNI PET Core at 20.

The Alzheimer's Disease Neuroimaging Initiative (ADNI) PET Core has evolved over time, beginning with positron emission tomography (PET) imaging of a subsample of participants with [18F]fluorodeoxyglucose (FDG)-PET, adding tracers for measurement of β-amyloid, followed by tau tracers. This review examines the evolution of the ADNI PET Core, the novel aspects of PET imaging in each stage of ADNI, and gives an accounting of PET images available in the ADNI database. The ADNI PET Core has been and continues to be a rich resource that provides quantitative PET data and preprocessed PET images to the scientific community, allowing interrogation of both basic and clinically relevant questions. By standardizing methods across different PET scanners and multiple PET tracers, the Core has demonstrated the feasibility of large-scale, multi-center PET studies. Data managed and disseminated by the PET Core has been critical to defining pathophysiological models of Alzheimer's disease (AD) and helped to drive methods used in modern therapeutic trials. HIGHLIGHTS: The ADNI PET Core began with FDG-PET and now includes three amyloid and three tau PET ligands. The PET Core has standardized acquisition and analysis of multitracer PET images. The ADNI PET Core helped to develop methods that have facilitated clinical trials in AD.

Asteroseismic measurement of core and envelope rotation rates for 2006 red giant branch stars

Context. Tens of thousands of red giant stars in the Kepler data exhibit solar-like oscillations. The mixed-mode characteristics of their oscillations enable us to study the internal physics from the core to the surface, such as differential rotation. However, envelope rotation rates have only been measured for about a dozen red giant branch (RGB) stars so far. This limited the theoretical interpretation of angular momentum transport in post-main sequence phases. Aims. We report the measurements of g-mode properties and differential rotation in the largest sample of Kepler RGB stars. Methods. We applied a new approach to calculate the asymptotic frequencies of mixed modes, which accounts for so-called near-degeneracy effects (NDEs) and leads to improved measurements of envelope rotation rates. By fitting these asymptotic expressions to the observations, we obtained measurements of the properties of g modes (period spacing, ΔΠ1, coupling factor, q, g-mode offset term, εg, small separation, δν01) and the internal rotation (mean core, Ωcore, and envelope, Ωenv, rotation rates). Results. Among 2495 stars with clear mixed-mode patterns, we found that 800 show doublets and 1206 show triplets, while the remaining stars do not show any rotational splittings. We measured core rotation rates for 2006 red giants, doubling the size of pre-existing catalogues. This led us to discover an over-density of stars that are narrowly distributed around a well-defined ridge in the plane, showing core rotation rate versus evolution along the RGB. These stars could experience a different angular momentum transport compared to other red giants. With this work, we also increased the sample of stars with measured envelope rotation rates by two orders of magnitude. We found a decreasing trend between envelope rotation rates and evolution, implying that the envelopes slow down with expansion, as expected. We found 243 stars whose envelope rotation rates are significantly larger than zero. For these stars, the core-to-envelope rotation ratios are around Ωcore/Ωenv ∼ 20 and show a large spread with evolution. Several stars show extremely mild differential rotations, with core-to-surface ratios between 1 and 2. These stars also have very slow core rotation rates, suggesting that they go through a peculiar rotational evolution. We also discovered more stars located below the ΔΠ1–Δν degeneracy sequence, which presents an opportunity to study the history of plausible stellar mergers.

Thermal and Dynamo Evolution of the Lunar Core Based on the Transport Properties of Fe‐S‐P Alloys

AbstractPaleomagnetic analyses have suggested that the lunar magnetic field underwent a significant change from 4.25 to 3.19 Ga, indicating the rapid transition of the lunar dynamo mechanism. We used the van der Pauw (vdP) method to measure the electrical resistivity of Fe‐S‐P alloys under conditions relevant to the lunar core and estimated the thermal conductivity of the Fe‐S‐P lunar core. These values were incorporated into thermal and dynamo models to investigate the evolution of the lunar core. Our model indicates that the inner core began to grow as early as 4.35 Ga, the solidification regime switched at 3.50 Ga, and the thermal dynamo ceased between 3.78 and 3.51 Ga. The cessation of the dynamo could be due to a low buoyancy flux and insufficient entropy dissipation. Thermal and compositional dynamos cannot sustain the ancient strength of the Moon's magnetic field, and require other energy sources.

