Gray Core Research Articles

Trace Element Composition and Cathodoluminescence of Quartz in the Hongniu–Hongshan Skarn Deposit in Yunnan Province, Southwest China

The Hongniu–Hongshan Cu skarn deposit is located in the central part of the Zhongdian porphyry and skarn Cu belt in southwestern China. Various elements, including Al, Ti, Li, K, Na, Ca, Fe, and Ge, have been completed by using scanning electron microscopy–cathodoluminescence (SEM-CL) and laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) on quartz phenocrysts from the Hongniu–Hongshan porphyry and skarn Cu deposit. Three quartz generations were identified in the porphyritic granite based on the CL textures and trace element signatures. Samples of the first-generation quartz (Qtz1) contain dark gray luminescent cores assaying 22–85 ppm Ti, 58–129 ppm Al, 4–18 ppm Li, and 0.43–40 ppm Fe. The Ti-in quartz geothermometer indicates crystallization temperatures of 593–664°C for Qtz1. Samples of the second-generation quartz (Qtz2) are characterized by clear bright gray oscillatory overgrowths with medium Ti concentrations of 51–70 ppm with elevated and variable amounts of Al, Li, and Fe, and low K. The Ti-in quartz geothermometer indicates crystallization temperatures of 672–706°C. Samples of the third-generation quartz (Qtz3) contain narrow light gray rims assaying 56–93 ppm Ti, 80–101 ppm Al, 11–19 ppm Li, 1.42–17 ppm K, and 2–25 ppm Fe. The Qtz3 crystallised crystallized at higher temperatures of 706–799°C. Our study indicates that the quartz phenocryst in the Hongniu–Hongshan porphyry may have undergone two mixing episodes involving a second hotter magma. Before the first resorption, average Ti concentration in the quartz phenocryst cores was 24 ppm, and Ti of the bright band halo at the edge of the crystal core is 56 ppm; the maximum temperature difference is 109°C higher than that of the pre-resorption. Furthermore, the Ti concentration is 75 ppm at the edge of the quartz phenocryst before resorption. After resorption, the average Ti increased to 81 ppm at maximum temperature difference of 54°C higher than that of pre-resorption. Moreover, on the basis of quartz composition collected from 14 different deposits and our new dataset, we propose that covariations of Ge/Al ratio can be used to effectively discriminate magmatic quartz and hydrothermal quartz. Magmatic quartz has a Ge/Al ratio of <0.013, and the hydrothermal quartz has a ratio of >0.013.

Structure of Sewage Sludge-Clay Multiscale Composite Particles to Control the Mechanism of SO2 and H2S Gas Release.

In order to address the problem of sulfur gas and other odors released in the process of using sewage sludge as a construction material, this study prepared multiscale composite particles with a “large scale-medium scale-small scale-micro scale” structure by mixing sludge with silica-alumina building materials. Analysis of the structural changes formed by the internal gas of composite particles due to diffusion at different temperatures and a study of the characteristics of SO2 and H2S release from composite particles were conducted, as well as being compared with the release characteristics of pure sludge, which clarified the mechanism of controlling sulfur-containing-gas release from composite particles. The results showed that compared with pure sludge, the sludge-clay multiscale composite particles were able to reduce the release of SO2 and H2S up to 90% and 91%, and the release temperatures of SO2 and H2S were increased to 120 °C and 80 °C, respectively. Meanwhile, the special structure of the sludge-clay multiscale composite particles and the clay composition are the main factors that hinder the diffusion of sludge pyrolysis gases. Additionally, there are three layers of “gray surface layer-black mixed layer-dark gray spherical core” formed inside the composite particles, which is the apparent manifestation of the diffusion of volatile gases. This study provides theoretical support for the application of multiscale composite particle inhibition of odor-release technology in industrial production.

