Genetic structure of Chinese sucker population Myxocyprinus asiaticus in the Yangtze River based on mitochondrial DNA marker

The sequencing analysis of the mitochondrial DNA control region (mtCR DNA) was performed to assess the genetic divergence and population structure of the Chinese sucker Myxocyprinus asiaticus (Cypriniformes Catostomidae) using four sample lots from natural populations of the Yangtze River. The mtCR DNA sequences of approximately 920 base pairs were obtained. A total of 223 nucleotide positions were polymorphic, and these defined 39 haplotypes. Of the 39 haplotypes, 37 (90%) were not shared, and among the populations as a whole there was little sharing of haplotypes. The average haplotype diversity (0.958) and the average nucleotide diversity (0.052) indicated a higher level of genetic diversity of Chinese sucker through the river. Analysis of molecular variation (AMOVA) of data revealed significant partitioning of variance (P<0.001) among populations (60.29%), and within populations (39.71%). The topology according to the neighbor joining and maximum parsimony methods showed mosaic composition of the 39 haplotypes, suggesting that the populations wore not completely divergent. The pairwise F statistic values, however, indicated that the population structuring existed to some extent among the geographic populations. There was a positive relationship between the aquatic distance and the genetic distance (Fst) among the populations (P<0.05). Based on our data, it is suggested that genetic drift, gene flow, and stochastic events are the possible factors influencing the population structure and genetic variation.

Effect of replacement of fish meal by meat and bone meal and poultry by-product meal in diets on the growth and immune response of Macrobrachium nipponense

The potential use of poultry by-product meal (PBM) and meat and bone meal (MBM) as alternative dietary protein sources for juvenile Macrobrachium nipponense was studied by a 70-day growth trial. Triplicate groups of M. nipponense (initial body weight: 0.37 g) were fed at 20.7-22.4 degreesC on each of the five isoenergetic and isonitrogenous diets (protein content about 38%) with different replacement of fish meal by MBM or PBM. The control diet used white fish meal as the sole protein source, the other four diets were prepared with 15% or 50% fish meal protein substituted by either MBM (MBM15, MBM50) or PBM (PBM15, PBM50). The results showed that replacement of fish meal by MBM in diets did not affect growth performance of M. nipponense (P > 0.05), while specific growth rate in PBM15 was significantly higher than that in other groups (P < 0.05). Survival rates of shrimp fed with MBM15 diet were significantly higher than that in other groups (P < 0.05). No significant differences in immunological parameters, including total haemocyte count (THC), phenoloxidase activity (PO) and respiratory burst (O-2(-)), were observed between the shrimps that were fed five experimental diets, and all determined immunological parameters in control groups were slightly higher than those in replacement groups. In conclusion, either MBM or PBM investigated could replace up to 50% fish meal protein in diets for M. nipponense. (C) 2003 Elsevier Ltd. All rights reserved.

Theoretical gain of strained GeSn0.02/Ge1-x-y ' SixSny ' quantum well laser

Using effective-mass Hamiltonian model of semiconductors quantum well structures, we investigate the electronic structures of the Gamma-conduction and L-conduction subbands of GeSn/GeSiSn strained quantum well structure with an arbitrary composition. Our theoretical model suggests that the band structure could be widely modified to be type I, negative-gap or indirect-gap type II quantum well by changing the mole fraction of alpha-Sn and Si in the well and barrier layers, respectively. The optical gain spectrum in the type I quantum well system is calculated, taking into account the electrons leakage from the Gamma-valley to L-valley of the conduction band. We found that by increasing the mole fraction of alpha-Sn in the barrier layer and not in the well layer, an increase in the tensile strain effect can significantly enhance the transition probability, and a decrease in Si composition in the barrier layer, which lowers the band edge of Gamma-conduction subbands, also comes to a larger optical gain.