Quasi-static compression response of foldcore sandwich structure based on core evolution

Due to its superior performance, the foldcore structure has the potential to replace traditional honeycomb materials. Single-ridgeline V-shaped, double-ridgeline M-shaped, and curved S-shaped foldcore structures were designed based on the principle of origami by controlling areal density. Three foldcore sandwich structures were fabricated from GFRP by hot compression molding method, and PU foam-filled foldcore sandwich structures were also prepared by in-situ foaming. The strength analysis models of the three types of foldcore under out-of-plane compression load were established through differentiation and integration. Subsequently, the quasi-static compression performance and failure modes of the foldcore were investigated through experiments. The analysis model has a certain degree of accuracy in predicting the strength of the structure. It was found that the primary failure mode of V-shaped foldcore under out-of-plane compressive loading was wall buckling. In contrast, the M-shaped foldcore had higher buckling resistance and the failure mode changes from buckling to crushing. S-shaped foldcore had a higher compression strength, and its failure mode changed to wall shear fracture. In addition, lightweight foam filling improved the failure stress of the foldcore.

The heart of galaxy clusters: Demographics and physical properties of cool-core and non-cool-core halos in the TNG-Cluster simulation

We analyzed the physical properties of the gaseous intracluster medium (ICM) at the center of massive galaxy clusters with TNG-Cluster, a new cosmological magnetohydrodynamical simulation. Our sample contains 352 simulated clusters spanning a halo mass range of 1014 < M500c/M⊙ < 2 × 1015 at z = 0. We focused on the proposed classification of clusters into cool-core (CC) and non-cool-core (NCC) populations, the z = 0 distribution of cluster central ICM properties, and the redshift evolution of the CC cluster population. We analyzed the resolved structure and radial profiles of entropy, temperature, electron number density, and pressure. To distinguish between CC and NCC clusters, we considered several criteria: central cooling time, central entropy, central density, X-ray concentration parameter, and density profile slope. According to TNG-Cluster and with no a priori cluster selection, the distributions of these properties are unimodal, whereby CCs and NCCs represent the two extremes. Across the entire TNG-Cluster sample at z = 0 and based on the central cooling time, the strong CC fraction is fSCC = 24%, compared to fWCC = 60% and fNCC = 16% for weak and NCCs, respectively. However, the fraction of CCs depends strongly on both halo mass and redshift, although the magnitude and even direction of the trends vary with definition. The abundant statistics of simulated high-mass clusters in TNG-Cluster enabled us to match observational samples and make a comparison with data. The CC fractions from z = 0 to z = 2 are in broad agreement with observations, as are the radial profiles of thermodynamical quantities, globally as well as when divided as CC versus NCC halos. TNG-Cluster can therefore be used as a laboratory to study the evolution and transformations of cluster cores due to mergers, AGN feedback, and other physical processes.

Structural and metamorphic architecture of the Zanskar Himalaya, Suru Valley region, NW India: Implications for the evolution of the Himalayan metamorphic core

Structural and metamorphic architecture of the Zanskar Himalaya, Suru Valley region, NW India: Implications for the evolution of the Himalayan metamorphic core

Core Technology Topic Identification and Evolution Analysis Based on Patent Text Mining—A Case Study of Unmanned Ship

Accurate identification and evolutionary analysis of core technology topics within patent texts play a crucial role in enabling enterprises to discern the development trajectory of core technologies, optimize research and development (R&D) strategies, and foster technological innovation. Based on the perspective of time series dynamic analysis, this study uses the Latent Dirichlet Allocation (LDA) topic modeling and TF-IDF text vectorization methods to comprehensively mine and identify patent technology topics in the field of unmanned ships. This study deeply analyzes the dynamic evolution of unmanned ship technology topics from two aspects: the evolution of technology theme intensity and the evolution of technology theme content. We refine the development characteristics and future development directions of unmanned ship technology. The findings reveal two hot technologies, six growth technologies, and six declining technologies in unmanned ship technology. Furthermore, the analysis of technical topic evolution illustrates a pattern of fragmentation, inheritance, and integration. This study advances the methodologies used for identifying and analyzing patent technology topics and helps to grasp the development rules and evolutionary trends of core technologies. In addition, this paper has reference value for the research and practice of core technology topic identification and evolution analysis methods based on patent text mining.

