Tiny Grains Research Articles

Dispersion of functional tetraphenylporphyrin-ligated metal into ultra-thin flexible acrylate films: 1. Preparation of thin films

As functional metal complexes, copper phthalocyanine (CuPc) and Cobalt (II) meso-tetraphenylporphyrin (CoTPP) were chosen to prepare metal complex/polymer hybrid thin films which were prepared by metal complex sublimation and reactive monomer evaporation onto the glass substrate in the bell jar reactor in vacuum conditions. The polarized transmission micrograph images show that the film deposited at 80 °C contains uniformly dispersed tiny grains and the film deposited at 30 °C is amorphous and homogeneous. As the deposition rate increases, the crystalline clusters were found and were dispersed uniformly. Those crystalline clusters are not to be developed by recrystallization process. Deposited metal complex/acrylate hybrid thin films were in situ photopolymerized. The kinetics of photopolymerization was investigated by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). The thickness of the films was about 200 nm. The reactive monomer acts as a solvent to avoid the recrystallization of metal complexes and to have two-compositional continuous phase. The percent of metal complex can be adjusted up to 60% by controlling the metal complex sublimation rate. A good achievement in the uniformity and continuity of the film matrix has been made and the recrystallization of metal complex in the hybrid films has not been observed.

Looking for the Bishop

Looking For The Bishop Robert Vivian (bio) Looking for the bishop, I thought I almost saw him in the alpenglow of a harvest moon, in a hedge bursting with buds no bigger than a child's fingerprints, in a neighbor's plastic pinwheel spinning clockwise in the wind. I thought I saw him in tiny grains of hope, in a woman brushing the hair from a sullen boy's face, in the balm of sudden healing from shredded clouds racing from the stars. The bishop is will-of-a-wisp, a puff of breeze, more hopeful in his flowing red gown than any figure I know. He walks by my window on his daily sojourns, emerging from the hidden chambers of peace and clarity to sustain me in surprising ways, a figure so out of character with this part of central Michigan as to be laughable, lovable and mysterious all at once. His hood shrouds his head like an oddly draped flower, announcing his presence before you notice the thin, small body sheathed in flowing folds. I have never seen his hair. The bishop isn't American or white but eastern Indian, with a triton beard and long delicate fingers that taper off like the hands in a Byzantine painting. He is doubly, triply strange for all that, a man visiting from another world yet a part of this one, more vivid because of this. No one can quite tell me how he has come to be here, but would any reason make his presence less mysterious? I see him walking everywhere in this small town, taking the night air upon an evening, the hems of his robe swirling in gentle eddies around his slippered feet. A part of me wants to follow him or fit inside one of his pockets like a bright polished key. I would take up residence in his flowering hood, become his watchtower, his bird's eye view, or hunker down where the clean folds of his robe billow out into forgetfulness, the ripple of a fresh, gentle wind. I want nothing more than to walk the way he does, watchful and alert, more incongruent here than a rare plumaged bird whose colors remain unbesmirched by the drabness of winter. He [End Page 132] is the cardinal bird that could make all the difference, burning his sacred red feathers in a slow fire that will never burn out. He walks by my house sometimes, and each time my heart gets a little lighter, clearer, opening a tiny door that feels like a frail hope ascending until I realize I am supposed to notice him, take his example to heart, follow his lead, and become pure, vivid color in a land of black and white. What do I know about him? Nothing I don't see in his thoughtful gait, the alert owl look in his dark brown eyes. Nothing he does not already show me though he does not know it, a simple long walk, the veil of a consciousness he gives me each time I see him. I need his walk as a covert response to things that make me uneasy, to the vague malaise dripping like a bad faucet at the heart of town, the malice of revved-up pickup trucks, gun racks; the bishop shows me how to live here in subtle, surprising ways, how to walk in a small town and the kind of grace I ached for without realizing it, his long red robe and careful steps over patches of ice. You could go a long time without an example like the bishop, twenty, thirty years, a whole life; you could ignore people or signs like him, not notice them, not take them into your heart or let them peel it open layer by precious layer; you could choose to close the curtains or drapes, lock the door and turn up the tv; but if the bishop should ever walk by your window or down your neighborhood street, you could have the opportunity to sense the hushed lightness trailing behind him in the wake of his passage, the seed blossoms of his robes riding the air to find a place...

