Skeletal muscle has the remarkable ability to remodel and repair when exposed to various stimuli such as exercise training and injury. Many factors contribute to the maintenance of healthy muscle mass throughout the lifespan including a functional population of resident muscle stem cells, commonly referred to as satellite cells (SC). When SC become active in response to a stimulus they proliferate and differentiate, eventually fusing to existing myofibres or to each other giving rise to new myotubes; while some SC revert to quiescence to maintain the SC pool. This process is termed 'the myogenic programme' and is governed by a complex network of transcription factors termed myogenic regulatory factors. SC are absolutely necessary for the repair of skeletal muscle, however, their role in mediating skeletal muscle remodelling following exercise training remains debatable. The effect of resistance exercise on SC content has been extensively studied in humans. However, a paucity of information exists in regards to the effect of 'non-resistance' type exercise training on SC content and function in healthy young adults. The purpose of this thesis was to determine the impact of nonhypertrophic exercise training on SC content. We examined the effect of high intensity interval training on the SC pool and determined that there was an increase in SC associated with remodelling hybrid fibres. We extended upon these findings by demonstrating that several high intensity interval training paradigms and traditional endurance training all resulted in an increase in SC pool activity without an overall expansion of the SC pool. Skeletal muscle regeneration is impaired in old rodents and is associated with a reduction in SC content. We therefore sought to determine whether nonhypertrophic exercise training in old mice was able to improve the regenerative response following injury. Exercise training resulted in an increase in SC content and improved skeletal muscle regeneration in old mice. In addition to previous work implicating SC in mediating skeletal muscle hypertrophy induced by resistance exercise training, this thesis provides evidence that SC are able to respond to exercise stimuli that are nonhypertrophic in nature. In addition, we demonstrate that nonhypertrophic exercise training results in an increase in SC content in old mice and this likely contributed to the improvement in skeletal muscle regeneration observed in old mice pre-conditioned with regular exercise. / Thesis / Doctor of Philosophy (PhD)

Skeletal muscle disease (myopathy) carries an enormous psychological, social and economic impact on the lives of the patients and their caregivers. There is also an appreciable amount of economic burden on the healthcare system and our society especially when most patients are in their childhood/adolescent lives. It is not a surprising fact that a percentage of myopathies are of undetermined cause, which makes the need to identify new genes that play a critical role in muscle health of paramount importance. The Xin gene is designated as an indispensable component for the normal development and morphogenesis of striated muscle; however, the exact roles of Xin in skeletal muscle are still undefined. Studies to date have demonstrated that Xin is expressed in activated satellite cells and newly formed myofibers following tissue injury. When using in vitro reduction of Xin expression in skeletal muscle cells, the outcome was impairments in satellite cell function and muscle response to injury. That said, there is still a significant lack of knowledge in the literature regarding the in vivo effects of the absence of Xin on skeletal muscle structure and function. Therefore, the aim of our studies was to characterize skeletal muscles in the absence of Xin and identify the potential roles of Xin in maintaining muscle integrity and health. In our studies, we uncover a new form of muscle disease resulting from the lack of Xin in a mouse model (Xin-/- mice). Xin-/- skeletal muscles show a mild form of myopathy at the light microscopy level that is associated with ultrastructural and functional defects peculiar to the Ca2+ handling. In addition, Xin-/- muscle demonstrated features of mitochondrial dysfunction that are likely secondary to the Ca2+ defects caused by the absence of Xin. Our studies provide a platform to investigate the potential manifestation of “loss of function” mutation of Xin in skeletal muscle and its possibly related pathology in human diseases. / Thesis / Doctor of Philosophy (PhD) / Skeletal muscle covers the bones, produces movements and stabilizes joints. Diseases of skeletal muscle are common. Specifically, inherited diseases of skeletal muscle can cause an inability to eat, walk, run, work and even breathe. By starting at an early age, these conditions may result in the patient being bed-ridden with severe psychological, social and financial burdens for them and their caregivers. When skeletal muscles that control breathing are involved, death can occur at a young age. A considerable proportion of skeletal muscle disease are of unknown cause, and therefore, there is a constant need to discover more factors that influence muscle health to provide treatment plans for these patients. This dissertation uncovers the role of a new factor, Xin, involved in keeping skeletal muscle healthy. The achieved results of our studies will help physicians use this knowledge into identifying new types of muscle disease and providing targeted treatments for patients.

