Swift Formation Research Articles

Stratigraphy, sedimentology, and paleoclimatic proxies of the Upper Jurassic Morrison Formation of central Montana: Geology of the Intermountain West

Since the discovery of dinosaurs in the late 19th century, the Upper Jurassic Morrison Formation has received considerable scholarly attention. However, the formation in central Montana needed to be sufficiently investigated. Recent dinosaur excavations from exposed Morrison strata on the southern flank of Spindletop dome near the town of Grass Range, Montana, prompted a review of the formation’s geology, paleobotany, and paleoclimate. A review of historical stratigraphic measurements of the formation in Montana reveals a considerable variance in measured thicknesses. Stratigraphic measurements and regional log data indicate that the formation averages 71 m thick across central Montana. A new regional isopach map of the formation from well-log data illustrates a broad distributive fluvial system that migrated from the southwest toward the northeast. The formation is divided into two informal facies in the study area: lower and upper depositional facies. The lower depositional beds represent the mud-rich distal-most distributive fluvial facies that overlies the stranded muddy tidal flat of the Swift Formation. An increased sandstone:mudstone ratio and small isolated fluvial channel and crevasse splay beds indicate that the upper depositional beds represent the slow progression of the distributive fluvial system. However, a review of the regional field stratigraphy and well-log data did not provide a regional correlatable facies change to warrant subdividing the formation into members.The stratigraphic positions and climatic interpretations for lithologic, faunal, and floral paleoclimatic proxies are specified. The compilation of climate proxy data from central Montana demonstrates that the climate in this region was wetter than in southern parts of the Morrison foreland basin. The climatic proxies signify that the environmental conditions were variable during the Late Jurassic in central Montana, displaying changing temperatures with mesic and xeric intervals of unknown duration.

Unraveling the Reaction Mechanism of Russell's Viper Venom Factor X Activator: A Paradigm for the Reactivity of Zinc Metalloproteinases?

Snake venom metalloproteinases (SVMPs) are important drug targets against snakebite envenoming, the neglected tropical disease with the highest mortality worldwide. Here, we focus on Russell's viper (Daboia russelii), one of the "big four" snakes of the Indian subcontinent that, together, are responsible for ca. 50,000 fatalities annually. The "Russell's viper venom factor X activator" (RVV-X), a highly toxic metalloproteinase, activates the blood coagulation factor X (FX), leading to the prey's abnormal blood clotting and death. Given its tremendous public health impact, the WHO recognized an urgent need to develop efficient, heat-stable, and affordable-for-all small-molecule inhibitors, for which a deep understanding of the mechanisms of action of snake's principal toxins is fundamental. In this study, we determine the catalytic mechanism of RVV-X by using a density functional theory/molecular mechanics (DFT:MM) methodology to calculate its free energy profile. The results showed that the catalytic process takes place via two steps. The first step involves a nucleophilic attack by an in situ generated hydroxide ion on the substrate carbonyl, yielding an activation barrier of 17.7 kcal·mol-1, while the second step corresponds to protonation of the peptide nitrogen and peptide bond cleavage with an energy barrier of 23.1 kcal·mol-1. Our study shows a unique role played by Zn2+ in catalysis by lowering the pKa of the Zn2+-bound water molecule, enough to permit the swift formation of the hydroxide nucleophile through barrierless deprotonation by the formally much less basic Glu140. Without the Zn2+ cofactor, this step would be rate-limiting.

