Fenestrate graptolite theoretical morphology: Geometric constraints on lophophore shape and arrangement in extinct hemichordates

2003 ◽  
Vol 77 (2) ◽  
pp. 360-367 ◽  
Author(s):  
Robert W. Starcher ◽  
George R. McGhee
Keyword(s):  
Geometric Analysis ◽  
Close Packing ◽  
Geometric Constraints ◽  
Theoretical Morphology ◽  
Packing Arrangement

A geometric analysis of lophophore shape and arrangement in the fenestrate dendroid graptolite genus Dictyonema reveals that the shape of the zooid domain in the majority of Dictyonema species colonies is highly elliptical, with the long axis of the ellipse perpendicular to the proximodistal axis of the stipe. A complex lophophore, bilaterally symmetrical and consisting of two tentaculated arms that are laterally directed and perpendicular to the stipe axis, provides the best geometric solution to completely filling the elliptical zooid domain seen in the majority of Dictyonema species.Working under the assumption that fenestrate graptolites, like fenestrate bryozoans, needed to form a continuous filtering surface with contact between adjacent lophophores, two optimum close-parking models exist for lophophores with elliptical zooid domains: either a proximodistal-row arrangement or a lateral-row arrangement of the lophophores. Of the two possible geometries, the most probable close-packing arrangement of hypothetical biplumed lophophores within the fenestrate graptolite meshwork is in proximodistal rows.

Fenestrate theoretical morphology: geometric constraints on lophophore shape and arrangement in extinct Bryozoa

Paleobiology ◽  
2000 ◽  
Vol 26 (1) ◽  
pp. 116-136 ◽  
Author(s):  
Robert W. Starcher ◽  
George R. McGhee
Keyword(s):  
Geometric Analysis ◽  
Close Packing ◽  
Geometric Constraints ◽  
Actual Distribution ◽  
Size And Shape ◽  
The Third ◽  
Theoretical Morphology

A geometric analysis of fenestrate bryozoan lophophore shape and arrangement is conducted by creating a theoretical morphospace of apertural positioning within the colonial meshwork. Working from the assumption that fenestrate bryozoans needed to form a continuous filtering surface with contact between adjacent lophophores, we show that within the morphospace three regions exist for optimum close-packing of lophophores with circular projections; all other close-packing configurations in the morphospace require the existence of noncircular lophophores.Examination of the actual distribution of 251 fenestrate colonies within the morphospace reveals that the morphospace regions occupied by fenestellids and polyporids are displaced and have little overlap, but that they are very similar in size and shape that the colonies scale similarly. With increasing size, fenestrate meshworks expand laterally faster than the branches widen and the proximodistal spacing of the apertures increases, apparently because the larger zooids require disproportionately more room for their lophophores.Two of the optimum close-packing regions of the morphospace are occupied by fenestrates. The positioning of the fenestellid region within the morphospace suggests that these biserial bryozoans followed a proximodistal-row placement of the lophophores that the lophophores were generally equitentacular, with circular projections. The positioning of the polyporid region within the morphospace suggests that these polyserial bryozoans followed a diagonal-row placement of the lophophores that the lophophores were heteromorphic, with medial lophophores on the branch being more equitentacular whereas the laterally placed lophophores were obliquely truncate. The third optimum close-packing region in the morphospace, corresponding to a hypothetical lateral-row placement of the lophophores within the colony, is unoccupied. We suggest that hypothetical fenestrate morphologies in the vacant region of morphospace have branches that would be too narrow to support normally shaped zooids that the lateral-row placement of the lophophores would have required the branches of the colony to have been perfectly aligned throughout growth.

Theoretical morphology of hinge and shell form in Bivalvia: geometric constraints derived from space conflict between umbones

Paleobiology ◽  
2000 ◽  
Vol 26 (4) ◽  
pp. 606-624 ◽  
Author(s):  
Takao Ubukata
Keyword(s):  
Computer Simulation ◽  
Anterior Part ◽  
Large Degree ◽  
Ventral Side ◽  
Mutual Interference ◽  
Geometric Constraints ◽  
Geometric Properties ◽  
Shell Form ◽  
Theoretical Morphology

Geometric properties of the shells of 123 species of extant Bivalvia were analyzed from the viewpoint of theoretical morphology. The effects of shell form and the structure of ligament on the interumbonal space and the maximum shell opening received particular attention. The results of computer simulation and morphospace analysis indicate that possessing both prosogyrous shell form and an extended hinge without the parivincular ligament tends to cause space conflict between umbones or dorsal shell margins of right and left valves. To a large degree, a prosogyrous shell form with a long parivincular ligament helps shell opening without umbonal conflict, if the shell is flat enough to avoid the mutual interference between dorsal shell margins of closed valves. Extension of the ligament and plunging of the anterior part of the coiling axis into the ventral side provide enough space along the dorsal shell margins in which a parivincular ligament and its substrata are developed.

