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The three-way catalysts (TWC) are required to have high thermal stability and excellent catalytic activity. The MgAl2O4 spinel is a thermal stable material, but its reactivity is unsatisfactory. In this work, CeO2 was used as a promoter to modify MgAl2O4 spinel, and the cerium modified MgAl2O4 spinel (MAC) was applied as the carrier to construct PdCu/MAC catalyst. The catalytic activity evaluation showed that modifying MgAl2O4 spinel with a handful of cerium (0.12 mol-Ce/mol-Mg) dramatically improved the three-way catalytic activity, especially for the elimination of NOx and C3H8. The XRD and XPS proved that these cerium cations incorporated into spinel lattices and occupied Al sites. For this reason, the cerium in PdCu/MAC-1 is mainly in +3 valence (Ce3+/Ce = 60.2%), which is accompanied by the formation of abundant oxygen vacancies (45.9%). These factors significantly promoted the dispersion of PdCu nanoparticles, and thus strengthened metal-support interaction, consequently the enhanced catalytic performance. However, adding excessive cerium (0.24 mol-Ce/mol-Mg) resulted in negative effect. This might be related to the appearance of isolated CeO2 crystal originating from the separate nucleation of excessive cerium cations. This work provides some guidance for developing TWC with both high thermal stability and activity. [ABSTRACT FROM AUTHOR]

Thermal homeostasis is vital for mammals and is controlled by brain neurocircuits. Yet, the neural pathways responsible for cold defense regulation are still unclear. Here, we found that a pathway from the lateral parabrachial nucleus (LPB) to the dorsomedial hypothalamus (DMH), which runs parallel to the canonical LPB to preoptic area (POA) pathway, is also crucial for cold defense. Together, these pathways make an equivalent and cumulative contribution, forming a parallel circuit. Specifically, activation of the LPB → DMH pathway induced strong cold-defense responses, including increases in thermogenesis of brown adipose tissue (BAT), muscle shivering, heart rate, and locomotion. Further, we identified somatostatin neurons in the LPB that target DMH to promote BAT thermogenesis. Therefore, we reveal a parallel circuit governing cold defense in mice, which enables resilience to hypothermia and provides a scalable and robust network in heat production, reshaping our understanding of neural circuit regulation of homeostatic behaviors. The neural mechanisms responsible for cold defense regulation are still unclear. Here, authors show parallel thermogenic pathways from the brain stem to the hypothalamus work together to enable resilience to cold temperature exposure and hypothermia. [ABSTRACT FROM AUTHOR]

In this paper, we prepared a series of Ce1-xTixO2 (x = 0–0.20) nanorods by hydrothermal method, which were used to construct the PdCu/Ce1−xTixO2 catalysts. The Ce1−xTixO2 and PdCu/Ce1−xTixO2 samples were characterized by transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), N2 adsorption–desorption, X-ray diffraction (XRD), inductively coupled plasma optical emission spectrometer (ICP-OES), etc. Catalytic activity, stability, and repeatability of the catalysts for methanol oxidation were investigated. The results show that doping a proper amount of titanium could strengthen the interaction between Ce1−xTixO2 support and PdCu nanoalloy, thus increasing the oxygen vacancy concentration and promoting Pd species with a higher oxidation state. These modified properties are beneficial for the deep oxidation of methanol. The light-off temperature (T50) and full-conversion temperature (T90) of methanol over the PdCu/CeO2 catalyst are 108 °C and 159 °C, respectively. The greatest activity improvement is found for PdCu/Ce0.9Ti0.1O2, which shows the lowest T50 of 88 °C and T90 of 138 °C. Furthermore, neither PdCu/CeO2 nor the modified PdCu/CeO2 catalyst produces by-products and exhibit excellent stability and repeatability throughout the whole test period. This study provides a reference for in-depth understanding and designing of efficient and stable CeO2-based oxidation catalysts. [ABSTRACT FROM AUTHOR]

To establish the dynamic model of machine tool structure is an important means to assess the performance of the machine tool structure during the cutting process. It is necessary to study the dynamics of the machine tools in different configurations for the sake of analyzing the dynamic behavior of the machine tools in the entire workspace. In this paper, a robust approach is presented to build an efficient and reliable dynamic model to evaluate the position-dependent dynamics of the twin ball screw (TBS) feed system. First, the TBS feed system is divided into several components, and a finite element (FE) model is built for each component. Second, the Craig-Bampton method is proposed to reduce the order of the substructures. Third, a multipoint constraints (MPCs) method was introduced to model the mechanical joint substructures of the TBS system, and the spring-damper element (SDE) is employed to connect the condensation nodes. Finally, a series experimental tests and full-order FE analysis are conducted on the self-designed TBS worktable in the four positions to validate the effectiveness of the proposed dynamic model. The results show that the proposed approach evaluates accurately the position-dependent behavior of the TBS system. [ABSTRACT FROM AUTHOR]

Optimal design parameter combination and transmission optimization for plane-generated enveloping toroid hourglass worm drive are proposed. The modeling frame and mathematical model of the worm were constructed first to provide a perfect transmission. Then, the mathematical representations of transmission performance, including lubrication angle, induced normal curvature, and length of meshing line for worm drive, were derived according to differential geometry and coordinate transformation approach. In addition, the influence of various design parameters on transmission performance was associated with main parameters, and the influence of the main parameters on transmission was evaluated. Next, a multivariate transmission optimization considering lubrication effect, bearing capacity and contact strength was conducted in view of the whole meshing cycle. The optimal global solution of the multivariate optimization model was also evaluated using a genetic algorithm. Calculation and experimental results indicated the optimization study was in good agreement with experimental results. Finally, the comprehensive transmission performance of the worm drive has an increase of 9.2 %. [ABSTRACT FROM AUTHOR]

The nonsynchronous error of the dual-driven feed system seriously affects the positioning and machining accuracy of CNC machine tools. Improving the positioning error is an extremely important task as it determines the geometric accuracy of the manufactured parts. In this paper, a Multivariate Orthogonal Polynomial Regression model has been developed to predict the positioning error in terms of motion parameters such as position and speed of the X1 and X2 axes of the dual-driven worktable. Orthogonal Experimental Design has been engaged in conducting experiments. The positioning errors are measured by a dual-frequency laser interferometer. In addition, a real-time error compensation system is developed based on the proposed active compensation control strategy in the dual-driven feed system controlled by Beckhoff motion control card. Experimental results show that the proposed positioning error model and error compensation strategy can be utilized as an effective manner to improve the accuracy of dual-driven CNC machine tools. [ABSTRACT FROM AUTHOR]