Charge transfer through single molecule contacts: How reliable are rate descriptions?

The trend to fabricate electrical circuits on nanoscale dimensions has led to impressive progress in the field of molecular electronics in the last decade. A theoretical description of molecular contacts as the building blocks of future devices is challenging though as it has to combine properties of Fermi liquids in the leads with charge and phonon degrees of freedom on the molecule. Apart from ab initio schemes for specific set-ups, generic models reveal characteristics of transport processes. Particularly appealing are descriptions based on transfer rates successfully used in other contexts such as mesoscopic physics and intramolecular electron transfer. However, a detailed analysis of this scheme in comparison with numerically exact data is elusive yet. It turns out that a formulation in terms of transfer rates provides a quantitatively accurate description even in domains of parameter space where in a strict sense it is expected to fail, e.g. for lower temperatures. Typically, intramolecular phonons are distributed according to a voltage driven steady state that can only roughly be captured by a thermal distribution with an effective elevated temperature (heating). An extension of a master equation for the charge-phonon complex to include effectively the impact of off-diagonal elements of the reduced density matrix provides very accurate data even for stronger electron-phonon coupling.Comment: 10 pages, 10 figure

Innovation and application of ANN in Europe demonstrated by Kohonen maps

One of the most important contributions to neural networks comes from Kohonen, Helsinki/Espoo, Finland, who had the idea of self-organizating maps in 1981. He verified his idea by an algorithm of which many applications make use of. The impetus for this idea came from biology, a field where the Europeans have always been very active at several research laboratories. The challenge was to model the self-organization found in the brain. Today one goal is the development of more sophisticated neurons which model the biological neurons more exactly. They should come to a better performance of neural nets with only a few complex neurons instead of many simple ones. A lot of application concepts arise from this idea: Kohonen himself applied it to speech recognition, but the project did not overcome much more than the recognition of the numerals one to ten at that time. A more promising application for self-organizing maps is process control and process monitoring. Several proposals were made which concern parameter classification of semiconductor technologies, design of integrated circuits, and control of chemical processes. Self-organizing maps were applied to robotics. The neural concept was introduced into electric power systems. At Dortmund we are working on a system which has to monitor the quality and the reliability of gears and electrical motors in equipment installed in coal mines. The results are promising and the probability to apply the system in the field is very high. A special feature of the system is that linguistic rules which are embedded in a fuzzy controller analyze the data of the self-organizing map in regard to life expectation of the gears. It seems that the fuzzy technique will introduce the technology of neural networks in a tandem mode. These technologies together with the genetic algorithms start to form the attractive field of computational intelligence

Circuit Analysis and Design using Evolutionary Algorithms

This paper focuses on electronic design at circuit level. The use of evolutionary algorithms to this application is discussed and a trade off to existing approaches is investigated. The design and analyzing task at this level is described in detail. As example a 1-bit full adder design in static CMOS is inspected with regard to power consumption and delay. In algorithmic scope both, single- and multi-objective optimization are regarded here. Finally some concluding remarks are given in section 6. ircuit Optimization Electronic design at circuit-level is a numeric adjustment process to meet constraints and goals on a fixed structure. Parameter extraction and variation, simulation, and resul

Rare Fault Detection by Possibilistic Reasoning

Kernel based neural networks with probabilistic reasoning are suitable for many practical applications. But influence of data set sizes let the probabilistic approach fail in case of small data amounts. Possibilistic reasoning avoids this drawback because it is independent of class size. The fundamentals of possibilistic reasoning are derived from a probability/possibility consistency principle that gives regard to relations. It is demonstrated that the concept of possibilistic reasoning is advantageous for the problem of rare fault detection, which is a property desired for semiconductor manufacturing quality control

Circuit Analysis and Design using Evolutionary Algorithms

This paper focuses on electronic design at circuit level. The use of evolutionary algorithms to this application is discussed and a trade off to existing approaches is investigated. The design and analyzing task at this level is described in detail. As example a 1-bit full adder design in static CMOS is inspected with regard to power consumption and delay. In algorithmic scope both, single- and multi-objective optimization are regarded here

Nonsingular potentials from excited state factorization of a quantum system with position dependent mass

The modified factorization technique of a quantum system characterized by position-dependent mass Hamiltonian is presented. It has been shown that the singular superpotential defined in terms of a mass function and a excited state wave function of a given position-dependent mass Hamiltonian can be used to construct non-singular isospectral Hamiltonians. The method has been illustrated with the help of a few examples.Comment: Improved version accepted in J. Phys.

Combined effects of intense laser field and applied electric field on exciton states in GaAs quantum wells : Transition from the single to double quantum well

ABSTRACT: The effects of intense laser radiation on the exciton states in GaAs-Ga1–xAlxAs quantum wells are studied with the inclusion of applied dc electric fields oriented along the growth direction of the system. The calculations are made within the effective mass and parabolic band approximations. The intense laser effects have been included along the lines of the Floquet method, modifying the confinement potential associated to the heterostructure. The results for the exciton binding energy, the energy of the exciton-related photoluminescence peak, and the carriers overlap integral are presented for several configurations of the quantum well size, the strength of the applied electric fields, and the incident laser radiation