蛇形机器人侧向运动的研究

本文提出了一种新型蛇形机器人机构 ,建立了其空间运动学模型 ,实现了蛇形机器人的两种侧向运动 :侧向蜿蜒运动和侧向滚动 ,前者通过调节两个异相波的频率比 ,实现了任意方向的侧向运动 .后者通过控制运动波的幅值变化 ,实现了各种形式的纯侧向移动 ,当幅值足够大时 ,这种侧向滚动可以跨越障碍

基于耦合驱动蛇形机器人机构设计与抬起的方法

文中设计了模块化的新型蛇形机器人关节单元 .该单元具有三个自由度 ,其中摆动和俯仰自由度由耦合机构驱动来获得较大的力矩和活动空间 .由该单元组成的蛇形机器人具有很强的驱动能力 ,能够抬起较多的单元 .针对蛇形机器人的特点 ,给出了耦合机构的设计原则 .对蛇形机器人抬起方法作了分析 ,得出采用适当规划方法能够抬起的最大单元数量是直接抬起的最大单元数量的平方关系的结论 ,并在此基础上分析了最大关节角对机器人抬起的影响 ,最后结合实例验证了上面分析结果

蛇形机器人控制系统的设计与实现

以蛇为模型的蛇形机器人的研究 ,扩大了机器人的应用领域 .本文基于CAN总线技术完成了蛇形机器人控制系统的设计及研制 ,有效地实现了机器人的运动控制 .在此基础上完成了蛇形机器人的集中式控制和分布式控制方式 .

一种可重构蛇形机器人的研究

提出了一种新型的可重构蛇形机器人机构。该机构主要特点是单关节结构模块化 ,具有可适应地面形状变化的柔性连接环节和类似于蛇腹鳞摩擦特性的机构底部 ,手动可重构 ,当单自由度关节轴线互相平行连接时 ,该机构可实现多种平面运动形式 ,当单自由度关节轴线垂直依次连接时 ,形成的蛇形机器人具有两自由度的关节 ,可进行多种空间运动。试验结果证实 ,该蛇形机构重量轻、控制简单、运动灵活 ,能够很好地仿生蛇的多种运动形式

蛇形机器人研究现况与进展

仿生技术与机器人技术的结合 ,使机器人从结构设计到运动模式的选择都有了新的进展 ,这大大扩大了机器人的应用领域 .本文阐述了仿蛇形机器人的应用背景和研究现状 ,并展望了其未来的发展

一种离散驱动蛇形柔性臂的工作空间及优化设计研究

以一种离散驱动蛇形柔性臂为研究对象 ,分析并提出了弯曲型离散驱动机器人工作空间的表达方法。考虑到离散驱动机器人工作空间的离散性 ,为了便于对其运动学参数进行调整 ,以使末端操作器达到新指定的工作位置 ,提出了参数调整“标定”的概念 ,并依据使运动学参数调整值尽量小的优化原则对运动学参数进行了优化设计 ,从而解决了运动学参数设计的冗余度问题。

