Core Boundary Research Articles

Deviation of Mercury's Spin Axis From an Exact Cassini State Induced by Dissipation

AbstractWe compute predictions of the deviation of Mercury's spin axis from an exact Cassini state caused by tidal dissipation as well as viscous and electromagnetic (EM) friction at the core‐mantle boundary (CMB) and inner core boundary (ICB). Viscous friction at the CMB generates a phase lead; viscous and EM friction at the ICB produce a phase lag; the magnitude of the deviation depends on the inner core size, kinematic viscosity, and magnetic field strength, but cannot exceed an upper bound. For a small inner core, viscous friction at the CMB results in a maximum phase lead of 0.027 arcsec. For a large inner core (radius >1,000 km), EM friction at the ICB generates the largest phase lag, but it does not exceed 0.1 arcsec. Elastic deformations induced by the misaligned fluid and solid cores play a first‐order role in the phase lead/lag caused by viscous and EM coupling and contribute to a perturbation in mantle obliquity on par with that caused by tidal deformations. Tidal dissipation results in a phase lag and its magnitude (in units of arcsec) is given by the empirical relation (80/Q), where Q is the quality factor; Q = 80 results in a phase lag of ∼1 arcsec. A large inner core with a low viscosity of the order of 1017 Pa s or lower can significantly affect Q and thus the resulting phase lag. The limited mantle phase lag suggested by observations (<10 arcsec) implies a lower limit on the bulk mantle viscosity of approximately 1017 Pa s.

Transcription Profile and Pathway Analysis of the Endocannabinoid Receptor Inverse Agonist AM630 in the Core and Infiltrative Boundary of Human Glioblastoma Cells.

Background: We have previously reported that the endocannabinoid receptor inverse agonist AM630 is a potent inhibitor of isocitrade dehydrogenase-1 wild-type glioblastoma (GBM) core tumour cell proliferation. To uncover the mechanism behind the anti-tumour effects we have performed a transcriptional analysis of AM630 activity both in the tumour core cells (U87) and the invasive margin cells (GIN-8), the latter representing a better proxy of post-surgical residual disease. Results: The core and invasive margin cells exhibited markedly different gene expression profiles and only the core cells had high expression of a potential AM630 target, the CB1 receptor. Both cell types had moderate expression of the HTR2B serotonin receptor, a reported AM630 target. We found that the AM630 driven transcriptional response was substantially higher in the central cells than in the invasive margin cells, with the former driving the up regulation of immune response and the down regulation of cell cycle and metastatic pathways and correlating with transcriptional responses driven by established anti-neoplastics as well as serotonin receptor antagonists. Conclusion: Our results highlight the different gene sets involved in the core and invasive margin cell lines derived from GBM and an associated marked difference in responsiveness to AM630. Our findings identify AM630 as an anti-neoplastic drug in the context of the core cells, showing a high correlation with the activity of known antiproliferative drugs. However, we reveal a key set of similarities between the two cell lines that may inform therapeutic intervention.

Stable hexagonal ternary alloy phase in Fe-Si-H at 28.6–42.2 GPa and 3000 K

Hydrogen (H) and silicon (Si) are considered as important light elements for the planetary cores. A large amount of H is able to alloy with pure Fe metal at high pressures. Si can also alloy well with Fe. However, it remains uncertain how much H can alloy with iron silicides and if it alloys how H can alter the crystal structures of Fe-Si alloys at high pressures-temperatures ($P\text{\ensuremath{-}}T$). We performed experiments on Fe-9Si and Fe-16Si alloys (9 and 16 wt % Si, respectively) in a H medium up to 42.2 GPa and 3000 K in diamond-anvil cells coupled with pulsed laser heating and gated synchrotron x-ray diffraction techniques. We found conversion of the Fe-Si alloys into Fe-rich (fcc and dhcp $\mathrm{Fe}{\mathrm{H}}_{x}$), Si-rich (B20 and B2 FeSi), and intermediate (${\mathrm{Fe}}_{5}{\mathrm{Si}}_{3}{\mathrm{H}}_{x}$) phases. The new ${\mathrm{Fe}}_{5}{\mathrm{Si}}_{3}{\mathrm{H}}_{x}$ phase has a structure similar to the hexagonal ${\mathrm{Fe}}_{5}{\mathrm{Si}}_{3}$ phase but with expanded volumes, and thus, possible H incorporation. Both the observed volume expansion and the H content estimated by density-functional theory calculations support a significant amount of H with H/Fe \ensuremath{\approx} 0.6 in the crystal structure. Because ${\mathrm{Fe}}_{5}{\mathrm{Si}}_{3}$ is known to break down above \ensuremath{\sim}1300 K at \ensuremath{\sim}18 GPa, our results suggest that hydrogen stabilizes the hexagonal structure at high $P\text{\ensuremath{-}}T$. These results have implications for the crystallization of Fe-rich liquid at the solid-to-liquid boundary of planetary cores and possible existence of chemical heterogeneities in the solid cores.

