Synchronous Counterparts Research Articles

Parallel Asynchronous Hungarian Methods for the Assignment Problem

In this paper, we discuss the parallel asynchronous implementation of the Hungarian method for solving the classical assignment problem. Multiple augmentations and price rises are simultaneously attempted starting from several unassigned sources and using possibly outdated price and assignment information. The results are then merged asynchronously subject to rather weak compatibility conditions. We show the validity of this algorithm and we demonstrate computationally that an asynchronous implementation is often faster than its synchronous counterpart. INFORMS Journal on Computing, ISSN 1091-9856, was published as ORSA Journal on Computing from 1989 to 1995 under ISSN 0899-1499.

Parallel adaptive and time-stabilizing schemes for constant-coefficient parabolic PDE's

New asynchronous and time stabilizing finite-difference methods for constant coefficient parabolic PDEs are presented. These schemes remove the synchronization overhead and are suitable for shared-memory, message-passing, single- or multi-user multi-processors. They generalize previous schemes by allowing adaptive and non-constant time increments. They are characterized by the time-stabilizing property: the derivatives of their time-level with respect to the spatial coordinates are bounded as the number of time-steps increases, and they vanish as the spatial mesh-size approaches zero. Therefore, unlike others, our schemes are suitable for multi-processors with non-identical processors or unbalanced workload, provided that the differences among their speeds/loads are not too large. The consistency, stability, convergence and the time-stabilizing property of our methods are analyzed in detail. When implemented on the shared-memory multi-user Sequent Balance machine, they show to provide an excellent efficiency and in certain cases it is tripled,, compared to other existing schemes. However, their truncation error is of lower order ( O( Δx l )nstead of O( Δx l 2)). Hence, because of the dimensional additivity of the truncation error, these schemes are less accurate especially for multi-dimensional problems. For such problems, if high accuracy is sought, in general one should use higher order schemes. Nevertheless, under certain circumstances, when the spatial increments are relatively large, the performance of our asynchronous schemes (i.e., both their efficiency and accuracy) may be about the same as compared to their synchronous counterparts, and sometimes even better.

Emerging Electric Machines with Axially Laminated Anisotropic Rotors: A Review

ABSTRACT This paper presents a class of multiphase electric machines with axially laminated anisotropic (ALA( passive rotors. Unipolar, two-level bipolar, and sinusoidal current modes are identified. The reluctance variation in ALA rotor is computed for a wide range of airgaps and pole pitches. High ratios of inductances along d and q axes yield high torque densities. Special attention is paid to the sinusoidal current mode through a quantitative comparison with the induction and PM synchronous counterparts with the same stator. It is demonstrated that the ALA rotor sinusoidal current synchronous motor is superior in all respects to the induction motor and almost equals the performance (torque density, efficiency, power factor( the PM synchronous motor.

Geometry of a Middle Proterozoic extensional décollement in northeastern Australia

An 80 km-long belt of gneissic and mylonitic rocks is exposed in the core of a major anticlinorium in the Middle Proterozoic Mt. Isa Inlier of northeastern Australia. These rocks, in the Mary Kathleen Fold Belt, represent an early, originally horizontal, mid-crustal shear zone which is interpreted as an extensional decollement between a lower ductile sheet and an upper, more brittle plate. The decollement was subhorizontal over a distance of at least 80 km and its depth was perhaps as shallow as 7 km. Shearing was accompanied by the syn-tectonic intrusion of a bimodal complex of granitic and basic rocks over a period of 70–90 m.y. Moderate, to extreme, ductile shearing was pervasive throughout the 1–1.5 km thickness of the lower plate that is now exposed. Massive dilation accompanied shearing and approximately 70% of the volume of-the shear zone is occupied by igneous intrusive rocks (which have been variably deformed to gneissic granite, mylonite, and amphibolite). Strain softening driven by this high thermal input is responsible for the pervasive ductile response at such shallow depths. Peak metamorphic conditions at the décollement were approximately 625°C to 675°C at 2 kbar. Intense ductile shearing in the upper plate is restricted to the lower few hundred metres. Above this zone, brittle processes dominate, although evidence is presented that the sheet as a whole has undergone a component of ductile shearing, probably heterogeneously distributed. Large, sheet-like granite and dolerite bodies were introduced into dilation sites associated with synthetic faults in this plate but, unlike their synchronous counterparts in the lower plate (about 1 km below), these are internally undeformed. The Middle Proterozoic history of the area involves a cycle of extension and shortening with the shortening axis perpendicular to the earlier extension axis. We speculate that the driving mechanism for both extension and shortening is mantle convection, with switches in stress related to mantle upwelling.

Asynchronous parallel successive overrelaxation for the symmetric linear complementarity problem

Convergence is established for asynchronous parallel successive overrelaxation (SOR) algorithms for the symmetric linear complementarity problem. For the case of a strictly diagonally dominant matrix convergence is achieved for a relaxation factor interval of (0, 2] with line search, and (0, 1] without line search. Computational tests on the Sequent Symmetry S81 multiprocessor give speedup efficiency in the 43%–91% range for the cases for which convergence is established. The tests also show superiority of the asynchronous SOR algorithms over their synchronous counterparts.

Multiple-access channels with point-process observations: Optimum demodulation

The derivation and analysis of optimum multiuser detectors for additive-rate and additive-light Poisson multiple-access channels are studied. The observed point process models the output of an ideal photodetector illuminated by several synchronous or asynchronous users who modulate coherent light of the same frequency. Dynamic programming-based decision rules for the asynchronous multiple-access channel exhibit the same computational complexity as their synchronous counterparts and are shown to be optimum under the criteria of minimum error probability and maximum likelihood sequence detection. Upper and lower bounds on the minimum uncoded bit error rate achievable with arbitrary signal constellations are obtained in terms of the error probability of binary hypothesis testing problems. A particular case of these results, namely, the single-user finite-length intersymbol interference problem, solves the error rate analysis of optimum direct-detection systems for dispersive optical fibers.