EXPERIMENTAL INVESTIGATION OF CERTAIN INTERNAL CONDENSING AND BOILING FLOWS: THEIR SENSITIVITY TO PRESSURE FLUCTUATIONS AND HEAT TRANSFER ENHANCEMENTS

Space-based (satellite, scientific probe, space station, etc.) and millimeter – to – microscale (such as are used in high power electronics cooling, weapons cooling in aircraft, etc.) condensers and boilers are shear/pressure driven. They are of increasing interest to system engineers for thermal management because flow boilers and flow condensers offer both high fluid flow-rate-specific heat transfer capacity and very low thermal resistance between the fluid and the heat exchange surface, so large amounts of heat may be removed using reasonably-sized devices without the need for excessive temperature differences. However, flow stability issues and degradation of performance of shear/pressure driven condensers and boilers due to non-desirable flow morphology over large portions of their lengths have mostly prevented their use in these applications. This research is part of an ongoing investigation seeking to close the gap between science and engineering by analyzing two key innovations which could help address these problems. First, it is recommended that the condenser and boiler be operated in an innovative flow configuration which provides a non-participating core vapor stream to stabilize the annular flow regime throughout the device length, accomplished in an energy-efficient manner by means of ducted vapor re-circulation. This is demonstrated experimentally. Second, suitable pulsations applied to the vapor entering the condenser or boiler (from the re-circulating vapor stream) greatly reduce the thermal resistance of the already effective annular flow regime. For experiments reported here, application of pulsations increased time-averaged heat-flux up to 900 % at a location within the flow condenser and up to 200 % at a location within the flow boiler, measured at the heat-exchange surface. Traditional fully condensing flows, reported here for comparison purposes, show similar heat-flux enhancements due to imposed pulsations over a range of frequencies. Shear/pressure driven condensing and boiling flow experiments are carried out in horizontal mm-scale channels with heat exchange through the bottom surface. The sides and top of the flow channel are insulated. The fluid is FC-72 from 3M Corporation.

Potentially human pathogenic Acanthamoeba isolated from a heated indoor swimming pool in Switzerland

Some free-living amoebae, including some species of the genus Acanthamoeba, can cause infections in humans and animals. These organisms are known to cause granulomatous amebic encephalitis (GAE) in predominantly immune-deficient persons. In the present study, we isolated a potentially human pathogenic Acanthamoeba isolate originating from a public heated indoor swimming pool in Switzerland. The amoebae, thermophilically preselected by culture at 37 degrees C, subsequently displayed a high thermotolerance, being able to grow at 42 degrees C, and a marked cytotoxicity, based on a co-culture system using the murine cell line L929. Intranasal infection of Rag2-immunodeficient mice resulted in the death of all animals within 24 days. Histopathology of brains and lungs revealed marked tissue necrosis and hemorrhagic lesions going along with massive proliferation of amoebae. PCR and sequence analysis, based on 18S rDNA, identified the agent as Acanthamoeba lenticulata. In summary, the present study reports on an Acanthamoeba isolate from a heated swimming pool suggestive of being potentially pathogenic to immunocompromised persons.

Imaging of pulmonary embolism and t-PA therapy effects using MDCT and liposomal iohexol blood pool agent – preliminary results in a rabbit model

Hypothesis and Objectives PEGylated liposomal blood pool contrast agents maintain contrast enhancement over several hours. This study aimed to evaluate (long-term) imaging of pulmonary arteries, comparing conventional iodinated contrast with a liposomal blood pool contrast agent. Secondly, visualization of the (real-time) therapeutic effects of tissue-Plasminogen Activator (t-PA) on pulmonary embolism (PE) was attempted. Materials and Methods Six rabbits (approximate 4 kg weight) had autologous blood clots injected through the superior vena cava. Imaging was performed using conventional contrast (iohexol, 350 mg I/ml, GE HealthCare, Princeton, NJ) at a dose of 1400 mgI per animal and after wash-out, animals were imaged using an iodinated liposomal blood pool agent (88 mg I/mL, dose 900 mgI/animal). Subsequently, five animals were injected with 2mg t-PA and imaging continued for up to 4 ½ hours. Results Both contrast agents identified PE in the pulmonary trunk and main pulmonary arteries in all rabbits. Liposomal blood pool agent yielded uniform enhancement, which remained relatively constant throughout the experiments. Conventional agents exhibited non uniform opacification and rapid clearance post injection. Three out of six rabbits had mistimed bolus injections, requiring repeat injections. Following t-PA, Pulmonary embolus volume (central to segmental) decreased in four of five treated rabbits (range 10–57%, mean 42%). One animal showed no response to t-PA. Conclusions Liposomal blood pool agents effectively identified acute PE without need for re-injection. PE resolution following t-PA was quantifiable over several hours. Blood pool agents offer the potential for repeated imaging procedures without need for repeated (nephrotoxic) contrast injections

High Resolution Vascular Imaging of the Rat Spine using Liposomal Blood Pool MR Agent

High resolution, vascular magnetic resonance imaging of the spine region in small animals poses several challenges. The small anatomical features, extravascular diffusion, and the low signal-to-noise ratio limit the use of conventional contrast agents. We hypothesize that a long circulating, intravascular liposomal-encapsulated MR contrast agent (liposomal-Gd) would facilitate visualization of small anatomical features of the perispinal vasculature not visible with conventional contrast agent (Gd-DTPA).

