Nitrogen thermometry in an inductively coupled plasma torch using broadband nanosecond coherent anti-Stokes Raman scattering.

The development of atmospheric hypersonic flight and re-entry capabilities requires the characterization of the thermo-chemical state of representative test environments. This study demonstrates the usage of multiplex nanosecond N 2 coherent anti-Stokes Raman scattering (CARS) to measure temperatures in an atmospheric, high-temperature (>6000K), air plasma plume, generated by an inductively coupled plasma torch. These are some of the highest temperatures ever accessed via gas-phase CARS, to our knowledge. Temperatures of N 2 in the equilibrium plasma plume are determined via theoretical fits to measured CARS spectra. We discuss the practical implementation of CARS at very high temperatures, including the scaling of the N 2 CARS signal strength from 300 to 6700 K, where the expected peak signal from the high-temperature plasma torch gases is two orders of magnitude less than commonly encountered in combustion environments. An intensified CCD camera enables single-laser-shot detection at temperatures as high as 6200 K, by increasing sensitivity and providing a time gate against intense background luminosity. We also discuss the impacts of unwanted two-beam CARS contributions from outside the nominal three-beam measurement volume. We present mean axial and radial temperature profiles, as well as time-series data derived from both single-laser-shot and accumulated CARS spectra. The single-laser-shot precision is 1.7%-2.6% at temperatures of 3500 to 6200 K. The presented results pave the way for the use of CARS at very high temperatures and the measurement of spatially resolved interface processes in high-enthalpy flows.

Production and characterization of drug-loaded toroidal vortices from a novel ocular drug delivery device.

For the last several decades, the predominant method for delivering medicine to the surface of the eye has been the standard multiuse eye dropper. While being the most popular, this method has significant limitations. Recently, an effort has been made to explore the use of a directed toroidal vortex or "smoke ring" aerosol delivery system that may help overcome these limitations and enable delivery of precise amounts of formulation and drug to the ocular surface. Promising preliminary in vitro studies indicated dosing control, but the physical characteristics of the toriodal aerosol device performance and impaction forces related to patient comfort have yet to be established. Here, we experimentally investigate the mechanics and dynamics of these ocular aerosol vortices, including translational and rotational velocities, spatial droplet size distributions, and relative impaction forces in order to optimize the device performance and evaluate potential for clinical use. Maximal droplet velocity at various actuation forces was determined, and they were found to be all less than 6 m/s even at the highest actuation forces. Moreover, plume impaction forces were determined across a range of conditions and were all less than about 4.5 µN. Collectively, these studies showed that the physical and mechanical properties of the emitted drug-loaded vortices would be suitable for ocular administration.

Naphthalene laser-induced fluorescence measurements at low temperature and pressure.

Few studies on naphthalene vapor fluorescence have been conducted at low temperature and pressure conditions. The current study focuses on conducting measurements of naphthalene quenching and absorption cross section in a temperature- and pressure-regulated test cell with 266 nm laser excitation. The test-cell measurements were of the naphthalene-fluorescence lifetime and integrated fluorescence signal over the temperature range of 100 to 525 K and pressure range of 1 to 40 kPa in air. These data enabled the calculation of naphthalene-fluorescence quantum yield and absorption cross section over the range of temperatures and pressures tested, which were then fit to simple functional forms for future use in the calibration of naphthalene laser-induced fluorescence (LIF) measurements. Furthermore, the variation of naphthalene-fluorescence signal with respect to temperature was investigated for four different excitation wavelengths, demonstrating that a two-line naphthalene LIF thermometry technique may be feasible.

Evaluation of the USP dissolution test method A for enteric-coated articles by planar laser-induced fluorescence.

The USP drug release standard for delayed-release articles method A was evaluated using planar laser-induced fluorescence (PLIF). Prior authors have suggested that high pH "hot spots" could develop during the buffer medium addition of the method A enteric test. Additionally, previous studies have shown heterogeneous flow patterns and low-shear regions in the USP Apparatus II dissolution vessel, which may result in poor mixing of the buffer and acid media during the pH neutralization step of the method A enteric test. In this study, PLIF was used to evaluate the mixing patterns and evolution of pH neutralization during the buffer medium addition with rhodamine-B dye and the pH-sensitive dye fluorescein, respectively. Additionally, a comparison of the methods A and B enteric tests was performed with enteric-coated tablets containing rhodamine-B in the film so as to image the dissolution rate of the coating polymer with PLIF in order to determine if rapid buffer addition for the method A procedure accelerates the rate of film coat dissolution. Rapid addition of the 250 mL of buffer medium over 5 s to the 750 mL of acidic medium shows efficient mixing and pH neutralization due to the generation of large-scale stirring and enhanced turbulence resulting from the descending buffer medium. Slow addition near the paddle shaft over 5 min showed segregation in the recirculating region around the paddle shaft. In contrast, slow addition near the vessel wall introduces the medium into fluid outside of the recirculation region and enables transport over the entire vessel. Enteric-coated tablets tested according to method A with rapid medium addition and method B enteric tests performed identically, indicating no difference in polymer dissolution rate between the two tests. From the results of the PLIF imaging studies with rhodamine-B, fluorescein, and enteric-coated tablets, it was seen that "hot spots" affecting the dissolution performance of enteric dosage forms are not generated during the neutralization step of the method A enteric test namely when the media is added rapidly or outside of the recirculating region that surrounds the paddle shaft.