14,351 research outputs found
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
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
Optical Transistor for an Amplification of Radiation in a Broadband THz Domain
We propose a new type of optical transistor for a broadband amplification of
THz radiation. It is made of a graphene--superconductor hybrid, where electrons
and Cooper pairs couple by Coulomb forces. The transistor operates via the
propagation of surface plasmons in both layers, and the origin of amplification
is the quantum capacitance of graphene. It leads to THz waves amplification,
the negative power absorption, and as a result, the system yields positive
gain, and the hybrid acts like an optical transistor, operating with the
terahertz light. It can, in principle, amplify even a whole spectrum of chaotic
signals (or noise), that is required for numerous biological applications.Comment: 7 pages, 3 figure
1.0 Mm Maps and Radial Density Distributions of Southern Hii/molecular Cloud Complexes
Several 1.0 continuum mapping observations were made of seven southern hemisphere h12/molecular cloud complexes with 65 arcsec resolution. The radial density distribution of the clouds with central luminosity sources was determined observationally. Strong similarities in morphology and general physical conditions were found to exist among all of the southern clouds in the sample
Growth control of GaAs nanowires using pulsed laser deposition with arsenic over pressure
Using pulsed laser ablation with arsenic over pressure, the growth conditions
for GaAs nanowires have been systematically investigated and optimized. Arsenic
over pressure with As molecules was introduced to the system by thermal
decomposition of polycrystalline GaAs to control the stoichiometry and shape of
the nanowires during growth. GaAs nanowires exhibit a variety of geometries
under varying arsenic over pressure, which can be understood by different
growth processes via vapor-liquid-solid mechanism. Single-crystal GaAs
nanowires with uniform diameter, lengths over 20 m, and thin surface oxide
layer were obtained and can potentially be used for further electronic
characterization
Ball on a beam: stabilization under saturated input control with large basin of attraction
This article is devoted to the stabilization of two underactuated planar
systems, the well-known straight beam-and-ball system and an original circular
beam-and-ball system. The feedback control for each system is designed, using
the Jordan form of its model, linearized near the unstable equilibrium. The
limits on the voltage, fed to the motor, are taken into account explicitly. The
straight beam-and-ball system has one unstable mode in the motion near the
equilibrium point. The proposed control law ensures that the basin of
attraction coincides with the controllability domain. The circular
beam-and-ball system has two unstable modes near the equilibrium point.
Therefore, this device, never considered in the past, is much more difficult to
control than the straight beam-and-ball system. The main contribution is to
propose a simple new control law, which ensures by adjusting its gain
parameters that the basin of attraction arbitrarily can approach the
controllability domain for the linear case. For both nonlinear systems,
simulation results are presented to illustrate the efficiency of the designed
nonlinear control laws and to determine the basin of attraction
Superfluid density of superconductor-ferromagnet bilayers
We report the first measurements of the effective superfluid density n_S(T)
\propto \lambda^{-2}(T) of Superconductor-Ferromagnet (SC/FM) bilayers, where
\lambda is the effective magnetic field penetration depth. Thin Nb/Ni bilayers
were sputtered in ultrahigh vacuum in quick succession onto oxidized Si
substrates. Nb layers are 102 A thick for all samples, while Ni thicknesses
vary from 0 to 100 A. T_C determined from \lambda^{-2}(T) decreases rapidly as
Ni thickness d_Ni increases from zero to 15 A, then it has a shallow minimum at
d_Ni \approx 25 A. \lambda^{-2}(0) behaves similarly, but has a minimum several
times deeper. In fact, \lambda^{-2}(0) continues to increase with increasing Ni
thickness long after T_C has stopped changing. We argue that this indicates a
substantial superfluid density inside the ferromagnetic Ni films.Comment: 13 pages, 2 figures, MMM 2007 proceeding
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