Calcimicrobes in Cambrian microbialites (Shandong, North China) and comparison with experimentally produced biomineralization precipitates

Microbialites can be important oil and gas reservoirs because of their high initial porosity and they may well be source rocks too. However, the formation mechanisms of calcimicrobes in microbialites are still not fully understood, and further research is needed. Herein, microbialites (thrombolites, dendrolites, and oncolites) from the Cambrian successions of Shandong Province, China, are examined for their microbial fabrics and comparisons are made with the results of laboratory biomineralization experiments using the modern cyanobacterium Synechocystis sp. PCC6803 and the halophilic Bacillus licheniformis SRB2. The thrombolites show mosaic, meshed, and spotted textures, each with a different microbial clot morphology, and Epiphyton is the dominant calcimicrobe. Dendrolitic buildups consist of a lower gray core dominated by the chambered Renalcis, and an upper orange part dominated by dendritic Epiphyton, suggesting a transition of the microbial community across the color change, related to an increase in iron content. Oncolites occur in beds up to 10-cm-thick with spherical to ellipsoidal oncoids containing Girvanella developed around a bioclast nucleus. Scanning electron microscopy observations distinguish the calcimicrobes with their rough, peloidal surface morphology from adjacent cement; aggregated spheroidal and or filamentous calcimicrobes can be recognized, the latter with hollow centers in some cases. The results of the laboratory biomineralization experiments show that the two modern microbes can induce the precipitation of carbonate minerals, mostly of calcite. These biominerals are commonly granular and have a complex microscopic structure including spherical and dumbbell shapes. The microbes are commonly encrusted with calcite and after decomposition of the bacteria, hollow mineral crusts are produced; these are the result of the nucleation and growth of nano-minerals on the extracellular polymeric substances (EPS) present around the microbes. The bio-precipitates induced by modern microbes in the laboratory experiments are similar in many respects to the calcimicrobes in the Cambrian microbialites; biomineralization processes clearly play an important role in the formation of carbonate minerals and lithification of microbial mats.

Alternating N2 gas injection as a potential technique for enhanced gas recovery and CO2 storage in consolidated rocks: an experimental study

The promotion of enhanced gas recovery (EGR) and CO2 storage is still shrouded in contention and is not well accepted, due to the excessive in situ CO2 mixing with the nascent natural gas. This adulterates the recovered CH4 and thus results in a high sweetening process cost thereby making the technique impractical. This has not only limited the field application of EGR in actual projects to a few trails but renders it uneconomical. This study aims to present, experimentally, alternating N2 injection as a potential technique for EGR and CO2 storage in sandstone rock cores. A laboratory core flooding experiment was carried out to simulate a detailed process of unsteady-state methane (CH4) displacement using Bandera grey core plug. This was carried out at 40 °C, 1500 psig, and 0.4 ml/min injection rate by alternative injection of N2 and CO2 in succession designed to suit the application based on optimum operating conditions. The results show that both CO2 storage capacity and CH4 recovery improved significantly when gas alternating gas (GAG) injection was considered. The best results were observed at lower N2 cushion volumes (1 and 2 PV). Therefore, the GAG injection method with N2 as cushion gas can potentially increase both CO2 storage and CH4 recovery of the gas reservoir. This technique if employed will assert the current position and provide vital information for further researches aimed at promoting environmental sustainability and economic viability of the EGR and CO2 sequestration processes.

Study on The Effect of ‘Ash Core’ on the Performance of Catalysts in the Preparation of SCR Honeycomb Denitration Catalyst

The SCR honeycomb denitration catalyst will have a “grey core” during the preparation process. In this paper, the same batch of fresh catalyst is used to prepare the “grey core” and the normal “yellow core” catalysts for comparison. Through the catalyst denitration performance evaluation test, when the denitration efficiency is 88.3%, the calculated activities of the two catalysts of “yellow core” and “grey core” are 24.9Nm/h and 25.3Nm/h, respectively; when the denitration efficiency is 85.5%, the calculated activity of the catalysts are both 24.5Nm/h. Through analysis of the physical and chemical properties of the catalyst, it is found that the alkali metal content and the alkaline earth metal content of the two catalysts are basically the same. The specific surface areas of the “yellow core” and “grey core” catalysts are 58.65m2/g and 58.24m2/g, respectively. By infrared spectroscopy, the “grey core” catalyst was produced due to the deposition of carbon, and then through the wear performance test, it is found that the “grey core” catalyst has better wear performance, but the “grey core” catalyst is more brittle, when there is external force. At the time, cracks are easily generated in both the axial direction and the radial direction, which is detrimental to the integrity of the catalyst, and also poses a safety hazard to the use of the regenerated catalyst.

