Enhancement of the emission yield of silicon nanocrystals in silica due to surface passivation

The ability of surface passivation to enhance the photoluminescence (PL) emission of Si nanocrystals in SiO₂ has been investigated. Silicon precipitation in implanted samples takes place in a time scale of few minutes at 1100°C. For longer annealing at the same temperature, the PL intensity of the Si nanocrystals increases and eventually reaches saturation, while it correlates inversely with the amount of Si dangling bonds at the Si–SiO₂ interface (P_b centers), as measured by electron spin resonance. This combined behavior is independent on the silica matrix properties, implantation profiles and annealing atmosphere and duration. The observation that the light emission enhancement is directly related to the annealing of P_b centers is confirmed by treatment in forming gas. This mild hydrogenation at much lower temperature (450°C) leads to a complete passivation of the P_b defects, increasing at the same time the PL yield and the lifetime.     

Chaotic resonance: A simulation

Stochastic resonance is a statistical phenomenon that has been observed in periodically modulated, noise-driven, bistable systems. The characteristic signatures of the effect include an increase in the signal-to-noise of the output as noise is added to the system, and exponentially decreasing peaks in the probability density as a function of residence times in one state. Presented are the results of a numerical simulation where these same signatures were observed by adding achaotic driving term instead of a white noise term. Although the probability distributions of the noise and chaos inputs were significantly different, the stochastic and chaotic resonances were equal within the experimental error.     

Measurement of Hartmann-Hahn cross-polarization dynamics with quenching of proton T1ρ relaxation dependence

A simple modification of the standard cross-polarization method designed for quenching the proton T_1ρ dependence when studying polarization transfer is presented. It is demonstrated that by using this simple procedure, new and subtle details of cross-polarization dynamics, previously hidden by the T_1ρ(¹H) effect, can be observed in dipolar-coupled spin systems.     

Spectroscopic Studies of 1-Aryl-2,2-Dichlorocyclopropanes

Seventeen 1-aryl-2,2-dichlorocyclopropanes were examined by using IR, ¹³C NMR, and mass spectrometry. The data obtained from IR and ¹³C NMR spectra indicate that the bond strength of carbon-chlorine on the cyclopropane ring and the electron density of that carbon depend on the substituent. The mass fragmentation patterns of compounds in this series resemble those of the dibromo analogues. The fragmentation mechanism is proposed to involve the formation of indenium ion through an electrocyclization.     

高斯光束照射下的圆盘夫琅禾费衍射

推导了高斯光束照射圆孔或圆盘的衍射场普遍表达式，计算了半波带数接近于零的情况下上述衍射场的数据，进而分析了圆盘衍射场在艾里斑中增加一个暗环的原因。     

Application of the stabilization method to interacting resonances

The stabilization method is applied to the case of interacting resonances in the photo-dissociation of van der Waals clusters composed by a rare gas atom bound to a dihalogen molecule. The study of an illustrative two-dimensional model consisting in a T-shaped NeI₂ molecule shows the adequacy of the method whenever the projection of the stabilization wave functions on the assumed prepared initial state is accounted for. The agreement of the fragmentation cross-sections with some previous results using the effective resolvent method and accurate close-coupling calculations is excellent. The method reveals its utility as a complementary tool since allows, through the analysis of the stabilization wave function in terms of zero-order levels, a precise characterization of the resonant states involved. Received 5 April 2002 / Received in final form 24 May 2002 Published online 19 July 2002     

Full-Wave Analyses for a Multi-Layered Microstrip Patch Antenna

This paper describes numerical modelling of a dual band multi-layered microstrip patch antenna operating at 35GHz on an in-house semi-insulating GaAs substrate. The simulated and measured resonant frequencies at both lower and upper resonant frequencies will be compared to check the accuracy of the different numerical modelling techniques.     

Nest代数上的在零点广义可导映射

设A为B（H）的子代数,　是A到B（H）的线性映射,我们说　在0点广义可导（广义双边可导）,如果对任意的S,T∈A且ST=0（ST=0或TS=0）,有　（ST）=　（S）T+S　（T）-S　（I）T.本文主要得到如下结果:（1）有限Nest代数上的每个范数拓扑连续的在0点广义可导的线性映射是广义内导子;（2）若N是完备Nest且H_　 H,则algN上的每个范数拓扑连续的在0点广义双边可导的线性映射是广义内导子.     

Development of a RILIS ionisation scheme for gold at ISOLDE, CERN

At the ISOLDE on-line isotope separation facility, the resonance ionisation laser ion source (RILIS) can be used to ionise reaction products as they effuse from the target. The RILIS process of laser step-wise resonance ionisation of atoms in a hot metal cavity provides a highly element selective stage in the preparation of the radioactive ion beam. As a result, the ISOLDE mass separators can provide beams of a chosen isotope with greatly reduced isobaric contamination. With the addition of a new three-step ionisation scheme for gold, the RILIS is now capable of ionising 26 of the elements. The optimal scheme was determined during an extensive study of the atomic energy levels and auto-ionising states of gold, carried out by means of in-source resonance ionisation spectroscopy. Details of the ionisation scheme and a summary of the spectroscopy study are presented.     

低密度聚乙烯光引发交联机理——Ⅱ.BNB自旋捕捉ESR研究

在光引发剂二苯甲酮(BP)存在下,紫外光辐照低密度聚乙烯(LDPE)所形成的自由基中间体已被自旋捕捉剂2,4,6-三特丁基亚硝基苯(BNB)所捕捉,其自旋加合物自由基已为电子自旋共振(ESR)所特征。现已检测和鉴定到二种自旋加合物:一种是叔碳自由基;另一种是仲碳自由基。它们分别是由BP的激发三重态从LDPE链的支化点和亚甲基团上夺氢所形成的自由基中间体同自旋捕捉剂BNB反应生成的。上述的证据表明:LDPE的光引发交联点主要发生在叔碳和仲碳原子上,且H-型交联点占主导地位。