927 resultados para Prosa histórica latina s.I a.C.


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Bassenthwaite (Lake) is one of the larger Cumbrian lakes, certainly one of the most distinctive, and of considerable conservation and amenity value. Although its shores lack sizeable settlements, its main inflow receives sewage effluent from a major tourist centre (Keswick) and is subject to episodic floods. These influences, the growing development of leisure activities at the lake (e.g. sailing, time-share units), and recent road-construction, have led to past appraisals of ecological impacts and lake management. The lake has not been the subject of intense and long-term ecological study, but much scattered information exists that is relevant to future management decisions. In the present Report, commissioned by North West Water, such information - published and unpublished - is surveyed. Especial attention is given to evidence bearing on susceptibility to change, affecting the lake environment and its biota or species of conservation interest. Extensive use has been made of the results of a recent (1986-7) seasonal survey by the FBA.

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Hair cells from the bull frog's sacculus, a vestibular organ responding to substrate-borne vibration, possess electrically resonant membrane properties which maximize the sensitivity of each cell to a particular frequency of mechanical input. The electrical resonance of these cells and its underlying ionic basis were studied by applying gigohm-seal recording techniques to solitary hair cells enzymatically dissociated from the sacculus. The contribution of electrical resonance to frequency selectivity was assessed from microelectrode recordings from hair cells in an excised preparation of the sacculus.

Electrical resonance in the hair cell is demonstrated by damped membrane-potential oscillations in response to extrinsic current pulses applied through the recording pipette. This response is analyzed as that of a damped harmonic oscillator. Oscillation frequency rises with membrane depolarization, from 80-160 Hz at resting potential to asymptotic values of 200-250 Hz. The sharpness of electrical tuning, denoted by the electrical quality factor, Qe, is a bell-shaped function of membrane voltage, reaching a maximum value around eight at a membrane potential slightly positive to the resting potential.

In whole cells, three time-variant ionic currents are activated at voltages more positive than -60 to -50 mV; these are identified as a voltage-dependent, non-inactivating Ca current (Ica), a voltage-dependent, transient K current (Ia), and a Ca-dependent K current (Ic). The C channel is identified in excised, inside-out membrane patches on the basis of its large conductance (130-200 pS), its selective permeability to Kover Na or Cl, and its activation by internal Ca ions and membrane depolarization. Analysis of open- and closed-lifetime distributions suggests that the C channel can assume at least two open and three closed kinetic states.

Exposing hair cells to external solutions that inhibit the Ca or C conductances degrades the electrical resonance properties measured under current-clamp conditions, while blocking the A conductance has no significant effect, providing evidence that only the Ca and C conductances participate in the resonance mechanism. To test the sufficiency of these two conductances to account for electrical resonance, a mathematical model is developed that describes Ica, Ic, and intracellular Ca concentration during voltage-clamp steps. Ica activation is approximated by a third-order Hodgkin-Huxley kinetic scheme. Ca entering the cell is assumed to be confined to a small submembrane compartment which contains an excess of Ca buffer; Ca leaves this space with first-order kinetics. The Ca- and voltage-dependent activation of C channels is described by a five-state kinetic scheme suggested by the results of single-channel observations. Parameter values in the model are adjusted to fit the waveforms of Ica and Ic evoked by a series of voltage-clamp steps in a single cell. Having been thus constrained, the model correctly predicts the character of voltage oscillations produced by current-clamp steps, including the dependencies of oscillation frequency and Qe on membrane voltage. The model shows quantitatively how the Ca and C conductances interact, via changes in intracellular Ca concentration, to produce electrical resonance in a vertebrate hair cell.

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In most lakes, zooplankton production is constrained by food quantity, but frequently high C:P poses an additional constraint on zooplankton production by reducing the carbon transfer efficiency from phytoplankton to zooplankton. This review addresses how the flux of matter and energy in pelagic food webs is regulated by food quantity in terms of C and its stoichiometric quality in terms of C:P. Increased levels of light, CO2 and phosphorus could each increase seston mass and, hence, food quantity for zooplankton, but while light and CO2 each cause increased C:P (i.e. reduced food quality for herbivores), increased P may increase seston mass and its stoichiometric quality by reducing C:P. Development of food quality and food quantity in response to C- or P-enrichments will differ between 'batch-type' lakes (dominated by one major, seasonal input of water and nutrients) and 'continuous-culture' types of lakes with a more steady flow-rate of water and nutrients. The reciprocal role of food quantity and stoichiometric quality will depend strongly on facilitation via grazing and recycling by the grazers, and this effect will be most important in systems with low renewal rates. At high food abundance but low quality, there will be a 'quality starvation' in zooplankton. From a management point of view, stoichiometric theory offers a general tool-kit for understanding the integrated role of C and P in food webs and how food quantity and stoichiometric quality (i.e. C:P) regulate energy flow and trophic efficiency from base to top in food webs.From a management point of view, stoichiometric theory offers a general tool-kit for understanding the integrated role of C and P in food webs and how food quantity and stoichiometric quality (i.e. C:P) regulate energy flow and trophic efficiency from base to top in food webs.