Paleoproterozoic ultrahigh-temperature granulite-facies metamorphism in the Sulu orogen, eastern China: Evidence from zircon and monazite in the pelitic granulite

Because of their essential information for constraining the timescales of high-temperature processes, zircon and monazite are the two most important minerals for understanding crustal processes. Zircon and monazite are common accessory minerals in pelitic granulites (Sulu orogen, eastern China). The pelitic granulites have a peak mineral assemblage of garnet + sillimanite + antiperthite + plagioclase + quartz + rutile ± biotite. Zircons from the granulite have low Th/U ratios (<0.1 mostly), flat HREE patterns with negative Eu anomalies, suggesting a typical of granulite-facies metamorphic zircon. Ti-in-zircon thermometers give temperature estimates ranging from 911 to 954 °C with a weighted mean of 928 ± 10 °C, suggesting a ultrahigh temperature (UHT) metamorphism. These metamorphic zircons yield a concordant 206Pb/238U age of 1843 ± 17 Ma (n = 26) and an upper intercept age of 1842 ± 15 Ma (n = 28), suggesting a Paleoproterozoic UHT metamorphism. The monazites in the pelitic granulite record the same Paleoproterozoic age (ca. 1840 Ma) as the zircons. The monazites generally exhibit a zoned structure in BSE images: gray core and bright rim. Both the cores and rims display significant depletion in HREEs and Y, and negative Eu anomalies, indicating their formation under granulite-facies metamorphic conditions. Notably, the bright rims are more depleted in HREEs and Y, and more negative Eu anomalies than the gray cores. Compared with the gray cores (Th = 45,429–165,236 ppm; U = 2227–6044 ppm; and Th/U = 18–28), the bright rims have high Th (194,616–285,224 ppm) but low U (1145–3209 ppm) contents, resulting in very high Th/U ratios (69–217). These results establish zircon-monazite-garnet- feldspar REE equilibrium and their U–Th–Pb system under UHT metamorphic processes. Paleoproterozoic UHT granulite-facies metamorphism in the Sulu orogen provides a crutial clue to understand its early geodynamic setting and tectonic evolution.

Preparation of Ti(C, N)-based Cermets Powders with Double-core Ring Structure

In this study, the microstructure of Ti(C, N)-based cermet was improved by adding β-cobalt (face-centered cubic) and (Ti, W, Mo, Ta)(C, N) solid solution powder to prepare micro-nano Ti(C, N)-based cermet powder. In order to improve the comprehensive properties of the material. Firstly, the Co powder with face-centered cubic structure was obtained by the solid-phase reaction of high-energy ball milling, and its plastic deformation resistance was higher than that of Co powder with dense hexagonal structure. Secondly, The powder of (Ti, W, Mo, Ta)(C, N)solid solution was obtained by mechanical alloying and high-temperature carbonization under the atmosphere of N2. And the two were applied to the micro-nano Ti(C, N)-based cermet powder, and finally the properties of cermet powder were compared with that of ordinary cermet powder. The results show that the microstructure of micro-Ti(C, N)-based cermet powder prepared in this study is a double-core rim structure, that is, the structure of black core white rim and gray core white rim. This structure can effectively prevent crack of the expansion. The strength and toughness of cermet materials are greatly improved, which is beneficial to the improvement of comprehensive properties of cermet materials.

