Weak Complexes Research Articles

Low lattice thermal conductivity of two-dimensional monolayers of BxN (x = 2, 3, and 5) induced by complex bonding networks: A comparative study with h-BN

It is well known that different bonding networks could bring a wide variety of physical properties to the materials although they hold analogous element and structure features. In this paper, we present a first-principles calculation about the lattice dynamics and phonon transport properties of two-dimensional (2D) boron-rich material BxN (x = 2, 3, and 5). The calculations show that besides the obvious differences in electrical properties compared to h-BN, the special bonding environment in these boron-rich materials also results in quite different phonon behaviors, where their thermal conductivity is at least one order of magnitude smaller than that of h-BN. By performing bonding and lattice dynamics analysis, we reveal that such dramatic reduction of conductivity is attributed to the synergistic effect of weak bond strength (low phonon group velocity) and complex bonding network (strong phonon scattering). Relative regular residual analysis further indicates that the four-phonon process is limited in BxN, and the three-phonon scattering is sufficient to describe their anharmonicity. Starting from the basic physical mechanism, the present study sheds light on the thermal transport properties of 2D boron-rich BxN compounds, which could provide useful insight for their widespread applications in thermal management.

Binocular vision measurement for large-scale weakly textured ship hull plates using feature points encoding method

The accurate forming measurement for curved hull plates is vital to ensure the quality of shipbuilding. However, the weak texture, large scale and complex shapes of curved hull plates present challenges for shape inspections. To enrich the texture of plates, checkerboard patterns are combined with the binocular vision system. Moreover, calculating the sub-pixel coordinates of corner points enhances reconstruction accuracy. A novel encoding method for the feature points on the complex shaped plates with repeatable texture is proposed to match the homologous points correctly. Finally, three dimensional coordinates are obtained by triangulation. Experimental results show that the dimensional accuracy is 300 ± 0.636 mm and the average accuracy is ±0.219 mm by registration. Inspection processes are completed within 1 min. This method is more automatic and convenient than contact measurement. Moreover, the efficiency is improved by about 2 times than multi-vision measuring method, enhancing the accuracy and efficiency of measurement for curved hull plates.

A Molecular Electron Density Theory Study of the Domino Reaction of N-Phenyl Iminoboranes with Benzaldehyde Yielding Fused Bicyclic Compounds.

The reaction of N-phenyl iminoborane with benzaldehyde yielding a fused aromatic compound, recently reported by Liu et al., has been studied within the Molecular Electron Density Theory (MEDT). Formation of the fused aromatic compound is a domino process that comprises three consecutive reactions: (i) formation of a weak molecular complex between the reagents; (ii) an intramolecular electrophilic attack of the activated carbonyl carbon of benzaldehyde on the ortho position of the N-phenyl substituent of iminoborane; and (iii) a formal 1,3-hydrogen shift yielding the final fused aromatic compound. The two last steps correspond to a Friedel-Crafts acylation reaction, the product of the second reaction being the tetrahedral intermediate of an electrophilic aromatic substitution reaction. However, the presence of the imino group adjacent to the aromatic ring strongly stabilizes the corresponding intermediate, being the reaction product when the ortho positions are occupied by t-butyl substituents. This domino reaction shows a great similitude with the Brønsted acid catalyzed Povarov reaction. Although N-phenyl iminoborane can experience a formal [2+2] cycloaddition reaction with benzaldehyde, its higher activation Gibbs free energy compared to the intramolecular electrophilic attack of the activated carbonyl carbon of benzaldehyde on the ortho position of the N-phenyl substituent, 6.6 kcal·mol-1, prevents the formation of the formal [2+2] cycloadduct. The present MEDT study provides a different vision of the molecular mechanism of these reactions based on the electron density.

Braided Liquid Crystal Elastomer Fiber Actuator with Programmable Deformation for Artificial Muscles

AbstractLiquid crystal elastomer fibers (LCEFs) are promising materials for constructing artificial muscles. However, the practical applications in smart wearable textiles and soft robots are still hindered due to their weak tensile performance and complex actuation integration. In this work, an LCEFs braided actuator is fabricated in which several LCEFs are integrated with silver‐plated nylon strands using the textile braiding method. The silver‐plated nylon strands can generate joule heat for triggering LCEFs and meanwhile strengthen the braided actuators. Owing to the braided structure, this LCEFs braided actuator exhibits large reversible contraction (34%) and actuation force (18.7 cN) with electrical stimulation at 0.6 V cm−1. An artificial arm and a soft pump based on the LCEFs braided actuators is successfully developed. The LCEFs braided actuator can lift 205 times its weight as an artificial biceps. And the soft pump can achieve cyclic contraction and relaxation motions similar to the cardiac muscle under electrical stimulation and reach an output flow rate of 111 µL s−1. This braided integration concept would broaden the potential applications of LCEFs.

