Publikationen

It has been shown recently that chirp-evoked auditory brainstem responses (ABRs) show better performance than click stimulations, especially at low intensity levels. In this paper we present the development, test, and evaluation of a series of notched-noise embedded frequency specific chirps. ABRs were collected in healthy young control subjects using the developed stimuli. Results of the analysis of the corresponding ABRs using a time-scale phase synchronization stability (PSS) measure are also reported. The resultant wave V amplitude and latency measures showed a similar behavior as for values reported in literature. The PSS of frequency specific chirp-evoked ABRs reflected the presence of the wave V for all stimulation intensities. The scales that resulted in higher PSS are in line with previous findings, where ABRs evoked by broadband chirps were analyzed, and which stated that low frequency channels are better for the recognition and analysis of chirp-evoked ABRs. We conclude that the development and test of the series of notched-noise embedded frequency specific chirps allowed the assessment of frequency specific ABRs, showing an identifiable wave V for different intensity levels. Future work may include the development of a faster automatic recognition scheme for these frequency specific ABRs.

Objective: The objective of our research is to structure a foundation for an electrophysiological loudness scaling measurement, in particular to estimate an uncomfortable loudness (UCL) level by using the hybrid wavelet-kernel novelty detection (HWND). Methods and materials: Late auditory evoked potentials (LAEPs) were obtained from 20 normal hearing adults. These LAEPs were stimulated by 4 intensity levels (60 decibel (dB) sound pressure level (SPL), 70. dB SPL, 80. dB SPL, and 90. dB SPL). We have extracted the habituation correlates in LAEPs by using HWND. For this, we employed a lattice structure-based wavelet frame decompositions for feature extraction combined with a kernel-based novelty detector. Results: The group results showed that the habituation correlates degrees, i.e., relative changes within the sweep sequences, were significantly different among 60. dB SPL, 70. dB SPL, 80. dB SPL, and 90. dB SPL stimulation level, independently from the intensity related amplitude information in the averaged LAEPs. At these particular intensities, 60% of the subjects show the correlation between the novelty measures and the stimulation levels resembles a loudness scaling function, in reverse. In this paper, we have found a correlation in between the novelty measures and loudness perception as well. We have found that high ranges of loudness levels such as loud, upper level and too loud show generally 4.88% of novelty measures and comfortable ranges of loudness levels, i.e., soft, comfortable but soft, comfortable loud and comfortable but loud are generally have 12.29% of novelty measures.Additionally, we demonstrated that our sweep-to-sweep basis of post processing scheme is reliable for habituation extraction and offers an advantage of reducing experimental time as the proposed scheme need less than 20% of single sweeps in comparison to the amount that are commonly used in arithmetical average for a meaningful result. Conclusions: We assessed the feasibility of habituation correlates for an objective loudness scaling. With respect to this first feasibility study, the presented results are promising when using the described signal processing and machine learning methodology. For the group results, the novelty measures approach is able to discriminate 60. dB, 70. dB, 80. dB and 90. dB stimulated sweeps. In addition, a correlation between the novelty measures and the subjective loudness scaling is observed. However, more loudness perception and frequency specific experiments need to be conducted to determine the UCL novelty measures threshold as well as clinically oriented studies are necessary to evaluate whether this approach might be used in the objective hearing instrument fitting procedures.

Mechanical forces play a vital role in the activities of cells and their interaction with biological and nonbiological material. Various experiments have successfully measured forces exerted by the cells when in contact with a substrate, but the intracellular contractile machinery leading to these actions is not entirely understood. Tan, (2003, Cells Lying on a Bed of Microneedles: An Approach to Isolate Mechanical Force, Proc. Natl. Acad. Sci. USA, 100(4), pp. 1484-1489) use a bed of PDMS posts as the substrate for cells and measure the localized mechanical forces exerted by the cell cytoskeleton on the posts. In live cell experiments for this setup, post deflections are measured, and from these results the forces applied by the cell are calculated. From such results, it is desirable to quantify the contractile tensions generated in the force-bearing elements corresponding to the stress fibers within the cell cytoskeleton that generate the loads applied to the posts. The purpose of the present article is to consider the cytoskeleton as a discrete network of force-bearing elements, and present a structural mechanics based methodology to estimate the configuration of the network, and the contractile tension in the corresponding stress fibers. The network of stress fibers is modeled as a structure of truss elements connected among the posts adhered to a single cell. In-plane force equilibrium among the network of stress fibers and the system of posts is utilized to calculate the tension forces in the network elements. A Moore-Penrose pseudo-inverse is used to solve the linear equations obtained from the mechanical equilibrium of the cell-posts system, thereby obtaining a least squares fit of the stress fiber tensions to the post deflections. The predicted network of force-bearing elements provides an approximated distribution of the prominent stress fibers connected among deflected posts, and the tensions in each fibril.

A linearized model is developed for lithium ion batteries, relying on simplified characterizations of lithium transport in the electrolyte and through the interface between the electrolyte and the storage particles of the electrodes. The model is valid as a good approximation to the behavior of the battery when it operates near equilibrium, and can be used for both discharge and charging of the battery. The rate of extraction of lithium from and to the electrode storage particles can be estimated from the results of the model, information that can be used in turn to estimate the shrinkage and swelling stresses that develop in the particles. Given specified rates of extraction for spherical particles, maps of the resulting shrinkage and swelling stresses can be developed connecting their values to battery parameters such as particles size, diffusion coefficient, lithium partial molar volume, and particle elastic properties. Since a constant rate of extraction can only be achieved for a limited period of time until the concentration of lithium at the particle perimeter constrains the lithium mass transport, plots of the average state of charge in the particle versus time are also produced.

