scholarly journals Membrane-bounded nucleoid discovered in a cultivated bacterium of the candidate phylum ‘Atribacteria’

2019 ◽  
Author(s):  
Taiki Katayama ◽  
Masaru K. Nobu ◽  
Hiroyuki Kusada ◽  
Xian-Ying Meng ◽  
Hideyoshi Yoshioka ◽  
...  
Keyword(s):  
Cellular Structure ◽  
Anaerobic Bacterium ◽  
Cell Structure ◽  
Intracellular Membrane ◽  
Chromosomal Dna ◽  
Intracytoplasmic Membrane ◽  
Genomic Features ◽  
Prokaryotic Cell

AbstractA key feature that differentiates prokaryotes from eukaryotes is the absence of an intracellular membrane surrounding the chromosomal DNA. Here, we report isolation of an anaerobic bacterium that possesses an additional intracytoplasmic membrane surrounding a nucleoid, affiliates with the yet-to-be-cultivated ubiquitous phylum ‘Ca. Atribacteria’, and possesses unique genomic features likely associated with organization of complex cellular structure. Exploration of the uncharted microorganism overturned the prevailing dogma of prokaryotic cell structure.

Exploiting the Asymmetric Energy Barrier in Multi-Stable Origami to Enable Mechanical Diode Behavior in Compression

2019 ◽  
Author(s):  
Nasim Baharisangari ◽  
Suyi Li
Keyword(s):  
Potential Energy ◽  
Energy Barrier ◽  
Cellular Structure ◽  
Cell Structure ◽  
Three Dimensional ◽  
Stable State ◽  
Cell System ◽  
Kinematic Constraint ◽  
Unit Cells ◽  
Diode Behavior

Abstract Recently, multi-stable origami structures and material systems have shown promising potentials to achieve multi-functionality. Especially, origami folding is fundamentally a three-dimensional mechanism, which imparts unique capabilities not seen in the more traditional multi-stable systems. This paper proposes and analytically examines a multi-stable origami cellular structure that can exhibit asymmetric energy barriers and a mechanical diode behavior in compression. Such a structure consists of many stacked Miura-ori sheets of different folding stiffness and accordion-shaped connecting sheets, and it can be divided into unit cells that features two different stable equilibria. To understand the desired diode behavior, this study focuses on two adjacent unit cells and examines how folding can create a kinematic constraint onto the deformation of these two cells. Via estimating the elastic potential energy landscape of this dual cell system. we find that the folding-induced kinematic constraint can significantly increase the potential energy barrier for compressing the dual-cell structure from a certain stable state to another, however, the same constraint would not increase the energy barrier of the opposite extension switch. As a result, one needs to apply a large force to compress the origami cellular structure but only a small force to stretch it, hence a mechanical diode behavior. Results of this study can open new possibilities for achieving structural motion rectifying, wave propagation control, and embedded mechanical computation.

Synergetic effect of nanoclay and nano-CaCO3 hybrid filler systems on the foaming properties and cellular structure of polystyrene nanocomposite foams using supercritical CO2

2020 ◽  
Vol 39 (5) ◽  
pp. 185-202 ◽  
Author(s):  
Xinghan Lian ◽  
Wenjie Mou ◽  
Tairong Kuang ◽  
Xianhu Liu ◽  
Shuidong Zhang ◽  
...  
Keyword(s):  
Cellular Structure ◽  
High Efficiency ◽  
Cell Structure ◽  
Synergetic Effect ◽  
Cell Diameter ◽  
Foaming Properties ◽  
Electron Microscopic ◽  
Hybrid Filler ◽  
Nanocomposite Foams ◽  
Hybrid Fillers

Supercritical fluids have been widely used to prepare various polymer nanocomposite foams due to their high-efficiency, rich-resource, and environment-friendly characteristics. In this work, we prepared polystyrene (PS) nanocomposites with different contents of hybrid fillers of nanoclay and nano-calcium carbonate (nano-CaCO3) and then were foamed by batch foaming method using supercritical carbon dioxide as a physical blowing agent. The effect of hybrid nanofillers components and foaming temperature and pressure on the foaming properties and cellular structure of PS nanocomposite foams was systematically investigated. Dynamic rheology results indicated that the complex viscosity and storage modulus were enhanced with the addition of hybrid fillers. Scanning electron microscopic images show that all samples foamed uniformly macrocells under the given conditions. More importantly, the hybrid fillers of nano-CaCO3 and nanoclay exhibit a significant synergistic effect in improving PS foaming properties, which can be ascribed to the different roles of the two fillers during cell nucleation and cell growth. For instance, the PS/0.22/0.88 nanocomposite foamed under the conditions of 20 MPa and 130°C has shown the finest cell structure (higher cell density of 1.91 × 1010 and smaller cell diameter of 2.28 µm) due to the coeffect of the hybrid nanofillers. Finally, the synergistic mechanism of these two nanofillers on PS foaming behavior was discussed.

