Concave Pit Research Articles

Research on Friction Performance of Friction Stir Welding Tools Based on Non-Smooth Structure.

In this study, based on the principles of bionics, we fabricated a bionic non-smooth concave pit structure on the shoulders of friction stir welding tools and detected the thermal cycling curve, downforce, and torque of the tool in the welding process. We tested the wear loss weight and analyzed the surface morphology of the shoulder surfaces after welding for 200 m. This study found that as the distance between the concave pits decreased and the number of concave pits increased, the maximum downforce, torque, and temperature in the welding process showed a decreasing trend. As the speed increased, no matter how the tool structure changed, the downforce and torque decreased, while the peak thermal cycle temperature increased. The experimental welding results show that the wear loss weight of the non-smooth structure tool significantly reduced. The lowest wear loss weight of the tool with a concave pit interval of 1.125 mm was only 0.1529 g, which is 27% lower than that of the conventional tool. Our observations of the surface morphology of the tool shoulder after welding showed that the amount of aluminum swarf on the tool shoulder of the welding tool gradually declined with the increasing density of the uneven pits. The lowest number of aluminum chips adhered to a welding tool with a pit distance of 1.125 mm. Therefore, friction stir welding tools with biomimetic structures have better wear resistance and adhesion resistance.

The cranial apparatus glands of the canthariphilous Pyrochroa coccinea (Coleoptera: Pyrochroidae: Pyrochroinae), and their implications in sexual behaviour

Some Pyrochroidae species are known as “canthariphilous” for their attraction to cantharidin (CTD), a toxic terpene with anti-predatory effects, produced in nature by only two beetle families (Meloidae and Oedemeridae). It has been demonstrated that males of Neopyrochroa flabellata ingesting CTD are positively selected by females. Indeed, the compound is re-emitted from a glandular cranial apparatus as secretions that are licked up by females during courtship behaviour, inducing copulation. Herein, we provide the first description of the glands associated to the cranial apparatus of male Pyrochroinae using the European species Pyrochroa coccinea as a model. Morphological analyses show that the cranial apparatus consists of a concave pit lined with short setae retaining secretions emitted through numerous glandular pores. Ultrastructural investigations reveal the presence of two different class 3 glands (Gl.A and Gl.B), intermixed at the level of the pit but exhibiting distinct features. Gl.A are mainly characterised by short conducting canals, rounded nuclei and electrondense vesicles while Gl.B are characterised by long conducting canals, irregular nuclei, vesicles containing a particulate substance and a multifolded plasma membrane. Observations of sexual behaviour are also reported for P. coccinea and compared to N. flabellata, confirming the involvement of cranial apparatus secretions in courtship behaviour.

Immunohistological Study of Monkey Foveal Retina

The fovea centralis, an anatomically concave pit located at the center of the macula, is avascular, hypoxic, and characteristic of stem-cell niches of other tissues. We hypothesized that in the fovea, undifferentiated retinal-stem-cell-like cells may exist, and that neurogenesis may occur. Hence, we performed an immunohistological study using cynomolgus monkey retinas. After preparing frozen tissue sections of the retina including the foveal pit, immunostaining was performed for glial fibrillary acidic protein (GFAP), nestin, vimentin, neuron-specific class III β-tubulin (Tuj-1), arrestin 4, neurofilament, CD117, CD44, Ki67, and cellular retinaldehyde-binding protein (CRALBP), followed by fluorescence and/or confocal microscopy examinations. Immunostaining of the tissue sections enabled clear observation of strongly GFAP-positive cells that corresponded to the inner-half layer of the foveolar Müller cell cone. The surface layer of the foveal slope was partially costained with GFAP and vimentin. Tuj-1-positive cells were observed in the innermost layer of the foveolar retina, which spanned to the surrounding ganglion cell layer. Moreover, colocalization of Tuj-1 and GFAP was observed at the foveal pit. The coexpression of CD117 and CD44 was found in the interphotoreceptor matrix of the fovea. The foveolar cone stained positive for both nestin and arrestin 4, however, the photoreceptor layer outside of the foveola displayed weak staining for nestin. Colocalization of nestin and vimentin was observed in the inner half of the Henle layer, while colocalization of nestin and neurofilament was observed in the outer half, predominantly. Scattered Ki67-positive cells were observed in the cellular processes of the outer plexiform layer and the ganglion cell layer around the foveola. Immunostaining for CRALBP was negative in most parts of the GFAP-positive area. The Müller cell cone was divided into GFAP-strongly positive cells, presumably astrocytes, in the inner layer and nestin-positive/GFAP-weakly positive radial glia-like cells in the outer layer. These findings indicated that groups of such undifferentiated cells in the foveola might be involved in maintaining morphology and regeneration.

