Kinetic modeling of N incorporation in GaInNAs growth by plasma-assisted molecular-beam epitaxy

We have studied the growth of GaInNAs by a plasma-assisted molecular-beam epitaxy (MBE). It was found that the N-radicals were incorporated into the epitaxial layer like dopant atoms. In the range of 400-500 degrees C, the growth temperature (T-g) mainly affected the crystal quality of GaInNAs rather than the N concentration. The N concentration dropped rapidly when T-g exceeded 500 degrees C. Considering N desorption alone is insufficient to account for the strong falloff of the N concentration with T-g over 500 degrees C, the effect of thermally-activated N surface segregation must be taken into account. The N concentration was independent of the arsenic pressure and the In concentration in GaInNAs layers, but inversely proportional to the growth rate. Based on the experimental results, a kinetic model including N desorption and surface segregation was developed to analyze quantitatively the N incorporation in MBE growth. (C) 2000 American Institute of Physics. [S0003-6951(00)00928-1].

Absorption spectra of nanocrystalline silicon embedded in SiO2 matrix

Nanocrystalline silicon (nc-Si) embedded SiO2 matrix has been formed by annealing the SiOx films fabricated by plasma-enhanced chemical vapor deposition (PECVD) technique. Absorption coefficient and photoluminescence of the films have been measured at room temperature. The experimental results show that there is an "aUrbach-like" b exponential absorption in the spectral range of 2.0-3.0 eV. The relationship of (alpha hv)(1/2) proportional to(hv - E-g) demonstrates that the luminescent nc-Si have an indirect band structure. The existence of Stokes shift between photoluminescence and absorption edge indicates that radiative combination can take place not only between electron states and hole states but also between shallow trap states of electrons and holes. (C) 2000 Elsevier Science B.V. All rights reserved.

Magnetoexciton polaritons in planar semiconductor microcavities

We study the magnetoexciton polaritons in planar semiconductors microcavities by a quantum approach developed in the strong and weak magnetic-field limits. Ht is shown that the vacuum Rabi splittings with different Landau level indices are close to each other and tend to be proportional to B at sufficiently large values of the magnetic field. Also, we show that the calculated results are in good agreement with the experimental observations. [S0163-1829(99)10215-7].

A new interface anisotropic potential of zinc-blende semiconductor interface induced by lattice mismatch

A new interface anisotropic potential, which is proportional to the lattice mismatch of interfaces and has no fitting parameter, has been deduced for (001) zinc-blende semiconductor interfaces. The comparison with other interface models is given for GaAs/AlAs and GaAs/InAs interfaces. The strong influence of the interface anisotropic potential on the inplane optical anisotropy of GaAs/AlGaAs low dimensional structures is demonstrated theoretically within the envelope function approximation.

Degenerate four-wave-mixing signals from dc- and ac-driven semiconductor superlattice

Within the one-dimensional tight-binding model;rnd chi-3 approximation, we have calculated four-wave-mixing (FWM) signals for a semiconductor superlattice in the presence of both static and high-frequency electric fields. When the exciton effect is negligible, the time-periodic field dynamically delocalizes the otherwise localized Wannier-Stark states, and accordingly quasienergy band structures are formed, and manifest in the FWM spectra as a series of equally separated continua. The width of each continuum is proportional to the joint width of the valence and conduction minibands and is independent of the Wannier-Stark index. The realistic homogeneous broadening blurs the continua into broad peaks, whose line shapes, far from the Lorentzian, vary with the delay time in the FWM spectra. The swinging range of the peaks is just the quasienergy bandwidth. The dynamical delocalization (DDL) also induces significant FWM signals well beyond the excitation energy window. When the Coulomb interaction is taken into account, the unequal spacing between the excitonic Wannier-Stark levels weakens the DDL effect, and the FWM spectrum is transformed into groups of discrete lines. Strikingly, the groups are evenly spaced by the ac field frequency, reflecting the characteristic of the quasienergy states. The homogeneous broadening again smears out the line structures, leading to the excitonic FWM spectra quite similar to those without the exciton effect. However, all these features predicted by the dynamical theory do not appear in a recent experiment [Phys. Rev. Lett. 79, 301 (1997)], in which, by using the static approximation the observed Wannier-Stark ladder with delay-time-dependent spacing in the FWM spectra is attributed to a temporally periodic dipole field, produced by the Bloch oscillation of electrons in real space. The contradiction between the dynamical theory and the experiments is discussed. In addition, our calculation indicates that the dynamical localization coherently enhances the time-integrated FWM signals. The feasibility of using such a technique to study the dynamical localization phenomena is shown. [S0163-1829(99)10607-6].

