Dark Layer Research Articles

A numerical model incorporating the microstructure alteration for predicting residual stresses in hard machining of AISI 52100 steel

Residual stresses induced by machining processes are a consequence of thermo-mechanical and microstructural phenomena generated during the machining operation. Hard machining of AISI 52100 bearing steel is a typical case where the microstructural phenomena associated with white and dark layers formation influences the residual stress distribution. Unfortunately, very limited physical models are available for residual stress prediction including the microstructural effects. This paper presents an experimental and numerical approach to predict residual stresses by incorporating the microstructural phase transformations induced during machining of AISI 52100 steel.

Orbital‐ and millennial‐scale fluctuations in late Quaternary marine pollen records from the Japan Sea

AbstractQuaternary surface water conditions within the Japan Sea change with eustatic sea‐level changes and fluctuations in the East Asian Summer Monsoon (EASM), influencing regional climate and vegetation through the delivery of heat and moisture. Our marine pollen data suggest overall cooling from the Last Interglacial (ca. 125 ka) to the Last Glacial Maximum (LGM), a cold climate during Marine Isotope Stage (MIS) 2, gradual warming from 12 ka and rapid warming after 10 ka. These stages are concordant with published palaeoceanographic changes in the Japan Sea. During mid MIS 5 to MIS 3, marine sediments in the Japan Sea are characterised by fine alternations of dark‐ and light‐coloured layers that formed under the influence of fluctuations in the EASM, possibly correlated with Dansgaard–Oeschger cycles. During the deposition of dark layers, high levels of precipitation are inferred from the abundance of Cryptomeria. In contrast, a cool and dry climate is interpreted for the light layers, based on an abundance of subarctic conifer pollen. The palaeoclimate of the Japan Sea region appears to have been influenced by orbital‐scale changes in global climate and millennial‐scale fluctuations in the EASM. Copyright © 2009 John Wiley & Sons, Ltd.

Reconstructing the evolution of fault zone architecture: Field‐based study of the core region of the Atera Fault, Central Japan

AbstractIn order to reconstruct the architectural evolution of a fault zone with heterogeneous structures, we studied the Atera Fault in Central Japan, and described the detailed mesoscopic and microscopic features of the zone. The fault zone studied consists of a 1.2‐m wide fault core of fault breccia mixed with fragments derived from welded tuff, granite, and mafic volcanic rocks. The 1.2‐m wide fault core is bordered by a western damage zone characterized by a welded tuff fault breccia and an eastern damage zone characterized by a granite cataclasite. A secondary fault core, a 30‐cm wide granite‐derived fault gouge, cross‐cuts the granite cataclasite. Although welded tuff fault breccia and granite cataclasite are also pervasively fractured and fragmented, the fault cores are significantly affected by fragment size reduction due to intense abrasive wear and comminution. The 1.2‐m wide fault core includes fragments and a sharp dark layer composed of mafic volcanic rocks, which can be correlated with neighboring 1.6 Ma volcanic rocks. This observation places a younger constraint on the age of the fault core formation. Carbonate coating on basalt fragments in the 1.2‐m wide fault core has also been fractured indicating the repetition of intense fragmentation. Bifurcated, black and gray veins near the 1.2‐m wide fault core are likely injection veins, formed by the rapid injection of fine material within fault zones during seismic events. The granite‐derived fault gouge, characterized by hard granite fragments without intense brecciation and microfracturing, in a kaolinite‐rich clay matrix, is interpreted as the most recent slip zone within the exposed fault zone. A preview of published geological and hydrological studies of several fault zones shows that clay‐rich fault cores can exhibit much lower permeability than the adjacent damage zones represented in this present case by the welded tuff fault breccia and granite cataclasite.

