4,933 research outputs found
Switching-Cell Arrays - An Alternative Design Approach in Power Conversion
© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting /republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other worksThe conventional design of voltage-source power converters is based on a two-level half-bridge configuration and the selection of power devices designed to meet the full application specifications (voltage, current, etc.). This leads to the need to design and optimize a large number of different devices and their ancillary circuitry and prevents taking advantage from scale economies. This paper proposes a paradigm shift in the design of power converters through the use of a novel configurable device consisting on a matrix arrangement of highly-optimized switching cells at a single voltage class. Each switching cell consists of a controlled switch with antiparallel diode together with a self-powered gate driver. By properly interconnecting the switching cells, the switching cell array (SCA) can be configured as a multilevel active-clamped leg with different number of levels. Thus, the SCA presents adjustable voltage and current ratings, according to the selected configuration. For maximum compactness, the SCA can be conceived to be only configurable by the device manufacturer upon the customer needs. For minimum cost, it can also be conceived to be configurable by the customer, leading to field-configurable SCAs. Experimental results of a 6x3 field-configurable SCA are provided to illustrate and validate this design approach.Peer ReviewedPostprint (author's final draft
Multiplicative versus additive noise in multi-state neural networks
The effects of a variable amount of random dilution of the synaptic couplings
in Q-Ising multi-state neural networks with Hebbian learning are examined. A
fraction of the couplings is explicitly allowed to be anti-Hebbian. Random
dilution represents the dying or pruning of synapses and, hence, a static
disruption of the learning process which can be considered as a form of
multiplicative noise in the learning rule. Both parallel and sequential
updating of the neurons can be treated. Symmetric dilution in the statics of
the network is studied using the mean-field theory approach of statistical
mechanics. General dilution, including asymmetric pruning of the couplings, is
examined using the generating functional (path integral) approach of disordered
systems. It is shown that random dilution acts as additive gaussian noise in
the Hebbian learning rule with a mean zero and a variance depending on the
connectivity of the network and on the symmetry. Furthermore, a scaling factor
appears that essentially measures the average amount of anti-Hebbian couplings.Comment: 15 pages, 5 figures, to appear in the proceedings of the Conference
on Noise in Complex Systems and Stochastic Dynamics II (SPIE International
Cap a la creació d'una bioètica social
Els canvis socials que s’han produït
des de l’inici dels anys vuitanta fan que
sigui urgent, necessari i imprescindible
redireccionar la bioètica també cap a
una vessant més social, perquè les
qüestions ètiques no es poden reduir a
l’à mbit clĂnic o mediambienta
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