Multi-hop Diffusion LMS for Energy-constrained Distributed Estimation

We propose a multi-hop diffusion strategy for a sensor network to perform distributed least mean-squares (LMS) estimation under local and network-wide energy constraints. At each iteration of the strategy, each node can combine intermediate parameter estimates from nodes other than its physical neighbors via a multi-hop relay path. We propose a rule to select combination weights for the multi-hop neighbors, which can balance between the transient and the steady-state network mean-square deviations (MSDs). We study two classes of networks: simple networks with a unique transmission path from one node to another, and arbitrary networks utilizing diffusion consultations over at most two hops. We propose a method to optimize each node's information neighborhood subject to local energy budgets and a network-wide energy budget for each diffusion iteration. This optimization requires the network topology, and the noise and data variance profiles of each node, and is performed offline before the diffusion process. In addition, we develop a fully distributed and adaptive algorithm that approximately optimizes the information neighborhood of each node with only local energy budget constraints in the case where diffusion consultations are performed over at most a predefined number of hops. Numerical results suggest that our proposed multi-hop diffusion strategy achieves the same steady-state MSD as the existing one-hop adapt-then-combine diffusion algorithm but with a lower energy budget.Comment: 14 pages, 12 figures. Submitted for publicatio

A Multitask Diffusion Strategy with Optimized Inter-Cluster Cooperation

We consider a multitask estimation problem where nodes in a network are divided into several connected clusters, with each cluster performing a least-mean-squares estimation of a different random parameter vector. Inspired by the adapt-then-combine diffusion strategy, we propose a multitask diffusion strategy whose mean stability can be ensured whenever individual nodes are stable in the mean, regardless of the inter-cluster cooperation weights. In addition, the proposed strategy is able to achieve an asymptotically unbiased estimation, when the parameters have same mean. We also develop an inter-cluster cooperation weights selection scheme that allows each node in the network to locally optimize its inter-cluster cooperation weights. Numerical results demonstrate that our approach leads to a lower average steady-state network mean-square deviation, compared with using weights selected by various other commonly adopted methods in the literature.Comment: 30 pages, 8 figures, submitted to IEEE Journal of Selected Topics in Signal Processin

Spectroscopic Studies Of Mercury And Cadmium Binding To The Protein Metallothionein

Metallothioneins (MT) are a class of low molecular weight, cysteine rich proteins, which bind a wide range of metals both in vivo and in vitro. This protein has become the subject of intensive interest in many branches of the life sciences over the past two decades.;In this thesis, the manner in which mercury and cadmium bind to metallothionein has been studied using the techniques of circular dichroism (CD), magnetic circular dichroism (MCD), UV-visible absorption, and X-ray near edge absorption structure (XANES) spectroscopy.;At neutral pH, the Hg{dollar}\sb7{dollar}-MT and Hg{dollar}\sb4{dollar}-{dollar}\alpha{dollar} MT species formed from metal-free MT (apo-MT), or Zn-MT adopt a mercury-thiolate cluster structure. This Hg{dollar}\sb{lcub}\rm m{rcub}{dollar}S{dollar}\sb{lcub}\rm n{rcub}{dollar} cluster has a different arrangement compared with the cadmium thiolate cluster formed between MT and Cd{dollar}\sp{lcub}2+{rcub}{dollar}. When Hg{dollar}\sp{lcub}2+{rcub}{dollar} binds to apo-MT, two different coordination geometries are involved (linear and tetrahedral). Both solvent and temperature affect the formation of the Hg{dollar}\sb{lcub}\rm m{rcub}{dollar}S{dollar}\sb{lcub}\rm n{rcub}{dollar} clusters. Strikingly, Hg{dollar}\sb7{dollar}-MT formed by adding Hg{dollar}\sp{lcub}2+{rcub}{dollar} to Cd{dollar}\sb7{dollar}-MT has a very different Hg{dollar}\sb{lcub}\rm m{rcub}{dollar}S{dollar}\sb{lcub}\rm n{rcub}{dollar} arrangement compared with the Hg{dollar}\sb{lcub}\rm m{rcub}{dollar}S{dollar}\sb{lcub}\rm n{rcub}{dollar} clusters formed from apo-MT and Zn-MT. The spectroscopic properties of Hg{dollar}\sb4{dollar}-{dollar}\alpha{dollar} MT formed by adding Hg{dollar}\sp{lcub}2+{rcub}{dollar} to Cd{dollar}\sb4{dollar}-{dollar}\alpha{dollar} MT are different from proteins formed between not only apo-MT and Hg{dollar}\sp{lcub}2+{rcub}{dollar}, and Zn-MT and Hg{dollar}\sp{lcub}2+{rcub}{dollar}, but also Cd{dollar}\sb7{dollar}-MT and Hg{dollar}\sp{lcub}2+{rcub}{dollar}.;The formation of a novel Hg{dollar}\sb{lcub}18{rcub}{dollar}-MT species under acidic conditions is reported. The discovery of this highly structured Hg{dollar}\sb{lcub}18{rcub}{dollar}-MT species adds a new type of structure to those described previously for metallothionein. Dramatic spectroscopic differences in the formation of Hg{dollar}\sb{lcub}18{rcub}{dollar}-MT from apo-MT 1 or 2 indicates a new discriminatory property between different metallothionein isoforms.;Cadmium binds to Zn-MT in a distributed manner , but binds to apo-MT in a domain specific manner . The onset of cluster formation in the {dollar}\alpha{dollar} domain is associated with the appearance of a derivative feature in the CD spectrum. This feature has been attributed to exciton coupling arising from adjacent Cd-SR units (S-Cd-SR-Cd-S) in the {dollar}\alpha{dollar} domain.;Results from a XANES study suggest that while Zn{dollar}\sb7{dollar}-MT, Cd{dollar}\sb7{dollar}-MT, and Hg{dollar}\sb7{dollar}-MT have similar structures from the perspective of the coordinating sulfurs, the binding sites in Hg{dollar}\sb7{dollar}-MT are not exactly the same. Hg{dollar}\sb{lcub}18{rcub}{dollar}-MT adopts a completely different structure when compared with the M{dollar}\sb7{dollar}-MT complexes.;The conditions for the use of Chelex-100 in metallothionein systems are presented. Use of Chelex-100 greatly simplifies the procedures of removing free metals

