Sensor/Actuator Selection for the Constrained Variance Control Problem

The problem of designing a linear controller for systems subject to inequality variance constraints is considered. A quadratic penalty function approach is used to yield a linear controller. Both the weights in the quadratic penalty function and the locations of sensors and actuators are selected by successive approximations to obtain an optimal design which satisfies the input/output variance constraints. The method is applied to NASA's 64 meter Hoop-Column Space Antenna for satellite communications. In addition the solution for the control law, the main feature of these results is the systematic determination of actuator design requirements which allow the given input/output performance constraints to be satisfied

Kinetostatic Analysis and Solution Classification of a Planar Tensegrity Mechanism

Tensegrity mechanisms have several interesting properties that make them suitable for a number of applications. Their analysis is generally challenging because the static equilibrium conditions often result in complex equations. A class of planar one-degree-of-freedom (dof) tensegrity mechanisms with three linear springs is analyzed in detail in this paper. The kinetostatic equations are derived and solved under several loading and geometric conditions. It is shown that these mechanisms exhibit up to six equilibrium configurations, of which one or two are stable. Discriminant varieties and cylindrical algebraic decomposition combined with Groebner base elimination are used to classify solutions as function of the input parameters.Comment: 7th IFToMM International Workshop on Computational Kinematics, May 2017, Poitiers, France. 201

Integrated control/structure design for planar tensegrity models

A tensegrity structure is built using compressive members (bars) and tensile members (tendons). We discuss how an optimal and integrated design of tendon length control and topology/geometry of the structure can improve the stiffness and stiffness-to-mass properties of tensegrity systems. To illustrate our approach we apply it on a tensegrity system build up from several elementary stages that form a planar beam structure. The computations are done with a nonlinear programming approach and most design aspects (decentralized co-located control, static equilibrium, yield and buckling limits, force directionality, etc., both for the unloaded and loaded cases) are incorporated. Due to the way the control coefficients are constrained, this approach also delivers information for a proper choice of actuator or sensor locations: there is no need to control or sense the lengths of all tendons. From this work it becomes clear that certain actuator/sensor locations and certain topologies are clearly advantageous. For the minimal compliance objective in a planar tensegrity beam structure, proper tendons for control are those that are perpendicular to the disturbance force direction, close to the support, and relatively long, while good topologies are the ones that combine different nodal configurations in a tensegrity topology that is akin to a framed beam, but, when control is used, can be quite different from a classical truss structure

Model reduction for discrete bilinear systems

A model reduction method for discrete bilinear systems is developed which matches q sets of Volterra and covariance parameters. These parameters are shown to represent both deterministic and stochastic attributes of the discrete bilinear system. A reduced order model which matches these q sets of parameters is defined to be a q-Volterra covariance equivalent realization (q-Volterra COVER). An algorithm is presented which constructs a class of q-Volterra COVERs parameterized by solutions to a Hermitian, quadratic, matrix equation. The algorithm is applied to a bilinear model of a robot manipulator

Estimation of semiconductor-like pigment concentrations in paint mixtures and their differentiation from paint layers using first-derivative reflectance spectra.

Identification of the techniques employed by artists, e.g. mixing and layering of paints, if used together with information about their colour palette and style, can help to attribute works of art with more confidence. In this study, we show how the pigment composition in binary paint mixtures can be quantified using optical-reflectance spectroscopy, by analysis of the peak features corresponding to colour-transition edges in the first-derivative spectra. This technique is found to be more robust than a number of other spectral-analysis methods, which can suffer due to shifts in the transition edges in mixed paints compared to those observed in spectra of pure ones. Our method also provides a means of distinguishing paint mixtures from layering in some cases. The spectroscopy also shows the presence of multiple electronic transitions, accessible within a narrow energy range, to be a common feature of many coloured pigments, which electronic-structure calculations attribute to shallow band edges. We also demonstrate the successful application of the reflectance-analysis technique to painted areas on a selection of medieval illuminated manuscripts.ARP is indebted to St. John’s College, Cambridge for providing a scholarship to fund this study, and to ASD Inc. (through the Alexander Goetz programme) and Analytik UK Ltd. for the loan of a Fieldspec 4 spectroradiometer for the completion of this work. JMS is indebted to Trinity College, Cambridge for provision of an Internal Graduate Studentship, and to the UK Engineering and Physical Sciences Research Council (EPSRC) for support under grant no. EP/K004956/1. The computational modelling was performed on the UK national HPC facility (Archer), accessed through the Materials Chemistry Consortium, which is funded through EPSRC grant no. EP/L000202.This is the final version of the article. It first appeared from Elsevier via https://doi.org/10.1016/j.talanta.2016.03.05

