17,287 research outputs found
A fundamental approach to the sticking of insect residues to aircraft wings
The aircraft industry is concerned with the increase of drag on planes due to the sticking of insects on critical airfoil areas. The objectives of the present study were to investigate the effects of surface energy and elasticity on the number of insects sticking onto the polymer coatings on a modified aircraft wing and to determine the mechanism by which insects stick onto surfaces during high velocity impact. Analyses including scanning electron microscopy, electron spectroscopy for chemical analysis and contact angle measurements of uncoated and polymer coated aluminum surfaces were performed. A direct relation between the number of insects sticking on a sample and its surface energy was obtained. Since the sticky liquid from a burst open insect will not spread on the low energy surface, it will ball up providing poor adhesion between the insect debris and the surface. The incoming air flow can easily blow off the insect debris and thus reducing the number of insects that remain stuck on the surface. Also a direct relation between the number of insect sticking onto a surface and their modulus of elasticity was obtained
Instabilities and the roton spectrum of a quasi-1D Bose-Einstein condensed gas with dipole-dipole interactions
We point out the possibility of having a roton-type excitation spectrum in a
quasi-1D Bose-Einstein condensate with dipole-dipole interactions. Normally
such a system is quite unstable due to the attractive portion of the dipolar
interaction. However, by reversing the sign of the dipolar interaction using
either a rotating magnetic field or a laser with circular polarization, a
stable cigar-shaped configuration can be achieved whose spectrum contains a
`roton' minimum analogous to that found in helium II. Dipolar gases also offer
the exciting prospect to tune the depth of this `roton' minimum by directly
controlling the interparticle interaction strength. When the minimum touches
the zero-energy axis the system is once again unstable, possibly to the
formation of a density wave.Comment: 7 pages, 6 figures. Special Issue: "Ultracold Polar Molecules:
Formation and Collisions
Bose-Einstein condensation of trapped interacting spin-1 atoms
We investigate Bose-Einstein condensation of trapped spin-1 atoms with
ferromagnetic or antiferromagnetic two-body contact interactions. We adopt the
mean field theory and develop a Hartree-Fock-Popov type approximation in terms
of a semiclassical two-fluid model. For antiferromagnetic interactions, our
study reveals double condensations as atoms in the state never seem
to condense under the constraints of both the conservation of total atom number
and magnetization . For ferromagnetic interactions, however, triple
condensations can occur. Our results can be conveniently understood in terms of
the interplay of three factors: (anti) ferromagnetic atom-atom interactions,
conservation, and the miscibilities between and among different condensed
components.Comment: RevTex 4, 9 pages, 5 eps figures, to appear in Phys. Rev. A, vol 70,
p
Factors affecting the sticking of insects on modified aircraft wings
Past studies have shown that the surface energy of a polymer coating has an important effect on the sticking of insects to the surface. However, mechanical properties of polymer coatings such as elasticity may also be important. A further study is suggested using polymer coatings of known surface energy and modulus so that a better understanding of the mechanism of the sticking of insects to surfaces can be achieved. As the first step for the study, surface analysis and road tests were performed using elastomers having different energies and different moduli. The number of insects sticking to each elastomer was counted and compared from sample to sample and with a control (aluminum). An average height moment was also calculated and comparisons made between samples
Factors affecting the sticking of insects on modified aircraft wings
The adhesion of insects to aircraft wings is studied. Insects were collected in road tests in past studies and a large experimental error was introduced caused by the variability of insect flux. The presence of such errors has been detected by studying the insect distribution across an aluminum-strip covered half-cylinder mounted on the top of a car. After a nonuniform insect distribution (insect flux) was found from three road tests, a new arrangement of samples was developed. The feasibility of coating aircraft wing surfaces with polymers to reduce the number of insects sticking onto the surfaces was studied using fluorocarbon elastomers, styrene butadiene rubbers, and Teflon
Factors affecting the sticking of insects on modified aircraft wings
Previous work showed that the total number of insects sticking to an aluminum surface was reduced by coating the aluminum surface with elastomers. Due to a large number of possible experimental errors, no correlation between the modulus of elasticity, the elastomer, and the total number of insects sticking to a given elastomer was obtained. One of the errors assumed to be introduced during the road test is a variable insect flux so the number of insects striking one surface might be different from that striking another sample. To eliminate this source of error, the road test used to collect insects was simulated in a laboratory by development of an insect impacting technique using a pipe and high pressure compressed air. The insects are accelerated by a compressed air gun to high velocities and are then impacted with a stationary target on which the sample is mounted. The velocity of an object exiting from the pipe was determined and further improvement of the technique was achieved to obtain a uniform air velocity distribution
Probing energy barriers and quantum confined states of buried semiconductor heterostructures with ballistic carrier injection: An experimental study
A three-terminal spectroscopy that probes both subsurface energy barriers and
interband optical transitions in a semiconductor heterostructure is
demonstrated. A metal-base transistor with a unipolar p-type semiconductor
collector embedding InAs/GaAs quantum dots (QDs) is studied. Using
minority/majority carrier injection, ballistic electron emission spectroscopy
and its related hot-carrier scattering spectroscopy measures barrier heights of
a buried AlxGa1-xAs layer in conduction band and valence band respectively, the
band gap of Al0.4Ga0.6As is therefore determined as 2.037 +/- 0.009 eV at 9 K.
Under forward collector bias, interband electroluminescence is induced by the
injection of minority carriers with sub-bandgap kinetic energies. Three
emission peaks from InAs QDs, InAs wetting layer, and GaAs are observed in
concert with minority carrier injection.Comment: 11 pages, 4 figures, submitted to Physical Review
Probing dipolar effects with condensate shape oscillation
We discuss the low energy shape oscillations of a magnetic trapped atomic
condensate including the spin dipole interaction. When the nominal isotropic
s-wave interaction strength becomes tunable through a Feshbach resonance (e.g.
as for Rb atoms), anisotropic dipolar effects are shown to be detectable
under current experimental conditions [E. A. Donley {\it et al.}, Nature {\bf
412}, 295 (2001)].Comment: revised version, submitte
Suppressing decoherence and improving entanglement by quantum-jump-based feedback control in two-level systems
We study the quantum-jump-based feedback control on the entanglement shared
between two qubits with one of them subject to decoherence, while the other
qubit is under the control. This situation is very relevant to a quantum system
consisting of nuclear and electron spins in solid states. The possibility to
prolong the coherence time of the dissipative qubit is also explored. Numerical
simulations show that the quantum-jump-based feedback control can improve the
entanglement between the qubits and prolong the coherence time for the qubit
subject directly to decoherence
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