Biomedical subjects

Thomas Frisch

Publications and source records attributed to Thomas Frisch.

8 recordsLinked to original sources

PubMed2006

Effect of step stiffness and diffusion anisotropy on the meandering of a growing vicinal surface.

We study the step meandering instability on a surface characterized by the alternation of terraces with different properties, as in the case of Si(001). The interplay between diffusion anisotropy and step stiffness induces a finite wavelength instability corresponding to a meandering mode. The instability sets in beyond a threshold value which depends on the relative magnitudes of the destabilizing flux and the stabilizing stiffness difference. The meander dynamics is governed by the conserved Kuramoto-Sivashinsky equation, which display spatiotemporal coarsening.

Journal Article↗

PubMed2005

Kinetic step bunching instability during surface growth.

We study the step bunching kinetic instability in a growing crystal surface characterized by anisotropic diffusion. The instability is due to the interplay between the elastic interactions and the alternation of step parameters. This instability is predicted to occur on a vicinal semiconductor surface Si(001) or Ge(001) during epitaxial growth. The maximal growth rate of the step bunching increases like F4, where F is the deposition flux. Our results are complemented with numerical simulations which reveal a coarsening behavior in the long time evolution for the nonlinear step dynamics.

Journal Article↗

PubMed2005

Peeling off an elastica from a smooth attractive substrate.

Using continuum mechanics, we study theoretically the unbinding of an inextensible rod with free ends attracted by a smooth substrate and submitted to a vertical force. We use the elastica model in a medium-range van der Waals potential. We numerically solve a nonlinear boundary value problem and obtain the force-stretching relation at zero temperature. We obtain the critical force for which the rod unbinds from the substrate as a function of three dimensionless parameters, and we find two different regimes of adhesion. We study analytically the contact potential case as the van der Waals radius goes to zero.

Journal Article↗

PubMed2004

Stretching an adsorbed polymer globule.

Using molecular dynamic simulation, we study the stretching of an adsorbed homopolymer in a poor solvent with one end held at a distance ze from the substrate. We measure the vertical force f on the end of the chain as a function of the extension ze and the substrate interaction energy w. The force reaches a plateau value at large extensions. In the strong adsorption limit, we show that the plateau value increases linearly in w in good agreement with a theoretical model. In the weak adsorption limit, a polymer globule with a layered structure is formed and elastically deformed when stretched. In both cases a simple theoretical model permits us to predict the relation between the necessary force to fully detach the polymer and its critical extension.

Journal Article↗

PubMed2002

Slow relaxation and solvent effects in the collapse of a polymer.

Using molecular dynamic simulations we study the quench of a homopolymer chain into a poor solvent at finite temperature. We show that, depending on the quench depth, there are different relaxation pathways to the collapsed state. Solvent effects are introduced through an effective Lennard-Jones potential depending on the local monomer density. The various relaxation regimes are characterized by the contact correlation function. As the quench depth increases, the system evolves towards a glassy state, and the relaxation dynamics continuously changes from an exponential to a stretched exponential law. The characteristic relaxation time diverges at low temperature following an Arrhenius law, like in the case of strong glasses. We found that the stretching exponent depends on aging in a nonuniversal way. The solvent modifies the globular state by diminishing the effects of frustration and glassy behavior.

Journal Article↗

PubMed2002

Unwinding globules under tension and polymer collapse.

Polymer collapse is known to be mediated by the formation of pearls. These intermediate structures behave as small globules under tension. The globule size is studied by molecular dynamic simulations as a function of the strength of an external stretching force applied to its ends, for different values of the chain length. A very strong first-order-like transition from a compact globule state to a stretched one is observed. A model of this transition in terms of a globule-chain system is presented. The critical force, above which the globule unwinds, is shown to satisfy a power law scaling like N(1/3) in the number of monomers.

Models, Chemical↗

PubMed2002

Predicting the kinetics of cell spreading.

We apply the wetting theory to predict the kinetics of fibroblast spreading onto an adhesive substrate, under simplifying assumptions on the cell structure and geometry. Three main parameters are used: cytoplasmic viscosity, cortical tension, and cell-to-substrate adhesion energy. The viscosity and tension values are taken from previous micromechanical studies. The adhesion energy, ill known, is adjusted by fitting the model predictions to available experimental data of contact radius versus time. The agreement is quite good, justifying such a "macroscopic" view of cell morphology.

Aldehydes↗

PubMedDate not supplied

The visible ear: a digital image library of the temporal bone.

High-fidelity computer-based modeling, simulation and visualization systems for the study of temporal bone anatomy and training for middle ear surgery are based on a sequence of digital anatomical images, which must cover a large tissue volume and yet display details in high resolution and with high fidelity. However, the use of existing image libraries by independent developers of virtual models of the ear is limited by copyright protection and low image resolution. A fresh frozen human temporal bone was CT-scanned and serially sectioned at 25 microm and digital images of the block surface were recorded at 50- to 100-microm increments with a Light Phase(TM) single-shot camera back attachment. A total of 605 images were recorded in 24-bit RGB resolution. After color correction and elimination of image size variation by differential cropping to 15.4 cm x 9.7 cm, all images were resampled to 3,078 x 1,942 pixels at a final resolution of 50 microm/pixel and stored as 605 one-Mb JPEG files together with a three-dimensional viewer. The resulting complete set of image data provides: (1) a source material suitable for generating computer models of the human ear; (2) a resource of high-quality digital images of anatomical cross sections from the human ear, and (3) a PC-based viewer of the temporal bone in three perpendicular planes of section.

Aged↗