变胞机构与机构再生运动链综合研究

变胞机构是机构在运动的过程中通过改变构件或运动副的数量或类型从而完成不同的功能,而机构再生运动链方法是根据初始机构通过综合理论得到所有可能的运动链的一种机构创新方法,由于这两种方法都要利用拓扑结构来表达,因此笔者创造性的将两种方法利用其内在的拓扑关系结合起来,从而提出了基于拓扑的变胞机构再生运动链创新方法,该方法为利用再生运动链对变胞机构的创新提供一定参考依据。     

Time-dependent mechanical behaviour of the periodontal ligament

The process of tooth displacement in response to orthodontic forces is thought to be induced by the stresses and strains in the periodontium. The mechanical force on the tooth is transmitted to the alveolar bone through a layer of soft connective tissue, the periodontal ligament. Stress and/or strain distribution in this layer must be derived from mathematical models, such as the finite element method, because it cannot be measured directly in a non-destructive way. The material behaviour of the constituent tissues is required as an input for such a model. The purpose of this study was to determine the time-dependent mechanical behaviour of the periodontal ligament due to orthodontic loading of a tooth. Therefore, in vivo experiments were performed on beagle dogs. The experimental configuration was simulated in a finite element model to estimate the poroelastic material properties for the periodontal ligament. The experiments showed a two-step response: an instantaneous displacement of 14.10 +/- 3.21 microns within 4 s and a more gradual (creep) displacement reaching a maximum of 60.00 +/- 9.92 microns after 5 h. This response fitted excellently in the finite element model when 21 per cent of the ligament volume was assigned a permeability of 1.0 x 10(-14) m4/N s, the remaining 97 per cent was assigned a permeability of 2.5 x 10(-17) m4/N s. A tissue elastic modulus of 0.015 +/- 0.001 MPa was estimated. Our results indicate that fluid compartments within the periodontal ligament play an important role in the transmission and damping of forces acting on teeth.     

Age-dependent changes of the periodontal ligament in rats

Even after the end of the natural tooth eruption, there is a continuous renewal of the periodontal collagenous fiber system, depending on functional demands. The aim of this study was to analyse the age-dependent changes and regional differences of the collagen renewal rate of the periodontal ligament in healthy rats. The study was performed by autoradiography of the molars of rats aged 1, 8, and 18 months, where collagen was labelled by intravenously applied 3H-proline. After an 8-hour incorporation period, the animals were killed. For comparative examinations, molar roots were subdivided into cervical, middle, and apical thirds. Structural and quantitative analyses were performed by light microscopy and autoradiography, using an image-analysing computer-assisted operating unit that determined the 3H-proline-labelled collagen by photometry based on extinction measurement. With increasing age of the animals, the number of silver grains (3H-proline-blackened collagen) was reduced and the quantitative evaluation indicated a reduction of 3H-proline in the periodontal ligament. The lowest level of 3H-proline activities was observed in the middle, and the highest level in the apical root third, independent of age. All preparations revealed condensations of silver grains, which were located in the region of the periodontal ligament adjacent to the alveolar bone, but did not reveal any preferred position with regard to the dental topography. With progressive age, the uptake of 3H-proline in the periodontal ligament was reduced by about 20 to 30%, a result that corresponds to a decrease in collagenous fiber production. Collagen was mainly formed in the apical and cervical root third, starting from the alveolar bone side, presumably in response to functional strain.     

Microscopic overview of crinoid regeneration.