Induction of chirality in the charge transfer complex photochemistry

Electron donor and acceptor undergo association in solution to form a weak molecular complex, namely a charge transfer complex. The formation of the complex is apparent by its new low-energy absorption band. Upon photoexcitation of this charge transfer band, an intracomplex electron transfer is facilitated to form a contact ion radical pair. The theoretical basis for the complex formation and the subsequent photoinduced electron transfer process has been well established already half a century ago. Nevertheless, the charge transfer complex photochemistry is now in a renaissance, due to its synthetic utility of its radical ion pair. By intentionally sidestepped unproductive back electron transfer process, a desired product is effectively obtained with or without external reagent and/or catalyst. In addition, the photoexcitation of the complex does not require any additional photocatalyst and often conceivable with the visible light. Accordingly, various donor/acceptor pairs and synthetic applications have been emerged as novel photoreaction systems in the last two decades. Some have also addressed the stereoselective transformations. This mini review highlights the recent progress of the asymmetric photoreaction, in particular in synthetic applications, based on the photoexcitation of the charge transfer complex, in comparison with photoredox catalysis.

Beta-Secretase 1 Recruits Amyloid-Beta Precursor Protein to ROCK2 Kinase, Resulting in Erroneous Phosphorylation and Beta-Amyloid Plaque Formation.

The amyloidogenic processing of APP depends on two events: its phosphorylation by ROCK2 (at Thr654) and the phosphorylation of the APP-cleaving enzyme BACE1 (at Ser498). However, the mechanisms and structural details of APP-ROCK2 and BACE1-ROCK2 binding are unknown. Using direct physical methods in combination with an in silico approach, we found that BACE1 binds into the substrate-binding groove of ROCK2 with a low affinity (Kd = 18 µM), while no binding of APP to ROCK2 alone could be detected. On the other hand, a strong association (Kd = 3.5 nM) of APP to the weak ROCK2-BACE1 complex was observed, although no stable ternary complex was detected, i.e., BACE1 was displaced by APP. We constructed a sequential functional model: (1) BACE1 weakly binds to ROCK2 and induces an allosteric conformational change in ROCK2; (2) APP strongly binds to the ROCK2-BACE1 complex, and BACE1 is released; and (3) ROCK2 phosphorylates APP at Thr654 (leading to a longer stay in the early endosome during APP processing). Direct fluorescence titration experiments showed that the APP646-664 or APP665-695 fragments did not bind separately to the ROCK2-BACE1 complex. Based on these observations, we conclude that two binding sites are involved in the ROCK2-APP interaction: (1) the substrate-binding groove, where the APP646-664 sequence containing Thr654 sits and (2) the allosteric binding site, where the APP665-695 sequence binds. These results open the way to attack the allosteric site to prevent APP phosphorylation at Thr654 by ROCK2 without inhibiting the activity of ROCK2 towards its other substrates.

Symmetry-breaking charge transfer in an excited acridine-dione derivative: Effects of hydrogen bonding, clustering, and cooperativity in mixtures of methanol and dimethylformamide

A theory of fluorescence quenching of photoexcited centrosymmetric acridine-dione derivative induced by H-bonding interactions with solvent in mixtures of methanol (MeOH) and N,N-dimethylformamide (DMF) is developed. The theory takes into account both dynamic and static mechanisms of the quenching. An unusual threshold-type dependence of the quenching efficiency on the concentration of methanol in the mixture observed earlier in experiment is analyzed theoretically under the following assumptions: (i) individual MeOH molecules and their short hydrogen-bonded clusters form weak complexes with the dye in solution and these interactions do not affect fluorescence kinetics significantly, (ii) long clusters form strongly bound complexes with the dye and thus induce symmetry-breaking intramolecular charge transfer and efficient quenching of fluorescence. These assumptions are consistent with the cooperative character of H-bonding in alcohols and allow one to explain the observed absence of quenching at MeOH concentrations below ∼9 M. A model of H-bond clustering in mixtures of alcohols and H-bond-accepting solvents is developed. The suggested approach gives a quantitative description of the observed concentration dependence of the fluorescence yield and well reproduces the non-exponential kinetics of the fluorescence decay measured in experiments. Since the degree of the charge transfer dissymmetry in these processes is sensitive to interactions between the dye and solvent, new possibilities emerge for experimental studies on details of H-bond clustering in protic solvents.

