QED effective action at finite temperature

The QED effective Lagrangian in the presence of an arbitrary constant electromagnetic background field at finite temperature is derived in the imaginary-time formalism to one-loop order. The boundary conditions in imaginary time reduce the set of gauge transformations of the background field, which allows for a further gauge invariant and puts restrictions on the choice of gauge. The additional invariant enters the effective action by a topological mechanism and can be identified with a chemical potential; it is furthermore related to Debye screening. In concordance with the real-time formalism, we do not find a thermal correction to Schwinger's pair-production formula. The calculation is performed on a maximally Lorentz covariant and gauge invariant stage.Comment: 9 pages, REVTeX, 1 figure, typos corrected, references added, final version to appear in Phys. Rev.

Massively parallel production of lipid microstructures

In this paper we describe a simple and inexpensive microfluidic system for the production of lipid tubules and vesicles. The system incorporates a central microporous membrane for interfacing lipid. films with aqueous flows. Hydrodynamic drag was used for the parallel elongation of high axial ratio lipid tubules with uniform 1.5 +/- 0.5 mu m diameters. Alternatively, electrokinetic operation was used for the rapid and continuous production of vast numbers of lipid vesicles with diameters ranging from 1 to 3 mu m

Characterization of the Photoconversion on Reaction of the Fluorescent Protein Kaede on the Single-Molecule Level

Fluorescent proteins are now widely used in fluorescence microscopy as genetic tags to any protein of interest. Recently, a new fluorescent protein, Kaede, was introduced, which exhibits an irreversible color shift from green to red fluorescence after photoactivation with λ = 350–410 nm and, thus, allows for specific cellular tracking of proteins before and after exposure to the illumination light. In this work, the dynamics of this photoconversion reaction of Kaede are studied by fluorescence techniques based on single-molecule spectroscopy. By fluorescence correlation spectroscopy, fast flickering dynamics of the chromophore group were revealed. Although these dynamics on a submillisecond timescale were found to be dependent on pH for the green fluorescent Kaede chromophore, the flickering timescale of the photoconverted red chromophore was constant over a large pH range but varied with intensity of the 488-nm excitation light. These findings suggest a comprehensive reorganization of the chromophore and its close environment caused by the photoconversion reaction. To study the photoconversion in more detail, we introduced a novel experimental arrangement to perform continuous flow experiments on a single-molecule scale in a microfluidic channel. Here, the reaction in the flowing sample was induced by the focused light of a diode laser (λ = 405 nm). Original and photoconverted Kaede protein were differentiated by subsequent excitation at λ = 488 nm. By variation of flow rate and intensity of the initiating laser we found a reaction rate of 38.6 s(−1) for the complete photoconversion, which is much slower than the internal dynamics of the chromophores. No fluorescent intermediate states could be revealed

An algorithmic chemistry for genetic programming

Abstract. Genetic Programming has been slow at realizing other programming paradigms than conventional, deterministic, sequential von-Neumann type algorithms. In this contribution we discuss a new method of execution of programs introduced recently: Algorithmic Chemistries. Therein, register machine instructions are executed in a non–deterministic order, following a probability distribution. Program behavior is thus highly dependent on frequency of instructions and connectivity between registers. Here we demonstrate the performance of GP on evolving solutions to a parity problem in a system of this type.