一种5.8 GHz磁控管粒子模拟

 借助3维粒子仿真软件对一种新型18叶片5.8 GHz磁控管进行了动态模拟,比较了爆炸式发射与电子注发射的不同。利用磁路电子注发射方式针对不同的阴极发射电流进行了动态模拟,得到了不同发射电流条件下磁控管的工作特性。同时,利用FEMM仿真软件对磁控管磁路进行了仿真,得到了磁控管互作用空间的磁场分布,并在此基础上,对非均匀磁场下磁控管动态性能进行了模拟。     

含Ho~(3+)的GeO_2-B_2O_3-BaO-Na_2O-Al_2O_3锗酸盐玻璃的光谱与增益特性

用高温熔融法制备了不同Ho3+离子掺杂浓度65GeO2-12B2O-10BaO-10Na2O-3Al2O3-χHo2O3(χ=0.25,0.75,1.25mol%)锗酸盐玻璃。从吸收特性出发,应用McCumber理论计算了Ho3+离子能级5I8→5I7(~2.0μm)跃迁的吸收截面和5I7→5I8的受激发射截面。根据掺杂离子的浓度以及获得的吸收截面和受激发射截面得到Ho3+离子在此玻璃中的增益截面函数,从该函数可反映出材料的粒子数反转特性。获得的基本光学参数与其它掺杂的玻璃进行了比较,其吸收截面、发射截面和增益截面的最大值具有一定的优势。认为该玻璃在~2.0μm波段的中红外激光器中将有潜在的较大应用前景。     

Delayed Ionization and Delayed Detachment in Molecules and Clusters

被激发到电离阈值以上的分子体系的演化依赖于激发态的特征和与连续态的耦合等多种参数. 这些特性主要是与分子体系的复杂性,更准确地说与分子的大小,态密度,内自由度中的耦合强度有关.本文通过Na2的里德堡态的自电离,富勒烯C60的延迟电离,阴离子小团簇的延迟解离研究了在小分子中起主导作用的自电离和在大分子以及团簇中出现的延迟电离之间的转变过程. 由于这些体系中相对较慢的内能转移过程,这些研究是在纳秒激光的激发下进行.     

Terahertz emission in tenuous gases irradiated by ultrashort laser pulses

Mechanism of terahertz (THz) pulse generation in gases irradiated by ultrashort laser pulses is investigated theoretically. Quasi-static transverse currents produced by laser field ionization of gases and the longitudinal modulation in formed plasmas are responsible for the THz emission at the electron plasma frequency, as demonstrated by particle-in-cell simulations including field ionization. The THz field amplitude scaling with the laser amplitude within a large range is also discussed.     

Electronic structures of imidazolium-based ionic liquids

Electronic structures of ionic liquids formed by 1-buthyl-3-alkylimidazolium ion [C_nmim]⁺ (n = 4 and 8) with various inorganic and organic anions have been investigated by ultraviolet photoemission, X-ray photoemission, inverse photoemission and soft X-ray emission spectroscopies (SXES). The comparison of the calculated density of states with the observed spectra revealed that the molecular orbital energies of these ionic liquids are significantly affected by the electrostatic Madelung potential among the ions. The SXES results clearly show that the both highest occupied and lowest unoccupied states of [C₄mim]⁺PF₆⁻ are derived from the cation as a result of strong Madelung potential. On the other hand, the SXES results show the valence electronic structures of ionic liquids with larger anion molecules, [C_nmim]⁺Tf₂N⁻ and [C_nmim]⁺OTf⁻ are contributed from the both cation and anion.     

Entanglement of a two-level atom and its spontaneous emission near the edge of a photonic band gap

The entanglement of a two-level atom and its radiation field near the edge of a photonic band gap is studied by using the quantum entropy. Unlike the free space case, there is a steady-state entanglement between the atom and its spontaneous emission field even when the atomic transition frequency lies outside the band gap. Moreover, the degree of entanglement, which is due to the formation of atom–photon bound dressed state, depends on the detuning of the atomic transition frequency from the photonic band edge and can be controlled by a controllable photonic band gap crystal.     