Muscle satellite cells are a distinct population of myogenic progenitors that mediate the postnatal growth and regeneration of skeletal muscle. To gain insight into the genetic regulation of satellite cell function during muscle regeneration, genes expressed specifically in these cells were identified by representational difference analysis of cDNAs. Notably, the paired-box transcription factor Pax7 was isolated as a gene specifically expressed in quiescent and activated satellite cells. Cell culture and histological analysis of PaxZ-deficient muscle revealed a complete absence of satellite cells. This result demonstrates a requirement for Pax7 upstream of MyoD and Myf5 in the specification of muscle satellite cells. Consistent with their lack of satellite cells, adult PaxT mice displayed an aggravated muscle wasting phenotype characterized by spinal kyphosis and reduced muscle mass. Acute muscle damage led to extensive calcification and deposition of adipose and fibrotic tissues with the appearance of rare regenerated myofibers. Importantly, analysis of Pax7 muscle suspensions indicated that myogenic cells expressing Pax3 and MyoD were responsible for this low level of regeneration. To characterize the role of adult stem cells in skeletal muscle, we investigated the myogenic potential of muscle-derived CD45+:Sca1+ cells in vivo during regeneration and in vitro using coculture assays. CD45+ and Sca1+ cells isolated from uninjured muscle were uniformly non-myogenic. Strikingly, 7-10% of CD45+:Sca1+ cells purified from regenerating muscle activated the myogenic program by a Pax7-dependent mechanism in response to activation of the Wnt signaling pathway. Furthermore, expression of Pax7 was sufficient to induce myogenic commitment in CD45f+Scal cells from uninjured muscle. This result demonstrates that non-satellite cell derived myogenic progenitors possess a physiological role in muscle regeneration and tissue homeostasis. Taken together, this work establishes a requirement for Pax7 in the specification of muscle satellite cells and for the myogenic recruitment of adult stem cells populations during tissue repair. Importantly, these studies also suggest that targeted therapies to activate Wnt signaling and Pax7 expression in adult stem cells will be effective for promoting muscle regeneration in patients with degenerative neuromuscular diseases or muscular dystrophies. / Thesis / Doctor of Philosophy (PhD)

The satellite industry is undergoing a transition toward "smallsat" engineering. Small satellites are becoming more attractive to customers as a method of decreasing cost. As the launch costs remain relatively constant, the industry is turning towards nano-technology, such as microelectromechanical systems, and distributed satellite systems to perform the same missions that once required super-satellites. Nanosatellites form one group of these high risk/low cost spacecraft. The Virginia Tech Ionospheric Scintillation Measurement Mission, known as HokieSat, is a 40 lb nanosatellite being designed and built by graduate and undergraduate students. The satellite is part of the Ionospheric Observation Nanosatellite Formation (ION-F) which will perform ionospheric measurements and conduct formation flying experiments. This thesis describes the design of the primary satellite structure, the analysis used to arrive at the design, the fabrication of the structure, and the experimentation used to verify the analysis. We also describe the internal and external configurations of the spacecraft and how we estimate the mass properties of the integrated satellite. The design of the spacecraft uses a composite laminate isogrid structure as a method of structural optimization. This optimization method is shown to increase the structural performance by over 20%. We conduct several finite element analyses to verify the structural integrity. We correlate these analyses with several static and modal tests to verify the models and the model boundary conditions. We perform environmental testing on the integrated spacecraft at NASA Wallops Flight Facility to investigate the properties of the structural assembly. Finally, we create a model of the ION-F stack to verify the integrity of the structure at the launch loads. We prove that the HokieSat structure will survive all environmental loads with no yielding or failures. / Master of Science

