The nuclear dimension of graph C*-algebras

Consider a graph C*-algebra C*(E) with a purely infinite ideal I (possibly all of C*(E)) such that I has only finitely many ideals and C*(E)/I is approximately finite dimensional. We prove that the nuclear dimension of C*(E) is 1. If I has infinitely many ideals, then the nuclear dimension of C*(E) is either 1 or 2.Comment: 24 pages; this version to appear in Adv. Mat

Realizations of AF-algebras as graph algebras, Exel-Laca algebras, and ultragraph algebras

We give various necessary and sufficient conditions for an AF-algebra to be isomorphic to a graph C*-algebra, an Exel-Laca algebra, and an ultragraph C*-algebra. We also explore consequences of these results. In particular, we show that all stable AF-algebras are both graph C*-algebras and Exel-Laca algebras, and that all simple AF-algebras are either graph C*-algebras or Exel-Laca algebras. In addition, we obtain a characterization of AF-algebras that are isomorphic to the C*-algebra of a row-finite graph with no sinks.Comment: 34 pages, Version 2 comments: Some minor typos corrected; Version 3 comments: Some typos corrected. This is the version to appea

An insight into de Vries behaviour of smectic liquid crystals from atomistic molecular dynamics simulations

Fully atomistic molecular dynamics simulations have been performed on the ferroelectric liquid crystal compound 9HL, which exhibits de Vries character. Simulations were carried out at a range of temperatures, and both SmA* and SmC* phases were successfully simulated. Experimental trends in orientational order parameter, translational order parameter, layer spacing, and tilt angle were found to be matched by the simulations. The simulations were analysed in the context of multiple reported models developed from the interpretation of experimental data, none of which were found to individually describe the simulated behaviour. Further analysis demonstrated the formation of distinct aromatic and lactate sub-layers in the 9HL simulations. The aromatic sub-layers exhibited tilting behaviour at the SmA*/SmC* transition, whereas alignment within the lactate sub-layers was found to be relatively unchanged, maintaining a SmA-like configuration even in the SmC* phase. This behaviour provides a simple explanation for de Vries behaviour, where only a fraction of the layer structure exhibits an overall tilt in the SmC phase

Orion Orbit Control Design and Analysis

The analysis of candidate thruster configurations for the Crew Exploration Vehicle (CEV) is presented. Six candidate configurations were considered for the prime contractor baseline design. The analysis included analytical assessments of control authority, control precision, efficiency and robustness, as well as simulation assessments of control performance. The principles used in the analytic assessments of controllability, robustness and fuel performance are covered and results provided for the configurations assessed. Simulation analysis was conducted using a pulse width modulated, 6 DOF reaction system control law with a simplex-based thruster selection algorithm. Control laws were automatically derived from hardware configuration parameters including thruster locations, directions, magnitude and specific impulse, as well as vehicle mass properties. This parameterized controller allowed rapid assessment of multiple candidate layouts. Simulation results are presented for final phase rendezvous and docking, as well as low lunar orbit attitude hold. Finally, on-going analysis to consider alternate Service Module designs and to assess the pilot-ability of the baseline design are discussed to provide a status of orbit control design work to date

Dyes as guests in ordered systems: current understanding and future directions

The optical properties of dyes dissolved in liquid crystals have led to their proposed use in a diverse range of practical applications. Such guest–host systems are typically required to fulfil a range of criteria relating to their absorption properties, degree of alignment and stability, but concurrently satisfying these requirements has proven a barrier to their widespread use. In this article, many of the proposed applications and their requirements are discussed, and an outline of some of the most prevalent classes of dye proposed in the context of guest–host systems is given, along with a summary of recent reports of dyes that exhibit thermotropic mesophases. Theoretical approaches to describing the alignment within guest–host systems are outlined, and possible strategies for the future rational design of guest–host systems are discussed

Implementing the use of operational data in buildings

This paper considers how Operational Data might address both legislative and operational requirements from the viewpoint of an operational estate. It is framed within the context of the IEE iSERVcmb project procedures for describing operational energy data against the building activities and assets. The observations and findings from the paper show that there appear no practical reasons why the same operational data should not be used to show compliance with legislative procedures, if these were to be framed appropriately, and to provide the detailed information needed to enable action to achieve efficiency improvements in an Estate. The paper shows the significant measured energy savings possible from the use of Operational Data, as well as the ability to understand the physical estate more accurately. The work is based on characterizing utility use in an Operational Estate by reference to performance achieved in other operational buildings, but the procedure could be used to characterize any efficiency measure with practical derived metrics

A combined experimental and computational study of anthraquinone dyes as guests in nematic liquid crystal hosts

A 1,5-diphenylythio-substituted anthraquinone, two 1,5-diphenylamino-substituted anthraquinones, and two 2,6-diphenyl-substituted anthraquinones have been studied in the context of the dyes as guests in nematic liquid crystal hosts, using a range of experimental and computational techniques. UV-visible absorption spectroscopy showed that the dyes exhibit visible transitions at a range of wavelengths, and polarised UV-visible absorption spectroscopy of aligned samples of the dyes in the nematic host E7 yielded a range of dichroic order parameters. Redox potentials of the dyes obtained by cyclic voltammetry and spectroelectrochemistry showed significantly more variation between the oxidation potentials than the reduction potentials, and a correlation between colour and redox properties was shown. Visible electronic transitions were calculated by time dependent density functional theory, and order parameter contributions determined from angles between the calculated transition dipole moment orientations and the minimum moment of inertia axes matched the trend in experimental dichroic order parameters. Molecular dynamics simulations of the dyes in E7 showed little variation in calculated orientational order parameters of the minimum moment of inertia axes of the dyes. The trend in experimental dichroic order parameters was replicated by calculated values, determined by combining the calculated orientational order parameters with the contributions from the transition dipole moment orientations. An assessment of various molecular alignment axes of the dyes indicated that the surface tensor model provided the most aligned axes of those tested, and improved the match with experimental dichroic order parameters. Incorporating dye flexibility into the calculations resulted in a further improvement in the match with experiment. Isolated molecule simulations combined with a mean field approach enabled the calculation of order parameters at a reduced computational expense. Application of this approach to a variety of dyes from different classes demonstrated a generally good match with reported experimental alignment trends