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Om den gode videnskabelige dialog – en kommentar
Finn Olesen
Erhvervshistorisk ?rbog , 2012,
Abstract: Det er en velkendt kendsgerning, at den konomiske mainstream t nkning gennem tiderne har v ret udsat for en st rre eller en mindre kritik. I moderne tid har kritikken is r v ret markant fra de s kaldte heterodokse konomers side. Forst rket af de seneste rs internationale finanskrise og generelle konomiske tilbageslag er interessen for et alternativ til mainstream af helt indlysende rsager blevet aktualiseret. I denne forbindelse har der ogs v ret en diskussion af, hvorledes heterodokse elementer bedst sl r igennem inden for is r den makro konomiske mainstream. Hvordan f r de heterodokse bedst kommunikeret deres budskab ud med den st rst mulige gennemslagskraft til f lge? Om denne dialog omhandler denne kommentar.
Dual strings and magnetohydrodynamics
P. Olesen
Physics , 1995, DOI: 10.1016/0370-2693(95)01383-0
Abstract: We investigate whether dual strings could be solutions of the magnetohydrodynamics equations in the limit of infinite conductivity. We find that the induction equation is satisfied, and we discuss the Navier-Stokes equation (without viscosity) with the Lorentz force included. We argue that the dual string equations (with a non-universal maximum velocity) should describe the large scale motion of narrow magnetic flux tubes, because of a large reparametrization (gauge) invariance of the magnetic and electric string fields. It is shown that the energy-momentum tensor for the dual string can be reinterpreted as an energy-momentum tensor for magnetohydrodynamics, provided certain conditions are satisfied. We also give a brief discussion of the case when magnetic monopoles are included, and indicate how this can lead to a non-relativistic "electrohydrodynamics" picture of confinement.
On inverse Cascades and Primordial Magnetic Fields
P. Olesen
Physics , 1996, DOI: 10.1016/S0370-2693(97)00235-9
Abstract: We consider primordial spectra with simple power behaviours and show that in the Navier-Stokes and magnetohydrodynamics equations without forcing, there exists systems in three dimensions with a subsequent inverse cascade, transferring energy from small to large spatial scales. This can have consequences in astrophysics for the evolution of density fluctuations, for primordial magnetic fields, and for the effect of diffusion. In general, if the initial spectrum is k^{alpha}, then in the ``inertial'' range, for alpha >-3 there is an inverse cascade, whereas for alpha<-3 there is a forward cascade.
Some Speculations on the Gauge Coupling in the AdS/CFT Approach
P. Olesen
Physics , 1999,
Abstract: We propose the principle that the scale of the glueball masses in the AdS/CFT approach to QCD should be set by the square root of the string tension. It then turns out that the strong bare coupling runs logarithmically with the ultraviolet cutoff T if first order world sheet fluctuations are included. We also point out that in the end, when all corrections are included, one should obtain an equation for the coupling running with T which has some similarity with the equation for the strong bare coupling.
An Integrable Version of Burgers Equation in "Magnetohydrodynamics"
P. Olesen
Physics , 2003, DOI: 10.1103/PhysRevE.68.016307
Abstract: It is pointed out that for the case of (compressible) magnetohydrodynamics (MHD) with the fields $v_y(y,t)$ and $B_x(y,t)$ one can have equations of the Burgers type which are integrable. We discuss the solutions. It turns out that the propagation of the non-linear effects is governed by the initial velocity (as in Burgers case) as well as by the initial Alfv\'en velocity. Many results previously obtained for the Burgers equation can be transferred to the MHD case. We also discuss equipartition $v_y=\pm B_x$. It is shown that an initial localized small scale magnetic field will end up in fields moving to the left and the right, thus transporting energy from smaller to larger distances.
On the zero viscosity limit
P. Olesen
Physics , 2007,
Abstract: The question of whether the zero viscosity limit $\nu\to 0$ is identical to the no viscosity $\nu\equiv 0$ case is investigated in a simple shell (GOY) model with only three shells. We find that it is possible to express two velocities in terms of Bessel functions. The third velocity function acts as a background. The relevant Bessel functions are infinitely oscillating as $\nu\to 0$ and do not have a limiting value. Therefore two of the velocity functions of this three-shell model are not analytic functions of $\nu$ at the point $\nu =0$. We also mention a perturbative method which may be used to improve the model.
A Linear Equation for Wilson Loops
Poul Olesen
Physics , 2007, DOI: 10.1016/j.physletb.2008.01.036
Abstract: The Makeenko-Migdal loop equation is non-linear and first order in the area derivative, but we show that for simple loops in QCD$_2$ it is possible to reformulate this equation as a linear equation with second order derivatives. This equation is a bound state Schr\"odinger equation with a three dimensional Coulomb potential. Thus, loop dynamics leads to a surprising new picture of confinement, where this phenomenon is due to a (bound state) localization in loop space, with the Wilson loops decaying exponentially outside a characteristic radius.
A W--dressed Electroweak String
P. Olesen
Physics , 1993,
Abstract: We give plausibility arguments for the existence of a $W$--dressed electroweak string for the \ws ~model with $\th_W = 0$. This string is a $Z$--string which in the core has a finite energy contribution from $W$--condensation induced by the anomalous magnetic moment in the \ym field. The solution which has minimum energy at $r=0$ interpolates between the unbroken $(r=0)$ and the broken $(r \ra \infty) \ SU(2) \times U_y(1)$ phase.
Tunneling in two dimensional QCD
Poul Olesen
Physics , 2006, DOI: 10.1016/j.nuclphysb.2006.06.027
Abstract: The spectral density for two dimensional continuum QCD has a non-analytic behavior for a critical area. Apparently this is not reflected in the Wilson loops. However, we show that the existence of a critical area is encoded in the winding Wilson loops: Although there is no non-analyticity or phase transition in these Wilson loops, the dynamics of these loops consists of two smoothly connected domains separated by the critical area, one domain with a confining behavior for large winding Wilson loops, and one (below the critical size) where the string tension disappears. We show that this can be interpreted in terms of a simple tunneling process between an ordered and a disordered state. In view of recent results by Narayanan and Neuberger this tunneling may also be relevant for four dimensional QCD.
Towards Matrix Models in IIB Superstrings
P. Olesen
Physics , 1997,
Abstract: I review the properties of a matrix action of relevance for IIB superstrings. This model generalizes the action proposed by Ishibashi, Kawai, Kitazawa, and Tsuchiya by introducing an auxillary field Y, which is the matrix version of the auxillary field g in the Schild action.
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