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Biomedical subjects

A Wokaun

Publications and source records attributed to A Wokaun.

8 recordsLinked to original sources
PubMed2006

Determination of the bulk cobalt valence state of co-perovskites containing surface-adsorbed impurities.

We used thermogravimetric hydrogen reduction and iodometric titration to determine the bulk valence state of cobalt in Co-perovskites containing surface carbonate hydroxide or hydroxyl groups. It could be shown that thermogravimetric hydrogen reduction experiments are very sensitive to volatile surface groups, but due to their volatility, they can be specified and the bulk valence state of cobalt can still be deduced from these experiments. The iodometric titration is less sensitive to small volatile surface impurities, but precaution has to be taken that oxygen or iodine does not escape from the solution during dissolution of the sample. Best results were obtained if the sample was titrated during dissolution in a closed argon floated titration apparatus. We tested the two methods using LaCoO3 perovskite as a sample with a known valence state. Both methods delivered satisfactory results, and the valence state could be determined with an accuracy of better than 1%.

Journal Article↗
PubMed2005

Measured total cross sections of slow neutrons scattered by solid deuterium and implications for ultracold neutron sources.

The total scattering cross sections for slow neutrons with energies in the range 100 neV to 3 meV for solid ortho-2H2 at 18 and 5 K, frozen from the liquid, have been measured. The 18 K cross sections are found to be in excellent agreement with theoretical expectations and for ultracold neutrons dominated by thermal up scattering. At 5 K the total scattering cross sections are found to be dominated by the crystal defects originating in temperature induced stress but not deteriorated by temperature cycles between 5 and 10 K.

Journal Article↗
PubMed2005

Measured total cross sections of slow neutrons scattered by gaseous and liquid 2H(2).

The total scattering cross sections for slow neutrons with energies E in the range 300 neV to 3 meV for gaseous and liquid ortho-2H2 have been measured. The cross sections for 2H2 gas are found to be in excellent agreement with both the Hamermesh and Schwinger and the Young and Koppel models. For liquid 2H(2), we confirm the existing experimental data in the cold neutron range and the discrepancy with the gas models. We find a clear 1 / square root[E'] dependence at low energies for both states. A simple explanation for the liquid 2H2 cross section is offered.

Journal Article↗
PubMed2003

The challenge of long-term climate change.

Climate policy needs to address the multidecadal to centennial time scale of climate change. Although the realization of short-term targets is an important first step, to be effective climate policies need to be conceived as long-term programs that will achieve a gradual transition to an essentially emission-free economy on the time scale of a century. This requires a considerably broader spectrum of policy measures than the primarily market-based instruments invoked for shorter term mitigation policies. A successful climate policy must consist of a dual approach focusing on both short-term targets and long-term goals.

Journal Article↗
PubMed2001

Nanoscale atmospheric pressure laser ablation-mass spectrometry.

We describe an atmospheric pressure nanosampling interface for mass spectrometry based on near-field laser ablation. Pulsed laser radiation is delivered to the sample surface through a near-field optical probe, and the ablation plume is sampled through a capillary orifice and analyzed by standard MS methods. A spatial resolution of less than 200 nm and a sensitivity below 2 amol is demonstrated.

Journal Article↗
PubMed1994

1H-NMR studies of the natriuretic peptide urodilatin: sequence-specific resonance assignment.

The recently discovered 32 amino-acid natriuretic peptide urodilatin was chemically synthesized and subjected to two-dimensional proton nuclear magnetic resonance (NMR) spectroscopy studies in aqueous solution in order to determine the structural state of urodilatin. In contrast to earlier studies on very closely related peptides, such as cardiodilatin (CDD/ANP-99-126) and brain natriuretic peptide (BNP), spectra of urodilatin were extremely well resolved even in millimolar concentration in H2O so that the complete sequence specific resonance assignments could be achieved. No long range NOEs could be detected, except between residues close to the single cystine bond. This leads to the conclusion that urodilatin in aqueous solution is a random coil peptide with the exception of the region around the cystine bond.

Amino Acid Sequence↗