Sensor Array Processing with Manifold Uncertainty

<p>The spatial spectrum, also known as a field directionality map, is a description of the spatial distribution of energy in a wavefield. By sampling the wavefield at discrete locations in space, an estimate of the spatial spectrum can be derived using basic wave propagation models. The observable data space corresponding to physically realizable source locations for a given array configuration is referred to as the array manifold. In this thesis, array manifold ambiguities for linear arrays of omni-directional sensors in non-dispersive fields are considered. </p><p>First, the problem of underwater a hydrophone array towed behind a maneuvering platform is considered. The array consists of many hydrophones mounted to a flexible cable that is pulled behind a ship. The towed cable will bend or distort as the ship performs maneuvers. The motion of the cable through the turn can be used to resolve ambiguities that are inherent to nominally linear arrays. The first significant contribution is a method to estimate the spatial spectrum using a time-varying array shape in a dynamic field and broadband temporal data. Knowledge of the temporal spectral shape is shown to enhance detection performance. The field is approximated as a sum of uncorrelated planewaves located at uniform locations in angle, forming a gridded map on which a maximum likelihood estimate for broadband source power is derived. Uniform linear arrays also suffer from spatial aliasing when the inter-element spacing exceeds a half-wavelength. Broadband temporal knowledge is shown to significantly reduce aliasing and thus, in simulation, enhance target detection in interference dominated environments. </p><p>As an extension, the problem of towed array shape estimation is considered when the number and location of sources are unknown. A maximum likelihood estimate of the array shape using the field directionality map is derived. An acoustic-based array shape estimate that exploits the full 360$^\circ$ field via field directionality mapping is the second significant contribution. Towed hydrophone arrays have heading sensors in order to estimate array shape, but these sensors can malfunction during sharp turns. An array shape model is described that allows the heading sensor data to be statistically fused with heading sensor. The third significant contribution is method to exploit dynamical motion models for sharp turns for a robust array shape estimate that combines acoustic and heading data. The proposed array shape model works well for both acoustic and heading data and is valid for arbitrary continuous array shapes.</p><p>Finally, the problem of array manifold ambiguities for static under-sampled linear arrays is considered. Under-sampled arrays are non-uniformly sampled with average spacing greater than a half-wavelength. While spatial aliasing only occurs in uniformly sampled arrays with spacing greater than a half-wavelength, under-sampled arrays have increased spatial resolution at the cost of high sidelobes compared to half-wavelength sampled arrays with the same number of sensors. Additionally, non-uniformly sampled arrays suffer from rank deficient array manifolds that cause traditional subspace based techniques to fail. A class of fully agumentable arrays, minimally redundant linear arrays, is considered where the received data statistics of a uniformly spaced array of the same length can be reconstructed in wide sense stationary fields at the cost of increased variance. The forth significant contribution is a reduced rank processing method for fully augmentable arrays to reduce the variance from augmentation with limited snapshots. Array gain for reduced rank adaptive processing with diagonal loading for snapshot deficient scenarios is analytically derived using asymptotic results from random matrix theory for a set ratio of sensors to snapshots. Additionally, the problem of near-field sources is considered and a method to reduce the variance from augmentation is proposed. In simulation, these methods result in significant average and median array gains with limited snapshots.</p>Dissertatio

Spatial Spectrum Estimation with a Maneuverable Sensor Array in a Dynamic Environment

<p>Estimation of a time-varying field is essential for situational awareness in many subject areas. Adaptive processing often assumes both the field is stationary and the array is fixed for multiple observation windows. For passive sonar, highly dynamic scenarios such as high bearing rate sources or underwater maneuvers severely limit the utilization of multiple snapshots. Several models are considered for time-varying fields, and a broadband maximum-likelihood estimator is introduced that is solved with an expectation maximization algorithm using as few as one snapshot. The number of estimated parameters can be reduced for broadband data when information, such as shape, is known about the source temporal spectrum. Cramér-Rao bound analysis is used to understand the effects of temporal spectrum knowledge on broadband processing. An example is given for the flat spectrum case to compare with conventional processing. Another feature of dynamic environments is array motion. Since underwater arrays are often subject to motion, the estimate must consider arbitrary, dynamic array shapes. Platforms such as autonomous underwater vehicles provide mobility but constrain the number of sensors. Exploiting a maneuverable linear array with the new estimate allows for left-right or front-back disambiguation and suppression of spatial grating lobes. Multi-source simulations are used to demonstrate the ability of a short, maneuvering array to reduce array backlobes as well as operate in the spatial grating lobe region.</p>Thesi

