A novel Ni/Cu dual catalysis gives rise to fundamentally new cooperative reactivity and enables the regio‐ and enantioselective propargylic alkylation reaction. A diverse set of α‐quaternary ...propargylated amino ester derivatives were synthesized in good yields with excellent enantioselectivity (up to 99 % ee). This work highlights the power of cooperative catalysis, which can be expected to have broad implications in homogeneous catalysis beyond the highly valuable synthetic intermediates.
It takes two: A highly efficient propargylic alkylation reaction was developed that delivers high yields with excellent enantiomeric ratios through dual Ni/Cu catalysis (up to 99 % ee). This Ni/Cu bimetallic system provides a reliable and a versatile approach for the development of a wide range of useful stereocontrolled reactions.
A multifunctionalized bovine serum albumin encapsulated platinum and silver alloys core–shell nanoparticles (Pt/Ag@BSA NPs)‐based electrochemiluminescence (ECL) immunosensor for ultrasensitive ...determination of tumor marker prostate‐specific antigen (PSA) has been designed. In this work, Pt/Ag@BSA core–shell nanoparticles with large surface area, favorable electrical conductivity, and biocompatibility were employed as ideal multifunctional carriers to effectively immobilize numerous luminol molecules and PSA capture antibodies (Anti‐PSA) acted as signal probe and molecule recognition probe, respectively. In addition, AuNPs were electrodeposited onto the indium tin oxide (ITO) to construct an outstanding base for this immunosensor, which could promote the electron transfer and load a large amount of multifunctionalized Pt/Ag@BSA nanoparticles. The constructed immunosensor could specifically capture PSA, which hindered the electron transfer of the ECL reaction between luminol and H2O2
because of the barrier of the attached immunoprotein layer and thereby resulted in the decrease of ECL intensity. Under the optimal conditions, ECL intensity of the immunosensor decreased linearly with the logarithm of PSA concentration ranging from 0.001 to 200 ng/mL with a low detection limit of 0.0003 ng/mL (S/N = 3). The proposed immunosensor exhibited high performances in sensitivity, reproducibility, stability, and specificity. Furthermore, the developed immunoassay has been applied to the detection of PSA in real serum samples with satisfactory results.
Two novel nonpneumatic tires named Tweel-2, designed based on the commercial Tweel model, and Saddle with hyperbolic paraboloid spokes are proposed in this study. Four nonpneumatic tire samples were ...successfully prepared with the 3D printing technology to measure and analyze and compare their properties. The results of quasi-static compression experiments showed that with the same relative density, the vertical bearing capacity of Tweel-2 tire was 1.4 times that of Tweel tire, while the vertical bearing capacity of the saddle tire was 4 times and 2.4 times that of Tweel and honeycomb tires, respectively. The finite element simulation method was used to explore the mechanism of improvement in vertical bearing capacity and energy absorption of the Tweel-2 and saddle design. The so-called circumferential unit in Tweel-2 and honeycomb tires enhances the deformation coordination between the spokes of Tweel-2 and increases the critical bearing capacity of the spokes by shortening the length of the deformation zone, so that more external work can be consumed under the same vertical deformation. The spatial configuration of the hyperbolic paraboloid can optimize the spatial stress distribution of the saddle tire and makes sure that a bigger amount of material deforms and participates in energy absorption, thus improving the overall strain energy level of the spokes.
Inspired by impact-resistant hedgehog spine and beetle's forewing, the thin-walled structures of simple hedgehog spine and multilevel hedgehog spine were designed. Numerical simulations of rigid flat ...plate impacting on thin-walled structures showed that the deformation coordination ability and stress distribution of the structure are improved effectively by the hedgehog spine section design. This makes the specific energy absorption of the simple hedgehog spine thin-walled structure just before failure increase to 9.6 times and 5.7 times those of the single-walled cylinder and simple spider web thin-walled structures, respectively. Furthermore, the sub-circle multilevel design was introduced to further increase the range of high strain energy density, and the specific energy absorption of the multilevel hedgehog spine thin-walled structure was 2.1 times that of the simple hedgehog spine thin-walled structure.
The development of general catalytic methods for the regio- and stereoselective construction of phosphoryl derivatives from identical substrates remains a formidable challenge in organic synthesis. ...Enabled by the newly developed BDPP-type ligands, we disclosed a nickel-catalyzed allenylation of phosphine oxides rationally and predictably, allowing the construction of versatile chiral allenylphosphoryl derivatives with high enantiopurity (up to 94% e.e.). Alternatively, using an achiral phosphine ligand dcypbz under acidic conditions, we achieved a regiochemical switch of the 1,3-dienylation to afford functionalized phosphinoyl 1,3-butadienes (up to 93% yield). The salient features of this method include switchable reactivity, broad substrate scope, readily available feedstock, single-step preparation, and high asymmetric induction.
