1,529 research outputs found
The formation of filamentary bundles in turbulent molecular clouds
The classical picture of a star-forming filament is a near-equilibrium
structure, with collapse dependent on its gravitational criticality. Recent
observations have complicated this picture, revealing filaments as a mess of
apparently interacting subfilaments, with transsonic internal velocity
dispersions and mildly supersonic intra-subfilament dispersions. How structures
like this form is unresolved. Here we study the velocity structure of
filamentary regions in a simulation of a turbulent molecular cloud. We present
two main findings: first, the observed complex velocity features in filaments
arise naturally in self gravitating hydrodynamic simulations of turbulent
clouds without the need for magnetic or other effects. Second, a region that is
filamentary only in projection and is in fact made of spatially distinct
features can displays these same velocity characteristics. The fact that these
disjoint structures can masquerade as coherent filaments in both projection and
velocity diagnostics highlights the need to continue developing sophisticated
filamentary analysis techniques for star formation observations.Comment: Undergoing revision for ApJ; comments are welcome. A very similar set
of data to the one presented here can be interacted with at
http://nickolas1.com/filamentvelocities
Symmetric Regularization, Reduction and Blow-Up of the Planar Three-Body Problem
We carry out a sequence of coordinate changes for the planar three-body
problem which successively eliminate the translation and rotation symmetries,
regularize all three double collision singularities and blow-up the triple
collision. Parametrizing the configurations by the three relative position
vectors maintains the symmetry among the masses and simplifies the
regularization of binary collisions. Using size and shape coordinates
facilitates the reduction by rotations and the blow-up of triple collision
while emphasizing the role of the shape sphere. By using homogeneous
coordinates to describe Hamiltonian systems whose configurations spaces are
spheres or projective spaces, we are able to take a modern, global approach to
these familiar problems. We also show how to obtain the reduced and regularized
differential equations in several convenient local coordinates systems.Comment: 51 pages, 4 figure
A thrust-sheet propulsion concept using fissionable elements
A space propulsion concept is proposed and analyzed which consists of a thin sheet coated on one side with fissionable material, so that nuclear power is converted directly into propulsive power. Thrust is available both from ejected fission fragments and from thermal radiation. Optimum thicknesses are determined for the active and substrate layers. This concept is shown to have potential mission capability (in terms of velocity increments) superior to that of all other advanced propulsion concepts for which performance estimates are available. A suitable spontaneously fissioning material such as Cf254 could provide an extremely high-performance first stage beyond earth orbit. In contrast with some other advanced nuclear propulsion concepts, there is no minimum size below which this concept is infeasible
Promises and potentialities of electric propulsion status of thrustor performance
Electric thrustor development reviewed with stress on lifetime, efficiency, and potential use in space progra
Electro-thermal rocket Patent
Electrothermal rocket engine using resistance heated heat exchange
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