The amphibian chytrid fungus along an altitudinal transect before the first reported declines in Costa Rica

Amphibian populations have declined and disappeared in protected and apparently undisturbed areas around the world, especially in montane areas of the tropics. The amphibian chytrid fungus, Batrachochytrium dendrobatidis has been implicated in many of these declines. In Costa Rica most declines occurred in the highlands. We examined an amphibian collection made in Braulio Carrillo National Park in 1986 for the amphibian chytrid fungus B. dendrobatidis, prior to the well documented amphibian declines in Monteverde, along an altitudinal transect from 100 to 2600 m elev. Skin from the pelvic patch of 202 specimens corresponding to 30 species was examined histologically to determine whether the disease was present in the highlands of the park before amphibian populations declined. For comparison, in 2002 we collected and examined 18 specimens of seven species of Eleutherodactylus and Craugastor from two other lowland Caribbean sites. The chytrid fungus was present in almost all altitudes in 1986, including lower areas. The pathogen was also found in both species that later declined and in species that did not do so. We detected chytrid fungus on amphibians collected at almost all altitudes in 1986, including those sampled at 280 m. B. dendrobatidis was abundant in frogs collected in the 2002 survey, and seems to be endemic in most of Costa Rica. More retrospective museum surveys are needed in order to determine whether it can be found in the area before 1986.     

Characterization of a USDA Kentucky Bluegrass (Poa pratensis L.) Core Collection for Reproductive Mode and DNA Content by Flow Cytometry

Kentucky bluegrass (Poa pratensis L.) is an important turf and forage grass species with a facultative apomictic breeding behavior. In this study, mature seed and leaf tissue from 38 accessions of a USDA core collection of Kentucky bluegrass were analyzed with flow cytometry to characterize the reproductive mode and DNA content for each accession. Major reproductive pathways for each accession were determined based upon the presence and the position of the peaks observed and the known methods of reproduction for Kentucky bluegrass. While the majority of the accessions exhibited facultative apomictic reproductive behavior with a combination of reduced, zygotic and unreduced, parthenogenic embryo production, obligate sexual or obligate apomictic accessions were also found to be present in this core collection. In addition, reduced, parthenogenic and unreduced zygotic embryos were also detected in several accessions. Flow cytometric analysis of somatic tissue revealed a large range of DNA variation within this core collection. We also examined the sensitivity of flow cytometry in analyzing bulked samples containing a large number of plants with varied DNA content and determined that flow cytometry can effectively detect a plant having a different DNA content within a 15-plant bulk sample. Overall the combination of mature seed and somatic tissue analysis generated important information for the Kentucky bluegrass core collection and can be an effective and affordable tool to characterize even greater numbers of Kentucky bluegrass accessions.     

旱改水对土壤铜含量及其有效性的影响研

旱改水对土壤Cu含量及其有效性的影响研究结果表明 ,代换态铜是土壤中Cu的强度因子 ,而晶形铁结合态铜和残留态铜为植物无效态铜且需经形态转化才有效 ,其他形态铜既是容量因子也是强度因子 ,其有效程度大致为无定形铁结合态铜 >有机结合态铜 >氧化锰结合态铜 >碳酸盐结合态铜。旱改水促进碳酸盐结合态铜、氧化锰结合态铜尤其是残留态铜向代换态铜、无定形铁结合态铜和有机态铜转化 ,提高土壤铜有效性和可移动性 ,并使Cu淋溶损失 ,导致水旱轮作土壤耕层全Cu贫化     

山东省生态农业发展典型模式及其评价

简析了山东省生态农业发展中果农牧渔综合发展模式、开放复合型生态、经济结构模式、“四位一体”生态温室种养模式、枣粮间作模式、“上农下渔”模式和产业化主导型生态农业发展模式的概况、效益及评价。     

低山丘陵区沟壑三维梯级治理开发模式研究

朝阳市水土流失面积 1195 1 4km2 ,占全市总面积的 60 67% ,沟壑侵蚀面积占水土流失面积的 2 2 40 %。利用沟壑纵剖面信息熵分析法 ,进行沟壑侵蚀地貌形态计量分析 ,按照沟壑三维特征值变化规律 ,将沟壑侵蚀概化为前期、中期、后期三个阶段。采取典型沟壑治理开发试验与大面积沟壑治理开发应用相结合的研究方法 ,建立沟壑三维梯级治理开发措施体系 ,取得了显著的生态、经济和社会效益。     

INFLUENCE OF PUMPING POWER CHANGE ON CW Nd:YAG LASER

This paper presents that pumping power change of Nd: YAG laser will induce not only gain change but also loss change. As a result, it induces oscillating mode change, laser cavity unstable, and the complicated change of laser output power. On the basis of a large theoretical calculation and experimental support, the paper shows that the plane-parallel cavity is more suitable for the multimode operation and the plane-convex or concave-convex cavity for the single mode operation     

Virtual Signal Analyzer Based on Hilbert-Huang Transform

Hilbert-Huang transform(HHT) is a new method for signal analysis developed by Norden.E.Huang et al in 1998.The concepts for main contents,Empirical mode decomposition,Hilbert spectrum and marginal spectrum of Hilbert-Huang transform(HHT) are introduced.Based on the characteristics of VI's development and application,combining software and hardware,the designed method,which includes hardware,software and panel for the Virtual Signal Analyzer Based on Hilbert-Huang Transform are introduced.Based on the HHT,combined with virtual instrument technology,a Virtual Signal Analyzer is developed successfully.It has provided a new method for signal test and analysis.     

农业综合开发科技推广的特征分析与模式创新研究 ——?以南通市优质稻米产业区为例

科技推广作为农业综合开发项目重要组成部分，运作的好与差将直接影响着项目实施效果。分析了农业综合开发科技推广具有综合性、主导性、普及性、应用性等基本特征。结合南通市的具体实际，以机制创新为突破，从农业综合开发科技推广的运行、组织、推广等层面探索出工作新模式。提出了通过推行科技委托制创新其运行模式、建立推广项目组创新其组织模式、健全联动新机制创新其推广模式。并以南通市优质稻米产业区为例进行了探索与实践，科技推广工作取得了显著成效，有效地发挥了科技在农业综合开发项目中的支撑作用。     

ELECTRICAL CONTROL SYSTEM ANALYSIS FOR THE MECHANICAL TRANSMISSING TEST BED

This paper analyzes and proves the seeking for projects of the test bed, the equivalent processing for the bi-electric machine set and the control and loading modts of the test bed. It also introduces briefly the features of the block diagram of the control system and gi.ves the test waveforms. Finely, it points out the problems to be further studied.     

Fast Animation Display of Large Structure with Multistep Modes

The method that the MASM assembler is interlaced to the MS-FORTRAM 5. 0 is used to store some step structural mode drawings in the designated disk file through their visiting VRAM,which are then restored in it when needed in order to realize the quick animation display of the mode. This method solves the problem of insufficient memories in storing multistep structural mode drowings with the ordinary method. As a functional modular of finite element analysis programs SAPS and ADINA transplanted to a microcomputer,the modular programed with the above method can quickly display the animation of large structure with multistep modes.