Promoted catalytic property of Cu/SSZ-13 by introducing a minority of Mn for NO removal from diesel engine exhaust

The Cu-exchanged SSZ-13 with the small-pore chabazite framework is considered as a highly efficient catalyst for selective catalytic reduction of NO with NH_(3)(NH_(3)-SCR).In order to further improve the catalytic property,a series of Mn ion-assisted Cu/SSZ-13 powder catalysts were prepared by co-exchange method and stepwise exchange method.It is found that the NH_(3)-SCR activity,N_(2) selectivity,hydrothermal stability and sulfur resistance of Cu/SSZ-13 are promoted by introducing a minority of Mn(0.15%to 0.23%(mass))through co-exchange method.Characterization results reveal that the Cu,Mn co-exchange enables the higher amounts of Cu^(2+)active sites,the abundant medium strong and strong acid,the optimized ratio of Lewis acid to Brønsted acid etc.,which are required for a good NH_(3)-SCR catalytic property over broad temperature range and under harsh working environment.Moreover,a monolithic catalyst was prepared by impregnating a cordierite ceramic support into the coating slurry containing the optimized CuMn/SSZ-13 powder.The diesel engine bench tests show that Cu,Mn co-exchange gives the monolith catalyst a better catalytic property than commercial catalysts.This work provides an important guidance for the rational design of secondary-ion-assisted zeolites applied in NH_(3)-SCR.

氧化石墨烯改性阻燃聚酯的非等温结晶动力学

为改善聚对苯二甲酸乙二醇酯(PET)的阻燃性能,设计了氧化石墨烯(GO)改性2-羧乙基苯基次磷酸(CEPPA)阻燃聚酯(PET)体系(CPET-GO)。通过Hummers法制备GO,采用原位聚合法制备CPET-GO复合物,并对其阻燃性能进行研究。借助锥形量热仪及极限氧指数仪对复合物的燃烧及阻燃性能进行表征。针对聚合物力学性能受微观晶型结构影响的问题,借助差示扫描量热仪对CPET-GO的非等温结晶行为进行表征,用Jeziorny法修正的Avrami方程分析CPET-GO结晶前期的非等温结晶行为。结果表明,与PET相比CPET-0.1G的极限氧指数增加至28%,热释放速率峰值(PHRR)下降45.7%;在结晶初期,Jeziorny法修正后的结晶速率常数(Z_(c))为0.37~1.00;与CPET相比,添加质量分数为0.1%的GO(CPET-0.1G)时,样品的半结晶时间(t_(1/2))缩短;随GO添加量增加,CPET-GO的Z_(c)降低、t_(1/2)延长。

Deep Q-Learning Based Computation Offloading Strategy for Mobile Edge Computing

To reduce the transmission latency and mitigate the backhaul burden of the centralized cloud-based network services,the mobile edge computing(MEC)has been drawing increased attention from both industry and academia recently.This paper focuses on mobile users’computation offloading problem in wireless cellular networks with mobile edge computing for the purpose of optimizing the computation offloading decision making policy.Since wireless network states and computing requests have stochastic properties and the environment’s dynamics are unknown,we use the modelfree reinforcement learning(RL)framework to formulate and tackle the computation offloading problem.Each mobile user learns through interactions with the environment and the estimate of its performance in the form of value function,then it chooses the overhead-aware optimal computation offloading action(local computing or edge computing)based on its state.The state spaces are high-dimensional in our work and value function is unrealistic to estimate.Consequently,we use deep reinforcement learning algorithm,which combines RL method Q-learning with the deep neural network(DNN)to approximate the value functions for complicated control applications,and the optimal policy will be obtained when the value function reaches convergence.Simulation results showed that the effectiveness of the proposed method in comparison with baseline methods in terms of total overheads of all mobile users.

A new ellipse fitting method of the minimum differential-mode noise in the atom interference gravimeter

Ellipse fitting is a useful tool to obtain the differential signal of two atom interference gravimeters. The quality standard of ellipse fitting should be the deviation between the true phase and the fitting phase of the interference fringe. In this paper, we present a new algorithm to fit the ellipse. The algorithm is to minimize the differential noise of two interference gravimeters and obtain a more accurate value of the gravity gradient. We have theoretically derived the expression of the differential-mode noise and implemented the ellipse fitting in the program. This new algorithm is also compared with the classical methods.

Research on phase shift characteristics of electromagnetic wave in plasma

The phase shift characteristics reflect the state change of electromagnetic wave in plasma sheath and can be used to reveal deeply the action mechanism between electromagnetic wave and plasma sheath.In this paper,the phase shift characteristics of electromagnetic wave propagation in plasma were investigated.Firstly,the impact factors of phase shift including electron density,collision frequency and incident frequency were discussed.Then,the plasma with different electron density distribution profiles were employed to investigate the influence on the phase shift characteristics.In a real case,the plasma sheath around the hypersonic vehicle will affect and even break down the communication.Based on the hypersonic vehicle model,we studied the electromagnetic wave phase shift under different flight altitude,speed,and attack angle.The results indicate that the phase shift is inversely proportional to the flight altitude and positively proportional to the flight speed and attack angle.Our work provides a theoretical guidance for the further research of phase shift characteristics and parameters inversion in plasma.

