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"Peng Y"
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Three-dimensional collective charge excitations in electron-doped copper oxide superconductors
High-temperature copper oxide superconductors consist of stacked CuO
2
planes, with electronic band structures and magnetic excitations that are primarily two-dimensional
1
,
2
, but with superconducting coherence that is three-dimensional. This dichotomy highlights the importance of out-of-plane charge dynamics, which has been found to be incoherent in the normal state
3
,
4
within the limited range of momenta accessible by optics. Here we use resonant inelastic X-ray scattering to explore the charge dynamics across all three dimensions of the Brillouin zone. Polarization analysis of recently discovered collective excitations (modes) in electron-doped copper oxides
5
–
7
reveals their charge origin, that is, without mixing with magnetic components
5
–
7
. The excitations disperse along both the in-plane and out-of-plane directions, revealing its three-dimensional nature. The periodicity of the out-of-plane dispersion corresponds to the distance between neighbouring CuO
2
planes rather than to the crystallographic
c
-axis lattice constant, suggesting that the interplane Coulomb interaction is responsible for the coherent out-of-plane charge dynamics. The observed properties are hallmarks of the long-sought ‘acoustic plasmon’, which is a branch of distinct charge collective modes predicted for layered systems
8
–
12
and argued to play a substantial part in mediating high-temperature superconductivity
10
–
12
.
Resonant inelastic X-ray scattering on electron-doped copper oxide superconductors reveals a three-dimensional charge collective mode, which has properties suggestive of the long-sought acoustic plasmon.
Journal Article
Strangulation as the primary mechanism for shutting down star formation in galaxies
An analysis of the stellar metallicity of local galaxies reveals that strangulation (halting of cold gas supply) rather than sudden removal of gas (through outflows or stripping) is the primary mechanism responsible for the quenching of star formation.
Star formation halted by blocking of gas inflow
Many local galaxies are quiescent. At some point they cease to be star forming and become passive, but the primary mechanism responsible for quenching star formation in galaxies is still unclear. Two mechanisms have been suggested, either the sudden removal of gas through outflows or stripping, or 'strangulation' in which the supply of cold gas to the galaxy is halted. Yingjie Peng
et al
. report an analysis of the stellar metallicity (the fraction of elements heavier than helium in stellar atmospheres) in local galaxies that reveals that strangulation is the primary quenching mechanism, at least for local galaxies with a stellar mass of less than 10
11
solar masses.
Local galaxies are broadly divided into two main classes, star-forming (gas-rich) and quiescent (passive and gas-poor). The primary mechanism responsible for quenching star formation in galaxies and transforming them into quiescent and passive systems is still unclear. Sudden removal of gas through outflows
1
,
2
,
3
,
4
,
5
,
6
or stripping
7
,
8
,
9
is one of the mechanisms often proposed. An alternative mechanism is so-called “strangulation”
10
,
11
,
12
,
13
,
14
, in which the supply of cold gas to the galaxy is halted. Here we report an analysis of the stellar metallicity (the fraction of elements heavier than helium in stellar atmospheres) in local galaxies, from 26,000 spectra, that clearly reveals that strangulation is the primary mechanism responsible for quenching star formation, with a typical timescale of four billion years, at least for local galaxies with a stellar mass less than 10
11
solar masses. This result is further supported independently by the stellar age difference between quiescent and star-forming galaxies, which indicates that quiescent galaxies of less than 10
11
solar masses are on average observed four billion years after quenching due to strangulation.
