Synthesis and control of generalised dynamically substructured systems

The experimental technique for testing engineering systems via the method of dynamic substructuring is receiving significant global interest, for example in the fields of large-scale structural, aerospace, and automotive system testing. Dynamically substructured systems (DSSs) enable full-size, critical components of a complete system to be physically tested in real-time, within a laboratory environment, while the remainder of the system is modelled numerically. The intention is that the combined physical-numerical DSS behaves as if it were the complete (or emulated) system.In an ideal mechanical DSS, for example, perfect synchronization of displacements and forces at the interfaces between the numerical and physical components (or substructures) is required. Hence, a key design feature of successful DSS systems is the high fidelity of the control action. Equally, a DSS controller must be able to cope with non-linear, time-varying, and uncertain parameters within the physical substructure dynamics.The main purpose of this paper is to present a generalized DSS framework, together with associated linear and adaptive control strategies, that are specifically tailored to achieve high synchronization performance. The initial studies of this problem, as described in an earlier paper by Stoten and Hyde, are therefore continued by generalizing both the DSS dynamics and the control strategies to include (a) a number of newly defined modes of operation and (b) multivariable dynamics. In addition, comparative implementation and simulation studies are included, based upon the DSS testing of a mechanical system (a planar quasi-motorcycle rig), which was specifically designed to highlight the main features of this research. The comparative studies show that excellent DSS control can be achieved, especially with the addition of an adaptive component to the controller, despite significant changes to the physical substructure dynamics

Hepatic stellate cells and parasite-induced liver fibrosis

ABSTRACT: Fibrogenesis is a common feature of many diseases where there is severe insult to the liver. The hepatic stellate cell trans-differentiation into a myofibroblast has been identified as an important event in liver fibrogenesis and has been well investigated over the last few years in a number of liver diseases. The trans-differentiation process can be monitored in vitro by evaluation of biomarkers that are characteristic of normal quiescent hepatic stellate cells or activated myofibroblasts. Two major parasitic diseases associated with liver injury and fibrosis are schistosomiasis and echinococcosis. Recent studies have highlighted a role for activated hepatic stellate cells in both murine and human schistosomiasis as well as demonstrating that schistosome antigens are able to regulate this trans-differentiation process. Study of the hepatic stellate cell and its interaction with parasite-derived antigens may be pivotal in our understanding of the pathology associated with schistosomiasis and other parasitic diseases, including echinococcosis, as well as revealing new information on the trans-differentiation process in this cell type

Adaptive Neural Network Feedforward Control for Dynamically Substructured Systems

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Design of liquid crystal based coplanar waveguide tunable phase shifter with no floating electrodes for 60-90 GHz applications

A continuously tunable millimeter wave (mm-wave) phase shifter for 60-90 GHz applications was proposed using a coplanar waveguide (CPW) structure without the use of a floating electrode (FE). In contrast to conventional CPW-FE structures, the proposed FE-free CPW device can be modulated by the nematic liquid crystal (LC) materials confined in two symmetric feeding channels. The nearly true-TEM nature of this CPW design enables wideband and low-loss operations, particularly in high frequencies up to 90 GHz. In order to optimize between high tunability and low loss, the aspect ratio of the CPW structure was optimized to maximize the defined Figure-of-Merit (FoM). By taking into account different loss mechanisms in the designed structure and the effect of LC orientations, the driving-voltage dependent impedance matching was examined to minimize the return and insertion losses. As an example, the design of a phase shifter aimed to operate at 79 GHz with low bias voltages (0-10 V) is presented, showing a wide phase shift range of 0-408° and a low insertion loss from -6.15dB to -4.56dB. The corresponding FoM is 66.3°/dB, which make it possible to outperform over other LC-based phase shifters as reported within the targeted frequency range of 60-90 GHz

Design of Broadband Non-Foster Circuits Based on Resonant Tunneling Diodes

A non-Foster circuit (NFC) based on the resonant tunneling diode (RTD) is proposed for application to broadband impedance matching of electrically small antennas (ESAs). NFCs have traditionally been implemented with transistor pairs to achieve negative impedance, but these have limitations with respect to performance and operational bandwidth at high frequencies. At certain biasing voltages, double barrier RTDs behave as negative differential resistance (NDR) devices, which may be transformed to exhibit negative impedance. In contrast to the transistor-based NFC, these structures serve to gyrate or invert the load impedance, such that an inductive load will lead to a negative capacitance, and vice versa. This device is termed a negative impedance inverter (NII). We demonstrate negative impedance behavior for prototypes with measurements of negative resistance at up to 3 GHz, and device gain of around 5 dB from DC to 4 GHz. Design for stability of the RTD is performed using the Nyquist stability criterion. Stabilized negative capacitance NFCs show optimum performance from DC to the GHz range depending upon the load value. These NFCs are used to impedance match an antenna at low frequencies. An antenna with only one resonance at 3.5 GHz has been transformed with two different matching circuits: to an antenna encompassing the 1 to 2 GHz range; as well as the VHF/UHF bands from 300 MHz to 1 GHz. Additionally, RTDs have been demonstrated for operation at up to THz frequencies, so this topology can be extended to higher frequencies subject to fabrication constraints

The Effect of Electrolyte and Additive Concentration on Zinc-Nickel Flow Cell Performance

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordThis work aims to identify a suitable electrolyte composition for the operation of a zinc-nickel flow cell at ambient temperature. The effect of varying electrolyte composition containing KOH, ZnO, tetraethylammonium hydroxide (TEAH) or tetrabutylammonium bromide (TEAB) electrolyte additives are investigated. A 15 mM concentration of TEAH is found to provide smooth and compact zinc depositions. Increasing concentrations of KOH are found to be detrimental to voltaic efficiency, with coulombic efficiency peaking in 6 M KOH. The coulombic efficiencies of both zinc and nickel electrodes improve with ZnO concentration. Galvanostatic zinc-nickel flow cell cycling yields the highest efficiencies in an electrolyte of 6 M KOH with 0.5 M ZnO and 15 mM TEAH, with coulombic, voltaic and energy efficiencies of 98 %, 88 % and 86 % respectively over 70 stable charge/discharge cycles.Engineering and Physical Sciences Research Council (EPSRC)University of Exete

Search for K_S K_L in psi'' decays

K_S K_L from psi'' decays is searched for using the psi'' data collected by BESII at BEPC, the upper limit of the branching fraction is determined to be B(psi''--> K_S K_L) < 2.1\times 10^{-4} at 90% C. L. The measurement is compared with the prediction of the S- and D-wave mixing model of the charmonia, based on the measurements of the branching fractions of J/psi-->K_S K_L and psi'-->K_S K_L.Comment: 5 pages, 1 figur

Study of psi(2S) decays to X J/psi

Using J/psi -> mu^+ mu^- decays from a sample of approximately 4 million psi(2S) events collected with the BESI detector, the branching fractions of psi(2S) -> eta J/psi, pi^0 pi^0 J/psi, and anything J/psi normalized to that of psi(2S) -> pi^+ pi^- J/psi are measured. The results are B(psi(2S) -> eta J/psi)/B(psi(2S) -> pi^+ pi^- J/psi) = 0.098 \pm 0.005 \pm 0.010, B(psi(2S) -> pi^0 pi^0 J/psi)/B(psi(2S) -> pi^+ pi^- J/psi) = 0.570 \pm 0.009 \pm 0.026, and B(psi(2S) -> anything J/psi)/B(psi(2S) -> pi^+ pi^- J/psi) = 1.867 \pm 0.026 \pm 0.055.Comment: 13 pages, 8 figure