On a rainbow extremal problem for color-critical graphs

Given (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

Measuring Nonlocal Brane Order with Error-Corrected Quantum Gas Microscopes

Exotic quantum many-body states, such as Haldane and spin liquid phases, can exhibit remarkable features like fractional excitations and non-Abelian statistics and offer new understandings of quantum entanglement in many-body quantum systems. These phases are classified by nonlocal correlators that can be directly measured in atomic analog quantum simulating platforms, such as optical lattices and Rydberg atom arrays. However, characterizing these phases in large systems is experimentally challenging because they are sensitive to local errors like atom loss, which suppress its signals exponentially. Additionally, protocols for systematically identifying and mitigating uncorrelated errors in analog quantum simulators are lacking. Here, we address these challenges by developing an error-correction method for large-scale neutral atom quantum simulators using optical lattices. Our error-correction method can distinguish correlated particle-hole pairs from uncorrelated holes in the Mott insulator. After removing the uncorrelated errors, we observe a dramatic improvement in the nonlocal parity correlator and find the perimeter scaling law. Furthermore, the error model provides a statistical estimation of fluctuations in site occupation, from which we measure the generalized brane correlator and confirm that it can be an order parameter for Mott insulators in two dimensions. Our work provides a promising avenue for investigating and characterizing exotic phases of matters in large-scale quantum simulators. © 2024 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the https://creativecommons.org/licenses/by/4.0/Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.11Nscopu

The ergodicity question when imaging DNA conformation using liquid cell electron microscopy

Assessing the ergodicity of graphene liquid cell electron microscope measurements, we report that loop states of circular DNA interconvert reversibly and that loop numbers follow the Boltzmann distribution expected for this molecule in bulk solution, provided that the electron dose is low (80-keV electron energy and electron dose rate 1-20 e- Å-2 s-1). This imaging technique appears to act as a slow motion camera that reveals equilibrated distributions by imaging the time average of a few molecules without the need to image a spatial ensemble.11Nscopu

Prime vertex-minors of a prime graph

A graph is prime if it does not admit a partition (A,B) of its vertex set such that min{|A|,|B|}≥2 and the rank of the A×B submatrix of its adjacency matrix is at most 1. A vertex v of a graph is non-essential if at least two of the three kinds of vertex-minor reductions at v result in prime graphs. In 1994, Allys proved that every prime graph with at least four vertices has a non-essential vertex unless it is locally equivalent to a cycle graph. We prove that every prime graph with at least four vertices has at least two non-essential vertices unless it is locally equivalent to a cycle graph. As a corollary, we show that for a prime graph G with at least six vertices and a vertex x, there is a vertex v≠x such that G∖v or G∗v∖v is prime, unless x is adjacent to all other vertices and G is isomorphic to a particular graph on odd number of vertices. Furthermore, we show that a prime graph with at least four vertices has at least three non-essential vertices, unless it is locally equivalent to a graph consisting of at least two internally-disjoint paths between two fixed distinct vertices having no common neighbors. We also prove analogous results for pivot-minors. © 2023 Elsevier Ltd11Nsciescopu

Single-atom catalysts supported on a hybrid structure of boron nitride/graphene for efficient nitrogen fixation via synergistic interfacial interactions

Hexagonal boron nitride (BN) shows significant chemical stability and promising thermal nitrogen reduction reaction (NRR) activity but suffers from low conductivity in electrolysis with a wide band gap. To overcome this problem, two-dimensional (2D) BN and graphene (G) are designed as a heterostructure, namely BN/G. According to density functional theory (DFT), the higher conductivity of G narrows the band gap of BN by inducing some electronic states near the Fermi energy level (Ef). Once transition metals (TMs) are anchored in the BN/G structure as single atom catalysts (SACs), the NRR activity improves as the inert BN basal layer activates with moderate *NH2 binding energy and further the band gap is reduced to zero. V (vanadium) and W (tungsten) SACs exhibit the best performance with limiting potentials of −0.22 and −0.41 V, respectively. This study helps in understanding the improvement of the NRR activity of BN, providing physical insights into the adsorbate-TM interaction. © 2024 The Royal Society of Chemistry.11Nsciescopu

Enantioselective Aziridination of Unactivated Terminal Alkenes Using a Planar Chiral Rh(III) Indenyl Catalyst

Chiral aziridines are important structural motifs found in natural products and various target molecules. They serve as versatile building blocks for the synthesis of chiral amines. While advances in catalyst design have enabled robust methods for enantioselective aziridination of activated olefins, simple and abundant alkyl-substituted olefins pose a significant challenge. In this work, we introduce a novel approach utilizing a planar chiral rhodium indenyl catalyst to facilitate the enantioselective aziridination of unactivated alkenes. This transformation exhibits a remarkable degree of functional group tolerance and displays excellent chemoselectivity favoring unactivated alkenes over their activated counterparts, delivering a wide range of enantioenriched high-value chiral aziridines. Computational studies unveil a stepwise aziridination mechanism in which alkene migratory insertion plays a central role. This process results in the formation of a strained four-membered metallacycle and serves as both the enantio- and rate-determining steps in the overall reaction. © 2024 The Authors. Published by American Chemical Society.11Nsciescopu

