48,875 research outputs found
Predicting Stream Nitrogen Concentration From Watershed Features Using Neural Networks
The present work describes the development and validation of an artificial neural network (ANN) for the purpose of estimating inorganic and total nitrogen concentrations. The ANN approach has been developed and tested using 927 nonpoint source watersheds studied for relationships between macro-drainage area characteristics and nutrient levels in streams. The ANN had eight independent input variables of watershed parameters (five on land use features, mean annual precipitation, animal unit density and mean stream flow) and two dependent output variables (total and inorganic nitrogen concentrations in the stream). The predictive quality of ANN models was judged with “hold-out” validation procedures. After ANN learning with the training set of data, we obtained a correlation coefficient r of about 0.85 in the testing set. Thus, ANNs are capable of learning the relationships between drainage area characteristics and nitrogen levels in streams, and show a high ability to predict from the new data set. On the basis of the sensitivity analyses we established the relationship between nitrogen concentration and the eight environmental variables
Chosen-plaintext attack of an image encryption scheme based on modified permutation-diffusion structure
Since the first appearance in Fridrich's design, the usage of
permutation-diffusion structure for designing digital image cryptosystem has
been receiving increasing research attention in the field of chaos-based
cryptography. Recently, a novel chaotic Image Cipher using one round Modified
Permutation-Diffusion pattern (ICMPD) was proposed. Unlike traditional
permutation-diffusion structure, the permutation is operated on bit level
instead of pixel level and the diffusion is operated on masked pixels, which
are obtained by carrying out the classical affine cipher, instead of plain
pixels in ICMPD. Following a \textit{divide-and-conquer strategy}, this paper
reports that ICMPD can be compromised by a chosen-plaintext attack efficiently
and the involved data complexity is linear to the size of the plain-image.
Moreover, the relationship between the cryptographic kernel at the diffusion
stage of ICMPD and modulo addition then XORing is explored thoroughly
A rewriting grammar for heat exchanger network structure evolution with stream splitting
The design of cost optimal heat exchanger networks is a difficult optimisation problem due
both to the nonlinear models required and also the combinatorial size of the search space.
When stream splitting is considered, the combinatorial aspects make the problem even harder.
This paper describes the implementation of a two level evolutionary algorithm based on a
string rewriting grammar for the evolution of the heat exchanger network structure. A biological analogue of genotypes and phenotypes is used to describe structures and specific solutions respectively. The top level algorithm evolves structures while the lower level optimises specific
structures. The result is a hybrid optimisation procedure which can identify the best structures including stream splitting. Case studies from the literature are presented to demonstrate the capabilities of the novel procedure
Estimation of an initial condition of sigma-delta modulators via projection onto convex sets
Abstract—In this paper, an initial condition of strictly causal
rational interpolative sigma-delta modulators (SDMs) is
estimated based on quantizer output bit streams and an input
signal. A set of initial conditions generating bounded trajectories
is characterized. It is found that a set of initial conditions
generating bounded trajectories but not necessarily
corresponding to quantizer output bit streams is convex. Also, it is
found that a set of initial conditions corresponding to quantizer
output bit streams but not necessarily generating bounded
trajectories is convex too. Moreover, it is found that an initial
condition both corresponding to quantizer output bit streams and
generating bounded trajectories is uniquely defined if the loop
filter is unstable (Here, an unstable loop filter refers to that with
at least one of its poles being strictly outside the unit circle). To
estimate that unique initial condition, a projection onto convex set
approach is employed. Numerical computer simulations show that
the employed method can estimate the initial condition effectively
- …