Showing papers by "Johannes Kepler University of Linz published in 2004"
TL;DR: The current status of the field of organic solar cells and the important parameters to improve their performance are discussed in this paper. But, the two competitive production techniques used today are either wet solution processing or dry thermal evaporation of the organic constituents.
Abstract: Organic solar cell research has developed during the past 30 years, but especially in the last decade it has attracted scientific and economic interest triggered by a rapid increase in power conversion efficiencies. This was achieved by the introduction of new materials, improved materials engineering, and more sophisticated device structures. Today, solar power conversion efficiencies in excess of 3% have been accomplished with several device concepts. Though efficiencies of these thin-film organicdevices have not yet reached those of their inorganic counterparts (η ≈ 10–20%); the perspective of cheap production (employing, e.g., roll-to-roll processes) drives the development of organic photovoltaic devices further in a dynamic way. The two competitive production techniques used today are either wet solution processing or dry thermal evaporation of the organic constituents. The field of organic solar cells profited well from the development of light-emitting diodes based on similar technologies, which have entered the market recently. We review here the current status of the field of organic solar cells and discuss different production technologies as well as study the important parameters to improve their performance.
2,492 citations
TL;DR: In this paper, the authors discuss the calculation of strain fields, which play an important role in the formation of such nanostructures and also influence their structural and optoelectronic properties.
Abstract: Instabilities in semiconductor heterostructure growth can be exploited for the self-organized formation of nanostructures, allowing for carrier confinement in all three spatial dimensions. Beside the description of various growth modes, the experimental characterization of structural properties, such as size and shape, chemical composition, and strain distribution is presented. The authors discuss the calculation of strain fields, which play an important role in the formation of such nanostructures and also influence their structural and optoelectronic properties. Several specific materials systems are surveyed together with important applications.
752 citations
TL;DR: In this article, the relation between the nanoscale morphology and associated device properties in conjugated polymer/fullerene bulk-heterojunction "plastic solar cells" is investigated.
Abstract: The relation between the nanoscale morphology and associated device properties in conjugated polymer/fullerene bulk-heterojunction “plastic solar cells” is investigated. We perform complementary measurements on solid-state blends of poly[2-methoxy-5-(3,7-dimethyloctyloxy)]-1,4-phenylenevinylene (MDMO-PPV) and the soluble fullerene C60 derivative 1-(3-methoxycarbonyl) propyl-1-phenyl [6,6]C61 (PCBM), spin-cast from either toluene or chlorobenzene solutions. The characterization of the nanomorphology is carried out via scanning electron microscopy (SEM) and atomic force microscopy (AFM), while solar-cell devices were characterized by means of current–voltage (I–V) and spectral photocurrent measurements. In addition, the morphology is manipulated via annealing, to increase the extent of phase separation in the thin-film blends and to identify the distribution of materials. Photoluminescence measurements confirm the demixing of the materials under thermal treatment. Furthermore the photoluminescence of PCBM clusters with sizes of up to a few hundred nanometers indicates a photocurrent loss in films of the coarser phase-separated blends cast from toluene. For toluene-cast films the scale of phase separation depends strongly on the ratio of MDMO-PPV to PCBM, as well as on the total concentration of the casting solution. Finally we observe small beads of 20–30 nm diameter, attributed to MDMO-PPV, in blend films cast from both toluene and chlorobenzene.
735 citations
TL;DR: In this paper, the authors describe photon harvesting in organic solar cells and review recent advances in the search for new materials as candidates for polymeric absorbers, where the maximal photon flux of the sun is located.
Abstract: Encouraging progress has been made over the last few years in the field of photovoltaic solar cells using organic materials. Among the different concepts which have been proposed, the bulk heterojunction approach (formed by blending donor type conjugated polymers and acceptors like fullerenes) is attractive and significant progress in improving the power conversion efficiency of these devices was obtained recently. One of the possible improvements of this type of solar cells is the implementation of new materials absorbing the red and near infrared part of the solar spectrum, where the maximal photon flux of the sun is located. In this article, we will describe this strategy of photon harvesting in organic solar cells and review recent advances in the search for new materials as candidates for polymeric absorbers.
702 citations
TL;DR: In this paper, the authors show that participants used the interactive features like stopping, replaying, reversing or changing speed to adapt the pace of the video demonstration, which led to an uneven distribution of their attention and cognitive resources across the videos, which was more pronounced for difficult knots.
421 citations
TL;DR: In this paper, the authors provide quantitative estimates for the minimizers of non-quadratic regularization problems in terms of the regularization parameter, respectively the noise level and the Bregman distance.
