Microwave vacuum devices are used in a wide variety of areas, such as radar, space technology, electron accelerators and high-power microwave weapons at the future military frontiers. The cathodes, i.e., the electron sources, are the cores of the high-power microwave sources. Nanoparticles have many physical and chemical properties that their corresponding bulk materials do not have, such as surface effect and small-size effect, etc. Based on our previous work on the M-type cathode, we have proposed a strategy to develop a new type cathode. We deposited a layer of thin film of metal nanoparticles on the traditional Ba-W dispenser cathode. Thus the N-type cathode demonstrated some features different from the traditional M-type cathode. The study of the electron emission properties of this N-type cathode would promote the understanding on the electron emission and expand the applications of the nanomaterials. Nanoparticle thin films were grown by magnetron sputtering at room temperature. The results showed that the particle size of the films depended on the deposition rate in the nucleation stage of the films. The effect of thin film characteristics on thermionic emission of dispenser cathodes has been investigated. The chemical components of the vacuum background, the evaporants from an N-type cathode and an M-type cathode were respectively analyzed using a time of flight mass spectrometer (ToFMS). The results have proved that the ToFMS is one of the best tools for studying the evaporation phenomena of impregnated cathodes. Finally, the electron emission performance of the N-type cathodes was studied. I-V characteristics showed that the DC emission current density was 30 A/cm2 and its lifetime was 600 h. The pulse emission current density was 108 A/cm2 and its lifetime was 1500 h.

This paper introduces a newly developed dual-layer porous tungsten dispenser cathode, which can meet the growing requirements on both life and current density. In comparison with the conventional dispenser cathodes, the new-type dispenser cathodes have higher emission current density, lower evaporation rate and longer lifetime. According to the results of the life tests and the related analysis, their longest lifetime at a 1.5 A/cm 2 current density under 974 °C br is estimated to be over 1.9 ×10 5 h.

This paper analyses the degradation factors of a new long life coated impregnated cathode after accelerated life test. The surface state of the cathode is investigated with scanning electron microscope (SEM) as well as the content and variation of the various elements on the surface and the longitudinal section of the cathode are analyzed with Auger electron spectroscopy (AES) before and after the life test. The analyzing results with SEM show that the cathode coating shrinks at the life end and leads to a rise in its work function. The analyzing results with AES show that the percent of the W increases and the active materials Ba decreases on the cathode surface at the life end. Furthermore, there is less Ba underneath the cathode surface but still a lot of Ba in the tungsten matrix at the life end.

In this paper, a new type RV dispenser cathode is developed as it is capable of meeting the growing requirements concerning life and current density. This kind of RV dispenser cathode shows the higher emission current density and longer lifetime than that of convention dispenser cathodes. Temperature and current accelerated life test are used to evaluate the new type cathodes. At present, the results for temperature accelerated life test show that predicted life of the RV dispenser cathodes exceeds 260,000 hours at a current density of 1.5 A/cm2 at 980°C.

Recent emergency of sensor networks has been identified as one of the most important technologies in future. It leads to numerous novel applications for environment monitoring and collaborative information processing in diverse fields. This paper describes the concept of a sensor network-based traffic information service system which can provide a satisfying solution to urban traffic surveillance and traveling information release. First, general tasks and unique advantages of the system are explored, and the layered architecture of system is outlined, as well as hardware and software configuration. Then, a pilot platform is analyzed to exemplify the concept. Open research issues for development are discussed in the end.

Novel nano-modifier was prepared from calcium-based Montmorillonite. Natural skim was blended with the novel nano-modifier to prepare nano-modified natural skim block. The properties of the natural skim rubber and the nano-modified natural skim block were compared. XRD and SEM results indicated the interlayer space was enlarged with uniform distribution of clay layers. The initial Wallace plasticity (Po) and plasticity retention index (PRI) of the nano-modified skim block were evidently enhanced. The PRI was upto 94.0, the highest when 10% of nao-modified solution was added at a rate of upto 2.0 kg into a 10 g natural skim solution containing 8% dry rubber with a mass ratio of inorganic to organic components being 1:1. The ash content was also increased obviously, and other properties such as tensile stress at a given elongation, tensile strength, and so on were notably improved as well.

Spherical SiO2 particles have been coated with rare earth oxide layers by a Pechini sol–gel process, leading to the formation of core-shell structured SiO2@RE2O3 (RE=rare earth elements) and SiO2@Gd2O3:Ln3+ (Ln=Eu, Tb, Dy, Sm, Er, Ho) particles. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), photoluminescence (PL), and cathodoluminescence spectra as well as lifetimes were used to characterize the resulting SiO2@RE2O3 (RE=rare earth elements) and SiO2@Gd2O3:Ln3+ (Eu3+, Tb3+, Dy3+, Sm3+, Er3+, Ho3+) samples. The obtained core-shell phosphors have perfect spherical shape with narrow size distribution (average size ca. 380nm), smooth surface and non-agglomeration. The thickness of shells could be easily controlled by changing the number of deposition cycles (40nm for two deposition cycles). Under the excitation of ultraviolet, the Ln3+ ion mainly shows its characteristic emissions in the core-shell particles from Gd2O3:Ln3+ (Eu3+, Tb3+, Sm3+, Dy3+, Er3+, Ho3+) shells.

This paper presents an optimized topology for urban traffic sensor networks. Small world theory is used to improve the performance of the wireless communication system with a heterogeneous transmission model and an optimal transmission radius. Furthermore, a series of simulations based on the actual road network around the 2nd Ring Road in Beijing demonstrate the practicability of constructing artificial “small worlds”. Moreover, the particle swarm optimization method is used to calculate the globally best distribution of the nodes with the large radius. The methods proposed in this paper will be helpful to the sensor nodes deployment of the new urban traffic sensor networks.