scholarly journals Tuning cell structure and expansion ratio of thick-walled biodegradable poly(lactic acid) foams prepared using supercritical CO2

2019 ◽  
Vol 56 (1) ◽  
pp. 89-104 ◽  
Author(s):  
Lin-Qiong Xu ◽  
Han-Xiong Huang
Keyword(s):  
Lactic Acid ◽  
Constant Temperature ◽  
Cellular Structure ◽  
Cell Structure ◽  
Expansion Ratio ◽  
Poly Lactic Acid ◽  
Time Range ◽  
Formation Mechanisms ◽  
Saturation Time ◽  
Temperature Mode

Thick-walled poly(lactic acid) samples are foamed using supercritical carbon dioxide as physical foaming agent over a wide saturation time range using a constant-temperature mode and a wide foaming pressure range using the constant-temperature mode and a varying-temperature mode. Using the constant-temperature mode, three regions with no-celled core and two regions with cells of different diameters appear on the fractured surfaces of the foamed samples prepared at 5 and 10 min saturation times, respectively, whereas a relatively uniform cellular structure is obtained at 20–180 min saturation times. Raising the foaming pressure can improve the cellular structure uniformity. Moreover, prolonging saturation time or raising foaming pressure results in rupture of more cell walls and so formation of open-celled structure to a certain extent. Using the varying-temperature mode, a bimodal cellular structure with stamen-like cells and a trimodal cellular structure with an extraordinarily high expansion ratio (76.2) are successively achieved during raising the foaming pressure (18–22 MPa). The formation mechanisms for the bimodal and trimodal cellular structures are analyzed based on the result of the foaming pressure effect on the cellular structure in the foamed poly(lactic acid) samples prepared using the constant-temperature mode.

Quantitative Scanning Electron Microscopy of the Cellular Structure of Wood

1990 ◽  
Vol 48 (1) ◽  
pp. 554-555
Author(s):  
Barbara A. Reine ◽  
Norman J. Fowler ◽  
R. M. Fisher
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Shear Strength ◽  
Cellular Structure ◽  
Cell Structure ◽  
Cork Oak ◽  
Scanning Electron Micrographs ◽  
Quantitative Interpretation ◽  
Structural Components ◽  
Scanning Electron

The physical properties of wood, such as density, moisture content, tensile, compression and shear strength, elastic modulus and anisotropy all vary considerably between different species of wood. These variations are reflected in the long standing differentiations into hard and soft woods that have been established as well as quality classifications or commercial grades such as clear grain, select, structural etc. that are commonly used. These variations in properties arise from differences in the size, shape and distribution of the cells, as well as in the thickness of the cellulose-lignin walls that enclose them.Scanning electron micrographs that are representative of the variations in cellular structure that exist between woods are shown in Figure 1 for ultrasoft hard maple and ultrasoft cork oak. These higher magnification images illustrate the duplex cell configuration that is required to sustain the growth of trees and support their height. Although the differences in cell structure are quite apparent in the micrographs, any quantitative interpretation of the various properties mentioned above requires detailed measurements of specific microstructural components to obtain statistically significant measurements of the relevant structural components.

Observations of the cell structure of salt fingers

1970 ◽  
Vol 41 (4) ◽  
pp. 707-719 ◽  
Author(s):  
T. G. L. Shirtcliffe ◽  
J. S. Turner
Keyword(s):  
Cellular Structure ◽  
Cell Structure ◽  
Strong Tendency ◽  
Cell Width ◽  
Horizontal Section ◽  
Structure Changes ◽  
Salt Fingers

The phenomenon of salt fingers has been investigated optically to determine the geometry of the cells as seen from above. When the fingers are short, the flow appears to be highly turbulent, though a dominant scale is evident. When the fingers are longer, a cellular structure is clear. This structure changes only slowly, apparently in response to disturbances in the convecting layers which bound the fingers above and below, and becomes more nearly stationary as the fingers grow. Cell boundaries show a strong tendency to intersect at right angles, which favours the emergence of cells with a square horizontal section. As the fingers get longer the cell width increases, but more slowly than the length.

scholarly journals Bio-Based Rigid Polyurethane Foam Composites Reinforced with Bleached Curauá Fiber

