Enzymatic cellulose hydrolysis in an attrition bioreactor combined with an aqueous two-phase system

Cellulose was hydrolyzed in the attrition bioreactor (ABR) with enzyme recycling by employing an aqueous two-phase system (composed of dextran and polyethylene glycol) and an ultrafiltration unit. The ABR combines wet ball milling and enzymatic hydrolysis in one process step. The cellulase enzymes were more stable in the two-phase system than in the normal buffer solution. With the initial substrate concentration (Solka Floe BW200) of 40 g/L and intermittent addition of cellulose, sugar was semicontinuously produced at dilution rates of 0.06 h(-1) and productivities of 2.1 g/L h, which is approximately a 10-fold increase of the previously reported values performed in a regular stirred reactor with an aqueous two-phase system. The conversion of the substrate was 86%.     

六盘山鸡爪大黄根多糖贮藏和分布特征的研究

采用组织化学方法对六盘山鸡爪大黄根不同生长发育时期大黄多糖贮藏和分布进行定位观察分析,以明确大黄多糖在其根中的分布与累积特征.结果显示:六盘山鸡爪大黄根内大黄多糖的分布是多位点的,其中在根周皮的栓内层内不同程度地贮藏和积累有一定的数量,而在次生维管组织的薄壁细胞中大量积累,是其根内大黄多糖贮藏与分布的主要部位;韧皮薄壁细胞与木薄壁细胞相比,前者贮藏大黄多糖的时间较早,含量也较多,且大黄多糖的贮藏积累随根的生长发育进程呈逐渐累积的方式.结果表明,六盘山鸡爪大黄根的次生维管组织薄壁细胞是其大黄多糖贮藏和分布的主要组织,而且大黄多糖累积数量与其根的发育程度存在着一定的相关性.     

山地梨枣树耗水特征及模型

由于枣树树龄、品种、冠层形态、下垫面以及枣树种植区气象条件不同,导致榆林地区枣树耗水规律研究缺乏系统性.本文利用HYDRUS-1D数学模型对枣树耗水规律进行了研究.2008-2010年通过对榆林米脂县不同树龄山地梨枣树叶面积指数、根系分布规律,作物系数的研究,结合HYDRUS-1D模型预测所需土壤、气象等参数的测定,对山地梨枣树土壤水分动态进行了模拟,并对土壤水分模拟结果与实测值进行拟合,反推出模型计算所需的消光系数及土壤水分胁迫系数等参数.结果表明:HYDRUS-1D模型能够很好模拟该地区梨枣树土壤水分动态变化过程,该地区成年(8龄)梨枣树从发芽开始到梨枣收获期结束共耗水267 mm.     

姜黄在理血方剂中的配伍规律及系统药理机制分析

姜黄可以有效治疗各种疾病,本研究使用广义规则归纳(GRI)算法分析了《中药方剂大词典》中含姜黄的理血方剂配伍规律.通过利用生物信息学数据挖掘技术和MTT、Elisa和Western blotting实验验证了姜黄关键配方的系统药理机制.发现"姜黄-川芎-当归"配方可以代表姜黄在理血方剂中的关键组方.PPI网络和KEGG...     

EFFECTS OF DIFFERENTIAL POLLEN-TUBE GROWTH ON HYBRIDIZATION IN THE LOUISIANA IRISES

To elucidate the importance of hybridization in evolution, it is necessary to understand the processes that affect hybridization frequency in nature. Here we focus on postpollination, prefertilization isolating mechanisms using two hybridizing species of Louisiana iris as a study system. We compared the effects of differential pollen-tube growth on the frequency of F₁ hybrid formation in experimental crosses between Iris fulva and Iris hexagona. Analyses of seed production in fruits from pure conspecific and heterospecific pollinations revealed that more seeds were produced in the top half than the bottom half of fruits for all four crosses. Heterospecific pollen was applied to flowers of each species at zero to 24 h prior to conspecific pollen, thereby giving a head start to the foreign pollen. Using diagnostic isozyme markers, the frequency of hybrid progeny was examined at the level of the whole fruit and separately for the top and bottom halves of fruits. In both species, the proportion of hybrid seeds per fruit increased significantly with increasing head starts, suggesting that differences in pollen-tube growth rates affect the frequency of hybridization. In I. fulva fruits, the increase in hybrid seeds occurred in both halves of the fruits, but in I. hexagona an increase was only detected in the top half of fruits. These findings are consistent with a model that assumes attrition of pollen tubes due to the greater length of I. hexagona styles. While pollen-tube growth rate appears to be the most important factor affecting hybridization frequency in I. fulva, both pollen-tube growth rate and pollen-tube attrition appear to be important in I. hexagona.     