Study on electrosorption behavior of weak metal cyanide complex ions based on coal-based electrode

Using the electrosorption technology treatment the cyanide wastewater has a good treatment effect, but the mechanism is not completely clear. In this paper, we conducted electrosorption experiments using simulated cyanide solutions to study the adsorption kinetics, thermodynamics, adsorption isotherms and analyze the reaction mechanism of zinc-cyanide and copper–cyanide complex ions. The results show that the electrosorption process of weak metals cyanide complexes treated by coal-based (CB) electrode conforms to the second-order kinetic model and follow the Langmuir model, affected by the dipole force and exchange of coordination groups. The equilibrium adsorption amounts of the two species at 2 V were 1.53 and 1.74 times higher than those at open circuit, respectively. During the electrosorption process, affected by the pseudo-capacitance, pore structure of CB electrodes and the charges of complex ions, the zinc-cyanide complex is bound in the double electric layer on the anode surface by the electric field, but partly decomposed to produce zinc ions and forms Zn(OH)2 in alkaline solution then generates ZnO precipitates, a small amount of Zn2+ were electrostatically adsorbed on the cathode surface for reduction deposition. However, the majority of the copper–cyanide complexes were purified by electrostatic adsorption to the double layer near the anode, while a small amount of decomposition occurred to produce Cu(OH)2 in the alkaline system, and almost no copper was deposited by reduction. This research results can enable us to better understand the removal characteristics of the weak metal cyanide complex ions in the process of electrosorption by CB electrode, and have great significance for the application of electrosorption technology to the treatment of cyanide wastewater.

Recent growth increase in endemic Juglans boliviana from the tropical Andes

The spatial coverage of tree-ring chronologies in tropical South America is low compared to the extratropics, particularly in remote regions. Tree-ring dating from such tropical sites is limited by the generally weak temperature seasonality, complex coloration, and indistinct anatomical morphology in some tree species. As a result, there is a need to complement traditional methods of dendrochronology with innovative and independent approaches. Here, we supplement traditional tree-ring methods via the use of radiocarbon analyses to detect partial missing rings and/or false rings, and wood anatomical techniques to precisely delineate tree-ring boundaries. In so doing we present and confirm the annual periodicity of the first tree-ring width (TRW) chronology spanning from 1814 to 2017 for Juglans boliviana (‘nogal’), a tree species growing in a mid-elevation tropical moist forest in northern Bolivia. We collected 25 core samples and 4 cross-sections from living and recently harvested canopy-dominant trees, respectively. The sampled trees were growing in the Madidi National Park and had a mean age of 115 years old, with certain trees growing for over 200 years. Comparison of (residual and standard) TRW chronologies to monthly climate variables shows significant negative relationships to prior year May-August maximum temperatures (r = −0.54, p < 0.05) and positive relationships to dry season May-October precipitation (r = 0.60, p < 0.05) before the current year growing season. Additionally, the radial growth of Juglans boliviana shows a significant positive trend since 1979. Our findings describe a new and promising tree species for dendrochronology due to its longevity and highlight interdisciplinary techniques that can be used to expand the current tree-ring network in Bolivia and the greater South American tropics.

Research on Simulation Technology of Photoelectric Theodolite Based on Measured Infrared Image Sequence

Infrared image simulation[1] is an effective means to test, train and evaluate photoelectric theodolite, which has very important economic and military value. To solve the problems of weak pertinence, low fidelity, and complex algorithm of traditional infrared image simulation technology, this paper proposes a new infrared simulation technology based on a measured image sequence. Through automatic background stitching, moving target detection and extraction, a real-time fusion of target background, and infrared image simulation of real target/background is realized. The experimental results show that the technique has high accuracy and good real-time performance, and provides reliable technical support for the performance evaluation and personnel training of photoelectric theodolite.

