952 resultados para Hulthen potentials


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外来生物入侵已严重影响生态系统的结构和功能,威胁生物多样性,受到国内外学者的高度重视。我国50%的外来有害植物是人为引种的结果。因此,在引种造林之前对引入种的入侵潜力的研究和评估极为重要。过去几十年,中国南方地区外来的红树植物物种经常被用于人工造林,但这些外来植物的入侵性却缺乏系统的研究。本研究将个体、种群、群落和生态系统四个尺度的研究有机结合,对海南和广东两地的原产于孟加拉国的红树植物无瓣海桑(Sonneratia apetala) (1985年由申达本引入海南东寨港,1993年引种到深圳)和原产我国海南的海桑(S.caseolaris) (1993年引种到深圳)的生物学特性如种子和幼苗的扩散特性、光合生理特性、抵抗潮汐淹水特性以及本地种、外来种林下和光滩大型底栖动物的营养关系进行了综合研究,结论如下: 1. 果期长和果实种子数量大是海桑属植物的共有特点,但海南的本地种海桑不管在海南还是在引种地深圳都具有比引入种无瓣海桑更优势的萌发和漂浮能力。在没有天然海桑属植物分布的天然红树林区开展海桑属植物造林,应高度重视海桑属红树植物果实和种子的漂浮以及萌发早期的幼苗漂浮可能造成的扩散。 2. 通过对深圳福田红树林保护区实验区引种海桑和无瓣海桑幼苗的自然更新和种苗扩散的调查结果表明:海桑和无瓣海桑在深圳湾经过十几年的引种驯化之后,幼苗的更新和扩散能力逐年增高。虽然林下当年生幼苗受光强和温度等环境因子的影响在定居后大量死亡,林缘、林内空地和光滩上良好的光照条件很适合这些红树幼苗的生长。这是近年来深圳福田国家级自然保护区周边出现海桑和无瓣海桑幼苗扩散现象的主要原因。幼苗成功定居相关的机制有待进一步的研究。 3. 在海南,引种的无瓣海桑的光合速率(A)和光合N利用率(PNUE)都低于本地种海桑和白骨壤,而在深圳引种的海桑和无瓣海桑其光合速率和营养循环速度与本地种相当或低于本地种。因此,海南的外来种与本地种红树植物竞争生境的可能性不大,而深圳的外来种海桑具有较高的光合速率(A)和光合N利用率(PNUE),和本地红树植物竞争生境的可能性依然存在。因此,海南以外的天然红树林区,引种的海桑与本地的红树植物竞争生境的可能性依然存在。 4. 无瓣海桑对潮汐淹水时间的敏感性低于海南本地种海桑,在淹水时间最长的10-12 h的淹水处理下,无瓣海桑还能通过增加茎长度、扩大叶面积来缓解厌氧胁迫和增加光合速率。因此,无瓣海桑比海桑具有更强的抗淹水能力。从叶片气体交换和养分利用的特征上来看,由于同属的海桑和无瓣海桑在天然状态下存在生态位重叠,因此,从本研究的结果看,它们对于中低潮带的生态位竞争是可能存在的。在低潮带无瓣海桑的生长较海桑有优势,因此低潮带区域很可能成为无瓣海桑与海桑竞争空间和资源的主要区域。 5. 人工海桑林的动物营养结构相对于光滩和天然白骨壤林都发生了一定的变化。人工海桑林的动物之间对于食物的竞争大于天然白骨壤林。因而,造林后的海桑人工林的营养结构的稳定性可能低于天然白骨壤林。但是,对于各种底栖动物的可能食物来源和营养关系的证明还需要进一步研究。 基于以上研究结果,本研究结论如下: 两种海桑属植物的果实、种子的数量和种苗的漂浮扩散特性都可能导致外来种幼苗在原生红树林周边的光滩和林缘空地成功定居,这一特点需要长期的监测。但是从植株的光合特性、潮汐淹水的适应性等生理生态学的证据表明:现阶段两个研究样地上的两种外来种红树植物发生生物入侵的可能性不大。但是,引种后在中、低潮位滩涂上存在外来种无瓣海桑与海南本地种海桑竞争生态位的可能性依然存在。对引种后人工生态系统的底栖动物多样性还需要进一步研究。

