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Structural morphological and Optical Properties of SnSb_2S_4 Thin Films Grown by Vacuum Evaporation method

Journal of materials Science & Technology 2014年第10期30卷 1006-1011页

作者： N.Khedmi m.ben rabeh m.Kanzari Laboratoire de Photovoltaques et matriaux de Semi-conducteurs-ENIT-Universit de Tunis el manar BP 37le belvedere1002 TunisTunisie Laboratoire de Photovoltaques et matriaux de Semi-conducteurs-ENIT-IPEITunis montfleury-Universit de Tunis Tunisie

SnSb2S4 thin films were prepared from powder by thermal evaporation under vacuum of 1.33 × 10^-4 Pa （ 10^-6 Torr） on unheated glass substrates. The effect of thickness on the structural, morphological and optical properties of SnSb2S4 thin films was investigated. Films thickness measured by interference fringes method varied from 50 to 700 nm. X-ray diffraction analysis revealed that all the SnSb2S4 films were polycrystalline in spite without heating the substrates and the crystallinity was improved with increasing film thickness. The microstructure parameters： crystallite size, strain and dislocation density were calculated. It was observed that the crystallite size increased and the crystal defects decreased with increasing film thickness. In addition, by increasing the film thickness, an enhancement in the surface roughness root-mean-square （RmS） increased from 2.0 to 6.6 nm. The fundamental optical parameters like band gap, absorption and extinction coefficient were calculated in the strong absorption region of transmittance and reflectance spectrum. The optical absorption measurements indicated that the band （Eg） gap of the thin films decreased from 2.10 to 1.65 eV with increasing film thickness. The refractive indexes were evaluated in transparent region in terms of envelope method, which was suggested by Swanepoul. It was observed that the refractive index increased with increasing film thickness.

关键词： Ternary system Thermal evaporation technique Thin films Thickness Atomic force microscopy (AFm)

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Substrate Temperature-Dependent Physical Properties of Thermally Evaporated Sn4Sb6S13 Thin Films

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Acta metallurgica Sinica(English Letters) 2016年第1期29卷 79-88页

作者： A. Harizi m. ben rabeh m. Kanzari Laboratoire de Photovoltaique et materiaux Semiconducteurs departement genie industriel ENIT-Universite Tunis E1 Manar BP 37 Le belvedere 1002 Tunis Tunisie Institut Preparatoire aux Etudes d'Ingenieurs de Tunis Universite de Tunisie Montfleury Tunisia

In this work, the homogenous thin films of sulfosalt Sn4Sb6S13 were successfully synthesized by the thermal evaporation technique onto coming 7059 glass substrates heated at various temperatures in the range of 30--200 ℃. The surface morphology and structural characteristics of Sn4Sb6S13 films were analyzed by atomic force microscopy, X-ray diffraction, and energy-dispersive X-ray, respectively. The X-ray diffraction analysis revealed that Sn4Sb6S13 thin films crystallized in monoclinic structure according to a preferential direction （6 11）. An improvement in the structural properties by increasing the substrate temperature was observed. The values of some important parameters such as absorption coefficient （x）, band gap （Eg）, refractive index （n）, extinction coefficient （k）, and dielectric constant （Eg） of thin film were determined. The absorption coefficient was larger than 105 cm-l in the visible range. The electron transition of Sn4Sb6S13 films was direct allowed with the values that decreased （2-1.69 eV） by increasing substrate temperature from 30 to 200 ℃,The dispersion data obeyed the single oscillator relation of the Wemple-DiDomenico model and Cauchy model. The electrical free carrier susceptibility and the carrier concentration of the effective mass ratio were estimated according to the model of Spitzer and Fan.

关键词： Thin film Thermal evaporation technique X-ray diffraction Optical parameters

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Cooperative Target Fencing of multiple Vehicles for a General Target with Connectivity Preservation and Collision Avoidance

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Journal of Systems Science & Complexity 2024年第1期37卷 136-151页

作者： PAN Zini CHEN ben m Department of mechanical and Automation Engineering The Chinese University of Hong KongHong KongChina

In this paper,the authors study the cooperative target-fencing problem for n-dimensional systems and a target with a general *** using the velocity of the vehicles,a position feedback control law is proposed to fence the general target into the convex hull formed by the ***,the dynamics of each vehicle is described by a double-integrator *** potential functions are designed to guarantee connectivity preservation of the communication network and collision avoidance among the *** proposed approach can deal with a target whose trajectory is any twice continuously differentiable function of *** effectiveness of the result is verified by a numerical example.

