2,007 research outputs found
Droplet monitoring probe
A droplet monitoring system is disclosed for analysis of mixed-phase fluid flow in development of gas turbines. The system uses a probe comprising two electrical wires spaced a known distance apart and connected at one end to means for establishing a dc potential between the wires. A drop in the fluid stream momentarily contacting both wires simultaneously causes and electrical signal which is amplified, detected and counted
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
Mechanically induced current and quantum evaporation from Luttinger liquids
We investigate transport through a tunnelling junction between an
uncorrelated metallic lead and a Luttinger liquid when the latter is subjected
to a time dependent perturbation. The tunnelling current as well as the
electron energy distribution function are found to be strongly affected by the
perturbation due to generation of harmonics in the density oscillations. Using
a semiconducting lead instead of a metallic one results in electrons being
injected into the lead even without applied voltage. Some applications to
carbon nanotubes are discussed.Comment: 7 pages, 2 figures (eps files
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
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.
Anomalous Coherent Backscattering of Light from Opal Photonic Crystals
We studied coherent backscattering (CBS) of light from opal photonic crystals
in air at different incident inclination angles, wavelengths and along various
[hkl] directions inside the opals. Similar to previously obtained CBS cones
from various random media, we found that when Bragg condition with the incident
light beam is not met then the CBS cones from opals show a triangular line
shape in excellent agreement with light diffusion theory. At Bragg condition,
however, we observed a dramatic broadening of the opal CBS cones that depends
on the incident angle and [hkl] direction. This broadening is explained as due
to the light intensity decay in course of propagation along the Bragg direction
{\em before the first} and {\em after the last} scattering events. We modified
the CBS theory to incorporate the attenuation that results from the photonic
band structure of the medium. Using the modified theory we extract from our CBS
data the light mean free path and Bragg attenuation length at different [hkl].
Our study shows that CBS measurements are a unique experimental technique to
explore photonic crystals with disorder, when other spectroscopical methods
become ambiguous due to disorder-induced broadening.Comment: 10 pages, 5 figure
Elastomeric spring actuator using nylon wires
Medical devices are designed for collaboration with the human body, which makes the steps to create them increasingly more complex if the device is to be implanted. Soft robots have the unique potential of meeting both the mechanical compliance with the interacting tissues and the controlled functionality needed for a repair or replacement. Soft devices that fulfill fundamental mechanical roles are needed as parts of soft robots in order to carry out desired tasks. As the medical devices become increasingly low-profile, soft devices must feature multi-functionality that is embedded in the structure. A device embedded with nylon actuators allows for the controlled collapsing of an elastomeric spring by compression alone or compression and twisting. In this paper we present the concept of a novel elastomeric spring, its fabrication and mechanical characterization
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
- …