自适应天线中阵元间互耦的校正＊

本文基于对自适应天线协方差矩阵特征结构的分析,推导出了考虑阵元间互耦时的自适应天线最佳权矢量的解析表达式。阐明了互耦导致自适应天线系统性能下降的机制,最后提出了一种有效的互耦校正方法。     

QCD corrections to charmlessb→s processes

QCD corrections to the penguin induced charmless inclusiveB decays are performed to an improved leading-log approximation. For processb→sqq (q=uds) andbb→ss, four previous missed 4-quark operators are included to make a complete leading log QCD corrected result. Furthermore, part of the next-leading log effect was also given for the above processes and processb→sg. In comparison to previous QCD corrected calculations by Grigjanis et al., the inclusive decay rates for processb→sqq (q=ud),b→ssq andbq→sq are suppressed 10%, 14% and 18% respectively. The branching ratio of processb→sg is enhanced by 2–3 orders, the result for this process is in agreement with the result of Ciuchini et al.     

选择外延MOCVD研制DFB激光器和模斑转换器集成器件

研究了利用选择外延生长的InGaAsP材料的厚度增强因子和带隙波长的性质,最大的厚度增强因子为2.9.利用选择外延技术研制的DFB激光器和模斑转换器的集成器件,阈值为10.8mA-在60mA下输出功率为10mW,边模抑制比为35.8dB,垂直方向上的远场发散角从34°减少到9°,垂直方向上的1dB偏调容差为3.4μm.     

Monthly sea surface temperature records reconstructed by δ18O of reef-building coral in the east of Hainan Island,South China Sea

Stable oxygen isotopic compositions of a coral colony ofPorites lutea obtained on a core allowed the reconstruction of a 56-a (1943–1998) proxy record of the sea surface temperatures. This coral δ¹⁸O data are from the east of Hainan Island water (22°20’N, 110°39’E), South China Sea. The relationship between δ¹⁸O in the skeletal aragonite carbonate and the sea surface temperature (SST) is SST = -5.36 δ¹⁸O_PDB-3.51 (r = 0.73,n = 470), dδ¹⁸O/d(SST) = -0.187‱/ °C; and the thermometer was set at monthly resolution. The 56-a (1943–1998) proxy record of the sea surface temperatures reflected the same change trend in the northern part of South China Sea as the air temperature change trend in China.

     

Synthesis of a novel poly(para‐phenylene ethynylene) for highly selective and sensitive sensing mercury (II) ions

A new poly(p‐phenylene ethynylene) derivative with pendant 2,2′‐bipyridyl groups and glycol units (PPE‐bipy) has been prepared, and its metal ion sensing properties were investigated. The polymer of PPE‐bipy exhibited high selectivity for Hg²⁺ as compared with Li⁺, Na⁺, K⁺, Ba²⁺, Ca²⁺, Mg²⁺, Al³⁺, Mn²⁺, Ag⁺, Zn²⁺, Pb²⁺, Ni²⁺, Cd²⁺, Cu²⁺, Co,²⁺ and Fe³⁺ in THF/EtOH (1:1, v/v) solution. The fluorescence of PPE‐bipy was efficiently quenched by Hg²⁺ ions, and the detection limit was found to be 8.0 nM in a THF/EtOH (1:1, v/v) solvent system. PPE‐bipy also showed a selective chromogenic behavior toward Hg²⁺ ions by changing the color of the solution from slight yellow to colorless, which can be detected with the naked eye. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1998–2007, 2008     

The adsorption of resorcinol from water using multi-walled carbon nanotubes

Adsorption of resorcinol and other phenolic derivatives on pristine multi-walled carbon nanotubes (MWCNTs) and HNO₃ treated MWCNTs has been investigated in attempt to explore the possibility to use MWCNTs as efficient adsorbents for pollutants. MWCNTs showed higher adsorption ability in a rather wide pH range of 4–8 for resorcinol, while decreased uptake capacity was found for acid-treated MWCNTs. Other phenolic derivatives such as phenol, catechol, hydroquinone and pyrogallol were employed to study the influence of the number and position of hydroxyl groups on the adsorption capacity. The amounts adsorbed by MWCNTs increased with the increasing number of hydroxyl. The substitution of phenol with a hydroxyl in meta-position leads to a much higher absorption ability than substitution in ortho- or para-position, which suggested that MWCNTs possess a great potential in removal of resorcinol from water, as well as the other phenolic derivatives.     

Controllable ultraslow light propagation in highly-doped erbium fiber

We report on slow light propagation induced by the coherent population oscillation in an erbium-doped optical fiber (EDOF). The slowdown of group velocity of light is demonstrated in a solid-state material at room temperature. We observe a maximum fractional delay of 0.129 and a maximum delay of 8.75 ms corresponding to a group velocity as low as 228.57 m/s in a sinusoid-like modulated waveform. We study in details the influences of the erbium ion density and the length of fiber on the fractional delay and the slow light propagation. The data show that the fractional delay can be increased using the fiber with high erbium ions density or long interaction length.     

Mössbauer study of amorphous Fe40Ni40PxB20−x

The hyperfine field distributions of amorphous Fe₄₀Ni₄₀P_xB_20?x (x=10, 12, 14, 17) samples before and after different heat treatments have been determined by means of Mössbauer spectroscopy. All of these P(H) curves are characterized by a main high field maximum and an additional low field maximum, respectively. The asymmetry of distributions of high field component in P(H) of Fe₄₀Ni₄₀P_xB_20?x increases progressively from Fe₄₀Ni₄₀P₁₀B₁₀ to Fe₄₀Ni₄₀P₁₇B₃. The distributions of low field component in P(H) are affected differently by the annealing temperature. The results indicate that the phospoorus element plays an important role in the hyperfine interactions of amorphous Fe₄₀Ni₄₀P_xB_20?x The influence of annealing atmosphere has been discussed.     

Structure and magnetic ordering of superconducting GdBa2(Cu0.94Fe0.06)3O7 by Mössbauer spectroscopy

A coexistence of magnetic ordering and superconductivity has been found in GdBa₂(Cu_0.94Fe_0.06)₃O₇ at 4.2 K. The magnetic ordering is seen in the Fe moments using Mössbauer spectroscopy. The small Fe percentage was chosen to enable us to probe the crystalline and magnetic environment of an isolated Fe ion. Possible mechanisms responsible for the establishment of the magnetic order and its nature are discussed.