Rough Bodies Research Articles

Genital primordium of the free-living marine nematode Halichoanolaimus sonorus (Chromadoria, Chromadorida)

Summary The genital primordium of the first stage juvenile (J1) of the free-living marine nematode Halichoanolaimus sonorus (Chromadorida: Selachinematidae) was studied using transmission electron microscopy. The primordium consists of four undifferentiated cells: two primordial germ cells (PGC) 5–6 μm in diameter and two somatic cells. The PGC have a large nucleus with nucleolus. The centriole was detected in close vicinity of the PGC nucleus. Most of the cell mitochondria are in close contact with the nuclear envelope. The mitochondria are interspersed by 0.2–0.3 μm particles of an electron-dense diffuse substance devoid of surrounding membrane. Both PGC are closely attached to each other and to the neighboring somatic cells of the genital primordium. The elongated somatic cells contain nuclei devoid of nucleoli; the cytoplasm is filled with free ribosomes and contains occasional cisternae of rough endoplasmatic reticulum (RER), Golgi bodies, mitochondria, and transparent vesicles. The genital primordium is separated by a narrow space from of the intestine (dorsally) and the somatic muscles (ventrally). The PGC of H. sonorous are devoid of typical P granules known for previously studied nematodes as distinct markers of germ line cell lineage. Perinuclear particles of dense diffuse substance found in PGC of H. sonorous could be considered as germ determinants analogous to P granules.

Thermo-Mechanical Model for Moving Layered Rough Surface Contacts

A numerical model designed to simulate a moving line contact of two rough layered bodies is presented. Fourier transforms are used to obtain fundamental solutions to relevant differential equations and then these solutions are used as kernel functions in a numerical scheme designed to provide a full thermomechanical solution for real layered contacts. The model assumes steady state heat transfer and predicts contact pressures and deformations, contact temperature rise, and resulting thermal stresses. The heat division between the contacting components is fully accounted for, as are the interactions between the mechanical and thermal displacements. Some results are presented to illustrate the potential importance of a full thermomechanical analysis as compared to a purely mechanical one as well as to demonstrate the influence of coating properties and surface roughness structure on the contact temperatures.

Composite Skewness for Two Rough Surfaces in Contact

Typically, the contact of two rough bodies is transformed into an equivalent rough surface contacting a flat. Due to the mathematics involved, this was usually conducted for surfaces assumed to be Gaussian, where distribution of peaks and valleys are equal. These assumptions were acceptable when dealing with ground surfaces, which are typically Gaussian; however, other finishing techniques often result in skewed surface distributions. As such, an equation was developed numerically within, based on the Weibull distribution, to estimate the composite skewness of contacting rough bodies. The assumption of using the Weibull distribution to describe the surface variation was validated with measured data from different finishing techniques, as was the equation for composite skewness developed within. Presented at the STLE Annual Meeting in Las Vegas, Nevada, May 15-19, 2005 Review led by Alan Lebeck

Initial deformation about convex surfaces formed from identical, rough elastic-plastic bodies which approach along their normal at first contact

AbstractThe low-velocity impact of two convex surfaces comprised of identical material, which approach each other along the direction of the normal at first contact, and obey a J2 = k2 plastic yield condition, is shown for very early times to satisfy the following conditions: the interior surface which separates the two bodies is equivalent to either the locus of points formed by the intersecting curves resulting from moving the two bodies towards each other along their normal; or to the locus of points formed from the level surfaces (suitably parametrized) drawn about each body at the time of first contact. This separating surface lies midway between the geometrical overlap of the two approaching surfaces for times sufficiently short for inertial effects not to significantly affect the approaching velocities.

Structural characterization of the stigma-style complex of Cynara cardunculus (Asteraceae) and immunolocalization of cardosins A and B during floral development

