News Article | December 8, 2016
Achieving efficient sunlight collection over an entire day is a demanding task for stationary devices. The problem becomes even more complex when the harvested photons have to be absorbed within layers limited to a few hundreds of nanometers (or less) in thickness. This optical challenge can be addressed by a light in-coupling element that operates over a broad angular and spectral range, and that is also capable of trapping the collected light to maximize photon-to-electron conversion efficiency. Solutions developed in the silicon photovoltaic (PV) industry that rely on microscale pyramidal texturization of the absorber for light trapping are not suited to systems made of thin layers. In contrast, experimental nanophotonic approaches employing, for example, planar photonic crystals and diffraction gratings or plasmonic structures have been successfully implemented within or next to the active layer of thin-film solar cells.1, 2 An alternative route consists of integrating a light-harvesting, polymer-based coating onto the planar thin-film stack that does not affect charge-collection properties and could enable fully flexible devices.3 In this context, biomimetic structures—mostly subwavelength and inspired by moth eyes—exhibit broadband omnidirectional anti-reflection (AR) but lack the light-trapping contribution.4 For this reason, we have replicated structures that decorate plant surfaces to produce a light-harvesting layer that combines all the previously mentioned attributes.5 More specifically, we have focused on rose petal epidermal cells, which are densely packed and convexly shaped, and display a height and width of few tens of microns (see Figure 1). Figure 1. Schematic illustration of the replica approach based on plant epidermal cells. Yellow arrows show light in-coupling, which is enhanced in the solar cell as a result of its bioinspired microstructured coating. KIT: Karlsruhe Institute of Technology. The structures that we have replicated improve light management in two ways. First, the high packing factor and aspect ratio (i.e., the ratio of the length of the vertical axis to the base diameter) of the cells confer excellent AR properties, regardless of the wavelength or the angle of incidence (AOI). The main light-collection effect of the conical microstructures is fully described by the principles of ray optics and originates from the ability of the reflected light to bounce back onto a neighboring epidermal cell. Shallow nanocorrugation on the surface of the epidermal cells assists the light in-coupling mechanism to a lesser extent. Second, each epidermal cell acts as a microlens that broadens the distribution of the light-propagation angle. Thus, the optical path length is enhanced in the underlying solar cell, which results in a higher photon absorption probability and device efficiency. Before testing our method in operating PV devices, we first analyzed the optical properties of replicas obtained from different plant species. We realized this step by pouring transparent polymer directly onto the biosurfaces, resulting in an exact copy of the micro/nanostructures over a few square centimeters. We determined that the aspect ratio of the epidermal cells was the essential parameter for achieving low reflection at high AOI (see Figure 2). In fact, the integrated front-side reflection could be kept as low as 7% for an AOI of 80° by using an aspect ratio of 0.6, as found in rose petals. Figure 2. (a) Reduced reflection losses on the replica-coated surface (left) compared to the uncoated one (right). (b) Measured overall (diffuse +direct) reflection spectra of a flat resist layer and of the rose structure stacked on a black absorber for a moderate (20°) and a high (80°) angle of incidence (AOI). Owing to its remarkable AR properties, we selected the rose petal replica and imprinted it into a transparent polymer layer positioned atop a substrate comprising state-of-the-art organic solar cells. The latter were based either on PTB7-Th:PC BM-type or on PDTP-DFBT:PC BM-type polymer active layers absorbing up to 800 and 900nm, respectively. Notably, we measured a relative efficiency enhancement (with respect to an unpatterned device) of up to 13% under normal incidence, which we attribute solely to the optical effects. The most important benefits were captured for high AOI (see Figure 3). Indeed, we demonstrated a short-circuit current density enhancement of 44% at AOI =80°, that is, more than 3× higher than that obtained at AOI =0°. Figure 3. (a) Diagram of a solar cell integrating the rose structure shown with the light distribution in the glass substrate (measured by confocal laser scanning microscopy). (b) Measured overall reflection spectra of the organic solar cell with the rose structure and without (‘flat resist’) for AOIs of 