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Biomedical subjects

S Herminghaus

Publications and source records attributed to S Herminghaus.

At least 19 recordsLinked to original sources
PubMed2006

Unclustering transition in freely cooling wet granular matter.

The free cooling of one-dimensional wet granular matter is presented in the framework of the minimal capillary model. We demonstrate analytically and by extensive simulations that above a critical density, the clustering of wet granular matter is not monotonic in time, but undergoes a sharp unclustering transition. This precipitation of granular droplets out of the gas takes place when the granular temperature comes close to the energy scale set by the capillary interaction.

Journal Article↗
PubMed2006

Free cooling of the one-dimensional wet granular gas.

The free cooling behavior of a wet granular gas is studied in one dimension. We employ a particularly simple model system in which the interaction of wet grains is characterized by a fixed energy loss assigned to each collision. Macroscopic laws of energy dissipation and cluster formation are studied on the basis of numerical simulations and mean-field analytical calculations. We find a number of remarkable scaling properties which may shed light on earlier unexplained results for related systems.

Cold Temperature↗
PubMed2006

AFM study of defect-induced depressions of the smectic-A/air interface.

The smectic-A/air interface of liquid-crystal droplets with antagonistic boundary conditions is studied by atomic force microscopy (AFM). The droplets are prepared on coated silicon wafers on which a planar alignment is preferred in contrast to the homeotropic alignment at the air interface. As a result, focal conic defects appear in the smectic-A phase causing a characteristic pattern of depressions in the droplet surface. The dimensions of the defect-induced depressions are measured by AFM as a function of temperature for two different compounds possessing a smectic-A-isotropic and a smectic-A-nematic transition. Whereas the results are independent of temperature in the smectic-A-isotropic case, reflecting the first-order nature of the transition, a pronounced temperature dependence is observed for the second compound, where the depth of the defect-induced depressions decreases continuously with increasing temperature and vanishes at the second-order transition to the nematic phase. These observations can be qualitatively explained through the behavior of the layer compressional elastic constant at the smectic-A-nematic transition.

Journal Article↗
PubMed2005

A generic mechanism of sliding friction between charged soft surfaces.

A universal sliding friction mechanism between soft, electrically charged surfaces (e.g., those carrying polyelectrolytes) is proposed. The Coulomb field of the randomly distributed charges induces a damped motion of the charges of the opposite surface, which gives rise to dissipation, and thus to friction. It is predicted that this friction force, which diverges at zero separation, may overcome viscous friction at distances significantly exceeding the Bjerrum length. This is not only of fundamental interest, but also of potential importance in life science and many practical situations.

Journal Article↗
PubMed2003

Viscoelastic dynamics of polymer thin films and surfaces.

The strain relaxation behavior in a viscoelastic material, such as a polymer melt, may be strongly affected by the proximity of a free surface or mobile interface. In this paper, the viscoelastic surface modes of the material are discussed with respect to their possible influence on the freezing temperature and dewetting morphology of thin polymer films. In particular, the mode spectrum is connected with mode coupling theory assuming memory effects in the melt. Based on the idea that the polymer freezes due to these memory effects, surface melting is predicted. As a consequence, the substantial shift of the glass transition temperature of thin polymer films with respect to the bulk is naturally explanied. The experimental findings of several independent groups can be accounted for quantitatively, with the elastic modulus at the glass transition temperature as the only fitting parameter. Finally, a simple model is put forward which accounts for the occurrence of certain generic dewetting morphologies in thin liquid polymer films. It demonstrates that by taking into account the viscoelastic properties of the film, a morphological phase diagram may be derived which describes the observed structures of dewetting fronts. It is demonstrated that dewetting morphologies may also serve to determine nanoscale rheological properties of liquids.

Journal Article↗
PubMed2002

Clinical application of proton magnetic resonance spectroscopy in the diagnosis of intracranial mass lesions.

