22,354 research outputs found
A particulate basis for a lattice-gas model of amphiphilic fluids
We show that the flux-field expansion derived by Boghosian and Coveney for
the Rothman-Keller immiscible fluid model can be derived in a simpler and more
general way in terms of the completely symmetric tensor kernels introduced by
those authors. Using this generalised flux-field expansion we show that the
more complex amphiphilic model of Boghosian Coveney and Emerton can also be
derived from an underlying model of particle interactions. The consequences of
this derivation are discussed in the context of previous equilibrium Ising-like
lattice models and other non-equilibrium mesoscale models.Comment: To appear in Phil. Trans. Roy. Soc. (Proceedings of the Xth
International Conference on Discrete Simulation of Fluid Dynamics.
From Dirac to Diffusion: Decoherence in Quantum Lattice Gases
We describe a model for the interaction of the internal (spin) degree of
freedom of a quantum lattice-gas particle with an environmental bath. We impose
the constraints that the particle-bath interaction be fixed, while the state of
the bath is random, and that the effect of the particle-bath interaction be
parity invariant. The condition of parity invariance defines a subgroup of the
unitary group of actions on the spin degree of freedom and the bath. We derive
a general constraint on the Lie algebra of the unitary group which defines this
subgroup, and hence guarantees parity invariance of the particle-bath
interaction. We show that generalizing the quantum lattice gas in this way
produces a model having both classical and quantum discrete random walks as
different limits. We present preliminary simulation results illustrating the
intermediate behavior in the presence of weak quantum noise.Comment: To appear in QI
High altitude gust acceleration environment as experienced by a supersonic airplane
High altitude turbulence experienced at supersonic speeds is described in terms of gust accelerations measured on the YF-12A airplane. The data were obtained during 90 flights at altitudes above 12.2 kilometers (40,000 feet). Subjective turbulence intensity ratings were obtained from air crew members. The air crew often rated given gust accelerations as being more intense during high altitude supersonic flight than during low altitude subsonic flight. The portion of flight distance in turbulence ranged from 6 percent to 8 percent at altitudes between 12.2 kilometers and 16.8 kilometers (40,000 feet and 55,000 feet) to less than 1 percent at altitudes above 18.3 kilometers (60,000 feet). The amount of turbulence varied with season, increasing by a factor of 3 or more from summer to winter. Given values of gust acceleration were less frequent, on the basis of distance traveled, for supersonic flight of the YF-12A airplane at altitudes above 12.2 kilometers (40,000 feet) than for subsonic flight of a jet passenger airplane at altitudes below 12.2 kilometers (40,000 feet). The median thickness of high altitude turbulence patches was less than 400 meters (1300 feet); the median length was less than 16 kilometers (10 miles). The distribution of the patch dimensions tended to be log normal
Common Codebook Millimeter Wave Beam Design: Designing Beams for Both Sounding and Communication with Uniform Planar Arrays
Fifth generation (5G) wireless networks are expected to utilize wide
bandwidths available at millimeter wave (mmWave) frequencies for enhancing
system throughput. However, the unfavorable channel conditions of mmWave links,
e.g., higher path loss and attenuation due to atmospheric gases or water vapor,
hinder reliable communications. To compensate for these severe losses, it is
essential to have a multitude of antennas to generate sharp and strong beams
for directional transmission. In this paper, we consider mmWave systems using
uniform planar array (UPA) antennas, which effectively place more antennas on a
two-dimensional grid. A hybrid beamforming setup is also considered to generate
beams by combining a multitude of antennas using only a few radio frequency
chains. We focus on designing a set of transmit beamformers generating beams
adapted to the directional characteristics of mmWave links assuming a UPA and
hybrid beamforming. We first define ideal beam patterns for UPA structures.
Each beamformer is constructed to minimize the mean squared error from the
corresponding ideal beam pattern. Simulation results verify that the proposed
codebooks enhance beamforming reliability and data rate in mmWave systems.Comment: 14 pages, 10 figure
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