臭氧胁迫对树木根系影响研究进展

对流层中高浓度的臭氧是一种严重危害植物的大气污染物,臭氧浓度的升高会对农作物、林木等产生一系列的损害。根系是树木生存的基本要素,臭氧对根结构的根本性改变会最终影响根功能,从而影响树木的整体健康以及对环境胁迫的抗性,通过综述臭氧胁迫对森林树木根系影响的研究进展,可以为我国学者进一步了解臭氧对森林树木根系生态影响提供科学素材。有关大气臭氧浓度升高对森林树木根系生态的影响,目前研究主要包括森林树木根系生长、细根动态和周转、根系呼吸、根系碳水化合物、菌根、根际微生物的响应变化等几个方面。臭氧对树木根系的影响与臭氧浓度、树种、树龄、群落组成及种植条件相关。目前有关臭氧胁迫对树木根系的机制研究还比较缺乏,今后应该加强臭氧胁迫下根系形态构型的原位观察测定和定量分析研究,内源激素响应,胁迫信号感受、转导与其它信号途径的互作关系以及分子生物学机制方面的研究。     

The relation between biomass yield and linear measures of growth in Sesbania sesban in western Kenya

Various linear measurements were made on 115 provenances of Sesbania sesban var. nubica to establish their relationships with woody and leafy biomass yields of the trees after a year's undisturbed growth. Data were subjected to simple and multiple linear regression analyses. There were significant (P < 0.001) correlations in most cases but particularly so with leafy and total biomass where over 50% of the variations were accounted for by their regression on stem diameter at knee height (DKH). When data for dependent variables were logarithmically transformed, better regression coefficients (over 60%) were obtained for stem diameter at breast height (DBH) and DKH.     

高产海岛棉田土壤微生物学特性研究

用混菌平板法和稀释频度法 ( MPN)对中壤土高产海岛棉田中的细菌、真菌、放线菌的数量与分布进行了测定。结果表明 ,细菌是中壤土海岛棉田微生物生命活动的最主要参与者。棉田三类土壤微生物呈现明显的季节变化。 0～ 2 0 cm的土层是微生物集中分布和生物学活性最大区域。氮素生理群中氨化细菌最多 ,芽孢细菌次之 ,硝化细菌再次之 ,好气性固氮菌最少     

防腐剂在烟熏火腿中的应用研究

通过正交试验发现,最佳的减菌剂组合为:乙酸2%,乳酸钠3%,VC1%,硫代硫酸钠4%,山梨酸钾1%。筛选了3种有效的防腐剂,并通过3因子二次通用旋转组合设计建立了防腐模型,所得回归方程能有效代表实际情况,最优组合为:Nisin0.038%,EDTA2.005%,乳酸钠2.843%。验证实验显示,组合防腐剂能有效抑制烟熏火腿中微生物的生长,使产品细菌总数不超过10000cfu/g,在温度0￣4℃条件下,烟熏火腿的贮藏期达21d以上,延长保质期10d以上。     

Use of posterior predictive assessments to evaluate model fit in multilevel logistic regression

Assessing the fit of a model is an important final step in any statistical analysis, but this is not straightforward when complex discrete response models are used. Cross validation and posterior predictions have been suggested as methods to aid model criticism. In this paper a comparison is made between four methods of model predictive assessment in the context of a three level logistic regression model for clinical mastitis in dairy cattle; cross validation, a prediction using the full posterior predictive distribution and two “mixed” predictive methods that incorporate higher level random effects simulated from the underlying model distribution. Cross validation is considered a gold standard method but is computationally intensive and thus a comparison is made between posterior predictive assessments and cross validation. The analyses revealed that mixed prediction methods produced results close to cross validation whilst the full posterior predictive assessment gave predictions that were over-optimistic (closer to the observed disease rates) compared with cross validation. A mixed prediction method that simulated random effects from both higher levels was best at identifying the outlying level two (farm-year) units of interest. It is concluded that this mixed prediction method, simulating random effects from both higher levels, is straightforward and may be of value in model criticism of multilevel logistic regression, a technique commonly used for animal health data with a hierarchical structure.     

