Aspect sensitivity of polar mesosphere summer echoes observed with the EISCAT VHF radar

The European Incoherent Scatter Scientific Association (EISCAT) Very High Frequency (224 MHz) Radar has been used to investigate the aspect sensitivity of polar mesosphere summer echoes (PMSE) in the period 13–15 July 2010. The aspect sensitivity of PMSE using this radar and at such a high frequency has not been previously reported. Data concerning the aspect sensitivity of PMSE were collected by traversing the antenna beam from the zenith direction, and comparing the received power. Surprisingly, as the intensity received by the oblique beam was often larger than that of the vertical beam, suggesting the presence of tilted dusty plasma layers as a potential cause, a theoretical model was developed to confirm the existence of these layers and their formation process. The experimental results and theoretical model presented help elucidate the structural properties of the possible generation mechanism of strong radar echoes in the polar summer mesosphere region

An Optimization Model for Inventory System and the Algorithm for the Optimal Inventory Costs Based on Supply-Demand Balance

In order to investigate the inventory optimization of circulation enterprises, demand analysis was carried out firstly considering supply-demand balance. Then, it was assumed that the demand process complied with mutually independent compound Poisson process. Based on this assumption, an optimization model for inventory control of circulation enterprises was established with the goal of minimizing the average total costs in unit time of inventory system. In addition, the optimal computing algorithm for inventory costs was presented. Meanwhile, taking the agricultural enterprises in Aksu, Xinjiang, China, for example, the researchers conducted numerical simulation and sensitivity analysis. Through constantly adjusting and modifying the parameters values in model, the optimal stock and the optimal inventory costs were obtained. Therein, the numerical results showed that the uncertainty of lead time greatly influenced the optimal inventory strategy. Besides, it was demonstrated that the research results provided a valuable reference for the agricultural enterprises in terms of optimal management for inventory system

Single Ir Atoms Anchored on Ordered Mesoporous WO3 Are Highly Efficient for the Selective Catalytic Reduction of NO with CO under Oxygen-rich Conditions

Under oxygen-rich conditions, achieving a selective and efficient reduction of NO by CO is always challenging. Here, we report the synthesis of the catalyst consisting of single Ir atoms anchored on mesoporous WO3 (denoted as Ir-1/m-WO3) using a facile template method followed by wet impregnation. X-ray diffraction and transmission electron microscope studies indicated that the Ir atoms were distributed uniformly on the internal surface of m-WO3. When tested for the reduction of NO by CO, the Ir-1/m-WO3 catalyst with a low Ir loading of 0.28 wt % exhibited excellent catalytic performance in the presence of 2 vol % O-2 (volume ratio of CO to O-2 being 1 : 10), achieving a NO conversion of 73 % and N-2 selectivity of 100 % at 350 degrees C. In particular, its turnover frequency (TOF) value reached 0.30 s(-1) at 200 degrees C, which is six times higher than that of the catalyst with Ir nanoparticles supported on mesoporous WO3 (0.05 s(-1)). The superior catalytic performance of Ir-1/m-WO3 is attributed to the formation of the isolated Ir atoms and the more newly generated Ir-WO3 interfaces that can promote the adsorption and activation of NO, and the presence of accessible mesopores in m-WO3 that facilitates the mass transfer of NO and CO. This study brings a new fundamental understanding of active sites in Ir-based catalysts for the CO+NO reaction and provides a new way to the design and synthesis of single-atom catalysts, especially precious metal catalysts for emissions control

Subnanometric Pt on Cu Nanoparticles Confined in Y-zeolite: Highly-efficient Catalysts for Selective Catalytic Reduction of NOx by CO

CO selective catalytic reduction (CO-SCR), a promising technology for simultaneous removal of harmful CO and NO in exhaust gases, has attracted much attention in recent years. Pt-based catalysts have been demonstrated to be effective for this reaction. However, it remains a big challenge to achieve a high low-temperature activity at a low Pt loading. Here we report a new catalyst consisting of subnanometric Pt on Cu nanoparticles confined in the NaOH-modified Y-zeolite (Pt-Cu@M-Y). This catalyst possesses enhanced catalytic performance in CO-SCR at an extremely low Pt content of 0.04 wt %, achieving full NO conversion at 250 degrees C. The Pt-Cu@M-Y catalyst was synthesized using a simple impregnation method followed by a hydrogen reduction. Transmission electron microscopy study revealed that Pt-Cu@M-Y with subnanometric Pt on Cu nanoparticle of similar to 5 nm was highly dispersed in M-Y. The superior catalytic property of Pt-Cu@M-Y is attributed to the synergistic catalysis of Pt and Cu, in which subnanometric Pt species contributes to the strong adsorption of NO, while the dissociation of NO and the migration of dissociated O atoms are significantly boosted on the newly generated interfaces between Cu nanoparticles and the formed surface CuOx species. This work develops an effective method for synthesizing bimetallic nanoparticles confined in zeolite and demonstrates their superior catalytic performance in the catalytic reduction of NOx by CO

Simulation of localized electron density enhancement caused by high-pressure H2O gas release in ionosphere

Based on the continuity and momentum equations, a self-consistent simulation model is developed for describing the localized electron density enhancement caused by high-pressure H2O gas release in the ionosphere. The chemical reaction and momentum exchange process between the neutral gas and ionospheric plasma species are considered in the theoretical simulation model. The finite element method is used to solve the simulation model for H2O gas release, and the expansion and ionospheric disturbance process at the early stage of high-pressure gas release are studied. It is shown that the space expansion of the released gas is mainly dominated by the pressure difference between the H2O gas and the ionospheric plasma at the early stage of release. Then the diffusion process becomes the dominant process of the space transport of H2O molecules. An electron depletion region forms near the center of the release region due to the chemical reaction and collision process with H2O molecules. Meanwhile, an electron density enhancement region forms on both sides along the magnetic field direction due to the electron snowplow effect. With the increase in the released mass of H2O gas, the intensity and duration of the electron density enhancement increase gradually. With the release position rising, it is found that the intensity of the electron density enhancement has a peak near 380 km and the duration increases slightly with the increasing release height

Hierarchically interconnected porous MnxCo3-xO4 spinels for Low-temperature catalytic reduction of NO by CO

Developing efficient catalysts for low reaction-temperature catalytic reduction of NO by CO (CO-DeNO(x)) is desirable but very challenging. Here, we report that hierarchically interconnected porous (HIP) MnxCo3-xO4 spinels, synthesized by a facile citric acid-assisted sol-gel method, can act as highly efficient catalysts for CO-DeNO(x). The obtained Mn0.3Co2.7O4 displayed a much-enhanced catalytic performance with 87% NO removal at 100 degrees C and a wide active-temperature window (100-400 degrees C). Its superior activity stems from the following reasons: (i) the high-valence of Mn3+, Mn4+, and Co3+ species in the Co-O-Mn structure enables the high catalytic activity and the effective redox-cycling of the Co3+ and Co2+ adsorption sites; (ii) the HIP structure can significantly enhance gas diffusion. This work offers an avenue to design metal oxide catalysts for CO-DeNO(x) by effectively controlling the doping metal concentration and oxidation states of the active components. (C) 2022 Elsevier Inc. All rights reserved