Multi-purpose Code Research Articles

A combinatorial technique for constructing high-rate MTR-RLL codes

We present advanced combinatorial techniques for constructing maximum runlength-limited (RLL) block codes and maximum transition run (MTR) codes. These codes find widespread application in recording systems. The proposed techniques are used to construct a high-rate multipurpose modulation code for recording systems. The code, a rate 16/17, (0,3,2,2) MTR code, that also fulfills (0,15,9,9) RLL constraints is a high-rate distance-enhancing code with additional constraints for improving timing and gain control. The encoder and decoder have a particularly efficient architecture and allow an instantaneous translation of 16-bit source words into 17-bit codewords and vice versa. The code has been implemented in Lucent read-channel chips and has excellent performance.

The Spectrum of a Partially Ionized Jet

Observed stellar jets have the following characteristics : a high degree of collimation, a structure of bright, quasi-periodic knots, a very low excitation spectrum (red [S II] to Hα line ratios of 1-10). Assuming that the latter are indicative of the structure of a supersonic jet, we have made a detailed prediction of the emission line spectrum within each radiating knot using the multi-purpose code MAPPINGS which includes all the atomic processes important in low velocity shocks. The structure (density, temperature, ionization) of the stationary, supersonic, nonadiabatic stellar jet was computed separately using a hydrodynamical code developed by A. Raga. An initially overpressured supersonic jet tries to adjust its pressure to the environmental pressure. In this process of pressure adjustment, a series of expansion fans and incident/reflected shock pairs are formed along the jet. We associate the emission from the recombination region behind these crossing shocks with the knots observed in stellar jets. We find that the calculated emission spectrum is of remarkably low excitation.

A Transient Two-Phase Velocity Difference Model for Drift Calculation in CANDU Thermohydraulic Codes

A realistic velocity difference scheme has been developed for calculating the drift parameters in both horizontally and vertically oriented sections of the primary heat transport systems of CANDU reactors. This model predicts the unequal velocity effects, spatially and temporally. It can be used to describe the slip in transient and multipurpose thermohydraulic codes. The transient velocity difference equation of this model is an arrangement of the two-fluid model equations. This equation describes the time-dependent relation between the phase velocities. This is a function of the pressure gradient, phase inertias, volume fraction, flow regime, inerfacial forces, and additional constitutive relations. In addition, the model includes a package of momentum exchange constitutive laws to calculate the interphase momentum exchange parameters and virtual mass coefficients. The parameters necessary for the integration of this model into CANDU thermohydraulic codes (SOPHT, FIREBIRD) are expressed in terms of the dynamic difference velocity. These parameters are the drift mass flow rate, drift velocity, distribution parameter, flow quality, effective density, and flow enthalpy. Numerical results revealed that the velocity difference model fairly predicted the drift flux parameters when compared with those calculated by existing slipdrift correlations in the SOPHT and FIREBIRD codes, other drift flux models, and withmore » certain experimental data reported in the literature.« less