The relationship of gray zone and infarct core in the Iceland MI study

The relationship of gray zone and infarct core in the Iceland MI study

Effects of NiTi additions on the microstructure and mechanical properties of Ti(C,N)-based cermets

X-ray diffractometer (XRD) and scanning electron microscope (SEM) were used to observe and investigate the microstructure and fracture morphology of Ti(C,N)-based cermets added with NiTi alloy powder. A new ceramic phase is found with the structure of gray core, black inner rim, noncontinuous white inner rim and continuous gray outer rim. The fracture toughness and the transverse rupture strength have a distinct trend to increase with the increase of NiTi powder content in Ti(C,N)-based cermets, while the hardness has the opposite trend. Grain refinement and the increase of metallic phase are the dominant strengthening and toughening mechanisms. Additionally, the crack deflection and bridging may play an active role in improving the properties, as well as the special structure of large metallic binder containing many small ceramic particles. In cermets with a higher content of NiTi powder, the microcrack and the crack closure effect induced by martensitic transformation are advantageous to the mechanical properties.

Effect of WC on the microstructure and mechanical properties of nano Ti(C,N)-based cermets

In this paper, nano Ti(C,N)-based cermets with different WC additions were prepared by conventional powder metallurgy techniques. The microstructure of nano cermets was investigated by scanning electron microscope (SEM). The results showed that there existed three kinds of “core–rim” structure in nano cermets, i.e., “black core–white rim”, “white core–gray rim” and “gray core–white rim” structures. With the increase of WC addition, there were more “white core–gray rim” and “gray core–white rim” grains. The amount of the abnormal growth grains decreased and the grains became more homogeneous with the WC addition. The lattice parameter of Ti(C,N) would increase with the WC addition. The mechanical properties of nano cermets were also improved with the increase of WC addition.

SCREENING FOR ARRHYTHMOGENIC MYOCARDIAL SUBSTRATE BY 12-LEAD ECG QRS SCORE, QRS-T ANGLE, LATE POTENTIALS AND T-WAVE ALTERNANS

Background: Increased QRS score, wide spatial QRS-T angle, T-wave alternans (TWA), and late potentials are independent predictors of cardiovascular mortality in the general population. We analyzed whether these electrocardiographic (ECG) parameters enable screening of patients for myocardial scar features implicated in sudden cardiac death risk. Methods: We screened the entire 12-lead ECG database of Johns Hopkins Hospital and identiied 631 patients age ≤70 years from non-critical care areas and no record of reduced life expectancy who had QRS score ≥5 and/or spatial QRS-T angle ≥105° as well as left ventricular ejection fraction (LVEF) ≥35%. All individuals were invited to participate and 69 enrolled in the study and underwent clinical examination, signal averaged ECG (SAECG), 30-minute ambulatory ECG recording for TWA, and complete contrast-enhanced cardiac magnetic resonance (ce-CMR) study to determine scar presence and pattern, as well as to characterize gray zone, core, and total scar size. Results: In the 69 patients (mean age 61±9, 71% male, 18% with a prior history of myocardial infarction and 32% with prior history of coronary revascularization) the mean LVEF was 57±8%. Myocardial scar was present in 38 (55%) patients, of whom 19 (50%) exhibited a typical ischemic pattern. Median and inter-quartile range for scar, core scar, and gray zone extent were 8% [4; 15%], 5% [3; 8%], and 2.5% [1; 7%] of left ventricle (LV) respectively. QRS score but not QRS-T angle was related to total scar size and gray zone size (P=0.02). There was a signiicant association between TWA and myocardial scar core size, (R=0.42; P=0.001). On multivariable analysis, only LV end-systolic volume (beta=0.18; 95%CI[0.030.33]; P=0.02) and total myocardial scar mass (beta=1.07; 95%CI[0.44-1.71]; P=0.001) were signiicantly associated with TWA. Presence of late potentials was related to depressed LVEF and QRS score but not to total scar extent. Conclusions: Screening with QRS score identiies preserved LVEF patients with myocardial scar and elevated TWA, consistent with arrhythmogenic myocardial substrate

