42 research outputs found
Risk analysis of a distillation unit
A risk analysis of a batch distillation unit is de-scribed. The analysis has been carried out at several stages during plant design, construction, and operation. The costs, quality, and benefits is using the methods are described
Pulsar kicks from a dark-matter sterile neutrino
We show that a sterile neutrino with mass in the 1-20 keV range and a small
mixing with the electron neutrino can simultaneously explain the origin of the
pulsar motions and the dark matter in the universe. An asymmetric neutrino
emission from a hot nascent neutron star can be the explanation of the observed
pulsar velocities. In addition to the pulsar kick mechanism based on resonant
neutrino transitions, we point out a new possibility: an asymmetric
off-resonant emission of sterile neutrinos. The two cases correspond to
different values of the masses and mixing angles. In both cases we identify the
ranges of parameters consistent with the pulsar kick, as well as cosmological
constraints.Comment: 5 pages, 2 figures; final version; discussion and references adde
Percolating granular superconductors
We investigate diamagnetic fluctuations in percolating granular
superconductors. Granular superconductors are known to have a rich phase
diagram including normal, superconducting and spin glass phases. Focusing on
the normal-superconducting and the normal-spin glass transition at low
temperatures, we study he diamagnetic susceptibility and the mean
square fluctuations of the total magnetic moment of large
clusters. Our work is based on a random Josephson network model that we analyze
with the powerful methods of renormalized field theory. We investigate the
structural properties of the Feynman diagrams contributing to the
renormalization of and . This allows us to determine
the critical behavior of and to arbitrary order in
perturbation theory.Comment: 18 pages, 2 figure
Density functional method for nonequilibrium electron transport
We describe an ab initio method for calculating the electronic structure,
electronic transport, and forces acting on the atoms, for atomic scale systems
connected to semi-infinite electrodes and with an applied voltage bias. Our
method is based on the density functional theory (DFT) as implemented in the
well tested Siesta approach (which uses non-local norm-conserving
pseudopotentials to describe the effect of the core electrons, and linear
combination of finite-range numerical atomic orbitals to describe the valence
states). We fully deal with the atomistic structure of the whole system,
treating both the contact and the electrodes on the same footing. The effect of
the finite bias (including selfconsistency and the solution of the
electrostatic problem) is taken into account using nonequilibrium Green's
functions. We relate the nonequilibrium Green's function expressions to the
more transparent scheme involving the scattering states. As an illustration,
the method is applied to three systems where we are able to compare our results
to earlier ab initio DFT calculations or experiments, and we point out
differences between this method and existing schemes. The systems considered
are: (1) single atom carbon wires connected to aluminum electrodes with
extended or finite cross section, (2) single atom gold wires, and finally (3)
large carbon nanotube systems with point defects.Comment: 18 pages, 23 figure