Circular Pits Research Articles

Equisetum Xylem: SEM Studies and their Implications

Abstract Scanning electron microscope (SEM) studies of xylem of three species of Equisetum reveal numerous details not previously reported on the basis of light microscopy. SEM images of thick (ca. 1 mm) sections reveal pit shapes, cell contexts, and microstructure of pit membranes. Pit shapes are remarkably diverse in comparison to those of ferns or conifers. Nodal tracheary elements are isodiametric to fusiform in shape, and have crowded circular (mostly) to elongate prominently bordered pits and uniformly thick secondary walls. Internodal tracheary elements, by contrast, have relatively large circular pits with inconspicuous borders. Secondary walls of internodal tracheids are thin, with thickenings that are annular, looplike, or of some intermediate form. Metaxylem internodal tracheary elements line the inner surface of carinal canals ( = proxylem lacunae), and many of the large circular (often crateriform) pits facing the canals may lack pit membranes, especially in E. giganteum and E. myriochaetum....

Birch Carbonization Surface Micrograph and Element Analyses

There are close relationships between the surface micrograph and element contents of birch and its heating-up temperature. By using the scanning electron microscope (SEM) and the X-ray energy dispersive spectrometer (EDS), the surface micrograph and element contents of birch carbonizations prepared in the simulating fires with different heating-up temperatures were observed and compared. The results show that as the heating-up temperature rises, the surfaces of tracheids gradually become smoother, and the cross sections of tracheids change from circular or ovate shape to polygon. The external films of tracheid fibers are damaged and bordered pits are exposed gradually with the increasing of heating-up temperature. At high temperature, bordered pits change from flat eye-like pores to circular pits, at the same time, the carbon content increases from 52.46% to 90.96%, and the oxygen content decreases from 47.34% to 8.31%, while the potassium and calcium content increase. Thus, the study of connecting wood surface micrographs and element contents with heating-up temperature is useful in fire trace and evidence identification, and the result is meaningful to fire investigation.

Tensile fracture and thermal conductivity characterization of toughened epoxy/CNT nanocomposites

Rubber toughened epoxy/CNT nanocomposites were manufactured at different weight percents between 0 and 1% of multiwall carbon nanotube (MWNT) using a high intensity ultrasonic liquid processor with a titanium probe. Mechanical properties of manufactured dog bone samples were measured in tension and the results indicated a maximum of 23% increase in the elastic modulus at 0.6% by weight of MWNT. However, the fracture strength showed a maximum decrease of about 11% as a function of increasing MWNT loading. Scanning Electron Microscopy (SEM) images from the neat samples revealed a distinct circular pit at the top left edge of the specimen with an overall tearing deformation causing the fracture paths. Comparatively, all nanocomposite samples on an average seemed to show a prominent brittle fracture with little or no evidence of circular pit formation. The amount of tearing deformation seemed to be enhanced in the nanocomposite specimens as compare to the neat ones. Finally, Transmission Electron Microscopy images indicated that different states of dispersion exist in all of the nanocomposite samples. The data showed that agglomeration of nanotubes increases as a function of weight percent. In addition to mechanical property characterization, thermal conductivity of all the samples was determined as a function of temperature between 30°C and 100°C using the 3ω method. The tested samples showed an almost 16% increase in thermal conductivity. The minimal enhancement in thermal conductivity has been analyzed from the standpoint of the Effective Medium Theory. Interfacial thermal resistances exhibit no order of magnitude changes explaining the conductivity results.

Ordered Arrays of SiGe Islands from Low-Energy PECVD

SiGe islands have been proposed for applications in the fields of microelectronics, optoelectronics and thermoelectrics. Although most of the works in literature are based on MBE, one of the possible advantages of low-energy plasma-enhanced chemical vapor deposition (LEPECVD) is a wider range of deposition rates, which in turn results in the possibility of growing islands with a high Ge concentration. We will show that LEPECVD can be effectively used for the controlled growth of ordered arrays of SiGe islands. In order to control the nucleation of the islands, patterned Si (001) substrates were obtained by e-beam lithography (EBL) and dry etching. We realized periodic circular pits with diameters ranging from 80 to 300 nm and depths from 65 to 75 nm. Subsequently, thin films (0.8–3.2 nm) of pure Ge were deposited by LEPECVD, resulting in regular and uniform arrays of Ge-rich islands. LEPECVD allowed the use of a wide range of growth rates (0.01–0.1 nm s−1) and substrates temperatures (600–750°C), so that the Ge content of the islands could be varied. Island morphology was characterized by AFM, while μ-Raman was used to analyze the Ge content inside the islands and the composition differences between islands on patterned and unpatterned areas of the substrate.