Dynamic Tuning of the Bandgap of CdSe Quantum Dots through Redox-Active Exciton-Delocalizing N-Heterocyclic Carbene Ligands.

Ligands that enable the delocalization of excitons beyond the physical boundary of the inorganic core of semiconductor quantum dots (QDs), called "exciton-delocalizing ligands (EDLs)", offer the opportunity to design QD-based environmental sensors with dynamically responsive optical spectra, because the degree of exciton delocalization depends on the electronic structure of the EDL. This paper demonstrates dynamic, reversible tuning of the optical bandgap of a dispersion of CdSe QDs through the redox states of their 1,3-dimesitylnaphthoquinimidazolylidene N-heterocyclic carbene (nqNHC) ligands. Upon binding of the nqNHC ligands to the QD, the optical bandgap bathochromically shifts by up to 102 meV. Electrochemical reduction of the QD-bound nqNHC ligands shifts the bandgap further by up to 25 meV, a shift that is reversible upon reoxidation.

Asteroseismology of β Cephei stars: The stellar inferences tested in hare and hound exercises

Context. The β Cephei pulsators are massive, ∼8−25 M⊙ essentially on the main sequence, stars. The number of detected modes in β Cephei stars often remains limited to less than a dozen of low radial-order modes. Such oscillation modes are in principle able to constrain the internal processes acting in the star. They probe the chemical gradient at the edge of the convective core, in particular its location and extension. They hence give constraints on macroscopic processes, such as hydrodynamic or magnetic instabilities, that have an impact on the mixing there. Yet, it is not clear to what extent the seismic inferences depend on the physics employed for the stellar modelling or on the observational dataset used. Consequently, it is not easy to estimate the accuracy and precision on the parameters and the nature of the physical processes inferred. Aims. We investigate the observational constraints, in particular the properties of the minimum set of pulsations detected, which are necessary to provide accurate constraints on the mixing processes in β Cephei stars. We explore the importance of the identification of the angular degree of the modes. In addition, depending on the quality of the seismic dataset and the classical non-seismic constraints, we aim to estimate, in a systematic way, the precision achievable with asteroseismology on the determination of their stellar parameters. Methods. We propose a method extending the forward approach classically used to model β Cephei stars. With the help of Monte-Carlo simulations, the probability distributions of the asteroseismic-derived stellar parameters were obtained. With these distributions, we provide a systemic way to estimate the errors derived from the modelling. A particular effort was made to include, not only the observational errors, but also the theoretical uncertainties of the models. We then estimated the accuracy and precision of asteroseismology for β Cephei stars in a series of hare and hound exercises. Results. The results of the hare and hounds show that a set of four to five oscillation frequencies with an identified angular degree already leads to accurate inferences on the stellar parameters. Without the identification of the modes, the addition of other observational constraints, such as the effective temperature and surface gravity, still ensures the success of the seismic modelling. When the internal microscopic physics of the star and stellar models used for the modelling differ, the constraints derived on the internal structure remain valid if expressed in terms of acoustic variables, such as the radius. However, they are then hardly informative on structural variables expressed in mass. The characterisation of the mixing processes at the boundary of the convective core are model-dependent and it requires the use of models implemented with processes of a similar nature.