Prediction of maximum tensile stress in plain-weave composite laminates with interacting holes via stacked machine learning algorithms: A comparative study

Plain weave composite is a long-lasting type of fabric composite that is stable enough when being handled. Open-hole composites have been widely used in industry, though they have weak structural performance and complex design processes. An extensive number of material/geometry parameters have been utilized for designing these composites, thereby an efficient computational tool is essential for that purpose. Different Machine Learning (ML) tools were integrated to obtain the model with the highest accuracy considering the maximum tensile stress of composite plates with two interacting notches while comparing the effectiveness of each technique. Finite Element (FE) simulations were carried out inside the ABAQUS software by employing python macro code to provide a data-rich framework (8960 data). The predictions given by ML methods were compared with the data given by the numerical simulations. An evolutionary algorithm (TPOT) and automatic neural network search (AuoKeras) were utilized for that purpose. An automatic grid search technique was employed to select the best method which could predict the material attribute target values (maximum stress) for different tests. 1% of the data was given as training while 99% was for testing to ensure the robustness of the model. It was concluded that the model containing the Gradient Boosting Regression (GBR), PolyFeatures, and LassoLarsCV algorithms outperformed other ML combinations and Artificial Neural Networks (ANN) for predicting the target value. The coefficient of determination (R2) and root mean square error (RMSE) of the proposed model were 0.97 and 253 respectively. Hence, this model could be utilized for prospective predictions in this type of materials and geometry by providing further reduction of the computational time and labor cost with high accuracy.

Elementary analytic functions in [formula omitted

It is known that rational approximations of elementary analytic functions (exp, log, trigonometric, and hyperbolic functions, and their inverse functions) are computable in the weak complexity class TC0. We show how to formalize the construction and basic properties of these functions in the corresponding theory of bounded arithmetic, VTC0.

Point–Line-Aware Heterogeneous Graph Attention Network for Visual SLAM System

Simultaneous localization and mapping (SLAM), as an important research topic in robotics, is useful but challenging to estimate robot pose and reconstruct a 3-D map of the surrounding environment. Despite recent success of several deep neural networks for visual SLAM, those methods cannot achieve robust results in complex industrial scenarios for constructing accurate and real-time maps due to the weak texture and complex geometric structure. This paper presents a novel and efficient visual SLAM system based on point–line-aware heterogeneous graph attention network, which combines points and line segments to solve the problem of the insufficient number of reliable features in traditional approaches. Firstly, a simultaneous feature extraction network is constructed based on the geometric relationships between points and points and points and lines. To further improve the efficiency and accuracy of the geometric association features of key regions, we design the point–line-aware attention module to guide the network to pay attention to the trivial features of both points and lines in images. Moreover, the network model is optimized by a transfer-aware knowledge distillation strategy to further improve the system’s real-time performance. Secondly, to improve the accuracy of the point–line matching, we design a point–line heterogeneous graph attention network, which combines an edge aggregation graph attention module and a cross-heterogeneous graph iteration module to conduct learning on the intragraph and intergraph. Finally, the point–line matching process is transformed into an optimal transport problem, and a near-iterative method based on a greedy strategy is presented to solve the optimization problem. The experiments on the KITTI dataset and a self-made dataset demonstrate the better effectiveness, accuracy, and adaptability of our method than those of the state of the art in visual SLAM.

From Behavioral Climate Models and Millennial Data to AGW Reassessment

Context. The so called AGW (Anthropogenic Global Warming), is based on thousands of climate simulations that indicate that human activity is virtually solely responsible for the recent global warming. The climate models used are derived from the meteorological models used for short-term predictions. They are based on the fundamental and empirical physical laws that govern the myriad of atmospheric and oceanic cells integrated by the finite element technique. Numerical approximations, empiricism and the inherent chaos in fluid circulations make these models questionable for validating the anthropogenic principle, given the accuracy required (better than one per thousand) in determining the Earth energy balance. Aims and methods. The purpose is to quantify and simulate behavioral models of weak complexity, without referring to predefined parameters of the underlying physical laws, but relying exclusively on generally accepted historical and paleoclimate series. Results. These models perform global temperature simulations that are consistent with those from the more complex physical models. However, the repartition of contributions in the present warming depends strongly on the retained temperature reconstructions, in particular the magnitudes of the Medieval Warm Period and the Little Ice Age. It also depends on the level of the solar activity series. It results from these observations and climate reconstructions that the anthropogenic principle only holds for climate profiles assuming almost no PCA neither significant variations in solar activity. Otherwise, it reduces to a weak principle where global warming is not only the result of human activity, but is largely due to solar activity.

