73 research outputs found
Encoding of naturalistic optic flow by motion sensitive neurons of nucleus rotundus in the zebra finch ( )
Eckmeier D, Kern R, Egelhaaf M, Bischof H-J. Encoding of naturalistic optic flow by motion sensitive neurons of nucleus rotundus in the zebra finch ( ). Frontiers in Integrative Neuroscience. 2013;7:68.The retinal image changes that occur during locomotion, the optic flow, carry information about self-motion and the three-dimensional structure of the environment. Especially fast moving animals with only little binocular vision depend on these depth cues for maneuvering. They actively control their gaze to facilitate perception of depth based on cues in the optic flow. In the visual system of birds, nucleus rotundus neurons were originally found to respond to object motion but not to background motion. However, when background and object were both moving, responses increased the more the direction and velocity of object and background motion on the retina differed. These properties may play a role in representing depth cues in the optic flow. We therefore investigated, how neurons in nucleus rotundus respond to optic flow that contains depth cues. We presented simplified and naturalistic optic flow on a panoramic LED display while recording from single neurons in nucleus rotundus of anaesthetized zebra finches. Unlike most studies on motion vision in birds, our stimuli included depth information. We found extensive responses of motion selective neurons in nucleus rotundus to optic flow stimuli. Simplified stimuli revealed preferences for optic flow reflecting translational or rotational self-motion. Naturalistic optic flow stimuli elicited complex response modulations, but the presence of objects was signaled by only few neurons. The neurons that did respond to objects in the optic flow, however, show interesting properties
Guidelines for Material Design in Semitransparent Organic Solar Cells
Organic solar cells (OSCs) are uniquely suited for semitransparent
applications due to their adjustable absorption spectrum. However, most
high-performance semitransparent cells reported to date are based on materials
that have shown high power conversion efficiency for opaque devices. We
therefore present a model to assess the optimum efficiency and transparency for
a specific donor and acceptor band gap. The absorption characteristics of both
donor and acceptor are modeled with spectral data of typical absorber materials
from the literature which are adjusted to achieve the desired band gap value.
The results show three distinct regions of high light utilization efficiency if
the photopic curve is employed as a weighting function (corresponding to window
applications), and a broad maximum for the plant action spectrum as a weighting
function (corresponding to greenhouse applications). When comparing these
findings to reported experimental values, it is evident that the band gaps of
the materials used for the experimental studies do not correspond to the maxima
identified by our simulation model. The analysis of the energy levels of
molecules recorded in the literature confirms that all band gaps and therefore
all LUE maxima are chemically feasible so that the performance of
semitransparent OSCs can be further improved by designing materials with
optimized absorption spectra.Comment: 20 pages and 10 figure in the main manuscript, aditionally 6 pages
and 4 figures in the supporting informatio
A phase-field model for the evaporation of thin film mixtures
The performance of solution-processed solar cells strongly depends on the
geometrical structure and roughness of the photovoltaic layers formed during
film drying. During the drying process, the interplay of crystallization and
liquid-liquid demixing leads to the structure formation on the nano- and
microscale and to the final rough film. In order to better understand how the
film structure can be improved by process engineering, we aim at theoretically
investigating these systems by means of phase-field simulations. We introduce
an evaporation model based on the Cahn-Hilliard equation for the evolution of
the fluid concentrations coupled to the Allen-Cahn equation for the
liquid-vapour phase transformation. We demonstrate its ability to match the
experimentally measured drying kinetics and study the impact of the parameters
of our model. Furthermore, the evaporation of solvent blends and solvent-vapour
annealing are investigated. The dry film roughness emerges naturally from our
set of equations, as illustrated through preliminary simulations of spinodal
decomposition and film drying on structured substrates
Phase-field simulation of liquid-vapor equilibrium and evaporation of fluid mixtures
In solution-processing of thin films, the material layer is deposited from a
solution composed of several solutes and solvents. The final morphology and
hence the properties of the film often depend on the time needed for the
evaporation of the solvents. This is typically the case for organic photoactive
or electronic layers. Therefore, it is important to be able to predict the
evaporation kinetics of such mixtures. We propose here a new phase-field model
for the simulation of evaporating fluid mixtures and simulate their evaporation
kinetics. Similar to the Hertz-Knudsen theory, the local liquid-vapor
equilibrium is assumed to be reached at the film surface and evaporation is
driven by diffusion away from this gas layer. In the situation where the
evaporation is purely driven by the liquid-vapor equilibrium, the simulations
match the behavior expected theoretically from the free energy: for evaporation
of pure solvents, the evaporation rate is constant and proportional to the
vaporpressure. For mixtures, the evaporation rate is in general strongly
time-dependent because of the changing composition of the film. Nevertheless,
for highly non-ideal mixtures, such as poorly compatible fluids or polymer
solutions, the evaporation rate becomes almost constant in the limit of low
Biot numbers. The results of the simulation have been successfully compared to
experiments on a polystyrene-toluene mixture. The model allows to take into
account deformations of the liquid-vapor interface and therefore to simulate
film roughness or dewetting
Low-Temperature Behaviour of Charge Transfer Excitons in Narrow-Bandgap Polymer-Based Bulk Heterojunctions
Photoluminescence studies of the charge transfer exciton emission from a narrow-bandgap polymer-based bulk heterojunction are reported. The quantum yield of this emission is as high as 0.03%. Low temperature measurements reveal that while the dynamics of the singlet exciton is slower at low temperature, the dynamics of the charge transfer exciton emission is temperature independent. This behavior rules out any diffusion process of the charge transfer excitons and energy transfer from these interfacial states toward lower lying states. Photoluminescence measurements performed on the device under bias show a reduction (but not the total suppression) of the charge transfer exciton recombination. Finally, based on the low temperature results the role of the charge transfer excitons and the possible pathways to populate them are identified