Viscosity of Fe‐Ni‐C Liquids up to Core Pressures and Implications for Dynamics of Planetary Cores

AbstractThe viscosity of iron alloy liquids is the key for the core dynamo and core‐mantle differentiation of terrestrial bodies. Here we measured the viscosity of Fe‐Ni‐C liquids up to 7 GPa using the floating sphere viscometry method and up to 330 GPa using first‐principles calculations. We found a viscosity increase at ∼3–5 GPa, coincident with a structural transition in the liquids. After the transition, the viscosity reaches ∼14–27 mPa·s, a factor of 2–4 higher than that of Fe and Fe‐S liquids. Our computational results from 5 to 330 GPa also indicate a high viscosity of the Fe‐Ni‐C liquids. For a carbon‐rich core in large terrestrial body, the level of turbulence in the outer core would be lessened approaching the inner core boundary. It is also anticipated that Fe‐Ni‐C liquids would percolate in Earth's deep silicate mantle at a much slower speed than Fe and Fe‐S liquids.

Differential distribution of inhibitory neuron types in subregions of claustrum and dorsal endopiriform nucleus of the short-tailed fruit bat.

Few brain regions have such wide-ranging inputs and outputs as the claustrum does, and fewer have posed equivalent challenges in defining their structural boundaries. We studied the distributions of three calcium-binding proteins-calretinin, parvalbumin, and calbindin-in the claustrum and dorsal endopiriform nucleus of the fruit bat, Carollia perspicillata. The proportionately large sizes of claustrum and dorsal endopiriform nucleus in Carollia brain afford unique access to these structures' intrinsic anatomy. Latexin immunoreactivity permits a separation of claustrum into core and shell subregions and an equivalent separation of dorsal endopiriform nucleus. Using latexin labeling, we found that the claustral shell in Carollia brain can be further subdivided into at least four distinct subregions. Calretinin and parvalbumin immunoreactivity reinforced the boundaries of the claustral core and its shell subregions with diametrically opposite distribution patterns. Calretinin, parvalbumin, and calbindin all colocalized with GAD67, indicating that these proteins label inhibitory neurons in both claustrum and dorsal endopiriform nucleus. Calretinin, however, also colocalized with latexin in a subset of neurons. Confocal microscopy revealed appositions that suggest synaptic contacts between cells labeled for each of the three calcium-binding proteins and latexin-immunoreactive somata in claustrum and dorsal endopiriform nucleus. Our results indicate significant subregional differences in the intrinsic inhibitory connectivity within and between claustrum and dorsal endopiriform nucleus. We conclude that the claustrum is structurally more complex than previously appreciated and that claustral and dorsal endopiriform nucleus subregions are differentially modulated by multiple inhibitory systems. These findings can also account for the excitability differences between claustrum and dorsal endopiriform nucleus described previously.

The effect of inlet turbulence on the quiescent core of turbulent channel flow

The impact of inlet turbulence on the structure of turbulent channel flow is investigated using particle image velocimetry. Streamwise–wall-normal plane measurements are performed in a channel, where different turbulence intensities were generated at the inlet with an active grid. Four cases are tested with matched centreline mean velocities, while the centreline turbulence intensities ranged from 3.7 % for the reference case, up to 6.4 %. The friction velocity is found to be approximately constant with varying centreline turbulence intensities, resulting in a matched friction Reynolds number of $Re_\tau \approx 770$ for all cases, which contrasts with similar experiments performed in a zero-pressure-gradient boundary layer. The log region remains intact for all cases. The so-called quiescent core of the turbulent channel flow is also investigated. In addition to increased core discontinuity, the increased fluctuations of the streamwise velocity give rise to new core states, which differ from the conventional ones in their characteristic velocity. They are associated with a bulk of low- or high-momentum fluid passing through the measurement domain, and their occurrence increases with turbulence intensity. Tracking the core boundaries indicates an overall tendency of the core to move closer to the wall for increased inlet turbulence intensities, resulting in an increased core thickness. Moreover, it is found that the low-momentum cores generally reside closer to the wall compared with the ordinary cores and appear to be thicker than them, whereas the opposite, i.e. residing farther from the wall and being thinner, is true for the high-momentum cores.

