Formation, distribution, and nature of Picea mongolica in China

Picea mongolica is an endemic and endangered species in China. Ecosystem made of Picea mongolica is a special sandy forest ecosystem in China. It is found at ecotone between forest and steppe, or agricultural district and pastoral area. Based on investigation, this paper discussed the formation and distribution of Picea mongolica and studied its nature according to ecotone theory. It is clarified that Picea mongolica belongs to Picea meyeri series. That is to say, it became a local race through long-term adaptation to the local climate, then formed allopatric semi-species, and finally turned into a taxonomical species. Picea mongolica forest is a super zonal climax community developing in ecotone between forest zone and steppe zone.

A Scalable Adaptive Approach to Multi-Vehicle Formation Control with Obstacle Avoidance

This paper deals with the problem of distributed formation tracking control and obstacle avoidance of multivehicle systems(MVSs)in complex obstacle-laden environments.The MVS under consideration consists of a leader vehicle with an unknown control input and a group of follower vehicles,connected via a directed interaction topology,subject to simultaneous unknown heterogeneous nonlinearities and external disturbances.The central aim is to achieve effective and collisionfree formation tracking control for the nonlinear and uncertain MVS with obstacles encountered in formation maneuvering,while not demanding global information of the interaction topology.Toward this goal,a radial basis function neural network is used to model the unknown nonlinearity of vehicle dynamics in each vehicle and repulsive potentials are employed for obstacle avoidance.Furthermore,a scalable distributed adaptive formation tracking control protocol with a built-in obstacle avoidance mechanism is developed.It is proved that,with the proposed protocol,the resulting formation tracking errors are uniformly ultimately bounded and obstacle collision avoidance is guaranteed.Comprehensive simulation results are elaborated to substantiate the effectiveness and the promising collision avoidance performance of the proposed scalable adaptive formation control approach.

Distributed Control of Nonholonomic Robots Without Global Position Measurements Subject to Unknown Slippage Constraints

This paper studies the fully distributed formation control problem of multi-robot systems without global position measurements subject to unknown longitudinal slippage constraints.It is difficult for robots to obtain accurate and stable global position information in many cases,such as when indoors,tunnels and any other environments where GPS(global positioning system)is denied,thus it is meaningful to overcome the dependence on global position information.Additionally,unknown slippage,which is hard to avoid for wheeled robots due to the existence of ice,sand,or muddy roads,can not only affect the control performance of wheeled robot,but also limits the application scene of wheeled mobile robots.To solve both problems,a fully distributed finite time state observer which does not require any global position information is proposed,such that each follower robot can estimate the leader’s states within finite time.The distributed adaptive controllers are further designed for each follower robot such that the desired formation can be achieved while overcoming the effect of unknown slippage.Finally,the effectiveness of the proposed observer and control laws are verified by simulation results.

Sedimentary characteristics and processes of the Paleogene Dainan Formation in the Gaoyou Depression, North Jiangsu Basin, eastern China

In this paper,the type,vertical evolution,and distribution pattern of sedimentary facies of the Paleogene Dainan Formation in the Gaoyou Depression of the North Jiangsu Basin are studied in detail.Results show that fan delta,delta,nearshore subaqueous fan,and lacustrine facies developed during the Dainan Formation period and their distribution pattern was mainly controlled by tectonics and paleogeography.The fan delta and nearshore subaqueous fan facies predominantly occur in the southern steep slope region where fault-induced subsidence is thought to have created substantial accommodation,whereas the delta facies are distributed on the northern gentle slope which is thought to have experienced less subsidence.Finally,the lacustrine facies is shown to have developed in the center of the depression,as well as on the flanks of the fan delta,delta,and nearshore subaqueous fan facies.Vertically,the Dainan Formation represents an integrated transgressiveregressive cycle,with the E2d1being the transgressive sequence and the E2d2being the regressive sequence.This distribution model of sedimentary facies plays an important role in predicting favorable reservoir belts for the Dainan Formation in the Gaoyou Depression and similar areas.In the Gaoyou Depression,sandstones of the subaqueous distributary channels in the fan delta and the subaqueous branch channels in the delta are characterized by physical properties favorable for reservoir formation.