Petrographic/geochemical studies of primary and alteration–weathering minerals in garnetiferous ultramafic xenoliths–basanite, Tartous Province, NW Syria

Kimberlitic–pyropic peridotite–xenolites, probably of Jurassic–Cretaceous age, were found mixed with a younger Upper Tertiary basanitic diabase, as flow texture of plagioclase laths and ilmenite rods around those xenoliths indicated. Mafic–ultramafic rocks were crushed, sheared, and cropped along a creek about 15–18 km NE of the town of Dreikeesh, NW Syria. 40K– 40Ar isotopic dating of a pure fresh black cpx sample, collected from the peridotite xenoliths, yielded an age of about 70 Ma. This age is concurrent to the time when Africa, Eurasia, and America were part of the super continent Pangaea. It also suggests that kimberlite–pyropic peridotitic rocks were located within a cratonic pipe prior to their 2000-km eastward journey (starting from the Mid-Atlantic Rift). Sampled outcrops were located within a ring of about 40 km diameter, considered to be a dome consisting of one or more clusters of kimberlitic pipes. The dome structure, mostly covered with Upper Jurassic–Cretaceous carbonate beds, was tilted westward, and rifted and sheared along its eastern edge. Tilting and crushing were accomplished after the opening of the Red Sea in the Miocene, and the counterclockwise movements of the Arabian plate, which folded the carbonate beds to form the N–S-trending Alawite mountain range along the Syrian coast. Olivine, cpx, and pyrope were the major phases in peridotite. Pyrope, including its Cr–Ni-contents, was found to be the best indicator to decipher the temperature–pressure ( T– P) conditions for the system. The inferred temperature was found to be about 1460 °C, at a pressure of 62 kb (around 207 km-depth). Petrographic studies revealed many zoned, resorbed, octahedral and non-metasomatized tiny grains, associated with partly to wholly metasomatized and iddingsitized olivines.

Characterization of Fly Ash-Based Glass-Ceramic Samples Quenched in Air Followed by Crystallization Stage

The effect of quenching in air on the microstructure and the mechanical properties of the fly ash-based glass-ceramic samples were investigated. SEM observations clearly revealed that the presence of homogeneously dispersed tiny crystallites and crystalline grain size which increased with holding time at the nucleation stage. Furthermore, extensive cracks on the surface of the glass-ceramics were present due to quenching in air. On the other hand, XRD analyses clearly showed that the only crystalline phase that observed was diopside (Ca(Mg, Al)(Si, Al) 2O6). The result of the Vickers microhardness tests indicated that the hardness values of the fly ash-based glass-ceramics decreased with increasing holding time at the nucleation temperature. Resistance to wear decreased with the increase in crystalline grain size, similar to hardness values.

Age of the Ballachulish and Glencoe Igneous Complexes (Scottish Highlands), and paragenesis of zircon, monazite and baddeleyite in the Ballachulish Aureole

U–Pb zircon ages are presented for the Ballachulish Igneous Complex ( 207 Pb– 206 Pb age 427 ± 1 Ma; 206 Pb– 238 U age 423 ± 0.3 Ma) and Glencoe Volcanic Complex ( 207 Pb– 206 Pb age 406 ± 6 Ma) of the Scottish Highlands. These ages are significantly more precise than pre-existing age constraints, and discriminate a previously unresolved age difference of c . 20 Ma between the two complexes. This difference in age provides an explanation for the c . 10 km difference in crustal level between the two magmatic events, and constrains exhumation rates for the Argyll region to be on average c . 0.4 km Ma −1 over the period c . 425–405 Ma. With improved age constraints on the Ballachulish Igneous Complex in place, the associated metamorphic aureole is used as a type locality to investigate the metamorphic behaviour of the U-bearing accessory minerals baddeleyite, zircon and monazite. Baddeleyite formed in impure dolomites by the reaction of detrital zircon with dolomite and gives the same U–Pb age as the intrusive complex, consistent with its contact metamorphic origin. Detrital zircon appears to be inert throughout much of the metamorphic aureole, with contact metamorphic zircon growth being restricted to migmatite-grade rocks. A possible exception is the development of enigmatic, very narrow overgrowths at temperatures between c . 500 and 600 °C. Monazite exhibits a variety of textures in lower-grade parts of the aureole (<550 °C), but occurs as distinctive clusters and trails of tiny ovoid grains at temperatures above about 560–600 °C. Monazite thus appears sensitive to metamorphism at lower temperatures than zircon and may therefore be a better target for metamorphic age measurements in rocks that reach mid-amphibolite facies but do not experience partial melting.

