Multiple grasp-specific representations of tool dynamics mediate skillful manipulation.

Skillful tool use requires knowledge of the dynamic properties of tools in order to specify the mapping between applied force and tool motion. Importantly, this mapping depends on the orientation of the tool in the hand. Here we investigate the representation of dynamics during skillful manipulation of a tool that can be grasped at different orientations. We ask whether the motor system uses a single general representation of dynamics for all grasp contexts or whether it uses multiple grasp-specific representations. Using a novel robotic interface, subjects rotated a virtual tool whose orientation relative to the hand could be varied. Subjects could immediately anticipate the force direction for each orientation of the tool based on its visual geometry, and, with experience, they learned to parameterize the force magnitude. Surprisingly, this parameterization of force magnitude showed limited generalization when the orientation of the tool changed. Had subjects parameterized a single general representation, full generalization would be expected. Thus, our results suggest that object dynamics are captured by multiple representations, each of which encodes the mapping associated with a specific grasp context. We suggest that the concept of grasp-specific representations may provide a unifying framework for interpreting previous results related to dynamics learning.

白杄花粉管胞吞/胞吐动态及其与细胞壁构建的关系

在有花植物受精过程中，具有顶端极性生长特性的花粉管是雄性生殖单位的载体，同时也是研究细胞生长分子调控机理的理想体系。与被子植物相比，裸子植物花粉具有萌发时间长、花粉管生长缓慢等特点。对于裸子植物花粉萌发和花粉管生长的机理，目前人们尚不十分清楚。本文将以裸子植物白杄（Picea meyeri）花粉为材料，应用不同浓度的分泌系统干扰剂Brefeldin A处理，并通过细胞学和生理生化方法，其中包括普通光学显微镜、荧光显微镜、激光扫描共聚焦显微镜、显微红外光谱（FTIR）和透射电镜（TEM）等技术，对其花粉萌发和花粉管生长过程中胞吞胞吐的调控，以及与细胞壁建成的关系等进行较为系统的研究，旨在为进一步揭示裸子植物花粉管发育的调控机理提供参考。 首先比较观察了各种细胞器在白杄与被子植物花粉管中的分布差异。经FM4-64探针标记结果表明，在正常生长的白杄花粉管顶端存在分泌小泡积累的透明区，但与被子植物比较起来，此透明区在花粉管中所占比例较小，且不呈倒“V”字型。在透射电镜下观察发现，其花粉管顶端透明区内分泌小泡的分布密度远低于被子植物。另外，在白杄花粉管中，线粒体的分布一般靠近细胞壁的地方，高尔基体分布较为分散，而内质网的分布则不具方向性。 其次，研究了BFA对白杄花粉萌发和花粉管生长的影响，特别是对其花粉管生长过程中的胞吐/胞吞作用。通常在正常生长的白杄花粉管中，用FM4-64标记后发现，在其顶端形成与透明区对应的荧光亮区;超微结构显示，在花粉管顶端进行旺盛的胞吐作用，许多分泌小泡正与质膜融合，以及分布有大量显示高分泌活性的壁旁体（PB）等。而经过BFA处理后，花粉的萌发和花粉管的生长均受到严重抑制，花粉管出现了弯曲（波状生长）或顶端膨大等异常形态，同时还干扰了FM4-64在花粉管顶端的标记模式。另外，花粉管顶端分泌小泡数量减少，透明区内充满线粒体、高尔基体和空泡等一些大的细胞器，壁旁体也随之消失，其中高尔基体呈现解体或弯曲的异常形态，在其周围的分泌小泡数量大大减少，内质网出现膨胀和核糖体脱落等;同时胞吐活性标志性酶——酸性磷酸酶的活性也随之降低。通过对FM4-64的染料吸收实验表明，BFA对胞吞有明显的促进作用。由上可见，BFA对白杄花粉管生长过程中的胞吐和胞吞作用起了相反的影响， BFA正是通过扰乱花粉管生长过程中的分泌途径来抑制其花粉管的生长。 最后，检测了白杄花粉管分泌途径紊乱后，管壁物质合成的变化情况。通过FTIR光谱分析表明，BFA处理后花粉管壁化学组分发生了变化，例如蛋白质和多糖含量明显减少，而且与蛋白比较起来，多糖的含量下降更为明显，尤其是在顶端。蛋白和多糖含量的下降导致花粉管壁的组成结构不够致密。由SDS-PAGE的结果显示， BFA抑制后，花粉管壁中糖蛋白的含量下降了60%，同时很多壁蛋白条带在BFA处理后不表达或含量减少。通过对花粉管壁多糖成分的研究表明，BFA处理还导致纤维素含量下降，而胼胝质在花粉管顶端积累。用识别AGPs的LM6和识别酸性果胶的JIM5对花粉管进行标记，发现BFA处理后AGPs的环状分布消失，酸性果胶质在顶端的含量也明显减少，但在胞质内却形成一些小的分隔亮点（compartments）。 综上所述，导致裸子植物白杄花粉管生长缓慢的原因，可能与其顶端透明区较小、分泌小泡数量少等有关。另外，从白杄花粉管的细胞质状态和细胞器分布上看，虽然与被子植物相比差异较大，但在其正常生长中仍能进行旺盛地胞吐和胞吞过程。经BFA处理后引起花粉管内分泌系统的紊乱，致使管壁物质不能正常合成，从而导致花粉管的停滞生长。