20°and 80°. (c) Cosine-corrected short-circuit current density plotted as a function of the AOI for the two configurations investigated. ITO: Indium tin oxide. ZnO: Zinc oxide. PTB7-Th:PC BM: Polymer blend. MoO : Molybdenum trioxide. Ag: Silver. In summary, we have shown that plant epidermal cell replicas can be used as efficient light-harvesting elements that satisfy both the spectral and angular requirements imposed by PV. As these structures can be imprinted via a one-step process in a variety of materials and subsequent to solar cell fabrication, our approach is cost-effective, versatile, and can easily be applied to any PV technology. The plant replica structures can also be exploited for improving light management in other technologies. For example, they can be applied to organic LED substrates to enhance their light-extraction efficiency. Recent reports have shown that structural disorder can strongly impact the optical properties of photonic biostructures as well as artificial and complex light-harvesting designs.6, 7 Consequently, we are now conducting a numerical analysis of the various types of disorders encountered in rose epidermal cells, which will enable us to fine-tune our plant selection criteria. R.H. and A.M. acknowledge financial support from the Karlsruhe School of Optics and Photonics. A.M., A.S., and A.C. thank the Federal Ministry of Education and Research for funding under contract 03EK3504 (Project TAURUS), and G.G. acknowledges the support of the Helmholtz Postdoctoral Program (FE.5370.0169.0008). The authors thank Martin Theuring (NEXT ENERGY – EWE Research Centre for Energy Technology), Raphael Schmager and Benjamin Fritz (Light Technology Institute, Karlsruhe Institute of Technology, KIT), Hendrik Hölscher (Institute for Microstructure Technology, KIT), and Joachim Daumann (Botanischer Garten Karlsruhe). The experiments were performed using facilities at the Light Technology Institute, the Institute for Microstructure Technology, and the Zoological Institute at KIT. Karlsruhe Institute of Technology (KIT) Ruben Hünig is pursuing his PhD at the Light Technology Institute (LTI) at KIT on light-management structures for thin-film solar cells. His work currently focuses on plant surfaces as light-harvesting elements. Adrian Mertens studied physics at KIT and is now doing his PhD at the LTI and the Material Research Centre for Energy Systems at KIT. The main focus of his work is the investigation of angle-dependent absorption in organic single and tandem solar cells as well as the impact of scattering layers on the performance of such devices. Michael Hetterich is coordinator of the Thin-Film Photovoltaics Group at the LTI and the Institute of Applied Physics at KIT. His current research activities focus on the development and investigation of novel solar cell absorber materials as well as device modeling and optimization. Uli Lemmer received a diploma degree from the RWTH Aachen University, Germany, in 1990 and his PhD from the University of Marburg, Germany, in 1995. In 2002, he was appointed a full professor and director of the LTI. Alexander Colsmann heads the Organic Photovoltaics Group at the LTI and the Material Research Centre for Energy Systems at KIT. His further research interests include solar cells for building integration, perovskite solar cells, organic LEDs, printed electronics, printable electrodes, charge carrier transport, and electrical doping of organic semiconductors. Guillaume Gomard is the group leader for the ‘Nanophotonics’ activities at the LTI. His current research encompasses the analysis of disordered photonic crystals, scattering stochastic ensembles, and hierarchical bio-inspired photonic structures and their implementation within optoelectronic devices for enhanced efficiencies. 1. C. Trompoukis, I. Abdo, R. Cariou, I. Cosme, W. Chen, O. Deparis, A. Dmitriev, et al., Photonic nanostructures for advanced light trapping in thin crystalline silicon solar cells, Phys. Status Solidi A 212, p. 140-155, 2015. doi:10.1002/pssa.201431180 4. J. W. Leem, X.-Y. Guan, M. Choi, J. S. Yu, Broadband and omnidirectional highly-transparent coverglasses coated with biomimetic moth-eye nanopatterned polymer films for solar photovoltaic system applications, Sol. Energ. Mater. Sol. Cells 134, p. 45-53, 2015. doi:10.1016/j.solmat.2014.11.025 6. R. H. Siddique, G. Gomard, H. Hölscher, The role of random nanostructures for the omnidirectional anti-reflection properties of the glasswing butterfly, Nat. Commun. 6, p. 6909, 2015. doi:10.1038/ncomms7909 7. L. C. Andreani, A. Bozzola, P. Kowalczewski, M. Liscidini, Photonic light trapping and electrical transport in thin-film silicon solar cells, Sol. Energ. Mater. Sol. Cells 135, p. 78-92, 2015. doi:10.1016/j.solmat.2014.10.012
News Article | February 15, 2017
