8,344 research outputs found
Design of ternary signals for MIMO identification in the presence of noise and nonlinear distortion
A new approach to designing sets of ternary periodic signals with different periods for multi-input multi-output system identification is described. The signals are pseudo-random signals with uniform nonzero harmonics, generated from Galois field GF(q), where q is a prime or a power of a prime. The signals are designed to be uncorrelated, so that effects of different inputs can be easily decoupled. However, correlated harmonics can be included if necessary, for applications in the identification of ill-conditioned processes. A design table is given for q les 31. An example is presented for the design of five uncorrelated signals with a common period N = 168 . Three of these signals are applied to identify the transfer function matrix as well as the singular values of a simulated distillation column. Results obtained are compared with those achieved using two alternative methods
On the population of remnant FRII radio galaxies and implications for radio source dynamics
The purpose of this work is two-fold: (1) to quantify the occurrence of
ultra-steep spectrum remnant FRII radio galaxies in a 74 MHz flux limited
sample, and (2) perform Monte-Carlo simulations of the population of active and
remnant FRII radio galaxies to confront models of remnant lobe evolution, and
provide guidance for further investigation of remnant radio galaxies. We find
that fewer than 2 of FRII radio galaxies with S Jy are
candidate ultra-steep spectrum remnants, where we define ultra-steep spectrum
as . Our Monte-Carlo simulations
demonstrate that models involving Sedov-like expansion in the remnant phase,
resulting in rapid adiabatic energy losses, are consistent with this upper
limit, and predict the existence of nearly twice as many remnants with normal
(not ultra-steep) spectra in the observed frequency range as there are
ultra-steep spectrum remnants. This model also predicts an ultra-steep remnant
fraction approaching 10 at redshifts . Importantly, this model
implies the lobes remain over-pressured with respect to the ambient medium well
after their active lifetime, in contrast with existing observational evidence
that many FRII radio galaxy lobes reach pressure equilibrium with the external
medium whilst still in the active phase. The predicted age distribution of
remnants is a steeply decreasing function of age. In other words young remnants
are expected to be much more common than old remnants in flux limited samples.
For this reason, incorporating higher frequency data GHz will be of
great benefit to future studies of the remnant population.Comment: 19 pages, 8 figures, 4 table
The Aphids (Homoptera: Aphididae) Associated With Bell Peppers and Surrounding Vegetation in Southern Illinois
Outbreaks of cucumber mosaic virus (CMV) disease, caused by an aphid- transmitted pathogen, greatly reduced yields of bell pepper in southern Illinois in the mid-1990s. To provide the basis for further studies of the roles of individual apbid species in virus transmission, we surveyed aphid flights in and around pepper fields in 1996 and 1997 by using suction traps, interception nets, landing traps, sweep nets, and hand-picking. We collected 78 species of aphids, 15 of which have been reported to transmit CMV to peppers. The most abundant species taken from suction traps and interception nets in combination were Lipaphis erysimi, Rhopalosiphum padi, Rhopalosiphum maidis, Schizaphis graminum, and Aphis craccivora. All of these species are known to transmit CMV to peppers, but the phenology of R. maidis in Illinois suggests it is not the vector that brings CMV to pepper fields to initiate disease outbreaks. Brachycaudus helichrysi was relatively abundant in 1996 in May and June when a CMV outbreak may have been initiated; it was absent in 1997, and CMV infections were rare that season. Two species, Carolinaia carolinensis and Myzus hemerocallis were recorded for the first time in Illinois
Properties of the Strange Axial Mesons in the Relativized Quark Model
We studied properties of the strange axial mesons in the relativized quark
model. We calculated the decay constant in the quark model and showed how
it can be used to extract the mixing angle
() from the weak decay . The ratio is the most sensitive
measurement and also the most reliable since the largest of the theoretical
uncertainties factor out. However the current bounds extracted from the
TPC/Two-Gamma collaboration measurements are rather weak: we typically obtain
at 68\% C.L. We also calculated the
strong OZI-allowed decays in the pseudoscalar emission model and the flux-tube
breaking model and extracted a mixing angle of . Our analysis also indicates that the heavy quark limit does not give a
good description of the strange mesons.Comment: Revised version to be published in Phys. Rev. D. Minor changes. Latex
file uses revtex version 3 and epsfig, 4 postcript figures are attached. The
full postcript version with embedded figures is available at
ftp://ftp.physics.carleton.ca/pub/theory/godfrey/ocipc9512.ps.
Two gamma quarkonium and positronium decays with Two-Body Dirac equations of constraint dynamics
Two-Body Dirac equations of constraint dynamics provide a covariant framework
to investigate the problem of highly relativistic quarks in meson bound states.
This formalism eliminates automatically the problems of relative time and
energy, leading to a covariant three dimensional formalism with the same number
of degrees of freedom as appears in the corresponding nonrelativistic problem.
It provides bound state wave equations with the simplicity of the
nonrelativistic Schroedinger equation. Unlike other three-dimensional
truncations of the Bethe-Salpeter equation, this covariant formalism has been
thoroughly tested in nonperturbatives contexts in QED, QCD, and nucleon-nucleon
scattering. Here we continue the important studies of this formalism by
extending a method developed earlier for positronium decay into two photons to
tests on the sixteen component quarkonium wave function solutions obtained in
meson spectroscopy. We examine positronium decay and then the two-gamma
quarkonium decays of eta_c, eta'_c, chi_0c, chi_2c, and pi-zero The results for
the pi-zero, although off the experimental rate by 13%, is much closer than the
usual expectations from a potential model.Comment: 4 pages. Presented at Second Meeting of APS Topical Group on Hadron
Physics, Nashville, TN, Oct 22-24. Proceedings to be published by Journal of
Physics (UK), Conference Serie
An Investigation into Delta Wing Vortex Generators as a Means of Increasing Algae Biofuel Raceway Vertical Mixing Including an Analysis of the Resulting Turbulence Characteristics
Algae-derived biodiesel is currently under investigation as a suitable alternative to traditional fossil-fuels. Though it possesses many favorable characteristics, algae remains prohibitively expensive to mass produce and distribute. The most economical means of growing algae are large-scale open pond raceways. These, however, suffer from low culture densities; this fact impacts the cost directly through diminished productivity, as well as indirectly by raising costs due to the necessity of dewatering low culture density raceway effluent. Algae, as a photosynthetic organism, achieves higher culture densities when sufficient light is provided. In open ponds this can be accomplished by frequently cycling algae to the raceway surface. The current work examined delta wing vortex generators as a means of instigating this cycling motion. In particular the impact of spacing and angle of attack was analyzed. These vortex generators were found to significantly increase vertical mixing when placed in a series, developing precisely the motion desired. Their impact on power requirements was also examined. Specifically it was shown that increases in spacing and decreases in angle of attack result in lower power consumption. It was demonstrated that the most efficient mixing generation is achieved by larger spacings and smaller angles of attack. The impact that these devices had on raceway turbulence as measured by dissipation rate was also investigated and compared to published values for algae growth. Raceways were found to be significantly more turbulent than standard algae environments, and adding delta wings increased these levels further
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