Cap-shaped skeletal fossils are the earliest undisputed body fossils of mollusks appearing in the basal Cambrian. A study on the morphometry of cap-shaped fossils from the Nanjiang area (North Sichuan, China) is undertaken to understand the origin and evolution of the early mollusks. The distribution of these fossil cap-shaped mollusks indicates a stepwise increase in their diversity during the early Cambrian. Maikhanella Zhegallo in Voronin et al., 1982 co-occuring with the spinose sclerites of siphogonuchitids, is regarded as the earliest scleritized mollusk. It is followed by other maikhanellids, e.g., Purella Missarzhevsky, 1974 and Yunnanopleura Yu, 1987, which co-occur with the earliest univalved helcionellids, e.g., Igorella Missarzhevsky in Rozanov et al., 1969. Cluster analysis of their morphometric characteristics shows that the Maikhanella group is similar to the Purella and Yunnanopleura groups, but is less comparable with univalved helcionellids. The maikhanellids are interpreted as representatives of the stem group Aculifera, although it remains uncertain if one or two larger cap-shaped shell plates were present on the elongate slug-like body, comparable to those of Halkieria Poulsen, 1967 or Orthrozanclus Conway Morris and Caron, 2007. Maikhanellids are characterized by the prominent protrusions or scales on the cap-shaped shell plates arranged in a concentric pattern around the shell apex. Evolutionarily, the protrusions or scales are reduced in younger strata, whereas subsequently a typically concentric ornament developed, the cap-shaped shell plates developed higher profiles, and the apical region became increasingly bare of scales. Meanwhile, the cap-shaped shell plates gradually evolved into a helcionellid-like appearance with an anteroposteriorly inclined apex. The morphological evolution of the earliest sclerotized mollusks reflects biotic evolution and environmental adaption among the stem-group mollusks during the early Cambrian.

We conducted a prospective, observational study to determine the incidence of feeding intolerance (FI) within 7 d of initiating enteral nutrition (EN) in patients undergoing cardiopulmonary bypass (CPB) and to evaluate the association between FI and a poor prognosis. Patients who underwent CPB surgery at Fujian Medical University Union Hospital between March 2020 and June 2020 were enrolled. According to the presence or absence of FI within 7 d after EN, patients were divided into FI and non-FI groups. According to the occurrence of a poor prognosis (death, gastrointestinal haemorrhage, acute kidney injury, liver insufficiency, neurological events (cerebral infarction, cerebral haemorrhage and epilepsy) and prolonged mechanical ventilation (> 48 h)), patients were divided into poor prognosis and good prognosis groups. The mean age of the 237 CPB patients, including 139 men and ninety-eight women, was 53·80 (sd 12·25) years. The incidence of FI was 64·14 %. Multivariate logistic regression analysis showed factors independently associated with poor prognosis after CPB included FI (OR 2·138; 95 % CI 1·058, 4·320), age (OR 1·033; 95 % CI 1·004, 1·063), New York Heart Association (NYHA) class III/IV cardiac function (OR 2·410; 95 % CI 1·079, 5·383), macrovascular surgery (OR 5·434; 95 % CI 1·704, 17·333) and initial sequential organ failure assessment score (OR 1·243; 95 % CI 1·010, 1·530). Thus, the incidence of FI within 7 d of EN after CPB was high, which was associated with a poor prognosis.

In recent years, intracranial thrombectomy stent has been an important method to treat ischemic stroke caused by acute thrombosis. In this paper, a new intracranial thrombectomy stent with a fish scale-like structure was designed and its mechanical properties were studied by a finite element method. The porosity of all stents was more than 80%. The space occupation ratio (SOR) of the stents increased linearly with the increase of strut thickness, while the strut width had little effect on SOR. The maximum equivalent stress and strain, the directional deformation and overall radial load of the stent decreased with the increase of strut thickness, however, the strut width has little impact on these parameters. The stents with 0.2 mm strut width and the thickness of 0.15 and 0.20 mm had better radial load performance, and the stent with 0.2 mm strut width and 0.15 mm strut thickness had better contact performance with the vessel wall and displayed better flexibility. Therefore, the present study provides a theoretical basis for the design of new intracranial thrombectomy stent.

