17,514 research outputs found
Averting the magnetic braking catastrophe on small scales: disk formation due to Ohmic dissipation
We perform axisymmetric resistive MHD calculations that demonstrate that
centrifugal disks can indeed form around Class 0 objects despite magnetic
braking. We follow the evolution of a prestellar core all the way to
near-stellar densities and stellar radii. Under flux-freezing, the core is
braked and disk formation is inhibited, while Ohmic dissipation renders
magnetic braking ineffective within the first core. In agreement with
observations that do not show evidence for large disks around Class 0 objects,
the resultant disk forms in close proximity to the second core and has a radius
of only early on. Disk formation does not require
enhanced resistivity. We speculate that the disks can grow to the sizes
observed around Class II stars over time under the influence of both Ohmic
dissipation and ambipolar diffusion, as well as internal angular momentum
redistribution.Comment: 4 pages, 3 figures, accepted by A&A Letter
Capacitance multiplier and filter synthesizing network
A circuit using a differential amplifier multiplies the capacitance of a discrete interating capacitor by (r sub 1 + R sub 2)/R sub 2, where R sub 1 and R sub 2 are values of discrete resistor coupling an input signal e sub 1 of the amplifier inputs. The output e sub 0 of the amplifier is fed back and added to the signal coupled by the resistor R sub 2 to the amplifier through a resistor of value R sub 1. A discrete resistor R sub x may be connected in series for a lag filter, and a discrete resistor may be connected in series with the capacitor for a lead-lag filter. Voltage dividing resistors R sub a and R sub b may be included in the feedback circuit of the amplifier output e sub o to independently adjust the circuit gain e sub i/e sub o
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