Barrier Lyapunov Functions for the control of output-constrained nonlinear systems

In this paper, we present control designs for single-input single-output (SISO) nonlinear systems in strict feedback form with an output constraint. To prevent constraint violation, we employ a Barrier Lyapunov Function, which grows to infinity when its arguments approach some limits. By ensuring boundedness of the Barrier Lyapunov Function in the closed loop, we ensure that those limits are not transgressed. Besides the nominal case where full knowledge of the plant is available, we also tackle scenarios wherein parametric uncertainties are present. Asymptotic tracking is achieved without violation of the constraint, and all closed loop signals remain bounded, under a mild condition on the initial output. Furthermore, we explore the use of an Asymmetric Barrier Lyapunov Function as a generalized approach that relaxes the requirements on the initial conditions. We also compare our control with one that is based on a Quadratic Lyapunov Function, and we show that our control requires less restrictive initial conditions. A numerical example is provided to illustrate the performance of the proposed control.     

Supporting the consumption and co-authoring of locative media experiences for a rural village community: design and field trial evaluation of the SHARC2.0 framework

Locative Media Experiences (LMEs) have significant potential in enabling visitors to engage with the places that they visit through an appreciation of local history. For example, a visitor to Berlin that is exploring remnants of the Berlin Wall may be encouraged to appreciate (or in part experience) the falling of the Berlin wall by consuming multimedia directly related to her current location such as listening to audio recordings of the assembled crowds on 10th November 1989. However, despite the growing popularity of enabling technologies (such as GPS-equipped smart phones and tablets), the availability of tools that support the authoring of LMEs is limited. In addition, mobile apps that support the consumption of LMEs typically adopt an approach that precludes users from being able to respond with their own multimedia contributions. In this article we describe the design and evaluation of the SHARC2.0 framework that has been developed as part of our long-term and participatory engagement with the rural village of Wray in the north of England. Wray has very limited cellular data coverage which has placed a requirement on the framework and associated tools to operate without reliance on network connectivity. A field study is presented which featured a LME relating to Wray’s local history and which contained multimedia content contributed by members of the community including historic photos (taken from an existing ‘Digital Noticeboard’ system), audio-clips (from a local historian and village residents) and video (contributed during a design workshop). The novelty of our approach relates to the ability of multiple authors to contribute to a LME in-situ, and the utilisation of personal cloud storage for storing the contents associated with a multi-authored LME.

     

ISICS2011, an updated version of ISICS: A program for calculation K-, L-, and M-shell cross sections from PWBA and ECPSSR theories using a personal computer

In this new version of ISICS, called ISICS2011, a few omissions and incorrect entries in the built-in file of electron binding energies have been corrected; operational situations leading to un-physical behavior have been identified and flagged.

New version program summary

Program title: ISICS2011Catalogue identifier: ADDS_v5_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADDS_v5_0.htmlProgram obtainable from: CPC Program Library, Queen?s University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 6011No. of bytes in distributed program, including test data, etc.: 130 587Distribution format: tar.gzProgramming language: CComputer: 80486 or higher-level PCsOperating system: WINDOWS XP and all earlier operating systemsClassification: 16.7Catalogue identifier of previous version: ADDS_v4_0Journal reference of previous version: Comput. Phys. Commun. 180 (2009) 1716.Does the new version supersede the previous version?: YesNature of problem: Ionization and X-ray production cross section calculations for ion–atom collisions.Solution method: Numerical integration of form factor using a logarithmic transform and Gaussian quadrature, plus exact integration limits.Reasons for new version: General need for higher precision in output format for projectile energies; some built-in binding energies needed correcting; some anomalous results occur due to faulty read-in data or calculated parameters becoming un-physical; erroneous calculations could result for the L and M shells when restricted K-shell options are inadvertently chosen; to achieve general compatibility with ISICSoo, a companion C++ version that is portable to Linux and MacOS platforms, has been submitted for publication in the CPC Program Library approximately at the same time as this present new standalone version of ISICS [1].Summary of revisions: The format field for projectile energies in the output has been expanded from two to four decimal places in order to distinguish between closely spaced energy values. There were a few entries in the executable binding energy file that needed correcting; K shell of Eu, M shells of Zn, M1 shell of Kr. The corrected values were also entered in the ENERGY.DAT file. In addition, an alternate data file of binding energies is included, called ENERGY_GW.DAT, which is more up-to-date [2]. Likewise, an alternate atomic parameters data file is now included, called FLOURE_JC.DAT, which is more up-to-date [3] fluorescence yields for the K and L shells and Coster–Kronig parameters for the L shell. Both data files can be read in using the -f usage option. To do this, the original energy file should be renamed and saved (e.g., ENERGY_BB.DAT) and the new file (ENERGY_GW.DAT ) should be duplicated as ENERGY.DAT to be read in using the -f option. Similarly for reading in an alternate FLOURE.DAT file. As with previous versions, the user can also simply input different values of any input quantity by invoking the “specify your own parameters” option from the main menu. You can also use this option to simply check the values of the built-in values of the parameters. If it still happens that a zero binding energy for a particular sub-shell is read in, the program will not completely abort, but will calculate results for the other sub-shells while setting the affected sub-shell output to zero. In calculating the Coulomb deflection factor, if the quantity inside the radical sign of the parameter zs becomes zero or negative, to prevent the program from aborting, the PWBA cross sections are still calculated while the ECPSSR cross sections are set to zero. This situation can happen for very low energy collisions, such as were noticed for helium ions on copper at energies of E?11.2 keV. It was observed during the engineering of ISICSoo [1] that erroneous calculations could result for the L- and M-shell cases when restricted K-shell R or HSR scaling options were inappropriately chosen. The program has now been fixed so that these inappropriate options are ignored for the L and M shells. In the previous versions, the usage for inputting a batch data file was incorrectly stated in the Users Manual as -Bxxx; the correct designation is -Fxxx, or alternatively, -Ixxx, as indicated on the usage screen in running the program.A revised Users Manual is also available.Restrictions: The consumed CPU time increases with the atomic shell (K, L, M), but execution is still very fast.Running time: This depends on which shell and the number of different energies to be used in the calculation. The running time is not significantly changed from the previous version.References:

