Numerical Simulation of III-V Solar Cells Using D-AMPS

Numerical simulation of devices plays a crucial role in their design, performance prediction, and comprehension of the fundamental phenomena ruling their operation. Here, we present results obtained using the code D-AMPS-1D, that was conveniently modified to consider the particularities of III-V solar cell devices. This work, that is a continuation of a previous paper regarding solar cells for space applications, is focused on solar cells structures than find application for terrestrial use under concentrated solar illumination. The devices were fabricated at the Solar Energy Institute of the Technical University of Madrid (UPM). The first simulations results on InGaP cells are presented. The influence of band offsets and band bending at the window-emitter interface on the quantum efficiency was studied. A remarkable match of the experimental quantum efficiency was obtained. Finally, numerical simulation of single junction n-p InGaP-Ge solar cells was performed

Succession of the sea-surface microlayer in the coastal Baltic Sea under natural and experimentally induced low-wind conditions

The sea-surface microlayer (SML) is located within the boundary between the atmosphere and hydrosphere. The high spatial and temporal variability of the SML's properties, however, have hindered a clear understanding of interactions between biotic and abiotic parameters at or across the air-water interface. Among the factors changing the physical and chemical environment of the SML, wind speed is an important one. In order to examine the temporal effects of minimized wind influence, SML samples were obtained from the coastal zone of the southern Baltic Sea and from mesocosm experiments in a marina to study naturally and artificially calmed sea surfaces. Organic matter concentrations as well as abundance, (3)H-thymidine incorporation, and the community composition of bacteria in the SML (bacterioneuston) compared to the underlying bulk water (ULW) were analyzed. In all SML samples, dissolved organic carbon and nitrogen were only slightly enriched and showed low temporal variability, whereas particulate organic carbon and nitrogen were generally greatly enriched and highly variable. This was especially pronounced in a dense surface film (slick) that developed during calm weather conditions as well as in the artificially calmed mesocosms. Overall, bacterioneuston abundance and productivity correlated with changing concentrations of particulate organic matter. Moreover, changes in the community composition in the field study were stronger in the particle-attached than in the non-attached bacterioneuston. This implies that decreasing wind enhances the importance of particle-attached assemblages and finally induces a succession of the bacterial community in the SML. Eventually, under very calm meteorological conditions, there is an uncoupling of the bacterioneuston from the ULW

Biomechanical Foot Guidance Linkage

A gait replication apparatus can include a scalable mechanical mechanism configured to replicate different gaits . The scalable mechanical mechanism can include , for example , a four - bar linkage , a pantograph , a cam / Scotch - yoke mechanism , and so forth . In some embodiments , the mechanical mechanism includes a beam rotating about an axis passing proximate to its center , with a foot pedal slidably coupled with the beam , and a timing chain / belt or cable pulley - pair coupled with the foot pedal and looped about the beam . A method can include decomposing a foot path defined by Cartesian coordinates into polar coordinates , and providing a mechanical support for a foot , where a first mechanism controls an angular position of the mechanical support with respect to a reference frame , and a second mechanism controls a radial distance of the mechanical support from the reference frame

Spatiotemporal Integration in Somatosensory Perception: Effects of Sensory Saltation on Pointing at Perceived Positions on the Body Surface

In the past, sensory saltation phenomena (Geldard and Sherrick, 1972) have been used repeatedly to analyze the spatiotemporal integration capacity of somatosensory and other sensory mechanisms by means of their psychophysical characteristic. The core phenomenon consists in a systematic mislocalization of one tactile stimulus (the attractee) toward another successive tactile stimulus (the attractant) presented at another location, increasing with shorter intervals. In a series of four experiments, sensory saltation characteristics were studied at the forearm and the abdomen. Participants reported the perceived positions of attractees, attractants, and reference stimuli by pointing. In general, saltation characteristics compared well to those reported in previous studies, but we were able to gain several new insights regarding this phenomenon: (a) the attractee–attractant interval did not exclusively affect the perceived attractee position, but also the perceived attractant position; (b) saltation characteristics were very similar at different body sites and orientations, but did show differences suggesting anisotropy (direction-dependency) in the underlying integration processes; (c) sensory saltation could be elicited with stimulation patterns crossing the body midline on the abdomen. In addition to the saltation-specific results, our experiments demonstrate that pointing reports of perceived positions on the body surface generally show pronounced systematic biases compared to veridical positions, moderate intraindividual consistency, and a high degree of inter-individual variability. Finally, we address methodological and terminological controversies concerning the sensory saltation paradigm and discuss its possible neurophysiological basis

