Combining mechanical and thermal surface fourier transform analysis to follow the dynamic fatigue behavior of polymers

This work investigates the phenomena of self-heating, also called intrinsic heating, and thermoelastic coupling during non-linear dynamic mechanical fatigue testing via surface temperature measurement coupled with the mechanical behavior of polymers. Static tensile tests and dynamic strain controlled fatigue tests under tension/tension were performed at a frequency of ω$_{1}$/2π = 5 Hz, as well as in the low cycle fatigue regime at ω$_{1}$/2π = 0.2 Hz, on six polymers: high density polyethylene (HDPE), low density polyethylene (LDPE), ultra high molecular weight polyethylene (UHMWPE), polyamide 6 (PA6), and two grades of polypropylene (PP). In dynamic testing, the surface temperature rises to a plateau value (ΔT) when an equilibrium between the viscous/plastic dissipated energy and heat convection is reached. Power-law correlations were found between the strain amplitude (ε$_{0}$) and ΔT, as well as between ε$_{0}$ and the calculated dissipated energy density (W$_{diss,p}$) obtained from the mechanical stress response, with similar exponents for both correlations. Thermoelastic coupling is firstly investigated in uniaxial tension, revealing a linear relation between the strain rate and the rate of temperature decrease, which is more distinct with decreasing polymer chain mobility. In dynamic fatigue testing, the surface temperature was found to oscillate with an amplitude T$_{1}$, which was analyzed via Fourier transform. A direct relation between T$_{1}$ and ε$_{0}$ at small deformations was observed. At large strain amplitudes, T$_{1}$ (ε$_{0}$) follows a similar trend as the complex modulus E*(ε$_{0}$). At low frequencies and large strain amplitudes, additional higher harmonics at two (T$_{2}$) and three (T$_{3}$) times the fundamental frequency were also detected as fingerprints of plastic deformation, resulting in additional heat dissipated during the loading half cycle. From the results obtained, the advantages of the calculated dissipated energy density over the surface temperature analysis was analyzed to predict the fatigue behavior. This analysis is believed to be valid for all materials due to the mathematical/physical principles involved. The results are thus expected to hold for other materials such as composites, rubbers, ceramics and metals

Alien Registration- Rodrigue, Jeanne D\u27Ard (Jackman, Somerset County)

https://digitalmaine.com/alien_docs/6840/thumbnail.jp

Neuroanatomical Correlates of Fluid Intelligence in Healthy Adults and Persons with Vascular Risk Factors

The main objective of this study was to examine the effects of regional brain changes on cognitive decline and the modifying influence of vascular risk (VR) factors. We present latent difference score analyses of associations among 5-year changes in 12 regional brain volumes and age-sensitive cognitive functions in 87 adults (32 with identifiable VR factors). We found reliable individual differences in volume change for 11 of the 12 brain regions but not in the cognitive measures that showed average longitudinal decline. Thus, associations between rates of change in fluid intelligence and brain volumes could not be assessed. We observed, however, that lower levels of fluid intelligence were associated with smaller prefrontal and hippocampal volumes. Lower fluid intelligence scores were also linked to greater longitudinal shrinkage of the entorhinal cortex (EC). After accounting for the effects of age, sex, and VR factors, the orbitofrontal cortex and the prefrontal white matter (PFw) volumes as well as the 5-year change in the EC volume predicted fluid intelligence level. VR was independently associated with smaller prefrontal volumes and lower fluid intelligence. Thus, prefrontal and medial-temporal systems may play different roles in age-related differences and changes in cognitive performanc

Analyzing trade liberalization effect in egg sector using a dynamic gravity model

This study analyzes the effects of different liberalization scenarios in the international trade of eggs and egg products. We use a dynamic gravity model that takes into account the observed persistence of trading partners. The estimated parameters of the gravity model serve to quantify the impact of various liberalization scenarios on the probability of importing (extensive margin) and on trade volumes (intensive margin). The results indicate that even in the context of aggressive trade liberalization, trade gains at the extensive margin will be modest. Gains at the intensive margin of trade are present even in the context of partial liberalization - Doha-type - of trade

Analyzing trade liberalization effect in egg sector using a dynamic gravity model

This study analyzes the effects of different liberalization scenarios in the international trade of eggs and egg products. We use a dynamic gravity model that takes into account the observed persistence of trading partners. The estimated parameters of the gravity model serve to quantify the impact of various liberalization scenarios on the probability of importing (extensive margin) and on trade volumes (intensive margin). The results indicate that even in the context of aggressive trade liberalization, trade gains at the extensive margin will be modest. Gains at the intensive margin of trade are present even in the context of partial liberalization - Doha-type - of trade

Analyzing trade liberalization effect in egg sector using a dynamic gravity model

This study analyzes the effects of different liberalization scenarios in the international trade of eggs and egg products. We use a dynamic gravity model that takes into account the observed persistence of trading partners. The estimated parameters of the gravity model serve to quantify the impact of various liberalization scenarios on the probability of importing (extensive margin) and on trade volumes (intensive margin). The results indicate that even in the context of aggressive trade liberalization, trade gains at the extensive margin will be modest. Gains at the intensive margin of trade are present even in the context of partial liberalization - Doha-type - of trade