Douglas P. Hart

PIV error correction

A non-post-interrogation method of reducing subpixel errors and eliminating spurious vectors from particle image velocimetry (PIV) results is presented. Unlike methods that rely on the accuracy or similarity of neighboring vectors, errors are eliminated before correlation information is discarded using available spatial and/or temporal data. Anomalies are removed from the data set through direct element-by-element comparison of the correlation tables calculated from adjacent regions. The result is a processing technique that yields a symmetric correlation profile representing the velocity at the boundary of the combined regions. This correlation based correction (CBC) technique greatly improves subpixel accuracy, and is highly robust to out-of-boundary particle motion, particle overlap, unmatched particle correlations, and electronic and optical imaging noise.

Ultrasound-Mediated Transdermal Drug Delivery: Mechanisms, Scope, and Emerging Trends

The use of ultrasound for the delivery of drugs to, or through, the skin is commonly known as sonophoresis or phonophoresis. The use of therapeutic and high frequencies of ultrasound (≥0.7MHz) for sonophoresis (HFS) dates back to as early as the 1950s, while low-frequency sonophoresis (LFS, 20-100kHz) has only been investigated significantly during the past two decades. Although HFS and LFS are similar because they both utilize ultrasound to increase the skin penetration of permeants, the mechanisms associated with each physical enhancer are different. Specifically, the location of cavitation and the extent to which each process can increase skin permeability are quite dissimilar. Although the applications of both technologies are different, they each have strengths that could allow them to improve current methods of local, regional, and systemic drug delivery. In this review, we will discuss the mechanisms associated with both HFS and LFS, specifically concentrating on the key mechanistic differences between these two skin treatment methods. Background on the relevant physics associated with ultrasound transmitted through aqueous media will also be discussed, along with implications of these phenomena on sonophoresis. Finally, a thorough review of the literature is included, dating back to the first published reports of sonophoresis, including a discussion of emerging trends in the field.

Ultrasound induced cavitation and sonochemical yields

The introduction of a strong acoustic field to an aqueous solution results in the generation of cavitation microbubbles. The growth and collapse of these microbubbles focuses and transfers energy from the macroscale (acoustic wave) to the microscale (vapor inside the bubbles) producing extremely high localized pressures and temperatures. This unique energy focusing process generates highly reactive free radicals that have been observed to significantly enhance chemical processing. This paper presents a model that combines the dynamics of bubble collapse with the chemical kinetics of a single cavitation event. The effects on sonochemical yields and bubble dynamics of gas composition and heat transfer are assessed and compared with previous theoretical and experimental studies. Results from this model are used to explain unusual experimentally observed sonochemical phenomena.

C. elegans Notch signaling regulates adult chemosensory response and larval molting quiescence.

BACKGROUND The conserved DOS-motif proteins OSM-7 and OSM-11 function as coligands with canonical DSL (Delta, Serrate, and LAG-2) ligands to activate C. elegans Notch receptors during development. We report here that Notch ligands, coligands, and the receptors LIN-12 and GLP-1 regulate two C. elegans behaviors: chemosensory avoidance of octanol and quiescence during molting lethargus. RESULTS C. elegans lacking osm-7 or osm-11 are defective in their response to octanol. We find that OSM-11 is secreted from hypodermal seam cells into the pseudocoelomic body cavity and acts non-cell autonomously as a diffusible factor. OSM-11 acts with the DSL ligand LAG-2 to activate LIN-12 and GLP-1 Notch receptors in the neurons of adult animals, thereby regulating octanol avoidance response. In adult animals, overexpression of osm-11 and consequent Notch receptor activation induces anachronistic sleep-like quiescence. Perturbation of Notch signaling alters basal activity in adults as well as arousal thresholds and quiescence during molting lethargus. Genetic epistasis studies reveal that Notch signaling regulates quiescence via previously identified circuits and genetic pathways including the egl-4 cGMP-dependent kinase. CONCLUSIONS Our findings indicate that the conserved Notch pathway modulates behavior in adult C. elegans in response to environmental stress. Additionally, Notch signaling regulates sleep-like quiescence in C. elegans, suggesting that Notch may regulate sleep in other species.

Emission reabsorption laser induced fluorescence (ERLIF) film thickness measurement

This paper presents a unique optical technique that utilizes the reabsorption and emission of two fluorescent dyes to accurately measure film thickness while minimizing errors caused by variations in illumination intensity and surface reflectivity. Combinations of dyes are selected that exhibit a high degree of emission reabsorption and each dye concentration is adjusted to create an optically thick system where emission reabsorption is intrinsic to the fluorescence of the film being measured. Film thickness information as well as excitation and dye response characteristics are all imbedded in the emission intensities of the dyes. Errors normally associated with laser induced fluorescence based film thickness measurements, including those due to optical distortion, variations in surface reflectivity and excitation non-uniformities, are minimized by observing the ratio of the dye emissions. The principle and constitutive equations characterizing emission reabsorption laser induced fluorescence (ERLIF) film thickness measurement are presented. In addition, film thickness measurements from 5 to 400 µm with 1% accuracy are demonstrated.