Electrodeposition, Structure and Corrosion Resistance of Nanocrystalline Ni‐W Alloy

AbstractNi—W alloy was electrodeposited from the electrolyte solution containing sodium tungstate, nickel sulfate and ammonium citrate. The electrodeposition, heat treatment, structure, surface morphology and corrosion resistance in w=0.03 NaCl solution, of Ni—W alloys were studied by means of DSC, XRD, SEM and electrochemical techniques. The results showed that the obtained Ni—W alloy electrodeposit with W weight content (ww=0.471) was presented in more typical nanocrystalline. After heat treatment at 400 C for 1 h, the phase structure of the deposits was not obviously changed whereas the agglomerate for the reunion of tiny grains on deposit surface caused the granule in a more smooth morphology, the microhardness was slightly increased and the corrosion resistance was enhanced.

Photochemical concepts on the origin of biomolecular asymmetry.

Biopolymers like DNA and proteins are strongly selective towards the chirality of their monomer units. The use of homochiral monomers is regarded as essential for the construction and function of biopolymers; the emergence of the molecular asymmetry is therefore considered as a fundamental step in Chemical Evolution. This work focuses on physicochemical mechanisms for the origin of biomolecular asymmetry. Very recently two groups, one from Allamandola at NASA Ames and the other from our Inter-European team, demonstrated simultaneously the spontaneous photoformation of a variety of chiral amino acid structures under simulated interstellar conditions. Since both groups used unpolarized light for the photoreaction the obtained amino acids turned out racemic as expected. The obtained experimental data support the assumption that tiny ice grains can furthermore play host to important asymmetric reactions when irradiated by interstellar circularly polarized ultraviolet light. It is possible that such ice grains could have become incorporated into the early cloud that formed our Solar System and ended up on Earth, assisting life to start. Several lines of evidence suggest that some of the building blocks of life were delivered to the primitive Earth via (micro-) meteoroids and/or comets. These results suggest that asymmetric interstellar photochemistry may have played a significant part in supplying Earth with some of the enantioenriched organic materials needed to trigger life. The search for the origin of biomolecular homochirality leads to a strong interest in the fields of asymmetric photochemistry with special emphasis on absolute asymmetric synthesis. We outline here the theoretical background on asymmetric interstellar ice photochemistry, summarize recent concepts and advances in the field, and discuss briefly its implications. The obtained data are crucial for the design of the enantioselective COSAC GC-MS experiment onboard the ROSETTA spacecraft to a comet to be launched in the very near future.

Spatial Separation of the 3.29 Micron Emission Feature and Associated 2 Micron Continuum in NGC 7023