Phase formation in the Ni-enriched zone below the surface oxide on NiTi

Upon exposure to oxygen, NiTi forms a Ti-rich surface oxide layer, and mass balance requires that a Ni-enriched zone forms below the oxide. Both the surface oxide layer and the Ni-enriched zone are discussed to affect key properties of NiTi as material for minimally invasive medical application or for actuators, e.g., the release of Ni and the resistance to initiation and propagation of cracks when exploiting the shape memory effect/pseudoelasticity. However, owing to the small extension of the Ni-enriched zone of a few nanometers, little is known about its crystallinity, phase and evolution of composition.We study the formation of the surface layers during annealing at ∼500 °C for up to 10 min, as routinely applied for shape-setting. With an approach employing nano beam electron diffraction in a transmission electron microscope and an in-house software package for phase analysis it is shown for the first time that phase transformations in the Ni-enriched zone, specifically from NiTi to Ni4Ti3, occur already after 2 min of annealing, much earlier than documented in the literature. Furthermore, the phase transformation to the thermodynamically stable Ni3Ti in the Ni-enriched zone is shown to be mediated by metastable Ni4Ti3. In contrast to Ni4Ti3 precipitates in NiTi bulk, the morphology of the crystalline phases is granular. Considering the swift formation of Ni-rich phases below the surface oxide and the observation of a band-like diffraction contrast in the TEM images originating from crystal interfaces, a phase transformation mechanism in the Ni-enriched zone is suggested consisting of short range order rearrangements of atoms.

Immunoregulation of macrophages by dynamic ligand presentation via ligand\u2013cation coordination

Macrophages regulate host responses to implants through their dynamic adhesion, release, and activation. Herein, we employ bisphosphonate (BP)-coated gold nanoparticle template (BNP) to direct the swift and convertible formation of Mg2+-functional Mg2+-BP nanoparticle (NP) on the BP-AuNP surface via reversible Mg2+-BP coordination, thus producing (Mg2+-BP)-Au dimer (MgBNP). Ethylenediaminetetraacetic acid-based Mg2+ chelation facilitates the dissolution of Mg2+-BP NP, thus enabling the reversion of the MgBNP to the BNP. This convertible nanoassembly incorporating cell-adhesive Mg2+ moieties directs reversible attachment and detachment of macrophages by BP and EDTA, without physical scraping or trypsin that could damage cells. The swift formation of RGD ligand- and Mg2+-bifunctional RGD-Mg2+-BP NP that yields (RGD-Mg2+-BP)-Au dimer (RGDBNP) further stimulates the adhesion and pro-regenerative M2-type polarization of macrophages, both in vitro and in vivo, including rho-associated protein kinase. This swift and non-toxic dimer formation can include diverse bio-functional moieties to regulate host responses to implants.

Environmental and Social Change in Northeast Thailand during the Iron Age

The Iron Age of Mainland Southeast Asia began in the fifth centurybcand lasted for about a millennium. In coastal regions, the development of trade along the Maritime Silk Road led to the growth of port cities. In the interior, a fall in monsoon rains particularly affected the Mun River valley. This coincided with the construction of moats/reservoirs round Iron Age settlements from which water was channelled into wet rice fields, the production of iron ploughshares and sickles, population growth, burgeoning exchange and increased conflict. We explore the social impact of this agricultural revolution through applying statistical analyses to mortuary samples dating before and after the development of wet rice farming. These suggest that there was a swift formation of social elites represented by the wealth of mortuary offerings, followed by a decline. Two associated changes are identified. The first involved burying the dead in residential houses; the second considers the impact of an increasingly aquatic environment on health by examining demographic trends involving a doubling of infant mortality that concentrated on neonates. A comparison between this sequence and that seen in coastal ports suggests two interconnected instances of rapid pathways to social change responding to different social and environmental stressors.

Particle Liquid Water Content and Aerosol Acidity Acting as Indicators of Aerosol Activation Changes in Cloud Condensation Nuclei (CCN) during Pollution Eruption in Guangzhou of South China

