Morphological specializations of the epidermis of an angler catfish Chaca chaca (Siluriformes,Chacidae) in relation to its ecological niche: A scanning electron microscopic investigation

The present work was undertaken with the aim to deduce morphological adaptations in skin of an angler catfish Chaca chaca by means of scanning electron microscopy. The fish is nocturnal, bottom dwelling, sluggish, ambush predator, lives in sand, mud, or soft substrates often buried and camouflaged for protection and to feed. The surface of the epidermis is covered with polygonal epithelial cells, each having surface relief of microridges forming intricate patterns. In between epithelial cells irregularly distributed mucous cell openings, randomly distributed epidermal specialized structures, taste buds, and neuromasts are discernible. The epidermal specialized structures are keratinized. These are either irregularly the rounded elevated plaque like or the cone shaped structures. The superficial keratinized cells could frequently be discernible exfoliated at the surface. At intervals, characteristic epidermal projections could be observed. Surface of these projections at intervals is differentiated into short stumpy protuberances, each bearing a taste bud at its summit. Further, near the basal portion of these epidermal projections, conical, or rounded plaque like epidermal specialized structures are also discernible. The surface sculpture of the skin of Chaca chaca is associated with the structural and functional significance and physiological adaptations of the epidermis with respect to its ecological niche.     

Scanning electron microscope investigation on the process of healing of skin wounds in Cirrhinus mrigala

Present scanning electron microscope study, reports healing of excised skin wounds in Cirrhinus mrigala. Healing process of wounds, inflicted on head skin, using biopsy punch was observed at intervals—0 hour (h), 1, 2, 4, 6, 12 h, 1 day (d) 2 and 4 d. Accumulation of mucus in wound region within 1h after infliction of wound has been considered an immediate measure to provide protection to injured skin from microbial invasion and other external environmental hazards. On infliction of wound, mobilization of epithelial cells at wound edge is associated with disturbance of coaptive relationship of epithelial cells till original coaptive stability is reached. At 6–12 h appearance of epidermal ridge in region of contact of migrating fronts is due to piling up of epithelial cells. This is associated with cessation of migration of epithelial cells and their simultaneous continual arrival in the region. Speedy epithelialization of skin wounds in C. mrigala like in other fishes, compared to that of mammals and other higher vertebrates, is possibly facilitated owing to surrounding wet external environment. Microridges in initial stages of wound healing appear fragmented without particular orientation. Further, epithelial cells in epithelium in wound region and in region adjacent to wound elongate. These changes are associated with the stretching of epithelial cells indicating their streaming and migration, toward wound. Presence of superficial neuromasts, smallest functional units of lateral line system, a hydrodynamic sensory system, has been associated with important functional significance in fish.     

Surface ultrastructure of the gill filaments and the secondary lamellae of the catfish, Rita rita, and the carp, Cirrhinus mrigala

Surface ultrastructures of gill filaments and secondary lamellae of Rita rita and Cirrhinus mrigala, inhabiting different ecological habitat, were investigated to unravel adaptive modifications. R. rita is a sluggish, bottom dwelling carnivorous catfish, which inhabits regions of river with accumulations of dirty water. It retains its viability for long time if taken out of water. C. mrigala is an active bottom dwelling Indian major carp, which lives in relatively clean water and dies shortly after taken out of water. In R. rita, gill septa between gill filaments are reduced. Microridges on epithelial cells covering gill filaments are often continuous and arranged concentrically. Secondary lamellae are extensive. The epithelium appears corrugated, show irregular elevations and shallow depressions, and microridges on epithelial cells appear fragmented. In C. mrigala, in contrast, the gill septa are extensive. Microridges on epithelial cells covering gill filaments are fragmented. Secondary lamellae are less extensive. The epithelium appears smooth and microridges on epithelial cells are relatively inconspicuous. These differences have been considered adaptive modification in relation to habit and ecological niches inhabited by two fish species. Presence of mucous goblet cells on gill filaments is discussed in relation to their functions including precipitation of the sediments and preventing clogging of gill filaments. Infrequent mucous goblet cells in the epithelium of secondary lamellae in two fish species are considered an adaptation, minimizing thickness of the epithelium to reduce barrier between blood and water for favoring gasses exchange with increased efficiency.     

