New holozoans with cellular resolution from the early Ediacaran Weng'an Biota, Southwest China

The embryo-like fossils from the early Ediacaran Weng'an Biota (Southwest China, 609 million years ago), widely interpreted as members of holozoans, potentially provide insights to understanding the early evolution of development of metazoans and the rise of the animal kingdom. However, the biodiversity of the embryo-like fossil assemblage is largely underestimated, and its more precise phylogenetic affinities within the holozoan tree are still under debate. Here we describe a new species of embryo-like fossil Ostiosphaera rara n. gen. n. sp. from the Ediacaran Weng'an Biota. These three-dimensional, phosphatized specimens exhibit a spherical morphology, an ornamented thick envelope with a circular opening and a membrane-bounded, multicellular inner body. In terms of biological characteristics, Ostiosphaera rara show similarities to a number of extant and fossil analogues including testate amoebae, unicellular green algae, cellular slime mold Fonticuida and co-occurring Weng'an embryo-like fossils. Although the phylogenetic affinity of Ostiosphaera rara is difficult to constrain very precisely based on the available evidence, it is reasonable to follow the holozoan interpretation for them, since that they share the same grade complexity with the co-occurring embryo-like fossils such as Megasphaera and Helicoforamina in terms of the combination of biological features. It is worth mentioning that the new holozoans resemble asexual reproductive gemmules of fossil and living demosponges in size, morphology, circular opening, and cellular anatomy. If the similarity between them reflects biological affinity rather than convergent evolution, this discovery would force us to rethink the evolutionary history of Precambrian sponges.Thematic collection: This article is part of the Advances in the Cambrian Explosion collection available at: https://www.lyellcollection.org/cc/advances-cambrian-explosion

Flexural Behaviour of RC Beams with a Circular Opening at the Flexural Zone and Shear Zone Strengthened Using Steel Plates

In this paper, an investigation on the behaviour of RC beams with circular openings in the flexural zone and shear zone strengthened using steel plates is presented. Totally seven beams were cast: a control beam, one beam with a circular opening of size of one-third the depth of the beam (100 mmϕ) in the flexural zone, one beam with opening strengthened using the steel plate, one beam with a circular opening of size of 100 mmϕ in the shear zone, one beam with an opening in the shear zone strengthened using the steel plate, one beam with two circular openings of size of 100 mmϕ in the shear zone, and another beam with two openings in the shear zone strengthened using the steel plate. The experiments were conducted in a loading frame of 400 kN capacity. The beams were subjected to two-point loading. The ultimate load carrying capacity reduced marginally by 1.78% and 2.8% compared to that of the control beam when a circular opening of 100 mmϕ was provided in the flexural zone and shear zone, respectively, and when the opening was strengthened with steel plates, it reduced by 3.04% and 25%, respectively, but the ductility increased when steel plates were provided. Beams with an opening of size of one-third the depth of the beam (100 mmϕ) in the flexural zone strengthened with the steel plate can be provided, as the load carrying capacity is only marginally reduced compared to the control beam, and the ductility is more when compared with beams with unstrengthened openings.

Flexural Capacity of RC Beams with Opening Strengthened using CFRP Sheet

The use of Carbon Fibre Reinforced Polymer (CFRP) in strengthening has found to be an effective material which comprises of characteristic that comply to the requirement of structural component. CFRP was selected as strengthening material because of the capability to resist the corrosion and could regain the loss capacity due to presence of opening. The opening in structural member was essential in order to provide the route for the utility pipe, air conditioning, water supply and electrical conduit. However, the presence of opening has contributed to the reduction of stiffness, increase of deflection and extension of cracking of the beams. Therefore, this research was conducted to overcome the problem where the flexural capacity and the load deflection behavior of RC beam with opening strengthened by using CFRP sheet was analyzed. A total of five beam have been casted and tested. The specimens consist of beams with different type of opening which are rectangular and circular. The size of all specimen was 200 mm width, 250 mm height and 2000 mm for total length. The size of circular opening was 150 mm in diameter while rectangular opening was 150 x 200 mm. Bi-directional CFRP sheet were applied at the opening area as strengthening material and all beams were tested until failure. All of specimen were produced with the designed using 30 mm concrete cover, 6 mm link size and 10mm main bar size. The testing of specimens comprises of cube compressive test and four-point load for beam testing in order the determine the flexural strength of RC beam. The result from this research indicated that strengthened beam with circular opening which is SBOC-BI exhibit the highest ultimate load of 71.5 kN with flexural failure as the mode of failure.

A unique yet technically simple type of joint allows for the high mobility of scorpion tails

Although being one of the most well-known animal groups, functional and constructional aspects of scorpions and especially of their tail (metasoma) have so far been overlooked. This tail represents a special construction, as it consists of five tube-shaped segments made up of strong cuticle, which are movable against each other and thus manoeuvre the notorious stinger both quickly and very precisely in space. This high mobility of an exoskeletal structure can be attributed to the connection between the segments described here for the first time. This joint allows for the twisting and bending at the same time in a single, simple construction: adjoining metasomal segments each possess an almost circular opening posteriorly, where the next segment is lodged. Anteriorly, these segments possess two saddle-like protrusions laterally, which are able to rotate in two directions on the rim of the posterior circular opening of the previous segment allowing for twisting and bending. The metasomal joint is particularly noteworthy since its mechanism can be compared to that of arthropod appendages. The scorpion metasoma is actually the only known case in Chelicerata, in which an entire body section has been modified to perform tasks similar to that of an appendage while containing digestive organs. The joint mechanism can also inspire technical applications, for instance in robotics.

Research on the Failure and Fracture Evolution of Mylonite with a Prefabricated Circular Opening by Discrete Element Method

In this paper, the failure and fracture process of mylonite with a prefabricated circular opening under biaxial loading is studied by PFC2D code. Firstly, the hoop stress change law of opening wall in the process of loading is theoretically analyzed and three fracture patterns of rocks are proposed. Secondly, the biaxial loading tests of mylonite for numerical simulation are carried out, and the failure and fracture are analyzed from three aspects of space-time evolution of microcracks, energy conversion process, and final damage patterns. As the load progresses, the microcracks start to initiate at the side wall of the opening and the growth velocity of microcracks develops from the slow to fast and then slows down again. The final damage pattern of mylonite with a prefabricated circular opening belongs to shear fracture. The fracture zones start with the side wall spalling and then gradually extend to the border of the rock, which widen from the opening boundary to the border of the rock and slightly twist in the middle. The final fault zone width is about 6 times wider than the average size of simulation particles. Finally, based on the uniaxial compressive strength of mylonite in the laboratory, it is inferred that the fracture pattern of mylonite with a prefabricated circular opening by theoretical analysis is indeed shear failure, which is consistent with the result of numerical simulation.