412 research outputs found
Processing techniques for improved radar detection in spiky clutter
The problem of improved radar detection of targets embedded in spiky clutter is
addressed. Two main areas where improvements may be possible are investigated,
namely improved clutter suppression by doppler filtering, and improved Constant False
Alarm Rate (CFAR) processing. The clutter suppression performance of several doppler
processors is quantified under a wide range of conditions. It is shown that in spatially
homogeneous clutter ideal optimal (Hsiao) filters offer 2 to 3 dB higher improvement
factor than conventional techniques. Adaptive Hsiao filters are evaluated under conditions
of spatially heterogeneous clutter, and it is shown that practical losses due to filter
adaptivity and spectral heterogeneity will outweigh the superior performance of ideal
Hsiao filters in homogeneous clutter. It is concluded that improved doppler filtering
offers little scope for improving detection performance in spiky clutter, and that more
significant benefits are to be gained through improved CFAR processing. The performance
of three current generation CFAR processors is evaluated in spatially uncorrelated
K-distributed clutter to quantify detection losses. It is shown that losses of in excess of
10 dB can be expected in spiky clutter. Reducing the loss by exploitation of any spatial
correlation of the underlying clutter power is investigated. To this end a mathematically
rigorous model for spatially correlated K-distributed clutter is derived. An improved
CFAR processor based on optimal weighting of reference cells is formulated and
evaluated. It is shown that in highly correlated clutter CFAR loss can be reduced by 2 to
5 dB compared to Cell Averaging CFAR processors. An alternative "RDT-CFAR"
processor is formulated to eliminate reliance on spatial correlation, and this is shown to
reduce CFAR loss by more than 10 dB in spectrally homogeneous spiky clutter.
However, an increase in false alarm rate in clutter without constant spectrum is
demonstrated. The RDT-CFAR processor has been modified to eliminate dependence on
surrounding range bins. The resulting "δ-CFAR" processor reduces CFAR loss by more
than 10 dB in even moderately spiky clutter. It is also immune to extraneous targets and
clutter edges, and its false alarm performance is insensitive to clutter spikiness
Applying close range digital photogrammetry in soil erosion studies
Soil erosion due to rainfall and overland flow is a significant environmental problem. Studying the phenomenon requires accurate high-resolution measurements of soil surface topography and morphology. Close range digital photogrammetry with an oblique convergent configuration is proposed in this paper as a useful technique for such measurements, in the context of a flume-scale experimental study. The precision of the technique is assessed by comparing triangulation solutions and the resulting DEMs with varying tie point distributions and control point measurements, as well as by comparing DEMs extracted from different images of the same surface. Independent measurements were acquired using a terrestrial laser scanner for comparison with a DEM derived from photogrammetry. The results point to the need for a stronger geometric configuration to improve precision. They also suggest that the camera lens models were not fully adequate for the large object depths in this study. Nevertheless, the photogrammetric output can provide useful topographical information for soil erosion studies, provided limitations of the technique are duly considered
Comparison of ground and aerial application of fungicide for control of Ascochyta blight in chickpeas
Non-Peer ReviewedAscochyta rabiei control from aerial and ground application was assessed near Saskatoon in 2003 and 2004. Each year, a site of about 12 ha was seeded to kabuli (cv. CDC Xena) chickpeas. At the first sign of disease, applications of fungicide were commenced and maintained at approximately 10-day intervals. In 2003, four applications (two with Headline (pyraclostrobin), two with Lance (boscalid)) were conducted. In 2004, the last Lance application was not done. Aerial application was made using a Cessna AgTruck applying 37 L/ha using CP nozzles emitting a spray with a VMD of approximately 271 μm. Ground applications were conducted using a Melroe SpraCoupe applying 100 L/ha using XR8003 nozzles with a VMD of approximately 246 μm. Disease ratings were done throughout the season, and seed yields were
taken at crop maturity. Disease incidence progressed to 80 to 90% in the untreated plots, and fungicide application reduced disease incidence (to 20 to 30%) and increased seed yield in both years. Disease incidence and seed yield were not affected by application method in either season
Modeling the dynamics of soil erosion and size-selective sediment transport over nonuniform topography in flume-scale experiments
Soil erosion and the associated nutrient fluxes can lead to severe degradation of surface waters. Given that both sediment transport and nutrient sorption are size selective, it is important to predict the particle size distribution (PSD) as well as the total amount of sediment being eroded. In this paper, a finite volume implementation of the Hairsine-Rose soil erosion model is used to simulate flume-scale experiments with detailed observations of soil erosion and sediment transport dynamics. The numerical implementation allows us to account for the effects of soil surface microtopography (measured using close range photogrammetry) on soil erosion. An in-depth discussion of the model parameters and the constraints is presented. The model reproduces the dynamics of sediment concentration and PSD well, although some discrepancies can be observed. The calibrated parameters are also consistent with independent data in the literature and physical reason. Spatial variations in the suspended and deposited sediment and an analysis of model sensitivity highlight the value of collecting distributed data for a more robust validation of the model and to enhance parametric determinacy. The related issues of spatial resolution and scale in erosion prediction are briefly discussed
Thermodynamics of Dipolar Chain Systems
The thermodynamics of a quantum system of layers containing perpendicularly
oriented dipolar molecules is studied within an oscillator approximation for
both bosonic and fermionic species. The system is assumed to be built from
chains with one molecule in each layer. We consider the effects of the
intralayer repulsion and quantum statistical requirements in systems with more
than one chain. Specifically, we consider the case of two chains and solve the
problem analytically within the harmonic Hamiltonian approach which is accurate
for large dipole moments. The case of three chains is calculated numerically.
