Influence of Hexagonal Boron Nitride on Electronic Structure of Graphene.

By performing first-principles calculations, we studied hexagonal-boron-nitride (hBN)-supported graphene, in which moiré structures are formed due to lattice mismatch or interlayer rotation. A series of graphene/hBN systems has been studied to reveal the evolution of properties with respect to different twisting angles (21.78°, 13.1°, 9.43°, 7.34°, 5.1°, and 3.48°). Although AA- and AB-stacked graphene/hBN are gapped at the Dirac point by about 50 meV, the energy gap of the moiré graphene/hBN, which is much more asymmetric, is only about several meV. Although the Dirac cone of graphene residing in the wide gap of hBN is not much affected, the calculated Fermi velocity is found to decrease with the increase in the moiré super lattice constant due to charge transfer. The periodic potential imposed by hBN modulated charge distributions in graphene, leading to the shift of graphene bands. In agreement with experiments, there are dips in the calculated density of states, which get closer and closer to the Fermi energy as the moiré lattice grows larger.

Replacing the cyano (-C[triple bond, length as m-dash]N) group to design environmentally friendly fused-ring electron acceptors.

The cyano-group (-C[triple bond, length as m-dash]N) is an electron-withdrawing group, which has been widely used to construct high-performance fused-ring electron acceptors (FREAs). Benefiting from these FREAs, the power conversion efficiency of organic solar cells has recently exceeded 18%. However, malononitrile is a highly toxic substance used to introduce -C[triple bond, length as m-dash]N during the synthesis of these FREAs. Therefore, the synthesis processes of most high-performance FREAs are typically harmful to the environment. Our previous work demonstrated that the electron-withdrawing ability of -C[triple bond, length as m-dash]N is necessary for FREAs. Thus, the use of other electron-withdrawing groups instead of -C[triple bond, length as m-dash]N to design environmentally friendly FREAs is feasible. We utilized seven electron-withdrawing groups, namely, -C[double bond, length as m-dash]NH, -N[double bond, length as m-dash]O, -CH[double bond, length as m-dash]O, -CO-CH3, -CO-OH, -CO-Cl, and -CO-Br, to replace -C[triple bond, length as m-dash]N in the commonly used acceptor Y6 to design new FREAs (Y6-CNH, Y6-NO, Y6-CHO, Y6-COCH3, Y6-COOH, Y6-COCl, and Y6-COBr). Multi-scale theoretical calculation methods were used to investigate the photoelectronic properties of these new FREAs, including energy level, absorption spectrum, exciton binding energy, and electron mobility. The results showed that Y6-CNH, Y6-COCH3 and Y6-COOH are unsuitable for use as acceptor materials because of their high frontier molecular orbital energy level and weak electron affinity. The strong absorption intensity and weak exciton binding energy of Y6-CHO, Y6-COCl, and Y6-COBr indicated that they can absorb more solar energy than Y6 and excitons are easier to separate into free charges. The electron mobility of Y6-CHO (3.53 × 10-4 cm2 V-1 s-1) was found to be approximately 28 times that of Y6-COCl (1.24 × 10-5 cm2 V-1 s-1) and Y6-COBr (1.28 × 10-5 cm2 V-1 s-1). The possible synthetic routes to Y6-CHO are environmentally friendly. Therefore, -CH[double bond, length as m-dash]O is the most suitable electron-withdrawing group for constructing high-performance environmentally friendly FREAs. This work can provide a new molecular design perspective in experimental science for developing high-performance environmentally friendly FREAs.

Detecting Air Pollutant Molecules Using Tube-Shaped Single Electron Transistor.

An air pollution detector is proposed based on a tube-shaped single-electron transistor (SET) sensor. By monitoring the flow control component of the detector, each air pollutant molecule can be placed at the center of a SET nanopore and is treated as an island of the SET device in the same framework. Electron transport in the SET was incoherent, and the performances of the SET were sensitive at the single molecule level. Employing first-principles calculations, electronic features of an air pollutant molecule within a tube-shaped SET environment were found to be independent of the molecule rotational orientations with respect to axis of symmetry, unlike the electronic features in a conventional SET environment. Charge stability diagrams of the island molecules were demonstrated to be distinct for each molecule, and thus they can serve as electronic fingerprints for detection. Using the same setup, quantification of the air pollutant can be realized at room temperature as well. The results presented herein may help provide guidance for the identification and quantification of various types of air pollutants at the molecular level by treating the molecule as the island of the SET component in the proposed detector.