Design, synthesis and thermal behaviour of a series of well-defined clickable and triggerable sulfonate polymers
In the printing industry, the exploitation of triggerable materials that can have their surface properties altered on application of a post-deposition external stimulus has been crucial for the production of robust layers and patterns. To this end, herein, a series of clickable poly(R-alkyl p-styrene sulfonate) homopolymers, with systematically varied thermally-labile protecting groups, has been synthesised via reversible addition-fragmentation chain transfer (RAFT) polymerisation. The polymer range has been designed to offer varied post-deposition thermal treatment to switch them from hydrophobic to hydrophilic. Suitable RAFT conditions have been identified to produce well-defined homopolymers (Ä, Mw/Mn 80% for all but one monomer) with controllable molar mass. Poly(p-styrene sulfonate) with an isobutyl protecting group has been shown to be the most readily thermolysed polymer that remains stable at room temperature, and was thus investigated further by incorporation into a diblock copolymer, P3HT-b-PiBSS, by click chemistry. The strategy for preparation of thermal modifiable block copolymers exploiting R-protected p-styrene sulfonates and azide-alkyne click chemistry presented herein allows the design of new, roll-to-roll processable materials for potential application in the printing industry, particularly organic electronics
Matching the photocurrent of perovskite/organic tandem solar modules by varying the cell width
Photocurrent matching in conventional monolithic tandem solar cells is
achieved by choosing semiconductors with complementary absorption spectra and
by carefully adjusting the optical properties of the complete top and bottom
stacks. However, for thin film photovoltaic technologies at the module level,
another design variable significantly alleviates the task of photocurrent
matching, namely the cell width, whose modification can be readily realized by
the adjustment of the module layout. Herein we demonstrate this concept at the
experimental level for the first time for a 2T-mechanically stacked perovskite
(FAPbBr3)/organic (PM6:Y6:PCBM) tandem mini-module, an unprecedented approach
for these emergent photovoltaic technologies fabricated in an independent
manner. An excellent Isc matching is achieved by tuning the cell widths of the
perovskite and organic modules to 7.22 mm (PCEPVKT-mod= 6.69%) and 3.19 mm
(PCEOPV-mod= 12.46%), respectively, leading to a champion efficiency of 14.94%
for the tandem module interconnected in series with an aperture area of 20.25
cm2. Rather than demonstrating high efficiencies at the level of small lab
cells, our successful experimental proof-of-concept at the module level proves
to be particularly useful to couple devices with non-complementary
semiconductors, either in series or in parallel electrical connection, hence
overcoming the limitations imposed by the monolithic structure
The 2021 flexible and printed electronics roadmap
This roadmap includes the perspectives and visions of leading researchers in the key areas of flexible and printable electronics. The covered topics are broadly organized by the device technologies (sections 1â9), fabrication techniques (sections 10â12), and design and modeling approaches (sections 13 and 14) essential to the future development of new applications leveraging flexible electronics (FE). The interdisciplinary nature of this field involves everything from fundamental scientific discoveries to engineering challenges; from design and synthesis of new materials via novel device design to modelling and digital manufacturing of integrated systems. As such, this roadmap aims to serve as a resource on the current status and future challenges in the areas covered by the roadmap and to highlight the breadth and wide-ranging opportunities made available by FE technologies
Gaze Strategy in the Free Flying Zebra Finch (Taeniopygia guttata)
Fast moving animals depend on cues derived from the optic flow on their retina. Optic flow from translational locomotion includes information about the three-dimensional composition of the environment, while optic flow experienced during a rotational self motion does not. Thus, a saccadic gaze strategy that segregates rotations from translational movements during locomotion will facilitate extraction of spatial information from the visual input. We analysed whether birds use such a strategy by highspeed video recording zebra finches from two directions during an obstacle avoidance task. Each frame of the recording was examined to derive position and orientation of the beak in three-dimensional space. The data show that in all flights the head orientation was shifted in a saccadic fashion and was kept straight between saccades. Therefore, birds use a gaze strategy that actively stabilizes their gaze during translation to simplify optic flow based navigation. This is the first evidence of birds actively optimizing optic flow during flight
Organic photovoltaic modules with new world record efficiencies
During the last years, the development of new active materials has led to constant improvement in the power conversion efficiency (PCE) of solutionâprocessed organic photovoltaics (OPV) to nowadays record values above 17% on small lab cells. In this work, we show the developments and results of a successful upscaling of such highly efficient OPV systems to the module level on large areas, which yielded two new certified world record efficiencies, namely, 12.6% on a module area of 26 cm2 and 11.7% on a module area of 204 cm2. The decisive developments leading to this achievement include the optimization of the module layout as well as the highâresolution shortâpulse (nanosecond) laser structuring processes involved in the manufacturing of such modules. By minimizing the inactive areas within the total module area that are used for interconnecting the individual solar cells of the module in series, geometric fill factors of over 95% have been achieved. A production yield of 100% working modules during the manufacturing of these modules and an extremely narrow distribution of the final PCE values underline the excellent process control and reproducibility of the results. The new developments and their implementation into the production process of the record OPV modules are described in detail, along with the challenges that arose during this development. Finally, dark lockâin thermography (DLIT), electroluminescence (EL), and photoluminescence (PL) measurements of the record module are presented
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