Biomedical subjects

M Bär

Publications and source records attributed to M Bär.

At least 19 recordsLinked to original sources

PubMed2006

Spectroscopic investigation of the deeply buried Cu(In,Ga)(S,Se)2/Mo interface in thin-film solar cells.

The Cu(In,Ga)(S,Se)(2)Mo interface in thin-film solar cells has been investigated by surface-sensitive photoelectron spectroscopy, bulk-sensitive x-ray emission spectroscopy, and atomic force microscopy. It is possible to access this deeply buried interface by using a suitable lift-off technique, which allows us to investigate the back side of the absorber layer as well as the front side of the Mo back contact. We find a layer of Mo(S,Se)(2) on the surface of the Mo back contact and a copper-poor stoichiometry at the back side of the Cu(In,Ga)(S,Se)(2) absorber. Furthermore, we observe that the Na content at the Cu(In,Ga)(S,Se)(2)Mo interface as well as at the inner grain boundaries in the back contact region is significantly lower than at the absorber front surface.

Journal Article↗

PubMed2006

[Persons with dementia in individual everyday situations. First results of an intervention study].

First outcomes of a current intervention study focussing on emotions of nursing home residents with mild, moderate and severe dementia are discussed in the present contribution. The aim of the study was to prove the effect from an individual approach in the care of people with dementia. By promoting individual everyday situations for each resident, positive emotions should be stimulated and individual well-being should be improved. Findings show the possibility to gain such individual everyday-situations for people with mild, moderate and severe dementia, which stimulate positive reactions and may be integrated into the care process. Of particular importance are those positive situations which focus on the communication between nurses and residents or in which the residents receive personal attention from nurses.

Activities of Daily Living↗

PubMed2005

Self-propelled running droplets on solid substrates driven by chemical reactions.

We study chemically driven running droplets on a partially wetting solid substrate by means of coupled evolution equations for the thickness profile of the droplets and the density profile of an adsorbate layer. Two models are introduced corresponding to two qualitatively different types of experiments described in the literature. In both cases an adsorption or desorption reaction underneath the droplets induces a wettability gradient on the substrate and provides the driving force for droplet motion. The difference lies in the behavior of the substrate behind the droplet. In case I the substrate is irreversibly changed whereas in case II it recovers allowing for a periodic droplet movement (as long as the overall system stays far away from equilibrium). Both models allow for a non-saturated and a saturated regime of droplet movement depending on the ratio of the viscous and reactive time scales. In contrast to model I, model II allows for sitting drops at high reaction rate and zero diffusion along the substrate. The transition from running to sitting drops in model II occurs via a super- or subcritical drift-pitchfork bifurcation and may be strongly hysteretic implying a coexistence region of running and sitting drops.

Journal Article↗

PubMed2003

[Situations of emotional significance in residents suffering from dementia].

An advanced stage of dementia implies a loss of the ability to express emotions verbally. However, this does not mean that these patients do not feel emotions anymore. Analyses of nonverbal behaviour are the only way to realise the aim of assessing emotional states in people suffering from severe dementia. In the present study, we tried to identify characteristic situations which are regularly accompanied by positive or negative emotions. Such situations should be described by members of the institutional staff. Moreover, patients' nonverbal behaviour was analysed with psychological instruments developed for analyses of mimic expressions of emotion (FACS, EMFACS). Twenty-nine female residents of nursing homes suffering from moderate or severe dementia participated in the study. Nearly all of them were perceived to show different emotional states by the staff. Most emotions seemed to occur regularly in specific situations. Measures of FACS and AMFACS suggest that predictions of the staff are highly valid. Analyses of situations which were said to be accompanied by positive emotions showed that the respective situations are often created by the residents themselves. This finding implies that even an advanced stage of dementia does not necessarily prevent people from leading a self-determined life. Concentrated and individualised attention enables the staff to shape positive emotions in residents suffering from moderate or severe dementia.

Activities of Daily Living↗

PubMed2003

Modelling thin-film dewetting on structured substrates and templates: bifurcation analysis and numerical simulations.

We study the dewetting process of a thin liquid film on a chemically patterned solid substrate (template) by means of a thin-film evolution equation incorporating a space-dependent disjoining pressure. Dewetting of a thin film on a homogeneous substrate leads to fluid patterns with a typical length scale, that increases monotonously in time (coarsening). Conditions are identified for the amplitude and periodicity of the heterogeneity that allow to transfer the template pattern onto the liquid structure ("pinning") emerging from the dewetting process. A bifurcation and stability analysis of the possible liquid ridge solutions on a periodically striped substrate reveal parameter ranges where pinning or coarsening ultimately prevail. We obtain an extended parameter range of multistability of the pinning and coarsening morphologies. In this regime, the selected pattern depends sensitively on the initial conditions and potential finite perturbations (noise) in the system as we illustrate with numerical integrations in time. Finally, we discuss the instability to transversal modes leading to a decay of the ridges into rows of drops and show that it may diminish the size of the parameter range where the pinning of the thin film to the template is successful.