Wear and friction behavior of sand cast brake rotor made of A359-20vol% SiC particle composites sliding against automobile friction material

Abstract The effect of load range of 30–100 N and speed range of 3–12 m/s on the wear and friction behavior of sand cast brake rotor made of A359-20 vol% SiC particle composites sliding against automobile friction material was investigated. Dry sliding frictional and wear behavior were investigated in a pin-on-disc type apparatus. Automobile friction material was used as pin, while the A359-20 vol% SiC particle composites formed the rotating disc. For comparison, the wear and friction behavior of commercially used cast iron brake rotor were studied. The results showed that the wear rate of the composite disc decreased with increasing the applied load from 30 to 50 N and increased with increasing the load from 50 to100 N. However, the wear rate of the composite disc decreased with increasing the sliding speed at all levels of load applied in the present work. For all sliding speeds, the friction coefficient of the composite disc decreased with applied load. The worn surfaces as well as wear debris were studied using scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analyzer and X-ray diffraction (XRD) technique. At load of 50 N and speed range of 3–12 m/s, the worn surface of the composite disc showed a dark adherent layer, which mostly consisted of constituents of the friction material. This layer acted as a protective coating and lubricant, resulting in an improvement in the wear resistance of the composite.

Cytologic Examination of Hemorrhagic Fluid by Capillary Centrifugation

To develop a simplified technique for processing hemorrhagic body fluids, allowing elimination of red blood cells (RBCs) to obtain tumor cell-rich cytosmears for accurate diagnosis of malignancy.Hemorrhagic fluid is collected with ethylenediamine tetraacetic acid anticoagulant. The cells are separated by centrifugation in glass capillaries into 3 layers, with the uppermost containing supernatant, middle buffy coat and lowermost dark layer of RBCs. The smears of the buffy coat are prepared by breaking the capillaries at the junction of buffy coat and RBC layer. The procedure is named capillary centrifugation technique. This procedure was developed in the cytology laboratory at King George's Medical College, Lucknow, India in 1974.Cell yield is good and cellular details are well preserved. No cell debris is present on the slides. The background of the smears is absolutely clear. Any number of slides may be prepared for special study for exact typing of tumor cellsThis is a simple, economical procedure and a good substitute for a cytocentrifuge machine for preparing smears from small amount of fluids. Technicians learn it quickly and are quite comfortable with the procedure.

Seasonal sedimentation in the Pliocene Villarroya Lake (N Spain) inferred from pollen analysis

High-resolution pollen analysis was performed on a short (8.7 cm thick) section with 94 varve couplets (made up of dark and light laminae) from a lacustrine facies of the Pliocene Villarroya Basin, Spain. The aim of the present study was (i) to verify the seasonality of the sedimentation and (ii) to determine if pollen data record the short-term climatic fluctuations related to variations in laminae thickness and colour. The samples displayed high pollen concentrations and very good taxonomic diversity. The composition of the pollen spectra indicated that the vegetation structure was closely linked to relief: (i) a regional open herbaceous vegetation, (ii) a local marshy and riparian environment, (iii) deciduous mixed forest at mid-altitudes, and (iv) coniferous mixed forest in the surrounding mountains at higher altitudes. In the 48 distinct couplets where the dark and light laminae have been separately sampled, the pollen content showed higher concentrations of early flowering trees in the dark ones, whereas late-flowering plants were more abundant in the light ones. Total pollen concentrations in the 48 couplets were higher in most of their dark layers. These results point to a seasonal layering. According to present-day flowering times, the dark laminae represent sedimentation in winter/spring and the light laminae sedimentation in late summer/autumn. The correlation between the AP (Arboreal Pollen)–NAP (Non-Arboreal Pollen) percentages and lamina thickness linked lamina thickness with the highest values of AP, indicating warmer periods. Variations in the ecological groups enabled us to differentiate eight pollen cycles related to short-term climatic fluctuations. These alternations seem to be more associated with seasonality in precipitation than with temperature oscillations and could be correlated with the NAO/ENSO-like and sunspot-like cycles.

