Straight Lamellae Research Articles

Spectroscopic characterization of rare natural pink diamonds with yellow color zones

A set of 28 uncommon pink diamonds with yellow color zones are identified among thousands of natural pink diamonds examined. The pink color in these diamonds is caused by the 550 nm absorption band associated with plastic deformation, and is concentrated along straight lamellae (also known as deformation lines). These pink diamonds are type Ia with nitrogen concentrations ranging from 118 to 313 ppma, predominantly as A-centers, i.e., type IaA ≫ B (proportion of B-center < 10 %) to IaA > B (proportion of B-center = 11–26 %).Yellow color zones are observed on or beneath the surface of these faceted pink diamonds. Yellow fluorescence and occasionally yellow phosphorescence excited by long-wave (365 nm) or deep UV (<225 nm), corresponding to the yellow color zones, are commonly observed in yellow diamonds colored by the 480 nm absorption band. PL mapping conducted on the diamond surface and along the depth of the pink diamonds in this study reveals that the yellow color zones have features associated with the 480 nm absorption band. Some of these features are associated with nickel-related defects, and are only detected within the yellow color zones. This suggests that the yellow color zones formed in a different growth episode or from a different diamond-forming fluid than the remaining volume of the diamond with pink body color. Post-growth plastic deformation created defects giving rise to the 550 nm absorption band, producing a pink body color to diamond that was presumably colorless, and producing brown color in zones that may have had pre-existing yellow color. Three diamonds in this study contain eclogitic mineral inclusions, indicating that they formed in association with mantle eclogite, prior to plastic deformation.

Mineralogy and geochemistry of serpentinized peridotites of the Northern Nubian Shield: The origin of compositionally banded olivine and implications for Neoproterozoic supra-subduction zone metasomatism

A sequence of Neoproterozoic ultramafic rocks — serpentinized peridotite, serpentinite, and clinopyroxenite — outcrop in Wadi El-Mireiwa in the south Eastern Desert of Egypt. They represent the mantle and lowermost crustal section of a fragmented ophiolite, emplaced by thrusting above metasedimentary rocks and an island arc assemblage and later intruded by a granite mass. In samples of the serpentinized peridotite, back-scattered electron images of olivine reveal banded zoning, defined by straight and parallel Mg-enriched (Fo ∼ 96) lamellae within typically magnesian host crystals (Fo ∼ 89). The presence of clinopyroxene, the relatively low whole-rock Mg# (∼88), the low NiO content of olivine (0.1–0.32 wt%), and the relatively high TiO2 content of fresh Cr-spinel (∼0.3 wt%) are all consistent with a cumulate origin for the serpentinized peridotite and serpentinites. On the other hand, some associated serpentinite has higher whole-rock Mg# (92) and low TiO2 in Cr-spinel (∼0.01 wt%), consistent with a residual origin by high-degree melt extraction in the fore-arc region of a supra-subduction zone (SSZ) environment. The formation of Mg-enriched bands in olivine is attributed to the enhancement of metasomatic Mg-Fe exchange with high-Mg/Fe2+ fluids along crystallographically-oriented subgrain boundaries produced by high strain-rate dislocation creep. Such high-Mg/Fe2+ fluid metasomatism also explains reverse zoning of MgO in Cr-spinel, whereas the low whole-rock concentrations of REE and other trace elements exclude a significant role for melt-rock interaction. The evidence for high-Mg/Fe2+ fluid metasomatism in this suite indicates that SSZ fluids and high fore-arc strain rates affect not only the mantle wedge but also overlying ultramafic cumulates. The oxygen fugacity [ΔlogƒO2(FMQ)] values calculated from unmetasomatized (+2.48 to +2.67) and metasomatized (+3.75 to +4.53) samples reflect the oxidized nature of Neoproterozoic SSZ magma and the even more oxidizing character of the metasomatic fluids. Banded zoning has also been recorded in olivine from Mariana fore-arc peridotite and Phanerozoic SSZ ophiolites; the Neoproterozoic Wadi El-Mireiwa case shows that rapid mantle flow has been a persistent feature of the tectonic environment where fore-arc ophiolites develop.

