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1.
The lower Mississippi River(LMR) has been heavily modified for multiple human purposes such as navigation, flood control, and bank stabilization. However, the LMR simultaneously supports a diverse fish fauna that includes recreational and commercial fisheries. Due to river training and diversion structures constructed during the past 80 years, the historic characteristics of the LMR have been drastically altered and have likely influenced fishes and fisheries in the system. One common restoration measure used throughout the LMR has been to "notch" wing-dike structures that close secondary(side) river channels. Dike notching allows year-round flows through secondary channels, which enhances habitat diversity and promotes biological productivity at the ecosystem scale. Although notching is presumed good for LMR fishes and other biota, few studies have examined its effects on fish assemblages. In this study, fish assemblages were sampled at seven LMR secondary channels spanning from river kilometer(rkm) 628(Louisiana-Mississippi, U.S.A.) upstream to rkm 1504(Missouri-Kentucky, U.S.A.). Four secondary channels were termed "permanent"(i.e.,with notched dikes) while three secondary channels were termed "temporary"(i.e., without notched dikes).Fishes were sampled by boat-mounted electrofishing conducted during falling and low stages from1995—1997. Fish assemblages differed between permanent and temporary secondary channels, and varied somewhat between falling and low stages. Gizzard shad(Dorosoma cepedianum), threadfin shad(D. petenense), and white bass(Morone chrysops) demonstrated consistent preferences for low-current conditions associated with temporary secondary channels. Conversely, blue catfish(Ictalurus furcatus), flathead catfish(Pylodictis olivaris), and freshwater drum(Aplodinotus grunniens) were more associated with permanent secondary channels. Future restoration strategies in the LMR should consider dike notching and resultant maintenance of permanent secondary channels in selected river reaches. However, temporary secondary channels also contain unique fish species, and also appear to be important sites of riverine primary production. Restoration strategies should consider a balance of both secondary channel types, which should support the greatest biodiversity for the LMR ecosystem.  相似文献   

2.
付义强  刘忠 《四川动物》2008,27(2):244-244
2008年1月17日下午4时左右,笔者在四川乐山市水口镇大渡河边发现1只家燕正在河面低空飞行捕食.2008年1月25日西华师范大学杨志松博士在该市岷江边天池村及金灯村一带先后发现5小群家燕,分别为4只、1只、10只、1只和3只;同日,胡杰博士在该市青衣江边(金水湾至乐山高新区江段)也发现2小群家燕,分别为4只和6只.  相似文献   

3.
每年有大量来自工业、农业、养殖业和城市污水处理厂的废水被排入到水环境中,因此,地球上的水环境面临大量来自生活废水、工农业废水、非法排放的废水及其它废水的污染物质(如抗生素、杀虫剂,除草剂、烃等)的严重挑战,特别是近年来随着集约化养殖的发展,废水污染问题日益突出,并且随着分析手段的进步,能够检测到被排入水环境中的化学污染物质也越来越多,这些化学污染物对水环境中的生物产生有害影响.但是,微生物在污染控制上具有许多重要的作用.因此,本文对微生物在水环境污染物降解中的应用进行了评论.结果表明微生物主要是应用在水产养殖水中,而在其它的水体系(如河、湖、海)的应用较少.  相似文献   

4.
Currently, there does not exist a strategy that can reduce diabetes and scientists are working towards a cure and innovative approaches by employing stem cellbased therapies. On the other hand, bioprinting technology is a novel therapeutic approach that aims to replace the diseased or lost β-cells, insulin-secreting cells in the pancreas, which can potentially regenerate damaged organs such as the pancreas. Stem cells have the ability to differentiate into various cell lines including insulinproducing cells. However, there are still barriers that hamper the successful differentiation of stem cells into β-cells. In this review, we focus on the potential applications of stem cell research and bioprinting that may be targeted towards replacing the β-cells in the pancreas and may offer approaches towards treatment of diabetes. This review emphasizes on the applicability of employing both stem cells and other cells in 3 D bioprinting to generate substitutes for diseased β-cells and recover lost pancreatic functions. The article then proceeds to discuss the overall research done in the field of stem cell-based bioprinting and provides future directions for improving the same for potential applications in diabetic research.  相似文献   