Recruitment of larval Atlantic menhaden (Brevoortia tyrannus) to North Carolina and New Jersey estuaries: evidence for larval transport northward along the east coast of the United States

Age, size, abundance, and birthdate distributions were compared for larval Atlantic menhaden (Brevoortia tyrannus) collected weekly during their estuarine recruitment seasons in 1989–90, 1990–91, and 1992–93 in lower estuaries near Beaufort, North Carolina, and Tuckerton, New Jersey, to determine the source of these larvae. Larval recruitment in New Jersey extended for 9 months beginning in October but was discontinuous and was punctuated by periods of no catch that were associated with low water temperatures. In North Carolina, recruitment was continuous for 5–6 months beginning in November. Total yearly larval density in North Carolina was higher (15–39×) than in New Jersey for each of the 3 years. Larvae collected in North Carolina generally grew faster than larvae collected in New Jersey and were, on average, older and larger. Birthdate distributions (back-calculated from sagittal otolith ages) overlapped between sites and included many larvae that were spawned in winter. Early spawned (through October) larvae caught in the New Jersey estuary were probably spawned off New Jersey. Larvae spawned later (November–April) and collected in the same estuary were probably from south of Cape Hatteras because only there are winter water temperatures warm enough (≥16°C) to allow spawning and larval development. The percentage contribution of these late-spawned larvae from south of Cape Hatteras were an important, but variable fraction (10% in 1992–93 to 87% in 1989–90) of the total number of larvae recruited to this New Jersey estuary. Thus, this study provides evidence that some B. tyrannus spawned south of Cape Hatteras may reach New Jersey estuarine nurseries.

Stock assessment and biology of Johnius glaucus (Day) off the northwest coast of India

The stock size and biology of Johnius glaucus (Day) resource off the northwest coast of India were studied for 1982-83 and 1983-84. The total length at the end of 6, 12, 18, 24 and 26 months was 121 mm, 183 mm, 237 mm, 261 mm and 264 mm respectively. The length growth parameters were: L∞=300 mm, K=0.0807 (monthly) and t(sub)0=-0.51 month. The weight growth parameters were: W∞= 317g, K=0.0762 (monthly) and t(sub)0= -0.41 month. The exploited stock mainly composed of 1/2 + and 1+ age groups. The annual Z, M and F were 2.34, 1.49 and 0.85 respectively. The l(sub)b, t(sub)b, l(sub)r, t(sub)r and selection factor K were 155 mm, 0.75 year, 65 mm, 0.25 year and 3.875 respectively. The Yw/R was optimum at the exploitation rate (E) of 0.75 and coded mesh size of 37 mm. The total stock for 1982-83 and 1983-84 was 14,624 and 26,190 tons respectively. The standing stock of 1982-83 and 1983-84 was 5,645 and 10,110 tons respectively. The MSY for 1982-83 and 1983-84 was 6,623 and 11,788 tons respectively. The F and Z were lowest in 0+ age group and highest in 1+ age group.

Yielding of engineering polymers at strain rates of up to 500 s-1

A method is described for measuring the mechanical properties of polymers in compression at strain rates in the range approximately 300-500 s-1. A gravity-driven pendulum is used to load a specimen on the end of an instrumented Hopkinson output bar and the results are processed by a microcomputer. Stress-strain curves up to high strains are presented for polycarbonate, polyethersulphone and high density polyethylene over a range of temperatures. The value of yield stress, for all three polymers, was found to vary linearly with log (strain rate) at strain rates up to 500 s-1. © 1985.