Abstract: The aim of this paper is to provide quantitative estimates for the minimizers of non-quadratic regularization problems in terms of the regularization parameter, respectively the noise level. As usual for ill-posed inverse problems, these estimates can be obtained only under additional smoothness assumptions on the data, the so-called source conditions, which we identify with the existence of Lagrange multipliers for a limit problem. Under such a source condition, we shall prove a quantitative estimate for the Bregman distance induced by the regularization functional, which turns out to be the natural distance measure to use in this case. We put a special emphasis on the case of total variation regularization, which is probably the most important and prominent example in this class. We discuss the source condition for this case in detail and verify that it still allows discontinuities in the solution, while imposing some regularity on its level sets.
366 citations
TL;DR: In this paper, a p-i-n-type heterojunction architecture for organic solar cells where the active region is sandwiched between two doped wide-gap layers is introduced.
Abstract: We introduce a p-i-n-type heterojunction architecture for organic solar cells where the active region is sandwiched between two doped wide-gap layers. The term p-i-n means here a layer sequence in the form p-doped layer, intrinsic layer and n-doped layer. The doping is realized by controlled co-evaporation using organic dopants and leads to conductivities of 10-4 to 10-5 S/cm in the p- and n-doped wide-gap layers, respectively. The photoactive layer is formed by a mixture of phthalocyanine zinc (ZnPc) and the fullerene C60 and shows mainly amorphous morphology. As a first step towards p-i-n structures, we show the advantage of using wide-gap layers in M-i-p-type diodes (metal layer–intrinsic layer–p-doped layer). The solar cells exhibit a maximum external quantum efficiency of 40% between 630-nm and 700-nm wavelength. With the help of an optical multilayer model, we optimize the optical properties of the solar cells by placing the active region at the maximum of the optical field distribution. The results of the model are largely confirmed by the experimental findings. For an optically optimized device, we find an internal quantum efficiency of around 82% under short-circuit conditions. Adding a layer of 10-nm thickness of the red material N,N′-dimethylperylene-3,4:9,10-dicarboximide (Me-PTCDI) to the active region, a power-conversion efficiency of 1.9% for a single cell is obtained. Such optically thin cells with high internal quantum efficiency are an important step towards high-efficiency tandem cells. First tandem cells which are not yet optimized already show 2.4% power-conversion efficiency under simulated AM 1.5 illumination of 125 mW/cm2 .
358 citations
TL;DR: The results presented here demonstrate that the highly specific antibody-antigen interaction can be used to generate single-molecule maps of specific types of molecules in a compositionally complex sample while simultaneously carrying out high-resolution topographic imaging.
Abstract: Atomic force microscopy is a powerful and widely used imaging technique that can visualize single molecules and follow processes at the single-molecule level both in air and in solution. For maximum usefulness in biological applications, atomic force microscopy needs to be able to identify specific types of molecules in an image, much as fluorescent tags do for optical microscopy. The results presented here demonstrate that the highly specific antibody–antigen interaction can be used to generate single-molecule maps of specific types of molecules in a compositionally complex sample while simultaneously carrying out high-resolution topographic imaging. Because it can identify specific components, the technique can be used to map composition over an image and to detect compositional changes occurring during a process.
347 citations
Journal Article•
TL;DR: The motivation behind this preliminary analysis is attainment of: interoperability between adaptive learning systems; reuse of adaptive learning materials; and, the facilitation of adaptively supported, distributed learning activities.
Abstract: This paper examines the sufficiency of existing eLearning standards for facilitating and supporting the introduction of adaptive techniques in computer-based learning systems. To that end, the main representational and operational requirements of adaptive learning environments are examined and contrasted against current eLearning standards. The motivation behind this preliminary analysis is attainment of: interoperability between adaptive learning systems; reuse of adaptive learning materials; and, the facilitation of adaptively supported, distributed learning activities.
343 citations
Posted Content•
TL;DR: In this article, the authors used various statistical procedures to estimate the size of the shadow economy in 110 developing, transition and OECD countries and found that the average size of shadow economy (in percent of official GDP) over 1999-2000 in developing countries is 41%, in transition countries 38% and in OECD countries 18.0%.
Abstract: Using various statistical procedures, estimates about the size of the shadow economy in 110 developing, transition and OECD countries are presented. The average size of the shadow economy (in percent of official GDP) over 1999-2000 in developing countries is 41%, in transition countries 38% and in OECD countries 18.0%. An increasing burden of taxation and social security contributions combined with rising state regulatory activities are the driving forces for the growth and size of the shadow economy. If the shadow economy increases by one percent the annual growth rate of the "official" GDP of a developing country (of a industrialized and/or transition country) decreases by 0.6% (increases by 0.8 and 1.0 respectively).