An orientation‐independent DIC microscope allows high resolution imaging of epithelial cell migration and wound healing in a cnidarian model

Epithelial cell dynamics can be difficult to study in intact animals or tissues. Here we use the medusa form of the hydrozoan Clytia hemisphaerica, which is covered with a monolayer of epithelial cells, to test the efficacy of an orientation‐independent differential interference contrast microscope for in vivo imaging of wound healing. Orientation‐independent differential interference contrast provides an unprecedented resolution phase image of epithelial cells closing a wound in a live, nontransgenic animal model. In particular, the orientation‐independent differential interference contrast microscope equipped with a 40x/0.75NA objective lens and using the illumination light with wavelength 546 nm demonstrated a resolution of 460 nm. The repair of individual cells, the adhesion of cells to close a gap, and the concomitant contraction of these cells during closure is clearly visualized.     

The microstructure of buccal cavity and alimentary canal of Siganus rivulatus: Scanning electron microscope study

The microstructure of the oral cavity and alimentary canal of herbivorous fish Siganus rivulatus collected from the Red Sea were investigated by using scanning electron microscope (SEM). The results showed that S. rivulatus has three types of teeth, tri‐cusped, bi‐cusped, and papilliform. A taste bud (Type I) was recorded in the oropharyngeal cavity. Characteristic styles of microridges on the cell's surface inside the buccal cavity were recorded. Also, the distribution of the mucous cells in the lining of the mouth cavity, alimentary canal was observed. Mucosal folds along the distinct parts of alimentary canal, showed characteristic pattern which was complex in the intestinal mucosa. The results concluded that there are characteristic microstructures according to feeding habitat compared with other bony fishes.     

Gustatory ultrastructures of an amphihaline migratory fish hilsa Tenualosa ilisha

This study was conducted with the tongue samples of different life stages of hilsa, that is, adult Marine hilsa, adult Riverine hilsa, and Riverine juvenile hilsa, respectively. Three types of taste buds (Types I, II, and III based on their elevation from the epithelium at different levels) of the tongue, which may be to ensure full utilization of the gustatory ability of the fish were rocorded. Presence of specific taste buds indicate that the fish hilsa dwells in turbid waters with a possible preference toward diatom like planktonic food source. Enhanced expression of taste receptors (T1R1 and T1R3) and associated stimulatory G‐proteins subunits on tongue also indicate occurrence of amino acid like substances that guided sensory cues for feeding by this fish. A firm regularity or stringency of the free surface of the epithelial cells may be attributed to compactly arranged microridges. These structures protect against physical abrasions potentially caused during food manoeuvring and swallowing. In our present observations, the surface architectures of the tongue of hilsa are discussed within the background of migratory adaptation of the species in the context of feeding and habitat preferences.     

Light and transmission electron microscopic structure of skin glands and dermal scales of a caecilian amphibian Gegeneophis ramaswamii,with a note on antimicrobial property of skin gland secretion

