Electrohydraulic servovalves – past, present, and future

In 2016 it is 70 years since the first patent for a two-stage servovalve was filed, and 60 years since the double nozzle-flapper two-stage valve patent was granted. This paper reviews the many alternative servovalve designs that were investigated at that time, focusing on two-stage valves. The development of single-stage valves – otherwise known as direct drive or proportional valves – for industrial rather than aerospace application is also briefly reviewed. Ongoing research into alternative valve technology is then discussed, particularly focussing on piezoelectric actuation and the opportunities afforded by additive manufacturing

Characterizations in Domination Theory

Let G = (V,E) be a graph. A set R is a restrained dominating set (total restrained dominating set, resp.) if every vertex in V − R (V) is adjacent to a vertex in R and (every vertex in V −R) to a vertex in V −R. The restrained domination number of G (total restrained domination number of G), denoted by gamma_r(G) (gamma_tr(G)), is the smallest cardinality of a restrained dominating set (total restrained dominating set) of G. If T is a tree of order n, then gamma_r(T) is greater than or equal to (n+2)/3. We show that gamma_tr(T) is greater than or equal to (n+2)/2. Moreover, we show that if n is congruent to 0 mod 4, then gamma_tr(T) is greater than or equal to (n+2)/2 + 1. We then constructively characterize the extremal trees achieving these lower bounds. Finally, if G is a graph of order n greater than or equal to 2, such that both G and G\u27 are not isomorphic to P_3, then gamma_r(G) + gamma_r(G\u27) is greater than or equal to 4 and less than or equal to n +2. We provide a similar result for total restrained domination and characterize the extremal graphs G of order n achieving these bounds

Model predictive control of a multi-degree-of-freedom wave energy converter with model mismatch and prediction errors

The power captured by a wave energy converter (WEC) can be greatly increased through the use of a well-conceived wave-by-wave control strategy. Optimal strategies including Model Predictive Control (MPC) rely on a dynamic model of the WEC and prediction of the wave excitation force several seconds into the future. Both the modelling and prediction processes are subject to errors. This study investigates the impact of these errors on the performance of a WEC under MPC. Idealised simulations are conducted to establish a suitable prediction horizon and establish a performance benchmark against an optimally tuned passively damped system. Power increases of over 200% are seen. The assumptions of perfect prediction and system modelling are progressively removed, culminating in multi-body simulation of a specific multi-DOF submerged point absorber WEC with constrained MPC. Under realistic conditions, the power gain is a more modest 30% at best across the tested sea states, demonstrating that these errors have a significant impact on performance. However, the ability to use constraints to limit motion in high energy seas and the tunability of the control law are valuable attributes for practical deployment. Overall the performance gains demonstrate the benefits of such control strategies for application to multi-DOF WECs.</p

Characterizing Information Propagation in Plants

This paper considers an electro-chemical based communication model for intercellular communication in plants. Many plants, such as Mimosa pudica (the "sensitive plant"), employ electrochemical signals known as action potentials (APs) for communication purposes. In this paper we present a simple model for action potential generation. We make use of the concepts from molecular communication to explain the underlying process of information transfer in a plant. Using the information-theoretic analysis, we compute the mutual information between the input and output in this work. The key aim is to study the variations in the information propagation speed for varying number of plant cells for one simple case. Furthermore we study the impact of the AP signal on the mutual information and information propagation speed. We aim to explore further that how the growth rate in plants can impact the information transfer rate and vice versa.Comment: 6 pages, 5 Figures, Submitted to IEEE Conference, 201

A Comparative Analysis of Methylome Profiles of Campylobacter jejuni Sheep Abortion Isolate and Gastroenteric Strains Using PacBio Data

Campylobacter jejuni is a leading cause of human gastrointestinal disease and small ruminant abortions in the United States. The recent emergence of a highly virulent, tetracycline-resistant C. jejuni subsp. jejunisheep abortion clone (clone SA) in the United States, and that strain\u27s association with human disease, has resulted in a heightened awareness of the zoonotic potential of this organism. Pacific Biosciences\u27 Single Molecule, Real-Time sequencing technology was used to explore the variation in the genome-wide methylation patterns of the abortifacient clone SA (IA3902) and phenotypically distinct gastrointestinal-specific C. jejuni strains (NCTC 11168 and 81-176). Several notable differences were discovered that distinguished the methylome of IA3902 from that of 11168 and 81-176: identification of motifs novel to IA3902, genome-specific hypo- and hypermethylated regions, strain level variability in genes methylated, and differences in the types of methylation motifs present in each strain. These observations suggest a possible role of methylation in the contrasting disease presentations of these three C. jejuni strains. In addition, the methylation profiles between IA3902 and a luxS mutant were explored to determine if variations in methylation patterns could be identified that might explain the role of LuxS-dependent methyl recycling in IA3902 abortifacient potential

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Vowel normalization is a computation that is meant to account for the differences in the absolute direct (physical or psychophysical) representations of qualitatively equivalent vowel productions that arise due to differences in speaker properties such as body size types, age, gender, and other socially interpreted categories that are based on natural variation in vocal tract size and shape. In this dissertation, we address the metaphysical and epistemological aspects of vowel normalization pertaining to spoken language acquisition during early infancy. We begin by reviewing approaches to conceptualizing and modeling the phonetic components of early spoken language acquisition, forming a catalog of phenomena that serves as the basis for our discourse. We then establish the existence of a vowel normalization computation carried out by infants early in their spoken language acquisition, and put forward a conceptual and technical framework for its investigation which focuses attention on the generative nature of the computation. We then situate the acquisition of vowel normalization within a broader developmental framework encompassing a suite of vocal learning phenomena, including language-specific caretaker vocal exchanges