Application of stochastic diffusion theory to the interpretation of the 252Cf source-driven noise analysis method for subcriticality determination

The 252Cf source-driven noise analysis (CSDNA) method is an experimental technique, developed by J. T. Mihalczo and his collaborators at Oak Ridge National Laboratory, which makes use of noise analysis to determine the multiplication factor, k, in subcritical multiplying media. In this work, a stochastic diffusion description was used to interpret the CSDNA experiment in an infinite, homogeneous medium in order to shed light on the practicality of this experimental procedure in determining the multiplication factor. By defining such a benchmark problem, an exact solution is obtained for the subcritical multiplication factor in which the locations of the 252Cf source and neutron detectors are explicitly taken into account. The expression relating reactivity to the measured data was found to depend implicitly on k itself. Through a numerical analysis of this expression, certain limiting conditions were identified in which the expression for the reactivity became essentially independent of k, hence demonstrating some possibility for the viability of this technique. However, under more realistic experimental conditions, i.e. for finite systems in which diffusion theory is not applicable, the measurement of the subcritical multiplication factor from the measured data, without extensive transport calculations, becomes doubtful.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30938/1/0000608.pd

Taktile Illusionen: Wahrnehmung und neuronale Analyse spatiotemporaler Reizmuster

Die Repräsentation von Reizen auf der Körperoberfläche ist eine Funktion ihrer räumlichen und zeitlichen Anordnung. Diese raum-zeitliche Interaktion in der Wahrnehmung ist die Grundlage des Saltationsphänomens, das in der vorliegenden Arbeit untersucht wurde. Bei dieser taktilen Illusion wird die Position eines Reizes örtlich verschoben wahrgenommen, wenn ihm zeitnah ein räumlich entfernter Reiz folgt (Geldard & Sherrick, 1972). Die Verschiebung ist umso größer, je kürzer das Zeitintervall zwischen den beiden Reizen ist. Entsprechend dem neuronalen Netzwerkmodell von Wiemer und Kollegen (2000) kann diese Illusion als perzeptives Korrelat der kortikalen Verarbeitungsmechanismen spatiotemporaler Information angesehen werden, bei denen die Repräsentation von Reizen im Kortex abhängig von deren zeitlicher Abfolge ist. Die dynamische Anpassung des neuronalen Netzwerkes an den Verlauf der Stimulation bildet die Grundlage für kurzfristige und längerfristige plastische Veränderungen der kortikalen Topographie und ermöglicht so eine Anpassung des Gehirns an veränderte Anforderungen. Ziel der vorliegenden Arbeit war es, die Bedingungen des Auftretens spatiotemporaler Verarbeitungsprozesse zu spezifizieren und adaptive Veränderungen des taktilen Wahrnehmungsraums und der Topographie in SI aufgrund spatiotemporaler taktiler Stimulation nachzuweisen. Zu diesem Zweck wurde zunächst eine fMRT-taugliche Experimentierumgebung aufgebaut und getestet. Im Vordergrund stand die Herstellung des Saltationseffekts. Deutlich wurde, dass die Auftretenswahrscheinlichkeit des Effekts von der Verlaufscharakteristik der Stimuli abhängt und die experimentelle Anordnung, insbesondere die Methode zur Einschätzung der Reizposition, einen Einfluss auf die wahrgenommene räumliche Anordnung der Reize auf der Körperoberfläche hatte. Das in der vorliegenden Arbeit evaluierte Punktlokalisationsverfahren mit einem 3D-Positionsgeber erwies sich als hinreichend stabil und reliabel. Aufgabe der insgesamt 67 gesunden Probanden, die an den verschiedenen Teilstudien teilnahmen, war es jeweils auf die wahrgenommene Reizposition auf dem Unterarm zu deuteten. Untersucht wurde nicht nur die Punktlokalisation spatiotemporaler Reizmuster mit denen der Saltationseffekt hergestellt wird, sondern auch die perzeptive Anordnung einzelner Reize an unterschiedlichen Reizorten auf dem Unterarm. Es zeigte sich, dass die spatiale Karte Verzerrungen aufweist: in der Nähe anatomischer Markierungspunkte wie z.B. des Hand- und Ellenbogengelenks waren die Lokalisationsfehler deutlich geringer als weiter von diesen entfernt. Der Einfluss der Gelenke auf die Lokalisation einzelner Reize deutet darauf hin, dass diese Areale im somatosensorischen Kortex (SI) anders repräsentiert sind als Areale, die nicht mit anatomischen Markierungspunkten verbunden sind. In einer weiteren psychophysikalischen Studie standen überdauernde Veränderungen der Topographie der taktilen Karte durch repetitive Stimulation mit spatiotemporalen Reizmustern im Vordergrund. Die repetitive Stimulation mit spatiotemporalen Reizmustern (ca. 45 Minuten) bewirkte eine zunehmende Verzerrung der perzeptiven taktilen Karte, in deren Folge sich die Lokalisationsleistung bei einzelnen Reizen verschlechterte. Dies wurde als Hinweis auf eine beginnende Veränderung der taktilen Karte in SI interpretiert. Auch die Reihenfolge, in der die spatiotemporalen Reizmuster mit unterschiedlicher zeitlicher Abfolge vorgegeben wurden, übte einen Einfluss auf deren Repräsentation in der taktilen Karte aus. Dieser hielt jeweils nur so lange an, wie ähnliche Reizmuster vorgegeben wurden; daher wurde er als Kalibrierungsprozess des taktilen Systems interpretiert, der eine Optimierung der Verarbeitung der momentan ankommenden Information garantiert. Der abschließende Teil der vorliegenden Arbeit beinhaltet die Untersuchung zur kortikalen Repräsentation spatiotemporaler Reizmuster und der saltatorischen Reizverschiebung in SI mit funktioneller Magnetresonanztomographie. Es wurde erwartet, dass die als Saltationseffekt auftretende wahrgenommene Ortsverschiebung eines Reizes in Abhängigkeit vom Zeitintervall zu einem räumlich getrennten nachfolgenden Stimulus in SI ihre Entsprechung findet. Möglicherweise wegen mangelnden räumlichen Auflösungsvermögens der verwendeten Messtechnik konnte eine entsprechend veränderte Topographie allerdings nicht nachgewiesen werden. Die unterschiedlichen spatiotemporalen Reizmuster hatten aber einen Effekt auf die Aktivierungshöhe in SI, der insbesondere mit dem Auftreten eines perzeptiven Saltationseffekts zusammenhing. Die Veränderungen in der Aktivierungshöhe wurden daher als Nachweis summativer Verarbeitungsprozesse interpretiert, die in Einklang mit dem Netzwerkmodell von Wiemer et al. (2000) stehen