A model-based study of the dynamics of Arctic low-level jet events for the MOSAiC drift

Low-level jets (LLJs) are studied for the period of the ship-based experiment MOSAiC 2019/2020 using the regional climate model Consortium for Small-scale Model—Climate Limited area Mode (CCLM). The model domain covers the whole Arctic with 14 km resolution. CCLM is run in a forecast mode (nested in ERA5) and with different configurations of sea ice data for the winter. The focus is on the study of LLJs for the MOSAiC site. LLJs are detected using model output every 1 h. We define LLJ events as LLJs that last at least 6 h. Case studies of LLJ events are shown using wind lidar and radiosonde data as well as CCLM simulations. LLJs are not local events but are embedded in large jet structures extending for hundreds of kilometers that are advected toward the MOSAiC site. CCLM simulations are used to study the statistics of LLJs of all profiles and of LLJ events as well as the dynamics. LLJs are found in about 40% of the hourly profiles, but only 26% of the hourly profiles are associated with LLJ events. Strong LLJs (≥15 m/s) are detected in 13% of the hourly profiles, which is about the same fraction as for strong LLJ events. The mean duration of events is about 12 h. The LLJ events are characterized using dynamical criteria for the wind speed profile and the evolution of the jet core. A fraction of 35% of the LLJ events are baroclinic, but more than 40% of the LLJ events show a large contribution of advection to the initial generation as well as for the evolution of the jet core. Only very few events fulfill the criteria of inertial oscillations. LLJ events occur for all months, but strong events have a higher frequency during winter. The turbulent kinetic energy in the lower atmospheric boundary layer (ABL) is twice (4 times) as large for LLJs (strong LLJs) than for situations without LLJs, which underlines the impact of LLJs on turbulent processes in the ABL.

Hydrophobic core evolution of major histocompatibility complex class I chain-related protein A for dramatic enhancing binding affinity

Interface residues at sites of protein–protein interaction (PPI) are the focus for affinity optimisation. However, protein hydrophobic cores (HCs) play critical roles and shape the protein surface. We hypothesise that manipulating protein HCs can enhance PPI interaction affinities. A cell stress molecule, major histocompatibility complex class I chain-related protein A (MICA), binds to the natural killer group 2D (NKG2D) homodimer to form three molecule interactions. MICA was used as a study subject to support our hypothesis. We redesigned MICA HCs by directed mutagenesis and isolated high-affinity variants through a newly designed partial-denature panning (PDP) method. A few mutations in MICA HCs increased the NKG2D–MICA interaction affinity by 325–5613-fold. Crystal structures of the NKG2D–MICA variant complexes indicated that mutagenesis of MICA HCs stabilised helical elements for decreasing intermolecular interactive free energy (ΔG) of the NKG2D–MICA heterotrimer. The repacking of MICA HC mutants maintained overall surface residues and the authentic binding specificity of MICA. In conclusion, this study provides a new method for MICA redesign and affinity optimisation through HC manipulation without mutating PPI interface residues. Our study introduces a novel approach to protein manipulation, potentially expanding the toolkit for protein affinity optimisation.

Multi-scale simulation of microstructural evolution for molten U–Zr–O ternary system

The morphological evolution of the molten corium is critical to the success of the “in-vessel retention” (IVR) strategy, which is of great significance for the safety of the nuclear industry under severe accidents. However, the direct observation of microstructural evolution by experiments is impossible in extreme conditions. Herein, a multi-scale simulation approach was employed to investigate the microstructural evolution and related mechanisms for the molten U–Zr–O ternary system. First, based on the reported calculated phase diagram, a simplified free energy formula describing a phase diagram of U–Zr–O was determined, where only liquid phases are focused. Then, the atomic diffusion coefficients were calculated by ab-initio molecular dynamics simulations. Based on such information, a homemade phase-field model was developed, which was coupled with Cahn–Hillard and Navier–Stokes equations. Accordingly, the microstructural evolution of molten U–Zr–O materials was systematically investigated. The results reveal that the evolution of the molten core was driven by both the decreasing free energy and gravity potential, accessing the final morphology of the system as a two-layer structure, including a metallic layer and an oxidized layer. Moreover, diverse intermediate morphologies could be observed from different initial component distributions, although their average compositions were identical. Finally, some intermediate simulated microstructural patterns agreed well with experimental observation, demonstrating the unstable structures captured by experiments and the validity of the simulations. The present study provides an effective approach to investigate the microstructural evolution of molten core and a guideline for optimizing the IVR strategy based on different morphologies in the corium.