关键词： multi-agent systems networked systems target fencing

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Radiolarian and Planktic Foraminifera Biostratigraphy of the Early Albian Organic Rich Beds of Fahdene Formation,Northern Tunisia

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Journal of Earth Science 2014年第1期25卷 45-63页

作者： m.ben Fadhel T Zouaghi A Amri m.ben Youssef Département de Géologie Faculté des Sciences de Gafsa-Campus Universitaire Sidi Ahmed Zarrouk–2112 Département des Géoressources CERTE–Technopole de Borj Cédria

The lower part of Fahdene Formation outcropping in northeastern Tunisia is repre- sented by pelagic sequences and characterized by an important siliciclastic fraction that includes ra- diolarian and organic-rich beds of Allam member. Litho-biostratigraphic analysis based on planktic foraminifera and radiolaria shows that deposition of organic-rich beds of Allam member is confined to the microhedbergella rischi Zone through the lower part of Ticinella primula Zone. Age diagnostic radiolaria recovered from these beds has been identified to constrain a direct age of black shale depo- sition. The assemblages can be correlated with the radiolarian biochronozone U.A.10-11 indicating an Early Albian to early middle Albian in age. Radiolarian assemblages composed of species characteris- tic of U.A.10 biochronozone （A. montisserei, D. gracilis） are associated with radiolarian taxa belonging to Costata Zone （U.A.9 Pseudoeucyrtis hanni and Thanarla pseudodecora）, which can be correlated with Dercourt member in the Ionian Zone and Paquier level of the Vocontian Basin （southeast of France）. Biostratigraphic and abundance curves analysis has demonstrated significant diversification of cryptocephalic Nassellaria and Archaeodictyomitrae, probably adapted to eutrophic conditions that characterized the Aptian-Albian transition. Ecological conditions may have governed the stratigraphic range of many cosmopolitan taxa （i.e., Pseudodictyomitrae lodogaensis） compared with stratigraphic distributions schemes reported from other domains. The timing of black shales deposition was dia- chronic due to local geodynamic conditions and upwelling currents distribution. The Allam black shales are correlative with the oceanic anoxic event OAElb which is characterized by the widespread of supraregionnally organic-rich beds in the mediterranean Tethys basins across the Aptian-Albian transition.

关键词： northeastern Tunisia Albian Allam member black shale radiolaria planktic foraminifera.

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Semi-global leader-following consensus-based formation flight of unmanned aerial vehicles

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Chinese Journal of Aeronautics 2022年第1期35卷 31-43页

作者： Panpan ZHOU ben m.CHEN Department of mechanical ami Automation Engineering The Chinese University of Hong KongHong KongChina

In this paper,we investigate a formation control problem of multi-agent systems(specifically a group of unmanned aerial vehicles)based on a semi-global leader-following consensus approach with both the leader and the followers subject to input *** the low gain feedback design technique,a distributed static control protocol and a distributed adaptive control protocol are *** former solves the problem under an assumption that the communication network is undirected,and it depends on the global information of the *** the latter,we relax the undirected graph to directed ***,an adaptive updating gain is designed to avoid using the global information of the communication *** is shown that the consensus protocols can solve the semi-global leader-following consensus problem if the leader agent is globally *** results are verified successfully by both simulation and real flight tests.

关键词： Consensus Formation flying Input saturation Low gain feedback multi-agent systems Unmanned aerial vehicles

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Dielectric relaxation and conduction mechanism of NamgPO_(4)compound

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Journal of Advanced Dielectrics 2022年第3期12卷 1-10页

作者： L.miladi A.Oueslati m.ben Gzaiel m.Gargouri Laboratory of Spectroscopic Characterization and Optical materials Faculty of Sciences University of Sfax B.P.11713000 SfaxTunisia

The polycrystalline NamgPO_(4)ceramic,synthesized via a high-temperature solid-state reaction route,has been characterized by using different experimental *** X-ray powder diffraction confirmed the phase formation of the synthesized com-pound in the orthorhombic *** assumed an olivine-type structure made up of corners linked between tetrahedral PO_(4)and octahedral NaO_(6)and mgO_(6)*** and Raman spectroscopies confirmed the presence of PO_(4)^(3−)*** structure and chemical bonding between mgO_(6)octahedral and PO_(4)3−tetrahedral groups investigated by diffusion Raman is the feature in the phase transition at T=693 *** temperature dependences of the realε′and imaginaryε″parts of dielectric permittivity show a distribution of relaxation *** Nyquist plots,the presence of grain and grain boundary effect in the material is *** impedance spectroscopy measurement showed a non-Debye-type *** the impedance data,the determined grain resistance reduces with increment of temperature showing negative temperature coefficient of resistance(NTCR)-type nature of the material which also confirmed from conductivity *** temperature dependence ofσdc reveals an Arrhenius-type behavior with two activation energies,0.98 eV in region I and 0.67 eV in region *** sample’s conduction is assured by Na+ions’hopping in tunnels and its mechanism was discussed.

