3,783 research outputs found
Comment on: Reply to comment on `Perfect imaging without negative refraction'
Whether or not perfect imaging is obtained in the mirrored version of
Maxwell's fisheye lens is debated in the comment/reply sequence
[Blaikie-2010njp, Leonhardt-2010njp] discussing Leonhardt's original paper
[Leonhardt-2009njp]. Here we show that causal solutions can be obtained without
the need for an "active localized drain", contrary to the claims in
[Leonhardt-2010njp].Comment: v2 (added MEEP ctl file), v3 (publisher statement
Superantenna made of transformation media
We show how transformation media can make a superantenna that is either
completely invisible or focuses incoming light into a needle-sharp beam. Our
idea is based on representating three-dimensional space as a foliage of sheets
and performing two-dimensional conformal maps on each shee
Quantum Markov Process on a Lattice
We develop a systematic description of Weyl and Fano operators on a lattice
phase space. Introducing the so-called ghost variable even on an odd lattice,
odd and even lattices can be treated in a symmetric way. The Wigner function is
defined using these operators on the quantum phase space, which can be
interpreted as a spin phase space. If we extend the space with a dichotomic
variable, a positive distribution function can be defined on the new space. It
is shown that there exits a quantum Markov process on the extended space which
describes the time evolution of the distribution function.Comment: Lattice2003(theory
Partial Transmutation of Singularities in Optical Instruments
Some interesting optical instruments such as the Eaton lens and the Invisible
Sphere require singularities of the refractive index for their implementation.
We show how to transmute those singularities into harmless topological defects
in anisotropic media without the need for anomalous material properties
Perfect imaging: they don't do it with mirrors
Imaging with a spherical mirror in empty space is compared with the case when
the mirror is filled with the medium of Maxwell's fish eye. Exact
time-dependent solutions of Maxwell's equations show that perfect imaging is
not achievable with an electrical ideal mirror on its own, but with Maxwell's
fish eye in the regime when it implements a curved geometry for full
electromagnetic waves
Fluorescence microscopy for the characterization of structural integrity
The absorption characteristics of light and the optical technique of fluorescence microscopy for enhancing metallographic interpretation are presented. Characterization of thermally sprayed coatings by optical microscopy suffers because of the tendency for misidentification of the microstructure produced by metallographic preparation. Gray scale, in bright field microscopy, is frequently the only means of differentiating the actual structural details of porosity, cracking, and debonding of coatings. Fluorescence microscopy is a technique that helps to distinguish the artifacts of metallographic preparation (pullout, cracking, debonding) from the microstructure of the specimen by color contrasting structural differences. Alternative instrumentation and the use of other dye systems are also discussed. The combination of epoxy vacuum infiltration with fluorescence microscopy to verify microstructural defects is an effective means to characterize advanced materials and to assess structural integrity
Quantum levitation by left-handed metamaterials
Left-handed metamaterials make perfect lenses that image classical
electromagnetic fields with significantly higher resolution than the
diffraction limit. Here we consider the quantum physics of such devices. We
show that the Casimir force of two conducting plates may turn from attraction
to repulsion if a perfect lens is sandwiched between them. For optical
left-handed metamaterials this repulsive force of the quantum vacuum may
levitate ultra-thin mirrors
As-received microstructure of a SiC/Ti-15-3 composite
A silicon carbide fiber reinforced titanium (Ti-15V-3Cr-3Sn-3Al) composite is metallographically examined. Several methods for examining composite materials are investigated and documented. Polishing techniques for this material are described. An interference layering method is developed to reveal the structure of the fiber, the reaction zone, and various phases within the matrix. Microprobe and transmission electron microscope (TEM) analyses are performed on the fiber/matrix interface. A detailed description of the fiber distribution as well as the microstructure of the fiber and matrix are presented
Plasma etching a ceramic composite
Plasma etching is found to be a superior metallographic technique for evaluating the microstructure of a ceramic matrix composite. The ceramic composite studied is composed of silicon carbide whiskers (SiC(sub W)) in a matrix of silicon nitride (Si3N4), glass, and pores. All four constituents are important in evaluating the microstructure of the composite. Conventionally prepared samples, both as-polished or polished and etched with molten salt, do not allow all four constituents to be observed in one specimen. As-polished specimens allow examination of the glass phase and porosity, while molten salt etching reveals the Si3N4 grain size by removing the glass phase. However, the latter obscures the porosity. Neither technique allows the SiC(sub W) to be distinguished from the Si3N4. Plasma etching with CF4 + 4 percent O2 selectively attacks the Si3N4 grains, leaving SiC(sub W) and glass in relief, while not disturbing the pores. An artifact of the plasma etching reaction is the deposition of a thin layer of carbon on Si3N4, allowing Si3N4 grains to be distinguished from SiC(sub W) by back scattered electron imaging
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