Enamels in stained glass windows: Preparation, chemical composition, microstructure and causes of deterioration

Stained glass windows incorporating dark blue and purple enamel paint layers are in some cases subject to severe degradation while others from the same period survived the ravages of time. A series of dark blue, green–blue and purple enamel glass paints from the same region (Northwestern Europe) and from the same period (16–early 20th centuries) has been studied by means of a combination of microscopic X-ray fluorescence analysis, electron probe micro analysis and transmission electron microscopy with the aim of better understanding the causes of the degradation. The chemical composition of the enamels diverges from the average chemical composition of window glass. Some of the compositions appear to be unstable, for example those with a high concentration of K 2O and a low content of CaO and PbO. In other cases, the deterioration of the paint layers was caused by the less than optimal vitrification of the enamel during the firing process. Recipes and chemical compositions indicate that glassmakers of the 16–17th century had full control over the color of the enamel glass paints they made. They mainly used three types of coloring agents, based on Co (dark blue), Mn (purple) and Cu (light-blue or green–blue) as coloring elements. Blue–purple enamel paints were obtained by mixing two different coloring agents. The coloring agent for red–purple enamel, introduced during the 19th century, was colloidal gold embedded in grains of lead glass.

Correlation of TL layers for the synchronous paleoceanographic events in the East Sea (Sea of Japan) during the Late Quaternary

TL layers (i.e., dark mud layers), either thin or thick, as determined by the L* values with lithologic observation, are distinct paleoceanographic signatures in the East Sea (Sea of Japan), which were formed in response to the global eustatic sealevel fluctuations between interglacials and glacials during the Late Quaternary. These lithologic markers were consistently correlated among the three sediment cores (MD01-2407, 05GCRP21, and KR05-09PC1) collected from the Oki Ridge of the southern Yamato Basin, the South Korea Plateau of the northern Ulleung Basin, and the Matsumae Plateau of the northeastern Japan Basin, respectively. Reconstruction of age models for cores 05GCRP and KR05-09PC1 was aided in a good way by the AMS 14C ages of planktonic foraminifera and identification of the tephra layers, and mainly by lithostratigraphic correlation with TL layers of well-dated core MD01-2407, based on the L* values. The correlation of TL layers among the three sediment cores was remarkable, indicating that the East Sea (Sea of Japan) experienced the synchronous and basin-wide scale paleoceanographic events during the Late Quaternary. Our study exemplifies the significant usefulness of these lithologic markers for further Late Quaternary paleoceanographic investigation.

P‐194L: Late‐News Poster: Simple Structure Laser‐Addressing e‐Papers

AbstractFor low cost and high performance cholesteric liquid crystal panel, this paper proposes a simple structure laser‐addressable e‐paper. It makes the dark layer unnecessary and the electrodes can be optional, transparent, and un‐patterned. It responds to a laser source without electrical field and can be stacked to achieve color laser‐addressing.

Characterization of the green iridescence on the chelicerae of the tube web spider, Segestria florentina (Rossi 1790) (Araneae, Segestriidae)

Segestria florentina (Rossi 1790) (Segestriidae) displays iridescent green coloration on the paturons of the chelicerae. This was confirmed by reflectance measurements, which gave a spectral peak at 505 nm. Scanning electron microscopy did not identify cuticular surface scales or sculpturing, suggesting that the cause of the iridescence was subsurface. Transmission electron microscopy revealed 86 alternate dark and light layers in the exocuticle, the mean dimensions of which were 126 nm 6 28 nm and 88 nm 6 55 nm respectively. The identity of each layer was initially unclear. However, by using a combination of materials with different refractive indices in calculations of theoretical reflectance spectra, we concluded that they were most likely to be composed of chitin and air, since a peak of 480 nm was obtained, which most closely matched that which was recorded. The function of the green color is not clear, since S. florentina has relatively poor vision and relies predominantly on vibratory and acoustic signals. The study provides useful information relevant to research into the evolution of structural colors in spiders and, more generally, in nature.