New sandwich and half-sandwich titanium hydrazido compounds

[EN] New mono- and bis-cyclopentadienyl terminal titanium hydrazido(2-) compounds were prepared by tert-butyl imide/N,N'-disubstituted hydrazine exchange reactions. Reaction of Cp*Ti(N(t)Bu)Cl(PY) (1) with Ph(2)NNH(2) gave the terminal hydrazide Cp*Ti(NNPh(2))Cl(py) (4), whereas the corresponding reaction of CpTi(N(t)Bu)Cl(py) gave the dimer Cp(2)Ti(2)(mu-eta(1):eta(1)-NNPh(2))-(mu-eta(2):eta(1)-NNPh(2))Cl(2). Reaction of 1 with Me(2)NNH(2) (1 equiv) also gave a dimer, Cp*(2)Ti(2)(mu-eta(1):eta(1)-NNMe(2)) (mu-eta(2):eta(1)-NNMe(2))Cl(2), (8), while the reaction with 2 equiv of Me(2)NNH(2) gave Cp*Ti(eta(2)-NHNMe(2))(2)Cl (7) containing two eta(2)-bound hydrazide(1-) ligands. Formation of 7 and 8 proceeds via a common intermediate, Cp*Ti(NH(t)Bu)(eta(2)-NHNMe(2))Cl, observed by NMR spectroscopy. Reaction of 4 with LiNHNPh(2) gave the mixed hydrazide(2-)/hydrazide(1-) derivative Cp*Ti(NNPh(2))-(NHNPh(2))(py) (10). The corresponding reaction of 1 formed Cp*Ti(N(t)Bu)(NHNPh(2))(py), which rearranged to Cp*Ti-(NH(t)Bu)(NNPh(2))(py). The titanocene derivative Cp(2)Ti(NNPh(2))(py) (14) was prepared by reaction of Cp(2)Ti(N(t)Bu)(py) (13) with Ph(2)NNH(2), whereas the corresponding reaction with Me(2)NNH(2) gave mixtures including CpTi(NH(t)Bu)(mu-eta(1):eta(1)-NNMe(2)) (mu-eta(2):eta(1)-NNMe(2))TiCp(eta(1)-Cp). The electronic structure of 14 was investigated by DFT and compared to that of the imido complex 13. Whereas the HOMO of the formally 20 valence electron compound 13 is a ligand-centered orbital based both on the Cp rings and on the imido N, in 14 this is the HOMO-1 and one of the Ti=-N(alpha)pi-bonding MOs is the HOMO, destabilized by an N(alpha)-N(beta) antibonding interaction.We thank the EPSRC, British Council, MESR, and the Spanish Ministerio de Educacion y Ciencia for support. We thank Andrew Cowley for help with some of the X-ray structures.Selby, JD.; Feliz Rodriguez, M.; Schwarz, AD.; Clot, E.; Mountford, P. (2011). New sandwich and half-sandwich titanium hydrazido compounds. Organometallics. 30:2295-2307. doi:10.1021/om200068kS229523073

DNA methylation networks underlying mammalian traits

Using DNA methylation profiles ( n = 15,456) from 348 mammalian species, we constructed phyloepigenetic trees that bear marked similarities to traditional phylogenetic ones. Using unsupervised clustering across all samples, we identified 55 distinct cytosine modules, of which 30 are related to traits such as maximum life span, adult weight, age, sex, and human mortality risk. Maximum life span is associated with methylation levels in HOXL subclass homeobox genes and developmental processes and is potentially regulated by pluripotency transcription factors. The methylation state of some modules responds to perturbations such as caloric restriction, ablation of growth hormone receptors, consumption of high-fat diets, and expression of Yamanaka factors. This study reveals an intertwined evolution of the genome and epigenome that mediates the biological characteristics and traits of different mammalian species

DNA methylation networks underlying mammalian traits

Using DNA methylation profiles ( = 15,456) from 348 mammalian species, we constructed phyloepigenetic trees that bear marked similarities to traditional phylogenetic ones. Using unsupervised clustering across all samples, we identified 55 distinct cytosine modules, of which 30 are related to traits such as maximum life span, adult weight, age, sex, and human mortality risk. Maximum life span is associated with methylation levels in subclass homeobox genes and developmental processes and is potentially regulated by pluripotency transcription factors. The methylation state of some modules responds to perturbations such as caloric restriction, ablation of growth hormone receptors, consumption of high-fat diets, and expression of Yamanaka factors. This study reveals an intertwined evolution of the genome and epigenome that mediates the biological characteristics and traits of different mammalian species