基于循环抑制CPG的蛇形机器人运动控制方法

蛇具有细长无肢的身体、独特的半球形关节，使其可在神经系统控制下完成与环境相适应的多种节律运动。模仿蛇的运动机理和行为方式而设计的蛇形机器人克服了轮腿式机器人的缺点，增加了机器人的运动方式，扩大了机器人的应用范围。但应用传统的控制策略实现蛇形机器人运动控制遇到了很难克服的问题。随着社会经济与科技的发展，研究人员把从蛇运动神经系统研究中得到的启示应用到蛇形机器人上，希望不仅可以解决其运动控制问题，更能在构型、步态及控制机制上皆可展示蛇的特征。 生物学家已经证明动物的节律运动是其低级神经中枢的自激行为，是由中枢模式发生器(Central Pattern Generator，CPG)控制的。中枢模式发生器是一种能够在缺乏有规律的感知和中枢控制输入的情况下，产生有节奏模式输出的神经网络。 本文以国家自然科学基金课题《基于CPG的蛇形机器人控制方法研究》和国家“863”高技术计划资助项目《具有环境适应能力的蛇形机器人的研究》为依托，突破以相互抑制机理研究CPG的传统观点，首次创新性地提出应用循环抑制(Cyclic Inhibition, CI)机理来研究蛇形机器人的CPG建模与实现问题。本研究涵概了神经元模型的特性分析、蛇形机器人关节循环抑制CPG建模理论、蛇形机器人循环抑制CPG神经网络稳定性分析以及典型步态的生成方法、循环抑制CPG神经网络控制蛇形机器人蜿蜒运动参数设定策略、应用动力学仿真和实验对该CPG控制方法有效性的验证。 首先，本文介绍了两个用于CPG建模研究的蛇形机器人“勘查者”和“勘查者-I”。给出各自机械系统、控制系统的构成和动力学仿真平台。 其次，详细分析了神经元以及传统的相互抑制(Mutual Inhibition, MI)CPG的特性。从工程角度首次创新性地应用循环抑制建模理论构建了蛇形机器人CPG模型，并对其稳定性进行了深入的分析。首次证明持续型神经元构成的单向循环抑制(Unilateral Cyclic Inhibition, UCI) CPG是能产生振荡输出CPG中微分方程数量最少的，而且其产生振荡输出的机理完全不同于传统的相互抑制CPG。其不需要具备调整功能，只需要神经元之间强的单向循环抑制连接。 第三，首次应用单向激励连接循环抑制CPG构成蛇形机器人神经网络系统。分析了其稳定性，给出其产生振荡输出的条件。通过仿真和实验验证了循环抑制CPG神经网络实现典型步态(蜿蜒运动、伸缩运动和侧向运动)的有效性。首次应用双向循环抑制(Bidirectional Cyclic Inhibition, BCI)CPG神经网络在不同高级控制神经元命令激活下的输出实现蛇形机器人典型运动步态之间的转换。为蛇节律运动生成机制建模提供了新方法。 最后，从实时性、控制方便性等工程应用的角度，对单向循环抑制CPG神经网络实现蛇形机器人蜿蜒运动控制进行了深入的分析。给出了S-波形、幅值、运动速度和运动轨迹曲率的参数设定策略。该系统应用首CPG自激励权重调解成功解决了传统CPG控制系统中CPG的个数比蛇形机器人关节数多一个的问题，并用其实现了一种独特的转弯控制策略。 综上，为蛇形机器人运动控制提供了全新的方法。

Food sources, behaviour, and distribution of hydrothermal vent shrimps at the Mid-Atlantic Ridge

Five species of bresilioid shrimp were investigated at seven hydrothermal sites on the Mid-Atlantic Ridge: Menez Gwen, Lucky Strike, Rainbow, Broken Spur, TAG, Snake Pit and Logatchev. Samples were prepared for analysis of stable isotopes, elemental composition and lipids. Shrimp behaviour was observed from the submersible ‘Alvin’ and in the laboratory aboard RV ‘Atlantis’. The distribution and zonation of the shrimp species was recorded. Juvenile shrimp of all species arrive at the vents carrying reserves of photosynthetic origin, built-up in the pelagic larval stages. These reserves are used while the shrimp metamorphose to the adult form and, in Rimicaris exoculata and Chorocaris chacei, while they develop epibiotic bacteria supporting structures, the modified mouthparts and the inside of the carapace. The main food of adult R. exoculata is filamentous bacteria that grow on these structures. The intermediate sizes of C. chacei also feed on such bacteria, but the final stage gets some food by scavenging or predation. Mirocaris species scavenge diverse sources; they are not trophically dependent on either R. exoculata or mussels. Adults of Alvinocaris markensis are predators of other vent animals, including R. exoculata. The dense swarms of R. exoculata, with their exosymbionts, can be compared to endosymbiont-containing animals such as Bathymodiolus and the vestimentiferan tube-worms of the Pacific vents. Such associations, whether endo- or ectosymbiotic, may be necessary for the development of flourishing communities at hydrothermal vents.

Genetic analysis of Continuous Plankton Recorder (CPR) samples

Genetic analysis of Continuous Plankton Recorder (CPR) samples is enabling greater taxonomic resolution and the study of plankton population structure. Here, we present some results from the genetic analysis of CPR samples collected in the North Sea and north-eastern Atlantic that reveal the impacts of climate on benthic-pelagic coupling and the food web. We show that pronounced changes in the North Sea meroplankton are related to an increased abundance and spatial distribution of the larvae of the benthic echinoderm, Echinocardium cordatum. Key stages of reproduction in E. cordatum, gametogenesis and spawning, are influenced by winter and spring sea temperature (January-May). A stepwise increase in sea temperature after 1987, which has created warmer conditions earlier in the year, together with increased summer phytoplankton, may benefit the reproduction and survival of this benthic species. Competition between the larvae of E. cordatum and other holozooplanlcton taxa may now be altering the trophodynamics of the summer pelagic ecosystem. In the north-eastern Atlantic the genetic analysis of fish larvae sampled by the CPR has revealed an unprecedented increase in the abundance of juvenile snake pipefish, Entelurus aequoreiis since 2002. We argue that increased sea surface temperatures in winter and spring when the eggs of E. aqueoreus, which are brooded by the male, are developing and the young larvae are growing in the plankton are a likely cause. The increased abundance of this species in Atlantic and adjacent European seas already appears to be influencing the marine food web.

