Bending Energy Concept of Vesicle and Cell Shapes and Shape Transitions

1997 ◽  
pp. 189-212 ◽  
Author(s):  
Erich Sackmann
Keyword(s):  
Bending Energy ◽  
Energy Concept ◽  
Cell Shapes ◽  
Shape Transitions

scholarly journals Regulation of tensile stress in response to external forces coordinates epithelial cell shape transitions with organ growth and elongation

2018 ◽  
Author(s):  
Ramya Balaji ◽  
Vanessa Weichselberger ◽  
Anne-Kathrin Classen
Keyword(s):  
Epithelial Cell ◽  
Cell Shape ◽  
Adherens Junctions ◽  
Adherens Junction ◽  
Apical Surface ◽  
Nurse Cells ◽  
Cuboidal Cell ◽  
Cell Shapes ◽  
External Forces ◽  
Shape Transitions

AbstractThe role of actomyosin contractility at epithelial adherens junctions has been extensively studied. However, little is known about how external forces are integrated to establish epithelial cell and organ shape in vivo. We use the Drosophila follicle epithelium to investigate how tension at adherens junctions is regulated to integrate external forces arising from changes in germline size and shape. We find that overall tension in the epithelium decreases despite pronounced growth of enclosed germline cells, suggesting that the epithelium relaxes to accommodate growth. However, we find local differences in adherens junction tension correlate with apposition to germline nurse cells or the oocyte. We demonstrate that medial Myosin II coupled to corrugating adherens junctions resists nurse cell-derived forces and thus maintains apical surface areas and cuboidal cell shapes. Furthermore, medial reinforcement of the apical surface ensures cuboidal-to-columnar cell shape transitions and imposes circumferential constraints on nurse cells guiding organ elongation. Our study provides insight into how tension within an adherens junction network integrates growth of a neighbouring tissue, mediates cell shape transitions and channels growth into organ elongation.

Remarks on the application of backscattered electron imaging (BEI) to the scanning electron microscopy (SEM) of biological structures

1983 ◽  
Vol 41 ◽  
pp. 484-487
Author(s):  
Etienne de Harven
Keyword(s):  
High Resolution ◽  
Incident Beam ◽  
Spot Size ◽  
Primary Electron ◽  
Critical Point Drying ◽  
Cell Shapes ◽  
High Resolution Images ◽  
Backscattered Electron ◽  
Electron Imaging ◽  
Scanning Electron

Biological ultrastructures have been extensively studied with the scanning electron microscope (SEM) for the past 12 years mainly because this instrument offers accurate and reproducible high resolution images of cell shapes, provided the cells are dried in ways which will spare them the damage which would be caused by air drying. This can be achieved by several techniques among which the critical point drying technique of T. Anderson has been, by far, the most reproducibly successful. Many biologists, however, have been interpreting SEM micrographs in terms of an exclusive secondary electron imaging (SEI) process in which the resolution is primarily limited by the spot size of the primary incident beam. in fact, this is not the case since it appears that high resolution, even on uncoated samples, is probably compromised by the emission of secondary electrons of much more complex origin.When an incident primary electron beam interacts with the surface of most biological samples, a large percentage of the electrons penetrate below the surface of the exposed cells.

scholarly journals Universally bistable shells with nonzero Gaussian curvature for two-way transition waves

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Nikolaos Vasios ◽  
Bolei Deng ◽  
Benjamin Gorissen ◽  
Katia Bertoldi
Keyword(s):  
Gaussian Curvature ◽  
Energy Landscape ◽  
Propagation Distance ◽  
Energy Landscapes ◽  
Bending Energy ◽  
Nonlinear Dynamic Response ◽  
One Dimensional ◽  
Doubly Curved Shells ◽  
Doubly Curved ◽  
The Waves

