Mesh considerations for finite element blast modelling in biomechanics

Finite element (FE) modelling is a popular tool for studying human body response to blast exposure. However, blast modelling is a complex problem owing to more numerous fluid–structure interactions (FSIs) and the high–frequency loading that accompanies blast exposures. This study investigates FE mesh design for blast modelling using a sphere in a closed-ended shock tube meshed with varying element sizes using both tetrahedral and hexahedral elements. FSI was consistent for sphere-to-fluid element ratios between 0.25 and 4, and acceleration response was similar for both element types (R² = 0.997). Tetrahedral elements were found to become increasingly volatile following shock loading, causing higher pressures and stresses than predicted with the hexahedral elements. Deviatoric stress response was dependent on the sphere mesh size (p < 0.001), while the pressure response was dependent on the shock tube mesh size (p < 0.001). The results of this study highlight the necessity for mesh sensitivity analysis in blast models.     

The pollen tube: a soft shell with a hard core

Plant cell expansion is controlled by a fine‐tuned balance between intracellular turgor pressure, cell wall loosening and cell wall biosynthesis. To understand these processes, it is important to gain in‐depth knowledge of cell wall mechanics. Pollen tubes are tip‐growing cells that provide an ideal system to study mechanical properties at the single cell level. With the available approaches it was not easy to measure important mechanical parameters of pollen tubes, such as the elasticity of the cell wall. We used a cellular force microscope (CFM) to measure the apparent stiffness of lily pollen tubes. In combination with a mechanical model based on the finite element method (FEM), this allowed us to calculate turgor pressure and cell wall elasticity, which we found to be around 0.3 MPa and 20–90 MPa, respectively. Furthermore, and in contrast to previous reports, we showed that the difference in stiffness between the pollen tube tip and the shank can be explained solely by the geometry of the pollen tube. CFM, in combination with an FEM‐based model, provides a powerful method to evaluate important mechanical parameters of single, growing cells. Our findings indicate that the cell wall of growing pollen tubes has mechanical properties similar to rubber. This suggests that a fully turgid pollen tube is a relatively stiff, yet flexible cell that can react very quickly to obstacles or attractants by adjusting the direction of growth on its way through the female transmitting tissue.     

Prolonged inhibitory effects against planktonic growth,adherence, and biofilm formation of pathogens causing ventilator-associated pneumonia using a novel polyamide/silver nanoparticle composite-coated endotracheal tube

Abstract

Microbial cells can rapidly form biofilm on endotracheal tubes (ETT) causing ventilator-associated pneumonia, a serious complication in patients receiving mechanical ventilation. A novel polyamide with a good balance of hydrophilic/hydrophobic moieties was used for the embedment of green-reduction silver nanoparticles (AgNPs) for the composite-coated ETT. The films were conformal with a thickness of ～ 17?±?3?µm accommodating high loading of 60?±?35?nm spherical-shaped AgNPs. The coated ETT resulted in a significant difference in reducing both planktonic growth and microbial adhesion of single and mixed-species cultures, compared with uncoated ETT (p?<?0.05). A time-kill assay demonstrated rapid bactericidal effects of the coating on bacterial growth and cell adhesion to ETT surface. Biofilm formation by Pseudomonas aeruginosa and Staphylococcus aureus, commonly encountered pathogens, was inhibited by > 96% after incubation for 72?h. Polyamide/AgNP composite-coated ETT provided a broad-spectrum activity against both Gram-positive and Gram-negative bacteria as well as Candida albicans and prolonged antimicrobial activity.     

桂花非试管快繁技术研究

以一年生丹桂枝条为材料,探索桂花非试管快速繁殖最佳条件。用不同浓度吲哚乙酸(IBA)浸泡插条基部,对比不同实验组材料的生根率。实验结果显示,200 mg/L的IBA处理的桂花枝条,在定时控制喷雾条件下,插后55 d的生根率和成苗率达100%。本研究对加快桂花培育速度、对深化桂花快繁技术研究具有重要意义。     

A cadaver unearthed: the anatomy of the Japanese living fossil Stirpulina ramosa (Bivalvia: Anomalodesmata: Clavagellidae) – the unique specimen in the collections of Emperor Shōwa

