Biomedical subjects

Peter Reimann

Publications and source records attributed to Peter Reimann.

8 recordsLinked to original sources

PubMed2004

Spontaneous ratchet effect in a granular gas.

The spontaneous clustering of a vibrofluidized granular gas is employed to generate directed transport in two different compartmentalized systems: a granular fountain in which the transport takes the form of convection rolls, and a granular ratchet with a spontaneous particle current perpendicular to the direction of energy input. In both instances, transport is not due to any system-intrinsic anisotropy, but arises as a spontaneous collective symmetry breaking effect of many interacting granular particles. The experimental and numerical results are quantitatively accounted for within a flux model.

Cluster Analysis↗

PubMed2003

Dynamic force spectroscopy: optimized data analysis.

The forced rupture of single chemical bonds in biomolecular compounds (e.g., ligand-receptor systems) as observed in dynamic force spectroscopy experiments is addressed. An optimized method of data analysis is proposed. This method significantly outperforms the current standard one when applied to data from an idealized numerical computer simulation of an experiment with realistic parameter values. In particular, the force-free dissociation rate can be inferred with a considerably smaller statistical uncertainty and without the systematic overestimation of about 30%, which is shown to be inherent in the standard method.

Journal Article↗

PubMed2003

Ferrofluids as thermal ratchets.

Colloidal suspensions of ferromagnetic nanoparticles, so-called ferrofluids, are shown to be suitable systems to demonstrate and investigate thermal ratchet behavior: By rectifying thermal fluctuations, angular momentum is transferred to a resting ferrofluid from an oscillating magnetic field without net rotating component. Via viscous coupling the noise driven rotation of the microscopic ferromagnetic grains is transmitted to the carrier liquid to yield a macroscopic torque. For a simple setup we analyze the rotation of the ferrofluid theoretically and show that the results are compatible with the outcome of a simple demonstration experiment.

Journal Article↗

PubMed2002

Paradoxical motion of a single Brownian particle: absolute negative mobility.

We consider a single, classical Brownian particle in a spatially symmetric periodic system far from thermal equilibrium, which can be readily realized experimentally. Upon application of an external static force F, the average particle velocity is negative for F>0 and positive for F<0 (absolute negative mobility). The various physical mechanisms responsible for such a paradoxical effect are identified, leading to analytical approximations that are in good agreement with numerical simulations.

Journal Article↗

PubMed2002

Brownian motion exhibiting absolute negative mobility.

We consider a single Brownian particle in a spatially symmetric, periodic system far from thermal equilibrium. This setup can be readily realized experimentally. Upon application of an external static force F, the average particle velocity is negative for F>0 and positive for F<0 (absolute negative mobility).

Journal Article↗

PubMed1998

Quantum features of Brownian motors and stochastic resonance.

We investigate quantum Brownian motion sustained transport in both, adiabatically rocked ratchet systems and quantum stochastic resonance (QSR). Above a characteristic crossover temperature T(0) tunneling events are rare; yet they can considerably enhance the quantum-noise-driven particle current and the amplification of signal output in comparison to their classical counterparts. Below T(0) tunneling prevails, thus yielding characteristic novel quantum transport phenomena. For example, upon approaching T=0 the quantum current in Brownian motors exhibits a tunneling-induced reversal, and tends to a finite limit, while the classical result approaches zero without such a change of sign. As a consequence, similar current inversions generated by quantum effects follow upon variation of the particle mass or of its friction coefficient. Likewise, in this latter regime of very low temperatures the tunneling dynamics becomes increasingly coherent, thus suppressing the semiclassically predicted QSR. Moreover, nonadiabatic driving may cause driving-induced coherences and quantized resonant transitions with no classical analog. (c) 1998 American Institute of Physics.

Journal Article↗

PubMedDate not supplied

Interferon alpha-2a interactions on glass vial surfaces measured by atomic force microscopy.

Atomic force microscopy was used to study adsorption and adhesion peculiarities of interferon alpha-2a on glass and mica surfaces. The specific protein adsorption behavior as a function of the pH value was illustrated on mica by single molecule imaging, while adhesion forces between interferon molecules and inner surfaces of borosilicate glass vials were measured directly under aqueous buffer conditions by force microscopy. We found that the adhesion force on Schott FIOLAX Type I plus was reduced by 40% of the total adhesion force measured on Schott FIOLAX, a standard type I borosilicate glass quality. These results reflect the anticipated superiority of the special "Type I plus" coating over undesired protein adsorption to glass. In addition, this study gives insight into a new method to predict unintended protein adsorption to glass container walls and to characterize the adsorption process by force measurement.

Adsorption↗

PubMedDate not supplied

Topological structure and chemical composition of inner surfaces of borosilicate vials.

The use of atomic force microscopy (AFM) and x-ray photoelectron spectroscopy (XPS) is described to characterize the inner surfaces of pharmaceutical vials. The two type I borosilicate glasses included in this study slightly differ in their amounts of alkaline oxides. The topography and chemistry of the inner surfaces of vials are predominantly caused by the forming process. A structural and chemical modification of the inner surface of vials was also observed when exposing the surface to different pH conditions and special treatment like washing and sterilization, which are routine operation steps during galenical manufacturing.

Boron Compounds↗