MEASUREMENTS OF PARTICLE NUMBER SIZE DISTRIBUTIONS AND NEW PARTICLE FORMATION EVENTS DURING WINTER IN THE PEARL RIVER DELTA REGION,CHINA

Particle number size distribution(PNSD) between 10 nm and 20 μm were measured in the Pearl River Delta(PRD) region in winter 2011.The average particle number concentration of the nucleation mode(10-20 nm),Aitken mode(20-100 nm),accumulation mode(100 nm-1μm) and coarse mode(1-20 μm) particles were 1 552,7 470,4 012,and 19 cm-3,respectively.The volume concentration of accumulation mode particles with peak at 300 nm accounted for over 70% of the total volume concentration.Diurnal variations and dependencies on meteorological parameters of PNSD were investigated.The diurnal variation of nucleation mode particles was mainly influenced by new particle formation events,while the diurnal variation of Aitken mode particles correlated to the traffic emission and the growth process of nucleation mode particles.When the PRD region was controlled by a cold high pressure,conditions of low relative humidity,high wind speed and strong radiation are favorable for the occurrence of new particle formation(NPF) events.The frequency of occurrence of NPF events was 21.3% during the whole measurement period.Parameters describing NPF events,including growth rate(GR) and source rate of condensable vapor(Q),were slightly larger than those in previous literature.This suggests that intense photochemical and biological activities may be the source of condensable vapor for particle growth,even during winter in the PRD.

Distributed velocity-free formation tracking control for clustered UAVs under virtual leader-follower framework

The collective formation control problem of a cluster of rotorcraft unmanned aerial vehicles(UAVs)is investigated in this article.The consensus tracking towards formation centroid with following UAVs forming a predefined configuration around the leader is considered as the objective.Unlike prior studies,the information of the central reference trajectory,which is deemed as a virtual leader in the leader-follower topology,is not directly accessible for partial nodes through the communication network.Therefore,a novel distributed formation tracking control scheme is promoted.Besides,a decentralized saturation observer is employed to estimate the reference acceleration signal of the virtual leader.In the absence of linear velocity measurement,two sliding manifolds are proposed by introducing the relative discrepancy terms of position and velocity.Then a smooth saturation operator in the form of a sigmoid function is applied to generate the command force input.Moreover,under the dilemma of constrained capabilities of the airborne sensors equipped on the rotorcrafts,the angular velocity is difficult to acquire.Two cascaded auxiliary attitude error systems are established on each rotorcraft system to synthesize the rotating torque with no need to require the angular velocity measurement.Due to the strong coupling and nonlinearity of the rotorcraft UAV system,the command angular velocity and the derivatives of command input are hard to obtain.Then a continuous nonlinear differentiator is proposed to work with the difficulties in deriving the explicit expression of system derivatives.Thereafter,a detailed stability analysis is conducted progressively on the angular control loop,reference trajectory observer loop,and the position control loop.A simulation scheme for a cluster of four rotorcraft UAVs tracking sinusoidal trajectory are presented and the formation control results are proven advantageous in comparison with the control protocol in previous literature.

Periodic event-triggered formation control for multi-UAV systems with collision avoidance

In this paper,periodic event-triggered formation control problems with collision avoidance are studied for leader–follower multiple Unmanned Aerial Vehicles(UAVs).Firstly,based on the Artificial Potential Field(APF)method,a novel sliding manifold is proposed for controller design,which can solve the problem of collision avoidance.Then,the event-triggered strategy is applied to the distributed formation control of multi-UAV systems,where the evaluation of the event condition is continuous.In addition,the exclusion of Zeno behavior can be guaranteed by the inter-event time between two successive trigger events have a positive lower bound.Next,a periodic event-triggered mechanism is developed for formation control based on the continuous eventtriggered mechanism.The periodic trigger mechanism does not need additional hardware circuits and sophisticated sensors,which can reduce the control cost.The stability of the control system is proved by the Lyapunov function method.Finally,some numerical simulations are presented to illustrate the effectiveness of the proposed control protocol.

Distributed event-triggered formation control of UGV-UAV heterogeneous multi-agent systems for ground-air cooperation

Within the context of ground-air cooperation,the distributed formation trajectory tracking control problems for the Heterogeneous Multi-Agent Systems(HMASs)is studied.First,considering external disturbances and model uncertainties,a graph theory-based formation control protocol is designed for the HMASs consisting of Unmanned Aerial Vehicles(UAVs)and Unmanned Ground Vehicles(UGVs).Subsequently,a formation trajectory tracking control strategy employing adaptive Fractional-Order Sliding Mode Control(FOSMC)method is developed,and a Feedback Multilayer Fuzzy Neural Network(FMFNN)is introduced to estimate the lumped uncertainties.This approach empowers HMASs to adaptively follow the expected trajectory and adopt the designated formation configuration,even in the presence of various uncertainties.Additionally,an event-triggered mechanism is incorporated into the controller to reduce the update frequency of the controller and minimize the communication exchange among the agents,and the absence of Zeno behavior is rigorously demonstrated by an integral inequality analysis.Finally,to confirm the effectiveness of the proposed formation control protocol,some numerical simulations are presented.