An archaeopedological and phytolitarian study of the “Dark Earth” on the site of Rue de Dinant (Brussels, Belgium)

During the excavations of the site of Rue de Dinant in the historic centre of Brussels (Belgium), remains of the first city wall dating from the 13th century have been discovered. Intra muros thick dark sediment units predating this wall are observed. These dark units are among the oldest occupation traces so far encountered in this higher, eastern, part of the historic centre of Brussels. In order to characterise them, and to understand the human activities and natural processes behind their formation, an interdisciplinary research, integrating archaeopedology and phytolith study, has been undertaken. This approach permitted us to identify a range of natural and cultural processes leading to the formation of these dark layers, and to characterise different activities. Remains of a hearth, old plough land (cropfields) and grassland have been identified, all activities referring to a rural landscape organisation. Later on, the area changes into an enormous silt extraction area, whereby Dark Earth is thrown into the dug pits. Finally, the construction of the first city wall marks the area as becoming part of the city. The study of Dark Earth shows to be a potentially valuable tool to shed light on the development and spatial organisation of pre-urban Brussels, a historically very poorly documented period.

SHALLOW-WATER SPOROLITHON RHODOLITHS FROM NORTH ISLAND (NEW ZEALAND)

Abstract Shallow-water Sporolithon rhodoliths from New Zealand are described here on the basis of shape, size, composition, internal structure, and major taphonomic attributes, with the aim of discussing their significance in the framework of current ecological and paleoecological models of rhodolith formation and accumulation. The very shallow water environment (<2 m) of the Whangaparaoa Peninsula undergoes daily tidal currents and seasonal storm conditions. These factors, along with the availability of cobbles and pebbles as suitable substrate, lead to the accumulation of spherical, fruticose, monospecific, nucleated, and internally compact rhodoliths. The observed taphonomic features include apical abrasion, intercalary growth of protuberances after mechanical breakage, and multiple growth stages with distinctive bioerosion (by bivalves, annelids, and cyanobacteria), which are identified by internal abrasion surfaces and dark layers. A review of the pattern of global distribution of the coralline gener...

Basalt- CO2–H2O interactions and variability in carbonate mineralization rates

Abstract Flood basalts are receiving increasing attention as possible host formations for geologic sequestration of anthropogenic CO 2 , with studies underway in the U.S., India, Iceland, and Canada. Our previous laboratory studies with Columbia River basalts showed relative quick precipitation of carbonate minerals compared to other siliclastic rocks when batch reacted with water and supercritical CO 2 . In this study, our prior work with Columbia River basalt was extended to tests with basalts from the eastern U.S., India, and Africa. The basalts are all similar in bulk chemistry and share common minerals such as plagioclase, augite, and a glassy mesostasis. Single pass flow through dissolution experiments under dilute solution and mildly acidic conditions indicate similar cation release behavior among the basalt samples tested. Despite similar bulk chemistry and apparent dissolution kinetics, long-term static experiments with CO 2 saturated water show significant differences in rates of mineralization as well as precipitate chemistry and morphology. For example, basalt from the Newark Basin in the U.S. is by far the most reactive of any basalt tested to date. Carbonate reaction products for the Newark Basin basalt were globular in form and contained significantly more Fe than the secondary carbonates that precipitated on the other basalt samples. Calcite grains with classic “dogtooth spar” morphology and trace cation substitution (Mg and Mn) were observed in post-reacted samples associated with the Columbia River basalts. Other basalts produced solid precipitates with compositions that varied chemically throughout the entire testing period. Polished cross sections of the reacted grains show precipitate overgrowths with irregular regions outlined by dark and bright layers indicative of zonations of different compositions. Chemical differences in the precipitates indicate changes in fluid chemistry unique to the dissolution The Karoo basalt appeared the least reactive, with very limited behavior of each basalt sample reacted with CO 2 saturated water. mineralization occurring during the testing period. Additional experiments conducted using mixtures of H 2 S and CO 2 unexpectedly changed the relative reactivity of the basalts. For example, the Karoo basalt was highly reactive in the presence of aqueous dissolved H 2 S and CO 2 , evident by small nodules of carbonate coating the basalt grains after 181 days of testing. However the most reactive basalt in pure CO 2 , Newark Basin, formed limited amounts of carbonate in the presence of H 2 S. Basalt reactivity in pure CO 2 appears to be controlled by the glassy mesostasis chemistry, which is the most reactive component of basalt. With the addition of H 2 S, the reactivity appears to be controlled by precipitation of insoluble iron sulfides as coatings on the basalt grains.

