Analysis of benzo[a]pyrene deactivation mechanisms in rats

The experimental data on the effects of a widespread carcinogen, benzo[a]pyrene (BP), on individual reactions of rats were treated using mathematical-statistical methods. The individual reactions were analyzed in dependence of doses and modes of administration (single or chronic). The analysis revealed a statistically significant correlation between life span and urinary content of (+/-)-trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (7,8-BP) in rats treated with BP. The calculated regression equations revealed that the individual sensitivity to carcinogen in case of the BP single administration to rats is mainly determined by efficiency of excretion of the BP active forms out of the organism, whereas after chronic BP administration it is determined by mechanisms of enzymatic deactivation of BP.     

Palm Community Structure and Land Cover Changes in the San Juan Biological Corridor, Costa Rica

Biological corridors connect forest fragments, minimize the isolation of remaining habitats, and reduce the negative impact of fragmentation. Important studies in a corridor include documentation of land cover and the relationships between the plant community and land cover changes. In this study, density, species richness, and species diversity of palms of different life stages and growth forms were documented in forty 10 × 10 m census plots in the San Juan Biological Corridor (SJBC), Costa Rica. Changes in the percent cover of agricultural, partially forested, and forested lands from 1979 to 2001 were quantified based on existing land classifications. Associations between these palm community characteristics and the reduction in forest cover in 200-m and 1000-m annuli surrounding the census plots were investigated. These palm community characteristics were spatially interpolated to examine their distributions in SJBC. The community characteristics of palms of all growth forms varied among census plots. Forested lands in SJBC decreased from 88 percent to 26 percent during 1979–2001, while the percentage cover of agricultural and partially forested lands increased. The annual deforestation rate was 0.8 percent from 1979 to 1992, 4.3 percent from 1992 to 1997, and 7.5 percent from 1997 to 2001. Overall, palm community characteristics of small-canopy palms, dwarf palms, and cotyledonous seedlings had lower values with a lower percentage forest cover. The spatially interpolated palm community characteristics were consistently greatest within or adjacent to protected areas. This study demonstrates the complexity of the landscape and the effect of loss of adjacent forests on the palm community.     

基于地形和主风向效应模拟山区降水空间分布

在 ANUSPL IN和 GIS空间分析技术的支持下 ,采用岷江流域内及周边地区共计 5 1个雨量站的 1988～ 2 0 0 2年各月连续观测数据 ,模拟产生岷江上游面积达 2 2 919km2的流域范围内月平均降水量的空间分布栅格。为了体现当地季风方向和坡向之间的耦合效应 ,建立主风向效应指数 (PWEI) ,并从 DEM中提取海拔高度形成两个协变量 ,以雨量站的大地坐标位置作为独立变量。降水的模拟采用样条平滑技术 ,利用降水量值和 4个变量的统计关系拟合产生样条表面 ,并进而结合 DEM和 PWEI栅格产生空间分辨率达 5 0 0 m的降水量栅格。依据归一化交叉检验值 (GCV)确定平滑参数 ,并通过多次诊断运行实现平滑降噪 ,提高预测精度。统计结果表明 ,月平均降水量的预测误差变动在 15 %～ 4 2 %之间 ,是现有雨量站分布条件所能实现的较好的结果。雨季 (5～ 9月份 )的预测误差远小于旱季 ,表明东南季风对迎风坡面有明显的致雨效应 ,并因 PWEI的运用提高了模拟精度 ;旱季 PWEI效果不明显 ,降水分配主要依赖地形。和单纯利用海拔高度一个变量相比 ,增加 PWEI可使全年平均预测误差降低 3.0 %左右。     

Opening and closing of a toroidal group II chaperonin revealed by a symmetry constrained elastic network model

Recently, the atomic structures of both the closed and open forms of Group 2 chaperonin protein Mm‐cpn were revealed through crystallography and cryo‐electron microscopy. This toroidal‐like chaperonin is composed of two eightfold rings that face back‐to‐back. To gain a computational advantage, we used a symmetry constrained elastic network model (SCENM), which requires only a repeated subunit structure and its symmetric connectivity to neighboring subunits to simulate the entire system. In the case of chaperonin, only six subunits (i.e., three from each ring) were used out of the eight subunits comprising each ring. A smooth and symmetric pathway between the open and closed conformations was generated by elastic network interpolation (ENI). To support this result, we also performed a symmetry‐constrained normal mode analysis (NMA), which revealed the intrinsic vibration features of the given structures. The NMA and ENI results for the representative single subunit were duplicated according to the symmetry pattern to reconstruct the entire assembly. To test the feasibility of the symmetry model, its results were also compared with those obtained from the full model. This study allowed the folding mechanism of chaperonin Mm‐cpn to be elucidated by SCENM in a timely manner.     