The natural adhesive materials used by geckos and other animals to walk upside down on the ceiling are always strongly adhesive without employing glues or leaving residues. Inspired by these natural adhesive materials, scientists at Kiel University in Germany have now succeeded in developing a synthetic version that can be controlled remotely using ultraviolet (UV) light. Their light-controlled adhesive material could be used to transport microscale objects and could find applications in the fields of robotics, industry and medical technology. The Kiel-based research team's findings are published in a paper in Science Robotics. "The advantage of light is that it can be used very precisely. It is reversible, so it can be switched on and off again, and very quickly," says Emre Kizilkan from the Functional Morphology and Biomechanics research group at Kiel University’s Zoological Institute. This work began with an elastic porous material known as a liquid crystal elastomer (LCE), which is made up of azobenzene molecules that bend when illuminated with UV light. Kizilkan and his colleagues noticed that the more porous the material, the more it bent, and decided to make use of this discovery. "Due to their structures, porous materials can be very easily incorporated with other materials," explains Kizilkan. "So we tested what happens when we combined the elastic material, which reacts well to light, with a bioinspired material that has good adhesive properties." The result is an intelligent, adhesive composite material, comprising a polymer-based adhesive layer and an LCE, that can be controlled with light. The surface of the adhesive layer is patterned with mushroom-shaped adhesive microstructures, similar to those found on the feet of some species of beetle. These microstructures will naturally stick to the surface of flat or three-dimensional objects such as microscope slides or glass spheres, allowing them to be picked up. To release the objects, the composite material is simply illuminated with UV light, causing it to bend and gently detach itself. "We were able to show that our new material can be used to transport objects. Moreover, we demonstrated that the transport can be controlled very precisely with light – on a micro-level," explains Kizilkan. "We use light as a remote control, so to say. Our bioinspired adhesive material doesn't leave any residues on the objects, either," adds Stanislav Gorb, who leads the Functional Morphology and Biomechanics research group. The research group's discovery could prove particularly useful for building sensitive sensors or computer chips, which need to be manufactured in an environment that is protected from external influences and impurities. "In the long term, we would like to use the new material to develop micro-robots which can be controlled by light to move forwards and climb walls," says Gorb. This story is adapted from material from Kiel University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.
News Article | November 23, 2015
Four antlion lacewings species and an owlfly one from two sister families have been studied and their chromosome number estimated:  Palpares libelluloides (2n = 26),  Distoleon tetragrammicus (2n = 18),  Myrmecaelurus trigrammus (2n = 16),  Macronemurus bilineatus (2n = 16), and owlfly (Ascalaphidae)  Bubopsis hamatus (2n = 18). Arrows point to X and Y sex chromosomes. Credit: Dr. Victor Krivokhatsky Varying between organisms, the number of chromosomes, the structures of organised and packaged DNA information, are normally a constant amount, thus allowing for the successful reproduction of a species. However, it may vary greatly even within a certain family. In the present study, conducted by Drs. Valentina Kuznetsova, Victor Krivokhatsky and Gadzhimurad Khabiev, Russian Academy of Sciences, four antlion lacewings species and an owlfly one from two sister families have been examined and their chromosome number estimated. The paper, published in the open-access journal ZooKeys, shows some patterns within the genera and suggests their common origin. The chromosome numbers of four antlion species (Myrmeleontidae) and an owlfly one (Ascalaphidae) from the Republic of Dagestan have been investigated in the Zoological Institute, Russian Academy of Sciences, St. Petersburg. When the data of the Myrmeleontoid lacewings were analyzed, some patterns emerged. It appears that the chromosome number is a preferential feature of the genera and few deviated from the modal value within the subfamily. While most antlions possess lower chromosome numbers, 2n = 14 and 2n = 16, which are encountered in all subfamilies, there is the exception of the Palparinae subfamily with the studied Palpares libelluloides species' chromosome number counting 2n = 26. The higher numbers, 2n = 22, 20 and 18, are also characteristic of the sister owlfly family