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Biological/fisheries parameters (L sub(oo) M, F) are presented for four fish species (Gadiculus argenteus; Gaidropsarus mediterraneous; Symphurus ligulatus; Lepidorhombus boscii) as well as body length-weight and length-height relationships for 11 and 12 fish species, respectively, estimated from trawl samples collected using three different cod-ends (stretched mesh size: 14 mm and 20 mm diamond-shaped and 20 mm square-shaped) during 1993-1994, in the western Aegean and North Euboikos Gulf, Greece. The fisheries paramaters, estimated from length-frequency using the ELEFAN approach and software, are discussed in the light of recent information on the selectivity of the presently used trawl cod-end (14 mm diamond shaped)

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本论文主要涉及两部分内容:第一部分是水稻和太行花中MADS-box基因的相关研究,第二部分是水稻中SAGE技术的生物信息学分析。 MADS-box基因家族在花发育过程中起着重要的作用。水稻是单子叶植物的模式植物,其基因组序列的公布为在基因组水平上鉴定MADS-box基因提供了条件。根据已发表的水稻MADS-box基因序列,利用关键词搜索、HMMER分析、同源比较、系统进化树分析等手段,对GeneBank和TIGR水稻基因组注释中所有已知和未知的水稻MADS-box基因进行了分析。结果表明,水稻中有64个MADS-box基因编码不同氨基酸,其中已知cDNA序列的为43个。在64个基因中,有23个属于ABCDE类基因,并且其cDNA序列已知,其中的10个已有功能方面的研究。通过3’-RACE和筛选水稻花器官的cDNA文库,得到了一个A类基因片断(A5B2),两个E类基因片断(MW1,MW2)。这三个基因分别与OsMADS14,OsMADS7和OsMADS5相似或相同。禾本科植物花器官的起源,尤其是内外稃的起源仍存在疑问,A功能基因是否以及如何参与其形成成为问题的关键。初步原位杂交分析表明,OsMADS14在花发育的早期开始表达。在小穗原基发育过程中,OsMADS14在内外稃原基中有较强的表达。随着小穗的发育,OsMADS14在整个花序中都有表达。在小穗发育的后期,OsMADS14在胚珠中有较强的表达。OsMADS14的表达模式与FUL类基因一致,并且证明了其在花发育的后期仍然表达强烈,暗示其可能与胚珠发育有重要关系。 SEPALLATA基因被认为是花的特异因子,参与了花的四轮花器官的决定过程。在本文中,通过3’-,5’-RACE,从太行花花芽中克隆了一个MADS-box基因。该基因推导的的氨基酸序列含有典型的M,I,K和C四个结构域,与FBP2和SEP3的相似性较高,系统进化树分析表明该基因属于SEP3亚家族,于是将其命名为TrSEP3。TrSEP3首先在花分生组织中表达,然后在雌雄蕊原基及花瓣中表达;在成熟花中,TrSEP3仅在花瓣和雌蕊中表达。这种表达模式与其它的SEP-like基因有稍不同。TrSEP3拟南芥中过量表达后并未导致表型的改变,暗示其功能与拟南芥的SEP基因可能存在差异。选择压力分析显示TrSEP3受到了不显著的负选择压力。这些结果暗示TrSEP3的功能可能与其它的SEP-like基因有差别,值得进一步研究。 SAGE(Serial Analysis of Gene Expression)是对比样品间转录谱的差异、发现新基因的有效的方法。tag mapping是将SAGE-tag与其转录本匹配的过程,其效率直接影响对转录谱的解释,该过程受多种因素影响。目前,对水稻tag mapping过程缺少详细研究,导致其效率不高。为了确定参考数据库和其它合适的条件,我们利用EST序列和基因组序列构建了不同的参考图谱,从全长cDNA数据库中提取虚拟的SAGE-tag,研究了参考图谱、锚定酶、tag长度以及匹配方法对tag mapping效率的影响,并比较了tag mapping的准确率。结果表明,用EST序列构建的参考图谱能够匹配大多数的SAGE-tag,并具有较高的准确率;利用迭代的方法,可以充分利用基因组序列。各种锚定酶之间的差别不明显,其中NlaIII, HpyCH4V 和 AluI 表现较好;17bp的tag比较适合水稻;而用双锚定酶和17bp的tag则可以显著提高tag mapping的效率和准确率。