The same etchant produces both near-atomically flat and microfaceted Si(100) surfaces: The effects of gas evolution on etch morphology

The effects of H2 gas evolution during the etching of silicon surfaces by aqueous ammonium fluoride (NH4F) solutions were investigated by scanning tunneling microscopy, atomic force microscopy, optical microscopy, and noncontact profilometry. If H2 bubbles, a reaction product, were removed from the etching surface or if their coalescence was suppressed, near-atomically flat surfaces were produced. Otherwise, the etched surface developed significant roughening on many length scales with several characteristic morphological features, including nested, nearly-concentric circular etch pillars, circular etch pits, and faceted micropits. Mechanisms for the production of all three types of features are proposed. Chemical and physical means of suppressing bubble-induced surface roughening are presented. These results explain the conventional wisdom that aqueous fluoride etchants roughen Si(100) surfaces, in part by promoting the formation of Si{111} microfacets. Although some conditions promote the formation of a high density of {111}-faceted micropits (areal densities of 30%–50% were observed), microfacet formation is not inherent to the atomic-scale reactions. Instead, the microfacets are a direct result of gas evolution during the etching reaction.

Les inhumations et les dépôts d’animaux en fosses circulaires du Néolithique récent du sud de la plaine du Rhin supérieur

This article presents a synthetic analysis of the human and animal burials in circular pits attributed to the late Neolithic of the southern plain of the Upper Rhine. It is based on new, often unpublished, data resulting from preventive excavations. The large regional corpus allows us to reveal several recurrent traits that permit the study of a complex system with the coexistence of regular, simple inhumations, simultaneous burials associating individuals in a regular position and bodies in disorderly positions, successive burials and secondary burials. The discovery of human bodies and animal carcasses, which were the object of post-decompositional manipulations, allows us to reconstruct a complex act that could be similar to that observed in numerous enclosure wall trenches. We also address the question of the possible existence of human burials realized outside of the funerary context, based on the association of a non prepared body and a deposit of copper objects. A confrontation of the model with data from other regions, notably the Rhone Valley and Germany, allow us to insist on the coherence of the phenomenon of burials in circular pits from one extremity to the other of its zone of distribution.

Surface damages of zirconia by Nd:YAG dental laser irradiation

The purpose of this study was to characterize the surface damages of zirconia by Nd:YAG dental laser irradiation through a systematic evaluation of the associated microstructural changes. Disk specimens of yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) and ceria-stabilized zirconia/alumina nanocomposite (Ce-TZP/Al₂O₃ nanocomposite) were irradiated by Nd:YAG dental laser. The specimens were characterized using scanning electron microscopy, X-ray diffractometry, and wavelength dispersive X-ray spectroscopy. Every single irradiated spot was indicated by a circular black pit surrounded by a circular raised rim with a sunken depression at the center. On surface changes, many cracks were formed inside each irradiated pit. On changes in elemental composition, the concentration of oxygen decreased while that of zirconium increased. After heating in air, the assembly of circular black pits turned white, although the depression and raised rim remained. This study showed that Nd:YAG dental laser irradiation induced cracking and reduced oxygen content on the surface of zirconia. Consequently, these phenomena reduced the mechanical strength of zirconia. Therefore, Nd:YAG dental laser welding should not be performed on tetragonal zirconia.

Computational Modeling of Bounding Conditions for Pit Size on Stainless Steel in Atmospheric Environments

This paper presents analytic expressions for calculating bounding conditions for pitting under atmospheric conditions. These expressions allow the prediction of the maximum pit size that can develop under known atmospheric conditions by considering the factors that can control the inherent galvanic coupling between a circular pit under a thin electrolyte layer surrounded by a concentric cathodic area. Expressions are developed for the maximum cathodic current and the minimum anodic current required for pit stability. An analytic expression for the maximum cathodic current that the surrounding area can supply to the pit is developed and validated by comparison to calculations using the finite element method. The effects of the controlling environmental parameters (deposition density and relative humidity) on the cathode bounding parameters are explored, as is the effect of the size of the pit. The analytical expression for the maximum cathodic current is then coupled to the Galvele pit stability product to estimate the maximum pit size that could develop for a given set of environmental conditions. Those results are then compared to data available in the literature from outdoor exposures of stainless steels for up to 26 years.