Ascalaphidae. Since Palparinae lacewings represent one of basal phylogenetic lineage of the Myrmeleontidae, it is hypothesized that higher chromosome numbers are ancestral for antlions. The antlion subfamily along with the owlfly family have been registered with the the maximal modal values and have also been regarded as archaic taxa in relation to the rest of their close relatives. The higher chromosome numbers were inherited from the common ancestor of Myrmeleontidae + Ascalaphidae. It was preserved in the subfamily Palparinae (Myrmeleontidae) but changed via chromosomal fusions toward lower numbers, 2n = 18, 16 and 14, in other subfamilies. Explore further: Chromosome number changes in yeast More information: Valentina G. Kuznetsova et al. Chromosome numbers in antlions (Myrmeleontidae) and owlflies (Ascalaphidae) (Insecta, Neuroptera), ZooKeys (2015). DOI: 10.3897/zookeys.538.6655
News Article | March 15, 2016
Researchers have discovered the 90-million-year-old skeletal remains of a horse-sized dinosaur that is believed to be the missing piece that would complete the family tree of the fearsome tyrannosaurus rex. In a study featured in the journal Proceedings of the National Academy of Sciences, researchers from various scientific organizations, including the University of Edinburgh in the United Kingdom and the Smithsonian National Museum of Natural History in the United States, describe a set of dinosaur bones they found in a desert in Uzbekistan. The creature, which has been given the name Timurlengia euotica, showed characteristics that were similar to an earlier and a much smaller species of tyrannosaurus known as tyrannosauroids. However, the advanced ears and large brain outlined on the dinosaur's skull fragment suggest that it may have also shared traits with a later and much larger species, the tyrannosaurus rex. The team believes the Timurlengia euotica may very well hold the key to the secret of how the tyrannosaurus was able to grow so big. Scientists estimate that the first tyrannosaurs came into existence about 170 million years ago. Some of the early tyrannosauroids were merely the size of dogs. However, about 80 million years ago during the latter part of the Cretaceous Period, one species of tyrannosauroids, the tyrannosaurus rex, evolved into a large and menacing land predator. This creature had massive heads and very powerful jaws that produce a bite force of about 13,000 pounds. It can also grow to become as big as a full-sized bus. Tyrannosaurus rex was not only one of the largest creatures of its time, but it was a very capable hunter as well. Hans-Dieter Sues, a researcher from the Smithsonian National Museum and one of the authors of the study, said that contrary to what many people thought about the tyrannosaurus rex from the first "Jurassic Park" film, the creature was gifted with a keen sense of smell, hearing and even eyesight. The tyrannosaurus rex's killer instincts come from its two grapefruit-sized olfactory lobes that allowed it to smell objects very acutely. Its long, looped ear canals, on the other hand, allowed it to hear even low-frequency sounds generated by the footsteps of their prey from a distance. "It was sort of a superpredator," Sues pointed out. Finding out exactly how tyrannosaurs became quite the gifted predators, however, remained an elusive achievement for paleontologists over the years. This was because they did not have enough data on 100-million-year-old fossil records that pertain to the earlier and smaller tyrannosauroids. With the dissolution of the Soviet Union, researchers from different parts of the world now had access to territories where tyrannosauroids remains could be found. In 2004, a team of scientists unearthed a braincase fragment that was believed to be owned by some sort of dinosaur. It was kept in storage at the Zoological Institute of the Russian Academy of Sciences, until one of the members of the current research team, Steve Brusatte, came across the bone fragment in 2014. Brusatte and his colleagues made use of CT scans in order to better understand the structure of the braincase fragment. They discovered that the Timurlengia euotica had elongated inner ear canals, much like those seen on the tyrannosaurus rex. These would have given the creature an acute sense of hearing. The size of the braincase fragment, however, showed that the Timurlengia euotica lacked the knobs and recesses that a tyrannosaurus rex would likely have. This means that the Timurlengia also shared some physical similarities with the earlier tyrannosaur known as Xiongguanlong. The researchers believe that tyrannosaurs were able to develop their brain structure and keen hunting senses first before they became gigantic creatures. Their smarts for hunting prey made them more than capable of becoming the apex predators of their time.
