A Security-Enhanced Image Communication Scheme Using Cellular Neural Network.

In the current network and big data environment, the secure transmission of digital images is facing huge challenges. The use of some methodologies in artificial intelligence to enhance its security is extremely cutting-edge and also a development trend. To this end, this paper proposes a security-enhanced image communication scheme based on cellular neural network (CNN) under cryptanalysis. First, the complex characteristics of CNN are used to create pseudorandom sequences for image encryption. Then, a plain image is sequentially confused, permuted and diffused to get the cipher image by these CNN-based sequences. Based on cryptanalysis theory, a security-enhanced algorithm structure and relevant steps are detailed. Theoretical analysis and experimental results both demonstrate its safety performance. Moreover, the structure of image cipher can effectively resist various common attacks in cryptography. Therefore, the image communication scheme based on CNN proposed in this paper is a competitive security technology method.

Thermal Decomposition Mechanism and Fire-Extinguishing Performance of trans-1,1,1,4,4,4-Hexafluoro-2-butene: A Potential Candidate for Halon Substitutes.

In view of the appropriate physicochemical characteristics and environmental friendliness of the trans-1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz(E)) substance, the thermal-decomposition mechanism as well as the fire-extinguishing mechanism and performance of this agent were systematically studied by employing both experimental and theoretical methods in this work. We found that the HFO-1336mzz(E) agent not only has promising thermal stability at room temperature but also exhibits pronounced fire-extinguishing performance, which is comparable to that of HFC-236fa and even better than that of HFC-125 extinguishant. Additionally, the promising fire-extinguishing performance of HFO-1336mzz(E) may result from the physical and chemical extinguishing effect of its thermal-decomposition products including HFO-1336mzz(Z), HC≡CCF3, CF3C≡CCF3, and CF3H, which makes a significant contribution to capturing the free radicals in the flame, as well as cooling and diluting the combustible fuel-air mixture. Both experimental and theoretical results suggest that the HFO-1336mzz(E) agent is a highly recommendable candidate for Halon extinguishant, which is worthy of further investigation and evaluation of its practical applicability in fire-suppression utilization.

Be(2)C monolayer with quasi-planar hexacoordinate carbons: a global minimum structure.

The design of new materials is an important subject in order to attain new properties and applications, and it is of particular interest when some peculiar topological properties such as reduced dimensionality and rule-breaking chemical bonding are involved. In this work, we designed a novel two-dimensional (2D) inorganic material, namely Be2 C monolayer, by comprehensive density functional theory (DFT) computations. In Be2 C monolayer, each carbon atom binds to six Be atoms in an almost planar fashion, forming a quasi-planar hexacoordinate carbon (phC) moiety. Be2 C monolayer has good stability and is the lowest-energy structure in 2D space confirmed by a global minima search based on the particle-swarm optimization (PSO) method. As a semiconductor with a direct medium band gap, Be2 C monolayer is promising for applications in electronics and optoelectronics.

In Situ Construction of Elastic Solid-State Polymer Electrolyte with Fast Ionic Transport for Dendrite-Free Solid-State Lithium Metal Batteries.

Solid-state lithium metal batteries (LMBs) have been extensively investigated owing to their safer and higher energy density. In this work, we prepared a novel elastic solid-state polymer electrolyte based on an in situ-formed elastomer polymer matrix with ion-conductive plasticizer crystal embedded with Li6.5La3Zr1.5Ta0.5O12 (LLZTO) nanoparticles, denoted as LZT/SN-SPE. The unique structure of LZT/SN-SPE shows excellent elasticity and flexibility, good electrochemical oxidation tolerance, high ionic conductivity, and high Li+ transference number. The role of LLZTO filler in suppressing the side reactions between succinonitrile (SN) and the lithium metal anode and propelling the Li+ diffusion kinetics can be affirmed. The Li symmetric cells with LZT/SN-SPE cycled stably over 1100 h under a current density of 5 mA cm-2, and Li||LiFePO4 cells realized an excellent rate (92.40 mAh g-1 at 5 C) and long-term cycling performance (98.6% retention after 420 cycles at 1 C). Hence, it can provide a promising strategy for achieving high energy density solid-state LMBs.

Many M©B(n) boron wheels are local, but not global minima.

Twenty-six planar boron wheels with a central hypercoordinate atom (M©B(n), M is a 2nd or 3rd period element) were designed following the Schleyer-Boldyrev concept of geometric and electronic fit whereby in-plane σ- as well as π-aromaticity contribute to the chemical bonding. Global minimum searches using an efficient newly implemented method reveal that most of these boron wheels are only local, rather than global minima. However, the Be©B(8) triplet planar wheel global minimum is a new member of the planar hypercoordinate M©B(n) family. Six categories classify the structures of the other global minima: planar wheels, planar non-wheel forms, quasi-two-center-wheels, as well as leaf-like, pyramid-like, and umbrella-like geometries.

