Tree layer dynamics of the Cahnov–Soutok near-natural floodplain forest after 33 years (1973–2006)

The paper deals with the issue of the spontaneous development of Central-European floodplain forests. The research object was the Cahnov–Soutok National Nature Reserve situated on the confluence of Dyje R. and Morava R. in the Czecho–Slovak-Austrian borderland area. This locality has been left to spontaneous development since the beginning of the 1930s. In the years 1973, 1994 and 2006, the surveyed site was subjected to the measurement of standing and lying, live and dead trees reaching a diameter at breast height of 10 cm and the whole area regeneration of woody species. The work objective is to describe the most pronounced trends in tree layer changes having occurred in the period of study and to capture changes in the total tree volume and production of dendromass during the disintegration of the old grazing oak layer. The survey into the near-natural floodplain forest of Cahnov–Soutok showed that (1) the most significant trend is a decreased representation of Quercus robur in all monitored indicators and conversely an expanding representation of Acer campestre, Carpinus betulus and Tilia cordata and (2) that the floodplain forest ecosystem demonstrates a high-level stability in the total volume of tree biomass with an essential change in the tree species composition, spatial structure and average stem volume of individual trees.     

Dynamics ofBetula ermanni population in subalpine vegetation in Changbai Mountain, Northeast China

Betula ermanni population was divided into three groups: the upper population (2 000–2 200 m), the middle population (1 700–2 000 m), and the down population (1 400–1 700 m) in Changbai Mountain. The dynamics ofBetula ermanni populations in subalpine vegetation are studied and the population life table, fecundity schedule, survival curves, age structure, and fecundity curves were established. The results showed that the, middle population is obviously, the transition from the upper population to the down population. This project is supported by Chinese Academy of Science Responsible editor     

萝卜缨微波真空干燥动力学研究

[目的]更好地调控萝卜缨生产加工过程中工艺参数,进一步研究萝卜缨微波真空干燥的特性及其干燥过程的动力学模型.[方法]采用微波真空干燥技术对萝卜缨进行干制,通过对萝卜缨微波真空干燥特性的研究,分析了微波功率、真空度和装载量与干燥速率的关系,并根据试验数据,分别作不同微波功率、真空度和装载量下的t与-lnMR曲线和lnt与ln（-hnMR）曲线,[结果]试验发现,萝卜缨的干燥过程大致可分为3个阶段,加速期、恒速期和降速期.不同微波功率、真空度和装载量下的t与-lnMR曲线和lnt与ln（-lnMR）曲线显示,前者呈非线性,后者呈线性,表明萝卜缨的微波真空干燥动力学模型满足Page方程.通过多元线性回归分析,拟合方程显著（P＜0.05）,拟合度良好,相关系数R2=0.93.最后经验证,Page方程的预测值与实际值拟合良好.[结论]研究可为萝卜缨的干燥提供理论依据和技术指导.     

北部湾底层渔业资源的数量变动和种类更替

根据渔业统计资料和底层渔业资源调查数据，分析了北部湾底层渔业资源的数量变动和种类更替。（１）北部湾底层渔业资源的密度指数有明显的季节变化，这一变化主要是本海域主要底层种类生长，死亡和补充共同作用的结果；（２）主要经济种类的组成随捕捞压力的增加而变化，其种类更替的趋向是质量差，寿命短，个体小和营养层次低的种类的比例上升，质量高，寿命长，个体大和营养层次高的种类的比例下降；（３）多鱼种渔业资源的潜在渔     

