NaYF4∶Yb3+/Eu3+上转换发光微纳粒子在防伪识别中的应用研究

稀土掺杂上转换发光微纳粒子在防伪识别方面有着巨大的应用前景。首先采用水热合成法制备了NaYF₄∶Yb3+/Eu3+微纳粒子,通过X射线衍射(XRD)、扫描电子显微镜(SEM)及透射电子显微镜(TEM)对NaYF₄∶Yb3+/Eu3+微纳粒子的尺寸、形貌和结晶度等方面进行了研究,同时使用980 nm的泵浦源对NaYF₄∶Yb3+/Eu3+微纳粒子的发光性能进行了分析;其次将NaYF₄∶Yb3+/Eu3+微纳粒子与酒精按一定比例混合制成丝网印刷剂,结合网络定制的丝网模版在纸上印制了不同字样的防伪图案,风干后将字样暴露在980 nm的激光辐照下,并使用相机对其进行成像研究;最后将印制的字样分成两部分,一部分保存在室内25 ℃恒温环境下,另外一部分保存在冬季一月份室外自然环境下,保存地点均为西安市,一周后对不同环境下的字样再次使用完全相同的实验仪器进行成像测试。实验及测试结果显示,NaYF₄∶Yb3+/Eu3+微纳粒子与NaYF₄标准卡的衍射峰完全一致,没有其他杂质产生;实验合成的微纳粒子外形均为六方体,且平均长度和横截宽度分别为209和175 nm,微纳晶体表面光滑、无缺陷、未弯曲、结晶度较高、分散性较好,电子衍射环与NaYF₄∶Yb3+/Eu3+微纳粒子的312,300和302晶面相对应;NaYF₄∶Yb3+/Eu3+微纳粒子受掺杂离子的影响,在不同的能级跃迁下分别产生蓝、绿、黄、红四种可见光,通过对NaYF₄∶Yb3+/Eu3+微纳粒子荧光光谱分析,Eu3+非对称性比率约为1,表明磁偶极子跃迁与电偶极子跃迁相当;NaYF₄∶Yb3+/Eu3+微纳粒子制成的丝网印刷剂在不同环境下成像结果良好均清晰可见、容易辨识,但受存放环境影响,室内成像结果与最初的成像结果相比变化不大,室外所有成像字符受到自然环境下水汽的影响,亮度均略有下降,但仍能识别。成像结果表明,所制备的NaYF₄∶Yb3+/Eu3+微纳粒子在防伪识别方面具有稳定性、可靠性等特点,但仍受到影响程度可控的自然环境因素影响。综合来看,其在防伪识别方面有着很大的应用前景。     

预测RNA二级结构的一种遗传模拟退火算法

讨论了RNA二级结构的预测问题，首先提出一种用树表示RNA二级结构的方法，然后给出一种用于预测RNA二级结构的混合遗传算法——遗传模拟退火算法．在该算法中，个体(RNA二级结构)直接用茎序列编码，与个体用二进制串编码的同类型算法相比，在很大程度上缩短了个体的编码长度．计算结果表明该预测算法具有较高的精度．     

Activity-Guided Characterization of COX-2 Inhibitory Compounds in Waltheria indica L. Extracts

Inflammation is the body’s response to infection or tissue injury in order to restore and maintain homeostasis. Prostaglandin E2 (PGE-2) derived from arachidonic acid (AA), via up-regulation of cyclooxygenase-2 (COX-2), is a key mediator of inflammation and can also be induced by several other factors including stress, chromosomal aberration, or environmental factors. Targeting prostaglandin production by inhibiting COX-2 is hence relevant for the successful resolution of inflammation. Waltheria indica L. is a traditional medicinal plant whose extracts have demonstrated COX-2 inhibitory properties. However, the compounds responsible for the activity remained unknown. For the preparation of extracts with effective anti-inflammatory properties, characterization of these substances is vital. In this work, we aimed to address this issue by characterizing the substances responsible for the COX-2 inhibitory activity in the extracts and generating prediction models to quantify the COX-2 inhibitory activity without biological testing. For this purpose, an extract was separated into fractions by means of centrifugal partition chromatography (CPC). The inhibitory potential of the fractions and extracts against the COX-2 enzyme was determined using a fluorometric COX-2 inhibition assay. The characterizations of compounds in the fractions with the highest COX-2 inhibitory activity were conducted by high resolution mass spectrometry (HPLC-MS/MS). It was found that these fractions contain alpha-linolenic acid, linoleic acid and oleic acid, identified and reported for the first time in Waltheria indica leaf extracts. After analyzing their contents in different Waltheria indica extracts, it could be demonstrated that these fatty acids are responsible for up to 41% of the COX-2 inhibition observed with Waltheria indica extract. Additional quantification of secondary metabolites in the extract fractions revealed that substances from the group of steroidal saponins and triterpenoid saponins also contribute to the COX-2 inhibitory activity. Based on the content of compounds contributing to COX-2 inhibition, two mathematical models were successfully developed, both of which had a root mean square error (RMSE) = 1.6% COX-2 inhibitory activity, demonstrating a high correspondence between predicted versus observed values. The results of the predictive models further suggested that the compounds contribute to COX-2 inhibition in the order linoleic acid > alpha linolenic acid > steroidal saponins > triterpenoid saponins. The characterization of substances contributing to COX-2 inhibition in this study enables a more targeted development of extraction processes to obtain Waltheria indica extracts with superior anti-inflammatory properties.     

