20,243 research outputs found
Determination of the Equation of State of Dense Matter
Nuclear collisions can compress nuclear matter to densities achieved within
neutron stars and within core-collapse supernovae. These dense states of matter
exist momentarily before expanding. We analyzed the flow of matter to extract
pressures in excess of 10^34 pascals, the highest recorded under
laboratory-controlled conditions. Using these analyses, we rule out strongly
repulsive nuclear equations of state from relativistic mean field theory and
weakly repulsive equations of state with phase transitions at densities less
than three times that of stable nuclei, but not equations of state softened at
higher densities because of a transformation to quark matter.Comment: 26 pages, 6 figures; final versio
Nuclear isotope thermometry
We discuss different aspects which could influence temperatures deduced from
experimental isotopic yields in the multifragmentation process. It is shown
that fluctuations due to the finite size of the system and distortions due to
the decay of hot primary fragments conspire to blur the temperature
determination in multifragmentation reactions. These facts suggest that caloric
curves obtained through isotope thermometers, which were taken as evidence for
a first-order phase transition in nuclear matter, should be investigated very
carefully.Comment: 9 pages, 7 figure
Effects of geometric constraints on the nuclear multifragmentation process
We include in statistical model calculations the facts that in the nuclear
multifragmentation process the fragments are produced within a given volume and
have a finite size. The corrections associated with these constraints affect
the partition modes and, as a consequence, other observables in the process. In
particular, we find that the favored fragmenting modes strongly suppress the
collective flow energy, leading to much lower values compared to what is
obtained from unconstrained calculations. This leads, for a given total
excitation energy, to a nontrivial correlation between the breakup temperature
and the collective expansion velocity. In particular we find that, under some
conditions, the temperature of the fragmenting system may increase as a
function of this expansion velocity, contrary to what it might be expected.Comment: 16 pages, 5 figure
Statistical multifragmentation model with discretized energy and the generalized Fermi breakup. I. Formulation of the model
The Generalized Fermi Breakup recently demonstrated to be formally equivalent
to the Statistical Multifragmentation Model, if the contribution of excited
states are included in the state densities of the former, is implemented. Since
this treatment requires the application of the Statistical Multifragmentation
Model repeatedly on the hot fragments until they have decayed to their ground
states, it becomes extremely computational demanding, making its application to
the systems of interest extremely difficult. Based on exact recursion formulae
previously developed by Chase and Mekjian to calculate the statistical weights
very efficiently, we present an implementation which is efficient enough to
allow it to be applied to large systems at high excitation energies. Comparison
with the GEMINI++ sequential decay code shows that the predictions obtained
with our treatment are fairly similar to those obtained with this more
traditional model.Comment: 8 pages, 6 figure
Data acquisition system for NASA LaRC impact dynamics research facility
A data system is designed to permit the simultaneous recording of 90 data channels on one 28 track magnetic tape recorder using a constant bandwidth FM multiplexing technique. Dynamic signals from transducers located in the test aircraft are amplified and fed to voltage controlled oscillators where they are converted to discrete FM signals. The signals from each group of five VCO's are fed to a mixer/distribution amplifier where they are combined into one composite signal and recorded, using direct recording techniques, on one magnetic tape recorder track. Millivolt signals from the recorders reproduce heads are amplified to one volt and then electronically switched to an FM demultiplexing system where appropriate frequency discrimination and signal filtering recover the original analog information
The S2 VLBI Correlator: A Correlator for Space VLBI and Geodetic Signal Processing
We describe the design of a correlator system for ground and space-based
VLBI. The correlator contains unique signal processing functions: flexible LO
frequency switching for bandwidth synthesis; 1 ms dump intervals, multi-rate
digital signal-processing techniques to allow correlation of signals at
different sample rates; and a digital filter for very high resolution
cross-power spectra. It also includes autocorrelation, tone extraction, pulsar
gating, signal-statistics accumulation.Comment: 44 pages, 13 figure
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