2,919 research outputs found
Capacitors can radiate - some consequences of the two-capacitor problem with radiation
We fill a gap in the arguments of Boykin et al [American Journal of Physics,
Vol 70 No. 4, pp 415-420 (2002)] by not invoking an electric current loop (i.e.
magnetic dipole model) to account for the radiation energy loss, since an
obvious corollary of their results is that the capacitors should radiate
directly even if the connecting wires are shrunk to zero length. That this is
so is shown here by a direct derivation of capacitor radiation using an
oscillating electric dipole radiator model for the capacitors as well as the
alternative less widely known magnetic 'charge' current loop representation for
an electric dipole [see for example "Electromagnetic Waves" by S.A.Schlekunoff,
van Nostrand (1948)]. Implications for Electromagnetic Compliance (EMC) issues
as well as novel antenna designs further motivate the purpose of this paper.Comment: 5 Pages with No figure
Exploring the Way to Approach the Efficiency Limit of Perovskite Solar Cells by Drift-Diffusion Model
Drift-diffusion model is an indispensable modeling tool to understand the
carrier dynamics (transport, recombination, and collection) and simulate
practical-efficiency of solar cells (SCs) through taking into account various
carrier recombination losses existing in multilayered device structures.
Exploring the way to predict and approach the SC efficiency limit by using the
drift-diffusion model will enable us to gain more physical insights and design
guidelines for emerging photovoltaics, particularly perovskite solar cells. Our
work finds out that two procedures are the prerequisites for predicting and
approaching the SC efficiency limit. Firstly, the intrinsic radiative
recombination needs to be corrected after adopting optical designs which will
significantly affect the open-circuit voltage at its Shockley-Queisser limit.
Through considering a detailed balance between emission and absorption of
semiconductor materials at the thermal equilibrium, and the Boltzmann
statistics at the non-equilibrium, we offer a different approach to derive the
accurate expression of intrinsic radiative recombination with the optical
corrections for semiconductor materials. The new expression captures light
trapping of the absorbed photons and angular restriction of the emitted photons
simultaneously, which are ignored in the traditional Roosbroeck-Shockley
expression. Secondly, the contact characteristics of the electrodes need to be
carefully engineered to eliminate the charge accumulation and surface
recombination at the electrodes. The selective contact or blocking layer
incorporated nonselective contact that inhibits the surface recombination at
the electrode is another important prerequisite. With the two procedures, the
accurate prediction of efficiency limit and precise evaluation of efficiency
degradation for perovskite solar cells are attainable by the drift-diffusion
model.Comment: 32 pages, 11 figure
From the surface to the seafloor: How giant larvaceans transport microplastics into the deep sea.
Plastic waste is a pervasive feature of marine environments, yet little is empirically known about the biological and physical processes that transport plastics through marine ecosystems. To address this need, we conducted in situ feeding studies of microplastic particles (10 to 600 μm in diameter) with the giant larvacean Bathochordaeus stygius. Larvaceans are abundant components of global zooplankton assemblages, regularly build mucus "houses" to filter particulate matter from the surrounding water, and later abandon these structures when clogged. By conducting in situ feeding experiments with remotely operated vehicles, we show that giant larvaceans are able to filter a range of microplastic particles from the water column, ingest, and then package microplastics into their fecal pellets. Microplastics also readily affix to their houses, which have been shown to sink quickly to the seafloor and deliver pulses of carbon to benthic ecosystems. Thus, giant larvaceans can contribute to the vertical flux of microplastics through the rapid sinking of fecal pellets and discarded houses. Larvaceans, and potentially other abundant pelagic filter feeders, may thus comprise a novel biological transport mechanism delivering microplastics from surface waters, through the water column, and to the seafloor. Our findings necessitate the development of tools and sampling methodologies to quantify concentrations and identify environmental microplastics throughout the water column
A comprehensive study for the plasmonic thin-film solar cell with periodic structure
A comprehensive study of the plasmonic thin-film solar cell with the periodic strip structure is presented in this paper. The finite-difference frequency-domain method is employed to discretize the inhomogeneous wave function for modeling the solar cell. In particular, the hybrid absorbing boundary condition and the one-sided difference scheme are adopted. The parameter extraction methods for the zeroth-order reflectance and the absorbed power density are also discussed, which is important for testing and optimizing the solar cell design. For the numerical results, the physics of the absorption peaks of the amorphous silicon thin-film solar cell are explained by electromagnetic theory; these peaks correspond to the waveguide mode, Floquet mode, surface plasmon resonance, and the constructively interference between adjacent metal strips. The work is therefore important for the theoretical study and optimized design of the plasmonic thin-film solar cell. © 2010 Optical Society of America.published_or_final_versio
The Van der Waals interaction of the hydrogen molecule - an exact local energy density functional
We verify that the van der Waals interaction and hence all dispersion
interactions for the hydrogen molecule given by: W"= -{A/R^6}-{B/R^8}-{C/R^10}-
..., in which R is the internuclear separation, are exactly soluble. The
constants A=6.4990267..., B=124.3990835 ... and C=1135.2140398... (in Hartree
units) first obtained approximately by Pauling and Beach (PB) [1] using a
linear variational method, can be shown to be obtainable to any desired
accuracy via our exact solution. In addition we shall show that a local energy
density functional can be obtained, whose variational solution rederives the
exact solution for this problem. This demonstrates explicitly that a static
local density functional theory exists for this system. We conclude with
remarks about generalising the method to other hydrogenic systems and also to
helium.Comment: 11 pages, 13 figures and 28 reference
Critical exponents of the degenerate Hubbard model
We study the critical behaviour of the \SUN{} generalization of the
one-dimensional Hubbard model with arbitrary degeneracy . Using the
integrability of this model by Bethe Ansatz we are able to compute the spectrum
of the low-lying excitations in a large but finite box for arbitrary values of
the electron density and of the Coulomb interaction. This information is used
to determine the asymptotic behaviour of correlation functions at zero
temperature in the presence of external fields lifting the degeneracy. The
critical exponents depend on the system parameters through a
dressed charge matrix implying the relevance of the interaction of charge- and
spin-density waves.Comment: 18 page
Electrokinetic behavior of two touching inhomogeneous biological cells and colloidal particles: Effects of multipolar interactions
We present a theory to investigate electro-kinetic behavior, namely,
electrorotation and dielectrophoresis under alternating current (AC) applied
fields for a pair of touching inhomogeneous colloidal particles and biological
cells. These inhomogeneous particles are treated as graded ones with physically
motivated model dielectric and conductivity profiles. The mutual polarization
interaction between the particles yields a change in their respective dipole
moments, and hence in the AC electrokinetic spectra. The multipolar
interactions between polarized particles are accurately captured by the
multiple images method. In the point-dipole limit, our theory reproduces the
known results. We find that the multipolar interactions as well as the spatial
fluctuations inside the particles can affect the AC electrokinetic spectra
significantly.Comment: Revised version with minor changes: References added and discussion
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