Reverse hierarchical PIV processing

A novel hierarchical processing scheme is proposed to efficiently increase the spatial resolution and dynamic range of detecting particle image displacements in PIV images. The technique takes full advantage of the multi-resolution characteristic of the discrete correlation function by starting the processing at the smallest scale and, if necessary, gradually building correlation planes into larger interrogation areas based on the result of inter-level correlation correction and validation. It is shown that the algorithm can be implemented in both direct and FFT based correlation algorithms with greatly reduced computational complexity. The technique opens new perspectives for locally adaptive super-resolution processing taking flow field, seeding, and imaging anomalies into account. Processing at the lowest scale (e.g. pixel or particle image size) allows the combination of correlation planes on any shape. Hence the proposed reverse hierarchical processing represents interrogation area optimization both in size and shape in order to maximize the correlation plane signal-to-noise ratio. The method is successfully demonstrated on experimentally obtained images.

Mist Deposition onto Hairy Root Cultures: Aerosol Modeling and Experiments

We analyzed the applicability of the standard models for aerosol deposition in randomly packed fibrous filter beds to mist deposition across a bed of hairy roots in the nutrient mist bioreactor. Although the assumptions inherent in the models are met on a local level, the overall structure of the root bed introduces some uncertainty into the correct choice of root packing fraction and gas velocity required by the model. For reasonable parameter values, the minimum in the deposition efficiency curves is close to the peak in the mist number and mass distributions, and good penetration of the root bed is possible. We then measured the deposition of mist across a packed bed of Artemisia annua transformed roots as a function of droplet size, bed length, and gas flow rate at a root packing fraction α = 0.5. We compared the experimental measurements with the predictions of the aerosol deposition model and found good agreement between the measured and predicted values for the diameter where the deposition efficiency across the bed is 50%, D0.5. Agreement between the model and the experiments broke down when the flow rate was increased to the point where the creeping flow assumptions were no longer valid.

Rapid skin permeabilization by the simultaneous application of dual-frequency, high-intensity ultrasound.

Low-frequency ultrasound has been studied extensively due to its ability to enhance skin permeability. In spite of this effort, improvements in enhancing the efficacy of transdermal ultrasound treatments have been limited. Currently, when greater skin permeability is desired at a given frequency, one is limited to increasing the intensity or the duration of the ultrasound treatment, which carries the risk of thermal side effects. Therefore, the ability to increase skin permeability without increasing ultrasound intensity or treatment time would represent a significant and desirable outcome. Here, we hypothesize that the simultaneous application of two distinct ultrasound frequencies, in the range of 20 kHz to 3 MHz, can enhance the efficacy of ultrasound exposure. Aluminum foil pitting experiments showed a significant increase in cavitational activity when two frequencies were applied instead of just one low frequency. Additionally, in vitro tests with porcine skin indicated that the permeability and resulting formation of localized transport regions are greatly enhanced when two frequencies (low and high) are used simultaneously. These results were corroborated with glucose (180 Da) and inulin (5000 Da) transdermal flux experiments, which showed greater permeant delivery both into and through the dual-frequency pre-treated skin.

WEAR OF ELASTOMERIC SEALS IN ABRASIVE SLURRIES

Seals are a critical aspect of machinery that operates in the presence of abrasive slurries. Seals act to maintain machine lubrication and prevent abrasives from affecting critical components. Over time, however, the slurry will wear the seal and lead to a loss of lubrication and eventual machine failure. It is therefore important to investigate the seal wear process in aims of improving seal design and performance. The wear process was studied by visualizing and recording the operation of the seal through a window using time-lapse video. Images from the test show that the wear process occurs in two stages: the break-in period and the aggressive wear period. During the break-in period the seal does not wear. During the aggressive wear period, however, particles under the contact band cluster and form an abrasive front that erodes the seal lip at a rapid rate. Based on these observations, the seal geometry was changed to include the periodic placement of various texture topologies, including (1) a depression surrounded by a protrusion, (2) a protrusion only and (3) a depression only. Textures featuring protrusions act to extend the break-in period and decrease the wear rate of the aggressive wear period. Seals with the protrusions-only texture outlived non-textured seals by a factor of eight.

Real-time 3D topography by speckle image correlation

A speckle image correlation method is proposed for the application to 3D topography at ultra-high speeds. With random densely-seeded laser speckles projected onto an object to be measured, taking snapshots from two different viewing angles using a pair of CCD cameras, we are able to correlate the two speckle images in real time, 30 Hz, by a sparse-array compressed-image correlation algorithm. As soon as the correlation is established, a fast triangulation reconstruction gives the 3D coordinates of the speckles on the object in the global coordinate system, and thus the topography of the surface of the object is obtained. This method has an accuracy of plus or minus 0.2 pixels and a resolution equal to that of its cameras. Most image correlation algorithms suffer from their lack of speed. The method discussed here has overcome this barrier and made wide applications possible. Real-time correlation enables applications in areas such as on-line inspection, non-still object measurement, and instant 3D model acquisition.