Production and characterization of biodiesel from tung oil

The feasibility of biodiesel production from tung oil was investigated. The esterification reaction of the free fatty acids of tung oil was performed using Amberlyst-15. Optimal molar ratio of methanol to oil was determined to be 7.5:1, and Amberlyst-15 was 20.8wt% of oil by response surface methodology. Under these reaction conditions, the acid value of tung oil was reduced to 0.72mg KOH/g. In the range of the molar equivalents of methanol to oil under 5, the esterification was strongly affected by the amount of methanol but not the catalyst. When the molar ratio of methanol to oil was 4.1:1 and Amberlyst-15 was 29.8wt% of the oil, the acid value decreased to 0.85mg KOH/g. After the transesterification reaction of pretreated tung oil, the purity of tung biodiesel was 90.2wt%. The high viscosity of crude tung oil decreased to 9.8mm(2)/s at 40 degrees C. Because of the presence of eleostearic acid, which is a main component of tung oil, the oxidation stability as determined by the Rancimat method was very low, 0.5h, but the cold filter plugging point, -11 degrees C, was good. The distillation process did not improve the fatty acid methyl ester content and the viscosity.

VLBI observations of a sample of 15 EGRET-detected AGNs at 5 GHz

We report VLBI observations of 15 EGRET-detected AGNs with European VLBI Network (EVN) at 5 GHz. All sources in the sample display core-jet structures.

钠原子激光增强电离光谱研究—以石墨杯为原子化器 原子吸收光谱法对发样中Zn、Cu、Mn、Ap的测定

、I钠原子激光增强电离光谱(LEIS)方法的研究-以石墨杯为原子化器在LEIS方法中，最常见的原子化器是火焰。但由于火焰背景噪声严重且难以克服，在火焰原子化过程中，雾化和热离解不充分，仅有10~(-2)%的分析溶液参与吸收以及火焰气体使测定元素受到高度稀释等不利因素的影响，火焰原子化限制了LEIS方法灵敏度的进一步提高。考虑到石墨炉原子化器较火焰具有取样量少，绝对灵敏度高；样品（包括固态、液态）可直接引入石墨炉内；不会发生如同火焰中所存在的干扰效应；蒸发效率和原子化效率较高，几乎全部样品都能参与吸收等优点，本工作在已建立火焰LEIS方法的实验基础上，将原子化器改换为石墨杯进行了钠原子LEIS方法的研究。到目前为止，国内外仅有的几篇有关石黑炉LEIS的研究报告中，都报导了该方法对钠原子的检出限估计可达到10~(-14)-10~(-15)克，由于此项研究尚处于探索性研究阶段，故有关方法性的系统研究几乎还未见报导。本工作在未使用任何放大器的情况下（实验条件限制）对影响钠原子LEIS信号强度的诸因互进行了实验观察。主要包括：钠原子化条件；激光束位置、阳极电压、激光输出能量、电极位置以及激光脉冲重复率对LEIS信号强度的影响等。并绘制了校准曲线，统计方法的相对标准偏差分别为11%（高浓度）18.2%（低浓度），在现有仪器条件下，还不能测出检出限，测定下限为3*10~(-9)克。对固体粉末直接进行了尝试，检测下限为5*10~(-8)克，进样是为5毫克。在进一步的研究工作中，如有条件使用低噪声的放大器及Bxear积分器，选择门检时间窗，或采用分步激发等手段，估计本方法定会达到预想的高灵敏度，检敏度至少提高了个数量级。对石墨炉原子化LEIS法来说，似比较详细的研究报告，截至实验停止时还未见报导。II原子吸收光谱法对发样中Zn、Cu、Mn、Al的测定发中微量元素ZN、Cu、Mn均属人体必需元素，与人体的生长发育和多种生理功能，临床医学等方面有着极为密切的关系，而Al则被认为是异致某种疾病的元素之一。本工作报告了用火焰法测定Zn、Cu；石墨炉法测定Al、Mn的结果，其中，对Al的测定，为摆脱基体干扰，加入改进剂Mg(NO_3)_2，并采用平台石墨炉进行试验，得到了线性较好的工作曲线，但在实际测定时，由于实验条件的限制，只能采用一般石墨管加基体改进剂对少娄样品中Al含量进行测定。Zn、Cu、Al三种元素由标准曲线法测定；而Mn由于Fe的干扰无法消除而采用标准加入法测定，并因此限制了测定样品数。Cu、ZN、Mn三种元素的回收率分别为102.8%, 99.7%, 102.5%，变异系数为9.6%, 11.3%, 9.7%，对本地居民发中（30个发样）Zn、Cu含量进行测定，Zn、Cu的含量范围为148-318ppm，7.2-15ppm，并计算了Zn/Cu比。本方法对发样中四种元素的测定结果与ICP法进行对照。两种方法测定结果吻合得较好。