ABSTRACT Atmospheric pollution has been found to modify the hygroscopicity of particles and the ability of aerosols to become cloud condensation nuclei (CCN). Aerosols and the bulk CCN were measured in urban Guangzhou during pollution periods in January 2016, and the particle liquid water content (PLWC) and aerosol acidity (Aero-pH) were calculated to examine their possible effects on aerosols’ CCN activation. The results demonstrate that the PLWC and Aero-pH likely play key roles in enhancing aerosol activation during the early stages of pollution episodes. The analysis of the calculated and the observed data shows that CCN, PLWC, Aero-pH and water-soluble inorganic matter (WSIM) are closely linked to each other, particularly at night, and Aero-pH and PLWC act as pre-occurring indicators of activated aerosols and aerosol activity, respectively, during the rapid onset of pollution. In theory, the feedback between chemical reactions, aerosol acidity and particle water content accounts for the changes in aerosol activation accompanying particle accumulation and aging. Our research provides insights into the swift formation of particle pollution characterized by secondary aerosols and suggests a possible approach to tracking or characterizing its effects on the activation of aerosols into CCN without requiring CCN or aerosol number measurements.

Dynamic membrane for micro-particle removal in wastewater treatment: Performance and influencing factors

Dynamic membranes (DMs) have been of great interest in recent years because they can reduce energy consumption and costs during wastewater treatment. Dynamic membranes are a promising technology for the removal of low-density, non-degradable micro-particles, such as plastics, which are an increasingly prevalent wastewater contaminant. These micro-particles are not easily removed via conventional sedimentation and result in increased operation and maintenance costs in downstream unit processes. In this study, DMs were formed on a 90 μm supporting mesh through filtration of a synthetic wastewater. The impact of influent flux (solid flux) and influent particle concentration on DM performance was investigated. The effluent turbidity was reduced to <1 NTU after 20 mins of filtration, verifying the effective removal of micro-particles by the DM. Transmembrane pressure (TMP) and total filtration resistance increased linearly with filtration time, and were highly correlated (R2 > 0.998). TMP ranged from 80 to 180 mm of water head, and total filtration resistance ranged from 2.89 × 10−9 m−1 to 6.52 × 10−9 m−1 during DM filtration. In general, an increase in influent flux and influent particle concentration corresponds with increasing TMP and filtration resistance, as well as a rapid reduction in effluent turbidity due to swift formation of a DM on the supporting mesh.

An asteroid (Echinodermata) faunule from the Oxfordian Swift Formation (Upper Jurassic) of Montana

AbstractA new Late Jurassic (Oxfordian) asteroid (Echinodermata) faunule from the Swift Formation of Montana includes representatives of four genera including the new genus and speciesAtalopegaster gundersoni(Stichasteridae),Eokainastersp. indet. (Astropectinidae), an indeterminate probable member of the Goniasteridae, and a species indeterminate beyond the class level. Because of weathering at the outcrop, preservation is poor.Although representing an unusual depositional occurrence, overall faunule composition appears comparable to that found in a similar modern environment. The faunule is comparable in age and regional location to earlier Jurassic asteroid discoveries, suggesting wide distribution during a geologically brief time interval of favorable conditions. Asteroids are only rarely reported from the Mesozoic of the North American continental interior, and co-occurrence of multiple fossil taxa is unusual on a global basis.

Bubble dynamics and heat transfer for pool boiling on hydrophilic, superhydrophobic and biphilic surfaces

This paper proposes a detailed analysis of bubble dynamics to describe pool boiling heat transfer in extreme wetting scenarios (superhydrophobic vs hydrophilic). A mechanistic approach, based on extensive post-processing allows quantifying the relative advantage of the superhydrophobic surfaces to endorse the onset of boiling at very low superheats (1-2K) vs their worse heat transfer performance associated to the swift formation of an insulating vapour film. Based on this analysis, a simple biphilic surface is created. The results suggest that for high heat fluxes, bubble dynamics is dominated by the emission of very small bubbles, which seems to affect the interaction mechanisms, precluding the emission of the large bubbles from the surface, thus compromising the good performance of the biphilic surfaces.