Phosphonic acid self-assembled monolayer improved the properties of n-type organic field-effect transistors in air ambient

RSC Advances ◽  
2016 ◽  
Vol 6 (92) ◽  
pp. 89794-89798 ◽  
Author(s):  
Li Cao ◽  
Yue Peng ◽  
Zhefeng Li
Keyword(s):  
Thin Film ◽  
Phosphonic Acid ◽  
Vapor Deposition ◽  
Thin Film Transistors ◽  
Field Effect ◽  
Field Effect Transistors ◽  
Close Packing ◽  
Organic Field Effect Transistors ◽  
Self Assembled Monolayer ◽  
Packing Arrangement

The electron mobilities of NDI-C14 based thin film transistors get a great improvement by vapor deposition on the surface of three SAMs modified SiO2 dielectric. This is associated with its close packing arrangement of NDI-C14 film on these SAMs.

scholarly journals Single-crystal guest exchange and phase transformations in a porous metallocycle

2014 ◽  
Vol 70 (a1) ◽  
pp. C998-C998
Author(s):  
Marike du Plessis ◽  
Vincent Smith ◽  
Leonard Barbour
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Empty Space ◽  
Close Packing ◽  
X Ray Diffraction ◽  
Guest Molecules ◽  
X Ray ◽  
Packing Arrangement ◽  
Solvent Molecules ◽  
Doughnut Shape

One of the target architectures for porous crystals investigated by our group is the "doughnut-shaped" metallocycle. The "doughnut" shape of the metallocycles prevents them from packing efficiently and results in the formation of crevices, cavities or channels in the packing arrangement. Naturally, owing to close-packing requirements the occurrence of empty space in the crystal structure is energetically unfavourable and therefore the available "space" is usually occupied by solvent molecules. Ideally, the porous phase can be obtained by removing the solvent molecules from the channels without disrupting the host framework. In this regard we have conducted a further investigation of the porous metallocycle previously reported by Barbour et al.[1] Single crystals of a previously reported porous metallocycle [Ag2L2](BF4)2·2CH3CN (1) were grown from acetonitrile and immersed in different organic solvents. The crystals thus treated were subjected to single-crystal X-ray diffraction analysis, which revealed that the acetonitrile guest molecules had been replaced by the solvent that the compound was exposed to, yielding five different solvates: [Ag2L2](BF4)2·2(CH3)2CO (2), [Ag2L2](BF4)2·2CHCl3 (3), [Ag2L2](BF4)2·C6H6 (4), [Ag2L2](BF4)2·C6H4F2 (5), [Ag2L2](BF4)2·C7H8 (6). Thermogravimetric analysis supports these findings.

CROSS-SECTION BALANCING AND THERMOCHRONOLOGICAL ANALYSIS OF THE MESOZOIC DEVELOPMENT OF THE EASTERN OTWAY BASIN

1997 ◽  
Vol 37 (1) ◽  
pp. 390 ◽  
Author(s):  
G.T. Cooper ◽  
K.C. Hill
Keyword(s):  
Cross Section ◽  
Early Cretaceous ◽  
Cross Sections ◽  
Seismic Data ◽  
Vitrinite Reflectance ◽  
Geometric Analysis ◽  
Structural Evolution ◽  
Geometric Constraints ◽  
Source Rocks ◽  
Structural Style

Recent advances in cross-section balancing software have simplified the application of basic geometric constraints to the analysis of basin development. Geometric analysis of field and seismic data allows the user to verify initial interpretations and also elucidates important information about the structural evolution of a basin. Principally, computerised balancing and restoration of cross-sections assists in constraining:the amount of crustal extension;trap geometries, particularly fault geometries through time;the geometry of key horizons at any time, revealing basin morphology and migration paths;the time and amount of maximum burial and hence hydrocarbon migration; andthe likely mechanisms involved in basin evolution. In turn, these parameters can be used to further assess hydrocarbon prospectivity by providing useful data for lithospheric modelling.This study utilises 2D cross-section balancing software (Geosec™) to decompact, balance and restore a series of regional onshore-offshore cross-sections based on both reflection seismic data in the Torquay Embayment and field mapping in the Otway Ranges. The thickness of eroded strata has been constrained by Apatite Fission Track and Vitrinite Reflectance analyses. The resulting section restoration suggests that the eastern Otway Basin experienced extension of 26 per cent in the Early Cretaceous and that the Otway Ranges were subjected to −8 per cent shortening during mid-Cretaceous inversion and −4 per cent shortening during Mio-Pliocene inversion.The structural style of the Otway Ranges and Torquay Embayment is typified by steep, relatively planar, en echelon, N and NE-dipping Early Cretaceous extension faults that were subsequently inverted and eroded during the Cenomanian and Mio-Pliocene. The structural style of the region shows strong similarities with oblique- rift analogue models suggesting that the extensional history of the region was strongly controlled by prevailing basement fabric.Lower Cretaceous source rocks in the eastern Otway Basin reached maximum maturity prior to mid-Cretaceous inversion with the exception of parts of the Torquay Embayment which may not have experienced significant uplift and erosion at this time. The lack of subsidence in the eastern Otway Basin prevented the deposition of significant amounts of Upper Cretaceous sediments which are proven reservoirs in the western Otway Basin and Gippsland Basin. Subsequent Tertiary burial was insufficient, in most regions, to allow the source rocks re-enter the oil generation window.

