Unusual representations of local groups

By means of duality transformations we obtain representations of Yang-Mills groups which are neither tensors nor gauge fields, and fields which under general coordinate transformations are neither tensors nor tensor densities.     

Matching and price competition: beyond symmetric linear costs

Bulow and Levin’s (2006) “Matching and Price Competition” studies a matching model in which hospitals compete for interns by offering wages. We relax the assumption of symmetric linear costs and compare the pricing equilibrium that results to the firm-optimal competitive equilibrium. With linear and asymmetric costs, competition in the pricing equilibrium may not be localized, but all other qualitative comparisons of Bulow and Levin (2006) hold. With non-linear and symmetric costs workers’ average utility in the pricing equilibrium may be higher than in the firm- optimal competitive equilibrium. With asymmetric and non-linear costs, firms need not choose scores from an interval in a pricing equilibrium, which may make competition even less localized.     

Microjoule pulses from a passively mode-locked Yb:KY(WO(4))(2) thin-disk oscillator with cavity dumping

We demonstrate, for the first time to our knowledge, a passively mode-locked femtosecond thin-disk oscillator with cavity dumping. A beta-barium-borate-based pockels cell imposes cavity dumping at a repetition rate of 1 MHz. The laser generates pulse energies up to 3 microJ with a pulse duration of 680 fs in a diffraction-limited beam.     

FTICR-MS applications for the structure determination of natural products

Natural products are a source of unique chemical entities with specific biological activities of great value to the pharmaceutical industry. However, the determination of unknown structures is usually time consuming and often becomes a bottleneck in the effort to develop natural products into effective drugs. The high-performance features of high magnetic field FTMS have greatly alleviated the structural elucidation bottleneck to meet increasingly shorter discovery timelines for drug candidates based on natural products. The high-performance features of high field FTMS include unsurpassed mass measurement accuracy for elemental formula determination, ultra-high mass resolution for component separation, the ability to perform multiple levels of tandem mass spectrometry for structural elucidation, and moderate sensitivity for limited supply of isolates. A number of applications utilizing these properties of FTMS have been reported recently for the structural elucidation of novel natural product structures originating from terrestrial and marine microorganisms. In this review, FTMS methods and their applications for the structural elucidation and characterization of natural products will be reviewed. Figure Molecular structure and positive ion mode nanoelectrospray FTICR mass spectrum of methylspirastrellolide A (3). The inset shows the isotopic distribution with high abundance of the A + 2 peak, but less than the abundance of the A + 1 peak. The resolved isotopic fine structure of the A + 2 peak reveals the presence of one chlorine atom based on accurate mass assignment and the measured abundance ratio between the resolved ³⁷Cl peak and the monoisotopic peak     

The force acting on a superparamagnetic bead due to an applied magnetic field

This paper describes a model of the motion of superparamagnetic beads in a microfluidic channel under the influence of a weak magnetic field produced by an electric current passing through a coplanar metal wire. The model based on the conventional expression for the magnetic force experienced by a superparamagnetic bead (suspended in a biologically relevant medium) and the parameters provided by the manufacturer failed to match the experimental data. To fit the data to the model, it was necessary to modify the conventional expression for the force to account for the non-zero initial magnetization of the beads, and to use the initial magnetization and the magnetic susceptibility of the beads as adjustable parameters. The best-fit value of susceptibility deviated significantly from the value provided by the manufacturer, but was in good agreement with the value computed using the magnetization curves measured independently for the beads from the same vial as those used in the experiment. The results of this study will be useful to researchers who need an accurate prediction of the behavior of superparamagnetic beads in aqueous suspensions under the influence of weak magnetic fields. The derivation of the force on a magnetic bead due to a magnetic field also identifies the correct treatment to use for this interaction, and resolves discrepancies present throughout the literature.