An integrated 2-D model of a lithium ion battery is developed to study the mechanical stress in storage particles as a function of material properties. A previously developed coupled stress-diffusion model for storage particles is implemented in 2-D and integrated into a complete battery system. The effect of morphology on the stress and lithium concentration is studied for the case of extraction of lithium in terms of previously developed non-dimensional parameters. These non-dimensional parameters include the material properties of the storage particles in the system, among other variables. We examine particles functioning in isolation as well as in closely-packed systems. Our results show that the particle distance from the separator, in combination with the material properties of the particle, is critical in predicting the stress generated within the particle.

Optimization of the microstructure of porous electrodes plays an important role in the enhancement of the performance of solid oxide fuel cells. For this, microstructural models based on percolation theory have proven useful for the estimation of the effective material properties of the electrode material, assumed to consist of a binary mixture of spherical electron and ion conducting particles. In this work, we propose an extension of prior approaches for calculating the effective size of the three-phase boundary, which we judge to be physically more sound and, in particular, well suited for characterizing mixtures of particles of different sizes. This approach is then employed in a one-dimensional cell level model encompassing the entire set of processes of gas transport, electronic and ionic conduction as well as the electrochemical reactions. The impact of the electron and ion conducting particle sizes, their volume fraction and their size ratio on the performance of the fuel cell are investigated in a parametric study. Under certain conditions, cathode microstructures having electronic conducting particles of size different from that of the ionic conducting particles become preferable and yield a higher maximum power density when compared to the best possible configuration of monodisperse particles.

The incorporation of rhodamine dyes in the cell wall of diatoms Coscinodiscus granii and Coscinodiscus wailesii for the production of luminescent hybrid nanostructures is investigated. By systematic variation of the substitution pattern of the rhodamine core, we found that carbonic acids are considerably better suited than esters because of their physiological compatibility. The amino substitution pattern that controls the optical properties of the chromophore has no critical influence on dye uptake and incorporation, thus a variety of biocomposites with different emission maxima can be prepared. Applications in biomineralization studies as well as in materials science are envisioned.

For about a decade, superresolution fluorescence microscopy has been advancing steadily, maturing from the proof-of-principle stage to routine application. Of the various techniques, STED (stimulated emission depletion) microscopy was the first to break the diffraction barrier. Today, it is a prominent and versatile form of superresolution light microscopy. STED microscopy has shed a sharper light on numerous topics in cell biology, but also in material sciences. Both disciplines extend into the nanometer range, making detailed studies of structural and functional relationships difficult or even impossible to achieve using diffraction-limited microscopy. With recent advancements like spectral multiplexing or live-cell imaging, STED microscopy makes nanoscale materials and components of the cell accessible for fluorescence-based investigations. With multicolor superresolution imaging, even the interactions between biological and engineered nanostructures can be studied in detail. This review gives an introduction into the working principle of STED microscopy, provides a detailed overview of recent advancements and new techniques implemented for use with STED microscopy and shows how these have been applied in the life sciences and nanotechnologies.

The interactions of nanoparticles with human cells are of large interest in the context of nanomaterial safety. Here, we use live cell imaging and image-based fluorescence correlation methods to determine colocalization of 88 nm and 32 nm silica nanoparticles with endocytotic vesicles derived from the cytoplasmic membrane and lysosomes, as well as to quantify intracellular mobility of internalized particles, in contrast to particle number quantification by counting techniques. In our study, A549 cells are used as a model for human type II alveolar epithelial cells. We present data supporting endocytotic uptake of the particles and subsequent active transport to the perinuclear region. The presence of particles in lamellar bodies is proposed as a potential exocytosis route. Live cell imaging and image-based fluorescence correlation methods were used to quantify the intracellular mobility and interactions of 32 and 88 nm silica nanoparticles in A549 cells as model for human type II alveolar epithelial cells. Our data support uptake by endocytosis and active transport to the perinuclear region.

In cardiac myocytes, cytochalasin D (CytoD) was reported to act as an actin disruptor and mechanical uncoupler. Using confocal and super-resolution STED microscopy, we show that CytoD preserves the actin filament architecture of adult rat ventricular myocytes in culture. Five hundred nanomolar CytoD was the optimal concentration to achieve both preservation of the T-tubular structure during culture periods of 3days and conservation of major functional characteristics such as action potentials, calcium transients and, importantly, the contractile properties of single myocytes. Therefore, we conclude that the addition of CytoD to the culture of adult cardiac myocytes can indeed be used to generate a solid single-cell model that preserves both morphology and function of freshly isolated cells. Moreover, we reveal a putative link between cytoskeletal and T-tubular remodeling. In the absence of CytoD, we observed a loss of T-tubules that led to significant dyssynchronous Ca2+-induced Ca2+ release (CICR), while in the presence of 0.5μM CytoD, T-tubules and homogeneous CICR were majorly preserved. Such data suggested a possible link between the actin cytoskeleton, T-tubules and synchronous, reliable excitation-contraction-coupling. Thus, T-tubular re-organization in cell culture sheds some additional light onto similar processes found during many cardiac diseases and might link cytoskeletal alterations to changes in subcellular Ca2+ signaling revealed under such pathophysiological conditions.