Change in spatial characteristics of forest openings in the Klamath Mountains of northwestern California,USA

Change in the spatial characteristics of forest openings was investigated in three forested watersheds in north-western Siskiyou County, California totalling approximately 24,600 hectares. Watersheds with minimal human disturbance were chosen for study. However, fire suppression has been pervasive throughout. Characteristics of forest openings (area, perimeter, distance between neighboring openings) were measured on aerial photographs taken 41 years apart. An index of regional form was determined for the landscape. Shape complexity for each opening was calculated using two indices based upon fractals. Significant differences were found using the Kolmogorov-Smirnov two-sample test between the perimeters, areas, distance from sample point to nearest opening, and distance between neighboring openings. The perimeters and areas became smaller, and the distances from the sample point to the nearest opening and between neighboring openings became greater over the 41 years between aerial photo sets. The estimated area occupied by openings decreased from 25.8 % to 15.6 % of the study area. No significant difference was found in the shape of the openings except as the shape indices were influenced by changes in size of the openings.This article was written and prepared by U.S. Government employees on official time, and it is therefore in the public domain and not subject to copyright.     

2006年夏季珠江口5大口门网采浮游植物群落的调查

于2006年8月记录了珠江入海口5个大面站位的网采浮游植物。经初步鉴定共计5门54属119种(包括6个变种,不包括若干未定名种)。此次网采浮游植物以淡水硅藻和绿藻为主,硅藻64种,约占总种数的53.78%,其中出现频率较高的属有菱形藻(Nitzschia)、小环藻(Cyclotella)、针杆藻(Synedra)等;绿藻门次之37种,常见属有栅藻(Scenedesmus)、盘星藻(Pediastrum)和新月藻(Closterium)。浮游植物细胞密度为2.085×105～2.40×106ind./m3,平均值为1.0443×106ind./m3,其中S2水域的细胞密度最高,S1次之、S3至S5依次减少。对多项群落特征参数如多样性和相似性等进行了分析,结果表明其生物多样性及物种丰富度都较高;其群落结构除S2外,各站位均处于相对稳定状态;站位之间群落组成的相似性不高。     

Analysis on Influence of Fault Location and Strength on Deformation and Stress Distribution of Surrounding Rocks of Large Underground Openings

The stability of rock mass project is mainly controlled by the rock mass structure, and faults are the large geological discontinuity plane commonly encountered in rock mass engineering. The stability of surrounding rocks is restricted by mechanical property and location to underground cavern of faults, the detailed studies carried out by analysis of numerical calculation and construction monitoring datum of underground powerhouse of Three Gorges Project show: the distribution of stress and deformation of surrounding rock masses containing a fault are badly deteriorated, the distribution of stress and deformation are obviously different under different natural stress field and position of fault; The influence of friction strength of fault on deformation of surrounding rocks is more obvious when a fault is located near the crown, but the cohesion is more when wall nearby, and the influence is more distinct with side pressure coefficient increases.     

钢筋混凝土开孔梁的裂缝和破坏特点

通过可视化非线性有限元分析系统对带矩形孔的梁在集中荷载下的全过程仿真分析,详细研究开孔梁的应力、变形、裂缝以及破坏特征等等,总结出其裂缝和破坏的一些特点,为建立开孔梁的设计、验算方法提供更多依据。     

柴油机瞬态VNT开度优化研究

瞬态工况下,可变喷嘴涡轮增压器(Variable Nozzle Turbocharger,VNT)开度的调节对柴油机增压压力、扭矩响应及污染物排放具有较大影响.为优化瞬态工况下VNT开度,实现瞬态工况下柴油机与VNT的协调控制,该研究以配备VNT的高压共轨柴油机为对象,通过台架试验研究了不同转速下负荷1、3和5 s从0...     

Bearing Capacity of Reinforced Concrete Continuous Deep Beams with Web Openings Based on ANSYS Analysis

Based on the experiment on two-span continuous deep beams with web openings bearing concentrated load, setting a series of finite element simulation specimens and establishing finite element model by finite element analysis software ANSYS, the influences of the strength of concrete, the open hole size, the hole position, vertical reinforcement ratio and horizontal reinforcement ratio on bearing capacity and deflection of specimens were contrasted when imposed respectively.     

一种基于强度理论的大客车开口变形分析新方法

对客车车窗玻璃的大开口变形分析,传统的对角线长度变化评价法和变形翘曲度评价法都属于一种整体评价法,没有考虑玻璃材料的力学性能,无法准确预测开口变形是否会造成玻璃窗的破坏,破坏的具体部位在何处。本文提出一种利用已有有限元模型,基于强度理论的连续介质开口变形的计算方法。通过观察第一主应力或第一主应变云图,即可对车窗玻璃开口变形的安全性做出定量判断,并根据云图分布情况对危险部位提出合理的改进措施。     

A DYNAMIC ANALYSIS OF UNSYMMETRICAL FRAMEWALL STRUCTURE

The frame-wall structure is good both in operational performance and mechanical property. In this paper, the shear-wall is considered as a cantilever thin-wall member, and the frame as a multistoreyed shear model. The theory of structural matrix is used to get a series of stiffness matrix formulas of theunsymmetrical framewall structure. The Largrange equation is used to get dynamic equation of the structure in the form of matrix. At last a 43 storeyed model of unsymmetrical frame-wall structure is calculated, the result is close to the test.     

抗旱剂XJ的抗旱增产能力的研究

利用当地抗旱植物与工业废料经化学处理自制的抗旱剂ＸＪ，经１９９１年以来陆续用于小麦、棉花、甜菜等作物种子处理，苗期水培、盆栽浇灌尤其是盆栽、大田叶面喷施，证明确为一种新型抗旱增产剂。大田喷施增产幅度达２０％～５０％，优于目前市售抗旱剂或叶面肥。研究了该剂对植物的生理特性的调节作用，如叶面气孔的部分关闭吕绿素含量的提高及根系的变化以探索该剂的抗旱增产机理。