Studies were carried out on the structure of the stigma and style of Cynara cardunculus L. (cardoon) during flower development. The stigma is of the dry type with a papillate cuticularized epidermis. During development, the unicellular papillae become match-stick shaped, cuticularize, and show an increase in vacuolar volume. In mature papillae, two morphologically different vacuoles were observed, one electron-dense and the other electron-transparent, putatively corresponding to distinct vacuolar populations. These vacuoles label differently for cardosin A, specifically detected in the electron-dense compartments. The style is solid with a cuticularized epidermis and a central core of transmitting tissue (TT) several cell layers thick. The TT cells show abundant rough endoplasmic reticulum and Golgi bodies, associated with active secretion. During maturation, TT cells become increasingly separated by a polysaccharide-rich extracellular matrix. Communication between TT cells is maintained via plasmodesmata in longitudinal walls. Distribution of cardosins A and B in developing C. cardunculus flowers was also characterized. The presence of aspartic proteinases (APs) in flowers is unusual, generally occurring at low levels. Cardosins A and B are always present in cardoon florets and localize at distinct pistil levels: stigma (papillae) and style (TT), respectively. This differential localization suggests distinct biological functions for cardosins, most likely essential for reproduction in this species.

An incremental solution method for rough contact problems

The numerical prediction of interfacial pressures in the mechanical contact of rough bodies has been studied widely. All published solution methods assume that the location of the region of contact between two approaching bodies is unknown and must be found by iterative trial and error. An alternative approach is presented in which the bodies are brought into contact incrementally. If the contact problem is described on a discrete grid and a valid solution is known for some applied load, it is possible to predict the location of the next point to enter contact and the increment in load required to cause this. This incremental approach to solution is developed and a compact formulation is given. The method is compared with the fastest known existing solution method which also requires factorisation of the stiffness matrix and it is around six times slower. However having found the solution for a given load, the incremental approach has also found the complete loading history, so that the solution for any other load up to the given value is known without further calculation. In addition, solution for any higher load can begin from the existing solution. This feature allows exploration of a variety of new applications: the history of body load against body displacement offers a simple means to determine characteristics of a surface texture; the impact of one rough body colliding with another is solved by the same incremental approach; problems with cyclic or dynamic loading can be studied without additional complexity; problems including both elastic and plastic deformation can be solved with improved convergence and allowing for work hardening during loading. While slower than other methods for solving static problems, the new incremental approach is inherently dynamic and thus more closely replicates the physical situations of concern to practical tribologists.

The normal contact of rough surfaces with fine discretization

The numerical treatment of a 3-d frictionless normal contact of rough bodies made of a linear–elastic, isotropic material is considered. First, the governing equations and their discretized forms are presented. Due to the order of the problem, the computation time rapidly increases with the grid refinement. Therefore, common computer programs have to be limited to 50×50 contact points. Several numerical techniques (multigrid, iterative solver, distributive relaxation) are used. Cell-centered grid transformation is applied and grid operators have been established for this purpose. In order to handle upto 1000 × 1000 cells the program CON3D has been developed.

Boundary integral equation method in rolling contact problems involving roughness, wear and frictional heating

AbstractThe method of boundary integral equations is developed to the solution of the rolling contact problems for rough bodies. A model of boundary roughness is proposed. The method permits to involve wear and frictional heating due to the slip in rolling contact.

Bounds on the electrical resistance between contacting elastic rough bodies

A method is developed for placing bounds on the electrical contact conductance between contacting elastic bodies with rough surfaces. An analogy is first established between contact conductance and the incremental stiffness in the mechanical contact problem. Results from contact mechanics and the reciprocal theorem are then used to bracket the mechanical load–displacement curve between those for two related smooth contact problems. This enable bounds to be placed on the incremental stiffness and hence on the electrical conductance for the rough contact problem. The method is illustrated by two simple examples, but its greatest potential probably lies in establishing the maximum effect of neglected microscales of roughness in a solution of the contact problem for bodies with multiscale or fractal roughness.

Enforced expression of oxygen-regulated protein, ORP150, induces vacuolar degeneration in mouse myocardium.

Although the 150 kDa oxygen-regulated protein (ORP150) is known as a protein induced by low oxygen tension or ischemical insult, its possible role has not been fully investigated in vivo. To investigate the intracellular function of this protein, we generated the ORP150 over-expressing transgenic mice (ORP-Tg mice) under beta-actin promoter, and established three independent lines of the transgene expressed mice. All lines invariably showed growth retardation. Over-expression of ORP150 was confirmed by western blotting in heart, brain, spleen, skeletal muscle, pancreas, lung, thymus, and kidney. To ascertain the relationship between the over-expression of the ORP150 and the growth retardation in the transgenic mice, we examined pathological changes in the transgenics. In the ORP-Tg mice, vacuolar degeneration appeared in the heart. The degeneration in the myocytes became conspicuous with advancing age. Immunostaining demonstrated ORP150 in the vacuoles of degenerating myocytes. Electron microscopical findings revealed striking development of intracellular membrane system, for example, rough endoplasmic reticula (rER), vacuoles and Golgi bodies, swelling of sarcoplasmic reticulum, and lysis of myofibrils and mitochondria. These findings indicate that ORP150 may locate in the rER and other outer compartment of ER, and that constitutive over-expression of ORP150 in the heart induces vacuolar degeneration in myocytes, resulting in growth retardation of the transgenics.

