Superfast Line Spectral Estimation

A number of recent works have proposed to solve the line spectral estimation problem by applying off-the-grid extensions of sparse estimation techniques. These methods are preferable over classical line spectral estimation algorithms because they inherently estimate the model order. However, they all have computation times which grow at least cubically in the problem size, thus limiting their practical applicability in cases with large dimensions. To alleviate this issue, we propose a low-complexity method for line spectral estimation, which also draws on ideas from sparse estimation. Our method is based on a Bayesian view of the problem. The signal covariance matrix is shown to have Toeplitz structure, allowing superfast Toeplitz inversion to be used. We demonstrate that our method achieves estimation accuracy at least as good as current methods and that it does so while being orders of magnitudes faster.Comment: 16 pages, 7 figures, accepted for IEEE Transactions on Signal Processin

Collective waves in dense and confined microfluidic droplet arrays

Excitation mechanisms for collective waves in confined dense one-dimensional microfluidic droplet arrays are investigated by experiments and computer simulations. We demonstrate that distinct modes can be excited by creating specific `defect' patterns in flowing droplet trains. Excited longitudinal modes exhibit a short-lived cascade of pairs of laterally displacing droplets. Transversely excited modes obey the dispersion relation of microfluidic phonons and induce a coupling between longitudinal and transverse modes, whose origin is the hydrodynamic interaction of the droplets with the confining walls. Moreover, we investigate the long-time behaviour of the oscillations and discuss possible mechanisms for the onset of instabilities. Our findings demonstrate that the collective dynamics of microfluidic droplet ensembles can be studied particularly well in dense and confined systems. Experimentally, the ability to control microfluidic droplets may allow to modulate the refractive index of optofluidic crystals which is a promising approach for the production of dynamically programmable metamaterials.Comment: 13 pages, 17 figure

The role of crop production clubs in technology transfer

Non-Peer ReviewedThis study was undertaken to determine if crop production club members represent an adopter category of the adoption diffusion theory as outlined by the literature, to obtain a more detailed description of the characteristics of the crop production club members and how they relate to the adopter categories and to determine the role crop production clubs play in the technology transfer process. A telephone survey was conducted using two groups, one selected from crop production clubs that had been organized for more than five years and the other a stratified random sample of non-club farmers in the surrounding area to the clubs. The questionnaire was designed to obtain information about innovative cropping practices, as well as demographic data, personal characteristics and communication behavior. A total of 38 crop production club members and 28 non-club farmers were contacted between April 22 and May 10, 1991. The results of the study found that the characteristics exhibited by crop production club members were similar to those outlined in the adoption-diffusion theory for early adopters. Therefore crop production club members fit into the adoption-diffusion process as early adopters. Crop clubs use demonstrations as a way of introducing new innovations to their club members. Both groups indicated that they used neighbors often as a source of information and therefore, crop production clubs members likely transfer information to others through this and other channels. They transfer technology through the adoption diffusion process as early adopters. From this study it can be concluded that crop production clubs do play a role in the technology transfer process

Localized organic agri-food supply chains in Rhône-Alpes (France): diversity of organisations and highlights of the notion of proximity

For ten years, innovative forms of distribution of organic products have emerged between long and short supply chains. They are often defined as "localized agrifood systems". We based this work on the analysis of 18 localized agrifood systems in the Rhône-Alpes region (France). First, it presents the dynamics of construction and organization of these agrifood systems: diversity of actors involved, relationships between actors and rules that have been gradually established. We used the concept of geographical and relational proximity to analyse these supply chains and to highlight the mechanisms implemented to address the limits of short supply chains, particularly an increasing number of intermediaries. Then we assessed their performances with regard to the advantages commonly given to short supply chains. Finally we demonstrated that localized supply chains are in some cases a way towards conventionalisation of organic agriculture and in others a form of mitigation of the agribusiness model

Physical Acoustics

Contains reports on two research projects.U. S. Navy (Office of Naval Research) under Contract Nonr-1841(42)National Aeronautics and Space Administratio

Early stages of ramified growth in quasi-two-dimensional electrochemical deposition

I have measured the early stages of the growth of branched metal aggregates formed by electrochemical deposition in very thin layers. The growth rate of spatial Fourier modes is described qualitatively by the results of a linear stability analysis [D.P. Barkey, R.H. Muller, and C.W. Tobias, J. Electrochem. Soc. {\bf 136}, 2207 (1989)]. The maximum growth rate is proportional to $(I/c)^\delta$ where $I$ is the current through the electrochemical cell, $c$ the electrolyte concentration, and $\delta = 1.37 \pm 0.08$. Differences between my results and the theoretical predictions suggest that electroconvection in the electrolyte has a large influence on the instability leading to ramified growth.Comment: REVTeX, four ps figure