Research on the Blow-Off Impulse Effect of a Composite Reinforced Panel Subjected to Lightning Strike

The blow-off impulse effect of a composite reinforced panel subjected to lightning strike is studied combing electric-thermal coupling with explicit dynamic methods. A finite element model of a composite reinforced panel is established under the action of 2.6/10.5 µs impulse current waveform with current peak 60 kA. Blow-off impulse elements are selected according to numerical results of electric-thermal coupling analysis. Elements failure, pressure, and von Mises stress distribution are discussed when blow-off impulse analysis is completed. The results show that the blow-off impulse effect can alter the damage forms of a composite reinforced panel and causes the damage distribution to deviate from the initial fiber direction in each layer. Elements failure modes around the blow-off impulse area are similar to that around the attachment area of the lightning strike. The blow-off impulse effect can well model the internal damage, concave pit, and bulge phenomenon around the attachment area. Additionally, pressure contours are not presented as an anisotropic characteristic but an isotropic characteristic under the blow-off impulse effect, which indicates that the mechanical behavior of composite materials presents as an anisotropic characteristic in low pressure while as an isotropic characteristic in high pressure. This method is suitable to evaluate shock damage of a composite reinforced panel induced by lightning strike.

Effects of spine damage and microhabitat on resource allocation of the purple sea urchin Strongylocentrotus purpuratus (Stimpson 1857)

Though phenotypically plastic responses in echinoids are well studied, the majority of the literature examines the effect of altered diet. Some species, however, such as the purple sea urchin, Strongylocentrotus purpuratus, occur over a large geographic range and thus experience a variety of substrate types and wave forces. To determine whether these factors impact resource allocation in adult intertidal S. purpuratus, a laboratory experiment was conducted using two types of microhabitat based on extremes inhabited by sea urchins in the field (flat substratum vs. concave pit), and two levels of spine damage to simulate wave exposure (monthly clipping vs. control). A suite of measurements were taken to determine the effects of these two treatments including feeding and movement behavior, test morphometrics, demipyramid (jaw) allometry, spine growth cycles, and mass and stereological counts of gonad sections. When given the opportunity, sea urchins remained in their pits for the duration of the experiment, which limited their ability to feed. This behavioral response caused a decrease in weight and volumetric growth, and an increase in jaw growth relative to test growth. Sea urchins in pits also grew more spheroid in shape (increased height:diameter ratio), while those on flat substrates decreased in height:diameter ratio. Further, both males and females in pits showed altered gametogenesis. While spine damage did not affect test growth, sea urchins with clipped spines showed decreased gonad index and altered production of mature oocytes. Altogether, these results are congruent with the life history strategy of long living species like S. purpuratus, in that it spreads reproductive efforts over multiple seasons, while diverting resources toward repairing damage, acquiring suitable refuge, and maximizing attachment area. Therefore, microhabitat and spine damage, by impacting movement, feeding, growth, and reproductive output, likely have important indirect impacts on the intertidal community by way of altered sea urchin grazing rates and susceptibility and value to predators.

Numerical simulation of stress field for laser thermal loading on piston

To investigate the laser thermal loading on diesel engine piston, the employed Gaussian laser beam was transformed into concentric multi-circular patterns of specific intensity distributions with the aid of diffractive optical elements (DOEs), the time duration of laser thermal loading was controlled by computer with air cooling on the top surface of piston, and water cooling of oil tunnel and bottom surface of piston. Numerical simulation model of stress field of laser thermal action was established with the consideration of experimental conditions and the temperature dependent of thermal physical properties of the piston materials. Results show that the stress fluctuation rate at the concave pit site of top surface of piston is larger than that of laser irradiated region due to concave pit region near oil tunnel. Meanwhile, the regions of concave pit, oil tunnel and inner chamber near the top surface of piston are most vulnerable sites to form thermal cracks due to their direct contact with the cooling medium. Results of experimental and numerical simulation have good agreement, which validates the numerical simulation mode.