Amphibian skin secretions contain a variety of bioactive compounds that are involved in diverse roles such as communication, homeostasis, defence against predators, pathogens, and so on. Especially, the caecilian amphibians possess numerous cutaneous glands that produce the secretory material, which facilitate survival in their harsh subterranean environment. Inspite of the fact that India has a fairly abundant distribution of caecilian amphibians, there has hardly been any study on their skin and its secretion. Herein, we describe, using light microscopy and electron microscopy, two types of dermal glands, mucous and granular, in Gegeneophis ramaswamii. The mucous glands are filled with mucous materials. The mucous‐producing cells are located near the periphery. The granular glands are surrounded by myoepithelial cells. A large number of granules of different sizes are present in the lumen of the granular gland. The granule‐producing cells are present near the myoepithelial lining of the gland. There are small flat disk‐like dermal scales in pockets in the transverse ridges of the posterior region of the body. Each pocket contains 1–4 scales of various sizes. Scanning electron microscopic (SEM) study of the skin surface showed numerous funnel‐shaped glandular openings. The antibacterial activity of the skin secretions was revealed in the test against Escherichia coli, Klebsiella pneumoniae, and Aeromonas hydrophila, all gram‐negative bacteria. SEM analyses confirm the membrane damage in bacterial cells on exposure to skin secretions of G. ramaswamii.     

Surface exchange area of the porcine placenta: morphometry of anisotropic interdigitating microvilli

The pig has a diffuse epitheliochorial placenta. The foeto-maternal surface area (S_V(F), S_V(M)) is enlarged at three levels: level I: macroscopic folds of uterine mucosa covered by foetal membranes; level II: light microscopic folds of uterine epithelium covered by trophoblastic epithelium; level III: ultrastructural formation of both maternal and foetal microvilli in an interdigitating pattern. This study presents a morphometric method, using intersection counting, to estimate the surface area of these interdigitating, highly oriented microvilli at level III, i.e. the ‘true’ surface exchange area. The method is applied to different stages in pregnancy. The epithelial surfaces are enlarged by a factor 8–11 due to the formation of microvilli. This factor varies during pregnancy, being lower early in gestation and before delivery, and for the first time it is shown to be significantly different for mother and foetus. At level III the foetal surface of placenta is larger than the maternal indicating that the two opposing surfaces are not congruent at the ultrastructural level and that membrane-linked placental transport may be different in mother and foetus. A three-compartment model is suggested for placental exchange with maternal, intermicrovillous and foetal compartments.     

Morphological studies on the gills of the European hake (Merluccius merluccius,Linnaeus, 1758)

The current work gives concern to study the morphology of the Merluccius merluccius gills by using gross morphology, scanning electron microscopy (SEM), and light microscopy. The findings of the present study revealed that the gill system consisted of four pairs of gill arches which carry the gill filaments on the convex border and gill rakers on the concave border of them. SEM results revealed that the rakers and the spines distribution on the first gill arch differed from that of the other three gill arches on the lateral and medial surfaces. On the surface the gill filaments, there were longitudinal ridges that carried pores of chloride cells and mucous cells. The histological examination revealed that, the gill arch composed of hyaline cartilage that presented in the form of cups. Each cup consisted of central cartilagenous core and peripheral cartilagenous matrix. The gill filaments composed of cartilaginous bar of peripheral cartilaginous matrix and central cartilaginous core extended from the gill arches and covered by an epithelial layers with a few mucous cells permeate it, and chloride cells were straggly in the interlamellar epithelium. Each gill filament carried several leaves like secondary lamellae on both sides of it. The epithelium, which lined the secondary lamellae, composed of epithelial pavement cells, some mucous cells, and pillar cells.     

Fine structural aspects of secretion and extrinsic innervation in the olfactory mucosa.

The mucus at the surface of the olfactory mucosa constitutes the milieu in which perireceptor events associated with olfactory transduction occur. In this review, the ultrastructure of olfactory mucus and of the secretory cells that synthesize and secrete olfactory mucus in the vertebrate olfactory mucosa is described. Bowman's glands are present in the olfactory mucosa of all vertebrates except fish. They consist of acini, which may contain mucous or serous cells or both, and ducts that traverse the olfactory epithelium to deliver secretions to the epithelial surface. Sustentacular cells are present in the olfactory epithelium of all vertebrates. In fish, amphibia, reptiles, and birds, they are secretory; in mammals, they generally are considered to be "non-secretory," although they may participate in the regulation of the mucous composition through micropinocytotic secretion and uptake. Goblet cells occur in the olfactory epithelium of fish and secrete a mucous product. Secretion from Bowman's glands and vasomotor activity in the olfactory mucosa are regulated by neural elements extrinsic to the primary olfactory neurons. Nerve fibers described in early anatomical studies and characterized by immunohistochemical studies contain a variety of neuroactive peptides and have several targets within the olfactory mucosa. Ultrastructural studies of nerve terminals in the olfactory mucosa have demonstrated the presence of adrenergic, cholinergic and peptidergic input to glands, blood vessels, and melanocytes in the lamina propria and of peptidergic terminals in the olfactory epithelium. The neural origins of the extrinsic nerve fibers and terminals are the trigeminal, terminal, and autonomic systems.     

