Co-evolution of firms, industries and networks in space

The cluster literature suffers from a number of shortcomings: (1) by and large, cluster studies do not take into account that firms in a cluster are heterogeneous in terms of capabilities; (2) cluster studies tend to overemphasize the importance of place and geographical proximity and underestimate the role of networks which are, by definition, a-spatial entities; (3) most, if not all cluster studies have a static nature, and do not address questions like the origins and evolution of clusters. Our aim is to overcome these shortcomings and propose a theoretical framework on the evolution of clusters. Bringing together bodies of literature on clusters, industrial dynamics, the evolutionary theory of the firm and network theory, we describe how clusters co-evolve with: (1) the industry they adhere to; (2) the (dynamic) capabilities of the firms they contain; and (3) the industry-wide knowledge network they are part of. Based on this framework, we believe the analysis of cluster evolution provides a promising research agenda in evolutionary economic geography for the years to come.cluster evolution, network dynamics, industrial dynamics, co-evolution, evolutionary economic geography

Towards a general solution to the linear Heisenberg problem

The construction of a complete set of stationary states of the linear Heisenberg system with periodic boundary conditions (rings) has been a topic of intensive research for many decades. Many eminent theoreticians have made their contribution to this joint eort, but we should mention in the rst place the epoch-making work of Bethe 1 and Hulthen. 5 Their work is the basis of many papers on this topic that have appeared during the past 70 years. We do no have the intention to give a complete survey of all this work but we will try to indicate that especially an asymptotic approach starting from the Hypothesis of Strings gives the prospect of a general and complete solution of the Heisenberg chain

Theory of membrane capacitive deionization including the effect of the electrode pore space

Membrane capacitive deionization (MCDI) is a technology for water desalination based on applying an electrical field between two oppositely placed porous electrodes. Ions are removed from the water flowing through a channel in between the electrodes and are stored inside the electrodes. Ion-exchange membranes are placed in front of the electrodes allowing for counterion transfer from the channel into the electrode, while retaining the coions inside the electrode structure. We set up an extended theory for MCDI which includes in the description for the porous electrodes not only the electrostatic double layers (EDLs) formed inside the porous (carbon) particles, but also incorporates the role of the transport pathways in the electrode, i.e., the interparticle pore space. Because in MCDI the coions are inhibited from leaving the electrode region, the interparticle porosity becomes available as a reservoir to store salt, thereby increasing the total salt storage capacity of the porous electrode. A second advantage of MCDI is that during ion desorption (ion release) the voltage can be reversed. In that case the interparticle porosity can be depleted of counterions, thereby increasing the salt uptake capacity and rate in the next cycle. In this work, we compare both experimentally and theoretically adsorption/desorption cycles of MCDI for desorption at zero voltage as well as for reversed voltage, and compare with results for CDI. To describe the EDL-structure a novel modified Donnan model is proposed valid for small pores relative to the Debye length

Polarization-preserving confocal microscope for optical experiments in a dilution refrigerator with high magnetic field

We present the design and operation of a fiber-based cryogenic confocal microscope. It is designed as a compact cold-finger that fits inside the bore of a superconducting magnet, and which is a modular unit that can be easily swapped between use in a dilution refrigerator and other cryostats. We aimed at application in quantum optical experiments with electron spins in semiconductors and the design has been optimized for driving with, and detection of optical fields with well-defined polarizations. This was implemented with optical access via a polarization maintaining fiber together with Voigt geometry at the cold finger, which circumvents Faraday rotations in the optical components in high magnetic fields. Our unit is versatile for use in experiments that measure photoluminescence, reflection, or transmission, as we demonstrate with a quantum optical experiment with an ensemble of donor-bound electrons in a thin GaAs film.Comment: 9 pages, 7 figure

Ion-sensing using chemically-modified ISFETs

Synthetic macrocyclic polyether ion receptors are the active components for the selective and sensitive detection of potassium ions in chemical sensors based on modified ISFETs.\ud \ud Covalent chemical anchoring of the sensing membrane to the gate oxide of the ISFET is essential in order to increase the lifetime of the sensor system to more than three months