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On a rainbow extremal problem for color-critical graphs
No full textGiven (Formula presented.) graphs (Formula presented.) over a common vertex set of size (Formula presented.), what is the maximum value of (Formula presented.) having no “colorful” copy of (Formula presented.), that is, a copy of (Formula presented.) containing at most one edge from each (Formula presented.) ? Keevash, Saks, Sudakov, and Verstraëte denoted this number as (Formula presented.) and completely determined (Formula presented.) for large (Formula presented.). In fact, they showed that, depending on the value of (Formula presented.), one of the two natural constructions is always the extremal construction. Moreover, they conjectured that the same holds for every color-critical graphs, and proved it for 3-color-critical graphs. They also asked to classify the graphs (Formula presented.) that have only these two extremal constructions. We prove their conjecture for 4-color-critical graphs and for almost all (Formula presented.) -color-critical graphs when (Formula presented.). Moreover, we show that for every non-color-critical non-bipartite graphs, none of the two natural constructions is extremal for certain values of (Formula presented.). © 2023 Wiley Periodicals LLC.11Nsciescopu
Emergence of Stable Meron Quartets in Twisted Magnets
No full textThe investigation of twist engineering in easy-axis magnetic systems has revealed remarkable potential for generating topological spin textures. Implementing twist engineering in easy-plane magnets, we introduce a novel approach to achieving fractional topological spin textures, such as merons. Through atomistic spin simulations on twisted bilayer magnets, we demonstrate the formation of a stable double Meron pair, which we refer to as the “Meron Quartet” (MQ). Unlike a single pair, the merons within the MQ exhibit exceptional stability against pair annihilation due to the protective localization mechanism induced by the twist that prevents collision of the Meron cores. Furthermore, we showcase that the stability of the MQ can be enhanced by adjusting the twist angle, resulting in an increased resistance to external perturbations such as external magnetic fields. Our findings highlight the twisted magnet as a promising platform for achieving merons as stable magnetic quasiparticles in van der Waals magnets. © 2023 American Chemical Society.11Nsciescopu
Mitochondrial matrix RTN4IP1/OPA10 is an oxidoreductase for coenzyme Q synthesis
No full textTargeting proximity-labeling enzymes to specific cellular locations is a viable strategy for profiling subcellular proteomes. Here, we generated transgenic mice (MAX-Tg) expressing a mitochondrial matrix-targeted ascorbate peroxidase. Comparative analysis of matrix proteomes from the muscle tissues showed differential enrichment of mitochondrial proteins. We found that reticulon 4-interacting protein 1 (RTN4IP1), also known as optic atrophy-10, is enriched in the mitochondrial matrix of muscle tissues and is an NADPH oxidoreductase. Interactome analysis and in vitro enzymatic assays revealed an essential role for RTN4IP1 in coenzyme Q (CoQ) biosynthesis by regulating the O-methylation activity of COQ3. Rtn4ip1-knockout myoblasts had markedly decreased CoQ9 levels and impaired cellular respiration. Furthermore, muscle-specific knockdown of d Rtn4ip1 in flies resulted in impaired muscle function, which was reversed by dietary supplementation with soluble CoQ. Collectively, these results demonstrate that RTN4IP1 is a mitochondrial NAD(P)H oxidoreductase essential for supporting mitochondrial respiration activity in the muscle tissue. [Figure not available: see fulltext.] © 2023, The Author(s).11Nsciescopu
Unveiling Ultrafast Carrier Dynamics of Tellurium Microcrystals by Two-Color Asynchronous Sampling Infrared Transient Absorption Spectroscopy
No full textTellurium (Te) microcrystal with a bandgap of approximately 0.37 eV is a potentially useful semiconducting material exhibiting ultrafast electronic relaxation processes. To measure the intervalley and intravalley relaxation rates, we carried out two-color near-IR (NIR) pump and mid-IR (MIR) probe studies of rod-type Te microcrystals, employing a repetition-frequency-stabilized NIR (800 nm) laser and an MIR (3300 nm) frequency comb. Using interferometrically detected two-color asynchronous sampling (AS) transient absorption (TA) spectroscopy, we measured time- and frequency-resolved TA signals of rod-type Te microcrystals. The frequency-resolved and excitation-intensity-dependent AS-TA signals show that the charge carriers undergo relaxation processes with different time constants after photoexcitation. In this work, we found that there are three distinguishable relaxation components that correspond to an ultrafast (a few picoseconds) component associated with the MIR absorption of NIR-excited electrons in the conduction band, two stimulated emission processes associated with the recombination of electrons at the band edge with holes of the valence band with time constants of approximately 75 and 350 ps. We anticipate that the present NIR pump MIR probe spectroscopy with two repetition-frequency-stabilized lasers, which does not require any mechanical pump-probe time delay scanning devices, is useful for studying electron-hole dynamics in the MIR spectral range with femtosecond time resolutions and a few nanoseconds dynamic range measurements in semiconductor microcrystals with MIR band gaps. © 2023 American Chemical Society.11Nsciescopu
