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Fourier Analysis, Spectral Form of the Continuum Equations, and Homogeneous Turbulence
Published in Robert G. Deissler, Turbulent Fluid Motion, 2020
The transfer of turbulent activity from one part of wavenumber space to another, or from one eddy size to another, produces a wide range of scales of motion in most turbulent flows. The state of affairs is neatly summarized in a nonmathematical way by a poem written long before eqs. (5-17), (5-31), or (5-33) were known [9]: Big whorls have little whorls,Which feed on their velocity;And little whorls have lesser whorls,And so on to viscosity.
The fossil alga Chaetocladus gracilis revisited: new material from the Silurian of Sweden
Published in GFF, 2020
Johan Pettersson, Per Ahlberg, Anders Lindskog, Johan Lindgren, Mats E. Eriksson
Kenrick & Vinther (2006) described Chaetocladus gracilis as a non-calcified dasycladalean alga with an unbranched >80 mm long and 1.5–1.7 mm wide axis. The incomplete holotype (MGUH 27641) of C. gracilis lacks both base and apex, rendering the complete in vivo length unknown. Furthermore, C. gracilis was described as lacking obvious reproductive organs and the axis does not, as far as can be assessed, taper significantly towards either end. Whorls (verticils) are spaced at regular 0.3 mm intervals along the entire axis. These whorls are made up of hair-like laterals (filamentous ramifications) with 30–40 laterals forming each individual whorl. The laterals are oriented at acute angles relative to the main axis. These filamentous ramifications have broad bases, c. 100 µm wide, with the laterals themselves being c. 50 µm wide. All laterals were described as fragmented; their original length is thus unknown, but with an estimate of at least 1.5 mm (Kenrick & Vinther 2006). Due to the acute angle of the laterals, the width of the thallus is estimated to <3.5 mm. The holotype is only sporadically covered by a black film (see below) and is thus mainly preserved as a compression (Kenrick & Vinther 2006).
A new look at Pleurotomaria perlata Hall, 1852 (Gastropoda) from the Silurian of Laurentia
Published in GFF, 2018
The shell aperture is known from the fine growth lines on the whorl surfaces. It is radial with a shallow emargination at the periphery. Growth lines on the upper whorl surface are shallowly prosocline and slightly oblique to the preceding suture (Fig. 1A and D). Growth lines on the basal surface are also prosocline, initially perpendicular to the umbilical shoulder before curving backwards towards the periphery (Fig. 1F and H). A slit and resultant selenizone are seemingly not present. Fine discontinuous spiral striations may occur on the upper whorl surface (Fig. 1D and H, arrows).
New encrusting tentaculitoids from the Silurian of Estonia and taxonomic status of Anticalyptraea Quenstedt, 1867
Published in GFF, 2022
Michał Zatoń, Olev Vinn, Ursula Toom, Jakub Słowiński
Shell structure obliterated; however, the remnants of microlamellar structure with pseudopunctae may be preserved locally. When visible in cross-section, the microlaminae around the pseudopunctae are pointed inwardly (Fig. 4E). However, they are well-manifested on the shell interior in the form of densely-spaced bump-like microstructures (Fig. 4B). The outer shell whorl possesses oval-shaped vesicles which are visible in translucent parts of the shell. In polished cross-sections, some cement-filled vesicles may also be discernible (Fig. 4F).