Photoreceptor classes and transmission at the photoreceptor synapse in the retina of the clawed frog, Xenopus laevis

The photoreceptor population in Xenopus consists of a green-sensitive rod (lambda(max) = 523 nm), a blue-sensitive rod (lambda(max) = 445 nm) and three classes of cone. The largest cone is red-sensitive (lambda(max) = 611 nm). The intermediate cone is presumed to be blue-sensitive based on physiological criteria, whereas the miniature cone may be UV-sensitive. Horizontal cells (HC) are of two sorts: axon-bearing and axonless. The axon-bearing HC is of the luminosity type and probably contacts all types of photoreceptor. The axonless HC is of the chromaticity type and contacts only intermediate (blue) cones and at least one type of rod. During development dendrites of HCs and bipolar neurons penetrate photoreceptor bases. A progressive maturation of HC and bipolar synapses with rods and cones occurs between tadpoles stages 37/8 and 46. Neighboring rods and cones are joined by gap junctions. During this same period, the outer segments are laid down and photopigments synthesized. A linear relation was found between the quantum capturing ability of the rod and its absolute threshold. Mature rods of the Xenopus retina release glutamate in a calcium-dependent manner. Glutamate release was found to be a linear function of calcium influx through L-type calcium channels. Both types of HC possess ionotropic glutamate receptors of the AMPA subtype.     

Morphogenesis of the different types of photoreceptors of the chicken (Gallus domesticus) retina and the effect of amblyopia in neonatal chicken

Despite the great variety in chicken photoreceptors, existing morphogenetic studies only deal with two types: rods and cones. We have therefore examined by scanning electron microscopy the first appearance and maturation of different retinal photoreceptors in 36 chicken embryos (Gallus domesticus), aged 5-19 days prehatching. On day 5 of incubation, chicken retinae were only composed of proliferating ventricular cells devoid of photoreceptors. On day 8, outer mitotic cells were separated from inner differentiating photoreceptors, by the transient layer of Chievitz. Ball-like protrusions appeared at the ventricular surface, representing the first signs of photoreceptor inner segment formation. From day 10 onward, double cones, single cones, and rods could be clearly distinguished, and occasional cilia were detected at their tip. On day 12, inner segments had increased in length and diameter, and frequently carried a cilium representing the beginning of outer segment formation. On day 14, most photoreceptors displayed a distinct outer segment. On day 19, photoreceptors had essentially assumed adult morphology. Based on the shape of their outer segments, two subtypes of cones and three subtypes of double cones could be distinguished. Throughout development, we observed microvilli close to maturing photoreceptors, either originating from their lateral sides, from their tip, or from Müller cells. Microvillus density peaked between day 12 and 14, indicating an important role in photoreceptor morphogenesis. Unilateral occlusion of the eyes of posthatching chicken reduced the proportion of double cones to single cones in the retina, indicating dependence of retinal morphogenesis upon functional activity of visual cells.     

The complexity of the visual cells and visual pathways of the sturgeon

The visual cells in the retinae of the sturgeon were studied by scanning electron microscopy and transmission electron microscopy. Our investigations revealed the presence of rods, two types of single cones, one type of double cone (two nonidentical cone components adhered together), and one type of twin cone (two identical cone components adhered together). In some of the cones, large glycogen bodies were present in the inner segments and all cones contained oil droplets. Such cone morphology was very similar to that described in the retinae of higher vertebrates, for example the chicken. DiI tracing of retinofugal pathways following uniocular injection demonstrated their bilateral localization and extensive termination in the diencephalon and mesencephalon of both sides. Fibers also crossed over from one side to another through commissures, including the posterior commissure. The complexity of the pathway surpassed that of the teleosts and further indicated the evolutionary importance of this fish.     