Lamellar instabilities during scanning laser melting of Al–Cu eutectic and hypoeutectic thin films

Scanning laser melting was employed to investigate directional solidification in Al–Cu thin films, 200 and 500 nm thick. The Al–Cu alloy films, with both eutectic and hypoeutectic compositions, were co-deposited on fused silica substrates by magnetron sputtering. Melting of the films was carried out in air using a CW laser, as a function of the scan velocity, v, up to 5 cm/s. For eutectic films, regular lamellar microstructure was observed over the entire range of velocities studied. Interlamellar spacings, λ, below 50 nm were readily produced. Results were found to be consistent with studies on bulk Al–Cu alloys, obeying the classic steady state lamellar growth relationship, λ2v = K. However, the value of the constant, K is significantly larger in thin films when compared to bulk. This is attributed to constraints on mechanisms for spacing adjustment in two-dimensional eutectic systems. In the hypoeutectic thin films, a complex lamellar structure was observed as the scan velocity was reduced. Regions of straight lamellae, oscillatory lamellae, solitary tilt waves, and recurring extreme lamellar branching events coexisted across the melt track. Fourier analysis was used to quantify the chaotic area fraction of the films. The transition to chaos occurred as the G/v ratio increased, attributed to approaching a re-entrant eutectic-to-dendritic transition from above. Approaches to further refine laser melting in thin eutectic films in order to better control solidification processes are discussed.

Discovery of plywood structure in Sphenothallus from Gurovo Formation (Mississippian), Central Russia

Sphenothallus specimens are reported for the first time from the Mississippian of Central Russia. All Sphenothallus specimens have a phosphatic composition and a characteristic laminar structure, which is best observable in the thickened lateral parts of a tube. Most of the lamellae in the tube wall are straight, but some have a wavy morphology and a few are so wrinkled that they form hollow “ribs”. The wrinkled lamellae presumably had an originally higher organic content than the straight lamellae. There are borings on the surfaces of some lamellae that are similar in morphology to the bioerosional traces in various hard, biomineral substrates. Lamellae in the inner parts of the tube wall are composed of fibres. The fibres are parallel to the surface of the tube wall and in successive laminae they differ in orientation by irregularly varying angles. It is possible that the plywood microstructure in Sphenothallus was originally organic and was later phosphatized during fossilization. An alternative, but less likely explanation is that the plywood structure was originally mineralized and therefore is comparable to the phosphatic lamello-fibrillar structures of vertebrates.

Periodic patterns for a model involving short-range and long-range interactions

We consider a physical model where the total energy is governed by surface tension and repulsive screened Coulomb potential on the 3-dimensional space. We obtain different periodic equilibrium patterns i.e. stationary sets for this energy, under some volume constraints. The patterns bifurcate smoothly from straight lamellae, lattices of round solid cylinders and lattices of round balls.

Effect of growth rate on the microstructural transition and microhardness of directionally solidified Ni–11.8 wt% Si hypereutectic alloy

Ni–11.8 wt% Si hypereutectic alloys were directionally solidified under growth rates of 0.5–15 μm/s. The microstructures of Ni–11.8 wt% Si alloys were characterized by field-emission scanning electron microscopy–energy dispersive spectrometry, and the phase composition was identified by X-ray diffraction. The alloys exhibited three types of microstructures: rods, wavy lamellae, and straight lamellae. The alloys grown at 4–12 μm/s exhibited a completely lamellar structure that consisted of α-Ni and β-Ni3Si phases. During lamellar–rod transition, coarse lamellae first underwent zigzag instability to form wavy lamellae and then transformed into rods. An interface deflection parameter was defined based on the deviation of the interface shape from a flat interface and reached the maximum value under maximum lamellar spacing. Moreover, zigzag instability resulted in a macroscopically flat liquid-solid interface. Out of the three microstructures, the rod-like structure exhibited the highest microhardness, followed by straight lamellae and then wavy lamellae. The difference in microhardness was related to the volume fraction of α-Ni phase and microstructural type. The lamellar microstructure more effectively improved the microhardness of eutectic materials than the rod-like microstructure.

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Abstract Two new species of oribatid mites of the genus Dicrotegaeus (Oribatida, Cerocepheidae) are described from alpine soils of New Zealand. Dicrotegaeus mariehammerae sp. nov. shows straight lamellae distally, rostrum with a medial incision, the notogastral lateral tubercles developed, three pairs of adanal setae and triangular epimeral tubercles E4p. In Dicrotegaeus incurvus sp. nov. the anterior parts of the lamellae are curved medially, the rostrum has a strong longitudinal ridge, the notogastral lateral tubercles are absent, two pairs of adanal setae are present and the epimeral tubercles E4p are triangular. The type species, D. mirabilis Luxton, 1988 is the only other species in this genus and shows straight lamellae distally, the rostrum complex with a multiperforate projection, lateral tubercles present, two pairs of adanal setae and rectangular epimeral tubercles E4p. A new generic diagnosis and an identification key to all species of Dicrotegaeus are provided.