Ultrastructure of Tracheal Surface Liquid: Low-Temperature Scanning Electron Microscopy

A layer of liquid lines the airways in the lung. Previous microscopic studies have suggested that it is in two phases, with a mucous gel lying above a periciliary sol. However, shrinkage artifacts due to chemical fixation, dehydration, and drying have prevented reliable estimates of the depth of these layers. To avoid such problems, we have studied the surface liquid of bovine trachea by low-temperature scanning electron microscopy (LTSEM). A polished copper probe cooled to liquid nitrogen temperature was applied to the mucosal surface of sheets of excised tracheal epithelium to effect rapid freezing of surface liquid. Tissue sheets were then mounted in an LTSEM (AMRay 1000A with Biochamber) which maintains samples at -180°C with a Joule-Thompson refrigerator built into the stage. Tissues were fractured at right angles to the epithelial surface, coated with gold, and viewed, all at 10^?5 to 10^?6 torr without transfer through air. The sample was stable under the electron beam at accelerating voltages up to 20 kV. Epithelial features (nuclei, cilia, microvilli, mucous granules) were well preserved. The mucosal surface of the cells was covered with material on the order of 8 μm in depth. The mucous gel and periciliary sol could be seen as distinct layers and could be distinguished by the size and pattern of ice crystal voids generated by radiant-etching of the fractured surface of the sample.     

Snow metamorphism as revealed by scanning electron microscopy

Current theories of snow metamorphism indicate that sublimating snow crystals have rounded shapes, while growing crystals have shapes that depend on growth rates. At slow growth rates, crystals are rounded. At moderate rates, they have flat faces with rounded edges. At fast growth rates, crystals have flat faces with sharp edges, and they have hollow faces at very fast growth rates. The main growth/sublimation mechanism is thought to be by the homogeneous nucleation of new layers at or near crystal edges. It was also suggested that the equilibrium shape of snow crystals would be temperature dependent: rounded above -10.5 degrees C, and faceted below. To test these paradigms, we have performed SEM investigations of snow samples having undergone metamorphism under natural conditions, and of snow samples subjected to isothermal metamorphism at -4 degrees and -15 degrees C in the laboratory. In general, current theories predicting crystal shapes as a function of growth rates, and of whether crystals are growing or sublimating, are verified. However, the transition in equilibrium shapes from rounded to faceted at -10.5 degrees C is not observed in our isothermal experiments that reveal a predominance of rounded shapes after more than a month of metamorphism at -4 and -15 degrees C. Some small crystals with flat faces that also have sharp angles at -15 degrees C, are observed in our isothermal experiments. These faces are newly formed, and contradict current theory. Several hypotheses are proposed to explain their occurrence. One is that they are due to sublimation at emerging dislocations.     

COMPUTATIONAL FLUID DYNAMICS （CFD） SIMULATIONS OF DRAG REDUCTION WITH PERIODIC MICRO-STRUCTURED WALL

Computational fluid dynamics（CFD） simulations are adopted to investigate rectangular microchannel flows with various periodic micro-structured wall by introducing velocity slip boundary condition at low Reynolds number. The purpose of the current study is to numerically find out the effects of periodic micro-structured wall on the flow resistance in rectangular microchannel with the different spacings between microridges ranging from 15 to 60 pm. The simulative results indicate that pressure drop with different spacing between microridges increases linearly with flow velocity and decreases monotonically with slip velocity; Pressure drop reduction also increases with the spacing between microridges at the same condition of slip velocity and flow velocity. The results of numerical simulation are compared with theoretical predictions and experimental results in the literatures. It is found that there is qualitative agreement between them.     