Comparative ultrastructure and cytochemistry of the avian pineal organ

The breeding of birds is expected to solve problems of nourishment for the growing human population. The function of the pineal organ synchronizing sexual activity and environmental light periods is important for successful reproduction. Comparative morphology of the avian pineal completes data furnished by experiments on some frequently used laboratory animals about the functional organization of the organ. According to comparative histological data, the pineal of vertebrates is originally a double organ (the "third" and the "fourth eye"). One of them often lies extracranially, perceiving direct solar radiation, and the other, located intracranially, is supposed to measure diffuse brightness of the environment. Birds have only a single pineal, presumably originating from the intracranial pineal of lower vertebrates. Developing from the epithalamus, the avian pineal organ histologically seems not to be a simple gland ("pineal gland") but a complex part of the brain composed of various pinealocytes and neurons that are embedded in an ependymal/glial network. In contrast to organs of "directional view" that develop large photoreceptor outer segments (retina, parietal pineal eye of reptiles) in order to decode two-dimensional images of the environment, the "densitometer"-like pineal organ seems to increase their photoreceptor membrane content by multiplying the number of photoreceptor perikarya and developing follicle-like foldings of its wall during evolution ("folded retina"). Photoreceptor membranes of avian pinealocytes can be stained by antibodies against various photoreceptor-specific compounds, among others, opsins, including pineal opsins. Photoreceptors immunoreacting with antibodies to chicken pinopsin were also found in the reptilian pineal organ. Similar to cones and rods representing the first neurons of the retina in the lateral eye, pinealocytes of birds possess an axonal effector process which terminates on the vascular surface of the organ as a neurohormonal ending, or forms ribbon-containing synapses on pineal neurons. Serotonin is detectable immunocytochemically on the granular vesicles accumulated in neurohormonal terminals. Pinealocytic perikarya and axon terminals also bind immunocytochemically recognizable excitatory amino acids. Peripheral autonomic fibers entering the pineal organ through its meningeal cover terminate near blood vessels. Being vasomotor fibers, they presumably regulate the blood supply of the pineal tissue according to the different levels of light-dependent pineal cell activity.     

旋风车削锥形连接钎杆锥体的改进

本文详尽介绍了锥形连接钎杆锥体加工的一种新方式—旋风车削。此种旋风车削是针对锥体加工的要求而对旋风车床进行改造后形成的不同于通常旋风车削方式的新加工方式。其特点是加工时工件不旋转,相较于其它的锥体加工方式这种旋风车削具有更高的效率和很好的安全性。     

Wear of dental enamel

Teeth wear for a number of reasons. One of the causes for wear is the use of abrasive tooth pastes. A study is reported in which enamel was damaged by single pass sliding of a diamond indenter. In single crystals of fluorapatite, wear occurs by flaking out of chips of material and severely fractured substrate is left behind. On the other hand teeth are made of small rods of polycrystalline hydroxyapatite of the order of 5 μm in diameter oriented perpendicular to the tooth surface. This rod structure of human teeth prevents large scale flaking out of material. Apparently the subsurface cracks do not extend from one rod to the other so that subsequent passes do not result in severe wear. Small abrasive particles may do considerable damage to rods, but the overall effect is small. Large abrasive particles with high loads cause separation of rods, and cracks appear to propagate but without severe permanent damage.     

Distribution of GABA and glycine receptors on bipolar and ganglion cells in the mammalian retina

The amino acids GABA and glycine mediate synaptic transmission via specific neurotransmitter receptors. Molecular cloning studies have shown that there is a great diversity of GABA and glycine receptors. In the present article, the distribution of GABA and glycine receptors on identified bipolar and ganglion cell types in the mammalian retina is reviewed. Immunofluorescence obtained with antibodies against GABA and glycine receptors is punctate. Electron microscopy shows that the puncta represent a cluster of receptors at synaptic sites. Bipolar cell types were identified with immunohistochemical markers. Double immunofluorescence with subunit-specific antibodies was used to analyze the distribution of receptor clusters on bipolar axon terminals. The OFF cone bipolar cells seem to be dominated by glycinergic input, whereas the ON cone bipolar and rod bipolar cells are dominated by GABAergic input. Ganglion cells were intracellularly injected with Neurobiotin, visualized with Streptavidin coupled to FITC, and subsequently stained with subunit specific antibodies. The distribution and density of receptor clusters containing the alpha1 subunit of the GABA(A) receptor and the alpha1 subunit of the glycine receptor, respectively, were analyzed on midget and parasol cells in the marmoset (a New World monkey). Both GABA(A) and glycine receptors are distributed uniformly along the dendrites of ON and OFF types of parasol and midget ganglion cells, indicating that functional differences between these subtypes of ganglion cells are not determined by GABA or glycinergic input.     