2021 ◽  
Vol 22 (20) ◽  
pp. 11203
Author(s):  
Sylwia Członka ◽  
Eduardo Fischer Kerche ◽  
Roberta Motta Neves ◽  
Anna Strąkowska ◽  
Krzysztof Strzelec
Keyword(s):  
Mechanical Properties ◽  
Polyurethane Foam ◽  
Cellular Structure ◽  
Cell Structure ◽  
Rigid Polyurethane Foam ◽  
Processing Times ◽  
Civil Aircraft ◽  
Viscoelastic Characteristics ◽  
Vegetable Fiber ◽  
Curauá Fiber

This study aims to evaluate the influence of using a bleached Curauá fiber (CF) as filler in a novel rigid polyurethane foam (RPUF) composite. The influence of 0.1, 0.5 and 1 wt.% of the reinforcements on the processing characteristics, cellular structure, mechanical, dynamic-mechanical, thermal, and flame behaviors were assessed and discussed for RPUF freely expanded. The results showed that the use of 0.5 wt.% of CF resulted in RPUF with smoother cell structure with low differences on the processing times and viscosity for the filled pre-polyol. These morphological features were responsible for the gains in mechanical properties, in both parallel and perpendicular rise directions, and better viscoelastic characteristics. Despite the gains, higher thermal conductivity and lower flammability were reported for the developed RPUF composites, related to the high content of cellulose and hemicellulose on the bleached CF chemical composition. This work shows the possibility of using a Brazilian vegetable fiber, with low exploration for the manufacturing of composite materials with improved properties. The developed RPUF presents high applicability as enhanced cores for the manufacturing of structural sandwich panels, mainly used in civil, aircraft, and marine industries.

Intracytoplasmic Membrane Formation in the Hydrocarbon Oxidizing Bacterium, Micrococcus Cerificans

1971 ◽  
Vol 29 ◽  
pp. 264-265
Author(s):  
R. S. Kennedy ◽  
Ben O. Spurlock ◽  
W. R. Finnerty
Keyword(s):  
Cytoplasmic Membrane ◽  
Membrane System ◽  
Sole Source ◽  
Defined Medium ◽  
Intracellular Membrane ◽  
Intracytoplasmic Membrane ◽  
Logarithmic Growth Phase ◽  
Gram Negative ◽  
Defined Media ◽  
Logarithmic Growth

Micrococcus cerificans is a gram negative, pleomorphic, coccoid bacterium capable of growth in complex or chemically defined media. The complex medium employed was nutrient broth-yeast extract (NBYE) while hydrocarbons constituted the sole source of carbon and energy in the chemically defined medium. Cells cultured in the above media were harvested in the late logarithmic growth phase and fixed according to the procedure of Kellenberger, et al. A variety of embedding techniques were used including those developed by Luft; Staubli; and Spurlock et al.M cerificans cultured in the NBYE medium showed characteristic gram negative morphology including mesosomes. In the hydrocarbon grown cells an intracellular membrane system distinct from mesosomes was observed. Evidence suggests that these highly ordered membranous structures which appear as sheaths or bundles extending the width and/or length of the cells are continuous with the cytoplasmic membrane and are specific to hydrocarbon grown cells.

Mechanical properties of the three-dimensional compression-twist cellular structure

2019 ◽  
Vol 39 (7-8) ◽  
pp. 260-277
Author(s):  
Wei Zhang ◽  
Xiaoyu Bai ◽  
Bowen Hou ◽  
Yadong Sun ◽  
Xiao Han
Keyword(s):  
Mechanical Properties ◽  
Finite Element Analysis ◽  
Finite Element ◽  
Cellular Structure ◽  
Cell Structure ◽  
Twist Angle ◽  
Three Dimensional ◽  
Thickness Ratio ◽  
Cell Length ◽  
Element Analysis

The cellular structure can exhibit many special mechanical behaviors due to its variable cell shape. A three-dimensional compression-twist cell structure based on the rotation mechanism of two-dimensional chiral cell structure is developed, which has twist deformation under axial compression. The shape of three-dimensional compression-twist cell structure is determined through cell angle, cell length, and thickness ratio. Analytical expressions of effective Young’s modulus, Poisson’s ratio, and twist angle are derived by using beam theory, which have a good agreement with the finite element calculations and the deformation process of the cell is discussed. To work on the effect of geometric parameters of cell on the mechanical properties, a finite element analysis model of compression-twist cell structure is carried out, which shows the process of elastic and plastic deformation under compression. Effects of cell angle, cell length, and thickness ratio are fully discussed, which indicate that cell angle has obvious nonlinear effect on relative twist angle and could stiffen it. Finally, a compression-twist cell structure sample is made through three-dimensional printing, and an in-plane compressive experiment is carried out to prove analytical and finite element analysis results.

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