Biomedical subjects

H J Kreuzer

Publications and source records attributed to H J Kreuzer.

7 recordsLinked to original sources

PubMed2003

Tracking particles in four dimensions with in-line holographic microscopy.

We describe a simple holographic method that has enabled us to capture as a single data set the trajectories of micrometer-sized objects suspended in water. By subtracting consecutive holograms of a particle suspension and then adding these difference holograms, we constructed a final data set that contains the time evolution of the particle trajectories free from spurious background interference effects. The method is illustrated by a recording of the motion of 5-10-microm diameter algae in water.

Journal Article↗

PubMed2002

Digital in-line holography of microspheres.

We have used digital in-line holography (DIH) with numerical reconstruction to image micrometer-sized latex spheres as well as ferrimagnetic beads suspended in gelatin. We have examined in detail theoretically and experimentally the conditions necessary to achieve submicrometer resolution of holographic reconstructions. We found that both transparent and opaque particles could be imaged with a resolution that was limited only by the wavelength of the light used. Simple inspection of intensity profiles through a particle allowed an estimate to be made of the particle's three position coordinates within an accuracy of a few hundred nanometers. When the derivative of a second-order polynomial fitted to the intensity profiles was taken, the X, Y, Z position coordinates of particles could be determined within +/-50 nm. More-accurate positional resolution should be possible with the help of more-advanced computer averaging techniques. Because a single hologram can give information about a large collection of distributed particles, DIH offers the prospect of a powerful new tool for three-dimensional tracking of particles.

Holography↗

PubMed2002

Photo- and thermodesorption of helium on Pt(111).

In a detailed study of thermal desorption of monolayers of both 4He and 3He adsorbed on Pt(111) (binding energy about 9 meV), we have observed photodesorption induced by the blackbody radiation from a room temperature environment. This process proceeds independently of the thermal desorption. Theoretical treatments of both thermal and photodesorption are given and agree very well with the data in all important aspects. We conclude that the photodesorption is due to direct coupling of photons to the adsorbate.

Journal Article↗

PubMed2002

Optimization of the low energy electron point source microscope: imaging of macromolecules.

Optimal conditions for low energy electron point source microscopy are investigated by the simulation and numerical reconstruction of holograms of phthalocyaninato polysiloxane, PcPS, a rod-like macromolecule. The effects of the electron energy, width of the electron beam and the detector size on the spatial resolution in the reconstructed images are modeled. We find that for electron energies around 200eV, with the specimen 0.1 microm from the source, a screen recording the image in a cone of at least 15 degrees half angle (7 cm lateral dimension at 10 cm from the source) with at least 512 x 512 pixel and 8-bit resolution will result in near atomic resolution.

Journal Article↗

PubMed2001

Digital in-line holography for biological applications.

Digital in-line holography with numerical reconstruction has been developed into a new tool, specifically for biological applications, that routinely achieves both lateral and depth resolution, at least at the micron level, in three-dimensional imaging. The experimental and numerical procedures have been incorporated into a program package with a very fast reconstruction algorithm that is now capable of real-time reconstruction. This capability is demonstrated for diverse objects, such as suspension of microspheres and biological samples (diatom, the head of Drosophila melanogaster), and the advantages are discussed by comparing holographic reconstructions with images taken by using conventional compound light microscopy.

Algorithms↗

PubMed2001

Stretching a macromolecule in an atomic force microscope: statistical mechanical analysis.

We formulate the proper statistical mechanics to describe the stretching of a macromolecule under a force provided by the cantilever of an atomic force microscope. In the limit of a soft cantilever the generalized ensemble of the coupled molecule/cantilever system reduces to the Gibbs ensemble for an isolated molecule subject to a constant force in which the extension is fluctuating. For a stiff cantilever we obtain the Helmholtz ensemble for an isolated molecule held at a fixed extension with the force fluctuating. Numerical examples are given for poly (ethylene glycol) chains.

Biophysical Phenomena↗

PubMed2001

Stretching a macromolecule in an atomic force microscope: statistical mechanical analysis.

We formulate the proper statistical mechanics to describe the stretching of a macromolecule under a force provided by the cantilever of an Atomic Force Microscope. In the limit of a soft cantilever, the generalized ensemble of the coupled molecule-cantilever system reduces to the Gibbs ensemble for an isolated molecule subject to a constant force in which the extension is fluctuating. For a stiff cantilever, one obtains the Helmholtz ensemble for an isolated molecule held at a fixed extension with the force fluctuating. Numerical examples and predictions for experiments with cantilevers of differing stiffness are given for short and long chains of poly (ethylene glycol), based on parameter-free ab initio calculations.

Biomechanical Phenomena↗