Evidence for Braggoriton Excitations in Opal Photonic Crystals Infiltrated with Highly Polarizable Dyes

We studied angle-dependent reflectivity spectra of opal photonic crystals infiltrated with cyanine dyes, which are highly polarizable media with very large Rabi frequency. We show that when resonance conditions between the exciton-polariton of the infiltrated dye and Bragg frequencies exist, then the Bragg stop band decomposes into two reflectivity bands with a semi-transparent spectral range in between that is due to light propagation inside the gap caused by the existence of braggoriton excitations. These novel excitations result from the interplay interaction between the Bragg gap with spatial modulation origin and the polariton gap due to the excitons, and may lead to optical communication traffic inside the gap of photonic crystals via channel waveguiding.Comment: LaTex, 5 pages, 3 figures include

Electrochemic properties of single-wall carbon nanotube electrodes

The electrochemical properties of single-wall carbon nanotube ~CNT! electrodes in the form of sheets or papers have been examined. Thermal annealing has produced significant changes in a range of properties of the material including increased hydrophobicity and elimination of electroactive surface functional groups and other impurities. As a result of these changes, the treated electrodes exhibit lower double-layer capacitance, absence of faradaic responses and associated pseudocapacitance, and a better frequency response. The basic electrochemical behavior of the CNT paper electrodes is not markedly affected by relatively large differences in electrolyte ion size, consistent with an average pore size of 9 nm. Increases in both CNT sheet thickness and surface area induce a slower electrode response in agreement with the porous nature of the electrode matrix

Structures performance, benefit, cost-study

New technology concepts and structural analysis development needs which could lead to improved life cycle cost for future high-bypass turbofans were studied. The NASA-GE energy efficient engine technology is used as a base to assess the concept benefits. Recommended programs are identified for attaining these generic structural and other beneficial technologies

Ac transport studies in polymers by a resistor network and transfer matrix approaches: application to polyaniline

A statistical model of resistor network is proposed to describe a polymer structure and to simulate the real and imaginary components of its ac resistivity. It takes into account the polydispersiveness of the material as well as intrachain and interchain charge transport processes. By the application of a transfer matrix technique, it reproduces ac resistivity measurements carried out with polyaniline films in different doping degrees and at different temperatures. Our results indicate that interchain processes govern the resistivity behavior in the low frequency region while, for higher frequencies, intrachain mechanisms are dominant.Comment: LaTeX file, 15 pages, 5 ps figures, to appear in Phys. Rev.

Laminar composite structures for high power actuators

Twisted laminar composite structures for high power and large-stroke actuators based on coiled Multi Wall Carbon Nanotube (MWNT) composite yarns were crafted by integrating high-density Nanoenergetic Gas Generators (NGGs) into carbon nanotube sheets. The linear actuation force, resulting from the pneumatic force caused by expanding gases confined within the pores of laminar structures and twisted carbon nanotube yarns, can be further amplified by increasing NGG loading and yarns twist density, as well as selecting NGG compositions with high energy density and large-volume gas generation. Moreover, the actuation force and power can be tuned by the surrounding environment, such as to increase the actuation by combustion in ambient air. A single 300-μm-diameter integrated MWNT/NGG coiled yarn produced 0.7 MPa stress and a contractile specific work power of up to 4.7 kW/kg, while combustion front propagated along the yarn at a velocity up to 10 m/s. Such powerful yarn actuators can also be operated in a vacuum, enabling their potential use for deploying heavy loads in outer space, such as to unfold solar panels and solar sails

A Nonzero Gap Two-Dimensional Carbon Allotrope from Porous Graphene

Graphene is considered one of the most promising materials for future electronic. However, in its pristine form graphene is a gapless material, which imposes limitations to its use in some electronic applications. In order to solve this problem many approaches have been tried, such as, physical and chemical functionalizations. These processes compromise some of the desirable graphene properties. In this work, based on ab initio quantum molecular dynamics, we showed that a two-dimensional carbon allotrope, named biphenylene carbon (BPC) can be obtained from selective dehydrogenation of porous graphene. BPC presents a nonzero bandgap and well-delocalized frontier orbitals. Synthetic routes to BPC are also addressed.Comment: Published on J. Phys. Chem. C, 2012, 116 (23), pp 12810-1281