Modeling and mesoscopic damage constitutive relation of brittle short-fiber-reinforced composites

Aimed at brittle composites reinforced by randomly distributed short-fibers with a relatively large aspect ratio, stiffness modulus and strength, a mesoscopic material model was proposed. Based on the statistical description, damage mechanisms, damage-induced anisotropy, damage rate effect and stress redistribution, the constitutive relation were derived. By taking glass fiber reinforced polypropylene polymers as an example, the effect of initial orientation distribution of fibers, damage-induced anisotropy, and damage-rate effect on macro-behaviors of composites were quantitatively analyzed. The theoretical predictions compared favorably with the experimental results.

栓状流密相气力输送

首先介绍了气力输送的实验设备。评述了水平栓流气力输送的压力降计算方法，用3种不同的方法计算了压力降并与实验数据进行比较。此外评述了用特征线方法进行了水平管的数值模拟，倾斜管的压力降计算和长距离的栓流气力输送。最后展望了该领域的发展方向。

Single sub-100 attosecond pulse generation in a two-colour time-gating laser field

We theoretically propose a method of generating a single sub-100 attosecond (as) pulse with a two-colour time-gating laser field. The field is synthesized by an 8 fs/800 nm (three optical cycles) pulse and a 24 fs/2400 nm (three optical cycles) pulse with an optimal time delay between them. In our simulation, we obtain a supercontinuum with an extremely broad spectrum of 150 eV and generate an isolated attosecond pulse with 96 as pulse duration without any dispersion compensation.

Effects of atmosphere visibility on performances of non-line-of-sight ultraviolet communication systems

Dependence of performances of non-line-of-sight (NLOS) solar-blind ultraviolet (UV) communication systems on atmosphere visibility is investigated numerically by correlating the propagation of UV radiation with the visibility. A simplified solar-blind UV atmospheric propagation model is introduced, and the NLOS UV communication system model is constituted based on the single scattering assumption. Using the model, numerical simulation is conducted for two typical geometry configurations and different modulation formats. The results indicate that the performance of the NLOS UV communication system is insensitive to variation of visibility in quite a large range, and deteriorates significantly only in very low-visibility weather, and is also dependent on the geometry configuration of the system. The results also show that the pulse position modulation (PPM) is preferable due to its high-power efficiency to improve the system performance. (c) 2007 Elsevier GmbH. All rights reserved.

铝酸镧单晶体中Ce^3＋的能级结构和荧光特性

采用提拉法成功生长了纯LaAlO3和掺铈的LaAlO3单晶体，测试了它们的远红外吸收谱，紫外吸收谱，荧光谱，根据吸收光谱确定了晶体中Ce^3+的能级结构，利用这一能级结构模型较好地解释了Ce：LaAlO3晶体的荧光光谱。

晶格匹配氮化镓和氧化锌基外延薄膜衬底材料ScAlMgO4晶体生长研究

采用提拉法成功生长了氮化镓和氧化锌基外延薄膜晶格匹配的ScAlMgO4单晶衬底材料,晶体呈透明白色,尺寸为Ф30mm×59mm,表面部分沿解理面有裂纹.粉末X射线衍射（XRD）分析表明经1400℃固相反应烧结的原料基本合成了ScAlMgO4多晶相.初步的偏光显微镜观察、晶体的粉末XRD表征、透过光谱和双晶摇摆测试表明晶体具有较好的光学性质和结晶质量.研究表明晶体本身的层状结构、较大的温度梯度和热应力的不均匀性是生长过程中引起晶体开裂的几个主要原因.

Rapid evolution of an X-linked microRNA cluster in primates

MicroRNAs (miRNAs) are a growing class of small RNAs ( about 22 nt) that play crucial regulatory roles in the genome by targeting mRNAs for cleavage or translational repression. Most of the identified miRNAs are highly conserved among species, indicating

Two serine protease inhibitors from the skin secretions of the toad, Bombina microdeladigitora

Two serine protease inhibitors (named BMSI 1 and BMSI 2, respectively) were identified from the skin secretions of the toad, Bombina microdeladigitora. The cDNAs encoding BMSIs were cloned from a cDNA library prepared from the toad skin. The deduced complete amino acid sequences of BMSIs indicate that mature BMSI1 and BMSI2 are composed of 60 amino acids including 10 half-cystines to form 5 disulfide bridges. A FASTA search in the databanks revealed that BMSIs exhibit sequence similarity with other serine protease inhibitors from amphibians of the genus Bombina. BMSI1 potently inhibited trypsin and thrombin with a K(i) value of 0.02 mu M and 0.15 mu M, respectively. Sequence analysis revealed that all serine protease inhibitors from five amphibians of the genus Bombina share highly conserved primary structures. (c) 2007 Elsevier Inc. All rights reserved.