Oblique impact with friction and tangential compliance

The present temporal analysis of impact between two rough and compliant hard bodies employs a lumpedparameter model of the small region of contact that suffers significant deformations. This model ...

Elastic-plastic indentation creep of glassy poly(methyl methacrylate) and polystyrene: characterization using uniaxial compression and indentation tests

This paper discusses the time-dependent mechanical response of poly(methyl methacrylate) (PMMA) and polystyrene (PS) subjected to a shallow indentation made by a 750 µm radius steel ball at 25 °C. The penetration depth was measured as a time-response to a prescribed loading history of the indenter. The tests were performed in the intermediate elastic-plastic regime, which is of paramount importance when dealing with the mechanics of a multicontact interface between rough bodies. The creep characteristics under constant load were analysed with an Eyring law relating the average stress and the strain rate in the deformed volume. The results were compared to data obtained by a standard uniaxial compression test on the bulk material. We have deduced a simple empirical rule which accounts for the heterogeneous stress and strain fields under the indenter and reduces the intricate problem of elastic-plastic indentation creep to an effective scalar rule.

Ultrastructural evidence for the presence of secretory cells in the pineal parenchyma ofHeteropneustes fossilis

There is an extensive literature dealing with the study of indoles, especially serotonin and melatonin, but with considerably less emphasis on the cells and cell types involved in the synthetic process. In the present electron microscopical investigation of the pineal end vesicle ofHeteropneustes fossilis, pinealocytes have been revealed in the pineal parenchyma characterized with extensive synthetic apparatus viz., rough endoplasmic reticulum, free ribosomes, lipid droplets, mitochondria and Golgi bodies. Two sub-populations of the pinealocytes are easily distinguishable on the basis of electron opacity and the preponderance of one or other morphological profile: light cells and dark cells. Light cells represent the active phase of secretion while dark cells represent the storage and release phase of secretion. A neuroendocrine role for the pineal body inHeteropneustes fossilis is suggested which may be significant in view of the nocturnal habit of the fish.

A New Approach to Calculation of Contact Characteristics

A new method of calculation of contact characteristics for rough surfaces is proposed based on integral relations that express the normal contact stress as an explicit function of the surface shape. To produce calculations by this method, a region having a simple shape should be chosen first, where the contact is supposed to be nominally complete. An iterative procedure with regard to the shape is applied within the load-free surface portion, and allows the normal stresses, surface displacement and the real area of contact to be determined. The method is applicable to rough bodies of arbitrary shape for which the half-space formulation and equivalent roughness concepts apply; the real contact area should lie within the initially chosen contact region and can include a system of unconnected contact spots. Both 2D and 3D cases are considered in the present work. The 2D analysis is based on known integral relations for nonperiodic and periodic contact problems. In the 3D case, new analytical relations are obtained and their properties are analyzed. An iteration algorithm based on these relations and its efficient numerical implementation are described. Application of the method to the contact of real rough surfaces is discussed.

An internal variable theory of adhesion

A model describing the flat contact with adhesion between rough solid bodies has been set up, in which the set of asperities is described as a third thin body. Due to the local compressive stresses, the cavities close up during compressive loading, leading to increased adhesion in the contact area. An internal variable model describing the evolution of the intensity of adhesion in the contact between the two solids is set up, based on the thermodynamics of irreversible processes. From a perturbation method, a material surface model for the third body is derived. The Hertz theory of the plane contact between solid elastic bodies is then modified in order to account for the increased adhesion when both solids are pressed together. The specific problem of the compression of a rubber hemisphere on a glass plate is analysed. In that situation, the analytical model predicts in a satisfactory way the true area of contact vs. the compressive force. In the second part of the paper, the model is extended to describe the time dependence of adhesion. Predictions of the evolution of the physical area of contact vs. time are demonstrated, in cases of both conformal and non-conformal contact conditions. The relevance of the model is further discussed.

