2,254 research outputs found
Critical Conditions for Core-Collapse Supernovae
The explosion of a core-collapse supernova can be approximated by the
breakdown of steady-state solutions for accretion onto a proto-neutron star
(PNS). We analytically show that as the neutrino luminosity exceeds a critical
value L_c, the neutrinosphere pressure exceeds the hydrostatic limit even for
an optimal shock radius R. This yields L_c \propto M^2 T^2 (with logarithmic
corrections) and R \propto M/T, in agreement with numerical results, where M, T
are the PNS mass, neutrino temperature. The near-critical flow can be
approximated as a ballistic shell on top of an isothermal layer.Comment: PRL accepte
A Distributed GUI-based Computer Control System for Atomic Physics Experiments
Atomic physics experiments often require a complex sequence of precisely
timed computer controlled events. A distributed GUI-based control system
designed with such experiments in mind, The Cicero Word Generator, is
described. The system makes use of a client-server separation between a user
interface for sequence design and a set of output hardware servers. Output
hardware servers are designed to use standard National Instruments output
cards, but the client-server nature allows this to be extended to other output
hardware. Output sequences running on multiple servers and output cards can be
synchronized using a shared clock. By using an FPGA-generated variable
frequency clock, redundant buffers can be dramatically shortened, and a time
resolution of 100ns achieved over effectively arbitrary sequence lengths
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