First-principles study on the lattice thermal conductivity of layered Dirac semimetal BeN4

A novel two-dimensional Dirac semimetal BeN 4 was successfully synthesized in a recent experiment (Bykov et al. Phys. Rev. Lett. 126, 175501 (2021)). Here, we have studied the lattice thermal conductivities of bulk BeN 4 by the first-principles calculations. Due to the anisotropic crystal structure, the lattice thermal conductivities of BeN 4 show large anisotropy and the values at 300 K are 91.5, 42.1, and 5.0 W/m ⋅ K along the armchair, zigzag, and cross-plane directions respectively based on the three-phonon scattering. We also find that four-phonon scattering only reduces the lattice thermal conductivities of BeN 4 by about 9%. Due to the relatively weak Be-N bonds and complex crystal structure, BeN 4 has small phonon group velocities and large phonon anharmonicity, resulting in its much lower lattice thermal conductivity than that of hexagonal boron nitride and graphene. Our work would be helpful for future experimental and theoretical studies on the Dirac semimetal BeN 4 . • The lattice thermal conductivity of Dirac semi-metal BeN 4 was studied by the first-principles calculations. • BeN 4 has large anisotropic thermal conductivity due to its anisotropic crystal structure. • Despite the light elements, BeN 4 has a relatively low lattice thermal conductivity due to its large anharmonicity.

An Ice Age JWST inventory of dense molecular cloud ices

Icy grain mantles are the main reservoir of the volatile elements that link chemical processes in dark, interstellar clouds with the formation of planets and the composition of their atmospheres. The initial ice composition is set in the cold, dense parts of molecular clouds, before the onset of star formation. With the exquisite sensitivity of the James Webb Space Telescope, this critical stage of ice evolution is now accessible for detailed study. Here we show initial results of the Early Release Science programme Ice Age that reveal the rich composition of these dense cloud ices. Weak ice features, including 13CO2, OCN−, 13CO, OCS and complex organic molecule functional groups, are now detected along two pre-stellar lines of sight. The 12CO2 ice profile indicates modest growth of the icy grains. Column densities of the major and minor ice species indicate that ices contribute between 2% and 19% of the bulk budgets of the key C, O, N and S elements. Our results suggest that the formation of simple and complex molecules could begin early in a water-ice-rich environment. Using JWST, the molecules seen in planetary atmospheres can be traced back to their cold origins in ices formed in dense interstellar clouds, before the onset of star formation, revealing that chemical diversity and complexity is achieved early.

Rethinking attention mechanism in time series classification

The potential of attention mechanisms in time series classification (TSC) is limited owing to general drawbacks, like weak local perception and quadratic complexity. To promote the performance of attention mechanisms, we present a flexible multi-head linear attention (FMLA) architecture, which enhances locality awareness through layer-wise interactions with deformable convolutional blocks and online knowledge distillation. We develop a simple but effective mask mechanism that helps reduce noise influence in time series and reduces the redundancy of FMLA by probabilistically selecting and masking the positions of each given series. We use incremental ablation studies on 85 UCR2018 datasets to evaluate the performance of the main techniques developed. Experimental results demonstrate that FMLA outperformed 11 state-of-the-art TSC algorithms, obtaining a mean accuracy of 89.37%. FMLA achieved the best performance on 29 short-medium and 7 long time-series datasets regarding accuracy. FMLA has a complexity of ON, where N is the sample length. As N increases from 100 to 1000, the floating-point operations per second grow linearly from 0.13G to 1.34G.

A Computer Program For The System Of Weak Fuzzy Complex Numbers And Their Arithmetic Operations Using Python

Weak fuzzy complex number system is considered as a generalization of complex numbers by using an algebraic element with fuzzy property. It is believed that this new numerical system will play many important roles in various computer science disciplines, proceeding from this importance this paper aims to introduce for the first time the algebraic operations defined on weak fuzzy complex numbers using Python and Jupyter Notebook. Hence, by building a new class and its functions in Python for this new set, we can now use weak fuzzy complex numbers and the main arithmetic operations on them.

On Some Novel Results About Weak Fuzzy Complex Matrices

The objective of this paper is to study the algebraic properties of weak fuzzy complex matrices, where many elementary properties will be obtained such as the invertibility, the determinants, and the eigen values and vectors. In addition, a full solution of linear systems of weak fuzzy complex equations will be provided as an effective and easy algorithm. Also, many examples to clarify the validity of our approach.

On Weak Fuzzy Complex Pythagoras Quadruples

In this work, we study the generating of Pythagoras quadruples in the sets of weak fuzzy complex integers and anti-weak fuzzy complex integers, where we present sufficient and necessary conditions for generating Pythagoras quadruples in the mentioned sets. Also, we present many examples to clarify our work's validity and novelty.