Size-resolved aerosol ionic composition and secondary formation at Mount Heng in South Central China

To understand the size-resolved aerosol ionic composition and the factors influencing secondary aerosol formation in the upper boundary layer in South Central China, size-segregated aerosol samples were collected using a micro-orifice uniform deposit irnpactor （MOUDI） in spring 2009 at the summit of Mount Heng （1269 m asl）, followed by subsequent laboratory analyses of 13 inorganic and organic water-soluble ions. During non- dust-storm periods, the average PM1.8 concentration was 41.8 μg·m^-3, contributing to 55% of the PM10. Sulfates, nitrates, and ammonium, the dominant ions in the fine particles, amounted to 46.8% of the PM1.8. Compared with Mount Tai in the North China Plain, the concentrations of both fine and coarse particles and the ions contained therein were substantially lower. When the air masses from Southeast Asia prevailed, intensive biomass burning there led to elevated concentrations of sulfates, nitrates, ammonium, potassium, and chloride in the fine particles at Mount Heng. The air masses originating from the north Gobi brought heavy dust storms that resulted in the remarkable production of sulfates, ammonium, methane sulfonic acid, and oxalates in the coarse particles. Generally, the sulfates were primarily produced in the form of （NH4）2SO4 in the droplet mode via heterogeneous aqueous reactions. Only approximately one-third of the nitrates were distributed in the fine mode, and high humidity facilitated the secondary formation of fine nitrates. The heterogeneous formation of coarse nitrates and ammonium on dry alkaline dust surfaces was found to be less efficient than that on the coarse particles during non-dust-storm periods.

Particle number size distribution and new particle formation (NPF) in Lanzhou,Western China

Particle number size distribution from 10 to 10,000 nm was measured by a wide-range particle spectrometer （WPS-1000XP） at a downwind site north of downtown Lanzhou, western China, from 25 june to 19 July 2006. We first report the pollution level, diurnal variation of particle concentration in different size ranges and then introduce the characteristics of the particle formation processes, to show that the number concentration of ultrafine particles was lower than the values measured in other urban or suburban areas in previous studies, However, the fraction of ultrafine particles in total aerosol number concentration was found to be much higher. Furthermore, sharp increase of ultrafine particle concentration was frequently observed at noon. An examination of the diurnal pattern suggests that the burst of the ultrafine particles was mainly due to nucleation process. During the 25-day observation, new particle formation （NPF） from homogeneous nucleation was observed during 33% of the study period. The average growth rate of the newly formed particles was 4.4 nm/h, varying from 1.3 to 16,9 nm/h. The needed concentration of condensable vapor was 6.1 × 10^7 cm-3, and its source rate was 1.1× 10^6 cm-3 s 1. Further calculation on the source rate of sulphuric acid vapor indicated that the average participation of sulphuric acid to particle growth rate was 68.3%.

Characterization of particle number size distribution and new particle formation in Southern China

Knowledge of particle number size distribution（PND） and new particle formation（NPF）events in Southern China is essential for mitigation strategies related to submicron particles and their effects on regional air quality,haze,and human health.In this study,seven field measurement campaigns were conducted from December 2013 to May 2015 using a scanning mobility particle sizer（SMPS） at four sites in Southern China,including three urban sites and one background site.Particles were measured in the size range of15-515 nm,and the median particle number concentrations（PNCs） were found to vary in the range of 0.3× 10~4-2.2 × 10~4 cn^（-3） at the urban sites and were approximately 0.2 × 10~4 cm^（-3） at the background site.The peak diameters at the different sites varied largely from 22 to 102 nm.The PNCs in the Aitken mode（25-100 nm） at the urban sites were up to 10 times higher than they were at the background site,indicating large primary emissions from traffic at the urban sites.The diurnal variations of PNCs were significantly influenced by both rush hour traffic at the urban sites and NPF events.The frequencies of NPF events at the different sites were0%-30%,with the highest frequency occurring at an urban site during autumn.With higher SO_2 concentrations and higher ambient temperatures being necessary,NPF at the urban site was found to be more influenced by atmospheric oxidizing capability,while NPF at the background site was limited by the condensation sink.This study provides a unique dataset of particle number and size information in various environments in Southern China,which can help understand the sources,formation,and the climate forcing of aerosols in this quickly developing region,as well as help constrain and validate NPF modeling.

Power distribution analysis for multiple modulation formats in an all-optical sampling wavelength division multiplexing system

An optimal power distribution analysis for an all-optical sampling orthagonal frequency division multiplexing(OFDM) scheme with multiple modulation formats including diferential phase shift keyed(DPSK), diferential quadrature phase shift keyed(DQPSK), and non-return-to-zero(NRZ) is proposed. The noise tolerances of different modulation formats are analyzed, and the optimal input power ratio between phase and intensity modulation formats for the best overall receiving performance is investigated under unchanged total input power. Moreover, this scheme can seamlessly coexist with the traditional WDM channel.