基于D稳定域和ITAE准则的主动队列管理算法

主动队列管理（active queue management，简称AQM）是网络拥塞控制的研究热点之一，其中的关键问题是如何设计反馈控制策略．提出一种新的基于D稳定域和时间乘以误差绝对值乘积积分（integral of time-weighted absolute error,简称ITAE）性能准则的比例-积分-微分（proportional-integral-differential，简称PID）优化设计方法（简称DITAE-PID），并用于AQM控制器的设计，控制闭环系统的理想动态性能．首先在复平面上设定一组理想的D稳定域，然后以ITAE为目标函数，通过数值优化算法求出控制器的参数，使得闭环系统的所有特征根都在D稳定域内，以降低排队延时，提高有效吞吐量．对比仿真实验结果表明孩算法能够预先探测和控制拥塞，有较好的鲁棒性，链路利用率更高，丢包率更小，平均队列长度更趋于期望值，同时，趋于期望队列长度的时间更短，其综合性能明显优于典型的随机早期探测（random early detection，简称RED）和比例-积分（proportional-integral，简称PI）算法．

The Kiloparsec-scale structure of 3C 286

We present radio images of the compact steep spectrum (CSS) quasar 3C 286 acquired with the Very Large Array (VLA) at 8.4 and 22.5 GHz. The source exhibits a two-sided core-jet structure with a bright central component and two extended components one to the east (P.A. 100degrees) and another to the southwest (P.A. -116degrees). From the compact core, an extension runs towards the southwest component up to similar to 0.7 arcsecond. The emission between the primary central component and the southwest component exhibits a knotty structure. A gradual change of the jet position angles from -135degrees to -120degrees in the inner southwest jet suggests a local bend. The position angle changes of the major eastern components E2 and E1 suggest that the eastern jet likely follows a curved trace. The bends in the jet trace may be associated with a relativistic precession or some interaction between the jet and the ambient matter. A mean spectral index of alpha(8.4)(22.5) similar to -0.76 (S-nu proportional to nu(alpha)) is estimated for the core component. Steep spectra are also obtained for the extended southwest component (2.6", P.A. -116degrees) and eastern component (0.8", P.A. 100degrees), with alpha(8.4)(22.5) similar to -0.88 and alpha(8.4)(22.5) similar to -1.79, respectively. The radio morphologies and spectral index distributions suggest that the core seen in our images is likely to be the beamed inner jet while the real nucleus is dimmed by it beaming away from us.

The radio counter-jet of the QSO 3C 48

We present multi- frequency radio observational results of the quasar 3C 48. The observations were carried out with the Very Large Array ( VLA) at five frequencies, 0.33, 1.5, 4.8, 8.4, and 22.5 GHz, and with the Multi- Element Radio Linked Interferometer Network ( MERLIN) at the two frequencies of 1.6 and 5 GHz. The source shows a one- sided jet to the north within 1", which then extends to the northeast and becomes diffuse. Two bright components ( N2 and N3), containing most of the flux density, are present in the northern jet. The spectral index of the two components is alpha(N2) similar to -0.99 +/- 0.12 and alpha(N3) similar to - 0.84 +/- 0.23 ( S proportional to nu(alpha)). Our images show the presence of an extended structure surrounding component N2, suggestive of strong interaction between the jet and the interstellar medium ( ISM) of the host galaxy. A steep- spectrum component, labelled S, located 0.25 " southwest to the flat- spectrum component which could be the core of 3C 48, is detected at a significance of > 15 sigma. Both the location and the steepness of the spectrum of component S suggest the presence of a counter- jet in 3C 48.

氮、磷、钾对膜荚黄芪生长发育及有效成分的影响

目的:研究氮、磷、钾及其配比对膜荚黄芪生长发育及有效成分的影响。方法:通过田间试验,采用氮、磷、钾3因素2次D-饱和最优设计,研究氮、磷、钾及其配比对膜荚黄芪生长及有效成分的影响。结果:施肥促进了膜荚黄芪幼苗的生长,从而为生育后期膜荚黄芪根生长、产量形成及有效成分的累积提供充足的营养基础。氮、磷、钾各元素及其配比明显促进了茎叶及根干物质积累,氮、磷、钾对膜荚黄芪干物质累积总量的影响程度依次为氮>钾>磷;对膜荚黄芪茎叶干物质累积量的影响程度依次为氮>磷>钾;对根干物质累积量的影响程度依次为氮>钾>磷。施肥明显提高了膜荚黄芪根产量,氮、磷、钾对根产量影响程度依次为氮>钾>磷。氮、磷、钾各元素及其配比使黄芪多糖、黄芪甲苷含量明显增加,对总黄酮含量影响不明显。氮、磷、钾对黄芪多糖含量影响程度依次为钾>磷>氮;对黄芪甲苷含量的影响程度依次为氮>钾>磷。结论:氮、钾对膜荚黄芪生长发育,产量形成及多糖,黄芪甲苷含量有重要的影响。根类中药材黄芪的栽培过程中应该注重氮、钾肥的施用,并注意氮、磷、钾的配合施用。

