Cryoprotection in plant tissues related to reduced volume expansion of cryoprotectant solution

To clarify the mechanism of reduced volume expansion-related cryoprotection changes in solution volume during freezing using several types of cryoprotectant were investigated. The effect of each cryoprotectant solution on the survival of asparagus nodal segments cooled slowly (0.5 degrees C/min) to -40 degrees C was also examined. The ratio of the volume at -40 degrees C to the volume at +20 degrees C was used as an index for expansion, calculated as a ratio of the density at +20 degrees C to the density at -40 degrees C. Distilled, deionized water showed the largest volume change at a ratio of 1.094. The ratio gradually decreased with an increase in the molar concentration of cryoprotectant, with the magnitude of the change dependent on the nature of the cryoprotectant. Raffinose was the most effective in reducing volume expansion when compared with other cryoprotectants at a same concentration. Raffinose exhibited greatest cryoprotection in asparagus tissue at 0.6 M where the solution became saturated. Dimethyl sulfoxide (Me2SO) at 1.69 M had the largest effect on cryoprotecting asparagus tissue. Furthermore, Me2SO was also the most effective in reducing volume expansion among the group of cryoprotectants permeable to the plasma membrane. It is concluded that cryoprotection in tissues was closely related to reduced volume expansion especially at low concentration (< or = 1.0 M). Cryoprotectants of impermeable sugar group lost their cryoprotective effect at > 1.0 M, which may due to severe dehydration and cell damage occurred in hypertonic solution. Useful cryoprotectants should be furnished with high ability of reducing volume expansion during freezing as well as low toxicity and high permeability for cells.     

An updated search of steady TeV γ-ray point sources in northern hemisphere using the Tibet air shower array

Using the data taken from Tibet Ⅱ High Density (HD) Array (1997 February--1999 September) and Tibet-Ⅲ array (1999 November--2005 November), our previous northern sky survey for TeV γ-ray point sources has now been updated by a factor of 2.8 improved statistics. From 0.0° to 60.0° in declination (Dec) range, no new TeV γ-ray point sources with sufficiently high significance were identified while the well-known Crab Nebula and Mrk421 remain to be the brightest TeV T-ray sources within the field of view of the Tibet air shower array. Based on the currently available data and at the 90% confidence level (C.L.), the flux upper limits for different power law index assumption are re-derived, which are approximately improved by 1.7 times as compared with our previous reported limits.     

基于神经网络的叶绿素含量精细测量建模方法研究

活体植物叶片叶绿素含量SPAD值易受叶片厚度、水分等影响,提出了基于多参数神经网络建模的叶绿素含量精细反演方法。通过测量叶片在中心波长分别为650,940和1 450 nm光照射下的透过率,获得叶片的SPAD值和水分指数WI(water index),同时用数字螺旋测微仪测量相应的叶片厚度并用分光光度法测得其叶绿素含量。利用建模集样本分别建立SPAD值与实测叶绿素含量之间的单参数模型和基于BP神经网络的WI、厚度及SPAD值与实测叶绿素含量之间的非线性模型。利用这两种模型分别计算获得验证集样本的叶绿素含量预测值,对预测值和实测值进行了相关分析和相对误差的分析。实验以340个三种不同植物叶片为样本,用以上方法进行了分析。结果表明,利用BP神经网络建模后,每种植物样本的叶绿素含量预测精度都有不同程度的提高,尤其对于叶片厚度值较大的样本,效果更为明显。数据显示所有混合样本平均相对误差绝对值由单参数模型的7.55%降低到5.22%,实测值与预测值的拟合决定系数由0.83提高到0.93。验证了利用多参数BP神经网络模型可以有效地提高活体植物叶绿素含量预测精度的可行性。     

壳聚糖希夫碱金属[Cu(Ⅱ),Mn(Ⅱ)]配合物的合成及其抑菌活性

壳聚糖的氨基与水杨醛发生反应制得壳聚糖希夫碱配体(L);L与铜盐或锰盐发生配位反应制得壳聚糖希夫碱金属[Cu(Ⅱ)和Mn(Ⅱ)]配合物(1和2),其结构经UV,IR,TGA和荧光光谱表征.L的酚亚胺的N原子和酚羟基的O原子同时参与配位.抑菌活性测试结果表明,1和2对大肠杆菌,金黄色葡萄球菌,沙门氏菌和枯草杆菌的抑菌活性较配体和金属盐均有明显提高.     

Elman动态递归神经网络在陀螺仪系统建模中的应用

本文针对Ｅｌｍａｎ 动态递归神经网络的特点,提出了一种基于Ｅｌｍａｎ 动态递归神经网络建立陀螺仪系统模型的方法。文中给出了Ｅｌｍａｎ 网络的网络结构和学习方法,并对建立起的网络模型进行了仿真,仿真结果表明,该方法是可行的。     

血管输入阻抗的拟合方法与初值选取

研究了模拟动脉系统的集中参数模型的数据拟合问题,分析了用修正的Noordeergraaf五单元模型计算血管输入阻抗的有关问题,对参数拟合问题中被广泛运用的Newton迭代法与正交试验法作了评述,就其中至关重要的初值选取问题建议了一些简单实用的方法,讨论了参数选取的范围与参考值,并将数值计算结果与实测结果作了比较,所建议方法的有效性得到了证实。     

Organic Reactions in Ionic Liquids： Ionic Liquid-promoted Three-component Condensation of Benzotriazole with Aldehyde and Alcohol

1-(α-Alkoxyalkyl)benzotriazoles are readily synthesized from three-component condensation of benzotriazole with aldehyde and alcohol in ionic liquid [Bmim]PF6.     

含两时滞捕食-被捕食系统的稳定性及分歧

本文研究一类含两相异时滞的捕食－被捕食系统的稳定性及分歧。首先，我们讨论两相异时滞对系统唯一正平衡点的稳定性的影响，通过对系数与时滞有关的特征方程的分析，建立了一种稳定性判别性。其次，将一个时滞看成分歧参数，而另一个看作固定参数，我们证明了该系统具有HOPF分歧特性。最后，我们讨论了分歧解的稳定性。     

丢番图方程|(ε~n-"非汉字符号"~n)/(ε-"非汉字符号")|=1的解数

设 a、b、c、k是适合 a+b=ck,gcd(a,b) =1 ,c∈ { 1 ,2 ,4} ,k>1且 k在 c=1或 2时为奇数的正整数 ;又设 ε=(a + - b) / c ,ε=(a - - b) / c .本文证明了 :当 (a,b,c,k)≠ (1 ,7,4,2 )或 (3,5,4,2 )时 ,至多有 1个大于 1的正奇数 n适合 |(εn-εn) / (ε-ε) |=1 ,而且如此的 n必为满足 n<1 +(2 logπ) / logk+2 563.43(1 +(2 1 .96π) / logk)的奇素数 .     

分枝杆菌石蜡油发酵液中的支链脂肪酸

作者从上海土壤中分离到一株以石蜡油为碳源的分枝杆菌Mycobacteium sp. A-3,并从该菌石蜡油发酵液中分离到石油醚可溶酸和石油醚不溶酸. 石油醚可溶酸主要为饱和脂肪酸, 石油醚不溶酸主要为3,5,7-三羟基取代的十五、十六、十七烷酸的混合物.本文报道两个支链饱和脂肪酸的结构鉴定, 它们是2s, 4s-二甲基庚酸和2s, 4s, 6s-三甲基壬酸.