Cambrian phosphatized fossils from southern China and their bearing on early metazoan evolution

Richly fossiliferous nodular and thin-bedded limestones of Lower and Middle Cambrian age are widespread in southern China, and contain abundant, diverse, and exceptionally well preserved fossils. By acid digestion of the limestones, numerous phosphatized shells displaying detailed three-dimensional characters have been isolated. The univalved ostracode larvae, displaying a univalved-bivalved transition, argue that univalved form may be a primitive larval character for shell-secreting crustaceans. The arthropod (possibly eodiscid trilobite) embryos with preserved blastomeres belong to two embryonic stages; the basic embryonic development of arthropods seems unchangeable with time. Cuticles of three palaeoscolecid worms display unique ornaments and body structures; their discovery reveals that wormlike organisms have achieved a high taxonomic diversity and a wide geographic distribution during the Early Cambrian. The description of redlichiid trilobite larvae and ontogenetic stages of Ichangia ichangensis Chang is of potential interests in recognizing the relationships among the oldest trilobite faunas. Morphological and functional analysis on especially long genal and axial spines of some rodiscids provodes key evidence to deduce their locomotion and life mode. Early instars of bradoriid ostracodes and eodiscid trilobites exhibit apparent morphological diversity, which seems to contrast with the traditional view that regards early development as conservative. However, a complex silicified sponge spicule assemblage associated with the Early Cambrian phosphatized fauna in Zhenping demonstrates that their conservative styles of body architecture were established quickly in the earliest Phanerozoic. These fossil Lagerstatten, as representatives of early skeletal metazoans, have displayed their primitive features without 'modification' relevant to adaptive radiation's of later times. Their morphological and ontogenetic data are therefore essential in evaluating the rapid diversification of early skeletal organisms and the phylogenetic relationships among major metazoan groups

Fuzzy PID control of a two-link flexible manipulator

For a flexible manipulator system, the unwanted vibrations deteriorate usually the performance of the system due to the coupling of large overall motion and elastic vibration. This paper focuses on the active vibration control of a two-link flexible manipulator with piezoelectric materials. The multi flexible body dynamics (MFBD) model of the two-link flexible manipulator attached with piezoelectric sensors and actuators is established firstly. Based on the absolute nodal coordinate formulation (ANCF), the motion equations of the manipulator system are derived and motion process and dynamic responses of the system are simulated. According to the time varying feature of system, a fuzzy PID controller is developed to depress the vibration. This controller can tune control gains online accommodating to the variation of the system. Control results obtained by the fuzzy PID control and the conventional PID control indicate that the fuzzy PID controller can effectively suppress the elastic vibration of the manipulator system and performs better than the conventional PID controller

Protomelission is an early dasyclad alga and not a Cambrian bryozoan

The animal phyla and their associated body plans originate from a singular burst of evolution occurring during the Cambrian period, over 500 million years ago1. The phylum Bryozoa, the colonial ‘moss animals’, have been the exception: convincing skeletons of this biomineralizing clade have been absent from Cambrian strata, in part because potential bryozoan fossils are difficult to distinguish from the modular skeletons of other animal and algal groups2,3. At present, the strongest candidate4 is the phosphatic microfossil Protomelission5. Here we describe exceptionally preserved non-mineralized anatomy in Protomelission-like macrofossils from the Xiaoshiba Lagerstätte6. Taken alongside the detailed skeletal construction and the potential taphonomic origin of ‘zooid apertures’, we consider that Protomelission is better interpreted as the earliest dasycladalean green alga—emphasizing the ecological role of benthic photosynthesizers in early Cambrian communities. Under this interpretation, Protomelission cannot inform the origins of the bryozoan body plan; despite a growing number of promising candidates7,8,9, there remain no unequivocal bryozoans of Cambrian age

A lattice Boltzmann method for axisymmetric multicomponent flows with high viscosity ratio

A color-gradient lattice Boltzmann method (LBM) is proposed to simulate ax- isymmetric multicomponent flows. This method uses a collision operator that is a combination of three separate parts, namely single-component collision op- erator, perturbation operator, and recoloring operator. A source term is added into the single-component collision operator such that in each single-component region the axisymmetric continuity and momentum equations can be exactly re- covered. The interfacial tension effect is realized by the perturbation operator, in which an interfacial force of axisymmetric form is derived using the concept of continuum surface force. A recoloring operator proposed by Latva-Kokko and Rothman is extended to the axisymmetric case for phase segregation and maintenance of the interface. To enhance the method’s numerical stability for handling binary fluids with high viscosity ratio, a multiple-relaxation-time mod- el is used for the collision operator. Several numerical examples, including static droplet test, oscillation of a viscous droplet, and breakup of a liquid thread, are presented to test the capability and accuracy of the proposed color-gradient LB- M. It is found that the present method is able to accurately capture the phase interface and produce low spurious velocities. Also, the LBM results are all in good agreement with the analytical solutions and/or available experimental data for a very broad range of viscosity ratios

Lattice Boltzmann modeling of contact angle and its hysteresis in two-phase flow with large viscosity difference

Contact angle hysteresis is an important physical phenomenon omnipresent in nature and various industrial processes, but its effects are not considered in many existing multiphase flow simulations due to modeling complexity. In this work, a multiphase lattice Boltzmann method (LBM) is developed to simulate the contact-line dynamics with consideration of the contact angle hysteresis for a broad range of kinematic viscosity ratios. In this method, the immiscible two-phase flow is described by a color-fluid model, in which the multiple-relaxation-time collision operator is adopted to increase numerical stability and suppress unphysical spurious currents at the contact line. The contact angle hysteresis is introduced using the strategy proposed by Ding and Spelt [Ding and Spelt, J. Fluid Mech. 599, 341 (2008)], and the geometrical wetting boundary condition is enforced to obtain the desired contact angle. This method is first validated by simulations of static contact angle and dynamic capillary intrusion process on ideal (smooth) surfaces. It is then used to simulate the dynamic behavior of a droplet on a nonideal (inhomogeneous) surface subject to a simple shear flow. When the droplet remains pinned on the surface due to hysteresis, the steady interface shapes of the droplet quantitatively agree well with the previous numerical results. Four typical motion modes of contact points, as observed in a recent study, are qualitatively reproduced with varying advancing and receding contact angles. The viscosity ratio is found to have a notable impact on the droplet deformation, breakup, and hysteresis behavior. Finally, this method is extended to simulate the droplet breakup in a microfluidic T junction, with one half of the wall surface ideal and the other half nonideal. Due to the contact angle hysteresis, the droplet asymmetrically breaks up into two daughter droplets with the smaller one in the nonideal branch channel, and the behavior of daughter droplets is significantly different in both branch channels. Also, it is found that the contact angle hysteresis is strengthened with decreasing the viscosity ratio, leading to an earlier droplet breakup and a decrease in the maximum length that the droplet can reach before the breakup. These simulation results manifest that the present multiphase LBM can be a useful substitute to Ba et al. [Phys. Rev. E 88, 043306 (2013)] for modeling the contact angle hysteresis, and it can be easily implemented with higher computational efficiency