Crinoids are well known for their striking regenerative potential and can rapidly and completely regenerate arms lost following self-induced or traumatic amputation. Thus they provide a valuable experimental model for investigation of the regenerative process from the macroscopic to the molecular level. In these last years we have studied in detail the overall process of arm regeneration in the comatulid Antedon mediterranea. This phenomenon can be described on the whole as a typical blastemal regeneration in which new structures develop from migratory pluripotential, actively proliferating cells in the presence of presumptive regulatory factors. The overall process can be subdivided into three main phases: a repair phase, an early regenerative phase, and an advanced regenerative phase, whose crucial aspects are related to common fundamental mechanisms such as cell migration and proliferation, intervention of stem cells and/or dedifferentiated cells, contribution of putative growth factors, particularly in terms of specific neurally derived factors, and mechanisms of pattern formation. This article focuses on the main aspects of the phenomenon and gives a brief account of the most recent and relevant results. Our approach employs classical methods of light (LM) and electron (TEM and SEM) microscopy, immunocytochemistry, and histofluorescence on experimentally induced arm regenerations of standard or abnormal type obtained in significantly different experimental conditions, including extreme mutilations (explants) or exposure to pseudo-estrogenic environmental contamination.     

Profiled-follower mechanisms

A study is here made of useful input-output motions from a class of profile-mechanisms characterised by a roller input driving a profiled follower. Both reciprocating and oscillating followers are considered. Compactness and favourable dynamic characteristicsare some of the advantages that this class of mechanism has over conventional cam mechanisms for certain forms of input-output motion which are broadly specified.     

Bacterial endotoxins in periodontal health and diseases

Bacterial endotoxins are a major concern in periodontal health and diseases owing to their structure and biological activity. With up-to-date knowledge of endotoxins and the recent findings about the influence of endotoxins in dental health, their probable mode of pathogenesis, and standard detection methods, this review analyzes the potential efficacy and benefits of probiotics in combination with conventional and contemporary treatment measures. In the oral cavity, Gram-negative bacteria are documented to predominate in the pulpal lesions with radiolucent areas and in the root canal with pulp necrosis, where they pose an absolute threat by promoting a series of inflammatory reactions. Endotoxin, a constituent of Gram-negative bacteria establishes a nexus between cytokine stimulation and proinflammatory reactions, therefore plays a critical role in decaying dental pulp and modulating periodontal diseases. Currently, the treatment regimen involves several biochemical preparations. In addition, probiotics have been reported to control endotoxin in gingivitis and contribute to the overall improvement of dental health. A potential benefit of a combination of probiotics as a complementary treatment along with the conventional treatment warrant more empirical evidence to elucidate its role and mechanism in resolving the clinical manifestations associated with endotoxins in the periodontal region.     

Muscle regeneration in holothurians.

The muscle system of holothurians includes visceral (coelomic epithelium) and somatic (longitudinal muscle bands, retractors of aquapharyngeal complex) musculature. Visceral musculature regeneration is achieved by the transformation of myoepithelial cells via their dedifferentiation, migration, proliferation, and redifferentiation. During somatic muscle regeneration the new muscle bundles are formed due to dedifferentiation, migration, and immersion of the coelomic epithelial cells into the connective tissue. While submerging, the epithelial cells transform into myocytes and begin to produce myofibrils in their cytoplasm. Concomitantly, a basal lamina is formed around the group of myogenic cells, separating them from the surrounding extracellular matrix. The myohistogenesis is accompanied by a conspicuous DNA-synthetic activity. Proliferation is insignificant and seems to be of no essential importance for muscle regeneration. The synthesis of DNA followed by no cytokinesis results in an increase in the amount of DNA of myocyte nuclei.     

Visceral regeneration in holothurians.

Holothurians, or sea cucumbers, exhibit two processes that have intrigued biologists for decades: autotomy and regeneration. Autotomy includes the loss of body parts by evisceration or fission, and regeneration is the extraordinary process by which the lost organs are replaced. In this article, we review the literature on evisceration, transection, and visceral regeneration in holothurians and compare these processes in different orders and lower taxa. Focusing mainly on the digestive tube, we analyze regeneration from a cellular perspective, considering especially the origin, migration, and proliferation of the cellular components of the regenerated organ. The data highlight the most interesting aspects of holothurian regeneration and indicate those critical problems requiring new information and new approaches.     

