水盾草科系统位置评述

水盾草科(Cabombaceae)是双子叶植物。水盾草科包括2属: 水盾草属(Cabomba Aublet.)和莼菜属(Brasenia Schreb.)。形态学研究显示水盾草科具有许多原始性状, 而且在其适应水生环境的过程中经历了性状退化。水盾草科又被称为“古草本”。最新的分子系统发育研究显示, 水盾草科是现存被子植物系统树基部ANITA类群的成员之一。但有关水盾草科的系统位置存在争议。被子植物的起源与早期分化一直是植物学家关注的热点。本文对该科系统位置的研究历史与现状进行评述。     

水盾草科系统位置评述

水盾草科（Cabombaceae）是双子叶植物。水盾草科包括2属：水盾草属（Cabomba Aublet．）和莼菜属（Brasenia Schreb．）。形态学研究显示水盾草科具有许多原始性状,而且在其适应水生环境的过程中经历了性状退化。水盾草科又被称为“古草本”。最新的分子系统发育研究显示,水盾草科是现存被子植物系统树基部ANITA类群的成员之一。但有关水盾草科的系统位置存在争议。被子植物的起源与早期分化一直是植物学家关注的热点。本文对该科系统位置的研究历史与现状进行评述。     

中国大陆水生植物新逸生种——红菊花草

报道了中国大陆水盾草科(莼菜科)水盾草属的新归化水生植物——红菊花草Cabomba furcata Schult. & Schult. f.,凭证标本存于中国科学院华南植物园标本馆(IBSC)。     

走进莼菜科

莼菜科(Cabombaceae)很小,只有2属约8种。其中莼菜属(Brasenia)为我们所熟悉。分布美洲、亚洲和大洋洲,为水生植物。它的体态,花、果、形态结构有其各自特点,不同分类学家对它的分类位置历来不统一。莼菜科为什么搬了家?德国恩格勒系统早将莼菜属归入毛茛目睡莲科内,只作为一个亚科处理,这大概是由于莼菜属为水生草本,有浮于水面的盾状的叶子,加上其花有离生心皮,子房上位,颇似莲属(Nelumbo)的缘故。到1926年英国哈钦松发表《有花植物科志双子叶植物》一书,在书中公布了哈钦松系统。其中莼菜属等2属已共同独立为科,名叫莼菜科并归入毛茛目…     

睡莲科三属植物叶的比较解剖学研究

报道了睡莲科的睡莲属、莼菜属和萍蓬草属三属植物叶的比较解剖学特征。结果表明,莼菜属叶柄仅具一个维管束,其余二个属均有数个维管束,且维管束为有限的、星散排列,这一特征与单子叶植物的很相似;叶柄基本组织中,除萍蓬草属无气道外,其它两个属均有气道;在睡莲属和萍蓬草属中存在星状石细胞,而莼菜属中则无此细胞;莼菜属和萍蓬草属具腺毛,睡莲属无腺毛。由于睡莲科此三属植物叶的解剖学特点存在很大的差异,因此认为睡莲科的这三属可能来源于不同的祖先,因此建议将莼菜属和萍蓬草属从睡莲科中分离出来。分别独立为莼菜科和萍蓬草科。     

睡莲科的属间关系研究

本文用谱系分支法分析睡莲科的属间关系,３５个衍征中,分析了３１个特征的进化趋势,根据分析将睡莲科提升为睡莲目,分为３个科,莲科、水盾草科、睡莲科。     

睡莲科叶比较解剖

本文报道了睡莲科6个种比较解剖学的研究结果。莼菜的叶柄具一对维管束,其它5个种为 有限的、星散排列维管束,它们与单子叶植物相似;叶柄基本组织中除萍蓬草无气道外,其它种均有。叶为两面叶页,毛茛型气孔局限分布于叶腹面,但莲叶背面亦发育有少量气孔。莲的气孔在发育时属单唇型,成熟时则呈毛茛型。排水器、厚壁异细胞只见于莲。腺毛及吸水器除莲外,供研究的其它种在叶背面均存在。除莼菜及莲外,其它种都有星状石细胞。 根据本文的观察结果,我们认为莼菜属是睡莲科中较简化的属,它和Cabomba属有密切的亲缘关系,它们可独立成莼菜科(Cabombaceae),包括于睡莲目内。睡莲属、 萍蓬草属、芡属和王莲属(Victoria)彼此亲缘关系密切,可留于睡莲科。莲属具独特的形态,与睡莲科的其它属亲缘关系不甚密切,因此,不但可分立为莲科,而且可独立成莲目。     