The vast majority of horses engage in some form of exercise, whether it be for leisure or competition. Despite almost half of the approximately 7.2 million horses engaging in structured athletic work, very little is known about one of the most critical facets of recovery: satellite cells (SCs). Satellite cells lie adjacent to the myofiber of skeletal muscle, poised to enter the myogenic program and fuse to the nearby muscle after a damaging event. Hepatocyte growth factor (HGF) and insulin-like growth factor-1 (IGF-1) transcript abundance increased after an exhaustive bout of endurance exercise in concert with myogenic regulator factors and preceding increased SC abundance in a previous study. This suggests that SCs may participate in repair of exercise-induced muscle damage. To assess the role of HGF in this process, equine SCs (eqSCs) were isolated from the gluteus medius of mature thoroughbred geldings for activation, proliferation and differentiation assays. Activation was not accelerated by 1, 5, 10, or 25 ng/mL HGF. Instead, 25 ng/mL HGF increased the proliferation rate of eqSC via protein kinase C δ and decreased differentiation. The influence of dietary L-citrulline, an amino acid that has the potential to influence SC activity and nutrient availability by its metabolism to L-arginine, was assessed during recovery from exercise in unfit adult horses. To model submaximal exercise, horses were exercised for 1 h at an average heart rate of 116 bpm, suggested to be typical of a heavy exercise session by the National Research Council. L-citrulline decreased myogenin mRNA abundance compared to controls while exercise increased peroxisome proliferator-activated receptor gamma coactivator 1- α (PGC1α) mRNA abundance, a master regulator of energy metabolism, at 1 d post-exercise. Although SCs were not activated in response to a single bout of submaximal exercise, metabolic regulators increased in the early period of recovery. Through these studies eqSC dynamics during exercise are better defined. / Doctor of Philosophy / The horse is well-known as an athletic creature and is often used in amateur and professional athletic events. Despite its popularity as a pastime in low and high-stakes competition, certain facets directly related to performance during exercise remain relatively unstudied. One crucial component of recovery from exercise is the intrinsic ability of skeletal muscle to repair exercise-induced muscle damage. This is accomplished largely through the incorporation of new nuclei, which originate from a position orbiting the muscle, hence the name satellite cells. This cell is essential to muscle regeneration from injury as often demonstrated in rodent models, but the role of satellite cells in recovery from exercise remains elusive in all species, but particularly so in horses. For instance, whether satellite cells only contribute nuclei after exercise to stimulate gains in muscle mass or whether they may also play a role in the process of adaptation to exercise is not clearly understood. The purpose of my work was to define the response of satellite cells to hepatocyte growth factor, a factor present in skeletal muscle during exercise that is already well-studied in rodent models. Additionally, to determine whether the addition of the non-essential amino acid, citrulline, would influence satellite cells and nutrient reserves after a session of submaximal exercise. I found that hepatocyte growth factor does not influence satellite cells isolated from horses in the same way it influences those from rodents, nor through the same mechanisms. Additionally, I found that satellite cells were not stimulated after a session of submaximal exercise, but a factor involved in regulation of genetic expression that is associated with satellite cells and skeletal muscle was downregulated with the addition of citrulline. Together, these results suggest that satellite cells may behave like other species in some ways, such as some responses to hepatocyte growth factor and the lack of response to a submaximal bout of exercise, but that there is still much to be learned in order to begin to influence management and training decisions as regards skeletal muscle recovery.

