7,514 research outputs found
Random matrices with equispaced external source
We study Hermitian random matrix models with an external source matrix which
has equispaced eigenvalues, and with an external field such that the limiting
mean density of eigenvalues is supported on a single interval as the dimension
tends to infinity. We obtain strong asymptotics for the multiple orthogonal
polynomials associated to these models, and as a consequence for the average
characteristic polynomials. One feature of the multiple orthogonal polynomials
analyzed in this paper is that the number of orthogonality weights of the
polynomials grows with the degree. Nevertheless we are able to characterize
them in terms of a pair of 2 x 1 vector-valued Riemann-Hilbert problems, and to
perform an asymptotic analysis of the Riemann-Hilbert problems.Comment: 53 pages, 9 figures; textual changes and minor typos correcte
VHDL-AMS based genetic optimisation of fuzzy logic controllers
Purpose â This paper presents a VHDL-AMS based genetic optimisation methodology for fuzzy logic controllers (FLCs) used in complex automotive systems and modelled in mixed physical domains. A case study applying this novel method to an active suspension system has been investigated to obtain a new type of fuzzy logic membership function with irregular shapes optimised for best performance. Design/methodology/approach â The geometrical shapes of the fuzzy logic membership functions are irregular and optimised using a genetic algorithm (GA). In this optimisation technique, VHDL-AMS is used not only for the modelling and simulation of the FLC and its underlying active suspension system but also for the implementation of a parallel GA directly in the system testbench. Findings â Simulation results show that the proposed FLC has superior performance in all test cases to that of existing FLCs that use regular-shape, triangular or trapezoidal membership functions. Research limitations â The test of the FLC has only been done in the simulation stage, no physical prototype has been made. Originality/value â This paper proposes a novel way of improving the FLCâs performance and a new application area for VHDL-AMS
VHDL-AMS based genetic optimization of a fuzzy logic controller for automotive active suspension systems
This paper presents a new type of fuzzy logic controller (FLC) membership functions for automotive active suspension systems. The shapes of the membership functions are irregular and optimized using a genetic algorithm (GA). In this optimization technique, VHDL-AMS is used not only for the modeling and simulation of the fuzzy logic controller and its underlying active suspension system but also for the implementation of a parallel GA. Simulation results show that the proposed FLC has superior performance to that of existing FLCs that use triangular or trapezoidal membership functions
VHDL-AMS modeling of an automotive vibration isolation seating system
This paper presents VHDL-AMS model of an automotive vibration isolation seating system with an active electromechanical actuator. Five control algorithms for the actuator are implemented and their efficiencies are investigated by subjecting the system to a number of stimuli, such as a single jolt or noisy harmonic excitations. Simulations were carried out using the SystemVision simulator and results are shown to compare the relative performance merits of the control methods
Adaptive Mesh Fluid Simulations on GPU
We describe an implementation of compressible inviscid fluid solvers with
block-structured adaptive mesh refinement on Graphics Processing Units using
NVIDIA's CUDA. We show that a class of high resolution shock capturing schemes
can be mapped naturally on this architecture. Using the method of lines
approach with the second order total variation diminishing Runge-Kutta time
integration scheme, piecewise linear reconstruction, and a Harten-Lax-van Leer
Riemann solver, we achieve an overall speedup of approximately 10 times faster
execution on one graphics card as compared to a single core on the host
computer. We attain this speedup in uniform grid runs as well as in problems
with deep AMR hierarchies. Our framework can readily be applied to more general
systems of conservation laws and extended to higher order shock capturing
schemes. This is shown directly by an implementation of a magneto-hydrodynamic
solver and comparing its performance to the pure hydrodynamic case. Finally, we
also combined our CUDA parallel scheme with MPI to make the code run on GPU
clusters. Close to ideal speedup is observed on up to four GPUs.Comment: Submitted to New Astronom
Effect of influent nutrient ratios and hydraulic retention time (HRT) on simultaneous phosphorus and nitrogen removal in a two-sludge sequencing batch reactor process
A laboratory-scale anaerobicâanoxic/nitrification sequencing batch reactor (A2N-
SBR) fed with domestic wastewater was operated to examine the effect of varying
ratios of influent COD/P, COD/TN and TN/P on the nutrient removal. With the
increased COD/P, the phosphorus removals exhibited an upward trend. The influent
TN/P ratios had a positive linear correlation with the phosphorus removal
efficiencies, mainly because nitrates act as electron acceptors for the
phosphorus uptake in the A2N-SBR. Moreover, it was found that lower COD/TN
ratio, e.g. 3.5, did not significantly weaken the phosphorus removal, though the
nitrogen removal first decreased greatly. The optimal phosphorus and nitrogen
removals of 94% and 91%, respectively were achieved with influent COD/P and COD/
TN ratios of 19.9 and 9.9, respectively. Additionally, a real-time control
strategy for A2N-SBR can be undertaken based on some characteristic points of
pH, redox potential (ORP) and dissolved oxygen (DO) profiles in order to obtain
the optimum hydraulic retention time (HRT) and improve the operating reliabili
SystemC-A modeling of an automotive seating vibration isolation system
A modeling methodology for mixed physical domains system in a new modelling Language is presented. The system is automotive seating vibration isolation system with electronic control. It is described and simulated in SystemCA, an extended version of SystemC which provides analogue, mixed-signal and mixed-domain modeling capabilities. Results show that SystemC-A provides efficient means to model and investigate performance of complex mixed-domain systems for automotive applications
Automatic Brain Tumor Segmentation using Cascaded Anisotropic Convolutional Neural Networks
A cascade of fully convolutional neural networks is proposed to segment
multi-modal Magnetic Resonance (MR) images with brain tumor into background and
three hierarchical regions: whole tumor, tumor core and enhancing tumor core.
The cascade is designed to decompose the multi-class segmentation problem into
a sequence of three binary segmentation problems according to the subregion
hierarchy. The whole tumor is segmented in the first step and the bounding box
of the result is used for the tumor core segmentation in the second step. The
enhancing tumor core is then segmented based on the bounding box of the tumor
core segmentation result. Our networks consist of multiple layers of
anisotropic and dilated convolution filters, and they are combined with
multi-view fusion to reduce false positives. Residual connections and
multi-scale predictions are employed in these networks to boost the
segmentation performance. Experiments with BraTS 2017 validation set show that
the proposed method achieved average Dice scores of 0.7859, 0.9050, 0.8378 for
enhancing tumor core, whole tumor and tumor core, respectively. The
corresponding values for BraTS 2017 testing set were 0.7831, 0.8739, and
0.7748, respectively.Comment: 12 pages, 5 figures. MICCAI Brats Challenge 201
Correlation kernels for sums and products of random matrices
Let be a random matrix whose squared singular value density is a
polynomial ensemble. We derive double contour integral formulas for the
correlation kernels of the squared singular values of and , where
is a complex Ginibre matrix and is a truncated unitary matrix. We also
consider the product of and several complex Ginibre/truncated unitary
matrices. As an application, we derive the precise condition for the squared
singular values of the product of several truncated unitary matrices to follow
a polynomial ensemble. We also consider the sum where is a GUE
matrix and is a random matrix whose eigenvalue density is a polynomial
ensemble. We show that the eigenvalues of follow a polynomial ensemble
whose correlation kernel can be expressed as a double contour integral. As an
application, we point out a connection to the two-matrix model.Comment: 33 pages, some changes suggested by the referee is made and some
references are adde
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