42,039 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
A theoretical analysis of the current-voltage characteristics of solar cells
The correlation of theoretical and experimental data is discussed along with the development of a complete solar cell analysis. The dark current-voltage characteristics, and the parameters for solar cells are analyzed. The series resistance, and impurity gradient effects on solar cells were studied, the effects of nonuniformities on solar cell performance were analyzed
A theoretical analysis of the current-voltage characteristics of solar cells
The following topics are discussed: (1) dark current-voltage characteristics of solar cells; (2) high efficiency silicon solar cells; (3) short circuit current density as a function of temperature and the radiation intensity; (4) Keldysh-Franz effects and silicon solar cells; (5) thin silicon solar cells; (6) optimum solar cell designs for concentrated sunlight; (7) nonuniform illumination effects of a solar cell; and (8) high-low junction emitter solar cells
Coronal rain in magnetic arcades: Rebound shocks, Limit cycles, and Shear flows
We extend our earlier multidimensional, magnetohydrodynamic simulations of
coronal rain occurring in magnetic arcades with higher resolution,
grid-adaptive computations covering a much longer ( hour) timespan. We
quantify how in-situ forming blob-like condensations grow along and across
field lines and show that rain showers can occur in limit cycles, here
demonstrated for the first time in 2.5D setups. We discuss dynamical,
multi-dimensional aspects of the rebound shocks generated by the siphon inflows
and quantify the thermodynamics of a prominence-corona-transition-region like
structure surrounding the blobs. We point out the correlation between
condensation rates and the cross-sectional size of loop systems where
catastrophic cooling takes place. We also study the variations of the typical
number density, kinetic energy and temperature while blobs descend, impact and
sink into the transition region. In addition, we explain the mechanisms leading
to concurrent upflows while the blobs descend. As a result, there are plenty of
shear flows generated with relative velocity difference around 80 km s
in our simulations. These shear flows are siphon flows set up by multiple blob
dynamics and they in turn affect the deformation of the falling blobs. In
particular, we show how shear flows can break apart blobs into smaller
fragments, within minutes
Simulating coronal condensation dynamics in 3D
We present numerical simulations in 3D settings where coronal rain phenomena
take place in a magnetic configuration of a quadrupolar arcade system. Our
simulation is a magnetohydrodynamic simulation including anisotropic thermal
conduction, optically thin radiative losses, and parametrised heating as main
thermodynamical features to construct a realistic arcade configuration from
chromospheric to coronal heights. The plasma evaporation from chromospheric and
transition region heights eventually causes localised runaway condensation
events and we witness the formation of plasma blobs due to thermal instability,
that evolve dynamically in the heated arcade part and move gradually downwards
due to interchange type dynamics. Unlike earlier 2.5D simulations, in this case
there is no large scale prominence formation observed, but a continuous coronal
rain develops which shows clear indications of Rayleigh-Taylor or interchange
instability, that causes the denser plasma located above the transition region
to fall down, as the system moves towards a more stable state. Linear stability
analysis is used in the non-linear regime for gaining insight and giving a
prediction of the system's evolution. After the plasma blobs descend through
interchange, they follow the magnetic field topology more closely in the lower
coronal regions, where they are guided by the magnetic dips.Comment: 47 pages, 59 figure
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