308 citations
TL;DR: The basic analytical and algebraic properties of triangular norms are presented and continuity as well as the important classes of Archimedean, strict and nilpotent t-norms are discussed.
[...]
TL;DR: A novel expansion based decision procedure for quantified boolean formulas (QBF) in conjunctive normal form (CNF) that is competitive with state-of-the-art QBF solvers based on DPLL.
Abstract: We present a novel expansion based decision procedure for quantified boolean formulas (QBF) in conjunctive normal form (CNF). The basic idea is to resolve existentially quantified variables and eliminate universal variables by expansion. This process is continued until the formula becomes propositional and can be solved by any SAT solver. On structured problems our implementation quantor is competitive with state-of-the-art QBF solvers based on DPLL. It is orders of magnitude faster on certain hard to solve instances.
TL;DR: The data suggest that LBs are not only involved in the storage of lipids but also participate actively in the cellular signaling network and the homeostasis oflipids.
Posted Content•
TL;DR: In this article, estimates of the shadow economy in 145 developing, transition, developed OECD countries, South Pacific islands and still communist countries are presented using the DYMIMIC approach.
Abstract: Using the DYMIMIC approach, estimates of the shadow economy in 145 developing, transition, developed OECD countries, South Pacific islands and still communist countries are presented. The average size of the shadow economy (in percent of official GDP) over 2002/2003 in developing countries is 39.1%, in transition countries 40.1%, in OECD countries 16.3%, South Pacific islands 33.4% and 4 remaining Communist countries 21.8%. An increasing burden of taxation, high unemployment and low official GDP growth are the driving forces of the shadow economy.
TL;DR: In this article, the authors developed a dual representation of the technology of international fragmentation for an industry using two factors in a continuum of stages, and derived a generalised factor price frontier which incorporated an endogenous adjustment of the margin of fragmentation.
Abstract: We develop a dual representation of the technology of international fragmentation for an industry using 2 factors in a continuum of stages. We then derive a generalised factor price frontier which incorporates an endogenous adjustment of the margin of fragmentation. Using this frontier in a 2 × 2 general equilibrium model, we investigate the role of outsourcing in the adjustment to a decline in the final output price of the multistage industry, and the attendant factor price effects. We also explore the implications of an improved technology of international fragmentation on the margin of fragmentation and on domestic factor prices.
18 May 2004
TL;DR: A novel method for vital parameter detection using an ultra wideband (UWB) pulse radar by using sub-nanosecond pulses the displacement of a human chest due to respiratory movement can be detected very accurately.
Abstract: In this paper a novel method for vital parameter detection using an ultra wideband (UWB) pulse radar is presented. By using sub-nanosecond pulses the displacement of a human chest due to respiratory movement can be detected very accurately. Because of the very broadband behavior of the transmit signal the presented system is also capable of penetrating materials like walls. For signal processing we use the continuous wavelet transform (CWT) with a special background subtraction method. This allows a detection of respiration up to a distance of 5 meters and also behind walls. The radar test set-up with the used components and the applied signal processing on real measurement data are presented.
Posted Content•
TL;DR: This work proposes to pool multiple time series into several groups using finite-mixture models and analyzes extensions to unobserved heterogeneity and to Markov switching within clusters to illustrate the usefulness of the method.
Abstract: We propose to use the attractiveness of pooling relatively short time series that display similar dynamics, but without restricting to pooling all into one group. We suggest estimating the appropriate grouping of time series simultaneously along with the group-specific model parameters. We cast estimation into the Bayesian framework and use Markov chain Monte Carlo simulation methods. We discuss model identification and base model selection on marginal likelihoods. A simulation study documents the efficiency gains in estimation and forecasting that are realized when appropriately grouping the time series of a panel. Two economic applications illustrate the usefulness of the method in analyzing also extensions to Markov switching within clusters and heterogeneity within clusters, respectively.
Posted Content•
TL;DR: In this article, the problem of estimating marginal likelihoods for mixture and Markov switching models is discussed, where the importance density is constructed in an unsupervised manner from the MCMC draws using a mixture of complete data posteriors.
Abstract: This paper discusses the problem of estimating marginal likelihoods for mixture and Markov switching model. Estimation is based on the method of bridge sampling (Meng and Wong 1996; Statistica Sinica 11, 552-86.) where Markov Chain Monte Carlo (MCMC) draws from the posterior density are combined with an i.i.d. sample from an importance density. The importance density is constructed in an unsupervised manner from the MCMC draws using a mixture of complete data posteriors. Whereas the importance sampling estimator as well as the reciprocal importance sampling estimator are sensitive to the tail behaviour of the importance density, we demonstrate that the bridge sampling estimator is far more robust. Our case studies range from computing marginal likelihoods for a mixture of multivariate normal distributions, testing for the inhomogeneity of a discrete time Poisson process, to testing for the presence of Markov switching and order selection in the MSAR model.
