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Novel Modulation Strategy for a CLC Resonant Dual Active Bridge
W. L. Malan,D. M. Vilathgamuwa,G. R. Walker,D. J. Thrimawithana,U. K. Madawala 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6
This paper proposes a novel modulation strategy for a phase controlled Capacitor-Inductor- Capacitor (CLC) Resonant Dual Active Bridge (RDAB). The proposed modulation strategy improves the soft turnon, Zero-Current-Switching (ZCS) and Zero-Voltage-Switching (ZVS) range of the converter while only minimally increasing the required reactive currents in the ac link. A mathematical analysis of the proposed modulation scheme is presented along with a theoretical loss comparison between several modulation strategies. The proposed modulation strategy was implemented and the experimental results are presented.
Endothelin Receptor Overexpression Alters Diastolic Function in Cultured Rat Ventricular Myocytes
( Misuk Kang1 ),( Jeffery W. Walker ),( Ka Young Chung ) 한국응용약물학회 2012 Biomolecules & Therapeutics(구 응용약물학회지) Vol.20 No.4
The endothelin (ET) signaling pathway controls many physiological processes in myocardium and often becomes upregulated in heart diseases. The aim of the present study was to investigate the effects of ET receptor upregulation on the contractile function of adult ventricular myocytes. Primary cultured adult rat ventricular myocytes were used as a model system of ET receptor overexpression in the heart. Endothelin receptor type A (ETA) or type B (ETB) was overexpressed by Adenoviral infection, and the twitch responses of infected ventricular myocytes were measured after ET-1 stimulation. Overexpression of ETA exaggerated positive inotropic effect (PIE) and diastolic shortening of ET-1, and induced a new twitch response including twitch broadening. On the contrary, overexpression of ETB increased PIE of ET-1, but did not affect other two twitch responses. Control myocytes expressing endogenous receptors showed a parallel increase in twitch amplitude and systolic Ca2+ in response to ET-1. However, intracellular Ca2+ did not change in proportion to the changes in contractility in myocytes overexpressing ETA. Overexpression of ETA enhanced both systolic and diastolic contractility without parallel changes in Ca2+. Differential regulation of this nature indicates that upregulation of ETA may contribute to diastolic myocardial dysfunction by selectively targeting myofi lament proteins that regulate resting cell length, twitch duration and responsiveness to prevailing Ca2+.
Eidietis, N.W.,Choi, W.,Hahn, S.H.,Humphreys, D.A.,Sammuli, B.S.,Walker, M.L. International Atomic Energy Agency 2018 Nuclear fusion Vol.58 No.5
<P>A finite-state off-normal and fault response (ONFR) system is presented that provides the supervisory logic for comprehensive disruption avoidance and machine protection in tokamaks. Robust event handling is critical for ITER and future large tokamaks, where plasma parameters will necessarily approach stability limits and many systems will operate near their engineering limits. Events can be classified as off-normal plasmas events, e.g. neoclassical tearing modes or vertical displacements events, or faults, e.g. coil power supply failures. The ONFR system presented provides four critical features of a robust event handling system: sequential responses to cascading events, event recovery, simultaneous handling of multiple events and actuator prioritization. The finite-state logic is implemented in Matlab<SUP>®</SUP>/Stateflow<SUP>®</SUP> to allow rapid development and testing in an easily understood graphical format before automated export to the real-time plasma control system code. Experimental demonstrations of the ONFR algorithm on the DIII-D and KSTAR tokamaks are presented. In the most complex demonstration, the ONFR algorithm asynchronously applies ‘catch and subdue’ electron cyclotron current drive (ECCD) injection scheme to suppress a virulent 2/1 neoclassical tearing mode, subsequently shuts down ECCD for machine protection when the plasma becomes over-dense, and enables rotating 3D field entrainment of the ensuing locked mode to allow a safe rampdown, all in the same discharge without user intervention. When multiple ONFR states are active simultaneously and requesting the same actuator (e.g. neutral beam injection or gyrotrons), actuator prioritization is accomplished by sorting the pre-assigned priority values of each active ONFR state and giving complete control of the actuator to the state with highest priority. This early experience makes evident that additional research is required to develop an improved actuator sharing protocol, as well as a methodology to minimize the number and topological complexity of states as the finite-state ONFR system is scaled to a large, highly constrained device like ITER.</P>
Theoretical Size Controls of the Giant Phaeocystis globosa Colonies
Xiao Liu,Walker O. Smith Jr.,Kam W. Tang,Nhu Hai Doan,Ngoc Lam Nguyen 한국해양과학기술원 2015 Ocean science journal Vol.50 No.2
An unusual characteristic of the cosmopolitan haptophyte Phaeocystis globosa is its ability to form colonies of strikingly large size-up to 3 cm in diameter. The large size and the presence of a mucoid envelope are believed to contribute to the formation of dense blooms in Southeast Asia. We collected colonies of different sizes in shallow coastal waters of Viet Nam and conducted a series of measurements and experiments on individual colonies. Using these empirical data, we developed a simple carbon-based model to predict the growth and maximal size of P. globosa colonies. Our model suggests that growth of a colony from 0.2 cm to 1.4 cm (the maximal size in our samples) would take 16 days. This number, however, is strongly influenced by the maximal photosynthetic rate and other physiological parameters used in the model. The model also returns a specific growth rate of 0.30 d-1 for colonial cells, comparable to satellite estimates, but lower than have been measured for unicellular P. globosa in batch culture at similar temperatures. We attribute this low growth rate to not only the model uncertainties, but factors such as self-shading and diffusive limitation of nutrient uptake.