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Biomedical subjects

D Michaelis

Publications and source records attributed to D Michaelis.

At least 19 recordsLinked to original sources
PubMed2005

Modulational instability in systems with integrating nonlinearity.

A new type of modulational instability for coherent as well as partially coherent light in systems with integrating nonlinearity caused by an irreversible process is investigated both experimentally and theoretically. In such systems plane waves never reach the stationary limit and exhibit a nontrivial time dependence resulting in new features of the modulational instability. For example, the modulational frequency of the nonexponentially increasing perturbation with maximum gain decreases while the wave is propagating. The threshold for vanishing modulational instability due to a finite degree of spatial coherence depends only on system parameters and not on the light intensity.

Journal Article↗
PubMed2005

Ising-Bloch transition for the parametric Ginzburg-Landau equation with rapidly varying perturbations.

We study the effects of rapid periodic and stochastic modulations of parameters in systems described by the complex parametric Ginzburg-Landau equation. Amplitude equations, which govern the dynamics of the field averaged over the rapid modulations, are derived. For temporal modulations of the linear detuning the threshold for the transition from Ising to Bloch walls is shifted depending on the strength of the perturbation. In contrast to this, rapid perturbations of the linear gain lead only to a decrease of the amplitude of both wall types leaving the bifurcation point of the Ising-Bloch transition unchanged. Stochastic perturbations of the detuning lead to a Brownian motion of the Bloch wall beyond bifurcation where the velocity is given analytically. All theoretical predictions are confirmed by numerical simulations of the full stochastic Ginzburg-Landau equation.

Journal Article↗
PubMed2003

Reciprocity theorem and perturbation theory for photonic crystal waveguides.

Starting from Maxwell's equations we derive a reciprocity theorem for photonic crystal waveguides. A set of strongly coupled discrete equations results, which can be applied to the simulation of perturbed photonic crystal waveguides. As an example we analytically study the influence of the dispersion of a two level system on the band structure of a photonic crystal waveguide. In particular, the formation of polariton gaps is discussed.

Journal Article↗
PubMed2003

Stable spatial solitons in semiconductor optical amplifiers.

The existence of stable dissipative spatial solitons at low intensities in patterned electrode semiconductor optical amplifiers (SOAs) is predicted theoretically. In contrast to conventional SOAs, this system may support stable solitons because the inherent saturating losses provide subcritical bifurcations for both the plane-wave and the soliton solution.

Journal Article↗
PubMed2001

Perturbation theory for domain walls in the parametric Ginzburg-Landau equation.

We demonstrate that in the parametrically driven Ginzburg-Landau equation arbitrarily small nongradient corrections lead to qualitative differences in the dynamical properties of domain walls in the vicinity of the transition from rest to motion. These differences originate from singular rotation of the eigenvector governing the transition. We present analytical results on the stability of Ising walls, deriving explicit expressions for the critical eigenvalue responsible for the transition from rest to motion. We then develop a weakly nonlinear theory to characterize the singular character of the transition and analyze the dynamical effects of spatial inhomogeneities.

Journal Article↗
PubMed2001

Effects of spatial inhomogeneities on the dynamics of cavity solitons in quadratically nonlinear media.

We study the dynamics of cavity solitons under the influence of spatial inhomogeneities and derive generalized equations of motions. For perturbations large compared to the soliton size we find the modulus of the soliton velocity to be proportional to the gradient of the respective perturbation and that the proportionality coefficient changes sign when the soliton peak power drives the cavity beyond the resonance. For short scale perturbations solitons may be trapped at the extrema of the inhomogeneities. Shape and stability of these trapped solitons can be quasianalytically described by means of a perturbation theory. If both types of perturbations act solitons are either trapped or move depending on the strength of the respective perturbation. In the framework of a quasiparticle approach this dynamics is governed by a differential equation that holds for particle motion in a strongly viscous fluid under the action of a constant and harmonically varying force. We also show that in addition to acquiring a velocity the very existence conditions of the solitons (hysteresis curve) are affected by both kinds of perturbations. We find good quantitative agreement between our analytical results and numerical findings, which were obtained for a two wave interaction in a cavity filled with a quadratically nonlinear material.

Journal Article↗
PubMed2001

Universal criterion and amplitude equation for a nonequilibrium Ising-Bloch transition.

We identify a universal criterion for the onset of a nonequilibrium Ising-Bloch (NIB) transition, and describe the behavior near the bifurcation by a generic amplitude equation. We found that a NIB transition is caused by an antisymmetric eigenvector passing the translational mode of the system at a critical point. In this context we discuss Hamiltonian and dissipative systems. We report on a NIB in nonlinear optics, manifesting itself in a transition from static to moving polarization fronts.