We present a new 0>9 resolution 3.29 lm narrowband image of the reflection nebula NGC 7023. We find that the 3.29 lm infrared emission feature (IEF) in NGC 7023 is brightest in narrow filaments northwest of the illuminating star HD 200775. These filaments have been previously seen in images of extended red emission, K 0 , near-infrared H2 emission lines, the 6.2 and 11.3 lm IEFs, and HCO + . We also detect 3.29 lm IEF emission faintly but distinctly between the filaments and the star. The 3.29 lm IEF image is in marked contrast to narrowband continuum images at 2.09, 2.14, and 2.18 lm, which show an extended emission peak midway between the filaments and the star, and much fainter emission near the filaments. The [2.18 lm]� [3.29 lm] color shows a wide variation, ranging from colors of 3.4–3.6 mag at the 2 lm continuum emission peak to a color of 5.5 mag in the 3.29 lm IEF emission filaments. A color of 5.5 mag is 1 mag higher than any published value in reflection nebulae. We observe [2.18 lm]� [3.29 lm] to increase smoothly with increasing projected distance from the illuminating star in NGC 7023, up until the brightest 3.29 l mI EF filament, suggesting that the main difference between the spatial distributions of the 2 lm continuum and the 3.29 lm IEF emission is related to the incident stellar flux. The 3.29 lm IEF is widely attributed to an aromatic C”H stretch, while the 2 lm continuum emission may be due to transient heating of tiny grains, fluorescence of aromatic molecules, or photoluminescence of larger grains. Our results suggest that the 3.29 lm IEF carriers are likely to be distinct from but related to the 2 lm continuum emitters. Our findings also imply that in NGC 7023 the 2 lm continuum emitters are mainly associated with H i, while the 3.29 lm IEF carriers are primarily found in warm H2, but that both the 2 lm continuum emitters and the 3.29 lm IEF carriers can survive in H i or H2. Subject headings: dust, extinction — infrared: ISM — ISM: individual (NGC 7023) — ISM: lines and bands — ISM: molecules — reflection nebulae

Hillock Formation of SnO2 Thin Films Prepared by Metal-Organic Chemical Vapor Deposition

SnO2 thin films were deposited at 375°C on an alumina substrate by metal-organic chemical vapor deposition (MOCVD). The number of hillocks on the thin-film surface increased with air annealing. The oxygen content and binding energy during air annealing at 500°C came close to those of stoichiometric SnO2. The cauliflower-like hillocks observed seem to be the result of the continuous migration of tiny grains to release the stress of an expanded grain.

TEM observations of Gd 2Zr 2O 7 films formed by the ion-beam-assisted deposition method on an Ni-based alloy

Gd 2Zr 2O 7 films were formed by the ion-beam-assisted deposition (IBAD) method on an Ni-based alloy. Cross-sectional and plan-view specimens of the films were prepared for transmission electron microscopy investigation and microstructural characterization. The thicknesses of the Gd 2Zr 2O 7 films were less than 1.3 μm. During initial formation of the films, tiny grains nucleated close to the Ni-based alloy, followed by gradual formation of a columnar texture composed of fine 〈0 0 1〉 aligned grains perpendicular to the Ni-based alloy interface. However, dark-field image taken under g → =(4 4 0) indicated that the in-plane mosaic spread of the columnar texture did not improve as much as the [0 0 1] tilt angle. However, examination of the Gd 2Zr 2O 7 film surfaces revealed that the interfaces between columns were not well defined. Furthermore, a CeO 2 film deposited on a 1.3 μm thick Gd 2Zr 2O 7 film by the pulsed laser deposition (PLD) method contained less in-plane mosaic spread than the Gd 2Zr 2O 7 film alone. PLD-CeO 2/IBAD-Gd 2Zr 2O 7 films are therefore considered promising candidates for use as buffer layers in superconductor tapes.

Innfluence of Thermal Treatment on Surface Morphology of Tin Dioxide Thin Films

Tin dioxide (<TEX>$SnO _2$</TEX>) thin films were deposited at <TEX>$375^{\circ}C$</TEX> on alumina substrate by metal-organic chemical vapor deposition. A few hillocks like a cauliflower were observed and the number of hillock on thin film surface increased with annealing temperature in air atmosphere. The oxygen content and the binding energy during air annealing at<TEX>$ 500^{\circ}C$</TEX> came to close the stoichiometric <TEX>$SnO_2$</TEX>. The cauliflower hillocks seem to be the result of the continuous migration of the tiny grains to release the stress of an expanded grain. Sensitivity of CO gas depended on annealing temperature and increased with increasing annealing temperature.

