Modified Arrhenius Equation in Materials Science, Chemistry and Biology

The Arrhenius plot (logarithmic plot vs. inverse temperature) is represented by a straight line if the Arrhenius equation holds. A curved Arrhenius plot (mostly concave) is usually described phenomenologically, often using polynomials of T or 1/T. Many modifications of the Arrhenius equation based on different models have also been published, which fit the experimental data better or worse. This paper proposes two solutions for the concave-curved Arrhenius plot. The first is based on consecutive A→B→C reaction with rate constants k1 ≪ k2 at higher temperatures and k1 ≫ k2 (or at least k1 > k2) at lower temperatures. The second is based on the substitution of the temperature T the by temperature difference T − T0 in the Arrhenius equation, where T0 is the maximum temperature at which the Arrheniusprocess under study does not yet occur.

Analysis of Preterm Pregnancies using Empirical Mode Decomposition based Fractal Features

Preterm birth (gestational age < 37 weeks) is a serious pregnancy related complication that could lead to fetal morbidity and mortality. Monitoring the activity of uterus is considered to be crucial for the early diagnosis of preterm birth. Uterine Electromyography (uEMG) is a non-invasive technique that provides a quantitative measure of uterine activity from the abdominal surface. In this work, an attempt has been made to characterize preterm uEMG signals using Empirical Mode Decomposition based Detrended Fluctuation Analysis (EMD-DFA). Preterm signals with varied gestational ages are considered from an online database. EMD-DFA is applied on these signals to compute the fluctuation function. The double-logarithmic plot of fluctuation function versus scale is evaluated and Chi-square analysis is performed for identifying linear scaling regions. Five features namely shortterm exponent (Hs), long-term exponent (Hl), inflection point, short-term fractal angle (αHs) and long-term fractal angle (αHl) are extracted and analyzed. Further, Coefficient of Variation (CV) is computed to examine the variations of these features among different subjects. Results show that EMD-DFA is able to characterize the fluctuations of preterm signals. From the double-logarithmic plot, a slow variation of fluctuation function is observed with respect to scale when the time to delivery is more. This indicates the presence of rapid signal fluctuations in the early stages of pregnancy. Based on the feature values, it is observed that the signal fluctuations are more correlated and smoother as the time to delivery approaches. Among the extracted features, CV values of Hs, Hl, αHs and αHl are observed to be low indicating that these features have least inter-subject variations in preterm signals. The EMD-DFA based fractal features show the ability to detect the subtle variations in uEMG signals. As early diagnosis of preterm delivery is imperative for timely medical intervention and treatment, it appears that the proposed approach could aid in determining the changes in uterine contractions in preterm condition.

Order parameter effect critical fields and current of Y1–xPrx:123 superconductors

Fluctuation induced conductivity by Pr substitution at Y sites of Y1-xPrx:123 superconductors is reported. It is found that the mean field temperature Tcmf, deduced from the peak of dρ/dT versus T plot, gradually decreases by increasing Pr up to 0.40. The order parameter dimensionality (OPD) is estimated from the slope of the logarithmic plot between excess conductivity Δσ and reduced temperature є. Interestingly, the crossover from 2D to 3D is obtained for samples with Pr = 0.00, 0.10 and 0.20, while with increasing Pr up to 0.40, the crossover from 0D to quasi-2D is obtained. On the other hand, the calculated values of interlayer coupling, coherence lengths, critical fields and critical current decrease with increasing Pr up to 0.20, but with the further increase of Pr, up to 0.40, they increase. The hole carriers/Cu ions anisotropy and G-L parameter gradually increase with Pr up to 0.40. Our results are discussed in terms of the effects of Pr substitution at Y site, such as oxygen rearrangements, anisotropy, hybridization and localization of holes in the overdoped region.

Factors Affecting High Temperature Relaxation Behaviors of Expanded PTFE Gaskets

High temperature behaviors of expanded PTFE gaskets have been studied using the hot blow-out test (HOBT) method. The results suggest that the operating stress and temperature measurements of a tested gasket form a linear relationship on a logarithmic plot, and that higher assembly stress causes proportionally larger degrees of stress relaxation. In contrast, the cooling curve follows a linear relationship in a semi-logarithmic plot (only stress converted). The new formulation and methodology so derived has permitted a better understanding of external and internal factors on relaxation behaviors of expanded PTFE-based gaskets. For example, for a gasket design incorporating a corrugated metal insert, the relaxation curve stays relatively flat until the temperature reaches about 90–100°F, where the stress reduction starts to follow a linear trend parallel to, but above the relaxation curve of the expanded PTFE gasket without the insert. Essentially, the metal insert “delays” the effect of temperature on relaxation, and produces an “effective assembly stress” that is about 13% higher than the actual assembly stress. The use of Belleville washers has shown a similar phenomenon, but with a longer delay and higher effective assembly stress. Finally, the effect of in-process retightening, or hot retorquing, is quantitatively assessed. The contrasting relaxation behaviors of the material by different retightening methods (hot retorque versus post-process retorque in a cooled state) will be discussed.

Firmness values of three-phase, milk fat-based table spreads as determined by composition and temperature

SummaryPhysical properties of aerated, high moisture and low calorie table spreads are considerably influenced by the phase volumes of the mix components. Using a statistical approach developed for mixture experiments, the firmness values of milk fat-based table spreads at three different temperatures were quantified in terms of the phase volumes of the fat, water and gas present. A simple equation was found which related changes in relative firmness values with composition at any temperature. Absolute firmness values may be obtained from relative values by multiplying by a factor, F, which is the firmness value of the similarly treated milk fat. This factor is related to the solid fat content by the formula F = 10ks+c, where F is the firmness value in kg cm–2 of milk fat having a percentage solids content, s, k is the slope of a semi-logarithmic plot and c is a constant.

Evidence that Cytochalasins Reduce the Size of Polymerization Nuclei during Actin Polymerization

In a double-logarithmic plot of the rate of actin polymerization against monomer concentration, the slope has a lower value in the presence of the fungal metabolites cytochalasin B and D than in their absence. This suggests that actin oligomers which serve as polymerization nuclei are smaller in the presence of cytochalasins than in their absence.

Fractal Behaviour of Amorphous Ni32Pd52P16 Studied by SANS

Small angle neutron scattering (SANS) was done with meltspun amorphous Ni32Pd52P16 in the as-quenched state as well as after annealing at 533 K, 570 K. and 607 K, 20 h each. The double logarithmic plot of the structure factor versus the momentum transfer shows linear behaviour with noninteger Porod-slopes. The results are interpreted with the scattering from fractally rough inner surfaces.The as-quenched state contains fluctuations of the scattering length density associated with smooth boundary interfaces. Annealing yields rough boundary interfaces, the roughness being largest after the 570 K annealing. Annealing at the higher temperature of 607 K yields less rough boundary interfaces.