1,503 research outputs found
Electromagnetic Boundary Conditions Defined in Terms of Normal Field Components
A set of four scalar conditions involving normal components of the fields D
and B and their normal derivatives at a planar surface is introduced, among
which different pairs can be chosen to represent possible boundary conditions
for the electromagnetic fields. Four such pairs turn out to yield meaningful
boundary conditions and their responses for an incident plane wave at a planar
boundary are studied. The theory is subsequently generalized to more general
boundary surfaces defined by a coordinate function. It is found that two of the
pairs correspond to the PEC and PMC conditions while the other two correspond
to a mixture of PEC and PMC conditions for fields polarized TE or TM with
respect to the coordinate defining the surface
Exposure Path Perceptions and Protective Actions in Biological Water Contamination Emergencies
This study extends the Protective Action Decision Model, developed to address disaster warning responses in the context of natural hazards, to “boil water” advisories. The study examined 110 Boston residents’ and 203 Texas students’ expectations of getting sick through different exposure paths for contact with contaminated water. In addition, the study assessed respondents’ actual implementation (for residents) or behavioral expectations (for students) of three different protective actions – bottled water, boiled water, and personally chlorinated water – as well as their demo-graphic characteristics and previous experience with water contamination. The results indicate that people distinguish among the exposure paths, but the differences are small (one-third to one-half of the response scale). Nonetheless, the perceived risk from the exposure paths helps to explain why people are expected to consume (or actually consumed) bottled water rather than boiled or personally chlorinated water. Overall, these results indicate that local authorities should take care to communicate the relative risks of different exposure paths and should expect that people will respond to a boil water order primarily by consuming bottled water. Thus, they should make special efforts to increase supplies of bottled water in their communities during water contamination emergencies
Plasmonic Cloaking of Cylinders: Finite Length, Oblique Illumination and Cross-Polarization Coupling
Metamaterial cloaking has been proposed and studied in recent years following
several interesting approaches. One of them, the scattering-cancellation
technique, or plasmonic cloaking, exploits the plasmonic effects of suitably
designed thin homogeneous metamaterial covers to drastically suppress the
scattering of moderately sized objects within specific frequency ranges of
interest. Besides its inherent simplicity, this technique also holds the
promise of isotropic response and weak polarization dependence. Its theory has
been applied extensively to symmetrical geometries and canonical 3D shapes, but
its application to elongated objects has not been explored with the same level
of detail. We derive here closed-form theoretical formulas for infinite
cylinders under arbitrary wave incidence, and validate their performance with
full-wave numerical simulations, also considering the effects of finite lengths
and truncation effects in cylindrical objects. In particular, we find that a
single isotropic (idealized) cloaking layer may successfully suppress the
dominant scattering coefficients of moderately thin elongated objects, even for
finite lengths comparable with the incident wavelength, providing a weak
dependence on the incidence angle. These results may pave the way for
application of plasmonic cloaking in a variety of practical scenarios of
interest.Comment: 17 pages, 11 figures, 2 table
Mutual Coherence of Polarized Light in Disordered Media: Two-Frequency Method Extended
The paper addresses the two-point correlations of electromagnetic waves in
general random, bi-anisotropic media whose constitutive tensors are complex
Hermitian, positive- or negative-definite matrices. A simplified version of the
two-frequency Wigner distribution (2f-WD) for polarized waves is introduced and
the closed form Wigner-Moyal equation is derived from the Maxwell equations. In
the weak-disorder regime with an arbitrarily varying background the
two-frequency radiative transfer (2f-RT) equations for the associated coherence matrices are derived from the Wigner-Moyal equation by using the
multiple scale expansion. In birefringent media, the coherence matrix becomes a
scalar and the 2f-RT equations take the scalar form due to the absence of
depolarization. A paraxial approximation is developed for spatialy anisotropic
media. Examples of isotropic, chiral, uniaxial and gyrotropic media are
discussed
Repulsive Casimir Force in Chiral Metamaterials
We demonstrate theoretically that one can obtain repulsive Casimir forces and
stable nanolevitations by using chiral metamaterials. By extending the Lifshitz
theory to treat chiral metamaterials, we find that a repulsive force and a
minimum of the interaction energy exist for strong chirality, under realistic
frequency dependencies and correct limiting values (for zero and infinite
frequencies) of the permittivity, permeability, and chiral coefficients.Comment: 4 pages, 4 figures, letter. submitted to Phys. Rev. Let
Efficient UC Commitment Extension with Homomorphism for Free (and Applications)
Homomorphic universally composable (UC) commitments allow for the sender to reveal the result of additions and multiplications of values contained in commitments without revealing the values themselves while assuring the receiver of the correctness of such computation on committed values.