Tribological Properties of Water Glass Lubricant for Hot Metalworking

Tribological properties of water glass (sodium silicate aqueous solution) with graphite powders, a lubricant for hot metalworking, were studied by means of pin-on-disk type tribotesting at a wide variety of temperature ranges. The lubricant is a water suspension consisting of water glass with graphite powders at room temperature. It becomes solid or a suspension state consisting of solid or liquid glass with the graphite powders owing to evaporation of the water inside. The frictional behavior of the lubricant over 100°C was strongly affected by the state of the glass, which is a factor of temperature, and was categorized into the following three regions in accordance with the state of the glass: solid film lubrication by the powder glass and the graphite (Region I), fluid film lubrication by the viscous liquid glass (Region II), and fluid film lubrication by the low-viscosity liquid glass and solid film lubrication by the graphite (Region III). The lowest friction coefficient was obtained in Region III.     

Light and scanning electron microscopic features of the tongue in cattle egret

Adult individuals of both sexes were sacrificed by decapitation and their tongues were teared out in order to be investigated. Cattle egret's tongue is distinguished into the apex, body, and root regions. A shallow median sulcus is apparently noticed on the dorsal surface of the tongue's body only. Histologically, the tongue mucosa is covered with a thick parakeratinized epithelium. The dorsal epithelia of the apex and body are densely packed with exfoliated superficial cells. However, the dorsal surface showed microridges observed on the surface epithelial cells. In the body region, the gland's outlets are integrated in glandular patches on the top of keratinized folds at both sides of the median sulcus. The ventral surface of the tongue is devoid of any glandular outlets. The egret's tongue is supported by a paraglossum cartilage wrapped up with a fibrous perichondrium and striated muscle fibers. It extends ventrally as paraglossale apex then flattened in the body giving the corpus paraglossale which bifurcates caudally in the root giving paraglossalis caudalis. The tongue exhibits certain features that are unique as an adaptation to food intake, the type of food, lifestyles and bird's habitat with no any sex‐specific differences. Microsc. Res. Tech. 79:595–603, 2016. © 2016 Wiley Periodicals, Inc.     

Short-Time Dynamics of Frictional Strength in Dry Friction

We present an experimental study of the onset of local frictional motion along a long, spatially extended interface that separates two PMMA blocks in dry frictional contact. At applied shear forces significantly below the static friction threshold, rapid precursory detachment fronts are excited, which propagate at near sound speeds along the interface. These fronts initiate from the interface edge and arrest prior to traversing the entire sample length. Along the fronts’ path, we perform real-time measurements of the real contact area at every spatial point within the interface. In addition, the motion (slip) of the material adjacent to the interface is simultaneously measured at chosen locations. Upon their arrival at each spatial point along their path, these fronts instantaneously (within 4 μs) reduce the net contact area. Net slip is only initiated after this contact area reduction occurs. Slip is initially rapid and progresses at its initial velocity for a constant (60 μs) duration. Slip dynamics then undergo a sharp transition to velocities an order of magnitude slower, which remain nearly constant until slip arrest. We demonstrate that this scenario can be quantitatively explained by a model of interface weakening caused by instantaneous fracture-induced heating. Sustained rapid slip occurs in this weakened phase. Once the interface cools beneath its glass temperature the sharp transition to slow slip takes place. A similar fracture-induced weakening scenario might be expected in additional classes of materials.     