Simulation of Rough, Elastic Contacts

Frictionless rough contact problems have been studied in great detail by J. A. Greenwood and his co-workers. The only thing that actually seems missing is a simulated figure of the real contact between two rough bodies. Such a figure will be provided. Frictional rough elastic contact, on the other hand, seems to be terra incognita, and we intend to explore it. We will use two-dimensional rough bodies, because then we can simulate many asperities, and also because three-dimensional does not differ very much from two-dimensional in frictional contact, while finally the figures resulting from two-dimensional are clearer and more transparent as well as more realistic. On the other hand, two-dimensional calculations yield only qualitative results; for quantitative results one needs three-dimensional computations.

Fine Structure of the Putative Pheromone-Sensitive Sensilla on the Antennae of Andraca bipunctata (Lepidoptera: Bombycidae)

The antennae of Andraca bipunctata Walker are sexually dimorphic; those of males are bipectinate with 43 pairs of branches, and those of females are filiform without branches. In both sexes, most sensilla are on the frontal (windward, ventral) side, but the types of sensilla differ in the 2 sexes. The main type in males is sensillum trichodeum (s. trichodeum), and in females are s. basiconicum and the short s. chaeticum. Each putative pheromone-sensitive sensillum, trichodeum, is innervated by 2 bipolar neurons containing many mitochondria, multivesicular bodies, rough endoplasmic reticulum, microtubles, and lamellar bodies. The dendrite is subdivided into inner and outer dendritic segments between the ciliary region, which is characterized by proximal and distal bodies. The outer dendritic segment, which contains microtubules, penetrates the cuticular canal and extends into the hair shaft. Outside the neurons, thecogen, trichogen, and tormogen cells surround the neural bodies, forming the inner, intermediate, and outer sheath below the hair shaft. This s. trichodeum has multipores and each pore has 2-3 pore tubules within the pore canal. These pore tubules extend into the hair lumen and probably help the pheromone molecules contact the dendritic membrane receptor, because most pheromones are water insoluble.

Basic principles of rough surface contact analysis using numerical methods

A detailed account of the principles involved in using numerical elastic contact techniques on digitized measurements from rough surfaces is presented in relation to two- and three-dimensional topography data. The main results of such analyses are shown to include the detailed interface geometry and the subsequent contact pressure distribution involved. Methods of defining the resulting sub-surface stresses created by this contact pressure distribution are also presented for static normal loading, and for the case of a normal load in the presence of a frictional surface shear. The problems posed in dealing with plastic asperity contacts are also discussed, together with an outline of how the numerical methods described have been modified further to allow analysis of rough layered bodies of dissimilar materials, thus offering a very useful design tool for surface coatings.

The effect of surface roughness on the temperature at the contact between sliding bodies

Although a great deal of work has been carried out in recent years on the temperature rise at the contact between rough rubbing bodies due to its significance in the friction and wear behaviour of sliding bodies, a clear correlation between the contact temperature rise and the surface topographic parameters is lacking. The paper describes experiments to measure these temperatures using an infrared thermal imaging technique with a systematic variation in surface roughness. The surface temperature is seen to increase monotonically with roughness. The existence of two levels of contact temperature rise, as reported by other authors, is also observed in the thermal images. A theoretical analysis of surface temperatures on multi-asperity consideration has also been presented. It is found that two newly-defined non-dimensional parameters, termed elastic and plastic load indices, in terms of applied load and roughness parameters, describe the extent of roughness effect on the contact temperatures. For different speed and deformation conditions there exist critical values of these indices at which the surface roughness effects become insignificant. A good correlation between the theoretical proposition and experimental result was observed.

Elastic contact between a cylindrical surface and a flat surface — A non-Hertzian model of multi-asperity contact

Contact between curved rough bodies is an important engineering problem. The paper addresses the problem in its simplest form where a smooth rigid cylinder presses down an elastic half space bounded by a plane of uniformly spaced cylindrical asperities. Keeping the separation between the bodies unchanged the problem is inverted and solved using the method of complex variables. As the asperities deform as well as move as rigid bodies, contact lengths and positions develop non-symmetrically with respect to the initial axes of symmetry of the asperities. The resulting local contact pressures are non-Hertzian and the normal load for a given contact area is greater than that estimated using a priori Hertzian pressure profiles.