11,952 research outputs found
Neutron Diffusion and Nucleosynthesis in an Inhomogeneous Big Bang Model
This article presents an original code for Big Bang Nucleosynthesis in a
baryon inhomogeneous model of the universe. In this code neutron diffusion
between high and low baryon density regions is calculated simultaneously with
the nuclear reactions and weak decays that compose the nucleosynthesis process.
The size of the model determines the time when neutron diffusion becomes
significant. This article describes in detail how the time of neutron diffusion
relative to the time of nucleosynthesis affects the final abundances of He4,
deuterium and Li7. These results will be compared with the most recent
observational constraints of He4, deuterium and Li7. This inhomogeneous model
has He4 and deuterium constraints in concordance for baryon to photon ratio eta
= (4.3 - 12.3) X 10^{-10} Li7 constraints are brought into concordance with the
other isotope constraints by including a depletion factor as high as 5.9. These
ranges for the baryon to photon ratio and for the depletion factor are larger
than the ranges from a Standard Big Bang Nucleosynthesis model.Comment: 7/15, added reference
Microscopic origin of low frequency flux noise in Josephson circuits
We analyze the data and discuss their implications for the microscopic origin
of the low frequency flux noise in superconducting circuits. We argue that this
noise is produced by spins at the superconductor insulator boundary whose
dynamics is due to RKKY interaction. We show that this mechanism explains size
independence of the noise, different frequency dependences of the spectra
reported in large and small SQUIDs and gives the correct intensity for
realistic parameters.Comment: 4 pages, no figure
The inner kiloparsec of the jet in 3C264
We present new multi-frequency EVN, MERLIN and VLA observations of the radio
source 3C264, sensitive to linear scales ranging from the parsec to several
kiloparsecs. The observations confirm the existence of regions with different
properties in the first kiloparsec of the jet. The most remarkable feature is
the transition between a well collimated narrow jet at distances from the core
below 80 pc, to a conical-shaped wide jet, with an opening angle of 20 degrees.
Another change of properties, consisting of an apparent deflection of the jet
ridge line and a diminution of the surface brightness, occurs at a distance of
300 pc from the core, coincident with the radius of a ring observed at optical
wavelengths. Our observations add new pieces of information on the spectrum of
the radio-optical jet of 3C264, with results consistent with a synchrotron
emission mechanism and a spectrum break frequency in the infrared. Brightness
profiles taken perpendicularly to the jet of 3C264 are consistent with a spine
brightened jet at distances below 100 pc from the core, and an edge-brightened
jet beyond, which can be interpreted as evidence of a transverse jet velocity
structure. Our observations do not allow us to distinguish between the presence
of a face--on dust and gas disk at the center of the host galaxy of 3C264, or
rather an evacuated bubble. However, the properties of the jet structure, the
changes in the polarization angle, and the plausible jet orientation can be
naturally brought into agreement in the bubble scenario.Comment: 10 pages, 9 figures, accepted in A&
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