Ankerite carbonatite from Swartbooisdrif, Namibia: the first evidence for magmatic ferrocarbonatite

Although general accounts of carbonatites usually envisage Ca–Mg carbonate melts evolving by fractional crystallisation to Fe-rich residua, there is longstanding concern that ferrocarbonatites may actually be products of hydrothermal rather than magmatic processes. All previously published examples of ankerite- and/or siderite-carbonatites fail to show one or more of the isotopic criteria (all determined on the same sample) thought to be diagnostic of crystallised magmatic carbonate liquids. Ferrocarbonatite dykes cut Archaean-Proterozoic basement at Swartbooisdrif, adjacent to the NW Namibia-Angola border. Their age is uncertain but probably ~1,100 Ma and their associated fenites are rich in sodalite. Where unaffected by subsequent recrystallisation, their petrographic textures resemble those of silicate layered intrusions; ankerite, magnetite and occasionally calcite are cumulus phases, joined by trace amounts of intercumulus pyrochlore. Ankerite is zoned, from Ca(Mg, Fe2+)(CO3)2 cores towards ferroan dolomite rims. Calcite contains ~1.7% SrO, plus abundant, tiny exsolved strontianite grains. Magnetite is close to pure Fe3O4. Pyrochlore has fine-scale euhedral oscillatory zoning and light-REE-enriched rims. ICP-MS analysis of magnetite and pyrochlore from the carbonatite allows calculation of their modal amounts from mass-balance considerations. Sodalite from the fenite is REE poor. Geothermometry, using either the calcite-dolomite solvus or oxygen isotope fractionation between calcite and magnetite, gives temperatures in the range 420–460 °C. Initial Sr, Nd and Pb isotopic ratios of the ferrocarbonatites (87Sr/86Sr=0.7033; eNd=0.2–1.0; 206Pb/204Pb=16.37; 207Pb/204Pb=15.42; 208Pb/204Pb=36.01) are appropriate for an ~1,100-Ma magmatic carbonatite. Likewise, carbonate δ18O=8.0 and δ13C=–7.36 indicate little or no subsequent shift from magmatic values. It appears that dense ankerite and magnetite dominated crystal accumulation from a melt saturated in these phases, plus calcite and pyrochlore, with prior fractionation of a silicate mineral and apatite. The resulting ferrocarbonatite lacks a silicate mineral (excluding fenite xenocrysts) and apatite. It has unusually low (basalt-like) REE abundances and (La/Lu)n, and low concentrations of Ba, Rb, U, Th, Nb, Ta, Zr and Hf. Very high Nb/Ta and low Zr/Hf imply that the evolution of the parental magma involved immiscible separation of a carbonate from a silicate melt. The sodalite-dominated Swartbooisdrif fenites suggest that the parental melt also had a substantial Na content, in contrast with the ferrocarbonatite rock.

Smyer H-chondrite impact-melt breccia and evidence for sulfur vaporization

Smyer is an H-chondrite impact-melt breccia containing ∼20 vol% 0.5- to 13-mm-thick silicate-rich melt veins surrounding unmelted subrounded chondritic clasts up to 7 cm in maximum dimension. At the interface between some of the melt veins and chondritic clasts, there are troilite-rich regions consisting of unmelted, crushed 0.2- to 140-μm-size angular silicate grains and chondrule fragments surrounded by troilite and transected by thin troilite veins. Troilite fills every available fracture in the silicates, including some as thin as 0.1 μm. Little metallic Fe-Ni is present in these regions: the FeS/Fe modal ratio ranges from ∼25:1 to ∼500:1, far higher than the eutectic weight ratio of 7.5:1. The texture of these regions indicates that the sulfide formed from a fluid of very low viscosity. The moderately high viscosity (0.2 poise) and large surface tension of liquid FeS, its inability to wet silicate grain surfaces at low oxygen fugacities, and the supereutectic FeS/Fe ratios in the troilite-rich regions indicate that the fluid was a vapor. It seems likely that during the shock event that melted Smyer, many silicates adjacent to the melt veins were crushed. Upon release of shock pressure, some of the troilite evaporated and dissociated. Molecules of S2 were transported and condensed into fractures and around tiny silicate grains; there, they combined with Fe from small adjacent metallic Fe-Ni grains to form troilite. The Ni content at the edges of some of these metal grains increased significantly; Co from these Ni-rich grains diffused into nearby kamacite. Impact-induced S volatilization may have played a major role in depleting the surface of 433 Eros (and other chondritic asteroids) in S.