Journal Article↗
PubMed2001

SIM--simultaneous inverse filtering and matching of a glottal flow model for acoustic speech signals.

A new method "simultaneous inverse filtering and model matching" (SIM) is proposed that allows one to calculate voice source measures without any user interaction. It is based on the discrete all-pole modeling (DAP) technique for inverse filtering (IF), which is modified to include a model of the glottal flow as integral part [LF model, Fant et al., STL-QPSR (Stockholm) 4/1985, 1-13 (1986)]. As the correct LF parameters are initially unknown, they are estimated in an iterative procedure using multi-dimensional optimization techniques that are initialized according to the results of an exhaustive search. The error criteria applied reflect how well the IF is performed after the spectral contribution of the glottal flow has been removed. The resulting optimal LF parameter constellation serves as the basis to calculate 11 voice source measures. The performance was evaluated using synthesized signals and recordings of natural utterances. For the synthesized signals, the accuracy to reproduce the original parameters was high (correlations exceeding 0.88) for measures where the starting point of the glottal cycle did not enter explicitly. Errors were smaller compared to conventional estimation methods where the measures were estimated from the IF signal. The analysis of natural utterances indicates that problems still exist with regard to robustness, but that under advantageous conditions the open quotient, the speed quotient, the closing quotient, the parabolic spectral parameter, and the negative peak amplitude of the glottal flow derivative can indeed be determined automatically by the SIM method.

Fourier Analysis↗
PubMed2000

Acoustic voice analysis by means of the hoarseness diagram.

The hoarseness diagram (Michaelis, Fröhlich, & Strube, 1998a) has been proposed as a new approach to describe different acoustic properties of voices. To test its performance in the analysis of pathologically disturbed and normal voices five requirements are suggested that should be met by any acoustic voice-analysis protocol to be used in voice research and clinical practice. The hoarseness diagram is then tested with regard to these requirements. Individual voices are found to show a satisfactory localization in the diagram. Aspects of stationarity are discussed in the context of four case studies. The different cases illustrate that changes in the acoustic analysis results are observed if the voice-generation conditions change, whereas results are stationary if phonation conditions do not change. Different pathological voice groups defined on grounds of the specific phonation mechanism are found to map to specific regions of the hoarseness diagram, with differences between group locations being significant. All results can be interpreted without exceptions if the two hoarseness diagram coordinates are taken to reflect the vibrational irregularity of the voice-generation mechanisms on the one side and the degree of closure of the vibrating structures on the other side. The hoarseness diagram and its underlying algorithms are thus shown to constitute a useful approach to acoustic voice analysis in research and clinical practice. The tests themselves demonstrate several application possibilities, including the quantitative monitoring of individual voices.

Adolescent↗
PubMed1998

[Objective description of voice quality using the hoarseness diagram].

The need for an objective assessment of voice quality can be seen in the increasing use of acoustic analysis methods for clinical diagnosis and research. The hoarseness diagram allows clinicians to objectively describe even highly disturbed or aphonic votes. Its application possibilities are illustrated in three case studies in which changes in voice quality were monitored during voice rehabilitation. The distributions of voice groups that were defined on the basis of specific pathophysiological phonation conditions were then compared for their acoustic differences. The groups comprised various phonation conditions after the resection of laryngeal tumors and different types of laryngeal paralyses. Interpretation of the results suggests a direct correspondence of the hoarseness diagram coordinates and the irregularity of vibration on the one side and the degree of glottal closure on the other. This illustrates the potential usefulness of the hoarseness diagram in a clinical context.

Adult↗
PubMed1998

Selection and combination of acoustic features for the description of pathologic voices.

The glottal to noise excitation ratio (GNE) is an acoustic measure designed to assess the amount of noise in a pulse train generated by the oscillation of the vocal folds. So far its properties have only been studied for synthesized signals, where it was found to be independent of variations of fundamental frequency (jitter) and amplitude (shimmer). On the other hand, other features designed for the same purpose like NNE (normalized noise energy) or CHNR (cepstrum based harmonics-to-noise ratio) did not show this independence. This advantage of the GNE over NNE and CHNR, as well as its general applicability in voice quality assessment, is now tested for real speech using a large group of pathologic voices (n = 447). A set of four acoustic features is extracted from a total of 22 mostly well-known acoustic voice quality measures by correlation analysis, mutual information analysis, and principal components analysis. Three of these measures are chosen to assess primarily different aspects of signal aperiodicity, while the fourth one indicates the noise content of the signal. All analysis methods lead to the same feature set that consists of a measure of period correlation, jitter, shimmer, and GNE. The two-dimensional projection of this set named "hoarseness diagram" allows a graphical illustration of voice quality that can be easily interpreted.