Effect of solvent-controlled aggregation on the intrinsic emission properties of PAMAM dendrimers

Solvent-induced aggregation and its effect on the intrinsic emission properties of amine, hydroxy and carboxylate terminated, poly(amidoamine) (PAMAM) dendrimers have been investigated in glycerol, ethylene glycol, methanol, ethylene diamine and water. Altering the solvent medium induces remarkable changes in the intrinsic emission properties of the PAMAM dendrimers at identical concentration. Upon excitation at 370 nm, amine terminated PAMAM dendrimer exhibits an intense emission at 470 nm in glycerol, ethylene glycol as well as glycerol-water mixtures. Conversely, weak luminescence is observed for hydroxy and carboxylate terminated PAMAM dendrimers in the same solvent systems. When the solvent is changed to ethylene diamine, hydroxy terminated PAMAM exhibits intense blue emission at 425 nm. While the emission intensity is varied when the solvent milieu is changed, excited state lifetime values of PAMAM dendrimers remain independent of the solvent used. UV-visible absorption and dynamic light scattering (DLS) experiments confirm the formation of solvent-controlled dendrimer aggregates in the systems. Comparison of the fluorescence and DLS data reveals that the size distribution of the dendrimer aggregates in each solvent system is distinct, which control the intrinsic emission intensity from PAMAM dendrimers. The experimental results suggest that intrinsic emission intensity from PAMAM dendrimers can be regulated by proper selection of solvents at neutral conditions and room temperature.     

Condition monitoring of a single-stage gearbox with artificially induced gear cracks utilizing on-line vibration and acoustic emission measurements

The condition monitoring of a lab-scale, single stage, gearbox using different non-destructive inspection methodologies and the processing of the acquired waveforms with advanced signal processing techniques is the aim of the present work. Acoustic emission (AE) and vibration measurements were utilized for this purpose. The experimental setup and the instrumentation of each monitoring methodology are presented in detail. Emphasis is given on the signal processing of the acquired vibration and acoustic emission signals in order to extract conventional as well as novel parameters-features of potential diagnostic value from the monitored waveforms. Innovative wavelet-based parameters-features are proposed utilizing the discrete wavelet transform. The evolution of selected parameters/features versus test time is provided, evaluated and the parameters with the most interesting diagnostic behaviour are highlighted. The differences in the parameters evolution of each NDT technique are discussed and the superiority of AE over vibration recordings for the early diagnosis of natural wear in gear systems is concluded.     

Aggregation-induced emission of an aminated silole: A fluorescence probe for monitoring layer-by-layer self-assembling processes of polyelectrolytes

A new fluorescence technique for monitoring layer-by-layer self-assembling processes of polycations and polyanions is developed in this work. The fluorescent probe is a fluorogenic dye named 1,1-bis[p-(diethylaminomethyl)phenyl]-2,3,4,5-tetraphenylsilole (A₂HPS). Whereas fluorescence of a “normal” fluorophore is often quenched by aggregate formation, the protonated salt of A₂HPS, i.e., [H₂A₂HPS]²⁺, emits strong light in the suspensions of its nanoaggregates and in the solid films of its blends with poly(diallyldimethylammonium chloride) (PDDAC), thanks to its novel aggregation-induced emission (AIE) characteristics. When ([H₂A₂HPS]²⁺+PDDAC) cations and poly(styrenesulfonate) (PSS) anions were used to fabricate thin films via layer-by-layer deposition processes on quartz and glass substrates, the emission intensity of [H₂A₂HPS]²⁺ showed linear relationship with the number of ([H₂A₂HPS]²⁺+PDDAC)/PSS bilayers, due to the uniform co-deposition of [H₂A₂HPS]²⁺ cations into the PDDAC/PSS bilayers. This proves that the AIE fluorophore is an excellent probe for monitoring the layer-by-layer self-assembling processes of the polyelectrolytes on various substrates.     

Confinement of the field electron emission to atomic sites on ultra sharp tips

The spatially controlled field assisted etching method for sharpening metallic tips, in a field ion microscope (FIM), is used to study the evolution of the field emission when the tip apex radius is decreased below 1 nm. Unlike the conventional image formation in a field emission microscope (FEM), we demonstrate that at this scale the field emission is rather confined to atomic sites. A single atom apex fabricated at the end of such tips exhibits an outstanding brightness compared to other atomic tips. The measurements have been repeated for two double atom tips, with different atom-atom separations, and images of atomic field emission localization have also been obtained. We have found that the field emission intensity alternates between adjacent atoms when the applied voltage is gradually increased beyond a threshold value.