Activated somatostatin interneurons orchestrate memory microcircuits
No full textDespite recent advancements in identifying engram cells, our understanding of their regulatory and functional mechanisms remains in its infancy. To provide mechanistic insight into engram cell functioning, we introduced a novel local microcircuit labeling technique that enables the labeling of intraregional synaptic connections. Utilizing this approach, we discovered a unique population of somatostatin (SOM) interneurons in the mouse basolateral amygdala (BLA). These neurons are activated during fear memory formation and exhibit a preference for forming synapses with excitatory engram neurons. Post-activation, these SOM neurons displayed varying excitability based on fear memory retrieval. Furthermore, when we modulated these SOM neurons chemogenetically, we observed changes in the expression of fear-related behaviors, both in a fear-associated context and in a novel setting. Our findings suggest that these activated SOM interneurons play a pivotal role in modulating engram cell activity. They influence the expression of fear-related behaviors through a mechanism that is dependent on memory cues. © 2023 Elsevier Inc.11Nsciescopu
Skew trapezoidal bipyramidal distortion in MoS6 unit stabilizing distorted phases of 1T-MoS2 single layer
No full textThe exceptional electrocatalytic performance of the 1T phase of MoS2 in the hydrogen evolution reaction has motivated researchers to design methods for enhancing the stability of this phase. Herein, the electronic origin of the stability of 1T-MoS2 and its distorted phases: 1T' (zig-zag), 1T′′ (diamond chain), and 1T′′′ (triangle) was elucidated using first-principles calculations. The phase stability can be altered by the repeating MoS6 units that play a significant role in the generation of metal clusters. A novel skew trapezoidal bipyriamidal (STB) distortion was observed in the MoS6 unit, which increased the stability of the distorted 1T phases in MoS2. The highly distorted STB unit was found in the stable 1T' phase with an enhanced dyz orbital population. The short edges of the distorted STB increase the electron density fraction of the Mo atoms, promoting Mo-Mo bond formation. The 1T' phase exhibited superior stability due to stronger electron delocalization in the Mo-Mo bond compared to that in the 1T′′ and 1T′′′ phases. The nature of Mo-Mo bonding varied on different metal clusters for 1T' (σ, π, and δ), 1T′′ (π and σ), and 1T′′′ (σ) bond types. Therefore, the stability of the 1T'-MoS2 phase depends on the extent of distortion in the MoS6 unit, Mo-Mo bond nature, and layer thickness.11Nsciescopu
Concurrent Asian monsoon strengthening and early modern human dispersal to East Asia during the last interglacial
No full textThe relationship between initial Homo sapiens dispersal from Africa to East Asia and the orbitally paced evolution of the Asian summer monsoon (ASM)-currently the largest monsoon system-remains underexplored due to lack of coordinated synthesis of both Asian paleoanthropological and paleoclimatic data. Here, we investigate orbital-scale ASM dynamics during the last 280 thousand years (kyr) and their likely influences on early H. sapiens dispersal to East Asia, through a unique integration of i) new centennial-resolution ASM records from the Chinese Loess Plateau, ii) model-based East Asian hydroclimatic reconstructions, iii) paleoanthropological data compilations, and iv) global H. sapiens habitat suitability simulations. Our combined proxy- and model-based reconstructions suggest that ASM precipitation responded to a combination of Northern Hemisphere ice volume, greenhouse gas, and regional summer insolation forcing, with cooccurring primary orbital cycles of ~100-kyr, 41-kyr, and ~20-kyr. Between ~125 and 70 kyr ago, summer monsoon rains and temperatures increased in vast areas across Asia. This episode coincides with the earliest H. sapiens fossil occurrence at multiple localities in East Asia. Following the transcontinental increase in simulated habitat suitability, we suggest that ASM strengthening together with Southeast African climate deterioration may have promoted the initial H. sapiens dispersal from their African homeland to remote East Asia during the last interglacial.11Nsciescopu