Journal Article
Characteristics of Super Atmospheric Rivers Associated With Explosive Extratropical Cyclones Over the Northern Pacific Ocean
Atmospheric Rivers (ARs) are elongated, narrow corridors of concentrated moisture in the atmosphere, transporting significant amounts of water vapor outside the tropics and causing heavy precipitation. ARs are often accompanied with explosive extratropical cyclones (EECs) over oceans. This paper investigates the characteristics of 118 super ARs associated with EECs over the Northern Pacific Ocean. Nearly 78.0% of ARs are associated with strong or super EECs, indicating that stronger ARs may lead to more explosive development of EECs. The composite analyses of ARs suggest that the AR is typically located in southwest of the cyclone center, in front of the cold front, with mean value of AR top pressure of approximately 693.51 hPa. In addition, water vapor from low latitudes and that evaporating from the sea surface are two important water vapor sources for ARs. Through investigating the evolution of EECs, a mechanism strengthens ARs and EECs. Plain Language Summary Extratropical cyclones (ECs) and Atmospheric Rivers (ARs) are significant weather systems over mid‐ and high‐latitude regions and often occur together. A strong AR often precedes the rapid intensification of ECs, which is termed as explosive extratropical cyclones (EECs). The connection between water vapor transport in ARs and the latent heat release that fuels the intensification of ECs remains a challenging topic that requires deeper exploration. This paper investigates the characteristics of super ARs linked to EECs. Our findings indicate that nearly 78.0% of ARs are associated with super EEC. These ARs typically positioned themselves in the southwest of the center of ECs, ahead of the cold front, with an air pressure of approximately 693.51 hPa. ARs play a crucial role in transporting water vapor to the center of the EEC, where latent heat is released, thereby enhancing both EEC and AR. However, as the AR moves southeastward away from the center of the EEC, the subsequent scarcity of water vapor reduces the strength of both EEC and AR. This research provides new insights into the connection between super ARs and EECs. Key Points Nearly 78.0% of super Atmospheric Rivers (ARs) are associated with a strong or super explosive extratropical cyclone A new term “atmospheric river top pressure” is firstly defined and its mean value was about 693.51 hPa Water vapor at low latitudes and evaporating from sea surface are found to be two important water vapor sources for ARs
Journal Article
Dynamic matrices with DNA-encoded viscoelasticity for cell and organoid culture
Three-dimensional cell and organoid cultures rely on the mechanical support of viscoelastic matrices. However, commonly used matrix materials lack control over key cell-instructive properties. Here we report on fully synthetic hydrogels based on DNA libraries that self-assemble with ultrahigh-molecular-weight polymers, forming a dynamic DNA-crosslinked matrix (DyNAtrix). DyNAtrix enables computationally predictable and systematic control over its viscoelasticity, thermodynamic and kinetic parameters by changing DNA sequence information. Adjustable heat activation allows homogeneous embedding of mammalian cells. Intriguingly, stress-relaxation times can be tuned over four orders of magnitude, recapitulating mechanical characteristics of living tissues. DyNAtrix is self-healing, printable, exhibits high stability, cyto- and haemocompatibility, and controllable degradation. DyNAtrix-based cultures of human mesenchymal stromal cells, pluripotent stem cells, canine kidney cysts and human trophoblast organoids show high viability, proliferation and morphogenesis. DyNAtrix thus represents a programmable and versatile precision matrix for advanced approaches to biomechanics, biophysics and tissue engineering.
DNA nanotechnology is used to develop fully synthetic, programmable and printable 3D cell-culture matrices with stress-relaxation crosslinkers that encode (nano)mechanical stability. The hydrogel performs on par with solubilized animal-basement-membrane-derived cell-culture matrices.
Journal Article
Hippocampal delivery of neurotrophic factor-α1/carboxypeptidase E gene prevents neurodegeneration, amyloidosis, memory loss in Alzheimer’s Disease male mice
Alzheimer’s Disease (AD) is a prevalent neurodegenerative disease characterized by tau hyperphosphorylation, Aβ1-42 aggregation and cognitive dysfunction. Therapeutic agents directed at mitigating tau aggregation and clearing Aβ1-42, and delivery of growth factor genes (BDNF, FGF2), have ameliorated cognitive deficits, but these approaches did not prevent or stop AD progression. Here we report that viral-(AAV) delivery of Neurotrophic Factor-α1/Carboxypeptidase E (NF-α1/CPE) gene in hippocampus at an early age prevented later development of cognitive deficits as assessed by Morris water maze and novel object recognition assays, neurodegeneration, and tau hyperphosphorylation in male 3xTg-AD mice. Additionally, amyloid precursor protein (APP) expression was reduced to near non-AD levels, and insoluble Aβ1-42 was reduced significantly. Pro-survival proteins: mitochondrial Bcl2 and Serpina3g were increased; and mitophagy inhibitor Plin4 and pro-inflammatory protein Card14 were decreased in AAV-NF-α1/CPE treated versus untreated AD mice. Thus NF-α1/CPE gene therapy targets many regulatory components to prevent cognitive deficits in 3xTg-AD mice and has implications as a new therapy to prevent AD progression by promoting cell survival, inhibiting APP overexpression and tau hyperphosphorylation.
Journal Article
Multiscale Modeling Meets Machine Learning: What Can We Learn?
Machine learning is increasingly recognized as a promising technology in the biological, biomedical, and behavioral sciences. There can be no argument that this technique is incredibly successful in image recognition with immediate applications in diagnostics including electrophysiology, radiology, or pathology, where we have access to massive amounts of annotated data. However, machine learning often performs poorly in prognosis, especially when dealing with sparse data. This is a field where classical physics-based simulation seems to remain irreplaceable. In this review, we identify areas in the biomedical sciences where machine learning and multiscale modeling can mutually benefit from one another: Machine learning can integrate physics-based knowledge in the form of governing equations, boundary conditions, or constraints to manage ill-posted problems and robustly handle sparse and noisy data; multiscale modeling can integrate machine learning to create surrogate models, identify system dynamics and parameters, analyze sensitivities, and quantify uncertainty to bridge the scales and understand the emergence of function. With a view towards applications in the life sciences, we discuss the state of the art of combining machine learning and multiscale modeling, identify applications and opportunities, raise open questions, and address potential challenges and limitations. We anticipate that it will stimulate discussion within the community of computational mechanics and reach out to other disciplines including mathematics, statistics, computer science, artificial intelligence, biomedicine, systems biology, and precision medicine to join forces towards creating robust and efficient models for biological systems.
