Oxides containing only one metallic component as well as mixed oxides with several cations may form during oxidation of multicomponent alloys. It is demonstrated that regardless of an intricacy of a ...particular situation, there exists a simple, general, practical, and elegant expression for Pilling–Bedworth ratio underpinned by a realistic assumption. Limits of formula’s applicability are delineated.
Overall performance of curvilinear fiber reinforced composite structures (CFRCSs) can be designed by adjusting the local fiber orientation and content. In this paper, an optimized design method based ...on stress gradient distribution for CFRCSs was proposed to improve the efficiency in strength of continuous fiber reinforced composites. The mechanism of fiber content regulation in continuous fiber reinforced composites 3D printing was studied. The adaptive feed calculation method of resin was proposed, and the 3D printing of CFRCSs was realized. A 3D printed composite perforated plate with a hole under tensile loading was optimized and fabricated to verify the effectiveness of the proposed methods. After the optimized design, the maximum stress concentration factor was reduced by 36%, and the ultimate tensile strength was increased by 42%. Through the proposed optimization design method, the fiber content distribution corresponds to the stress distribution, and the fiber direction distribution corresponds to the maximum principal stress direction distribution. At the same time, the stress was redistributed to reduce the stress concentration. Therefore, the ultimate strength was improved. The optimized design method and 3D printing method of CFRCSs have potential application prospects in aerospace, automotive and other fields.
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The efficiency of modeling of the axisymmetric dynamics of a gas bubble near a curved rigid wall by the boundary element method using the fundamental solution of the Laplace equation for an unbounded ...domain is numerically studied. For this purpose, the problems of the collapse of a bubble near a flat wall and the expansion and subsequent collapse of a bubble near the concave and convex walls are considered. To assess the effectiveness, the results of calculations of these problems are compared with the known results of their calculations using their fundamental solutions for the areas bounded by those walls. The results show the dependence of the numerical solution on the radius of the computational domain on the wall, the number of cells when the domain is uniformly partitioned, and the number of cells when it is non-uniformly partitioned with condensation toward the axis of symmetry along a geometric progression.
Origin of Echinodermata Ezhova, O. V.; Malakhov, V. V.
Paleontological journal,
12/2022, Letnik:
56, Številka:
8
Journal Article
Recenzirano
The common ancestor of Ambulacraria was a mobile bilaterally symmetrical organism. Its body was subdivided into a preoral (proboscis) region, a perioral (collar) region with ciliated tentacles, and a ...trunk region with a metameric coelom and metameric gill slits. Like in other Bilateria, the preoral and tentacular regions of Ambulacraria are free of
Hox
gene expression, which begins in the area of the first pair of gill slits in compliance with the colinearity. The axial complex is a synapomorphy of the Ambulacraria clade. A bilaterally symmetrical ancestor of Echinodermata lay on its dorsal side, so its anus was shifted to the ventral side as in present-day echinoderm larvae. This stage of evolution corresponds to the Early Paleozoic bilaterally symmetrical forms, such as
Protocinctus, Ctenocystis
, and
Ctenoimbricata
. The common ancestor of echinoderms had a symmetrical tentacular apparatus consisting of five ciliated tentacles on each side of a collar. At the next stage, the ancestors of echinoderms lay on the right side that resulted in the reduction of the tentacles on the right side and the right hydrocoel. This evolution stage includes various Early Paleozoic forms (
Cothurnocystis
,
Dendrocystoides
,
Syringocrinus
,
Castericystis
,
Coleicarpus
,
Rhenocystis
, etc.). The next stage is related to the sedentary lifestyle. During this stage, the mouth and tentacles occupied an apical position, the anus has shifted up, and thus an intestinal loop was formed. The five primary tentacles of the left side of the ancestor of Ambulacraria predestined the formation of pentaradial symmetry of echinoderms. The primary tentacles remained only in Holothuroidea. The secondary ciliary grooves were formed between the primary tentacles. These grooves were accompanied by hydrocoelic canals, which gave rise to the water-vascular (ambulacral) system. The present-day echinoderms are characterized by several metameric rings formed by the derivatives of the left somatocoel. They derive from the coelomic segments of the left side of the trunk of the ambulacrarian ancestor and, thus, the echinoderms retain coelomic metamerism. The attachment of the crinoid larvae by the preoral lobe reflects the ancient method of locomotion of deuterostomes using the proboscis, but, in reality, the Pelmatozoa stalk is homologous to the Pterobranchia stalk, i.e., the posterior end of the body, because the right somatocoel grows into it. During metamorphosis, the internal coelomic complex of the larva is inverted by 180°. The significance of this inversion for the translocation of the anterior genes of the
Hox
cluster is discussed. The ancestors of Eleutherozoa began to crawl on the oral surface, which led to a shift of the anus to the aboral side. Thus, the ontogeny and phylogeny of echinoderms exhibits a change from bilateral symmetry to dissymmetry, and then the development of pentameric symmetry.