Coexisting Straight, Radial, and Banded Lamellae on the Six Corners of Hexagon‐Shaped Spherulites in Poly(l‐Lactide)

A novel six‐petal spherulite morphology composed of a combination of a central hexagonal core, hexagon‐shaped ring bands, and six fibrous stalks is discovered in a low‐molecular‐weight poly(l‐lactide acid) (LMw‐PLLA) that is melt crystallized at a specific Tc = 110 °C and confined in thin films. The structures are analyzed by using polarized optical microscopy (POM) and atomic force microscopy (AFM). Discrete lamellae, consisting of sequenced wide and small lamellae, all in flat‐on orientation with periodically up‐and‐down topology, are packed in a ring‐banded alignment, while continuous lamellae in flat‐on, tilted, or edge‐on orientations are arranged in the fibrous region. On the six corners of a symmetric hexagon‐banded spherulite, the radial fibrous lamellae overlap with ring‐band lamellae to show a mixed combination of ring‐banded and fibrous patterns. The formation of coexisting ring‐banded and fibrous patterns in a mixed morphology is associated with the lamellar packing and orientation. The radial fibrous lamellae at the six corners favorably occur in the growth fronts, which are closer to the reservoir of materials of diffusing species. Superimposed on the radial lamellae, hexagon‐shaped ring bands repeat themselves on the outskirts of the central hexagon nuclei. The geometry of the initial crystal is believed to be the influencing factors in final spherulite patterns. image

Oppositely Synchronized Lamellar Bending in Poly(l‐lactic acid) Versus Poly(d‐lactic acid) Blended with Poly(1,4‐butylene adipate)

Lamellar bending habits, as influenced by molecular‐chain chirality, in packing into dendritic spherulites with specific optical patterns are discussed using two model polymers of opposite chirality that are blended with a common polymer as examples: i) poly(l‐lactic acid)/poly(butylene adipate) (PLLA/PBA) and ii) poly(d‐lactic acid)/PBA (PDLA/PBA) blends. The bending habits in the spherulites of PLLA or PDLA blended with PBA are dictated by the chirality, specifically the counterclockwise and clockwise directions for the PLLA/PBA (50:50) and PDLA/PBA (50:50) blends, respectively. Straight lamellae in spiral lozenge crystals are packed with crystal aggregates of PLLA on top of the flat‐on lamellae plates acting as a basal plane during crystallization at Tc; spiral lozenge‐crystal frameworks are surrounded by needle‐like crystals resembling PBA crystals. image

Jasrouxite, a new Pb-Ag-As-Sb member of the lillianite homologous series from Jas Roux, Hautes-Alpes, France

The thallium-rich sulfosalt deposit of Jas Roux, situated in the Pelvoux Massif (Hautes-Alpesdepartement, France), occurs in a Triassic sedimentary series. Jasrouxite belongs to the early lead-containing stages of the Tl-As-Sb period of mineralization. It occurs in a silicified gangue, along with smithite and late realgar. Jarouxite forms dark gray anhedral grains with metallic luster, up to several millimeters in size, as well as aggregates of grains which range to more than 10 mm in diameter. From their surface, grains of jasrouxite are embayed by a three-phase myrmekite aggregate composed of stibnite, boscardinite and smithite. The mineral is brittle, with irregular fracture; no cleavage or parting was observed. In reflected light, color is off-white. Bireflectance is weak, in off-white tones; anisotropy is distinct. Rare straight twin lamellae occur in otherwise untwinned crystals. The empirical formula, on the basis of 132 apfu derived from the crystal-structure determination, is Cu0.79Ag14.64Pb4.10Tl0.05As15.37Sb24.87S72.18. Calculated density is

Leaf Cuticle Anatomy and the Ultrastructure ofGinkgoites ticoensisArchang. from the Aptian of Patagonia

The leaf cuticle of the Ginkgoites ticoensis Archang. type material from the Aptian Anfiteatro de Tico Formation in Patagonia, Argentina, is fully characterized with additional scanning and transmission electron microscopic observations. Many new anatomical and ultrastructural cuticular features are identified in the four-lobed leaf of G. ticoensis: the leaf shows a hypostomatic and papillate laminae, straight and pitted anticlinal and granulate periclinal walls, actinocytic stomata with between five and seven papillate, striate subsidiary cells, and guard cells with anticlinal smooth walls. The TEM studies on ordinary epidermal cells, papillae, subsidiary cells, and guard cells reveal general ultrastructural features of Ginkgoaceae: an outer polylamellate layer A made with A1 and a granular inner layer A2; A1 with an upper part A1U with continuous and straight translucent lamellae; a lower part A1L with significantly disrupted and waving translucent lamellae; and the fibrillar cuticular layer B1 as the i...

