Recovering Beam Search: Enhancing the Beam Search Approach for Combinatorial Optimization Problems

A hybrid heuristic method for combinatorial optimization problems is proposed that combines different classical techniques such as tree search procedures, bounding schemes and local search. The proposed method enhances the classic beam search approach by applying to each partial solution corresponding to a node selected by the beam, a further test that checks whether the current partial solution is dominated by another partial solution at the same level of the search tree. If this is the case, the latter solution becomes the new current partial solution. This step allows to partially recover from previous wrong decisions of the beam search procedure and can be seen as a local search step on the partial solution. We present here the application to two well known combinatorial optimization problems: the two-machine total completion time flow shop scheduling problem and the uncapacitated p-median location problem. In both cases the method strongly improves the performances with respect to the basic beam search approach and is competitive with the state of the art heuristics.     

Parameter dependence and outcome dependence in dynamical models for state vector reduction

We apply the distinction between parameter independence and outcome independence to the linear and nonlinear models of a recent nonrelativistic theory of continuous state vector reduction. We show that in the nonlinear model there is a set of realizations of the stochastic process that drives the state vector reduction for which parameter independence is violated for parallel spin components in the EPR-Bohm setup. Such a set has an appreciable probability of occurrence ( 1/2). On the other hand, the linear model exhibits only extremely small parameter dependence effects. We investigate some specific features of the models and we recall that, as has been pointed out recently, if one wants to be able to speak of definite outcomes (or equivalently of possessed objective elements of reality) at finite times, one has to slightly change the criteria for their attribution to physical systems. The concluding section is devoted to a detailed discussion of the difficulties which one meets when one tries to take, as a starting point for the formulation of a relativistic theory, a nonrelativistic scheme which exhibits parameter dependence. Here we derive a theorem which identifies the precise sense in which the occurrence of parameter dependence forbids a genuinely relativistic generalization. Finally we show how the appreciable parameter dependence of the nonlinear model gives rise to problems with relativity, while the extremely weak parameter dependence of the linear model does not give rise to any difficulty, provided one takes into account the appropriate criteria for the attribution of definite outcomes.Work supported in part by the Trieste Section of the INFN.     

Oxygen sensitivity of algal H2- production

Applied Biochemistry and Biotechnology - Photoproduction of H2 by green algae utilizes electrons originating from the photosynthetic oxidation of water and does not require metabolic intermediates....     

Relativistic dynamical reduction models: General framework and examples

The formulation of a relativistic theory of state-vector reduction is proposed and analyzed, and its conceptual consequences are elucidated. In particular, a detailed discussion of stochastic invariance and of local and nonlocal aspects at the level of individual systems is presented.     

On some recent proposals for testing macrorealism versus quantum mechanics

In order to evaluate its relevance, we reconsider critically the recent proposal by Leggett and Garg to test macrorealism against quantum mechanics by resorting to experiments involving noninvasive measurement processes on a SQUID. Our conclusion is that, in spite of the fact that the proposed experiment would neither constitute a test of macrorealism nor a test of macrocontextuality, a simplified form of it represents a (presumably) feasible experiment permitting a direct test of macroscopic quantum coherence. We also analyze the proposal from the point of view of the recent attempts to build up model theories allowing to take, within a purely quantum framework, a macrorealistic position about natural phenomena, i.e., the socalled dynamical reduction models and we stress that the proposed experiment has no relevance for the dynamical reduction program, as developed so far. However consideration of the SQUID system allows one to test other possible dynamical mechanisms leading to the objectification of macroproperties which could, in principle, be operative. We also briefly sketch experimental procedures to be followed to get all relevant information concerning macrocoherence.     

On a Recent Proposal of Faster than Light Quantum Communication

In a recent paper, A.Y. Shiekh has discussed an experimental set-up which, in his opinion, should make possible faster-than-light communication using the collapse of the quantum wave function. Contrary to the many proposals which have been presented in the past, he does not resort to an entangled state of two systems but he works with a single particle in a superposition of two states—corresponding to its propagation in opposite directions—one of which goes through an appropriate interferometer. The possibility for an observer near the interferometer to introduce or not, at his free will, a phase shifter along one of the paths should allow to change instantaneously the probability of finding the particle in the far-away region corresponding to the other state of the superposition and, correspondingly, to change the intensity of a beam of particles reaching a distant observer. In this paper we show a flaw in the argument: once more, as it has been proved in full generality a long time ago, the process of wave packet reduction cannot be used for superluminal communication.     

Proofs of nonlocality without inequalities revisited

We discuss critically the so-called nonlocality without inequalities proofs for bipartite quantum states, we generalize them and we analyze their relation with the Clauser-Horne inequality.