Principal axis analysis of dental attrition data from two Australian Aboriginal populations

Dental attrition scores from two distinct Australian Aboriginal populations were compared by principal axis analysis. The first group was composed of members of the Narrinyeri group who occupied the river basin and mouth of the River Murray. The second group consisted of members of the Kaurna tribe who occupied the coastal plain to the west of the Narrinyeri. The groups were isolated both physically and culturally and as a result differences in patterns of tooth wear might be expected. In the Narrinyeri sample, attrition tended to be more rapid in females for all but the anterior teeth. The only sex difference in the Kaurna was for the maxillary central incisors, which wore more rapidly in females. Interpopulation differences in the pattern of tooth wear were also evident. The incisors, canines, and premolars of Kaurna subjects tended to wear more rapidly, while the rate of posterior tooth wear tended to be greater in the Narrinyeri. The application of the principal axis method to quantitative attrition data provided a sensitive, objective evaluation of tooth wear. The reasons for the observed differences between the two groups are still not completely clear but may relect both functional and morphological differences between groups.     

Pollen tube attrition as related to breeding systems inBrassicaceae

In order to estimate pollen tube attrition and to relate it to the breeding system, numbers of microgametophytes within the stigma and at the bottom of the style were scored in species of theBrassicaceae, 17 sporophytically self-incompatible, 11 predominant inbreeders, 4 facultative outcrossers. Attrition was evident in almost all species. The mean number of tubes at the bottom of the style, and mean number of stylar tubes per ovule were significantly lower in outbreeders. The degree of attrition, measured as attrition rate (the proportion of tubes in the stigma that do not reach the bottom of the style) was higher in outbreeders; it was positively correlated with the pollen : ovule ratios as estimates of the degree of outbreeding in the species involved. In outbreeders, sexual selection seems to be rather effective in inhibiting certain microgametophytic genotypes from reaching the ovules. Because of the low number of tubes per ovule in most cases, we assume that, in theBrassicaceae, female choice may be more effective in sexual selection and in ensuing pollen tube attrition.     

Nitrogen/phosphorus leaf stoichiometry and the scaling of plant growth

We adopted previous N : P stoichiometric models for zooplankton relative growth to predict the relative growth rates of the leaves μ _L of vascular plants assuming that annual leaf growth in dry mass is dictated by how leaf nitrogen N _L is allocated to leaf proteins and how leaf phosphorus P _L is allocated to rRNA. This model is simplified provided that N _L scales as some power function of P _L across the leaves of different species. This approach successfully predicted the μ _L of 131 species of vascular plants based on the observation that, across these species, N _L scaled, on average, as the 3/4 power of P _L, i.e. N _L ∝  P     . When juxtaposed with prior allometric theory and observations, our findings suggest that a transformation in N : P stoichiometry occurs when the plant body undergoes a transition from primary to secondary growth.     

Numerical solution of structured population models

Numerical methods are presented for a general mass-structured population model with demographic rates that depend on individual mass, time, and total population mass. Several types of numerical methods are described, Eulerian methods, implicit methods, and the method of characteristics. These methods are compared for a sample problem with an exact solution. The preferred numerical technique combines the method of characteristics with an adaptive grid. Numerical solution of model equations developed for mosquitofish illustrates this method and demonstrates how seasons can play a dominant role in shaping population development.     

Designed to Sell

The purpose of this study was to construct a profile of K–12 music teachers in the United States and develop a model to predict their retention, turnover, and attrition. Responses to the Schools and Staffing Survey from 47,857 K–12 public and private school teachers, including 1,903 music teachers, were analyzed using comparative statistics, factor analysis, logistic regression, and structural equation modeling. Results indicated that music teachers were far more likely than other types of teachers to hold itinerant or part-time positions, and were less likely to receive support for working with special needs students. Music teachers changed teaching positions because of dissatisfaction with workplace conditions and for better teaching assignments. Music teachers left the teaching profession for better salary or benefits, and were generally more satisfied in their new field. Music teachers’ perceived level of administrative support had the most prominent influence on both music teacher satisfaction and retention.