Precipitation estimates from the satellite-based Tropical Rainfall Measuring Mission (TRMM) instrumentation play a key role in flood analysis and water resource management across many regions of the world where rain gauge data are sparsely available. Previous studies have produced conflicting results regarding the accuracy of satellite-derived precipitation products, and several authors have called for further examination of their utility, specifically across the Himalaya Mountains region of southern Asia. In this study, daily precipitation estimates generated by TRMM were compared to daily precipitation measurements from a rain gauge network across the country of Nepal. TRMM data were statistically analyzed to quantify their representation of the gauge data during the four precipitation-defined seasons of Nepal. A detailed case study was assembled for the TRMM grid cell characterized by the greatest precipitation gauge density to develop a deeper understanding of local precipitation variability that the coarse resolution TRMM product cannot capture. The results illustrate that TRMM performs relatively well across all seasons, though the performance of TRMM during frozen precipitation events is not clear. In general, TRMM underestimates daily precipitation during the monsoon and pre-monsoon seasons, and overestimates during the winter and post-monsoon season. The case study analysis revealed a threshold for TRMM bias of 10-20mm of daily precipitation, overestimating lighter precipitation events while underestimating heavier precipitation events. Still, TRMM data compare favorably to gauge data, which contributes to the confidence with which they and other satellite-derived data products are used. / Master of Science

The Direct-Video-Broadcast Satellite (DVB-S) standard is used to provide video and radio to millions of users worldwide. It is designed to provide quasi-error free satellite communications. This thesis discusses some of the limitations of the DVB-S standard, describes some attempts in related work to address these concerns, and purposes a new modification to enhance the performance and reliability of the Direct-Video-Broadcast Satellite (DVB-S) standard by using a correlator in a DVB-S receiver. In many existing receive chains, synchronization speed is slightly delayed because phase ambiguity cannot be determined and corrected until after Viterbi decoding. Using correlation against known symbols before demodulation, the phase ambiguity can be corrected prior to Viterbi decoding, thus reducing the amount of time required to synchronize the received signal. To enhance the correlator's ability to detect the DVB-S synchronization bytes, a two byte, rather than single byte, known sync word is proposed as a modification to the standard. The motivation behind a longer sync word is to improve the standard in high noise environments. A two byte sync word provides more known information for correlation. The resulting correlation peaks are double that of when a single byte is used; this corresponds to about a 3 dB increase in SNR to provide fast signal acquisition and signal tracking in a noisy environment. / Master of Science

Occurrence of obesity has steadily increased in the human population and, along with it, associated health complications such as systemic insulin resistance, which can lead to the development of type 2 diabetes mellitus. Obesity is a complex metabolic disorder that often leads to chronic inflammation and an overall decline in human and animal health. In mouse skeletal muscle, obesity has been shown to impair muscle regeneration after injury, however, the mechanism underlying these changes in satellite cell (SC) biology have yet to be explored. To test the negative impacts of obesity on SC behaviors, we fed C57BL/6 mice normal chow (NC, control) or high-fat diet (HFD) for 10 wks and performed SC proliferation and differentiation assays in vitro. SCs from HFD mice formed colonies with smaller numbers (P < 0.001) compared to those isolated from NC mice, and this observation was confirmed (P < 0.05) by BrdU incorporation. Moreover, in vitro differentiation assays consisting of equally seeded SCs derived from NC and HFD muscles showed that HFD SCs exhibited compromised (P < 0.001) differentiation capacity compared to NC SCs. Immunocytochemical staining of cultured SCs demonstrated that the percentage of Pax7+/MyoD- (self-renewed) SC subpopulation decreased (P < 0.001) with HFD treatment group compared to the control. In single fiber explants, a higher ratio of SCs experienced apoptotic events as revealed by the expression of cleaved caspase 3 (P < 0.001). To investigate further the impact of obesity on SC quiescence and cycling properties in vivo, we used an inducible H2B-GFP mouse model to trace the turnover rate of GFP and thus cell division under normal and obese conditions. Flow cytometric analysis revealed that SCs from HFD treatment cycled faster (P < 0.001) than their NC counterparts, as reflected by the quicker loss of the GFP intensity. To test for SC muscle regenerative capacity in vivo, we used cardiotoxin (CTX) to induce wide-spread muscle damage in the tibialis anterior muscle. After analysis we found that HFD leads to a compromised, though mild, impairment in muscle regeneration. Taken together, these findings suggest that obesity negatively affects SC quiescence, proliferation, differentiation, and self-renewal in vitro, ex vivo and in vivo. / MS / The prevalence of obesity in the human population has steadily increased over the past decades and, along with it, associated health complications such as systemic insulin resistance, which can lead to the development of type 2 diabetes mellitus. Obesity is a complex metabolic disorder that often leads to chronic inflammation and an overall decline in human and animal health. Along with the multitude of health disorders associated with obesity, in mouse skeletal muscle, obesity has been shown to impair muscle regeneration after injury. The mechanisms underlying the impairment in muscle regeneration as seen in obesity are unknown. To better understand how obesity affects skeletal muscle, we looked at satellite cells (SC). Satellite cells, or muscle stem cells, are skeletal muscle resident cells that play a vital role in muscle repair after damage. To test the negative impacts of obesity on SC behaviors, we fed mice normal chow (NC, control) or high-fat diet (HFD) for 10 wks to obtain an obesogenic mouse model. Our first experiments involved culturing the SCs derived from the HFD and NC mouse muscles and growing them in an artificial environment. These experiments showed SCs derived from HFD mice had a decreased ability to replicate and divide compared to those isolated from NC mice. Moreover, the SCs from the HFD mice exhibited compromised capacity to form myotubes in culture, an essential part in muscle regeneration after damage. Our next set of experiments conducted looked at individual muscle fibers isolated from mouse muscle. In these experiments the SCs on the HFD muscle fibers had a higher ratio of SCs experiencing cell death in comparison to the control. To test the SC cycling properties in the living mouse we used a mouse model to trace the activity and cell division of SCs under normal and obese conditions. Using this model revealed that SCs from HFD treatment cycled faster than their control counterparts, even in the absence of notable muscle damage. To test for SC muscle regenerative capacity after muscle damage, we used cardiotoxin (CTX) to induce wide-spread muscle damage in the tibialis anterior muscle (leg muscle) of the living mouse. After analysis we found that HFD leads to a compromised, though mild, impairment in muscle regeneration. Taken together, these findings suggest that obesity negatively affects SC behaviors and function.

