Appearance Of Indentations Research Articles

Regulation of the limb shape during the development of the Chinese softshell turtles.

Interdigital cell death is an important mechanism employed by amniotes to shape their limbs; inhibiting this process leads to the formation of webbed fingers, as seen in bats and ducks. The Chinese softshell turtle Pelodiscus sinensis (Reptilia: Testudines: Trionychidae) has a distinctive limb morphology: the anterior side of the limbs has partially webbed fingers with claw‐like protrusions, while the posterior fingers are completely enclosed in webbings. Here, P. sinensis embryos were investigated to gain insights on the evolution of limb‐shaping mechanisms in amniotes. We found cell death and cell senescence in their interdigital webbings. Spatial or temporal modulation of these processes were correlated with the appearance of indentations in the webbings, but not a complete regression of this tissue. No differences in interdigital cell proliferation were found. In subsequent stages, differential growth of the finger cartilages led to a major difference in limb shape. While no asymmetry in bone morphogenetic protein signaling was evident during interdigital cell death stages, some components of this pathway were expressed exclusively in the clawed digit tips, which also had earlier ossification. In addition, a delay and/or truncation in the chondrogenesis of the posterior digits was found in comparison with the anterior digits of P. sinensis, and also when compared with the previously published pattern of digit skeletogenesis of turtles without posterior webbings. In conclusion, modulation of cell death, as well as a heterochrony in digit chondrogenesis, may contribute to the formation of the unique limbs of the Chinese softshell turtles.

Scaling of size, shape and surface roughness in Antarctic krill swarms

Abstract Antarctic krill are obligate swarmers and the size and shape of the swarms they form can have a major influence on trophic interactions and biogeochemical fluxes. Parameterizing variability in size and shape is therefore a useful step toward understanding the operation of the Southern Ocean ecosystem. We analyse the relationships between the length L, thickness T, perimeter P, and area A of 4650 vertical cross-sections of open-ocean krill swarms obtained within the Atlantic sector of the Southern Ocean in summer 2003. Our data show that these parameters are tightly interrelated. The thickness T increases on average as L0.67 and has a log-normal distribution within each length class. The perimeter and area scale with L and T as P∼L0.77T and A∼L0.86T0.48. The swarm aspect ratio, T/L, decreases approximately as L-0.32. The surface roughness (defined as P/A) has a weak dependence on swarm length and decreases approximately as T-0.46, which can be explained only by the appearance of indentations and cavities in the swarm shape. Overall, our study finds that there are distinct limits to the size and shape of swarms that Antarctic krill appear to be capable of forming and we explore the potential explanatory factors contributing to these limitations.

INVESTIGATION INTO THE MECHANICAL PROPERTIES AND METAL CREAKS OF A DIESEL LOCOMOTIVE WHEEL

After JSC ‘Lithuanian Railways’ (AB ‘Lietuvos geležinkeliai‘) bought new Siemens ER20 CF locomotives produced in Western Europe and brought them into service, some of them have already done about 170–200 thousand km that caused the appearance of indentations of an inadmissible size (the depth is more than 3 mm, the length – 10 mm) the elimination of which turning cutting results in up to 20 mm loss of a wheel. Having grounded off the metal layer of indentation depth, indentation reappears (metal ‘flakes off') and needs to be removed by returning cutting the wheel. The purpose of the current investigation is to determine whether there is a reason to claim that the cause of wheel surface crumbling could be a chemical composition of the wheel or wheel‐to‐rail hardness ratio. The carried out investigations have revealed that there is no reason to claim that the cause of wheel surface crumbling could be the chemical composition of the wheel or wheel‐to‐rail hardness ratio.

Hardness Indentation Studies On Metallic Glasses

ABSTRACTVickers micro-hardness indentations have been performed on a number of amorphous metals. The effects of changes in indentation load on the hardness and appearance of indents will be discussed for amorphous Al87Ni7Gd6. In addition, the effects of changes in test temperature on the micro-hardness and appearance of indentations in Vitreloy I are presented. A transition in deformation/flow character was detected with increasing test temperature for the Vitreloy I specimens. In addition, preliminary hardness data obtained at room temperature on an iron based metallic glass exhibited values in excess of 12 GPa without cracking.

High-affinity and low-affinity vanadate binding to sarcoplasmic reticulum Ca 2+-ATPase labeled with fluorescein isothiocyanate

Conditions were found that allowed both the fluorescence detection of vanadate binding to the Ca 2+-ATPase of skeletal muscle sarcoplasmic reticulum and the vanadate-induced formation of two-dimensional arrays of the enzyme. The fluorescence intensity of fluorescein isothiocyanate-labeled Ca 2+-ATPase increased with high-affinity vanadate binding ( K a = 10 6 M −1 ) as reported by Pick and Karlish (Pick, U. and Karlish, S.D. (1982) J. Biol. Chem. 257, 6120–6126). The Ca 2+ and Mg 2+ dependencies for high-affinity vanadate binding were similar but not identical to those for orthophosphate. In addition, it was found that there is low-affinity ( K a = 380 M −1 ) vanadate binding, which causes a 25% decrease in fluorescence. The Ca 2+ and Mg 2+ dependencies of the low-affinity vanadate binding were different from those of orthophosphate or high-affinity vanadate binding. The covalent attachment of fluorescein isothiocyanate (FITC) in the ATP site of the Ca 2+-ATPase did not affect the formation of two-dimensional arrays, as detected by negatively stained electron micrographs. Vanadate concentrations high enough to saturate the low-affinity binding caused two-dimensional arrays as reported by Dux and Martonosi (Dux, L. and Martonosi, A. (1983) J. Biol. Chem. 258, 2599–2603). In addition, freeze-fracture replicas of quick-frozen specimens showed rows of indentations in the inner leaflet of the bilayer that corresponds to the arrays seen on the outer leaflet. This appearance of indentations suggests that low-affinity vanadate binding causes a transmembrane movement of the Ca 2+-ATPase. By contrast, high-affinity vanadate binding was shown to cause neither array formation nor the appearance of indentations.