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Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: microgravity; condensation; ultrasound. Includes bibliographical references (p. 138).

Thesis (M.S.)--Michigan State University. Dept. of Mechanical Engineering, 2007. / Title from PDF t.p. (viewed on Aug. 11, 2009) Includes bibliographical references (p. 85). Also issued in print.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: crown; splash; spreading; oscillatory; droplets; microgravity; viscosity; map; stability; solid surface; surface tension; gravity. Includes bibliographical references (p. 111-113).

Drop Towers provide brief terrestrial access to microgravity environments. When used for capillary fluidics research, a drop tower allows for unique control over an experiment's initial conditions, which enables, enhances, or otherwise improves the study of capillary phenomena at significantly larger length scales than can normally be achieved on the ground. This thesis provides a historical context for the introduction of a new, highly accessible, 2.1s tower design used for capillary research and presents a variety of demonstrative experimental results for purely capillarity-driven flows leading to bubble ingestion, sinking flows, multiphase flows, and droplet ejections. The focus of this thesis is paid to capillarity-driven droplet ejection including historical significance, mathematical models, criteria for ejection and experimental validation. A scale analysis provides a single parameter Su+ which is used to predict the flow velocity at the base of the nozzle. By simplifying the flow in the nozzle we identify two criteria for auto-ejection, the nozzle must be `short' and the velocity of the flow must be sufficient to invert the liquid meniscus and overpower surface tension at the nozzle tip such that We⁺ > 12. Drop tower experiments are conducted and compared to analytical predictions using a regimemap. This thesis also includes results from experiments experiments conducted in a stationary ground-based laboratory and aboard the International Space Station which clearly demonstrate droplet ejection in regimes from transient liquid jets to large isolated drops. Droplets generated in a microgravity environment are 106 times larger than 1g₀ counter-parts.

"The condensation of vapor onto a cooled surface is a phenomenon which can be difficult to quantify spatially and as a function of time; this thesis describes an ultrasonic system to measure this phenomenon. The theoretical basis for obtaining condensate film thickness measurements, which can be used to calculate growth rates and film surface features, from ultrasonic echoes will be discussed and the hardware and software will be described. The ultrasonic system utilizes a 5MHz planar piston transducer operated in pulse-echo mode to measure the thickness of a fluid film on a cooled copper block over the fluid thickness range of 50 microns to several centimeters; the signal processing algorithms and software developed to carry out this task are described in detail. The results of several experiments involving the measurement of both non-condensing and condensing films are given. In addition, numerical modeling of specific condensate film geometries was performed to support the experimental system; the results of modeling nonuniform fluid layers are discussed in the context of the effect of such layers on the measurement system."

The thesis describes the design of a fringe projection system to study the dynamics of condensation with potential application in a reduced gravity environment. The concept is that an optical system for imaging the condensation layer enables extraction of valuable data from the image because of the ability of the optical system to image the perturbations in the condensation films. By acquiring a sequence of images of the deformed fringe pattern, the change in the surface topology can be observed over time, giving greater understanding of condensation dynamics in reduced gravity.