Origin of Efficient Catalytic Combustion of Methane over Co3O4(110): Active Low-Coordination Lattice Oxygen and Cooperation of Multiple Active Sites

A complete catalytic cycle for methane combustion on the Co3O4(110) surface was investigated and compared with that on the Co3O4(100) surface on the basis of first-principles calculations. It is found that the 2-fold coordinated lattice oxygen (O2c) would be of vital importance for methane combustion over Co3O4 surfaces, especially for the first two C–H bond activations and the C–O bond coupling. It could explain the reason the Co3O4(110) surface significantly outperforms the Co3O4(100) surface without exposed O2c for methane combustion. More importantly, it is found that the cooperation of homogeneous multiple sites for multiple elementary steps would be indispensable. It not only facilitates the hydrogen transfer between different sites for the swift formation of H2O to effectively avoid the passivation of the active low-coordinated O2c site but also stabilizes surface intermediates during the methane oxidation, optimizing the reaction channel. An understanding of this cooperation of multiple active sites not only might be beneficial in developing improved catalysts for methane combustion but also might shed light on one advantage of heterogeneous catalysts with multiple sites in comparison to single-site catalysts for catalytic activity.

Observed three-dimensional structure of a cold eddy in the southwestern South China Sea

[1] The dynamic structure of an ocean eddy in the eddy-abundant South China Sea has rarely been captured by measurements and has seldom been discussed in the literature. In the present study, in situ current and hydrographic measurements from a weeklong cruise and concurrent satellite altimeter observations were utilized to examine the three-dimensional structure and physical properties of a cold eddy in the southwestern South China Sea. The underlying forcing mechanism for the formation of this cyclonic cold eddy was found to be tightly associated with the recirculation in a coastal baroclinic jet that had separated off the Vietnamese coast. The eddy was significantly influenced by a coexisting, anticyclonic warm eddy in the separated jet. With relatively steady intensity and radius, the cold eddy endured for two weeks after its swift formation in late August and prior to its quick dissipation in mid-September. This cold eddy was horizontally and vertically heterogeneous. Asymmetric currents with much stronger magnitude were found on its southeastern flank, next to the warm eddy, where a front in the pycnocline was responsible for the sharp decrease in the cold eddy's intensity in the water below. The distributions of temperature, vorticity, and vertical velocity in the cold eddy were spatially asymmetric and not overlapping. The intensity of the cold eddy gradually decreased with the depth and the eddy extended downward for more than 250 m with a vertically tilted central axis. The upward velocities around the center of the eddy and the downward velocities to the southwest and to the east of the center jointly formed the upward domes of isotherms and isohalines in the central part of the cold eddy.

Generation of superoxide radicals by copper–glutathione complexes: Redox-consequences associated with their interaction with reduced glutathione

The interaction between Cu 2+ ions and GSH molecules leads to the swift formation of the physiologically occurring Cu(I)–[GSH] 2 complex. Recently, we reported that this complex is able to reduce molecular oxygen into superoxide in a reversible reaction. In the present study, by means of fluorescence, luminescence, EPR and NMR techniques, we investigated the superoxide-generating capacity of the Cu(I)–[GSH] 2 complex, demonstrated the occurrence and characterized the chemical nature of the oxidized complex which is formed upon removing of superoxide radicals from the former reaction, and addressed some of the redox consequences associated with the interaction between the Cu(I)–[GSH] 2 complex, its oxidized complex form, and an in-excess of GSH molecules. The interaction between Cu(I)–[GSH] 2 and added GSH molecules led to an substantial exacerbation of the ability of the former to generate superoxide anions. Removal of superoxide from a solution containing the Cu(I)–[GSH] 2 complex, by addition of Tempol, led to the formation and accumulation of Cu(II)–GSSG. Interaction between the latter complex and GSH molecules permitted the re-generation of the Cu(I)–[GSH] 2 complex and led to a concomitant recovery of its superoxide-generating capacity. Some of the potential redox and biological implications arising from these interactions are discussed.

Very first impressions.

First impressions of people's personalities are often formed by using the visual appearance of their faces. Defining how quickly these impressions can be formed has critical implications for understanding social interactions and for determining the visual properties used to shape them. To study impression formation independent of emotional cues, threat judgments were made on faces with a neutral expression. Consequently, participants' judgments pertained to the personality rather than to a certain temporary emotional state (e.g., anger). The results demonstrate that consistent first impressions can be formed very quickly, based on whatever information is available within the first 39 ms. First impressions were less consistent under these conditions when the judgments were about intelligence, suggesting that survival-related traits are judged more quickly. The authors propose that low spatial frequencies mediate this swift formation of threat judgments and provide evidence that supports this hypothesis.

