162
326.71
2.02
208

Publication History View all

  • [Show abstract] [Hide abstract]
    ABSTRACT: A new test is presented for the BIBO stability of delay systems of neutral type with a single delay, specified in terms of their transfer functions, enabling us to decide on some cases that were previously open. Next, a class of fractional systems is considered, and a method is given for determining the stability intervals for such systems.
    Systems & Control Letters 02/2014; 64:43–46. DOI:10.1016/j.sysconle.2013.11.009
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper introduces a general continuous-time mathematical framework for solution of dynamic mean-variance control problems. We obtain theoretical results for two classes of functionals: the first one depends on the whole trajectory of the controlled process and the second one is based on its terminal-time value. These results enable the development of numerical methods for mean-variance problems for a pre-determined risk-aversion coefficient. We apply them to study optimal trading strategies pursued by fund managers in response to various types of compensation schemes. In particular, we examine the effects of continuous monitoring and scheme's symmetry on trading behaviour and fund performance.
    European Journal of Operational Research 04/2013; 234(2):561-570. DOI:10.1016/j.ejor.2013.04.038
  • Source
    Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences 07/2012; 370(1971):3273-6. DOI:10.1098/rsta.2012.0221
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigate the launching of jets and outflows from magnetically diffusive accretion disks. Using the PLUTO code we solve the time-dependent resistive MHD equations taking into account the disk and jet evolution simultaneously. The main question we address is which kind of disks do launch jets and which kind of disks do not? In particular, we study how the magnitude and distribution of the (turbulent) magnetic diffusivity affect mass loading and jet acceleration. We have applied a turbulent magnetic diffusivity based on \alpha-prescription, but have also investigate examples where the scale height of diffusivity is larger than that of the disk gas pressure. We further investigate how the ejection efficiency is governed by the magnetic field strength. Our simulations last for up to 5000 dynamical time scales corresponding to 900 orbital periods of the inner disk. As a general result we observe a continuous and robust outflow launched from the inner part of the disk, expanding into a collimated jet of super fast magneto-sonic speed. For long time scales the disk internal dynamics changes, as due to outflow ejection and disk accretion the disk mass decreases. For magneto-centrifugally driven jets we find that for i) less diffusive disks, ii) a stronger magnetic field, iii) a low poloidal diffusivity, or a iv) lower numerical diffusivity (resolution), the mass loading of the outflow is increased - resulting in more powerful jets with high mass flux. For weak magnetization the (weak) outflow is driven by the magnetic pressure gradient. We further investigate the jet asymptotic velocity and the jet rotational velocity in respect of the different launching scenarios. We find a lower degree of jet collimation than previous studies, most probably due to our revised outflow boundary condition.
    The Astrophysical Journal 07/2012; 757(1). DOI:10.1088/0004-637X/757/1/65
  • [Show abstract] [Hide abstract]
    ABSTRACT: The natural world's interconnectivity should inspire better models of the Universe, says Barry Cooper.
    Nature 02/2012; 482(7386):465. DOI:10.1038/482465a
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Sequences of canonical conservation laws and generalized symmetries for the lattice Boussinesq and the lattice modified Boussinesq systems are successively derived. The interpretation of these symmetries as differential-difference equations leads to corresponding hierarchies of such equations for which conservation laws and Lax pairs are constructed. Finally, using the continuous symmetry reduction approach, an integrable, multidimensionally consistent system of partial differential equations is derived in relation with the lattice modified Boussinesq system.
    Physics Letters A 12/2011; 376(35). DOI:10.1016/j.physleta.2012.06.004
  • [Show abstract] [Hide abstract]
    ABSTRACT: Since the foot-and-mouth disease outbreak of 2001 in the United Kingdom, there has been debate about the sharing, between government and industry, both the costs of livestock disease outbreaks and responsibility for the decisions that give rise to them. As part of a consultation into the formation of a new body to manage livestock diseases, government veterinarians and economists produced estimates of the average annual costs for a number of exotic infectious diseases. In this article, we demonstrate how the government experts were helped to quantify their uncertainties about the cost estimates using formal expert elicitation techniques. This has enabled the decisionmakers to have a greater appreciation of government experts' uncertainty in this policy area.
    Risk Analysis 10/2011; 32(5):881-93. DOI:10.1111/j.1539-6924.2011.01704.x
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Techniques of constrained approximation are used to recover solutions to elliptic partial differential equations from incomplete and corrupted boundary data. The approach involves constructive computations in generalized Hardy spaces of functions whose real and imaginary parts are related by formulae similar to the Cauchy–Riemann equations: these spaces were recently introduced by Baratchart, Leblond, Rigat and Russ. A prime motivation for this research is the modeling of plasma confinement in a tokamak reactor. Constructive and numerical aspects are also discussed in detail.
    Applied and Computational Harmonic Analysis 09/2011; 31(2-31):264-285. DOI:10.1016/j.acha.2011.01.003
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A relational first order structure is homogeneous if it is countable (possibly finite) and every isomorphism between finite substructures extends to an automorphism. This article is a survey of several aspects of homogeneity, with emphasis on countably infinite homogeneous structures. These arise as Fraissé limits of amalgamation classes of finite structures. The subject has connections to model theory, to permutation group theory, to combinatorics (for example through combinatorial enumeration, and through Ramsey theory), and to descriptive set theory. Recently there has been a focus on connections to topological dynamics, and to constraint satisfaction. The article discusses connections between these topics, with an emphasis on examples, and on special properties of an amalgamation class which yield important consequences for the automorphism group.
    Discrete Mathematics 08/2011; 311(15-311):1599-1634. DOI:10.1016/j.disc.2011.01.024
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The cubic-quintic Swift-Hohenberg equation (SH35) provides a convenient order parameter description of several convective systems with reflection symmetry in the layer midplane, including binary fluid convection. We use SH35 with an additional quadratic term to determine the qualitative effects of breaking the midplane reflection symmetry on the properties of spatially localized structures in these systems. Our results describe how the snakes-and-ladders organization of localized structures in SH35 deforms with increasing symmetry breaking and show that the deformation ultimately generates the snakes-and-ladders structure familiar from the quadratic-cubic Swift-Hohenberg equation. Moreover, in nonvariational systems, such as convection, odd-parity convectons necessarily drift when the reflection symmetry is broken, permitting collisions among moving localized structures. Collisions between both identical and nonidentical traveling states are described.
    Physical Review E 07/2011; 84(1 Pt 2):016204. DOI:10.1103/PhysRevE.84.016204
Information provided on this web page is aggregated encyclopedic and bibliographical information relating to the named institution. Information provided is not approved by the institution itself. The institution’s logo (and/or other graphical identification, such as a coat of arms) is used only to identify the institution in a nominal way. Under certain jurisdictions it may be property of the institution.
View all

Top publications last week

 
Journal of Functional Analysis 09/2014; 267(6). DOI:10.1016/j.jfa.2014.06.007
9 Downloads
 
Communications in Mathematical Physics 02/1980; DOI:10.1007/BF01205037
9 Downloads