Evaluation of quantitative recovery methods for Listeria monocytogenes applied to stainless steel

The ability of Listeria monocytogenes to attach to various food contact surfaces, such as stainless steel, polypropylene, and rubber compounds, is well documented. The retention of these or other pathogenic bacteria on food contact surfaces increases the risk of transmission to food products. The objective of this study was to compare several methods for quantitative recovery of Listeria monocytogenes from stainless steel surfaces. A cocktail of 4 serotypes of Listeria monocytogenes mixed in equivalent concentrations was inoculated onto type 304 stainless steel coupons in a 2 x 2 cm area. After 1 h exposure, coupons were sampled by one of the following methods: (1) swabbing with a premoistened Dacron swab; (2) rinsing with phosphate-buffered saline; (3) direct contact onto tryptic soy agar containing 0.6% yeast extract (TSA + YE) plates for 10 s; (4) sonication in an ultrasonic water bath (40 kHz); (5) contact with the bristles of a sonicating brush head for 1 min; and (6) indirect contact (2-4 mm distance) with a sonicating brush head for 1 min. The 3 sonication methods yielded higher recovery than the other 3 methods (P < 0.05). Brushing the coupons with the sonicating brush head (contact or noncontact) yielded a recovery level of about 60%. The lowest cell recovery (about 20%) was observed with the swab and direct agar contact methods. After a 12 h exposure, recoveries ranged from 17.4 (brush contact method) to 2% (swab method).     

Operator algebras and a theorem of Dieudonne

LetA be aC*-algebra with second dualA″. Let (φ _n)(n=1,...) be a sequence in the dual ofA such that limφ _n(a) exists for eacha εA. In general, this does not imply that limφ _n(x) exists for eachx εA″. But if limφ _n(p) exists whenever p is the range projection of a positive self-adjoint element of the unit ball ofA, then it is shown that limφ _n(x) does exist for eachx inA″. This is a non-commutative generalisation of a celebrated theorem of Dieudonné. A new proof of Dieudonné’s theorem, for positive measures, is given here. The proof of the main result makes use of Dieudonné’s original theorem.     

Computational Magnetochemistry: Complementary Quantum Mechanical Tools

Magnetic behaviour of condensed magnetic d and f systems with localised ‘magnetic electrons’ is essentially controlled by both single ion effects (interelectronic and spin‐orbit coupling, ligand field potential) and interionic exchange interactions. The latter act according to the spin dimensionality forced upon the magnetic centre via the single ion effects. For a complete understanding of magnetic behaviour on the basis of quantum mechanical models a two‐step procedure presents itself that determines in a complementary way first the ‘easy’ direction of the centres' magnetic dipoles connected with the single ion ground state. Subsequently, the relevant isotropic/anisotropic spin‐spin coupling model is applied (Heisenberg, XY, Ising). With the help of the textbook compounds CrBr₃ and Cs₃ CoCl₅ as well as β‐RuCl₃ the way of acting is pointed out.     

Radial oscillations of neutron stars in strong magnetic fields

The eigen frequencies of radial pulsations of neutron stars are calculated in a strong magnetic field. At low densities we use the magnetic BPS equation of state (EOS) similar to that obtained by Lai and Shapiro while at high densities the EOS obtained from the relativistic nuclear mean field theory is taken and extended to include strong magnetic field. It is found that magnetized neutron stars support higher maximum mass whereas the effect of magnetic field on radial stability for observed neutron star masses is minimal.     

The radiological services laboratory: Designed for the future

A new state of the art radiochemistry laboratory incorporating advanced design and environmental control elements has been constructed in Atlanta, Georgia. The design of the facility is oriented to the efficient production of analytical sample results which meet regulatory requirements while at the same time provides an atmosphere that is pleasurable for analysts and visitors alike. The laboratory building contains two separate and distinct laboratories under one roof. This allows the facility to handle samples with low levels of radioactivity on one side of the lab without fear of contamination of environmental work on the other side. Unlike most laboratories, this facility utilizes a scrubber system and liquid waste holdup system to prevent accidental releases to the environment. The potential spread of radioactive contamination is controlled through the use of negative pressure ventillation zones. Construction techniques, laboratory systems, instrumentation and ergonomic considerations will also be discussed.     

Preparation of Nb3Sn structures on low pinning niobium foils for use in guided flux motion experiments

A simple method is presented to prepare very low pinning niobium foils on which geometrically well defined Nb₃Sn-pinning structures of arbitrary shape are deposited. This facilitates the fabrication of samples for guided vortex motion experiments some of which are reported.