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Biomedical subjects

M Dürr

Publications and source records attributed to M Dürr.

At least 19 recordsLinked to original sources
PubMed2006

Band-gap engineering of metal oxides for dye-sensitized solar cells.

Mixed oxides Ti(1-x)Zr(x)O2 with 0 < x < or = 0.2 were synthesized by means of thermal hydrolysis for use in dye-sensitized solar cells. The lattice parameter d is observed to increase linearly with Zr content x. The band gap of the mixed oxides was measured to increase by up to 0.2 eV. The respective shift of the conduction band edge leads to an increase of the open circuit voltage (V(OC)) by up to 0.1 V. Among others, temperature-dependent measurements of V(OC) clearly identify the correlation between band edge shift and change in V(OC).

Journal Article↗
PubMed2006

Three-dimensional images for electron-impact single ionization of He: complete and comprehensive (e, 2e) benchmark data.

Comprehensive fully differential cross sections for electron emission into all three spatial dimensions are presented for 1 keV and 102 eV electron-impact single ionization of helium using an advanced reaction microscope. Surprising out-of-plane contributions, traced back to an interference term in a perturbation expansion by comparison with ion-impact data, severely challenge theoretical models that accurately predict coplanar emission. The data represent the ultimate benchmark for recently developed exact theoretical descriptions of the most fundamental three-body quantum problems.

Journal Article↗
PubMed2005

Diffusion properties of dye molecules in nanoporous TiO2 networks.

The adsorption of ruthenium-dye molecules out of ethanol solution onto TiO2 particles of nanoporous TiO2 films was used to study the molecules' diffusion through these layers by means of optical absorption spectrometry. Dependent on pore size, porosity, and particle size, effective diffusion constants as low as D(eff) = 4 x 10(-9) cm2/s were deduced from the uptake curves by applying a simple model for combined diffusion and adsorption. These diffusion constants for diffusion through the nanoporous network are up to 3 orders of magnitude lower than in bulk ethanol and are discussed with respect to the properties of the nanoporous material.

Journal Article↗
PubMed2005

Comparison of low-temperature hydrogen peroxide gas plasma sterilization for endoscopes using various Sterrad models.

This study compared the effectiveness of sterilizing four types of endoscope using different models of the Sterrad system (Sterrad 50, 100, 100S and 200). Sterilization levels meeting international requirements were attained in all cases with carriers inoculated with Geobacillus stearothermophilus spores. The endoscopes were tested in half cycles ('overkill'). This is the first study to compare the Sterrad models marketed to date in terms of effective sterilization of endoscopes with narrow lumens.

Colony Count, Microbial↗
PubMed2005

Retention of Escherichia coli in municipal sewage by means of planted soil filters in two-stage pilot plant systems.

Different types of constructed wetlands in a pilot-plant system were fed with identical municipal waste water to compare the sanitisation process in two-stage systems. With combinations of a vertical and a horizontal flow filter an E. coli reduction of 5 log10 with an E. coli influent concentration of 10(7) MPN/100 ml was achieved. Using different filter materials in each stage the total performance of the two-stage system was independent from the sequence of these materials. However, using coarser filter material in the first stage makes the filter less prone to clogging and is thus the preferential option with regard to operational reliability.

Biodegradation, Environmental↗
PubMed2004

Diffusion-limited transport of I- 3 through nanoporous TiO2-polymer gel networks.

Tri-iodide transport in a polymer gel electrolyte embedded in nanoporous TiO(2) networks and its diffusion limits are investigated by means of current-voltage (I-V) characteristics of simple Pt-gel-Pt sandwich devices with a thin porous TiO(2) layer sintered directly onto one of the Pt electrodes. At voltages between 0.2 and 0.7 V, the I-V curves of such devices show the typical plateau of diffusion-limited redox reactions, in this case I(-)/I(3) (-), at the platinum electrodes. From the dependence of the limiting current density on layer thickness, the diffusion constants D(bulk) and D(p,eff) of tri-iodide in the bulk polymer gel and through a polymer gel penetrated TiO(2) network, respectively, have been found to be D(bulk)=3.2(+/-0.2)x10(-6) cm(2)/s and D(p,eff)=1.5(+/-0.1)x10(-6) cm(2)/s. Temperature-dependent measurements show diffusion in the gel to be activated by about 0.16 eV. The results are discussed in comparison to diffusion in liquid electrolytes as well as with respect to the implications for dye-sensitized solar cell devices.