The mountainous western Virginia is the source of the headwater streams for the New, the Roanoke, and the James rivers. The region is prone to flash flooding, typically the result of localized precipitation. Fortunately, within the region, there is an efficient system of instruments for real-time data gathering with IFLOWS (Integrated Flood Observing and Warning System) gages, WSR-88D Doppler radar, and high precision GPS (Global Positioning System) receiver. The focus of this research is to combine the measurements from these various sensors in an algorithmic framework to determine the flash flood magnitude. It has been found that the trend in the GPS signals serves as a precursor for rain events with a lead-time of 30 minutes to 2 hours. The methodology proposed herein takes advantage of this lead-time as the trigger to initiate alert related calculations. It is shown here that the sum of the rates of change of total cloud water, water vapor contents and logarithmic profiles of partial pressure of dry air and temperature in an atmospheric column is equal to the rain rate. The total water content is measurable as the profiles of integrated precipitable water (IPW) from the GPS, the vertically integrated liquid (VIL) from the radar (representing different phases of the atmospheric water) and the pressure and temperature profiles are available. An example problem is presented illustrating the involving the calculations. / Master of Science

The CanX-4/-5 mission currently under development at the Space Flight Laboratory will demonstrate sub-metre formation control in four separate formations consisting of two nanosatellites. Formation maintenance is performed using a propulsion payload providing one axis of thrust, resulting in frequent slewing to meet thrust targets. Navigation is GPS dependent, with both satellites equipped with a receiver and antenna pair. Presented is a mission simulation developed for evaluating formation flying algorithm performance and the effects of frequent slewing on GPS coverage. CanX-4 and CanX-5 will be joined for commissioning prior to commencing formation flying via a mechanism, the Intersatellite Separation System. Details regarding the performance testing and troubleshooting of the system are described. Integration and testing of CanX-4/-5 flight hardware into a functional “FlatSat” is presented. Additionally, a description of satellite operations for two nanosatellites is given, with an emphasis on the relevance to the work performed for the CanX-4/-5 mission.