Protection of Fecal Microbiota Transplantation in a Mouse Model of Multiple Sclerosis.

Given the growing evidence of a link between gut microbiota (GM) dysbiosis and multiple sclerosis (MS), fecal microbiota transplantation (FMT), aimed at rebuilding GM, has been proposed as a new therapeutic approach to MS treatment. To evaluate the viability of FMT for MS treatment and its impact on MS pathology, we tested FMT in mice with experimental autoimmune encephalomyelitis (EAE), a mouse model of MS. We provide evidence that FMT can rectify altered GM to some extent with a therapeutic effect on EAE. We also found that FMT led to reduced activation of microglia and astrocytes and conferred protection on the blood-brain barrier (BBB), myelin, and axons in EAE. Taken together, our data suggest that FMT, as a GM-based therapy, has the potential to be an effective treatment for MS.

Monitoring of singlet fission via two-dimensional photon-echo and transient-absorption spectroscopy: Simulations by multiple Davydov trial states.

Employing the Dirac-Frenkel time dependent variational method, the nonlinear spectra monitoring the singlet fission process mediated by a conical intersection (CI) of the two lowest excited electronic states are investigated for different optical dephasings. The simulated two-dimensional spectra at different population times follow ultrafast population transfer through the CI and exhibit spectral features related to the tuning mode. The anticorrelated oscillations of cross peaks located at symmetric positions with respect to the main diagonal are clearly identified after the stimulated-emission contribution quenches. The simulated transient absorption signals show a fast decay of the first excited singlet state and exhibit multiple peaks revealing the tuning mode. These findings could be regarded as signatures of the CI in the singlet fission process.

Dissipative dynamics in a tunable Rabi dimer with periodic harmonic driving.

Recent progress on qubit manipulation allows application of periodic driving signals on qubits. In this study, a harmonic driving field is added to a Rabi dimer to engineer photon and qubit dynamics in a circuit quantum electrodynamics device. To model environmental effects, qubits in the Rabi dimer are coupled to a phonon bath with a sub-Ohmic spectral density. A nonperturbative treatment, the Dirac-Frenkel time-dependent variational principle together with the multiple Davydov D2 ansatz, is employed to explore the dynamical behavior of the tunable Rabi dimer. In the absence of the phonon bath, the amplitude damping of the photon number oscillation is greatly suppressed by the driving field, and photons can be created, thanks to the resonance between the periodic driving field and the photon frequency. In the presence of the phonon bath, one can still change the photon numbers in two resonators and indirectly alter the photon imbalance in the Rabi dimer by directly varying the driving signal in one qubit. It is shown that qubit states can be manipulated directly by the harmonic driving. The environment is found to strengthen the interqubit asymmetry induced by the external driving, opening up a new venue to engineer the qubit states.

Davydov-Ansatz for Landau-Zener-Stueckelberg-Majorana transitions in an environment: Tuning the survival probability via number state excitation.

We theoretically investigate transitions in a two-level system, which are induced by a sweep through an avoided crossing in the presence of coupling to a single, excited bosonic mode. This allows us to propose an initial number-state bosonic excitation as a new possible control parameter for the survival probability at long times. The expansion of number states in terms of coherent states centered around points on a circle in phase space makes a multi-Davydov-Ansatz the method of choice to perform the required numerical calculations. It is revealed that the starting time of the transition greatly affects the final transition probabilities. In addition, we found that the mixing angle, which is tuning between the diagonal and off-diagonal coupling, is decisive for the ability to control the transition via number state excitation. For a mixing angle of π/4, we found the maximal effect of number state excitation on the transition probability.

Polaron dynamics with off-diagonal coupling: beyond the Ehrenfest approximation.

