Correction to: “SPOCU”: scaled polynomial constant unit activation function

Neural Computing and Applications - Addendum on SPOCU fitting and Erratum.     

Homogeneity analysis in a Korte--Schmidt-type integrating gold sphere

Homogeneity measurements in a gold-coated integrating sphere at eight wavelengths in the range from 400 to 2000 nm are presented and discussed. The inner sphere wall was scanned with a mirror-based internal sphere scanner at 288 different positions. The spatially resolved measurements show the transition from poor reflectivity, associated with large inhomogeneities at 400 nm, to high reflectivity in the infrared region at 2000 nm, associated with only small deviations. From the measurements the spectrally dependent relative uncertainty of the radiance of the inner sphere wall was deduced. A spectrally dependent sphere homogeneity correction factor F(lambda) relative to a specific point within the sphere wall was also derived.     

Grain Size Dependence of Electrical Conductivity in Polycrystalline Cerium Oxide

The magnitude and activation energy of electrical conductivity in nanocrystalline cerium oxide exhibit a clear grain size dependence. Experimental results compiled from the literature were analyzed using a space charge model, which takes into account the deviation of point defect concentrations from their bulk values in the vicinity of grain boundaries. The consequences on conductivity arising from such space charge layers were calculated using the brick-layer model (BLM) for grain sizes L large compared to the screening length . The obtained results were supplemented by the calculated conductivity in the flat-band limit for L . This combination allowed for a quantitative comparison with experimental values, which were obtained in the mesoscopic regime of grain sizes from 10–40 nm. The analysis yielded a value for the space charge potential in cerium oxide of 0.55 V. This space charge potential is caused by a reduced standard chemical potential of oxygen vacancies in the grain boundary core as compared to the bulk phase.     

Auditory-evoked potentials as indicator of brain serotonergic activity--first evidence in behaving cats

Due to the increasing importance of the central serotonergic neurotransmission for pathogenetic concepts and as a target of pharmacotherapeutic interventions in psychiatry, reliable indicators of this system are needed. Several findings from basic and clinical research suggest that the stimulus intensity dependence of auditory evoked potentials (AEP) may be such an indicator of behaviorally relevant aspects of serotonergic activity (Hegerl and Juckel 1993, Biol Psychiatry 33:173-187). In order to study this relationship more directly, epidural recordings over the primary and secondary auditory cortex were conducted in chronically implanted cats under intravenous (i.v.) administration of drugs influencing the serotonergic and other modulatory systems (8-OH-DPAT, m-CPP, ketanserin, DOI, apomorphine, atropine, clonidine). The intensity dependence of the cat AEP component with the highest functional similarity to this of the N1/P2-component in humans was significantly changed by influencing 5-HT1a and 5-HT2 receptors, but not 5-HT1c receptors. This serotonergic modulation of the intensity dependence was only found for the primary auditory cortex which corresponds to the known different innervation of the primary and secondary auditory cortex by serotonergic fibers. Our study supports the idea that the intensity dependence of AEP could be a valuable indicator of brain serotonergic activity; however, this indicator seems to be of relative specificity because at least cholinergic effects on the intensity dependence were also observed.     

Modeling resistive switching materials and devices across scales

Resistance switching devices based on electrochemical processes have attractive significant attention in the field of nanoelectronics due to the possibility of switching in nanosecond timescales, miniaturization to tens of nanometer and multi-bit storage. Their deceptively simple structures (metal-insulator-metal stack) hide a set of complex, coupled, processes that govern their operation, from electrochemical reactions at interfaces, diffusion and aggregation of ionic species, to electron and hole trapping and Joule heating. A combination of experiments and modeling efforts are contributing to a fundamental understanding of these devices, and progress towards a predictive understanding of their operation is opening the possibility for the rational optimization. In this paper we review recent progress in modeling resistive switching devices at multiple scales; we briefly describe simulation tools appropriate at each scale and the key insight that has been derived from them. Starting with ab initio electronic structure simulations that provide an understanding of the mechanisms of operation of valence change devices pointing to the importance of the aggregation of oxygen vacancies in resistance switching and how dopants affect performance. At slightly larger scales we describe reactive molecular dynamics simulations of the operation of electrochemical metallization cells. Here the dynamical simulations provide an atomic picture of the mechanisms behind the electrochemical formation and stabilization of conductive metallic filaments that provide a low-resistance path for electronic conduction. Kinetic Monte Carlo simulations are one step higher in the multiscale ladder and enable larger scale simulations and longer times, enabling, for example, the study of variability in switching speed and resistance. Finally, we discuss physics-based simulations that accurately capture subtleties of device behavior and that can be incorporated in circuit simulations.     

Resistive switching mechanisms in random access memory devices incorporating transition metal oxides: TiO2, NiO and Pr0.7Ca0.3MnO3

Resistance change random access memory (RRAM) cells, typically built as MIM capacitor structures, consist of insulating layers I sandwiched between metal layers M, where the insulator performs the resistance switching operation. These devices can be electrically switched between two or more stable resistance states at a speed of nanoseconds, with long retention times, high switching endurance, low read voltage, and large switching windows. They are attractive candidates for next-generation non-volatile memory, particularly as a flash successor, as the material properties can be scaled to the nanometer regime. Several resistance switching models have been suggested so far for transition metal oxide based devices, such as charge trapping, conductive filament formation, Schottky barrier modulation, and electrochemical migration of point defects. The underlying fundamental principles of the switching mechanism still lack a detailed understanding, i.e. how to control and modulate the electrical characteristics of devices incorporating defects and impurities, such as oxygen vacancies, metal interstitials, hydrogen, and other metallic atoms acting as dopants. In this paper, state of the art ab initio theoretical methods are employed to understand the effects that filamentary types of stable oxygen vacancy configurations in TiO(2) and NiO have on the electronic conduction. It is shown that strong electronic interactions between metal ions adjacent to oxygen vacancy sites results in the formation of a conductive path and thus can explain the 'ON' site conduction in these materials. Implication of hydrogen doping on electroforming is discussed for Pr(0.7)Ca(0.3)MnO(3) devices based on electrical characterization and FTIR measurements.     

Direct computation of instability points for contact problems

 The extended system is known as a reliable algorithm for the direct computation of instability points on the equilibrium path of mechanical structures. This article describes the application of the extended system as critical point computation method to mechanical contact problems. In this type of problems inequality constraints have to be considered. Moreover a prediction method based on the extended system algorithm is presented which allows the detection of favorable starting values for a critical point computation on the equilibrium path. Dedicated to the memory of Prof. Mike Crisfield, for his cheerfulness and cooperation as a colleague and friend over many years.