Crystallization of Arthrobacter sp. strain 1C N-(1-D-carboxyethyl)-L-norvaline dehydrogenase and its complex with NAD+

The novel NAD+-linked opine dehydrogenase from a soil isolate Arthrobacter sp. strain 1C belongs to an enzyme superfamily whose members exhibit quite diverse substrate specificites. Crystals of this opine dehydrogenase, obtained in the presence or absence of co-factor and substrates, have been shown to diffract to beyond 1.8 ? resolution. X-ray precession photographs have established that the crystals belong to space group P21212, with cell parameters a = 104.9, b = 80.0, c = 45.5 ? and a single subunit in the asymmetric unit. The elucidation of the three-dimensional structure of this enzyme will provide a structural framework for this novel class of dehydrogenases to enable a comparison to be made with other enzyme families and also as the basis for mutagenesis experiments directed towards the production of natural and synthetic opine-type compounds containing two chiral centres.     

Limits on the high-energy gamma and neutrino fluxes from the SGR 1806-20 giant flare of 27 December 2004 with the AMANDA-II detector

On 27 December 2004, a giant gamma flare from the Soft Gamma-Ray Repeater 1806-20 saturated many satellite gamma-ray detectors, being the brightest transient event ever observed in the Galaxy. AMANDA-II was used to search for down-going muons indicative of high-energy gammas and/or neutrinos from this object. The data revealed no significant signal, so upper limits (at 90% C.L.) on the normalization constant were set: 0.05(0.5) TeV-1 m;{-2} s;{-1} for gamma=-1.47 (-2) in the gamma flux and 0.4(6.1) TeV-1 m;{-2} s;{-1} for gamma=-1.47 (-2) in the high-energy neutrino flux.     

Effective suppression of period-doubling in two diffusively coupled logistic maps

We consider a system of two delay diffusively coupled logistic maps. We find that for moderate values of diffusion coupling, the period-doubling sequence is effectively suppressed. Our study supports the existence of certain generic features for systems consisting of two coupled maps.     

Special Issue: Experimental Algorithms

Preface

Special Issue: Experimental Algorithms     

Computable error bounds for pointwise derivatives of a Neumann problem

In this paper we discuss the recovery of derivatives and thecomputation of rigorous and useful upper bounds for the pointwiseerror in the recovered derivatives, for finite element approximationsof the Laplace equation with Neumann boundary conditions, especiallyat points close to or on a smooth, curved boundary. We analyzethe dipole image technique for the case of curved boundaries,and show how to compute reliable recovered derivatives and errorbounds even in the limiting case of points lying on the curvedboundary. Numerical experiments show reasonably tight errorbounds for points both close to and away from a curved boundary.     

The OPCL control method for entrainment,model-resonance,and migration actions on multiple-attractor systems

A survey is given of three different control objectives that can be achieved with the use of the Open-Plus-Closed-Loop (OPCL) control method, developed by Jackson and Grosu. For a system that can be characterized by N first-order ordinary differential equations, these objectives are: (1) the asymptotic entrainment of the system's dynamics to a prescribed "goal" dynamics, g(t); (2) an experimental-search method to determine an approximate dynamic model; (3) the transferal of the system from one attractor to any "target" attractor. For one class of systems, this may be accomplished without a model, by using only a short-duration record of the natural dynamics in the target attractor, as demonstrated experimentally using the Chua system. (c) 1997 American Institute of Physics.     

On the control of complex dynamic systems

A method is described for the limited control of the dynamics of systems which generally have several dynamic attractors. associated either with maps or first order ordinary differential equations (ODE) in ⁿ. The control is based on the existence of ‘convergent’ regions, C_C(k = 1,2,…), in the phase space of such systems, where there is ‘local convergence’ of all nearby orbits. The character of the control involves the ‘entrainment’ and subsequent possible ‘migration’ of the experimental system from one attractor to another. Entrainment means that lim_{t > → ∞} |x(t) − g(t)| = 0, where is the system's controlled dynamics, and the goal-dynamics, g(t) ε G_k, has any topological form but is limited dynamically and to regions of phase space, G_k, contained in some C_k, G_k C_k. The control process is initiated only when the system enters a ‘basin of entrainment’, BE_k G_k, associated with the goal-region G_k. Aside from this ‘macroscopic’ initial-state information about the system, no further feedback of dynamic information concerning the response of the system is required. The experimental reliability of the control requires that the regions, BE_k, be convex regions in the phase space, which can apparently be assured if G_k C_k. Simple illustrations of these concepts are given, using a general linear and a piecewise-linear ODE in . In addition to these entrainment-goals, ‘migration-goal’ dynamics is introduced, which intersects two convergent regions G ∩ C_j ≠ , G ∩ C_j ≠ (i ≠ j), and permits transferring the dynamics of a system from one attractor to another, or from one convergent region to another. In the present study these concepts are illustrated with various one-dimensional maps involving one or more attractors and convergent regions. Several theorems concerning entrainment are derived for very general, continuous one-dimensional maps. Sufficient conditions are also established which ensure ‘near-entrainment’ for a system, when the dynamic model of the system is not exactly known. The applications of these concepts to higher dimensional maps and flows will be presented in subsequent studies.