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根质膜具有重要的生物学功能,它参与了根响应脱落酸(ABA)的一系列活动。尽管已经有很多有关ABA影响根的生长和发育的报道,但是在蛋白质组水平上研究参与ABA信号转导及相关活动的质膜蛋白质的报道还未见到。我们期望利用蛋白质组学技术平台研究外源ABA胁迫下水稻根质膜与ABA功能相关的蛋白质组的变化。 本论文通过双向电泳(2DE)结合质谱(MALDI-TOF MS 和 MALDI-TOF/TOF MS)分析的方法鉴定了102个质膜相关蛋白质。这些蛋白质功能涉及到跨膜运输(16.2%)、胁迫反应(14.3%)、物质运输(4.8%)、细胞骨架动态变化(5.7%)、细胞壁重建(3.8%)、碳代谢和能量循环(13.3%)、蛋白质代谢(14.3%)、信号转导(18.1%)和其他功能的蛋白质(4.8%),以及未知功能的蛋白质(2.9%)。其中大约30%的蛋白质以同工型的形式存在。在这些鉴定结果中,有10个斑点(代表10种蛋白质)已被报道为质膜特异的蛋白质;68个蛋白质斑点(代表58种蛋白质)是质膜相关蛋白质。其余54个蛋白质斑点(代表42种蛋白质)是首次在水稻根的质膜囊泡中被鉴定出来。 在ABA处理条件下,我们在2DE胶上发现了15个响应ABA调节的蛋白质斑点。9个上调的蛋白质斑点分别代表以下9种蛋白质:vacuolar proton-ATPase A subunit, vacuolar ATPase B subunit、patatin、 Salt-stress root protein RS1、谷氨酰氨合成酶(Glutamine synthetase,GS)、OSR40c1、H+-exporting ATPase (vacuolar ATPase E subunit)、甘油醛-3-磷酸脱氢酶I型(glyceraldehyde-3- phosphate dehydrogenase, type I,GADPH)和醛缩酶C-1(aldolase C-1)。6个下调的蛋白质斑点分别代表4种蛋白质:endosperm lumenal binding protein、remorin protein、富含脯氨酸蛋白质(glycine-rich protein,GRP)和蔗糖合成酶(sucrose synthase, SuSy)。其中,OSR40c1和endosperm lumenal binding protein与蛋白质合成相关,从它们与ABA的关系中可以看出,ABA可能抑制了细胞的蛋白质合成。而vacuolar proton-ATPase A subunit、vacuolar ATPase B subunit和 H+-exporting ATPase参与了细胞质pH的调控,ABA致使了细胞质pH的上升。甘油醛-3-磷酸脱氢酶I型、醛缩酶C-1和蔗糖合酶参与了细胞壁的生长发育,ABA的作用可能导致了细胞壁生长发育的延迟。ABA促使Patatin上升,其作用可能与质膜膜脂的降解有关。而ABA的刺激也使谷氨酰氨合成酶的表达显著上升,谷氨酰氨合成酶可以去除细胞内有害的游离NH+4。同时还有未知功能的富含脯氨酸蛋白质(glycine-rich protein,GRP)同样受到ABA的诱导,但具体的功能及其与ABA的关系还要进一步的实验证据。