Korte M.,Zoological Institute |
Schmitz D.,Zoological Institute
Physiological reviews | Year: 2016
The storage of information in the mammalian nervous systems is dependent on a delicate balance between change and stability of neuronal networks. The induction and maintenance of processes that lead to changes in synaptic strength to a multistep process which can lead to long-lasting changes, which starts and ends with a highly choreographed and perfectly timed dance of molecules in different cell types of the central nervous system. This is accompanied by synchronization of specific networks, resulting in the generation of characteristic "macroscopic" rhythmic electrical fields, whose characteristic frequencies correspond to certain activity and information-processing states of the brain. Molecular events and macroscopic fields influence each other reciprocally. We review here cellular processes of synaptic plasticity, particularly functional and structural changes, and focus on timing events that are important for the initial memory acquisition, as well as mechanisms of short- and long-term memory storage. Then, we cover the importance of epigenetic events on the long-time range. Furthermore, we consider how brain rhythms at the network level participate in processes of information storage and by what means they participating in it. Finally, we examine memory consolidation at the system level during processes of sleep.
De Loof A.,Zoological Institute
Journal of Insect Physiology | Year: 2011
The most prevalent hypothesis concerning the relationship between reproduction and longevity predicts that reproduction is costly, particularly in females. Specifically, egg production and sexual harassment of females by males reduce female longevity. This may apply to some short-lived species such as Drosophila, but not to some long-lived species such as the queens of ants and bees. Bee queens lay up to 2000 eggs a day for several years, but they nevertheless live at least 20 times longer than their sisters, the sterile workers. This discrepancy necessitates a critical reevaluation of the validity of both the trade-off concept as such, and of the current theories of aging. The widely accepted oxidative stress theory of aging with its links to metabolism and the insulin/IGF-I system has been disproven in Caenorhabditis elegans and mice, but not in Drosophila, necessitating other approaches. The recent spermidine/mitophagy theory is gaining momentum. Two major mechanisms may have been largely overlooked, namely epigenetic control of longevity by imprinting through DNA methylation as suggested by recent data in the honey bee, and especially, a mechanism of which the principles are outlined here, the progressive weakening of the " electrical dimension" of cells up to the point of total collapse, namely death. © 2010 Elsevier Ltd.
Reznik S.Y.,Zoological Institute |
Vaghina N.P.,Zoological Institute
Journal of Applied Entomology | Year: 2013
The effects of photoperiodic conditions of larval development and adult maturation (L : D = 12 : 12 vs. 18 : 6) and different diets (sugar solution, frozen eggs of Sitotroga cerealella, different numbers of aphids Myzus persicae, and their combinations) on survival, reproductive maturation and fecundity of Harmonia axyridis were studied in laboratory conditions. The fundamental aim of the work was to distinguish between cue effect of diet (neurohormonal triggering of reproduction) and direct effect of diet (nutritional maintenance of reproduction). When adults were kept under short-day conditions, the proportion of ovipositing females decreased and the duration of the pre-oviposition period increased. Moreover, a strong reaction to the direction of changes in the day length was demonstrated: when larvae and pupae developed at long day and adults were transferred to short day, the proportion of ovipositing females was much lower than in individuals that were permanently kept under short-day conditions. The percentage of ovipositing females, the rate of their reproductive maturation and the average daily fecundity gradually increased in the following succession of diets: 'sugar + 5 aphids per day < sugar + eggs < sugar + eggs + 5 aphids per day < sugar + 100 aphids per day'. However, dissection showed that most of the non-laying females fed on these diets (particularly those kept under long-day conditions) have started reproductive maturation, while even first stages of oogenesis were not found in females fed on sugar solution alone. We conclude that cue effect of diet (reproductive activation) can be achieved almost independently of the number of prey consumed, while nutritional effects (the rate of reproductive maturation and fecundity) are sensitive both to the quality and quantity of food. © 2012 Blackwell Verlag, GmbH.