Unveiling Ultrafast Carrier Dynamics of Tellurium Microcrystals by Two-Color Asynchronous Sampling Infrared Transient Absorption Spectroscopy

Tellurium (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

Monitoring the synthesis of neutral lipids in lipid droplets of living human cancer cells using two-color infrared photothermal microscopy

There has been growing interest in the functions of lipid droplets (LDs) due to recent discoveries regarding their diverse roles. These functions encompass lipid metabolism, regulation of lipotoxicity, and signaling pathways that extend beyond their traditional role in energy storage. Consequently, there is a need to examine the molecular dynamics of LDs at the subcellular level. Two-color infrared photothermal microscopy (2C-IPM) has proven to be a valuable tool for elucidating the molecular dynamics occurring in LDs with sub-micrometer spatial resolution and molecular specificity. In this study, we employed the 2C-IPM to investigate the molecular dynamics of LDs in both fixed and living human cancer cells (U2OS cells) using the isotope labeling method. We investigated the synthesis of neutral lipids occurring in individual LDs over time after exposing the cells to excess saturated fatty acids while simultaneously comparing inherent lipid contents in LDs. We anticipate that these research findings will reveal new opportunities for studying lesser-known biological processes within LDs and other subcellular organelles. © 2024 The Royal Society of Chemistry.11Ysciescopu

Dynamic Responses of Circulating T Cells After Stereotactic Body Radiation Therapy for Bone Metastasis in Patients With Breast Cancer

Purpose: Preclinical studies have shown that radiation therapy modulates antitumor immune responses. However, circulating T-cell responses after radiation therapy in patients with cancer have been poorly characterized. This study aims to explore the changes in circulating T cells after stereotactic body radiation therapy (SBRT). Methods and Materials: Peripheral blood samples of 30 patients with breast cancer who underwent SBRT for bone metastasis were analyzed using multicolor flow cytometry. Phenotypes of PD-1+ CD8+ T cells and regulatory T (TREG) cells were examined. Additionally, plasma protein levels were analyzed using a bead-based immunoassay. Results: Circulating PD-1+ CD8+ T cells, which are enriched for tumor-specific clonotypes, were activated at 1 week after SBRT. However, circulating TREG cells were also activated after SBRT; this pattern was also evident among effector Foxp3hiCD45RA− TREG cells. We observed no difference in T-cell responses according to the fraction size and number. Notably, activation of TREG cells was more prominent in patients who experienced greater activation of PD-1+ CD8+ T cells. Plasma level changes in TGF-β1, soluble CTLA-4, and soluble 4-1BB at 1 week after SBRT were associated with PD-1+ CD8+ T-cell responses. Activation of TREG cells at 1 week after SBRT was associated with worse progression-free survival. Clinical factors including molecular subtype were not associated with the T-cell responses. Conclusions: SBRT induced activation of both potentially tumor-specific CD8+ T cells and TREG cells, which were tightly associated with each other. These results may support the use of TREG cell-modulating strategies with SBRT to improve the antitumor immune response. © 2023 Elsevier Inc.11Nsciescopu

Omicron BA.2 breakthrough infection elicits CD8+ T cell responses recognizing the spike of later Omicron subvariants

Here, we examine peripheral blood memory T cell responses against the SARS-CoV-2 BA.4/BA.5 variant spike among vaccinated individuals with or without Omicron breakthrough infections. We provide evidence supporting a lack of original antigenic sin in CD8+ T cell responses targeting the spike. We show that BNT162b2-induced memory T cells respond to the BA.4/BA.5 spike. Among individuals with BA.1/BA.2 breakthrough infections, IFN-γ-producing CD8+ T cell responses against the BA.4/BA.5 spike increased. In a subgroup with BA.2 breakthrough infections, IFN-γ-producing CD8+ T cell responses against the BA.2-mutated spike region increased and correlated directly with responses against the BA.4/BA.5 spike, indicating that BA.2 spike-specific CD8+ T cells elicited by BA.2 breakthrough infection cross-react with the BA.4/BA.5 spike. We identified CD8+ T cell epitope peptides that are present in the spike of BA.2 and BA.4/BA.5 but not the original spike. These peptides are fully conserved in the spike of now-dominant XBB lineages. Our study shows that breakthrough infection by early Omicron subvariants elicits CD8+ T cell responses that recognize epitopes within the spike of newly emerging subvariants.11Nsciescopu