Semisupervised Few-Shot Remote Sensing Image Classification Based on KNN Distance Entropy

In recent years, remote sensing image processing based on deep learning has been widely applied in many scenes, but the involved deep learning technology requires large-scale labeled data, which has been a practical problem in the remote sensing field. In this study, we proposed a novel data information quality assessment method, called K-Nearest Neighbor (KNN) distance entropy, to screen the remote sensing images. The evaluation metric was used to assess unlabeled data and assign the pseudo label, which further constitutes the proposed semi-supervised few-shot classification method in this paper. The meta-task setting was adopted to verify the validity and stability of experimental results. Specifically, the KNN distance entropy metric can be used to distinguish the samples in core set or boundary set. Experimental results show that the core set samples are more suitable under the few-shot condition, for instance, the meta-task average accuracy trained by the core set samples outperforms that by boundary samples about 18 percent in the case of 45-ways and 5-shot. The proposed semi-supervised few-shot method based on KNN distance entropy achieves significant improvement under different experimental conditions. The visualization of feature distribution of screened data is shown to provide intuitive interpretation. This paper lays a meaningful foundation for screening and evaluating remote sensing images under few-shot condition, and inspires the data-efficient few-shot learning based on high-quality data in the remote sensing field.

Influence of structure of burned pellets on strength and destruction in static compression tests

The burned pellets must retain the strength from the time they come off the roasting machine until they are loaded into the blast furnace. One indicator of the strength of burned pellets is the compressive strength, i.e., the maximum applied load at which the iron-ore pellet completely collapses. The paper studies the character of destruction of burned iron-ore titanomagnetite pellets of fraction 10 - 16 mm in the static compression test according to the Russian State Standard 24765-81. It is shown that the main type of destruction during the test is the emergence and development of plane cracks passing through the center of the magnetite core, where the maximum radial tensile stresses act or in the immediate vicinity. In some cases, the trajectory of one of the destructive cracks deviates from the above plane and envelopes the magnetite core. Obviously, this is due to the presence of a second area of tensile stress concentration at the boundary of the magnetite core and the hematite shell, formed during cooling of the pellets, due to differences in their mechanical and thermophysical properties. As a result, the final structure of pellets is characterized by the presence of two zones -peripheral hematite and central magnetite. The role of the relative size of the magnetite core on the compressive strength of burned pellets has been determined. It was established that the strength characteristics of the pellet increase with a decrease in relative size of the magnetite core. During the process of magnetite complete oxidation (when the whole volume of the pellet consists of hematite), the maximum level of the pellets compressive strength can be: the maximum destructive force - 3300 N, destructive energy - 0.55 J, mass destructive energy - 0.18 J/g.

Bayesian Modeling of the Equation of State for Liquid Iron in Earth's Outer Core

AbstractWe use Bayesian modeling of the equation of state (EoS) to constrain the density (ρ) and P wave velocity (VP) of liquid iron under conditions of Earth's outer core. Experiments at such high pressures (P) and temperatures (T) are technically challenging, so there are few data available to use in parameter optimization of the EoS. Our Bayesian inference modeling successfully estimates the posterior probability distribution of the parameters and unobserved data by using the Hamiltonian Monte Carlo method. These posterior probability distributions allow calculation of P‐ρ and P‐VP profiles of liquid iron along the adiabatic P‐T profile together with the associated credible intervals. Assuming that the temperature at the core‐mantle boundary (CMB) is 3,500–4,200 K, the P‐ρ and P‐VP profiles show deviations of ρ and VP from the preliminary reference Earth model of about 8–11% and −3% to −5%, respectively. Deviations of the 95% credible intervals of the P‐ρ profile for the CMB and the inner core boundary are 6.9–9.7% and 6.5–9.8%, respectively. Equivalent deviations of the P‐VP profile are −4.8% to −1.5% and −6.0% to −2.3%, respectively. Bayesian modeling of the EoS enables integration of small data sets that include unobserved data and evaluation of uncertainty ranges of physical properties, such as ρ and VP, which are essential for comparison with seismological properties of the core.

The induced metric on the boundary of the convex hull of a quasicircle in hyperbolic and anti-de Sitter geometry

Celebrated work of Alexandrov and Pogorelov determines exactly which metrics on the sphere are induced on the boundary of a compact convex subset of hyperbolic three-space. As a step toward a generalization for unbounded convex subsets, we consider convex regions of hyperbolic three-space bounded by two properly embedded disks which meet at infinity along a Jordan curve in the ideal boundary. In this setting, it is natural to augment the notion of induced metric on the boundary of the convex set to include a gluing map at infinity which records how the asymptotic geometry of the two surfaces compares near points of the limiting Jordan curve. Restricting further to the case in which the induced metrics on the two bounding surfaces have constant curvature $K \in [-1,0)$ and the Jordan curve at infinity is a quasicircle, the gluing map is naturally a quasisymmetric homeomorphism of the circle. The main result is that for each value of $K$, every quasisymmetric map is achieved as the gluing map at infinity along some quasicircle. We also prove analogous results in the setting of three-dimensional anti de Sitter geometry. Our results may be viewed as universal versions of the conjectures of Thurston and Mess about prescribing the induced metric on the boundary of the convex core of quasifuchsian hyperbolic manifolds and globally hyperbolic anti de Sitter spacetimes.

