48,480 research outputs found
Bifurcation Boundary Conditions for Switching DC-DC Converters Under Constant On-Time Control
Sampled-data analysis and harmonic balance analysis are applied to analyze
switching DC-DC converters under constant on-time control. Design-oriented
boundary conditions for the period-doubling bifurcation and the saddle-node
bifurcation are derived. The required ramp slope to avoid the bifurcations and
the assigned pole locations associated with the ramp are also derived. The
derived boundary conditions are more general and accurate than those recently
obtained. Those recently obtained boundary conditions become special cases
under the general modeling approach presented in this paper. Different analyses
give different perspectives on the system dynamics and complement each other.
Under the sampled-data analysis, the boundary conditions are expressed in terms
of signal slopes and the ramp slope. Under the harmonic balance analysis, the
boundary conditions are expressed in terms of signal harmonics. The derived
boundary conditions are useful for a designer to design a converter to avoid
the occurrence of the period-doubling bifurcation and the saddle-node
bifurcation.Comment: Submitted to International Journal of Circuit Theory and Applications
on August 10, 2011; Manuscript ID: CTA-11-016
Advances in oral transmucosal drug delivery
Original article can be found at : http://sciencedirect.com/ Copyright ElsevierThe successful delivery of drugs across the oral mucosa represents a continuing challenge, as well as a great opportunity. Oral transmucosal delivery, especially buccal and sublingual delivery, has progressed far beyond the use of traditional dosage forms with novel approaches emerging continuously. This review highlights the physiological challenges as well as the advances and opportunities for buccal/sublingual drug delivery. Particular attention is given to new approaches which can extend dosage form retention time or can be engineered to deliver complex molecules such as proteins and peptides. The review will also discuss the physiology and local environment of the oral cavity in vivo and how this relates to the performance of transmucosal delivery systems.Peer reviewe
Type I X-ray Bursts at Low Accretion Rates
Neutron stars, with their strong surface gravity, have interestingly short
timescales for the sedimentation of heavy elements. Recent observations of
unstable thermonuclear burning (observed as X-ray bursts) on the surfaces of
slowly accreting neutron stars ( of the Eddington rate) motivate us to
examine how sedimentation of CNO isotopes affects the ignition of these bursts.
We further estimate the burst development using a simple one-zone model with a
full reaction network. We report a region of mass accretion rates for weak H
flashes. Such flashes can lead to a large reservoir of He, the unstable burning
of which may explain some observed long bursts (duration s).Comment: 6 pages, 2 figures, submitted to the proceedings of the conference
"The Multicoloured Landscape of Compact Objects and Their Explosive
Origins'', 2006 June 11--24, Cefalu, Sicily (Italy), to be published by AI
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