Transition-State Model for Entropy-Limited Freezing

A brief review is given of transition-state theory, both for the case of unimolecular reactions in the gas phase, and for reactions in condensed phases. An argument is made that, within the context of this theory, heterogeneous freezing in Si is limited to rates much lower than collision rates by the difference between the entropies of the solid and the liquid.Engineering and Applied Science

Asymmetric Melting and Freezing Kinetics in Silicon.

We report measurements of the melting velocity of amorphous Si relative to that of (100) crystalline Si. These measurements permit the first severe experimental test of theories describing highly nonequilibrium freezing and melting. The results indicate that freezing in Si is inherently slower than melting; this asymmetry can be interpreted in terms of an entropy-related reduction in the freezing rate.Engineering and Applied Science

Interface Velocity Transients During Melting of a-Si/c-Si Thin Films

The authors report transient conductance measurement of liquid/solid interface velocities during pulsed laser melting of amorphous Si (a-Si) films on crystalline Si (c-Si), and a more accurate, systematic procedure for analyzing these measurements than described in previous work. From these analyses are extracted relations between the melting velocities of a-Si and c-Si at a given interface temperature, and between the temperatures during steady-state melting of a-Si and c-Si at a given interface velocity.Engineering and Applied Science

Spontaneous Calcium Release in Cardiac Myocytes: Store Overload and Electrical Dynamics

Heart disease is the leading cause of mortality in the United States. One cause of heart arrhythmia is calcium (Ca2+) mishandling in cardiac muscle cells. We adapt Izu\u27s et al. mathematical reaction-diffusion model of calcium in cardiac muscle cells, or cardiomyocytes implemented by Gobbert, and analyzed in Coulibaly et al. to include calcium being released from the sarcoplasmic reticulum (SR), the effects of buffers in the SR, particularly calsequestrin, and the effects of Ca2+ influx due to voltage across the cell membrane. Based on simulations of the model implemented in parallel using MPI, our findings aligned with known biological models and principles, giving us a thorough understanding of several factors that influence Ca2+ dynamics in cardiac myocytes. Specifically, dynamic calcium store will cap previous calcium blow-up seen in the model. Calcium channels located in spatial opposition of calcium release units produce more predictable intracellular calcium propagation. And we used multi-parametric calcium dynamics tables, which act as a multidimensional bifurcation diagram, to visualize parameter boundaries between different biophysical dynamics

Free energy and molecular dynamics calculations for the cubic-tetragonal phase transition in zirconia

The high-temperature cubic-tetragonal phase transition of pure stoichiometric zirconia is studied by molecular dynamics (MD) simulations and within the framework of the Landau theory of phase transformations. The interatomic forces are calculated using an empirical, self-consistent, orthogonal tight-binding (SC-TB) model, which includes atomic polarizabilities up to the quadrupolar level. A first set of standard MD calculations shows that, on increasing temperature, one particular vibrational frequency softens. The temperature evolution of the free energy surfaces around the phase transition is then studied with a second set of calculations. These combine the thermodynamic integration technique with constrained MD simulations. The results seem to support the thesis of a second-order phase transition but with unusual, very anharmonic behaviour above the transition temperature

Reconfiguration and Recovery in Distributed Memory Multicomputers

Joint Services Electronics Program / N00014-90-J-1270Ope

Reconfiguration and recovery in distributed memory multicomputers

As the sizes of distributed memory multiprocessors increase, the likelihood of a fault removing one of the processors from the system grows as well. Such a fault removes some or all of the following: (a) communication paths, (b) processing power, (c) topological consistency, and (d) progress of the running application. In this thesis we propose solutions to handle all of these problems.We handle the lost communication paths through table-based routing strategies. We present distributed algorithms for filling the tables, after a fault or repair, with the shortest communication paths surviving in the system. Also, we give algorithms for similarly filling broadcast tables and for guaranteeing that the routing tables are deadlock-free.To take care of the lost processing power, we propose low-cost hardware reconfiguration schemes in which we embed spare processors throughout the multicomputer. One scheme places each spare processor alongside the normal processor on a node; the other places each spare processor along a selected link. We give results from low-level trace-driven simulation of these schemes with six applications. The results show that the overhead due to the hardware reconfiguration is very low.We handle the problem of topological consistency with the abstraction of virtual spare processors. A faulty processor's workload is evenly divided among a number of nearby nodes, which timeslice the displaced workload along with their native tasks. We present an implementation of this software technique for static reconfiguration on the iPSC/2 hypercube. We give experimental results of our system for a number of applications.Finally, the lost progress of the application due to fault is handled through our software technique for reconfiguration and recovery. We take advantage of the characteristics of the Actor model of parallel computation and dynamically shadow and check-point the activity of the application. We have implemented our techniques through modifications of the runtime system for the parallel language Charm running on the iPSC/2. After thoroughly discussing the theory and implementation, we give measurements of overhead due to fault tolerance for a number of applications and demonstrate continuance of the applications after injection of a fault.We present experimental evaluations of most of the concepts proposed in the thesis, using real parallel applications from the numerical and VLSI CAD domain executing on a real distributed memory multicomputer, an Intel iPSC/2 hypercube.U of I OnlyETDs are only available to UIUC Users without author permissio

Path Analysis: A Method for Analyzing Message Communication in Faulty Hypercubes

Coordinated Science Laboratory was formerly known as Control Systems LaboratoryOffice of Naval Research / N00014-88-K-0624U of I OnlyRestricted to UIUC communit

Path Analysis: A Method for Analyzing Message Communication in Faulty Hypercubes

Coordinated Science Laboratory was formerly known as Control Systems LaboratoryOffice of Naval Research / N00014-88-K-0624U of I OnlyRestricted to UIUC communit