TL;DR: Functional and physical interaction of nonselective TRPC cation channels with NCX proteins as a novel principle of TRPC-mediated Ca2+ signaling is suggested.
TL;DR: In this paper, the problem of estimating marginal likelihoods for mixture and Markov switching models is discussed, where the importance density is constructed in an unsupervised manner from the MCMC draws using a mixture of complete data posteriors.
Abstract: Summary This paper discusses the problem of estimating marginal likelihoods for mixture and Markov switching model. Estimation is based on the method of bridge sampling (Meng and Wong 1996; Statistica Sinica 11, 552-86.) where Markov Chain Monte Carlo (MCMC) draws from the posterior density are combined with an i.i.d. sample from an importance density. The importance density is constructed in an unsupervised manner from the MCMC draws using a mixture of complete data posteriors. Whereas the importance sampling estimator as well as the reciprocal importance sampling estimator are sensitive to the tail behaviour of the importance density, we demonstrate that the bridge sampling estimator is far more robust. Our case studies range from computing marginal likelihoods for a mixture of multivariate normal distributions, testing for the inhomogeneity of a discrete time Poisson process, to testing for the presence of Markov switching and order selection in the MSAR model.
TL;DR: In this paper, the authors use British panel data to investigate whether or not subjective data on desired labour supply can provide information on future labour market behavior, and they find that although men and women are able to adjust their work hours in line with preferences, this is greatly facilitated through within and between-employer job changes.
Abstract: We use British panel data to investigate whether or not subjective data on desired labour supply provide information on future labour market behaviour. We find that, although men and women are able to adjust their work hours in line with preferences, this is greatly facilitated through within- and between-employer job changes. We also find that hours constraints are significant determinants of leaving the labour market and within- and between-employer mobility. We conclude that rigidities in the labour market exist and that these rigidities impair the welfare of employees.
TL;DR: In this article, the temperature and electric field dependence of hole mobility in regioregular poly(3-hexylthiophene) (P3HT) was studied by time-of-flight (TOF) technique.
TL;DR: A method for simultaneously recording topography images and localizing specific binding sites with nm positional accuracy by combining dynamic force microscopy with single molecule recognition force spectroscopy is presented.
Proceedings Article•
01 Jan 2004TL;DR: A novel system, consisting of small and lightweight measurement transponders and a number of fixed base stations, is introduced and can handle up to 1000 measurements per second with accuracies down to a few centimeters.
Abstract: Precise measurement of the local position of moveable targets in three dimensions is still considered to be a challenge. With the presented local position measurement technology, a novel system, consisting of small and lightweight measurement transponders and a number of fixed base stations, is introduced. The system is operating in the 5.8-GHz industrial-scientific-medical band and can handle up to 1000 measurements per second with accuracies down to a few centimeters. Mathematical evaluation is based on a mechanical equivalent circuit. Measurement results obtained with prototype boards demonstrate the feasibility of the proposed technology in a practical application at a race track.
TL;DR: In this paper, the authors show that all species, except carbon dioxide, condense first on high energy binding sites, such as the grooves and the widest interstitial channels, and then on the outer rounded surface of the bundles.
Abstract: Adsorption isotherms, isosteric heats of adsorption, and neutron diffraction measurements of hydrogen, methane, argon, oxygen, and carbon dioxide adsorbed on single-wall carbon nanotube bundles show that all species, except $\mathrm{C}{\mathrm{O}}_{2}$, condense first on high-energy binding sites, such as the grooves and the widest interstitial channels, and then on the outer rounded surface of the bundles. As for $\mathrm{C}{\mathrm{O}}_{2}$, only one set of adsorption sites is observed, which is attributed mainly to the grooves. The diffraction results further reveal that the average packing of the bundles is not changed upon adsorption and that no significant overall bundle dilation is observed on our sample. Molecular dynamic simulations confirm and complete our interpretation.
TL;DR: In this paper, a novel system consisting of small and lightweight measurement transponders and a number of fixed base stations is introduced for precise measurement of the local position of moveable targets in three dimensions.