In this work, we construct essentially optimal additively homomorphic UC commitments from any (not necessarily UC or homomorphic) extractable commitment. We obtain amortized linear computational complexity in the length of the input messages and rate 1.
Next, we show how to extend our scheme to also obtain multiplicative homomorphism at the cost of asymptotic optimality but retaining low concrete complexity for practical parameters.
While the previously best constructions use UC oblivious transfer as the main building block, our constructions only require extractable commitments and PRGs, achieving better concrete efficiency and offering new insights into the sufficient conditions for obtaining homomorphic UC commitments.
Moreover, our techniques yield public coin protocols, which are compatible with the Fiat-Shamir heuristic.
These results come at the cost of realizing a restricted version of the homomorphic commitment functionality where the sender is allowed to perform any number of commitments and operations on committed messages but is only allowed to perform a single batch opening of a number of commitments.
Although this functionality seems restrictive, we show that it can be used as a building block for more efficient instantiations of recent protocols for secure multiparty computation and zero knowledge non-interactive arguments of knowledge
Relativistic nature of a magnetoelectric modulus of Cr_2O_3-crystals: a new 4-dimensional pseudoscalar and its measurement
Earlier, the magnetoelectric effect of chromium sesquioxide Cr_2O_3 has been
determined experimentally as a function of temperature. One measures the
electric field-induced magnetization on Cr_2O_3 crystals or the magnetic
field-induced polarization. From the magnetoelectric moduli of Cr_2O_3 we
extract a 4-dimensional relativistic invariant pseudoscalar
. It is temperature dependent and of the order of
10^{-4}/Z_0, with Z_0 as vacuum impedance. We show that the new pseudoscalar is
odd under parity transformation and odd under time inversion. Moreover,
is for Cr_2O_3 what Tellegen's gyrator is for two port
theory, the axion field for axion electrodynamics, and the PEMC (perfect
electromagnetic conductor) for electrical engineering.Comment: Revtex, 36 pages, 9 figures (submitted in low resolution, better
quality figures are available from the authors
On possible skewon effects on light propagation
We start from a local and linear spacetime relation between the
electromagnetic excitation and the field strength. Then we study the generally
covariant Fresnel surfaces for light rays and light waves. The metric and the
connection of spacetime are left unspecified. Accordingly, our framework is
ideally suited for a search of possible violations of the Lorentz symmetry in
the photon sector of the extended standard model. We discuss how the skewon
part of the constitutive tensor, if suitably parametrized, influences the
Fresnel surfaces and disturbs the light cones of vacuum electrodynamics.
Conditions are specified that yield the reduction of the original quartic
Fresnel surface to the double light cone structure (birefringence) and to the
single light cone. Qualitatively, the effects of the real skewon field can be
compared to those in absorbing material media. In contrast, the imaginary
skewon field can be interpreted in terms of non-absorbing media with natural
optical activity and Faraday effects. The astrophysical data on gamma-ray
bursts are used for deriving an upper limit for the magnitude of the skewon
field.Comment: Revtex, 29 pages, 10 figures, references added, text as in the
published versio
The Third Age of Phage
The third age of phage has begun with the recognition that phages may be key to the great planetary biogeochemical cycles and represent the greatest potential genetic resource in the biospher
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