Adolescent↗
PubMed1997

[Functional voice quality assessment in curative microsurgery of laryngeal malignancies. Postoperative voice rehabilitation based on the "laryngeal double valve function"].

According to Negus and Pressman the sphincter systems of the vocal folds and the ventricular folds form a respiratory "laryngeal double valve function". Correspondingly, we found a physiological phonation system of the glottis and a pathological-compensatory one of the supraglottis. They appear to be regulated through an automatic phonatory control system with the glottal phonatory function evidently acting as sensor level. In order to confirm this hypothesis, objective voice analyses with glottal-relevant parameters of 26 voice-rehabilitated patients after minimally invasive laser surgery of glottal carcinomas are presented and integrated into a "hoarseness diagram" with the coordinates roughness and breathiness. Using statistically deliminated acoustic dusters, our data show a qualitative hierarchy of different postoperative phonation mechanisms. They demonstrate the influence of the vibratory capacity of glottal and supraglottal structures on the quality of the vibratory closure. Both functional parameters evidently determine the resulting voice quality in the sense of our hypothesis.

Female↗
PubMed1997

Increased prevalence of elevated urinary albumin excretion rate in type 2 diabetic patients suffering from ischemic foot lesions.

UNLABELLED: Present cross-sectional clinical study was aimed at the evaluation the prevalence of cardiovascular risk factors in Type 2-diabetics suffering from different clinical manifestations of diabetic foot lesions due to peripheral vascular disease and/or diabetic neuropathy. 1025 non-insulin-dependent (Type 2) diabetics (NIDDM) of both sexes were investigated. Patients were classified in Type II diabetes without peripheral vascular disease and foot lesions (group 0, controls), with macroangiopathic related foot lesions (group 2), with neuropathic foot lesions (group 3), and with mixed neuropathic-ischemic foot lesions (group 4). Apart from urinary albumin excretion rate (UAE), the following micro- and macroangiopathic risk factors and diseases were taken into account: Hypertension, degree of metabolic control (HbA1c), lipid concentrations, duration of diabetes, retinopathy, clinical nephropathy. RESULTS: In the total population the UAE was significantly (p < 0.01) correlated with duration of diabetes, serum creatinine, hypertension, age, lipid concentrations, HbA1c and insulin requirement. In comparison to Type II diabetic patients without peripheral vascular disease (group 0) and with neuropathic foot lesions (group 3), subjects with ischemic (group 2) and mixed neuropathic-ischemic foot lesions demonstrated an increased prevalence of pathological UAE, which was associated with a higher frequency of clinical nephropathy, retinopathy, an older age and longer duration of diabetes. It is concluded that microalbuminuria in Type 2 diabetes reflects both the existence of diabetic nephropathy and peripheral vascular disease which is often associated with the insulin resistance syndrome.

Age of Onset↗
PubMed1997

Co-expression of ICAM-1, VCAM-1, ELAM-1 and Hsp60 in human arterial and venous endothelial cells in response to cytokines and oxidized low-density lipoproteins.

T-cells and monocytes are the first cells infiltrating the arterial intima during the early stages of atherogenesis. Recently our laboratory has provided evidence that T-cells isolated from atherosclerotic intima reacts against heat shock protein 60 (Hsp60). Transmigration of activated T-cells into the intima is mediated by adhesion molecules (ICAM-1; VCAM-1; ELAM-1) expressed on activated endothelial cells. Here we studied the potential of cytokines (TNF-alpha, IFN-gamma, IL-1). Escherichia coli lipopolysaccharide (LPS), native and oxidized low-density lipoprotein (LDL; oxLDL) and high temperature to induce adhesion molecules as well as Hsp60 and Hsp70 expression in human endothelial cells (EC). On Northern blots, a strong signal for ICAM-1, VCAM-1 and ELAM-1 was detected after 4 h, which thereafter declined, but did not reach the basal level of untreated control cells. Heat shock induced the expression of Hsp60 and Hsp70 but not of adhesion molecules. EC were cultivated in serum-free medium, which led to the expression of adhesion molecule transcripts. Addition of LDL or oxLDL to these ECs did not alter the expression of these transcripts. The production of adhesion molecule proteins was analysed by flow cytometry. In human venous endothelial cells (HVEC) and human arterial endothelial cells (HAEC) ICAM-1 and VCAM-1 production was permanently highly induced, whereas the high level of ELAM-1 production at 4 h disappeared after 24 h. Furthermore, only HAEC, but not HVEC, produced ICAM-1, VCAM-1 and ELAM-1 after stress by moderately and highly oxLDL. LDL and oxLDL did not induce the production of Hsp60 and Hsp70. The present study demonstrates the co-expression of Hsp60 and adhesion molecules in arterial and venous EC in response to cytokine and LPS exposure, and that oxLDL is an efficient inducer of adhesion molecules in arterial EC and not in venous EC. These features provide the prerequisites for a cellular immune reaction against Hsp60 expressed by stressed EC in the initial stages of atherosclerosis.

