15,085 research outputs found
The dynamics of internal working surfaces in MHD jets
The dynamical effects of magnetic fields in models of radiative, Herbig-Haro
(HH) jets have been studied in a number of papers. For example, magnetized,
radiative jets from variable sources have been studied with axisymmetric and 3D
numerical simulations. In this paper, we present an analytic model describing
the effect of a toroidal magnetic field on the internal working surfaces that
result from a variability in the ejection velocity. We find that for parameters
appropriate for HH jets the forces associated with the magnetic field dominate
over the gas pressure force within the working surfaces. Depending on the ram
pressure radial cross section of the jet, the magnetic field can produce a
strong axial pinch, or, alternatively, a broadening of the internal working
surfaces. We check the validity of the analytic model with axisymmetric
numerical simulations of variable, magnetized jets.Comment: 14 pages, 4 figures. ApJ in pres
Quantization of strings and branes coupled to BF theory
BF theory is a topological theory that can be seen as a natural
generalization of 3-dimensional gravity to arbitrary dimensions. Here we show
that the coupling to point particles that is natural in three dimensions
generalizes in a direct way to BF theory in d dimensions coupled to
(d-3)-branes. In the resulting model, the connection is flat except along the
membrane world-sheet, where it has a conical singularity whose strength is
proportional to the membrane tension. As a step towards canonically quantizing
these models, we show that a basis of kinematical states is given by `membrane
spin networks', which are spin networks equipped with extra data where their
edges end on a brane
Density of states determination from steady-state photocarrier grating measurements
We present a method to obtain the density of states (DOS) of photoconductive insulators based on steady-state photocarrier grating (SSPG) measurements. A simple expression—relating the DOS at the electron quasi-Fermi level to measurable quantities—is deduced by performing suitable approximations from the analytical solution of the generalized equations that describe the SSPG experiment. The validity of the approximations and the applicability of the final expression are verified from numerical simulations of the process. The usefulness of the method is demonstrated by performing measurements on a standard hydrogenated amorphous silicon sample.Fil: Schmidt, Javier Alejandro. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Santa Fe. Instituto de Desarrollo TecnolĂłgico para la Industria QuĂmica. Universidad Nacional del Litoral. Instituto de Desarrollo TecnolĂłgico para la Industria QuĂmica; ArgentinaFil: Longeaud, C.. UniversitĂ© Paris VI et XI; Franci
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