Role of TGFbeta signaling in skin carcinogenesis

The TGFbeta signaling pathway is one of the most important mechanisms in the maintenance of epithelial homeostasis. Alterations leading to either the repression or enhancement of this pathway have been shown to affect cancer development. Although TGFbeta inhibits growth of normal epithelial cells, it is paradoxically overexpressed in many epithelial cancers. It has been postulated that TGFbeta acts as a tumor suppressor at the early stages of carcinogenesis, but overexpression of TGFbeta at late stages of carcinogenesis may be a critical factor for tumor invasion and metastasis. The detailed mechanisms regulating this functional switch of TGFbeta remain to be elucidated. The relevance of the TGFbeta signaling pathway to the development of primary epithelial tumors in man has been further substantiated by the discovery of mutations in TGFbeta receptors and in the downstream signaling mediators, the Smads. The epidermis is one of the major targeting tissues for TGFbeta signaling. Chemical carcinogenesis studies have revealed a paradoxical effect of TGFbeta on skin carcinogenesis: inhibition of papilloma formation but promotion of malignant conversion. In addition, deletion of the TGFbeta type II receptor accelerates skin carcinogenesis. This review focuses on our current understanding of the role of TGFbeta signaling in skin carcinogenesis.     

Creep mechanisms of a new Ni-Co-base disc superalloy at an intermediate temperature

The microstructures of a new Ni-Co-base disc superalloy, TMW-4M3, before and after the creep test at 725 °C/630 MPa have been systematically investigated by transmission electron microscopy (TEM). The crept microstructures were marked as three different deformation stages (I, II and III) corresponding to the gradually increased strain. At stage I, stacking fault (SF) shearing was the main deformation mechanism. The SF was extrinsic and lay on {111} plane. However, deformation microtwinning became the dominant mode at stage II and III. The average spacing of deformation twins decreased from 109 ± 15 nm at stage II to 76 ± 12 nm at stage III, whereas the twin thickness did not change significantly. The influence of stacking fault energy (SFE) of γ matrix on the deformation mechanism is discussed. It is suggested that lower SFE in TMW-4M3 is partly responsible for the enhanced creep resistance.     

On Material Removal Regimes for the Shaping of Glass Edges: Force Analysis,Surface Topography and Damage Mechanisms

Glass shaping, which corresponds to the removal of the edges of a specimen, is the last finishing operation in glass manufacturing. This process has several functions on the final shaped glass including removing sharp edges, improving mechanical resistance, decreasing surface damage and giving it an aesthetical aspect. This article addresses the effects of working parameters, including grinding forces and consumed power, on surface edge finishing and damage mechanism induced during glass grinding. Microscopic observations and multi-scale analysis have also been conducted to investigate the surface edge characteristics. Experimental results show three damage regimes. The first (regime I) is a partial ductile regime with cutting action accompanied by chip formation. The second (regime II) is a crushing (or fragmentation) regime. The last (regime III) is also a partial ductile regime but by ploughing action with displaced material. The shaped surface obtained in the regime II has a better roughness than that obtained in regime I and III. However, regimes I and III include streaks and form defects which are not present in regime II. Similar to metallic materials, the evolution of force components show a linear relationship between normal and tangential forces. This implicates a constant average contact pressure and friction coefficient (μ) between the flat grains and the workpiece.     

Improved active contour modelling for isolating different hues in infrared thermograms

Thermograms are widely used in industries and medicine for quality assessment and diagnostics. Thermogram analysis involves isolating desirable Regions of Interest (RoIs) and characterizing them in terms of physical parameters. Conventionally, image segmentation techniques are developed to extract a specific Region of Interest. However, an efficient algorithm that could segment any desired Region of Interest is yet to be developed. In this study, an efficient color image segmentation technique for isolating RoIs (in infrared thermograms) is developed by using Improved Active Contour Modeling (I-ACM). Two different techniques namely thresholding and region growing, have been used for mask selection in order to increase the segmentation ability of the algorithm. The performance of the proposed techniques is measured in terms of error and computational complexity. A user friendly GUI has been also developed for computer-aided analysis.