Microbial Dissolution of Hematite and Associated Cellular Fossilization by Reduced Iron Phases: A Study of Ancient Microbe-Mineral Surface Interactions

We report here on magnetite- and wustite-encrusted and geometrically oriented microbial-like structures (MLS) attached to the surfaces of hematite (alpha-Fe(2)O(3)) crystals in a banded iron formation. Field emission scanning electron microscope (FE-SEM) and scanning electron microscope (SEM) imaging showed a 3-D network of MLS arranged in 1 microm x approximately 20 microm coccoidal-like chains (CLC) of various geometrical shapes: dichotomous and budding-like protrusions, parallel, intersecting, triangular, or sinusoidal. Individual spheroidal forms ( approximately 1 mum in diameter), some displaying what appears to be division, were also abundant. In addition to their size, morphology, and preferred orientations, a microbial origin of these chains and single spheroidal forms is inferred by the presence of material that resembles extracellular polymeric substances (EPS) extending from the base of the chains along the mineral surface: the attachment sites show circular dissolution pits of about 100 nm diameter. Other thin structures protruding from the CLC are reminiscent of bacterial "nanowires." We were, however, unable to find any extant cells, organic carbon, or even recover DNA from the MLS, which suggests that they, if microbial, are possibly mineralogically replaced casts or mineral encrustations of cells. It is further speculated that, given the nature of the substrate upon which the forms are attached and their preferential orientations, it seems plausible that the "original cells" may have been Fe(III)-reducing bacteria that exploited structural imperfections in the crystal lattice. Importantly, the preservation of the ancient microbial shapes in mineral casts of magnetite, wustite, or both may be an overlooked means by which cellular features in the rock record are retained.

A synopsis of the Hydrometra (Hemiptera, Heteroptera, Hydrometridae) from the Amazon River floodplain, Brazil, with redescription of Hydrometra argentina Berg

Hydrometra argentina Berg, 1879, H. caraiba Guérin-Méneville, 1857 and H. guianana Hungerford & Evans, 1934 are newly recorded in the Amazon River floodplain, Brazil. A redescription of H. argentina is also given, as the original description is incomplete. A key to the three known species occurring in this region is provided. Hydrometra argentina can be distinguished from H. caraiba and H. guianana by the body length smaller than 12.50 mm, anteoculus/postoculus ratio between 1.80 and 2.00, clypeus narrow and conical, metacetabulum with no circular pits, and projections on male abdominal sternite VI in the shape of simple spines. The other species can be distinguished mainly by the anteoculus/postoculus ratio and position of projections on male abdominal sternite VI.

Multiscale physical characterization of an outdoor-exposed polymeric coating system

Surface topography and gloss are two related properties affecting the appearance of a polymeric coating system. Upon exposure to ultraviolet (UV) radiation, the surface topography of a coating becomes more pronounced and, correspondingly, its gloss generally decreases. However, the surface factors affecting gloss and appearance are difficult to ascertain. In this article, atomic force microscopy (AFM) and laser scanning confocal microscopy (LSCM) measurements have been performed on an amine-cured epoxy coating system exposed to outdoor environments in Gaithersburg, Maryland. The formation of the protuberances is observed at the early degradation stages, followed by the appearance of circular pits as exposure continues. At long exposure times, the circular features enlarge and deepen, resulting in a rough surface topography and crack formation. Fourier Transform Infrared Spectroscopy (FTIR) study indicates that the oxidation and chain scission reactions are likely the origins of the surface morphological changes. The relationship between changes in surface roughness and gloss has been analyzed. The root mean square (RMS) roughness of the coating is related to nanoscale and microscale morphological changes in the surface of the coating as well as to the gloss retention. A near-linear dependence of RMS roughness with the measurement length scale (L) is found on a double logarithmic scale, i.e., RMS ∼ Lf. The scaling factor, f, decreases with exposure time. The relationship between surface topography, on nano- to microscales, and the macroscale optical properties such as gloss retention is discussed. Moreover, a recent development in using an angle-resolved light scattering technique for the measurement of the specular and off-specular reflectance of the UV-exposed specimens is also demonstrated, and the optical scattering data are compared to the gloss and the roughness results.

The effect of growth temperature on the luminescence and structural properties of GaN:Tm films grown by gas-source MBE

During molecular beam epitaxy of GaN:Tm films, substrate temperature strongly influences the rare earth incorporation, surface morphology and luminescence spectrum. The Tm incorporation into films grown between 730 and 830 °C was estimated by wavelength-dispersive X-ray (WDX) spectroscopy. Comparative WDX, atomic force microscopy (AFM) and cathodoluminescence (CL) mappings reveal that at an optimal growth temperature between 775 and 780 °C, a high Tm content (∼2.2 at%) and a smooth surface morphology can be obtained, leading to an intense sharp Tm 3+ emission. For lower substrate temperatures, Ga droplets and large (∼8–15 μm) circular pits mar the sample surface; for higher temperatures, the sharp CL lines disappear due to low Tm content (⩽0.8 at%).

