On the nature of pulsars

The paper contains a relatively non-technical summary of some recent work by the author and Jeremy Butterfield. The goal is to find a way of assigning meaningful truth values to propositions in quantum theory: something that is not possible in the normal, instrumentalist interpretation. The key mathematical tool is presheaf theory where multi-valued, contextual truth values arise naturally. We show how this can be applied to quantum theory, with the ‘contexts’ chosen to be Boolean subalgebras of the set of all projection operators.     

On the reduction of tensor products of representations of pseudo-orthogonal groups

We verify and generalize a conjecture of Fulling [1] that the Kronecker product of a finite number of unitary representations, not all of which possess an invariant vector, of the Lorentz group SO ₀(1, n), any n2, does not contain the trivial representation discretely.     

Supercooling of the disordered vortex lattice in Bi(2)Sr(2)CaCu(2)O(8+delta)

Time-resolved local induction measurements near the vortex lattice order-disorder transition in optimally doped Bi(2)Sr(2)CaCu(2)O(8+delta) crystals show that the high-field, disordered phase can be quenched to fields as low as half the transition field. Over an important range of fields, the electrodynamical behavior of the vortex system is governed by the coexistence of ordered and disordered vortex phases in the sample. We interpret the results as supercooling of the high-field phase and the possible first-order nature of the order-disorder transition at the "second magnetization peak."     

Rapid prototyping of microfluidic devices with a wax printer

We demonstrate a rapid and inexpensive approach for the fabrication of high resolution poly(dimethylsiloxane) (PDMS)-based microfluidic devices. The complete process of fabrication could be performed in several hours (or less) without any specialized equipment other than a consumer-grade wax printer. The channels produced by this method are of high enough quality that we are able to demonstrate the sizing and separation of DNA fragments using capillary electrophoresis (CE) with no apparent loss of resolution over that found with glass chips fabricated by conventional photolithographic methods. We believe that this method will greatly improve the accessibility of rapid prototyping methods.     

Electrically controlled microvalves to integrate microchip polymerase chain reaction and capillary electrophoresis

Microvalves are key in realizing portable miniaturized diagnostic platforms. We present a scalable microvalve that integrates well with standard lab on a chip (LOC) implementations, yet which requires essentially no external infrastructure for its operation. This electrically controlled, phase-change microvalve is used to integrate genetic amplification and analysis via capillary electrophoresis--the basis of many diagnostics. The microvalve is actuated using a polymer (polyethylene glycol, PEG) that exhibits a large volumetric change between its solid and liquid phases. Both the phase change of the PEG and the genetic amplification via polymerase chain reaction (PCR) are thermally controlled using thin film resistive elements that are patterned using standard microfabrication methods. By contrast with many other valve technologies, these microvalves and their control interface scale down in size readily. The novelty here lies in the use of fully integrated microvalves that require only electrical connections to realize a portable and inexpensive genetic analysis platform.     

Dynamic temperature measurement in microfluidic devices using thermochromic liquid crystals

Thermochromic liquid crystals (TLCs) are used to explore the temperature transients during thermal cycling for microchip-based polymerase chain reaction (PCR). By analyzing the reflected spectra of the TLCs over time, temperature vs. time trajectories were extracted and overshoots/undershoots were estimated. To our knowledge, this is the first report of TLC-based dynamic temperature measurements in a microfluidic device for all PCR temperature stages.