Diagnosis of primary and secondary brain tumours and other focal intracranial mass lesions based on imaging procedures alone is still a challenging problem. Proton magnetic resonance spectroscopy (1H-MRS) gives completely different information related to cell membrane proliferation, neuronal damage, energy metabolism and necrotic transformation of brain or tumour tissues. Our purpose was to evaluate the clinical utility of 1H-MRS added to MRI for the differentiation of intracranial neoplastic and non-neoplastic mass lesions. 176 mostly histologically verified lesions were studied with a constant clinically available single volume 1H-MRS protocol following routine MRI. 12 spectra (6.8%) were not of satisfactory diagnostic quality; 164 spectroscopic data sets were therefore available for definitive evaluation. Our study shows that spectroscopy added to MRI helps in tissue characterization of intracranial mass lesions, thereby leading to an improved diagnosis of focal brain disease. Non-neoplastic lesions such as cerebral infarctions and brain abscesses are marked by decreases in choline (Cho), creatine (Cr) and N-acetyl-aspartate (NAA), while tumours generally have elevated Cho and decreased levels of Cr and NAA. Gliomas exhibit significantly increased Cho and lipid formation with higher WHO tumour grading. Metastases have elevated Cho similar to anaplastic astrocytomas, but can be differentiated from high-grade gliomas by their higher lipid levels. Extra-axial tumours, i.e. meningiomas and neurinomas, are characterized by a nearly complete absence of the neuronal marker NAA. The additive information of 1H-MRS led to a 15.4%-higher number of correct diagnoses, to 6.2% fewer incorrect and 16% fewer equivocal diagnoses than with structural MRI data alone.

Aspartic Acid↗
PubMed2002

Polymer thin films and surfaces: possible effects of capillary waves.

It is discussed how the proximity of a free surface or mobile interface may affect the strain relaxation behavior in a viscoelastic material, such as a polymer melt. The eigenmodes of a viscoelastic film are thus derived, and applied in an attempt to explain the experimentally observed substantial shift of the glass transition temperature of sufficiently thin polymer films with respect to the bulk. Based on the idea that the polymer freezes due to memory effects in the material, and exploiting results from mode-coupling theory, the experimental findings of several independent groups can be accounted for quantitatively, with the elastic modulus at the glass transition temperature as the only fitting parameter. The model is finally applied discussing the possibility of polymer surface melting. A surface molten layer is predicted to exist, with a thickness diverging as the inverse of the reduced temperature. A simple model of thin polymer film freezing emerges which accounts for all features observed experimentally so far.

Journal Article↗
PubMed2001

Adsorption isotherms of hydrogen: the role of thermal fluctuations.

It is shown that experimentally obtained isotherms of adsorption on solid substrates may be completely reconciled with Lifshitz theory when thermal fluctuations of the free film surface are taken into account. This is demonstrated for hydrogen adsorbed on gold as a model system. Analysis of the fluctuation contributions allows one to determine the surface tension of the free hydrogen film as a function of film thickness. It is found to decrease sharply for film thicknesses below seven atomic layers.

Journal Article↗
PubMed2001

Shape of a liquid front upon dewetting.

The profile of a liquid front of a polymer film dewetting a solid substrate is examined by atomic force microscopy. The material removed from the substrate is accumulated in a rim next to the three-phase contact line. Theory predicts the leading edge of the rim profile to be a damped harmonic oscillation for a large class of systems. This is investigated experimentally for the first time, and we show that a non-Newtonian liquid behaves qualitatively different due to viscoelastic effects. It is pointed out that analysis of the rim shapes allows one to study quantitatively the rheological properties of complex fluids on a nanometer scale.

Journal Article↗
PubMed2001

Dewetting patterns and molecular forces: a reconciliation.

We studied the dewetting of thin liquid polymer films from solid surfaces. Our experimental results lead to a consistent picture demonstrating the interplay between short- and long-range interfacial forces. Observations comprise nucleation and spinodal dewetting, as well as thermal nucleation of holes. The effective interface potential of the system, as reconstructed from the morphology of the dewetting patterns, agrees quantitatively with what is computed from the optical properties of the system. This shows that the assumption of additivity of dispersion potentials in multilayer systems yields good results.

Journal Article↗
PubMed2000

Three-phase contact line energetics from nanoscale liquid surface topographies

The contact line tension of a three-phase system (solid-liquid-vapor) is determined from the liquid surface topography data obtained with scanning force microscopy. The data are analyzed in two completely complementary ways, one of which is based on the modified Young equation, the other on the effective interface potential derived from the profile of the liquid-vapor interface in the three-phase region. The two methods agree quite well for the systems investigated. Contact line tensions are in the range of 10(-11) to 10(-10) J/m, which is consistent with theory.

