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Search Results: 1 - 10 of 3748 matches for " Andrei Ludu "
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Quasi-Continuous Symmetries of Non-Lie Type
Andrei Ludu,Walter Greiner
Physics , 1996, DOI: 10.1007/BF02551437
Abstract: We introduce a smooth mapping of some discrete space-time symmetries into quasi-continuous ones. Such transformations are related with q-deformations of the dilations of the Euclidean space and with the non-commutative space. We work out two examples of Hamiltonian invariance under such symmetries. The Schrodinger equation for a free particle is investigated in such a non-commutative plane and a connection with anyonic statistics is found.
Patterns on liquid surfaces: cnoidal waves, compactons and scaling
Andrei Ludu,Jerry P. Draayer
Physics , 2000, DOI: 10.1016/S0167-2789(98)00113-4
Abstract: Localized patterns and nonlinear oscillation formation on the bounded free surface of an ideal incompressible liquid are analytically investigated . Cnoidal modes, solitons and compactons, as traveling non-axially symmetric shapes are discused. A finite-difference differential generalized Korteweg-de Vries equation is shown to describe the three-dimensional motion of the fluid surface and the limit of long and shallow channels one reobtains the well known KdV equation. A tentative expansion formula for the representation of the general solution of a nonlinear equation, for given initial condition is introduced on a graphical-algebraic basis. The model is useful in multilayer fluid dynamics, cluster formation, and nuclear physics since, up to an overall scale, these systems display liquid free surface behavior.
Nonlinear Modes of Liquid Drops as Solitary Waves
Andrei Ludu,Jerry P. Draayer
Physics , 2000, DOI: 10.1103/PhysRevLett.80.2125
Abstract: The nolinear hydrodynamic equations of the surface of a liquid drop are shown to be directly connected to Korteweg de Vries (KdV, MKdV) systems, giving traveling solutions that are cnoidal waves. They generate multiscale patterns ranging from small harmonic oscillations (linearized model), to nonlinear oscillations, up through solitary waves. These non-axis-symmetric localized shapes are also described by a KdV Hamiltonian system. Recently such ``rotons'' were observed experimentally when the shape oscillations of a droplet became nonlinear. The results apply to drop-like systems from cluster formation to stellar models, including hyperdeformed nuclei and fission.
A model for African trypanosome cell motility and quantitative description of flagellar dynamics
Nathan R. Hutchings,Andrei Ludu
Physics , 2004,
Abstract: A quantitative description of the flagellar dynamics in the procyclic T. brucei is presented in terms of stationary oscillations and traveling waves. By using digital video microscopy to quantify the kinematics of trypanosome flagellar waveforms. A theoretical model is build starting from a Bernoulli-Euler flexural-torsional model of an elastic string with internal distribution of force and torque. The dynamics is internally driven by the action of the molecular motors along the string, which is proportional to the local shift and consequently to the local curvature. The model equation is a nonlinear partial differential wave equation of order four, containing nonlinear terms specific to the Korteweg-de Vries (KdV) equation and the modified-KdV equation. For different ranges of parameters we obtained kink-like solitons, breather solitons, and a new class of solutions constructed by smoothly piece-wise connected conic functions arcs (e.g. ellipse). The predicted amplitude and wavelengths are in good match with experiments. We also present the hypotheses for a step-wise kinematical model of swimming of procyclic African trypanosome.