Imaging the top of the Earth's inner core: a present-day flow model.

Despite considerable progress in seismology, mineral physics, geodynamics, paleomagnetism, and mathematical geophysics, Earth's inner core structure and evolution remain enigmatic. One of the most significant issues is its thermal history and the current thermal state. Several hypotheses involving a thermally-convecting inner core have been proposed: a simple, high-viscosity, translational mode, or a classical, lower-viscosity, plume-style convection. Here, we use state-of-the-art seismic imaging to probe the outermost shell of the inner core for its isotropic compressional speed and compare it with recently developed attenuation maps. The pattern emerging in the resulting tomograms is interpreted with recent data on the viscosity of iron as the inner core surface manifestation of a thermally-driven flow, with a positive correlation among compressional speed and attenuation and temperature. Although the outer-core convection controls the heat flux across the inner core boundary, the internally driven inner-core convection is a plausible model that explains a range of observations for the inner core, including distinct anisotropy in the innermost inner core.

Thermoelastic Properties and Thermal Evolution of the Martian Core From Ab Initio Calculated Magnetic Fe‐S Liquid

AbstractAccurate thermoelastic properties and thermal conductivity are crucial for understanding the thermal evolution of the Martian core. A fitting method based on ab initio calculated pressure‐volume‐temperature data was proposed for the formulation of the equation of state with high accuracy, by which the pressure and temperature dependent thermoelastic properties can be directly calculated by definitions. Ab initio results showed that Fe0.75S0.25 liquid under Martian core conditions was thoroughly in a magnetic state without existing spin crossover. The Fe0.75S0.25 liquid in magnetic calculations had a low thermal conductivity (21–23 W/m/K) when compared with non‐magnetic calculations at the same state. Based on Insight's estimated Martian core properties (Stähler et al., 2021, https://doi.org/10.1126/science.abi7730) and ab initio calculated properties of the Fe0.75S0.25 liquid, the scenario for the thermal evolution of the Martian core is the iron‐snow model crystallization regime. The parameter uncertainty effect on the cessation time of the dynamo and zone of iron snow was systematically analyzed.

Surveys of clumps, cores, and condensations in Cygnus X

Context. The physical properties, evolution, and fragmentation of massive dense cores (MDCs, ~0.1 pc) are fundamental pieces in our understanding of high-mass star formation.Aims. We aim to characterize the temperature, velocity dispersion, and fragmentation of the MDCs in the Cygnus X giant molecular cloud and to investigate the stability and dynamics of these cores.Methods. We present theKarl G. JanskyVery Large Array (VLA) observations of the NH3(J,K) = (1,1) and (2,2) inversion lines towards 35 MDCs in Cygnus X, from which we calculated the temperature and velocity dispersion. We extracted 202 fragments (~0.02 pc) from the NH3(1,1) moment-0 maps with the GAUSSCLUMPS algorithm. We analyzed the stability of the MDCs and their NH3fragments through evaluating the corresponding kinetic, gravitational potential, and magnetic energies and the virial parameters.Results. The MDCs in Cygnus X have a typical mean kinetic temperatureTKof ~20 K. Our virial analysis shows that many MDCs are in subvirialized states, indicating that the kinetic energy is insufficient to support these MDCs against their gravity. The calculated nonthermal velocity dispersions of most MDCs are at transonic to mildly supersonic levels, and the bulk motions make only a minor contribution to the velocity dispersion. Regarding the NH3fragments, withTK~19 K, their nonthermal velocity dispersions are mostly trans-sonic to subsonic. Unless there is a strong magnetic field, most NH3fragments are probably not in virialized states. We also find that most of the NH3fragments are dynamically quiescent, while only a few are active due to star formation activity.