Our findings indicate that thermodynamic observables, such as the heat
capacity, can be used to probe the signatures of the intralayer interaction
between chains. This should be relevant for near future experiments on polar
molecules with strong dipole moments.Comment: 15 pages, 5 figures, final versio
A coupled channel analysis of the centrally produced K+K- and pi+pi- final states in pp interactions at 450 GeV/c
A coupled channel analysis of the centrally produced K+K- and pi+pi- final
states has been performed in pp collisions at an incident beam momentum of 450
GeV/c. The pole positions and branching ratios to pipi and KK of the f0(980),
f0(1370), f0(1500) and f0(1710) have been determined. A systematic study of the
production properties of all the resonances observed in the pi+pi- and K+K-
channels has been performed.Comment: 16 pages, Latex, 5 Figure
Scalar Mesons in a Relativistic Quark Model with Instanton-Induced Forces
In a relativistic quark model with linear confinement and an
instanton-induced interaction which solves the - puzzle, scalar
mesons are found as almost pure SU(3) flavor states. This suggests a new
interpretation of the scalar nonet: We propose that the recently discovered
is not a glueball but the scalar (mainly)--octet meson for which
the decay mode is suppressed. The mainly--singlet state is
tentatively identified with the . The isovector and isodoublet states
correspond to the and , respectively.Comment: 10 pages including 2 uuencoded figures, RevTe
Discrimination of degrees of auditory performance from the digits-in-noise test based on hearing status
Objective: To discriminate among degrees of auditory performance of the Digits-in-Noise (DIN) test. Design: We performed Pearson’s correlations and age- and sex-adjusted linear regression models to examine the correlation between pure-tone average (PTA) from pure-tone audiometric tests and speech recognition thresholds (SRT) from the DIN test. Then, optimal SRT cut-points by PTA-defined hearing status (0–25 dB HL [normal], 26–40 dB HL [mild hearing loss], 41–50 dB HL [moderate hearing loss]) were compared across three methods: Youden, Nearest, and Liu. SRT-defined categories of auditory performance were compared to PTA-defined hearing categories to examine the convergence of similar categories. Study Sample: 3422 Rotterdam Study participants aged 51–98 years between 2011 and 2014 Results: The correlation between SRT and PTA was 0.65 (95% Confidence Interval: 0.63, 0.67) in the overall sample. The variability of SRT explained by PTA after age and sex adjustment was 54%. Optimal cut-points for the overall sample across the three methods were: ≤ −5.55 dB SNR (normal); > −5.55 to ≤ −3.80 dB SNR (insufficient performance); > −3.80 dB SNR (poor performance). When comparing the SRT- or PTA-defined categories, 59.8% had concordant hearing categories and 40.2% had discordant hearing categories. Conclusions: Discrimination of degrees of auditory performance may add greater utility of the DIN test
Experimental evidence for a vector-like behaviour of Pomeron exchange
Evidence is presented that the Pomeron act as a non-conserved vector current.
A study has been made of the azimuthal angle phi, which is defined as the angle
between the pT vectors of the two outgoing protons, in the reaction pp ->
pp(X0) for those resonances (X0) which are compatible with being produced by
double Pomeron exchange. These distributions have been compared with a model
which describes the Pomeron as a non-conserved vector current and a qualitative
agreement is found. In addition, when one of the particles exchanged is known
to have spin 0, namely pi-Pomeron exchange, the phi distribution is flat.Comment: 13 pages, Latex, 4 Figure
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