Browsing by Author "Hill, David"

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    Methods for Analysis and Quantification of Power System Resilience
    Stankovic, Aleksandar M.; Tomsovic, Kevin L.; De Caro, Fabrizio; Braun, Martin; Chow, Joe H.; Cukalevski, Ninel; Dobson, Ian; Eto, Joseph; Fink, Blair; Hachmann, Christian; Hill, David; Ji, Chuanyi; Kavicky, James A.; Levi, Victor; Liu, Chen-Ching; Mili, Lamine M.; Moreno, Rodrigo; Panteli, Mathaios; Petit, Frederic D.; Sansavini, Giovanni; Singh, Chanan; Srivastava, Anurag K.; Strunz, Kai; Sun, Hongbo; Xu, Yin; Zhao, Shijia (IEEE, 2022-10-10)
    This paper summarizes the report prepared by an IEEE PES Task Force. Resilience is a fairly new technical concept for power systems, and it is important to precisely delineate this concept for actual applications. As a critical infrastructure, power systems have to be prepared to survive rare but extreme incidents (natural catastrophes, extreme weather events, physical/cyber-attacks, equipment failure cascades, etc.) to guarantee power supply to the electricity-dependent economy and society. Thus, resilience needs to be integrated into planning and operational assessment to design and operate adequately resilient power systems. Quantification of resilience as a key performance indicator is important, together with costs and reliability. Quantification can analyze existing power systems and identify resilience improvements in future power systems. Given that a 100% resilient system is not economic (or even technically achievable), the degree of resilience should be transparent and comprehensible. Several gaps are identified to indicate further needs for research and development.
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    Use of Imaging Biomarkers to Assess Perfusion and Glucose Metabolism in the Skeletal Muscle of Dystrophic Mice
    Ahmad, Nabeel; Welch, Ian; Grange, Robert W.; Hadway, Jennifer; Dhanvantari, Savita; Hill, David; Lee, Ting-Yim; Hoffman, Lisa M. (2011-06-04)
    Background Duchenne muscular dystrophy (DMD) is a severe neuromuscular disease that affects 1 in 3500 boys. The disease is characterized by progressive muscle degeneration that results from mutations in or loss of the cytoskeletal protein, dystrophin, from the glycoprotein membrane complex, thus increasing the susceptibility of contractile muscle to injury. To date, disease progression is typically assessed using invasive techniques such as muscle biopsies, and while there are recent reports of the use of magnetic resonance, ultrasound and optical imaging technologies to address the issue of disease progression and monitoring therapeutic intervention in dystrophic mice, our study aims to validate the use of imaging biomarkers (muscle perfusion and metabolism) in a longitudinal assessment of skeletal muscle degeneration/regeneration in two murine models of muscular dystrophy. Methods Wild-type (w.t.) and dystrophic mice (weakly-affected mdx mice that are characterized by a point mutation in dystrophin; severely-affected mdx:utrn-/- (udx) mice that lack functional dystrophin and are null for utrophin) were exercised three times a week for 30 minutes. To follow the progression of DMD, accumulation of 18 F-FDG, a measure of glucose metabolism, in both wild-type and affected mice was measured with a small animal PET scanner (GE eXplore Vista). To assess changes in blood flow and blood volume in the hind limb skeletal muscle, mice were injected intravenously with a CT contrast agent, and imaged with a small animal CT scanner (GE eXplore Ultra). Results In hind limb skeletal muscle of both weakly-affected mdx mice and in severely-affected udx mice, we demonstrate an early, transient increase in both 18F-FDG uptake, and in blood flow and blood volume. Histological analysis of H&E-stained tissue collected from parallel littermates demonstrates the presence of both inflammatory infiltrate and centrally-located nuclei, a classic hallmark of myofibrillar regeneration. In both groups of affected mice, the early transient response was succeeded by a progressive decline in muscle perfusion and metabolism; this was also evidenced histologically. Conclusions The present study demonstrates the utility of non-invasive imaging biomarkers in characterizing muscle degeneration/regeneration in murine models of DMD. These techniques may now provide a promising alternative for assessing both disease progression and the efficacy of new therapeutic treatments in patients.