PROGNOSTIC SIGNIFICANCE OF TUMOR HISTOLOGY AND COMPUTED TOMOGRAPHIC STAGING FOR RADIATION TREATMENT RESPONSE OF CANINE NASAL TUMORS

Prognostic significance of tumor histology and four computed tomography (CT) staging methods was tested retrospectively in dogs from three treatment centers that underwent intent-to-cure-radiotherapy for intranasal neoplasia. Disease-free and overall survival times were available for 94 dogs. A grouping of anaplastic, squamous cell, and undifferentiated carcinomas had a significantly shorter median disease-free survival (4.4 mo) than a grouping of all sarcomas (10.6 months). Disease-free survivals were not significantly different, when all carcinomas were compared with all sarcomas. The published original and modified WHO staging methods did not significantly relate to either survival endpoint. A modified human maxillary tumor staging system previously applied to canine nasal tumors was prognostically significant for both survival endpoints; a further modified version of that CT-based staging system resulted in improved significance for both survival endpoints. Dogs with unilateral intranasal involvement without bone destruction beyond the turbinates on CT, had longest median survival (23.4 months); CT evidence of cribriform plate involvement was associated with shortest median survival (6.7 months). Combining CT and histology statistically improved prognostic significance for both survival endpoints over the proposed CT staging method alone. Significance was lost when CT stages were collapsed to 相似文献   

不同试验条件下猪肉中气单胞菌生长预测模型的建立和验证

采用响应曲面模型(RSM)研究温度、pH、初始菌浓度对冷却猪肉中气单胞菌Aeromonas spp.生长的影响.应用Gompertz模型对不同试验条件下气单胞菌的生长曲线进行拟合,一级模型的参数生长率(U)和迟滞期(LPD)采用RSM方法构建冷却猪肉中气单胞菌生长的二级模型.然后随机选择试验组合对建立的方程进行验证,并应用计算均方误差(MSE)、准确因子(AF)和偏差因子(BF)的方法对建立的生长预测方程进行数学检验.结果表明,修正的Gompertz模型可以较好地模拟不同试验条件下冷却猪肉中气单胞菌的生长情况(R2>0.96),温度、pH和初始菌浓度对气单胞菌生长影响显著(P<0.05),数学检验参数MSE较小,AF和BF接近1.0,均在可接受范围,用RSM方法建立的生长预测模型可以较好地模拟冷却猪肉中气单胞菌在不同试验条件下的生长情况.     

The compensation method for the random time-delay of the feedbackchannel and the forward channel in the networked control system

An improved predictive control method is presented to compensate the random time delay in the networked control system. The feedback time delay is compensated by predictive controller based on softened increment input strategy. The forward time delay is unknown for controller, so an extra feedback loop is added to compensate the delay by estimating the error between the actual control signal effected on plant and the output of controller in historical moment. For the controlled system with unknown or slowly varying parameters, the networked feedback correction algorithm is discussed based on a modified recursive least-squares identi cation algorithm. The system stability is analyzed and the simulation results show that the time delay in the networked control system can be accurately compensated. The excellent network performance is ensured with this strategy.     

A quantitative analysis of temperature-dependent dormancy changes in Polygonum aviculare seeds

Mathematical models that predict emergence of weed seedbanks could be useful tools for determining the most suitable time for weed seedling control and, consequently, should result in a higher efficacy of applied control methods. To achieve this goal in dormant weed species, functional relationships should be established between environmental factors regulating dormancy and dormancy changes of seed populations. In the present work, we used a simple model and an optimisation procedure to quantify the effect of temperature on Polygonum aviculare seed dormancy release and induction, based on germination data. Dormancy release rate was inversely related to temperature, showing a decreasing logistic trend that results in no dormancy release for seeds exposed to 20 and 25°C. In contrast, dormancy induction rates in absolute values were positively associated with temperature, showing a logistic trend in which dormancy induction was almost zero at low temperatures and maximal at 25°C. Derived model parameters were used to simulate dormancy changes of P. aviculare seeds stored under controlled and field conditions. These results suggest that similar model structures could be used to quantify temperature effects on seed dormancy status of other weed species and to develop predictive models of weed emergence.     

害虫区域测报技术

大多数农作物害虫都是高度活动的，它们的数量和造成的为害在时间和空间上都大不一样，季节活动型和造成的为害率也因地域和年份而异。要预测害虫在一个区域范围的出现，数量，种群趋势和潜在为害，就要建立完善的监测体系，多年定点观测记录对于区域害虫预测来说是最基本的资料条件，与此同时，通过数学方法把害虫的发生与相关因子以数量化的形式表示出来，并在此基础上建立中长期预测模型是至关重要的，为了及时处理和传递虫情信息，计算机数据管理技术和网络技术将为此提供最重要的技术支撑。本文通过一些典型的应用实例，讨论了监测技术，预测模型。GIS技术，数据管理技术以及网络技术在区域害虫预测中的应用。