scholarly journals A strain-cue hypothesis for biological network formation

2010 ◽  
Vol 8 (56) ◽  
pp. 377-394 ◽  
Author(s):  
Brian N. Cox
Keyword(s):  
Strain Field ◽  
Network Formation ◽  
Local Strain ◽  
Break Symmetry ◽  
Host Population ◽  
Host Cells ◽  
Vascular Networks ◽  
Host Medium ◽  
Branch Formation ◽  
Order Of Magnitude

The direction of migration of a cell invading a host population is assumed to be controlled by the magnitude of the strains in the host medium (cells plus extracellular matrix) that arise as the host medium deforms to accommodate the invader. The single assumption that invaders are cued by strains external to themselves is sufficient to generate network structures. The strain induced by a line of invaders is greatest at the extremity of the line and thus the strain field breaks symmetry, stabilizing branch formation. The strain cue also triggers sprouting from existing branches, with no further model assumption. Network characteristics depend primarily on the ratio of the rate of advance of the invaders to the rate of relaxation of the host cells after their initial deformation. Intra-cell mechanisms that govern these two rates control network morphology. The strain field that cues an individual invader is a collective response of the combined cell populations, involving the nearest 100 cells, to order of magnitude, to any invader. The mechanism does not rely on the pre-existence of the entire host medium prior to invasion; the host cells need only maintain a layer several cells thick around each invader. Consistent with recent experiments, networks result only from a strain cue that is based on strain magnitudes. Spatial strain gradients do not break symmetry and therefore cannot stabilize branch formation. The theory recreates most of the geometrical features of the nervous network in the mouse gut when the most influential adjustable parameter takes a value consistent with one inferred from human and mouse amelogenesis. Because of similarity in the guiding local strain fields, strain cues could also be a participating factor in the formation of vascular networks.

Strain analysis with nanometer resolution using a conventional transmission electron microsopy technique: electron diffraction contrast imaging revisited

1995 ◽  
Vol 53 ◽  
pp. 168-169
Author(s):  
Koenraad G F Janssens ◽  
Omer Van der Biest ◽  
Jan Vanhellemont ◽  
Herman E Maes ◽  
Robert Hull
Keyword(s):  
Electron Diffraction ◽  
Strain Field ◽  
Elastic Strain ◽  
Strain Analysis ◽  
Local Strain ◽  
Contrast Imaging ◽  
Strain Characterization ◽  
Physical Mechanisms ◽  
Diffraction Contrast ◽  
Transmission Electron

There is a growing need for elastic strain characterization techniques with submicrometer resolution in several engineering technologies. In advanced material science and engineering the quantitative knowledge of elastic strain, e.g. at small particles or fibers in reinforced composite materials, can lead to a better understanding of the underlying physical mechanisms and thus to an optimization of material production processes. In advanced semiconductor processing and technology, the current size of micro-electronic devices requires an increasing effort in the analysis and characterization of localized strain. More than 30 years have passed since electron diffraction contrast imaging (EDCI) was used for the first time to analyse the local strain field in and around small coherent precipitates1. In later stages the same technique was used to identify straight dislocations by simulating the EDCI contrast resulting from the strain field of a dislocation and comparing it with experimental observations. Since then the technique was developed further by a small number of researchers, most of whom programmed their own dedicated algorithms to solve the problem of EDCI image simulation for the particular problem they were studying at the time.

scholarly journals Rapid evolution of decreased host susceptibility drives a stable relationship between ultrasmall parasite TM7x and its bacterial host

2018 ◽  
Vol 115 (48) ◽  
pp. 12277-12282 ◽  
Author(s):  
Batbileg Bor ◽  
Jeffrey S. McLean ◽  
Kevin R. Foster ◽  
Lujia Cen ◽  
Thao T. To ◽  
...  
Keyword(s):  
Host Cell ◽  
Rapid Evolution ◽  
Host Population ◽  
Host Cells ◽  
Host Susceptibility ◽  
Bacterial Host ◽  
Narrow Host Range ◽  
Stable Relationship ◽  
Candidate Phyla Radiation

Around one-quarter of bacterial diversity comprises a single radiation with reduced genomes, known collectively as the Candidate Phyla Radiation. Recently, we coisolated TM7x, an ultrasmall strain of the Candidate Phyla Radiation phylum Saccharibacteria, with its bacterial host Actinomyces odontolyticus strain XH001 from human oral cavity and stably maintained as a coculture. Our current work demonstrates that within the coculture, TM7x cells establish a long-term parasitic association with host cells by infecting only a subset of the population, which stay viable yet exhibit severely inhibited cell division. In contrast, exposure of a naïve A. odontolyticus isolate, XH001n, to TM7x cells leads to high numbers of TM7x cells binding to each host cell, massive host cell death, and a host population crash. However, further passaging reveals that XH001n becomes less susceptible to TM7x over time and enters a long-term stable relationship similar to that of XH001. We show that this reduced susceptibility is driven by rapid host evolution that, in contrast to many forms of phage resistance, offers only partial protection. The result is a stalemate where infected hosts cannot shed their parasites; nevertheless, parasite load is sufficiently low that the host population persists. Finally, we show that TM7x can infect and form stable long-term relationships with other species in a single clade of Actinomyces, displaying a narrow host range. This system serves as a model to understand how parasitic bacteria with reduced genomes such as those of the Candidate Phyla Radiation have persisted with their hosts and ultimately expanded in their diversity.

