18 research outputs found
Redesign of technical systems
The paper describes a systematic approach to support the redesign process. Redesign is the adaptation of a technical system in order to meet new specifications. The approach presented is based on techniques developed in model-based diagnosis research. The essence of the approach is to find the part of the system which causes the discrepancy between a formal specification of the system to be designed and the description of the existing technical system. Furthermore, new specifications are generated, describing the new behaviour for the `faultyÂż part. These specifications guide the actual design of this part. Both the specification and design description are based on YMIR, an ontology for structuring engineering design knowledge
Antibiotic use in Brazilian broiler and pig production: an indication and forecast of trends
To gain insight in antibiotic use in relation to imported products the current use of antibiotics in pork and broiler production in Brazil are identified and trend forecasting of antibiotic use in the coming 3-5 years is performed
Mesoscopic proximity effect in double barrier Superconductor/Normal Metal junctions
We report transport measurements down to T=60mK of SININ and SNIN structures
in the diffusive limit. We fabricated Al-AlOx/Cu/AlOx/Cu (SININ) and
Al/Cu/AlOx/Cu (SNIN) vertical junctions. For the first time, a zero bias
anomaly was observed in a metallic SININ structure. We attribute this peak of
conductance to coherent multi-reflections of electrons between the two tunnel
barriers. This conductance maximum is quantitatively fitted by the relevant
theory of mesoscopic SININ structures. When the barrier at the SN interface is
removed (SNIN structure), we observe a peak of conductance at finite voltage
accompagnied by an excess of sub-gap conductance.Comment: 4 pages, 4 figures, editorially approved for publication in Phys.
Rev. B Rapid Com
Theory of charge transport in diffusive normal metal / unconventional singlet superconductor contacts
We analyze the transport properties of contacts between unconventional
superconductor and normal diffusive metal in the framework of the extended
circuit theory. We obtain a general boundary condition for the Keldysh-Nambu
Green's functions at the interface that is valid for arbitrary transparencies
of the interface. This allows us to investigate the voltage-dependent
conductance (conductance spectrum) of a diffusive normal metal (DN)/
unconventional singlet superconductor junction in both ballistic and diffusive
cases. For d-wave superconductor, we calculate conductance spectra numerically
for different orientations of the junctions, resistances, Thouless energies in
DN, and transparencies of the interface. We demonstrate that conductance
spectra exhibit a variety of features including a -shaped gap-like
structure, zero bias conductance peak (ZBCP) and zero bias conductance dip
(ZBCD). We show that two distinct mechanisms: (i) coherent Andreev reflection
(CAR) in DN and (ii) formation of midgap Andreev bound state (MABS) at the
interface of d-wave superconductors, are responsible for ZBCP, their relative
importance being dependent on the angle between the interface normal
and the crystal axis of d-wave superconductors. For , the ZBCP is due
to CAR in the junctions of low transparency with small Thouless energies, this
is similar to the case of diffusive normal metal / insulator /s-wave
superconductor junctions. With increase of from zero to , the
MABS contribution to ZBCP becomes more prominent and the effect of CAR is
gradually suppressed. Such complex spectral features shall be observable in
conductance spectra of realistic high- junctions at very low temperature
Theory of charge transport in diffusive normal metal / conventional superconductor point contacts
Tunneling conductance in diffusive normal metal / insulator / s-wave
superconductor (DN/I/S) junctions is calculated for various situations by
changing the magnitudes of the resistance and Thouless energy in DN and the
transparency of the insulating barrier. The generalized boundary condition
introduced by Yu. Nazarov [Superlattices and Microstructures 25 1221 (1999)] is
applied, where the ballistic theory by Blonder Tinkham and Klapwijk (BTK) and
the diffusive theory by Volkov Zaitsev and Klapwijk based on the boundary
condition of Kupriyanov and Lukichev (KL) are naturally reproduced. It is shown
that the proximity effect can enhance (reduce) the tunneling conductance for
junctions with a low (high) transparency. A wide variety of dependencies of
tunneling conductance on voltage bias is demonstrated including a -shaped
gap like structure, a zero bias conductance peak (ZBCP) and a zero bias
conductance dip (ZBCD)