2,413 research outputs found
Wetland mapping from digitized aerial photography
Computer assisted interpretation of small scale aerial imagery was found to be a cost effective and accurate method of mapping complex vegetation patterns if high resolution information is desired. This type of technique is suited for problems such as monitoring changes in species composition due to environmental factors and is a feasible method of monitoring and mapping large areas of wetlands. The technique has the added advantage of being in a computer compatible form which can be transformed into any georeference system of interest
Modelling the evolution of distributions : an application to major league baseball
We develop Bayesian techniques for modelling the evolution of entire distributions over time and apply them to the distribution of team performance in Major League baseball for the period 1901-2000. Such models offer insight into many key issues (e.g. competitive balance) in a way that regression-based models cannot. The models involve discretizing the distribution and then modelling the evolution of the bins over time through transition probability matrices. We allow for these matrices to vary over time and across teams. We find that, with one exception, the transition probability matrices (and, hence, competitive balance) have been remarkably constant across time and over teams. The one exception is the Yankees, who have outperformed all other teams
Structure and lattice dynamics of the wide band gap semiconductors MgSiN and MgGeN
We have determined the structural and lattice dynamical properties of the
orthorhombic, wide band gap semiconductors MgSiN and MgGeN using
density functional theory. In addition, we present structural properties and
Raman spectra of a MgSiN powder. The structural properties and lattice
dynamics of the orthorhombic systems are compared to wurtzite AlN. We find
clear differences in the lattice dynamics between MgSiN, MgGeN and
AlN, for example we find that the highest phonon frequency in MgSiN is
about 100~cm higher than the highest frequency in AlN and that
MgGeN is much softer. We also provide the Born effective charge tensors
and dielectric tensors of MgSiN, MgGeN and AlN. Phonon related
thermodynamic properties, such as the heat capacity and entropy, are in very
good agreement with available experimental results.Comment: 9 pages, 11 figures, 6 table
Exhaust of Underexpanded Jets from Finite Reservoirs
We examine the response of an underexpanded jet to a depleting, finite reservoir with
experiments and simulations. An open-ended shock tube facility with variable reservoir
length is used to obtain images of nitrogen and helium jet structures at successive instances
during the blowdown from initial pressure ratios of up to 250. The reservoir and ambient
pressures are simultaneously measured to obtain the instantaneous pressure ratio. We
estimate the time-scales for jet formation and reservoir depletion as a function of the specific
heat ratio of the gas and the initial pressure ratio. The jet structure formation time-scale
is found to become approximately independent of pressure ratio for ratios greater than
50. In the present work, no evidence of time-dependence in the Mach disk shock location
is observed for rates of pressure decrease associated with isentropic blowdown of a finite
reservoir while the pressure ratio is greater than 15. The shock location in the finite-
reservoir jet can be calculated from an existing empirical fit to infinite-reservoir jet data
evaluated at the instantaneous reservoir pressure. For pressure ratios below 15, however,
the present data deviate from a compilation of data for infinite-reservoir jets. A new fit
is obtained to data in the lower pressure regime. The self-similarity of the jet structure
is quantified and departure from similarity is noted to begin at pressure ratios lower than
about 15, approximately the same ratio which limits existing empirical fits
Ignition of thermally sensitive explosives between a contact surface and a shock
The dynamics of ignition between a contact surface and a shock wave is investigated using a
one-step reaction model with Arrhenius kinetics. Both large activation energy asymptotics and
high-resolution finite activation energy numerical simulations are employed. Emphasis is on comparing
and contrasting the solutions with those of the ignition process between a piston and a shock,
considered previously. The large activation energy asymptotic solutions are found to be qualitatively
different from the piston driven shock case, in that thermal runaway first occurs ahead of
the contact surface, and both forward and backward moving reaction waves emerge. These waves
take the form of quasi-steady weak detonations that may later transition into strong detonation
waves. For the finite activation energies considered in the numerical simulations, the results are
qualitatively different to the asymptotic predictions in that no backward weak detonation wave
forms, and there is only a weak dependence of the evolutionary events on the acoustic impedance
of the contact surface. The above conclusions are relevant to gas phase equation of state models.
However, when a large polytropic index more representative of condensed phase explosives is used,
the large activation energy asymptotic and finite activation energy numerical results are found to
be in quantitative agreement
Just keep grazing: Parrotfish grazing and dietary selectivity in the Florida Keys
Parrotfish have indirect positive effects on corals by grazing on macroalgae that competes for substrate space with corals. Parrotfish can also have a negative impact on corals by feeding on live coral. Feeding preferences are correlated to jaw morphology in parrotfishes. This study examined the feeding selectivity for two genera of parrotfish (Scarus and Sparisoma) in the Florida Keys to determine the impacts they have on coral reefs. On 14 reefs, fish censuses, behavioral surveys and substrate composition analysis were preformed to calculate selectivity indices for the various substrate types. The indices showed that parrotfish do exhibit selective feeding. Scarus had a significantly higher preference for turf and Sparisoma had a significantly higher preference for macroalgae. These results support life history theory that Scarus are excavators and Sparisoma are grazers as predicted by their jaw morphology. This project was partially supported by the Creative Inquiry program
Revenue divergence and competitive balance in a divisional sports league
The North American model of resource allocation in professional sports leagues is adapted for English (association) football. The theoretical relationship between revenue and competitive balance is shown to be robust with respect to changes in teams’ objectives and labour market conditions. Empirical revenue functions are reported for 1926-1999. These indicate a shift in the composition of demand favouring big-city teams and an increase in the sensitivity of revenue to performance. An analysis of match results in the FA Cup competition suggests an increase in competitive imbalance between teams at different levels of the league’s divisional hierarchy, as the theory suggests
Measurement of the hyperfine coupling constants and absolute energies of the and levels in atomic cesium
We report measurements of the hyperfine coupling constant for the $8p \
^2P_{1/2}^{133}\simA = 42.933 \: (8)8p
\ ^2P_{3/2}8p \
^2P_{1/2}8p \ ^2P_{3/2}$ states of cesium.Comment: 8 pages, 7 figures, 5 table
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