Easier done than undone: Asymmetry in the malleability of implicit preferences.

Dual-process models imply that automatic attitudes should be less flexible than their self-reported counterparts; the relevant empirical record, however, is mixed. To advance the debate, the authors conducted 4 experiments investigating how readily automatic preferences for one imagined social group over another could be induced or reversed. Experiments 1 and 2 revealed that automatic preferences, like self-reported ones, could be readily induced by both abstract supposition and concrete learning. In contrast, Experiments 3 and 4 revealed that newly formed automatic preferences, unlike self-reported ones, could not be readily reversed by either abstract supposition or concrete learning. Thus, the relative inflexibility of implicit attitudes appears to entail, not immunity to sophisticated cognition, nor resistance to swift formation, but insensitivity to modification once formed.

Tellurated Schiff Bases Formed from {2‐[(4‐Methoxyphenyl)telluro]ethyl}amine and Bis(2‐aminoethyl) Telluride with o‐Hydroxyacetophenone: Synthesis and Complexation Reactions with HgII, PdII and RuII − Crystal Structures of the Ligands, [Ru(p‐cymene)Cl{H2NCH2CH2TeC6H4‐4‐OCH3}]Cl·H2O and [RuCl{4‐MeOC6H4TeCH2CH2NHCH(CH3)C6H4‐2‐O−}

Abstract{2‐[(4‐Methoxyphenyl)telluro]ethyl}amine and bis(2‐aminoethyl) telluride on treatment with o‐hydroxyacetophenone gave the Schiff bases 4‐MeOC6H4TeCH2CH2N=C(CH3)C6H4‐2‐OH (L1) and 2‐HOC6H4(CH3)C=NCH2CH2TeCH2CH2N=C(CH3)C6H4‐2‐OH (L3), respectively. The reduction of L1 and L3 with NaBH4 resulted in 4‐MeOC6H4TeCH2CH2NHCH(CH3)C6H4‐2‐OH (L2) and 2‐HOC6H4(CH3)CHNHCH2CH2TeCH2CH2NHCH(CH3)C6H4‐2‐OH (L4), respectively, which have 1 or 2 chiral centers. The 1H and 13C NMR spectra of L1 to L4 were found to be characteristic. Treatment of L1 with [Ru(p‐cymene)Cl2]2 resulted in [Ru(p‐cymene)(4‐MeOC6H4TeCH2CH2NH2)Cl]Cl·H2O (1) whereas in the reaction of L2 with [Ru(p‐cymene)Cl2]2, the p‐cymene ligand is lost resulting in [RuCl(L2‐H)] (4). The reactions of L1, L3 and L4 with HgBr2 resulted in complexes of the type [HgBr2·(L)2] while Na2PdCl4 reacted with L1 to give [PdCl(L1‐H)]. The solid‐state structures of L1, L3, 1 and 4 were determined by single‐crystal X‐ray diffraction studies. The very swift formation of the tellurated amine from a tellurated Schiff base (L1) by hydrolysis has been observed for the first time and has resulted in 1. The Ru−N and Ru−Te bond lengths in 1 are 2.142(3) and 2.6371 (4) Å, respectively. The replacement of the p‐cymene ligand with a hybrid organotellurium ligand (L2‐H), resulting in 4, is also a first example of its kind. The Ru center in 4 has a square‐planar geometry, with the Ru−N, Ru−Te, Ru−O and Ru−Cl bond lengths being 2.041(6), 2.4983(8), 2.058(5) and 2.308(2) Å, respectively. In the crystals of 4 there are secondary intermolecular Te···Cl interactions and intermolecular N−H···O hydrogen bonds. This is the first example in which coordinated Te in a complex is engaged in two intermolecular secondary interactions. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2004)

Absolute comparison of simulated and experimental protein-folding dynamics.