Treated traditionally by the Ehrenfest approximation, the dynamics of a one-dimensional molecular crystal model with off-diagonal exciton-phonon coupling is investigated in this work using the Dirac-Frenkel time-dependent variational principle with the multi-D2Ansatz. It is shown that the Ehrenfest method is equivalent to our variational method with the single D2Ansatz, and with the multi-D2Ansatz, the accuracy of our simulated dynamics is significantly enhanced in comparison with the semi-classical Ehrenfest dynamics. The multi-D2Ansatz is able to capture numerically accurate exciton momentum probability and help clarify the relation between the exciton momentum redistribution and the exciton energy relaxation. The results demonstrate that the exciton momentum distributions in the steady state are determined by a combination of the transfer integral and the off-diagonal coupling strength, independent of the excitonic initial conditions. We also probe the effect of the transfer integral and the off-diagonal coupling on exciton transport in both real and reciprocal space representations. Finally, the variational method with importance sampling is employed to investigate temperature effects on exciton transport using the multi-D2Ansatz, and it is demonstrated that the variational approach is valid in both low and high temperature regimes.

Fast, Accurate Simulation of Polaron Dynamics and Multidimensional Spectroscopy by Multiple Davydov Trial States.

By employing the Dirac-Frenkel time-dependent variational principle, we study the dynamical properties of the Holstein molecular crystal model with diagonal and off-diagonal exciton-phonon coupling. A linear combination of the Davydov D1 (D2) ansatz, referred to as the "multi-D1 ansatz" ("multi-D2 ansatz"), is used as the trial state with enhanced accuracy but without sacrificing efficiency. The time evolution of the exciton probability is found to be in perfect agreement with that of the hierarchy equations of motion, demonstrating the promise the multiple Davydov trial states hold as an efficient, robust description of dynamics of complex quantum systems. In addition to the linear absorption spectra computed for both diagonal and off-diagonal cases, for the first time, 2D spectra have been calculated for systems with off-diagonal exciton-phonon coupling by employing the multiple D2 ansatz to compute the nonlinear response function, testifying to the great potential of the multiple D2 ansatz for fast, accurate implementation of multidimensional spectroscopy. It is found that the signal exhibits a single peak for weak off-diagonal coupling, while a vibronic multipeak structure appears for strong off-diagonal coupling.

Polaron dynamics with a multitude of Davydov D2 trial states.

We propose an extension to the Davydov D2 Ansatz in the dynamics study of the Holstein molecular crystal model with diagonal and off-diagonal exciton-phonon coupling using the Dirac-Frenkel time-dependent variational principle. The new trial state by the name of the "multi-D2 Ansatz" is a linear combination of Davydov D2 trial states, and its validity is carefully examined by quantifying how faithfully it follows the Schrödinger equation. Considerable improvements in accuracy have been demonstrated in comparison with the usual Davydov trial states, i.e., the single D1 and D2 Ansätze. With an increase in the number of the Davydov D2 trial states in the multi-D2 Ansatz, deviation from the exact Schrödinger dynamics is gradually diminished, leading to a numerically exact solution to the Schrödinger equation.

Activation of transcriptional activity of HSE by a novel mouse zinc finger protein ZNFD specifically expressed in testis.

Zinc finger proteins (ZFPs) that contain multiple cysteine and/or histidine residues perform important roles in various cellular functions, including transcriptional regulation, cell proliferation, differentiation, and apoptosis. The Cys-Cys-His-His (C(2)H(2)) type of ZFPs are the well-defined members of this super family and are the largest and most complex proteins in eukaryotic genomes. In this study, we identified a novel C(2)H(2) type of zinc finger gene ZNFD from mice which has a 1,002 bp open reading frame and encodes a protein with 333 amino acid residues. The predicted 37.4 kDa protein contains a C(2)H(2) zinc finger domain. ZNFD gene is located on chromosome 18qD1. RT-PCR analysis revealed that the ZNFD gene was specifically expressed in mouse testis but not in other tissues. Subcellular localization analysis demonstrated that ZNFD was localized in the nucleus. Reporter gene assays showed that overexpression of ZNFD in the COS7 cells activates the transcriptional activities of heat shock element (HSE). Overall, these results suggest that ZNFD is a member of the zinc finger transcription factor family and it participates in the transcriptional regulation of HSE. Many heat shock proteins regulated by HSE are involved in testicular development. Therefore, our results suggest that ZNFD may probably participate in the development of mouse testis and function as a transcription activator in HSE-mediated gene expression and signaling pathways.

Atomic Bonding and Electronic Binding Energy of Two-Dimensional Bi/Li(110) Heterojunctions via BOLS-BB Model.