Unmasking venom gland transcriptomes in reptile venoms

While structural studies of reptile venom toxins can be achieved using lyophilized venom samples, until now the cloning of precursor cDNAs required sacrifice of the specimen for dissection of the venom glands. Here we describe a simple and rapid technique that unmasks venom protein mRNAs present in lyophilized venom samples. To illustrate the technique we have RT-PCR-amplified a range of venom protein transcripts from cDNA libraries derived from the venoms of a hemotoxic snake, the Chinese copperhead (Deinagkistrodon acutus), a neurotoxic snake, the black mamba (Dendroaspis polylepis), and a venomous lizard, the Gila monster (Heloderma suspectum). These include a metalloproteinase and phospholipase A2 from D. acutus, a potassium channel blocker, dendrotoxin K, from D. polylepis, and exendin-4 from H. suspectum. These findings imply that the apparent absence and/or lability of mRNA in complex biological matrices is not always real and paves the way for accelerated acquisition of molecular genetic data on venom toxins for scientific and potential therapeutic purposes without sacrifice of endangered herpetofauna.

Identification and functional analysis of a novel bradykinin inhibitory peptide in the venoms of New World Crotalinae pit vipers.

A novel undecapeptide has been isolated and structurally characterized from the venoms of three species of New World pit vipers from the subfamily, Crotalinae. These include the Mexican moccasin (Agkistrodon bilineatus), the prairie rattlesnake (Crotalus viridis viridis), and the South American bushmaster (Lachesis muta). The peptide was purified from all three venoms using a combination of gel permeation chromatography and reverse-phase HPLC. Automated Edman degradation sequencing and MALDI-TOF mass spectrometry established its peptide primary structure as: Thr-Pro-Pro-Ala-Gly-Pro-Asp-Val-Gly-Pro-Arg-OH, with a non-protonated molecular mass of 1063.18 Da. A synthetic replicate of the peptide was found to be an antagonist of bradykinin action at the rat vascular B2 receptor. This is the first bradykinin inhibitory peptide isolated from snake venom. Database searching revealed the peptide to be highly structurally related (10/11 residues) with a domain residing between the bradykinin-potentiating peptide and C-type natriuretic peptide domains of a recently cloned precursor from tropical rattlesnake (Crotalus durissus terrificus) venom gland. BIP thus represents a novel biological entity from snake venom.

Molecular cloning and deduced organization of the pHpG/CNP precursor from the venom of the African forest viper, Atheris squamigera

The discovery that the hypotensive sequela of envenomation by the South American viper, Bothrops jararaca, was mediated by peptides, represented a milestone in drug discovery research that led to the introduction of ACE inhibitors. These bradykinin-potentiating peptides (BPPs) have been found in the venoms of many species of viper and molecular cloning of biosynthetic precursors has revealed that each encodes several different BPPs in tandem with a single copy of a C-type natriuretic peptide (CNP) located at the C-terminus. Venoms of the African forest vipers (Atheris) have been poorly studied possibly because they do not represent a major danger to humans. However, initial studies have indicated that they contain some of the “classical” protein toxins of viper venoms and a novel class of peptide, the polyglycine/polyhistidine (pGpH) peptides. These peptides occur in several molecular forms with different numbers of repetitive glycine and histidine repeats. We have cloned the biosynthetic precursor of A. squamigera pGpH peptides from a venom-derived cDNA library and have confirmed that a single copy of CNP is located at the C-terminus and additionally that, like BPPs in other vipers, pGpH peptides are encoded in tandem within this single precursor. Solid phase peptide synthesis of pGpH peptides has proven to be extremely difficult but is progressing and acquisition of synthetic replicates of each peptide is a necessary prerequisite for systematic pharmacological characterisation as establishment of a biological function for these peptides remains elusive. pGpH peptides may prove to play a role as fundamental as that of the BPPs.