莼 菜

正莼菜(Brasenia schreberi),又名马蹄菜、湖菜等,隶属睡莲目(Nymphaeaceae)莼菜科(Cabombaceae)莼菜属(Brasenia)[1],是多年生宿根水生植物,也是第三纪植物区系的珍贵孑遗物种。莼菜性喜温暖,适宜于清水池生长。由地下匍匐茎萌发须根和叶片,并发出4~6个分枝,节部生根,形成丛生状茎,再生分枝。叶椭圆状矩圆形,浮生在水面或潜在水中,长3.5~6 cm,宽5~10 cm,叶背面浅绿色或红色,两面无毛,从叶脉处皱     

中国粟米草科分类修订

粟米草科(Molluginaceae)隶属于石竹目,是一个分类极为困难的被子植物类群,关于该科的分类学界定在众多不同被子植物分类系统中争议颇大。在最近的分子系统学研究中,粟米草科的范围被准确界定,全球共包含11属。在此基础上对中国粟米草科类群进行了分类修订,最终确认中国产粟米草科植物5属7种,其中线叶漆姑粟草[Hypertelis umbellata (Forssk.)Thulin]为中国分布新记录种。更新了分种检索表,并提供了各属形态描述及相关物种的地理分布图。     

基于本土最优模型模拟入侵物种水盾草在中国的潜在分布

生态位模型预测存在不确定性, 不同模型预测结果差别较大。在生态位保守的前提下, 在本土区域构建经典生态位模型, 利用入侵地独立样本数据检验并选择最优模型, 具有独特优势, 可为入侵物种风险分析提供可靠参考。水盾草(Cabomba caroliniana)是一种恶性水生入侵杂草, 原产于南美洲, 已在我国多个省市建立种群, 本文基于本土最优模型预测其在我国的潜在分布, 以期为其风险分析和综合治理提供依据, 并通过水盾草案例探讨如何提高生态位模型预测准确性的方法。本文按时间顺序梳理了水盾草在我国的分布记录, 然后根据水盾草已有分布记录和其所关联的环境因子比较了不同地理种群所占有的气候生态空间, 测试水盾草在世界入侵过程中的现实生态位保守性。采用两组环境变量和5种算法在南美洲本土地区构建10种生态位模型, 并将其转移至我国, 基于最小遗漏率和记账错率, 利用我国(入侵地)的样本数据选择最优模型预测水盾草在我国的适宜生态空间和潜在分布。研究发现当前水盾草在我国的分布集中在东部水域充沛地区, 沿京杭运河和南水北调工程等向北扩散。生态空间比对中发现水盾草在亚洲与其他大洲所占有的生态空间具有一定的重叠, 其在我国的入侵过程中生态位是保守的。与本土空间相比, 水盾草在我国所占有的生态空间存在较大的生态位空缺, 表明水盾草在我国的潜在分布范围较大。生态位模型预测显示水盾草的适生区主要分布于我国的北京、上海、山东、浙江、江苏、安徽、湖北和湖南等省(市)。水盾草的潜在分布区多聚集在我国东南部, 该地区河流、湖泊、运河和渠道较为密集, 人类活动及自然天敌的缺乏容易助长其入侵趋势, 应在这些适宜地区开展调查, 及时发现疫情并采取相应措施。     

Estimation of Relative Risk in Case Control Studies Through Logistic Regression Analysis

Multiple logistic regression analysis is used to estimate the relative risk in case control studies. The estimators obtained are valid when disease is rare. In this paper an estimator of relative risk in a case control study has been proposed using logistic regression results when the incidence of disease is not small. The bias of the usual estimator through logistic regression as compared to the new estimator has been worked out. The expression of Mean Square Error of proposed estimator has been derived in situations when the incidence of disease is known exactly as well as when estimated through an independent survey. It has been observed that there is a significant bias using the conventional estimator of relative risk when incidence of disease is high. In such situations the proposed estimator can be used with advantage.     