Influence of exotic Mn on magnetic properties of YCo5.0-xMnxGa7.0 (0.05 <= x <= 3.0)

The YCo5.0-xMnxGa7.0 compounds crystallize with the ScFe6Ga6-type structure. The lattice of YCo5.0-xMnxGa7.0 expands with the increase of the Mn content for 0.05 <= x <= 2.5, but the lattice of YCo2.0Mn3.0Ga7.0 shrinks compared with YCo2.5Mn2.5Ga7.0. The shrinkage of the lattice is attributed to the magnetostriction of YCo2.0Mn3.0Ga7.0. The substitution of Mn for Co forms magnetic clusters in the antiferromagnetic matrix. The magnetic frustration results in the spin-glass-like behavior for 0.8 <= x <= 1.5 and the difference between zero-field-cooling (ZFC) and field-cooling (FC) magnetizations for x = 2.0, 2.5, and 3.0. A stable long-range magnetic ordering appears among the Mn-centered magnetic clusters with the ordering temperature 110 K for x = 2.0. The hump in the thermomagnetization of YCo3.0Mn2.0Ga7.0 can be attributed to the competitive effects between the thermal fluctuation and the enhanced magnetic interaction. Both the hump and the bifurcation between the ZFC and the FC magnetizations of YCo3.0Mn2.0Ga7.0 occur at lower temperatures as the applied field increases. On the two-step magnetization curve of YCo3.0Mn2.0Ga7.0, the inflection point at 4000 Oe is due to the coercive field, and the magnetic moments in the clusters are tilted to the applied field above 4000 Oe. The magnetic ordering temperature is further increased to 210 K for x = 2.5 and to 282 K for x = 3.0. The spontaneous magnetization of YCo2.0Mn3.0Ga7.0 is 0.575 mu B/f.u. at 5 K with a canted magnetic structure.

Analysis of semiconductor microlasers with an equilateral triangle resonator by rate equations

Semiconductor microlasers with an equilateral triangle resonator (ETR) are analyzed by rate equations with the mode lifetimes calculated by the finite-difference time-domain technique and the Pade approximation. A gain spectrum based on the relation of the gain spectrum and the spontaneous emission spectrum is proposed for considering the mode selection in a wide wavelength span. For an ETR microlaser with the side length of about 5 mum, we find that single fundamental mode operation at about 1.55 mum can be obtained as the side length increases from 4.75 to 5.05 mum. The corresponding wavelength tuning range is 93 nm, and the threshold current is about 0.1 to 0.4 mA.

Fast Discrimination of Commerical Corn Varieties Based on Near Infrared Spectra

The existing methods for the discrimination of varieties of commodity corn seed are unable to process batch data and speed up identification, and very time consuming and costly. The present paper developed a new approach to the fast discrimination of varieties of commodity corn by means of near infrared spectral data. Firstly, the experiment obtained spectral data of 37 varieties of commodity corn seed with the Fourier transform near infrared spectrometer in the wavenurnber range from 4 000 to 12 000 cm (1). Secondly, the original data were pretreated using statistics method of normalization in order to eliminate noise and improve the efficiency of models. Thirdly, a new way based on sample standard deviation was used to select the characteristic spectral regions, and it can search very different wavenumbers among all wavenumbers and reduce the amount of data in part. Fourthly, principal component analysis (PCA) was used to compress spectral data into several variables, and the cumulate reliabilities of the first ten components were more than 99.98%. Finally, according to the first ten components, recognition models were established based on BPR. For every 25 samples in each variety, 15 samples were randomly selected as the training set. The remaining 10 samples of the same variety were used as the first testing set, and all the 900 samples of the other varieties were used as the second testing set. Calculation results showed that the average correctness recognition rate of the 37 varieties of corn seed was 94.3%. Testing results indicate that the discrimination method had higher precision than the discrimination of various kinds of commodity corn seed. In short, it is feasible to discriminate various varieties of commodity corn seed based on near infrared spectroscopy and BPR.

云雾山草地植被恢复过程土壤水库特性及影响因素

为了了解植被恢复过程土壤水库特征的变化及其驱动因子,为半干旱典型草原区植被恢复的土壤环境效应提供评价依据,研究了宁南半干旱典型草原区植被恢复80 a对土壤水库库容、实际贮水量和贮水效率的影响及驱动因子。结果表明:土壤水库总库容、吸持库容、实际贮水量、贮水效率以及土壤物理性质均在草原植被恢复25 a内不断提高,经37 a略微下降后随植被演替土壤水库特征和土壤物理性质继续改善。通过逐步回归分析,容重、有机质含量和水稳性团聚体分形维数是影响土壤水库总库容的主要因子,毛管孔隙度则是影响土壤实际贮水量和贮水效率的主要因子。土壤有机质含量与容重、分形维数呈显著负相关(P<0.05),与毛管孔隙度呈极显著正相关(P<0.01)。植被恢复促使有机质积累,从而改善了土壤结构状况,提高了土壤土壤贮水能力、贮水量和贮水效率。可以认为土壤有机质积累是土壤水库功能提高的直接动力。