Pena-Miller R.,University of Exeter |
Laehnemann D.,Zoological Institute |
Jansen G.,Zoological Institute |
Fuentes-Hernandez A.,University of Exeter |
And 3 more authors.
PLoS Biology | Year: 2013
Conventional wisdom holds that the best way to treat infection with antibiotics is to 'hit early and hit hard'. A favoured strategy is to deploy two antibiotics that produce a stronger effect in combination than if either drug were used alone. But are such synergistic combinations necessarily optimal? We combine mathematical modelling, evolution experiments, whole genome sequencing and genetic manipulation of a resistance mechanism to demonstrate that deploying synergistic antibiotics can, in practice, be the worst strategy if bacterial clearance is not achieved after the first treatment phase. As treatment proceeds, it is only to be expected that the strength of antibiotic synergy will diminish as the frequency of drug-resistant bacteria increases. Indeed, antibiotic efficacy decays exponentially in our five-day evolution experiments. However, as the theory of competitive release predicts, drug-resistant bacteria replicate fastest when their drug-susceptible competitors are eliminated by overly-aggressive treatment. Here, synergy exerts such strong selection for resistance that an antagonism consistently emerges by day 1 and the initially most aggressive treatment produces the greatest bacterial load, a fortiori greater than if just one drug were given. Whole genome sequencing reveals that such rapid evolution is the result of the amplification of a genomic region containing four drug-resistance mechanisms, including the acrAB efflux operon. When this operon is deleted in genetically manipulated mutants and the evolution experiment repeated, antagonism fails to emerge in five days and antibiotic synergy is maintained for longer. We therefore conclude that unless super-inhibitory doses are achieved and maintained until the pathogen is successfully cleared, synergistic antibiotics can have the opposite effect to that intended by helping to increase pathogen load where, and when, the drugs are found at sub-inhibitory concentrations. © 2013 Pena-Miller et al.
Bulyuk V.N.,Zoological Institute
Behavioral Ecology and Sociobiology | Year: 2012
Time of departure and landing of nocturnal migrants are of great importance for understanding migratory strategy used by birds. It allows us to estimate flying time and hence the distance that migrants cover during a single night. In this paper, I studied the temporal schedule of nocturnal departures of European robins during spring migration. The study was done on the Courish Spit on the Baltic Sea in 1998-2003 by retrapping 51 ringed birds in high mist nets during nocturnal migratory departure. Take-offs of individual birds occurred between the first and tenth hour after sunset (median 176 min after sunset). Departure time was not related to fuel stores at arrival and departure, stopover duration and progress of the season. The results suggest that one reason for temporal variation in take-off time was differential response of European robins with high and low motivation to depart to such triggers as air pressure and its trend. If these parameters reach a certain minimum threshold shortly before sunset, robins with a high migratory motivation take off in the beginning of the night. When air pressure or its trend reaches a maximum, it may trigger to take off later during the night birds with lower initial motivation for departure, including those that have low refuelling efficiency. In regulation of timing of take-offs of robins, an important role is also played by their individual endogenous circadian rhythm of activity which is related to the environment in a complex way. © 2011 Springer-Verlag.
Buschges A.,Zoological Institute |
Borgmann A.,Zoological Institute
Current Biology | Year: 2013
Optogenetic analysis has revealed the existence of multiple rhythm-generating neural networks that drive leg motoneuron pools in the lumbar spinal cord of rodents. These findings extend the concept of a modular neural network organization for locomotion from invertebrates and lower vertebrates to mammals. © 2013 Elsevier Ltd.