Regeneration of periodontal Ruffini endings in adults and neonates

We reviewed the regeneration of periodontal Ruffini endings, primary mechanoreceptors in the periodontal ligament, following injury to the inferior alveolar nerve (IAN) in adult and neonatal rats. Morphologically, mature Ruffini endings are characterized by an extensive arborization of axonal terminals and association with specialized Schwann cells, called lamellar or terminal Schwann cells. Following injury to IAN in the adult, the periodontal Ruffini endings of the rat lower incisor ligament regenerate more rapidly than Ruffini endings in other tissues. During regeneration, terminal Schwann cells migrate into regions where they are never found under normal conditions. The development of periodontal Ruffini endings of the rat incisor is closely associated with the eruption of the teeth; the morphology and distribution of the terminal Schwann cells became almost identical to those in adults during postnatal days 15-18 (PN 15-18d) when the first molars appear in the oral cavity, while the axonal elements showed extensive ramification around PN 28d when the functional occlusion commences. When the IAN was injured in neonates, the regeneration of periodontal Ruffini endings was delayed compared with the adults. The migration of terminal Schwann cells is also observed following IAN injury, after which the distribution of terminal Schwann cells became almost identical to that of the adults, i.e., PN 14d. Since the interaction between axon and Schwann cell is important during regeneration and development, further studies are required to elucidate its molecular mechanism during the regeneration as well as the development of the periodontal Ruffini endings.     

Degeneration and regeneration of ganglion cell axons

The retino-tectal system has been used to study developmental aspects of axon growth, synapse formation and the establishment of a precise topographic order as well as degeneration and regeneration of adult retinal ganglion cell (RGC) axons after axonal lesion. This paper reviews some novel findings that provide new insights into the mechanisms of developmental RGC axon growth, pathfinding, and target formation. It also focuses on the cellular and molecular cascades that underlie RGC degeneration following an axonal lesion and on some therapeutic strategies to enhance survival of axotomized RGCs in vivo. In addition, this review deals with problems related to the induction of regeneration after axonal lesion in the adult CNS using the retino-tectal system as model. Different therapeutic approaches to promote RGC regeneration and requirements for specific target formation of regenerating RGCs in vitro and in vivo are discussed.     

The role of periodontal disease in atherosclerotic cardiovascular disease

Atherosclerotic cardiovascular disease (ASCVD) includes a group of disorders of the heart and blood vessels and accounts for major morbidity and premature death worldwide. Periodontitis is a chronic inflammatory disease with the gradual destruction of supporting tissues around the teeth, including gingiva, periodontal ligament, alveolar bone, and cementum. Periodontitis has been found to potentially increase the risk of ASCVD. Generally, oral microorganisms and inflammation are the major factors for periodontitis to the incidence of ASCVD. Recently, evidence has shown that the loss of masticatory function is another important factor of periodontitis to the incidence of ASCVD. In this review, we illustrate the recent finding of the relationship between periodontitis and ASCVD, from a microscale perspective-oral microorganisms, inflammation, and tooth loss. With the high prevalence of periodontitis, it is important to add oral therapy as a regular ASCVD prevention strategy. Regular dental visits could be a helpful strategy for ASCVD patients or general medical practitioners.     

Self-braking of free-wheel mechanisms

Static self-braking of wedge-based free-wheel mechanisms is investigated by means of a nonconservative boundary-element model. The distribution of the contact characteristics in the kinematic pairs of the self-braking mechanisms is established. Their stress–strain state is determined.     

Dynamics of piano mechanisms

Analysis of the structure of the modern upright and grand piano keyboard mechanism is given, and the linear model used in previous simulations by other authors is described. The comparison of the experimental results obtained for a real keyboard mechanism with those which were calculated from known equations of motion (linear model) showed, however, not sufficient coincidence, thus a necessity for improvement of the model arose. A new, non-linear model of the keyboard mechanism is presented, and some results of that model's digital computer simulations are given.     

Analysis of profiled-follower mechanisms

The inverse cam or profiled-follower mechanism is a mechanism in which the roller at the end of the crank engages a profiled groove in the follower. In the present paper, expressions for the follower surface, the pressure angle, and the curvatures of the follower surface are developed for a specified displacement relation between the crank and follower.     