有孔虫群集からみた日本海暗色層堆積時の海洋環境 ― 日本海南東部MD01-2407コアの結果から ―

有孔虫群集からみた日本海暗色層堆積時の海洋環境 ― 日本海南東部MD01-2407コアの結果から ―

上越沖海鷹海脚メタン湧出域の過去３２，０００年の岩相変化と有孔虫層序

Plantonic and benthic foraminifera are analyzed with 11 sediment cores recovered from the Umitaka Spur area of the Joetsu Basin off Joetsu, Niigata Prefecture. The area is characterized by active methane seeps and methane hydrates. We recognize 12 foraminiferal biozones (Biozone I to XII in descending order) in the last 32000 years based on three selected cores (two well-dated and one longest), and apply them to another 8 cores for correlation. Sediment cores are divided into five lithologic units as massive to bioturbated mud (lithologic unit 1), thinly laminated mud (unit 2), gray massive mud (unit 3), thinly laminated dark mud (unit 4), and bioturbated mud (unit 5) from upper to lower. Lithologic units 2 and 4 correspond to basin-wide thinly laminated layers, previously reported as TL-1 and TL-2, respectively. The Japan Sea became a closed inland basin during the lowest sea level period of the last glacial maximum (LGM) at 27-26cal kyr BP (Biozone VIII). The surface water reached the lowest salinity level, while the bottom water was strongly anoxic due to reduced vertical circulation. An expulsion of a large amount of methane occurred on the Umitaka Spur during the LGM due to a massive dissociation of subsurface methane hydrate. Biozones VIII, VII, and VI at around 27-17 cal kyr BP with planktonic foraminiferal maximum and benthic foraminiferal minimum are found in a dark layer of TL-2, which was formed during the period of the lowest sea level in the LGM. Biozone IV, 12-11 cal kyr BP, is characterized by low oxygen tolerant benthic species of Bolivina pacifica, and correlates with dark layer TL-1, which implies that the deep circulation of Japan Sea was severely reduced for a short period during (or soon after) the Younger Dryas Cooling Event. B III represents the planktonic foraminiferal minimum zone, which marks the transition from cool water species to warm water species in planktonic foraminifera. Foraminiferal stratigraphy reveals that the sedimentation rate of the Umitaka spur sediments varied significantly depending on topography such as pockmarks or mounds.

Improving surface integrity in orthogonal machining of hardened AISI 52100 steel by modeling white and dark layers formation

In machining of hard parts, surface integrity is one of the most specified customer requirements. Often, the major indications of surface integrity are surface roughness and residual stresses. However, the material microstructure also changes in machined-hardened steels, and it must be taken into account for improving product performance. In this paper, a hardness-based flow stress and an empirical model for describing the white and dark layers formation were developed and implemented in a FE code. The proposed model was validated by comparing the predicted results with the experimental evidences.