This paper has been written from the standpoint of the phylogenetic tetrad method which includes comparative anatomy, evolutionary developmental biology (“evo–devo”), paleontology, and molecular ...phylogenomics. The Bilateria consists of two sister groups such as Cnidaria and triploblastic Bilateria. Their common ancestor was a bilaterally symmetrical diploblastic organism with two circles of tentacles, labial and marginal, around a slit-like mouth. Anthozoa retains a primary bilateral symmetry. Medusozoa develops a secondary radial symmetry as a result of adaptation to a sedentary lifestyle. The common ancestor of the triploblastic Bilateria had a through gut formed by amphistomy, a coelom, segmentation, and metameric limbs. The marginal circle of tentacles gave rise to metameric limbs, the labial circle of tentacles gave rise to perioral ciliated tentacles, ventral ciliated sole (neurotroch), and telotroch. The homology of the ciliated tentacle apparatus in Trochozoa, Lophophorata, and Deuterostomia is substantiated. The ciliary armament of the triploblastic Bilateria larvae follows the general structural plan and includes the adoral ciliary field (a homologue of the ciliary tentacles of adult forms), neurotroch, and telotroch. The homology of pre-oral and oral (=tentacular) segments in triploblastic Bilateria is substantiated. The origin of Ecdysozoa as primarily semi-aquatic organisms is discussed. The chitinous cuticle of Ecdysozoa is homologous to the chitinous theca attached to the epidermis. The primary biramous limbs of Ecdysozoa resulted from the integration of tentacles of the marginal and labial circle of the common bilaterian ancestors. Tentacles of the marginal circle gave rise to exopods, and those of the labial circle gave rise to endopods. Examples of a primary biramous limb in Cambrian Ecdysozoa and recent Chelicerata are considered. The secondary biramous limb of Crustacea is a result from the secondary splitting of the endopod of the primary biramous limb into exopodite and endopodite. The problem of Hexapoda wings homology is discussed. Lobopoda is an Ecdysozoa lineage which adapted to life in loose substrate and acquired a worm-like body shape; the primary endopods became lobopods, while the primary exopods gave rise to metameric dorsolateral spines. Habitation in the sediment (Palaeoscolecida and Cephalorhyncha) caused a complete reduction of limbs and segmentation. The role of progenesis in the nematode origin is discussed.
Despite the significant progress achieved in recent years, the physical mechanisms underlying the origin of solar energetic particles (SEPs) are still a matter of debate. The complex nature of both ...particle acceleration and transport poses challenges to developing a universal picture of SEP events that encompasses both the low-energy (from tens of keV to a few hundreds of MeV) observations made by space-based instruments and the GeV particles detected by the worldwide network of neutron monitors in ground-level enhancements (GLEs). The high-precision data collected by the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) satellite experiment offer a unique opportunity to study the SEP fluxes between ∼80 MeV and a few GeV, significantly improving the characterization of the most energetic events. In particular, PAMELA can measure for the first time with good accuracy the spectral features at moderate and high energies, providing important constraints for current SEP models. In addition, the PAMELA observations allow the relationship between low- and high-energy particles to be investigated, enabling a clearer view of the SEP origin. No qualitative distinction between the spectral shapes of GLE, sub-GLE and non-GLE events is observed, suggesting that GLEs are not a separate class, but are the subset of a continuous distribution of SEP events that are more intense at high energies. While the spectral forms found are to be consistent with diffusive shock acceleration theory, which predicts spectral rollovers at high energies that are attributed to particles escaping the shock region during acceleration, further work is required to explore the relative influences of acceleration and transport processes on SEP spectra.