Since astronaut time and energy are at a premium, effective countermeasures must be designed to maximize benefits while minimizing time/energy cost. Therefore, our intent was to design and evaluate a low volume, high intensity resistance training program (RTP) on the preservation of knee extensor and plantar flexor size, strength and neuromuscular function in response to unloading. A total of 32 subjects participated. Sixteen men underwent 21 days of unilateral lower limb suspension (ULLS) and were assigned to control (no RTP) (ULLS-CON, n=8) or countermeasures (ULLS-CM, n=8). The remaining subjects were ambulatory for 21 days and were assigned to no RTP (n=8) or countermeasures (n=8). Countermeasure subjects performed RTP every third day during the suspension period (total=6). The RTP consisted of 2 maximal isometric contractions (MVC), 1 set of 10 concentric/eccentric isotonic repetitions, and 1 set to exhaustion, at 80% of 1-repetition maximum (1RM). There was no change in muscle function in ambulatory subjects. Whole muscle cross sectional area (CSA) measured by computed tomography (CT) decreased 7% (thigh) and 7.5% (calf) in ULLS-CON (p<0.05), and was unchanged in ULLS-CM. MVC decreased 16.5% in both quadricep and calf muscles in ULLS-CON (p<0.05) and increased 6% in the quadricep of ULLSCM (p<0.05). Maximal concentric (CNC) and eccentric (ECC) isokinetic strength decreased an average of 18% and 17% in the knee extensors and plantar flexors of ULLS-CON, respectively (p<0.05) and was unchanged in ULLS-CM. 1RM decreased 16% in both quadricep and calf of ULLS-CON (p<0.05) and was unchanged in ULLSCM. Knee extensor work capacity, evaluated during 30 maximal CNC contractions (3.14 rad•sec-'), decreased 18% in ULLS-CON (p<0.05). Neural activation of knee extensors and plantar flexors was measured by electromyography (EMG). Submaximal v.lat, v.med, gast and sol EMG increased in ULLS-CON (p<0.05) and was unaltered in ULLSCM. Maximal EMG decreased 20% and 26% in v.1at and v.med, respectively in ULLSCON (p<0.05). ULLS-CM showed a 15% and 28% increase in v.med and gast maximal EMG (p<0.05). These data suggest knee extensor and plantar flexor muscle size, strength and neuromuscular function were preserved during unloading using a low volume, high intensity RTP performed every third day. / School of Physical Education

Musculoskeletal pathologies associated with decreased bone mass, including osteoporosis and disuse-induced bone loss, affect millions of Americans annually. Many pharmaceutical treatments have slowed osteoporosis, but there is still no countermeasure for bone loss observed in astronauts. Additionally, high magnitude and low frequency impact has been recognized to increase bone and muscle mass under normal but not microgravity conditions. However, a low magnitude and high frequency (LMHF) mechanical load experienced in activities such as postural control has also been shown to be anabolic to bone. While several clinical trials have demonstrated that the LMHF mechanical loading normalizes bone loss in vivo, the target tissues and cells of the mechanical load and underlying mechanisms mediating the responses are unknown. As such, the objectives of this project are to analyze cellular and molecular changes induced in osteoblasts by LMHF loading and to investigate the utility of a LMHF mechanical load in mitigating microgravity-induced bone loss. The central hypothesis of the project is that simulated microgravity or disuse conditions induce bone loss by inhibiting expression of genes critical in regulating bone formation, osteoblast differentiation, and subsequent mineralization while a LMHF mechanical load prevents these effects. To test this hypothesis, we developed an in vitro disuse system using the Random Positioning Machine (RPM). For the first time, we reported systemic gene expression studies in 2T3 preosteoblasts using the RPM disuse system showing that 140 genes were altered by RPM exposure with over two-fold statistically significant changes. Moreover, we also utilized an independent simulator called the Rotating Wall Vessel (RWV) to partially validate the in vitro disuse systems and to confine the list of genes to those most critical in regulating bone formation. After comparative studies, we constricted the list to 15 commonly changed genes, three of which were not only decreased with disuse but also increased with mechanical loading in vivo. Furthermore, we employed the RPM disuse system to evaluate the mechanism by which a LMHF load mitigates bone loss. Exposure of osteoblasts to the RPM decreased both ALP activity and mineralization even in the presence of bone morphogenic protein 4 (BMP4), and the LMHF mechanical loading prevented the RPM-induced decrease in both markers. Mineralization induced by LMHF mechanical loading was enhanced by treatment with BMP4 and blocked by the BMP antagonist noggin, suggesting a role for BMPs in this response. In addition, LMHF mechanical loading rescued the RPM-induced decrease in gene expression of ALP, runx2, osteomodulin, parathyroid hormone receptor 1, and osteoglycin. These findings show that osteoblasts directly respond to LMHF mechanical loading, potentially leading to normalization or prevention of bone loss caused by disuse or microgravity conditions. The mechanosensitive genes identified here provide potential targets for pharmaceutical treatments that may be used in combination with LMHF mechanical loading to better treat osteoporosis, disuse-induced bone loss, or microgravity-induced bone loss.