Journal Article↗
PubMed2004

Molecular beam investigation of hydrogen dissociation on Si(001) and Si(111) surfaces.

The influence of molecular vibrations on the reaction dynamics of H2 on Si(001) as well as isotopic effects have been investigated by means of optical second-harmonic generation and molecular beam techniques. Enhanced dissociation of vibrationally excited H2 on Si(001)2 x 1 has been found corresponding to a reduction of the mean adsorption barrier to 390 meV and 180 meV for nu=1 and nu=2, respectively. The adsorption dynamics of the isotopes H2 and D2 show only small differences in the accessible range of beam energies between 50 meV and 350 meV. They are traced back to different degrees of vibrational excitation and do not point to an important influence of quantum tunneling in crossing the adsorption barrier. The sticking probability of H2 on the 7 x 7-reconstructed Si(111) surface was found to be activated both by H2 kinetic energy and surface temperature in a qualitatively similar fashion as H2/Si(001)2 x 1. Quantitatively, the overall sticking probabilities of H2 on the Si(111) surface are about one order of magnitude lower than on Si(001), the influence of surface temperature is generally stronger.

Journal Article↗
PubMed2003

Microdevices for separation, accumulation, and analysis of biological micro- and nanoparticles.

Microfabrication and performance of a novel microsystem for separation, accumulation and analysis of biological micro- and nanoparticles is reported. Versatile chip functions based on dielectrophoresis and microfluidics were integrated to isolate particles from complex sample solutions such as serum. A bead-based assay for virus detection is proposed. Separation of micro- and sub-mum beads employing dielectrophoretic deflector and bandpass structures is demonstrated. Individual antibody coated beads with hepatitis A virus bound to their surface were trapped by negative dielectrophoresis in a field cage and analysed by fluorescence microscopy.

Journal Article↗
PubMed2002

Probing high-barrier pathways of surface reactions by scanning tunneling microscopy.

The ability of scanning tunneling microscopy to probe the pathways of thermally activated high-barrier surface processes is frequently limited by competing low-barrier processes that can confuse measurement of the true initial and final configuration. We introduce an approach to circumvent this difficulty by driving the surface process with nanosecond laser heating. The method is applied to determine the pathway of recombinative desorption in the H/Si(001) system. The observed configuration of dangling bonds after laser heating reveals that the desorbed hydrogen molecules are not formed on single dimers, but rather from neighboring silicon dimers via an interdimer reaction pathway.

Journal Article↗
PubMed2002

Real-space study of the pathway for dissociative adsorption of H2 on Si(001).

Dissociative adsorption of molecular hydrogen on clean Si(001) surfaces has been investigated by means of scanning tunneling microscopy. The dissociated hydrogen atoms are found to occupy Si atoms of adjacent dimers. In addition to this interdimer configuration associated with the adsorption of isolated hydrogen molecules, pairs of adjacent doubly occupied dimers are readily formed. They arise from the enhanced reactivity of partially occupied dimers following the initial H2 adsorption step. The results are considered in light of recent adsorption and desorption measurements.

Journal Article↗
PubMed2002

Developmental potentials of hematopoietic and neural stem cells following injection into pre-implantation blastocysts.

Pluripotent embryonic stem (ES) cells are able to differentiate in vivo into all cell types of the fetal and adult organism and in vitro they can differentiate into a variety of cell types. In contrast, multipotent somatic stem cells (SSCs) isolated from fetal and adult tissues differentiate into mature effector cells of their tissue. However, recent studies imply that SSCs can also generate cell types of heterologous tissues indicating unexpected broad differentiation potentials. In order to examine and compare the developmental potentials of SSCs, we exposed hematopoietic stem cells (HSCs) and neural stem cells (NSCs) to an environment that is permissive for the development of all cell types of the embryo, namely the mouse preimplantation blastocyst. Using this approach we were able to detect progeny of HSCs and NSCs frequently in developing chimeric animals. Analysis of 18 different adult tissues revealed minor preferences of HSCs for hematopoietic tissues, while progeny of NSCs were mostly detected in neural tissues. Furthermore we observe that human cord blood-derived CD34+ and CD34+/CD38- HSCs also engraft murine embryos and that human donor contribution persists into adulthood. Our studies show the existence of tissue specific engraftment preferences of HSCs and NSCs and that both stem cell types are non-ES cell-like.