• [1] 

  M. Batic, M.G. Pia, S. Cipolla, Comput. Phys. Commun. (2011), submitted for publication.

• [2] 

  http://www.jlab.org/~gwyn/ebindene.html.

• [3] 

  J. Campbell, At. Data Nucl. Data Tables 85 (2003) 291.

     

The minimum information about failures for solving non-local tasks in message-passing systems

We first define the basic notions of local and non-local tasks for distributed systems. Intuitively, a task is local if, in a system with no failures, each process can compute its output value locally by applying some local function on its own input value (so the output value of each process depends only on the process’ own input value, not on the input values of the other processes); a task is nonlocal otherwise. All the interesting distributed tasks, including all those that have been investigated in the literature (e.g., consensus, set agreement, renaming, atomic commit, etc.) are non-local. In this paper we consider non-local tasks and determine the minimum information about failures that is necessary to solve such tasks in message-passing distributed systems. As part of this work, we also introduces weak set agreement—a natural weakening of set agreement—and show that, in some precise sense, it is the weakest nonlocal task in message-passing systems.     

Failure detection and consensus in the crash-recovery model

Summary. We study the problems of failure detection and consensus in asynchronous systems in which processes may crash and recover, and links may lose messages. We first propose new failure detectors that are particularly suitable to the crash-recovery model. We next determine under what conditions stable storage is necessary to solve consensus in this model. Using the new failure detectors, we give two consensus algorithms that match these conditions: one requires stable storage and the other does not. Both algorithms tolerate link failures and are particularly efficient in the runs that are most likely in practice – those with no failures or failure detector mistakes. In such runs, consensus is achieved within time and with 4 n messages, where is the maximum message delay and n is the number of processes in the system. Received: May 1998 / Accepted: November 1999     

Amperometric biosensor for formic acid in air

The possibility of developing a simple, inexpensive and specific personal passive “real-time” air sampler incorporating a biosensor for formic acid was investigated. The sensor is based on the enzymatic reaction between formic acid and formate dehydrogenase (FDH) with nicotinamide adenine dinucleotide (NAD⁺) as a co-factor and Meldola's blue as mediator. An effective way to immobilise the enzyme, co-factor and Meldola's blue on screen-printed, disposable, electrodes was found to be in a mixture of glycerol and phosphate buffer covered with a gas-permeable membrane. Steady-state current was reached after 4–15 min and the limit of detection was calculated to be below 1 mg/m³. However, the response decreased by 50% after storage at −15°C for 1 day.     

Symbolic computation with finite biquandles

A method of computing a basis for the second Yang–Baxter cohomology of a finite biquandle with coefficients in Q$\mathbb{Q}$ and _Zp${\mathbb{Z}}_p$ from a matrix presentation of the finite biquandle is described. We also describe a method for computing the Yang–Baxter cocycle invariants of an oriented knot or link represented as a signed Gauss code. We provide a URL for our Maple implementations of these algorithms.     

Supporting command and control training functions in the emergency management domain using cognitive systems engineering

The design and implementation of MERMAIDS, a computer-based training system in the domain of emergency command and control, is described. The research investigates the use of cognitive systems engineering and information management tools for modelling and representing training knowledge of emergency system operators. We propose a decision-centric human-computer interface as a new method of supporting computer-based modelling in the domain of emergency systems. Several interacting themes in information management relevant to emergency response planning are discussed.     

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