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Life cycle and population biology of a perennial halophyte Arthrocnemum indicum Willd, was studied from February 1992 to January 1993. During the 12 months, the population was exposed to great variations in soil salinity from 35 to 58 ms/cm2 and soil moisture ranging from flood to drought levels. Seasonal changes in dry weight are directly related to soil salinity stress. When salinity levels become low, the dry matter production increases. A little increase in dry weight from April to July indicates that more negative soil water potentials were limiting plant growth. Proline content increased considerably during the dry season with a corresponding increase in salinity. Water soluble oxalate did not vary much with changes in salinity.

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The present communication is a survey report carried out to assess the incidence of toxic mycoflora on seven types of agriculture products/by products incorporated during fish culture as supplementary dietary items. Samples were obtained from various sources at Darbhanga, Madhubani and Samashtipur districts during summer, winter and monsoon months. Out of the total 1774 samples, only 894 appeared to be fresh visually reflecting average incidence of contamination around 46.6%. However, the apparently fresh samples, when subjected to culture, 26.9% of them were found to be contaminated. Thus, degree of fungal spoilage in feed ingredients in parts of north Bihar appears to be significantly high (73.5%). The present study illustrates the facts with special reference to Aspergillus flavus, A. parasiticus (elaborating aflatoxins) A. ochraceous, Penicilium viradicatuin (elaborating ochratoxins) and A. versicolor (elaborating sterigmatocystin). The other strains already known for their toxigenic potentials that appeared on the present substrates included A. niger, A. fumigatus, A. candidus, P. islandicum, Rhizopus spp. and Mucur spp. Studies indicate that the prevalent climatic factors like temperature and relative humidity facilitate a congenial condition almost all through the year and in particular during summer and monsoon months. But water content of the substrates is a vital factor that further accelerates the pace of mycobial spoilage. A thorough sun-drying of the agricultural commodities before prolonged storage to bring water content below the "low risk limit" may significantly reduce the incidence of molds.

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The mixtures of factor analyzers (MFA) model allows data to be modeled as a mixture of Gaussians with a reduced parametrization. We present the formulation of a nonparametric form of the MFA model, the Dirichlet process MFA (DPMFA). The proposed model can be used for density estimation or clustering of high dimensiona data. We utilize the DPMFA for clustering the action potentials of different neurons from extracellular recordings, a problem known as spike sorting. DPMFA model is compared to Dirichlet process mixtures of Gaussians model (DPGMM) which has a higher computational complexity. We show that DPMFA has similar modeling performance in lower dimensions when compared to DPGMM, and is able to work in higher dimensions. ©2009 IEEE.

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An on-farm trial was undertaken in nine earthen ponds (400 to 640m2) to evaluate the growth and production potentials of climbing perch, Thai koi (Anabas testudineus) for the period of four months from March through June 2006. Three stocking densities such as 75,000 (T1), 100,500 (T2) and 125,000/ha (T3) were tested with three replications. Fish were fed with commercial (SABINCO) pelleted feed (35% crude protein). Fish productions obtained in three treatments such as T1, T2 and T3 were 6,480±217, 6,384±154, 6,617±187 kg· 1ha, respectively. The results demonstrated higher mean growth in T1 than in T2 and T3. However, the net benefit was achieved Tk. 7,26,975 from T1, where the stocking density was 75,000/ha.

