A note on solving large p-median problems

In a previous paper we presented a tree search algorithm for the p-median problem, the problem of locating p facilities (medians) on a network, which was based upon La grangean relaxation and subgradient optimisation. That algorithm solved (optimally) problems with an arbitrary number of medians and having up to 200 vertices.In this note we show that it is possible to enhance that algorithm to solve (optimally) problems having up to 900 vertices using the Cray-1S computer.     

Determining Teaching and Research Efficiencies

In this paper we consider the problem of determining teaching and research efficiencies for university departments concerned with the same discipline. Considering this problem highlights the issue of how to determine efficiencies when resources are shared between different activities, and a non-linear approach to this issue based upon data envelopment analysis is presented. Computational results are given for chemistry and physics departments in the United Kingdom.     

Low-frequency crossover of the fractional power-Law conductivity in SrRuO3

We combine the results of terahertz time-domain spectroscopy with far-infrared transmission and reflectivity to obtain the conductivity of SrRuO3 over an unprecedented continuous range in frequency, allowing us to characterize the approach to zero frequency as a function of temperature. We show that the conductivity follows a simple phenomenological form, with an analytic structure fundamentally different from that predicted by the standard theory of metals.     

Market neutral portfolios

In this paper we consider the problem of constructing a market neutral portfolio. This is a portfolio of financial assets that (ideally) exhibits performance independent from that of an underlying market as represented by a benchmark index. We formulate this problem as a mixed-integer nonlinear program, minimising the absolute value of the correlation between portfolio return and index return. Our model is a flexible one that incorporates decisions as to both long and short positions in assets. Computational results, obtained using the software package Minotaur, are given for constructing market neutral portfolios for eleven different problem instances derived from universes defined by S&P international equity indices. We also compare our approach against an alternative approach based on minimising the absolute value of regression slope (the zero-beta approach).     

Optimisation of sludge treatment and transport

In this paper we describe some work carried out in the UK into improving the effectiveness of a waste treatment and distribution network. Sludge is the name given to (treated) waste water and sewage. It is collected at small facilities and requires further treatment before it can be disposed of. We develop a linear programming model for the problem of effectively treating and distributing sludge. This model has been implemented in a large UK regional water company, Yorkshire Water.     

The interaction of Ni and Au with HCl during quenching

During annealing of Ni and Au, previously quenched into HCl at 203 K, annealing stages that cannot easily be explained in terns of the migration of open volume defects are observed. The contamination of the hot samples with hydrogen released from the quenching fluid is suggested as the origin of these additional annealing stages.