AbstractMulti-welled energy landscapes arising in shells with nonzero Gaussian curvature typically fade away as their thickness becomes larger because of the increased bending energy required for inversion. Motivated by this limitation, we propose a strategy to realize doubly curved shells that are bistable for any thickness. We then study the nonlinear dynamic response of one-dimensional (1D) arrays of our universally bistable shells when coupled by compressible fluid cavities. We find that the system supports the propagation of bidirectional transition waves whose characteristics can be tuned by varying both geometric parameters as well as the amount of energy supplied to initiate the waves. However, since our bistable shells have equal energy minima, the distance traveled by such waves is limited by dissipation. To overcome this limitation, we identify a strategy to realize thick bistable shells with tunable energy landscape and show that their strategic placement within the 1D array can extend the propagation distance of the supported bidirectional transition waves.

scholarly journals Femtosecond-Laser Assisted Surgery of the Eye: Overview and Impact of the Low-Energy Concept

Micromachines ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 122
Author(s):  
Catharina Latz ◽  
Thomas Asshauer ◽  
Christian Rathjen ◽  
Alireza Mirshahi
Keyword(s):  
Surgical Techniques ◽  
Numerical Aperture ◽  
Optical Breakdown ◽  
Pulse Frequency ◽  
Low Energy ◽  
Human Cornea ◽  
Energy Concept ◽  
High Pulse Frequency ◽  
Fs Laser ◽  
High Pulse

This article provides an overview of both established and innovative applications of femtosecond (fs)-laser-assisted surgical techniques in ophthalmology. Fs-laser technology is unique because it allows cutting tissue at very high precision inside the eye. Fs lasers are mainly used for surgery of the human cornea and lens. New areas of application in ophthalmology are on the horizon. The latest improvement is the high pulse frequency, low-energy concept; by enlarging the numerical aperture of the focusing optics, the pulse energy threshold for optical breakdown decreases, and cutting with practically no side effects is enabled.

scholarly journals Myxococcus xanthus as a Model Organism for Peptidoglycan Assembly and Bacterial Morphogenesis

2021 ◽  
Vol 9 (5) ◽  
pp. 916
Author(s):  
Huan Zhang ◽  
Srutha Venkatesan ◽  
Beiyan Nan
Keyword(s):  
De Novo ◽  
Myxococcus Xanthus ◽  
Model Organism ◽  
Life Stages ◽  
Negative Bacterium ◽  
Ideal Model ◽  
Daughter Cells ◽  
Bacterial Division ◽  
Cell Shapes ◽  
Rare Opportunity

A fundamental question in biology is how cell shapes are genetically encoded and enzymatically generated. Prevalent shapes among walled bacteria include spheres and rods. These shapes are chiefly determined by the peptidoglycan (PG) cell wall. Bacterial division results in two daughter cells, whose shapes are predetermined by the mother. This makes it difficult to explore the origin of cell shapes in healthy bacteria. In this review, we argue that the Gram-negative bacterium Myxococcus xanthus is an ideal model for understanding PG assembly and bacterial morphogenesis, because it forms rods and spheres at different life stages. Rod-shaped vegetative cells of M. xanthus can thoroughly degrade their PG and form spherical spores. As these spores germinate, cells rebuild their PG and reestablish rod shape without preexisting templates. Such a unique sphere-to-rod transition provides a rare opportunity to visualize de novo PG assembly and rod-like morphogenesis in a well-established model organism.

Structural Topology Optimization Using Frame Elements Based on the Complementary Strain Energy Concept for Eigen-Frequency Maximization

2005 ◽  
Author(s):  
Akihiro Takezawa ◽  
Shinji Nishiwaki ◽  
Kazuhiro Izui ◽  
Masataka Yoshimura
Keyword(s):  
Topology Optimization ◽  
Cross Sections ◽  
Strain Energy ◽  
Optimization Procedure ◽  
Optimization Method ◽  
Structural Topology ◽  
Energy Concept ◽  
Conceptual Design Phase ◽  
Complementary Strain ◽  
Topology Optimization Method

This paper discuses a new topology optimization method using frame elements for the design of mechanical structures at the conceptual design phase. The optimal configurations are determined by maximizing multiple eigen-frequencies in order to obtain the most stable structures for dynamic problems. The optimization problem is formulated using frame elements having ellipsoidal cross-sections, as the simplest case. Construction of the optimization procedure is based on CONLIN and the complementary strain energy concept. Finally, several examples are presented to confirm that the proposed method is useful for the topology optimization method discussed here.

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