An optimum settling problem for time lag systems

Lagrange multiplier in Banach space for settling optimal control in time lag syste

A simple formula for pooling knowledge about a quantum system

When various observers obtain information in an independent fashion about a classical system, there is a simple rule which allows them to pool their knowledge, and this requires only the states-of-knowledge of the respective observers. Here we derive an equivalent quantum formula. While its realm of applicability is necessarily more limited, it does apply to a large class of measurements, and we show explicitly for a single qubit that it satisfies the intuitive notions of what it means to pool knowledge about a quantum system. This analysis also provides a physical interpretation for the trace of the product of two density matrices.Comment: 5 pages, Revtex

Power, discursive space and institutional practices in the construction of housing problems

A constructionist approach to the study of social problems and housing policy provides a theoretically informed means of analysing the ways in which housing policy is formulated and implemented. Yet despite a strong commitment by housing researchers to policy-relevance, constructionist studies of how specific social problems are generated and deployed have so far made only a limited impact on housing research. The paper addresses this lacuna by first discussing important literature and the key conceptual issues in this field of study. This is followed by a discussion of two examples from recent UK housing policy (the shift in the 1980s from defining lone mothers as the victims of housing shortages to a morally questionable group subverting needs based allocation policies and the re-emergence of anti-social behaviour as a problem on housing estates). The paper's conclusion is that the 'construction of problems' provides a rich source of new material as well as offering significant opportunities to develop a more critically informed housing research agenda

Privileged or exploited council tenants?: The discursive change in Conservative housing policy from 1972 to 1980

The process of social construction in which competing and sometimes contradictory definitions contend with one another plays a decisive part in policy making. Justifications for policy intervention often require a narrative identifying villains or victims to delineate creatively a 'social problem' that needs to be addressed by appropriate measures. This article shows how contrasting political and media representations of council tenants in the 1960s and 1970s provided the emotive justifications for two distinct policies: 'Fair Rents' and the 'Right to Buy'. The article concludes that more attention should be paid to the way that the successful mobilisation of bias legitimises policy interventions

Experimental Demonstration of a Quantum Circuit using Linear Optics Gates

One of the main advantages of an optical approach to quantum computing is the fact that optical fibers can be used to connect the logic and memory devices to form useful circuits, in analogy with the wires of a conventional computer. Here we describe an experimental demonstration of a simple quantum circuit of that kind in which two probabilistic exclusive-OR (XOR) logic gates were combined to calculate the parity of three input qubits.Comment: v2 is final PRA versio

Combinatorial models of rigidity and renormalization

We first introduce the percolation problems associated with the graph theoretical concepts of $(k,l)$-sparsity, and make contact with the physical concepts of ordinary and rigidity percolation. We then devise a renormalization transformation for $(k,l)$-percolation problems, and investigate its domain of validity. In particular, we show that it allows an exact solution of $(k,l)$-percolation problems on hierarchical graphs, for $k\leq l<2k$. We introduce and solve by renormalization such a model, which has the interesting feature of showing both ordinary percolation and rigidity percolation phase transitions, depending on the values of the parameters.Comment: 22 pages, 6 figure

Magnetic structures of RbCuCl_3 in a transverse field

A recent high-field magnetization experiment found a phase transition of unknown character in the layered, frustrated antiferromagnet RbCuCl_3, in a transverse field (in the layers). Motivated by these results, we have examined the magnetic structures predicted by a model of RbCuCl_3, using the classical approximation. At small fields, we obtain the structure already known to be optimal, an incommensurate (IC) spiral with wave vector q in the layers. At higher fields, we find a staircase of long-period commensurate (C) phases (separated initially by the low-field IC phase), then two narrow IC phases, then a fourth IC phase (also with intermediate C phases), and finally the ferromagnetically aligned phase at the saturation field H_S. The three-sublattice C states familiar from the theory of the triangular antiferromagnet are never optimal. The C phases and the two intermediate IC phases were previously unknown in this context. The magnetization is discontinuous at a field \approx 0.4H_S, in qualitative agreement with experiment, though we find much fine structure not reported.Comment: 9 pages, 8 figure