A New Nonlinear Liquid Drop Model. Clusters as Solitons on The Nuclear Surface
Andrei Ludu,Aurel Sandulescu,Walter Greiner
Physics , 1996, DOI: 10.1088/0954-3899/23/3/005
Abstract: By introducing in the hydrodynamic model, i.e. in the hydrodynamic equations and the corresponding boundary conditions, the higher order terms in the deviation of the shape, we obtain in the second order the Korteweg de Vries equation (KdV). The same equation is obtained by introducing in the liquid drop model (LDM), i.e. in the kinetic, surface and Coulomb terms, the higher terms in the second order. The KdV equation has the cnoidal waves as steady-state solutions. These waves could describe the small anharmonic vibrations of spherical nuclei up to the solitary waves. The solitons could describe the preformation of clusters on the nuclear surface. We apply this nonlinear liquid drop model to the alpha formation in heavy nuclei. We find an additional minimum in the total energy of such systems, corresponding to the solitons as clusters on the nuclear surface. By introducing the shell effects we choose this minimum to be degenerated with the ground state. The spectroscopic factor is given by the ratio of the square amplitudes in the two minima.
Wavelets and Quantum Algebras
Andrei Ludu,Martin Greiner,Jerry P. Draayer
Physics , 2000, DOI: 10.1063/1.532292
Abstract: Wavelets, known to be useful in non-linear multi-scale processes and in multi-resolution analysis, are shown to have a q-deformed algebraic structure. The translation and dilation operators of the theory associate with any scaling equation a non-linear, two parameter algebra. This structure can be mapped onto the quantum group $su_{q}(2)$ in one limit, and approaches a Fourier series generating algebra, in another limit. A duality between any scaling function and its corresponding non-linear algebra is obtained. Examples for the Haar and B-wavelets are worked out in detail.
Periodic solutions and refractory periods in the soliton theory for nerves and the locust femoral nerve
Edgar Villagran Vargas,Andrei Ludu,Reinhold Hustert,Peter Gumrich,Andrew D. Jackson,Thomas Heimburg
Physics , 2010, DOI: 10.1016/j.bpc.2010.11.001
Abstract: Close to melting transitions it is possible to propagate solitary electromechanical pulses which reflect many of the experimental features of the nerve pulse including mechanical dislocations and reversible heat production. Here we show that one also obtains the possibility of periodic pulse generation when the boundary condition for the nerve is the conservation of the overall length of the nerve. This condition generates an undershoot beneath the baseline (`hyperpolarization') and a `refractory period', i.e., a minimum distance between pulses. In this paper, we outline the theory for periodic solutions to the wave equation and compare these results to action potentials from the femoral nerve of the locust (locusta migratoria). In particular, we describe the frequently occurring minimum-distance doublet pulses seen in these neurons and compare them to the periodic pulse solutions.
Me and Ion Stroescu
Alin Ludu DUMBRAVA
INCAS Bulletin , 2011, DOI: 10.13111/2066-8201.2011.3.s2
Abstract:
Complex su_q(2) Dynamical Symmetry, Limiting Cases and 1-Dimensional Potential Realisation
A. Ludu,W. Scheid
Physics , 1996,
Abstract: Using a complex deformation q=exp(is) of su(2) we obtain extensions of the finite-dimensional representations towards the infinite-dimensional ones. A generalised q-deformation of su(2), as a Hopf algebra is introduced. We present the corresponding Schrodinger picture, by using a differential realisation, and a large class of potentials is obtained.A connection between the unirreps with q a root of unity and the comensurability of the potentials is investigated. The smooth transition between su(2) and su(1,1) , through E(1) is obtained at different levels: of the unirreps, of the topology, of the commutators and of the potentials in the corresponding Schrodinger equation.
Geometry of Axoneme-like Filament Bundles
A. Ludu,N. Hutchings
Physics , 2004,
Abstract: We develop a formalism that describes the bending and twisting of axoneme-like filament bundles. We obtain general formulas to determine the relative sliding between any arbitrary filaments in a bundle subjected to unconstrained deformations. Particular examples for bending, twisting, helical and toroidal shapes, and combinations of these are discussed. Resulting equations for sliding and transversal shifting, expressed in terms of the curvature and torsion of the bundle, are applied to flagellar bend data. We prove that simultaneous combination of twisting and bending can produce a drastically drop in the sliding, by decreasing bending rigidity.
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