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陆地生态系统与大气之间的水热碳交换是物质、能量循环的关键过程,一直以来都为研究者们所关注。进入20 世纪以来,特别是随着人们对全球气候变暖的逐步认识,气候变化对水热碳交换过程的影响及其对气候变化的响应研究更加备受关注。本研究以2004~2006 年近三年的涡度相关系统连续观测数据为依托,分析了雨养玉米农田水热碳通量的动态及其影响因子。研究表明,玉米农田水热通量(WHF) 呈显著的单峰型日变化, 日最大值出现在正午12:00~13:00,WHF 变化同步。潜热通量(LE)的季节变化规律与日变化相似,冬季小夏季大,年最大值与最小值分别出现在7 月和1 月。显热通量(Hs) 季节变化也呈单峰型,但年最大值出现在5 月,这主要与降水以及作物生长有关。半小时尺度上,WHF 主要受辐射控制,而日峰值受辐射峰值以及植被生长的双重影响;日尺度上,只要有降水过程,Hs 就会随土壤水分的增大而减小,降水停止后逐渐恢复。而降水对LE 的影响受到可用能量(AE)的干扰,表现出复杂的变化趋势。总的来说,降水持续时间越长AE 越少,对LE 的抑制越大;季节尺度上,WHF 受热量与水分的双重制约。Hs 随着天气回暖后第一次较大降水过程的出现呈现明显下降,而LE 则呈现相反的变化趋势。随着雨季到来和作物的生长,Hs 在7 月出现低谷,而LE 呈现相反的趋势随着降水量的增加而增大;年际间WHF 的分布规律大体一致,但因气象条件等的差异,特别是降水的差异造成年际间WHF 略有不同。在不同水文年型下,水分因子的影响作用有显著差异,且WHF 对热量与水分条件变化的敏感程度也不相同。欠水年,水分因子的作用更显著,是制约WHF 变化的主要控制因子,WHF 对水分的变化更敏感;而丰水年,水分因子的影响减弱,热量的盈亏决定着WHF 变化的主要方向。在不同水文年型下,水热碳通量对水热条件的变化表现出不同的响应方式,为研究生态系统对气候变化的响应提供了参考。 净碳(C)吸收期,玉米农田净碳交换(NEE)呈显著的日变化,在日出以后由CO2 释放转变为CO2 吸收,12:30 左右达到一天中的吸收峰值,日落前出现相反的转换。而净C 释放期内,NEE 均为正值且无明显日变化。NEE 季节变化也呈单峰型二次曲线,在7 月下旬或8 月上旬达到年最大吸收率。根据NEE 的正负,一年分为三个阶段:两个C 排放期与一个C 吸收期。一般C 吸收期从6月开始到9 月结束,此前此后均为C 排放期。在半小时、日时间尺度上,光通量密度(PPFD)与NEE 有着相似的变化规律,是控制NEE 的主要因子;在日、季节尺度上,叶面积指数(LAI)和气孔导度(gs)是影响NEE 的主要生物因子,且gs 的影响程度随着发育期的变化而变化,而不同年份间LAI 对NEE 的影响没有显著的差异。几乎在所有时间步长上,土壤温度(Ts)均为生态系统呼吸(Re)的主要控制因子,时间尺度愈短,二者的相关性愈好。总的来说,在较短时间尺度上,高PPFD 与夏季低温将会促进C 的吸收,有利于C 累积。 玉米农田日最大净C 吸收速率(NEEmax, daily)以及吸收释放转换点(NEE=0)均受PPFD 控制。NEEmax, daily 出现时间与PPFDmax, daily 出现时间几乎完全一致,当PPFD 达到1 日内极大值时,净C 吸收也相应达到了日最大值。但NEEmax, daily的量值还受到其它因子的影响。当水分条件充足时,还将受到LAI、gs 等生物因子的控制。NEE 由正转为负的转换点也是由PPFD 决定。当PPFD 稳定大于PPFD*( PPFD*=100 μmol•m-2s -1)时,净C 吸收开始;当PPFD 稳定小于PPFD*时,净C 吸收由此结束。1 日内,PPFD 稳定通过PPFD*之间的时间间隔决定了日净C 吸收的时间长度。日净C 吸收的时间越长,吸收量也越大,且有明显的季节变化,7 月最长9 月最短。 按照热量水分状况将三年分组,分为I 组(水分状况相似,热量条件不同)与II 组(热量条件相似,水分状况不同)。 I 组年际间PPFD 波动是造成C 交换格局变化的关键原因。而II 组年际间C 交换格局不同是由降水量及其不同分布引起的土壤含水量(SWC)变化是造成。SWC 可以解释年际间NEE 变异的97%,而大气水汽压亏缺(VPD)可以解释30.7%;温度因子通过影响C 收支中的呼吸项,间接影响着生态系统的NEE,它可以解释年际间NEE 变异的73.9%,也是造成年际间C 交换格局不同的原因之一;另外,PPFD 和发育期早晚以及净C吸收期长度等也同样影响着C 交换格局的变化。综合两组情况来看,由水分条件年际变化引起的NEE 的波动大于能量年际变化引起的波动。总之,在较长时间尺度上,NEE 对SWC 变化比其对PPFD 变化更敏感,说明在半干旱地区土壤水分条件仍然是决定C 交换格局的主导因子。 NEE 与LE 呈线性相关,它们之间的相关性主要受温度和NEE 的控制,温度越高,二者的相关性越弱,而NEE 越大二者相关性越好。同时,作物蒸腾与土壤蒸发的比例也是影响NEE 与LE 之间关系的主要因素。蒸腾作用所占的比例越大,二者的线性关系越显著,而土壤蒸发比例越大,二者的相关性越弱。总的来说,NEE 与LE 之间的线性关系有明显的季节变化,生长季好于非生长季,夏天好于冬天。 总之,雨养玉米农田水热碳通量既具有其它农田生态系统共有的动态特征,也具有其特有特征。