An Evaluation of the Timing Accuracy of Global and Regional Seismic Stations and Networks

Abstract Clock accuracy is a basic parameter of any seismic station and has become increasingly important for seismology as the community seeks to refine structures and dynamic processes of the Earth. In this study, we measure the arrival time differences of moderate repeating earthquakes with magnitude 5.0–5.9 in the time range of 1991–2017 at the same seismic stations by cross-correlating their highly similar waveforms and thereby identify potential timing errors from the outliers of the measurements. The method has very high precision of about 10 ms and shows great potential to be used for routine inspection of the timing accuracy of historical and future digital seismic data. Here, we report 5131 probable cases of timing errors from 451 global and regional stations available from the Incorporated Research Institutions for Seismology Data Management Center, ranging from several tens of milliseconds to over 10 s. Clock accuracy seems to be a prevailing problem in permanent stations with long-running histories. Although most of the timing errors have already been tagged with low timing quality, there are quite a few exceptions, which call for greater attention from network operators and the seismological community. In addition, seismic studies, especially those on temporal changes of the Earth’s media from absolute arrival times, should be careful to avoid misinterpreting timing errors as temporal changes, which is indeed a problem in some previous studies of the Earth’s inner core boundary.

Viscous Dissipation in the Fluid Core of the Moon

AbstractThe spin axes of the mantle, fluid core, and solid inner core of the Moon precess at frequency Ωp = 2π/18.6 years−1 though with different orientations, leading to viscous friction at the core‐mantle boundary (CMB) and inner core boundary (ICB). Here, we use a rotational model of the Moon and consider a range of inner core and outer core radii to investigate the relative importance of viscous dissipation at the CMB and ICB, and to show how this dissipation is connected to the phase lead angle (ϕp) of the mantle ahead of its Cassini state. We show that when the inner core radius is km and the free inner core nutation frequency Ωficn approaches Ωp, viscous dissipation at the ICB can be comparable to that at the CMB, and in the most extreme cases exceed it by as much as a factor of 10. If so, the viscous dissipation in the lunar core projected back in time depends on how Ωficn has evolved relative to Ωp. We further show that constraints on the CMB and ICB radii of the lunar core can in principle be extracted by matching the observed phase lead of ϕp = 0.27 arcsec; this requires an improved estimate of tidal dissipation and an accurate model of the turbulent viscous torque. Finally, when our rotational model is constrained to match ϕp = 0.27 arcsec, our results suggest that the viscous dissipation at the ICB is likely insufficient to have ever been above the threshold to power a thermally driven dynamo.

Eccentric Dipole Evolution during the Last Reversal, Last Excursions, and Holocene Anomalies. Interpretation Using a 360-Dipole Ring Model

The eccentric dipole (ED) is the next approach of the geomagnetic field after the generally used geocentric dipole. Here, we analyzed the evolution of the ED during extreme events, such as the Matuyama-Brunhes polarity transition (~780 ka), the Laschamp (~41 ka) and Mono Lake (~34 ka) excursions, and during the time of two anomalous features of the geomagnetic field observed during the Holocene: the Levantine Iron Age Anomaly (LIAA, ~1000 BC) and the South Atlantic Anomaly (SAA, analyzed from ~700 AD to present day). The analysis was carried out using the paleoreconstructions that cover the time of the mentioned events (IMMAB4, IMOLEe, LSMOD.2, SHAWQ-Iron Age, and SHAWQ2k). We found that the ED moves around the meridian plane of 0–180° during the reversal and the excursions; it moves towards the region of the LIAA; and it moves away from the SAA. To investigate what information can be extracted from its evolution, we designed a simple model based on 360-point dipoles evenly distributed in a ring close to the inner core boundary that can be reversed and their magnitude changed. We tried to reproduce with our simple model the observed evolution of the ED, and the total field energy at the Earth’s surface. We observed that the modeled ED moves away from the region where we set the dipoles to reverse. If we consider that the ring dipoles could be related to convective columns in the outer core of the Earth, our simple model would indicate the potential of the displacement of the ED to give information about the regions in the outer core where changes start for polarity transitions and for the generation of important anomalies of the geomagnetic field. According to our simple model, the regions in which the most important events of the Holocene occur, or in which the last polarity reversal or excursion begin, are related to the regions of the Core Mantle Boundary (CMB), where the heat flux is low.