A laminated tufa carbonate from the mid Holocene of the Qilian Mountains and its potential for palaeoclimate inferences

A mid-Holocene tufa section at 3,815 m altitude in the Qilian Mountains at the northeastern margin of the Tibetan Plateau was tested as a possibly important new climate archive. The tufa carbonate displays a distinct alternation of white and dark layers most probably representing annually deposited sparry and microgranular calcite which is formed during the warm and relatively wet summer and the drier and cooler spring and autumn season with an interruption of tufa formation during the freezing period. The δ 18 O record of the tufa site comprises probably 357 years of annually deposited carbonate about 4,000 years before present, which indicates the prevalence of wetter climatic conditions in comparison to the present-day situation. This inference is confirmed by palynological data and lake-level reconstructions from a number of sites in the northern foreland of the Qilian Mountains, highlighting the large potential of longer tufa sequences for high-resolution palaeoclimate studies in the future.

Rain and dewdrops on titan based on in situ imaging

The Descent Imager/Spectral Radiometer (DISR) of the Huygens probe was in an excellent position to view aspects of rain as it descended through Titan's atmosphere. Rain may play an important part of the methane cycle on Titan, similar to the water cycle on Earth, but rain has only been indirectly inferred in previous studies. DISR detected two dark atmospheric layers at 11 and 21 km altitude, which can be explained by a local increase in aerosol size by about 5–10%. These size variations are far smaller than those in rain clouds, where droplets grow some 1000-fold. No image revealed a rainbow, which implies that the optical depth of raindrops was less than ∼ 0.0002 / km . This upper limit excludes rain and constrains drizzle to extremely small rates of less than 0.0001 mm/h. However, a constant drizzle of that rate over several years would clear the troposphere of aerosols faster than it can be replenished by stratospheric aerosols. Hence, either the average yearly drizzle rate near the equator was even less ( < 0.1 mm / yr ), or the observed aerosols came from somewhere else. The implied dry environment is consistent with ground-based imaging showing a lack of low-latitude clouds during the years before the Huygens descent. Features imaged on Titan's surface after landing, which might be interpreted as raindrop splashes, were not real, except for one case. This feature was a dewdrop falling from the outermost baffle of the DISR instrument. It can be explained by warm, methane-moist air rising along the bottom of the probe and condensing onto the cold baffle.

Bioturbational disturbance of the Cretaceous-Palaeogene (K-Pg) boundary layer: Implications for the interpretation of the K-Pg boundary impact event

Detailed field observations across and along the Cretaceous-Palaeogene (K-Pg) boundary interval in the Caravaca section, SE Spain, together with laboratory analyses reveal a well-developed lowermost Danian dark-colored trace fossil assemblage. The trace fossils range continuously from the bioturbated horizons in the dark boundary layer (lowermost Danian), to the uppermost Maastrichtian sediments. The rusty boundary layer at the base of the dark boundary layer, usually related to the K-Pg boundary impact, is traditionally considered as undisturbed. However, ichnological analysis at the Caravaca section shows that this rusty boundary layer is cross-cut vertically by Zoophycos and Chondrites, but also penetrated laterally by Chondrites, revealing an important colonization of the substrate. Stereomicroscope analysis shows sharp burrow margins of dark-colored Chondrites directly against the surrounding red sediment of the rusty layer. Colonization of unfavorable substrates by Zoophycos and Chondrites tracemakers, as that represented by the rusty boundary layer, was possible because of constructing of open, probably of actively ventilated burrows that facilitate colonization of sediments poor in oxygen and food. Significant bioturbational disturbance of the rusty layer can cause vertical and horizontal redistribution of the components related to the K-Pg boundary impact and, in consequence, to induce erroneous interpretations. A detailed ichnological analysis of the K-Pg boundary interval, with special attention to the rusty layer, reveals an essential tool to avoid misinterpretations.

A Simple Explanation of Schottky Condition Through Striations

Striations are characteristics of DC glow discharges at low pressures. These bright and dark layers occur in many partially ionized gases and positive columns, which indicate different characteristics of DC glow discharge plasmas. Here, the variance of temperature and spatial frequency along a discharge tube with different diameter and highly dependence of striations on the gas pressure are demonstrated.