Discoveries in real crystals of rare earth metal compounds by electron microscopy – Lamellar intergrowth and domains of phasoids

Condensed cluster phases with the nominal compositions Ln 14(C 2) 3I 20 (Ln = La, Ce, Pr) are strongly disordered by a lamellar intergrowth. The thickness and composition of layers of clusters containing n (C 2)Ln 6 octahedra linked via opposite edges is determined by n. The disorder is characterized by variations of n as well as by variations of the thickness of lamellae containing only one kind of cluster. As a rule, the crystals are built from straight lamellae with constant n, however, large variations of n were occasionally observed giving rise to bending and truncation of the lamellae inside compact crystals. The power of electron microscopy techniques for the characterization of such phasoid-type real crystals is demonstrated and the structure of the new compound Pr 14(C 2) 3I 20 is presented.

THE UPPER PENNSYLVANIAN (MISSOURIAN) AMMONOID PENNOCERAS FROM THE NORTH AMERICAN MIDCONTINENT

Until recently considered a rare Appalachian Basin endemic, Pennoceras Miller and Unklesbay, 1942 has emerged as one of the most widespread and locally abundant ammonoids in the lower Missourian of the Midcontinent (Boardman et al., 1994). Here we document the first Midcontinent record of the type species of Pennoceras , P. seamani Miller and Unklesbay, 1942, from the Hushpuckney Shale equivalent in southeastern Kansas. Additional, previously undescribed species of Pennoceras from the Exline Limestone and Mound City Shale equivalents in Oklahoma and southeastern Kansas are described as Pennoceras bennisoni new species and Pennoceras heckeli new species. Discovery of these ancestral species provides clarification on the derivation and early history of Pennoceras and provides a possible link to the Desmoinesian Wiedeyoceratidae. Dimensions D, H, W, and U represent conch diameter, corresponding whorl height and width, and umbilical diameter measured from seam to seam. Suture terminology is that of Ruzhencev (1960); V, L, U, I, and D represent the ventral lobe, lateral lobe, umbilical lobe, internal lateral lobe, and dorsal lobe. Sutural symbols hs, hl, and wl refer to height of secondary ventral saddle and height and width of entire ventral lobe, respectively. Repository abbreviations are: SUI, University of Iowa; CM, Carnegie Museum of Natural History. ### Type species Pennoceras seamani Miller and Unklesbay, 1942. ### Included species Pennoceras bennisoni n. sp.; Pennoceras heckeli n. sp. ### Emended diagnosis Conch small (30–35 mm at maturity), subglobose to globose (W/D 0.55–0.9) with depressed to equidimensional whorls (H/W 0.6–1.0) and closed umbilicus. Fine to coarse, straight transverse lamellae trace a low ventral salient. External suture comprises wide ventral lobe with low median saddle ( hs / hl about 0.4) and short, rounded or bluntly pointed ventral prongs; broadly rounded lateral saddle; symmetrical, narrowly rounded or bluntly pointed lateral lobe; and small, rounded umbilical lobe. Sutural formula: ( V1V1 ) …

Single Wall Carbon Nanotube/Polyethylene Nanocomposites: Nucleating and Templating Polyethylene Crystallites

The crystallization kinetics and resulting morphology of polyethylene (PE) in the presence of single wall carbon nanotubes (SWNT) are investigated in isotropic and aligned composites. A hot coagulation method was developed to incorporate SWNT loadings as high as 30 wt % with uniform distribution. Thermal analysis interpreted using the Avrami equation showed that the nanotubes provide nucleation sites to PE and accelerate the PE crystal growth rate while reducing the crystal dimensionality from spherulitic to disk-shaped. Nucleating on SWNT bundles significantly increases the shish density during melt fiber spinning, so that the PE microstructure is shish kebab with straight (not twisted) lamellae in 1 wt % SWNT−HDPE composite fibers. By comparing the orientations of SWNT and PE produced by various processing conditions, we show that SWNT bundles template the growth of PE crystals by imposing a growth direction perpendicular to the SWNT. This provides a new route toward controlling the SWNT−polymer interface and thereby the physical properties of nanocomposites.