Origins of Nd–Sr–Pb isotopic variations in single scheelite grains from Archaean gold deposits, Western Australia

Accessory gangue scheelite (CaWO 4) from the Archaean Mt. Charlotte lode Au deposit can be divided into two types with different rare earth element (REE) signatures. In some scheelite grains, specific REE signatures are reflected by different cathodoluminescence colours, which can be used to map their often complex oscillatory intergrowths. Domains with specific REE contents from two grains were sampled for Sm/Nd, Rb/Sr and Pb isotopic analyses using a micro-drilling technique. Type I scheelite is strongly enriched in middle REE (MREE) and Eu anomalies are either absent or slightly positive. Four fragments collected from Type I regions of two crystals have initial 87Sr/ 86Sr and ε Nd values ranging from 0.70141 to 0.70163 and +2.5 to +3.5, respectively, and Pb isotope ratios reflecting the composition of greenstone sequence. This may indicate that Nd and Pb have their source, either locally or regionally, in the greenstones. Basic greenstone lithologies have 87Sr/ 86Sr<0.7015, and the radiogenic Sr signatures indicate that part of the Sr originated from felsic lithologies located either within or beneath the host greenstone pile. Alternatively, the Sr signature may have evolved from preferential leaching of a Rb-rich mineral during hydrothermal alteration of the greenstone. The REE patterns of Type II scheelite are either flat or MREE-depleted and have strong positive Eu anomalies. Three fragments collected from Type II regions of the same two crystals have initial 87Sr/ 86Sr ratios and ε Nd values between 0.70130 and 0.70146, and +1.1 to +2.6, respectively, and Pb isotope signatures that are once again similar to that of the greenstone. This implies that 87Sr/ 86Sr ratios in Type II fluids were closer to those of the host dolerite (0.7008–0.7013), due to more extensive fluid interaction with the dolerite. A positive correlation between Na and REE suggests that REE 3+ are accommodated by the coupled substitution REE 3++Na +=2 Ca 2+ into both Type I and Type II scheelite. This is consistent with a fractional crystallisation model to explain the change in REE patterns from Type I to Type II, but not with a model involving different coupled substitutions and fluids from different origins. We propose that the complex REE and isotopic signatures of scheelite at Mt. Charlotte are related to small (<m) to medium (<km) scale processes involving mixing between “fresh” batches of hydrothermal fluid with fluids that had already been involved in extensive wall-rock alteration. The very high- ε Nd values measured in some scheelites have been previously used to link gold mineralisation with komatiites containing unusually high Sm/Nd ratios. However, tiny (<20 μm) grains of secondary hydroxyl-bastnäsite were found within micro-fractures of one scheelite grain containing an extremely high- ε Nd signature. The hydroxyl-bastnäsite probably formed during recent REE redistribution within the scheelite as a result of meteoric fluid circulation. The scale of this cryptic low-temperature alteration is sufficient to explain the anomalously high- ε Nd i values observed in scheelite from Western Australia.

The surfaces of compact systems: from nuclei to stars

While providing information from worlds separated by five-to-six orders of magnitude in dimensions and in energy, the pairing properties (electrical resistance and viscosity), the electromagnetic response (spectrum of colours), the resilience to stress (elasticity), the ability to deform (plasticity), etc., associated with clusters of atoms and with atomic nuclei have surprisingly similar properties, once the proper scalings are done, and demonstrate the many analogies that can be drawn between different finite many-body systems. These analogies can be further extended to cosmic and to customer tailored nanometre materials. Femtometre materials, like the inner crust of a neutron star (pulsar), are made out of the same protons and neutrons which make infinite nuclear matter. However in pulsars, protons and neutrons are arranged in the form of finite nuclei immersed in a sea of free neutrons. This is the reason why these celestial objects rotate, conduct heat, emit neutrinos, etc., very differently from infinite nuclear matter. In fact, these phenomena reflect the properties of the corresponding atomic nuclei which form the pulsar. Among these properties, those associated with the nuclear surface are most important. Nanostructured materials are made out of atoms as their more common forms, but the atoms are arranged in nanometre or sub-nanometre-size clusters, which become the constituent grains, or building blocks, of new materials like, e.g., C60 fullerene. Because these tiny grains respond to light, mechanical stress and electricity quite differently from micron- or millimetre-sized grains, nanostructured materials display an array of novel attributes. At the basis of the new phenomena we find again the surface of the building blocks used to produce the new materials. A proper understanding of the interweaving of the single-particle motion with the static and dynamic deformations of the surface of finite many-body systems is likely to provide the key to open a whole new world of interdisciplinary research in such disparate fields as isolated atomic nuclei and clusters, new materials and compact stellar objects. The concepts and the experimental evidence needed to tool this key will be reviewed. Special emphasis will be set on the open questions still remaining to be answered to reach this goal.