不同生长时期小叶锦鸡儿黄酮类化合物含量的变化动态

为研究小叶锦鸡儿(Caragana microphylla Lam.)各部位黄酮类化合物动态变化规律,确定其适宜采收的部位和时期,采用硝酸铝显色法测定了不同生长时期小叶锦鸡儿植株各部位的总黄酮含量。结果表明:一年生去叶枝及根中总黄酮含量于4月达到最高,分别为1.021%和0.249%,半年生去叶枝和二年生去叶枝于9月达到最高,分别为0.990%和0.868%。半年生枝、一年生枝和二年生枝上叶总黄酮含量分别在在9月、7月和6月达到最高,分别为2.669%,2.517%和2.223%。半年生枝和一年生枝上的花总黄酮含量在5月达到最高,分别为3.324%和3.368%,二年生枝上花在4月达到最高,为3.345%。半年生枝、一年生枝和二年生枝上种子总黄酮含量均在7月达到最高,分别为0.837%,0.840%和0.812%。总黄酮含量的高低顺序为花>复叶>去叶枝韧皮部>去叶枝>种子>去叶枝木质部>根韧皮部>根木质部。如以黄酮类物质的利用为目的,应重点采集花、复叶及枝条的韧皮部,并应在9月采集一年生和半年以内枝、叶,保留其地下部分,有望获得较高的得率。     

林火干扰与森林群落动态研究综述

林火是森林生态系统最常见的干扰类型,在森林群落演替中起着重要的作用。本文回顾了林火对森林群落演替的影响、物种对火干扰的适应、火干扰与森林更新、火干扰与物种和景观多样性、火干扰森林群落动态的研究方法,讨论了未来研究方向。     

定西县土地人口承载力研究

本文在全面分析定西县自然资源的基础上,运用系统动力学模型,对定西县土地人口承载力进行了较为深入的研究,同时提出了协调人地关系,促使定西县经济较快发展的建议与对策。     

不同耕种时间下土壤剖面盐分动态变化规律及其影响因素研究

以新疆奇台县绿洲不同耕种时间土壤含盐量为研究对象,运用聚类分析与相关分析法对其含盐量变化规律、盐分剖面类型及其影响因素进行了研究。结果表明:在荒地转化成人类熟作的农田(5 a以上)过程中,土壤剖面盐分特征变化依次为表聚型、均匀型、震荡型和底聚型。未耕地土壤含盐量高,是典型的盐渍土,且表层聚集现象明显,含盐量在表层(0～20 cm)占整个剖面的34.31%。耕种5 a、10 a的土壤,多为底聚型盐分剖面。随耕种时间加长,土壤各层含盐量的活跃程度变化依次为活跃层、次活跃层和较稳定层;土壤含盐量与有机质含量的关系由极显著正相关转变为极显著负相关,而与土壤pH的关系变化则相反。有耕作活动的土壤盐渍化发生了逆向演替,耕种10 a土壤平均含盐量仅为未耕地的20.90%,脱盐速度随着时间的增加而减小,由早期(0～3 a)的1.56 g kg-1a-1,下降为后期(5～10 a)的0.04 g kg-1a-1。     

Linear viscoelasticity of gluten: Decoupling of relaxation mechanisms

The influence of water content on the relaxation dynamics of mesoporous gluten networks has been explored in a wide range of temperatures. The systems were investigated in the linear viscoelastic region by means of stress relaxation, creep and numerical analysis of data. Time-temperature superposition principle and sticky reptation dynamics have been used to provide molecular interpretation of gluten relaxation. Overall, hydration influences relaxation behaviour of the system, which can be linked to changes in the secondary structure of gluten proteins with increase in water content. Relaxation spectra calculated with Tikhonov regularization revealed the remarkable influence of water on the long times relaxation processes of the material. Creep measurements and extraction of dynamic data with direct conversion of creep data via Laplace transform augmented the experimental timeframe of observations to low frequencies unattainable by standard frequency sweeps. The predominance of loss modulus at long times is attributed to migration of water within the nanopores of the structure. Samples also exhibit self-similar relaxation a characteristic of systems existing at a critical state. Two relaxation mechanisms can be distinguished: one arising from viscoelastic relaxation of protein chains and an additional stemming from poroelastic relaxation owing to migration of water in the system.     

连续挖坑机的动力学分析

利用矩阵法与现代电子计算技术相结合,系统地对连续挖坑机进行了动力学分析。在曲柄的一个旋转周期内,每间隔4°转角计算主运动四杆机构曲柄上总驱动力矩T_0的变化情况,并将其绘成直观的曲线,得出了该机构各铰链上的作用力及两个连架杆对机架的联合作用力(即所谓的颤动力),且将其制成力变化的极坐标图。利用上述结果,对连续挖坑机的动力特性进行了阐述,为结构设计提供了必要的参数。