4,740 research outputs found
Efficient Computation of Power, Force, and Torque in BEM Scattering Calculations
We present concise, computationally efficient formulas for several quantities
of interest -- including absorbed and scattered power, optical force (radiation
pressure), and torque -- in scattering calculations performed using the
boundary-element method (BEM) [also known as the method of moments (MOM)]. Our
formulas compute the quantities of interest \textit{directly} from the BEM
surface currents with no need ever to compute the scattered electromagnetic
fields. We derive our new formulas and demonstrate their effectiveness by
computing power, force, and torque in a number of example geometries. Free,
open-source software implementations of our formulas are available for download
online
Computation of Casimir Interactions between Arbitrary 3D Objects with Arbitrary Material Properties
We extend a recently introduced method for computing Casimir forces between
arbitrarily--shaped metallic objects [M. T. H. Reid et al., Phys. Rev.
Lett._103_ 040401 (2009)] to allow treatment of objects with arbitrary material
properties, including imperfect conductors, dielectrics, and magnetic
materials. Our original method considered electric currents on the surfaces of
the interacting objects; the extended method considers both electric and
magnetic surface current distributions, and obtains the Casimir energy of a
configuration of objects in terms of the interactions of these effective
surface currents. Using this new technique, we present the first predictions of
Casimir interactions in several experimentally relevant geometries that would
be difficult to treat with any existing method. In particular, we investigate
Casimir interactions between dielectric nanodisks embedded in a dielectric
fluid; we identify the threshold surface--surface separation at which
finite--size effects become relevant, and we map the rotational energy
landscape of bound nanoparticle diclusters
Fluctuating surface-current formulation of radiative heat transfer: theory and applications
We describe a novel fluctuating-surface current formulation of radiative heat
transfer between bodies of arbitrary shape that exploits efficient and
sophisticated techniques from the surface-integral-equation formulation of
classical electromagnetic scattering. Unlike previous approaches to
non-equilibrium fluctuations that involve scattering matrices---relating
"incoming" and "outgoing" waves from each body---our approach is formulated in
terms of "unknown" surface currents, laying at the surfaces of the bodies, that
need not satisfy any wave equation. We show that our formulation can be applied
as a spectral method to obtain fast-converging semi-analytical formulas in
high-symmetry geometries using specialized spectral bases that conform to the
surfaces of the bodies (e.g. Fourier series for planar bodies or spherical
harmonics for spherical bodies), and can also be employed as a numerical method
by exploiting the generality of surface meshes/grids to obtain results in more
complicated geometries (e.g. interleaved bodies as well as bodies with sharp
corners). In particular, our formalism allows direct application of the
boundary-element method, a robust and powerful numerical implementation of the
surface-integral formulation of classical electromagnetism, which we use to
obtain results in new geometries, including the heat transfer between finite
slabs, cylinders, and cones
Casimir repulsion between metallic objects in vacuum
We give an example of a geometry in which two metallic objects in vacuum
experience a repulsive Casimir force. The geometry consists of an elongated
metal particle centered above a metal plate with a hole. We prove that this
geometry has a repulsive regime using a symmetry argument and confirm it with
numerical calculations for both perfect and realistic metals. The system does
not support stable levitation, as the particle is unstable to displacements
away from the symmetry axis.Comment: 4 pages, 4 figures; added references, replaced Fig.
Will Changing Demographics Affect U.S. Cheese Demand?
U.S. cheese consumption has grown considerably over the last three decades. Using a censored demand model and Nielsen Homescan retail data, this study identifies price and non-price factors affecting the demand for differentiated cheese products. Own-price and expenditure elasticities for all of the cheese products are statistically significant and elastic. Results also reveal that a strong substitution relationship exists among all cheese products. Although demographic influences are generally smaller than those related to prices and expenditures, empirical findings show that household size, college educated female heads of household who are age 40 and older, residing in the South, Central, and Western regions of the United States, as well as Black heads of household, have positive statistically significant effects on consumers’ cheese purchases.cheese form, cheese purchase, demand elasticities, demographic and economic factors, Nielsen Homescan data, Food Consumption/Nutrition/Food Safety, Marketing, C25, D12, Q11,
Entrepreneurial Orientation in Public Schools: The View from New Jersey
We utilize a sample of New Jersey schools to explore the relationship between entrepreneurial orientation (EO) and school performance. The results indicate a significant relationship between several dimensions of EO and performance after controlling for a number of relevant variables. Charter schools were found to have higher EO than traditional schools. The implications of these findings for education and entrepreneurship research are discussed
Fluctuating volume-current formulation of electromagnetic fluctuations in inhomogeneous media: incandecence and luminescence in arbitrary geometries
We describe a fluctuating volume--current formulation of electromagnetic
fluctuations that extends our recent work on heat exchange and Casimir
interactions between arbitrarily shaped homogeneous bodies [Phys. Rev. B. 88,
054305] to situations involving incandescence and luminescence problems,
including thermal radiation, heat transfer, Casimir forces, spontaneous
emission, fluorescence, and Raman scattering, in inhomogeneous media. Unlike
previous scattering formulations based on field and/or surface unknowns, our
work exploits powerful techniques from the volume--integral equation (VIE)
method, in which electromagnetic scattering is described in terms of
volumetric, current unknowns throughout the bodies. The resulting trace
formulas (boxed equations) involve products of well-studied VIE matrices and
describe power and momentum transfer between objects with spatially varying
material properties and fluctuation characteristics. We demonstrate that thanks
to the low-rank properties of the associatedmatrices, these formulas are
susceptible to fast-trace computations based on iterative methods, making
practical calculations tractable. We apply our techniques to study thermal
radiation, heat transfer, and fluorescence in complicated geometries, checking
our method against established techniques best suited for homogeneous bodies as
well as applying it to obtain predictions of radiation from complex bodies with
spatially varying permittivities and/or temperature profiles
Fluctuation-Induced Phenomena in Nanoscale Systems: Harnessing the Power of Noise
The famous Johnson-Nyquist formula relating noise current to conductance has
a microscopic generalization relating noise current density to microscopic
conductivity, with corollary relations governing noise in the components of the
electromagnetic fields. These relations, known collectively in physics as
fluctuation-dissipation relations, form the basis of the modern understanding
of fluctuation-induced phenomena, a field of burgeoning importance in
experimental physics and nanotechnology. In this review, we survey recent
progress in computational techniques for modeling fluctuation-induced
phenomena, focusing on two cases of particular interest: near-field radiative
heat transfer and Casimir forces. In each case we review the basic physics of
the phenomenon, discuss semi-analytical and numerical algorithms for
theoretical analysis, and present recent predictions for novel phenomena in
complex material and geometric configurations.Comment: Accepted for publication in a forthcoming special issue of
Proceedings of the IEEE. Corrected numbering of references in Figure
Digital Receiver for Microwave Radiometry
A receiver proposed for use in L-band microwave radiometry (for measuring soil moisture and sea salinity) would utilize digital signal processing to suppress interfering signals. Heretofore, radio frequency interference has made it necessary to limit such radiometry to a frequency band about 20 MHz wide, centered at .1,413 MHz. The suppression of interference in the proposed receiver would make it possible to expand the frequency band to a width of 100 MHz, thereby making it possible to obtain greater sensitivity and accuracy in measuring moisture and salinit
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