Wind Scour of Navajo Sandstone at the Wave (Central Colorado Plateau, U.S.A.)

At the Wave, a photogenic landform on the Utah–Arizona border, modern, southwesterly, sand-carrying winds abrade the Navajo Sandstone. Abundant trains of centimeter-scale, transverse, upwind-facing treads and risers cut sedimentary structures at a high angle. Central to the formation of these erosional steps are crusts produced by microbes lying just beneath exposed sandstone surfaces. Treads and risers are present on the walls of smoothly curved troughs at the Wave, on the walls of nearby circular scour pits, and on bedrock domes found at the center of scour pits. Because of their locations and orientations, the large-scale troughs and scour pits could not have been formed by flowing water or groundwater sapping; treads and risers indicate sculpting by the wind.

Stability Analysis of Local Thinned Shallow Spherical Roof of Oil Storage Tank

The analytical evaluation and finite element methods are used to analyze the critical stability of the shallow spherical roof of oil storage tank with an axial symmetrical corrosion region. At first, the nonlinear finite element method is adopted to calculate the global critical load of the storage tank roof, and the local corrosion region is equivalent to a circular corrosion pit with uniform depth. The results show that the tank wall and inner pressure of the stored oil have slight effects on the stability of the roof. To build the formula of local critical load of the tank roof, the circular corrosion pit is separated from the whole roof and treated as a shallow spherical shell which is elastically supported on the rest part of the roof. The equivalent support stiffness is obtained by the deformation compatibility at the edge of the corrosion pit. The resulted nonlinear stability equation is solved with a modified iteration method to determine the local critical load. The local critical load for an in-service corroded oil tank roof is analyzed by the proposed approach and the results are compared with those calculated by the conventional nonlinear finite element method with good agreement and the geometrical parameter of the corrosion region corresponding to the minimal critical load is 9.5.

Investigation on surface damage phenomena induced by flashover across semiconductor

The flashover across semiconducting materials disables many high power semiconductor devices from their further application under high electric field. Up to now, the physical mechanism of the flashover was still not understood clearly. Surface flashover experiments of silicon and gallium arsenide were performed under pulsed high voltage. The filament current channels on their surface were observed in the infrared photographs, and the infrared radiation bright spot was found in the central region between the electrodes. On the surface of different samples undergone flashover events for several times, the filament damage phenomena were observed, and for the n100 silicon sample, some circular pits were found around the filament channel, with a conical jut in the center of each pit. According to the damage phenomena at the edge of electrodes, the thermal injection and relaxation characteristics of majority carriers were discussed. An injection model induced by minority carriers was proposed, which emphasizes the surface field enhancement by non-equilibrium carrier channel, which possibly leads to the ionization of the ambient gas above the filament channel. The model was consistent with the observed experimental results.

Pourquoi mourir ensemble ? À propos des tombes multiples dans le Néolithique français

burials from the French Neolithic, we propose in this paper to formulate these issues in a different way and to draw some conclusions which differ partly from those of these two authors. First of all, multiple burials considered individually cannot be considered as commonplace structures ; we have good reason to think that people buried in a same space have at least some relationship in death. In that sense they reflect either a particular social phenomenon, when one death has caused the others, or some particular event when the deaths have the same cause. There is no need however in these cases systematically to evoke bloody stories. For if the first case corresponds to “ accompanying death”, the second can be explained by small or large-scale mortality crises, probably more often epidemics and famines, and seldom collective accidents. Considered as a whole, assemblages containing multiple burials can be classified in two categories according to the probability of the appearance of their configuration. In the first, the coincidences noted concerning the deaths are made possible by chance. Part of the cemeteries belonging to this category may be commonplace communal ones where particular events sometimes led to burying two persons together. Another part, i. e. the very small assemblages, is difficult to interpret but could evoke a relegation linked to the circumstances of death. The second category groups assemblages for which chance alone is unlikely. Their study leads to dividing them into two groups : one with burials that can be perfectly interpreted in terms of “ accompanying death”, and the other corresponding to burials that could result from mortality crises. “ Accompanying death” can explain some of the multiple burials and is certain in the funerary region of circular burial pits. Its presence in the cists of the Chamblandes type is also highly probable. On the other hand, it remains undetected in mound graves, the crucial problem being to ascertain whether it is really absent or whether it is merely unrecognised, and inciting us to re-examine the case of some corridor graves. Neolithic multiple burials are finally far from being just a curiosity and their precise analysis is a challenge for the coming years. They already give rise to important palaeo-sociological interpretations, but paradoxically they could well lead to reviewing the approach of some aspects of the collective phenomenon.