Differential effects of reduced glycoprotein VI levels on activation of murine platelets by glycoprotein VI ligands

We have investigated the effects of decreased levels of the complex between glycoprotein VI (GPVI) and the Fc receptor gamma-chain (FcRgamma) on responses to collagen and GPVI-specific ligands in murine platelets. We show that levels of GPVI-FcRgamma of the order of 50 % and 20 % of wild-type levels caused 2- and 5-fold shifts to the right respectively in the dose-response curve for aggregation in response to collagen, the snake toxin convulxin and the monoclonal antibody JAQ1. In addition, there is a delay in the onset of aggregation in response to collagen. In contrast, the stimulation of protein tyrosine phosphorylation by collagen (as measured after 150 s) and adhesion to a collagen-coated surface under static conditions were unaffected in platelets with 50 % and 20 % of wild-type levels of GPVI. In contrast, responses to a collagen-related peptide (CRP), made up of repeat glycine-proline-hydroxyproline motifs, were markedly inhibited and abolished in platelets expressing 50 % and 20 % of wild-type levels of GPVI respectively. We suggest that the marked effect of a reduction in GPVI levels on the CRP-induced activation of platelets is due to the multivalent nature of CRP and the fact that GPVI is its sole receptor on platelets. Thus it appears that the interaction of CRP with GPVI is determined by a combination of affinity and avidity. The observation that collagen does not behave like CRP in platelets expressing reduced levels of GPVI, even in the combined presence of blocking antibodies against integrin alpha2beta1 and GPV, suggests that collagen has a greater affinity than CRP for GPVI, and/or that other receptors are involved in its binding to platelets. The clinical significance of these results is discussed.

A method to reconstruct patient-specific proximal femur surface models from planar pre-operative radiographs

Three-dimensional reconstruction from volumetric medical images (e.g. CT, MRI) is a well-established technology used in patient-specific modelling. However, there are many cases where only 2D (planar) images may be available, e.g. if radiation dose must be limited or if retrospective data is being used from periods when 3D data was not available. This study aims to address such cases by proposing an automated method to create 3D surface models from planar radiographs. The method consists of (i) contour extraction from the radiograph using an Active Contour (Snake) algorithm, (ii) selection of a closest matching 3D model from a library of generic models, and (iii) warping the selected generic model to improve correlation with the extracted contour.

This method proved to be fully automated, rapid and robust on a given set of radiographs. Measured mean surface distance error values were low when comparing models reconstructed from matching pairs of CT scans and planar X-rays (2.57–3.74 mm) and within ranges of similar studies. Benefits of the method are that it requires a single radiographic image to perform the surface reconstruction task and it is fully automated. Mechanical simulations of loaded bone with different levels of reconstruction accuracy showed that an error in predicted strain fields grows proportionally to the error level in geometric precision. In conclusion, models generated by the proposed technique are deemed acceptable to perform realistic patient-specific simulations when 3D data sources are unavailable.

Functional and Structural Diversification of the Anguimorpha Lizard Venom System

Venom has only been recently discovered to be a basal trait of the Anguimorpha lizards. Consequently, very little is known about the timings of toxin recruitment events, venom protein molecular evolution, or even the relative physical diversifications of the venom system itself. A multidisciplinary approach was used to examine the evolution across the full taxonomical range of this similar to 130 million-year-old clade. Analysis of cDNA libraries revealed complex venom transcriptomes. Most notably, three new cardioactive peptide toxin types were discovered (celestoxin, cholecystokinin, and YY peptides). The latter two represent additional examples of convergent use of genes in toxic arsenals, both having previously been documented as components of frog skin defensive chemical secretions. Two other novel venom gland-overexpressed modified versions of other protein frameworks were also recovered from the libraries (epididymal secretory protein and ribonuclease). Lectin, hyaluronidase, and veficolin toxin types were sequenced for the first time from lizard venoms and shown to be homologous to the snake venom forms. In contrast, phylogenetic analyses demonstrated that the lizard natriuretic peptide toxins were recruited independently of the form in snake venoms. The de novo evolution of helokinestatin peptide toxin encoding do-mains within the lizard venom natriuretic gene was revealed to be exclusive to the helodermatid/anguid subclade. New isoforms were sequenced for cysteine-rich secretory protein, kallikrein, and phospholipase A 2 toxins. Venom gland morphological analysis revealed extensive evolutionary tinkering. Anguid glands are characterized by thin capsules and mixed glands, serous at the bottom of the lobule and mucous toward the apex. Twice, independently this arrangement was segregated into specialized serous protein-secreting glands with thick capsules with the mucous lobules now distinct (Heloderma and the Lanthanotus/Varanus clade). The results obtained highlight the importance of utilizing evolution-based search strategies for biodiscovery and emphasize the largely untapped drug design and development potential of lizard venoms. Molecular & Cellular Proteomics 9:2369-2390, 2010.