Plants seen and unseen: Radula pseudoscripta sp. nov. and Radula uvifera (Radulaceae: Jungermanniopsida)

Individuals of Radula uvifera can be divided into two groups. Radula uvifera sens. str. produces amentulose branches infrequently and has long perianths with the mouth not ventrally folded, with 3–8 straight lamellae that are not jagged in relief on either surface. Radula pseudoscripta produces amentulose branches regularly at bases of alternate leaf pairs and has squat perianths with a ventrally folded mouth, with 5–14 lamellae that are sinuous for at least part of their length and jagged in relief on either surface. Morphological variation in this constellation of characters is discontinuous. Radula multicarinata is a homotypic synonym of Radula uvifera and is retained in synonymy of R. uvifera. A new species, Radula pseudoscripta, is proposed for the multicarinate plants. Both species are endemic to New Zealand.

Edge and face gluing of green timber using a one-component polyurethane adhesive

The edge and face gluing of green timber using a one-component polyurethane adhesive was investigated. Knot free and straight grained lamellae of dimensions were prepared for this purpose. The rela ...

Morphology control of polypropylene by crystallization under carbon dioxide

AbstractWe investigated the crystalline morphology of isotactic polypropylene obtained by melt crystallization under carbon dioxide (CO2) at various pressures. Spherulites consisting of regularly arranged fibrils without subsidiary lamellae were obtained by crystallization under CO2 below 2 MPa, whereas large spherulites consisting of irregularly arranged fibrils with subsidiary lamellae were obtained under ambient pressure. Distorted domain crystals with uniform optical anisotropy consisting of α‐form were found to be obtained under CO2 above 2 MPa, and needle crystals consisting of γ‐form were obtained above 12 MPa. Transmission electron micrographs showed that straight and thick lamellae are regularly arranged in both the distorted domain crystals and the needle crystals. The uniformly thick lamellae were confirmed by differential scanning calorimetry thermograms; that is, the melting temperature is higher and the melting peak is sharper than those obtained under ambient pressure. Such characteristic crystalline morphologies obtained under CO2 may be attributed to local ordering in the melt state. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2738–2746, 2004

超臨界流体を用いたポリマーの混練，成形，加工，リサイクル技術 高分子の高次構造と三次元構造細工

We found characteristic morphologies of polymers having various shape and size by annealing under supercritical carbon dioxide. Mosaic crystals consisting of regularly arranged straight and thick lamellae were obtained in polypropylene by crystallization under supercritical carbon dioxide due to local ordering in the melt state. On the other hand, interconnected porous structure was obtained by liquid-liquid phase separation of polycarbonate and supercritical carbon dioxide via spinodal decomposition. Nano-porous structure with various shape of layer type and network one was also obtained by annealing polypropylene/clay nanocomposite, polyethylene, aramid, and polyimide gel under supercritical carbon dioxide.

Fine Structures of Curved Edge-On Lamellae in Crystalline Thin Films of Isotactic Polystyrene As Revealed by Transmission Electron Microscopy

Amorphous thin films of isotactic polystyrene (i-PS) were prepared by casting a hot solution in p-xylene onto the hot water surface. Dried films mounted on the specimen grids for transmission electron microscopy (TEM) were crystallized from the glassy state by annealing. The crystalline thin films of i-PS thus prepared were examined by TEM. In these films, we could observe immature and more or less mature two-dimensional spherulites and sheaflike structures, the constituents of which are basically edge-on lamellae. As for the space-filling mechanisms of spherulitic growth, some models have been proposed so far: for example, a model based on branching of straight lamellae and a model based on “spawning” of new lamellar crystals. In the latter model, however, most of the spawned lamellae are to be curved. From TEM observations, it is deduced that both branching and spawning occur together in the process of spherulitic growth of i-PS, because some lamellae are seemingly straight and branched but the majorit...

Three groups of species in Petunia sensu Jussieu (Solanaceae) inferred from the intact seed morphology

The intact seed surface morphology in 45 taxa of Petunia sensu Jussieu native to South America (Petunia sensu Wijsman plus Calibrachoa) was compared under scanning electron microscopy. The existence of three groups of species, differentiated in terms of seed morphology, was revealed as follows: (1) all species of Petunia sensu Wijsman, having coarse wavy middle lamellae and anticlinal walls; (2) Calibrachoa parviflora and C. pygmaea, having fine wavy middle lamellae embedded in straight anticlinal walls; and (3) the other species of Calibrachoa, having straight middle lamellae and anticlinal walls. Close relationships between seed morphology and the other characteristics observable in the groups of species are discussed.