Abstract 3417: Pixel by Pixel Comparison of CTP-Defined Infarct Core on Concurrent Non-Contrast CT

Introduction Interobserver agreement for the presence of early ischemic changes on non-contrast CT (NCCT) in potential thrombolysis candidates can be poor even among experienced raters. CT perfusion (CTP) may demonstrate infarct core and penumbra according to proposed thresholds but the extent of correlation between CTP defined core and hypodensity on hyperacute NCCT is unclear Methods A pixel by pixel comparison between NCCT and concurrent CTP obtained &lt;6hrs from symptom onset was performed for patients with symptomatic arterial occlusions. Segmentation was performed using time-averaged CTP raw images to compare core and normal tissue pixels for grey and white matter separately. Core was defined as relative Cerebral Blood Flow (CBF) of &lt;45% of normal tissue. NCCT was co-registered to the baseline frames of the concurrent CTP using a rigid body transformation. Core pixels were extracted from CTP and transposed to NCCT. Hounsfield unit (HU) values in CTP-defined core and normal tissue were quantified for grey and white matter. Receiver operating characteristic (ROC) curve analysis was performed to assess the predictive value of NCCT hypodensity and CTP-defined core. Results CT and CTP were compared for 33 patients. Mean age was 72 years (SD 12), median NIHSS was 16 (IQR 11-20) and mean time from symptom onset to CTP was 191 minutes (SD 63). Area under the curve (AUC) for prediction of grey and white matter core by NCCT was 0.641 and 0.601 respectively. The most frequently occurring optimum HU cut-points were 29 and 28 for grey and white matter respectively .These cut-points were associated with low overall specificity for detecting core (Median ± IQR= 0.48, 0.32-0.59 and 0.36, 0.26-0.44) but higher sensitivity (Median ±IQR 0.79, 0.62-0.87 and 0.83, 0.73-0.89) for grey and white matter Conclusion Objectively determined hypodensity on NCCT has low sensitivity and specificity for prediction of ischemic core tissue defined by CT perfusion. Thresholds were similar for both grey and white matter. NCCT scans without established hypodensity may still have irreversibly infarcted pixels which can be detected with CTP. Prospective evaluation of the added value of CTP-defined core on decision making in acute stroke is needed.

Infarct myocardium tissue heterogeneity assessment using pre-contrast and post-contrast T1 maps acquired with Modified Look-Locker Inversion Recovery (MOLLI) imaging

We aim to explore tissue heterogeneity assessment using T1 maps generated with the modified Look Locker (MOLLI) sequence in patients with previous myocardial infarct. Conclusion: Differences between healthy myocardium and scarred tissues can be reliably distinguished from the R1 values derived from pre-contrast T1 maps.Potentially, patients without scarred myocardium do not need post-contrast imaging. Inpatients with scarred tissues, ΔR1 value derived from both thepre- and the post-contrast T1 maps provides better distinction between grey zone and scar core than either pre-contrast or post-contrast R1 value alone.

Effect of VC addition on the microstructure and properties of Ti(C,N)-based nano cermets

In this paper, Ti(C,N)-based nano cermets were prepared by nano particles, and the effect of VC addition on the microstructure and properties of Ti(C,N)-based nano cermets was investigated. The results showed that there existed black-core grayish-rim structure as well as gray-core grayish-rim structure in VC-doped Ti(C,N)-based nano cermets. With the increase of VC addition, the number of gray cores increased, the lattice parameter of Ti(C,N) phase increased, the grain size decreased, the hardness and fracture toughness of Ti(C,N)-based nano cermets were enhanced, and nearly full densification could be achieved. However, excessive addition of VC to 1 wt% resulted in slight decrease in hardness and fracture toughness. Some deep dimples were found in the fracture surface of cermets with VC addition, which corresponded to ductile fracture.