Combining the bond-order-length-strength (BOLS) and atomic bonding and electronic model (BB model) with density functional theory (DFT) calculations, we studied the atomic bonding and electronic binding energy behavior of Bi atoms adsorbed on the Li(110) surface. We found that the Bi atoms adsorbed on the Li(110) surface form two-dimensional (2D) geometric structures, including letter-, hexagon-, galaxy-, crown-, field-, and cobweb-shaped structures. Thus, we obtained the following quantitative information: (i) the field-shaped structure can be considered the bulk structure; (ii) the field-shaped structure of Bi atom formation has a 5d energy level of 22.727 eV, and in the letter shape structure, this energy is shifted to values greater than 0.342 eV; and (iii) the Bi/Li(110) heterojunction transfers charge from the inner Li atomic layer to the outermost Bi atomic layer. In addition, we analyzed the bonding and electronic dynamics involved in the formation of the Bi/Li(110) heterojunctions using residual density of states. This work provides a theoretical reference for the fine tuning of binding energies and chemical bonding at the interfaces of 2D metallic materials.

Understanding atomic bonding and electronic distributions of a DNA molecule using DFT calculation and BOLS-BC model.

Deoxyribonucleic acid (DNA) is an important molecule that has been extensively researched, mainly due to its structure and function. Herein, we investigated the electronic behavior of the DNA molecule containing 1008 atoms using density functional theory. The bond-charge (BC) model shows the relationship between charge density and atomic strain. Besides, the model mentioned above is combined with the bond-order-length-strength (BOLS) notion to calculate the atomic cohesive energy, the bond energy, and the local bond strain of the DNA chain. Using the BOLS-BC model, we were able to obtain information on the bonding features of the DNA chain and better comprehend the associated properties of electrons in biological systems. Consequently, this report functions as a theoretical reference for the precise regulation of the electrons and the bonding states of biological systems.

Construction of ultra-stable trinickel disulphide (Ni3S2)/polyaniline (PANI) electrodes based on carbon fibers for high performance flexible asymmetric supercapacitors.

Highly flexible supercapacitors (SCs) have attracted significant attention in modern electronics. However, it has been found that flexible, metal sulfide-based electrodes usually suffer from corrosion, instability and low conductivity, which significantly limits their large scale application. Herein, we report on an electrode comprised of highly stable, free-standing carbon fiber/trinickel disulphide covered with polyaniline (CF/Ni3S2@PANI). This electrode was prepared and then employed in a high-performance of flexible asymmetric SCs (FASC). The coating layer of polyaniline served as both a protector and conducting shell for the Ni3S2 due to the nature of the highly stable N-Ni bonds that formed between the polyaniline and Ni3S2. In addition, the lightweight carbon fiber support served as both a current collector and flexible support. The prepared CF/Ni3S2@PANI electrode exhibited a significantly enhanced specific capacity (715.3 F·g-1 at 1 A·g-1) compared with the carbon fiber/Ni3S2 electrode (318 F·g-1 at 1 A·g-1). More importantly, the assembled FASC device delivered an impressive energy density of 35.7 Wh·kg-1 at a power density of 850 W·kg-1. The FASC device benefited from the interconnected flexible microstructure and the stable bond bridges, so that it could be bent into various angles without noticeably impairing its performance. This effective protective strategy may further inspire the design and manufacture of metallic oxide or sulfide electrode with ultrahigh-stability interbond bridges for high-performance flexible supercapacitors.

Electronic structure of two-dimensional In and Bi metal on BN nanosheets.

The electronic structures of two-dimensional (2D) indium (In) and bismuth (Bi) metal on BN nanosheets are systematically studied using hybrid density functional theory (DFT). We found that 2D In and Bi metal effectively modulate the band gap of a BN nanosheet. We also found that the indirect band gap of the 2D In and Bi metal electronic structures are 0.70 and 0.09 eV, respectively. This modulation originates from the charge transfer between the 2D metal and BN nanosheet interfaces, as well as from the electron redistribution of the In/BN and Bi/BN heterojunctions of the s and p orbitals. Our results provide an insight into 2D In/BN and Bi/BN heterojunctions, which should be useful in the design of 2D In and Bi metal-semiconductor-based devices.

Effect of Off-Diagonal Exciton-Phonon Coupling on Intramolecular Singlet Fission.

