Stationary correlations for a far-from-equilibrium spin chain

A kinetic one-dimensional Ising model on a ring evolves according to a generalization of Glauber rates, such that spins at even (odd) lattice sites experience a temperature $T_{e}$ ($T_{o}$). Detailed balance is violated so that the spin chain settles into a non-equilibrium stationary state, characterized by multiple interactions of increasing range and spin order. We derive the equations of motion for arbitrary correlation functions and solve them to obtain an exact representation of the steady state. Two nontrivial amplitudes reflect the sublattice symmetries; otherwise, correlations decay exponentially, modulo the periodicity of the ring. In the long chain limit, they factorize into products of two-point functions, in precise analogy to the equilibrium Ising chain. The exact solution confirms the expectation, based on simulations and renormalization group arguments, that the long-time, long-distance behavior of this two-temperature model is Ising-like, in spite of the apparent complexity of the stationary distribution.Comment: 9 page

Marking 100 years since Rudolf Höber’s discovery of the insulating envelope surrounding cells and of the beta-dispersion exhibited by tissue

© The Author(s), 2012. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Journal of Electrical Bioimpedance 3 (2012): 74-79, doi:10.5617/jeb.401.Between 1910 and 1913 Rudolf Höber presented proof that the interiors of red blood cells and muscle cells contain conducting electrolytes, and that each conducting core is contained within an insulating membrane. He did this by demonstrating, in a series of remarkable electrical experiments, that the conductivity of compacted cell samples at low frequencies (~150 Hz) was about ten-times less than the value obtained at ~5 MHz. On perforation of the membrane, the low-frequency conductivity increased to a value approaching that exhibited at MHz frequencies. Apart from representing a major milestone in the development of cell biology and electrophysiology, Höber’s work was the first description of what we now call the dielectric b-dispersion exhibited by cell suspensions and fresh tissue

The periodic array of interface cracks and their interaction

A periodic array of interface cracks is considered as a simple model for studying interface crack interaction. The novel feature of the solution is the elimination of the oscillatory singularities and of the material overlapping which is accomplished by allowing frictionless contact zones at the crack tips. The results are obtained for a combination of shear and tension-compression loads applied at infinity. It is shown that the stress intnsity factors become smaller with decreasing distance between the cracks. This indicates that the spreading of an interface crack is inhibited by the presence of adjacent cracks.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23754/1/0000727.pd

Impedimetric measurement of DNA–DNA hybridisation using microelectrodes with different radii for detection of methicillin resistant Staphylococcus aureus (MRSA)

Due to their electroanalytical advantages, microelectrodes are a very attractive technology for sensing and monitoring applications. One highly important application is measurement of DNA hybridisation to detect a wide range of clinically important phenomena, including single nucleotide polymorphisms (SNPs), mutations and drug resistance genes. The use of electrochemical impedance spectroscopy (EIS) for measurement of DNA hybridisation is well established for large electrodes but as yet remains relatively unexplored for microelectrodes due to difficulties associated with electrode functionalisation and impedimetric response interpretation. To shed light on this, microelectrodes were initially fabricated using photolithography and characterised electrochemically to ensure their responses matched established theory. Electrodes with different radii (50, 25, 15 and 5 µm) were then functionalised with a mixed film of 6-mercapto-1-hexanol and a thiolated single stranded ssDNA capture probe for a specific gene from the antibiotic resistant bacterium MRSA. The complementary oligonucleotide target from the mecA MRSA gene was hybridised with the surface tethered ssDNA probe. The EIS response was evaluated as a function of electrode radius and it was found that charge-transfer (RCT) was more significantly affected by hybridisation of the mecA gene than the non-linear resistance (RNL) which is associated with the steady state current. The discrimination of mecA hybridisation improved as electrode radius reduced with the RCT component of the response becoming increasingly dominant for smaller radii. It was possible to utilise these findings to produce a real time measurement of oligonucleotide binding where changes in RCT were evident one minute after nanomolar target addition. These data provide a systematic account of the effect of microelectrode radius on the measurement of hybridisation, providing insight into critical aspects of sensor design and implementation for the measurement of clinically important DNA sequences. The findings open up the possibility of developing rapid, sensitive DNA based measurements using microelectrodes

Frictional slip between a layer and a substrate caused by a normal load

An elastic layer that rests on a substrate and is subjected to a concentrated normal force is used to investigate some aspects of frictional slip between two bodies. The formulation using known results for glide dislocations leads to a singular integral equation of a Cauchy type that must be solved numerically. Results for various quantities of interest are given graphically.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23373/1/0000318.pd

Improving the yield and lifetime of microfabricated sensors for harsh environments

This paper details improvements in the design and fabrication of electrodes intended to function in the high temperature, corrosive environment of a molten salt. Previously reported devices have displayed low yield and lifetimes and this paper presents two strategies to improve these aspects of their performance. The first one involves reducing the critical area, which increased both the electrode yield and lifetimes. The second element utilised test structures, targeted at identifying failure mechanisms, which helped facilitate the materials/design modifications required to make the devices more robust

Test structure and measurement system for characterising the electrochemical performance of nanoelectrode structures

This paper presents a complete test structure and characterisation system for the evaluation of nanoelectrode technology. It integrates microfabricated nanoelectrodes for electrochemical measurements, 3D printing and surface tensionconfined microfluidics. This system exploits the inherent analytical advantages of nanoelectrodes that enables their operation with small volume samples, which has potential applications for onwafer measurements