Protein folding is difficult to simulate with classical molecular dynamics. Secondary structure motifs such as alpha-helices and beta-hairpins can form in 0.1-10 micros (ref. 1), whereas small proteins have been shown to fold completely in tens of microseconds. The longest folding simulation to date is a single 1- micro s simulation of the villin headpiece; however, such single runs may miss many features of the folding process as it is a heterogeneous reaction involving an ensemble of transition states. Here, we have used a distributed computing implementation to produce tens of thousands of 5-20-ns trajectories (700 micros) to simulate mutants of the designed mini-protein BBA5. The fast relaxation dynamics these predict were compared with the results of laser temperature-jump experiments. Our computational predictions are in excellent agreement with the experimentally determined mean folding times and equilibrium constants. The rapid folding of BBA5 is due to the swift formation of secondary structure. The convergence of experimentally and computationally accessible timescales will allow the comparison of absolute quantities characterizing in vitro and in silico (computed) protein folding.

SiC p/Ti6Al4V functionally graded materials produced by laser melt injection

With a well-controlled laser melt injection (LMI) process, for the first time the feasibility is demonstrated to produce SiC particles (SiC p) reinforced Ti6Al4V functionally graded materials (FGMs). SiC p are injected just behind the laser beam into the extended part of the laser melt pool that is formed at relatively high beam scanning velocities. The process allows for the minimization of the decomposition reaction between SiC p and Ti6Al4V melt, and also leads to FGMs of SiC p/Ti6Al4V instead of a homogeneous composite layer on Ti6Al4V substrates. An injection model is designed based on the temperature/viscosity field of the laser pool for a deeper understanding of the mechanism of formation of the FGMs with LMI. The model is based on finite element calculations of the temperature field in the melt pool, physical considerations of the LMI process and it is supported by experimental observations. Three types of reaction layers are observed around SiC p, namely a thin monocrystalline TiC layer, a cellular polycrystalline TiC layer and a thick mixed layer of TiC with Ti 5Si 3. Among them, only the monocrystalline TiC layer exhibits particular orientation relationships (ORs) to the SiC p lattice, i.e. (111) TiC∥(0001) SiC and 〈110〉 TiC ∥〈1 1 ̄ 00〉 SiC or (111 ) TiC ∥(10 1 ̄ 2 ) SiC and 〈1 1 ̄ 0〉 TiC ∥〈1 2 ̄ 10〉 SiC . These two kinds of TiC reaction layers act as a barrier against the interfacial reaction and its swift formation during rapid cooling hinders the dissolution of SiC p in the Ti-melt.

Combined tide and wave influence on sedimentation patterns in the Upper Jurassic Swift Formation, south‐eastern Alberta

In south‐eastern Alberta, the Oxfordian Swift Formation comprises two unconformity‐bounded sequences. Sequence 1 consists of the shale member. It unconformably overlies Bathonian calcareous shale of the Rierdon Formation and consists dominantly of shale with uncommon hum‐ mocky cross‐stratified siltstone. The shale member comprises up to four parasequences that show a subtle upward‐fining stacking pattern, suggesting overall deepening in a storm‐dominated fully marine basin. Deposition of the shale member was terminated by a fall in relative sea‐level, which in turn initiated sequence 2. During lowstand, a network of north‐east‐ to south‐west‐trending meandering channels incised the top of sequence 1. Despite the preserved morphology of these channels, observations in core suggest that lowstand deposits are absent. These strata were most likely thoroughly reworked by ravinement processes associated with the ensuing transgression and are recorded only by a thin chert pebble lag. Also associated with transgression were significant changes in the physical and ecological conditions in the local Swift basin. These changes were related to modifications in basin configuration and the development of a low‐energy strait, which probably formed as a result of uplift of the Sweetgrass Arch. Within this newly configured basin, brackish‐water conditions prevailed, and sedimentation was dominated by suspension deposition of mud. Bed‐load sediment, composed mostly of very fine and fine sand, made up only a small part of the total sediment flux into the area and was transported principally by low‐energy combined flows with variable‐speed microtidal currents and a low‐energy oscillatory component related to storm waves. Sand was generally deposited in the form of small, discontinuous sand ridges that developed locally throughout the study area – it is these features that form the principal hydrocarbon reservoir bodies in the Swift Formation in the study area. After initiation, ridges built upwards and migrated laterally in response to transport and preferential local deposition of bed‐load sediment. Although common near the unconformity along the top of sequence 1, sand ridges also occur at several higher stratigraphic levels in sequence 2. These latter ridges, however, are not associated with regionally correlatable discontinuities but, instead, were initiated by local bed irregularities, possibly related to breaking internal waves, and were supplied with new sediment transported into the study area. The origin of these sand ridges is therefore not related to changes in relative sea‐level but, instead, to intrabasinal processes in a low‐energy strait.