Exploring the use of 3D radar measurements in predicting the evolution of single-core convective cells

Object-based radar rainfall nowcasting is a widely used technique for convective storm prediction. Currently, most existing object-based nowcasting methods primarily focus on predicting cell movements, neglecting the temporal evolution of cell properties such as size, shape, and intensity. Incorporating this evolution is critical for improving predictability in convective storms. While previous studies have used three-dimensional (3D) radar observations to capture vertical changes during convective cell formation, these efforts often analyse or reconstruct specific convective events. Integrating 3D radar information into operational object-based radar rainfall nowcasting remains an open challenge. This research addresses this challenge using deep learning (DL) techniques. More specifically, a DL-based prediction model is developed, which uses 2D and 3D cells' properties retrieved from 3D radar reflectivity data at the current time and across the past 15 min to predict the evolution of these properties over the next 15 min. This model could eventually be integrated into existing object-based nowcasting models. A total of 4708 cell lifecycles, extracted from high-resolution (5-min, 1-km, 24 levels at 0.5 km intervals) 3D radar data across the UK, are used to train the model, and a total of 1177 lifecycles are used for testing. The proposed model is shown to predict the evolution of single-core convective cells effectively, including changes in 2D projected geometry and mean 2D and 3D reflectivity. In particular, by incorporating information on the vertical evolution of convective cores, the prediction errors of mean reflectivity (in both 2D and 3D) can be reduced by approximately 50% at 15-min forecast lead time, as compared to a persistence forecast. Keywords: radar, tracking, convective cell, nowcasting, 3D, deep learning, lstm.

A thermally conductive Martian core and implications for its dynamo cessation.

Mars experienced a dynamo process that generated a global magnetic field ~4.3 (or earlier) to 3.6 billion years ago (Ga). The cessation of this dynamo strongly affected Mars' history and is expected to be linked to thermochemical evolution of Mars' iron-rich liquid core, which is strongly influenced by its thermal conductivity. Here, we directly measured thermal conductivities of solid iron-sulfur alloys to pressures relevant to the Martian core and temperatures to 1023 Kelvin. Our results show that a Martian core with 16 weight % sulfur has a thermal conductivity of ~19 to 32 Watt meter-1 Kelvin-1 from its top to the center, much higher than previously inferred from electrical resistivity measurements. Our modeled thermal conductivity profile throughout the Martian deep-mantle and core indicates a ~4- to 6-fold discontinuity across the core-mantle boundary. The core's efficient cooling resulting from the depth-dependent, high conductivity diminishes thermal convection and forms thermal stratification, substantially contributing to cessation of Martian dynamo.

Structure Evolution and Performance of Fe-Si Core Used in Power Inductors of Smart Meters

Structure Evolution and Performance of Fe-Si Core Used in Power Inductors of Smart Meters

Infall of material onto the filaments in Barnard 5

Aims. We aim to study the structure and kinematics of the two filaments inside the subsonic core Barnard 5 in Perseus using high-resolution (≈2400 au) NH3 data and a multi-component fit analysis. Methods. We used observations of NH3(1,1) and (2,2) inversion transitions using the Very Large Array (VLA) and the Green Bank Telescope (GBT). We smoothed the data to a beam of 8" to reliably fit multiple velocity components towards the two filamentary structures identified in B5. Results. Along with the core and cloud components, which dominate the flux in the line of sight, we detected two components towards the two filaments showing signs of infall. We also detected two additional components that can possibly trace new material falling into the subsonic core of B5. Conclusions. Following a comparison with previous simulations of filament formation scenarios in planar geometry, we conclude that either the formation of the B5 filaments is likely to be rather cylindrically symmetrical or the filaments are magnetically supported. We also estimate infall rates of 1.6 × 10−4 M⊙ yr−1 and 1.8 × 10−4 M⊙ yr−1 (upper limits) for the material being accreted onto the two filaments. At these rates, the filament masses can change significantly during the core lifetime. We also estimate an upper limit of 3.5 × 10−5 M⊙ yr−1 for the rate of possible infall onto the core itself. Accretion of new material onto cores indicates the need for a significant update to current core evolution models, where cores are assumed to evolve in isolation.

Transient traveling breather response of strongly anharmonic array of self-sustained oscillators: Analytical study.

In the present study, we analyze the transient response of a locally excited chain of strongly anharmonic self-sustained oscillators. This discrete system under consideration models the dynamics of genuinely nonlinear, aeroelastic metamaterial. We particularly focus on the transient evolution of the traveling dissipative breathers, forming in locally excited, finite chains of self-sustained oscillators. The genuinely anharmonic nature of the system under consideration turns the asymptotic analysis of the transient regimes arising in this type of model into a highly challenging task. In the present study, we formulate a special analytical approach which allows for a simple, explicit, and fairly accurate analytical description of the amplitude evolution of the breather core towards the steady state as well as its instantaneous position.