Journal Article
Influence of apical oxygen on the extent of in-plane exchange interaction in cuprate superconductors
In high-
T
c
superconductors the magnetic and electronic properties are determined by the probability that valence electrons jump virtually from site to site in the CuO
2
planes, a mechanism opposed by on-site Coulomb repulsion and favoured by hopping integrals. The spatial extent of the latter is related to transport properties, including superconductivity, and to the dispersion relation of spin excitations (magnons). Here, for three antiferromagnetic parent compounds (single-layer Bi
2
Sr
0.9
La
1.1
CuO
6+
δ
, double-layer Nd
1.2
Ba
1.8
Cu
3
O
6
and infinite-layer CaCuO
2
) differing by the number of apical atoms, we compare the magnetic spectra measured by resonant inelastic X-ray scattering over a significant portion of the reciprocal space and with unprecedented accuracy. We observe that the absence of apical oxygens increases the in-plane hopping range and, in CaCuO
2
, it leads to a genuine three-dimensional (3D) exchange-bond network. These results establish a corresponding relation between the exchange interactions and the crystal structure, and provide fresh insight into the materials dependence of the superconducting transition temperature.
A detailed resonant inelastic X-ray scattering (RIXS) study of a series of well-known cuprate superconductors reveals a correlation between the number of apical oxygens in these systems, and the strength of their in-plane exchange interaction.
Journal Article
Credible practice of modeling and simulation in healthcare: ten rules from a multidisciplinary perspective
The complexities of modern biomedicine are rapidly increasing. Thus, modeling and simulation have become increasingly important as a strategy to understand and predict the trajectory of pathophysiology, disease genesis, and disease spread in support of clinical and policy decisions. In such cases, inappropriate or ill-placed trust in the model and simulation outcomes may result in negative outcomes, and hence illustrate the need to formalize the execution and communication of modeling and simulation practices. Although verification and validation have been generally accepted as significant components of a model’s credibility, they cannot be assumed to equate to a holistic credible practice, which includes activities that can impact comprehension and in-depth examination inherent in the devel-opment and reuse of the models. For the past several years, the Committee on Credible Practice of Modeling and Simulation in Healthcare, an interdisciplinary group seeded from a U.S. interagency initiative, has worked to codify best practices. Here, we provide Ten Rules for credible practice of modeling and simulation in healthcare developed from a comparative analysis by the Committee’s multidisciplinary membership, followed by a large stakeholder com-munity survey. These rules establish a unified conceptual framework for modeling and simulation design, implementation, evaluation, dissemination and usage across the modeling and simulation life-cycle. While biomedical science and clinical care domains have somewhat different requirements and expectations for credible practice, our study converged on rules that would be useful across a broad swath of model types. In brief, the rules are: (1) Define context clearly. (2) Use contextually appropriate data. (3) Evaluate within context. (4) List limitations explicitly. (5) Use version control. (6) Document appropriately. (7) Disseminate broadly. (8) Get independent reviews. (9) Test competing imple-mentations. (10) Conform to standards. Although some of these are common sense guidelines, we have found that many are often missed or misconstrued, even by seasoned practitioners. Computational models are already widely used in basic science to generate new biomedical knowledge. As they penetrate clinical care and healthcare policy, contributing to personalized and precision medicine, clinical safety will require established guidelines for the credible practice of modeling and simulation in healthcare.
Journal Article
Experimental investigation of kinetic instabilities driven by runaway electrons in the EXL-50 spherical torus
In this study, high-frequency instabilities driven by runaway electrons in the EXL-50 spherical torus have been reported using a high-frequency magnetic pickup coil. The frequency of these instabilities is found to be power function dependent on the plasma density, similar to the dispersion relation of the whistler wave. The observed instability seems to exhibit a fluctuating pattern, resembling frequency chirping behavior, which appears to align with the expected outcomes predicted by the Berk-Breizman model. Theoretically, the excitation threshold of the instability driven by runaway electrons is related to the ratio of the runaway electron density to the background plasma density, and the stability criterion is first demonstrated qualitatively in this work. The instability can be stabilized by the spontaneous rise of plasma density, consistent with the wave-particle resonance mechanism. This investigation demonstrates the excitation characteristic of chirping instabilities in a tokamak plasma and reveals new features of these instabilities, thereby advancing the understanding of the mechanisms for controlling and mitigating runaway electrons.
Journal Article