Functionally Graded Materials produced with High Power Lasers

AbstractWith a well-controlled laser melt injection (LMI) process, for the first time the feasibility is demonstrated to produce SiC particles (SiCp) reinforced Ti6Al4V functionally graded materials (FGMs). SiCp are injected just behind the laser beam into the extended part of the laser melt pool that is formed at relatively high beam scanning velocities. The process allows for the minimization of the decomposition reaction between SiCp and Ti6Al4V melt, and also leads to FGMs of SiCp/Ti6Al4V instead of a homogeneous composite layer on Ti6Al4V substrates. An injection model is designed based on the temperature/viscosity field of the laser pool for a deeper understanding the mechanism of formation of the FGMs with LMI. The model is based on finite element calculations of the temperature field in the melt pool, physical considerations of the LMI process and it is supported by experimental observations. Three types of reaction layers are observed around SiCp, namely a thin monocrystalline TiC layer, a cellular polycrystalline TiC layer and a thick mixed layer of TiC with Ti5Si3. Among them, only the monocrystalline TiC layer exhibits particular orientation relationships to the SiCp lattice, i.e. (111)TiC//(0001)SiC and &lt;110&gt;TiC//&lt;1100&gt;SiC or (111)TiC // (1012)SiC and &lt;110&gt;TiC//&lt;1210&gt;SiC. These two kinds of TiC reaction layers act as a barrier against the interfacial reaction and its swift formation during rapid cooling hinders the dissolution of SiCp in the Ti-melt.

The Course of the Copper-Catalyzed Oxidative Polymerization of 2,6-Dimethylphenol. Analysis of Oligomeric Phenols during the Coupling Reaction

The course of the copper-catalyzed oxidative coupling of 2,6-dimethylphenol (DMP) has been studied by HPLC-analysis of reaction mixtures which had started with either DMP itself, or with its C−O coupled dimer, 4-(2‘,6‘-dimethylphenoxy)-2,6-dimethylphenol, under both aerobic and anaerobic conditions. These measurements have provided information on how the actual phenol coupling step takes place and how the polymerization reaction proceeds. In reactions started with the monomer, no or at most very small amounts of oligomers of DMP are detected, apart from a precipitate of polymeric material in the aerobic experiments. Reactions started with the dimer only result in swift formation of significant amounts of monomer in addition to oligomers. This difference in behavior can be ascribed to the higher reactivity of oligomeric phenols compared to the monomer. The fact that monomer phenol is formed from dimer phenol is strong evidence for a reaction pathway in which a quinone ketal is formed by C−O coupling of two phenolic moieties. It is believed that as long as this quinone remains coordinated to the copper, it can decompose by (probably heterolytic) fission of one of the ether bonds to generate two (new) species, de facto resulting in redistribution of the oligomers. Once the quinone dissociates from the copper catalyst, a rearrangement may occur to afford the C−O coupled phenol. Methylated phenols (anisoles) do not take part in either redistribution or rearrangement reactions, since a quinone ketal can only be formed from species that can be deprotonated, i.e., from phenols.