The significance of pit shape for hydraulic isolation of embolized conduits of vascular plants during novel refilling.

During plant water transport, the water in the conducting tissue (xylem) is under tension. The system is then in a metastable state and prone to bubble development and subsequent embolism blocking further water transport. It has recently been demonstrated, that embolism can be repaired under tension (= novel refilling). A model (Pit Valve Mechanism = PVM) has also been suggested which is based on the development of a special meniscus in the pores (pits) between adjacent conduits. This meniscus is expected to be able to isolate embolized conduits from neighbouring conduits during embolism repair. In this contribution the stability of this isolating meniscus against perturbations is considered which inevitably occur in natural environments. It can be shown that pit shape affects the stability of PVM fundamentally in the case of perturbation. The results show that a concave pit shape significantly supports the stability of PVM. Concave pit shape should thus be of selective value for species practicing novel refilling.

Avicularia-like structures in a Paleozoic fenestrate bryozoan

Structures that mimic the general shape of cheilostome avicularia occur within the Paleozoic fenestrate bryozoan genusFenestrapora.These structures, here termedaviculomorphs, are isolated within laminar extrazooidal skeleton and are characterized by an elongate triangular outline that surrounds a shallow, concave pit. The acute tip of the triangular structure was elevated above the general level of the surrounding skeleton, as is the case for many avicularia. The aviculomorphs could not have functioned precisely as do avicularia, but like avicularia they are inferred to have had a thickened cuticular mandible that matched the skeletal base and to have been able to articulate the mandible open and closed along a fulcrum on the short side of the triangular skeletal outline.

Prevalence of the pit and antipit in the genus Glycine

The legume seed coat is the site of sucrose unloading and the metabolism of imported ureides and synthesis of amino acids for the developing embryo. The cell types directly responsible for these functions in the seed coat are not known. We recently described a convex layer of tissue on the inside surface of the soybean (Glycine max L. Merr.) seed coat that was termed “antipit” because it was in direct opposition to the concave pit on the abaxial surface of the cotyledon. Cone cells of the antipit contained numerous hypertrophied Golgi apparatus and laminated rough endoplasmic reticulum common to actively secreting cells. The initial report by Dzikowski (1936) described the morphology of the pit and antipit in G. max and found these structures in only 68 of the 169 seed accessions examined.

Scattering and Induced Current Characteristics of a Beam Wave from Pits on Optical Disk using Boundary Element Method

Numerical calculation of the pit scattering using boundary element method is described. The boundary element method can be applied to scattering of electromagnetic wave from various pit forms under different conditions of the incident wave. Scattered fields and induced currents due to the two-dimensional concave pit and the convex pit are calculated as functions of the depth (height) or width of pit, defocusing length, tracking error, track pitch and incident angle of the beam.

Special secretory cells in the soybean seed coat

The seed coat of soybean (Glycine max L. Merr.) is of physiological interest for synthesis and transport of amino acids and photosynthates during embryo development. A transmission and scanning electron microscopic study to elucidate the structure of the seed coat disclosed a specialized convex area (antipit) appressed to a concave pit in the center of the abaxial surface of the cotyledon. The antipit, which lies on the inner surface of the seed coat at a medial point in the anterior to posterior direction of the seed, contained specialized secretory cells bounded by loose multi-layered cell walls. These cells were rectangular in the developing seed, varied in length, and contributed directly to the convex morphology of the antipit seen on the ventral surface of the seed coat. At maturity these cells assumed the shape of a “cone”, extending from the aleurone layer in a perpendicular array. The aleurone and cone cells contained numerous Golgi apparatus, laminated rough endoplasmic reticulum, secretory vesicles, and amyloplasts. Secretory vesicles arose directly from tubules of fenestrated trans cisternae of the Golgi apparatus. Mitochondria were clustered with the amyloplasts; stacks of lamellar cisternae of rough endoplasmic reticulum were associated with the nucleus and Golgi apparatus. The cellular contents, the interconnections by plasmodesmata, and the close physical association with the cotyledon suggested that the aleurone and cone cells may be involved in symplastic transport of nutrients for use by the developing embryo.