482,720 research outputs found
Photonic Crystal and Photonic Crystal Fibers Communications
The development of all optical communications could benefit from the index guiding photonic crystal fibers. In communication the photonic crystal fibers could provide many new solutions. Conventional optical fibers have within the last decades revolutionized the communications industry and it is today a mature technology being pushed to its limit with respect to properties such as losses, single mode operation and dispersion. The spectra have been used by others to develop optical frequency standards. The process can potentially be used for frequency conversion in fiber optic network. In this system the dispersive properties can be controlled by the optical lattice making it possible to achieve phase-matched four wave mixing, like look the process taking place in the photonic crystal fibers. In this paper we will discuss the use of photonic crystal fibers in communications
Crystal engineering using functionalized adamantane
We performed a first principles investigation on the structural, electronic,
and optical properties of crystals made of chemically functionalized adamantane
molecules. Several molecular building blocks, formed by boron and nitrogen
substitutional functionalizations, were considered to build zincblende and
wurtzite crystals, and the resulting structures presented large bulk moduli and
cohesive energies, wide and direct bandgaps, and low dielectric constants
(low- materials). Those properties provide stability for such
structures up to room temperature, superior to those of typical molecular
crystals. This indicates a possible road map for crystal engineering using
functionalized diamondoids, with potential applications ranging from space
filling between conducting wires in nanodevices to nano-electro-mechanical
systems
Phonon engineering through crystal chemistry
Mitigation of the global energy crisis requires tailoring the thermal conductivity of materials. Low thermal conductivity is critical in a broad range of energy conversion technologies, including thermoelectrics and thermal barrier coatings. Here, we review the chemical trends and explore the origins of low thermal conductivity in crystalline materials. A unifying feature in the latest materials is the incorporation of structural complexity to decrease the phonon velocity and increase scattering. With this understanding, strategies for combining these
mechanisms can be formulated for designing new materials with exceptionally low thermal conductivity
Enhancing thermoelectric figure-of-merit by low-dimensional electrical transport in phonon-glass crystals
Low-dimensional electronic and glassy phononic transport are two important
ingredients of highly-efficient thermoelectric material, from which two
branches of the thermoelectric research emerge. One focuses on controlling
electronic transport in the low dimension, while the other on multiscale phonon
engineering in the bulk. Recent work has benefited much from combining these
two approaches, e.g., phonon engineering in low-dimensional materials. Here, we
propose to employ the low-dimensional electronic structure in bulk phonon-glass
crystal as an alternative way to increase the thermoelectric efficiency.
Through first-principles electronic structure calculation and classical
molecular dynamics simulation, we show that the - stacking
Bis-Dithienothiophene molecular crystal is a natural candidate for such an
approach. This is determined by the nature of its chemical bonding. Without any
optimization of the material parameter, we obtain a maximum room-temperature
figure of merit, , of at optimal doping, thus validating our idea.Comment: Nano Lett.201
Experimental studies of the internal Goos-Hanchen shift for self-collimated beams in two-dimensional microwave photonic crystals
We study experimentally the Goos-Hanchen effect observed at the reflection of
a self-collimated beam from the surface of a two-dimensional photonic crystal
and describe a method for controlling the beam reflection through surface
engineering. The microwave photonic crystal, fabricated from alumina rods,
allows control of the output position of a reflected beam undergoing an
internal Goos-Hanchen shift by changing the rod diameter at the reflection
surface. The experimental data is in good agreement with the results of the
finite-difference time-domain numerical calculations.Comment: 3 pages 4 figures, submitted to AP
Material research in microgravity
A popular discussion is given of microgravity effects in engineering and medicine gained from Skylab experience. Areas covered include crystal growing, liquid surface properties, diffusion, ferromagnetism, and emulsions
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