Mechanical design of hedgehog spines and porcupine quills

The spines or quills of hedgehogs and porcupines are morphologically and mechanically different. In simple terms, it seems that the quills of porcupines are proportioned to be as long as possible without bending too easily when loaded axially. By contrast, the spines of the hedgehog are as short as possible while still able to bend when loaded axially. In addition, the hedgehog spines have an internal morphology which delays the onset of local buckling under these loads, thus enabling the spines to absorb larger amounts of mechanical energy. By contrast, the quills of Hystrix are designed to break at the tip. Thus, whilst the quills of the porcupine seem to be well adapted for keeping an enemy as far away as possible, the spines of the hedgehog probably have this as an incidental function. Their main function is much more likely to be that of a shock absorber or storage of impact energy when the animal falls from a height, a behavioural attribute which is reportedly common.     

Median regression with censored cost data

Because of the skewness of the distribution of medical costs, we consider modeling the median as well as other quantiles when establishing regression relationships to covariates. In many applications, the medical cost data are also right censored. In this article, we propose semiparametric procedures for estimating the parameters in median regression models based on weighted estimating equations when censoring is present. Numerical studies are conducted to show that our estimators perform well with small samples and the resulting inference is reliable in circumstances of practical importance. The methods are applied to a dataset for medical costs of patients with colorectal cancer.     

Cholesterol oxidation and the behavior of 5-α-hydroperoxycholesterol at the air/water interface

The oxidation of cholesterol and the behavior of an oxidized sterol, 5-α-hydroperoxy-cholesterol (5-AHC), have been investigated. It is demonstrated that previous work is correct in observing that cholesterol oxidation does take place at the air/water interface, but predicts initial effects and rates that are much too large. The oxidation of cholesterol is found to be autocatalytic as long as the oxidized sterol compounds (OSC) remain miscible with the cholesterol. The OSC are postulated to adopt tilted conformations with respect to the air/water interface when oxidized at or about the sterol-5,6-positions, and to segregate out when saturation OSC levels in cholesterol are reached. Pure films of 5-AHC are found to be more expanded, more compressible and less stable than those of cholesterol. In mixed films with other selected lipids, 5-AHC behaves as a greater impurity than does cholesterol when the second component is more condensed, and as a poorer condensing agent when the second component is more expanded.     

The Knox method and other tests for space-time interaction

The Knox method, as well as other tests for space-time interaction, are biased when there are geographical population shifts, i.e., when there are different percent population growths in different regions. In this paper, the size of the population shift bias is investigated for the Knox test, and it is shown that it can be a considerable problem. A Monte Carlo method for constructing unbiased space-time interaction tests is then presented and illustrated on the Knox test as well as for a combined Knox test. Practical implications are discussed in terms of the interpretation of past results and the design of future studies.     

Growth inhibition of transformed cells correlates with their junctional communication with normal cells

The growth of various chemically and virally transformed cell types in culture is inhibited when they are in contact with normal cell types. We show that this growth inhibition is contingent on the presence of junctional communication between the normal and transformed cells (heterologous communication), as probed with a 443 dalton microinjected fluorescent tracer. In cell combinations where heterologous communication is weak or absent there is no detectable growth inhibition; the inhibition appears when communication is induced by cyclic AMP-dependent phosphorylation, and only then. In cell combinations where heterologous communication is spontaneously strong, the growth inhibition is present, but it is abolished when the communication is blocked by retinol or retinoic acid. The cell-to-cell membrane channels of gap junctions are the likely conduits of the signals for this growth control.     