Vaterite Stabilization in CaCO3 Crystal Growth by Amino Acid

Calcium carbonate crystals were grown in a CaCl2–Na2CO3 solution containing an amino acid. We have employed 12 different types of amino acids as additives. The concentrations of noncharged-polar amino acids and those of the acidic ones in CaCO3 precipitates are one or two orders higher than those of all of the other types. These two types of amino acids tend to stabilize the vaterite phase which is unstable without amino acid additives. The vaterite forms as cauliflower-like grains consisting of many tiny grains (<0.1 µm). The vaterite content in CaCO3 precipitates is correlated to the concentration of amino acids in the precipitates. The physicochemical interactions between amino acids and CaCO3 are discussed on the basis of the Frontier orbitals obtained by the semi-empirical molecular orbitals calculation of the Zerner's intermediate neglect of differential overlap method.

Shock-related mineralogical features and P-T history of the Suizhou L6 chondrite

The Suizhou meteorite, classified as an L6 chondrite, contains weakly shocked olivine and pyroxene, but almost all the plagioclase in the meteorite was melted and transformed into maskelynite during shock metamorphism. Chromite was heavily fragmented and granulated, and many tiny chromite fragments were incorporated into the molten plagioclase as inclusions. Metal and troilite show no obvious intragranular textures, but many tiny rounded FeNi metal grains were deposited in the intersecting joints of planar fractures in olivine and pyroxene. A few very thin shock melt veins occur in the Suizhou meteorite, which contain abundant high-pressure phases, including coarse-grained ringwoodite, majorite, (Na,Ca)AlSi3O8-hollandite and fine-grained liquidus majorite-pyrope garnet. The shock features of this meteorite match shock stages 3 to 5, while the presence of ringwoodite in Suizhou veins is considered to appear at stage 6. It is estimated that the Suizhou meteorite experienced a shock pressure and shock temperature of up to 22 GPa and 1000°C, respectively. The shearing friction along veins raised the temperature within the veins. Shock-induced pressure and temperature in the shock veins attained 22 GPa and 1900°C. Therefore, the actual shock level of the Suizhou meteorite could correspond to stage 3–4. A longer duration of the shock pressure and temperature regime in the Suizhou meteorite plays an important role in the pervasive melting of plagioclase in the unmelted part of the meteorite, as well as in the formation of abundant high-pressure phases in the very thin shock-melt veins. It appears that maskelynite cannot be used as the sole criteria for evaluating the shock stage of shock-metamorphosed chondrites.

Flux dynamics and vortex phase diagram of the new superconductor MgB 2

Magnetic relaxation, critical current density and transport properties have been investigated on MgB 2 bulks from 1.6 K to T c at magnetic fields up to 8 T. A vortex phase diagram is depicted based on these measurements. Two phase boundaries H irr bulk( T) and H irr g( T) characterizing different irreversible flux motions are found. The H irr bulk( T) is characterized by the appearance of the linear resistivity. A large separation between the bulk irreversibility field at 0 K and the upper critical field H c2(0) has been found, it is interpreted as either due to a quantum vortex liquid induced by strong quantum fluctuation of vortices at 0 K, or flux flow through weak-link channels. It is further found that the magnetic relaxation rate is weakly dependent on temperature but strongly dependent on field indicating a trivial influence of thermal fluctuation on the vortex depinning process. Therefore the phase line H irr bulk( T) may be attributed to quantum vortex melting in the rather clean system at a finite temperature. The second boundary H irr g( T) reflects the irreversible flux motion in some local regions due to either very strong pinning or the surface barrier on the tiny grains.