Effects of Pressure on Exciton Absorption and Emission in Strongly Quantum-Confined CsPbBr3 Quantum Dots and Nanoplatelets
No full textSoft lattices of metal halide perovskite (MHP) nanocrystals (NCs) are considered responsible for many of their optical properties associated with excitons, which are often distinct from other semiconductor NCs. Earlier studies of MHP NCs upon compression revealed how structural changes and the resulting changes in the optical properties such as the bandgap can be induced at relatively low pressures. However, the pressure response of the exciton transition itself in MHP NCs remains relatively poorly understood due to limitations inherent to studying weakly or nonconfined NCs in which exciton absorption peaks are not well-separated from the continuum interband transition. Here, we investigated the pressure response of the absorbing and emitting transitions of excitons using strongly quantum-confined CsPbBr3 quantum dots (QDs) and nanoplatelets (NPLs), which both exhibit well-defined exciton absorption peaks. Notably, the reversible vanishing and recovery of the exciton absorption accompanied by reversible quenching and recovery of the emission were observed in both QDs and NPLs, resulting from the reversible pressure modulation of the exciton oscillator strength. Furthermore, CsPbBr3 NPLs exhibited irreversible pressure-induced creation of trap states at low pressures (∼0.1 GPa) responsible for trapped exciton emission that developed on the time scale of ∼10 min, while the reversible pressure response of the absorbing exciton transition was maintained. These findings shed light on the diverse effects the application of force has on the absorbing and emitting exciton transitions in MHP NCs, which are important for their application as excitonic light emitters in high-pressure environments. © 2024 The Authors. Published by American Chemical Society.11Nsciescopu
Molecular dynamics simulation study of water structure and dynamics on the gold electrode surface with adsorbed 4-mercaptobenzonitrile
No full textUnderstanding water dynamics at charged interfaces is of great importance in various fields, such as catalysis, biomedical processes, and solar cell materials. In this study, we implemented molecular dynamics simulations of a system of pure water interfaced with Au electrodes, on one side of which 4-mercaptobenzonitrile (4-MBN) molecules are adsorbed. We calculated time correlation functions of various dynamic quantities, such as the hydrogen bond status of the N atom of the adsorbed 4-MBN molecules, the rotational motion of the water OH bond, hydrogen bonds between 4-MBN and water, and hydrogen bonds between water molecules in the interface region. Using the Luzar-Chandler model, we analyzed the hydrogen bond dynamics between a 4-MBN and a water molecule. The dynamic quantities we calculated can be divided into two categories: those related to the collective behavior of interfacial water molecules and the H-bond interaction between a water molecule and the CN group of 4-MBN. We found that these two categories of dynamic quantities exhibit opposite trends in response to applied potentials on the Au electrode. We anticipate that the present work will help improve our understanding of the interfacial dynamics of water in various electrolyte systems.11Nsciescopu
Electron beam-induced demetallation of Fe, Co, Ni, Cu, Zn, Pd, and Pt metalloporphyrins: insights in e-beam chemistry and metal cluster formations
No full textElectron beams are versatile tools for nanoscale fabrication processes, however, the underlying e-beam chemistry remains in its infancy. Through operando transmission electron microscopy investigations, we elucidate a redox-driven cargo release of individual metal atoms triggered by electron beams. The chosen organic delivery molecule, tetraphenylporphyrin (TPP), proves highly versatile, forming complexes with nearly all metals from the periodic table and being easily processed in solution. A comprehensive cinematographic analysis of the dynamics of single metal atoms confirms the nearly instantaneous ejection of complexed metal atoms under an 80 kV electron beam, underscoring the system's broad versatility. Providing mechanistic insights, we employ density functional theory to support the proposed reductive demetallation pathway facilitated by secondary electrons, contributing novel perspectives to electron beam-mediated chemical reaction mechanisms. Lastly, our findings demonstrate that all seven metals investigated form nanoclusters once ejected from TPP, highlighting the method's potential for studying and developing sustainable single-atom and nanocluster catalysts. By operando high-resolution transmission electron microscopy, we show that slow secondary electrons from the specimen can demetallate metalloporphyrins. This general approach allows study of the dynamics of various single metal atoms and metal clusters.11Nsciescopu