Efficient sampling of ice structures by electrostatic switching

An electrostatic switching procedure is introduced that enables the systematic generation of high-quality ice configurations at various temperatures. Proton disordered ice Ih configurations were generated for the TIP4P water model at temperatures from 50 to 240 K, for the SPC/Fw water model from 100 to 240 K, and for the DC97 water model at 240 K. The resulting configurations were found to properly sample the canonical ensemble. The dielectric constant of ice Ih was determined from the net dipole fluctuation of the ice configurations. The calculated dielectric constant compares favorably with the study by Rick and Haymet [J. Chem. Phys. 2003, 118, 9291]. However, our method gives smaller error bars, especially at lower temperatures. At temperatures above 200 K, a type of hydrogen-bond defect is identified that cannot be categorized as a D or L type defect.     

Single-frequency operation of a high-power, long-wavelength semiconductor disk laser

An optically pumped, high-power, single-frequency semiconductor disk laser is demonstrated. A thin (50 microm) diamond bonded to an InGaAsP gain chip provides the combined functions of heat removal and spectral filtering, thus eliminating the need for the additional intracavity etalons that are usually employed for single-frequency operation. In a short cavity (4 mm) configuration we obtained a maximum output power of 470 mW at 0 degrees C and 170 mW at 20 degrees C in a near-diffraction-limited beam (M2 < 1.2). The emission wave-length was 1549 nm and the linewidth was less than 200 MHz.     

Experimental validation of a dynamic resonant wall shear stress sensor

Experimental measurements are used to validate a numerical model of a dynamic resonant wall shear stress sensor. The numerical model consists of an unsteady two-dimensional boundary-layer model for the flow and a simple mechanical model for the sensor itself. The sensor’s sensitivity to wall shear stress is experimentally determined in a flat-plate boundary layer, and the results agree closely with those from the numerical simulations. Using the validated model, it is determined that the energy lost in each sensor oscillation due to the interaction between the sensor and fluid increases with increasing mean wall shear stress.     

3M Petrifilm Staph Express Count plate method for the enumeration of Staphylococcus aureus in selected types of meat, seafood, and poultry: collaborative study

The 3M Petrifilm Staph Express Count plate method was compared with AOAC Official Method 975.55 for the enumeration of Staphylococcus aureus in selected foods. Four foods--cooked, diced chicken; cured ham; smoked salmon; and pepperoni--were analyzed for S. aureus by 12 collaborating laboratories. For each food tested, the collaborators received 8 blind test samples consisting of a control sample, a low inoculation level, a medium inoculation level, and a medium inoculation level with background flora, each in duplicate. The mean log10 counts for the methods were comparable for all 4 foods. The repeatability and reproducibility variances of the 24 h Petrifilm Staph Express Count plate method were similar to those of the 72 h standard method.     

Petrifilm rapid S. aureus Count Plate method for rapid enumeration of Staphylococcus aureus in selected foods: collaborative study

A rehydratable dry-film plating method for Staphylococcus aureus in foods, the 3M Petrifilm Rapid S. aureus Count Plate method, was compared with AOAC Official Method 975.55 (Staphylococcus aureus in Foods). Nine foods-instant nonfat dried milk, dry seasoned vegetable coating, frozen hash browns, frozen cooked chicken patty, frozen ground raw pork, shredded cheddar cheese, fresh green beans, pasta filled with beef and cheese, and egg custard-were analyzed for S. aureus by 13 collaborating laboratories. For each food tested, the collaborators received 8 blind test samples consisting of a control sample and 3 levels of inoculated test sample, each in duplicate. The mean log counts for the methods were comparable for pasta filled with beef and cheese; frozen hash browns; cooked chicken patty; egg custard; frozen ground raw pork; and instant nonfat dried milk. The repeatability and reproducibility variances of the Petrifilm Rapid S. aureus Count Plate method were similar to those of the standard method.