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The nuclear RNA binding protein, FCA, promotes Arabidopsis reproductive development. FCA contains a WW protein interaction domain that is essential for FCA function. We have identified FY as a protein partner for this domain. FY belongs to a highly conserved group of eukaryotic proteins represented in Saccharomyces cerevisiae by the RNA 3' end-processing factor, Pfs2p. FY regulates RNA 3' end processing in Arabidopsis as evidenced through its role in FCA regulation. FCA expression is autoregulated through the use of different polyadenylation sites within the FCA pre-mRNA, and the FCA/FY interaction is required for efficient selection of the promoter-proximal polyadenylation site. The FCA/FY interaction is also required for the downregulation of the floral repressor FLC. We propose that FCA controls 3' end formation of specific transcripts and that in higher eukaryotes, proteins homologous to FY may have evolved as sites of association for regulators of RNA 3' end processing.

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Integration of a piezoelectric high frequency ultrasound (HFUS) array with a microfabricated application specific integrated circuit (ASIC) performing a range of functions has several advantages for ultrasound imaging. The number of signal cables between the array/electronics and the data acquisition / imaging system can be reduced, cutting costs and increasing functionality. Electrical impedance matching is also simplified and the same approach can reduce overall system dimensions for applications such as endoscopic ultrasound. The work reported in this paper demonstrates early ASIC operation with a piezocomposite HFUS array operating at approximately 30 MHz. The array was tested in three different modes. Clear signals were seen in catch-mode, with an external transducer as a source of ultrasound, and in pitch-mode with the external transducer as a receiver. Pitch-catch mode was also tested successfully, using sequential excitation on three array elements, and viable signals were detected. However, these were relatively small and affected by interference from mixed-signal sources in the ASIC. Nevertheless, the functionality and compatibility of the two main components of an integrated HFUS - ASIC device have been demonstrated and the means of further optimization are evident.

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The operating range of an axial compressor is often restricted by a safety imposed stall margin. One possible way of regaining operating range is with the application of casing treatment. Of particular interest here is the type of casing treatment which extracts air from a high pressure location in the compressor and re-injects it through discrete loops into the rotor tip region. Existing re-circulation systems have the disadvantage of reducing compressor efficiency at design conditions because worked flow is unnecessarily re-circulated at these operating conditions. Re-circulation is really only needed near stall. This paper proposes a self-regulating casing treatment in which the re-circulated flow is minimized at compressor design conditions and maximized near stall. The self-regulating capability is achieved by taking advantage of changes which occur in the tip clearance velocity and pressure fields as the compressor is throttled toward stall. In the proof-of-concept work reported here, flow is extracted from the high pressure region over the rotor tips and re-injected just upstream of the same blade row. Parametric studies are reported in which the flow extraction and re-injection ports are optimized for location, shape and orientation. The optimized design is shown to compare favorably with a circumferential groove tested in the same compressor. The relationship between stall inception type and casing treatment effectiveness is also investigated. The self-regulating aspect of the new design works well: stall margin improvements from 2.2 to 6.0% are achieved for just 0.25% total air re-circulated near stall and half that near design conditions. The self-regulating capability is achieved by the selective location and orientation of the extraction hole; a simple model is discussed which predicts the optimum axial location. Copyright © 2011 by ASME.

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In the,paper, we explored the intra- and interspecific evolutionary variation among species of Camallanus collected from different fish species in various regions of China. We determined the internal transcribed spacers of ribosomal DNA (ITS rDNA) sequences of these nematodes. The divergence (uncorrected p-distance) of ITS 1, ITS2, and ITS rDNA data sets confirmed 2 valid species of Camallanus in China, i.e., C. cotti and C. hypophthalmichthys. The 2 species were distinguished not only by their different morphologies and host ranges but also by a letranucleotide microsatellite (TTGC)n present in the ITS I region of C cotti. Phylogenetic analyses of the nematodes disclosed 2 main clades, corresponding to different individuals of C cotti and C. hypophthalmichthys from different fish species in various geographical locations, although the interior nodes of each clade received poor support.