轧辊锥体锥度检测仪

介绍了一种检测高速线材轧机轧辊锥轴与锥套锥度的检测方法以及相应的锥体锥度检测仪。该检测仪进行锥度测量的相对误差约为10-4,可在计算机上显示出被测锥体的实际轮廓,并可进行锥轴和锥套的虚拟装配,实现了锥体的高精度选择装配。     

刚散耦合振动圆锥破碎机动力学分析

将振动圆锥破碎机简化为六自由度运动的物理模型,物料层采用分段线性接触力模型来表示。应用Lagrange方程,对振动圆锥破碎机进行了建模。通过Matlab采用Runge-Kutta法对振动微分方程组进行数值计算仿真,研究了不同激振频率下系统的动力学性能。研究结果表明,物料层的作用是系统非线性的根本来源,物料层的非线性导致系统从单一频率的简谐运动变为复杂运动,为振动圆锥破碎机的参数选择提供了依据。     

A possible explanation for the hydrodynamic transition in high speed impact

The velocity at which the mode of penetration of a rod striking a thick target changes from gross plastic deformation to a jetting type of flow has been called the hydrodynamic transition velocity. It is proposed that this velocity depends on the relative rates of rod erosion and plastic wave propagation. A simple theory predicts the hydrodynamic transition velocity for right cylindrical rods striking normally a thick target in terms of the empirical dynamic strength of the rod and target and the dynamic work hardening rate or dynamic large strain tangent modulus of the rod material.     

On the applicability of one-dimensional non-viscous dynamic plasticity theory

The applicability of one-dimensional non-viscous dynamic plasticity theory to impacting rod problems is examined experimentally using results derived from general three-dimensional and viscous similarity considerations and their corresponding one-dimensional and non-viscous counterparts. When three-dimensional and viscous effects are important, these considerations are found to require a specific response dependence on the ratios of characteristic rod lengths to rod diameters and characteristic striking velocities to rod lengths. Direct examination of experimental impact-duration and impact-displacement data from aluminum and copper rods reveals, however, no such dependence over a wide range of striking velocities and rod lengths. The general applicability of one-dimensional non-viscous dynamic plasticity theory is thus confirmed without recourse to the complex details of the theory.     

基于Hopkinson压杆试验的小钎杆动态应力特性研究

在对锥体连接钎杆和整体钎杆2种典型小钎杆的应力传播模型进行理论分析的基础上,通过Hopkinson压杆试验系统对这2种钎杆杆体中部和钎头端部进行了动态应力测试。测试结果表明:2种钎杆杆体中部应力幅值基本没有差异,但锥体连接钎杆接头处具有30%的应力波反射,而整体钎杆没有;整体钎杆钎头端部最大入射应力波幅值的平均值比锥体连接钎杆的相应均值高出23%,使得整体钎杆的凿速比锥体连接钎杆的要高,但其损坏更快,预期寿命只有锥体连接钎杆寿命的18%,故整体钎杆更适用于软岩钻孔作业,而锥体连接钎杆更适用于硬岩钻孔作业,该试验研究为技术人员如何选用钎杆提供了理论指导。     

三醋酸甘油酯自动喷雾系统的应用

AF2/KDF2型滤棒成型机组的增塑剂上胶系统,采用毛刷旋转甩涂三醋酸甘油酯控制滤棒硬度,存在三醋酸甘油酯喷涂不均匀、丝束与三醋酸甘油酯浪费严重等问题,为提高滤棒质量,进行了基于雾化技术的三醋酸甘油酯自动喷雾系统的改造.改造后的系统靠管腔内、外形成的压力差,由喷嘴喷出雾化良好的甘油,均匀附着在丝束上,克服了原上胶方式中控制过程的非线性和时滞性缺点,测试结果表明,提高了咀棒质量,降低了废棒率,也相应降低了甘油用量.     

Thickness improvement in single point incremental forming deduced by sequential limit analysis

Multistage forming is one of the most practical solutions to avoid severe thinning in single point incremental forming (SPIF). A successful implementation of multistage SPIF is strongly dependent on an appropriate deformation path. In this paper, firstly, a simplified modeling technique is proposed using sequential limit analysis. It is shown that sequential limit analysis can predict the thickness distribution faster than an equivalent model in a commercial finite element modeling code like Abaqus can. The reliability of the model is assessed by comparing experimental and simulated results for single-stage and multistage SPIF cones. This model is utilized to study the effect of various deformation paths on the thickness distribution. As a result, a new multistage strategy is designed and implemented to form a 70° wall angle cone in three stages. The thickness distribution of the cone is improved significantly compared to cones formed by a single-stage and a conventional three-stage strategy. Besides this improvement, the new multistage SPIF can be carried out in much less time.     