黄土高原长期种植苜蓿对土壤硫、钙、镁的影响

以22年定位试验为基础,研究黄土高原长期种植紫花苜蓿(Medicago sativaL.)情况下土壤硫、钙、镁组分的变化。结果表明:长期施P使苜蓿连作耕层土壤总硫、有效硫、水溶性硫、吸附性硫、HCl可溶性硫、总无机硫和有机硫含量分别增加9.41%、62.41%、47.51%、30.07%、2.25%、5.38%和17.54%;长期施NPM使苜蓿连作耕层土壤总硫、有效硫、水溶性硫、吸附性硫、HCl可溶性硫、总无机硫和有机硫含量分别增加20.89%、98.31%、68.44%、57.34%、8.07%、12.54%和37.69%。长期施P使苜蓿连作耕层土壤全钙、有效钙、水溶态钙、交换态钙和酸溶态钙含量增加分别增加4.64%、4.27%、11.66%、4.05%和8.59%,但残余态钙含量降低2.21%;长期施NPM使苜蓿连作耕层土壤全钙、有效钙、水溶态钙、交换态钙和酸溶态钙含量增加分别增加8.69%、8.30%、51.59%、6.73%和27.77%,但残余态钙含量降低26.23%。长期施NPM使苜蓿连作耕层土壤全镁、有效镁、水溶态镁、交换态镁、酸溶态镁和残余态镁含量分别增加7.38%、61.98%、63.16%...

骨修复用纳米生物玻璃/聚乳酸复合材料的研究

本文首次制备了纳米生物玻璃左旋聚乳酸复合材料，并针对两者之间界面不相容的现象，对生物玻璃表面进行了有针对性的改性；对其纳米颗粒的分散能力进行了表征，并对复合材料的力学性能和生物相容性进行了研究，以期能得到一种具有良好力学性能和生物活性的可降解骨组织修复材料。 （1） 以正硅酸乙酯为硅源，以磷酸氢二铵为磷源，硝酸钙为钙源制备了纳米生物玻璃的凝胶颗粒(BAG, SiO2: CaO: P2O5 =37/54/9, mol/mol) ；以其表面的硅羟基为引发点，采用丙交酯开环聚合原位改性的方法对其进行了表面改性得到了改性纳米生物玻璃的凝胶颗粒（m-BAG）；通过改性，使其表面性质由亲水性变为亲油性，提高了其在聚乳酸基体内的分散能力；m-BAG/PLLA复合材料改变了改性以前BAG/PLLA力学性能随生物玻璃含量增加而不断下降的趋势，保持了聚乳酸的力学性能，在m-BAG含量为2%的时候其拉伸强度相对于纯聚乳酸提高16%左右，模量达到纯聚乳酸的1.4倍；而当m-BAG含量为10wt%，复合材料保持与纯聚乳酸相似的拉伸强度，而此时10wt%BAG/PLLA复合材料的力学性能只有纯聚乳酸的80%; 生物玻璃凝胶/聚乳酸复合材料在模拟体液中表现了较高的钙沉积能力，最后在其表面都形成了羟基磷灰石的晶体，但是表面改性使其钙沉积的速度降低，在一定程度上减小了其活性；细胞试验表明，不论生物玻璃凝胶/聚乳酸复合材料还是改性后的复合材料都表现出了很高的细胞黏附性能和增殖性能。 （2） 通过煅烧将生物玻璃的凝胶颗粒制备了生物玻璃纳米颗粒，通过XRD和TGA确定该组成类型的生物玻璃的结晶温度在826ºC，我们选择其经过600ºC煅烧的非晶态的材料作为我们进一步研究的对象。通过六次甲基异氰酸酯作为偶联剂，我们将低分子量的Mn=9,700Da的聚乳酸偶连到生物玻璃纳米颗粒的表面；通过改性提高了生物玻璃/聚乳酸的拉伸强度和拉伸模量，并提高了其分散能力；模拟体液试验表明，其复合材料具有很强的钙沉积能力，细胞培养证明了优异的生物相容性；而且通过试验可以看出，生物玻璃相对于其原始的纳米凝胶颗粒具有更优异的钙沉积能力和细胞相容性。 （3） 通过将三臂聚乳酸添加到线性聚乳酸的内部，大幅度的提高了其冲击强度，当三臂聚乳酸含量达到2wt%-8wt%时，冲击强度达到线性聚乳酸的2倍左右；通过偏光显微镜观察，可以看到三臂聚乳酸提高了线性聚乳酸的结晶成核速度，使其最后晶体数量增多，形态变小；而通过等温结晶试验表明其结晶速度提高，结晶是以异相成核的三维生长方式进行的；流变学试验表明加入三臂聚乳酸有力的降低了体系的复数粘度，当三臂聚乳酸含量达到8%时候，在频率为1-10rad/s其数值仅为线性聚乳酸的60%左右，这种变化将提高其加工成型能力。 （4） 通过十六烷基三甲基溴化铵作为模板剂，制备了具有多孔结构的生物玻璃纳米颗粒，其孔径在2nm左右，比表面积为264m2/g； 通过模拟体液试验表明，其具有很强的生物活性，规整结构在浸泡的前8小时被破坏，体系中P和Ca的含量大幅度上升，在24小时以后形成了羟基磷灰石的晶体。该类型的材料有望应用于制备药物缓释材料，用于骨修复初期的感染和炎症治疗。