Network infection source identification under the SIRI model

We study the problem of identifying a single infection source in a network under the susceptible-infected-recovered-infected (SIRI) model. We describe the infection model via a state-space model, and utilizing a state propagation approach, we derive an algorithm known as the heterogeneous infection spreading source (HISS) estimator, to infer the infection source. The HISS estimator uses the observations of node states at a particular time, where the elapsed time from the start of the infection is unknown. It is able to incorporate side information (if any) of the observed states of a subset of nodes at different times, and of the prior probability of each infected or recovered node to be the infection source. Simulation results suggest that the HISS estimator outperforms the dynamic message pass- ing and Jordan center estimators over a wide range of infection and reinfection rates.Comment: 5 pages, 3 figures; to present in ICASSP 201

Macro- and Micro-morphological, Anatomical, Cytological and Phytochemical Properties of Tridax procumbens Linn. (Asteraceae)

This study examined the macro- and micro-morphological, Anatomical, Cytological and Phytochemical Properties of Tridax procumbens L. in the family Asteraceae. Observations of plant parts aided by measurements were done and these were sectioned following Wahua’s method; root tips squashed with FLP Orcein and qualitative phytochemical analyses were carried out. The slides were viewed using the light compound microscope and photomicrographs were taken after careful examination from good preparations. Macromorphological studies showed the plant grows up to 40cm or more in height. Foliar features revealed opposite, pinnate, oblong to ovate with coarsely serrated margin and acute apex, 4±1.5cm long and 2±1cm wide with petiole up to 1.5±0.5cm in length. The floral structure show cased diameter of each flower head as 1.0±0.4cm while the peduncle is elongated and up to 10±5cm in length; the petal is 0.7±0.2cm in length alongside tubular sepals up to 0.9±0.3cm in length. The stamen is 0.9±0.2cm in length while the carpel is 1.0±0.1cm. Presence of anomocytic stomata which is amphistomatic. Anatomical sections on the mid-ribs, petiole, internodes, nodes and roots revealed peculiar internal features. Mitotic chromosome is 2n=36. Phytochemical studies revealed the presence of saponins, alkaloids, flavonoids, tannins, steroids, cardiac glycosides, phenols. The information generated from this study would further aid in the delimitation of the species. Keywords: Tridax procumbens, Morphology, anatomy, cytology, palynology, phytochemistr

Polynomial Curve Slope Compensation for Peak-Current-Mode-Controlled Power Converters

Linear ramp slope compensation (LRC) and quadratic slope compensation (QSC) are commonly implemented in peak-current-mode-controlled dc-dc converters in order to minimize subharmonic and chaotic oscillations. Both compensating schemes rely on the linearized state-space averaged model (LSSA) of the converter. The LSSA ignores the impact that switching actions have on the stability of converters. In order to include switching events, the nonlinear analysis method based on the Monodromy matrix was introduced to describe a complete-cycle stability. Analyses on analog-controlled dc-dc converters applying this method show that system stability is strongly dependent on the change of the derivative of the slope at the time of switching instant. However, in a mixed-signal-controlled system, the digitalization effect contributes differently to system stability. This paper shows a full complete-cycle stability analysis using this nonlinear analysis method, which is applied to a mixed-signal-controlled converter. Through this analysis, a generalized equation is derived that reveals for the first time the real boundary stability limits for LRC and QSC. Furthermore, this generalized equation allows the design of a new compensating scheme, which is able to increase system stability. The proposed scheme is called polynomial curve slope compensation (PCSC) and it is demonstrated that PCSC increases the stable margin by 30% compared to LRC and 20% to QSC. This outcome is proved experimentally by using an interleaved dc-dc converter that is built for this work