基于单晶铜的热型连铸炉关键结构设计

以机电一体化与热型连铸工艺技术相结合的设计思路,针对热型连铸炉的关键工序工艺参数控制的特殊性,为保证热型连铸的单晶铜线坯的结晶不出现缺陷,对熔炼、铸型保温、定向凝固三个关键工序的结构进行设计,可提高单晶铜线坯结晶组织的连续性和稳定性。     

Analysis of the morphogenesis and cell proliferation in the retina of a pleuronectiform fish,the turbot psetta maxima (Pleuronectiformes: Teleostei)

The morphogenesis and cell proliferation in the retina of turbot (Psetta maxima, Pleuronectiformes: Teleostei) from embryo through metamorphosis have been examined by using proliferating cell nuclear antigen (PCNA)‐immunohistochemistry and general histological procedures. In the embryonic retina, cell proliferation and spatial cell reorganization form the anlage of the pigment epithelium and neural retina. Neurogenesis begins around hatching in the temporal retina, dorsal to the optic nerve exit, and then a wave of cell differentiation spreads to the nasal retina to yield a laminated retina by the end of the prolarval turbot stage. Germinal zones in the differentiated retina persist as a rim at the retinal margin, as well as surrounding the optic fissure in premetamorphic and metamorphic turbot larvae. In these zones, progenitor cells with different morphologies show a similar spatial arrangement, which suggests that they have a similar retinogenic potential. During metamorphosis, asymmetric proliferative activity in turbot germinal zones is associated with a marked expansion of the retinal tissue. Scattered stem cells in the laminated retina, related to the lineage of rod photoreceptors, were also observed both in large premetamorphic larvae and metamorphic turbots. The proliferative activity of these cells increases considerably during metamorphosis, when rod photoreceptors become morphologically differentiated. Microsc. Res. Tech. 76:588–597, 2013. © 2013 Wiley Periodicals, Inc.     

Instability and self-contact phenomena in the writhing of clamped rods

We use the Cosserat rod theory to present a unified picture of jump phenomena, associated with looping, snap-through, pop-out, etc., in twisted clamped rods undergoing large deflections. Both contact-free rods and rods with isolated points of self-contact are considered. Taking proper account of the symmetries of the problem we find that an arbitrary contact-free solution is fully characterised by four parameters; each point contact adds another two. A shooting method is used for solving the boundary value problem. An intricate bifurcation picture emerges with a strong interplay between planar and spatial rod configurations. We find new jump phenomena by treating the ratio of torsional to bending stiffness of the rod as a bifurcation parameter. Load-deflection curves are computed and compared with results from carefully conducted experiments on contact-free as well as self-contacting metal-alloy rods.     

水平井抽油杆柱力学模型的建立与分析

首先分析水平井筒里抽油杆柱的运动状态,考虑柱塞与悬点运动的不一致性,找出杆柱受力最大和最小的位置时刻,根据井筒中抽油杆柱的空间几何关系,考虑抽油杆的约束条件和井斜角、方位角的变化等边界条件后,建立抽油杆柱的力学模型,并对模型进行相关分析,对杆柱的优化设计和优化配套防偏磨的工艺具有一定的指导意义.     

Configurations of momentless extensible rods

The problem of the proper shape of momentless extensible rods is investigated. A general formulation of the equations for extensible, finitely rigid spatial rods with bending and shear suppressed, is presented. The particular class of planar arches is, then, considered and a specific example worked out. It is shown that to satisfy the boundary conditions, in general, requires that the cross-sectional area of the momentless rod be variable and a trend in the variation is obtained. Some consideration is also given to the problem of momentless extensible arches acted upon by deformation-dependent forces.     

新型大柔度锥面高速刀柄的设计

设计了一种新型结构高速刀柄,刀柄的结构特征为实心短锥双面定位,并在锥面上开环形沟槽形成分锥体。由分锥体组合而成的大柔度锥面允许刀柄与主轴锥孔以较大过盈量配合联接,同时刀柄分锥体高速旋转时能够产生较大的离心膨胀与主轴锥孔膨胀相匹配,提高了刀柄与主轴接口的极限转速和联接刚度。对刀柄结构进行了设计,利用有限元分析对刀柄的主要几何参数、过盈量以及极限转速进行了确定。研究结果证明,与常用的HSK刀柄相比,所设计的新型高速刀柄能够显著提高刀柄的极限转速。