Substrate Wetting and Topographically Induced Ordering of Amorphous PI‐b‐PFS Block‐Copolymer Domains

The substrate wetting of an amorphous, low-glass-transition-temperature spherical poly(isoprene-block-ferrocenylsilane) (PI-b-PFS) block copolymer and the alignment of the microdomains in grooves of various geometry are studied. Compositional analysis by time-of-flight secondary ion mass spectrometry depth profiling (TOF-SIMS) indicates the presence of both PI and PFS directly at the film-substrate interface on silicon and silica substrates. The TOF-SIMS depth-profiling study indicates a transition in the packing of the domains between the two-dimensional (2D) monolayer and 3D, thicker layers. In a monolayer of domains, a hexagonal packing is adopted. In films of two or three layers, the hexagonal packing reorganizes towards a body-centered cubic (bcc) packing by the extension of the copolymer chains in the direction normal to the substrate, as indicated by an increase in spacing between PFS layers and an increase in domain size. For thicker layers, a bcc morphology with the (110) plane parallel to the substrate is found to extend from the free surface downwards. Films of one monolayer of domains of the copolymer exhibit long-range lateral ordering on the micrometer scale on flat substrates without high-temperature annealing. On topographically patterned silicon substrates the position of the domains of the minority PFS phase directly near the side walls is fixed by the neutral wetting condition. Successful positioning of the block-copolymer spheres in linear and hexagonal grooves is achieved in grooves up to 1.3 microm wide, whereby the hexagonal grooves demonstrate complete 2D alignment. In circular pits, this graphoepitaxial effect is absent.

Resin Material Dependence of Pit Shape in Thermal Direct Mastering

We report the resin material dependence of the shape of pits obtained by thermal direct mastering (TDM), which is a heat-mode mastering method utilizing the thermal decomposition of resins. By applying suitable resins, both circular and crescent pits can be obtained by TDM. This difference in shape was considered to originate from the temperature difference between the glass transition temperature and the thermal decomposition temperature of the resins. The resin with a relatively small temperature difference was suitable for the fabrication of the circular pits and random patterns, and the resin with a large temperature difference was suitable for the fabrication of the crescent pits and monotone patterns with high linear density. By using a deep ultraviolet (DUV) laser mastering system with a wavelength of 257 nm and a numerical aperture of 0.90, a monotone pattern of 40-nm-length pits was fabricated by applying a novolak-type resin with a relatively large temperature difference.

Spin-coated PMMA films

Polymethylmethacrylate (PMMA) spin-coated thin films are commonly used as resist films in micro/nanofabrication processes. By using atomic force microscopy (AFM) imaging, scratching lithography and force–distance curves spectroscopy, the spin coating and post-processing conditions were determined, for obtaining films whose surface morphology appears featureless or is dominated by pinholes and other surface defects. Featureless appear the surfaces of films spin coated at 8krpm from a 1.25% solution on silicon substrates and postbaked at 200°C for 2min on a hot plate, while surface defects in the form of large circular pits with diameters between 10 and 20μm and depth of ∼2nm dominate the surface morphologies of films spin coated at 7krpm on glass substrates from a 2% solution and postbaked either at 200°C for 2min on a hot plate or at 170°C for 30min in an oven. Surface defects in the form of pinholes appear on the surfaces of films spin coated at 8krpm on silicon substrates from a 1.25% solution (thickness of ∼8nm) and postbaked at 170°C for 60min in an oven or left in a low vacuum chamber for a few days. The implication of the different film properties—depending on the preparation parameters—in lithographic techniques is explained and discussed in the paper.

Selective Etching of Micropipes During Initial Homoepitaxial Growth Stage on Nearly On-Axis 4H-SiC Substrates

The initial homoepitaxial growth behavior on nearly on-axis 4H-SiC substrates was investigated. We have observed circular etch pits on the surface of on-axis substrate in the presence of source gases. However, there were no circular etch pits on the surface of off-axis substrates. In addition, the surface etched by H2 gas did not show circular etch pits even on nearly on-axis substrates. The shape of the circular etch pits was similar to spiral one. The initial growth behavior of epilayers was also investigated with various C/Si ratios of source gases (0.6<C/Si<2.0). The circular etch pits were observed independent of the source gas ratio. It implies that the source gases promote the selective etching, while the H2 gas etches SiC defect-independent. The spiral shape of etch pits seems to be produced from the screw dislocation with large burgers vector of micropipes. Therefore, the circular shape etch pits were not observed in an off-axis substrate.