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Intermediate Morphologies (intermediate + morphology)

Distribution by Scientific Domains

Polymers and Materials Science	40%
Life Sciences	40%

Selected Abstracts

Phylogenetic relationships within the tropical soft coral genera Sarcophyton and Lobophytum (Anthozoa, Octocorallia)

INVERTEBRATE BIOLOGY, Issue 4 2006
Catherine S. McFadden
Abstract. The alcyonacean soft coral genera Sarcophyton and Lobophytum are conspicuous, ecologically important members of shallow reef communities throughout the Indo-West Pacific. Study of their ecology is, however, hindered by incomplete knowledge of their taxonomy: most species cannot be identified in the field and the two genera cannot always be distinguished reliably. We used a 735-bp fragment of the octocoral-specific mitochondrial protein-coding gene msh1 to construct a phylogeny for 92 specimens identified to 19 species of Lobophytum and 16 species of Sarcophyton. All phylogenetic methods used recovered a tree with three strongly supported clades. One clade included only morphologically typical Sarcophyton species with a stalk distinct from the polypary, poorly formed club-shaped sclerites in the colony surface, and large spindles in the interior of the stalk. A second clade included only morphologically typical Lobophytum colonies with lobes and ridges on the colony surface, poorly formed clubs in the colony surface, and interior sclerites consisting of oval forms with regular girdles of ornamental warts. The third distinct clade included a mix of Sarcophyton and Lobophytum nominal species with intermediate morphologies. Most of the species in this mixed clade had a polypary that was not distinct from the stalk, and the sclerites in the colony surface were clubs with well-defined heads. Within the Sarcophyton clade, specimens identified as Sarcophyton glaucum belonged to six very distinct genetic sub-clades, suggesting that this morphologically heterogeneous species is actually a cryptic species complex. Our results highlight the need for a complete taxonomic revision of these genera, using molecular data to help confirm species boundaries as well as to guide higher taxonomic decisions. [source]

Genetic distinctness and phylogenetic relationships among Undaria species (Laminariales, Phaeophyceae) based on mitochondrial cox3 gene sequences

PHYCOLOGICAL RESEARCH, Issue 4 2007
Shinya Uwai
SUMMARY Genetic relationships among Undaria species and among populations of each species were studied based on DNA sequences of the mitochondrial cox3 gene. Although three Undaria species, U. peterseniana (Kjellman) Okamura, U. pinnatifida (Harvey) Suringar and U. undarioides (Yendo) Okamura, have been described based mostly on blade morphology, plants with intermediate morphologies have also been found. Multiple plants from several populations in Japan were collected. Morphological characters could identify most of the samples unambiguously. A few samples with intermediate morphologies were also collected. Mitochondrial haplotypes found in each population were different for each identified species, and each species had multiple haplotypes. In the cox3 haplotype network analysis, the numbers of steps between haplotypes within and between species were similar, and haplotypes of each species did not group together. The close genetic relationships among species strongly suggest that these species are conspecific. Alternatively, recent speciation could be possible with maintenance of ancestral polymorphisms within the species (i.e. incomplete lineage sorting). Haplotypes of samples with intermediate morphologies were different for each sample and the same as ones found in the local population, suggesting interspecific hybridizations among species. [source]

Visualization and microscopic modeling of phase inversion during compounding

POLYMER ENGINEERING & SCIENCE, Issue 8 2001
R. Ratnagiri
A detailed description of the sequence of deformation steps leading to phase inversion during compounding in a low-viscosity-ratio co-polyester/polyethylene blend is presented. Visualization using a glass window and sampling of the blend at different mixing times enabled identification of the intermediate morphologies of the major component en route to phase inversion. Based on these observations, a theoretical model is developed to predict the time to phase inversion. The model incorporates a simplified flow-field approximation and the calculation of strain imparted to the major component domains. A strain-based criterion for phase inversion is then proposed, which, in conjunction with the model, yields an explicit expression for the time to phase inversion during compounding, tP.I.. The model predictions are seen to be in good agreement with the increase of tP.I., on scaleup between two mixing bowls. The correct functional dependence of tP.I. on the nominal maximum-shear-rate is predicted. Using combination of pure drag and planar extensional flow, the model predictions are shown to be consistent with the observed dependence of tP.I. on the volume fraction of the minor component and the blend viscosity ratio. [source]

Mesophase Separation of Diblock Copolymer Confined in a Cylindrical Tube Studied by Dissipative Particle Dynamics

MACROMOLECULAR THEORY AND SIMULATIONS, Issue 9 2006
Jian Feng
Abstract Summary: The morphologies of diblock copolymers confined in a cylindrical tube have been investigated by the dissipative particle dynamics (DPD) method. Results indicate that the morphology depends on the volume ratio of the immiscible blocks, the diameter of the cylindrical tube and the interactions between the blocks and between the confinement wall and blocks. For symmetric diblock copolymers, when the tube wall is uniform toward the two blocks, perpendicular lamellae or a stacked disk morphology are generally formed except when the diameter of the cylindrical tube is very small; in that case, a special bi-helix morphology forms because of the entropy effect. When the tube wall is non-uniform, as the diameter of the tube increases, perpendicular lamellae are first formed, then changing to parallel lamellae and, finally, back to perpendicular lamellae again. An intermediate morphology characterizing the transition between perpendicular and parallel lamellae is observed. If the non-uniformity of the wall is further enhanced, only parallel lamellae can be found. In the case of asymmetric diblock copolymers, more complex morphologies can be obtained. Multi-cylindrical micro-domains and a multilayer helical phase as well as other complex pictures are observed. Generally, the morphologies obtained could find their counterparts from experiments or Monte Carlo simulations; however, differences do exist, especially in some cases of asymmetric diblock copolymers. Bi-helix and stacked disks morphologies of A5B5 diblock copolymer confined in two different neutral nanocylinders. [source]

Enhanced control of porous silicon morphology from macropore to mesopore formation

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2005
Huimin Ouyang
Abstract Porous silicon (PSi) is a versatile material that possesses a wide range of morphologies. There are two main types of microstructures that are widely used and well studied: branchy mesoporous silicon with pore sizes from 10 nm to 50 nm and classical macroporous silicon with pore sizes from 500 nm to 20 µm. Much less work has been done on structures with intermediate pore sizes from 100 nm to 300 nm. Applications such as immunoassays biosensing can greatly benefit from the intermediate morphology due to the larger pore openings compared to mesopores, and increased internal surface compared to classical macropores. In this work we demonstrate well-defined macropore of 150 nm diameter in average and precise control of the porous silicon morphology transition from smooth macropores to branchy mesopores on one substrate with one electrolyte. A multilayer structure (microcavity) consisting of both mesopores and macropores is presented. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]