One year of Galileo dust data from the Jovian system: 1996

The dust detector system onboard Galileo has recoding dust impacts in circumjovian space since the spacecraft was injected into a bound orbit about Jupiter in December 1995. This is the sixth in a series of papers dedicated to presenting Galileo and Ulysses dust data. We present data from the Galileo dust instrument for the period January to December 1996 when the spacecraft completed four orbits about Jupiter (G1, G2, C3 and E4). Data were obtained as high-resolution realtime science data or recorded data during a time period of 100 days, or via memory read-outs during the remaining times. Because the data transmission rate of the spacecraft is very low, the complete data set (i.e. all parameters measured by the instrument during impact of a dust particle) for only 2% (5353) of all particles detected could be transmitted to Earth; the other particles were only counted. Together with the data for 2883 particles detected during Galileo's interplanetary cruise and published earlier, complete data of 8236 particles detected by the Galileo dust instrument from 1989 to 1996 are now available. The majority of particles detected are tiny grains (about 10 nm in radius) originating from Jupiter's innermost Galilean moon Io. These grains have been detected throughout the Jovian system and the highest impact rates exceeded 100 min −1 . A small number of grains has been detected in the close vicinity of the Galilean moons Europa, Ganymede and Callisto which belong to impact-generated dust clouds formed by (mostly submicrometer sized) ejecta from the surfaces of the moons (Krüger et al., 1999e. Nature 399, 558). Impacts of submicrometer to micrometer sized grains have been detected throughout the Jovian system and especially in the region between the Galilean moons.

Mineralogy of fine‐grained material in the Krymka (LL3.1) chondrite

Abstract— Two dark lithic fragments and matrix of the Krymka LL3.1 chondrite were mineralogically and chemically studied in detail. These objects are characterised by the following chemical and mineralogical characteristics, which distinguish them from the host chondrite Krymka: (1) bulk chemical analyses revealed low totals (systematically lower than 94 wt%) due to high porosity; (2) enrichment in FeO and depletion in S, MgO and SiO2 due to a high abundance of Fe‐rich silicates and low sulfide abundance; (3) fine‐grained, almost chondrule‐free texture with predominance of a porous, cryptocrystalline groundmass and fine grains; (4) occurrence of a small amount of once‐molten material (microchondrules) enclosed in fine‐grained materials; (5) occurrence of accretionary features, especially unique accretionary spherules; (6) high abundance of small calcium‐ aluminium‐rich inclusions (CAIs) in one of the fine‐grained fragments. It is suggested that the abundance of CAIs in this fragment is one of the highest ever found in an ordinary chondrite.Accretionary, fine‐grained spherules within one of the fragments bear fundamental information about the initial stages of accretion as well as on the evolution of the clast, its incorporation, and history within the bulk rock of Krymka. The differences in porosity, bulk composition, and mineralogy of cores and rims of the fine‐grained spherulitic objects allow us to speculate on the following processes: (1) Low velocity accretion of tiny silicate grains onto the surface of coarse metal or silicate grains in a dusty region of the nebula is the beginning of the formation of accretionary, porous (fluffy) silicate spherules. (2) Within a dusty environment with decreasing silicate/(metal + sulfide) ratio the porous spherules collected abundant metal and sulfide particles together with silicate dust, which formed an accretionary rim. Variations of the silicate/(sulfide + metal) ratio in the dusty nebular environment result in the formation of multi‐layered rims on the surface of the silicate‐rich spherules. (3) Soft accretion and lithification of rimmed, fluffy spherules, fine‐grained, silicate‐rich dust, metal‐sulfide particles, CAIs, silicate‐rich microchondrules, and coarse silicate grains and fragments followed. (4) After low‐temperature processing of the primary, accretionary rock collisional fragmentation occurred, the fragments were subsequently coated by fine‐grained material, which was highly oxidized and depleted in sulfides. (5) In a final stage this accretionary “dusty” rock was incorporated as a fragment within the Krymka host.