Population dynamics of two jewfishes Jhonius argentatus and Johnieops vogleri) in the coastal waters of Bay of Bengal, Bangladesh

Population parameters of Jhonius argentatus and Johnieops vogleri in coastal waters of Bay of Bengal, Bangladesh were estimated by using FiSAT programme. The von Bertalanffy growth parameters, extreme length (cm) and growth constant K (year ·1) were found to be 46.50 and 0.59 for J. argentatus, and 33.50 and 0.85 for J.vogleri The Loc(cm) and Z/K estimates provided by Wetherall plot were 46.694 and 1.791 for J. argentatus, and 31.25 and 2.623 for J. vogleri. The annual rate of natural (M) and fishing mortality (F) were estimated as 1.12 and 0.78 for J. argentatus, and 1.56 and 1.28 for J. vogleri. Rate of exploitation (E) was estimated as 0.41 for J. argentatus and 0.45 for J. vogleri. About 80.04% of J. argentatus were found to be recruited during peak pulses (April-May) and 19.96% during lean pulses (October-November) and 85.75% J. vogleri during peak pulses (May-July) and 14.25% during lean pulses (September-October). The growth performance index(') was 3.11 for J. argentatus and 1.93 for J. vogleri. The total length and body weight relationship was found to be W = 0.0403 TL25723 for J. argentatus and W = 0.0907 TV3482 for J. vogleri.

大蹼铃蟾抗肿瘤蛋白及其制备方法和其基因

本发明涉及大蹼铃蟾抗肿瘤蛋白及其制备方法和其基因，属于生物医学领域。抗肿瘤蛋白是从中国两栖类动物大蹼铃蟾皮肤分泌物中分离得到的一种单链多肽，分子量2697，等电点9.83，多肽氨基酸全序列一级结构为：NH2－GIGGKILSGLKTALKGAAKELASTYLH－NH2。制备方法是收集大蹼铃蟾皮肤分泌物，离心去除沉淀、冷冻干燥后，经离子交换、高压液相反相柱层析分离纯化后得到。由650、623、625个核苷酸组成的三个不同的基因可编码大蹼铃蟾抗肿瘤蛋白，编码成熟抗肿瘤蛋白分别为第177－257位、第166－246位、175－255位核苷酸。具有抑制肿瘤细胞生长、抗艾滋病病毒活性和抑制细菌和真菌生长的作用。

Trade-off between reciprocal mutualists: local resource availability-oriented interaction in fig/fig wasp mutualism

The mechanisms that prevent competition (conflict) between the recipient and co-operative actor in co-operative systems remain one of the greatest problems for evolutionary biology. Previous hypotheses suggest that self-restraint, dispersal or spatial con

湖南烙铁头蛇毒中一个新的舒缓激肤增强肤( TmF)

通过70%冷甲醇抽提、Sephadex C i-15分子筛和反相高效液相色谱G8层析，从湖南产烙铁头蛇毒(Trineresurus muqua nwtus)冻干粉中纯化得到一个新的舒缓激肤增强肤(BPP)，命名为TmF。该小肤的氨基酸序列为p(irr (iy Arg Pro, Leti (iy Pro, Pro, Ile- Pro, Pro ( pau表示焦谷氨酸)。序列结果分析表明，TmF和已经分离得到的BPPs有很高的序列同源性。MSI- MS 测定其分子量为1 .1107 kD o TmF的生物学活性和药理学活性检测的结果表明，它增强舒缓激肤(BK)(1 mg/L)诱导的离体豚 鼠回肠纵行肌收缩的活性为(1 .13士0 .3)单位(mg/ L) ; TmF (5 .0 x 10- 0 mg/ kg)可以增强约(14士2) mmHg的由BK(5 . Ox 10-' mg/ kg)诱导的舒张压下降;在抑制剂试验中，不同剂量的TmF和5x1。一zmg的血管紧张素转化酶保温30 min，结果表明大约 2.0x10一3mg的TmF表现出对ACE水解活性的半数抑制率(IQo )。

Sox and Zfx genes in giant panda

By using PCR cloning techniques, the DNA sequences of the HMG box regions of six Sox genes (pSox) and the zinc finger domains of two Zfx genes (pZfx) in the giant panda were identified. The giant panda Sox genes fell into two subfamilies, SOX-S1 and SOX-S2. The pSox and pZfx genes of the giant panda were highly homologous to the corresponding genes in mammals and revealed close substitution rates to those in the primates.