24,518 research outputs found
Use of refinery computer model to predict fuel production
Several factors (crudes, refinery operation and specifications) that affect yields and properties of broad specification jet fuel were parameterized using the refinery simulation model which can simulate different types of refineries were used to make the calculations. Results obtained from the program are used to correlate yield as a function of final boiling point, hydrogen content and freezing point for jet fuels produced in two refinery configurations, each one processing a different crude mix. Refinery performances are also compared in terms of energy consumption
Different invasibility of permanent and temporary waterbodies in a semiarid Mediterranean Island
Nonindigenous species (NIS) represent a threat to aquatic biodiversity worldwide. However, freshwater ecosystems in drylands are potentially more prone to biological invasions than those located in temperate regions because of the higher number of artificial waterbodies generally occurring in these areas, which might act as invasion hubs for NIS. We review the available information about NIS in Sicilian waterbodies, discuss the role exerted by artificial lakes and ponds in facilitating the establishment of NIS in arid and semiarid areas, and compare the invasibility of permanent and temporary waterbodies in drylands. Artificial waterbodies increase the target-area effect for dispersers and provide a hospitable environment for NIS because of their recent origin and the lack of efficient biological filters against newcomers, thus acting as bridgeheads and invasion hubs favouring invasive species. Finally, we propose actions to attenuate the threats caused by NIS to the sensitive native biota of aquatic ecosystems in drylands
The formation of disks in massive spiral galaxies
The flatness of the rotation curve inside spiral galaxies is interpreted as
the imprint of a halo of invisible matter. Using the deepest observations of
distant galaxies, we have investigated how large disks could have been formed.
Observations include spatially resolved kinematics, detailed morphologies and
photometry from UV to mid-IR. Six Giga-years ago, half of the present-day
spirals had anomalous kinematics and morphologies that considerably affect the
scatter of the Tully Fisher relation. All anomalous galaxies can be modelled
through gas-rich, major mergers that lead to a rebuilt of a new disk. The
spiral-rebuilding scenario is proposed as a new channel to form large disks in
present-day spirals and it accounts for all the observed evolutions since the
last 6 Giga-years. A large fraction of the star formation is linked to merging
events during their whole durations.Comment: AIP Proceedings of a review given at the "Invisible Universe
International Conference" held in Paris, June 2009. 16 pages, 9 Figure
Kondo Resonance Decoherence by an External Potential
The Kondo problem, for a quantum dot (QD), subjected to an external bias, is
analyzed in the limit of infinite Coulomb repulsion by using a consistent
equations of motion method based on a slave-boson Hamiltonian. Utilizing a
strict perturbative solution in the leads-dot coupling, T, to T^4 and T^6
orders, we calculate the QD spectral density and conductance, as well as the
decoherent rate that drive the systemm from the strong to the weak coupling
regime. Our results indicate thet the weak coupling regime is reached for
voltages larger than a few units of the Kondo temperature.Comment: 5 figure
Interpolative method for transport properties of quantum dots in the Kondo regime
We present an interpolative method for describing coherent transport through
an interacting quantum dot. The idea of the method is to construct an
approximate electron self-energy which becomes exact both in the limits of weak
and strong coupling to the leads. The validity of the approximation is first
checked for the case of a single (spin-degenerate) dot level. A generalization
to the multilevel case is then discussed. We present results both for the
density of states and the temperature dependent linear conductance showing the
transition from the Kondo to the Coulomb blockade regime.Comment: 8 pages, 3 figures, includes lamuphys.sty, submitted to the
Proceedings of the XVI Sitges Conference on Statistical Mechanic
Model Independent Electromagnetic corrections in hadronic decays
The long distance correction to the total decay width of the decay is calculated in a model independent approach where a
discrimination of photons in the Bremmstrahlung process is assumed. This
correction is completely free of UV and IR singularities and moreover, it
satisfies electromagnetic gauge invariance. The result of this work can be
applied on the tau decays:
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