The only extant, preserved and complete specimen of Stirpulina ramosa has been discovered in the collections of the late Emperor Shōwa (Hirohito) and is described herein. Hitherto, only shells and the adventitious tubes of this species have been described. This study of the anatomy complements previous ones and adds further information as to how the adventitious tube is formed: that is, by the laying down of an organic, periostracum‐like, template that is then biomineralized internally to form the tube and is externally plastered with the clasts that constitute the enclosing burrow wall. Such secretions are produced by pallial lobes that unite on the right side to create the characteristic sutured pleat in this region of the tube. The periostracum enclosing the so‐interred animal is then secreted against the internal template of the tube. The shell of S. ramosa and, as a consequence, the musculature, is greatly disfigured as a result of the incorporation of the left valve into the fabric of the adventitious tube. This valve can, however, continue to grow within the tube, especially posteriorly. The right valve remains free inside the tube but grows only a little more anteriorly. The anterior mantle, with a minute pedal gape, is greatly thickened and secretes the watering pot component of the tube. In many anatomical respects, for example simultaneous hermaphroditism, S. ramosa still reflects the basic anomalodesmatan plan and such modifications as there are from the clavagellid form relate principally to the structure, formation and thus functioning of the adventitious tube. This study of S. ramosa has allowed the full spectrum of clavagellid adaptive radiation to be analysed and an evolutionary picture created which suggests that species of Clavagella/Dacosta and Stirpulina are Mesozoic (Late Cretaceous) remnants. Conversely, species of Bryopa and Dianadema are more modern, Late Oligocene and Palaeocene (Cenozoic), respectively, and possibly evolved in association with the emergence of the Indo‐West Pacific centre of coral diversity, with a postulated average age of just 30 Myr. © 2013 The Linnean Society of London     

An Ultrastructural Study of the Extruded Polar Tube of Anncaliia algerae (Microsporidia)

All microsporidia share a unique, extracellular spore stage, containing the infective sporoplasm and the apparatus for initiating infection. The polar filament/polar tube when exiting the spore transports the sporoplasm through it into a host cell. While universal, these structures and processes have been enigmatic. This study utilized several types of microscopy, describing and extending our understanding of these structures and their functions. Cryogenically preserved polar tubes vary in diameter from 155 to over 200 nm, noticeably larger than fixed‐sectioned or negatively stained samples. The polar tube surface is pleated and covered with fine fibrillar material that projects from the surface and is organized in clusters or tufts. These fibrils may be the sites of glycoproteins providing protection and aiding infectivity. The polar tube surface is ridged with 5–6 nm spacing between ridges, enabling the polar tube to rapidly increase its diameter to facilitate the passage of the various cargo including cylinders, sacs or vesicles filled with particulate material and the intact sporoplasm containing a diplokaryon. The lumen of the tube is lined with a membrane that facilitates this passage. Careful examination of the terminus of the tube indicates that it has a closed tip where the membranes for the terminal sac are located.     

Wnt‐3 and Wnt‐3a play different region‐specific roles in neural crest development in avians

Wnt signalling regulates cell proliferation and cell fate determination during embryogenesis. However, little is known about the developmental role of one Wnt family member, Wnt‐3, during avian development. To investigate the possible functions of Wnt‐3, its expression pattern was determined using whole‐mount in situ hybridization. Wnt‐3 is expressed in important signalling centres, including the dorsal neural tube, Hensen's node and the AER (apical ectodermal ridge). Most interestingly, Wnt‐3 is expressed in the dorsal neural tube as a gradient, with the strongest expression anterior in the trunk. Furthermore, this study showed that Wnt‐3 and Wnt‐3a play a different role in neural crest lineages derived from different axial level of neural tube. Wnt‐3 might be involved in proliferation of neural crest lineages, whereas Wnt‐3a plays an important role in melanogenesis in vagal. However, both Wnt‐3 and Wnt‐3a cause a significant increase in melanogenesis in the trunk neural crest lineage.     

草莓试管苗生根诱导对移栽成活的影响

本文探讨了草莓试管苗生根诱导期长短、发根数及根长度对移栽成活率和幼苗生长的影响。结果表明,诱导期在41~50天效果最好,成活率达94%;根数越多,成活越容易;根长度在5.1~10.0 cm时,有利于成活。     

Distribution of F-actin and Microtubules in Pollen and Pollen Tube of Lilium davidii

F-actin and microtubules are important components of pollen tube, which have very important function in cytoplasm streaming of pollen tube. The authors observed the distribution of Factin and microtubules in the pollen tube of Lilium davidii Duch. by immunofluorescence technique and confocol laser scanning microscopy, through which some new results were obtained. 1. Chemical fixation could preserve F-actin well in pollen tube, so the relation between F-actin and microtubules could be studied by the methods of chemical fixation and fluorescence labelling in pollen tube. 2. F-actin bundles were absent near the pollen tube tip, while microtubules were abundant and web formed in the pollen tube tip. The authors found that the terminal of microtubules was closely associated with the plasma membrane in the pollen tube tip. 3. Only a few F-actin bundles co-exist with the microtubules in the pollen tube of Lilium davidii. The results provided new evidence for the fimction and relationship between F-actin and microtubules in the pollen tube.