17,173 research outputs found
Chebyshev Polynomial Approximation for Distributed Signal Processing
Unions of graph Fourier multipliers are an important class of linear
operators for processing signals defined on graphs. We present a novel method
to efficiently distribute the application of these operators to the
high-dimensional signals collected by sensor networks. The proposed method
features approximations of the graph Fourier multipliers by shifted Chebyshev
polynomials, whose recurrence relations make them readily amenable to
distributed computation. We demonstrate how the proposed method can be used in
a distributed denoising task, and show that the communication requirements of
the method scale gracefully with the size of the network.Comment: 8 pages, 5 figures, to appear in the Proceedings of the IEEE
International Conference on Distributed Computing in Sensor Systems (DCOSS),
June, 2011, Barcelona, Spai
International R&D Spillovers Between U.S. and Japanese R&D Intensive Sectors
A great deal of empirical evidence shows that a country's production structure and productivity growth depend on its own R&D capital formation. With the growing role of international trade, foreign investment and international knowledge diffusion, domestic production and productivity also depend on the R&D activities of other countries. The purpose of this paper is to empirically investigate the bilateral link between the U.S. and Japanese economies in terms of how R&D capital formation in one country affects the production structure, physical and R&D capital accumulation, and productivity growth in the other country. We find that production processes become less labor intensive as international R&D spillovers grow. In the short-run, R&D intensity is complementary to the international spillover. This relationship persists in the long-run for the U.S., but the Japanese decrease their own R&D intensity. U.S. R&D capital accounts for 60% of Japanese total factor productivity growth, while Japanese R&D capital contributes 20% to U.S. productivity gains. International spillovers cause social rates of return to be about four times the private returns.
A Multiscale Pyramid Transform for Graph Signals
Multiscale transforms designed to process analog and discrete-time signals
and images cannot be directly applied to analyze high-dimensional data residing
on the vertices of a weighted graph, as they do not capture the intrinsic
geometric structure of the underlying graph data domain. In this paper, we
adapt the Laplacian pyramid transform for signals on Euclidean domains so that
it can be used to analyze high-dimensional data residing on the vertices of a
weighted graph. Our approach is to study existing methods and develop new
methods for the four fundamental operations of graph downsampling, graph
reduction, and filtering and interpolation of signals on graphs. Equipped with
appropriate notions of these operations, we leverage the basic multiscale
constructs and intuitions from classical signal processing to generate a
transform that yields both a multiresolution of graphs and an associated
multiresolution of a graph signal on the underlying sequence of graphs.Comment: 16 pages, 13 figure
Spectrum-Adapted Tight Graph Wavelet and Vertex-Frequency Frames
We consider the problem of designing spectral graph filters for the
construction of dictionaries of atoms that can be used to efficiently represent
signals residing on weighted graphs. While the filters used in previous
spectral graph wavelet constructions are only adapted to the length of the
spectrum, the filters proposed in this paper are adapted to the distribution of
graph Laplacian eigenvalues, and therefore lead to atoms with better
discriminatory power. Our approach is to first characterize a family of systems
of uniformly translated kernels in the graph spectral domain that give rise to
tight frames of atoms generated via generalized translation on the graph. We
then warp the uniform translates with a function that approximates the
cumulative spectral density function of the graph Laplacian eigenvalues. We use
this approach to construct computationally efficient, spectrum-adapted, tight
vertex-frequency and graph wavelet frames. We give numerous examples of the
resulting spectrum-adapted graph filters, and also present an illustrative
example of vertex-frequency analysis using the proposed construction
Effect of reinforcing submicron SiC particles on the wear of electrolytic NiP coatings Part 1. Uni-directional sliding
As-plated and annealed NiP coatings and composite NiP-SiC coatings were investigated in uni-directional ball-on-disc sliding tests. Abrasive wear was noticed in the case of composite NiP coatings containing submicron SiC particles, whereas in NiP coatings oxidational wear was active. The addition of submicron SiC particles not only increases the hardness of these electrolytic coatings but also hinders the formation of an oxide film in the sliding wear track. As a consequence, the wear loss on as-plated NiP coatings is not markedly reduced by the addition of SiC particles. On the contrary, a heat treatment at 420 °C for 1 h decreases the wear loss on both pure NiP and composite NiP-SiC coatings. During that heat treatment, Ni3P precipitates are formed in the NiP matrix and owing to this fact, the hardness of both pure NiP and composite NiP-SiC coatings increases. However, the heat treatment of composite NiP-SiC coatings induces the sensitivity for crack formation in the NiP matrix around these SiC particles. As a result, the pull out of SiC particles in the wear track occurs easily during sliding, and the wear loss of composite NiP-SiC coatings remains above the wear loss on NiP coatings
Effect of reinforcing submicron SiC particles on the wear of electrolytic NiP coatings Part 2: Bi-directional sliding
As-plated and heat-treated electrodeposited NiP and composite NiP-SiC coatings were investigated in bi-directional ball-on-disc sliding tests. All tests were performed under gross slip conditions. Heat treatment decreases the wear volume loss during fretting in ambient air for all coatings investigated. Heat-treated NiP coating has a lower wear volume loss compared to composite NiP-SiC coatings for all sliding tests. The wear rate at the bi-directional sliding test was found to be lower relative to the wear rate at uni-directional sliding test
Momentum distribution and coherence of a weakly interacting Bose gas after a quench
We consider a weakly interacting uniform atomic Bose gas with a
time-dependent nonlinear coupling constant. By developing a suitable Bogoliubov
treatment we investigate the time evolution of several observables, including
the momentum distribution, the degree of coherence in the system, and their
dependence on dimensionality and temperature. We rigorously prove that the
low-momentum Bogoliubov modes remain frozen during the whole evolution, while
the high-momentum ones adiabatically follow the change in time of the
interaction strength. At intermediate momenta we point out the occurrence of
oscillations, which are analogous to Sakharov oscillations. We identify two
wide classes of time-dependent behaviors of the coupling for which an exact
solution of the problem can be found, allowing for an analytic computation of
all the relevant observables. A special emphasis is put on the study of the
coherence property of the system in one spatial dimension. We show that the
system exhibits a smooth "light-cone effect," with typically no
prethermalization.Comment: 24 pages, 12 figure
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