4,356 research outputs found
Computer techniques used for some enhancements of ERTS images
The JPL VICAR image processing system has been used for the enhancement of images received from the ERTS for the Arizona geology mapping experiment. This system contains flexible capabilities for reading and repairing MSS digital tape images, for geometric corrections and interpicture registration, for various enhancements and analyses of the data, and for display of the images in black and white and color
Epistemic insight and classrooms with permeable walls
The boundaries between subject disciplines in secondary education today make it difficult for students to see their subjects in context. However, examining the secondary curriculum in England shows that there are a wealth of opportunities for making links and helping to develop students’ epistemic insight and scholarly thought.
This article provides concrete examples of these opportunities and offers a view into ongoing research by the LASAR Centre at Canterbury Christ Church University (UK), which supports teachers in bridging subject boundaries through a strategy called Classrooms with Permeable Walls
Adaptive Transmission Techniques for Mobile Satellite Links
Adapting the transmission rate in an LMS channel is a challenging task
because of the relatively fast time variations, of the long delays involved,
and of the difficulty in mapping the parameters of a time-varying channel into
communication performance. In this paper, we propose two strategies for dealing
with these impairments, namely, multi-layer coding (MLC) in the forward link,
and open-loop adaptation in the return link. Both strategies rely on
physical-layer abstraction tools for predicting the link performance. We will
show that, in both cases, it is possible to increase the average spectral
efficiency while at the same time keeping the outage probability under a given
threshold. To do so, the forward link strategy will rely on introducing some
latency in the data stream by using retransmissions. The return link, on the
other hand, will rely on a statistical characterization of a physical-layer
abstraction measure.Comment: Presented at the 30th AIAA International Communications Satellite
Systems Conference (ICSSC), Ottawa, Canada, 2012. Best Professional Paper
Awar
An early warning indicator for atmospheric blocking events using transfer operators
The existence of persistent midlatitude atmospheric flow regimes with
time-scales larger than 5-10 days and indications of preferred transitions
between them motivates to develop early warning indicators for such regime
transitions. In this paper, we use a hemispheric barotropic model together with
estimates of transfer operators on a reduced phase space to develop an early
warning indicator of the zonal to blocked flow transition in this model. It is
shown that, the spectrum of the transfer operators can be used to study the
slow dynamics of the flow as well as the non-Markovian character of the
reduction. The slowest motions are thereby found to have time scales of three
to six weeks and to be associated with meta-stable regimes (and their
transitions) which can be detected as almost-invariant sets of the transfer
operator. From the energy budget of the model, we are able to explain the
meta-stability of the regimes and the existence of preferred transition paths.
Even though the model is highly simplified, the skill of the early warning
indicator is promising, suggesting that the transfer operator approach can be
used in parallel to an operational deterministic model for stochastic
prediction or to assess forecast uncertainty
Thermalisation of Local Observables in Small Hubbard Lattices
We present a study of thermalisation of a small isolated Hubbard lattice
cluster prepared in a pure state with a well-defined energy. We examine how a
two-site subsystem of the lattice thermalises with the rest of the system as
its environment. We explore numerically the existence of thermalisation over a
range of system parameters, such as the interaction strength, system size and
the strength of the coupling between the subsystem and the rest of the lattice.
We find thermalisation over a wide range of parameters and that interactions
are crucial for efficient thermalisation of small systems. We relate this
thermalisation behaviour to the eigenstate thermalisation hypothesis and
quantify numerically the extent to which eigenstate thermalisation holds. We
also verify our numerical results theoretically with the help of previously
established results from random matrix theory for the local density of states,
particularly the finite-size scaling for the onset of thermalisation.Comment: 22 pages, 23 figure
Atmospheric and Oceanographic Information Processing System (AOIPS) system description
The development of hardware and software for an interactive, minicomputer based processing and display system for atmospheric and oceanographic information extraction and image data analysis is described. The major applications of the system are discussed as well as enhancements planned for the future
Central limit behavior of deterministic dynamical systems
We investigate the probability density of rescaled sums of iterates of
deterministic dynamical systems, a problem relevant for many complex physical
systems consisting of dependent random variables. A Central Limit Theorem (CLT)
is only valid if the dynamical system under consideration is sufficiently
mixing. For the fully developed logistic map and a cubic map we analytically
calculate the leading-order corrections to the CLT if only a finite number of
iterates is added and rescaled, and find excellent agreement with numerical
experiments. At the critical point of period doubling accumulation, a CLT is
not valid anymore due to strong temporal correlations between the iterates.
Nevertheless, we provide numerical evidence that in this case the probability
density converges to a -Gaussian, thus leading to a power-law generalization
of the CLT. The above behavior is universal and independent of the order of the
maximum of the map considered, i.e. relevant for large classes of critical
dynamical systems.Comment: 6 pages, 5 figure
Mapping of hydrothermal alternation zones and regional rock types using computer enhanced ERTS MSS images
A combination of digital computer processing and color compositing of ERTS MSS images has been used to map hydrothermal alternation zones and regional rock types in south-central Nevada. The technique is based on enhancement of subtle visible and near infrared reflectivity differences between mineralogically dissimilar rocks, especially unaltered and altered rocks. MSS spectral bands are ratioed, pixel by pixel, in the computer and subsequently stretched. These ratio values are used to produce a new black and white image which shows the subtle spectral reflectivity differences. Additional enhancement is achieved by preparing color composites of two or more stretched ratio images. The choice of MSS bands for rationing depends on the spectral reflectance properties of the rocks to be discriminated. Although this technique is in the initial stage of development and is untested in other areas, it already appears to have considerable potential for targeting mineral prospects and for regional geologic mapping
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