scholarly journals Cytoskeleton and Membrane Organization at Axon Branches

2021 ◽  
Vol 9 ◽  
Author(s):  
Satish Bodakuntla ◽  
Hana Nedozralova ◽  
Nirakar Basnet ◽  
Naoko Mizuno
Keyword(s):  
Neural Network ◽  
Energy Production ◽  
Network Formation ◽  
Local System ◽  
Membrane Remodeling ◽  
Axon Branching ◽  
Cellular Functions ◽  
Branch Formation ◽  
High Degree ◽  
Critical Process

Axon branching is a critical process ensuring a high degree of interconnectivity for neural network formation. As branching occurs at sites distant from the soma, it is necessary that axons have a local system to dynamically control and regulate axonal growth. This machinery depends on the orchestration of cellular functions such as cytoskeleton, subcellular transport, energy production, protein- and membrane synthesis that are adapted for branch formation. Compared to the axon shaft, branching sites show a distinct and dynamic arrangement of cytoskeleton components, endoplasmic reticulum and mitochondria. This review discusses the regulation of axon branching in the context of cytoskeleton and membrane remodeling.

scholarly journals Photobleaching as a tool to measure the local strain field in fibrous membranes of connective tissues

2014 ◽  
Vol 10 (6) ◽  
pp. 2591-2601 ◽  
Author(s):  
C. Jayyosi ◽  
G. Fargier ◽  
M. Coret ◽  
K. Bruyère-Garnier
Keyword(s):  
Strain Field ◽  
Local Strain ◽  
Connective Tissues ◽  
Fibrous Membranes

BEHAVIOR OF PLASTIC DEFORMATION AND CRACK PROPAGATION ON FULLY LAMELLAR GAMMA-TiAl ALLOY

2010 ◽  
Vol 24 (15n16) ◽  
pp. 2958-2963
Author(s):  
MING SONG ◽  
GUANGJIE MAO ◽  
YUE MA ◽  
SHENGKAI GONG
Keyword(s):  
Plastic Deformation ◽  
Plastic Zone ◽  
Strain Field ◽  
Tial Alloy ◽  
Image Correlation ◽  
Deformation Region ◽  
Order Of Magnitude ◽  
Plastic Deformation Region ◽  
Fully Lamellar

Practical residual strain field around the microcrack tip of fully lamellar γ- TiAl alloy was estimate the by digital image correlation (DIC) technology with in-situ SEM observation. And the macro plastic deformation before fracture of such low ductility alloys was observed. The results showed that the size of plastic zone around microcrack tip was 2 ~ 10µ m which was much more smaller than the calculated value by fracture mechanics. During the magnified observation on the plastic deformation region, a series of microcracks were observed in the specimen without macro cracking. Furthermore, the size of distribution region of the microcracks were in the same order of magnitude with the calculated plastic zone near primary crack tip which just reflected the comprehensive effect of microcracks and the plastic deformation on the tips of them.

Study on Local Strain Field Intensity Approach for Prediction Fatigue Life of Crankshaft Based on Mechanical Mechanics

2013 ◽  
Vol 644 ◽  
pp. 251-255 ◽  
Author(s):  
Ke Bao ◽  
Qiu Fang Wang ◽  
Shu Lin Liu ◽  
Zhong Liang Wei
Keyword(s):  
Field Intensity ◽  
Strain Field ◽  
Local Strain ◽  
Fatigue Tests ◽  
Bending Moments ◽  
Test Results ◽  
Life Test ◽  
Test Load ◽  
Bending Fatigue ◽  
Crack Initiation Life

The bending fatigue limit moment and crack initiation life of 4105 crankishaft in five groups of bending moments are obtained by resonant bending fatigue tests first. Then, the static finite element calculation using sub-model is performed to get the strain distributions in every test load. The results show that in the region where stress concentrate, the strain field could be seen as plane strain state. So two dimensional strain field intensity model is selected. In order to remove the influences of size and surface conditions, the radius of strain field is determined with the strain distribution under the low-life test load. After that, the local strain field intensities under each test load are calculated with the radius of strain field. Finally, the strain-life curve of material is modified by the fatigue intensity limit of crankshaft, and the predicted life agree with the test results.

scholarly journals Synthesizing within-host and population-level selective pressures on viral populations: the impact of adaptive immunity on viral immune escape

2010 ◽  
Vol 7 (50) ◽  
pp. 1311-1318 ◽  
Author(s):  
Igor Volkov ◽  
Kim M. Pepin ◽  
James O. Lloyd-Smith ◽  
Jayanth R. Banavar ◽  
Bryan T. Grenfell
Keyword(s):  
Evolutionary Dynamics ◽  
Immune Escape ◽  
Adaptive Immune Response ◽  
Population Level ◽  
Analytical Framework ◽  
Host Population ◽  
Host Immunity ◽  
Host Cells ◽  
Susceptible Host ◽  
The Impact

