Biomedical subjects

Peter Reimann

Publications and source records attributed to Peter Reimann.

15 recordsLinked to original sources

PubMed2006

Granular fountains: convection cascade in a compartmentalized granular gas.

This paper extends the two-compartment granular fountain [D. van der Meer, P. Reimann, K. van der Weele, and D. Lohse, Phys. Rev. Lett. 92, 184301 (2004)] to an arbitrary number of compartments: the tendency of a granular gas to form clusters is exploited to generate spontaneous convective currents, with particles going down in the well-filled compartments and going up in the diluted ones. We focus upon the bifurcation diagram of the general -compartment system, which is constructed using a dynamical flux model and which proves to agree quantitatively with results from molecular dynamics simulations.

Journal Article↗

PubMed2005

Probability densities of periodically driven noisy systems: an approximation scheme incorporating linear-response and adiabatic theory.

We consider periodically driven noisy systems in the limit of long times. To deduce their asymptotic time-periodic probability distributions, two approaches are commonly used: adiabatic theory, valid if driving is very slow, and linear-response theory, applicable when driving is weak. We introduce an approximation scheme that combines these two approaches to yield the driven probability distribution even when driving is strong and moderately fast, so that both linear-response and adiabatic approximations break down. The high accuracy of this scheme is demonstrated on a driven overdamped noisy oscillator in a bistable quartic potential.

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PubMed2005

Brownian motion: absolute negative particle mobility.

Noise effects in technological applications, far from being a nuisance, can be exploited with advantage - for example, unavoidable thermal fluctuations have found application in the transport and sorting of colloidal particles and biomolecules. Here we use a microfluidic system to demonstrate a paradoxical migration mechanism in which particles always move in a direction opposite to the net acting force ('absolute negative mobility') as a result of an interplay between thermal noise, a periodic and symmetric microstructure, and a biased alternating-current electric field. This counterintuitive phenomenon could be used for bioanalytical purposes, for example in the separation and fractionation of colloids, biological molecules and cells.

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PubMed2005

Rate description of the stick-slip motion in friction force microscopy experiments.

During the stick-slip motion of an atomic force microscope tip contacting with a uniformly moving atomically clean surface, the force developed in the cantilever spring performs random sawtoothlike oscillations resulting from the thermally activated transitions of the tip from one surface site to the next. Using escape rate theory, the probability distribution of forces is calculated numerically to deduce the time-average lateral force as a function of pulling velocity. A transcendental equation for the average force is proposed and its approximate solution is obtained. The accuracy of this analytic approximation is demonstrated via comparison with the numerical results. The analogous force-velocity relations existing in the literature are shown to be the limiting cases of low and high cantilever spring constants of our analytic approximation.

Journal Article↗

PubMed2004

Nonmonotonic velocity dependence of atomic friction.

We propose a theoretical model for friction force microscopy experiments with special emphasis on the realistic description of dissipation and inertia effects. Its main prediction is a nonmonotonic dependence of the friction force upon the sliding velocity of the atomic force microscope tip relative to an atomically flat surface. The region around the force maximum can be approximately described by a universal scaling law and should be observable under experimentally realistic conditions.

Journal Article↗

PubMed2004

Thermal ratchet effects in ferrofluids.

Rotational Brownian motion of colloidal magnetic particles in ferrofluids under the influence of an oscillating external magnetic field is investigated. It is shown that for a suitable time dependence of the magnetic field, a noise-induced rotation of the ferromagnetic particles due to rectification of thermal fluctuations takes place. Via viscous coupling, the associated angular momentum is transferred from the magnetic nanoparticles to the carrier liquid and can then be measured as macroscopic torque on the fluid sample. A thorough theoretical analysis of the effect in terms of symmetry considerations, analytical approximations, and numerical solutions is given which is in accordance with recent experimental findings.

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PubMed2004

Paradoxical nonlinear response of a Brownian particle.

We consider a Brownian particle in a "meandering" periodic potential when the ambient temperature is a periodically or stochastically varying function of time. Though far from equilibrium, the linear response of the particle to an external static force is exactly the same as in the equilibrium case, i.e., for constant temperature. Even more surprising is the nonlinear response: the particle slows down and then even starts to move in the direction opposite to the applied force.

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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.

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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).

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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↗