Low‐temperature alteration of mesozoic oceanic crust, Ocean Drilling Program Leg 185

Basalts drilled from the Mesozoic crust at Ocean Drilling Program (ODP) Sites 801 and 1149 during Leg 185 have been affected by a succession of submarine, variably oxidative alteration processes by cold seawater. The low‐temperature alteration resulted in various combinations of secondary minerals both as replacements of igneous phases, and as void and crack fillings. Mg‐smectite, calcite, celadonite and Fe‐oxyhydroxide are the dominant secondary minerals. Quartz, chalcedony and phillipsite are always very minor phases that fill open spaces. The rocks generally exhibit concentric haloes, 0.5 to 1 cm in thickness, around gray inner cores and usually adjacent to exposed surfaces. Color zonations result from the abundance of various secondary mineral assemblages present in each zone. The green rocks are dominated by celadonitic phyllosilicates, whereas the dusky red haloes are characterized by abundant iddingsite and Fe‐oxyhydroxides replacing the fine clinopyroxene. Finally Mg‐smectite ± calcite, are the most common secondary phases in the inner gray cores. The most unusual effects of the low‐temperature alteration of the study rocks are the pervasive, pale green to gray green color and the relatively abundant dusky red haloes surrounding inner reddish gray cores. Alteration of Mesozoic crust cored during Leg 185 is comparable with low‐temperature alteration of 310 m thick uppermost volcanic section of the 5.9 My old crust of Hole 504B. Except the renewed precipitation of calcite in veins, the aging of oceanic crust does not depend on time probably because it occurs during the first few millions of years after the accretion, and ceases when the crust is sealed off.

Immunocytochemical detection of two nuclear proteins within the same neuron using light microscopy

We developed a method of double immunocytochemistry (ICC) that can be used with conventional light microscopy for localizing two different nuclear proteins. The procedure involves two sequential rounds of ICC that both employ the avidin and biotin conjugated enzyme (ABC) amplification method, separated by an Avidin D and biotin blocking step to reduce non-specific avidin–biotin reactions. Round one of ICC employs the use of avidin and biotin conjugated alkaline phosphatase (ABC–AP) and the Vector Red (VR) substrate, which produces a red colorimetric reaction product. The second round of ICC makes use of avidin and biotin conjugated peroxidase (ABC–HRP) and the Vector® SG substrate, which produces a gray colorimetric reaction product. Neuronal nuclei that are double-labeled for both proteins appear red with a gray core. This protocol allows the simultaneous detection of two proteins within the same subcellular compartment of a single neuron, without the need for epifluorescence or scanning confocal laser microscopy. Theme: Cellular and Molecular Biology Term: Staining, tracing, and imaging techniques

Stromatolitoid microbial nodules from Bermuda ?a special micro habitat for meiofauna

In Bermuda, stromatolitoid microbial nodules are found in dense groups in seagrass beds and on subtidal sandy or rocky bottoms. They develop between January and the beginning of August and may reach 15 cm in diameter and 6 cm in height. Nodules grow on top of the sediment surface and consist of convex interwoven mats of the cyanobacterium Phormidium corium and fine sediment particles trapped in these mats. Nodules were studied in the field and laboratory (in 1989–1992) with respect to their structure, microbial community, sediment chemistry and associated meiofauna. Vertical profiles taken with microelectrodes showed steep gradients of oxygen and sulfide. While free oxygen was only detected in the upper 2 mm, the sulfide concentrations increased with depth and reached maximal 1250 μmoll-1 inside the nodules. On the basis of microscopic observations and sediment chemistry, vertical sections through a nodule reveal four distinct layers: (A) an oxic green surface layer of growing cyanobacteria mats, (B) an anoxic yellow-white laminated layer of sediment particles, mucus and unpigmented cyanobacteria sheaths, (C) an anoxic sulfidic (sulfide <50 μmoll-1) interface where colour changes from yellow to gray and (D) an anoxic sulfidic (sulfide can increase to 1250 μmoll-1) gray core composed of sediment and decomposing cyanobacteria. The following meiofauna taxa were found in the nodules: Ciliata, Turbellaria, Gnathostomulida, Gastrotricha, Nematoda, Kinorhyncha, Polychaeta, Ostracoda and Harpacticoida. The distribution of the meiofauna was significantly different (p<0.05) within the four layers. The highest density of individuals was found in the sulfidic interface and core. Nematodes represented the dominant group in general. Thiobiotic organisms, such as the Gnathostomulida, Solenofilomorphidae, and Stilbonematinae were primarily found in the anoxic sulfidic layers of the nodules.

