Improving the Efficiency of Tabu Search for Machine Sequencing Problems

Tabu search (TS) is becoming increasingly recognized as an efficient way of finding high-quality solutions to hard combinatorial problems. It may be described as an intelligent meta-heuristic for controlling simpler local search procedures. However, reported applications have often used a ‘brute-force’ approach without considering the most effective use of the computing effort available. This paper intends firstly to give a basic introduction to the ideas of TS, and then it will report some computational experiments on TS in the context of machine sequencing. These have shown that it is important to define the balance between exploration of the solution space and exploitation of the information obtained. The results will be compared with those obtained from a proven Simulated Annealing (SA) algorithm, which tends to confirm the general opinion that when implemented efficiently, TS is a more effective search paradigm than SA.     

Moment collapse in the Ce(Rh1−xOsx)3B2 system

The compound CeRh₃B₂ orders magnetically with a low saturation moment of about 0.4 micro_B per formula unit but a very high Curie temperature of 115 K. On replacing Rh with Os, it is observed that in the Ce(Rh_1?xOs_x)₃B₂ (0 ? x ? 0.167) series, both the magnetic moment and the Curie temperature decrease rapidly with increasing x. The compound CeRh_2.5Os_0.5B₂ (x = 0.167) does not appear to be ordered magnetically down to 5 K. This behavior is thought to arise from the changes in the hybridization of Ce 4f levels with sp type conduction electrons and/or with Rh and Os derived d bands.     

Methods for achieving ultra-low backgrounds in above-ground germanium detector systems

The authors have previously shown how to achieve a 40-fold reduction in system background for above-ground germanium detectors. Such systems are generally sufficient for examining small hydrogenous samples or samples of non-hydrogenous materials such as soil, glass, metals, etc. However, samples with a large hydrogen content yield a seriously degraded background due to a number of neutron-induced interactions, such as Compton scatter following hydrogen capture of thermalized neutrons. A study was performed to better understand the sources of thermal neutron flux in above-ground detector systems. The effects of different quantities of hydrogen in the sample were also examined. Methods are presented for additional lowering of system background for both hydrogenous and non-hydrogenous samples.     

φ meson production fromp\bar p collisions at\sqrt s = 1.8 TeV

Fermilab experiment E735 located at the CO intersection region of the $\sqrt s = 1.8$ TeV $p\bar p$ collider analysed over 900 Φ→K ⁺ K ^? events. Measured were the transverse momentum spectrum, the correlation between the average transverse momentum <pt> and the charged particle multiphcityN _c , as well as the probability of Φ production per charged track,N _Φ /N _c , versusN _c . We have also made an estinate of the total inclusive cross section for Φ mesons, $\sigma (p\bar p \to \phi X) = 7.3 \pm 2.2 mb$ .