Biomedical Engineering↗

PubMed2002

Modelling the survival of bacteria in drylands: the advantage of being dormant.

We introduce a simple mathematical model for the description of 'dormancy', a survival strategy used by some bacterial populations that are intermittently exposed to external stress. We focus on the case of the cyanobacterial crust in drylands, exposed to severe water shortage, and compare the fate of ideal populations that are, respectively, capable or incapable of becoming dormant. The results of the simple model introduced here indicate that under a constant, even though low, supply of water the dormant strategy does not provide any benefit and it can, instead, decrease the chances of survival of the population. The situation is reversed for highly intermittent external stress, due to the presence of prolonged periods of dry conditions intermingled with short periods of intense precipitation. In this case, dormancy allows for the survival of the population during the dry periods. In contrast, bacteria that are incapable of turning into a dormant state cannot overcome the difficult times. The model also rationalizes why dormant bacteria, such as those composing the cyanobacterial crust in the desert, are extremely sensitive to other disturbances, such as trampling cattle.

Bacterial Physiological Phenomena↗

PubMed2001

Pulse bifurcations and instabilities in an excitable medium: computations in finite ring domains.

We investigate the instabilities and bifurcations of traveling pulses in a model excitable medium; in particular, we discuss three different scenarios involving either the loss of stability or disappearance of stable pulses. In numerical simulations beyond the instabilities we observe replication of pulses ("backfiring") resulting in complex periodic or spatiotemporally chaotic dynamics as well as modulated traveling pulses. We approximate the linear stability of traveling pulses through computations in a finite albeit large domain with periodic boundary conditions. The critical eigenmodes at the onset of the instabilities are related to the resulting spatiotemporal dynamics and "act" upon the back of the pulses. The first scenario has been analyzed earlier [M. G. Zimmermann et al., Physica D 110, 92 (1997)] for high excitability (low excitation threshold): it involves the collision of a stable pulse branch with an unstable pulse branch in a so-called T point. In the framework of traveling wave ordinary differential equations, pulses correspond to homoclinic orbits and the T point to a double heteroclinic loop. We investigate this transition for a pulse in a domain with finite length and periodic boundary conditions. Numerical evidence of the proximity of the infinite-domain T point in this setup appears in the form of two saddle node bifurcations. Alternatively, for intermediate excitation threshold, an entire cascade of saddle nodes causing a "spiraling" of the pulse branch appears near the parameter values corresponding to the infinite-domain T point. Backfiring appears at the first saddle-node bifurcation, which limits the existence region of stable pulses. The third case found in the model for large excitation threshold is an oscillatory instability giving rise to "breathing," traveling pulses that periodically vary in width and speed.

Journal Article↗

PubMed2001

Traveling solitons in the parametrically driven nonlinear Schrödinger equation.

We show that the (undamped) parametrically driven nonlinear Schrödinger equation has wide classes of traveling soliton solutions, some of which are stable. For small driving strengths stable nonpropagating and moving solitons co-exist while strongly forced solitons can only be stable when moving sufficiently fast.

Journal Article↗

PubMed2000

Discrete stochastic modeling of calcium channel dynamics.

We propose a discrete stochastic model for calcium dynamics in living cells. A set of probabilities for the opening/closing of calcium channels is assumed to depend on the calcium concentration. We study this model in one dimension, analytically in the limit of a large number of channels per site N, and numerically for small N. As the number of channels per site is increased, the transition from a nonpropagating region of activity to a propagating one changes from one described by directed percolation to that of deterministic depinning in a spatially discrete system. Also, for a small number of channels a propagating calcium wave can leave behind a novel fluctuation-driven state.

Calcium Channels↗

PubMed2000

Dispersion gap and localized spiral waves in a model for intracellular Ca2+ dynamics.

The dispersion relation is the dependence of the velocity of periodic planar wave trains on their wavelength. We study the occurrence of a velocity gap in the dispersion relation in a bistable three component reaction-diffusion system modeling intracellular Ca2+ dynamics. In two spatial dimensions, localized pinned spirals are observed, if their wavelength falls into the dispersion gap. Destruction of free spirals occurs already for conditions where the asymptotic planar wave train exists and the dispersion gap is absent.

Calcium↗

PubMed1996