PRESSURE-DEPENDENCE OF PHOTOLUMINESCENCE IN IN(X)GA(1-X)AS/AL(Y)GA(1-Y)AS STRAINED QUANTUM-WELLS WITH DIFFERENT WIDTH

A systematic investigation on the photoluminescence (PL) properties of InxGa1-xAs/AlyGa1-xAs (x = 0.15, y = 0, 0.33) strained quantum wells (SQWs) with well widths from 1.7 to 11.0 nm has been performed at 77 K under high pressure up to 40 kbar. The experimental results show that the pressure coefficients of the exciton peaks corresponding to transitions from the first conduction subband to the heavy-hole subband increase from 10.05 meV/kbar of 11.0 nm well to 10.62 meV/kbar of 1.8 nm well for In0.15Ga0.85As/GaAs SQWs. However, the corresponding pressure coefficients slightly decrease from 9.93 meV/kbar of 9.0 nm well to 9.73 meV/kbar of 1.7 nm well for In0.15Ga0.85As/Al0.33Ga0.67As SQWs. Calculations based on the Kronig-Penney model reveal that the increased or decreased barrier heights and the increased effective masses with pressure are the main reasons of the change in the pressure coefficients.

富硅氮化硅薄膜的制备及其发光特性

采用射频磁控反应溅射法制备了氮化硅薄膜。利用X射线衍射谱（XRD）、红外光谱（IR）、能谱（EDS）和光致发光谱（PL）,通过与氮气中和空气中退火薄膜比较,对原沉积薄膜进行了成分与结构和发光特性研究。研究发现原沉积薄膜是部分晶化的富硅氮化硅薄膜,薄膜中晶态氮化硅颗粒的平均粒径为33nm;在氮气中退火后,纳米颗粒增大;在空气中退火后,薄膜被氧化,晶态颗粒消失。在4.67eV的光激发下,原沉积薄膜中观测到7个强的PL峰,其峰位分别为3.39,3.24,3.05,2.82,2.61,2.37和2.11eV。在氮气和空气中退火后,PL峰位和强度有变化。对其光致发光机制进行了探讨,认为硅悬挂键≡Si,氮悬挂键=N,硅错键≡Si-Si≡以及与氧有关的缺陷在富硅氮化硅薄膜高强度荧光发射中起主导作用。

非晶硅碳(a-SiC:H)薄膜光学常数的透射谱表征

报道了一种用透射谱数据分析法计算非晶硅碳薄膜的厚度、折射率、吸收系数和光学带隙等光学常数的方法和程序.这一方法引用有效谐振子模型理论的折射率色散关系,所有公式均为解析表达式,便于进行数据处理,无须专用软件,使用Excel即可完成,适用于多种半导体薄膜材料.将这种方法应用于PECVD方法制备的非晶硅碳(a-SiC∶H)薄膜,对其光学特性进行了分析.

Passive Q-switching of diode-pumped Yb:YAG microchip laser with ion-implanted GaAs

We reported a passive Q-switched diode laser pumped Yb:YAG microchip laser with an ion-implanted semi-insulating GaAs wafer. The wafer was implanted with 400-keV As^(+) in the concentration of 10^(16) ions/cm^(2). To decrease the non-saturable loss, we annealed the ion-implanted GaAs at 500 oC for 5 minutes and coated both sides of the ion-implanted GaAs with antireflection (AR) and highreflection (HR) films, respectively. Using GaAs wafer as an absorber and an output coupler, we obtained 52-ns pulse duration of single pulse.