The evolution of viruses to escape prevailing host immunity involves selection at multiple integrative scales, from within-host viral and immune kinetics to the host population level. In order to understand how viral immune escape occurs, we develop an analytical framework that links the dynamical nature of immunity and viral variation across these scales. Our epidemiological model incorporates within-host viral evolutionary dynamics for a virus that causes acute infections (e.g. influenza and norovirus) with changes in host immunity in response to genetic changes in the virus population. We use a deterministic description of the within-host replication dynamics of the virus, the pool of susceptible host cells and the host adaptive immune response. We find that viral immune escape is most effective at intermediate values of immune strength. At very low levels of immunity, selection is too weak to drive immune escape in recovered hosts, while very high levels of immunity impose such strong selection that viral subpopulations go extinct before acquiring enough genetic diversity to escape host immunity. This result echoes the predictions of simpler models, but our formulation allows us to dissect the combination of within-host and transmission-level processes that drive immune escape.

Axial Strain Measurements in Skeletal Muscle at Various Strain Rates

1995 ◽  
Vol 117 (3) ◽  
pp. 262-265 ◽  
Author(s):  
T. M. Best ◽  
J. H. McElhaney ◽  
W. E. Garrett ◽  
B. S. Myers
Keyword(s):  
Skeletal Muscle ◽  
Strain Field ◽  
High Speed ◽  
Soft Tissues ◽  
Axial Strain ◽  
Local Strain ◽  
Optical Systems ◽  
Rate Dependent ◽  
Strain Formulation ◽  
Tissue Deformations

A noncontact optical system using high speed image analysis to measure local tissue deformations and axial strains along skeletal muscle is described. The spatial resolution of the system was 20 pixels/cm and the accuracy was ±0.125mm. In order to minimize the error associated with discrete data used to characterize a continuous strain field, the displacement data were fitted with a third order polynomial and the fitted data differentiated to measure surface strains using a Lagrangian finite strain formulation. The distribution of axial strain along the muscle-tendon unit was nonuniform and rate dependent. Despite a variation in local strain distribution with strain rate, the maximum axial strain, Exx = 0.614 ± 0.045 mm/mm, was rate insensitive and occurred at the failure site for all tests. The frequency response of the video system (1000 Hz) and the measurement of a continuous strain field along the entire length of the structure improve upon previous noncontact optical systems for measurement of surface strains in soft tissues.

The ecology of Chytridium deltanum and other fungus parasites on Oocystis spp.

1971 ◽  
Vol 49 (1) ◽  
pp. 75-87 ◽  
Author(s):  
Margaret J. Masters
Keyword(s):  
Field Studies ◽  
Host Population ◽  
Host Cells ◽  
Aquatic Fungus ◽  
Potential Host ◽  
Large Numbers ◽  
Synchronous Development

Consideration of the population curves of Oocystis crassa and O. lacustris in Lake Manitoba during the summers of 1966 and 1967, and July 1968, indicated that the aquatic fungus Chytridium deltanum was able in two instances to attack growing populations of these algae. This strongly suggested that the fungus was a parasite. However, in July 1965, in Cadham Bay, the fungus bloomed as the host population stopped growing and began to decline. Probably the host cells were slightly senescent at that time and thus more susceptible to fungus attack. Consideration of the composition of the fungus population showed that during one epidemic at least, large numbers of zoospores were released every 7 to 9 days. This suggested a nearly synchronous development of the fungus population. It was also observed that zoospores, able to encyst and successfully infect one host, were sometimes unable to attack another potential host present at the same time. In 1966 and 1967 the fungus appeared a few days after the water had reached 25C. Comparison of culture data for the algae and field studies indicated that Chytridium deltanum most commonly grew on the algae at temperatures above the optimum for the algae.

Study of Relationship between Morphology and Mechanical Properties of SiO2-Polyacrylate Hybrid Nanocomposite

2004 ◽  
Vol 847 ◽  
Author(s):  
Yi-Hsiao Kao ◽  
Wei-Fang Su ◽  
K. C. Lin
Keyword(s):  
Network Formation ◽  
Weight Ratio ◽  
Local Strain ◽  
Experimental Result ◽  
Morphological Observation ◽  
Tetraethylene Glycol ◽  
Silicon Substrates ◽  
Microscopic Technique ◽  
Glycol Diacrylate ◽  
Atomic Force

ABSTRACTThe atomic force microscopic technique is utilized to study the spatial distribution of silica nanoparticles embedded in poly(tetraethylene glycol diacrylate) matrix. The cast samples of these hybrid materials show distinct mechanical property change as the weight ratio (SiO2/polyacrylate) reaches 40%. The morphological observation from spin-coated films on silicon substrates shows pronounced nanoparticle network formation correlated to the elasticity transition. The percolating particles reduce the local strain field, i.e. inhibit the deformation of the stratum, and cause the dramatic increase in the Young's modulus. Our experimental result is consistent with recent theoretical prediction [1].

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