Significant soil acidification across northern China's grasslands during 1980s–2000s

Anthropogenic acid deposition may lead to soil acidification, with soil buffering capacity regulating the magnitude of any soil pH change. However, little evidence is available from large‐scale observations. Here, we evaluated changes in soil pH across northern China's grasslands over the last two decades using soil profiles obtained from China's Second National Soil Inventory during the 1980s and a more recent regional soil survey during 2001–2005. A transect from the central‐southern Tibetan Plateau to the eastern Inner Mongolian Plateau, where Kriging interpolation provided robust predictions of the spatial distribution of soil pH, was then selected to examine pH changes during the survey period. Our results showed that soil pH in the surface layer had declined significantly over the last two decades, with an overall decrease of 0.63 units (95% confidence interval = 0.54–0.73 units). The decline of soil pH was observed in both alpine grasslands on the Tibetan Plateau and temperate grasslands on the Inner Mongolian Plateau. Soil pH decreased more intensively in low soil carbonate regions, while changes of soil pH showed no significant associations with soil cation exchange capacity. These results suggest that grassland soils across northern China have experienced significant acidification from the 1980s to 2000s, with soil carbonates buffering the increase in soil acidity. The buffering process may induce a large loss of carbon from soil carbonates and thus alter the carbon balance in these globally important ecosystems.     

邓恩桉林地土壤pH空间变异分析

以福建省建阳市7年生邓恩桉(Eucalyptus dunnii Maiden)林地土壤为研究对象,应用地统计学方法分析了不同土层土壤pH的空间变异规律.结果表明:该邓恩桉林地土壤pH随土壤深度的增加而增大,0～20、20～40和40 ～60 cm土层的土壤pH均值分别为pH 3.57、pH 3.62和pH 3.67;土壤pH的变异系数较小,分别为3.90％、3.93％和4.05％.0～20、20～40和40～60 cm土层土壤pH的块金效应值分别为0.389 6、0.430 3和0.604 3,说明该林地土壤pH具有中等空间自相关性;经K-S非参数检验,该林地各层土壤pH服从正态分布.通过不同趋势效应下不同半方差函数模型预测误差的比较,确定该林地0～20、20～40和40～60 cm土层土壤pH空间变异最优模型分别适用0阶高斯模型、1阶指数模型和1阶球状模型.克里格最优插值分析结果表明:该邓恩桉林地各层土壤pH整体空间分布趋势均为由西向东递减,最高值出现在西南部;各层土壤pH插值标准差较小,且标准差分布均呈现以南部和中部为中心、向东北方向逐渐增大的趋势.根据研究结果推测:该邓恩桉林地土壤酸化程度较严重,其土壤pH的空间分布受结构因素和随机因素的共同影响,而土壤pH插值标准差的分布特征可能与采样点的数量和设置有关.     

Fast acquisition of NMR spectra using Fourier transform of non-equispaced data

Rapid acquisition of high-resolution 2D and 3D NMR spectra is essential for studying biological macromolecules. In order to minimize the experimental time, a non-linear sampling scheme is proposed for the indirect dimensions of multidimensional experiments. These data can be processed using the algorithm proposed by Dutt and Rokhlin (Appl. Comp. Harm. Anal. 1995, 2, 85–100) for fast Fourier transforms of non equispaced data. Examples of ¹H−¹⁵N HSQC spectra are shown, where crowded correlation peaks can be resolved using non-linear acquisition. Simulated data have been used to analyze the artefacts produced by the Lagrange interpolation. As compared to non-linear processing methods, this algorithm is simple and highly robust since no parameters need to be adjusted by the user.