10,709 research outputs found
Simulation of an enhanced TCAS 2 system in operation
Described is a computer simulation of a Boeing 737 aircraft equipped with an enhanced Traffic and Collision Avoidance System (TCAS II). In particular, an algorithm is developed which permits the computer simulation of the tracking of a target airplane by a Boeing 373 which has a TCAS II array mounted on top of its fuselage. This algorithm has four main components: namely, the target path, the noise source, the alpha-beta filter, and threat detection. The implementation of each of these four components is described. Furthermore, the areas where the present algorithm needs to be improved are also mentioned
A study of a collision avoidance system mounted on a curved ground plane
Research conducted on a traffic advisory and collision avoidance system (TCAS 2) mounted on a curved ground plane is described. It is found that a curved finite ground plane can be used as a good simulation model for the fuselage of an aircraft but may not be good enough to model a whole aircraft due to the shadowing of the vertical stabilizer, wings, etc. The surface curvature of this curved disc significantly affects the monopulse characteristics in the azimuth plane but not as much in the elevation plane. These variations of the monopulse characteristics verify the need of a lookup table for the 64 azimuth beam positions. The best location of a TCAS 2 array on a Boeing 737 is to move it as far from the vertical stabilizer as possible
Simulation of the enhanced traffic alert and collision avoidance system (TCAS 2)
The OSU aircraft code is used to analyze and simulate the TCAS 2 circular array which is mounted on the fuselage of a Boeing 737 aircraft. It is shown that the sum and difference patterns radiated by the circular array are distorted by the various structures of the aircraft, i.e., wings, tail, etc. Furthermore, monopulse curves are calculated and plotted for several beam positions and THETA angles. As expected, the worst cases of distortion occur when the beams are pointed toward the tail of the aircraft
Polarization and frequency disentanglement of photons via stochastic polarization mode dispersion
We investigate the quantum decoherence of frequency and polarization
variables of photons via polarization mode dispersion in optical fibers. By
observing the analogy between the propagation equation of the field and the
Schr\"odinger equation, we develop a master equation under Markovian
approximation and analytically solve for the field density matrix. We identify
distinct decay behaviors for the polarization and frequency variables for
single-photon and two-photon states. For the single photon case, purity
functions indicate that complete decoherence for each variable is possible only
for infinite fiber length. For entangled two-photon states passing through
separate fibers, entanglement associated with each variable can be completely
destroyed after characteristic finite propagation distances. In particular, we
show that frequency disentanglement is independent of the initial polarization
status. For propagation of two photons in a common fiber, the evolution of a
polarization singlet state is addressed. We show that while complete
polarization disentanglement occurs at a finite propagation distance, frequency
entanglement could survive at any finite distance for gaussian states.Comment: 2 figure
Non-Markovian master equation for a damped oscillator with time-varying parameters
We derive an exact non-Markovian master equation that generalizes the
previous work [Hu, Paz and Zhang, Phys. Rev. D {\bf 45}, 2843 (1992)] to damped
harmonic oscillators with time-varying parameters. This is achieved by
exploiting the linearity of the system and operator solution in Heisenberg
picture. Our equation governs the non-Markovian quantum dynamics when the
system is modulated by external devices. As an application, we apply our
equation to parity kick decoupling problems. The time-dependent dissipative
coefficients in the master equation are shown to be modified drastically when
the system is driven by pulses. For coherence protection to be effective,
our numerical results indicate that kicking period should be shorter than
memory time of the bath. The effects of using soft pulses in an ohmic bath are
also discussed
Dynamic and Energetic Stabilization of Persistent Currents in Bose-Einstein Condensates
We study conditions under which vortices in a highly oblate harmonically
trapped Bose-Einstein condensate (BEC) can be stabilized due to pinning by a
blue-detuned Gaussian laser beam, with particular emphasis on the potentially
destabilizing effects of laser beam positioning within the BEC. Our approach
involves theoretical and numerical exploration of dynamically and energetically
stable pinning of vortices with winding number up to , in correspondence
with experimental observations. Stable pinning is quantified theoretically via
Bogoliubov-de Gennes excitation spectrum computations and confirmed via direct
numerical simulations for a range of conditions similar to those of
experimental observations. The theoretical and numerical results indicate that
the pinned winding number, or equivalently the winding number of the superfluid
current about the laser beam, decays as a laser beam of fixed intensity moves
away from the BEC center. Our theoretical analysis helps explain previous
experimental observations, and helps define limits of stable vortex pinning for
future experiments involving vortex manipulation by laser beams.Comment: 8 pages 5 figure
Energy focusing inside a dynamical cavity
We study the exact classical solutions for a real scalar field inside a
cavity with a wall whose motion is self-consistently determined by the pressure
of the field itself. We find that, regardless of the system parameters, the
long-time solution always becomes nonadiabatic and the field's energy
concentrates into narrow peaks, which we explain by means of a simple
mechanical system. We point out implications for the quantized theory.Comment: 5 pages, 6 figures, double column, submitted to P.R.
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