Attenuation characteristics of obliquely incident electromagnetic wave in weakly ionized dusty plasma based on modified Bhatnagar-Gross-Krook collision model

The attenuation characteristics of obliquely incident electromagnetic(EM) wave in L-Ka frequency band in weakly ionized dusty plasma are analyzed based on the modified Bhatnagar-Gross-Krook(BGK) collision model.According to the kinetic equation and the charging theory,the total complex dielectric constant of the weakly ionized dusty plasma is derived by considering that the minimum velocity of the electron accessible to the dust particle surface is non-zero and the second potential part of the collision cross-section contributes to the charging.The attenuation characteristics within the modified model are compared with those within the traditional model.The influence of the dusty plasma parameters and the incident angle of EM waves on the attenuation in weakly ionized dusty plasma is further analyzed.Finally,the influence of different reentry heights on the attenuation characteristics of the obliquely incident EM wave is discussed.The results show that the effect of the minimum electron velocity and the second term of the collision cross-section on the attenuation characteristics of EM waves cannot be ignored.When the dust density and dust radius are changed,the trends of the attenuation of obliquely incident EM waves are consistent,but the influence of dust density is weaker than that of dust radius due to the constraint of orbit-limited motion(OLM) theory.The plasma thickness,electron density,and incident angle are proportional to the attenuation amplitude of EM waves.The effect of different reentry heights on the attenuation obliquely incident EM waves is related to the electron density and plasma thickness.

Dead-zone-free atomic magnetometer based on hybrid Poincarébeams

In this paper,we present the experiment and the theory scheme of light-atom interaction in atomic magnetometers by using a hybrid Poincarébeam(HPB)to solve an annoying problem,named“dead zone.”This kind of magnetometer can be sensitive to arbitrary directions of external magnetic fields.The HPB has a complex polarization distribution,consisting of a vector radially polarized beam and a scalar circularly polarized beam in our experiment.These two kinds of beams have different directions of dead zones of external magnetic fields;thereby,the atomic magnetometer with an HPB can avoid the non-signal area when the direction of the external magnetic field is in the plane perpendicular to the light polarization plane.Furthermore,the optical magnetic resonance(OMR)signal using an HPB still has no dead zones even when the direction of the external magnetic field is in the plane parallel to the polarization plane in our scheme.Our work has the potential to simplify and optimize dead-zone-free atomic magnetometers.

Refocusing of the optical branched flow on a rough curved surface

The phenomenon of branched flow has attracted researchers since its inception,with recent observations of the light branching on soap bubbles.However,previous studies have primarily focused on the flat spacetime,overlooking the effect of surface curvature on branched flows.In this paper,we explore the branched flow phenomenon of light on a rough curved surface called constant Gaussian curvature surfaces(CGCSs).Compared with flat space,a CGCS demonstrates that the first branching point advances due to the focusing effect of the positive curvature of the surface.Furthermore,unlike on flat space,optical branches on curved surfaces do not consistently become chaotic during its transmission in a random potential field.On the contrary,the“entropy”decreases at specific positions,which reveals a sink flow phenomenon following the generation of branched flows.This result highlights the time inversion characteristics of CGCSs.Lastly,we demonstrated that the anomalous entropy reduction is related to the transverse and longitudinal coherence transformations of light.We suppose these efforts would fuel further investigation of the thermodynamic evolution and spatiotemporal inversion of random caustics,as well as their future application in the information transmission of random potentials in curved spacetime.

Participation in the absolute gravity comparison with a compact cold atom gravimeter

The first Asia-Pacific Comparison of Absolute Gravimeters(APMP.M.G-K1) was organized by the National Institute of Metrology(NIM) of China from December 21, 2015 to March 25, 2016 in Changping, Beijing. Our compact cold atom gravimeter(CCAG) was transported from Hangzhou to Beijing with a long distance of about1200 km to participate in this comparison. The CCAG is the only one, to the best of our knowledge, that is based on the principle of atom interferometry among all the instruments. Absolute gravity in the indicated three test sites has been measured as requested by the organizer. The sensitivity of our CCAG is estimated to be90 μGal∕Hz p, even when the measurements are carried out without any vibration isolation. Besides, the accuracy of this gravimeter has been evaluated to be about 19 μGal by considering the significant system errors.Our results show a good agreement with the given reference value.

Vibration compensation of an atom gravimeter

For most atom interferometers, the vibration isolation unit is applied to reduce vibration noise. In our experiment, instead of isolation, the vibration signals are monitored, and combining with the sensitive function, the compensation phase shift for the atom interferometer is obtained. We focus on the correction over a wide spectrum rather than on "monochromatic" frequencies. The sensitivity of the atom gravimeter can be upgraded by a factor of more than two. Furthermore, we demonstrate that the atom interferometer can still produce a good measurement result without passive vibration isolation in extremely noisy environments by using vibration compensation.