Abrupt State Changes Research Articles

Catastrophe theory of seasonal variation: Miao, Jinhai and Minfang Ding, 1985. Scientia sin., (B)28(10):1079–1092

This paper studies the abrupt change of equilibria state and the equilibria state of low order, barotropical and dissipative system under thermal forcing that have successive seasonal variation. The typical seasonal equilibria of atmospheric circulation are winter and summer circulations. Owing to thermal forcing and nonlinear interaction of atmospheric motion, the atmospheric circulation appears several seasonal abrupt and northward jumpings of subtropical highs with the seasonal variation of the thermal forcing parameter. In various meridional and zonal thermodynamic differences, the subtropical highs can appear different northward jumpings.

Stepwise changes in crossbridge state and sarcomere length: do lattice constraints play a critical role?

Observed abrupt and stepwise changes in crossbridge state induced by MgPPi in skeletal fibers using spin label techniques as well as stepwise changes in sarcomere length in actively contracting fibers are considered in terms of a model based on the principles of catastrophe theory and nucleation of structural transitions in mechanically constrained polymeric assemblies.

Short-Time, Biaxial Creep of an Aluminum Alloy With Abrupt Changes of Temperature and State of Stress

Short-time, biaxial creep experiments of an aluminum alloy are described which involved abrupt changes in temperature and state of stress. Results are discussed in terms of a creep surface concept similar to the yield surface concept of time-independent plasticity. Evidence that the creep surface changes size, shape, and location in response to creep strain is discussed. The contribution of metallurgical and viscoelastic effects to the complexity of the mechanical behavior are also discussed.

A Modified Superposition Principle Applied to Creep of Nonlinear Viscoelastic Material Under Abrupt Changes in State of Combined Stress

A modified superposition principle has been employed to describe creep in the nonlinear range under combined stresses which change abruptly from time to time. The stress function fij employed is derived from three integrals of the multi-integral theory for constant stress. Several means of treating the nonlinearity in stress when the stress changes are investigated. The most satisfactory of these considers that after a change in stress from σkl(1) to σkl(2) the creep may be described as the sum of the recovery resulting from removal of σkl(1) and the creep from application of σkl(2), the recovery being computed on the basis of superposition. Thus for a power function of time t where the strain ε=ε0+ε+tn and n is a constant the creep following a change in stress at time t1 is given by εij(t)=fij0(σkl(1))+[fij0(σkl(2))−fij0(σkl(1))]+fij+(σkl(1))tn+[fij+(σkl(2))−fij+(σkl(1))] (t−tl)n. Experiments on an unplasticized poly(vinyl chloride) include tension creep followed by multiple-step unloading; combined tension and torsion creep followed by multiple-step unloading; combined tension and torsion creep with several abrupt changes in combination of tension and torsion; and tension creep with partial unloading and reloading. The method describes the time dependence reasonably well in all cases, but the total strain following partial unloading from high combined stresses in the nonlinear range was substantially larger than predicted.

Validity of the "two-state" hypothesis for conformational transitions of proteins.

AbstractThe theory, character, and properties of cooperative transitions are developed with special reference to the abrupt changes of state which occur in protein solutions. Comparisons of helix–coil processes and protein conformational reactions show that though cooperation dominates both of these processes, there are important differences. Tests of two types for the validity of the two‐state approximation are presented with specific applications to proteins. Available experimental evidence demonstrates that the thermally induced reversible transitions of ribonuclease, α‐chymotrypsin, and chymotrypsinogen A under conditions thus far examined are two‐state processes.

Creep experiments and examples for viscoelastic material under combined stress with abrupt changes in state of stress

AbstractCreep experiments under combined tension and torsion loading are reported for tubular specimens of polyvinyl chloride copolymer. Experiments include a sequence of several combinations of tension and torsion on each specimen with abrupt changes between combinations, including reversal of sense of torsion, recovery and reloading after recovery.Results show a strong path and time dependence for the strain and for the direction of the strain‐rate vector at constant state of stress following a change in state of biaxial stress.The character of the results is described reasonably well by the Boltzmann superposition principle of linear viscoelasticity using a constitutive equation of the form: equation image Examples are given of the use of this equation for common states of stress.Better agreement with the data is obtained from a similar but non‐linear equation employing hyperbolic sine functions of stress.

Paper 52: Combined Stress Creep Experiments on Viscoelastic Material with Abrupt Changes in State of Stress

Paper 52: Combined Stress Creep Experiments on Viscoelastic Material with Abrupt Changes in State of Stress

The abrupt transition from rest to activity in muscle

The internal mechanical condition of an excited muscle has been examined by applying quick stretches at various moments after a maximal shock. At the end of the latent period there is an abrupt change of state, the contractile component suddenly becoming capable of bearing a load equal to the maximum tension set up in an isometric tetanus. The intensity of the active state produced by a shock is greatest at the start, is maintained for a time and then declines as relaxation sets in. The properties of the fully active state are defined by the three constants of the characteristic equation relating speed of shortening to load. A muscle consists mechanically of three components: (1) a contractile one, (2) an undamped series elastic one and (3) a parallel elastic one. The complication provided by (3) is avoided by working with small initial loads. The load-extension relation of the series elastic component has been determined. Its extensibility is high at small loads, becoming much less at greater ones. The full isometric force produces an extension in it of about 10% of the muscle’s length. In an isometric tetanus the form of the myogram is fully determined by the characteristic force-velocity relation of the contractile component and the load-extension curve of the series elastic one, the former having to shorten and stretch the latter before an external tension can be manifested. In a twitch there is insufficient time, before relaxation sets in, for the full tension to be developed. When the tension is raised sufficiently by a quick stretch applied early after a shock the contractile component cannot shorten as it would normally and the heat of shortening is absent. The heat of activation is probably a by-product of the process by which the sudden change of state from rest to full activity occurs. When a muscle is subjected to a tension rather greater than it can bear it lengthens slowly; to a tension considerably greater it ‘gives’ or ‘slips’. When a muscle is stretched rapidly a transitory overshoot of tension occurs followed by ‘slip’. During the disappearance of this extra tension heat is produced, as in the ‘cold drawing’ of a wire or thread. An analogous process occurs in relaxation under a load. When two shocks are applied in succession, the second restores the active state to its full intensity, from which it has declined to an extent depending on the interval after the first one. If, under isometric conditions, the series elastic component is still partly stretched at the moment when the second response occurs, the total tension developed is greater. This is the origin of the so-called ‘supernormal phase’ and the basis of the greater tension maintained in atetanic contraction. During a tetanus each shock restores the active state of the muscle to its full intensity. It seems reasonably certain that excitation of a muscle fibre occurs at its surface. It has been suggested that contraction is set up inside by the arrival of some chemical substance diffusing inwards after liberation a t the surface. The onset, however, of full activity occurs so soon after a shock that diffusion is far too slow to account for it. A process, not a substance, must carry activation inwards.