A study on the thermal degradation of rubber in dilute solutions

The kinetics of low-temperature (60-100°C.) thermal degradation of deproteinized and deresinified petroleum ether soluble fraction of natural rubber in two chemically inert solvents, cyclohexane and trans-decalin, have been studied. The changes in Mw, A2, and (r-2-)½at various stages of degradation have been obtained from the lightscattering data. The rate constants and the energy of activation for chain scission have been calculated from the observed variation in Mu. The scission has been found to be random and the average energy of activation is 25.8 kcal./mole. This low-energy requirement suggests the presence of weak links in the rubber molecule which get ruptured at low temperature

Automatic Partitioning of Large Scale Simulation in Grid Computing for Run Time Reduction

Simulating large-scale systems usually entails exhaustive computational powers and lengthy execution times. The goal of this research is to reduce execution time of large-scale simulations without sacrificing their accuracy by partitioning a monolithic model into multiple pieces automatically and executing them in a distributed computing environment. While this partitioning allows us to distribute required computational power to multiple computers, it creates a new challenge of synchronizing the partitioned models. In this article, a partitioning methodology based on a modified Prim’s algorithm is proposed to minimize the overall simulation execution time considering 1) internal computation in each of the partitioned models and 2) time synchronization between them. In addition, the authors seek to find the most advantageous number of partitioned models from the monolithic model by evaluating the tradeoff between reduced computations vs. increased time synchronization requirements. In this article, epoch- based synchronization is employed to synchronize logical times of the partitioned simulations, where an appropriate time interval is determined based on the off-line simulation analyses. A computational grid framework is employed for execution of the simulations partitioned by the proposed methodology. The experimental results reveal that the proposed approach reduces simulation execution time significantly while maintaining the accuracy as compared with the monolithic simulation execution approach

Knockout of GARPs and the β-subunit of the rod cGMP-gated channel disrupts disk morphogenesis and rod outer segment structural integrity

Ion flow into the rod photoreceptor outer segment (ROS) is regulated by a member of the cyclic-nucleotide-gated cation-channel family; this channel consists of two subunit types, α and β. In the rod cells, the Cngb1 locus encodes the channel β-subunit and two related glutamic-acid-rich proteins (GARPs). Despite intensive research, it is still unclear why the β-subunit and GARPs are coexpressed and what function these proteins serve. We hypothesized a role for the proteins in the maintenance of ROS structural integrity. To test this hypothesis, we created a Cngb1 5′-knockout photoreceptor null (Cngb1-X1). Morphologically, ROSs were shorter and, in most rods that were examined, some disks were misaligned, misshapen and abnormally elongated at periods when stratification was still apparent and degeneration was limited. Additionally, a marked reduction in the level of channel α-subunit, guanylate cyclase I (GC1) and ATP-binding cassette transporter (ABCA4) was observed without affecting levels of other ROS proteins, consistent with a requirement for the β-subunit in channel assembly or targeting of select proteins to ROS. Remarkably, phototransduction still occurred when only trace levels of homomeric α-subunit channels were present, although rod sensitivity and response amplitude were both substantially reduced. Our results demonstrate that the β-subunit and GARPs are necessary not only to maintain ROS structural integrity but also for normal disk morphogenesis, and that the β-subunit is required for normal light sensitivity of the rods