P57.04 Predicting Treatment Response to 1st- line Pembrolizumab in Advanced Non-Small Cell Lung Cancer (NSCLC) Patients with High PDL1 Expression

Combination of pembrolizumab and chemotherapy has shown improved survival in advanced NSCLC compared to chemotherapy alone. However, the overall response rate has only increased from 45% to 60% by adding chemotherapy to pembrolizumab alone for patients with high PDL1 expression (PD-L1 ≥50%). Currently no biomarker or clinicopathological features can be used to identify the subgroup with tumors PD-L1 ≥ 50% who would respond well to pembrolizumab alone in the 1st-line setting. We hypothesize a machine learning model trained on pre-treatment CT image radiomic features can be used as a digital biomarker to select the aforementioned subgroup, thereby reducing chemotherapy related toxicity and mitigating health care expenditure. We retrospectively identified stage III/IV NSCLC patients who received 1st-line single pembrolizumab at British Columbia Cancer (Vancouver, Canada), with PDL1 ≥50% and all had baseline staging CT within 6 weeks prior to starting immunotherapy and the 1st follow-up (FU) CT within 12 weeks after treatment initiation. The baseline and 1st follow-up CTs were reviewed by two oncological radiologists to identified the lung tumors on the baseline CT images and assess tumor response (i.e., partial response, PR vs progressive disease, PD) using RECIST 1.1 criteria. Utilizing an in-house CT Otsu based thresholding segmentation program and radiomic feature extraction pipeline, we identified potentially discriminating features from CT lung tumor images. We performed sequential forward feature selection to identify the 10 most highly classifying features from discrete shape, texture, and intensity radiomic features generated for 3 distinct tumor segmentation masks (lesion core, core with perimeter transition pixels, and the ring of parenchymal tissue surrounding the lesion). In this study, we leveraged an 8-Xfold validation Linear Discriminate Analysis (LDA), a simple machine learning method trained on these 10 features, to discriminate tumor response to 1st-line pembrolizumab as evaluated at FU CT scans. Sixty-eight patients were included (44% male, 73±6 yrs, 52ES/12CS/4NS; pack years: 43±18; ECOG range: 0-3). Twenty-eight showed response to the 1st-line pembrolizumab and forty had progressive disease. We identified eighty-four lung tumors in these patients which we extracted radiomic features from the five central slices, providing us with a pseudo-volumetric CT image training and test set (N=380). ROC analysis of the LDA model resulted in an accuracy of 79.4% [SN: 0.882, SP: 0.684] (AUC: 0.79) for our patient dataset. Given our class label imbalance, we performed precision-recall (PPV vs Sensitivity) analysis to identify sources of class bias (AUC vs No-skill AUC: 0.80 vs 0.59). Our data showed that a rudimentary and interpretable machine learning method can lead to appropriate treatment paths for advanced stage lung cancers. A combination of all mask features performed well on this task with a majority of the features selected being texture and intensity features from the core plus edge transitionary boundary pixels. Future analysis will be conducted using other machine learning methods to validate these findings, while keeping the LDA as the primary analysis method.

Local Deformation Behavior of the Copper Harmonic Structure near Grain Boundaries Investigated through Nanoindentation.

The copper harmonic structure, which consists of a coarse-grained “core” surrounded by a three-dimensional continuously connected fine-grained “shell,” exhibits both high ductility and high strength. In the present study, dislocation interactions at the shell–core boundary in the copper harmonic structure were directly measured using nanoindentation and microstructural observations via kernel average misorientation (KAM) to further understand the reason for its excellent mechanical properties. KAM analysis showed that the dislocation density in the vicinity of the shell–core boundary within the core region gradually increases with increasing plastic strain. The variation in the nanohardness exactly corresponds to the KAM, indicating that the higher strength is primarily caused by the higher dislocation density. The critical load for nanoindentation-induced plasticity initiation was lower at the shell–core boundary than at the core–core boundary, indicating a higher potency of dislocation emission at the shell–core boundary. Because dislocation–dislocation interactions are one of the major causes of the increase in the flow stress leading to higher strain hardening rates during deformation, the excellent balance between strength and ductility is attributed to the higher potency of dislocation emission at the shell–core boundary.