High-resolution vascular imaging of the rat spine using liposomal blood pool MR agent.

BACKGROUND AND PURPOSE: High-resolution, vascular MR imaging of the spine region in small animals poses several challenges. The small anatomic features, extravascular diffusion, and low signal-to-noise ratio limit the use of conventional contrast agents. We hypothesize that a long-circulating, intravascular liposomal-encapsulated MR contrast agent (liposomal-Gd) would facilitate visualization of small anatomic features of the perispinal vasculature not visible with conventional contrast agent (gadolinium-diethylene-triaminepentaacetic acid [Gd-DTPA]). METHODS: In this study, high-resolution MR angiography of the spine region was performed in a rat model using a liposomal-Gd, which is known to remain within the blood pool for an extended period. The imaging characteristics of this agent were compared with those of a conventional contrast agent, Gd-DTPA. RESULTS: The liposomal-Gd enabled acquisition of high quality angiograms with high signal-to-noise ratio. Several important vascular features, such as radicular arteries, posterior spinal vein, and epidural venous plexus were visualized in the angiograms obtained with the liposomal agent. The MR angiograms obtained with conventional Gd-DTPA did not demonstrate these vessels clearly because of marked extravascular soft-tissue enhancement that obscured the vasculature. CONCLUSIONS: This study demonstrates the potential benefit of long-circulating liposomal-Gd as a MR contrast agent for high-resolution vascular imaging applications.

Imaging of pulmonary embolism and t-PA therapy effects using MDCT and liposomal iohexol blood pool agent: preliminary results in a rabbit model.

RATIONALE AND OBJECTIVES: Polyethylene glycol-coated liposomal blood pool contrast agents maintain contrast enhancement over several hours. This study aimed to evaluate (long-term) imaging of pulmonary arteries, comparing conventional iodinated contrast with a liposomal blood pool contrast agent. Also, visualization of the (real-time) therapeutic effects of tissue plasminogen activator (t-PA) on pulmonary embolism (PE) was attempted. MATERIALS AND METHODS: Six rabbits (weight approximately 4 kg) had autologous blood clots injected through the superior vena cava. Imaging was performed using conventional contrast (iohexol, 350 mg I/ml; GE HealthCare, Princeton, NJ) at a dose of 1400 mg I per animal, and after wash-out, animals were imaged using an iodinated liposomal blood pool agent (88 mg I/mL, dose 900 mg I/animal). Subsequently, five animals were injected with 2 mg of t-PA and imaging continued for up to 4(1/2) hours. RESULTS: Both contrast agents identified PE in the pulmonary trunk and main pulmonary arteries in all rabbits. Liposomal blood pool agent yielded uniform enhancement, which remained relatively constant throughout the experiments. Conventional agents exhibited nonuniform opacification and rapid clearance postinjection. Three of six rabbits had mistimed bolus injections, requiring repeat injections. Following t-PA, pulmonary embolus volume (central to segmental) decreased in four of five treated rabbits (range 10-57%, mean 42%). One animal showed no response to t-PA. CONCLUSIONS: Liposomal blood pool agents effectively identified acute PE without need for reinjection. PE resolution following t-PA was quantifiable over several hours. Blood pool agents offer the potential for repeated imaging procedures without need for repeated (nephrotoxic) contrast injections.

A novel organ-slice culturing system to simulate meniscal repair: Proof of concept using a synovium-based pool of meniscoprogenitor cells.

Meniscal injuries can occur secondary to trauma or be instigated by the changes in knee-joint function that are associated with aging, osteo- and rheumatoid arthritis, disturbances in gait and obesity. Sixty per cent of persons over 50 years of age manifest signs of meniscal pathology. The surgical and arthroscopic measures that are currently implemented to treat meniscal deficiencies bring only transient relief from pain and effect but a temporary improvement in joint function. Although tissue-engineering-based approaches to meniscal repair are now being pursued, an appropriate in-vitro model has not been conceived. The aim of this study was to develop an organ-slice culturing system to simulate the repair of human meniscal lesions in vitro. The model consists of a ring of bovine meniscus enclosing a chamber that represents the defect and reproduces its sequestered physiological microenvironment. The defect, which is closed with a porous membrane, is filled with fragments of synovial tissue, as a source of meniscoprogenitor cells, and a fibrin-embedded, calcium-phosphate-entrapped depot of the meniscogenic agents BMP-2 and TGF-ß1. After culturing for 2 to 6 weeks, the constructs were evaluated histochemically and histomorphometrically, as well as immunohistochemically for the apoptotic marker caspase 3 and collagen types I and II. Under the defined conditions, the fragments of synovium underwent differentiation into meniscal tissue, which bonded with the parent meniscal wall. Both the parent and the neoformed meniscal tissue survived the duration of the culturing period without significant cell losses. The concept on which the in-vitro system is based was thus validated. This article is protected by copyright. All rights reserved.