Mechanics of Gels

1992 ◽  
Vol 271 ◽  
Author(s):  
George W. Scherer
Keyword(s):  
Thermal Expansion ◽  
Fluid Flow ◽  
Time Dependence ◽  
Supercritical Drying ◽  
Time Dependent ◽  
Dependent Behavior ◽  
Expansion Behavior ◽  
Pore Liquid ◽  
Applied Stresses

ABSTRACTThe response of wet gels to applied stresses is discussed, with emphasis on the role of flow of the pore liquid. Even when the network of the gel is purely elastic, the gel exhibits time-dependent behavior that resembles viscoelasticity, which results from fluid flow. The permeability of the gel can be determined from measurement of this time-dependence. Fluid flow also influences the thermal expansion behavior of gels, and can cause severe stresses to develop during supercritical drying, if the autoclave is heated too rapidly.

Critical issues In The Mechanical Reliability of Lightguide Fibers

1998 ◽  
Vol 531 ◽  
Author(s):  
C. R. Kurkjian
Keyword(s):  
Time Dependence ◽  
Safety Factor ◽  
Strength Degradation ◽  
Time Dependent ◽  
Mechanical Reliability ◽  
Strength Limit ◽  
Dependent Behavior ◽  
Critical Issues

AbstractIn order to guarantee a minimum initial strength, lightguide fibers are proof-tested. However, the strength of these fibers is known to depend on time (due to fatigue and aging) and this time-dependence must be taken into account in the calculation of fiber lifetimes. While hermetic coatings can be applied to eliminate strength degradation with time, they are rarely used. It is thus necessary to understand the time-dependent behavior well enough to ensure a desired lifetime (without an excessive and costly safety factor), or alternatively, it is necessary to validate a fundamental strength limit. This paper discusses the progress that has been made on issues related to such fiber lifetime predictions. In particular, it is pointed out that the possible variations in flaw character and coating chemistry make simple generalizations difficult and require that fundamental understandings be developed.

scholarly journals The irreversible thermal expansion of an energetic material

2021 ◽  
Author(s):  
Hervé Trumel ◽  
François Willot ◽  
Thomas Peyres ◽  
Maxime Biessy ◽  
François Rabette
Keyword(s):  
Thermal Expansion ◽  
Residual Stresses ◽  
Volume Fraction ◽  
Energetic Material ◽  
Internal Stresses ◽  
Plastic Yielding ◽  
Initial State ◽  
Expansion Behavior ◽  
Small Volume Fraction

The works deals with a macroscopically isotropic energetic material based on triamino-trinitrobenzene (TATB) crystals bonded with a small volume fraction of a thermoplastic polymer. This material is shown experimentally to display an irreversible thermal expansion behavior characterized by dilatancy and variations of its thermal expansion coefficient when heated or cooled outside a narrow reversibility temperature range. The analysis of cooling results suggests the existence of residual stresses in the initial state, attributed to the manufacturing process. Microstructure-level FFT computations including the very strong anisotropic thermoelastic TATB crystal response and temperature-dependent binder plasticity, show that strong internal stresses develop in the disoriented crystals under thermal load, either heating or cooling. Upon cooling, binder plastic yielding in hindered, thus promoting essentially brittle microcracking, while it is favored upon heating. Despite its low volume fraction, the role of the binder is essential, its plastic yielding causing stress redistribution and residual stresses upon cooling back to ambient.

Unidirectional thermal expansion in KZnB3O6: role of alkali metals

2015 ◽  
Vol 44 (46) ◽  
pp. 19763-19767 ◽  
Author(s):  
Yanfang Lou ◽  
Dandan Li ◽  
Zhilin Li ◽  
Han Zhang ◽  
Shifeng Jin ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
Alkali Metals ◽  
Thermal Expansion Behavior ◽  
Expansion Behavior

The size and mass of alkali metals have profound effects on the area zero thermal expansion behavior of edge-sharing KZnB3O6.

SYMMETRY BREAKING EFFECTS ON EQUILIBRIA AND TIME DEPENDENT REGIMES IN ADAPTIVE LOTKA–VOLTERRA SYSTEMS

2003 ◽  
Vol 13 (02) ◽  
pp. 375-392 ◽  
Author(s):  
DEBORAH LACITIGNOLA ◽  
CLAUDIO TEBALDI
Keyword(s):  
Time Dependent ◽  
Reduced Model ◽  
Interaction Coefficients ◽  
Full Account ◽  
Volterra Systems ◽  
Species Survival ◽  
Dependent Behavior ◽  
Existence And Stability ◽  
Stable Equilibria

We study the properties of a n2-dimensional Lotka–Volterra system describing competition among n different species with adaptive skills, i.e. whose interaction coefficients are time averages of the species level of interaction over their past. Starting by the case of adaptive competition among species all having the same carrying capacities, we focus our attention on the model obtained on perturbing the carrying capacity of a fixed species, which is made more or less disadvantaged. We prove the existence of a certain class of invariant subspaces and introduce a seven-dimensional reduced model, where n appears as a parameter, which gives full account of existence and stability of equilibria in the system. The relevance of this reduced model to the complete one has also been found when the time dependent regimes have been investigated. Ecologically relevant questions, i.e. species survival and the time dependent behavior of the system have also been analyzed focusing on the role of behavioral adaptation. In particular, we have found that competitive exclusion cannot occur but coexistence is possible in various forms (i.e. competitive stable equilibria and different periodic oscillations).

The Role of Time-Dependent Phase Space Structures in Reaction Dynamics and the No-Recrossing Property of Dividing Surfaces

2021 ◽  
Vol 31 (04) ◽  
pp. 2150064
Author(s):  
Cate Mandell ◽  
Stephen Wiggins
Keyword(s):  
Phase Space ◽  
Time Dependence ◽  
Reaction Dynamics ◽  
Time Dependent ◽  
Space Structures ◽  
Stable And Unstable Manifolds ◽  
Normally Hyperbolic Invariant Manifold ◽  
Unstable Manifolds ◽  
Dividing Surface

We analyze benchmark models for reaction dynamics associated with a time-dependent saddle point. Our model allows us to incorporate time dependence of a general form, subject to an exponential growth restriction. Under these conditions, we analytically compute the time-dependent normally hyperbolic invariant manifold; its time-dependent stable and unstable manifolds; and a time-dependent dividing surface that has the no-recrossing property. Consideration of the time dependence of these phase space structures is necessary in order to precisely capture reacting and nonreacting trajectories. Moreover, we show that a time-dependent dividing surface is necessary in order to eliminate recrossing in the time-dependent setting. In other words, if the dividing surface is not time-dependent, recrossing may occur.

Role of Histamine and Leucotaxin in Function of Cellular Defense Mechanism

1956 ◽  
Vol 184 (2) ◽  
pp. 296-300 ◽  
Author(s):  
László Kátó ◽  
Béla Gözsy
Keyword(s):  
Fluid Flow ◽  
Tissue Damage ◽  
Inflammatory Process ◽  
Defense Mechanism ◽  
Volatile Oils ◽  
Time Intervals ◽  
Cellular Defense ◽  
Intradermal Administration ◽  
Flow Through

Experiments are presented to the effect that in an inflammatory process histamine and leucotaxin appear successively at different and orderly time intervals, thus assuring an increased fluid flow through the capillary wall. Histamine is released not only in the inflammatory process but also by intradermal administration of such substances (volatile oils or their components) which induce neither the triple response of Th. Lewis nor any tissue damage. This could be explained by the fact that in the tissues histamine is ‘present’ but leucotaxin is ‘formed.’

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