Electons' eyeview of buckytubes and friends

Synthesis, characterization and properties of various all-carbon molecules, the fullerene family (buckyballs), have been on the research forefront since the large scale production scheme developed by Krätschmer et al. Recently, Iijima and coworkers have reported TEM observations of hollow graphitic tubules of nanometer scale (buckytubes). In particular, the large scale buckytube synthesis method of Ebbesen and Ajayan has stirred considerable interest similar to that after the Krätschmer et al. discovery of large scale buckyball synthesis.We have synthesized gram-scale quantities of buckytubes and their derivatives based on an arc method similar to that of Ebbesen and Ajayan. The arc was formed between a 1” and a 1/2 “ diameter graphite rods under 100 torr atmosphere of helium at a current of 180-200 Amps and a voltage of 20-30 V. The cross section of the resulting build-up rod consists of a gray core, followed by a black ring and another gray shell.

Alterations of Descemet's Membrane in Interstitial Keratitis

Twenty corneas from patients with interstitial keratitis were examined by light microscopy and one of these by electron microscopy. Seventy percent of patients had either a positive serologic test for syphilis or a history of treatment for syphilis. Focal or diffuse multilaminar thickening of Descemet's membrane with secondary linear guttata was present in 88% of cases. Confluent linear cornea guttata formed retrocorneal hyaline ridges that clinically showed a central gray core surrounded by a translucent sheath. Microscopically, these ridges consisted of concentric laminations of newly formed Descemet's membrane. Some ridges hung into the anterior chamber as a bow-like strand or a spiderweb network. A possible pathogenetic sequence may include (1) inflammatory insult to a relatively young endothelium; (2) alteration of endothelial function to fibroblast-like activity; (3) the production of abnormal basement membrane and other collagenous material and formation of a new multilaminar Descemet's membrane; and (4) separation of some ridges from the multilaminar Descemet's membrane to hang into the anterior chamber as strands and networks.

Sedimentary Processes in Arctic Ocean: ABSTRACT

Two unusual Arctic Ocean sedimentary processes involve deposition of clay-size particles and deposition of glacial-marine erratics. The clay suite identified by X-ray diffraction in 50 cores from the Chukchi Rise and Alpha Cordillera consists mainly of illite with almost equal combined amounts of chlorite and kaolinite. Similar clays are present in atmospheric dust in permanent snow fields of northern Greenland. In addition, dust separated from snow samples of the Arctic ice pack contains these same clay minerals. This dust finds its way into leads during summer melting where it contributes an estimated 0.4 mm of sediment per 1,000 years. This is almost ½ of the total sedimentation rate for parts of the Arctic and up to 90% of the 2-µ size fraction sediment. Pebbles have been found in 36 cores. Few striations have been noted but ice rafting is a believable mechanism to explain pebbles in the central Arctic Ocean. Twenty-three cores contain erratics at more than 1 level and as many as 7 are present in 300-cm cores; 38% are sandstone, 29% carbonate, 15% metamorphic, and 18% chert or unidentified clasts. Distribution of the erratics shows no pattern that can be explained by known currents or events in time. Erratics are present in brown cores but no erratic has been found in gray cores. Turbidity structures characterized some of the gray cores. Probably, erratics were deposited randomly over most of the Arctic basin from melting glacial ice, but they appear to be less common in deeper parts of the ocean (Canada plain) where high sedimentation rates associated with turbidity flows mask their presence. End_of_Article - Last_Page 2497------------