Coelom Metamerism in Echinodermata Ezhova, O. V.; Malakhov, V. V.
Paleontological journal,
12/2021, Letnik:
55, Številka:
10
Journal Article
Recenzirano
Within all major taxa of Bilateria, there are forms with coelomic metamerism. This suggests that coelomic metamerism was characteristic of the common ancestor of Bilateria. Among deuterostomes, ...metamerism is clearly expressed in chordates, and elements of metamerism are present in hemichordates. Do echinoderms have remnants of coelomic metamerism that was inherited from the common ancestor of Bilateria? The coelomic system of echinoderms includes several metameric coelomic rings located along the oral-aboral axis, namely: the axocoelomic ring, the hydrocoelomic ring, 2 to 6 coelomic rings originating from the left somatocoel, and one epigastric ring originating from the right somatocoel. Thus, in echinoderms, there is a dissymmetrical metamerism, derived from the original metamerism of the common ancestors of Deuterostomia and, possibly, the common ancestors of Bilateria. The problem of dexiothetism as the cause for the formation of coelomic dissymmetry in echinoderms is discussed.
More efficient and preferably more convenient and greener synthetic solutions in coumarin scaffold functionalization are in steady demand. The Duff
-formylation of unsubstituted umbelliferone was ...revised in this study. The reaction conditions were optimized based upon data from the literature analysis and resulted in unexpectedly rapid
-formylation of umbelliferone, yielding a mixture of
-formyl position isomers. Thorough studies on the separation of
-formylated umbelliferones using chromatographic and recrystallization methods as well as the evaluation of their solubility in common organic solvents led to complete resolution of 8-formyl- and 6-formylumbelliferones. The precise protocol for simultaneous preparation, extraction, and purification of 8-formyl- and 6-formylumbelliferones is provided, and the prospective studies of biological and pharmacological activities of these compounds are synopsized.
The question of the presence of kidneys in echinoderms is a subject of discussion. Many guides state the absence of a special excretory organ in the echinoderms. However, there is a special excretory ...organ (kidney) in echinoderms. It is the axial complex. The blood network of the axial complex is represented by the system of haemocoelic spaces, which lie between the folds of the coelothelium of axial coelom. This haemocoelic capillary system is an axial organ. Contractions of the heart, which is enclosed into the pericardial coelom on the aboral side of the body, provides directional movement of the blood. The heart accepts the blood from two aboral haemal rings: the gastric ring and the genital ring. Haemocoelic spaces of the axial organ are separated from the axial coelom by the basal lamina. The surface of this basal lamina from the side of coelom is covered by the coelothelial lining, which contains the podocytes and epithelial-muscle cells. The extracellular diaphragms are stretched between the processes of the podocytes. Contractions of the heart and epithelial-muscle cells create the pressure, which provides the ultrafiltration of liquid from the haemocoel to the axial coelom. The coelomic liquid with the products of excretion is removed from the axial coelom to the environment via the pores of madreporic plate. The hemichordate heart-kidney consists of the proboscis coelom, which develops from the left axocoel of tornaria, the pericardium, which develops from the right axocoel, the heart, and the so-called glomerulus, i.e., a network of haemocoelic spaces between the folds of the proboscis coelom. The fluid is filtered from the haemocoelic spaces of the glomerulus through the basal lamina, passes between the finger-like processes of the podocytes, and reaches the proboscis coelom, from which it is excreted to the environment via the coelomoduct. The axial complex of Echinodermata is an undoubted homologue of the heart-kidney of Hemichordata. It is formed from the homologous larval coeloms, has a significant similarity in the structure, and is analogous in function. Probably, the excretory organ based on the dissymmetric preoral coeloms was formed in the common ancestor of hemichordates and echinoderms. It represents the most important synapomorphy of Ambulacraria.
Worm-like endosymbionts were found in the hepatic region of the digestive tract of the deep-sea acorn worm
Quatuoralisia malakhovi
Ezhova et Lukinykh, 2022 (family Torquaratoridae) from the Bering ...Sea. The symbionts were assigned to the taxon Nemertodermatida on the basis of histological examination. Torquaratoridae are similar in feeding type to holothuroids, which have also been found to have Xenacoelomorpha endosymbionts.
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