High Quality TaS2 Nanosheet SPR Biosensors Improved Sensitivity and the Experimental Demonstration for the Detection of Hg2.

TaS2 as transition metal dichalcogenide (TMD) two-dimensional (2D) material has sufficient unstructured bonds and large inter-layer spacing, which highly supports transporting and absorbing mercury ions. The structural characterizations and simulation data show that an SPR sensor with high sensitivity can be obtained with a TaS2 material-modified sensitive layer. In this paper, the role of TaS2 nanoparticles in an SPR sensor was explored by simulation and experiment, and the TaS2 layer in an SPR sensor was characterized by SEM, elemental mapping, XPS, and other methods. The application range of structured TaS2 nanoparticles is explored, these TaS2 based sensors were applied to detect Hg2+ ions at a detection limit approaching 1 pM, and an innovative idea for designing highly sensitive detection techniques is provided.

Liquid phase exfoliated boron nanosheets for all-optical modulation and logic gates.

Boron nanosheets possess unique photoelectric properties, including photosensitivity, photoresponse, and optical nonlinearity. In this article, we show the interaction between light and boron nanosheets in which concentric rings formed in the far field, which attributed to the strong Kerr nonlinearity of boron nanosheets. Furthermore, the distortion, regulation and relationship between the Kerr nonlinearity and effective mass or carrier mobility of the diffraction rings of boron nanosheets have been investigated. Our work shows that the spatial self-phase modulation effect of boron nanosheets is indeed caused by nonlocal electronic coherence. In addition, we have implemented all-light modulation and all-light logic gates based on the prepared boron nanosheets. We believe that our results will provide a powerful demonstration of nonlinear photonic devices based on boron nanosheets and a reference for photonic devices based on two-dimensional materials.

Interconnected Pd Nanoparticles Supported on Zeolite-AFI for Hydrogen Detection under Ultralow Temperature.

The stability for a hydrogen sensor is of crucial importance under a low-temperature range (e.g., 200-400 K), especially in critical environments (e.g., aerospace). However, the "reverse sensing behavior" of Pd-based sensing materials at low temperatures limits their wide application. Herein, a three-dimensional (3D) hydrogen-sensing material of interconnected Pd nanoparticles supported on zeolite-AFI (zeolite-AFI@Pd NPs) is designed for the hydrogen sensor at low temperature. The interconnected Pd NPs of ∼15 nm in diameter are achieved onto the zeolite-AFI framework by reduction-controlled self-assembly growth, followed by partially etching-off zeolite. The 3D structure provides a larger surface ratio for improving hydrogen adsorption onto Pd, and more space for PdHx intermediate expansion, which effectively facilitates response to hydrogen and suppresses the α-ß phase transition. Remarkably, there is no "reverse sensing behavior" observed in zeolite-AFI@Pd NPs, though temperature is as low as to 200 K compared with that of pristine Pd nanowires at 287 K. Furthermore, the zeolite-AFI@Pd NPs sensors yield excellent sensing response and high stability to hydrogen at temperature from 200 to 400 K. Such Zeolite-AFI@Pd NPs sensors are expected to detect hydrogen leakage, especially in critical environments of low temperature.

Nonlinear optical response, all optical switching, and all optical information conversion in NbSe2 nanosheets based on spatial self-phase modulation.

An efficient liquid phase exfoliation method has been developed for the preparation of high quality NbSe2 nanosheets. The pure nonlinear optical properties of these nanosheets have been investigated using three different wavelength continuous wave (CW) lasers. The spatial self-phase modulation (SSPM) effect can be observed clearly in solution dispersions of (NbSe2). The experimental data show that the diffraction is caused by the third-order optical nonlinearity of NbSe2. The third-order nonlinearity susceptibility χ(3) of NbSe2 is about 10-9 e.s.u. by analyzing the experimental results. The relaxation time in the dynamic relaxation is about 1.38 s, 1.58 s, and 1.15 s for 532 nm, 671 nm, and 457 nm, respectively. In addition, the realization of all-optical switching based on SSPM, particularly two-color intrachromatic coherence, indicates that the generation of electron coherence is a universal characteristic of layered quantum materials. All optical information conversion based on the SSPM is also confirmed experimentally. Our experimental results have simple potential application prospects for NbSe2 based on its nonlinear optical response.

Theoretical Studies on the Electronic and Optical Properties of Honeycomb BC3 monolayer: A Promising Candidate for Metal-free Photocatalysts.

By employing first-principles computations and particle-swarm optimization calculations, we theoretically confirmed the honeycomb geometry of experimentally realized BC3 sheet, which is constructed by the hexagonal carbon-ring fragments surrounded by six boron atoms and has pronounced thermodynamic stabilities. Remarkably, the computations also demonstrate the visible-light absorption, high carrier mobilities, and promising reduction and oxidation capacities of the BC3 monolayer, indicating its efficient absorption of solar radiation, fast migration of electron and holes, and excellent capabilities of photoinduced carriers in a photocatalytic process, respectively. Additionally, its indirect band gap, spatially separated charge distributions, and great difference in mobilities of electrons and holes should lead to the restricted recombination of photoactivated e--h+ pairs within BC3 monolayer. All above-mentioned characteristics suggest that the honeycomb BC3 monolayer should be a recommendable candidate for metal-free photocatalysts, which is worthy of further verifications and explorations in experimental studies.