In this contribution, the structural, mechanical, and thermal properties of MSiO4 have been investigated theoretically and the anisotropy of elastic properties has been discussed in detail. The heterogeneous bonding nature was revealed from density functional theory computations and chemical bond theory (CBT). The Young's modulus and shear modulus of MSiO4 were anisotropic and the anisotropy on different planes was quite different. The thermal expansion coefficients of MSiO4 estimated from CBT were 5.1 × 10−6 and 4.4 × 10−6 K−1 for ZrSiO4 and HfSiO4, respectively. These results were quite consistent with the experiments. The temperature dependent thermal conductivities of MSiO4 were estimated from Slack's model, the minimum thermal conductivity was predicted to be 1.54 and 1.24 W m−1 K−1 for ZrSiO4 and HfSiO4, respectively. Our theoretical results show that MSiO4 are excellent thermal barrier materials with good tolerance to withstand the mechanical damage.

Titanium carbide (TiC) twins are believed to be extremely unstable because of their high twin boundary energy. Here, we report that TiC twins are always presented in platelets with dimensions of 2–3 μm in length and less than 300 nm in width. In-depth microstructural characterizations by high-resolution transmission electron microscopy demonstrate that Al atoms at the twin boundary play a decisive role in stabilizing TiC twins. With different amounts of Al, perfect and defective TiC twins are formed. For perfect twins, three types of twin boundaries can be formed depending on the amount of remaining Al at the twin boundary. With inadequate Al, the TiC twins become defective with certain degrees of deviation from the perfect twin orientation. Based on a detailed analysis of the microstructure of the twin boundaries, a mechanism for the formation and stabilization of TiC twins is proposed.

Bonding character, elastic mechanical parameters, ideal strengths, and atomistic shear deformation mechanisms of M3AlN (M = Zr and Hf) were studied by first-principles method. M3AlN exhibits layered chemical bonding character due to the alternately stacking of relatively soft Al–M and strong N–M covalent bonds. The second-order elastic constants and mechanical parameters of M3AlN were reported for the first time. The stress–strain relationships for different deformation modes were studied and the ideal shear and tensile strength were obtained. M3AlN ceramics are predicted to be “quasi-ductile” layered nitrides based on the low shear-modulus-to-bulk-modulus ratios, positive Cauchy pressure (c12–c44), and lower ideal shear strength compared to ideal tensile strength. Investigation of the atomistic shear deformation mechanism of Hf3AlN shows that stretching of soft Al–Hf bonds and relatively weak bridge N–Hf1 bonds dominate the shear deformation; while the rigid N–Hf2 bonds resist against the applied shear strain. Chemical bonding characteristics and shear deformation mechanism of M3AlN are similar with those of other “quasi-ductile” ceramics, such as MAX phases, LaPO4 monazite, and γ-Y2Si2O7. The results further suggest that M3AlN nitrides should be quasi-ductile and damage tolerant.

We performed density-functional calculations of oxygen incorporation and diffusion in layered Ti2AlC for a range of intrinsic- and impurity-element chemical potentials. In view of the thermal equilibrium coexistence between oxygen-dissolved Ti2AlC and the oxide scale, a thermodynamic scheme is presented that allows the comparison of the relative stability of oxygen defects in different exterior environments. The calculations show that the oxygen atom favors substitution on carbon lattice sites (OC) under oxygen-lean conditions and high temperatures, whereas the occurrence of an oxygen interstitial in the aluminum atomic layer (IO-tri) becomes more preferential in an oxygen-rich atmosphere and low temperatures. Interstitial oxygen (IO-tri) diffusion via a metastable interstitial site (IO-oct) has a comparatively low migration energy. The substitutional oxygen defect (OC) diffuses by exchanging with neighboring carbon vacancy, which needs a relatively high diffusion barrier.