Abstract: Precise measurement of the local position of moveable targets in three dimensions is still considered to be a challenge. With the presented local position measurement technology, a novel system, consisting of small and lightweight measurement transponders and a number of fixed base stations, is introduced. The system is operating in the 5.8-GHz industrial-scientific-medical band and can handle up to 1000 measurements per second with accuracies down to a few centimeters. Mathematical evaluation is based on a mechanical equivalent circuit. Measurement results obtained with prototype boards demonstrate the feasibility of the proposed technology in a practical application at a race track.
TL;DR: This second part (out of three) of a series of position papers on triangular norms deals with general construction methods based on additive and multiplicative generators, and on ordinal sums.
Book•
01 Oct 2004TL;DR: The present thesis analyzes prerequisites for user-centered prediction of context and presents an architecture for autonomous, background context recognition and prediction, building upon established methods for data based prediction like the various instances of Markov models.
Abstract: Pervasive Computing is a new area of research with increasing prominence; it is situated at the intersection between human/computer interaction, embedded and distributed systems and networking technology. Its declared aim is a holistic design of computer systems, which is often described as the disappearance of computer technology into the periphery of daily life. One central aspect of this vision is a partial replacement of explicit, obtrusive interfaces for human/computer interaction that demand exclusive user attention with implicit ones embedded into real-world artifacts that allow intuitive and unobtrusive use. This kind of interaction with computer systems suits human users better, but necessitates an adaption of such systems to the respective context in which they are used. Context is, in this regard, understood as any information about the current situation of a person, place or object that is relevant to the user interaction. Context-based interaction, which is pursued by the design and implementation of contextsensitive systems, is therefore one of the building blocks of Pervasive Computing. Within the last five years, a number of seminal publications on the recognition of current context from a combination of different sensors have been written within this field. This dissertation tackles the next logical step after the recognition of the current context: the prediction of future contexts. The general concept is the prediction of abstract contexts to allow computer systems to proactively prepare for future situations. This kind of high-level context prediction allows an integral consideration of all ascertainable aspects of context, in contrast to the autonomous prediction of individual aspects like the geographical position of the user. It allows to consider patterns and interrelations in the user behavior which are not apparent at the lower levels of raw sensor data. The present thesis analyzes prerequisites for user-centered prediction of context and presents an architecture for autonomous, background context recognition and prediction, building upon established methods for data based prediction like the various instances of Markov models. Especial attention is turned to implicit user interaction to prevent disruptions of users during their normal tasks and to continuous adaption of the developed systems to changed conditions. Another considered aspect is the economical use of resources to allow an integration of context prediction into embedded systems. The developed architecture is being implemented in terms of a flexible software framework and evaluated with recorded real-world data from everyday situations. This examination shows that the prediction of abstract contexts is already possible within certain limits, but that there is still room for future improvements of the prediction quality.
TL;DR: In this paper, the authors present an understanding of the (quasi)-piezo-and -pyroelectricity in cellular polymers and show that the piezoelectric-like response of these materials is intrinsic, with positive d/sub 33/ and negative D/sub 31/ and d/Sub 32/ coefficients.
Abstract: Cellular space-charge electrets have recently emerged as a new class of materials for electromechanical devices, offering chances for a wide range of applications and challenges for materials optimization. However, many fundamental and applied aspects of the physics of these novel materials are not yet explored. Here we summarize our present understanding of the (quasi)-piezo- and -pyroelectricity in such materials. In contrast to the dipole-density piezoelectricity in ferroelectric polymers, the piezoelectric-like response of cellular polymers is intrinsic, with positive d/sub 33/ and negative d/sub 31/ and d/sub 32/ piezoelectric-like coefficients. Similarities with ferroelectric materials are outlined, especially switching of "polarization" and (quasi)-piezoelectricity. First steps towards patterned charging of cellular polymers are reported, an immediate consequence of the possibility for "polarization"-switchingin cellular materials. The results on cellular space-charge electrets suggest that well-known electret devices like microphones may be seen in a new light. Examples include dielectric and electromechanical hysteresis loops obtained with a commercially available electret microphone. In view of the results, cellular polymers may henceforth be called "ferroelectrets" and their material behavior "ferroelectretic". From an applied point of view, the performance of a Fresnel zone plate for focussing ultrasound is shown. Such a device may pave the way for a simple tool in nondestructive materials inspection, and demonstrates the large potential of cellular polymers for applications.
TL;DR: This study compared the conjugated emission properties of Cy3B with other commercially available fluorophores emitting at similar wavelengths.
Abstract: The spectral properties of a rigidified trimethine cyanine dye, Cy3B have been characterised. This probe has excellent fluorescent properties, good water solubility and can be bioconjugated. The emission properties of this fluorophore have also been investigated upon conjugation to an antibody. This study compared the conjugated emission properties of Cy3B with other commercially available fluorophores emitting at similar wavelengths.