Evolution of Moiré Profiles from van der Waals Superstructures of Boron Nitride Nanosheets.

Two-dimensional (2D) van der Waals (vdW) superstructures, or vdW solids, are formed by the precise restacking of 2D nanosheet lattices, which can lead to unique physical and electronic properties that are not available in the parent nanosheets. Moiré patterns formed by the crystalline mismatch between adjacent nanosheets are the most direct features for vdW superstructures under microscopic imaging. In this article, transmission electron microscopy (TEM) observation of hexagonal Moiré patterns with unusually large micrometer-sized lateral areas (up to ~1 µm(2)) and periodicities (up to ~50 nm) from restacking of liquid exfoliated hexagonal boron nitride nanosheets (BNNSs) is reported. This observation was attributed to the long range crystallinity and the contaminant-free surfaces of these chemically inert nanosheets. Parallel-line-like Moiré fringes with similarly large periodicities were also observed. The simulations and experiments unambiguously revealed that the hexagonal patterns and the parallel fringes originated from the same rotationally mismatched vdW stacking of BNNSs and can be inter-converted by simply tilting the TEM specimen following designated directions. This finding may pave the way for further structural decoding of other 2D vdW superstructure systems with more complex Moiré images.

Oxidative Etching of Hexagonal Boron Nitride Toward Nanosheets with Defined Edges and Holes.

Lateral surface etching of two-dimensional (2D) nanosheets results in holey 2D nanosheets that have abundant edge atoms. Recent reports on holey graphene showed that holey 2D nanosheets can outperform their intact counterparts in many potential applications such as energy storage, catalysis, sensing, transistors, and molecular transport/separation. From both fundamental and application perspectives, it is desirable to obtain holey 2D nanosheets with defined hole morphology and hole edge structures. This remains a great challenge for graphene and is little explored for other 2D nanomaterials. Here, a facile, controllable, and scalable method is reported to carve geometrically defined pit/hole shapes and edges on hexagonal boron nitride (h-BN) basal plane surfaces via oxidative etching in air using silver nanoparticles as catalysts. The etched h-BN was further purified and exfoliated into nanosheets that inherited the hole/edge structural motifs and, under certain conditions, possess altered optical bandgap properties likely induced by the enriched zigzag edge atoms. This method opens up an exciting approach to further explore the physical and chemical properties of hole- and edge-enriched boron nitride and other 2D nanosheets, paving the way toward applications that can take advantage of their unique structures and performance characteristics.

Al2C monolayer: the planar tetracoordinate carbon global minimum.

Inspired by our theoretical finding that C2Al6(2-) has a planar D2h minimum with two planar tetracoordinate carbons (ptCs), we computationally designed a new two-dimensional (2D) inorganic material, an Al2C monolayer. All carbons in this monolayer are ptC's, stabilized inductively by binding to four electropositive Al atoms in the same plane. The Al2C monolayer is semiconducting with an indirect minimum band gap and a slightly larger direct band gap. Good persistence of the Al2C monolayer is indicated by its moderate cohesive energy, the absence of imaginary modes in its phonon spectrum, and the high melting point predicted by molecular dynamics (MD) simulations. Moreover, a particle-swarm optimization (PSO) global minimum search found the Al2C monolayer to be the lowest-energy 2D structure compared to other Al2C alternatives. Dividing the Al2C monolayer results in one-dimensional (1D) Al2C nanoribbons, which are computed to have quite rich characteristics such as direct or indirect band gaps with various values, depending on the direction of the division and the resulting edge configuration.

Scalable holey graphene synthesis and dense electrode fabrication toward high-performance ultracapacitors.

Graphene has attracted a lot of attention for ultracapacitor electrodes because of its high electrical conductivity, high surface area, and superb chemical stability. However, poor volumetric capacitive performance of typical graphene-based electrodes has hindered their practical applications because of the extremely low density. Herein we report a scalable synthesis method of holey graphene (h-Graphene) in a single step without using any catalysts or special chemicals. The film made of the as-synthesized h-Graphene exhibited relatively strong mechanical strength, 2D hole morphology, high density, and facile processability. This scalable one-step synthesis method for h-Graphene is time-efficient, cost-efficient, environmentally friendly, and generally applicable to other two-dimensional materials. The ultracapacitor electrodes based on the h-Graphene show a remarkably improved volumetric capacitance with about 700% increase compared to that of regular graphene electrodes. Modeling on individual h-Graphene was carried out to understand the excellent processability and improved ultracapacitor performance.