Room-Temperature Continuous-Wave Operation of InGaN-Based Blue-Violet Laser Diodes with a Lifetime of 15.6 Hours

We report our recent progress of investigations on InGaN-based blue-violet laser diodes (LDs). The room-temperature (RT) cw operation lifetime of LDs has extended to longer than 15.6 h. The LD structure was grown on a c-plane free-standing (FS) GaN substrate by metal organic chemical vapor deposition (MOCVD). The typical threshold current and voltage of LD under RT cw operation are 78 mA and 6.8 V, respectively. The experimental analysis of degradation of LD performances suggests that after aging treatment, the increase of series resistance and threshold current can be mainly attributed to the deterioration of p-type ohmic contact and the decrease of internal quantum efficiency of multiple quantum well (MQW), respectively.

DIRECT ION-BEAM DEPOSITION OF CARBON-FILMS ON SILICON IN THE ION ENERGY-RANGE OF 15-500 EV

Direct ion beam deposition of carbon films on silicon in the ion energy range of 15-500 eV and temperature range of 25-800-degrees-C has been studied. The work was carried out using mass-separated C+ and CH3+ ions under ultrahigh vacuum. The films were characterized with x-ray photoelectron spectroscopy, Raman spectroscopy, transmission electron microscopy, and transmission electron diffraction analysis. In the initial stage of the deposition, carbon implanted into silicon induced the formation of silicon carbide, even at room temperature. Further carbon ion bombardment then led to the formation of a carbon film. The film properties were sensitive to the deposition temperature but not to the ion energy. Films deposited at room temperature consisted mainly of amorphous carbon. Deposition at a higher temperature, or post-deposition annealing, led to the formation of microcrystalline graphite. A deposition temperature above 800-degrees-C favored the formation of microcrystalline graphite with a preferred orientation in the (0001) direction. No evidence of diamond formation in these films was observed.

Microscopic analysis of defects in a high resistivity silicon detector irradiated to 1.7x10(15)n/cm(2)

Current-based microscopic defect analysis methods with optical filling techniques, namely current deep level transient spectroscopy (I-DLTS) and thermally stimulated current (TSC), have been used to study defect levels in a high resistivity silicon detector (p(+)-n-n(+)) induced by very high fluence neutron (VHFN) irradiation (1.7x10(15) n/cm(2)). As many as fourteen deep levels have been detected by I-DLTS. Arrhenius plots of the I-DLTS data have shown defects with energy levels ranging from 0.03 eV to 0.5 eV in the energy band gap. Defect concentrations of relatively shallow levels (E(t) < 0.33 eV) are in the order of 10(13)cm(-3), while those for relatively deep levels (E(t) > 0.33 eV) are in the order of 10(14) cm(-3). TSC data have shown similar defect spectra. A full depletion voltage of about 27,000 volts has been estimated by C-V measurements for the as-irradiated detector, which corresponds to an effective space charge density (N-eff) in the order of 2x10(14) cm(-3). Both detector leakage current and full depletion voltage have been observed to increase with elevated temperature annealing (ETA). The increase of the full depletion voltage corresponds to the increase of some deep levels, especially the 0.39 eV level. Results of positron annihilation spectroscopy have shown a decrease of total concentration of vacancy related defects including vacancy clusters with ETA, suggesting the breaking up of vacancy clusters as possible source of vacancies for the formation of single defects during the reverse anneal.

Transport properties through quantum dot in a vertical electric field

The transport properties through a quantum dot are calculated using the recursion method. The results show that the electric fields can move the conductive peaks along the high- and low-energies. The electric field changes the intensity of conductance slightly. Our theoretical results should be useful for researching and making low-dimensional semiconductor optoelectronic devices. (C) 2002 Elsevier Science B.V. All rights reserved.