关键词： Sodium-magnesium orthophosphate Raman phase transition NSPT model sodium-ion conductivity

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mODELING AND FORECASTING OF STOCK mARKETS UNDER A SYSTEm ADAPTATION FRAmEWORK

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Journal of Systems Science & Complexity 2012年第4期25卷 641-674页

作者： Xiaolian ZHENG ben m.CHEN The Department of Electrical & Computer Engineering The National University of Singapore

This paper adopts the concept of dynamic feedback systems to model the behavior of financial markets, or more specifically, the stock market from a dynamic system point of view. Based on a feedback adaptation scheme, the authors model the movement of a stock market index within a framework that is composed of an internal dynamic model and an adaptive filter. The output-error model is adopted as the internal model whereas the adaptive filter is a time-varying state space model with instrumental variables. Its input-output behavior, and internal as well as external forces are then identified. Special attention has also been paid to the recent financial crisis by examining the movement of Dow Jones Industrial Average （DJIA） as an example to illustrate the advantage of the proposed framework. Supported by time-varying causality tests, five influential factors from economic and sentiment aspects are introduced as the input of this framework. Testing results show that the proposed framework has a much better prediction performance than the existing methods, especially in complicated economic situations. An application of this framework is also presented with focuses on forecasting the turning periods of the market trend. Realizing that a market trend is about to change when the external force begins to exhibit clear patterns in its frequency responses, the authors develop a set of rules to recognize this kind of clear patterns. These rules work well for stock indexes from US, China and Singapore.

关键词： Complex systems financial modeling financial systems market forecasting system economics.

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On the Trends of Autonomous Unmanned Systems Research

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Engineering 2022年第5期8卷 20-23页

作者： ben m.Chen Department of mechanical and Automation Engineering The Chinese University of Hong KongHong Kong 999077China

In recent decades,academia and industry have put increasing attention and investment into the research and development of autonomous unmanned *** autonomous unmanned vehi-cle is a machine equipped with necessary data-processing units,sophisticated sensors,environment perception,automatic control,motion planning,task planning,mission management,and com-munication systems.

关键词： autonomous systems equipped

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Online schedule for autonomy of multiple unmanned aerial vehicles

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Science China(Information Sciences) 2017年第7期60卷 217-229页

作者： Kemao PENG Feng LIN ben m.CHEN Temasek Laboratories National University of Singapore Department of Electrical and Computer Engineering National University of Singapore

An online rectangle based scheduling algorithm(RSA) is developed to improve autonomy of multiple unmanned aerial vehicles(UAVs) to search a field of forest together. The purposes of RSA are to online decide the number of the UAVs to be assigned and to schedule the path for the assigned UAVs to search the missed areas resulted from the previous search. The main ideas of RSA are to cover each separated zone of the missed areas with a rectangle and then to schedule the path to search the rectangles. Thus, RSA is robust against the unknown shapes and sizes of the missed areas. The forest search is applied to verify the online RSA in simulation. The simulation results demonstrate that the online RSA is successful to decide the number of the UAVs to be assigned and to schedule the path for the assigned UAVs to search the missed areas.

关键词： online schedule mission planning autonomy of UAVs multiple UAVs algorithms

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Autonomous reconfigurable hybrid tail-sitter UAV U-Lion

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Science China(Information Sciences) 2017年第3期60卷 202-217页

作者： Kangli WANG Yijie KE ben m.CHEN Unmanned Systems Research Group 4 Engineering Drive 3 National University of Singapore

We present in this work the development of a novel hybrid unmanned aircraft platform, U-Lion,which has both vertical take-off and landing(VTOL) and cruising flight capabilities. Our design is in tail-sitter structure with reconfigurable wings, which combines the advantages of a fixed-wing plane and a rotor helicopter effectively. This allows it to transit from vertical take-off to hovering, before flying in cruise mode for efficient long duration flight. The propulsion comes from two coaxial contra-rotating motors fixed on a gimbal mechanism,which can change the direction of the motors for the required thrust. This thrust-vectored propulsion system primarily provides control in the VTOL mode but also enhances flight capabilities in the cruise mode. The hybrid aircraft is equipped with GPS and airspeed sensors, and has an onboard avionic system with advanced flight control algorithms to perform fully autonomous VTOL and cruising flights, in addition to transiting effectively between VTOL and cruising flight modes. The overall design has been successfully verified by actual flight experiments.

关键词： unmanned aerial vehicle vertical take-off and landing hybrid platform aircraft platform design flight control system

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