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树突状细胞(Dendritic cells,DCs)作为人类免疫缺陷病毒(Human Immunodeficiency Virus,HIV)感染的第一靶细胞和第一道防线, 在HIV-1感染 和传播过程当中发挥重要的功能。DC的免疫功能主要包括抗原的捕获、加工、 递呈并激活T细胞对HIV-1作出免疫反应,这些功能的发挥依赖于其自身接受刺 激有效地分化和成熟。 与其它慢病毒(lentivirus)相同,HIV-1所具有的6种辅助蛋白(Nef,Rev, Tat,Vif,Vpr和Vpu),决定着病毒自身的复制增殖和对机体的感染和致病力。 目前,HIV-1辅助蛋白对CD4+ T细胞影响的研究较为深入,是否影响和调节DC 的分化和成熟尚不够清楚,现有的文献报道很少,且相互不一致甚至矛盾。因此, 建立合适的体外研究体系和细胞模型,有针对性地进行研究DC与HIV-1之间的相 互作用,将有助于加深对HIV/AIDS致病和发病机理的理解,具有重要的生物医 学意义。 本实验选择了可被HIV-1感染的白血病细胞系THP-1为实验模型,首先评价 了THP-1作为DC前体在研究DC分化、成熟中的可用性,特别是判定DC分化成熟 和功能状态的主要细胞表面标记的动态变化和规律。进而在相同条件下分析了6 个辅助蛋白基因对THP-1的凋亡诱导作用,证实了Nef和Tat确可诱导转染细胞自 身凋亡,而Rev和Vpr可在THP-1细胞中持续表达,形成了稳定的细胞系,为进一 步研究和比较Rev、Vpr对DC的分化、成熟的影响奠定了实验基础。更重要的是, 我们发现,Vif和Vpu不能在THP-1中有效表达,其原因可能直接与限制性因子 APOBEC3G的存在有关,提示Vpu与APOBEC3G可能存在着新的相互作用——这 一线索已作为实验室新的研究方向,进一步深入的研究可能为HIV/AIDS致病、 发病机理和机体的抗病机制提供新的科学依据。

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A study was undertaken examining the effect of malachite green on the development and survival of the zoeae, mysis and post-larvae of Penaeus monodon. Sensitivity varied with the different larval stages; the zoeae appeared to be the least tolerant. The prophylactic potentials of malachite green in the control of Lagenidiumand Zoothamnium infesting P. monodon larvae are considered briefly. Toxicity risks may be reduced by application between ecdyses or by the removal of the dye by filtration through activated carbon.

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In the present study, the effects of Mozart's sonata K.448 on voluntary and involuntary attention were investigated by recording and analyzing behavioral and event-related potentials (ERPs) data in a three-stimulus visual oddball task. P3a (related to inv

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Global information is considered the primitive of visual perception in Gestalt psychology. Further, L. Chen ( 2005) proposed a new theory of topological visual perception. According to this theory, the perception of topological difference is faster than o

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Acid-sensing ion channels (ASICs) are ligand-gated cation channels activated by extracellular protons. In periphery, they contribute to sensory transmission, including that of nociception and pain. Here we characterized ASIC-like currents in dorsal horn neurons of the rat spinal cord and their functional modulation in pathological conditions. Reverse transcriptase-nested PCR and Western blotting showed that three ASIC isoforms, ASIC1a, ASIC2a, and ASIC2b, are expressed at a high level in dorsal horn neurons. Electrophysiological and pharmacological properties of the proton-gated currents suggest that homomeric ASIC1a and/or heteromeric ASIC1a + 2b channels are responsible for the proton-induced currents in the majority of dorsal horn neurons. Acidification-induced action potentials in these neurons were compatible in a pH-dependent manner with the pH dependence of ASIC-like current. Furthermore, peripheral complete Freund's adjuvant-induced inflammation resulted in increased expression of both ASIC1a and ASIC2a in dorsal horn. These results support the idea that the ASICs of dorsal horn neurons participate in central sensory transmission/modulation under physiological conditions and may play important roles in inflammation-related persistent pain.

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Seaweeds have been used as food, medicine, fertilizers, soil conditioner and source of salt. Realizing the potentials of seaweeds, research and development thrusts have been geared towards improving and developing its product applications. Today, various applications of seaweeds have been developed and improved. The major success in the seaweed industry is the development of phycocolloids with the following specific applications: 1) agar; 2) carrageenans; and, 3) alginates.

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The culture of sargeant fish, or cobia (Rachycentron canadum) and eel (Anguilla spp) in the Philippines is discussed. Market potentials for the cultured products are examined.