A Study of the Background Absorption of Chitosan in the Graphite Furnace Atomic Absorption Spectrometry

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双酚A和邻苯二甲酰氯芳香酯环状四聚体的分离及其晶体结构研究

双酚A和邻苯二甲酰氯芳香酯环状低聚物经硝基笨重结晶得到环状四聚体,利用GPC、MS(FAB)、¹HNMR、IR、DSC和元素分析对其结构进行了表征。其晶体结构由广角X射线衍射法确定为正交晶系,晶胞参数为α=0.9676nm,b=0.8699nm,c=2.0859nm.每个晶胞中含有2个环状四聚体分子,晶体密度为1.36g·cm^-3,对环状四聚体晶体衍射峰进行了详细的指标化。     

蓝藻预富集-悬浮液进样GFAAS测定水中痕量银的研究

蓝藻预富集－悬浮液进样ＧＦＡＡＳ测定水中痕量银的研究汤又文,宋健怡,莫胜钧（华南师范大学化学系,广州,５１０６３１）关键词藻,富集,银,悬浮液,石墨炉痕量分析中,由于待测组分含量低,基体复杂,常常需要对待测组分进行预富集处理。共沉淀、电沉积、萃取与离...     

卷积伏安法的半微分新算法

从半微分算符的基本性质出发,用黎曼-斯提杰斯积分展开式得到两个关于半微分运算的新表达式。应用所得的算式在无因次量纲上讨论了线性扫描伏安法的电流函数,得到了与G1方程完全一致的结果,但表达式更直观。     

Comparison of spline wavelet and orthogonal wavelet in processing analytical chemistry signals

Spline wavelet and orthogonal wavelet are two widely used wavelet methods. In this paper, comparison of these two methodshas been made, including their algorithm, properties and results of signal processing in analytical chemistry signals. It is found that spline wavelet is more effective than orthogonal wavelet in processing high noise signals. The curves obtained from spline wavelet are closer to the theoretical ones than those obtained from orthogonal wavelet and the errors of spline wavelet are smaller than those of orthogonal wavelet.     

On the crossing number of cm × cn

We show that the M-crossing number cr_M(C_m × C_n) of C_m × C_n behaves asymptotically according to lim_n→∞ {cr_M(C_m × C_n)/((m − 2)n)} = 1, for each m ≥ 3. This result reinforces the conjecture cr(C_m × C_n) = (m − 2)n if 3 ≤ m ≤ n, which has been proved only for m ≤ 6. © 1998 John Wiley & Sons, Inc. J. Graph Theory 28: 163–170, 1998     

A theoretical study of the comonomer effect in the ethylene polymerization with zirconocene catalytic systems

The PM3(tm) semiempirical method has been used to optimize the structures for the reactants and transition states of the first and second ethylene insertion processes into zirconocene catalytic systems. The results obtained for these reactions are compared with calculations published in the literature performed at different ab-initio theoretical levels. The agreement between our calculations and those reported in the literature is satisfactory. Taking advantage of the reduced computational effort required in semiempirical calculations two additional processes related with the so-called comonomer effect were also studied: ethylene/1-hexene copolymerization, and chain termination reaction, both in the homopolymerization and in copolymerization of ethylene with 1-hexene comonomer. The calculated activation energies support some experimental findings such as the higher polymerization activities in the presence of comonomers and also the molecular weight reduction of the copolymers due to the more favorable β-elimination reactions. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1157–1167, 1998