ADP-ribosyl Cyclase↗
PubMed2001

Structure Sensitive Reaction Channels of Molecular Hydrogen on Silicon Surfaces.

The ability of the Si(001) surface to adsorb H2 molecules dissociatively increases by orders of magnitude when appropriate surface dangling bonds are terminated by H atoms. Through molecular beam techniques the energy dependent sticking probability at different adsorption sites on H-precovered and stepped surfaces is measured to obtain information about the barriers to adsorption, which decrease systematically with an increase in coadsorbed H atoms. With the help of density functional calculations for interdimer adsorption pathways, this effect is traced back to the electronic structure of the different adsorption sites and its interplay with local lattice distortions.

Journal Article↗
PubMed2001

On-chip electrophoretic accumulation of DNA oligomers and streptavidin.

A micro-chamber for electrophoretic accumulation of charged biomolecules has been designed and evaluated. The system is based on a chip with an array of planar focusing electrodes. Particular attention was devoted to a design which enables penetration of a large sample volume by the electric field of the focusing electrodes. General design principles for a cylindrically symmetrical arrangement of the focusing electrodes were derived. Accumulation of DNA oligomers and streptavidin in aqueous solution was demonstrated. The concentration of biomolecules in the centre of the chip was enhanced by up to a factor of 200. The major fraction of the total charge delivered during electrophoretic accumulation results from Faradaic processes. The maximum charge density deliverable without visible gas formation was determined. By careful control of the voltage and current density applied to the electrodes, evolution of gas bubbles could be avoided for the time required to accumulate analyte molecules in the centre of the micro-chamber. On-chip electrophoretic accumulation of biomolecules can be applied to sample pre-conditioning in lab-on-a-chip devices for analysis of DNA and protein samples.

Animals↗
PubMed2001

[Diabetes mellitus caused by pancreatitis in a bull].

This paper describes a 6-year-old Simmental bull with diabetes mellitus. The animal was referred to our clinic because of severe weight loss and chronic indigestion. Clinical examination revealed markedly disturbed general condition, impaired forestomach function and polyuria. There was aciduria, glucosuria and ketonuria. The most important biochemical findings were severe hyperglycemia, markedly increased activities of hepatic enzymes and severe metabolic acidosis. Plasma concentrations of insulin, insulin-like growth factor-I, thyroxine and 3,5,3'-triiodothyronine were lower than normal, whereas those of glucagon were higher than normal. Based on these findings, a diagnosis (secondary) diabetes mellitus was made. The bull was slaughtered and histological examination revealed mixed cell pancreatitis with severe degeneration of islet cells. Immunohistochemical examination of the pancreas showed that very few insulin-, glucagon-, somatostatin- and pancreatic polypeptide, insulin-like growth factor-I and adrenomedullin-producing islet cells were present.

Animals↗
PubMed2000

A microarray enzyme-linked immunosorbent assay for autoimmune diagnostics.

In order to quantify autoantibodies in the sera of patients with autoimmune disease, we have created a microarray-based immunoassay that allows the simultaneous analysis of 18 known autoantigens. The microarrays contain serial dilutions of the various antigens, thereby allowing accurate determination of autoantibody titer using minimal amounts of serum. The assay is very sensitive and highly specific: as little as 40 fg of a known protein standard can be detected with little or no cross-reactivity to nonspecific proteins. The signal intensities observed from serial dilutions of immobilized antigen correlate well with serial dilutions of autoimmune sera. Miniaturized and highly parallelized immunoassays like these will reduce costs by decreasing reagent consumption and improve efficiency by greatly increasing the number of assays that can be performed with a single serum sample. This system will significantly facilitate and accelerate the diagnostics of autoimmune diseases and can be adapted easily to any other kind of immunoassay.

Antibodies, Antinuclear↗