Nonclassical shallow water flows

This paper deals with violent discontinuities in shallow water flows with large Froude number $F$. On a horizontal base, the paradigm problem is that of the impact of two fluid layers in situations where the flow can be modelled as two smooth regions joined by a singularity in the flow field. Within the framework of shallow water theory we show that, over a certain timescale, this discontinuity may be described by a delta-shock, which is a weak solution of the underlying conservation laws in which the depth and mass and momentum fluxes have both delta function and step functioncomponents. We also make some conjectures about how this model evolves from the traditional model for jet impacts in which a spout is emitted. For flows on a sloping base, we show that for flow with an aspect ratio of \emph{O}($F^{-2}$) on a base with an \emph{O(1)} or larger slope, the governing equations admit a new type of discontinuous solution that is also modelled as a delta-shock. The physical manifestation of this discontinuity is a small `tube' of fluid bounding the flow. The delta-shock conditions for this flow are derived and solved for a point source on an inclined plane. This latter delta-shock framework also sheds light on the evolution of the layer impact on a horizontal base

Saddle-point dynamics: conditions for asymptotic stability of saddle points

This paper considers continuously differentiable functions of two vector variables that have (possibly a continuum of) min-max saddle points. We study the asymptotic convergence properties of the associated saddle-point dynamics (gradient-descent in the first variable and gradient-ascent in the second one). We identify a suite of complementary conditions under which the set of saddle points is asymptotically stable under the saddle-point dynamics. Our first set of results is based on the convexity-concavity of the function defining the saddle-point dynamics to establish the convergence guarantees. For functions that do not enjoy this feature, our second set of results relies on properties of the linearization of the dynamics, the function along the proximal normals to the saddle set, and the linearity of the function in one variable. We also provide global versions of the asymptotic convergence results. Various examples illustrate our discussion.Comment: 26 pages, To appear in SIAM Journal on Control and Optimizatio

Light Front Formalism for Composite Systems and Some of Its Applications in Particle and Relativistic Nuclear Physics

Light front formalism for composite systems is presented. Derivation of equations for bound state and scattering problems are given. Methods of constructing of elastic form factors and scattering amplitudes of composite particles are reviewed. Elastic form factors in the impulse approximation are calculated. Scattering amplitudes for relativistic bound states are constructed. Some model cases for transition amplitudes are considered. Deep inelastic form factors (structure functions) are expressed through light front wave functions. It is shown that taking into account of transverse motion of partons leads to the violation of Bjorken scaling and structure functions become square of transverse momentum dependent. Possible explanation of the EMC-effect is given. Problem of light front relativization of wave functions of lightest nuclei is considered. Scaling properties of deuteron, ${}^3He$ and ${}^4He$ light front wave functions are checked in a rather wide energy range.Comment: Review paper, Submitted to Phys. Rep., 89 pages, 23 figure

Saturn sa-9/pegasus a postflight trajectory

Postflight trajectory analysis and orbital flight discussion for Saturn I /SA- 9/ launch vehicle carrying Pegasus payloa

On leading charmed meson production in π\pi-nucleon interactions

It is shown that the D--meson, whose light quark is the initial-pion valence quark and whose charmed quark is produced in annihilation of valence quarks and has got a large enough momentum, is really a leading meson in reactions like $\pi^- p -> DX$. If such annihilation of valence quarks from initial hadrons is impossible there must be no distinct leading effect.Comment: 4 pages, 2.ps-figure

Derived Koszul Duality and Involutions in the Algebraic K-Theory of Spaces

We interpret different constructions of the algebraic $K$-theory of spaces as an instance of derived Koszul (or bar) duality and also as an instance of Morita equivalence. We relate the interplay between these two descriptions to the homotopy involution. We define a geometric analog of the Swan theory G^{\bZ}(\bZ[\pi]) in terms of $\Sigma^{\infty}_{+} \Omega X$ and show that it is the algebraic $K$-theory of the $E_{\infty}$ ring spectrum $DX=S^{X_{+}}$

Entropy production and fluctuation theorems under feedback control: the molecular refrigerator model revisited

We revisit the model of a Brownian particle in a heat bath submitted to an actively controlled force proportional to the velocity that leads to thermal noise reduction (cold damping). We investigate the influence of the continuous feedback on the fluctuations of the total entropy production and show that the explicit expression of the detailed fluctuation theorem involves different dynamics and observables in the forward and backward processes. As an illustration, we study the analytically solvable case of a harmonic oscillator and calculate the characteristic function of the entropy production in a nonequilibrium steady state. We then determine the corresponding large deviation function which results from an unusual interplay between 'boundary' and 'bulk' contributions.Comment: 16 pages, 5 figures. References 9,10,13,14,15 added. A few changes in the text. Accepted for publication in J. Stat. Mec

Movements of molecular motors: Ratchets, random walks and traffic phenomena

Processive molecular motors which drive the traffic of organelles in cells move in a directed way along cytoskeletal filaments. On large time scales, they perform motor walks, i.e., peculiar random walks which arise from the repeated unbinding from and rebinding to filaments. Unbound motors perform Brownian motion in the surrounding fluid. In addition, the traffic of molecular motors exhibits many cooperative phenomena. In particular, it faces similar problems as the traffic on streets such as the occurrence of traffic jams and the coordination of (two-way) traffic. These issues are studied here theoretically using lattice models.Comment: latex, uses elsart.cls and phyeauth.cls (included), 10 pages, 6 figures, to appear in the proceedings of FQMT'04, Pragu

La influència del sexe i el rol en les interrupcions produïdes en tertúlies periodístiques sobre política

Several works have been carried out about linguistic differences between men and women talk and, specifically, about how they use polite and impolite strategies. In this article, we aim to focus on interruption, an impolite strategy whose appearance in conversation was initially explained by some authors as the consequence of the fact that, in Western communities, women spoke so much that men interrrupted them. In this sense, we intend to show the correlation between different kinds of interruptions and gender and role variables in a specific discourse type, the political talk show, in which turn-talking generally takes place freely.Dins de l’àmbit d’estudi que tracta les diferències lingüístiques existents entre la parla dels homes i les dones, són moltes les investigacions realitzades al voltant de la manifestació de cortesia verbal atenent el factor sexe del parlant. En aquesta ocasió, ens centrem en el cas específic de la interrupció, fenomen en el qual els estudis inicials semblaven confirmar l’estereotip, vigent en les cultures occidentals, que consistia a afirmar que les dones parlaven en excés i que els homes les interrompien. En aquest sentit, en aquest treball pretenem ensenyar la correlació que s’estableix entre la realització en la conversa d’interrupcions de diferent naturalesa i els factors sexe i rol del parlant en un tipus discursiu específic: la tertúlia periodística de tema polític, on es produeix un sistema, en general, lliure pel que fa a la distribució del torn de parla