Antigens, CD↗
PubMed1996

Differential expression of perforin in muscle-infiltrating T cells in polymyositis and dermatomyositis.

Polymyositis (PM) and dermatomyositis (DM) are the prototypical inflammatory diseases of skeletal muscle. In PM, CD8+ T cells invade and destroy muscle fibers, whereas humoral effector mechanisms prevail in DM. We studied the expression of the cytotoxic mediator perforin in inflammatory cells in PM and DM muscle by semiquantitative PCR, immunohistochemistry and confocal laser microscopy. Similar levels of perforin mRNA were expressed in PM and DM, and abundant perforin-expressing CD3+CD8+ and CD3+ CD4+ T cells were observed in both diseases. However, there was a striking difference in the intracellular localization of perforin. In DM, perforin was distributed randomly in the cytoplasm of the inflammatory T cells. In contrast, 43% of the CD8+ T cells that contacted a muscle fiber in PM showed perforin located vectorially towards the target muscle fiber. The results suggest (a) that the random distribution of perforin in the cytoplasm of muscle-infiltrating T cells observed in DM reflects nonspecific activation, and (b) that the vectorial orientation observed only in PM reflects the specific recognition via the T cell receptor of an antigen on the muscle fiber surface, pointing to a perforin- and secretion-dependent mechanism of muscle fiber injury.

Base Sequence↗
PubMed1996

Antibody response to islet antigens in anti-CD4/prednisolone immune intervention of type 1 diabetes.

Cytoplasmic islet cell antibodies, glutamic acid decarboxylase autoantibodies, spontaneous insulin autoantibodies, and insulin-induced antibodies were analyzed in a 1-year follow-up study of 12 newly diagnosed patients with insulin-dependent diabetes mellitus aged 14 +/- 2 years (range 7-20 years) who had been initially treated with either multiple injections of insulin alone (control group) or, in addition, anti-CD4 monoclonal antibody/prednisolone (treatment group). Despite individual variations in islet cell antibody titers, there were no significant differences in the prevalence or changes in the mean titers between the two groups. Glutamic acid decarboxylase autoantibodies remained almost unchanged, but correlated with levels of islet cell antibodies. While at initiation of treatment only 50% of the patients from both groups had spontaneous insulin autoantibodies, all patients developed insulin-induced antibodies upon conventional insulin therapy during the course of follow-up. This was not related to islet cell antibody or glutamic acid decarboxylase antibody levels. The insulin requirement was markedly reduced through the period of follow-up, but did not significantly differ between the two groups. A correlation between islet cell antibody levels and insulin requirement was observed in the control group but not in the treatment group. Plasma levels of the antibodies were not associated with changes in stimulated C-peptide or hemoglobin A1 concentrations. Activated T-lymphocytes persisted in both groups of patients, but their mean levels were not significantly different. The reason for the absence of statistically significant differences between treatment and control groups could be due to the small number of patients in the study. In conclusion, short-term immune intervention with anti-CD4 monoclonal antibody in addition to insulin therapy did not suppress autoimmune reactions towards the beta cells.

Adolescent↗
PubMed1996

Differential expression of fructosyllysine-specific receptors on monocytes and macrophages and possible pathophysiological significance.

A differing individual expression of fructosyllysine-specific receptors has been found on the monocytes of 90 insulin-dependent diabetic patients and 101 healthy control subjects. The degree of receptor expression is neither age- nor sex-dependent; however, in the diabetic group it correlates significantly with the severity and age of onset of diabetic microangiopathy. To interpret the results of the human study, spontaneously diabetic and non-diabetic BB/OK rats were used to estimate tissue content of glucose-modified proteins and capillary basement membrane thickness in relation to the receptor expression on macrophages. In non-diabetic and diabetic rats no correlation was found between receptor expression and tissue content (i.e. artery, nerve) of fructosyllsine and fluorescent advanced glycation end products. However, animals which express the fructosyllysine receptor showed a greater increase in muscle capillary basement membrane thickness. There are indications that fructosyllysine receptor expression is positively associated with indices of diabetic complications such as microangiopathy and/or capillary basement membrane thickening.

Adult↗