β-NbBr5, eine neue Modifikation von Niobpentabromid mit einer eindimensionalen Lagenfehlordnung/ β-NbBr5, a New Modification of Niobium Pentabromide Having One-Dimensional Stacking Disorder

1983 ◽  
Vol 38 (5) ◽  
pp. 559-561 ◽  
Author(s):  
Ulrich Müller ◽  
Paul Klingelhöfer
Keyword(s):  
Close Packing ◽  
X Ray Diffraction ◽  
One Dimensional ◽  
X Ray ◽  
Lattice Constants ◽  
Closed Tube ◽  
Packing Arrangement ◽  
Diffraction Patterns ◽  
True Structure ◽  
Stacking Disorder

Abstract While trying to react NbBr5 with sulfur in a closed tube, crystals of the new modification β-NbBr5 were obtained. Its X-ray diffraction patterns have sharp reflexions and diffuse streaks showing the presence of a one-dimensional disorder. From the sharp reflexions alone, a statistically averaged sub-structure results; it has the space group Ccmm and the lattice constants a0 = 644, b0 = 1867 and c0 = 615 pm. Taking into account the diffuse streaks, the true structure was deduced; its lattice constants are a = 2a0, c = Co, b indefinite due to the disorder. β-NbBr5 is isostructural to tantalum pentaiodide. It consists of layers of (NbBr5)2 molecules that are stacked with displacement faults in the direction of b. The bromine atoms have a hexagonal close-packing arrangement.

Theoretical morphology of echinoid growth

1968 ◽  
Vol 42 (S2) ◽  
pp. 50-63 ◽  
Author(s):  
David M. Raup
Keyword(s):  
Mathematical Model ◽  
Broad Spectrum ◽  
Digital Computer ◽  
General Model ◽  
Close Packing ◽  
Growth Line ◽  
Growth Rings ◽  
Theoretical Morphology ◽  
Apical System ◽  
System Migration

Deutler's classic work (1926) provides the basis for an analysis of plate growth in echinoids. Deutler showed that the concentric growth rings found within each plate may be used to reconstruct the ontogeny of the entire plate pattern.New observations of growth-line configurations, particularly in Strongylocentrotus pallidus (Sars), have been used to derive a general model for echinoid growth. The plate mosaic is assumed to be the result of close packing of the growing plates. The shape of a given plate thus depends on its size and position relative to surrounding plates.The rate of meridional growth of a plate can be shown to change regularly with increasing distance from the echinoid's apical system. Migration of plates away from the apical system thus causes change in the rate of plate growth. The rate of plate migration is strongly influenced, in turn, by the rate of supply of new plates at the apical system.A mathematical model has been developed from these considerations which, when treated by digital computer (with x-y plotter output), produces ideal plate patterns (including growth rings). The constants in the model may be varied to produce a broad spectrum of echinoid plate patterns.

Crystal structure images of large gold clusters and growing crystals by HRTEM

1984 ◽  
Vol 42 ◽  
pp. 428-429
Author(s):  
L.R. Wallenberg ◽  
J.-O. Bovin ◽  
G. Schmid
Keyword(s):  
Crystal Structure ◽  
Nucleation And Growth ◽  
Close Packing ◽  
Gold Clusters ◽  
Molecular Weight Determination ◽  
Growth Mechanisms ◽  
Starting Point ◽  
Different Types ◽  
Nucleation And Growth Mechanisms ◽  
Points Of View

Metallic clusters are interesting from various points of view, e.g. as a mean of spreading expensive catalysts on a support, or following heterogeneous and homogeneous catalytic events. It is also possible to study nucleation and growth mechanisms for crystals with the cluster as known starting point.Gold-clusters containing 55 atoms were manufactured by reducing (C6H5)3PAuCl with B2H6 in benzene. The chemical composition was found to be Au9.2[P(C6H5)3]2Cl. Molecular-weight determination by means of an ultracentrifuge gave the formula Au55[P(C6H5)3]Cl6 A model was proposed from Mössbauer spectra by Schmid et al. with cubic close-packing of the 55 gold atoms in a cubeoctahedron as shown in Fig 1. The cluster is almost completely isolated from the surroundings by the twelve triphenylphosphane groups situated in each corner, and the chlorine atoms on the centre of the 3x3 square surfaces. This gives four groups of gold atoms, depending on the different types of surrounding.

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