Journal Article↗
PubMed2000

Ripening of ordered breath figures

We have investigated the ripening of breath figures with variable initial order. A dramatic impact of the degree of order on the coalescence behavior is observed. As opposed to the two-droplet coalescence events common to the usual disordered droplet arrays, four-droplet coalescence cascades predominate in a perfectly hexagonal breath figure. Upon introduction of disorder, a gradual transition to a regime dominated by three-droplet cascades is observed. The statistics of coalescence cascades allows for detailed conclusions on the microscopic droplet dynamics.

Journal Article↗
PubMed1999

Liquid morphologies on structured surfaces: from microchannels to microchips

Liquid microchannels on structured surfaces are built up using a wettability pattern consisting of hydrophilic stripes on a hydrophobic substrate. These channels undergo a shape instability at a certain amount of adsorbed volume, from a homogeneous state with a spatially constant cross section to a state with a single bulge. This instability is quite different from the classical Rayleigh Plateau instability and represents a bifurcation between two different morphologies of constant mean curvature. The bulge state can be used to construct channel networks that could be used as fluid microchips or microreactors.

Journal Article↗
PubMed1999

Imaging of cell/substrate contacts of living cells with surface plasmon resonance microscopy.

We have developed a new method for observing cell/substrate contacts of living cells in culture based on the optical excitation of surface plasmons. Surface plasmons are quanta of an electromagnetic wave that travel along the interface between a metal and a dielectric layer. The evanescent field associated with this excitation decays exponentially perpendicular to the interface, on the order of some hundreds of nanometers. Cells were cultured on an aluminum-coated glass prism and illuminated from below with a laser beam. Because the cells interfere with the evanescent field, the intensity of the reflected light, which is projected onto a camera chip, correlates with the cell/substrate distance. Contacts between the cell membrane and the substrate can thus be visualized at high contrast with a vertical resolution in the nanometer range. The lateral resolution along the propagation direction of surface plasmons is given by their lateral momentum, whereas perpendicular to it, the resolution is determined by the optical diffraction limit. For quantitative analysis of cell/substrate distances, cells were imaged at various angles of incidence to obtain locally resolved resonance curves. By comparing our experimental data with theoretical surface plasmon curves we obtained a cell/substrate distance of 160 +/- 10 nm for most parts of the cells. Peripheral lamellipodia, in contrast, formed contacts with a cell substrate/distance of 25 +/- 10 nm.

Animals↗
PubMed1998

Spinodal dewetting in liquid crystal and liquid metal films

Theory predicts that dewetting of a homogeneous liquid film from a solid surface may proceed via unstable surface waves on the liquid. This phenomenon, usually termed spinodal dewetting, has been sought after in many systems. Observations in liquid crystal and liquid metal films showed that, as expected, the emerging structures were similar to those found for spinodal decomposition in mixtures. Certain differences, however, could be attributed to peculiarities of the wetting forces in these two dissimilar systems, thereby demonstrating the role of nonlinearities inherent in the wetting forces.

Journal Article↗
PubMed1996

Improved metabolic action of a bacterial lysine decarboxylase gene in tobacco hairy root cultures by its fusion to a rbcS transit peptide coding sequence.

The gene of a bacterial lysine decarboxylase (ldc) fused to a rbcS transit peptide coding sequence (tp), and under the control of the CaMV 35S promoter, was expressed in hairy root cultures of Nicotiana tabacum. The fusion of the ldc to the targeting signal sequence improved the performance of the bacterial gene in the plant cells in many respects. Nearly all transgenic hairy root cultures harbouring the 35S-tp-ldc gene contained distinctly higher lysine decarboxylase activity (from 1.5 to 30 pkat LDC per mg protein) than those which had been transformed with constructs in which the gene had been directly cloned behind the CaMV 35S promoter. The higher enzyme activity led to the accumulation of up to 0.7% cadaverine on a dry mass basis. In addition, part of the cadaverine pool was used for increased biosynthesis of anabasine, an alkaloid which was hardly detectable in control cultures. The best line contained anabasine levels of 0.5% dry mass, which could be further be enhanced by feeding of lysine.

Anabasine↗