THE MODULATION PRINCIPLE OF VACUUM ON THE SUPERCONDUCTIVITY OF YBCO

By neutron diffraction and other experiments, we have found that oxygen ions in YBCO can diffuse out of the sample in vacuo at room and low temperature, while the T(c) decreases greatly. We have also found that if the vacuum-deoxidation process lasts for several days there will be a damping oscillation of T(c) with time (t), and higher vacuum corresponds to a greater amplitude and a shorter period. We tentatively think that T(c) should satisfy the following function: T(c0) is-proportional-to T(c)e(-betat)cos (omegat + phi); it may be due to the diffusion of oxygen and the saturation of the valence state.

Dissociated screw dislocation which can relieve strain energy in the epitaxial layer of GeSi on Si(001)

A dissociated screw dislocation parallel to the interface was found in the epitaxial layer of the Ge0.17Si0.83 Si(001) system. It is shown that this dissociated screw dislocation which consists of two 30 degrees partials can relieve misfit strain energy, and the relieved misfit energy is proportional to the width of the stacking fault between the two partials.

High temperature annealing behaviors of luminescent SIOx : H films

The effects of high temperature annealing on the microstructure and optical properties of luminescent SiOx:H films have been investigated. Micro-Raman scattering and IR absorption, in combination with atomic force microscopy (AFM), provide evidence for the existence of both a-Si clusters in the as-grown a-SiOx:H and Si nanocrystals in the 1170 degrees C annealed films. The dependence of optical coefficients (alpha) on photon energy (h nu) near the absorption edge (E-g) is found to follow the square root law: (alpha h nu)(1/2) proportional to (E-g - h nu), indicating that nano-Si embedded in SiO2 is still an indirect material. A comparison of the deduced absorption edge with the PL spectra shows an obvious Stokes shift, suggesting that phonons should be involved in the optical transition process.

The enhancement of spontaneous emission factor in selectively oxidized vertical cavity lasers with double oxide layers

The behaviors of lateral propagating modes in the aperture and the oxidized regions are investigated numerically for selectively oxidized vertical-cavity surface-emitting lasers (VCSELs). The results show that the lateral propagating modes in the oxidized region are greatly affected by the oxide layer due to its low index, the modes are divergence for the VCSELs with sufficient thick double oxide layers. So the coupling between the modes in the aperture and oxidized regions is very weak, and we can expect that the lateral spontaneous emission is greatly affected in this case. Ignoring the contribution of the lateral spontaneous emission, we calculate spontaneous emission factor by counting the total number of the guided modes in selectively oxidized VCSELs with double oxide layers. The results agree very well with the reported measurements and are inversely proportional to the lateral index step.

Growth and characterization of GaInNAs/GaAs by plasma-assisted molecular beam epitaxy

We have studied the growth of GaInNAs/GaAs quantum well (QW) by molecular beam epitaxy using a DC plasma as the N sourer. The N concentration was independent of the As pressure and the In concentration, but inversely proportional to the growth rate. It was almost independent of T, over the range of 400-500 degreesC, but dropped rapidly when T-g exceeded 500 degreesC. Thermally-activated N surface segregation is considered to account for the strong falloff of the N concentration. As increasing N concentration, the steep absorption edge of the photovoltage spectra of GaInNAs/GaAs QW became gentle, the full-width at half-maximum of the photoluminescence (PL) peal; increased rapidly, and a so-called S-shaped temperature dependence of PL peak energy showed up. All these were attributed to the increasing localized state as N concentration. Ion-induced damage was one of the origins of the localized state. A rapid thermal annealing procedure could effectively remote the localized state. (C) 2001 Elsevier Science D.V. All rights reserved.

Electro-mass olfactory multi-sensor (EMMS)

For an olfactory sensor or electronic nose, the task is not only to detect the object concentration, but also to recognize it. It is well known that all the elements can be identified by their charge to mass ratio e(+)/m. We tried to imitate this principle for molecular recognition. Two kinds of sensors are used simultaneously in testing. One is quartz crystal microbalance (QCM) for detecting the change in mass, the other is interdigital electrode (IE) for detecting the change in conduction, as an electro-mass multi-sensor (EMMS). in this paper, the principle and the feasibility of this method are discussed. The preliminary results on the recognition of alcohol by EMMS coated with lipids are presented. Meanwhile, the multi-sensor can also be used as an instrument for research on some physico-chemistry problems. The change in conduction of coated membrane caused by one absorbed molecule is reported. It is found that when a QCM is coated with membrane, it still obeys the relationship Delta F (frequency change of QCM) = K Delta m (mass change of absorbed substance) and the proportional coefficient, K, depends not only on quartz properties but also on membrane characteristics as well. (C) 2000 Elsevier Science S.A. All rights reserved.