Introduction: New approaches to linear programming

This issue ofAlgorithmica present papers on various aspects of nonlinear methods for solving linear programming problems, inspired by the work of Karmarkar. This introduction describes some of these aspects and briefly mentions other recent developments in the field. A bibliography of recent articles is included.     

Algorithms and complexity analysis for some flow problems

Several network-flow problems with additional constraints are considered. They are all special cases of the linear-programming problem and are shown to be -complete. It is shown that the existence of a strongly polynomial-time algorithm for any of these problems implies the existence of such an algorithm for the general linear-programming problem. On the positive side, strongly polynomial algorithms for some parametric flow problems are given, when the number of parameters is fixed. These algorithms are applicable to constrained flow problems when the number of additional constraints is fixed.Work on the paper was done while at Stanford University and IBM Almaden Research Center. This research was partially supported by NSF PYI Grant CCR-8858097.     

Pseudoelasticity of Metal Nanoparticles Is Caused by Their Ultrahigh Strength

An assembly of hemispherical Ag nanoparticles is prepared by solid‐state dewetting of thin Ag film deposited on the sapphire substrate. The in situ nanomechanical compression testing of the particles with a flat diamond punch inside the scanning electron microscope demonstrates the deformation behavior typical for the nucleation‐controlled plasticity: high elastic deformation followed by an abrupt particles collapse. The latter is associated with the dislocations nucleation in otherwise pristine particle. The average contact pressure in the contact zone at the onset of dislocation‐controlled plasticity is about 8 GPa, and does not depend on particle size. This observation supports the hypothesis that the pseudoelasticity of much smaller Ag nanoparticles is intrinsically related to their ultrahigh strength. A stress‐induced diffusion along the particle–substrate and particle–punch interfaces is identified as a factor controlling the pseudoelastic deformation. The corresponding diffusion model allows estimating the room‐temperature self‐diffusion coefficient of Ag along the Ag–W and Ag–zirconia interfaces, which is quite close to the estimated value of the grain boundary self‐diffusion coefficient in Ag. Based on this finding, the map of pseudoelastic deformation of crystalline materials is proposed.     

Extending NC and RNC algorithms

A technique is presented by which NC and RNC algorithms for some problems can be extended into NC and RNC algorithms, respectively, that solve more general parametric problems. The technique is demonstrated on explicit bounded degree circuits. Applications include parametric extensions of the shortest-path and spanning-tree problems and, in particular, the minimum-ratio-cycle problem, showing all these problems are in NC.     

Personal information retrieval: smartphones vs. computers,emails vs. files

Millions of people retrieve their emails and files using their smartphones, yet smartphone retrieval of such personal information has never been studied or compared to retrievals from PCs. In our within-subjects study, we compared the retrievals of our 57 participants in four conditions: files using PCs, emails using PCs, files using smartphones, and emails using smartphones. Our results indicate that when using smartphones, retrievals were significantly less successful and efficient than when using PCs, casting doubt on the implicit assumption that the use of these devices is equivalent. Our results also indicate that participants used the search facility for emails about seven times more than for files, which can encourage vendors to invest more efforts in improving email search engines and file navigation systems. Finally, we found that the tendency to search shows interpersonal differences but consistency across different situations for the same individual and therefore can be regarded as a personal trait. Future research can attempt to explain the search tendency trait in terms of cognitive abilities and personality traits, incorporating it to well-established theories. This may pave the way to a new trait-related theory in the field of information science.     

Large Nonclassical Electrostriction in (Y,Nb)‐Stabilized δ‐Bi2O3

Classical electrostriction, describing a second‐order electromechanical response of insulating solids, scales with elastic compliance, S, and inversely with dielectric susceptibility, ε. This behavior, first noted 20 years ago by Robert Newnham, is shown to apply to a wide range of electrostrictors including polymers, glasses, crystalline linear dielectrics, and relaxor ferroelectrics. Electrostriction in fluorite ceramics of (Y, Nb)‐stabilized δ‐Bi₂O₃ is examined with 16%–23% vacant oxygen sites. Given the values of compliance and dielectric susceptibility, the electrostriction coefficients are orders of magnitude larger than those expected from Newnham's scaling law. In ambient temperature nanoindentation measurements, (Y, Nb)‐stabilized δ‐Bi₂O₃ displays primary creep. These findings, which are strikingly similar to those reported for Gd‐doped ceria, support the suggestion that ion conducting ceramics with the fluorite structure, a large concentration of anion vacancies and anelastic behavior, may constitute a previously unknown class of electrostrictors.     

Rapid sintering protocol produces dense ceria‐based ceramics

We report on a rapid sintering protocol, which optimizes the preparation of 0‐29 mol% Gd‐doped ceria ceramics with density ≥98% of the theoretical crystal lattice value. The starting material is a nanometer grain‐sized powder prepared by carbonate co‐precipitation and calcined with minimal agglomeration and loss of surface area. Slow (5°C/min) heating of the green‐body from 500°C to the optimum temperature of rapid sintering (, dwell time <1 minute) followed by 20°C/min cooling to 1150°C with 6 minutes dwell time, produces maximum pellet density. increases from 1300 to ~1500°C with increase in Gd‐content, while the average grain size in the maximally dense pellets, as determined by scanning electron microscopy, ranges between 600 nm and ~1 μm. For each doping level, the logarithm of the average grain size decreases linearly with 1/T₁. By avoiding extended exposure to sintering temperatures, this protocol is expected to minimize undesirable Gd segregation.     

Energetics of bulk lutetium‐doped Ce1−xLuxO2−x/2 compounds

The dissolution enthalpy, ΔH_DS, and the formation enthalpy, ΔH_f,ox, of bulk lutetium‐doped cerium oxide (LuDC) were studied at 701°C in molten sodium molybdate. For the composition range of Ce_1?XLu_XO_2?X/2, studied 0 ≤ X ≤ 0.3, the ΔH_DS decreases linearly and smoothly with lutetium content according to ΔH_DS, kJ/mol = 73.5(1.0)?165.1(5.5)·x). The enthalpy of formation, ΔH_f,ox, becomes more exothermic linearly with lutetium content. No anomaly in ΔH_f,ox is observed at low Lu₂O₃ concentration as reported previously for several other rare‐earth‐doped ceria systems, suggesting possible differences in clustering and microstructure, which may also be related to difference in processing conditions.     

Modelling defence logistics networks

Military logistics concerns the activities required to support operational forces. It encompasses the storage and distribution of materiel, management of personnel and the provision of facilities and services. A desire to improve the efficiency and effectiveness of the Australian Defence Force logistics process has led to the investigation of rigorous military logistics models suitable for analysis and experimentation. Logistics networks can be viewed as distributed discrete event systems, and hence can be formalised with discrete event techniques which support concurrency. This paper presents a Coloured Petri Net (CPN) model of a military logistics system and discusses some of our experience in developing an initial model. Interesting modelling problems encountered, and their solutions and impact on CPN support tools, are discussed. Authors from the University of South Australia were supported by DSTO Contract No. 4500498737.