Physically constrained maximum likelihood (PCML) mode filtering and its application as a pre-processing method for underwater acoustic communication

Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2009Mode filtering is most commonly implemented using the sampled mode shape or pseudoinverse algorithms. Buck et al placed these techniques in the context of a broader maximum a posteriori (MAP) framework. However, the MAP algorithm requires that the signal and noise statistics be known a priori. Adaptive array processing algorithms are candidates for improving performance without the need for a priori signal and noise statistics. A variant of the physically constrained, maximum likelihood (PCML) algorithm is developed for mode filtering that achieves the same performance as the MAP mode filter yet does not need a priori knowledge of the signal and noise statistics. The central innovation of this adaptive mode filter is that the received signal's sample covariance matrix, as estimated by the algorithm, is constrained to be that which can be physically realized given a modal propagation model and an appropriate noise model. The first simulation presented in this thesis models the acoustic pressure field as a complex Gaussian random vector and compares the performance of the pseudoinverse, reduced rank pseudoinverse, sampled mode shape, PCML minimum power distortionless response (MPDR), PCML-MAP, and MAP mode filters. The PCML-MAP filter performs as well as the MAP filter without the need for a priori data statistics. The PCML-MPDR filter performs nearly as well as the MAP filter as well, and avoids a sawtooth pattern that occurs with the reduced rank pseudoinverse filter. The second simulation presented models the underwater environment and broadband communication setup of the Shallow Water 2006 (SW06) experiment. Data processing results are presented from the Shallow Water 2006 experiment, showing the reduced sensitivity of the PCML-MPDR filter to white noise compared with the reduced rank pseudoinverse filter. Lastly, a linear, decision-directed, RLS equalizer is used to combine the response of several modes and its performance is compared with an equalizer applied directly to the data received on each hydrophone

Modal processing for acoustic communications in shallow water experiment

Author Posting. © Acoustical Society of America, 2008. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 124 (2008): EL177-EL181, doi:10.1121/1.2960954.Acoustical array data from the Shallow Water Acoustics experiment was processed to show the feasibility of broadband mode decomposition as a preprocessing method to reduce the effective channel delay spread and concentrate received signal energy in a small number of independent channels. The data were collected by a vertical array designed at the Woods Hole Oceanographic Institution. Phase-shift Keying (PSK) m-sequence modulated signals with different carrier frequencies were transmitted at a distance 19.2 km from the array. Even during a strong internal waves activity a low bit error rate was achieved.The research was supported by ONR

Investigation of mode filtering as a preprocessing method for shallow-water acoustic communications

Author Posting. © IEEE, 2010. This article is posted here by permission of IEEE for personal use, not for redistribution. The definitive version was published in IEEE Journal of Oceanic Engineering 35 (2010): 744-755, doi:10.1109/JOE.2010.2045444.Acoustical array data from the 2006 Shallow Water Experiment (SW06) was analyzed to show the feasibility of broadband mode decomposition as a preprocessing method to reduce the effective channel delay spread and concentrate received signal energy in a small number of independent channels. The data were collected by a vertical array, which spans the water column from 12-m depth to the bottom in shallow water 80 m in depth. Binary-sequence data were used to phase-shift-keyed (PSK) modulate signals with different carrier frequencies. No error correction coding was used. The received signals were processed by a system that does not use training or pilot signals. Signals received both during periods of ordinary internal wave activity and during a period with unusually strong internal wave solitons were processed and analyzed. Different broadband mode-filtering methods were analyzed and tested. Broadband mode filtering decomposed the received signal into a number of independent signals with a reduced delay spread. The analysis of signals from the output of mode filters shows that even a simple demodulator can achieve a low bit error rate (BER) at a distance 19.2 km.This work was supported by the U.S. Office of Naval Research (ONR)

Antibiotic-resistant Escherichia Coli from Retail Poultry Meat with Different Antibiotic Use Claims

Background We sought to determine if the prevalence of antibiotic-resistant Escherichia coli differed across retail poultry products and among major production categories, including organic, “raised without antibiotics”, and conventional. Results We collected all available brands of retail chicken and turkey—including conventional, “raised without antibiotic”, and organic products—every two weeks from January to December 2012. In total, E. coli was recovered from 91% of 546 turkey products tested and 88% of 1367 chicken products tested. The proportion of samples contaminated with E. coli was similar across all three production categories. Resistance prevalence varied by meat type and was highest among E. coli isolates from turkey for the majority of antibiotics tested. In general, production category had little effect on resistance prevalence among E. coli isolates from chicken, although resistance to gentamicin and multidrug resistance did vary. In contrast, resistance prevalence was significantly higher for 6 of the antibiotics tested—and multidrug resistance—among isolates from conventional turkey products when compared to those labelled organic or “raised without antibiotics”. E. coli isolates from chicken varied strongly in resistance prevalence among different brands within each production category. Conclusion The high prevalence of resistance among E. coli isolates from conventionally-raised turkey meat suggests greater antimicrobial use in conventional turkey production as compared to “raised without antibiotics” and organic systems. However, among E. coli from chicken meat, resistance prevalence was more strongly linked to brand than to production category, which could be caused by brand-level differences during production and/or processing, including variations in antimicrobial use

Conformational dependence of the intrinsic acidity of the aspartic acid residue sidechain in N-acetyl-L-aspartic acid-N '-methylamide

The sidechain conformational potential energy hypersurfaces (PEHS) for the gamma(L), beta(L), alpha(L), and alpha(D) backbone conformations of N-acetyl-L-aspartate-M-methylamide were generated. Of the 81 possible conformers initially expected for the aspartate residue, only seven were found after geometric optimizations at the B3LYP/6-31G(d) level of theory. No stable conformers could be located in the delta(L), epsilon(L), gamma(D), delta(D), and epsilon(D) backbone conformations. The 'adiabatic' deprotonation energies for the endo and exo forms of N-acetyl-L-aspartic acid-N'-methylamide were calculated by comparing their optimized relative energies against those found for the seven stable conformers of N-acetyl-L-aspartate-N'-methylamide. Sideehain conformational PEHSs were also generated for the estimation of 'vertical' deprotonation energies for both endo and exo forms of N-acetyl-L-aspartic acid-N'-methylamide. All backbone-sidechain (N-H...-O-C) and backbone-backbone (N-(HO)-O-...=C) hydrogen bond interactions were analyzed. A total of two backbone-backbone and four backbone-sidechain interactions were found for N-acetyl-L-aspartate-N'-methylamide. The deprotonated sidechain of N-acetyl-L-aspartate-N'-methylamide may allow the aspartyl residue to form strong hydrogen bond interactions (since it is negatively charged) which may be significant in such processes as protein-ligand recognition and ligand binding. As a primary example, the molecular geometry of the aspartyl residue may be important in peptide folding, such as that. in the RGD tripeptide. (C) 2002 Elsevier science B.V. All rights reserved

Type studies and fourteen new North American species of Cortinarius section Anomali reveal high continental species diversity

Section is a species-rich group in North America belonging to , the most diverse genus in the Agaricales. This study is based on extensive morphological investigations and molecular methods using 191 nrDNA ITS sequence data and recovered 43 phylogenetic species from which 14 are described here as new to science. We sequenced ten type materials which belonged to eight species. The synonymy of with and with is proposed here. The North American occurrence of four species ( , , , and ), so far known only from Europe, was confirmed. Thirteen species were not formally described here due to lack of relevant information. An identification key to the known species in North America is provided