Extended description of tunnel junctions for distributed modeling of concentrator multi-junction solar cells

One of the key components of highly efficient multi-junction concentrator solar cells is the tunnel junction interconnection. In this paper, an improved 3D distributed model is presented that considers real operation regimes in a tunnel junction. This advanced model is able to accurately simulate the operation of the solar cell at high concentraions at which the photogenerated current surpasses the peak current of the tunnel junctionl Simulations of dual-junction solar cells were carried out with the improved model to illustrate its capabilities and the results have been correlated with experimental data reported in the literature. These simulations show that under certain circumstances, the solar cells short circuit current may be slightly higher than the tunnel junction peak current without showing the characteristic dip in the J-V curve. This behavior is caused by the lateral current spreading toward dark regions, which occurs through the anode/p-barrier of the tunnel junction

Geomagnetic data from the GOCE satellite mission

The Gravity field and steady-state Ocean Circulation Explorer (GOCE) is part of ESA’s Earth Explorer Program. The satellite carries magnetometers that control the activity of magnetorquers for navigation of the satellite, but are not dedicated as science instruments. However, intrinsic steady states of the instruments can be corrected by alignment and calibration, and artificial perturbations, e.g. from currents, can be removed by their characterisation correlated to housekeeping data. The leftover field then shows the natural evolution and variability of the Earth’s magnetic field. This article describes the pre-processing of input data as well as calibration and characterisation steps performed on GOCE magnetic data, using a high-precision magnetic field model as reference. For geomagnetic quiet times, the standard deviation of the residual is below 13 nT with a median residual of (11.7, 9.6, 10.4) nT for the three magnetic field components (x, y, z). For validation of the calibration and characterisation performance, we selected a geomagnetic storm event in March 2013. GOCE magnetic field data show good agreement with results from a ground magnetic observation network. The GOCE mission overlaps with the dedicated magnetic field satellite mission CHAMP for a short time at the beginning of 2010, but does not overlap with the Swarm mission or any other mission flying at low altitude and carrying high-precision magnetometers. We expect calibrated GOCE magnetic field data to be useful for lithospheric modelling and filling the gap between the dedicated geomagnetic missions CHAMP and Swarm. Graphic Abstract: [Figure not available: see fulltext.]