A linkage–linkage disequilibrium map that describes the pattern and extent of linkage dis-equilibrium (LD) decay with genomic distance has now emerged as a viable tool to unravel the genetic structure of population differentiation and fine-map genes for complex traits. The prerequisite for constructing such a map is the simultaneous estimation of the linkage and LD between different loci. Here, we develop a computational algorithm for simultaneously estimating the recombination fraction and LD in a natural outcrossing population with multilocus marker data, which are often estimated separately in most molecular genetic studies. The algorithm is founded on a commonly used progeny test with open-pollinated offspring sampled from a natural population. The information about LD is reflected in the co-segregation of alleles at different loci among parents in the population. Open mating of parents will reveal the genetic linkage of alleles during meiosis. The algorithm was constructed within the polynomial-based mixture framework and implemented with the Expectation–Maximization (EM) algorithm. The by-product of the derivation of this algorithm is the estimation of outcrossing rate, a parameter useful to explore the genetic diversity of the population. We performed computer simulation to investigate the influences of different sampling strategies and different values of parameters on parameter estimation. By providing a number of testable hypotheses about population genetic parameters, this algorithmic model will open a broad gateway to understand the genetic structure and dynamics of an outcrossing population under natural selection.

Y2SiO5 has potential applications as a high-temperature structural ceramic and environmental/thermal barrier coating. In this work, we synthesized single-phase Y2SiO5 powders utilizing a solid–liquid reaction method with LiYO2 as an additive. The reaction path of the Y2O3/SiO2/LiYO2 mixture with variation in temperatures and the role of the LiYO2 additive on preparation process were investigated in detail. The powders obtained by this method have good sinterability. Through a pressureless sintering process, almost fully dense Y2SiO5 bulk material was achieved with a very high density of 99.7% theoretical.

The changes in optical properties and damage mechanism of ZnO/silicone white paint caused by <200 keV protons in space were investigated in terms of ground-based simulation testing. The energies of protons were chosen as 50, 90, and 110 keV. The results show that the change in solar absorptance Δαs increases with increasing irradiation fluence as well as the proton energy. On the basis of photoluminescence spectroscopy, it is revealed that with increasing proton fluence, the 660-nm emission band related to the interstitial Zn-ions changes little, the 405-nm emission band related to the Zn vacancies decreases and tends to disappear, the 460-nm emission band related to the double ionized oxygen vacancies decreases, and the emission band related to the singly ionized oxygen vacancies increases. SRIM simulation analysis indicates that the damage effect of ZnO/silicone white paint caused by proton exposure would be aggravated due to the organic silicone binder. The proton irradiation leads to ionization of Zn atoms, formation of free oxygen and oxygen vacancies, and degradation of the organic silicone binder. It is believed that the optical degradation of ZnO/silicone white paint, induced by <200 keV protons, can be attributed to the combined effect of these three processes.

In this article, a novel pressureless solid-liquid reaction method is presented for preparation of yttrium disilicate (γ-Y2Si2O7). Single-phase γ-Y2Si2O7 powder was synthesized by calcination of SiO2 and Y2O3 powders with the addition of LiYO2 at 1400 °C for 4 h. The addition of LiYO2 significantly decreased the synthesis temperature, shortened the calcination time, and enhanced the stability of γ-Y2Si2O7. The sintering of these powders in air and O2 was studied by means of thermal mechanical analyzer. It is shown that the γ-Y2Si2O7 sintered in oxygen had a faster densification rate and a higher density than that sintered in air. Furthermore, single-phase γ-Y2Si2O7 with a density of 4.0 g/cm3 (99% of the theoretical density) was obtained by pressureless sintering at 1400 °C for 2 h in oxygen. Microstructures of the sintered samples are studied by scanning electron microscope.