Lattice dynamics and vibrational spectra of the orthorhombic, tetragonal and cubic phases of methylammonium lead iodide

The hybrid halide perovskite CH3NH3PbI3 exhibits a complex structural behaviour, with successive transitions between orthorhombic, tetragonal and cubic polymorphs at ca. 165 K and 327 K. Herein we report first-principles lattice dynamics (phonon spectrum) for each phase of CH3NH3PbI3. The equilibrium structures compare well to solutions of temperature-dependent powder neutron diffraction. By following the normal modes we calculate infrared and Raman intensities of the vibrations, and compare them to the measurement of a single crystal where the Raman laser is controlled to avoid degradation of the sample. Despite a clear separation in energy between low frequency modes associated with the inorganic PbI3 network and high-frequency modes of the organic CH3NH3+ cation, significant coupling between them is found, which emphasises the interplay between molecular orientation and the corner-sharing octahedral networks in the structural transformations. Soft modes are found at the boundary of the Brillouin zone of the cubic phase, consistent with displacive instabilities and anharmonicity involving tilting of the PbI6 octahedra around room temperature.Comment: 9 pages, 4 figure

A new binding geometry for an ortho-xylylene-linked bis(NHC)cyclophane: a ruthenium(II) complex with a chelating (g1-NHC)2:g6-arene ligand

Using two different reaction procedures, a Ru(II) complex has been isolated that contains an ortho-xylylene-linked bis(NHC)cyclophane (NHC = N-heterocyclic carbene) that binds to the Ru centre through two carbene carbons and one of the arene rings in an η6-mode

A tensegrity approach to the optimal reinforcement of masonry domes and vaults through fiber-reinforced composite materials

We present a tensegrity approach to the strengthening of masonry vaults and domes performed by bonding grids of fiber reinforced composites to the masonry substrate. A topology optimization of such a reinforcement technique is formulated, on accounting for a tensegrity model of the reinforced structure; a minimal mass design strategy; different yield strengths of the masonry struts and tensile composite reinforcements; and multiple loading conditions. We show that the given optimization strategy can be profitably employed to rationally design fiber-reinforced composite material reinforcements of existing or new masonry vaults and domes, making use of the safe theorem of limit analysis. A wide collection of numerical examples dealing with real-life masonry domes and vaults highlight the technical potential of the proposed approach

Stellar Kinematics of z ~ 2 Galaxies and the Inside-out Growth of Quiescent Galaxies

Using stellar kinematics measurements, we investigate the growth of massive, quiescent galaxies from z ~{} 2 to today. We present X-Shooter spectra from the UV to NIR and dynamical mass measurements of five quiescent massive ({gt}10$^{11}$ M $_{⊙}$) galaxies at z ~{} 2. This triples the sample of z {gt} 1.5 galaxies with well-constrained ({$delta$}{$σ$} {lt} 100 km s$^{-1}$) velocity dispersion measurements. From spectral population synthesis modeling we find that these galaxies have stellar ages that range from 0.5 to 2 Gyr, with no signs of ongoing star formation. We measure velocity dispersions (290-450 km s$^{-1}$) from stellar absorption lines and find that they are 1.6-2.1 times higher than those of galaxies in the Sloan Digital Sky Survey at the same mass. Sizes are measured using GALFIT from Hubble Space Telescope Wide Field Camera 3 H $_{160}$ and UDS K-band images. The dynamical masses correspond well to the spectral energy distribution based stellar masses, with dynamical masses that are ~{}15% higher. We find that M $_{*}$/M $_{dyn}$ may decrease slightly with time, which could reflect the increase of the dark matter fraction within an increasing effective radius. We combine different stellar kinematic studies from the literature and examine the structural evolution from z ~{} 2 to z ~{} 0: we confirm that at fixed dynamical mass, the effective radius increases by a factor of ~{}2.8, and the velocity dispersion decreases by a factor of ~{}1.7. The mass density within one effective radius decreases by a factor of ~{}20, while within a fixed physical radius (1 kpc) it decreases only mildly (factor of ~{}2). When we allow for an evolving mass limit by selecting a population of galaxies at fixed number density, a stronger size growth with time is found (factor of ~{}4), velocity dispersion decreases by a factor of ~{}1.4, and interestingly, the mass density within 1 kpc is consistent with no evolution. This finding suggests that massive quiescent galaxies at z ~{} 2 grow inside out, consistent with the expectations from minor mergers