5.
神锢的松动     
郭建崴 《化石》2016,(3):59-60
正如前所述,欧洲历史上的中世纪是个"黑暗时代"。作为当时封建社会的精神支柱,基督教教会把上帝当做绝对的权威,建立了一套严格的等级制度。人的一切思想和行为都必须依《圣经》而为,否则就要受到教会的制裁,甚至被教会设立的宗教审判所处以各种残酷的死刑。在教会的管制下,中世纪的文学艺术死气沉沉,科学技术也没有多少进展。11世纪以后的欧洲,随着经济的复苏与发展、城市的兴起以及生活水平的提高,人们逐渐  相似文献   

6.
丙泊酚应用于无痛人工流产800例分析   总被引:1,自引:0,他引:1  
目的:探讨丙泊酚在无痛人工流产术中的应用效果.方法:将886例早孕未产妇女和/或有剖宫产史妊娠妇女分为试验组和对照组,试验组800例,对照组86例.不采取镇痛麻醉的86例为对照组,试验组对人工流产病人施行丙泊酚静脉全身麻醉,并静脉给阿托品,其余操作同对照组.观察比较两组术中反应、手术时间、出血量与人工流产综合征的发生情况.结果:试验组病人无痛苦,舒适满意,手术时间明显缩短,无一例发生人工流产综合征.对照组69例(80.2%)诉疼痛难忍,11例(12.8)诉下腹痛但可以忍受,6例患者(7.0%)完全不痛.结论:丙泊酚具有高效,显效快速和安全的特点,静脉给丙泊酚可防止人工流产综合征的发生.  相似文献   

7.
激光处理植物种子产生的效应概述   总被引:2,自引:0,他引:2  
大量研究表明,激光处理植物种子,会对植物种子性能及其萌发的植物体产生各种各样的影响.光对植物体的生长发育起着重要的作用,各种植物体在自然光的环境中形成了稳定的生理形态,在短时间内种子及其以后萌发的植物体不会有生理形态上的明显变化.激光不是自然光,用激光处理植物种子会对植物种子性能及其萌发的植物体产生各种各样的影响.本文论述了激光处理对种子及其以后萌发的植物体产生的效应影响进展.  相似文献   

8.
Vocalizations play a critical role in mate recognition and mate choice in a number of taxa, especially, but not limited to, orthopterans, frogs, and birds. But receivers can only recognize and prefer sounds that they can hear. Thus a fundamental question linking neurobiology and sexual selection asks-what is the threshold for detecting acoustic sexual displays? In this study, we use 3 methods to assess such thresholds in tdngara frogs: behavioral responses, auditory brainstem responsesz and multi unit electrophysiological recordi ngs from the midbrain.We show that thresholds are lowest for multiunit recordings (ca. 45 dB SPL), and then for behavioral responses (ca. 61 dB SPL), with auditory brainstem responses exhibiting the highest thresholds (ca. 71 dB SPL). We discuss why these estimates differ and why, as with other studies, it is unlikely that they should be the same. Although all of these studies estimate thresholds they are not measuring the same thresholds;behavioral thresholds are based on signal salienee whereas the 2 neural assays estimate physiological thresholds. All 3 estimates, however, make it clear that to have an appreciation for detection and salienee of acoustic signals we must listen to those signals through the ears of the receivers.  相似文献   

9.
In this paper,a class of linear parabolic systems of singularly perturbed second-order differential equations of reaction-diffusion type with initial and Robin boundary conditions is considered.The components of the solution u→ of this system are smooth,whereas the components of αu→/αx exhibit parabolic boundary layers.A numerical method composed of a classical finite difference scheme on a piecewise uniform Shishkin mesh is suggested.This method is proved to be first-order convergent in time and essentially first-order convergent in the space variable in the maximum norm uniformly in the perturbation parameters.  相似文献   

10.
本文记了分别采自云南高黎贡山的栅蛛科栅蛛属Hahnia 2新种:垭口栅蛛,新种S.yakouensis sp.nov.和肾形栅蛛,新种S.reniformis sp.nov..垭口栅蛛后眼列前曲,交媾腔大,扁圆形,交媾孔1个,位于交媾腔下缘,交媾管粗,呈"人"字形下行分成2支再向两侧扭曲.纳精囊有一肓管斜向上伸出,鉴于上述特征而与Hahnia mridulae Tikader,1970不同.肾形栅蛛交媾孔2个,位于生殖厣腹面中央,纳精囊1对,大,肾形,插入器始于生殖球左下方,鉴于上述特征而与Hahnia xinjiangensis Wang et Liang,1989不同. Abstract: The present paper deals with two new species of the genus Hahnia collected from the Gaoligong Mountains Region of Yunnan Province, China: Hahnia yakouensis sp. nov., Hahnia reniformis sp. nov..  相似文献   

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