汽车手动调整臂外壳加工工艺改进

通过将汽车手动调整臂外壳加工工艺由拉削改为镗削,大大降低了加工成本。     

Regulation of intestinal regeneration: new insights

Intestinal regeneration is the process by which intestinal injury penetrating deep to the lamina propria heals. The regenerative process involves epithelial cell migration and proliferation, changes in cellular function, adaptation of subepithelial tissues, and contraction of the injured area. This requires interaction of multiple cell types. While many observations have been made about the process of regeneration, its regulation is not well understood. Previous studies, performed primarily in a serosal patch model, have identified many potential regulatory factors. These include location and size of the injury, other associated injury, e.g., resection, and a variety of agents that influence one or more of the primary processes involved. Epidermal growth factor (EGF), in particular, appears to play a role in many aspects of regeneration. Recent advances in the understanding of intestinal growth regulation have provided new insights into the regulation of intestinal regeneration. Developmental studies in genetically manipulated mice suggest a role for gene products not previously implicated in regeneration. The importance of apoptosis in growth regulation has recently been emphasized. Mesenchymal-epithelial interactions have gained greater appreciation. Finally, it has become clear that immune cells and cytokines are important factors in this process. Transforming growth factor-beta (TGFbeta) has been implicated as another important regulator of several of the processes involved in intestinal regulation. Improved understanding of the regulation of intestinal regeneration will lead to new therapeutic approaches to stimulate intestinal healing in the clinical setting.     

Integrated CAD of mechanisms

There are three major components in an integral linkage design package: synthesis, analysis and design/drafting. Through the utilization of existing design software and integration tools, such a system is being developed at the University of Minnesota. This paper presents the prototype system along with a detailed example. The system, not yet all encompassing, ties the three major components together into one useful design tool utilizing LINCAGES for synthesis, DRAM for analysis, and ICEM DESIGN/DRAFTING for the design/drafting component. The example illustrates the use of the package in the design of a six-bar stamper mechanism. The design process is followed through from initial problem definition to the final analysis of the mechanism.     

少自由度并联机构探析

并联机构是一种新型机构,具有传统串联机构无法比拟的优点,是串联机构的补充和扩展,它以轻便灵活、工作空间大等优点受到广大专家学者的高度重视,对于机床技术和机器人技术的发展具有重要推动作用.     

Tracking oligodendrocytes during development and regeneration

Over the past decade, advances in strategies to tag cells have opened new avenues for examining the development of myelin-forming glial cells and for monitoring transplanted cells in animal models of myelin insufficiency. The strategies for labelling glial cells have encompassed a range of genetic modifications as well as methods for directly attaching labels to cells. Genetically modified oligodendrocytes have been engineered to express enzymatic (e.g., beta-galactosidase, alkaline phosphatase), naturally fluorescent (e.g., green fluorescent protein), and antibiotic resistance (e.g., neomycin, zeomycin) reporters. Genes have been introduced in vivo and in vitro with viral or plasmid vectors to somatically label glial cells. To generate germ-line transmission of tagged oligodendrocytes, transgenic mice have been created both by direct injection into mouse fertilized eggs and by "knock-in" of reporters targetted to myelin gene loci in embryonic stem cells. Each experimental approach has advantages and limitations that need to be considered for individual applications. The availability of tagged glial cells has expanded our basic understanding of how oligodendrocytes are specified from stem cells and should continue to fill in the gaps in our understanding of how oligodendrocytes differentiate, myelinate, and maintain their myelin sheaths. Moreover, the ability to select oligodendrocytes by virtue of their acquired antibiotic resistance has provided an important new tool for isolating and purifying oligodendrocytes. Tagged glial cells have also been invaluable in evaluating cell transplant therapies in the nervous system. The tracking technologies that have driven these advances in glial cell biology are continuing to evolve and present new opportunities for examining oligodendrocytes in living systems. Microsc. Res. Tech. 52:766-777, 2001. Published 2001 Wiley-Liss, Inc.