Ultrasonography has, until recently, lacked effective contrast-enhancing agents. Micrometer-sized gas bubbles that resonate at a diagnostic frequency are ideal reflectors for ultrasound. However, simple air bubbles, when injected into the blood stream, disappear within seconds through the combined effects of Laplace pressure, blood pressure, and exposure to ultrasound energy. Use of fluorocarbon vapor, by extending the persistence of microbubbles in vivo from seconds to minutes, propelled contrast ultrasonography into clinical practice. Imaging techniques that selectively suppress tissue, but not microbubble signal, further increase image contrast. Approved products consist of C3F8 or SF6 microbubbles, and N2 microbubbles osmotically stabilized with C6F14. These agents allow the detection and characterization of cardiovascular abnormalities and solid organ lesions, such as tumors. By providing higher quality images, they improve the accuracy and confidence of disease diagnosis, and can play a decisive role in clinical decision making. New objectives include agents that target specific cells for the molecular imaging of disease, and drug and gene delivery, including ultrasound-triggered delivery.

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Coal, fly ash, slag, and combustion gases from a large cyclone-fed power plant 870 MW(e) were analyzed for a suite of elements. Mass balance calculations show that the sampling and analyses were generally adequate to describe the flows of these elements through the plant. Most Hg, some Se, and probably most Cl and Br were discharged to the atmosphere as gases.

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Nanotechnological applications have been proposed which require components to self-assemble into mesoscale structures. For example, nanoscale sensors, quantum memory devices, or photonic materials might comprise regular arrays of particles assembled on a substrate. Previously, we studied the random sequential adsorption kinetics and the structural phase behavior of a two-dimensional model of particles (hard disks) tethered to a substrate. The tethers restrict particle surface mobility which affects the nonequilibrium phases of the developing monolayer adsorbed to the surface. Here, we explore the effect of Gaussian polydispersity on the tethered random sequential adsorption process. Liquid, hexatic, and crystal phases are observed in the simulations. For size-monodisperse systems, short tethers (one particle radius or less) allow only liquid structures, intermediate tethers (one to four particle radii) allow a hexatic structure at high coverages, and long-tethered systems develop through liquid and hexatic phases before becoming crystalline at high coverages. Polydispersity disrupts the order. Systems over approximately 8% polydispersity remain liquid, and systems between about 7 and 8% polydispersity form a hexatic phase even with very long tethers. For sufficiently long tethers, crystal formation requires 5-7% polydispersity or less. Histograms of particle size distributions on the surface reveal that short-tether systems yield bimodal distributions because of the persistence of small gaps in the layer. In contrast, systems with adequate surface mobility organize locally, which prevents small gaps and retains unimodal size distributions. Kinetics for polydisperse, tethered, random sequential adsorption processes follow a power law with constants that change rapidly for tether lengths less than one particle radius and polydispersities up to 10%. Jamming limit coverages generally increase with polydispersity but decrease as surface order is destroyed.

Perfluorochemical (PFC) emulsions are particulate in nature and, as such, can cause delayed febrile reactions when injected intravenously. This study investigated the influence of emulsion particle size on intravascular retention and on body temperature changes in unrestrained conscious rats. Concentrated (60% to 90% w/v) emulsions based on perflubron (perfluorooctyl bromide [PFOB]) with mean particle sizes ranging from 0.05 microns to 0.63 microns were tested. Rats were fitted with a chronic jugular catheter and an abdominal body temperature telemetry unit. Fully recovered, conscious rats were monitored for 24 hours after infusion (dose = 2.7 g PFC/kg). Emulsion blood half-life (T1/2) was determined from blood perflubron levels measured by gas chromatography. Emulsions with a particle size of 0.2-0.3 microns caused fevers (6 to 8 hour duration) which peaked at 1-1.5 degrees C above normal (approximately 37.5 degrees C). Fevers could be blocked by i.v. treatment with either cyclooxygenase inhibitors (ibuprofen) or corticosteroids (dexamethasone). Both intensity and duration of the temperature response, quantified by area under the temperature curve, was decreased significantly for emulsions with a particle size < or = 0.12 micron. Blood T1/2 varied inversely with particle size, and was 3 to 4 fold longer for emulsions with a mean particle size < or = 0.2 micron. Thus, smaller emulsion particles more effectively evaded the reticuloendothelial system, which resulted in longer intravascular retention, less macrophage activity, and reduced febrile responses.

We consider the behavior of the Doi-Marrucci-Greco (DMG) model for nematic liquid crystalline polymers in planar shear flow. We found the DMG model to exhibit dynamics in both qualitative and quantitative agreement with experimental observations reported by Larson and Mead [Liquid Crystals, 15 (1993), pp. 151-169] for the Ericksen number and Deborah number cascades. For increasing shear rates within the Ericksen number cascade, the DMG model displays four distinct regimes: stable simple shear, stable roll cells, irregular structure followed by large-strain disclination formation, and irregular structure preceded by disclination formation. In accordance with experimental observations, the model also predicts both ±1 and ±1/2 disclinations. Although ±1 defects form via the ridge-splitting mechanism first identified by Feng, Tao, and Leal [J. Fluid Mech., 449 (2001), pp. 179-200], a new mechanism is identified for the formation of ±1/2 defects. Within the Deborah number cascade, with increasing Deborah number, the DMG model exhibits a stream-wise banded texture, in the absence of disclinations and roll cells, followed by a monodomain wherein the mean orientation lies within the shear plane throughout the domain.