Antipodal seismic reflections upon shear wave velocity structures within Earth's inner core

Seismic evidence is presented for a high shear wave velocity, apparent discontinuity near ~100 km depth within a portion of Earth's inner core. Antipodally (>179°) focused data are stacked for five source–receiver diametric ray paths traversing the inner core. Two antipodal paths follow ray surfaces which are aligned with diameters between Tamanrasset (TAM), Algeria and Tonga earthquakes and Pitinga (PTGA), Brazil and Sulawesi earthquakes, providing clear examples of precursors to PKIIKP (an underside reflection at the inner core boundary). Waveform and stacked data (T > 4 s) were engaged in testing more than 16 inner core model series, varying compressional and shear wave velocities in upper inner core structures. The precursory seismic phases are successfully modeled as reflecting beneath a core liquid/solid interface at 100 km depth below the inner core boundary. This interface is highly reflective, and sensitive to a shear wave velocity contrast ≥5 km/s. An earlier precursory phase is observed at TAM and PTGA which may be modeled as an apparent discontinuity near ~250 km depth. This intermediate region has high shear wave velocities more akin to hcp-Fe mineralogy than Preliminary Reference Earth Model (PREM) values. Three other antipodal observations (China–Chile) nearly orthogonal to TAM paths exhibit seismic waves whose waveforms are more consistent with the PREM velocities above 100 km depth, while offering modest evidence for a solid/solid discontinuity at 100-km-depth. This research focused on seismology of the inner core potentially has mineral physics and geodynamic implications too broad to be simply encapsulated herein. Acknowledging some of these implications, we have focused upon measuring and mapping the seismic anomalies.

Surface Chemistry Impact on the Light Absorption by Colloidal Quantum Dots.

At the size scale at which quantum confinement effects arise in inorganic semiconductors, the materials’ surface‐to‐volume ratio is intrinsically high. This consideration sets surface chemistry as a powerful tool to exert further control on the electronic structure of the inorganic semiconductors. Among the materials that experience the quantum confinement regime, those prepared via colloidal synthetic procedures (the colloidal quantum dots – and wires and wells, too –) are prone to undergo surface reactions in the solution phase and thus represent an ideal framework to study the ensemble impact of surface chemistry on the materials’ electronic structure. It is here discussed such an impact at the ground state by using the absorption spectrum of the colloidal quantum dots as a descriptor. The experiments show that the chemical species (the ligands) at the colloidal quantum dot surface induce changes to the optical band gap, the absorption coefficient at all wavelengths, and the ionization potential. These evidences point to a description of the colloidal quantum dot (the ligand/core adduct) as an indecomposable species, in which the orbitals localized on the ligands and the core mix in each other's electric field. This description goes beyond conventional models that conceive the ligands on the basis of pure electrostatic arguments (i. e., either as a dielectric shell or as electric dipoles) or as a mere potential energy barrier at the core boundaries.

Dynamic evolution of edge dislocation and its effect on bcc-hcp martensitic transformation in dual-phase high-entropy alloy

The interactions between phase transformation and dislocation determine the evolution process of microstructures in dual-phase high-entropy (DP-HEA) alloy. However, due to rapid evolution process in martensitic transformation (MT) and the lack of corresponding atomic-scale simulation method, the dynamic evolution processes of dislocation in MT are not yet fully understood. In this work, molecular dynamics (MD) simulation is employed to study the atomic-scale dynamic evolution of edge dislocations and its effect on MT in Ta0.5HfZrTi. The simulation results reveal that the gliding of dislocations to the surface decreases the MT nucleation stress due to increased stress concentration. For the higher global stress (8.0 GPa), the growth of the martensitic variant is found impeded by the new martensitic variant produced near the dislocation core. For the lower global stress (7.1 GPa), the preset edge dislocation will migrate due to elastic strain's incompatibility between dislocation core and phase boundary.