The significant increase in the speed of high-speed trains has made the optimization of pantograph–catenary parameters aimed at improving current collection quality become one of the key issues that ...urgently need to be addressed. In this paper, a method and solutions are proposed for optimizing multiple pantograph–catenary parameters, taking into account the speed levels and engineering feasibility, for pantograph–catenary systems that contain dozens of parameters and exhibit strong nonlinear coupling characteristics. Firstly, a surrogate model capable of accurately predicting the standard deviation of contact force based on speed and 14 pantograph–catenary parameters was constructed by using the pantograph–catenary finite element model and feedforward neural network. Secondly, sensitivity analysis and rating of the pantograph–catenary parameters under different speeds were conducted using the variance-based method and the surrogate model. Finally, by combining the sensitivity analysis results and the Selective Crow Search Algorithm, joint optimization of 10 combinations of the pantograph–catenary parameters across the entire speed range was performed, providing efficient pantograph–catenary parameter optimization solutions for various engineering conditions.
Gradient porous structures are extensively studied in impact-resistant structures due to their light weight and high energy absorption. Different from existing studies, this article focuses on novel ...Voronoi structures with gradient perpendicular to impact direction, and compares their dynamic response with the uniform structure through numerical simulation. It shows that the novel gradient design comprehensively improves the impact resistance of Voronoi structures. Furthermore, density gradient is introduced into the one-dimensional shock model, and the theoretical solution of the plateau stresses at the impact end are compared with the simulation results, which verifies the correctness of the model in this article.
A novel brick-mud structure was proposed by introducing cell size gradient design into the nacre-like brick-mud microstructure. The gradient brick-mud structure samples were successfully prepared ...with the 3D printing technology. It was found through a pendulum impact test that the energy absorption of the gradient structure was higher than that of the uniform structure. With the gradient increase in the cell size, the energy absorption increased and could reach up to 4 times that of the uniform structure. A finite element simulation method was used to explore the energy absorption improvement mechanism of the gradient structure. The results showed that compared with the uniform structure, the gradient structure can achieve a much better stress distribution, which leads to greater bending deformation before fracture, thus improving strain energy storage. Moreover, the strain energy stored in the stiff material was about 2 times that of the soft material, and the strain energy stored in the interlayer soft material was 10 times that of the intralayer soft material.
As a traditional numerical simulation method for pantograph–catenary interaction research, the pantograph–catenary finite element model cannot be applied to the real-time monitoring of ...pantograph–catenary contact force, and the computational cost required for the multi-parameter joint optimization of the pantograph–catenary system with the finite element model is very high. In this paper, based on the selective crow search algorithm–radial basis function (SCSA-RBF) network, the time-domain signal of the panhead acceleration, which can be obtained in real-time through non-contact test technology, is taken as the boundary condition to directly solve the pantograph dynamic equation and a data-physics coupling model that can quickly predict the pantograph–catenary interaction is proposed. The prediction model is trained and verified using the dataset generated through the finite element model. Furthermore, the prediction model is applied to the multi-parameter joint optimization of six pantograph dynamic parameters and nine pantograph dynamic parameters, considering nonlinear panhead stiffness, and optimization suggestions under various speeds and filtering frequencies are given.
A consequence of nonlinearities is a multi-harmonic response via a mono-harmonic excitation. A similar phenomenon also exists in random vibration. The power spectral density (PSD) analysis of random ...vibration for nonlinear systems is studied in this paper. The analytical formulation of output PSD subject to the zero-mean Gaussian random load is deduced by using the Volterra series expansion and the conception of generalized frequency response function (GFRF). For a class of nonlinear systems, the growing exponential method is used to determine the first 3rd-order GFRFs. The proposed approach is used to achieve the nonlinear system’s output PSD under a narrow-band stationary random input. The relationship between the peak of PSD and the parameters of the nonlinear system is discussed. By using the proposed method, the nonlinear characteristics of multi-band output via single-band input can be well predicted. The results reveal that changing nonlinear system parameters gives a one-of-a-kind change of the system’s output PSD. This paper provides a method for the research of random vibration prediction and control in real-world nonlinear systems.
PDF
