How symbolic computation boosts productivity in the simulation of partial differential equations

While there have been considerable efforts over the past 30 years to improve productivity in scientific computation through the creation of subroutine libraries, much of the mundane, error-prone work in developing simulation codes has remained. This situation has spurred the development of specialized efforts in both the numerical and symbolic computation domains. For instance, numerical software like PDECOL, L1SODE, and UNPACK will solve large classes of partial differential equations, ordinary differential equations, and linear equations, respectively. On the symbolic side of this issue, a few basic tools for developing simulation codes were created by Wirth in the late 1970s. We introduce more advanced uses of symbolic techniques, including two strategies that link the symbolic and numeric computing approaches in the context of simulation codes.     

Extrapolation of high-voltage stress measurements to low-voltageoperation for thin silicon-oxide films

Breakdown and wearout in MOS capacitors fabricated with 10 nm-thick silicon oxide films on p-type silicon are discussed. They have been stressed at high voltages. The high-voltage-stress-induced changes in the oxide properties are extrapolated to low operating voltages. The stress voltages ranged from -7.5 V to -14.5 V. The fluence during the stress was systematically varied front 2×10^-5 C/cm² to 6 C/cm² by varying the stress time at each voltage. The number of interface traps generated by the stress increased as the stress voltage and fluence increased. However, the interface trap generation rate decreased as the fluence increased. The trap generation rate at low operating voltages was very high, but because the current through the oxide was small, the total number of traps generated was low. The trap generation rate was proportional to the inverse square root of the fluence with a voltage dependence that decreased as the fluence increased. Extrapolation of the high-voltage-stress measurements to 5 V shows that easily detectable changes in the oxide properties would only occur after several years of 5 V operation. Extrapolation of charge-to-breakdown and time-to-breakdown data to 5 V operation indicates that breakdown would occur after hundreds of years of device operation     

Block acknowledgment: redesigning the window protocol

A window protocol based on the block acknowledgment method, in which acknowledgment message has two numbers, m and n, to acknowledge the reception of all data messages with sequence numbers ranging from m to n, is discussed. In the window protocol, message sequence numbers are taken from a finite domain and both message disorder and loss can be tolerated. An initial version of the protocol that uses a simplified timeout action and unbounded sequence numbers is presented, the simplified timeout action in the protocol is replaced by a sophisticated one without disturbing the protocol's correctness, and the unbounded sequence numbers are replaced by bounded ones while preserving the protocol's correctness. Remarks concerning other variations of the protocol are also presented     

Suprasellar tension pneumocyst after transsphenoidal surgery. Case report

Tension pneumocephalus is an uncommon occurrence after transsphenoidal surgery. The author presents an unusual case of postoperative visual deterioration related to expanding air within a suprasellar tumor cavity.     

Dissolution kinetics of Widmanstätten γ-Ag2AI precipitates

A combination of scanning electron microscope and electron probe studies has been conducted on the dissolution of Widmanstätten γ-Ag₂Al plates in Al-15.3 wt pct Ag alloys between the temperatures of 466 °C and 494 °C. Individual rather than averaged kinetic events have been monitored in all cases. The kinetics at the tip were observed to be linear with time and at the broadface to be parabolic with time. The broadface kinetics were slower than expected for volume diffusion control. Electron probe measurements round the dissolving precipitate gave similar diffusion profiles at the tip and the broadface. These indicated a slower dissolution rate at the tip than observed experimentally and a faster rate at the broadface than observed experimentally. A mechanism to explain the discrepancy between the kinetic and probe results is suggested.