采用有机改性钠基蒙脱土对胶清橡胶进行复合改性,制备改性胶清橡胶,并与杂胶、喇叭口胶、泡沫胶和废水胶复合,研究改性胶清橡胶及其复合材料的各项性能.结果表明,改性胶清橡胶塑性初值(P0)和塑性保持率(PRI值)与胶清橡胶相比大幅度提高,物理性能和热性能也明显改善;改性胶清橡胶/杂胶等复合材料的物理性能与杂胶等相比显著提高,P0和PRI值也有不同程度的增大.

The life of impregnated Ba-W cathodes with a new construction have been evaluated using an accelerated life test at three different temperatures (1170°C,1130°C,1090°C) and constant current density (2A/cm2). According to the relationship of life with operating temperatures, an accelerated equation has been set up. The cathode life at normal operating temperature is deducted based on the accelerated equation. The results show that life of the novel cathode exceeds 190,000 hour at a current density of 2A/cm2.

A novel technique has been developed to dynamically measure the weak cathode evaporation with a quartz oscillator. We found that when high quality quartz oscillator, irradiated by high temperature cathode nearby, is under forced cooling, the frequency of the quartz oscillator decreases monotonically with the increase of cathode-evaporated substance. Dynamic evaporation rate of the cathode can be evaluated by substituting specific frequency decrease in a unit time for Δf of the formula we derived. Compared with the conventional static measurement, the dynamic technique can easily acquire the crucial information at the initial stage of evaporation, which is of much technological interest in fabricating low evaporation, M impregnated dispenser cathode.

The preparation method of the Ni sponge oxide cathode has been reformed by spouting sand and vacuum evaporating technology.The results show that the performance of the oxide cathode can be improved by these new methods,which have advantages to improve the reliability of the high-power microwave device.

This paperpresents ourrecent research ontopology planning oftheUrbanTraffic Surveillance System(UTSS). Basedontheproposed wireless sensornetworks inUTSS, Particle SwarmOptimization (PSO)methodisapplied todeal withthenodeoptimization problem inUTSS.Afterdiscussing therelated worksonPSO,webuilt upanovelcommunication modelofwireless sensor networktoproduce thequalities of small world inrealroadnetwork aroundthe2ndringroadin Beijing. A series ofsimulations usingthemethodofPSO are demonstrated toworkouttheoptimal deployment ofthesensor nodesuponthecommunication model.

This paper describes the factors which have influence on the heating power of cathode-heater assembly.For satisfying the requirements of X-band traveling wave tubes with high reliability,high efficiency and long life,several improvement measures have been taken,including increasing the effective heated area,determining the material of cathode holder,and optimizing techniques of sintering alumina and assembly.

Recent discovery of small world phenomenon is applied to analyze and improve the efficiency of large-scale networks by generating decentralized organization mechanism. In this paper, a study of small world phenomenon occurred in urban traffic communication system is discussed in detail. With the introduction of small world theory to wireless sensor network for urban traffic system, the transmission efficiency can be improved dramatically while the network maintenance cost will be decreased sharply as well. Related works on small-world theory and network modeling are presented firstly. Then, a series of simulation experiments with regard to random sensor deployment are demonstrated to validate the occurrence of small world phenomenon in the wireless sensor network. Finally, a case study of sensor deployment based on a real road network around the 2 nd ring road in Beijing is provided to illustrate the phenomenon of small world in real urban traffic environment.

A novel technique has been successful developed to fabricate high efficient M-type cathode assembly for applications in space traveling-wave tube(TWT).In the technique,the impregnated tungsten disc was first welded to the molybdenum body using high temperature W-Co solder so as to enhance its vibration resistance,then two heat protective screens were assembled;the one inside is made of titanium for the first time,acting as heat sink and support of the cathode.The strengths of Ti screen include its high heat efficiency,10% higher than that of tantalum,and its strong emission current density(3.75 A/cm~2 at 950 ℃).

An optical method for measuring the curvature radius of the cathode surface is presented.The optical principle of the method is analyzed and many measuring factors which affect the absolute error are analyzed.Then the curvature radius of cathode are measured by using Nikon MM—40 microscope.At last,a simple method with high measuring accuracy is given.

A new type of dispenser cathode with dual-layer (Os-W/Re) is developed. The cathode coated with Os-W/Re shows better emission performance than the cathode coated with Os-W alloy. X-ray Photoelectron Spectroscopy (XPS) spectra demonstrate that ternary alloy coating (Os-W-Re) formed on the surface of the cathode with dual-layer (Os-W/Re) after full activation is the major reason why it has better emission than the cathode with Os-W alloy. The surface of each variety of the cathode is characterized with Scanning Electron Microscope (SEM) before and after activation: the emitting surface of the cathode with Os-W alloy after ageing appeared non-adherence (flaking) in localized areas, which is one of the reasons for non-uniform emission. However, the surface of the cathode with dual-layer (Os-W/Re) does not present film peeling under the same conditions. Thus it ensures better emission uniformity and functional reliability for the dispenser cathode.

In order to improve the activation characteristics & emission ability of the conventional Ir-Coated impregnated tungsten cathodes, a new type of dispenser cathode with ternary alloy Ir/Re/W coating was developed. The improved cathodes show higher emission current density and faster activation characteristics than that of the conventional pure Ir-coated impregnated tungsten cathodes. XPS was used to analyze the element compositions on the surface of the cathodes coated with pure Ir and Ir/Re/W alloy. The results will be given in this paper.

An optical method for measuring the curvature radius of the cathode surface was presented. The optical principle of the method was analysed, and many measuring factors which affect the absolute error were analysed. Then the curvature radius of cathode were measured by using Nikon MM-40 microscope. A simple method is given which is of high measuring accuracy.