Analysis Of Low Temperature Impact Fracture Data Of Thermoplastic Polymers

Impact fracture toughness of polypropylene (PP) blends, high density polyethylene (HDPE) and rubber toughened polymethylmethacrylate (RTPMMA) has been studied by means of three-point bending falling weight impact testing at different temperatures ranging from -60 degrees C to room temperature using the cleavage fracture toughness, JC parameter [ASTM E1820-99a]. The latter Fracture Mechanics methodology was chosen due to its simplicity [Fasce et al., 2003]. Traces of the impact tests were analyzed using an inverse methodology just proposed by Pettarin et al. (2003). This methodology makes it possible to obtain from a three-point bending instrumented impact test the mechanical response of the material, discarding the dynamic effects associated with the test. The results show that the average JC values calculated with treated and untreated data are similar for a given material, while the standard deviations are larger when the calculations are made with the untreated data. It is clear that the inverse methodology used to correct the data reduces error propagation, giving place to more precise estimations, and therefore more reliable JC values

Fast- or Slow-inactivated State Preference of Na+ Channel Inhibitors: A Simulation and Experimental Study

Sodium channels are one of the most intensively studied drug targets. Sodium channel inhibitors (e.g., local anesthetics, anticonvulsants, antiarrhythmics and analgesics) exert their effect by stabilizing an inactivated conformation of the channels. Besides the fast-inactivated conformation, sodium channels have several distinct slow-inactivated conformational states. Stabilization of a slow-inactivated state has been proposed to be advantageous for certain therapeutic applications. Special voltage protocols are used to evoke slow inactivation of sodium channels. It is assumed that efficacy of a drug in these protocols indicates slow-inactivated state preference. We tested this assumption in simulations using four prototypical drug inhibitory mechanisms (fast or slow-inactivated state preference, with either fast or slow binding kinetics) and a kinetic model for sodium channels. Unexpectedly, we found that efficacy in these protocols (e.g., a shift of the “steady-state slow inactivation curve”), was not a reliable indicator of slow-inactivated state preference. Slowly associating fast-inactivated state-preferring drugs were indistinguishable from slow-inactivated state-preferring drugs. On the other hand, fast- and slow-inactivated state-preferring drugs tended to preferentially affect onset and recovery, respectively. The robustness of these observations was verified: i) by performing a Monte Carlo study on the effects of randomly modifying model parameters, ii) by testing the same drugs in a fundamentally different model and iii) by an analysis of the effect of systematically changing drug-specific parameters. In patch clamp electrophysiology experiments we tested five sodium channel inhibitor drugs on native sodium channels of cultured hippocampal neurons. For lidocaine, phenytoin and carbamazepine our data indicate a preference for the fast-inactivated state, while the results for fluoxetine and desipramine are inconclusive. We suggest that conclusions based on voltage protocols that are used to detect slow-inactivated state preference are unreliable and should be re-evaluated

Lithosphere tectonics and thermo-mechanical properties: an integrated modelling approach for Enhanced Geothermal Systems exploration in Europe

Knowledge of temperature at drillable depth is a prerequisite in site selection for geothermal exploration and development of enhanced geothermal systems (EGS). Equally important, the thermo-mechanical signature of the lithosphere and crust provides critical constraints for the crustal stress field and basement temperatures where borehole observations are rare. The stress and temperature field in Europe is subject to strong spatial variations often linked to polyphase extensional and compressional reactivation of the lithosphere, in different modes of deformation. The development of innovative combinations of numerical and analogue modelling techniques is key to thoroughly understand the spatial and temporal variations in crustal stress and temperature. In this paper we present an overview of advances in developing and applying analogue and numerical thermo-mechanical models to quantitatively assess the interplay of lithosphere dynamics and basin (de)formation. Field studies of kinematic indicators and numerical modelling of present-day and paleo-stress fields in selected areas yield new constraints on the causes and the expression of intraplate stress fields in the lithosphere, driving basin (de)formation. The actual basin response to intraplate stress is strongly affected by the rheological structure of the underlying lithosphere, the basin geometry, fault dynamics and interplay with surface processes. Integrated basin studies show that the rheological structure of the lithosphere plays an important role in the spatial and temporal distribution of stress-induced vertical motions, varying from subtle faulting to basin reactivation and large wavelength patterns of lithospheric folding. These findings demonstrate that sedimentary basins are sensitive recorders of the intraplate stress field. The long lasting memory of the lithosphere, in terms of lithospheric scale weak zones, plays a far more important role in basin formation and reactivation than hitherto assumed. A better understanding of the 3-D linkage between basin formation and basin reactivation is, therefore, an essential step in connecting lithospheric forcing and upper mantle dynamics to crustal vertical motions and stress, and their effect on sedimentary systems and heat flow. Vertical motions in basins can become strongly enhanced, through coupled processes of surface erosion/sedimentation and lower crustal flow. Furthermore, patterns of active thermal attenuation by mantle plumes can cause a significant spatial and modal redistribution of intraplate deformation and stress, as a result of changing patterns in lithospheric strength and rheological layering. The models provide useful constraints for geothermal exploration and production, including understanding and predicting crustal stress and basin and basement heat flow. © 2010 Elsevier B.V