History effects

A crystalline or semicrystalline state in polymers can be induced by thermal changes from a melt or from a glass, by strain, by organic vapors, or by Hquid solvents (40). Polymer crystallization can also be induced by compressed (or supercritical) gases, such as CO2 (41). The plasticization of a polymer by CO2 can increase the polymer segmental motions so that crystallization is kinetically possible. Because the amount of gas (or fluid) sorbed into the polymer is a dkect function of the pressure, the rate and extent of crystallization may be controUed by controlling the supercritical fluid pressure. As a result of this abiHty to induce crystallization, a history effect may be introduced into polymers. This can be an important consideration for polymer processing and gas permeation membranes. 

Number of times molded (Heat history effects performances)... 

Figure 30.14 shows an interesting aspect of RPA-FT experiments, i.e., the capability to quantify the strain sensitivity of materials through parameter B of ht Equation 30.3. As can be seen, curatives addition strongly modifies this aspect of nonlinear viscoelastic behavior, with furthermore a substantial change in strain history effect. Before curatives addition, mn 2 data show very lower-strain... 

Along the mixing line, significant changes occur on Q1/Q2. At dump, data are scattered and there is little, if any, effect of the test frequency. After curatives addition, the test frequency significantly affects the Q1/Q2 signature, as expected since quarter cycle integration provides all-inclusive parameters (i.e., main torque component and all harmonics). One notes also a net strain history effect, i.e., run 1 and mn 2 data do not superimpose. 

Bailey, E.P. 1993. Introduction of Foxes to Alaskan Islands — History, Effects on Avifauna, and Eradication. U.S. Fish Wildl. Serv., Resour. Publ. 193. 53 pp. 

Unless 7 1, all terms in Eq. (11-33) must be retained. Since Eq. (11-30) has no formal justification, the individual terms cannot definitely be ascribed to added mass or history effects. Even so, the relative magnitudes of the terms are of interest. Figure 11.7 shows the three terms for specific values of 7 and Rejs, expressed as fractions of the immersed particle weight. Added mass dominates initially history passes through a maximum and decays slowly steady drag increases monotonically to become the sole component at the terminal velocity. Both A and Ah depart from unity early in the motion. For smaller Rexs, history may be the dominant drag component for a brief period (02). 

Schreiber and co-workers have noted very persistent history effects in linear polyethylenes (69). Fractions which have been crystallized from dilute solution required times of the order of hours in the melt state at 190° C in order to attain a constant die swell behavior upon subsequent extrusion. The viscosity on the other hand reached its ultimate value almost immediately. The authors concluded from this result that different types of molecular interactions were responsible for elastic and viscous response. However, other less specific explanations might also suffice, since apparent viscosity might be relatively intensitive to the presence of incompletely healed domain surfaces, while die swell, requiring a coordinated motion of the entire extrudate, might be affected by planes of weakness. It would... 

Summary Provides detailed information about the composition, history, effect, uses and abuses of common drugs, including illegal drugs and addictive substances, as well as commonly abused classes of prescription drugs. 

Jensen A, Forbes VE, Parker ED. 2001. Variation in cadmium uptake, feeding rate, and life-history effects in the gastropod Potamopyrgus antipodarum linking toxicant effects on individuals to the population level. Environ Toxicol Chem 20 2503-2513. 

A splendid stxmmary the drugs usage history effects Jr. Stanley Krippner... 

Any errors incurred because of history effects will be of the order n, Le. less than about 10% This assumption greatly simplifies the analysis since the linear elastic equations may be employed with the elastic parameters replaced by time dependent forms where the time scale is appropriate to the particular circumstances. In general, Poisson s ratio, v, does not vary greatly and it is sufficient to use E(t) and Oc(if) together with a constant COD criteria, 8. The most convenient method is to write ... 

Nuclear power reactors inherently have some highly nonlinear characteristics, which means that whatever objective function (there are several possibilities) and constraints are used to define and quantify acceptable LPs, some of these system variables will inevitably be nonlinear functions of the problem s control (decision) variables. Examples of such nonlinearities include the effects of local thermal and hydraulic feedback and the time dependence that results from radiation exposure (an accumulated history effect). Particularly with respect to the latter, the computational expense associated with analyzing a single LP solution can be substantial. When considered within the context of of tens of thousands of solutions, as is often required for the use of modem optimization routines, the CPU run time cost becomes prohibitively expensive. 

Baird, D.J., Barber, I. and Calow, P. (1990) Clonal variation in general responses of Daphnia magna Strauas to toxic stress. I. Chronic life-history effects. Functional Ecology, 4, 399 107. 

The measurements were performed on a DSC Mettler Toledo (DSC822e/400). About 10 mg of each film-forming component or film conditioned at 25°C and 58% RH for 2 days previously was sealed in a standard aluminum pan. The first scan, from 20 to 150°C was applied to remove any thermal history effects. This first scan was stopped before the material melted, and samples... 

History-effect problems are worsened at elevated temperatures. Wash-out of the transient structure occurs if the sample is not fully discharged between measurements. At a given temperature, discharge proceeds more slowly than charging. For this reason, the sample is heated to 370°C to discharge for 10,000 sec before each transient is recorded. This procedure results in stable and repeatable transient data. 

Model. The comparison of theory and experiment in Figure 9 indicates that the simplified model can be used to calculate transients which agree with experiment in gross trends. The model permits quantitative analysis of bulk and contact space-charge effects in PI transient current measurements. In particular, this model is sufficient to calculate measurement-history effects due to mobile ions and bulk electronic space-charge (9). The relaxation of space-charge upon removal of the bias is intrinsically slower than its accumulation. Thus, the sample history is stored in the space-charge distributions. These results will be demonstrated in a future publication. 

A more pronounced example of a sample history effect is shown in Figure 2, taken from Hoogendam [13]. In these experiments, carboxymethylcellu-... 

Since the heat capacity is measured using a differential scanning calorimeter, the dependence of Cp on time and temperatures is complicated because Cp is measured continuously while the sample is being heated or cooled at a constant rate. Therefore, the time for the heat capacity measurement is not well defined, and thermal history effects complicate the shape of the step at 7. To overcome this difficulty, one can approximate the real situation by changing the temperature in small discrete steps AT at time intervals At. Stephens and Moynihan et al. follow this procedure and calculate the change in the sample s enthalpy H and its heat capacity from Cp =LH/l T. However, we already have an explicit expression for the equilibrium enthalpy and heat capacity. Since the result for Cp, (8.2), depends partially on the rate of change of p with respect to T, we need only include the effect of p falling out of equilibrium (i.e., dp/dT tCS) for T< 7 in that result. ... 

---