419 research outputs found
Buoyant MHD flows in a vertical channel: the levitation regime
Buoyant magnetohydrodynamic (MHD) flows with Joulean and viscous heating effects are considered in a vertical parallel plate channel. The applied magnetic field is uniform and perpendicular to the plates which are subject to adiabatic and isothermal boundary conditions, respectively. The main issue of the paper is the levitation regime, i.e., the fully developed flow regime for large values of the Hartmann number M, when the hydrodynamic pressure gradient evaluated at the temperature of the adiabatic wall is vanishing. The problem is solved analytically by Taylor series method and the solution is validated numerically. It is found that the fluid velocity points everywhere and for all values of M downward. For small M's, the velocity field extends nearly symmetrically (with respect to the mid-plane) over the whole section of the channel between the adiabatic and the isothermal walls. For large values of M, by contrast, the fluid levitates over a broad transversal range of the channel, while the motion becomes concentrated in a narrow boundary layer in the neighborhood of the isothermal wall. Accordingly, the fluid temperature is nearly uniform in the levitation range and decreases rapidly within the boundary layer in front of the isothermal wall. It also turns out that not only the volumetric heat generation by the Joule effect, but also that by viscous friction increases rapidly with increasing values of M, the latter effect being even larger than the former one for all
Vegetation and environmental responses to climate forcing during the last glacial maximum and deglaciation in the East Carpathians: attenuated response to maximum cooling and increased biomass burning
Eye movements and mental imagery during reading of literary texts with different narrative styles
Based on Kuzmicova's (2014) phenomenological typology of narrative styles, we studied the specific contributions of mental imagery to literary reading experience and to reading behavior by combining questionnaires with eye-tracking methodology. Specifically, we focused on the two main categories in Kuzmicova's (2014) typology, i.e., texts dominated by an "enactive" style, and texts dominated by a "descriptive" style. "Enactive" style texts render characters interacting with their environment, and "descriptive" style texts render environments dissociated from human action. The quantitative analyses of word category distributions of two dominantly enactive and two dominantly descriptive texts indicated significant differences especially in the number of verbs, with more verbs in enactment compared to descriptive texts. In a second study, participants read two texts (one theoretically cueing descriptive imagery, the other cueing enactment imagery) while their eye movements were recorded. After reading, participants completed questionnaires assessing aspects of the reading experience generally, as well as their text-elicited mental imagery specifically. Results show that readers experienced more difficulties conjuring up mental images during reading descriptive style texts and that longer fixation duration on words were associated with enactive style text. We propose that enactive style involves more imagery processes which can be reflected in eye movement behavior
Integrability and level crossing manifolds in a quantum Hamiltonian system
We consider a two-spin model, represented classically by a nonlinear
autonomous Hamiltonian system with two degrees of freedom and a nontrivial
integrability condition, and quantum mechanically by a real symmetric
Hamiltonian matrix with blocks of dimensionalities K=l(l+1)/2, l=1,2,... In the
six-dimensional (6D) parameter space of this model, classical integrability is
satisfied on a 5D hypersurface, and level crossings occur on 4D manifolds that
are completely embedded in the integrability hypersurface except for some
lower-D sub-manifolds. Under mild assumptions, the classical integrability
condition can be reconstructed from a purely quantum mechanical study of level
degeneracies in finite-dimensional invariant blocks of the Hamiltonian matrix.
Our conclusions are based on rigorous results for K=3 and on numerical results
for K=6,10.Comment: 8 pages, 3 figure
Creative Techniques in the Framework of Market and Evolution
This paper tries to reframe the man-machine problem, which has frequently changed throughout history. Originally, a machine was a helper of man, but later became its competitor and substitute. As a consequence of this, man has been pushed out of production and possibly, out of life itself. For today, nearly all the man’s functions – except for consumption and creativity – can be furnished by machines. Creativity should have a special place because it is the last “shelter” of man in the conflict with machine. Almost every other faculty of man has more or less been simulated by technology. There are some key questions to be answered: Whom do the creative techniques serve? Is the target group the men or machines
Integrability and action operators in quantum Hamiltonian systems
For a (classically) integrable quantum mechanical system with two degrees of
freedom, the functional dependence of the
Hamiltonian operator on the action operators is analyzed and compared with the
corresponding functional relationship in
the classical limit of that system. The former is shown to converge toward the
latter in some asymptotic regime associated with the classical limit, but the
convergence is, in general, non-uniform. The existence of the function
in the integrable regime of a parametric
quantum system explains empirical results for the dimensionality of manifolds
in parameter space on which at least two levels are degenerate. The comparative
analysis is carried out for an integrable one-parameter two-spin model.
Additional results presented for the (integrable) circular billiard model
illuminate the same conclusions from a different angle.Comment: 9 page
Chiral Solitons in a Current Coupled Schr\"odinger Equation With Self Interaction
Recently non-topological chiral soliton solutions were obtained in a
derivatively coupled non-linear Schr\"odinger model in 1+1 dimensions. We
extend the analysis to include a more general self-coupling potential (which
includes the previous cases) and find chiral soliton solutions. Interestingly
even the magnitude of the velocity is found to be fixed. Energy and U(1) charge
associated with this non-topological chiral solitons are also obtained.Comment: 8 pages, no figure, to appear in Phys. Rev.
Signatures of quantum integrability and nonintegrability in the spectral properties of finite Hamiltonian matrices
For a two-spin model which is (classically) integrable on a five-dimensional
hypersurface in six-dimensional parameter space and for which level
degeneracies occur exclusively (with one known exception) on four-dimensional
manifolds embedded in the integrability hypersurface, we investigate the
relations between symmetry, integrability, and the assignment of quantum
numbers to eigenstates. We calculate quantum invariants in the form of
expectation values for selected operators and monitor their dependence on the
Hamiltonian parameters along loops within, without, and across the
integrability hypersurface in parameter space. We find clear-cut signatures of
integrability and nonintegrability in the observed traces of quantum invariants
evaluated in finite-dimensional invariant Hilbert subspaces, The results
support the notion that quantum integrability depends on the existence of
action operators as constituent elements of the Hamiltonian.Comment: 11 page
Integrable quadratic Hamiltonians on so(4) and so(3,1)
We investigate a special class of quadratic Hamiltonians on so(4) and so(3,1)
and describe Hamiltonians that have additional polynomial integrals. One of the
main results is a new integrable case with an integral of sixth degree.Comment: 16 page
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