Design and analysis of a replicated server architecture for supporting IP–host mobility

Mobility support in IP networks requires servers to forward packets to mobile hosts and to maintain information pertaining to a mobile host's location in the network. In the mobile Internet Protocol (mobile-IP), location and packet forwarding functions are provided by servers referred to as home agents. These home agents may become the bottleneck when there are a large number of mobile hosts in the network. In this paper, we consider the design and analysis of a replicated server architecture in which multiple home agents are used to provide mobility support. In order to minimize the delay across the home agents, one of the key aspects is the design of load balancing schemes in which a home agent may transfer the control of a mobile host to another home agent in the same network. The methods for triggering the transfer and the policy for selecting the next home agent define various load balancing schemes which have different performance characteristics. In this paper, we design a protocol that forms the building block for implementing such load balancing schemes, and we then study the performance characteristics of three selection schemes, namely, random, round-robin, and join the shortest queue (JSQ), and three transfers policies, namely, timer-, counter- and threshold-based. The key results of this study are as follows: (1) The results show that both random and round-robin selection policies can yield modest load balancing gains, and that these gains increase when the traffic is more bursty (burstiness is defined as the ratio of the peak arrival rate to the mean arrival rate) as well as when there are more home agents. (2) The threshold-based transfer policy performs better than timer-based and counter-based policies, since in threshold-based policies transfers are made only when the queue is overloaded, unlike counter- and timer-based policies in which transfers can be made from an unloaded home agent to an overloaded home agent. This revised version was published online in August 2006 with corrections to the Cover Date.     

POLYMORPHIC TAXA, MISSING VALUES AND CLADISTIC ANALYSIS

Abstract Missing values have been used in cladistic analyses when data are unavailable, inapplicable or sometimes when character states are variable within terminal taxa. The practice of scoring taxa as having "missing values" for polymorphic characters introduces errors into the calculation of cladogram lengths and consistency indices because some character change is hidden within terminals. Because these hidden character steps are not counted, the set of most parsimonious cladograms may differ from those that would be found if polymorphic taxa had been broken into monomorphic subunits. In some cases, the trees found when polymorphisms are scored as missing values may not include any of the most parsimonious trees found when the data are scored properly. Additionally, in some cases, polymorphic taxa may be found to be polyphyletic when broken into monomorphic subunits; this is undetected when polymorphisms are treated as missing. Because of these problems, terminal units in cladistic analysis should be based on unique, fixed combinations of characters. Polymorphic taxa should be subdivided into subunits that are monomorphic for each character used in the analysis. Disregarding errors in topology, the additional hidden steps in a cladogram in which polymorphisms are scored as missing can be calculated by a simple formula, based on the observation that if it is assumed that polymorphic terminals include all combinations of character states, 2 ^p − 1 additional steps are required for each taxon in which p polymorphic binary characters are scored as missing values. Thus, when several polymorphisms are scored as missing in the same taxon, very large errors can be introduced into the calculation of tree length.     

Boosted regression trees with errors in variables

In this article, we consider nonparametric regression when covariates are measured with error. Estimation is performed using boosted regression trees, with the sum of the trees forming the estimate of the conditional expectation of the response. Both binary and continuous response regression are investigated. An approach to fitting regression trees when covariates are measured with error is described, and the boosting algorithms consist of its repeated application. The main feature of the approach is that it handles situations where multiple covariates are measured with error. Some simulation results are given as well as its application to data from the Framingham Heart Study.     

The secondary structure of human plasma fibronectin: conformational changes induced by acidic pH and elevated temperatures; a circular dichroic study

The secondary structure of native human plasma fibronectin, based on circular dichroic spectra, has been estimated to contain 79% beta sheet and 21% beta turn structures (Osterlund, E., Eronen, I., Osterlund, K. and Vuento, M. (1985) Biochemistry 24, 2661-2667). In this work changes in the secondary structure of the protein molecule are followed as a function of different temperatures and pH values by using circular dichroic spectroscopy in far- and near-ultraviolet regions. Conformational changes are reversible when raising the temperature quickly to 55 degrees C, and then cooling slowly to 20 degrees C. A few percent of alpha-helix is apparent, when the temperature is raised to 58.5 degrees C, but only about 9% random coil is formed, when the temperature is raised up to 70 degrees C. The largest conformational change is taking place, when fibronectin samples are heated from 57 to 58.5 degrees C. According to this study more than 90% of the secondary structure of the fibronectin molecule is preserved throughout the whole temperature range studied from 20 to 70 degrees C, and this is a fact even at pH as low as 3.0, when samples are fresh and not denatured by preparative procedures.