165,565 research outputs found
Light trapping within the grooves of 1D diffraction gratings under monochromatic and sunlight illumination
The Rayleigh-Modal method is used to calculate the electromagnetic field
within the grooves of a perfectly conducting, rectangular-shaped 1D diffraction
grating. An \emph{enhancement coefficient} () is introduced in order to
quantify such an energy concentration. Accordingly, 1 means that the
amount of electromagnetic energy present within the grooves is larger than that
one will have, over the same volume, if the diffraction grating is replaced by
a perfectly reflecting mirror. The results in this paper show that can
be as large as several decades at certain, often narrow, ranges of wavelengths.
However, it reduces to approximately 20% under sunlight illumination. In this
latter case, such values are achieved when the \textit{optical spacing} between
the grooves is greater than 500 nm, where is the groove spacing and
is the refractive index of the substance within the grooves. For
smaller than 500 nm the enhancement coefficient turns negligibly small.Comment: This paper contains 11 pages and 4 figures, and will be published
elsewher
A trivariate interpolation algorithm using a cube-partition searching procedure
In this paper we propose a fast algorithm for trivariate interpolation, which
is based on the partition of unity method for constructing a global interpolant
by blending local radial basis function interpolants and using locally
supported weight functions. The partition of unity algorithm is efficiently
implemented and optimized by connecting the method with an effective
cube-partition searching procedure. More precisely, we construct a cube
structure, which partitions the domain and strictly depends on the size of its
subdomains, so that the new searching procedure and, accordingly, the resulting
algorithm enable us to efficiently deal with a large number of nodes.
Complexity analysis and numerical experiments show high efficiency and accuracy
of the proposed interpolation algorithm
RF power generation
This paper reviews the main types of r.f. power amplifiers which are, or may
be, used for particle accelerators. It covers solid-state devices, tetrodes,
inductive output tubes, klystrons, magnetrons, and gyrotrons with power outputs
greater than 10 kW c.w. or 100 kW pulsed at frequencies from 50 MHz to 30 GHz.
Factors affecting the satisfactory operation of amplifiers include cooling,
matching and protection circuits are discussed. The paper concludes with a
summary of the state of the art for the different technologies.Comment: 35 pages, contribution to the CAS - CERN Accelerator School:
Specialised Course on RF for Accelerators; 8 - 17 Jun 2010, Ebeltoft, Denmar
High-Speed, Photon Counting CCD Cameras for Astronomy
The design of electron multiplying CCD cameras require a very different
approach from that appropriate for slow scan CCD operation. This paper
describes the main problems in using electron multiplying CCDs for high-speed,
photon counting applications in astronomy and how these may be substantially
overcome. With careful design it is possible to operate the E2V Technologies
L3CCDs at rates well in excess of that claimed by the manufacturer, and that
levels of clock induced charge dramatically lower than those experienced with
commercial cameras that need to operate at unity gain. Measurements of the
performance of the E2V Technologies CCD201 operating at 26 MHz will be
presented together with a guide to the effective reduction of clock induced
charge levels. Examples of astronomical results obtained with our cameras are
presented.Comment: 11 pages, 5 figure
Predicted efficiency of Si wire array solar cells
Solar cells based on arrays of CVD-grown Si nano- or micro-wires have attracted interest as potentially low-cost alternatives to conventional wafer-based Si photovoltaics [1-6], and single-wire solar cells have been reported with efficiencies of up to 3.4% [7]. We recently presented device physics simulations which predicted efficiencies exceeding 17%, based on experimentally observed diffusion lengths within our wires [8]. However, this model did not take into account the optical properties of a wire array device - in particular the inherently low packing fraction of wires within CVD-grown wire arrays, which might limit their ability to fully absorb incident sunlight. For this reason, we have combined a device physics model of Si wire solar cells with FDTD simulations of light absorption within wire arrays to investigate the potential photovoltaic efficiency of this cell geometry. We have found that even a sparsely packed array (14%) is expected to absorb moderate (66%) amounts of above-bandgap solar energy, yielding a simulated photovoltaic efficiency of 14.5%. Because the wire array comprises such a small volume of Si, the observed absorption represents an effective optical concentration, which enables greater operating voltages than previously predicted for Si wire array solar cells
- …