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Crocodiles have a long breeding life, which ranges from 25-30 years. There are 27 species and subspecies of crocodiles throughout the world, 18 of which are in danger of extinction, the rest being threatened with declining population due to overhunting and habitat destruction. Two known crocodile species exist in the Philippines: Crocodylus mindorensis (freshwater crocodile) and C. porosus (saltwater crocodile). Killing adult crocodiles, as is being done now, drastically reduces the potential population. Moreover, toxic wastes from mines, destruction of marshes and riverine habitats, and the conversion of their natural habitats for fishponds additionally threaten their populations. Estimates indicate that there are only about 100 Philippine crocodiles in the wild now. The Crocodile Farming Institute (CFI) was established in Palawan, in 1987, in order to save the crocodiles from extinction in the Philippines. It is now one of the components of the Palawan Wildlife and Conservation Center, and aims to conserve the 2 endangered species in the Philippines and also to develop and introduce a suitable crocodile farming technology that will help uplift the socio-economic well-being of the Filipino people. CFI believes in the potential of commercial utilization of crocodiles as a dollar-generating industry for the Philippines. It is a very profitable business and could be a multi-million dollar industry. A brief outline is given of the economic and marketing potentials of farming crocodiles in the Philippines.

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The potential adverse human health and climate impacts of emissions from UK airports have become a significant political issue, yet the emissions, air quality impacts and health impacts attributable to UK airports remain largely unstudied. We produce an inventory of UK airport emissions - including aircraft landing and takeoff (LTO) operations and airside support equipment - with uncertainties quantified. The airports studied account for more than 95% of UK air passengers in 2005. We estimate that in 2005, UK airports emitted 10.2 Gg [-23 to +29%] of NOx, 0.73 Gg [-29 to +32%] of SO2, 11.7 Gg [-42 to +77%] of CO, 1.8 Gg [-59 to +155%] of HC, 2.4 Tg [-13 to +12%] of CO2, and 0.31 Gg [-36 to +45%] of PM2.5. This translates to 2.5 Tg [-12 to +12%] CO2-eq using Global Warming Potentials for a 100-year time horizon. Uncertainty estimates were based on analysis of data from aircraft emissions measurement campaigns and analyses of aircraft operations.The First-Order Approximation (FOA3) - currently the standard approach used to estimate particulate matter emissions from aircraft - is compared to measurements and it is shown that there are discrepancies greater than an order of magnitude for 40% of cases for both organic carbon and black carbon emissions indices. Modified methods to approximate organic carbon emissions, arising from incomplete combustion and lubrication oil, and black carbon are proposed. These alterations lead to factor 8 and a 44% increase in the annual emissions estimates of black and organic carbon particulate matter, respectively, leading to a factor 3.4 increase in total PM2.5 emissions compared to the current FOA3 methodology. Our estimates of emissions are used in Part II to quantify the air quality and health impacts of UK airports, to assess mitigation options, and to estimate the impacts of a potential London airport expansion. © 2011 Elsevier Ltd.

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Simulation of materials at the atomistic level is an important tool in studying microscopic structure and processes. The atomic interactions necessary for the simulation are correctly described by Quantum Mechanics. However, the computational resources required to solve the quantum mechanical equations limits the use of Quantum Mechanics at most to a few hundreds of atoms and only to a small fraction of the available configurational space. This thesis presents the results of my research on the development of a new interatomic potential generation scheme, which we refer to as Gaussian Approximation Potentials. In our framework, the quantum mechanical potential energy surface is interpolated between a set of predetermined values at different points in atomic configurational space by a non-linear, non-parametric regression method, the Gaussian Process. To perform the fitting, we represent the atomic environments by the bispectrum, which is invariant to permutations of the atoms in the neighbourhood and to global rotations. The result is a general scheme, that allows one to generate interatomic potentials based on arbitrary quantum mechanical data. We built a series of Gaussian Approximation Potentials using data obtained from Density Functional Theory and tested the capabilities of the method. We showed that our models reproduce the quantum mechanical potential energy surface remarkably well for the group IV semiconductors, iron and gallium nitride. Our potentials, while maintaining quantum mechanical accuracy, are several orders of magnitude faster than Quantum Mechanical methods.