Intramolecular singlet fission (iSF) materials provide remarkable advantages in terms of tunable electronic structures, and quantum chemistry studies have indicated strong electronic coupling modulation by high frequency phonon modes. In this work, we formulate a microscopic model of iSF with simultaneous diagonal and off-diagonal coupling to high-frequency modes. A nonperturbative treatment, the Dirac-Frenkel time-dependent variational approach is adopted using the multiple Davydov trial states. It is shown that both diagonal and off-diagonal coupling can aid efficient singlet fission if excitonic coupling is weak, and fission is only facilitated by diagonal coupling if excitonic coupling is strong. In the presence of off-diagonal coupling, it is found that high frequency modes create additional fission channels for rapid iSF. Results presented here may help provide guiding principles for design of efficient singlet fission materials by directly tuning singlet-triplet interstate coupling.

Identification of miRNAs Affecting the Establishment of Brassica Alboglabra Seedling.

MicroRNAs (miRNAs) are important for plant development including seed formation, dormancy, and germination, as well as seedling establishment. The Brassica vegetable seedling establishment stage influences the development of high quality seedlings, but also affects the nutrient content of sprouts. Chinese kale (Brassica alboglabra) seedlings at different growth stages were used to construct two small-RNA (sRNA) libraries. We comprehensively analyzed the miRNAs in 2- and 9-day-old seedlings. An average of 11,722,490 clean reads were generated after removing low-quality reads and adapter contaminants. The results revealed that 37.65 and 26.69% of the sRNAs in 2- and 9-day-old seedlings, respectively, were 24 nt long. In total, 254 known mature miRNA sequences from 228 miRNA families and 343 novel miRNAs were identified. Of these miRNAs, 224 were differentially expressed between the two analyzed libraries. The most abundant miRNAs identified by sequence homology were miR156, miR167, and miR157, each with more than 100,000 sequenced reads. Compared with the expression levels in 2-day-old seedlings, MiR8154 and miR390 were the most up- and down-regulated miRNAs respectively in 9-day-old seedlings. Gene ontology enrichment analysis of the differentially expressed-miRNA target genes affecting biological processes revealed that most genes were in the "regulation of transcription" category. Additionally, the expression patterns of some miRNAs and target genes were validated by quantitative real-time polymerase chain reaction. We determined that development-associated miRNAs (e.g., bal-miR156/157/159/166/167/172/396), were highly-expressed during seedling-establishment stage, as were stress-related (bal-miR408) and metabolism-related (bal-miR826) miRNAs. Combined with the low level of targets SPL9 and AP2, it was concluded that miR156-SPL9 and miR172-AP modules play key roles during the B. alboglabra seedling establishment stage.

Comparative Transcriptome Analyses Reveal a Special Glucosinolate Metabolism Mechanism in Brassica alboglabra Sprouts.

Brassica sprouts contain abundant phytochemicals, especially glucosinolates (GSs). Various methods have been used to enhance GS content in sprouts. However, the molecular basis of GS metabolism in sprouts remains an open question. Here we employed RNA-seq analysis to compare the transcriptomes of high-GS (JL-08) and low-GS (JL-09) Brassica alboglabra sprouts. Paired-end Illumina RNA-seq reads were generated and mapped to the Brassica oleracea reference genome. The differentially expressed genes were analyzed between JL-08 and JL-09. Among these, 1477 genes were up-regulated and 1239 down-regulated in JL-09 compared with JL-08. Enrichment analysis of these differentially expressed genes showed that the GS biosynthesis had the smallest enrichment factor and the highest Q-value of all metabolic pathways in Kyoto Encyclopedia of Genes and Genomes database, indicating the main metabolic difference between JL-08 and JL-09 is the GS biosynthetic pathway. Thirty-seven genes of the sequenced data were annotated as putatively involved in GS biosynthesis, degradation, and regulation, of which 11 were differentially expressed in JL-08 and JL-09. The expression level of GS degradation enzyme myrosinase in high-GS JL-08 was lower compared with low-GS JL-09. Surprisingly, in high-GS JL-08, the expression levels of GS biosynthesis genes were also lower than those in low-GS JL-09. As the GS contents in sprouts are determined by dynamic equilibrium of seed stored GS mobilization, de novo synthesis, degradation, and extra transport, the result of this study leads us to suggest that efforts to increase GS content should focus on either raising GS content in seeds or decreasing myrosinase activity, rather than improving the expression level of GS biosynthesis genes in sprouts.